Recent Advancements in Polymeric Materials for Electrochemical Energy Storage (Green Energy and Technology) [1st ed. 2023] 981994192X, 9789819941926

Citation preview

Green Energy and Technology

Ram K. Gupta   Editor

Recent Advancements in Polymeric Materials for Electrochemical Energy Storage

Green Energy and Technology

Climate change, environmental impact and the limited natural resources urge scientific research and novel technical solutions. The monograph series Green Energy and Technology serves as a publishing platform for scientific and technological approaches to “green”—i.e. environmentally friendly and sustainable—technologies. While a focus lies on energy and power supply, it also covers “green” solutions in industrial engineering and engineering design. Green Energy and Technology addresses researchers, advanced students, technical consultants as well as decision makers in industries and politics. Hence, the level of presentation spans from instructional to highly technical. **Indexed in Scopus**. **Indexed in Ei Compendex**.

Ram K. Gupta Editor

Recent Advancements in Polymeric Materials for Electrochemical Energy Storage

Editor Ram K. Gupta Department of Chemistry National Institute for Materials Advancement Pittsburg State University Pittsburg, KS, USA

ISSN 1865-3529 ISSN 1865-3537 (electronic) Green Energy and Technology ISBN 978-981-99-4192-6 ISBN 978-981-99-4193-3 (eBook) https://doi.org/10.1007/978-981-99-4193-3 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

Polymeric materials possess several unique characteristics such as tunable electrical and electronic structure, redox activity, multifunctionality, high porosity and surface area, and the ability to make nanocomposites with enhanced electrochemical performance. This book covers the synthesis of various polymeric materials, their electrochemical behavior, strategies to enhance electrochemical characteristics, and recent development in electrochemical energy storage devices. Understanding the chargetransport mechanism in polymers, properties of individual components in composite, and architectural aspects of the devices are some of the important studies which are covered in this book which are much needed for the fabrication of advanced energy devices. The main purpose of this book is to provide current, state-of-the-art knowledge, fundamental mechanisms, design strategies, and future challenges in electrochemical energy storage devices using polymeric materials. The key goals for advanced energy devices are to deliver high energy and power density, improve safety, use widely available materials, reliability, cycle life, and have low production cost. In this book, the fundamentals and working principles of electrochemical energy devices such as supercapacitors and batteries will be covered. This book explores new approaches for the synthesis of polymeric materials and their composites to broaden the vision for researchers to explore advanced materials for electrochemical energy applications. The future applications and challenges in polymeric materials are also explored. All the chapters are covered by experts in these areas making this a suitable textbook

v

vi

Preface

for students and providing new directions to researchers and scientists working in polymers, energy, and nanotechnology. Ram K. Gupta Associate Professor of Polymer Chemistry, Department of Chemistry, National Institute for Materials Advancement Pittsburg State University Pittsburg, KS, USA

Contents

Materials for Electrochemical Energy Storage: Introduction . . . . . . . . . . . Phuong Nguyen Xuan Vo, Rudolf Kiefer, Natalia E. Kazantseva, Petr Saha, and Quoc Bao Le

1

Design/Types of Electrochemical Energy Devices . . . . . . . . . . . . . . . . . . . . . Shibyendu Nikhar, Gaurav Awasthi, and Pawan Kumar

15

Polymer-Based Electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tapas Das, Sanjeev Verma, Vikas K. Pandey, and Bhawna Verma

33

Conducting Polymers for Electrochemical Energy Storage Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. A. U. Madhushani and Ram K. Gupta Conductive Polymer and Composites for Supercapacitor Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shilpa Pande, Bidhan Pandit, Shoyebmohamad F. Shaikh, and Mohd Ubaidullah Polymer-Based Nanocomposites for Supercapacitors . . . . . . . . . . . . . . . . . . Sagar Jariwala, Yash Desai, and Ram K. Gupta

49

71

93

Polymer-Carbon Nanocomposites for Supercapacitors . . . . . . . . . . . . . . . . 113 Pragati Chauhan, Mansi Sharma, Dinesh Kumar, and Rekha Sharma Polymer-Metal Oxides Nanocomposites for Supercapacitors . . . . . . . . . . . 131 R. Rajalakshmi and N. Ponpandian Polymer-Metal Sulfides Nanocomposites for Supercapacitors . . . . . . . . . . 151 Shrestha Tyagi, Himani, Anuj Kumar, and Beer Pal Singh Polymeric Materials for Nanosupercapacitors . . . . . . . . . . . . . . . . . . . . . . . . 167 Mert Akın ˙Insel and Selcan Karaku¸s

vii

viii

Contents

Polymer-MOFs Nanocomposite for Supercapacitor . . . . . . . . . . . . . . . . . . . 187 Abhijeet S. Shelake, Onkar C. Pore, Rajendra V. Shejwal, Dhanaji G. Kanase, and Gaurav M. Lohar The Active Role of Conjugate Polymer Composites in Electrochemical Storage: A Themed Perspective on Polymer-MOF Nanocomposites for Metal-Ion Batteries . . . . . . . . . . . . . . . 211 Sowjanya Vallem and Joonho Bae Redox-Active Polymeric Materials Applied for Supercapacitors . . . . . . . . 229 Rudolf Kiefer, Phuong Nguyen Xuan Vo, Natalia E. Kazantseva, Petr Saha, and Quoc Bao Le Polymeric Nanocomposites for Flexible Supercapacitors . . . . . . . . . . . . . . 245 Sanjeev Verma and Bhawna Verma Polymeric Materials for Flexible Supercapacitors . . . . . . . . . . . . . . . . . . . . . 263 Rasmita Barik, Saurabh Kumar Pathak, and Agni Kumar Biswal Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Achayalingam Ramesh, Sourabh Basu, and M. Sterlin Leo Hudson Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries . . . . . . . . 299 Hamid Dehghan-Manshadi, Mohammad Mazloum-Ardakani, and Soraya Ghayempour Polymer-Chalcogen Composites for Metal-Ion Batteries . . . . . . . . . . . . . . . 313 Sakshi Gautam, Anjali Banger, Nirmala Kumari Jangid, and Manish Srivastava Polymeric Materials for Metal-Sulfur Batteries . . . . . . . . . . . . . . . . . . . . . . . 329 Jiadeng Zhu, Yucheng Zhou, Qiang Gao, and Mengjin Jiang Polymer-Based, Flexible, Solid Electrolyte Membranes for All-Solid-State Metal-Ion Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 E. M. Sreeja, Merin K. Wilson, A. Abhilash, and S. Jayalekshmi Polymer Materials for Metal-Air Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 Arpana Agrawal Polymeric Materials for Metal-Air Batteries . . . . . . . . . . . . . . . . . . . . . . . . . 383 Mansi Sharma, Pragati Chauhan, Dinesh Kumar, and Rekha Sharma Polymeric Materials for Flexible Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Aparajita Pal and Narayan Chandra Das Polymeric Materials for Nanobatteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 Anurag Tiwari and Rajendra Kumar Singh Materials and Applications of 3D Print for Solid-State Batteries . . . . . . . 433 Apurba Das and Pintu Barman

Contents

ix

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical Treatment to Obtain Materials with Highly Improved Capacitive Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 Thalita Centofanti, Maria de A. Silva, Mariana G. Segatelli, and César R. T. Tarley Advanced Polymers and Composites for Actuators in Robotics and Bioelectronics: Materials and Technologies . . . . . . . . . . . . . . . . . . . . . . 467 Massimo Mariello Methods and Technologies for Recycling Energy Storage Materials and Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489 Neha Thakur, Pradipta Samanta, and Sunita Mishra

Materials for Electrochemical Energy Storage: Introduction Phuong Nguyen Xuan Vo, Rudolf Kiefer, Natalia E. Kazantseva, Petr Saha, and Quoc Bao Le

Abstract Energy storage devices (ESD) are emerging systems that could harness a high share of intermittent renewable energy resources, owing to their flexible solutions for versatile applications from mobile electronic devices, transportation, and load-leveling stations to extensive power conditioning. The last decades have witnessed considerable developments in supercapacitors and batteries with superior energy density and remarkably long cycle life that could continually store and deliver much energy to portable and stationary applications. The substantial development of new, cheaper, eco-friendly, superior polymer-based nanocomposites has gained considerable interest in advancing the existing ESD behaviors. The ease of processing, the simple tunability of arrangements, and the synergetic interaction between the polymer and the inorganic counterparts that allow remarkable electronic conductivity, specific surface area, and charge of the nanocomposites have presented great opportunities for economic viability for efficient energy conversion. Keywords Electrochemical storage devices · Metal-ion batteries · Redox flow batteries · Supercapacitors · Polymer-based nanocomposites

1 Introduction Our present energy use relies on the vast storage of fossil fuels, exposing its weaknesses and vulnerabilities to the energy and climate crisis chaos. Advancing the sustainable transition to renewables to bring affordable energy, jobs, economic P. N. X. Vo Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam R. Kiefer Conducting Polymers in Composites and Applications Research Group, Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam N. E. Kazantseva · P. Saha · Q. B. Le (B) University Institute, Tomas Bata University, Nad Ovˇcírnou 3685, 760 01 Zlin, Czech Republic e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_1

1

2

P. N. X. Vo et al.

growth, and a resilient environment to the people and communities on earth has become more critical than ever. From 2010 to 2021, the cumulative capacity of installed wind power worldwide has increased significantly from 180.8 GW to approximately 430 GW. The growth of solar PV power generation grew from merely 32 to 1002.9 TWh (Source: IEA [1, 2]). The IEA reports that the development of renewable electricity is accelerating worldwide faster than ever, with an expectedly additional 50% increase over the next five years. In harvesting intermittent energy from the record growth of renewables and bringing about the decarbonization of our global energy systems, energy storage is a prerequisite. The fundamental idea of efficient energy storage is to transfer the excess of power or energy produced into a form of storable energy and to be quickly converted on demand for a wide variety of applications and load sizes. To enable energy storage to limit the intertwined crisis of energy and climate change, significantly, long-term, regionally-tailored storage in affordable net-zero electricity systems predominantly powered by renewable energy is essential. In other words, if the storage of renewable energy is destined to transform our electricity grids, electric vehicles, and domestic appliances towards carbon-free, then solutions of energy storage must satisfy crucible criteria, including (i) long duration of power delivery (in days); (ii) sufficient power delivery to cope with peak spikes; and (iii) being scalable, adaptable, environmental/ climate-friendly and economically viable. Many well-developed and emerging technologies exist for renewable energy storage in practically all forms of energy, including mechanical, chemical, electrochemical, electrical, and thermal energies. Among the many available options, electrochemical energy storage systems with high power and energy densities have offered tremendous opportunities for clean, flexible, efficient, and reliable energy storage deployment on a large scale. They thus are attracting unprecedented interest from governments, utilities, and transmission operators. There are many developing chemistries in the electrochemical storage field and many of which are promising. This chapter introduces concepts and materials of the matured electrochemical storage systems with a technology readiness level (TRL) of 6 or higher, in which electrolytic charge and galvanic discharge are within a single device, including lithiumion batteries, redox flow batteries, metal-air batteries, and supercapacitors. The TRL aims to measure a system’s maturity of technology components. There has recently been a scale from 1 to 9, the TRL’s most mature technology.

2 Fundamental Electrochemical Storage Technologies 2.1 Batteries Batteries are electrochemical cells that rely on chemical reactions to store and release energy (Fig. 1a). Batteries are made up of a positive and a negative electrode, or the so-called cathode and anode, which are submerged in a liquid electrolyte. The cathode

Materials for Electrochemical Energy Storage: Introduction

3

Fig. 1 Schematic configuration of a a metal-ion rechargeable battery, b a regular capacitor, and c a supercapacitor [3, 4]

and anode chambers in batteries are separated by a micro-permeable separator, which only allows ions to pass through. Batteries work on a concept associated with the electrochemical potentials of metals, which are the tendency of the metal to lose electrons. The battery performance can be indicated by how much energy it can deliver on demand (i.e., power density) and how much energy it stores (i.e., energy density). More than 200 years ago, Alessandro Volta created an external flow of electricity from the first cell using two metals (Zn and Ag) with different electrochemical potentials. In 1991, Sony Corp. made the first commercial model of lithium-ion battery (LiB), which was invented by Yoshino et al. [3], followed by Ali Eftekhari’s invention of potassium-ion battery (KiB) in 2004 [4] and Aquion Energy’s first model of sodium-ion battery (SiB or NiB) in 2009 [5]. They are rechargeable and again based on the same concept of electrochemical potential. The metal-ion batteries store charges by employing metal ions as the charge carrier, meaning the metal ions move back and forth between the cathode and the anode through the electrolyte during charge and discharge. Lithium has only one electron in its outer shell in the electrochemical series and the highest tendency to lose an electron. In addition, the low density of Li (0.534 g cm−3 ) helps to reduce the overall mass and volume of the LiBs, thus improving both gravimetric and volumetric energy densities (i.e., the energy stored per unit weight and unit volume) of the LiBs. Moreover, the low redox potential (− 3.040 V vs. NHE) and high theoretical specific capacity (3860 mAh g−1 and 2061 mAh cm−3 ) of Li enables the LiBs to operate at relatively high cell voltage, which also increases the energy density of the LiBs [6]. Therefore, the LiB has the highest energy density per unit volume and mass among commercial rechargeable metal-ion batteries (Fig. 2). Remarkably, the LiBs possess relatively high energy density (up to 200 Wh/kg and 450 Wh/L), with high energy efficiency (more than 95%) and long cycle life (3000 cycles at the deep discharge of 80%) [7–10]. Because of its rapid response, modularization, and flexible installation, the LiB technology has been widely used in diverse

4

P. N. X. Vo et al.

Fig. 2 Gravimetric and volumetric energy densities of various rechargeable metal-ion batteries [7]

applications, including portable devices, power tools, electric cars, home storage backup (e.g., Tesla’s Powerwall), satellites (e.g., REIMEI’s battery) and utility-scale storage (e.g., Tesla’s PowerPack). The Tesla 100-MW PowerPack in South Australia is currently the largest lithium-ion battery (LiB) power plant. It was installed to be paired with the Hornsdale wind farm, and recently it has been expanded by 50% to 150 MW to increase its capacity for smoothing out temporary spikes in demand. Though the LiB is a remarkably advancing technology that has deeply penetrated every corner of our life since its advent, it poses many drawbacks and concerns, including high cost, fire risk, capacity fade over time, and the requirement for the battery management system to be protected from temperature extremes. The LiBs typically deliver their power over up to 4 h at a time. Though the LiB price is dropped significantly since 2010, the current cost of 4-h discharge of LiBs remains too expensive for most grid-scale applications due to the scarcity of crucial metal (Li, Ni, Co, Mn) resources [11] and the sophisticated protection systems to prevent dangerous overcharging and explosion [12]. The standard design of a battery pack with cells connected in parallel to increase capacity has shown an uneven current distribution, varied thermal gradients, and interconnected resistances [13]. These issues accelerate battery pack degradation, as seen in the example of a 75 kWh Tesla Model S which uses about 4680 cylindrical cells arranged into 96 cells in series and 46 cells in parallel, providing 500 km of range. While an individual cell and the battery pack initially perform the same, after 1200 cycles, the single cell loses 28% of its original capacity, whereas the battery pack reduces to 35% after only 750 cycles [14]. Overcharge, excessive charge rate, and extreme load conditions during utilization are the most significant factors contributing to the loss of LiB energy due to solid-electrolyte interface growth and active material loss at the negative electrode (e.g., Li plating) [15]. Moreover, the recyclability of LiBs is generally poor due to challenges in separating materials. Therefore, much research and development have been going on to find cheap, reliable, and long-lasting energy storage solutions that

Materials for Electrochemical Energy Storage: Introduction

5

use abundant, safe, reusable, and sustainable materials to complement the LiBs by delivering the day-worth of continuous power. Redox flow batteries (RFBs) are a promising complement to LiBs, with stateof-the-art technologies, including vanadium redox flow batteries (VRFBs) and zincbromine redox flow batteries (ZBRFBs). Organic RFBs, which use naturally abundant elements like C, H, and O, can also store and release energy. The basic setup of an RFB combines designs from both a battery and a fuel cell configuration, with two tanks of electrolyte liquid containing aqueous solutions of redox-active cathodic and anodic materials (Fig. 3). One tank serves as a positive electrolyte, and the other as a negative electrolyte, with a cell stack in between. The solutions from each tank are pumped into the cell stack, where a thin ion-exchanged membrane separates the ions. As the RFB discharges, ions in the negatively charged solution release electrons through an oxidation process, which move towards an electrode in the cell stack, go through a circuit and return to another electrode on the other side. This electrode feeds the electrons into the positively charged solution through a reduction process, with positively charged hydrogen ions flowing across the membrane to maintain charge balance. The whole cycle is entirely reversible. While the amount of stored energy in LiBs is related to the amount of solid active materials, such as graphite for the anode and transition metal oxide for the cathode, RFBs rely on the amount of liquid active materials stored in tanks. The number of cell stacks and the volume of the cell tanks determines the power capacity and stored energy of RFB systems. It makes RFBs an economical and robust alternative for energy storage at the grid scale. A liquid electrolyte, mainly aqueous, makes RFB systems highly durable and long-lasting. They can also be easily scaled up without the risk of fire or explosion and are recyclable due to the separation of the electrolytes. However, RFBs have lower volumetric energy densities than LiBs for a similar output due to the volume of electrolyte flow delivery and less compact systems (Fig. 4). Specifically, the stored energy density of the RFBs only ranges from 25 to 35 Wh/L, and round-trip efficiencies of up to 57–75% in kW-class systems, but the lifespan of the RFBs typically lasts from 15,000 to 20,000 charge/discharge cycles at Fig. 3 Schematic configuration of a redox flow battery [15]

6

P. N. X. Vo et al.

Fig. 4 Comparison of power rating and discharge time for lithium-ion battery, redox flow battery, metal-air flow battery, and pumped hydropower [17, 18]

the deep discharge of 90% or more [16]. The RFB setup is cheaper, recyclable, and safe in operation, which are attractive selling points for grid transmission operators and offers the commercialization potential for the smaller version of the power wall systems for domestic homeowners.

2.2 Supercapacitors Unlike the battery, a capacitor does not rely on chemical reactions to function. No chemical reactions are involved in the capacitor’s energy storage mechanism. Instead, the regular capacitor stores potential energy electrostatically. The typical capacitor consists of two conductive metal plates (electrodes), typically made from aluminum and separated by a dielectric insulating material such as ceramic (Fig. 1b). When a potential difference is applied between the electrodes, an electric field established between the electrodes polarizes the dielectric material, accumulating an equal amount of positive and negative charges. This separation of charges allows the device to store energy and release it quickly. While the battery takes longer to be charged and loses its usable energy over time and use, the capacitor only takes seconds to be charged and retains its capacity over time since there are no changes on the electrodes in regular operation. Therefore, capacitors are used in almost every circuit board to power the circuit for any short power supply interruption. Capacitor banks are commonly found in large buildings for correcting current–voltage lagging when many inductive loads are placed into the circuit [19] or for smoothing full-wave rectification output [20]. Although the energy stored in a capacitor is determined by its capacitance, which can be increased by enlarging the electrode surface area and reducing the distance between the electrodes,

Materials for Electrochemical Energy Storage: Introduction

7

the capacitor still has a lower energy density than a LiB due to the relatively high permittivity extraction, low leakage of current density, and high breakdown voltage. Recent advances in inkjet-printable ink formulations have enabled the deposition of dielectric films [21] that are micron or sub-micron thick. However, a capacitor with relatively high permittivity extraction, low current density leakage, and high breakdown voltage still has a lower energy density than a LiB [22–24]. The LiBs offer high energy densities but suffer from slow power delivery, whereas regular capacitors provide fast but limited energy densities. To compete with fossil fuels, faster and higher-power energy storage systems are needed for renewables. The electrochemical supercapacitor fills this gap between the rechargeable battery and the regular capacitor. Its design resembles a battery’s, with an electrolyte on either side of an insulator (Fig. 1c). A supercapacitor can store hundreds or even thousands of times more energy than a regular capacitor. When the supercapacitor is charged, the charger connects across the electrodes, and negative ions attach to the electrode from the electrolyte, forming electric double boundary layers. The attraction force between the electrode and the electrolyte is electrostatic. The supercapacitor’s ability to store electrical charges is due to the electric double layer, which aligns positive and negative charges across the electrode and electrolyte solution, making it an electrical double-layer capacitor (EDLC). Its charge storage capacity sets a supercapacitor apart from a regular capacitor, which depends on the distance between metal plates and the available surface area. While the distance between metal plates in a conventional capacitor is in the micron scale, the supercapacitor has a narrower distance in the nanoscale range. This reduction in distance, combined with a larger electric field formed in the proximity of the electrodes and higher dielectric permittivity, allows for significantly greater energy storage. Developing new active materials with a much larger surface area of 1000–2000 m2 g−1 enhances the storage capacity of supercapacitors even further [25]. Even though intensive research has been carried out to make supercapacitors more universally applicable, the supercapacitors’ progress still cannot compete with the LiBs regarding high specific energy and long-term energy storage. The LiBs commonly store a large amount of energy as high as 150–200 Wh kg−1 but are confined by their low power density (below 1000 W kg−1 ) and poor cycle life (usually less than 3000 cycles). In contrast, the supercapacitors can provide much higher power density (10 kW kg−1 ), long cycle life (exceeding 1 × 105 cycles), and fast charge–discharge processes (within seconds) but suffer from much lower energy density (only 5–10 Wh kg−1 ) [26]. Therefore, the supercapacitor has been found to have the most considerable potential for hybrid applications. A fantastic example of how effective supercapacitors can be seen in Switzerland, where buses are exposed to charging stations at various stops along their routes [27]. Only 15 s are needed to top the energy charge off and a few minutes for a full charge. Tesla Model S Plaid+ [28], Toyota Yaris Hybrid-R concept car [29], or Lamborghini high-powered Sián FKP-37 [30] take advantage of the superior power density of supercapacitors in power regeneration during system deceleration (i.e., energy recharging).

8

P. N. X. Vo et al.

3 Material of Choice for Electrodes and Electrolytes The combination of supercapacitor and/or battery-based technologies has been shown to reduce the workload and intensity level of LiBs, extending their lifespan by reducing their exposure to more demanding tasks [31]. The success of the ESD market is attributed to the development of flexible advanced storage components that can conform to various shapes and endure mechanical deformations in different states. Additionally, the development of scalable, reliable, and cost-effective manufacturing methods for active materials and storage devices has played a significant role in the success of the ESD market [32]. While increasing the energy density and battery lifespan remain necessary, current active materials used in LiBs pose environmental and geopolitical issues that must be addressed. A significant factor determining the final cost of rechargeable batteries is the cost of active materials for electrodes and electrolytes. Active cathode materials often comprise more than 50% of the total cost [31]. Typical automotive LiBs containing resource-limited Cobalt (Co), lithium (Li), and nickel (Ni) in the cathode with commonly used LiB cathode chemistries are lithium nickel cobalt manganese oxide (NCM) [32], lithium nickel cobalt aluminum oxide (NCA) [33], or lithium iron phosphate (LFP) [34]. Battery technology is constantly improving, and new and improved chemistries are expected to emerge in the future. However, strategic efforts are being made to replace expensive and resource-limited metals such as Co and Li with abundant commodity-scale inorganic materials with readily available material production infrastructure to reduce costs and ensure availability. It has led to the preference for low-cost metals such as Iron, Zinc, Copper, Aluminum, and Silicon and their alloys as battery electrodes, which undergo liquid/solid transformation, due to their abundance, recyclability, and eco-friendliness. Using solid active materials based on these abundant elements would lower costs. A notable example is Tesla’s tabless 4680 battery cells, which feature a new cell design and modified material chemistry, resulting in higher energy density, ease of manufacturing, and lower costs [17]. In addition to the cell design with internal ‘shingled spiral’ construction to alleviate thermal issues and simplify the manufacturing process, the Tesla cathode enriched with Ni eliminates the need for Cobalt, reducing the Tesla’s cathode cost per kWh by 15%. Tesla also improves silicon chemistry by stabilizing it with an elastic ion-conducting polymer coating, allowing for a higher percentage of cheap silicon to be used in cell manufacture. Altogether these changes create an expected 56% improvement in Tesla’s cost per kWh. Polymers are the materials of choice for electrochemical energy storage devices because of their relatively low dielectric loss, high voltage endurance, gradual failure mechanism, lightweight, and ease of processability. An encouraging breakthrough for the high efficiency of ESD has been achieved in ESD employing nanocomposites of polymers. Over the past decades, a wide range of nanostructured composites with varying chemical compositions (e.g., inorganic ceramics, metal oxides/ phosphide/sulfide/carbide, organic molecules) and dimensions (0-D nanoparticles, 1-D nanorods or nanowires, 2-D nanosheets, 3-D frameworks) have been blended

Materials for Electrochemical Energy Storage: Introduction

9

Fig. 5 Schematic illustration of synergetic effects from the introduction of advanced nanostructured fillers as composites to the polymer matrix in ESDs [18, 45]

with the polymer matrix in an attempt to take physical/chemical properties, porosity, and surface area, charge conduction, scalability and processability of the ESDs to the next level of flexibility, multifunctionality and integration (Fig. 5) [35–44]. Advantages of large surface areas, high pore volumes, modulated pore structures, unique d-electrons configurations, low-cost nature, and synergistic effects of porous transition metal-based nanomaterials, such as oxides, sulfide, phosphide, and carbides, have emerged as promising alternatives for the next generation of ESDs [35, 36]. Owing to the large mass density, high surface area, and metallic conductivity, high-aspect-ratio 1-D nanostructures, such as carbon nanofibers, nanowires, and nanotubes, or 1-D nanostructured metal nitrides have been explored for enhancing strength, electrical conductivity, and thermal stability in advanced energy harvesting and energy storage technologies [42]. The ion-conducting network formed by the 1-D ionic conductors made it possible to develop flexible all-solid-state batteries without sacrificing their electrochemical performance and safety. Carbon nanostructures, particularly graphene, have shown significant potential and have been considered a breakthrough in material science since their discovery. Graphene, a widely studied 2-D material, is composed of carbon atoms packed closely together in a honeycomb-like structure, possessing a high surface area (1654–2600 m2 g−1 ), electrical conductivity (100–2000 S cm−1 ), thermal conductivity (2000– 3000 Wm K−1 ), tensile strength (1.2 MPa for nanoporous graphene, 130 GPa for single-crystalline graphene), and outstanding fatigue resistance [43]. Its potential applications are still being discovered and are considered beyond what has been explored thus far. Many concrete and realistic applications of graphene are hitting the market, including ESDs. Graphene-based ESDs have been demonstrated to have excellent performance characteristics and are getting ready to show off colossal news

10

P. N. X. Vo et al.

for plug-in hybrid vehicles [44]. Graphene balls, in which silicon oxide nanoparticles are coated with graphene sheets, are used as the cathode or the protective layer on the anode to increase the volumetric density of a complete cell by 28%. The cell retains almost 80% capacity after 500 cycles [46]. The outstanding electrical conductivity of graphene makes it possible for cells to deliver highly high currents while ensuring fast charging, which is especially beneficial for high-capacity automobile batteries or fast device-to-device charging. The high heat conductance of graphene also implies that graphene-based batteries can run cooler, extending their lifespan. This 2-D architecture has many intriguing qualities, such as high flexibility, strength, and weight, making graphene appealing to battery researchers. Metal–organic frameworks (MOFs) are another emerging class of ordered porous materials with a 3-D modular nature of metal nodes and organic linkers, thus allowing for fine chemical and structural control tunability for specific ESD needs in ESDs [47, 48].

4 Conclusions and Future Perspectives Electric vehicles can never be a proper competitor for internal combustion engine cars until the consumer can charge them up in more or less the same amount of time as it takes to fill up a tank of fossil fuels. In the vast majority of grid operations, the grids continue to generate the bulk of the day-to-day from fossil fuels like coal and gas or nuclear energy, restricting the extent to which intermittent renewables have been able to replace them. Though it might seem challenging to have a smooth energy transition to renewables and actualize a carbon-free grid, plenty of astonishing ideas are experimenting in the global race of developing a new form of energy storage chemistry for mass production of ESD facilities with appreciable electrochemical performances to supply massive energy on a large scale. However, the cost of lithium-ion batteries remains relatively high, making it challenging to implement them on a large scale for grid-level energy storage. Furthermore, the upper limit of 4 h for discharge is generally considered the minimum time window for peak operations on most grids, making it difficult to rely solely on lithium-ion batteries for longer-term energy storage needs. To address this challenge, researchers and industry experts are exploring the potential of complementary technologies, such as battery-based or supercapacitor-based technologies, to deliver longer-term energy storage solutions that can provide days of continuous discharge. Supercapacitors, in particular, have shown promise due to their ability to quickly store and discharge energy and withstand many charge and discharge cycles. Combining these technologies may create a comprehensive energy storage solution that can support the reliable delivery of low-cost renewable energy throughout the year. In addition to these efforts, there are ongoing research and development efforts to improve the efficiency and capacity of existing technologies, such as developing new chemistries and electrode materials, improving the design of energy storage systems, and streamlining the manufacturing process. The goal is to make energy

Materials for Electrochemical Energy Storage: Introduction

11

storage systems more affordable, reliable, and scalable, accelerating the transition to a sustainable, renewable energy future. Acknowledgements This work was supported by the Horizon Europe project TwinVECTOR of the European Union (Grant Agreement No. 101078935).

References 1. IEA (2022) Wind Electricity, IEA, Paris. https://www.iea.org/reports/wind-electricity, License: CC BY 4.0 2. IEA (2022) Solar PV, IEA, Paris. https://www.iea.org/reports/solar-pv, License: CC BY 4.0 3. Yoshino A, Sanechika K, Nakajima T (1985) US4668595A and JP9769585, filling date (priority) May 10, 1985. Secondary battery 4. Eftekhari A (2004) Potassium secondary cell based on Prussian blue cathode. J Power Sources 126:221–228 5. Whitacre JF, Wiley T, Shanbhag S, Wenzhuo Y, Mohamed A, Chun SE, Weber E, Blackwood D, Lynch-Bell E, Gulakowski J, Smith C, Humphreys D (2012) An aqueous electrolyte, sodium ion functional, large format energy storage device for stationary applications. J Power Sources 213:255–264 6. Lin D, Liu Y, Cui Y (2017) Reviving the lithium metal anode for high-energy batteries. Nat Nanotech 12:194–206 7. Kubota K, Dahbi M, Hosaka T, Kumakura S, Komaba S (2018) Towards K-ion and Na-ion batteries as “beyond Li-ion”. Chem Rec (New York, N.Y.) 18(4):459–479 8. Purvins A, Sumner M (2013) Optimal management of stationary lithium-ion battery system in electricity distribution grids. J Power Sources 242:742–755 9. Crawford AJ, Huang Q, Kintner-Meyer MCW et al (2018) Lifecycle comparison of selected Li-ion battery chemistries under grid and electric vehicle duty cycle combinations. J Power Sources 380:185–193 10. Valant C, Gaustad G, Nenadic N (2019) Characterizing large-scale, electric-vehicle lithium ion transportation batteries for secondary uses in grid applications. Batteries 5(1):8 11. Weil M, Ziemann S, Peters J (2018) The issue of metal resources in Li-ion batteries for electric vehicles. In: Pistoia G, Liaw B (eds) Behaviour of lithium-ion batteries in electric vehicles: battery health, performance, safety, and cost. Springer, 59–74 12. Chen Y, Kang Y, Zhao Y, Wang L, Liu J, Li Y, Liang Z, He X, Li X, Tavajohi N, Li B (2021) A review of lithium-ion battery safety concerns: the issues, strategies, and testing standards. J Energy Chem 59:83–99 13. Liu X, Ai W, Marlow MN, Patel Y, Wu B (2019) The effect of cell-to-cell variations and thermal gradients on the performance and degradation of lithium-ion battery packs. Appl Energy 248:489–499 14. Carter R, Huhman B, Love CT, Zenyuk IR (2018) X-ray computed tomography comparison of individual and parallel assembled commercial lithium iron phosphate batteries at end of life after high rate cycling. J Power Sources 381:46–55 15. Shchurov NI, Dedov SI, Malozyomov BV, Shtang AA, Martyushev NV, Klyuev RV, Andriashin SN (2021) Degradation of lithium-ion batteries in an electric transport complex. Energies 14(23):8072 16. Sánchez-Díez E, Ventosa E, Guarnieri M, Trovò A, Flox C, Marcilla R, Soavi F, Mazur P, Aranzabe E, Ferret R (2021) Redox flow batteries: Status and perspective towards sustainable stationary energy storage. J Power Sources 481:228804 17. A Closer Look at Tesla’s New 4680 cell battery pack—FutureCar.com—via @FutureCar_ Media

12

P. N. X. Vo et al.

18. Wu ZS, Zhou G, Yin LC, Ren W, Li F, Cheng HM (2012) Graphene/metal oxide composite electrode materials for energy storage. Nano Energy 1:107–131 19. Kodsi SKM, Cañizares CA, Kazerani M (2006) Reactive current control through SVC for load power factor correction. Electric Pow Sys Res 76:701–708 20. Hartog JR, Craney PJ (2012) US201261678423P, filing date (priority) August 01, 2012. Power assist for use of high-power X-ray generators to operate from low power single phase supply lines 21. Tehrani BK, Mariott C, Cook BS, Roselli L, Tentzeris MM (2016) Development, characterization, and processing of thin and thick inkjet-printed dielectric films. Org Electron 29:135–141 22. Xiong L, Hu J, Yang Z, Li X, Zhang H, Zhang G (2022) Dielectric properties investigation of metal-insulator-metal (MIM) capacitors. Molecules 27:3951 23. Wang B, Huang W, Chi L, Al-Hashimi M, Mark TJ, Fachetti A (2018) High-k gate dielectrics for emerging flexible and stretchable electronics. Chem Rev 118(11):5690–5754 24. Kim ES, Liang JG, Wang C, Cho MY, Oh JM, Kim NY (2019) Inter-digital capacitors with aerosol-deposited high-K dielectric layer for highest capacitance value in capacitive supersensing applications. Sci Rep 9:680 25. Forouzandeh P, Kumaravel V, Pillai SC (2020) Electrode materials for supercapacitors: a review of recent advances. Catalysts 10:969 26. Zhai Y, Dou Y, Zhao D, Fulvio PF, Mayes RT, Dai S (2011) Carbon materials for chemical capacitive energy storage. Adv Mater 23:4828 27. Electric Buses: Where and How to Charge Them? - Alliance for an Energy Efficient Economy (aeee.in) 28. Engineering Analysis Of New Tesla Model S Plaid Supercar (insideevs.com) 29. Toyota details its triple-motor, super capacitor-powered Yaris Hybrid-R (newatlas.com) 30. Lamborghini built a supercapacitor into its Sián hybrid for a faster, smoother ride (popsci.com) 31. Lemian D, Bode F (2022) Battery-supercapacitor energy storage systems for electrical vehicles: a review. Energies 15:5683 32. Kim Y (2012) Lithium nickel cobalt manganese oxide synthesized using alkali chloride flux: morphology and performance as a cathode material for lithium ion batteries. ACS Appl Mater Interfaces 4(5):2329–2333 33. Tran M-K, DaCosta A, Mevawalla A, Panchal S, Fowler M (2021) Comparative study of equivalent circuit models performance in four common lithium-ion batteries: LFP, NMC, LMO, NCA. Batteries 7:51 34. Spears BM, Brownlie WJ, Cordell D et al (2022) Concerns about global phosphorus demand for lithium-iron-phosphate batteries in the light electric vehicle sector. Commun Mater 3:14 35. Hou R, Gund GS, Qi K, Nakhanivej P, Liu H, Li F, Xia BY, Park HS Hybridization design of materials and devices for flexible electrochemical energy storage. Energy Storage Mater 19:212–241 36. Tan DQ (2020) The search for enhanced dielectric strength of polymer-based dielectrics: a focused review on polymer nanocomposites. J Appl Polym Sci 137:e49379 37. Rabuffi M, Picci G (2002) Status quo and future prospects for metallized polypropylene energy storage capacitors. IEEE Trans Plasma Sci 30:1939–1942 38. Wang X, Kim M, Xiao Y, Sun Y-K (2016) Nanostructured metal phosphide-based materials for electrochemical energy storage. J Mater Chem A 4:14915–14931 39. Liu X, Huang J-Q, Zhang Q, Mai L (2017) Nanostructured metal oxides and sulfides for lithium-sulfur batteries. Adv Mater 29:1601759 40. Zhong Y, Xia X, Shi F, Zhan J, Tu J, Fan HJ (2016) Transition metal carbides and nitrides in energy storage and conversion. Adv Sci 3:1500286 41. Díez-Pascual AM (2020) Carbon-based polymer nanocomposites for high-performance applications. Polymers 12:872 42. Han JT, Cho JY, Kim JH, Jang JI, Kim JS, Lee HJ, Park JH, Chae JS, Roh H-K, Lee W et al (2019) Structural recovery of highly oxidized single-walled carbon nanotubes fabricated by kneading and electrochemical applications. Chem Mater 31:3468–3475

Materials for Electrochemical Energy Storage: Introduction

13

43. Wang Y, Li S, Yang H, Luo J (2020) Progress in the functional modification of graphene/ graphene oxide: a review. RSC Adv 10:15328–15345 44. Das HT, Haripradad K, Balaji TE (2021) Graphene and its analogous 2D-layered materias for flexible persistent energy storage devices in consumer electronics. In: Kamble G (ed) 2D Functional nanomaterials 45. Seok D, Jeong Y, Han K, Yoon DY, Sohn H (2019) Recent progress of electrochemical energy devices: metal oxide-carbon nanocomposites as materials for next-generation chemical storage for renewable energy. Sustainability 11:3694 46. Son IH, Park JH, Park S et al (2017) Graphene balls for lithium rechargeable batteries with fast charging and high volumetric energy densities. Nat Commun 8:1561 47. Baumann AE, Burns DA, Liu B et al (2019) Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices. Commun Chem 2:86 48. Kaneti YV, Tang J, Salunkhe RR, Jiang XC, Yu AB, Wu KC-W, Yamauchi Y (2017) Nanoarchitectured design of porous materials and nanocomposites from metal organic frameworks. Adv Mater 29:1604898

Design/Types of Electrochemical Energy Devices Shibyendu Nikhar, Gaurav Awasthi, and Pawan Kumar

Abstract Electrochemical energy devices, such as batteries and fuel cells, are a crucial part of modern energy systems and have numerous applications, including portable electronic devices, electric vehicles, and stationary energy storage systems. In this chapter, we provide an overview of the design and types of these devices, including their principles of operation, key performance parameters, and materials used in construction. We also discuss the challenges and opportunities for improving their performance and sustainability, as well as the potential for integrating them into various energy systems. The materials used in construction and the choice of electrolyte are important design considerations, and researchers have explored a range of options in both areas. Additionally, efforts to increase energy density, power density, and lifetime, as well as reduce environmental impact, are key areas of research in this field. This chapter aims to provide students and researchers with a comprehensive understanding of electrochemical energy devices and their role in modern energy systems. Keywords Electrochemical energy devices · Batteries · Fuel cell · Electrolyte

1 Introduction Electrochemical energy devices (EEDs), such as fuel cells and batteries, are an important part of modern energy systems and have numerous applications, including portable electronic devices, electric vehicles, and stationary energy storage systems [1]. These devices rely on chemical reactions to produce or store electrical energy and can convert chemical energy into electricity with high efficiency [1]. There are several S. Nikhar Chandigarh University, Ludhiana-Chandigarh State Hwy, Punjab 140413, India G. Awasthi · P. Kumar (B) Materials Application Research Laboratory, Department of Nano Sciences and Materials, Central University of Jammu, Jammu, UT of J&K 181143, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_2

15

16

S. Nikhar et al.

types of EEDs, including batteries, fuel cells, and hybrid systems. Batteries are types of storage devices that collect energy in the form of chemical reactions and then transform that energy into electricity using an external circuit [2]. Fuel cells, on the other hand, generate electricity directly from chemical reactions, typically using hydrogen and oxygen as reactants [2]. Hybrid systems combine elements of both batteries and fuel cells and can be used to store and generate electricity [2]. The design of EEDs is a key factor in their performance and efficiency. Materials used in construction, electrolyte materials, and performance parameters all contribute to the performance and operation of these devices [3]. In addition, researchers have focused on improving the performance and sustainability of EEDs, including efforts to increase energy density, power density, and lifetime, as well as reduce environmental impact [3].

1.1 Applications of Electrochemical Energy Devices Recent years have seen a rise in the implementation of EEDs for grid-scale energy storage. This is particularly relevant as the world transitions towards renewable energy sources, which are often intermittent and require energy storage to be dispatched when needed. Batteries have emerged as a realistic choice for grid-scale energy storage because of their energy density and relatively low cost. One of the primary advantages of EEDs is their high energy density, which allows them to store substantial levels of energy in a limited space. This makes them ideal for use in portable applications where weight and size are major concerns [4]. EEDs, such as fuel cells and, batteries have a broad range of applications in various industries. Commonly, batteries are used to power portable electronic devices, such as laptops and smartphones, as well as electric vehicles. They are also being increasingly utilized for grid-scale energy storage to provide a reliable source of power during periods of high demand or without renewable energy sources such as wind energy and solar energy [5]. In addition, EEDs are being explored for use in the military and aerospace sectors. The high energy density and portability of batteries make them suitable for use in military equipment, while the efficiency and clean emissions of fuel cells make them a potential option for powering aircraft [5]. Increasing interest is also being shown in the application of EEDs for residential and commercial applications. For example, building-integrated fuel cells can be used to generate electricity and heat for homes and businesses, while portable fuel cells can be used as a source of power backup in case of a blackout [5]. LIBs have also seen significant improvements, particularly for use in electric vehicles (EVs). These batteries have a high energy density, long cycle life, and low self-discharge rate, making them an attractive choice for EVs [6]. Other electrochemical storage technologies, such as supercapacitors and redox flow batteries, have also been developed for use in renewable energy systems. These devices have the advantage of high-power density and rapid charging and discharging capabilities, making them suitable for applications that require rapid delivery of high power [7].

Design/Types of Electrochemical Energy Devices

17

2 Design of Electrochemical Energy Devices Generally, EEDs contain two electrodes that are used to transmit and store electrons in chemical form. These electrodes are separated either by a membrane or a separator. A common ion, which participates in both electrochemical reactions, connects the two unique electrochemical processes occurring at the two electrodes. For the transport of the common ion, electrolyte plays an important role here. Solid-state devices with basic anode, membrane, and cathode designs can only store energy at the electrode– electrolyte interface up to the thickness of the electrodes. The flow battery stores and releases energy in the redox states of liquid oxidants and reductants. Since it is possible to circulate redox liquids by turning enormous reservoirs into an energyconversion tool/device [8]. Different type of EEDs is shown in Figs. 1, 2 and 3. These devices can decouple power from energy. In the case of gas-based EEDs Hydrogen based electrolytes are used. In general, compared to other fuel cell types, polymer electrolyte fuel cells (PEFCs) based on hydrogen operate at lower temperatures (< 120 °C). These EEDs generate energy by separating hydrogen and oxygen through an ion-exchange membrane, as well as heat as a by-product of the reaction [8, 9].

2.1 Material Used in Construction Various nano-based materials are used in the construction of the EEDs. Generally, all EEDs contain two electrodes i.e., anode and cathode. The electrodes are composed of a conductive material and serve as a support for the catalyst as well as a channel for electron delivery to the bipolar plates [13].

Fig. 1 The interface structure of solid-state lithium metal batteries. Adapted from Ref. [10]. Copyright The Authors, some rights reserved; exclusive licensee Wiley. Distributed under a Creative Commons Attribution License 4.0

18

S. Nikhar et al.

Fig. 2 A schematic diagram of a redox flow battery. Adapted from Ref. [11]. Copyright The Authors, some rights reserved; exclusive licensee Springer. Distributed under a Creative Commons Attribution License 2.0 Fig. 3 A diagrammatic representation of a hydrogen fuel battery. Adapted with permission [12] Copyright (2020), Elsevier

Metal Oxides—Metal oxides have gained significant interest due to the high electron storage capacity and emissivity in an energy storage device via a chemical redox process. For the high performance of EEDs researchers used various metal oxides for the electrode materials e.g., TiO2 , V2 O5 , MnO2 , Fe2 O3 , Co3 O4 , NiO, and CuO. These metal oxides are distinguished by price and several important performance metrics, such as power density, energy density, safety, and lifespan [14].

Design/Types of Electrochemical Energy Devices

19

Due to its high abundance and accessibility of raw ingredients, MnO2 has been viewed as a sustainable material. MnO2- based products have low-energy synthesis and production techniques which reduced carbon footprints with enhanced electrochemical properties [14]. When we compared it to other metal oxides, nickel oxide (NiO) has various advantages for supercapacitors, including a theoretically significant high Cs of 2000 Fg−1 , strong chemical/thermal stability, cost-efficiency, nontoxicity, and Eco-friendliness. The implementation of NiO-based EEDs by their cyclic stability and low electrical conductivity. To enhance electrical activity, NiO has been fabricated with multiple morphologies, including, nanofibers, nanoflowers, nanospheres, etc. [15]. Graphene and Graphene-based Materials—Graphene is a monolayer of carbon atoms with sp2 hybridization arranged in a hexagonal lattice. It is an allotrope of carbon and a building block of graphite, fullerenes, and carbon nanotubes. Graphite is used as a material for EEDs because of its exceptional qualities, including as low weight, chemical inertness, reasonable cost, and high surface area [16]. When graphene participates in an energy-storage mechanism, it is considered as an active material. It can operate as a catalyst in metal-air batteries, store ions (such as Li+ or Na+ in metal-ion batteries), keep electrostatic charges on the electrode double-layer, or any combination of these [16]. The usage of graphene/polymer nanocomposites in supercapacitors is incredibly attractive. Graphene/polyaniline-based nanomaterials are simple to synthesize electrochemically or chemically with capacitances ranging from 233 Fg−1 to 1046 Fg−1 based on their composition. Although graphene/polymer composites (polyaniline/graphene) are flexible and hold their features even when mechanically stressed, they are perfect for portable and wearable electronics [17]. In terms of energy storage devices, 3D graphene frameworks have greater promise than irregularly aggregated graphene because of their higher mechanical strength, high surface area, continuous electron-transport pathways, and quick ion diffusion capabilities. Metal–Organic Framework (MOF)—MOF is an example of porous material. Their flexible design enables for extensive synthetic tunability, allowing for precise chemical and structural control. These qualities make MOFs a promising option for next-generation energy storage systems. For the installation of innovative reservoirs for electrons in metal-ion batteries electrodes, MOFs’ high synthetic tunability is very helpful. Metal nodes that are redox-active are common in MOF fabrication and have been widely investigated both in anode and cathode materials [18]. In the case of lithium-ion batteries (LIBs), MOFs are used as electrodes as well as the cathode. Iron-based MOFs like MIL-53 (Fe), MIL-68(Fe), and MIL 101(Fe) are used as cathodic materials in LIBs [19]. Despite iron-based MOF, lithium-based MOF (Li2 (VO)2 (HPO4 )2 (C2 O4 )) also used as cathode material. This Li MOF shows a high electrochemical plateau at 3.9 V with 80 mAh/g of reversible capacity after 25 cycles [20]. Zn-based MOFs are generally used as anodic materials for LIBs. Zn-based MOF-177 was first reported in 2006 as anodic material for LIBs with ~ 400 mAh/g discharge capacity and 105 mAh/g charge capacity [21]. Despite ZnZnbasedOF, Cobalt-based MOF is also used. Co2 (OH)2 BDC is used as an anode in

20

S. Nikhar et al.

LIBs. This MOF shows 650 mAh/g reversible capacity at 50 mA/g current density after 100 cycles in the range of 0.02–3.0 V [22]. MXenes—A two-dimensional transition metal carbide, nitride, or carbonitride known as MXene with exceptionally accessible hydrophilic surfaces [23]. MXenes are being investigated as electrode materials due to their improved structural characteristics and a high number of active sites for rapid charge transfer and redox reactions. The presence of more surface functional groups helps to MXenes’ improved chargestorage mechanism [23]. V2 CTx , Nb2 CTx, Ti2 CTx are some examples of MXenes used in batteries. M2 X MXenes like Nb2 C, Ti2 C, Sc2 C, and V2 C with low molecular weight and high gravimetric capacities make them promising materials for electrodes in batteries [24]. Despite ion batteries, MXenes are also used in capacitors. Ti3 C2 Tx is the most extensively researched MXene for electrochemical capacitors [24]. Miscellaneous—EEDs based on biomass and biochar have gained popularity because they are inexpensive, safe, eco-friendly, and function well electrochemically. The electrolyte, binder, and membrane of the EEDs are prepared by extracting or converting organic molecules from biomass materials. For these various species of algae such as Chlorella, Nannochloropsis, Gelidium, Schizochytrium, Spirulina, etc. are used [25]. To increase the capacity of materials for EEDs different materialbased hybrid composites like graphene with metal oxides, graphene with MXenes, graphene with carbon nanotubes, MOF derived metal oxides are also used.

2.2 Electrolyte Materials An electrolyte is a critical component of EEDs, with its qualities having a significant impact on the energy capacity, cyclability, rate performance, and safety of all EEDs. In most cases, an electrolyte is a liquid that helps in the conduction of electricity by the transport of ions not electrons. We can say electrolyte act as a conductor in the case of ions and insulators in the case of electrons [26]. Figure 4 shows the classifications of electrolytes used in EEDs.

3 Types of Electrochemical Energy Devices Electrochemical energy devices are a form of energy storage and conversion technology that generates electricity through chemical reactions. These energy sources rely on redox (reduction–oxidation) processes, a type of chemical reaction, to produce electricity. These reactions, in which electrons are transferred from one species to another, can result in the generation of an electric current. These devices can be classified into three main categories: batteries, fuel cells, and hybrid systems.

Design/Types of Electrochemical Energy Devices

21

Fig. 4 Classification of electrolytes used in EEDs. Adapted with permission [27]. Copyright (2020), Elsevier

3.1 Batteries Batteries for electrochemical storage devices are an essential technology for modern society, as they allow us to store electrical energy for use in many different applications, including grid-level energy storage, portable electronic devices, and electric vehicles. The basic principle of operation of a battery is the conversion of chemical energy into electrical energy through a process called an electrochemical conversion. There have been many developments in batteries for electrochemical storage devices in recent years. Here is a summary of some of the latest research in this area. Development of high-energy density LIBs: developments are ongoing to improve the energy density of LIBs, which are utilized extensively in a variety of portable electronic products in addition to electric automobiles. One recent development in this area is the use of high-capacity cathode materials, such as lithium-rich cathodes and high-voltage cathodes, which can raise the energy density of LIBs [28]. Development of lithium-sulfur batteries: Lithium-sulfur (Li–S) batteries have the potential to provide high energy densities at low cost. Researchers have made progress in improving the stability and cycling performance of Li–S batteries, which are still under development for practical use [29]. Development of flow batteries: Flow batteries are a type of electrochemical storage device that uses a liquid electrolyte that is injected into the cell when it is being charged and discharged. They have the potential to provide large-scale energy storage for grid-level applications [30].

22 Table 1 Battery used in electrochemical energy storage application with their type, mechanism, and reaction type

S. Nikhar et al.

Battery type

Mechanism name

Reaction type

Lead-acid

Redox

Discharge

Lithium-ion

Intercalation

Charge/discharge

Nickel–cadmium

Redox

Charge/discharge

Sodium-sulfur

Redox

Charge/discharge

Flow

Redox

Charge/discharge

Nickel-metal hydride

Redox

Charge/discharge

Zinc-carbon

Discharge

Discharge

Alkaline

Discharge

Discharge

Nickel-zinc

Redox

Charge/discharge

Lithium-polymer

Intercalation

Charge/discharge

Zinc-air

Discharge

Discharge

Silver-zinc

Redox

Charge/discharge

Lithium-sulfur

Redox

Charge/discharge

Lead–carbon

Redox

Charge/discharge

Nickel–iron

Redox

Charge/discharge

Development of supercapacitors: Electrochemical capacitors, often known as supercapacitors, can store and deliver electrical energy very quickly, making them suitable for applications that require fast charging and discharging. Researchers are working on improving the energy density of supercapacitors to make them more practical for use in portable electronic devices and electric vehicles [31]. Table 1 shows the batteries with applicability in electrochemical storage devices.

3.2 Fuel Cells Electrochemical energy conversion devices that produce electricity by electrochemically mixing fuel and an oxidant are known as fuel cells. Since they can run constantly if the fuel and oxidant are available, they are sometimes seen as a battery alternative for storing electrical energy [32]. Fuel cells are categorized according to the type of electrolyte used. Such as solid oxide fuel cells (SOFCs), phosphoric acid fuel cells (PAFCs), proton exchange membrane fuel cells (PEMFCs), alkaline fuel cells (AFCs), and molten carbonate fuel cells (MCFCs) [32]. The anode of a fuel cell is where the fuel is oxidized to generate protons and electrons. The protons are transported through an ion-conducting electrolyte to the cathode, where they react with oxygen to produce water. The electrons, on the other hand, are forced to travel through an external circuit to reach the cathode, generating an electrical current [32]. Figure 5 shows the working mechanism of the fuel cell, The overall reaction can be expressed as:

Design/Types of Electrochemical Energy Devices

23

Fig. 5 Scheme diagram for working of a fuel cell: adapted from Ref. [35]. Copyright The Authors, some rights reserved; exclusive licensee EDP Science. Distributed under a Creative Commons Attribution License 4.0

Fuel + Oxidant → Electricity + Water One of the main advantages of fuel cells is their high efficiency, which can reach up to 60–80% depending on the type of fuel cell [33]. They are also relatively quiet, produce no emissions, and have a long lifespan compared to batteries. However, fuel cells have a higher cost and require a continuous supply of fuel and oxidants, which limits their practical applications [33]. One of the most widely used fuel cells is the PEMFC, which uses a protonconducting polymer membrane as the electrolyte. PEMFCs operate at relatively low temperatures (around 80 °C) and have a fast response time, making them suitable for portable and transportation applications. AFCs, on the other hand, use an aqueous alkaline solution as the electrolyte and can operate at higher temperatures (up to 300 °C). AFCs have a higher energy density and are more tolerant to impurities, but they suffer from a slower response time and lower efficiency compared to PEMFCs. PAFCs, MCFCs, and SOFCs are also used in various applications, but they have lower efficiencies and higher operating temperatures compared to PEMFCs and AFCs [34] (Table 2).

3.3 Hybrid System Hybrid systems for EEDs have received a considerable amount of focus recently because of their potential to improve the efficiency and performance of energy storage systems. These systems typically combine two or more different types of energy

24

S. Nikhar et al.

Table 2 Different types of fuel cells Fuel cell type

Mechanism name

Reaction type

Proton exchange membrane fuel cell (PEMFC)

Proton-exchange

Electrolysis

Alkaline fuel cell (AFC)

Hydrogen–oxygen

Electrolysis

Phosphoric acid fuel cell (PAFC)

Hydrogen–oxygen

Electrolysis

Solid oxide fuel cell (SOFC)

Oxygen-ion

Oxidation–reduction

Direct methanol fuel cell (DMFC)

Hydrogen–oxygen

Electrolysis

Molten carbonate fuel cell (MCFC)

Hydrogen–oxygen

Electrolysis

Polymer electrolyte membrane fuel cell (PEMFC) Proton-exchange

Electrolysis

Direct carbon fuel cell (DCFC)

Hydrogen–oxygen

Electrolysis

Regenerative fuel cell (RFC)

Hydrogen–oxygen

Electrolysis

Zinc-air fuel cell (ZAFC)

Hydrogen–oxygen

Electrolysis

Bacterial fuel cell (BFC)

Microbial metabolism Oxidation–reduction

Enzyme-based fuel cell (EBFC)

Enzyme-catalysed

Bio electrochemical system (BES)

Microbial metabolism Oxidation–reduction

Organic fuel cell (OFC)

Redox reactions

Oxidation–reduction

Hydrogen fuel cell (HFC)

Hydrogen–oxygen

Electrolysis

Electrolytic fuel cell (EFC)

Hydrogen–oxygen

Electrolysis

Biofuel cell (BFC)

Microbial metabolism Oxidation–reduction

Microbial fuel cell (MFC)

Microbial metabolism Oxidation–reduction

Enzymatic fuel cell (EZFC)

Enzyme-catalysed

Oxidation–reduction

Direct ethanol fuel cell (DEFC)

Hydrogen–oxygen

Electrolysis

Oxidation–reduction

storage technologies, such as batteries and supercapacitors, to achieve better overall performance. The working principle of hybrid systems for EEDs involves the use of different energy storage technologies in combination to achieve better overall performance and efficiency [36]. A hybrid supercapacitor serves as an illustration of a hybrid system, it combines the high energy density of a battery with the highpower density of a supercapacitor. The working principle of a hybrid supercapacitor involves the use of two different types of electrodes: one that can store energy through an electrochemical reaction and another that can store energy through electrostatic attraction. These two types of electrodes are typically connected in parallel, allowing the device to store and discharge energy quickly while also maintaining a high energy density [2]. The supercapacitor or other energy storage device is used to improve the overall power density and cycling stability of the battery, while the LIBs provide the necessary energy density. Table 3 Gives an idea about the types of hybrid systems available as EEDs.

Design/Types of Electrochemical Energy Devices

25

Table 3 Hybrid system types Type of hybrid system

Working mechanism

Reaction type

Redox flow battery hybrid

Energy is stored in the redox flow battery and used to power an electrochemical reaction in the other component

Redox reactions

Battery-supercapacitor hybrid

Energy is stored in the battery and used to power an electrochemical reaction in the supercapacitor

Redox reactions

Fuel cell-battery hybrid

Energy is stored in the battery and used to power a chemical reaction in the fuel cell

Electrolysis

Thermal energy storage-battery hybrid

Energy is stored in the battery and used to power a thermal energy storage system

Not applicable

Hybrid flow battery-supercapacitor system

Energy is stored in the flow battery and used to power Redox an electrochemical reaction in the supercapacitor reactions

Solar panel-battery hybrid system

Energy from the solar panel is used to charge the battery, which can then be used to power an electrical load

Not applicable

LIBs-redox flow battery Energy is stored in the LIBs and used to power an hybrid electrochemical reaction in the redox flow battery

Redox reactions

Hybrid solid-state lithium battery-supercapacitor system

Energy is stored in the lithium battery and used to power an electrochemical reaction in the supercapacitor

Redox reactions

Nickel-metal hydride battery-supercapacitor hybrid

Energy is stored in the nickel-metal hydride battery and used to power an electrochemical reaction in the supercapacitor

Redox reactions

Hybrid energy storage system using phase change materials

Energy is stored in phase change materials and used to Not power an electrical load applicable

4 Challenges and Opportunities for Improving Electrochemical Energy Devices Batteries and fuel cells are examples of EEDs that are crucial technologies for storing and transforming chemical energy into electricity. However, there are several challenges and opportunities for improving these devices to increase their efficiency, durability, and sustainability. One major challenge is the development of highperformance, low-cost electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) [37]. The effectiveness of metal-air batteries and fuel cells depends on these processes, but they are often limited to using expensive and scarce precious metal catalysts, such as platinum and iridium. Attempts to develop non-precious metal catalysts other than precious metals, such as nitrogendoped carbon materials and transition metal oxides, have shown promise, but there is still room for improvement in terms of their activity and stability [38].

26

S. Nikhar et al.

4.1 Increasing Energy Density and Power Density Electrochemical energy devices play a crucial role in providing portable and renewable energy solutions. However, several challenges need to be addressed to improve their performance and increase their adoption. One of the most difficult issues is boosting the energy and power density of these devices. The quantity of energy held per unit of mass or volume is known as energy density. While, power density refers to the rate at which energy can be delivered per unit mass or volume. These two factors are important for portable and mobile applications as they determine the size, weight, and runtime of the device [39]. There are several approaches to improving the energy density and power density of EEDs. One approach is to use high-energy–density materials as electrodes and electrolytes. For example, in LIBs lithium is used as the anode material, which offers a high energy density. However, the use of lithium can be limited due to cost and availability issues. Therefore, researchers are exploring alternative materials, such as silicon and graphene, which have a higher energy density but are still facing challenges in terms of their stability and cycling performance [40]. Additionally, using a hybrid device, such as a battery-supercapacitor hybrid, can improve the power density and extend the lifespan of the device [41]. There are also several opportunities for improving EEDs by increasing their energy density and power density. Another approach is to charge these devices using renewable/sustainable energy sources like the sun and wind. This can reduce the reliance on fossil fuels and decrease the carbon footprint of the devices. Additionally, the use of smart grids and energy management systems can improve the efficiency of these devices by optimizing the charging and discharging process [42].

4.2 Improving Lifetime and Durability Electrochemical energy storage devices despite having many applicability challenges in improving the lifetime and durability of these devices. Further, some of the key challenges and opportunities for improving the lifetime and durability of EEDs have been discussed. One of the main challenges facing EEDs is their limited lifetime. Batteries, for example, degrade over time due to a variety of factors, such as electrode degradation and the development of solid electrolyte interphase (SEI) layers [41]. Fuel cells are also subject to degradation over time, with factors such as membrane degradation and catalyst poisoning. Improving the lifetime of these devices is critical for their widespread adoption in a variety of uses including grid-scale energy storage and electric vehicles [32]. The development of novel materials represents one of the primary potentials for increasing the longevity of EEDs. For example, researchers have been investigating new electrode materials, such as silicon and lithium metal, which have the potential to significantly increase the energy density of batteries [43].

Design/Types of Electrochemical Energy Devices

27

The development of novel manufacturing techniques is one of the best ways to increase the robustness of EEDs. For example, investigating new methods for producing battery electrodes, such as three-dimensional printing, which have the potential to improve the mechanical stability of the electrodes [43, 44].

4.3 Reducing Environmental Impact Recent advancements in the materials, manufacturing processes, and recycling and disposal methods for EEDs have the potential to increase their sustainability and decrease their environmental impact. These devices are essential for powering numerous applications, including portable electronics and electric vehicles. However, the production and disposal of these devices can have a significant impact on the environment. The challenges and opportunities associated with improving these devices while minimizing environmental harm are a topic of ongoing research and discussion. One of the paramount challenges in enhancing the performance of EEDs is the identification and implementation of more efficient and cost-effective materials. The utilization of materials such as lithium and cobalt in LIBs, while common, presents limitations as they are considered rare and expensive, thereby rendering them less environmentally sustainable and accessible. To overcome these limitations, researchers are investigating alternative materials such as silicon and lithiumsulfur, which exhibit the potential to improve performance while decreasing costs [45]. Furthermore, Sodium-ion batteries (NIBs) have been proposed as an alternative due to their utilization of abundant and inexpensive materials, such as sodium and aluminum, while maintaining high performance and low cost [45]. Another challenge is the need for improved manufacturing processes to reduce the environmental impact caused by these devices. Methods that are energy-efficient and produce fewer emissions need to be developed. For example, using renewable energy sources during production or recycling materials and by-products can mitigate the impact. Moreover, recycling critical metals such as cobalt, lithium, nickel, and manganese can have a positive impact on the environment by reducing greenhouse gas emissions, energy consumption, and the use of primary resources.

5 Integrating Electrochemical Energy Devices into Energy Systems Batteries and fuel cells are two examples of EEDs that have the potential to be very important in the integration of renewable energy sources into the grid. These devices can store energy produced by intermittent sources, like wind and solar, and release it when necessary to fulfil demand. Some of them are explained below.

28

S. Nikhar et al.

5.1 Stationary Energy Storage Stationary energy storage systems are critical components for integrating EEDs into modern energy systems. These systems serve as a buffer between the intermittent and variable generation of renewable energy sources and the constant demand for energy from the grid. By holding extra energy in reserve during times of low demand and releasing it when demand is high, stationary energy storage systems enable more efficient and stable integration of renewable energy sources into the grid [46]. Overall, the integration of EEDs into energy systems requires the use of stationary energy storage systems to buffer the variable and intermittent generation of renewable energy sources. Both LIBs and redox flow batteries are widely researched and implemented types of stationary energy storage systems that have shown great potential for meeting the energy storage needs of modern energy systems.

5.2 Portable Electronic Devices Portable electronic devices have become an integral part of modern society, with a wide range of applications in both personal and professional settings. These devices, such as smartphones, laptops, and tablets, rely on energy storage devices to function, which is typically in the form of rechargeable batteries. The integration of EEDs into portable electronic devices enables their use in various locations and settings, without being tethered to an electrical outlet [47]. A widely used type of EEDs for portable electronic devices is LIBs. These batteries have a high energy density, long life, and low self-discharge rate, making them wellsuited for portable electronic devices. Additionally, recent advancements in materials science and engineering have led to the development of LIBs with improved safety and performance characteristics, further increasing their viability as energy storage devices for portable electronic devices [46]. Despite EEDs solid state batteries (SSBs) are also used ae portable electronic devices. These SSBs use a solid electrolyte, rather than a liquid electrolyte as in LIBs, which can increase safety and improve the performance characteristics of the device. Recently researchers are more interested in using solid-state batteries in portable electronic devices as they exhibit good cycle performance, high energy density, and safety advantages [48].

5.3 Electric Vehicles Electric vehicles (EVs) also rely on electrochemical energy storage devices, specifically batteries, to power their electric motors. EVs offer several advantages over traditional gasoline-powered vehicles, including lower operating costs, lower emissions, and increased energy security, by reducing dependence on fossil fuels [49]. The

Design/Types of Electrochemical Energy Devices

29

use of electric vehicles is expected to continue to grow in coming years as the technology improves and costs continue to decrease. To the greatest of requirements and customer satisfaction, the current generation LIBs are still unable to power electric vehicles. The limiting factors include charging times, safety issues, the distance, and the price. The current generation of LIBs does not meet the requirements for use in electric vehicles in terms of safety, energy density, power density, and cyclic stability to use more technical terms. Therefore, our goal has been to develop nanostructured electrode materials, such as active nanoparticles (such as LiFePO4 , LiNiMnCoO2 , SiO2 , etc.), graphenic carbon, “decorating” conducting reinforcements (graphene or carbon nanotubes), Si nanowires, etc., via careful optimization/ management of the processing conditions. In addition to the detailed materials and electrochemical studies/engineering, In-depth investigations/understandings are also conducted using several new in situ techniques such as phase evolutions in electrodes during electrochemical Li-insertion/removal and stress monitoring during discharge/charge) [49].

6 Future Research Directions in Electrochemical Energy Device Design and Technology Since the demand for clean and sustainable energy sources continues to grow, EEDs such as batteries and fuel cells have emerged as promising technologies for meeting this demand. However, there are still several obstacles to overcome before the full potential of these technologies can be realized. We will discuss the current state of the art in electrochemical energy device design and technology and highlight some of the key areas in which future research is needed. One of the most significant fields of study in the field of EEDs is the development of more efficient and stable electrodes. Since LIBs are widely used in a variety of applications, it have high energy densities but also faces issues of capacity fading, safety, and thermal stability. Hence, current research focuses on the creation of novel electrode materials, such as silicon and tin, which have the opportunity for major advancement in the energy density and stability of LIBs [50]. Additionally, advanced fabrication techniques, such as 3D printing, are being investigated as a way to create more complex and efficient electrode structures.

7 Conclusion In conclusion, EEDs play a vital role in the transition towards clean and sustainable energy sources. The design and types of these devices are crucial to achieving high performance and efficiency. The chapter has provided an overview of the current state of the art in electrochemical energy device design and technology, including

30

S. Nikhar et al.

the principles of design, materials used in construction, electrolyte materials, and performance parameters. The different types of EEDs, such as batteries, fuel cells, and hybrid systems were also discussed, each with its unique characteristics and applications. Despite their potential, there are still several challenges that must be addressed to progress the performance of EEDs. Research efforts are being directed towards increasing energy density and power density, improving lifetime and durability, and reducing environmental impact. The integration of these devices into larger energy systems such as stationary energy storage, portable electronic devices, and electric vehicles also poses challenges and opportunities for future research.

References 1. Trahey L, Brushett FR, Balsara NP, Ceder G, Cheng L, Chiang YM, Crabtree GW (2020) Energy storage emerging: a perspective from the Joint Center for Energy Storage Research. Proc Natl Acad Sci 117(23):12550–12557 2. Kamel AA, Rezk H, Abdelkareem MA (2021) Enhancing the operation of fuel cellphotovoltaic-battery-supercapacitor renewable system through a hybrid energy management strategy. Int J Hydrogen Energy 46(8):6061–6075 3. Xing F, Bi Z, Su F, Liu F, Wu ZS (2022) Unraveling the design principles of batterysupercapacitor hybrid devices: from fundamental mechanisms to microstructure engineering and challenging perspectives. Adv Energy Mater 12(26):2200594 4. Wilberforce T, Alaswad A, Palumbo A, Dassisti M, Olabi AG (2016) Advances in stationary and portable fuel cell applications. Int J Hydrogen Energy 41(37):16509–16522 5. Kennedy KM, Ruggles TH, Rinaldi K, Dowling JA, Duan L, Caldeira K, Lewis NS (2022) The role of concentrated solar power with thermal energy storage in least-cost highly reliable electricity systems fully powered by variable renewable energy. Adv Appl Energy 6:100091 6. Hannan MA, Lipu MH, Hussain A, Mohamed A (2017) A review of lithium-ion battery state of charge estimation and management system in electric vehicle applications: challenges and recommendations. Renew Sustain Energy Rev 78:834–854 7. Emmett RK, Roberts ME (2021) Recent developments in alternative aqueous redox flow batteries for grid-scale energy storage. J Power Sources 506:230087 8. Liu J, Wang J, Xu C, Jiang H, Li C, Zhang L, Shen ZX (2018) Advanced energy storage devices: basic principles, analytical methods, and rational materials design. Adv Sci 5(1):1700322 9. Navarro-Suárez AM, Shaffer MS (2022) Designing structural electrochemical energy storage systems: a perspective on the role of device chemistry. Front Chem 9:810781 10. Li S, Zhang SQ, Shen L, Liu Q, Ma JB, Lv W, Yang QH (2020) Progress and perspective of ceramic/polymer composite solid electrolytes for lithium batteries. Adv Sci 7(5):1903088 11. Weber AZ, Mench MM, Meyers JP, Ross PN, Gostick JT, Liu Q (2011) Redox flow batteries: a review. J Appl Electrochem 41:1137–1164 12. Phuc NHH, Xian OY, Atsunori M (2020) New developments in hydrogen fuel cells. New Dimens Prod Util Hydrog 273–298 13. Ram F, Shanmuganathan K (2021) Nanocellulose-based materials and composites for fuel cells. Nanocellulose Based Compos Electron 259–293 14. Zhao W, Rubio SJB, Dang Y, Suib SL (2022) Green electrochemical energy storage devices based on sustainable manganese dioxides. ACS ES T Eng 2:20–42 15. Dhas SD, Maldar PS, Patil MD, Waikar MR, Sonkawade RG, Moholkar AV (2022) Sol-gel synthesized nickel oxide nanostructures on nickel foam and nickel mesh for a targeted energy storage application. J Energy Storage 47:103658 16. Raccichini R, Varzi A, Passerini S, Scrosati B (2014) The role of graphene for electrochemical energy storage. Nat Mater 14(3):271–279

Design/Types of Electrochemical Energy Devices

31

17. Pumera M (2011) Graphene -based nanomaterials for energy storage. Energy Environ Sci 4:668–674 18. Baumann AE, Burns DA, Liu B, Thoi VS (2019) Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices. Commun Chem 21(2):1–14 19. Zhao Y, Song Z, Li X, Sun Q, Cheng N, Lawes S, Sun X (2016) Metal organic frameworks for energy storage and conversion. Energy Storage Mater 2:35–62 20. Shahul Hameed A, Nagarathinam M, Schreyer M, Reddy MV, Chowdari BVR, Vittal JJ (2013) A layered oxalatophosphate framework as a cathode material for Li-ion batteries. J Mater Chem A 1:5721–5726 21. Li X, Cheng F, Zhang S, Chen J (2006) Shape-controlled synthesis and lithium-storage study of metal-organic frameworks Zn4O(1,3,5-benzenetribenzoate)2. J Power Sources 160:542–547 22. Gou L, Hao LM, Shi YX, Ma SL, Fan XY, Xu L, Li DL, Wang K (2014) One-pot synthesis of a metal–organic framework as an anode for Li-ion batteries with improved capacity and cycling stability. J Solid State Chem 210:121–124 23. Gogotsi Y, Anasori B (2019) The rise of MXenes. ACS Nano 13:8491–8494 24. Anasori B, Lukatskaya MR, Gogotsi Y (2017) 2D metal carbides and nitrides (MXenes) for energy storage. Nat Rev Mater 22(2):1–17 25. Parsimehr H, Ehsani A (2020) Algae-based electrochemical energy storage devices. Green Chem 22:8062–8096 26. Xia L, Yu L, Hu D, Chen GZ (2017) Electrolytes for electrochemical energy storage. Mater Chem Front 1:584–618 27. Iqbal MZ, Zakar S, Haider SS (2020) Role of aqueous electrolytes on the performance of electrochemical energy storage device. J Electroanal Chem 858:113793 28. Xiang J, Wei Y, Zhong Y, Yang Y, Cheng H, Yuan L, Huang Y (2022) Building practical high-voltage cathode materials for lithium-ion batteries. Adv Mater 2200912 29. Wang H, Chen S, Fu C, Ding Y, Liu G, Cao Y, Chen Z (2021) Recent advances in conversion-type electrode materials for post lithium-ion batteries. ACS Mater Lett 3(7):956–977 30. Fan X, Liu B, Liu J, Ding J, Han X, Deng Y, Zhong C (2020) Battery technologies for grid-level large-scale electrical energy storage. Trans Tianjin Univ 26:92–103 31. Beidaghi M, Gogotsi Y (2014) Capacitive energy storage in micro-scale devices: recent advances in design and fabrication of micro-supercapacitors. Energy Environ Sci 7(3):867–884 32. Ibrahim OA, Navarro-Segarra M, Sadeghi P, Sabaté N, Esquivel JP, Kjeang E (2022) Microfluidics for electrochemical energy conversion. Chem Rev 122(7):7236–7266 33. Alaswad A, Omran A, Sodre JR, Wilberforce T, Pignatelli G, Dassisti M, Olabi AG (2020) Technical and commercial challenges of proton-exchange membrane (PEM) fuel cells. Energies 14(1):144 34. Aminudin MA, Kamarudin SK, Lim BH, Majilan EH, Masdar MS, Shaari N (2022) An overview: current progress on hydrogen fuel cell vehicles. Int J Hydrogen Energy 35. O’Hayre RP (2017) Fuel cells for electrochemical energy conversion. In: EPJ Web of conferences, vol 148. EDP Sciences, p 00013 36. Hassan F, Jamil F, Hussain A, Ali HM, Janjua MM, Khushnood S, Li C (2022) Recent advancements in latent heat phase change materials and their applications for thermal energy storage and buildings: a state of the art review. Sustain Energy Technol Assess 49:101646 37. Ahmed MS, Choi B, Kim YB (2018) Development of highly active bifunctional electrocatalyst using Co3 O4 on carbon nanotubes for oxygen reduction and oxygen evolution. Sci Rep 8(1):2543 38. Bhatt MD, Lee JY (2020) Advancement of platinum (Pt)-free (non-Pt precious metals) and/ or metal-free (non-precious-metals) electrocatalysts in energy applications: a review and perspectives. Energy Fuels 34(6):6634–6695 39. Cerdas F, Titscher P, Bognar N, Schmuch R, Winter M, Kwade A, Herrmann C (2018) Exploring the effect of increased energy density on the environmental impacts of traction batteries: a comparison of energy optimized lithium-ion and lithium-sulfur batteries for mobility applications. Energies 11(1):150

32

S. Nikhar et al.

40. Wang C, Yang C, Zheng Z (2022) Toward practical high-energy and high-power lithium battery anodes: present and future. Adv Sci 9(9):2105213 41. Gao S, Zhang L, Qiao Y, Dong P, Shi J, Cao S (2016) Electrodeposition of polyaniline on threedimensional graphene hydrogel as a binder-free supercapacitor electrode with high power and energy densities. RSC Adv 6(64):58854–58861 42. Huang Y, Wang L, Guo W, Kang Q, Wu Q (2016) Chance constrained optimization in a home energy management system. IEEE Trans Smart Grid 9(1):252–260 43. Li J, Adewuyi K, Lotfi N, Landers RG, Park J (2018) A single particle model with chemical/ mechanical degradation physics for lithium-ion battery state of health (SOH) estimation. Appl Energy 212:1178–1190 44. Kidambi PR, Chaturvedi P, Moehring NK (2021) Subatomic species transport through atomically thin membranes: present and future applications. Science 374(6568):eabd7687 45. Liu T, Zhang Y, Jiang Z, Zeng X, Ji J, Li Z, Liang C (2019) Exploring competitive features of stationary sodium ion batteries for electrochemical energy storage. Energy Environ Sci 12(5):1512–1533 46. Olabi AG, Wilberforce T, Sayed ET, Abo-Khalil AG, Maghrabie HM, Elsaid K, Abdelkareem MA (2022) Battery energy storage systems and SWOT (strengths, weakness, opportunities, and threats) analysis of batteries in power transmission. Energy 254:123987 47. Tu J, Torrente-Rodríguez RM, Wang M, Gao W (2020) The era of digital health: a review of portable and wearable affinity biosensors. Adv Func Mater 30(29):1906713 48. Kim JG, Son B, Mukherjee S, Schuppert N, Bates A, Kwon O, Park S (2015) A review of lithium and non-lithium based solid state batteries. J Power Sources 282:299–322 49. Aijaz I, Ahmad A (2022) Electric vehicles for environmental sustainability. In: Smart technologies for energy and environmental sustainability, pp 131–145 50. Wang W, Xie Z, Li K, Yu S, Ding L, Zhang FY (2022) Recent progress in in-situ visualization of electrochemical reactions in electrochemical energy devices. Curr Opin Electrochem 101088

Polymer-Based Electrolytes Tapas Das, Sanjeev Verma, Vikas K. Pandey, and Bhawna Verma

Abstract The extensive use of electronic devices in various fields of medical science, self-automated robots, roll-up displays, and wearable devices has increased the demand for portable energy storage devices. The energy storage devices have the potential to withstand the fear of fossil fuel scarcity along with controlling global warming. There are various energy storage devices like capacitors, fuel cells, supercapacitors, and batteries. Out of all these energy storage devices, supercapacitors and batteries are capturing the attention of researchers and industrialists due to their high specific energy, specific power, cycle life, cost, and portability. Electrolyte plays a vital role in enhancing electrochemical performances and the cycle life. Aqueous, ionic, and polymer electrolytes are used in batteries and supercapacitors. The corresponding electrolyte has its advantages and disadvantages. Aqueous electrolytes exhibit high specific capacitance, but they have spillage issues. Ionic electrolytes have a very wide potential window but the ion mobility is very slow, which results in lower specific capacitances. But polymer electrolytes do not have a spillage issue and can provide a good potential stability window, thereby enhancing the energy density of the system. The research on various polymer electrolytes will be discussed extensively. Finally, the existing issues along with perspectives have been addressed in this chapter. Keywords Nanowire · Flexible device · Supercapacitor · Battery · Nanomaterial

T. Das · S. Verma · V. K. Pandey · B. Verma (B) Department of Chemical Engineering and Technology, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India e-mail: [email protected] T. Das National Institute of Technology, Rourkela, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_3

33

34

T. Das et al.

1 Introduction One of the most significant worldwide challenges is the development of technology that can replace non-renewable energy sources and slow down the depletion of limited fossil fuels [1, 2]. Electrochemical energy storage, like batteries and supercapacitors, perform better than other devices because of their high specific energy, ease of maintenance, lightweight, and tremendous electrochemical potentials [3–7]. However, the widespread use of extremely volatile and explosive organic solvents in the liquidbased electrolytes used in lithium batteries limits the batteries’ long-term viability as there are safety concerns regarding the risk of fire and explosion. Additionally, solid-polymer electrolyte interphase (SEI) layers are unstable and frequently occur when highly active lithium metal reacts with liquid electrolytes, leading to the development of dangerous lithium dendrites [8]. Studies on solid polymer electrolytes, which can replace liquid electrolytes and help resolve these problems, have recently increased [9]. Polymer electrolytes-based electrochemical energy storage devices can achieve a better energy density by using fewer electrolytes. Additionally, electrochemical energy storage devices based on polymer electrolytes will be secure and have a long lifespan. Solid electrolytes are often divided into two categories: solid electrolytes based on polymers (PSEs) and inorganic solid electrolytes (ISEs). Solid sulfide electrolytes and solid oxide electrolytes make up the majority of the constituent ISE materials. Numerous solid oxide electrolytes, including perovskite-type, Na super conductor (NASICON) ionic-type, garnet-type, and LixPOyNz (LiPON)-based materials, as well as solid sulphide electrolytes, including glass–ceramic Li2SP2S5, Li10GeP2S12 (LGPS), and thio-Li superionic conductor (thio-LISICON) have been developed due to their reasonable electrochemical stability and high ionic conductivity under ambient conditions [10]. However, all these ISEs have a high interfacial resistance due to their stiffness and brittleness as well as their low mechanical compliance with the electrodes. PSEs provide good processability, excellent safety, and improved mechanical compatibility with electrodes because they combine an alkali metal salt-free solid matrix with a polymer host in place of a liquid solvent. Although foldable solid-state electrochemical energy storage devices are essential power accessories for the rapidly evolving wearable and flexible electronic devices, their increased flexibility will make them especially well-suited for these applications [11]. More importantly, the PSEs’ strong adhesivity, lowers interface charge transfer resistance, as well as improved interfacial stability, can account for the fluctuations in electrode volume that take place during cycling [12]. However, compared to liquid electrolytes and ISEs, most of the single-component polymer electrolytes have lower ionic conductivities. PSEs for energy storage, especially lithium batteries, need naturally have higher values of ionic conductivities above 10–4 S/cm to assure stable functioning. PSEs’ ionic conductivity can be increased by adding liquid plasticizers to the polymer, but this comes at the expense of their mechanical qualities [13]. Because of this, rigidityconductivity inconsistencies and non-uniform ion distribution frequently occur in

Polymer-Based Electrolytes

35

Fig. 1 Polymer electrolyte development and characteristics

polymer electrolytes. To make matters worse, the anode of lithium batteries may occasionally produce harmful lithium dendrites. On the contrary side, it has recently been shown that a variety of popular polymer matrix architectures and the introduction of inorganic fillers (such as active fast-ion conductive materials and inert ceramics) to PSEs are efficient ways to attain higher values of ionic conductivities to enable high-performance electrochemical energy storage without compromising the other different benefits of PSEs (Fig. 1). In order to fully understand the impact that polymer matrices play in the performance of the electrolyte, we outline the most recent developments of the stateof-the-art PSEs in this chapter. The focus then shifts to two distinct types of PSE: solid polymer composite electrolytes (SPCEs) and PSEs with structurally engineered polymer matrix. In addition, PSE applications in today’s hotly debated fields are introduced. These electrochemical energy storage devices include flexible lithiumion batteries, lithium-sulfur batteries, and lithium-ion all-solid-state batteries A few perspectives and prospective approaches for PSEs are provided in the final section.

2 Polymer Matrices for Polymer Electrolytes Even though single-component polymer electrolytes find it challenging to meet all requirements at once due to the rapid development of various energy storage devices, research on the fundamental chemical structures of single-component polymer matrices can offer a solid basis and clear directions to assist in the investigations of multicomponent polymer-based electrolytes with exceptional performances. The structural features of PSEs and the most popular polymer matrices have been shown in Fig. 2.

36

T. Das et al.

Fig. 2 Chemical structures of various polymer matrices in polymer electrolyte

2.1 Polyacrylonitrile Polyacrylonitrile (PAN), comprising the electron-withdrawing and polar and C≡N, has a wide electrochemical window, excellent electrochemical stability, significant mechanical strength, and great thermal stability. Particularly, PAN-based electrolytes, due to their high oxidation resistance potential are suitable for high-voltage cathode materials with higher energy density [14]. In PAN/LiClO4 -based systems, Li ions can establish comb-like connections with up to four C-N groups in the PAN chain. However, the ionic conductivity of a dry PAN/LiClO4 solid polymer electrolyte is still as low as ~ 10–7 S/cm, which is comparable to a PEO-based electrolyte [15]. The PAN-based electrolyte’s ionic conductivity can occasionally be controlled by the movement of PAN polymer chains despite reports that LiTFSI could lower the crystallinity of PAN [16]. This is in contrast to the mechanism exhibited by PEObased solid electrolytes. However, in LiTFSI, the imide anion, which has a huge ion delocalization that makes ion dissociation easier, is stabilized by two powerful electron-withdrawing groups on the nitrogen atom. In some cases, ionic conductivities of up to ~ 10–6 S/cm have been recorded for dry LiTFSI-PAN solid polymer electrolytes [17]. Wang and coworkers showed that plasticizers may effectively prevent the connections between PAN and Li+ and boost PAN-based solid electrolytes’ ionic conductivity [18]. The addition of inorganic fillers to PAN is an alternative method to plasticizers for enhancing ionic conductivity. Additionally, the research group of Wang demonstrated that the surface-modified ceramic fillers could serve as charge carrier sources, improving ionic conductivity according to the Lewis acid–base theory [19]. PAN is not readily soluble in the majority of volatile solvents, such as methanol, acetone, and THF but is commonly dissolved in organic solvents having a high boiling

Polymer-Based Electrolytes

37

point, such as dimethylsulfoxide (DMSO) or N, N-dimethylformamide (DMF) to produce a homogeneous polymer solution. However, these solvents require a lot of energy to evaporate, which could pose a problem for the mass production of PAN-based PSEs [20].

2.2 Poly(Ethylene Oxide) Due to its excellent mechanical characteristics and outstanding compatibility with electrodes, high molecular weight poly(ethylene oxide) (PEO) has received a lot of attention for energy storage applications and mainly lithium polymer batteries as a polymer matrix. The repeat units of the polymer chain, –CH2–CH2–O–, have been shown to contain lithium ions, and the backbone’s segmental motion provides adequate ion dynamics [21]. However, semicrystalline PEO has a low ionic conductivity at ambient temperature because of the dense chain packing, which precludes it from effectively transporting lithium ions [22]. It is commonly accepted that ion transport through main-chain segmental movements rises fast upon lowering crystallinity or rising temperature above the glass-transition temperature. In contrast to conventional inorganic alkali salts, LiTFSI (bis(trifluoromethane) sulfonamide lithium) exhibits high thermal, chemical, and electrochemical stability and possesses a flexible anion, CF3 -SO2 -N-SO2 -CF3 − (TFSI− ). This anion helps reduce the crystallinity of PEO chains. Additionally, a TFSI− with a highly delocalized charge distribution may have weaker interactions with Li+ and TFSI− , which would promote the dissociation of lithium salts [23]. For lithium-ion batteries with this kind of PSEs, the operating temperature must be more than 60 °C. These PSEs would melt and lose their dimensional stability at such high temperatures, which would lead to non-homogeneity and a reduced capacity to control the development of Li dendrites during cycling.

2.3 Polyacrylates The lithium salts are easily dissociated by the functional ester groups of polyacrylates (PAs), which can donate electrons and can interact with the cations of alkali salts. Additionally, PAs are economical and have strong interfacial compatibilities. These benefits make PAs promising as PSE matrices. Generally, polycyanoacrylate (PCA) and polymethyl methacrylate (PMMA) are two popular alternatives [24]. At 25 °C, PMMA has a 96% amorphous content, making it a lightweight and translucent polymer that is ideal for facilitating ion transport [25]. Fourier transforms infrared (FTIR) spectroscopy was used by Shukla and Thakur to prove that the PMMA matrix’s –C=O is the only place where Li+ may coordinate [26]. PMMA possesses the advantages listed above, however, its brittleness and frequent poor ionic conductivity at room temperature preclude their use in real-world applications. For

38

T. Das et al.

PMMA-based PSEs, practical solutions have been implemented to overcome these problems, including the addition of liquid plasticizers and surfactants, the addition of inorganic fillers, and the blending with other polymers. The functional nitrile group in PCA, another promising PA-based matrix, provides great electrochemical stability and excellent binding. Additionally, the interaction of Li ions with ester and nitrile groups in PCA facilitates the dissolution of the salt and the transmission of charge. Future-based rechargeable Li batteries, mainly high-potential window batteries with huge specific energy, seem to be a perfect candidate for PCA-based polymer electrolytes, in light of these advantages [27]. However, PCA-based electrolytes typically need liquid solvents as plasticizers to increase ionic conductivity, which results in PCA-based electrolytes having insufficient mechanical properties and high flammability.

2.4 Aliphatic Polycarbonates Due to their extremely polar carbonate groups and oxygen atoms that coordinate with Li+ , aliphatic polycarbonates (APCs) have been shown to be substitute polymer matrices for PSEs. APCs may have a higher dielectric constant and better salt solubility due to the sequential arrangement of their polar carbonate groups [28]. Different APCs have been employed in PSEs for future-generation lithium batteries since they offered good compatibility with Li metal, a wide electrochemical window, and improved ionic conductivity. These APCs include poly(trimethylene carbonate) (PTMC), poly(vinylene carbonate) (PVC), poly(ethylene carbonate) (PEC), and poly(propylene carbonate) (PPC). In PSEs built on APCs, segmental motion, local relaxation, and amorphous phase all aid in Li-ion conduction [29]. Additionally, Wang et al. employed PPC to show that sectional breakdown of polymer might reduce the degree of crystallinity in the case of APCs when in close enough proximity to the Li electrode [30]. The interfacial resistance would decrease with degrading products entering the space between the electrolyte and Li metal. As a consequence, the ionic conductivity of APC-based electrolytes has greatly increased. They frequently have worse mechanical strength, though. In order to address this problem, new substrates for APC-based systems have been added, including three-dimensionally organized macroporous polyimide, polybutadiene rubber, rigid frame cellulose nonwoven, and polyurethane [31]. Even though a number of polymer matrices, such as PAN, PEO, PAs, and APCs, have shown promising properties in PSEs, several problems such as lower electrochemical window for PEO, and low ionic conductivity, instability of PAN against Li, and inferior mechanical strength for Pas and APCs which restricts their use in real-world applications. It is urgently necessary to develop new polymer matrices with a wide electrochemical window at room temperature, remarkable mechanical stability, and strong ionic conductivity.

Polymer-Based Electrolytes

39

3 Polymer Electrolyte with an Architectural Designed Polymer Matrix The intrinsic architecture of PSEs has been the subject of numerous studies up to this point, to enhance performance, particularly by utilizing the synergistic effects provided by various but dominant polymer chains. PSEs with modified polymer matrices have better ionic conductivity because they can diminish crystalline polymer zones without going through phase separation. Additionally, creating network polymers or adding stiff chains as backbones can strengthen PSEs, which inhibits the development of Li dendrites. Furthermore, even when under stress from the environment, these electrolytes preserve good shape. From these investigations, it has been found that mixing, single-ion polymer building, crosslinking, interpenetration, and copolymerization are the most effective and often employed methods for creating uniform PSEs exhibiting desirable performance.

3.1 Copolymer-Based Solid Polymer Electrolyte The ordered structure of the polymer matrix might be disrupted by a copolymer that adds a monomer unit to a homopolymer system by increasing the percentage of amorphous domains. According to how the comonomer units are arranged throughout the chain, copolymers may be broadly classified into graft copolymers, block copolymers, random copolymers, and alternating copolymers [32]. In PSE, both graft and block copolymers have received a great deal of attention. In a block copolymer, the first block is responsible for ionic conduction whereas the second block is in charge of mechanical strength. When a graft copolymer is utilized, the main chain keeps its mechanical strength while the oligomeric grafts improve ionic conductivity. Consequently, copolymer-based electrolytes can be produced under ambient conditions with good mechanical characteristics and respectable ionic conductivity. The dimensional stability of PSEs can also be improved through copolymerization. Although pure PC-based PSEs frequently prevent their realistic deployment due to poor mechanical features, PC-based electrolytes nonetheless offer strong ionic conductivity and are compatible with lithium metal anodes. By copolymerizing polycarbonated diol (PCDL), 1,6-hexamethylene diisocyanate (HDI), and diethylene glycol, hard polyurethane (PU) segments were added to the PC chains in order to solve this problem [31]. Combining LiTFSI with a copolymer solid electrolyte (PCPU) led to improved stretching and flexibility. In the case of PSEs, the hydrogen bonding between the carbonate and the urethane groups and the stiff domains generated by the PU segments enabled a very substantial elongation at a break of 2000%. Higher ionic conductivities can only be attained at high temperatures above 10–4 S/cm.

40

T. Das et al.

3.2 Interpenetrating Structured Polymer Electrolytes A network of separate crosslinked polymer molecules without any covalent interactions between them is called an interpenetrating polymer network (IPN). Networks in IPN cannot be separated without rupturing chemical connections due to the partially interlaced structures that are inherent to the material. This greatly enhances the compatibility and dimensional stability of the two immiscible phases. Additionally, due to the distinctive form, crystalline domains in an IPN would nearly completely disappear, which is very advantageous for improving ion conduction [32]. Usually, sequential or simultaneous polymerization is used to create an IPN. A self-supporting IPN (INSPE) was created by Tong et al. using simultaneous ring-opening polymerization [33]. Based on chemical interactions between epoxy and amine groups, bisphenol A diglycidyl ether (BPDE) and a star-shaped copolymer (3PPEGM-co-GMA) were simultaneously crosslinked with polyetherdiamine (ED2003), creating an IPN PSE in the presence of lithium salt. The threearm copolymer and LiTFSI were used to obtain a maximum ionic conductivity of 5.6 × 10–5 S/cm at 25 °C by adjusting the amount of GMA in the mixture. Due to the formation of the network structure and the presence of ester bonds in the polymer backbone, this electrolyte is thermally stable up to 350 °C.

3.3 Polymer Electrolyte with Cross-Linking The process of crosslinking involves joining two polymer chains together via a covalent connection or a brief string of chemical bonds. Crosslinking can enhance the thermal stability and tensile strength of polymer electrolytes as well as their dynamic storage modulus. Despite having a comparable structure to PEO, Poly(tetrahydrofuran) (PTHF) has been shown to have a greater transference number and lithium-ion conductivity than PEO. This is explained by the fact that PTHF’s main chain contains fewer oxygen heteroatoms, which avoids the excessive O-Li+ coordination that occurs in PEObased PSEs [34]. PTHF’s weaker Li+ coordination is a benefit, but the material’s low melting point, weak mechanical characteristics, and poor thermal stability still prevent extensive use of PTHF-based PSEs [35]. By combining a polymer network with carbamate groups, Bao and coworkers created a thermally stable PSE based on crosslinked PTHF (xPTHF) to solve these problems while also enhancing mechanical strength and thermal stability [36].

Polymer-Based Electrolytes

41

3.4 Simple Blending Based Polymer Electrolyte Polymer blends are actual combinations of two or more polymers with various molecular structures that could dissolve in one another. Blended polymer electrolytes frequently combine the desirable characteristics of the various polymers to establish a compromise between electrochemical window, thermal stability, mechanical strength, and ionic conductivity for high-performance PSEs. The polymer blending method is practical, effective, and economical when compared to alternative approaches [37]. According to Tao et al., PEO’s crystallinity can be reduced and the mechanical strength of the PSE increased when PEO is combined with thermoplastic polyurethane (TPU) and LiTFSI [38]. The ionic conductivity may reach up to 5.3 × 10–4 S/cm at 60 °C when the TPU/PEO ratio was at its ideal of 3. When compared to Li/Li+ , the potential window of up to 5 V was obtained as determined by linear sweep voltammetry for the TPU/PEO/LiTFSI electrolyte.

4 Composite Polymer Electrolyte Composite polymer electrolytes combine the benefits of both inorganic and organic components by incorporating inorganic fillers into polymer hosts. Due to their remarkable performance in lithium batteries, composite polymer electrolytes have gained more and more attention in recent years [39]. In composite polymer electrolytes, the inorganic fillers can either be stacked as a separate layer that is firmly adhered to the polymer film or they can be evenly scattered in a polymer matrix. The composite polymer electrolytes created by both techniques of fabrication offer better mechanical and structural stability, a bigger electrochemical window, and less interfacial resistance. They also have enhanced ionic conductivity. Surface interactions between an inorganic material and the polymer host can prevent the polymer host from crystallizing. As a result of the Lewis acid–base interaction, some functional groups can also aid in the dissociation of lithium salts, hence boosting the number of cations that transfer. Inorganic fillers employed in composite polymer electrolytes can be categorized as active or passive (inert) fillers based on how much they assist in Li-ion transport [40]. Although their size and shape may affect the composite polymer electrolyte’s ionic conductivity, passive fillers do not promote ionic transport. As ion conductors, active inorganic fillers can actively take part in ion transmission inside the composite polymer electrolyte.

4.1 Polymer-Passive (Inert) Filler Electrolytes To create solid polymer-passive filler composite electrolytes, a variety of inert oxide ceramic materials, including SiO2 , Al2 O3 , TiO2 , ZrO2 , ZnAl2 O4 , and CeO2 ,

42

T. Das et al.

have been widely used. A PEO-based polymer electrolyte’s ionic conductivity and mechanical strength might be significantly improved by adding 10 vol.% Al2 O3 particles, according to research by Weston et al. in 1982 [41]. The ionic conductivity of the composite polymer electrolyte was examined by Dissanayake et al. [42]. They observed that when particle size decreased, ionic conductivity improved. The increased surface area of smaller particles was used to explain the relationship between increasing ionic conductivity and particle size because By interacting well with filler’s O/OH groups, ions can create highly efficient ion conduction routes on the filler surface. The development of inert oxides with large surface areas has received a lot of attention recently. Lin and coworkers reported ultrafine SiO2 (MUSiO2 ) particles, which were monodispersed by in situ hydrolysis of tetraethyl orthosilicate in a PEO solution, to increase effective interfacial areas and sustain strong polymer-ceramic interactions between polymers and inert ceramics [43]. By successfully avoiding the agglomeration of fillers, this approach produced high monodispersity as well as excellent particle dispersion, as both of them are responsible for greater boosted the effective surface area for Lewis acid–base interaction. The ionic conductivity of PEO-MUSiO2 SPCE is an order of magnitude better than that of the silica-based composite electrolyte created by straightforward mechanical mixing. The in-situ generated electrolyte also exhibits a significant electrochemical potential window of up to 5.5 V without any anodic degradation. Aluminosilicate, also known as halloysite (Al2 Si2 O5 (OH)4 ), is a nano clay that Lin and colleagues synthesized and utilized in PEO-LiTFSI matrix as an organic filler [44]. They employed it as an inorganic filler in the. However, Lithium salt may be dissolved by the negatively charged silica surface of the halloysite nanotube (HNT), which can also absorb Li ions from the surface, contrary to expectations that TFSI- anions would be connected to the inner surface, which was made up of positively charged –Al–OH groups. Lithium ions were successfully able to enter the tubular channels due to the Lewis acid– base interactions between HNT, LiTFSI, and PEO. This significantly reduced the amount of distance that Li ions had to travel and thereby significantly reducing the distance that Li ions had to travel. Because of this, the synthesized SPCE displayed an impressive ionic conductivity of 1.11 × 10–4 S/cm at 25 °C.

4.2 Active Fillers-Based Polymer Electrolytes An active filler in the composite solid electrolyte is anticipated to form novel lithiumion-based pathways, which are thought to be the primary cause of the enhancement in ionic conductivity. A passive filler also contributes to reducing the polymer crystallinity. For an active filler, high degrees of electrochemical, chemical, and mechanical stability are also important. Metal oxides such as garnet-type, perovskitetype, and NASICON-type ceramics have received the most research focus as active fillers [45].

Polymer-Based Electrolytes

4.2.1

43

Garnet-Type Ceramic Polymer Electrolytes

These types of fillers have been utilized frequently in composite polymer electrolytes due to their non-flammability and broad electrochemical window. The usual chemical formula of garnet is M3 N2 (XO4 )3 , where M, N, and X, respectively, hold eight, six, and four coordinated cationic sites [46]. Since it was initially published in 2007, the garnet-type lithium solid-state electrolyte Li7 La3 Zr2 O12 (LLZO) has garnered a lot of interest [47]. Numerous studies have shown that composite electrolytes made of polymer and LLZO offer a workable approach for enhancing the overall electrochemical capabilities. Lithium-ion channels in a PEO-LLZO particle-based composite electrolyte were tracked using Li NMR spectroscopy [48].

4.2.2

Perovskite-Type Ceramic Polymer Electrolytes

Solid electrolytes based on perovskite-type follow the formula ABO3 , where A is Ca, Sr, or La and B are Ti or Al. Some A sites can receive Li, which results in the formula Li3x La2/3-x TiO3 . Perovskite ceramics are highly thermally stable and stable at high voltages, making them attractive fillers in composite polymer electrolytes [49].

4.2.3

NASICON Type Ceramic Polymer Electrolytes

Numerous researchers have become interested in the Na superionic conductor (NASICON)-type ceramics because of its exceptional ionic conductivity at high room-temperature and environmental durability [50]. NASICON-type of materials can maintain their original structures and transform into Li-ion-based inorganic fillers when Na is swapped out for Li. These substances often have the chemical formula LiM2 (PO4 )3 , where M stands for Ti, Ge, or Zr. It is possible to enhance the electrocatalytic activity of NASICON-type ceramics by substituting ions for various elements with various valences in the framework [51]. If the interfacial problem is resolved, it appears that generating composite polymer electrolytes with polymer-active fillers is a potential strategy for building electrolytes with good characteristics. Other potential strategies for improving composite polymer electrolytes include creating inorganic fillers with 3D connections to create ionic-percolated frameworks and strengthening the connections between active fillers and matrix.

44

T. Das et al.

5 Summary and Perspective Polymer electrolytes, comprising electrolyte salts and polymer matrices, have the capability to deliver better overall attributes, like mechanical strength, ionic conductivity, thermal stability, and non-flammability as compared to inorganic solid electrolytes and liquid electrolytes. For lithium batteries used in flexible and wearable electronics, portable electronics, and electric vehicles, where high energy density, great reliability, and durable mechanical properties are crucial, polymer electrolytes must be carefully considered. The discussion of novel design concepts, methodologies, and working mechanisms in the case of novel polymer electrolytes, primarily based on the four most popular matrices, PAN, PEO, PA, and APC, has provided this chapter with an overview of the significant advancements made in the development of polymer electrolytes in recent years. In this chapter, polymer electrolytes are categorized into two categories: composite polymer electrolytes and polymer electrolytes with architecturally defined polymer matrixes. Excellent mechanical properties, thermal stability, and nonflammability have been shown by many polymer electrolytes. The most crucial and difficult performance criterion for polymer electrolytes, ionic conductivity, has been significantly improved, with several polymer electrolytes achieving ion conductivity values of more than 10–4 S/cm at room temperature. Although there have been many advancements made in polymer electrolytes, there are still many obstacles to be overcome before they can be used in commercial electrochemical energy storage. • First, because of their better mechanical robustness and higher ionic conductivity at elevated temperatures, crosslinked polymers are fascinating candidates for polymer electrolyte hosts since they ensure the steady functioning of lithium batteries based on them. Even though certain polymer electrolytes’ ionic conductivity is close to 10–3 S/cm under ambient temperatures, liquid electrolytes utilized in commercial applications typically have an ionic conductivity of 10–3 –10–2 S/ cm. Although the ionic conductivity of some polymer electrolytes is close to 10–3 S/cm in ambient conditions, it is nonetheless less than the industry norm of 10–3 –10–2 S/cm for liquid electrolytes used in commercial applications. A low energy density is obtained with these types of polymer electrolytes as they exhibit lower electrochemical potential windows which is insufficient for use with high-voltage cathodes. It is desirable to create new, low-cost polymer matrices with wide, high-conductance electrochemical windows that can be produced at room temperature. High-strength electro spun nonwoven membranes with porous frameworks are better solutions for polymers with high ionic conductivity but low mechanical properties. Additionally, lithium salt anions can improve the performance of polymer electrolytes because they offer more interfacial stability during cycle operations over Li metal and aggressive intermediates. • The addition of inorganic fillers to polymer electrolytes is a simple way to increase ionic conductivity at ambient temperature and widen the possible window for polymer electrolytes. Phase separation and short-ranged lithium-ion conduction channels would occur from insufficient interfaces and limited contact between

Polymer-Based Electrolytes

45

organic and inorganic materials, negating the beneficial effects of fillers on the characteristics of polymer electrolytes. Promising approaches to address the aforementioned problems include changing the surface of inorganic fillers and introducing interlayers of adhesive coating to inorganic–organic interfaces. This strategy has had only sporadic success, though, because the interactions between polymers and inorganic materials are so intricate and case-by-case. More research is required to fully understand the interactions in a wide range of systems, which will aid in the development of innovative composite electrolytes with enhanced interfacial stability. • The performance of composite polymer electrolytes can be improved by using polymer-inorganic layered electrolytes with continuous lithium-ion routes and independent continuous phases for each component to prevent the agglomeration of inorganic materials. • The solid-state lithium batteries’ rate capability and cycle stability are both significantly influenced by the electrolyte/electrode interfacial characteristic. A tiny amount of liquid electrolyte is frequently utilized to moisten the surfaces between electrolytes and electrodes in order to establish excellent polymer electrolyte/ electrode interactions. The interfaces can only be slightly improved using this method; it is not a permanent fix. The cathode and solid electrolyte are commonly coupled by hot pressing, which is widely followed to create the bilayer framework of the cathode and electrolyte.

References 1. Verma S, Pandey VK, Verma B (2022) Facile synthesis of graphene oxide-polyaniline-copper cobaltite (GO/PANI/CuCo2O4) hybrid nanocomposite for supercapacitor applications. Synth Met 286 2. Pandey VK, Verma S, Verma B (2022) Polyaniline/activated carbon/copper ferrite (PANI/AC/ CuF) based ternary composite as an efficient electrode material for supercapacitor. Chem Phys Lett 802:139780 3. Sabihuddin S, Kiprakis AE, Mueller M (2015) A numerical and graphical review of energy storage technologies. Energies 8:172–216 4. Verma S, Das T, Pandey VK, Verma B (2022) Nanoarchitectonics of GO/PANI/CoFe2O4 (graphene oxide/polyaniline/cobalt ferrite) based hybrid composite and its use in fabricating symmetric supercapacitor devices. J Mol Struct 133515 5. Pandey VK, Verma S, Das T, Verma B (2022) Supercapacitive behavior of polyaniline-waste derived carbon-copper cobaltite based ternary composite. Bioresour Technol Rep 20:101255 6. Das T, Pandey VK, Verma S, Pandey SK, Verma B (2022) Optimization of the ratio of aniline, ammonium persulfate, para -toluenesulfonic acid for the synthesis of conducting polyaniline and its use in energy storage devices. Int J Energy Res 46:19914–19928 7. Das T, Verma B (2022) Facile synthesis of bimetallic CuFe2O4 based ternary hybrid composites for supercapacitor electrodes and optimization of weight ratio of the individuals on the basis of their electrochemical performances. Mater Technol 37:2552–2566 8. Zhang SS (2013) Liquid electrolyte lithium/sulfur battery: fundamental chemistry, problems, and solutions. J Power Sources 231:153–162

46

T. Das et al.

9. Wu Z, Xie Z, Yoshida A, Wang Z, Hao X, Abudula A, Guan G (2019) Utmost limits of various solid electrolytes in all-solid-state lithium batteries: a critical review. Renew Sustain Energy Rev 109:367–385 10. Liu Q, Geng Z, Han C, Fu Y, Li S, He Y, Kang F, Li B (2018) Challenges and perspectives of garnet solid electrolytes for all solid-state lithium batteries. J Power Sources 389:120–134 11. Zhou J, Qian T, Liu J, Wang M, Zhang L, Yan C (2019) High-safety all-solid-state lithiummetal battery with high-ionic-conductivity thermoresponsive solid polymer electrolyte. Nano Lett 19:3066–3073 12. Zhao Q, Liu X, Stalin S, Khan K, Archer LA (2019) Solid-state polymer electrolytes with in-built fast interfacial transport for secondary lithium batteries. Nat Energy 4:365–373 13. Agrawal RC, Pandey GP (2008) Solid polymer electrolytes: materials designing and all-solidstate battery applications: an overview. J Phys D Appl Phys 41:223001 14. Hu P, Chai J, Duan Y, Liu Z, Cui G, Chen L (2016) Progress in nitrile-based polymer electrolytes for high performance lithium batteries. J Mater Chem A 4:10070–10083 15. Zhou D, Shanmukaraj D, Tkacheva A, Armand M, Wang G (2019) Polymer electrolytes for lithium-based batteries: advances and prospects. Chem 5:2326–2352 16. Li J, Huang X, Chen L (2000) X-ray diffraction and vibrational spectroscopic studies on PAN-LiTFSI polymer electrolytes. J Electrochem Soc 147:2653 17. Wu B, Wang L, Li Z, Zhao M, Chen K, Liu S, Pu Y, Li J (2016) Performance of “polymer-in-salt” electrolyte PAN-LiTFSI enhanced by graphene oxide filler. J Electrochem Soc 163:A2248– A2252 18. Wang Z (1999) Spectroscopic investigation of interactions among components and ion transport mechanism in polyacrylonitrile based electrolytes. Solid State Ionics 121:141–156 19. Wang Z, Hu Y, Chen L (2005) Some studies on electrolytes for lithium ion batteries. J Power Sources 146:51–57 20. Jia W, Li Z, Wu Z, Wang L, Wu B, Wang Y, Cao Y, Li J (2018) Graphene oxide as a filler to improve the performance of PAN-LiClO4 flexible solid polymer electrolyte. Solid State Ionics 315:7–13 21. Meyer WH (1998) Polymer electrolytes for lithium-ion batteries. Adv Mater 10:439–448 22. Tan R, Gao R, Zhao Y, Zhang M, Xu J, Yang J, Pan F (2016) Novel organic-inorganic hybrid electrolyte to enable LiFePO4 quasi-solid-state li-ion batteries performed highly around room temperature. ACS Appl Mater Interfaces 8:31273–31280 23. Marzantowicz M, Dygas JR, Krok F, Łasi´nska A, Florja´nczyk Z, Zygadło-Monikowska E, Affek A (2005) Crystallization and melting of PEO:LiTFSI polymer electrolytes investigated simultaneously by impedance spectroscopy and polarizing microscopy. Electrochim Acta 50:3969–3977 24. Zhang H, Zhang J, Ma J, Xu G, Dong T, Cui G (2019) Polymer electrolytes for high energy density ternary cathode material-based lithium batteries. Electrochem Energy Rev 2:128–148 25. Xu H, Zhang H, Ma J, Xu G, Dong T, Chen J, Cui G (2019) Overcoming the challenges of 5 V Spinel LiNi 0.5 Mn 1.5 O4 cathodes with solid polymer electrolytes. ACS Energy Lett 4:2871–2886 26. Shukla N, Thakur AK (2009) Role of salt concentration on conductivity optimization and structural phase separation in a solid polymer electrolyte based on PMMA-LiClO4. Ionics (Kiel) 15:357–367 27. Chai J, Zhang J, Hu P, Ma J, Du H, Yue L, Zhao J, Wen H, Liu Z, Cui G, Chen L (2016) A high-voltage poly(methylethyl α-cyanoacrylate) composite polymer electrolyte for 5 V lithium batteries. J Mater Chem A 4:5191–5197 28. Ye S, Wang S, Lin L, Xiao M, Meng Y (2019) CO2 derived biodegradable polycarbonates: synthesis, modification and applications. Adv Ind Eng Polym Res 2:143–160 29. Zhang J, Yang J, Dong T, Zhang M, Chai J, Dong S, Wu T, Zhou X, Cui G (2018) Aliphatic polycarbonate-based solid-state polymer electrolytes for advanced lithium batteries: advances and perspective. Small 14:1800821 30. Wang C, Zhang H, Li J, Chai J, Dong S, Cui G (2018) The interfacial evolution between polycarbonate-based polymer electrolyte and Li-metal anode. J Power Sources 397:157–161

Polymer-Based Electrolytes

47

31. Bao J, Shi G, Tao C, Wang C, Zhu C, Cheng L, Qian G, Chen C (2018) Polycarbonatebased polyurethane as a polymer electrolyte matrix for all-solid-state lithium batteries. J Power Sources 389:84–92 32. Jenkins AD, Kratochvíl P, Stepto RFT, Suter UW (1996) Glossary of basic terms in polymer science (IUPAC Recommendations 1996). Pure Appl Chem 68:2287–2311 33. Tong Y, Lyu H, Xu Y, Prasad Thapaliya B, Li P, Sun X-G, Dai S (2018) All-solid-state interpenetrating network polymer electrolytes for long cycle life of lithium metal batteries. J Mater Chem A 6:14847–14855 34. Alamgir M, Moulton RD, Abraham KM (1991) Li+-conductive polymer electrolytes derived from poly(1,3-dioxolane) and polytetrahydrofuran. Electrochim Acta 36:773–782 35. Akbulut O, Taniguchi I, Kumar S, Shao-Horn Y, Mayes AM (2007) Conductivity hysteresis in polymer electrolytes incorporating poly(tetrahydrofuran). Electrochim Acta 52:1983–1989 36. Mackanic DG, Michaels W, Lee M, Feng D, Lopez J, Qin J, Cui Y, Bao Z (2018) Crosslinked poly(tetrahydrofuran) as a loosely coordinating polymer electrolyte. Adv Energy Mater 8:1800703 37. Bao J, Qu X, Qi G, Huang Q, Wu S, Tao C, Gao M, Chen C (2018) Solid electrolyte based on waterborne polyurethane and poly(ethylene oxide) blend polymer for all-solid-state lithium ion batteries. Solid State Ionics 320:55–63 38. Tao C, Gao M-H, Yin B-H, Li B, Huang Y-P, Xu G, Bao J-J (2017) A promising TPU/PEO blend polymer electrolyte for all-solid-state lithium ion batteries. Electrochim Acta 257:31–39 39. Liu Y, Xu B, Zhang W, Li L, Lin Y, Nan C (2020) Composition modulation and structure design of inorganic-in-polymer composite solid electrolytes for advanced lithium batteries. Small 16:1902813 40. Wan J, Xie J, Mackanic DG, Burke W, Bao Z, Cui Y (2018) Status, promises, and challenges of nanocomposite solid-state electrolytes for safe and high performance lithium batteries. Mater Today Nano 4:1–16 41. Weston J, Steele B (1982) Effects of inert fillers on the mechanical and electrochemical properties of lithium salt-poly(ethylene oxide) polymer electrolytes. Solid State Ionics 7:75–79 42. Dissanayake MAKL, Jayathilaka PARD, Bokalawala RSP, Albinsson I, Mellander B-E (2003) Effect of concentration and grain size of alumina filler on the ionic conductivity enhancement of the (PEO)9LiCF3SO3:Al2 O3 composite polymer electrolyte. J Power Sources 119–121:409– 414 43. Lin D, Liu W, Liu Y, Lee HR, Hsu P-C, Liu K, Cui Y (2016) High ionic conductivity of composite solid polymer electrolyte via in situ synthesis of monodispersed SiO2 nanospheres in poly(ethylene oxide). Nano Lett 16:459–465 44. Lin Y, Wang X, Liu J, Miller JD (2017) Natural halloysite nano-clay electrolyte for advanced all-solid-state lithium-sulfur batteries. Nano Energy 31:478–485 45. Liu Y, He P, Zhou H (2018) Rechargeable solid-state Li-air and Li-S batteries: materials, construction, and challenges. Adv Energy Mater 8:1701602 46. O’Callaghan MP, Powell AS, Titman JJ, Chen GZ, Cussen EJ (2008) Switching on fast lithium ion conductivity in garnets: the structure and transport properties of Li 3+ x Nd 3 Te 2–x Sb x O 12. Chem Mater 20:2360–2369 47. Murugan R, Thangadurai V, Weppner W (2007) Fast lithium ion conduction in garnet-type Li7La3Zr2O12. Angew Chemie Int Ed 46:7778–7781 48. Zheng J, Tang M, Hu Y (2016) Lithium ion pathway within Li 7 La 3 Zr 2 O 12 -polyethylene oxide composite electrolytes. Angew Chemie 128:12726–12730 49. Stramare S, Thangadurai V, Weppner W (2003) Lithium lanthanum titanates: a review. Chem Mater 15:3974–3990 50. Goodenough JB, Hong H-P, Kafalas JA (1976) Fast Na+-ion transport in skeleton structures. Mater Res Bull 11:203–220 51. Epp V, Ma Q, Hammer E-M, Tietz F, Wilkening M (2015) Very fast bulk Li ion diffusivity in crystalline Li 1.5 Al 0.5 Ti 1.5 (PO4)3 as seen using NMR relaxometry. Phys Chem Chem Phys 17:32115–32121

Conducting Polymers for Electrochemical Energy Storage Applications K. A. U. Madhushani and Ram K. Gupta

Abstract With the invention of conducting polymers (CPs) starting in the nineteenth century, they have achieved incredible attraction in the field of energy storage due to their tunable electrochemical properties. Mainly, the chemistry behind the CP material exhibits a great relationship between structure and property that contributes to the discovery of modified materials for numerous applications. The characteristic features of nanostructured conducting materials including high porosity and large surface area result in high specific capacitance, superior conductivity, simplicity in synthesis, and low production cost. However, considering the structural features and electrochemical performances, this becomes an effective electrode material in various electrochemical energy devices such as supercapacitors, solar cells, batteries, fuel cells, sensors, etc. To date, there are several varieties of CPs are developed as a result of extensive research. The doping activities and π-conjugated chains affect the electrochemical redox reaction resulting in high conductivity of the CPs. This chapter discusses in detail CP materials related to various synthesis technologies, and how CPs are used for energy generation such as solar cells, fuel cells, and for energy storage such as batteries, supercapacitors, and flexible devices. Furthermore, recent research findings related to CP-based flexible devices are expected to be explored in this chapter. Keywords Conducting polymer · Solar cells · Batteries · Supercapacitors · Flexible devices

K. A. U. Madhushani · R. K. Gupta (B) Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA e-mail: [email protected] National Institute for Materials Advancement, Pittsburg State University, Pittsburg, KS 66762, USA © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_4

49

50

K. A. U. Madhushani and R. K. Gupta

1 Introduction The growth of the population and the expansion of science and technology are two major aspects that affect the increment of the need for fossil fuel energy consumption. This leads to causing so many troubles not only for humans but also for living beings. As a solution, although natural energy sources like solar, tidal, water and air can be used as alternative resources, their availability is limited due to some factors such as season, climate, geography and time, etc. Because of these unavoidable circumstances, scientists turned their attention to finding an eco-friendly, effective, reliable source of energy that could be helped in both energy generation and storage for future purposes. This led to innovative photovoltaic cells (PVCs), fuel cells (FCs) as energy conversion devices, supercapacitors (SCs), and batteries playing a vital role in energy storage (Fig. 1). Electrode material and electrolytes are critical factors in electrochemical performance in energy storage applications. Over the past decades, various types of electrode materials have been used to fabricate electrochemical energy storage devices (EESDs) to achieve a better function of energy conversion and energy storage. The energy storage capacitance is different from the composition of the electrode materials. It is significantly discovered that there are lots of practices that have been carried out to tune the properties of different electrode materials. Composing with more conductive materials, and heteroatom doping are some of them. Considering their unique characteristics of high conductivity, long life span, costeffectiveness, eco-friendliness, etc., polymeric materials have attracted great attention in ongoing research studies [1]. After the invention of conducting polymers (CPs) in 1960, several types of CPs, for instance, polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh), poly(3,4 ethylenedioxythiophene) (PEDOT), polyacetylene (PA), and poly(phenylenevinylene) (PPV) were discovered as a result of extensive research projects (Fig. 2). The tunability of properties, the presence of redox activity,

Fig. 1 Scheme of electrochemical energy storage

Conducting Polymers for Electrochemical Energy Storage Applications

51

Fig. 2 Structural configurations of a PANI, b PPy, c PTh, and d PEDOT. Adapted with permission [2]. Copyright © 2019 John Wiley and Sons

doping-dedoping behavior, and the chemical structure of those materials have a major impact on energy storage. Tuning the features of CPs and composite polymeric materials has been developed for energy storage applications. According to those facts, this can be used in manufacturing many devices like electronic devices, SCs, sensors, and batteries [2]. Typically, CPs show pseudocapacitance properties as a result of the reversible redox reactions that occur on the surface of the electrode material [1]. In SCs, the specific capacitance of the pseudocapacitor is relatively higher than that of an electric double-layer capacitor (EDLC). This is because the faradaic reaction can transfer more ions compared with electrostatic adsorptions that occur in EDLC. As a pseudocapacitive material, CP maintains a high specific capacitance and conductivity based on its ion motion, availability of solvated counterions, and simple kinetics. Chemically, both graphene and CPs consist of sp2 -conjugated carbon molecules, there is a distinguishable bandgap in CPs. However, due to the presence of a bandgap in CPs, the hetero-atom doping process leads to enhancing the conductivity of CPs by forming a new energy level between the bandgap. The p-doping involves the removal of electrons from the valence band (oxidation) while n-doping promotes the introduction of electrons into the conduction band (reduction). In the following equations, A− and C+ are denoted by counter anion and counter ion, respectively. p − doping : C P + n A− → C P n+ (A− )n + ne−

(1)

n − doping : C P + ne− + nC + → (C + )n C P n−

(2)

52

K. A. U. Madhushani and R. K. Gupta

Fig. 3 Doping mechanism in graphene and conducting polymers. Adapted with permission [3]. Copyright © 2016, American Chemical Society

Here, charged ions are moved in the form of charged polarons (radical ions) and bipolarons (dianions/dications) within the polymer. In doping/dedoping steps, counterions are capable of keeping neutrality within the system (Eqs. 1 and 2). In that sense, the charge formation differs from the mechanism of doping atoms. For instance, PPy has a specific bandgap that contributes to improving conductivity. During the pdoping of PPy, bipolaron or carbocation occurs by removing two electrons from the polymer chain. With increasing dopant concentration, bipolaronics are further formed after the saturation limit. This results in a new bandgap where the energy levels overlap. Due to this mechanism, the conductivity of PPy was improved through increased charge transfer (Fig. 3) [3].

2 Synthesis and Characterization of Conducting Polymers Mainly, CPs can be synthesized in two ways. One method is a chemical method that is carried out via oxidative polymerization by using oxidants like ammonium persulfate and Fe+3 . Electrochemical polymerization is another way to form CPs in various forms of films, sponges, hydrogels, and powders. Apart from those two, some techniques such as photochemical, methathesis, concentrated emulsion, pyrolysis, plasma polymerization, and inclusion are used for the fabricating different types of CPs having diverse morphological features like nanotubes, nanowires, nanofibers, nanoarrays, and nanorods. These structural variations of CPs facilitate changes in volume, surface area, and porosity, leading to large differences in chemical performances [2].

Conducting Polymers for Electrochemical Energy Storage Applications

53

2.1 Electrochemical Method The electrochemical method has been considered to be the most popular approach to obtaining CPs because of its many benefits. Similar to the chemical polymerization technique, the electrochemical method follows the same mechanism, the difference is that this method uses oxidizing potential instead of an oxidizing agent. Electropolymerization is performed using a three-electrode system which contains a polymer solvent dispersion in the electrolyte. This technique leads to the formation of a thin film of CPs on the conductive surface. CPs can be synthesized in a single-section glass cell and no large instruments need for the synthesis route. In that sense, through this technique, CPs are obtained at the required level of uniformity and thickness. Anodic oxidation of electroactive functional monomers is widely used for the synthesis of CPs, while cathodic reduction is rarely applied. In previous experiments which were done by using the oxidation method, the production of thin film and doping counter ions have taken place in sequences producing polymer films and doping counter ions are taken place instantaneously, for example, the synthesis of PANI, PTh can be done through this technique [4]. Dubal et al. [5] fabricated PPy with various nanostructures of nano bricks, nanosheets, and nanobelts on stainless steel surfaces by altering the scan rate of deposition in the potentiodynamic mode. The electrochemical polymerization of PPy was done using a conventional procedure. First, the neutral monomer of PPy was oxidized into a radical cation. Then, aromatization and oxidation of dimer occur more rapidly than monomer conversion. In particular, it is necessary to be potential should be high enough to oxidize the monomer, and the coupling of two radicals results in the formation of PPy. The reaction mechanism of PPy can be illustrated in Fig. 4. There are some advantages to this method. One of them is the tunability of the thickness of the CP film by altering the electrochemical parameters like oxidation potential, time, and electrolyte. Furthermore, these CP films can be deposited on any internal and external surfaces with different geometries, such as cylindrical, and flat surfaces. These fabricated CP films with high conductivity can be used for electrode modifications and this is a green technique as it does not use oxidizing agents.

2.2 Chemical Method-Oxidative Polymerization Due to mass production at low cost, the synthesis of CPs through the chemical reactions of polymerization/reduction/oxidation of monomers is widely used for various purposes. Among those, oxidative polymerization which is carried out using oxidants like ammonium persulfate and Fe+3 very attractive. This is because of its high value of quantity and quality production at lower production costs. PANI, PPy, and PTh are some examples that can easily be synthesized using this technique. But, it has been found that the electrochemical performance and mechanical properties of CPs obtained by this are lower compared to electrochemical methods. Maintaining high

54

K. A. U. Madhushani and R. K. Gupta

Fig. 4 Reaction mechanism of polypyrrole by electropolymerization. Adapted with permission [5]. Copyright © 2012, Royal Society of Chemistry

stability is a considerable factor while using chemical polymerization. Herein, the reactivity and solubility of the oligomers and low molecular weight monomers lead to the production of high molecular weight polymers. When oligomers precipitate out from the solution, the polymerization can propagate heterogeneously, reducing the concentration of invisible monomers and reactive polymers. Thus, the sometimes higher molecular weight can not be reached if the chemical polymerization is failed, resulting in the formation of mechanically unstable coatings on the walls of the vessel. However, with the selection of suitable solvents and appropriate oxidants, successful polymerization results in the production of cation radicals at the proper site of the monomers. Overall, the chemical method is an effective method to synthesize conductive polymers with better electrochemical properties [4].

2.3 Photochemical Method The benefits of easy synthesis, cheapness, low energy required, the relatively fast processing speed of reactions, and the usage of aqueous solvents in replace of organic solvents make this method more popular among others. The specialty here is that the product made through this technology mainly affects the control of environmental pollution. This process is completed through three different steps: initiation, propagation, and polymerization. In the first step, photoinitiators are undergone electronic excitation under UV/visible radiation, resulting in reactive radicals being produced. Next, these radicals are reacted with monomers to form actives species of ion pairs or chain-initiators which contribute to occur ionic and radical photopolymerization, respectively. Finally, polymeric chains are formed by transferring chains or connecting or disproportionating those active species. Through this technique, different types of CPs, for instance, PPy, and PTh, PANI were produced. In 1992, Rabeck et al. [6] discovered this production of PPy by cationic photoinitiators, opening a new way for CPs innovation. It has already been found that PPy can

Conducting Polymers for Electrochemical Energy Storage Applications

55

be polymerized in HClO4 or tetraethylammonium tetrafluoroborate solution used as catalysts by exposure to long UV radiation time (15 h). This research group synthesized PPy using iron-arene salts [η-C5 H5 )Fe(η-arene)] which are considered cationic photoinitiators under UV/visible light. Herein, as initiating step, Fe(II) fragments are oxidized into Fe(III). This polymerization takes place in the presence of oxygen. Thus, the conductivity of the formed PPy is relatively low, resulting in poor electrochemical performances. Later in 1994, the PTh photopolymerization procedure was first discovered by Shimidzu et al. [7]. Herein, benzothiophene was photopolymerized in a solution of methylene cyanide containing chloroform (electronic acceptor) and tetramethylammonium bromide (salt) using a 500 W xenon lamp. PTh made using this method gives the same electronic and molecular structure as those prepared chemically.

2.4 Concentrated Emulsion Method This method is based on the mechanism of free radical polymerization. This follows the heteroatom phase procedure placing three segments such as monomer droplet, latex particle, and water segments. Herein, the solvent and one of the above segments act as the monomer and the initiator respectively. After the polymerization, the synthesized polymers exist as soluble components either in the solvent or monomer. Because of the mixture of hydrophobic monomer and hydrophilic initiator, this method holds a micelle-forming surfactant. In that sense, emulsions of monomer droplets in water initialize the polymerization and concentrated emulsions (CEs) act as precursors for latexes of polymers. These CEs have a large volume fraction in the dispersed phase which is a value greater than 0.74/0.99. At a low volume fraction of the continuous phase, the dispersed phase is made with polyhedral cells by separating thin layers of the continuous phase (Fig. 5). With the addition of a dispersed phase as dropwise into surfactant contained continuous phase, the CEs are formed. There are some reasons which affect the use of CEs as a route for polymerization. One of these is the ordered arrangement of the surfactant molecules which contributes to the rate of conversion. Another one is the lower mobility of the cells in the surfactant layer creates the gel effect and this helps to enhance the rate of the polymerization and the molecular weight of the polymer because this gel effect delays the termination of biomolecular reactions. Moreover, this maintains the structure of emulsions and controls the size of latexes by changing the cell size of CEs [8].

2.5 Pyrolysis Method This method is based on the chemical degradation of materials at elevated temperatures in an inert atmosphere. This can be applied for small quantities of sample synthesis and this is a simple technique that does not require much time for the sample

56

K. A. U. Madhushani and R. K. Gupta

Fig. 5 Graphic design of concentrated emulsions Oil surfactant film

Water

preparation. The presence of monomer species is studied using spectroscopic analysis. Commonly, natural and synthetic polymers are synthesized through pyrolysis gas chromatography. The rate of temperature, substrate type, presence of oxygen, and other chemicals are the main factors that affect the performance of the pyrolysis method. This follows three main degradation steps random scission, side group scission, and monomer reversion. Mainly, this process is carried out with heat treatment which causes combustion and gasification phenomena that contribute to the partial or full oxidation of the material. This occurs as an endothermic reaction ending in the formation of high-energy products [9].

3 Conducting Polymers for Energy Generation 3.1 Photovoltaic Cells As a solution to rising global temperatures due to CO2 emissions, solar energy which is a non-carbon energy source can be considered an ecofriendly way of generating electrical energy. Photovoltaic cells also known as solar cells, are designed as an energy conversion devices that can convert solar power into electricity due to the effect of photovoltaics. In addition to power generation, this is very useful as a photodetector that can measure the intensity of light or detect light/any electromagnetic radiation close to the visible range. Mainly, there are different types of PVCs such as dye-sensitized PVC (DS-PVC), quantum dot PVC, perovskite PVC, bifacial PVC, organic PVC (O-PVC), and polymer PVC (P-PVC). Among them, O-PVC and P-PVC made of thin films of PPV and DS-PVCs fabricated with PEDOT are some examples of CP-based PVCs. It has been found that the energy conversion efficiency of CPs is relatively low compared to that of inorganic components. In 2013, Guo et al. [10] reported that P-PVC had a power conversion efficiency (PCE) of 3% while other organic materials reached 11.1%.

Conducting Polymers for Electrochemical Energy Storage Applications

57

When considering the working mechanism of the P-PVCs, this device operates under four basic steps. Initially, this process starts with the absorption of the electrons, and photons from the light source. The electrons are transferred from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) by leaving a hole in HOMO. As the second step, created excitons move towards to donor–acceptor (D-A) border. Subsequently, the excited electron is transmitted among LUMO energy levels from D to A. Then, the presence of a hole in the D site and electrons in the A site is strongly connected as pairs by the coulomb effect. Finally, with the pair separation, free electrons and holes move toward the cathode and anode, respectively (Fig. 6). After collecting electrons and holes at each electrode, charge generation in PVC is complete [11]. Although most PVCs made of single crystallines such as silicon and semiconductor materials give high performances, the problem with that is the high production cost for both techniques and materials. As a better solution, research has found that organic DS- PVCs are a very cost-effective method, as they use relatively cheap solution-based materials. As an example, Mozer et al. [12] synthesized a porous flexible electrode for solid-state dye-sensitized solar cells by using vapor-phase polymerized conducting polymer (PEDOT), polytetrafluoroethylene (Goretex), and Au, current collector metal ion. The porous structure of this electrode provides

Fig. 6 Schematic representation of energy generation mechanism in polymer photovoltaic cell. Adapted from Ref. [11]. Copyright © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license

58

K. A. U. Madhushani and R. K. Gupta

the space for the reactivity of the reactant agents resulting in high performance in energy conversion, storage, and electrocatalytic activities. The pore filling of the TiO2 photoanode hinders the efficiency of this device. To remedy this, electroactive porous CPs were embedded in the pores, for instance, PPy was synthesized using the electrochemical method used for this filling. However, the main limitation of these PVCs is the lack of reproducibility of gold/platinum as a current collector. In this device, to maintain a good physical link between two incompressible electrodes, TiO2 must be completely even and defect-free within a large surface area. Further, through the post-manufacture ionic liquid treatment, the conductivity of PEDOT can be enhanced. This group tested this device by connecting the photoanode and Goretex-Au-PEDOT to a potentiostat by supping 0.2 V. Then they observed that the current increased slightly when the light was turned on (Fig. 7). This is a great innovation for the large-scale, reproducible, cost-effective production of solar cells. As another innovation, Yim et al. [13] produced semitransparent O-PVCs using CP anode and silver nanowire (AgNW) cathode. In this study, they modified the CP to achieve high performance in these devices. So, they used poly (3,4 ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT: PSS) as an anode material. Previously, Kaltenbrunner et al. [14] discovered that poly(3-hexylthiophene-2,5-diyl): [6, 6]-phenyl-C61-butyric acid methyl ester (P3 HT: PCBM) in O-PVCs using highly conductive PEDOT:PSS on plastic substrate exhibited high PCE. In that sense, Yim and his group used this concept in their experiment by fabricating electrodes in P3 HT: PCBM. Then, the anode and cathode of this device showed relatively high PCEs of 2.0% and 2.3%, respectively. This modernization in CP materials has paved the way

Fig. 7 a Schematic representation and layer structure of a solid-state dye-sensitized solar cell using photoelectrochemically deposited PEDOT as a hole conductor. SEM images of b the Goretex-AuPEDOT cross-section and the photoanode surface c after and d before PEDOT deposition. Adapted with permission [12]. Copyright © 2010 American Chemical Society

Conducting Polymers for Electrochemical Energy Storage Applications

59

for the fabrication of high PCE optoelectronic devices used in various applications [13].

3.2 Fuel Cells Focusing on green energy technology, FCs are being introduced to replace power producers using fossil fuel as an environmentally friendly energy generation device. This has a higher capability of conversion of chemical energy of fuel into DC electricity. These are very effective in generating energy because they do not need to be charged like batteries. Depending on the working temperature, there are three types of FC. They are, low-temperature FC, medium-temperature FC, and high-temperature FC (Fig. 8). Among those FCs, CPs involve in the production of low-temperature based FCs, for instance, polymer electrolyte membrane FC. Under this category proton-exchange membrane FC (PEMFC) is the most popular due to its unique characteristics of low weight, low working thermal range, fast beginning time, excellent ratio of power/weight, and, high power density. Thus, its main problems are the high cost of perfluorosulfonated polymer electrolyte and noble catalyst (platinum), the low reduction rate of oxygen, and the low longevity of the membrane used between two electrodes in this device. Herein, this membrane is permeable only for protons not for electrons. This acts as a separator of the anode and cathode while avoiding reacting gases [1]. The issues arising from PEMFC can be overcome by using alkaline anion exchange membrane (AEM) FCs. This is because they use low-budget, less-value metallic electrocatalysts. Thus, it is quite challenging to find a suitable hydroxide ion CP membrane with excellent mechanical properties for use in this device. In that sense, Lee et al. [15] have synthesized an AEMFC using fluorene-contained hydroxide ion CPs to achieve higher performances in this device. The important facts in using fluorene-containing compounds are the chemical strength and excellent film-forming ability. In addition, Li et al. [16] developed a

Fig. 8 Classification of fuel cells based on operating temperature

60

K. A. U. Madhushani and R. K. Gupta

composite of SPEEKK/polyaniline for membrane formation in the DMFC. Due to its convenient structure, ease of storage of ethanol, and low operating temperature range, this device has high demand in various applications such as electronic devices and automobiles. Here, the compatibility, conductivity, and behavior of the film increase with the addition of PANI. This happens due to the hydrogen bonding interaction between anion groups and sulfonated acid. The main purpose of introducing PANI into SPEEKK film was to avoid the flow of methanol through the membrane. This group has stated that this composite was effective material for the membrane of DMFC which helps to improve the properties of this device. These are just a few examples of past studies on CPs that apply to fuel cell fabrication.

4 Conducting Polymers for Energy Storage 4.1 Batteries With the development of sustainable energy storage devices, scientists were able to innovate batteries that tend to attract popularity in various fields. Nowadays, there is no doubt that every nook and corner is covered with batteries, for instance, many electronic devices (computers, mobiles, watches), wearable sensors, and automobiles are controlled by battery power. The activity of each device mainly depends on the performance, functionality, and processbility of batteries such as metal-ion (lithiumion, sodium-ion), metal-supfur, metal-air, etc. Typically, they have unique properties of high energy density, high specific capacity, long cyclic stability, etc. The only problem with that is lower power density. In 1991, Sony started commercializing batteries using inorganic transitional metal compounds as cathode materials. Later, the electrochemically active organic materials including CPs, organic free radicals, organo-sulfur, and carbonyl compounds become more popular with their redox activities. Considering electrochemical properties linked with the pliability and structural features, CPs have gained considerable attraction in the industrial-scale production of batteries. Among CPs, PPy, PANI, PEDOT, PTh, and their derivatives are most commonly used in battery fabrications. In batteries, the conductivity of CPs depends on the doping mechanism. As discussed earlier, oxidation (p-doping) and reduction (n-doping) of neutral CP by combination with dopants (counterions) are introduced as doping functions. The movements of counteranions and countercations in the doping/dedoping process in CPs are correlated with the charge/discharge activity of CPs. Due to the electrochemical steadiness in the p-doped phase, CP acts as a cathode in the Li-ion batteries (LIBs) while carbon plays the role of an anode (Fig. 9). During discharging step, dopants and lithium ions are released from the cathode and anode into the electrolyte, respectively. As the charging process begins, it is deposited on the carbon material, meanwhile, oxidation of CP occurs by emitting electrons [17].

Conducting Polymers for Electrochemical Energy Storage Applications

61

Fig. 9 Schematic diagram of discharge process in lithium-ion battery based on p-doped CP cathode and carbon anode. Adapted with permission [17]. Copyright © 2019 American Chemical Society

Recent research has found that sodium-ion batteries (SIBs) can be replaced with LIBs. Due to the low availability of Li ions on Earth, it is necessary to find an alternative source to replace this. Therefore, novel research has led to carrying out experiments with sodium materials due to their high availability. Both have the same properties as they are alkali metals. For this reason, their mechanism of action in both batteries is also similar. However, the higher radius of sodium (Na) ion compared to lithium-ion limits the application of SIBs. Thus, the high interspace of Na ion provides a soft character to the system which allows CPs to accommodate SIBs [1]. Through modification of CPs with oxidation–reduction favored materials, the performance of the batteries can be improved. Various studies have been conducted to date around these research areas. Although the properties of CPs can change with the change of doping level, in some cases, exceeding the doping levels causes irreversible disruption of CPs. Therefore it was required to consider the doping amount while proceeding with this technique of CPs. And also, there is another matter with CPs. That is, the decrease in discharge voltage as it varies with the charge–discharge process and the amount of doping. Emerging CPs with redox functional groups such as carbonyls, metal complexes, organosulfur and radical compounds are considered the best solution to overcome those issues. This can be done in several ways, by doping the material to the polymer as counterions or covalently attaching to the polymer backbone as pendants. In addition to the doping/dedoping behaviors, this helps to remove and insert Li/Na ions in the battery. Overall, these redox-doped CPs show better performance in battery devices than using individual CPs [17]. In n-doped CP-based metal ion batteries, n-type CP and p-type CP with redoxactive groups act as anode, and cathode, respectively. Most research has been carried out using PANI, PTh, etc. For instance, Jimenez et al. [18] used lithium-doped PANI to fabricate LIBs. The benefits of using PANI are high electrical conductivity, high coulombic efficiency, and long cyclic stability. In PANI, three different states

62

K. A. U. Madhushani and R. K. Gupta

of fully reduced leucoemaraldine base (LB), conducting emeraldine salt (ES), and completely oxidized pernigraniline (PNB) are involved in the doping mechanism. The anode material, Li-doped PANI, was prepared using lithium proton exchange in a Li-containing electrolyte. This happened due to the interaction between the negatively charged N atoms of the ES and cations (Li+ ). This group has discovered that this electrode material achieved 4.25 V discharge voltage, 208 mAh/g of specific capacitance, and 99% coulombic efficiency after 400 cycles resulting in higher stability of LIBs. Nowadays, most of the research has proven that in p-doped CP-based batteries, both anode and cathode are made with p-type CPs. In that sense, PPy, PEDOT, PTh are mainly used to synthesize those. For instance, Emanuelsson et al. [19] synthesized metal ion batteries using modified PEDOT, PEDOT-benzoquinone [BQ]) as a positive electrode, PEDOT-anthraquinone [AQ] as a negative electrode. In this device, the specific capacities of PEDOT-BQ and PEDOT-AQ showed as 120 mAh/g and 103 mAh/g, respectively at a cell potential of 0.5 V. In those compounds, BQ and AQ are connected as pendants to the backbone polymer of PEDOT to conduct redox polymer. The oxidation and reduction reactions that occur in the anode and cathode are shown in Fig. 10. The backbone of this polymer provides enough facilities to transfer ions within this structure while preventing dissolving in an electrolyte solution. This group used pyridine-based electrolytes containing proton donors and acceptors. There are some drawbacks that have been found by this team. This CP act as the conducting phase in a particular voltage range, otherwise, it shows insulating properties beyond this limit. Considering the high conductivity of this CP without using other conductive promoters, it is effective to use this in that potential difference. Further, the chemical performance of the PEDOT-AQ electrode is relatively low in an acidic medium or aqueous medium. Hydrophobic AQ can be applied as a solution to this issue. This group suggested that by improving the working potential and stabilty of the cathode material, and modifyning the electrolyte, the device could be developed as industrial-scale production.

4.2 Supercapacitors Supercapacitors, also known as ultracapacitors have become a tremendous device among other EESDs because of their unique features of high power density, high specific capacitance, fast charge/ discharge rate, and long cyclic stability. The problem with that is lower energy density compared with others. However, most recent research has found some techniques to improve the energy density of SCs. The type of electrode material is a very decisive factor in the fabrication SCs. These electrochemical capacitors are more popular in the application of aerospace, automobiles, bio-sensors, portable electronic devices, etc. [20]. Based on the energy storage mechanism, SCs are classified into three categories, electrical double-layer capacitors (EDLCs), pseudocapacitors (PCs), and hybrid capacitors (HCs). In that sense, the electrodes of EDLC are made of high surface areas of carbon materials

Conducting Polymers for Electrochemical Energy Storage Applications

63

Fig. 10 Redox reaction mechanism of PEDOT-based battery. Adapted with permission [19]. Copyright © 2017 American Chemical Society

such as activated carbon, carbon nanotubes, and carbon aerogels. This device stores energy via electrostatic charge accumulation at the electrode/electrolyte interface. Usually, EDLC exhibits high power density while showing low rate capability and low specific capacitance. In PCs, conducting polymers and transition metal oxides are the two main electrode materials that generate charge via rapidly reversible redox reactions. With compared to EDLC, PCs show higher specific capacitance. HCs are fabricated by using those two types of electrodes. Mainly, energy is stored on those devices by transferring charged ions at or near the surface of the electrodes. Due to excellent conductivity and high charge density, facile synthesis and lowcost CPs have a better performance compared to metal oxides and carbons. In particular, nano-structured CPs with high surface area and porosity are considered to be the best electrode materials for SC applications. Based on the usage of various types of doped CPs and other doping forms of CPs, there are three types of conducting polymer-based supercapacitors. They are completely identical p-type doped CPs, different p-type doped CPs, and combined n-type doped and p-type doped CPs. The main feature of the type I-CPs based SCs is their discharge ions quantity is half of the charge ones and the potential difference between two poles is relatively small value because both electrodes are identical. But the electrode materials of type-II SCs are composed of different p-type doped CPs. Therefore, this device has a higher potential window at a fully charged state. The problem with this type of device is that the charging process can not be reversed. This affects the working life of these SCs which limits their use. The final type the CP-based SC is composed of two different doped CPs. At a fully charged state, p-doped CPs can act as an anode and the cathode is represented by n-doped ones while enhancing the voltage difference between those

64

K. A. U. Madhushani and R. K. Gupta

two electrodes. This resulted in superior features such as a greater working potential window, and better super capacitance leading to a promising device. Moreover, a lower resistance in the internal circuit results in higher conductivity and better cyclic stability. By considering all the facts, it can be concluded that type III CP-based SCs have more advantages when compared with others [20] For instance, Dubal et al. [5] fabricated high-performance SC using porous PPy that was synthesized by electropolymerization. It is known that materials that are composed of nanostructures such as nanotubes, nanoribbons, nanobelts, nano bricks, and nanosheets have higher electrical conductivity due to the high surface area and porosity. Herein, this group experimented to find effective PPy by comparing the electrochemical performances in three different nanostructures of PPy. The ppy was deposited onto pure stainless steel foil to fabricate the electrodes. With the increase of the scan rate of deposition, the crystallinity of the polymer decreases by shortening the length of the polymer chain. Consequently, nanobelt, nano bricks, and nanosheet structures were obtained with deposition of the surface of PPy at a scan rate of 50 mV/ s, 100 mV/s, and 200 mV/s respectively PPy (Fig. 11). 0.5 M H2 SO4 was used as the electrolyte. In that sense, nanosheets showed a higher surface area of 3.71 m2 /g compared to nanobelts and nano bricks. According to that, cyclic voltammetry and galvanostatic charge–discharge tests proved that the highest specific capacitance of 568 F/g (at 2 mV/s) was exhibited from the multilayer nanosheet structured PPy [5]. The main issues with CPs are slow ion transport, and their lower cycle stability. Because of that, high-stability materials composed with CPs as composites are used to fabricate supercapacitors. As an example, Sahoo et al. synthesized graphene (GN)/ PPy nanofiber nanocomposite as electrode material for SC applications [21]. As discussed in Sect. 2, PPy nanofibers are synthesized using chemical, electrochemical,

Fig. 11 (i) Different forms of polypyrrole synthesized by electropolymerization with SEM images. Adapted with permission [5]. Copyright © 2012, Royal Society of Chemistry

Conducting Polymers for Electrochemical Energy Storage Applications

65

and microemulsion polymerization. This research group aimed to fabricate hybrid SC using GN/PPy composite as electrode material capable of both faradic and nonfaradic reactions. In this device, energy is stored due to anion and cation movements at the interface of the GN/PPy electrode and the electrolyte (Fig. 12). GN can increase the reactivity of the PPy nanofiber due to its high surface area and porosity. It has already been found that the conductivity of GN and PPy is 0.54 S/cm and 0.29 S/ cm respectively. But, this composite exhibited an electrical conductivity of 1.45 S/ cm at RT (302 K), which is higher than the individual materials. Moreover, PPy has the ability to increase capacity through redox reactions, and nanocomposites can improve it to a higher value. The highest capacitance of 466 F/g at 10 mV/s scan rate was showed by GN/PPy based SC in 1 M KCl electrolyte. Compared with past records of the composite of different conducting materials, this combination showed higher performance of SC. Also, this composite material maintained 85% capacitance retention after 600 cycles at a scan rate of 10 mV/s. The intermolecular bonding between GN and PPy nanofibers retained the regular structure without changing throughout the charge/discharge processes, resulting in high stability of the composite. From that, it is confirmed that an extended network of the composite structure is effective in overcoming the stability issue of CPs.

Fig. 12 Schematic illustration of the charging-discharging process. Adapted with permission [21]. Copyright © 2012, Elsevier

66

K. A. U. Madhushani and R. K. Gupta

5 Conducting Polymers Based Flexible Devices Based on all the feasible properties of eco-friendliness, controllable conductivity, doping, and dedoping capability, high flexibility, and ease of preparation, CPs are in great demand for the production of flexible devices. It has been significantly discovered that many recently developed flexible and wearable electronic devices are fabricated with CP-based materials due to their redox activity, high charge density, polymeric structure, ability to bend, stretch, and fold in any direction without compromising functionality. Because of the lower cyclic stability of CPs, it is quite challenging to improve the chemical performances of flexible energy storage devices while maintaining high mechanical properties. When reviewing past studies, it seems that CPs are selected as the most favorable materials for supercapacitors by comparing their electrochemical properties. Depending on the availability and application, the forms of CPs used for flexible CP-based supercapacitors vary as nanosheets, nanowalls, nanorods, nanofibers, hybrid films, powder, and hydrogels. Morphological changes in CPs play a decisive role in the electrochemical performance of SCs. One of the issues regarding CPs, low cyclic stability, can be overcome by making composites with CPs. In flexible SC fabrication, numerous CP-based composites are made by coupling CP with graphene oxide, metal oxides, carbon nanotubes (CNTs), etc. In 2022, Hong et al. [22] synthesized flexible SCs using PPy nanofoam (PPyNF) and CNT-based multilayered electrodes. Customized thermoplastic polyurethane (TRU) was taken to improve the flexibility of this device. The electrodes were synthesized by applying thin coatings of CNT/PANI on the TRU surface, then a three-dimensional conductive PPyNF active layer was applied on top of this layer. This flexible SC device was made as a sandwiched-like structure. The interlayer interactions within the system are enhanced through the polymerization of PPyNF. This group found that when applying horizontal force this membrane shows a high extension rate of 220% without damage. To demonstrate the mechanical properties of TPU/CNT/PANI and TPU/CNT/PPyNF composite electrodes, they were tested by bending and twisting (Fig. 13). In this test, it was confirmed that TPU/CNT/ PPyNF has excellent flexibility compared to other ones. Due to the strong bonding interactions between the layers, TPU/CNT/PPyNF was not damaged during twisting, but this could not be observed in TPU/CNT/PANI sample due to its lack of uniform layer form. Distinguishable features such as nanoporous structure can be observed clearly in SEM images of TPU/CNT/PPyNF. CNT in the center provides more space for electron transfer leading to higher conductivity and supports enhancing bonding interactions resulting in higher cyclic stability. Moreover, PPyNF provides higher porosity to the surface area that contributes to more charge storage and it helps to retain the flexibility of the TPU/CNT film. Considering all the characteristics, this group decided to fabricate the SC device with TPU/CNT/PPyNF composites instead using PANI. This composite exhibited 712 mF/cm2 of capacitance at 5 mV/s (scan rate) and 85% of capacitance retenition after 10,000 cycles, a capacity of 98.5% indicated high stretching ablity even at a angle of 90°.

Conducting Polymers for Electrochemical Energy Storage Applications

67

Fig. 13 Fabrication process for the TPU/CNT/PPyNF and TPU/CNT/PAni systems with multilayered structures established using in situ polymerization methodology. a TPU (5 wt%) was added in DMF solvent and stirred continuously for 4 h at 200 rpm until all pellets were dissolved. b (i) Then, 0.5 wt% of that TPU content was added into the container and continuously stirred, and sonication was carried out for proper dispersion. The resulting solution was solvent casted at ambient conditions to obtain TPU/CNT films. (ii) The as-fabricated TPU/CNT composite stretchable backbone offered high flexibility and stretchability when subjected to various mechanical stresses. c The PAni and PPy layers were grown on the TPU/CNT stacked system with in situ polymerization. d The PAni active layer formed only an extremely thin top layer on the TPU/CNT substrate, while the PPyNF was grown into a thicker (200–300 μm) foam layer with good adhesion. e TPU/CNT/PAni samples demonstrated desirable mechanical performance in flexibility and bending tests. f TPU/ CNT/PPyNF also performed well in flexing and bending without any dusting or other mechanical deformation. Adapted with permission [22]. Copyright © 2022, American Chemical Society

CP-based PVCs play a vital role in energy storage necessity in various applications such as robotics, textile, medical, etc. In order to achieve high performance in these fields, this device should have certain properties of lightweight, large surface area, higher flexibility, etc. In that sense, a polymer-based solar cell device that has a thickness of less than 2 μm and high PCE was discovered by Kaltenbrunner et al. [14]. The specialty of this invention is that the thickness and lightness of these flexible OPVCs are ten times greater than that of other PVCs according to the analytical reports of the time. Considering PVCs available in the market, they showed a PCE of 1.5% and a lifespan of 1 year. Further, they have recorded that some well-known companies produce PVCs by achieving a high PCE of 10–11%. Thus, the mechanical properties of these devices mainly depend on the substrate material used in fabrication. In this study, polyethylene terephthalate (PET) substrate with a thickness of 1.4 μm less than spider silk, was used as substrate. Ultrathin O-PVC was fabricated using PEDOT: PSS (one electrode), Ca/Ag evaporated metal electrode, P3HT: PCBM, PET (as substrate)

68

K. A. U. Madhushani and R. K. Gupta

showing a total thickness of 1.9 μm. The metal electrode in this device provides ultra-bending flexibility for this device. Further, they have demonstrated that PVCs becomes shrink while increasing compressive strain at 30 and 50% (Fig. 14). They found that 50% of compressive strain was equal to 100% of tensile strain. Herein, this device shows 4.2% of PCE, a specific weight of 10 W/g with high flexibility. Overall, the PEDOT: PSS materials can be considered as highly stretchable, costeffective, and conductive materials compared to the tertiary oxides which are mostly used for solar cells. This material has a high ability to achieve both long durability and efficiency while retaining extreme flexibility and being lightweight. Wang et al. [23] fabricated a CP-based battery composed of styryl-substituted dialkoxyterthiophene (poly(OC10 DASTT), PPyPF6 , and LiPF6 as anode, cathode, and electrolyte, respectively. The poly(OC10 DASTT) compound was synthesized

Fig. 14 a Schematic representation of flexible O-PVC, b demonstration of bending PVC device using human air, c diffentaiate the stretchy PVCs prepared by connecting the PVC to a pre-stretched elastomer at 30 and 50% percentage of compressive strain, d illustration of stretchability, e SEM image of PET surface in PVC. Adapted with permission [14]. Copyright © 2012, The authors. Published by Springer Nature

Conducting Polymers for Electrochemical Energy Storage Applications

69

through the casting method. In that case, neutral undoped poly(OC10 DASTT) was dissolved in chloroform solution and this was dropped into two different flat surfaces of Ni/Cu-coated nonwoven polyester, and carbon-fiber mat to synthesize the thin film of anode material. Subsequently, this group found that the two substrates exhibited better electrical conductivity and that the anode of the battery fabricated with poly (OC10 DASTT) on the polyester-based textile substrate exhibited a higher capacity of 39.1 mAh/g, excellent dishcrage efficiency (94%), greater steadiness, and better rate capability. This was a remarkable innovation in the textile industry that could be developed on an industrial scale.

6 Conclusion Over the decades, many efforts have been pointed toward CP materials for energy storage functions due to their considerably attractive features. Through this chapter, novel experiments on the synthesis and characterization of CP materials, and some of the successful and innovative research works on CP-based devices used for energy generation and storage have been briefly discussed. Furthermore, the explanation of novel innovations has been extended to modified flexible devices fabricated through the polymerization of nano-structured CPs on flexible substrates. Considering the recent research on CP-based apparatus, it is true that several drawbacks and challenges still exist in some cases, but some of them have overcome through advanced experiments as described in the previous sections. Thus, further experimental measures should be achieved to improve the chemical performance of those devices including cyclic stability, power, and energy density. Most research has been carried out on the lab scale and many practical challenges have to be faced when they moved to industrial usage. Therefore, extra attention should be paid to the mass production of such devices in industrial-scale applications. In that sense, long-term research and development studies on different CP materials with diverse techniques would be effective to conclude successful products. It is supposed that all the drawbacks, and unexpected results of current experiments, will pave the way for other findings. Obviously, no one can deny that in the next 10 years, SCs will take over the power device market by replacing Li-ion-based ones. There is great future demand for CP-based energy storage devices due to their benfbenefitslow cost, lightweight, long lifetime, and chemical performance. By putting all the facts together, the research and innovations on CP-based devices such as PVCs, FCs, SCs, and batteries, have made a significant evolutionary change in the energy storage application. In conclusion, it is believed that the content of this chapter will be useful in getting ideas for innovations in this field.

70

K. A. U. Madhushani and R. K. Gupta

References 1. Kausar A (2017) Overview on conducting polymer in energy storage and energy conversion system. J Macromol Sci, Part A: Pure Appl Chem 54:640–653 2. Han Y, Dai L (219) Conducting polymers for flexible supercapacitors. Macromol Chem Phys 220 3. Bryan AM, Santino LM, Lu Y, Acharya S, D’Arcy JM (2016) Conducting polymers for pseudocapacitive energy storage. Chem Mater 28:5989–5998 4. Kumar R, Singh S, Yadav BC, Nagar D (2015) Conducting polymers: synthesis, properties and applications. Int Adv Res J Sci, Eng Technol 2 5. Dubal DP, Lee SH, Kim JG, Kim WB, Lokhande CD (2012) Porous polypyrrole clusters prepared by electropolymerization for a high performance supercapacitor. J Mater Chem 22:3044–3052 6. Rabek JF, Lucki J, Zuber M, Qu BJ, Shi WF (1992) Polymerization of pyrrole by cationic photoinitiators 7. Saika T, Lrieb M, Shimidzuc T (1994) Thiophene oligomers with a photoswitch 8. Ruckenstein E (n.d.) Concentrated emulsion polymerization 9. Chemistry and Physics of Fire and Liquid Fuels 4.1 DEFINITION OF FIRE 4.1.1 Basic Conditions A/Fire Triangle 2007 10. Guo C, Lin YH, Witman MD, Smith KA, Wang C, Hexemer A, Strzalka J, Gomez ED, Verduzco R (2013) Conjugated block copolymer photovoltaics with near 3% efficiency through microphase separation. Nano Lett 13:2957–2963 11. Murad AR, Iraqi A, Aziz SB, Abdullah SN, Brza MA (2020) Conducting polymers for optoelectronic devices and organic solar cells: a review. Polymers (Basel) 12:1–47 12. Mozer AJ, Panda DK, Gambhir S, Romeo TC, Winther-Jensen B, Wallace GG (2010) Flexible and compressible goretex-PEDOT membrane electrodes for solid-state dye-sensitized solar cells. Langmuir 26:1452–1455 13. Yim JH, Joe SY, Pang C, Lee KM, Jeong H, Park JY, Ahn YH, de Mello JC, Lee S (2014) Fully solution-processed semitransparent organic solar cells with a silver nanowire cathode and a conducting polymer anode. ACS Nano 8:2857–2863 14. Kaltenbrunner M, White MS, Głowacki ED, Sekitani T, Someya T, Sariciftci NS, Bauer S (2012) Ultrathin and lightweight organic solar cells with high flexibility. Nat Commun 3 15. Lee WH, Mohanty AD, Bae C (2015) Fluorene-based hydroxide ion conducting polymers for chemically stable anion exchange membrane fuel cells. ACS Macro Lett 4:453–457 16. Li X, Chen D, Xu D, Zhao C, Wang Z, Lu H, Na H (2006) SPEEKK/polyaniline (PANI) composite membranes for direct methanol fuel cell usages. J Memb Sci 275:134–140 17. Jia X, Ge Y, Shao L, Wang C, Wallace GG (2019) Tunable conducting polymers: toward sustainable and versatile batteries. ACS Sustain Chem Eng 7:14321–14340 18. Jiménez P, Levillain E, Alévêque O, Guyomard D, Lestriez B, Gaubicher J (2017) Lithium n-doped polyaniline as a high-performance electroactive material for rechargeable batteries. Angew Chem 129:1575–1578 19. Emanuelsson R, Sterby M, Strømme M, Sjödin M (2017) An all-organic proton battery. J Am Chem Soc 139:4828–4834 20. Su DY, Liu ZG, Jiang L, Hao J, Zhang ZJ, Ma J (2019) Conducting polymers in supercapacitor application. IOP Conf Ser Earth Environ Sci 21. Sahoo S, Dhibar S, Hatui G, Bhattacharya P, Das CK (2013) Graphene/polypyrrole nanofiber nanocomposite as electrode material for electrochemical supercapacitor. Polymer (Guildf) 54:1033–1042 22. Hong SH, Shi HH, Naguib HE (2022) Polypyrrole nanofoam/carbon nanotube multilayered electrode for flexible electrochemical capacitors. ACS Appl Energy Mater 5:4059–4069 23. Wang CY, Ballantyne AM, Hall SB, Too CO, Officer DL, Wallace GG (2006) Functionalized polythiophene-coated textile: a new anode material for a flexible battery. J Power Sources 156:610–614

Conductive Polymer and Composites for Supercapacitor Applications Shilpa Pande, Bidhan Pandit, Shoyebmohamad F. Shaikh, and Mohd Ubaidullah

Abstract After the addition of dopants, conducting polymers with their own electrical conductivity were created. In addition to a polymer backbone, they also have a system of conjugated bonds. As a result of the conjugation, the polymers may now move electrons both along and across their chains (interchain hopping). Doping (of both p- and n-type) with acids and other substances produce conductivity. Both chemical and electrochemical approaches might be used to accomplish doping. The use of conducting polymer in electrochemical performances may be traced back to this finding. Doping can be accomplished by the application of voltage (in the form of electrons or holes). The charge may be stored and the capacitor’s defining double layer can develop. Moreover, charging and discharging may take place over a broad range of voltages, making them a promising option for energy storage in conjunction with power plants. Several methods, including electrochemical and chemical oxidation, have been used to oxidize the conducting monomer. When it comes to electrode material for supercapacitors or batteries, polyaniline is one of the most researched and commonly used conducting polymers. This chapter delves further into the topic of supercapacitor composites based on polymer electrolytes. Energy storage systems like supercapacitors and lithium and other ion batteries were analysed for their software development and fundamental design constraints, as well as their limitations and future and present possibilities for enhancing energy storage technology. The goal of this Chapter is to make it easier to collect and analyze data on this polymer, which should open up new avenues of inquiry. S. Pande (B) Department of Applied Physics, Laxminarayan Institute of Technology, R T M Nagpur University, Nagpur, Maharashtra 440033, India e-mail: [email protected] B. Pandit Department of Materials Science and Engineering and Chemical Engineering, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganés, Madrid, Spain e-mail: [email protected]; [email protected] S. F. Shaikh · M. Ubaidullah Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_5

71

72

S. Pande et al.

Keywords Charge storage · Conducting polymers · Electroactive materials · Supercapacitor · Pseudo capacitor

1 Introduction The functional composite material’s unique characteristic has been recognized for decades. Polymers have thousands or millions of monomer units. Polymers mostly insulate. Polymers separate from metals due to their weak electrical conductivity. In the early 1900s, a novel class of organic polymers having electrical conductivity was discovered [1]. Most electrically conducting polymers have a wide conjugation system with single and double bonds alternatively dispersed across the backbone. Most electrically conductive polymers share this structure. Conjugated polymers are stiff and miscible with most organic solvents. Alternating single and double bonds make the structure fragile. Linked side chains influence solubility and processability, while dopant ions give conducting polymers mechanical, electrical, and optical properties [2]. Conducting polymers can be separated from other polymers by their crystalline and amorphous shapes.

1.1 Overview of Conductive Polymer and Composites Functional polymer composites have improved electrical and thermal conductivity. Scientists have been mixing insulating polymers with conductive components to give polymers conductivity, low ionization potential, high electron affinities, and low energy optical transmission. Since polyacetylene was discovered, interest in conducting polymers has increased, leading to the invention of new ones (PA). Polyaniline (PANI), poly-thiophene (PTH), polypyrrole (PPy), poly(para-phenylene) (PPP), polyfuran (PF), and poly(phenylenevinylene) are the most common kinds of CP, although there are many more (PPV). A polymer composite’s electrical conductivity depends on filler distribution, aspect ratio, shape, size, filler conductivity and matrix interaction, water absorption, polymer matrix type, form, surface energy, orientation, and processing processes [3, 4]. Figure 1 compares the polymer’s conductivity range and fluctuations to others. Due to their ductility, low weight, electrical conductivity, and corrosion resistance, conductive polymer composites (CPCs) provide good metallic conductor alternatives. Delocalization of p bonds in conducting polymers is closely related to disorder states. State delocalization by polarons, bipolarises, solitons, and other charge carriers helps the insulator-to-metal phase transition. Conducting polymers conduct electricity via carrier concentration and mobility. Doping keeps carriers flowing, which increases conductivity. CPC material undergoes an insulator/conductor transition when the concentration of conductive filler

Conductive Polymer and Composites for Supercapacitor Applications

73

Fig. 1 Conductivity of conductive polymers compared to those of other materials, from quartz (insulator) to copper (conductor). Polymers may also have conductivities corresponding to those of semiconductors

increases [5]. New conductive channels in the polymer matrix may form as conductive dopants increase, perhaps increasing the material’s electrical conductivity. Interchain, intramolecular, and inter-particle transport make up polymer conductivity. These three elements constitute a complicated resistive network that influences carrier movement. Recent technological advances have made CPCs useful in sensors, circuit device components, fuel cell electrodes, batteries, and fuel cell bipolar plates [6].

1.2 Supercapacitor Applications Energy storage capacity has grown in significance for the economic and social development of countries undergoing profound change. A discussion about reducing our reliance on non-renewable fuel sources, substituting them with alternative energy sources, and re-evaluating the effectiveness of our current technologies has been sparked by a number of factors, including the rising cost of fuel, geological upheaval, and global climate change. Modern civilization and the planet will require efficient electrical storage systems built on cutting-edge materials with excellent electrochemical characteristics. The necessity for the creation of practical and efficient electronic systems is expanding, necessitating the development of more efficient energy storage systems (ESSs). A supercapacitor’s “capacitance,” or its ability to hold an electrical charge, is expressed in units called farads (F). The surface area of the two electrodes facing in different directions is directly related to the quantity of electrical energy that may be stored (capacitance). Applying the aforementioned equation to the CV curves, the specific capacitance was computed: C = Q/(Vm)

74

S. Pande et al.

where m(g) is the mass of the active materials, Q(C) is the average charge across the charging and discharging cycle, C(Fg) is the specific capacitor, and V(V) is the potential window. The following equation may be computed to obtain the discharge specific capacitance while analysing discharge curves [7]:   C = It/ m V where I(A) means the discharge current, t(s) denotes the time needed to discharge across a potential range of V, and V(V) denotes the potential windows. m(g) denotes the mass of the active materials, or the majority of the total electrode materials. The supercapacitor is a milestone in electrical energy storage technology. Figure 2 shows the latest supercapacitor. Supercapacitors have higher SE and SP than batteries and capacitors over their lifespan [8]. Supercapacitors have two electrodes, a separator, and electrolyte liquid. Safety and performance require hermetically sealed enclosures. Polymer gel electrolytes reduce leakage and maintain performance. Flexible and transparent displays, E-skins, and smart clothes require energy storage [9]. Supercapacitors are either pseudo capacitors or electrical double layer capacitors (EDLCs). Electrochemically, cations and anions store energy on double-layer capacitor (EDLC) electrodes. Pore size and homogeneity affect electrode performance. EDLCs utilise high-surface-area carbon materials like graphene, carbon nanotubes, and activated carbon. Redox processes make conducting polymers (CPs) and transition metal oxides/hydroxides pseudo-capacitors capacitance-producing. Pseudocapacitors may have higher specific capacitances than EDLCs due to the faradic process across the core. Supercapacitors’ electrode materials determine energy retention. Conducting polymers should beat carbon and RuO2 in electrical conductivity, surface roughness, chemical integrity, and faradic charge transfer [10].

2 Synthetic Strategies of Conducting Polymer Composites When two or more nanoparticles or nanosized things are connected using a suitable procedure, a composite material, or nanocomposites, is created with new physical properties and many possible applications. Scientists have exploited ordinary polymers’ strength as one component of nanocomposites [5] to maximise nanoparticle technology. Preliminary methods include harsh, gentle, and self-templating. Hard templating includes material construction, functional surface augmentation, and partial template removal. The hard templating approach involves duplicating particle nanostructures or employing nanochannels as templates for new structures. Nanostructures are formed through molecular self-assembly [11]. Soft templating methods like microemulsion and reversed-microemulsion synthesis build new nanostructures from scratch, but non-template (self-template) synthesis replicates an existing nanostructure through

Conductive Polymer and Composites for Supercapacitor Applications

75

Fig. 2 The schematic representation of supercapacitor development and challenges

chemical and/or physical interactions. Self-templating/interfacial approaches eliminate the need for a secondary template, saving time and money on synthetic procedures. CP formulation and synthesis have improved during the past 20 years [12]. Electrical conductivity is determined by the morphology of the conductive polymer composites and the architecture of the conductive network routes introduced into the composite matrix.

2.1 Chemical Synthesis of CPC Monomers are oxidised or reduced, then polymerized, to make CPs. The technology may allow cheap mass production. Many experiments have been done to improve oxidative polymerization production and quality. The chemical approach does not involve electrochemical processes. Stability is the key to chemical polymerization after conjugation. Electrochemical synthesis produces higher-quality materials than chemical synthesis, albeit at the expense of product quality. High-molecular-weight polymerization requires soluble and reactive oligomers and low-molecular-weight polymers. Monomer production must ensure polymerization. When chemical polymerization fails due to low molecular weight, the reaction vessel rims create a brittle coating. However, the technique selectively applies an oxidant to form cation radicals at the ideal monomer site, enhancing solubility.

76

S. Pande et al.

2.2 Electrochemical Polymerization Electrochemical polymerizations complicate polymer synthesis. Polymerization cells have three electrodes: monomer, solvent, and electrolyte. Controlled electrodes form functioning electrodes, or polymerization surfaces. The reference electrode’s constant potential allows reading the working electrode’s voltage. The counter or auxiliary electrode stops the electrolyte from resisting current. The counter electrode is commonly overlooked but essential to synthesis [13]. If the reference electrode is small, the counter electrode’s electrical and ionic transport can limit system transfer. If chemically inert, the ideal counter electrode has a contact area ten times bigger than the electrode surface. The SHE or any standard reference electrode with a known voltage could be the reference electrode [14]. However, most typical electrodes contain water, requiring a separate polymerization solvent–water interface. A voltage may change this contact’s junction potential. The reduction and oxidation of a conventional redox pair before and after electrochemical testing can verify safety. Even in two-electrode systems like galvanostatic polymerization, understanding the electrode potential-monomer oxidation relationship is difficult without a reference electrode. Figure 3 simplifies electrochemical polymerization, which produces PEDOT nanostructures and PPy polymer nanowires.

Fig. 3 Schematic depiction of PPy nanowires polymerization by electrochemical polymerization method. Adapted from Ref. [15]. Copyright The Authors, some rights reserved; exclusive licensee Royal Society of Chemistry. Distributed under a Creative Commons Attribution License 3.0 (CC BY) https://creativecommons.org/licenses/by/3.0/

Conductive Polymer and Composites for Supercapacitor Applications

77

2.3 Photo-Induced Polymerization Radiation starts photoinduced polymerization. Most monomers do not create enough starting species when exposed to light, hence photo initiators are commonly added [16]. Photoexcitation releases free radicals or ions from the unstable chemical. A large quantum yield from homolysis generates numerous radicals, which initiate quickly. Dissolving the light initiator in the reactive monomer generates and consumes radicals or ions in a chain reaction, producing a waxy polymer. Fast initiation increases bimolecular closure, allowing polymerization with short kinetic chains. This provides precision molecular weight management of the final product. Photoinitiation can use UV, visible, or other radiation. Multifunctional monomers cause photoinduced polymerization to crosslink in most industrial processes that involve ultraviolet light. This well-known UV curing technique turns monomers, light initiators, and additives into solids in a crystalline or rubbery state [17]. The method is intriguing because it can be done at room temperature without a solvent, turns a liquid monomer into a solid layer quickly, and modifies mechanical and physical–chemical properties.

2.4 Chemical Oxidative Polymerization After conjugation, solubility is chemical polymerization’s most essential structural factor. Oligomers and low-molecular-weight polymers must be reactive and solventcapable to polymerize into big molecules. If an oligomer crystallises, heterogeneous polymerization must occur, which becomes less likely as monomer and reactive polymer concentrations decrease. Failure chemical polymerization may leave the reaction vessel walls with an unstable mechanical covering. Chemical polymerization can place cation radicals on the monomer exactly by regulating the oxidant. FeCl3 is the most common oxidant. The polymer is kept in a solvent after oxidant removal. Chemical oxidation guides polymer to any suitable surface for coating. This method produces conductive polymers, however electrochemical polymers are more effective [18]. The thickness of the insulating barrier between a polymer-deposited electrode and the polymer may hinder charge transfer. Doping the polymer, which helps ions and electricity migrate, dramatically improves its conductivity.

2.5 Significant Difference Between Chemical and Electrochemical Methods Chemical polymerization synthesises most redox polymers. Electrochemically active groups are added before polymerization (pre-functionalized polymers) or after

78

S. Pande et al.

coating to make polymer film electrodes (post coating functionalization). Electrochemical polymerization uses ion-exchange polymers. Electrochemical polymerization can make thin-layer sensors and hybrid polymer film electrodes for conducting applications. We prioritise potential control since it’s crucial to manufacturing high-quality products and constructing the polymer film that will operate as an anode throughout production. Chemical synthesis is the most viable way to produce the device’s large amount of polymer. Chemical synthesis yields the most, yet it produces undesired by products. Electrochemical polymerization affects polymer shape and supramolecular structures such Nano globules, nanotubes, and microspheres. Electrochemical methods include voltage cycling between the oxidised conducting and neutral insulating states or redox agents can change the polymer’s oxidation state. Electrochemical polymerization’s electrode rotation affects film form, conductivity, and speed. Electrochemical techniques scale better than chemical synthesis. The smaller anode limits this method’s product output. The procedure’s advantage over a chemical technique is its thickness and form customization. Regulating some electrochemical parameters may help.

2.6 In Situ Copolymerization Technique In situ polymerization is a practical preparation process. It’s polymer research terminology. Fusing nanoparticles with polymers creates polymer nanocomposites [19]. The nanoparticles and low molecular weight liquid monomer or precursor are mixed first. Polymerization begins with the correct initiator and energy in a homogenous mixture. The initiator receives polymerization-initiating energy. After polymerization, polymer molecules attach to nanoparticles, creating the nanocomposite. In situ polymerization creates polymer nanocomposites by polymerizing precursor polymer molecules with a low viscosity (usually less than 1 Pa) in a short time. The polymer must have desirable mechanical properties and no side products. In situ polymerization in solutions containing the conducting polymer’s monomer and suspension of these components was the most common approach for generating nanocomposites of conducting polymers with CNTs, MNPs, or GN nanosheets. A monomer and a suspension of nanoparticles were mixed to make nanocomposites, which were microwaved with an oxidising agent.

2.7 Direct Deposition Polymerization Method Direct polymerization polymerizes metal foams and conductors. Making metal foam starts with a polymeric foam sacrificial specimen. This specimen modelled the product’s open cellular structure (dodecahedron cells). Electroplating Ni atoms

Conductive Polymer and Composites for Supercapacitor Applications

79

uniformly coats the specimen. Spraying alloying components at high-temperature homogenization destroys the polymeric substrate [5]. Polymers covered metal foams with different pore sizes. After a 10-s aerograph application at 2 cm from the specimen surface, the wet painted froth was posttreated with a regulated air flow to ensure uniform coating dispersion. Up to six paint treatments with intermittent drying achieved the required coating thicknesses and flow resistance pore sizes. Serial sectioning and 3D optical measurements ensured coating uniformity in test and control samples.

3 Composites Depending on Conducting Polymers for Supercapacitor Applications Due to their many beneficial qualities, such as their high electrical conductivity value, simple solution processing, electrochemical stability, low cost, and reversibility among the redox states by doping/dedoping procedures, conducting polymers (CPs) have recently gained popularity as candidate materials for use in supercapacitors. One p-dopable CP is used by Type I SCs, two p-dopable CPs are used by Type II SCs, and either p or n may be used to dope Type III SCs. Chemical or electrochemical approaches allow for rapid, binder-free CP deposition onto current collectors. This can be accomplished with relative ease.

3.1 Asymmetric Supercapacitors Asymmetric supercapacitors have two electrode materials (ASC). Redox (Faradic) processes drive one electrode, while electric double-layer absorption/distribution drives the other (i.e., non-Faradic or electrostatic processes) [20]. Aqueous electrolytes outperform organic ones in safety, capacitance, and ionic conductivity. The most essential electrode materials for aqueous ASCs enable power sources with higher energy density at greater power densities than conventional capacitors. Most ASC constituents are pseudocapacitive, porous carbon, lithium intercalation compounds, graphene oxide, and conductive polymers. Electrodeposition can make all polymer-dependent ASCs without carbonaceous components in one step [21]. In the most significant case ever, PEDOT conducting polymer was chosen as the negative electrode material because it has electrochemical activity over a wide potential window of roughly 1.4 V. Asymmetric solid-state supercapacitors with polyaniline (PANI) positive electrodes were made on Au-coated plastic PEN substrates [22].

80

S. Pande et al.

3.2 Flexible Supercapacitors Flexible supercapacitors have a long lifespan and high power density in a tiny unit. They’re supercapacitors. Black phosphorus, graphene, aramid nanofiber, and other CP films are composited to make flexible hybrid film electrodes for film-type flexible CP supercapacitors [23]. A hybrid hydrogel electrode created a programmable solidstate supercapacitor with high energy density and areal specific capacitance [24]. Hybrid CP hydrogels have been created to address the mechanical and adjustability challenges of pure CP-dependent conductive hydrogels for flexible supercapacitors. One-dimensional (1D) fibre supercapacitors make clothing electronics easy. CNT and graphene-based flexible supercapacitors have been developed recently [25]. Wetspun, solution-dried, and dip-coated flexible supercapacitors can have high pseudo capacitance [26].

3.3 Significant Challenges in Supercapacitors These supercapacitors’ specific energy and coulombic efficiency depend on the redox processes’ electroactive material (EAM). Low capacitance negative electrode materials reduce performance [27]. Super-capacitors need a quantum leap in specific power and energy as the market grows. To compete with lithium-ion batteries, supercapacitors must increase their existing fast charging and discharging rates, long cycle life (greater than 10,000 cycles), and wide working temperature range. Wearable electronics, backup power supplies, cell phones, computers, video cameras, and signal transmitters use high-performance supercapacitors. Cyclic durability is shown by capacity retention after a given number of discharge/charge cycles or work hours. This measure determines supercapacitor lifespan. Stability and ageing cause electrolyte degradation, which is exacerbated by high temperatures and voltages. SC cells last long because activated carbon electrodes are chemically and electrochemically inert. Battery electrode materials’ delayed phase shift kinetics during charging and draining create cycle instability. Cycle testing rapidly degrades conducting polymer electrode materials, causing low cyclic stability. Growing conductive polymers break their molecular chains. Changing the polymer film’s molecular structure or layer spacing increases its cyclic stability. Nanomaterials can improve ion adsorption, expedite electrolyte transit to the redox active site, and reduce ion distance. Thus, the electrode’s cyclic stability and process kinetics improve [18]. The coatingencapsulant synergy makes the combined process ultra-long cycle stable. The coating protects the material’s structure, making it more cyclically stable”. These low current density values are surprising given that capacitance retention after 600 cycles is less than 60% [28]. A supercapacitor’s electrodes and other components bond after several cycles. Electric double-layer capacitors outperform pseudo and regular supercapacitors in cyclic stability. Phyllic electrolytes promote electrochemical reactions and

Conductive Polymer and Composites for Supercapacitor Applications

81

cyclic stability. To study high-performance supercapacitors with good cycle stability, electrolyte-phylicity must be balanced for charging and discharging without harming or dissolving the structure.

3.4 Binary Composites Depending on Conducting Polymers for Supercapacitor Applications Composite materials outperform their constituents in mechanical stability, electrochemical activity, etc. However, the volumetric shrinking of certain CPs during dedoping reduces cycle stability, necessitating CP performance improvements in these areas. Composites with metal oxide, ferrite particle, and carbon-based fibre reinforcement can achieve this goal [29]. Particles, flakes, or fibres in CP binary nanocomposite reinforcing phases generate two-part structures. The reinforcing phase joins the CP matrix phase. Combining CPs with other components creates binary and ternary nanocomposites. A conductive polymer must have a nanoscale reinforced component to work with a solid-phase conducting material like metal or ceramic (1–100 nm). Graphene and its derivatives combined with carbon derivatives create common binary composites and low-complexity composites. Many researchers have considered integrating nanomaterials with polymers due to their efficient electrical behaviour, which can be generated by electronic interactions of structural modifications in the binary components of polymers [30].

3.4.1

Conductive Binary Polymer-Carbon Composites

Many carbon compounds can be utilised as supercapacitor electrodes (also known as EDLC). Activated/porous carbon, carbon aerogels, organised mesoporous carbons, carbon from carbides, carbon nanotubes, and graphene are some examples. Electrochemical polymerization, interfacial polymerization, and chemical polymerization can produce carbon-based nanocomposites [31]. Carbon-based materials have high conductivity and a huge surface area, making them ideal for supercapacitor electrodes. Carbon black particles and carbon fibres provide polymer composites conductivity. Carbon fibres are long strands of carbon atoms. Carbon particles’ chainlike aggregate structures make them more likely to form a conductive network than metal powder. To maximise capacitance, carbon compounds are copolymerized with conducting polymers containing nanostructures. Carbon-based materials are used to make supercapacitor electrodes because they are very conductive and stable.

82

3.4.2

S. Pande et al.

Binary Polymer-Graphene Conductive Composites

Graphene and its derivatives affect composite materials’ morphologies, structural stabilities, and electrical characteristics, improving CPs’ electrochemical performances. However, several factors other than graphene affect conductive polymer supercapacitors. Supercapacitors have specialised capacitance, cycle stability, discharging, and charging characteristics. Electrolyte, graphene characteristics, composite graphene dispersion/aggregation, intrinsic CP properties, and polymerization process are other considerations [32].

3.4.3

Binary Polymer-CNT-Based Conducting Composites

Percolation explains thermoplastic composites’ electrical conductivity. Conductivity-filler content relationship (commonly named as percolation threshold). The synthesis polymer, nanotube, and solvent can impact the percolation threshold [34]. In-situ chemical oxidative polymerization with different surfactants and insertion into an insoluble and infusible polymer matrix controlled PPy-CNT nanocable size. Changing the mass ratio of pyrrole to carbon nanotubes can accurately adjust nanocable diameter. Its synthetic composite conductivity was 100 times higher than pure PPy and temperature dependent. MWCNT-PPy composite films’ low cost and high charge storage capacity may assist supercapacitors and secondary batteries (many times more than that of either CNT or PPy). CNT-polymer matrix interactions may increase features. An alternating electric field may vary the capacitance of electrochemically generated PPy-CNT composite sheets. Cycle voltammography showed 76% capacitance retention in PPy, CNT/PPy supercapacitors [25].

3.4.4

Binary Polymer-Porous, Mesoporous-Based Conductive Composites

3D carbon materials are more conductive than 1D and 2D carbon. Three-dimensional carbon compounds like mesoporous and porous carbon, as well as other threedimensional carbon materials, are potential electrode materials for supercapacitors due to their high conductivity and simple access to electrolytes. Polymer-graphene replaced graphene during hydrothermal treatment, enhancing the composite’s porosity. The suggested method produces a porous composite with good electrolyte accessibility, even with a large polymer mass contribution [35]. Hierarchically porous nanostructures accelerate electrode/electrolyte contact, ion transport, and electron exchange, increasing power density and rate capability. Electrolyte ions cannot reach all electrode micropores [36]. When 3D carbon material hole diameters match electrolyte ion sizes, capacitance is optimal.

Conductive Polymer and Composites for Supercapacitor Applications

83

3.5 Binary Conducting Polymer-Metal (Sulphides, Metal Oxides, Metal Hydroxides, Etc.) Composites Recent research has focused on the charge requirement for multivalence metal cation synergy. The composite’s synergistic composition makes electrode ion and charge movement easier, improving redox processes. Transition metal-dependent electrodes were also studied because to their superior metallic conductivity, redox reaction sites, and electrochemical stability over monometallic oxides [6]. Electrodes must be made stronger. A blend of metal oxides, metal sulphides [37, 38, 39, 40, 41], and metal hydroxides during composite manufacture improved their mechanical characteristics and electrical conductivity.

3.5.1

Ruthenium Oxide (RuO2 )

Recent Li-ion battery electrodes use RuO2 . RuO2 has shown strong electrocatalytic capabilities in many electrochemical processes. The molecular orbital (MO) theory described RuO2 ’s extraordinary isotropic charge transfer and thermodynamic stability. RuO2 , a preferred electrode material for EES applications, has strong electroactivity in both amorphous and crystalline forms. Cyclic voltammetry is needed to understand electrode surface redox reactions. The RuO2 /solution interface can store energy like an electric capacitor before discharging it. RuO2 crystal microorientations can affect electrochemical properties. In ruthenium oxides, proton or cation insertion from the electrolyte and electrochemical interconversions between metal oxidation states create pseudo capacitance. KOH stored voltametric charges better than HClO4 across the same voltage range. Alkaline environments allow oxygen evolution, stabilising surface Ru atoms with higher oxidation states [42]. RuO2 /polyaniline nanocomposites show that a favourable electrochemical deposition cycle can produce a high active surface area based-porous in 1 M H2 SO4 .

3.5.2

Manganese Dioxide (MnO2 )

Manganese dioxide (MnO2 ) high’s capacitance, low cost, abundant natural supply, and lack of environmental impact have made it popular in energy storage. MnO2 ’s poor electrical conductivity and high dissolvability limit its performance, making it unsuitable for developing technology. MnO2 is a common electrode material for metal-ion batteries and supercapacitors. Noble metals in composite materials boost MnO2 electrochemical performance. Scientists have produced many nanostructured MnO2 -based electrodes with customizable morphologies, hierarchical porous topologies, high pore diameters, and large electroactive regions to increase charge storage. Due to their unique atomic arrangements, polymorphs have different surface characteristics, crystal structure pore and channel sizes, and chemical selectivity for various electrolyte ions. Polypyrrole increased MnO2 ’s capacitance [43]. The

84

S. Pande et al.

Fig. 4 CV curves of different electrodes NiO/Ni(OH)2 /PEDOT electrode at different scan rates and cycling performance of the electrode. Adapted with permission [45], Copyright 2016, American Chemical Society

capacitance of nanoscale MnO2 powder could reach 294 F/g [44]. High-temperature electrochemical processing produces coaxial MnO2 /PEDOT nanowires on anodized alumina (AAO). This technique builds a hierarchical MnO2 architecture on a functionalized carbon nanotube before polymerizing with PEDOT.

3.5.3

Conducting Polymer/nickel Oxide–hydroxide Composites

Nickel oxide (NiO) and nickel hydroxide (Ni(OH)2 ) have been considered for use in composites with conducting polymers as electrochemical devices for supercapacitors due to their low cost, unique redox reaction, ease of synthesis, and relatively high theoretical specific capacitance (2584 F/g for NiO and 2081 F/g for Ni(OH)2 ). A flower-shaped PANI-NiO nanostructure was formed on nickel foams for binder-free electrodes. These nanostructures may retain 70% of their initial specific capacitance of 2565 F/g at 1 A/g when the current density is ten times higher [45]. Figure 4 shows how covering the PNC’s surface with a thin layer of protective PEDOT improves the electrical conductivity and integrity of NiO/Ni(OH)2 /PEDOT composites. The flower-shaped 3D nanostructure has a remarkable specific capacity of 4 mA/cm2 and a maximum yield of 82.2% after 1000 long-term cycles. Ni-based polymer nanocomposite has simplified, secured, and efficiently produced high-performance hybrid energy storage technologies.

3.5.4

Composites of Conductive Polymers Metal Oxide–hydroxides

Metal oxide or hydroxide supercapacitor electrode materials have higher energy densities than carbon-based and conductive polymers. The electrode materials’

Conductive Polymer and Composites for Supercapacitor Applications

85

surfaces and cores transport electrons for metal oxides/hydroxides, allowing for high capacitances. Scientists have produced polymer-metal oxide/hydroxide composites for supercapacitors [22]. These composites have high specific capacitances and cycle stabilities. The composites’ conductive polymers use space steric hindrance and the electrostatic effect to prevent metal oxide/hydroxide particles from clumping and dispersing. Conductive polymers and metal oxides/hydroxides like vanadium oxides (V2 O5 ) [39], cobalt monoxide (CoO), and hematite can be used to make supercapacitor electrodes (a-Fe2 O3 ). V2 O5 ’s fast ion transport, caused by its various oxidation states, layered structure, and surface/bulk redox interactions, has garnered interest.

3.5.5

Conductive Polymers Incorporating Metal Sulphides

Transition metal sulphides have fewer intercalation pseudo-capacitance reports than metal oxides. Ion intercalation and de-intercalation between supercapacitor layers is slow. Thus, improving rate performance requires increasing electrical conductivity and interlayer gaps. It’s fascinating that some transition metal sulphides carry electricity. PPy was evenly deposited as a sheet-like component on CuS microspheres, resulting in standard specific capacitance and outstanding cycle stability [30, 46]. The homogeneous integration of PPy into the sheet-like component structure on the CuS surface produces pseudocapacitive CuS microspheres. Simple solvothermal synthesis at 150 °C yields CuS microspheres with interwoven sheetlike subunits. This method requires no surfactant or mould. Electrochemical tests reveal that the CuS/PPy composite electrode has great cycle stability and capacity in supercapacitors.

4 Ternary Composites of Conducting Polymers for Supercapacitor Applications Binary composites of CPs with graphene and its derivatives offer superior electrochemical properties as compared to pure CPs. Researchers have tested a number of combinations of graphene/CP composites with metal sulphides, metal oxides, and non-metal oxides in order to improve their electrochemical performance in SCs. Ternary composites perform better electrochemically than binary composites. Better performance from CPs, graphene, and other materials is coupled with shorter diffusive paths thanks to improved Supercapacitance performance. Graphene, metal oxides, and CP ternary composites can be used to reduce nanoparticle segregation and boost cycle stability. Graphene/CP composites utilise ternary composite metals and metal oxides or sulphides for their conductivity and pseudo capacitance. The addition of a non-metallic, low-conductivity material to graphene/CP composites may improve their electrochemical performance.

86

S. Pande et al.

4.1 Metal Oxide-Based Ternary Nanocomposites Conducting polymers made from nanocomposites of rare earth oxides or transition metal oxides may increase energy density by increasing their specific capacitance. Nanoparticles in polymer matrixes make good energy storage electrodes due to their increased electrochemical properties. NiO and Co3 O4 are more studied than other transition metal oxides due to their high theoretical capacitance, significant reaction activity, and natural occurrence. Faradaic interactions with Ni and Co ions may boost electrochemical effects. A straightforward chemical synthesis produced this Pr2 O3 , NiO, and Co3 O4 ternary nanocomposite [47]. In cyclic voltammetry, the ternary nanocomposite had a greater specific capacitance than the binary ones. The polymer matrix improves ion transport and core–shell shapes increase surface-dependent electrochemical properties, increasing capacitance.

4.2 Ferrite-Based Ternary Nanocomposites In recent years, scientists have generated various ternary ferrite nanocomposites using carbon derivatives. Polyaniline has high electrical conductivity and specific capacitance. There’s little surface area, and volume varies quickly when charging and discharging. Ferrite metal oxide electrodes have high capacitance but a reduced surface area. Graphene oxide/polymer electrodes have a huge surface area but low specific capacitance. Due to its huge voltametric area and good interlinking arrangement, the ternary GO/PANI/CoFe2 O4 Ferrite material has the highest current and capacitance. The ternary composite scan rate boosts EDLC and decreases pseudo capacitance. Charge storage determines this feature. Electrolyte ions cannot reach the active material’s surface at high scan rates. At 20 A/g, the GO/PANI/CoFe2 O4 composite had an even higher coulombic efficiency of 89.12%. After 5000 CV cycles, Verma et al. [48] found that manufactured ferrite-based materials retained 79.03% of their initial capacitance (shown in Fig. 5). The GO/PANI/ CoFe2 O4 ferrite-based ternary conducting polymer material had a greater specific capacitance than related binary materials. Graphene oxide (GO) reduces PANI molecule volumetric contraction and expansion in the ternary GO/PANI/CoFe2 O4 composite, increasing stability. CoFe2 O4 improves charge transport in the ternary composite. The ternary system had good electrochemical properties, making supercapacitor devices predictable.

4.3 Graphene/Carbon Nanotubes/Polyaniline Ternary Nanocomposites Chemically doped graphene is used as a supercapacitor electrode due to its high specific capacitance, fast rate, and good cycle performance. This was done to boost

Conductive Polymer and Composites for Supercapacitor Applications

87

Fig. 5 GCD (Galvonostatic charge–discharge) plot a At 1A/g of different samples, b at different current density of the ternary sample, c changes of specific capacitance varies with scan rate using 3E and symmetric 2E system. d Ragone plot, e changes of coulombic efficiency with current density for ternary composites, f Retention (%) of capacitance up to 5000 cycles. Adapted with permission [48], Copyright 2022, Elsevier

energy storage capacity. Electro-deposition of polyaniline onto reduced graphene oxide/carbon nanotubes/polyaniline (S-rGO/CNTs/PANI) composite films produced durable and flexible membranes. Liu Dong et al. reveals that all electrodes have optimal capacitive characteristics at low frequency, with the best conductivity or lowest internal resistance, regardless of polarisation impedance (Fig. 6) [49]. To test cycling robustness, many S-rGO/CNTs/PANI composite membrane electrode iterations were cycled 2000 times in 1.0 M H2 SO4 at 0.1 V/s. All electrodes demonstrated exceptionally high cycling stabilities, and S levels correlated negatively with

88

S. Pande et al.

Fig. 6 Cycling stability of the S-rGO/CNTs/PANI-10, S-rGO/CNTs/PANI-15, S-rGO/CNTs/ PANI-20 and S-rGO/CNTs/PANI-25 composite membrane electrodes by CV cycles in 1.0 MH2 SO4 aqueous solution at a scan rate of 0.1 V/s [49]. Adapted with permission [49], Copyright 2017, Elsevier

cycle stability. S-rGO nanosheets, which are hydrophilic, retained 95.02% specific capacitance.

4.4 Polyaniline/Polypyrrole/Carbon Nanotubes Ternary Nanocomposites Electrically conducting polymers like PANI, PPy, PEDOT, and others are studied and used due to their favourable physicochemical properties, such as electrically tunable permeability, strong supercapacitors, flexibility, simple processability from solution, and reversible electrochemical doping/dedoping. Reversible charging and discharging at the electrode/electrolyte interface is shown by the perfect rectangular cyclic voltammograms of the PANI/PPy and Metal oxide ternary nanocomposites at varied scan speeds. Redox cycling affects electrode mechanical stability due to mass insertion/ejection in polymer chains and chain flaws in the polymer matrix caused by recurrent swelling and shrinking. PANI/PPy and metal oxide ternary nanocomposites were stable electrolytes without redox reactions. Symmetrical CV curves optimise capacitive properties at the electrode/electrolyte contact under operational conditions. Polymer interacts with KMnO4 to form structured, homogeneous charge storage structures. Metal oxide molecules in a polymer matrix appear to degrade CV performance at high scan rates. Use the anode-specific range from 0.02 to 1.5 V [30, 31]. The higher maximum voltage window will increase capacities, but not for all anode materials. Asymmetric supercapacitors were developed to increase energy density and operating voltage window.

Conductive Polymer and Composites for Supercapacitor Applications

89

Conducting polymer composites have several benefits: Accessible and practical smart material behaviour includes reduced weight, low energy usage, corrosion resistance, and strength from extra materials. Its degradation resistance, lack of solubility in advanced circumstances, and inefficient cell-polymer interaction are negatives. Biodegradable composites are a response to environmental consciousness and pollution reduction. New polymerization methods using supercritical CO2 and chemicals may be profitable and reduce harmful waste. Its high modulus and corrosion resistance make disposal and reuse challenging. Expiration debris, faulty components, and discarded samples add to the polymer composite garbage pile. Developing nations recycle mechanical and chemical polymer composite waste. Ecological health requires assessing an item’s life cycle from design through disposal. Enhancing regulatory evaluation and monitoring will encourage clean processing, applications, biodegradation, recycling, and reprocessing.

5 Conclusions, Future Prospects and Challenges Energy storage devices are increasingly using compact, flexible, and wearable supercapacitors. Cycle life is crucial for working supercapacitors. This chapter covers conducting polymer composite fabrication, cyclic stability, and performance. Conducting polymer electrodes have poor performance and cyclic stability. Mixing conducting polymers with other materials efficiently can create composite electrode materials to address these difficulties. Composite nanostructures in conducting polymer composite electrodes boost energy density and cycle stability. Compared to theoretical values, conductive polymer composite capacitance values are low. Conducting polymers can improve their capacitance despite being created with hydroxides, metal oxides, and sulfides. Despite some basic research, ternary conductive polymer composite electrodes for batteries and supercapacitors haven’t received much attention. Hybrid nanostructures may be more stable in multiphase systems, making batteries and supercapacitors more efficient. Conductive polymer composite electrodes will provide flexible, intelligent, and cost-effective energy storage. Over the past decade, researchers have been increasingly interested in and successful at studying conductive polymer composites. Electrochemical performance must improve energy density, capacitance rate retention, self-discharging, and cost. Acknowledgements Bidhan Pandit acknowledges the CONEX-Plus programme funded by Universidad Carlos III de Madrid (UC3M) and the European Commission through the MarieSklodowska Curie COFUND Action (Grant Agreement No 801538).

90

S. Pande et al.

References 1. Zhang L, Du W, Nautiyal A, Liu Z, Zhang X (2018) Recent progress on nanostructured conducting polymers and composites: synthesis, application and future aspects. Sci China Mater 61(3):303–352. https://doi.org/10.1007/s40843-017-9206-4 2. Li Z, Xu K, Pan Y (2019) Recent development of supercapacitor electrode based on carbon materials. Nanotechnol Rev 8(1):35–49. https://doi.org/10.1515/ntrev-2019-0004 3. Mohd Radzuan NA, Sulong AB, Sahari J (2017) A review of electrical conductivity models for conductive polymer composite. Int J Hydrogen Energy 42(14):9262–9273. https://doi.org/ 10.1016/j.ijhydene.2016.03.045 4. Gangopadhyay R, De A (2000) Conducting polymer nanocomposites: a brief overview. Chem Mater 12(3):608–622. https://doi.org/10.1021/cm990537f 5. Sisido M (2015) Encyclopedia of polymeric nanomaterials. https://doi.org/10.1007/978-3-64229648-2 6. Yang D (2012) Application of nanocomposites for supercapacitors: characteristics and properties. Nanocomposites—New Trends Dev, pp 1–55. https://doi.org/10.5772/50409 7. Jiang H, Yang L, Li C, Yan C, Lee PS, Ma J (2011) High-rate electrochemical capacitors from highly graphitic carbon-tipped manganese oxide/mesoporous carbon/ manganese oxide hybrid nanowires. https://doi.org/10.1039/C1EE01032H 8. Narayanan S, Pankajakshan AE, Padmanabhan VT, Joseph A (2022) Conducting polymer nanocomposites for supercapacitors. In: Polymer Nanocomposites in Supercapacitors. CRC Press, pp 17–41. https://doi.org/10.1201/9781003174646-2 9. Zhao C, Jia X, Shu K, Yu C, Wallace GG, Wang C (2020) Conducting polymer composites for unconventional solid-state supercapacitors. J Mater Chem A 8(9):4677–4699. https://doi.org/ 10.1039/c9ta13432h 10. González A, Goikolea E, Barrena JA, Mysyk R (2016) Review on supercapacitors: technologies and materials. Renew Sustain Energy Rev 58:1189–1206. https://doi.org/10.1016/J.RSER. 2015.12.249 11. Pang H, Xu L, Yan DX, Li ZM (2014) Conductive polymer composites with segregated structures. Prog Polym Sci 39(11):1908–1933. https://doi.org/10.1016/j.progpolymsci.2014. 07.007 12. Pan L et al (2010) Conducting polymer nanostructures: Template synthesis and applications in energy storage. Int J Mol Sci 11(7):2636–2657. https://doi.org/10.3390/ijms11072636 13. Kondawar SB (2022) Conducting polymer nanocomposites for supercapacitors. Accessed Oct 16 2022 [Online]. Available: http://www.polymer-books.com 14. Callegari V, Demoustier-Champagne S (2011) Using the hard templating method for the synthesis of metal-conducting polymer multi-segmented nanowires. Macromol Rapid Commun 32(1):25–34. https://doi.org/10.1002/marc.201000486 15. Cui S, Zheng Y, Liang J, Wang D (2016) Conducting polymer PPy nanowire-based triboelectric nanogenerator and its application for self-powered electrochemical cathodic protection. Chem Sci 7(10):6477–6483. https://doi.org/10.1039/C6SC02562E 16. Bella F, Bongiovanni R (2013) Photoinduced polymerization: an innovative, powerful and environmentally friendly technique for the preparation of polymer electrolytes for dye-sensitized solar cells. J Photochem Photobiol C Photochem Rev 16:1–21. https://doi.org/10.1016/j.jphoto chemrev.2013.03.002 17. Nguyen DN, Yoon H (2016) Recent advances in nanostructured conducting polymers: from synthesis to practical applications. Polymers (Basel) 8(4):1–53. https://doi.org/10.3390/pol ym8040118 18. Huang S, Zhu X, Sarkar S, Zhao Y (2019) Challenges and opportunities for supercapacitors. APL Mater 7(10):100901. https://doi.org/10.1063/1.5116146 19. Hammad AS, Noby H, Elkady MF, El-Shazly AH (2018) In-situ polymerization of polyaniline/ polypyrrole copolymer using different techniques. IOP Conf Ser Mater Sci Eng 290(1):0–8. https://doi.org/10.1088/1757-899X/290/1/012001

Conductive Polymer and Composites for Supercapacitor Applications

91

20. Singh A, Chandra A (2015) Significant performance enhancement in asymmetric supercapacitors based on metal oxides, carbon nanotubes and neutral aqueous electrolyte. Sci Rep 5. https:/ /doi.org/10.1038/srep15551 21. Volkov AV et al (2019) Asymmetric aqueous supercapacitor based on p- And n-type conducting polymers. ACS Appl Energy Mater 2(8):5350–5355. https://doi.org/10.1021/acsaem.9b00853 22. Kurra N, Wang R, Alshareef HN (2015) All conducting polymer electrodes for asymmetric solid-state supercapacitors. J Mater Chem A 3(14):7368–7374. https://doi.org/10.1039/C5T A00829H 23. Liu H et al (2018) Electrically conductive polymer composites for smart flexible strain sensors: a critical review. J Mater Chem C 6(45):12121–12141. https://doi.org/10.1039/C8TC04079F 24. Huang H, Abbas SC, Deng Q, Ni Y, Cao S, Ma X (2021) An all-paper, scalable and flexible supercapacitor based on vertically aligned polyaniline (PANI) nano-dendrites@fibers. J Power Sources 498:229886. https://doi.org/10.1016/J.JPOWSOUR.2021.229886 25. Shown I, Ganguly A, Chen LC, Chen KH (2015) Conducting polymer-based flexible supercapacitor. Energy Sci Eng 3(1):2–26. https://doi.org/10.1002/ESE3.50 26. He N et al (2019) Mordant inspired wet-spinning of graphene fibers for high performance flexible supercapacitors. J Mater Chem A 7(12):6869–6876. https://doi.org/10.1039/C8TA12 337C 27. El-Kady MF et al (2015) Engineering three-dimensional hybrid supercapacitors and microsupercapacitors for high-performance integrated energy storage. Proc Natl Acad Sci U S A 112(14):4233–4238. https://doi.org/10.1073/pnas.1420398112 28. Shaikh NS et al (2022) Novel electrodes for supercapacitor: Conducting polymers, metal oxides, chalcogenides, carbides, nitrides, MXenes, and their composites with graphene. J Alloys Compd 893:161998. https://doi.org/10.1016/J.JALLCOM.2021.161998 29. Omar FS, Numan A, Duraisamy N, Ramly MM, Ramesh R, Ramesh R (2017) Binary composite of polyaniline/copper cobaltite for high performance asymmetric supercapacitor application. Electrochim Acta 227:41–48. https://doi.org/10.1016/J.ELECTACTA.2017.01.006 30. Ashritha MG, Hareesh K (2020) A review on graphitic carbon nitride based binary nanocomposites as supercapacitors. J Energy Storage 32:101840. https://doi.org/10.1016/J.EST.2020. 101840 31. Jain R, Mishra S (2021) Conducting polymer carbon-based binary hybrid for supercapacitors. Handb Supercapacitor Mater, pp. 205–224. https://doi.org/10.1002/9783527824779.CH7 32. Azman NHN, Mamat @ Mat Nazir MS, Ngee LH, Sulaiman Y (2018) Graphene-based ternary composites for supercapacitors. Int J Energy Res 42(6):2104–2116. https://doi.org/10.1002/ ER.4001 33. Zhao F, Zhang G, Zhao S, Cui J, Gao A, Yan Y (2018) Fabrication of pristine graphene-based conductive polystyrene composites towards high performance and light-weight. Compos Sci Technol 159:232–239. https://doi.org/10.1016/J.COMPSCITECH.2018.02.013 34. Nayak SK, Mohanty S, Unnikrishnan L (2017) Trends and applications in advanced polymeric materials. Trends Appl Adv Polym Mater, pp 1–310. https://doi.org/10.1002/9781119364795 35. Moyseowicz A, Gryglewicz G (2020) High-performance hybrid capacitor based on a porous polypyrrole/reduced graphene oxide composite and a redox-active electrolyte. Electrochim Acta 354:136661. https://doi.org/10.1016/J.ELECTACTA.2020.136661 36. Ji C, Liu Y, Li Y, Su X, Xu J, Lu L (2021) Facile preparation and excellent microwave absorption properties of cobalt-iron/porous carbon composite materials. J Magn Magn Mater 527:167776. https://doi.org/10.1016/J.JMMM.2021.167776 37. Pande SA, Pandit B, Sankapal BR (2017) Electrochemical approach of chemically synthesized HgS nanoparticles as supercapacitor electrode. Mater Lett 209:97–101. https://doi.org/10.1016/ j.matlet.2017.07.084 38. Karade SS, Agarwal A, Pandit B, Motghare RV, Pande SA, Sankapal BR (2019) First report on solution processed α- Ce2 S3 rectangular microrods: an efficient energy storage supercapacitive electrode. J Colloid Interface Sci 535:169–175. https://doi.org/10.1016/j.jcis.2018.09.076 39. Pande SA, Pandit B, Sankapal BR (2019) Vanadium oxide anchored MWCNTs nanostructure for superior symmetric electrochemical supercapacitors. Mater Des 182:107972. https://doi. org/10.1016/j.matdes.2019.107972

92

S. Pande et al.

40. Pandit B, Pande SA, Sankapal BR (2019) Facile SILAR processed Bi2 S3 :PbS solid solution on MWCNTs for high-performance electrochemical supercapacitor. Chin J Chem 37:1279–1286. https://doi.org/10.1002/cjoc.201900222 41. Patil S, Raut S, Pandit B, Pandey SN, Pande SA, Sankapal B (2021) Web-analogues onedimensional iron hydroxide@cadmium hydroxide nanostructure: electrochemical supercapacitor. J Mater Sci: Mater Electron 32:22472–22480. https://doi.org/10.1007/s10854-021-067 33-5 42. Laha S et al (2019) Ruthenium oxide nanosheets for enhanced oxygen evolution catalysis in acidic medium. Adv Energy Mater 9(15):1803795. https://doi.org/10.1002/AENM.201803795 43. Bai MH, Liu R, Yang XB, Yu Z, Wang Y, Zhao Z (2018) Polypyrrole and manganese oxide composite materials with high working voltage and excellent cycling stability. ChemistrySelect 3(38):10574–10579. https://doi.org/10.1002/SLCT.201802311 44. Wang Q, Zhang Z, Zhang Z, Zhou X, Ma G (2018) Facile synthesis of MXene/MnO2 composite with high specific capacitance. J Solid State Electrochem 23(2):361–365. https://doi.org/10. 1007/S10008-018-4143-4 45. Yang H, Xu H, Li M, Zhang L, Huang Y, Hu X (2016) Assembly of NiO/Ni(OH)2 /PEDOT nanocomposites on contra wires for fiber-shaped flexible asymmetric supercapacitors. ACS Appl Mater Interfaces 8(3):1774–1779. https://doi.org/10.1021/acsami.5b09526 46. Dhilip Kumar R, Nagarani S, Sethuraman V, Andra S, Dhinakaran V (2022) Investigations of conducting polymers, carbon materials, oxide and sulfide materials for supercapacitor applications: a review. Chem Pap 2022 76(6):3371–3385. https://doi.org/10.1007/s11696-022-021 24-0 47. Naveed ur Rehman M et al (2021) Facile synthesis and characterization of conducting polymermetal oxide based core-shell PANI-Pr2O–NiO–Co3 O4 nanocomposite: as electrode material for supercapacitor. Ceram Int 47(13):18497–18509. https://doi.org/10.1016/j.ceramint.2021. 03.173 48. Verma S, Das T, Pandey VK, Verma B (2022) Nano architectonics of GO/PANI/CoFe2 O4 (graphene oxide/polyaniline/cobalt ferrite) based hybrid composite and its use in fabricating symmetric supercapacitor devices. J Mol Struct 1266:133515. https://doi.org/10.1016/j.mol struc.2022.133515 49. Liu D, Du P, Wei W, Wang H, Wang Q, Liu P (2017) Flexible and robust sandwichstructured S-doped reduced graphene oxide/carbon nanotubes/polyaniline (S-rGO/CNTs/ PANI) composite membranes: excellent candidate as free-standing electrodes for highperformance supercapacitors. Electrochim Acta 233:201–209. https://doi.org/10.1016/j.electa cta.2017.03.040

Bidhan Pandit is now a Marie Curie CONEX-Plus researcher at University Carlos III de Madrid (UC3M), Madrid, Spain. He received his Ph.D. degree (2019) in Physics from Visvesvaraya National Institute of Technology (India) and joined as CNRS Postdoctoral Research Fellow at the Institut Charles Gerhardt Montpellier (ICGM), Université de Montpellier (France). His previous scientific interests focus on the synthesis of nanostructures and fabrication of flexible devices for supercapacitor applications. His current research focus includes the synthesis of cathode materials for lithium, sodium and potassium-ion batteries, as well as the in situ/operando X-ray based characterizations for the understanding of battery mechanisms.

Polymer-Based Nanocomposites for Supercapacitors Sagar Jariwala, Yash Desai, and Ram K. Gupta

Abstract In response to the charging global scenario, energy storage and harvesting have become the prime focus of scientists and researchers. Tremendous interest has been generated over the last decade in developing more and more efficient energy storage devices. One such device is a supercapacitor, which has evolved as a potential contender to bridge the gap between rechargeable batteries and conventional capacitors. Supercapacitors possess high specific power, moderate energy density, excellent reversibility, and long cycle life compared to batteries. In this chapter, supercapacitors using polymer-based nanocomposites to enhance electrochemical performance are discussed. Polymer nanocomposites have been offering excellent qualities such as thermal, mechanical, and structural properties without compromising the electrochemical performance. Nanofillers such as graphene oxide owing to their hydrophilic nature provide a better interaction of polar molecules or polymers to form intercalated or exfoliated nanocomposites. The chapter covers recent development where polymer nanocomposites are synthesized using conventional materials such as chalcogens and metal oxides for the manufacturing of flexible supercapacitors as a breakthrough in energy storage devices. Keywords Supercapacitors · Conducting polymers · Nanocomposites · Chalcogens · Flexible supercapacitors

1 Introduction Batteries and supercapacitors (SCs) have received tremendous attention due to their increasing importance to our daily life. Batteries store and deliver charges through faradic processes giving out high energy density but low power density [1]. On the S. Jariwala · Y. Desai · R. K. Gupta (B) Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA e-mail: [email protected] National Institute for Materials Advancement, Pittsburg, KS 66762, USA © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_6

93

94

S. Jariwala et al.

other hand, SCs store and deliver charges through electrochemical double layers, featuring high energy density, long cycling stability, less maintenance, and more environmental friendliness. Nevertheless, there remains the challenge to improve the volumetric capacitance rather than the gravimetric capacitance, because portable electronic devices deliver maximum energy in a very limited geometric shape [2]. SCs have been mainly classified into three types which is discussed in the later parts of this chapter. Furthermore, to improve the electrochemical properties of the SCs it becomes hard to achieve the desired performance through conventional materials such as carbon, chalcogens, and metal oxide which are generally used to manufacture SC’s electrode materials. It becomes necessary to incorporate this material with some conducting polymer and nano-fillers to provide better structural stability by producing free-standing electrode materials accompanied with better electrochemical performance [3]. For this purpose, the synthesis of nanomaterials becomes an important task. These nanomaterials are produced through several techniques such as melt intercalation, exfoliation adsorption, in-situ polymerization, and other techniques. Whereas, the above-listed techniques are the ones that have been used mostly because of their being easy operation and providing high-quality materials at a lower cost [4]. With the advancement in materials, researchers are looking forward to making novel devices that provide high electrochemical properties accompanied by good thermal and mechanical properties. Here mechanical properties mainly refer to flexible electronic devices such as smartwatches and smartphones. Apart from the electrode, electrolytes have also been a great area of research as the current SCs mainly work on liquid-state electrolytes which have many drawbacks such as corrosion of electrodes due to leaks of the solvent. Because of solvent evaporation, polymer gel electrolytes have been in light in the present day so they could give out flexible energy storage devices in an efficient, convenient, and environmentally friendly way. The polymer gel and solid-state electrolytes don’t have any hazards like leaks and drying ending up in usage for a various number of applications. Even for the polymer gel electrolytes, nanofillers have been beneficial in providing better properties in terms of thermal and mechanical and they even enable the better transfer of ions throughout the system [5]. The topics being covered in the chapter would get an understanding of the synthesis of nanocomposites along with the application of those nanocomposites for manufacturing electric energy storage devices particularly supercapacitors.

2 Methods for Synthesis of Polymeric Nanocomposites Polymer nanocomposites can be hybrid organic–inorganic materials with at least one dimension of the filler phase less than 100 nm. They are synthesized via various methods that can be categorized into four major routes: melt intercalation, exfoliation adsorption, template synthesis, and in-situ polymerization. Three distinct microstructures are obtained based on the method and material used consisting of unintercalated,

Polymer-Based Nanocomposites for Supercapacitors

95

Fig. 1 Types of composite microstructures, a intercalated, b unintercalated (phase separated), and c exfoliated (nanocomposite). Adapted with permission [6]. Copyright © 2000 Elsevier

intercalated, or exfoliated as shown in Fig. 1 which illustrates the arrangement and composition of layered silicate nanoparticles with a polymer.

2.1 Melt Intercalation Melt intercalation is a conventional approach for synthesizing thermoplastic polymer nanocomposites. The process involves annealing the polymer matrix at high temperatures, adding the filler, and finally kneading the composite to achieve uniform distribution. It has the advantage of being environmentally friendly due to the lack of solvent. It is considered compatible with industrial processes such as injection molding and extrusion making it more convenient to utilize and economical. Some researchers synthesized recycled high-impact polystyrene (PS)/organoclay nanocomposites by melt intercalation. Two different speeds and two types of clay fillers each with a surfactant were used. The temperature was varied between 150 and 190 °C in the processing zones. The high-impact polystyrene was ball milled before mixing to increase the surface area and dispersion. It was reported that the high speed of mixing at 600 rpm yielded nanocomposites with a better dispersion than the ones processed at 450 rpm [7]. Many other polymeric nanocomposites have been manufactured through the intercalation process, one such synthesis was carried out by synthesizing poly(1-caprolactone)/organo- modified montmorillonites (MMTs) nano-composites by a twin screw extruder whose length was 1200 mm and L/D ratio of 48 [8]. The extrusion was conducted at 140 °C at 250 rpm and with a melt

96

S. Jariwala et al.

Fig. 2 TEM images of polymer clay nanocomposites at 3 wt% of a Nanofil5, b C30B, and c Nanofil2. Adapted with permission [8]. Copyright © 2009 Elsevier

flow rate of 3 kg/h. Several clay materials consisting of C30B clay material yielded an intercalated/exfoliated structure, however, Nanofils5 and Nanofils2 gave rise to intercalated nanocomposite as shown in Fig. 2.

2.2 Exfoliation Adsorption Unlike in melt intercalation, the driving force behind exfoliation adsorption is gained by the desorption of solvent which compensates for the decreased entropy of the confined intercalated chains. This method is considered good for the intercalation of polymers with little or no polarity. Researchers composed styrene butadiene rubber (SBR) with graphene nanocomposites using the solution intercalation technique (Fig. 3). Graphene platelets were obtained from the graphite-intercalated compound by processing them through thermal shock and treating them in tetrahydrofuran (THF) while being ultrasonicated. The solution was then added to the SBR mixture and mechanically mixed at 200 rpm followed by sonication for 1 h below 30 °C. Evaporation of the solvent was done at 60 °C, ethanol was used to precipitate, collect, wash, and structures were obtained. Moreover, the researchers compared those results with those obtained from melt mixing, and better exfoliation and dispersion were achieved in the former. More interlayer spacing is available for the polymer to intercalate comprising a lower percolation threshold and higher mechanical properties obtained [9].

Polymer-Based Nanocomposites for Supercapacitors

97

Fig. 3 Synthesis flow chart for SBR/graphene nanocomposite by solution mixing. Adapted with permission [9]. Copyright © 2013 Elsevier

2.3 In-Situ Polymerization Both thermos-plastic and thermoset nanocomposites can be manufactured using insitu polymerization process. It also permits the grafting of polymers on the filler surface, which indirectly improves the properties of the final composite. With better dispersion and intercalation of the fillers in the polymer matrix. Using this method, Polypyrrole (PPy)/graphene oxide (GO) composites were synthesized via liquid– liquid interfacial polymerization. To accomplish this, GO sheets were produced by treating graphite with H2 SO4 and KMnO4 giving out graphite oxide and ultrasonicating it for 30 min. The reaction mixture of GO and PPy was obtained through the solvent by rotary evaporation [10]. The same reaction chronology is demonstrated in Fig. 4. The above-discussed various methods have been extensively used in producing polymeric nanocomposite for manufacturing of electrical energy storage devices.

3 Introduction to Supercapacitor Supercapacitors are widely used in power storage and supply and backup power applications because of their fast charge–discharge characteristics, longer lifespans, and outstanding power densities. These properties are enabled due to the electrostatic charge storage mechanism of SCs, which also limits their energy density to about 5 Wh/kg. SCs may be classified into electrochemical double-layer capacitors (EDLCs) or pseudocapacitors, respectively, based on electrostatic and faradic charge storage mechanism. SC also has other distinguishing factors between the active materials with which they are made wherefore, EDLC electrodes are mostly porous carbon, whereas pseudocapacitors mostly have oxide-based electrodes. To further satisfy

98

S. Jariwala et al.

Fig. 4 PPy/GO-based nanocomposite synthesized through solution based in-situ polymerization. Adapted with permission [10]. Copyright © 2012 Elsevier

future electrochemical energy storage demands, hybrid supercapacitors combine the best qualities of EDLCs and pseudocapacitors. Figure 5 displays the energy storage methods of all three types of supercapacitors and the electrode, electrolyte, and separator, which are the three essential components of a supercapacitor.

3.1 Electrochemical Double-Layer Capacitors EDLCs store charges by electrostatic charge absorption at the electrode–electrolyte boundary. An electrical double layer is formed between an electrode and the electrolyte. The layer normally consists of absorbed ions and diffused ionic layers. Figure 6 depicts the three classical models used to describe the mechanism at the boundary: the Helmholtz model, the Gouy-Chapman model, and the Gouy-ChapmanStern model. Helmholtz developed the earliest and simplest double-layer model in 1879, which considered the concept of charge separation at the interface between the electrode and the electrolyte solution. The Gouy-Chapman model was based on the thermal mobility of ions at the boundary, which results in the concentration of ions with opposite charges at the diffused double layer. Gouy-Chapman-Stern models combine the two previous models by introducing a more realistic physical phenomenon at the boundary. When a supercapacitor is charged, an electrostatic force of attraction is generated at the electrode–electrolyte interphase, which contains an oppositely charged double layer. The thickness of this double layer is typically within the Debye length (1–10 nm) and is dictated by the electrolyte concentration

Polymer-Based Nanocomposites for Supercapacitors

99

Fig. 5 Schematic representation of a EDLC, b pseudocapacitor, and c hybrid capacitor. Adapted with permission [11]. Copyright © 2022 Elsevier

and permittivity, as well as the electrolyte structure at the boundary. The high performance of EDLCs is partly attributed to the intrinsic properties of the porous carbon materials which provide high surface area and rapid electrostatic response. About 95% of total EDLC production is based on porous activated carbon (AC) electrodes. AC provides high specific capacitance, tunable porosity, high electrical conductivity, and outstanding electrochemical stability as well as chemical inertness. Higher efficiencies are obtained by fine-tuning the porosity and surface area with an optimized combination of nano, meso, and micropores.

3.2 Pseudocapacitors Pseudocapacitors use oxide-based electrodes such as RuO2 and MnO2 , to mimic the electrochemical storage of EDLCs via redox processes. Pseudocapacitors have substantially higher levels of charge storage and energy density than EDLCs. The

100

S. Jariwala et al.

Fig. 6 Schematic diagram of EDL models based on positively polarized electrodes in a solvent. a Helmholtz model, b Gouy-Chapman model, and c Gouy-Chapman model. The dashed lines indicated the potential drop in each model. Adapted with permission [12]. Copyright © 2020 The Royal Society of Chemistry

capacitive behavior is initiated as a Faradaic reaction involving monolayers of electrochemically active species. This is distinct from the electrostatic phenomena observed in EDLCs. The first documented pseudocapacitance in transition metal oxides was the charge storage in a ruthenium oxide layer in sulfuric acid discovered in the 1970s. Pseudocapacitors use transitional metal oxides and conductive polymers as active materials and are prone to capacitive decay, low conductivity, and structural instability. Pseudocapacitive materials are often combined with carbons to synergistically improve capacitance and energy density.

3.3 Hybrid Supercapacitors The energy storage of supercapacitors is based on charge accumulation or reversible redox processes. Hybrid supercapacitors have both high capacitance and energy storage capability due to higher charge accumulations and redox reactions. They have gotten a lot of attention because of their proclivity for mixing the qualities of their constituents (EDLC and pseudocapacitor). The possibilities for such blends are components aimed at energy storage. A hybrid supercapacitor is a mix of EDLC and pseudocapacitor, which provides better performance than the individual components. In a pseudocapacitor, energy storage is achieved through quick reproducible redox reactions between electroactive components which are placed on active electrode materials and an electrolytic solution. The energy storage process of hybrid supercapacitors has higher energy and power densities. As a result, they are more likely to be used in energy-efficient systems than other energy-storage devices. In comparison to batteries and fuel cells, hybrid supercapacitors reach the pinnacle of power density, although they have a significantly lower power density than regular capacitors.

Polymer-Based Nanocomposites for Supercapacitors

101

4 Polymeric Nanocomposites for Supercapacitor 4.1 Polymer-Carbon Nanocomposites Great interests have been generated over the past decades in terms of developing more viable energy storage devices. Supercapacitors are one such type, which has come out as a potential contestant to be a bridge the gap between rechargeable batteries and conventional capacitors due to high specific power, excellent reversibility, moderate energy density, and long cycle life [13]. One of the most basic and prime components of these supercapacitors are the electrodes, which are made from three main groups of materials, that consist of carbonaceous materials, transition metal oxides/hydroxides, and conducting polymer. Carbon-based materials work as EDLC and offer excellent cyclic stability and long service lifetime due to excellent thermal, chemical, and thermal stability. However, active electrode surface area and pore size distribution due to the absence of chemical reactions limit the charge storage capacity of the supercapacitors. Due to this, carbon materials such as CNTs, graphene, reduced graphene oxide, carbon black, and other materials have been combined with one or more of the other two groups of materials to form hybrid electrodes exhibiting improved power density and capacitance. Keeping this idea in mind, some researchers combined multiwalled carbon nanotubes (MWCNTs) as carbon material, with copper oxide (CuO) as a transition metal oxide and polyaniline (PANI) from the conducting polymers group. To further improve the specific capacitance of the electrode, CuO/ NiO as NiO has a bit higher theoretical specific capacitance than CuO [14]. The addition of a robust electrical conductor such as MWCNT, should not only provide a large contact area but also allow fast cation transfer between the electrolyte and the electrode. The presence of PANI further improves the performance and stability of the composite without compromising the conductivity of the product. Once the composite was synthesized, the working electrodes were prepared by mixing 80 wt% of the active material with 20 wt% of Nafion and dispersed in 2-propanol to obtain a slurry and then drop cast on a glassy carbon electrode before drying at room temperature for 1 h. All electrochemical measurement was carried out on an electrochemical workstation at room temperature in a three-electrode cell containing NaOH aqueous electrolyte in which the as-prepared electrode, platinum wire, and Ag/AgCl were used as the working, counter, and reference electrodes respectively. Cyclic Voltammetry (CV) tests were carried out in the frequency range from 100 kHz to 0.1 Hz. All in all, the polymer-carbon nanocomposite electrode displayed reduced charge transfer resistances which improved the specific capacitance of the electrode and showed up to 83% capacitance retention after 1500 charge–discharge cycles providing exceptional cyclic stability, thus being a promising material composite for supercapacitor application [14]. Several studies have been published where different combinations of materials have been applied [15–18], one such study was proposed by Saptarshi et al. where they fabricated polymer carbon-based nanocomposite with an easy and cost-effective procedure for high-performance supercapacitor electrodes [19].

102

S. Jariwala et al.

Graphene (Gr)-single-walled carbon nanotube (SWCNT)- poly(3-methyl thiophene) (PMT) ternary nanocomposite was synthesized. They observed Gr and SWCNTs enhanced the electrochemical properties. For the synthesis of the nanocomposite, the conventional in-situ chemical oxidative polymerization method was used. Firstly, 50 mg of Gr, 50 mg of SWCNTs, 2 g of CTAB, and 100 ml of CHCl3 were taken in a 200 ml beaker and sonicated for 1 h at room temperature to disperse the Gr and SWCNTs. In a 500 mL round bottom flask, 50 mL of CHCl3 and 2 g of FeCl3 were sonicated for 30 min at room temperature. Then, the suspension was added to the FeCl3 solution and stirred for 15 min. In a 100 mL beaker, 1 mL of 3-methyl thiophene monomer was dissolved in CHCl3 . Then, the monomer solution was added slowly to Gr/SWCNTs solution and stirred for 24 h at a constant speed and constant temperature. The ternary nanocomposite was washed with methanol, distilled water, and ethanol several times; and then vacuum dried at room temperature for 1 h. The same synthesis procedure is presented in Fig. 7. Electrochemical properties of the nanocomposite and pure PMT as well as SWCNTs-PMT, Gr-PMT were tested on cyclic voltammetry at various scan rates of 5, 10, 20, 50, 100, and 200 mV/s within a potential window from 0 to 0.8 V as shown in Fig. 8 [19]. It was observed that the CV curves of all the electrode materials are rectangular, attesting to excellent supercapacitor behavior. Gr-SWCNTs-PMT as displayed in Fig. 8d ternary nanocomposite showed a maximum specific capacitance of 561 F/g at a scan rate of 5 mV/s. While the other curves are for pure PMT, SWCNTs-PMT, and Gr-PMT and they were good as long as for the supercapacitor application. These exceptional properties might be due to several reasons such as highly accessible surface area due to the use of carbon-based materials SWCNTs and Gr, PMT coated on these carbon-based materials build a bridge for quick transfer of cations from the electrolyte to the electrode. The electrode material also possessed 93% specific capacitance over 1000 charge–discharge cycles. The nanocomposite material had high thermal stability at higher temperatures. Based on the above properties, this Fig. 7 Representation of ternary polymer-metal oxide nanocomposite synthesis process. Adapted with permission [19]. Copyright © 2014 American Chemical Society

Polymer-Based Nanocomposites for Supercapacitors

103

Fig. 8 Cyclic voltammograms at different scan rates of a pure PMT, b SWCNTs–PMT, c Gr– PMT, and d Gr–SWCNTs–PMT ternary nanocomposite. Adapted with permission [19]. Copyright © 2014 American Chemical Society

and several other combinations of polymer carbon-based nanocomposite are looked at as potential electrode materials for high-performance supercapacitor electrodes [20–22].

4.2 Polymer-Metal Oxide Nanocomposites Transition metal oxides are found in abundance in nature and, therefore, are easily accessible and processed at low cost. Nevertheless, they don’t possess good cyclic stability through the redox reactions by not being completely reversible and showing low electrical conductivity. Furthermore, it is worth stating that most of the metal oxides are classified as semiconductors, referring to an extensive band gap energy that triggers poor electron transfer. To overcome these drawbacks, researchers have incorporated metal oxides with several conducting polymers which improve the electrochemical performance of the electrode materials. Additionally, these conducting polymers and metal oxides have been enabled with several nanofillers such as

104

S. Jariwala et al.

graphene oxide, SWCNTs, and many more. These nanofillers improve the structural framework of the electrode materials combined with improved faradic charge transfer [23]. Following these theories, researchers synthesized electrode material nanocomposites consisting of Fe2 O3 , polypyrrole, and reduced graphene oxide. Firstly, graphene oxide was prepared through an oxidation exfoliation reaction and coated on Fe2 O3 and ultrasonicated through a hydrothermal reaction which gave out ferrous oxide-graphene nanocomposite. Once the composite was synthesized, it was processed under an in-situ polymerization reaction where HCl-dissolved polypyrrole was applied as the top layer of the platelets the same is represented in Fig. 9 [24]. The polymer-nanocomposite possessed high electrochemical performance such as high cyclic stability accompanied by good mechanical and chemical properties. Apart from the above-discussed processes of polymerization, polymer-metal oxidebased supercapacitors have also been made through the state-of-the-art technique of additive manufacturing. Herein, activated carbon, graphene, and Mn3 O4 nanocomposite. In this process, the first step was the ink formulation for additive manufacturing wherefore commercial Ag nanoparticle ink was used for the current collector and the printed pattern was annealed at 120 °C for 2 h to obtain an end-to-end resistance of 0.6 Ω. The supercapacitor ink also contains 4.9 g of activated carbon, 1.4 g of carbon black, and 0.7 g of PVDF in a solvent consisting of 12 g of terpineol. The powders were ball-milled to nanometer size and sonicated to minimize agglomeration and optimize dispersion in ink formulations. For the gel electrolyte layer, propylene carbonate served as a solvent, polyvinylidene difluoride (PVDF) served as the polymer matrix, and lithium perchlorate as a salt and displayed a viscous gel texture upon cooling. The organic electrolyte ensures higher stability than aqueous electrolytes in test prototypes [25]. At the printing phase, the current collector, active layer, and electrolyte were printed by direct filament writing through sequential layer-by-layer printing as described in Fig. 10. Electrochemical measurements including CV, galvanostatic charge, and discharge were carried out. Wherefore, the CV curves for EDLC at an applied voltage of 0– 0.8 V at various scan rates (5–100 mV/s). However, the system included resistive behavior at high scan rates, all curves displayed clear hysteresis, indicative of electrochemical capacitive behavior. The areal capacitance and volumetric capacitance values were 165.8 F/g and 16.72 F/cm3 , respectively at a current density of 2 A/g.

Fig. 9 Presentation of the fabrication of the ternary polypyrrole/ Fe2 O3 /rGO composite. Adapted with permission [24]. Copyright © 2017 Elsevier

Polymer-Based Nanocomposites for Supercapacitors

105

Fig. 10 Presentation of layer-by-layer printing of current collector, an active layer, and electrolyte in two types of configurations EDLC and PsC. Adapted with permission [25]. Copyright © 2020 American Chemical Society

The gravimetric power density and energy density of EDLC were 160.71 W/g and 7.74 Wh/kg and in this power measurement range areal power density and energy density are 1.49 mW/cm2 and 9.280 μWh/cm2 for EDLC, and 1.610 mW/cm2 and 7.431 μWh/cm2 for PC. Overall, the energy performance of the printed supercapacitors is relatively higher than those of previously reported printed supercapacitor devices [26, 27]. The two-step-ink formulation ad binder optimization maximized the functionality of the active material while maintaining high printability. The surface properties obtained by the incorporation of nano-graphene and metal oxide on the PVDF substrate provide a uniform surface that improves the output performance. A stable conductance lowers the series resistance, increasing the usability of the active layers. Therefore, providing a high surface-to-volume ratio of the in-plane thin-film electrodes [25]. The remarkable results demonstrate the exciting commercial application of polymer-metal-based nanocomposite for high-performance, environmentfriendly, and low-cost electrical energy storage devices, this process can also combine with additive manufacturing for quick production as discussed in the above parts of the chapter [24]. Apart from polymer-metal oxide nanocomposites, several other materials such as polymer chalcogen nanocomposites have been used for manufacturing supercapacitors and the same will be discussed in the upcoming topics of this chapter.

4.3 Polymer-Chalcogens Nanocomposites The global demands for energy and the noticeable depletion of fossil fuels during the past decades have caused an energy crisis and environmental concerns. Scientists and researchers have been working on proposing several novel alternatives for manufacturing energy storage devices such as supercapacitors and batteries from different

106

S. Jariwala et al.

nanomaterials to give out more efficient energy storage devices [28]. Many nanocomposite materials have been developed such as carbon-polymer, and metal oxidepolymer-based nanocomposites as discussed in the previous parts of the chapter, but still these proposals aren’t enough to tackle the energy storage crisis of the world. For such instances, researchers have been working on polymer-chalcogen-based nanocomposites to add up another material that would be beneficial for energy storage and delivery with enhanced performance [29]. Based on this idea, some researchers reported the synthesis of 2D metallic niobium disulfide nanoflakes, produced by liquid phase exfoliation, and to enhance the functionality of the nanoflakes, they were treated with 3-mercapto-1-propane sulfonate salt. The functionalized NbS2 was incorporated in sulfonated poly ethyl ether ketone to form a nanocomposite electrolyte exhibiting high mechanical stability of 38.3 MPa. The solid-state electrolytes were produced in the form of self-standing membranes, which were directly sandwiched by two electrodes, composed of activated carbon 72 wt%, single layer graphene 8 wt%, and carbon black 10 wt% to assemble the supercapacitor as represented in Fig. 11. Results showed that NbS2 -SPEEK nanocomposite electrolyte and proton conducting binder can achieve a specific capacitance of 116 F/g at 0.02 A/g, optimal rate capability of 76 F/g at 10 A/g, and excellent electrochemical stability over the galvanostatic charge–discharge cycles [29]. The above-discussed mechanical strength of the nanocomposite also suggested that the materials could have a potential application in flexible electrochemical energy storage systems. Another study was conducted by Ke-Jing et al. where they synthesized layered CuS/multi-walled carbon nanotube nanocomposites for supercapacitor electrode materials through a one-step hydrothermal process. The main idea behind this research was CuS is an abundant and inexpensive material with several applications and even provides unique chemical and physical properties when being used as an electromaterial for supercapacitors [30]. However, CuS being a semiconductor and possessing low conductivity it is necessary to incorporate it with other nanomaterials such as SWCNT which provide high surface area and electrical conductivity, and well-controlled nanostructure, surface functionality, and cyclicity can be achieved through this nanocomposite material. The galvanostatic charge–discharge cycles displayed 90% retention after 600 cycles and suggest that the material could

Fig. 11 Representation of f-NbS2 /SPEEK nanocomposite synthesis and preparation of solid-state electrolyte materials. Adapted with permission [29]. Copyright © 2022 American Chemical Society. The article was published using Creative Commons License

Polymer-Based Nanocomposites for Supercapacitors

107

lead to a novel application of high-performance supercapacitors [31]. Apart from CuS, many other chalcogen materials have been composed with several nanofiller and polymers making ternary polymer-chalcogen nanocomposite. Therefore, researchers combined graphene and MoS2 with polyaniline to give out a next-generation material for supercapacitor applications. The synthesis was carried out through a solution exfoliation technique with N-methyl-2-pyrrolidone (NMP) as the solvent with further addition of 50 mg of graphite powder in 10 ml of NMP. The mixture was sonicated in an ultrasonic bath at 33 kHz for 8 h. The dispersion was then allowed to settle overnight and centrifuged at 1500 rpm for 30 min. The same exfoliation method was used for dispersing MoS2 and sonicated for 4 h. PANI nanocomposite was prepared with graphene by in situ chemical oxidative polymerization. The ternary nanocomposite of PANI, graphene, and MoS2 was added from their respective dispersion of NMP. The mixture was stirred for 15 min at room temperature and sonicated for 45 min at 33 kHz. Once the sonication was successful the solution was kept for 24 h to complete the polymerization and vacuum dried for 24 h at 60 °C. The respective synthesis is represented in Fig. 12. The electrode materials were tested for electrochemical analysis through cyclic voltammetry curves measured at a scan rate of 50 mV/s with a potential window of − 0.4 to 1.0 V. The rectangular shape of the CV curves confirms the suitability of the prepared nanocomposites as electrode materials for supercapacitor materials. The nanocomposite material also showed good cyclic stability with 96.67% retention and the highest energy density of 2.650 Wh/kg at a power density of 119.212 W/kg [32]. The respective properties of the electrode materials are due to the inter-crosslinking and intercalation with the nanoflakes of the negative electrode materials with PANI nanorods maintaining an equilibrium between charge carriers during the redox reaction.

Fig. 12 Schematic diagram of the experiment: a binary nanocomposite of PANI and graphene, b ternary nanocomposite of PANI/Graphene/MoS2 , Dispersion of MoS2 graphene nanosheets followed by in-situ polymerization of PANI. Adapted with permission [32]. Copyright © 2018 Elsevier

108

S. Jariwala et al.

5 Polymeric Nanocomposites for Flexible Supercapacitor Supercapacitors have been extensively investigated in recent decades, which display a typical density of 5–10 Wh/kg and provide these enhanced properties through electrodes having high surface area separated by a porous separator with liquid electrolyte. However, liquid electrolytes have several disadvantages such as leakage, corrosion of electrodes, and limited geometry shape that eventually limits their practical applications. For such consequences, it becomes necessary to research synthesizing novel gel polymer electrolytes or polymer solid-state electrolytes (PSE) without compromising ionic conductivity. These polymer electrolytes are synthesized through solvent-free techniques which fix the reduction of ionic conductivity due to solvent evaporation. On the other hand, they also provide high wettability and flexibility, unlike liquid electrolytes. Herein, to build flexible supercapacitors, Cheng et al. developed an electrical-ionic hybrid polymer nanocomposite electrode by adopting a novel thermally stable and non-corrosive PSE, poly(vinylidene fluorideco-hexafluoropropylene)/lithium bis(ox-alato)borate (PVDF-HFP/LiBOB) and, as a host substrate stacked 2D graphene oxide (GO)/1D carbon nanotubes continuous network. The fabrication process of a supercapacitor is illustrated in Fig. 13. Where the process consisted of three main steps PSE preparation, fabricating electrodes, and assembling supercapacitors. The PSE was fabricated through a facile drop casting method wherefore, PVDF-HFP pellet and LiBOB powder were dissolved in DMF and vacuum dried to get the free-standing structure film evaporating the DMF. To get the polymer-nanocomposite electrodes GO/CNT/PSE were dissolved in NMP giving out a slurry with the weight ratio of 1:4:1 of the respective materials. The electrode and electrolyte were packed in an EDLC configuration through hot lamination. The inter-percolating electrical-ionic network electrode structure provides significant access of ions to the surface of the capacitive material by improving electrode/electrolyte contact. The polymer nanocomposite electrode showed a significant specific gravimetric capacitance of 267 F/g at 1 A/g and was comparable to carbon-based electrodes in liquid electrolytes based on the researcher’s study. Supercapacitors also displayed an outstanding lifetime with capacitance retention of 88% even after 20,000 charge–discharge cycles on an operation window of 1.8 V and excellent flexibility as expected with nearly zero decay in capacitance after 10,000 times bending tests. In another study flexible supercapacitors were manufactured through poly(3,4 ethylene dioxythiophene){PEDOT} polystyrene sulfonate and modulated through nanofiller graphene oxide. PEDOT-based conducting polymers have been promising materials to be used as flexible supercapacitors [34]. To manufacture the electrode film deposition method with drop casting in the silicone molds and dried in air for 72 h. PEDOT/PSS + GO + glucose (GGO-PEDOT) free-standing films obtained were then annealed for 1 h at 140 °C on a hot plate in an N2 atmosphere to disperse GO and glucose in the mixture. Upon successful preparation of the polymer nanocomposite electrode material, it was tested for a specific capacitance of 8.57 F/g at a scan rate of 100 mV/s in pristine conditions [35]. The CV curve of the nanocomposite film

Polymer-Based Nanocomposites for Supercapacitors

109

Fig. 13 Schematic representation for preparing the PSE film and GO/CNT/PSE-based solvent-free supercapacitors. Adapted with permission [33]. Copyright © 2019 The Royal Society of Chemistry

presented a broad approximately rectangular shape when tested upon the doublelayer configuration capacitor indicating that the material is potentially suitable to be used as electrode material for supercapacitors. From the above study, we could relate the application of polymer-based nanocomposite for flexible supercapacitors without compromising the electrochemical properties of the electrical energy storage device [35]. This facile property of flexibility and extensive mechanical ability in supercapacitors will help create new devices while being a huge leap in the range of applications.

6 Conclusion In summary, we discussed the past and current research being conducted incorporating polymers with several other materials such as carbon, chalcogen, and metal oxide-based materials to synthesize electrodes and solid-state electrolytes for supercapacitors. These materials had also been enabled with nanomaterials such as SWCNT, graphene oxide, and many more which provide better mechanical and thermal properties while acting as conducting materials that enhanced the electrochemical performance of the energy storage devices. Basic information about the working principle and mechanism of the several supercapacitors was also discussed. We also discussed different synthesis methods for manufacturing polymeric nanocomposites, while they were used by the researchers in their respective projects. For the most part, it was noticed that the supercapacitor developed with the nanocomposite displayed top-notch properties which would increase their number of applications commercially. However, the amount of research being done to manufacture energy storage devices through polymeric materials and other nanocomposites is

110

S. Jariwala et al.

still less when viewing the global energy demand scenario but the promising results from the present works give hope and enthusiasm to work on novel nanocomposite synthesis techniques and usage of these nanocomposites in specialty application such as manufacturing flexible devices with high specific capacitance combined with impressive power density.

References 1. Zhou G, Li F, Cheng HM (2014) Progress in flexible lithium batteries and future prospects. Energy Environ Sci 7:1307–1338 2. Moussa M, El-Kady MF, Abdel-Azeim S, Kaner RB, Majewski P, Ma J (2018) Compact, flexible conducting polymer/graphene nanocomposites for supercapacitors of high volumetric energy density. Compos Sci Technol 160:50–59 3. Soneda Y (2013) Carbons for supercapacitors. In: Handbook of advanced ceramics materials, applications, processing, and properties, 2nd edn. Elsevier Inc., pp 211–222 4. Liu P, Yan J, Guang Z, Huang Y, Li X, Huang W (2019) Recent advancements of polyanilinebased nanocomposites for supercapacitors. J Power Sources 424:108–130 5. Dai H, Zhang G, Rawach D, Fu C, Wang C, Liu X, Dubois M, Lai C, Sun S (2021) Polymer gel electrolytes for flexible supercapacitors: recent progress, challenges, and perspectives. Energy Storage Mater 34:320–355 6. Alexandre M, Dubois P (2000) Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials. Mater Sci Eng R Rep 28:1–63 7. Chimanowsky Junior JP, Soares IL, Luetkmeyer L, Tavares MIB (2014) Preparation of highimpact polystyrene nanocomposites with organoclay by melt intercalation and characterization by low-field nuclear magnetic resonance. Chem Eng Process Process Intensif 77:66–76 8. Labidi S, Azema N, Perrin D, Lopez-Cuesta JM (2010) Organo-modified montmorillonite/ poly(ε-caprolactone) nanocomposites prepared by melt intercalation in a twin-screw extruder. Polym Degrad Stab 95:382–388 9. Araby S, Meng Q, Zhang L, Kang H, Majewski P, Tang Y, Ma J (2014) Electrically and thermally conductive elastomer/graphene nanocomposites by solution mixing. Polymer (Guildf) 55:201– 210 10. Bora C, Dolui SK (2012) Fabrication of polypyrrole/graphene oxide nanocomposites by liquid/ liquid interfacial polymerization and evaluation of their optical, electrical and electrochemical properties. Polymer (Guildf) 53:923–932 11. Mensah-Darkwa K, Ampong DN, Yeboah D, Agyekum E, Gupta RK (2022) Biomass/biowastes for electrochemical energy storage. In: Handbook of energy materials, pp 1–42 12. Shao H, Wu YC, Lin Z, Taberna PL, Simon P (2020) Nanoporous carbon for electrochemical capacitive energy storage. Chem Soc Rev 49:3005–3039 13. Patrice S, Yuri G, Bruce D (2014) Where do batteries end and supercapacitors begin? Science (80–) 343:1208–1210 14. Chakraborty I, Chakrabarty N, Senapati A, Chakraborty AK (2018) CuO@NiO/Polyaniline/ MWCNT nanocomposite as high-performance electrode for supercapacitor. J Phys Chem C 122:27180–27190 15. Singhal R, Fagnoni J, Thorne D, LeMaire PK, Martinez X, Zhao C, Gupta RK, Uhl D, Scanley E, Broadbridge CC (2019) Study of MnO2-graphene oxide nanocomposites for supercapacitor applications. MRS Adv 4:777–782 16. Mitchell E, Jimenez A, Gupta RK, Gupta BK, Ramasamy K, Shahabuddin M, Mishra SR (2015) Ultrathin porous hierarchically textured NiCo2O4–graphene oxide flexible nanosheets for high-performance supercapacitors. New J Chem 39:2181–2187

Polymer-Based Nanocomposites for Supercapacitors

111

17. Singhal R, Thorne D, Lemaire PK, Martinez X, Zhao C, Gupta RK, Uhl D, Scanley E, Broadbridge CC, Sharma RK (2020) Synthesis and characterization of CuS, CuS/graphene oxide nanocomposite for supercapacitor applications. AIP Adv 10:35307 18. Al Dream J, Zequine C, Siam K, Kahol PK, Mishra SR, Gupta RK (2019) Electrochemical properties of graphene oxide nanoribbons/polypyrrole nanocomposites C 5:18 19. Dhibar S, Bhattacharya P, Ghosh D, Hatui G, Das CK (2014) Graphene—single-walled carbon nanotubes—poly (3-methylthiophene) ternary nanocomposite for supercapacitor electrode materials. Ind Eng Chem Res 53:13030–13045 20. Palchoudhury S, Ramasamy K, Gupta RK, Gupta A (2019) Flexible supercapacitors: a materials perspective. Front Mater 5:1–9 21. Zequine C, Bhoyate S, de Souza F, Arukula R, Kahol PK, Gupta RK (2020) Recent advancements and key challenges of graphene for flexible supercapacitors. In: ACS symposium series, 2020, pp 49–77 22. Bhoyate S, Kahol PK, Gupta RK (2020) Broadening the horizon for supercapacitor research via 2D material systems. In: Revaprasadu N (ed) Nanosci, vol 6. The Royal Society of Chemistry, pp 120–149 23. Chee WK, Lim HN, Harrison I, Chong KF, Zainal Z, Ng CH, Huang NM (2015) Performance of flexible and binderless polypyrrole/graphene oxide/zinc oxide supercapacitor electrode in a symmetrical two-electrode configuration. Electrochim Acta 157:88–94 24. Ehsani A, Heidari AA, Shiri HM (2019) Electrochemical pseudocapacitors based on ternary nanocomposite of conductive polymer/graphene/metal oxide: an introduction and review to it in recent studies. Chem Rec 19:908–926 25. Seol ML, Nam I, Ribeiro EL, Segel B, Lee D, Palma T, Wu H, Mukherjee D, Khomami B, Hill C, Han JW, Meyyappan M (2020) All-Printed in-plane supercapacitors by sequential additive manufacturing process. ACS Appl Energy Mater 3:4965–4973 26. Zhu C, Liu T, Qian F, Han TYJ, Duoss EB, Kuntz JD, Spadaccini CM, Worsley MA, Li Y (2016) Supercapacitors based on three-dimensional hierarchical graphene aerogels with periodic macropores. Nano Lett 16:3448–3456 27. Areir M, Xu Y, Harrison D, Fyson J (2017) 3D printing of highly flexible supercapacitor designed for wearable energy storage. Mater Sci Eng B Solid-State Mater Adv Technol 226:29– 38 28. Yan C, Jin M, Pan X, Ma L, Ma X (2020) A flexible polyelectrolyte-based gel polymer electrolyte for high-performance all-solid-state supercapacitor application. RSC Adv 10:9299– 9308 29. Bagheri A, Bellani S, Beydaghi H, Eredia M, Najafi L, Bianca G, Zappia MI, Safarpour M, Najafi M, Mantero E, Sofer Z, Hou G, Pellegrini V, Feng X, Bonaccorso F (2022) Functionalized metallic 2D transition metal dichalcogenide-based solid-state electrolyte for flexible all-solidstate supercapacitors. ACS Nano 16:16426–16442 30. Jhan JY, Huang YW, Hsu CH, Teng H, Kuo D, Kuo PL (2013) Three-dimensional network of graphene grown with carbon nanotubes as carbon support for fuel cells. Energy 53:282–287 31. Huang KJ, Zhang JZ, Xing K (2014) One-step synthesis of layered CuS/multi-walled carbon nanotube nanocomposites for supercapacitor electrode material with ultrahigh specific capacitance. Electrochim Acta 149:28–33 32. Palsaniya S, Nemade HB, Dasmahapatra AK (2018) Synthesis of polyaniline/graphene/MoS2 nanocomposite for high performance supercapacitor electrode. Polymer (Guildf) 150:150–158 33. Chi C, Li Y, Li D, Huang H, Wang Q, Yang Y, Huang B (2019) Flexible solvent-free supercapacitors with high energy density enabled by electrical-ionic hybrid polymer nanocomposites. J Mater Chem A 7:16748–16760 34. Li Z, Ma G, Ge R, Qin F, Dong X, Meng W, Liu T, Tong J, Jiang F, Zhou Y, Li K, Min X, Huo K, Zhou Y (2016) Free-standing conducting polymer films for high-performance energy devices. Angew Chem—Int Ed 55:979–982 35. Díez-Pascual AM, Rahdar A (2022) Graphene-based polymer composites for flexible electronic applications. Micromachines 13:1–18

Polymer-Carbon Nanocomposites for Supercapacitors Pragati Chauhan, Mansi Sharma, Dinesh Kumar, and Rekha Sharma

Abstract Due to their ability to resist large capacitors and many battery capacities when properly arranged, the application of highly conductive polymer nanomaterials for superconductors has increased during the last few years. Furthermore, researchers have looked at the usage of nanomaterials comprising electrically conductive polymers including nonconducting and conducting nanoparticles, like cellulose nanocrystals and carbon nanotubes. Supercapacitors, fuel cells, and batteries are examples of unusual electric-operated devices. Due to their superior electrochemical performance, amazing specific power, great cycle life, and quick charging and discharging rates, supercapacitors have attracted a lot of attention. Supercapacitors made from conducting polymers (CPs) also provide greater specific energy and energy density, making them a more flexible and cost-effective energy storage solution. Because of its potential applications in various fields including sensors, supercapacitors, and fuel cells, CP has become the focus of many studies over the years. The chapter begins with the introduction of conducting materials and is followed by various synthesis methods for CPs. The purpose of this chapter is to enlighten the readers about the benefits and drawbacks of implementing such materials in supercapacitors as well as potential topics for further research. Keywords Capacitors · Superconductors · Sensors · Electrochemical · Supercapacitors

P. Chauhan · M. Sharma · R. Sharma Department of Chemistry, Banasthali Vidyapith, Rajasthan 304022, India D. Kumar (B) School of Chemical Sciences, Central University of Gujarat, Gandhinagar 382030, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_7

113

114

P. Chauhan et al.

1 Introduction Due to their wide range of uses in things like power management, electromagnetic absorber, enhanced computer chips, specific optical systems, biomaterials, detectors, and improved computer chips and conduction composite compounds have received something of interest. The fabrication of conductive polymer/carbon material (CP/ CM) nanocomposite as well as its usage are the main topics of this chapter since such applications are among the very thoroughly researched rising attention about energyrelated concerns [1]. According to the growing quantity of papers on the subject, several researchers are interested in the processes of synthesizing CP/CM materials in addition to their characteristics and applicability. The primary CP/CM compound manufacturing techniques, in addition to their characteristics and applications in the power management domains, are covered in four segments of this chapter. The fabrication of CPs not only from refined carbon materials but also from composite materials will receive great interest. The importance of adsorbents has been well recognized, not only because of the wide variety of morphological characteristics displayed by them. Some examples of these adsorbents are activated carbon (AC), carbon black (CB), carbon nanotube (CNT), carbon fiber (CF), activated carbon fiber (ACF), graphene (G), fullerene, graphene oxide (GO), reduced graphene oxide (rGO), carbon xerogels, etc. CMs have been touted as interesting applicants in addition to the qualities derived from their inherent characteristics. Regarding these, it is important to draw attention to its usage in adsorbents, catalysts, medicinal uses, sensors/biosensors, photovoltaic solar cells, and energy applications (fuel cells, batteries, capacitors, etc.). Such characteristics, combined with its affordable price, give these viable options for building various combinations. Although CPs were found in 1963, much study has been carried out. A thorough investigation of CPs as well as their uses in detectors and supercapacitors, among many other things, was started by MacDiarmid. The family of polymerics known as “Synthetic metals” has multiple sp2 carbonyl groups on coupled equipped and massive resonation arrangements, which enable the dipolar movement of electric charge. Because of their exceptional qualities in electrochemical energy storage uses carbon-related compounds such as AC, CNTs, and G stand amongst a wide range of options as the greatest contender for resolving this issue. As a result, compounds created by mixing the above mentioned elements with CPs will be discussed, as well as latest events using these compounds in the area of superconductors will also be emphasized [2].

1.1 Conducting Polymers When initial discoveries in the late 1970s, CPs had generated a lot of attention on a global scale. CPs often referred to as synthetic material, typically consist of p-orbital elements and/or an alternated single as well as double-linked framework, resulting in

Polymer-Carbon Nanocomposites for Supercapacitors

115

Fig. 1 Various applications of conducting polymers

a continuous layer of dipolar bonds. The final product is mostly to blame which was produced by electrical high thermal conductivity due to its conductive polymer characteristics. This significant massive difference in permeability is caused by an oxidation propagation phase on the polymer’s pillar that involves either the withdrawal of electrons (positive doping, or p-doping), or the adding of electrons (negative doping, or n-doping). The above method alters the number of attacks generated per unit quantity. This procedure, known as electrochemical reactions, modifies the characteristics of the polymeric, like conductivity, volume, and visible light absorption, leading to a wide range of applications, including electrochromic devices, chemical and biosensors, field emission display, supercapacitors, surface protection, data storage and many more. Various applications of CPs are shown in Fig. 1. Chemical, photochemical, or electrochemical reactions can be used to carry out such oxidative reactions. Electrochemistry is one of these strategies that are naturally advantageous for advanced battery uses. Nevertheless, p-doped CPs are effectively used as favorable electrocatalysts for electromechanical disk drives because n-doped CPs are unstable, particularly in the condition of water and oxygen. In fact, according to p-doping with such a doping concentration of around 0.3 as well as 0.5 per monomeric unit, positive ions are produced on the polymeric matrix. Notably, depending on the degree of performance enhancing drugs and the make-up of the polymer, the produced charge density can either come in form of a radical-cation (RC, also known as polaron) or dictation (DC, bipolar on). Conjugated electron donor systems are exhibited by most of the common p-type CPs. These materials can be coupled with conjugated electron acceptor materials, such as CNTs and graphene which was resulting in the formation of composites through stacking and electrostatic interactions. The possibilities of combining common CPs with carbon-related materials (activated carbon, CNTs, and graphene) are thus highlighted in this chapter to create a synergetic effect and improve the cycling performances of the resulting composites. As indicated, the arrangement of the polymeric chains on the carbon networks is crucial for the development of strong composites. From this perspective, a thorough

116

P. Chauhan et al.

knowledge of the polymeric process as well as the impact of synthesized circumstances on the shape as well as physical biochemical characteristics of CPs is still difficult to achieve and calls for more research [3].

2 Methods of Synthesis of Conducting Polymer/Carbon Material Composites The most popular ways for creating CPs or CP/CM compounds are chemical and electrochemical processes. The quantity of CP generated via the electrical process is constrained by the working electrode in which the polymer takes place, whereas the chemical treatment often results in powdery nanoparticles that can be readily expanded. As a result, electrochemically produced CPs are typically formed as a layer on the interface of the electrode. Other approaches to the production of CP/ CM hybrids exist in addition to these two, such as physical mixing, layer-by-layer (LBL) assembly, electrodeposition, electrospinning, and chemical grafting.

2.1 Chemical Polymerization Method Simple oxidizing of monomers in solutions using oxidizing reagents like (NH4 )2 S2 O8 , K2 Cr2 O7 , FeCl3 , KMnO4 , etc. constitutes the biochemical production of CPs. As soon as there are sufficient polymeric molecules as well as an effective oxidizing agent in the solutions, the mass synthesis in this instance is not constrained. Because it offers a low-cost and effective means of obtaining significant quantities of polymer, it is favored in the sector. Even so, the acquired polymer exhibits lower electrical properties and a low rate of uniformity when compared to compare to conventional techniques methods. This disadvantage may worsen if the polymers take place within the CMs’ permeability since transport issues may prevent the oxidizing of the monomers and the following interaction among two radical’s ionic species. This is why a prior polymeric adsorbent step is necessary for the synthesizing of CP/ CM composite materials to enable an appropriate dispersion of the oxidizing agent and prevent diffusion issues while acquiring a greater level of uniformity. In this respect, several CMs have been investigated for one’s interaction with various CPs [4]. Samples of combinations and certain features of CP/CM compounds created by an electrochemical polymer. To tackle the condition in this problem, a few of the most typical CP/CM composite pairings will be quickly detailed in the succeeding subcategories. Various examples of CP/CM are shown in Table 1, which are synthesized by chemical method.

Polymer-Carbon Nanocomposites for Supercapacitors

117

Table 1 CP/CM composites synthesized by chemical method CP

CM

Oxidant

AC/F g−1

Thickness/nm

References

PANI

SWCNT

(NH4 )2 S2 O8

–

10

[7]

PANI

MWCNT

(NH4 )2 S2 O8

424 (1 M H2 SO4 )

45–60

[8]

PANI

AC

(NH4 )2 S2 O8

316 (1 M H2 SO4 )

–

[9]

PANI

ACF

(NH4 )2 S2 O8

233 (1 M H2 SO4 )

0.5

[10]

PANI

CF

(NH4 )2 S2 O8

180 (1 M H2 SO4 )

84

[11]

PEDOT

SWCNT

FeCl3

–

2–6

[12]

PEDOT

MWCNT

Fe (ClO4 )3 / FeCl3

160 (1 M TEABF4 in acetonitrile)

–

[13]

PPy

MWCNT

FeCl3

200 (1 M H2 SO4 )

–

[14]

PPy

GO

FeCl3

165 (6 M KOH)

–

[15]

2.1.1

CP/CNT Composites

Given that they can be sufficiently dispersed, CNTs may be thought of as a highly intriguing solid supportive since it enables the homogenous dispersion of CPs. Furthermore, CNTs may maintain CP as an electrode layer despite volumetric changes brought by the intercalation as well as depletion of atoms throughout the dating and de-doping processes. The purest CPs have poor physical characteristics. To create CP/CNT compositions for superconductors employing Ppy, PANI, PEDOT, etc., CNTs have been extensively researched [5]. For example, Li and colleagues produced SWCNT/PANI that demonstrated a positive rapport. Chargetransfer compound production took the place of Van der Waals force and exhibited a PANI surface area of 10 nm with SWCNTs having such a width of 12 nm. Additionally, a rise in electrical properties was seen while the number of SWCNTs grew, which was described by connecting connections among various conductive PANI domains. To create a compound that was lighter and much more elastic than that produced by traditional CNT/PANI hybrids, Meng et al. developed a material that resembled a sheet (buck paper of 25 m) utilizing PANI as CP and MWCNT [6]. That MWCNT/ PANI compound was 30 m wide and included 75 wt.% PANI. A homogenous and condensed PANI coating was found to cover the CNTs based on SEM characterization. Such adaptable MWCNT/PANI compounds’ creation portends a tremendous breakthrough for prospective uses. The fabrication of materials for dye-sensitized solar cells (DSSC) is further utilized for CP/CNT. The electrocatalytic reducing performance of CP/CM compounds is also strong, making them acceptable for use as DSSC conductors. Productivity increased with the addition of a modest quantity of MWCNT to PEDOT. Excellent conductance materials were produced by chemically polymerizing MWCNT/PEDOT compound with CNTs being the centers.

118

2.1.2

P. Chauhan et al.

CP/graphene Composites

As a distinctive 2D crystalline structure with outstanding characteristics, graphene presents exceptional prospects to meet the rising worldwide power requirements. Significant strides in the realm of power generation as well as advancements in graphene-based products have been made in current years. Among the substances considered the greatest suitable for usage as the electrodes in rising composite superconductors is a CP/G mixture. N-doped GPPy electrodes with such a large resistance were created by Lai and colleagues [16]. This finding is more significant than that from NH2 -graphene/PPy or GO/PPy, which are also encouraging results. Compared to their separate elements, G/PPy hybrids have also demonstrated better specific capacitance. Additionally, the distinct G/CP compound electrical, mechanical, optical, chemical, and structural capabilities have sparked attention in the sensors industry.

2.1.3

CP/activated Carbon Composite

Although CNTs or Gs had received a lot of attention, little research has been done just on the mechanical synthesis of CPs using AC. Another initial research was completed by Ryu and colleagues and involved the application of aniline monomers on AC as well as subsequently polymer in acidic media. It was claimed that such an AC/ PANI ratio might regulate the PANI accumulation. Relative to the AC, the AC/PANI enhanced the particular capacity by approximately 41%. Comparable composites were created by Zhou and colleagues. However, users came to the same conclusion that the AC/PANI ratio has no bearing on the regularity of PANI patterns [17]. The in-situ copolymer AC/PANI hybrid was previously employed by Yan and colleagues as an electrode component in capacitance deionization. Despite having poor conductance, AC/PANI had a conductance that was almost four percent greater than that of the initial AC. With just an AC/PANI composite, Zengin and colleagues obtained a specific capacitance of 16 S cm−1 . The impact of interface composition on the creation of AC/PANI electrodes was investigated by Bleda-Martnez and colleagues. A manual combining technique and a biochemical procedure were both used to create several AC/PANI hybrids. The AC had been produced using anthracite via a KOH-chemical setup process, and oxygen molecules were then removed through heat treatment. Subsequently, several axial loads of AC/PANI were synthesized using both CMs. This was found as the unprocessed AC (228 F g−1 ) had a greater permeability as well as more oxygen vacancy molecules than the hightemperature AC (125 F g−1 ). There were significant variations in the combinations because of the various interface chemicals of the CMs even which will be discussed later [18].

Polymer-Carbon Nanocomposites for Supercapacitors

119

2.2 Electrochemical Polymerization Method When using the electrolytic approach to create CPs, molecules are typically oxidized in solutions using either a steady voltage or cyclic voltammetry within a predetermined range. In a particular instance, many variables, including the solvent, electrolyte, quantity of monomer, and pH, have an impact on the procedure. Additionally, the voltage, current, or temperature at where every polymer polymerizes differently, resulting in a CP having a top standard of uniformity. As a result, electromechanical approaches can readily regulate the polymerization process, as well as the incorporated energies employed in electrosynthesis could also readily manage the quantity of output [19]. In such an aspect, an electromechanical approach is preferable to a chemical one. A variety of CPs, carbon, metal oxides and other compounds may be easily, affordably, and adaptably synthesized using electrochemical processes for use as functional polymers in supercapacitors. Different electrochemical syntheses are discussed below in Fig. 2. Additionally, electrolytic polymers may be carried out in tiny quantities at ambient temperature and atmospheric pressures having improved selectivity and sensitivity. It enables the customization of the shape that immediately affects the characteristics of the nanoparticles. Because of this, the electromechanical approach is a useful technique for producing CP nanoparticles. Several electrochemical methods, including the steady-state step approach, the potentiodynamic technique, and numerous potentiates stages had been utilized to improve the properties of CMs and CPs. Examples of CP/CM composites are shown below in Table 2, which are synthesized by the electrochemical method. Fig. 2 Electrochemical synthesis for supercapacitors

120

P. Chauhan et al.

Table 2 CP/CM composites synthesized by electrochemical method CP

CM

Technique

C/F g−1

Thickness/ nm

References

PANI

SWCNT

CV; 20.2 to 1.2 V/ SCE

–

–

[20]

PANI

SWCNT

Galvanostatic 0.75 V/SCE

55 (1 M H2 SO4 )

15

[21]

PANI

CF

Potentiostic deposition 0.894 V/ Ag/AgCl

80 (0.5 M Na2 SO4 ) 150

[22]

PANI

AC

Potentiodynamic 0.75 V, 1.0 V/ Ag/ AgCl

350–450 (1 M HCl 1 0.5 KCl)

[23]

PANI

ACF

Potentiostatic 0.3 V 21.05 V/RHE

233 (0.5 M H2 SO4 ) 0.5

[24]

PEDOT

MWCNT

Galvanostatic

150 (1 M TEABF4 / – AN)

[25]

PEDOT

GO

Potentiostatic 1.05, 0.92 V/Ag/AgCl

-

–

[26]

PPy

SWCNT

Galvanostatic 2 mA cm

202 (1 M KCl)

–

[27]

PPy

MWCNT

Potentiostatic deposition 0.70 V/ SCE

192 (0.5 M KCl)

–

[28]

2.2.1

–

CP/CNT Composites

In various articles, electrochemical techniques had been used to deposit CPs over CNTs. One of the most effective conductive polymers for covering CNTs includes PPy as well as PANI. Utilizing the potentiodynamic stage technique, Huang et al. synthesized SWCNT/PANI compounds having various proportions [29]. It was shown as the level of PANI causes resistivity to rise quickly. This finding indicates both SWCNT and PANI have a powerful connection that can help CNT as well as polymer matrix exchange electrons. PANI/SWCNT composite sheets were created by Liu and colleagues using an electrochemical manufacturing and breakdown approach. Owing to more polycrystalline PANI areas, a large capacitor of 502 F g−1 was attained following 90 cycles, and following electron degradation, the capacitive reactance was 707 F g−1 . To create an extremely thin as well as homogenous sheet for utilization as electrodes, Jun Ge and colleagues produced PANI/SWCNT composite parts. The promise for translucent and adaptable power storing systems is demonstrated by the ultra-compact, visually homogenous, transparent, electrically conducting films. That exhibits a substantial capacitance (220 F g−1 ) with an SWCNT concentration of just 10.0 mg/cm2 as well as 59 wt.% PANI. Chen and colleagues developed coatings on Pt/Ti for CNT/PPy hybrids. The huge contact surface of a

Polymer-Carbon Nanocomposites for Supercapacitors

121

CNT/PPy compound was shown to produce greater electrochemical efficiency than those produced in the lack of CNTs, finding that materials are particularly intriguing as electrodes for reusable batteries [30]. To use a galvanostatic approach, Wang and colleagues produced SWCNTs/PPy compounds, resulting in an SWCNT/PPy sheet with less barrier than just that produced by other researchers. Because of its high price, PEDOT/CNT has indeed been mentioned only infrequently. Again, to produce a PEDOT coating atop CNT in the organic solvent, Lota and colleagues utilized a galvanostatic technique, yielding a capacitor voltage of 150 F g−1 .

2.2.2

CP/G Compounds

A biochemical detector having excellent sensitivities to identify hydrogen was produced using a fine sheet of PANI/G hybrids manufactured using an in situ electrical technique. To make versatile, homogenous PPy/G compound sheets to be utilized as supercapacitor electrodes, a straightforward procedure was adopted.

2.2.3

CP/AC Composites

PANI/AC may be made utilizing three alternative electrochemical methods, which are described anon that uses the findings of Bleda Martnez and colleagues as an illustration Potentiostatic step method.

Potentiodynamic Method From a lower point of 0.3 V to several upper possibilities (0.75 and 1.0 V), the potentiostat step approach was used unless a total electric arc of 2 C was attained. Both the presence as well as lack of AC were used to carry out all the PANI polymerization. A dual sheet sword’s initial impact on the current decrease and the deposition new method may be characterized as two distinct zones. The one-dimensional network expansion by straight monomer-unit integration into the pre-existing PANI film was what led to the present rise. At 0.75 V, polymerization proceeded more slowly than at 1 V. The synthesis so over AC takes less time at both higher possibilities than the synthesis immediately over the bare graphite due to the high surface area of the AC [31].

The Potentiodynamic Polymerization By employing 30 cycles of 0.75 V from 0 to 1 V, cyclic voltammetry was used to measure the open circuit potential polymers. The polarization curves polymerization’s penultimate 30th cycle up to 1 and 0.75 V, correspondingly. The polymer rate of PANI/AC compounds crosslinked up to 1 V was greater compared to compounds

122

P. Chauhan et al.

polymerization up to 0.75 V. This happens because, at greater potentials, more aniline compounds underwent oxidation before being integrated into polymeric chains. Due to their greater contact area as compared to the graphene, the specimens with AC had a larger current.

Multiple Potentiostatic Steps Method 200 different potentiostatic pulses were applied to the electrode surface using this approach. A lower potential of 0.3 V was brought to a higher potential of 0.75 or 1 V and maintained for 4 s. The prospective electrode was brought to a lower point for 4 s and then brought to the higher possibility for 4 s using a polarization current shift. Up to the experiment’s conclusion, these stages were repeated. The current was found to be greater for pulses between 0.3 and 1 V, indicating that more electrodeposited polyaniline was produced as a result of more radical monomer production that needed to be polymerized. The chronopotentiometry experiments validated the relationship between the capacitance increase and PANI redox processes, demonstrating the effectiveness of PANI electrodeposition [32]. To understand their characteristics as potential electrodes for supercapacitors, the electrodes produced by each electrochemical polymerization method were examined using a variety of techniques, including chronopotentiometry, cyclic voltammetry, electrochemical impedance spectroscopy, and infrared spectroscopy. The outcomes showed that the capacitance value for the composites was higher than that produced by the mixing method utilizing the information from both separate materials. By boosting the charge transport kinetics as well as the electron dipoles of a CP, a greater use of the polymer’s characteristics results in this complex formation. Additionally, the composite showed improved electrical conductivity compared to the pure AC, highlighting the polymer’s beneficial role in the process. The composites made using the potentiodynamic approach have greater electrical conductivity than those made using other electro-polymerization techniques as the PANI framework is more uniform in the such composite. For single-step potentiostatic techniques, the samples showed more capacitance and performance improvement at high current densities. It was shown that samples made using multistep potentiostatic procedures performed similarly to those made using single-step potentiostatic methods as well as potentiodynamic methods. These findings corroborated the need to carefully choose the electro-polymerization process conditions following the needs of the intended composite’s application [33].

2.2.4

CP/ACF Composites

By using chemical and electrochemical polymeric techniques, Salinas-Torres and collaborators created ACFPANI materials. The cyclic voltammetry results of each of the compounds and the pure ACF are displayed in contrast to PANI/carbon compounds, the carbon substance exhibits a quasi-rectangular geometry associated

Polymer-Carbon Nanocomposites for Supercapacitors

123

with the production of a natural electronic dual sheet. The electrochemical levels are very clearly characterized in the specimen produced by electrochemical polymer chains than they appear in the specimen produced by conventional polymerization, which can be observed. Whenever PANI is produced chemically, that one was linked to intermediate by-products, but the electrochemically created composite has distinct peaks linked to bigger chains with minimal flaws. In comparison to virgin ACF, all composites enhanced inductance by approximately 40%. By using chemical and electrochemical polymeric techniques, Salinas-Torres and collaborators created the ACFPANI composite [34].

2.3 Other Synthesis Methods Although chemical or electrochemical polymeric techniques have been used to manufacture the majority of CP/CM composite, these are additional approaches to the synthesis of CP/CM composite materials.

2.3.1

Mechanical Mixing Method

Pure PANI was created to create AC-PANI compounds using a mechanical combining technique. Following the creation of purified PANI, the composite was made by combining various ratios of PANI, AC, acetylene black, and binder (PVDF copolymer). It is evident that mechanically combining PANI and AC results in a reduction in the micropores of a resultant composite, which becomes greater as the polyaniline content is raised. Additionally, the voltammogram significantly changes, becoming more like the form of pure PANI, when the quantity of polyaniline approaches a particular level. Additionally, all of the combinations with PANI had capacitances that were greater than those of clean AC. The scientists attributed this modification to restrictions for ion diffusion as well as migration within the majority of polyaniline and increased resistivity for the layer’s thicker construction. By mechanically combining PEDOT and MWCNTs, on the opposite side, Lota and colleagues also created overlayed electrodes. The combination produced a 120 F g−1 capacitor voltage in an acid media [35].

2.3.2

Layer-By-Layer (LbL) Assembly

By layer-by-layer (LbL) assembling synthesized MWCNTs and PANI nanomaterials, polymer conductors for electrolytic capacitors or microbatteries were produced. Rechargeable cells may achieve high internal capacitance as well as high voluminous capacity using these LbL-PANI/MWCNT films. Additionally, rate-dependent galvanostatic experiments demonstrated that LbL-PANI/MWNT films can produce

124

P. Chauhan et al.

significant power and rising energy density. They might be potential positively charged electrode elements for coating microbatteries or supercapacitors [36].

3 Graphene-Based Nanocomposites Graphene had been extensively studied in many basic and practical fields since it was initially introduced by A. Geim and K. Novoselov the originally synthesized 2D compound with a central particle thick. Following this, graphene is made up of a unique horizontal carbon sheet having an sp2 hybridized composition. Why is graphene, in comparison to other families of materials, so important? Intriguing properties are produced by this 2D arrangement, including a large particular contact area, strong thermal/electrical conductance, outstanding mechanical/chemical durability, and amazing elasticity and visibility. Due to its exceptional qualities, graphene, and relevant items are well suited for a variety of applications, including synthetic skin and muscles, power storage and distributed generation, and transistors. Theoretically specific capacity of single sheet graphene is computed as 21 F/cm2 , which results in a quantity of 550 F g−1 whenever the entire surface is utilized for charge storage through the development of an electrical double layer [37]. Graphene sheets tend to aggregate, and their electrochemically accessible surface is drastically reduced because of interactions with layering as well as van der Waal interactions, which limits ion transport. As a result, clean graphene performs far worse in practice than it does in theory. Various materials (such as CNTs, polymers, nanoparticles, etc.) must be combined with graphene to create a hybrid system to prevent or at least limit the restacking phenomena and to create room for ions to diffuse [38].

3.1 Polymer/graphene Composites Since the beginning of the graphite era in 2004, scientists have been eager to combine graphite with other materials, leading to an enormous number of papers during the past ten years. The creation of polymer/graphene composites has therefore been the subject of several articles. Graphene/polyurethane, epoxy, polystyrene (PS), poly (vinylidene fluoride) (PVDF), polycarbonate (PC), etc. were often the subjects of extensive research. From a straightforward mixing of graphene as well as a polymer to a more intricate process, different groups have used different methods for the production and processing of the described composites. For instance, a three-step process was described for generating homogeneously distributed graphene in the PS matrix. A steady solution with isocyanate-functionalized graphene was produced after the graphene was processed with benzyl isocyanate in dimethylformamide for approximately 24 h (GO). Subsequently, the PS was added, resulting in a mechanical combination of PS/GO that underwent a chemical method with the aid of hydrazine

Polymer-Carbon Nanocomposites for Supercapacitors

125

to produce PS/rGO. Because of this, the final product had strong electrical properties (0.1 S/m) and an infiltration limit of 0.1 vol% at room temperature. Electrical CPs began to interact with graphite in this environment of investigating the potential for the construction of novel composites, leading to the development of a new form of composite. The addition of conductive polymers enabled the substrate’s graphite to have better electrical conductivity [39]. In 2008, Hong et al. presented the first study on the synthesis process of graphene employing a conductive polymer (i.e., PEDOT doped with polystyrene sulfonate). Since then, a great deal of research has been put into developing this family of materials for a variety of uses, such as (bio)sensors, supercapacitors, batteries, and electrocatalysis. Although the usage of a variety of polymer electrolytes to form a continuous graphene surface, the three unique types of combinations outlined in the preceding section continued to be the most significant ones. The proposed specific capacity for PANI, PPY, and PEDOT is consecutively 750, 620, and 210 F g−1 from the perspective of specific capacity [40].

3.2 Polyaniline/Graphene Freestanding Via employing a graphene “Paper,” PANI-coated graphene paper (GPCP) was created in situ electro-polymerization (AEP) of aniline. The entire process in addition to the finished item. A foldable graphene electrode was created by filtering the graphene suspension used to create the graphene paper (also known as G-paper). The PANI was then electrochemically polymerized using oxide layer polarization in aniline solvent and placed onto G-paper that used a three-electrode arrangement. Due to the improved connectivity between graphene layers in the presence of PANI, some as GPCP had a better mechanical stress of 12.6 MPa. Due to the improved connectivity among graphene layers in the addition of PANI, GPCP had a higher structural tension of 12.6 MPa. But as also demonstrated by BET and CV (6 or 3 A/g for pure and transformed graphene at 0.1 V@20 mV/s, correspondingly) the surface area is significantly reduced [41]. Some over of conductive fillers to the spaces in the graphite network may be the cause. However, the redox capacitor produced by the electrolytic doping of PANI causes the capacitance to be enhanced in the existence of PANI. Gravimetric as well as volumetric capacitors, which represent the cycling capability, are determined to have a particular inductance of 233 F g−1 and 135 F/cm3 , accordingly. As a result, raising the network’s permeability, such as by introducing CNTs, may be predicted to increase the specific capacity of this device [42].

126

P. Chauhan et al.

3.3 Polypyrrole/Graphene PPY has now been tightly associated with things relating to graphene and has the second-greatest predicted specific capacity among various conductive polymers, resulting in extremely active nanocomposite with improved cycle efficiency. Low electron potential (easier oxidation reaction), greater water soluble, and prepare-bycheap procedures are some benefits of PPY over all other CPs. Similar to materials with PANI-covered graphene, PPY@G-related composites may likewise be made using oxidative or electrochemical polymerization. The microstructure and shape of the PPY@G might, however, differ from the PANI composite materials due to differences in chemical structure and physical–chemical characteristics [43]. PPYlayered graphene-related compounds were looked into for the exact purpose as early as PANI@G-based compounds were disclosed as the active layer for superconductors. Liu et al. described the electrolytic polymerization of pyrrole in the presence of sulfonated graphene (SG) to produce PPY-coated SG-suitable biomaterials for supercapacitors. Sulfonic acid compounds from graphite films function as anionic dopants during the electrolytic production of PPY from a molecular perspective. To create a composite with increased conductivity from 99 S/m (pure PPY) to over 500 S/m, the SG sheets are consequently incorporated into the polymer matrix.

3.4 Thiophene-Based Polymers/Graphene Despite polythiophene’s theoretically weak specific capacity, it would be gravely neglectful to not consider the potential connection of PTh with graphene again for the creation of supercapacitors. Recent developments in the use of polythiophene@graphene as just an activated compound in superconductors are given in the section that follows. Different strategies have previously been suggested to optimize the mixture of both elements, PTh, and graphene because the micro structuration of composites plays a vital role in producing higher performance [44]. Contrary to other conductive polymers, thiophene-based polymers have now been extensively employed in a widely accessible form, via a straightforward combination with substances containing graphene, to produce an activated composite with improved performance. One of the most popular thiophene variants, PEDOT: PSS, was initially employed as a conducting wrapper to improve the storage capacity of MnO2 adorned graphene layers (GMP). Highly porous MnO2 nanomaterials with a petal shape were synthesized by anodic polarisation upon a graphene substrate (polyester textiles covered with graphene, R = 700 /sq.). The resulting substrate was then exposed to two or three “dip and dry” sessions in a solution of commonly produced PEDOT: PSS (Clevios, 1: 10 diluted PH1000 solution). Upon completion, the polymeric loading is approximately 0.2 mg/cm2 . As a baseline, a similar technique was used with the SWCNTs suspended, producing G@MnO2 @SWCNTs (GMC) [45].

Polymer-Carbon Nanocomposites for Supercapacitors

127

4 Conclusion and Future Outlook Since they have a huge contact area, are chemically stable, simple to manufacture, and possess a long cycling life. Porosity carbon atoms have received substantial study as components for many electrochemical uses, with double-sheet capacitors. The poor conductance of the very carbon-based materials as well as the fact that the battery technology happens primarily through a dual layers process are two significant limitations in the instance of dual-layer capacitors, though. Substantial research has been done to try to boost electrical conductivity, which might improve the device’s capacity, as well as add pseudo capacitance contribution, which could improve the amount of electricity stored. The incorporation of a thin conductive polymer sheet is one intriguing method. By choosing the production technology and subsequently creating new and distinct qualities for the pure carbon material, this method makes it possible to create various composite materials. Overall, the CP@carbon-based composites have demonstrated excellent characteristics and performance, but they are still plagued by several problems. The consistency of CP-based composites throughout cycling remains difficult. Additionally, although it is not frequently noted in the majority of the published studies, superconductors still have a good self-rate compared to traditional Li-ion batteries, which is one of their key downsides. Several routes might be taken for the advancement of CP-based superconductors in the future. To effectively synthesize composites, it is important to: I. II. III. IV. V. VI. VII.

Comprehend how distinct materials interact with one another. Gain insight into these interactions. Investigate the various interactions among electrocatalysts and electrolytes. Increase the cyclability of SC. Investigate the effects of n-doping on CP. Enhance the connection of polymer electrolytes with carbon-based templates. Enhance the capacitive assembly. The price of the supercapacitors must be brought down in addition to their improved performances. Upcoming opportunities for developing highperforming systems include combining a battery and bank in the very same device, or supercapacitors hybrids. This arrangement enables the use of both aspects’ favorable characteristics.

References 1. Gabe A, Mostazo-López MJ, Salinas-Torres D, Morallón E, Cazorla-Amorós D (2017) Synthesis of conducting polymer/carbon material composites and their application in electrical energy storage. Hybrid polymer composite materials, pp 173–209 2. Pham Truong TN, Banet P, Aubert PH (2021) Conducting polymers nanowires with carbon nanotubes or graphene-based nanocomposites for supercapacitors applications. Conjugated polymer nanostructures for energy conversion and storage applications, pp 445–497

128

P. Chauhan et al.

3. Fan JA, Yeo WH, Su Y, Hattori Y, Lee W, Jung SY, Zhang Y, Liu Z, Cheng H, Falgout L, Bajema M (2014) Fractal design concepts for stretchable electronics. Nat Commun 5(1):1–8 4. Zhang N, Chen J, Huang Y, Guo W, Yang J, Du J, Fan X, Tao C (2016) A wearable all-solid photovoltaic textile. Adv Mater 28(2):263–269 5. Chang SY, Cheng P, Li G, Yang Y (2018) Transparent polymer photovoltaics for solar energy harvesting and beyond. Joule 2(6):1039–1054 6. González A, Goikolea E, Barrena JA, Mysyk R (2016) Review on supercapacitors: technologies and materials. Renew Sustain Energy Rev 58:1189–1206 7. Zhong C, Deng Y, Hu W, Qiao J, Zhang L, Zhang J (2015) A review of electrolyte materials and compositions for electrochemical supercapacitors. Chem Soc Rev 44(21):7484–7539 8. Benny A, George S, Mishra M (2018) Energy: polymer supercapacitors. Encyclopaedia of polymer application. Taylor and Francis, pp 990–1008 9. Abdelhamid ME, O’Mullane AP, Snook GA (2015) Storing energy in plastics: a review on conducting polymers & their role in electrochemical energy storage. RSC Adv 5(15):11611– 11626 10. Laheäär A, Przygocki P, Abbas Q, Béguin F (2015) Appropriate methods for evaluating the efficiency and capacitive behavior of different types of supercapacitors. Electrochem Commun 60:21–25 11. Zhao X, Dong M, Zhang J, Li Y, Zhang Q (2016) Vapor-phase polymerization of poly (3, 4ethylenedioxythiophene) nanofibers on carbon cloth as electrodes for flexible supercapacitors. Nanotechnology 27(38):385705 12. Luo J, Zhong W, Zou Y, Xiong C, Yang W (2016) Preparation of morphology-controllable polyaniline and polyaniline/graphene hydrogels for high-performance binder-free supercapacitor electrodes. J Power Sources 319:73–81 13. Liu H, Song H, Chen X, Zhang S, Zhou J, Ma Z (2015) Effects of nitrogen-and oxygencontaining functional groups of activated carbon nanotubes on the electrochemical performance in supercapacitors. J Power Sources 285:303–309 14. Han J, Li Q, Peng C, Shu N, Pan F, Wang J, Zhu Y (2020) Increasing S dopant and specific surface area of N/S-codoped porous carbon by in-situ polymerization of PEDOT into biomass precursor for high-performance supercapacitor. Appl Surf Sci 502:144191 15. Tong L, Skorenko KH, Faucett AC, Boyer SM, Liu J, Mativetsky JM, Bernier WE, Jones WE Jr (2015) Vapor-phase polymerization of poly (3, 4-ethylenedioxythiophene)(PEDOT) on commercial carbon coated aluminum foil as enhanced electrodes for supercapacitors. J Power Sources 297:195–201 16. Gao Z, Zhang X, Zhang K, Yuen MM (2015) Growth of vertically aligned carbon nanotube arrays on Al substrates through controlled diffusion of catalyst. J Phys Chem C 119(27):15636– 15642 17. Afzal A, Abuilaiwi FA, Habib A, Awais M, Waje SB, Atieh MA (2017) Polypyrrole/carbon nanotube supercapacitors: technological advances and challenges. J Power Sources 352:174– 186 18. Warren R, Sammoura F, Teh KS, Kozinda A, Zang X, Lin L (2015) Electrochemically synthesized and vertically aligned carbon nanotube–polypyrrole nanolayers for high-energy storage devices. Sens Actuators, A 231:65–73 19. Hsia B, Marschewski J, Wang S, In JB, Carraro C, Poulikakos D, Grigoropoulos CP, Maboudian R (2014) Highly flexible, all solid-state micro-supercapacitors from vertically aligned carbon nanotubes. Nanotechnology 25(5):055401 20. Fang Y, Jiang X, Niu L, Wang S (2017) Constructing polypyrrole/aligned carbon nanotubes composite materials as electrodes for high-performance supercapacitors. Mater Lett 190:232– 235 21. Lagoutte S, Aubert PH, Pinault M, Tran-Van F, Mayne-L’Hermite M, Chevrot C (2014) Poly (3methylthiophene)/vertically aligned multi-walled carbon nanotubes: electrochemical synthesis, characterizations, and electrochemical storage properties in ionic liquids. Electrochim Acta 130:754–765

Polymer-Carbon Nanocomposites for Supercapacitors

129

22. Chang ZH, Feng DY, Huang ZH, Liu XX (2018) Electrochemical deposition of highly loaded polypyrrole on individual carbon nanotubes in carbon nanotube film for supercapacitor. Chem Eng J 337:552–559 23. Vignal T, Banet P, Pinault M, Lafourcade R, Descarpentries J, Darchy L, Hauf H, Reynaud C, Mayne-L’Hermite M, Aubert PH (2020) Electropolymerized poly (3-methylthiophene) onto high density vertically aligned carbon nanotubes directly grown on aluminum substrate: application to electrochemical capacitors. Electrochim Acta 350:136377 24. Ghosh S, Holade Y, Remita H, Servat K, Beaunier P, Hagège A, Kokoh KB, Napporn TW (2016) One-pot synthesis of reduced graphene oxide supported gold-based nanomaterials as robust nanocatalysts for glucose electrooxidation. Electrochim Acta 212:864–875 25. Bonaccorso F, Colombo L, Yu G, Stoller M, Tozzini V, Ferrari AC, Ruoff RS, Pellegrini V (2015) Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage. Science 347(6217):1246501 26. Kar P, Sardar S, Liu B, Sreemany M, Lemmens P, Ghosh S, Pal SK (2016) Facile synthesis of reduced graphene oxide–gold nanohybrid for potential use in industrial waste-water treatment. Sci Technol Adv Mater 17(1):375–386 27. Yang Z, Chabi S, Xia Y, Zhu Y (2015) Preparation of 3D graphene-based architectures and their applications in supercapacitors. Prog Nat Sci: Mater Int 25(6):554–562 28. Xu G, Jarjes ZA, Desprez V, Kilmartin PA, Travas-Sejdic J (2018) Sensitive, selective, disposable electrochemical dopamine sensor based on PEDOT-modified laser scribed graphene. Biosens Bioelectron 107:184–191 29. Yue R, Wang H, Bin D, Xu J, Du Y, Lu W, Guo J (2015) Facile one-pot synthesis of Pd–PEDOT/ graphene nanocomposites with hierarchical structure and high electrocatalytic performance for ethanol oxidation. J Mater Chem A 3(3):1077–1088 30. Gao Y (2017) Graphene and polymer composites for supercapacitor applications: a review. Nanoscale Res Lett 12(1):1–17 31. Jin J, Mu H, Wang W, Li X, Cheng Q, Wang G (2019) Long-life flexible supercapacitors based on nitrogen-doped porous graphene@ π-conjugated polymer film electrodes and porous quasi-solid-state polymer electrolyte. Electrochim Acta 317:250–260 32. Yu J, Xie F, Wu Z, Huang T, Wu J, Yan D, Huang C, Li L (2018) Flexible metallic fabric supercapacitor based on graphene/polyaniline composites. Electrochim Acta 259:968–974 33. Gao S, Zhang L, Qiao Y, Dong P, Shi J, Cao S (2016) Electrodeposition of polyaniline on threedimensional graphene hydrogel as a binder-free supercapacitor electrode with high power and energy densities. RSC Adv 6(64):58854–58861 34. Shen H, Li H, Li M, Li C, Qian L, Su L, Yang B (2018) High-performance aqueous symmetric supercapacitor based on polyaniline/vertical graphene/Ti multilayer electrodes. Electrochim Acta 283:410–418 35. Li P, Jin Z, Peng L, Zhao F, Xiao D, Jin Y, Yu G (2018) Stretchable all-gel-state fiber-shaped supercapacitors enabled by macromolecularly interconnected 3D graphene/nanostructured conductive polymer hydrogels. Adv Mater 30(18):1800124 36. Hong X, Zhang B, Murphy E, Zou J, Kim F (2017) Three-dimensional reduced graphene oxide/polyaniline nanocomposite film prepared by diffusion driven layer-by-layer assembly for high-performance supercapacitors. J Power Sources 343:60–66 37. Wu J, Wang J, Huang X, Bai H (2018) A self-assembly route to porous polyaniline/reduced graphene oxide composite materials with molecular-level uniformity for high-performance supercapacitors. Energy Environ Sci 11(5):1280–1286 38. Zhang L, Wang W, Cheng J, Shi Y, Zhang Q, Dou P, Xu X (2018) Skeleton networks of graphene wrapped double-layered polypyrrole/polyaniline nanotubes for supercapacitor applications. J Mater Sci 53(1):787–798 39. Wang H, Yu Z, El-Kady MF, Anderson M, Kowal MD, Li M, Kaner RB (2019) Graphene/ oligoaniline based supercapacitors: towards conducting polymer materials with high rate charge storage. Energy Storage Mater 19:137–147 40. Liu Y, Zhang B, Xu Q, Hou Y, Seyedin S, Qin S, Wallace GG, Beirne S, Razal JM, Chen J (2018) Development of graphene oxide/polyaniline inks for high performance flexible microsupercapacitors via extrusion printing. Adv Func Mater 28(21):1706592

130

P. Chauhan et al.

41. Li R, Yang Y, Wu D, Li K, Qin Y, Tao Y, Kong Y (2019) Covalent functionalization of reduced graphene oxide aerogels with polyaniline for high performance supercapacitors. Chem Commun 55(12):1738–1741 42. Park H, Kim JW, Hong SY, Lee G, Kim DS, Oh JH, Jin SW, Jeong YR, Oh SY, Yun JY, Ha JS (2018) Microporous polypyrrole-coated graphene foam for high-performance multifunctional sensors and flexible supercapacitors. Adv Func Mater 28(33):1707013 43. Barakzehi M, Montazer M, Sharif F, Norby T, Chatzitakis A (2019) A textile-based wearable supercapacitor using reduced graphene oxide/polypyrrole composite. Electrochim Acta 305:187–196 44. Qu G, Cheng J, Li X, Yuan D, Chen P, Chen X, Wang B, Peng H (2016) A fiber supercapacitor with high energy density based on hollow graphene/conducting polymer fiber electrode. Adv Mater 28(19):3646–3652 45. Zhou H, Zhai HJ, Han G (2016) Superior performance of highly flexible solid-state supercapacitor based on the ternary composites of graphene oxide supported poly (3, 4-ethylenedioxythiophene)-carbon nanotubes. J Power Sources 323:125–133

Polymer-Metal Oxides Nanocomposites for Supercapacitors R. Rajalakshmi and N. Ponpandian

Abstract Conducting polymers (CP) in a supercapacitor are used as pseudocapacitive materials compared to double-layer capacitors as their redox reactions are fast promoting excellent power capability and superior specific charges. Their conductive nature surpasses carbon-based supercapacitors but their cycle life is generally poor. To overcome many of these deficiencies, incorporating a composite with metal oxides is beneficial as they serve a variety of electrochemical properties. The options for selecting a metal oxide are vast in the periodic table according to the need of the pseudocapacitance behavior. The synergistic impact of the nanometal oxides combined with the conductivity of the CPs could promote better active sites to enhance the overall electrochemical performance of the supercapacitors. This chapter introduces the basic background on supercapacitors and their types leading to the synthesis techniques of conducting polymers and metal oxides to serve as efficient electrode materials for supercapacitor application. Finally, a full discussion on the physicochemical and electrochemical performance of major CP’s like polyaniline (PANI), poly(3,4-ethylene-dioxythiophene) (PEDOT), and polypyrrole (PPy) with different types of metal oxide are discussed in brief. The chapter is concluded with suggestions for further research and development in the existing field. Keywords Polymers · Metal oxide · Nanocomposites · Supercapacitors · Energy storage

1 Introduction The decline in the availability of non-renewable resources has led to the development of alternative energy sources to tackle climate breakdown and the fuel crisis. Research focusing on electrochemical energy storage or conversion is in huge demand owing R. Rajalakshmi · N. Ponpandian (B) Department of Nanoscience and Technology, Bharathiar University, Coimbatore, Tamil Nadu 641046, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_8

131

132

R. Rajalakshmi and N. Ponpandian

to their exceptional power and energy densities with high withstanding capability scaling them up for daily mankind or high-end industrial applications [1]. Among the list of competent devices like fuel cells and batteries, supercapacitors are a hot topic as they are advantageous with their long cyclic life, ease in the reversibility of their state, high specific energies, and abundant options for fabrication of different types of supercapacitors from solid state to flexible and transparent [2–4]. There are different types or divisions of supercapacitors established depending on their ability to store charges. One division is the EDLCs also known as the electrical double-layer capacitors where the charge accumulation occurs physically due to the adsorption and desorption of the reactants between the electrode and the electrolyte interface. The selection of materials for EDLC type includes mainly carbon nanotubes (CNTs) with an emphasis on carbon-based materials. Pseudocapacitors fall under the second division where reversible fast-redox reactions from various metal oxides/hydroxides/sulfides/phosphides and also include conductive polymers are utilized for the energy storage process. There is also another category called the hybrid supercapacitors which are also known as battery-type supercapacitors and utilize faradic and EDLC-type mechanisms to store charge. The selection of materials for the hybrid supercapacitors also varies depending on the specific target of an increase in the faradaic or EDLC property of the supercapacitor [5]. The need in a supercapacitor application where the energy density should be stocked up sufficiently could not be handled efficiently by EDLC materials where the role of pseudocapacitor materials is contributed [6]. Introducing conducting polymers (CPs) as an integral part of the pseudocapacitor component mainly targets to increase the conductive nature of the electrode material thereby reducing self-discharge and elevating the energy stored through the redox mechanism. The conjugated bond in the polymer chain forms the backbone of the selection of the CP to deliver high electrochemical performance [7, 8]. Metal oxides of various natures including a majority of transition and rare earth elements are also in long use as a pseudocapacitor material to resolve the inadequacies of low energy density and conductivity of electrical double-layer (EDL) capacitors containing carbon. The use of pristine CPs as pure pseudocapacitor electrodes hinders the cycle stability compared to carbon-based materials in the EDLC type. Another vast group of materials exhibiting pseudocapacitive behavior are the metal oxides with their oxidation states favoring flexible faradaic reactions and possessing large theoretical values of capacitance. Their fabrication techniques are also facile including mostly chemical methods. However, metal oxides have their shortcomings as they cannot confine to the structural stability of standing as an electrode to deliver high current density and the low electronic conductivity is also an added drawback [9, 10]. Therefore, the gap between the complications faced by the conducting polymers and the metal oxides could be bridged by combining these two to form composites of binary or ternary compositions and design electrodes to store a greater amount of charge as well as increase the longevity of the pseudocapacitors with superior specific energies.

Polymer-Metal Oxides Nanocomposites for Supercapacitors

133

2 Electronically Conducting Polymers (CPs) for Supercapacitors The Conducting polymers (CPs) could serve the purpose of a supercapacitor electrode due to their inherent electronic and pseudo-capacitive properties. The main advantage is their flexibility which could be opted for substrate-free electrodes in capacitor applications. The important and frequently used CPs include Polyaniline (PANI), Polypyrrole (PPy), and poly(3,4-ethylene-dioxythiophene) (PEDOT) [11]. The physicochemical and electrochemical characteristics of the most prominent CPs are tabulated in Table 1. Polyaniline (PANI) is a long-chain conjugated with an interconvertible benzenoid ring that could be synthesized by various electrochemical or chemical routes [12]. It is a prominent conducting polymer with fast kinetics and good electrical conductivity. However, the polymer suffers from shrinking and swelling during the intercalation/deintercalation processes causing mechanical instability. Polypyrrole (PPy) is also a widely investigated conducting polymer that is π-electron conjugated. The main advantage of this polymer over other conducting polymers is its ecofriendliness with rarer toxicological complications and the existence of anionic surfactants highly improves the conductivity to be used in even alkaline conditions [13]. The succeeding polymer is the PEDOT also known as Poly(3,4ethylenedioxythiophene), which is a regularly employed CPon account of its high work function, superior physical and chemical steadiness with flexible filmforming capacity. Nevertheless, PEDOT also has some shortcomings as poor solubility, swelling, and shrinking at the time of intercalation processes considered to shorten the span of cyclic stability and the existing conduct of supercapacitors [14]. Solutions to improve the existing downsides also include ameliorating them with binary and ternary composites of metal oxides. Other conducting polymers prove useful such as poly(3,4-methylenedioxy pyrrole) PEDOP, polyindole (Pind), polythiophene (PTh),etc. which are also included in the chapter (Fig. 1). Table 1 Physical and electrochemical properties of the most prominent CPs [11] Conducting polymers

Molecular Dopant Potential Cs Cs weight (g) level window (Theoretical) (Measured) range (F g−1 ) (F g−1 ) (V)

Polyaniline

93

0.5

0.7

750

240

Polypyrrole

67

0.33

0.8

620

530

Polythiophene

84

0.33

0.8

485

-

0.33

1.2

210

92

Poly(3,4-ethylenedioxythiophene) 142

134

R. Rajalakshmi and N. Ponpandian

Fig. 1 Structural illustration of different conducting polymers (CPs). Adapted with permission [11]. Royal Society of Chemistry under a Creative Commons Attribution License 4.0 (CC BY)

3 Metal Oxides for Pseudocapacitors Materials scientists review the properties of metal oxides as pseudocapacitive materials owing to their exceptional physicochemical properties and reliability in electrochemical systems [15]. The most commonly used metal oxides are RuO2 , MnO2 , Fe2 O3 , TiO2 , V2 O5, and MoO3 [9, 10]. One of the highly efficient and durable surface redox materials for use as a pseudocapacitor is the ruthenium oxide that exists in different phases (RuO2 and RuO2 xH2 O) [16]. But considering the cost-effectiveness of the sample, it is rather used in small proportions along with a high percentage of various other materials for pseudocapacitors. Reigning the category for high values of specific capacitance, cost sustainability, sufficient enough for production, lowtoxic and a large amount of the previous investigations carried out are MnO2 and Mn3 O4 [17]. As a characteristic of efficient electrode material for use of a pseudocapacitor, Fe2 O3, and Fe3 O4 have also received a lot of attention since their theoretical capacitance and the possibility to work in a wide negative potential window with effectiveness in cost and toxicity is an added advantage [18]. Recently, vanadium oxides (V2 O5 , VO2 , V2 O3 ) areconsideredcapableentrants due to their intrinsic properties being advantageous, especially for withstanding high resistance in storing charges. Nevertheless, their poor electrical conductivity and structural instability have been improved by proposed techniques such as hybridization with highly conductive materials [19]. Apart from that, a material whose conductivity due to the bandgap is exceptionally good and the synthesizing strategies are of ease to obtain the desired crystal phase and specifically, the capacitance of 1112 F/g deducted theoretically are all considered exuberant for the n-type semiconductor WO3 for use in an SC. Among the polymorphs of Titanium oxide (TiO2 ), TiO2 (B) is approached for intercalation purposes in a pseudocapacitor as the structure is more exposed to surface relation reactions [20]. Considering the metal Molybdenum, the orthorhombic and the metastable states of MoO3 render good stability for application in supercapacitors than MoO2

Polymer-Metal Oxides Nanocomposites for Supercapacitors

135

[21]. Among various metal oxides, NiO, a p-type semiconductor possesses excellent features of long durability, electrochemical stability, and different synthesizing possibilities to be used as an electrode material. Various other metal oxides from the rare earth group (CeO2 , Eu2 O3 , Pr6 O11 ) have also contributed to the capacitive ability to be implemented for the application of a supercapacitor [22, 23].

4 Synthesis Techniques Involved 4.1 Synthesis Techniques for Conducting Polymers The synthesizing strategies involved for CPs are mainly through chemical, electrochemical, and redox reactions using light. The chemical synthesis method involves the connection of the carbon–carbon bond of monomers by the insertion of simple monomers under various environmental parameters. An enormous amount of polymerization methods have also been put into practice to upsurge the quantitative and qualitative yield of the CPs. Most of the prominent CPs such as PANI. PPy, PEDOT, etc., [18, 24–26] are prepared by chemical polymerization. An alternative method is the electrochemical synthesis method which is cost-effective as it could be prepared on a substrate and is also advantageous for its reproducibility. The electrochemical conditions of constant current or potential are favored for the preparation technique. At times, cyclic voltammetry is also performed especially on the anodic side where the oxidation process occurs to deposit the polymer onto the substrate rather than the insignificant cathodic reduction. Several external factors are responsible to influence the deposition rate such as the alkalinity or acidity of the medium of interaction and the concentration of the monomers as well as the electrochemical parameters such as the potential applied for polymerization, temperature, time, etc. In this electropolymerization process, the primary step is to generate a radical cation and when a monomer is introduced to react with the cation a protonated dimer is produced to finally yield an oxide by the electro-oxidation step (Fig. 2) [18]. Additionally, lightinduced reactions are applied to create flexible substrates of CPs like PPY, PANI, etc., Other methods of synthesis of CPs include emulsion, solid state, pyrolysis, plasma, etc.,Over againlately, CPs involving the attachment of other co-polymer blocks are also attained through template-assisted synthesis techniques for hybrid structures.

4.2 Synthesis Techniques of Metal Oxides The physicochemical characteristics such as crystal structure, morphology, defects types, dispersity, etc., of the metal oxide are determined vastly by the choice of synthesis technique adopted. The synthesis techniques involved in the fabrication of metal oxide nanoparticles, especially for supercapacitor applications require a

136

R. Rajalakshmi and N. Ponpandian

Fig. 2 a The process of synthesis of Ti-Fe2 O3 @PEDOT on CC substrate illustrated schematically. b The morphology of Ti-Fe2 O3 @PEDOT NRs viewed by SEM. c The HRTEM images with the lattice spacings with the elemental mapping of d Fe, e Ti, and f S respectively. Adapted with permission [18]. Copyright (2015) WILEY-VCH

qualitative approach rather than the yield. The methods of synthesis can be broadly classified into chemical methods, further described as the solution state synthesis and physical methods also called the vapor state synthesis methods. Some of the solution state practices include the sonochemical method, co-precipitation, sol–gel, Solvothermal, and microwave-assisted method. The physical methods are primarily the laser ablation method, chemical vapor synthesis method, combustion method, and template-free mediated synthesis [22]. In the sonochemical method, intensified ultrasonic vibrations are introduced into the precursor solution containing the metallic salts which cause alternate compression and relaxation leading to acoustic cavitation in an implosive pattern. These shock waves will lead to the formation of the oxide particles in the presence of air at elevated temperatures and after the settlement/cooling recrystallizes the formation of the obtained products. A wide range of metal oxides including TiO2 , CeO2 , MoO3 , V2 O5 , etc., have been synthesized by this method. Another state-of-the-art method is the co-precipitation method involving the precipitate formation of oxo-hydroxide solutions of a metal salt precursor in a solution by using NaOH, KOH, (C2 H5 )4 NOH, etc., as agents to precipitate the metal oxides. When the threshold concentration of the solution is reached, nucleation begins to spurt and the growth phase naturally follows. A wide range of metal oxides especially magnetic nanoparticles are synthesized by using this technique [4, 6, 27].

Polymer-Metal Oxides Nanocomposites for Supercapacitors

137

An alternative approach is a solvothermal method where the organometallic precursor solution is dispersed in an appropriate solvent and subjected to reasonably good thermodynamic conditions (temperature and pressure) for deriving the final product. The chemical and thermodynamic parameters could be tuned to obtain highly crystalline metal oxide nanostructures. An advantage of implementing this technique is that Oswald’s ripening process leading to nucleation paves the way to produce different morphological entities necessary for heightening the electrochemical performance of nanometal oxide materials. Core–shell metal oxides of Fe3 O4 and many other morphological structures such as V2 O5 nanobelts (Fig. 3) are produced by this technique. A chemical solution deposition also known as sol–gel is a chemical path that includes the metalorganic compound precursors, to form the respective oxo-hydroxide constituents and condense them to form hydroxide components that could be calcined to derive the metal oxide counterpart. The microwave-assisted method is also gaining popularity as it requires fairly low energy rapid to nucleate and form small, highly monodisperse particles using microwave irradiation [9, 10]. Although the physical/vapor state synthesis techniques are rarely used except for the exceptional quality of high-end crystalline materials in supercapacitor applications, the most used method is the laser ablation technique where metal oxide nanomaterials are produced by colliding with laser irradiation under high vacuum conditions. The resultant is a qualitative thin film of appropriate thickness when the time of irradiation is managed well. ZnO, Fe2 O3 , SnO2 , iron-oxide, Al2 O3 , and also some ternary compositions of metal oxides are prepared by this method. A similar approach is chemical vapor deposition (CVD), where high temperature is exposed to the precursor materials in a gaseous state such as Ar (inert gas) to decompose

Fig. 3 a TEM images of V2 O5 nanobelts, b The same TEM image of a in a higher magnification c The calculated interplanar distance of V2 O5 , d The SAED pattern of i V2 O5 /PEDOP ii pristine V2 O5 and iii the PEDOP polymer, e TEM image of PEDOP, f smaller and g higher magnification Tem image of PEDOP/V2 O5 nanocomposite. Adapted with permission [28]. Royal Society of Chemistry

138

R. Rajalakshmi and N. Ponpandian

into the respective metal oxide. Defect-free oxides of various morphologies could be attained by this technique. The least used technique is the combustion method as the rate of evaporation of precursors is at stake. The process is complex due to the coupling of flame chemistry and oxide production being difficult to control. The final template/surface-mediated synthesis is an amalgamation of different physical and chemical routes (sol–gel, chemical polymerization, CVD, etc.,). The anticipated morphology of the template chosen, be it rods or tubules could be fabricated by this method with an emphasis on managing the porosity. Highly monodisperse nanostructures with enhanced activity displaying highly reactive surfaces could be attained by this method.

5 Composites of Polyaniline and Metal Oxide as Electrodes for Supercapacitors 5.1 Binary Compositions The metal oxide MnO2 was composited with the conducting polymer PANI to form the (PANI)/MnO2 composite through the pulse electrodeposition method. When compared to the Cs of the pure polymer form of PANI (662 F g−1 ), the PANI/ MnO2 composite exhibited a dynamically higher specific capacitance of 810 F g−1 at 0.5 A g−1 . The durability was also strong with the cycle life maintained at 86.3% of its initial capacitance [29]. In this study, the pseudocapacitance contribution from the MnO2 and PANI had a direct variation in the mass activity of the individual components. Conceptually similar work has also been carried out by Prasad and Miura where a matrix consisting of PANI and MnO2 achieved a good specific capacitance of 715 Fg−1 . When introducing one-dimensional architectures with co-axial fibers of PANI-δ-MnO2 in the same electrolyte (0.1 M Na2 SO4 ) a Cs of 383 Fg−1 was reported [30]. PANI insertion is also found to increase the lattice spacing of δ-MnO2 . The mechanistic insights of charge storage were studied in a single polymorph of δ-MnO2, where the morphology (nanoflower) played a major role along with the CP—PANI as the active area, increased from 17 to 106 m2 g−1 thereby increasing the ion diffusion coefficient and intercalation capacitance [31]. A chemical reaction involving polymerization produced fibrous PANI–MnO2 nanocomposite [32] This fibrous catalyst enriched the specific energy of a fuel cell (microbial) than its pure equivalent (PANI) displaying a P of 0.0588 Wm−2 . The capacitance touched 525 F g−1 at 2 A g−1 . Apart from fibers, α-MnO2 nanotubes (MNTs) were composited with PANI by in situ polymerization. The PANI–MnO2 nanotube hybrid nanocomposite corresponded to a maximum specific capacitance of 626 F g−1 and an energy density of 17.8 Wh kg−1 , from the GCD curve measurements at 2 A g−1 [33].

Polymer-Metal Oxides Nanocomposites for Supercapacitors

139

A hierarchical hollow Co3 O4 electrode composited with PANI through in situ polymerization path produced nanocage structures that drastically improved the electron transport rate and lowered the contact resistance of the electrode material. The Co3 O4 /PANI electrode material unveiled at 1 A g−1 a high specific capacitance of 1301 F g−1 and maintained a stability of 10% less than the initial capacitance after 2000 cycles. An energy density of 41.5 Wh kg−1 at 0.8 kW kg−1 and a power density of 15.9 kW kg−1 at 18.4 Wh kg−1 was conveyed by the device assembled with the composite electrode [34]. Furthermore, the in situ polymerization method also paved way for the Co3 O4 /PANI electrode to exhibit a core–shell structure witha low ion transmission path and the least resistance with anextraordinary Cs (1184 F g−1 at 1.25 A g−1 ) and a degradation in cyclic stability of 15.1% after 1000 cycles [25]. The electrode nanocomposite consisting of vanadium oxide (V2 O5 ) and polyaniline (PANI) exposed nanowire-like morphology through the electro-codeposition method of introducing V2 O5 into the PANI polymer substrate. The flexible symmetric supercapacitor exhibited an extensive potential window of 1.6 V and a maximum Cs of 443 F g−1 crossing a retention factor of 92% after 5000 cycles [19]. Combining rare earth oxides with CPs such as CeO2 /polyaniline nanostructure showed superior redox reaction based on the superior electrochemical properties of the combo nanocomposites. The CeO2 /PANI nanostructure displayed improved specific capacitance of 1452 F g−1 at a current density of 2 A g−1 , compared to CeO2 (927 F g−1 at 2 A g−1 ) maintaining excellent stability upto 1500 cycles. The polymer composition was exploited for an asymmetric supercapacitor which possessed high capacity (256 F g−1 at 2 mV s−1 ) with an impeccable E (75 Wh kg−1 ) and extraordinary (566 W kg−1 )[35]. PANI nanowire arrays engulfed into the TiO2 nanotubes showed excellent reactivity and fast diffusion path delivering a Cs (732 F g−1 at 1 A g−1 ), and only 26% of the E (36.6 Wh kg−1 ) was lost at 6000 W kg−1 . Polyaniline/black TiO2 nanotubes (PANI/H-TiO2 NTs) were fabricated by blending electrochemical deposition and a reduction reaction to attain a highly capacitive electrode material. The PANI/HTiO2 NTsrevealedaCs of 999 F g−1 at 0.6 A g−1 while degrading a percentage of 29.8 of the initial capacitance after 2000 GCD cycles[12]. Furthermore, a thin film consisting of a composite of TiO X -polyaniline (PANI) was synthesized using an electrochemical deposition technique showing granular porous morphologies improving the P and E values at ∼ 31.2 kW/kg and ∼ 35.2 Wh/kg, respectively over 1000 charge–discharge cycles [20]. Considering mixed oxides nanocomposites with PANI such as CoMoO4 .0.75H2 O, metal molybdates were formed due to multiple oxidation states displaying a good Cs of 380 F g−1 achieved at 1 A g−1 current density accompanied with a high E of 42.7 Wh/kg at a power delivery rate of 450 W/kg (Fig. 4) [36] A facile coprecipitation technique produced nanoplatelet-like Ca2 V2 O7 nanostructures [37]. The nanoplatelets when combined with PANI in 6 M KOH electrolyte delivered aCsof 542 F g−1 at 1 A g−1 which is greater than pristine Ca2 V2 O7 (202 F g−1 ). The composition also displayed an admirable retention capacitance delivering 84.2% efficiency after 1000 cycles of its initial discharge capacitance at 5 A g−1 .

140

R. Rajalakshmi and N. Ponpandian

Fig. 4 a Deviationin the specific capacitance values of pristine (CoMoO4 .0.75H2 O) and composite (CoMoO4 .0.75H2 O/PANI)at different current density values, b cyclic stability, c The Ragone plot of both the samples and d Deviation in the specific capacitance values of both the samples at different scan rate (mV/s). Adapted with permission [36]. Royal Society of Chemistry

5.2 Ternary Compositions Introducing ternary compositions enhances the existing properties and targets specific improvements of the electrochemical behavior. A ternary composition with Ag/ MnO2 /PANI was synthesized using the pulsed potential electrodeposition procedure. The electrical conductivity was drastically increased from 66 to 83% from the uniform vermicular morphology in a 0.5 M LiClO4 electrolyte exhibiting a specific capacitance of 800 F g−1 from the charge–discharge measurements [4]. An optimum Cs of 216 Fg−1 was delivered with high endurance when a ternary composite was introduced with CNT forming a MnO2 /PANI@CNTelectrode [10].

Polymer-Metal Oxides Nanocomposites for Supercapacitors

141

6 Composites of Polypyrrole and Metal Oxide as Electrodes for Supercapacitors 6.1 Binary Compositions The Polypyrrole polymer was composited with MnO2 nanofilmto enhance the electrode performance demonstrating (∼ 45.6 mF cm−2 ) with an areal capacitance (25.9 mF cm−2 ) but poor retention scalability as almost half of the initial capacitance was lost when the scan rate was increased to 250 mV s−1 ) [38]. Hydrothermally synthesized γ-MnO2 was composited with PPy to obtain γ-MnO2 /PPy by electrochemical polymerization of pyrrole. The (PPy/MnO2 ) composite was fabricated to be scaled up for an asymmetric supercapacitor device. The electrode only displayed 73.7 F g−1 in its pure form before composition with PPy but then rose to a Cs 141.6 F g−1 , improving the reactive area measured from BET to be 125 m2 g−1 which was only 64 m2 g−1 before composite formation[39]. Nanorods of MoO3 coated with PPyvia hydrothermal in-situ chemical oxidative polymerization provided a specific capacitance of 687 F g−1 at a current density of 1 A g−1 . The nanorod composite remarkably enhanced the capacitance retention (83%) after 3000 cycles [40]. Similar works of nanobelt MoO3 with PPy contributed to 76% capacity retention after 10,000 cycles in an asymmetric supercapacitor. The composite MoO3/ PPy attributed to 17% degradation after 600 cycles. After 10,000 cycles, 11.8% of the initial capacitance was worn out. In terms of stability, the positive side contributed to 2.5% of the loss whereas the negative side suffered upto 13.8% loss of its initial Cs after 6000 cycles. A nanorod morphology of MnMoO4 and PPypolymer lost 19.4% of the stability test after 1000 cycles [9]. CoO nanowire array with polypyrrole (PPy) was grown on a 3D nickel foam to improve the electrode performance by shortening the ion diffusion pathway. This led to an excellent specific capacitance (2223 F g–1 ) approaching the exceptionally least capacitance loss (0.2%) after 2000 cycles. The electrode architecture paved the way for a device setup with a maximum voltage of 1.8 V demonstrating a high E (∼ 43.5 Wh kg–1 ), and an outstanding P (∼ 5500 W kg–1 at 11.8 Wh kg–1 ) [41]. A core–shell nanorod electrode material consisting of Co3 O4 /PPysynthesized through the hydrothermal route and depositing the metal oxide through electrodeposition revealed only 2% loss after 5000 cycles and exhibited a good reactive space with areal capacitance (1.02 F cm−2 )[42]. CeO2 particles were surface-functionalized in different ways with PPy to form CeO2 /PPy nanocomposite as an electrode material to form an asymmetric supercapacitor. The composite revealed a high Cs of 193 F g−1 when considering the pristine form, 0.6 F g−1 (CeO2 ) and 127 F g−1 (PPy) respectively. The composite electrode also revealed a good stable capacitance of 10% loss after 500 cycles [22]. The aminefunctionalized Pr6 O11 nanoparticles through in situ surface-initiated polymerization technique were composited with polypyrrole (Pr6 O11 /PPy) demonstrating a Cs of 400 F g−1 at 10 mA cm−2 (GCD). However, the capacitance dropped to 60% of the initial capacitance after 750 cycles [23].

142

R. Rajalakshmi and N. Ponpandian

Fig. 5 The galvanostatic charge–discharge curves of a PPY/CuO/Eu2 O3 from small to high current densities, b PPY, PPY/CuO, and PPY/CuO/Eu2 O3 at 1 A g−1 , c The specific capacitances values of pure polymer, PPY/CuO and PPY/CuO/Eu2 O3 nanocomposites represented in a 3D graph, d Cyclic voltagramms of the nanocomposite PPY/CuO/Eu2 O3 at different scan rates and, e Cyclic voltagramms of PPY, PPY/CuO and PPY/CuO/Eu2 O3 at a fixed scan rate. Adapted with permission [24]. Royal Society of Chemistry

6.2 Ternary Compositions A high capacitance electrode material comprising manganese oxide@nitrogen doped graphene oxide/polypyrrole (MnO2 @NGO/PPy) composite synthesized through hydrothermal chemical reaction depicted improved capacitance of 480 Fg−1 compared to its binaryMnO2 @NGO electrode (360 F g−1 ) at 0.5 A g−1 [15]. The charge transport properties necessary for supercapacitance application could be enhanced by introducing a rare-earth metal oxide such as Eu2 O3 . A ternary composition consisting of PPY/CuO/Eu2 O3 developed interconnected mesoporous networks to reduce the internal resistance (Fig. 5). This composition exhibited a maximum Cs of 320 F g−1 at 1 A g−1 and also established an excellent columbic efficiency [24].

7 Composites of PEDOT and Metal Oxide as Electrodes for Supercapacitors 7.1 Binary Compositions The PEDOT, poly(3,4-ethylene-dioxythiophene) conducting polymer has received immense attention in the field of SCs owing to its excellent conductivity, good capacitive behavior, high stability, and high-end mechanical flexibility. Rios and coworkers introduced electrodeposition of (PEDOT/MnO2 ) over a PEDOT-modified

Polymer-Metal Oxides Nanocomposites for Supercapacitors

143

titanium substrate. The PEDOT/MnO2 /PEDOT sandwich electrode was optimized to deliver excellent capacitive response possessing a high Cs (487.5 F g−1 at 1 A g−1 ) [43]. Further, a coaxial MnO2 /PEDOT nanowire composite on Ausputtered nanoelectrodes comprising different shapes and models showed the highest Cs (270 F g−1 at 0.70 V vs. Ag/AgCl) [17]. Zhang et al. presented a MnO2 @PEDOT@MnO2 composite which represented a core–shell-branch structure by incorporating an electrodeposition approach. The GCD test revealed a maximum Cs of 449 F g−1 at 0.5 A g−1 [3]. TiO2 fibers prepared by electrospinning process and coated with PEDOT through vapor-phase polymerization process had cyclic stability of 9.8%loss after 1000 cycles. A combination of TiO2 /PEDOT nanofibers achieved a Cs of 87.9 F g−1 [44]. A fusion of (PEDOT) with poly(4-styrene sulfonic acid) (PSS) and TiO2 electrode fabricated with peroxotitanic acid (PTiA) revealed a capacity retention loss of 20% after 10,000 cycles and maintaining a 48% loss after 32,000 cycles to be applied as a symmetric supercapacitor cell configuration[26]. V2 O5 nanobeltswith a PEDOT combination yielded a hybrid electrode material showing an E of 223 Wh kg−1 at a P of 3.8 kW kg−1 withstanding 90% of its capacitance after 5000 cycles [28]. The pseudocapacitance behavior of RuO2 /PEDOT nanotubes electrode exhibited high Cs and redox capability. The flexible PEDOT kept the metal oxide from fragmenting and peeling off whereas the metal oxide kept the PEDOT structure in shape. The composite electrode consisting of RuO2 /PEDOT nanotube reached a high P of 20 kW kg−1 while losing only 20% of its energy density (28 Wh kg−1 ). The charging and the discharging ability of the composite revealed a high specific capacitance (1217 F g−1 ) [27]. With the help of microwave irradiation and in situ chemical polymerization, a nanocomposite with 1 wt.% of RuO2 and organic PEDOT was successfully prepared. The composite when subjected to galvanostatic charge– discharge measurements maintained 76.2% after 1,000 continuous cycles. A specific capacitance of 153.3 F g−1 at a current density of 150 mA g−1 revealed the synergistic effect of the polymer PEDOT and RuO2 xH2 O[45].

7.2 Ternary Compositions Ti doping into Fe2 O3 oxide and successfully compositing it with PEDOT exhibited a significant capacitance enhancement and remarkable cyclic stability with an exceptionally high energy density (0.89 mWh cm−3 ). A high-performing asymmetric solidstate device was built with MnO2 as the anode and the Ti-Fe2 O3 /PEDOT composite as the cathode (Fig. 6) [18]. A PEDOT-PSS-RuO2 xH2 O electrode was employed by electrochemically loading Hydrous RuO2 particles loaded into PEDOT doped with polystyrene sulfonic acid (PSS). A high Cs (653 F g−1 ) was achieved with the nanocomposite electrode [16]. A similar work produced with RuO2 /PEDOT: PSS hybrid transparent thin film (93% transparency) demonstrated historically high areal capacitance (1.2 mF/cm2 ) and good stability over 10,000 charge/discharge cycles. The thin film consisting

144

R. Rajalakshmi and N. Ponpandian

Fig. 6 a Cyclic voltagramms of MnO2 electrode and Ti-Fe2 O3 @PEDOT composite electrode at a constant scan rate − 100 mV s−1 , b cyclic voltagramms of the MnO2 //Ti-Fe2 O3 @PEDOT supercapacitor working at different voltage windows, c cyclic voltagramms of the optimized device recorded at different scan rates, d GCD curves of the optimized device containing MnO2 //Ti-Fe2 O3 @PEDOT recorded at different current densities, e plot of the areal capacitance and capacitance retention from the GCD curves of the MnO2 //Ti-Fe2 O3 @PEDOT ASC device at different current densities and f cyclic voltagramms recorded for the MnO2 //Ti-Fe2 O3 @PEDOT asymmetric capacitor device under different bending angles fixed at 100 mV s−1 . Adapted with permission [18]. Copyright (2015) WILEY-VCH

of RuO2 /PEDOT: PSS served as a cathode and the PEDOT: PSS counterpart was the anode forming an asymmetric solid-state device. It displayed a maximum P of 147 μW/cm2 and an E of 0.053 μWh/cm2 with a superficially high capacitance in terms of its area (1.06 mF/cm2 ) [46]. A cost-effective solid-state supercapacitor comprising of three-dimensional nanoflowers of NiO/Ni(OH)2 with PEDOT delivered a high Cs (404.1 mF cm–2 ) at 4 mA cm–2 and a degradation of 17.8% of capacitance retention after 1000 cycles[47]. A highly sophisticated Ni–Mn–Co ternary oxide and PEDOT–PSS hybrid were hierarchically synthesized via a solvothermal–coprecipitation combined with an oxidative route[14]. The ratio of PSS incorporated into the ternary composite differed in the range of 0.5–2 and the composite consisting of 1.5% of PSS exhibited an outstanding specific capacitance (1234.5 F g−1 ) compared to 1% PSS composite (1032.7 F g−1 ). The cause could be ascribed to the doping component PSS imparting abundantly branched chains to the PEDOT structure thereby improving the rigidity and effectively reducing the volume changes of the metal oxides during cycling. The capacitance retention of the PEDOT–PSS/NMCO electrode declined to 83.7% after 1000 cycles when the current density was as high as 5 A g−1 . The electrode elevated to a power density output of 5500 W kg−1 delivering 21.4 W h kg−1 energy density. A ternary nanocomposite of SnO2 and two-dimensional graphene was merged with PEDOTviaa one-pot synthesis method. The GE/SnO2 /PEDOT as an electrode material was tested in two different electrolytes 1 M H2 SO4 and 1 M Na2 SO4 which

Polymer-Metal Oxides Nanocomposites for Supercapacitors

145

displayed Cs of 184 F g−1 and 180 F g−1 respectively. In the H2 SO4 electrolyte, the E reached 22 Wh Kg−1 at a P of 238.3 W kg−1 whereas the E dropped to 17.1 Wh kg−1 delivering a high P (5803.3 W kg−1 ). The composite presented outstanding stability with zero loss of capacitance after 5000 cycles in 1 M H2 SO4 at 1 A g−1 whereas, in the case of Na2 SO4 electrolyte, the retention percentage dropped to 70% in the same conditions. The enhanced electrochemical property of GE/SnO2 /PEDOT electrodes could be credited to the well-designed ternary nanostructure components and the synergistic effects occurring at the composite/electrolyte interface [6]. A core–shell nanoplatelet array (NPA) with CoAl-layered double hydroxide (LDH) and PEDOT was developed on a bendable foil substrate of Ni. The LDH@PEDOT core/shell NPA as a high-performance pseudocapacitor exhibited a Cs of 672 F/g by galvanostatic discharge measurements at 1 A/g.Furthermore, due to the abundant energy-storage capacity of the hybrid NPA electrode, an excellent rate competency with specific energy (9.4 Wh/kg) at 40 A/g. Additionally, excellent cycling stability was established with degradation of 7.5% of its original capacitance retained after 5000 cycles[48].

8 Other Conducting Polymers (CPs) for Supercapacitors A nanorod morphology of Co3 O4 with a poly(3,4-methylenedioxy pyrrole) PEDOP polymer was grown on a carbon cloth substrate which displayed a Cs (407 F g−1 at 1 A g−1 ) and a degradation of 22% loss after 5000 cycles. The E was 29.9 Wh kg−1 at a P of 0.15 kW kg−1 [49]. Another common conducting polymer is the polyindole (Pind). A nanocomposite of Co3 O4 and Pindpolymer was synthesized which demonstrated a Cs of 1805 F g−1 at 2 A g−1 [7]. The conducting polymer polythiophene (PTh) was penetrated by electropolymerization method into the TiO2 nanotubes (TNTs) revealing a Cs of 640 F g−1 [50]. TNTs were also conjugated with conducting 1D PTh nanofibers showing potential supercapacitor responses, exhibiting a high specific capacitance of 1052 F g−1 (Fig. 7)[8].

9 Conclusion The development of efficient electrode materials for supercapacitor application is very well the need of the hour, acknowledging the future energy demands. Conducting polymers are widely used in charge storage applications to enhance the conducting nature of electrode materials. Nanostructured metal oxides are also easily synthesized with high specific energies and cyclic stability, proven to greatly improve the ionic path enhancements necessary for supercapacitor application. The two counterparts have their respective pros and cons, hence a bridged relationship could be initiated to overcome the cons by forming nanocomposites. A brief outlook on the major conducting polymers along with their respective binary and ternary compositions

146

R. Rajalakshmi and N. Ponpandian

Fig. 7 a CV curves of bare TiO2 nanotubes and composites of TiO2 nanotubes with PTh at a constant can rate 5 mV s−1 , b CV curves of TiO2 nanotubes with PTh nanocomposite at different scan rates, GCD curve of PTh–TNTs at 2 A g−1 , d the change in Cs representing the loss percentage at different cycle numbers, e FESEM image of the top view of bare TiO2 nanotubes, f TEM image of the top view of bare TiO2 nanotubes, g FESEM image of the top view of PTh– TNTs (inset representing the magnified top view), h TEM image of the top view of PTh– TNTs (inset representing the magnified top view), i FESEM image of the top view of PTh–Ti foil and j TEM image of the top view of PTh–Ti foil. Adapted with permission [50]. Royal Society of Chemistry

with metal oxides are discussed with their electrochemical performances. In short, it is highly recommended to substantially improve factors such as longevity and energy densities which could be realized by a proper understanding of the mechanistic views for selecting appropriate materials to satisfy the existing hindrances for scaling supercapacitors to the next level.

References 1. Ahn JM, Inamdar AI, Jo Y, Kim J, Jung W, Im H, Kim H (2014) TiOX -polyanilne composite films for high-performance supercapacitors. J Korean Phys Soc 64(2):182–185 2. Ambade RB, Ambade SB, Shrestha NK, Nah Y-C, Han S-H, Lee W, Lee S-H (2013) Polythiophene infiltrated TiO2 nanotubes as high-performance supercapacitor electrodes. Chem Commun 49(23):2308–2310 3. Ambade RB, Ambade SB, Shrestha NK, Salunkhe RR, Lee W, Bagde SS, Lee S-H (2017) Controlled growth of polythiophene nanofibers in TiO2 nanotube arrays for supercapacitor applications. J Mater Chem A 5(1):172–180 4. Ansari SA, Parveen N, Han TH, Ansari MO, Cho MH (2016) Fibrous polyaniline@manganese oxide nanocomposites as supercapacitor electrode materials and cathode catalysts for improved power production in microbial fuel cells. Phys Chem Chem Phys 18(13):9053–9060 5. Badwal SPS, Giddey SS, Munnings C, Bhatt AI, Hollenkamp AF (2014) Emerging electrochemical energy conversion and storage technologies. Front Chem 2:2296–2646 6. Bahloul A, Nessark B, Briot E, Groult H, Mauger A, Zaghib K, Julien CM (2013) Polypyrrolecovered MnO2 as electrode material for supercapacitor. J Power Sources 240:267–272 7. Bai M-H, Liu T-Y, Luan F, Li Y, Liu X-X (2014) Electrodeposition of vanadium oxide–polyaniline composite nanowire electrodes for high energy density supercapacitors. J Mater Chem A 2(28):10882–10888

Polymer-Metal Oxides Nanocomposites for Supercapacitors

147

8. Balasubramaniam S, Mohanty A, Balasingam SK, Kim SJ, Ramadoss A (2020) Comprehensive Insight into the Mechanism Material Selection and Performance Evaluation of Supercapatteries. Nano-Micro Lett 12(1):85 9. Chen J, Xia Z, Li H, Li Q, Zhang Y (2015) Preparation of highly capacitive polyaniline/black TiO2 nanotubes as supercapacitor electrode by hydrogenation and electrochemical deposition. ElectrochimicaActa 166:174–182 10. Chen L, Yuan C, Gao B, Chen S, Zhang X (2009) Microwave-assisted synthesis of organic– inorganic poly(3,4-ethylenedioxythiophene)/RuO2 xH2 O nanocomposite for supercapacitor. J Solid State Electrochem 13(12):1925 11. De B, Banerjee S, Pal T, Verma KD, Tyagi A, Manna PK, Kar KK (2020) Transition metal oxide/carbon-/electronically conducting polymer-based ternary composites as electrode materials for supercapacitors. In: Kar KK (ed) Handbook of nanocomposite supercapacitor materials II: performance, pp 387–434 12. Fu, L., Qu, Q., Holze, R., Kondratiev, V. v, & Wu, Y. Composites of metal oxides and intrinsically conducting polymers as supercapacitor electrode materials: the best of both worlds? J Mater Chem A 7(25):14937–14970 13. Hai Z, Gao L, Zhang Q, Xu H, Cui D, Zhang Z, … Xue C (2016) Facile synthesis of core– shell structured PANI-Co3 O4 nanocomposites with superior electrochemical performance in supercapacitors. Appl Surf Sci 361:57–62 14. Han J, Dou Y, Zhao J, Wei M, Evans DG, Duan X (2013) Flexible CoAl LDH@PEDOT core/ shell nanoplatelet array for high-performance energy storage. Small 9(1):98–106 15. Huang L-M, Lin H-Z, Wen T-C, Gopalan A (2006) Highly dispersed hydrous ruthenium oxide in poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) for supercapacitor electrode. ElectrochimicaActa 52(3):1058–1063 16. Huang M, Li F, Dong F, Zhang YX, Zhang LL (2015) MnO2 -based nanostructures for highperformance supercapacitors. J Mater Chem A 3(43):21380–21423 17. Jaidev JRI, Mishra AK, Ramaprabhu S (2011) Polyaniline–MnO2 nanotube hybrid nanocomposite as supercapacitor electrode material in acidic electrolyte. J Mater Chem 21(44):17601– 17605 18. Jiang H, Ma J, Li C (2012) Polyaniline–MnO2 coaxial nanofiber with hierarchical structure for high-performance supercapacitors. J Mater Chem 22(33):16939–16942 19. Kalair A, Abas N, Saleem MS, Kalair AR, Khan N (2021) Role of energy storage systems in energy transition from fossil fuels to renewables. Energy Storage 3(1):e135 20. Kim J, Ju H, Inamdar AI, Jo Y, Han J, Kim H, Im H (2014) Synthesis and enhanced electrochemical supercapacitor properties of Ag–MnO2 –polyaniline nanocomposite electrodes. Energy 70:473–477 21. Namsheer K, Rout CS (2021) Conducting polymers: a comprehensive review on recent advances in synthesis, properties and applications. RSC Adv 11(10):5659–5697 22. Liu R, Duay J, Lane T, Bok Lee S (2010) Synthesis and characterization of RuO2 /poly(3,4ethylenedioxythiophene) composite nanotubes for supercapacitors. Phys Chem Chem Phys 12(17):4309–4316 23. Liu R, Duay J, Lee SB (2011) Electrochemical formation mechanism for the controlled synthesis of heterogeneous MnO2 /Poly(3,4-ethylenedioxythiophene) nanowires. ACS Nano 5(7):5608–5619 24. Liu T, Shao G, Ji M, Wang G (2015) Polyaniline/MnO2 composite with high performance as supercapacitor electrode via pulse electrodeposition. Polym Compos 36(1):113–120 25. Majumder M, Choudhary RB, Thakur AK, Kumar U (2017) Augmented gravimetric and volumetric capacitive performance of rare earth metal oxide (Eu2 O3 ) incorporated polypyrrole for supercapacitor applications. J Electroanal Chem 804:42–52 26. Majumder M, Choudhary RB, Thakur AK, Karbhal I (2017) Impact of rare-earth metal oxide (Eu2 O3 ) on the electrochemical properties of a polypyrrole/CuO polymeric composite for supercapacitor applications. RSC Adv 7(32):20037–20048 27. Mandal M, Ghosh D, Giri S, Shakir I, Das CK (2014) Polyaniline-wrapped 1D CoMoO4 ·0.75H2 O nanorods as electrode materials for supercapacitor energy storage applications. RSC Adv 4(58):30832–30839

148

R. Rajalakshmi and N. Ponpandian

28. Misnon II, Jose R (2017) Synthesis and electrochemical evaluation of the PANI/δ-MnO2 electrode for high performing asymmetric supercapacitors. New J Chem 41(14):6574–6584 29. Nallappan M, Gopalan M (2018) Fabrication of CeO2/PANI composites for high energy density supercapacitors. Mater Res Bull 106:357–364 30. Raj RP, Ragupathy P, Mohan S (2015) Remarkable capacitive behavior of a Co3 O4 –polyindole composite as electrode material for supercapacitor applications. J Mater Chem A 3(48):24338– 24348 31. Ramesh G, Palaniappan S, Basavaiah K (2018) One-step synthesis of PEDOT-PSS•TiO2 by peroxotitanium acid: a highly stable electrode for a supercapacitor. Ionics 24(5):1475–1485 32. Ramesh S, Yadav HM, Karuppasamy K, Vikraman D, Kim H-S, Kim J-H, Kim HS (2019) Fabrication of manganese oxide@nitrogen doped graphene oxide/polypyrrole (MnO2 @NGO/ PPy) hybrid composite electrodes for energy storage devices. J Market Res 8(5):4227–4238 33. Reddy BN, Deshagani S, Deepa M, Ghosal P (2018) Effective pseudocapacitive charge storage/ release by hybrids of poly(3,4-ethylenedioxypyrrole) with Fe3 O4 nanostructures or Co3 O4 nanorods. Chem Eng J 334:1328–1340 34. Reddy BN, Mukkabla R, Deepa M, Ghosal P (2015) Dual purpose poly(3,4ethylenedioxypyrrole)/vanadium pentoxide nanobelt hybrids in photoelectrochromic cells and supercapacitors. RSC Adv 5(40):31422–31433 35. Ren X, Fan H, Ma J, Wang C, Zhang M, Zhao N (2018) Hierarchical Co3 O4 /PANI hollow nanocages: synthesis and application for electrode materials of supercapacitors. Appl Surf Sci 441:194–203 36. Tang P, Zhao Y, Xu C (2013) Step-by-step assembled poly(3,4-ethylenedioxythiophene)/ manganese dioxide composite electrodes: tuning the structure for high electrochemical performance. ElectrochimicaActa 89:300–309 37. Thiagarajan K, Theerthagiri J, Senthil RA, Madhavan J (2017) Simple and low cost electrode material based on Ca2 V2 O7 /PANI nanoplatelets for supercapacitor applications. J Mater Sci: Mater Electron 28(22):17354–17362 38. Tong L, Liu J, Boyer SM, Sonnenberg LA, Fox MT, Ji D, … Jones WE (2017) Vapor-phase polymerized poly(3,4-ethylenedioxythiophene) (PEDOT)/TiO2 composite fibers as electrode materials for supercapacitors. ElectrochimicaActa 224:133–141 39. Wang C, Zhan Y, Wu L, Li Y, Liu J (2014) High-voltage and high-rate symmetric supercapacitor based on MnO2-polypyrrole hybrid nanofilm. Nanotechnology 25(30):305401 40. Wang W, Lei W, Yao T, Xia X, Huang W, Hao Q, Wang X (2013) One-pot synthesis of graphene/ SnO2 /PEDOT ternary electrode material for supercapacitors. ElectrochimicaActa 108:118–126 41. Wang X, Wang T, Liu D, Guo J, Liu P (2016) Synthesis and electrochemical performance of CeO2 /PPy nanocomposites: interfacial effect. Ind Eng Chem Res 55(4):866–874 42. Wang X, Yang C, Wang T, Liu P (2011) Praseodymium oxide/polypyrrole nanocomposites for electrochemical energy storage. ElectrochimicaActa 58:193–202 43. Wu X, Meng L, Wang Q, Zhang W, Wang Y (2017) A flexible asymmetric fiberedsupercapacitor based on unique Co3 O4 @PPy core-shell nanorod arrays electrode. Chem Eng J 327:193–201 44. Wu X, Wang Q, Zhang W, Wang Y, Chen W (2016) Nanorod structure of Polypyrrole-covered MoO3 for supercapacitors with excellent cycling stability. Mater Lett 182:121–124 45. Yang H, Xu H, Li M, Zhang L, Huang Y, Hu X (2016) Assembly of NiO/Ni(OH)2 /PEDOT nanocomposites on contra wires for fiber-shaped flexible asymmetric supercapacitors. ACS Appl Mater Interfaces 8(3):1774–1779 46. Yin C, Yang C, Jiang M, Deng C, Yang L, Li J, Qian D (2016) A novel and facile one-pot solvothermal synthesis of PEDOT–PSS/Ni–Mn–Co–O hybrid as an advanced supercapacitor electrode material. ACS Appl Mater Interfaces 8(4):2741–2752 47. Zeng Y, Han Y, Zhao Y, Zeng Y, Yu M, Liu Y, Lu X (2015) Advanced Ti-Doped Fe2 O3 @PEDOT core/shell anode for high-energy asymmetric supercapacitors. Adv Energy Mater 5(12):1402176 48. Zhang C (John), Higgins TM, Park S-H, O’Brien SE, Long D, Coleman JN, Nicolosi V (2016) Highly flexible and transparent solid-state supercapacitors based on RuO2 /PEDOT:PSS conductive ultrathin films. Nano Energy 28:495–505

Polymer-Metal Oxides Nanocomposites for Supercapacitors

149

49. Zhang X, Zeng X, Yang M, Qi Y (2014) Investigation of a branchlike MoO3/Polypyrrole hybrid with enhanced electrochemical performance used as an electrode in supercapacitors. ACS Appl Mater Interfaces 6(2):1125–1130 50. Zhou C, Zhang Y, Li Y, Liu J (2013) Construction of high-capacitance 3D CoO@Polypyrrole nanowire array electrode for aqueous asymmetric supercapacitor. Nano Lett 13(5):2078–2085

Polymer-Metal Sulfides Nanocomposites for Supercapacitors Shrestha Tyagi, Himani, Anuj Kumar, and Beer Pal Singh

Abstract In recent years, there is an urgent need for energy storage for the development of renewable, clean, and sustainable alternative energy sources and to overcome emerging ecological problems. Supercapacitors as novel devices are at the forefront of various energy storage devices owing to their potential applications in photovoltaics, aerospace, railways, hybrid electric vehicles, wind power generation, and wearable electronics. In this context, metal sulfides are considered promising electrode materials due to their exciting physical and chemical properties along with their high specific capacity, which is several times higher than that of carbon/ graphite-based materials. Metal sulfides are widely distributed in nature and are capable of undergoing redox transitions with a variety of metal ion valence states. Due to their superior redox reversibility and comparatively high specific capacitances, nanostructured metal sulfides like MoS2 , NiCo2 S4 , CuSx , NiSx , and CoSx have attracted a lot of attention. However, these sulfide electrodes have some limitations in practical applications due to their inferior rate performance and cycling stability. In order to achieve improved electrochemical performance, incorporating various polymer matrices including polythiophene, polyaniline, polypyrrole, and poly [3,4-ethylenedioxythiophene] with metal Sulfides are an advanced category of substance used for storing energy. This chapter deals with the recent development, challenges, and future perspectives of polymer-metal sulfide nanocomposites-based supercapacitors. These polymer-metal sulfide nanocomposites can be used as efficient electrode materials owing to their redox reactions, variable oxidation states, less cost, high electrical conductivity, and stability. Keywords Metal Sulfide · Polymers · Nanocomposites · Supercapacitor · Energy storage

S. Tyagi · Himani · A. Kumar (B) · B. P. Singh Department of Physics, Chaudhary Charan Singh University, Meerut 250004, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_9

151

152

S. Tyagi et al.

1 Introduction High-performance energy storage technologies must be invented in order to combat pollution, global warming, and the continual exhaustion of fossil fuels like coal, oil, and natural gas. To achieve a balance between ubiquitous energy demands and environmental concerns, investment in energy storage devices, specifically lithium-ion batteries (LIBs) and supercapacitors (SCs), is considered necessary to bring a green energy future. Discovering possible energy resources with excellent cyclic retention, better thermal stability, high energy, power density, and improved operational safety is especially important given the widespread applications of energy storage issues [1]. Supercapacitors emerged as promising candidates for cutting-edge devices for energy storage and are frequently utilized in portable electronics, automotive systems, and other applications. An electrolyte, an anode, a cathode, and a separator incorporated between both parallel-facing electrodes make up the majority of a traditional supercapacitor system. MSs (Metal Sulfides) such as Molybdenum disulfide (MoS2 ), Copper Sulfide (CuSx ), Nickel Sulfide (NiSx ), and Cobalt Sulfide (CoSx ) have gained prominence as the leading candidates for SCs over recent years. Their distinctive physical and chemical characteristics, such as enhanced electrical conductivity, better mechanical strength, and improved thermal stability compared to their corresponding metal oxides, as well as the complex redox chemistry which is usually several times greater than that of carbon-based materials that contribute significantly to their high specific capacity and capacitance, set them apart from other electrode materials. Their poor rate performance and cycling stability, however, make it difficult for these sulfide electrodes to be used in practical applications [2]. Consequently, significant research has been put into improving the performance and cycling stability of electrode materials for supercapacitors (SCs) in order to realize highly efficient energy storage of Metal Sulfides (MSs). The advancement of novel ideas such as doping, functionalization, composites, and hybridization with conductive matrices produce new nanostructures thus opening up the possibility for enhanced electrochemical performance of MSs [3]. To achieve improved electrochemical performance, incorporating various polymer matrices including polythiophene, polyaniline, polypyrrole, and poly [3,4ethylenedioxythiophene] with metal sulfides are an advanced category of substance used for storing energy. Due to the interactions between the surface of the polymer matrix and the nanofillers, the components of metal sulfide/polymer nanocomposite materials can combine the properties of the two components. Polymers improve the adsorption of metal sulfide onto the collector and the surface area between metal sulfide and electrolyte resulting in enhanced electrochemical performance. The interface between the polymer and MSs can cause new or improved phenomena in addition to various distinguishing characteristics [4]. This chapter presents the most recent advancements, difficulties, and potential applications of supercapacitors based on polymer-metal sulfide nanocomposites. These polymer-metal sulfide nanocomposites owing to their redox reactions, variable oxidation states, low cost, high electrical conductivity, and stability make them suitable for use as effective electrode materials.

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

153

2 Electrode Material for Supercapacitors The most important part of energy storage devices is the electrode material, which has a significant impact on the way the device as a whole performs electrochemically. Since the electrode materials used have a considerable effect on the efficiency of supercapacitors, researchers have developed and incorporated electrode architectures based on nanomaterials with a variety of chemical compositions and morphologies. There are three main types of supercapacitors. Electrical double-layer capacitors (carbon-based materials such as porous carbons, carbon nanotubes/nanofibers, ulphide, etc.), pseudo capacitors, and hybrid (transition metal chalcogenides that include oxides, ulphides, nitrides, Mxenes, nitrides, carbonitrides, conducting polymers, etc. [5]. A substantial specific capacitance and a large number of active sites have been characterized in polymer-based pseudo supercapacitors, although their kinetics are quite low. Also, The good electrical conductivity, numerous active sites, and affordable costs of the metal ulphides like MoS2 , SnS2 , CoS2 , and NiS have attracted a lot of attention as the potential electrode material for pseudo capacitors. Because these three kinds of supercapacitors operate in different ways, therefore different electrode materials are required. In the search for the best possible metal resource, relatively inexpensive, and feasible electrode materials concerning improved gravimetric and volumetric energy densities, several transition-based sulfide materials are reportedly being screened for supercapacitors. Metal sulfides (MS) are useful for a wide range of emerging applications because they are readily available in a variety of crystalline structures, morphology, shapes, compositions, and sizes. Some sulfides exhibit layered structures that are thought to be very beneficial for EES because they benefit from readily available large surface area and interlayer gaps for efficient ionic intercalation/decalation. CuSbS2 3D pyramidal architectures have recently been reported by Das et al. for overcoming power densities and energy densities of 3248.78 W kg−1 and 12.63 W h kg−1 even without carbon support, respectively. The impressive performance was thought to be due to the exposed 111 facet’s abundance of active redox sites and the 3D pyramids’ large surface area [6]. Zinc cobalt sulfides were recently reported with a bead curtain-like morphology in conducting nickel foam substrate, and they were able to achieve high capacitances 837 Cg−1 , which was due to morphological structure having high porosity and conductivity [7]. Therefore, in order to achieve significant electrochemical performance, tailored sulfide electrode materials with controllable crystalline composition are required. Polymer metal sulfide nanocomposites’ outstanding properties have drawn the attention of researchers. The polymer component offers mechanical and thermal durability, whereas the metallic component provides electrical conductivity. Due to the interfacial interaction between polymers and nanostructured materials, the physical and chemical properties of constituent materials are quite different from that of nanoparticles [8]. The method used to prepare polymer metal sulfide nanocomposites has a significant impact on the composite’s properties. In comparison to the polymer matrix, metal sulfide nanoparticles are extremely capable of improving the thermal stability of the resultant nanocomposite. It could be caused by a decline in the

154

S. Tyagi et al.

material’s volatilization. Additionally, there is hardly much thermal energy transmission due to the presence of metal sulfide fillers at the interstitial points throughout the polymeric chains. Because the polymeric substance adsorbs the metal sulfides like CdS, ZnS, etc., there is less segmental mobility, which prevents chain transmission. There are different strategies to fabricate polymer-metal sulfide composites such as the In-situ polymerization technique, intercalation method, sol–gel method, solution cast method, and more. The techniques used to synthesize polymer metal sulfide composites have a notable impact on both the physical and chemical properties of the composite.

3 Synthesis Strategies of Polymer-Metal Sulfide Nanocomposites Compatibility is a key factor in achieving a polymer blend or nanocomposite with the specified qualities. The techniques used to synthesize polymer metal sulfide composites have a notable impact on both the physical and chemical properties of the composite. In practice, systems with poor performance come from the chemical differences between polymers, or the polymer matrix and nanoparticles. The morphology and characteristics of the material are affected by the synthesizing techniques. Depending on the types of the polymeric matrix, the Nano filler, and the required parameters for the final product, the right procedure is chosen. In comparison to the polymer matrix, metal sulfide nanoparticles are extremely capable of improving the thermal stability of the resultant nanocomposite. It could be caused by a decline in the material’s volatilization. Additionally, there is hardly much thermal energy transmission. Due to the presence of metal sulfide fillers at the interstitial points throughout the polymeric chains. Because the polymeric substance adsorbs the MSs like CdS, ZnS, etc., there is less segmental mobility, which prevents chain transmission. There are different strategies to fabricate the polymer-metal sulfide composites briefly described here.

3.1 In Situ Polymerization Technique Latin’s phrase In-situ means “in position” in its direct translation. With the help of a chemical reaction, a very small and thermodynamically stable reinforcing phase is created within a matrix using this technology. The process of joining monomer molecules to create large polymer molecules is known as polymerization. The sonication method is used to scatter nanoparticles in a liquid monomer or relatively low-molecular-weight precursors as well as in their solution. The liquid monomer solution is then combined with an oxidizing agent to start the polymerization, and

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

155

the solution is filtered to extract the sample. Because the polymers are intercalated in the layers, this approach is frequently utilized to create layered structured nanofiller-incorporated polymer nanocomposites.

3.2 Sol–gel Method The sol–gel method has shown to be an affordable and easy technology. This process involves the dispersion of solid nanoparticles in liquid (a sol) and agglomerating together to form a continuous 3D network expanding throughout the liquid (a gel). To synthesize metal sulfide polymer composite sol–gel method is opted which is a bottom-up approach. In the sol–gel method, hydrolysis of metal alkoxides forms a sol (colloidal suspension) and undergoes evaporation of water called condensation, which results in the formation of the network between gel formed by polymerization. The whole gel creates a network of connections as time lengthens. The polymer network for the development of layered crystals becomes the nucleating agent which further promotes the layered crystal growth. This method has the potential of providing materials with various morphologies. High specific surface area (SSA) with improved electrochemical behavior are the main advantages of electrode material prepared by this method, which is also controllable in terms of temperature, surfactant, solvent, and reaction time changes. The schematic representation of the typical sol–gel method is shown in (Fig. 1). Fig. 1 Schematic representation of the sol–gel method

156

S. Tyagi et al.

3.3 Intercalation Method There are various strategies have been used to synthesize polymer composites. The polymer inclination method is amongst the most widely used methods. Intercalation is the process of introducing cations into the bulk lattice of such solid electrode materials. The polymer and organically altered lamellar clay fillers are disseminated in an organic polar solution as part of the procedure. Layers of lamellar clay are easily distributed in the solvent. For achieving the optimal degree of organophilic clay exfoliation in this method the selection of solvent is the critical factor. The dissolved polymer can be absorbed by the layers of expanding silicates. This procedure requires several hours. After solvent evaporation, the layers finally reassemble and create an intercalated structure.

3.4 Solution Cast Method Solution casting is a top-down technique for producing polymer nanocomposite matrices. It is predicated on the breakdown of the aggregated nanofillers and mixing with the molten polymer matrix above the glass transition temperature. Continuous heating, stirring, and reflux can be used to dissolve the target polymer in a particular solvent until a viscous, clear solution is achieved. Moreover, the filler can be uniformly mixed and ultrasonically agitated in a different kind of solvent to dissolve it. Following that, mixing both batches while stirring them at room temperature for an entire night will confirm that the fillers were distributed uniformly throughout the polymer solution. At normal temperatures, the solvents used in the casting on Petri dishes will evaporate, creating the ideal nanocomposite coating.

4 Polymer-Metal Sulfide Nanocomposites for Supercapacitors To form polymer-metal sulfide nanocomposites several nanoscale fillers (metal sulfides) with different shapes and sizes can be mixed with polymers to make them technologically viable, thermally stable, and with good mechanical properties. Nanostructured metal sulfides like molybdenum disulfide (MoS2 ), copper sulfide (CuSx ), nickel sulfide (NiSx ), and cobalt sulfide (CoSx ) have attracted interest recently and have been combined with conducting polymers as a new kind of energy storage material because of their outstanding redox reversibility and relatively high specific capacitances. Various polymer/metal sulfide nanocomposites utilized for supercapacitor application are briefly described here.

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

157

4.1 Polymer-Molybdenum Disulfide Nanocomposites Composites of polymer and molybdenum disulfide (MoS2 ) show outstanding electrochemical performance as they exhibit enhanced ionic conductivity and large specific capacitance than other metal oxides [9]. Hybridization of MoS2 with conductive polymers results in enhanced electrochemical performance. This collective behavior can be ascribed to the formation of superior heterointerfaces and enhanced morphology of the hybrid. Among various transition metal chalcogenides, MoS2 has a good capability, high specific capacitance, and long cycle life. For example, the constituent material molybdenum disulfide (MoS2 ) and polyaniline (PANI) have exhibited a relatively low specific capacitance of 98 Fg−1 and 298 Fg−1 respectively while the composite PANI/MoS2 exhibited a high specific capacitance of 575 Fg−1 at 1 Ag−1 with enhanced morphology [10]. Wang et al. in presence of ammonium persulfate synthesized intercalated composite poly (3,4-ethylene dioxythiophene)/ MoS2 show outstanding capacity retention of 90% and specific capacitance of 405 Fg−1 prepared via an In-situ polymerization technique [11]. Fu et al. synthesized polyaniline (sPANI)/ MoS2 nanocomposite via the hydrothermal method, the schematic representation is shown in (Fig. 2). To obtain enhanced morphology he used polyvinylpyrrolidone (PVP) as a surfactant. The high specific surface area is the result of PVP hindering the crystallization of MoS2 to produce nano spherical fluffy morphology and hence good specific capacitance [12]. Charge transfer is facilitated by the multilayer structure, and the composite’s stability is increased by tight contact between heterointerfaces. For instance, Zhao et al. reported a smooth surface, maximum porosity, and a high surface area of 25 m2 /g by synthesizing a metallic 1-T- MoS2 -PANI thin nanosheet contains alternatively arranged monolayers of 1 T- MoS2 and PANI [13]. Tang et al. synthesized single-layered MoS2 /PPy nanocomposites in the presence of ammonium persulfate ((NH4 ) 2 S2 O8 , APS) solution by an in situ oxidative polymerization of pyrrole monomers. The nanocomposites have an enhanced cycling stability of Fig. 2 Schematic representing the synthesis process of sPANI-MoS2 [12]. Adapted with permission [12], Copyright (2017), Elsevier

158

S. Tyagi et al.

85% after 4000 cycles, excellent rate capability, and a large specific capacitance of about 700 Fg− 1 at 10 mV s−1 [14]. Yang et al. fabricated PANI coated with carbonshell fabricated on 1 T MoS2 monolayers (MoS2 /PANI@C). This hybrid matrix showed excellent specific capacitance of 678 Fg−1 (1 mVs−1 ) and capacity retention of 80% on 10,000 consecutive cycles. These characteristics are equivalent to the greatest overall performance attained for SCs electrodes made of conducting polymers [15]. Ren et al. prepared a 3D tubular MoS2 /PANI nanostructure with PANI nanowire arrays vertically aligned on the external and internal surfaces of the 3D tubular MoS2 , and they reported an improved specific capacitance of 552 Fg−1 at 0.5 Ag−1 and an exceptional rate capability of 82% from 0.5 to 30 Ag−1 [16]. A straightforward microwave-assisted heating technique was used by Firmiano et al. to create the layered MoS2 /graphene hybrid nanosheets, resulting in electrodes for supercapacitors with a high specific capacitance of 265 Fg−1 [17].

4.2 Polymer-Copper Sulfide Nanocomposites Nanoporous CuS, a high-performance electrode material for supercapacitor applications, displays extremely high specific capacitance (814 F/g at 1 A/g) with good rate capability and cycle life. Accordingly, an enhanced specific capacitance of 305 Fg-1 @ current density of 2 Ag-1 , was achieved by Hsu et al. through the creation of hierarchical nanostructures made of CuS nanowire (Figure 3) arrays directly fabricated on copper foil. The electrode demonstrated improved capacitance retention efficiency of 87% on 5000 consecutive GCD [18]. Ramesan et al fabricated Ppy/CuS (polypyrrole/copper sulfide) nanocomposites by an In-situ chemical oxidative polymerization in presence of [(NH4 )2 S2 O8 ] (ammonium persulfate) in an aqueous medium. CuS/PPy composite exhibits improved surface morphology with good adhesion and better uniformity [19]. CuS nanoparticles with varying crystalline phases exist in various stoichiometric compositions. Copper sulfide nanoparticles can be very helpful in enhancing the PVA/PVP blend’s mechanical properties. The surface polarity of the mix composites that arise determines their mechanical characteristics. Ramesan et al synthesized the polymer blend matrix of PVA/PVP with varying concentrations of copper sulfide (CuS) via the solution cast technique. The addition of CuS nanoparticles gave the PVA/PVP blend a crystalline character due to the interaction of CuS nanoparticles with the polymer matrix. The thermal stability of all blends adds more attention to the pure blend because intermolecular interactions exist between the particles of the polymer blend [20]. Due to its unique qualities, including high transmittance, ease of processing, non-corrosiveness, and strong thermal stability across a wide temperature range, water-soluble poly (vinyl alcohol) (PVA) is one of the most promising polymers. This makes it an ideal matrix for energy storage applications. By in situ oxidation polymerizing pyrrole in the presence of the CuS solution, a CuS@PPy composite electrode is synthesized. The CuS@PPy composite, which contains 16.7 weight

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

159

Fig. 3 a FESEM images of Cu(OH)2 nanowires (NWs) SEM images of sulfonation-treated Cu(OH) 2 NWs at a reaction time of b 1 h, c 2 h, d 4 h at room temperature [18]. Adapted with permission [18], Copyright (2014), Elsevier

percent of CuS, has a considerable specific capacitance of 427 Fg-1 (at 1 Ag-1 ) and can maintain 88% of that capacitance even after 1000 cycles [21].

4.3 Polymer-Nickel Sulfide Nanocomposites Polymer-nickel sulfide nanocomposites are widely studied by researchers for their applications in supercapacitors. Peng and coworkers fabricated a conductive PPy/ NiS/bacterial cellulose membrane as an electrode via in-situ polymerization technique in the presence of iron (III) chloride hexahydrate with varying concentrations of Nickel (10mL, 50mL, 100mL) and designated as NiS/BC-10, NiS/BC-50, and NiS/BC-100 and reported power density of 39.5 WKg-1 , the energy density of 239 WhKg-1 and specific capacitance of 713 Fg-1 [22]. Wang et al. produced NiCo2 S4 /PPy nanotubes grown on CNFs (Carbon nanofibres) and exhibited enhanced specific capacitance of 9.781 F cm−2 at 5 mA cm−2 with remarkable stability and good capacity retention [23]. When designing composites, which may be utilized as substrates or wrapped in units to improve the specific

160

S. Tyagi et al.

surface area of nickel and cobalt sulfides, requires careful consideration of the size and structure of conducting polymers [24]. Reddy and others using a reliable solution cast technique developed (PVA)/NiS Polyvinyl alcohol hybrid composite films by dispersing NiS NPs (0–3 wt%) in the PVA matrix. However, in the temperature range (40 °C–140 °C) the dielectric behavior of these films was studied at a frequency range of 50 Hz–20 MHz. The remarkable increase in the dielectric characteristics of the nanocomposites is evidence that there is also a strong interaction between the polymer matrix and the nanofiller. PVA/NiS nanocomposite film with 3 wt% NiS NPs loading was found to have a dielectric constant value of 154.55 at 50 Hz and 140 °C. These findings imply that NiS NPs were uniformly distributed throughout the PVA matrix [25]. PANI/NiS films (0.5–2 wt%) were synthesized by dispersing various weight percentages of NiS nanoparticles in the monomer. The creation of nanocomposite films included a dip-coating method. By adopting an innovative and affordable chemical oxidation process, highly conducting polyaniline films with improved structural and conducting characteristics were successfully created. To test the effectiveness of this method, the microstructure and electrical characteristics of these films were examined. It was unexpected to observe the production of homogenous, well-adherent coatings with improved dc conducting characteristics [26].

4.4 Cobalt Sulfide-Polymer Nanocomposite Given their specific capacitance, good rate capability, as well as excellent cycling stability, and low-cost transition metal sulfides such as cobalt sulfide (CoS), have been regarded as one of the most viable pseudocapacitor materials [27]. Moreover, cobalt sulfide’s low electrical conductivity and mechanical unreliability restrict its use to some extent [28]. For this reason, several researchers have attempted to enhance the electrochemical characteristics of carbon materials by combining them with cobalt sulfide-based binary composites or their ternary composites with conducting polymers [29]. Cobalt sulfide exists in different phases such as Co3 S 4 , Co2 S3 and CoS2 , Co4 S3 , Co9 S8 , and CoS. For instance, Zhang et al. have reported excellent capacity retention and specific capacitance of 1040 Fg−1 at a current density of 0.5 Ag−1 by fabricating the unique CoS2 (cobalt sulfide) ellipsoids with anisotropic tube-like cavities using cobalt carbonate as precursor via thermal decomposition and sulfidation process [30]. Similarly, Liu and coworkers reported a specific capacitance of 764 Fg−1 at a current density of 2 Ag−1 and capacity retention of nearly 85% after 500 cycles by synthesizing cobalt disulfide (CoS1.097 ) via a one-step solvothermal method [27]. For electrochemical energy storage devices, conducting polymers such as PANI (polyaniline) are the most promising because of their low cost, high degree of flexibility, and multi-redox states [31]. In this context, a ternary composite PANIrGO–CoS was synthesized via an in-situ polymerization method by Heydari et al. and reported remarkable cycling stability after 1000 cycles showing capacity retention of 90.1%. Furthermore, the PANI-rGO-CoS composite demonstrates a specific capacitance of 431 Fg−1 at a current density of 0.5 Ag−1 . The ternary composite’s

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

161

interactions with its constituent parts may have synergistic enhancing effects that support the high-performance super capacitance [32]. An interesting natural nanofibrous substance with a three-dimensional, interconnected network structure with a high degree of polymerization and better crystallinity is bacterial cellulose (BC). BC has a special structure that results in a plethora of hydrogen bonding, which gives it a lot of specific surface area and enough porosity to support other functionalized materials as well as act as a substrate for other nanostructures [33]. For instance, Peng and coworkers successfully synthesized the hybrid nanofibrous composite PPy/CoS/BC with better compatibility and enhanced morphology for supercapacitor applications. With the introduction of cobalt sulfide, the capacity retention maintains at 62.4% after 300 cycles and the specific capacitance reaches upto 614 Fg−1 at current density 0.70 Ag−1 while the retention of Ppy/BC composite is only effective up to 21.7% after 300 cycles shown in (Fig. 4) [34]. Wang et al. fabricated the 2D hybrid nanosheets for the application of supercapacitors. In this research work, PEI (polyethyleneimine) mediated cobalt sulfide/graphene (G-P-CoS) hybrid was designed which showed the specific capacitance of 320 Fg−1 at a current density of 1 Ag−1 and excellent cycling stability after 20,000 cycles [35].

Fig. 4 a Galvanostatic charge–discharge curves of the supercapacitors using the PPy/Co S/BC and Ppy-BC electrodes at a current density of 0.8 mA cm−2 , b cycling stability at a current density of 0.8 mA cm−2 (coulombic efficiency in inset), c specific capacitance of Ppy/CoS/BC-50 and Ppy-BC electrodes at different current densities, d ragone plots of the supercapacitors using Ppy/CoS/BC-50 and Ppy-BC electrodes [34]. Adapted with permission [34], Copyright (2016), Elsevier

162

S. Tyagi et al.

4.5 Other Metal Ulphides Polymer Composites Several other metal sulfide polymer composites have been reported for highperformance supercapacitors. Fang et al. synthesized a hybrid composite of surface structured microspheres of copper sulfide/poly (N-isopropylacry-lamideco-methacrylic acid) (CuS/PNIPAM-MAA) via the polymeric mini gel template method. It is believed that the resulting size and morphology of the composites may be controlled by the network structure of mini gels, which may direct and regulate the precipitation of metal sulfides [36]. Pb methacrylate microgels were studied to create PbS nanocomposites, which were subsequently copolymerized into a polystyrene matrix [37]. Zhang and his coworkers reported a reversible capacity of 416 mAh g–1 after 700 cycles delivered by (PANI/OC/SeS2 ) composite using a one-step in situ technique. This polyacrylonitrile/organic carbon/selenium sulfide composite demonstrates excellent electrochemical properties by heating the mixture of (PANI) with SeS2 powder in a vacuum [38]. Reddy and coworkers opted for the green synthesis approach to synthesize PVA/ZnS nanocomposite films using orange fruit peel to prepare ZnS nanoparticles. Furthermore, the solution cast technique was used to incorporate nanoparticles into the PVA polymer matrix. The composite evidenced the better thermal stability and homogenous distribution of NPs into the PVA matrix demonstrating the enhanced energy storage applications [39]. Yasoda et al. reported the MnS/GO/PANI nanocomposite synthesized via in situ polymerization technique and studied for various electrochemical properties. When PANI is added to MnS/GO, the interfacial contact between the various pore sizes increases, resulting in improved specific capacitance of 822 F/g at 10 mV/s and 315 F/g at 200 mV/s [40].

5 Recent Trends and Challenges in Supercapacitors The past half-century has been focused to develop clean and renewable energy sources due to the rapid increase in environmental pollution and a significant decrease in fossil fuels which resulted due to high demand for uninterrupted energy [41]. The estimated world energy demand as of 2012 from fossil fuels was 13.731 billion tons of oil equivalent (BTOE) and it is expected to increase18.30 BTOE in 2035. The need for effective and efficient energy conversion/storage devices has motivated scientists to design compact and clean energy storage devices that will be beneficial for society, and electrochemical supercapacitors are one of them [42]. Supercapacitors can bridge the gap of, specific power, cell voltage, and operating cost between batteries and conventional dielectric capacitors [43]. The amount of total stored energy per unit volume is the energy density which is relatively higher in the case of batteries than that of supercapacitors followed by, high self-discharge, low operation voltages, and relatively high costs of production [44]. The electrochemical performance and quality of the electrode materials, as well as the electrical

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

163

conductivity, surface area, wetting behaviors of the electrodes, and permeability of the electrolyte used, are what determine the performance and high cost of the supercapacitor. Also, composite electrode materials have higher environmental stability and are less expensive, which helps them overcome the drawbacks of single-substance electrode materials in the application of real-world settings. The finer details of polymer electrolyte-based supercapacitors are being controlled by a number of groups, including improving the interaction of GPEs with the electrodes, improving the mechanical and electrochemical properties of the polymerbased electrolytes, and optimizing the properties of the liquid component in gel polymer electrolytes GPEs. [45]. Zichen Xu et al. reported the excellent super capacitance properties of polymer-metal sulfide composites, Zinc Sulfide-reduced Graphene Oxide-Polyaniline (ZnS/RGO/PANI) after 1000 cycles shows remarkable cyclic stability of 160% at 1 A g−1 and discharge Cs (Specific Capacitance) is 1045.3 F g−1 . The Pd (Power density) of the above polymer matrix when measured in two electrode symmetric system is 18.0 kW kg−1 , while the Ed (Energy density) is 349.7 Wh kg−1 . The polymer blend Zinc Sulfide-reduced Graphene Oxide-Polyaniline (ZnS/RGO/PANI) exhibits discharge-specific capacitance of 722.0 F g−1 and cycle stability of 76.1% at 1 A g−1 after 1000 cycles. Furthermore, for the two-electrode system, ZnS/RGO/PANI demonstrated the discharge voltage up to 1.6 V and the voltage range of the electrode composites in 6 M KOH electrolyte [46]. Similarly, The specific capacitance and cycle stability of MoS2 /PPy (695 F g−1 , 85% at 1 A g−1 after 4000 cycles) are significantly higher than those of PPy (200 F g−1 , 60% at 1 A g−1 after 4000 cycles), reported by Tang et al. for synthesizing solution-based methodology to tunable growth of PPy ultrathin films on 2D MoS2 monolayers [14]. In another study, Li et al. successfully synthesized MoS2 /RGO@PANI electrode composite through a two-stage synthetic method, and the specific capacitance and cycle stability after 3000 loops of MoS2 /RGO@PANI at 1 A g−1 were 1224 F g−1 and 82.5%, which were better than those of pure PANI as 774 F g−1 and 70.2% [47]. Xu et al. proposed a proton transport mechanism of PANI in dense nanocomposites, indicating that PANI was a dual electronic-ionic conductivity polymer that acted not only as a pseudocapacitive active material for high energy storage but also as a proton conductor that realized a proton transport from the interfaces of electrode/ electrolyte to the inner of dense particles [48]. To completely comprehend and utilize the capacitive properties of polymer-based nanocomposites, it is imperative to define the charging mechanism. In retrospect, we can confidently state that polymer-metal sulfide nanocomposites can be used to create high-performance supercapacitors, but additional investigation is required to satisfy the demands of next-generation supercapacitors.

164

S. Tyagi et al.

6 Conclusions In this chapter, we focus on the most recent studies on the application of polymermetal sulfide nanocomposites as an electrode for supercapacitors. In order to address future demands for the storage of clean and renewable energy for a variety of applications, including electronic gadgets, hybrid-electric vehicles, and large commercial machinery, supercapacitors have been acknowledged as the perfect storage devices. In supercapacitor applications, the development of polymer-metal sulfide nanocomposite electrode materials has drawn a lot of attention because it has been demonstrated to significantly improve the ion/electron transport through their enlarged SSA, thereby increasing the specific capacitance. The morphology, pore size, and surface area should all be taken into account because the design and ideal conditions for the fabrication of superior features are still very challenging to achieve. In conclusion, the study of polymer-based nanocomposites is an important area that links polymers to various types of materials. The utilization rate of polymers and other materials used as reinforcers in devices is improved by the pairing of outstanding properties of polymers and some other types of material.

References 1. Rajkumar M, Hsu C, Wu T, Chen M, Hu C (2015) Advanced materials for aqueous supercapacitors in the asymmetric design. Prog Nat Sci Mater Int 1–18 2. Online VA, Rui X, Yan Q (2014) Nanostructured metal sul fi des for energy storage 9889–9924 3. Rehman J, Eid K, Ali R, Fan X, Murtaza G, Faizan M, Laref A, Zheng W, Varma RS (2022) Engineering of transition metal sulfide nanostructures as efficient electrodes for high-performance supercapacitors. ACS Appl Energy Mater 5:6481–6498 4. Nie N, Hu M, Liu J, Wang J, Wang P, Wang H, Ji Z, Chen Z, Huang Y (2021) The application of polymer nanocomposites in energy storage devices. Polym Nanocomposite Mater 157–187 5. Chatterjee DP, Nandi AK (2021) A review on the recent advances in hybrid supercapacitors. J Mater Chem A 9:15880–15918 6. Das A, Mohapatra M, Basu S (2021) Expeditious synthesis of 3D pyramidal faceted CuSbS2 architectures manifesting unrivalled pseudo capacitive energy storage. Mater Lett 289:129412 7. Xu L, Xi Y, Sun X, Zhao P, Zhu F, Yin J, Chen L, Hu J, Li X (2021) Hierarchically novel beadcurtain-like zinc-cobalt sulfides arrays toward high energy density hybrid supercapacitors via morphology engineering. J Power Sources 489:229535 8. Idumah CI, Ezeani EO, Nwuzor IC (2020) A review: advancements in conductive polymers nanocomposites 60:756–783 9. Kumar KS, Choudhary N, Jung Y, Thomas J (2018) Recent advances in two-dimensional nanomaterials for supercapacitor electrode applications. ACS Energy Lett 3:482–495 10. Huang KJ, Wang L, Liu YJ, Wang HB, Liu YM, Wang LL (2013) Synthesis of polyaniline/2-dimensional graphene analog MoS2 composites for high-performance supercapacitor. Electrochim Acta 109:587–594 11. Wang J, Wu Z, Yin H, Li W, Jiang Y (2014) Poly(3,4-ethylenedioxythiophene)/MoS2 nanocomposites with enhanced electrochemical capacitance performance. RSC Adv 4:56926–56932 12. Fu G, Ma L, Gan M, Zhang X, Jin M, Lei Y, Yang P, Yan M (2017) Fabrication of 3D Spongiashaped polyaniline/MoS2 nanospheres composite assisted by polyvinylpyrrolidone (PVP) for high-performance supercapacitors. Synth Met 224:36–45

Polymer-Metal Sulfides Nanocomposites for Supercapacitors

165

13. Zhao C, Ang JM, Liu Z, Lu X (2017) Alternately stacked metallic 1T-MoS2/polyaniline heterostructure for high-performance supercapacitors. Chem Eng J 330:462–469 14. Tang H, Wang J, Yin H, Zhao H, Wang D, Tang Z (2015) Growth of polypyrrole ultrathin films on MoS2 monolayers as high-performance supercapacitor electrodes. Adv Mater 27:1117–1123 15. Yang C, Chen Z, Shakir I, Xu Y, Lu H (2016) Rational synthesis of carbon shell coated polyaniline/MoS 2 monolayer composites for high-performance supercapacitors 16. Ren L, Zhang G, Yan Z, Kang L, Xu H, Shi F, Lei Z, Liu ZH (2015) Three-dimensional tubular MoS2/PANI hybrid electrode for high rate performance supercapacitor. ACS Appl Mater Interfaces 7:28294–28302 17. Da Silveira Firmiano EG, Rabelo AC, Dalmaschio CJ, Pinheiro AN, Pereira EC, Schreiner WH, Leite ER (2014) Supercapacitor electrodes obtained by directly bonding 2D MoS2 on reduced graphene oxide. Adv Energy Mater 4:1301380 18. Hsu Y, Chen Y, Lin Y (2014) Electrochimica acta synthesis of copper sulfide nanowire arrays for high-performance supercapacitors. Electrochim Acta 139:401–407 19. Ramesan MT (2012) In Situ synthesis, characterization and conductivity of copper sulphide/ polypyrrole/polyvinyl alcohol blend nanocomposite 51:1223–1229 20. Ramesan MT, Jayakrishnan P, Anilkumar T, Mathew G (2018) Influence of copper sulphide nanoparticles on the structural, mechanical and dielectric properties of poly(vinyl alcohol)/ poly(vinyl pyrrolidone) blend nanocomposites. J Mater Sci Mater Electron 29:1992–2000 21. Peng H, Ma G, Sun K, Mu J, Wang H, Lei Z (2014) High-performance supercapacitor based on multi-structural CuS@polypyrrole composites prepared by in situ oxidative polymerization. J Mater Chem A 2:3303–3307 22. Peng S, Fan L, Wei C, Bao H, Zhang H, Xu W, Xu J (2016) Polypyrrole/nickel sulfide/bacterial cellulose nanofibrous composite membranes for flexible supercapacitor electrodes. Cellulose 23:2639–2651 23. Wang Q, Wu X, Huang J, Chen S, Zhang Y, Dong C, Chen G, Wang L, Guan H (2022) Enhanced microwave absorption of biomass carbon/nickel/polypyrrole (C/Ni/PPy) ternary composites through the synergistic effects. J Alloys Compd 890:161887 24. Yan M, Yao Y, Wen J, Long L, Kong M, Zhang G, Liao X, Yin G, Huang Z (2016) Construction of a hierarchical NiCo2S4@PPy core-shell heterostructure nanotube array on Ni foam for a high-performance asymmetric supercapacitor. ACS Appl Mater Interfaces 8:24525–24535 25. Reddy PL, Deshmukh K, Kováˇrík T, Reiger D, Nambiraj NA, Lakshmipathy R, Khadheer Pasha SK (2020) Enhanced dielectric properties of green synthesized nickel sulphide (NiS) nanoparticles integrated polyvinylalcohol nanocomposites. MRE 7:064007 26. Batool A, Kanwal F, Abbas A, Riaz S, Naseem S (2014) Novel method to synthesize highly conducting polyaniline/nickel sulfide nanocomposite films and the study of their structural, magnetic, and electrical properties. IEEE Trans Magn 50 27. Liu S, Mao C, Niu Y, Yi F, Hou J, Lu S, Jiang J, Xu M, Li C (2015) Facile synthesis of novel networked ultralong cobalt sulfide nanotubes and its application in supercapacitors. ACS Appl Mater Interfaces 7:25568–25573 28. Mao M, Mei L, Wu L, Li Q, Zhang M (2014) Facile synthesis of cobalt sulfide/carbon nanotube shell/core composites for high performance supercapacitors. RSC Adv 4:12050–12056 29. Ghosh D, Giri S, Das CK (2013) Preparation of CTAB-assisted hexagonal platelet Co(OH)2/ graphene hybrid composite as efficient supercapacitor electrode material. ACS Sustain Chem Eng 1:1135–1142 30. Zhang L, Bin Wu H, Lou XW (2012) Unusual CoS2 ellipsoids with anisotropic tube-like cavities and their application in supercapacitors. Chem Commun 48:6912–6914 31. Konwer S (2016) Graphene oxide-polyaniline nanocomposites for high performance supercapacitor and their optical, electrical and electrochemical properties. J Mater Sci Mater Electron 27:4139–4146 32. Heydari H, Gholivand MB (2016) Polyaniline/reduced graphene oxide–cobalt sulfide ternary composite for high-performance supercapacitors. J Mater Sci Mater Electron 28:3607–3615 33. Hu W, Chen S, Yang J, Li Z, Wang H (2014) Functionalized bacterial cellulose derivatives and nanocomposites. Carbohydr Polym 101:1043–1060

166

S. Tyagi et al.

34. Peng S, Xu Q, Fan L, Wei C, Bao H, Xu W, Xu J (2016) Flexible polypyrrole/cobalt sulfide/ bacterial cellulose composite membranes for supercapacitor application. Synth Met 222:285– 292 35. Wang M, Yang J, Liu S, Hu C, Li S, Qiu J (2019) Polyethyleneimine-mediated fabrication of two-dimensional cobalt sulfide/graphene hybrid nanosheets for high-performance supercapacitors. ACS Appl Mater Interfaces 11:26235–26242 36. Fang Y, Bai C, Zhang Y (2004) Preparation of metal sulfide–polymer composite microspheres with patterned surface structures. Chem Commun 4:804–805 37. Cui T, Cui F, Zhang J, Wang J, Huang J, Lü C, Chen Z, Yang B (2006) From monomeric nanofibers to PbS nanoparticles/polymer composite nanofibers through the combined use of γ-irradiation and gas/solid reaction. J Am Chem Soc 128:6298–6299 38. Zhang W, Wang H, Zhang N, Liu H, Chen Z, Zhang L, Guo S, Li D, Xu J (2019) One-step in situ preparation of polymeric selenium sulfide composite as a cathode material for enhanced sodium/potassium storage. ACS Appl Mater Interfaces 11:29807–29813 39. Reddy PL, Deshmukh K, Chidambaram K, Ali MMN, Sadasivuni KK, Kumar YR, Lakshmipathy R, Pasha SKK (2019) Dielectric properties of polyvinyl alcohol (PVA) nanocomposites filled with green synthesized zinc sulphide (ZnS) nanoparticles. J Mater Sci Mater Electron 30:4676–4687 40. Yasoda KY, Kumar S, Kumar MS, Ghosh K, Batabyal SK (2021) Fabrication of MnS/GO/PANI nanocomposites on a highly conducting graphite electrode for supercapacitor application. Mater Today Chem 19:100394 41. Yan J, Wang Q, Wei T, Fan Z (2014) Recent advances in design and fabrication of electrochemical supercapacitors with high energy densities. Adv Energy Mater 4 42. Tasnin W, Saikia LC (2018) Performance comparison of several energy storage devices in deregulated AGC of a multi-area system incorporating geothermal power plant. IET Renew Power Gener 12:761–772 43. Huang J, Sumpter BG, Meunier V (2008) A universal model for nanoporous carbon supercapacitors applicable to diverse pore regimes, carbon materials, and electrolytes. Chem A Eur J 14:6614–6626 44. Simon P, Gogotsi Y, Dunn B (2014) Where do batteries end and supercapacitors begin?, Science 343:1210–1211 45. Huang Z, Li L, Wang Y, Zhang C, Liu T (2018) Polyaniline/graphene nanocomposites towards high-performance supercapacitors: a review. Compos Commun 8 46. Xu Z, Zhang Z, Yin H, Hou S, Lin H, Zhou J, Zhuo S (2020) Investigation on the role of different conductive polymers in supercapacitors based on a zinc sulfide/reduced graphene oxide/conductive polymer ternary composite electrode. RSC Adv 10 47. Li X, Zhang C, Xin S, Yang Z, Li Y, Zhang D, Yao P (2016) Facile synthesis of MoS2/ reduced graphene oxide@polyaniline for high-performance supercapacitors. ACS Appl Mater Interfaces 8:21373–21380 48. Xu Y, Tao Y, Li H, Zhang C, Liu D, Qi C, Luo J, Kang F, Yang QH (2017) Dual electronicionic conductivity of pseudo-capacitive filler enables high volumetric capacitance from dense graphene micro-particles. Nano Energy 36:349–355

Polymeric Materials for Nanosupercapacitors ˙ Mert Akın Insel and Selcan Karaku¸s

Abstract The fabrication of polymeric materials-based nanosupercapacitors with unique properties such as an ultra-fast charge–discharge rate and high specific capacitance for high-performance energy sources has advanced rapidly in recent years. Experiments on the performance, charge storage mechanisms, and capacitance of polymeric nanostructure-based supercapacitors, in particular, are gaining traction in electrochemical energy storage nanotechnologies. This chapter gives points to all aspects of synthesis methods, surface characterizations, performances, and energy storage mechanisms of polymeric materials-based supercapacitors. Furthermore, there has been great attention to the preparation and performance of resins, biopolymers, carbon nanofiber networks, nano-hybrid materials, nanocellulosebased materials, polymer/metal oxide nanocomposites, and conductive polymer/ graphene/metal nanoparticles for supercapacitor applications. Finally, some new strategies for nanoplatforms, as well as a comprehensive understanding of the unique properties, current limitations, and future outlook of advanced nanostructure-based supercapacitors, were highlighted. Keywords Nanopolymers · Nanosupercapacitors · Synthesis · Supercapacitor applications · Supercapacitor performance

M. A. ˙Insel Department of Chemical Engineering, Faculty of Chemical-Metallurgical Engineering, Yıldız Technical University, Istanbul 34210, Turkey S. Karaku¸s (B) Department of Chemistry, Faculty of Engineering, Istanbul University-Cerrahpa¸sa, 34320 Istanbul, Turkey e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_10

167

168

M. A. ˙Insel and S. Karaku¸s

1 Introduction Fossil fuel use has increased over time, creating greenhouse effects that pose a major threat to the environment and to human life. To deal with the current problems of energy crises and pollution, it is essential to develop renewable and clean energy sources [1]. The development of technological systems for net-zero energy conversion and climate-neutral storage became critical. In recent years, there has been a symbolically growing interest in developing emerging technologies. Significant work has been put into upgrading more sustainable energy storage technologies, such as batteries and capacitors [2]. Supercapacitors (SCs) were created as a consequence of the limitations placed on the use of traditional capacitors and batteries in highhanded technologies because of their low energy density, low power density, etc. [3]. Researchers in both academia and industry have been drawn to energy conversion and storage devices with remarkable efficiency and stability [4]. As a result, they continued to face significant difficulties in the development and design of SCs. Supercapacitors or electrochemical capacitors (ECs) are a class of energy-storage devices that incorporate a variety of active materials, such as transition metal oxides, activated carbons, conductive polymers, and nitrides, as well as electrolytes and separators, into their construction [2, 5–8]. SCs are devices that can store electrochemical energy and discharge it at high current densities thanks to their large electrochemically active surface areas [9]. They are generally classified into two distinct groups: electric double-layer SCs (EDLCs) and faradaic SCs (FSCs) [9, 10]. EDLCs store and discharge energy by utilizing the adsorption and desorption of ions [11]. When the EDLC is charged, negative and positive ions are adsorbed on the anode and cathode side adsorbents, respectively. Ions are desorbed to the electrolyte during discharge, resulting in high power densities. FSCs, on the other hand, utilize fast and reversible half-cell redox reactions, and for that reason, they are also known as pseudo capacitors [11, 12]. The working principles of these supercapacitors are illustrated in Fig. 1. While FSCs can provide higher power densities than EDLCs due to the use of redox reactions, they are more prone to swelling or shrinking, are mechanically less stable, and thus have a noticeably shorter lifecycle [11, 13, 14]. There are also some hybrid-type supercapacitors (HSCs) that have been researched recently, which combine both methods with the aim of enhancing their advantages [15]. Asymmetric SCs (ASCs) have recently emerged as a result of significant advances in nano polymeric electrode science, and they hold promising potential for future supercapacitor applications. While SCs and nanoSCs (NSCs) can provide high power densities, reliably long life cycles, and security, they lack the ability to store sufficient energy per mass of the capacitor (1000) electrochemical cycles, which is crucial in determining if the constructed SC is stable over a sufficient period or not. These metrics are computed in most studies, which makes them useful when trying to evaluate the performance of novel SCs. Herein, the performance metrics from

178

M. A. ˙Insel and S. Karaku¸s

the most recently published articles that produced NSCs by using novel nanopolymers are collected. Table 1 shows the performance of these NSCs in terms of type, method, and performance metrics. For further information about the recent advances in nanopolymer electrodes for NSCs, we would like to encourage the readers to investigate the references given in Table 1.

6 Future Outlook of Nanostructure-Based Supercapacitors The increasing usage of fossil fuels and the huge greenhouse problem that has resulted from the booming global economy since the turn of the twenty-first century are now fundamental obstacles to the sustainable advancement of human civilization. To significantly increase the use of renewable energy sources, an advanced nanomaterials-based industry must be built with efficient energy storage as a fundamental component. Currently, green SCs are primarily employed in portable electronic devices, but they are also used in more specialized applications in the domains of defense, aerospace, and healthcare systems. Due to their low cost and generally developed technology, NCs are anticipated to be employed in a variety of applications and play a vital role in the development of a sustainable society in the future. The SC technology has advanced steadily and methodically over the past few years. At this point in their research, the SC technology is being thoroughly investigated as potential candidates for use as energy storage devices in practical, everyday scenarios. SCs have demonstrated a number of enormous benefits, such as high power density, long cycling life, and quick recharging, but other crucial aspects of these electronics still need to be improved for commercial scale application. Supercapacitors’ primary component, the electrode materials, controls how well they store energy. By using various approaches to control the characteristics of electrode materials, scientists have made every attempt to build advanced electrode materials that are highly effective, economical, and environmentally friendly. The design and engineering of these electrode materials remain a significant issue, nevertheless. Low compatibility between electrodes and electrolytes, low energy density, and high cost are some of the significant limitations that must be effectively solved in the near future. Future NCs will be developed in a variety of ways, but they will all strive for the same thing: high energy power, density, capacity, and longer cycle lifetimes. In this review article, the most recent developments in the study and creation of NSC electrodes have been outlined. Comprehensive surveys of the EDLC-type, hybrid electrodes, and pseudocapacitive capabilities and performances have been carried out in order to identify recent innovations in SC technology. The efficiency of SCs is very dependent on the active material, just like any other energy storage system. For increasing SCs’ performance, high electroactive surface areas are particularly required. Various carbon materials have all experienced incredible growth in this context. Improved electrochemical performance is also another benefit of the nanoelectrodes’ high redox activity. Considering this, binary, ternary, and quaternary

Polymeric Materials for Nanosupercapacitors

179

Table 1 Comparison of performance of polymer-based electrodes for NSCs Electrode

Supercapacitor type

Synthesis method

Performance metrics*

Year

Refs.

ZnO/SnO2 :rGO

FSC

Hydrothermal

ED = 17.34 Wh/kg PD = 2000 W/kg SCa = 3238 F/g ECR = 91.54%

2023

[12]

Co/Zn bimetallic organic framework on carbon fibers

HSC

N/A

ED = 124.6 Wh/kg PD = 49.2 W/kg SCa = 284.4 F/g ECR = 94%

2023

[15]

Polymer derived honeycomb-like carbon nanostructure

EDLC

Solvothermal

ED = 260.18 Wh/kg PD = 935.91 W/kg SCa = 3328 F/g ECR = 95%

2023

[18]

rGO/TiO2 /PANI

EDLC

In-situ Polymerization

ED = 7.79 Wh/kg PD = 8910 W/kg SCa = 692.87 F/g ECR = > 99%

2021

[21]

Ni/Co-based Nanoscale coordination polymers

ASC

Facile Self-assembly

ED = 43.7 Wh/kg PD = 594.9 W/kg SCa = 1160.2 F/g ECR = 66%

2022

[23]

Cobalt sulfide nanosheets on polypyrrole nanowires

ASC

Direct Utilization

ED = 51.1 2023 Wh/kg PD = 800 W/ kg SCa = 860 C/ g ECR = 92%

[26]

(continued)

M. A. ˙Insel and S. Karaku¸s

180 Table 1 (continued) Electrode

Supercapacitor type

Synthesis method

Performance metrics*

Year

Refs.

POAP/MoS2 /MnO2

FSC

Hydrothermal

ED = 37.64 2022 Wh/kg PD = 500 W/ kg SCa = 529 F/ g ECR = 94%

[30]

KCuCl3 /PANI

FSC

Solvothermal

ED = 438.12 Wh/kg PD = 1.6 W/ kg SCa = 2434 F/g ECR = 94%

2022

[32]

D-DABA-Ni/Co MOF

ASC

Solvothermal and Ultrasonication

ED = 85.56 2023 Wh/kg PD = 400 W/ kg SCa = 621 C/ g ECR = 88.92%

[33]

CCP-N @ Co/Ni LDH// CCP-N

ASC

Co-precipitation

ED = 48.1 Wh/kg PD = 576.8 W/kg SCa = 1319.4 F/g ECR = 82.2%

2023

[34]

BCN-PANI

FSC

Electrodeposition

ED = 25.3 2022 Wh/kg PD = 10 kW/ kg SCa = 672.0 F/g ECR = 89.6%

[38]

S-NaI-Gly

EDLC

Solvothermal

ED = 1.6 2022 Wh/kg PD = 300 W/ kg SCa = 8.80 F/g ECR = 93%

[48]

(continued)

Polymeric Materials for Nanosupercapacitors

181

Table 1 (continued) Electrode

Supercapacitor type

Synthesis method

Performance metrics*

Year

Refs.

NiCoFe2O anchored PVA/PVP

ASC

Solution Combustion & Microwave

ED = 3.67 Wh/kg PD = 246.49 W/kg SCa = 13.49 F/g ECR = 99.39%

2022

[49]

*ED Energy Density, PD Power Density, SCa Specific Capacity, ECR Electrical Capacitance Retention

metal/metal oxide-based nanoelectrodes have been produced by combining metal oxides with carbon nanomaterials. In the never-ending quest for higher NSC efficiency, several conducting polymer and MXene-based nanostructures have been integrated with graphene, borophene, or MXene in recent years. Furthermore, NSCs have been coupled with other power sources such as secondary batteries, solar cells, and fuel cells for the fabrication of modern integrated energy storage and conversion systems. All things considered, it can be concluded that technological breakthroughs in SC electrodes have been totally satisfying. However, there are a few obstacles that still need to be cleared before advanced NSCs will be capable of supporting the continually increasing energy demands. Environmental contamination is one of the century’s biggest issues. Green and low-cost synthesis methods and strategies for SC electrochemical devices are vital in this situation. Carbon nanomaterials produced from biomass have been designed to fulfill this requirement. The carbon-based electrodes, however, have poor porosity, and conductivity. Therefore, a significant problem for researchers is to optimize the manufacturing of these materials for SC electrodes at an industrial scale. From a cost perspective, a large cost is required to manufacture NSCs. Among electrode alternatives, two-dimensional, layered nanostructures are particularly expensive. A low total cost is crucial for effective nanodevice commercialization. Although the fabrication of separators and electrolytes is essential to SC technology, the majority of studies that have been published lately have focused on the development and modification of electrode materials. While solid-state devices have been shown to have low capacitances, aqueous devices often have low operating potential. The manufacture of high-performance SCs is gaining momentum thanks to appropriate design and electrolyte selection. Another tricky topic is managing the mass deposition of pseudocapacitive electrode materials. Overloading of active materials can, however, assist in reducing both electrolyte leaching and specific capacitance since this specific capacitance is negatively correlated to the electrode mass. Optimizing this parameter is crucial. Another significant problem is the poor cycle stability required to deliver polymer-based electrodes with volume changes

182

M. A. ˙Insel and S. Karaku¸s

during the charge/discharge cycle. Conductive polymers with various surface properties, including spherical, tubular, fiber, etc., have been investigated to limit volume expansion. These recently developed nanomaterials have high conductivity, porosity, and capacitance. It would be ideal to produce polymer nanomaterials with superior mechanical strength without surrendering their inherent capacitance. Self-discharge is yet another major issue for NSCs. Compared to other energy storage devices, the self-discharge efficiency of NSCs is high; hence, lowering it is essential for their commercial viability. The electrochemical performances of MXene-based electrode nanomaterials have recently been shown to be promising. However, it is currently difficult to synthesize MXene-based electrodes with their unique morphologies. Additionally, little research has been reported on how these nanoelectrodes will be used in practice. Similar to other energy storage systems, there is still a huge discrepancy between large-scale, commercially feasible fabrication processes and lab-developed fabrication processes for nanostructure-based electrodes. For NSCs to be effectively marketed, this issue must be solved. High-performance and economical energy storage technologies must be developed immediately to deal with the world’s urgent current problems. Although a strong basis has been laid, the promise of nanostructure-based SCs has not yet been fully realized. In summary, with recent developments in nanotechnology, SC technology is being investigated and developing quickly. Using nanomaterials of various sizes, SC electrodes have significantly improved in all areas when it comes to their outstanding electrochemical characteristics. We anticipate having a wide range of items readily available for the use of SC technology in a variety of applications very soon, thanks to the ongoing improvement of existing materials and the contribution of inventive research that results in new electrode compositions and nanostructures.

References 1. Wang L, Wu J, Fu S (2023) A mini review of recent progress in Mo-based electrode materials for supercapacitors. Inorg Chem Commun 148:110329 2. Dong W, Xie M, Zhao S, Qin Q, Huang F (2023) Materials design and preparation for high energy density and high power density electrochemical supercapacitors. Mater Sci Eng R Rep 152:100713 3. Bhat SA, Kumar V, Kumar S, Atabani AE, Anjum Badruddin I, Chae K-J (2023) Supercapacitors production from waste: a new window for sustainable energy and waste management. Fuel 337:127125 4. Ashish Kumar A, Dakeshwar Kumar V, Berdimurodov E (2023) Recent trends in noble-metals based composite materials for supercapacitors: a comprehensive and development review. J Indian Chem Soc 100(1):100817 5. Cao L, Wang C, Huang Y (2023) Structure optimization of graphene aerogel-based composites and applications in batteries and supercapacitors. Chem Eng J 454:140094 6. Mohan M, Shetti NP, Aminabhavi TM (2023) Recent developments in MoS2-based flexible supercapacitors. Mater Today Chem 27:101333 7. Melkiyur I, Rathinam Y, Kumar PS, Sankaiya A, Pitchaiya S, Ganesan R et al (2023) A comprehensive review on novel quaternary metal oxide and sulphide electrode materials for

Polymeric Materials for Nanosupercapacitors

8.

9. 10.

11. 12.

13.

14.

15.

16.

17. 18. 19. 20.

21.

22.

23.

24. 25. 26. 27.

183

supercapacitor: origin, fundamentals, present perspectives and future aspects. Renew Sustain Energy Rev 173:113106 Mandal S, Hu J, Shi SQ (2023) A comprehensive review of hybrid supercapacitor from transition metal and industrial crop based activated carbon for energy storage applications. Mater Today Commun 34:105207 Sarno M (2019) Nanotechnology in energy storage: the supercapacitors. Stud Surf Sci Catal 179:431–458 Borras N, Estrany F, Alemán C (2017) Nanophase-segregation in the dielectric layer enhances the charge storage capacity of polymeric electrochemical supercapacitors. Org Electron 51:322–331 González A, Goikolea E, Barrena JA, Mysyk R (2016) Review on supercapacitors: technologies and materials. Renew Sustain Energy Rev 58:1189–1206 Shanmugapriya V, Arunpandiyan S, Hariharan G, Bharathi S, Selvakumar B, Arivarasan A (2023) Enhanced supercapacitor performance of ZnO/SnO2:rGO nanocomposites under redox additive electrolyte. J Alloy Compd 935:167994 Shafiei N, Nasrollahzadeh M, Hegde G (2021) Chapter 10—Biopolymer-based (nano)materials for supercapacitor applications. In: Nasrollahzadeh M (ed) Biopolymer-based metal nanoparticle chemistry for sustainable applications, Elsevier, pp 609–671 Zhu ZZ, Wang GC, Sun MQ, Li XW, Li CZ (2011) Fabrication and electrochemical characterization of polyaniline nanorods modified with sulfonated carbon nanotubes for supercapacitor applications. Electrochim Acta 56(3):1366–1372 Chen X, Li Y, Li L, Zhu Q, Liang B, Zhao J et al (2023) Co/Zn bimetallic organic framework nanoparticles on carbon fibers as cathode for a high-performance rechargeable aqueous Zn-ion hybrid supercapacitor. Scripta Materialia 225 Dai Z, Xue L, Zhang Z, Gao Y, Wang J, Gao Q et al (2020) Construction of single-phase nickel disulfide microflowers as high-performance electrodes for hybrid supercapacitors. Energy Fuels 34(8):10178–10187 Huang S, Zhu X, Sarkar S, Zhao Y (2019) Challenges and opportunities for supercapacitors. APL Materials. 7(10) Das SK, Pradhan L, Jena BK, Basu S (2023) Polymer derived honeycomb-like carbon nanostructures for high capacitive supercapacitor application. Carbon 201:49–59 Majumdar D (2021) Review on current progress of MnO2-based ternary nanocomposites for supercapacitor applications. ChemElectroChem 8(2):291–336 Martínez-Cartagena ME, Bernal-Martínez J, Banda-Villanueva A, Enríquez-Medrano J, Lechuga-Islas VD, Magaña I et al (2022) Biomimetic synthesis of PANI/graphitic oxidized carbon nitride for supercapacitor applications. Polymers 14(18) Yoruk O, Bayrak Y, Ates M (2022) Design and assembly of supercapacitor based on reduced graphene oxide/TiO2/polyaniline ternary nanocomposite and its application in electrical circuit. Polym Bull 79(5):2969–2993 Chetibi L, Bounab MO, Benmkideche A, Hamana D, Achour S (2022) Realization and characterization of flexible supercapacitors based on doped graphene electrodes. J Solid State Electrochem 26(11):2457–2467 Ma Q, Cui F, Zhang J, Yan Y, Cui T (2022) Facile access to Ni/Co-based nanoscale coordination polymers for the boosted electrochemical performance of asymmetric supercapacitors. ACS Appl Energy Mater 5(10):12165–12173 Hong SH, Shi HH, Naguib HE (2022) Polypyrrole nanofoam/carbon nanotube multilayered electrode for flexible electrochemical capacitors. ACS Appl Energy Mater 5(4):4059–4069 He Y, Ning X, Wan L (2022) Ultrathin graphene oxide@polypyrrole nanosheets as a supercapacitor electrode with high areal specific capacitance. Polym Bull 79(10):9075–9091 Liu A, Tang L, Gong L, Tang J (2022) Cobalt sulfide nanosheets decorated on polypyrrole nanowires for improved charge storage in supercapacitors. Ceramics Int Abdollahifar M, Huang SS, Lin YH, Lin YC, Shih BY, Sheu HS et al (2018) High-performance carbon-coated ZnMn2O4 nanocrystallite supercapacitors with tailored microstructures enabled by a novel solution combustion method. J Power Sources 378:90–97

184

M. A. ˙Insel and S. Karaku¸s

28. Shireesha K, Chidurala SC (2022) Impact of hybridization on specific capacitance in hybrid NiO/V2O5@graphene composites as advanced supercapacitor electrode materials. Appl Surf Sci Adv 12 29. Kumar P, Mathpal MC, Inwati GK, Swart HC, Roos WD (2022) Graphene oxide based semiconducting nanomaterial’s composites for environmental applications. Nanoscale Compound Semiconduct Optoelectron Appl 407–431 30. Heydari H, Abdouss M, Mazinani S, Shayeh JS, Bazargan AM (2022) Facile electrosynthesis and characterization of Poly Ortho Amino Phenol/MoS2/MnO2 nanocomposite as a new supercapacitor. J Energy Storage 48:103905 31. Park C, Samuel E, Kim BY, An S, Lee HS, Yoon SS (2023) Supersonically sprayed self-aligned rGO nanosheets and ZnO/ZnMn2O4 nanowires for high-energy and high-power-density supercapacitors. J Mater Sci Technol 137:193–204 32. Riaz M, Munawar T, Mukhtar F, Nadeem MS, Manzoor S, Ashiq MN et al (2022) Facile synthesis of polyaniline-supported halide perovskite nanocomposite (KCuCl3/PANI) as potential electrode material for supercapacitor. J Mater Sci: Mater Electron 33(32):24462–24476 33. Song S, Ma X, Li W, Zhang B, Sun J, Deng C (2023) The influence of solvent controlled morphology on capacitive properties of metal-organic frameworks based on polyaminocarboxybenzene ligands. Colloids Surf A 656:130350 34. Yan C, Jia S, Wei J, Guan J, Shao Z (2023) Efficient dual conductive network based on layered double hydroxide nanospheres and nanosheets anchored in N-carbon nanofibers for asymmetric supercapacitors. J Alloys Compounds 930 35. Yaqoob T, Rani M, Neffati R, Janjua NK, Khan S, Arshad M et al (2023) Novel GO/ LiCr2O4 nanocomposite synthesis, characterizations and electrode testing for electrochemical applications. Mater Sci Eng B: Solid-State Mater Adv Technol 287 36. Cruz IF, Freire C, Araújo JP, Pereira C, Pereira AM (2018) Chapter 3—Multifunctional ferrite nanoparticles: from current trends toward the future. In: El-Gendy AA, Barandiarán JM, Hadimani RL (eds) Magnetic nanostructured materials, Elsevier, pp 59–116 37. Karaku¸s S, Albayrak ˙I, Üllen NB, Insel MA, Kilislio˘glu A (2022) Preparation, characterization and evaluation of a novel CMC/Chitosan-α-Fe2O3 nanoparticles-coated 17–4 PH stainlesssteel foam. Polym Bull 79(6):4133–4151 38. Shi D, Yang M, Zhang B, Hu H, Ai Z, Shao Y et al (2022) Design of boron carbonitridespolyaniline (BCN-PANI) assembled supercapacitor with high voltage window. J Colloid Interface Sci 626:544–553 39. Güney H, ˙Iskendero˘glu D, Güldüren ME, Dem˙ir KÇ, Karadeniz SM (2022) An investigation on CuO thin films grown by ultrasonic spray pyrolysis at different substrate temperatures: structural, optical and supercapacitor electrode characterizations. Opt Mater 132 40. Onwudiwe DC (n.d.) Microwave-assisted synthesis of PbS nanostructures 41. Mayakkannan M, Siva V, Murugan A, Shameem A, Thangarasu S, Bahadur SA (2023) Microwave-assisted synthesis of ternary transition metal ferrite: structural, morphological, optical, magnetic and electrochemical properties. Physica E: Low-Dimensional Syst Nanostruct 147 42. Kumar R, Youssry SM, Joanni E, Sahoo S, Kawamura G, Matsuda A (2022) Microwaveassisted synthesis of iron oxide homogeneously dispersed on reduced graphene oxide for highperformance supercapacitor electrodes. J Energy Storage 56 43. Song F, Ao X, Chen Q (2022) 2D−3D hybrid hierarchical porous carbon with intrinsic and external defects for high energy density supercapacitors. J Alloys Compounds 928 44. Xu Z, Kong L, Wang H, Ma Q, Shen X, Wang J et al (2022) Soft-template assisted preparation of hierarchically porous graphitic carbon nitride layers for high-performance supercapacitors. J Appl Polym Sci 139(39) 45. Zhang XF, Zuo XH, Zhu WJ, Che PL, Shi DW, Chen SS (2022) Morphology and electrochemical properties of NiCo2O4 powders prepared by a facile hydrothermal method. Ceram Int 48(14):20984–20995 46. Kambale SV, Lokhande BJ (2023) Morphologically modified CuO nanorod structure @ stainless steel as high performing supercapacitor electrode prepared by spray pyrolysis. Mater Chem Phys 295

Polymeric Materials for Nanosupercapacitors

185

47. Srinivasan SKV, Santo J, Penumakala PK (2022) Effect of surface modification of printed electrodes on the performance of supercapacitors. J Energy Storage 56:106043 48. Hamsan MH, Abdul Halim N, Demon SZN, Sa’aya NSN, Kadir MFZ, Abidin ZHZ et al (2022) SCOBY-based bacterial cellulose as free standing electrodes for safer, greener and cleaner energy storage technology. Heliyon 8(10) 49. Siva V, Murugan A, Shameem A, Thangarasu S, Bahadur SA (2022) A facile microwaveassisted combustion synthesis of NiCoFe2O4 anchored polymer nanocomposites as an efficient electrode material for asymmetric supercapacitor application. J Energy Storage 48 50. Shao Y, El-Kady MF, Sun J, Li Y, Zhang Q, Zhu M et al (2018) Design and mechanisms of asymmetric supercapacitors. Chem Rev 118(18):9233–9280

Polymer-MOFs Nanocomposite for Supercapacitor Abhijeet S. Shelake, Onkar C. Pore, Rajendra V. Shejwal, Dhanaji G. Kanase, and Gaurav M. Lohar

Abstract Among energy storage devices, supercapacitors have attracted increasing attention in recent years. In order to achieve improvement in performance and electrochemical properties; different nanostructured electrode materials have been studied. MOFs are attracting considerable attention as electrode materials in supercapacitor applications due to their high porosity, high surface area, variable distribution of pores, easy synthesis, and great structural flexibility. Besides these excellent properties, MOF showed inherently poor electronic conductivity. The hard metal ions and redox inactive ligands exist in MOF creating a high energy barrier for charge transport resulting in low performance in supercapacitor applications. In order to enhance of supercapacitor performance of MOFs, it is better to blend highly efficient pseudocapacitive materials. Conducting polymers (CPs) are highly efficient pseudocapacitive materials and extensively studied for the supercapacitor application. Conductive polymers are considered good candidates for materials in the field of energy storage because of their superior electronic conductivity, water absorptivity, flexibility, relatively cheapness, ease of synthesis, and so on. Recently, many researchers are working on Polymer-MOFs nanocomposites for the application of energy storage devices. In this chapter, we aim to explore the Polymer-MOFs nanocomposites and their use in the application of supercapacitors. In the beginning, polymer-MOF nanocomposites with their synthesis processes and their supercapacitor performance are mentioned. Lastly, the discussion on the benefit, challenges, and prospects of polymer-MOF nanocomposites in the field of supercapacitors are mentioned. Keywords Supercapacitor · Metal-Organic frameworks · Conducting polymers

A. S. Shelake · O. C. Pore · R. V. Shejwal · G. M. Lohar (B) Department of Physics, Lal Bahadur Shastri College of Arts, Science and Commerce, Satara, Maharashtra 415002, India e-mail: [email protected] A. S. Shelake · D. G. Kanase Department of Chemistry, Dr. Patangarao Kadam Mahavidyalaya College, Sangli, Maharashtra 416416, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_11

187

188

A. S. Shelake et al.

1 Introduction As a human beings, energy is one of the most important aspects of our lives today. Energy plays a vital role in human development; the global energy need is increasing day by day. There are two main sources of energy, renewable energy, and nonconventional energy. The non-conventional energy sources are slowly depleting, so we have shifted to renewable energy, but storage is the key need right now. Supercapacitors (SCs) is also called electrochemical capacitors, used as energy storage devices on the basis of storage mechanisms they are classified into two categories. Electrochemical double-layer capacitor (EDLC) can store energy by ion adsorption or non-radically and pseudo-capacitors stores energy by fast surface redox reaction or faradically [1]. Another type is hybrid SCs which consist of two different types of material or different charge storage mechanism electrodes and the separator used to isolate these electrodes electrically and also an electrolyte. To enhance the energy density of hybrid SCs, it consists a redox/faradaic type reaction electrode or a battery type electrode with an EDLCs type electrode (generally carbon-based material). It has been observed that metal oxides like RuO2 , MnO2 , NiO, Co3 O4 , Fe2 O3 , TiO2 , SnO2 , V2 O5 have excellent redox activity and high theoretical specific capacity and are used as electrode materials for SCs application [2]. Transition mixed metal oxide and their composite are also good candidates in the field of energy storage [3]. CPs are also used as SCs material for the last few decades. Polyaniline (PANI), Polypyrrole (PPy), and Polythiophenes (PTh) play important roles in the field of CPs [4]. Polymers consist of identical physicochemical properties of flexibility, transparency, good toughness and blending, doping/dedoping which improved self-healing, and electrochemical activities. As a result, it can be used in a variety of applications such as energy conversion devices like fuel cells, photocatalysis, Photovoltaics and solar cells, energy storage devices, SCs, and lithium-ion battery electrode [5–7]. MOFs are a class of crystalline material with high porosity and colossal inner surface area. The MOFs are known for their unique properties, including high surface area, adjustable interior surface properties, and the ability to modify the pore size [8]. MOFs are a novel class of porous material that consists of organic linkers with metallic nodes, their pore structures can be easily modified by replacing the bridging organic ligands. As an energy storage material, MOFs are attractive because of their properties such as high porosity and surface area, charge conduction, stability, synthetic tunability, and so forth. These materials have certain limitations such as relatively low stability in the air environment, lack of sufficient conductivity, low cyclic performance, mechanical and chemical stability, and low sp. capacitance hence we need to modify/introduce another material and prepare a composite that overcomes the problem in the field of SCs [9–11]. High electrical conductivity is an important requirement for SCs because it helps in the charge transfer kinetics and it also helps to operate at high power. CPs have been characteristics to become a promising material in SCs because of their properties such as good conductivity, flexibility, cheapness, and ease of synthesis. Nevertheless, CPs suffer from chemical instability when using a strong acid or base as an electrolyte

Polymer-MOFs Nanocomposite for Supercapacitor

189

polymer undergoes rapid degradation which may destroy the mechanical robustness or softness of polymers. The main challenge in CPs is long-term cycling stability, during the charge/discharge process polymer is oxidized or reduced and also ions of electrolyte intercalate on the surface or inside to maintain charge neutrality and reduce the stability of the material [12]. This problem is overcome by blending or by preparing a composite of CPs and MOFs. In the field of SCs, the flexibility of electrodes was thoroughly studied, thus if we used polymer nanocomposite electrodes achieving flexibility without loss of sp. capacitance. The composite of MOFs/CPs will be the future of SCs because it enhances the stability of the material and increases their electrochemical performance. Combining MOFs with CPs is a strategy to improve the sp. capacitance of electrode material, cyclic stability, energy, and power density throughout the performance of electrode material. Composite of MOFs-Polymer are also helpful to fabricate the flexible SCs which can further be used in electronic devices such as smartwatches and wearable devices [11, 13]. So, the present chapter is focused on the synthesis of the metal–organic framework, conducting polymers, and their composites. The chapter is focused on the development of MOF-polymer-based nanostructures and their supercapacitor performance. The polymers like polyaniline, polypyrrole, and polythiophene composite with different MOF and based supercapacitors with well-developed nanostructures have been briefly explained.

2 Metal–Organic Framework MOFs are a new class of material it is building blocks of diverse inorganic metals/ metal-oxo clusters and organic linkers. MOFs are synthesized by combining the metals with different organic linkers they are combined and form a building block-like structure which is illustrated in Fig. 1a. A MOF has the advantage of tunability, pore size, and surface area, and we can change the structure of MOFs by changing organic linkers, and it can also be easily modified after synthesis. The other advantages of MOFs themselves have a unique structure it consists of a metal ion that easily undergoes the redox reaction and is directly used as electrode material [11]. Ni-based layered two-dimensional Ni-MOFs were first used by Yang et al. [16] for SCs application which showed high sp. capacitance and good cyclic stability. The morphological study of Ni-MOF exhibited a loosely sheet-like structure, the material showed a layered structure and build a one-dimensional (1D) chain of Ni-MOF. These layers are connected by hydrogen bonding between Ni-Coordinated molecules. Ni-MOFs were synthesized by hydrothermal route, a capacitance of 1127 F/g was showed and 90% retention after 3000 cycles was achieved. Yan et al. [17] synthesized Ni-MOF via hydrothermal route, and the prepared Ni-MOF was labeled as P0-P3 on the basis of different ultrasonic times 0 m, 20 min, 40 min, and 1 h respectively. The surface area was studied using Brunauer-Emmett Teller (BET) accordion-like (P3) had a surface area of 117.42 m2 /g Ni-MOF (P0) had 99.53 m2 /g which revealed that

190

A. S. Shelake et al.

Fig. 1 a Schematic illustration of synthesis of MOF. b Diagrammatic illustration of synthesis of MOF. c Schematic illustration of synthesis of MOF. d SEM image of Ni-MOF-1:6 and e SEM image of Ni-MOF 1:1. a Adapted with permission [11], Copyright (2022), Elsevier. b Adapted with permission [14], Copyright (2019), Elsevier and c–e Adapted with permission [15], Copyright (2018), Elsevier

accordion-like Ni-MOF has a higher surface area than bulk Ni-MOF (P0) it indicates the accordion-like Ni-MOF provide a large surface area and enhances the electrochemical performance. The Ni-MOF (P3) electrode exhibited an sp. capacitance of 823 F/g at 7.0 A/g. The cyclic stability of the electrode was good electrode retained 96.5% of its previous capacitance after the completion of 5000 cycles. The flexible solid-state fabricated device (accordion-like Ni-MOF//AC) showed a sp. capacitance 230 mF/cm2 at 1.0 mA/cm2 with 92.8% of capacity retention after completion of 5000 cycles. Device exhibited a maximum energy density of 4.18 mWh cm−3 and maximum a power density of 231.2 mW cm−3 . Spherical mesocrystals of FA-Ni (FA-Folic acid) was prepared by Zhao et al. [14] via hydrothermal route schematic

Polymer-MOFs Nanocomposite for Supercapacitor

191

representation of synthesis is illustrated in Fig. 1b. FA formed a co-ordinate bond with Ni (II) ions and formed sphere like structure, and sphere contains hollow nanotubes present on the sphere helps in fast transport of electron and electrolyte ion. The fabricated electrode delivered a sp. capacitance of 912 F g−1 at current density of 0.5 A g−1 and showed good cyclic stability of about 89% capacitance retention after 2000 cycles at 10 A g−1 . The fabricated asymmetric SCs (ASCs) device delivered sp. capacitance of 78.2 F g−1 at current density of 1 A g−1 and as a result of 8000 cycles, the ASCs retained 97.6% of their initial capacitance. Du et al. [15] prepared Ni-MOF by one-step hydrothermal which showed method which showed hierarchical porous morphology schematic presentation of hydrothermal synthesis illustrated Fig. 1c. They prepared a different sample where trimesic acid: Ni2+ ratio was kept as 1:6, 1:4, 1:2 and 1:1 orderly, and then sample labeled as Ni-MOF 1–6, Ni-MOF 1-4, Ni-MOF 1-2 and Ni-MOF 1-1. Morphological study explored when mole ratio of trimesic acid and Ni2+ 1:6 all the Ni-MOF synthesized showed o hierarchical porous structure Fig. 1d, but when mole ratio was kept as 1:4 the spherical was formed of Ni-MOF and when molar ratio was kept 1:1 the spherical structure Fig. 1e was formed and showed a smooth surface. The specific surface area of synthesized Ni-MOF 1-6, Ni-MOF 1-4, Ni-MOF 1-2 and Ni-MOF 1-1 are 40.36, 28.2, 23.36 and 5.24 m2 g−1 respectively. The sample of NiMOF 1-6 showed hierarchical porous structure of Ni-MOF and exhibited a highest specific area such large surface area can provide a more active sites and enhance the electrochemical performance of material. According to the electrochemical analysis, hierarchical porous Ni-MOF (Ni-MOF 1-6) demonstrated the highest sp. capacitance and the largest average area of CV. Prepared electrode of Ni-MOF (Ni-MOF 1-6) exhibited sp. capacitance of 1057 F g−1 at current density of 1 A g−1 with good rate capability of 63.4% (649 F g−1 ) up to 30 A g−1 . Ni-MOF electrode retained 70% capacitance of its original value after 2500 charge discharge cycles at 10 A g−1 . The fabricated ASCs with AC which exhibit sp. capacitance of 87 F g−1 at a current density of 0.5 A g−1 and showed energy density of 21.05 Wh kg−1 at power density of 0.44 kW kg−1 and high-power density of 6.03 kW kg−1 at energy density of 5.36 Wh kg−1 . Gao et al. [18] synthesized Ni-MOF via single step hydrothermal route with some modification using a solution of DMF (N, N-dimethylformamide) and water instead of pure DMF. The synthesized Ni- MOF are indicated as Ni-MOF-I (2:1 DMF-water) and Ni-MOF-II (Pure DMF). According to SEM analysis, Ni-MOFI exhibited a loosely stacked layer-cuboid structure combined with a mesoporous structure which is beneficial for charge transfer and ion transport. As a result, NiMOF-I showed a better sp. capacitance than Ni-MOF-II which are respectively 804 F g−1 at 432 at current density of 1 A g−1 . The prepared ASCs device showed a high energy density of 31.5 Wh kg−1 at a power density of 800 Wh kg−1 . Wang et al. [19] prepared Co-MOF by hydrothermal method out of theses Co-MOF 6 h (the sample synthesized for time 6 h) delivered good sp. capacitance of about 450.86 F g−1 at a current density of 0.5 A g−1 and showed high supercapacitive performance than another sample. Prepared electrode showed about 95% capacitive retention over 1000 cycles. Cobalt-based pillar layered like MOF synthesized by Xiao et al. [20]

192

A. S. Shelake et al.

by hydrothermal method and SEM study revealed pillar-layered like 3D structure. Prepared Co-MOF compound electrode showed 75.5 F g−1 at current densities of 0.5 A g−1 and delivered 94% sp. capacitance retention of its initial value after 3000 cycles. Zhu et al. [21] prepared hierarchical Co-MOF by facile solvothermal method. Prepared Co-MOF electrode showed a high areal sp. capacitance of 13.6 at current densities of 2 mA cm−2 with superior rate capability. The morphological study showed hierarchical nanosheet on the nickel foam (NF) substrate. The fabricated ASCs device delivered high energy density of 1.7 mW h cm−2 at a power density of 4.0 mW cm−2 and 69.7% of capacitance retention over 2000 cycles at a constant current density of 50 mA cm−2 . 3D hierarchically structured Co-MOF supported on NF (Co-MOF/NF) are showed superior capacitive performance than a powder CoMOF. Wang et al. [22] synthesized Ultrathin NiCo-MOF Nanosheet by ultrasonic method. Surface area of material was studies using BET the Ni-MOF, Co-MOF and NiC0-MOF showed surface area of 44.8, 34.9 and 54.6 m2 g−1 respectively. The prepared Ni-Co-MOF electrode showed sp. capacitance of 1202.1 F g−1 at current density of 1 A g−1 and exhibited 89.5% capacitance retention of its initial capacitance after 5000 cycles. The fabricated ASCs device of NiCo-MOF delivered a sp. capacitance of 158.1 F g−1 at 10 A g−1 and the device delivered a high energy density of 49.4 Wh kg−1 with a power density of 562.5 W kg−1 in voltage window of 1.5 V. Zhang et al. [23] synthesized Co-MOF labelled as (CBC) and nanowires microsphere shaped Co-BTC labelled (CBNWM) synthesized via hydrothermal method. SEM study revealed morphology of CBC was like prismatic crystal and CBNWM as like microsphere shape. It revealed that nanowire microsphere was provide more active sites and enhance the electrochemical performance of material. The electrochemical study showed a sp. capacitance of CBC 608 F g−1 while CBNWM showed a sp. capacitance of 1020 F g−1 at 5 mV s−1 which was higher than CBC. The prepared CBNWM electrode showed a sp. capacitance of 1020 F g−1 at scan rate of 5 mV s−1 with 81.4% of capacity retention after 3000 cycles. The fabricated ASCs device showed an energy density of 34.4 Wh kg−1 with the power density of 375.3 W kg−1 .

3 Conducting Polymer Polymer is a repeating unit of monomer which makes larger molecule, the repetition of monomer is linear or branched or interconnected. Conducting Polymer increases the conductivity of composite because of it consist a π-conjugated bond which increases the electron cloud. PANI [24], PPy [25], PTh [25] are some commonly used conducting polymer in the energy storage filed.

Polymer-MOFs Nanocomposite for Supercapacitor

193

3.1 Polyaniline (PANI) PANI is a conducting polymer which are widely used in energy storage (ES) application due to its variable oxidation state and its doping characteristics which leads toward high specific pseudocapacitance. Stable nanostructured PANI electrode was synthesized Dhwale et al. [24] by chemical bath deposition (CBD) method. In CBD method the rate of precipitation is very helpful in development of thin films. These method offers an easy and controlled direct growth of nanostructures on the conducting substrate surface. The electrode of PANI showed a sp. capacitance of 503 F g−1 at 10 mV s−1 . The electrode showed good stability upto 10,000 cycles after several CV cycles there is small decrease of its initial sp. capacitance it indicates that an electrode was stable in nature. Kim et al. [26] prepared flexible electrode from Nafion/PANI nanofiber. Using the PAN/Au/PVDF materials, 235 F g−1 of sp. capacitance was achieved, and 245 F g−1 of discharge capacitance was achieved at 100 mV s−1 . The use of Nafion coating enhanced the stability of these PAN/Au/PVDF materials and a sp. capacitance of 180 F g−1 was observed after 10,000 cycles at 100 mV s−1 . Li et al. [27] synthesized PANI/Sodium alginate by template-induced method, formed mat like network, the prepared electrode exhibited a sp. capacitance of 2093 F g−1 . Khdary et al. [28] synthesized mesoporous PANI (M-PANI) on glassy carbon (GC) electrode by electrochemical polymerization. M-PANI showed excellent cyclic stability the electrode showed 83% of initial capacitance after 1000 cycles. The prepared electrode showed a high sp. capacitance of 532 F g−1 .

3.2 Polypyrrole (PPy) PPy is an important candidate in a branch of conducting polymer due to its high conductivity, flexibility and good mechanical properties. PPy is used as an energy storage material by number of researchers. There are various ways to synthesis of PPy out of which Interfacial polymerization [25], electrochemical pulse polymerization [29] etc. are widely used. Yang et al. [25] prepared via oil/water interfacial polymerization which exhibited a maximum sp. capacitance of 261 F g−1 at 25 mV s−1 and showed 75% of capacitance retention after 1000 cycles. Sharma and co-workers [29] synthesized PPy through electrochemical pulse polymerization the prepared electrode showed sp. capacitance of 400 F g−1 with 20% of sp. capacitance decay after 5000 cycles [29]. Wang et al. [30] prepared by pulse current polymerization method the electrode delivered a high specific power of 110.9 kW kg−1 and specific energy of 18.4 Wh kg−1 . Dubal et al. [31] synthesized porous PPy cluster by electropolymerization method the electrode delivered a sp. capacitance of 586 F g−1 at scan rate of 2 mV s−1 and showed 91% of charge/discharge efficiency.

194

A. S. Shelake et al.

3.3 Polythiophene (PTh) and Its Derivatives Researcher has taken interest in PTh and its derivatives in recent few years because of its conductivity. Darcy et al. [32] prepared through chemical vapor deposition, with a scan rate of 5 mV s−1 , prepared electrodes showed 175 F g−1 specific capacitance and galvanostatic discharges had 160 F g−1 specific capacitance at 1 A g−1 current density. At a current density of 1 A g−1 , electrodes retained 94% of their capacitance after 1000 charge/discharge cycles. of 175 F g−1 at a scan rate of 5 mV s−1 and galvanostatic charge discharge showed a sp. capacitance of 160 F g−1 at a current density of 1 A g−1 electrode showed 94% capacitance retention after 1000 charge/ discharge cycles at current density of 1 A g−1 . Patil et al. [33] prepared PTh thin film by successive ionic layer adsorption and reaction (SILAR) method. The electrode showed a highest sp. capacitance of 252 F g−1 at the scan rate of 5 mV s−1 and it exhibited a specific energy 4.86 Wh kg−1 and specific power 363.36 W kg−1 . The prepared electrode showed an 85% cyclic stability after 1000 cycles. Senthikumar et al. [34] synthesized PTh by catalyzed oxidative polymerization a prepared PTh electrode showed a highest sp. capacitance of 117 F g−1 at scan rate 5 mV s−1 .

4 MOF-Polymer Composite MOFs has become a promising candidate in a field of energy storage and used as an electrode material for SCs due to their functionalities and high porosity. Electrode prepared from pristine MOFs material has certain limitation such as chemically instability, cyclic stability, electrical conductivity etc. To overcome these problems, the best approach is to enhance the conductivity of MOF by blending or by preparing of composite with highly conductive phases. Recently researchers are working on MOF-CPs composite which helps to improves a chemical stability and conductivity of pristine MOFs [35, 36]. CPs are offering some advantages like easy for fabrication, environment friendly and as a result we fabricated as free-standing electrode for SCs device. Free-standing electrode have advantages like easy to handle, therefore it offers to upscale potential in industry. In many cases it is observed that when we incorporate the CPs in MOFs or preparing a composite of MOFs/CPs it enhances the electrochemical performance of electrode. In case of CPs after few charge/discharge cycles they undergo an internal change as like shrinking or swelling such problems are overcome with to prepare a MOFs@CPs hybrid material. MOFs@CPs allows a tremendous advantage in SCs field because it enhance the cycling stability, free standing/self-support, charge transport, environment friendly, mechanical robustness etc. Moreover, π-π conjugations between organic ligand of MOFs and CPs helpful to enhance the performance. There are several ways to synthesis MOFs@CPs which include mainly in-situ chemical polymerization, in-situ electrochemical polymerization, in-situ method, physical mixing. MOFs is further modified at post synthesis time. However, the application of MOFs in SCs device have some barrier by their

Polymer-MOFs Nanocomposite for Supercapacitor

195

low conductivity and poor stability. Herein, solution is that to prepare a composite of MOFs with conducting polymer which enhance the stability and tackle this issue [11].

4.1 MOF-PANI Based SCs PANI is usually used CPs in SCs application and it is also used in the hybrid material or in composite material with MOFs. Published composite and hybrids of MOFs and CPs are summarized in Table 1. MOFs/CP composite is synthesized by various method, in-situ chemical oxidation is widely used method to synthesize into/onto MOF/PANI nanostructure [35], simple room temperature synthesis [37], hydrothermal method [38], chemical oxidation polymerization method [36] etc. Liu et al. [13] synthesized ZIF-67@PANI network by low temperature agitation and solvent evaporation method. The purpose of study was to enhance the electrochemical supercapacitor performance of ZIF-67 suffered from poor electrical conductivity, by interweaving the conducting polymer PANI. The fabrication process of bare ZIF67 and ZIF-67@PANI network is as shown in Fig. 2a, b respectively. The energy storage mechanism of ZIF-67@PANI network in alkaline electrolyte is depicted in Fig. 2c. The ZIF-67@PANI network contains both EDLC and reversible redox reactions during the charge storage. The EDLC capacitance is attributed the pore structure of ZIF-67@PANI network while the cobalt ions and PANI are responsible for reversible redox reactions. The optimized ZIF-67@PANI network exhibited maximum sp. capacity of 1123.6 C g−1 at 1 A g−1 and showed capacity retention of 92.2% over 9000 cycles. For practical application they prepared ZIF-67@PANI network based ASCs supercapacitor device. The two devices connected in series could lit the commercial red LED. Guo et al. [35] synthesized carbonized Zn-MOF/PANI by simple in situ chemical oxidative polymerization method. The synthesis method of carbonized Zn-MOF/ PANI is illustrated in the Fig. 3a. The CV curves of optimized Zn-MOF/PANI composite at different scan rate are shown in Fig. 3b. The GCD curve of optimized ZnMOF/PANI composite at different current densities is provided in Fig. 3c. The better supercapacitor performance of Zn-MOF/PANI composite is attributed to the better morphology. It provides high electrical conductivity and reduced diffusion resistance of electrolyte. The prepared carbonized Zn-MOF/PANI electrode exhibited a sp. capacitance of 477 F g−1 at a current density of 1 A g−1 . Shao et al. [39] synthesized PANI/UiO composite, Zr-MOF (UiO-66) was prepared by hydrothermal method and PANI were prepared by polymerization method. The composite PANI/UiO-66 was synthesized via situ-polymerization. The SEM image of PANI/UiO-66 composite is given in Fig. 4a. It showed PANI and UiO-66 channels are combined together. When polymer (PANI) was incorporated into MOF pores (UiO-66), its transport properties changed. This is due to noncovalent interaction between PANI moieties and UiO-66 moieties or charge transfer interactions. This resulted in an increase in conjugate delocalization length of PANI

Hydrothermal

Hydrothermal

Hydrothermal

Ni-Trimesic Acid

Ni-H2 BDC

Ni-Folic acid

Co-MOF

Co-ZIF

Co-MOF

NiCo-MOF

3

4

5

6

7

8

9

1

Zn-MOF/PANI

MOF-Polymer

Hydrothermal

Ni-PTA

2

In-Situ Chemical oxidative polymerization

Hydrothermal

Hydrothermal

Hydrothermal

Hydrothermal

Hydrothermal

Ni-BDC

1

Synthesis method

Electrode material

Sr. No.

Sp. capacitance (F g−1 )

1020 F g−1 (5 mV s−1 )

13.6 cm−2 (2 mA cm−2 )

450.89 F g−1 (0.5 A g−1 )

912 F g−1 (0.5 A g−1 )

804 Fg−1 (1 A g−1 )

1057.2 F−1 (1 A g−1 )

823 F g−1 (7.0 A g−1 )

Sandwich structure

477 F g−1 (1 A g−1 )

Wrinkled nanosheets 1202.1 F g−1 (1 A g−1 )

Microsphere

Hexagon-like microblocks

Hydrothermal method

Spherical mesocrystals

Layer cuboid structure

Nanosheets like structure

Nanosheets likes

Loosely packed sheet 1127 F g−1 (0.5 A g−1 ) like structure

Morphology

Table 1 Summary of electrochemical supercapacitor properties of MOF and MOFs/CPs composite material Stability

Electrolyte

3 M KOH

6 M KOH

1 M KOH

Good cyclic stability

89.5% after 5000 cycles

81.4% after 3000 cycles

66.7% after 2000 cycles

1 M H2 SO4

2 M KOH

1 M NaOH

2 M KOH

95% after 1000 6 M KOH cycles

97.6% after 8000 cycles at 10 A g−1

Retention of 2 M KOH 302 F g−1 after 5000 cycles

70% after 2500 3 M KOH

96.5% after 5000 cycles at 1.4 A −1

93–91% after 3000 cycles

References

(continued)

[35]

[23]

[49]

[21]

[19]

[14]

[18]

[15]

[17]

[16]

196 A. S. Shelake et al.

Ni-MOF/PANI

PANI/MIL-101

Co-MOF/PANI

ZIF-67@PANI

5

6

7

8

1

MOF-PPy

Room Temperature Synthesis

PANI/Cu-MOF

4

MOF-PPy

Situ polymerization

PANI/UiO-66

3

In-Situ network

In-Situ

In-situ chemical oxidative polymerization method

In-situ Polymerization

In-situ Polymerization

Chemical oxidation polymerization

Co-MOF/PANI

2

Synthesis method

Electrode material

Sr. No.

Table 1 (continued)

Hybrid structure

Octahedral

Nanocage like structure

Hierarchical structure

Nanosheet

Uniform semi-spherical

Nanofiber

Matrix

Morphology

554.4 F g−1 (0.5 A g−1 )

1123.65 C g−1 (A g−1 )

504 F g−1 (1 A g−1 )

1197 F g−1 (1 A g−1 )

3626.4 mF cm−2 (2 mA cm−2 )

734 F g−1 (5 mV s−1 )

1015 F g−1 (1 A g−1 )

162.5 C g−1 (0.4 A g−1 )

Sp. capacitance (F g−1 ) Stability

1 M H2 SO4

2 M KOH

6 M KOH

1 M H2 SO4

1 M KOH

Electrolyte

Good cyclic stability upto 10,000 cycles

92.3% at 5 A g−1 after 9000 cycles

1 M Na2 SO4

1 M KOH

90% after 5000 1 M KOH GCD cycles at 2 Ag−1

90% after 10,000 cycles

81.6% after 10,000 cycles

93.6% capacitance remains after 4000 cycles

91% of after 5000

Specific capacity of 416% after 3000 cycles

(continued)

[40]

[13]

[43]

[41]

[38]

[37]

[39]

[36]

References

Polymer-MOFs Nanocomposite for Supercapacitor 197

Hydrothermal

Chemical oxidation method

PPy-d-MOF

Ni-MOF-PPy

3

4

Morphology

Sp. capacitance (F g−1 )

Micro block form sheet like structure

Octahedrons

1815.4 F g−1 (1 A g−1 )

354 F g−1 (25 mV s−1 )

Modified chemical Flower Like structure 715.6 F g−1 (0.3 A g−1 ) oxidation

Ni-MOF PPy

2

Synthesis method

Electrode material

Sr. No.

Table 1 (continued) Stability

–

70% capacitance retention after 2500 cycles

80% capacitance retention

2 M KOH + 0.1 M K4 Fe(CN)6

1.0 M KCl

3 M KOH

Electrolyte

[46]

[45]

[44]

References

198 A. S. Shelake et al.

Polymer-MOFs Nanocomposite for Supercapacitor

199

Fig. 2 a Schematic illustration of fabrication ZIF-67. b Schematic illustration of fabrication ZIF67@PANI. c Charge storage mechanism of ZIF-67@PANI. a–c Adapted with permission [13], Copyright (2021), Elsevier

as well as an improved carrier transfer capability. When we added MOF (UiO-66) it increases the range of the π electron and the electron cloud which helps in π-π interaction between the UiO-66 and PANI. The addition of PPy tubes in the MOF increases electron transfer between MOF particle as well as it maintains the high effective porosity of MOF and also provide flexibility to MOFs [40]. The prepared electrode showed sp. capacitance up to 1015 F g−1 at 1 A g−1 and sp. capacitance remains 91% after 5000 cycles. Neisi et al. [37] synthesized PANI/Cu-MOF nanocomposite by two step process included polymerization of aniline and then prepared aniline was treated with prepared Cu-MOF. The CV curves of prepared PANI/Cu-MOF rectangular shaped indicated material was ideal (EDLC). The electrochemical study showed that PANI/ Cu-MOF composite electrode showed a sp. capacitance of 734 F g−1 which was higher than sp. capacitance of bare Cu-MOF (558 F g−1 ). PANI/Cu-MOF and Cu-MOF showed capacitance retention about respectively 98% and 93.6% after

200

A. S. Shelake et al.

Fig. 3 a Illustration of synthesis process of carbonized Zn-MOF/PANI composite. b CV curves of carbonized Zn-MOF/PANI composite at different scan rates. c GCD curves of carbonized Zn-MOF/ PANI composite at different current densities. a–c Adapted with permission [35], Copyright (2016), Elsevier

4000 cycles. Using Electrochemical Impedance Spectroscopy (EIS), it was demonstrated that a composite electrode composed of PANI and Cu-MOF exhibits a better capacitance behavior than the pure Cu-MOF electrode. Iqbal et al. [36] synthesized Co-MOF by hydrothermal method, PANI was synthesized by chemical oxidation polymerization method and finally MOF/PANI composite was prepared. The Morphology analysis of MOF/PANI matrix was done by SEM study. Figure 4b shows the SEM micrograph of MOF/PANI matrix. The formed MOF/PANI matrix provides more active site for charge storage. The electrochemical measurement was carried in 1 M KOH as an electrolyte using three electrode system. Fig. 4c shows the comparative GCD curves of MOF and MOF/PANI matrix. The prepared MOF/PANI composite electrode showed specific capacity of 162.5 C g−1 at the current density of 0.4 A g−1 which is higher than bare MOF. The

Polymer-MOFs Nanocomposite for Supercapacitor

201

Fig. 4 a SEM micrograph of PANI/UiO-66 composite. b SEM image of MOF/PANI matrix, c comparative GCD curves of MOF and MOF/PANI matrix. d A graph of specific capacity and coulombic efficiency versus cycle number of fabricated AC//MOF/PANI supercapattery device (Inset: photograph of practical application of AC//MOF/PANI supercapattery device with glowing red LED. a Adapted with permission from [39], Copyright (2018), Elsevier. b–d Adopted with permission [36], Copyright (2020), Elsevier

fabricated ASCs device exhibited a high energy density of 23.2 Wh kg−1 with high power density of 1600 W kg−1 . The synthesized cobalt incorporated MOFs showed a poor electrochemical performance which was enhanced by blending Co-MOF with PANI. Figure 4d shows the graph of specific capacity and coulombic efficiency versus cycle number of fabricated AC//MOF/PANI supercapattery device. The fabricated device exhibited outstanding stability of 164% even after 3000 cycles. The inset of Fig. 4d presents the photograph of practical application of AC//MOF/PANI supercapattery device with glowing red LED. The prepared composite high sp. capacitance than pristine Co-MOFs it indicates the MOFs/PANI composite is favorable candidate in SCs field [36]. Cheng et al. [38] synthesized Ni-MOF/PANI by two step methods. In the first step PANI was coated onto NF (Nickel Foam) by in-situ polymerization of aniline and in second step Ni-MOF nanosheet arrays grown onto PANI/NF by hydrothermal method. The areal capacitance of Ni-MOF/PANI/NF, Ni-MOF/NF, PANI/NF and Ni-MOF powder at 2 mA cm−2 are 3626.4, 2275.1, 1202.6 and 567.6 mF cm−2 respectively. The Ni-MOF/PANI/NF showed high areal capacitance than another electrode. The rate capacity of Ni-MOF/PANI/NF 71.3% at 50 mA cm−2 which

202

A. S. Shelake et al.

is higher than PANI/NF (70.6%), Ni-MOF/NF (60.5%) and Ni-MOF (29.9%). The device was fabricated using AC (anode) Ni-MOF (cathode) the ASCs device delivered high sp. capacitance of 113.6 at 1 A g−1 and ASCs device showed 81.6% of initial sp. capacitance was retained after 10,000 charge–discharge cycles. The ASCs device delivered high energy density of 45.6 Wh kg−1 at power density 850 W kg −1 . Wang et al. [41] prepared hierarchical porous PANI/MIL-101 nanocomposite. Using GCD in a three-electrode system, the electrochemical properties of the PANI/ MIL-101 composite electrode materials were investigated. The PANI/MIL-101 electrode exhibited sp. capacitance of 1197 F g−1 at 1 A g−1 and showed capacitance retention rate of almost 90% after 10,000 cycles. The fabricated device delivered a high sp. capacitance of 371 F g−1 at 0.5 A g−1 with high energy density of 7 Wh kg−1 and a power density of 2000 W kg−1 for a 0.8 V potential window. GCD testing was performed at 2.5 A g−1 , and the device showed high cyclic stability, maintaining a sp. capacitance of approximately 81% after 10,000 cycles. Wang et al. [42] synthesized ZIF-67 by hydrothermal process further the powered ZIF-67 applied onto carbon cloth (CC) and prepare electrode. PANI was prepared by electrochemical process and deposited on ZIF-67-CC electrochemical process where ZIF-67-CC used as working electrode. The prepared PANI-ZIF-67-CC exhibited a sp. capacitance of 2146 mF cm−2 at 10 mV s−1 . Furthermore, the PANI-ZIF-67CC device exhibited a sp. capacitance of 35 mF with a maximum power density of 0.8335 W cm−3 (0.245 W cm−2 ) as well as a maximum energy density of 0.0161 mWh cm−3 (0.0044 mWh cm−2 ). Srinivasan et al. [43] fabricated Co-MOF/PANI composite where MOF prepared by facile synthesis method and aniline synthesized via in-situ chemical oxidative polymerization method. Based on GCD studies, the Co-MOF/PANI composite showed sp. capacitance of 504 F g−1 at the current density of 1 A g−1 , and its stability was sustained at 90% after 5000 cycles of GCD.

4.2 MOF-PPy Based SCs Xu et al. [40] synthesized three-dimensional networked MOF (ZIF-17) with conductive PPy tubes for flexible supercapacitor. The schematic illustration of fabrication procedure of MOF-PPy is provided in Fig. 5a. The FESEM image of optimized ZIFPPy network is as shown in Fig. 5b. As shown in FESEM image the ZIF polyhedra are well dispersed and connected to the PPy tubes. The prepared MOF-PPy network exhibited a sp. capacitance of 554.4 F g−1 at a current density of 0.5 A g−1 . Also, the optimized MOF-PPy network exhibited 90.7% capacity retention over 10,000 cycles. For application purpose they also fabricated flexible supercapacitor device based on MOF-PPy network. The CV curves of ZIF-PPy flexible supercapacitor device at different bending angles @ 5 mV s−1 are provided in Fig. 5c. The inset of Fig. 5c shows the digital photograph of ZIF-PPy flexible supercapacitor device. The GCD curves of different configurations of device are provided in Fig. 5d. The three devices connected in series can reach the potential window of 1.8 V. The as

Polymer-MOFs Nanocomposite for Supercapacitor

203

prepared flexible supercapacitor device delivered a stable performance in between potential window 0.6 V and exhibited high areal capacitance of 225.8 mF cm−2 . Wang et al. [44] synthesized a Ni-MOF-PPy composite, via a simple wet chemical method, in this method firstly they prepared PPy after that some amount of Ni-MOF dispersion was introduced into the PPy and getting the Ni-MOF-PPy composite. The Ni-MOF-PPy electrode exhibited a specific capacitance of 715.6 F g−1 at 0.3 A g−1 current density. The fabricated PPy-MOF//AC ASCs device showed an energy density of 40.1 Wh kg−1 at a power density of 1500.6 W kg−1 . Patterson et al. [45] synthesized PPy decorated metal–organic framework by hydrothermal method out of which PPy-d-MOFs sample exhibited a maximum sp. capacitance of 354 F g−1 at 25 mV s−1 and retains 70% of initial value after completion of 2500 cycles. Quin et al. [46] synthesized Ni-MOF-PPy by facile chemical oxidation technique the Ni-MOF-PPy composite exhibited a sp. capacitance of 1845.4 F g−1 at a current density of 1 A g−1 . The electrochemical performance was studied in KOH, Sp. capacitance of whole system was enhance 6.1% after addition of K4 Fe(CN)6 in regular KOH electrolyte because of synergistic effect between K4 Fe(CN)6 and Ni-MOFPPy material, introducing of K4 Fe(CN)6 created new channel for charge transport and faradaic redox reaction. As a result of the ASCs device construction, an energy density of 38.5 Wh kg−1 was achieved at 7000 W kg−1 and 87.8% capacitance retention was demonstrated after 3000 cycles. Liu et al. [47] synthesized NiCoMOF@PNTs (polypyrrole nanotubes) by simple ultrasonic method. The prepared electrode of NiCo-MOF@PNTs delivered a maximum sp. capacitance of 1109 F g−1

Fig. 5 a Schematic illustration of fabrication process of ZIF-PPy hybrid material. b FESEM micrograph of ZIF-PPy hybrid material. c CV curves of ZIF-PPy flexible supercapacitor device at different bending angles @ 5 mV s−1 (Inset: the digital photograph of ZIF-PPy flexible supercapacitor device). d GCD curves of different configurations of device. a–d Adapted with permission [40], Copyright (2017), American Chemical Society

204

A. S. Shelake et al.

at 0.5 A g−1 . It was observed that the NiCo-MOF@PNTs//AC device fabricated has a high energy density of 41.2 Wh kg−1 at a power density of 375 W kg−1 with a capacitance retention of 79.1% after 10,000 cycles.

4.3 MOF-PTh Based SCs Shi et al. [48] synthesized Ni-MOF/poly(3,4-ethylenedioxythiophene) (PEDOT) composite Ni-MOF synthesized via hydrothermal method and composite via chemical vapor deposition (CVD) Fig. 6a. The SEM image of Ni-MOF/PEDOT composite showed PEDOT combined with Ni-MOF core shell structure Fig. 6b. The GCD study of Ni-MOF/PEDOT at different current densities is as shown in Fig. 6c. It was found that the Ni-MOF/PEDOT composite electrode had a high sp. capacitance of 1401 F g−1 at current density of 0.5 A g−1 after 1000 cycles, and that it had retained 80.6% of its initial sp. capacitance after the process. The fabricated ASCs device exhibited a high energy density of 40.6 Wh kg−1 at a power density of 450 W kg−1 .

5 Future Prospective There is need to enhance the performance of SCs materials for commercialization or to fabrication devices it is possible when we prepare a composite of material. Most of the MOF’s composite discussed above are just combination of a MOFs and CPs are single materials. Hence multiple MOFs material or even MOFs derived metal oxides are combined with CPs deserve further research. For commercialization of Polymer-MOFs based nanocomposite type SCs we require the fabrication of electrode that can fulfil all of the major performance criteria addressed in this review: high sp. capacitance and capacity retention, chemically stable, high electrical conductivity, long-term cyclic stability, high power density and energy density, mechanical robustness, and scalable production.

6 Summary and Conclusion Developing advanced supercapacitors with enhanced electrochemical performance requires the search for new materials. MOFs are a candidate from 2D material can be useful for high surface area and high energy density. In summary in these chapter, we discussed about the MOFs-CPs composite material for SCs application. Electrochemical SCs are used as promising device for energy storage. Polymer-MOFs nanocomposite are the future of flexible SCs because of its own materials properties. Flexible SCs are the future of foldable electronic devices. Combining of MOFs-CPs are effective strategy to enhance the sp. capacitance and overall SCs performance

Polymer-MOFs Nanocomposite for Supercapacitor

205

Fig. 6 a The fabrication process of Ni-MOF/PEDOT composite. b SEM image of Ni-MOF/PEDOT composite. c GCD study of Ni-MOF/PEDOT-50 at different current densities. a–c Adapted with permission [48], Copyright (2022), Elsevier

of electrode material. In this chapter we are deals with strategies to enhance the SCs performance, chemical as well as cyclic stability of MOFs with different CPs material. In these book chapter composite of MOFs-CPs was classified according to composite of MOFs and CPs. In general MOFs composite are divide into three main type that is MOF-PANI, MOFs-PPy and MOFs-PTh derivatives. MOFs@CPs will become an admirable material in a field of SCs filed (Table 2).

206

A. S. Shelake et al.

Table 2 Summary of electrochemical supercapacitor properties of MOF and MOFs/CPs composite-based supercapacitor devices Capacitance

Energy density

Power density

Stability

Referencs

Ni-MOF//AC

230 mF cm−2 (1.0 mA cm−2 )

4.18 mWh cm−3

231.2 mW cm−3

92.8% of capacity retention after 5000

[17]

Ni-MOF//AC

88 F g−1 (1 A g−1 )

31.5 Wh kg−1

800 Wh kg−1

Good cyclic stability upto 5000 cycles

[18]

FA-Ni//AC

78.2 F g−1 (1 A g−1 )

27.81 Wh kg−1

1001.16 W kg−1

97.6% after 8000 CD cycles

[14]

Co-MOF//AC

–

1.7 mWh cm−2

4.0 mW cm−2

69.7% after 2000 cycles

[21]

NiCo-MOF//AC

158.1 F g−1 (0.5 A g−1 )

49.4 Wh kg−1

562.5 W kg−1

76.3% after 5000 cycles

[22]

CBNWM//AC

110 F g−1 (0.5 A g−1 ) 34.4 Wh kg−1

375.3 W kg−1

120.5% after 5000 cycles

[23]

Ni-MOF//AC

113.6 F g−1 (1.0 A g−1 )

850 W kg−1

81.6% after 10,000 cycles

[38]

[13]

Electrode material MOF

45.6 Wh kg−1

MOF-Polymer ZIF-67@PANI// ZIF-67@PANI

512 F g−1 (1.0 A g−1 ) 71.1 Wh kg−1

504.72 W kg−1

92.3% after 9000 cycles

MOF/PANI//AC

104.3 C g−1 (1.0 A g−1 )

23.2 Wh kg−1

1600 W kg−1

146% after [36] 3000 cycles

PANI/MIL-101 (SSD)

371 F g−1 at (0.5 A g−1 )

7 Wh kg−1

2000 W kg−1

81% after [41] 10,000 GCD cycle

Ni-MOF-PPy//AC

395.2 F g−1 (0.2 A g−1 )

40.1 Wh kg−1

1500.6 W kg−1

–

[44] (continued)

Polymer-MOFs Nanocomposite for Supercapacitor

207

Table 2 (continued) Electrode material

Capacitance

Energy density

Power density

Stability

Referencs

Ni-MOF@PPy//AC

141.5 F g−1 (0.5 A g−1 )

38.5 Wh kg−1

7000 W kg−1

90.2% after 3000 cycles

[46]

NiCoMOF@PNTs// 1109 F g−1 (0.5 A AC g−1 )

41.2 Wh kg−1

375 W kg−1

79.1% after 10,000 cycles

[47]

90.3 F g−1 (0.5 A g−1 ) 40.6 Wh kg−1

450 W kg−1

73.4% after 1000 cycle

[48]

Ni_MOF/PEDOT// AC

References 1. Simon P, Gogotsi Y (2008) Materials for electrochemical capacitors. Nature Mater 7(11):845– 854 2. Zhou L, Li C, Liu X, Zhu Y, Wu Y, van Ree T (2018) Metal oxides in supercapacitors. Metal Oxides Energy Technol 169–203 3. Pore OC, Fulari AV, Shejwal RV, Fulari VJ, Lohar GM (2021) Review on recent progress in hydrothermally synthesized MCo2 O4 /rGO composite for energy storage devices. Chem Eng J 426:131544 4. Meng Q, Cai K, Chen Y, Chen L (2017) Research progress on conducting polymer based supercapacitor electrode materials. Nano Energy 36:268–285 5. Relekar BP, Fulari AV, Rath MC, Fulari VJ, Lohar GM (2020) Modification in porous MnO2 / PANI composite using high-energy electron irradiation for electrochemical supercapacitor. J Mater Sci: Mater Electron 31:11741–11747 6. Ghosh S, Maiyalagan T, Basu RN (2016) Nanostructured conducting polymers for energy applications: towards a sustainable platform. Nanoscale. 8:6921–6947 7. Relekar BP, Fulari AV, Lohar GM, Fulari VJ (2019) Development of porous manganese oxide/polyaniline composite using electrochemical route for electrochemical supercapacitor. J Electron Mater 48:2449–2455 8. Furukawa H, Ko N, Go YB, Aratani N, Choi SB, Choi E, Yazaydin AÖ, Snurr RQ, O’Keeffe M, Kim J, Yaghi OM (1979) Ultrahigh porosity in metal-organic frameworks. Science 329(2010):424–428 9. Mehtab T, Yasin G, Arif M, Shakeel M, Korai RM, Nadeem M, Muhammad N, Lu X (2019) Metal-organic frameworks for energy storage devices: Batteries and supercapacitors. J Energy Storage 21:632–646 10. Wang KB, Xun Q, Zhang Q (2020) Recent progress in metal-organic frameworks as active materials for supercapacitors. Energy Chem 2:100025 11. Dˇedek I, Kupka V, Jakubec P, Šedajová V, Jayaramulu K, Otyepka M (2022) Metal-organic framework/conductive polymer hybrid materials for supercapacitors. Appl Mater Today 26:101387 12. Wang Z, Zhu M, Pei Z, Xue Q, Li H, Huang Y, Zhi C (2020) Polymers for supercapacitors: Boosting the development of the flexible and wearable energy storage. Mater Sci Eng R Rep 139:100520 13. Liu PY, Zhao JJ, Dong ZP, Liu ZL, Wang YQ (2021) Interwoving polyaniline and a metalorganic framework grown in situ for enhanced supercapacitor behavior. J Alloys Compd 854:157181

208

A. S. Shelake et al.

14. Zhao J, Li Q, Han L, Liu R (2019) Spherical mesocrystals from self-assembly of folic acid and nickel (II) ion for high-performance supercapacitors. J Colloid Interface Sci 538:142–148 15. Du P, Dong Y, Liu C, Wei W, Liu D, Liu P (2018) Fabrication of hierarchical porous nickel based metal-organic framework (Ni-MOF) constructed with nanosheets as novel pseudo-capacitive material for asymmetric supercapacitor. J Colloid Interface Sci 518:57–68 16. Yang J, Xiong P, Zheng C, Qiu H, Wei M (2014) Metal–organic frameworks: a new promising class of materials for a high performance supercapacitor electrode. J Mater Chem A Mater 2:16640–16644 17. Yan Y, Gu P, Zheng S, Zheng M, Pang H, Xue H (2016) Facile synthesis of an accordion-like Ni-MOF superstructure for high-performance flexible supercapacitors. J Mater Chem A Mater 4:19078–19085 18. Gao S, Sui Y, Wei F, Qi J, Meng Q, He Y (2018) Facile synthesis of cuboid Ni-MOF for high-performance supercapacitors. J Mater Sci 53:6807–6818 19. Wang Z, Chen J, Bi R, Dou W, Wang K, Mao F, Wu H, Wang S (2020) Supercapacitor and oxygen evolution reaction performances based on morphology-dependent Co-MOFs. J Solid State Chem 283:121128 20. Xiao GB, Yao XQ, Xie H, Ma HC, Yan PJ, Qin DD (2019) Dinuclear cobalt-based pillarlayered-like MOF as an electrode material for supercapacitor and photocatalysis activity. Polyhedron. 162:39–44 21. Zhu G, Wen H, Ma M, Wang W, Yang L, Wang L, Shi X, Cheng X, Sun X, Yao Y (2018) A selfsupported hierarchical Co-MOF as a supercapacitor electrode with ultrahigh areal capacitance and excellent rate performance. Chem Commun 54:10499–10502 22. Wang Y, Liu Y, Wang H, Liu W, Li Y, Zhang J, Hou H, Yang J (2019) Ultrathin NiCoMOF nanosheets for high-performance supercapacitor electrodes. ACS Appl Energy Mater. 2:2063–2071 23. Zhang H, Wang J, Sun Y, Zhang X, Yang H, Lin B (2021) Wire spherical-shaped Co-MOF electrode materials for high-performance all-solid-state flexible asymmetric supercapacitor device. J Alloys Compd 879:160423 24. Dhawale DS, Vinu A, Lokhande CD (2011) Stable nanostructured polyaniline electrode for supercapacitor application. Electrochim Acta 56:9482–9487 25. Yang Q, Hou Z, Huang T (2015) Self-assembled polypyrrole film by interfacial polymerization for supercapacitor applications. J Appl Polym Sci 132 26. Kim BC, Kwon JS, Ko JM, Park JH, Too CO, Wallace GG (2010) Preparation and enhanced stability of flexible supercapacitor prepared from Nafion/polyaniline nanofiber. Synth Met 160:94–98 27. Li Y, Zhao X, Xu Q, Zhang Q, Chen D (2011) Facile preparation and enhanced capacitance of the polyaniline/sodium alginate nanofiber network for supercapacitors. Langmuir 27:6458–6463 28. Khdary NH, Abdesalam ME, el Enany G (2014) Mesoporous polyaniline films for high performance supercapacitors. J Electrochem Soc 161:G63–G68 29. Sharma RK, Rastogi AC, Desu SB (2008) Pulse polymerized polypyrrole electrodes for high energy density electrochemical supercapacitor. Electrochem Commun 10:268–272 30. Wang J, Xu Y, Wang J, Du X (2011) Toward a high specific power and high stability polypyrrole supercapacitors. Synth Met 161:1141–1144 31. Dubal DP, Lee SH, Kim JG, Kim WB, Lokhande CD (2012) Porous polypyrrole clusters prepared by electropolymerization for a high performance supercapacitor. J Mater Chem 22:3044–3052 32. D’Arcy JM, El-Kady MF, Khine PP, Zhang L, Lee SH, Davis NR, Liu DS, Yeung MT, Kim SY, Turner CL, Lech AT, Hammond PT, Kaner RB (2014) Vapor-phase polymerization of nanofibrillar poly(3,4- ethylenedioxythiophene) for supercapacitors. ACS Nano 8:1500–1510 33. Patil BH, Jagadale AD, Lokhande CD (2012) Synthesis of polythiophene thin films by simple successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application. Synth Met 162:1400–1405 34. Senthilkumar B, Thenamirtham P, Kalai Selvan R (2011) Structural and electrochemical properties of polythiophene. Appl Surf Sci 257:9063–9067. https://doi.org/10.1016/J.APSUSC. 2011.05.100

Polymer-MOFs Nanocomposite for Supercapacitor

209

35. Guo SN, Zhu Y, Yan YY, Min YL, Fan JC, Xu QJ, Yun H (2016) (Metal-Organic Framework)-Polyaniline sandwich structure composites as novel hybrid electrode materials for high-performance supercapacitor. J Power Sources 316:176–182 36. Iqbal MZ, Faisal MM, Ali SR, Farid S, Afzal AM (2020) Co-MOF/polyaniline-based electrode material for high performance supercapattery devices. Electrochim Acta 346:136039 37. Neisi Z, Ansari-Asl Z, Dezfuli AS (2019) Polyaniline/Cu(II) metal-organic frameworks composite for high performance supercapacitor electrode. J Inorg Organomet Polym Mater 29:1838–1847 38. Cheng Q, Tao K, Han X, Yang Y, Yang Z, Ma Q, Han L (2019) Ultrathin Ni-MOF nanosheet arrays grown on polyaniline decorated Ni foam as an advanced electrode for asymmetric supercapacitors with high energy density. Dalton Trans 48:4119–4123 39. Shao L, Wang Q, Ma Z, Ji Z, Wang X, Song D, Liu Y, Wang N (2018) A high-capacitance flexible solid-state supercapacitor based on polyaniline and metal-organic framework (UiO-66) composites. J Power Sources 379:350–361 40. Xu X, Tang J, Qian H, Hou S, Bando Y, Hossain MSA, Pan L, Yamauchi Y (2017) Threedimensional networked metal-organic frameworks with conductive polypyrrole tubes for flexible supercapacitors. ACS Appl Mater Interfaces 9:38737–38744 41. Wang Q, Shao L, Ma Z, Xu J, Li Y, Wang C (2018) Hierarchical porous PANI/MIL-101 nanocomposites based solid-state flexible supercapacitor. Electrochim Acta 281:582–593 42. Wang L, Feng X, Ren L, Piao Q, Zhong J, Wang Y, Li H, Chen Y, Wang B (2015) Flexible solidstate supercapacitor based on a metal-organic framework interwoven by electrochemicallydeposited PANI. J Am Chem Soc 137:4920–4923 43. Srinivasan R, Elaiyappillai E, Nixon EJ, Sharmila Lydia I, Johnson PM (2020) Enhanced electrochemical behaviour of Co-MOF/PANI composite electrode for supercapacitors. Inorganica Chim Acta 502:119393 44. Wang B, Li W, Liu Z, Duan Y, Zhao B, Wang Y, Liu J (2020) Incorporating Ni-MOF structure with polypyrrole: enhanced capacitive behavior as electrode material for supercapacitor. RSC Adv 10:12129–12134 45. Patterson N, Xiao B, Ignaszak A (2020) Polypyrrole decorated metal–organic frameworks for supercapacitor devices. RSC Adv 10:20162–20172 46. Qin Z, Xu Y, Liu L, Liu M, Zhou H, Xiao L, Cao Y, Chen C (2022) Ni-MOF composite polypyrrole applied to supercapacitor energy storage. RSC Adv 12:29177–29186 47. Liu Y, Wang Y, Chen Y, Wang C, Guo L (2020) NiCo-MOF nanosheets wrapping polypyrrole nanotubes for high-performance supercapacitors. Appl Surf Sci 507:145089 48. Shi L, Yang W, Zha X, Zeng Q, Tu D, Li Y, Yang Y, Xu J, Chen F (2022) In situ deposition of conducting polymer on metal organic frameworks for high performance hybrid supercapacitor electrode materials. J Energy Storage 52:104729 49. Wang X, Liu X, Rong H, Song Y, Wen H, Liu Q (2017) Layered manganese-based metal– organic framework as a high capacity electrode material for supercapacitors. RSC Adv 7:29611–29617

The Active Role of Conjugate Polymer Composites in Electrochemical Storage: A Themed Perspective on Polymer-MOF Nanocomposites for Metal-Ion Batteries Sowjanya Vallem and Joonho Bae

Abstract In recent years, the hybrid structures of polymer-integrated metal-organic framework (MOF) have become a trending research domain in the field of electrochemical energy storage (EES) because polymers play a fundamental role in energy storage systems as electrolytes, separators, and active materials with limited obstructions. MOFs are a novel category of crystalline porous compounds that have an inherently huge surface area, which makes them fascinating for a wide variety of applications and recommended candidates for next-generation energy technologies. However, their utility in metal-ion batteries (MIBs) is mitigated due to limited mechanical durability and electrical conductivity. Conversely, the malleability, highenvironmental resistance, docility, cost-effectiveness, and lightweight nature of conjugated polymers (CPs) make them flexible for several portable applications. Reportedly, the integration of MOF with polymer can influence its structure, and polymers can modulate the nucleation and characteristics of MOFs. Hence, the hybridization of MOF crystalline architecture with flexible CPs leads to disparate composites that retain a feasible electronic structure for ion/electron transportation, a huge surface area, and porosity, all of which are flexible for the collection and accumulation of charges. Herein, we spotlight the recent advancements in the electrochemical performance of polymer-MOF hybrids as active material, electrolytes, and separators in various MIBs which are fabricated using polymer polymerization within MOFs, grafting polymers to MOFs, and growth of MOFs on polymer templates. Finally, the perspectives of polymer-MOFs are discussed, which may provide useful information on the futuristic fabrication of polymer-MOF composites for flexible EES. Keywords Hybrid polymer-MOFs · Flexible · Metal-ion batteries · Self-healing · Multifunctional composites

S. Vallem · J. Bae (B) Department of Physics, Gachon University, 1342, Seongnam-si, Gyeonggi-do 461-701, South Korea e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_12

211

212

S. Vallem and J. Bae

1 Introduction In this modern era, there is a high demand for sustainable and portable electronic vehicles, electronic devices, and aerospace systems that are searching for new electrochemical storage materials with reliable performance. Yet, lithiumion batteries (LIB) have reached the commercial level and are used in electronic gadgets due to their high energy density, lightweight nature, and cycle longevity. Persuasively, considerable research on the developments of LIBs pursued the prestigious Nobel prize in 2019 [1]. Due to the limited abundance of lithium sources in the Earth’s crust, atlternative batteries such as Zn, Na, Al, and K-ion batteries are also being developed for energy storage. However, the biggest challenges in front of MIBs, include limited specific capacity and rate performance. Reportedly, most investigations on LIBs focus on graphite-based anode materials, which primarily rely on the reversible Li-ion intercalation in their structure and can offer a maximum specific capacity of ∼ 372 mAh g−1 , setting a higher limit on the total energy density of LIBs [2]. Furthermore, a major issue of LIBs is dendrite formation, which erodes the battery performance. Apart from LIBs, making other metal-ion (Na, Al, Zn, and K-ion) rechargeable batteries are facing challenges in adequate engineering strategies for their larger storage capability and cycle longevity in which fabricating electrodes with hybrid materials has become a good choice to mitigate the hurdles of MIBs. Recently, MOF-derived metal oxides, chalcogenides, carbides, and phosphides nanostructures have been used as anode materials for MIBs [3]. Despite the favorable attributes of existing materials, their chemical and physical limitations hinder electrochemical performance. Therefore, the focus of developments has shifted to the hybridization of hetero-nanostructures. For example, polymers and conductive carbon-based composites are synthetically feasible, cost-effective, and scalable, but are hindered due to the low physical and chemical durability for device deployment. Whereas, several MOF-derived materials have a huge surface area, good electrical conductivity, and tunable attributes, rendering them excellent materials for next-generation energy storage [4]. Due to the diverse physicochemical functions of CP, they are playing a vital role in domestic life and technology. The conjugated carbon chain of organic polymers has alternative single and double bonds, which are responsible for their unique electronic and optical features. CPs are not only conducive but also mechanically flexible, lightweight, transparent, wettable, and have a tunable structure, as well as facile synthesis methods [5]. More interestingly, CPs are capable of storing charge via the redox reaction mechanism and compatible with many electrolytes, endowing them suitable as sustainable electrode materials and separators. These unique properties of CPs have led to tremendous interest in utilizing them in various cutting-edge EES devices. In addition to this, the high packing density of CPs renders them useful in carbon electrodes to enhance the volumetric performance of the associated devices [6]. Electrical and optical properties of polymers mainly rely on attached dopants to monomer units and synthetic parameters. Despite their attractive properties, the electrode materials made up of CP for electrochemical energy storage devices easily

The Active Role of Conjugate Polymer Composites in Electrochemical …

213

suffer from structural damage due to severe volume expansion and contraction during the charging/discharging [7]. Hence, the hybridization of polymers-structure with suitable materials could be the persistent solution to mitigate structural destruction. MOFs, on the other hand, are crystalline-porous architectures with periodically arranged metal ions surrounded by organic linkers, forming a symmetric hollow structure with uniform porosity that provides an extremely huge surface area (103 ∼104 m2 g−1 ). Additionally, MOFs can exhibit unique structural diversity due to their segmental combination of metals and linkers, making them more attractive compared to other porous structures and feasible for achieving the required structure and chemical functionalities [6]. Owing to their atom-level uniformity, tunable porosity, structural diversity, feasible network topology, dimension, geometry, and reactive functionality, MOFs become highly recommended candidates for next-generation EES technologies [8]. MOF accommodates redox-active metal centers, particularly transition metals such as Co, Fe, Ni, and Mn which exhibit efficient electrochemical activity. Ion-selective MOF membranes have been utilized in EES applications. However, MOFs face issues with poor electrical conductivity and chemical stability. Therefore, remedial approaches have been adopted to mitigate these problems through the utilization of MOF-derived metal compounds and carbonaceous composites [9, 10], among which hybridization of MOF structures with different structures is beneficial to boost performance in various applications. This chapter focuses on polymer-MOF nanostructures as electrode material, separator, and electrolytes for MIBs. Figure 1 shows the basic structure of MOFs and their attributes, which can be improved through hybridization with polymers. Precisely, the synthesis routes employed for the hybridization of MOF materials with polymers and their improved electrochemical performance for MIBs have been discussed. In the end, the prospects of MIBs with a polymer-MOF hybrid structure are presumed.

Fig. 1 The basic structure of MOFs and their improved attributes after the incorporation of polymers. Adapted with permission [11]. Copyright (2021) Royal society of chemistry

214

S. Vallem and J. Bae

2 Brief Outline of Synthetic Approaches of Polymer-MOF Hybrids To date, extensive literature on design strategies of both MOF and CP has been reported elsewhere [10, 12, 13]. Comprehensively, the synthetic approaches are broadly classified as, the top-down approach through which post-prepared MOFs can be polymerized whereas the bottom-up approach describes hybridization during the formation of MOF. Several elegant synthetic approaches for polymer-MOF materials have been reported that are categorized into five distinct strategies, (1). insitu polymerization in MOF, (2). mixed matrix membranes, (3). polymer-templated MOFs, (4). MOF synthesis using polymeric ligands, and (5) polymer-grafted MOFs (Fig. 2). These approaches are used widely to tailor polymer-MOF hybrids for several applications, including sensors, catalysis, electrodes, and energy storage applications.

2.1 In-Situ Polymerization in MOF Here, the monomers will directly polymerize inside the pores of MOF in the gas or liquid phase through heat, light, and chemical reaction promoters, or direct reactions between monomers and MOF particles. After polymerization, the polymer chain can establish its growth compatible with MOF pores and get trapped in MOF architecture (Fig. 3). Otherwise, strong intermolecular interactions occur between MOF walls and polymer. The in-situ approach is feasible to introduce linear polymers with controllable repeated monomer units in MOF structure [15]. Fig. 2 Schematic illustration of hybridization approaches of polymer-MOFs. Re-created based on Ref. [14]

The Active Role of Conjugate Polymer Composites in Electrochemical …

215

Fig. 3 Schematic illustration of in-situ polymerization in the MOF structure. Adapted with permission [16]. Copyright (2020) American Chemical Society

2.2 Mixed Matrix Membranes The mixed matrix membrane (MMM) is used to integrate rigid porous material into the flexible polymer. These types of membranes are widely utilized for the selective separation of various gases due to high fluxes and better selectivity, as well as separators for rechargeable batteries to tackle dendrites and poly-shuttling species for facile ion diffusion [17, 18]. The successful development of MMMs is greatly associated with optimization and control over the subtle interaction, which depends on the properties of polymer and particles. However, methodological optimization of synthetic parameters is critical for good MMM performance [19]. The conventional fabrication of polymer-MOF MMM includes the solution dispersion followed by a casting approach. Through this strategy, the MOF particles can suspend in a volatile solvent and then mixed well with polymer dissolved solution until mixed particles homogeneously disperse in the medium. This wellmixed mixture is known as “MOF ink,” which could be cast into a membrane and allowed to dry to evaporate solvents to produce standalone MMM (Fig. 4). A wide variety of MOF-polymer materials were tailored using casting methods for several specific applications [20].

Fig. 4 Schematic view of the convectional MMM approach of polymer-MOF hybridization. Adapted with permission [21]. Copyright (2015) Wiley publishing group

216

S. Vallem and J. Bae

Fig. 5 An example of a polymer-templated MOF approach. Adapted with permission [22]. Copyright (2020) American Chemical Society

2.3 Polymer-Templated MOFs The structural features of MOFs, such as crystalline phase, size, shape, and porosity, can be controlled using organic polymers. In contrast to MOF templates, organic polymer templates have the advantage of facilitating many coordination sites, selfassembling ability, and vast tunability towards desired applications. Though several reports discuss polymer template versatility in metal oxides, mineral morphology, and soft matter structures, the control over the growth of MOF is still in the beginning stages. An example of a synthetic approach of polymer templated MOF (polystyrene (PS) template for ZIF) is shown in Fig. 5.

2.4 MOF Synthesis Using Polymeric Ligand The poly-MOF is a unique and attractive strategy to construct MOF hybrids, beneficial to controlling molecular weight, structure, polymer composition, and the load inside MOF, consequently leading to control over shape, size, and colloidal stability. Hence, processability of MOF can be improved based on requirements. However, precise care has to be taken during the polymeric ligand (PoL) synthesis, and synthetic parameters at which MOF crystallizes could be accordingly elucidated. The kinematical and entropy disorders due to the implementation of polymeric ligands are quite challenging factors that show an impact on the regularity of the polymeric chain and symmetry of the structure. In certain instances, this could be beneficial but anticipated by the reactive nature of PoLs. The molecular weight and functionality of PoL are also influential factors on the polymeric backbone of the targeted out-structure of MOF. For instance, the alkyl space-linkers and the applicability of this method have a key role in the versatility of crystalline phases of MOF. Another interesting factor that needs to be explored is its functionality on the polymeric backbone [15].

The Active Role of Conjugate Polymer Composites in Electrochemical …

217

2.5 Polymer-Grafted MOFs Polymers can be grafted on/into MOF through the covalently connected polymer chain to the MOF surface to enhance their compatibility with matrix components. Grafting-to and grafting-from are two typical approaches to polymer-functionalized surfaces. The grafting-to method involves end-functionalizing pre-made polymers with reactive groups that are complimentary to the surface functionality to which the chain is grafted. This method has the considerable benefit of allowing the polymer to be thoroughly characterized before surface grafting. However, the grafting-to method facilitates limited grafting density, which restricts the mass fractions of the polymer that can be obtained. Whereas the surface of the polymer is functionalized with initiator groups at the beginning of the grafting-from process, through which high mass fractions and extremely dense brushes of polymer can be produced. Though characterizing the polymer brushes is difficult, most analytical procedures call for cleaving and isolating polymer chains from the surface. Earlier research on MOFpolymer hybrids was also focused on layer-by-layer deposition of polymer chains on MOF surfaces or straightforward absorption of the chains. The current literature on grafting polymer through covalently attached polymer chains to MOF particles mostly focuses on grafting-to and grafting-from techniques. The classification of polymer-MOF hybridization techniques is given in Table 1. Table 1 Classification of polymer-MOF hybridization strategies Types of hybridization

Sub-classification

References

Polymerization of MOF

Radical polymerization

[23]

Oxidative polymerization

[24]

Electro-polymerization

[16]

Ionic polymerization

[15]

Coordination-insertion polymerization

[25]

Polycondensation polymerization

[26]

Cycloaddition polymerization

[27]

MOF-ink filler casting on polymer

[17–19, 28]

Covalently connected MOF-polymer MMM

[14]

Polymer-templated MOFs

Various kinds of polymer templates for MOF

[14, 15]

Poly-MOF (polymer ligands for MOF)

Direct synthesis Exchanging ligands

[15, 29]

Polymer-grafted MOFs

Grafting-to Grafting- from Grafting-through

[30, 31]

Mixed-matrix membranes

218

S. Vallem and J. Bae

3 Why Polymer-MOFs Are Attractive for MIBs The adaptable structural advantages of polymer-MOF can enhance the performance of MIBs in several essential parts, including separators, electrolytes, and anode/ cathode materials with high porosity, redox-active functionalities, exceptional host– guest chemistry, and flexibility. Reportedly, polymer-MOF hybridization establishes chemical, mechanical, and thermal stability [15]. In contrast to the bare MOF, polymer-MOF hybrids can effectively resist structural phase transformation/ distraction and endure in extremely humid and/or acidic and/or basic mediums, which represents significant progress in chemical and mechanical stability. Additionally, polymer inclusion can assist in the isolation of MOFs that were previously inaccessible because of their instability, and the requirement of heat and vacuum during functionalization. These factors render the hybridization of polymer-MOF a promising approach to maintaining the structural geometry and, inhibited porosity of MOFs. This will enable them to live longer and operate better in a range of different environments, which will benefit sustainable applications [14]. Current research on polymer-MOF composites focuses on their exceptional interior surface area and pore volume, customizable pore sizes and shapes, regularity of MOF geometry, and the combined benefits of polymers, such as a high density of reactive groups and processability. For rechargeable batteries, all these factors collectively contribute to the installation of electron reservoirs that support excellent electrical conductivity and facilitated porosity for ion percolation. The majority of functional linkers are inhibited with subunits such as benzene, imidazole, pyridine, or thiophene that can be electrochemically active due to the presence of redox-active sites and also behave as electron reservoirs. Interestingly, the theoretical capacity may increase beyond the limits of metal nodes due to the cross-linkers with accessible oxidation/reduction potentials without compromising porosity/framework integrity. Controlling particle size also enhances electrochemical stability by mitigating volume expansion through interparticle spacing. Furthermore, hierarchically porous polymer-MOFs with large exterior surface areas improve the electrode–electrolyte interface, facilitating faster charge transportation due to the abundance of ion transport channels and low diffusion lengths, offering better cycling performance than monolithic MOF crystallites. The CP interaction with MOF could enhance a wide range of accessible oxidation states of redox-active metals or linkers. Further, the chemical plasticity of polymerMOFs allows the inclusion of multi-electron redox-active metal nodes and linkers to provide better specific capacities [8]. The design criteria of MIBs incorporating CP-MOFs involve selection of favorable functional characteristics such as porosity, morphology, conductivity, and redoxactive sites. These characteristics make CP-MOFs efficient integral components of batteries. Increased electron/ion storage capacity has a significant impact on future polymer-MOFs for MIBs. To date, polymer-MOF hybrids with multifunctional versatility, are adopted to develop various integral parts of MIBs.

The Active Role of Conjugate Polymer Composites in Electrochemical …

219

4 Recent Advancements in Polymer-MOF Composites for MIBs High-power applications, such as batteries for electric cars, require a quick energy supply over a short period and intermittent use. Therefore, the materials used for the battery fabrication must have low contact resistance, quick charge transfer kinetics, and enough transport routes to carry out redox processes at the high applied currents during charge/discharge. Yet, high-rate batteries are facing substantial safety risks due to the possible damage of cells from dendrite growth, volume expansion, and heating issues due to incorrect material selection. Flexible and robust polymer-MOF hybrids can be tailored to mitigate these issues by maintaining exceptional electrode contact through their large surface area. Additionally, energy storage systems are also needed to supply a consistent power supply in harsh environmental circumstances. Pushing the boundaries of these environmental conditions exposes current battery technologies to risks and unreliability. Due to their mechanical, chemical, and thermal endurance, polymer-MOFs are utilized as separators, electrode materials, and solidstate electrolytes to push the boundaries of battery technology and work effective and safe operation in extreme conditions. This section discusses the outcomes of recent articles on polymer-MOF composites designed for MIBs published in 2020–2022.

4.1 Separators The electronic insolubility of polymers makes them naturally suitable as battery separators, but in a combination of MOF fillers, polymer-MOF structures became attractive remedy to immobilize shuttling species and mitigates dendrite formation due to their adjustable porosity and ionic conductivity. The resulting polymer-MOF incorporated separator is reffered to as an “ionic sieve” as it transports metal ions while preventing dissolvable dendrites from reaching the anode/cathode. Li–S batteries (LSBs) are highly preferred for MIBs due to their high energy density. A separator composed of polydopamine (PDA) assisted zeolitic imidazolate8 (ZIF-8) layer on polyolefin was fabricated for LSBs. This functional separator efficiently trapped polysulfides, promoted lithium-ion transport, and offered high specific capacity (711 mAh g−1 at 2 °C). It exhibited a low capacity degradation rate of only 0.013% per cycle, outperforming conventional separator in terms of electrolyte wettability, thermal stability, and lithium-ion transference number [32]. Whereas, Anwar and his group demonstrated a PCN-250(Fe)-coated porous polypropylene (PPy) membrane to mitigate the polyselenide shuttle and improve Li+ transportation of Li-Se batteries (LSeBs). The PCN separator acted as a selective barrier, tackling polyselenides and allowing steady lithiation/delithiation during repeated cycles. It achieved a high discharge capacity of 423 mAh g−1 at 0.2 °C and a Coulombic efficiency of greater than 98% after 500 cycles. Since PCN-separator demonstrated

220

S. Vallem and J. Bae

reliable and reversible electrochemical activity for LSeBs, this may also be suitable for alkali-metal and alkali-metal chalcogenide battery systems [18]. Further, the combination of poly(vinylidene fluoride) (PVDF) and MOF-808 was used for LIBs which enhanced the porosity, surface area, ionic conductivity, and electrolyte absorption of the separator. MOF-808 fillers were added to the liquid electrolyte to enhance capacity retention and reduce capacity fading during high C-rate performance. Indeed, PVDF/MOF-808 membranes exhibited a capacity of 68 mAh g−1 at a 2 °C rate during charge–discharge testing in Li/C-LiFePO4 half-cells. The long-term steady cycling behavior of the PVDF/MOF-808 separator exhibits approximately 100% of Coulombic efficiency. The electrolyte accessibility through this membrane was significantly increased due to the meso- and micro-porous polymer with the well-arranged microporous system of the MOFs [17]. A special design of Co-MOF/polyacrylonitrile (CO-MOF/PANI) membranes prepared via electrospinning approach and was utilized for the NCM811||separator||Li battery system. The MOF/PANI separator exhibited exceptional thermal stability, remarkable electrolyte absorption (794 ± 30%), high ionic conductivity (2.83 mS cm−1 at 25 °C), and substantial electrochemical window (5.2 V vs. Li+ /Li). The Li||separator||Li half-cell remained stable at 5 mA cm−2 for 1000 h. The Li+ transference number was increased up to 0.74, which was 64.4% greater than that of the PANI-separator, because of a strong electrostatic contact between MOF and PF− 6 in the electrolyte that prevents anions from moving. Whereas, the NCM811||10% MOF/PANI separator||Li battery system exhibited a 166.3 mAh g−1 initial discharge capacity with 81.3% capacity retention after 250 cycles at 5 °C [33]. Similarly, Zhou et al. used electrospinning and the subsequent liquid phase chemical vapor deposition (LPCVD) techniques to develop a double-layered MOF-PANI/rGO-PANI nanofiber membrane. In this strategy, along with good mechanical and thermal stability, the MOF architecture associated with nanofibers was vital to adsorb polysulfides, establish cycle stability, and supported a high Li+ transference number (0.81). Further, LSBs made up of this separator offered a high starting capacity of 1302 mAh g−1 at 0.5 °C and the capacity degradation rate was merely 0.03% per cycle over 600 cycles at a high rate of 5 °C. More interestingly, the Li–S battery produced a high areal capacity of 7.8 mAh cm−2 after 50 cycles despite having a high sulfur loading of 7.7 mg cm−2 . The DFT calculations also supported the crucial role of the MOF-PANI layer on electrochemical performance [34]. A distinguish MMM was fabricated with a multiplex of poly(vinylidene fluorideco-hexafluoropropylene) (PVDF-HFP) with UiO-66-NH2 , MOF-808, and MIL125 nanofillers using the solvent-casting method. The characteristic membrane structure disclosed a reduction in the shape of the porous structure of MOF with the polymeric matrix, extended pore diameters, and changes in the PVDF-HFP chains and domain arrangements. The inclusion of MOF in MMM increased the wettability, absorption, and charge transport of the PVDF-HFP separators. Whereas, PVDFHFP/UiO-66-NH2 MMM demonstrates a decreased half-cell resistance, exceptional cycle consistency, and high-rate discharge capacity [35].

The Active Role of Conjugate Polymer Composites in Electrochemical …

221

4.2 Electrolytes Conventional electrolytes used in batteries are generally made up of combustible organic solvents which have safety concerns, and reliability issues for high-energy– density rechargeable batteries. Solid-state electrolytes are being used to replace solution electrolytes, and suitable materials should have a perfect metal-ion transference number and strong ionic conductivity (over 10–4 S cm−1 at ambient temperature). Polymer-MOFs may enable high ion mobility through open channels, solvent inclusion, and soft chemical interactions. Furthermore, compared to solid inorganic compounds, polymer-MOF hybrids are more compatible with carbon-composed electrodes. An electrolyte composed of poly(ethylene oxide) (PEO) and UiO-66 fillers for LIBs in which the coordination of UiO-66 and lithium salt and oxygen in the PEO chain considerably promoted the ionic conductivity (3.0 × 10–5 S cm−1 at 25 °C and 5.8 × 10–4 S cm−1 at 60 °C), Li+ transport, stability, and extended potential window (to 4.9 V). Further, the durability of prepared Li cells was extended to 1000 h (at 0.15 mA cm−2 , and 60 °C) [36]. In another approach, Liu and coworkers described the facile photopolymerization of boronic-ester crosslinking monomer (BEM) and poly(ethyleneglycol)diacrylate (PEGDA) in the co-existence of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and MOF to produce a poly(caprolactone) modified MOF (MOF-PCL) composite polymer electrolyte (CSPE) for LIBs. In this multiplex, MOF-PCL increased the ion percolation and electrochemical stability, boron facilitated the more transit of Li-ions. The resulting CSPE has established a high upper limit of the potential window (5.29 V) and a higher Li-ion transference number (0.59). Further, the LiFePO4 /Li cell composed of CSPE extended cycling stability and rate performance [37]. Later on, Wen et al. fabricated a free-standing flexible composite SPE (CSPE) membrane via the solutionpouring method, which was grown from random copolymerization of trifluoroethylmethacrylate (TFEMA) with polyethyleneglycolmethacrylate (PEGMA), lithium salt, and MOF-5. The solid battery LiFePO4 /CSPE/Li offered capacity retention of 92.2% after 25 cycles, [38]. Yang et al. synthesized a unique MOF (UiO-66)-Li-ion conductor in which only the untrammeled Li+ is allowed to travel through the porous channel because the negative ions are covalently linked to the MOF. Further, the conductivity of MOF was improved due to the addition of cationic organic solvents such as ethylene carbonate (EC) and propylene carbonate (PC). When the temperature was raised from 25 to 90 °C, the conductivity of UiO-66 was increased from 6 × 10–5 to 1.1 × 10–4 S cm−1 and the potential window was extended to 5.2 V. In the absence of a plasticizer, the electrolyte exhibited single-ion conducting behavior with a high Li+ transference number of 0.90 at 25 °C. With the addition of EC and PC, the ionic conductivity of MOF reached 7.8 10–4 S cm−1 at 25 °C. Finally, Li|MOF|LiFePO4 batteries offered excellent rate capacity and cycle durability [39]. Further, the physical and electrochemical characteristics of the composite polymer electrolyte (CPE) had been improved through the addition of UiO-66-NH2 @SiO2 [40] which established a high number of Li+ passage through the CPE and also

222

S. Vallem and J. Bae

improved electrode–electrolyte interfacial properties and homogeneous Li+ flux between two electrodes. The author also claimed that the properties of UiO-66NH2 including superior chemical and thermal stability have a greater possibility for all-solid-state lithium-polymer batteries even at higher temperatures.

4.3 Cathode and Anodes The polymer-MOFs can be essential components of metal-ion cathodes and anodes because of their adaptable structure, redox performance, high porosity, and exceptional host–guest chemistry. For instance, lithium-stabilizing ligand moieties and redox-active metal centers can enhance the volume of lithium ions storage, increasing the theoretical capacity. Ion transit can be facilitated by the inherent porosity of MOFs, which can offer extensive interfacial contact with the electrolyte and allow the reversible storage of metal ions. Additionally, the contribution of flexible CP with MOF has a high scope to mitigate volume expansion issues. A polymer-templated MOF was used to design a core–shell structured nitrogendoped polystyrene@ZIF (PS@ZIF), which further transformed into Co (single-atom) hollow-porous carbon (CoSA-HC) via one-step pyrolysis. The Se@CoSA-HC cathodes provided a good electrochemical performance with a capacity of 564 mAh g−1 at 0.1 C and long durability (5000 cycles) with 100% Coulombic efficiency. In brief, this report describes the following benefits of designed structures, high utilization of selenium storage sites, a larger electrode–electrolyte interface area, shorter mass– charge migration lengths, minimizing the adsorption energy barriers, providing large interior void spaces which buffer volume expansion during lithiation and improved electrode conductivity. This study lays the groundwork for a fresh approach based on polymer-templated MOF-derived active materials for high-power EES devices [22]. The MOF-polymer was used to produce ZnO–C@SiOC anode material via suspension polymerization (Poly[(dimethylsilylene)diacetylene], PDSDA) for LIBs. The microporous architecture of ZnO-C@SiOC abounds with oxygen vacancies and strong molecular interaction allowed rapid passage of Li-ions through the electrolyte and efficient encapsulation of ZnO-C. Additionally, the coordination of the ZnO-C network with the amorphous SiOC network raises the abundance of active sites and allows more Li+ transportation with facile ionic diffusion. The ZnO-C@SiOC nanocomposite demonstrated an impressive retention capacity of 472 mAh g−1 after 1000 cycles at 0.8 A g−1 with excellent cycle stability over 350 h. Furthermore, the ZnO-C@SiOC anode together with the LiFePO4 cathode offered a capacity of 388 mAh g−1 over 180 cycles at 0.1 A g−1 with the dominant pseudocapacitive behavior. High energy density and the feasibility of designed materials are responsible for short ionic diffusion and quick electron transit [41]. To overcome the problems with solubility and the poor electrical conductivity of organic electrode compounds, Chu et al. designed an N-doped carbon framework for SIB cathodes via in-situ polymerization of poly (3,4,9,10-perylenetetracarboxylic

The Active Role of Conjugate Polymer Composites in Electrochemical …

223

dianhydride ethylene diamine) (PI) with N-doped carbon matrix (NC) (ZIF-8derivative) composites. The battery design included a commercial disodium terephthalate (NaTP) anode and synthesized PI@NC cathode, which exhibited a specific capacity of 125 mAh g−1 at 0.1 A g−1 with an exceptional capacity retention of 96.2% after 200 cycles. The author claimed that the improved electrochemical performance of the PI@NC electrode was due to the crucial involvement of conductive frameworks and organic compounds [42]. In 2022, Konstantin and his team synthesized PANI/Fe-BTC composites through in-situ polymerizations of aniline in the presence of Fe-BTC. The interaction between PANI and MOF enabled a significant enhancement in pseudo-faradic current. The author claimed that adding Fe-BTC to PANI-based composites improved their electrochemical responsiveness, and a lower percentage of PANI contribution also enabled stable MOF accessibility [43] for electrochemical functionalities. Later on, a facile MOF-on-MOF self-templated strategy was used to design a core-double-shelled architecture (Fe7 S8 /C@ZnS/N– C@C) composed of ZnS and Fe7 S8 /C. The MOF-on-MOF with a ZIF-8 shell, MIL-53 core, and polymer resorcinol and formaldehyde (RF) was synthesized via a layer-by-layer assembly approach (MIL-53@ZIF-8@RF). After the sublimation of sulfur, a hierarchical carbon matrix was obtained with a thrived interfacial and tiered distribution of active material. This structure provided fast sodium-ion reaction kinetics, excellent pseudocapacity, good tolerance to volume fluctuations, and a stepwise sodiation/desodiation reaction mechanism. The Fe7 S8 /C@ZnS/N–C@C anode was sustainable until 10,000 cycles, and produced a high capacity of 364.7 mAh g−1 at a current density of 5.0 A g−1 , with just 0.00135% capacity loss per cycle [44]. Similarly, bimetallic ZnNi-MOF/PANI nanofibers were thermally decomposed to synthesize nitrogen- and oxygen-doped porous carbon nanofibers (PCNFs). The author claimed the capability of PCNFs to improve the nucleation and adsorption of Na with low energy, dendrite-free characteristics, and stability of Na metal anodes [45]. For potassium-ion batteries (KIBs), the active material was derived from MOF/PANI nanofiber via electrospinning of ZIF-67 nanocubes, PANI, and DMF. Co0.85 Se@C nanoboxes were subsequently transformed into carbon nanofibers (Co0.85 Se@CNFs) after carbonization and selenidation processes. In this derivative, a large surface area of Co0.85 Se@C nanoboxes with sufficient void space reduces the volume expansion for better cycle stability. During potassiation/depotassisation, the strong CNF network improved electronic conductivity and stabilized the integral structure. Consequently, this special nanoarchitecture demonstrated high cycling stability as an anode material for KIBs (299 mAh g−1 at 1 Ag−1 after 400 cycles) [46]. In a case study of Zn-air batteries (ZABs), an active material fabricated from carbon nanotube integrated single cobalt atoms with Co9 S8 nanoparticles (CoSA + Co9 S8 /HCNT), which derived from ZnS-templated ZIF-67-PDA through pyrolysis. This material exhibited an impressive power density (PD) of 177.33 mW cm−2 . Additionally, in the combination of all-solid-state flexible rechargeable ZAB, CoSA + Co9 S8 /HCNT offered a PD of 51.85 mW cm−2 [47]. Later on, a simple PPy tubedirected templating approach was used to synthesize a bifunctional catalyst called Co@hNCTs, which had Co nanoparticles enclosed in hollow nitrogen-doped carbon

224

S. Vallem and J. Bae

tubes. The surfactant-treated PPy nanotubes typically served as the structure-guiding templates to forming ZIF-67 nanocrystals. The ZIF-67/PPy nanotube composite was transformed into Co@hNCTs after carbonization at 800 °C. These Co@hNCTs cathodes demonstrated long-term cyclability (over 500 h) for ZABs [48]. The above-mentioned advantages of MOF-polymers-based structures seem to be excellent remedies for most of the issues that are encountered by MIBs. The electrochemical improvements of polymer-MOF-derived structures as separators and active materials are summarized in Table 2. Table 2 Polymer-MOF architectures used for separators and active materials of MIBs and their improved performance Name of polymer and MOF used

Type of component

PDA/ZIF-8

Separator

PPy/PCN-250(Fe) Separator

Type of battery

Performance (capacity-scan rate-cycle longevity) (mAh/g-C or A/ g-cycles)

References

LSB

711-2-500

[32]

LSeB

423-0.2-500

[18]

PVDF/MOF-808

Separator

LIB

68-2-150

[17]

PANI/Co-MOF

Separator

LIB

166.3-5-250

[33]

PVDF-HFP/ UiO-66-NH2

Separator

LIB

85-2-200

[35]

PVDF-HFP/ MOF-808

64-2-200

PVDF-HFP / MIL-125

73-2-200

Co-MOF-PANI/ rGO-PANI

Separator

Li–S

441-5-600

[34]

PS@ZIF

Cathode

Li-Se

564-0.1-100

[22]

ZIF-8@PDSDA

Anode

LIB

940-0.1-430

[41]

SIB

125-0.1A/g-200

[42]

N-doped ZIF-8/PI Cathode ZnNi-MOF/PANI

Anode

SIB

80-0.5-1000

[45]

ZIF-67/PANI

Anode

KIB

299-1 A/g-400

[46]

ZIF-67/PPy

Cathode

ZAB

51.33 mF/cm2 and PD of 51.85 mW/ cm2

[47]

ZIF-67/PPy

Cathode

ZAB

746 mAh/g at 10 mA/cm2 and PD of 149 mW/cm2 and cycle stability up to 500 h

[48]

The Active Role of Conjugate Polymer Composites in Electrochemical …

225

5 Conclusion and Perspective To develop energy storage capabilities of upcoming devices, discovering novel materials is essential. Polymer-MOFs are unique and multifunctional structures compared to pristine MOFs or polymers, which could be modified by altering the concentration or type of additives, choosing suitable manufacturing techniques, and functionalizing the surface of the additives. Notably, the multifunctional feasibility of these materials extends their utility in all integral functional parts of batteries. The great safety, flexibility, and electrochemical functional features make them attractive materials for next-generation EES technologies. MIBs benefit from recent advancements in polymer-MOF functional materials for energy storage applications. Due to the synergistic interaction between CP and MOFs, EES devices have dramatically better electrochemical characteristics compared to traditional EES devices. However, there are still some practical difficulties. Despite having advantageous properties, precise structural alterations and impacts on the electrochemical process of polymer-MOF composites are yet unknown. Understanding their working mechanism is essential to produce high-quality, lowcost electrode materials. One of the biggest issues with polymer-MOF composite electrodes is production cost. Concerning scalability and processability, top-down approaches of polymer-MOF could use the synthetic diversity of MOFs to facilitate the utilization of inexpensive ligands, and metal precursors in the form of oxides, hydroxides, or carbonates. Along with this, more exposure to less energy-consuming approaches such as mechanochemical and microwave irradiation synthetic routes [49] could be better choices for large-scale manufacturing. Especially in the case of MIBs, the exposure of hybridization of the variety of novel MOFs with selfhealing conductive polymers such as PPy, PANI, and poly 3,4-ethlenedioxythiophene (PEDOT) could be the solution to mitigate critical issues of cycle-longevity and volume expansion. Although some literature on PANI and PPy-based MOF hybrids for LIBs is appreciable, further improvements and new combinations of self-healingCP integrated MOF are recommended to extend their application to all MIBs. Noteworthily, the self-healing and conductive functionalities of polymers are the main factors in attaining the structural feasibility and ion percolation of symmetric porous MOFs, making them ideal for excellent ionic conductivity, homogeneity, and very elasticity. The diversity of these combined properties makes it rational for various active roles as active cathode/anode, separator, and electrolyte materials for MIBs which can eventually avoid dendrite growth, and further enhance the cycle stability. Finally, the recently synthesized Ni-backboned polymer [50] is opening up opportunities to explore interesting functionalities in the combination of MOF for EES, however, synthetic challenges still need to be overcome. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF2021R1A2C1008272).

226

S. Vallem and J. Bae

References 1. Manthiram A (2020) A reflection on lithium-ion battery cathode chemistry. Nat Commun 11:1550 2. Muruganantham R, Gu Y-J, Song Y-D, Kung C-W, Liu W-R (2021) Ce-MOF derived ceria: Insights into the Na-ion storage mechanism as a high-rate performance anode material. Appl Mater Today 22:100935 3. Zhong M, Kong L, Li N, Liu Y-Y, Zhu J, Bu X-H (2019) Synthesis of MOF-derived nanostructures and their applications as anodes in lithium and sodium ion batteries. Coord Chem Rev 388:172–201 4. Liang Z, Zhao R, Qiu T, Zou R, Xu Q (2019) Metal-organic framework-derived materials for electrochemical energy applications. Energy Chem 1:100001 5. Kim D, Kim DW, Hong WG, Coskun A (2016) Graphene/ZIF-8 composites with tunable hierarchical porosity and electrical conductivity. J Mater Chem A 4:7710–7717 6. Thakur AK, Majumder M, Patole SP, Zaghib K, Reddy MV (2021) Metal-organic frameworkbased materials: advances, exploits, and challenges in promoting post Li-ion battery technologies. Mater Adv 2:2457–2482 7. Wu F, Liu Z, Wang J, Shah T, Liu P, Zhang Q, Zhang B (2021) Template-free self-assembly of MXene and CoNi-bimetal MOF into intertwined one-dimensional heterostructure and its microwave absorbing properties. Chem Eng J 422:130591 8. Baumann AE, Burns DA, Liu B, Thoi VS (2019) Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices. Commun Chem 2:86 9. Mehek R, Iqbal N, Noor T, Amjad MZ Bin, Ali G, Vignarooban K, Khan MA (2021) Metalorganic framework based electrode materials for lithium-ion batteries: a review. RSC Adv 11:29247–29266 10. Zhao R, Liang Z, Zou R, Xu Q (2018) Metal-organic frameworks for batteries. Joule 2:2235– 2259 11. Unnikrishnan V, Zabihi O, Ahmadi M, Li Q, Blanchard P, Kiziltas A, Naebe M (2021) Metalorganic framework structure-property relationships for high-performance multifunctional polymer nanocomposite applications. J Mater Chem A 9:4348–4378 12. Mechili M, Vaitsis C, Argirusis N, Pandis PK, Sourkouni G, Zorpas AA, Argirusis C (2022) Research progress in Metal-organic framework based nanomaterials applied in battery cathodes. Energies 15:5460 13. Xu JH, Di DC, Chen P, Tan LH, Chen CB, Fu JJ (2020) Intrinsic self-healing polymers for advanced lithium-based batteries: advances and strategies. Appl Phys Rev 7:031304 14. Kalaj M, Bentz KC, Ayala S, Palomba JM, Barcus KS, Katayama Y, Cohen SM (2020) MOF-Polymer hybrid materials: From simple composites to tailored architectures. Chem Rev 120:8267–8302 15. Yang S, Karve VV, Justin A, Kochetygov I, Espín J, Asgari M, Trukhina O, Sun DT, Peng L, Queen WL (2021) Enhancing MOF performance through the introduction of polymer guests. Coord Chem Rev 427:213525 16. Begum S, Hassan Z, Brase S, Tsotsalas M (2020) Polymerization in MOF-confined nanospaces: tailored architectures, functions, and applications. Langmuir 36:10657–10673 17. Valverde A, Gonçalves R, Silva MM, Wuttke S, Fidalgo-Marijuan A, Costa CM, Vilas-Vilela JL, Laza JM, Arriortua MI, Lanceros-Mendez S, Fernsndez de Luis R (2020) Metal-organic framework based PVDF separators for high rate cycling lithium-ion batteries. ACS Appl Energy Mater 3:11907–11919 18. Hossain MA, Tulaphol S, Thapa AK, Rahaman MS, Jasinski JB, Wang H, Sunkara MK, Syzdek J, Ozdemir OK, Ornstein JM, Sathitsuksanoh N (2021) Metal-organic framework separator as a polyselenide filter for high-performance lithium-selenium batteries. ACS Appl Energy Mater 4:13450–13460

The Active Role of Conjugate Polymer Composites in Electrochemical …

227

19. Winarta J, Meshram A, Zhu F, Li R, Jafar H, Parmar K, Liu J, Mu B (2020) Metal-organic framework-based mixed-matrix membranes for gas separation: An overview. J Polym Sci 58:2518–2546 20. Denny MS, Moreton JC, Benz L, Cohen SM (2016) Metal-organic frameworks for membranebased separations. Nat Rev Mater 1:16078 21. Denny MS Jr, Cohen SM (2015) In Situ Modification of Metal-organic frameworks in mixedmatrix membranes. Angew Chemie Int Ed 54:9029–9032 22. Tian H, Tian H, Wang S, Chen S, Zhang F, Song L, Liu H, Liu J, Wang G (2020) High-power lithium-selenium batteries enabled by atomic cobalt electrocatalyst in hollow carbon cathode. Nat Commun 11:5025 23. Schmidt BVKJ (2020) Metal-organic frameworks in polymer science: Polymerization catalysis, polymerization environment, and hybrid materials. Macromol Rapid Commun 41:1900333 24. Khatun A, Yadav A, Zhang S, Saha S (2022) Transforming an insulating metal-organic framework into electrically conducting metal-organic framework conducting polymer composites. Mater Today Chem 24:100981 25. Comito RJ, Fritzsching KJ, Sundell BJ, Schmidt RK, Dinca M (2016) Single-site heterogeneous catalysts for olefin polymerization enabled by cation exchange in a metal-organic framework. J Am Chem Soc 138:10232–10237 26. Tsotsalas M, Liu J, Tettmann B, Grosjean S, Shahnas A, Wang Z, Azucena C, Addicoat M, Heine T, Lahann J, Overhage J, Brase S, Gliemann H, Woll C (2014) Fabrication of highly uniform gel coatings by the conversion of surface-anchored metal-organic frameworks. J Am Chem Soc 136:8–11 27. Park IH, Chanthapally A, Lee HH, Quah HS, Lee SS, Vittal JJ (2014) Solid-state conversion of a MOF to a metal-organo polymeric framework (MOPF) via [2+2] cycloaddition reaction. Chem Commun 50:3665–3667 28. Kulak H, Thur R, Vankelecom IFJ (2022) MOF/Polymer mixed-matrix membranes preparation: effect of main synthesis parameters on CO2 /CH4 separation performance. Membranes 12:425 29. Pastore VJ, Cook TR, Rzayev J (2018) Polymer-MOF hybrid composites with high porosity and stability through surface-selective ligand exchange. Chem Mater 30(23):8639–8649 30. Maity N, Dawn A (2020) Conducting polymer grafting: recent and key developments. Polymers 12:709 31. Giliopoulos D, Zamboulis A, Giannakoudakis D, Bikiaris D, Triantafyllidis K (2020) Polymer/ metal-organic framework nanocomposites for biomedical applications. Molecules 25:1–28 32. Wu X, Zhou C, Dong C, Shen C, Shuai B, Li C, Li Y, An Q, Xu X, Mai L (2022) Polydopamine-assisted in-situ formation of dense MOF layer on polyolefin separator for synergistic enhancement of lithium-sulfur battery. Nano Res 15:8048–8055 33. Yang L-Y, Cao J-H, Cai B-R, Liang T, Wu D-Y (2021) Electrospun MOF/PAN composite separator with superior electrochemical performances for high energy density lithium batteries. Electrochim Acta 382:138346 34. Zhou C, He Q, Li Z, Meng J, Hong X, Li Y, Zhao Y, Xu X, Mai L (2020) A robust electrospun separator modified with in situ grown metal-organic frameworks for lithium-sulfur batteries. Chem Eng J 395:124979 35. Barbosa JC, Gonçalves R, Valverde A, Martins PM, Petrenko VI, Márton M, Fidalgo-Marijuan A, Fernández de Luis R, Costa CM, Lanceros-Mendez S (2022) Metal-organic framework modified poly(vinylidene fluoride-co-hexafluoropropylene) separator membranes to improve lithium-ion battery capacity fading. Chem Eng J 443:136329 36. Liang F, Wen Z (2021) MOF/Poly(Ethylene Oxide) composite polymer electrolyte for solidstate lithium battery. J Inorg Mater 36:332–336 37. Liu Y, Zeng Q, Chen P, Li Z, Chen A, Guan J, Wang A, Zhang L (2022) Modified MOF-based composite all-solid-state polymer electrolyte with improved comprehensive performance for dendrite-free Li-ion batteries. Macromol Chem Phys 223:2100325 38. Wen W, Wang Z, Wang A, Zeng Q, Chen P, Wen X, Li Z, Li Z, Liu W, Zhang L (2021) A Metalorganic framework-5-incorporated all-solid-state composite polymer electrolyte membrane with enhanced performances for high-safety lithium-ion batteries. Energy Technol 9:2000808

228

S. Vallem and J. Bae

39. Yang H, Liu B, Bright J, Kasani S, Yang J, Zhang X, Wu N (2020) A Single-ion conducting UiO-66 metal-organic framework electrolyte for all-solid-state lithium batteries. ACS Appl Energy Mater 3:4007–4013 40. Angulakshmi N, Zhou Y, Suriyakumar S, Dhanalakshmi RB, Satishrajan M, Alwarappan S, Alkordi MH, Stephan AM (2020) Microporous metal-organic framework (MOF)-based composite polymer electrolyte (CPE) mitigating lithium dendrite formation in all-solid-state lithium batteries. ACS Omega 5:7885–7894 41. Idrees M, Batool S, Javed MS, Ud Din MA, Imran M, Chen Z (2022) Preferred coordination of polymers at MOFs enables improved lithium-ion battery anode performance. Mater Chem Front 6:1690–1705 42. Chu R, Song H, Ullah Z, Guan Z, Zhang Y, Zhao L, Chen M, Li W, Li Q, Liu L (2020) ZIF-8 derived nitrogen-doped carbon composites boost the rate performance of organic cathodes for sodium ion batteries. Electrochim Acta 362:137115 43. Milakin KA, Gavrilov N, Pasti IA, Moravkova Z, Acharya U, Unterweger C, Breitenbach S, Zhigunov A, Bober P (2020) Polyaniline-metal organic framework (Fe-BTC) composite for electrochemical applications. Polymer 208:122945 44. Cao D, Kang W, Wang W, Sun K, Wang Y, Ma P, Sun D (2020) Okra-Like Fe7 S8 /C@ZnS/NC@C with core-double-shelled structures as robust and high-rate sodium anode. Small 16:1–11 45. Mubarak N, Ihsan-Ul-Haq M, Huang H, Cui J, Yao S, Susca A, Wu J, Wang M, Zhang X, Huang B, Kim J-K (2020) Metal-organic framework-induced mesoporous carbon nanofibers as an ultrastable Na metal anode host. J Mater Chem A 8:10269–10282 46. Atangana Etogo C, Huang H, Hong H, Liu G, Zhang L (2020) Metal-organic-frameworksengaged formation of Co0.85 Se@C nanoboxes embedded in carbon nanofibers film for enhanced potassium-ion storage. Energy Storage Mater 24:167–176 47. Li Y, Cao R, Li L, Tang X, Chu T, Huang B, Yuan K, Chen Y (2020) Simultaneously integrating single atomic cobalt sites and Co9 S8 nanoparticles into hollow carbon nanotubes as trifunctional electrocatalysts for Zn-Air batteries to drive water splitting. Small 16:1–10 48. Zhou Q, Zhang Z, Cai J, Liu B, Zhang Y, Gong X, Sui X, Yu A, Zhao L, Wang Z, Chen Z (2020) Template-guided synthesis of Co nanoparticles embedded in hollow nitrogen doped carbon tubes as a highly efficient catalyst for rechargeable Zn-air batteries. Nano Energy 71:104592 49. Raptopoulou CP (2021) Metal-organic frameworks: Synthetic methods and potential applications. Materials 14:310 50. Zeng K, Yang Y, Xu J, Wang N, Tang W, Xu J, Zhang Y, Wu Y, Xu Y, Wang G, Chen P, Wang B, Sun X, Jin G, Peng H (2023) Metal-backboned polymers with well-defined lengths. Angew Chemie Int Ed 62:e202216060

Redox-Active Polymeric Materials Applied for Supercapacitors Rudolf Kiefer, Phuong Nguyen Xuan Vo, Natalia E. Kazantseva, Petr Saha, and Quoc Bao Le

Abstract Energy demand has become a significant factor in maintaining global economic stability. However, overusing fossil fuels in the last century has resulted in severe problems, such as climate change and a dangerous reliance on limited natural resources. As a result, the development of alternative energy resources has become imperative, and attention has shifted to energy storage devices and energy harvesting. Alongside batteries, supercapacitors (SCs) have emerged as promising technology due to their unique advantages. One key advantage of SCs is that they can be fabricated using various materials, many of which are not resource-limited. Among these materials, conductive polymers and naturally abundant polymers such as cellulose have become increasingly popular in SC electrode applications due to their high capacitance and pseudocapacitance, which can result in improved SC performance. Moreover, these materials can also use abandoned materials that contribute to plastic and waste pollution. This chapter provides an overview of recent research and future directions in polymer applications for SC development, which may offer a potential solution for the future energy supply. Keywords Electrochemical devices · Supercapacitors · Conducting polymers · Cellulose · Hydrogels

R. Kiefer Conducting Polymers in Composites and Applications Research Group, Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam P. N. X. Vo Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam N. E. Kazantseva · P. Saha · Q. B. Le (B) University Institute, Tomas Bata University, Nad Ovˇcírnou 3685, 760 01 Zlin, Czech Republic e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_13

229

230

R. Kiefer et al.

1 Introduction SCs usually contain many mesoporous materials that can store a large amount of charge (energy) and, in the ideal case, have high-capacity retention over several thousand cycles. The first SC was invented in the 1960s by Standard oil company (SOHIO) in a simplified design using activated charcoal as electrode materials separated by a thin insulator, with its first application in backup power for computer memory maintenance. The first electrochemical devices were designed to operate at low voltage in an electrolyte, and this basic principle is still used in today’s designs. This chapter covers the various materials used in capacitors and the polymers that make up these devices. Different mesoporous carbon particles are nowadays applied from carbide-derived carbon (CDC), carbon nanotubes (CNT), activated carbon aerogels (ACA), and reduced graphene oxide (rGO), as well as the combination of those with different inorganic additives. There are two classes of capacitors, depending on the principle of their action: electric double capacitors (EDLC) based on carbon materials where at charging/discharging, an electrical double layer (EDL) is formed over ioninjection [1], and pseudocapacitors (PCs) based on different metal oxides such as polyoxometalates and conducting polymers belonging to the faradaic process where charging/discharging occurs over oxidation/reduction [2]. We focus on the electrode material (SCs), their charging/discharging capability, and properties such as conductivity and mesoporous structure. The electrochemical SCs occur in electrode systems (2-electrode or 3-electrode) where the electrolytes play an essential role in their ionic conductivity, size, and mobility. In the case of CNT materials mainly following the EDL process, the charging at positive voltage leads to positive charges created on CNT defects with EDL formation regarding the ions (anions) of the electrolyte. CNT and carbon-related materials such as CDC and ACA also have actuation functionalities. In contrast, over-induced ion injection changes in C–C length occur [3]. Conducting polymers are often used as a matrix, providing better conductivity (ionic and electronic) which enhances the stability and capacity of the embedded carbon particles [4]. Using conducting polymers as a matrix for carbon particles, it also needs to consider that reversible volume change leads to actuation properties. It is an issue for SCs materials in delamination. Mass-production printing technology is getting more favored. Furthermore, conducting polymers such as PEDOT:PSS are preferred due to their high conductivity and liquid form that can solubilize carbon particles. Recent research [5] revealed that printed PEDOT:PSS with ACA is possible but has an issue with delaminations. With the growing emphasis on green technology, natural polymers such as chitosan and cellulose are attracting significant attention for their potential use as ion reservoirs. Research is focused on developing flexible supercapacitors with high specific capacitance and improved flexibility, self-healing properties, and electrolyte reservoirs. Researchers are exploring conducting polymers, metal oxides, carbon particles, and organic metal frameworks to achieve these goals. The most recent research in this area has been conducted using hydrogels. [6].

Redox-Active Polymeric Materials Applied for Supercapacitors

231

The new trend to acquire mass production of flexible supercapacitors is focused on 2D and 3D printing [7], with some examples in each section.

2 EDLC and PC and Their Principal Mechanism of Action Upon the working mechanism, SCs can absorb and release the charge quickly. SCs have two subdivisions: Electrochemical Double Layer Capacitors (EDLCs) and Pseudocapacitors. Generally, each SC has two conducting electrodes, insulating dielectric material, and a separator. When an SC performs, under voltage applied, the opposite charges are accumulated on the surface of each electrode, making the electrical fields that make its energy storage. The EDLC and pseudocapacitor’s working mechanisms are shown in Fig. 1. As shown in Fig. 1a, the charges accumulate at the surfaces between electrodes and electrolytes when voltage is applied. EDLC function is caused by the electrons moving from the anode to the cathode through the external circuit. Inside the cell, anions move toward the cathode, and cations move toward the anode. The storage capacitance of SCs results from those charged particles accumulated at the interfaces of electrodes. During the discharging processes, electrons and ions move in reverse. This mechanism explains why there is no Faradaic reaction in EDLC [8]. On the other hand, pseudocapacitor (also called faradic supercapacitor) has a different working principle from EDLC (Fig. 1b). During the charge/discharge process, fast and reversible faradaic reactions occur at the inner surfaces of electrodes and electrolytes. The ions made by reactions travel through the double layers of SC. The faradaic processes inside SCs lead to higher energy density and better specific capacitance than EDLC. Pseudocapacitors are also hindered by their low power density and lack of cycling stability. However, due to the wide range of materials, such as metal oxides and conducting polymers, pseudocapacitors play a significant role in

Fig. 1 a The EDLC and b Pseudocapacitor [5]

232

R. Kiefer et al.

energy storage devices. The combination of materials has potential applications due to the working conditions of devices [8]. As shown in Fig. 1, one SC can be defined as two capacitors in series containing electrodes and electrolytes interfacing with each other. Usually, the overall capacitance (CT ) of the electrodes can be expressed as follows [9]: 1 1 1 = + CT C1 C2

(1)

When considering the capacitances of discrete electrodes, C1 and C2 , in a supercapacitor (SC), the total capacitance (CT ) can be calculated by adding the capacitances of both electrodes. However, if the SC is symmetrical, C1 and C2 are equal, and CT can be calculated as half of the sum of both capacitances. CS , which is commonly used to evaluate an SC’s capacitance, can be calculated using various methods, such as normalizing to the device’s surface area, volume, or mass or using the electric and relative dielectric constant, the specific surface area of the electrodes, and their separation distance. One standard method for calculating Cs is by using the galvanostatic charge–discharge curves. It should be noted that if one of the electrodes has a smaller capacitance, it dominates the overall CT , resulting in an imbalanced SC [10]. The specific capacitance of the two-electrode SC value can be calculated as follows: Cs = 4

I.Δt m t .ΔV

(2)

where I is the average anodic and cathodic current, Δt is the time taken for the discharge process, ΔV is the discharge potential, and mt is the total weight of active materials of two electrodes. In case the SC has two similar electrodes materials with the same mass (ms ), Cs can be defined as: Cs = 2

I.Δt m s .ΔV

(3)

The specific energy E(J) stored inside SC can be determined via the specific capacitance as: E=

1 C(ΔV )2 2

(4)

It can be noted that SC voltage decreases linearly with the state of charge [11]. The phenomenon leads to the use of energy stored inside SC may not be used at all. Therefore, one strategy to increase an SC’s energy density is increasing its capacitance and working potential. However, each material and device have a limit. While the capacitance depends on the materials’ properties, an SC’s working potential must follow the safety instruction since a significant increase in working potential would cause seriously unpredicted problems. One factor of an SC is the maximum instantaneous power Pmax that can be delivered. It is calculated via the equivalent resistance

Redox-Active Polymeric Materials Applied for Supercapacitors

233

(R) of the cell as follows: Pmax =

(ΔV )2 4R

(5)

The electrochemical properties of an SC are mainly dependent on its components. Every change in electrode material, electrolyte, or separator may cause a significant difference in the working performance of an SC. For the SC design to work with polymeric materials is a potential reaching strategy to improve SC working performance in the future.

3 Conducting Polymer Nanocomposites Combining pseudocapacitors (metal oxides or conducting polymers) with EDLC materials enhances performance with better flexibility, conductivity, and capacitance [2]. EDLC materials have high cycle stability and power density, but their drawbacks are reduced energy density. Pseudocapacitors have high energy density and can provide improved electronic and ionic conductivity due to conducting polymers. Different conducting polymers such as polypyrrole (PPy), polyaniline (PANI), and polythiophene (PTh, PEDOT) have been chosen to combine carbon-related EDLC with envisaged performance in flexibility, capacitance, and energy density [12]. The disadvantages of conductive polymers are their low cycle stability due to the drainage of ionic charge carriers [13] and their conductivity, obtained only in the oxidized state. Metal oxides belong to the redox-reactive capacitors, with conducting polymers or in the ternary combination of CP, MO, and carbon materials (2PCs with EDLCs). There are many options for combining various materials. One of them is the use of nanomaterials in binary or triple combinations. Figure 2a gives some examples of flexible SCs in binary and ternary combinations of PEDOT:PSS with MnO2 (Fig. 2a), PPy included rGO and MnO2 (Fig. 2b), and electropolymerization of PPy with either POM (PTA phosphotungstic acid) and in combination with CDC (Fig. 2c). Conducting polymers in oxidative polymerization requires oxidants (APS, FeCl3 ), and once they are formed, no solvent can dissolve them. Oxidative polymerization can be done by putting monomers in an oxidant solution where colloidal particles sink to the bottom or creating thin films on substrates. Combining inorganic metals (SiO2 , MnO2 , polyoxometalates (POMs), and others) leads to a more stable form of those nanomaterials where the CP is functionalized as the binder. Metal oxides like manganese oxides have high pseudocapacitance (theoretically of about 1370 F g−1 [17]) and fast reaction kinetics. The disadvantages of MnO2 are that its conductivity is very low; therefore, it is usually combined with either carbon materials or conducting polymers. Figure 2a displays such a system where MWCNT are solubilized with the help of TritonX in solution, adding PEDOT:PSS (40%) wrapped around MWCNT (4%), and an electrode was formed where MnO2 was electrodeposited on the surface

234

R. Kiefer et al.

Fig. 2 a PEDOT:PSS wrapped around MWCNT with MnO2 electrodeposition showing the scheme of formation, SEM image of the electrode, MnO2 electrodeposition time given specific capacitance and capacity retention. Aadapted with permission [14], Copyright 2022, Elsevier. b Ternary combination of PPy and MnO2 nanoparticles incorporated in rGO sheets showing scheme and SEM of obtained composite with cyclic voltammetry of compounds in aqueous Na2 SO4 (1 M) electrolyte with specific capacitance retention (1000 cycles). Aadapted with permission from Ref. [15], Copyright 2022, Elsevier. c Binary and ternary combination of PPy doped with dodecyl benzene sulfonate in aqueous solution or ethylene glycol solution with the addition of POM (PTA) and addition of PTA + CDC forming PPy-PT (EG) and PPyCDC-PT (EG) composites (PT phosphotungstic anions). The SEM images are shown, and the specific capacitance against applied current densities in LiTFSIPC and LiTFSI-aq electrolytes. Adapted with permission of Ref. [16], Materials, Copyright 2022, MDPI

of PEDOT:PSS/MWCNT. The specific capacitance at optimal deposition time of MnO2 found at 900 s with specific capacitance shown 428.2 F g−1 (10 mV s−1 , 0.1 M Na2 SO4 ) and capacity retention (4 A g−1 ) of 82% after 2000 cycles. Other conducting polymers, such as PPy, are often applied, as shown in Fig. 2b, by using rGO nanosheet with adding MnO2 and PPy nanoparticles and investigating their specific capacitance in 1 M Na2 SO4 by changing rGO:MnO2 :PPy ratio. The best specific ccapasitance was achieved with a ratio of 2: 1: 2, detected at 682 F g−1 (scanning speed of 5 MV S-1) with a power of 89% (1000 cycles) [15]. Electropolymerization of CP, including MO, such as POM, and carbon-related particles, such as CDC, is another way to combine binary and ternary composites (Fig. 2c). The advantages of electropolymerization compared to oxidative polymerization (Fig. 2a, b) are better electronic conductivity, avoiding overoxidation and degradation, and being suitable for flexible electrodes in supercapacitor devices. POMs are polyanion metal clusters having two or more transition metals. For example, the Keggin anion [PW12 O40 ]3− (there are many other POM types of several transition metals linked over oxo clusters) has been shown in different combinations of conducting polymers (PPy and PANI), enhancing their pseudocapacitance [18]. Carbon particles (modified or POMs) can be directly added to monomer solution as additional dopants forming stable composites to include different particles. The binary combination of PPy with POM polymerized in EG solvent (PPyPT EG) in aqueous NaClO4 (0.1 M) had 130

Redox-Active Polymeric Materials Applied for Supercapacitors

235

Table 1 Specific capacitance Cs, electrolytes applied, and retention rate of CP composites Composites

Cs

Electrolyte

Retention (cycles)

References

rGO/ Cu-MOF@PANI

276.6 F g−1 (0.5 A g−1 )

H2 SO4 (1 M) aq

92.5% (5000)

[19]

rGO/Fe2 O3 -PANI

281.1 F g−1 (0.5 A g−1 )

HCl aq

76% (3000)

[20]

PPy/DBS-PT

223 F g−1 (0.09 A g−1 )

LiTFSI (0.1 M) 94% (1200) aq

[21]

PPy + C3 N4

810 F g−1 (0.2 A g−1 )

LiClO4 -ACN (0.1 M)

92% (6000)

[22]

PMo12 /PPy/CNT

1308 F g−1 (1 A g−1 )

IL (1 M)

81.5% (3000)

[23]

F g−1 , and with CDC forming PPyCDC-PT EG showed 190 F g−1 at 0.05 A g−1 [16] with capacity retention of 90% (1000 cycles). The electropolymerized composites’ primary focus is supercapacitors and dual functionality in actuators or sensors. There are a lot of different combinations of CP with MO and carbon-related materials, as shown in Table 1. Table 1 demonstrates which metal oxide applied with and without carbon materials using CP leads to acceleration of the specific capacitance. Accordingly, the best specific capacitance is achieved with POMs (PMo12 ) in combination with PPy and CNT, besides PPy + C3 N4 (carbon nitride) also shows promising capacitance. Numerous research and combination of CP with metal oxide and carbon are reported annually. The study aims to develop 3D-printed SCs that allow the homogeneous distribution of carbon particles in the composite.

4 Cellulose-Based Supercapacitor Composites Cellulose is one of the most abundant natural polymers (polysaccharides) consisting of β-1,4 D-glucose units, where its strength (tensile strength 7.5–7.7 GPa [24], more potent than Kevlar fiber) is referred to as inter- and intra-molecular hydrogen bonds. To obtain flexible supercapacitors, research using cellulose with the combination of nanocarbon materials and other pseudocapacitors is conducted [24]. The main direction of the cellulite study (Microcrystalline Elgulose MCC, Nano-Cellulose NC, bacterial cellulose of BC) is associated with its use as a matrix in fiber, paper, and textiles [25]. There are various methods, such as grafting, plasma treatment, or coatings. In this section, we focus on only a few, including dissolving cellulose and adding particles in suspension with fiber formation in electrospinning or printing [26] and coatings on cellulose fibers. Their application varied from SCs, batteries, sensors, actuators, and flexible electronics. Figure 3 gives examples of cellulosebased composites with different information and components.

236

R. Kiefer et al.

Fig. 3 Formation of cellulose composites showing in a In situ polymerization using PPy (oxidative polymerization with APS) and cellulose nanofibers (CFs) forming PPy@CFs and with doping of AQS (anthraquinone sulfonate) and para-toluene sulfonate (p-TSA) forming composite PPy:AQS/ p-TSA@CFs. The scheme of formation is shown, as well as the SEM images of PPy@CFS and PPy:AQS/p-TSA@CFs, with specific capacitance against the current density and capacity retention of both samples. Adapted with permission [27], Copyright 2022, MDPI. b Electrospinning of the core material of CNT with nano-cellulose (CNC) forming with polyvinylalcohol (PVA) and polyacrylic acid (PAA) a fiber network (SEM image). PANI (polyacrylonitrile) are chemically polymerized on those (PANI@ CNT-CNC/PVA-PAA) with different polymerization times with specific capacitance determined in H2 SO4 (1 M) in the flat and bending twisted state. Adapted with permission [28]. Copyright 2022, American Chemical Society. c Printing of PEDOT:PSS (P:P) with cellulose forming an ink where activated carbon (AC) and carbon black (CB) are added and printed on substrates showing the procedure, the ratios of P:P cellulose to AC and CB, and their ternary plots of the specific capacitance normalized. Adapted with permission [29], Copyright 2022, Elsevier

The simple form to obtain flexible cellulose composites are coatings of cellulose fibers using pyrrole monomer cellulose nanofibers and making in-situ oxidative polymerization with APS (ammonium persulfate) (Fig. 3a). Different dopants are also used to increase the charging/discharging rate with AQS and p-TSA forming PPy:AQS/p-TSA@CFs. The specific capacitance (pseudocapacitors) for PPy:AQS/ p-TSA@CFs showed 829.8 F g−1 (PPy@CFs had 261.9 F g−1 ) at 0.2 A g−1 (0.6 M H2 SO4 ) with capacity retention after 1000 cycles showed 96% retention [27]. To bring carbon particles into cellulose, the cellulose has to be dissolved using ionic liquids, which break the most commonly applied inter-intramolecular hydrogen bonds between cellulose units. Carbon particles can be mixed within, and such suspension can be applied for extrusion or wet spinning. One example of given extrusion with recently including activated carbon aerogels (ACA) or carbide-derived carbon (CDC) forming Cell-ACA with specific capacitance found at 48 F g−1 and

Redox-Active Polymeric Materials Applied for Supercapacitors

237

Cell-CDC at 36 F g−1 (0.2 A g−1 ) in lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in propylene carbonate (PC) [30]. Recent work applied regenerated cellulose with functionalized CNT ( f -CNT, introducing carboxyl groups on CNT over acid treatments), forming films. MnO2 was electrodeposited on cellulose/f -CNT films, and the specific capacitance of the composite did reach 7.95 F cm−2 (1 mA cm−2 ) in 1 M H2 SO4 with capacity retention of 79% (10.000 cycles). In contrast, the inclusion of PPy in Cellulose with f -CNT had an areal capacitance of 2.15 F cm−2 at the same current density with capacity retention above 100% after 5000 cycles [31]. Electrospinning is now applied to many composites. Figure 3b shows crystalline nano-cellulose (CNC) with CNT (8 wt.%) in PVA and PAA solution. When electrospinning, nanofibers of CNT-CNC/ PVA-PAA are made. Due to their low conductivity, PANI was chemically coated (oxidative polymerization) at 3 h, 6 h, 9 h, and 12 h on the nanofibers forming PANI@CNT-CNC/PVA-PAA composites [28]. The best results were obtained with a duration of 6 h: the lower effect of the coating of nano-pores on the fiber (PaNI@CNC-CNT/PVA-PAA) was achieved, with a specific capacitance of 155.5 F g−1 (1 A g−1 , 1 M H2 SO4 and capacity retention (2000 cycles) in flat (92%), bending (90%) and twisted (89%) formation. Another direction using MWCNT cellulose composites forming over electrospinning fibers is additional carbonization of those with capacitance achieved (6 wt.% MWCNT) found at 145 F g−1 (10 A g−1 ) in 6 M KOH [32]. Making fibers or films over extrusion or electrospinning is not applicable in most cases to mass production. Therefore if composite can be printed on flexible substrates, more precise paper supercapacitors can be formed [29] within Fig. 3c to reflect such printing technology. The composition of the ink was made by PEDOT:PSS cellulose, which functionalized as glue for activated carbon (AC) and carbon black (CB). The specific capacitance can be optimized with the variation of those components (Fig. 3c). The combination AC/CB P:P cellulose showed the best particular capacitance up to 100–105 F g−1 , with the second best found for AC/P:P cellulose with 82–85 F g−1 (Fig. 3c) at the current density of 0.2–0.4 A g−1 (electrolyte 1 M NaCl) [29]. Besides numerous combinations of cellulose with EDLC or PCs, their application is not limited to supercapacitors aiming at printable electronics, sensors, actuators, and several more [33].

5 Flexible Hydrogel Supercapacitors For SC electrodes, the charging/discharging capabilities, the pore size of the applied material, and the electronic and ionic conductivity are essential. As seen in previous sections, conducting polymers or cellulose plays a vital role in the SC performance in the matrix where those SC materials are embedded. Hydrogels (at least 10 wt% water) are known for their flexibility, excellent ionic conductivity, highly stretchable, self-healing, and low-temperature resistance [34]. In general, those hydrophilic polymers as host materials are water soluble same for cross-linkage agents that

238

R. Kiefer et al.

form the hydrogels that became insoluble in water but had high water affinity. Different cross-linkages are made over thermo-condensation, self-assembling, ionic gelation, electrostatic, and chemical (hydrogen bonds, ionic bonds, and hydrophobic interactions). The most applied polymers for such are polyvinyl alcohol (PVA) with H2 SO4 having excellent ion conductivity up to 82 mS cm−1 or polyacrylamide (PAAm) with the addition of Ca2+ or alginate having 33.7 mS cm−1 forming self-healing hydrogels applied as the matrix in several combinations of CPs, MO and carbon materials. Recent research used activated carbon cloth in combination with MnO2 in PVA/H2 SO4 hydrogel, establishing a self-healing flexible hydrogel with specific capacitance found at 886.7 mF cm−2 (1 mA cm−2 ) with capacitance retention at 87% (10.000 cycles) [35]. Another combination using PAAm as a hydrogel matrix with cellulose and in-situ polymerization of PANI revealed a specific capacitance of 835 mF cm−2 (1 mA cm−2 ) with a capacity retention of 96% after 5000 cycles [36]. Having an excellent ionic conductivity network also conducting polymers used as such are coming more in focus with past research [37] showing that PPy chemically oxidized with ammonium persulfate (APS) and NaDBS did lead to PPy hydrogels having a specific surface area up to 425.8 m2 g−1 and specific capacitance of 159.1 F g−1 . PANI hydrogels using APS as an oxidant have been established with a specific capacitance of 750 F g−1 (1 A g−1 ) [4]. Furthermore, PEDOT:PSS presented as the first hydrogel is widely applied for its good electronic (88 S cm−1 ) and ionic conductivity, with a specific capacitance of 202 mF cm−2 (0.54 mA cm−2 ) and retention of 100% after 10,000 cycles [38], while other reported a specific capacitance of 158 F g−1 (50 mV s−1 ) with capacitance retention of 85% after 2000 cycles [39]. Figure 4 gives some examples of hydrogels in combination with conducting polymers, including carbon materials and MO. Figure 4a shows rGO /Mn/Cu MOF hydrogels with the addition of PANI (insitu polymerization using APS), forming M1P and M2P. The specific capacitance at current density 0.5 A g−1 of M1 was found at 163 F g−1 , M2 at 135 F g−1 , and M1P at 225.8 F g−1 , and the best in this study showed M2P with 276.6 F g−1 . Due to PANI degradation, the best capacity retention of M1 and M2 was found at 92% (1 A g−1 , 5000 cycles) [19]. There are some drawbacks to using conducting polymers to obtain the flexibility of hydrogels, with most conducting polymers’ stretchability found to be smaller than 10%. PANI is the most applied conducting polymer in hydrogels with the combination of cellulose nanofiber (TEMPO + borax) forming TOCNF with CNT and PANI (in situ polymerization with different amounts of PANI using APS as an oxidant) and PVA (Fig. 4b). The specific capacitance of TOCNF-CNT@PANIPVA-2 (mass ration ANI to TOCNF 1:1) had 226.8 F g−1 (0.4 A g−1 , 6 M KOH) with capacitance retention (bending, twisting) at 85% (1000 cycles) [40]. Recent research (Fig. 4c) showed that using ideal candidates for hydrogels (PANI/PVA) in combination leads to stretchable conducting polymers interpenetrating double networks. To obtain microstructure, liquid-phase synthesized hydrogels (LpG) PANI/ PVA were applied, and for hierarchical nanostructure formation, ice-templating and polymerization at low temperatures are made to get ice-templating gels (ItG) [41]. Those double interpenetrating networks’ (ItG) stretchability is 29-fold improved

Redox-Active Polymeric Materials Applied for Supercapacitors

239

Fig. 4 a Reduced graphene oxide (rGO) used as a matrix with the addition of Mn/Cu metal– organic framework (MOF) and PANI forming hydrogel SCs showing formation procedure of M1 (rGO/Mn-MOF aerogel), M2 (rGO/Cu-MOF), M1P (rGO/Mn-MOF@PANI) and M2P (rGO/CuMOF@PANI). The SEM images of M2P are shown, and the specific capacitance of all samples in 1 M H2 SO4 . Adapted with permission [19]. Copyright 2022, Scientific Reports, Springer Nature. b Nanocellulose fiber combined with polyvinyl alcohol (PVA)-borax and TEMPO forming TOCNF combined with CNT and PANI in hydrogels (TOCNF-CNT@PANI-PVA) showing SEM images and interaction scheme of different components with specific capacitance against current densities (electrolyte 6 M KOH). The self-healing scheme and bending/twisted capacitance retention are shown as well. Adapted with permission [40]. Copyright 2022, MDPI. c PANI/PVA hydrogels either made conventional in the liquid phase (LpG) or over ice templating and polymerization at low temperature (ItG) forming a double interpenetrating network. The ItG has improved mechanical, electrical, and electrochemical properties. Adapted with permission [41]. Copyright 2022, Elsevier

(Fig. 4c). The electrical conductivity was 89 times better with a specific capacitance twofold higher (compared to LpG), showing 888 Fg−1 (1 M H2 SO4 , 0.5 A g−1 ) with capacity retention of 90% (1000 cycles, 10 Ag−1 ). The application range of such high stretchable SCs can be found in strain sensors for motion detection or in stretchable electronics [41].

6 Future Perspective The current industry demand for flexible supercapacitors necessitates innovation to achieve excellent capacitance, stretchability, lightweight, and high charging/ discharging properties with a small applied voltage range. These flexible supercapacitors can be made either for bulk production or micro-fabrication in mass production. Researchers have developed various types of flexible supercapacitors, with some

240

R. Kiefer et al.

exhibiting excellent capacitance and durability. A promising approach is the combination of pseudocapacitors and electrical double-layer capacitors using conducting polymers, cellulose, carbon, and metal oxides, which can provide capacitance up to 1000 F g−1 [13]. One drawback of flexible supercapacitors is their complex formulation, making mass production expensive and reproducibility challenging. However, advancements in printed electronics have led to the development of electrodes that can function as supercapacitors [42], as shown in Fig. 3c, using materials such as PEDOT:PSS, cellulose, and carbon particles [29]. When PEDOT:PSS is printed on a flexible substrate that provides good surface adhesion and no delamination, a specific capacitance of up to 193 F g−1 can be achieved in an aqueous electrolyte, with values around 100 F g−1 in an organic electrolyte [43]. Another direction in developing flexible supercapacitors is 3D printing, which is well-suited for producing special microdevices for specific applications [44]. Table 2 overviews the latest developments in printed flexible supercapacitor materials. It highlights the potential of printed flexible electrodes to achieve high specific capacitance even in micro-fabrication. This technology, including 3D or 4D printing, offers many perspectives for various highly efficient applications [50]. Researchers have recently demonstrated a 4D printed material that can change its shape in response to temperature changes, showing potential for energy storage applications. Overall, flexible supercapacitors offer many advantages for various applications, but their complex formulation and mass production challenges still need to be addressed. Advances in printed electronics, especially 3D and 4D printing, offer new possibilities for developing high-capacity, stretchable, and lightweight supercapacitors. These developments could pave the way for new energy storage applications like wearables and internet devices. Table 2 Printing (ink-jet, 2D, and 3D) of flexible supercapacitors, specific capacitance Cs , applied electrolyte, and capacity retention Materials

Procedure

Specific capacitance (scan rate)

MnHCF-MnOx/ Screen-printing 467 F g−1 (1 A g−1 ) rGO

Electrolyte Retention References (cycles) 0.5 M Na2 SO4

80.4% (5000)

[45]

1M H2 SO4

64% (500)

[46]

81.5% (1000)

[47]

93% (3000)

[48]

88% (10.000)

[49]

Graphene

Ink-jet printing 192 F g−1 (20 mV s−1 )

RuO2 / PEDOT:PSS/ graphene

Screen-printing 820 F g−1 (0.5 A g−1 ) 0.5 M H2 SO4

PEDOT:PSS/ MnO2

3D printing micro SCs

135.4 mF cm−2 (0.08 mA cm−2 )

PEDOT:PSS/ CNT/rGO

4D printing

21.7 F g−1 (0.5 A g−1 ) PVA-KCl

PVA-LiCl

Redox-Active Polymeric Materials Applied for Supercapacitors

241

Acknowledgements This work was also supported by the Horizon Europe project TwinVECTOR of the European Union (Grant Agreement No. 101078935).

References 1. Cao Y, Li S, Xu C, Ma X, Huang G, Lu C, Li Z (2021) Mechanisms of porous carbon-based supercapacitors. ChemNanoMat 7:1273–1290 2. Liu L, Zhao H, Lei Y (2019) Review on nanoarchitectured current collectors for pseudocapacitors. Small Methods 3:1–25 3. Kosidlo U, Omastova M, Micusik M, Ciric-Marjanovic G, Randriamahazaka H, Wallmersperger T, Aabloo A, Kolaric I, Bauernhansl T (2013) Nanocarbon based ionic actuators-a review. Smart Mater Struct 22:104022 4. Han Y, Dai L (2019) Conducting polymers for flexible supercapacitors, macromol. Chem Phys 220. https://doi.org/10.1002/macp.201800355 5. Põldsalu I, Harjo M, Tamm T, Uibu M, Peikolainen AL, Kiefer R (2017) Inkjet-printed hybrid conducting polymer-activated carbon aerogel linear actuators driven in an organic electrolyte. Sensors Actuators, B Chem 250:44–51 6. Bashir, K. Hasan, M. Hina, R. Ali Soomro, M.A. Mujtaba, S. Ramesh, K. Ramesh, N. Duraisamy, R. Manikam (2021) Conducting polymer/graphene hydrogel electrodes based aqueous smart supercapacitors: a review and future prospects. J Electroanal Chem 898:115626 7. Kumar S, Saeed G, Zhu L, Hui KN, Kim NH, Lee JH (2021) 0D to 3D carbon-based networks combined with pseudocapacitive electrode material for high energy density supercapacitor: a review. Chem Eng J 403:126352 8. Le QB, Kiefer R, Dao TT, Kazantseva NE, Saha P (2022) Recent and future research related to the use of conducting polymers for supercapacitors. In: Gupta RK (ed) Springer International Publishing, Cham, pp 289–309 9. Zhong C, Deng Y, Hu W, Qiao J, Zhang L, Zhang J (2015) A review of electrolyte materials and compositions for electrochemical supercapacitors. Chem Soc Rev 44:7484–7539 10. Simon P, Gogotsi Y (2008) Materials for electrochemical capacitors. Nat Mater 7:845–854 11. Hall PJ, Mirzaeian M, Fletcher SI, Sillars FB, Rennie AJR, Shitta-Bey GO, Wilson G, Cruden A, Carter R (2010) Energy storage in electrochemical capacitors: designing functional materials to improve performance. Energy Environ Sci 3:1238 12. Meng Q, Cai K, Chen Y, Chen L (2017) Research progress on conducting polymer based supercapacitor electrode materials. Nano Energy 36:268–285 13. Shown I, Ganguly A, Chen LC, Chen KH (2015) Conducting polymer-based flexible supercapacitor. Energy Sci Eng 3:2–26 14. Lee HU, Yin JL, Park SW, Park JY (2017) Preparation and characterization of PEDOT:PSS wrapped carbon nanotubes/MnO2 composite electrodes for flexible supercapacitors. Synth Met 228:84–90 15. Zhou H, Yan Z, Yang X, Lv J, Kang L, Liu ZH (2016) RGO/MnO2 /polypyrrole ternary film electrode for supercapacitor. Mater Chem Phys 177:40–47 16. Tran CB, Zondaka Z, Le QB, Velmurugan BK, Kiefer R (2021) Polypyrrole with phosphor tungsten acid and carbide-derived carbon: change of solvent in electropolymerization and linear actuation. Materials (Basel) 14:6302 17. Yin C, Zhou H, Li J (2019) Facile one-step hydrothermal synthesis of PEDOT:PSS/MnO2 nanorod hybrids for high-rate supercapacitor electrode materials. Ionics (Kiel) 25:685–695 18. Genovese M, Lian K (2017) Polyoxometalates: molecular metal oxide clusters for supercapacitors. In: DeepakPG-R, Dubal P (eds) Metal oxides supercapacitors. Elsevier Inc., pp 133–164

242

R. Kiefer et al.

19. Le QB, Nguyen T-H, Fei H, Bubulinca C, Munster L, Bugarova N, Micusik M, Kiefer R, Dao TT, Omastova M, Kazantseva NE, Saha P (2022) Electrochemical performance of composite electrodes based on rGO, Mn/Cu metal–organic frameworks, and PANI. Sci Rep 12:1–13 20. Martins VHN, Siqueira NMS, Fonsaca JES, Domingues SH, Souza VHR (2021) Ternary nanocomposites of reduced graphene oxide, polyaniline, and iron oxide applied for energy storage. ACS Appl Nano Mater 4:5553–5563 21. Zondaka Z, Harjo M, Khan A, Khanh TT, Tamm T, Kiefer R (2018) Optimal phosphotungstinate concentration for polypyrrole linear actuation and energy storage. Multifunct Mater 1:14003 22. Gonçalves R, Paiva RS, Lima TM, Paixão MW, Pereira EC (2021) Carbon nitride/polypyrrole composite supercapacitor: boosting performance and stability. Electrochim Acta 368 23. Wang M, Zhang Y, Zhang T, Li Y, Cui M, Cao X, Lu Y, Peng D, Liu W, Liu X, Wang T, Huang Y (2020) Confinement of single polyoxometalate clusters in molecular-scale cages for improved flexible solid-state supercapacitors. Nanoscale 12:11887–11898 24. Moon RJ, Martini A, Nairn J, Simonsen J, Youngblood J (2011) Cellulose nanomaterials review: structure, properties and nanocomposites. Chem Soc Rev 40:3941–3994 25. Dutta S, Kim J, Ide Y, Ho Kim J, Hossain MSA, Bando Y, Yamauchi Y, Wu KCW (2017) 3D network of cellulose-based energy storage devices and related emerging applications. Mater Horizons 4:522–545 26. Zhao D, Zhu Y, Cheng W, Chen W, Wu Y, Yu H (2021) Cellulose-Based flexible functional materials for emerging intelligent electronics. Adv Mater 33:1–18 27. Yang S, Qian X (2022) Conductive PPy @ cellulosic paper hybrid electrodes with a redox active dopant for high capacitance and cycling stability. Polymers (Basel) 14:2634 28. Han J, Wang S, Zhu S, Huang C, Yue Y, Mei C, Xu X, Xia C (2019) Electrospun coreshell nanofibrous membranes with nanocellulose-stabilized carbon nanotubes for use as high-performance flexible supercapacitor electrodes with enhanced water resistance, thermal stability, and mechanical toughness. ACS Appl Mater Interfaces 11:44624–44635 29. Belaineh D, Brooke R, Sani N, Say MG, Håkansson KMO, Engquist I, Berggren M, Edberg J (2022) Printable carbon-based supercapacitors reinforced with cellulose and conductive polymers. J Energy Storage 50:104224 30. Kiefer R, Elhi F, Puust L, Peikolainen AL, Tamm T (2022) Dual function composite fibers of cellulose with activated carbon aerogel and carbide derived carbon. J Appl Polym Sci 139:1–12 31. Jyothibasu JP, Kuo DW, Lee RH (2019) Flexible and freestanding electrodes based on polypyrrole/carbon nanotube/cellulose composites for supercapacitor application. Cellulose 26:4495–4513 32. Deng L, Young RJ, Kinloch IA, Abdelkader AM, Holmes SM, De Haro-Del Rio DA, Eichhorn SJ (2013) Supercapacitance from cellulose and carbon nanotube nanocomposite fibers. ACS Appl Mater Interfaces 5:9983–9990 33. Agate S, Joyce M, Lucia L, Pal L (2018) Cellulose and nanocellulose-based flexible-hybrid printed electronics and conductive composites—a review. Carbohydr Polym 198:249–260 34. Cao X, Jiang C, Sun N, Tan D, Li Q, Bi S, Song J (2021) Recent progress in multifunctional hydrogel-based supercapacitors. J Sci Adv Mater Devices 6:338–350 35. Fan Z, Ren J, Zhang F, Gu T, Zhang S, Ren RP, Lv YK (2022) A flexible and self-healing supercapacitor based on activated carbon cloth/MnO2 composite. J Mater Sci 57:1281–1290 36. Li Y, Gong Q, Liu X, Xia Z, Yang Y, Chen C, Qian C (2021) Wide temperature-tolerant polyaniline/cellulose/polyacrylamide hydrogels for high-performance supercapacitors and motion sensors. Carbohydr Polym 267:118207 37. Temmer R, Kiefer R, Aabloo A, Tamm T (2013) Direct chemical synthesis of pristine polypyrrole hydrogels and their derived aerogels for high power density energy storage applications. J Mater Chem A 1:15216–15219 38. Cheng T, Zhang YZ, Wang S, Chen YL, Gao SY, Wang F, Lai WY, Huang W (2021) Conductive hydrogel-based electrodes and electrolytes for stretchable and self-healable supercapacitors. Adv Funct Mater 31:1–27 39. Bhat MA, Rather RA, Shalla AH (2021) PEDOT and PEDOT:PSS conducting polymeric hydrogels: a report on their emerging applications. Synth Met 273:116709

Redox-Active Polymeric Materials Applied for Supercapacitors

243

40. Wang H, Biswas SK, Zhu S, Lu Y, Yue Y, Han J, Xu X, Wu Q, Xiao H (2020) Self-healable electro-conductive hydrogels based on core-shell structured nanocellulose/carbon nanotubes hybrids for use as flexible supercapacitors. Nanomaterials 10:1–21 41. Zhao Y, Zhang B, Yao B, Qiu Y, Peng Z, Zhang Y, Alsaid Y, Frenkel I, Youssef K, Pei Q, He X (2020) Hierarchically structured stretchable conductive hydrogels for high-performance wearable strain sensors and supercapacitors. Matter 3:1196–1210 42. Liang J, Jiang C, Wu W (2021) Printed flexible supercapacitor: Ink formulation, printable electrode materials and applications. Appl Phys Rev 8 43. Põldsalu I, Rohtlaid K, Nguyen TMG, Plesse C, Vidal F, Khorram MS, Peikolainen AL, Tamm T, Kiefer R (2018) Thin ink-jet printed trilayer actuators composed of PEDOT:PSS on interpenetrating polymer networks. Sens Actuators, B Chem 258:1072–1079 44. Park SH, Goodall G, Kim WS (2020) Perspective on 3D-designed micro-supercapacitors. Mater Des 193:108797. https://doi.org/10.1016/j.matdes.2020.108797 45. Liang J, Tian B, Li S, Jiang C, Wu W (2020) All-printed MnHCF-MnOx-based highperformance flexible supercapacitors. Adv Energy Mater 10:1–10 46. Ervin MH, Le LT, Lee WY (2014) Inkjet-printed flexible graphene-based supercapacitor. Electrochim Acta 147:610–616. https://doi.org/10.1016/j.electacta.2014.10.006 47. Cho S, Kim M, Jang J (2015) Screen-printable and flexible RuO2 nanoparticle-decorated PEDOT:PSS/graphene nanocomposite with enhanced electrical and electrochemical performances for high-capacity supercapacitor. ACS Appl Mater Interfaces 7:10213–10227 48. Li D, Yang S, Chen X, Lai WY, Huang W (2021) 3D wearable fabric-based microsupercapacitors with ultra-high areal capacitance. Adv Funct Mater 31:1–7 49. Zhou Y, Parker Y, Joshi P, Naskar AK, Glass JT, Cao C (2021) 4D printing of stretchable supercapacitors via hybrid composite materials. Adv Mater Technol 6 50. Kuang X, Roach DJ, Wu J, Hamel CM, Ding Z, Wang T, Dunn ML, Qi HJ (2019) Advances in 4D printing: materials and applications. Adv Funct Mater 29:1–23

Polymeric Nanocomposites for Flexible Supercapacitors Sanjeev Verma and Bhawna Verma

Abstract Polymeric-based flexible supercapacitors have received much attention due to their variable conductivity, good cyclic stability, different doping natures, and also eco-friendly processability. Polymeric-based flexible supercapacitors can be made effectively by incorporating polymeric materials into flexible substrates. In this chapter, new advancements in the study and creation of flexible supercapacitors based on polymeric materials are reviewed in detail. We focus on the electrochemical properties of conducting polymers based on polymeric materials, such as pure polymeric and polymeric-based hybrids in supercapacitors. The most recent developments in creating binary and ternary polymeric-based flexible materials with polymeric bases are described. Furthermore, the future and current scenario of polymeric-based materials in supercapacitors are also addressed. In the last, we examine the prime areas in research and development for commercializing polymeric-based supercapacitors. Keywords Conducting polymers · Flexible · Energy storage · Supercapacitor · Nanocomposites

1 Introduction Renewable and clean energy storage and conversion are becoming more and more necessary due to the depletion of fossil fuels, global warming, and climate change. In light of this, extensive effort has been put into creating supercapacitors and other ecologically friendly high-power energy storage devices [1]. Supercapacitors often referred to as electrochemical capacitors or ultracapacitors, are crucial for storing

S. Verma · B. Verma (B) Department of Chemical Engineering and Technology, Indian Institute of Technology, Banaras Hindu University, Varanasi, Uttar Pradesh 221005, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_14

245

246

S. Verma and B. Verma

Fig. 1 Schematic illustration of supercapacitor mechanism

energy and recycling. Additionally, the rapid growth of wearable and flexible electronics necessitates using bendable, stretchable, or foldable flexible supercapacitors as the power source. The best power source for lightweight electronic vehicles and portable/wearable electronics is thought to be flexible supercapacitors. Like conventional supercapacitors, flexible supercapacitors are flexible, lightweight storage systems for electrochemical energy with enormous power densities and extended cycle stability [2, 3]. Due to their unique charge storage techniques, flexible supercapacitors can also be classified into two classes such as EDLCs (electrical double-layer capacitors) and pseudocapacitors (Fig. 1). The effective surface area and pore size distribution of the electrode active materials have a significant impact on the EDLC’s capacitance values, which is related with the ion accumulation via electrostatic force at the interface of electrode and electrolyte. In contrast, pseudocapacitors have approximately higher capacitances because of the quick and reversible nature of faradic reactions occurring at or near the interface [4]. For EDLCs, carbon nanomaterials like CNTs (carbon nanotubes) and graphene make great electrode materials, whereas CPs (conducting polymers) and transition metal oxides/hydroxides make excellent electrode materials for pseudocapacitors [5]. Because of its higher conductivity nature, simplicity in formation, and great inherent flexibility, CPs have been identified as the group of materials that hold the most promise for flexible supercapacitors. The polymer backbones including electron delocalization has made it possible to create a variety of consolidate polymers with alternate double and single bonds and unique electrical characteristics [6]. CPs, such as PANI (polyaniline), PPy (polypyrrole), PEDOT (poly(3,4-ethylenedioxythiophene)), and PTh (polythiophene), have garnered a lot of attention recently. The fact that sensors, supercapacitors, batteries, and modern electric devices have leveraged CPs’ reverse doping-dedoping behavior for many suitable applications is particularly intriguing. By changing the doping amount, it is possible to modify the conductivity

Polymeric Nanocomposites for Flexible Supercapacitors

247

of CPs over a range of around 13 orders of magnitude. CPs can be made via electrochemical polymerization into a variety of states, like sponges, films, hydrogels, and powders or by the oxidative polymerization utilizing popular oxidant agents (such as ammonium persulfate). Different synthetic and/or processing approaches, such as seeding, soft/hard template aided, electrochemical and interfacial polymerization, and post-synthesis electrospinning, have also been used to produce a wide range of morphologies, including nanofibers, nanowires, nanotubes, nanorods, nanorings, and nanoarrays [7]. Due to the wide variety of CPs that are available in various morphologies and shapes, there is a lot of potential for creating flexible supercapacitors based on CPs. But CP-based supercapacitors often have low cycle stability because CPs vary in volume during the doping-dedoping process. Therefore, creating CP-based flexible composites electrode with optimal mechanical and spongy nanostructures for flexible supercapacitors is a major problem [8]. In this chapter, we give a detailed analysis of current advancements in the study and creation of CP-based supercapacitors. First, we discuss the different conducting polymers including electrochemical functionality for energy storage applications. The discussions that follow focus on recent developments in flexible energy storage supercapacitor based on hybrid structures of CPs. The usage of different CPs for flexible supercapacitors is then discussed, including the relationship between the built-in nanostructure and the performance of the flexible CP-based active electrodes in terms of electrochemistry. Also highlighted are the existing difficulties and potential outcomes for CP-based supercapacitors.

2 Flexible Supercapacitor Materials In a flexible assembly, a flexible electrode with excellent electrochemical characteristics, a suitable electrolyte, and a separator make up a flexible supercapacitor (Fig. 2). Supercapacitors have been thoroughly researched in recent years using three main category of materials like different carbon-based materials, CPs, and various transition metal oxides (MOx ). The non-faradic carbon-based materials (such as different activated carbons, graphene and its derivatives, CNTs, and carbon fibers) have high surface area, whereas metal oxides (Fe2 O3 , V2 O5 , MnO2 , and RuO2 , etc.) and CPs (like polyaniline, polythiophene, and polypyrrole) are successfully and frequently treated as the faradaic pseudocapacitors electrode materials [9]. The exhibited chargestorage capability and surface area of the electroactive carbon-based materials determine the specific capacitance of EDLCs. The quick ion sorption at electrode and electrolyte interface responsible for the very high power capability of EDLCs [10]. But the non-Faradaic charge-storing mechanism in EDLCs places a restriction on their specific capacitance. The redox charge transfers storage mechanism that occurs in the majority of the active electrode materials causes the pseudocapacitors to display much higher capacitance comparable to EDLCs.

248

S. Verma and B. Verma

Fig. 2 Representation of flexible supercapacitor

For instance, carbon-based materials are stable and capable of high power densities, but their low specific capacitance prevents them from being used in high energy– density devices. The wide charge–discharge potential range, double layer capacitance, and pseudocapacitance of metal oxides/hydroxides are present, but their application is constrained by their low conductivity, low surface area, poor stability, toxicity, and higher cost. The benefits of CPs include their higher capacitance values, strong conductivity, ease of production, and low cost, but their performances are limited by their lower cyclic and mechanical stability [11]. Mainly, among the range of active materials investigated for energy applications, CPs have garnered more interest in flexible applications in recent years because of its polymeric flexible nature, that is an essential prerequisite for flexible electric devices. Specific capacitance in carbon materials typically falls around 300 F/g, whereas CPs and MOx can reach values of approximately 1000 F/g. A hybrid composites, which combines two or more different materials as aforementioned, can also attain higher capacitance around 2000 F/g (Fig. 3). This is in addition to the three kinds of materials stated above. It has been clearly established over the last few years that the creation of hybrid nanomaterials represents new strategies for controlling and optimizing the structural, mechanical, and physical characteristics of active materials, resulting in improved performance for supercapacitors [12, 13]. To increase the energy density, stability, and capacitance values, different hybrid structures including MOx /CPs, CPs/CNTs, CPs/GO, and MOx /CNTs have been formed. However, in addition to the individual active components, the shape, and the interfacial properties also affect the properties of composite electrodes [14]. Contrary to flexible supercapacitors, conventional capacitors need the formation of flexible active components, including high-performance current collectors with flexible active electrode materials (flexibility). Due to their intrinsic flexibility and polymeric composition, which makes them ideal for flexible supercapacitor applications, CPs are more promising than other conventional active electrode materials. The most popular methods for building CPs-based supercapacitors are wet chemical polymerization and electrochemical polymerization (electro polymerization). The classic slurry-based wet chemical polymerization process still faces difficulties with respect to the manufacturing and performance of CPs-based flexible supercapacitors [15, 16]. Traditionally, binders and additives are combined with the slurry-based

Polymeric Nanocomposites for Flexible Supercapacitors

249

Fig. 3 Comparison of different supercapacitor material based on their capacitance values

chemically polymerized CPs to create the electrode. Because of the high innate resistance and interfacial resistances of the binder/linker materials, these electrodes perform poorly due to the slow diffusion of charge during the faradic process. To growth the CPs directly onto the suitable current collectors, direct-growth approach has been used for supercapacitor energy application in order to get enhance device performance. Horng et al. initially showed nanowires of polyaniline (PANI-NWs) on carbon cloth made using the electro polymerization procedure by utilizing the direct growth approach [17]. The most suitable method for binder independent manufacturing of hybrid composites on a selected flexible collector is the direct electro polymerization approach. The fast ions transport, lower inner resistance, and binder free formation of active materials on flexible current collector could be responsible for reaching extremely high capacitance values, which became a very favorable move toward the synthesis of flexible material supercapacitor devices in the future.

3 Flexible Conducting Polymer Supercapacitors CPs are organic polymers that move electricity throughout the chain of the polymer through a conjugated bond structure. The reversible redox behavior, lower cost, and higher charge density than costly MOx , CPs have been thoroughly investigated for ES (electrochemical system) applications during the past two decades. Because of its higher pseudocapacitance values and electrical conductivity, PANI, PPy, and derivatives of PTh have received the most attention among all types of CPs as active material electrodes for electrochemical storage. Due to their extreme flexibility and ease of manufacture, CPs are now thought highly attractive materials for flexible electrode supercapacitor applications [18, 19]. The morphology of CPs affects how well they work electrochemically. In the literature, CPs have been successfully produced and used in a variety of forms, including nanowalls, nanorods, nanosheets, and bulky powder. Due to unique features of different conducting routes, higher volume/ surface contribution, and surface interactions in nanoscale range dimensions, CPs nanostructures with higher porosity and surface area manifest superior performances.

250

S. Verma and B. Verma

Recent studies have shown that 1-dimensional CPs nanostructures can obtain higher pseudocapacitances in comparison to their bulk/bare counterparts [20].

3.1 PANI (Polyaniline) PANI consist of remarkable doping-dedoping feature and changeable oxidation degree, which results in higher pseudocapacitance value, PANI considered most favorable conducting polymers, has been employed extensively as cheaper material of positive electrode in electrochemical energy storage applications. Despite reports that the protonated PANI emeraldine version has very low conductivity, but most researched CPs because of environmental resilience and high doping level (Fig. 4). The working potential window of p-type PANI can theoretically be extended to about 0.7 V, and its highest theoretical-specific capacitance can reach 2000 F/g. The maximum doping level of p-type PANI can substantively be achieved to 0.5 (i.e., two monomer units per dopant) [21, 22]. PANI has been produced utilizing a variety of substrates, including flexible substrate, stainless steel, nickel, carbon, and carbon cloth, or combined with a variety of substances for use in ES. Numerous studies on PANI-based supercapacitors in the literature show that their specific capacitance can range from 30 to 3000 F/g. Such divergence is dependent on a number of variables, including the polymerization procedure, electroactive material’s ionic movement path length, dopant concentration, and structural morphology. High surface area and nanoscale structures, which are possible in the presence of different dopants in optimal conditions, are the ideal conditions for the creation of PANI-based pseudocapacitors. Li et al. used an easy solution approach to create the bulk amounts of the nanostructured PANI/SA (polyaniline/sodium alginate) composite [23]. With sizes ranging from 50 to 100 nm, the PANI/SA nanofiber electrode displayed good electrochemical characteristics. When compared to chemically polymerized pure PANI, electropolymerized PANI had a greater specific capacitance (2093 F/g). According to reports, electropolymerized PANI demonstrated a 2300 F/g of specific capacitance with consistent charging/discharging cyclic stability up to 1000 cycles when used with a Ni-electrode and Triton X-100 [24]. Another study used the potentiodynamic approach to deposit PANI on porous carbon and achieved 1600 F/g of specific capacitance at 2.2 A/g current density [25]. An electrochemical capacitance that was electrochemically coated on porous carbon by PANI was fairly adherent and persistent for a significant number of cycles (till 1000 cycles) at 19.8 A/g current density. The creation of aligned and ordered structures of PANI, has drawn more attention recently due to their better potential for energy storage. Kulia et al. used a supramolecular block copolymer on transparent ITO as nanotemplate to demonstrate PANI nanorods vertically aligned ordered arrays [26]. The PANI nanorods with nanospacing shown remarkable electrochemical behavior with 3407 F/g of capacitance value. This extremely high specific capacitance measurement for PANI nanorods is incoherent. Peng et al. have noted that the redox stoichiometry of charge

Polymeric Nanocomposites for Flexible Supercapacitors

251

Fig. 4 Different structure of polyaniline

storage and current knowledge of PANI’s electrochemical chemistry cannot match such a high specific capacitance value [27]. Additionally, their theoretical calculations and experimental findings demonstrated that higher capacitance values could only have resulted from a calculation or experiment error based on PANI nanorods underestimated mass. Consequently, extreme caution is required for CPs based supercapacitors research or another redox-active material in order to obtain correct results. The template-based synthesis approach is exceedingly intricate and not appropriate for mass production. The creation of template-free PANI nanostructures has recently received a lot of attention. Kim et al. constructed a PANI electrode nanofiber on a gold painted PVDF (polyvinylidene fluoride/co-hexafluoropropylene) substrate to demonstrate a unique idea for flexible supercapacitor with higher stability electrode based on PANI [28]. To signify the stable flexible supercapacitor, they encased the PANI nanorods on PVDF in Nafion. Generally speaking, while having low cycle stability, the PANI-based supercapacitor electrode has a very outstanding specific capacitance value. To develop flexible PANI-based supercapacitors, the stability issue must be resolved, and a variety of hybrid materials with an appropriate research are needed. Recent cutting-edge research has shown that the supercapacitive characteristics of PANI-based flexible supercapacitors are positively impacted by the addition of graphene and CNTs nanoscale templates [29].

252

S. Verma and B. Verma

3.2 PPy (Polypyrrole) The high energy density, low cost, strong thermal stability, quick charge–discharge mechanism, and high conductivity of PPy, the most signify CPs for the redox energy storage application, make it stand out from the competition (Fig. 5). The active specific area of electrode and electrode preparation techniques affect the faradic electrochemical performance of the PPY-based hybrid nanomaterials in similar to PANI. Anions with a multiple and single charges are frequently added to PPy. The cross-linked PPy is said to have a very high capacitance due to the active material’s strong ion diffusivity and porosity [30, 31]. However, because dopants have less penetrated in inner locations of the backbone polymer, PPy which has grown more densely and thickly on the current collector has a lower capacitance. In recent years, PPy has received a lot of attention in CPs-based research since it may be utilized to prepare the pseudocapacitor electrode chemically or electrochemically. In the presence of excessive surfactants, chemical oxidation-polymerization can produce a variation of PPy nanostructures, but it is very challenging to construct an active electrode for an electrochemical application caused by higher internal resistance of binder. An et al. created a Carbon/PPy nanocomposite for use in supercapacitors by chemical oxidation polymerization, resulting in 433 F/g specific capacitance [32]. In pTS-doped C/PPy hybrid composites in aqueous Na2 SO4 solution, Kumar et al. recently showed 395 F/g of specific capacitance [33]. Supercapacitor use makes up the majority of the electropolymerization process’s utilization for the direct development of PPy on suitable substrate. Dubal et al. showed different PPy nanostructures on a stainless-steel using the electro-polymerization process for energy storage application [34]. The nanosheets of PPy displayed the best 586 F/g of specific capacitance in comparison to other nanostructures. Future applications of flexible supercapacitors may benefit from this PPy nanosheet construction on a suitable flexible substrate. A unique method for creating a very stable nafion-doped PPy electrode for ES use was demonstrated by Kim et al. [30]. It’s interesting to note that PPy has recently concentrated heavily on developing flexible electrodes due to their higher conductivity and flexibility than polythiophene and polyanilines. A straightforward “soak and polymerization” technique for creating PPy-coated paper has been developed by Yuan et al. [35]. With a 1 mWh/ cm3 of energy density and 0.27 W/cm3 of power density, the flexible paper/PPy

Fig. 5 Chemical structure of polypyrrole

Polymeric Nanocomposites for Flexible Supercapacitors

253

nanocomposite electrode material displayed a 0.42 F/cm2 capacitance. By observing the current at 0.5 V voltage, the stability of the paper coated with PPy at various curvature (bending) states was determined. After 100 cycles of bending, the conductivity of paper with PPy-coating remained stable. This technique has sparked a lot of interest in related sectors because it is one of the low-cost options that might be used to produce conductive paper-based electrodes on a wide scale for flexible electronics and energy storage applications. To achieve high capacitance for electrochemical energy application, a major development is required because this material has not yet been produced with high performance.

3.3 PTh (Polythiophene) and Its Derivatives P and n-type CPs are both possible for polythiophene (PTh) and its derivatives. Generally, PTh has low conductivity, although p-doped CPs are very stable in humid and air. In comparison to PANI or PPy, the PTh-based electrode typically has a lower specific capacitance, but its prime advantage is higher potential window operation. It is easier to build asymmetric supercapacitor based on CPs with large negative potential window. All thiophene-based polymers have been utilized successfully in supercapacitor applications, although PEDOT, PMeT (poly (3-methyl thiophene)), and PFPT (poly(3-(4-fluorophenyl) thiophene)) are the most well-known and widely used (Fig. 6). These polymers reported specific capacitance values to fall between 70 and 200 F/g. Due to its great environmental stability for the past few years, PEDOT has been investigated as one of the most promising pseudocapacitor materials [36, 37].

Fig. 6 Chemical representation of different polymers

254

S. Verma and B. Verma

For prospective ES applications, Liu et al. shown PEDOT via electropolymerization in ionic electrolyte [38]. Samui et al. have also published a C/PMeT material electrode in a solid type gel electrolyte for use in supercapacitors [39]. In a thorough investigation, Kearns et al. showed that adding adequate, effective, and reversible faradic couplings to PTh-based material might increase the power and energy density of pseudocapacitor, in addition, enhance the PTh-based polymer’s faradaic charge storage capacity [40]. To increase the ions storing capacity of PTh-based supercapacitor, they have developed a cheaper triarylamine/thiophene co-polymer using an electrocopolymerization procedure. Triarylamine-thiophene copolymer’s chemical make-up, as well as it’s significantly greater and more durable capacitance than bare poly (bi-thiophene) [41]. A novel category of dendritic CPs such as pTTPA (poly(tris(thiophenylphenyl)amine)) has been described by Robert et al. At 50 mV/s scan rate, this pTTPA dendritic based material electrode displayed a 950 F/g specific capacitance in organic electrolyte [42]. The PTh-based ES application now has a new avenue to pursue due to this adaptable amorphous polymer film. Osterholm et al. recently showed the flexible supercapacitor electrode behavior of PEDOTfilms in organic gel and ionic electrolytes [43]. Nejati et al. used a different technique to create the PTh ultrathin films inside porous activated carbon texture, which raised 250% and 50% of volumetric and specific capacitance, in comparison to pure activated carbon [44]. In case of highly effective and conducting nanofibrillar material electrode that displayed 175 F/g specific capacitance, D’Arcy et al. recently manufactured structures of poly (3,4-ethylene dioxythiophene) using vapor-phased polymerization [45]. Strong adherence between the coated CPs on suitable current collector is achieved by this unique technology using the vapor phase polymerization procedure, as demonstrated by low internal resistance and good cyclic stability. This type of PTh-based electrochemical studies represent a positive breakthrough for the flexible energy storage technology that is based on CPs.

4 Flexible Supercapacitors Based on Composite Materials Due to their low cost, higher charge density, ease of fabrication, and excellent environmental stability CPs are regarded as one of the most alluring supercapacitor materials. However, CPs’ insufficient cycle stability, severely limits their practical application. Few shortcomings of different CPs material based pseudocapacitive devices may be effectively solved by methods for the production of hybrid materials that combine CPs with metal oxide or different carbon materials. The highly stable supercapacitive performance of hybrid nanocomposites mainly based on different CPs along with graphene derivatives, CNTs, carbon cloths, and MOx (MnO2 , CoO3 , RuO2 ) has been demonstrated. This is primarily due to increased faradic nature and conductivity of different CPs based materials by the integration of CNTs, MOx , and GO. Hybrid material electrodes have been investigated not just to increase conductivity and cycle life, but also unlock the prospect of new physical characteristics dependent on the different atoms and its interrelationships. Due to the former’s higher

Polymeric Nanocomposites for Flexible Supercapacitors

255

stability, conductivity, and mechanical strength as well as the availability of carbon nanostructures in a variety of forms, recent developments in flexible different CPsbased material supercapacitors primarily focus on binary composite based on carbon materials rather than other composites.

4.1 Composites Based on Carbon Materials with CPs 4.1.1

Using CNTs

The high conductivity and mechanical toughness of CNTs are widely known properties. The use of single-wall and multi-wall CNTs (also known as SWCNTs and MWCNTs, respectively) as EDLCs has been thoroughly investigated. Many studies widely described that the appearance of a faulty, thin, amorphous film on periphery of the CNTs could increase the capacitance values because of more ions buildup. Assessment of the literature on materials electrode manufactured from different CPs revealed the benefit of having a higher pseudocapacitance value. While, the mechanical instability of different CPs-based electrochemical electrode is one of its main weaknesses. This is because of the significant volume change, recurrent swelling or shrinking, and charge release or insertion during again and again charging/ discharging cycles. Following this, the CPs with CNTs-based binary hybrid materials have been thoroughly investigated, and investigations have shown an attractive refinement in the functionality and mechanical stability of the electrode active materials. For example, Gupta et al. produced a SWCNTs/PANI nanocomposite successfully and attained 463 F/g specific capacitance based on mass-normalization and 2.7 F/ cm2 specific capacitance based on area-normalization [46]. In a different tactic, Li et al. created an original core–shell PPy/CNT sponge and showed how it could be used as a very suitable supercapacitor material with excellent capacitance(300 F/g) [47].

4.1.2

Using Graphene Oxide/Graphene

Graphene offers a wide range of possible uses in electrochemical energy storage systems, mostly due to its exceptional unit thick 2-dimensional shape, huge thermal or electric conductivity, excellent compactness, intrinsic stretchability, and enormous surface area. Combining CPs and graphene derivatives materials to create hybrid composites in order to create flexible substrate electrodes has become a popular technique in recent years. The highly porous film texture of graphene governs the shape of CPs in the graphene/polymer composite in addition to making it easier for electrolyte ions to move between electrodes and increase the specific capacitance. A one-step co-electrodeposition technique was used by Zhou et al. to create GO/ PPy nanocomposite films. During the electrochemical polymerization, the comparatively large anionic GO was captured in nanomaterial of PPy, where it served as a

256

S. Verma and B. Verma

weak electrolyte and as a charge-balancing dopant [48]. Through intrinsic reductions of GO in the appearance of PPy nanowires, Zhang et al. recently demonstrated a flexible composite membrane comprising RGO and PPy. Direct linking of two electrode membranes in the absence of a conductive additive or binder, has been used to create a symmetric supercapacitor [49]. The large areal capacitance of 175 mF/cm2 and outstanding cycling stability was attained by the supercapacitor.

4.2 Composites Based on Metal Oxides The most attractive materials for the upcoming generation of electrochemical system is MOx , which offer better capacitance values due to large number of redox processes than interfacial double layer storage in carbon-based materials. These electrode materials’ limited structural stability, which results in quickly capacitance drop during frequently charging and discharging, is a result of the significant volume fluctuation. The low capacitive characteristics of MOx are another effect of poor electrical conductivity. As opposed to this, CPs’ added flexible polymeric nature and strong electrical conductivity are also advantages. Because of this, it is anticipated that MOx and CPs will exhibit considerable synergistic effects when combined at the molecular level, and these effects could result in the creation of innovative flexible supercapacitors with enhanced capacitance capabilities that surpass those of each component material. An amazing 2223 F/g has been claimed by Zhou et al. for a hybrid made of 3-dimensinal CoO/PPy [50]. In its research, they developed an asymmetric supercapacitor using aqueous electrolyte with 1.8 V maximum potential window that had exceptionally high power density (5500 W/kg @ 11.8 Wh/kg), high energy density (43.5 Wh/kg), and excellent cycle stability. Li et al. recently showed how to make an ES electrode using a CNT@PPy@MnO2 core–shell [51]. The higher electrochemical performance in their study was due to the synergic effect of MnO2 and PPy in conductive porous CNT framework. These nanohybrids of MOx composites along with CPs, in our opinion, can create novel possibilities for flexible electrochemical storage technology.

5 Challenges It is clear that various carbon-based and metal oxide-based materials with suitable CPs can influence the development of nanohybrids based on CPs, and flexible devices architecture offers a crucial method for improving flexible supercapacitor performance. Furthermore, according to study, the faradaic ions diffusion electrochemical process, stability of the active electrode materials, and the complete supercapacitive behavior, can all be impacted by the composite creation. Additionally, it was discovered that CPs-based composites had the best performance in the majority of the studies when they were put directly on suitable flexible collector substrate.

Polymeric Nanocomposites for Flexible Supercapacitors

257

It should be highlighted that even though the CPs-based nanocomposites exhibit higher capacitance values, their electrochemical performances such as energy density, cycle stability, and power density are far away from being applicable in real-world industrial settings. Additionally, while the majority of research has been focused on performance of supercapacitor materials, less attention has been paid on the supercapacitor cell optimization and its impact on performance, including cyclic stability, energy, and power density. Therefore, it should be very necessary for actual and practical application of energy storage devices to carefully focus on the energy and power density research of the entire supercapacitor system as well as much advanced analysis of interfacial mechanism and inner resistances. As a result, based on the types of electrochemical cells and their uses, it is important to set some common industry benchmarks, like different dimensional parameters, active electrode structures, electrolyte selection, and its performance.

6 Future Prospective and Present Scenario Redox materials based on CPs are revolutionizing applications for flexible pseudocapacitors. The potential for new, inexpensive, lightweight, and highly flexible devices is even larger in future. In the next decade, it is anticipated that these CPsbased supercapacitors would significantly reduce the market share of the current Li-ion batteries to meet the huge demand of energy storage flexible devices. High conductivity, flexibility, faradic specific capacitance, and ease of fabrication for wearable flexible and ultrathin electronic gadgets are the distinguishing characteristics of CPs-based supercapacitors. The flexible energy devices based on CPs can be quickly incorporated and attached into clothes which can be easily stretched or folded into particular shape of energy storage devices. Depending upon electrode material design features, selecting suitable electrolytes along with proper active electrode materials is crucial for enhancing electrochemical outcome. Also well known that improving the working potential range is the best strategy to accelerate the supercapacitors’ power and energy densities. Furthermore, electrolyte electrochemical stability and the production of some gaseous items at the anode and cathode during the voltammetric measurements limit the safe or withstanding operating proper voltage window in electrochemical operation. The functioning potential window of ionic liquid and organic based electrolytes might be improved around 2 times more compare to aqueous electrolytes, according to an advanced supercapacitor electrolyte study. Another crucial factor is the electrodes’ ESR (equivalent series resistance), which has an inverse relationship with the supercapacitor power density. Therefore, reducing the intrinsic material resistance and the interfacial (contact) resistance between current collector and CPs-based materials would be crucial to enhancing ions transport and obtaining higher specific power. The development of coreshell CPs/MOx or CPs/C hybrid composites on suitable collector, as well as the direct growth of MOx nanostructures or carbon-based structures on collector, have all recently been attempted as solutions to the existing

258

S. Verma and B. Verma

problem. The direct electrode-design approach, in comparison to powder-type supercapacitor active materials, can enhance power density by lowering contact resistance and ESR between CPS-based materials and current collector.

7 Conclusion Over the past few years, research and development on flexible supercapacitors based on CPs have advanced quickly. Supercapacitors based on CPs have received a lot of attention as potential new platforms for flexible electrochemical energy storage. This study has summarily covered current developments, including few fruitful and encouraging study projects reaching higher value of capacitance belonging to flexible supercapacitors made of CPs. We believe that this evaluation will spark fresh ideas in the search for logical designs for flexible devices that use CPs-based pseudocapacitors that are more effective. However, it is clear that there are still a number of problems to be solved before supercapacitor capabilities like energy density, power density, and cycle stability, are appropriate for real-world industrial applications. Further developments are required to take benefit of the huge operating potential window in ionic electrolyte and obtain a high energy density and power density. Advancement of the extensive commercial electronics applications also needs further work. To clarify the impacts of polymer topology and in-situ doping on pure and hybrid CPs material, as well as the ways in which those discoveries might be employed to direct future development efforts, extensive research is required.

References 1. Verma S, Das T, Pandey VK, Verma B (2022) Nanoarchitectonics of GO/PANI/CoFe2 O4 (Graphene Oxide/polyaniline/Cobalt Ferrite) based hybrid composite and its use in fabricating symmetric supercapacitor devices. J Mol Struct 133515 2. Wang Q, Wang X, Xu J, Ouyang X, Hou X, Chen D, Wang R, Shen G (2014) Flexible coaxialtype fiber supercapacitor based on NiCo2O4 nanosheets electrodes. Nano Energy 8:44–51 3. Jiang J, Li Y, Liu J, Huang X, Yuan C, Lou XW (2012) Recent advances in metal oxide-based electrode architecture design for electrochemical energy storage. Adv Mater 24:5166–5180 4. Verma S, Verma B (2022) Graphene-based nanomaterial for supercapacitor application. In: Nanostructured materials for supercapacitors, pp 221–244 5. Verma S, Pandey VK, Verma B (2022) Synthesis and supercapacitor performance studies of graphene oxide based ternary composite. Mater Technol 1–17 6. Das T, Pandey VK, Verma S, Pandey SK, Verma B (2022) Optimization of the ratio of aniline, ammonium persulfate, para-toluenesulfonic acid for the synthesis of conducting polyaniline and its use in energy storage devices. Int J Energy Res 7. Feng Z-Q, Wu J, Cho W, Leach MK, Franz EW, Naim YI, Gu Z-Z, Corey JM, Martin DC (2013) Highly aligned poly(3,4-ethylene dioxythiophene) (PEDOT) nano- and microscale fibers and tubes. Polymer (Guildf) 54:702–708

Polymeric Nanocomposites for Flexible Supercapacitors

259

8. Pandey VK, Verma S, Verma B (2022) Polyaniline/activated carbon/copper ferrite (PANI/AC/ CuF) based ternary composite as an efficient electrode material for supercapacitor. Chem Phys Lett 802:139780 9. Verma S, Pandey VK, Verma B (2022) Facile synthesis of graphene oxide-polyaniline-copper cobaltite (GO/PANI/CuCo2 O4 ) hybrid nanocomposite for supercapacitor applications. Synth Met 286:117036 10. Verma S, Das T, Pandey VK, Verma B (2022) Facile and scalable synthesis of reducedgraphene oxide using different green reducing agents and its characterizations. Diam Relat Mater 129:109361 11. Canales M, Torras J, Fabregat G, Meneguzzi A, Alemán C (2014) Polyaniline emeraldine salt in the amorphous solid state: Polaron versus bipolaron. J Phys Chem B 118:11552–11562 12. Yu G, Hu L, Liu N, Wang H, Vosgueritchian M, Yang Y, Cui Y, Bao Z (2011) Enhancing the supercapacitor performance of graphene/MnO2 nanostructured electrodes by conductive wrapping. Nano Lett 11:4438–4442 13. Li Q, Liu J, Zou J, Chunder A, Chen Y, Zhai L (2011) Synthesis and electrochemical performance of multi-walled carbon nanotube/polyaniline/MnO2 ternary coaxial nanostructures for supercapacitors. J Power Sources 196:565–572 14. Pandey VK, Verma S, Das T, Verma B (2022) Supercapacitive behavior of polyaniline-waste derived carbon-copper cobaltite based ternary composite. Bioresour Technol Rep 20:101255 15. Huang Y, Li H, Wang Z, Zhu M, Pei Z, Xue Q, Huang Y, Zhi C (2016) Nanostructured Polypyrrole as a flexible electrode material of supercapacitor. Nano Energy 22:422–438 16. Inamuddin H (2019) Abbas Kashmery, Polyvinylidene fluoride/sulfonated graphene oxide blend membrane coated with polypyrrole/platinum electrode for ionic polymer metal composite actuator applications. Sci Rep 9:1–11 17. Horng Y-Y, Lu Y-C, Hsu Y-K, Chen C-C, Chen L-C, Chen K-H (2010) Flexible supercapacitor based on polyaniline nanowires/carbon cloth with both high gravimetric and area-normalized capacitance. J Power Sources 195:4418–4422 18. Rudge A, Raistrick I, Gottesfeld S, Ferraris JP (1994) A study of the electrochemical properties of conducting polymers for application in electrochemical capacitors. Electrochim Acta 39:273–287 19. Kim J-Y, Kim KH, Kim KB (2008) Fabrication and electrochemical properties of carbon nanotube/polypyrrole composite film electrodes with controlled pore size. J Power Sources 176:396–402 20. Peng C, Zhang S, Jewell D, Chen GZ (2008) Carbon nanotube and conducting polymer composites for supercapacitors. Prog Nat Sci 18:777–788 21. Neves S, Polo Fonseca C (2002) Influence of template synthesis on the performance of polyaniline cathodes. J Power Sources 107:13–17 22. Li H, Wang J, Chu Q, Wang Z, Zhang F, Wang S (2009) Theoretical and experimental specific capacitance of polyaniline in sulfuric acid. J Power Sources 190:578–586 23. Li Y, Zhao X, Xu Q, Zhang Q, Chen D (2011) Facile preparation and enhanced capacitance of the polyaniline/sodium alginate nanofiber network for supercapacitors. Langmuir 27:6458–6463 24. Girija TC, Sangaranarayanan MV (2006) Polyaniline-based nickel electrodes for electrochemical supercapacitors—Influence of Triton X-100. J Power Sources 159:1519–1526 25. Mondal SK, Barai K, Munichandraiah N (2007) High capacitance properties of polyaniline by electrochemical deposition on a porous carbon substrate. Electrochim Acta 52:3258–3264 26. Kuila BK, Nandan B, Böhme M, Janke A, Stamm M (2009) Vertically oriented arrays of polyaniline nanorods and their super electrochemical properties. Chem Commun 5749 27. Peng C, Hu D, Chen GZ (2011) Theoretical specific capacitance based on charge storage mechanisms of conducting polymers: comment on ‘vertically oriented arrays of polyaniline nanorods and their super electrochemical properties.’ Chem Commun 47:4105 28. Kim BC, Kwon JS, Ko JM, Park JH, Too CO, Wallace GG (2010) Preparation and enhanced stability of flexible supercapacitor prepared from nafion/polyaniline nanofiber. Synth Met 160:94–98

260

S. Verma and B. Verma

29. Dai L, Chang DW, Baek J-B, Lu W (2012) Carbon nanomaterials for advanced energy conversion and storage. Small 8:1130–1166 30. Kim BC, Ko JM, Wallace GG (2008) A novel capacitor material based on nafion-doped polypyrrole. J Power Sources 177:665–668 31. Wang J, Xu Y, Wang J, Du X (2011) Toward a high specific power and high stability polypyrrole supercapacitors. Synth Met 161:1141–1144 32. An H, Wang Y, Wang X, Zheng L, Wang X, Yi L, Bai L, Zhang X (2010) Polypyrrole/carbon aerogel composite materials for supercapacitor. J Power Sources 195:6964–6969 33. Kumar A, Singh RK, Singh HK, Srivastava P, Singh R (2014) Enhanced capacitance and stability of p-toluenesulfonate doped polypyrrole/carbon composite for electrode application in electrochemical capacitors. J Power Sources 246:800–807 34. Dubal DP, Lee SH, Kim JG, Kim WB, Lokhande CD (2012) Porous polypyrrole clusters prepared by electropolymerization for a high performance supercapacitor. J Mater Chem 22:3044 35. Yuan L, Yao B, Hu B, Huo K, Chen W, Zhou J (2013) Polypyrrole-coated paper for flexible solid-state energy storage. Energy Environ Sci 6:470 36. Snook GA, Chen GZ (2008) The measurement of specific capacitances of conducting polymers using the quartz crystal microbalance. J Electroanal Chem 612:140–146 37. Laforgue A, Simon P, Sarrazin C, Fauvarque J-F (1999) Polythiophene-based supercapacitors. J Power Sources 80:142–148 38. Liu K, Hu Z, Xue R, Zhang J, Zhu J (2008) Electropolymerization of high stable poly(3,4ethylenedioxythiophene) in ionic liquids and its potential applications in electrochemical capacitor. J Power Sources 179:858–862 39. Sivaraman P, Thakur A, Kushwaha RK, Ratna D, Samui AB (2006) Poly(3-methyl thiophene)activated carbon hybrid supercapacitor based on gel polymer electrolyte. Electrochem SolidState Lett 9:A435 40. Kearns JT, Roberts ME (2012) Enhanced performance of triarylamine redox electrodes through directed electrochemical polymerization. J Mater Chem 22:2392–2394 41. Kearns JT, Roberts ME (2012) Synthesis of high-charge capacity triarylamine–thiophene redox electrodes using electrochemical copolymerization. J Mater Chem 22:25447 42. Roberts ME, Wheeler DR, McKenzie BB, Bunker BC (2009) High specific capacitance conducting polymer supercapacitor electrodes based on poly(tris(thiophenylphenyl)amine). J Mater Chem 19:6977 43. Österholm AM, Shen DE, Dyer AL, Reynolds JR (2013) Optimization of PEDOT films in ionic liquid supercapacitors: demonstration as a power source for polymer electrochromic devices. ACS Appl Mater Interfaces 5:13432–13440 44. Nejati S, Minford TE, Smolin YY, Lau KKS (2014) Enhanced charge storage of ultrathin polythiophene films within porous nanostructures. ACS Nano 8:5413–5422 45. D’Arcy JM, El-Kady MF, Khine PP, Zhang L, Lee SH, Davis NR, Liu DS, Yeung MT, Kim SY, Turner CL, Lech AT, Hammond PT, Kaner RB (2014) Vapor-phase polymerization of nanofibrillar poly(3,4-ethylenedioxythiophene) for supercapacitors. ACS Nano 8:1500–1510 46. Gupta V, Miura N (2006) Influence of the microstructure on the supercapacitive behavior of polyaniline/single-wall carbon nanotube composites. J Power Sources 157:616–620 47. Li P, Shi E, Yang Y, Shang Y, Peng Q, Wu S, Wei J, Wang K, Zhu H, Yuan Q, Cao A, Wu D (2014) Carbon nanotube-polypyrrole core-shell sponge and its application as highly compressible supercapacitor electrode. Nano Res 7:209–218 48. Zhu C, Zhai J, Wen D, Dong S (2012) Graphene oxide/polypyrrole nanocomposites: onestep electrochemical doping, coating and synergistic effect for energy storage. J Mater Chem 22:6300 49. Zhang J, Chen P, Oh BHL, Chan-Park MB (2013) High capacitive performance of flexible and binder-free graphene–polypyrrole composite membrane based on in situ reduction of graphene oxide and self-assembly. Nanoscale 5:9860

Polymeric Nanocomposites for Flexible Supercapacitors

261

50. Zhou C, Zhang Y, Li Y, Liu J (2013) Construction of high-capacitance 3D CoO@polypyrrole nanowire array electrode for aqueous asymmetric supercapacitor. Nano Lett 13:2078–2085 51. Li P, Yang Y, Shi E, Shen Q, Shang Y, Wu S, Wei J, Wang K, Zhu H, Yuan Q, Cao A, Wu D (2014) Core-double-shell, carbon nanotube@polypyrrole@MnO2 sponge as freestanding, compressible supercapacitor electrode. ACS Appl Mater Interfaces 6:5228–5234

Polymeric Materials for Flexible Supercapacitors Rasmita Barik, Saurabh Kumar Pathak, and Agni Kumar Biswal

Abstract The ever-growing demand for portable, flexible, bendable, and advanced energy storage devices is high because of their high degrees of mechanical deformability. The polymer-based flexible supercapacitors are tremendously successful in achieving enhanced energy storage performance which further leads to advanced practical application. Flexible supercapacitors developed with conducting polymers and polymer-based materials with high redox active-specific capacitance (SC) and inherent elastic polymeric nature show unparalleled advantages over other established electrode materials (metal oxides/sulfides). The innovation of new polymeric materials depends on their superior physical/chemical properties such as charge production, transportation, diffusion, and assortment, proving it as one of the best answers for flexible supercapacitors. In this present book chapter, the synthesis of polymeric materials with a high surface area, high porosity, small pore size, good electrical conductivity like high energy density (ED) and power density (PD), and associated polymeric electrolyte, substrates are discussed. Furthermore, this chapter also gives an elaborative insight into the futuristic advanced flexible materials for electronic applications. Keywords Conducting polymers · Composites · Flexible · Wearable · Supercapacitors

R. Barik (B) Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi 110016, India e-mail: [email protected] S. K. Pathak Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, USA A. K. Biswal Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_15

263

264

R. Barik et al.

1 Introduction Energy is one of the most essential needs for human beings and it became a critical issue with the depletion of natural sources in the twenty-first century. This can be fulfilled from the available traditional energy sources like solar, wind, water, etc., or storage devices such as thermoelectric, fuel cells, etc. Out of these, extensive research was done on manmade storage devices. The development of ideal electrochemical energy storage devices like supercapacitors is bridging the gap between traditional capacitors and batteries and can be a long-term solution for this field that can minimize the use of natural resources [1, 2]. Electrochemical supercapacitors (ESs) from the last two decades have emerged as one of the most fascinating, environment-friendly, low-cost, and promising renewable energy storage devices, as compared to batteries with good mechanical, and electrochemical properties such as high-power density (> 10 kW kg−1 ), and faster charging/discharging capacity, etc. Renewable and advanced energy storage devices are of low cost, sustainable, environmentally friendly, have high energy density (ED) and high power density, and have stable, fast, and long charge–discharge cycles, etc. [1, 2]. The development of ES started after several transitions through hybrid electric devices from 1957 to achieve a long life cycle (100,000). Traditional supercapacitors are the sandwiched sealed device of two working electrodes (Anode and cathode) separated by a separator in presence of liquid electrolytes, but due to liquid electrolyte leakage and rigid structure practical application is restricted. Therefore, future ESs need to be modified to their more convenient forms which may easily be adaptable to upcoming electronics [3]. The future electronics (such as electric vehicles, portable devices, touch screens, smart electronics, roll-up displays, wearable sensors, etc.) need to be flexible, twistable, and deformable while the previous existing mediums are hard, brittle, and rigid. Energy storage devices owning high flexibility, lightweight, and high safety increases their usage in electronics. Besides, the flexible energy storage devices must be nontoxic, nonflammable, shape-conformable, and efficient in electrochemical properties [3]. Compared to conventional supercapacitors, flexible ESs with a flexible substrate with highly conductive and can act as both a current collector and electrode [4]. The charge storage mechanism in flexible supercapacitors follows two types of mechanism: (i) Electric double-layer capacitors (EDLC) have resulted from the charge accumulation and separation at electrode/electrolyte interface and most used materials are carbon-based materials, carbon nanotubes, graphene, etc.) and (ii) Pseudocapacitors have resulted from the fast and reversible faradic redox reactions occurs at or near the electrode, in presence of valence states of different pseudocapacitive materials such as conducting polymers, metal oxides, metal nitrides, and sulfides, etc. The use of polymeric materials can result in high porosity in materials hence enhancing the pseudocapacitor electrochemical properties [3, 5]. Among all conducting polymers (CPs), polyaniline (PANI), polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) PEDOT, polythiophene (PTh), polyparaphenylene (PPP) and polyindole (PI), etc. are mostly used electrode materials for flexible

Polymeric Materials for Flexible Supercapacitors

265

supercapacitors due to their high conductivity, high capacity, ease of synthesis, environmental friendliness, low cost, large porosity, wide potential window, synthesis feasibility, and high intrinsic flexibility [1, 2]. Among them, PANI is the most studied CPs with outstanding surface area and the highest theoretical capacitance of 750 F/g as compared to PPy (620 F/g), PEDOT (210 F/g), and PTh (485 F/g).[5] The reverse doping–dedoping property of CPs coerced the engineering of highperformance polymeric materials considering the high polymeric (long chain) or highly conducting pathways, high surface-to-volume ratio, and surface interactions etc. for the development of both electrodes and electrolytes for supercapacitors. The CPs can be synthesized via oxidative polymerizations (electrospinning, in-situ polymerization, electrochemical, hard-soft template-assisted, seeding etc.) or by electrochemical polymerization in different forms (powder, films, hydrogels, sponges, nanofiber, nanowire, nanoarray, nanorod, nano ring, etc.). Flexible polymer-based supercapacitors are categorized into various types depending on the nature of CPs and device fabrication. Type I (p-type polymers, PANI/PPy/Polythiopene) and type III (n-type or a donor–acceptor polymer) are ascribed to the symmetric configuration (both anode and cathode are the same) while Type II (two different p-type polymers differentiated as negative and positive electrodes) and type IV (n-type or donor − acceptor polymers) supercapacitors are asymmetric types (different anode and cathode) [6, 7]. The poor conductivity and cyclic stability limit the commercial use of polymer for flexible supercapacitors. The use of efficient, advanced, flexible supercapacitors is in high demand owing to their suitable supporting properties such as ultrafast charging/ discharging capability, outstanding PD, and sustained cycling life. The continuing research efforts on the development of highly capacitive, electrolyte, and improved polymeric materials, are still in progress. Predominantly, the CPs or CPs-based composites are explored for practical applications owing to their high theoretical standards, and high surface area which facilitates the faster dispersion of electrolyte ions. Further, the introduction of carbon and carbon-based materials such as graphene, and carbon nanotubes (CNTs), into the CPs matrix, plays a crucial role in enhancing the SC system. The interaction of both materials helps in improving the capacity and cycling ability of energy-storage applications [8]. Long-chain polymers with low cost and high conductivity have emerged as electrode materials for flexible ESs. Further, the various CP-based composites such as polymer/carbon, polymer/metal oxides/ sulfides, copolymers, etc. are developed with optimized porous microstructures and mechanical properties [6, 7]. The present book chapter focused on polymer and polymer-based energy materials for flexible supercapacitors (Fig. 1). The first part explains the different polymers and their synthesis methods, the designing of flexible supercapacitors, and device fabrication in the current scenario. In the second part, the advantages and disadvantages associated with polymer-based flexible substrates and electrolytes in flexible ESs are discussed. Finally, future scopes with possible strategies to develop advanced flexible supercapacitors are discussed.

266

R. Barik et al.

Fig. 1 Polymer materials for flexible supercapacitors: polymers, synthesis methods, polymeric composites, and polymers for supercapacitors device fabrication

2 Types of Polymers and Their Composites for Flexible Supercapacitors Conducting polymers and their composites are the most attractive materials with good intrinsic conductivity and low band gaps (1–3 eV), while conventional polymers have a band gap of 10 eV. CPs with suitable morphology and architecture have faster charge–discharge kinetics. CPs are one of the most used ideal electrode materials for supercapacitors due to facile synthesis, high electrochemical, and mechanical properties, and environmental friendliness. Polymers can store charge over their volume due to their outstanding ability for rapid and faster doping and dedoping. Furthermore, CPs such as Polyaniline/Polypyrrole /PEDOT and their composites with metal oxide/sulfide, carbon, etc. are used for advanced and flexible supercapacitors. Traditional CPs (such as PANI and PPy) with high theoretical capacitances, high surface area, and higher porosity based on their nanoscale dimension, surface interaction, conducting pathways, and high surface-to-volume ratio show better performance. But the practical application of CPs is restricted by their poor stability during the charge/ discharge cycle, which leads to the swelling/shrinkage of the polymer chain, and thus insufficient ionic carriers are released. To modify the properties of CPs, CPsmetal oxides, CPs-carbon materials, copolymers, and polymer hydrogels are also made as electrode active materials used for the supercapacitors to further improve electrochemical performance.

Polymeric Materials for Flexible Supercapacitors

267

2.1 Different Conducting Polymers Polyaniline/Polypyrrole/Polythiophene/PEDOT are mostly used conductive polymers. They are important organic materials where redox behavior helps in charge storage, and release and helps in the development of high-performance pseudocapacitors. During the oxidation process, the ions are transferred toward the polymer backbone while in the reduction process, the ions are unrestricted within the electrolyte [9]. CP-based supercapacitors show high ED (~ 10 Wh/kg versus ~ 5 Wh/kg) and lower PD (~ 2 kW/kg versus ~ 4 kW/kg). Arvas et al. followed the electro-polymerization method to develop PPY and PANI-based materials on carbon felt. The developed supercapacitor shows an areal capacitance of 4000 mF/cm2 at a current density (CD) of 10 mV/s with a specific ED of 18.8 Wh/kg and PD of 1875 W/kg. The enhanced SC is obtained due to the 2-sulfonic acid addition to PPy which facilitates the electron transfer in 1 M H2 SO4 electrolyte and electrode materials [10]. Ju et al. successfully polymerized aniline in NaCl solution and highly porous and intercrossed honeycomb-like PANI structure for flexible and foldable all-solid-state supercapacitors, with high SC value of 480 F/ g [11]. Huang and his group developed a high-concentration, viscoelastic, additivefree, and free-standing supercapacitor from PEDOT: PSS (polystyrene sulfonate) [12]. The diversity of microstructures reduces the strain and stress of the electrodes and provides a great degree of freedom for the development of stretchable electrodes. There are various flexible/stretchable supercapacitors devices have been developed via the 3D-Printing method. The 3D-printed CP electrode can be stretched to 150% or bent to 180° and delivers a high area capacitance of 990 mF/cm2 with 74.7% capacity retention after 14,000 cycles. Therefore, the synthesis methods for polymerization also play a vital role. Carbon nanofibers (CNFs) synthesized by polyacrylonitrile show excellent electrochemical properties owing to their high specific surface area. The free-standing CNF-based stable supercapacitor developed by Chee et al. shows an SC value of 100 F/g [13]. Further, the redox behavior of polymers creates mechanical stress in the flexible device system which develops more internal resistance, instability, and self-discharge property. Owing to these behaviors, various polymer composites are required to irradiate the dilemma. While it is expected that carbon-based metal oxide materials will show better cycle stability with an increased SC, ED, and PD.

2.2 Polymer/carbon Composites Portable flexible electronic devices are becoming more and more attractive due to their small size and lightweight. Previously carbon-based polymer nanocomposites (CPNCs) are extensively used in automotive, packing, aerospace, and energy accumulation sectors. Because of their easy processing, configuration adaptability,

268

R. Barik et al.

lightweight, and flexibility. They are also used in batteries, fuel cells, and supercapacitors. Polymers have good mechanical flexibility, and low-density properties. Due to these advantages, polymeric materials are considered as flexible electrodes/ current collectors [1, 2]. Carbon-based materials such as CNTs, CNFs, and graphene are the most used carbon sources with outstanding mechanical strength, high conductivity, low density, and high surface area, in electrochemical energy storage properties. Polymer sponges (e.g., melamine foam), cotton, silk fibers, bioproducts (peels, leaves, etc.), and specially treated wood can be carbonized into carbons. Apart from the direct use of polymers (polyacrylonitrile (PAN), polyvinyl alcohol (PVA), and polyvinylpyrrolidone, etc.), there are other shape-forming methods such as electrospinning, dry-jet wet-spinning, and wet spinning methods are used to prepare polymer based flexible energy storage devices [13]. The polymer/carbon-based composites such as CPs/CNTs, polymer nanowire array/SWCNT composites, nitrogen-doped graphene in polyacrylic acid/polyaniline (NG-PAA/PANI) composites, Electrospun CNFs/ CNTs/PANI Ternary Composites, etc. are used for the flexible supercapacitor study. PANI is embedded into the polymer matrix of polymethyl methacrylate, polycarbonate, poly (vinyl alcohol), polyvinyl carbazole, etc. As they are mostly insulators, to enhance conductivity carbon-based materials such as CNFs/CNTs are introduced in the polymer matrix to enhance both the mechanical and electrochemical properties. These electrode materials are used by carbon cloth working electrodes. A very expensive textile electrode carbon cloth (CC) is mostly used as a working electrode because of its high surface area, high conducting, and excellent current collector. The micro and nanopores of carbon cloth with hierarchical, almost scaleinvariant pore distribution help in the diffusion of the electrolyte ions into the electrode material. Wang et. al reports the NG-PAA/PANI composites for the fabrication of flexible supercapacitor (shown in Fig. 2). NG-PAA/PANI shows a capacitance of 68 F/g at 1 A/g, which is 13 times larger than earlier reported similar PAA/PANI composite [14]. While the PANI/SWCNT/cloth material reported by Wang et al. shows a high SC of 410 F/g with high-rate capability and good stability [15]. The poly (3-hexyl-thiophene 2, 5-diyl)/SWCNTs showed an SC of 245.8 F/g at 0.5 A/g on a graphite sheet in the electrolyte 0.1 M LiClO4 electrolyte [16].

2.3 Polymer/Metal Oxide/Sulfide) Composites In the past few years, massive investigations have been carried out in the improvement of existing polymer/metal oxide/sulfide based energy materials for advanced energy storage device applications. So, in search of stable, and highly conducting energy materials the researchers tried to develop some CPs based on different metal oxide/sulfide materials. The presence of metal oxides/hydroxides/sulfides facilitates mechanical stability and sustains the volume change during the charge–discharge cycles. CPs with excellent optical and electronic properties are suitable for supercapacitor applications. The porous structure of PEDOT provides superior electrolytic

Polymeric Materials for Flexible Supercapacitors

269

Fig. 2 i The polymer-based NG-PAA/PANI for flexible electrode preparation and their supercapacitor study, ii the fabrication of an all-solid-state capacitor. Adapted from [14] Copyright The Authors (2016), Springer Nature. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

access, but it has a lower mass-SC as compared to PANI and PPy. Polypyrrole loses its conductivity during the charge–discharge cycle because of the morphology collapse which results in poor stability and reduced capacity. The combination of TMOs, metal sulfides, and CPs and their derivatives display good redox reactions which makes the advanced material for pseudocapacitors [1, 2]. However, polypyrrole loses its conductivity during the charge–discharge cycle because of the morphology collapse results in poor stability and reduced capacity. Therefore, the PPy composite materials such as PPy/carbon, and PPy/metal oxide composites need extensive examination. Among all polymers polyaniline (PANI) is the most studied polymer with its interconvertible benzenoid ring and quinoid structure which results in high SC. However, its lower mechanical stability during the charge–discharge process causes shrinking and swelling to yield a poor life cycle. Therefore, a controlled synthesis of metal-oxide nanocomposite and CPs are required to develop polymer-based pseudocapacitors [9]. Polypyrrole is the cheapest among polymers with simple synthesis and high theoretical capacitance. [17, 18] Graphene-doped metal oxides (iron oxide) ternary composites with PPy are developed to achieve high gravimetric and areal capacitance supercapacitors. The N-doped PPy/N-PCM shows excellent supercapacitive behavior with SC of 237.5 F/g. The flexible electrode is highly stable at 10 A/g with a capacitance retention of 88.53% shown in Fig. 3 [17]. Co(III) complex and PPy composite thin films developed by Parne et al. show a higher SC of 668 F/g at 0.45 A/g. Herein the economical Co(III) is electrochemically deposited on the high

270

R. Barik et al.

Fig. 3 i The Schematic representation of polymer-based film formation on GCE from pyrrole and CoN4 complex by electrochemical deposition method and their electrochemical study at 0.1 M HClO4 . Adapted from [17]. Copyright The Authors (2020), Springer Nature. Distributed under a Creative Commons Attribution License 4.0 (CC BY). ii The schematic presentation of Ppy/N-PCM synthesis and their electrochemical analysis compared with Ppy/N-PCM, Ppy/rGO-C, and pure Ppy. Adapted from [18]. Copyright The Authors (2019), Springer Nature. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

electrically conducting polymer PPy which has the ability to store huge amounts of energy and is highly stable even after several charge–discharge cycles [18]. Barik et al. successfully synthesized PANI-modified CuV2 O6 layered nanosheets for energy storage device applications via the co-precipitation method followed by in-situ polymerization for the flexible supercapacitor formation with 375 F/g at 4 A/g and good rate capability [19]. PANI@Fe−Ni co-doped Co3 O4 was developed by Usman et al. and shows 1171 F/g at the CD of 1 A/g followed by 84% of capacity retention after 200 cycles. Initially, the hydrothermal and annealing method is employed for the synthesis of Fe−Ni co-doped Co3 O4 followed by the addition of aniline and stirring [20]. MnO2 –PPy–carbon, and V2 O5 –PANI–carbon fiber composites developed by Liu et al. show excellent electrochemical behavior. MnO2 is electrodeposited onto the carbon fiber at a scan rate of 10 mV/s in the aqueous solution of Mn(NO3 )2 and NaNO3 with an applied potential range of 0.4 V to 1.3 V versus the saturated calomel electrode (SCE). By using 5% (v:v) PPy monomer and 0.2 M NaClO4 solution, the Ppy film is formed at voltage − 0.8 V and yields a conductive encapsulation of MnO2 – CNF structures and shows a high areal capacitance of 0.613 F/cm2 at 1.5 mA/cm2 CD The device is stable up to 5000 cycles and demonstrates as a promising candidate for extensive applications. Liu et al. [21] Manganese and iron oxides are electrodeposited on polyimide film for the formation of flexible micro-supercapacitor by the laserinduced self-generated method. The laser-induced method helps in generating large numbers of pores by controlling the irradiation energy inside the conductor. This process helps in producing a flexible highly conducting micro supercapacitor with ED of 16.3 mWh/cm3 and PD of 3.54 W/cm3 at a high voltage range of 1.5 V [22].

Polymeric Materials for Flexible Supercapacitors

271

2.4 Co-Polymer The CPs and their composites are widely used electrode materials for the flexible supercapacitor. Basically, polymers can be used in their copolymer forms where they are covalently bonded with two or more distinct and incompatible monomers. They can be categorized as di-block, tri-block, tetra-block, etc. They have reverse doping–dedoping properties which further help to improve the pore size and ionic conductivity. The copolymers deliver versatile tools for the development of nanomaterials for flexible supercapacitors due to the strong phase of block copolymers [23]. Wang et al. report the synthesis of copolymers with SC of 227.88 F/g at CD of 4 mA/cm2 , [24]. While Wang et al. [25] report the phytic acid-doped poly(aniline-copyrrole) copolymer which results in SC of 639 F/g and retains capacitance 62.3% after 1000 cycles at 3 A/g CD. Further, Sharma et al. worked on π-conjugated polymers (naphthalene diimide or perylene diimide (PDI) as acceptor and benzodithiophene (BDT) as donor component) for flexible supercapacitor electrodes with SC of 113 F/ g at 4000 cycles stability and almost 100% retention in PCLiClO4 organic electrolyte [6]. The supercapacitor industry mostly depends on activated carbons, due to their excellent properties (inert chemical activity, high surface area, better pore size distribution, and low cost). The copolymer with a carbon source and a sacrificial block plays the most vital role in the preparation of hierarchical carbon for the supercapacitor application. They are chemically and thermally stable with high contents of nitrogen within the activated carbon source even after carbonization [6, 26]. Nitrogendoped carbon derived from copolymer shows an enriched surface area of 2104.5 m2 / g and further shows SC 257 F/g at 0.5 A/g CD. Again, conducting polymer hydrogel (CPH) is proven as another prospective candidate for flexible supercapacitors. They basically possess a unique threedimensional porous network structure and facilitate the electrochemical interaction by diffusing electrolyte ions into the inner electrode between the electrode/electrolyte interface. There are two methods being reported for the synthesis of CPHs. The first one is the addition of smaller molecules (dopants, crosslinkers, gelators) to monomers of CPs to form crosslinked structures. The other method involves the growth of polymer crosslinked 3D hydrophilic networks in presence of initiators. Networks [27–38]. Most hydrophilic soft polymers are electrochemically inactive and electrical insulators. The CPH can be formed by the chemical or physical interactions of rigid conductive polymers in a hydrogel matrix. Therefore, the combination of soft polymers and rigid conducting polymers will help in improving the mechanical properties and will avoid the destruction of network structures. Among all polymers, polyaniline, and polypyrrole hydrogels are proven as the most feasible electrode materials with rigid, fragile, and hydrophobic properties for flexible supercapacitors. The poly(aniline-co-pyrrole)/PVA hydrogels are synthesized via in situ copolymerization of aniline and pyrrole in presence of phytic acid and PVA, which shows ED

272

R. Barik et al.

of 22 Wh/kg and PD of 125 W/kg with 81.7% of capacitance retention. All-hydrogelstate flexible symmetric supercapacitor in presence of PACP/PVA-0.8 hydrogel electrode and PVA/H2 SO4 gel electrolyte with areal capacitance of 350 mF/cm2 is developed by Tao et al. [27]. Zhang et al. in 2017 fabricated flexible supercapacitors with poly(ethylene oxide) and terminal poly(acrylamide) hybrid hydrogel, which shows an SC value of 919 F/g at CD 0.5 A/g [28]. Again, the PANI − PVA hydrogel shows tensile strength (16.3 Mpa), and large elongation at break (407%), having an electrochemical capacitance of 1053 F/g. These attempts further help in developing conductive hybrid hydrogels with robust mechanical properties and electrochemical behavior for futuristic flexible supercapacitors.

3 Methods for the Synthesis of Polymers for Flexible Supercapacitors The vigorous research work is carried out on conductive polymeric materials or organic polymers as supercapacitor materials because of their large specific pseudocapacitance, easy availability, low cost, and simplistic synthesis method. In addition to this, supercapacitor materials or devices are mostly fabricated from polymeric materials or their composites. There are different techniques like in situ polymerization, electrospinning, electrochemical polymerization, and interfacial polymerizations, for flexible efficient supercapacitors.

3.1 In Situ Polymerization Synthesis Method for Supercapacitors One of the most common chemical polymerization techniques is in situ polymerization, where polymers are synthesized from their monomers in presence of oxidizing agents in aqueous phase followed by direct filtration. Initially, in situ polymerization is invented to produce nanofibers, nanoparticles, nanorods. Soudan and his coworkers chemically synthesized a series of conductive polymers for supercapacitor applications by varying the amount of FeCl3 . They polymerized monomers into electrode materials with SC 245 C/g and ED 68 Wh/kg. However, their instability leads to a composite formation where polymers are combined with inorganic moieties through in situ polymerization of monomers. Yuanyuan et al. developed a compressible and flexible supercapacitor by in situ interfacial polymerization of Melamine foam (MF) and polypyrene (PPy) [29]. The electrode MF/Ppy shows high deformation tolerance and excellent supercapacitor properties. The polymer-based supercapacitor shows good cyclic stability with high ED i.e. 75.95 μWh/cm2 , and PD 5.82 mW/cm2 .

Polymeric Materials for Flexible Supercapacitors

273

3.2 Electrochemical Polymerization The electrochemical polymerization technique is used to develop new supercapacitor materials because of its easy templating of ionic materials onto the required electrodes. There are two different ways such as two electrodes and a three-electrode system for electrodeposition as shown in Fig. 4 [30]. A two-electrode system can be configured by positive and negative electrodes dipped in their corresponding electrolyte where the ionic movements are carried with the help of supplied voltage. A Three-electrode system has a working electrode, counter electrode, and reference electrode where the current flows from the working electrode to the counter electrode. Feng and his co-workers developed PANI/graphene electrode materials by one-step electrochemical synthesis. Initially, aniline monomers are adsorbed onto the modified graphene oxide sheets, then the electrochemical polymerization method is followed [31]. In another study, polyaniline/titanium oxide/graphene hybrid (PANI/TiO2 /GN) based electrode material for supercapacitors was developed using simple polymerization of PANI on TiO2 and graphene [32]. In situ polymerization of aniline is carried out in presence of titanium isopropoxide and graphene oxide and results in a good surface area with a high SC of 403 F/g at CD 2 A/g. In addition to these, other polymeric hybrid materials PAN/graphene, NG-PAA/PANI, etc. for supercapacitors using in-situ polymerization are also developed.

3.3 Interfacial Polymerization Generally, most of the supercapacitor research works are extensively carried out on metal oxides/conductive polymers and carbon-based electrode materials. Polymerbased composite materials show pseudocapacitance. However, polymeric materials are not stable electrode materials. Therefore, a controlled synthetic method and addition of its composites can produce stable electrode materials. In this regard, the interfacial polymerization technique is obtained to synthesize stable intrinsic electrically conductive polymer polypyrrole composites with NaVO3 .[33] The polymerization technique involves the simple dissolution of pyrrole monomer FeCl3 and NaVO3 in water where polymerization did at the interfaces of water and organic solvents. The resulting 40% NaVO3 composite shows excellent SC of 391 F/g and good cyclic stability with high specific ED of 14 Wh/kg.

3.4 Electrospinning Nowadays, the electrospinning method is one of the most employed techniques to design 1D fibers sized from micro to nanometers for supercapacitors. 1D fibers with excellent mechanical properties (flexibility, portability, transparency), high ED, and

274

R. Barik et al.

Fig. 4 Schematic presentation of electrochemical synthesis of polymers. Adapted from [30]. Copyright The Authors (2020), Springer Nature. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

PD, make it a future applicant for flexible supercapacitors. The electron transfer/ conduction is facilitated by the axial orientation, and it further reduces the carrier transport path during the flow of polymer solution from a spinneret, and fibers are collected by the collector with the supply of high voltage. Hou et al. synthesized needle-like polyaniline/graphitized ECNF composite electrode for supercapacitors with high SC of 976.5 F/g at CD of 0.4 A/g [34]. Thielk et al. studied the formation of electrospun fibers from polymeric solution and after carbonization, they used the carbon nanofibers for the supercapacitor studies (Fig. 5). The uniform fibers show SC of 103.64 F/g at CD 0.25 A/g, with stability up to 6000 charge–discharge cycles. [35] However, to develop flexible wearable ESCs, conventional electrodes are striving to achieve the requirements.

4 Polymer-Based Substrates for Flexible Supercapacitors The substrates are playing the most vital role in flexible supercapacitors. Polymeric materials with low density, low cost, and smooth processing, offers mechanical flexibility and strength for flexible supercapacitors. Although nickel foam, carbon

Polymeric Materials for Flexible Supercapacitors

275

Fig. 5 i Schematic presentation of Electrospinning method, ii nanofiber formation and iii their electrochemical study. Adapted from [35]. Copyright The Authors (2022), Frontiers Journals. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

cloths, graphite sheets, and aluminum foils, are abundantly used due to their high conductivity, flexibility, and high porosity but the polymer-based substrates (foams/ sponges), papers, hydrogels, and textile materials have been reflected as the most ideal substrates [4]. Polymer hydrogels have a self-healing property with hydrogen bonds, coordination bonds, and supramolecular host–guest interactions making them one of the most encouraging substrates. Polymer carbon nanofibers with high mechanical strength, porosity, and conductivity have emerged as one of the best substrates for supercapacitors. Poly(acrylonitrile) (PAN), polyvinyl pyrrolidone (PVP), and (PVA) are mostly used polymers for CNF preparation followed by carbonization [36]. Non-conductive properties of textile/yarn substrates can be modified with metals, polymers, carbons, etc. by dip-coating, polymerization, and electro-plating methods. Cho et al. developed a graphene/CPs-based composite film, for flexible supercapacitor applications (Fig. 6). This film is flexible in nature, with high degrees of bending or twisting without losing the device integrity, and can be a feasible option for roll-to-roll manufacture [37]. Polymer-based conductive ethylene–vinyl acetate copolymer used as substrate for MnO2 deposition and formation of MnO2 /EVA/CNT for supercapacitor studies with high conductivity of 12.1 S/m and ED of 9.4 Wh/ kg with 3% capacitance loss over 5000 cycles [38]. Likewise, melamine foam-based substrates, electrochemically deposited PPy on gold-sputtered layers, cellulose fibers papers, polymer hydrogels, etc. are also used as working substrates for the flexible supercapacitors.

5 Polymer Based Electrolytes for Flexible Supercapacitors Polymer-based electrolytes play an important role for flexible supercapacitors. Since the first report in 1970, there are many polymer electrolytes have been conceptualized and investigated. Polymer-based electrolytes are important class of electrolytes, due

276

R. Barik et al.

Fig. 6 Schematic presentation of metallic paper (MP)-based supercapacitor electrode. using ligandmediated layer-by-layer assembly between hydrophobic metal (or metal oxide) nanoparticles and tris(2-aminoethyl) amine molecules. Adapted from [37]. Copyright The Authors (2017), Springer Nature. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

to their long polymeric chains and high concentration of ions, for the development of non-flammable and non-toxic energy storage and conversion devices. Other properties such as flexibility, mechanical stability, adhesion to electrodes, structural stability during the charging and discharging cycle, etc. make them good candidates [39]. The preparation of polymer electrolytes is broadly divided into two categories i.e., physical, and chemical methods. The physical methods generally include physical crosslinking, an entanglement of chains, and electrostatic interactions, whereas in chemical method the bond formation takes place leading to 3D network gels, which further divided into three categories as monomer cross-linking, polymer cross-linking, and carrier graft copolymerization [40]. Based on the method of preparation and materials involved the polymer electrolytes have been categorized in the following types: (i) Solvent-free polymer electrolytes, (ii) solvent polymer electrolytes, (iii) plasticized polymer electrolytes, (iv) polyelectrolytes, (v) rubbery electrolytes, (vi) porous polymer electrolytes, (vii) Gel polymer electrolytes, and (viii) composite polymer electrolytes [41]. PVA-based electrolytes have gained attention due to their high conductivity. Along with a number of polymer hosts such as poly-acrylic acid, poly-ethyl oxide, polyacrylate, poly(vinylidene fluoride-co-hexafluoropropylene), poly-(methyl methacrylate),

Polymeric Materials for Flexible Supercapacitors

277

and many more are used for the gel polymer electrolytes. Further, the addition of some organic solvents (such as diethyl methyl formamide, ethylene glycol, etc.) or aqueous solutions of potassium hydroxide, sulfuric acid, and phosphorous acid to the polymer results in gel electrolytes and hydrogel redox-active electrolytes [39]. The main drawback regarding polymer electrolytes is comparatively low conductivity as compared to conventional electrolytes but free from corrosion, packing, and leakage issue. Therefore, research is still going on to develop some advanced flexible polymer-based electrolytes for energy storage devices. However, gel polymer electrolytes lose their efficiency in low temperatures due to the presence of water. Still, there is a lot to be explored in the field of polymer electrolytes, and their fabrication methods to increase conductivity.

6 Future Perspective of Polymeric Materials for Flexible Supercapacitors Supercapacitors have been widely accepted as superior energy storage devices because of their faster and high energy storage capacity. In the past few years, significant research has led to progress all the way from conventional to flexible supercapacitor devices. Carbon nanomaterials played a major role in bringing the era of flexible devices but due to the poor conductivity further research focused on carbon-based graphene and CNTs resulted in enhanced conductivity. These materials also have some drawbacks, which include structural instability and overall activity. So, the transition metal oxides and conducting polymers-based supercapacitors were able to solve problems to some extent. The CPs emerged as a solution because of their high theoretical specific capacitance, electrical conductivity, voltage window, porosity, adjustable redox properties, and environment-friendly nature. Various approaches have been attempted to improve their performance which includes the formation of primary, secondary, and tertiary nanocomposites with transition metal oxides and carbon nanomaterials. But due to their low conductivity and poor stability, polymeric materials limit their practical applications. Various studies have been conducted to enhance the research in flexible supercapacitors. In a recent study, a used newspaper has been used as an electrode after dipping it in graphite and depositing Ppy polymer over it, promoting sustainability. To enhance energy density of hydrogel-based electrolytes have been used in recent times. Natural polymer lignin-based Fe3+ -rich, high-conductivity hydrogels with tunable mechanical properties are used for supercapacitor application. The low ED and high cost remain the major challenge in this field, one of the approaches to solve this problem is to combine EDLC material with pseudocapacitive material. The polymer-based carbon fibers are the most promising electrode materials as discussed above while structural instability is still associated with polymers. Some new materials like CoN-Ni3 N/N–C nanosheets show some promising results and

278

R. Barik et al.

give new hope to developing new technology with better stability. To make the device environment-friendly, natural polymers are being explored. Solid polymer electrolytes are an important component in the development of flexible energy storage technology and using molecular dynamics the distribution of ions in the electrolyte can be predicted to further improve the performance. MOFs and COFs contribute a lot to the advancement of energy storage materials. So, the compatibility of polymers as well as the geometry, lattice matching, hydrophobicity, flexibility, and stability with MOFs and COFs may be a promising solution to gain high conductivity for the efficient device. In recent years computational chemistry has played important role in the development of materials related to the component of energy storage devices. Along with experimental techniques models and simulation of new concepts of materials and electrolytes can complement the understanding of the mechanism, the further scope for improvement supercapacitors. Self-healing polymeric materials hold great promise for the future of SCs. In-situ doping, and modification of polymer architecture may be a suitable solution for the synthesis of CPs. Polymeric electrolytes are playing an important role in the new generation devices. CPs suffer from poor conductivity, but some solid strategies are required to convert the polymeric materials to future energetic materials. 3D printing technology will be one of the most conventional methods for their application for wearable and skin-attached electronic devices. So, 3D printing technology must be explored for flexible supercapacitors.

7 Conclusions Last several years polymeric materials and their research for the development of flexible supercapacitors have been improved precipitously. In this book chapter, the different polymeric materials and their composites are discussed. Various synthesis methods are discussed with their advantages and disadvantages. The research till date has proved that CPs holds great potential for the energy storage devices due to their properties complimenting the criteria required for flexible devices. However, it is obvious that there are several issues associated with the polymeric materials for flexible supercapacitor development such as poor conductivity, less stability, limits its industrial applications, and needs further revisions. This can be achieved by lowering the cost of materials, increasing the cyclic stability, and improving the fabrication method to enhance energy density and storage capacitance. Further, the mechanical stability can be resolved using different architectures for the electrodes, substrates, and electrolytes. Conclusively there is still a lot of research yet to be done in the field of materials related to supercapacitors and they can be reliable for the future along with large-scale energy storage devices. Additional efforts must be given for the large-scale flexible, wearable supercapacitor fabrication. A healthier and more mature knowledge of polymeric materials will be helpful in encouraging future research.

Polymeric Materials for Flexible Supercapacitors

279

Acknowledgements RB is grateful to Institute Postdoctoral Fellowship provided by IIT Delhi. SP is grateful to Case Western Reserve University, USA for providing the Ph.D. fellowship. AKB is thankful to the University of Washington, USA for the postdoctoral fellowship.

References 1. Han Y, Dai L (2019) Conducting polymers for flexible supercapacitors. Macromol Chem Phys 220(3):1800355 2. Shown I, Ganguly A, Chen L-C, Chen K-H (2015) Conducting polymer-based flexible supercapacitor. Energy Sci Eng. 3(1):2–26 3. Dubal DP, Chodankar NR, Kim D-H, G.-Romero P (2018) Towards flexible solid-state supercapacitors for smart and wearable electronics. Chem Soc Rev 47:2065–2129 4. Shang K, Gao J, Yin X, Ding Y, Wen Z (2021) An overview of flexible electrode materials/ substrates for flexible electrochemical energy storage/conversion devices. Eur J Inorg Chem 7:606–619 5. Liu L, Niu Z, Chen J (2016) Unconventional supercapacitors from nanocarbon-based electrode materials to device configurations. Chem Soc Rev 45:4340–4363 6. Sharma S, Soni R, Kurungot S, Asha SK (2019) Rylene diimide-based alternate and random copolymers for flexible supercapacitor electrode materials with exceptional stability and highpower density. J Phys Chem C 123:2084–2093 7. Uke SJ, Mardikar SP, Kumar A, Kumar Y, Gupta M, Kumar Y (2021) A review of π-conjugated polymer-based nanocomposites for metal-ion batteries and supercapacitors. R Soc Open Sci. 8(10):210567 8. Holze R (2017) Metal oxide/conducting polymer hybrids for application in supercapacitors, metal oxides in supercapacitors. Metal Oxides 219–245 9. Siwal SS, Zhang Q, Devi N, Thakur VK (2020) Carbon-based polymer nanocomposite for high-performance energy storage applications. Polymers 12(3):505 10. Arvas MB, Yazar S, Sahin Y (2022) Electrochemical synthesis and characterization of selfdoped aniline 2-sulfonic acid-modified flexible electrode with high areal capacitance and rate capability for supercapacitors. Synth Met 285:117017 11. Ju G, Khan MA, Zheng H, An Z, Wu M, Zhao H, Xu J, Zhang L, Bilal S, Zhang J (2019) Honeycomb-like polyaniline for flexible and folding all-solid-state supercapacitors. Front Mater Sci 13:133–144 12. Yang J, Cao Q, Tang X, Du J, Yu T, Xu X, Cai D, Guan C, Huang W (2021) 3D-Printed highly stretchable conducting polymer electrodes for flexible supercapacitors. J Mater Chem A 9:19649–19658 13. Chee WK, Lim HN, Zainal Z, Harrison I, Huang NM, Andou Y, Chong KF, Pandikumar A (2017) Electrospun nanofiber membranes as ultrathin flexible supercapacitors. RSC Adv 7:12033–12040 14. Wang Y, Tang S, Vongehr S, Syed JA, Wang X, Meng X (2016) High-performance flexible solidstate carbon cloth supercapacitors based on highly processible N-graphene doped polyacrylic acid/polyaniline composite. Sci Rep 6, Article number:12883 15. Wang K, Zhao P, Zhou X, Wu H, Wei Z (2011) Flexible supercapacitors based on clothsupported electrodes of conducting polymer nanowire array/SWCNT composites. J Mater Chem 21:16373–16378 16. Vu V-P, Mai V-D, Lee S-H (2023) Hybrid carbon nanofiller/polymer composites as self-healable current collector electrodes for use in high-performance flexible metal-free supercapacitors. J Alloys Compd 93:167823 17. Feng M, Lu W, Zhou Y, Zhen R, He H, Wang Y, Li C (2020) Synthesis of polypyrrole/nitrogendoped porous carbon matrix composite as the electrode material for supercapacitors. Sci Rep 10, Article number:15370

280

R. Barik et al.

18. Parne CM, Chhetri BP, Mitche TB, Watanabe F, Kannarpady G, RanguMagar AB, Zhou H, Alghazali KM, Biris AS, Ghosh A (2019) Sci Rep 9:5650 19. Barik R, Barik G, Tanwar V, Ingole PP (2022) Supercapacitor performance and charge storage mechanism of brannerite type CuV2 O6 /PANI nanocomposites synthesis with their theoretical aspects. Electrochim Acta 410:140015 20. Usman M, Adnan M, Ahsan MT, Javed S, Butt MS, Akram MA (2021) In situ synthesis of a polyaniline/Fe–Ni codoped Co3 O4 composite for the electrode material of supercapacitors with improved cyclic stability. ACS Omega 6(2):1190–1196 21. Liu W, Liu N, Shi Y, Chen Y, Yang C, Tao J, Wang S, Wang Y, Su J, Li L, Gao Y (2015) A wire-shaped flexible asymmetric supercapacitor based on carbon fiber coated with a metal oxide and a polymer. J Mater Chem A 3:13461–13467 22. Lee J, Seok J, Son S, Kang B, Yang M (2017) High-energy, flexible micro-supercapacitors by one-step laser fabrication of a self-generated nanoporous metal/oxide electrode. J Mater Chem A 5:24585–24593 23. Liu T, Liu G (2019) Block copolymers for supercapacitors, dielectric capacitors and batteries. J Phys: Condens Matter 31:233001 24. Wang W, Zhu F, Dai Y, Zhang H, Lei J (2016) Electrosynthesis and performance of poly(aniline/ pyrrole) copolymer. Int J Electrochem Sci 11:4000–4006 25. Wang Y, Ma W-B, Guo L, Song X-Z, Tao X-Y, Guo L-T, Fan H-L, Liu Z-S, Zhu Y-B, Wei X-Y (2020) Phytic acid-doped poly(aniline-co-pyrrole) copolymers for supercapacitor electrodes applications. J Mater Sci Mater 31:6263–6273 26. Tong Y-X, Li X-M, Xie L-J, Su F-Y, Li J-P, Sun G-H, Gao Y-D, Zhang N, Wei Q, Chen C-M (2016) Nitrogen-doped hierarchical porous carbon derived from block copolymer for supercapacitor. Energy Storage Mater 3:140–148 27. Tao X-Y, Wang Y, Ma W-B, Ye S-F, Zhu K-H, Guo L-T, Fan H-L, Liu Z-S, Zhu Y-B, Wei X-Y (2021) Copolymer hydrogel as self-standing electrode for high performance all-hydrogel-state supercapacitor. J Mater Sci 56:16028–16043 28. Zhang G, Chen Y, Deng Y, Wang C (2017) A triblock copolymer design leads to robust hybrid hydrogels for high-performance flexible supercapacitors. ACS Appl Mater Interfaces 9:36301– 36310 29. Sun Y, Jia D, Zhang A, Tian J, Zheng Y, Zhao W, Cui L, Liu J (2019) Synthesis of polypyrrole coated melamine foam by in-situ interfacial polymerization method for highly compressible and flexible supercapacitor. J Colloid Interface Sci 557:617–627 30. Lv H, Pan Q, Song Y, Liu X-X, Liu T (2020) A Review on Nano-/microstructured materials constructed by electrochemical technologies for supercapacitors. Nano-Micro Lett. 12:118 31. Feng X-M, Li R-M, Ma Y-W, Chen R-F, Shi N-E, Fan Q-L, Huang W (2011) One-step electrochemical synthesis of graphene/polyaniline composite film and its applications. Adv Funct Mater 21(15):2989–2996 32. Parveen N, Ansari MO, Han TH, Cho MH (2017) Simple and rapid synthesis of ternary polyaniline/titanium oxide/graphene by simultaneous TiO2 generation and aniline oxidation as hybrid materials for supercapacitor applications. J Solid State Electrochem 21:57–68 33. Naseeb I, Almashhadani HA, Macadangdang RR Jr, Ullah S, Khan MF, Kamran M, Qureshi N, Naseeb F (2022) Interfacial polymerization synthesis of polypyrrole and sodium metavanadate (PPy/NaVO3 ) composite as an excellent performance electrode for supercapacitors. Results Chem 4:100446 34. He S, Hu X, Chen S, Hu H, Hanif M, Hou H (2012) Polyaniline nanowires on graphite nanofibers: hierarchical micro/nanoarchitecture for high performance supercapacitors. J Mater Chem 22:5114–5120 35. Thielke MW, Guzman SL, Tafoya JPV, Tamayo EG, Herazo CIC, Hosseinaei O, Sobrido AJ (2022) Full lignin-derived electrospun carbon materials as electrodes for supercapacitors. Front Mater 9:859872 36. Chee WK, Lim HN, Zainal Z, Huang NM, Harrison I, Andou Y (2016) Flexible graphene-based supercapacitors: a review. J Phys Chem C 120(8):4153–4172

Polymeric Materials for Flexible Supercapacitors

281

37. Ko Y, Kwon M, Bae WK, Lee B, Lee SW, Cho J (2017) Flexible supercapacitor electrodes based on real metal-like cellulose papers. Nat Commun 8, Article number:536 38. Zhang Z, Wang W, Li C, Wei L, Chen X, Tong Y, Mai K, Lu X (2014) Highly conductive ethylene–vinyl acetate copolymer/carbon nanotube paper for lightweight and flexible supercapacitors. J Power Sources 248:1248–1255 39. Pal B, Yang S, Ramesh S, Thangadurai V, Jose R (2019) Electrolyte selection for supercapacitive devices: a critical review. Nanoscale Adv 1:3807–3835 40. Hashmi SA, Yadav N, Singh MK (2020) Polymer electrolytes for supercapacitor and challenges. Polymer electrolytes. Wiley, pp 231–297 41. Bhat TS, Patil PS, Rakhi RB (2022) Recent trends in electrolytes for supercapacitors. J Energy Storage 50:104222

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors Achayalingam Ramesh, Sourabh Basu, and M. Sterlin Leo Hudson

Abstract The creation of more flexible and adaptable energy storage technology having high power and energy densities is necessary for the development of nextgeneration electronic devices. A variety of high-tech electronic gadgets, from microelectronics to automotive applications, need high-performance energy storage technologies. The supercapacitor is a potential energy storage alternative that provides high power density for energy storage and conversion devices. The performance of the active electrode material has a major impact on the supercapacitors’ ability to store energy. In order to find an electrode material that gives high power and energy densities for supercapacitors, substantial research is being conducted in this area. One of the promising electrode materials that offer excellent energy storage capability to supercapacitors is metal phosphide (MPs). MPs are a potential material for energy storage devices due to their good electrical conductivity and a high degree of chemical stability. Recently, polymer-metal phosphide nanocomposites are becoming a feasible material for supercapacitor applications due to their ultra-flexibility and compactivity. This chapter provides a summary of the most recent advancements in MPs and polymer-based MPs for supercapacitor applications. Keywords Metal-phosphides · Conducting polymer · Flexible supercapacitor · Polymer-metal phosphide composite

1 Introduction The creation of flexible supercapacitors of the next generation requires high-capacity electrode materials. The electrode materials must have high power and energy densities and be able to tolerate external stress and damage in order to have an energy

A. Ramesh · S. Basu · M. Sterlin Leo Hudson (B) Department of Physics, Banaras Hindu University, Uttar Pradesh, Varanasi 221005, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_16

283

284

A. Ramesh et al.

storage device with a long lifespan. Metal complexes with oxygen/hydroxide functionalities (Redox materials) offer greater specific capacitance (CS ) and energy densities as compared to carbon-based nanostructured materials. Due to the presence of redox functionalities, these metal complexes possess poor electrical conductivity [1] and greater electrolyte corrosion [2]. In order to achieve favourable charge/ discharge performance, conductive additives (carbon black, graphene, CNTs, carbon nanofibers, and conducting polymers) are employed to make these electrode materials electrically conductive [3–6]. Moreover, numerous metals that have been conjugated with sulfur, phosphorous, boron, carbon, and nitrogen have intriguing properties such as high electrical conductivity and good chemical stability, hence they are being considered as prospective electrode materials for energy storage applications [7]. MPs are interesting electrode materials for energy applications as they exhibit good electrical conductivity, higher electrolytic accessibility, and higher chemical stabilities when compared to metal oxides and metal hydroxides [8, 9]. MPs are also well suited for use as stable electrode materials due to their greater thermal stability and good environmental resistance. As a result, electrodes made of MPs can be used in energy storage and conversion technologies such as, batteries, sensors, water purification, water splitting, [10, 11] solar cells and catalysis [7]. Recently, numerous MPs have been studied as novel electrode materials in symmetric and asymmetric supercapacitors and have shown great performance with enhanced CS . These MPs include copper phosphide (CuP, Cu3 P), nickel phosphide (NiP), and cobalt phosphide (CoP) [12]. Although phosphorus-rich material have low ionic character, by increasing metal ions, the electrical conductivity of MPs can be increased. This increase in metal ion concentration may increase the availability of free electrons in MPs, resulting an enhancement in its electrical conductivity [8]. Since pure metal and metal-rich phosphides have similar binding energies, the addition of a secondary metal phosphide enhances the redox site properties while maintaining chemical stability [13]. Due to the their variable valence states available for redox processes, bimetallic and ternary transition MPs such as NiCoP, [14] ZnNiP, [15] NiFeP, [16] CuCoP, [17] ZnNiCoP [18] and FeCoNiP [19] have attracted significant interest due to their superior capacitance performance, which is higher than the mono-MPs [12, 13]. While designing flexible appliances, conductive polymers (CPs) of polyethylenedioxythiophene (PEDOT), polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) plays a vital role due to their flexibility and superior electrical conductivity [20]. These polymers can give exceptional electrical contact and flexibility to the composite materials. Additionally, CPs are used for a variety of energy storage applications due to their distinctive redox reactions, inexpensive preparation techniques, and increased storage capacities [21]. MPs and CPs composite have demonstrated greater potential for energy storage in flexible electronic appliances. The addition of CPs provides conductive pathways for electrons to go through MPs surfaces, facilitating efficient electrochemical reactions on the surface of MPs [22]. This chapter will present updates on MPs and polymer-MP nanocomposites and examine their advancement in supercapacitor applications in addition to the electrochemical performance analysis of these materials.

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

285

2 Metal Phosphides (MPs) MPs are generally prepared through phosphorization of metal or metal oxide precursors. These MPs exhibit excellent electrochemical properties because of their exceptional electrical conductivity and outstanding redox activity. MPs are typically categorized as either mono- MPs (consist of only one type of metallic element for example, nickel phosphide, cobalt phosphide, iron phosphide etc.), binary MPs (consist of two different types of metallic element for example, nickel cobalt phosphide, iron cobalt phosphide etc.), or ternary MPs (consist of multiple intermetallic phosphides). These MPs have very good chemical stability and possess numerous redox states on its structure. Thus, the structural morphology of MPs determines its electrochemical characteristics. As a result, several efforts have been undertaken to synthesize MPs through various techniques and adopted different strategies to improve their electrochemical characteristics. One such strategy for improving the electrochemical characteristics of MPs was by employing conductive additives such as CNTs, graphene, and CPs. Figure 1 shows the schematic representation of different types of MPs.

2.1 Mono-Metal Phosphides Mono-MPs such as cobalt phosphides (CoPs) and nickel phosphides (NiPs) have good electrochemical stability [23] and possess high theoretical capacitance [24]. Fig. 1 Classification of metal phosphides

286

A. Ramesh et al.

The redox activity and distinct charge transfer and storage properties of MPs attract research attention for electrochemical energy storage. In addition to having a greater theoretical capacitance, NiPs is also a cost-effective and environmentally-friendly material. Several nickel phosphide compounds such as NiP, NiP2 , NiP3 , Ni2 P, Ni3 P4 , Ni5 P4 , and Ni12 P5 , are now being researched for use in supercapacitors [25]. Recently, greater CS value of 1625 F g-1 at 1 A g−1 was reported for electrode fabricated using 3-dimensional (3D) hollow NiP microspheres prepared from nickel-metal– organic frameworks (Ni-MOFs) and measured capacitance loss (CL ) after 10,000 cycles was 35%.[26] The electrode fabricated using hydrothermal phosphorization derived nanostructured Ni2 P shows a superior CS of 2031 mF cm−2 (2539 F g−1 ) at 1 mA cm−2 and 2859 mF cm−2 (3574 F g−1 ) at 5 mV s−1 , respectively [27]. After 2500 galvanostatic charge discharge (GCD) cycles, the Ni2 P electrode shows a CL of 10.7% in comparison to its initial charge/discharge cycle. In another study, yolk-shell type Ni3 P was prepared by using solvothermal method. The electrode fabricated using Ni3 P with activated carbon demonstrated a CS of 170.8 F g−1 at 0.5 A g−1 [28]. This electrode has a CL of 4.4% after 3500 GCD cycles at 2 A g−1 . In a different work, P. Sun et al. [29] investigated the electrochemical properties of 3D Ni3 P nanostructure. The electrode fabricated using 3D Ni3 P nanostructure as an active electrode material shows the CS of 1761 mF cm−2 (1048 F g−1 ) at 5 mA cm−2 . The hydrothermal method derived Ni12 P5 hollow nanocapsule reported by H. Wan et al. [30] exhibit CS value of 949 F g−1 at 1 A g−1 . After 2000 GCD cycles determined at 5 A g−1 , the electrode has a capacitance retention (CR ) of 81%. The CR was calculated from the difference in the capacitance value measured between the initial and final GCD cycles. Like NiPs, CoPs have high electrical and thermal conductivity as well as good chemical stability [31]. Crystalline phases of CoPs family such as CoP, Co2 P, CoP2 , and CoP3 exhibit superior electrochemical performance. Han et al. [32] recently synthesized CoP nanoneedles through hydrothermal method which yields a specific capacity of 403.5 C g−1 , at 1 A g−1 . They have observed that 73% of the initial capacitance was retained after 1000 GCD cycles at 5 A g−1 . However, phosphorization of CoP nanoneedles leads to an enhanced capacitance of 422.4 C g−1 with much improved cyclic stability of 99% (CR ) after 10,000 cycles at 5 A g−1 . Hollow nanoflower like Co2 P structure derived by using thermal decomposition was reported to have a CS value of 412.7 F g−1 at 1 A g−1 in 6 M KOH solution. After 10,000 GCD cycles at 5 A g−1 , the CS of Co2 P was found to increase from 285.9 to 360.9 F g−1 .[33] Another work by Jiang et al. [34] report the excellent electrochemical properties of CoP3 grown on Ni foam, which exhibit a CS value of 3000 mF cm−2 (1632 F g−1 ) at 2.5 mA cm−2 , with the CR of 81.4% after 10,000 GCD cycles. Furthermore, the addition of Ni to CoP3 increased the CS of the electrode to 2780 F g−1 with a CR of 90.2% after 10,000 GCD cycles. Iron phosphide (FeP) is another intriguing mono-MP that has recently attracted considerable research attention as a substitute for Ni and Co-based phosphides in electrochemical energy storage applications [35]. Luo et al. [36] recently reported an areal capacitance of 438.39 mF cm−2 for FeP nanorods. However, after 5000 cycles, the CR of FeP has significantly dropped to 24.19%. The addition of conductive

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

287

polymer in FeP was found to improve the cyclic stability. Liang et al. [37] observed that FeP nanotube arrays on carbon cloth-based negative electrodes exhibit a CS of 149.11 F g−1 and a high areal capacitance of 300 mF cm−2 at 1 mA cm−2 . The addition of reduced graphene oxide (rGO) to the FeP coated electrode increased its capacitance. The FeP with rGO as an additive has a CS of 376.50 F g−1 at 1 A g−1 and good cyclic stability, retaining 82.5% of its initial capacitance after 5000 cycles. However, when measured at 6 A g−1 the cyclic stability was reduced to 71.7% [38]. Nanostructured Copper(I) phosphides (Cu3 P) have excellent electrochemical properties. Cu3 P is environmentally friendly and more chemically stable than CuP. Nonetheless, there hasn’t been much research done on Cu3 P so far. Chen et al. [39] synthesized Cu3 P nanotubes (~ 5 nm diameter) array on copper foil through electrooxidation followed by the phosphorization method. The Cu3 P nanotubes array electrode has a CS of 300 F g−1 at 2.5 mA cm−2 and the CR of 81.9% after 5000 GCD cycles at 10 mA cm−2 . Jin et al. [40] examined the electrochemical properties of Cu3 P nanocrystals. The Cu3 P nanocrystals electrode has an excellent CS of 992.4 and 318.5 F g−1 at 2 and 400 mV s−1 , respectively with no noticeable CL even after 10,000 GCD cycles at 10 A g−1 . Kumar et al. [41] recently reported that hexagonal Cu3 P platelets synthesized using CVD technique and graphene as an additive have a CS of 1095 F g−1 at 10 mV s−1 with a CR of 95% after 3000 GCD cycles. Furthermore, combination of Co and Fe along with CuP exhibits a higher CS of 1290 C g−1 at 1 A g−1 with good cyclic stability (94.8%) even after 5000 GCD cycles, according to the report [42].

2.2 Bimetal Phosphide Transition metals (TMPs) have the ability to chemically combine with a variety of metals and exhibit a metalloid-like character, which aids in the enhancement of their electrochemical properties. Bimetallic phosphides are becoming a popular electrode material for supercapacitors due to their high electrical conductivity and superior electrochemical response. The availability of more free electrons in metal-rich MPs increases its electrical conductivity. As a result, when phosphorus is conjugated with transition metals to form TMPs, the metal-rich phosphide phases can transport more freely accessible electrons, improving electrical conductivity and forming an electrochemical feedback [13]. Co and Ni have received a lot of interest as potential supercapacitor electrode materials because of their similar electrochemical redox potentials. These redox materials can aid the reversible Faradaic reactions in the electrodes. Zhang, et al. [12] determined the variation in the CS values while varying the Co concentration in CoNiP/CNF, which is shown in Fig. 2. He measured a higher CS value of 3093 F g−1 (capacity of 1237.2 C g−1 ) at 50 mV s−1 when the Co:Ni ratio was 1:9 in CoNiP/CNF composite (Co0.1 Ni0.9 P/CNF) electrode. Furthermore, even at a higher current density of 500 A g−1 a higher CS of ~ 2996 F g−1 (capacity of 1198.4 C g−1 ) was observed for Co0.1 Ni0.9 P/CNF electrode. Lower CS was observed when the Co:Ni ratio was increased or decreased from 1:9.

288

A. Ramesh et al.

Fig. 2 a Specific capacitances/capacities of CoNiP/CNF composite estimated from the CV curves (measured at 50 mV s−1 ), when the Co:Ni ratio is varied from Co0 Ni1 P to Co1 Ni0 P. b Specific capacitances/capacities versus current density curve of Co0.1 Ni0.9 P/CNF at different current densities. Adapted with permission [12], Copyright (2019), American Chemical Society

Several binary MPs have recently gained popularity as a supercapacitor electrode material. During electrochemical reaction, mixed MPs of Co–Ni phosphides, [43] Ni–Fe phosphides, Cu–Co phosphides and Co–Mn phosphides contribute to redox reaction. Other binary MPs such as Ni–Mo phosphides, Co–Mo phosphides, and Zn–Ni phosphides possess excellent structural stability during the electrochemical reactions [44]. Li et al. [16] reported a higher CS of 3017.8 F g−1 (1358 C g−1 ) at 5 mA cm−2 for the electrode fabricated using freestanding NiFeP nanosheets. Moreover, these NiFeP were found to have good cyclic stability with a 94.7% CR even after 10,000 GCD cycles. Bimetallic NiFeP nanosheets were found to show much improved electrochemical performance than monometallic NiP nanosheets. Recently, Moosavifard et al. [17] reported a CS value of 1946 F g−1 (4.86 F cm−2 ) at 5 mA cm−2 for the electrode fabricated using CuCoP hollow microspheres. It also exhibits very good cyclic stability with a 92.7% CR after 6000 GCD cycles. More recently, Xiang et al. [45] synthesized layered flower like structure of CoP–Mn3 P through hydrothermal method. The CoMn3 P sample exhibit a CS of 2714 F g−1 at 1 A g−1 with 83.1% CR after 10,000 cycles. Hierarchical 3D nanosheet arrays of ZnNiP was reported to have a specific capacity of 384 mA h g−1 at 2 mA cm−2 and a CR of 93.05% after 20,000 GCD cycles [15].

2.3 Ternary Metal Phosphide Compared to mono and binary MPs, ternary MPs have more redox active sites and superior electrical conductivity due to the presence of multiple intermetallic phases and structural defects caused by multi-metal ions. Hence, ternary MPs exhibit superior electrochemical characteristics than mono and binary MPs. The electrochemical properties of NiCoP nanoneedles grown on porous MnP nanosheets supported by Ni

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

289

foam (NF/MnP/NiCoP) was investigated by Hong et al. [47]. The CS of the NF/MnP/ NiCoP electrode was found to increase from 880 F g− 1 to 2310 F g− 1 after 1270 GCD cycles, due to the activation of electrode during GCD cycles. Figure 3 depicts the schematic method employed for the preparation of Ni/MnP/NiCoP composite and its electrochemical characteristics. Huang et al. [46] reported the growth of NiCoMoP on carbon cloth and found a CS of 433 F g−1 at 1 A g−1 . Moreover, the NiCoP with CoNiMoP exhibit a specific capacity of 1366 C g−1 at 2 A g−1 with 94% CR after 6000 GCD cycles. Xie et al. [19] described the synthesis and electrochemical properties of free-standing FeCoNiP nanosheet arrays on carbon cloth, having a capacity of 593.0 C g−1 at 1 A g−1 and a CR of 84.2% after 5000 GCD cycles. Lei et al. [18] determined a high CS of 2820 F g−1 (1269 C g−1 ) at 3 A g−1 and a CR of 92% after 10,000 GCD cycles at 2 A g−1 for the electrode fabricated using ZnNiCoP grown on Ni foam. Recently, Saleh et al. [48] reported a very high CS of 3380 F g−1 (having capacity of 1690 C g−1 ) at 1 A g−1 for MnNiCoP, having Mn:Ni:Co ratio 1:1:1 prepared by electrodeposition followed by PH3 plasma treatment. Furthermore, the sample has very good cyclic stability of 96% CR after 8000 GCD cycles at 10 A g−1 .

Fig. 3 a Schematic diagram depicting the preparation method used for NF/MnP/NiCoP composite on Ni foam, b specific capacitance versus current density curve, determined at different cycles, c GCD cycle measured with capacitance performance. Adapted with permission [47], Copyright (2022), Elsevier

290

A. Ramesh et al.

3 Polymer-Metal Phosphide Composites MPs exhibit excellent electrochemical properties when combined with CPs such as Poly(3,4-ethylenedioxythiophene) (PEDOT), Polyaniline (PANI), Polypyrrole (PPy), Polyacrylamide (PAM) and Polythiophene (PTh). Several studies on MPs and CPs have recently been conducted in order to find flexible electrode materials for electrochemical energy storage. Luo et al. [36] created a low-cost negative electrode stabilised for long-term redox reactions using PEDOT and iron phosphide (FeP) nanorods. The FeP/PEDOT composite electrode show significant increase in the capacitance value of 790.59 mF cm−2 at 1 mA cm−2 , whereas that of FeP nanorods electrode shows a capacitance of 438.39 mF cm-2 at the same current density. The addition of PEDOT was found to be effective in lowering the series and the charge transfer resistances, as well as providing a protective conductive coating around the FeP nanorods, resulting in significantly improved mechanical and charge discharge cyclic stability. Figure 4 represents the various types of MPs and their tendency to make composite with various conductive polymers, as well as their superior performance in charge-discharge cycles of electrochemical energy storage devices. Nayak et al. [9] reported an enhancements in specific capacity of 369.18 C g−1 for Ni12 P5 /PANI composite due to the higher conductivity and increased number of redox active sites. The specific capacities of the composite’s individual components, Ni12 P5 and PANI were 216.2 and 282.94 C g−1 , respectively, at a scan rate of 3 mV s−1 . An asymmetric supercapacitor fabricated using Ni12 P5 /PANI composite and activated carbon as the positive and negative electrodes, Whatman filter paper as separator and Fig. 4 Different polymer metal phosphide composites for energy storage applications

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

291

2 M aq. KOH as electrolyte solution. The supercapacitor has the maximum energy density of 21.9 Wh kg−1 and a power density of 373.6 W kg−1 at 0.5 A g−1 . Another study by Liu et al. [49] demonstrated the improved electrochemical performance of PPy/Ni2 P composite, having CS of 476.5 F g−1 at 1 A g−1 . They have investigated the electrochemical behaviour of Ni2 P/PPy composite at different mass ratio of Ni2 P and PPy. The optimal electrochemical performance was observed for 30 wt.% of Ni2 P in the Ni2 P/PPy composite. The Ni2 P in the composite increases mechanical strength and reduces the swelling and shrinking of conductive polymer, leading to an improved electrochemical performance of Ni2 P/PPy composite. Bimetallic TMPs with CPs composite were found to have superior electrochemical characteristics due the creation of higher faradaic redox centres and a stable crystal structure. In addition to CPs, conducting CNFs have also been investigated for improving the conductivity and structural stability of bimetallic TMPs. Zhang et al. [12] described the synthesis of ultrafine crystals of CoNiP by wet-chemical reduction of metal precursors followed by phosphorization. They have found that, for optimal element ratio (Co:Ni:P = 0.1:0.9:1) in the bimetallic Cox Ni1−x P/CNF composites, the capacitance increased significantly. The CNFs in the composite provide a conductive pathway for electrons, and their reticular structure aids in ion diffusion and electrolyte permeation. The Co and Ni metal ratio in the composite also plays a significant role for the material performances The CV curves shows a shift in redox peak toward negative potential side as the Co concentration is increased in the Cox Ni1-x P/CNF composites then a redox peak shift toward positive potential was observed when the stoichiometric ratio for Co:Ni exceeds 1:1 in Cox Ni1-x P/CNF composites. This suggests that a strong electronic interaction between Co and Ni facilitates the oxidation of Ni. As a result, changes in the Co:Ni ratio cause changes in the faradaic properties and the pseudo nature of the material. CNF was used by Gopalakrishanan et al. [50] to modify the electrochemical properties of Ni1 Co9 P. CNFs improves the conductivity, electron transport kinetics and electrochemical stability of Ni1 Co9 P, resulting in an increase in CS from 160 F g−1 to 200 F g−1 . Recently, composites of CPs like PANI, PPy and carbon materials such as CNTs, templated carbon have recently been used to enhance the overall conductivity, pseudo-capacitance and flexibility of bimetallic TMPs. Shi et al. [51] studied the use of carboxylic CNT (c-CNT) and PPy to improve the electrochemical performance of NiCoP. The NiCoP @CNT@PPy composite was prepared by using a simple hydrothermal method, and its electrochemical properties were tested over a wide range of operating temperatures and bending angles. The capacitance of NiCoP attached with c-CNT framework and PPy polymer composite exhibit higher CS than NiCoP and NiCoP@c-CNT. NCP@CNT10@PPy6 was reported to have a CS of 1807.8 F g−1 at 1 A g−1 , whereas, NiCoP, NiCoP @CNT10 and NiCoP @PPy6 were found to have CS of 1388.2, 1570.5 and 1426.4 F g−1 , respectively. The PPy improves the conductivity of active electrode material, while the tubular c-CNT penetrates into NiCoP structure, creating gaps for the diffusion of ions and effectively assisting in electron transfer throughout the material. The ASC device fabricated using the composite has a capacitance of 127.9 F g−1 at 1 A g−1 and a series resistance Rs of 0.53 Ω, highlighting the composite’s effective charge transfer. The fabricated

292

A. Ramesh et al.

Fig. 5 Schematic representation of electronic/ ionic transport in the NCP@CNT10@PPy6. Adapted with permission [51], Copyright (2022), Elsevier

electrochemical device has energy and power densities of 34.8 Wh kg−1 and 700 W kg−1 , respectively as well as a stable CR over wide range of temperatures and bending angles. Figure 5 shows the schematic diagram representing the electronic/ ionic transport mechanism in the NiCoP@CNT10@PPy6 composite. There is currently a high demand for flexible energy storage devices that can be easily incorporated into apparel in order to develop smart clothing and wearable electronics. The use of fabrics and textiles has also been investigated by incorporating suitable nanocomposites with stretchable textiles. Sun et al. [52] recently developed a spandex textile based stretchable asymmetric supercapacitor using bimetallic NiCoP. A two-step electroless deposition technique was used to modify spandex textile (ST) with polymer decorated with Ni. The stretchable Ni@NiCoP ST was then created by depositing a layer of NiCoP onto modified ST. Even after two weeks of exposure to open air, a negligible change in the resistance of Ni@NiCoP ST was observed. Furthermore, the Ni@NiCoP ST exhibits stable capacitance behaviour even at 80 °C and can withstand maximum stress up to 11.59 MPa due to the reinforcement of the fibre in the composite. At a scan rate of 5 mV s−1 , the areal and gravimetric capacitances of Ni@NiCoP ST were found to be 877.6 mF cm−2 and 713 F g−1 , respectively. The Ni@NiCoP ST has symmetric charging and discharging and a low series resistance of 4.16 Ω. The asymmetric supercapacitor (ASC) device made with stretchable electrodes of Ni@NiCoP ST and Ni@NiCoP ST/SWCNT separated by a PAM membrane soaked in 1 M KOH has an equivalent series resistance of 6.02 Ω, a CS of 171.4 mF cm−2 and a CR of 98%, after 6000 cycles at 100 mVs−1 . The practical energy storage capability and adoptability of the Ni@NiCoP ST in a wearable electronic device was demonstrated by charging the ASC device using flexible solar cells under the light illumination of 40 mW cm−2 for 32.5 s. The output current derived from ASC device for this charging condition was observed to be 2.5 mA for 142.9 s. Yue et al. [53] investigated the electrochemical properties of PPy supported with core–shell heterogeneous intertwined CoP nanowires grown on Ni-foam (PPy@CoP). The PPy@CoP electrode with a mass loading of 2.69 mg cm−2 has

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

293

a CS of 443 C g−1 at 1 A g−1 , and a CR of 92% after 5000 cycles at 5 A g−1 . The hybrid supercapacitor device with nitrogen doped CNT (N-CNT) as a negative electrode and PPy@CoP as a positive electrode has a capacity of 183 C g−1 at 1 A g−1 , and energy and power densities of 38.1 Wh kg−1 and 7502 W kg−1 , respectively. Similarly, Li et al. [54] used a two-step electrochemical process to create PPy fibres decorated with NiP nanoparticles. The PPy fibres were found to effectively prevent the aggregation of NiP nanoparticles during charging/discharging cycles, thereby improving the structural strength of the composite to withstand long-term charging/ discharging cycles. Furthermore, the intertwined PPy fibres in the NiP nanoparticle composite provide numerous pathways for proper electrolyte ion interaction through the electroactive sites. The PPy@NiP nanoparticle composite has a CS of 364 mAh g−1 at 3 A g−1 and a CR of 91% after 5000 charge–discharge cycles at 10 A g−1 . The ASC device, which was made of PPy@NiP nanoparticle composite as the positive electrode and N-CNT as the negative electrode, has a working potential of up to 1.6 V and a CS of 72 mAh g−1 at 1 A g−1 . After 5000 cycles at 5 A g−1 , it retains 94% of its initial capacity and has a Coulombic efficiency of 91%. Sun et al. [29] reported that the use of porous carbon improved the CS of 3D Ni3 P nano-network. The use of sulphonated polystryene (SPS) helps the cross-linkage of PS in the CF@NiCoNiPC composite. It also aids in the formation of a homogeneous nano-network of CF@NiCoNiPC composite, resulting in a higher capacitance of 1761 mF cm−2 at 5 mA cm−2 and good cyclic stability. The ASC device made from CF@NiCoNiPC nano-composite electrode was found to have a capacitance of 516.7 mF cm−2 and energy and power densities of 34.2 Wh kg−1 and 513 W kg−1 , respectively. Table 1 summarises recently reported electrochemical results for polymer-based MP composites.

4 Conclusion This chapter focuses on the recent advancement in metal phosphides (MPs) and its potential application in electrochemical energy storage. Here the different classes of MPs (mono metallic phosphides, bimetallic phosphides and ternary metallic phosphides) and their capacitance as well as their cyclic stabilities are discussed. The reported results suggest that compared to mono and bimetallic phosphide, the ternary MPs are potential candidate for supercapacitor application owing to higher redox behaviour, electrical stability, and chemical stability. Polymers are now been investigated as an effective additive to enhance the conductivity and flexibility of the MPs and thus can be utilized in flexible electronic gadgets. However, the specific capacity and long-term stability of the MP-polymer remain the bottleneck and yet to be resolved. The MP-polymer composite would be of great interest for the development of flexible smart electronic wearables. There is an immense scope of research on polymers for enhancing the electrochemical performance and strengthening the composite for stable cyclic performance of supercapacitor electrodes. However, it is less explored and have potential research focus on this area.

294

A. Ramesh et al.

Table 1 Electrochemical characteristics of polymer-based MP composites Active material

Electrolyte

Electrode setup

Specific capacity/ capacitance

PPy@CoP

2 M KOH

Three electrode setup

443 C g−1 at 93% after 5000 [53] 1 A g−1 cycles at 5 A g−1

2 M KOH

Two electrode setup

183 C g−1 at 91% after 5000 1 A g−1 cycles at 5 A g−1

PPy/Ni2 P

1 M Na2 SO4

Three electrode setup

476.5 F g−1 at 1 A g−1

NiCoP@CNT10@PPy6

3 M KOH

Three electrode setup

1807.8 F g−1 75% after 8000 [51] cycles at 3 at 1 A g−1 A g−1

two electrode setup

127.9 F g−1 at 1 A g−1

80% after 8000 cycles at 3 A g−1

Capacitance retention/ cyclability

Refs

89% after 3000 [49] cycles at 1 A g−1

NiP-PANI composite

2 M KOH

Two electrode setup

105.5 C g−1 at 0.5 A g−1

89% after 4000 [9] cycles at 3 A g−1

FeP/PEDOT

1 M Na2 SO4

Three electrode setup

790.59 mF cm−2 at 1 mA cm−1

81.17% after 5000 cycles

[36]

References 1. Hong F, Yue B, Hirao N, Liu Z, Chen B (2017) Significant improvement in Mn2O3 transition metal oxide electrical conductivity via high pressure. Sci Rep 7:44078. https://doi.org/10.1038/ srep44078 2. Li H, Gao Y, Wang C, Yang G (2015) A simple electrochemical route to access amorphous mixed-metal hydroxides for supercapacitor electrode materials. Adv Energy Mater 5:1401767. https://doi.org/10.1002/aenm.201401767 3. Ramesh A, Basu S, Ganesan V, Soni PK, Manivannan S, Kandasamy J, Leo Hudson MS, Shaz MA (2023) Tuning the electrochemical capacitance of carbon nanosheets by optimizing its thickness through controlling the carbon precursor in salt-template. Energy Storage e445. https://doi.org/10.1002/est2.445 4. Yang G, Takei T, Zhu Y, Iranmanesh E, Liu B, Li Z, Wang J, Hiralal P, Amaratunga GAJ, Fontaine O, Zhou H (2021) Constructing an efficient conductive network with carbonbased additives in metal hydroxide electrode for high-performance hybrid supercapacitor. Electrochim Acta 397:139242. https://doi.org/10.1016/j.electacta.2021.139242 5. Chen X, Wang P, Feng Z, Meng C, Zhang Y (2022) Conductive polymer intercalated vanadium oxide on carbon cloth for fast ammonium-ion storage in supercapacitor applications. Chem Eng J 445:136747. https://doi.org/10.1016/j.cej.2022.136747 6. Wang G, Shao Z, Yu Z (2007) Comparisons of different carbon conductive additives on the electrochemical performance of activated carbon. Nanotechnology 18:205705. https://doi.org/ 10.1088/0957-4484/18/20/205705

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

295

7. Liu Y, McCue AJ, Li D (2021) Metal phosphides and sulfides in heterogeneous catalysis: electronic and geometric effects. ACS Catal 11:9102–9127. https://doi.org/10.1021/acscatal. 1c01718 8. Wang X, Kim H-M, Xiao Y, Sun Y-K (2016) Nanostructured metal phosphide-based materials for electrochemical energy storage. J Mater Chem A 4:14915–14931. https://doi.org/10.1039/ C6TA06705K 9. Nayak S, Kittur AA, Nayak S (2022) Nickel phosphide-polyaniline binary composite as electrode material using chitosan biopolymer electrode binder for supercapattery applications. Mater Today Proc 54:912–922. https://doi.org/10.1016/j.matpr.2021.11.221 10. Xiao P, Chen W, Wang X (2015) A review of phosphide-based materials for electrocatalytic hydrogen evolution. Adv Energy Mater 5:1500985. https://doi.org/10.1002/aenm.201500985 11. Callejas JF, Read CG, Roske CW, Lewis NS, Schaak RE (2016) Synthesis, characterization, and properties of metal phosphide catalysts for the hydrogen-evolution reaction. Chem Mater 28:6017–6044. https://doi.org/10.1021/acs.chemmater.6b02148 12. Zhang N, Li Y, Xu J, Li J, Wei B, Ding Y, Amorim I, Thomas R, Thalluri SM, Liu Y, Yu G, Liu L (2019) High-performance flexible solid-state asymmetric supercapacitors based on bimetallic transition metal phosphide nanocrystals. ACS Nano 13:10612–10621. https://doi. org/10.1021/acsnano.9b04810 13. Aziz SKT, Kumar S, Riyajuddin S, Ghosh K, Nessim GD, Dubal DP (2021) Bimetallic phosphides for hybrid supercapacitors. J Phys Chem Lett 12:5138–5149. https://doi.org/10.1021/ acs.jpclett.1c00562 14. Anuratha KS, Su Y-Z, Huang M-K, Hsieh C-K, Xiao Y, Lin J-Y (2022) High-performance hybrid supercapacitors based on electrodeposited amorphous bimetallic nickel cobalt phosphide nanosheets. J Alloys Compd 897:163031. https://doi.org/10.1016/j.jallcom.2021.163031 15. Nguyen TT, Balamurugan J, Kim NH, Lee JH (2018) Hierarchical 3D Zn–Ni–P nanosheet arrays as an advanced electrode for high-performance all-solid-state asymmetric supercapacitors. J Mater Chem A 6:8669–8681. https://doi.org/10.1039/C8TA01184B 16. Li S, Hua M, Yang Y, Huang W, Lin X, Ci L, Lou J, Si P (2019) Self-supported multidimensional Ni–Fe phosphide networks with holey nanosheets for high-performance all-solid-state supercapacitors. J Mater Chem A 7:17386–17399. https://doi.org/10.1039/C9TA04832D 17. Moosavifard SE, Kaverlavani SK, Shamsi J, Bakouei A (2017) Hierarchical multi-shelled nanoporous mixed copper cobalt phosphide hollow microspheres as a novel advanced electrode for high-performance asymmetric supercapacitors. J Mater Chem A 5:18429–18433. https:// doi.org/10.1039/C7TA06514K 18. Lei X, Ge S, Tan Y, Wang Z, Li J, Li X, Hu G, Zhu X, Huang M, Zhu Y, Xiang B (2020) High capacity and energy density of Zn–Ni–Co–P nanowire arrays as an advanced electrode for aqueous asymmetric supercapacitor. ACS Appl Mater Interfaces 12:9158–9168. https://doi. org/10.1021/acsami.9b17038 19. Xie M, Zhou M, Zhang Y, Du C, Chen J, Wan L (2022) Freestanding trimetallic Fe–Co– Ni phosphide nanosheet arrays as an advanced electrode for high-performance asymmetric supercapacitors. J Colloid Interface Sci 608:79–89. https://doi.org/10.1016/j.jcis.2021.09.159 20. Meng Q, Cai K, Chen Y, Chen L (2017) Research progress on conducting polymer based supercapacitor electrode materials. Nano Energy 36:268–285. https://doi.org/10.1016/j.nan oen.2017.04.040 21. Ryu KS, Kim KM, Park N-G, Park YJ, Chang SH (2002) Symmetric redox supercapacitor with conducting polyaniline electrodes. J Power Sources 103:305–309. https://doi.org/10.1016/ S0378-7753(01)00862-X 22. Wang Q, Wang J, Wang H, Zhan J, Zhu Y, Zhang Q, Shen Q, Yang H (2019) TiO2-C nanowire arrays@polyaniline core-shell nanostructures on carbon cloth for high performance supercapacitors. Appl Surf Sci 493:1125–1133. https://doi.org/10.1016/j.apsusc.2019.07.102 23. Li F, Bu Y, Lv Z, Mahmood J, Han G-F, Ahmad I, Kim G, Zhong Q, Baek J-B (2017) Porous cobalt phosphide polyhedrons with iron doping as an efficient bifunctional electrocatalyst. Small 13:1701167. https://doi.org/10.1002/smll.201701167

296

A. Ramesh et al.

24. Qu G, Sun P, Xiang G, Yin J, Wei Q, Wang C, Xu X (2020) Moss-like nickel-cobalt phosphide nanostructures for highly flexible all-solid-state hybrid supercapacitors with excellent electrochemical performances. Appl Mater Today 20:100713. https://doi.org/10.1016/j.apmt. 2020.100713 25. Patil SS, Patil PS (2022) Status review of nickel phosphides for hybrid supercapacitors. Nanoscale 14:16731–16748. https://doi.org/10.1039/D2NR05139G 26. Ma X, Chen J, Yuan B, Li Y, Yu L, Zhao W (2022) Three-dimensional hollow nickel phosphate microspheres with controllable hoya-like structure for high-performance enzymeless glucose detection and supercapacitor. Appl Surf Sci 588:152928. https://doi.org/10.1016/j.apsusc.2022. 152928 27. He G, Song Y, Wang L (2019) In situ synthesis of Ni2P nanostructures on Ni foam for high-performance supercapacitors. Ionics (Kiel) 25:3927–3934. https://doi.org/10.1007/s11 581-019-02927-4 28. Ding L, Chen L, Ma Z, Zhang X, Zhang K, Zhu G, Yu Z, Deng J, Chen F, Yan D, Xu H, Yu A (2020) High-performance asymmetrical hybrid supercapacitor based on yolk-shell Ni3P nanoparticles constructed by selective etching. Electrochim Acta 357:136875. https://doi.org/ 10.1016/j.electacta.2020.136875 29. Sun P, Qiu M, Huang J, Zhao J, Chen L, Fu Y, Cui G, Tong Y (2020) Scalable threedimensional Ni3P-based composite networks for flexible asymmertric supercapacitors. Chem Eng J 380:122621. https://doi.org/10.1016/j.cej.2019.122621 30. Wan H, Li L, Chen Y, Gong J, Duan M, Liu C, Zhang J, Wang H (2017) One pot synthesis of Ni12P5 hollow nanocapsules as efficient electrode materials for oxygen evolution reactions and supercapacitor applications. Electrochim Acta 229:380–386. https://doi.org/10.1016/j.ele ctacta.2017.01.169 31. Wang J, Liu Z, Zheng Y, Cui L, Yang W, Liu J (2017) Recent advances in cobalt phosphide based materials for energy-related applications. J Mater Chem A 5:22913–22932. https://doi. org/10.1039/C7TA08386F 32. Han R, Guan L, Zhang S, Lin Y, Tao J (2021) Boosted cycling stability of CoP nanoneedles based hybrid supercapacitor with high energy density upon surface phosphorization. Electrochim Acta 368:137690. https://doi.org/10.1016/j.electacta.2020.137690 33. Cheng M, Fan H, Xu Y, Wang R, Zhang X (2017) Hollow Co2P nanoflowers assembled from nanorods for ultralong cycle-life supercapacitors. Nanoscale 9:14162–14171. https://doi.org/ 10.1039/C7NR04464J 34. Jiang J, Li Z, He X, Hu Y, Li F, Huang P, Wang C (2020) Novel Skutterudite CoP3–based asymmetric supercapacitor with super high energy density. Small 16:2000180. https://doi.org/ 10.1002/smll.202000180 35. Tian L, Yan X, Chen X (2016) Electrochemical activity of iron phosphide nanoparticles in hydrogen evolution reaction. ACS Catal 6:5441–5448. https://doi.org/10.1021/acscatal.6b0 1515 36. Luo J, Zheng Z, Kumamoto A, Unah WI, Yan S, Ikuhara YH, Xiang X, Zu X, Zhou W (2018) PEDOT coated iron phosphide nanorod arrays as high-performance supercapacitor negative electrodes. Chem Commun 54:794–797. https://doi.org/10.1039/C7CC09163J 37. Liang B, Zheng Z, Retana M, Lu K, Wood T, Ai Y, Zu X, Zhou W (2019) Synthesis of FeP nanotube arrays as negative electrode for solid-state asymmetric supercapacitor. Nanotechnology 30:295401. https://doi.org/10.1088/1361-6528/ab0620 38. Zardkhoshoui AM, Davarani SSH (2019) Designing a flexible all-solid-state supercapacitor based on CuGa2O4 and FeP-rGO electrodes. J Alloys Compd 773:527–536. https://doi.org/ 10.1016/j.jallcom.2018.09.135 39. Chen Y-C, Chen Z-B, Lin Y-G, Hsu Y-K (2017) Synthesis of copper phosphide nanotube arrays as electrodes for asymmetric supercapacitors. ACS Sustain Chem Eng 5:3863–3870. https:// doi.org/10.1021/acssuschemeng.6b03006 40. Jin Y, Zhao C, Wang Y, Jiang Q, Ji C, Jia M (2017) Large-scale production of Cu3P nanocrystals for ultrahigh-rate supercapacitor. Ionics (Kiel) 23:3249–3254. https://doi.org/10.1007/s11581017-2267-7

Polymer-Metal Phosphide Nanocomposites for Flexible Supercapacitors

297

41. Kumar S, Aziz SKT, Kumar S, Riyajuddin S, Yaniv G, Meshi L, Nessim GD, Ghosh K (2020) Three-dimensional graphene-decorated copper-phosphide (Cu3P@3DG) heterostructure as an effective electrode for a supercapacitor. Front Mater 7. https://doi.org/10.3389/fmats.2020. 00030 42. Andikaey Z, Ensafi AA, Rezaei B (2021) Iron-doped cobalt copper phosphide/phosphate composite with 3D hierarchical flower-like structures as electrodes for hybrid supercapacitors. Electrochim Acta 393:139061. https://doi.org/10.1016/j.electacta.2021.139061 43. Wang Z, Wang H, Ji S, Wang X, Zhou P, Huo S, Linkov V, Wang R (2020) Hollow-structured NiCoP nanorods as high-performance electrodes for asymmetric supercapacitors. Mater Des 193:108807. https://doi.org/10.1016/j.matdes.2020.108807 44. Zong Q, Liu C, Yang H, Zhang Q, Cao G (2021) Tailoring nanostructured transition metal phosphides for high-performance hybrid supercapacitors. Nano Today 38:101201. https://doi. org/10.1016/j.nantod.2021.101201 45. Xiang F, Dong Y, Yue X, Zheng Q, Lin D (2022) High-capacity CoP-Mn3P nanoclusters heterostructures derived by Co2MnO4 as advanced electrodes for supercapacitors. J Colloid Interface Sci 611:654–661. https://doi.org/10.1016/j.jcis.2021.12.118 46. Huang Y, Luo C, Zhang Q, Zhang H, Wang M-S (2021) Rational design of three-dimensional branched NiCo-P@CoNiMo-P core/shell nanowire heterostructures for high-performance hybrid supercapacitor. J Energy Chem 61:489–496. https://doi.org/10.1016/j.jechem.2021. 02.005 47. Hong X, Deng C, Wang G, Wang X, Dong W (2023) Composition and morphology transition of NF/MnP/NiCoP composite electrode induced by charge/discharge activation. Chem Eng J 451:139036. https://doi.org/10.1016/j.cej.2022.139036 48. Saleh AA, Amer A, Sayed DM, Allam NK (2021) A facile electrosynthesis approach of Mn–Ni– Co ternary phosphides as binder-free active electrode materials for high-performance electrochemical supercapacitors. Electrochim Acta 380:138197. https://doi.org/10.1016/j.electacta. 2021.138197 49. Liu S, Chen Y, Ren J, Wang Y, Wei W (2019) An effective interaction in polypyrrole/ nickel phosphide (PPy/Ni2P) for high-performance supercapacitor. J Solid State Electrochem 23:3409–3418. https://doi.org/10.1007/s10008-019-04443-x 50. Gopalakrishnan A, Yang D, Ince JC, Truong YB, Yu A, Badhulika S (2019) Facile one-pot synthesis of hollow NiCoP nanospheres via thermal decomposition technique and its freestanding carbon composite for supercapacitor application. J. Energy Storage. 25:100893. https:/ /doi.org/10.1016/j.est.2019.100893 51. Shi X, Sun L, Li X, Wu L, Qian J, Wang J, Lin Y, Su S, Sun C, Zhang Y, Zhang Y (2022) Highperformance flexible supercapacitor enabled by Polypyrrole-coated NiCoP@CNT electrode for wearable devices. J Colloid Interface Sci 606:135–147. https://doi.org/10.1016/j.jcis.2021. 08.016 52. Sun P, Qiu M, Li M, Mai W, Cui G, Tong Y (2019) Stretchable Ni@NiCoP textile for wearable energy storage clothes. Nano Energy 55:506–515. https://doi.org/10.1016/j.nanoen.2018. 10.067

298

A. Ramesh et al.

53. Yue C, Hu B, Huang W, Liu A, Guo Z, Mu J, Zhang X, Liu X, Che H (2021) Construction of polypyrrole nanowires@cobalt phosphide nanoflakes core–shell heterogeneous nanostructures as high-performance electrodes for supercapacitors. J Electroanal Chem 899:115656. https:// doi.org/10.1016/j.jelechem.2021.115656 54. Li Z, Yu R, Yue C, Tian T, Guo Z, Mu J, Zhang X, Wang G, Zhang Z, Che H (2022) Nickel phosphide nanoparticles decorated on polypyrrole nanowires as battery-type electrodes for hybrid supercapacitors. Synth Met 291:117163. https://doi.org/10.1016/j.synthmet.2022.117163

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries Hamid Dehghan-Manshadi, Mohammad Mazloum-Ardakani, and Soraya Ghayempour

Abstract Metal-ion batteries are important devices to convert and save the energy of fossil fuels to renewable energy. Improving the efficiency of these batteries requires the use of materials with special properties and innovative engineering design. Polymer-metal oxide nanocomposites are one important useful material in designing effective energy storage systems such as solar cells, supercapacitors, batteries, and others. They have been utilized in metal-ion batteries due to their role in improving electrical and optical properties. This chapter presents an outlook on the challenges in the synthesis and application of polymeric nanocomposites based on various metal oxides such as cobalt oxide, vanadium oxide, tin oxide, manganese oxide, and others in the design and preparation of metal-ion batteries. Keywords Nanocomposites · Metal-ion batteries · Metal oxides · Conductive polymers · Discharge capacity

1 Introduction Metal-ion batteries are one of the most important power sources for portable electronic devices. The four basic ingredients of metal-ion batteries are: Two electrodes (anode and cathode), an electrolyte, and a separator. Usually, a metal oxide and a porous carbonous material have been used as the cathode and anode, respectively. During the discharge stage, the ions abandon the anode electrode and transfer to the cathode electrode after passing the electrolyte and separator sectors. To obtain H. Dehghan-Manshadi Thin Layer and Nanotechnology Laboratory, Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST), P.O. Box 33535-111, Tehran, Iran M. Mazloum-Ardakani (B) Department of Chemistry, Faculty of Science, Yazd University, Yazd, Iran e-mail: [email protected] S. Ghayempour Department of Textile Engineering, Faculty of Engineering, Yazd University, Yazd, Iran © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_17

299

300

H. Dehghan-Manshadi et al.

a high-efficiency metal-ion battery, there is a need to use materials with special features in their structure [1, 2]. The advantages of lithium-ion batteries such as excellent energy density, good storage efficiency, low self-discharge rate, eco-friendly property, ultra-long cycle life, low maintenance cost, and inconsiderable memory effects lead to the special attention of researchers to them. Nonetheless, limited reserves of lithium, high expense, and safety challenges of lithium-ion batteries lead to the turning of researchers to the more available metals such as aluminum, magnesium, zinc, sodium, and potassium [3–5]. Aluminum as the most available metal can be used as a renewable energy source in metal-ion batteries. Aluminum-ion batteries have been considered by researchers due to their lightweight, low-cost, and abundant aluminum. Also, aluminum creates a high charge storage capacity of 2980 mA h g−1 /8046 mAh cm−3 and a low oxidation/reduction potential [6]. The magnesium-ion batteries are a useful alternative to lithium-ion batteries due to their high abundance, high volumetric capacity, low reduction potential, safety, and ecofriendly. In these batteries, in which magnesium metal acts as the anode, they never form dendrites during plating—stripping cycles. However, confined electrochemical oxidative stability of their electrolytes, slow transfer of magnesium ions to the cathode, and irreversible conversion of Mg2+ to metal magnesium at the anode are the important disadvantages of magnesium-ion batteries [7]. Zinc is another useful metal as the anode electrode due to its good theoretical capacity (820 mAh g−1 ) and excellent energy density (5851 mAh mL−1 ). Also, zinc (II) ions can create a more storage capacity with the ability to transfer two electrons per atom in comparison to lithium or sodium ions with the ability to transfer one electron [8]. The working principle of sodium and potassium-ion batteries is the same as an operation of lithium-ion batteries so that sodium and potassium ions were inserted into the cathode and anode materials. Sodium-ion batteries have the advantages of the abundance of sodium, similarity to the approach of lithiumion batteries, and inexpensive, but the larger ionic radius of sodium prevents from storage of sodium ion through electrochemical reaction via graphite as the anode. Evaluation of potassium-ion batteries is attractive for researchers because of low standard electrode potential, an abundance of potassium, and low desolvation energy. Comparison of standard electrode potential of potassium ion (− 2.93 V versus SHE) and sodium ions (− 2.71 V versus SHE) indicates a more negative potential of potassium resulting create battery with excellent properties such as good energy density and great operating voltage. However, they have several problems such as low cycle stability and poor reversible capacity [9, 10].

2 Metal Oxide-Based Polymeric Nanocomposites Many metal oxides with different morphologies and structures have been synthesized and utilized as the electrode compositions in metal-ion batteries, but they have restrictions such as restricted electrochemical active sites and low conductivity. A

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries

301

solution to this problem is applying the conductive polymers in preparation of metalion batteries due to their mechanical properties, specific processability and good conductivity. Therefore, they can form a suitable conductive matrix for preparation of metal-ion batteries, which prevent from the mechanically decomposition of active materials during the charging/discharging process. Also, conductive polymers can be improved the electrode lifetime, rate capability and thermal stability of metal-ion batteries through synergistic interaction with inorganic compounds [11–13]. On the other hand, synthesis and application of metal oxide nanocomposites using conductive polymers can be improved conductivity, stability and electrochemical behavior of metal-ion batteries. Various polymer-metal oxides nanocomposites have been synthesized suitable metal oxide for application as the cathode, anode, electrolyte or separator of metal-ion batteries. Among the transition metal oxides, cobalt oxide is one of the most evaluated electrode compositions in metal-ion batteries and supercapacitors owing to high ability to charge storing in the electrode and rich redox activity. They have several advantages such as earth abundance, low cost, and good environmental compatibility. Among the types of cobalt oxides, CoO and Co3 O4 are the most common ones owing to their excellent chemical and physical characterizations. Co3 O4 with spinel structure obtain a relative good theoretical capacity of 890 mAh g−1 for lithiumion batteries [14–16]. Other most representative electrode materials are the variety of vanadium oxides. They have been applied as the cathode materials in metal-ion batteries due to natural layered structures and excellent electrochemical performance [17]. Tin oxide (SnO2 ) and their derivatives have been used as the active anode materials according to their high theoretical specific capacity in comparison to graphite and obtain a great energy density when used in a in lithium-ion batteries. The two-step lithiation and de-lithiation reactions of SnO2 are as follows: SnO2 + 4Li+ + 4e− → Sn + 2Li2 OSn

(1)

Li2 OSn + xLi+ + xe− → Lix Sn 0 ≤ x ≤ 4.4

(2)

As seen in Eqs. 1 and 2, The first discharge leads to create the metal tin and Li2 O through interaction between lithium ion and oxygen in structure tin oxide. Li2 O formation and interaction of metal tin with lithium ion carries out due to high irreversible capacity of tin oxide. Also, a solid interphase film obtains through interaction between high active tin and electrolyte, which enhance the irreversible capacity fading [18–20]. Disadvantage of SnO2 -based active materials in metal-ion batteries is rapid capacity degradation during charge–discharge cycles because of the huge volume variation of SnO2 . This issue can be attributed to the particles trituration and mechanical stress during the alloying/dealloying process with lithium ions. On the other hand, the cutoff voltage can effects on the storage capacity, so that high cutoff voltage results in change of the volume, destruction of the lithium oxide matrix and reduction of storage capacity. Above problems can be resolved using change the

302

H. Dehghan-Manshadi et al.

method of SnO2 synthesis. Preparation of a nanocomposite using an appropriate polymer may be useful for obtain a high-efficiency active electrode in metal-ion batteries [11, 19, 20]. Manganese oxides are interesting because of their inexpensive preparation, high capacity retention, abundance, eco-friendly, and low toxicity. Various valence of MnO2 states (0, + 2, + 3 and + 4) and ability of transfer 4 electrons for per MnO2 molecules leads to a relative good theoretical specific capacity (1232 mAh g−1 for 4 electrons). They can act as the anode and cathode electrodes in lithium-ion and aqueous metal-ion batteries, respectively. A wide range of their applications are reported for zinc ion batteries. Because, the most electrode materials usable for insertion/extraction of lithium ions are not appropriate for zinc-ion batteries because of their electrostatic interactions with the host lattice of zinc as a divalent ion. Mnbased cathodes is good candidate due to obtain a better energy density against other cathode types. Although, the low natural conductivity, poor rate performance, inferior cycling sustainability, and the dissolution of manganese-based cathode electrodes leads to low reaction rate and rapid loss of capacity. Several solutions have been proposed to solve this problem; such as add an extra values of manganese ions to electrolyte, perform the hybridization process, and modification of their crystalline structure [5, 8, 21]. Nickel oxide is other metal oxide applied as the anode materials in metal-ion batteries due to its good theoretical capacity, long cycle life, abundance and ecofriendly. Electrochemical properties of NiO-based anodes in metal-ion batteries depend on their morphology such as crystallinity, particle size, surface area and porosity. However, the rapid capacity drop and voltage fade because of destruction of the cathode electrode during utilization of battery are the important challenges in NiO-based anodes in metal-ion batteries [22, 23]. MXenes are referred to a group of two-dimensional transition metal carbides or nitrides with general formula of Mn+1 Xn Tx (M: transition element like titanium, tantalum, niobium, manganese, zirconium, vanadium, chromium and molybdenum; X: carbon or nitrogen; T: oxygen, fluorine or hydroxyl as the terminating group, n: the number of carbon or nitrogen elements (which can change between 1 and 3); x: the number of terminating groups). The existence of terminal groups in structure of MXenes leads to hydrophilic property that is important in anodes of lithium-ion batteries [24, 25]. Conductive characterizations and band gap of MXenes are related to presence of metallic and covalent bonds in their structure. Recently, they have been interested by researchers as an appropriate alternatives to carbonious nanostructure compounds because of their good conductivity, adjustability of functional groups, and great surface/volume ratio. Fabrication of a composite containing polymer and MXene is carried out through covalent and hydrogen, which assists to uniform formation and support of obtain a MXene compound with three-dimensional structure [26, 27]. MXenes have been widely applied as the filler material in synthesis of polymeric composites owing to their hydrophilic surfaces, good mechanical features, and high conductivity. Mechanical and thermal properties of MXenes improve through preparation of their composite with a polymer. Also, incorporating of active groups on

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries

303

structure of MXenes during etching process increases the relevance between their flakes and polymeric chains [26].

3 Application of Metal Oxide-Based Polymeric Nanocomposites in Metal-Ion Batteries Metal-ion batteries have several advantages and disadvantages according to the characteristics of the used material in their components including electrodes (anode and cathode), electrolyte and separator. The main components of a typical ion-metal batteries are displayed in Fig. 1. The chemical reactions in cathode and anode are based on the used materials of the electrode. Generally, during the discharge process, the metal ions transform from the anode electrode to the cathode electrode through electrolyte and the electrons move from the anode to the cathode. The charging process is the opposite of the discharging process. In this process, a power source should be help to move metal ions from the cathode to the anode [28].

3.1 Cathode Materials The composition of electrodes has a critical task in the efficiency, stability, and storage capacity of batteries especially metal-ion batteries. A composition with high porosity or layered structure is an effective ideal material for cathode electrode of batteries. Vanadium and manganese oxides and their derivatives are two common metal oxide Fig. 1 The main components of a typical ion-metal batteries

304

H. Dehghan-Manshadi et al.

applied as the cathode electrode in metal-ion batteries. They lead to intercalation and deintercalation of the ions between the electrolyte and electrode [17, 29–31]. One of the important challenges in Zn-ion batteries is preparation of a stable composition as the cathode electrode for good storage of zinc ion. Vanadium oxides and their derivatives are widely used as the active composition for cathode section of zinc-ion batteries due to their natural layered structures and excellent electrochemical performance. Sun et al. in 2021 [17] synthesized a active composite film containing vanadium pentoxide (V2 O5 .nH2 O), reduced graphene oxide (rGO) and polyvinyl alcohol (PVA) by a one-step hydrothermal procedure and utilized as the standing cathode electrode for solid-state zinc-ion batteries. According to their results, PVA leads to increase V2 O5 .nH2 O layer space, create a network between rGO and H2 O through hydrogen bonds, and enhance the mechanical features of the synthesized composite. An excellent electrochemical capacity (481 mAh g−1 ) and a good energy density (708 Wh kg−1 ) are the important results of this work. In other study, Zhang et al. in 2022 [30] presented a strategy for solve the challenges of zinc-ion batteries including low conductivity, small ion diffusion coefficient, and dissolution of cathode electrode. They synthesized V2 O5 -polypyrrole nanobelt composite by in-situ polymerization of pyrrole on the vanadium oxide. Polypyrrole is the most commonly used conductive polymers owing to its conductivity, non-toxicity, low-cost, and simple production. Although, polymerization of pyrrole carried out by high-temperature hydrothermal method, therefore, invention of an easy, safe, and effective technique for synthesis of V2 O5 -polypyrrole composite is indispensable. In the reported method by Zhang et al., vanadium oxide was used both as the cathode material and as an oxidant for polymerization. The synthesized nanocomposite indicated an discharge capacity of 441 mAh g−1 at 0.1 A g−1 and a capacity retention of 95.92% after 2000 cycles. The synthesized V2 O5 -polypyrrole composite helps to increase the conductivity, create the oxygen vacancies and prohibit from the dissolution of vanadium [30]. Recently, Sun et al. [29] fabricated a core–shell V2 O5 ·nH2 O nanobelts@polyaniline composite and used as the cathode electrode in zinc-ion batteries. They claimed V2 O5 ·nH2 O despite having a good capacity, its cycle stability is low because of damage its structure through rapid transformation of zinc ions. Application of the synthesized polymeric composite led to cycle stability of 98% after 2000 cycles at 2 A g−1 . As mentioned, manganese oxides and their derivatives are a suitable cathode material in zinc-ion batteries because of their good theoretical capacity. However, the gradual dissolution of MnO2 in the electrolyte during the insertion of zinc ions decrease the capacity and cycling process. Coating of MnO2 with a conductive polymer can prevents from its dissolution. Mao et al. in 2020 [31] prepared a MnO2 /rGO/polyaniline (PANI) aerogel composite and utilized as the cathode electrode in aqueous zinc-ion batteries. Application of the prepared composite leads to increase the electrical conductivity and prevent the dissolution of MnO2 . A capacity retention of 82.7% after 600 cycles were obtained using the prepared composite. The compressed structure of the synthesized MnO2 /rGO/PANI leads to improve the composite stability and the interaction between battery materials. Also, the coated layer of polyaniline prevents the dissolution of MnO2 and help to improvement

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries

305

of conductivity and storage capacity. Application of polypyrrole as the conductive polymer to protection of manganese oxide is reported by several researchers [5, 32]. For instance, Huang et al. in 2021 [5] proposed a process including synthesis of molten-salt and polypyrrole thin-layer on the surface of MnO2 /Mn2 O3 nanocomposite for utilization as the cathode electrode in zinc-ion batteries. The most their important results can be mentioned to specific capacity of 289.8 mAh g−1 and cycle stability of 96.7% after 1000 cycles. In other study, Liao et al. in 2021 [32] synthesized a composite containing β-MnO2 and polypyrrole and utilized as the cathode composition in aqueous zinc-ion batteries. They attributed the enhanced electrochemical performance of the synthesized β-MnO2 /polypyrrole composite to good conductivity of polypyrrole nanostructures and three-dimensional structure composed from β-MnO2 nanorods and polypyrrole nanowires.

3.2 Anode Materials Graphite as the commercial anode electrode in preparation of lithium-ion batteries has disadvantages including low theoretical specific capacity and high-cost of preparing a high purity graphite. Therefore, recent developments have been carried out on the use of different compound as the anode materials. Cobalt oxide is a common metal oxide applied as the anode electrode in metal-ion batteries. Guo et al. in 2016 [33] prepared a nitrogen-doped porous carbon nanospheres/cobalt oxide nanocomposite using carboxymethyl chitosan and utilized as the anode materials for lithium-ion batteries. Carboxymethyl chitosan containing amino groups was used as the source of carbon and nitrogen. They attributed the good electrochemical performance of the prepared nanocomposite to the synergic effects of the Co3 O4 nanoparticles, the porosity of its structure, and the existence of nitrogen functional groups in the structure of the prepared nanocomposite. Although cobalt oxide has represented good electrochemical performance, some its disadvantages such as the scarce natural resources, toxicity, and high cost can be limited its applications in electrochemical energy storage devices. Some of the solutions to these problems are the use of more eco-friendly and inexpensive metals such as magnesium, nickel, copper, vanadium, and others in synthesize binary metal cobaltite and synthesis of cobalt nanocomposites. Cobalt oxide-based nanocomposites can be utilized as the active anode in preparation of metal-ion batteries with high reversible capacity [34, 35]. In a study, a nanocomposite containing CoV2 O4 / rGO as the active material and carboxymethyl cellulose/styrene butadiene rubber as the binder was fabricated by Muruganantham et al. in 2020 [9] and utilized as the anode for sodium ion batteries. Insertion/extraction process of sodium ion in metal oxide-based anode electrodes leads to pulverization of the active materials, high volume changes, and reduce the electrical contact. The synthesized conductive nanocomposite acts as a network to hold the electrical contact and correct the cycle stability and capacity of battery.

306

H. Dehghan-Manshadi et al.

Tin oxide is another useful metal oxide as the anode electrode in metal-ion batteries. Several studies has been reported on synthesis of various nanocomposites containing tin oxide and polypyrrole and their usage for preparation of anode electrodes in metal-ion batteries [13, 20, 36–39]. In a study, Liu et al. in 2014 [20] synthesized core–shell SnO2 –polypyrrole nanocomposites through a two steps procedure including a hydrothermal technique and an chemical-polymerization method. The synthesized nanocomposite was utilized as the anode electrode in a lithium-ion battery. The core–shell structure of the synthesized nanocomposite and the synergic effect among polypyrrole and tin oxide lead to increase cycling stability. Also, the polypyrrole layer prevents the pulverization of tin oxide and aggregation of the tin oxide/metallic tin spheres. The hollow area in tin oxide nanospheres reduces the volume changes during charging and discharging process. In another study, Du et al. in 2016 [36] proposed a strategy to decrease the volume change of SnO2 via trapping SnO2 particles on the synthesized polypyrrole nanotubes to obtain a SnO2 nanocomposite. SnO2 @polypyrrole nanotubes were synthesized using polymerization and a microwave-based method. Application of the synthesized nanocomposite as the anode electrode leads to cycling stability of 790 mAh.g–1 at 200 mA.g–1 after 200 cycles. Another study was reported by Yuan et al. in 2017 [37] on preparation of SnO2 / polypyrrole hollow spheres by a two step process including liquid-phase deposition procedure and polymerization. Application of the synthesized SnO2 /polypyrrole nanocomposites as the anode electrode in lithium-ion battery resulted in a capacity of 899 mAh.g−1 at the current density of 100 mA.g−1 after 600 cycles. The high conductivity, rapid diffusion of lithium ion, and enough space to prevent the volume changing can be related to synergic effect of polypyrrole layer and SnO2 spheres. Tian et al. in 2021 [11] offered a solution to achieve good conductivity and low volume changes using synthesis of a nanocomposite inclusive of polyvinylpyrrolidone, thin oxide and p-toluenesulfonic acid-doped polypyrrole through electrospinning/chemical two step method. The good electrochemical performance of the synthesized nanocomposite confirmed by obtain cycle capacity of 654.7 mAh.g−1 after 500 cycles at 500 mA.g−1 . The synthesized nanocables leads to increase conductivity and reduce volume changes due to strong synergistic effects of their nanoarchitecture. Recently, Li et al. in 2022 [38] coated polypyrrole on the hierarchical tin oxide nanospheres to improve the conductivity and preserve their multi-shelled spatial structure during charge/discharge process. The stable charge/discharge of 580 mAh.g−1 during 5000 cycles and improve the energy density are the important results of their study. Also, Liu et al. in 2022 [39] synthesized a three-dimensional nitrogen-doped mesoporous carbon/tin oxide nanocomposite using a wet-impregnation and coated with polypyrrole layers using in-situ polymerization method. The prepared nanostructure was applied as the anode electrode in lithium-ion batteries. The obtained product provides a reversible capacity of 591 mAh.g−1 at 1 A.g−1 after 1000 cycles. MXenes are other compounds that are widely applied as the electrode composition. Among various synthesized MXenes, Ti3 C2 Tx has been widely utilized as the ideal matrices for active electrode composition in metal-ion batteries and supercapacitors because of hydrophilic surface, relative good electrical conductivity, high stability and having a good condition for the growth of titanium dioxide [40].

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries

307

Application of pure Ti3 C2 Tx MXenes in batteries is low-efficiency due to low conductivity and poor capacity of titanium dioxide. Application of carbonaceous materials as the functional additives and addition of nitrogen-doped carbons are the solutions for enhance the conductivity and electrochemical performance of titanium dioxide. However, lithium-storage of titanium dioxide is limited due to compact two-dimensional structure which cannot supply an enough space for penetration of electrolyte and diffusion of lithium ions. This issue can be solved by hybridization with an effective active substance with larger theoretical specific capacity and three-dimensional structure [24, 40–42]. For example, Zhang et al. in 2020 [42] prepared a three-dimensional composite as the anode electrode including titanium dioxide, nitrogen-doped carbon and a pyrrhotite with chemical formula of Fe7 S8 . The composite was prepared using an in-situ polymerization with Ti3 C2 Tx in an alkaline medium. Their evaluation showed a cycle stability of 282 mAh g−1 after 1000 cycles at 4 A g−1 . Three-dimensional urchin-like structure of synthesized TiO2 leads to create an enough space to enhance the contact surface between electrolyte and electrode. Also, it shorts the diffusion length of lithium ion and reduces the volume changes. On the other hand, nitrogen-doped carbon improve the conductivity, facilitate the electron transfer and prevent the aggregation of pyrrhotite.

3.3 Electrolyte The electrolyte as the effective section for transporting lithium ions is a complex mixture of various organic and non-aqueous constituents. The liquid electrolytes acts as a carrier which supply a way for the transport of ions between the cathode and anode electrodes. Their chalanges are including self-discharge of the battery due to interactions with active materials in electrode surfaces, destroying the battery structure using metal dendritic growth during charging/discharging process and permeation of flammable electrolytes. Application of solid electrolytes replacing liquid electrolytes, modification of electrolyte composition, the use of flame-retardant materials, application of artificial solid–electrolyte interphase to stabilize the anode interface and utilization of meal nanocomposite anodes are the proposed solution for this problems [43]. The existing challenges for electrolytes in metal ion batteries are indicated in Fig. 2. MXenes are an appropriate metal oxide to design and synthesize diverse electrolytes. MXenes have ability of application as the advanced inorganic electrolyte because of their great specific surface and numerous surface functional groups. However, they suffer from aggregation and restacking of the two-dimensional nanosheets, which limits their electrochemical performance. A nanocomposite containing MXenes and a polymer should be synthesized to obtain excellent performance [44, 45]. In a research, Pan et al. in 2019 [24] prepared MXenebased nanocomposite polymer electrolytes through dispersing of Ti3 C2 Tx into a poly(ethylene oxide)/bis(tri-fuoromethane)sulfonimide Li complex. Based in their

308

H. Dehghan-Manshadi et al.

Fig. 2 Challenges of electrolytes and separators in metal-ion batteries

results, application of two-dimensional MXenes leads to ionic conductivity enhancement and increase the efficiency of lithium-ion batteries in comparison to the dimensionless and one-dimensional nanofillers. Nanocomposite polymer electrolyte containing 3.6 wt% MXene indicated the best conductivity. They attributed the high performance of the prepared nanocomposite to its two-dimensional morphology, the well diffusion of the flakes in the polymeric matrix, and having a surface with high functional groups. In contrast to lithium, sodium and potassium-ion batteries with non-aqueous electrolytes, zinc- ion batteries need an aqueous electrolyte to enhance their durability, safety and ion conductivity, and reduce the cost and manufacturing complexity. On the other hand, the anode electrodes of aqueous zinc-ion batteries have ability of side interactions like the hydrogen evolution and deactivation reactions. This limits the durability of zinc ion batteries [45]. In an evaluation, Chen et al. in 2021 [45] prepared a solid polymer electrolyte using poly(vinylidene fluoride-cohexafluoropropylene (PVHF), poly(methyl acrylate) (PMA) and MXenes. In this study, a solution containing lithium fluoride and hydrochloric acid was used to scratch the aluminum layer of Ti3 AlC2 to obtain the MXene (Ti3 C2 Tx ). Interaction between PMA and PVHF matrix led to obtain an electrolyte with homogeneous dispersed MXenes. The prepared solid polymer electrolyte was used as the electrolyte part in zinc-ion batteries. The cycle stability of 10,000 cycles at 2C was the important result of their evaluation. There are very few reports on the effects of V2 O5 on the efficiency of electrolyte in metal-ion batteries. Helen et al. in 2022 [46] added V2 O5 into chitosan polymer owing to its features like large surface, less toxicity and chemical stability. They prepared an electrolyte containing chitosan as the host polymer, V2 O5 , and MgCl2 salt (70 wt%) for application as the electrolyte in magnesium-ion batteries. Their results showed that the existence of V2 O5 meliorated the features of the chitosanbased electrolytes. The conductivity of 1.4 × 10−3 S cm−1 was the important results of the prepared composite electrolytes. This can be related to the reduction of the

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries

309

crystalline degree by adding V2 O5 filler, which leads to obtain a more conduction ways and increase the mobility of magnesium ions.

3.4 Separator The separators have an important section of metal-ion batteries due to their effect on charging/discharging efficiency of batteries. In addition, they play an important role in safety of metal-ion batteries through physical separation of the anode and cathode electrodes, because their contact with each other can be create an internal short circuit followed by an explosion, fire or thermal escape. The porous polymeric materials like polypropylene (PP), polyethene (PE) or a combination of them (for example PP/PE/ PP multilayers) have been utilized in common metal-ion batteries due to their high porosity, good chemical durability and special mechanical characterizations. When using PP/PE/PP as the separator, increase the internal temperature of the battery to above the melting point of PE (~ 130 °C) leads to melting of PE and blocking of the pores of PP layers. This prevent the transfer of lithium ions. However, they are several disadvantages (Fig. 2), such as possibility of internal short-circuiting due to thermal contraction at high temperatures, and increase of the ohmic resistance because of wettability to the electrolyte. Therefore, there are still many challenges for further research in this part of the battery [2, 47]. Zirconium dioxide is a crystalline metal oxide. Application of ZrO2 particle layers leads to create an electro-spun separator with reduced-size uniform pores. Also, zirconium dioxide can be enhance the ability of separator in electrolyte retention and the cycle stability metal-ion batteries through decrease the separator porosity and capability of uptake the electrolyte [2, 47]. In a research, Liu et al. in 2019 [47] applied PP and PE to preparation of nanocomposite of ZrO2 as the separator in lithium-ion batteries. For this purpose, they coated zirconium dioxide nanoceramic on the surface of a PP/PE/PP separator through modification with dopamine followed by a sol–gel process. The modified separator exhibits a specific capacity of 203.7 mAh g−1 . The mechanical, electrochemical and physical characterizations of separator have been enhanced by applied modification process [47]. Preparation of a separator with layerby-layer structure for metal-ion batteries, can be improved its mechanical properties. Xiao et al. in 2020 [2] prepared a multilayer composite using electrospinning of PVA nanofibers and electrospraying of zirconium dioxide nanoparticles and used as the separator in lithium-ion batteries. The synthesized PVA-ZrO2 separator showed ionic conductivity of 2.19 mS cm−1 and electrolyte wettability with uptake of 350%. Composites containing MXene can be used as the separator in metal-ion batteries. In a study, Likitaporn et al. in 2022 [48] prepared a composite containing polyacrylonitrile, polyurethane and Ti3 C2 Tx by electrospinning method and used as the high efficiency separator in zinc-ion batteries. The mixture of polyacrylonitrile/ polyurethane with a ratio of 75/25 leads to create a smooth electro-spun fibers. The values of 0–10 wt% of MXene were added to the mixture to obtain composite

310

H. Dehghan-Manshadi et al.

containing Ti3 C2 MXene micro-sheets. The electrolyte uptake of 2214%, and the excellent charge/discharge stability were obtained using the prepared membrane.

4 Conclusion Metal-ion batteries are one of the most important and popular batteries in the market due to their ability to be recharged. The most common ones are lithium-ion batteries, but efforts have been carried out to use other metal ions to prepare batteries with better characteristics. One of these efforts is the application of metal oxide nanocomposites in various nanocomponents of metal-ion batteries including as cathode, anode, electrolyte, and separator. In this chapter, the challenges in this field and the research to solve them have been collected. It is expected that better results will be achieved in this field by synthesize and apply nanocomposites containing new metal oxides with special structures using hierarchical methods.

References 1. Manthiram A (2017) An outlook on lithium ion battery technology. ACS Cent Sci 3(10):1063– 1069 2. Xiao W, Song J, Huang L, Yang Z, Qiao Q (2020) PVA-ZrO2 multilayer composite separator with enhanced electrolyte property and mechanical strength for lithium-ion batteries. Ceram Int 46(18, Part A), 29212–29221 3. Qi W, Shapter JG, Wu Q, Yin T, Gao G, Cui D (2017) Nanostructured anode materials for lithium-ion batteries: principle, recent progress and future perspectives. J Mater Chem A 5(37):19521–19540 4. Wu R, Sun J, Xu C, Chen H (2021) MgCo2 O4 -based electrode materials for electrochemical energy storage and conversion: a comprehensive review. Sustain Energy Fuels 5(19):4807–4829 5. Huang A, Zhou W, Wang A, Chen M, Chen J, Tian Q, Xu J (2021) Self-initiated coating of polypyrrole on MnO2 /Mn2 O3 nanocomposite for high-performance aqueous zinc-ion batteries. Appl Surf Sci 545:149041 6. Elia GA, Kravchyk KV, Kovalenko MV, Chacón J, Holland A, Wills RGA (2021) An overview and prospective on Al and Al-ion battery technologies. J Power Sources 481:228870 7. Chen L, Bao JL, Dong X, Truhlar DG, Wang Y, Wang C, Xia Y (2017) Aqueous Mg-ion battery based on polyimide anode and prussian blue cathode. ACS Energy Lett 2(5):1115–1121 8. Lian S, Sun C, Xu W, Huo W, Luo Y, Zhao K, Yao G, Xu W, Zhang Y, Li Z, Yu K, Zhao H, Cheng H, Zhang J, Mai L (2019) Built-in oriented electric field facilitating durable ZnMnO2 battery. Nano Energy 62:79–84 9. Muruganantham R, Lu J-S, Liu W-R (2020) Spinel rGO wrapped CoV2 O4 nanocomposite as a novel anode material for sodium-ion batteries. Polymers 10. Min X, Xiao J, Fang M, Wang W, Zhao Y, Liu Y, Abdelkader AM, Xi K, Kumar RV, Huang Z (2021) Potassium-ion batteries: outlook on present and future technologies. Energy Environ Sci 14(4):2186–2243 11. Tian F, Zhang Y, Liu L, Shi Q, Li J, Zhao Q, Zhang Y, Cheng Y, Zhou C, Yang S, Song X (2021) Thermally reshaped polyvinylpyrrolidone/SnO2 @p-toluenesulfonic acid-doped polypyrrole nanocables with high capacity and excellent cycle performance as anode for lithium-ion batteries. J Alloy Compd 867:159067

Polymer-Metal Oxides Nanocomposites for Metal-Ion Batteries

311

12. Dubal D, Jagadale A, Chodankar NR, Kim D-H, Gomez-Romero P, Holze R (2019) Polypyrrole nanopipes as a promising cathode material for li-ion batteries and li-ion capacitors: two-in-one approach. Energ Technol 7(2):193–200 13. Tian Z, Yu H, Zhang Z, Xu X (2018) Performance improvements of cobalt oxide cathodes for rechargeable lithium batteries. ChemBioEng Reviews 5(2):111–118 14. Wang X, Li M, Chang Z, Wang Y, Chen B, Zhang L, Wu Y (2015) Orientated Co3 O4 nanocrystals on MWCNTs as superior battery-type positive electrode material for a hybrid capacitor. J Electrochem Soc 162(10):A1966 15. Haghshenas M, Mazloum-Ardakani M, Tamaddon F, Nasiri A (2021) CoFe2 O4 @methyl cellulose core-shell nanostructure and their hybrids with functionalized graphene aerogel for high performance asymmetric supercapacitor. Int J Hydrogen Energy 46(5):3984–3995 16. Mei J, Liao T, Ayoko GA, Bell J, Sun Z (2019) Cobalt oxide-based nanoarchitectures for electrochemical energy applications. Prog Mater Sci 103:596–677 17. Sun J, Zhang Y, Liu Y, Jiang H, Dong X, Hu T, Meng C (2021) Hydrated vanadium pentoxide/ reduced graphene oxide-polyvinyl alcohol (V2 O5 ·nH2 O/rGO-PVA) film as a binder-free electrode for solid-state Zn-ion batteries. J Colloid Interface Sci 587:845–854 18. Usman Hameed M, Ullah Dar S, Ali S, Liu S, Akram R, Wu Z, Butler IS (2017) Facile synthesis of low-dimensional SnO2 nanostructures: an investigation of their performance and mechanism of action as anode materials for lithium-ion batteries. Physica E: Low-dimensional Syst Nanostruct 91:119–127 19. Zhu X, Jan SS, Zan F, Wang Y, Xia H (2017) Hierarchically branched TiO2 @SnO2 nanofibers as high performance anodes for lithium-ion batteries. Mater Res Bull 96:405–412 20. Liu R, Li D, Wang C, Li N, Li Q, Lü X, Spendelow JS, Wu G (2014) Core–shell structured hollow SnO2 –polypyrrole nanocomposite anodes with enhanced cyclic performance for lithium-ion batteries. Nano Energy 6:73–81 21. Guo X, Yang S, Wang D, Chen A, Wang Y, Li P, Liang G, Zhi C (2021) The energy storage mechanisms of MnO2 in batteries. Curr Opin Electrochem 30:100769 22. Ata ur R, Iftikhar M, Latif S, Jevtovic V, Ashraf IM, El-Zahhar AA, Abdu Musad Saleh E, Mustansar Abbas S (2022) Current advances and prospects in NiO-based lithium-ion battery anodes. Sustain Energy Technol Assessments 53:102376 23. Yang H, Wu H-H, Ge M, Li L, Yuan Y, Yao Q, Chen J, Xia L, Zheng J, Chen Z, Duan J, Kisslinger K, Zeng XC, Lee W-K, Zhang Q, Lu J (2019) Simultaneously dual modification of Ni-rich layered oxide cathode for high-energy lithium-ion batteries. Adv Func Mater 29(13):1808825 24. Pan Q, Zheng Y, Kota S, Huang W, Wang S, Qi H, Kim S, Tu Y, Barsoum MW, Li CY (2019) 2D MXene-containing polymer electrolytes for all-solid-state lithium metal batteries. Nanoscale Adv 1(1):395–402 25. Zhao M-Q, Torelli M, Ren CE, Ghidiu M, Ling Z, Anasori B, Barsoum MW, Gogotsi Y (2016) 2D titanium carbide and transition metal oxides hybrid electrodes for Li-ion storage. Nano Energy 30:603–613 26. Krishnaiah P, Awan HTA, Walvekar R, Manickam S (2022) MXene-based composites and their applications. In: Khalid M, Grace AN, Arulraj A, Numan A (eds) Fundamental aspects and perspectives of MXenes. Springer International Publishing, Cham, pp 53–86 27. Jin X, Wang J, Dai L, Liu X, Li L, Yang Y, Cao Y, Wang W, Wu H, Guo S (2020) Flame-retardant poly(vinyl alcohol)/MXene multilayered films with outstanding electromagnetic interference shielding and thermal conductive performances. Chem Eng J 380:122475 28. Shea JJ, Luo C (2020) Organic electrode materials for metal ion batteries. ACS Appl Mater Interfaces 12(5):5361–5380 29. Sun J, Zhao Y, Liu Y, Jiang H, Chen D, Xu L, Hu T, Meng C, Zhang Y (2023) Synthesis of V2 O5 ·nH2 O nanobelts@polyaniline core–shell structures with highly efficient Zn2+ storage. J Colloid Interface Sci 633:923–931 30. Zhang Y, Huang R, Wang X, Wang Z, Song B, Du Y, Lu Q, Chen X, Sun J (2022) Facile large-scale preparation of vanadium pentoxide -polypyrrole composite for aqueous zinc-ion batteries. J Alloy Compd 907:164434

312

H. Dehghan-Manshadi et al.

31. Mao J, Wu F-F, Shi W-H, Liu W-X, Xu X-L, Cai G-F, Li Y-W, Cao X-H (2020) Preparation of polyaniline-coated composite aerogel of MnO2 and reduced graphene oxide for high-performance zinc-ion battery. Chin J Polym Sci 38(5):514–521 32. Liao X, Pan C, Pan Y, Yin C (2021) Synthesis of three-dimensional β-MnO2 /PPy composite for high-performance cathode in zinc-ion batteries. J Alloy Compd 888:161619 33. Guo L, Ding Y, Qin C, Li W, Du J, Fu Z, Song W, Wang F (2016) Nitrogen-doped porous carbon spheres anchored with Co3 O4 nanoparticles as high-performance anode materials for lithium-ion batteries. Electrochim Acta 187:234–242 34. Liu S, Ni D, Li H-F, Hui KN, Ouyang C-Y, Jun SC (2018) Effect of cation substitution on the pseudocapacitive performance of spinel cobaltite MCo2 O4 (M = Mn, Ni, Cu, and Co). J Mater Chem A 6(23):10674–10685 35. Alqahtani DM, Zequine C, Ranaweera CK, Siam K, Kahol PK, Poudel TP, Mishra SR, Gupta RK (2019) Effect of metal ion substitution on electrochemical properties of cobalt oxide. J Alloy Compd 771:951–959 36. Du X, Yang T, Lin J, Feng T, Zhu J, Lu L, Xu Y, Wang J (2016) Microwave-assisted synthesis of SnO2 @polypyrrole nanotubes and their pyrolyzed composite as anode for lithium-ion batteries. ACS Appl Mater Interfaces 8(24):15598–15606 37. Yuan J, Chen C, Hao Y, Zhang X, Zou B, Agrawal R, Wang C, Yu H, Zhu X, Yu Y, Xiong Z, Luo Y, Li H, Xie Y (2017) SnO2 /polypyrrole hollow spheres with improved cycle stability as lithium-ion battery anodes. J Alloy Compd 691:34–39 38. Li B, Bi R, Yang M, Gao W, Wang J (2022) Coating conductive polypyrrole layers on multiple shells of hierarchical SnO2 spheres and their enhanced cycling stability as lithium-ion battery anode. Appl Surf Sci 586:152836 39. Liu X, Zhu S, Liang Y, Li Z, Wu S, Luo S, Chang C, Cui Z (2022) 3D N-doped mesoporous carbon/SnO2 with polypyrrole coating layer as high-performance anode material for Li-ion batteries. J Alloy Compd 892:162083 40. Huang J, Meng R, Zu L, Wang Z, Feng N, Yang Z, Yu Y, Yang J (2018) Sandwich-like Na0.23 TiO2 nanobelt/Ti3 C2 MXene composites from a scalable in situ transformation reaction for long-life high-rate lithium/sodium-ion batteries. Nano Energy 46:20–28 41. Lim E, Shim H, Fleischmann S, Presser V (2018) Fast and stable lithium-ion storage kinetics of anatase titanium dioxide/carbon onion hybrid electrodes. J Mater Chem A 6(20):9480–9488 42. Zhang X, Li J, Li J, Han L, Lu T, Zhang X, Zhu G, Pan L (2020) 3D TiO2 @nitrogen-doped carbon/Fe7 S8 composite derived from polypyrrole-encapsulated alkalized MXene as anode material for high-performance lithium-ion batteries. Chem Eng J 385:123394 43. Zhang S, Long T, Zhang H-Z, Zhao Q-Y, Zhang F, Wu X-W, Zeng X-X (2022) Electrolytes for multivalent metal-ion batteries: current status and future prospect. Chemsuschem 15(21):e202200999 44. Zhao Q, Zhu Q, Miao J, Zhang P, Wan P, He L, Xu B (2019) Flexible 3D porous MXene foam for high-performance lithium-ion batteries. Small 15(51):1904293 45. Chen Z, Li X, Wang D, Yang Q, Ma L, Huang Z, Liang G, Chen A, Guo Y, Dong B, Huang X, Yang C, Zhi C (2021) Grafted MXene/polymer electrolyte for high performance solid zinc batteries with enhanced shelf life at low/high temperatures. Energy Environ Sci 14(6):3492– 3501 46. Helen PA, Ajith K, Diana MI, Lakshmi D, Selvin PC (2022) Chitosan based biopolymer electrolyte reinforced with V2 O5 filler for magnesium batteries: an inclusive investigation. J Mater Sci: Mater Electron 33(7):3925–3937 47. Liu L, Wang Y, Gao C, Yang C, Wang K, Li H, Gu H (2019) Ultrathin ZrO2 -coated separators based on surface sol-gel process for advanced lithium ion batteries. J Membr Sci 592:117368 48. Likitaporn C, Okhawilai M, Kasemsiri P, Qin J, Potiyaraj P, Uyama H (2022) High electrolyte uptake of MXene integrated membrane separators for Zn-ion batteries. Sci Rep 12(1):19915

Polymer-Chalcogen Composites for Metal-Ion Batteries Sakshi Gautam, Anjali Banger, Nirmala Kumari Jangid, and Manish Srivastava

Abstract Lithium-chalcogen batteries (LCBs) have gotten a lot of attention as nextgeneration energy storage systems because of their high theoretical capacities, high energy density, and low cost when compared to the most recent lithium-ion batteries (LIBs). Nevertheless, their practical applications are severely inhibited by some drawbacks, such as the dramatic volume expansion of elemental chalcogen, the dissolution and shuttling of intermediates in ether electrolytes, and dendrite growth on metal anodes. Functional components, such as chalcogen hosts, binder, and interlayer, using various polar materials, have been introduced to address these issues. Bio-derived materials are among them and are regarded as novel eco-friendly alternatives. In this chapter, the authors focus on the unique physical, chemical, and environmental properties of bio-derived materials used in LCBs, including active host materials and polymer binders. We hope that the present report can provide some new insights and directions for future research on high-performance alkaline chalcogen batteries (ACBs). Keywords Lithium-ion batteries · Lithium-chalcogen batteries · Alkali chalcogen batteries · Bio-derived material · Energy storage

1 Introduction The advancement of science and technology has the potential to impact all aspects of humanity. This is especially true for LIBs, which are commonly used in everyday human life. Now, portable and stationary electronics, electric vehicles, and stationary energy storage are all possible with LIB. In addition, they allow the rapid exchange of S. Gautam · A. Banger · N. K. Jangid (B) Department of Chemistry, Banasthali Vidyapith, Banasthali, Rajasthan 304022, India e-mail: [email protected] M. Srivastava Department of Chemistry, Central University of Allahabad, Allahabad, Uttar Pradesh 211002, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_18

313

314

S. Gautam et al.

information without the restrictions (such as power outages) inherent in distributed power systems (i.e., the national grid). In terms of environmental protection, LIB allows the use of intermittent, clean, and renewable energy sources such as solar, wind, tidal, and earth heat, which reduces the need for fossil fuels, cleans the environment and limits the generation of pollution and waste at specified domains or levels [1]. However, the use of conventional LIBs based on Li+ intercalation chemistry is constrained by the gradual approach of their theoretical energy density limits, which prevents them from being used in novel applications like electric vehicles. Breaking the limit requires the development of new electrode systems and materials capable of triggering new chemical processes for electrochemical storage. The LCBs, based on redox reactions of Li with chalcogen elements (S, Se, and Te) to trigger two-electron redox reactions between anode and cathode materials, show the ability to store and generate more power than conventional LIBs, making them prime candidates for emerging storage markets. Due to their high theoretical energy efficiency (2560 Wh kg−1 or 2860 Wh L−1 ), low cost, and S-toxicity-free nature, lithium-sulfur (Li–S) batteries have been identified by many organizations, including the US Department of Energy and the National Energy Administration of China, as a potential solution for high-energy electrochemical storage in the near future. As the apparent conductivity density of Se (3265 mAh cm−3 ) is roughly equivalent to that of S (3461 mAh cm−3 ), another alternative system, Lithium-Selenium (Li-Se) batteries, has an energy density comparable to that of the Li–S system, suggesting potential for volume-sensitive applications, such as devices, mobile electronics, and spacecraft. The high electronic conductivity of bulk Se (1 × 10–3 S cm−1 , about 24–25 orders of magnitude higher than S) and compatibility with conventional liquid electrolytes, particularly carbonates, are additional benefits of Li–Se systems. Research on the Li-Se combination advances our knowledge of LCBs and paves the way for the creation of useful rechargeable Li batteries with high energy and a long life [2].

2 A Short Introduction to Li Batteries Based on Chalcogen Cathodes S has been used as a cathode material since Herbet & Ulam patented a 1° battery in 1962 that used a Li alloy or Li as the anode and sulfur as the cathode. This practice dates back to the 1960s. 1°, 2°, or 3° saturated fatty amines have been used to dissolve perchlorate, iodide, bromide, or chlorate alkaline electrolytes. Propyl, butyl, and amyl amines are preferred among these solvents. These metal-sulfur batteries’ theoretical energy density was then calculated by Bhaskara, who then filed for a patent on it. In order to create rechargeable Li–S batteries, liquid electrolytes based on ether solvents, particularly 1,3-dioxolane (DOL), were used in the 1980s. Recently, the cathode materials Se and Te for rechargeable alkaline batteries have been studied.

Polymer-Chalcogen Composites for Metal-Ion Batteries

315

The Amine group first proposed selenium as a cathode material for rechargeable Li batteries in 2012. They discovered that in carbonate electrolytes, the Se cathode exhibits conductivity and improved cyclic stability along with an operating voltage of 2 V compared to Li+ /Li and an apparent capacity density of 3253 mAh cm−3 that is comparable to that of S (2.2 V compared to Li+ /Li; 3467 mAh cm−3 ). As a result, it has demonstrated that it is possible to develop high-energy rechargeable batteries for sophisticated data storage applications while keeping material costs low. Numerous follow-up studies have been published because of the new chalcogen cathode’s electrochemical characteristics, which have sparked a great deal of interest in this subject [3]. Te cathode use in Li rechargeable batteries has been the subject of independent research groups led by professors Chunsheng Wang from the University of Maryland, College Park, and Shu-Hong Yu from the University of Science and Technology of China since 2014. They discovered that Te, like S/Se, has a high capacity density (2621 mAh cm−3 ), but Te also exhibits higher electronic conductivity and faster reaction kinetics due to its quasi-metallic nature. Investigating the Te versus Li electrochemistry also revealed a transition that may be distinct from the contentious claims of polytelluride formation. In addition to using pure elements as cathodes, Se and Te have demonstrated the ability to form S-miscible inter chalcogen compounds, which greatly improve the storage efficiency of rechargeable batteries.

3 LCBs Electrochemical Principles For a better understanding of their electrochemical differences, the physicochemical properties of sulfur, selenium, and tellurium are compared before delving into the workings of LCBs (Table 1) [4]. The solubility of polychalcogenides in the electrolyte, for example, has a significant impact on the electrochemical performance of S, Se, and Te and can result in different electrochemical activities. For instance, Chau et al., discovered that trigonal Se induces a single-phase transformation while amorphous Se undergoes multi-step photochemistry, highlighting the significance of the selenium phase in Li-Se batteries [5]. In addition, the chalcogen elements have different electrical conductivities. Se and Te are semi-metals and semiconductors, while S is an insulator. S has a low rate potential and requires a considerable amount of additional carbon to improve the reaction kinetics because of the significant difference in conductivity. Because Te has a significantly higher density (6.24 g/ cm3 ), Li-Te batteries have the same volumetric capacity as Li-Se and Li–S batteries, which is essential for practical use where space is limited. The melting point (M.P.) of chalcogen increases with atomic number. As a result, the application of melt permeation to produce carbon/Te composites has inherent limitations such as lower operating mass loads, less safety, and increased cost. In this section, we will discuss in depth the electrochemical concepts of Li–S, Li-Se, and Li-Te batteries. Li–S batteries: Batteries in Li–S ether electrolytes frequently show a multi-step redox reaction that is known as a two-step charge/discharge configuration [6]. As can be seen in (Fig. 1), during discharge, sulfate (S8 ) molecules interact with the

316

S. Gautam et al.

Table 1 Parameters of different chalcogens are summarized in detail Element

Electronic conductivity (S m−1 )

S

5 × 10−28

2.07

Monoclinic (ring-like S8 )

32.1

115

Se

1 × 10–3

4.81

Rhombohedral (Se6 ), trigonal (chain-like Se8 )

79.0

221

Te

2 × 102

6.24

Trigonal (chain-like Te8 )

127.6

450

Mass density (g cm−3 )

Crystal structure

Mole mass (g mol−1 )

M.P. (°C)

lithium-ion to produce a number of soluble intermediates, including Li2 S8 , Li2 S6 , and Li2 S4 . A plain discharge of less than or equal to 2.1 V results from additional photochemistry that transforms a long-chain polysulfide into a solid and insoluble short-chain polysulfide (i.e., Li2 S) deposited on the electrode. Reversible reactions with the intermediate, Li2 S8 or S, take place during charging. Li–S batteries go through oxidation reactions as they transition from solid to liquid to solid during charge and discharge cycles. For instance, it has been discovered that the cyclo-S8 cathode and the carbonate electrolyte are incompatible because the higher-order polysulfides will interact nucleophilically with the carbonate solvent and cause battery failure after the initial discharge. The researchers then discovered that in the carbonate electrolyte, the S2-4 sulfur molecules are confined to space, and covalently bonded organic sulphur has an inclined plateau along with a unique discharge configuration [7]. Li–Se batteries: The theoretical bulk capacities of both Li-Se (3253 mAh cm−3 ) and Li–S (3467 mAh cm−3 ) are equivalent as congeners of sulfur. But it shows a

Fig. 1 Charge/discharge profiles of LCBs in carbonate-based and ether-based electrolytes liquid electrolyte. a Li–S batteries, b Li–Se batteries, c Li–Te batteries. Adapted with permission [4], Copyright [2021], Elsevier

Polymer-Chalcogen Composites for Metal-Ion Batteries

317

significantly lower theoretical gravimetric capacity (675 mAh g−1 ) than Li–S (1675 mAh g−1 ) [8]. The widespread use of Li-Se batteries is also hampered by a number of reasons, such as the pendulum effects caused by the dissolution of intermediate polyselenides in ether-based electrolytes, the volume expansion of se during cycling, and active losses [9]. In ether and carbonate electrolytes, Li-Se batteries behave in different ways. With the exception of a slightly lower redox potential, the operation of Li-Se batteries in ether-based electrolytes is similar to that of Li–S batteries [10]. Two discharge plateaus at ~ 2.1 and ~ 1.9 V, respectively, demonstrate the typical reduction of Se to Li2 Sen (n ≥ 4) to Li2 Se2 , and finally Li2 Se. During charging, there is only one plateau, which might be caused by possible overlap (Fig. 1). Li-Se batteries behave the same as Li–S batteries when using an ether-based electrolyte. Se cathodes, in contrast to cyclo-S8 , are notable for being compatible with carbonate electrolytes. Li–Te batteries: Li-Te batteries have a volumetric capacity that is comparable to Li–S and Li-Se batteries (2558 mAh cm−3 ) because Te is a chalcogen element that belongs to the same family as S and Se. Li-Te batteries have a lower theoretical weight capacity (419 mAh g−1 ) than Li–S (1675 mAh g−1 ) and Li-Se (675 mAh g−1 ) batteries because Te has a higher molecular weight [11]. Wang and Yu’s team used the Te cathode for rechargeable Li batteries for the first time in 2014. According to reports, Li2 Te formation involves a single-step phase transition mechanism called the Li-Te redox reaction in carbonate electrolytes (Fig. 1). The insoluble ditellurides, or Li-Te, are transformed into Te after loading. As a result, the S and Se electrodes in the ether electrolyte and the Te electrodes both experience pendulum motion issues. It should be noted that there is an ongoing discussion about how polytellurides are formed. Additionally, during photochemistry, the cathode of Te experiences a significant volume expansion of about 200%, which has a rapid degradative effect on long-term cyclic stability. ACBs have inherent flaws in their active materials that prevent them from being used in practical applications. Low conductivity, significant volume changes during discharge, and efficient shuttle reactions from soluble intermediates (metal polysulfide [PSs] and metal polyselenide [PSes]). These serious problems cause metal chalcogen batteries to have a shorter cycle life, a lower coulomb efficiency, and inaccurate reproducibility. Numerous studies have suggested functional components as hosts for active materials, polymer electrolytes, intercalators, and polymeric binders in an effort to solve these problems. Polar materials, such as metal-based compounds, carbon doped with heteroatoms, and naturally polar materials, are frequently found in functional components. Among them, bio-based materials are of great interest because they have the potential to make ACB commercially viable. Bio-based materials contain different functional groups with unique chemical and physical properties. In addition to their eco-friendliness and reasonable cost, they comply with global environmental laws. In this chapter, we aim to provide an overview of current trends in biomaterials research for the ACB by discussing and evaluating relevant modeling studies from the development stage to their positive poles. The objective of this chapter is to provide

318

S. Gautam et al.

new perspectives for the development of advanced ACBs that do not adversely affect nature.

4 Bio-derived Materials for Alkali Metal–Chalcogen Batteries Bio-Derived Materials as Functional Hosts of Active Materials: The hosts of chalcogen materials for ACBs can successfully suppress the PSs & Pses shuttle effects by physically trapping and accommodating the volume changes of the chalcogens during cycling, thereby improving conductivity. Porous carbon made from biological materials has unique chemical properties that can improve the suppression of shuttle PSs and PSes effects. comparison to conventional porous carbon (Super-P, Ketjen Black, and CMK-3). Numerous chalcogenide hosts have been developed, and each one is based on the inherent structural properties and chemical composition of materials obtained through biological processes (detailed in Table 2). To convert natural raw materials into substances with an appropriate electron or ion path for use in batteries, the majority of scientists have used the carbonization technique (high-temperature calcination above 400 °C or the hydrothermal technique). Activators like KOH, NaOH, and CaCO3 were used to simultaneously activate and carbonize porous structures. Yeon et al., in their investigation of the aforementioned natural structural characteristics, identified lignin-derived porous carbon as a sulfur Table 2 Various chalcogenides host from bio-derived materials, fabrication method sources, & structure Sources SEM and TEM

Fabrication method

References

Sucrose

Dehydration

“Adapted with permission from Ref. [15], Copyright [2019], ACS

Lignin

KOH activation “Adapted with permission from Ref. [12], Copyright [2019], Elsevier

Fluffy catkins

ZnCl2 template Adapted with permission from Ref. [16], Copyright [2020], Elsevier

Polymer-Chalcogen Composites for Metal-Ion Batteries

319

host. Lignin is a potent candidate for hierarchically structured carbon nanomaterials because of its aromatic structure, sustainability, abundance, and affordability (in contrast to its counterparts that use fossil fuels) [12]. It has been established that the original composition of ginkgo nuts provides a rich environment rich in N and S. Liu et al., used porous honeycomb carbon made from ginkgo nuts as a sulfur host. The electrical conductivity and PSs/PSes affinity of heteroatom-doped porous carbon are higher. In contrast to earlier studies that only discussed porous carbon doped with a single heteroatom, more recent studies have focused on porous carbon doped with two or three heteroatoms (such as nitrogen, sulfur, or oxygen). Porous carbons include nitrogen and oxygen dual-doped carbon [13], double and oxygendoped carbon (derived from Cyclosorus), [14], and nitrogen and phosphorus-doped carbon (derived from yarn). The material-supported functional hosts displayed distinct qualities when compared to natural materials. Ghosh et al., introduced cardanol benzoxazine, an agro-waste copolymer rich in sulfur, as an active component for sodium-sulfur batteries (NSBs). Due to the in-situ formation of the polymer backbone, these materials allowed for the homogeneous distribution of sulfur while maximizing its utilization. Raghunandanan et al., claim that manganese oxide is used in hemp-derived carbon as a sulfur host, producing PSs absorbents in addition to increasing conductivity. To create a biocarbon from bacteria, Duan et al., used graphene as the sulfur host and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as the carbon host. Beginning with biological materials at the macroscale, the use of biological materials at the micro- and nanoscales can help advance research into new resources. Bio-Derived Materials as Functional Polymer Binders: Important sulfur cathode components such as polymeric binders have shown efficient electrode integration, ensuring effective connections between the interfaces of active materials, current collectors, and conductive carbons during cycling while also controlling the electrode materials. Binder’s ability to function as an electrochemical regulator capable of preventing PSs rearrangement and facilitating electron and ion transport has been enhanced as knowledge of the multiphase conversion chemistry of ACB has grown. Previously, the binder’s role was merely that of a simple mechanical stabilizer [17]. Due to their plentiful natural supply, high mechanical strength, environmental friendliness, and wealth of functional groups with effective lithium polysulfide anchors, biomaterials have attracted a lot of interest as binder additives or polymer binders. Furthermore, biopolymer purification for food additives, pharmaceuticals, and cosmetics has already been created, and it is straightforward to adapt it to other industries. Earlier research focused on the bonding properties of bio-derived materials and the identification of bio-derived polymers, but recently the attention has shifted to the chemical and physical properties of modified binders. Chitosan, a substance derived from mussels, shrimp, and crabs, has a lot of potential as a binding agent for ACBs. (Poly[β-1/4]-2-amino-2-deoxy-Dglucopyranose) structure (which results in

320

S. Gautam et al.

electrochemical stability, abundant hydrogen bonding, and straightforward lithiumion transport pathways via flexible ether linkages) confers favorable mechanical properties. In addition, chitosans’ plentiful NH2 and OH groups significantly strengthen its bond with the current collector and increase its affinity for PSs and PSes (to control shuttle effects) [18]. A graphene oxide-based multifunctional network binder for Li–S batteries that contains less chitosan was presented by Kim et al., Chitosan and graphene oxide combine in an aqueous solution to form a homogeneous network that enhances mechanical properties, controls the PSs in the electrochemical redox system, and creates a quick electrical path through the binder system. Deng et al., and Pan et al., presented modified chitosan functional groups for use in Li–S battery binders. Chitosan’s PSs capture efficiency was improved by substituting acryloyl glycine amide and nitrocatechol for its amine groups [19]. A dual cross-linked network capable of providing excellent PSs affinity while having substantial mechanical strength to stabilize the electrode was presented by Deng et al., as an advanced binder design over a modified functional group. Their combination with functional polymers offers a novel strategy for enhancing ACB and is based on biopolymer design. A strong biopolymer network was demonstrated by Liu et al., using guar gum and xanthan gum as binders. Both polymers’ mechanical properties were enhanced by intramolecular bonding between their functional groups, which led to stable battery performance on a heavily loaded sulfur cathode. A 3Dreinforced free-standing sulfur cathode with a hybrid binder made of sodium alginate and polyaniline was described by Ghosh et al. Bio-Derived Materials as Functional Interlayers: A promising technique for enhancing the cycling of ACB batteries through interlayer insertion has recently come to light in several studies. The first to suggest using carbon paper for interlayer insertion was Manthiram et al. [20]. Utilizing the interlayer offered a fresh method for increasing battery performance. Research on the cathode’s exteriors has advanced because of advancements made in research on the cathode’s interiors (host, binder, and conductive agent). To improve the electrochemical performance of ACBs, a wide variety of interlayers based on carbon, metal compounds, and polymers have been carefully examined during the interlayer development process. Work has been done to control soluble PSs/PSes via fixation and conversion, and an interlayer that will promote the formation of conductive and polar networks has also been attempted. Any carbonaceous material derived from biological material, such as through the process described earlier, can generally be used as an active material for coating a commercial separator after carbonization. Interlayers relating to heteroatomic (nitrogen, sulfur, and oxygen-doped) carbon have been described, like carbon materials made from biological material in the host. Numerous materials with biological origins can be produced using polysaccharides, amino acids, and other organic compounds. The process of making porous carbon doped with heteroatoms is simple. An oxygen-rich carbon-based aerogel made from sweet potato was reported by Zhu et al., as an active interlayer material. Nitrogen- and oxygen-doped porous carbon derived from crab shells have been shown by Huang et al., to be an efficient PSs shuttle effect suppressant [21]. Other materials decorated with biological metal compounds

Polymer-Chalcogen Composites for Metal-Ion Batteries

321

have been discovered, and the interlayer is thought to be responsible for their catalytic properties. Carbon spheres with yeast-derived MnO decorations were suggested as interlayer coating materials by Feng et al. [22] through powerful chemical adsorption, polar MnO was used to successfully block PSs. The development of Li–S batteries was aided by the opening of new pathways for the preparation of carbon-coated materials made possible using metal oxides in conjunction with carbon derived from biomass to create new coated separators. Free-standing interlayers made of SnO2 nanoparticles and carbon nanofibers derived from bacterial cellulose were described by Celik et al. In addition to improved adsorption effects and the use of active material(s), mixing metal oxides with pyrolyzed bacterial cellulose further decreased the contribution of tin oxide to cellular resistance. Additionally, the free-standing interlayer might enhance the function of the current interlayer by facilitating electron and ion transport in sulfur cathodes. Zheng et al., described a carbon microtubular textile made from cotton waste that was a freestanding interlayer with an optimized structure that allowed for straightforward carbonization and the preservation of the original material structure. Yang et al., reported a carbon-felt interlayer made of rice paper. Rice paper is famous for being used in traditional Chinese painting and calligraphy. It is made of specific natural plants, such as rice straw and sandalwood. The prepared interlayer demonstrated a synergistic effect for PSs capture using its own absorbents in conjunction with coulombic ion repulsion mechanisms using a functional polymer. The electrochemical performance of ACBs was significantly enhanced by the chemical and structural advantages of bio-derived materials shown in Table 3. Table 3 Various interlayers obtained from bio-derived materials; sources, types, and functions Sources

Types

Functions

References

Carb-shell

Carbon materials for interlayer High utilization of active [21] materials regulation of PS shuttle affects Enhancements in the electronic conductivity

Lignin

Carbon materials for interlayer Accommodation of the volume [23] change of sulfur regulation of PS shuttle affects enhancements in the electronic conductivity

Silk nanofiber Freestanding interlayer

Regulation of PS shuttle effects

[24]

Cotton

Freestanding interlayer

Regulation of PS shuttle effects Enhancements in the electronic conductivity

[25]

Yeast

Carbon materials for interlayer High utilization of active [22] materials regulation of PS shuttle effects Enhancements in the electronic conductivity Facile lithium-ion diffusion

322

S. Gautam et al.

Bio-Derived Materials for Functional Polymer: The safety and lifespan of batteries can be increased with inexpensive options like electrolyte-fixed ACBs. Solid-state electrolytes fall into two categories: inorganic and polymer electrolytes. Inorganic metal oxides (such as NASICON types Li1.3 Al0.3 Ti1.7 [PO4 ]3 and Li7 La3 Zr2 O12 ) are used to make solid-state electrolytes [26]. In comparison to liquid and solid inorganic electrolytes, polymer electrolytes have several advantages, such as superior flexibility, better safety features, reduced PSs/PSes effects, and improved processability. Additionally, they are more resistant to the changing volume of an electrode during the charge and discharge process. However, these are constrained by time-consuming procedures, expensive precursors, and poor physical attributes. Additionally, under specific circumstances, the growth of metal anode dendrites in polymer electrolytes can be restricted or even prevented [27, 28]. Most of the biomass is composed of cellulose (30–50 wt%), hemicellulose (25–30 wt%), and lignin (10–20 wt%). Numerous active functional groups, including hydroxyl, carbonyl, and carboxyl, can be found in lignin molecules. Hydroxyl groups are expected to form hydrogen bonds with anions in Li-salts and highly electronegative PSs during the charge–discharge process. Excellent mechanical properties, an electrochemical stability window, ionic conductivity, thermal stability, and compatibility with Li-ion battery electrodes were all characteristics of the lignocellulose-based polymer electrolyte. Zhu et al., described a polymer electrolyte based on soy protein isolate (SPI). Given that SPI is a plentiful renewable resource that is safe for the environment and has a greater number of functional groups, which greatly facilitate lithium ion transport while immobilizing PSs, it is an environmentally friendly framework for polymer electrolytes in LIBs. Many of the aforementioned biological elements could be utilized as ACB polymer electrolytes. Chitosan, for instance, has a corkscrew-like chain structure because it contains glucosamine monomers connected by glycosidic bonds. Chitosan disaggregates lithium salts, adsorbs organic solvents, facilitates lithium ion transport, and inhibits PSs and PSes shuttle effects as a result of its unique chemical composition and functional groups. Furthermore, the formation of stable solidelectrolyte interfaces (SEI) with uniform lithium deposition and stripping during cycling can prevent the growth of dendrites on the lithium surface. Another strong contender for a stable ACB for both electrodes is sodium alginate (chalcogen cathode and alkali metal anode). It is well known that sodium alginate has excellent heat resistance, excellent ionic conductivity (to alkali metal ions), and is mechanically and electrochemically stable. Sun et al., reported that a polymer electrolyte based on sodium alginate demonstrated enhanced interfacial compatibility at the electrode interface with low interfacial resistance in LIBs [29]. Polymer electrolytes based on biological materials are anticipated to be further researched and optimized in the future due to their favorable environmental and economic properties over traditional solid polymer electrolytes (SPEs).

Polymer-Chalcogen Composites for Metal-Ion Batteries

323

5 High-Performance Alkali Metal–Chalcogen Batteries Achieved by Bio-derived Materials Lithium–Sulfur: Sulfur frequently degrades battery performance because of its insulating properties, massive volume expansion during the charge–discharge process, and the PS pendulum effect. The PSs pendulum effect needs to be fixed in order to achieve high performance. The mechanism of the formation of soluble PSs in the shuttle effect is shown below. In the first stage, soluble long-chain PSs are produced, which dissolve in the organic electrolyte (Li2 Sx, where x = 4–8). In the second phase, it transforms into an insoluble PS (Li2 S2 or Li2 S). The equations for the first stage of discharge (2.2–2.4 V) are (x/8) S8 + 2e− + 2Li + = Li2 Sx (x = 4–8), and those for the second stage of discharge (below 2.2 V) are (2x − 2) e− + (2x − 2) Li + = xLi2 S (x = 4–8). To maximize the Li–S batteries’ energy density, high sulfur loading, and a low electrolyte/sulfur ratio should be achieved in Li–S battery research. The electrolyte/ sulfur ratio and sulfur content greater than 5 mg/cm2 have been identified as critical metrics for high-performance Li–S batteries by Manthiram’s group. These metrics typically allow Li–S batteries to operate for extended periods of time with high capacity retention and recharge in ten or even a few minutes. High-performance Li– S batteries should therefore have the advantages of high sulfur content, high-speed capability, long cycle life, and a low electrolyte/sulfur ratio. These advantages, which are listed in (Table 4), can be attained by using bio-derived materials, creating the possibility of practically employable Li–S batteries. High Sulfur Loading: Low sulfur content affects the majority of sulfur cathodes. For instance, by using a short-branched protein as a functional binder additive to adsorb PSs, Chen et al., were able to achieve high sulfur loading. While the long-branched zein residues could only take up a small number of PSs, the shortbranched gelatin residues were able to open up the binding sites and trap the PSs in a “molecular cage.” Short-branched gelatin is an effective binder additive for cathodes to achieve high sulfur loading because of its high PS-capturing capacity. Tu et al., added gum arabic to a conductive carbon nanofiber film as a PS shielding interlayer with specific oxygen-containing functional groups. High reversible areal capacities of 4.77 and 10.8 mAh/cm2 with high sulfur loadings of 6 and 12 mg/ cm2 , respectively, could be achieved in the Li–S system based on the interlayer. Babu et al., produced graphene-like N-doped carbon sheets using bagasse as a sulfur host. A sulfur loading of 12 mg cm−2 and an area capacity of 12 mAh/cm2 were achieved by stacking several cathode layers. These studies have demonstrated that high-performance ACBs with a high sulfur loading of > 5 mg/cm2 can successfully use bio-derived materials [31]. High-Rate Capability: One important component for the potential use of Li–S batteries is thought to be rate capability. The high-rate performance of Li–S batteries allows for quick charging. Capacotton fabric (CCF), which is produced quickly and has a remarkable capacity for Li–S batteries to adsorb electrolytes, is one potential outcome of bio-derived materials. The ability of Li–S batteries to repurpose the

High rate performance Long-term cycling stable performance

Saponin 0.8–1

732

826

High sulfur loading

Soy protein 5.6

835

≈ 1.2

High rate performance Long-term stable cycling performance

Chitosan

Loading (mg cm−2 ) 887

Sulfur loading 3

Advantage

Gram-positive Long-term stable cycling performance bacteria Bacillus subtilis

Sources

638

735

543

482

Initial capacity (mAh g−1 )

38.0

43.2

32.4

28.7

Final capacity (mAh g−1 )

Table 4 High-performance Li–S batteries achieved by bio-derived materials in the last three years

1000

100

700

1000

Final capacity/ theoretical capacity (%)

2 C

0.3 Ag-1

1 C

5 C

Cycle current density

[19]

[30]

[18]

[27]

References

324 S. Gautam et al.

Polymer-Chalcogen Composites for Metal-Ion Batteries

325

absorbed electrolyte and contain the electrolyte’s PS dissolution with it in the 3D CCF interlayer improved their performance. The 3D CCF interlayer significantly improved rate performance, as demonstrated by the Li–S batteries based on it, which demonstrated 645.7 mAh g−1 at the sixth cycle after being activated at 0.1 C for five cycles and maintained 569.2 mAh g−1 at 4 C after 200 cycles. The Li–S batteries based on the 3D CCF interlayer can be controlled to have a low electrolyte/sulfur ratio, which is also significant to note (30 and 40 μL for 2 and 5 mg cm−2 cathode, respectively). In order to create chitosan sulfateethylamide glycinamide (CSEG), Yi et al., converted chitosan. CSEG was used as the binder for sulfur cathodes. The initial capacity of the CSEG-based sulfur cathode was 835.1 mAh g−1 , and it continued to maintain 543.5 mAh g−1 at 1 C after 700 cycles, demonstrating 96.4% Coulombic efficiency and a low initial capacity fading rate of 0.049% per cycle. Even at a very high current density of 20 C, the CSEG-based sulfur cathode displayed a remarkable reversible capacity of 194.4 mAh g−1 . The outstanding electrochemical performance is attributed to the high confining capacity of PSs and the efficient inhibition of the diffusion and shuttle of PSs. As a result, bio-derived materials can support ACBs’ high performance, which significantly serves to reinforce their superiority in high-performance ACBs [32]. Long-Term Stable Cycling Performance: Li–S batteries typically have poor long-term stable cycling performance due to PS dissolving in the electrolyte and low sulfur conductivity, but this performance can be greatly enhanced by using bioderived materials. With a performance of 1040 mAh g−1 at 0.2 A g−1 after 100 cycles and good rate capability at various current densities, SDC@TiO2 /S outperformed SDC/S electrodes, TiO2 /S, and pure S. Polar PS movement is restricted and slowed down by the TiO2 shell, but non-polar sulfur can be adsorbent and hosted in porous carbon [33]. With an average capacity loss of 0.016% per cycle and a Coulombic efficiency of 99.5%, the SDC@TiO2 -S cathode demonstrated a stable ultra-long cycling performance of 569 mAh g−1 after 1500 cycles at 1.5 A g−1 . According to reports, a trustworthy carbonized cotton fabric (CCC) interlayer for Li–S batteries has been created from used cotton fabric. The long Li–S batteries’ lifetime was made possible by the CCC interlayer acting as an upper current collector and PS barrier. The Li–S batteries kept their high initial capacity of 827 mAh g−1 while maintaining 498 mAh g−1 after 1000 cycles at 1 C. Chitosan and reduced graphene oxide were combined to create a multifunctional network binder for Li– S batteries by Kim et al., (rGO). Chitosan had a variety of functional groups that effectively controlled the pendulum effect of PS, in contrast to rGO, which enhanced electrical conductivity and constrained sulfur volume expansion. So it is essential to use bio-based materials to increase the cycle life and stability of Li–S batteries [34]. Low Electrolyte/Sulfur Ratio: Electrolytes make up a large portion of the mass fraction of Li–S batteries. The low electrolyte/sulfur ratio required to maximize the energy density of Li–S batteries can be achieved with the aid of biologically derived materials. Yi et al., described PACEC as a high-performance binder for sulfur cathodes (polyphosphate acid cross-linked ethylamide urea chitosan). The high PSs affinity of the PACEC binder reduced the pendulum effect of PSs and improved the mechanical properties of the sulfur cathode.

326

S. Gautam et al.

Despite the fact that the Li–S battery ratio was significantly higher, the electrolyte/ sulfur ratio was tightly controlled at 6 μL mg−1 . The Li–S batteries’ energy density rose as a result of the low electrolyte/sulfur ratio, which also reduced overall weight. The PACEC binder-based sulfur cathode had an initial areal capacity of 17.5 mAh/ cm2 and a coulombic efficiency of 99.3% despite having a low electrolyte/sulfur ratio of 6 μL/mg, and a high sulfur concentration of 14.8 mg/cm2 . Even though bioderived materials can be used to achieve an electrolyte/sulfur ratio of6 μL/mg, more research on these materials is necessary to improve the electrochemical performance of Li–S batteries [35].

6 Conclusions and Outlook LCBs with high theoretical capacities and energy densities have been recognized as promising alternatives to LIBs. However, the practical application of LCBs is hindered by the severe volume expansion of chalcogen cathodes, sluggish redox reaction kinetics, problematic Li dendrite growth, and dissolution and diffusion of intermediates in ether-based electrolytes. Bio-derived materials, which are earthabundant, sustainable, environmentally friendly, and low-cost, have been adopted to resolve these issues with much improved electrochemical performance. Due to these advantages, bio-derived materials are widely used in rechargeable ACBs as active hosts, interlayers, binders, or solid electrolytes. This chapter introduces bio-derived materials that achieve high performance in rechargeable ACBs. The various functional groups in bio-derived materials can effectively reduce the shuttle effect of PSs and PSes, while the porous structure of bioderived materials is beneficial for encapsulating active materials. Meanwhile, the bio-derived materials demonstrated stronger chemical binding to PSs and PSes by doping heteroatoms or modifying them with polar materials, indicating that this is an effective strategy for improving the future performance of ACBs. Despite the success of bio-derived materials used in high-performance ACBs, some problems still need to be solved. (1) The bio-derived materials can improve the ionic conductivity of SPEs at room temperature, but the ACBs with these SPEs cannot show the same high-rate capability and long-term stable cycling performance as compared with the batteries based on liquid electrolytes. Thus, more bio-derived materials should be found for safe and high-performance solid ACBs operated at room temperature. (2) Some bio-derived materials naturally have special structures such as wrinkle surfaces, micro- or nanopores, and laminated structures. Using these structures, we can easily prepare a special electrode or battery structure without a previously complex process, which will lead to advanced-performance ACBs. By addressing these problems, high-performance ACBs achieved by bio-derived materials will be able to go one step further in practical applications.

Polymer-Chalcogen Composites for Metal-Ion Batteries

327

References 1. Zhou J, Liu Y, Zhang S, Zhou T, Guo Z (2020) Review article –metal chalcogenides for potassium storage. InfoMat 2(3):437–465 2. Wang WP, Zhang J, Yin YX, Duan H, Chou J, Li SY, Yan M, Xin S, Guo YG (2020) A rational configuration of electrolyte for high-energy and long-life lithium–chalcogen batteries. Adv Mater 32(23) 3. Wang YH, Li XT, Wang WP, Yan HJ, Xin S, Guo YG (2020) Review article-chalcogen cathode and its conversion electrochemistry in rechargeable Li/Na batteries. Sci China Chem 63(10):1402–1415 4. Ma L, Wu J, Lv Y, Li B, Jin Z (2021) Rational design of carbon nanotube architectures for lithium–chalcogen batteries: advances and perspectives. Energy Storage Mater 42:723–752 5. Zhou X, Gao P, Sun S, Bao D, Wang Y, Li X, Wu T, Chen Y, Yang P (2015) Amorphous, crystalline and crystalline/amorphous selenium nanowires and their different (De)lithiation mechanisms. Chem Mater 27(19):6730–6736 6. She ZW, Sun Y, Zhang Q, Cui Y (2016) Designing high-energy lithium–sulfur batteries. Chem Soc Rev 45(20) 7. Wu J, Liu J, Lu Z, Lin K, Lyu YQ, Li B, Ciucci F, Kim JK (2019) Non-flammable electrolyte for dendrite–free sodium-sulfur battery. Energy Storage Mater 23:8–16 8. Liu Y, Si L, Zhou X, Liu X, Xu Y, Bao J, Dai Z (2014) A Selenium -confined microporous carbon cathode for ultrastable lithium-selenium batteries. J Mater Chem A 2(42):17735–17739 9. Zhang J, Xu Y, Fan L, Zhu Y, Liang J, Qian Y (2015) Graphene-encapsulated selenium/polyaniline core-shell nanowires with enhanced electrochemical performance for Li-Se batteries. Nano Energy 13:592–600 10. Luo C, Xu Y, Zhu Y, Liu Y, Zheng S, Liu Y, Langrock A, Wang C (2013) Selenium@ mesporous carbon composite with superior lithium and sodium storage capacity. ACS Nano 7(9):8003– 8010 11. Zhang J, Yin YX, You Y, Yan Y, Guo YG (2014) A high-capacity tellurium @ carbon anode material for lithium–ion batteries. Energ Technol 2(9–10):757–762 12. Yeon JS, Park SH, Suk J, Lee H, Park HS (2020) Confinement of sulfur in the micropores of honeycomb-like carbon derived from lignin for lithium-sulfur battery cathode. Chem Eng J 382:122946 13. Liu J, Xiao SH, Zhang Z, Chen Y, Xiang Y, Liu X, Chen JS, Chen P (2020) Naturally derived honeycomb- like N, S-codoped hierarchical porous carbon with MS2 ( M=Co, Ni) decoration for high performance Li-S battery. Nanoscale 12(8):51144–55124 14. You X, Liu L, Zhang M, Walle MD, Li Y, Liu YN (2018) Novel biomass derived hierarchical porous carbon for lithium sulfur batteries. Mater Lett 217:167–170 15. Xiong P, Han X, Zhao X, Bai P, Liu Y, Sun J, Xu Y (2019) Room-temperature potassium–sulfur batteries enabled by microporous carbon stabilized small-molecule sulfur cathodes. ACS Nano 13(2):2536–2543 16. Yuan H, Huang JQ, Peng HJ, Titirici MM, Xiang R, Chen R, Liu Q, Zhang Q (2018) A review of functional binders in lithium–sulfur batteries. Adv Energy Mater 2018 Nov 8(31):1802107 17. Lee SH, Lee JH, Nam DH, Cho M, Kim J, Chanthad C, Lee Y (2018) Epoxidized natural rubber/ chitosan network binder for silicon anode in lithium-ion battery. ACS Appl Mater Interfaces 10(19):16449–16457 18. Yi H, Lan T, Yang Y, Zeng H, Zhang T, Tang T, Wang C, Deng Y (2019) A robust aqueousprocessable polymer binder for long-life, high-performance lithium sulfur battery. Energy Storage Mater 1(21):61–68 19. Kim S, Cho M, Lee Y (2010) Saponin-containing multifunctional binder toward superior long-term cycling stability in Li–S batteries. J Mater Chem A 8(20):10419–10425 20. Long L, Wang S, Xiao M, Meng Y (2016) Polymer electrolytes for lithium polymer batteries. J Mater Chem A 4(26):10038–10069 21. Lee JH, Kim S, Cho M, Chanthad C, Lee Y, Crosslinked gel polymer electrolytes for Si anodes in Li-ion batteries. J Electrochem Soc 166(13):A2755

328

S. Gautam et al.

22. Sun YY, Wang YY, Li GR, Liu S, Gao XP (2019) Metalophilic gel polymer electrolyte for in situ tailoring cathode/electrolyte interface of high-nickel oxide cathodes in quasi-solid-state Li-ion batteries. ACS Appl Mater Interfaces 11(16):14830–14839 23. Wu K, Hu Y, Cheng Z, Pan P, Jiang L, Mao J, Ni C, Gu X, Wang Z (2019) Carbonized regenerated silk nanofiber as multifunctional interlayer for high-performance lithium-sulfur batteries. J Membr Sci 15:592:117349. 24. Zheng B, Li N, Yang J, Xi J (2019) Waste cotton cloth derived carbon microtube textile: a robust and scalable interlayer for lithium–sulfur batteries. Chem Commun 55(16): 2289–2292 25. Peng HJ, Huang JQ, Zhang Q (2017) A review of flexible lithium–sulfur and analogous alkali metal–chalcogen rechargeable batteries. Chem Soc Rev 46(17):5237–5288 26. Su YS, Manthiram A (2012) Lithium–sulphur batteries with a microporous carbon paper as a bifunctional interlayer. Nat Commun 3(1):1–6 27. Shao H, Ai F, Wang W, Zhang H, Wang A, Feng W, Huang Y (2017) Crab shell-derived nitrogen-doped micro-/mesoporous carbon as an effective separator coating for high energy lithium–sulfur batteries. J Mater Chem A 5(37):19892–19900 28. Feng G, Liu X, Wu Z, Chen Y, Yang Z, Wu C, Guo X, Zhong B, Xiang W, Li J (2020) Enhancing performance of Li–S batteries by coating separator with MnO@ yeast-derived carbon spheres. J Alloys Compounds, pp 817:152723 29. Lai YH, Kuo YT, Lai BY, Lee YC, Chen HY (2019) Improving lithium-sulfur battery performance with lignin reinforced MWCNT protection layer. Int J Energy Res 43(11):5803–5811 30. Fu X, Scudiero L, Zhong WH (2019) A robust and ion-conductive protein-based binder enabling strong polysulfide anchoring for high-energy lithium–sulfur batteries. J Mater Chem A 7(4):1835–1848 31. Han J, Chen X, Xi B, Mao H, Feng J, Xiong S (2018) High –surface –area nitrogen/phosphorous dual-doped hierarchical porous carbon derived from biochar for sulfur holder. Chem Sel 3(36):10175–10181 32. Wang T, Zhu J, Wei Z, Yang H, Ma Z, Ma R, Zhou J, Yang Y, Peng L, Fei H, Lu B (2019) Bacteria-derived biological carbon building robust Li–S batteries. Nanoletters 19(7):4384– 4390 33. Fan L, Li Z, Kang W, Cheng B (2020) Biomass-derived tube-like nitrogen and oxygen dualdoped porous carbon in the sulfur cathode for lithium sulfur battery. Renew Energy 155:309– 316, 2020 Aug 1 34. Wang X, Hao X, Xia Y, Liang Y, Xia X, Tu J (2019) A polyacrylonitrile (PAN)-based doublelayer multifunctional gel polymer electrolyte for lithium-sulfur batteries. J Membr Sci 582:37– 47 35. Babu DB, Ramesha K (2019) Melamine assisted liquid exfoliation approach for the synthesis of nitrogen doped graphene-like carbon nano sheets from bio-waste bagasse material and its application towards high areal density Li-S batteries. Carbon 144:582–590

Polymeric Materials for Metal-Sulfur Batteries Jiadeng Zhu, Yucheng Zhou, Qiang Gao, and Mengjin Jiang

Abstract Polymeric materials have attracted tremendous attention for their applications in metal-sulfur batteries due to their unique properties, which have been widely used for each component of a cell based on the corresponding requirements. Thus, this chapter aims to deliver an overview of the research by utilizing polymeric materials in metal-sulfur batteries, mainly focusing on lithium-sulfur (Li–S) batteries. A brief introduction to Li–S batteries is first given, followed by the advantages of polymers performed in Li–S batteries. Applications of polymeric materials in Li– S batteries associated with the integrated designs have been further discussed. A perspective regarding the broad applications of polymers has also been presented at the end to provide insightful comments in this area. Keywords Polymeric materials · Metal-sulfur batteries · Polysulfides · Dendrites · Shuttle effect

J. Zhu (B) Smart Devices, Brewer Science Inc., 524 N Boonville Ave, Springfield, MO 65806, USA e-mail: [email protected] Y. Zhou Department of Mechanical and Aerospace Engineering, University of Virginia, 122 Engineer’s Way, Charlottesville, VA 22904, USA Q. Gao School of Chemistry and Chemical Engineering, Yangzhou University, No. 180 Siwangting Road, Yangzhou 225002, China M. Jiang College of Polymer Science and Engineering, Sichuan University, No. 24 South Section 1, Yiyuan Road, Chengdu 610065, China © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_19

329

330

J. Zhu et al.

1 Introduction Polymeric materials have received significant attention during the past few decades because of their unique features, including high flexibility, easy processing, multifunctional groups, exceptional binding and adhesion ability, good mechanical performance, etc. [1–4]. Therefore, polymeric materials have been extensively explored in wearable electronics, resistant materials, energy storage, filtration, etc. [5–8]. As an appealing electrochemical energy storage system, lithium-ion batteries (LIBs) have been widely utilized in electronics, mobile devices, grid energy, etc., during the last 40 years [9]. With the high demand for energy storage capability to boost their working time for smartphones, laptops, electric vehicles, etc., batteries with high energy densities are extremely desired [10, 11]. There are two main approaches to enhancing the energy density of the batteries: (i) improving the working voltage of the cell, and (ii) increasing its capacity. While for a conventional Li-ion cell, an oxide or a phosphate cathode and a graphite anode are commonly used, which have limited capacities with a fixed working voltage. Therefore, other alternative high-capacity electrodes should be investigated to meet the requirements [12–15]. In this regard, lithium-sulfur (Li–S) battery, as a representative of metal-sulfur batteries, has received remarkable interest because both lithium and sulfur can deliver high theoretical capacities of 1675 and 3800 mAh/g, respectively, which have one order of magnitude higher compared to the current lithium iron phosphate and graphite [16, 17]. In addition, sulfur is environmentally friendly and abundant. Moreover, lithium owns a low negative potential, enabling a significant enhancement of the cell’s energy density [18]. Nevertheless, the commercialization of Li–S batteries have not been realized yet mainly due to the following four issues: (i) poor conductivity of sulfur and its intermediates, (ii) volume change of sulfur electrodes, (iii) polysulfides shuttle effects, and (iv) safety concerns of the lithium dendrite growth and flammable organic electrolytes [19, 20]. Up to date, many studies regarding the utilization of polymeric materials have been done to address these issues by creating and developing novel sulfur hosts, solid-state polymer electrolytes (SPEs), gel polymer electrolytes (GPEs), multifunctional separators, and interlayers, which are mainly attributed to their outstanding flexibility, multifunctionality, robust mechanical properties, and excellent processability [21, 22]. The advantages and progress of polymeric materials for achieving highperformance Li–S batteries will be reviewed and discussed to provide audiences with a better understanding of utilizing polymers in this field. It begins with an introduction of Li–S batteries followed by their electrochemical working mechanism and challenges. Then, the advantages of polymers have been claimed along with their applications in Li–S batteries from four aspects: (a) rotational cathode design; (b) functional separators and interlayers; (c) novel electrolytes; and (d) the Li anode protection. Some perspectives related to the existing challenges, opportunities, and directions are proposed to show the importance of advanced Li–S cells via polymeric materials, accelerating their development for practical Li–S cells.

Polymeric Materials for Metal-Sulfur Batteries

331

2 Overview of Metal-Sulfur Batteries Metal-sulfur batteries are recognized as promising candidates to substitute current Li-ion batteries due to the high capacity and energy density nature of sulfur, as well as its low cost [23–28]. Among different types of metal-sulfur batteries, Li– S batteries are identified as the representative. Nevertheless, multiple challenges have been hindering the development and commercialization of these energy storage systems. The following chapter will introduce the working mechanism of metalsulfur batteries and the major challenges they are facing by using Li–S batteries as an example.

2.1 Working Mechanism of Li–S Batteries The high capacity and energy density of Li–S batteries benefit from the multistep working mechanism that has been primarily discussed and acknowledged [28]. During the whole process, a large number of electrons are exchanged between the lithium metal and sulfur, which can be illustrated by S8 + 16Li+ + 16e– ↔ 8Li2 S [29]. The stepwise discharge process can be described as the conversion from crystalline S8 to S8 2− and S6 2− (solid to liquid), S8 2− and S6 2− to S4 2− (liquid to liquid), S4 2− to Li2 S2 (liquid to solid), and Li2 S2 to Li2 S (solid to solid) (Fig. 1a). This can also be represented by a double-staged discharge curve where phase-changed processes are shown as flat stages, whereas same-phase processes are illustrated as steep curves. The opposite stepwise process occurs when a battery is charging, where all Li2 S change back to crystalline S8 and are stored to be discharged again.

Fig. 1 a Schematic for working mechanism of a Li–S battery and polysulfide shuttle effect. Adapted with permission [37], Copyright (2016). b Schematic illustration of the dendritic Li growth. Adapted with permission [39], Copyright (2020), Elsevier

332

J. Zhu et al.

2.2 Challenges Despite its high capacity and energy density, the commercialization of the Li–S battery is highly hindered by many challenges. Among them, four major challenges are discussed in detail below.

2.2.1

Insulating Nature of Sulfur and Its Intermediates

Electrodes with high conductivities in batteries are crucial since they ensure an unobstructed pathway for electrons to travel. However, sulfur and its intermediates are considered insulators since sulfur only exhibits a conductivity of 5 × 10−30 S cm−1 at room temperature [30]. This leads to the fact that sulfur cannot be used by itself in a battery, and a highly conductive framework is needed to hold sulfur and provide a conductive network for electrons. One of the most commonly seen conductive materials to support sulfur is carbon-based materials, including graphite, carbon black, and carbon nanotubes/nanowires [31]. Recent research has opened other potential conductive materials with proper structures, such as various types of conductive polymers [32].

2.2.2

Volume Expansion

Due to the phase change of crystalline S8 and Li2 S during the battery operation, sulfur suffers from a huge volume expansion of 78%, which usually collapses its combining framework [33]. The fracture of cathodes causes a random redistribution of active materials, leading to undesired polarization and fast capacity decay. This also potentially brings the detachment of sulfur from its framework, resulting in a relapse of non-conductive sulfur and, thus, a loss of active materials [34]. A viable way of addressing this issue is to design a porous or hollow structure that can provide a large surface area for sulfur volume change. In addition, the choice of materials that possess excellent mechanical properties can also help soothe the volume expansion of sulfur. Besides carbon-based materials with hollow structures, the conductive polymer is also a promising candidate as it usually exhibits significant mechanical properties along with excellent processability [32].

2.2.3

Shuttle Effect

Polysulfides are a series of sulfur-based long-chain molecules (Li2 SX (4 ≤ x ≤ 8)), which are soluble in common electrolytes. These molecules can be generated even a battery is at rest due to the Li-ion-containing electrolytes. They show the sizes of 0.5–5 nm depending on the number of chained sulfurs, which is much smaller than the pore sizes of common separators (several tens’ nanometers at least) [35–37]. The

Polymeric Materials for Metal-Sulfur Batteries

333

small sizes of polysulfides allow them to diffuse through the common separators, reach the Li metal, and further react with it automatically, resulting in a waste of active materials and, eventually, poor longevity (Fig. 1a). Many efforts have been devoted to overcoming this challenge, such as material and structure design toward cathodes, pore size adjustment and functional group embedment toward separators, and component optimization toward electrolytes [38].

2.2.4

Lithium Dendrite Growth

Apart from issues with sulfur, attributed to the active nature of lithium, the safety issue is always one of the major challenges within not only Li–S batteries but also many other Li-based batteries. As the operation of the battery, Li ions travel back and forth, and the randomly distributed Li ions prefer to accumulate at the uneven surface to form dendrites to lower surface energy [39, 40]. When these dendrites grow long enough, they possibly pierce the separator and contact the cathode, leading to localized short circuits, which results in a low lifespan of the battery and even fire hazards (Fig. 1b) [39]. Many scientists have found that the recipe of electrolytes plays a critical role in the form of dendritic Li, therefore, a promising route to suppress it is to optimize the electrolytes or even consider solid-state/gel electrolytes [40]. Other methods include a better design of cathode structure to enable an even contact between Li-ions and sulfur, an improvement of separators within Li–S batteries, and even inserting interlayers.

3 Advantages of Polymeric Materials in Metal-Sulfur Batteries To date, polymers have been considered one of the most promising materials for obtaining high-performance Li–S batteries due to their abovementioned features, which are favorable for being used as cathode hosts, outstanding absorbents/adsorbents for polysulfides, multifunctional interlayers, and solidstate/gel electrolytes [34]. For example, conductive polymers such as polyaniline (PANI), polypyrrole (PPy), poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) have been performed as the sulfur host, which could not only improve the electrical conductivity of the electrode but also suppress the shuttle effect. Besides conventional porous polyolefin (i.e., polyethylene (PE), polypropylene (PP)) based separators, other polymers including but not limited to polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyimide, etc. and their composites have been prepared and utilized as the separator for Li–S batteries, which are targeting on addressing the shuttle effect of polysulfides and the Li dendrite growth because of their outstanding barrier effect on polysulfide migration and good mechanical properties [12, 19]. Moreover, polymer-based electrolytes are another research hotspot

334

J. Zhu et al.

to replace liquid organic electrolytes, which can both restrain the polysulfide shuttle effect and solve safety concerns [41, 42]. It’s worth mentioning that polymers with such unique properties have been thoroughly investigated by acting as sulfur electrodes host, fine-tuning the separators, working as interlayers and electrolytes, etc., to boost the performance of Li–S cells, improving their commercialization capability.

4 Applications of Polymeric Materials in Metal-Sulfur Batteries 4.1 Cathodes Cathodes as the main component in metal-sulfur batteries have been widely studied using polymers. As a provider of active sulfur, the stability and integrality of cathodes are the base of the battery performance, however, challenges including sulfur’s low conductivity, volume expansion, and shuttle effects are hindering the practical applications. Polymers, especially highly conductive polymers, can effectively help optimize the cathodes due to polymers’ versatility [43]. Different ways of using polymers to improve cathodes have been attempted. Among all, three major routes emerge and show promising results regarding metal-sulfur cathode improvement. Polymers possess active sites that can connect with sulfur to form binary or even ternary composites and be used as cathodes. Several methods can achieve such bonding. Inverse vulcanization is one of the most commonly seen approaches to produce sulfur-based polymer cathodes at a relatively low cost, which usually requires a continuous stirring process for a couple of hours in an oil bath at a temperature above 100 °C [44]. For example, Gracia et al. synthesized a copolymer from the radical polymerization of sulfur and divinyl benzene (DVB)) in all-solid-state Li–S cells via inverse vulcanization [45]. Thanks to DVB, polysulfides tend to form ≡C-(S)n –C≡ structure and be diminished, leading to a weaker shuttle effect. As a result, the cell with such a copolymer exhibited decent sulfur utilization with an initial capacity of 1100 mAh g−1 . Simmonds et al. [46] and Zhang et al. [47] also applied this method and obtained poly(sulfur-random-1,3-diisopropenylbenzene) (poly(S-rDIB)) and poly(sulfur-random-styrene) (poly(S-r-Sty)), respectively, from elemental sulfur and polymers. They extended the lifespan of Li–S batteries to 500 cycles and 1000 cycles, respectively. Besides, other methods have also been studied to construct sulfur-polymer composites that performed as cathodes for Li–S batteries. Sang et al. used condensation reactions to obtain a series of organosulfur polymers (BTTP) from 1,3,5-benzenetrithiol (BTT) and elemental sulfur, which could load a high sulfur content of 72 wt% (Fig. 2a) [48]. Another intriguing sulfur-polymer product was produced by vigorous stirring using commercial vegetable oil and sulfur, which could achieve an even higher sulfur content (80 wt%) [49].

Polymeric Materials for Metal-Sulfur Batteries

335

Fig. 2 a Schematic of the BTTP/S binary cathode obtained by condensation reactions. Adapted with permission [48], Copyright (2021), Elsevier. b Schematic of the PANI layer-coated sulfur cathode. Adapted with permission [51], Copyright (2017), IOP Publishing. c Schematic and SEM images of the SPEEK composite coated separator produced from vacuum filtration with a thickness of 0.7 µm. Adapted with permission [54], Copyright (2018), American Chemical Society. d Schematic of the pVIDZ coated separator prepared by iCVD technique with an ultrathin thickness. Adapted with permission [57], Copyright (2021), American Chemical Society. e Schematic of the PVA/CMC composite separator suppressing shuttle effect and Li dendrites. Adapted with permission [60], Copyright (2020), Elsevier

In addition to being directly utilized as cathodes, polymers can also serve other functions regarding cathode improvement. For example, polymers can be coated on the surface of sulfur and its substrates to deal with sulfur volume expansion and the shuttle effect. Li et al. coated PPy onto the acetylene black/sulfur (AB/S) binary composite to achieve the AB/S/PPy ternary composite by chemical oxidation polymerization [50]. The PPy layer effectively protected the cathode from volume expansion and sulfur shuttling, leading to better capacity and stability compared to AB/ S-only and sulfur-only batteries. Moon et al. transfer-printed a conducting polymer, PANI, on a sulfur cathode to suppress polysulfide dissolution, which achieved an extremely high capacity-retention rate of 96.4% even after 200 cycles (Fig. 2b) [51]. Moreover, Cheng et al. explored a new type of polymer synthesized by homogeneous reactions to substitute the conventional binder, PVDF [52]. They applied sulfonated

336

J. Zhu et al.

poly(ether ether ketone) (SPEEK) as a binder to assemble cathodes for Li–S batteries and showed a better performance compared with PVDF-based batteries.

4.2 Separators and Interlayers Besides cathodes, another promising component to be modified that can help suppress the polysulfide shuttle effect and even improve Li-ion traveling is the separator. Separators are originally designed to separate the cathode and anode from touching and causing short circuits [53]. They have always been the safety insurance to stabilize batteries, therefore, in metal-sulfur batteries, especially Li–S batteries, scientists have also been using them for inhibiting the shuttle effect and dendritic Li growth. Separators in Li–S batteries are usually porous PP membranes, and two pathways have been studied to endow more functions: (i) design a new polymer separator to substitute PP, and (ii) coat PP or other commercial separators with functional polymers. Commercial separators with proper porous sizes can physically prevent the cathode and anode from touching, thus, coating other functional polymers onto the separators can easily add extra functions to the separators. This is also the majority approach, as of now, to modify separators. Those resultant coating layers are generally named interlayers. Depending on the thickness of the coating, various methods have been explored, including vacuum filtration, blade coating, electrostatic layerby-layer (LBL) self-assembly, chemical vapor deposition (CVD), and vapor-phase polymerization. The first two methods can usually coat the layer with a thickness of micron level, which are the most commonly seen methods along with a low cost. For example, Babu et al. reported a permselective SPEEK composite-coated separator with a thickness of 0.7–0.9 µm using vacuum filtration (Fig. 2c) [54]. Li et al. constructed a cationic polymer-based coating prepared through a reaction between tri(4-imidazolylphenyl)amine (TIPA) and cyanuric chloride by a facile blade-coating method, and the thickness was measured to be around 5.3 µm [55]. The LBL selfassembly also introduces the coating layer with a thickness of micron level. Shi et al. applied this approach to deposit positively charged poly(diallyl dimethyl ammonium chloride) (PDDA) wrapped covalent triazine framework (CTF) (CTF@PDDA) and negatively charged PEDOT: PSS with a thickness of 1.5–4.5 µm [56]. The latter two methods can form a nano-sized layer, which is relatively more costly yet introduced less weight and volume, leading to better energy density. For instance, Lim et al. coated a polyvinylimidazole (pVIDZ) nanolayer onto the commercial separator through an initiated CVD technique with a thickness of only 70–100 nm (Fig. 2d) [57]. Li et al. used in-situ vapor-phase polymerization to coat PPy onto a commercial separator with a thickness of only 15–25 nm [58]. PPy has often been selected as the coating polymer for separators. It can address both polysulfide and Li challenges, as well as improve the electrochemical performance of batteries due to several advanced features, such as its hydrophilic surface, functional groups, good conductivity, and low-cost synthesis.

Polymeric Materials for Metal-Sulfur Batteries

337

Compared to coating a mature commercial separator, designing a novel separator to solve challenges is more complex and thus, there are much fewer reports on that yet the basic aims are the same. For example, Sun et al. integrated the concepts of electrode and separator by coating a layer of poly(m-phenylene isophthalamide) (PMIA) onto the electrode via a non-solvent induced phase separation (NINP) process and using the integrated electrode as both the cathode and separator [59]. The flexible PMIA provided a volume expansion buffer and the amide and pore structure of PMIA endowed assistance to prevent the shuttle effect and dendritic Li growth. The same strategy can be used to produce a polyvinyl alcohol (PVA)/sodium carboxylmethyl cellulose (CMC) composite separator with threedimensional ion-selective nanochannels, where the carboxylate groups of –COO– and oxygen-containing –OH groups on it could help minimize both polysulfide shuttling and Li dendrite growth (Fig. 2e) [60]. Apart from that, designing new structures for separators is also a potential path to overcome the challenges. Lee et al. designed a spiderweb-like sandwich-type functional nanomats with top and bottom layers of carbon nanotube-wrapped polyetherimide (PEI) and a middle layer of poly(1-ethyl3-methylimidazolium) bis(trifluoromethane sulfonyl)imide (PVIm[TFSI], polyionic liquid)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) nanomat on the PE separator, which could significantly suppress the shuttle effect while ensuring facile Li-ion transport [61].

4.3 Electrolytes As discussed earlier, polymers, especially conductive polymers, have been widely investigated to design novel cathodes and modify the separator to improve the electrode conductivity, minimize their volume expansion, and address the polysulfide shuttle effect [42, 62]. Nevertheless, the current flammable liquid organic electrolyte is still a concern, which may generate other problems including potential leakage, explosion, and fire. In addition, the Li dendrite growth caused by the uneven nucleation and inferior reversibility during the Li plating/stripping process has not been solved. Thus, due to their good thermal and mechanical properties along with excellent processability, polymer electrolytes have been further explored for Li–S cells, which have been considered as promising methods to get rid of the traditional organic electrolyte, suppress the shuttle effect, and inhibit the growth of Li dendrite. Depending on their compositions, polymer electrolytes can be mainly divided into two categories, which are solid-state polymer electrolytes (SPEs) and gel polymer electrolytes (GPEs), respectively. Among the polymer matrix candidates, polyethylene oxide (PEO) has been extensively investigated mainly ascribed to its good mechanical properties and outstanding processability. However, the relatively low room-temperature ionic conductivity attributed to the formation of crystallites in PEO systems has significantly impeded their practical applications. Therefore, other polymers, including but not limited to PVDF, PVDF-HFP, PAN, etc., have also been explored [34]. Theoretically, SPEs are

338

J. Zhu et al.

the ideal solution for Li–S batteries since they can not only fully suppress the shuttle effect but also minimize Li dendrite growth. For example, Lin et al. introduced corn starch, which performed as a solid electrolyte host, providing remarkable lithium-ion transportability even at room temperature [63]. Briefly, lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) with different concentrations (from 20 to 60 wt%) was mixed with the reacted corn starch/dimethyl sulfoxide (DMSO) solution. The resultant mixtures were further dried to obtain the electrolyte films, whose ionic conductivities were then evaluated. The result indicated an optimal ionic conductivity of 3.39 × 10–4 S cm−1 at 25 °C, which was way better than that of PEO composites prepared in this work. The cell with such SPE could deliver an initial capacity of 1442 mAh g−1 and a capacity retention of 93% compared to the second discharge capacity at 0.1 C and 25 °C. However, a severe capacity decay could be found for the cell tested at 2 C and 45 °C, which might be attributed to the relatively low ionic conductivity and poor interfacial contact. In addition, the weight content of sulfur in the cathode was only 30.1%, which could not meet the practical requirement. In contrast, GPEs, which are intermediates between liquid and solid electrolytes, not only improve the overall ionic conductivity but also reduce the resistance. Therefore, they have received tremendous attention recently [42]. In-situ gelation of a pentaerythritol tetraacrylate (PETEA)/azobisisobutyronitrile (AIBN) solution was performed to obtain the PETEA-based GPE with an extremely high ionic conductivity of 1.13 × 10–2 S cm−1 at 25 °C, which was comparable with that of liquid electrolyte (1.19 × 10–2 S cm−1 ) (Fig. 3a, b) [64]. It was probably attributed to the good compatibility between the polymer matrix and the liquid electrolyte along with the unique symmetrical star structure with four C=C bonds of each PETEA molecule, which could significantly increase the crosslink density and enhance its ion mobility. Figure 3c shows that the cell with this PETEA-derived electrolyte could achieve a capacity of 744.1 mAh g−1 after 100 cycles at 0.1 C, and a capacity retention of 63.4% could be obtained, which was much better compared to that of the cell using the liquid electrolyte (31.2%). The improved electrochemical performance was ascribed to the PETEA-based GPE, which could strongly enhance the flexibility of passivating layer against the sulfur volume expansion and effectively minimize the polysulfide dissolution and the interfacial reaction between the electrolyte and electrodes. The corresponding working principle is illustrated in Fig. 3d. Although GPEs could provide decent ionic conductivity and low interfacial resistance, there are still two main challenges regarding the practical applications, which are interfacial instability and poor cycling life. In summary, both SSEs and GPEs have been extensively explored, while their practical applications in Li–S batteries should be comprehensively evaluated regarding their robustness and stability to demonstrate their application capability.

Polymeric Materials for Metal-Sulfur Batteries

339

Fig. 3 a A representative structure of the prepared PETEA electrolyte, b conductivity comparison of the PETEA-derived GPE and the traditional liquid electrolyte and c the related cells’ performance, d schematic illustration of the polysulfide immobilization mechanism using the PETEA-based GPE. Adapted with permission [64], Copyright (2016), Elsevier

4.4 Anode Protection Due to its high theoretical capacity (3860 mAh g−1 ) and low redox potential (− 3.04 V vs. standard hydrogen electrode), Li has been recognized as a promising anode candidate for high-energy–density rechargeable batteries. Despite such unique properties, the use of Li has been greatly hindered by the uncontrollable Li dendrite growth. In addition, the resultant polysulfides can react with Li and form inactive layers, resulting in poor cycling stability of the cells [65]. In this regard, polymeric materials have been widely studied to protect the Li anode by blocking the diffusion of polysulfides and impeding the Li dendrite growth because of their good elasticity and mechanical properties. Liu et al. developed a protective layer by crosslinking polydimethylsiloxane (PDMS), named Silly Putty (SP) [66], which could be served as a stable interface between the Li anode and the electrolyte. The corresponding chemical structure of the polymer is shown in Fig. 4a. According to the rate of the Li growth, the flowability and stiffness of the resultant polymer could reversibly switch, helping resolve the issues of dendrites (Fig. 4b, c). Compared with the other two coatings (siloxane crosslinked PDMS and uncross-linked PDMS-free polymer chains), a high Coulombic efficiency along with low hysteresis of Li plating/stripping overpotential could be achieved even at a high current density of 1 mAh cm−2 by using this protective SP

340

J. Zhu et al.

layer, which could be ascribed to its “solid–liquid” characteristic arising from the internal dynamic cross-linking. Besides PDMS, other polymers like polystyrene (PS) have also been researched for obtaining better-performance Li metal cells. For instance, interconnected poly(styrene-co-divinyl-benzene) (P(S-DVB)) microspheres obtained by Lee et al. were performed to protect the Li anode, suppressing the Li dendrites growth [67]. Briefly, P(S-DVB) microspheres were first dispersed in tetrahydrofuran (THF), and a doctor blade was used to cast the resultant solution on a Li metal foil. THF could be evaporated at room temperature after that. Then, another UV cross-linkable oligomer diethylene glycol diacrylate (DEGDA)/photo-initiator 2-hydroxy-2-methyl propiophenone (HMPP)/THF solution was coated on the top of the microsphere arrays,

Fig. 4 a The chemical structure of SP. The growth of Li dendrites with the unprotected b and protected c Li anodes. Adapted with permission [66], Copyright (2017), American Chemical Society. d Schematic diagram indicating the procedure of these protective P(S-DVB) microspheres crosslinked with DEGDA. e–h Schematic images showing the mechanism of microsphere protection. Adapted with permission [67], Copyright (2017), American Chemical Society

Polymeric Materials for Metal-Sulfur Batteries

341

followed by evaporation of THF, which was later cured by UV with a power of 40 W and wavelength of 365 nm for 1 h (Fig. 4d). The corresponding working mechanism is shown in Fig. 4e–h, in which the external pressure caused by the high-modulus microspheres could minimize the Li dendrite growth. Meanwhile, the Li ions might be uniformly deposited due to the evenly distributed micropores. Overall, how to utilize polymeric materials to achieve high-performance Li–S batteries has been discussed. Nevertheless, more robust approaches should be further explored to enhance the energy density and cycling performance of Li–S cells along with suppressing the Li dendrite growth and the polysulfide dissolution.

5 Conclusions and Perspectives Attributed to the high theoretical capacity and energy density, metal-sulfur batteries, especially Li–S batteries, have been considered the next-generation energy storage devices. Besides, sulfur is environmentally friendly at a low cost. Nevertheless, there are still several challenges that block their commercialization such as the insulation nature and big volume change of sulfur, the shuttle effect of polysulfides, the Li dendrite growth, etc. Polymeric materials are one of the promising candidates used in metal-sulfur batteries to address the abovementioned issues because of their unique properties, and the corresponding applications have been discussed in detail, including but not limited to being performed as the cathodes host, adsorbents/absorbents towards polysulfides, multi-functional interlayers/separators, solidstate/gel electrolytes, etc. Even though tremendous studies have been done so far, more fundamental research and testing conditions (i.e., high materials loading, fast charging/discharging, etc.) are demanded in this field to further expand possibilities. At the same time, cost-effective synthesis approaches are highly desired as well to further enhance their overall practical applications. What’s more, polymer composites should also be explored to have synergistic effects of polymers and the couple components, providing multifunctionality for achieving better metal-sulfur batteries. We hope that polymeric materials can be further utilized to solve the main challenges and help realize the practical applications of metal-sulfur batteries with such expanding research.

References 1. Upton BM, Kasko AM (2016) Strategies for the conversion of lignin to high-value polymeric materials: review and perspective. Chem Rev 116:2275–2306 2. Chen Z, Wang M, Mo Y, Zhang C, Wang Y, Gao C, Zhu J, Gao J, Shen M, Gao Q (2022) A breathable and reliable thermoplastic polyurethane/Ag@K2 Ti4 O9 composite film with asymmetrical porous structure for wearable piezoresistive sensors. J Mater Chem C 10:12986–12997 3. Zhu J, Lim J, Lee C-H, Joh H-I, Kim HC, Park B, You N-H, Lee S (2014) Multifunctional polyimide graphene oxide composites via in-situ polymerization. J Appl Polym Sci 131:40177

342

J. Zhu et al.

4. Li Y, Shen Q, Shen J, Ding X, Liu T, He J, Zhu C, Zhao D, Zhu J (2021) Multifunctional fibroblasts enhanced via thermal and freeze-drying treatments of aligned electrospun nanofiber membranes. Adv Fiber Mater 3:26–37 5. Wang Y, Zhu J, Shen M, Gao C, Wang M, Zhao C, Gao J, Gao Q (2022) Three-layer coreshell Ag/AgCl/PEDPT:PSS composite fibers via a one-step single-nozzle technique enabled skin-inspired tactile sensors. Chem Eng J 442:136270 6. Gao Q, Li C, Wang M, Zhu J, Wang P, Zhu C, Zhu P, Gao C (2022) A highly adhesive, self-healing and perdurable PEDOT:PSS/PAA-Fe3+ gel enabled by multiple non-covalent interactions for multi-functional wearable electronics. J Mater Chem C 10:6271–6280 7. Wang P, Wang M, Zhu J, Wang Y, Gao J, Gao C, Gao Q (2021) Surface engineering via selfassembly on PEDOT:PSS fibers: biomimetic fluff-like morphology and sensing application. Chem Eng J 425:131551 8. Wang Y, Wang M, Wang P, Zhou W, Chen Z, Gao Q, Shen M, Zhu J (2021) Urea-treated wetspun PEDOT:PSS fibers for achieving high-performance wearable supercapacitors. Compos Commun 27:100885 9. Zhu J, Lu Y, Chen C, Ge Y, Jasper S, Leary JD, Li D, Jiang M, Zhang X (2016) Porous onedimensional carbon/iron oxide composite for rechargeable lithium-ion batteries with high and stable capacity. J Alloys Compd 672:79–85 10. Li D, Wang H, Luo L, Zhu J, Li J, Liu P, Yu Y, Jiang M (2021) An electrospun separator based on sulfonated polyoxadiazole with outstanding thermal stability and electrochemical properties for lithium-ion batteries. ACS Appl Energy Mater 4:879–887 11. Chung SH, Manthiram A (2019) Current status and future prospects of metal-sulfur batteries. Adv Mater 31:1901125 12. Zhu J, Cheng H, Zhu P, Li Y, Gao Q, Zhang X (2022) Electrospun nanofibers enabled advanced lithium-sulfur batteries. Acc Mater Res 3:149–160 13. Yu Y, Zhu J, Zeng K, Jiang M (2021) Mechanically robust and superior conductive n-type polymer binders for high-performance silicon anodes in lithium-ion batteries. J Mater Chem A 9:3472–3481 14. Yu Y, Gao H, Zhu J, Li D, Wang F, Jiang C, Zhong T, Jiang M (2021) Ionic/electronic conductivity regulation of n-type polyoxadiazole lithium sulfonate conductive polymer binders for high-performance silicon microparticle anodes. Chin Chem Lett 32:203–209 15. Yu Y, Zhu J, Gao H, Yang C, Chen S, Zhang S, Jiang M (2020) Preparation and characterization of a class of self-doping aromatic polyoxadiazole electrochromic materials. J Appl Polym Sci 137:49406 16. Gao H, Mao J, Li D, Yu Y, Yang C, Qi S, Liu Q, Zhu J, Jiang M (2020) Lithium sulfonated polyoxadiazole as a novel single-ion polymer electrolyte in lithium-ion batteries. J Electrochem Soc 167:070518 17. Zhu P, Yan C, Zhu J, Zang J, Li Y, Jia H, Dong X, Du Z, Zhang C, Wu N, Dirican M, Zhang X (2019) Flexible electrolyte-cathode bilayer framework with stabilized interface for room-temperature all-solid-state lithium-sulfur batteries. Energy Storage Mater 17:220–225 18. Li Y, Zhu J, Zhu P, Yan C, Jia H, Kiyak Y, Zang J, He J, Dirican M, Zhang X (2018) ZrO2 confined in porous nitrogen-doped carbon nanofiber used as a novel separator in lithium-sulfur batteries with a long lifespan. Chem Eng J 349:376–387 19. Zhu J, Chen C, Lu Y, Zang J, Jiang M, Kim D, Zhang X (2016) Highly porous polyacrylonitrile/ graphene oxide membrane separator exhibiting excellent anti-self-discharge feature for highperformance lithium-sulfur batteries. Carbon 101:272–280 20. Zhu P, Zhu J, Yan C, Dirican M, Zang J, Jia H, Li Y, Kiyak Y, Tan H, Zhang X (2018) In-situ polymerization of nanostructured conductive polymer on 3D sulfur/carbon nanofiber composite matrix as a cathode for high-performance lithium-sulfur batteries. Adv Mater Interfaces 5:1701598 21. Selvan RK, Zhu P, Yan C, Zhu J, Dirican M, Shanmugavani A, Lee YS, Zhang X (2018) Biomass-derived porous carbon modified glass fiber separator as polysulfide reservoir for Li-S batteries. J Colloid Interface Sci 513:231–239

Polymeric Materials for Metal-Sulfur Batteries

343

22. Zhu J, Yildirim E, Aly K, Shen J, Chen C, Lu Y, Jiang M, Kim D, Tonelli AE, Pasquinelli MA, Bradford PD, Zhang X (2016) Hierarchical multi-component nanofiber separators for lithium polysulfide capture in lithium-sulfur batteries: an experimental and molecular modeling study. J Mater Chem A 4:13572–13581 23. Zhu P, Zang J, Zhu J, Lu Y, Chen C, Jiang M, Yan C, Dirican M, Selvan RK, Kim D, Zhang X (2018) Effect of rGO reduction degree on the performance of polysulfide rejection in lithiumsulfur batteries. Carbon 126:594–600 24. Yu X, Manthiram A (2020) A progress report on metal-sulfur batteries. Adv Funct Mater 30:2004084 25. Li Y, Zhu J, Zhu P, Yan C, Jia H, Kiyak Y, Zang J, He J, Dirican M, Zhang X (2018) Glass fiber separator coated by porous carbon nanofiber derived from immiscible PAN/PMMA for highperformance lithium-sulfur batteries derived from polymer blends. J Membr Sci 552:31–42 26. Zhu P, Zhu J, Zang J, Chen C, Lu Y, Jiang M, Yan C, Selvan KR, Zhang X (2017) A novel bi-functional double-layer rGO-PVDF/PVDF composite nanofiber membrane separator with enhanced thermal stability and effective polysulfide inhibition for high-performance lithiumsulfur batteries. J Mater Chem A 5:15096–15104 27. Zhu J, Ge Y, Kim D, Lu Y, Chen C, Jiang M, Zhang X (2016) A novel separator coated by carbon for achieving exceptional high-performance lithium-sulfur batteries. Nano Energy 20:176–184 28. Li T, Bai X, Gulzar U, Bai YJ, Capiglia C, Deng W, Zhou X, Liu Z, Zaccaria RP (2019) A comprehensive understanding of lithium-sulfur battery technology. Adv Funct Mater 29:1901730 29. Wild M, O’Neill L, Zhang T, Purkayastha R, Minton G, Marinescu M, Offer GJ (2015) Lithium sulfur batteries, a mechanistic review. Energy Environ Sci 8:3477–3494 30. Xu H, Jiang Q, Zhang B, Chen C, Lin Z (2020) Integrating conductivity, immobility, and catalytic ability into high-N carbon/graphene sheets as an effective sulfur host. Adv Mater 32:1906357 31. Li M, Carter R, Douglas A, Oakes L, Pint CL (2017) Sulfur vapor-infiltrated 3D carbon nanotube foam for binder-free high areal capacity lithium-sulfur battery composite cathodes. ACS Nano 11:4877–4884 32. Liu K, Zhao H, Ye D, Zhang J (2022) Recent progress in organic polymers-composited sulfur materials as cathodes for lithium-sulfur battery. Chem Eng J 417:129309 33. Shaibani M, Mirshekarloo MS, Singh R, Easton CD, Cooray MCD, Eshraghi N, Abendroth T, Dörfler S, Althues H, Kaskel S, Hollenkamp AF, Hill MR, Majumder M (2022) Expansiontolerant architectures for stable cycling of ultrahigh-loading sulfur cathodes in lithium-sulfur batteries. Sci Adv 6:eaay2757 34. Zhu J, Zhu P, Yan C, Dong X, Zhang X (2019) Recent progress in polymer materials for advanced lithium-sulfur batteries. Prog Polym Sci 90:118–163 35. Wang YX, Lai WH, Chou SL, Liu HK, Dou SX (2019) Remedies for polysulfide dissolution in room-temperature sodium-sulfur batteries. Adv Mater 32:1903952 36. Zhu J, Yanilmaz M, Fu K, Chen C, Lu Y, Ge Y, Kim D, Zhang X (2016) Understanding glass fiber membrane used as a novel separator for lithium-sulfur batteries. J Membr Sci 504:89–96 37. Duan L, Zhang F, Wang L (2016) Cathode materials for lithium sulfur batteries: design, synthesis, and electrochemical performance, in alkali-ion batteries. London, United Kingdom: IntechOpen 38. Gu S, Sun C, Xu D, Lu Y, Jin J, Wen Z (2018) Recent progress in liquid electrolyte-based Li-S batteries: shuttle problem and solutions. Electrochem Energy Rev 1:599–624 39. Gao X, Zhou YN, Han D, Zhou J, Zhou D, Tang W, Goodenough JB (2020) Thermodynamic understanding of Li-dendrite formation. Joule 4:1864–1879 40. Li D, Luo L, Zhu J, Qin H, Liu P, Sun Z, Lei Y, Jiang M (2021) A hybrid lithium sulfonated polyoxadiazole derived single-ion conducting gel polymer electrolyte enabled effective suppression of dendritic lithium growth. Chin Chem Lett 33:1025–1031 41. He Y, Ren X, Xu Y, Engelhard MH, Li X, Xiao J, Liu J, Zhang JG, Xu W, Wang C (2019) Origin of lithium whisker formation and growth under stress. Nat Nanotechnol 14:1042–1047

344

J. Zhu et al.

42. Qian J, Jin B, Li Y, Zhan X, Hou Y, Zhang Q (2021) Research progress on gel polymer electrolytes for lithium-sulfur batteries. J Energy Chem 56:420–437 43. Dirlam PT, Glass RS, Char K, Pyun J (2017) The use of polymers in Li-S batteries: a review. J Polym Sci Part A: Polym Chem 55:1635–1668 44. Gomez I, Mecerreyes D, Blazquez JA, Leonet O, Youcef HB, Li C, Gómez-Cámer JL, Bondarchuk O, Rodriguez-Martinez L (2016) J Power Sources 329:72–78 45. Gracia I, Youcef HB, Judez X, Oteo U, Zhang H, Li C, Rodriguez-Martinez LM, Armand M (2018) S-containing copolymer as cathode material in poly(ethylene oxide)-based all-solidstate Li-S batteries. J Power Sources 390:148–152 46. Simmonds AG, Griebel JJ, Park J, Kim KR, Chung WJ, Oleshko VP, Kim J, Kim ETT, Glass RS, Soles CL, Sung YE, Char K, Pyun J (2014) Inverse vulcanization of elemental sulfur to prepare polymeric electrode materials for Li-S batteries. ACS Macro Lett 3:229–232 47. Zhang Y, Griebel JJ, Dirlam PT, Nguyen NA, Glass RS, Mackay ME, Char K, Pyun J (2017) Inverse vulcanization of elemental sulfur and styrene for polymeric cathodes in Li-S batteries. J Polym Sci Part A: Polym Chem 55:107–116 48. Sang P, Song J, Guo W, Fu Y (2021) Hyperbranched organosulfur polymer cathode materials for Li-S battery. Chem Eng J 415:129043 49. Hoefling A, Lee YJ, Theato P (2017) Sulfur-based polymer composites from vegetable oils and elemental sulfur: a sustainable active material for Li-S batteries. Macromol Chem Phys 218:1600303 50. Li S, Li H, Zhu G, Jin B, Liu H, Jiang Q (2019) Improved electrochemical performance of Li-S battery with carbon and polymer-modified cathode. Appl Surf Sci 479:265–272 51. Moon S, Yoo JK, Jung YH, Kim JH, Jung YS, Kim DK (2017) Effective suppression of polysulfide dissolution by uniformly transfer-printed conducting polymer on sulfur cathode for Li-S batteries. J Electrochem Soc 164:A6417–A6421 52. Cheng M, Li L, Chen Y, Guo X, Zhong B (2016) A functional binder-sulfonated poly(ether ether ketone) for sulfur cathode of Li-S batteries. RSC Adv 6:77937–77943 53. Huang X (2011) Separator technologies for lithium-ion batteries. J Solid State Electrochem 15:649–662 54. Babu DB, Giribabu J, Ramesha K (2018) Permselective SPEEK/Nafion composite-coated separator as a potential polysulfide crossover barrier layer for Li-S batteries. ACS Appl Mater Interfaces 10:19721–19729 55. Li Z, Jiao S, Yu D, Zhang Q, Liu K, Han J, Guo Z, Liu J, Wang L (2021) Cationic-polymerfunctionalized separator as a high-efficiency polysulfide shuttle barrier for long-life Li-S battery. ACS Appl Energy Mater 4:2914–2921 56. Shi QX, Yang CY, Pei HJ, Chang C, Guan X, Chen FY, Xie XL, Ye YS (2021) Layer-by-layer self-assembled covalent triazine framework/electrical conductive polymer functional separator for Li-S battery. Chem Eng J 404:127044 57. Lim WG, Oh S, Jeong J, Jang W, Shim KI, Kim S, Han JW, Im SG, Lee J (2021) Ultrathin and bifunctional polymer-nanolayer-embedded separator to simultaneously alleviate Li dendrite growth and polysulfide crossover in Li-S batteries. ACS Appl Energy Mater 4:611–622 58. Li Y, Wang W, Liu X, Mao E, Wang M, Li G, Fu L, Li Z, Eng AYS, Seh ZW, Sun Y (2019) Engineering stable electrode-separator interfaces with ultrathin conductive polymer layer for high-energy-density Li-S batteries. Energy Storage Mater 23:261–268 59. Sun CC, Song YZ, Yan Y, Yuan JJ, Huang Z, Fang LF, Zhu BK (2020) Integrating flexible PMIA separator and electrode for dealing with multi-aspect issues in Li-S batteries. Electrochim Acta 359:136987 60. Chen Y, Zhou G, Zong W, Ouyang Y, Chen K, Lv Y, Miao YE, Liu T (2021) Porous polymer composite separators with three-dimensional ion-selective nanochannels for high-performance Li-S batteries. Compos Commun 25:100679 61. Lee YH, Kim JH, Kim JH, Yoo JT, Lee SY (2018) Spiderweb-mimicking anion-exchanging separators for Li-S batteries. Adv Funct Mater 28:1801422 62. Zhu J (2016) Advanced separator selection and design for high-performance lithium-sulfur batteries. North Carolina State University, Ph.D. dissertation

Polymeric Materials for Metal-Sulfur Batteries

345

63. Lin Y, Li J, Liu K, Liu Y, Liu J, Wang X (2016) Unique starch polymer electrolyte for high capacity all-solid-state lithium sulfur battery. Green Chem 18:3796–3803 64. Liu M, Zhou D, He YB, Fu Y, Qin X, Miao C, Du H, Li B, Yang QH, Lin Z, Zhao TS (2016) Novel gel polymer electrolyte for high-performance lithium-sulfur batteries. Nano Energy 22:278–289 65. Wang Y, Sahadeo E, Rubloff G, Lin CF, Lee SB (2019) High-capacity lithium sulfur battery and beyond: a review of metal anode protection layers and perspective of solid-state electrolytes. J Mater Sci 54:3671–3693 66. Liu K, Pei A, Lee HR, Kong B, Liu N, Lin D, Liu Y, Liu C, Hsu PC, Bao Z, Cui Y (2017) Lithium metal anodes with an adaptive “solid-liquid” interfacial protective layer. J Am Chem Soc 139:4815–4820 67. Lee YG, Ryu S, Sugimoto T, Yu T, Chang WS, Yang Y, Jung C, Woo J, Kang SG, Han HN, Doo SG (2017) Dendrite-free lithium deposition for lithium metal anodes with interconnected microsphere protection. Chem Mater 29:5906–5914

Polymer-Based, Flexible, Solid Electrolyte Membranes for All-Solid-State Metal-Ion Batteries E. M. Sreeja, Merin K. Wilson, A. Abhilash, and S. Jayalekshmi

Abstract A brief introduction to the theoretical aspects, experimental synthesis procedures and electrochemical characterization techniques of polymer-based, flexible, and solid electrolyte membranes for developing all solid-state metal ion batteries form the central theme of this chapter. Although extensive research work is being carried out globally in this direction, there are many challenges yet to be addressed effectively, for developing commercial standard all solid-state metal ion batteries for applications in the automobile industry. One of the main challenges is to reduce the electrode-solid electrolyte barrier for facilitating easy ion transport and enhance metal ion conductivity to the range exhibited by liquid electrolytes. Polymer-based solid electrolytes have many advantages of high flexibility and mechanical stability and the availability of simple and cost-effective synthesis routes. Identifying suitable plasticizers, metal salts, and nano-filler materials to enhance the amorphous nature of the polymer host material and reduce its glass transition temperature is one of the most viable means to achieve high metal ion conductivity for polymer-based solid electrolytes. Keywords Solid polymer electrolyte · Nanofiller · Hopping mechanism

1 Introduction Energy needs are always having top priority in any society around the world. Environmental pollution worries are growing as energy consumption rises. The dangers associated with the use of fossil fuel are getting worse. To mitigate these negative aspects and our dependence on fossil fuels, technologies for alternative energy based on solar power and wind that use renewable resources need to be created and implemented. However, solar and wind energies are intermittent. Hence it is mandatory E. M. Sreeja · M. K. Wilson · A. Abhilash · S. Jayalekshmi (B) Department of Physics, Cochin University of Science and Technology, Cochin, Kerala 682022, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_20

347

348

E. M. Sreeja et al.

to develop efficient and economical energy storage systems for storing the energy produced by renewable sources. One of the best options for electrical energy storage is the use of rechargeable batteries. Metal-ion batteries are electrochemical energy conversion and storage systems that use only one type of ion to shuttle between the negative and positive electrodes during charge–discharge cycles. Because of the abundance and availability of starting materials, as well as the high energy density and stable electrochemical behavior, alkali and alkaline metals such as lithium, sodium, and magnesium based rechargeable energy storage devices are currently being widely investigated. Lithium being the lightest metal, lithium-ion battery is the best-known example of this concept, also known as the rocking-chair battery [1]. Electrolyte is considered to be the primary component of the electrochemical cell, separating the cathode from the anode in any electrochemical device and acts as the charge transport medium. Commonly used electrolytes can be found in liquid, gel and solid forms. Liquid electrolytes appear to be the most conductive of the three options. However they are sometimes volatile and vulnerable to evaporation, corrosion and leakage. It can cause the formation of unstable solid electrolyte interface (SEI) on the anode surface which affects adversely the cell performance. Gel-type electrolytes can reduce the complications related to safety issues, as they acquire the characteristics of both solid and liquid electrolytes. But they have poor mechanical properties and structural instability. Solid-state electrolytes are the better and more reliable choice to resolve the safety issues without compromising the structural and mechanical properties [2]. Solid electrolytes have two categories comprising of inorganic solid electrolytes and solid polymer electrolytes. Most commonly studied solid electrolytes are shown in Fig. 1 [3, 4]. Polymer based, flexible, solid electrolyte membranes to be used for all solid state metal ion batteries constitute the focal theme of this chapter.

Fig. 1 Most commonly studied solid electrolytes with examples

Polymer-Based, Flexible, Solid Electrolyte Membranes …

349

1.1 Solid Polymer Electrolytes (SPE) Solid polymer electrolytes have got tremendous attention due to easy processability, non-flammability, flexibility and light weight. Furthermore, SPEs are more attractive because they can accommodate electrode volume changes through elastic and plastic deformations. They act as both the solid electrolyte and the separator in rechargeable metal-ion batteries, sandwiched between the anode and the cathode. They possess a number of advantages over liquid electrolytes including (i) flexibility (ii) compactness (iii) laminated solid-state structures (iv) minimum leakage issues (v) low discharge in batteries (vi) elasticity relaxation under stress conditions (vii) availability in different geometries and (viii) easy processing methods [5]. But the ionic conductivity of SPEs is generally less than the necessary conductivity of 10–3 Scm−1 . Their low ionic conductivity at various temperatures, caused primarily by the presence of the polymer’s crystalline phase, limits their wide applications. Numerous studies, including the synthesis of novel polymer matrices, have been conducted to achieve an optimal balance between the amorphous and crystalline phases in SPE to achieve the required ionic conductivity and mechanical properties. Performance of the solid polymer electrolyte can be improved by reducing crystallinity, increasing the proportion of the amorphous region and the concentration of ions in the system, decreasing the polymer electrolyte system’s glass transition temperature, and improving lithium/sodium- ion capacity. SPEs are synthesized by dissolving inorganic salts in polymer matrix. The polymer acts as the host for the transmission of ions through the motion of polymer segments. Electrostatic forces are responsible for the interactions of polar groups in polymers with metal ions from salt. Chemical properties of the functional groups attached to the polymer backbone, distance between and composition of functional groups, degree of branching, molecular weight, chemical properties and charge of metal cation and counter ions are some important factors that may affect the polymer-metal ion interactions [6]. In order to be used in electrochemical devices, SPEs should possess the following properties: • • • • • • • •

Good ionic conductivity of the order between 10−4 and 10−2 S cm−1 Mechanical stability is required for device operation to be safe and long-lasting Wide electrochemical stability window Good thermal stability Electrochemical compatibility with electrodes Sustainability Low cost Low toxicity.

Various polymer electrolytes have been developed from different polymers such as, poly (ethylene oxide) (PEO), Cellulose, polyvinylidene fluoride (PVDF), poly(vinyl alcohol) (PVA), polyacrylonitrile (PAN), chitosan, poly(methyl methacrylate) (PMMA), and poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), to name a few [2]. Of these, SPEs based on polyethylene oxide (PEO) are the most

350

E. M. Sreeja et al.

promising because of their potential to provide good solubility for lithium, magnesium sodium salts. Inorganic salts improve ionic conductivity by reducing crystallinity of the polymer host. This is because polymer salts are biphasic, consisting of both amorphous and crystalline phases. In order to facilitate good ion transport, the ethylene oxide (EO) units of PEO should have a high donor number for Li+ and high chain flexibility. Furthermore, PEO has high Li+ solvability and dielectric constant [7]. However PEO based electrolytes generally show low ionic conductivity at room temperature. Many approaches have recently been taken to increase the ionic conductivity of PEO-based electrolytes.

1.2 Strategies to Improve Ionic Conductivity of PEO Based SPEs Inorganic salts Using inorganic salts in polymer electrolytes (PE) can improve electrical stability and conductivity in a variety of solvents. Ionic conductivity, chemical stability, and mechanical strength are all determined by the interaction between the polymer host and the inorganic salt. Low salt lattice energy and high polymer dielectric constant aid in the solubilization of inorganic salts in polymer chains. Non-metal salts and lithium/sodium salts are examples of generally preferred inorganic salts. Ammonium acetate (CH3 COONH4 ) has been chosen for its plasticizing effect in non-metal salts. Through hydrogen bonding, the acetate ion (CH3 COO− ) helps in salt solvation. In the synthesis of PE, salts such as MgTf, NaYF4 , NaI, NaClO4, NaTf, LiNO3 , LiPF6 , LiCF3 SO3 , LiClO4 , LiOX, and LiBF4 have been used as charge carriers. PEO is the most promising PE due to its high solubility in lithium salts. Nano filler One of the promising methods for improving the morphological and electrochemical properties of PEO is the addition of nano fillers. Nano fillers have a higher surface area that allows efficient contact with the electrolytes, increasing cell capacity, shortening lithium/sodium diffusion pathways, and facilitating lithium/sodium insertionextraction reactions. The addition of nanoparticles is expected to inhibit local reorganization of chains in the polymer and decrease polymer crystallization, resulting in high Li-ion transport [8]. There are inorganic and organic nano fillers. Inorganic nano fillers are more suitable for enhancing ionic conductivity and mechanical stability. Al2 O3 , SiO2 , TiO2 , LiAlO2 are some examples for inorganic fillers. Composite polymer electrolytes can be prepared by incorporating nano filler into a polymer salt matrix. Type of filler and particle size have high impact on conduction improvement. Conductivity enhancement improves with the surface area of the filler particles. Compared to conventional particles, the higher surface area of nano-sized fillers has preferred effects on improving SPE performance [9].

Polymer-Based, Flexible, Solid Electrolyte Membranes …

351

Plasticizer Plasticization is an important method for increasing amorphous phase in PEOLiX electrolytes. Plasticizers are additives that attempt to improve ion plasticity and mobility, thereby increasing ionic conductivity at room temperature. They are commonly used in the preparation of polymer electrolytes. Plasticizers increase ion mobility by dissolving more charge carriers. Dimethyl carbonate (DMC), dioctyl adipate (DOA), DBP, DEC, PC, and EC are examples of low molecular weight plasticizers [10]. Blending The process of combining polymers with or without chemical bonding is known as polymer blending. Combining PEO with other polymers will increase the percentage of amorphous phase. Polymer blending has been widely used in the development of new polymeric materials with a wide range of applications. The major benefits of combining polymers are ease of preparation and control over physical properties. Crosslinking method Cross-linked polymers have a number of advantageous properties. Structure of a polymer solution is fixed by cross-linking. The resulting polymer network is elastic and mechanically strong. It can expand by absorbing water or chemical solvents. Covalent chemical bonds or physical interactions are used to form cross connections. The amorphous form of linear PEO can be stabilized by crosslinking with welldeveloped polymer network structures. Crosslinking between polymer chains makes it difficult for crystallization to occur. Heat or UV light, initiators, and radiation sources are commonly used in crosslinking [11].

1.3 Preparation Methods of SPE SPEs can be prepared by several methods including solution casting, phase inversion and electro spinning techniques. Solution casting The most traditional and simplest method of making solid polymer electrolyte (SPE) membranes is solvent casting. In this process, the salt and polymer are dissolved in right solvents before casting onto the right substrates. After being allowed to dry at either ambient conditions or a higher temperature inside an oven, the solvent is allowed to evaporate. Depending on the needs, solution casting process can be carried out inside a glove box or at room temperature. SPE membrane is a free-standing one, with typical thickness in the millimeter range.

352

E. M. Sreeja et al.

Phase inversion Phase inversion is a method of demixing. Here a homogeneous polymer solution is immersed in a coagulation bath and converted into two phases. This conversion can be accomplished in a variety of ways like immersion precipitation, thermally induced phase separation (TIP), evaporation induced phase separation (EIP) and vapour induced phase separation (VIP). Among these, immersion precipitation is the widely used approach. Here, the polymer solution is cast on a suitable support and submerged in the coagulation bath containing a non-solvent. The solvent enters the non-solvent, and the non-solvent enters the polymer solution. This exchange will continue until demixing takes place. As a result, the homogeneous polymer solution gets separated into two distinct phases. One is the polymer-rich phase, which is an asymmetric membrane, and the other is the liquid-rich phase [12]. Electro spinning technique Electro spinning method is capable of generating membranes of fibers with a high surface area-to-volume ratio. Additionally, the electro spun membranes have higher thermal stability compared to the solution-cast membranes.

2 Theory of Solid Polymer Electrolytes (SPEs) Solid polymer electrolyte membranes are ideally perfect insulators with good ionic conductivity. They are usually amorphous or near amorphous in nature and crystallinity can be varied by introducing variations in additives or plasticizers which effectively improve ionic conductivity of the membranes. The dielectric properties of these membranes using simple electrical theory are discussed in the following theory sections [1, 2].

2.1 Dielectric Loss and Dissipation Factor When SPE membrane, which is a dielectric material, is subjected to an AC voltage or any oscillating field, resulting polarization P and displacement current D also vary periodically with time. But in general, polarization P and displacement current D may lag behind in phase relative to applied electric field E. If E = E 0 cos ωt then we have D = D0 cos(ωt − δ) where δ is the phase angle. D = D0 cos ωt cos δ + D0 sin ωt sin δ

Polymer-Based, Flexible, Solid Electrolyte Membranes …

353

D = D1 cos ωt + D2 sin ωt where D1 = D0 cos δ, D2 = D0 sin δ For most dielectric materials, D0 is proportional to E0 but DE00 is frequency dependent, and frequency dependent dielectric constant or relative permittivity is defined as, ε'' (ω) =

D0 cos δ D1 = E0 E0

ε'' (ω) =

D0 sin δ D2 = E0 E0

These two terms are combined to get the single complex dielectric constant as in Eq. (1) ε∗ (ω) = ε' (ω) − iε'' (ω)

(1)

Then the relation between displacement current D and electric field E can be expressed as D = ε∗ E 0 eiωt Or D = ε' (ω)E 0 cos ωt + ε'' (ω)E 0 sin ωt and there exists a relation tan δ =

ε'' (ω) ε' (ω)

(2)

since ε' (ω) and ε'' (ω) are frequency dependent real and imaginary parts of dielectric constant. The phase angle δ is also a frequency dependent quantity. The energy loss is proportional to tan δand hence it is called dielectric loss factor or dissipation factor. It represents the amount of energy that is dissipated in the SPE membrane when an electric field is applied across it.

2.2 Conduction Mechanisms Majority of insulators typically conducts non-ohmically above 1 MVcm−1 and ohmically below 0.1 MVcm−1 . While non-ohmic conduction can be inherent, ohmic

354

E. M. Sreeja et al.

Fig. 2 Schematic diagram of various conduction mechanisms in solid polymer electrolyte membranes a at high fields b at low fields

conduction is caused by impurities and inhomogeneity. It applies irrespective of ionic or electronic conduction. It is not always applicable to insulators, especially those that are amorphous, since band theory of conduction has been created for metals and semiconductors. By appropriately modifying band theory, the theory of polarons is used to assess conduction in SPE membranes. High field conduction Electronic conduction Conduction mechanism can be the effect of different processes which are classified into four types as illustrated in Fig. 2a, b. • HOMO (Highest occupied molecular orbital) to LUMO (Lowest unoccupied molecular orbital) transition: By raising the temperature, which is depicted as process a, Schottky emission from the electrode, depicted as process b and thermal excitation from defect levels to the LUMO, depicted as process c, electrons can be lifted from HOMO to LUMO. • Tunneling processes: Tunneling can occur directly between defect level and LUMO (process e), HOMO and LUMO (process f), HOMO to electrode (process g), or directly between two electrodes (process h) if the SPE membrane is thin enough to allow these processes. • Impurity conduction: It is used to refer to electrons hopping from one trapping center to another without going up into the LUMO (process i). • Space charge effects: There could be a buildup of space charges which affects the total impedance. In the limit, charge accumulation from the trapped electrons or electrons in the LUMO will balance the supplied voltage.

Polymer-Based, Flexible, Solid Electrolyte Membranes …

355

Ionic conduction It is also feasible for ions, frequently in the form of impurities or defects, to move through the SPE membranes under the influence of an electric field in addition to the methods outlined above for allowing electrons to do so. This is depicted in Fig. 2b as process j. Low field conduction If the SPE membrane is thin enough, direct tunneling between the electrodes can occur at low fields (h). Generally, for applications in metal ion batteries, membranes or films that are thicker than 100 μm are used. Electronic-impurity conduction and ionic conduction, take place in insulating SPE membranes at low fields and ambient temperatures. Impurity conduction: Electrons will go from one trap to the next in impurity conduction, without entering the LUMO (process i). Hoping will take place as a result of typical impurity conduction between the traps. If there are many electrons in the LUMO, limited mobility of the hopping electrons will likely hide any effects they might have. Impurity conduction is more likely to be visible in an insulator due to the relatively low density of thermally produced free carriers in the LUMO. Ionic conduction: Ionic conduction is the result of migration of impurities or defects present in the SPE membranes. Ions move by hopping over barriers of energy φ and separation l under applied field E and three types of behavior are observed as E is increased: (a) For E < 105 Vcm−1 and Eel > kb T, the number of current carriers is increased by the field. Since multiple hops also occur in this region, the analysis is complex. In real life, it could be difficult to explain the difference between ionic and electronic currents, especially if the activation energy is high. Electronic conduction is typically linked with an activation energy of less than 0.1 eV and high mobility, whereas a value of more than 0.6 eV and low mobility can represent either ionic conduction or electronic conduction. But a number of things will influence the differentiation. Polarization effects may be brought about by the accumulation of space charges at the electrodes or by dielectric relaxation and if ion transport does

356

E. M. Sreeja et al.

take place, material will be transported between the electrodes and can be detected chemically.

2.3 Ion Transport in SPE Membranes One crucial factor in deciding whether the SPE membrane is practically suitable and effective for device applications, is ionic conductivity. When calculating ionic conductivity of an electrolyte, the bulk resistance from the Nyquist plot obtained using EIS (electrochemical impedance spectroscopy) is used. To ensure a linear current–voltage relationship for impedance measurement, the solid polymer electrolyte is exposed to a low potential, typically 10 mV. The following equation illustrates the Nernst-Einstein relationship, which states that the ionic conductivity, is directly proportional to the ion diffusion coefficient, D as shown in the following equation [13]: σ =

e2 n D kb T

(5)

where e is elementary charge, n is the number of ions, kb is Boltzmann constant and T, temperature. Since the electrolyte consists of salts that can ionize into cations and anions, Eq. (5) can be written as follows: σ = σ+ + σ− =

e2 (n + D+ + n − D− ) kb T

(6)

where σ+ and σ− are the ionic conductivity of cations and anions respectively, n+ is the number of cations, n− is the number of anions, D+ is the cationic diffusion coefficient and D− is the anionic diffusion coefficient. The movements of ions are varied in the electrolyte system, depending on whether it is liquid, solid or gel. Inorganic salts are often dissolved in a polymer host matrix containing functional groups to form a solid polymer electrolyte. Through electrostatic contact, the functional groups assist in solvating the salts into ions. Many studies refer to the mobility of ions in polymer matrix as being associated with the segmental movement of the polymer chains, just like in the context of Brownian motion [14]. Because of this, it is thought that ion movements can take place only in amorphous polymers, where the polymer chains can move around freely while carrying the ions. It is commonly known that polymer matrices with low glass transition temperatures, Tg, have increased polymer chain mobility and flexibility. The relation between ionic conductivity and Tg can be explained by the Vogel-Tammann-Fulcher (VTF) equation, given below (

σ = σ0 T

1/2

−β exp T − (Tg − 50K )

) (7)

Polymer-Based, Flexible, Solid Electrolyte Membranes …

357

where σ 0 is pre-exponential factor and β is the term related to activation energy. Based on Eqs. (6) and (7), by raising the number density of mobile ions and decreasing the Tg value, a polymer electrolyte’s ionic conductivity can be enhanced. The simplest solution to meet the aforementioned requirements is to incorporate plasticizers with high dielectric constants into the polymer electrolyte. High dielectric constants help in accelerating salt dissociation and increasing the number density of mobile ions by weakening the forces that hold salt ions together. By making the polymer electrolyte layer more amorphous and offering more coordination sites for ions to conduct, plasticizers also help to make easy pathways for ions to travel. Diffusion coefficient of ions, D, can also be determined from the following equation D=

d2 4τ2 δ 2

(8)

dκ where d is the thickness of the electrolyte membrane or film, τ2 = ω1 and δ = Aεε 0 (here ω is the angular frequency taken at the minimum value of impedance in Bode plot; κ is double layer capacitance; ε is dielectric constant of the electrolyte and ε0 is the permittivity of free space). κ values can be obtained by fitting the Nyquist plot of the electrolyte based on the series connection of bulk resistance, Rb , and constant phase element, CPE. The mobility, μ, and number density, n, of ions can be obtained by using the following equations:

μ=

eD kb T

n=

σ eμ

Relationship between σ, n and μ can be expressed as [15]: σ = neμ n values can also be calculated from the famous Rice and Roth model which was originally developed to describe the conducting behavior for super-ionic conductors [16] σ =

( ) ) ( 2 (Z e)2 −E a n E a τ exp 3 mkb T kb T

(9)

where Ea is the activation energy; e is the electron charge; m is the mass of ions; Z is the vacancy of conducting species and τ = l/ν, where l is the distance between two trapping sites and ν is the velocity of ions, which is given by

358

E. M. Sreeja et al.

√ v=

2E a m

(10)

Ea is the minimum energy required for an ion to hop in between sites, and it can be obtained from the Arrhenius equation, as shown below ( σ = σ0 exp

Ea kb T

) (11)

where σ0 is the pre-exponential factor. A low Ea value is required for high conductivity. Ionic conductivity can also be calculated using Eq. (12) in terms of bulk resistance obtained using Nyquist plot of EIS analysis. σ=

t Rb A

(12)

where Rb is the bulk resistance obtained from the complex AC impedance plot, A is the area and t, the thickness of the solid polymer electrolyte membrane [17]. Ion transport in polymer electrolytes typically occurs by hopping and is associated with the segmental motion of the polymer chains [18]. The conduction mechanism of solid polymer electrolyte, in all-solid-state metal ion cell, using it as separator cum electrolyte is illustrated in Fig. 3a and the corresponding energy diagram is shown as schematic in Fig. 3b.

Fig. 3 a Schematic diagram of conduction mechanism in solid polymer electrolyte based all solid state metal ion cell, b schematic energy diagram of a solid polymer electrolyte. The energy separation of HOMO and LUMO of polymer electrolyte is Eg . ΦA and ΦC are the anode and cathode work functions respectively. The formation of SEI layer results in kinetic stability for which the condition is μa > LUMO and/or μC < HOMO layer

Polymer-Based, Flexible, Solid Electrolyte Membranes …

359

3 Characterization Techniques 3.1 Ionic Conductivity—Electrochemical Impedance Spectroscopy Electrical impedance is the term used to describe a material’s hindrance to the flow of an alternating current (ac). Oliver Heaviside originally established the impedance idea in relation to electrical circuits in the 1880s [1]. This concept was further expanded by A. E. Kennelley by using vector diagrams and complex number representations [2]. Frequency of the applied alternating signal affects impedance. Variation of impedance of a system with frequency can be measured and is represented in a complex plane with frequency as an implicit variable. Impedance spectroscopy is a potent tool in materials research and for studying electrochemical systems and processes. Impedance spectroscopy is based on determining the impedance of an electrochemical system in response to a small ac signal. Since impedance is a complex number, both its real and imaginary components can be used to express it. The phase shift between the applied signal and the current through the material and the impedance’s magnitude can be used to determine the real and imaginary components of impedance. From the phase shift, it is possible to determine how resistive, capacitive, or inductive can be, the material, system, or process. In impedance spectroscopy technique, a small amplitude alternating signal is applied across the sample. Current through the sample is measured. The applied ac signal E(t) guarantees that the current response I(t) to the alternating voltage is linear or pseudo-linear. Frequency is also the same as that of the voltage applied, albeit it is phase shifted. The complex impedance of the sample, denoted as Z, is the voltage to current ratio, or E(t)/I(t). Impedance is frequency (f) dependent since E(t) and I(t) vary with frequency. A spectrum of Z versus f (ω) can be obtained for the frequency of choice. A typical sample sandwiched between two electrodes is subjected to the small amplitude ac voltage indicated by the equation E(t) = E 0 sin ωt

(13)

Here Eo is the maximum voltage and ω = 2πf is the angular frequency of the ac signal. The response ac current flowing through the sample is given by I (t) = I0 sin(ωt + θ )

(14)

where θ is a phase difference between current and voltage. Here the current leads the voltage by a phase θ. The impedance of the sample is the ratio between the ac excitation and the ac response and is given by

360

E. M. Sreeja et al.

E(t) I (t)

(15)

E 0 sin ωt I0 sin(ωt + θ )

(16)

Z= Z=

Z is a function of frequency and has a magnitude of Z0 and a phase angle θ, given by E0 I0

Z0 =

(17)

Since ac impedance of a system Z(ω) is a complex quantity, it has a real Z' (ω) and an imaginary Z'' (ω) component and can be represented as Z (ω) = Z ' (ω) + j Z '' (ω)

(18)

Here the real part Z ' (ω) = Z 0 cos θ

(19)

and the imaginary part Z '' (ω) = Z 0 sin θ

(20)

The phase angle of Z(ω) is given by θ = tan−1

(

Z '' (ω) Z ' (ω)

) (21)

In the traditional method of impedance spectroscopy, Z is measured as a function of frequency f (ω = 2πf) for a sample over a large frequency range and Z'' (ω) against Z' (ω) are plotted at different frequencies. The resultant graph, often known as a complex impedance plot or Nyquist plot, provides data on a wide range of characteristics pertaining to how the system under examination operates. An intrinsic flaw of the Nyquist plot is its inability to capture the frequency at which a specific impedance is exhibited by the system. This drawback is rectified in the bode plot, in which the real part on the X axis is replaced with logarithmic frequency. In the Nyquist plot the horizontal axis represents the real impedance, Z' (ω). The vertical axis represents the imaginary impedance, Z'' (ω). The bulk resistance Rb of the sample is indicated by the intercept of the plot with the Z' axis. The sample’s reactance X is shown on the vertical axis. For a sample in the form of a disc or film, the bulk resistance can be written as Rb = ∴ρ=

ρt A

(22)

Rb A t

(23)

Polymer-Based, Flexible, Solid Electrolyte Membranes …

361

Here ρ denotes the resistivity of the material, t is the length or thickness of the sample, and A is the area of cross-section of the sample. The conductivity, σ of the sample is given by σ = ∴σ =

1 ρ

(24) t

Rb A

(25)

Since Rb can be obtained from the Nyquist plot and t and A are known, σ can be determined. Equivalent circuit fitting approach is another method for calculating the bulk resistance of an impedance plot. The impedance spectra of ideal systems have semicircles with centers on the horizontal Z' -axis and vertical spikes. The spectra for real systems typically include depressed or warped semicircles and slanted or curved spikes. The nature of the electrolyte/electrode contact, the electrolyte’s nonhomogeneous characteristics and the electrolyte’s scattered microscopic properties are the common causes of depressed semicircles. Rough electrode/electrolyte interfaces, charge transfer across the electrode/electrolyte interface and species diffusion in the electrolyte or electrode can all lead to slanted or curved spikes. In short, the bulk material is represented by the depressed semicircle, whereas the electrical double layer (EDL) is represented by the slanted spike. A typical impedance plot of electrolyte sandwiched between two blocking electrodes and the corresponding simple equivalent circuit are illustrated in Fig. 4a, b. Impedance spectra that deviate from ideal behavior can be described by a novel circuit parameter known as the constant phase element (CPE). The CPE often possesses the characteristics of R and C. The depressed semicircle and slanted spike in the impedance plots may be fitted using an equivalent circuit. The selection of right equivalent circuit is important to ensure that the impedance plot is completely fitted. A parallel resistor and CPE can represent the depressed semicircle portion, and a

Fig. 4 a A typical impedance plot of electrolyte sandwiched between two blocking electrodes and b the corresponding simple equivalent circuit

362

E. M. Sreeja et al.

CPE can represent the slanted spike. Combining R//CPE in series with another CPE, as illustrated in Fig. 4b, generate the equations of real and imaginary impedance, and both equations will fit the impedance plot in Fig. 4a. The bulk resistance of the sample is represented by the resistor (R) in the circuit. Ionic conductivity of each sample can be calculated by using the value of R obtained from the fitting method and substituting it in the equation of conductivity.

3.2 DC Polarization—Total Ionic Transport Number and Cationic Transference Number Wagner’s DC polarization method can be used to calculate the total ionic transport number (tion ). By applying a fixed dc voltage ΔV across the sample with structure SS/ SPE/SS, where SS stands for stainless steel which acts as the blocking electrode and SPE stands for solid polymer electrolyte, the dc current developed can be observed as a function of time. The following equation gives the value of tion and Fig. 5 shows a typical DC polarization curve of PEO/PVDF blend based SPE film with 15 weight% of LiNO3 . tion =

I T − Ie IT

(26)

Here IT is the total current and Ie the residual current. Theoretical value of total ion transport number is unity which indicates there is no electron contribution to carrier transport. In real systems, its value is very close to unity indicating that the overall conductivity of the sample is predominantly ionic and electron contribution to carrier transport is quite negligible. Very important physical parameter for battery electrolytes in both applied and fundamental regards is the cation transference number. Looking at the ionic radius Fig. 5 A typical DC polarization curve of SPE film with 15 weight % of LiNO3

Polymer-Based, Flexible, Solid Electrolyte Membranes …

363

of cations in comparison with typical salt anions, the cation is much smaller and should move faster through the electrolyte at first glance if the charges of both ions are equal. In reality this is not observed for most of the electrolytes. This is due to solvation effects that are more severe when small and polarizing ions are considered. DC polarization method described by Bruce and Evans is applied to identify the contributions of individual species. These contributions are quantified by the transference number t+ , which is defined by the amount of current transported by cation I+ in relation to the total current I. t+ =

I+ I+ = I+ + I− I

(27)

In this method, metals which can reversibly exchange cations but blocking to the anions are used as electrodes. Since the applied potential difference in this two-electrode setup affects both ions in the same way, the transference number can also be written in terms of ionic conductivities, given by, t+ =

R σ+ σ+ = = σ+ + σ− σ R+

(28)

where R is the total electrolyte resistance characterized by a parallel connection of anionic resistance R=

R+ R− (R+ + R− )

(29)

The symmetrical cell is polarized with a DC voltage ΔV and the total conductivity of the electrolyte can be determined at time t = 0. In this case, the initial overall resistance of the system for a potentiostatic situation is given by ΔV = R0S E I + R I0

(30)

Here I0 denotes initial current and R0S E I denotes initial serial resistance due to solid electrolyte interface (SEI) at the electrodes. Initial current in the system drops until a constant equilibrium current is reached which only originates from the non-blocking ionic species. Applied voltage causes the migration of ions in the electric field. As the metal electrodes are reversible only for cations, the anions accumulate at the anode, lowering their concentration at the cathode. Due to this effect, a concentration gradient is established. Motion of anions is reduced and eventually comes to a complete stop. As a result, the cations are the only conducting species whereby the electric current is reduced. In the steady state, the overall resistance is given by

364

E. M. Sreeja et al.

ΔV SE I = R∞ + R+ I∞

(31)

SE I Here I∞ denotes steady state current and R∞ denotes steady state serial resistance due to solid electrolyte interface (SEI) at the electrodes. Combining Eqs. (28), (30) and (31), the expression for t+ can be deducted as

( ) I∞ ΔV − I0 R0S E I ) t+ = ( SE I I0 ΔV − I∞ R∞

(32)

DC polarization technique is generally carried out to obtain the initial (I0 ) and SE I can be obtained from the steady state (I∞ ) currents. The values of R0S E I and R∞ impedance plot, before the polarization and after the steady state has been reached.

3.3 Linear Sweep Voltammetry The energy density and capacity of an electrochemical cell are critical parameters that are tied to the voltage window of the cell electrolyte. Electrochemical stability window (ESW) enables the user to use the battery safely and provides information about the interfacial resistance with the electrodes. The difference between the oxidation and reduction potentials is denoted as ESW. As a result, ESW is tested prior to cell fabrication. Because rechargeability (reversibility) is a crucial property of metal ion batteries, oxidation and reduction must occur within this voltage limit. Linear sweep voltammetry is the technique used in SS/SPE/metal configuration to investigate the electrochemical stability window of the SPEs. Measurements are carried out in a potential window at a low scan rate and at a particular voltage, sudden onset of current occurs owing to the decomposition of the electrolyte. This breakdown voltage is referred to as the electrochemical stability window of the electrolyte.

3.4 Conclusions Developing all solid state metal ion batteries with high energy density, cycling stability and operational safety is mandatory for the commercial growth of next generation electric and hybrid electric vehicles. Identifying the best category of solid polymer electrolytes, capable of being grown as free standing and flexible membranes or films with impressive metal ion conductivity, comparable to that of liquid electrolytes, thermal and mechanical stability and high electrochemical stability window is the prime research goal to be addressed and achieved. Our research group has put in extensive efforts in this direction and attempts are continuing with novel types of hybrid materials and approaches to develop all solid state metal ion batteries based on lithium, sodium and magnesium with highly impressive performance characteristics.

Polymer-Based, Flexible, Solid Electrolyte Membranes …

365

References 1. Liu Y, Holze R (2022) Metal-Ion Batteries. Encyclopedia 2022, 2(3)1611–1623. https://doi. org/10.3390/encyclopedia 2. Teo LP, Buraidah MH, Arof AK (2021) Development on solid polymer electrolytes for electrochemical devices. Molecules 26:6499. https://doi.org/10.3390/molecules26216499 3. Karabelli D, Birke KP, Weeber M (2021) A performance and cost overview of selected solid-state electrolytes: race between polymer electrolytes and inorganic sulfide electrolytes. Batteries 7:18. https://doi.org/10.3390/batteries7010018 4. Lau J, Deblock RH, Butts DM, Ashby DS, Choi CS, Dunn BS (2018) Sulfide solid electrolytes for lithium battery applications. Adv Energy Mater 8(27). https://doi.org/10.1002/aenm.201 800933 5. Kuila T, Acharya H, Srivastava SK, Samantaray BK, Kureti S (2007) Enhancing the ionic conductivity of PEO based plasticized composite polymer electrolyte by LaMnO3 nanofiller. Mater Sci Eng: B 137:217–224. https://doi.org/10.1016/j.mseb.2006.11.023 6. Aziz SB, Woo TJ, Kadir MFZ, Ahmed HM (2018) A conceptual review on polymer electrolytes and ion transport models. J Sci Adv Mater Devices 3(1):1–17. https://doi.org/10.1016/j.jsamd. 2018.01.002 7. Yua Q, Jianga K, Yub C, Chena X, Zhanga C, Yaoa Y, Jianga B, Longa H (2021) Recent progress of composite solid polymer electrolytes for all-solid-state lithium metal batteries. Chin Chem Lett 32(9):2659–2678. https://doi.org/10.1016/j.cclet.2021.03.032 8. Zhang Q, Liu K, Ding F, Liu X (2017) Recent advances in solid polymer electrolytes for lithium batteries. Nano Res 10:4139–4174. https://doi.org/10.1007/s12274-017-1763-4 9. (Kelvin) Fua K, Gonga Y, Daib J, Gonga A, Hana X, Yao Y, Wanga C, Wang Y, Chen Y, Yan C, Li Y, Wachsman ED, Hu L (2016) Flexible, solid-state, ion-conducting membrane with 3D garnet nanofiber networks for lithium batteries. PNAS 113. https://doi.org/10.1073/pnas.160 0422113 10. Wang J, Yang J, Shen L, Guo Q, He H, Yao X (2021) Synergistic effects of plasticizer and 3D framework toward high- performance solid polymer electrolyte for room-temperature solidstate lithium batteries. ACS Appl Energy Mater 4(4):4129–4137. https://doi.org/10.1021/acs aem.1c00468 11. Ben H, Garcia-calvo O, Lago N, Devaraj S, Armand M (2016) Cross-linked solid polymer electrolyte for all-solid-state rechargeable lithium batteries. Electrochim Acta 220:587–594. https://doi.org/10.1016/j.electacta.2016.10.122 12. Murata K, Izuchi S, Yoshihisa Y (2000) An overview of the research and development of solid polymer electrolyte batteries. Electrochim Acta 45:1501–1508 13. Teo LP, Buraidah MH, Arof AK (2021) Development on solid polymer electrolytes for electrochemical devices. Molecules 26(21) 14. Golodnitsky D, Strauss E, Peled E, Greenbaum S (2015) Review—on order and disorder in polymer electrolytes. J Electrochem Soc 162(14):A2551–A2566 15. Arof AK, Naeem M, Hameed F, Jayasundara W (2014) Quasi solid state dye-sensitized solar cells based on polyvinyl alcohol (PVA) electrolytes containing I-/I3- redox couple. Opt Quantum Electron 46(1):143–154 16. Ahmed HT, Abdullah OG (2020) Impedance and ionic transport properties of protonconducting electrolytes based on polyethylene oxide/methylcellulose blend polymers. J Sci Adv Mater Devices 5(1):125–133 17. Jinisha B, KM A, Manoj M, Pradeep P, Jayalekshmi J (2017) Development of a novel type of solid polymer electrolyte for solid state lithium battery applications based on lithium enriched poly (ethylene oxide) (PEO)/poly (vinyl pyrrolidone) (PVP) blend polymer. Electrochim Acta 235:210–222. https://doi.org/10.1016/j.electacta.2017.03.118 18. Zhou Q, Ma J, Dong S, Li X, Cui G (2019) Intermolecular chemistry in solid polymer electrolytes for high-energy-density lithium batteries. Adv Mater 31(50):1–21 19. Kittel C (1996) Introduction to solid state physics. John Wiley and Sons Inc., Singapore, pp 380–392

366

E. M. Sreeja et al.

20. Dekker AJ (2012) Solid state physics. Macmillan Publishers India Ltd., Delhi, pp 133–178 21. Lamb DR (1967) Electrical conduction mechanism in thin insulating films. Methuen, Landon 22. Maissel LI, Glang R (1970) Handbook of thin film technology. McGraw-Hill Book Company, New York, pp 16–33

Polymer Materials for Metal-Air Battery Arpana Agrawal

Abstract Metal-air batteries are one of the fascinating powering devices for today’s electronic gadgets owing to their theoretical high energy density. The main components of a metal-air battery include electrodes (anode and cathode) and electrolytes. For the fabrication of metal-air batteries, polymeric materials are considered to be one of the most potential candidate materials serving as either electrode material and/ or electrolyte due to their outstanding flexibility and excellent mechanical properties. Accordingly, the present chapter provides a critical overview of various polymericbased materials including polypyrrole conducting polymers, polyaniline, poly(3,4ethylenedioxythiophene) polystrene, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, polytetrafluroethylene, anion exchange polymer, poly(ethylene oxide), poly(vinyl alcohol), xanthan, κ-carrageenan based alkaline hydrogels, sagogel, etc. that can be successfully employed for the preparation of either electrodes and/ or electrolytes of metal-air batteries including zinc-air, lithium-air, aluminum-air or magnesium-air batteries. Few recent studies on the utility of several polymeric materials-based metal-air batteries have also been reported. Keywords Metal-air batteries · Polymeric materials · Electrochemical performances · Polymer-based electrolytes

1 Introduction Metal-air batteries (MABs) have attracted immense research interest from the viewpoint of technological importance [1]. They serve as one of the most effective devices for powering various portable, flexible, and wearable electronic gadgets of our modern society. The main components of a MAB include the electrodes i.e., air cathode and metal anode, and electrolytes. Based on the metal anode employed, they A. Agrawal (B) Department of Physics, Shri Neelkantheshwar Government Post-Graduate College, Khandwa 450001, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_21

367

368

A. Agrawal

can be named an aluminum-air battery (AAB) [2], magnesium-air battery (MgAB) [3], zinc-air battery (ZAB) [4], lithium-air battery (LAB) [5], etc. To design or prepare these components, polymeric materials are considered one of the most important materials. It is noteworthy to mention here that air cathode plays a vital role to examine the electrochemical performances of a MAB and hence in the case of polymeric material-based electrodes, they mainly act as cathode catalysts which facilitates improving the electrochemical properties including the specific capacity, life, density, etc. Apart from the cathode catalyst, polymeric materials can also be used as a shielding/protecting coating layer deposited on the metal anode in order to diminish the occurrence of its corrosion. Another most important utility of polymeric materials is the preparation of electrolytes for MABs. Initially, the batteries were discovered with aqueous electrolytes with alkaline electrolytes based on KOH/H2 O solution or quasi-neutral electrolytes comprising of various salts dissolved in water such as NaCl, NH4 Cl, (NH4 )SO4, etc. which are considered to be abundantly available, harmless, cost-effective and can be fabricated easily. However, with aqueous or liquid electrolytes, there always remains an issue of leakage, dendrite formation, and evolution of corrosive layer onto metal anodes that significantly hinders the electrochemical performances of MABs and can be skirted exploiting polymer-based electrolytes. In 1973, the very first conducting polymer, namely poly(ethylene oxide) (PEO) was discovered by Wright et al. [6], which revolutionized the field of polymer-based electrolytes for MABs which are usually semi-solid- or all-solid-state electrolytes. However, allsolid-state electrolytes have comparatively low ionic conductivity as compared to semi-solid-state electrolytes. Polymer alkaline gel-based electrolyte was reported to be employed for designing all-solid-state AAB [7]. Lin et al. [8], reported the fabrication of nano-engineered polymer electrolyte-based solid-state ZAB having high durability. Several polymeric materials have been nowadays opted as alternative and effective electrolytes because of their ability to reduce the leakage issues of MABs. Additionally, their thermal stability, ion transport capability, high elastic modulus, good deformation resistance, excellent mechanical properties even under several deforming circumstances along with flexibility can be exploited to fabricate potential wearable MABs. So far, several researchers have successfully employed various polymer-based materials consisting of polypyrrole (PPy) conducting polymers, PEO, polyaniline (PANI), poly(3,4-ethylenedioxythiophene) polystyrene (PEDOT), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), polyacrylamide (PAM), polytetrafluroethylene, polyacrylic acid (PAA), anion exchange polymer (AEP), poly(vinyl alcohol) (PVA), polymethyl methacrylate (PMMA), xanthan, κ-carrageenan based alkaline hydrogels, etc. for the fabrication of various MABs. It is noteworthy to mention here that polymer electrolytes can be categorized on the basis of their sources and composition and physical state. Depending upon the sources, polymer electrolytes may be naturally occurring such as chitosan, rice/ corn starch, k-carrageenam, etc., or synthetic polymers which are mainly the dispersion of liquid electrolytes in the polymer matrix. Lizundia and Kundu have compiled

Polymer Materials for Metal-Air Battery

369

various naturally occurring biopolymer-based materials serving as either electrolytes or separators for battery applications [9]. PVA, PAA, PEO, PAM, sodium polyacrylate (PANa), etc., are commonly employed synthetic polymers and their molecular structures are provided in Fig. 1a. Depending upon the composition and physical state, polymers can be classified as gel-polymer electrolytes, solid polymer electrolytes, composite polymer electrolytes, and double-network gel-polymer electrolytes. Fan et al. [10], constructed highly durable ZAB with porous structured nanocomposite gel polymer-based electrolyte. Highly conductive double network hydrogel for ZAB is discussed by Sun et al. [11]. PAA and κ-carrageenan based hybrid network hydrogels have also been reported for AAB [12]. Gaele et al. [13] and Wang et al. [14], discussed the potentiality of dual electrolytes for fabricating AAB possessing excellent electrochemical characteristics. A plasticized polymer membrane-based electrolyte separator was also reported by Elia and Hassoun for fabricating lithium–oxygen (Li– O2 ) batteries possessing excellent electrochemical performances (highest capacity obtained ~ 25,000 mAhg−1 ) [15]. To prepare the polymer membrane-based electrolyte, a mixture of PEO20 LiCF3 SO3 and ZrO2 membrane was swelled in a solution of tetraethylene glycol dimethyl ether and LiCF3 SO3 . Figure 1b shows the photograph of the

Fig. 1 a Molecular structure of few commonly employed polymers in MABs; b Photograph of the plasticized polymer membrane-based electrolyte; c Galvanostatic cyclic response of the fabricated Li–O2 battery at 100 mA g−1 [15]. Adapted with permission [15]. Copyright (2015) Copyright The Authors, some rights reserved; exclusive licensee [Nature Publishing]. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

370

A. Agrawal

plasticized polymer membrane-based electrolyte. The galvanostatic cyclic response of the fabricated Li–O2 battery at 100 mA g−1 was depicted in Fig. 1c. It should be noted here that among all the above-mentioned polymers, synthetic gel-polymer electrolytes are widely employed for fabricating various MABs including ZAB, MgAB, LAB, AAB, etc., and are semi-solid-state electrolytes (in-between liquid and all-solid-state), obtained by adding organic solvents or plasticizers into dry polymer-based substrates. This leads to improved ionic conductivity ~ 104 Scm−1 at 300 K and encourages flexibility. Few polymer electrolytes can also serve as efficient separators and/or substrates in their original form or via coating them on paper substrates or carbon-based textile/cloths which facilitates minimal use of electrolytes via capillary action. The proper choice of electrode and electrolyte materials is one of the decisive factors to examine and improve the battery performance and hence their practical utility. Accordingly, this chapter presents an overview of various polymeric materials either (natural or synthetic) utilized for the fabrication of MABs. Few recent studies performed in this field have also been discussed.

2 Polymeric Materials for Metal-Air Batteries Polymeric materials are immensely utilized for the fabrication of MABs either in the form of electrode materials or electrolytes. This section describes the various polymeric materials serving as either electrode materials or electrolytes.

2.1 Polymeric Materials as Electrode Materials Several polymeric materials including PPy conducting polymers, PANI, PEDOT, polytetrafluroethylene, AEP, etc. can be employed as the electrode materials and mainly serve as the shielding cover to minimize the possibility of corrosion of the metal anode, or as cathode catalyst and hence improve the battery performances including the stability or the capacity. Zhang et al. [16], have reported the fabrication of Li-O2 batteries consisting of PPy-based conducting polymers doped with Cl− (PPy-Cl) and ClO4 − (PPy-ClO4 − ) serving as efficient cathode catalyst, Li as anode and alkyl carbonate as electrolyte. They showed that the LAB made up of PPy-Cl exhibits enhanced capacity and cycle stability as compared to LAB with PPy-ClO4 − . The preparation of a novel air cathode structure consisting of entangled carbonized polyaniline nanotubes (Co3 O4 e-cPANI) for the fabrication of LAB was also reported [17]. The fabricated battery with Co3 O4 -e-cPANI based cathode exhibits outstanding cycle stability of 226 cycles at 1000 mAhg−1 . Badam et al. [18], have demonstrated the construction of Li–O2 batteries employing bis(imino)acenaphthenes iron complex (BP-Fe) as a cathode catalyst. This complex possesses high electrochemical activities. Cui et al. [19],

Polymer Materials for Metal-Air Battery

371

have also fabricated Li–O2 batteries employing PANI/reduced graphene oxide (rGO) foam as cathode material. The battery shows a discharge capacity of 36,010 mAhg−1 and outstanding cycle stability of 500 cycles at 500 mAhg−1 . PEDOT/ MnO2 /carbon paper-based composite cathode is also reported for fabricating AAB [2]. For the cathode, initially the open tunnel structured MnO2 catalyst was synthesized by employing a hydrothermal approach followed by the deposition of PEDOT polymer on MnO2 /carbon paper via oxidative chemical vapor deposition technique. Anodes can also be made via polymer coating to lessen their corrosion. Deyab et al. [20], have fabricated AAB using a polymer-coated anode. This polymer-coated anode was made by coating PANI and carbon nanofibers (CNFs) onto the Al anode (Al/ PANI@CNF) which facilitates the reduction of corrosion of the anode and also helps in circumventing the release of hydrogen gas (up to 92%). The battery shows highcapacity density and high energy density at 10 mA/cm2 . The same group has also [21] utilized polymeric materials for shielding Zn electrodes in ZAB. They have prepared a novel nanocomposite by incorporating Zn-phthalocyanines (ZnPc) nanoparticles in PANI (PANI@ZnPc) and have deposited this onto the surface of the Zn anode. Zhang et al. [22], have also reported the coating of polymer on the Al anode to minimize the corrosion of the anode in AAB. They have prepared a porous structured polytetrafluroethylene hydrophobic membrane which was physically absorbed onto the surface of the anode. The fabricated AAB shows a capacity of 1126 mAhg−1 at a current density of 10 mA/cm2 . PANI polymer-coated Zn anode for ZAB was also discussed and prepared via the sonochemical method [23]. Wang et al. [24], have developed flexible ZAB using multiwalled carbon nanotubes (MWCNTs) bridged with Zn particles as an anode, MWCNT-based catalytic layer coated on flexible carbon cloth as cathode, and PAA and PVA-coated paper separator/substrate which enhance the electrolytic storage capacity. Figure 2a pictorially illustrates the sandwich layered structured ZAB with photographs of various different layers and assembled ZAB (Fig. 2b–e). To prepare the electrodes, initially, anode and cathode pastes were prepared. For anode paste, zinc, bismuth oxide, and highly pure MWCNTs were mixed together in a polymeric binder (PEDOT: PSS), and then applied to the current collectors. For cathode paste, electrolytic manganese di-oxide powder and MWCNTs were mixed in a polymeric binder (PEDOT: PSS) and were then coated on flexible carbon cloth serving as a cathode. The polymeric binder PEDOT: PSS was utilized to increase the conductivity and flexibility of the electrodes. Figure 3a–f show the scanning electron microscopy (SEM) images of the electrode materials namely, cathode catalytic layer, anode with MWCNTs, battery grade zinc, copolymer improved paper separator, separator intersection, and MWCNT. The discharging curves of the battery were also examined under the varying amount of MWCNTs in the anode as illustrated in Fig. 3g which clearly shows an improved cell performance with an increased amount of MWCNTs. However, after a certain limit of MWCNTs in an anode, crack formation begins and hence, it is highly imperative to increase the volume of binder along with increasing the amount of MWCNTs which ensures the integrity and flexibility of the anodes.

372

A. Agrawal

Fig. 2 a Schematic illustration of layered structured ZAB; Photographs of MWCNT based catalytic layer caked on flexible carbon cloth serving as cathode (b); PAA and PVA polymer boosted paper separator/substrate (c); zinc metal anode (d); assembled ZAB (e). Adapted with permission [24]. Copyright (2017) Elsevier

Jia et al. [3], have reported the fabrication of a biocompatible magnesium-air bioelectric battery employing silk fibroin-PPy (SF-PPy) film-based cathode, Mg alloy as an anode, and phosphate-buffered saline as electrolyte. The cathode was prepared by coating PPy onto the silk substrate which possesses comparatively good conductivity (1.1 Scm−1 ). The fabricated magnesium-air bioelectric battery possesses a room temperature discharge capacity of 3.79 mAhcm−2 at 10 μA cm−2 and a significantly high specific energy density (4.70 mWh cm−2 ). Fabrication of extremely flexible and transparent ZAB was reported by Kwon et al. [25], as shown in Fig. 4a along with their optical microscopy images. The fabricated ZAB consists of an electrodeposited Zn metallic anode as a current collector, KOH-PAA gel as an electrolyte, and a highly transparent cathode-AEP separator assembly. To produce the cathode-AEP separator assembly, a catalyst paste was initially prepared to comprise a dispersion solution of Pt/C and Ir/C in isopropylalcohol along with a Nafion binder. This solution was continuously stirred mechanically and cast on the cathode followed by drying at 50 °C. After, this, the AEP solution was layered onto a polyethylene terephthalate (PETE) substrate with heating at 50 °C and air drying for 90 min. To assemble the AEP separator and cathode mesh, the cathode mesh was simply kept on the AEP separator and left for overnight drying. The process of conjoining the AEP separator and cathode leads to the formation of voids in the open spaces of the mesh as can be seen in Fig. 4a (top right) which may be due

Polymer Materials for Metal-Air Battery

373

Fig. 3 SEM scans of cathode catalytic layer (a); anode with MWCNTs (b); battery grade zinc (c); copolymer improved paper separator (d); separator intersection (e); MWCNTs (f). g Discharge results of the fabricated ZAB consisting of different amounts of MWCNTs and volume of binder in the anode. Adapted with permission [24]. Copyright (2017) Elsevier

to the gradual seep of the AEP resin towards the wire. Figure 4b schematically illustrates the mechanism of pore formation via the polymer grip of the cathode mesh wires. Once all the components were prepared, the complete ZAB assembly was constructed by placing the electrolyte in between the anode and cathode-separator assembly. Figure 4c shows the utility of the fabricated ZAB for powering white LED and Fig. 4d reveals the dependency of voltage and power density on current density. Figure 4e depicts the galvanostatic discharge results of the ZAB at two different current densities (1 mAcm−2 and 5 mAcm−2 ), which indicates a relatively higher specific capacity at 1 mAcm−2 (70 mAhg−1 ) as compared to those obtained at 5 mAcm−2 (684 mAhg−1 ).

374

A. Agrawal

Fig. 4 a Pictorial representation of transparent bendable ZAB along with the optical image of pore formations onto the open spaces of cathode -anion exchange polymer separator assembly and top view of battery’s configuration. b Mechanism of pore formation via polymer grip of the cathode mesh wires. c Photograph of white LED powered by the fabricated ZAB. d Voltage and power density dependence on current density, e Galvanostatic discharge curves of ZAB at 1 mAcm−2 and 5 mAcm−2 . Adapted with permission [25]. Copyright (2015) Copyright The Authors, some rights reserved; exclusive licensee [Nature Publishing]. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

2.2 Polymeric Materials as Electrolyte Materials Various natural polymers such as xanthan, κ-carrageenan based alkaline hydrogels, sagogel, etc. as well as synthetic polymers including PAN, PAA, poly(carbonateether), PVA-KOH gel polymer, etc. have been successfully employed as electrolytes in MABs and ensures upgrading of the battery performances. DiPhalma et al. [26], reported natural polymers, particularly Xanthan and κ-carrageenan based hydrogels as effective electrolytes for AABs. Sago gel-based electrolyte was employed by Marsi et al. [27], for the fabrication of ZAB. Zhang et al. [28], discussed the fabrication of flexible ZAB utilizing nanocellulose/graphene oxide-based electrolyte. Xanthan- HCl hydrogel-based solid and acid electrolytes has also been used for

Polymer Materials for Metal-Air Battery

375

AAB [29]. Chitosan hydrogel membranes, a natural polymer, can also be for fabricating eco-friendly Al-air coin cells [30]. Despite the success of such natural polymers, synthetic gel-polymer-based electrolytes are much more widely employed for fabricating various MABs including ZAB, LAB, AAB, MgAB, etc. Fan et al. [31], have examined the environmental stability of the PVA-KOH gel polymer electrolyte employed for the fabrication of sandwich-structured ZAB which is highly imperative for practical utility. For the preparation of gel polymer electrolyte, a mixture of PVA powder and deionized water undergoes magnetic stirring at 90 °C for 90 min followed by the addition of KOH electrolyte with continuous stirring to form a uniform viscous solution. This prepared solution was then cooled to form a thick polymer film. Carbon cloth loaded with Co3 O4 catalyst served as the cathode and Zn foil were used as an anode. Figure 5a and b depict the field emission scanning electron microscopy (FESEM) image and energy dispersive X-ray diffraction (EDX) images of PVA-KOH-based gel polymer electrolyte, respectively. FESEM image clearly shows the formation of homogenous material with high density while the EDX results reveal the presence and uniform dispersion of C, O, K elements, suggesting its effective crosslinking. Elemental mapping images of C, O, K elements of PVA-KOH-based gel polymer electrolyte are represented in Fig. 5c–f, respectively. Figure 5g depicts the pictures of the PVA-KOH membrane subsequent to air exposure after various time intervals ranging from 0–24 h. Figure 5h demonstrates the galvanostatic responses (@3 mAcm−3 ) of fabricated ZAB employing air-exposed (exposure time: 0, 2, 4, 6, 8 h) PVA-KOH gel polymer electrolyte membrane. It has been found that the cycling life decreases from 12.5 h to 1 h upon increasing the exposure time from 0 to 8 h. Wu et al. [32], compared the performances of alkaline ZAB and PVA/PAA polymer electrolyte-based AAB. The acrylamide-based polymer gel was also claimed to be an effective polymer electrolyte for flexible MABs [33]. Miao et al. [34], also reported PAM alkaline gel-based electrolyte for ZABs. Yu et al. [35], have demonstrated the fabrication of flexible sandwich structured AAB employing solidstate polymer alkaline gel electrolyte, Mn3 O4 catalyst incorporated CNFs acting as bending resistant cathodes prepared via direct electrospinning, Al metal as anode. The bending-resistant cathode was prepared as follows: initially, a mixture of MnO3 and DMF was ball milled using ZrO2 balls at 200 rpm for 2 min. The prepared suspension after removal of ZrO2 balls was dissolved in polyacrylonitrile (PAN) to form a precursor solution which was then undergoing magnetic stirring for 6 h at 60 °C to ensure the uniformity of the solution. This solution was utilized for electrospinning. After electrospinning, the electrospun fibers were got accumulated on the rotating drum of the electrospinning setup and were covered with nickel foam and air dried for 24 h. Figure 6a schematically illustrates the overall fabrication process of the air cathode using the electrospinning approach and Fig. 6b gives the sandwich design of AAB. The obtained films undergo a heat treatment where it was hot pressed at 230 °C with 200 MPa pressure for 30 min followed by carbonization at 900 °C under an Ar atmosphere (heating rate: 5 °C/min for 1 h). This heat treatment ensures the creation and encapsulation of Mn3 O4 in CNFs. Figure 6c and d show the SEM images of electrospun CNFs before and after heat treatment, respectively,

376

A. Agrawal

Fig. 5 FESEM (a) and EDX (b) profiles of PVA-KOH based gel polymer electrolyte. c–f Elemental mapping images of C, O, and K of PVA-KOH based gel polymer electrolyte. g Pictures of PVAKOH membrane subsequent to air exposure after various time intervals ranging from 0–24 h. h Galvanostatic response of of fabricated ZAB employing air exposed (exposure time: 0, 2, 4, 6, 8 h) PVA-KOH gel polymer electrolyte membrane at 3 mAcm−3 . Adapted with permission [31]. Copyright (2019) Copyright The Authors, some rights reserved; exclusive licensee [The Authors]. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

which clearly show a little rougher surface with a reduced diameter (250 nm) of carbon nanofibers after heat treatment as compared to CNF (400 nm) without heat treatment which is a consequence of decomposition of PAN. They have also examined the current density-dependent rate discharge performance and galvanostatic discharge performances at 2 mAcm−2 of the fabricated AAB as shown in Fig. 6e and f, respectively. Rate discharge curves clearly show stable voltage plateaus at 1.72 V to 1.08 V, indicating excellent stability of AAB. From Fig. 6f, the specific capacity at 2.0 mAcm−2 was found to be 1273 mAhcm−2 . Planar sandwich structured ZAB was also reported by Fu et al. [36], utilizing Zn anode, PVA-based polymer electrolyte, and LaNiO3 /NCNT filled carbon cloth as cathode, with an excellent energy density of 581 Wh kg−1 at 25 A kg−1 . Highly flexible and durable ZABs were fabricated by Li et al. [37], using near-neutral polymer electrolytes. Wang et al. [38], have designed an all-solid-state flexible ZAB with alkaline anion polymer as an electrolytic membrane. Highly stretchable water-resistant ZAB was also reported to be obtained from polymer-based double network hydrogel electrolytes [39]. Dual network hydrogel also serves as an electrolyte to fabricate highly stretchable ZABs [40]. Zhou et al. [41], demonstrated the use of CO2 -ionized PVA electrolyte for ZAB. Organohydrogel electrolytes and sodium polyacrylate hydrogel electrolytes were also reported for quasi-solid-state ZABs and solid-state ZABs [42]. Tran et al. [43], investigated the electrochemical performances of ZAB

Polymer Materials for Metal-Air Battery

377

Fig. 6 a Schematic representation of the overall fabrication process of the air cathode using electrospinning approach. b Sandwich design of AAB. c, d SEM profiles of electrospun fibers before and after heat treatment, respectively. Current density dependent rate discharge performance e and galvanostatic discharge responses at 2 mAcm−2 of the fabricated AAB (f). Adapted with permission [35]. Copyright (2020) Copyright The Authors, some rights reserved; exclusive licensee [MDPI, Basel, Switzerland]. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

with alkaline gel polymer-based electrolytes. The same group has also systematically studied the composition effect of gel polymer-based electrolytes for ZAB [44]. Recently, Chen et al. [1], reported MXene, a biodegradable polymer electrolyte for rechargeable ZAB which facilitates enhancing the durability of the battery. Polymeric materials can also be exploited as separators for various MABs. Hwang et al. [45], reported a separator membrane made up of polymerized ionic liquids to effectively improve the life and cycle stability of ZAB. They have employed this membrane on a selective ion transport channel. Such polymer-based selective ion transport channel has also been discussed by Kim et al. [4]. Elia et al. [5], have discussed the applicability of tetra glyme-based electrolytes for Li–O2 batteries and have also examined the effect of electrolytes on the carbon electrode during the operation of Li–O2 battery. Abrahim and Zhang [46], reported a sandwich-structured Li–O2 battery consisting of Li metal foil acting as an anode, carbon composite air cathode, and Li+ conductive PAN polymer-based electrolyte membrane. The polymer-based electrolyte membrane was prepared by heating a mixture of PAN, ethylene carbonate, propylene carbonate, and LiPF6 at 135 °C until a uniform homogenous solution is obtained. This homogenous solution was then sandwiched between the Teflon-coated

378

A. Agrawal

stainless-steel mesh and finally rolled to get membranes. The fabricated Li–O2 battery is highly rechargeable with an open circuit voltage ~ 3 V. Fabrication of sandwich-structured LAB comprising of a composite anode made up of reduced graphene oxide and Li metal, air cathode, and LiI and SiO2 -based gel polymer electrolyte was demonstrated by Guo et al. [47]. The gel polymer electrolyte also serves as a protective shield for the anode and exhibits excellent ion conductivity (1.01 mScm−1 ) with flame-resistant properties. SiO2 -based gel polymer electrolytes when utilized for MABs; aim to improve their functionalities even at high temperatures and hence facilitate flame-resistant characters. Similarly, SiO2 -based gel polymer electrolyte was also employed by Hu et al. [48], for constructing Na– CO2 batteries. Gel polymer electrolytes with ionic liquids have also been reported to be a potential candidate to fabricate a quasi-solid-state Li–O2 battery [49]. Li–O2 batteries with huge reaction zone employing polymer electrolytes have also been demonstrated [50]. Although polymers have been immensely employed as electrolytes in MABs, there still exist several shortcomings that one has to look at before utilizing them for the fabrication of MABs. Such restrictions include low ionic conductivity, interfacial contact issues between the electrodes and electrolytes, electrode wettability, etc. To circumvent such shortcomings, it is better to incorporate some dopants so that the crosslinking can be improved or polymer blending can also opt.

3 Conclusions In conclusion, polymeric materials employed either in the form of electrode/separator material or electrolyte have significantly encouraged the progress of MABs. Though the MABs were initially developed using aqueous/alkaline electrolytes, there exist several limitations such as dendrite formation, interfacial matching, metal electrode corrosion, etc. that hinder their large-scale production with high performance. All such issues can be circumvented by employing polymeric materials for the fabrication of MABs. Appreciable advancements in this field ensure the excellent control of metal corrosion with broad electrochemical windows. In this chapter, encouraging outcomes based on the utility of various polymeric materials for electrodes/ separators/electrolytes for MABs have been presented. However, additional efforts are still required to realize the commercialization of superior MABs. Continuous innovative efforts in the field along with technological advancements will definitely lead to the development of excellent stability and performance of MAB systems.

Polymer Materials for Metal-Air Battery

379

References 1. Chen Z, Li W, Yang X, Ke C, Chen H, Li Q, Guo J, He Y, Guo Z, Liang X (2022) Gel polymer electrolyte with MXene to extend cycle lifespan of flexible and rechargeable Zinc-Air batteries. J Power Sources 523:231020 2. Kuo YL, Wu CC, Chang WS, Yang CR, Chou HL (2015) Study of poly (3, 4ethylenedioxythiophene)/MnO2 as composite cathode materials for aluminum-air battery. Electrochim Acta 176:1324–1331 3. Jia X, Wang C, Zhao C, Ge Y, Wallace GG (2016) Toward biodegradable Mg–air bioelectric batteries composed of silk fibroin–polypyrrole film. Adv Funct Mater 26:1454–1462 4. Elia GA, Park JB, Scrosati B, Sun YK, Hassoun J (2013) Investigation of the carbon electrode changes during lithium oxygen cell operation in a tetraglyme-based electrolyte. Electrochem Commun 34:250 5. Kim HW et al (2016) Artifcially engineered, bicontinuous anion-conducting/-repelling polymeric phases as a selective ion transport channel for rechargeable zinc–air battery separator membranes. J Mater Chem A 4:3711–3720 6. Fenton DE, Parker JM, Wright PV (1973) Complexes of alkaii metal ions with poly(ethylene) oxide. Polymer 14:589 7. Zhang Z, Zuo C, Liu Z, Yu Y, Zuo Y, Song Y (2014) All-solid state Al-air batteries with polymer alkaline gel electrolyte. J Power Sources 251:470–475 8. Lin C, Shinde SS, Li X, Kim DH, Li N, Sun Y, Song X, Zhang H, Lee CH, Lee SU, Lee JH (2018) Solid-state rechargeable zinc-air battery with long shelf life based on nanoengineered polymer electrolyte. Chem Sus Chem 11:3215–3224 9. Lizundia F, Kundu D (2021) Advances in natural biopolymer-based electrolytes and separators for battery applications. Adv Funct Mater 31:2005646 10. Fan X, Liu J, Song Z, Han X, Deng Y, Zhong C, Hu W (2019) Porous nanocomposite gel polymer electrolyte with high ionic conductivity and superior electrolyte retention capability for long cycle-life flexible zinc-air batteries. Nano Energy 56:454–462 11. Sun N, Lu F, Yu Y, Su L, Gao X, Zheng L (2020) Alkaline double-network hydrogels with high conductivities, superiormechanical performances, and antifreezing properties for solid-state zinc-air batteries. ACS Appl Mater Interfaces 12:11778–11788 12. Zhang S, Wang Y, Li Y, Wei M, Miao L, Wang K (2022) Hybrid double-network hydrogels of poly(acrylicacid) and κ-carrageenan for detachable solid Al-air batteries. POWER-D-2200504. https://doi.org/10.2139/ssrn.4055075 13. Gaele MF, Migliardini F, DiPalma TM (2021) Dual solid electrolytes for aluminium-air batteries based on polyvinylalcohol acidic membranes and neutral hydrogels. J Solid State Electrochem 25:1207–1216 14. Wang L, Liu F, Wang W, Yang G, Zheng D, Wu Z, Leung MK (2014) A high-capacity dualelectrolyte aluminum/air electrochemical cell. RSC Adv 4:30857–30863 15. Elia GA, Hassoun J (2015) A polymer lithium-oxygen battery. Sci Rep 5:1–8 16. Zhang J, Sun B, Ahn HJ, Wang C, Wang G (2013) Conducting polymer-doped polyprrrole as an effective cathode catalyst for Li–O2 batteries. Mater Res Bull 48:4979–4983 17. Li C, Liu D, Xiao Y, Liu Z, Song L, Zhang Z (2019) Mesoporous Co3 O4 -rods-entangled carbonized polyaniline nanotubes as an efficient cathode material toward stable lithium–air batteries. ACS Appl Energy Mater 2:2939–2947 18. Badam R, Shibuya M, Mantripragada BS, Ohira M, Zhou L, Matsumi N (2022) BIAN-based durable polymer metal complex as a cathode material for Li–O2 battery applications. Polym J 54:1355–1366 19. Cui R, Xiao Y, Li C, Han Y, Lv G, Zhang Z (2020) Polyaniline/reduced graphene .oxide foams as metal-free cathodes for stable lithium–oxygen batteries. Nanotechnology 31:445402 20. Deyab MA, Mohsen Q (2021) Suppressing corrosion and hydrogen gas evolution in aluminum– air batteries via conductive nanocomposites. J Power Sources 506:230171 21. Deyab MA, Mele G (2019) Polyaniline/Zn-phthalocyanines nanocomposite for protecting zinc electrode in Zn-air battery. J Power Sources 443:227264

380

A. Agrawal

22. Zhang S, Wang Y, Li Y, Wei M, Wang K (2022) Anticorrosion of hydrophobic membrane on aluminum electrode for alkaline quasi solid Al-air batteries. J Power Sources 545:231907 23. Jo YN, Kang SH, Prasanna K, Eom SW, Lee CW (2017) Shield effect of polyaniline between zinc active material and aqueous electrolyte in zinc-air batteries. Appl Surf Sci 422:406–412 24. Wang Z, Meng X, Wu Z, Mitra S (2017) Development of flexible zinc–air battery with nanocomposite electrodes and a novel separator. J Energy Chem 26:129–138 25. Kwon O, Hwang HJ, Ji Y, Jeon OS, Kim JP, Lee C, Shul YG (2019) Transparent bendable secondary zinc-air batteries by controlled void ionic separators. Sci Rep 9:1–9 26. DiPalma TM, Migliardini F, Caputo D, Corbo P (2017) Xanthan and κ-carrageenan based alkaline hydrogels as electrolytes for Al/air batteries. Carbohyd Polym 157:122–127 27. Masri MN, Nazeri MFM, Mohamad AA (2010) Sagogel polymer electrolyte for zinc-air battery. Adv Sci Technol 72:305–308 28. Zhang J, Fu J, Song XP, Jiang GP, Zarrin H, Xu P, Li KC, Yu AP, Chen ZW (2016) Laminated cross-linked nanocellulose/graphene oxide electrolyte for flexible rechargeable zinc-air batteries. Adv Energy Mater 6:1600476 29. Migliardini F, DiPalma TM, Gaele MF, Corbo P (2018) Solid and acid electrolytes for Al-air batteries based on xanthan-HCl hydrogels. J Solid State Electr 22:2901–2916 30. Liu Y, Sun Q, Yang X, Liang J, Wang B, Koo A, Li R, Li J, Sun X (2018) High-performance and recyclable Al-air coin cells based on eco-friendly chitosan hydrogel membranes. ACS Appl Mater Interfaces 10:19730–19738 31. Fan X, Liu J, Ding J, Deng Y, Han X, Hu W, Zhong C (2019) Investigation of the environmental stability of poly (vinyl alcohol)–KOH polymer electrolytes for flexible zinc–air batteries. Frontiers Chem 7:678 32. Wu GM, Lin SJ, Yang CC (2006) Alkaline Zn-air and Al-air cells based on novel solid PVA/ PAA polymer electrolyte membrane. J Membr Sci 280:802−808 33. Tan MJ, Li B, Chee P, Ge X, Liu Z, Zong Y, Loh XJ (2018) Acrylamide-derived freestanding polymer gel electrolyte for flexible metal-air batteries. J Power Sources 400:566–571 34. Miao H, Chen B, Li S, Wu X, Wang Q, Zhang C, Sun Z, Li H (2020) All-solid-state flexible zinc-air battery with polyacrylamide alkaline gel electrolyte. J Power Sources 450:227653 35. Yu Y, Zuo Y, Liu Y, Wu Y, Zhang Z, Cao Q, Zuo C (2020) Directly electrospun carbon nanofibers incorporated with Mn3 O4 nanoparticles as bending-resistant cathode for flexible Al-air batteries. Nanomaterials 10:216 36. Fu J, Lee DU, Hassan FM, Yang L, Bai Z, Park MG, Chen Z (2015) Flexible high-energy polymer-electrolyte-based rechargeable zinc–air batteries. Adv Mater 27:5617–5622 37. Li Y, Fan X, Liu X, Qu S, Liu J, Ding J, Han X, Deng Y, Hu W, Zhong C (2019) Long batterylife flexible zinc–air battery with near-neutral polymer electrolyte and nanoporous integrated air electrode. J Mater Chem A 7:25449–25457 38. Wang M, Xu N, Fu J, Liu Y, Qiao J (2019) High-performance binary cross-linked alkaline anion polymer electrolyte membranes for all-solid-state supercapacitors and flexible rechargeable zinc–air batteries. J Mater Chem A 7:11257–11264 39. Li M, Kong H, Liu C-S (2021) Small molecule-based supramolecular-polymer double network hydrogel electrolytes for ultra-stretchable and waterproof Zn–air batteries working from 50 to 100 °C. Energy Environ Sci 14:4451–4462 40. Ma L, Chen S, Wang D, Yang Q, Mo F, Liang G, Li N, Zhang H, Zapien JA, Zhi C (2019) Superstretchable zinc–air batteries based on an alkaline-tolerant dual network hydrogel electrolyte. Adv Energy Mater 9:1803046 41. Zhou Y, Pan J, Ou X, Liu Q, Hu Y, Li W, Wu R, Wen J, Yan F (2021) CO2 ionized poly(vinyl alcohol) electrolyte for CO2 -tolerant Zn-air batteries. Adv Energy Mater 11:2102047 42. Wang Q, Feng Q, Lei Y, Tang S, Xu L, Xiong Y, Fang G, Wang Y, Yang P, Liu J, Liu W, Xiong X (2022) Quasi-solid-state Zn-air batteries with an atomically dispersed cobalt electrocatalyst and organohydrogel electrolyte. Nat Commun 13:3689 43. Tran TNT, Chung H-J, Ivey DG (2019) A study of alkaline gel polymer electrolytes for rechargeable zinc–air batteries. Electrochim Acta 327:135021

Polymer Materials for Metal-Air Battery

381

44. Tran TNT, Aasen D, Zhalmuratova D, Labbe M, Chung HJ, Ivey DG (2020) Compositional effects of gel polymer electrolyte and battery design for zinc-air batteries. Batteries Supercaps 3:917–927 45. Hwang HJ, Chi WS, Kwon O, Lee JG, Kim JH, Shul YG (2016) Selective ion transporting polymerized ionic liquid membrane separator for enhancing cycle stability and durability in secondary Zinc-air battery systems. ACS Appl Mater Interfaces 8:26298–26308 46. Abraham KM, Jiang Z (1996) A polymer electrolyte-based rechargeable lithium/oxygen battery. Electrochem Soc 143 47. Guo Z, Li J, Xia Y, Chen C, Wang F, Tamirat AG, Wang Y, Xia Y, Wang L, Feng S (2018) A flexible polymer-based Li–air battery using a reduced graphene oxide/Li composite anode. J Mater Chem A 6:6022–6032 48. Hu X, Zhang Y, Wang P, Matios E, Li W (2022) Suppression of gas crossover and dendrite growth in sodium-gas batteries across a wide operating temperature range. ACS Nano 16:17965–17972 49. Jung KN, Lee JI, Jung JH, Shin KH, Lee JW (2014) A quasi-solid-state rechargeable lithium– oxygen battery based on a gel polymer electrolyte with an ionic liquid. Chem Commun 50:5458 50. Bonnet-Mercier N, Wong RA, Thomas ML, Dutta A, Yamanaka K, Yogi C, Ohta T, Byon HR (2014) A structured three-dimensional polymer electrolyte with enlarged active reaction zone for Li–O2 batteries. Sci Rep 4:7127

Polymeric Materials for Metal-Air Batteries Mansi Sharma, Pragati Chauhan, Dinesh Kumar, and Rekha Sharma

Abstract The growing demand for energy coincides with a growing need for sustainable energy alternatives. Storage systems are important mechanisms of future energy grids as they act as a buffer for intermittent and renewable energy sources. Therefore, it is crucial to design a modern electrochemical storage system that is advanced, efficient, and eco-friendly and combines it with resource abundance. These days, metalair battery (MAB) is gaining attention among these technologies and has recently been undergoing research. The advantages of metal-air batteries include the fact that they are eco-friendly, non-noxious, low cost, and will not harm the environment. A metal-air battery has become the most promising power storage system of the modern era with its high-power density. Aluminium air batteries, lithium-air batteries, magnesium air batteries, zinc air batteries, and sodium air batteries, are examples of the most conventional metal-air batteries. Several polymers are used in metal-air batteries, for instance, poly (vinylpyrrolidone), poly (vinyl chloride), poly (acrylonitrile), poly (vinylidene fluoride-co-hexafluoropropylene), and poly (vinylidene fluoride). In this chapter, we have assessed the most recent advances from a technical point of view and analyzed their practical and business implications. Several factors limit the progress of industrial-scale metal–air batteries, including the low number of cycles, low discharge rates, discharge products at the cathode, side reactions inside the battery, and lithium anode oxidation. The present chapter will discuss the upcoming perspective, important issues, applicability, and challenges in the presented developed field. Ongoing research to overcome these barriers is also discussed. Keywords Metal-air batteries · Electrolyte · Aluminium-air batteries · Lithium-air batteries · Magnesium-air batteries · Zinc-air batteries · Sodium-air batteries · Polymers M. Sharma · P. Chauhan · R. Sharma Department of Chemistry, Banasthali Vidyapith, Rajasthan 304022, India D. Kumar (B) School of Chemical Sciences, Central University of Gujarat, Gandhinagar 382030, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_22

383

384

M. Sharma et al.

1 Introduction Growing economic growth has led to significant increases in energy demand. The conventional non-renewable energy sources available on earth include coal, oil, and natural gas but these resources are scarce. Renewable energy sources are inherently intermittent and unreliable, and the time of peak energy production and demand are often mismatched. This poses a great challenge to the widespread implementation of renewable energy in the energy sector. Thus, the creation of new energy technologies is crucial for a sustainable civilization. To solve these problems, large-scale energy storage systems must be created to balance the load and reduce the peak of renewable energy output [1, 2]. Renewable energies like wind and solar have been created to ensure a secure and sustainable energy source. The only concern is that these energies are geographically limited and intermittent. Therefore, reliable electrical energy storage systems are necessary to ensure reliable and efficient power delivery. Innovative metal-air batteries, supercapacitors, and biofuel batteries are among the best possibilities for addressing energy storage demands. Due to their flexibility to fulfill a variety of grid functions and the absence of geological or geographic limitations, electrochemical systems have become one of the most popular energy storage technologies. There are various battery solutions, including lead acid batteries and lithium-ion batteries, which are highly efficient and popular with consumers. Different components of metal-air batteries are represented in Fig. 1. These batteries serve a wide range of purposes and are extremely useful in our everyday lives [3, 4]. Over the last two decades, lithium-ion batteries (LIBs) have dominated the global consumer market for rechargeable batteries. LIBs are most disadvantageous when considering a sustainable and renewable economy due to their high costs as well as concerns over fire hazards and environmental issues. The energy and power densities of LIBs could yet be increased even if they are effective in their current applications. It is also possible to store energy as lead acid batteries (LABs), but lead is poisonous and there is no established recycling sector for it. Improvements to LIBs and LABs are urgently needed because of the rising demand for electric cars. Despite several advantages and benefits, LIBs have numerous issues. It is fragile and would work better in a protected circuit. Additional than 30% more efficiency cannot be achieved. As a result, they are not particularly useful for transportation. The higher energy Fig. 1 The components in the metal-air battery (MAB)

Polymeric Materials for Metal-Air Batteries

385

capacity, cost-effectiveness, and environmental friendliness of metal-air batteries have also attracted significant attention [5]. A MAB is a form of electrochemical cell in which metal oxidation and air reduction take place. There are two parts to a MAB: an anode consisting of metal embedded in an electrolyte, and a cathode made up of air. Anodes can be made of a variety of metals, including alkali metals like lithium, potassium, or sodium, alkaline earth metals like calcium and magnesium, metalloids like silicon and aluminium, and transition metals like iron and zinc. Electrolytes may vary depending on the type of anode used from hydrous to non-hydrous. There is also a reduction electrode consisting of air, whose anode and cathode are separated by separators. Since cathodic oxygen provides a limitless supply of energy from the atmosphere and does not need to be stored, MABs are a unique energy storage method [6]. Several polymers are used in metal-air batteries for instance poly (vinylpyrrolidone), poly (vinyl chloride), poly (acrylonitrile), poly (vinylidene fluoride-cohexafluoropropylene), and poly (vinylidene fluoride). Additionally, different kinds of polymers, including polyvinyl alcohol (PVA)-polyethylene oxide (PEO)-glass fiber mat, poly (epichlorohydrin-co-ethylene oxide) P (ECH-co-EO), and PVA-poly (epichlorohydrin) (PECH) doped with KOH, were utilized as Zinc air batteries (ZABs) electrolytes in the beginning. Major technological obstacles have also been noted, and potential fixes have been addressed. It has also been discussed how to produce high-performance rechargeable MABsusing cutting-edge sophisticated manufacturing techniques, including 3D printing and laser processing [7–9].

2 History In 1932, Maiche sold its first commercial product, the non-rechargeable Zn air battery. Over the years, a lot of research and progress has been made in the field of MABs. Aqueous and non-aqueous protic batteries were developed as a result of this research. Early battery discoveries used aqueous electrolytes, anodic metals like magnesium, aluminium, and iron, and an air cathode. Non-aqueous electrolyte combinations were developed after the disadvantages of aqueous electrolytes were discovered. These batteries are affordable because they can use natural oxygen as the cathode source and inexpensive metals as the anode. A broad timeline of the history of metal-air batteries represents in Fig. 2. Since MABs have a higher heat capacity and power density than other parallel batteries, particularly for EVs, they seem to be one of the most promising candidates for upcoming requirements [10]. The most sophisticated type of primary and secondary cells are metal-air batteries. These batteries are occasionally categorized as fuel cells because air is always moving inside the cell in these batteries between the electrodes. The MAB is a neglected breakthrough that was created in 1878. Aqueous ZABs were the subject of the earliest known study inMABs, and they were created using cutting-edge techniques to be on par with modern batteries. A brief chronology from 1878 to 2019 was provided by Hao Fan Wang and Qing XV, along with an update on the state of MAB research. The

386

M. Sharma et al.

Fig. 2 The schematic representation shows the history of metal-air batteries

chemistry of metal-air batteries is still improving, and that is a positive development. Historically, the first Zn-air battery (ZAB) was proposed in 1878 [11].

3 A Range of Battery Types Commercial lithium-ion batteries (LIBs) are in high demand in the electronics sector, but they are only about three to thirty times as efficient as MABs in terms of energy density. The world has been fascinated with Li and Zn metals as anodic metals. There is a theoretical possibility that LIBs (with Li2 O2 as the discharge product) can exhibit higher values of energy density and specific heat capacity (11,429 Wh/kg and 3,860 mAh/g, respectively), and that their voltage can reach 2.96 V. Zn-air batteries (ZABs) are around five times more advanced thanLIBs in terms of theoretical energy density, with a figure of 1350 Wh/kg. Both lead acid batteries (LABs) and Zn-air batteries (ZABs) are far less expensive than lithium-ion batteries in terms of price. The other MABs also have their unique advantages if we look at them. For instance, aluminiumair batteries display the bulk volume capacity (8040 Ah/L) while sodium-air batteries display lower charge overpotentials. Chunlion Wang discussed the advancements in cathode, anode, and electrolyte production techniques as well as the advances made in terms of battery performance. It has been found that conventional alloys are better suited to be used as anode electrode materials than alloys with nanocomposites because they can reduce other secondary reactions and increase electrical discharge capability [12–14].

Polymeric Materials for Metal-Air Batteries

387

3.1 Zinc-Air Battery A ZABis the best choice for applications that require small currents, such as hearing aids. They are the only ones in this category that have been successful and commercialized as primary cells. Zinc-oxygen systems provide arguably the fastest and most dependable route to a functional secondary MAB, even though their shelf life and recharge capacity are constrained. The ZAB was the first battery in the MAB category to be created in 1878. Multiphase electrolytes were used to conduct the Zn deposition and the oxygen evolution reaction (OER), leading to the creation of a polymer electrolyte-based ZAB and a new dendrite-resistant ZAB. In addition to galvanostatic discharge and electrochemical impedance spectroscopy (EIS), X-ray diffraction and scanning electron microscope (SEM) were used to explore the electrochemical properties of these batteries [5].

3.2 Aluminium-Air Battery Electric vehicles (EVs) may make excellent use of the aluminium-air battery (AAB) as a power source. Theoretically, it has an energy density of roughly 8100 Wh/kg, which is incredibly high and far superior toLIBs. There is a new AAB with a non-aqueous organic electrolyte. It consists of tetra-butyl-ammonium fluoride trihydrate salt dissolved in non-aqueous solvents such as PC/TEG-DME, CAN, etc. Another form of aluminum-air battery uses standard 1-ethyl-3-methylimidazolium chloride, an electrolyte of alkali metal chloride (AlCl3 ), and electrodes of platinum or copper (Pt/C) for gas diffusion [15].

3.3 Sodium-Air Battery Sodium air batteries (SABs) have a high specific heat energy of 1683 Watts-hour/kg (theoretical value), making them a new class of MABs. SAB is used in transportation due to their high salt content, low cost, and eco-friendliness. Similar to other metalair batteries, SABs also contain an anode and a cathode, as well as an electrolyte with a separator inside the battery box. This study used EDS, XRD, SEM, and Raman Spectroscopy to investigate the electrochemical properties of sodium air batteries containing carbon fiber gas diffusion layer (GDL) and sodium triflate salt [15].

388

M. Sharma et al.

3.4 Lithium-Air Battery K. Abraham created the initial second-generation (rechargeable)LAB. It had an electrically conducting membrane with Li+ at the anode and an air cathode with carbon embedded in it. Maximum LABs, which are quite advanced compared to Li-ion batteries and have the potential to be a strong competitor for electrical energy storage systems (EES), may have the maximum energy density (about 3458-Wh/kg, theoretical values) in the MAB family. Since the oxygen electrode’s creation in 1996, extensive research has been done to increase its electrochemical reversibility [16].

3.5 Vanadium-Air Battery The (VO2 + /VO2 + couple) that the oxygen on the cathode substitutes for serves as the electrolyte in most cases. Vanadium air battery (VAB) might have a good shelf life and be completely refillable over a limited number of cycles. A vanadium air battery, also known as a redox flow battery, uses vanadium as the anode, air as the reduction electrode, and VOSO4 in H2 SO4 as the electrolyte [17].

3.6 Magnesium-Air Battery It consists of Mg in combination with reduced air at the cathode and anode. Activated carbon is typically the foundation of a reducing electrode. Based on the electrode position of the electrolyte material, Metal sheets, and an aquaphobic polymer layer are sometimes used along with catalysts. Finding the ideal electrolyte combination has been a crucial hurdle in the advancement of secondary magnesium batteries. Using SEM, FTIR, and EIS characteristics, we were able to illustrate and explain the electrochemical behavior of an ionic liquid that contained magnesium in a polymeric electrolyte. XPS, mass spectroscopy, and FTIR, techniques were used to characterize the discharge behavior of a magnesium-air battery using tri-hexyl (tetradecyl) phosphonium chloride as the electrolyte [18].

3.7 Potassium-Air Battery In 2013, Ohio State University developed potassium-oxygen batteries. In addition to being twice as capable of storing a charge as current lithium-ion batteries. Compared

Polymeric Materials for Metal-Air Batteries

389

to lithium-air batteries, these batteries might perform better. An additional potassium air battery under development uses KPF6 dissolved in the ether as the electrolyte. They demonstrated its electrochemical behavior using XRD and Raman spectroscopy [5].

3.8 Calcium-Air Battery Calcium is abundant in the earth’s crust compared to Na and Mg. The most prominent, best, and safest metals inMABsselection, calcium has been shown to have a wide range of applications when combined with an aqueous electrolyte. In 1988, researchers created a calcium air battery using binary molten salts of CaCl2 and Cao as solid electrolytes. Air batteries made of calcium have the potential to have a high electrical density at a lower production cost [19].

3.9 Si, Sn, Fe, and Ge-Air Batteries Fe, Ge, Sn, and Si are less popular metals in metal-air batteries. In 2015, Hyungkuk Ju showed a Tin air storage cell based on a solid electrolyte that operates at high temperatures (750 0 C). SEM and EDX element mapping studies were used to demonstrate the Sn’s potential for thermal oxidation at temperatures close to its melting point. The metal-air batteries proposed by Ein-Eli in 2010 used ionic liquids for electrolytes, air for cathodes, and silicon for anodic metals. They performed XPS, energy-dispersive X-ray spectroscopy, and scanning electron microscopy research to understand electrochemical behavior. The metal-air battery is based on Ge with a precise interfacial structure and an effective PGE structure was manufactured in 2013. A series of analyses were performed on their electrochemical properties using SEM, XPS, and X-ray diffraction and they utilized a hierarchical nanoporous anode. Fe has many advantages from the standpoint of battery design: it is strong and promises to deliver adequate energy per unit of mass. A lot of industrial research potential was available in the 1970s and early 1980s when iron-air batteries were combined with alkaline electrolytes. Iron-air batteries with alkaline electrolytes have a theoretical open-circuit voltage of 1.28 V and a theoretical specific heat energy of 764 Wh/kg [5, 20, 21].

4 Various Electrolytes in Metal-Air Batteries A crucial element of MABs is the electrolyte. The efficiency of batteries is a key component. Metal air systems each have their characteristics regarding the electrolyte. The selection criteria for electrolytes are represented in Fig. 3. According to

390

M. Sharma et al.

their electrolytes, MABs can be divided into two types traditionally. Water or moisture do not affect protic or aqueous electrolytes, whereas aprotic or non-aqueous electrolytes can be influenced by atmospheric moisture. Non-aqueous aprotic electrolyte frequently uses reactive metals in aqueous electrolytes. Different types of polymer electrolytes are represented in Fig. 4. In contrast to aqueous MABs, non-aqueous MABs are still in the early stages of development. Lithium, Sodium, and Potassium are three excellent examples [22].

4.1 Metal-Air Batteries Based on Non-aqueous Electrolytes 4.1.1

Electrolyte for Ionic Liquid

Ionic liquids are a type of electrolyte that is not water-based. There are two different kinds of cations present in them: • Big organic cations of organic and inorganic anions. • Organic solvent alkali metal ions, such as organic ethers, carbonates, and esters. A novel non-aqueous primary silicon air battery was created in 2010. A special form of air batteries using non-aqueous primary silicon as the electrolyte. The battery was designed with the following components: anode and cathode. Heavily doped silicon wafers as the anode. 1-ethyl-3-methylimidazolium oligofluoro hydrogenate [EMI (HF)2–3 F] ionic-liquid electrolyte as electrolyte and oxygen as well as air at the cathode. The resulting electrolyte exhibits low corrosion, and the typical cell potential ranges from 0.8 to 1.1 with current densities of 10 to 300 A/cm2 . Significantly a nonaqueous aluminium-air system contains an electrolyte-based battery with 1-ethyl-3methylimidazolium oligo fluoro hydrogenate, which is non-aqueous at room temperature. It produces 140 mAh/cm2 and 1.5 mA/cm2 current density, and 25 A/cm2

Fig. 3 Schematically represents the criteria for electrolytes

Polymeric Materials for Metal-Air Batteries

391

Fig. 4 The schematic flow chart represents the polymer electrolyte on a different basis

corrosion current is observed for aluminium corrosion. High stability and minimal corrosion rates are demonstrated by the results of the linear polarisation experiment. In 2014, Ravel et al. used an EMI AlCl3 ionic liquid electrolyte for an Al air battery that was operated at room temperature. The capacity of this battery is 71 mAh/cm, and it has a low self-discharge rate. As part of his research in 2017, Deyab utilized 1-Allyl3-Methylimidazolium bis (trifluoromethylsulfonyl) imide (IL) in alkaline medium (4.0 N NaOH) for ionic liquid measurements. The resulting electrolyte reduces the rate of H2 gas evolution and corrosion while increasing the capacity density to a maximum of 2554 mA/g [23, 24].

4.1.2

Solid Electrolyte

Solid-state electrolytes differ from aqueous electrolytes in that they possess both wettability and conductivity. A solid electrolyte made of AlCl3 , urea, and glycerin was used to construct a rechargeable secondary aluminium air system. Aluminium chloride served as the anode, and polyvinylidene difluoride (PVDF) and titanium nitride (TiN) were combined to create the air cathode. This combination was flattened using a pelletizer at a pressure range of 4351 psi and then employed as the cathode. They asserted that various analyses, including XPS, scanning electron microscopy, and EDX, had demonstrated that the battery’s by-products, aluminium oxide, and aluminium hydroxide, were not produced. Additionally, it had been demonstrated that a stable electrochemical reaction was occurring because an active surface layer was present, which they claimed prevented these by-products from forming. Ionic liquids, sulphones, sulphoxides, amides, nitriles, esters, and alkyl carbonates, are only a few examples of the several solid electrolytes. A ceramic, solid electrolyte-based sodium-air battery with Na3 Zr2 Si2 PO12

392

M. Sharma et al.

(NASICON, a sodium superionic conductor) was also created. The exclusive technique for an oxygen transport type battery for Mg-air solid oxide batteries was disclosed by Atsushi Inoishi. This battery used Ca-stabilized ZrO2 as an electrolyte [25, 26].

4.1.3

Biopolymer/composite/polymer/electrolyte

A plasticized polymer electrolyte with a polyacrylonitrile (PAN) base was used to create the non-aqueous and polymeric electrolyte used in Abraham and Jiang’s (1996) secondary (rechargeable) LAB. Lithium ions are transferred from the Li anode to the oxygen cathode during the discharge process, which can be halted by employing plasticized polymers based on polyacrylonitrile as a separator and an electrolyte that will protect the cathode from the anode and electrolyte medium. Batteries with polymeric electrolytes are particularly well suited for small portable devices. Znair batteries were made using the basic glass-fiber-mat composite polymer electrolyte PEO-PVA, which has outstanding (1.2 V) electrochemical stability as well as mechanical strength in the solid state [27]. The cathode and electrolyte of mg air batteries were made of biocompatible conducting polymers. Choline nitrate (ClNO3 ) is encapsulated in the chitosan and is a highly biocompatible biopolymer to create a biocompatible electrolyte. The battery is more mechanically stable because of the natural polymer electrolytes, which also have higher ionic conduction of 8.9 × 10–3 S/cm. An overall volumetric energy capacity of 3.9 W/L is produced by the battery when it is assembled. This battery is used in medical intensive care devices like patient cardiac pacemakers. Most of the solid-state Aluminium-air batteries utilised a basic gel electrolyte based on polyacrylic acid (PAA). Mg-air batteries were also discovered. It has a biologically compatible cathode. It is made of polypyrrole-para (toluene sulfonic acid) and a biologically compatible electrolyte made of ClNO3 , both of which are embedded in the biopolymer chitosan. According to the study, a poly (vinylidene fluoride-hexafluoro propylene) polymer-based complex gel electrolyte with Al-doped Li0.33 La0.56 TiO3 particles shielded by silicon oxide (SiO2 ) film was created for Li-air batteries [28]. A flexible Zinc-air sandwich battery with a distinctive permeable shaped polyvinyl alcohol (PVA)-based nano-complex polymer electrolyte was created with the addition of SiO2 (GPE). This robust, free-standing gel polymer electrolyte (PGE) for aluminium-air batteries and zinc-air batteries exhibits great tensile strength and higher conduction of ions. An innovative paper Al-air battery was created that may prevent corrosion, simplify the battery system, and require less electrolyte storage. Its low production cost is a significant benefit. An affordable, dense, adaptable cotton-based aluminium-air battery with great implementation, simplicity, as well as compactness was also created. An ethylene oxide-based polymer electrolyte and molten sodium make up the single aprotic rechargeable sodium-air battery [29].

Polymeric Materials for Metal-Air Batteries

393

4.2 Metal Air Batteries Created on Aqueous Electrolyte There is a significant limitation to using Li metal with aqueous electrolytes due to its tendency to react violently with water. An electrode of Li was covered with a layer of glass ceramic in two thousand four. This prevented the metallic electrode from interacting with water while yet permitting the necessary electrochemical reaction. It is LiOH.H2 O instead of Li2 O2 that is responsible for discharge in alkaline aqueous electrolytes. In these systems, the separator-anode interface appears to be where LiOH.H2 O precipitates. This decreases the possibility of the cathode’s pores clogging in any way. This was found in aprotic lithium-air batteries [30].

4.2.1

Alkaline Electrolyte

To increase the application of AA5052 aluminium-air batteries, ethylene glycol is mixed with dicarboxylic acids such as C4 H6 O4 for the electrolyte additives and C6 H10 O4 as the electrolyte for the electrolyte additives. The development in battery electrolytes has led to improvements in Zn-air batteries which vary from non-aqueous electrolytes and aqueous electrolytes that contain ionic liquid electrolytes, solid polymer, as well as combined electrolytes. The problems with alkaline electrolytes or the ability of solution for ZABs are also discussed. They propose a protic basic electrolyte containing KOH, KF, and K2 CO3 that is saturated with ZnO [30].

4.2.2

Hybrid Electrolyte

Zinc air battery performance has been improved by using hybrid electrolytes that include ionic liquid electrolytes, aqueous electrolytes, non-aqueous electrolytes, and solid polymer electrolytes.

4.2.3

Room Temperature Ionic Liquid (RTIL)

It is a melted compound that sustains its liquid state at room temperature or lower than when it is used in aqueous metal-air batteries. These are highly thermally stable and do not easily catch fire. Consequently, gained more awareness as a replacement for alkaline electrolytes. It was demonstrated that adding water to the room-temperature ionic liquid electrolyte (RTIL) used in Zn-air batteries had a positive impact on ionic interaction. The zinc-air system utilizes a molten Li0.87 Na0.63 K0.50 CO3 eutectic electrolyte [31].

394

4.2.4

M. Sharma et al.

Quasi-Solid Flexible Electrolyte

Alkaline aqueous electrolyte with polymers is used in general as a quasi-solid versatile electrolyte. Researchers developed a superhydrophobic quasi-solid electrolyte (SHQSE) for LABs to avoid dendrite growth in moist conditions. It was also possible to create a battery system with an electrolyte based on gel polymer based on gelatin in a basic form. This adaptable ZABs cable type has successfully operated with an exterior load in the past [32].

5 Fundamental Concepts of Polymer Electrolytes The natural or synthetic materials that make up polymer electrolytes (PEs) are made up of a liquid electrolyte that is spread in a matrix of high molecular weight polymer that may transport charged species. In addition to solid-state batteries and flexible batteries, their thin film capacity has made them useful. They can be utilized directly as separators, and electrolytes in electrochemical devices. The viscoelastic or simply flexible properties of polymers are mixed with the amorphous features of liquid electrolytes in the PEs, which have an impact on both mechanical and electrochemical properties. Large-scale production of PEscould be accomplished using a variety of well-developed production processes due to the polymeric materials’ excellent workability and ease of processing [33]. Additionally, the polymer matrix’s architecture is incredibly adaptable, making it promising to change the pore size of polymer electrolytes by selecting particular beginning components like cross-linkers, polymers, monomers, and as well as by utilizing co-polymerization. A few flaws must be fixed with PEs, including their diminished mechanical ability, electrode wettability, insufficient electrolyte/ electrode interfacial contact low ionic conduction, as well as ion transfer coefficient. Examples of common techniques employed by researchers to get around these constraints include polymer blending, improving cross-linking, including dopants, and adding plasticizers or inorganic fillers [34]. The preparation of PEs used in Al-air batteries has been achieved using a variety of preparation methods, including mixing at ambient temperature, solution casting, freeze–thaw processes, and UV photopolymerization. Physical or chemical crosslinking is used to create the matrix of PEs. A cross-linking is created by forming weaker interactions, such as hydrogen bonds and ionic bonds, to enhance the material’s pliability and self-healing abilities. A cross-linking agent is required for chemical cross-linking, which creates irreversible and strong covalent bonds that offer mechanical power. Using the solution casting approach, for example, it is possible to create physically cross-linked PEs by merely combining the polymer with the liquid electrolyte. Conversely, chemically cross-linked polymer electrolytes (PEs) are often made from a precursor combination that includes a cross-linker, an initiator, and a

Polymeric Materials for Metal-Air Batteries

395

monomer or polymer. Usually, ammonium persulfate (NH4 )2 S2 O8 (APS) or potassium persulfate K2 S2 O8 (KPS) were utilized as initiators, and triallyl amine or MBA and (N, N' -methylene-bis(acrylamide)) were used as cross-linkers [35, 36]. One of the criteria affecting the stiffness of the polymer electrolyte during chemical cross-linking is the degree to which the polymer matrix is cross-linked. It can be modified by adjusting the cross-linkers concentration. The material’s mechanical strength increases with increasing cross-linking density. The electrolyte/electrode interface must be optimized to guarantee even a sufficient contact.

6 Gel Polymer Electrolytes An electrolyte based on gel polymer is a framework of cross-linked polymers in three dimensions (3D) that include a significant quantity of liquid electrolytes within their interstices and are categorized as quasi-solid polymer electrolytes. The polymer matrix’s capacity to absorb liquid allows it to swell without disintegrating. The term “hydrogel” refers to polymer gels if the solvent is an aqueous, alkaline, acidic, as well as salty solution. Hydrogels can hold water because polar hydrophilic groups are present like SO3 H (carrageenan), COOH (PAA, xanthan), NH2 (chitosan, PAM), OH (xanthan, carrageenan, agarose, PEO, and PVA), and along polymer chains. These functional groups serve as cross-linking active sites whose bonds are strong enough to prevent matrix dissolution as well as to have a strong propensity for absorbing water. In the end, the molecular system that permeates the whole volume serves as a matrix, allowing it to manage the absorption of water as well as support the swelled form of the meshwork [37]. While gel polymer electrolytes (GPEs) have several distinguishing qualities, including fluffiness, softness, viscoelasticity, and hydrophilicity. The swelling feature is one of the most significant ones. Additionally, they offer versatility, which is a growing development priority, particularly for wearable devices. GPEs provide several benefits over aqueous solutions, including increased safety, excellent wettability toward electrodes, higher ionic conductivity, the ability to reduce the dendritic formation of metal anodes, and the potential to expand the electrochemical stability window. They may occasionally have weak mechanical strength [38].

7 Solid Polymer Electrolytes In comparison to GPEs, solid polymer electrolytes (SPEs) contain fewer liquid electrolytes and typically take the form of membranes. Polymers, initiators, and crosslinkers are typically present in viscous solutions that are used to prepare SPEs. A thin solid electrolyte is created by evaporating the solution after it has been cast in molds. Compared to GPUs, they have higher mechanical strength and rigidity and can also function as separators.

396

M. Sharma et al.

The ionic conductivity of SPEs may be lower, and there may not be enough electrolyte/electrode contact at the interface. This explains why electrochemical devices sometimes use SPEs immersed in electrolyte solutions. SPEs have distinct advantages due to their unique characteristics, including superior thermal and electrochemical stability, increased safety, and leakproof properties in wearable electrochemical gadgets [39].

8 Composite Polymer Electrolytes Composite polymer electrolytes are a class of hybrid organic–inorganic electrolytes made of a chain of inorganic fillers like ZnO, SiO2 powders, glass fiber mats, and organic polymer macromolecules. Polymer crystalline structures are distorted by plasticizers such as ceramics, which enhance the plasticization process. Fillers are additionally applied in Lithium-ion batteries to weaken the connection between polymer chains, facilitating Li-salt dissociation as well as diminishing the Li+ coordination. Dinoto et al. go into great detail about the methods used to characterize the structure and electrical conductivity of Composite polymer electrolytes (CPEs) as well as the processes utilized to create them. Alkaline Zn -air and Li-air batteries are the primary research subjects for CPEs used in MABs. There have been reports of polymer electrolytes created with ZnO filler that was utilized in Al-air batteries as corrosion inhibitors [40].

9 Conclusion and Prospective Future In summary, metal-air batteries should be considered a system that stores energy for different technologies after the various aspects of metal-air batteries have been discussed and evaluated. Metal-air batteries are used in electrical vehicles and transportable electronics to store energy and control the flow of energy among renewable energy generators. It is cheaper to use an air cathode, and it can be electrolyzed with water or salt solutions in many cases. Consequently, metal-air batteries become less expensive, and we can operate the vehicle more economically. The environmentally sustainable nature of this battery will be enhanced by the use of green electrolytes and the use of less toxic metals as anodes. We must lower carbon emissions if we want a planet that can sustain life. Petroleum products emit substantial amounts of carbon dioxide into the atmosphere, which is why sources of renewable energy, like solar power, wind power, and hydropower, were developed. In 2030, over thirty-four million electric vehicles (including hybrid, plug-in hybrid electric vehicles (PHEVs), as well as battery electric vehicles (BEVs)) will be sold. As a result, more energy-storing devices are needed, which can potentially be used as power storage units. Cost-effective batteries must have elevated power density,

Polymeric Materials for Metal-Air Batteries

397

an extended shelf life, and be eco-friendly. Several MABs could be discovered in modern tools like electrically powered automobiles, connectors in hybrid electric vehicles, robotics, as well as storage devices for electric power. In recent years, electrochemical windows and control of anodic corrosion have experienced a rising trend of success. We hope to have given scientists helpful information for developing novel electrolytes for such exciting energy change technologies. The world that emits fewer CO2 emissions is the sustainable one. According to the International Energy Agency (IEA) . The number of electric vehicles on the road must reach fifty million by 2030 if we assume that we will reach the zero-carbon emission (0-CE) mark by 2050.

References 1. Rehman A, Ma H, Ozturk I, Ulucak R (2022) Sustainable development and pollution: the effects of CO2 emission on population growth, food production, economic development, and energy consumption in Pakistan. Environ Sci Pollut Res 1–12 2. Worku AK, Ayele DW, Habtu NG, Admasu BT, Alemayehu G, Taye BZ, Yemata TA (2022) Energy storage technologies; recent advances, challenges, and prospectives. In: Planning of hybrid renewable energy systems, electric vehicles and microgrid: modeling, control and optimization. Springer Nature Singapore, Singapore, pp 125–150 3. Bajolle H, Lagadic M, Louvet N (2022) The future of lithium-ion batteries: exploring expert conceptions, market trends, and price scenarios. Energy Res Soc Sci 93:102850 4. Olabi AG, Sayed ET, Wilberforce T, Jamal A, Alami AH, Elsaid K, Rahman SMA, Shah SK, Abdelkareem MA (2021) Metal-air batteries—a review. Energies 14(21):7373 5. Salado M, Lizundia E (2022) Advances, challenges, and environmental impacts in metal–air battery electrolytes. Mater Today Energy 28:101064 6. Wang HF, Xu Q (2019) Materials design for rechargeable metal-air batteries. Matter 1(3):565– 595 7. Olabi AG, Abbas Q, Shinde PA, Abdelkareem MA (2022) Rechargeable batteries: technological advancement, challenges, current and emerging applications. Energy 126408 8. Armand M, Axmann P, Bresser D, Copley M, Edström K, Ekberg C, Guyomard D, Lestriez B, Novák P, Petranikova M, Porcher W (2020) Lithium-ion batteries–current state of the art and anticipated developments. J Power Sources 479:228708 9. Liu Q, Liu R, He C, Xia C, Guo W, Xu ZL, Xia BY (2022) Recent progress on advanced polymer-based electrolytes in zinc–air batteries. eScience 10. Buckingham R, Asset T, Atanassov P (2021) Aluminum-air batteries: a review of alloys, electrolytes and design. J Power Sources 498:229762 11. Xu X, San Hui K, Dinh DA, Hui KN, Wang H (2019) Recent advances in hybrid sodium–air batteries. Mater Horiz 6(7):1306–1335 12. Placke T, Kloepsch R, Dühnen S, Winter M (2017) Lithium ion, lithium metal, and alternative rechargeable battery technologies: the odyssey for high energy density. J Solid State Electrochem 21:1939–1964 13. Shi X, Bi Y, Esan OC, An L (2022) Membranes for vanadium-air redox flow batteries. In: 60 years of the Loeb-Sourirajan membrane. Elsevier, New York, pp 155–175 14. Wang W, Lu YC (2021) The potassium-air battery: far from a practical reality? Acc Mater Res 2(7):515–525 15. Deyab MA, Mohsen Q (2021) Improved battery capacity and cycle life in iron-air batteries with ionic liquid. Renew Sustain Energy Rev 139:110729 16. Chawla N (2019) Recent advances in air-battery chemistries. Mater Today Chem 12:324–331

398

M. Sharma et al.

17. Yu Y, Gao S, Hu S (2021) Si modified by Zn and Fe as anodes in Si-air batteries with ameliorative properties. J Alloy Compd 883:160902 18. Wei W, Xu J, Xu M, Zhang S, Guo L (2018) Recent progress on Ge oxide anode materials for lithium-ion batteries. Sci China Chem 61:515–525 19. Gelman D, Shvartsev B, Ein-Eli Y (2019) Challenges and prospect of non–aqueous nonalkali (NANA) metal–air batteries. In: Electrochemical energy storage: next generation battery concepts, pp 127–168 20. Yu T, Yang X, Yang R, Bai X, Xu G, Zhao S, Duan Y, Wu Y, Wang J (2021) Progress and perspectives on typical inorganic solid-state electrolytes. J Alloy Compd 885:161013 ˙ 21. Siekierski M, Piszcz M, Zukowska G (2021) Electrolytes for metal-air batteries. In: Designing electrolytes for lithium-ion and post-lithium batteries. Jenny Stanford Publishing, Tayler and Francis, Abingdon, pp 215–291 22. Loupe N, Doan J, Gurau B, Smotkin ES (2017) Electrochemical energy storage: current and emerging technologies. In: Handbook of industrial chemistry and biotechnology, pp 1695–1727 23. Yan H, Zhang X, Yang Z, Xia M, Xu C, Liu Y, Yu H, Zhang L, Shu J (2022) Insight into the electrolyte strategies for aqueous zinc ion batteries. Coord Chem Rev 452:214297 24. Upasham S, Banga IK, Jagannath B, Paul A, Lin KC, Muthukumar S, Prasad S (2021) Electrochemical impedimetric biosensors, featuring the use of room temperature ionic liquids (RTILs): special focus on non-faradaic sensing. Biosens Bioelectron 177:112940 25. Lu J, Jaumaux P, Wang T, Wang C, Wang G (2021) Recent progress in quasi-solid and solid polymer electrolytes for multivalent metal-ion batteries. J Mater Chem A 9(43):24175–24194 26. Wang Y, Kwok H, Pan W, Zhang H, Leung DY (2019) Innovative paper-based Al-air batteries as a low-cost and green energy technology for the miniwatt market. J Power Sources 414:278–282 27. Pan W, Wang Y, Kwok HY, Leung DYC (2019) A low-cost portable cotton-based aluminum-air battery with high specific energy. Energy Proc 158:179–185 28. Tan MJ, Li B, Chee P, Ge X, Liu Z, Zong Y, Loh XJ (2018) Acrylamide-derived freestanding polymer gel electrolyte for flexible metal-air batteries. J Power Sources 400:566–571 29. Liu Q, Pan Z, Wang E, An L, Sun G (2020) Aqueous metal-air batteries: fundamentals and applications. Energy Storage Mater 27:478–505 30. Worku AK, Ayele DW, Habtu NG (2021) Recent advances and future perspectives in engineering of bifunctional electrocatalysts for rechargeable zinc–air batteries. Mater Today Adv 9:100116 31. Wu S, Yi J, Zhu K, Bai S, Liu Y, Qiao Y, Ishida M, Zhou H (2017) A super-hydrophobic quasisolid electrolyte for Li–O2 battery with improved safety and cycle life in humid atmosphere. Adv Energy Mater 7(4):1601759 32. Tan P, Chen B, Xu H, Zhang H, Cai W, Ni M, Liu M, Shao Z (2017) Flexible Zn–and Li–air batteries: recent advances, challenges, and future perspectives. Energy Environ Sci 10(10):2056–2080 33. Chen L, Li B, Zhu L, Deng X, Sun X, Liu Y, Zhang C, Zhao W, Chen X (2021) A PVA/ LiCl/PEO interpenetrating composite electrolyte with a three-dimensional dual-network for all-solid-state flexible aluminum–air batteries. RSC Adv 11(62):39476–39483 34. Zhao Q, Stalin S, Zhao CZ, Archer LA (2020) Designing solid-state electrolytes for safe, energy-dense batteries. Nat Rev Mater 5(3):229–252 35. Di Palma TM, Migliardini F, Gaele MF, Corbo P (2019) Physically cross-linked xanthan hydrogels as solid electrolytes for Al/air batteries. Ionics 25:4209–4217 36. Bashir S, Hina M, Iqbal J, Rajpar AH, Mujtaba MA, Alghamdi NA, Wageh S, Ramesh K, Ramesh S (2020) Fundamental concepts of hydrogels: synthesis, properties, and their applications. Polymers 12(11):2702 37. Miao H, Chen B, Li S, Wu X, Wang Q, Zhang C, Sun Z, Li H (2020) All-solid-state flexible zinc-air battery with polyacrylamide alkaline gel electrolyte. J Power Sources 450:227653 38. Ngai KS, Ramesh S, Ramesh K, Juan JC (2016) A review of polymer electrolytes: fundamental, approaches and applications. Ionics 22:1259–1279 39. Arya A, Sharma AL (2017) Polymer electrolytes for lithium-ion batteries: a critical study. Ionics 23(3):497–540

Polymeric Materials for Metal-Air Batteries

399

40. Gaele MF, Di Palma TM (2022) Polymer electrolytes for Al-air batteries: current state and future perspectives. Energy Fuels 36(21):12875–12895

Polymeric Materials for Flexible Batteries Aparajita Pal and Narayan Chandra Das

Abstract During the last decade innovative small-scale flexible batteries have stimulated significant attention worldwide. They possess a promising potential to act as alternative, renewable, green, and sustainable energy resources for the nextgeneration flexible and wearable devices. Their development is of critical importance to overcome key limitations in energy storage technologies; to improve the cell safety, stability, and cycle life; to ensure the smooth functioning of flexible electronic systems; to protect the environment and human health as well. Recently polymeric materials have emerged as auspicious candidates for these batteries due to their unique attributes, e.g., ease of processing, low cost, environmental friendliness, high flexibility, high strength, excellent conductivity, structural diversity, and versatility. Using conductive nanomaterials along with polymers is now a target of investigation which revolutionize the electrical and electronic industries over conventional nonflexible materials. The focus of this chapter is on the current research progress of polymeric materials and their composites with different nanomaterials to date in the context of their potential implementation in flexible batteries. Some major concerns and perspectives for future development are also highlighted which will help to give valuable insights into new research directions by designing and developing more promising, scalable, affordable, flexible, rechargeable, and wearable energy storage technologies. Keywords Polymer · Polymer/nanomaterial composites · Flexible battery · Flexible and wearable electronics · Energy storage

A. Pal · N. C. Das (B) Rubber Technology Centre, Indian Institute of Technology, Kharagpur, West Bengal 721302, India e-mail: [email protected] A. Pal e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_23

401

402

A. Pal and N. C. Das

1 Introduction An efficient electrochemical energy storage device is a primary requirement in the field of portable electronics. The current research is aimed at developing smaller, lighter, stretchable, and thinner batteries, to be used in smart, roll-on, or foldable displays, soft electronics, actuators, and wearable sensors. Developing intrinsically conductive flexible electrodes along with structural modification is the best approach. For developing an intrinsically conductive device, the influence of three components of the battery needs to be evaluated separately, i.e., electrodes, electrolyte, and separator. Firstly, the binder used in the electrode matrix and the adhesive to attach the electrode to the current collector is generally electrochemically inactive and cause a reduction in the conductivity and cyclic stability of the device. Secondly, liquid organic electrolytes despite having high ionic conduction, suffer from safety issues and leakage problems. And in the case of the solid-state electrolytes (SSE) in spite of being safer as no toxic organic solvent is used, are rigid and suffer from low ionic conduction. Recently different polymeric materials have emerged as predominant candidates for these flexible batteries due to their unique attributes, e.g., ease of processing, low cost, environmental friendliness, high stretchability, high strength, excellent conductivity, structural diversity, and versatility. Using conductive nanoparticles (NPs) embedded polymeric matrix is now a target of investigation which revolutionizes the modern era of energy harvesting devices. Nano additives include carbonaceous materials like graphene, carbon nanotube (CNT), carbon nano fibre (CNF) and activated carbon, different metal and metal oxide nanostructures, etc. The current chapter is focused on the study of intrinsically pliable yet conductive materials for application in flexible batteries. Various organic, inorganic, or biopolymer-based nanocomposite electrodes, gel polymer electrolytes, and semipermeable nanoporous membrane separators are mainly focused on in the current study.

2 Function of Polymer Materials in Flexible Batteries 2.1 Polymer Material as a Binder for Electrode The polymer binder acts as a cohesive agent between the active material and conductive additives. Based on the characteristics of the polymeric binder the morphology of the electrode, current conductivity, mechanical property, thermal resistance, and electrochemical performance of the device gets radically influenced. A low level of binder fails to maintain a co-continuous morphology. Hence, the obtained electrochemical conductivity of the electrode will be inferior. The factors like rheological properties, molecular weight of the polymer, presence of the polar and non-polar groups in the polymer backbone, etc. help in determining the preparation method of the electrode slurry, its stability, thermal resistance, and types of solvent used [1]. Furthermore, the distribution of filler particles on the binder matrix, i.e., the

Polymeric Materials for Flexible Batteries

403

microstructure of the slurry is also determined by the rheological data obtained. The distribution of the polymer binder on the active material depends upon the surface chemistry of the polymer material. Improper distribution can lead to failure to maintain sufficient adhesion between the active particles, causing a substantial increase in the internal resistance of the device. Polymeric binders can be broadly classified into three categories- synthetic, naturally derived, and conductive polymer based.

2.1.1

Synthetic Binder

Polyvinylidene fluoride (PVDF) is mainly used as a binder to maintain the structural integrity of cathode material in Li-ion batteries. Jeena et al. [2] has developed a copolymer-based binder poly (tert-butyl acrylate-co-triethoxyvinylsilane) or TBAco-TEVS to enhance the electrochemical performance of the silicon (Si) anode of the Li-ion battery. This ultimately improves the battery stability and increases the specific capacitance. Different random copolymers are synthesized varying the molar ratio of TBA and TEVS. Approximately 21% of TEVS in the copolymer generates superior performance along with stability for the Si anode. The specific capacitance of nearly 2551 mA h−1 is obtained over 100 cycles of charging-discharging. Moreover, upon heating at a certain temperature, the copolymer TBA-co-TEVS forms an interconnected crosslinked three-dimensional (3D) network. This helps in reducing the pulverization of the Si-particles. In another approach, a bio-derived acidic resin ‘rosin’ is used as an additive in the conventional PVDF binder. It is an eco-friendly material. This composite binder is used for Li4 Ti5 O12 (LTO) anode in Li-ion batteries. The addition of rosin forms new functional groups which are confirmed by Fourier Transform Infrared Spectra (FTIR spectra). Additionally, it leads to partial disruption of the crystallites, as observed with the melting temperature (Tm ) reduction from Differential Scanning Calorimetry (DSC) study. As the crystallinity of the polymer binder decreases, it becomes more flexible leading to better dispersion of the conductive additive and binder material. PVDF is a semi-crystalline material. Li-ion transport from this crystalline phase into the active material gets hindered, as parts of the active material are covered with the binder substance. Reduction in crystallinity due to the addition of rosin in the PVDF matrix helps in faster ion transport. At 40 wt.% of rosin additive in PVDF binder, the highest cyclic stability is obtained with a specific capacitance of 164 mAh g−1 at the 110th cycle [3]. In order to further improve the properties, lithium-polyacrylate (Li-PAA) polymer binder is developed mainly for alloy anode material. Linear PAA is an example of polyelectrolytes. Its aqueous solution is neutralized by adding strong bases (LiOH, NaOH, KOH etc.). Thus, the disarrayed colloidal solution is converted to structured gel. As a result, this gives an alternative way to form polymeric gels by neutralization of the aqueous solution of linear polyelectrolytes. The gel formed with linear PAA is reversible compared to the covalently crosslinked PAA gel [4]. In this study, water is used as a solvent to provide desired viscosity to the slurry during processing. The shape of the charging-discharging loops after multiple cycles remains the same

404

A. Pal and N. C. Das

indicating stability in electrochemical performance [5]. And after the 100th cycle, 60% of the initial capacity retains in the system. Polymethacrylic acid (PMA) and polyvinyl alcohol (PVA) are also widely investigated as binder materials. Due to the presence of surface functionalities, a positive effect is observed in suppressing the volume expansion of the electrode during the lithiation process. Besides, polyethylene oxide (PEO), poly (methyl methacrylic acid) (PMMA), polytetrafluoroethylene (PTFE), epoxy resin, poly (amic acid), etc. are also reported as potential candidates for the same category. The copolymer poly (isobutylene-alt-maleic anhydride) helps in reducing electrolyte decomposition in Li-ion batteries [6]. For Li–S battery amino groups containing binders are used as they can suppress the polysulfide dissolution. Hexamethylene diisocyanate polymerized with polyethyleneimine has been used as a binder material and is reported to obtain high cyclic stability for the Li–S battery [7]. However, the main issue with the synthetic binder is the use of toxic solvents which have raised serious environmental concerns.

2.1.2

Bio-derived Polymer as a Binder

Noerochim et al. have reported using CMC binder for composite conductive material. The device withstands an approximate capacity of 473 mAh g−1 for more than 100 cycles [8]. In another study, graphite is used as an anode material for Li-ion batteries. The graphite particles are pretreated with 0.5–1.5 wt.% gelatin. Gelatin is a polyelectrolyte material produced from the denaturalization of collagen and acts as an adhesive agent to maintain the cohesive force between small particles in aqueous dispersions. Here, gelatin-modified graphite particles are used as anode material and the subsequent effect on the electrochemical properties is examined [9]. Lignin is also evaluated as a binder material. It is reported that lignin can simultaneously act as a binder and conductive additive for Si-based negative electrodes in Li-ion batteries. The composite mixture of Si-nanoparticle (Si-NP) and lignin is coated on a copper substrate and heat treated at 800 °C [10]. At that high-temperature lignin undergoes some inner conformational changes or cyclization. Thus, a conductive additive is formed in situ by converting Si-lignin slurry to Si-carbon. Depending on the temperature and time of the treatment various microstructures are formed which further dictate the balance between gained conductivity and retained flexibility. Figure 1a shows the SEM micrograph of lignin-coated Si-NPs after heat treatment with a dimension in the range of 90–170 nm. The SEM image further confirms that the NPs form a well-connected network throughout the composite. From Fig. 1b–c, the High-Resolution Transmission Electron Microscopy (HRTEM) image indicates the crystalline Si-NPs are coated with a thin layer of the amorphous carbon layer. Further, Na-alginate also shows potential application as an electrode binder. The rheological property of Na-alginate is investigated based on the addition of different wt.% of conductive additives mainly graphite and carbon black [11]. The study displays promising results in terms of electrochemical performance and cyclic

Polymeric Materials for Flexible Batteries

405

Fig. 1 a SEM micrograph and b TEM image of Si-NP coated with Lignin after heat treatment c HRTEM image showing Si-NP. Adapted with permission [10]. Copyright 2016, American Chemical Society

stability. Different bio-based polysaccharides are investigated in order to observe their performance as a binder material for Si-anode in Li-ion batteries. Xanthan gum, guar gum, and agar [12] provide superior performance in terms of energy density and cyclic stability. To elaborate, xanthan gum has various functional groups like carboxyl, ester, and hydroxyl in the polymeric backbone. Therefore, it contributes to the availability of a larger number of active bonding sites for the active material, conductive filler, and the current collector, providing better integrity to the Si-anode under high volume change [13]. Polysaccharides also perform as a porous binder material. Chitosan is a linear polysaccharide, derived from the deacetylation process of chitin. The degree of deacetylation is mainly 60–100%. According to the work of Lee et al., chitosan

406

A. Pal and N. C. Das

is blended with epoxidized natural rubber to accommodate the uncontrolled expansion (variation of volume) of the Si-anode. The binder serves as an adhesive material as well as provides elasticity to the electrode. Chitosan helps in anchoring the Si particles and natural rubber provides a flexible matrix with high stretchability. The battery exhibits a specific capacity in the range of 1350 mAh g−1 after 1600 cycles of charging-discharging [14]. The protein-based binder material is also substantially studied [15].

2.1.3

Conductive Polymer as a Binder

Non-conductive polymers are insulating materials. However, conductive polymer additives act as both binder material and conductive filler. Poly(ethylenedioxythiophene) (PEDOT) is an optically transparent flexible conductive material. In case of Li-ion battery, it is reported to show inferior discharging capacity due to poor intercalation of Li-ions into the PEDOT matrix. However, in Li-air battery (Li–O2 ), the PEDOT matrix does not need to hold the Li-ion during the lithiation process, but it only helps in promoting a continuous electrically conducting surface for absorption and diffusion of oxygen and subsequent reduction phenomena [16]. PEDOT suffers from poor solubility which is further improvised by using a composite mixture of PEDOT: PSS-Poly(ethylenedioxythiophene): Poly(styrene sulfonate). This is called a composite polymer consisting of two ionomers. The composite is prepared by mixing aqueous sulfonated polystyrene with ethylenedioxythophene (EDOT) monomer. PEDOT: PSS composite has both high electrical and ionic conductivity. The range of electrical conductivity obtained is as high as 4600 S cm−1 . The presence of an oxygen atom in the PEDOT: PSS structure helps in forming string interaction with the polysulfides. It is reported to suppress the polysulfide shuttle in Li–S batteries through this mechanism. Additionally, a divalent Mg2+ ion is used which acts as a crosslinker for PSS in PEDOT: PSS system. The 3D crosslinked binder structure can withstand the volume change phenomena with lithiation and delithiation cycles. The initial capacity obtained is greater than 1000 mAh g−1 and subsequently, after 250 cycles as high as 74% retention of the capacity is observed through cyclic voltammetry at 0.5C rate [17]. Polyaniline (PANI) is another important conductive polymer material. It can act as a multifunctional binder for cathode material in Li–S batteries. In one approach, sulfur-loaded activated carbon composite is prepared for the cathode material where polyaniline as a binder material for the electrode adheres to sulfur and conductive carbon additive by van der Waals force or electrostatic interaction. Further, sulfuric acid-doped PANI is used as a binder material. The level of doping is determined using X-ray Photoelectron Spectroscopy (XPS) as 22%. To rate the overall performance of the device, the capacity retention using sulfuric acid doped PANI binder compared to conventional PVDF binder is increased by about 104%.

Polymeric Materials for Flexible Batteries

407

In a subsequent study, colloidal polypyrrole (PPy) is chosen as a conductive binder material. The polymerization of pyrrole is performed using cerium ammonium nitrate. As a result, the conductive colloidal PPy is prepared in a single step in dimethylformamide (DMF). Colloidal PPy- Si NP composite electrode helps in accommodating the large volume change issue of the Si-anode [18]. Further, colloidal PPy is used with PVDF and poly (vinylpyrrolidone) PVP to improve the cyclic stability of the battery.

2.2 Polymer-Based Flexible Electrodes for Battery Fabrication of flexible electrodes is challenging. Low active mass loading in the cell can cause poor electrochemical performance and early delamination of the active material. Hence, there is always needed to make a balance between the electrochemical performance and multiple flexing, compression, or stretching behavior. The flexible electrode architecture can be of three types—wave, spring, and Kirigami to achieve multidirectional stretchability [19]. Different polymer nanocomposite with various architectural design is further elaborated. Due to the large surface area and short pathways for mass transport the nanostructured conductive polymers have been considered very crucial to study for battery applications. Conductive polymers exhibit highly ∏-conjugated structures. The typical conductivities of the polymers are as follows, for polyaniline 0.01–5 S cm−1 , polyacetylene 3–1000 S cm−1 , polypyrrole 0.3–100 S cm−1 , polythiophene 2–150 S cm−1 , etc. In many applications PPy acts as a coating layer for different metal oxides in flexible electrode applications. The coating film either helps in protecting the metal oxide from oxidation or increases conductivity. Additionally, with the polymeric layer coating the composite electrode can prevent structural collapsing due to rapid volume change with every charging-discharging phenomenon. Polypyrrole (PPy) can be used as both a conductive additive or active material for flexible electrodes in batteries. PPy flexible films can be fabricated using the vapor phase polymerization method. Vapor phase polymerization is a simple, inexpensive, and scalable method. The high electrochemical performance is achieved due to layered arrangement of the pyrrole chains. This highly ordered structural characteristic of the PPy film is obtained due to following the vapor phase polymerization technique. PPy film based anodic material shows high specific capacitance in the range of 284.9 and 177.4 mAh g−1 in the case of Li-ion and Na-ion batteries respectively [20]. To impart higher conductivity the conjugated structure is subjected to further doping. The Li+ charge storage mechanism is performed by n-doping of PPy. The Li+ or Na+ is stored in the conductive polymer backbone. Due to the combination with oxygen atoms, Li–O, Na–O bond formation occurs. The ordered layered structure of PPy gets disrupted over the discharging process. During charging the Li–O and Na–O bond break and the ordered planar structure of the PPy polymer is restored. Here, it is reported that the d-spacing between the polymeric layer increases to accommodate intercalated ions and further restores during de-intercalation. It has

408

A. Pal and N. C. Das

a shape memory effect that can self-adapt according to the intercalated ionic radius. Hence, the device gives a stable electrochemical performance as there is no change occurring in the orderly structural arrangement of the polymeric chain layers of PPy under repeated charging-discharging process. Li-ion battery with the PPy composite electrode shows a stable discharging capacity of 216 mAh g−1 at a 10C charging rate after 1000 cycles with negligible capacity fading. During discharge, the cations Li+ or Na+ are stored in the spacing between the polymeric chains of PPy. The spacing plays a very crucial role in indicating the rate of intercalation, and de-intercalation process of the cations. For Na+ , the rate will be slow compared to the Li+ ion kinetics due to the large atomic radius of Na. In another study, PPy-reduced graphene oxide (rGO) composite film is introduced as an electrode material. By electrochemical reduction of graphene oxide, it is incorporated in PPy dopant. In the SEM micrograph, it is detected that the composite film possesses a wrinkled surface morphology with a porous structure. The porous structure contributes to a high surface area and can accommodate the volume swelling phenomena. The porous nature of the film is a result due to the physical nature of the graphene sheet. The composite porous film is further characterized using UV–visible spectroscopy, FTIR, and Raman spectra. The composite is used as a cathode material in flexible Li-ion batteries. It shows high-capacity retention and excellent cyclic stability [21]. In some applications, polythiophene as anode polymeric material and poly anthraquinone as cathode material are also introduced. But being expensive in nature they cannot be applied on a commercial scale. Polyaniline (PANI) is another conducting polymeric material that has been extensively studied due to its good redox reversibility, stability in cyclic performance, and easy synthesis method. CNT/PANI nanocomposite electrode material is investigated as flexible electrode material for Li-ion batteries. PANI nanoparticles are coated onto CNT film by an electrochemical deposition method. The importance of incorporating carbonaceous nanostructures like CNT, and graphene into the electrochemically active polymeric matrix is to further improve the resulting conductivity so that high energy density can be obtained. In another approach, a layer-by-layer synthesis method of polyaniline on a CNT sheet is analyzed for electrode application [22]. Layer by layer approach is chosen for flexible battery application. It consists of repetitive and sequential immersion of substrate into an aqueous solution of completely functionalized material. With this method, an ultrathin conformal electrode can be developed. Polyaniline nanofibers are fabricated by rapid polymerization of aniline monomer in a protonic (HCl) medium. Carboxylic acid functionalized multiwalled carbon nanotubes (MWCNTs) are used. This method can be described as a scalable production method for water-dispersible polyaniline nanofibre. From Fig. 2a, the surface atomic composition of the film as studied by XPS spectra gives the presence of carbon (88.6%), oxygen (9.5%), and nitrogen (3.7%). Further, in Fig. 2b, the N 1 s spectrum indicates that most of the nitrogen is in amine form. To improve the mechanical property in terms of tensile strength, bending, and compressibility, a heat treatment process is introduced. The composite film undergoes heat treatment at 180 °C for 12 h. The resulting material shows different pore morphology. Altered pore size helps in controlled interdiffusion of ions and increased conductivity

Polymeric Materials for Flexible Batteries

409

due to microstructural changes. The PANI/MWCNT composite electrode developed in this layer-by-layer technique displays a high power density 220 Wh g−1 and an energy density 100 kW g−1 . According to Ge et al. [23], a single-walled carbon nanotube (SWCNT)-PANIbased hybrid aerogel is synthesized for application in flexible free-standing electrodes. Aerogels are 3D network system that consists of several micro and mesodimensional pores. The ultra-porous nature of aerogel helps in creating a large specific surface area and a disordered open structure that can withstand high swelling during the lithium de-lithiation process due to better stress dissipation. Additionally, it can intake a high% of electrolytes. The ion transport resistance for the material is very low promoting faster diffusion. Here, the active materials are infiltrated into the aerogel template. Aniline is in situ polymerized within wet SWCNT hydrogel material. The study also observed the morphological evaluation of the PANI nanostructures from nanoparticles to porous nanofibers to nanoribbons. Owing to the inherent Fig. 2 a XPS spectra showing the surface atomic composition of the PANI/ MWCNT film b N 1 s spectrum. Adapted with permission [22]. Copyright 2011, American Chemical Society

410

A. Pal and N. C. Das

flexibility of the PANI nanoribbons and their double interpenetrating nature, the nanocomposite can be bent up to 180° without losing any significant aspect of its conductivity. The chemical nature of the growth of PANI nanoribbons on the SWCNT aerogel is characterized under FT-IR and UV–visible spectra. In another approach, textile fabric composite material is used as electrodes [24]. Functionalized polyterthiophenes are polymerized using the electropolymerization method on nickel or copper-coated polyester (PET) fabric. The coated fabric substrate shows high conductivity as well as high conformability with muscle movement. To compare the electrochemical performance of the flexible battery, another semirigid and rigid substrate (carbon mat and stainless-steel mesh) is also used for the electropolymerization of functionalized polyterthiophenes. Nickel or copper-coated non-woven PET fabric shows more even growth of the nano layer of the polymer film compared to the other substrates. Additionally, a fabric surface provides more roughness for adhering to the polymeric film, resulting in maintaining the integrity of the electrode during repetitive charging-discharging cycles. Paper-based electrode materials are another example of lightweight flexible batteries. In one similar study, MWCNT is inserted into an ethyl cellulose polymer matrix. The surface area is increased to a great extent ensuring high electrochemical performance. The composite electrode MWCNT/ ethyl cellulose shows a capacity in the range of 70–240 mAh g−1 at a charging rate of 0.1C. It also exhibits good capacity retention as over 50 cycles the device loses only 5% of its initial value [25]. 3D structured textile materials are most favorable for flexible energy storage device applications. According to Zhu et al. [26], a vanadium pentoxide (V2 O5 ) coated textile fabric is used as electrode material. The coating can be applied by either chemical vapor deposition (CVD), electrospinning, in situ growth, or hydrothermal method. In this study, hollow nanoparticles of V2 O5 are synthesized using the hydrothermal method. The as-synthesized nanolayer on the substrate increases the specific surface area of the electrode and creates more active sites for better storage of the Li-ions. The specific capacity has been significantly improved when these hollow nanoparticles are used instead of solid ones. Hollow particles have more void spaces which can incorporate easily the volume swelling of the electrode due to lithiation. It further helps in reducing the stress strain developed into the electrode due to the intercalation and de-intercalation process. It delivers a high specific capacitance of 222.4 mAh g−1 even after 500 charging and discharging cycles. Kirigami electrodes are fabricated mainly for deformable battery applications. This architectural design is achieved using an innovative printing method. The ink is made with proper viscosity and deposited on a polydimethylsiloxane (PDMS) template. A customized Kirigami soft PDMS template is used as a free-standing patterned electrode. It can be easily taken out upon drying. After lifting up, the electrode is placed on top of a micro fiber-based textile fabric which further undergoes heat-treatment for a permanent setting. The viscous ink is prepared by lithium titanium oxide nanoparticle, CNT, and PVDF scaffold mixing in an N-methyl2-pyrrolidone solvent system. The flow behavior of the ink is very crucial. The fabricated Kirigami electrode is tested under different mechanical stress- bending, stretching, and twisting [27].

Polymeric Materials for Flexible Batteries

411

The most potential innovation of this century is 3D printing technology. This shows great applicability in fabricating flexible electronics. The main challenge is formulating the printing ink as specific additives need to be introduced to maintain high conductivity along with the right viscosity. In general, printing ink consists of active material, a conductive filler, and binder material. The extrusion rate of the polymeric ink is controlled using a flow meter. Another crucial factor is controlling the barrel pressure. According to Praveen et al. [28], a self-standing electrode is fabricated using the 3D printing technique. Vapor phase-grown carbon fiber is used as a current collector for the electrode. The solid loading concentration in the printing ink is maintained at 80 mg mL−1 . As per the rheological study, the ink shows shear thinning behavior at a high shear rate which helps in uniform printing. The increase in PVDF content enhances the mechanical property but at a certain loss in conductivity values. The increase in polymer loading decreases the void spaces and blocks the ion diffusion pathways. In another study [29], a PDMS-based 3D sponge structured electrode is fabricated using the 3D printing technique. PDMS has great potential for stretchable battery applications, especially for wearable bio-monitoring devices. The high scale demand for health monitoring devices has skyrocketed the need for efficient wearable flexible batteries which are an integrated part of the system. Additionally, the wearable electrochemical device should perform consistently with minimum adhesion issues to the skin surface. However, with stable adhesion, biocompatibility is another primary requirement for developing skin-adhering bio-devices. PDMS is chemically inert and most suitable in terms of skin compatibility. In this study, the homogeneous loading of active material on PDMS is studied using SEM micrographs. The cross-sectional morphology of the sponge is also investigated to analyze the overall porosity in the structure, pore size, interconnectivity, and pore distribution in the matrix. Further, in a different approach, CNT/ PDMS composite is fabricated using the phase separation method. The pore size obtained is 30–50 µm. The PDMS composite porous electrode undergoes 70% stretchability on fracture strain. The specific capacitance of the device is obtained as 190 mAh g−1 based on the CNT loading.

2.3 Polymer Electrolytes for Flexible Battery Application Liquid electrolyte possesses the chance of leakage due to undergoing continuous mechanical stress–strain with the charging-discharging cycles. However, despite the risk of leakage, it has a high conductivity of 10–3 S cm−1 . They are generally nonaqueous in nature otherwise water can react with lithium. Another alternative is organic solvent-based electrolytes which ensure rapid diffusion of Li-ion through the electrolyte medium and stable solid electrolyte interface formation (SEI). One of the other primary requirements is that the electrolyte should withstand the normal operating voltage range without any deterioration. Electrolyte materials for flexible batteries can be divided into two broad categories based on their composition—solid polymer electrolyte (SPE) and gel polymer electrolyte (GPE).

412

2.3.1

A. Pal and N. C. Das

Solid Polymer Electrolyte (SPE)

Solid polymer-based electrolytes are mainly developed as they can be safer compared to liquid electrolytes. They are cost-effective, made using simple processing methods, non-flammable, lighter in weight, able to resist dendrite formation, and can withstand mechanical deformations. Solid polymers can act both as electrolyte and separator materials simultaneously. They are fundamentally composed of Li salts incorporated into a polymer (PEO, PMMA, PVDF, PAN) matrix. The most significant factor is the stable performance of the electrolyte under continuous volume change with a repetitive charging-discharging cycle. The commercialization of solid polymer electrolytes is quite challenging in the field of flexible, high-energy density Li-ion batteries. The limitation of SPE is unsatisfactory Li ion conductivity at room temperature. The nature of ion transport is based on the type of SPE used. For solvent-free SPE, the Li-ion transports through the amorphous region of the polymer matrix where the chain segmental motion occurs above the glass transition temperature. On the contrary, for solvent-based SPE which is mainly called gel polymer electrolyte (GPE), the ion transport occurs through the liquid phase, and the polymer phase acts as a host material. For example, in PEO, the crystalline and amorphous phases show co-existence. Here, the amorphous part mainly participates in ion conduction. The incorporation of additives is one of the several aspects of handling the issue of unsatisfactory conductivity with solvent-free SPE systems. Figure 3 depicts in situ synthesis of SiO2 nanospheres within the PEO matrix. The interaction between the nanospheres and the polymeric chains can be of two typeschemical bonding between the PEO polymer chain ends and the surface hydroxyl groups of the monodisperse SiO2 (MUSiO2 ) NPs and mechanical wrapping of PEO chains on the NPs during its growth. The additives can help in enhancing ionic transport, ion diffusion, high voltage stability, mechanical strength, and resistance to dendritic layer formation at the electrolyte–electrode interface. Ceramics as additives of SPEs can increase the ionic conductivity of the modified PEO electrolyte by one order of magnitude as compared to pristine PEO electrolyte material. Figure 4 shows the ionic conductivity of four different electrolyte systems with varying temperatures from 0 to 90 °C. Considerably high ionic conductivity is observed in the case of mechanically mixed PEO-fumed SiO2 CPE compared to pristine PEO (ceramicfree SPE). The sample with the incorporation of ex-situ synthesized MUSiO2 spheres in the PEO matrix is defined as ex situ CPE, showing further enhancement in performance due to a higher degree of monodispersity of MUSiO2 compared to fumed SiO2 particles. However, the in situ synthesized SiO2 -PEO CPE significantly facilitates ion transport compared to the other three electrolyte systems. At elevated temperatures (60 °C), its ionic conductivity value is observed as high as 10–3 S cm−1 which is analogous to the performance of liquid electrolytes [30]. Further, the incorporation of additives like Al2 O3 , SiO2 , TiO2 , ZrO2 , CNT, graphene, CNF, etc. is also reported. Besides, different functional additives are incorporated to impart special properties like flame retardancy, high voltage stability, thermal resistance, self-healing, and shape memory properties.

Polymeric Materials for Flexible Batteries

413

Fig. 3 Schematic diagram showing the decreasing ordered structure of PEO matrix due to synthesis of PEO-SiO2 composite polymer electrolyte (CPE) by in situ hydrolysis of tetraethyl orthosilicate (TEOS). Adapted with permission [30]. Copyright 2015, American Chemical Society

Fig. 4 Comparison of ionic conductivity of different electrolytes using Arrhenius plots. Adapted with permission [30]. Copyright 2015, American Chemical Society

2.3.2

Gel Polymer Electrolyte (GPE)

It can be fabricated by trapping metal-ion-containing solution in polymer gel type membrane of PEO, PVA, etc. The main advantage of using GPE is subsequent deterioration in the dendrite formation. GPEs can be prepared following hot pressing, electrospinning, and phase inversion methods. The liquid additives in GPEs can be categorized broadly into two types- organic solvents and ionic liquids. Common organic solvents namely ethyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, etc. are used as additive materials for GPE fabrication. On the contrary, ionic liquids are composed of molten salts in a liquid state where the positive and negative charges are bound electrostatically. According to the study of Liu et al. [31], a novel gel polymer electrolyte is developed based on pentaerythritol tetra

414

A. Pal and N. C. Das

acrylate (PETEA). PETEA-based GPE is fabricated by in situ gelation of precursor solution in a sealed container. 1.5 wt.% PETEA and 0.1 wt.% azobisisobutyronitrile (AIBN) initiator is used in the precursor solution. The electrolyte marks a high ionic conductivity in the range of 1.13 × 10–2 S cm−1 for Li–S battery. It also displays excellent rate performance and cyclic stability by overcoming the issue of solubility and the shuttle effect of the polysulfides.

2.4 Polymer Material as Separator Separators can be of different types—microporous polymeric film, nanocomposite membrane, non-woven fabric, and electro-spun nanofiber mat. In the wet spinning method, the combination of plasticizer-polymer dope is extruded at a defined flow rate, followed by coagulation in a non-solvent. The pore formation occurs due to phase separation forming polymer-rich and polymer-lean phases. Dry fabrication of the separator is performed through the melt spinning method. Another category is a non-woven textile fabric-based separator which is obtained by the random laying of fibers into a fiber mat structure. This method produces a uniform and mechanically stable separator membrane with 90% porosity. Micro or nanometer-sized fillers are incorporated into the polymer membrane to impart high mechanical strength, better wettability, thermal resistance, and selective ion diffusion capability. Polyolefins are widely used as a separator material for commercial Li-ion batteries. Polypropylene (PP) and polyethylene (PE) are mainly used in the monolayer separators where the pore size is 0.3–0.5 µm, and overall porosity is maintained at 30–40%. The large pore size helps in easy ion transport through the separator. However, it is reported that small pores with better interconnectivity and even distribution are more efficient in preventing any kind of internal short circuits between the two electrodes. Multilayer membrane for separator is another approach to enhance the safety issue of the device. It can be a bilayer (PE-PP) or trilayer (PE-PP-PE) composition which helps in a thermal shutdown of the cell. In the event of increasing temperature, PE melts due to its low melting temperature (Tm = 110 °C) collapsing the pores. It immediately blocks the Li-ion transport through the separator. Despite having so many benefits, polyolefins as a separator material can undergo thermal shrinkage resulting in internal short circuit generation. Different strategies are followed to improve the performance of the PE membrane. High surface area metal oxide nanoparticles like ZnO, SiO2 , TiO2 , etc. have been incorporated in the PE membrane. The modified PE membrane shows the ability to absorb impurities, enhance wettability with the electrolyte, and give a stable cyclic performance compared to pristine PE separator material. The nanostructures are mainly coated using the CVD method on the PE membrane surface which further increases its thermal resistance property. In another study, PE-PP sheath-core fiber is prepared by the air-laid method and then reinforced with nano silica to improve thermal stability. The nano-silica reinforced PE-PP nonwoven matrix as separator shows a reduction in thermal shrinkage value to 3% compared to 37% in commercially available Celgard® separator material. Besides

Polymeric Materials for Flexible Batteries

415

PP and PE, microporous sponge-like PVDF is also used as separator material which is fabricated using the phase separation method.

3 Conclusion and Future Perspective Polymeric materials have become an integral part of flexible battery applications. As discussed in the chapter, polymer materials are widely used in fabricating all three major parts of a battery- electrode, electrolyte, and separator. For binder material in electrodes, PVDF and carboxymethylcellolose (CMC) are cost-effective and the most commonly used material. They can also impart good cohesive force, better interaction with the electrolyte, and appropriate Li-ion transport. The surface chemistry of the polymeric binder is also modified in several approaches for better adhesion properties by improving its interaction through H-bonding or van der Waals force with the active materials. Bio-sourced materials, being sustainable, open a completely new horizon of study as a polymer binder material. Lignin, alginate, and chitosan are some of the principal biomaterials in this aspect. Future research needs more attention to analyze the usability of these biomaterials as a replacement for conventional ones. Besides, different conductive polymer-based binders are also explored as they reduce the need of separately using an active material. This is termed an eco-friendly approach as low active mass loading is required. In terms of electrolytes, the GPEs are more suitable for flexible battery applications showing stretchability along with high ionic conductivity. But there is always a safety concern that needs to be further addressed in future research. For separators, polyolefins are mostly used. However, they suffer issues such as thermal shrinkage which provides a wide field of opportunities for future research direction.

References 1. Costa CM, Lizundia E, Lanceros-Méndez S (2020) Polymers for advanced lithium-ion batteries: state of the art and future needs on polymers for the different battery components. Progress Energy Combust Sci 79 2. Jeena MT, Bok T, Kim SH, Perk S, Kim JY, Park S, Ryu JH (2016) A siloxane-incorporated copolymer as an in situ cross-linkable binder for high performance silicon anodes in Li-ion batteries. Nanoscale 8:9245–9253 3. Kim SJ, Lee BR, Oh ES (2015) Application of a bio-derivative, rosin, as a binder additive for lithium titanium oxide electrodes in lithium-ion batteries. J Power Sources 273:608–612 4. Masiak M, Hyk W, Stojek Z, Ciszkowska M (2007) Structural changes of polyacids initiated by their neutralization with various alkali metal hydroxides. Diffusion studies in poly(acrylic acid)s. J Phys Chem B 111:11194–11200 5. Li J, Le DB, Ferguson PP, Dahn JR (2010) Lithium polyacrylate as a binder for tin-cobalt-carbon negative electrodes in lithium-ion batteries. Electrochim Acta 55:2991–2995 6. Ku JH, Hwang SS, Ham DJ, Song MS, Shon JK, Ji SM, Choi JM, Doo SG (2015) Poly(isobutylene-alt-maleic anhydride) binders containing lithium for high-performance Li-ion batteries. J Power Sources 287:36–42

416

A. Pal and N. C. Das

7. Chen W, Qian T, Xiong J, Xu N, Liu X, Liu J, Zhou J, Shen X, Yang T, Chen Y, Yan C, Chen W, Xiong J, Qian T, Xu N, Liu X, Liu J, Zhou J, Shen X, Yang T, Chen Y, Yan C (2017) A new type of multifunctional polar binder: toward practical application of high energy lithium sulfur batteries. Adv Mater 29:1605160 8. Noerochim L, Wang JZ, Chou SL, Li HJ, Liu HK (2010) SnO2 -coated multiwall carbon nanotube composite anode materials for rechargeable lithium-ion batteries. Electrochim Acta 56:314–320 9. Bele M, Gaberscek M, Dominko R, Drofenik J, Zupan KY, Komac P, Kocevar K, Musevic I, Pejovnik S (2002) Gelatin-pretreated carbon particles for potential use in lithium ion batteries. Carbon 40:1117–1122 10. Chen T, Zhang Q, Pan J, Xu J, Liu Y, Al-Shroofy M, Cheng Y-T (2016) Low-temperature treated lignin as both binder and conductive additive for silicon nanoparticle composite electrodes in lithium-ion batteries. ACS Appl Mater Interfaces 8(47):32341–32348 11. García A, Culebras M, Collins MN, Leahy JJ (2018) Stability and rheological study of sodium carboxymethyl cellulose and alginate suspensions as binders for lithium ion batteries. J Appl Polym Sci 135:46217 12. Nur S, Zamri AM, Sulaiman MA, Ismail S, Masri MN (2017) Bacto-agar and commercial agar as binder for porous zinc anode. Solid State Phenom 264:136–139 13. He J, Zhong H, Wang J, Zhang L (2017) Investigation on xanthan gum as novel water soluble binder for LiFePO4 cathode in lithium-ion batteries. J Alloys Compd 714:409–418 14. Lee SH, Lee JH, Nam DH, Cho M, Kim J, Chanthad C, Lee Y (2018) Epoxidized natural rubber/ chitosan network binder for silicon anode in lithium-ion battery. ACS Appl Mater Interfaces 10:16449–16457 15. Choi DW, Choy KL (2020) Spider silk binder for Si-based anode in lithium-ion batteries. Mater Des 191:108669 16. Amanchukwu CV, Gauthier M, Batcho TP, Symister C, Shao-Horn Y, D’arcy JM, Hammond PT (2016) Evaluation and stability of PEDOT polymer electrodes for Li−O2 batteries. J Phys Chem Lett 7(19):3770–3775 17. Yan L, Gao X, Thomas JP, Ngai J, Altounian H, Leung KT, Meng Y, Li Y (2018) Ionically crosslinked PEDOT: PSS as a multi-functional conductive binder for high-performance lithium– sulfur batteries. Sustain Energy Fuels 2:1574–1581 18. Yayla I˙IA, Yuca N, Sezer E, Ustamehmeto˘glu B (2022) Colloidal polypyrrole as binder for silicon anode in lithium ion batteries. Energy Storage 4(4):e338 19. Islam J, Chowdhury FI, Raza W, Qi X, Rahman MR, Das J, Uddin J, Zabed HM (2021) Toward polymer composites based and architectural engineering induced flexible electrodes for lithium-ion batteries. Renew Sustain Energy Rev 148:111302 20. Yuan T, Ruan J, Zhang W, Tan Z, Yang J, Ma Z-F, Zheng S (2016) Flexible overoxidized polypyrrole films with orderly structure as high-performance anodes for Li-and Na-ion batteries. ACS Appl Mater Interfaces 8(51):35114–35122 21. Yang Y, Wang C, Yue B, Gambhir S, Too CO, Wallace GG (2012) Electrochemically synthesized polypyrrole/graphene composite film for lithium batteries. Adv Energy Mater 2:266–272 22. Hyder MN, Lee SW, Cebeci FÇ, Schmidt DJ, Shao-Horn Y, Hammond PT (2011) Layerby-layer assembled polyaniline nanofiber/multiwall carbon nanotube thin film electrodes for high-power and high-energy storage applications. ACS Nano 5:8552–8561 23. Ge D, Yang L, Honglawan A, Li J, Yang S (2014) In situ synthesis of hybrid aerogels from single-walled carbon nanotubes and polyaniline nanoribbons as free-standing, flexible energy storage electrodes. Chem Mater 26:1678–1685 24. Wang CY, Tsekouras G, Wagner P, Gambhir S, Too CO, Officer D, Wallace GG (2010) Functionalised polyterthiophenes as anode materials in polymer/polymer batteries. Synth Met 160:76–82 25. Tripathi B, Srivastava N, Sharma KB, Zagorskiy D, Katiyar RS (2017) MWNT/cellulose based nanocomposite electrodes for ultrafast flexible Li-ion battery. Macromol Symp 376:1700042

Polymeric Materials for Flexible Batteries

417

26. Zhu Y, Yang M, Huang Q, Wang D, Yu R, Wang J, Zheng Z, Wang D (2020) V2 O5 textile cathodes with high capacity and stability for flexible lithium-ion batteries. Adv Mater 32:1906205 27. Bao Y, Hong G, Chen Y, Chen J, Chen H, Song WL, Fang D (2020) Customized kirigami electrodes for flexible and deformable lithium-ion batteries. ACS Appl Mater Interfaces 12:780–788 28. Praveen S, Sim GS, Shaji N, Nanthagopal M, Lee CW (2022) 3D-printed self-standing electrodes for flexible Li-ion batteries. Appl Mater Today 26:100980 29. Liu W, Chen Z, Zhou G, Sun Y, Lee HR, Liu C, Yao H, Bao Z, Cui Y (2016) 3D porous sponge-inspired electrode for stretchable lithium-ion batteries. Adv Mater 28:3578–3583 30. Lin D, Liu W, Liu Y, Lee HR, Hsu PC, Liu K, Cui Y (2016) High ionic conductivity of composite solid polymer electrolyte via in situ synthesis of monodispersed SiO2 nanospheres in poly(ethylene oxide). Nano Lett 16:459–465 31. Liu M, Zhou D, He YB, Fu Y, Qin X, Miao C, Du H, Li B, Yang QH, Lin Z, Zhao TS, Kang F (2016) Novel gel polymer electrolyte for high-performance lithium–sulfur batteries. Nano Energy 22:278–289

Polymeric Materials for Nanobatteries Anurag Tiwari and Rajendra Kumar Singh

Abstract The demands for dimensionally small portable electronic devices are increasing rapidly. These demands can be extensively fulfilled by developing nanobatteries. Advancements in nanotechnology and nanobattery integrated systems can deliver high power and energy density in small spaces. Furthermore, it has a longer life, a shorter charging time, and better safety than traditional batteries. However, the miniaturization of batteries is a significant technological challenge in the development of nanobatteries. The use of nano-sized electrode materials and nanocomposite electrolytes plays a crucial role in nanobatteries. Solid electrolytes are a fascinating choice due to their good mechanical properties along with the high ionic conductivity of nanoparticles. Because of their flexibility, polymeric materials provide excellent contact between nano electrodes and electrolytes. The fabrication of nanobatteries by using polyaniline, polypyrrole, polythiophene, and other nano-structured conducting polymers leads to high-performance device applications. Moreover, nano-sized cathode materials such as LiMn2 O4 nanotubes, nano-LiCoO2 , sulfur-carbon nanocomposite, sulfur-conducting polymer nanocomposite, etc., and nano-sized Si, SnO, Sb, graphene, etc. as anodes are widely used in nanobatteries. The dimension of nanoparticles is comparable with the path length of diffusion during a redox reaction, which leads to reversible and efficient performance. This chapter contains a detailed investigation of the components of nanobatteries, such as electrolyte (nano-composite of polymer membranes and solid electrolyte) and electrode (cathode and anode) materials, which have the potential to overcome the shortcomings of conventional batteries like explosion risk due to volume expansion. The utilization of novel polymeric materials and nano-sized electrodes in nanobatteries is a revolutionary research aspect for next-generation device applications. Keywords Nanobatteries · Nanocomposite · Copolymerization · Nanofillers

A. Tiwari · R. K. Singh (B) Ionic Liquid and Solid-State Ionics Lab, Department of Physics, Institute of Science, Banaras Hindu University, Varanasi 221005, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_24

419

420

A. Tiwari and R. K. Singh

1 Introduction Due to advancements in the field of nanotechnology, there is increasing attention to miniaturized-sized electronic devices for producing power on demand. Lithium/ sodium and some other micro and or nano-sized batteries are potential candidates for this point of view. However, it is very difficult to fabricate a single such device having good performance parameters using lithium/sodium-based miniaturized batteries. Currently, there is a major dependency on portable electronic devices. To make it sustainable, a dimensionally small and compact power supply is needed. Shrinking the size of electrochemical power sources is useful to build portable devices and such energy storage systems are building blocks for technological development [1]. Advanced nanotechnology can lead the future of technological development due to the compact size of components and improved safety. For the electronic devices in the nano-size range, “nanobatteries” are the primary focus in the pharmaceutical and semiconductor industries. Nanobatteries, in contrast to conventional batteries containing harmful electrolytes, are typically fabricated with non-hazardous materials, making them another reason why they are considered environmentally friendly [2]. Nanobattery does not mean only nano-sized batteries, but also refers to enhancing the macroscopic battery performance by using nanotechnology. The contact area between the electrode and the electrolyte is maximized at the nanoscale without losing their characteristics. Furthermore, the dimension of nanoparticles is comparable with the path length of diffusion during the redox reaction which leads to reversible and efficient performance. In the macro and micro-sized active materials, the reach of external electrons and ions is up to the surface, i.e., the major part of the bulk remains unused, specifically at higher current rates Fig. 1. Thus, the effective capacity of such active materials appears relatively low, while for the nano-sized materials, the maximum capacity of the substance can be utilized. The objective of achieving the theoretical capacity of the active materials in battery applications can be achieved through the application of nanotechnology. Nanobatteries have been used extensively in a variety of fields, including micro-electromechanical systems, computer chips, electrochemical/optical nano sensors, and medical devices that may be implanted in patients for the purpose of carrying out specific diagnostic or therapeutic treatments. The nanobatteries developed by using nanomaterials have comparatively higher capacity, an improved charge–discharge process, compact size, and better sustainability. Also, the performances of conventional Li+ ion batteries are being improved using nanostructured electrodes and nanocomposite polymer electrolytes. The conventional Li+ ion batteries cannot be charged and discharge at low temperatures due to the formation of solid electrolyte interphase (SEI) layer between the electrodes and electrolyte, and also the charge–discharge process is sluggish due to the large diffusion pathway of Li+ ion [3]. Similar to conventional batteries, nano-batteries also comprise of anode, cathode, electrolyte, and separator. Several types of nanomaterials have been explored for lithium-ion battery electrodes. Cadmium sulfide (CdS) quantum dots (QDs) or nanocrystals (NCs) were synthesized by a chemical process and were fabricated into

Polymeric Materials for Nanobatteries

Idle

Active material

421

Nanosizing

Ion

Electron

Fig. 1 Effect of nanosizing of active material

a nano battery device by using the PVV/Li: graphite/CdS/Al combination. CdS QDs made a significant contribution to the enhanced performance of the nano battery by boosting the charge carrier’s mobility, which led to an increase in the number of recombination events involving ions of CdS QDs and Li. The fabrication of a CdS nano battery device using a semiconductor material including Li has been achieved, and the nano battery has been successfully operated at a few voltages while maintaining a decent performance [4]. Nanostructured anode used in nanobatteries includes C/Si nanocomposite [5], graphene [6], nano-SnO [7], core–shell Sn@Cu nanoparticles [8], nano-TiNb2 O7 [9], antimony hollow nanospheres [10], and MoO3 /conducting polymer nanocomposite [11]. While nanostructured cathodes in nano batteries include different kinds of nanomaterials such as LiMn2 O4 nanotubes [12], nanoscaled Zn-doped LiMn2 O4 [13], nano-CeO2 -coated nanostructure LiMn2 O4 [14], spinel LiMn2 O4 nanorods [15], nano-LiCoO2 [16], nanosulfur/poly-pyrrole/graphene nanocomposite [17], and sulfur-conducting polymer nanocomposite [18]. Also, conventional solid state polymer electrolyte used in Li+ ion batteries suffer from poor ionic conductivity; however, use of nanocomposite polymer electrolytes has significantly overcome this issues [19]. Moreover, The crystallisation kinetics of the PEO polymer chains were significantly enhanced as a result of the incorporation of a variety of nanoparticles (TiO2 , SiO2 , and Al2 O3 ) into the polymer and thus considered as most suitable electrolyte for nanobatteries [1]. The polymeric materials improve the electrochemical performance, rate capability, cyclic stability and capacity retention over pristine materials. Additionally, it offers a number of advantages, including enhanced thermal and mechanical stability, a leakage resistant feature, flexibility, safety, increased ionic conductivity, and decreased interface resistance [20]. In several areas like Bio-sensing, Actuating, Energy conversion, polymer based batteries etc., nano-sized conducting polymers have shown potential. From the above discussion, it can be seen that polymeric materials have extensive use in enhancing the performance of electrodes as well as electrolyte material in nanobatteries. Therefore, in the present chapter, the basic principle, components of nanobatteries, and applications of polymeric material have been discussed.

422

A. Tiwari and R. K. Singh

2 Nanobatteries: Principle and Components Basically, the batteries consist of three major components, which are the anode, cathode, and electrolyte. Shrinking the size of these components in the micro and/ or nano scale leads to an efficient electrochemical power storage device. The array of cathode, electrolyte, and anode can be fabricated on an electrically insulating substrate such that huge amounts of nano batteries can be built in a very small area, e.g., ~105 in 1 cm2 . When these nano batteries are connected in series and parallel combination by coating technique, these tiny batteries might be able to produce even 100 times more power and energy density than the thin film batteries of similar size [21].

2.1 Nanostructured Cathode Material A large number of studies are reported for various nanostructured cathode materials such as LiMn2 O4 nanotubes [12], nano-SiO2 -coated LiMn2 O4 [22], nanoscaled Zndoped LiMn2 O4 [13], nano-CeO2 -coated nanostructure LiMn2 O4 [14], nano-LiCoO2 [16], graphene [23], nanosulfur/polypyrrole/graphene nanocomposite [17], sulfurconducting polymer nanocomposite [18], nanofibrous selenium and its polypyrrole and graphene composite [24] with the high electrical conductivity, flat and smooth surface, highly organized, consistent as well as enhanced in aspects of its mechanical durability. A high-capacity reduced graphene oxide nanosulfur nanocomposite (RGOSNC) cathode is synthesised by hydrothermal treatment in the presence of ethylenediamine (EDA) for use in lithium sulfur batteries (LiSBs) [25]. Moreover, the preparation of LiSBs cathodes for rechargeable batteries with a high capacity and a long cycle life, copolymerization of sulfur nanoparticles is accomplished. This is performed to alleviate the dissolution of the active ingredient, sulfur, into the electrolyte during the charging and discharging process. The sulfur nanoparticles are loaded onto a conducting carbon-rich graphitic carbon nitride (GCN) framework for fast electro kinematics. This implements the advantage of polymeric material in order to prevent degradation of sulfur in order to achieve high capacity and a long cycle life [26]. Cathodes for specific lithium nanobatteries were constructed using V2 O5 that was confined inside the pores of Al2 O3 filter membranes. From the XRD, unique characteristics of V2 O5 as partially crystalline in the bulk form and purely amorphous in the aluminum oxide membrane are identified. The loading of V2 O5 xerogel with 35 weight percent carbon nanotubes resulted in the production of a nanocomposite cathode material with better performance [27]. Cathodes were constructed using composite particles that included carbon nanofibers (NFs) and were linked together using a binder. These particles are grown on the active sites of materials such as polyamidoimide polyimide, polysulfone, polyamide, polytetrafluoroethylene, and/ or polyphenylene sulfide. These materials are suitable for use in secondary batteries

Polymeric Materials for Nanobatteries

423

that employ non-aqueous electrolytes [28]. In a different approach to the fabrication of cathodes, the composite material includes both carbon nanofibers and carbon that is not carbon nanofibers, Li alloyed with Sn and/or Sicilcon, and a catalyst element chosen from the group consisting of Mn, Cu, Co, Ni, Fe, and/or Mo for the purpose of speeding the development of carbon NFs. High electrical conductivity and good initial charging/discharging characteristics or cycling performance are both advantages of this composite active material. It was proposed that a high-yield method could be developed for the synthesis of low polydispersity carbon microspheres, nanofibers, nanocrystals, nanotubes, or nanospheres by chemical transformation. This method involves dispersing a self-polymerizing end-capped tetrayne in the solvent, then heating of dispersed self-polymerizing end-capped tetrayne to produce polymeric material, which contains polymer nanoparticle [29]. Additionally, carbon-based materials have been used to increase the capability of electrodes namely cathodes as they have a high surface area and uniform pores. Therefore, nanostructured graphitic carbon electrodes are used in nanobatteries. For example, new carbon nanofibers have been reported by Li et al. [30], which were synthesized by pyrolyzing conducting polymers. These carbon nanofibers had an average pore width of 27.98 nm and about 74.5 m2 /g of specific surface area. Mao et al. [31] described a three-dimensional network of reduced graphene oxide i.e., poly(3,4-ethylenedioxythiophene) (rGO/PEDOT) composites by using laser-assisted performance and in-situ vapour phase polymerization. There is a rising degree of technological interest in surface-modified cathode active materials for battery durability, and improvement of stable shells from unstable conditions. Modifying the cathode’s surface is the simplest method for boosting performance. Even in severely oxidised states, structural stabilization, strong cyclability, and thermal stability have been achieved with the modification of cathode active material. The material displays not only a very highly reversible capacity dependent on the particle bulk composition, but also strong cycle and safety qualities. This is because of the stability of the concentration-gradient outer layer, which is maintained by the surface composition [32].

2.1.1

Role of Polymeric Material in Improving the Cathode Performance

The nanostructured polymer-cathode composite has gained a lot of attention over the span of the last two decades. Such a type of composite consists of conducting organic polymers such as polypyrrole, polyaniline, and polyacetylene interleaved between the layers of the oxide lattice. The composite of polymer and oxide is very attractive, as both polymer and oxide are electrochemically active. The most common example of this type of composite is V2 O5 /polyaniline nanocomposite film fabricated by a layer-by-layer technique, which significantly improved the intercalation capacity. Inspired by this, later, polymer polyaniline was replaced by blends of chitosan and poly(ethylene oxide) (PEO) which can intercalate 1.77 mol of lithium-ions and thus delivered higher capacity The enhanced electrochemical performance of V2 O5 /blend

424

A. Tiwari and R. K. Singh

was because there are a greater number of sites that are electrochemically active and lithium diffuses more quickly throughout the composite material [33]. Nanostructured polymer-cathode composite has also significant role in improving the performance of Li–S batteries. Generally, elemental sulfur has highest theoretical capacity density ~ 1672 mAh/g but it suffers from low utilization of active material due to the hindrance of sulfur particles by insulated reaction products and the dissolution of polysulfides that transfer into the Li anode that causes lithium corrosion. Thus, to overcome these issues, nano dispersed composites with sulfur embedded in a conductive polymer matrix were prepared by heating the polyacrylonitrile (PAN) and sublimed sulfur. This composite has successfully prevented the dissolution of polysulfides and prove a promising cathode for Li–S batteries [19]. Nitrogen (heteroatom) doping in RGO (RGOSNC) provide easy electron migration path through the conducting RGO framework and stabilises intermediate polysulfide to prevent loss of active material during the electrochemical performance with the advantage of material’s 3D interconnected porous conductive architecture. Furthermore, as cathode material for rechargeable LiSBs, a nano sulfur copolymer coated carbon-rich graphitic carbon nitride (GCN) nanosheet host that is mesoporous, conductive, and has a high specific surface area has been described to show high capacity along with long cyclability [26]. In another report, a sulfur nanocomposite with poly (ethylene dioxythiophene) (PEDOT) was synthesized via membrane assisted precipitation technique. Because of the encapsulation of a conducting PEDOT shell, the diffusion of polysulfides is reduced, self-discharging and the shuttle effect are mitigated, and the cycle stability is thereby improved. The synthesis of S/PEDOT core/shell nanoparticles and their use as cathode materials for Li/S batteries are shown here in the form of a schematic Fig. 2 [34].

Fig. 2 Schematic image of S/PEDOT core/shell nanoparticles, along with depiction of their utilization in Li/S batteries. Adapted with permission [34], Copyright (2013), Springer Nature

Polymeric Materials for Nanobatteries

425

2.2 Nanostructured Anode Materials Similar to cathode materials, nanostructured anode materials have also gained wide attention in the past two decades in advanced nanoscience and nanotechnology as they offer short mass and charge diffusion distances, improve energy density, life cycle, and rate capability of batteries. In commercial lithium ion batteries, graphitic anode materials are used due to the ease of Li+ ion intercalation and de-intercalation. Although the theoretical capacity of a graphite anode is 372 mAhg−1 , the demand of enhanced capacity with high retention has become predominant in recent years. A lot of research has gone into discovering amorphous carbon nanoparticles to further enhance the performance of carbon nanoparticles as Li+ ion battery anodes. One of the commercial aims of developing high-performance anodes is to replace the current commercial graphite materials in the not-too-distant future by making use of nanotechnology to achieve a capacity of 500 mAh/g or higher [35]. Sulfides, phosphates, carbonaceous materials, and metal oxides are just a few of the nanomaterials that have been employed as anode material for Li+ ion batteries because they offer the important characteristics of being readily available, chemically stable, recyclable, and inexpensive. Designing electrodes that work at such a tiny scale is a significant technical challenge in itself. It is envisaged that the nano-structured surface of graphitic carbon will function as the electrode in nanobatteries. In general, the chemical, structural morphology, and functional characteristics of carbon-based materials are all homogeneous. They possess shells with a high surface area that have pores distributed evenly throughout. Because of their own nature, the pores have a significant effective surface area, which, in turn, results in an increase in the number of locations on the nanostructure where a chemical reaction or catalysis might potentially take place. In addition, pores may be functionalized in order to boost their chemical and electrochemical activity for lithium nano batteries. Ultrathin coating ( 90% capacity retention up to 105 cycles [37].

426

A. Tiwari and R. K. Singh

A three-dimensional anode of composite α-Fe2 O3 /Polypyrrole, synthesized by chemical polymerization, enhanced the rate performance and specific areal capacity. The iron foil used as the current collector for the composite anode and fast ion transport, a unique nano-array structure which provide sufficient space for volume change during cyclicng [38]. Silicon alloys offer the greatest specific capacity when employed as anode material for lithium-ion batteries; yet, the dramatic volume shift that is inherent in their utilization creates severe hurdles when attempting to achieve stable cycling performance. Using a functional conductive polymer binder in composite electrodes allowed for SiO electrodes to be cycled in a manner that maintained their high gravimetric capacity (more than 1000 mAh/g) with good capacity retention over the long cycling performance (> 500 cycles) [39]. Intensive tapping of nano-Si is an attractive anode option because it may reduce the generally high irreversible capacities for silicon nano-materials, but the tiny surface area makes the design of appropriate polymeric binders very difficult. A high tap density nano-Si anode is developed using a synthetic conductive polymer binder, Poly(1-pyrenemethyl methacrylate-co-methacrylic acid) (PPyMAA), with electrical conductivity and adhesion capabilities. The PPyMAA binder’s facilitation of high tap-density nano-Si-based high-capacity anodes is a significant step towards the implementation as a viable product [40]. For the nano Si anode based Li+ ion batteries, Wang et al. reported Palladium-catalyzed direct arylation of 3-(2-ethylhexyl)thiophene or 3,3’-di(2-ethylhexyl)bithiophene and dimethyl-2,5dibromoterephthalate leads to the synthesis of polymer binders, followed by saponification, which exhibits efficient movement of charges and ions throughout the duration of 1000 cycles [41].

2.3 Electrolytes for Nano Batteries Ions and electrons both move around simultaneously during battery operation. Ions are transported through the electrolyte, whereas, electrons are produced at the anode and travel via an external circuit to reach the cathode. The electrode is responsible for the storage of charge in the successive levels of the stack, while the electrolyte serves as a kind of carpet for the ions. The rate at which lithium ions move to and from the spacer that is located between the electrodes is directly proportional to the capacity of the battery. In spite of the fact that the electrode plays an important part in the stability and safety of batteries, the electrolyte is also an essential component, and because of the dual roles that it plays, it requires careful consideration when selecting it. Between the electrodes is a separator, which serves two purposes: it prevents a short circuit from occurring and it provides a medium for ion movement [19]. In general, solid polymer electrolytes that have the capacity to transport alkali metal cations in solid phases are of special value for moderating the electrochemical performance of solid state batteries. The inter-polar cell separator is an essential part of every battery, and it may take the form of an ion-exchange membrane, a microporous membrane,

Polymeric Materials for Nanobatteries

427

or polymer electrolyte, depending on the type of battery. Conventional batteries use organic solvent based electrolytes, which suffer from various safety and portability concerns. To overcome these issues, solid polymer based electrolytes are being used extensively in macro as well as nanobatteries. A variety of polymeric materials such as PVdF-HFP, PEO, and PMMA and their composites with different nanofillers are widely used. A previous study on polyethylene oxide (PEO) shows the decreasing confinement size in the micro to nano range leads to enhancement of ionic conductivity, two orders higher than its film with the same composition. There is a possibility that the orientation of the polymer chains in the pores contributes to improved conductivity. These membranes also display improved conductivity in a direction perpendicular to the plane of the thin electrolyte layer. This structure is most suitable for the polymer electrolytes for implementation in nano battery applications [41].

2.3.1

Role of Polymeric Material in the Electrolyte

Among the many different alternatives, polymer electrolytes (PEs) feature numerous advantageous properties, including high flexibility and superior processability, which makes them interesting candidates for attaining high performance in nano battery applications. A significant number of studies have been carried out on the incorporation of nano-inorganic fillers in PEs. Nano-sized inorganic fillers such as SiO2 , TiO2 , ZnOx , Al2 O3 , and ZrO2 are some of the most common types used today. The nano fillers enhance the physical and mechanical properties of the polymer. The overall effect on ionic conductivity depends on several factors, like particle size, amount, and type of filler. Chung et al. reported the effect on the addition of inorganic nano-fillers and it was reported that the ionic conductivity of PE increases by two orders of magnitude at room temperature [42, 43]. Karpagavel et al. reported the blending of polymers to enhance the performance of solid-state lithium batteries. A lithium bromide ionic salt distributed with polyvinylpyrrolidone (PVP)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) blend polymershaves been synthesized by solution casting and utilized as an electrolyte [44]. Furthermore, Mishra et al. reported the PVdF-HFP based gel polymer electrolyte for sodium ion batteries with improved cycling performance [45]. Singh et al. reported a freestanding/flexible nano-composite gel polymer electrolyte for high-temperature Li-battery applications. The electrolyte was prepared by incorporating MCM-41 nano filler in PVdF-HFP polymer by using a solution cast technique [46].

3 Application of Nanobatteries in Various Field Nanobatteries have been widely used in various fields such as healthcare sector, defence, aerospace, industry, electronics, etc., as described below (Fig. 3).

428

A. Tiwari and R. K. Singh

Fig. 3 Schematic presentation of application of nanobatteries in various fields

3.1 Electronics Nanobatteries have revolutionized the electronic market. Li+ ion batteries with nano particle electrodes have been widely used in electric cars because of their better electrochemical performance. The electrical generator is built up with nano structured material, as they produce watts of electrical power by walking. Nanobatteries make the technology more powerful by reducing the size and cost as well as increasing its capabilities. Thus, with the use of nano batteries, gaming, texting, and tweeting can be done continuously without worrying about battery. Also, nanobatteries with silicon-graphene anode materials have great applications in smart phones, tablets, computers, stationary power, and vehicle electrification because of their significantly higher energy storage capacity than those conventional ion batteries.

3.2 Biomedical Nanobatteries are an interesting and potentially useful technology for use in medical instruments. Under implanted biomedical devices, the use of Li+ ion batteries demonstrates outstanding qualities such as biocompatibility, extended life, ultra-high safety, and consistency in the demanding working circumstances that exist inside the human body. It is suggested that lithium-ion batteries be used in the design of various biomedical devices such as pacemakers, implanted radio transmitters, stomach stimulators, smart gesture gloves, fitness and mobility trackers, and wearable biosensors. The devices are worn directly on the skin of the human body. As a result, they are required to be able to survive significant changes in human mobility and the biological conditions in which they operate, such as stress, pressure, and temperature. Incorporating

Polymeric Materials for Nanobatteries

429

polymeric materials into nanobatteries not only makes them more flexible, but also increases the electrode electrolyte compatibility throughout a wide range of body temperatures due to their adhesive properties.

3.3 Aerospace When the combustion of fossil fuel during flight operations is considered, significant changes may be seen in the quantity of greenhouse gas that is released into the environment. Despite the fact that weight is a significant constraint in aeronautical applications, Li-ion batteries have been shown to be of great use to the aircraft sector. The nanobatteries, having a light weight and sufficiently high energy and power density, can contribute to the development of aerospace applications.

4 Summary In the prevailing state of the industry, there is a significant need for electrical products that have a smaller size. Because electronic gadgets are becoming smaller, the size of their energy storage devices also has to become smaller and efficient. The development of nanobatteries has the potential to meet these needs in a significant way. It is abundantly clear that the term “nanobattery” refers not only to nanosized batteries but also to the process of improving the performance of macroscopic batteries by using nanotechnology. Recent developments in nanotechnology and integrated nanobatteries have made it possible to store a significant amount of power and energy in a very tiny area. Additionally, in comparison to conventional batteries, it has a longer life, a quicker charging time, and a higher level of safety. However, shrinking the battery is still an important challenge on the way towards the development of nanobatteries. Nanobatteries rely heavily on the use of nano-scale electrode materials and nanocomposite electrolytes in order to function efficiently. Polymeric materials offer very good contact to be made between the nano electrodes and the electrolytes. Nano-structured conducting polymers such as polyaniline, polypyrrole, and polythiophene are used in the manufacture of nanobatteries, which have found use in high-performance electronic applications. Moreover, the nano-sized cathode materials such as, LiMn2 O4 nanotubes, nano-LiCoO2 , sulfur-carbon nanocomposite, sulfur-conducting polymer nanocomposite, etc. and nano-sized Si, SnO, graphene, etc. as anodes are discussed in detail. For the use of next-generation devices, one innovative component of nanobattery research is the exploitation of new polymeric materials and nano-sized electrodes in the device.

430

A. Tiwari and R. K. Singh

References 1. Singh N, Kumar A, Riaz U (2022) Conducting polymer-based micro-and nano-batteries for biomedical applications: a short review. ChemistrySelect 7(27):e202201302 2. Kianfar E, Hassani Joshaghani A, Razavikia SA (2020) Introducing the application of nanotechnology in lithium-ion battery 3. Ma S, Jiang M, Tao P, Song C, Wu J, Wang J, Deng T, Shang W (2018) Temperature effect and thermal impact in lithium-ion batteries: a review. Prog Nat Sci Mater Int 28:653–666 4. Kadim A (2022) Fabrication of nano battery from CdS quantum dots and organic polymer. Kuwait J Sci 49(1) 5. Depeursinge A, Racoceanu D, Iavindrasana J, Cohen G, Platon A, Poletti P-A, Müller H (2010) Fusing visual and clinical information for lung tissue classification in high-resolution computed tomography. Artif Intell Med 50(1):13–21 6. Kim H, Seo D-H, Kim S-W, Kim J, Kang K (2011) Highly reversible Co3 O4 /graphene hybrid anode for lithium rechargeable batteries. Carbon 49(1):326–332 7. Li H, Huang X, Chen L (1999) Electrochemical impedance spectroscopy study of SnO and nano-SnO anodes in lithium rechargeable batteries. J Power Sources 81:340–345 8. Kim MG, Sim S, Cho J (2010) Novel core-shell Sn–Cu anodes for lithium rechargeable batteries prepared by a redox-transmetalation reaction. Adv Mater 22(45):5154–5158 9. Tang K, Mu X, van Aken PA, Yu Y, Maier J (2013) “Nano-pearl-string” TiNb2 O7 as anodes for rechargeable lithium batteries. Adv Energy Mater 3(1):49–53 10. Hou H, Jing M, Yang Y, Zhu Y, Fang L, Song W, Pan C, Yang X, Ji X (2014) Sodium/lithium storage behavior of antimony hollow nanospheres for rechargeable batteries. ACS Appl Mater Interfaces 6(18):16189–16196 11. Liu Y, Zhang BH, Xiao SY, Liu LL, Wen ZB, Wu YP (2014) A nanocomposite of MoO3 coated with PPy as an anode material for aqueous sodium rechargeable batteries with excellent electrochemical performance. Electrochim Acta 116:512–517 12. Tang W, Hou Y, Wang F, Liu L, Wu Y, Zhu K (2013) LiMn2 O4 nanotube as cathode material of second-level charge capability for aqueous rechargeable batteries. Nano Lett 13(5):2036–2040 13. Arumugam D, Paruthimal Kalaignan G, Vediappan K, Lee CW (2010) Synthesis and electrochemical characterizations of nano-scaled Zn doped LiMn2 O4 cathode materials for rechargeable lithium batteries. Electrochimica Acta 55(28):8439–8444 14. Arumugam D, Paruthimal Kalaignan G (2010) Synthesis and electrochemical characterization of nano-CeO2 -coated nanostructure LiMn2 O4 cathode materials for rechargeable lithium batteries. Electrochim Acta 55(28):8709–8716 15. Kim DK, Muralidharan P, Lee H-W, Ruffo R, Yang Y, Chan CK, Peng H, Huggins RA, Cui Y (2008) Spinel LiMn2 O4 nanorods as lithium ion battery cathodes. Nano Lett 8(11):3948–3952 16. Tang W, Liu LL, Tian S, Li L, Yue YB, Wu YP, Guan SY, Zhu K (2010) Nano-LiCoO2 as cathode material of large capacity and high rate capability for aqueous rechargeable lithium batteries. Electrochem Commun 12(11):1524–1526 17. Zhang Y, Zhao Y, Konarov A, Gosselink D, Soboleski HG, Chen P (2013) A novel nanosulfur/polypyrrole/graphene nanocomposite cathode with a dual-layered structure for lithium rechargeable batteries. J Power Sources 241:517–521 18. Qiu L, Zhang S, Zhang L, Sun M, Wang W (2010) Preparation and enhanced electrochemical properties of nano-sulfur/poly (pyrrole-co-aniline) cathode material for lithium/sulfur batteries. Electrochim Acta 55(15):4632–4636 19. Sharma SK, Sharma G, Gaur A, Aray A, Mirsafi FS, Abolhassani R, Rubahn H-G, Yu J-S, Mishra YK (2022) Progress in electrode and electrolyte materials: path to all-solid-state Li-ion batteries (ASSLIB). Energy Adv 20. Singh SK, Dutta D, Singh RK (2020) Enhanced structural and cycling stability of Li2 CuO2 coated LiNi0.33Mn0.33Co0.33O2 cathode with flexible ionic liquid-based gel polymer electrolyte for lithium polymer batteries. Electrochim Acta 343:136122 21. Clement B, Lyu M, Sandeep Kulkarni E, Lin T, Hu Y, Lockett V, Greig C, Wang L (2022) Recent advances in printed thin-film batteries. Engineering

Polymeric Materials for Nanobatteries

431

22. Arumugam D, Paruthimal Kalaignan G (2008) Synthesis and electrochemical characterizations of Nano-SiO2 -coated LiMn2 O4 cathode materials for rechargeable lithium batteries. J Electroanal Chem 624(1–2):197–204 23. Kim H, Lim H-D, Kim S-W, Hong J, Seo D-H, Kim D-C, Jeon S, Park S, Kang K (2013) Scalable functionalized graphene nano-platelets as tunable cathodes for high-performance lithium rechargeable batteries. Sci Rep 3(1):1506 24. Kundu D, Krumeich F, Nesper R (2013) Investigation of nano-fibrous selenium and its polypyrrole and graphene composite as cathode material for rechargeable Li-batteries. J Power Sources 236:112–117 25. Tiwari RK, Singh SK, Gupta H, Srivastava N, Meghnani D, Mishra R, Patel A, Tiwari A, Tiwari VK, Singh RK (2022) Multifaceted ethylenediamine and hydrothermal assisted optimum reduced GO-nanosulfur composite as high capacity cathode for lithium-sulfur batteries. Electrochem Sci Adv 2(1):e202100025 26. Tiwari RK, Singh SK, Srivastava N, Mishra R, Meghnani D, Patel A, Tiwari A, Tiwari VK, Singh RK (2022) Conducting carbon rich graphitic carbon nitride nanosheets with attached nano sulfur copolymer as high capacity cathode for long-lifespan lithium-sulfur battery. Batteries Supercaps 5(12):e202200282 27. Dewan C, Teeters D (2003) Vanadia xerogel nanocathodes used in lithium microbatteries. J Power Sources 119:310–315 28. Vullum F, Teeters D, Nytén A, Thomas J (2006) Characterization of lithium nanobatteries and lithium battery nanoelectrode arrays that benefit from nanostructure and molecular selfassembly. Solid State Ionics 177(26–32):2833–2838 29. Lowy DA, Patrut A (2008) Nonobatteries: decreasing size power sources for growing technologies. Recent Pat Nanotechnol 2(3):208–219 30. Li C, Yin X, Chen L, Li Q, Wang T (2009) Porous carbon nanofibers derived from conducting polymer: synthesis and application in lithium-ion batteries with high-rate capability. J Phys Chem C 113(30):13438–13442 31. Mao X, He X, Xu J, Yang W, Liu H, Yang Y, Zhou Y (2019) Three-dimensional reduced graphene oxide/poly (3, 4-ethylenedioxythiophene) composite open network architectures for microsupercapacitors. Nanoscale Res Lett 14(1):1–11 32. Myung S-T, Amine K, Sun Y-K (2010) Surface modification of cathode materials from nano-to microscale for rechargeable lithium-ion batteries. J Mater Chem 20(34):7074–7095 33. Kianfar E (2019) Recent advances in synthesis, properties, and applications of vanadium oxide nanotube. Microchem J 145:966–978 34. Chen H, Dong W, Ge J, Wang C, Wu X, Lu W, Chen L (2013) Ultrafine sulfur nanoparticles in conducting polymer shell as cathode materials for high performance lithium/sulfur batteries. Sci Rep 3(1):1910 35. Wu J, Cao Y, Zhao H, Mao J, Guo Z (2019) The critical role of carbon in marrying silicon and graphite anodes for high-energy lithium-ion batteries. Carbon Energy 1(1):57–76 36. Dakshayini BS, Reddy KR, Mishra A, Shetti NP, Malode SJ, Basu S, Naveen S, Raghu AV (2019) Role of conducting polymer and metal oxide-based hybrids for applications in ampereometric sensors and biosensors. Microchem J 147:7–24 37. Li C-H, Sengodu P, Wang D-Y, Kuo T-R, Chen C-C (2015) Highly stable cycling of a lead oxide/ copper nanocomposite as an anode material in lithium ion batteries. RSC Adv 5(62):50245– 50252 38. Liu J, Zhou W, Lai L, Yang H, Lim SH, Zhen Y, Yu T, Shen Z, Lin J (2013) Three dimensionals α-Fe2O3/polypyrrole (Ppy) nanoarray as anode for micro lithium ion batteries. Nano Energy 2(5):726–732 39. Zhao H, Wang Z, Lu P, Jiang M, Shi F, Song X, Zheng Z, Zhou X, Fu Y, Abdelbast G, Xiao X, Liu Z, Battaglia VS, Zaghib K, Liu G (2014) Toward practical application of functional conductive polymer binder for a high-energy lithium-ion battery design. Nano Lett 14(11):6704–6710 40. Zhao H, Wei Y, Qiao R, Zhu C, Zheng Z, Ling M, Jia Z, Bai Y, Fu Y, Lei J, Song X, Battaglia VS, Yang W, Messersmith PB, Liu G (2015) Conductive polymer binder for hightap-density nanosilicon material for lithium-ion battery negative electrode application. Nano Lett 15(12):7927–7932

432

A. Tiwari and R. K. Singh

41. Wang K-L, Chen K-T, Yi Y-H, Hung Y-H, Tuan H-Y, Horie M (2019) High-performance lithium ion batteries combining submicron silicon and thiophene–terephthalic acid-conjugated polymer binders. ACS Sustain Chem Eng 8(2):1043–1049 42. Chung SH, Wang Y, Persi L, Croce F, Greenbaum SG, Scrosati B, Plichta E (2001) Enhancement of ion transport in polymer electrolytes by addition of nanoscale inorganic oxides. J Power Sources 97:644–648 43. Boaretto N, Meabe L, Martinez-Ibañez M, Armand M, Zhang H (2020) Polymer electrolytes for rechargeable batteries: from nanocomposite to nanohybrid. J Electrochem Soc 167(7):070524 44. Karpagavel K, Sundaramahalingam K, Manikandan A, Vanitha D, Manohar A, Nagarajan ER, Nallamuthu N (2021) Electrical properties of lithium-ion conducting poly (vinylidene fluorideco-hexafluoropropylene)(PVDF-HFP)/polyvinylpyrrolidone (PVP) solid polymer electrolyte. J Electron Mater 50(8):4415–4425 45. Mishra R, Singh SK, Gupta H, Tiwari RK, Meghnani D, Patel A, Tiwari A, Tiwari VK, Singh RK (2021) Polar β-phase PVdF-HFP-based freestanding and flexible gel polymer electrolyte for better cycling stability in a Na battery. Energy Fuels 35(18):15153–15165 46. Singh SK, Dutta DP, Gupta H, Srivastava N, Mishra R, Meghnani D, Tiwari RK, Patel A, Tiwari A, Singh RK (2022) Electrochemical investigation of double layer surface-functionalized Li-NMC cathode with nano-composite gel polymer electrolyte for Li-battery applications. Electrochim Acta 435:141328

Materials and Applications of 3D Print for Solid-State Batteries Apurba Das and Pintu Barman

Abstract Additive manufacturing has emerged as one of the most enticing techniques over the past few decades and has practically revolutionized almost every manufacturing sector, from energy storage to the biomedical industry. For energy storage, solid-state batteries (SSBs) have numerous advantages such as safety, reliability, mechanical robustness, stability, and conductivity. The development of highly conducting solid-state electrolytes is a strikingly new feature that has improved the energy density of the next-generation SSBs. 3D printing has provided a viable alternative for scaling the production of SSBs, endowing the fabrication process with advantages such as enhancing the contact of surfaces between the battery layers, thus enabling the decrease of interfacial resistance. Additionally, the compatibility of 3D processing technology with ceramic and polymeric materials to construct architectural motifs for SSBs makes it stand out. In this chapter, the authors wish to discuss the evolving aspects of additive manufacturing techniques in the fabrication of SSBs from a broader prospect that includes several state-of-the-art improvements over the existing technology. A comprehensive overview of the technology will be included to provide a framework for researchers to understand the recent achievements and contribute to future developments. Keywords 3D printing · Solid-state batteries · Energy storage · Electrolytes · Polymer

A. Das (B) Department of Physics, Handique Girls College, Guwahati, Assam 781001, India e-mail: [email protected] P. Barman Department of Physics, Kamrup College, Chamata, Assam 781306, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_25

433

434

A. Das and P. Barman

1 Introduction The global demand to decrease carbon emissions for mitigating climate change challenges depends highly on the complete electrification of transportation systems which accounts for 25% of global carbon emissions [1]. The electrification process demands high-energy density, rechargeable, and safe batteries that can be used in electric vehicles and smart grids [2]. In order to meet future driving requirements (> 300 miles per charge), estimates suggest that batteries for electric vehicles (EV) need to have energy density (> 500 Wh/kg). The criteria of energy density up to 220 Wh/kg and the vehicle range have been partially met by the commercialization of energy-dense cathodes like LiNiMnCoO2 (NMC) and LiNiCoAlO2 (NCA) [3]. This energy density is not achievable with conventional Li-ion battery (LIB) systems, which employ graphite anodes with a specific capacity of just 350 mAh/g. [1]. An attractive way to increase energy density is to replace these typical graphite electrodes with Li metal (specific capacity 3860 mAh/g) [1]. It has also been observed that conventional Liion batteries have severe safety concerns, such as the risk of igniting the organic solvents used as electrolytes. In addition, lithium dendrite formation caused by inhomogeneous charging of the anode can short circuit the liquid organic electrolytes leading to pivotal damage of battery life [2]. Lastly, batteries meant for EVs need to have fast charging/discharging ability, especially during the ignition or accelerating process of the vehicles [4]. The current liquid electrolyte-based batteries have a low Li-ion transference number (< 0.5), which compels manufacturers to reduce the rate of charging/discharging so as to preserve the battery life, causing a severe limitation upon its power and energy density [4]. To address these limitations, a lot of impetus has been laid in the past decades to develop a high-power density for fast charging LIB. Research demands an ideal electrolyte with good mechanical properties, high Li-ion transference number, and ionic conductivity to meet the requirements. For instance, the problem of dendrite formation can be eliminated if the modulus of the electrolytes is twice that of the Li-metal [4]. Thus, it is essential that Li-ion batteries must have flexible but high Young’s modulus separators, leading to a superior resistance against dendrite formation, promoting the use of all-solid-state-lithium-ion-batteries (ASSLBs) [4]. Moreover, the risks associated with the leakage or explosion of the organic liquid electrolytes can be averted using ASSLBs. In the context of the solid-state electrolytes (SSE) used in ASSLBs, it is possible to categorize them into three types: solid polymer electrolyte (SPE), solid inorganic electrolyte (SIE), and their hybrids [4]. Some of the essential properties of SSE are shown in the form of an illustration in Fig. 1. However, despite all the advantages, a critical issue that limits SSBs to functional areas is the high interfacial impedance between the electrolytes and the electrodes. In addition, the modest active mass loading (1 mg/cm2 ) and lengthy ionic diffusion routes in electrodes, is much smaller in comparison to 12 mg/cm2 for LiCoO2 cathode and 6 mg/cm2 for graphite anodes as dictated for commercial applications [6]. The quickest way to address the shortcomings is to increase the contact area

Materials and Applications of 3D Print for Solid-State Batteries

435

Fig. 1 The characteristics of solid-state electrolytes (left partition). The electrolytes must possess certain characteristics that will help them perform optimally inside the batteries. For designing the batteries, it is important that a researcher pay attention to all the four categories, as a synergy between all of these properties shall lead to better performance of the batteries. Towards the right side of the partition, a 3D printed cell is prepared and some of its properties such as the capacity of the printed cells and its voltage are shown in (C) and (D). Adapted with permission [5], Copyright (2018), American Chemical Society

of the batteries by resorting to 3D structured components in batteries that will ultimately decrease interfacial impedance [6]. The 3D structured components will also improve the mass loading of the active materials. Various techniques are available for processing the 3D structured components, out of which semiconductor-processing methods and photo patterning are worth mentioning [7]. However, the processing cost associated with these methods is very high and are unable to produce customized 3D structures. These drawbacks can be eliminated using 3D printing technologies such as selective laser melting (SLM), stereolithography (SLA), electrophoretic deposition (EPD), laminated object manufacturing (LOM) and direct ink writing (DIW) [7]. In this chapter, we shall be focused on studying the details of the 3D processing techniques that can be employed for fabricating ASSLBs and the crucial developments that led to ASSLB. A comprehensive analysis of the advantages and drawbacks associated with the 3D printing techniques shall be discussed, and advances in the research methodology to deliver high powered fast charging/discharging batteries shall be taken up in the following sections.

2 Literature Survey In recent years, if we compare additive manufacturing (AM) to other technologies, it has been deemed one of the cutting-edge technologies because of its efficiency in producing complex designed structures at a relatively low cost [8]. In the additive manufacturing (AM) process, a computerized 3D solid model is prepared, which is then modified by an additive manufacturing machine. Finally, this model is utilized for producing 3D objects by layer-by-layer material deposition process

436

A. Das and P. Barman

[9]. The American Society for Testing and Materials classifies additive manufacturing into seven major categories: material extrusion, binder jetting, material jetting, powder bed fusion, sheet lamination, directed energy deposition, and vat photo-polymerization. These categories can be further broken down into numerous subbranches as shown in Fig. 2. Recently, various 3D techniques such as stereolithography (SLA) [10], selective laser sintering (SLS) [11], Laser Metal Deposition (LMD) [12], Laminated Object Manufacturing (LOM) [13], direct ink writing (DIW), etc., have been adopted for fabricating various devices. SLA is the first commercially available AM technique, where UV light has been used to convert a liquid photosensitive resin into a sliced solid-state layer and adhere them to the previous layer to build the structure. In the SLS method, a layer of powder is spread out before being selectively scanned by a laser, whereas in LMD, a focused high-power laser beam is used to melt the powders that are spread and deposited on the local surface. In the LOM process, a laser is used to cut a sheet of material along the contours of the part’s geometry as defined by the computer-aided design (CAD) model, which is stretched out on a flexible substrate. The DIW is a 3D fabrication process in which a computer-controlled nozzle has been utilized to distribute ink to create a freeform structure. In 3D printing, almost all types of materials can be used, and this process can be utilized in a wide range of applications. 3D printing technology has also been adopted in manufacturing electrochemical energy storage devices (EES) with a variety of geometries to enhance their mechanical property, power density, and energy density [14, 15]. This technique offers the possibility of manufacturing the entire EES device and its accompanying electronics in a single manufacturing step, which reduces production costs and is less expensive than producing and assembling the parts individually. Despite various 3D printing methods, DIW has gained considerable interest worldwide for the fabrication of next-generation batteries with intricate microstructures and superior performance due to its simplistic printing mechanism and affordable manufacturing process. Additionally, the DIW process offers various materials, length scales, and an exceptional structural finish [16, 17]. In 2013, Sun and co-workers [18] successfully manufactured Li-ion batteries with a 3D-interdigitated design, which may be considered one of the first attempts to fabricate a 3D-printed battery where a LiFePO4 based (LFP) cathode and an Li4 Ti5 O12 -based (LTO) anode were printed simultaneously onto a gold current collector. In this work, commercially available liquid electrolytes were used to fill the space between the pre-printed electrodes, following which all other components are packed in the 3D interdigitated micro battery architecture. Compared to the majority of conventionally made lithium-ion batteries previously mentioned in the literature, this approach offered superior areal energy and power densities. Fu et al. [19] reported a similar technique of 3D-interdigitated architecture, where they modify the LFP cathode and LTO anode composite inks by using graphene oxide (GO) to enhance the electrical conductivity of the device. After annealing the printed electrodes, the GO will be converted into reduced graphene oxide (r-GO), which increases the electrical conductivity of two electrodes from 10–4 –10–6 S/cm to 6.1–31.6 S/cm, respectively.

Materials and Applications of 3D Print for Solid-State Batteries

437

Fig. 2 Different branches and sub-branches of 3D-printing technology. The 3D printing technology has different technologies to accomplish the printing of the batteries. Each process has their own advantages and have been explored for reporting the new generation of the 3D printed solid-state batteries

In another report by Wein et al. [20], they discussed the design and electrochemical performance of a 3D printed LIB, where a semisolid biphasic electrode liquid was introduced, which improved the cell’s performance up to ten times as compared to conventional 3D interdigitated micro battery. In this process, along with the electrode inks of LPO and LTO, they mixed Ketjenblack (KB) carbon particles, creating a percolative network in the electrode solution; as a result, the rheological and ionic properties of the solution improved. Although the key benefit of using such liquid electrolyte devices is their reduced cost, the main concern lies within the safety requirement, which is the top priority of such rechargeable batteries. In this respect, the concept of solid-state electrolytes has been introduced, which has replaced liquid electrolytes in terms of safety, stability, flexibility, and excellent mechanical properties. The primary concern related to solid-state electrolyte devices is the high cell area-specific resistance (ASR), which can be minimized by manufacturing the electrolytes using 3D printing technology. Blake et al. [14] described a method for fabricating high-performing, thermally stable and flexible ceramic-polymer electrolytes that may be printed directly over the electrode without impacting the performance of any individual layers. For the first time, Li7 La3 Zr 2 O12 (LLZ) garnet was used by

438

A. Das and P. Barman

McOwen et al. [21] as a prototype solid electrolyte material to develop many solidstate electrolyte inks. This study prints and sinters a sample of potential structures, displaying thin, nonplanar, complicated constructions built mainly of LLZ solid electrolytes. It may be possible to create solid-state batteries with a significantly lower cell ASR and improved energy and power density by further investigation and improvement of electrolyte structure through 3D printing technology. Cheng et al. [22] reported a novel method of fabrication of hybrid polymer-based solid-state electrolytes using direct ink writing 3D printing at an elevated temperature. Due to their high viscosities and low melting temperatures, polymer-based electrolytes are excellent candidates for 3D printed inks. Such electrolytes could efficiently address several safety concerns, such as flammability and shorting issues inside a solid-state battery. The stability, mechanical robustness, conductivity, and practicality of the ideal solid-state electrolytes for LIBs must all be balanced. The materials for SSEs are expected to be electronically insulating but must have ionic conductivity at room temperature. For batteries that are configured in bulk, the conductivities are in the range of 10–4 S/cm–10–3 S/cm; however, in the thin film configuration, conductivities as low as 10–6 S/cm are acceptable.

3 Methodology of Additive Manufacturing of SSB’s The generation of 3D objects with the aid of digital printing methodologies is known as 3D printing or additive manufacturing. A CAD file instructs the printer to create the 3D object by connecting or deposition of materials layer by layer. There are numerous advantages of digital printing technology over subtractive or non-digital printing and fabrication methods. 3D printing technology has produced complex designs with resolution down to the order of microns and high surface area. It naturally incorporates the advantage of minimal wastage of the starting materials, thereby contributing to the low production cost. Additionally, the process is highly flexible as it allows crucial alterations by change of the CAD file that accounts for its scalability and rapid prototyping. The design of the CAD file and the architectural motifs of the solid-state LIB present quite a challenge for the researchers and require many optimizations of the processing conditions. For the bulk SSBs, designing the composite cathode consisting of 3D microstructures with micron-sized pores and electronically conducting ceramic matrices is very complex. Further, the composite cathode must be intercalated with an ionically conducting phase that can be either polymeric, ceramic, or a hybrid material. Aerosol jet (AJ) printing and laser-based SLA have successfully created scaffolds for the cathode matrix. Once the scaffolds are in place, the jetting process like inkjet (IJ) and AJ printing can be used to deposit electrolytes covering the entire porous structures. After the base scaffold is generated, the next stage of 3D printing is forming an interface between the composite cathode and bulk electrolyte. For the desired application, the direct write and the jetting techniques are best for depositing micron-thick layers of ceramic, polymeric, or hybrid materials. The disadvantage of

Materials and Applications of 3D Print for Solid-State Batteries

439

these methods lies in the large thickness of the deposited layer and the absence of flexibility in controlling the thickness. Techniques like fused deposition modeling have been reported in the literature and are highly useful if fast deposition rates are needed. Nevertheless, similar to the previous methods, the large thickness and the inability of thickness control present a significant drawback. In those conditions, sintering solid inorganic electrolytes using SLM is the best alternative for simultaneous consolidation. It has been observed that high aspect ratio features associated with the 3D interdigitated configurations to generate high volume energy densities can be achieved using the direct write printing techniques, which, as mentioned previously, provide micron-sized resolution. These technique needs to be paired up with another process that offers to integrate the electrolyte. Such an integration process can be readily achieved by the IJ or AJ printing process. However, the FDM process is more suited in this case due to its ability to create high aspect ratio features, which are not available with the previous techniques. Similarly, SLA can also be used as an alternative to FDA for creating high aspect ratio features. It is essential to mention here that the 3D printing techniques usually are incapable of matching the nanoscale spatial resolution of advanced thin film deposition techniques such as the physical vapor deposition process; the film-forming techniques like IJ and AJ provide viable alternatives. A schematic diagram of the architectural form of the 3D battery and its fabrication by the aforementioned methods and the challenges associated with their fabrication have been depicted in Fig. 3.

Fig. 3 A schematic diagram of architectural forms of 3D batteries and the different methods of fabrication of batteries. The acronyms used to describe the printing process: DIW (direct ink writing), SLS (selective laser selection), SLA (stereo lithography), LIFT (Laser induced forward transfer), AJ (aerosol jet), FDM (fused deposition modelling), and IJ (inkjet). The lines in the brown-font describes the challenges associated with the different 3D manufacturing process

440

A. Das and P. Barman

4 Materials Available for the Digital Printing of Solid-State Electrolytes The most difficult aspect of making solid-state batteries is depositing the solid electrolyte and composite cathode materials in accordance with the dimensions and resolutions necessary for the architectural motifs. As pointed out, various printing methods are available, and the majority of the necessary processes for post-printing consolidation change depending on the electrolyte composition. Some of the printing techniques, along with the associated materials, are discussed below. A schematic of the 3D printing process for fabrication of porous micro lattice electrode using the aerosol printing technology is shown in Fig. 4. Similarly, the idea of ink-jet printing technology in generating SSBs are included in Fig. 4b.

Fig. 4 a A schematic diagram of an aerogel printer, printing porous micro-lattice electrodes with interconnected networks. Adapted with permission [23], Copyright (2020), Elsevier. In b, we show the schematic diagram of the Inkjet printing technology and the process involved therein. Adapted with permission [24], Copyright (2015), Elsevier

Materials and Applications of 3D Print for Solid-State Batteries

441

4.1 3D Printing of Solid Polymer-Based Electrolytes Solid polymer electrolytes may now be digitally manufactured in place of ionic liquids since they are in high demand. There are reports showing the use of materials such as lithium salt dissolved in polyethylene oxide (PEO) to create solid polymer batteries using the IJ printing technology. The fundamental challenge associated with printing the electrolytes with IJ is the viscosity associated with the concentrated solution of the polymers [24]. If the viscosity is very high, it goes outside the range printable by IJ. To do away with the problem, a process is adopted where they formulate an ink, one of which includes an initiator, the monomeric polymer precursor, and the lithium salt. In the other process, two pairs of ink are formulated, where one contains the lithium salt and the monomeric precursor, and the other contains a polymerization catalyst. In both cases, the results are found to be similar [25]. Ink including electrode materials, an activator, and a polyether polymer material with a cross-linking group is used in a similar way to print the composite cathode/ electrolyte. When the ink has been printed successfully, a cross-linking process is used to create a composite electrode with a built-in polymer electrolyte. These restrictions are lifted in the DIW process, where the viscosity restrictions are completely eliminated so that the concentrations and molecular weights of the printable polymers can be accommodated for a wider variety [24].

4.2 3D Printed Gel Polymer-Based Electrolytes Gel polymer electrolytes have also been studied in parallel with solid polymer electrolytes, and significant progress has been made towards the fabrication of the actual solid-state batteries. For instance, by DIW of a complete lithium-ion battery, a solidelectrolyte layer of poly-vinylidene fluoride (PVDF)-co-Hexafluoropropylene (HFP) was printed across the interdigitation gaps in between a lithium iron phosphate/ graphene oxide (LFP/GO) cathode and lithium titanate /graphene oxide (LTO/GO) anode [26]. After printing both the cathode and the anode layers, the PVDF-co-HFP was deposited, and then it was submerged in a common liquid electrolyte to create a gel polymer electrolyte. The arrangement demonstrated a very promising initial discharge capacity of 91 mAhg−1 at a rate of 50 mAg−1 . The DIW of a PVDF-coHFP material and its performance as a separator indicated the development of a fully solid-state 3D printed interdigitated lithium-ion battery [5]. Finally, a 3D gel polymer electrolyte based on polyethylene glycol (PEG) was recently produced using micro stereolithography. It is advantageous that micro stereolithography has a better spatial resolution (~ 10 µm), if the technique could be applied to the fabrication of suitable solid polymer electrolytes, it would pave the way for the 3D printing of electrolytes with intricate interdigitated patterns [27].

442

A. Das and P. Barman

4.3 3D Printed Gel Ceramic-Based Electrolytes One of the primary examples of 3D printed oxide-based lithium-ion-conducting inorganic electrolytes is the recent direct write of Li7 La3 Zr 2 O12 (LLZ). For the process, two ink formulations were developed [28]. One formulation includes benzyl butyl phthalate (BBP) as a binder, Menhaden fish oil dispersion, polyvinyl butyral (PVB), plasticizers, and a solvent system of n-butanol and α-terpinol. The second ink system depends on the binder system that exhibits Bingham plasticity. It is specially designed for 3D interdigitated battery configurations and has a higher aspect ratio of self-supporting structures. Both these inks were printed on LLZ substrates to demonstrate the variety of LLZ structures attainable and how they vary with the ink rheology. The conformal ink, on the other hand, was printed on a mylar substrate, which, after sintering, produced a free-standing film of 10 µm thickness. The 100-µm layers that are typically formed are far thicker than the 10 µm layer thickness [29]. This work paved the path for the 3D printing of the Li-ion solid electrolytes. This work showed the viability of the traditionally adopted type casting techniques for the ceramic materials that could be manufactured additively using the Li-ion-conducting solid-phase electrolytes. SLA demonstrated a different strategy for digitally printing microstructured inorganic solid polymer electrolytes by replicating the polymer templates in the opposite direction. In the technique, the electrolytes used are lithium aluminium germanium phosphate (LAGP) powder, which is filled in the 3D printed polymer cast. The polymer cast vaporizes off during the sintering process and leaves out a porous scaffold made entirely of LAGP powder [30]. To enhance the mechanical strength, the scaffolds are filled up with an inert ceramic, which is also essential in maintaining the ambient conductivities in the range of ~ 10–4 S/cm, a value required for solid-state electrolytes.

5 Future Materials for 3D Printing and the Associated Challenges The digital printing of batteries is still in its initial days, and most 3D printed batteries heavily rely on ionic liquids and polymer electrolyte systems. Recently, effort has focused on printing sodium superionic conductor (NASICON) ceramic electrolytes and highly structured garnet. It has been demonstrated that the ceramic electrolyte structures utilised in these systems can be manufactured in both high and low aspect ratios. However, it has been identified that in the recent future, there are much scope to expand the selection of materials used for designing electrolytes to achieve the 3D printing of ASSLBs. For instance, a ceramics-reinforced polymer matrix has not been used in 3D printing. Using the ceramic-polymer matrix can help improve the mechanical strength and conductivity apart from preserving the excellent processability of the polymers.

Materials and Applications of 3D Print for Solid-State Batteries

443

Similarly, 3D printing of ceramic electrolytes has much scope for expansion, especially in post-deposition processing that allows their fabrication in battery cells. Such information would be crucial in designing of ceramic electrolyte/lithium metal anode battery systems. Again, with respect to solid polymer electrolytes, there are excellent opportunities for the use of new polymers that enhance the cross-linking, and at the same time, have excellent room temperature conductivities or mechanical strength compared to the standard PEO electrolytes. Over and above, a lot of research needs to be conducted to optimize the printing parameters to incorporate a broader range of materials for the generation of 3D printed batteries. Researchers must be able to show the macro-scale integration of the printed batteries into the structures they require to power on the micro- and mesoscales in order to progress the digitally printed solid-state batteries for rugged usage in powering electronics. Some potential future materials that can be used to develop the next generation of 3D printed batteries are discussed briefly in the following section.

5.1 Polymer Based Materials Polymer electrolytes have undergone several exciting improvements in the last few years, and 3D printing of such polymeric materials depends highly on the nature of the material (melt or solution). It is essential to determine earlier if the digital printing of these electrolytes in melt or solution form would lead to better results. In the case of PEO polymer, a room temperature conductivity of 10–4 S/cm has been achieved by grinding followed by pressing with tetraglyme, lithium salt, and a photo-induced hydrogen abstractor with the predominant role of initiating a free-radical chain reaction to interlink the PEO [31, 32]. This modification of PEO allows the material to be compatible with FDM, which has the distinct advantage of allowing solventfree deposition of polymeric materials. Similarly, the modified PEO also goes with SLA that depends on the photoactivity of the formulation. However, it is essential to mention that the solvent-free deposition of PEO shall not apply to IJ or AJ techniques that needs viscosities lesser than 10 cPs and 500 cPs, respectively. However, there might be other highly conducting polymers processed via solutions and are compatible with IJ and AJ printing methods. In this regard, mention can be made of jeffamine films, which are solution-processed and has better room temperature conductivity.

5.2 Ceramic Polymer Composites The field of ceramic has proven to be an astonishing achievement in additive manufacturing technology because of its ability to create intricate designs while enhancing the production efficiency and manufacturing approach. Ceramic composites might be produced and enhance their mechanical properties by employing powder-based

444

A. Das and P. Barman

3D printing technology such as FDM, SLA, IJ, etc. For solid-state batteries, ceramic composite electrolytes are shown to be more effective in terms of room temperature conductivity and mechanical properties than polymer or hybrid polymer-ceramic composite electrolytes. The main challenge of 3D manufacturing ceramic electrolytes, as well as, recognizing their excellent conductivity in battery configuration, entails developing a method or chemical to remove the grain boundaries that appear in electrolytes without affecting the interfacial resistance of battery electrodes and electrolytes. This can be overcome by manufacturing the electrode ink from substances, which has low sintering temperatures and suitable interface formation with the electrode materials. Recently, Yamada et al. [33] developed highly conducting surfacemodified ceramic electrolytes with non-sintered low grain boundary resistance. Here, the concept of defects distribution has been used to manufacture the core– shell ceramic electrolytes, where the surface of a highly conductive core material Li1.3 Al0.3 Ti1.7 (PO4 )3 (LATP) was coated with a poorly conductive shell material Li2 SiO3 (LSO). This method enhances the conductivity of the core electrolyte material, and the overall conductivity of the final electrolyte is found to be ~ 10–6 Scm−1 , which is a lower value to be used as composite electrodes of SSBs. The limitations that appeared in the direct ink method for a 3D printing solid-state battery can be overcome by switching to the SLA method, where shape formation and sintering of the electrolytes take place simultaneously in a single step, which alternately decreases the electrolyte/electrolyte grain boundary resistance and interfacial resistance of electrode/electrolyte.

5.3 Hybrid Polymer-Ceramic Composites Since each type of solid electrolyte (polymer or ceramic) exhibits a variety of advantages and disadvantages in terms of mechanical properties and conductivities, the challenge of manufacturing an ideal solid electrolyte that combines high conductivity with good mechanical properties is one of the biggest concerns till date. In this regard, researchers have put effort into combining these two electrolytes to produce a composite electrolyte to get the best possible result in enhanced conductivity and mechanical property. An ionically conducting ceramic phase is an essential component of the ideal polymer/ceramic composite material because it not only improves the amorphicity of the polymer but also offers a low resistance channel for ionic conduction. In order to expand their range in the field of 3D printing technology, ceramic fillers have been added to a PEO-based polymer matrix to improve the ionic conductivity and the interfacial property in contact with the electrodes. The filler size and its properties are found to be crucial elements for enhancing the electrochemical properties of polymer electrolytes. A report by Corce et al. [34] showed that the highest conductivity could be achieved in a nanocomposite polymer-ceramic electrolyte when nanoparticle size ceramic powder has been mixed with polymer matrix, which makes them ideal for most additive manufacturing techniques. A colloidal dispersion of ceramic nanoparticles and polymers has been developed for the AJ and

Materials and Applications of 3D Print for Solid-State Batteries

445

IJ printing procedures, while a solvent-free formulation has been used for the FDM technique.

6 Conclusions Solid-state batteries are now regarded as the industry leader among rechargeable battery technologies due to their significantly improved performance in terms of power and energy maintenance, which meets the requirements of growing energy storage needs, and can be used in many portable electronic gadgets. The next generation SSBs with more complex structures and many other features can be obtained by utilizing the latest 3D printing techniques, a promising and quickly expanding area of recent technology. This review briefly discusses the various aspects of 3D printing and their applications in developing SSBs. These factors have been associated with manufacturing various types of solid electrolytes and their future challenges. The advantages of 3D printed SSBs are low fabrication cost, complex structures, high surface area with control up to micrometric scale, and minimal material loss. Additionally, because the entire process can be managed from the outside, this technology reduces the several manufacturing phases of SSBs to a one-step procedure. Various customshaped SSBs such as micro-batteries and fibre-type batteries are achievable using 3D printing technology and integrated directly into a variety of powered wearable devices. The most challenging aspect of making solid-state batteries is depositing solid electrolyte and composite cathode materials with the necessary dimensions and resolutions, which are overcome by producing various types of solid electrolytes using 3D printing methods, as discussed in Sect. 4. Although the use of 3D printing in the production of SSBs is still in its early stages, the introduction of new materials and form factors might significantly increase this industry in the upcoming years.

References 1. Zaman W, Hatzell KB (2022) Processing and manufacturing of next generation lithium-based all solid-state batteries. Curr Opin Solid State Mater Sci 26:101003 2. Ding Y, Cano ZP, Yu A, Lu J, Chen Z (2019) Automotive li-ion batteries: current status and future perspectives, electrochem. Energy Rev 21(2):1–28 3. Hwang S, Kim SM, Bak SM, Chung KY, Chang W (2015) Investigating the reversibility of structural modifications of LixNiyMnzCo1-y-zO2 cathode materials during Initial charge/ discharge, at multiple length scales. Chem Mater 27:6044–6052 4. Li Y, Wang F, Huang B, Huang C, Pei D, Liu Z, Yuan S, Hou S, Cao G, Jin H (2022) A high power density solid electrolyte based on polycaprolactone for high-performance all-solid-state flexible lithium batteries. Electrochim Acta 424:140624 5. Reyes C, Somogyi R, Niu S, Cruz MA, Yang F, Catenacci MJ, Rhodes CP, Wiley BJ (2018) Three dimensional printing of a complete lithium ion battery with fused filament fabrication. ACS Appl Energy Mater 1:5268

446

A. Das and P. Barman

6. He Y, Chen S, Nie L, Sun Z, Wu X, Liu W (2020) Stereolithography three-dimensional printing solid polymer electrolytes for all-solid-state lithium metal batteries. Nano Lett 20:7136–7143 7. Kong D, Wang Y, Huang S, Zhang B, Von Lim Y, Sim GJ, Valdivia P, Alvarado Y, Ge Q, Yang HY (2020) 3D printed compressible quasi-solid-state nickel-iron battery. ACS Nano 14:9675–9686 8. Huang SH, Liu P, Mokasdar A, Hou L (2013) Additive manufacturing and its societal impact: a literature review. Int J Adv Manuf Technol 67:1191–1203 9. Guo N, Leu MC (2013) Additive manufacturing: technology, applications and research needs, Front. Mech Eng 8:215–243 10. Jacobs PF (1992) In: Reid DT (ed) Rapid prototyping & manufacturing: fundamentals of stereolithography. SME Publication, Dearborn 11. Beaman JJ, Barlow JW, Bourell DL, Barlow JW, Crawford RH, McAlea KP (1997) Solid freeform fabrication: a new direction in manufacturing. Springer, New York, pp 23–49 12. Mazumder J, Schifferer A, Choi J (1999) Direct materials deposition: designed macro and microstructure. Mater Res Innov 3:118–131 13. Feygin M, Hsieh B (1991) Laminated object manufacturing (LOM): a simpler process. In: Proceedings of solid freeform fabrication symposium, Austin, TX, pp 123–130 14. Blake AJ, Kohlmeyer RR, Hardin JO, Carmona EA, Maruyama B, Berrigan JD, Huang H, Durstock MF (2017) 3D printable ceramic–polymer electrolytes for flexible high-performance Li-ion batteries with enhanced thermal stability. Adv Ener Mater 7(1602920):1–10 15. Wang Y, Chen C, Xie H, Gao T, Yao Y, Pastel G, Han X, Li Y, Zhao J, Fu KK, Hu L (2017) 3D-printed all-fiber Li-ion battery toward wearable energy storage. Adv Funct Mater 27(1703140):1–8 16. Lewis JA, Gratson GM (2004) Direct writing in three dimensions. Mater Today 7:32–39 17. Lewis JA (2006) Direct ink writing of 3D functional materials. Adv Funct Mater 16:2193–2204 18. Sun K, Wei TS, Ahn BY, Seo JY, Dillon SJ, Lewis JA (2013) 3D Printing of interdigitated Li-ion microbattery architectures. Adv Mater 25:4539–4543 19. Fu K, Wang Y, Yan C, Yao Y, Chen Y, Dai J, Lacey S, Wang Y, Wan J, Li T, Wang Z (2016) Graphene oxide-based electrode inks for 3D-printed lithium-ion batteries. Adv Mater 28:2587– 2594 20. Wei TS, Ahn BY, Grotto J, Lewis JA (2018) 3D printing of customized Li-ion batteries with thick electrodes. Adv Mater 30(1703027):1–7 21. McOwen DW, Xu S, Gong Y, Wen Y, Godbey GL, Gritton JE, Hamann TR, Dai J, Hitz GT, Hu L, Wachsman ED (2018) 3D-printing electrolytes for solid-state batteries. Adv Mater 30(1707132):1–7 22. Cheng M, Jiang Y, Yao W, Yuan Y, Deivanayagam R, Foroozan T, Huang Z, Song B, Rojaee R, Shokuhfar T, Pan Y, Lu J, Shahbazian-Yassar R (2018) Elevated-temperature 3D printing of hybrid solid-state electrolyte for Li-ion batteries. Adv Mater 30(1800615):1–10 23. Ollinger M, Kim H, Sutto T, Pique A (2006) Laser printing of nanocomposite solid-state electrolyte membranes for Li micro-batteries. Appl Surf Sci 252(23):8212–8216 24. Delannoy P-E, Riou B, Lestriez B, Guyomard D, Brousse T, Le Bideau J (2015) Towards fast and cost-effective ink-jet printing of solid electrolyte for lithium microbatteries. J Power Sources 274:1085 25. McOwen DW, Xu S, Gong Y, Wen Y, Godbey GL, Gritton JE, Hamann TR, Dai J, Hitz GT, Hu L (2018) 3D printing Electrolytes for Solid-State Batteries. Adv Mater 30:1707132 26. Fu K, Wang Y, Yan C, Yao Y, Chen Y, Dai J, Lacey S, Wang Y, Wan J, Li T (2016) Graphene oxide-based electrodes inks for 3D-printed lithium-ion batteries. Adv Mater 28:2587 27. Chen Q, Xu R, He Z, Zhao K, Pan L (2017) Printing 3D gel polymer electrolyte in lithium-ion microbattery using stereolithography. J Electrochem Soc 164:A1852 28. Richerson DW, Lee WE (2018) Modern ceramic engineering: properties, processing, and use in design. CRC Press, Boca Raton 29. Young D, Sukeshini AM, Cummins R, Xiao H, Rottmayer M, Reitz T (2008) Ink-jet printing of electrolyte and anode functional layer for solid oxide fuel cells. J Power Sources 184:191

Materials and Applications of 3D Print for Solid-State Batteries

447

30. Sukeshini MA, Cummins R, Reitz TL, Miller RM (2009) Ink-jet printing: a versatile method for multilayer solid oxide fuel cells fabrication. J Am Ceram Soc 92:2913 31. Sukeshini AM, Gardner P, Meisenkothen F, Jenkins T, Miller R, Rottmayer M, Reitz TL (2011) Aerosol jet printing and microstructure of SOFC electrolyte and cathode layers. ECS Trans 35:2151 32. Zhu Y, Li J, Saleh MS, Pham H, Plateau TP, Panat R, Park J (2020) Towards high-performance, Li-ion batteries via optimized three-dimensional micro-lattice electrode architectures. J Power Sources 476(228593):1–18 33. Yamada H, Tsunoe D, Shiraishi S, Isomichi G (2015) Reduced grain boundary resistance by surface modification. J Phys Chem C 119:5412–5419 34. Croce F, Persi L, Ronci F, Scrosati B (2000) Nanocomposite polymer electrolytes and their impact on the lithium battery technology. Solid State Ionics 135:47–52

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical Treatment to Obtain Materials with Highly Improved Capacitive Current Thalita Centofanti, Maria de A. Silva, Mariana G. Segatelli, and César R. T. Tarley

Abstract Poly(organosilanes) are organic–inorganic polymers composed of the main inorganic chain (Si–O-Si) and organic groups or hydrogen that when exposed to thermal treatment conditions in an inert atmosphere, turn into silicon oxycarbide (SiOC) based ceramic materials. Some attractive highlights of SiOC derived from silicon polymers include high thermal and chemical stabilities, low densities, and good mechanical, optical, and electrical properties. These properties allow their use in several technological applications such as high-temperature receivers, ceramic coatings for high-temperature corrosion, ceramic membranes for water purification, high-resistance fibers, luminescent thin films, voltammetric sensors, and supercapacitors. In this work, SiOC ceramic materials were produced from 1,3,5,7-tetramethyl1,3,5,7-tetravinylcyclotetrasiloxane (D4Vi) crosslinked via radical reaction, which after acid treatment showed notable characteristics for electrical properties, as greater exposure of the Cfree phase and expressive values of the specific area. Specific capacitance values demonstrated that the application of SiOC materials in the supercapacitors field is promising. Thus, poly(organosilanes)-derived SiOC materials showed to be a viable option for the production of ceramic supercapacitors. Keywords SiOC ceramics · Polysiloxanes · HF etching · Supercapacitors

T. Centofanti · M. de A. Silva · M. G. Segatelli · C. R. T. Tarley (B) Chemistry Department, State University of Londrina, Celso Garcia Cid, PR 445, Km, 380, Zip Code 10.011, Londrina, PR, Brazil e-mail: [email protected] C. R. T. Tarley Chemistry Institute, Bioanalytical National Institute of Science in Technology (INCT), State University of Campinas (UNICAMP), 13083-970, Campinas, SP, Brazil © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_26

449

450

T. Centofanti et al.

1 Introduction 1.1 Polymer Derived Ceramics (PDCs) Quaternary, ternary and secondary systems involving silicon, oxygen, carbon, boron, and nitrogen atoms consist of the main Si-containing ceramics groups fabricated by the polymer pyrolysis route. Different combinations of polymeric precursors and synthesis techniques make it possible to obtain materials with excellent thermal, mechanical, and electrical properties [1, 2]. The great interest in this preparation method is due to the advantages over the conventional method of preparing ceramics. The conventional method involves reactions in the solid state at high temperatures of approximately 2400 °C, generating products exclusively in powder form, with large particles and little chemical homogeneity [3]. However, the polymer pyrolysis method uses lower temperatures (between 800 and 1500 °C) and reagents in the liquid state, which allows the association of polymer processing techniques, giving rise to final products in different forms such as fibers, films, filters, and monolithic, thus expanding the application potential of this materials class [1, 4]. The characteristics of the PDCs depend on several factors including the polymer chemistry (structure and composition) and pyrolysis conditions such as temperature, time, isotherm, and atmosphere, which can be inert or reactive, oxidizing phases present in the ceramic matrix or incorporating them during the process, forming new phases [5]. Following, the discussions addressed in this book chapter will be restricted to PDCs derived from polysiloxanes.

1.2 Polysiloxanes Polysiloxanes are polymers consisting of an inorganic silicon backbone bonded to oxygen simultaneously and organic groups (methyl, vinyl, phenyl) or hydrogen, as shown in Fig. 1. The chemical stability of polysiloxanes at elevated temperatures is a consequence of the main chain, in which the strong bond between silicon and oxygen atoms confer resistance and flexibility to the material [6]. The molecular architecture of polymeric precursors and knowledge about structural evolution, which involves curing processes and polymer-ceramic transformation, are relevant parameters when the aim is to improve the performance of ceramic materials in certain applications [5, Fig. 1 Representation of the general polysiloxane structure, where R indicates organic groups or hydrogen

R

1

Si R

2

O n

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

451

7]. Various types of syntheses can be used for cross-linking of silicones, one of them is the use of a metal-free system using free radicals as reaction initiators. Firstly, an initiator, from the peroxide decomposition, is added to the monomer to convert some molecules into radicals. The initiator breaks into radicals, and each radical attaches to a monomer chain containing an unsaturated bond, converting it to a radical. This radical reacts with another monomer, adding a new subunit that propagates the chain [8, 9]. The choice of starting monomers can generate distinct molecular architectures in the polymeric precursors. Cyclic monomers normally generate more opened and less compact structures due to the void spaces among the cycles, in contrast to linear polymers that reveal more compact structures [7].

1.3 Polysiloxanes to SiOC Ceramics Conversion Preparation of SiOC ternary systems using silicon polymers is based on three main processes: polymer synthesis using previously selected silicon monomers or oligomers; molding step to obtain structures with high crosslinking density and, finally, controlled pyrolysis, which includes important structural transformations during heating. From room temperature to 400 °C, the organic–inorganic transition process begins, in which the degradation of the polymeric network and volatile compounds release occurs depending on the reaction mechanism [10]. At temperatures close to 800 °C, the transition from polymeric network to non-crystalline ceramics generally takes place, which is based on the structure containing tetrahedral silicon sites [11]; At temperatures above 1200 °C, Si sites undergo continuous rearrangements in the ceramic matrix and the crystallization processes are now favored, resulting in the silicon carbide (β-SiC), silica (SiO2 ) and graphite (Cgraphitic ) formation [12, 13]. During the mineralization stage (~ 1000 °C), a metastable non-crystalline ceramic matrix is usually obtained, composed of SiO4, SiO3 C, SiO2 C2, SiOC3, and SiC4 sites randomly distributed, named in the literature as Q, T, D, M, and C units, respectively [10, 11]. In addition to this structural fraction, the volatile hydrocarbons released and the organic content of the polymeric precursor play a great role in the residual carbon phase formation in the matrix, consisting of Csp3 and Csp2 domains. The use of polymeric precursors containing saturated organic groups (methyl, ethyl, and propyl) generally results in ceramics with a lower free carbon amount when compared to unsaturated groups (vinyl and phenyl) [12]. Thus, the proportion of this phase can be controlled by the molecular structure of the selected precursors. Above 1200 °C, some crystallization processes occur. The first one is the carbothermal reduction, in which carbon is reduced by silica sites or sites rich in Si–O bonds, forming the SiC semiconductive phase, as represented by the global (Eq. 3) and partial equations (Eqs. 1 and 2) [13, 14]: C(s) + SiO2(s) → SiO(g) + CO(g)

(1)

452

T. Centofanti et al.

2C(s) + SiO(g) → SiC(s) + CO(g)

(2)

3C(s) + SiO2(s) → SiC(s) + 2CO(g)

(3)

In addition to carbothermal reduction reaction, continuous rearrangements of silicon sites take place in the ceramic matrix, according to reactions pointed out in the Eqs. 4–6. SiO3 C(s) + SiOC(s) → SiO2 C2(s) + SiO4(s)

(4)

SiO2 C2(s) + SiO3 C(s) → SiOC3(s) + SiO4(s)

(5)

SiO3 C(s) + SiO3 C(s) → SiC4(s) + SiO4(s)

(6)

At higher temperatures, SiOC decompose resulting in the phase separation of ceramic matrix, as represented in Eq. 7 [11]. 2SiOC(s) → SiC(s) + SiO2(s) + C(s)

(7)

Despite the structural transformation in the ceramic matrix involves the combination of the two processes, one of them is favored in relation to the other. It was reported that greater carbon content in the precursor leads to structural transformations in the ceramic, as represented by the Eq. 3, while the contrary provides better conditions for the phase separation reactions (Eq. 7), without involving significant mass loss. These processes are not independent of each other and may occur one after the other [14, 15]. As aforenmentioned, the crystallization process in materials occurs at high temperatures and involves phase separation and carbothermal reduction reactions, which reveal desirable characteristics for electrochemical applications, due to the SiC and free carbon formation. In addition to choice of suitable polymeric precursors, the heating involving isotherms at high temperatures can be used to intensify this process in the resulting ceramics [16]. The potential of these materials in electrical applications is mainly due to the presence of semiconductive and conductive phases (SiC and Cgraphitic ) formed in the ceramic matrix, by means the previously mentioned reactions. Though, insulating domains compose of SiO2 can negatively influence the electron percolation, resulting in unsatisfactory electrical performance [17].

1.4 Hydrofluoric Acid (HF) Etching Rich silicon-oxygen domains, such as SiO2 clusters and SiO2 nanocrystals can affect the electrical behavior of this materials class due to the insulating nature of these

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

453

phases. These domains can be removed and/or minimized by chemical treatment with aqueous hydrofluoric acid (HF) solution [18, 19], according to reaction in Eq. 8. SiO2(s) + 6HF(aq) → H2 SiF6(g) + 2H2 O(l)

(8)

The advantage of this method is that Si–O bonds are attacked by the fluoride anion, whereas Si–C bonds (less ionic character), domains composed of SiOx Cy and free carbon are not attacked in the process. Therefore, the dissolution of rich silica regions results in more porous SiOC ceramics at the end of the process, with considerable enhancement at the specific area and, consequently, the contact surface of the material [18, 20, 21]. The combination of crystalline phases and high specific area provided by the chemical treatment are promising strategies to improve the electrical properties of polysiloxanes derived SiOC ceramics.

1.5 Electrochemical Capacitors Supercapacitors, also called electrochemical capacitors, are energy storage devices that combine the typical properties of batteries with those of ordinary capacitors, such as high energy density and high power, respectively [22]. Supercapacitors can be divided into two main categories, depending on the active material and type of mechanism involved in the charge storage process. They are electrochemical double-layer capacitors (EDLCs) and pseudocapacitors. In EDLCs, charge accumulation occurs through the rapid ions adsorption at the electrode-solution interface. Thus, it is possible to infer that the performance of this material depends on the specific area, roughness, volume and pore size present in the active material. Materials commonly used as EDLCs are carbon derivatives, such as nanotubes, graphene, and activated in [22–24]. In pseudocapacitors, charge storage occurs through the charge transfer process at the electrode-solution interface. Materials classified in this group are some transition metal oxides and hydroxides and conductive polymers. However, the low mechanical stability and low conductivity of some of these materials affect the behavior of these supercapacitors [24, 25]. Due to this, a combination of these materials is made to have desired characteristics in terms of power, energy, and stability in the final material. Furthermore, some materials used as electrochemical capacitors share some common features, including large specific area and high porosity, good surface wettability, high electrical conductivity, long cycle stability (> 100,000 cycles), easy manipulation of morphology (size, pore distribution and particle size) and thermodynamic stability for a wide applied potential range [26, 28]. These devices have been widely studied due to the high demand for electricity focusing on high-performance, low-cost, and environmentally friendly power devices [22].

454

T. Centofanti et al.

2 Experimental 2.1 Synthesis of Polymeric Precursor Polymeric precursor was obtained by radical polymerization involving the 1,3,5,7tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (D4 Vi) cyclic monomer and 1 wt. % of dicumyl peroxide as catalyst. The mixture was magnetically stirred for 1 h and submitted to 380 °C for 5 h, under inert argon atmosphere for crosslinking. The resulting polymer presented yellow color and bubbles.

2.2 Preparation of SiOC Ceramic Materials Polymeric precursor was submitted to controlled pyrolysis process using a hightemperature oven containing an adapted alumina tube (EDG10P-S), under constant argon flow. The polymer was heated from 25 to 1500 °C and maintained for 1, 3, and 5 h at final temperature. Following, the polymers were cooled down to 25 °C. The maximum temperature and isotherm conditions were chosen due to the important structural transformations caused in the ceramic matrix (redistribution reactions and crystallization and phases segregation processes). Ceramics obtained were ground and sieved at ≤ 106 μm for better control of the particles size for further chemical treatment and characterizations.

2.3 Hydrofluoric Acid (HF) Etching About 0.5000 g of the obtained ceramics were immersed in 25 mL of a 20% (v/v) HF aqueous solution for 48 h in a polypropylene flask. After that, the ceramics were washed with ultrapure water and dried at 100 °C for 8 h in an oven [26].

2.4 Code of SiOC Ceramic Materials Table 1 compiles the codes of ceramic materials obtained at 1500 °C during 1, 3 and 5 h before and after HF treatment.

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical … Table 1 Code of synthesized materials

Starting reagent D4 Vi

455

Isotherm times at 1500 °C (h)

Without HF

Ceramics With HF

1

C1h

C1h_HF

3

C3h

C3h_HF

5

C5h

C5h_HF

2.5 Characterization Techniques The thermal stability and degradation events of the polymeric networks were analyzed in a thermogravimetric analyzer (PerkinElmer, TGA 4000). Approximately 15 mg of powdered polymers were heated from 30 to 900 °C, with a heating rate of 10 °C min−1 and nitrogen flow of 20 mL min−1 . Fourier transform infrared (FT-IR) spectra of the polymeric precursor and respective ceramics were obtained on a Fourier transform infrared spectrometer (Bruker® , Vertex 70) with a platinum attenuated total reflectance (ATR) accessory. All spectra were registered in the 2000–400 cm−1 range, with 16 scans and spectral resolution of 4 cm−1 . X-ray diffraction (XRD) patterns of ceramic samples were acquired on a diffractometer (PANalytical, X’Pert PRO MPD, Malvern Panalytical) with CuKα radiation, in the technique Bragg Brentano geometry. The voltage and current were 40 kV and 30 mA, respectively. The segregated carbon phase in the ceramic matrices was evaluated by Raman spectroscopy on a confocal spectrometer (WITec confocal equipment, Alpha300+) with an excitation laser of 532 nm and resolution of 8 cm−1 . Raman spectra were deconvoluted with the Lorentzian function by using the Origin 2017® software. The correlation coefficient were > 0.98 for all the cases. Nitrogen gas physisorption at 77 K experiments were conducted on an automatic N2 gas adsorption instrument (Quantachrome, Nova 1200e) to obtain the specific surface area (SSA), average pore volume (APV) and diameter (APD) values. Prior to analyses, the powdered samples were heated at 350 °C for 2 h, under vacuum. SA values were determined by the Brunauer-EmmetTeller (B.E.T.) method [27], using the adsorption isotherms, whereas the desorption isotherms were used for determining the APV and APD values, according to Barret-Joyner-Halenda (B.J.H.) method [28].

2.6 Electrochemical Assays Electrochemical measurements were performed using a potentiostat/galvanostat (PalmSense) using Ag/AgCl 3.0 mol L−1 as reference electrode, and an auxiliary platinum electrode. Working electrodes were prepared with each of the SiOC ceramics before and after the chemical treatment. To obtain the working electrodes, pastes were prepared with the powdered ceramic material in the ceramic:nujol® 80:20 (% m/m) proportion and introduced into the cavity of a paste electrode. For cyclic voltammetry

456

T. Centofanti et al.

measurements, KOH at 3 mol L−1 was used as support electrolyte. Electrochemical impedance spectroscopy (EIS) analyses were performed on a PalmSens 4 potentiostat/galvanostat (Palm Instruments BV® ), controlled by PSTrace 5.9 software (Palm Instruments BV® ), using potassium hexacyanoferrate (K3 [Fe(CN)6 ]) at 1 mmol L−1 concentration in 1 mol L−1 KCl as an electrochemical probe. Measurements were recorded at half-wave potential, in the frequency range from 100 kHz to 0.1 Hz, with 7 points per decade, and potential amplitude of 10 mV.

3 Results and Discussion 3.1 Structure Characterization and Thermal Stability of the Polymeric Precursor Polymerization involving radical reactions of the polymeric precursor system, according to the literature [7], results in a three-dimensional network of D4 Vi monomers bonded to each other by ethyl, propyl, and butyl bridges, from the combination of terminal organic groups (–CH3 and –CH=CH2 ), as represented in Fig. 2. FT-IR spectra of the D4 Vi monomer and polymeric precursor are shown in Fig. 3a. Absorptions bands assigned to νSi–O–Si, νSi–CH3 , νSi–CH–CH2 , νCH=CH2 and νCsp3 -H at 1080, 1262, 1404, 1595, 2968 cm−1 , respectively, were observed for the starting cyclic silicone [29]. Carbon bridges formed after polymerization reaction were evidenced by the arising of a band at 2890 cm−1 region, characteristic of νC–H of aliphatic groups. Polymeric precursor revealed high thermal stability, with mass loss of only 25% up to 900 °C, as illustrated in Fig. 3b. The more intense first event (427–665 °C), exhibited in DTG curve, was attributed to the polymeric network degradation, including the breakage of non-crosslinked Si–C terminations. The second thermal degradation event, in the 700–800 °C range, is characteristic of the mineralization process from polymeric network to ceramic matrix, in which rearrangements of the silicon sites give rise to silicon oxycarbide formation [30]. Characterization of SiOC Ceramic Materials Ceramic materials produced before (C1h, C3h, and C5h) and after chemical treatment with hydrofluoric acid (HF) aqueous solution (C1h_HF, C3h_HF, and C5h_HF) were characterized by infrared spectroscopy and the FT-IR spectra can be seen in Fig. 4. All materials before chemical treatment revealed absence of organic groups and three absorption bands attributed to νSi–O–Si, νSi–C and δSi–O, typical of SiOC ceramic matrices [29]. Though, a markable diminishing of νSi–O–Si and δSi–O was verified in the HF-treated ceramics (C1h_HF, C3h_HF, and C5_HF), confirming the partial removal of rich Si–O regions in the ceramic matrices after using hydrofluoric acid. XRD patterns of ceramic materials before and after HF treatment are shown in Fig. 5.

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

457

Fig. 2 Schematic representation of the polymeric precursor synthesized by radical polymerization at 380 °C for 5 h, using dicumyl peroxide as catalyst

All ceramic materials revealed diffraction signals at 35.8°, 60° and 70° (2θ), corresponding to (111), (220) and (311) crystallographic planes of SiC phase. In addition, the halo centered at 24° (2θ) is assigned to random distribution of tetrahedral Si sites (SiOx Cy ) in the ceramic matrix [31]. HF treatment promoted a visible amorphization in the ceramic samples (Fig. 5b) when compared with those without treatment (Fig. 5a), as can be noticed by the broadening diffraction signals of SiC, more evident

458

T. Centofanti et al.

Fig. 3 FT-IR spectra of the D4 Vi monomer and polymeric precursor (a) and TG and DTG curves of the synthesized polymeric precursor (b)

Fig. 4 FT-IR spectra of ceramic materials obtained before (C1h, C3h, and C5h) and after chemical treatment with hydrofluoric acid (HF) aqueous solution (C1h_HF, C3h_HF, and C5h_HF)

halo at 24° (2θ) and arising of a hump at 43° (2θ), ascribed to turbostratic carbon [31]. The chemical treatment usually acts in the Si sites mainly composed of Si– O bonds (SiO4 , SiO3 C, SiO2 C2 , and SiOC3 ), leaving more exposed the SiC4 and Cfree domains. However, the results suggest that there are still phases containing Si–O bonds, indicating that the complete dissolution of these sites is difficult to be achieved due to the complex matrix of this materials class [21]. Residual carbon phase (or Cfree ) was characterized by Raman spectroscopy and spectra of all ceramic materials were displayed in Fig. 6. All ceramics showed D and G bands around 1350 and 1580 cm−1 , respectively, typical of carbon-containing materials. D mode corresponds to “disorder” band and indicates the presence defects in carbon structure, thereby is inactive in perfect graphitic arrangements. G band is attributed to in

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

459

Fig. 5 XRD patterns of ceramic materials obtained before (a) and after chemical treatment with hydrofluoric acid (HF) aqueous solution (b)

plane stretching of Csp2 pairs, having E2g symmetry and appears for all organized Csp2 , present in cyclic and linear structures [32]. Notably, the presence of Csp2 is responsible for assigning conductive property to the Cfree phase. Intensity and full width at half maximum (FWHM) values were compiled in Table 2. More intense D and G bands in combination with lower FWHM values for HFtreated ceramics (Table 2) are in agreement with spectra profiles (Fig. 6). The evolution of both D and G bands indicates that carbon free phase was more exposed in the ceramic matrices after partial removal of rich Si–O sites with HF aqueous solution. Moreover, the predominance of D band over G band in all ceramics confirmed the disordered nature of the Cfree phase. The amorphization verified after chemical treatment in XRD patterns (Fig. 5b) was corroborated with Raman spectroscopy, by comparing the D band intensities between HF-treated with the analogous HF non-treated samples (Fig. 6 and Table 2). Fig. 6 Raman spectra of ceramic materials obtained before (C1h, C3h, and C5h) and after chemical treatment with hydrofluoric acid (HF) aqueous solution (C1h_HF, C3h_HF, and C5h_HF)

460

T. Centofanti et al.

Table 2 Intensity (I) and full width at half maximum (FWHM) values of the D and G bands of ceramics obtained before and after chemical treatment with hydrofluoric acid (HF) aqueous solution, extracted from deconvoluted Raman spectra Material

ID C1h

FWHM (cm−1 )

Intensity (cps) 325

IG

D

G

178

104

77

C1h_HF

996

567

93

68

C3h

319

176

98

84

C3h_HF C5h C5h_HF

1190

590

91

75

271

132

102

81

1123

696

89

69

Textural characteristics of the ceramic materials were characterized by N2 gas physisorption and the specific surface area (SSA), average pore volume (APV) and pore diameter (APD) values were illustrated in Table 3. Notably, the HF treatment increased the specific surface area and diminished the pore diameter of ceramic samples, without significative influence of isotherm time. Before chemical treatment, the pores were concentrated between 4.0 and 7.9 nm and after HF treatment, ceramics revealed mostly microporosity character with pores around 2 nm [33]. This markable increase is due to the effective removal of domains containing Si–O bonds, thus resulting in pores [19]. Probably, the pores size formed after chemical treatment is equivalent to the removed sites, which according to PenãAlonso [34], are domains at nanoscale, corroborating with the results obtained in this work. Table 3 Specific surface area (SSA), average pore volume (APV) and pore diameter (APD) values for ceramic materials before and after chemical treatment with HF aqueous solution

Material

SSA (m2 g−1 )a

C1h

39.2

2.7

4.0

C1h_HF

537

2.9

2.2

C3h

1.8

0.3

7.9

C3h_HF

600

4.5

2.3

C5h

90.6

10.5

5.2

C5h_HF

536

6.5

2.4

a

APV (× 10−2 cm3 g−1 )b

APD (nm)b

Specific surface area was calculated by the B.E.T. (BrunauerEmmet-Teller) method [33] b Average pore volume and diameter were calculated by the B.J.H. (Barret-Joyner-Halenda) method using the desorption isotherms [33]

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

461

3.2 Electrochemical Characterizations Ceramic materials were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Figure 7 displays the Nyquist impedance plots (Fig. 7a, b) and cyclic voltammograms (Fig. 7c) of ceramic materials obtained before and after HF treatment. Load transfer resistance (RTC) values, equivalent to the semicircle diameter observed in the impedance spectra [35], were obtained by fitting the conventional Randles circuit to the experimental data and were shown in Table 4. As shown in Table 4, RTC values decreased for the ceramic materials obtained with the longest isotherm times, and an even more expressive decrease was verified after HF treatment. This demonstrates that the electron conduction property of SiOC ceramic was favored by means the longer annealing times and, mainly through the removal of Si–O domains by HF chemical treatment. Cyclic voltammograms of the ceramic materials before and after HF treatment were evaluated using KOH at 5 mol L−1 as electrolyte. Only HF-treated ceramics

Fig. 7 Nyquist impedance plots of ceramic materials before (a) and after HF treatment (b). Cyclic voltammograms of ceramic materials after HF treatment (C1h_HF, C3h_HF and 5h_HF), using support electrolyte KOH 5 mol L−1 and 50 mV s−1 (c)

462 Table 4 Load transfer resistance (RTC ) values for ceramic materials obtained before C1h, C3h, and C5h) and after HF treatment (C1h_ HF, C3h_HF, and C5h_HF)

T. Centofanti et al.

Material

RTC (Ohm)

C1h

20,380 1486

C1h_HF

19,400

C3h

365

C3h_HF

7110

C5h

359

C5h_HF

showed typical behavior of capacitors, as can be seen in Fig. 7c. The better electrochemical performance of these ceramics most probably is related to exposure of the Cfree phase and higher SSA values, achieved by removal of Si–O sites after HF treatment. Studies reported that generally the higher the SSA value, the greater the charge accumulation capacity at the electrode/electrolyte interface is [36, 37]. Capacitance (C) values of HF-treated ceramics were determined from the cyclic voltammograms, according to Eq. 9 [38]. ∫

C=

id V 2Vs ΔV

(9)

∫ where id V is the integrated area of the voltammogram, V is the scan rate, and ΔV is the investigated potential range. Specific capacitance (Cs) was obtained by dividing the capacitance (C) value by the mass (m) of the material: Cs =

C m

(10)

Specific capacitance values obtained were 84.8; 106.8 and 142.3 F g−1 for C1h_ HF, C3h_HF, and C5_HF, respectively. The obtained values have magnitude order similar to specific capacitance values reported in the literature for SiOC matrices produced for application as supercapacitors [39, 40]. Isotherm times in combination with chemical treatment with HF aqueous solution played a great role to tune the microstructure of SiOC-based materials for applications as supercapacitors. The longest isotherm time allowed obtaining a ceramic material with typical characteristic of double-layer capacitor [41] due to almost rectangular voltammogram shape of C5h_HF sample.

4 Conclusion This work demonstrated that SiOC ceramic materials produced from controlled pyrolysis of a polymeric precursor obtained by radical polymerization of cyclic silicone monomers (D4 Vi), are promising to be used as supercapacitors.

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

463

Chemical treatment with HF aqueous solution changed the microstructure of the SiOC materials, improving their electron conduction properties. Removed rich Si–O domains with the aid of acidic treatment allowed a better exposing of the residual carbon (Cfree ) phase, which presents conductive nature, as demonstrated by Raman spectroscopy. In addition, the removal of these sites resulted in highly SiOC ceramics, with greater microporous amount and high specific area, thus revealing desirable conditions for charge storage. The isotherm time associated to chemical treatment played a great role to improve the conductive and porosity of SiOC materials. In summary, the achieved electrical features in the SiOC ceramics produced from polymer precursors bring out novel technological applications for this Sipolymer derived ceramics class, focusing on experimental conditions that directly favor enhancement of electrical conduction.

References 1. Colombo P, Mera G, Riedel R, Sorarù GD (2010) Polymer-derived ceramics: 40 Years of research and innovation in advanced ceramics. J Am Ceram Soc 93:1805–1837 2. Pradeep Advisor V, Domenico Soraru G (2013) Study of silicon oxycarbide (SiOC) as anode materials for Li-ion batteries. J Am Ceram Soc 1–7 3. Segal D. Chemical synthesis of ceramic materials. J Mater Chem 7:1297–1305 4. Greil P (2000) Polymer derived engineering ceramics. Adv Eng Mater 2:339–348 5. Belyaeva EI, Baklanova NI, Suchkova GA, Belyaev EY (2005) The peculiarities of transformation of organosilicon polymer into ceramic products under mechanochemical treatment. J Eur Ceram Soc 25:521–528 6. Dvornic PR, Lenz RW (1990) High temperature siloxane elastomers. Wepf, p 44 7. Sousa BF, Yoshida IVP, Ferrari JL, Schiavon MA (2012) Silicon oxycarbide glasses derived from polymeric networks with different molecular architecture prepared by hydrosilylation reaction. J Mater Sci 48;5 8. Colas A, Curtis J (2004) Silicones biomaterials: history and chemistry. biomaterials science: an introduction to materials in medicine. In: Biomaterials science, 2nd ed. Elsevier, pp 80–86 9. Deriabin Kv, Dobrynin Mv, Islamova RM (2020) A metal-free radical technique for crosslinking of polymethylhydrosiloxane or polymethylvinylsiloxane using AIBN. Dalton Trans 49:8855–8858 10. Godoy NV, Pereira JL, Duarte EH, Tarley CRT, Segatelli MG (2016) Influence of activated charcoal on ceramic’s structural and morphological characteristics based on silicon oxycarbide (SiOC): a promising approach to obtain a new electrochemical sensing platform. Mater Chem Phys 175:33–45 11. Sorarù GD, Modena S, Guadagnino E, Colombo P, Pantano JEC (2002) Chemical durability of silicon oxycarbide glasses. J Am Ceram Soc 85:1529–1531 12. Rangarajan S, Aswath PB (2011) Role of precursor chemistry on synthesis of Si-O-C and Si-O-C-N ceramics by polymer pyrolysis. J Mater Sci 46:2201–2211 13. Schiavon MA, Gervais C, Babonneau F, Soraru GD (2004) Crystallization behavior of novel silicon boron oxycarbide glasses. J Am Ceram Soc 87:203–208 14. Saha A, Raj R (2007) Crystallization maps for SiCO amorphous ceramics. J Am Ceram Soc 90:578–583 15. Schiavon MA, Ferrari JL, Hojamberdiev M, Yoshida IVP (2015) Silicon oxycarbide glasses from polysiloxanes. Quim Nova 38:972–979 16. Bréquel H, Parmentier J, Walter S, Badheka R, Trimmel G, Masse S, Babonneau F (2004) Systematic structural characterization of the high-temperature behavior of nearly stoichiometric silicon oxycarbide glasses. Chem Mater 16:2585–2598

464

T. Centofanti et al.

17. Cordelair J, Greil P (2000) Electrical conductivity measurements as a microprobe for structure transitions in polysiloxane derived Si–O–C ceramics. J Eur Ceram Soc 20:1947–1957 18. Gangadhar J, Ramachandran S, Ravindran S (2020) Study on effect of structure and surface/ physical characteristics of a silicon oxycarbide by hydrofluoric acid etching. 6:353–361 19. Biasetto L, Peña-Alonso R, Sorarù GD, Colombo P (2008) Etching of SiOC ceramic foams. Adv Appl Ceram 107:106–110 20. Xia K, Li C, Zhao S, Li Y, Duan L, Liu X (2022) Effect of HF and NaOH etching on the composition and structure of SiOC ceramics. Ceram Int 48:1789–1795 21. Assefa D, Zera E, Campostrini R, Soraru GD, Vakifahmetoglu C (2016) Polymer-derived SiOC aerogel with hierarchical porosity through HF etching. Ceram Int 42:11805–11809 22. Forouzandeh P, Kumaravel V, Pillai SC (2020) Electrode materials for supercapacitors: a review of recent advances. Catalysts 10:969 23. Wu G, Tan P, Wang D, Li Z, Peng L, Hu Y, Chen W (2017) High-performance supercapacitors based on electrochemical-induced vertical-aligned carbon nanotubes and polyaniline nanocomposite electrodes. Sci Rep 2017:7 24. Kim BK, Sy S, Yu A, Zhang J (2015) Electrochemical supercapacitors for energy storage and conversion. In: Handbook of clean energy systems. Wiley, pp 1–25 25. Meng Q, Cai K, Chen Y, Chen L (2017) Research progress on conducting polymer based supercapacitor electrode materials. Nano Energy 36:268–285 26. Dibandjo P, Graczyk-Zajac M, Riedel R, Pradeep VS, Soraru GDA (2012) Lithium insertion into dense and porous carbon-rich polymer-derived SiOC ceramics. J Eur Ceram Soc 32:2495– 2503 27. George A, Stephen Brunauer B (1938) Adsorption of gases in multimolecular layers 300 contribution from the bureau of chemistry and sons adsorption of gases in multimolecular layers. J Am Chem Soc 60(2):309–319 28. Baugh OF, Barrett EP, Joyner LG, Halenda PP (1951) The volume and area distributions in porous substances. J Am Chem Soc73(1):373–380 29. Coates J (2000) Interpretation of infrared spectra. A Practical Approach 30. Iastrenski MF, Silva CPR, Tarley TCR, Segatelli MG (2019) Influence of molecular architecture of Si-containing precursors and HF chemical treatment on structural and textural features of silicon oxycarbide (SiOC) materials. Ceram Int 45:21698–21708 31. Cullity BD, Stock Stuart R (1956) Elements of x-ray diffraction, 3rd ed. Pearson Education 32. Ferrari AC, Robertson J (2004) Raman spectroscopy of amorphous, nanostructured, diamondlike carbon, and nanodiamond. Philos Trans R Soc A: Math Phys Eng Sci 362:2477–2512 33. Pan J, Pan J, Cheng X, Yan X, Lu Q, Zhang C (2014) Synthesis of hierarchical porous silicon oxycarbide ceramics from preceramic polymer and wood biomass composites. J Eur Ceram Soc 34:249–256 34. Peña-Alonso R, Sorarù GD, Raj R (2006) Preparation of ultrathin-walled carbon-based nanoporous structures by etching pseudo-amorphous silicon oxycarbide ceramics. J Am Ceram Soc 89:2473–2480 35. Ragoisha GA, Bondarenko AS (2005) Potentiodynamic electrochemical impedance spectroscopy. Electrochim Acta 50:1553–1563 36. Lozano-Castello D, Cazorla-Amorós D, Linares-Solano A, Shiraishi S, Kurihara H, Oya A (2003) Influence of pore structure and surface chemistry on electric double layer capacitance in non-aqueous electrolyte. Carbon 41(9):1765–1775 37. Heimböckel R, Hoffmann F, Fröba M (2019) Insights into the influence of the pore size and surface area of activated carbons on the energy storage of electric double layer capacitors with a new potentially universally applicable capacitor model. Phys Chem Chem Phys 21(6):3122– 3133 38. Kissinger PT, Heineman WR (1983) Cyclic voltammetry. J Chem Educ 60:702–706 39. Pazhamalai P, Krishnamoorthy K, Sahoo S, Mariappan VK, Kim SJ (2020) Carbothermal conversion of siloxene sheets into silicon-oxy-carbide lamellae for high-performance supercapacitors. Chem Eng J 387:123886

Preparation of Silicon Polymer-Derived Ceramics Upon Chemical …

465

40. Tolosa A, Krüner B, Jäckel N, Aslan M, Vakifahmetoglu C, Presser V (2016) Electrospinning and electrospraying of silicon oxycarbide-derived nanoporous carbon for supercapacitor electrodes. J Power Sources 313:178–188 41. Duan L, Ma Q, Mei L, Chen Z (2015) Fabrication and electrochemical performance of nanoporous carbon derived from silicon oxycarbide. Microporous Mesoporous Mater 202:97–105

Advanced Polymers and Composites for Actuators in Robotics and Bioelectronics: Materials and Technologies Massimo Mariello

Abstract Actuators represent a key technology that allows converting electrical, magnetic, or chemical stimuli into mechanical motions/deformations and they have been used in recent years in several fields (e.g. robotics, soft automation, medical surgery, tissue engineering, bioelectronics, and biomedical implantable devices). These transducers can rely on different working principles and materials: electromechanical/magnetomechanical, chemical, or thermal. Standard metallic or ceramic actuators are rigid, bulky, not shape-adaptable, usually based on mechanical arms, and complex architectures not suitable for miniaturization. The recent advances in microelectronics have boosted the development and employment of novel advanced actuators that are based on soft, flexible, or stretchable polymeric materials. Polymers are characterized by well-known properties such as high variability of mechanical strains and stresses, light mass, easy processability, tunability of their flexibility, and biocompatibility. This chapter describes the current research status and main advances in polymer-based actuators, highlighting several transduction mechanisms, materials, and device architectures, for applications in robotics and wearable/ implantable bioelectronics. Keywords Soft actuators · Transducers · Polymers · Composites · Robotics · Bioelectronics

M. Mariello (B) Écolecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Processing of Advanced Composites, Institute of Materials, Route Cantonale, 1015 Lausanne, Switzerland e-mail: [email protected] Écolecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Soft Bioelectronic Interfaces, Neuro-X Institute, Chemin des Mines, CH-1202 Genève, Switzerland Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, Oxford OX3 7DQ, United Kingdom © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_27

467

468

M. Mariello

1 Introduction Actuators represent a key technology that allows converting electrical, magnetic, or chemical stimuli into mechanical motions or deformations and they have been used in recent years in several fields, such as robotics, soft automation, microfabrication, medical surgery, tissue engineering, bioelectronics, and biomedical implantable devices [1]. These transducers can rely on different working principles, depending on the materials and the operating mechanisms on which they are based, i.e. electromechanical/magneto-mechanical, chemical, thermal, etc. Conventional metallic or ceramic actuators include hydraulic and pneumatic actuators, and electrical motors: these are effective, providing high power and fast response time, but they are stiff, bulky, noisy, not shape-adaptable, usually based on mechanical arms and complex architectures not suitable for miniaturization or for biological environments. Soft actuators present several advantages against their standard counterparts. Their flexibility/rigidity can in fact be easily tuned by acting on their physical or chemical structure, depending on the final application. In addition, polymers are lightweight, easily processable and most of them biocompatible. Soft actuators can adapt to dynamic and complex morphologies, finding applications in the field of wearable technologies, including robotics, haptic devices, smart textiles for rehabilitation, body assistance, virtual reality, etc. The requirements of wearable actuators include a compatible modulus to the human body, a wide range of motion, a large strain energy density, a low fatigue rate and optimal reliability. Most of the recent soft actuators are inspired from biological muscles and animal limbs, although it is challenging to replicate their functions, and this hinders the full implementation of soft actuators in industrial contexts [1]. The chapter is devoted to the description of current research status in polymerbased actuators for applications in robotics and wearable/implantable bioelectronics, with focus on several transduction mechanisms, materials and device architectures. The chapter is organized as follows. The second section (“Overview of actuation mechanisms”), is focused on different kinds of actuation that can be adopted to convert multiple forms of energy into mechanical energy. The third section (“Soft actuators for robotics and bioelectronics: materials and technologies”) regards the description of the main soft devices used as actuators, in particular based on polymers and polymeric composites, with the most important state-of-the-art examples. A detailed classification of the materials used for each category is presented, as well as for the main applications of the actuators (artificial muscles, soft robotics, haptic displays, soft grippers, implantable biomedical devices). The fourth section includes a summary of the chapter and some concluding remarks related to the future development perspectives of soft polymer-based actuators.

Advanced Polymers and Composites for Actuators in Robotics …

469

2 Overview of Actuation Mechanisms The mechanisms of actuation can be classified in terms of the physical domains involved in the devices, which always lead to the conversion of a source energy to mechanical energy. Another classification can be based on the material selection, regarding the use of hard or soft substrates, their fabrication processes and the structural designs and architectures to achieve pre-determined motions and deformations. The following sections review and describe the principal actuation mechanisms illustrated in Fig. 1.

2.1 Electromagnetic Actuation Electromagnetic actuation (EMA) is the most standard method adopted for small and large actuators for automotive, industrial automation, protection systems etc., and it is based on the conversion of electrical energy into mechanical energy, which occurs

Fig. 1 Schematic of the most common actuation mechanisms, with their application fields

470

M. Mariello

in the air gap separating a stator and a rotor. An electric current is generally driven in an electric circuit and the induced magnetic field is exploited to produce mechanical forces and torques, according to the laws of electromagnetic induction, the Faradays’ and Biot-Savart’s laws and the Lorentz force. Electromagnetic actuators (EMAs) can be classified into electrical motors, solenoid actuators and moving-coil actuators, relays and MEMS switches. In particular, MEMS EMAs are microfabricated devices that rely on the electromagnetic interaction between magnets or magnetic materials with electrical coils. Although these actuators are miniaturized and can be adopted for portable systems, they are rigid and the integration of the magnets into the microdevice as well as the microfabrication of three-dimensional magnetic coils is still an unsolved challenge.

2.2 Electromechanical Actuation Electromechanical actuation (EMcA) relies on an electrical input, which can be represented by an electric motor or and electromechanical transducer. The electrical energy is transformed into mechanical energy during the actuation and the motion of the electrical components, i.e. the rotary motion of the motor, is then converted into a linear displacement. Even though electric motors are precise, efficient and easy to control, they are not suitable for human–robot interactions and they cannot be used for developing soft compliant actuators. Hence, the most recent electromechanical actuators are based on other principles. Two main groups can be identified for EMcA: the first category includes the series elastic actuators (SEAs) [2] and the second contains the mechanically-adjustable-compliance and controllable-equilibrium-position actuators (MACCEPAs) [3].

2.3 Fluidic Actuation The principle of fluidic actuation (FA) is based on a pneumatic input and it relies on tuning the fluid pressure inside a network of small channels of a soft (mostly elastomeric) embodiment: the in/out flow generates an overall motion of this embodiment for gripping or locomotion purposes. By designing and controlling properly the pneumatic input, it is possible to actuate soft robots with multiple degrees of freedom and complex deformations [1]. FA is effective in providing large deformations and compliance, but it requires bulky pumping equipment and it is less endurable than EMA. The drawbacks of this actuation mechanism are given by the need of bulky pumping equipment, and low motion speed. Specific strategies have been explored to overcome this problem, for instance with spherical caps which undergo isochoric snapping under pressure at volume-controlled conditions [4], thus overcoming the viscous resistance.

Advanced Polymers and Composites for Actuators in Robotics …

471

2.4 Electrostatic/Electrically-Driven Actuation Electrostatic actuation (ESA) or electrically-driven actuation (EdA), is based on the conversion of electrostatic energy into mechanical energy; in particular, the Maxwell stress in a dielectric material induces a mechanical deformation. Different categories of electrostatic/electrically-driven actuators can be classified, according on the specific working principle exploited. Dielectric elastomer actuators (DEAs) rely on the application of an electric field through a flexible dielectric elastomeric membrane (usually silicone or acrylic) sandwiched between two electrodes, which induces a thickness contraction (due to the Coulombian attraction of opposite charges) and lateral expansion (due to the elastomer incompressibility). Thus, the electrical input is converted into an overall mechanical deformation and this electrostriction effect reversibly restores the initial shape and film thickness after the electrodes discharge. To achieve the maximum performances, DEAs need an initial pre-stretch and a rigid frame. Other strategies to obtain larger strains and higher energy density rely on shape-morphing DEAs which consist of embedded internal electrodes between elastomeric layers, or interdigitated DEAs for multi-axial actuation.

2.5 Electrohydraulic (EH) and Electrohydrodynamic (EHD) Actuation A combination of electrostatic and fluidic actuation gives rise to the hydraulically amplified self-healing electrostatic actuators (HASESA), which use both hydraulic and electrostatic forces to contract linearly under an applied voltage, similarly to a muscle, and self-heal electrically after a dielectric breakdown. The actuator consists of rectangular flexible pouches filled with a liquid dielectric and partially covered with electrodes. Under the application of a voltage, electrostatic forces displace the liquid dielectric causing a decrease in the inter-electrode distance due to Maxwell forces. Thus, the liquid is pushed towards the uncovered portions of the pouch inducing a bulging effect: due to the shell’s inextensibility, this effect induces a linear contraction of the actuator. This category of actuation can be further classified into two groups: electro-elastic and thermo-plastic actuation. Electrohydrodynamic actuation (EHDA) is very similar to HASESA actuation: it exploits high electric fields to actuate a dielectric fluid enclosed in elastomeric channels. The purpose of this technique is to develop stretchable soft electrohydrodynamic pumps: these systems are very advantageous for soft wearable actuators because they enable bi-directional pumping and provide high performances in terms of flow rate, light mass and low power consumption. Two possible configurations can be adopted to realize a stretchable soft pump. The first one is conduction pumping with inclined capacitors which allow a net flow of ions between two adjacent pairs of electrodes, and the second is the charge injection using interdigitated electrodes. In the latter

472

M. Mariello

case, under a high enough electric field, field emission takes place, inducing electrons tunneling from the cathode into the dielectric liquid and the generated ions are then accelerated towards the anode, transferring a momentum to the other molecules.

2.6 Electrothermal Actuation Electrothermal actuation (ETA) relies on the Joule effect to generate heating due to a current flow through a resistive material: the heating is exploited to induce expansion or contraction in the actuator, thanks to shape memory effects or thermo-responsive twisted fibers or yarns. Differently from other actuators, ETA actuators require low driving voltages and can produce large forces and displacements, without involving electrostatic or magnetic fields; they are also quite controllable without undesired hysteresis effects, so they are suitable for integration into MEMS systems, for manipulating biological samples, for miniaturization, for actuation in microcantilever-based sensing and probing. Moreover, ESA can also be combined and coupled with piezoresistive or piezoelectric sensors. The main drawback is the slow switching speed due to the large time constants of thermal processes. Different types of designs and working principles can be exploited by ESA actuators, i.e. hot-and-cold-arm or U-shaped actuator, Chevron actuator, bimorph ETA actuator, etc. Other types of ETA actuators are not conventional and can be classified into (i) expanding bars, (ii) silicon-polymer stack, (iii) tweezing deflection (microspring) and (iv) combined geometry.

2.7 Passive Indirect Actuation Passive indirect actuation (PIA) is a type of actuation that is not triggered by an active mechanism but depends on the deformation transmitted through tendons from external motors, similarly to biological tendons. PIA-based actuators can provide fast and accurate deformations and high forces, and they are suitable for soft wearable applications, especially for patients’ assistance and rehabilitation, and also multifingered soft grippers, soft pumps and compliant robotic arms. The main drawback of this actuation mechanism is the need of external motors which hinder a further downscaling and miniaturization.

2.8 Magnetomechanical Actuation Magnetimechanical actuation (MMA) consists of controlling the actuators with an applied external magnetic field, whose amplitude, gradient and direction can be

Advanced Polymers and Composites for Actuators in Robotics …

473

modulated with high temporal resolution. The interaction of this field with the magnetic properties of the actuators allows a fine control of the output torques and forces, complex time-varying deformations, multimodal locomotion, a deep tissue penetration and other complex functions. The inhomogeneities of magnetic fields as well as the arrangement of magnetic domains in ferromagnetic materials or the alignment of magnetic nanoparticles in soft materials can be exploited to achieve diverse deformations [5]. MMA is suitable for minimally invasive soft actuators and for applications in drug delivery, but it can also be harnessed to generate heat remotely to activate the actuators in a contact-less modality, e.g. magnetically-induced liquid-to-gas phase transitions, through high-frequency magnetic fields [6].

2.9 Chemical, Thermal, Optical, Acoustic Actuation Other types of actuation harness different sources. An example is the chemical actuation (CA) which exploits chemical stimuli and species to actuate soft materials. These can be responsive to humidity, ionic strength, pH, chemical solvents or vapors, surface tension or others. Temperature is another parameter that can be used to induce heating and actuate soft materials, which are then called thermo-responsive [7]. Optical actuation (OA) exploits light as a wireless stimulus for soft actuators, with high temporal and spatial resolution, with the aid of optical lenses, choppers, optical fibers, etc. The actuation can be in particular driven by wavelength-selective or wide-spectrum light sources, which triggers some specific photochemical/photothermal reactions inside the stimulated material, shape memory effects, thermal strains, phase transitions or changes of other properties [8]. Acoustic actuation (AA) relies on the conversion of acoustic waves into motion through the integration of oscillatory resonant elements into the actuator, which must lay in the focal plane of the ultrasound waves: two main groups can be distinguished, i.e. bubble-based actuators and flexible-oscillating-structure actuators [9].

3 Soft Actuators for Robotics and Bioelectronics: Materials and Technologies The actuation mechanisms described in the previous Section find real and practical applications with several devices and systems proposed in current and past works. Soft actuators may in general be classified into (i) tethered and (ii) untethered actuators. Tethered actuators are triggered by elements (cables, tendons, etc.) attached to the actuator body and to external motors, by onboard electronics or soft pumps, providing large force output and agile deformation. Untethered actuators are instead supplied by contactless stimuli, they can be entirely soft or only have few rigid parts, they are wirelessly controlled and easily scalable, but they provide smaller output

474

M. Mariello

forces than the tethered counterparts and their self-sustained functioning is challenging. In this Section, the main categories of tethered and untethered soft actuators are described, with highlight on real devices and working mechanisms.

3.1 EMAs Against rigid EMAs, the new generation of EMA devices consists of soft electromagnetic actuators (SEMAs), proposed and described by Mao et al. [10]. The replacement of solid metal coils with elastomer-embedded liquid–metal channels or the use of magnetic particles (e.g. NdFeB), allows to design and fabricate stretchable, durable and programmable cm-scale shape-morphing systems with complex shapes and deformations. The basic principle of these actuators is that a magnet induces the Lorentz force onto the liquid–metal coils which are pulled and pushed. The main drawback is the size requirement, in fact the coils should be wider than the magnet and this impedes the miniaturization of the SEMAs, as well as the solid bonding between the magnet and the coils. Mao et al. [10] provided six main design strategies to decouple the magnet from the soft actuator. Muzalifah et al. [11] fabricated a PDMS-based flexible membrane composite with NdFeB magnetic particles (density up to 30 vol%) through MEMS technology and with a permanent magnet integrated in the system’s structure (Fig. 2a). The actuator exhibits a deflection of 9.16 μm at 6 vol% particle density and 8.14 μm at 25 vol% particle density for a flat and embossed configuration, respectively, under an applied magnetic field of 0.98 mT. The device is adopted in a compact micropump for Labon-Chip applications. Ni et al. [12] presented a planar in-contact check valve-based PDMS micropump, fabricated through PDMS replica and bonding techniques: in the system a couple of check valves are based on a planar stopper–flap configuration allowing for the incorporation of the pump chamber into a single layer (Fig. 2b). The micropump can efficiently generate a maximum flow rate of 41 μL min−1 and reliably operate against high backpressures up to 25 kPa, thus being suitable for the integration in various lab-on-chip and actuation systems, such as automated implantable drug delivery systems.

3.2 Piezoelectric Actuators Piezoelectric actuators are engineered transducers based on materials (i.e. piezoelectric) that are able to convert intrinsically electrical energy into mechanical energy. Under the application of an external stress, the crystalline structure is deformed and the internal dipoles inside the material undergo an irregular rearrangement, leading to a surface charge density which can be collected via electrodes: this is the direct piezoelectric effect, exploited in sensors and energy harvesters. The reverse piezoelectric effect, instead, is harnessed in actuators and relies on the generation of a strain/stress

Advanced Polymers and Composites for Actuators in Robotics …

475

Fig. 2 a Scheme, photo and fabrication process of a PDMS-based flexible membrane composite with NdFeB magnetic particles for soft electromagnetic actuation. Adapted with permission [11] Copyright (2016) Elsevier. b Schematic structure of a planar in-contact check valve-based PDMS micropump, fabricated using simple PDMS replica and bonding techniques. Adapted with permission [12] Copyright (2010) IOP Publishing Ltd.

after the application of an electric field/voltage. The theory of piezoelectricity, with all the fundamental constitutive equations and relationships among strain, stress and electric field, can be consulted in several works and reviews [13]. There are several classes of piezoelectric materials (i.e. single-crystal piezoceramics, polycrystalline piezoceramics, piezoelectric polymers and piezocomposites) [13, 14], synthesized in different forms (single crystals, bulk or thin films and nanomaterials). The mostly used piezoelectric material is Lead zirconate titanate or Pb(Zrx Ti1-x )O3 (PZT). This is

476

M. Mariello

a piezoceramic with a perovskite structure and with high piezoelectric performances. However, PZT is a ferroelectric material, so it needs a poling process to exhibit piezoelectricity, it is brittle and with high dielectric constants, and the presence of lead in its structure makes it unsuitable for biocompatible applications [15]. Hence, novel lead-free piezoelectric materials have been studied and employed in transducers, sensors and actuators. Barium titanate (BaTiO3 , BTO) is a well-known lead-free piezoelectric material: it is ferroelectric, with high piezoelectric parameters, low Curie temperature, high dielectric constants, and it can be grown as thick and thin films as well as nanomaterials [16]. Other lead-free piezoceramics include potassium/sodium niobite ((K,Na)NbO3 , KNN) [17], aluminium nitride (AlN) and zinc oxide (ZnO). ZnO can be synthesiszed in different forms, i.e. thin films as well as nanostructured materials [18], and exhibits moderate piezoelectric coefficients, low dielectric constant and a resulting high piezoelectric voltage constant. AlN is a III-nitride wurtzite-phase non-ferroelectric compound that can be deposited as poling-less piezoelectric thin films directly on soft/flexible substrates for sensing, energy harvesting and actuation applications [19–24]. Olivares et al. [25] exploited a Mo/AlN/Mo actuator on a silicon nitride structural layer, reporting a deflection of 3.5 μm for a 350-μm-long bridge under the application of an actuation voltage of 16 V (Fig. 3a). Ultrathin (100 nm) AlN piezoelectric layers were used by Sinha et al. [26] to fabricate vertically deflecting nanoactuators, achieving deflections as large as 40 nm from 18 μm-long and 350 nm-thick multilayer cantilever bimorph beams with 2 V actuation (Fig. 3b). Besides piezoceramics, piezoelectric polymers represent an interesting alternative to PZT with the advantages of high intrinsic flexibility, light mass, high strain capability and ease of processing. Polyvinylidene fluoride (PVDF) and its copolymer polyvinylidene fluoridetrifluoroethylene (P(VDF-TrFE)) exhibit the largest piezoelectric constants among piezo-polymers and are suitable for the realization of soft actuators. They are generally spin-coated, extruded, biaxially/uniaxially-oriented or electrospun, and the films commonly undergo a process of electrical poling to enhance their piezoelectricity [14]. Pabst et al. [27] presented all inkjet-printed piezoelectric polymer actuators based on P(VDF-TrFE) sandwiched between silver electrodes on a PET substrate (Fig. 3c). The piezoelectric d31 coefficients are measured to be approximately 7–9 pm/V with resulting significant actuator deflections for applications in micropumps for microfluidic Lab-on-Chip systems.

3.3 DEAs DEAs rely on the generation of electrostatic stresses induced by the application of a voltage across an insulating elastomer. The stresses are due to the charge separation and the attraction of opposite charges provokes a reduction in the elastomer thickness. These soft actuators are mainly fabricated by planar methods, with the production of films and membranes that are mechanically assembled in a system with at least two

Advanced Polymers and Composites for Actuators in Robotics …

477

Fig. 3 a Mo/AlN/Mo actuator on a silicon nitride structural layer: (i) fabrication process, (ii-iii) SEM images (ii) after actuation voltage and (iii) in relaxed state; (iv) XRD spectrum of AlN and Mo; (v) Deflection-voltage curve. Adapted with permission [25] Copyright (2005) Elsevier. b AlNbased Vertically deflecting nanoactuators. Adapted with permission [26] Copyright (2009) AIP Publishing. c P(VDF-TrFE)-based all inkjet-printed piezoelectric polymer actuators. (i) Printing and sintering of bottom electrode, (ii) printing and tempering of piezoelectric layer, (iii) printing and sintering of top electrode, (iv) cross section of the actuator, (v–vi) photos of the actuators, (vii–viii) deflection-voltage curves for cantilever and membrane actuators, (ix–x) resonance curves for cantilever and membrane actuators. Adapted with permission [27] Copyright (2013) Elsevier

478

M. Mariello

electrodes. The actuation in this simple case yields an in-plane expansion and outof-plane shrinking. In addition, bending, rolling or pre-strain can be applied onto these planar structures, obtaining more complex shapes for DEAs. Pre-straining in particular is very useful to avoid the use of rigid frames for pre-stretching the elastomers. Other approaches to fabricate 3D DEAs rely on stacking of individual planar layers or sequential deposition of active materials via inkjet printing and spray coating are other approaches to fabricate 3D DEAs. Chortos et al. [28] reported on a method for fabricating 3D interdigitated DEAs for in-plane contractile actuation (Fig. 4a). The interdigitated electrodes are made of a conductive elastomer ink encapsulated with a self-healing dielectric matrix composed of a plasticized, chemically crosslinked polyurethane acrylate. The devices exhibit breakdown fields of 25 V/μm and actuation strains up to 9%. DEAs are widely used for the fabrication of artificial muscles in exoskeletons and rehabilitation robots, because they provide large deformations and fast responses, even though the driving voltage required for their operation is high (~ kV). Singlefilm DEAs are thin to minimize the actuation voltage but in this way the force outputs and the displacements are limited (< 10 N, < 1 cm), thus multilayer strategies can be applied. Shintake et al. [29] proposed a method to fabricate monolithically stacked DEAs without any manual process of alternatively stacking electrode and dielectric layers (Fig. 4b): this technique consists of molding the elastomer (PDMS) with microfluidic channels and injecting liquid metal (i.e. eutectic gallium indium or EGaIn), to act as electrode. A comprehensive description of the DEA materials and the main types of DEA actuators can be found in the work of Guo et al. [30].

3.4 Triboelectric Actuators Triboelectricity consists of charge generation and redistribution on the surfaces of two dissimilar materials that come into contact or slide over each other. The effect is known as contract electrification and can be exploited by collecting charges through electrodes into an external circuit, generating an alternating current and voltage, which is the main operating principle of the triboelectric nanogenerators (TENGs), introduced in 2012 [31]. The triboelectric materials are usually flexible or soft polymers, which confer flexibility/stretchability to the device, and this makes these systems a promising option for self-powered actuation devices in soft robotics. TENGs represent ideal converters to transform ambient mechanical energy into electricity and the high output voltages can be exploited as electrostatic driving forces to manipulate charged droplets or to trigger soft ESA or EdA actuators in micro-/ nano-robotics, microfluidic systems and cell separation systems. In fact, the electrostatic stress generated by an electrostatic actuator, such as a DEA, is a function of the material total permittivity and also the applied electric field generated by the TENG. Nie et al. [32] combined the electrowetting technique with a freestanding TENG to fabricated a mini-vehicle by using four droplets to carry a pallet (Fig. 4c). The motion of the TENG can provide the driving energy for powering the mini vehicle,

Advanced Polymers and Composites for Actuators in Robotics …

479

480

M. Mariello

◄Fig. 4 a Printed DEA devices with (i) vertical and (ii) horizontal electrodes. Schematic illustration of the fabrication process of printing of interdigitated DEAs and dielectric matrix infilling. (iv) Multinozzle printhead. (v) Photo of a 3D DEA device. (vi–vii) 3D DEA with interdigitated electrodes arranged in (vi) a quadrant architecture or (vii) in an annular design. Adapted with permission [28] Copyright (2019) Wiley. b Monolithic stacked DEAs with silicone elastomer and liquid metal. (i) elastomeric matrix with a 3D printed inner part; (ii) matrix after dissolution of the inner part; (iii) matrix after liquid metal injection. (iv) Fabrication process flow. (v) Performances of the DEAs. Adapted with permission [29] Copyright (2021) Creative Commons Attributions License (CC BY). c (i) Schematic of the self-powered microfluidic transport system based on TENG and electrowetting. (ii) Performances of the system driving a mini vehicle. Adapted with permission [32] Copyright (2018) American Chemical Society. d Integration process and actuation performances of TENG and EAP. Adapted with permission from [34] Copyright (2018) America Chemical Society

achieving 1 m/s as the highest controllable velocity. Chen et al. [33] fabricated a conjunction system comprising a single-electrode TENG, based on a nanopatterned Kapton film and an Al electrode layer, and a DEA actuator, capable of generating a clamping force of about 0.2 N. Xu et al. [34] presented a self-powered electroadhesion (EA) system with three TENGs in parallel connection and an EA patch made of interdigitated electrodes sandwiched by a silicone encapsulation and a Kapton film (Fig. 4d): thanks to the high voltage output generated by the TENGs (up to 7000 V with a charge supplement), the resulting adhesion forces are high enough to enable the handling and manipulation of various objects (metal sheets, wafers, glass, paper, etc.), reaching up to 6.7 N, enabling the pickup of a 0.35 kg metal block.

3.5 Shape-Memory-Polymers Actuators Shape-memory polymers (SMPs) have the peculiar characteristics of restoring their original shape from a deformed secondary shape under the application of an appropriate stimulus. The working mechanism of SMPs is derived from a dual segment system composed of cross-links and switching segments with a transition temperature. Above this temperature, the material can be mechanically deformed into whichever shape: after cooling below the aforementioned temperature this shape can be maintained for long time but heating again the SMP will lead to a complete automatic recovery of the original permanent shape. The cross-links are then highly elastic and generally present in a crystalline phase or in a chemically bonded network, whereas the switching segments consist of a reversible entanglement responsible of the temporary shape and related to the melting or glass transition. The most common application of these materials regards the artificial muscles, which can be fabricated with different methods (twist insertion, shape fixation, or others) and are widely exploited in the fields of biomimetics and soft robotics.

Advanced Polymers and Composites for Actuators in Robotics …

481

SMP actuators do not need specific sophisticated linkage design and they can be activated by different types of stimuli, so they are called thermal-, photo-, electricalactuated SMP artificial muscles. Differently from other materials used for artificial muscles, SMPs are advantageous for their easy preparation, low price, high elasticity and self-healing capabilities, and they can mimic remarkably the behavior of natural muscles. Behl et al. [35] proposed a polyester urethane internally anisotropic network with a poly ω-pentadecalactone (PPDL) and PCL segment (Fig. 5a). The network anisotropy required for the shape-memory effect is set in this case with no external forces but through specific steps of heating and reheating; other methods to achieve this purpose consist of producing core–shell composites, bilayer polymeric laminates, crystalline polymeric multi-networks, glassy thermoset-stretched liquid crystalline networks, epoxy-based shape-memory lightly cross-linked networks, 3D printed thermoplastic/elastomer networks, etc. Hua et al. [36] experimented shape-memory hydrogels to produce thermoresponsive shape-memory actuators (Fig. 5b): in particular, they report a multipleresponsive upper-critical-solution-temperature (UCST) bilayer hydrogel actuator based on the complex of poly(acrylic acid) (PAAc) and poly(acrylamide) (PAAm). Due to the hydrogen bonding between the two polymers, the swelling of the PAAm layer induces a bending and the amplitude of actuation behavior could be tuned by adjusting the composition of the layers. The realized actuator is also responsive to urea and salts.

3.6 Ionically-Conductive-Polymers Actuators Soft actuators based on ionic polymers rely on conductive materials where the conduction is due to ions and not electrons, with several advantages, i.e. low voltage and power requirements, flexibility, softness, and biomimetic behaviour. An ionicpolymer-actuator (IPA) is basically composed of an ion-exchange membrane and a pair of electrodes attached to opposite surfaces of the ionic polymer. The basic principle of an IPA is based on electromigration: ions are charged particles which in solution tend to bind to solvent molecules forming solvated cations. When a voltage is applied between the opposite sides of the IPA, the charged solvated ions have a direction migration effect through the liquid phase microstructure of the electrolyte, accumulating on one side and depleting the other side. The result is a mechanical local strain that induces a deformation of the actuator. Two main categories of IPAs can be distinguished. Ionic polymer-metal composites (IPMC) consist of a perfluorinated ionomer membrane sandwiched between two metal electrodes and neutralised with the necessary number of mobile ions and fixed counterions. An intermediate layer is made of metal particles embedded in a polymer matrix containing the ionomer, some cations (i.e. alkali metal ions) and a solvent (water or ionic liquids) [37] (Fig. 6a). Bulky gel actuators (BGAs) are made of a base polymer (i.e. polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)), imidazoliumtype and ammonium-type ionic liquids and carbon nanotubes (CNTs). The structure

482

M. Mariello

Fig. 5 a (i) Schematic of reversible bidirectional shape-memory effect in copolymer networks. (ii) Deformation devices (gripper and reversible fixator) from PPD-PCL for reversible bidirectional shape-memory effect. Adapted with permission [35] Copyright (2013) John Wiley and Sons. b (i) Synthesis of asymmetric PAAm/PAAc hydrogel actuator and mechanism of temperatureinduced actuation. (ii) Actuation behaviors of the asymmetric hydrogels with different shapes. (iii) Amphibious self-actuation behaviors of asymmetric hydrogel actuating flowers. Adapted with permission [36] Copyright (2019) American Chemical Society

of a BGA includes a gel-like self-standing electrolyte film sandwiched between two electrodes and composed of ionic liquid and base polymer [38] (Fig. 6b). IPAs have been used for active microcatheters, micropumps, tactile displays, biomimetic microrobots.

3.7 Liquid–Crystal-Polymers Actuators Liquid crystal polymers (LCPs) are materials characterized by anisotropic elasticity and the combination of the molecular order of a crystalline solid with the fluidity of an isotropic liquid, thus they can achieve strain rates of > 120%/s. LCPs are generally

Advanced Polymers and Composites for Actuators in Robotics …

483

crosslinked to obtain liquid crystal elastomers (LCEs), with plenty of monomeric side-chains, or liquid crystal networks (LCNs), more crosslinked. Owing to the specific microstructure, the anisotropic chain conformation is temporarily lost upon heating, yielding a contraction, whereas after cooling the ordered phase is restored and the original shape is regained. A crucial requirement for LCEs is the alignment

484

M. Mariello

◄Fig. 6 a (i) Pd Dendritic interfacial electrodes. (ii) Deformation evolutions of IPMC actuators after different impregnation electroplating cycles. Adapted with permission [37]. Copyright (2017) American Chemical Society. b (i) Bulky-gel-based bimorph actuator fabricated by layer-by-layer casting. (ii) Performances of a BGA in response to alternating square-wave electric potentials. Adapted with permission [38]. Copyright (2005) Wiley–VCH Verlag GmbH & Co. c (i) Unloaded deformation of LCE laminates. (ii) Soft weightlifting with LCE laminates: stroke and specific work under load. Adapted with permission [40]. Copyright (2017) American Chemical Society. d Actuation modes of photothermally-driven LCP actuators: (i, ii) Reversible bending toward the light source, (iii) reversible contraction under load, (iv, v) Reversible bending away from the light source, (vi) light-driven locomotion. Adapted with permission [41]. Copyright (2018) Creative Commons Attribution 4.0 International License

of the liquid crystal portions: this can be performed by mechanical orientation of a gelled network or a viscous monomer solution, or by harnessing the diamagnetic or dielectric anisotropy of the monomers [39]. A limitation of LCEs is that force outputs increase with increasing film thickness, however, the preparation of very thick (> 50 μm) LCEs by surface anchoring is challenging. Guin et al. [40] proposed a method to produce arbitrarily thick LCEs with a continuous composition, via directed self-assembly by photoalignment (Fig. 6c). This technique consists of laminating many LCE films bonded with interfacial layers of the same composition which serve to take on the residual orientation of the adjacent LCE layers. The shape transformations in LCEs can be triggered by different stimuli, for instance by UV and visible light. Dong and Zhao [41] reviewed the basic principles of LCPs and all the main actuation modes of photothermally-driven LCPs (Fig. 6d): reversible bending toward the light source, reversible contraction/extension under a load, reversible bending away from the light source.

4 Conclusion: Summary and Challenges In this Chapter the state of the art of soft actuators for robotics and bioelectronics have been presented with a focus on the current advances in employed materials, technologies and device architectures. Their practical commercial deployment is still limited mostly because of their requirements in terms of actuation voltages, materials selection, fabrication processes and force outputs. Hence, new challenges need to be addressed for the next future of this technology and they are summarized in Fig. 7. The first challenge regards the material selection and design to replace rigid and bulk components and to introduce physical intelligence into the actuation system. The bistability of spherical membranes or dome-shaped structures, snap-through instabilities, kirigami and origami design strategies can be exploited to introduce asymmetries, to increase the overall flexibility of the actuator or to create shapemorphing inflatable structures.

Advanced Polymers and Composites for Actuators in Robotics …

485

Fig. 7 Schematic of the main challenges for the future deployment and commercialization of soft actuators in robotics and bioelectronics

The second challenge is adaptivity and multimodality, especially for human– machine interfaces, haptic and biomedical devices: biological actuators (hands, octopi, plants) exhibit the greatest adaptivity to complex environments and to different tasks or interacting objects. A multimodal performance implies a certain degree of reconfigurability as well as feedback loops based on electrical or optical signals. Machine learning and neural networks represent a useful tool to deal with the multiple interactions between the actuator and the surroundings. The third challenge regards the scalability and reproducibility of the fabrication process of soft actuators, which depend on the material and structural consistency, thus automated controlled processes are required. Additionally, large-scale production is still limited for these technologies both because the synthesis and fabrication processes are confined to research labs and because soft actuators need to be combined with other fields’ technologies in order to find practical applications and commercialization. The fourth challenge is the actuators’ reliability and durability. Soft actuators are very vulnerable to impacts, punctures, injuries and self-healing (intrinsic or extrinsic) materials are attracting an increasing interest since they can repair the device and restore its functionality. Finally, recycling and end-of-life handling of soft actuators represents another challenge in the context of sustainability and waste management. Biodegradable and

486

M. Mariello

bioresorbable materials can be useful to minimize the waste generation but they suffer for limited durability and lower performances.

References 1. Li M, Pal A, Aghakhani A, Pena-Francesch A, Sitti M (2021) Soft actuators for real-world applications. Nat Rev Mater 7:235–249 2. Leal Junior AG, Actuator SE (2016) Design, analysis and comparison. In: de Andrade RM, Filho AB (eds) Recent advances in robotic systems. ED1—Guanghui Wang. IntechOpen, Rijeka, p 10 3. Van Ham R, Van Damme M, Vanderborght B, Verrelst B, Lefeber D (2006) MACCEPA: the mechanically adjustable compliance and controllable equilibrium position actuator. In: Proceedings of CLAWAR 2006—9th international conference climbing walk. Robots Support Technol. Mob. Mach. 12–14 Sept 2006 Bruss, Belg, pp 196–203 4. Gorissen B, Melancon D, Vasios N, Torbati M, Bertoldi K (2020) Inflatable soft jumper inspired by shell snapping. Sci Rob 5:eabb1967 5. Zhang J, Ren Z, Hu W, Soon RH, Yasa IC, Liu Z, Sitti M (2021) Voxelated three-dimensional miniature magnetic soft machines via multimaterial heterogeneous assembly. Sci Robot 6:eabf0112 6. Mirvakili SM, Sim D, Hunter IW, Langer R (2020) Actuation of untethered pneumatic artificial muscles and soft robots using magnetically induced liquid-to-gas phase transitions. Sci Robot 5:eaaz4239 7. Jin B, Song H, Jiang R, Song J, Zhao Q, Xie T (2018) Programming a crystalline shape memory polymer network with thermo- and photo-reversible bonds toward a single-component soft robot. Sci Adv 4:eaao3865 8. Li M, Kim T, Guidetti G, Wang Y, Omenetto FG (2020) Optomechanically actuated microcilia for locally reconfigurable surfaces. Adv Mater Deerfield Beach Fla 32:e2004147 9. Kaynak M, Dirix P, Sakar MS (2020) Addressable acoustic actuation of 3D printed soft robotic microsystems. Adv Sci 7:2001120 10. Mao G, Drack M, Karami-Mosammam M, Wirthl D, Stockinger T, Schwödiauer R, Kaltenbrunner M (2020) Soft electromagnetic actuators. Sci Adv 6:eabc0251 11. Mohd. Said M, Yunas J, Pawinanto RE, Majlis BY, Bais (2016) PDMS based electromagnetic actuator membrane with embedded magnetic particles in polymer composite. Sens Actuat Phys 245:85 12. Ni J, Huang F, Wang B, Li B, Lin Q (2010) A planar PDMS micropump using in-contact minimized-leakage check valves. J Micromechan Microeng Struct Dev Syst 20:095033 13. Mariello M (2022) Recent advances on hybrid piezo-triboelectric bio-nanogenerators: materials, architectures and circuitry. Nanoenergy Adv 2:1 14. Mariello M, Qualtieri A, Mele G, De Vittorio M (2021) Metal-free multilayer hybrid PENG based on soft electrospun/-sprayed membranes with cardanol additive for harvesting energy from surgical face masks. ACS Appl Mater Interfaces 13:20606 15. Mariello M (2022) Advanced lead-free piezoelectric materials: ceramics, polymers, and composites. In: Gupta R (ed) Handbook of energy materials. Springer Nature, Singapore, pp 1–41 16. Gao J, Xue D, Liu W, Zhou C, Ren X (2017) Recent progress on BaTiO3 -based piezoelectric ceramics for actuator applications. Actuators 6:3 17. Zhang S-W, Zhou Z, Luo J, Li J-F (2019) Potassium-sodium-niobate-based thin films: lead free for micro-piezoelectrics. Ann Phys 531:1800525 18. Wang Z (2004) Zinc oxide nanostructures: growth, properties and applications. J Phys Condens Matter 16:R829

Advanced Polymers and Composites for Actuators in Robotics …

487

19. Mariello M, Guido F, Mastronardi VM, Giannuzzi R, Algieri L, Qualteri A, Maffezzoli A, De Vittorio M (2019) Reliability of protective coatings for flexible piezoelectric transducers in aqueous environments. Micromachines 10 20. Mariello M, Guido F, Mastronardi VM, Todaro MT, Desmaële D, De Vittorio M (2019) Nanogenerators for harvesting mechanical energy conveyed by liquids. Nano Energy 57:141 21. Mariello M, Fachechi L, Guido F, De Vittorio M (2021) Multifunctional Sub-100 μm thickness flexible piezo/triboelectric hybrid water energy harvester based on biocompatible AlN and soft parylene C-PDMS-EcoflexTM . Nano Energy 83:105811 22. Mariello M, Blad TWA, Mastronardi VM, Madaro F, Guido F, Staufer U, Tolou N, De Vittorio M (2021) Flexible piezoelectric AlN transducers buckled through package-induced preloading for mechanical energy harvesting. Nano Energy 85:105986 23. Mariello M, Guido F, Algieri L, Mastronardi VM, Qualtieri A, Pisanello F, De Vittorio M (2021) Microstructure and electrical properties of novel piezo-optrodes based on thin-film piezoelectric aluminium nitride for sensing. IEEE Trans Nanotechnol 20:10 24. Mariello M, Fachechi L, Guido F, Vittorio M (2021) Conformal, ultra-thin skin-contact-actuated hybrid piezo/triboelectric wearable sensor based on AlN and parylene-encapsulated elastomeric blend. Adv Funct Mater 2101047 25. Olivares J, Iborra E, Clement M, Vergara L, Sangrador J, Sanz-Hervás A (2005) Piezoelectric actuation of microbridges using AlN. Sens Actuat Phys 123–124:590 26. Sinha N, Wabiszewski GE, Mahameed R, Felmetsger VV, Tanner SM, Carpick RW, Piazza G (2009) Piezoelectric aluminum nitride nanoelectromechanical actuators. Appl Phys Lett 95:053106 27. Pabst O, Perelaer J, Beckert E, Schubert US, Eberhardt R, Tünnermann A (2013) All inkjetprinted piezoelectric polymer actuators: characterization and applications for micropumps in lab-on-a-chip systems. Org Electron 14:3423 28. Chortos A, Hajiesmaili E, Morales J, Clarke DR, Lewis JA (2020) 3D printing of interdigitated dielectric elastomer actuators. Adv Funct Mater 30:1907375 29. Shintake J, Ichige D, Kanno R, Nagai T, Shimizu K (2021) Monolithic stacked dielectric elastomer actuators. Front Robot AI 8 30. Guo Y, Liu L, Liu Y, Leng J (2021) Review of dielectric elastomer actuators and their applications in soft robots. Adv Intell Syst 3:2000282 31. Mariello M, Scarpa E, Algieri L, Guido F, Mastronardi VM, Qualtieri A, De Vittorio M (2020) Novel flexible triboelectric nanogenerator based on metallized porous PDMS and parylene C. Energies 13:1625 32. Nie J, Ren Z, Shao J, Deng C, Xu L, Chen X, Li M, Wang ZL (2018) Self-powered microfluidic transport system based on triboelectric nanogenerator and electrowetting technique. ACS Nano 12:1491 33. Chen X, Jiang T, Yao Y, Xu L, Zhao Z, Wang ZL (2016) Stimulating acrylic elastomers by a triboelectric nanogenerator—toward self-powered electronic skin and artificial muscle. Adv Funct Mater 26:4906 34. Xu L et al (2018) Giant voltage enhancement via triboelectric charge supplement channel for self-powered electroadhesion. ACS Nano 12:10262 35. Behl M, Kratz K, Zotzmann J, Nöchel U, Lendlein A (2013) Reversible bidirectional shapememory polymers. Adv Mater 25:4466 36. Hua L, Xie M, Jian Y, Wu B, Chen C, Zhao C (2019) Multiple-responsive and amphibious hydrogel actuator based on asymmetric UCST-type volume phase transition. ACS Appl Mater Interfaces 11:43641 37. Wang Y, Liu J, Zhu Y, Zhu D, Chen H (2017) Formation and characterization of dendritic interfacial electrodes inside an ionomer. ACS Appl Mater Interfaces 9:30258 38. Fukushima T, Asaka K, Kosaka A, Aida T (2005) Fully plastic actuator through layer-by-layer casting with ionic-liquid-based bucky gel. Angew Chem Int Ed 44:2410 39. Kularatne RS, Kim H, Boothby JM, Ware TH (2017) Liquid crystal elastomer actuators: synthesis, alignment, and applications. J Polym Sci Part B Polym Phys 55:395

488

M. Mariello

40. Guin T, Settle MJ, Kowalski BA, Auguste AD, Beblo RV, Reich GW, White TJ (2018) Layered liquid crystal elastomer actuators. Nat Commun 9:1 41. Dong L, Zhao Y (2018) Photothermally driven liquid crystal polymer actuators. Mater Chem Front 2:1932

Methods and Technologies for Recycling Energy Storage Materials and Device Neha Thakur, Pradipta Samanta, and Sunita Mishra

Abstract The limited reserve of non-renewable energy sources and increased demand for energy due to technological development and higher quality lifestyle has shifted the research directions towards the use of alternative renewable energy sources. As renewable energy can’t be instant, there is a great need to develop advanced energy storage devices for sustainable energy. The requirement of highpower density, high charge capacitance, and long cyclic stability of batteries and supercapacitors has made them promising device for storage but with the disadvantage of adding environmental pollution due to different metal ions and toxic materials of the scrapped batteries and capacitors. This has led to the development of various technologies for recycling energy storage materials and devices to reduce environmental hazards. This chapter gives an insight into the processes of heat treatment, chemical treatments, metallurgy methods, etc. for the recycling of the materials of storage devices along with the extraction and recovery of metals and other carbon-based materials from cathode, anode, and electrolytes. Keywords Metal-ion batteries · Supercapacitors · Renewable energy · Recycling

1 Introduction With the increase in energy demands, the need for energy storage devices has also increased to replenish finite energy sources. The most used storage devices are batteries and supercapacitors (SCs). As these storage devices possess a certain life span, their decomposition becomes an important task to manage. The extraction of these resources in raw form is a costly affair, and the appending processing to get the actual products adds further a huge cost to it. So recycling is the best option to cut N. Thakur · P. Samanta · S. Mishra (B) Academy of Scientific and Innovative Research, AcSIR Headquarters, CSIR-HRDC Campus, Sector 19, Kamla Nehru Nagar, Ghaziabad, UP 201002, India e-mail: [email protected] CSIR—Central Scientific Instruments Organisation, Sector – 30 C, Chandigarh 160030, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 R. K. Gupta (ed.), Recent Advancements in Polymeric Materials for Electrochemical Energy Storage, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4193-3_28

489

490

N. Thakur et al.

the cost by extracting useful materials at the end of their useful life. Batteries and SCs are the most widely used energy storage system. Metal ion batteries have been a dominant energy source used in various applications in different sectors. Among metal ion batteries, lithium-ion batteries (LIBs) are highly preferred due to their high energy density, long life cycle, and most importantly zero maintenance. The ample use of these batteries leads to a growing amount of waste at their disposal. Thus, to maintain the balance between waste materials and the environment, the best possible solution is waste management by recycling. The recycling process can be classified based on the material extraction process used for the electrodes, electrolytes, and various other materials as shown in Fig. 1. Another widely used energy storage device, SCs, are highly desirable over batteries due to their high power-carrying capacities, low weight and maintenance, and durability. A typical SC consists of conducting electrodes like carbon-based materials, metal oxides, conducting polymers, metal nitrides, various composites, etc., and the electrolytes like H2 SO4 , KOH, KCl, LiOH, etc. [1].

Fig. 1 Schematic diagram of the various methods used for the recycling of energy storage devices

Methods and Technologies for Recycling Energy Storage Materials …

491

2 Need for Recycling The world’s total fuel consumption for the year 2018 has been reported to be 11,743.6 million tons of oil, which accounts for the 84.7% of the world’s total energy consumption. A large part of this consumption is sustained by exploiting fossil fuels [2]. Also, the use of fossil fuels has resulted in a huge amount of carbon released into the atmosphere along with other harmful gases. To prevent damage to the environment and sustain the energy demands using non-renewable resources, a new idea of a carbon– neutral approach has been introduced. Batteries and SCs have been widely used as energy storage devices for various applications but it has limited life spans. In the year 2018, the installation capacity of LIBs was more than 86%. Once the life span is over, there is a dire need to decompose the spent devices as these storage devices are made of many toxic chemicals and materials which can harm the environment in one way or the other when left unaddressed at their disposal.

3 Recycling of SCs The recycling of the SC is done using shredding and sieving followed by the chemical treatment which is used to retrieve the reusable materials from it. These retrieved materials can be further used in other applications. The recycling process of SCs has not been much explored compared to the batteries, though the conventional procedures of both devices are similar.

3.1 Extraction of Electrodes Mechanical shredding is done to reduce the size of the SCs by paper cut machine as shown in Fig. 2. All the corresponding components like electrolyte, electrode material, current collector, and even the paper used as a separator can be retrieved by this process [3]. Shredding is carried out under a chemical hood to prevent the transmission of hazardous vapors into the environment. In The current collector of SCs have graphene as thin films, so its extraction includes scraping it out from the collector’s surface. The scrapped materials are placed in the round-bottom flask and heated in the presence of nitrogen. This results in the evaporation of the various solvents present on the electrode [4]. Similarly, retrieval of the activated carbons (ACs) from the SC electrode is initiated by discharging and pre-treating the collected shredded scrap. The collective is mixed with N-methyl-2-pyrrolidine (NMP) under ultrasonic conditions. The impurities from the ACs are also removed by heating the slur in the presence of nitrogen and then washing the slur with DI and further drying produces pure ACs [5].

492

N. Thakur et al.

Fig. 2 Supercapacitor recycling process. Adapted from [3]. Copyright The Authors, some rights reserved; exclusive licensee (Elsevier). Distributed under a Creative Commons Attribution License 4.0

3.2 Extraction of Electrolyte The recovery of electrolyte material like tetraethyl ammonium tetrafluoroborate (TEABF4 ) and other constituents like acetonitrile (ACN), and polyvinylidene difluoride (PVDF) is done using a facile and cost-effective method. TEABF4 and PVDF are separated from the carbonaceous mixture using their solubility in water and in butanone respectively. The slur is then filtered and washed using distilled water. Drying using rotator evaporator lefts with 59.3% ACN and further centrifuging the residue leads to 1.4 g of TEABF4 [5]. Other than the organic electrolytes, hydrogelbased electrolytes, and electrodes can be easily recycled using water heated at 80 °C [6].

4 Recycling of LIBs and Their Different Components Material LIBs mainly consist of four components, namely cathode, anode, electrolyte, and separator. Various oxides of Li have been used in cathode, such as LiCoO2 (LCO), LiNi0.5 Mn1.5 O4 (LNMO), LiNiO2 , LiMn2 O4 , LiFePO4 , LiNix Coy Mn1-x-y O2 , Ni-rich layered oxides, Li-rich layered oxides (LLOs) and so forth. The explored anode materials are alloy material, conversion-type anode materials (CTAMs), siliconbased compounds, and carbon-based compounds, including both graphitic carbon (GC) and non-graphitic carbons (NGC). LiPF6 , LiClO4 , LiBF4 , etc., as solutes and organic solvents diethyl carbonate (DEC), dimethyl sulfoxide (DMSO), and propylene carbonate (PC) are generally used as electrolytes of LIBs. Single and multi-layer of polyolefine (PO), polypropylene (PP), and polyethylene (PE) are commonly used

Methods and Technologies for Recycling Energy Storage Materials …

493

as a separator to avoid direct contact between anode and cathode and prevent internal short circuits.

5 Pretreatment Process Recycling of batteries can be primarily classified based on the treatment methodologies used such as pyrometallurgy, hydrometallurgy, and direct recycling. Before starting any process, batteries are fully discharged and pretreated by different methods. The most commonly used pretreatments are described below.

5.1 Thermal Pre-treatment Thermal treatments are used to decompose PVDF binder, acetylene black, conductive carbon, etc. The electrolyte decomposes at 250–300 °C; PVDF binder at 500 °C, and at around 600 °C Li metal oxide partially reduces to lower Li oxides and Li carbonate [7]. Bi et al. explored the low-temperature thermal pretreatment for Li iron phosphate (LFP) battery recycling [8]. After discharging and disassembling, cathode plates are given thermal treatment at varying temperatures (210, 240, 270, 300, and 330 °C) and time (60, 90, 120, and 150 min) and then cooled. The partially brittle cathode active material is scrapped off from Al foil by mechanical stress such as vibration as well as by crushing it for 20 s. Sun et al. used the vacuum pyrolysis method for the separation of cathode active material of LiCoO2 from Al foil [9]. After discharging, dismantling, and separation, cathode electrodes are placed into the vacuum pyrolysis system with a system pressure of less than 1.0 kPa, and heated to 600 °C for 30 min. The volatile components condense in the condenser and non-condensable gases are extracted by a vacuum pump. After the treatment, Li cobalt oxide is separated from Al foil by peeling it off.

5.2 NaOH Dissolution Method The extraction of Al from cathode material is carried out at a constant S/L ratio (1:10 g mL−1 ) and varying concentrations (0.25–3.75 mol L−1 ) of NaOH by varying the temperature from 30 to 70 °C keeping the leaching time up to 300 min [10]. Gaye et al. have used hydrometallurgical pretreatment of LIBs cathode material using NaOH as solvent [11]. After discharging, manual dismantling, and separation of cathode material from plastic and metal cells, it is dried in an oven at 50 °C for 24 h. A dried cathode is cut into small pieces and dissolved in different concentrations (2N, 3N, 4N) of NaOH with an L/S ratio of 10/1 for 5 h at room temperature. After leaching, the black cathode residue is separated by filtration. A similar approach is

494

N. Thakur et al.

used for the separation of Al metal from cathode material wherein during dissolution by NaOH, the aluminum at the surface is dissolved, and then separated from the cathode material [12]. The chemical reaction for this treatment is stated below: Al2 O3 + 2NaOH + 3H2 O → 2Na[Al(OH4 )]

(1)

2Al + 2NaOH + 6H2 O → 2Na[Al(OH4 )] + 3H2

(2)

5.3 Solvent Dissolution and Ultrasonic-Assisted Separation The cathode material is attached to aluminum foil using a PVDF binder in Li batteries. The stripping of cathode material from aluminum foil is done by ultrasonic cleaning [13]. The cathode material is separated from Al foil using NMP, N– N-dimethylformamide (DMF), N–N-dimethylacetamide (DMAC), N–N-dimethyl sulfoxide (DMSO), and ethanol as wetting agents [14]. Under optimum ultrasonic power (240 W), process temperature (70 °C), and time (90 min), using NMP as a cleaning solvent, achieved peel-off efficiency is approximately 99%. A similar approach is used by Lei et al. for the delamination of LMO and NMC LIB electrodes by ultrasonic treatment [15]. After disassembly and rinsing by dimethyl carbonate (DMC), an electrode is placed directly underneath high power sonotrode (operating frequency 20 kHz and maximum power 2200 W) in a solvent tank with a 3 mm gap in between the sonotrode and electrode. The power density of 120 W cm−2 and a wetting agent (solution of 0.05 M citric acid and 0.1 M NaOH) is used for the ultrasonic delamination of the anode, and NMC cathode respectively. The dispersed active material coating is easily recovered via filtration of the solvent. The delamination can be done in less than 10 s by this approach.

6 Metal Recycling/Extraction Process After the pretreatment of spent LIBs, different metallurgy methods are adopted for the recovery of active materials mainly from the cathode part. The main approaches include direct recycling, pyrometallurgy, hydrometallurgy, biometallurgy, electrochemical extraction, etc.

Methods and Technologies for Recycling Energy Storage Materials …

495

6.1 Direct Physical Recycling/Regeneration Process Direct physical recycling/regeneration processes can mainly be classified as hydrothermal re-lithiation, solid-state re-lithiation, and electrochemical re-lithiation.

6.1.1

Hydrothermal Re-lithiation

Hydrothermal treatment for regeneration of degraded Li manganese oxide (LiMn2 O4 ) oxide cathode is done by taking 0.25 g cycled LiMn2 O4 in a Teflon-lined autoclave, containing Li hydroxide (LiOH) with varying concentrations of 0.02, 0.1, and 0.4 M and heating it at 180 °C for different time periods [16]. After treatment, pH is adjusted to neutral, and the material is dried in a vacuum at 80 °C overnight. After 6 h of treatment with 0.1 M solution, the Li concentration reaches a pristine level. The extraction of electrolytes is explored by heating the cathode material and separating the graphite anode of spent LCO batteries by direct recycling [17]. After discharging of LIBs using sodium bicarbonate brine solution and extraction of an electrolyte by liquid carbon dioxide, the whole cells are shredded. The shredded residues are placed into a blender and after delamination, electrode materials are separated from plastics, copper/aluminum, and current collector by filtration. The recovered material is a mixture of the cathode, carbon black, binder, and graphite which is treated hydrothermally with 4 M aqueous Li solution. After removal of the binder by froth flotation, harvested material is agitated using water and surfactant that separates carbon (float) and metal oxide (sink). The graphitic float is collected and vacuum dried at 120 °C after rinsing with HNO3 , DI, and acetone. Collected healed cathode material is dried in air at 800 °C.

6.1.2

Solid-State Re-lithiation

The spent LiCoO2 batteries are recycled and regenerated after solid-state synthesis with Li2 Co3 . After the separation of Al foil and removal of acetylene black by calcination in air at 800 °C for 2 h, 100 g of cathode powder is mixed with Li2 Co3 (Li and Co in a molar ratio of 1.05:1) and again calcined in air at 800–950 °C for 12 h to get regenerated LiCoO2 . The discharge capacity of regenerated batteries varied from 148.7 to 152.4 mAh g−1 [18]. The direct recycling of LiNi1-x-y Cox Mny O2 cathode material from spent LIBs is done by the mechno-chemical activation and solid-state sintering method [19]. The cathode material of LiFePo4 batteries is regenerated using the solid phase sintering method [20]. After leaching the cathode material with NMP, DMF, dimethyl acetamide, and acetone at different temperature conditions, the filtrated black powder is collected and dried at 60 °C for 24 h. Dried LiFePo4 is treated with N2 in a tube heating furnace for 15 min and then regeneration is done

496

N. Thakur et al.

at various temperatures for 8 h by solid phase sintering with new LiFePo4 powder. Battery capacities by this method can reach over 120–144 mA h g−1 .

6.1.3

Electrochemical Re-lithiation

Zhang et al. explored electrochemical re-lithiation for LiCoO2 cathode using Li2 SO4 solution [21]. Waste Lix CoO2 is used as the working electrode, platinum plate as the anode electrode, and Ag/AgCl with saturated KCL as the reference electrode. All electrodes are immersed in Li2 SO4 solution with varying concentrations of 0.1, 0.3, 0.5, or 1 M. The constant cathode current is applied to insert Li+ into waste Lix CoO2 . The time to reach stable cathode potential decreases with the increase in solution concentration at a particular applied current density.

6.2 Pyrometallurgy Pyrometallurgy is the recycling technology that allows the extraction of pure metal at very high temperatures. The flow chart for the recycling of various spent batteries is shown in Fig. 3 [21]. The spent batteries are dissembled, preheated, pyrolyzed, and then smelted. The preheating temperature (< 300 °C) is maintained to ensure full evaporation of the electrolyte as well as to avoid explosive hazards at higher temperatures. The smelting process enables the extraction of base metals like Ni, Co, Li, and Fe [22]. The extraction of Li is done by selective pyrolysis. The Co Alloys and the Li concentrate are processed using hydrometallurgy and stored in the form of LiCO3 . A similar process is used to extract Li from a mixture of spent 18,650-type batteries [23]. The retrieval is obtained in the form of LiCO3 from the crystal structure of Li transition metal. The mixture is first crushed into fine nano particles and then pyrolyzed at 30 K min−1 in a vacuum. Further washing with diluted water left the recycled Li source while the graphite left in the filter is burnt away to recover the transition metal oxide. In another study, a spent battery from a phone is taken and pretreated which includes discharging, dismantling and mechanical crushing, etc. [24].

6.2.1

Microwave-Assisted (MW) Pyrolysis

MW-assisted pyrolysis for recycling of spent LIBs is done in three major steps: (a) roasting, (b) leaching, (c) precipitation. The MW-assisted pyrolysis as shown in Fig. 4 contained 8 MW generators of 6 W each, out of which six are used in the study to control atmospheric vulnerabilities. Generators are sequentially activated for 30 s to impart radiation over the sample placed in a crucible inside the reactor [25].

Methods and Technologies for Recycling Energy Storage Materials …

497

Fig. 3 Process flow for the recycling of cathode and anode materials using various spent batteries. Adapted from [21]. Copyright The Authors, some rights reserved; exclusive licensee [Elsevier]. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

The system also has an IR camera for the continuous monitoring of the temperature variation in the sample through the crucible. Further, a study to demonstrate the liberation of electrode material from the foil surface in a Li-ion battery is conducted using a pyrolysis process [26]. The results suggested that the liberation efficiency of 99.79 and 99.60% can be achieved for the cathode and anode respectively. Since pyrometallurgy includes the burning of the positive as well as negative material altogether at higher temperatures, a technique is suggested to lower the processing temperature [27]. Pyrolysis in presence of graphite leads to a coupling reaction and reduced the threshold of the reaction from 1426 to 1173.2 K.

498

N. Thakur et al.

Fig. 4 Schematic diagram of microwave-assisted pyrolysis plant. Adapted from [25]. Copyright The Authors, some rights reserved; exclusive licensee [MDPI]. Distributed under a Creative Commons Attribution License 4.0 (CC BY)

6.2.2

Pyrolysis and the Floating Process

The pyrolysis and the floating process are used to enhance the liberation efficiency of the spent batteries [28]. The spent batteries are given pretreatment and then the extracted cathode–anode (LiCoO2 -graphite) mix is fed to the tube furnace under a controlled temperature for the pyrolysis. Further, in the floatation process, the anode gets attached to the bubbles as is hydrophobic and vice versa. With additional filtration and drying, an impressive liberation of efficiency of 98.23% for the cathode and 98.89% for the anode is obtained.

6.2.3

Physical Separation

The pyrolysis in combination with the physical separation method is used to extract around 99.91% of organic electrolyte and other metals respectively from the batteries. While the pyrolysis is responsible for the electrolyte retrieval, the residue treatment with color-based segregation, high-pressure water cleaning, and flotation process enables the extraction of 99.34% Al, 96.25% Cu, and 49.67% of cathode active materials [29]. A bunch of household batteries is physically pretreated for the retrieval of main battery components like zinc (Zn), MnO (manganese oxide), and steel scrap. The laboratory-based pyrolysis process enabled 99% of Zn and the residue contained mainly MnO2 slur with minor impurities [30]. The temperature and exposure time are important parameters that determine the composition of the material recycled from the spent battery [31]. Nowadays Nickel, Cobalt, and Manganese (NCM) batteries are extensively used as an electrochemical power supply. A green facile recycling method has been used for the extraction of these spent NCM. Spray pyrolysis in addition

Methods and Technologies for Recycling Energy Storage Materials …

499

to leaching using acetic acid and hydrogen peroxide has led to 99% regeneration of each of the metals Ni, Co, and Mn [32]. Various studies over the past ensured the role of temperature and its optimization in the process of pyrolysis. A similar effort has been done to determine the pyrolysis temperature and the vacuum pressure for the efficient separation of the effective powder and the Al foil from the spent batteries. The results concluded that a 600 °C and 1000 Pa temperature and vacuum pressure respectively can increase the recovery rate of the cathode to 98.04% [33]. The reduction of cathode material optimizes the overall liberation properties of the cathode and helps in the removal of the organic binders [34]. Since pyrolysis has been a widely used recycling process for batteries over the decade, understanding its actual kinetics can still be sometime confusing or unclear. So, there is a dire need to focus on it for a better understanding of the reaction mechanism and its outcomes. Among the various other methods of recycling cathode material like incineration, dynamic pyrolysis, and vacuum pyrolysis, incineration is highly efficient. It could recover 95% of the cathode material at a temperature higher than 550 °C [35]. A novel process using pyrolysis is developed for recycling. In this process, the separator and the organic binders are collected in the form of oil and gases and the cathode recovery increased to more than 99.5% [36]. In general, The process of pyrolysis is preferred over the incinerating process [37].

6.2.4

Green Recovery Methods

The research community has widely explored hydrometallurgy, pyrometallurgy, biometallurgy, and direct recycling process for metal recovery. As various harsh chemicals are used for hydrometallurgy and high-temperature treatment for the pyrometallurgy process, these treatments take a toll on economic and energy consumption in the form of carbonization. Pine sawdust can be used as a cost-effective, facile, and green reducing agent that lowers the pyrolysis temperature. The recovery rate of Li and Co thorough the process comes out to be 94 and 97% respectively [38]. The wastewater generated during the chemical treatment for the separation of Al foil from the binder increases overall recycling cost. So, a critical analysis of the pyrolysis is of utmost importance for reactor designing, and optimization and also to remove the hazardous aspects [39].

6.3 Hydrometallurgy Hydrometallurgy mainly deals with the extraction of active cathode materials from spent LIBs by different inorganic and organic acids.

500

6.3.1

N. Thakur et al.

Inorganic Acid Leaching

Several inorganic acids such as HCl, HNO3 , and H2 SO4 have been used by different researchers as leaching agents for the leaching of cathode materials. Shu-guang et al. extracted Co and Li from the cathode material of a LiCoO2 battery by using H2 SO4 as leachant and hydrogen peroxide (H2 O2 ) as reducing agent [40]. Separated cathode active materials are dissolved in H2 SO4 and H2 O2 solution and after removal of impurities by filtration and adjustment of pH to 5, (NH4 )2 C2 O4 is added to leaching solution and CoC2 O4 .2H2 O precipitate is obtained. After filtration of suspending liquid, CoC2 O4 .2H2 O precipitate is collected and dried, and Na2 CO3 solution is added to the filtrate to precipitate Li2 CO3 . The leaching process and different precipitations can be chemically represented as: 2LiCoO2 (s) + 3H2 SO4 (aq) + H2 O2 (aq) → 2CoSO4 (aq) + Li2 SO4 (aq) + 4H2 O(g) + O2 (g)

(3)

CoSO4 (aq) + (NH4 )2 C2 O4 (aq) → CoC2 O4 (s) + (NH4 )2 SO4 (aq)

(4)

2Li + Na2 CO3 → Li2 CO3 ↓ +2Na+

(5)

The recovery of valuable metals from spent LIBs is explored using HCl as media [41]. After crushing, sieving, and magnetic separation, LIBs cathode material is added to 4 M HCl in a glass reactor vessel at a controlled temperature, and stirred for 180 min. The leaching reaction can be represented as: 2LiCoO2 (s) + 8HCl(aq) → 2LiCl(aq) + 2CoCl2 (aq) + Cl2 (g) + 4H2 O(aq) (6) Post neutralization by NaOH, Ni and Co recovery is done by direct precipitation with the addition of Na2 CO3 , resulting in nickel–cobalt rich precipitate; and solvent extraction by Cyanex 272 as extractant, tributyl phosphate as phase modifier and sulfonated kerosene as diluent. The vacuum and syringe filtration is used to separate the supernatant, product liquid solution (PLS), and precipitates. Li2 CO3 recovery was done by increasing the concentration of neutralized PLS, by evaporation, and by the addition of Na2 CO3 to initiate Li2 CO3 precipitation. At L/S ratio of 10 and at a temperature of 80 °C, the recovery of Li, Co, and Ni are 3069, 20,480 and 2626 mg L−1 , respectively. Besides these metals, Cu, Mn, and Al are also recovered. Jung et al. have studied selective leaching and recovery of LiNO3 from a mix of LiNix Coy Mnz O2 and LiCoO2 , LIB cathode material by roasting after leaching with HNO3 [42]. After removing organic compounds by pretreatment from mix of LiNix Coy Mnz O2 and LiCoO2 and leaching with 10 M HNO3 for 10 min, the nitrate compounds (LiNO3 , Co(NO3 )3 , Ni(NO3 )2 , and Mn(NO3 )2 ) are produced. Roasting it at varying temperatures (200–700 °C) and time (1-10 h) decompose the nitrate

Methods and Technologies for Recycling Energy Storage Materials …

501

compounds except the Li nitrate. The conversion of nitrate compounds into metal oxide compounds at a specific temperature during roasting can be represented as: 1 M(NO3 )2 (s) → MO(s) + 2NO2 (g) + O2 (g) 2

(7)

The selective Li leaching in DI water at room temperature with S/L ratio of 10 mL/g at optimum roasting temperature of 275 °C yielded 80% of Li.

6.3.2

Organic Acid Leaching

Tannic acid and acetic acid are used synergistically for cobalt and Li recovery from spent LiCoO2 LIBs [43]. 1 g of separated cathode powder was added to mixture of tannic acid and acetic acid and long homogenization for 12 h was done using an orbital shaker. After that the leached solution was separated from the solid residue. Tannic acid oxidation by insoluble Co3+ in LIB resulted in producing soluble Co2+ . The reaction with tannic acid and acetic acid is given below: 152LiCoO2 + C55 H40 O54 → 152Li+ + 152Co2+ + 55CO2 + 456OH− 8LiCoO2 + CH3 COOH + 18H2 O → 8Li+ + 8Co2+ + 2CO2 + 24OH−

(8) (9)

Metal recovery can be calculated as R = (C E X V )/(Co X m)

(10)

where CE is the metal concentration in leached solution, Co is the thermal content in cathode powder (mg/g) and V is the leaching agent volume (L). The effect of acid concentration, pulp density, and leaching time is also explored for the above mentioned process. Li, nickel, cobalt, and manganese are recovered from a mix of LiCoO2 and LiNi0.5 Co0.2 Mn0.3 O2 spent LIBs using L-tartaric acid as leachant and H2 O2 as reducing agent [44]. After separation, cathode active materials are added to a heated solution (40–80 °C temperature) of L-tartaric acid (0.25–2.5 M) and H2 O2 (0–5 vol %), and the reaction is allowed to mix for 300 min. The pulp density varied from 14 to 33 g/L. The leaching reaction can be represented as: 2LiCoO2 (s) + 3C4 H6 O6 (aq) + H2 O2 (aq) → C4 H4 O6 Li2 (aq) + 2C4 H4 O6 Co(aq) + 4H2 O(l) + O2 (g)

(11)

10LiNi0.5 Co0.2 Mn0.3 O2 (s) + 15C4 H6 O6 (aq) + 5H2 O2 (aq) → 5C4 H4 O6 Li2 (aq) + 5C4 H4 O6 Ni(aq) + 5C4 H4 O6 Co(aq) + 3C4 H4 O6 Mn(aq) + 20H2 O(l) + 5O2 (g)

(12)

502

N. Thakur et al.

Leaching efficiencies obtained are 99.31, 99.07, 98.64, and 99.31% for Ni, Mn, Li, and Co respectively at optimum conditions.

6.4 Biometallurgy Biometallurgy is the process where dissolution, precipitation, and recovery of valuable metals from spent LIBs are done by inorganic and organic acids produced by micro-organisms bacteria, and fungi. The bioleaching process is explored for the recovery of Co and Li from spent LIBs using the fungus Aspergillusniger MM1 and SG1 and, Acidithiobacillus thiooxidans 80,191 bacteria [45]. In bioleaching by fungal strains, 50 ml of sterile sucrose medium containing sucrose (100 g/L), NaNO3 (1.5 g/L), KH2 PO4 (0.5 g/L), MgSO4 .7H2 O (0.025 g/L), KCl (0.025 g/L) and yeast extract (1.6 g/L), 0.25% (w/v) autoclaved LIB powder and 0.5 mL A. niger MM1/ SG1 are put into conical flux and incubated at 30 °C. In another bioleaching process, A. niger is cultivated in sucrose medium followed by centrifugation and separation and then 50 ml of cell-free medium is taken and autoclaved LIBs powder (0.25%, w/ v) is added to it. Recovery of dissolved Co from leached solution is done by the addition of Na2 S, NaOH, and Na2 C2 O4 at room temperature to precipitate CoS, Co(OH)2 , CoC2 O4 .2H2 O respectively. Li recovery is done through Li2 CO3 precipitation by the addition of Na2 CO3 . The precipitation reaction for both can be expressed as follows: Co2+ (aq) + Na2 S → CoS(s) + 2Na+ (aq)

(13)

Co2+ (aq) + 2NaOH → Co(OH)2 (s) + 2Na+ (aq)

(14)

Co2+ (aq) + Na2 C2 O4 + 2H2 O → CoC2 O4 · 2H2 O(s) + 2Na+ (aq) 2Li+ (aq) + Na2 CO3 → Li2 CO3 (s) + 2Na+ (aq)

(15) (16)

Bacterial bioleaching is done similarly to fungal bioleaching except using sterile basal 317 as a medium. The metal dissolution for bacteria can be described as: ◦

S + H2 O + 3/2O2 → H2 SO4 (produced by A. thiooxidans)

(17)

H2 SO4 + M → MSO4 + 2H+ (M = Metal)

(18)

Solubilization is more for both fungal and bacterial bioleaching by second process and approximately 80–82% Co and 100% Li is removed by A. niger MM1/SG1 while 23% Co and 66% Li removal is achieved by A. thiooxidans.

Methods and Technologies for Recycling Energy Storage Materials …

503

6.5 Electrochemical Extraction The slurry electrolysis is used for the recovery of Li and manganese from spent LiMn2 O4 batteries [46]. In a cylinder-shaped slurry electrolyzer, graphite cathode and ruthenium-plated titanium anode are placed in a filter cloth separated cathode and anode chamber, filled with a mixture of H2 SO4 and MnSO4 electrolyte. The electrolyte is heated to 363 K and scrap LiMn2 O4 is added to the cathode chamber. At the cathode, Li is leached into the electrolyte and the reaction involve is given below: LiMn2 O4 + e + 4H+ → Li+ + MnO2 + Mn2+ + 2H2 O

(19)

LiMn2 O4 + H+ → HMn2 O4 + Li+

(20)

HMn2 O4 + 3H+ + e → Mn2+ + 2H2 O + MnO2

(21)

Generated MnO2 is leached into electrolyte as Mn2+ and is oxidized to Mn4+ and deposits MnO2 in the anode chamber. Removal of Mn2+ as Mn(OH)2 precipitate is done by the addition of NaOH. The reaction taking place at anode is given as: MnO2 + 4H+ + 2e → Mn2+ + 2H2 O

(22)

Mn2+ + 2OH− → Mn(OH)2 ↓

(23)

After the removal of Mn2+ and filtration and evaporation, Na2 CO3 is added to get Li2 CO3 precipitate. Li and Mn leaching are more than 99% and 92%. High purity Li2 CO3 (99.59 wt%) and MnO2 (92.33 wt%) are obtained by this approach.

7 Anode Material Recovery During different metallurgical treatments mainly active cathode materials are extracted as it contains valuable metal components. However, in recent years, extraction of active materials from the anode of LIBs has also been explored. The separation of carbon anode material is done by ultrasound leaching method from spent LIBs using ultra-pure water having specific conductivity of 0.055 µS/cm as a solvent [47]. Peeling off the packaging and shell of the spent LIBs and separation of the cathode, anode, and diaphragm are done mechanically. Carbon in anode material is separated from copper foil by ultrasonic leaching method. 0.25 g anode material is dried at 120 °C for 1 h and then carbon powder is separated from copper foil after cooling. Both materials are separately dried at 120 °C for 1 h and collected. At industrial level, carbon material and copper foil are separated by hammer crushing followed

504

N. Thakur et al.

by vibration sieving. After crushing, the obtained particle size of copper foil is more than 0.250 mm and while size of carbon powder is less than 0.125 mm so they get separated according to their size and shape. The air separation method is used for the particles of size in the range of 0.125–0.250 mm. The spent anode of LIBs contains 11.70–13.06% Li which comes from solid electrolyte interface (SEI) film and LiPF6 electrolytes. Among the existence of Li as Li2 Co3 , Li2 O, LiF, RCO2 Li, CH3 OLi, and (ROCO2 Li)2 compounds in SEI film, LiF is a major compound. Liu et al. have explored the potential of alkaline roasting by using NaOH to separate and recover insoluble LiF from graphite anode of LiCoO2 , LiNi0.5 Co0.2 Mn0.3 O2 , and LiFePO4 cathode LIBs [48]. After the separation of anode material from copper foil, the graphite from different anodes are mixed with NaOH in different mass ratios (2:1, 1:1, 1:2 and 1:4), and the mixtures are roasted in a tube furnace at 100–400 °C temperature for 0.5–3 h with a heating rate of 5 °C min−1 . After roasting, Li and graphite are separated by leaching with DI water and followed by filtration. Obtained graphite is vacuum dried at 80 °C for 12 h and Li is recovered from the filtrate solution. The achieved leaching efficiency for Li is nearly 100%. The reaction of LiF with NaOH can be represented as: LiF + NaOH → NaF + LiOH

(24)

8 Conclusions Increase use of electronic gadgets for a better lifestyle and the recent trend to use electric vehicles and hybrid electric vehicles, demands more use of batteries and SCs. Recycling of energy storage devices like spent metal ion batteries and, SCs can restore the limited reserves of raw materials for the different components of these devices. A detailed recycling methods and technologies such as hydrometallurgy, pyrometallurgy, heat and chemical treatments for the extraction of electrodes, electrolytes and active material and metals are explored categorically. Though some technologies have been adopted for industrial-scale recycling, more research is needed in this area for environment-friendly and efficient extraction and recovery of valuable materials. A better battery and supercapacitor collection policy also needs to be implemented by the government for this purpose.

References 1. Huang B, Pan Z, Su X, An L (2018) Recycling of lithium-ion batteries: recent advances and perspectives. J Power Sources 399:274–286

Methods and Technologies for Recycling Energy Storage Materials …

505

2. Chen H, Ling M, Hencz L, Ling HY, Li G, Lin Z, Liu G, Zhang S (2018) Exploring chemical, mechanical, and electrical functionalities of binders for advanced energy-storage devices. Chem Rev 118:8936−8982 3. Jiang G, Pickering SJ (2016) Recycling supercapacitors based on shredding and mild thermal treatment. Waste Manage 48:465–470 4. Jiang G, Pickering SJ (2017) Recycling graphene from supercapacitor electrodes as reinforcing filler for epoxy resins. Waste Biomass Valor 10(1):215–221 5. Wu F, Zhao T, Yao Y, Jiang T, Wang B, Wang M (2020) Recycling supercapacitor activated carbons for adsorption of silver (I)and chromium (VI) ions from aqueous solutions. Chemosphere 238:124638 6. Wang H, Dai L, Chai D, Ding Y, Zhang H, Tang J (2020) Recyclable and tear-resistant all-in-one supercapacitor with dynamic electrode/electrolyte interface. J Colloid Interf Sci 561:629–637 7. Babanejad S, Ahmed H, Andersson C, Samuelsson C, Lennartsson A, Hall B, Arnerlöf L (2018) High-temperature behavior of spent Li-Ion battery black mass in inert atmosphere. J Sustain Metall 8:566–581 8. Bi H, Zhu H, Zu L, Gao Y, Gao S, Peng J, Li H (2021) Low-temperature thermal pretreatment process for recycling inner core of spent lithium iron phosphate batteries. Waste Manage Res 39(1):146–155 9. Sun L, Qiu K (2011) Vacuum pyrolysis and hydrometallurgical process for the recovery of valuable metals from spent lithium-ion batteries. J Hazard Mater 194:378–384 10. Ferreira DA, Prados LMZ, Majuste D, Mansur MB (2009) Hydrometallurgical separation of aluminum, cobalt, copper and lithium from spent Li-ion batteries. J Power Sources 187:238–246 11. Gaye N, Gueye RS, Ledauphin J, Balde M, Seck M, Wele A, Diaw M (2019) Alkaline leaching of metals from cathodic materials of spent lithium-ion batteries. Asian J Appl Chem Res 3(2):1–7 12. Amalia D, Singh P, Zhang W, Nikoloski AN (2021) Influence of alkaline pre-treatment on acid dissolution of cathode material of 18650 lithium battery. IOP Conf Ser Earth Environ Sci 882:012001 13. Li J, Shi P, Wang Z, Chen Y, Chang CC (2009) A combined recovery process of metals in spent lithium-ion batteries. Chemosphere 77(8):1132–1136 14. He LP, Sun SY, Song XF, Yu JG (2015) Recovery of cathode materials and Al from spent lithium-ion batteries by ultrasonic cleaning. Waste Manage 46:523–528 15. Lei C, Aldous I, Hartley JM, Thompson DL, Scott S, Hanson R, Anderson PA, Kendrick E, Sommerville R, Ryder KS, Abbott AP (2021) Lithium ion battery recycling using high-intensity ultrasonication. Green Chem 23:4710–4715 16. Gao H, Yan Q, Xu P, Liu H, Li M, Liu P, Luo J, Chen Z (2020) Efficient direct recycling of degraded LiMn2 O4 cathodes by one-step hydrothermal relithiation. ACS Appl Mater Interfaces 12:51546–51554 17. Sloop S, Crandon L, Allen M, Koetje K, Reed L, Gaines L, Sirisaksoontorn W, Lerner M (2020) A direct recycling case study from a lithium-ion battery recall. Sustain Mater Technol 25:e00152 18. Nie H, Xu L, Song D, Song J, Shi X, Wang X, Zhang L, Yuan Z (2015) LiCoO2 : recycling from spent batteries and regeneration with solid state synthesis. Green Chem 17:1276–1280 19. Meng X, Hao J, Cao H, Lin X, Ning P, Zheng X, Chang J, Zhang X, Wang B, Sun Z (2019) Recycling of LiNi1/3 Co1/3 Mn1/3 O2 cathode materials from spent lithium ion batteries using mechanochemical activation and solid state sintering. Waste Manage 84:54–63 20. Song X, Hu T, Liang C, Long HL, Zhou L, Song W, You L, Wu ZS, Liu JW (2017). Direct regeneration of cathode materials from spent lithium iron phosphate batteries using a solid phase sintering method 2017. RSC Adv 7:4783–4790 21. Zhang L, Zhenming X, He Z (2020) Electrochemical relithiation for direct regeneration of LiCoO2 materials from spent lithium-ion battery electrodes. ACS Sustain Chem Eng 8:11596– 11605 22. Assefi M, Maroufi S, Yamauchi Y, Sahajwalla V (2020) Pyrometallurgical recycling of Li-ion, Ni–Cd and Ni–MH batteries: a minireview. Curr Opin Green Sustain Chem 24:26–31

506

N. Thakur et al.

23. Zhou LF, Yang D, Du T, Gong H, Luo WB (2020) The current process for the recycling of spent lithium ion batteries. Front Chem 8:578044 24. Xiao J, Li J, Xu Z (2017) Novel approach for in-situ recovery of lithium carbonate from spent lithium ion batteries using vacuum metallurgy. Environ Sci Technol 51(20):11960–11966 25. Zhang G, He Y, Feng Y, Wang H, Zhu X (2018) Pyrolysis-ultrasonic-assisted flotation technology for recovering graphite and LiCoO2 from spent lithium-ion batteries. ACS Sustain Chem Eng 6(8):10896–10904 26. Diaz F, Wang Y, Moorthy T, Friedrich B (2018) Degradation mechanism of nickel-cobaltaluminum (NCA) cathode material from spent lithium-ion batteries in microwave-assisted pyrolysis. Metals 8:565 27. Zhang G, He Y, Feng Y, Wang H, Zhang T, Xie W, Zhu X (2018) Enhancement in liberation of electrode materials derived from spent lithium-ion battery by pyrolysis. J Cleaner Prod 199:62–68 28. Mao J, Li J, Xu Z (2018) Coupling reactions and collapsing model in the roasting process of recycling metals from LiCoO2 batteries. J Cleaner Prod 205:923–929 29. Zhang G, Du Z, He Y, Wang H, Xie W, Zhang T (2019) A sustainable process for the recovery of anode and cathode materials derived from spent lithium-ion batteries. Sustainability 11:2363 30. Zhong X, Liu W, Han J, Jiao F, Qin W, Liu T, Zhao C (2018) Pyrolysis and physical separation for the recovery of spent LiFePO4 batteries. Waste Manage 89:83–93 31. Ebin B, Petranikova M, Steenari BM, Ekberg C (2019) Recovery of industrial valuable metals from household battery waste. Waste Manag. Res 37(2):168–175 32. Lombardo G, Ebin B, Foreman MR, St J, Steenari BM, Petranikova M (2019) Chemical transformations in Li-Ion battery electrode materials by carbothermic reduction. ACS Sustain Chem Eng 7:13668−13679 33. Zheng Y, Wang S, Gao Y, Yang T, Zhou Q, Song W, Zeng C, Wu H, Feng C, Liu J (2019) Lithium nickel cobalt manganese oxide recovery via spray pyrolysis directly from the leachate of spent cathode scraps. ACS Appl. Energy Mater 2(9):6952–6959 34. Li W, Yang S, Liu N, Chen Y, Xi Y, Li S, Jie Y, Hu F (2019) Study on vacuum pyrolysis process of cathode sheets from spent lithium-ion batteries. Mineral Metals Mater Ser 421–435 35. Zhang G, Yuan X, He Y, Wang H, Xie W, Zhang T (2020) Organics removal combined with in situ thermal-reduction for enhancing the liberation and metallurgy efficiency of LiCoO2 derived from spent lithium-ion batteries. Waste Manage 115:113–120 36. Lombardo G, Ebin B, Steenari BM, Alemrajab M, Karlsson I, Petranikova M (2021) Comparison of the effects of incineration, vacuum pyrolysis and dynamic pyrolysis on the composition of NMC-lithium battery cathode-material production scraps and separation of the current collector. Resour Conserv Recycl 164:105142 37. Tao R, Xing P, Li H, Wu Y, Li S, Sun Z (2021) Full-component pyrolysis coupled with reduction of cathode material for recovery of spent LiNixCoyMnzO2 lithium-ion batteries. ACS Sustain Chem Eng 9:6318–6328 38. Balachandran S, Forsberg K, Lemaître T, Vieceli N, Lombardo G, Petranikova M (2021) Comparative study for selective lithium recovery via chemical transformations during incineration and dynamic pyrolysis of EV Li-Ion batteries. Metals 11:1240 39. Zhou F, Qu X, Wu Y, Zhao J, Gao S, Wang D, Yin H (2022) Vacuum pyrolysis of pine sawdust to recover spent lithium ion batteries: the synergistic effect of carbothermic reduction and pyrolysis gas reduction. ACS Sustain Chem Eng 10:1287–1297 40. Yu S, Zhang B, Xiong J, Yao Z, Wu D, Liu J, Xu S, Tang J (2021) Pyrolysis kinetic study of cathode material derived from spent lithium ion batteries (LIBs): Comparison of different models. J Air Waste Manage Assoc 71(7):844–850 41. Shu-guang Z, Wen-zhi H, Guang-ming L, Xu Z, Xiao-jun Z, Ju-wen H (2012) Recovery of Co and Li from spent lithium-ion batteries by combination method of acid leaching and chemical precipitation. Trans Nonferrous Met Soc China 22:2274–2281 42. Porvali A, Aaltonen M, Ojanen S, Velazquez-Martinez O, Eronen E, Liu F, Wilson BP, SernaGuerrero R, Lundström M (2019) Mechanical and hydrometallurgical processes in HCl media for the recycling of valuable metals from Li-ion battery waste. Resour Conserv Recycl 142:257– 266

Methods and Technologies for Recycling Energy Storage Materials …

507

43. Jung Y, Yoo B, Park S, Kim Y, Son S (2021) Study on roasting for selective lithium leaching of cathode active materials from spent lithium-ion batteries. Metals 11:1336 44. Prasetyo E, Muryanta WA, Anggraini AG, Sudibyo S, Amin M, Muttaqii MA (2022) Tannic acid as a novel and green leaching reagent for cobalt and lithium recycling from spent lithium-ion batteries. J Mater Cycles Waste Manage 24:927–938 45. He LP, Sun SY, Mu YY, Song XF, Yu JG (2017) Recovery of lithium, nickel, cobalt, and manganese from spent lithium-ion batteries using L-tartaric acid as a leachant. ACS Sustain Chem Eng 5:714–721 46. Biswal BK, Jadhav UU, Madhaiyan M, Ji L, Yang EH, Cao B (2018) Biological leaching and chemical precipitation methods for recovery of CO and li from spent lithium-ion batteries. ACS Sustain Chem Eng 6:12343–12352 47. Li Z, He L, Zhao ZW, Wang D, Xu W (2019) Recovery of lithium and manganese from scrap LiMn2 O4 by slurry electrolysis. ACS Sustain Chem Eng 7:16738–16746 48. Yang L, Yang L, Xu G, Feng Q, Li Y, Zhao E, Ma J, Fan S, Li X (2019) Separation and recovery of carbon powder in anodes from spent lithium-ion batteries to synthesize grapheme. Sci Rep 9:9823 49. Liu D, Qu X, Zhang B, Zhao J, Xie H, Yin H (2022) Alkaline roasting approach to reclaiming lithium and graphite from spent lithium-ion batteries. ACS Sustainable Chem. Eng. 10:5739– 5747