Preface

The tremendous demand for energy for miniaturized portable and wearable electronic devices has inspired intense research on lightweight, flexible energy storage devices for commercial applications such as smartwatches, mobile phones, flexible displays, electronic skin and implantable medical devices. The speedy progress in flexible electronics has sparked wide-ranging endeavors in exploring coordinating power sources as flexible supercapacitor devices. Flexible supercapacitors are flexible, wearable devices that deliver high-power density, high specific capacitance, fast charge/discharge processes, long cycle life, low cost, and environmental friendliness. They hold enormous potential to meet the rapidly expanding market for portable and wearable electronics. Designing flexible supercapacitors requires essential architectures such as electrodes, electrolytes, and substrate materials that become robust, flexible, and durable under mechanical deformations without sacrificing the electrochemical performance. These flexible supercapacitors are promising energy technologies that can supplement or even substitute batteries in portable and flexible electronics; however, research and development (R&D) studies need to be conducted for their large-scale commercialization. Therefore, awareness and knowledge of flexible supercapacitors is crucial for advanced energy research.

This book presents a comprehensive overview of flexible supercapacitors using engineering nanoarchitectures mediated by functional nanomaterials and polymers as electrodes, electrolytes, separators, etc., for advanced energy applications. Various aspects of flexible supercapacitors, including capacitor electrochemistry, evaluating parameters, operating conditions, characterization techniques, different types of electrodes, electrolytes, and flexible substrates are covered. Since it is probably the first book of its type to systematically describe the recent developments and progress in flexible supercapacitor technology, it will help readers understand fundamental issues and solve problems. This book is the result of the commitment of top researchers with various backgrounds and expertise in the flexible power sources field. Those working in science, research, industry, or academia will benefit from the information archived herein relating to the fields of flexible power sources, solid-state electrochemistry, advanced energy storage material science, energy, electronics, advanced materials, and wearable science. It will be a very helpful reference source for generating innovative ideas in the field of energy storage material for wearable/flexible industry applications and also useful in resolving current industry issues. A summary of the information included in the 21 chapters is given below.

Chapter 1 discusses the types of electrode materials and the role they play in the high performance of flexible supercapacitors. Device preparation is described as well as the integration of flexible supercapacitors in various applications.

Chapter 2 highlights flexible fiber-shaped electrodes for flexible supercapacitors. Supercapacitors have an incredible impact on electrochemical devices in energy storage systems. To meet the rapid consumer demand for wearable and portable devices a new class of energy devices employ flexible fibrous electrodes/supercapacitors. These fiber-shaped flexible electrodes have garnered great attention for use in miniaturized microscale devices and the modern textile industry.

Chapter 3 discusses recent developments in graphene-based flexible supercapacitors, the structural morphology of flexible graphene-based electrodes and methods used to fabricate them, and the electrochemical performance of the devices.

Chapter 4 mainly discusses the preparation of polymer-based electrode materials. Also highlighted are the various prominent characterization techniques to elucidate the intercorrelation between physicochemical and performance properties of polymer-based electrode materials. The new reinforced polymer-based electrode materials for flexible supercapacitor applications are also discussed.

Chapter 5 thoroughly reviews the energy storage system and types of capacitor modeling. The structure, types of flexible supercapacitors and industrial applications are introduced.

Chapter 6 discusses the types of electrolytes for flexible supercapacitors and their salient features. Various electrolytes such as polyethylene glycol, polyvinylidene fluoride, ionic liquid and redox-active materials-based electrolytes are discussed along with their effect on the performance of flexible supercapacitors.

Chapter 7 discusses the preparation and properties of carbon-derived composite materials such as CNT-conducting polymer, CNT-metal oxide, activated carbon-conducting polymer, and activated carbon-metal oxide. The main focus of this chapter is to provide an overview of the latest progress in the development of flexible supercapacitors beyond graphene.

Chapter 8 highlights the various synthesis processes for making biomass-derived electrode materials, their recent developments and the associated challenges for the near future. After a brief general introduction, the chapter moves on to discuss various electrode materials used for flexible supercapacitors; biomass-derived carbon materials and their different activation processes like physical, chemical and other activations; and carbonization processes using the hydrothermal method, pyrolysis method, etc. The possible incorporation of biomass-based electrodes in flexible supercapacitors and the challenges for using biomass-derived materials in the near future are also discussed in detail.

Chapter 9 portrays the importance and applicability of conducting polymer electrolytes, especially in flexible supercapacitors. The components of supercapacitors and their configurations are discussed in detail along with the role of conducting polymer-based electrolytes and their significance in the performance of flexible supercapacitors. The essential enhancing parameters of such electrolytes, including their consequences and electrochemical activity, are also elaborated.

Chapter 10 discusses the various inorganic electrode materials used in flexible supercapacitors. These flexible inorganic-based electrodes have great potential in the field of stretchable, lightweight and intrinsic fast charging and discharging performance.

Chapter 11 focuses on different new generation materials used for flexible supercapacitor electrodes. Also, in order to predict future trends, the direction towards developing new materials exhibiting superior electrochemical performance and their feasibility in practical applications are discussed.

Chapter 12 briefly describes flexible supercapacitors and their flexible components with a concise outline of innovative cell designs. Additionally, there is an overview of the principle behind the energy-storage mechanism and the anode and cathode materials used for asymmetric supercapacitors.

Chapter 13 provides detailed insights into the gradual development and latest accomplishments achieved with aqueous electrolyte-based flexible supercapacitors. Advantages of low production costs, eco-friendliness, non-flammability, and many other attractive factors have motivated scientists to design these smart devices to meet the high rising energy demands of modern society.

Chapter 14 presents systematic evaluations of different kinds of micro-supercapacitor configurations, possible strategies of fabrication, and state-of-the-art electrode materials. Discussions on designing asymmetric micro-supercapacitors and the influence of electrolytes on enhancing charge-storage properties are also provided. Finally, the challenges of current technologies and possible solutions are highlighted.

Chapter 15 discusses the categories of supercapacitors and their mode of action. Different types of nanomaterials, including metallic, non-metallic and graphene-based hybrid, are discussed in detail for their self-healable properties to modify the electrodes in supercapacitors. The major focus is given to those nanomaterials that increase the self-healing properties of supercapacitors with enhanced capacitance.

Chapter 16 discusses the recent advancements for the fabrication of flexible and stretchable electrode supercapacitors using metal oxides, 2D materials, carbon, conductive polymers, and various hybrid nanocomposites. Moreover, possible applications of flexible/stretchable supercapacitors using these electrode materials, along with upcoming opportunities and challenges in this emerging field, are also discussed.

Chapter 17 discusses the classification of flexible supercapacitors and various superconducting materials. Additionally, different fabrication methods, namely, electrochemical deposition, chemical bath deposition (CBD), inkjet printing spray deposition, sol-gel technique, and direct writing method are discussed in detail.

Chapter 18 deals with the fundamental aspects of flexible supercapacitors with naturally inspired electrodes for energy storage systems. The mechanisms and principle behind energy storage in supercapacitors along with its essential parameters are presented. The use of common and naturally occurring materials and their electrochemical behavior is also discussed.

Chapter 19 focuses on advances in the field of high-performance ionic liquid electrolytes for flexible supercapacitors. After a brief discussion of the fundamentals, developments in the field of ionic liquids are presented. Design perspectives like electrolyte-electrode hybridization,...