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About this book

This book delivers a comprehensive overview of the characteristics of several types of materials that are widely used in the current era of supercapacitors; namely, architectured carbon materials, transition metal oxides and conducting polymers. It provides readers with a complete introduction to the fundamentals of supercapacitors, including the development of new electrolytes and electrodes, while highlighting the advantages, challenges, applications and future of these materials.

This book is part of the Handbook of Nanocomposite Supercapacitor Materials. Supercapacitors have emerged as promising devices for electrochemical energy storage, playing an important role in energy harvesting for meeting the current demands of increasing global energy consumption. The handbook covers the materials science and engineering of nanocomposite supercapacitors, ranging from their general characteristics and performance to materials selection, design and construction. Covering both fundamentals and recent developments, this handbook serves a readership encompassing students, professionals and researchers throughout academia and industry, particularly in the fields of materials chemistry, electrochemistry, and energy storage and conversion. It is ideal as a reference work and primary resource for any introductory senior-level undergraduate or beginning graduate course covering supercapacitors.

Table of Contents

Frontmatter

Chapter 1. Characteristics of Capacitor: Fundamental Aspects

Abstract
The capacitor is a passive electrical device, used to collect electrical energy by generating a potential difference. It is generally consisting of combination of two conductors placed next to each other separated by dielectric medium. The performance of a capacitor expressed in terms of the capacitance (C) depends on the dimension/geometry of the plate/electrode and the dielectric constant of the material, where the dielectric can be defined by insulating medium having permittivity, with no AC power losses or DC leakage. The capacitor shows different response to AC and DC sources. These are mainly used to supply power in several electronic and electrical systems. Therefore, this chapter provides the fundamental aspects of the capacitors and their basic properties. It emphasizes on the parallel plate model, the basic terminologies associated with the capacitors along with the equivalent circuits of the capacitor and its response to the externally applied AC and DC sources. It also describes about different types of capacitors that are being fabricated using different materials and different construction techniques. These different types of capacitors provide some unique properties.
Jitendra Tahalyani, M. Jaleel Akhtar, Jayesh Cherusseri, Kamal K. Kar

Chapter 2. Capacitor to Supercapacitor

Abstract
Supercapacitors bridge the gap between conventional electrolytic capacitors and batteries. These are capacitors with electrochemical charge storage. The basic equations used to describe the capacitors are same in the case of supercapacitors but their mechanism of energy storage is different. Various electrode-active materials such as activated carbon, mesoporous carbon, carbon nanotubes, graphene, etc., are invariably used in the supercapacitors with high performance. Both aqueous and organic electrolytes are used in supercapacitors but high voltage can only be delivered by the supercapacitors manufactured with organic electrolytes. However, the cycle life of aqueous electrolyte-based supercapacitors is high when compared with the organic ones. The present and future flexible and wearable technologies necessitate the development of flexible solid-state capacitors to supply them power. Supercapacitors are found applications in a variety of fields such as electronics industry, hybrid electric vehicles, and power supplies. The two major demerits of the present supercapacitors are low energy density and high cost. Hence, novel low-cost supercapacitors should be developed with high energy density to fulfill the needs of society. The present chapter discusses the Faradaic and non-Faradaic processes, types of supercapacitors, structure—i.e., electrode, electrolyte, electrolyte membrane, and current collector—key parameters for estimation of performance, electrochemical characterizations, etc.
Soma Banerjee, Prerna Sinha, Kapil Dev Verma, Tanvi Pal, Bibekananda De, Jayesh Cherusseri, P. K. Manna, Kamal K. Kar

Chapter 3. Characteristics of Transition Metal Oxides

Abstract
Transition metal oxides (TMOs) are the oxides of d-block elements in the periodic table with partially filled d-sub-shell. They have attracted the research community with their unique and fabulous properties such as magnetic, optical and electrochemical. The novel properties have envisaged them in many practical applications such as energy storage (e.g., supercapacitors, lithium-ion batteries, etc.), nonvolatile memory devices, sensors, solar cells and infrared detectors. The ability to modulate the physical as well as chemical properties helps in designing novel devices with tunable properties and hence enhances the industrial importances. This chapter mainly focusses on discussing the characteristics of TMOs including physical, chemical, surface, electronic, magnetic, optical, thermoelectric, electrochemical, etc. Synthesis techniques for TMOs are discussed in detail. The environmental impact of these materials along with their potential applications is also included.
Alekha Tyagi, Soma Banerjee, Jayesh Cherusseri, Kamal K. Kar

Chapter 4. Characteristics of Activated Carbon

Abstract
The wise use of natural resources is the necessity of today’s growing demand for energy for human civilization. The utilization of sustainable natural resources such as biomass and biomass waste has been noticed in the recent trend for the societal benefit and need. In this context, activated carbon has been used for decades in applications such as environmental remediation, energy storage and resource recovery. Biomass-derived activated carbon has attracted great attention because of natural porosity, hierarchical structure and inherent heteroatom doping characteristics. In this review, different synthesis mechanisms to derive biochar from a variety of biomass along with property dependence of activating agents have been discussed. Furthermore, morphology, physiochemical property, structural and elemental characterization have also been discussed in detail. Various applications of activated carbon derived from natural and waste biomass have been included to have a broad overview of this fascinating form of carbon.
Prerna Sinha, Soma Banerjee, Kamal K. Kar

Chapter 5. Characteristics of Graphene/Reduced Graphene Oxide

Abstract
Graphene, the thinnest two-dimensional material, is extensively explored by interdisciplinary fields of research communities due to the excellent electronic, mechanical, optical and thermal properties. This chapter provides a comprehensive review of the structure, synthesis, properties and applications of graphene/reduced graphene oxide. Graphene, the one atomic thick layer of sp2 hybridized carbon atoms arranged in honeycomb lattice, is the building block of all carbon materials such as graphite, carbon nanotubes and fullerenes. It can be synthesized by different techniques such as micromechanical cleavage, exfoliation and chemical vapour deposition. It has also been commonly synthesized from the reduction in graphene oxide. The reduction of graphene oxide again is also carried out either by using hazardous chemicals or by green approach. This chapter also discusses the properties of graphene/reduced graphene oxide, which makes them a potential material in diverse applications. The potential fields of applications of graphene/reduced graphene oxide include medicine, electronics, energy devices, sensors, environmental and many more.
Pankaj Chamoli, Soma Banerjee, K. K. Raina, Kamal K. Kar

Chapter 6. Characteristics of Carbon Nanotubes

Abstract
Carbon nanotubes (CNTs) are the materials of modern age having diverse applications in every sector. This article discusses the structure, synthesis, properties, purification, and application aspects of CNTs. CNTs can be classified based on tube structure and shapes. This chapter elaborates single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), and double-walled nanotubes (DWNTs) in brief. In addition, researches are going on worldwide to generate CNTs of variable shapes such as coiled, waved, bent, beaded, junction CNTs. CNTs can be synthesized by chemical and physical routes. The most common method of CNT production is chemical vapour deposition (CVD) technique that can produce pure CNTs in large quantities. This article also opens up the present aspects of growth mechanism of CNTs. The unique combination of electrical, thermal, and mechanical properties of CNTs makes them a potential performer in the number of fields such as supercapacitors, fuel cells, energy devices, high strength composites, biomedical, chemical. However, the application of CNTs is still somehow limited and yet to reach the desired plateau due to the purification, large-scale production, and toxicity issues.
Soma Banerjee, Kamal K. Kar

Chapter 7. Characteristics of Carbon Nanofibers

Abstract
Carbon nanofibers (CNFs) are fibrous nanostructures of sp2-hybridized carbon having partial structural similarity with carbon nanotubes (CNTs). This chapter reviews the structure, synthesis techniques, properties and applications of CNFs. CNFs can be produced either by vapor phase growth using chemical vapor deposition or by carbonization of pre-synthesized polymer nanofibers. Both techniques offer an easy synthesis of CNFs as compared to that of CNTs. The synthesis techniques affect their structure as well as properties significantly. CNFs, owing to their graphitic structure, offer unique properties such as high mechanical strength, corrosion resistance, thermal and electronic conductivities. In view of their unique properties, CNFs have drawn significant attention toward their use in advanced applications such as electrochemical power generation and storage, high-strength composites, sensors, adsorbents. Promising advancements project CNFs as the futuristic materials for lithium-ion batteries, supercapacitors, fuel cells and solar cells.
Raghunandan Sharma, Kamal K. Kar

Chapter 8. Characteristics of Conducting Polymers

Abstract
Conducting polymers (CPs) have gained recent attention from the research community due to the extraordinary combination of properties including tunable electrical conductivity, easy route of preparation, light in weight, easy to process, etc. These exclusive properties enable the use of CPs in many intriguing applications including modern electrochemical devices. The commonly adopted synthesis strategies utilized for the synthesis of CPs include chemical and electrochemical polymerization routes. The electrical conductivity of CPs can be tuned easily by altering the types of doping and concentration of doping. This chapter also discusses the efficacy and benefits of dopants to improve the conduction properties of common CPs. The new application areas of CPs comprise supercapacitors, sensors, solar cells, corrosion inhibitors, light-emitting diodes, EMI shielding, electrochromic devices, transistors, and many more. This review provides concise yet comprehensive introductory information on the CPs including the types of common CPS, their mechanism of conduction, attractive properties, and diverse application areas to have a broad overview of this field of research.
Tanvi Pal, Soma Banerjee, P. K. Manna, Kamal K. Kar

Chapter 9. Characteristics of Electrode Materials for Supercapacitors

Abstract
Device performance is based on the individual properties of the materials and performance of the components in the working environments. For example, the fabrication of high-performance supercapacitors and the electrode material should have a high specific surface area and high electrical conductivity along electrical and thermal stability. For different charge storage mechanisms in supercapacitors like electrical double-layer capacitors, pseudocapacitors and hybrid capacitors, and different types of electrode materials are proposed. Electrode materials of a supercapacitor decide the storage of charge in the device and thereby the capacitance of the final device. The effective surface area including electrical conductivity remains the parameter of importance to produce high capacitance. Carbon materials are proposed as the electrode material by storage of the charge at the surface of the material via electrical double-layer capacitance. High surface area, appropriate pore size, pore size distribution and the presence of functional groups complement the capacitance of the device. Some commonly used carbon-based materials of interest are graphite, graphene, carbon nanotube, activated carbon, etc. Other materials of importance remain metal oxides, conducting polymers, metal–organic frameworks, MXenes, black phosphorus, metal nitrides, etc. This chapter provides a short yet comprehensive overview of the characteristics of suitable electrode material for supercapacitor devices. Activated carbon, carbon nanotubes, graphene, polyaniline (PANI), polypyrrole (PPY) and polythiophene (PTH) are examples of some of the suitable electrode materials.
Kapil Dev Verma, Prerna Sinha, Soma Banerjee, Kamal K. Kar

Chapter 10. Characteristics of Electrolytes

Abstract
Electrolytes play a major role in determining the energy-storage capacity of the electrochemical supercapacitor devices. It consists of solvent, dissociated positive and negative ions, or pure salt, i.e., a solvent-free ionic liquid. The properties of an electrolyte depend on a number of parameters such as size of the ion and concentration, conductivity, interaction between electrolyte, electrode materials, etc. In this chapter, the types of electrolytes used in electrochemical supercapacitors have been discussed in detail. Based on chemical nature, the electrolytes can be classified in various groups, i.e., aqueous, organic, ionic liquid, solid state, redox, etc. This chapter also points out the effect of these electrolytes on the cell voltage, specific capacitance, and other important parameters for electrochemical double layer, asymmetric, and hybrid supercapacitor devices.
Kapil Dev Verma, Soma Banerjee, Kamal K. Kar

Chapter 11. Characteristics of Separator Materials for Supercapacitors

Abstract
Separator in a supercapacitor is used as a sandwich between two electrodes. The essential functions of separator materials remain the prevention of the device from short circuit, storage of electrolyte into its pores, and passage of ions during charging and discharging processes. Material selection for the separator also plays an important role in deciding the final performance of the supercapacitor devices. Ionic conductivity of the separator affects the power and energy density. For safety purpose, thermal stability of the separator is very important. For the flexible electronic devices, bendable separators of high mechanical strength are needed. Separator should have optimum porosity and high electrolyte uptake such that it can provide adequate electrolyte ions to the electrode. The example of the most commonly used separator is polyolefin materials. This chapter deals with the importance of the separator materials, the governing equations, and essential parameters.
Kapil Dev Verma, Prerna Sinha, Soma Banerjee, Kamal K. Kar, Manas K. Ghorai

Chapter 12. Characteristics of Current Collector Materials for Supercapacitors

Abstract
Current collector has a major role in electrochemical performance and cycle stability of supercapacitor. It collects electrons and supports the electrode material. Conductivity and contact resistance with the electrode material of a current collector have a direct influence on the power density and capacitance of a supercapacitor. Current collector should have high electrical conductivity, high mechanical strength/modulus, lightweight, high thermal stability, high electrochemical stability and low cost. Metal foam and metal foil type current collector are used in general, in which metal foam provides the highest performance. For flexible supercapacitor, carbon fiber is generally used as the current collector.
Kapil Dev Verma, Prerna Sinha, Soma Banerjee, Kamal K. Kar

Chapter 13. Applications of Supercapacitors

Abstract
Supercapacitors are the most promising energy storage devices that bridge the gap between capacitors and batteries. They can reach energy density close to the batteries and power density to the conventional capacitors. Several researches have been carried out in the field of supercapacitors for the development of promising electrode and electrolyte materials as well as device fabrications to breakthrough in energy storage systems with diverse applications in electronics. They have a broad range of applications as they can deliver a huge power within a very short time. This chapter provides the detailed applications of supercapacitors in several sectors like consumer and portable electronics, transportation and vehicles, power backup, biomedical, military, aerospace, etc.
Soma Banerjee, Bibekananda De, Prerna Sinha, Jayesh Cherusseri, Kamal K. Kar

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