Handbook of Nanocomposite Supercapacitor Materials III

Supercapacitors are energy storage devices, which display characteristics intermediate between capacitors and batteries. Continuous research and improvements have led to the development of supercapacitors and its hybrid systems and supercapacitors, which can replace traditional batteries. The comparison among different energy storage devices has been introduced in the present chapter. The timeline for the development of supercapacitors is also mentioned along with the introduction of different charge storage mechanisms in supercapacitors. Supercapacitors mainly consist of four components electrodes, electrolyte, separator, and current collector. The different types of supercapacitors have been introduced including the novel quantum supercapacitor. For hybrid energy management configurations, supercapacitors and batteries are used together to mask their limitations of the low energy density and power density, respectively. For miniaturized devices, on-chip supercapacitors and on-chip energy management systems are also discussed. The principles of the most widely used electrochemical characterization techniques and parameters have been incorporated in the chapter.

Supercapacitors are electrochemical energy storage devices that can be used to store a large amount of energy. It delivers excellent electrochemical performances such as high capacitance, high power density, and long cyclic stability at low cost. In contrast with other energy storage devices, its charge storage mechanism is simple, which makes its charging and discharging process highly reversible. Based on the charge storage mechanism, its electrode material can be categorized as EDLC and pseudocapacitor. EDLC capacitor stores charge electrostatically whereas, reversible redox reaction occurs in pseudocapacitance. Here, the charge is stored via the Faradaic process. The further improvement in the performance is done by the formation of composite electrode material, the introduction of nanostructure electrode, assembling a hybrid capacitor by introducing battery electrode material, and assembly of an asymmetric supercapacitor. Various combinations of electrode and electrolyte material in different types of configuration provide a synergistic effect of both types of charge storage mechanism and wide operating potential range. The main aim is to obtain a high energy density device without compromising other parameters such as power density, rate capability, and cyclic stability. This chapter extensively deals the various materials used in supercapacitors, types of charge storage mechanisms, types of supercapacitor assembly i.e., symmetric supercapacitors, asymmetric supercapacitors, battery-supercapacitor hybrid devices, etc., and their performance to the type of electrode material.

Nowadays, flexible solid-state supercapacitors (FSSCs) are the most emerging energy storage devices in modern miniatured technologies. With increasing the use of micro- and flexible electronic devices such as wearable electronic suits, microsensors, and biomedical equipment, the demand of FSSCs is increasing exponentially. These electronic devices focused on the integration of many components in single compact system that must be flexible in nature, lightweight, smaller in dimension, unbreakable and should be available at competitive price. Although the FSSCs device fabrication is in the early stage of development, there is a significant effort to investigate the new strategies to fulfill the demand of advanced energy technology. Therefore, exploring the novel approaches always remains an important academic and industrial challenge to the researchers. The chapter mainly focuses on the advancement of FSSCs devices with its all components such as current collector, electrode materials, and electrolytes. The chapter also discusses the strategies of fabrication techniques, types of FSSCs, design, evaluation of performance of FSSCs device step by step. Hence, the chapter gives an idea about the recent progress and challenges of the FSSCs devices.

CPs are known for their astonishing electrical and electrochemical properties. Characteristic features are tunable conductivity, structural flexibility, mild synthesis and processing conditions; chemical and structural diversity makes them excellent candidate for different fields of interest. Since the first introduction of CPs, it still remains relevant to discuss and grow rapidly in different fields of applications with various modern advancements. This chapter aims to revisit the journey and recent advancements of CPs in the field of energy storage systems like supercapacitors. Supercapacitors are one of the popular modern energy storage systems as they have many advantages like high power density, long cycle life, moderate to high capacitance, tunable rate capability, simple construction and low processing cost. Despite many advantages, supercapacitor is still facing many major challenges such as limited potential window, low energy density and sluggish rate kinetics. CPs have been considered as one of the excellent candidates for supercapacitor as they show miscellaneous redox nature, amazing electrical conductivity, good flexibility and many others. Therefore, substantial discussion is required to discuss the supercapacitors and its advantages and disadvantages, recent advancements, future challenges and new possibilities. This review focuses on the synthesis, processing and chemical modifications of various CPs with various interesting properties and their electrodes used for the advancements of supercapacitors which is the need of the hour.

Supercapacitors and conventional capacitors follow a similar charge storage mechanism. However, they differ from each other, as supercapacitors store a large amount of charge due to the extremely high surface area of the conducting electrodes. The charge storage mechanism of supercapacitors is based on either formation of an electric double layer, where adsorption and desorption of ions take place, or the Faradaic process, where reversible redox reaction occurs. The efficiency of a supercapacitor depends upon its components like electrodes, electrolyte, separator and current collectors. Among all the components, the electrode plays a major role to store a large amount of charge at its surface. So, characteristics of the electrode such as porosity, surface morphology, surface area, electrical conductivity are taken into account for selecting suitable electrode material for supercapacitor. Activated carbon, CNT, graphene, carbon aerogel, metal compounds, conducting polymers, and their composites are among various materials, which have been commonly used as electrodes and discussed in detail to select the best material with the concept of various material indices using Ashby’s chart in this review.

Supercapacitors have gained crucial advantages among various energy storage devices such as batteries, capacitors, and fuel cells. The efficiency of supercapacitors depends on various aspects that depend on its components. These components include electrodes, electrolyte, current collectors, and separator. Electrode store charges, electrolyte provide necessary ions, current collector transfers the charge from the electrode to external circuit, and separator acts as a membrane, which prevents the device from short circuit. The choice of separator material plays a vital role in the design of a supercapacitor. Its main function is to separate cathode and anode electrode material in supercapacitors to prevent short circuit. It is mainly present in the form of a porous membrane in order to provide easy ion transfer. The common material used as separator includes glass fiber, cellulose, ceramic fibers, or polymeric film materials. This chapter mainly describes functions served and characteristics required for separators and its materials, respectively, which are chosen according to those functions. Finally, the selection of separator material is justified with the help of various material indices using Ashby’s chart.

Non-conventional energy storage devices such as batteries, supercapacitors, and fuel cells are finding more applications due to increasing environmental concerns for energy distribution and storage. Supercapacitors charge very fast and have higher energy density than a conventional capacitor and higher power density than batteries. A lot of research is being done to improve the efficiency and performance of supercapacitors by making the right choice for electrodes, electrolytes, separators, and current collectors. Among all the components, electrolytes serve the purpose of balancing charge in supercapacitor and provide necessary ions to form an electrical connection between electrodes. The electrolyte materials used in supercapacitor can be classified as organic, aqueous, ionic liquids, solid-state, and redox-active electrolytes and are chosen according to their properties, ultimate applications, and physical state of the supercapacitor. This chapter explains the functions of electrolytes, classification of electrolytes, i.e., aqueous electrolytes, organic electrolytes, ionic electrolytes, etc., characteristics required for electrolytes, i.e., conductivity, viscosity, ionic concentration, electrochemical stability, thermal stability, dissociation, toxicity, volatility and flammability, cost, etc., performance of various electrolytes, performance metrics and their relationships, selection of electrolyte material in detail with the support of various material indices using Ashby’s chart.

The supercapacitor is a step-up device in the field of energy storage and has a lot of research and development scope in terms of design, its parts fabrication, and energy storage mechanism. The main function of the current collector is to collect and conduct electric current from electrodes to power sources. It also provides mechanical support to electrodes. To meet the required properties of the current collector materials should have minimum contact resistance, high electric conductivity, and good bonding capacity with electrodes. The bonding capacity can be increased by modifying the surface of the current collector, which is mainly carried out using industrial picoseconds laser device. Different types of materials are being used for the current collector, where the selection of materials depends upon the cost of materials and its suitability toward particular applications. Most commonly used conventional metals like copper (Cu), aluminum (Al), nickel (Ni), etc. are being replaced by advanced materials such as nanostructured or composite materials. In addition to this, the demand for flexible electronics is growing rapidly nowadays, and these devices require a material with enhanced properties. This review discusses various components of supercapacitors, i.e., electrode materials, electrolyte materials, separators, binders and current collectors, functions of current collectors, specifications of current collectors, various materials used as current collectors, various parameters that affect the performance of current collectors, i.e., thickness, temperature, electrolytes, etc., dimensions of current collectors, screening of current collectors using constraints, various governing equations used for electrical conductivity, thermal conductivity, tensile strength, mass, bending strength, etc., and various material indexes used to select the best materials using Ashby charts.

Intelligent energy storage systems utilize information and communication technology with energy storage devices. Energy management systems help in energy demand management and the effective use of energy storage devices. Supercapacitor management systems have been developed for supercapacitor usage during demand within safe operating limits. Supercapacitors and batteries are used together with the help of hybrid energy management configurations. Rule-based, optimization-based, and artificial intelligence-based energy management strategies are deployed for hybrid energy storage systems. The main parameters are adaptability, reliability, and robustness. Computational complexity is a driving parameter for using these techniques in online or offline mode.

The global supercapacitor market is expected to grow at a rapid rate in the coming years owing to the rising demand for supercapacitors in various applications. These supercapacitors are available in varying sizes, capacitances, voltage ranges, etc., and are sometimes tailor-made for certain applications. The markets in the Asia—Pacific region—are expected to grow at the highest rates with China being at the forefront. At present it is currently dominated by a few major players such as Murata Technology, Maxwell Technologies, Eaton Corporation, Nippon Chemi-Con, Nesscap among others. These major players are focussing immensely on research and development of supercapacitors to meet further demands as well as maintain their competitive advantage over the others. The current chapter deals with the trends in the supercapacitor market and also sheds light on the properties of supercapacitors cells and modules manufactured by key market players.

Supercapacitors exhibit large power density, fast charge and discharge capability, and long cycle stability. These characteristics find applications in transportation, energy and utilities, aerospace, military, electronics, industrial, and medical fields. Supercapacitors are currently used as one of the most efficient energy storage systems replacing batteries in many applications. In the transportation and aerospace sector, supercapacitor-based hybrid energy storage systems are widely utilized for improved efficiency. The use of supercapacitors in various sectors such as automotive, energy, medicine, electronics, aerospace, and defense is presented with consideration of the various products offered by manufacturers. The application of supercapacitor in portable and wearable electronics and medical sectors is discussed in detail. In this chapter, most of the possible application areas of supercapacitors along with manufacturers are discussed in detail.