Handbook of Nanocomposite Supercapacitor Materials IV

Supercapacitors (SCs) are the essential module of uninterruptible power supplies, hybrid electric vehicles, laptops, video cameras, cellphones, wearable devices, etc. SCs are primarily categorized as electrical double-layer capacitors and pseudocapacitors according to their charge storage mechanism. Various nanostructured carbon, transition metal oxides, conducting polymers, MXenes, and metal–organic frameworks based on electroactive materials are extensively studied for practical application. Moreover, electroanalytical techniques such as cyclic voltammetry (CV), constant current charge–discharge (CCCD), and electrochemical impedance spectroscopy (EIS) are used to evaluate the performance parameters like operating potential window, specific/areal/volumetric capacitance, equivalent series resistance, time constant, energy density, and power density of the assembled device/cell. Furthermore, the contribution of different charge storage mechanisms like the capacitive and diffusion-limited processes is estimated via several electrochemical methods such as CV recorded at different scan rates to obtain the relationship between voltammetric current and scan rate, a voltammetric charge and scan rate, and step potential electrochemical spectroscopy. Additionally, the key performance metrics such as mass loading, capacitance, potential window, cycle stability, leakage current, dwelling time, equivalent series resistance, time constant, device configuration and energy, and power densities of SCs need to study carefully for practical application.

A supercapacitor is a type of electrochemical energy storage device that holds charge both electrostatically and electrochemically. High power density, high energy density, long cycle life, and wide operating temperature range properties make supercapacitor different form other energy storage devices. The supercapacitor has four essential components: electrode, electrolyte, current collector, and separator. In which electrode material selection is the most important factor for the charge storage mechanism. Different types of electrode materials like carbon-based electrode material, transition metal oxides, transition metal dichalcogenides, and conducting polymers are used in supercapacitor applications. Electrode material should have high electrical conductivity, high surface area, lightweight, and low cost for high performance. This article will discuss different electrode materials with their electrochemical performances in supercapacitors.

MXenes are two-dimensional (2D) transition metal carbides, nitrides, or carbonitrides that display layered structure, rich surface chemistry, superior hydrophilicity, and intrinsic electronic conductivity. Since the very first report on MXenes (Ti₃C₂T_x) in 2011, the focus on MXenes has increased exponentially due to their favorable properties for a diverse range of applications including energy storage, thanks to their high conductivity, redox activity, and electrochemically active surface. In this chapter, we have targeted the current advances, achievements, and challenges in MXenes research on supercapacitors in a concise manner. In the beginning, an overview of various synthetic approaches for 2D MXenes are presented, and then, their structural aspects and properties are summarized. Moreover, MXenes and their composites-based supercapacitors are discussed highlighting their potential in such energy storage devices. Finally, few challenges and perspectives are provided to encourage the further improvement of MXenes in supercapacitors.

Micro-supercapacitors have high power density, long lifetime, quick charge, and applications in wearable devices and portable electronics. The functioning of micro-supercapacitors is mainly dependent on the charge storage mechanism in electrodes. A laser is a promising tool to pattern supercapacitor electrodes by photothermal, photochemical, etc. The laser provides a fast, efficient, cheap, and low defect fabrication of supercapacitor. The different laser parameters that affect the final device are discussed in the article. The various processes associated with lasers and their effects on materials are elaborated. Different materials exhibit electric double-layer behavior, pseudocapacitance, or hybrid nature. The progress in laser-derived materials in each type of charge storage mechanism and the final direct laser-based fabrication of supercapacitors focusing on recent areas are mentioned in detail.

In the past few decades, energy-storage technology has evolved rapidly as dependence on renewable energy sources have increased due to drastic changes in energy demands. A supercapacitor finds many applications that need high peak power and energy boosts, such as wireless sensor networks, regenerative braking in vehicles, IoT applications, RF transmissions, backup power supply, transport sector, energy harvesting systems, industrial and consumer electronics. Though the lab-scale supercapacitors perform well, there is considerable scope of improvement for commercially scalable supercapacitors. Low-cost, simple-processing, and high-performance material provides a possible solution for large-scale industrial efficient energy storage systems that can bridge the gap between lab-based energy storage technologies and large-scale commercial applications. The performance deteriorates with an increase in the size of devices due to the internal resistances from non-active materials such as binders and additives, and heating issues. To address these challenges, designer electrode structures such as self-standing architectures, mesh-type electrodes, and fractal design can be viable solutions to enhance the performance of large-scale energy storage devices. Industrial byproducts in the form of waste can be recycled and processed to synthesize cost-effective electrode materials. In addition, the fabrication of electrodes by printing techniques and additive nanomanufacturing has gained significant scientific attention as they are cost-effective and economical for the production of energy storage devices. Printing techniques such as inkjet, micro-gravure, and 3D printing possess the merit of easy manufacturing steps to produce scalable supercapacitors.

Supercapacitors are devices that store energy for a large variety of applications. There has been recent interest in sustainable technologies to fabricate energy storage devices. Additive manufacturing methods such as three-dimensional (3D) printing are being developed to manufacture such devices. There have been numerous ongoing developments in the 3D printing of supercapacitors. 3D printing of supercapacitors offers advantages over conventional fabrication methods. In a consistently changing technological landscape, it is critical to take stock of the developments till date and understand how 3D printing could evolve in the future in the supercapacitor technology. This chapter presents an overview of the main 3D printing technologies to make supercapacitors. The chapter describes the methods, their salient features, merits, and limitations, from the perspective of their application in developing supercapacitors. The chapter also delves into the materials used to 3D print supercapacitors, primarily those related to electrodes and electrolytes. Finally, the chapter presents an outlook into the future prospects of 3D printing-based development of supercapacitors.

Atomic layer deposition (ALD), an advanced and modified version of chemical vapor deposition (CVD), has become one of the state-of-the-art technologies for depositing high quality thin films with precise thickness control over a variety of planar as well as complex three-dimensional structures. In contrast to CVD, the thin film growth via ALD involves chemical reactions between the precursor (in gaseous phase) and surface species in a self-limiting fashion, which allows extremely uniform deposition of desired materials on virtually any substrate feature. Although the materials presently being used in energy storage devices are performing close to their theoretical limits in bulk form, the recent developments in nanotechnology allow for extracting novel properties from their nanosized forms. This poses ALD as an ideal technique for designing high-performance supercapacitor (SC) electrode materials possessing fast charge transfer kinetics and improved energy and power delivery with better cycling and rate performances. This chapter presents a summary of the recent advances on the use of ALD to design SCs with desirable structures and the ensuing properties. In addition, the present challenges and potential opportunities for future exploration of ALD to achieve desired electrochemical performance of next generation SCs are also pointed out.

Binder restricts electrode material’s performance by increasing the contact resistance and preventing electrolytes from utilizing the whole surface area of the electrode. A binder-free supercapacitor is a new approach for improving the performance of supercapacitors by growing or depositing the active material on the conducting substrate. It will also increase the flexibility and energy density of the supercapacitor device because dead mass has been removed. Binder-free electrode material can be fabricated by physical, thermal, and electrical methods. This article discusses different fabrication methods and performances of binder-free electrodes for supercapacitor applications.

The demand for energy storage devices is growing daily in stationaries and mobile applications. Commercial supercapacitors require a high (at least 30%) active electrode material mass of the whole device to fulfill particular applications’ energy and power density demands. Therefore, high mass loading supercapacitors have greatly interested in researching high-specific capacitance electrodes for the commercial application of high-energy storage devices. High mass loading in supercapacitor fabrication is challenging because of the sluggishness of electrical and ion migration kinetics. The commercial level supercapacitor requires high mass loading greater than 10 mg cm⁻² or film thickness of 150–200 µm. These are scaleable production parameters. On the other hand, the strategies adopted to lower the production cost reduce the supercapacitor’s performance. To overcome the adverse effects, researchers and scientists take many synthesis approaches to increase the pore distribution, the proper pore size for electrolytes, and improve the active surface area of electrode materials. Chemical vapor deposition, layer by layer deposition, aerogel, and hydrogel methods are used to create an advanced porous structure that provides an easy ion diffusion path. Apart from doping heteroatoms, intercalation in a layered structure and surface medication increase the active surface area, which controls the electrochemical performance of high mass loading supercapacitors. But the ion diffusion in electrode materials largely depends on the proper pore size, which quickly provides the path.

Polymer-electrolytes, used in commercial energy devices, need to have small liquid components to achieve the desired electrochemical properties. Besides this, these polymer electrolytes have a low cationic transference number and slow ion movement. To get rid of these drawbacks, polymer-in-salt-electrolytes (PISEs) were hypothesized in the 1990s. In PISEs, ion transport is decoupled from polymer segment movement and it occurs through ion cluster, resulting in much faster ion transport in comparison to SIPEs (salt-in-polymer-electrolytes) and cationic transference number is also supposed to approach 1. Unfortunately, a polymer host which can accommodate a large amount of salt above the threshold value required for continuous ion cluster formation, and retain mechanical properties, is still to be identified. Till now, the approach has been to get a mixture of salts in the molten state and then add a small amount of polymer to get a solid morphology. Even after trying a variety of permutation combinations of salt, polymers, and additives, the targeted conductivity (10^–4 S/cm) along with good mechanical properties is rarely reported. Owing to the state-of-art of electronic device technology which has reached to flexible device stage, the present-day energy devices (and hence the electrolytes) need to be flexible. Recently, a facile protocol, which does not use any sophisticated instruments and/or complicated chemical procedures, for the synthesis of PISEs using starch (a renewable polymer) as host polymer, has been reported. Conductivity up to 0.1 S/cm has been achieved in the flexible (bendable, stretchable, and twistable) morphology which can be easily cut into different shapes and sizes. Electrochemical-Stability-Window (ESW) is also quite good (>2.5 V). These electrolytes are quite stable with respect to ambient change. Presently, a new concept of Water-In-Polymer-Salt-Electrolyte (WIPSE) is being investigated. Because of the water-absorbing nature of starches, starch-based PISEs seem to inherently have this benefit also, and probably it is the reason for the exceptionally high conductivity observed in these materials. To the best of the author’s knowledge such high conducting, flexible, and economical PISE membranes were not reported in literature except for crosslinked-starch polymer host-based membranes.

This chapter deals with understanding the effect of external magnetic field on the performance of supercapacitors fabricated using magnetically responsive materials, i.e. magneto-electric supercapacitors. Further, a simple theoretical model is also provided to explain the experimental data. A new theoretical model is required because the conventional models used to explain the supercapacitive behaviour do not have any terms, which consider the possibility of changing magnetic fields and its impact on electrochemical behaviour.

With the advancement in the technology, application of microelectronic gadget has seen an upsurge. The progress of the microscale devices is significantly dependent on the development of microscale energy storage devices with outstanding charge storage properties. Supercapacitors have long cycle life and higher power density as compared to the rechargeable batteries. These are reasons why it is tempting to integrate the modern electronic gadgets with micro-supercapacitors as the energy storing mode. Despite the tremendous research dedicated in this field, there are still some challenges faced and needs more research to further improve the physical as well as the electrochemical properties of the micro-supercapacitor devices. In this chapter, we have discussed about the various device architecture designs and the state of art of it. Further different device preparation methods have been discussed with outlining their advantages and the disadvantages. This is following by a short and precise discussion about the patterning and micro-supercapacitor systems which have been developed recently. We have also discussed in detail various works reporting the various applications of MSCs in different fields. Lastly, the chapter has concluded on a note of the future direction of research assumed in this field. The architecture design of the micro-supercapacitors (MSCs) and brief description of the reaction mechanism have been provided. This is followed by the device preparation methods. We have also discussed in brief the device patterning and various systems integrating MSCs. Finally, discussion about applications and future developments have been discussed.

Nowadays, the increasing demand for energy storage devices and high-power density compared to batteries makes promising supercapacitor candidates for commercial application. Shape memory properties are seamlessly integrated with the supercapacitor to fulfill the stable energy requirement of flexible devices. Considerable research gained attention to developing shape memory supercapacitors in electrochemical energy devices. Different shape memory materials have been used to assemble the device and study the electrochemical performance, cyclic stability, etc. We have reviewed and explained shape memory materials types, such as shape memory alloy (SMA) and shape memory polymer (SMP). Both types of material have unique intrinsic shape memory properties such as strain recovery (R_r), shape fixity (R_f), and recovery time. Mainly heat-triggered shape memory material is used in the application, and its transition temperature largely depends on the material and material composition. The flexibility of the shape memory device depends on the design, architecture, materials, etc.; wire-shaped and planar devices have been studied extensively. Symmetric and asymmetric shape memory supercapacitors have been reviewed. Apart from this principle behind shape memory properties, the design aspect and electrochemical performance of recent advancements in SMSC have been reported.

The supercapacitor is an energy storage device that has the potential to replace traditional energy storage technologies such as batteries. Fast charge and discharge cycle, high power density, high operating temperature range, long cycle lifetime, and economic properties make supercapacitors unique. The supercapacitor has been widely used in different applications like hybrid vehicles, renewable energy storage, medical equipment, and electronic devices. With the advancement of current wearable electronic gadgets, a flexible and self-healing supercapacitor is required. Flexible supercapacitors can often endure some bending and stretching stains, so mechanical damage or micro-cracks can degrade the electrochemical performance of supercapacitors. Micro-crack diagnosis and self-healing prevent sudden failure and economic losses. Intrinsic and extrinsic self-healing mechanisms are used during repairing. Since self-healing supercapacitors are developing rapidly, but still, these are in infancy because of many limitations like high cost and lower performance. Despite the constraints of self-healing supercapacitors, the research potential for self-healing supercapacitors is unlimited. This article will discuss various fabrication methods of self-healing electrode material and self-healing electrolyte materials with their electrochemical performances in supercapacitor.

For centuries, optics have been used in various applications like mirrors, lenses, microscopes, and telescopes. The technology has been developed to maneuver photons, which have the potential to replace electronic devices with better speed, lower cost, and more security. The precision and characterization equipment based on electrons and photons required for the fabrication of sophisticated devices have applications in the forensic, medical, scientific, and education fields. The fabrication of optical chips and the processes involved with commercial status is discussed. The status of optical transmission systems and infrastructure being developed based on fibers and wireless depending on losses with applications is stated in the article. The manufacturing processes and hardware fabrication requires simulation, automation, and computational effort to save cost and time. All the devices require energy consumption, which can be sustainably fulfilled through renewable energy, energy storage systems, and good governance. The miniaturized devices require integrated small-size energy storage capabilities like laser fabricated on-chip micro-supercapacitors. The article elaborates on all these aspects of optics required for universal access to energy for humankind.

Uses of supercapacitors are increasing in the electronics field due to their properties and sustainability. Controlling this E-Waste generation by supercapacitors should be considered seriously to overcome the upcoming problem of E-waste management. Recycling supercapacitors is cost-effective and beneficial for the environment because it keeps dangerous elements out after the device has completely degraded. Due to its high capacitance and high energy density, ruthenium oxide (RuO₂) is a frequently used electrode material in supercapacitor devices and a good choice in this sector. This chapter discusses the recycling of RuO₂ electrode material-based supercapacitors. RuO₂ was extracted by the chemical extraction method. Sonication, chemical separation, and thermal decomposition methods were used to extract RuO₂. Used RuO₂ was removed from the device by sonication and then oxidized in RuO₄ by oxidizing agent ceric ammonium nitrate. RuO₄ is in a gas form and absorbed by paraffin oil and again reduced in RuO₂. So crystalline RuO₂ was extracted from paraffin oil via filtration. The extraction of crystalline RuO₂ is confirmed by XRD, showing clear and sharp peaks. Another electrochemical performance of the supercapacitor based on recycled RuO₂ material was investigated.