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In this paper, the design of high energy density dielectric capacitors for energy storage in vehicle, industrial, and electric utility applications have been considered in detail. The performance of these devices depends primarily on the dielectric constant and breakdown strength characteristics of the dielectric material used. A review of the literature on composite polymer materials to assess their present dielectric constants and the various approaches being pursued to increase energy density found that there are many papers in which materials having dielectric constants of 20–50 were reported, but only a few showing materials with very high dielectric constants of 500 and greater. The very high dielectric constants were usually achieved with nanoscale metallic or carbon particles embedded in a host polymer and the maximum dielectric constant occurred near the percolation threshold particle loading. In this study, an analytical method to calculate the dielectric constant of composite dielectric polymers with various types of nanoparticles embedded is presented. The method was applied using an Excel spreadsheet to calculate the characteristics of spiral wound battery cells using various composite polymers with embedded particles. The calculated energy densities were strong functions of the size of the particles and thickness of the dielectric layer in the cell. For a 1000 V cell, an energy density of 100–200 Wh/kg was calculated for 3–5 nm particles and 3–5 µ thick dielectric layers. The results of this study indicate that dielectric materials with an effective dielectric constant of 500–1000 are needed to develop dielectric capacitor cells with battery-like energy density. The breakdown strength would be 300–400 V/µ in a reverse sandwich multilayer dielectric arrangement. The leakage current of the cell would be determined from appropriate DC testing. These high energy density dielectric capacitors are very different from electrochemical capacitors that utilize conducting polymers and liquid electrolytes and are constructed much like batteries. The dielectric capacitors have a very high cell voltage and are constructed like conventional ceramic capacitors.

Although recognized as an important component of all energy storage and conversion technologies, electrochemical supercapacitators (ES) still face development challenges in order to reach their full potential. A thorough examination of development in the technology during the past decade, Electrochemical Supercapacitors for Energy Storage and Delivery: Fundamentals and Applications provides a comprehensive introduction to the ES from technical and practical aspects and crystallization of the technology, detailing the basics of ES as well as its components and characterization techniques. The book illuminates the practical aspects of understanding and applying the technology within the industry and provides sufficient technical detail of newer materials being developed by experts in the field which may surface in the future. The book discusses the technical challenges and the practical limitations and their associated parameters in ES technology. It also covers the structure and options for device packaging and materials choices such as electrode materials, electrolyte, current collector, and sealants based on comparison of available data. Supplying an in depth understanding of the components, design, and characterization of electrochemical supercapacitors, the book has wide-ranging appeal to industry experts and those new to the field. It can be used as a reference to apply to current work and a resource to foster ideas for new devices that will further the technology as it becomes a larger part of main stream energy storage.

The combination of oxime compounds with conducting polymers shows great potential in improving supercapacitor technology. This research examines the combined impacts of oximes and copolymers in composite electrodes by systematically exploring electrochemical methods. At the first stage of this work, novel Vic-dioxime-based oxime compounds were synthesized and named as [Ni(LoxH) 2 ], [Cu(LoxH) 2 ] and [Co(LoxH) 2 ].2H 2 O. They were incorporated into copolymer matrices through electrochemical way simultaneously with copolymer production. Analysis of the electrode materials through spectroscopic (FT-IR), microscopic (SEM–EDS) and electrochemical techniques (cyclic voltametric scan rate optimization, galvanostatic charge–discharge tests at different currents, long-cycle stability test and electrochemical impedance spectroscopy before extended cycling) provided insights into the structural and electrochemical characteristics of the composites. Areal capacitances at 10 mV s −1 were determined as 488.4 mFcm −2 , 286.0 mFcm −2 and 260.9 mFcm −2 for [Cu(LoxH) 2 ]@PGE/(PAn-co-PPy), [Ni(LoxH) 2 ]@PGE/(PAn-co-PPy) and [Co(LoxH) 2 ]@PGE/(PAn-co-PPy), respectively. Capacitance retention was 95% at the end of 1000 cycle in [Cu(LoxH) 2 ]@PGE/(PAn-co-PPy) electrode.

Architecture of fibrous building blocks with ordered structure and high electroactivity that enables quick charge kinetic transport/intercalation is necessary for high-energy-density electrochemical supercapacitors. Herein, we report a heterostructured molybdenum disulfide@vertically aligned graphene fiber (MoS 2 @VA-GF), wherein well-defined MoS 2 nanosheets are decorated on vertical graphene fibers by C–O–Mo covalent bonds. Benefiting from uniform microfluidic self-assembly and confined reactions, it is realized that the unique characteristics of a vertical-aligned skeleton, large faradic activity, in situ interfacial connectivity and high-exposed surface/porosity remarkably create efficiently directional ionic pathways, interfacial electron mobility and pseudocapacitive accessibility for accelerating charge transport and intercalation/de-intercalation. Resultant MoS 2 @VA-GF exhibits large gravimetric capacitance (564 F g −1 ) and reversible redox transitions in 1 M H 2 SO 4 electrolyte. Furthermore, the MoS 2 @VA-GF-based solid-state supercapacitors deliver high energy density (45.57 Wh kg −1 ), good cycling stability (20,000 cycles) and deformable/temperature-tolerant capability. Beyond that, supercapacitors can realize actual applications of powering multicolored optical fiber lamps, wearable watch, electric fans and sunflower toys. Graphical Abstract

A pair of polyaniline (PANIs) samples was prepared from HCl or H 2 SO 4 electrolytes containing 0.01 M of aniline, and then subjecting them to electropolymerization. The morphology, structure, and properties of the samples were characterized using scanning electron microscope, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The results demonstrate that the capacitance and morphology of the product depend exclusively on the reactive medium used. The PANI was used as a material electrode in a supercapacitor, and the electrochemical performance of the elaborated electrodes was evaluated using cyclic voltammetry, galvanostatic charge/discharge measurement, and electrochemical impedance spectroscopy. The optimal results for the specific capacitance of the PANI films were achieved under a 5-mVs −1 scan rate, ranging from 410.35 F/g for the FTO/PANI-H 2 SO 4 to 758.72 F/g for the FTO/PANI-HCl.

Hydrated and non-hydrated rGO-MnMoO 4 nanocomposites (rGO-MnMoO 4 and rGO-MnMoO 4 .1H 2 O) are synthesized by an easy hydrothermal method for use as supercapacitor electrodes. These nanocomposites are in situ grown onto the nickel foam. These nanocomposites are characterized via their structure, morphology, and chemical bonding. The electrochemical performance of these nanocomposites was measured as the supercapacitor electrodes. The morphological study of the samples reveals that the calcination process changes the morphology of nanocomposites from nanoflakes to cross-nanosheets for the hydrated and non-hydrated nanocomposites, respectively. The results showed that the cooperation of both the GO and the hydrated compound has a synergistic effect on the electrochemical performance of nanocomposites. The rGO-MnMoO 4 .1H 2 O nanocomposite at a scan rate of 5 mV s −1 in 1 M KOH electrolyte shows the highest specific capacitance of 855.6 F g −1 . It was found that the diffusion-limited process has a main contribution (than the capacitive process) to the storage mechanism of hydrated and non-hydrated rGO-MnMoO 4 nanocomposites. Also, the investigation of the storage mechanism contribution reveals that this mechanism depends on the scan rate. The designed quasi-solid-state symmetric supercapacitor device of rGO-MnMoO 4 .1H 2 O with KOH/PVA gel electrolyte can deliver a high energy density of 7.81 Wh kg −1 and a high power density of 2500 W kg −1 . Also, the assembled quasi-solid-state symmetric supercapacitor (SSC) exhibits a capacitance retention of 77.7% after 5000 cycles.

Flexible electrochemical supercapacitors (FESCs) are emerging as innovative energy storage systems, characterized by their stable performance, long cycle life, and portability/foldability. Crucial components of FESCs, such as electrodes and efficient electrolytes, have become the focus of extensive research. Herein, we examine deep eutectic solvent (DES)–based polymer gel systems for their cost-effective accessibility, simple synthesis, excellent biocompatibility, and exceptional thermal and electrochemical stability. We used a mixture a DES, LiClO4–2-Oxazolidinone as the electroactive species, and a polymer, either polyvinyl alcohol (PVA) or polyacrylamide (PAAM) as a redox additive/plasticizer. This combination facilitates a unique ion-transport process, enhancing the overall electrochemical performance of the polymer gel electrolyte. We manufactured and used LiClO4–2-Oxazolidinone (LO), polyvinyl alcohol–LiClO4–2-Oxazolidinone (PVA–LO), and polyacrylamide–LiClO4–2-Oxazolidinone (PAAM–LO) electrolytes to synthesize an MnO2 symmetric FESC. To evaluate their performance, we analyzed the MnO2 symmetric FESC using various electrolytes with cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The FESC featuring the PVA–LO electrolyte demonstrated superior electrochemical and mechanical performances. This solid-state MnO2 symmetric FESC exhibited a specific capacitance of 121.6 F/g within a potential window of 2.4 V. Due to the excellent ionic conductivity and the wide electrochemical operating voltage range of the PVA–LO electrolyte, a high energy density of 97.3 Wh/kg at 1200 W/kg, and a long-lasting energy storage system (89.7% capacitance retention after 5000 cycles of GCD at 2 A/g) are feasibly achieved. For practical applications, we employed the MnO2 symmetric FESCs with the PVA–LO electrolyte to power a digital watch and a light-emitting diode, further demonstrating their real-world utility.

Recent research has employed porous nano metal oxides (MOs) to store electrochemical energy. Some researchers have been interested in dual and ternary MOs, and more complicated metal oxide composite materials utilized in supercapacitors. This review discusses the electrochemical capacitive efficiency of metallic nanostructures doped in nickel oxide (NiO), methodologies, charge storage mechanisms, and recent research articles because of its better thermal stability, good chemical stability, cost-effective materials, superior theoretical morals of specific capacitance, natural richness, and environmental friendliness. The numerous different metals-doped NiO and their composite oxides have demonstrated good structural strength, reversible capacity, and extensive cycle lifetime. Researchers have indeed investigated nanostructured electrode materials for electrochemical supercapacitor applications.

Structural and electrochemical behaviors of electrophortically-deposited Fe3O4 and Fe3O4@C nanoparticles on carbon fiber (CF) were investigated. The nanoparticles were synthesized via a green-assisted hydrothermal route. The as-prepared samples were characterized by x-ray diffraction, transmission and scanning electron microscopies, Fourier transform infrared and UV–visible spectroscopies as well as by a vibration sample magnetometer. Surprisingly, the saturation magnetization (Ms) of the Fe3O4@C (~ 26.99 emu/g) was about 20% higher than that of Fe3O4 nanoparticles. A rather rectangular CV curve for both the elecrophortically-deposited Fe3O4 and Fe3O4@C on CF indicated the double-layer supercapacitor behavior of the samples. The synergistic effects of double shells improved the electrochemical behavior of Fe3O4@CF. The Fe3O4@C@CF composite exhibited a higher specific capacitance of ~ 412 F g−1 at scan rate of 0.05 V/s compared to the Fe3O4@CF with a value of ~ 193 F g−1. The superb electrochemical properties of Fe3O4@C@CF confirm their potential for applications as supercapacitors in the energy storage field.

Nanoflake bismuth ferrite thin film was synthesized by means of electrodeposition technique at room temperature. The morphology and phase evaluation of the synthesized electrode were analyzed using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and surface wettability techniques. Specifically, the bismuth ferrite nanoflake electrode exhibited high specific capacitance of 72.2 F g −1 at a current density of 1 A g −1 , and high rate capability with 37 % retention of capacitance even up to 20A g −1 , and excellent cycling stability with 82.8 % retention of the initial capacitance after 1500 charge/discharge cycles, supporting that the bismuth ferrite thin-film electrode could be a potential candidate for supercapacitor application.