Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

https://hal.archives-ouvertes.fr/hal-02417326/document

Materials for electrochemical capacitors

Hybrid supercapacitors with their improved performance in energy density without altering their power density have been in trend since recent years. The hybrid supercapacitor delivers higher specific capacitance in comparison to the existing electric double layer capacitor (EDLC) and pseudocapacitors. Generally, the asymmetric behavior of hybrid supercapacitors which is the combination of EDLC and pseudocapacitor acts as an enhancer in its respective capacitance values. This asymmetric approach marks a new beginning towards the much-needed pollution free, long lasting and proficient energy-storing performance. Corresponding to their utilization in hybrid electric vehicles and similar sort of power necessity based devices; the research in developing new advanced storage devices finds an enormous and vast future ahead. The most significant factor for the energy efficient applications demands a considerably higher ratio of surface to the volume by incorporation of new materials. This review article gives an overview of recent advances in the development of hybrid supercapacitors, storage mechanism, criteria of formation, components, different electrode and electrolyte materials, electrochemical profile assessment, design fabrication and their applications.

A review on recent advances in hybrid supercapacitors: Design, fabrication and applications

An asymmetric supercapacitor (ASC) is a supercapacitor based on two different electrode materials. One electrode is based on redox (Faradic) reactions with or without non-faradic reactions, and the other one is mostly based on electric double-layer (non-Faradic or electrostatic) absorption/desportion. Aqueous electrolytes have higher ionic conductivity, larger capacitance and better safety than the organic electrolytes. Herein, some key electrode materials for aqueous ASCs are primarily reviewed, which provide a new direction for power sources to have higher energy density at high power densities, compared with traditional capacitors. Their negative electrode materials include carbonaceous materials (porous carbons, carbon nanotubes and graphene), oxides (V2O5 and MoO3) and their composites, and their positive electrode materials include carbonaceous materials, oxides (RuO2, MnO2, MoO3, V2O5, PbO2, Co3O4), Ni(OH)2, intercalation compounds (LiCoO2, LiMn2O4, Li[NiCoMn]1/3O2, NaMnO2 and KMnO2). We describe the latest work on these electrode materials, and a particular focus is directed to the fabrication and electrochemical performance of various nanostructured electrode materials and some assembled ASCs. Finally, the future trends and prospects on advanced energy storage materials are suggested.

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Electrode materials for aqueous asymmetric supercapacitors

Hierarchical porous nickel oxide and carbon as electrode materials for asymmetric supercapacitor

A novel zinc-ion hybrid supercapacitor for long-life and low-cost energy storage applications

A hybrid capacitor (HC) with an aqueous electrolyte solution was assembled using a Zn negative electrode and an activated carbon (AC) positive electrode. The electrochemical properties of the HC were compared with an electric double-layer capacitor (EDLC) having two AC electrodes. The HC cell successfully functioned as an electrochemical capacitor, with a maximum operating voltage of 1.4 V, which was 1.5 times higher than that of the EDLC cell, and a specific capacitance of ca. 3.7 times higher than that of the EDLC cell. In addition, the HC cell displayed high-rate dischargeability comparable to that of the EDLC cell. Due to these advantages, the HC cell was found to be superior to the EDLC cell in terms of energy and power density. The HC could be a promising candidate for water-based electrochemical capacitors with high energy and power densities.

http://esl.ecsdl.org/content/10/12/A261.full.pdf

Tomoko Morimoto

Papers

Electrochemical Characterization of a Hybrid Capacitor with Zn and Activated Carbon Electrodes