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

Carbon materials for the electrochemical storage of energy in capacitors

Carbon properties and their role in supercapacitors

Electrical energy storage (EES) is one of the most critical areas of technological research around the world. Storing and efficiently using electricity generated by intermittent sources and the transition of our transportation fleet to electric drive depend fundamentally on the development of EES systems with high energy and power densities. Supercapacitors are promising devices for highly efficient energy storage and power management, yet they still suffer from moderate energy densities compared to batteries. To establish a detailed understanding of the science and technology of carbon/carbon supercapacitors, this review discusses the basic principles of the electrical double-layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes. We summarize the key aspects of various carbon materials synthesized for use in supercapacitors. With the objective of improving the energy density, the last two sections are dedicated to strategies to increase the capacitance by either introducing pseudocapacitive materials or by using novel electrolytes that allow to increasing the cell voltage. In particular, advances in ionic liquids, but also in the field of organic electrolytes, are discussed and electrode mass balancing is expanded because of its importance to create higher performance asymmetric electrochemical capacitors.

Carbons and Electrolytes for Advanced Supercapacitors

This paper presents the results obtained on the electrochemical behavior of electrochemical capacitors assembled in nonaqueous electrolyte. The first part is devoted to the electrochemical characterization of carbon-carbon 4 cm2 cells systems in terms of capacitance, resistance, and cyclability. The second part is focused on the electrochemical impedance spectroscopy study of the cells. Nyquist plots are presented and the impedance of the supercapacitors is discussed in terms of complex capacitance and complex power. This allows the determination of a relaxation time constant of the systems, and the real and the imaginary part of the complex power vs. the frequency plots give information on the supercapacitor cells frequency behavior. The complex impedance plots for both a supercapacitor and a tantalum dielectric capacitor cells are compared. © 2003 The Electrochemical Society. All rights reserved.

https://iopscience.iop.org/article/10.1149/1.1543948/pdf

Electrochemical Characteristics and Impedance Spectroscopy Studies of Carbon-Carbon Supercapacitors

Electrochemical characterization has been carried out for two types of phenolic resin‐based activated carbon‐fiber cloths (ACFC)—ACFC(a) and (b)—as polarizable electrodes. The specific surface areas of ACFC(a) and ACFC(b) were 1630 and 1060 m2g−1, respectively. The differential capacitance of ACFC(a) in organic electrolyte, which was determined by cyclic voltammetry, was 113 F g−1 at 0.1V vs. SCE. The capacitive current of ACFC(a) was almost constant in the range between −1.5 and 1.5V vs. SCE at 25° and −25°C, while that of ACFC(b) decreased under cathodic polarization, especially at −25°C. In accordance with the result of cyclic voltammetry, the temperature dependence of capacitance in the electric double‐layer capacitors with ACFC(a) and an organic electrolyte was small, and that of the capacitors with ACFC(b) was large. It was found that the temperature dependence of the capacitors with ACFC and an organic electrolyte was mainly influenced by the pore size distribution of ACFC electrodes.

https://iopscience.iop.org/article/10.1149/1.2086158/pdf

Electrochemical Characterization of Activated Carbon‐Fiber Cloth Polarizable Electrodes for Electric Double‐Layer Capacitors

An electric double layer capacitor which comprises a pair of polarizable electrode (4, 5), composed of electrically-conductive substrates (1) coated with layers formed on said substrates, of a mixture of activated carbon with a water-soluble material-based binding agent, optionally including an agent for improving electric conductivity, facing with each other by being interposed with a separator (6), and an electrolyte is disclosed.

Electric double layer capacitor and method for producing the same

Effect of concentration of surface acidic functional groups on electric double-layer properties of activated carbon fibers

A polarizable electrode body which has as a constituting member a paper-type body having activated carbon fiber and a fibrous binding medium as its composition, and also a electric double-layer capacitor having the polarizable electrode body as its constituting member. In comparison with a conventional simple polarizable electrode body of activated carbon fiber fabric, higher integration can be made and charged electric charge per unit volume can be increased, and the electric charge to be stored in the polarizable electrode body can be easily adjusted.

Akihiko Yoshida

Papers

Electrochemical Characterization of Activated Carbon‐Fiber Cloth Polarizable Electrodes for Electric Double‐Layer Capacitors

Electric double layer capacitor and method for producing the same

Effect of concentration of surface acidic functional groups on electric double-layer properties of activated carbon fibers

Polarizable electrode body and method for its making

Advanced capacitors and their application