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

[Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Advanced Materials for Energy Storage

Electrolytes and interphases in Li-ion batteries and beyond.

Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage.

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/Science313,%201760.pdf

Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer

Carbon materials have attracted intense interests as electrode materials for electrochemical capacitors, because of their high surface area, electrical conductivity, chemical stability and low cost. Activated carbons produced by different activation processes from various precursors are the most widely used electrodes. Recently, with the rapid growth of nanotechnology, nanostructured electrode materials, such as carbon nanotubes and template-synthesized porous carbons have been developed. Their unique electrical properties and well controlled pore sizes and structures facilitate fast ion and electron transportation. In order to further improve the power and energy densities of the capacitors, carbon-based composites combining electrical double layer capacitors (EDLC)-capacitance and pseudo-capacitance have been explored. They show not only enhanced capacitance, but as well good cyclability. In this review, recent progresses on carbon-based electrode materials are summarized, including activated carbons, carbon nanotubes, and template-synthesized porous carbons, in particular mesoporous carbons. Their advantages and disadvantages as electrochemical capacitors are discussed. At the end of this review, the future trends of electrochemical capacitors with high energy and power are proposed.

Carbon Materials for Chemical Capacitive Energy Storage

Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Influence of the solvent properties on the characteristics of a double layer capacitor

The advanced carbide-derived carbon based supercapacitor

Electrochemical double-layer capacitors with micro-to-nanoporous electrodes based on activated carbon utilize the gross interface between carbon and the electrolyte, which fills the pores of two main classes, (i) micrometer voids between agglomerates of carbon grains and (ii) micro-to-nanometer pores inside agglomerates and grains. The bigger pores provide good transport of ions throughout the layer whereas the smaller pores generate a large interfacial area. This essentially bifunctional architecture prompted us to combine two complementary concepts in the pertinent theory of double-layer capacitors, viz. linear transmission line models and self-affine fractal models. The merit of this structure-based approach, involving also the effect of hindrance of ionic conductivity in nanopores, is that it relates basic structural characteristics to the dynamic performance. Practically, with no fitting parameters, it reproduces the main features of recently reported complex impedance data. This refers to the effect of electrode thickness, constant phase angle (CPA) and crossover between CPA and non-CPA behavior. Routes toward the optimization of the capacitor architecture for the largest possible static capacitances and rapid charging-discharging are explored. The comparison of calculated optimum capacitance values with recent experimental data reveals remarkable reserves for advanced structural design.

Enn Lust

Papers

Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Influence of the solvent properties on the characteristics of a double layer capacitor

The advanced carbide-derived carbon based supercapacitor

Optimized Structure of Nanoporous Carbon-Based Double-Layer Capacitors

Electrochemical characteristics of nanoporous carbide-derived carbon materials in non-aqueous electrolyte solutions