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

In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

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A review of electrode materials for electrochemical supercapacitors

This tutorial review provides a brief summary of recent research progress on carbon-based electrode materials for supercapacitors, as well as the importance of electrolytes in the development of supercapacitor technology. The basic principles of supercapacitors, the characteristics and performances of various nanostructured carbon-based electrode materials are discussed. Aqueous and non-aqueous electrolyte solutions used in supercapacitors are compared. The trend on future development of high-power and high-energy supercapacitors is analyzed.

Carbon-based materials as supercapacitor electrodes

Li-ion battery technology has become very important in recent years as these batteries show great promise as power sources that can lead us to the electric vehicle (EV) revolution. The development of new materials for Li-ion batteries is the focus of research in prominent groups in the field of materials science throughout the world. Li-ion batteries can be considered to be the most impressive success story of modern electrochemistry in the last two decades. They power most of today's portable devices, and seem to overcome the psychological barriers against the use of such high energy density devices on a larger scale for more demanding applications, such as EV. Since this field is advancing rapidly and attracting an increasing number of researchers, it is important to provide current and timely updates of this constantly changing technology. In this review, we describe the key aspects of Li-ion batteries: the basic science behind their operation, the most relevant components, anodes, cathodes, electrolyte solutions, as well as important future directions for R&D of advanced Li-ion batteries for demanding use, such as EV and load-leveling applications.

Challenges in the development of advanced Li-ion batteries: a review

Carbon properties and their role in supercapacitors

We characterized activated carbon electrodes for electrical double-layer capacitor (EDLC) systems. High-surface-area carbons were prepared by carbonization of cotton cloth at elevated temperatures (up to 1050°C), followed by activation at 900°C by oxidation with CO 2 during different time periods. Specific surface areas and characteristic pore sizes obtained from gas adsorption isotherms were correlated with those obtained from ion electroadsorption at the electrical double layer. Electrolytes studied included aqueous LiCI, NaCI, and KCl solutions and nonaqueous propylene carbonate solutions with LiBF 4 and (C 2 H 5 ) 4 NBF 4 salts. We found clear evidence that the porous carbons thus formed exhibit ion sieving properties, and that increasing activation time systematically increases the average pore sizes of these carbons. The electric double layer (EDL) capacity of these samples (calculated from voltammetric measurements) depends strongly on the adsorption interaction of the ions in the pores, and hence the relationship between the average pore size and the effective ion size determines the specific EDL capacitance of these samples. The following order of dimension of adsorbed species was found, based on the ion sieving of the various synthesized carbons of different average pore size N 2 ; Na + (aq); Cl - (3.6 A) < BF 4 - < TEA + (PC) < Li + (PC).

https://iopscience.iop.org/article/10.1149/1.1393557/pdf

Carbon Electrodes for Double‐Layer Capacitors I. Relations Between Ion and Pore Dimensions

Long term stability of capacitive de-ionization processes for water desalination: The challenge of positive electrodes corrosion

Knudsen diffusion in microporous carbon membranes with molecular sieving character

Carbonaceous materials are widely used in electrochemistry. All allotropic forms of carbons—graphite, glassy carbon, amorphous carbon, fullerenes, nanotubes, and doped diamond—are used as important electrode materials in all fields of modern electrochemistry. Examples include graphite and amorphous carbons as anode materials in high-energy density rechargeable Li batteries, porous carbon electrodes in sensors and fuel cells, nano-amorphous carbon as a conducting agent in many kinds of composite electrodes (e.g., cathodes based on intercalation inorganic host materials for batteries), glassy carbon and doped diamond as stable robust and high stability electrode materials for all aspects of basic electrochemical studies, and more. Amorphous carbons can be activated to form very high specific surface area (yet stable) electrode materials which can be used for electrostatic energy storage and conversion [electrical double-layer capacitors (EDLC)] and separation techniques based on electro-adsorption, such as water desalination by capacitive de-ionization (CDI). Apart from the many practical aspects of activated carbon electrodes, there are many highly interesting and important basic aspects related to their study, including transport phenomena, molecular sieving behavior, correlation between electrochemical behavior and surface chemistry, and more. In this article, we review several important aspects related to these electrode materials, in a time perspective (past, present, and future), with the emphasis on their importance to EDLC devices and CDI processes.

Abraham Soffer

Papers

Carbon Electrodes for Double‐Layer Capacitors I. Relations Between Ion and Pore Dimensions

Long term stability of capacitive de-ionization processes for water desalination: The challenge of positive electrodes corrosion

Knudsen diffusion in microporous carbon membranes with molecular sieving character

The electrochemistry of activated carbonaceous materials: past, present, and future

The effect of the flow-regime, reversal of polarization, and oxygen on the long term stability in capacitive de-ionization processes