Double-layer capacitor

Tanahashi, 1., Yoshida, A. and Nishino, A., Electrochemical characterization of activated carbon fiber cloth polarizable electrodes for electric double layer capacitors. J. Electrochem. Soc., 1990, 137(10), 3052 3056. 

Ishikawa, M., Morita, M., lhara, M. and Matsuda, Y., Electric double layer capacitor composed of activated carbon fiber cloth electrodes and solid polymer electrolytes containing alkylammonium salt, J. Electrochem. Soc., 1994, 141(7), 1730 1734. 

Ishikawa, M., Sakamoto, A., Morita, M., Matsuda, Y. and Ishida, K., Effect of treatment of activated carbon fiber cloth electrodes with cold plasma upon performance of electric double layer capacitors, J. Power Sources, 1996, 60(2), 233 238. 

Work in this area has been conducted in many laboratories since the early 1980s. The electrodes to be used in such a double-layer capacitor should be ideally polarizable (i.e., all charges supplied should be expended), exclusively for the change of charge density in the double layer [not for any electrochemical (faradaic) reactions]. Ideal polarizability can be found in certain metal electrodes in contact with elelctrolyte solutions free of substances that could become involved in electrochemical reactions, and extends over a certain interval of electrode potentials. Beyond these limits ideal polarizability is lost, owing to the onset of reactions involving the solvent or other solution components. 

In recent years, many types of double-layer capacitors have been built with porous or extremely rough carbon electrodes. Activated carbon or materials produced by carbonization and partial activation of textile cloth can be used for these purposes. At carbon materials, the specific capacity is on the order of 10 J,F/cm of trae surface area in the region of ideal polarizability. Activated carbons have specific surface areas attaining thousands of mVg. The double-layer capacity can thus attain several tens of farads per gram of electrode material at the surfaces of such carbons. 

It follows from these data that the (theoretical) specific capacity of the active materials of such a double-layer capacitor may attain 100 F/g. This is many orders of magnitude above the values characterizing other capacitor types (film and electrolytic). For this reason such capacitors have also become known as super- or ultracapacitors. 

The operation of a double-layer capacitor is tied to a displacement of electrolyte ions. In a fully charged capacitor, anions accumulate as counterions in the solution layer next to the positively charged electrode while the eoncentration of the cations decreases. At the negative electrode, the opposite situation is seen. During discharge, the ionic concentrations level out to the bulk solution values by migration and diffusion. 

The total capacity of a ruthenium oxide electrode [the usual double-layer capacity plus the pseudocapacity of reaction (21.4)] is rather high (i.e., several hundred F/g), even more than at the electrodes of carbon double-layer capacitors. The maximum working voltage of ruthenium oxide pseudocapacitors is about 1.4 V. 

Burke AF, Miller M. Characteristics and Applications of Advanced Ultracapacitors. Proceedings of the 12th International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Deerfield Beach, Florida, USA, Dec. 9-11, 2002. 

High porosity carbons ranging from typically microporous solids of narrow pore size distribution to materials with over 30% of mesopore contribution were produced by the treatment of various polymeric-type (coal) and carbonaceous (mesophase, semi-cokes, commercial active carbon) precursors with an excess of KOH. The effects related to parent material nature, KOH/precursor ratio and reaction temperature and time on the porosity characteristics and surface chemistry is described. The results are discussed in terms of suitability of produced carbons as an electrode material in electric double-layer capacitors. 

Porous carbons are among the most attractive electrode materials for electric double layer capacitors (EDLC), where the charge accumulation occurs mainly by electrostatic attraction forces at the clcctrode/electrolyte interface [1-3]. Advantages of this class of materials include high surface... 

Gryglewicz G., Lorenc-Grabowska E., Lota G., Frackowiak E., Machnikowski J., Coal-based mesoporous activated carbons for double-layer capacitors, Carbon 03, International Conference on Carbon, CD-ROM Proc., paper 292, Oviedo 2003. 

GENERAL PROPERTIES OF IONIC LIQUIDS AS ELECTROLYTES FOR CARBON-BASED DOUBLE LAYER CAPACITORS... 

Fig. 7. A schematic diagram of an electric double-layer capacitor using active carbon electrodes.

Fig. 18b.5. (a) The capacitor-like metal solution interface, the double layer, (b) The equivalent circuit with solution resistance and overall double-layer capacitor, (c) Charging current transient resulting from a step-potential at... 

ECs are another promising electrical energy storage device with a higher energy density than electrical capacitors, and a better rate capability and cycling stability than LIBs [32]. Carbon-based electric double layer capacitors and metal oxide- or polymer-based pseudocapacitors are two main types of ECs. The charge-... 

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