Energy storage in electrochemical capacitors based on carbon materials

ENERGY STORAGE IN ELECTROCHEMICAL CAPACITORS BASED ON CARBON MATERIALS 

An electrochemical capacitor is a device which consists of a pair of ideally polarizable electrodes which are immersed in an electrolyte, and physically separated by a porous membrane through which ions can diffuse (Fig. 2). In a true electrochemical capacitor, the electrical energy storage is based on the separation of charged species in an electrical double layer at foe electrode/electrolyte interface. 

Electrochemical capacitors operate with the same principles as conventional electrostatic capacitors which consist of two conducting materials separated by a dielectric. The capacitance C (in Farad) is expressed as Eq. (1)  

In addition to their high capacitance compared to dielectric capacitors, EDLCs present much better reversibility and cycleabilily than any secondary battery because they do not undergo any charge transfer reaction. By contrast with a secondary battery, the practical cycle-life of an EDLC is limited by its engineering rather than by its chemistry. 

Some effect resembling to capacitance can arise when the transfer of a faradaic charge is proportional, or approximately proportional, to the applied voltage as in Eq. (3)  

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