Energy density, double-layer capacitance

As a result, by adjusting the CNT density in the nanopores, the ratio of the discharge from the double layer capacitance and the Li deintercalation can be controlled and the performance of the electrochemical cell can be designed for any purpose, for example, high energy density or high specific power. 

In Chapter 9 we have shown the thermodynamic relationships among the surface tension, y, (which is the same as the excess surface Gibbs energy), the excess charge density on the metal, qM, the double layer capacitance, Cai, and the surface excess of a particular species, F,- (cf. Eqs. (9.8) to (9.14)). 

The principle of EDLC operation is very simple and is based on the well-known electrical or double layer phenomenon. The device operates within a potential range in which no Faradaic reactions take place, and thus the behavior is fully capacitive. Polarization of the electrodes in opposite directions leads to accumulation of opposite charges at the electrode-solution interfaces. The higher the electrode surface area and the polarity of the electrolyte solution and its ionic concentration, the higher are the capacity and energy density of these devices. The capacitance C and the accumulated electrostatic energy E stored are given by Eqs. (2) and (3), respectively [44] ... 

The double-layer capacitor is one of the electrochemical capacitors showing intermediate performances between conventional capacitors and rechargeable batteries from the viewpoint of energy and power densities. Although the terms supercapacitor and ultracapacitor are often used for double-layer capacitors, in a sense that they have higher capacitance than conventional capacitors (ceramic, film, aluminum electrolytic, or tantalum electrolytic capacitors), these terms are not to be used because they are the trademarks of certain companies products. 

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