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The charge-storage mechanism and the design of the ultracapacitor are described. Based on a ceramic with an extremely high specific surface area and a metallic substrate, the ultracapacitor provides extremely high energy densities and exhibits low ESR (equivalent series resistance). The combination of low ESR and extremely low inductance provides the ultracapacitor with a very high power density and fast risetime as well. As a double-layer capacitor, the ultracapacitor is not constrained by the same limitations as dielectric capacitors. Thus, although its discharge characteristics and equivalent circuit are similar to those of dielectric capacitors, the capacitance of the ultracapacitor increases with the ceramic loading on the substrate and its ESR is inversely proportional to the cross-sectional area of the device. The ultracapacitor is composed of an inline stack of electrodes, which leads to an extremely low inductance device, and it exhibits interesting frequency dependence. The ultracapacitor principle has been extended to nonaqueous electrolytes and to a wide temperature range.>
Bullard et al. (Sun,) studied this question.