Performance of Asymmetric Electric Double Layer Capacitors — Predominant Contribution of the Negative Electrode

Abstract

Asymmetric capacitors with a non-aqueous electrolyte were constructed by using various carbons as negative and positive electrodes in order to study their performance. For asymmetric capacitors where the ratio of the BET surface area, SBET, of the negative carbon electrode to that of the positive carbon electrode was less than 1.7, the capacitance of the electric double layer was strongly governed by the negative carbon electrode. Their rate performance, as evaluated from the ratio of the capacitance at 200 mA to that at 20 mA, C200/C20, was determined by the mesoporous surface area of the negative carbon electrode. What is important, however, is that the negative carbon electrode in capacitors governs their characteristics, viz. their capacitance and rate performance. This conclusion was arrived at by constructing asymmetric electric double layer capacitors employing carbons with different pore structures as the negative and positive electrodes. The present result provides information which is important ...