Characterization of activated carbons for electric double layer capacitor and its attention

Abstract

In this review, it is explained how to characterize the activated carbon electrode for electric double layer capacitor (EDLC) and what points to pay attention to. Both of the power density and energy density of EDLC can be obtained using two-electrode type cell by constant power method or constant current method. The power density depends on the energy density. Additionally, the end of discharge voltage controls them. It is necessary to conduct the acceleration life-test at high charge-voltage and high temperature condition using two-electrode type cell for characterizing the cycle performance of EDLC. An overestimation of BET specific surface area often causes misunderstanding the correlation of the surface area and the capacitance of activated carbons. The BET specific surface area should be calculated in consideration of the analysis condition. The capacitance in ethylimidazolium-type ionic liquid cannot be measured by three-electrode cell with Li/Li⁺ reference electrode since lithium metal is reactive to the ionic liquid. The surface modification of lithium metal by HF can suppress the reaction to use Li/Li+ reference electrode in the ionic liquid.