Journal of Power Sources, Vol.267, 411-420, 2014
Impedance analysis of porous carbon electrodes to predict rate capability of electric double-layer capacitors
Electrochemical impedance analysis is performed to predict the rate capability of two commercial activated carbon electrodes (RP20 and MSP20) for electric double-layer capacitor. To this end, ac impedance data are fitted with an equivalent circuit that comprises ohmic resistance and impedance of intra-particle pores. To characterize the latter, ionic accessibility into intra-particle pores is profiled by using the fitted impedance parameters, and the profiles are transformed into utilizable capacitance plots as a function of charge discharge rate. The rate capability that is predicted from the impedance analysis is well-matched with that observed from a charge discharge rate test. It is found that rate capability is determined by ionic accessibility as well as ohmic voltage drop. A lower value in ionic accessibility for MSP20 is attributed to smaller pore diameter, longer length, and higher degree of complexity in pore structure. (C) 2014 Elsevier B.V. All rights reserved.
Keywords:Electric double-layer capacitor (EDLC);Electrochemical impedance spectroscopy (EIS);Rate capability;Porous electrode;Transmission-line model with pore size distribution (TLM-PSD);Activated carbon