Development of equivalent circuit model for electric double-layer capacitors reflecting pore structure of activated carbon

Abstract

In this study, an equivalent circuit model of electric double-layer capacitors (EDLCs) reflecting a branched-pore structure for activated carbon was developed. Geometrical parameters such as pore diameter, pore depth, and branch number of the macropore, mesopore, and micropore were estimated from the analysis of the electrochemical impedance for EDLCs, combining theoretical equations and an equivalent circuit model. The developed equivalent circuit model was applied to charge/discharge simulations of EDLCs. The experimental and simulated cell voltages during pulsed-current charge were found to be in excellent agreement. Distributions of currents and voltages in the macropore, mesopore, and micropore during pulsed-current charges were discussed using equivalent circuit simulations. Electric-double layers were charged in order of the macropore, the mesopore, and the micropore. It was suggested that charge delays of the mesopore and the micropore originated from both solution resistances in pores and the branch structure of the pore for activated carbon.