Effect of particle size of activated carbon on rate performance of electric double layer capacitors

High surface area activated carbon (AC) obtained by KOH activation was pulverized by ultrasonic air-jet pulverization equipment and the effect of particle size of AC on rate performance of electric double layer capacitors (ECs) was investigated by electrochemical impedance spectrometry using an equivalent circuit model based on a mixed kinetic and charge transfer control. The model parameters were extracted by Marquardt fitting method. The series solution resistance, polarization resistance and Warburg resistance were obtained. It is found that both the series solution resistance and polarization resistance are independent of the particle size while the Warburg resistance determined by the mass transport resistance or diffusion coefficient of ions within pores of AC particles governs the rate capability of the AC based ECs, owing to the short diffusion length of ions within pores of AC particles.