Effect of pore size in activated carbon on the response characteristic of electric double layer capacitor

Abstract

The effect of pore size on the response characteristic of an electric double layer capacitor (EDLC) was closely examined. A series of phenol-resin-based activated carbon (AC) samples was prepared as average pore size from 0.94 to 1.68 nm by KOH activation by varying the activation temperature and KOH/carbonized phenol-resin ratio. The impedance properties of pouch-type EDLC cells prepared using AC samples were evaluated by applying an alternating current at 3 V between 10 mHz and 100 kHz for confirming the response characteristic. The cell based on the AC with a largest pore size (1.68 nm) showed fast response frequency, and had a high dielectric relaxation time constant as calculated from the response frequency value. The AC with the largest pore size, which consisted of both micropores (>1 nm) and mesopores (2–4 nm), was confirmed to facilitate extremely low electrolyte-diffusion resistance during the formation of the electric double layer, implying that the large pores lead to fast and stable response frequency. The presented findings suggest that AC with a largest pore size as the electrode leads to superior capacitance and response frequency characteristics in the alternating current than those of an AC with a smaller pore size.