Performance of electric double-layer capacitors using carbons prepared from phenol-formaldehyde resins by KOH etching

Phenol-formaldehyde resins were used to produce carbons with different porosities by KOH etching. Through the introduction of a binder, carbon-binder composites were prepared to serve as electrodes in electric double-layer capacitors. Nitrogen adsorption was used to characterize the porous structure of the carbons and electrodes. The performance of the capacitors in 1 M H2SO4 was investigated with charge-discharge cycling experiments. The faradaic leakage current and the specific capacitance of the electrodes were found to increase with the specific surface area, while the resistance determined from the IR drop showed an opposite trend. The increased electrode resistance, which would probably result from the increased diffusion path in the pores upon etching, has caused a decrease in the capacitance per unit carbon area. A specific capacitance larger than 100 F/g was achieved with an electrode consisting of 80% carbon particles with a specific surface area of 1900 m(2)/g and 20% polyvinylidenefluoride as the binder. (C) 2001 Elsevier Science Ltd. All rights reserved.