Electrochemical properties of modified carbon electrodes for electric double layer capacitors

To improve capacitance and energy density of electric double layer capacitors (EDLCs), plasma surface treatments were carried out on surface of activated carbon sheets, and optimal conditions for the treatment were discussed. Operating gas pressure of argon was 20 Pa, and activated carbon sheets were set up so that they were covered with the dc glow discharge at 70 W. Electrochemical properties, including cyclic voltammetry (CV) and cole–cole plot of EDLCs in organic electrolyte, were examined. The results showed that capacitance of the plasma-treated EDLC increased to 11% in comparison with that of untreated one. The enhancement in specific capacitance was mainly attributable to increasing of ratio of surface area of the activated carbon sheets.