2. Experimental Procedure

Activated carbon(MSP-20) for an active electrode material was provided from Kansai Coke & Chemicals Co.. Super-P(M.M.M. Carbon Co., Belgium) and polyvinylidene fluoride(Sigma-Aldrich) were employed as a conductive additive and a binder, respectively. The preparation procedure for a coin-type EDLC cell was briefly presented in Fig. 1. Active material(activated carbon) and conductive additive were thoroughly mixed using a planetary ball mill (Xiamen Tmaxcn Inc.)with different ball-milling times. The ball-milling time was varied from 0 to 60 min with an interval of 10 min, in order to investigate the effect of mixing of active material and conductive additive on the electrochemical performance of EDLC electrode in organic electrolyte. Known amount of binder(polyvinylidene fluoride. 10 wt.%) in 1-methyl-2-pyrrolidone(NMP) was added to the mixed powder to form slurry, and subsequently, the resulting solution was vigorously stirred for 30 min. The mass ratio of active material:conductive additive:binder was fixed at 80:10:10. The slurry was coated onto the aluminum foil(current collector) by a doctor-blade apparatus with a gap of 22μm, and then, the coated electrode was dried at 70 o C in vacuo. Finally, the dried foil was pressed using a double-roll press at 80 o C to yield the electrode sheet. The prepared electrode were denoted as AC_X(X = 0, 10, 20, 30, 40, 50, and 60), where X represents ball-milling time(min).

Coin-type EDLC cell(CR2032) is composed of two symmetrical carbon electrodes,PP PE separator (Xiamen Tmaxcn Inc.), organic electrolyte, SUS cap, spacer and so on(Fig. 1). Prior to the coin cell packaging, the punched electrode was soaked in battery electrolyte (1M tetraethylammonium tetrafluoroborate in acetonitrile,Xiamen Tmaxcn Inc.) for 1 day in a vacuum glove box (Xiamen Tmaxcn Inc.)filled with argon. The carbon electrodes with a diameter of 18 mm were opposed to each other and the cellulose separator with a diameter of 19 mm was placed between the electrodes. Finally, coin-type cell was sealed using a coin cell crimper (Xiamen Tmaxcn Inc.).