By varying the cation size of quaternary ammonium salts, approximately 10% higher capacitance was achieved with trimethylethylammonium BF4 and trimethylpropylammonium BF4 relative to tetraethylammonium BF4 using microporous activated carbon (AC) electrodes. The ions carried solvation shells in the bulk electrolytes, but became desolvated within the narrow AC pores when the electrochemical double-layer capacitor was charged to a high potential. The capacitance depended on the size of the cation rather than that of the BF4 anion because the anion is smaller than the quaternary ammonium ions. The capacitance was found to be proportional to the reciprocal radii of the neat cations. The effective radius of the asymmetric trimethylpropylammonium ion was estimated to be 0.314 nm based on the present results.

: In the study, a room temperature ionic liquids as a co-solvent was used to evaluate the feasibility with various electrodes in Li-ion batteries. 1-Ethyl-1-methyl piperidinium bis(trifluoromethanesulfonyl)imide(PP12 TFSI) is an ionic liquid that melts at 85 o C. Pure PP12 TFSI is not able to be used as an electrolyte because it is a solid salt at room temperature. PP12 TFSI is mixed with EC/DEC(1/1 vol.%) to prepare mixed solvents. The electrolyte 1.5 M LiPF 6 in a mixed solvent having 44 wt.% PP12 TFSI is prepared to evaluated the various electrodes. The electrolytes provides good cycles life of cells with LiNi 0.5 Mn 1.5 O 4 (LNMO), LiFePO 4 (LFP), Li 4 Ti 5 O 12 (LTO) and artificial graphite. Further improvement of the cell performances can be accomplished by enhancing wettability of electrolytes to electrodes.