Allyl-functionalized ionic liquids as electrolytes for electric double-layer capacitors

Double-layer capacitor electrolytes employing allyl-functionalized ionic liquids as electrolytes with solvents have been evaluated. Imidazolium cations with allyl groups enabled the high capacitances and low resistances of electric double-layer capacitor (EDLC) cells at a wide range of temperature in spite of the large cation sizes and low ionic conductivities of the electrolytes compared to imidazolium with saturated alkyl groups, 1-ethyl-3-methylimidazolium (EMIm). The improvement of EDLC performance was noted particularly in the case of diallylimidazolium (DAIm) cation and TFSA anion. The substitution of the vinyl group increased the high capacitance only at 298 K and decreased the capacitance at low temperature and direct current resistance (DC-IR) at 243 and 298 K. The butenyl group deteriorated the capacitance and DC-IR at 243 and 298 K. The stability of EDLC cell of DAIm–BF4/PC was inferior to that of EMIm–BF4/PC. The addition of DMC to PC improved the stability.