Room-temperature phosphonium ionic liquids for supercapacitor application

Ionic liquids (ILs) have been used as electrolytes for supercapacitors. Two phosphonium salts such as trihexyl(tetradecyl.)phosphonium bis(trifluoromethylsulfonyl)imide (IL1) and trihexyl(tetradecyl) phosphonium dicyanamide (IL2) have been selected for this target. To decrease the viscosity of ILs, a small amount of acetonitrile (from 5 to 25 wt %) was added. Supercapacitor based on activated carbon (AC) as electrodes and IL1 with 25 wt % of acetonitrile supplied capacitance values of 100 F/g at a high operating voltage of 3.4 V. Such a supercapacitor reached a high energy of ∼ 40 Wh/kg, and a good cyclability. © 2005 American Institute of Physics.