Application of Low-Viscosity Ionic Liquid to the Electrolyte of Double-Layer Capacitors

Abstract

The performance of a double-layer capacitor (DLC) composed of activated carbon electrodes and 1-ethyl-3-methylimidazolium fluoride (EMIF)⋅2.3HF, which has extremely high conductivity with low viscosity, was examined and compared with those using the popular ionic liquid EMIBF4,EMIBF4, conventional aqueous electrolyte 35 wt % H2SO4,H2SO4, and nonaqueous electrolyte 1 M Et3MeNBF4Et3MeNBF4 /propylene carbonate. The DLC using EMIF⋅2.3HF showed an intermediate capacitance and internal resistance between the aqueous and nonaqueous electrolyte systems due to its intermediate double-layer capacitance and electrolytic conductivity. EMIF⋅2.3HF afforded much higher capacitance than EMIBF4EMIBF4 even at low temperatures, however, it had a lower decomposition voltage (∼2 V), resulting in lower energy density. The capacitance of EMIF⋅2.3HF was extremely dependent on the applied voltage. © 2003 The Electrochemical Society. All rights reserved.