Ionic Liquids with Low Melting Points and Their Application to Double-Layer Capacitor Electrolytes

Abstract

Ionic liquids, 1-ethyl-3-methylimidazolium hexafluorotantalate and hexafluoroniobate were synthesized by a new method. They showed lower melting points and higher decomposition temperatures than popular due to larger anion size. Electrolytic conductivities of these ionic liquids were about 6 mS cm−1 at 25°C. Lowering the melting point of ionic liquids did not result in the improvement of low-temperature characteristics of carbon double-layer capacitors, however, the new ionic liquids showed long life compared with and at 3.0 V, 70°C. The derivatives of the new ionic liquids having a methyl group in 2-position (1-ethyl-2,3-dimethylimidazolium salts) were not ionic liquids at room temperature. © 2002 The Electrochemical Society. All rights reserved.