Electrochemical Properties of Imidazolium Salt Electrolytes for Electrochemical Capacitor Applications

The specific ionic conductivity, dynamic viscosity, and electrochemical stability of several imidazolium salts are reported as neationic liquids and their solutions in several organic solvents. The temperature dependence of conductivity and viscosity are analyzed for 1‐ethyl‐3‐methylimidazolium and 1,2‐dimethyl‐3‐n‐propylimidazolium salts, and the influence of theanions bis(trifluoromethylsulfonyl)imide , bis(perfluoroethylsulfonyl)imide , hexafluoroarsenate , hexafluorophosphate , and tetrafluoroborate on these properties are discussed. These imidazolium salts make possible electrolytes with high concentration (>3 M), high room temperature conductivity (up to 60 mS/cm), and a wide window of stability . Differential scanning calorimetric results confirm a large glass phase for the ionic liquids, with substantial (>80°C) supercooling. Thermal gravimetric results indicate the imidazolium salts with and anions to be thermally more stable than the lithium salt analogs. The Vogel‐Tammann‐Fulcher interpretation accurately describes the conductivity temperature dependence. © 1999 The Electrochemical Society. All rights reserved.