Ionic conductivity of nonflammable ternary electrolyte consisting of ionic liquid and fluorinated alkylphosphate for advanced electrochemical capacitors

Abstract

A novel ternary electrolyte system that consists of 1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)amide (EMITFSA), LiTFSA, and tris(trifluoroethyl)phosphate (TFEP) has been developed as a nonflammable electrolyte for advanced electrochemical capacitors. The ionic conductivity of the system depended much on the electrolyte composition. Higher contents of EMITFSA gave higher conductivity in both binary EMITFSA-TFEP and ternary EMITFSA-LiTFSA-TFEP systems, whereas higher molar ratio of LiTFSA decreased the conductivity of the ternary system due to increased viscosity. In the systems keeping constant molar ratios of EMITFSA and LiTFSA, the conductivity showed maxima at ca. 70mol% of TFEP, where the concentration of the charge carriers (ions) and the mobility of the species are balanced. Brief tests of a symmetric cell composed of activated carbon electrodes revealed that the present ternary component system work as a nonflammable electrolyte in carbon-based electrochemical capacitors. © The Electrochemical Society of Japan, All rights reserved.