Physical and electrochemical properties of phosphonium ionic liquids derived from trimethylphosphine

Room-temperature ionic liquids based on phosphonium cations derived from trimethylphosphine are presented. The bis(fluorosulfonyl)amide-based ionic liquids showed relatively low melting point, low viscosity and high conductivity when compared to those of the corresponding bis(trifluoromethylsulfonyl)amide-based ionic liquids. The bis(trifluoromethylsulfonyl)amide-based ionic liquids were thermally stable up to at least 380 °C. The voltammetric analysis suggested that the ionic liquids exhibited high electrochemical stability. The bis(fluorosulfonyl)amide-based ionic liquids showed larger redox response of lithium than the bis(trifluoromethylsulfonyl)amide-based ionic liquids.