Low viscous and highly conductive phosphonium ionic liquids based on bis(fluorosulfonyl)amide anion as potential electrolytes

The physical and electrochemical properties of room-temperature ionic liquids based on quaternary phosphonium cations together with a bis(fluorosulfonyl)amide anion are presented in this report. The bis(fluorosulfonyl)amide-based phosphonium ionic liquids were relatively low-melting, low viscous and highly conductive when compared to those of the corresponding bis(trifluoromethylsulfonyl)amide-based ionic liquids. Particularly, the ionic liquids containing a methoxy group in the phosphonium cations indicated very low viscosities and high conductivities. The FSA-based phosphonium RTILs were thermally stable up to nearly 300 °C. The voltammetric analysis suggested that the bis(fluorosulfonyl)amide-based phosphonium ionic liquids showed high electrochemical stability similar to the corresponding bis(trifluoromethylsulfonyl)amide-based ionic liquids.