Dimethylthioformamide-derived ionic liquids: Synthesis, characterization and application as supercapacitor electrolyte

Abstract

Amide-derived ionic liquids (ILs), especially dimethylformamide (DMF)-derived ILs, have been recently attractive as potential electrolyte with high conductivity and decent electrochemical window, but very poor thermal stability. Here dimethylthioformamide (DMTF) that contains a sulfur atom instead of the oxygen atom in DMF was used to prepare a series of new ILs. DMTF-based ILs exhibit significantly improved thermal stability, with thermal decomposition temperature up to 351 °C, which is about 150 °C higher than that of their DMF counterparts. All of the DMTF ILs are liquid at ambient temperature and show moderate to good physicochemical properties, including density, refractive index, surface tension, viscosity and conductivity. The dynamic viscosity and conductivity obey both the Arrhenius and VFT temperature dependence. Although the electrochemical properties, i.e. conductivity and electrochemical window, of DMTF ILs are inferior to DMF ILs, [C1-DMTF]NTf2 with relatively high conductivity and wide electrochemical window gives decent performance as supercapacitor electrolyte, with specific capacitance of 90 F·g−1 at a stable operating voltage of 2.0 V.