Sulfonium Bis(trifluorosulfonimide) Plastic Crystal Ionic Liquid as an Electrolyte at Elevated Temperature for High-Energy Supercapacitors

This study describes the use of the ionic liquid trimethylsulfonium bis(trifluorosulfonimide) [Me3S][TFSI] as an electrolyte for carbon-based supercapacitors at temperatures up to 80 degrees C. [Me3S] [TFSI] is synthesized by a metathesis reaction, possesses a low melting point (T-m = 45.5 degrees C), and presents crystal plastic behavior indicated by a strong organizational structure with many possible conformations corresponding to several solid-solid phase transitions Ts-s. Furthermore, [Me3S][TFSI] is thermally stable up to T = 280 degrees C and presents a high conductivity up to 20.42 mS cm(-1) at 80 degrees C and a low viscosity, 3 mPa s, at the same temperature. The combination of a good cycling ability with high capacities up to 150 F g(-1) at elevated voltage and temperature, i.e., Delta E = 3 V, T = 80 degrees C, enables the realization of supercapacitors with high specific energies at high temperatures.