Asymmetric sulfonium-based molten salts with TFSI− or PF6− anion as novel electrolytes

A novel series of molten salts based on asymmetric sulfonium cations ([R1R2RS]+, wherein R1, R2 = CH3, R = C2H5, n-C4H9, n-C6H13, n-C8H17, corresponding to S112+, S114+, S116+, S118+, respectively) with TFSI− or PF6− anion as novel electrolytes have been prepared and characterized. Some of the physical and electrochemical properties of the salts, including thermal property, density, solubility in common solvents, conductivity, and electrochemical stability have been investigated. Three types of phase transition behavior and two types of decomposition behavior have been observed for these molten salts on heating. In the case of [R1R2RS]+ PF6−, which have much higher solubility in water compared to those with imidazolium cation which have only alkyl groups. In addition, the Arrhenius equation approximately describes the relationship between conductivity and temperature for some of these sulfonium-based molten salts with TFSI− anion in the high temperature region studied. The electrochemical windows are approximately 4.1 V for S112TFSI and S114TFSI, which are liquid at room temperature (25 °C).