Synthesis of new fluorine-containing room temperature ionic liquids and their physical and electrochemical properties

Abstract An improved synthesis of fluorine-containing room temperature ionic liquids (FRTILs) is described. Twelve FRTILs are synthesized, in which the fluorinated cations based on N -methyl pyrrolidinium (MPy), 1-methly imidazolium (MIm) and diethylsulfide (DES) are associated with anions, such as dicyanamide (DCA) or bis(trifluoromethane sulfonyl)imide (TFSI). The molecular structures of these FRTILs were confirmed by FT-IR, 1 H-NMR, 13 C-NMR and elemental analysis. The FRTILs have been investigated for their potential as electrolyte solvents, especially for lithium-sulfur (Li-S) batteries. Thermal behaviors were also studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) showing excellent thermal stability, exceeding 150 °C, for all FRTILs. Some of their physicochemical properties were determined, including density, flammability, viscosity, and miscibility with polar and nonpolar solvents. Due to the high viscosity of FRTILs, two low viscosity ILs (co-solvent thinners), [MImEt] [DCA] and [MImEt] [TFSI], have been synthesized and used to dilute the FRTILs. The resulting ternary electrolyte systems, LiTFSI in 1:1 wt.% FRTILs/thinner, were characterized by their ionic conductivity and electrochemical stability.