The effect of cation structure to the physicochemical and electrochemical properties of quaternary ammonium ionic liquids

Abstract

Ionic liquids (ILs) based on aliphatic quaternary ammonium cations and bis(trifluoromethanesulfonyl)imidur anions (R1R2R3R4N+TFSI) are synthesized and physicochemically and electrochemically characterized for using as electrolytes in lithiumion batteries. The alkyl ammonium cation structure was investigated by changing the alky chain length of R1, R2, R3, R4 alkyl substituents. The results of thermal properties (melting point, crystallization, and glass transition temperature), viscosity, ionic conductivity, and electrochemical stability combined with HOMO/LUMO calculation explained the cation structure - properties relation as well as predicted the optimized ionic liquids for replacing the conventional electrolytes in lithium-ion batteries.