Structure−Properties Relationships of Lithium Electrolytes Based on Ionic Liquid

Abstract

Low-melting ionic liquid, IL, based on small aliphatic quaternary ammonium cations ([R(1)R(2)R(3)NR](+), where R(1), R(2), R(3) = CH(3) or C(2)H(5), R = C(3)H(7), C(4)H(9), C(6)H(13), C(8)H(17), CF(3)C(3)H(6)) and imide anion were prepared and characterized. The physicochemical and electrochemical properties of these ILs, including melting point, glass transition, and degradation temperatures; viscosity; density; ionic conductivity; diffusion coefficient; and electrochemical stability, were determined. Heteronuclear Overhauser NMR spectroscopy experiments were also performed to point out the presence of pair correlation between the different moieties. The LiTFSI addition effect on the IL properties was studied with the same methodology. Some nanoscale organization with segregation of polar and apolar domains was observed. ILs with small alkyl chain length or fluorinated ammonium exhibit very high electrochemical stability in oxidation.