CONDUCTIVITY AND VISCOSITY OF SOLUTIONS OF LICF3SO3, LI(CF3SO2)2N, AND THEIR MIXTURES

The high level of charge delocalization of the Li(CF3SO2)2N anion reduces ion pairing in nonaqueous electrolytes. This overrides the higher viscosity of the imide-containing solutions making the electrolytes much more conductive than those containing LiCF3SO3, especially in low dielectric ether-based solvent systems commonly used in secondary lithium batteries. In more viscous solvent systems (1:1 propylene carbonate:1,2-dimethoxyethane) or at low temperatures, the imide affords less of an advantage in conductivity due to the more important role of viscosity. The cyclic imide Li-SO2-(CF2)4-SO2-N gives more viscous and less conductive solutions than does Li(CF3SO2)2N. The degree of dissociation in 1:1 PC:DME appears to be LiPF6 almost-equal-to LiAsF6 > LiClO4 almost-equal-to Li(CF3SO2)2N almost-equal-to Li-SO2-(CF2)4-SO2-N >> LiBF4 >> LiCF3SO3