Effects of Solvent Composition on Liquid Range, Glass Transition, and Conductivity of Electrolytes of a (Li, Cs)PF6 Salt in EC-PC-EMC Solvents

Electrolytes of 1 M LiPF6 (lithium hexafluorophosphate) and 0.05 M CsPF6 (cesium hexafluorophosphate) in EC-PC-EMC (ethylene carbonate-propylene carbonate ethyl methyl carbonate) solvents of varying solvent compositions were studied for the effects of solvent composition on the lower limit of liquid range, glass transition temperature (as a reflection of viscosity), and electrolytic conductivity. In addition, a ternary phase diagram of EC-PC-EMC was constructed, and crystallization temperatures of EC and EMC were calculated to assist the interpretation and understanding of the change of liquid range with solvent composition. A function based on the Vogel-Fulcher-Tammann equation was fitted to the conductivity data in their entirety and was plotted as conductivity surfaces in solvent composition space for more direct and clear comparisons and discussions. Changes of viscosity and dielectric constant of the solvents with their composition, in relation to those of the solvent components, were found to be underlying many of the processes studied.