Change of conductivity with salt content, solvent composition, and temperature for electrolytes of LiPF6 in ethylene carbonate-ethyl methyl carbonate

We measured the electrolytic conductivities of the electrolytes of LiPF6 in ethylene carbonate-ethyl methyl carbonate at different salt contents, solvent compositions, and temperatures in the ranges of their practical values. To these data, we fitted a fourth degree trivariate polynomial and obtained a close fit. We then plotted this function as surface and contour plots in the coordinates of salt content and solvent composition for a series of temperatures. These plots showed the change of conductivity with the simultaneous changes of salt content and solvent composition and the influence of temperature on this change, thus mapping the locations for the optimal combinations of salt content and solvent composition for maximum conductivity of the electrolytes at desired temperatures. Here we also discuss and interpret qualitatively the trends found in the change of conductivity with salt content, solvent composition, and temperature, based on the dependency on the same variables of these three factors: the number of dissociated ions in the electrolyte, the dielectric constant of the solvent. and the viscosity of the electrolyte. (C) 2001 The Electrochemical Society.