Phase diagrams, molar volumes, heat capacities, conductivities and viscosities of some lithium salts in aprotic solvents

Abstract

A general study of the properties of electrolytes in aprotic solvents was undertaken in order better to understand and control the factors which limit the performance of lithium batteries at low temperatures. The properties measured are solid-liquid phase diagrams, apparent molar volumes and heat capacities, conductivities and viscosities. Most of the data are for two electrolytes (LiBr and LiClO 4) in five aprotic solvents (1,2-dimethoxyethane, acetonitrile, γ-butyrolactone, dioxolane and to a lesser extent propylene carbonate). The low concentration thermodynamic data cannot be analysed unambiguously in terms of solvation effects because the Debye-Hückel limiting slope is unknown and it is difficult to account correctly for ion association. Our study shows that, according to the phase diagrams, the presence of solvates is largely responsible for the trends in the thermodynamic properties of the solutions at high concentration. When ion pairing is not a dominating factor, the trends in the conductivities of the lithium salts are qualitatively similar and tend to those of the molten salt or the molten solvates at high mole fractions. Lithium salts are strongly associated in 1,2-dimethoxyethane but at the same time are highly soluble. This electrolyte system has many unique properties.