Physicochemical and electrochemical properties of lithium trifluoromethanesulfonate solutions in sulfolane-1.3-dioxolane mixtures

The physicochemical properties (specific ion conductivity, viscosity, and density) of 1.0M solutions of LiSO3CF3 in sulfolane – 1.3-dioxolane mixtures in the temperature range of 30–50°C are studied. The specific ion conductivity isotherms is shown to pass through their maximum at a 1.3-dioxolane content of about 60 mol % (1.75×10–3 Ω–1 cm–1, 30°C). It is found that the viscosity and corrected (for viscosity) conductivity of the studied solutions decrease as the 1.3-dioxolane content increases and the temperature grows. It is concluded that the activation energies of the conductivity and viscous flow, as well as their ratio, decrease as the 1.3-dioxolane content increases. Self-diffusion coefficients of all components of the studied electrolyte solutions are estimated by NMR spectroscopy, and lithium cation transport numbers are calculated. The transport number of lithium cation is found to vary nonlinearly depending on the solution composition, viz. the maximum value (0.56) is reached when the ratio of sulfolane:1.3-dioxolane ≈ 2:3, which correlates with the position of the maximum on the conductivity isotherm. The melting points of 1.0M LiSO3CF3 solutions in mixtures of sulfolane with 1.3-dioxolane are shown to decrease as the content of the latter increases. It is noted that when the content of 1.3-dioxolane is more than 50 mol %, electrolyte solutions are in the liquid phase state at temperatures below –70°С.