Physicochemical and Electrochemical Properties of Lithium Trifluoromethanesulfonate Solutions in Sulfolane Mixtures of 1.3-Dioxolane

Abstract

A study is performed of the physicochemical properties (specific ion conductivity, viscosity, and density) of 1.0M solutions of LiSO₃CF₃ in mixtures of sulfolane and 1.3-dioxolane in the 30–50°C range of temperatures. It is shown that the isotherms of specific ion conductivity pass through a maximum at contents of 1.3-dioxolane around 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 fall as the content of 1.3-dioxolane and temperature rise. It is concluded that the activation energies of conductivity and viscous flow fall as the content of 1.3-dioxolane grows. NMR spectroscopy is used to estimate the self-diffusion coefficients of all components of the studied electrolyte solutions and calculate the transport numbers of lithium cations. It is been established that the transport numbers of lithium cations change nonlinearly, depending on the composition of the solution. The maximum value (0.56) is reached at a sulfolane : 1.3-dioxolane ratio of around 2 : 3, which correlates with the position of the maximum on the conductivity isotherm. It is shown that the melting points for 1.0 M solutions of LiSO₃CF₃ in mixtures of sulfolane and 1.3‑dioxolane fall as the content of the latter rises. It is noted that when the content of 1.3-dioxolane is more than 50 mol %, electrolyte solutions are in a liquid phase at temperatures below −70°C.