Evaluation of the Solution Properties of Binary Mixtures of Dimethyl Sulphoxide and Tetrahydrofuran for Magnesium-Ion Battery Electrolyte

Abstract

This study evaluates the solution properties of binary dimethyl sulphoxide (DMSO)/tetrahydrofuran (THF) mixtures containing magnesium perchlorate (Mg(ClO₄)₂) for potential application as magnesium-ion battery electrolytes. Binary DMSO/THF mixtures were prepared over DMSO mole fractions of 1.00, 0.85, 0.75, 0.50, 0.25, 0.15 and 0.00, and measurements were performed from 25 to 55 °C. Mg(ClO₄)₂ concentrations of 0.1, 0.5, 1.0 and 2.0 M were investigated. Density, kinematic and dynamic viscosity, as well as electrical/molar conductivity were measured. On the other hand dielectric constant, critical ion-pair distance, Grunberg–Nissan interaction parameter and excess properties were calculated. Density and viscosity decreased generally with increasing THF fraction and temperature, whereas salt addition increased the viscosity of the electrolyte solutions. The highest reported molar-conductivity value in the supplied dataset was 3.025 S m² mol⁻¹ at X_DMSO = 0.50 for 1.0 M Mg(ClO₄)₂. At 25 °C, the salt-containing mixtures   were predominantly negative for excess molar volumes, although small positive deviations occurred at selected compositions and concentrations. Excess viscosity and excess Gibbs free energy of activation also showed composition- and concentration-dependent deviations. The dielectric constant decreased with increasing THF fraction, while the calculated critical distance and Grunberg–Nissan parameter varied with composition. These results indicate that combining DMSO and THF can modify the balance between ion dissociation and mobility, although the optimum composition should be regarded as system-specific.