The theoretical volumetric capacity of Mg-ion batteries is far higher than state-of-the-art Li-ion batteries (3833mAh/cm³ for Mg vs. 850 mAh/cm³for Li). The development of suitable Mg-conductive electrolytic solutions has been a major barrier to Mg-ion technology: at present there is a need for liquids with wide anodic stability windows, whose interfaces allow plating and stripping of Mg with high coulombic efficiency and low deposition overpotential.

We have produced a number of Mg-conductive electrolytes by direct reaction of inorganic chloride salts with suspensions of Mg powder in nonaqueous solvents. The Mg-carrying cation in these electrolytes is presumably similar to the one that provides conductivity in the recently discovered magnesium aluminum chloride complex (MACC) electrolyte [1,2], but there is apparently no metal-complex anion, and no need for an auxiliary Lewis acid during synthesis.

The chemically synthesized Mg-conductive electrolyte formed by reacting ZnCl₂ with Mg in tetrahydrofuran is stable up to 3.0 V vs. Mg/Mg²⁺, and produces an ionic conductivity of 0.24 mS/cm at room temperature. Cyclic voltammetry shows reversible Mg plating and stripping on platinum. The deposition overpotential of freshly synthesized electrolyte is below 200mV, and the coulombic efficiency of plating and stripping approaches 100%. Over a period of a week, the coulombic efficiency of plating/stripping only decays by 5%; the deposition overpotential increases more substantially with aging, however. Electrochemical Impedance Spectroscopy (EIS) was used to analyze the transport properties of the solutions. Other properties, such as composition and structure of electrolytic solutions, the morphology of Mg deposits, and thermal stability will be also discussed to explore the precise mechanism by which this and Mg electrolytes formed by other chloride salts form, as well as their feasibility for future magnesium battery applications.

1. Barile, Christopher J. et al. J. Phys. Chem. C 118.48 (2014): 27623-27630
2. Vardar, Gulin, et al. Chem. Mater. 28.21 (2016): 7629-7637