(25f) Magnesium Deposition from Sulfone-Ether Electrolytes

Rechargeable batteries with magnesium metal anodes are of recent research interest due to their potential for high energy density and the widespread availability of magnesium. Magnesium electrolyte research has focused almost exclusively on ethereal solvents. Here, we demonstrate that select electrolytes based on sulfone-tetrahydrofuran mixtures are able to support reversible magnesium metal electrodeposition and dissolution with reasonably low underpotentials and overpotentials, respectively, and with significantly enhanced thermal stability relative to a pure tetrahydrofuran electrolyte. Analogous formulations based on different sulfones, however, do not facilitate deposition or dissolution. We demonstrate via electrospray ionization mass spectrometry (ESI MS) and nuclear magnetic resonance spectroscopy (NMR) that both a mixed solvation shell (sulfone plus tetrahydrofuran) and a sufficiently high ratio of Mg₂Cl₃⁺ cations to MgCl⁺ cations appears necessary to support reversible behavior.