Structure and compatibility of a magnesium electrolyte with a sulphur cathode

TLDR

Magnesium metal is a promising anode for rechargeable batteries, but its coupling with low‑cost sulphur cathodes requires a non‑nucleophilic electrolyte. The study demonstrates that crystallizing the active species from hexamethyldisilazide magnesium chloride and aluminum trichloride produces a non‑nucleophilic electrolyte. Crystallization identified the electroactive species [Mg₂(μ‑Cl)₃·6THF]⁺ and improved voltage stability and coulombic efficiency, while XPS confirmed successful sulphur–magnesium sulfide conversion.

Abstract

Magnesium metal is an ideal rechargeable battery anode material because of its high volumetric energy density, high negative reduction potential and natural abundance. Coupling Mg with high capacity, low-cost cathode materials such as electrophilic sulphur is only possible with a non-nucleophilic electrolyte. Here we show how the crystallization of the electrochemically active species formed from the reaction between hexamethyldisilazide magnesium chloride and aluminum trichloride enables the synthesis of a non-nucleophilic electrolyte. Furthermore, crystallization was essential in the identification of the electroactive species, [Mg2(μ-Cl)3·6THF]+, and vital to improvements in the voltage stability and coulombic efficiency of the electrolyte. X-ray photoelectron spectroscopy analysis of the sulphur electrode confirmed that the electrochemical conversion between sulphur and magnesium sulfide can be successfully performed using this electrolyte. Magnesium is an ideal rechargeable battery anode material, but coupling it with a low-cost sulphur cathode, requires a non-nucleophilic electrolyte. Kimet al. prepare a non-nucleophilic electrolyte from hexamethyldisilazide magnesium chloride and aluminium trichloride, and show its compatibility with a sulphur cathode.