Zinc Blende Magnesium Sulfide in Rechargeable Magnesium-Sulfur Batteries

Magnesium-sulfur batteries are one of the most promising next-generation battery systems due to their high energy density, low cost, and high level of safety. However, the reaction mechanisms are not well understood, and in particular, the discharge reaction products have not yet been identified. Here we show that zinc blende magnesium sulfide is observed as a reaction product after discharging in magnesium-sulfur batteries. When magnesium reacts electrochemically with sulfur in a sulfone-based magnesium electrolyte, sulfur becomes amorphous consisting of magnesium and sulfur in the cathode. In this study, it has been found that the amorphous material has an unusual local structure, which is not related to the most stable rock salt phase of magnesium sulfide but rather the metastable zinc blende phase. It was indicated that this material realizes the reversibility of magnesium-sulfur batteries.