A Passivation-Free Solid Electrolyte Interface Regulated by Magnesium Bromide Additive for Highly Reversible Magnesium Batteries

Highly reversible Mg battery chemistry demands a suitable electrolyte formulation highly compatible with currently available electrodes. In general, conventional electrolytes form a passivation layer on the Mg anode, requiring the use of MgCl 2 additives that lead to severe corrosion of cell components and low anodic stability. Herein, for the first time, we conducted a comparative study of a series of Mg halides as potential electrolyte additives in conventional magnesium bis(hexamethyldisilazide)-based electrolytes. A novel electrolyte formulation that includes MgBr 2 showed unprecedented performance in magnesium plating/stripping, with an average Coulombic efficiency of 99.26% over 1000 cycles at 0.5 mA/cm 2 and 0.5 mAh/cm 2 . Further analysis revealed the in situ formation of a robust Mg anode–electrolyte interface, which leads to dendrite-free Mg deposition and stable cycling performance in a Mg–Mo 6 S 8 battery over 100 cycles. This study demonstrates the rational formulation of a novel MgBr 2 -based electrolyte with high anodic stability of 3.1 V for promising future applications.