Robust Solid-Electrolyte Interphase via Si–O Molecular Engineering for Durable Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) remain limited by interfacial instability under large areal capacity and current density, where dissolution of solid-electrolyte interphase (SEI) components remains underexplored. Here, we identify solvation-driven dissolution of organic interphase species as a key origin of rapid cell failure and address it through a Si–O molecular engineering strategy using tris(trimethylsilyl) phosphate (TMSP). TMSP sterically regulates the Mg2+ solvation, weakens solvent coordination, and increases anion participation, thereby reducing unstable solvent-derived organics. Meanwhile, its preferential interfacial decomposition yields silicate/silicide and dissolution-resistant organosilicon species, forming a stronger, smoother, and more dissolution-resistant SEI. The optimized electrolyte enables reversible Mg||Mg cycling for over 3400 h at 20 mA cm–2 and 4 mAh cm–2, while maintaining a wide operating-temperature range from −20 to 55 °C and broad cathode compatibility. This work reveals SEI dissolution as a critical degradation pathway and provides a cost-effective electrolyte design strategy for durable RMBs.