Solution-Derived Artificial In/MgI2 Interphase Enables Kinetically Stable Mg Metal Anodes

Rechargeable magnesium batteries (RMBs) emerge as a promising alternative to postlithium battery systems due to their intrinsic advantages of magnesium metal anodes. However, the lack of a stable solid electrolyte interphase (SEI) on magnesium severely limits their interfacial reversibility and cycling life. Herein, we propose a simple solution-based surface engineering strategy to construct a robust artificial SEI layer on Mg metal through displacement reactions between Mg and InI3. The resulting In/MgI2@Mg electrode features a homogeneous and compact interphase composed of electrochemically favorable In, MgI2, and InMg alloy. This artificial SEI significantly enhances Mg2+ stripping/plating reversibility, lowers interfacial resistance, and suppresses passivation. The modified Mg anode exhibits a cycling lifespan of 725 h with a low overpotential of ∼80 mV, excellent rate performance, and a reduced activation energy of 17.92 kJ mol–1. When paired with a Mo6S8 cathode, the In/MgI2@Mg-based RMB delivers a high reversible capacity of 74.4 mAh g–1 (higher than 54.7 mAh g–1 of the bare Mg-based RMB), a reduced voltage hysteresis of 0.2 V, and superior Coulombic efficiency over extended cycling. This work highlights the effectiveness of iodide-mediated interfacial chemistry for stabilizing Mg metal anodes.