Interphase Self‐Optimization Enables Stable Magnesium Anode in Hydrogel Electrolyte

ABSTRACT Magnesium metal is a promising anode material for high‐energy and cost‐effective aqueous batteries, but the issue associated with corrosion reaction and surface passivation is more severe than the commonly studied metals such as Zn. Current strategies either rely on aggressively dissolving corrosion products with the sacrifice of active metal or attempt to suppress passivation with limited effect. In this work, a dynamic evolution of a self‐optimized interphase on the Mg anode surface is triggered through formulating a tridentate chelant and MgCl 2 based hydrogel electrolyte. At the anode‐electrolyte interface, chelant‐mediated solvation mitigates the water‐induced parasitic reactions, kinetically enabling a complete conversion of the MgO byproduct into a magnesium oxychloride interphase. This interphase is dynamic stable and Mg 2+ ‐conductive, rendering reversible Mg plating/stripping for over 600 h at 0.1 mA cm −2 in symmetric cells. Furthermore, 2 V‐class hybrid cells by paring the Mg anode with three different cathodes show stable charges and discharges up to 500 cycles (capacity retention is 69%).