Insights into Hyper-Efficient Construction of Compact Artificial SEI for Highly Reversible Mg Metal Anode

The practical applications of Mg metal anodes in rechargeable magnesium batteries (RMBs) have been seriously hindered due to the unstable anode interface. Herein, a simple and hyper-efficient hydrolysis of metal chloride strategy is proposed to obtain a dense layer of artificial SEI on the surface of the Mg anode. Based on the variations of relative compactness density (rρ_c), the morphology and electrochemical properties of the artificial SEI layer can be precisely regulated. Moreover, the surface-reconstructed In/MgCl₂@Mg electrode can achieve an ultralong cycle life of 1500 cycles at a current density of 3 mA cm^–2 and 1 mA h cm^–2 as well as a low overpotential (0.25 V). Consequently, a stable cycle capacity can also be maintained at 1C after 1000 cycles in full cell configurations, matching with the Mo₆S₈ cathode. This study provides a novel design concept and quantitative criteria for the specific preparation of efficient Mg anodes.