Bifunctional Synergistic Mg@SnSb SEI for Low Interfacial Reaction Energy Barriers and Stable Cycling of High‐Performance Rechargeable Magnesium Batteries

Abstract The formation of a stable passivation layer and the strong electrostatic interactions impede the diffusion of magnesium ions (Mg 2+ ) at the Mg anode surface. Construction of an artificial solid electrolyte interphase (SEI) layer presents a promising approach to overcome these limitations. This study develops a synergistic and structurally stable Mg@SnSb SEI through an in situ reaction between the anode and a Tin trifluoromethanesulfonate and antimony chloride (Sn(OTf) 2 ‐SbCl 3 ‐based) electrolyte, featuring a low LUMO (lowest unoccupied molecular orbital). The in situ formed multi‐phase SEI effectively reduces the interfacial reaction barriers and facilitates Mg 2+ diffusion during both the plating and the stripping processes. Additionally, the formation of nano‐grained microstructure enhances the uniformity of Mg plating/stripping and suppresses the decomposition of the OTf anions and DME solvent molecules. The Mg anode incorporating the Mg@SnSb SEI exhibits an exceptionally low overpotential of less than 0.07 V and an ultra‐long cycle life exceeding 1500 h. In full‐cell tests using Mg@SnSb||Mo 6 S 8 , the system achieved exceptional electrochemical performance, maintaining over 94% of its initial capacity after more than 400 cycles.