Magnesium bromide/aniline magnesium bromide sustained-release layer enables highly efficient Mg metal anode

• The reaction of Mg and p-bromoaniline is used to constructs a functional layer • The functional layer sustained-releases MgBr 2 /RMgBr to optimize the anode interphase. • The study on the effect of MgBr 2 dissolution on solvation structure of electrolyte. • The electrochemical performance improvement by sustained-release layer strategy. The application of conventional electrolytes in rechargeable magnesium batteries is obstructed by their incompatibility with Mg metal anode. Herein, a functional layer with sustained-release effect is constructed on Mg metal by chemical reaction between p-bromoaniline and Mg to realize compatibility between conventional electrolyte and Mg anode in the long cycle. It is proved that the functional layer contains a large amount of MgBr 2 , aniline magnesium bromide and their derivatives, which are released into the electrolyte. The experiment and theoretical calculation certified that the dissolved MgBr 2 alters the Mg 2+ solvation structure distribution and accelerates the desolvation process dramatically. Compared to adding additives to the electrolyte directly, the residual sustained-release layer maintains the freshness of SEI and is more conducive to the formation of Br − coordinated Mg 2+ . As a result, Mg electrodes with this functional layer maintains a low polarization voltage of 0.2–0.4 V at a high current density of 1.0 mA cm −2 above 1000 h without short circuit. The Mg||Mo 6 S 8 battery presents a low overpotential of ∼ 0.25 V during discharge/charge and remains 68.6 mAh/g after 300 cycles at the current density of 25 mA g −1 , confirming the practicability of this strategy.