A Bismuth-Based Protective Layer for Magnesium Metal Anode in Noncorrosive Electrolytes

Rechargeable magnesium (Mg) metal batteries are provided with potential advantages over lithium counterparts with respect to volumetric capacity and natural abundance (equivalent to low cost and sustainability). However, Mg metal anodes suffer from surface passivating behavior among numerous conventional Mg electrolytes, leading to irreversible Mg plating/stripping behavior. Herein, a modified Mg metal anode with a bismuth (Bi)-based artificial protective layer has been obtained via a facile solution process (soaking briefly in bismuth trichloride solution). This Bi-based protective layer is mainly composed of ion-conducting Bi metal and corresponding alloy and electronically insulating magnesium chloride. Various electrochemical tests and interface characterizations have proved that the protected Mg electrodes effectively inhibit the harmful parasitic reaction between Mg metal and noncorrosive Mg electrolyte, which further enables suppression of uneven growth during repeated Mg stripping/plating. More importantly, the assembled Mg–Cu2–xS and Mg–O2 full batteries utilizing the as-modified Mg anodes all deliver remarkably improved performance owing to the superior protection properties of a Bi-based artificial layer. These novel findings will inspire lot of efforts to modify the Mg metal anode with targeted surface coatings for high-performance rechargeable Mg batteries.