Reversible Mg-Metal Batteries Enabled by a Ga-Rich Protective Layer through One-Step Interface Engineering

Practical applications of Mg-metal batteries (MMBs) havebeen plaguedby a critical bottleneck-he formation of a native oxide layeron the Mg-metal interface-which inevitably limits the use ofconventional nontoxic electrolytes. The major aim of this work wasto propose a simple and effective way to reversibly operate MMBs incombination with Mg-(TFSI)(2)-diglyme electrolyte by forminga Ga-rich protective layer on the Mg metal (GPL@Mg). Mg metal wascarefully reacted with a GaCl3 solution to trigger a galvanicreplacement reaction between Ga3+ and Mg, resulting inthe layering of a stable and ion-conducting Ga-rich protective filmwhile preventing the formation of a native insulating layer. Variouscharacterization tools were applied to analyze GPL@Mg, and it wasdemonstrated to contain inorganic-rich compounds (MgCO3, Mg-(OH)(2), MgCl2, Ga2O3, GaCl3, and MgO) roughly in a double-layered structure.The artificial GPL on Mg was effective in greatly reducing the highpolarization for Mg plating and stripping in diglyme-based electrolyte,and the stable cycling was maintained for over 200 h. The one-stepprocess suggested in this work offers insights into exploring a cost-effectiveapproach to cover the Mg-metal surface with an ion-conducting artificiallayer, which will help to practically advance MMBs.