Alloying electrode coatings towards better magnesium batteries

Abstract : Mastering the metal-electrolyte interface is mandatory for the development of reliable rechargeable magnesium batteries. Nevertheless, most of the current electrolytes contain chlorides species to bypass the surface passivation of magnesium, making them corrosive to other cell components and potentially irrelevant for industrial application. Here, we demonstrate a novel approach to bypass the use of such electrolytes via the mediation of an alloy-type interface prepared by coating the surface of a magnesium electrode with liquid gallium. The chemical alloying induces the formation of a surface layer, mainly composed of the intermetallic Mg2Ga5, enabling significantly improved electrochemical performance with a simple chloride-free Mg(TFSI)2/DME electrolyte. Sensibly less-polarized and more stable plating/stripping is observed with symmetric cells, and longer cycle life is achieved in full cells with positive electrodes based on sulphur- and organic composites. This alloy-based surface protection opens the door to electrolytes firstly considered as non-compatible with magnesium metal, and consequently paves the way to the application of metal electrodes in practical magnesium batteries.