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 chloride 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. Chemical alloying induces the formation of a surface layer, mainly composed of 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 at a current density of 0.1 mA cm⁻², and longer cycle life is achieved in full cells with positive electrodes based on sulphur and organic composites. This proof-of-concept offers room for improvement in the coating protocol and could be tuned with other liquid metals. More importantly, it opens the door to electrolytes previously considered as non-compatible with magnesium metal, and consequently paves the way for the application of metal electrodes in practical magnesium batteries.