Mg Plating in Nonethereal Electrolyte Solutions: Fact or Misconception?

Abstract

Rechargeable Mg metal batteries (RMMBs) have garnered significant attention due to their outstanding electrochemical energy storage performance. Ether solvents are widely used as a primary component of RMMB electrolytes because of their excellent compatibility with Mg metal. However, the poor anodic stability of ethers hinders the development of high-energy-density RMMBs. To address this limitation, researchers have explored novel electrolyte formulations based on nonethereal solvents. However, the interpretation of reported results remains controversial due to a lack of solid experimental evidence confirming Mg plating reactions in such media. This article provides an overview of Mg electrochemistry in both ethereal and nonethereal electrolyte systems. Comprehensive cyclic voltammetry studies on the electrochemical Mg plating/stripping activity in various electrolyte systems reaffirm that only a limited range of solvents-including ethers, amines, and dialkylsulfones-support reversible Mg plating/stripping. In contrast, Mg plating is rarely observed in nitrile, amide, carbonate, and phosphate electrolytes, despite voltammograms exhibiting seemingly reversible responses. These findings caution researchers against assuming voltammetric responses correspond to Mg plating/stripping without solid evidence of Mg deposits. Finally, a protocol for assessing whether proposed (uncommon) electrolyte systems genuinely support Mg plating/stripping is presented.