High-entropy Electrolyte Enables High Reversibility and Long Lifespan for Magnesium Metal Anodes

Abstract

The stable cycling of Mg-metal anodes is limited by several problems, including sluggish electrochemical kinetics and passivation at the Mg surface. In this study, we present a high-entropy electrolyte composed of lithium triflate (LiOTf) and trimethyl phosphate (TMP) co-added to magnesium bis(trifluoromethane sulfonyl)imide (Mg(TFSI)2/1,2-dimethoxyethane (DME) to significantly improve the electrochemical performance of Mg-metal anodes. The as-formed high-entropy Mg2+-2DME-OTf−-Li+-DME-TMP solvation structure effectively reduced the Mg2+-DME interaction in comparison with that observed in traditional Mg(TFSI)2/DME electrolytes, thereby preventing the formation of insulating components on the Mg-metal anode and promoting its electrochemical kinetics and cycling stability. Comprehensive characterization revealed that the high-entropy solvation structure brought OTf− and TMP to the surface of the Mg-metal anode and promoted the formation of a Mg3(PO4)2-rich interfacial layer, which is beneficial for enhancing Mg2+ conductivity. Consequently, the Mg-metal anode achieved excellent reversibility with a high Coulombic efficiency of 98 % and low voltage hysteresis. This study provides new insights into the design of electrolytes for Mg-metal batteries.