An artificial interphase enables the use of Mg(TFSI)2-based electrolytes in magnesium metal batteries

Due to the good safety and high energy density, rechargeable Mg-metal batteries (RMMBs) have been regarded as a potential competitor of Li-metal batteries (LMBs). However, the Mg(TFSI)2-based conventional electrolytes will cause large overpotential in reversible plating/stripping attributed to the high ion transport impedance of the electrolyte decomposition products. Here, an artificial interphase composed of amorphous (a-) MgCl2@polymer on the Mg-metal surface is prepared by in-situ chemical reaction of metallic Mg with H3PO4 and SiCl4 in sequence, and can effectively inhibit the electrolyte decomposition and facilitate Mg2+ transport, which plays the role of solid electrolyte interface (SEI) on Mg anode. The Mg-Mg symmetrical cell with modified Mg electrode exhibits lower overpotential (~0.25 V) and interfacial impedance than bare Mg electrode in 0.5 M Mg(TFSI)2/DME electrolyte. The voltage hysteresis in the Mg-S and Mg-Mo6S8 batteries with the modified Mg anode is greatly improved compared to bare Mg anode. This work provides a new idea for future applications of passivation-free Mg-metal anode technology in the MMBs based on conventional electrolytes.