An ultra-dilute Mg(TFSI)2 based electrolyte enabling reversible Mg metal anode

Mg metal anodes experience significant passivation of harmful side reactions in conventional electrolyte consisting of magnesium bis(trifluoromethane sulfonyl)imide (Mg(TFSI)₂) in 1,2-dimethoxyethane (DME), which critically impedes the advancement of high-performance rechargeable magnesium batteries. Herein, an innovative electrolyte system comprising an ultra-dilute 0.02 M Mg(TFSI)₂ in DME with 4-chlorobutyl methyl ether (CME) as co-solvent is strategically devised. This unique formulation effectively suppresses the formation of TFSI⁻-derived passivation byproducts while simultaneously facilitating the establishment of protective Cl-rich interphase, thereby achieving exceptional reversibility in Mg plating/stripping processes. Remarkably, Mg electrodes demonstrate stable cycling performance with a minimal overpotential of 70 mV at 0.1 mA cm⁻² in the optimized 0.02 M Mg(TFSI)₂-DME/CME electrolyte. More impressively, the system maintains reversible electrochemical operation for 400 h even at 2 mA cm⁻². This work presents a novel electrolyte formulation for overcoming the limitations of Mg metal anode in conventional Mg(TFSI)₂ based electrolytes, offering new perspectives for the development of next-generation rechargeable magnesium batteries.