A Mg2+/Li+ hybrid electrolyte with regulated interfacial chemistry for highly reversible and stable rechargeable magnesium batteries

Rechargeable magnesium batteries (RMBs) are promising candidates for next-generation energy storage systems because of their high energy density and intrinsic safety. However, severe Mg anode passivation and non-uniform Mg deposition in conventional electrolytes greatly undermine their reversibility and cycling stability. Herein, we develop a rationally designed dual-salt electrolyte based on Magnesium trifluoromethanesulfonate (Mg(OTf) 2 ) and LiCl in dimethoxyethane (DME), which overcomes the solubility limitations of conventional single-salt magnesium electrolytes. The optimized 0.3 M Mg(OTf) 2 + 0.5 M LiCl/DME electrolyte enables complete dissolution of both salts and delivers excellent electrochemical performance, including an expanded anodic stability window of up to 4.60 V (vs. Mg 2+ /Mg). Mg||Mg symmetric cells exhibit ultra-long cycling stability over 4000 h at 0.5 mA cm −2 with a low and stable overpotential of 0.15 V, while Mg||Ti cells achieve an average Coulombic efficiency (CE) of 98.5% over 3000 cycles at 0.5 mA cm −2 . In addition, Mg||MnO 2 full cells deliver an initial discharge capacity of 100 mAh g −1 at 1 C and retain 73.6% of the initial capacity after 5000 cycles. Mechanistic studies reveal that Cl¯ regulates the Mg 2+ solvation structure by entering the inner coordination sphere and promotes the formation of a MgCl 2 -rich solid electrolyte interphase (SEI), which suppresses parasitic reactions and enables dendrite-free, stable Mg deposition. These findings provide an effective electrolyte design strategy for developing high-performance and long-life rechargeable magnesium batteries.