Synergistic halide and phosphate ester electrolytes for overcoming corrosion and interfacial challenges in magnesium batteries

Abstract

The practical development of rechargeable magnesium batteries is fundamentally limited by anode passivation, electrolyte-induced corrosion, and sluggish interfacial Mg²⁺ transport. Herein, we develop a universal electrolyte design strategy that exploits the synergy between halides and phosphate esters to address these long-standing challenges. Typically, the incorporation of SiBr₄ and tris(trimethylsilyl) phosphate (TMSP) extends the electrochemical stability window of the electrolyte from 2.75 to 3.94 V and reconstructs the solvation environment toward bis(trifluoromethanesulfonyl)imide (TFSI⁻) and TMSP-dominated coordination, significantly lowering the Mg²⁺ desolvation barrier. Preferential reduction of SiBr₄ and TMSP yields a cross-linked, inorganic-rich interphase comprising Mg₃(PO₄)₂, MgSiO₃, and MgBr₂, which enables fast Mg²⁺ transport and effectively suppresses parasitic reactions. Meanwhile, Mg₃(PO₄)₂ and MgSiO₃ within the interphase serve as robust scaffolds that immobilize soluble MgBr₂, further reinforcing interfacial stability. Besides, the electron-rich PO groups in TMSP further stabilize reactive SiBr₃⁺ intermediates, thereby preventing electrolyte acidification and corrosion. Consequently, Mg‖Mg symmetric cells cycle stably for 1800 h with a low overpotential of 0.14 V. Mg‖Mo cells reach a peak coulombic efficiency of 99.97% at 3.4 V after the activation process. Full cells with a Mo₆S₈ cathode deliver a capacity of 80 mAh g⁻¹ with only 0.08% fading over 500 cycles, and Mg‖polyaniline–intercalated V₂O₅ (PANI–V₂O₅) cells achieve 160 mAh g⁻¹ at a cut-off voltage of 2.6 V. This synergistic regulation concept is generalizable to other halides and phosphate esters, providing new mechanistic insights and a general framework for designing stable electrolytes for multivalent batteries.