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

## TL;DR

A new electrolyte design for magnesium batteries improves stability and performance by combining halides and phosphate esters to reduce corrosion and enhance ion transport.

## Contribution

A universal electrolyte strategy using synergistic halides and phosphate esters to address Mg2+ transport and interfacial stability in magnesium batteries.

## Key findings

- The electrolyte extends the electrochemical stability window from 2.75 to 3.94 V.
- Mg‖Mg symmetric cells cycle stably for 1800 h with a low overpotential of 0.14 V.
- Full cells with Mo6S8 cathodes show 80 mAh g−1 capacity with minimal fading over 500 cycles.

## 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 P

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O 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.

A synergistic halide and phosphate ester electrolyte regulates Mg2+ solvation and forms a robust inorganic-rich interphase, suppressing corrosion, enhancing Mg2+ transport, and providing a general framework for high-voltage multivalent batteries.