Stabilizing Magnesium Anodes in Rechargeable Magnesium Batteries via Fluorinated Cyclic Ether Electrolyte Additive

ABSTRACT Rechargeable magnesium batteries (RMBs) are gaining significant attention as next‐generation energy storage due to high theoretical volumetric energy density, abundance, and low cost of Mg metal. However, practical development remains constrained by surface passivation, cycling instability, and scarcity of compatible electrolytes. In this study, we explore the incorporation of fluorinated cyclic ethers in Mg[Al(hfip) 4 ] 2 /diglyme‐based electrolytes. The addition of 10 vol.% fluorinated cyclic ether improves the electrochemical performance of Mg metal, evidenced by improved coulombic efficiency (98.2% to 99.1%), cycling life (15 vs 90 cycles of Mg plating/stripping at 2 mA cm −2 and 2 mAh cm −2 ), and oxidative stability (3.7 V to 4.1 V vs Mg 0 /Mg 2+ ). The optimized electrolyte also enables stable and prolonged cycling in high‐voltage Mg||polyaniline cells, achieving 75% capacity retention over 500 cycles at 1C. Operando electrochemical impedance spectroscopy, supplemented by scanning electron microscopy and X‐ray photoelectron spectroscopy, was employed to explain the improvement. The electrochemical bottleneck processes occurring on the Mg metal anode without fluorinated ether addition were determined to be incomplete electrode activation, high surface area deposits formed during plating, and passivation of such deposits. These findings highlight the potential of fluorinated ether additives in improving Mg metal performance and advancing electrolyte design for next‐generation RMBs.