Dual‐Anion‐Dominated Electrolyte Design Manipulating Coordination and Boron‐Rich Interphase for Self‐Healing and Long‐Life Mg Metal Anode

Practical magnesium electrolyte options are limited by magnesium salt solubility in organic solvents and compatibility with metallic magnesium anode/cathode materials. Herein, a dual‐anion electrolyte system (YBTFC) consisting of 0.2 m magnesium chloride (MgCl2) and 0.4 m dibutylboron trifluoromethanesulfonate (TFBA) in 1,2‐Dimethoxyethane (DME) solvent to regulate the coordination chemistry and the interface structure is proposed. As an anion receptor, TFBA facilitates Lewis‐acid‐base reactions that foster the dissociation of insoluble MgCl2 and the formation of bi‐anions. The CF3SO3− modulates the solvation sheath to reduce DME coordination strength and penetrates Mg passive films, enabling reversible plating. Concurrently, the bulky B(CF3SO3)4− preferentially decomposes into boron‐rich interphases, enhancing Mg2⁺ transport kinetics while suppressing contact ion pair formation to extend operational temperature range. This combination of exceptional durability, low‐temperature operation (−30 °C), and inherent interfacial self‐healing is rarely observed in boron‐based electrolytes. Critically, the boron‐rich nature of YBTFC electrolyte facilitates B‐O interphase formation on both electrode interfaces. Accordingly, the Mg|YBTFC|Mo6S8 cell achieves a discharge specific capacity of 50 mAh g−1 and outstanding cycling stability of 4500 cycles at a 3C rate. Overall, tailoring Mg2+ coordination chemistry and constructing a boron‐rich interphase via a dual‐anion electrolyte provides a viable approach for realizing long‐life, high‐rate‐performance magnesium batteries.