Exploiting a high-performance magnesium-fluoride battery prototype enabled by anion-receptor-mediated electrolyte.

Rechargeable magnesium batteries have emerged as a competitive next-generation energy storage technology owing to their abundant resources and inherent safety. The development of Mg batteries, especially regarding specific energy, has been compromised by the lack of high-performance positive electrodes. Here, we design an anion-receptor-mediated all-phenyl-complex electrolyte that enables the electrochemical cooperation between fluoride and magnesium, and develop a Mg | |FeO0.7F1.3 battery prototype. The anion receptor of tris(pentafluorophenyl)borane alters the chemical compositions of electrolyte and regulates its solvation structures via dipole-ion and dipole-dipole interactions with chloride-based ionic species and solvent molecules. The tailored electrolyte mitigates the chloride-originated anodic instability and upgrades the desolvation kinetics of cationic carriers. The dual-cation co-driven conversion-type Mg | |FeO0.7F1.3 batteries exhibit the high reversible capacities in a wide temperature range, delivering 354 mAh g⁻¹ at 25 °C and 177 mAh g⁻¹ at -20 °C. Moreover, the high reversibility over 500 cycles with a low capacity decay rate of 0.054% per cycle can be realized when confined to intercalation chemistry. This work provides an anion receptor-based electrolyte design strategy that expands positive material horizons for magnesium batteries to high-energy fluorides.