Unlocking Ultra‐Long Cycling Stability in Fluorophosphate Cathodes via Electrostatic Interaction Regulation and Enhanced V─O Covalency

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ABSTRACT Polyanionic Na 3 (VO) 2 (PO 4 ) 2 F is a promising cathode for sodium‐ion batteries (SIBs) due to its stable structural framework and high operating voltage. However, its practical application is hindered by low electronic conductivity and sluggish Na + diffusion kinetics, which originate from the strong Coulombic attraction between Na + and the framework anions, and the Na + ‐Na + repulsion. In this study, we propose a novel anion engineering strategy involving simultaneous Br doping and Na vacancy. Theoretical and experimental analyses reveal that the partial substitution of O 2− with less electronegative Br − induces local charge redistribution, which enhances V 3d─O 2p orbital hybridization and strengthens V─O covalent bonds, improving structural stability and narrowing bandgap. The resulting charge compensation creates sodium vacancies that alleviate electrostatic repulsion among Na + ions, facilitating Na + diffusion. Moreover, Br doping expands interlayer spacing and mitigates charge transfer resistance. Consequently, the electrode exhibits exceptional long‐term cyclability (62.07 mAh g −1 after 90,000 cycles at 20 C) and superior rate capability (85.93 mAh g −1 at 100 C). The full cell paired with a hard carbon achieves high energy density and excellent cycling stability. This work provides a feasible and effective anionic doping approach for designing long‐life SIBs.

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