Oxygen‐Vacancy Engineering of Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Enables Fast and Wide‐Temperature Sodium Storage

The polyanionic cathode Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) is regarded as a promising cathode for sodium‐ion batteries owing to its low cost, intrinsic safety, and robust framework stability. However, the strongly localized electronic structure and sluggish Na + transport kinetics impose coupled limitations on its rate capability and stability. Herein, we demonstrate a defect‐engineering strategy to activate coupled electronic‐ionic transport through the rational introduction of oxygen vacancies into NFPP. Combined experimental investigations and density functional theory calculations reveal that oxygen vacancies act as dual‐functional kinetic regulators by simultaneously reconstructing the local Fe–O electronic environment and facilitating Na + migration. The defect‐induced electronic redistribution narrows the bandgap and accelerates electron transport (over 7 times), while expanded Na + diffusion pathways and reduced migration energy barriers enable rapid ion diffusion (over 6 times). Consequently, the oxygen vacancy‐enriched NFPP cathode delivers exceptional cycling stability with 90.46% capacity retention after 7000 cycles at an ultra‐high rate of 20 C. This work establishes oxygen‐vacancy engineering as an effective strategy for coupled transport regulation in polyanionic cathodes and provides fundamental insights into defect‐mediated kinetic enhancement for advanced sodium‐ion batteries.