Synergistic Engineering of Iron and Oxygen Vacancies Enables Fast Kinetics in Na 3.12 Fe 2.44 (P 2 O 7 ) 2 Cathodes for Superior Rate and Ultra‐Stable Sodium‐Ion Batteries

ABSTRACT High‐performance cathode materials are essential for the commercialization of sodium‐ion batteries (SIBs) in large‐scale energy storage. However, the NASICON‐type Na 3.12 Fe 2.44 (P 2 O 7 ) 2 cathode with promising structural stability and electrochemical properties has been plagued by sluggish electronic and ionic kinetics. To address this, we develop a series of superior rate and ultra‐stable Na 3.12‐2x Fe 2.44+x (P 2 O 7 ) 2 (NFPO) cathodes through a deliberate bulk defect‐engineering strategy that enables precise control of iron vacancies (V Fe ) and oxygen vacancies (V O ). Structural characterizations confirm that the material retains phase‐pure triclinic P ‐1 framework and the introduction of V Fe –V O divacancies, which induce an upshift of the valence band. Remarkably, density functional theory (DFT) calculations elucidate a dual‐functional mechanism, as V Fe and V O not only narrow the band gap but also drastically reduce the Na + migration barrier by 1.317 eV. Benefiting from this dual kinetic enhancement, the optimized NFPO@C (x = −0.1) cathode exhibits superior rate capability with a reversible capacity of 129.6 mAh g −1 at 1C, and exceptional cycling stability, retaining 99.6% of its capacity (100.8 mAh g − 1 ) after 12 000 cycles at 20C. This study establishes rational Fe and O divacancy engineering as an effective strategy to synergistically boost electronic/ionic transport, offering a generalizable paradigm for advanced polyanionic compounds in next‐generation energy storage.