Breaking “Fe 3+ Trap” to Reconstruct Electron/Ion Transport Networks in Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 for High‐Performance Sodium‐Ion Batteries

ABSTRACT Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 is a promising cathode material for sodium‐ion batteries due to its low cost, high safety, and long cycle life. However, its practical application is seriously constrained by the inherent low electrical conductivity and sluggish diffusion kinetics. This study identifies the Fe 3+ trap exist within Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 , which directly undermine the conduction network and do not participate in the reversible redox processes. Therefore, this study proposes a valence regulation strategy to restore and further enhance the electron/ion transport network. The formation of the Fe 3+ trap is effectively inhibited by Sn/Cl co‐modification. Due to the low energy level of 4d orbitals of Sn, the local electronic environment is modulated, thereby enhancing the Fe─O d‐p orbitals hybridization. Simultaneously, due to the lower electronegativity of Cl compared to O, the electrostatic attraction between Cl and Na is weaker, thus enhancing the Na + diffusion kinetics. Based on this, the optimized sample delivers high‐rate performance (84.65 mAh g −1 at 100 C) and superior cycle stability (90.35% after 5000 cycles at 20 C), This study provides a novel theoretical perspective for resolving the issue of mixed‐valuence state of metal‐ion in cathode materials.