Enhancing Kinetic Performance and Structural Stability of Na ₄ Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ ) Cathode via La Doping Defect Engineering

Abstract Due to the strong electronegativity of P in the anion group and the strong P─O covalent bond, NFPP exhibits low electronic and ionic conductivity, hindering its rate capability. A doping modification strategy of selecting La ³⁺ with a large ion radius at Na site has been designed, and the nano‐micro architectural Na _4‐3x La _x □ _2x Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ )/C (0≤x≤0.04) cathode material with Na vacancies is successfully synthesized via a scalable preparation route. Introducing positively charged substitutional point defects and charged vacancies through doping La ³⁺ not only broadens the Na ⁺ transport channels but also reduces lattice stress and stabilizes the crystal bulk structure during long‐term cycling for La ³⁺ as pillars. Additionally, high valence La ³⁺ doping enhances the effective charge carrier concentration and improves material conductivity. Consequently, the kinetic performance of Na ⁺ migration is significantly enhanced. The optimal Na _3.91 La _0.03 □ _0.06 Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ )/C (NFPP/C‐La3) exhibits the best electrochemical performance. The synthesized NFPP/C‐La3 exhibits excellent rate performance (99.45 mAh g ⁻¹ at 20 C) and long‐term cycle stability (92.36% of capacity retention over 1000 cycles at 10 C). These results provide the importance and prospect of the high valence ion doping for NFPP/C with high rate stability.