Enhancing Kinetic Performance and Structural Stability of NaFe(PO)(PO) Cathode via La Doping Defect Engineering.

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 with a large ion radius at Na site has been designed, and the nano-micro architectural NaLa□Fe(PO)(PO)/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 not only broadens the Na transport channels but also reduces lattice stress and stabilizes the crystal bulk structure during long-term cycling for La as pillars. Additionally, high valence La doping enhances the effective charge carrier concentration and improves material conductivity. Consequently, the kinetic performance of Na migration is significantly enhanced. The optimal NaLa□Fe(PO)(PO)/C (NFPP/C-La3) exhibits the best electrochemical performance. The synthesized NFPP/C-La3 exhibits excellent rate performance (99.45 mAh g 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.