Enhancing Kinetic Performance and Structural Stability of Na4Fe3(PO4)2(P2O7) 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 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.