Y‑Doped Na₄Fe₃(PO₄)₂(P₂O₇) as a High-Performance Cathode Material for Sodium-Ion Batteries

The Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) cathode material for sodium-ion batteries (SIBs) is modified through a facile yttrium (Y)-doping approach. The crystal structures, surface morphologies, and electrochemical performances of the pristine and Y-doped samples are comparatively investigated. The results indicate that the structure and morphology of the material are almost unchanged after Y doping. Doping with an appropriate amount of Y can enhance the electronic conductivity and electrochemical kinetics of the material, leading to superior electrochemical performance. Among the four samples prepared with different Y-doping levels, the optimum one exhibits the highest capacity of 115.8 mAh g^–1 (0.1C, 2–4 V, 1C = 129 mA g^–1), as well as outstanding cycling stability and rate capability (retaining a capacity of 87.8 mAh g^–1 after 3000 cycles at 20C, with a retention of 92.7%). Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements after cycling reveal that Y doping can stabilize the material structure, thereby further enhancing its lifespan during long-term cycling.