A Cobalt‐Mediated Facet Engineering for High‐Voltage Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ Cathodes

ABSTRACT Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP), with its high specific capacity and excellent structural stability, is a promising cathode material for sodium‐ion batteries. This study reveals the structural regulation mechanism of cobalt‐doped Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 cathode materials and demonstrates their optimization effects on the high‐voltage performance of sodium‐ion batteries. By combining multi‐scale characterization with electrochemical testing, we reveal that Co substitution for Fe can induce lattice expansion, stabilize the (210) crystal plane, and enhance Na + diffusion. Na 4 Fe 2.7 Co 0.3 (PO 4 ) 2 P 2 O 7 (NFCPP‐3) exhibits remarkable rate performance (82.3 mAh g −1 at 100C) and long‐term cycling stability (85.6% after 5000 cycles at 10C). DFT calculations show cobalt doping significantly enhances the material's adaptability under high voltage conditions by reducing the formation energy of the (210) crystal plane (E f : 0.158→0.151 eV) and Na + migration energy barriers (0.807 → 0.623 eV). Furthermore, full cell testing (NFCPP‐3//HC) confirms practical application potential, with a capacity retention of 82 mAh g −1 at 10C and 94.1% after 450 cycles at 1C. This study provides a new perspective for developing cathode materials for high‐voltage and high‐rate sodium‐ion batteries.