Anion‐Driven <i>d</i> – <i>p</i> Orbital Hybridization in Na _3.12 Fe _2.44 (P ₂ O ₇ ) ₂ for High‐Performance Sodium‐Ion Batteries

ABSTRACT Iron‐based polyanionic compounds have emerged as some of the most promising cathode materials for sodium‐ion batteries (SIBs) owing to their intrinsic structural robustness, long cycle life, and high safety, which make them well‐suited for low‐cost, large‐scale energy storage. Among them, Na 3.12 Fe 2.44 (P 2 O 7 ) 2 (NFPO) suffers from inherently limited rate capability and cycling stability. In this work, we propose an anion‐doping‐driven orbital hybridization strategy in which partial substitution of P 5+ by Si 4+ simultaneously modulates the electronic structure and Na + transport kinetics of NFPO. Combined experimental and theoretical analyses demonstrate that the lower electronegativity of Si strengthens Fe─O covalency, thereby reinforcing structural stability, while its electron‐donating character enhances Fe 3d─O 2p hybridization, optimizing bonding─antibonding interactions and accelerating redox kinetics. Benefiting from these synergistic effects, the NFPO‐Si5 cathode delivers a reversible capacity of 116.6 mAh g −1 at 0.05 C, approaching the theoretical limit of 117 mAh g −1 , and maintains 84.8% capacity retention after 14000 cycles at 20 C. These findings elucidate the fundamental role of orbital hybridization in governing both electrochemical capacity and long‐term durability, and more importantly, establish a generalizable design principle for developing next‐generation high‐performance cathode materials for sodium‐ion batteries.