Orbital Coupling and Electron Delocalization Engineered at Fe/V Heterointerfaces for Enhanced Cathode Performance in Sodium‐Ion Batteries

Sodium iron fluorophosphate (Na 2 FePO 4 F, NFPF) is considered a promising candidate for sodium‐ion batteries (SIBs) cathode materials due to low cost and abundant resources, but its practical application is limited by sluggish kinetics and low energy efficiency. An orbital‐level electronic structure modulation strategy by constructing NFPF‐Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) heterojunction was proposed to reconstruct electron‐ion synergistic transport channels for performance enhancement. Density functional theory (DFT) reveals that interfacial FeV 3d orbital coupling can enhance electron delocalization through upshifting of the d x 2 − y 2 orbital, which synergistically enhances electron delocalization across the heterointerface and boosts electronic conductivity by 20‐fold. Synchrotron radiation, X‐ray absorption spectroscopy, and DFT further confirm that the interfacial local electric field optimizes Na + diffusion path by modulating its coordination environment and forming new electronic pathways at the interface. Analysis of the distribution of relaxation times also illustrates the faster reaction kinetics. The NFPF–NVPF cathode delivers a specific capacity of 120.9 mAh g −1 at 0.2 C (113.6 mAh g −1 for NFPF) and exhibits a high capacity retention of 81.7% compared to 60.9% for NFPF and 75.9% for the mixing composites. This study offers a novel approach for multi‐objective optimization of “electron conduction‐ion diffusion‐structural stability.”