Fluorination-enabled synergistic engineering of lattice and interface in Na2FePO4F cathode for enhanced sodium-ion storage

The development of sodium-ion batteries is limited by the intrinsic kinetics and stability of cathode materials. Herein, we develop a synergistic engineering strategy for concurrently regulating the lattice structure and interfacial properties of Na2FePO4F cathode via a novel fluorination approach. This approach triggers a lattice reconstruction, widening Na+ migration channels and strengthening the Fe–F bond, thereby facilitating Na+ diffusion and enhancing framework stability. Simultaneously, this strategy promotes the formation of a defect-rich interface that accelerates interfacial charge transfer and enhances pseudocapacitive sodium storage. These synergistic effects achieve remarkable performance, including excellent rate capability (80.2 mAh g−1 at 5 C) and exceptional full-cell cyclability (89.3% capacity retention after 200 cycles at 1 C). This work provides a physical insight into the design of high-performance fluorinated electrodes through concurrent lattice and interface engineering.