NaPO₂F₂ additive to regulate robust electrode/electrolyte interphases for high-voltage sodium-ion batteries

High-voltage sodium-ion batteries (SIBs) are emerging as promising candidates for large-scale energy storage systems due to their abundant sodium source and high energy density. However, the instability of the electrode-electrolyte interphase remains a critical barrier to the potential use of high-voltage SIBs. Herein, sodium difluorophosphate (NaDFP) and fluoroethylene carbonate (FEC) serve as functional electrolyte additives to stabilize the interface of the high-voltage cathode. The oxidative competition between FEC and NaDFP facilitates the robust formation of the cathode-electrolyte interface (CEI) layer, enriched with inorganic components such as NaF/NaPO_xF_y. The highly conductive NaF/NaPO_xF_y and inorganics provide fast ion transport pathways and mechanical strength, thereby mitigating the decomposition of carbonates and NaPF₆. The half-cell equipped with BE2F+0.5DFP demonstrates 93.9% capacity retention at 4.3 V across 600 cycles, showcasing excellent cycling capability. Full HC∥NVOPF cells exhibit sustained performance with 91.69% capacity retention and a capacity of 91.57 mA·h/g over 1000 cycles at a 5C rate. This study is poised to garner increased scholarly interest in the domain of rational electrolyte formulation for practical applications.