Constructing Dissolution–Resistant Interphases for Long‐Life Sodium‐Ion Batteries at Elevated Temperatures

Rechargeable sodium-ion batteries (SIBs) utilizing NaPF₆-carbonate electrolytes consistently exhibit unsatisfactory cycle life at elevated temperatures, posing a significant challenge for their large-scale commercialization. This is mainly caused by the instability of interphase layers at elevated temperatures, especially the high solubility of interphase components (especially NaF) in carbonate solvents. In this study, a novel additive of sodium difluorobis(oxalato) phosphate (NaDFBOP) is synthesized and introduced into NaPF₆-carbonate electrolytes to enhance the cycle life of commercial SIBs composed of NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) cathode and hard carbon (HC) anode, particularly at 50 °C. Specifically, the NaDFBOP enables NFM/HC SIBs to retain 85.45% of initial capacity after 1000 cycles at 30 °C and 90.76% after 500 cycles at 50 °C. Theoretical calculations reveal that DFBOP⁻ anions enter the first solvation shell of Na⁺, and NaDFBOP exhibits a strong propensity for decomposition. Characterizations suggest that NaDFBOP favors the formation of dissolution-resistant robust interphase layers enriched of dissolution-resistant oxalate-containing species and inorganic NaF, which have strong mutual binding energy. This work underscores the critical importance of designing functional additives and constructing dissolution-resistant robust interphases to enhance the elevated temperature cycle life of SIBs.