Interface Engineering with Multiple Functional Groups Coupling for High-Voltage and Wide-Temperature Sodium Metal Batteries

High-voltage sodium metal batteries (SMBs) with layered oxide cathodes face safety and stability challenges due to electrolyte decomposition and unstable electrode/electrolyte interphases. This study proposes a multifunctional electrolyte design strategy coupling nitrile, fluorine, and ether groups to enhance the high-voltage stability. The optimized electrolyte promotes formation of a thin, uniform cathode electrolyte interphase containing N/F-rich components (CN-, CNO-, NaN_xO_y, NaF) and a NaF-rich solid electrolyte interphase, effectively inhibiting electrolyte degradation and transition-metal dissolution. The modified electrolyte enables SMBs to deliver a 103.4 mAh g^–1 initial capacity at 10 C (2.0–4.5 V) with 99.63% average Coulombic efficiency over 200 cycles. Moreover, it supports stable operation across −20 to 60 °C, providing design insights for high-voltage wide-temperature SMBs.