A Dual-Interface Stabilizing Additive for High-voltage Sodium Metal Batteries.

High-voltage sodium metal batteries (SMBs) suffer from fast degradation stemming from the interfacial incompatibility between electrolytes and electrodes. In this study, potassium 3-pyridyltrifluoroborate (KPBF3) is proposed as a dual-interface electrolyte additive, where the pyridine moiety can effectively modulate the anion's electronic structure, lowering its lowest unoccupied molecular orbital energy level and enhancing its binding affinity for Na+. This promotes the preferential reductive decomposition of PBF3 -, forming a robust NaF-rich solid electrolyte interphase that suppresses Na dendrite growth. Simultaneously, the cleavage of B─F bonds facilitates the formation of a thin and uniform NaF-rich cathode electrolyte interphase (CEI), significantly suppressing electrolyte oxidation and greatly improving the high-voltage stability. Consequently, Na||Na symmetric cells achieve an ultra-long cycling life of 6000 h at 5 mA cm-2, while Na||Cu cells exhibit a high average Coulombic efficiency (ACE) of 99.89%. Moreover, Na||Na3V2(PO4)2F3 cells demonstrate 90.8% capacity retention over 10000 cycles at 10 C and 4.3 V, and 90.0% retention after 2500 cycles at 4.4 V. Notably, this additive also enables SMBs with a low N/P ratio of 2.65 to deliver a high capacity retention of 88.4% after 1000 cycles.