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 (KPBF 3 ) 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 PBF 3 − , 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||Na 3 V 2 (PO 4 ) 2 F 3 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.