Homogeneous and Mechanically Stable SEI Enables Sodium-Metal Batteries for Extreme Working Conditions

Sodium metal has attracted considerable interest as an anode for next-generation high-energy-density sodium-metal batteries, owing to its superior specific capacity, low electrochemical potential, and economic viability. Despite the advantages, sodium-metal anodes encounter critical challenges, such as side reactions and dendrite growth, which diminish Coulombic efficiency and compromise long-term cycling performance. In this work, a multifunctional artificial NaF-Zn hybrid interfacial layer is in situ formed on the sodium metal surface. Both NaF and Zn exhibit strong binding affinity for PF 6 − , which facilitates Na + desolvation and accelerates the formation of a homogeneous and NaF-rich solid-electrolyte interphase (SEI). The resulting homogeneous and mechanically stable SEI enhances Na ion transport, reduced the side reactions and suppresses the dendrite formation. Consequently, the symmetric cells based on NaF-Zn modified Na operate stably for 1900 h at a high current density of 3 mAh cm −2 , while the full cell with Na 3 V 2 (PO 4 ) 3 cathode maintains stability for 8000 cycles at a high rate of 20C with a capacity retention of 75%. Moreover, the full cell demonstrated outstanding stability even under extreme working conditions, including low temperatures of −20 °C, high cathode loading, and reduced N/P ratios.