Robust SEI and Uniform Na Deposition Enabled by Sodiophilic Interface for Durable Anode‐Free Sodium Metal Batteries Across Ambient and Subzero Conditions

ABSTRACT Anode‐free sodium metal batteries (AFSMBs) are regarded as promising next‐generation energy storage device because of their exceptionally high energy density and low cost. However, their practical application is still hindered by uncontrolled sodium dendrites growth and unstable solid electrolyte interface (SEI) formation. To address these challenges, a sodiophilic Ag interface was in situ constructed on the copper foil current collector to regulate the uniform Na deposition and promote a stable SEI formation. Combined theoretical calculations and experimental analysis revealed that the Ag interface enables uniform Na deposition by enhancing sodiophilicity and homogenizing the electric field, while also promoting the decomposition of NaPF 6 to form a robust and thin SEI. Consequently, the Ag─Cu||Na asymmetric cells exhibited stable cycling for over 1100 cycles with a high Coulombic efficiency of 99.87% at 1 mA cm −2 . Moreover, AFSMBs paired with Na 3 V 2 (PO 4 ) 3 cathode delivered a capacity retention of 70% after 500 cycles at 2C. Furthermore, the AFSMBs also maintained stable cycling over 150 cycles at −20°C under 0.05C. These results demonstrate the significant potential of introducing a sodiophilic interfacial layer to regulate uniform sodium deposition and promote stable SEI formation, thereby enabling high‐performance anode‐free sodium metal batteries across ambient and subzero conditions.