Single‐Atom Engineering for Synergistic Nucleation and Interfacial Regulation Enabling Durable Anode‐Free Sodium Metal Batteries

Abstract Anode‐free sodium metal batteries (AFSMBs) are highly promising candidates for low‐cost, sustainable, and high‐energy‐density storage systems. However, their practical deployment is challenged by uncontrolled dendrite growth and unstable solid electrolyte interphase (SEI) formation. To address these issues, a highly reversible and robust Na metal host enabled by atomic Bi sites is devised, coordinated in a unique N 3 ‐Bi‐S 1 moiety anchored on interconnected carbon tubes (Bi‐N 3 S 1 @CT). Crucially, this designed remarkably sodiophilic Bi single‐atom promotes uniform Na nucleation with minimal Na + consumption, enabling durable and highly reversible Na plating/stripping, while effectively suppressing electrolyte over‐decomposition and fostering the formation of robust inorganic‐rich SEI films, as supported by comprehensive theoretical calculations and experimental analyses. Consequently, Bi‐N 3 S 1 @CT achieves an extraordinary average Coulombic efficiency (CE) of 99.6% over 900 cycles at 12 mA cm −2 and 6 mAh cm −2 , along with long‐term durability of 1000 h at 10 mA cm −2 and 10 mAh cm −2 in symmetric cells. Notably, an anode‐free pouch cell paired with a high‐loading Na 3 V 2 (PO 4 ) 3 cathode exhibits decent cyclability over 240 cycles at 1C while maintaining good rate capability. This work demonstrates a promising strategy to simultaneously enhance energy density and stability in AFSMBs via atomic‐level sodiophilicity regulation and SEI engineering.