Electronic structure-driven sodiophilicity enables stable anode-free sodium batteries

Anode-free sodium metal batteries (AFSBs) offer high energy density and low cost by removing excess anodes, but their practical use is limited by low Coulombic efficiency and rapid capacity decay from irreversible sodium loss during repeated plating and stripping. Since all sodium in AFSBs forms during initial deposition, sodium nucleation and growth on current collectors strongly affect battery performance and safety. We identify the d-band center (ε_d) of collector surfaces as a unifying electronic structure descriptor for governing sodium-related behaviors. Tests and calculations show a volcano-type relationship between ε_d and sodium nucleation overpotential, with intermediate ε_d balancing sodium binding and diffusion for uniform, reversible deposition. We engineered a thin TiO₂ interphase to tune ε_d optimally, enabling 4000 stable cycles (99.82% average Coulombic efficiency). AFSBs and pouch cells exhibit long life and energy density (325 watt-hours per kilogram) on a full positive/negative electrode mass basis, offering a generalizable framework for rational interface design in anode-free battery systems.