Intermetallic Layers with Tuned Na Nucleation and Transport for Anode-Free Sodium Metal Batteries

Sodium metal batteries without pre-deposited Na (anode-free) and with a limited amount of Na metal (anode-less) have attracted increasing attention due to their competitive energy density and the high abundance of sodium. However, severe interfacial issues result in poor cycling stability and low Coulombic efficiency. Here, the lightweight interphase layers composed of intermetallic nanoparticles (Sn-Cu and Sn-Ni) are applied to improve Na plating/stripping behaviors. These layers provide uniform seeding sites with high sodiophilicity and support fast ion transport. A reversible Na plating/stripping behavior, featuring a high Coulombic efficiency of ∼99.95% with a minor standard deviation of 0.0013, for 500 cycles at 1 mA cm^-2 and 1 mAh cm^-2 is achieved on SnCu-coated Al. Consequently, the anode-free Na₃V₂(PO₄)₃ full cell with a high loading of 7.6 mg cm^-2 exhibits a capacity retention of 90% after 200 cycles. This strategy provides an effective pathway toward anode-free sodium metal batteries.