Tailoring alloy-reaction-induced semi-coherent interface to guide sodium nucleation and growth for long-term anode-less sodium-metal batteries

Sodium metal batteries are emerging as promising energy storage technologies owing to their high-energy density and rich resources. However, the challenge of achieving continuous operation at high areal capacity hinders the application of this system. Here, a robust two-dimensional tin/sodium–tin alloy interface was introduced onto an Al substrate as an anode via an industrial electroplating strategy. Unlike the widely accepted in situ formation of Na₁₅Sn₄ alloys, the formation of Na₉Sn₄ alloys results in a semi-coherent interface with sodium due to low lattice mismatch (20.84%), which alleviates the lattice stress of sodium deposition and induces subsequent dense sodium deposition under high areal capacity. In addition, the strong interaction of Sn with anions allows more PF₆⁻ to preferentially participate in the interfacial solvation structure, thereby facilitating the formation of a thin (10 nm) NaF-rich solid electrolyte interface. Therefore, the substrate can withstand a high areal capacity of 5 mA h cm⁻², exhibiting a high average Coulombic efficiency of 99.7%. The full battery exhibits long-term cycling performance (600 cycles) with a low decay rate of 0.0018% per cycle at 60 mA g⁻¹.