Chemically pre-sodiated Na₁₅Sn₄ interphase enables high-reversibility anode-less sodium metal batteries

Anode-free batteries promise high energy density but suffer from dendrites, dead sodium, and cathode Na depletion that slow ion diffusion and charge transfer. We introduce the facile chemical pre-sodiation of Cu current collectors to form a Na15Sn4@Cu coating, which enhances Na affinity, supports uniform nucleation, and suppresses dendrites. Operando XRD confirms improved Na diffusion in NaNi0.5Mn0.5O2, yielding markedly enhanced reversible capacity and cyclability for anode-less sodium-metal batteries.