One-Step Synthesis of Na–Sn Alloy with Internal 3D Na₁₅Sn₄ Support for Fast and Stable Na Metal Batteries

Na metal batteries are promising next-generation batteries but are constrained by the high reactivity of metallic Na. Here, we address this challenge by using a one-step-synthesized Na–Sn alloy anode with 1.6 at. % Sn. This anode has interconnected and sodiophilic Na15Sn4 backbones, which structurally support Na, enable faster Na+/Na redox kinetics, and guide dendrite-free Na plating with more stable solid-electrolyte interfaces. The composite Na@Na15Sn4 anode enabled very stable cycling of symmetric cells even at 5.0 mA cm–2 and improved the stability of full cells coupled with 3.0 mAh cm–2 Na3V2(PO4)3 cathodes to >90% capacity retention for 300 cycles.