Mechanical Stable and Ion Pump Interface Design Through Heterogeneous Interphase Layer for Dendrite‐Free Sodium Metal Batteries

Sodium-metal batteries (SMBs) emerge as a promising alternative to lithium-metal systems but face intrinsic challenges of unstable electrode/electrolyte interfaces and rampant dendrite growth, which compromise cyclability and safety. Here, a multifunctional heterogeneous interphase layer (IMS-Na) with an ion pumping function on metallic sodium is constructed. This is enabled via an in situ reaction of Sb₂Se₃ powder with Na at room temperature by forming a Na₃Sb/Na₂Se hybrid structure as an artificial SEI layer. This artificial SEI layer synergizes ion pumping Na₃Sb with high ionic conductivity (adsorption energy: -1.31 eV, migration barrier: 0.49 eV) and mechanically stable Na₂Se with electronic insulation (bandgap: 2.11 eV) and mechanical robustness (Young's modulus: 60.63 GPa). The ion pumping Na₃Sb homogenizes the "hot spot" to suppress dendrite formation while the mechanically stable Na₂Se ensures the durability of the interface, which synergically enables dendrite-free Na deposition. As a result, the IMS-Na anode achieves ultralow polarization (30 mV) and unprecedented cycling stability (1535 h at 0.5 mA cm^-2) in carbonate electrolytes. Paired with a Na₃V₂(PO₄)₃ cathode, the full cell delivers long-term stability (1400 cycles) and high-rate capacity (102 mAh g^-1 at 2 A g^-1). This work establishes a design paradigm for artificial SEI layers, balancing ionic transport, electronic insulation, and mechanical resilience, critical for advancing high-energy-density metal batteries.