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

Abstract 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 Sb 2 Se 3 powder with Na at room temperature by forming a Na 3 Sb/Na 2 Se hybrid structure as an artificial SEI layer. This artificial SEI layer synergizes ion pumping Na 3 Sb with high ionic conductivity (adsorption energy: −1.31 eV, migration barrier: 0.49 eV) and mechanically stable Na 2 Se with electronic insulation (bandgap: 2.11 eV) and mechanical robustness (Young's modulus: 60.63 GPa). The ion pumping Na 3 Sb homogenizes the “hot spot” to suppress dendrite formation while the mechanically stable Na 2 Se 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 Na 3 V 2 (PO 4 ) 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.