A Series of Hybrid Multifunctional Interfaces as Artificial SEI Layer for Realizing Dendrite Free, and Long-Life Sodium Metal Anodes

Sodium metal (Na) anodes are considered the most promising anode for high-energy-density sodium batteries because of their high capacity and low electrochemical potential. However, Na metal anode undergoes uncontrolled Na dendrite growth, and unstable solid electrolyte interphase layer (SEI) formation during cycling, leading to poor coulombic efficiency, and shorter lifespan. Herein, a series of Na-ion conductive alloy-type protective interface (Na-In, Na-Bi, Na-Zn, Na-Sn) is studied as an artificial SEI layer to address the issues. The hybrid Na-ion conducting SEI components over the Na-alloy can facilitate uniform Na deposition by regulating Na-ion flux with low overpotential. Furthermore, density functional study reveals that the lower surface energy of protective alloys relative to bare Na is the key factor for facilitating facile ion diffusion across the interface. Na metal with interface layer facilitates a highly reversible Na plating/stripping for ≈790 h, higher than pristine Na metal (100 h). The hybrid self-regulating protective layers exhibit a high mechanical flexibility to promote dendrite free Na plating even at high current density (5 mA cm⁻²), high capacity (10 mAh cm⁻²), and good performance with Na₃V₂(PO₄)₃ cathode. The current study opens a new insight for designing dendrite Na metal anode for next generation energy storage devices.