In situ reconstructed dual-functional interfacial layer induced by spontaneous vanadium fluoride reaction for highly stable sodium metal batteries

To ensure even distribution of sodium ions in sodium-metal batteries, various components must be incorporated to strengthen the surface mechanically, suppress dendritic growth, and create an ideal solid electrolyte interphase (SEI) characterized by robust adhesion, superior electrical conductivity, and exceptional mechanical durability. A novel bifunctional artificial interfacial protective layer was first designed by in-situ deposition and reconfiguration of vanadium fluoride on the surface of sodium metal. This reaction produced two components, V and NaF, in a spontaneous manner. It has been demonstrated that NaF offers excellent ionic conductivity and electronic insulation, facilitating the rapid adsorption of Na⁺ onto the electrode surface without reduction. In contrast, vanadium exhibits exceptional sodiophilicity, effectively regulating the uniform deposition of sodium ions to promote a stable deposition-stripping cycle. Additionally, the multiphase interfacial layer comprising NaF/V offers both chemical and electrochemical stability, along with a notably high Young’s modulus of 17.7 GPa, thus ensuring the long-term stability and safety of the device. Sodium metal anodes as inhibitors of dendrite growth, the VF_x/Na demonstrates prolonged cycling stability of up to 1000 h at 0.5 mA cm⁻² and 1 mAh cm⁻² in symmetric cell. In the electrochemical test of a full battery with a Na₃V₂(PO₄)₃ cathode, the VF_x/Na electrode showed superior performance, maintaining a specific capacity of 76.3 mAh g⁻¹ at a current density of 5 A g⁻¹ for a stable cycle of 4000 turns.