Chemically presodiated Sb with a fluoride-rich interphase as a cycle-stable anode for high-energy sodium ion batteries

Abstract

Antimony (Sb) is a high capacity and low potential alloy anode for developing high-energy sodium ion batteries (SIBs), but in practical applications it suffers from low initial coulombic efficiency (ICE) and poor cyclability due to its interfacial instability during cycles. In this work, we report a controllable and effective presodiation strategy to eliminate the large irreversible Na loss of Sb anodes by a chemical reaction with biphenyl sodium (Na-Bp). Surface analysis reveals that the presodiated Sb-pNa anode further initiates a selective decomposition of the electrolyte to form a NaF-rich SEI film on the Sb surface, which not only mitigates undesired side reactions with electrolyte solvents, but also significantly inhibits the mechanical fracture of the Sb lattice during cycling. Accordingly, the Sb-pNa electrode demonstrates a greatly elevated ICE of ∼100% and a superior capacity retention of 500 mA h g⁻¹ over 300 cycles at a high rate of 2000 mA g⁻¹, much better than the pristine Sb electrode with an ICE of ∼75% and a capacity retention of 80 mA h g⁻¹. When paired with a Na₃V₂(PO₄)₃ cathode, the assembled Sb-pNa//Na₃V₂(PO₄)₃ full cell exhibits a high ICE of >95.0% and an energy density of 232 W h kg⁻¹, respectively, reflecting a full utilization of the electrode-active materials. This work suggests a new avenue to tackle many fundamental obstacles of alloy anodes, thereby opening up new possibilities for developing low-cost and high energy density SIBs.