High-Performance Bismuth Anodes Enabled by Double-Layer Coating Structure of Silica and Nitrogen-Doped Carbon for...

Bismuth (Bi) is a highly attractive anode material for sodium-ion batteries (SIBs). However, the significant volume expansion during cycling leads to rapid electrochemical performance degradation. Herein, this study constructs a double-layer coating structure with a rigid SiO₂ inner layer and a flexible nitrogen-doped carbon outer layer simultaneously coated on the surface of bismuth nanoparticles (denoted as Bi@SiO₂@NC). Thanks to this unique SiO₂@NC double-layer coating structure, the Bi@SiO₂@NC achieves rapid ion/electron transport, optimized interface stability, and good structural reversibility, effectively improving the electrode conductivity and maintaining the structural integrity during the cycling process. Electrochemical test results show that the Bi@SiO₂@NC anode delivers a reversible capacity of 318.2 mAh g^-1 at 0.1 A g^-1 and exhibits superior rate capability (308.5 mAh g^-1 at 20 A g^-1) and exceptionally long cycling lifespan (256.2 mAh g^-1 after 6000 cycles at 1.0 A g^-1). The full cell constructed in combination with Na₃V₂(PO₄)₃ still maintains a discharge capacity of 83.7 mAh g^-1 after 120 cycles at 0.5 A g^-1, demonstrating outstanding cycling stability. This multi-functional synergistic coating strategy offers an effective strategy for the rational structural optimization of high-performance bismuth-based anodes and holds significant reference value for the construction of high-energy-density and long-duration sodium-ion batteries.