High‐Performance Bismuth Anodes Enabled by Double‐Layer Coating Structure of Silica and Nitrogen‐Doped Carbon for Sodium‐Ion Batteries

ABSTRACT

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 SiO ₂ inner layer and a flexible nitrogen‐doped carbon outer layer simultaneously coated on the surface of bismuth nanoparticles (denoted as Bi@SiO ₂ @NC). Thanks to this unique SiO ₂ @NC double‐layer coating structure, the Bi@SiO ₂ @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@SiO ₂ @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 Na ₃ V ₂ (PO ₄ ) 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.