Scalable Carbonthermal Synthesis of Hierarchical Bi@C Anode for Superior Sodium‐Ion Batteries

Bismuth (Bi) has emerged as a promising anode material for sodium‐ion batteries (SIBs) due to its ultrahigh theoretical volumetric specific capacity (3765 mAh cm −3 ). However, Bi anodes undergo volume fluctuation during Na + insertion/extraction, which leads to the destruction of the electrode structure, resulting in capacity decay and poor cycle life. Herein, hierarchical Bi@C micro‐bricks were fabricated via a scalable carbothermal reduction method. Due to the unique hierarchical structure, the carbon matrix effectively suppresses the volume expansion of the Bi anode and preserves the structural stability during cycling. Compared to pure Bi, this Bi@C demonstrates dramatically enhanced cycling stability and maintains a stable capacity of 335.09 mAh g −1 after 700 cycles at 0.5 A g −1 . Even at 1.0 A g −1 , this hierarchical Bi@C micro‐bricks also retains a capacity of 307.32 mAh g −1 after 900 cycles. Furthermore, the dynamic performance analysis confirms that this carbon composite multilevel structure design strategy effectively enhanced the diffusion kinetics of Na + , thus resulting in superior rate capability and cycling stability. These findings provide valuable insights for developing a hierarchical alloy composite anode with high performance for SIBs.