Micro-sized porous bulk bismuth caged by carbon for fast charging and ultralong cycling in sodium-ion batteries

Bulk bismuth, which has a large tap density and low specific surface area, is considered a promising anode material for sodium-ion batteries. However, bulk bismuth suffers from pulverization upon cycling and sluggish sodium-ion diffusion. Herein, we report micro-sized porous bulk bismuth particles caged by carbon (P-Bi/C) with micro- and nanoscale elements as anodes for sodium-ion batteries. Bicontinuous nanopores provide buffer spaces to accommodate volume expansion of bismuth during cycling, while interconnected bismuth nanoligaments maintain excellent electrochemical stability. Moreover, the reversible formation of NaBi and hexagonal Na3Bi phases with high sodium-ion diffusivity enables fast electron and ion transport. The P-Bi/C anode has a high initial Coulombic efficiency of 95.2%, a high rate capability of 153.2 mAh g−1 at 150C (1C = 400 mA g−1), and excellent cycling stability for over 20,000 cycles. This work aims to advance practical applications for bismuth in fast-charging sodium-ion batteries.