Enhanced Fast‐Charging and Longevity in Sodium‐Ion Batteries through Nitrogen‐Doped Carbon Frameworks Encasing Flower‐Like Bismuth Microspheres

Abstract Micro‐sized bismuth (Bi) is recognized for its high volumetric capacity and suitable working potential, making it a promising anode candidate for sodium‐ion batteries (SIBs). However, its substantial volume changes and slow reaction kinetics during cycling detrimentally affects the SIB performance. Theoretical prediction uncovers a previously unexplored favorable attribute that bonding between nitrogen within a carbon coating and Bi atoms facilitates Na + ingress into the Bi bulk, significantly enhancing Bi‐Na alloying reactions, mitigating volume expansion, and preventing Na‐dendrite formation. Experimentally, the study innovatively engineers a flower‐like micro‐sized Bi encapsulated within an elastic, nitrogen‐doped carbon framework (FBi@NC) working as an efficient anode for SIBs. This design enables FBi@NC anode achieving a high tap density of 2.86 g cm −3 and delivering a remarkable volumetric capacity of 1100 mAh cm −3 at 1 mA cm − 2 . It also exhibits exceptional rate capability (368.2 mA h g −1 at 30 A g −1 ) and super durable cyclability (10 000 cycles with 318.8 mA h g −1 at 5 A g −1 , retaining 82% capacity). Full cells with Na 3 V 2 (PO 4 ) 3 cathodes demonstrate superior rate and cycling performances. Crucially, this study elucidates the underlying Na + ‐storage mechanisms and the contributory factors to performance enhancement, providing vital insights for the development of high‐energy and stable SIBs.