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

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 Na3V2(PO4)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. Guided by theoretical insights, this study has reported an efficient anode of a flower-like micro-sized bismuth encapsulated within an elastic, nitrogen-doped carbon framework for Na-ion batteries, yielding synchronously a large reversible volumetric capacity, high-rate capability, and long-term durability. Its underlying Na+-storage mechanisms and origins of the performance enhancement are thoroughly elucidated through extensive experimental characterizations and theoretical analyses. image