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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. [ABSTRACT FROM AUTHOR]

Alloying‐type antimony (Sb) with high theoretical capacity is a promising anode candidate for both lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). Given the larger radius of Na+ (1.02 Å) than Li+ (0.76 Å), it was generally believed that the Sb anode would experience even worse capacity degradation in SIBs due to more substantial volumetric variations during cycling when compared to LIBs. However, the Sb anode in SIBs unexpectedly exhibited both better electrochemical and structural stability than in LIBs, and the mechanistic reasons that underlie this performance discrepancy remain undiscovered. Here, using substantial in situ transmission electron microscopy, X‐ray diffraction, and Raman techniques complemented by theoretical simulations, we explicitly reveal that compared to the lithiation/delithiation process, sodiation/desodiation process of Sb anode displays a previously unexplored two‐stage alloying/dealloying mechanism with polycrystalline and amorphous phases as the intermediates featuring improved resilience to mechanical damage, contributing to superior cycling stability in SIBs. Additionally, the better mechanical properties and weaker atomic interaction of Na−Sb alloys than Li−Sb alloys favor enabling mitigated mechanical stress, accounting for enhanced structural stability as unveiled by theoretical simulations. Our finding delineates the mechanistic origins of enhanced cycling stability of Sb anode in SIBs with potential implications for other large‐volume‐change electrode materials. [ABSTRACT FROM AUTHOR]