In situ Electrochemical Construction of Bismuth Nanoparticles: Harnessing Intrinsic Favorable Heterointerfaces and Structural Confinement to Augment Sodium Storage

Metallic bismuth (Bi), exhibiting remarkable theoretical specific and volumetric capacities alongside a low and stable operational voltage, stands out as an attractive anode candidate. Herein, in situ formed ultrafine Bi nanoparticles (ISFU‐Bi) using BiOBr as the starting electrode material, featuring distinct NaBr‐Na 2 O, NaBr‐Bi, and Na 2 O‐Bi heterointerfaces, are formed through electrochemical construction. The abundantly generated heterointerfaces confer the following advantages for sodium storage. First, the in situ generated Na 2 O and NaBr uniformly and tightly encapsulate Bi nanoparticles, effectively mitigating the volume expansion of Bi during sodiation. Second, Na 2 O‐Bi and NaBr‐Bi heterointerfaces facilitate charge transport and enhance conductivity. Thirdly, ISFU‐Bi achieves high structural stability and rapid electron transport without the incorporation of carbon‐based materials, ensuring a high specific capacity. As a result, ISFU‐Bi demonstrates remarkable rate capability (248.5 mA h g −1 at 80 A g −1 ), high specific capacity (394.8 mA h g −1 at 1 A g −1 ), and exceptional cyclability (with a retention of 86.9% after 13000 cycles at 10 A g −1 ). Both NaBr‐Bi and Na 2 O‐Bi heterointerfaces are theoretically verified to present a conductive nature and facilitate Na + migration. Notably, at the Na 2 O‐Bi interface, a localized reconstruction of the electronic structure occurs due to strong electronic coupling between Bi and Na 2 O, enhancing interface diffusion kinetics.