Corncob-shaped Bi/V2O3 heterostructure encapsulated into N-doped carbon nanoshell for enhanced sodium-ion storage

Corncob-shaped Bi/V 2 O 3 @NC composite was designed and constructed. • Bi/V 2 O 3 @NC composite delivers 266.9 mAh g −1 at 1 A g −1 , and high rate performance. • Bi/V 2 O 3 heterostructure and carbon shell ease volume expansion for stable cycling. • Phase transition mechanism of Bi/V 2 O 3 @NC composite during cycling was investigated. Bismuth (Bi) is considered a promising anode candidate for alkali metal-ion batteries owing to its abundant natural reserves, outstanding theoretical capacity, intrinsic conductivity, and moderate charge/discharge potential. However, during cycling, it suffers from pulverization and agglomeration, leading to severe volume expansion, structural collapse, and rapid capacity decay. In addition, its sluggish alloying reaction kinetics limits the rate capability and practical applications. To address these challenges, a corncob-shaped Bi/V 2 O 3 @NC composite is designed, in which Bi and V 2 O 3 nanoparticles are uniformly encapsulated within a nitrogen-doped carbon nanoshell. This hierarchical architecture shortens ion/electron transport pathways and provides abundant electrochemically active sites. The Bi/V 2 O 3 heterointerface mitigates the volume expansion of Bi during cycling while enhancing reversible capacity, as evidenced by the stable cycling performance. The nitrogen-doped carbon coating suppresses volume deformation, enhances electrode conductivity, and facilitates ion diffusion, contributing to improved structural stability and electrochemical kinetics. Benefiting from these structural features, the Bi/V 2 O 3 @NC delivers a reversible capacity of 206.5 mAh g −1 at 10 A g −1 and retains 233.4 mAh g −1 after 3500 cycles at 5 A g −1 . Electrochemical analysis and ex situ characterization reveal that this performance originates from the synergistic effect of surface-capacitive and diffusion-controlled processes, with a high capacitive contribution (93.8% at 1.2 mV s −1 ) enabling fast kinetics. The sodium storage mechanism involves reversible alloying (Bi ↔ NaBi ↔ Na 3 Bi) and intercalation (V 2 O 3 ↔ Na x V 2 O 3 ) reactions, as confirmed by ex situ XRD. This work provides a design strategy for metal/metal oxide heterostructures and offers insights into the electrochemical mechanisms of alloy-based anodes for sodium-ion batteries. Download: Download high-res image (301KB) Download: Download full-size image