Carbon-coated bismuth–zinc oxide heterojunction microspheres as anode materials for lithium-ion batteries

Bismuth is a promising anode material for next-generation energy storage systems due to its high theoretical volumetric capacity. However, its practical application is hindered by severe structural instability arising from large volume changes during cycling. Drawing inspiration from conversion/alloying-based anode design strategies, hierarchical micro/nano-structured Bi/ZnO@C composites is developed to mitigate rapid capacity fading and enhance electrochemical performance. The optimized Bi/ZnO@C anode exhibits outstanding reversibility and cycling stability, delivering high gravimetric and volumetric capacities of 797 mAh g⁻¹ and 1546 mAh cm⁻³, respectively, after 180 cycles at 0.1 A g⁻¹, and retaining 379 mAh g⁻¹ after 1000 cycles at 1.0 A g⁻¹—surpassing the performance of conventional Bi-based anodes. Furthermore, a full-cell configuration paired with a LiCoO₂ cathode achieves a high energy density of 829 Wh L⁻¹. This exceptional performance is attributed to the uniform dispersion of Bi and ZnO nanoparticles within a carbon microsphere matrix, which forms beneficial heterointerfaces and defect structures. These features effectively accommodate (de)lithiation-induced stress, preserve continuous ion/electron transport pathways, and promote rapid ion and charge transfer. Ex situ characterizations combined with density functional theory (DFT) simulations confirm enhanced Li⁺ adsorption capability, accelerated reaction kinetics, reduced charge-transfer resistance, and improved structural integrity of the Bi/ZnO@C electrode.