Synergistic sodium storage in bismuth-loaded polycellular carbon spheres: high diffusion kinetics and stability

Abstract

Bismuth (Bi), a promising alloy-type anode material for sodium-ion storage, has garnered significant interest due to its high theoretical capacity, environmental friendliness, and safety. However, during cycling, Bi undergoes substantial volume expansion, leading to fragmentation, which can cause short circuits and capacity degradation. In this study, we introduce a new method for synthesizing porous polycellular carbon spheres as a carbon framework and achieving bismuth loadings within the carbon structure. The carbon framework stabilizes the structure during cycling, while also dispersing the Bi metal within its pores. This effectively mitigates volume expansion and fragmentation of bismuth, and improves the reaction kinetics of the electrode. For sodium-ion half batteries, the electrode achieves a high discharge capacity (404.2 mA h g⁻¹ at 1 A g⁻¹) and stable cycling performance (reversible capacity of 389 mA h g⁻¹ after 1500 cycles at 1 A g⁻¹). Furthermore, capacity decay remains below 2% at current densities up to 5 A g⁻¹. This work offers a promising strategy for alloy-type materials and paves the way for future practical applications.