A biomolecular self-assembly assisted synthesis strategy for ultra-small bismuth nanoparticles toward ultra-high-rate sodium-ion storage

Abstract

Bismuth (Bi), as an alloy-type anode material, has garnered significant attention in the development of sodium-ion hybrid capacitors (SIHCs) due to its high theoretical capacity. However, Bi-based anodes suffer from limited rate capability caused by volume expansion during repeated sodiation/desodiation processes. This work proposed a self-assembly assisted synthesis strategy, utilizing the polyphenol coordination characteristics of tannic acid (TA), to construct a BiTA precursor. Strong coordination interactions between the catechol groups of TA and Bi³⁺ form a stable organic–metal structure, which is subsequently pyrolyzed and reduced to obtain ultrafine Bi nanoparticles embedded in a carbon matrix (Bi/C–H). The synthesized Bi/C–H anode could effectively mitigate the inherent volume expansion of Bi, while the carbon-encapsulated Bi particles ensure excellent conductivity. During cycling, the Bi electrode evolves into finer, closely interconnected particles, contributing to superior electrochemical performances. The Bi/C–H-based sodium-ion half-cell demonstrates remarkable rate capability, delivering reversible specific capacities of 316.7 and 309.1 mA h g⁻¹ at current densities of 50 and 80 A g⁻¹, respectively. The assembled Bi/C–H//PC sodium-ion hybrid capacitor achieves a reversible capacitance of 58 F g⁻¹ at 10 A g⁻¹, corresponding to an energy density of 63 W h kg⁻¹, exhibiting both outstanding rate performance and high energy density.