Bismuth and its nanocomposite: Reaction mechanism and rational nanocomposite fabrication process for superior sodium-ion battery anodes

Bismuth has garnered attention as a promising anode material for Na-ion batteries (NIBs) because of its high volumetric capacity and appropriate operating potential. However, the large and repeated volume variations of the Bi anode during sodiation/desodiation lead to a poor electrochemical performance; thus, a rational design for Bi-based materials is essential for their application to NIB anodes. First, the Na reaction pathway of Bi was analyzed using various cutting-edge ex situ analysis tools. Subsequently, two different types of Bi-based nanocomposite materials were prepared to enhance the Na storage performance of Bi: one is an amorphous carbon (a-C)-modified Bi nanocomposite (Bi@a-C) fabricated via mechanical treatment and the other is a metal-organic framework (MOF)-derived polyhedral Bi nanocomposite (p-Bi@C) fabricated via chemical treatment. The Na storage performance of p-Bi@C is much higher than that of Bi@a-C because of the homogeneous anchoring effect of Bi nanocrystals in the MOF-derived polyhedral C matrices, which have robust and high Na-ion conduction. The p-Bi@C delivered a highly reversible capacity (302 mAh g(-1) over 100 cycles) and high rate capability (205 mAh g(-1) at 2C). Therefore, this study provides a rational design of Bi-based nanocomposite materials for application to high-performance NIB anodes.