Facile Synthesis of a Honeycomb-Like Nano-Bi/N-Doped C Composite as an Anode for Sodium-Ion Batteries with Superb Cycle Stability

A new honeycomb-like nano-Bi/N-doped C composite is synthesized through simple physical blending followed by pyrolysis, using polyvinylpyrrolidone and bismuth nitrate pentahydrate as starting materials. In the synthesized composite, the particle sizes of Bi nanospheres are concentrated in 4–16 nm, and most of them are embedded in N-doped C. When used as an anode for sodium-ion batteries, it displays a stable reversible capacity of around 285 mAh g–1 at 5 A g–1. After the electrode was cycled for 20 000 times, the capacity remained at 283 mAh g–1, with 88.4% capacity retention relative to the second discharge capacity (320 mAh g–1). The honeycomb-like nano-Bi/N-doped C anode presents an interface and charge transfer resistance of less than 2 Ω and fast Na+ diffusion coefficients of around 10–6 cm2 s–1. Full cells composed of the honeycomb-like nano-Bi/N-doped C anode and the sodium vanadium phosphate/reduced graphene oxide cathode exhibit high energy density and excellent cycle performance. This work demonstrates the feasibility of synthesizing high-performance Bi/C composites through facile and scalable methods using inexpensive starting materials.