Integrating Bi@C Nanospheres in Porous Hard Carbon Frameworks for Ultrafast Sodium Storage

Abstract Sodium‐ion batteries (SIBs) have emerged as an alternative technology because of their merits in abundance and cost. Realizing their real applications, however, remains a formidable challenge. One is that among the limitations of anode materials, the alloy‐type candidates tolerate fast capacity fading during cycling. Here, a 3D framework superstructure assembled with carbon nanobelt arrays decorated with a metallic bismuth (Bi) nanospheres coated carbon layer by thermolysis of Bi‐based metal–organic framework nanorods is synthesized as an anode material for SIBs. Due to the unique structural superiority, the anode design promotes excellent sodium‐storage performance in terms of high capacity, excellent cycling stability, and ultrahigh rate capability up to 80 A g −1 with a capacity of 308.8 mAh g −1 . The unprecedented sodium‐storage ability is not only attributed to the unique hybrid architecture, but also to the production of a homogeneous and thin solid electrolyte interface layer and the formation of uniform porous nanostructures during cycling in the ether‐based electrolyte. Importantly, deeper understanding of the underlying cause of the performance improvement is illuminated, which is vital to provide the theoretical basis for application of SIBs.