Bi-Doped Commercial Hard Carbon with Enhanced Slope Capacity to Deliver Superior Rate Performance for Sodium-Ion Batteries

Hard carbon (HC) suffers from the issues of unsatisfactory sodium storage capacity and inferior rate performance, severely hindering its practical application. Enhancing the slope capacity of commercial HC is considered an optimal strategy for improving its rate performance. Bismuth metal is well-known for its exceptional rate capability and low-temperature performance. Herein, we report an effective approach for regulating the surface structure of commercial HC anodes by introducing bismuth nanoparticles and increasing oxygen functional groups. Particularly, polyvinylpyrrolidone self-assembled micelles were selected as the "core '' to facilitate the adsorption of Bi3+, which enables the nanocrystallization of the Bi-HC material to yield a carbon-coated Bi structure. Compared to commercial HC, the Bi-HC anode exhibits a significantly enhanced slope capacity (increase from 90 to 120 mAh g-1 at 0.1 A g-1) and rate capability (increase from 70 to 250 mAh g-1 at 2 A g-1) in the ether electrolyte. This surface regulation strategy offers a promising pathway for the development of high-performance HC anodes and the construction of efficient sodium-ion batteries.