Review of Hard Carbon Anodes for Sodium‐Ion Batteries: Mechanisms, Precursors, and Modification Strategies

Sodium‐ion batteries (SIBs) have become important supplement to lithium‐ion batteries for the similar properties of sodium to lithium, ions storage mechanism, and huge reserve. Among varies of anode materials, hard carbon (HC) stands out as the most promising anode for large‐scale SIBs, owing to its high reversible capacity and rate capability, low sodiation potential, cost‐effective production, and abundant precursor sources such as biomass and industrial waste. However, some issues consist in HC‐based anodes such as low initial Coulombic efficiency, poor cycling stability, and inferior rate performance which seriously limit the practical application. More depth study on the Na + storage mechanism and material modification strategy is needed to improve the HC anode performance. Herein, a comprehensive review including Na + storage mechanism in HC, precursors classification, performance issues, and the related modification methods is provided. Furthermore, the future research direction is presented. It is believed that this review can provide an overall understanding about HC materials for the scholars who will devote to research on HC anode.