Biomass Precursors for Hard Carbon Anodes in Sodium-Ion Batteries: Structural Characteristics and Performance Relationships

Sodium-ion batteries (SIBs) have become a crucial supplementary technology for large-scale energy storage due to abundant sodium resources and their low cost. Biomass-derived hard carbon materials have been considered as one of the most promising anode materials for commercial SIBs. However, the inherent structures of different biomass materials vary significantly, which directly affects the electrochemical performance of the resulting hard carbon anode materials. In this review, raw materials are classified into four types based on the natural structure characteristics of biomass: fibrous, granular, dense, and special. This review highlights the structural characteristics of each biomass type and their influence on sodium storage performance. The carbonization process, including the treatment of raw materials before carbonization, the parameter control during the carbonization process, and the surface optimization after carbonization, is proposed as an effective strategy for regulating the structure of biomass-derived hard carbon. The existing structural deficiencies in current carbon materials are also analyzed. Finally, the selection of biomass precursors and the structural regulation strategies for commercial SIBs are discussed.