Biomass‐Derived Hard Carbon Anodes for Sodium‐Ion Batteries: Source, Synthesis, and Advanced Characterization

Against the backdrop of global energy transition toward low‐carbon systems and the implementation of China's “Dual Carbon” strategic objectives, sodium‐ion batteries (SIBs) have emerged as a critical complementary technology to lithium‐ion batteries due to their resource abundance, cost‐effectiveness, and superior low‐temperature performance. Among key components, hard carbon anode materials are regarded as the most promising candidates for SIBs owing to their low sodiation potential (<0.1 V vs Na/Na + ), high reversible capacity, long cycle life, and economic feasibility. This review focuses on biomass‐derived hard carbon materials, systematically summarizing research progress in sodium storage mechanisms, raw material sources (e.g., cellulose, starch, shells), preparation processes (pretreatment, carbonization strategies, post‐treatment), and advanced characterization techniques (e.g., interlayer spacing, closed pores, sodium clusters) employed across studies. The necessity of combining advanced characterization with experiments is further emphasized in the text to quantitatively analyze the correlation between microstructure characteristics and electrochemical performance. Only by establishing a plateau that collaboratively links the sources of biomass precursors, synthesis process parameters, and energy storage mechanisms, covering the entire process from “precursor → process → structure → performance”, can the hard carbon derived from biomass be elevated from an accidental product to a mature anode material for SIBs with adjustable structure and designable performance, and promote the practical application process of SIBs.