Precise Decoupling of Biomass Components to Engineer Hard Carbon Microcrystalline Architecture for Enhanced Sodium‐Ion Storage Performance

Extensive research on biomass-derived hard carbon (HC) anodes for sodium-ion batteries has aimed to optimize sodium storage through precise manipulation of precursor structures. Existent methods, involving harsh acids or corrosive reagents, typically raise production costs, pose safety hazards, and cause unwanted carbon loss, reducing precursor utilization efficiency. To overcome these issues, this study introduces a mild, environmentally friendly, and scalable approach utilizing selective sulfonation of raw bamboo. This method enhances lignin hydrophilicity, facilitating partial delignification via solid-liquid separation. Subsequent carbonization of the cellulose-enriched precursor yields HC with thin-layered pseudo-graphitic domains, enlarged interlayer spacing, and dense closed-pore structures. The resulting anodes achieve a reversible capacity of 348 mAh g^-1 at 30 mA g^-1 with an initial Coulombic efficiency of 84.2%, excellent rate capability (241 mAh g^-1 at 900 mA g^-1), and superior cycling stability (97.8% capacity retention after 500 cycles at 500 mA g^-1). Ex situ XRD and XPS analyses further indicate an adsorption-intercalation/filling mechanism. This sustainable pretreatment not only enhances electrochemical performance but also supports efficient lignosulfonate recovery, promoting comprehensive and high-value utilization of lignocellulosic biomass in energy storage applications.