Preparation of hard carbon anode materials for high-performance sodium-ion batteries by dual composition-structure modulation

Biomass-derived hard carbon has emerged as an anode material for sodium-ion batteries due to its cost-effectiveness and sustainability, but faces challenges in commercialization due to low sodium storage capacity and heterogeneity of precursors. This work presents a one-step acidothermal pretreatment strategy that rationally engineers walnut shell precursors through selective component modulation—effectively removing hemicellulose while reducing amorphous cellulose and acid-soluble lignin. The optimized precursor (RW-2) achieves balanced cellulose (48.9 %) and acid-insoluble lignin (49.6 %) composition with hierarchical porosity, enabling the synthesis of architecturally superior hard carbon (HC-2). The derived hard carbon (HC-2) integrates expanded interlayer spacing, hierarchical porosity, and defect-rich interfaces, synergistically enhancing sodium storage via intercalation-adsorption hybrid mechanisms. Electrochemically, HC-2 achieves a high reversible capacity (356 mAh/g at 20 mA/g), exceptional rate capability (280 mAh/g at 1000 mA/g) and sustained cyclability (79.3 % retention over 600 cycles at 1000 mA/g). By correlating precursor composition evolution with carbon microstructure, this work establishes a universal biomass engineering paradigm that decouples precursor heterogeneity from performance limitations while elucidating defect-mediated storage dynamics. The strategy provides a scalable pathway toward sustainable, high-performance sodium-ion battery anodes, bridging agricultural waste valorization with advanced energy storage technologies.