Cellulose swelling chemistry enables biomass-derived hard carbons with high-rate plateau capability for sodium ion batteries

Cellulose-rich biomass combines low cost, natural abundance and flexible microstructural tunability, thereby positioning itself as one of the most attractive precursors for fabricating high-performance hard carbons (HCs) anodes used in sodium-ion batteries (SIBs). However, constructing closed-pore structures within the robust macromolecular cellulose of biomass remains challenging for extending the plateau capacity and enhancing the diffusion kinetics of HCs. Herein, we propose an innovative swelling pretreatment strategy for cellulose using lithium hydroxide (LiOH) as the swelling reagent. Molecular dynamics simulations reveal that hydrated lithium ions penetrate the crystalline regions of cellulose and remain trapped during low-temperature drying, subsequently generating steam vapor upon carbonization to create closed pores. As a proof of concept, after swelling treatment with a moderate LiOH solution, the optimized ramie-derived HCs enables a superior rate capability of 195.7 mAh g −1 at an ultra-high rate of 6,000 mA g −1 . Combined in-/ex-situ characterization and GITT analysis delineate a three-stage sodium ions diffusion/storage process in HCs, uncovering the competitive kinetics between side reactions and the closed-pore dominated sodium cluster formation mechanism, which provides crucial insight for optimizing high-rate performance in SIBs. Overall, this study advances the mechanistic understanding of high-rate sodium storage and presents a novel material design strategy, offering valuable guidance for the development of next-generation biomass-derived anode materials for SIBs.