Stepwise Carbonization of Bagasse into Defect-Ordered Hard Carbons with Enriched Ion Channels for High-Plateau Sodium-Ion Storage

Bagasse, owing to its low cost and high carbon yield, is a promising precursor for hard-carbon anodes in sodium-ion batteries (SIB). Regulating the microcrystalline state and pore architecture during pyrolysis is key to boosting Na+ storage behavior. Here, the pyrolysis kinetics is controlled via stepwise carbonization to construct a defect-ordered island structure within the cellulose-derived carbon skeleton. Retaining sp3-hybridized carbon at low temperatures creates the Na+ channel, while acid cleaning selectively dissolves residual metal oxides, removing the electrochemical inert phase and promoting improved ion diffusion. This process also enriches active sites and interlayer spacing in the hard carbon, boosting capacity in the plateau region. In addition, the ash-catalyzed formation of local sp2 graphite microcrystals provides electron transport nodes, optimizing Na+ diffusion and electronic conductivity. Accordingly, the assembled SIB achieves a high reversible capacity of 378 mAh g−1 at 0.1C and an initial coulombic efficiency of 97%, with the plateau capacity accounting for 59.1% of the total reversible capacity. This work presents a universal thermochemical approach for engineering high-performance carbon anodes with high closed porosity from low-cost biomass precursors, advancing the development of sustainable and efficient SIBs.