Facile fabrication of cellulose-derived hard carbon for high-rate performance sodium-ion batteries by regulating degrees of polymerization

Hard carbon materials are considered as one of the most commercially promising anode materials for sodium-ion batteries because of their abundant resources, cost-effectiveness and stable cycling performance. However, to rationally regulate the graphitic microcrystalline and pore structure of hard carbon toward advanced sodium storage performance remains a daunting challenge. Here, a simple molecular engineering strategy is developed to synthesize hard carbon featuring diverse graphitic microstructures and pore structures by modulating the polymerization degree of cellulose through pretreatment. Remarkably, cellulose with an appropriate degree of polymerization is cross-linked during the pyrolysis process, forming large layer spacings and multi-layer short graphite microcrystalline structures, resulting in the formation of a rich closed-pore structure. As a consequence, the optimized hard carbon delivers a reversible capacity of 344.5 mA h g-1 at 0.05 A g-1 and a superior rate performance of 251.2 mA h g-1 at 2 A g-1. Moreover, it demonstrates a plateau capacity retention rate of 85.2% under high current density conditions. Additionally, dynamic analysis and in situ X-ray diffraction (XRD) elucidate the electrochemical advantages and sodium storage mechanisms. This study fundamentally sheds light on the molecular design of cellulose-based hard carbon materials thereby showcasing their substantial potential for application in cost-effective and environmentally friendly energy storage devices.