Tailoring pretreatment-mediated microcrystalline structure of starch-based hard carbon for high-performance sodiumion batteries

The principal challenge in optimizing biomass-derived hard carbon (HC) is the concurrent enhancement of specific capacity, cycling durability, and rate performance, as these properties are closely related to the disordered carbon network and abundant pore structure. However, inadequate controllability of morphology, insufficiently regulated pore structures, and the complexity of post-processing modifications hinders the practical application of HC. In this work, a high-temperature and high-pressure expansion pretreatment technique is proposed to regulate the structure of starch precursors, enabling the precise design of ordered graphitic-like microcrystals and closed pores within HC. The optimized starch-based HC displayed remarkable electrochemical efficiency, with a reversible capacity of 332.0 mAh g^-1, an initial Coulombic efficiency of 90.4%, and stable cycling over 3000 cycles. Meanwhile, advanced full-cell utilizing Na₄Fe₃(PO₄)₂P₂O₇ cathode achieve stable cycling performance exceeding 1000 cycles, demonstrating outstanding performance. This research innovatively employs a green expansion process to achieve structural regulation of HC, thereby providing an environmentally friendly and economically viable technical pathway for its large-scale production.