Cobalt-mediated microcrystalline engineering of starch-derived hard carbon for fast-charging sodium-ion batteries

Starch is a highly attractive precursor for hard carbon anodes in sodium-ion batteries (SIBs) owing to its abundance, renewability, and high carbon yield. However, starch-derived hard carbons synthesized via direct pyrolysis often suffer from low plateau capacity and poor rate capability, limiting their practical application. To address these challenges, we propose a cobalt-catalyzed defect-repair strategy to engineer the microcrystalline of starch-derived hard carbons. This approach induces the formation of quasi-long-range ordered graphitic microcrystallites and mitigates structural defects, while simultaneously introducing hierarchical mesoporosity. The optimized microstructure significantly enhances Na+ diffusion kinetics and electrical conductivity, resulting in boosted plateau capacity and rate performance. Consequently, the anode delivers a high specific capacity of 336 mAh g-1 with a plateau capacity of 185 mAh g-1 at 0.05 A g-1, and retains 89 % of its capacity after 600 cycles. Even at an ultrahigh current density of 5 A g-1, it maintains 201 mAh g-1 total capacity and 144 mAh g-1 plateau capacity, substantially outperforming conventional starch-derived carbons. This study highlights the potential of cobalt-mediated structural engineering to advance biomass-based anodes for high-energy and high-power SIBs.