Sulfur-Enriched Porous Carbon Derived from Corn Silk for Electrochemical Sodium Storage

Biomass-derived carbons are promising sodium-ion battery anodes because they combine renewable feedstocks, tunable pore structures, and adjustable surface chemistry. However, many biomass carbons still show limited specific capacity and unsatisfactory initial coulombic efficiency. Here, corn silk was used as the carbon precursor, and potassium-sulfate-assisted carbothermal reduction was applied to produce sulfur-enriched porous carbon. Sulfur incorporation introduced C-S-related active sites and high-voltage redox features near 2.1/1.5 V. The optimized SC1400 electrode delivered an initial discharge capacity of 365.94 mAh g-1 at 0.1 A g-1 and an initial coulombic efficiency of 84.52%. It retained 342 mAh g-1 after 500 cycles at 1 A g-1, corresponding to more than 93% capacity retention. The improved cycling stability originates from the coupled effects of a defect-rich framework, enlarged interlayer spacing, and sulfur-containing surface species. Density functional theory calculations are consistent with stronger Na adsorption after sulfur incorporation. Density functional theory calculations support that sulfur incorporation enhances sodium-ion adsorption energy. This work provides a practical route for converting agricultural waste into biomass-derived carbon anodes for sodium-ion batteries.