Thiourea-modified silk cotton carbon as an efficient sulfur host: A green approach for advanced aluminum-sulfur battery

Aluminum-sulfur batteries (AlSBs) hold immense promise for sustainable energy storage due to their high theoretical energy density and low-cost materials. However, rapid capacity fading caused by polysulfide shuttling and sluggish reaction kinetics limits their practical viability. Herein, thiourea-modified, biomass-derived carbon (DSC-800), synthesized from silk cotton, is a high-performance sulfur host for AlSBs. DSC-800 achieves a hierarchical porous structure, nitrogen, sulfur co-doping, and enhanced graphitic ordering through hydrothermal treatment and carbonization, enabling effective polysulfide confinement and improved ion and electron transport. The DSC-800-S cathode, with a current density of 100 mA g⁻¹, has an initial discharge capacity of 535 mAh g⁻¹ and retains 200 mAh g⁻¹ (37.4 % retention) after 160 cycles, greatly outperforming the SC-800-S counterpart, which retains only 20 mAh g⁻¹ equivalent over the same period. Impedance spectroscopy and cyclic voltammetry further confirm that the hierarchical porosity and heteroatom doping synergistically mitigate polysulfide shuttling and reduce charge-transfer resistance. This work demonstrates the viability of sustainable biomass-derived carbons for advanced sulfur cathodes and delivers a scalable approach to increase the cycling stability of AlSBs for large-scale energy storage applications.