The regeneration of harmful activated sludge into an energy source is an important strategy for municipal sludge treatment and recycling. Herein, SiO2-modified N,S auto-doped porous carbon (NSC@SiO2) with high conductivity (70 S m–1) is successfully obtained through a simple calcination method of the activated sludge from wastewater treatment. Further, P-doped NSC@SiO2 (NSPC@SiO2) is designed to achieve a higher surface area (891 m2 g–1 vs 624 m2 g–1), a larger pore volume (0.87 cm3 g–1 vs 0.08 cm3 g–1), and more carbon defects. Due to its special structure, NSPC@SiO2 is used as a sulfur host of lithium–sulfur batteries. The results of polysulfide adsorption experiments, S 2p X-ray photoelectron spectra (XPS), Li2S nucleation experiments, polysulfide symmetric cells, measurement of the galvanostatic intermittent titration (GITT), polarization voltage difference, lithium-ion diffusion rate, and Tafel slope verified that NSPC@SiO2 greatly improved the adsorption capacity of polysulfides, lowered the barrier to Li2S formation and the internal resistances of cells, and accelerated Li+ ion diffusion and the reaction kinetics of polysulfide conversion, resulting in the excellent performance of polysulfide capture and superior rate performance and cyclic stability. By comparing NSPC@SiO2 with NSC@SiO2, a higher initial capacity (1377 mAh g–1 vs 1150 mAh g–1 at 0.1C), better rate capacity (912 mAh g–1 vs 719 mAh g–1 at 2C), and low capacity decay (0.094% per cycle within 200 cycles) are obtained. Our work provides direction for the treatment, disposal, and resource utilization of activated sludge.

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