Regeneration of Activated Sludge into SiO 2 -Decorated Heteroatom-Doped Porous Carbon as Advanced Electrodes for Li-S Batteries.

The regeneration of harmful activated sludge into an energy source is an important strategy for municipal sludge treatment and recycling. Herein, SiO 2 -modified N,S auto-doped porous carbon (NSC@SiO 2 ) 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@SiO 2 (NSPC@SiO 2 ) is designed to achieve a higher surface area (891 m 2 g -1 vs 624 m 2 g -1 ), a larger pore volume (0.87 cm 3 g -1 vs 0.08 cm 3 g -1 ), and more carbon defects. Due to its special structure, NSPC@SiO 2 is used as a sulfur host of lithium-sulfur batteries. The results of polysulfide adsorption experiments, S 2p X-ray photoelectron spectra (XPS), Li 2 S 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@SiO 2 greatly improved the adsorption capacity of polysulfides, lowered the barrier to Li 2 S 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@SiO 2 with NSC@SiO 2 , 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.