Porous SiOCN with ultrafine CoSe2 nanoparticle modified separators for promoting polysulfides capture and redox kinetics in lithium-sulfur batteries

Ultrafine CoSe2 nanoparticle/porous silicon oxycarbonitride composite (CoSe2/P-SiOCN) is developed as modifying material of separator to improve the electrochemical performance of lithium-sulfur batteries by promoting polysulfides (LiPSs) trapping and the redox kinetics of sulfur species. CoSe2/P-SiOCN is prepared through pyrolyzing the Schiff-base-SiO2 precursors with Co2+ ions, subsequent selenylation and removal of silica domain. The conventional separator is modified by coating CoSe2/P-SiOCN on the side for facing sulfur cathode. In this structural design, the porous structure of silicon oxycarbonitride (P-SiOCN) functions as polysulfides trapping and support matrix of CoSe2 nanoparticles, while the ultrafine CoSe2 nanoparticles (similar to 7.8 nm) can efficiently promote the redox kinetics of sulfur species. The cell with CoSe2/P-SiOCN modified separator exhibits better cycling and rate performance than that with P-SiOCN modified separator and the pristine separator. At 1 C, the cell delivers a high reversible discharge capacity of 568.1 mAh g(-1) after 400 cycles with a low capacity decay of 0.042 % per cycle.