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 (~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.