Long-term stability of lithium-sulfur batteries via synergistic integration of nitrogen-doped graphitic carbon-coated cobalt selenide nanocrystals within porous three-dimensional graphene-carbon nanotube microspheres

Three-dimensional porous microspheres consist of highly conductive reduced graphene oxide-carbon nanotube (rGO-CNT) framework with well-embedded cobalt selenide (CoSe2) nanocrystals coated with N-doped graphitic carbon (NGC) were synthesized (referred as "P-CoSe2@NGC/rGO-CNT" microspheres) and utilized as an electrocatalytic interlayer to enhance the performance of lithium-sulfur (Li-S) batteries. The incorporation of the NGC layer and rGO-CNT framework not only enhances the electronic conductivity significantly but also offers numerous conductive pathways (primary and secondary) for efficient electron transport. Macropores (phi = 100nm) formed by the decomposition of PS nanobeads (phi = 200 nm) guarantee effective electrolyte penetration and short diffusion pathways. Moreover, the CoSe2 nanocrystals offer a multitude of polar active sites that effectively anchor polysulfide intermediates, reducing the loss of active material. Benefiting from the nanostructure merits, Li-S cells featuring a P-CoSe2@NGC/rGO-CNT-coated separator and a conventional sulfur electrode demonstrated outstanding rate capability (up to 2.0 C) and remarkable cycling stability (1000 cycles at 2.0 C). Even under more demanding cell conditions, such as high sulfur content (71 %), high sulfur loading (4.6 mg cm-2), and low E/S (5.6 mu L mg-1) ratio, the cell exhibits impressive cycling stability with 420 cycles at 0.1 C, along with feasible rate performance up to 0.3 C.