Win-win cooperation of boron-doped C3N5 porous nanosheets and CoSe2 nanorods for promoting cathodic sulfur conversion in lithium–sulfur batteries

Abstract

Integration of carbon-based materials with transitional metal compounds offers an efficient protocol for promoting cathodic sulfur conversion in lithium–sulfur batteries (LSBs). In this study, boron-doped C₃N₅ (B–C₃N₅) porous nanosheets and CoSe₂ nanorods have been coupled to form CoSe₂@B–C₃N₅ nanocomposite by involving B–C₃N₅ porous nanosheets in the hydrothermal synthesis of CoSe₂ nanorods. The B–C₃N₅ porous nanosheets with ample nitrogen-rich sites and boron dopants can favor sulfur accommodation, moderate lithium polysulfides (LiPSs) adsorption, electrolyte penetration and volume expansion tolerance. The CoSe₂ nanorods with metal-like conductivity and good electrocatalytic activity facilitate sulfur conversion. By establishing a powerful win–win cooperation, the optimized CoSe₂@B–C₃N₅–1 composite reveals intensified LiPSs adsorption capability and catalytic conversion kinetics, decreased internal resistances during Li₂S nucleation/activation, more efficient Li₂S deposition, smaller electrolyte and charge transfer resistances, and superior Li⁺ ions diffusion kinetics. As a result, the CoSe₂@B–C₃N₅–1 cathode achieves high capacities of 1066 mAh g⁻¹ for the first cycle and 663 mAh g⁻¹ by the 300th cycle at 0.2C. The CoSe₂@B–C₃N₅–1 cathode also shows desirable stability of specific capacity at 2C for 1000 cycles, with a low decay rate of 0.045 % per cycle. Density functional theory calculations indicate that the synergistic interaction between B–C₃N₅ and CoSe₂ significantly improves the ability to adsorb polysulfides. The strategy of combining C₃N₅ and CoSe₂ in this study can be popularized to promote the electrochemical performance of C₃N₅ and CoSe₂.