Advanced cobalt-based hierarchical and gradient armor catalysts for high-performance Li–S batteries over a wide temperature range

Abstract

Developing efficient and long-lasting cathode catalysts is crucial for preparing high-performance lithium–sulfur (Li–S) batteries. Here, we designed and synthesized hierarchical, gradient, and multi-dimensional Co@NCNN armor catalysts by pyrolyzing g-C₃N₄ in the presence of cobalt nitrate. The unique structure of the Co@NCNN armor catalysts combines 0D Co nanoparticles and outer carbon protective shells, which adsorb and confine LiPSs, as well as 1D carbon nanotubes and 2D carbon nanosheets, which enhance the sulfur load and block LiPS diffusion, respectively. XANES and XPS analysis showed that Co–Co bonds with different Co valence states are the main catalytic sites for LiPSs. In situ XRD experiments and Li₂S deposition tests demonstrated that the Co@NCNN armor catalysts can accelerate the liquid–solid conversion process, resulting in an initial discharge capacity of 1388.9 mA h g⁻¹ at 0.5 C, an excellent area capacity of 5.05 mA h cm⁻² and a sulfur load of 6.1 mg cm⁻². More importantly, the robust carbon layer protects the highly active inner cobalt nanoparticles, enabling them to perform 1000 cycles at a current density of 7 C, with a capacity decay rate of 0.048% per cycle, and maintain stability over a wide temperature range of 0 to 60 °C.