Cobalt-embedded hierarchically-porous hollow carbon microspheres as multifunctional confined reactors for high-loading Li-S batteries

Highlights: • The hierarchical hollow carbon sphere is synthesized based on Kirkendall effect. • The porous carbon shell selectively confines polysulfide and permits Li+ diffusion. • Encapsulated Co facilitates chemical affinity and catalyzes sulfur conversion. • The hollow sphere shows a large surface area to accommodate up to 90.5 wt% sulfur. • The Li-S cell exhibits excellent performance at high sulfur content/loading. The shuttle effect of dissolved polysulfides migrating to and depositing on anodes often leads to low round-trip efficiency and short cycle life for lithium-sulfur (Li-S) batteries. Herein, we report the rational design of cobalt-embedded nitrogen-doped hollow carbon microspheres (Co@N-HCMSs) as a multifunctional sulfur host for Li-S batteries. The hollow carbon microspheres exhibit large central cavities wrapped by a hierarchically porous shell, showing a large surface area of 1954 m² g⁻¹. Furthermore, the carbon shells display a unique porous architecture, in which small pores are scattered on the outside and large pores are inside, thereby functioning as a selection barrier to confine polysulfides and diffuse Li⁺ simultaneously. Moreover, the highly dispersed cobalt nanoparticles in the porous shell activate the surrounding N-doped carbon layer, which not only promote chemical adsorption of polysulfides but also catalyze polysulfide conversion. This facilitation effect has been confirmed by Bader charge and density function theory (DFT) calculations. When applied in Li-S batteries, the sulfur-impregnated Co@N-HCMSs cathode material exhibits excellent electrochemical performances, especially with a high sulfur content of 90.5 wt% and a high areal sulfur loading of 5.1 mg cm⁻².