Nitrogen-Doped Carbon Nanotube Forests Planted on Cobalt Nanoflowers as Polysulfide Mediator for Ultralow Self-Discharge and High Areal-Capacity Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries with high theoretical energy density have caught enormous attention for electrochemical power source applications. However, the development of Li-S batteries is hindered by the electrochemical performance decay that resulted from low electrical conductivity of sulfur and serious shuttling effect of intermediate polysulfides. Moreover, the areal capacity is usually restricted by the low areal sulfur loadings (1.0-3.0 mg cm). When the areal sulfur loading increases to a practically accepted level above 3.0-5.0 mg cm, the areal capacity and cycling life tend to become inferior. Herein, we report an effective polysulfide mediator composed of nitrogen-doped carbon nanotube (N-CNT) forest planted on cobalt nanoflowers (N-CNTs/Co-NFs). The abundant pores in N-CNTs/Co-NFs can allow a high sulfur content (78 wt %) and block the dissolution/diffusion of polysulfides via physical confinement, and the Co nanoparticles and nitrogen heteroatoms (4.3 at. %) can enhance the polysulfide retention via strong chemisorption capability. Moreover, the planted N-CNT forest on N-CNTs/Co-NFs can enable fast electron transfer and electrolyte penetration. Benefiting from the above merits, the sulfur-filled N-CNTs/Co-NFs (S/N-CNTs/Co-NFs) cathodes with high areal sulfur loadings exhibit low self-discharge rate, high areal capacity, and stable cycling performance.