Synthesis of CoO nanocrystals decorated porous carbon nanotube microspheres as sulfur host for high performance Li/S batteries

Lithium-sulfur (Li/S) batteries are promising portable energy storage devices if the defects of insufficient conductivity and obvious shuttle effect can be effectively suppressed. In this work, a unique caddice-like ball carbon nanotubes/CoO (CNTs/CoO) microspheres have been synthesized through a facile spray drying and following calcination method. By using cobalt acetate (Co(CHCOO)2) as a cobalt source, polymethyl methacrylate (PMMA) as a pore former and CNTs as the supporting frame, the as-prepared CNTs/CoO microspheres endowed with enriched interconnected pores and abundant scattered CoO nanoparticles on CNT walls. CNTs provided physical adsorption platforms for adsorption of polysulfides while ensuring the conductivity of the overall material. Polycrystalline CoO nanoparticles are uniformly deposited on CNT walls, providing additional confinement of polysulfides by strong chemical adsorption. In addition, the different content of CoO in the microspheres was regulated by the amount of added cobalt source during the preparation process. With both physical entrapment by CNTs and strong chemical interaction with CoO nanocrystals, this unique design can effectively promote the active material utilization and inhibit the shuttle effect. When employed as the sulfur host, an excellent electrochemical performance was achieved on the resulting sulfur-impregnated CNTs/CoO (S-CNTs/CoO) composite with the sulfur content of 73.0%. The obtained S-CNTs/CoO microspheres delivered an exceptional initial discharge capacity of 1340 mAh g-1 and a prominent cycling stability of 1116 mAh g-1 after 100 cycles at 0.2 C, as well as a superb rate capability of 600 mAh g-1 and 506 mAh g-1 at 2.0 C and 3.0 C, respectively. The results revealed that the S-CNTs/CoO composite was an enviable cathode material and showed an excellent potentiality in the application of Li/S batteries.