Multifunctional effects of hollow flower-like CoTiO microspheres wrapped by reduced graphene as sulfur host in Li-S battery.

The poor conductivity of sulfur, the shuttle effect and sluggish redox reaction kinetics of lithium polysulfides (LiPSs) are considered the main obstacles to the practical application of Lithium-sulfur (Li-S) batteries. Thus, it is urgent to design multifunctional host materials to eliminate these obstacles. Herein, we designed a hollow flower-like CoTiO wrapped by reduced graphene oxide (h-CoTiO@rGO) as sulfur host materials. The hollow structure of h-CoTiO@rGO not only endows sufficient space for high sulfur loading, but also physically and chemically confines the shuttle effect of LiPSs through the formation of Co-S chemical bonding. The large specific surface area and excellent electrocatalytic ability of h-CoTiO@rGO provide amounts of active sites to accelerate the redox reaction of LiPSs. Meanwhile, the conductive reduced graphene oxide (rGO) covered on the surface of CoTiO microspheres offers an interconnected conductive network to support the fast electron/ion transfer. Profit from these merits, the battery employing the multifunctional h-CoTiO@rGO as sulfur host exhibited excellent cycling stability with an ultralow capacity fading of 0.0127 % per cycle after 500 cycles at 1C. Even the battery with high sulfur loading of 5.2 mg/cm still delivered a high area capacity of 5.02 mAh/cm, which was competitive with the commercial Li-ion batteries. Therefore, the competitive capacity and superior cycling stability suggest that the h-CoTiO@rGO/S cathode is a potential candidate for high-performance Li-S batteries.