Cobalt-Doped Vanadium Nitride Yolk-Shell Nanospheres @ Carbon with Physical and Chemical Synergistic Effects for Advanced Li-S Batteries.

Lithium-sulfur (Li-S) battery has been attracting increasing attention because of its high energy density and the presence of abundance of sulfur. However, its commercialization is still restricted owing to the low conductivity of sulfur, large volume expansion, and a severe polysulfide-shuttle effect. To address these problems, here, we have reported for the first time a simple template-free solvothermal method combined with a subsequent calcination method to prepare cobalt-doped vanadium nitride (VN) yolk-shell nanospheres, encapsulated in a thin layer of a nitrogen-doped carbon (Co-VN@C) composite as an ideal sulfur host. Benefiting from the unique structural advantages and the synergistic effect of conductive VN, cobalt, and nitrogen-doped carbon (NC), the obtained composite could not only facilitate the kinetics of polysulfide conversion as a functional catalyst but also physically confine and chemically absorb the polysulfides effectively. With these advantages, the batteries present a high initial discharge capacity of 1379.2 mAh g-1 at 0.1 C (1 C is defined as 1675 mA g-1), good rate performance, and excellent cycling performances (∼715 mAh g-1 at 0.5 C after 200 cycles and ∼600 mAh g-1 at 1 C after 300 cycles, respectively), even with a high areal sulfur loading of 4.07 mg cm-2 (∼830 mAh g-1 at 0.2 C after 100 cycles). These results demonstrate that the rationally designed multifunctional sulfur host material Co-VN@C has great potential for application in Li-S batteries.