Nano-confined synthesis of multi yolk-shell Co-NC@N-HCSs hybrid as sulfur host for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) battery has been considered as one promising rechargeable battery with ultrahigh theoretical energy density. However, its practical application is mainly hindered by volume expansion during cycling and irreversible shuttle effect of soluble lithium polysulfides (LiPSs). Herein, we reported a rational design and fabrication of multi yolk-shell Co-NC@ nitrogen doped hollow carbon spheres (Co-NC@N-HCSs) as sulfur host for high performance Li-S batteries via a nano-confined synthesis strategy. The growth mechanism of multi yolk-shell ZIF-67s@N-HCSs nanostructure was studied and the ZIF-67 yolks were tunable by changing the reactant concentration. Regarding to multi yolk-shell Co-NC@N-HCSs hybrid, the nitrogen doped carbon shell provides effective physical confinement, abundant sulfur loading space and volume expansion alleviation, while the multi polar Co-NC yolks can enhance the internal electron conductivity inside the cavity and offer stronger chemisorption capability for LiPSs as well as catalytic effects on the redox reaction of LiPSs. Benefiting from the unique multi yolk-shell design, the S/Co-NC@N-HCSs electrode with sulfur content of 80.82 wt%, exhibits high discharge capacity of 1173 mAh g−1 at 0.1C and 995.8 mAh g−1 at 1C. It also shows long cycle life up to 450 cycles with a slow capacity decay rate of 0.13% per cycle. The electrochemical performance of S/Co-NC@N-HCSs is obviously promoted compared with S/N-HCSs, suggesting its potential to develop high performance lithium sulfur batteries.