A sulfur host based on cobalt-graphitic carbon nanocages for high performance lithium-sulfur batteries

Owing to the high theoretical specific capacity of sulfur (1675 mA h g(-1)), lithium-sulfur batteries display fascinating potential for high-capacity energy storage. However, their practical applications are still hindered by the fast capacity decay and poor cycling stability. In this work, a sulfur host based on MOF-derived cobalt-graphitic carbon nanocages is prepared by annealing the MOF (ZIF-67) in a H-2/Ar atmosphere. This unique structure can provide both the physical encapsulation of polysulfides by the graphitic carbon shell and chemical entrapment of polysulfides by the Co nanoparticles embedded in the carbon shell. In addition, the nanocages with inner void space not only allow a relatively higher loading content of sulfur but also alleviate the volume expansion of sulfur upon lithiation. As a result, the GC-Co electrodes with a high sulfur loading content of 77 wt% display a high specific capacity at different current densities and long-term cycling performance of 500 cycles at 1C with an ultra-low capacity decay of 0.015% per cycle.