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Sulfur-loaded monodisperse carbon nanocapsules anchored on graphene nanosheets as cathodes for high performance lithium–sulfur batteries

There is a growing demand to enhance the electrical conductivity of the cathode and to restrain the fast capacity decay during a charge–discharge process in lithium–sulfur (Li–S) batteries. This can be accomplished by developing novel methods for the synthesis of nanostructured materials that can act as effective cathode hosts. In this study, monodisperse carbon nanocapsules with a diameter of ∼20 nm anchored on a graphene nanosheet (MCNC/G) were prepared by a facile strategy, which involved mixing of iron-oleate and graphene, heat treatment, and finally, acid etching of iron oxide nanoparticles. This simple synthesis method could be suitable for mass production. We loaded MCNC/G with sulfur by a melting process, and tested the performance of the resulting MCNC/G–sulfur (MCNC/G–S) composites as the cathode material. As a result, the MCNC/G–S electrode infiltrated with 60 wt% sulfur delivers a high and stable reversible capacity of 525 mA h g−1 after 100 cycles at a 0.5 C-rate with good capacity retention and excellent rate capability (630.5 mA h g−1 at a high current density of 1C). The improved electrochemical performance could be attributed to the monodisperse carbon nanocapsules in the MCNC/G composite, which lead to small volume expansion and physical confinement of sulfur due to the void spaces inside the carbon nanocapsules during the charge–discharge process. Thus, these uniquely structured monodisperse carbon nanocapsules anchored on graphene nanosheets can be promising candidates for other energy storage applications.