Microwave synthesis of rGO/ZnS nanocomposite as cathodic material for Li-S batteries

Nowadays, the production of energy through renewable sources has been continuously increasing in order to limit the utilization of fossil fuels. Therefore, the development of safer energy storage systems with better performances is at the center of the scientific research. In this context, lithium sulfur (Li-S) battery is a promising technology due to the high gravimetric energy density (2600 Wh/kg) and its low environmental impact. Herein, we report an innovative synthesis of a composite material composed of reduced graphene oxide (rGO) sheets and ZnS nanoparticles. In particular, the microwave approach allows to dramatically reduce the time (15 minutes at 190 °C) to obtain the material, it is energy savings and can guarantee a higher reproducibility compared to the traditional hydrothermal route. The combination of carbonaceous materials and metal oxide is very interesting since the former are able to provide an excellent electronic conductivity while the latter have a strong affinity with polysulfides (LiPSs), which is fundamental to mitigate the shuttle effect, one of the main issues of Li-S battery. Moreover, it has been recently reported that metal oxides may act as catalyst to promote the oxidation of LiS2, another important factor that can limit the parasitic reactions. The rGO/ZnS nanocomposite was fully characterized from a chemical physical point of view (XPS, XRD, FESEM, TEM and TGA). Above all, the XPS results showed that the rGO structure was modified during the MW synthesis, resulting in a nitrogen and sulfur doping of the material, which could help to form a good interaction with LiPSs by increasing the polarity of the material. The composite was then used as sulfur host by using the melt infusion technique to produce cathodes which were subsequently tested in half cells, showing high rate capability and cycling stability.