A double-layered sulfur cathode exploiting the effect of high entropy oxides synthesized by microwave irradiation for excellent performances of lithium–sulfur batteries

The Lithium-sulfur (Li-S) battery has an obvious advantage in energy density due to the high theoretical capacities of the sulfur cathode (ca. 1672 mA h g−1) and the lithium anode (ca. 3862 mA h g−1), with the potential to achieve 500–600 W h kg−1 in the next few years. One of the major drawbacks of the Li-S cell comes from the reduction of sulfur at the cathode, which results in a large accumulation of LiPSs in the electrolyte. This in turn increases the electrolyte viscosity inducing high charge transfer resistance accompanied by sluggish redox kinetics. To date, carbon matrices are used as S hosts since they can prevent dissolution of the LiPSs mostly by physical interaction and increase the conductivity of sulfur at the cathode. Another effective way to limit LiPSs diffusion and shuttle effect to the anode is the use of metal components that anchor LiPSs and accelerate their conversion to solid Li2S. In this respect, high entropy metal oxides, HEO, have attracted significant attention because of their multifunctional behavior due to the incorporation of different cations in a single-phase solid solution. They can effectively immobilize LiPSs by chemical interaction accounting for the synergistic effects among the various metal ions. In this work, we have successfully prepared high entropy oxides HEO, (Mg, Cu, Co, Ni, Zn)O, by microwave-irradiation using metal nitrates as starting precursors. The microwave-irradiation is an effective synthetic route to produce HEO nanoparticles exploiting several advantages over conventional or wet methods. It assures fast speed, nanoscale and high purity products and low cost. XRD, TEM, XPS analyses confirmed the face-centered cubic crystalline structure of the oxides, the nanosize of the synthesized particles and the presence of all the five metallic species in the structure. Afterward, we have designed an integrated cathode architecture, consisting of ball-milled commercial sulfur and Ketjen black carbon powders coated by the HEO layer through a simple doctor‐blading technique. The cell response was then analyzed showing a synergistic effect through the use of the cathode coating method, resulting in a high capacity electrode that displayed around 650 mAh/g at the 250th cycle.