Thin-Layered Molybdenum Disulfide Nanoparticles as an Effective Polysulfide Mediator in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are attractive as sulfur offers an order of magnitude higher charge-storage capacity than the currently used insertion-compound cathodes. However, their practical viability is hampered by low electrochemical stability and efficiency, which results from severe polysulfide (LiPS) shuttling during cycling. We present here thin-layered MoS2 nanoparticles (MoS2-NPs) synthesized through a one-pot method and coated onto a commercial polymeric separator (as MoS2-NP-coated separator) as an effective LiPS mediator, facilitated by the nanodimension, polar interactions, and the better edge-binding sites of the MoS2-NPs. The resulting MoS2-NPs have an interlayer spacing of 0.55 nm and are stacked with a few layers. At a sulfur loading of 4.0 mg cm-2, the Li-S cell with a MoS2-NP-coated separator attains a peak discharge capacity of 983 mA h g-1, improving the electrochemical utilization of sulfur. The cell is able to maintain a high capacity of 525 mA h g-1 after 150 cycles at a C/5 rate. The MoS2-NPs are able to effectively anchor the LiPS species to their large S2- anions, enhancing the redox accessibility of sulfur cathodes and enabling better capacity retention.