Mixed phase 2D Mo_0.5W_0.5S₂alloy as a multi-functional electrocatalyst for a high-performance cathode in Li-S batteries

Lithium-sulfur batteries present unique polysulfide chemistry and exhibit a high theoretical energy density of 2600 W h kg-1. However, soluble lithium polysulfides (LiPSs) tend to shuttle during battery cycling and corrode the Li anode; this leads to an eventual performance fading in the Li-S battery. This shuttle effect can be reduced by accelerating the conversion of dissolved polysulfides to insoluble LiPSs and back to sulfur. Herein, a novel 2D Mo0.5W0.5S2 alloy with a 2H (semiconducting)-1T (metallic) mixed-phase is synthesized on carbon nanotubes (CNTs) by a two-step process of co-sputtering and sulfurization. The cathode comprising 2D Mo0.5W0.5S2-CNTs exhibits the synergistic effect of accelerated electron transfer, a higher LiPS binding effect, and good catalytic performance, as confirmed by our electrochemical analysis. As a result, the Li-S battery cell assembled with the 2D Mo0.5W0.5S2/CNT/S cathode shows a high specific capacity of 1228 mA h g-1 at 0.1C and a much higher cycling stability as compared to the pristine cathodes. Our results confirm that the 2D Mo0.5W0.5S2 alloy catalyst deposited on the CNTs can effectively prevent polysulfide shuttling and offer a viable solution to overcome the technical challenges in the development of practical Li-S batteries.