Mixed phase 2D Mo0.5W0.5S2 alloy as a multi-functional electrocatalyst for a high-performance cathode in Li–S batteries

Abstract

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 Mo_0.5W_0.5S₂ 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 Mo_0.5W_0.5S₂–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 Mo_0.5W_0.5S₂/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 Mo_0.5W_0.5S₂ 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.