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The complex surface chemistry that dictates the interaction between MXene and polysulfides - the formation of thiosulfate via consumption of -OH surface groups, followed by Lewis acid-base interaction between the exposed Ti atoms and polysulfides - is unravelled. Interweaving carbon nanotubes between the MXene layers creates a porous, conductive network with high polysulfide adsorptivity, enabling sulfur hosts with excellent performance even at high loading (5.5 mg cm ).

The lithium‐sulfur battery is a compelling energy storage system because its high theoretical energy density exceeds Li‐ion batteries at much lower cost, but applications are thwarted by capacity decay caused by the polysulfide shuttle. Here, proof of concept and the critical metrics of a strategy to entrap polysulfides within the sulfur cathode by their reaction to form a surface‐bound active redox mediator are demonstrated. It is shown through a combination of surface spectroscopy and cyclic voltammetry studies that only materials with redox potentials in a targeted window react with polysulfides to form active surface‐bound polythionate species. These species are directly correlated to superior Li‐S cell performance by electrochemical studies of high surface area oxide cathodes with redox potentials below, above, and within this window. Optimized Li‐S cells yield a very low fade rate of 0.048% per cycle. The insight gained into the fundamental surface mechanism and its correlation to the stability of the electrochemical cell provides a bridge between mechanistic understanding and battery performance essential for the design of high performance Li‐S cells.

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