Enlarged interlayer of separator coating enabling high-performance lithium–sulfur batteries

Lithium–sulfur batteries have been intensively studied due to their high theoretical energy density and abundant sulfur resources. However, their commercial application is hindered by the low redox kinetics and high sulfur losses. In principle, in the design of cathodes and separators, the adsorption toward lithium-polysulfides should be enhanced and the conversion of soluble high-order lithium-polysulfides should be catalyzed. Herein, a KV₃O₈·0.75H₂O separator is designed as an effective lithium-polysulfides mediator in lithium–sulfur batteries. The intercalated K⁺ would enlarge the interlayer spacing of vanadium oxides, preventing the collapse of the layer structure and improving the electrical/ion conductivity of the interface. Moreover, the KV₃O₈·0.75H₂O modified separator possess a prior adsorption and high redox kinetics toward lithium-polysulfides due to the enhanced diffusion kinetics, which guarantees the high-rate capability and efficient utilization of sulfur. As a result, lithium–sulfur batteries exhibit a high capacity of 1362 mAh·g⁻¹ and a long lifespan with a low capacity loss of 0.073% per cycle. This work may provide an alternative way to establish a functional separator to balance the adsorption and conversion of polysulfides during the redox back and forth.