Defect-induced-reduced Au quantum Dots@MXene decorated separator enables lithium-sulfur batteries with high sulfur utilization

Abstract

Although lithium-sulfur (Li-S) batteries have a high theoretical energy density, their practical applications are limited by rapid capacity fading and poor cycling stability due to the dissolution of high-order polysulfides in electrolytes and the sluggish kinetics of the solid-state Li2S2/Li2S redox reaction. Herein, a polysulfide sorbent and redox reaction catalytic promoter, Au quantum dots (Au QDs)-decorated MXene nanosheet, is designed by proposing defect-induced-reduced Ti3C2Tx (MXene) to improve the performance of Li-S batteries. The polar surface functional groups and high electronic conductivity of the MXene boost the conversion of sulfur/polysulfides and restrict the dissolution of the polysulfide shuttle. The Au QDs catalyst reduces the conversion reaction activation energy to achieve rapid solid-state Li2S2/Li2S reaction kinetics. Due to the adsorption-catalysis synergistic effect between MXene and Au QDs, an initial discharge capacity of 1,500 mA h g-1 is obtained, corresponding to a sulfur utilization of 90%. A Li-S battery based on the Au QDs@MXene-decorated separator exhibits a capacity retention rate of 71.0% for 300 cycles at 1 C.