Oxidized Nb2C MXene as catalysts for lithium-sulfur batteries: Mitigating the shuttle phenomenon by facilitating catalytic conversion of lithium polysulfides

Extensive research has been devoted to lithium-sulfur (Li-S) batteries due to their overwhelming promises and advantages such as high theoretical capacity (1675 mAh g−1), extremely cost effectiveness and abundance and availability of sulfur. Nevertheless, a sluggish electrochemical kinetics of the battery limited by a slow conversion of lithium polysulfide (LiPSs) intermediates and LiPSs shuttle effect severely hinder its development towards industrial application. Herein, we designed the oxidized Nb2C MXene with amorphous carbon (Nb2O5/C) composites as sulfur host using CO2 treatment to address the above issues. The Nb2O5/C composites with high conductivity are directly employed as sulfur hosts for Li-S battery capable to remarkably mitigate the shuttle phenomenon due to a combined effect of their LiPSs trapping ability and catalytic activity towards their accelerated conversion. Meanwhile, the unique layered structure of the composite facilitates ion transfer and accommodates the volume changes of the cathode during cycling. With this rational design, the resultant Li-S batteries exhibit superior electrochemical performance with a high initial specific capacity of 745 mAh g−1 at 1.0 C and a reversible capacity of 620 mAh g−1 at a high rate cycling at 3.0 C.