Developing a MXene quantum dot-based separator for Li–S batteries

The shuttle effect of polysulfides seriously hinders the practical application of lithium–sulfur (Li–S) batteries, and separator modification is supposed to be an effective way to solve this issue. Herein, MXene quantum dots (MQDs) were self-assembled on the surface of g-C3N4 sheets (g-C3N4@MQDs) by electrostatic adsorption principles to construct a functional layer on a Celgard separator. Making MXene into quantum dots was conducive to solving the agglomeration issue of its sheets, providing more active sites to capture the dissolved polysulfides. Moreover, the MQDs could also work as an electrocatalyst to further facilitate the Li2S catalytic conversion, obtaining a high deposition current and capacity (257.4 mA h g−1). Attributed to the regulation effect of MQDs toward the kinetic behavior of polysulfides, the shuttle effect was effectively mitigated. An as-fabricated Li–S battery with a heterostructured g-C3N4@MQD-based separator achieved a high specific capacity of 1433 mA h g−1 at 0.1 C, excellent rate performance (532 mA h g−1 at 4 C), and good cycling performance (0.024% capacity fading per cycle after 1000 cycles at 2 C). The rational design of the g-C3N4@MQD-based separator not only broadens the application of MQDs, but also presents new insights to develop high-performance Li–S batteries.