Ultrafine Mo2N Quantum Dots Embedded in N-Doped Graphene Sheets Enable Efficient Adsorption-Catalytic Transformation of Polysulfides

Abstract

Because of the high theoretical energy density of 2600 Wh kg^–1, lithium–sulfur batteries (LSBs) are anticipated to be among the next generation of high-energy-density storage technologies. However, the practical application of LSBs has been severely hampered by the significant shuttle effect and slow redox kinetics of polysulfides (LiPSs). To address the above problems, in this paper, the concept of quantum dots (QDs) was introduced to design and synthesize Mo₂N QD-modified N-doped graphene nanosheets (marked as Mo₂N-QDs@NG), which were used as separator modification materials for LSBs. The experimental results demonstrated that the introduction of Mo₂N QDs avoids stacking of graphene sheets and provides more active sites for the conversion of LiPSs. Moreover, Mo₂N enhances the chemical fixation and catalyzes the liquid–solid conversion of soluble LiPSs by forming Mo–S and Li–N bonds with LiPSs. Additionally, establishing Mo–C bonds with Mo₂N, N-doped graphene sheets can facilitate the transport of electrons and ions and physically prevent the diffusion of LiPSs, thus creating a highly conducting carbon structure to support electrochemical reactions. Benefiting from the synergistic effect of chemical immobilization and catalysis of Mo₂N QDs with the physical confinement of NG, Mo₂N-QDs@NG-PP batteries exhibit enhanced electrochemical performance.