Screening Conductive MXenes for Lithium Polysulfide Adsorption

Abstract MXenes are promising passive components that enable lithium‐sulfur batteries (LSBs) by effectively trapping lithium polysulfides (LiPSs) and facilitating surface‐mediated redox reactions. Despite numerous studies highlighting the potential of MXenes in LSBs, there are no systematic studies of MXenes’ composition influence on polysulfide adsorption, which is foundational to their applications in LSB. Here, a comprehensive investigation of LiPS adsorption on seven MXenes with varying chemistries (Ti₂CT_x, Ti₃C₂T_x, Ti₃CNT_x, Mo₂TiC₂T_x, V₂CT_x, Nb₂CT_x, and Nb₄C₃T_x), utilizing optical and analytical spectroscopic methods is performed. This work reports on the influence of polysulfide concentration, interaction time, and MXenes’ chemistry (transition metal layer, carbide and carbonitride inner layer, surface terminations and structure) on the amount of adsorbed LiPSs and the adsorption mechanism. These findings reveal the formation of insoluble thiosulfate and polythionate complex species on the surfaces of all tested MXenes. Furthermore, the selective adsorption of lithium and sulfur, and the extent of conversion of the adsorbed species on MXenes varied based on their chemistry. For instance, Ti₂CT_x exhibits a strong tendency to adsorb lithium ions, while Mo₂TiC₂T_x is effective in trapping sulfur by forming long‐chain polythionates. The latter demonstrates a significant conversion of intermediate polysulfides into low‐order species. This study offers valuable guidance for the informed selection of MXenes in various functional components benefiting the future development of high‐performance LSBs.