Lattice constant-dependent anchoring effect of MXenes for lithium-sulfur (Li-S) batteries: a DFT study

The anchoring effect of the cathode plays a significant role in improving the performance of lithium-sulfur (Li-S) batteries. MXenes, a new class of two-dimensional materials, have been reported to be effective sulfur hosts for Li-S batteries. However, previous studies mainly focused on Ti-based MXenes, while other potential transition metal MXenes have not been systematically explored. In the present work, we thoroughly investigated the interactions between lithium polysulfides (LiPSs) and a Ti₂CO₂ substrate, as well as six other M₃C₂O₂ (M = Cr, V, Ti, Nb, Hf and Zr) MXenes using density functional theory (DFT) calculations. It is found that all six M₃C₂O₂ systems possess trapping ability towards soluble LiPSs, largely attributed to the strong Li-O interactions between the LiPSs and the surface of the M₃C₂O₂. Among them, Cr₃C₂O₂ exhibited the strongest anchoring effect with the largest E_b. More importantly, a monotonical relationship between the binding energies and the lattice constants of M₃C₂O₂ was identified, which indicated that M₃C₂O₂ MXenes with a smaller lattice constant tend to exhibit a stronger anchoring effect. Furthermore, all six M₃C₂O₂ MXenes showed metallic properties during the whole process. Our results shed light on the future rational selection and design of MXenes acting as sulfur hosts in Li-S batteries and on the potential to improve host-guest interactions in other energy storage systems.