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

Abstract

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.