Behavior of Li-ion on the surface of Ti3C2–T (T = O, S, Se, F, Cl, Br) MXene: Diffusion barrier and conductive pathways

After obtaining Ti 3C 2 MXene structures terminated with O, S, Se, F, Cl, and Br, we calculate the energy barrier for Li-ion diffusion on the surface of each MXene, being the first to report on the Li-ion diffusivity in Cl and Br terminated Ti 3C 2. We find that the Ti 3C 2Cl 2 MXene has the lowest diffusion barrier, substituting the Ti 3C 2S 2 reported in the literature so far. In addition, a study on the adsorption energies indicates that the top binding position is the most stable adsorption position for the Li-ion. Furthermore, it is shown that the adsorption energy depends on the electronegativity of the termination atoms, as well as the distance between the terminations, the Li, and the surface Ti-atoms. Finally, we show that the bond valence sum method provides an indication of the transition state of the Li-ion and can serve as a comparison tool for the diffusion barriers of different structures.