It is clear from Fig. that the binding energies of all the sites are negative, indicating Li can be adsorbed at any of the locations. The single Li/Mg ion prefers to locate at the S2 site of Ti 2 CSO MXene, where S2 is at the O-surface. In Ti 2 CSSe MXene, the preferable sites are at S-surface, i.e., S3 is for Li and S4 is for Mg.