High-throughput screening of ion adsorption and diffusion on Sulfur-functionalized MXenes for battery electrode applications

Two-dimensional materials composed of transition metal carbides and nitrides (MXenes) are poised to revolutionize energy conversion and storage. MXenes exhibit the high capacity needed for electrodes in ion batteries and the high-power rate needed for supercapacitors. Also, it has been shown that adding Sulfur terminations decreases diffusion barrier for some ions. In this work, we tested adsorption of various adatoms (Ca, Mg, Na, Al, and Zn) on nine CM₂S₂ monolayers (M: Cr, Hf, Mo, Nb, Ta, Ti, V, W, Zr). We found that Ca binds the most strongly to all of the MXenes, and that Zn binds the weakest in dilute concentrations. Due to the thickness of CM2S2 layers, adatom-adatom interactions are screened in double-sided ion adsorption. In addition to these, we conducted cluster expansion simulations in order to study coverage dependent adsorption energies and open-circuit operating voltages (OCV). For the adatom having positive OCV, the migration of adatoms across the monolayers are studied with nudge elastic band method. This work searches for possible ion candidates to be used on sulfur-functionalized MXene layered materials to be used for battery electrode applications and will be terminal work on battery applications of two dimensional materials.