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Using the BVS method, we calculate Li-ion pathways and diffusion barriers in the interface between silicene and MgCl2, MgBr2 and MgI2 substrates and we show that the results are in good agreement with the previously published DFT studies. In addition, we showcase that BVS does not need the exact crystal structure as we examine different initial positions for the Li ion and different interface heights without affecting the calculated BVSE. Furthermore, we show that surface diffusion BVS calculations can be used to roughly optimize the interface, thus completely foregoing DFT geometry optimization calculations. Here, we propose that BVS can substitute DFT as a quick filter when searching for low migration barriers in silicene-based materials, providing good enough accuracy. [ABSTRACT FROM AUTHOR]

After obtaining Ti 3 C 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 3 C 2. We find that the Ti 3 C 2 Cl 2 MXene has the lowest diffusion barrier, substituting the Ti 3 C 2 S 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. [ABSTRACT FROM AUTHOR]

We study Li and, for the first time, K, Mg and Zn ion intercalation on the surface of the Zr 2 CS 2 MXene monolayer, taking advantage of the fact that the S terminations lower the diffusion barrier of the ions. We find that the Zr 2 CS 2 -Li, Zr 2 CS 2 -K and Zr 2 CS 2 -Mg structures are identical, with only Zr 2 CS 2 -Zn differing as to the position of the ion and Zn detaching from the MXene's surface during migration. Regarding the use of Zr 2 CS 2 as anode material in ion batteries, we examine as criteria the adsorption energy, diffusion barrier energy and open-circuit voltage for each of the ions considered. We show that the K ion has higher mobility, as well as lower open-circuit voltage. These results lead to the fact that KIB have fastest charge/discharge rates and higher energy density than LIB, MIB, and ZIB when it comes to the use of S-terminated, Zr-based materials as negative (anode) electrodes. KIB, therefore, seem the best alternative to LIB, especially after taking under consideration K's low cost and abundance of resources. • S termination atoms lower the ion diffusion barrier on the surface of the Zr 2 CS 2 MXene. • The Zn ion detaches from the Zr 2 CS 2 surface during migration. • KIB have fastest charge/discharge rates and higher energy density when using the Zr 2 CS 2 MXene as anode electrode. • KIB seem the best alternative to LIB after taking under consideration K's low cost and abundance of resources [ABSTRACT FROM AUTHOR]

Obtaining the structure of the Ti 3 C 2 S 2 MXene using Density Functional Theory, we study here for the first time the adsorption and diffusion of an Mg ion on the surface of the MXene. We find a very strong adsorption and the lowest energy barrier for Mg diffusion in Ti 3 C 2 -based materials reported so far. This value, equal to 0.049 eV, is comparable to the one for the diffusion of a Li ion on the surface of the Ti 3 C 2 Cl 2 MXene reported in previous studies, which was equal to 0.03 eV. The Ti 3 C 2 S 2 MXene could, therefore, potentially present as the best option for an anode electrode in Mg-ion batteries, while offering a safer, lower cost alternative to Li-ion batteries. • Ti 3 C 2 S 2 MXene can potentially be the best option for an anode electrode in Mg-ion batteries. • Mg ions on the surface of the Ti 3 C 2 S 2 MXene show strong adsorption. • Mg-ions on the surface of the Ti 3 C 2 S 2 MXene have the lowest migration energy barrier reported so far. [ABSTRACT FROM AUTHOR]