Janus SnXY (X/Y = O, S, Se, Te, X ≠ Y) monolayers for sodium ion storage anodes: In view of first principles understanding

The exploration of two-dimensional (2D) anode materials with fascinating theoretical specific capacity and ion diffusion rate has been paid much attention in the domain of alkali ion batteries. In this present contribution, the potency of monolayer Janus SnXY (X/Y = O, S, Se, Te, X ≠ Y) to function as an anode material for Na-ion batteries (SIBs) is anticipated upon the ground of first-principles calculations. The outcomes indicate that the cohesion energies of all the SnXY are positive, signifying that they are energetically stabilized. The distribution of electrons in the SnXY structure is strongly dependent on the electronegativity of the atoms on both sides, and the higher the electronegativity, the more electrons are gathered. Meanwhile, the larger (smaller) charge transfer between Sn atoms and X/Y atoms enhances (weakens) the bond strength and leads to a decrease (increase) in the interlayer spacing. In service, Na atoms tend to be steadily adsorbed at the top of O, Sn, Se and Te, and a large number of electrons are transferred from Na atoms to SnXY. SnXY exhibits a metallic state after embedding, increasing its own electrical conductivity. Particularly, the SnSSe has a low diffusion barrier of 0.12 eV and a high Na storage capacity of 1380 mAh/g. These insights demonstrate that monolayer Janus SnXY is a prospective anode material for SIBs possessing high storage capacity and rapid charge/discharge rates.