MX ( M = Ge, Sn; X = S, Se) sheets: theoretical prediction of new promising electrode materials for Li ion batteries

Exploring new electrode materials is one of the key solutions to the development of lithium ion batteries. In this work, via density functional theory calculations, we explored the interaction of Li with recently synthesized two-dimensional structures, MX (M = Ge, Sn; X = S, Se) sheets. Our studies revealed the following results: (1) Li atoms can spontaneously and rapidly load onto MX sheets, and finally form a stable configuration with adsorption energies of -1.82, -1.70, -1.76 and -1.86 eV for GeS, GeSe, SnS and SnSe sheets, respectively; (2) the activation barriers of Li atoms along the zigzag direction are about 0.19, 0.26, 0.30 and 0.36 eV for GeS, GeSe, SnS and SnSe sheets, respectively, which can be activated at room temperature; (3) at a relatively large content, MX sheets can still hold Li atoms strongly with very low adsorption energies, effectively insuring the thermodynamic stability of the electrode materials; (4) the results reveal remarkable average voltages, which are about 1.98, 2.12, 2.69 and 2.22 V for GeS, GeSe, SnS and SnSe sheets, respectively; (5) the calculated capacities are about 256, 178, 89 and 136 mA h g(-1) for GeS, GeSe, SnS and SnSe sheets, respectively, still larger than those of conventional electrode materials; (6) after lithiation, a semiconductor-to-conductor transition was observed, facilitating the electron movement in the MX sheets. All of these properties successfully show that MX (M = Ge, Sn; X = S, Se) sheets are potential electrode materials for application in high-performance lithium ion batteries.