First-Principles Study of Monolayer p e n t a - Co S 2 as a Promising Anode Material for Li / Na -ion Batteries

Using first-principles calculations, we investigate the properties of the ${\mathrm{Co}\mathrm{S}}_{2}$ monolayer pentagonal structure as a possible anode material for $\mathrm{Li}$- and $\mathrm{Na}$-ion batteries. The geometrical optimization reveals that the metal atom prefers to be adsorbed on the hollow site, and that the diffusion barrier of $\mathrm{Li}$ and $\mathrm{Na}$ can be as low as 0.22 eV, which would allow a relatively fast diffusion on the surface. Moreover, our calculations demonstrate that the ${\mathrm{Co}\mathrm{S}}_{2}$ monolayer has a theoretical specific capacity of 653.31 and $326.77\phantom{\rule{0.2em}{0ex}}\mathrm{mAh}\phantom{\rule{0.2em}{0ex}}{\mathrm{g}}^{\ensuremath{-}1}$ for $\mathrm{Li}$ and $\mathrm{Na}$, respectively, which in the case of $\mathrm{Li}$ is larger than the capacity of other two-dimensional materials used as an anode material. Overall, the ${\mathrm{Co}\mathrm{S}}_{2}$ monolayer in this structure shows excellent electrochemical properties, making it a promising candidate for use as the anode material in metal-ion batteries.