A first-principles study of sodium adsorption and diffusion on phosphorene.

The structural, electronic, electrochemical as well as diffusion properties of Na doped phosphorene have been investigated based on first-principles calculations. The strong binding energy between Na and phosphorene indicates that Na could be stabilized on the surface of phosphorene without clustering. By comparing the adsorption of Na atoms on one side and on both sides of phosphorene, it has been found that Na-Na exhibits strong repulsion at the Na-Na distance of less than 4.35 Å. The Na intercalation capacity is estimated to be 324 mA h g(-1) and the calculated discharge curve indicates quite a low Na(+)/Na voltage of phosphorene. Moreover, the diffusion energy barrier of Na atoms on the phosphorene surface at both low and high Na concentrations is as low as 40-63 meV, which implies the high mobility of Na during the charge/discharge process.