A First-principles study of Na adsorption and diffusion on graphene nanoflakes under the effect of external electric field as an anode material for Na-ion battery

In this work the interaction between Na ion and graphene surface with the absence and the presence of external electric field (EEF) applied perpendicular to the surface was investigated. M06-2X/6-31G(d) DFT calculations were performed to describe the adsorption and diffusion properties. Meaning of the binding energy and scanning the potential energy surface (PES) of the charged molecular systems in the presence of EEF is different from that in the absence of electric field as the binding energy is an anisotropic characteristic which depends on the orientation of molecules with respect to the EEF. With the electric field increased from 0.0 a.u to 0.02 a.u , the diffusion barriers were decreased from 24 to 20 Kj/mol , for the Na ion in the graphene nanoflakes. We concluded that the external electric field can increase the charging speed of rechargeable ion batteries based on the graphene anode materials.