First-principles study of phosphorene and graphene nanoflakes under the effect of external electric field as an anode material for Li-ion battery

Lithium ion batteries (LIBs) have been the subject of intense investigations due to their good cycling performance, high storage capacity and high energy density [1]. Despite all the studies, finding excellent anodes with good electrical conductivity and high reversible lithium storage are still under development [2]. Therefore, in this research we investigated materials with improved properties for use in the anode electrode of Li-ion batteries, using first-principles calculations. For this purpose, two-dimensional materials such as graphene and phosphorene because of their large surface-to-volume ratio and unique electronic properties are used. In this work the adsorption mechanism of Li metal atom and Li-ion in the absence, and presence, of a perpendicularly external electric field on the P54H18 phosphorene surface and C54H18 graphene surface (Fig 1) has been investigated using M05-2X/6-31G(d,p) density functional theory (DFT) and compare the results with those of C54H18 graphene surface [3]. The structural characteristics, charge transfer, electric surface potential (ESP) maps, equilibrium distances between atom/ion and the graphene or phosphorene surface and dipole moments of the atom/ion–graphene or phosphorene complexes were investigated (Table 1). In contrast to C54H18 graphene, interactions between Li metal atoms and Li-ions with P54H18 phosphorene surface are quite strong due to its highly reactive buckled hexagonal structure (Fig 2). As a consequence of structural properties adsorption height, most stable adsorption site and energy barrier against Li diffusion are also discussed here. electric field(a.u.) Eint(Kjol/mol) Dipole Moment (a. u.) R(Å) 0.000 -206.90 6.97 1.57 0.001 -213.25 9.06 1.59 0.002 -217.13 11.09 1.60 0.003 -220.76 13.13 1.62 0.004 -224.12 15.19 1.63 0.005 -227.24 17.26 1.66 Table1. Interaction energy, dipole moment and equilibrium distances between Li atom and the P54H18 surface related to electric field 180 Figure 1. During the calculations the applied electric field was perpendicular to the grapheme surface Here, it is shown that graphene has very limited Li storage capacity and low surface area than the phosphorene. As our models are in good agreement with previous predictions, this finding presents, a possible avenue for creating better anode material that can replace with graphene for higher capacity and better cycling performance of LiBs. Figure2. Interaction energy between Li atom and the P54H18 surface related to electric field