Adsorption mechanisms of lithium oxides (LixO2) on a graphene-based electrode: A density functional theory approach

We computationally modeled the adsorptive behavior of O-2, Li, LiO2, and Li2O2 on graphene using density functional theory (DFT) in an effort to understand the mechanisms by which lithium oxides (LixO2) and oxygen reduction reaction (ORR) products adsorb onto graphene-based electrodes during lithiumair battery operation. O-2 weakly adsorbed onto graphene with a binding energy of -0.111 to -0.089 eV, whereas Li strongly adsorbed onto graphene with relatively large binding energy of -1.079 to -0.774 eV. The LiO2 formation energy (-2.453 eV) was much lower than the LiO2 adsorption energy (-0.450 eV) on graphene, indicating that after Li and O-2 had associated, LiO2 adsorbed onto the graphene surface. Among the various Li2O2 adsorption configurations, the parallel configurations in which Li2O2 was oriented along the graphene axis (-0.630 to -0.611 eV) were more favorable than the perpendicular configurations (-0.513 to -0.475 eV). Consequently, more charges were transferred from Li to graphene in a parallel orientation. (C) 2015 Elsevier B.V. All rights reserved.