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

We computationally modeled the adsorptive behavior of O2, 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 lithium-air battery operation. O2 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 O2 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.