Li ion diffusion dynamics on Li oxides and peroxides surfaces

Li ion diffusion in the discharge products of the Li-O2 batteries is relevant to the performance of the battery. In this paper, Li ad-atom and Li-vacancy diffusion at the Li2O and Li2O2 surfaces are studied from first principles calculations. Li diffusion are considered on the energetically most favorable surfaces Li2O-(111) and Li2O2 (112̅0), which are obtained from calculating the surface energies of low index surfaces. Results show that Li diffusion on the Li2O-(111) is very slow at room temperature with energy barriers of 0.45 eV and 0.98 eV for Li ad-atom migration and vacancy migration, respectively. On the other hand, Li diffusion on Li2O2 (112̅0) surface is even more difficult. Li-vacancy migration energy barrier is 0.75 eV, while Li ad-atom migration is prohibited with an energy barrier of 1.87 eV. These results give explanations to the poor rate performance of the Li-O2 batteries and also suggest a possible Li2O phase formation mechanism at the Li2O2 surface.