Structural and Electronic Properties of Small Stoichiometric (Li2O2)n Clusters and Relevance to Li–O2 Batteries

Abstract

Stoichiometric (Li2O2)n clusters (n = 1–6) were systematically studied by density functional theory calculations with hybrid B3LYP functional. The most stable structures of these clusters are triplet except for the Li2O2 monomer. In the Li2O2 monomer, the closed shell singlet is strongly favored. There are superoxide-like characteristics in terms of bond lengths and spin in the stoichiometric peroxide lithium clusters, which may have implications for the formation and decomposition of peroxide lithium in Li–O2 batteries. Furthermore, the growth process of the lowest energy structures of (Li2O2)n clusters is “ring-like” (n = 2) → “rectangle-like” (n = 3,4) → “Y-like” (n = 5) → “disc-like” (n = 6) feature, this growth pattern is in good agreement with the experimental observation at the initial phase of discharge in the Li–O2 battery. In addition, the values of energy gaps for the (Li2O2)n clusters are much smaller than the band gap of bulk phase, and thus the (Li2O2)n cluster can enhance the electron conductivity in the peroxide lithium. The frontier molecular orbitals analysis indicates that there are π* antibonding on the surface of (Li2O2)n clusters, making their structures more stable. Finally, the PES of (Li2O2)n clusters have been simulated, we hope that our simulated PES can be compared with future experimental data.