Structure of Lithium Peroxide

The reliable identification of lithium oxide species, especially lithium peroxide (Li2O2), is of vital importance to the study of Li-air batteries. Previous X-ray diffraction studies of Li2O2 resulted in the proposal of two disparate structures by Feher and Foppl. In this Letter, we assess these competing Li2O2 structures using a combination of the following X-ray and first-principles techniques: (i) high-energy X-ray diffraction (XRD), (ii) comparisons of the measured nonresonant inelastic X-ray scattering (NIXS) spectra with those computed from first principles using the Bethe-Salpeter equation (BSE), and (iii) comparison of thermochemistry data with the formation enthalpies obtained from density functional theory (DFT) calculations using a hybrid functional. All three approaches result in the identification of Foppl's proposal as the more appropriate structure for Li2O2. The measured and computed spectra and data presented in this Letter are useful as benchmarks for future characterization of Li2O2. SECTION: Molecular Structure, Quantum Chemistry, General Theory