Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 39: Focussed session: Frontiers of electronic structure theory: Strong correlations from first principles III (jointly with TT)

O 39.8: Vortrag

Mittwoch, 28. März 2012, 12:15–12:30, HE 101

Electron conductivity of Li2O2 in Li-air batteries — •Juan María García Lastra and Kristian Thygesen — Center for Atomic-scal Design. Technical University of Denmark.

The development of non-aqueous Li-air batteries in the late 90s and the rapidly growing demands for better and more sustainable methods for energy storage, have recently spurred a great deal of interest in the material Li2O2. The main limiting factor in the performance of reversible Li-air batteries, namely the large potential losses at realistic current densities, is believed to be related to poor intrinsic transport properties of Li2O2 and/or the carbon- Li2O2 interface. Li2O2 is a wide-gap insulator material (4.9 eV gap) and thus is only able to transport electrons if it contains some kind of defect. Li+ ion vacancies have been detected by means of X-ray diffraction (XRD) and X-Ray Absorption Near Edge Spectroscopy (XANES) in Li2O2 during the discharge of the Li-air batteries. These defects are believed to be the responsible for the electronic transport in Li2O2. Nevertheless, the transport mechanism is not yet clear. In a previous paper from our group it was proposed that Li+ vacancies create electron holes in the valence band of Li2O2, which gives rise to the electronic conduction. However, recent optical absorption experiments have revealed strong excitonic effects in Li2O2 , which point towards to the creation of Li+-Superoxide pairs, instead of holes in the valence band. In this work I will present confirmation of the last hypothesis through DFT+U calculations and propose possible routes for improving Li2O2 electron conductivity through doping.