CONICET | Buscador de Institutos y Recursos Humanos

Inelastic X-ray scattering spectroscopy in Li-intercalated graphiteThe high-energy consumption in our day-to-day life can be balanced by harvesting power from pollution-free renewable energy sources. However, the latter requires from adequate energy carriers, which allow proper storage and distribution of energy. In this regard, the lithium ion battery is currently considered as an effective energy storage device and is involved in much active research in the electrochemical community. Li-intercalated graphite (LIG) is of particular interest both as the best studied intercalation compound but also due to its relevance for present day rechargeable battery technology.In the present work we investigate near edge fine structure at the Li and C K-edge in electrochemically prepared LIG in stages I and II by means of inelastic X-ray scattering spectroscopy. An inelastic X-ray scattering (IXS) experiment with high energy resolution provides information about electronic excitations by measuring the double differential scattering cross section as a function of the energy and momentum transfer. The present work applies IXS spectroscopy in the regimes of scattering from valence and core electrons to investigate electron excitation dynamic in LIG in stages I and II. In the former regime, collective and single particle like excitations of valence electrons can be investigated. In the latter, IXS gives the possibility of measuring absorption edges in the soft X-ray or VUV energy range, but with the advantages of using hard X-rays. Making use of the momentum transfer dependence of the IXS cross section, excitation channels other than dipolar can be investigated when core electrons are excited to empty states. This is a unique property of a spectroscopic technique based on a scattering process. We also present first-principles calculations results obtained for both stages to support the analysis obtained for the experimental results. Density functional theory calculations were performed using the Quantum Espresso package with Van der Waals interactions (DFT-D). Ultra soft pseudopotentials were employed with the Perdew-Wang approximation for exchange and correlation in the PW91 functional. The Kohn-Sham orbitals and charge density were expanded in plane-waves basis set up to 880 and 8800 eV for stage I and 1500 and 15000 eV for stage II, respectively. The Brillouin zone was sampled 13 x 13 x 13 irreducible Monkhorst-Pach k-point grid for both stages and 11 numbers of bands (nbnd) were considered for each atom to study de unoccupied states. The convergence threshold for the total energy at each electronic calculation was set to 1.36 x 10-7 eV.