Inelastic X-ray scattering spectroscopy of Li stage intercalation in graphite

S. CEPPI; D. BARRACO; M. OTERO; C. ROBLEDO; G. LUQUE; G. STUTZ; E. LEIVA

Buenos Aires

Congreso; 20th Topical Meeting of the International Society of Electrochemistry, Advances in Lithium and Hydrogen Electrochemical Systems for Energy Conversion and Storage; 2017

The 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 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). Ultrasoft pseudopotentials were employed with the GGA approximation for exchange and correlation in the PBE functional.The theoretical results are in close accordance with the experimental measurements allowing studying the electronic density characteristics of the materials [Figure 1]. For the first time stage II samples were measured permitting to define the physical disturbance of the unoccupied states of carbon atoms upon lithium insertion.