Core-Level RIXS as a Tool for Analyze Charge-Related Variations on the Li4Ti5O12 Compound

F. OLIVA; A. MIGLIORI; JOSE ROBLEDO; A. KARYDAS; H.J. SÁNCHEZ; JUAN JOSÉ LEANI; M. CZYZYCKI; C. PEREZ

Rio de Janeiro

Seminario; Latin American Seminar of Analysis by X-Ray Techniques (SARX); 2016

Universidade do Estado do Rio de Janeiro Instituto

Nowadays, renewable energy resources as well as more efficient energy storage systems have taken a starring role, since more sustainable energy systems are being demanded due mainly to the increasing needs of modern society together with the collateral effects of conventional energy sources. This situation has driven to a search for improved electrochemical storage systems that can safely store energy from sustainable sources, proving the energy needed, for example, for transportation and residential uses.As an example of everyday technology, the use of portable electronic devices has been feasible thanks to the lithium-ion batteries (LIB). The energy storage capacity of the LIB system is 5 times higher than lead-acid batteries, and it shows an average voltage of 3.8 V per cell in comparison with the average 2.0-2.2 V of the lead-acid batteries. In addition, lithium-ion batteries have the advantage of lower weight, higher energy density and faster charge and discharge rates compared to other similar battery technologies.Even though they are the most widely batteries employed in portable electronics, it is important to attend several issues regarding safety, and to improve its energy storage capacity in order to be used at larger scales, in, for example, electric vehicles. Lithium titanate, Li4Ti5O12 (LTO), is a promising candidate for anode material at the moment because of many its advantages. Due to this, a better knowledge regarding the LTO structure and how changes are related with its ulterior performance is of great importance.In this work, Resonant Inelastic X-ray Scattering (RIXS) has been used for studying titanium local environment changes in the LTO molecule when different levels of charge are applied. As complementary technique, XANES spectra of the Ti-K edge were also measured.The measurements were carried out at the Brazilian Synchrotron Light Source (LNLS, Campinas) in the D09B beamline and at ELETTRA Sincrotrone Trieste (Italy) in the IAEA end-station of the XRF-beamline. Several samples with different levels of charge (not charged, partially charged and fully charged) were studied. Reflection geometry was used together with monochromatic photons of 4900 eV (just beneath the K absorption edge of titanium) for the RIXS measurements and XANES spectra were acquired scanning the incident beam energy in the range 4930-5080 eV, i.e., around the Ti-K edge.For data analysis, and in order to discriminate the changes on the titanium chemical state of the LTO molecule, Principal Component Analysis (PCA) was used on both RIXS and XANES spectra.The results show that RIXS allows the detection of minor changes in the structure of the lithium-based compound due to the particular level of charge. In this way, typical chemical studies as the ones performed with conventional absorption techniques (XANES, EXAFS) can be achieved with this technique, with the advantageous characteristics of shorter measuring times and suppressing any energy scan during the analysis, between others.