X-ray diffraction and EXAFS analysis of materials for lithium-based rechargeable batteries
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XRay Diffraction and EXAFS Analysis of Materials for LithiumBased Rechargeable Batteries M. D. Sharkova, M. E. Boikoa, A. V. Bobyla, E. M. Ershenkoa, E. I. Terukova, and Y. V. Zubavichusb a
Ioffe PhysicalTechnical Institute, Russian Academy of Sciences, ul. Politekhnicheskaya 26, St. Petersburg, 194021 Russia email: [email protected] b National Research Centre “Kurchatov Institute”, pl. Kurchatova 1, Moscow, 123182 Russia Received February 22, 2013
Abstract—Lithium iron phosphate LiFePO4 (triphylite) and lithium titanate Li4Ti5O12 are used as compo nents of a number of active materials in modern rechargeable batteries. Samples of these materials are studied by Xray diffraction and extended Xray absorption fine structure (EXAFS) spectroscopy. Hypotheses about the phase composition of the analyzed samples are formulated. DOI: 10.1134/S1063774513070171
INTRODUCTION Compounds such as lithium iron phosphate LiFePO4 (known also under the name triphylite) and lithium titanate Li4Ti5O12 are active materials used in modern rechargeable batteries. It is known that these compounds prepared by chemical methods can con tain foreign phases which can differ in the size, shape, and even physical state. Hence, samples of triphylite or lithium titanate may be composed of either perfect crystalline or amorphous grains. Such samples can be successfully studied by combined methods. First, the atomic structure was investigated by extended Xray absorption fine structure (EXAFS) spectroscopy, which is sensitive to materials in any physical state. Second, the structure of the crystalline components of the sample was studied by Xray diffraction.
The Fe KEXAFS spectra recorded for both sam ples of LiFePO4 are shown in Fig. 1. Figure 2 displays the EXAFS spectrum at the Ti Kedge for the titanate sample. Both triphylite samples were studied also by Xray diffraction. Figure 3 shows the Xray diffraction (XRD) data for lithium iron phosphate samples 1 and 2, respectively. The Xray diffraction data were collected on a Bruker D8DISCOVER instrument in the Ioffe Phys icalTechnical Institute of the Russian Academy of Sciences using monochromated CuKα beams (the Absorption, arb. units 1.05
EXPERIMENTAL DATA MEASUREMENTS Two samples of triphylite and one sample of lithium titanium were prepared by chemical etching in the St. Petersburg State Technological Institute (Techni cal University). The EXAFS spectra of all samples (at the Ti Kedge for titanate and at the Fe Kedge for phosphate) were measured at the Structural Materials Science beamline on the SIBIR2 synchrotron radia tion source at the National Research Centre “Kur chatov Institute” (NRC KI). The measurements were performed in the reflection mode using two ionization chambers filled with N2–Ar gas mixtures. The energy was scanned using a Si(111) channelcut monochro mator. For one of the samples (sample 1), the EXAFS spectrum was repeatedly recorded 3 months after the first spectrum. One EXAFS spectrum was measured for another tr
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