Synchrotron X-Ray Absorption Study of LiFePO4 Electrodes

Synchrotron X-Ray Absorption Study of LiFePO4 Electrodes

TitleSynchrotron X-Ray Absorption Study of LiFePO4 Electrodes
Publication TypeJournal Article
Year of Publication2005
AuthorsOtto Haas, Aniruddha Deb, Elton J Cairns, Alexander Wokaun
JournalJournal of The Electrochemical Society
Volume152
Issue1
PaginationA191-A196
ISSN00134651
Keywordselectrochemical electrodes, iron compounds, lithium compounds, secondary cells, XANES
Abstract

LiFePO4 was investigated in practical Li-ion intercalation electrodes used for Li-ion batteries by applying X-ray absorption spectroscopy (XAS). A special in situ XAS cell was constructed to charge and discharge the LiFePO4 electrodes at current densities typically used in Li-ion batteries. Ex situ XAS measurements were made with technically relevant electrodes developed by Hydro-Québec power research using LiPF6 as an electrolyte and ethylene carbonate/dimethyl carbonate as a solvent. The X-ray absorption spectra were measured at the initial state [containing mainly LiFePO4, Fe(II)], which corresponds to the uncharged state of the battery and at the delithiated state [FePO4, Fe(III)], which corresponds to the battery’s charged state. The X-ray absorption near-edge structure region of the X-ray absorption spectra showed a substantial Fe K-edge shift after the electrode was electrochemically oxidized. The pre-edge features of the X-ray absorption spectra revealed high spin configuration for the two oxidation states [Fe(II), d6 and Fe(III), d5]. Reasonable ligand field stabilization energies could be extracted from the pre-edge features. Using the data analysis program EXAFSPAK with the FEFF8 code provided in this program, the EXAFS spectrum and its Fourier transformed radial structure function could be simulated satisfactorily, where only single scattering paths were used for this simulation.

DOI10.1149/1.1833316
Short TitleJ. Electrochem. Soc.