Synchrotron X-Ray Absorption Study of LiFePO4 Electrodes

Abstract

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 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 as an electrolyte and ethylene carbonate/dimethyl carbonate as a solvent. The X-ray absorption spectra were measured at the initial state [containing mainly Fe(II)], which corresponds to the uncharged state of the battery and at the delithiated state 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), and Fe(III), 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. © 2004 The Electrochemical Society. All rights reserved.