Raman and FTIR Spectroscopic Study of LixFePO4 ( 0 ⩽ x ⩽ 1 )

Abstract

A series of compounds, was prepared by chemical delithiation and investigated with Fourier transform infrared (FTIR) and Raman spectroscopy for the first time. Sample homogeneity with respect to Fe and P was analyzed with an electron microprobe. The imaging capabilities of the electron microprobe reveal larger-sized particles (10-20 μm diam) and fine intergranular particles (⩽1 μm). Elemental analysis with the electron microprobe demonstrates that the particles are relatively homogeneous. Thus, the electron microprobe may be used in conjunction with other instruments that are more commonly used to investigate particle morphology, such as scanning or transmission electron microscopes. Isotopic substitution experiments show that the symmetric and antisymmetric bending vibrations of the anion are highly mixed with translatory vibrations. Consequently, no band in the IR spectrum of may be assigned solely as a lithium ion “cage” mode. Spectroscopic measurements of the series demonstrate that the intramolecular modes of are particularly sensitive to the extraction of ions from and the accompanying oxidation of to Spectroscopic data suggest that the effective force constants (band frequencies), dipole moment derivatives (FTIR intensities), and polarizability derivatives (Raman intensities) change as is converted into Together, the data strongly support the two-phase shell model of delithiation. © 2004 The Electrochemical Society. All rights reserved.