Raman and FTIR Spectroscopy Investigations of Carbon-Coated LixFePO4 Materials

Abstract

Raman and Fourier transform infrared (FTIR) spectroscopy investigations were performed on carbon-coated materials differing by the temperature of their thermal treatments (575 and ) and by their electrochemical performance, with that obtained at a higher temperature showing larger reversible capacity and better capacity retention at high rates. Raman spectra gave information on the carbon located at the surface of the particles, which was shown for the two samples to be highly disordered with small in-plane correlation lengths . A UV Raman study has shown that these carbon coatings contain almost no -type carbon hybridization. This study has also highlighted again that the -type -type C ratio cannot be determined straightforwardly from Raman spectra recorded with visible excitation (such as ), and thus that no direct correlation can be done between the Raman band intensity ratio and the -type -type C ratio; a UV Raman study is necessary to get the true information on the -type C contribution. The baseline and absolute intensity of the FTIR spectra were shown to be sensitive to changes in the electronic conductivity of the samples. Furthermore, good crystallinity was maintained for materials upon cycling, showing good reversibility of the lithium deintercalation∕intercalation reaction.