Raman spectroscopy of carbon-coated LiCoPO(4) and LiFePO(4) olivines

The effect of laser power on the Raman spectra of two carbon-coated nano-powders of LiCoPO(4) and LiFePO(4) olivine cathode materials were investigated. In the ambient atmosphere at a moderate laser power, the phenomenon of the removal of the carbon coating layer from both samples was detected. The olivine structure of LiCoPO(4)-C powder therefore remains unchanged during the prolonged exposure to a 4.3 mW laser beam. The mild removal of the carbon layer makes it possible to analyze the details of the LiCoPO(4) structure in air without interference from carbon. LiFePO(4)-C powder, together with carbon layer gasification, undergoes oxidative decomposition by the oxygen with the formation of Li(3)Fe(2)(PO(4))(3) and Fe(2)O(3), even at a laser power of 1 mW. Thus, care should be taken when measuring and interpreting the Raman spectra of this material both in air and in an inert atmosphere, as obvious decomposition of the LiFePO(4) olivine structure takes place even at a moderate power of the excitation laser. A comparative study of the stability of these two carbon-coated nano powders under laser beam irradiation and heating was carried out with the use of TGA-mass spectrometry. (C) 2011 Elsevier B.V. All rights reserved.