Acta Phys. -Chim. Sin. ›› 2008, Vol. 24 ›› Issue (05): 873-879.doi: 10.3866/PKU.WHXB20080524

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Synthesis of LiFePO4 and Thermal Dynamics of the Precursor

RUAN Yan-Li; TANG Zhi-Yuan   

  1. School of Material Science and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300160, P. R. China; School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China
  • Received:2007-10-16 Revised:2008-02-27 Published:2008-05-05
  • Contact: RUAN Yan-Li

Abstract: Olivine LiFePO4 cathode materials were synthesized by a solid state method in an inert atmosphere. The thermal decomposition processes taking place in the solid state mixture of Li2CO3, FeC2O4·2H2O, and NH4H2PO4 were investigated using TG-DTA and XRD techniques. The dynamic study of the precursor was also investigated using TG-DTA at different heating rates. The decomposition proceeded through three well-defined steps while TG curves closely corresponded to the theoretical mass loss. The apparent activation energy of each stage was calculated using the Doyle-Ozawa and Kissinger methods. The calculated results were 134.3, 122.2, 173.2 kJ·mol-1 for Ozawa method and 102.4, 128.1, 145.3 kJ·mol -1 for Kissinger method. The coefficients of reaction order, frequency factor, and dynamic equations were also determined. Based on the results of the dynamic study, the cathode material LiFePO4 was synthesized by optimized step-sintering method. The crystal structure and the electrochemical performance were characterized by X-ray powder diffraction (XRD), scan electron microscopy (SEM), and galvanostatical charge-discharge testing. The results showed that the material had a single crystal olivine structure with homogeneous grain sizes, and exhibited excellent electrochemical performance at 0.1C rate.

Key words: LiFePO4, Differential thermal analysis, Solid state synthesis, Dynamic equation