Kinetic Studies on the Synthesis of Monoclinic Li3V2(PO4)3 via Solid-State Reaction

The data obtained by thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (XRD) measurements of the stoichiometric mixture of LiNO3, NH4VO3, and NH4H2PO4 were analyzed by both the Flynn-Wall-Ozawa (FWO) and Friedman-Reich-Levi (FRL) methods. The whole solid state reaction process could be divided into four stages corresponding to alpha values of 0.03-0.20, 0.30-0.60, 0.70-0.80, and 0.90-0.99. The nucleation of LiVP2O7 (alpha = 0.70-0.80) is a determining step of the four-reaction processes, for which the mechanism of random nucleation and subsequent growth, described by the Avrami-Erofeev equation (n = 4) G(alpha) = [-ln(1 - alpha)](4), was assumed. Moreover, the Gibbs free energy of activation Delta G*, enthalpy of activation Delta H*, and entropy of activation Delta S* at maximum temperature of the peak for the determining step were 99.24 kJ.mol(-1), 199.97 kJ.mol(-1), and 136.30 J. mol(-1).K.(-1), respectively. Finally, XRD analyses confirmed that the Li3V2(PO4)(3) synthesized by the precursor route is a pure phase.