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 α values of 0.03-0.20, 0.30-0.60, 0.70-0.80, and 0.90-0.99. The nucleation of LiVP₂O₇ (α = 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(α) = [-ln(1 - α)]⁴, was assumed. Moreover, the Gibbs free energy of activation ΔG*, enthalpy of activation ΔH*, and entropy of activation ΔS* 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.