Studies of thermal decomposition kinetics and temperature dependence of thermodynamic functions of the new precursor LiNiPO4·3H2O for the synthesis of olivine LiNiPO4

Abstract

The olivine LiNiPO4 was synthesized via the calcination of the new precursor LiNiPO4·3H2O at 600 °C. The precursor was obtained from low-temperature (50 °C) wet chemical reaction. The results from XRD, FTIR, AAS/AES and TG/DTG/DTA techniques confirmed the formula of the title compounds. The SEM results indicated the morphologies of the hydrate precursor as thin plate particles and the calcined product as small bead particles. The BET surface area of the final calcined product at 600 °C is much higher (5.807 m2 g−1) than that reported in the literature (0.25 m2 g−1). The kinetic triplet [activation energy, E, pre-exponential factor, A, and the most probable mechanism function, g(α)] and the thermodynamic functions of activated complexes (ΔS ≠, ΔH ≠ and ΔG ≠) for the dehydration step of LiNiPO4·3H2O were determined and discussed. The mechanism of the dehydration process is the single-step A3/2 (assumed random nucleation and its subsequent growth). New information, namely the isobaric molar heat capacity, experimental entropy, enthalpy and Gibbs energy changes as function of temperature (K) of LiNiPO4·3H2O and LiNiPO4, was evaluated from the DSC data by third-order polynomial fitting and reported for the first time. The calculated corresponding thermodynamic functions from kinetic parameters are compared and discussed.