Non-isothermal kinetics study on synthesis of LiFePO4 via carbothermal reduction method

Abstract

Non-isothermal kinetics of lithium ion phosphate synthesis via carbothermal reduction method with raw materials Li2CO3, FePO4·2H2O and C6H12O6·2H2O is studied by thermogravimetry-differential scanning calorimetry (TG–DSC) technology. The results indicate the synthesis process can be divided into two stages: dehydration and LiFePO4 formation. The apparent activation energy and natural logarithm frequency factor (lnA-value) for dehydration reaction is respectively 83.4±4.7kJmol−1 and 22.1±1.5s−1, and that for LiFePO4 formation reaction is in turn 184.2±10.4kJmol−1 and 28.3±1.9s−1. Additionally, the mechanism for dehydration and LiFePO4 formation stages is Avrami's A1.5 and A4, respectively. Furthermore, the dehydration process is diffusion controlled, and the crystallization of LiFePO4 formation is controlled by nuclei being formed randomly and growing in three-dimensions, and the kinetic equations for each stage are shown as follows:Dehydration stage: [−ln(1−a)]2/3=3.96×109 exp−8.34×104RTt;LiFePO4 formation stage: [−ln(1−a)]1/4=1.95×1012 exp−1.84×105RTt;where α is the fractional conversion, T the calcination temperature (K), t the calcination time (s), R the gas constant (8.314Jmol−1K−1).