Reaction Kinetics of the Intermediate in Synthesis of LiCoPO<sub>4</sub> by Solid-State Reaction

Abstract

A precursor NH4CoPO4 containing Li + was synthesized using a low temperature solid-state reaction with ammonium dihydrogen phosphate, cobalt acetate, and lithium hydroxide. LiCoPO4 powder was manufactured by high temperature baking. The products were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA). The results showed that the formation of the intermediates was effected by the baking atmosphere. NH4CoPO4 containing Li + was dehydrated and deaminated in air at 210−500 °C and then the (CoHPO4·LiCoPO4·Co2(OH)PO4·Li3PO4) intermediate (acid-base community) was emerged during the reaction process. The intermediate formation reaction mechanism followed the interfacial reaction power-law with an apparent activation energy of 50.0 kJ·mol - 1 . The kinetic function was found to be g(x)= (1−α) - 1 . The intermediate was dehydrated to form LiCoPO4 with an average apparent activation energy of 54.2 kJ·mol −1 . The formation of the intermediate was not affected by the process of crystallization or non- crystallization of the materials. High temperatures accelerated the decomposition reaction of the intermediate and then the formation of LiCoPO4 crystals. A perfect crystal of LiCoPO4 was obtained by the decomposition of the intermediate at temperatures higher than 550 °C.