Reaction Kinetics of the Intermediate in Synthesis of LiCoPO 4 by Solid-State Reaction

Abstract

A precursor NH 4 CoPO 4 containing Li + was synthesized using a low temperature solid-state reaction with ammonium dihydrogen phosphate, cobalt acetate, and lithium hydroxide. LiCoPO 4 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. NH 4 CoPO 4 containing Li + was dehydrated and deaminated in air at 210-500 °C and then the (CoHPO 4 · LiCoPO 4 · Co 2 (OH)PO 4 · Li 3 PO 4 ) 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 LiCoPO 4 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 noncrystallization of the materials. High temperatures accelerated the decomposition reaction of the intermediate and then the formation of LiCoPO 4 crystals. A perfect crystal of LiCoPO 4 was obtained by the decomposition of the intermediate at temperatures higher than 550 °C. © Editorial office of Acta Physico-Chimica Sinica.