Urea decomposition enhancing the hydrothermal synthesis of lithium iron phosphate powders: Effect of the lithium precursor

摘要

The synthesis of LiFePO4 (hereafter referred as LFP) using urea as a reducing agent under hydrothermal conditions was investigated. The synthesis was carried out by varying the temperature (150-200 degrees C), at different times from 6 to 24 h, and using different precursors of Li ions (LiCl, LiNO3, LiOH, and Li2SO4), to determine the effect of these parameters on the crystallization process of the reaction products. These were characterized by XRD, FT-IR, and FE-SEM. The results showed that the differences in the lattice parameters calculated by Rietveld refinement are affected by the synthesis temperature. In addition, the crystallization of single-phase LiFePO4 powders was achieved by the urea decomposition that occurred at reaction times longer than 12 h and at moderate temperatures (170-180 degrees C). The crystallization of LFP particles was promoted by a dissolution-precipitation mechanism, but it was not conducted in a single step, because intermediate secondary phases were produced at reaction intervals below 6 h. A crystal growth stage involving the dissolution-crystallization of intermediate secondary phases led to the formation of large particle agglomerates of LiFePO4 exhibiting a flower-like morphology when the synthesis was carried out using Li2SO4. When LiCl, LiOH, and LiNO3 were used, large bulky agglomerates were obtained. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.