LFP(LiFePO4) 양극활물질 공정부산물로부터 탄산리튬 회수 연구

Abstract

LFP(LiFePO4) is a cathode material composed of Li, Fe, and PO4 by adding iron phosphate instead of Co in LCO(LiCoO2), and has a hexahedral phosphate structure. LFP is an olivine structure and has higher lattice structure stability than a layered structure due to the strong covalent bond of P-O. It is difficult to apply the CO2 thermal reaction process used in a layered cathode active material because of the strong covalent bond of P-O. Therefore, this research conducted the H2 thermal reaction to recover lithium carbonate from the LFP cathode active material process byproducts. A phase was separated into lithium phosphate(Li3PO4) and iron phosphide(Fe2P) through an H2 thermal reaction from LFP, and optimal phase separation conditions with Li3PO4 were derived according to conditions such as reaction temperature and reaction time. Thereafter, the Li3PO4 and Fe2P were separated using a difference in solubility in water, and a Li recovery rate in accordance with conditions such as a solid-liquid ratio and leaching time was investigated. The aqueous solution of Fe2P and Li3PO4 separated by the water leaching process was dried at 90°C or higher for 24 hours. In order to recover Li2CO3 from the Li3PO4 powder recovered after drying, CaCO3 powder and Li3PO4 powder were mixed to perform a CO2 thermal reaction process. Phase-separated from Li3PO4 to Li2CO3 and Ca2P2O7 through a thermal reaction with CaCO3 powder, and optimal phase separation conditions to Li2CO3 were derived according to conditions such as reaction temperature, weight ratio of Li3PO4 and CaCO3, reaction time, and the like. Thereafter, the Li recovery rate according to conditions such as a solid-liquid ratio and leaching time was investigated using the difference in solubility of Li2CO3 and Ca2P2O7 in water. The aqueous solution of Ca2P2O7 and Li2CO3 separated by the water leaching process was dried at 90°C or higher for 24 hours. As a result of the optimal condition test calculated in each process, the Li recovery rate is 93.02% for Li3PO4, and 93.59% for Li2CO3.