Lithium Ion Extraction from Orthorhombic LiMnO2in Ammonium Peroxodisulfate Solutions

Well-crystallized orthorhombic LiMnO2was prepared by a flux method with a (LiCl+LiOH) mixture as the flux. The study of Li+extraction from the orthorhombic LiMnO2was carried out batchwise using a solution containing an oxidizing agent (0.5 mol· dm-3(NH4)S2O8). Lithium ions could be extracted from the LiMnO2without the dissolution of manganese. The time course of Li+extraction showed that the Li+extraction proceeded in three steps with different extraction rates. Chemical analysis showed that the reaction progressed mainly by a redox mechanism. A structural transformation of orthorhombic LiMnO2phase to spinel LiMn2O4took place at the first and second steps, accompanied by the Li+extraction. The structural transformation could be explained well by considering the migration not only of all the lithium ions but also of half of the manganese ions in both oxygen frameworks. The topotactic extraction of Li+from LiMnO2gave a rodlike manganese oxide with a spinel structure. A model of the Li+extraction process was proposed as well as a model for the structural transformation from the orthorhombic LiMnO2to spinel LiMn2O4. The Li+insertion into the Li+-extracted sample did not proceed in a mixed solution containing 0.1mol·dm-3LiOH and 0.5 mol· dm-3LiI.