Combining Aqueous and Solid-Phase Analysis to Improve Understanding of Sulfuric Acid-Based Leaching of LCO

The leaching of LiCoO₂ particles was investigated by combining aqueous analysis (inductively coupled plasma-optical emission spectroscopy) with solid-phase analysis methods (X-ray diffraction, X-ray photoelectron spectroscopy). The most common industrial leaching mixture, H₂SO₄ and H₂O₂, was used to understand the ongoing processes on the material level rather than performing an empirical improvement of a hydrometallurgical process. Instead, the reactions inside the bulk and on the surface of the LiCoO₂ particles during leaching are investigated. LiCoO₂ undergoes different structural phase transitions at the surface as well as in the bulk when leached with sulfuric acid due to strong lithium loss and the oxidation of cobalt. A stable outer shell with a delithiated core forms during leaching, which causes leaching limitations. Adding enhancing agents, e.g., H₂O₂ or S₂O₈^2-, results in higher conversion rates, which is explained by the reduction of the cobalt at the surface, forming soluble species. Thus, the phase transitions to the stable lithium-depleted phase are avoided, and complete leaching is possible.