Combining aqueous and solid-phase analysis to improve the understanding during sulfuric-acid based leaching of LCO

The leaching of LiCoO₂ particles was investigated 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, causing leaching limitations. Adding enhancing agents, e.g. H₂O₂ or S₂O82-, results in higher conversion rates, which is explained by the reduction of the cobalt at the surface forming soluble species. Thus, no stable lithium-depleted phase is formed as passivation layer and completed leaching is possible.