While it is commonly known that layered LixCoO2 transforms to a mixture of stoichiometric LiCoO2 and Co3O4 at elevated temperature, little experimental detail exists on the role time and temperature play in the transformation process or on the occurrence of possible intermediate phases. In this article we follow the thermal decomposition of LixCoO2 by characterizing its decomposition products after short and long-term isothermal annealing at 350 degrees C. X-ray diffraction and transition electron microscopy observations are complemented by electron energy loss spectroscopy and magnetic susceptibility measurements thus allowing the combination of structural and electronic information. Our results indicate that the charge balance upon Li extraction from LiCoO2 is in parts accomplished by oxidation of Co3+ to Co4+. in the annealed powder we observe an intermediate Li-Co-O phase of cubic spinel structure before the end products Co3O4 and CoO are formed. (C) 2010 Elsevier B.V. All rights reserved.