Stoichiometric lithium cobalt oxide (LiCoO2) has been synthesized by solid state reaction of mixtures of the system Co-0.5Li(2)CO(3) after mechanical activation by high energy milling. The differences in the reaction mechanism and in product stoichiometry with respect to what happens when starting from the non activated (physical) system have been brought into evidence by TG analysis. Furthermore it has been shown that stoichiometric LiCoO2 is obtained by a 200 h annealing of the activated mixture at temperatures as low as 400 degrees C. Finally, it has been revealed that longer activation times (150 h) result in Co oxidation to Co3O4 that, in turn, hampers the formation of stoichiometric LiCoO2. (c) 2006 Published by Elsevier B.V.