Novel Li1+xCo1-xO2 compositions were prepared by two synthesis methods: solid-state reaction between Li2O2 and Co3O4 under high pressure and mechanochemically assisted reaction between CoOOH and LiOH center dot H2O. Variation of the Li-to-Co ratio in the precursor mixture from 1.0 to 1.5 resulted in the formation of Li1+xCo1-xO2 compositions with x-0.12. The structure and cationic distribution in Li1+xCo1-xO2 were monitored by XRD powder analysis, TEM analysis and Li-6 MAS NMR spectroscopy. Pure Li1+xCo1-xO2 with Li2Ti2O4-type spinel structure was obtained under high pressure only. Mechanochemically assisted synthesis at 400 degrees C yielded layered LiCoO2 with a small amount of spinet-type Li1+xCo1-xO2. The spinet modification of LiCoO2 is able to accommodate extra Li, so that the Li-to-Co ratio is higher than 1. The layered modification of LiCoO2 is more rigid with respect to the accommodation of more than one lithium atom. (C) 2011 Elsevier B.V. All rights reserved.