Layered Li1+x(Ni0.425Mn0.425Co0.15)1−xO2 materials (x = 0 and 0.12) have been prepared by a coprecipitation method. The substitution of × Li+ ions for × metal ions in the transition metal layers leads to an increase in the average transition metal oxidation state for charge compensation, which was found to be due to the oxidation of Ni2+ ions into Ni3+ ions. The refinement in the R-3m space group of the X-ray diffraction data has shown an increasing lamellar character for the structure of these materials, with increasing overlithiation. Electron diffraction has revealed the presence of a √3.ahex. × √3.ahex. superstructure due to a cationic ordering in the transition metal layers, those being packed with faults along the chex.-axis. From an electrochemical point of view, the reversible capacity in the 2–4.3V decreased with overlithiation, in agreement with a decreasing amount of exchangeable electrons.
