Li[Co1-zAlz]O-2 (O <= z <= 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief Non-stoichiometric Li-x[Co0.9Al0.1]O-2 samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co+Al)=0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Li-x[Co0.9Al0.1]O-2 samples suggest the solid solution limit is between Li/(Co+Al)= 1.1 and 1.2. Electrochemical studies of the Li[Co1-zAlz]O-2 samples were used to measure the rate of capacity reduction with Al content, found to be about -250 +/- 30 (mAh/g)/(z=1). Literature work on Li[Ni1/3Mn1/3Co1/3-zAlz]O-2, Li[Ni1-zAlz]O-2 and Li[Mn2-yAly]O-4 demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co1-zAlz]O-2 in electrolyte. (C) 2009 Elsevier Ltd. All rights reserved.