Comparative study of Li[Co1−zAlz]O2 prepared by solid-state and co-precipitation methods

LiCo_1−zAl_z]O₂ (0 ≤ 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_xCo_0.9Al_0.1]O₂ 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_xCo_0.9Al_0.1]O₂ samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the LiCo_1−zAl_z]O₂ 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 LiNi_1/3Mn_1/3Co_1/3−zAl_z]O₂, LiNi_1−zAl_z]O₂ and LiMn_2−yAl_y]O₄ 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 LiCo_1−zAl_z]O₂ in electrolyte.