Comparison of the chemical stability of Li1-xCoO2 and Li1-xNi0.85Co0.15O2 cathodes

The chemical stability of the layered Li1-xCoO2 and Li1-xNi0.85Co0.15O2, cathodes is compared by monitoring the oxygen content with lithium content (1-x) in chemically delithiated samples. The Li1-xCoO2 system tends to lose oxygen from the lattice at deep lithium extraction while the Li1-xNi0.85Co0.15O2 system does not lose oxygen at least for (1 -x) > 0.3. This difference seems to result in a lower reversible (practical) capacity (140 mA h/g) for LiCoO2 compared to that for LiNi0.85Co0.15O2 (180 mA h/g). The loss of significant amount of oxygen leads to a sliding of oxide layers and the formation of a major P3 and a minor O1 phase for the end member CoO2-delta with delta = 0.33. In contrast, Ni0.85CO0.15O2-delta with a small amount of delta = 0.1 maintains the initial O-3 layer structure. (C) 2002 Elsevier Science.