Electrochemical and physical properties of the LixNi1$minus;yCoyO2 phases

A crystal chemistry study of the LiNi1−yCoyO2 system has been realized. These materials exhibit a layered structure (R 3m-O3 type) for 0≤y≤1. They have been used as positive electrode in lithium batteries. Up to 0.6 lithium atom can be reversibly deintercalated for cell voltages lying in the 3.5–4 V range. For 0≤y≤0.5, the shape of all the charge curves is very similar with a small decrease in potential when y increases due to the influence of cobalt which, however, does not participate significantly in the redox process. For materials with a larger cobalt amount (y≥0.6) the nickel ions are first oxidized to the tetravalent state, before the cobalt ions. This behavior is confirmed by the evolution of the electronic properties versus the lithium amount.