ELECTROCHEMICAL AND PHYSICAL-PROPERTIES OF THE LIXNI1-YCOYO2 PHASES

A crystal chemistry study of the LiNi1-yCoyO2 system has been realized. These materials exhibit a layered structure (R3m-O3BAR type) for 0 less-than-or-equal-to y less-than-or-equal-to 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 less-than-or-equal-to y less-than-or-equal-to 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 greater-than-or-equal-to 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.