The relationship between the composition of lithium nickel oxide and the loss of reversibility during the first cycle

A quantitative relationship between the reversibility of the intercalation/de-intercalation process and the amount z of extra-nickel ions within the lithium layers has been demonstrated by specific electrochemical studies of Li1-xNi1+zO2 cells. The oxidation of extra-nickel ions from divalent to trivalent state during the first electrochemical charge, leads to an irreversible shrinkage of the interslab space, and as a consequence, to a loss of reversibility in the first cycle. The re-intercalation composition limit is thus directly related to the concentration of extra-nickel ions. However, the overall reversibility can be recovered by a forced discharge up to the starting composition.