Structural Instability of Delithiated Li[sub 1−x]Ni[sub 1−y]Co[sub y]O[sub 2] Cathodes

The structural stability of layered cathodes has been assessed by investigating the crystal chemistry of chemically delithiated subjected to mild heating and comparing the data with that for The delithiated samples exhibit a decrease in ratio at temperatures as low as 50°C due to a migration of the ions from the nickel layer to the lithium layer. The rate of change in the ratio increases with increasing degree of delithiation (charging) and heating temperature and time, but decreases with increasing cobalt content. For example, the ratio of decreases from 5.11 to 5.01 after heating at 70°C for 11 days, whereas that of does not show a change under identical conditions. The decrease in ratio is also observed after mild heating of lithium cells consisting of charged electrodes.