Stability of LiNi0.6Mn0.2Co0.2O2 as a Cathode Material for Lithium-Ion Batteries against Air and Moisture

LiNi0.6Co0.2Mn0.2O2 (C622), a Ni-rich cathode material, was prepared and its durability tested in air and moisture. For the test, C622 was stored in a glovebox and in a humidity chamber at 50% RH. For each sample, the cell performance was tested in terms of the specific capacity, rate capability, and cycling stability; the changes in the crystal structure were also investigated. The results indicate that when C622 is stored in a humidity chamber, severe degradation occurs in all measurements relating to the cell performance, whereas when it is stored in a glovebox, no degradation is seen. This indicates that C622 is very sensitive to air and moisture. A larger quantity of residual lithium compounds, which are by-products of the reaction between the cathode material, CO2, and moisture in the air, could be seen on the surface of the C622 that was stored in a humidity chamber when compared to the one stored in a glovebox. The formation of residual lithium compounds and the corresponding changes in the crystal structure of C622 kept in the humidity chamber may be the reason for the degradation in the cell performance.