Influence of CO2 in the Li-ion battery-production atmosphere on the sorption kinetics of Li[Ni0.6Co0.2Mn0.2]O2 and its effect on cell performance

Water inside a Li-ion battery (LiB) can be detrimental to its performance and even degrade cathode active materials (CAM) in combination with CO2 during production. This degradation may originate from sorption of water and CO2 in CAM. Moisture management aims to control this sorption process, minimize degradation, and reduce water carried into the cell during production. Controlling these sorption processes requires understanding the kinetics that restrict the mass uptake of water and CO2 in CAM. This manuscript provides time-resolved sorption data for Li[Ni0.6Co0.2Mn0.2]O2 (NMC-622) and Li[Ni0.8Co0.1Mn0.1]O2 (NMC-811) cathodes as electrodes and NMC-622 CAM as powder in various humid atmospheres. The exposed material was processed to full coin cells and electrochemically tested. The sorption behavior of cathodes in air at 72%-RH is restricted by kinetics depending on material chemistry. Experiments showed the difference in sorption behavior of NMC-622 in humid atmospheres with and without CO2. The exposure of CAM to humid atmospheres with various CO2 concentrations showed that cell performance decreases with increasing CO2 concentration in the atmosphere – linking a defined mass uptake of NMC-622 from water and CO2 to a capacity loss. The overall mass uptake detected at industrially relevant conditions in NMC-622 in four days is ∼250 wt-ppm, which has little but noticeable effect on cell performance.