Impact of humidity on moisture resorption and resulting electrochemical performance of Gr/NMC622-based Li-ion batteries

Moisture management is an integral part of modern battery production. However, there is only little information available about the level of humidity in the production environment after which detrimental effects on cell performance set in. In this study, we investigate the impact of industry relevant levels of humidity on moisture resorption and electrochemical performance of Gr/NMC622-based Li-ion batteries utilizing two types of separator (one polyolefin and one with ceramic coating). The moisture resorption behaviour of all cell components was analysed in detail using Karl Fischer titration (KFT) and a magnetic suspension balance. The electrochemical performance was evaluated using PAT-cells that were assembled under identical humidity conditions and in parallel with the KFT sample preparation. We found a stable electrochemical performance for low dew points and an increase in irreversible capacity and internal resistance once a critical dew point was exceeded. By correlating residual moisture data and electrochemical performance, a common critical residual moisture content could be identified. The presented method allows, for the first time, to quantify the impact of residual cell moisture on electrochemical performance with high precision.