Water uptake of tape-cast cathodes for lithium ion batteries

High-performance ceramic-based cathodes (e.g. NMC, LFP) are the backbone of lithium ion batteries. The production of cathodes is based on ceramic manufacturing technologies (powder processing, slurry, tape casting). The minimization of the water content in the fabricated battery is a crucial point in its manufacturing. This work is focused on the kinetics of water uptake in tape-cast cathode materials (NMC, LFP). The cathode foils were exposed to atmospheres with varying humidity and the water content was determined by means of coulometric Karl-Fischer titration. Conversely, the tendency of the cathodes to release residual water is examined. Additionally, electrochemical investigations were performed on cathode foils containing defined amounts of water. Galvanostatic charge-discharge experiments were conducted in 2-electrode Swagelok® cells versus graphite anodes. It could be shown that the influence of residual water on the cell performance is very complex. On the one hand, the residual water causes side reactions. On the other hand, low water content obviously supports the formation of the solid electrolyte interface (SEI) on the anode.