The Impact of the C‐Rate on Gassing During Formation of NMC622 II Graphite Lithium‐Ion Battery Cells.

Formation is considered a cost and time intensive production step in industrial production of lithium‐ion batteries (LIBs). One solution for improvement is an acceleration of the formation step by applying higher C‐rates. In this study, formation protocols with up to 2 C were applied to LiNi0.6Mn0.2Co0.2O2 (NMC622) II graphite pouch cells with a nominal capacity of 5 Ah. The formation protocols utilizing higher C‐rates result in a decrease in overall formation time, but also in increased gassing due to additional electrolyte decomposition. The resulting gas phase was quantitatively determined using gas chromatography‐barrier discharge ionization detection (GC‐BID) and with regard to gas volume by making use of the Archimedes principle. Main formation gases in these cells were identified as CO and C2H4. Increased C‐rates altered certain decomposition reactions. Especially the CO evolution was increased. Nevertheless, gassing was smallest for 0.1 C and increased with lower and higher C‐rate. In case of too low C‐rates hydrogen was identified as the main formation gas. However, higher gassing was not correlated with higher capacity loss during formation. Furthermore, the dependence of the C‐rate on gassing was found to be dependent on the graphite material. [ABSTRACT FROM AUTHOR]