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

Abstract

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.

Combining multi-modal non-destructive techniques to investigate ageing and orientation effects in automotive Li-ion pouch cells

“…This gas firstly is produced due to the formation of the solid electrolyte interphase (SEI). 59 Then, as the cell is cycled and ages, further reactions with electrolyte and the internal structure of the cell will lead to further evolution. 60 Gas has a far greater acoustic impedance than solid electrode or liquid electrolyte.…”

Lithium-ion battery cell formation: status and future directions towards a knowledge-based process design

“…162 The produced gas amount also depends on the formation current and voltage. 182,[184][185][186] Leißing et al investigated the influence of different C-rates on gassing. 184 Gassing was found to be caused by both SEI formation and unspecific decomposition.…”

“…182,[184][185][186] Leißing et al investigated the influence of different C-rates on gassing. 184 Gassing was found to be caused by both SEI formation and unspecific decomposition. Both very slow and very fast formation led to an increase in non-specific gassing, but the species observed differed.…”

Methods for Quantifying Expansion in Lithium-Ion Battery Cells Resulting from Cycling: A Review

“…Cell dilation is described as the main expansion influence. Leißing et al [109] investigated the influence of the C-rate on the gassing behavior of NMC622/graphite cells with nominal capacity of 5 Ah. To determine the amount of gas which is produced on formation cycles, the same apparatus as Aiken et al is used [108].…”