Increased Moisture Uptake of NCM622 Cathodes after Calendering due to Particle Breakage

Abstract

As moisture presents a critical contamination in lithium-ion batteries (LIBs), electrodes and separators need to be post-dried before cell assembly. The moisture adsorption, desorption and re-adsorption of electrodes during processing is strongly dependent on their material system, manufacturing route and microstructure. The microstructure, in turn, is significantly defined by the coating density, which is adjusted by calendering. As a consequence, the calendering step is expected to directly influence the moisture sorption behavior of electrodes. This is why the influence of different coating densities and structural properties on the moisture content of NCM622 cathodes was investigated in this study. For increasing density, an increasing moisture content was detected by Karl Fischer Titration and sorption measurements. SEM and BET analyses showed an increasing amount of NCM622 particle breakage, accompanied by a rising surface area. Hence, the increased moisture uptake of cathodes with higher density is mainly caused by a higher surface area, which results from particle cracking and breakage during calendering. Electrochemical analysis showed that the increased active surface area of cathodes with higher densities leads to a good performance during formation and at low C-rates. However, the reduced porosity impairs the ionic conductivity and causes capacity loss at higher C-rates.

Evaluation of Deformation Behavior and Fast Elastic Recovery of Lithium‐Ion Battery Cathodes via Direct Roll‐Gap Detection During Calendering

“…However, particle breakage or fractioning in the cause of calendering is reported in the literature and may also be an origin for plastic deformation besides particle rearrangement. [ 12,15,31 ] As Figure 5a shows for higher mass loadings, higher maximum densities are reached, starting from ρ C = 3.18 g cm −3 for 200 g m −2 up to 3.41 g cm −3 for 350 g m −2 .…”

“…However, applying high load during compaction may lead to the appearance of particle cracks, causing accelerated cell aging, as reported for LMO [12] and NMC. [13,14] Huttner et al [15] observed an increased moisture uptake for NMC622-based cathodes with higher electrode density and addressed this behavior to a rising surface area caused by particle breakage through higher calendering forces. Bockholt et al [13] also examined the correlation between the mixing and calendering process, showing improved capacity retention for electrodes with an intensive dry-mixing process route.…”

Current Status of Formulations and Scalable Processes for Producing Sulfidic Solid‐State Batteries

“…One aspect may be the fact that the SE cannot fill the pores of the primary particles within the polycrystalline active material. Moreover, high pressures during compaction can cause a breakage of the polycrystalline material [93,104] . As mentioned before, the higher surface of the single crystalline material can result in a higher degradation because of the larger contact area to the electrolyte.…”

Tailored Digitalization in Electrode Manufacturing: The Backbone of Smart Lithium‐Ion Battery Cell Production

“…[ 116 ] The moisture content as an additional product parameter in combination with the coating density has been studied in the literature. [ 126 ] Figure 6 summarizes the parameters in the calendering process. It should be mentioned that, based on the defined reference process, the slitting process is followed after calendering and is not considered here.…”

“…The surface finish is another property influenced by the calendering process. [118,125] Product parameters such as coating width, [118] mass loading, [119] coating density, [117] and the pore size distribution [126] are additional aspects that are considered in setting up the process parameters. Similar to the drying process, the quality of the electrode concerning common electrode defects, such as the camber effect, is another product parameter to be considered in the calendering process.…”