Microstructure formation of lithium-ion battery electrodes during drying – An ex-situ study using cryogenic broad ion beam slope-cutting and scanning electron microscopy (Cryo-BIB-SEM)

Drying of Lithium‐Ion Battery Anodes for Use in High‐Energy Cells: Influence of Electrode Thickness on Drying Time, Adhesion, and Crack Formation

“…On the other hand, as shown in Figure , a larger amount of elastic SBR binder disappears from the particle–substrate interface. It might be assumed that it is transported to the electrode surface as was shown to occur with PVDF binder for NMP‐based electrodes . Larger amounts of binder at the electrode surface might be able to compensate some of the stresses that developed during the drying process to a certain extent.…”

“…In addition, EDS was used to track the evolving distribution of the binder during the drying process, showing its accumulation on the film surface during capillary transport. Hypothesis is that additives are dragged along with the solvent through the capillaries to the surface, which seems to be the case for carbon black as well as for the binder . In further investigations, a correlation between drying velocity, electrode adhesion on the substrate, and cell performance has been proven, indicating that high drying velocities lead to a depletion of binder at the interface between the substrate and active material.…”

“…This means, there is no diffusional limitation for solvent transport within the porous electrode, reducing the drying rate after the end of film shrinkage, which can be explained by capillary transport of solvent to the electrode surface. However, it could also be shown that for electrodes with state‐of‐the‐art thickness of about , some liquid clusters remain within the electrodes' microstructure, which have not been emptied by capillary transport and thus have to evaporate on site and move through the inner pore structure, not in the liquid phase but in the gaseous phase during the drying process . The number of liquid clusters though seems to be negligible for state‐of‐the art electrodes, since it is not reflected in the drying curve that is still governed by a constant drying rate.…”

Manufacturing Process for Improved Ultra‐Thick Cathodes in High‐Energy Lithium‐Ion Batteries

“…The electrode microstructure is a direct result of the fabrication process, which represents a sequence of complex individual steps that mutually influence each other and, therefore, demand a high level of quality monitoring . To generate thick electrodes with an appropriate microstructure, a fundamental understanding of the governing processes such as mixing, drying, or calendering occurring during electrode manufacturing and their impact on component distribution is needed.…”

“…During drying, an enrichment of binder at the electrode surface, called binder migration, can occur. Binder migration was already investigated using real‐time fluorescence microscopy, electrochemical impedance spectroscopy (EIS), Raman spectroscopy, and broad ion beam (BIB) milling and scanning electron microscopy (SEM) under cryogenic conditions (Cryo‐BIB‐SEM), and can be attributed to capillary forces and diffusion. In thick electrodes, where more solvent needs to be evaporated compared with thin electrodes and mechanical stability is one key issue, binder migration needs special attention due to the correlation of local binder concentration to the adhesion of the electrode composite to the substrate.…”