Electrode Shedding
- Negative electrodes are prone to powder shedding
- Main reason：1.Formula issues,insufficient bonding strength leading to material loss；2.Excessive baking temperature,rapid solvent evaporation resulting in SBR bleeding.Insufficient adhesive between the material and the current collector leading to material loss
Coating Scratch
- Scratches on the coating are often manifested as one or more unpainted marks on the coating
- Main reasons：1.Ineffective particle removal during sieving,and these particles can block the coating blade. Need a feeler gauge to clear the blockage；2.After coating for a period of time, due to the appearance of slurry dry material, the coating blade is blocked.
Note: The image is shared by Shengxia Weiyang
Electrode Cracking
The negative electrode cracks and sheds powder, which is a common problem caused by over-baking. Specifically, the temperature is too high or the time is too long during the drying process of the electrode.
Electrode Curling
- During the process of single-sided coating, observed that the outer edges of the electrode curled upward
- This phenomenon is mainly caused by two reasons. One is when the solid content of the slurry is relatively low, the excessive evaporation of solvent leads to severe shrinkage of the slurry. The other is that some adhesives with relatively large drying shrinkage may also cause this curling if the baking speed is too fast
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Coating Cratering (white spots)
Observing the location of the white spots under SEM, at the center of the white spots,found some foreign materials that are not part of the internal materials of the electrode.
Coating Cratering (white spots)
Surface cratering is essentially caused by the surface tension gradient generated during film formation. This phenomenon is known as the Maragoni effect.
The basic composition of coating slurry typically includes three main components: binder, powder material, and dispersion medium. Additionally, there may be various functional auxiliary materials. The mismatch of surface tension among these materials is the primary cause of cratering.However, factors such as the viscosity of the coating, the fluidity of the liquid film, the wind speed and oven temperature during drying and film formation, conditions and equipment status during the heat treatment stage, and others can all influence the surface tension and its action process, thereby inducing the occurrence of cratering.
Due to the presence of low surface tension particles (such as powder, oil droplets, etc., referred to as “contaminants”) in the flowable film surface before curing, the central surface tension becomes lower, causing the fluid to migrate towards the centered on the contaminants, ultimately forming a circular depression with higher edges than the center – cratering. In other words, there are substances with low surface tension in the center of the cratering, and there is a surface tension difference between them and the surrounding coating. This difference is the driving force for the formation of cratering, promoting the migration of surrounding liquid in a 360-degree direction away from the contaminants (as shown in Figure 2).
Electrode Bright Spots
After the coating process, the appearance of the electrode is not obvious. However, upon cold pressing, numerous bright spots become evident on the surface of the electrode.
Use optical microscope to analysis these bright spots(to be discussed in the next slide.)
Under different magnifications, found the particles in the normal areas were uniformly distributed, while there were large aggregations of small particles in the bright spot areas
Coating Stripes
There are obvious stripe patterns on the coating roller, and the stripes can also be clearly seen on the coated electrode
By reducing the coating viscosity, the situation has been significantly improved (high viscosity is not suitable for slurry leveling and can easily lead to this phenomenon)
Coating Abnormalities Summary
Company introduction
Welcome to Canrd Company (Canrd stands for “Creating Avenues for New Research Development”，website: www.canrd.com ). We specialized in:
- Electrochemical experiment consumables, including coin cell cases, cathodes, anodes, electrodes, electrolytes, and various other materials.
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We have strong research and development capabilities.If you are interested, please feel free to contact us at any time.
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