1.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
2.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.
3.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.
4.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
5.Coating White Spots
The white spots are primarily caused by bubbles in the slurry. During the post-coating resting period, bubbles can be clearly seen emerging, and these bubbles result in prominent white spots after drying
6.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.
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).
7.Electrode Bright Spots
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
8.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)
9.Coating Abnormalities Summary
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11. Q & A
During the Q&A session at the end of the course, everyone was more enthusiastic and raised many questions. Dr. Ke patiently answered each question and also collected suggestions for the course.
Harbin Institute of Technology, Sodium-ion Battery:
"Assuming 100mg of active material + conductive agent + binder, with a coating weight of about 1mg/cm², what is the typical volume of the system used? Just a rough range."
Dr. Ke:
"This isn't fixed. Different materials and different solid contents result in varying slurry densities."
Breeze:
"How is the amount of NMP controlled? Is it proportional to PVDF, or is it based on experience?"
Dr. Ke:
"The amount of NMP determines the solid content, which in turn affects viscosity. In industrial settings, this is adjusted based on the desired solid content and viscosity, often guided by experience. Slurries generally have specific solid content requirements that must be met. PVDF solutions typically have a concentration—around 5% is common in laboratory settings."
Actually, I'm a Good Person:
"How can the adjustable scraper maintain a consistent level across both sides and align to a reference point? For example, if I want to coat 100µm, how do I set it to zero? There must be some error, right?"
Dr. Ke:
"The adjustable scraper's level is controlled by two knobs for thickness adjustment. A practical approach is to first set it to zero and then adjust both sides uniformly to the desired thickness."
Silhouette:
"Hello, our lab has both types of devices, but the adjustable scraper tends to coat unevenly on both sides and can't pause while coating. Can we use something like alcohol as a lubricant on the scraper's path to reduce friction on the aluminum foil surface?"
Dr. Ke:
"Adding alcohol as a lubricant on foil is not recommended. It's better to control the issue at the source."
HELLO TOMORROW:
"After coating, there are particles present—what’s the cause, and how can this be avoided? Even after grinding for a long time, they persist."
Dr. Ke:
"Particles after coating require a root cause analysis. The main reasons are:
1.Material particles weren't ground finely enough—screen the slurry;
2.Poor dispersion of slurry, such as conductive agents agglomerating—improve dispersion techniques;
3.Gelation of slurry, which creates particles—control conditions to prevent gelation."
Silhouette:
"What impact does uneven surface density have on final battery performance? Apologies, I missed the class on this due to experiments."
Dr. Ke:
"Uneven surface density can lead to mismatched capacities between the anode and cathode on a microscopic level. Overcoating risks lithium plating, while undercoating affects capacity. You can revisit past courses on our official WeChat account, Korod."
Wanderer:
"Recently, during coating and drying, thinner coatings are fine, but thicker ones crack. I’m working on full cells, and thin electrodes lack capacity. What should I do?"
Dr. Ke:
"Thinner electrodes indeed affect capacity. If you lack time to optimize the formula, avoid overly thick coatings to reduce process issues. During vacuum drying, rapid evaporation often causes cracking. Use gentler baking to minimize this. Common causes of electrode cracking include:
1.Large surface area of material particles reducing effective adhesive amount—reduce particle surface area or use stronger adhesives;
2.Low solid content in the formula causes uneven adhesive distribution—lower drying speed (slow bake at low temperature), increase solid content, or use stronger adhesives;
3.Insufficient adhesive content in the formula—increase adhesive content to improve inter-particle bonding;
4.Excessive coating thickness leading to high solvent content and stress during evaporation—reduce coating thickness, increase adhesive, or use better binders.
To enhance adhesion between the coating and the current collector, consider using a carbon-coated collector to prevent coating shrinkage and cracking."
Balsam Pear:
"Does everyone sieve the slurry before coating?"
Dr. Ke:
"Sieving is done after adjusting the slurry viscosity and before coating preparation."
(￣o￣) . z Z:
"Should sodium-ion batteries also avoid vacuum drying? Sodium-ion materials are very hygroscopic, so I thought vacuum drying would be better."
Dr. Ke:
"If sodium-ion materials absorb moisture, this would primarily occur during the mixing process, not just during drying. During the drying process, the high temperature usually causes solvent evaporation, making moisture absorption unlikely."
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