Why do electrodes crack during lithium battery coating? How to solve it?
1. Detailed reasons for the cracking of the pole piece
1. Slurry problem
The slurry viscosity is not suitable:
- Viscosity is too high: The slurry has poor fluidity, making it difficult to spread evenly during coating and prone to cracking.
- Viscosity is too low: The slurry tends to flow, resulting in uneven coating thickness and cracking after drying.
Uneven slurry dispersion:
- Active materials, conductive agents and binders are not fully dispersed, resulting in local stress concentration.
- Agglomerated particles exist in the slurry, forming weak points during coating.
Poor slurry rheology:
- The slurry is not thixotropic enough and cannot maintain uniform thickness after coating.
Insufficient binder content:
- The binder (such as PVDF, CMC) content is too low, the electrode has insufficient mechanical strength and is prone to cracking after drying.
2. Improper coating process parameters
·Coating speed is too fast:
- The slurry cannot be spread sufficiently, resulting in uneven coating and cracking after drying.
Uneven coating thickness:
- Improper adjustment of the coating head or scraper leads to local over-thickness or over-thinness and uneven shrinkage stress during drying.
Drying temperature is too high or too fast:
- The surface dries quickly while the interior remains wet, creating internal stresses that lead to cracking.
Improper coating gap setting:
- The gap between the coating head and the current collector is uneven, resulting in uneven slurry distribution.
3. Current collector problem
The surface of the current collector is rough:
- The surface is uneven or has defects, resulting in uneven adhesion of the slurry.
Uneven current collector tension:
- The current collector tension fluctuates during the coating process, causing the pole piece to deform or crack.
Insufficient cleanliness of current collector:
- There is oil or dust on the surface, which affects the adhesion of the slurry.
4. Environmental factors
Humidity is too high or too low:
- Too high humidity: The slurry absorbs moisture, which slows down the drying process and easily generates internal stress.
- Humidity too low: The slurry dries too quickly, causing cracking.
Large temperature fluctuations:
- Unstable ambient temperature affects the rheology of the slurry and the drying uniformity.
5. Material properties
Active substance particles are too large:
- Particles that are too large will result in uneven stress distribution in the slurry, which will cause cracking after drying.
Poor dispersion of conductive agent:
- Agglomeration of conductive agents (such as carbon black) leading to local stress concentrations.
Improper selection of adhesive:
- The poor compatibility between the binder and the active material results in insufficient pole piece strength.
2. Detailed solution to the cracking of pole pieces
1. Optimize slurry formulation
Adjust the slurry viscosity:
- Use rheological additives (such as CMC, PAA) to adjust the slurry viscosity to ensure it is suitable for coating process.
- Determine the optimal viscosity range through experiments (usually 3000-8000 mPa·s).
Improve slurry dispersion:
- Use a high-speed mixer, ball mill or ultrasonic dispersing equipment to ensure that the slurry is evenly dispersed.
- Add dispersants (such as Tween-80) to improve particle dispersion.
Optimize binder content:
- Appropriately increase the binder content (such as increasing PVDF from 2% to 3%-5%) to improve the strength of the electrode.
Adjust solid content:
- Control the solid content of the slurry between 40% and 60% to ensure uniform coating.
2. Optimize coating process parameters
Control coating speed:
- Adjust the coating speed (usually 0.5-2 m/min) according to the characteristics of the slurry to ensure uniform spreading of the slurry.
Adjust coating thickness:
- Ensure uniform coating thickness (usually 100-200 μm) by adjusting the doctor blade gap or coating head pressure.
Optimize drying process:
- Use staged drying: pre-dry at low temperature (such as 60℃), and then gradually increase the temperature (such as 80℃-120℃) to completely dry.
- Control the drying speed to avoid rapid drying of the surface.
Calibrate coating gap:
- Regularly calibrate the gap between the coating head and the current collector to ensure uniform coating.
3. Improve the quality of current collector
Improve the surface quality of the current collector:
- Use current collectors with smooth and uniform surfaces (such as copper foil, aluminum foil).
- Surface treatment of the current collector (e.g. electrochemical polishing).
Control the current collector tension:
- Keep the current collector tension stable during coating (usually 10-30 N/m).
Clean the current collector:
- Use alcohol or deionized water to clean the current collector to remove surface oil and dust.
4. Control environmental conditions
Adjust the ambient humidity:
- Control the coating environment humidity between 30%-50%.
Stable ambient temperature:
- Ensure that the coating environment temperature is constant (usually 20℃-25℃).
Add environmental control equipment:
- Install constant temperature and humidity equipment in the coating workshop.
5. Material Improvement
Optimize the particle size of active substances:
- Use nano-scale or sub-micron active materials to reduce internal stress concentration.
Improve the dispersion of conductive agent:
- Use highly dispersible conductive agents (such as Super P, CNTs).
Choose the right adhesive:
- Use adhesives with better bonding properties (such as SBR, PAA) to improve the toughness of the electrode.
6. Equipment maintenance and improvement
Regular maintenance of coating equipment:
- Clean key parts such as coating head and scraper to ensure no wear and blockage.
Introducing advanced coating technology:
- Use slit coating, micro gravure coating and other technologies to improve coating uniformity.
Automated control:
- Introduce automated coating equipment to reduce human operation errors.
3. Precautions in actual operation
1. Slurry preparation:
- Strictly weigh materials according to the recipe to ensure slurry consistency.
- After stirring, let the slurry stand to defoam to avoid bubbles affecting the coating quality.
2. Coating process monitoring:
- Monitor coating thickness, speed and drying temperature in real time and adjust parameters in time.
- Take samples regularly to test the quality of electrodes and deal with problems promptly if found.
3. Equipment calibration:
- Regularly calibrate coating equipment and testing instruments to ensure process stability.
4. Personnel training:
- Provide professional training to operators to improve operational standardization and problem-solving capabilities.
Summarize:
The reasons for the cracking of lithium battery pole pieces during the coating process are complex and involve multiple aspects such as slurry, process, current collector, environment and materials. The problem of pole piece cracking can be effectively solved by optimizing the slurry formula, adjusting the coating process parameters, improving the quality of the current collector, controlling environmental conditions and improving material properties. In addition, regular maintenance of equipment and introduction of advanced coating technology can further improve the coating quality.
Canrd Brief Introduce
Canrd use high battery R&D technology(core members are from CATL) and strong Chinese supply chain to help many foreign companies with fast R&D. We provide lab materials, electrodes, custom dry cells, material evaluation, perfomance and test, coin/pouch/cylindrical cell equipment line, and other R&D services.
Email:contact@canrd.com Phone/Wechat/WhatsApp:+86 19867737979
Canrd Company Vedio/Website:www.canrud.com
1. Slurry problem
The slurry viscosity is not suitable:
- Viscosity is too high: The slurry has poor fluidity, making it difficult to spread evenly during coating and prone to cracking.
- Viscosity is too low: The slurry tends to flow, resulting in uneven coating thickness and cracking after drying.
Uneven slurry dispersion:
- Active materials, conductive agents and binders are not fully dispersed, resulting in local stress concentration.
- Agglomerated particles exist in the slurry, forming weak points during coating.
Poor slurry rheology:
- The slurry is not thixotropic enough and cannot maintain uniform thickness after coating.
Insufficient binder content:
- The binder (such as PVDF, CMC) content is too low, the electrode has insufficient mechanical strength and is prone to cracking after drying.
2. Improper coating process parameters
·Coating speed is too fast:
- The slurry cannot be spread sufficiently, resulting in uneven coating and cracking after drying.
Uneven coating thickness:
- Improper adjustment of the coating head or scraper leads to local over-thickness or over-thinness and uneven shrinkage stress during drying.
Drying temperature is too high or too fast:
- The surface dries quickly while the interior remains wet, creating internal stresses that lead to cracking.
Improper coating gap setting:
- The gap between the coating head and the current collector is uneven, resulting in uneven slurry distribution.
3. Current collector problem
The surface of the current collector is rough:
- The surface is uneven or has defects, resulting in uneven adhesion of the slurry.
Uneven current collector tension:
- The current collector tension fluctuates during the coating process, causing the pole piece to deform or crack.
Insufficient cleanliness of current collector:
- There is oil or dust on the surface, which affects the adhesion of the slurry.
4. Environmental factors
Humidity is too high or too low:
- Too high humidity: The slurry absorbs moisture, which slows down the drying process and easily generates internal stress.
- Humidity too low: The slurry dries too quickly, causing cracking.
Large temperature fluctuations:
- Unstable ambient temperature affects the rheology of the slurry and the drying uniformity.
5. Material properties
Active substance particles are too large:
- Particles that are too large will result in uneven stress distribution in the slurry, which will cause cracking after drying.
Poor dispersion of conductive agent:
- Agglomeration of conductive agents (such as carbon black) leading to local stress concentrations.
Improper selection of adhesive:
- The poor compatibility between the binder and the active material results in insufficient pole piece strength.
1. Optimize slurry formulation
Adjust the slurry viscosity:
- Use rheological additives (such as CMC, PAA) to adjust the slurry viscosity to ensure it is suitable for coating process.
- Determine the optimal viscosity range through experiments (usually 3000-8000 mPa·s).
Improve slurry dispersion:
- Use a high-speed mixer, ball mill or ultrasonic dispersing equipment to ensure that the slurry is evenly dispersed.
- Add dispersants (such as Tween-80) to improve particle dispersion.
Optimize binder content:
- Appropriately increase the binder content (such as increasing PVDF from 2% to 3%-5%) to improve the strength of the electrode.
Adjust solid content:
- Control the solid content of the slurry between 40% and 60% to ensure uniform coating.
2. Optimize coating process parameters
Control coating speed:
- Adjust the coating speed (usually 0.5-2 m/min) according to the characteristics of the slurry to ensure uniform spreading of the slurry.
Adjust coating thickness:
- Ensure uniform coating thickness (usually 100-200 μm) by adjusting the doctor blade gap or coating head pressure.
Optimize drying process:
- Use staged drying: pre-dry at low temperature (such as 60℃), and then gradually increase the temperature (such as 80℃-120℃) to completely dry.
- Control the drying speed to avoid rapid drying of the surface.
Calibrate coating gap:
- Regularly calibrate the gap between the coating head and the current collector to ensure uniform coating.
3. Improve the quality of current collector
Improve the surface quality of the current collector:
- Use current collectors with smooth and uniform surfaces (such as copper foil, aluminum foil).
- Surface treatment of the current collector (e.g. electrochemical polishing).
Control the current collector tension:
- Keep the current collector tension stable during coating (usually 10-30 N/m).
Clean the current collector:
- Use alcohol or deionized water to clean the current collector to remove surface oil and dust.
4. Control environmental conditions
Adjust the ambient humidity:
- Control the coating environment humidity between 30%-50%.
Stable ambient temperature:
- Ensure that the coating environment temperature is constant (usually 20℃-25℃).
Add environmental control equipment:
- Install constant temperature and humidity equipment in the coating workshop.
5. Material Improvement
Optimize the particle size of active substances:
- Use nano-scale or sub-micron active materials to reduce internal stress concentration.
Improve the dispersion of conductive agent:
- Use highly dispersible conductive agents (such as Super P, CNTs).
Choose the right adhesive:
- Use adhesives with better bonding properties (such as SBR, PAA) to improve the toughness of the electrode.
6. Equipment maintenance and improvement
Regular maintenance of coating equipment:
- Clean key parts such as coating head and scraper to ensure no wear and blockage.
Introducing advanced coating technology:
- Use slit coating, micro gravure coating and other technologies to improve coating uniformity.
Automated control:
- Introduce automated coating equipment to reduce human operation errors.
1. Slurry preparation:
- Strictly weigh materials according to the recipe to ensure slurry consistency.
- After stirring, let the slurry stand to defoam to avoid bubbles affecting the coating quality.
2. Coating process monitoring:
- Monitor coating thickness, speed and drying temperature in real time and adjust parameters in time.
- Take samples regularly to test the quality of electrodes and deal with problems promptly if found.
3. Equipment calibration:
- Regularly calibrate coating equipment and testing instruments to ensure process stability.
4. Personnel training:
- Provide professional training to operators to improve operational standardization and problem-solving capabilities.
Summarize:
The reasons for the cracking of lithium battery pole pieces during the coating process are complex and involve multiple aspects such as slurry, process, current collector, environment and materials. The problem of pole piece cracking can be effectively solved by optimizing the slurry formula, adjusting the coating process parameters, improving the quality of the current collector, controlling environmental conditions and improving material properties. In addition, regular maintenance of equipment and introduction of advanced coating technology can further improve the coating quality.
Canrd Brief Introduce
Canrd use high battery R&D technology(core members are from CATL) and strong Chinese supply chain to help many foreign companies with fast R&D. We provide lab materials, electrodes, custom dry cells, material evaluation, perfomance and test, coin/pouch/cylindrical cell equipment line, and other R&D services.
Email:contact@canrd.com Phone/Wechat/WhatsApp:+86 19867737979
Canrd Company Vedio/Website:www.canrud.com
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