1.Coating Basics
Purpose：To uniformly coat a fluid slurry onto the surface of a metal foil, dry it, and produce a battery electrode
Principle:The coating roller rotates to carry the slurry, and the amount of slurry transferred is adjusted by adjusting the gap between the blade and the roller. The relative rotation of the back roller and the coating roller is used to transfer the slurry onto the substrate. Subsequently, the solvent in the slurry is evaporated through drying and heating, causing the solid matter to adhere to the substrate.
Note: Taking transfer coating as an example
2.Common Coating Methods
3.Coating Process
Note: The cathode slurry typically uses NMP as a solvent.
Therefore, a NMP recovery device is added to the drying system during the coating process
4.Coating Mechanism
Control Points：
(1)Liquid Level of Slurry in Hopper (Liquid Level Control)
(2)Temperature of Slurry During Coating Process (Constant Temperature)
(3) Blade Gap
(4)Coating Speed
(5)Speed Ratio Between Coating Roller and Back Roller
Note: Taking transfer coating as an example
5.Drying System
Control Points for the Drying Process：
(1)Coating Speed
(2)Temperature Control of Each Oven
(3)Air Nozzle Blowing Speed
Common Issues：
(1)Electrode Cracking
(2)Elecrtode Curling
(3)Incomplete Drying of Electrode
(4)Electrode Delamination
6.Electrode Coating Method
Commonly Used Foil Materials：
Cathode Aluminum Foil：9~16um
Anode Electrode Copper Foil：6~12um
Due to specific needs, carbon-coated copper foil or aluminum foil may also be used for the copper and aluminum foil.
Continuous Coating
Currently, there are two main types of coating methods: continuous and intermittent coating
Coating Width: less than 650mm
Maximum Coating Speed: 70 meters per minute (m/min)
Intermittent Coating
7.Transfer Coating
Unwinding Hopper Transfer Coating
Coating wet film Oven Drying Dry Film Output
Rewinding
8.Extrusion Coating
Unwinding Extrusion Coating Oven Drying
Dry Film Output Rewinding Transit Tank(Preventing slurry settling)
Online Thickness Monitor Dust and Moisture Hood
(control particle size and positive electrode coating humidity)
9.Monitoring Methods
To maintain the consistency of the produced electrode, important parameters that need to be controlled during the coating process include:
1，Coating Weight(weighing，online x-ray，β-ray monitoring)
2，Coating Dimension(flexible tape measure，micrometer，online optical fiber measurement)
3，Coating Appearance(visual inspection，electrode adhesion test)
Weight thickness dimension
Monitoring is typically carried out using the aforementioned methods
10.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 Official Web Canrd Company Vedio Canrd Company profile
Website : www.canrud.com
11.
Q & A
As with the previous two sessions, everyone actively participated in the Q&A segment, raising a variety of questions. During this time, Dr. Ke also provided a summary of the causes of electrode cracking. True to form, Dr. Ke from Kelude patiently addressed each question raised by the participants, providing thorough explanations one by one.
Analysis of Causes for Electrode Cracking by Kelude
Dr. Ke summarized the causes of electrode cracking, which primarily occur due to insufficient bonding strength between the particles of porous electrode materials. Common reasons for cracking include:
1.High Specific Surface Area of Material Particles:
The strong adhesive absorption on large surface areas reduces the effective binder between particles, leading to weak bonding.
Solutions: Decrease the apparent specific surface area of particles, reduce the use of high-BET materials, increase binder content, or use binders with stronger adhesion.
2.Low Solid Content in the Formula:
Rapid solvent evaporation during coating leads to uneven binder distribution, causing weak bonding in certain areas and cracking.
Solutions: Slow down drying speed (low-temperature drying), increase solid content to reduce solvent, or use stronger binders.
3.Issues with Formula Ratios:
For instance, insufficient binder content.
Solution: Increase binder content to enhance inter-particle adhesion.
4.Excessive Coating Thickness:
Higher solvent content in thick coatings results in larger drying stress, causing cracking.
Solutions: Reduce coating thickness, increase binder amount, or switch to a more effective binder.
Additionally, enhancing the adhesion between the coating and the current collector can prevent cracking. For example, carbon-coated current collectors can mitigate coating shrinkage and cracking.
Participant Q&A Highlights
Blue Storm:
"What happens if the slurry is simply poured onto the current collector to dry instead of using blade coating?"
Dr. Ke:
"This method would make it hard to control areal density, which might lead to excessive areal density. This could affect battery rate performance and reduce material Utilization efficiency."
Original Intent:
"Is areal density controlled by adjusting the gap between the coating roller and the substrate?"
Dr. Ke:
"No, it is controlled by adjusting the gap between the coating roller and the doctor blade."
Lemon C:
"What about extrusion coating?"
Dr. Ke:
"In extrusion coating, areal density is controlled by the flow rate of the metering pump."
Lithium Battery - Novice:
"Does the drying process always require high temperature and long duration?"
Dr. Ke:
"It depends on the oven. Longer ovens can use lower temperatures. Drying time is usually within 30 minutes. The drying temperature is typically around 85°C for the negative electrode and 110°C for the positive electrode."
Just a Boy:
"Will the electrode material fall off during winding after coating?"
Dr. Ke:
"Normally, it won't fall off if the adhesion is adequate. Adhesion quality is a key appearance metric, and material shedding is unacceptable."
Original Intent:
"Is humidity control necessary during coating and slurry preparation?"
Dr. Ke:
"Yes, especially for the positive electrode. Positive electrode coating workshops typically monitor both temperature and humidity."
Flying Dream of Yan:
"What are the benefits of carbon-coated aluminum foil?"
Dr. Ke:
"Carbon-coated aluminum foil offers many advantages: mitigates cracking, reduces resistance, and improves adhesion. It's commonly used in lithium-sulfur collectors, lithium iron phosphate electrodes, and other materials with poor conductivity or low binder content."
Silent Angel:
"What causes coating defects like pits?"
Dr. Ke:
"Pits are often caused by air bubbles."
West:
"How does coating speed affect the process?"
Dr. Ke:
"Too fast, and the coating might not dry completely; too slow, and overdrying might occur."
Balsam Pear:
"What solutions exist for severe cracking in cathode carriers?"
Dr. Ke:
"This issue stems from the material's large specific surface area, which absorbs most of the binder, leaving insufficient adhesive between particles. Solutions include using carbon-coated aluminum foil, optimizing the formula, or reducing the material's specific surface area."
Lithium Battery - Novice:
"Why not maintain a constant drying temperature?"
Dr. Ke:
"If the temperature is constant, the electrode heats up too quickly during initial drying, which can lead to cracking."
Just a Baby:
"What is curling?"
Dr. Ke:
"Curling occurs when the edges of the foil shrink inward and bend."
Silent Angel:
"What causes edge bulging in coatings?"
Dr. Ke:
"Edge bulging is caused by excess slurry overflowing to the edges, resulting in thicker edges that bulge during winding. Adding a Mylar (PET film) near the doctor blade can resolve this issue."
Wax Piglet:
"How does β-ray monitoring work? Is it different from X-ray?"
Dr. Ke:
"β-ray monitoring requires specialized equipment installed at the coating machine's tail end. The principles differ; for instance, negative electrodes often use X-ray, while positive electrodes use β-ray."
Streamlet:
"How can high-loading negative electrodes (e.g., 10 mg/cm²) be achieved?"
Dr. Ke:
"The formula needs to be adjusted to ensure adequate adhesion at higher areal densities, and the drying process must also be carefully controlled."
West:
"How is the coating thickness tested?"
Dr. Ke:
"Currently, thickness is measured on the wet film."
This session provided comprehensive insights into coating techniques, troubleshooting, and optimization strategies for lithium-ion battery manufacturing.
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