Lithium-ion Battery Manufacturing Process – Coating Technology

The coating process of lithium batteries is a key production technology that involves evenly applying positive and negative electrode slurries onto substrates (such as aluminum foil or copper foil) to form a special functional film layer.

I. Coating Process

The coating process is a technology based on the study of fluid properties, which applies one or multiple layers of liquid onto a substrate. In the manufacturing of lithium batteries, the coating process is mainly used to evenly apply positive and negative electrode slurries onto foil materials to form the battery electrodes. The coating process has a significant impact on the performance of lithium batteries, including capacity, internal resistance, cycle life, and safety.

II. Coating Methods

There are currently two main methods for applying electrode slurries in lithium batteries:

1. Comma Roll Transfer Coating: The coating roll drives the slurry, adjusts the slurry transfer amount through the gap of the comma scraper, and uses the rotation of the backing roll and the coating roll to transfer the slurry onto the substrate. This method is suitable for slurries with lower viscosity and results in thinner coatings.

2. Slot Die Coating: The coating liquid is extruded through the slot of the coating die under certain pressure and flow rate and transferred onto the substrate. This method has the advantages of fast coating speed, high precision, uniform wet thickness, and prevention of contamination, with high slurry utilization rates. It is suitable for slurries with higher viscosity and can be used for multi-layer coating.

III. Coating Process Steps

The lithium battery coating process usually includes the following steps:

1. Equipment Startup Confirmation: Check the environmental temperature and humidity, open the air source valve, and confirm that the equipment is in a normal state.

2. Simulation Coating: Select the operation panel screen and run a simulation coating to check if the equipment is functioning properly.

3. Foil Threading: Place the substrate in the middle of the unwind device’s conveying shaft, secure it with an air gun, and manually pass the foil under the two pressure bars through the rewinder, backing roll, etc.

4. Set Parameters and Start: Set the rotation speed, oven temperature, and other parameters according to production requirements, start the backing roll manually, feed the foil into the oven, and then pass it through the floating roll, conveying roll, etc.

5. Pre-coating Adjustment: This includes selecting the operation panel, setting tension, correction, hot air temperature rise, and other steps, as well as installing the slurry pipe, loading material, adjusting the liquid level sensor, etc.

6. Coating: Coat according to the set process parameters while monitoring the coating quality.

7. Preparation for Second Side Coating: Refer to the process flow for foil threading or splicing, confirm the coating gap, backing roll gap, etc., and set the process parameters.

8. Second Side Coating: Perform the second side coating and conduct the first piece confirmation and inspection.

9. Cleaning and Finishing: After production, clean the equipment, sweep the working area, and turn off the power and air source.

IV. The Impact of Coating Process on Lithium Battery Performance

The impact of the coating process on lithium battery performance is mainly reflected in the following aspects:

1. Coating Drying Temperature: If the drying temperature is too low, the electrodes may not be completely dry; if the temperature is too high, it may cause cracking or peeling of the surface coating.

2. Coating Area Density: If the coating area density is too small, the battery capacity may not reach the nominal capacity; if the coating area density is too large, it can lead to material waste and potential safety hazards.

3. Coating Size and Thickness: The size and thickness of the coating also have a significant impact on battery performance. Sizes that are too small or too large may cause the internal positive electrode not to be completely wrapped by the negative electrode, affecting battery performance; thickness that is too thin or too thick will affect the subsequent electrode rolling process.

V. Coating Defects and Influencing Factors

During the coating process, various defects may occur, such as thick at the head and thin at the tail, double-sided thick edges, dotted dark spots, rough surface, and foil exposure. These defects may be caused by various factors, such as unstable slurry properties, insufficient precision of coating equipment, and improper setting of coating process parameters. To reduce coating defects and improve coating quality and yield, it is necessary to strictly control the properties of the slurry, the precision of the coating equipment, and the coating process parameters.

The coating process of lithium batteries is one of the key processes in the manufacturing of lithium batteries. By choosing the appropriate coating method, strictly controlling the coating process parameters, and reducing coating defects, high-quality and high-performance lithium battery products can be produced.