Lithium-ion battery coating process selection

Coating is the next process after the slurry coating following the completion of the preparation of the slurry, is the paste polymer, molten polymer or polymer melt coating on paper, cloth, plastic film to make composite materials. Coating in the design process can accurately use the best coating, drying process, balance the relationship between the two, and ultimately affect the overall technical performance of the coating.

A. Lithium-ion battery coating method

Battery coating machine is the key process equipment for the production of power lithium-ion battery cells. At present, the lithium-ion battery electrode coating process is mainly scraper type, roller coating transfer type and slit extrusion type.

1、Scraper coating

The foil substrate passes through the coating roller and directly contacts the slurry trough. The excess slurry is coated on the foil substrate, and the gap between the scraper and the substrate determines the coating thickness when the substrate passes between the coating roller and the scraper, while the excess slurry is scraped off the reflux, and a uniform coating is thus formed on the substrate surface.

The main squeegee type is the comma squeegee. Comma scraper is one of the key components in the coating head, generally in the round roller surface along the bus line processed into a comma-like edge, this scraper has high strength and hardness, easy to control the coating volume and coating accuracy, suitable for high solid content and high viscosity of the slurry.

2、Roller coating transfer type

The coating roller rotates to drive the slurry, adjusts the slurry transfer volume by comma squeegee gap, and transfers the slurry to the substrate using the rotation of the backing roller and coating roller. Roll coating transfer coating consists of two basic processes:

(1) The coating roll rotation drives the slurry through the metering roll gap to form a certain thickness of slurry layer.

(2) The thickness of the paste layer is transferred to the foil by the rotation of the coating roll and backing roll in opposite directions to form the coating.

3. Slot extrusion coating

As a sophisticated wet coating technology, the working principle is that the coating solution is transferred to the substrate by squeezing and spraying along the slit of the coating die at a certain pressure and flow rate. Compared to other coating methods, slit extrusion coating has many advantages, such as fast coating speed, high precision, uniform wet thickness; the coating system is closed to prevent the entry of contaminants in the coating process, high slurry utilization, the ability to maintain stable slurry properties, and can be coated in multiple layers at the same time. And can adapt to different slurry viscosity and solid content range, compared with the transfer coating process has a stronger adaptability.

B, lithium-ion battery coating process selection

Coating process is complex, while the impact of the coating effect of more factors, such as: the manufacturing accuracy of the coating equipment, the smoothness of the operation of the equipment and the control of dynamic tension in the coating process, the size of the air volume in the drying process and the temperature control curve will affect the effect of the coating, so it is extremely important to choose the right coating process.

The general choice of coating method needs to be considered from the following aspects, including: the number of layers to be coated, the thickness of the wet coating, the rheological properties of the coating solution, the required coating accuracy, the coating support or substrate, the coating speed, etc.

In addition to the above factors, it must also be combined with the specific conditions and characteristics of the pole chip coating. The characteristics of lithium-ion battery electrode coating are: double-sided single-layer coating; thicker wet coating of slurry (100~300um); non-Newtonian high-viscosity fluid for slurry; high required precision of electrode coating, similar to that of film coating; coating support body of 10~20um thickness of aluminum and copper foil; and the speed of electrode coating is not high compared to that of film coating.

Considering the above factors, the general laboratory equipment tends to use the scraper type, consumer lithium-ion batteries tend to use the roller coating transfer type, and power batteries tend to use the slit extrusion method.

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