How to prevent the problem of coating dark marks on lithium-ion batteries

The accuracy of the pole piece coating is very high, and the thickness deviation is about 3um, so the equipment is very demanding. Control points (1) To ensure the consistency of coating as much as possible, pay attention to the change of slurry viscosity, the change of liquid level on the hopper, and the change of coating speed during operation; (2) The thin layer of slurry on the aluminum foil enters the oven Dry and remove NMP solvent (NMP boiling point 202°C, flash point 95°C). If drying is too slow, the coating surface has fluidity, the thickness is unstable, and the drying is too fast, and the surface forms a PVDF film. The volatilization of the internal NMP solvent will cause the surface layer to wrinkle. In order to ensure the uniform evaporation of NMP, segmented drying is usually used. The middle section has the highest temperature. The positive electrode is generally 100-130°C, if the negative electrode adopts an aqueous system, the drying temperature is generally 75-90°C; in the drying process, NMP volatilizes, and the composition of the coating slurry is constantly changing, so the amount of NMP solvent in the preparation of the slurry and the temperature rise The method and heating time have an impact on this; (3) The heating temperature or time is not enough, it is difficult to remove the liquid in the slurry, so that part of the binder is dissolved, causing the active material to peel off; if the heating temperature is too high, the binder will occur Crystallization will also peel off the active material, which will cause a short circuit in the cell. In addition, improper drying temperature and drying time will also cause aluminum foil oxidation and electrode wetting; (4) Coating and drying must be the first three inspections-thickness, quality, and size meet the requirements, and the corresponding drawing should be inspected on time. Pulp speed, baking time, gap, etc. Lithium-ion battery coating dark marks Explanation about coating streak dark marks: dark marks are caused by uneven thickness on the surface of the pole piece during coating, and chromatic aberration appears, showing the appearance of dark marks. The uneven thickness may be caused by (1) the uneven surface thickness of the pole piece due to foreign matter on the knife edge or uneven surface of the knife edge (with gaps) during the drawing process; (2) before or after rolling There are linear traces. It is mostly caused by particles that have not opened the knife edge, or a small dry slurry stuck on the knife edge. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: What are the power supply requirements for UPS power lithium-ion batteries in the communication room?