How to solve the problem of lithium-ion battery coating dark mark

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

The coating process of the lithium-ion battery is to apply the slurry to the collector, and dry is removed the solvent in the slurry. When the lithium-ion battery is coated, there is more likely to have dark marks and wrinkles, and the general coating is different: the slurry wet coating is thick, the slurry is a Newton high viscosity fluid, fluid flow is Required shear stress, change with flow rate. Adjustment of coating thickness is difficult to carry out a standard manner, which is also difficult in coating machine coating.

It is very high in the proficiency of the operator. The accuracy of the polar coating is very high, the thickness is 3. Therefore, it is very high for equipment requirements.

Control points (1) should ensure the consistency of coating as much as possible, should pay attention to changes in slurry viscosity, changes in the height of the hopper, changes in the coating speed; (2) the thin layer of the slurry on the aluminum foil into the oven Dry, remove NMP solvent (NMP boiling point 202 ¡ã C, flash point 95 ¡ã C). Drying is too slow, the surface of the coating is fluidity, the thickness is unstable, the drying is too fast, the surface forms a PVDF film layer, and the internal NMP solvent volatilizes can cause the surface layer to wrinkle, in order to ensure the average evaporation of NMP, usually use segmented drying, The highest temperature in the middle section. The positive electrode is generally 100-130 ¡ã C, if the aqueous system is used, the drying temperature is generally 75-90 ¡ã C; and the drying process NMP volatilizes, the composition of the coating paste is constantly changing, so the amount of NMP solvent of the slurry, temperature rise The mode and heating time have an impact; (3) The heating temperature or time is not enough, it is difficult to remove the liquid in the slurry, so that the partial binder is dissolved, resulting in peeling of the active substance; the heating temperature is too high, then the binder occurs Crystallization, also peels the active substance, thereby causing short circuit in the battery.

In addition, the drying temperature and drying time are not appropriately caused by aluminum foil oxidation and polarity igniting; (4) coating and drying should be the first three inspection - thickness, quality, size meet the requirements, and test the corresponding pull on time Slurry speed, baking time, gap, etc. Explanation of dark laces of coating strips: Darkness is due to coating, the surface portion of the polar surface is uneven, the color difference occurs, and the appearance is dark. The difference in thickness is might be (1) due to the blade of foreign matter or the surface of the knife in the slurry (have a gap), causing a phenomenon that the surface thickness of the pole surface is uneven; (2) after the roller pressure or the roller pressure Linear traces.

Due to the particles that are not open due to the knife, or a small dry slurry card is caused on the kn.

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