What are the major problems in the processing and manufacturing of lithium battery pole pieces

The foil substrate passes through the coating roller and directly contacts the slurry tank. The excess slurry is coated on the foil substrate. When the substrate passes between the coating roller and the doctor blade, the gap between the doctor blade and the substrate determines the coating. At the same time, the excess slurry is scraped off and reflowed, thereby forming an even coating on the surface of the substrate. The squeegee type is critical to the comma squeegee. The comma blade is one of the key components in the coating head. Generally, a comma-like blade is produced along the bus bar on the surface of the round roller. This blade has high strength and hardness, and is easy to control the coating amount and coating accuracy. It is suitable for High solid content and high viscosity slurry. 2. Roller coating transfer type The coating roller rotates to drive the slurry, adjusts the slurry transfer amount through the comma doctor gap, and uses the rotation of the back roller and the coating roller to transfer the slurry to the substrate. The process is shown in Figure 2. Roll coating transfer coating contains two basic processes: (1) The rotation of the coating roller drives the slurry to pass through the metering roller gap to form a slurry layer of a certain thickness; (2) The slurry layer of a certain thickness passes through the coating roller and the opposite direction. The back roll rotates to transfer the slurry to the foil to form a coating. 3. Slit extrusion coating is a precise wet coating technology. The working principle is that the coating liquid is extruded and ejected along the gap of the coating die under a certain pressure and flow rate and transferred to the substrate. Compared with other coating methods, it has many advantages, such as fast coating speed, high precision, and average wet thickness. The coating system is closed, it can guard against the entry of pollutants during the coating process, the slurry utilization rate is high, the slurry properties can be kept stable, and multi-layer coating can be carried out at the same time. And can adapt to different slurry viscosity and solid content range, and has stronger adaptability compared with transfer coating process. To form a stable and average coating, the lithium battery coating process must meet these conditions at the same time: (1) The slurry properties are stable, no sedimentation, viscosity, solid content, etc. do not change. (2) The supply of slurry is stable, and an average and stable flow state is formed inside the die. (3) The coating process forms a stable flow field between the die and the coating roller within the coating window. (4) Stable foil travel, no tape sliding, severe jitter and wrinkles. The lithium battery coating operation window is an important process parameter for slit coating. In actual processing, when the process parameters exceed the range of the operation window, coating defects will appear. However, there are many types of defects in the coating film, and the reasons are different. This article focuses on the slit extrusion coating of lithium batteries, decomposing several common defects, and giving corresponding treatment methods. Common defects are a little defect, edge effect, jagged defect and so on. Point Defects 1. The pinhole defects of stomata bubbles are easier to understand. The bubbles in the wet film migrate from the inner layer to the surface of the film, and break on the surface of the film to form pinhole defects. Air bubbles mainly come from mixing, coating liquid transportation and coating process. 2. Various particles of foreign body shrinkage appear. The presence of foreign particles causes the wet film on the surface of the particles to have a low surface tension area, and the liquid film migrates to the periphery of the particles, forming shrinkage point defects. 3. Agglomerate particle protrusions. If the slurry is stirred unevenly and the conductive agent is not dispersed, such defects will appear when agglomerates are formed. Large areas of protrusions appear on the surface of the lithium battery pole pieces. If you zoom in to observe these places, you will find this It is an agglomerate of conductive agent. It is important to improve the slurry mixing process to eliminate this defect. 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: How to judge the quality of lithium battery test equipment?