Lithium Coating Shrinkage Hole And Its Solution
Lithium battery coating shrinkage hole is a common coating defect in the coating process of lithium ion battery electrode, which is mainly manifested as a round or nearly round depression on the surface of the electrode plate. This defect not only affects the appearance quality of the electrode sheet, but also may have a negative impact on the performance of the battery, such as reducing the battery capacity, increasing the internal resistance, and affecting the battery cycle life.The following is a detailed analysis of the lithium battery coating shrinkage hole:
一、 Cause analysis
Surface tension gradient:The formation of shrinkage pores is fundamentally caused by the surface tension gradient generated during film formation, which is called the Maragoni effect. The surface tension mismatch between materials is the main cause of shrinkage.
Presence of particles: In the coating process, if there are particles with low surface tension on the film surface (such as powder, oil droplets, etc.), these particles will cause the central surface tension to be low, and the fluid will migrate around the center of the pollutant, and eventually form a circular sag with the edge higher than the center, that is, a shrinkage hole.
Process parameters: the viscosity, fluidity, drying wind speed and oven temperature of the coating may change the surface tension and its action process, thus inducing the production of shrinkage holes.
二、Solution
For the shrinkage hole problem of lithium coating, the following solutions can be adopted:
Material surface structure modification:
By modifying the surface of the graphite material, increasing the polarity group, increasing its hydrophilicity, thereby improving its compatibility with the coating and reducing the production of shrinkage holes.
Adjust the molecular structure of the adhesive:
By adjusting the molecular structure of the active component of the adhesive, reducing the content of its polar groups, effectively reducing the surface tension of the LA type water-based adhesive product, improving the degree of its wetting of the graphite material, thereby reducing the formation of shrinkage holes.
Add surface active dispersant:
Surfactant dispersants such as PVP and CMC are added to the slurry to ensure the emulsification and dispersion of particles with low surface tension, and to improve the dispersion ability of graphite materials in water, that is, to improve the degree of water wetting of graphite materials, thereby reducing the generation of shrinkage holes.
Optimized coating process parameters:
Process parameters such as viscosity, fluidity, drying speed and oven temperature are controlled to reduce the influence of surface tension gradient and its action process on coating quality.
Increase slurry viscosity:
Increasing the viscosity of the slurry helps to reduce the migration and aggregation of particles during the flow, thus reducing the chance of shrinkage holes.
Shorten drying time:
Proper shortening of drying time can reduce the change of surface tension during drying and help to reduce the formation of shrinkage holes.
三、Precautions in practical application
In the actual production process, it is necessary to choose the right solution according to the specific situation, and constantly optimize the process parameters. At the same time, it is also necessary to strengthen the quality control and monitoring in the production process, and timely find and deal with quality problems such as coating shrinkage holes. In addition, regular maintenance and maintenance of production equipment is also one of the important measures to ensure the stability of coating quality.
In summary, the lithium battery coating shrinkage hole is a complex problem, which needs to be comprehensively analyzed and solved from many aspects such as materials, processes and equipment. By taking the above measures, the occurrence rate of coating shrinkage holes can be effectively reduced, and the performance and stability of lithium-ion batteries can be improved.
