Influence Factors of Thermal Shrinkage of Alumina Ceramic/Lithium Battery Separator
Ceramic coatings are popular choices, such as alumina coatings, boehmite coatings. The thermal shrinkage performance of the coating on the separator plays a decisive role in the thermal shrinkage performance of the entire lithium-ion battery separator.
1. The particle size of alumina
Particles with smaller particle sizes are relatively easy to obtain larger bulk densities. The thermal shrinkage rate of the ceramic coating film with the larger particle-like spherical alumina particles is higher than that with the smaller particle size. This is precisely because the particles with smaller particle size obtain a ceramic coating film with a larger bulk density, and a larger bulk density will lead to a smaller thermal shrinkage rate.
2. The original crystal form/morphology of alumina
Due to the shape of the quasi-spherical primary crystal, it is easy to form a higher bulk density, and thus its thermal shrinkage performance is better. On the contrary, the flaky original crystal is not easy to form a denser stack, and there are many voids in the loose stack, which will cause adverse effects during the thermal shrinkage process, resulting in excessive thermal shrinkage.
3. Types of binders
Different kinds of adhesives were selected, respectively mixed with alumina dispersion to form a coating solution, which was coated on the PE base film, and the thermal shrinkage rate of the coating in the MD and TD directions at 130 °C for 1 h was tested respectively.
4. The amount of binder
A coating solution was prepared with different content of binder and alumina dispersion, and coated on PE base film, and the thermal shrinkage rate of the coating in MD and TD directions at 120°C for 1 h was tested respectively. Within a certain range, with the increase of binder content, the thermal shrinkage performance of the coating film becomes worse. First of all, the adhesive itself is a polymer material, which shrinks under heat. When the content increases, the shrinkage rate increases; the corresponding alumina content, which mainly plays a role in heat shrinkage, decreases, and the thermal shrinkage performance of the coating film deteriorates; finally, with the adhesion With the increase of the agent content, the bulk density of the coating becomes smaller, and the liquid leads to the deterioration of its thermal shrinkage performance.
5. Coating thickness
As the coating thickness increases, the thermal shrinkage of ceramic coatings decreases significantly.
The ceramic coating film is mainly composed of a base film with poor thermal shrinkage performance and a coating with better thermal shrinkage performance. When the support strength of the coating is less than the heat shrinkage stress of the base film, the heat shrinkage performance of the ceramic coating film for lithium batteries is poor. When the support strength of the coating is equal to or higher than the heat shrinkage stress of the base film, the ceramic coating film for lithium batteries has poor performance. The heat shrinkage performance is improved.
