What is the impact of the separator on the performance of lithium batteries?

What kind of influence does the diaphragm have on the performance of lithium batteries? The diaphragm itself is not only a poor conductor of electrons, but also has the characteristics of electrolyte ion passing. The diaphragm material must have good chemical and electrochemical stability, good mechanical properties, and maintain a high degree of wettability to the electrolyte during repeated charging and discharging. The interface compatibility between the separator material and the electrode and the retention of the separator to the electrolyte all have an important impact on the charge and discharge performance and cycle performance of lithium batteries. Lithium battery requirements for diaphragm 1. Thickness The uniformity of diaphragm thickness is a particularly important quality index, which directly affects the appearance quality and internal performance of the diaphragm roll. It must be strictly controlled during processing. In a highly automated diaphragm processing line, the diaphragm thickness is automatically detected and controlled by a highly accurate online non-contact thickness gauge and a fast feedback control system. The thickness uniformity of the diaphragm includes longitudinal thickness uniformity and lateral thickness uniformity. Among them, the lateral thickness uniformity is particularly important, and it is generally required to be controlled within 1 micron. 2. The pore size lithium battery diaphragm material itself has a microporous structure, and the distribution of micropores in the entire diaphragm material should be uniform. The electrode particles currently used are generally on the order of 10 microns, and the pore diameter is generally 0.03-0.12um. If the aperture is too small, resistance will be added. If the aperture is too large, it will easily make the positive and negative electrodes contact or be pierced by dendrites and short circuit. Generally speaking, the submicron pore size membrane is sufficient to prevent the direct passage of electrode particles. Of course, some problems such as micro short circuit caused by poor electrode surface treatment and more dust are not excluded. 3. Porosity Porosity is the volume percentage of pores in the volume of the monomer film, which is related to the density of the raw resin and the film. The size of the porosity has a certain relationship with the internal resistance, but the absolute value of the porosity between different kinds of diaphragms cannot be directly compared. The porosity of the existing lithium battery separator is between 40%-50%. 4. Wetability In order to ensure that the internal resistance of the lithium battery is not too large, it is required that the diaphragm can be completely infiltrated by the electrolyte used in the battery. On the one hand, the degree of wettability is related to the diaphragm material itself, and on the other hand, the surface and internal microstructure of the diaphragm are closely related. Better wettability is conducive to improving the affinity between the diaphragm and the electrolyte, expanding the contact surface between the diaphragm and the electrolyte, thereby increasing the ion conductivity, and improving the charge and discharge performance and capacity of the battery. The wettability can be measured by measuring its liquid absorption rate and liquid holding rate. 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: How are high-quality lithium batteries for electric vehicles made?