Analysis of Physicochemical Properties of Lithium-ion Battery Separator

Consistency: Due to different preparation processes, the consistency of lithium-ion battery separators may vary greatly. This consistency includes its own characteristics, such as closure temperature and apparent consistency, such as the uniformity and thickness of holes observed under an electron microscope. Physical and chemical properties of lithium ion battery separator 1. Wetting and wetting speed. The poor wettability of the separator will increase the resistance of the separator and the lithium-ion battery, which will affect the cycle performance and charge-discharge efficiency of the lithium-ion battery. The wettability of the diaphragm refers to the speed at which the electrolyte enters the micropores of the diaphragm, which is related to the surface energy, pore size, porosity, and curvature of the diaphragm. 2. Absorption rate of the diaphragm. Since the lithium-ion battery separator material has the function of electrolyte, it must meet the following conditions: it is sufficient to ensure that the ion channel is unblocked, the liquid absorption rate and in the battery system, there will inevitably be many side-uses and consume a large amount of electrolyte, so it must There is sufficient reserve, otherwise it will cause the lack of new electrolyte interface resistance, and will also accelerate the consumption of electrolyte. This will be a vicious circle, so the absorption rate of the fluid diaphragm is an important parameter. 3. Chemical stability. The diaphragm should remain stable for a long time in the electrolyte, and must not react with the electrolyte and electrode materials under strong redox conditions. The chemical stability of the diaphragm is evaluated by measuring the corrosion resistance and the expansion and contraction rate of the electrolyte. 4. Thermal stability. Lithium-ion batteries will release heat during charging and discharging, especially when they are short-circuited or overcharged, a large amount of heat will be released. Therefore, when the temperature rises, the diaphragm should maintain the original integrity and certain mechanical strength, and continue to serve as the isolation between the positive and negative electrodes to prevent the occurrence of short circuits. 5. Diaphragm resistance. The membrane resistivity is actually the resistivity of the electrolyte in the micropores, which is related to many factors, such as porosity, pore curvature, electrolyte conductivity, film thickness, and the wetting of the electrolyte to the membrane material. Sex and so on. It is a more commonly used AC impedance method for testing diaphragm resistance. Because the film is very thin, there are often defects, which add errors in the measurement results. Therefore, we often use multiple samples and take the average. 6. Self-closing performance. When the temperature is higher than a certain temperature, an exothermic reaction occurs inside the lithium-ion battery, leading to self-heating. In addition, due to charger failure, safety current failure, etc., the battery will be overcharged or external short-circuit, and a lot of heat will be generated in these situations. Because of the thermoplastic polyolefin material, when the temperature is close to the melting point of the polymer, the ion-conducting membrane of the porous polymer becomes the insulating layer without loopholes, shrinks the pores, and causes the shutdown phenomenon, which prevents the ions from continuing to form a circuit and protect the battery, so the polyolefin separator can Supply additional protective batteries. The important purpose of the separator is to separate the positive and negative electrodes of lithium-ion batteries to prevent contact and short-circuit between the positive and negative electrodes. In addition, it also has the function of allowing electrolyte ions to pass through. It is understood that the quality of the separator directly affects the capacity, cycle capacity and safety performance of the lithium-ion battery. The excellent performance of the separator has an important purpose for improving the overall performance of the battery. 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: What are the advantages of lithium iron phosphate batteries as power lithium batteries for electric vehicles?