Basic parameters and performance requirements of lithium battery separator materials

From an academic point of view, the diaphragm is inert in the battery, that is, the diaphragm is not an essential part of the battery, but is only a requirement for the industrialized processing of the battery. Generally speaking, there is an air permeability parameter in the lithium battery separator, or Gurley number. This number means the time required for a certain volume of gas to pass through a certain area of u200bu200bthe diaphragm under certain pressure conditions. The volume of gas is generally 50cc, and some companies will also mark 100cc, and the final result will be twice as bad. ●Infiltration degree In order to ensure that the internal resistance of the lithium battery is not too large, the diaphragm is required to be completely infiltrated by the electrolyte used in the battery. There is no recognized testing standard in this regard. ●Chemical stability, in other words, requires lithium battery separators to be inert in electrochemical reactions. After several years of industrial inspection, it is generally believed that the current diaphragm material PE or PP meets the requirements of chemical inertness. ●Thickness For power lithium batteries, due to the mechanical requirements of the assembly process, thicker diaphragms are often required. Of course, safety is also very important for large power batteries, and thicker diaphragms often mean better safety at the same time. Sex. ●Aperture Generally speaking, in order to prevent the direct contact of electrode particles, it is very important to prevent the electrode particles from directly passing through the diaphragm. The electrode particles currently used are generally on the order of 10 microns. Generally speaking, the sub-micron pore size membrane is sufficient to prevent the direct passage of electrode particles. Of course, it is not ruled out that some electrode surfaces are not treated well, and some such as micro particles caused by more dust are not excluded. Short circuit, etc. ●The thermally stable diaphragm should be thermally stable within the temperature range (-20C~60C) where the lithium battery is used. Generally speaking, PE or PP materials currently used in diaphragms can meet the above requirements. ●Porosity Currently, the porosity of separators for lithium batteries is about 40%. 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 performance of lithium battery separator materials requires lithium batteries to be composed of positive and negative electrode materials, electrolyte, separator and battery casing. As the third pole of the battery, the diaphragm is one of the key internal components in the lithium battery. After the diaphragm absorbs the electrolyte, it can isolate the positive and negative electrodes to prevent short circuits and allow the conduction of lithium ions. When overcharged or the temperature rises, the diaphragm blocks current conduction through closed pores to prevent explosion. The advantages of the diaphragm performance determine the battery's interface structure and internal resistance, which in turn affect the battery's capacity, cycle performance, charge and discharge current density and other key characteristics. Excellent performance separators play an important role in improving the overall performance of lithium batteries. 1. Wetting ability and wetting speed: better wetting ability is beneficial to improve the affinity between the diaphragm and the electrolyte, expand the contact surface between the diaphragm and the electrolyte, thereby adding ion conductivity and improving the charge and discharge performance of the battery And capacity. The wettability of the diaphragm to the electrolyte can be measured by measuring its liquid absorption rate and liquid holding rate. 2. Chemical stability: The diaphragm should maintain long-term stability in the electrolyte and not react with the electrolyte and electrode materials. Its chemical stability is evaluated by measuring the corrosion resistance of the electrolyte and the rate of expansion and contraction. 3. Thermal stability: The battery will release heat during charging and discharging, especially when it is short-circuited or overcharged, a large amount of heat will be released. Therefore, when the temperature rises, the separator should maintain the original integrity and certain mechanical properties, and play the role of isolating the positive and negative electrodes and preventing short circuits. 4. Safety protection performance: With the gradual expansion of the application range of lithium batteries, especially in the field of power lithium-ion batteries, the safety of lithium batteries has become the most important link for lithium battery manufacturers. As the most critical core material of lithium batteries, higher requirements are also placed on the separator. Disclaimer: The articles published on this website are all from the Internet. If there is any infringement, please contact to delete it. 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: Are lithium batteries more environmentally friendly than lead-acid batteries?