Brief analysis of the diaphragm performance of lithium-ion batteries

The membrane characteristic separator of lithium ion batteries is located between the positive electrode and the negative electrode. Its important function is to separate the active material of the positive electrode and the negative electrode to prevent the two electrodes from contacting and short-circuiting. In addition, in the electrochemical reaction, the necessary electrolyte can maintain the formation of ion movement channels. The separator material is not conductive, and different types of batteries use different separators. Regarding lithium-ion batteries, since the electrolyte is an organic solvent system, its membrane must have the following characteristics. 1. In the battery system, its chemical stability is good, and the material can withstand organic solvents. 2. High mechanical strength and long service life. The ionic conductivity of organic electrolytes is lower than that of aqueous systems. In order to reduce resistance, the electrode area must be as large as possible, so the film must be thin. When the battery system is abnormal, the temperature will rise. In order to prevent danger, when the rapid heat generation temperature (120~140℃) starts, the thermoplastic film will melt and the micropores will be closed to become an insulator, preventing the electrolyte from passing through, thereby achieving the purpose of blocking current. 5. From the perspective of a lithium ion battery, it should be fully saturated with organic electrolytes and maintain a high penetration rate during repeated charging and discharging. The commonly used membrane material for batteries is a porous membrane made of cellulose or fabric or synthetic resin. Lithium-ion batteries generally use high-strength, thin-film polyolefin porous membranes, commonly used separator polypropylene (PP) and polyethylene (PE) microporous membranes, as well as copolymers of propylene and ethylene, and polyethylene homopolymers. Among them, Celgard's The diaphragm is representative. In recent years, the application of polymer electrolytes in lithium-ion batteries has been commercialized. In lithium-ion batteries, the polymer electrolyte is not only a channel for ion migration, but also a barrier between the positive and negative materials. Polymer electrolytes can be divided into solid polymer electrolytes and gel polymer electrolytes. As a practical polymer electrolyte membrane, the following requirements must be met: the transfer coefficient of lithium ions is basically unchanged to eliminate concentration polarization; (3) The negligible electrical conductivity ensures effective isolation between electrodes; (4) The electrode material has high chemical and electrochemical stability; the price is low, and the chemical composition is suitable to ensure environmental friendliness. Due to the low room temperature conductivity of solid polymer electrolytes, it is difficult to realize commercialization. The gel polymer electrolyte realizes ion conductivity through liquid electrolyte molecules fixed in the polymer network, not only has the stability of solid polymers, but also has the high ion conductivity of liquid electrolytes, and has good application prospects. The polymer electrolyte and polyethylene and polypropylene membrane together form a polymer lithium ion battery membrane. The colloidal polymer is covered or filled in the microporous membrane. Compared with the non-membrane polymer electrolyte lithium ion battery, it has better performance, such as : It can provide better protection when the internal short-circuit occurs; it can reduce the thickness of the electrolyte layer; it can provide sufficient security when charging; (4) it has better mechanical properties and thermal stability. It can be seen that polyethylene and polypropylene membranes play an important role in ionic cell membranes due to their special structure and properties, unless there is a real liquid-free polymer electrolyte. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete it. Previous: How can the lithium-ion battery be charged to facilitate people's use?