Understand the role of the lithium ion battery diaphragm

Source: 2020 - 03 - 24 o hits: the role of lithium ion battery diaphragm lithium ion battery of the four main data is the cathode. Electrolyte and anode data barrier. Baffle block is the main purpose of the positive and negative, prevent electronic through, while at the same time allowing ions, the end of the lithium ion rapid charge and discharge cycle between the positive and negative transfer. Barrier function directly affect the internal resistance of the battery. Discharge capacity, cycle life and battery safety features. The narrower the clearance, the higher the porosity, the smaller the battery internal resistance, the better the performance of high-speed discharge. Lithium ion battery clearance is a kind of porous plastic film, including woven film, non-woven film ( Non-woven fabric) Film, film, etc. Because of polyolefin material excellent mechanical properties, chemical stability and the performance of the relatively cheap commercial lithium-ion batteries cracks mainly polyolefin microporous membrane, including polyethylene ( PE) Single layer and polypropylene ( PP) Single layer and PP/PE/PP three-layer composite film. Air gap production difficulty lies in pore-forming process and matrix data. Pore-forming engineering technology including the product stability of the production equipment and manufacturing technics of clearance holes; The base material containing polypropylene, polyethylene materials and additives. Polyolefin production technology of air gap is divided into two kinds of dry method and wet method. Dry process is divided into one-way stretch and two-way stretching method. Dry uniaxial tensile process under low temperature tensile membrane formation micro defects, defect at high temperatures extend outward form pores. Due to its for single shaft structure, flat microporous structure and longer, transverse strength is relatively poor, but its advantage is transverse thermal contraction smaller. Celgard has the technology patents. Ube later bought the patent, in this way produce single PP three layer PE and PP/PE/PP composite membrane. Dry biaxial stretching technique consists of nucleation of polypropylene crystal improver, produce different density between different phase, in the process of drawing microporous crystal formation. The process by the institute of chemistry, Chinese Academy of Sciences, independent research and development. Xinxiang Greg new energy information co. , LTD. Technology co. , LTD, cooperating with Chinese Academy of Sciences of guilin the single-layer PP film production. Wet process is also known as hot phase separation. Adding pore forming agent polyolefin resin ( Such as liquid hydrocarbon, or some small molecules) , heating, melting, then pressed into a membrane, and then stretched at high temperature. Extraction solvent elution of residual pore forming material, after drying can be used for the preparation of interpenetrating microporous membrane materials, mainly used in single layer PE film. In this way the company including Japan agms ( Asahi Kasei Oriental) And American Entek. Dry drawing process is simple, no pollution. However, stretching is relatively small, this method is about 3 to 1, pore size and clear than difficult to operate. When stretching, membrane perforation to preparation. Wet preparation of microporous membrane aperture small and uniform, which can stretch up to 5 - 7, not easy to punch. It can be made into a thinner film, make the battery capacity and higher density. The microporous structure of the isolation is very important to the safety of the battery. When the battery overcharge or overheating, clearance may clog pores, open circuit is formed within the cell, limit current rise and prevent further raise the temperature. Baffle obturator temperature associated with the substrate used. PP membrane has high sealing temperature and melt temperature. Polyethylene film obturator low temperature, melting temperature is low. Melting temperature means that at this temperature or higher temperature, completely melt and narrow clearance, electrode internal short circuit of high temperature, lead to disintegration of battery and explosion. Therefore, the safety of the lithium ion battery is usually need to lower the obturator temperature and higher melting point. The application of multilayer composite film is a combination of both, the advantages of PE can be used as the fuse between the two layers of PP. Now there is a new technology can be coated with ceramic material wall, improve the heat resistance of the wall.