Analyze the processing technology of lithium iron battery separator

Lithium-iron battery separator processing technology The processing technology of lithium-iron battery separators is mainly divided into dry drawing method and wet drawing method. Lithium battery separators must have many characteristics, and special requirements are put forward for their processing technology. The processing technology includes raw material formula and rapid formula adjustment, micropore preparation technology, and complete set of equipment independent design technology. The unidirectional dry drawing process is to process high-orientation polypropylene or polyethylene films with low crystallinity by processing hard elastic fibers. The film is stretched at low temperature to form micro-defects, and then pulled open at high temperature to form micro-pores. At present, more than one-third of my country's processing capacity adopts the dry double-drawing process, and the products occupy a large proportion in the low-end market. It is processed by wet processing, also called phase separation or thermally induced phase separation, wet liquid hydrocarbons or small molecular substances are mixed with polyolefin resins, after melting, heating to form a homogeneous mixture, then cooling the phase separation, the inhibition of the diaphragm, and then heating to The melting point temperature near the diaphragm and the orientation of the biaxially stretched molecular chains, the holding time, and the residual volatile substances in the eluting solvent can be prepared by microporous membrane materials. The wet method can not only prepare interpenetrating microporous membrane materials, but also can prepare lithium battery separators with higher longitudinal and lateral strength. At present, the wet process is mainly used to process single-layer lithium battery separators. Process principle of lithium battery separator 1. Drying method First, the polyolefin resin is melted, extruded, and blown into a crystalline polymer film. Then, crystallization heat treatment and annealing are performed to obtain a highly oriented film structure. The drying process can also be divided into unidirectional stretching and bidirectional stretching. 2. Wet method The traditional wet method mainly uses the phase conversion method, and the TIPS thermally induced phase separation method is an important method used in recent years. The principle of crystalline polymers, thermoplastic polymers and small molecule chemical substances with high boiling point diluent mixtures (such as paraffin oil), form a homogeneous solution at high temperature, and then reduce the temperature of the solution, solid-liquid separation or liquid-liquid separation, extraction After the diluent of the small molecule chemical substance is removed, a thermoplastic and crystalline polymer porous film is formed. The important characteristics of the wet lithium battery separator are high cost, large investment, high equipment requirements, long construction period, long processing period, energy consumption and use of organic solvents during processing. However, the wet method can better control the pore size, distribution and porosity, so it is usually used to make high-end films. The dry raw material is PP, and the wet raw material is PE. Generally speaking, the melting point of PP is around 170°C, while the melting point of PE is around 140°C. Therefore, although the thickness of the wet-processed separator is relatively thin, the lower melting temperature makes the separator easy to shrink at high temperatures, resulting in a short circuit of the battery, and the safety of the battery cannot be guaranteed. Coating inorganic nanoparticles or high temperature resistant organic chemicals on the surface of the film can improve the high temperature safety performance of the film and make up for the defects of wet processing. Lithium battery separator drying process single drawing process feeding: PE, PP and other raw materials and additives are pretreated according to the formula, and then sent to the extrusion system. Fluidization: The pretreated raw materials are melted and plasticized in the extrusion system and then extruded from the die. The melt fluidizes to form a base film with a specific crystalline structure. Heat treatment: heat treatment of the base film to obtain a hard elastic film. Stretching: stretch the hard elastic film through cold and heat to form a nanoporous film. Slitting: According to customer requirements, the nano-microporous film is cut into finished films. Wet asynchronous drawing method feeding: PE, pore former and other raw materials are pre-processed and delivered to the extrusion system according to the formula. Flow delay: The pretreated raw material is melted and plasticized in a twin-screw extrusion system, and then the melt is extruded from the die. Longitudinal stretching: Longitudinal stretching of the flowing thick plate. 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. Previous article: How to maintain the computer battery?