Analysis of the advantages of wet processing technology and dry processing technology for lithium battery diaphragm

In the field of wet diaphragms, the country is still in the early stage of import substitution. In the field of dry-process diaphragms, the white paper believes that the current dry-process diaphragms are basically relatively mature, and the competition is more fierce than wet-process diaphragms, and they can basically completely replace imported diaphragms, facing downward pressure on prices. The wet processing process mixes liquid hydrocarbons or some small molecular substances with polyolefin resins, heats and melts them to form an even mixture, then cools down for phase separation, presses the membrane, and then heats the membrane to a temperature close to the melting point for bidirectional Stretching makes the molecular chain oriented, and finally keeps the temperature for a certain time, and the residual solvent is eluted with volatile substances to prepare interpenetrating microporous membrane materials. The dry process lithium battery process can be subdivided into a uniaxial stretching process and a biaxial stretching process. The dry uniaxial stretching process is to process hard elastic fibers to prepare highly oriented polypropylene or polyethylene films with low crystallinity, and then high-temperature annealing to obtain oriented films with high crystallinity. This film is first stretched at low temperature to form micro-defects, and then at high temperature the defects are pulled apart to form micro-pores. In the dry biaxial stretching process, by adding a β crystal modifier with nucleation purpose to polypropylene, the difference in density between different phases of polypropylene is used, and the crystal form changes during the stretching process to form micropores, which are used for processing Single-layer PP film. At present, more than one-third of my country's output uses the dry double-drawing process, and products occupy a large proportion in the low-end market. Scope of application: large-scale lithium-ion power lithium-ion battery. The battery separator technology is now mature, whether it is a battery separator manufactured by a dry method or a wet method. The many characteristics that lithium battery separators must have have put forward special requirements for their processing technology. The processing technology includes raw material formula and rapid formula adjustment, micropore preparation technology, and independent design of complete equipment. Dry method can be subdivided into uniaxial stretching process and biaxial stretching process. The dry uniaxial stretching process is to process hard elastic fibers to prepare highly oriented polypropylene or polyethylene films with low crystallinity. In the high-temperature annealing process, a film with high crystallinity is obtained. This kind of film is first stretched at low temperature to form micro-defects, and then at high temperature, the defects are pulled apart to form micro-pores. At present, more than one-third of my country's output uses the dry double-drawing process, and products occupy a large proportion in the low-end market. Scope of application: Large-scale lithium-ion power lithium-ion battery lithium battery wet processing technology, also known as phase separation method or thermally induced phase separation method. The wet method process mixes liquid hydrocarbons or some small molecular substances with polyolefin resin, and after heating and melting, An even mixture is formed, then the temperature is lowered for phase separation, the membrane is compressed, and the membrane is heated to a temperature close to the melting point, and the membrane is heated to a temperature close to the melting point, and the molecular chains are oriented by biaxial stretching. , Can prepare the interpenetrating microporous membrane material. The wet processing technology can not only prepare interpenetrating microporous membrane materials, but also the processed lithium battery separator has higher longitudinal and lateral strength. At present, the wet processing technology is urgently used to process single-layer lithium battery separators. Range of use: high-performance lithium batteries, etc. In terms of physical and mechanical properties, the dry uniaxial stretching process has more advantages. However, the lithium battery separator processed by the wet processing technology has high porosity and good air permeability, which can meet the requirements of high current charging and discharging of power lithium-ion batteries. On the contrary, because the wet processing technology uses polyethylene substrate, the melting point of the polyethylene substrate is only 140℃. Therefore, compared with the lithium battery separator processed by the dry processing technology, the lithium battery separator processed by the wet processing technology has the Poor thermal stability. The dry molding process needs to go through the steps of melt extrusion→high-stretching→cooling→heat solution→stretching→heat setting→slitting and rewinding.The mold temperature machine controls the extrusion temperature during the melt extrusion process to ensure the material's availability. fluidity. The water chiller cools down the cooling roller during the cooling stage, and the mold temperature machine heats it up in the heat solution stage. Wet processing technology, also known as phase separation method or thermally induced phase separation method. The wet processing method mixes liquid hydrocarbons or some small molecular substances with polyolefin resin, heats and melts, forms an average mixture, and then cools down for phase separation and compression Obtain the membrane, and then heat the membrane to a temperature close to the melting point, perform biaxial stretching to align the molecular chains, and finally keep it warm for a certain period of time to elute the remaining solvent with volatile substances. In general, the lithium battery separator technology is now mature, whether it is a battery separator manufactured by a dry method or a wet method. But the dry method does not need to extract this step, the cost is lower than the wet method, and the stability is poorer than the wet method. 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: Explain the development direction of UPS battery industry in detail