Process technology and development trend of lithium battery diaphragm industry

The wet method of lithium battery diaphragm is mainly used in the manufacture of polyethylene (PE) diaphragm. Since the process uses a mixture of paraffin oil and PE to make holes, and solvent extraction is used to remove them after the stretching process, this process is called a wet process. The wet technique involves stretching the film in two directions, so it is divided into simultaneous stretching and stepwise stretching. There has always been a debate about whether synchronous stretching or stepwise stretching is more advanced. Disputes are embodied in the aspects of product quality, efficiency, and process adaptability. From the comparison of the microstructure of the product, the diaphragm manufactured by the synchronous stretching process has higher porosity, more uniform pore distribution, and better thickness uniformity; at the same time, the synchronously stretched product has uniform strength and higher yield, which is theoretically integrated The performance is better. If we compare the production efficiency and the process adaptability of lithium-ion batteries, we can't judge the pros and cons for the time being. The only difference is the difference in equipment level and process maturity of different companies. From the user feedback, the difference in performance between the two products is not obvious. 2. Dry technology Dry technology is mainly used in the manufacture of polypropylene (PP) diaphragms. Dry technology mainly includes 3 kinds of technology: blown film + unidirectional stretching, cast sheet + unidirectional stretching and bidirectional stretching. Relatively speaking, dry technology has simpler process, lower equipment cost and lower production efficiency than wet technology. 3. Semi-dry process technology The semi-dry process is used in the manufacture of polyethylene (PE) diaphragms and is a newly introduced method in recent years. It also needs to use a pore former to occupy the place, and then use the method of evaporation to remove. The non-woven method (Non-Woven) is currently mainly used in the manufacture of polyester (PET) non-woven fabric and ceramic particle composite separators. The large pores that must exist in the non-woven fabric bring a higher short-circuit risk to the composite diaphragm. This shortcoming restricts the application of non-woven diaphragms and requires a breakthrough improvement in process technology. 4. Non-woven fabric method non-woven fabric diaphragm base material usually uses polyethylene terephthalate (PET, melting point up to 225°C) and polyimide (PI, melting point over 500°C), which has obvious advantages in heat resistance . At the same time, due to its three-dimensional pore structure, it can effectively prevent the short-circuit phenomenon caused by acupuncture and improve the liquid retention rate. At present, domestic and foreign companies have achieved many results in the research, application and performance optimization of non-woven fabric separators, but there have not been successful cases of large-scale commercial applications in lithium-ion batteries. The development trend of lithium battery diaphragm technology The development of power lithium battery has clarified the direction and put forward specific requirements for the development of diaphragm. The development of power lithium batteries consists of three elements: improving energy density, ensuring safety, and reducing costs. The specific energy of the monomer will reach more than 300Wh/kg, the specific energy of the system will strive to reach 260Wh/kg, and the cost will be reduced to less than 1 yuan/Wh. Correspondingly, the requirements for lithium battery separators are two aspects: higher safety, and more conducive to battery performance. From the aspect of conducive to the performance of lithium-ion batteries, it is necessary to further optimize the structural characteristic parameters and consistency of the separator. Such as thickness, reasonable value of porosity, optimized pore size, optimized pore size distribution, etc. In addition, the consistency of the diaphragm is always the core issue of large-scale production. Lithium battery separators mainly include polyolefin separators and non-woven separators. Polyolefin materials have excellent mechanical properties, chemical stability and relatively inexpensive characteristics. Therefore, polyolefin microporous membranes such as PE and PP have been widely used in the early stage of lithium ion battery research and development, and have become the mainstream direction of lithium battery separators. 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: Why does the lithium polymer battery have zero voltage? How to deal with it?