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New materials are the development trend, the wet coating is extremely promising

      Polyolefin diaphragm is the current mainstream diaphragm, the most mature technology, but there are lower melting temperature and low strength defects. Polyolefin diaphragm development of the earliest, the production process has been very mature, with non-toxic, corrosion-resistant and the battery temperature is too high to automatically shut down the pores to prevent the short circuit of the advantages of the current occupies an absolute dominant position. However, the melting point of polyolefin-based separator is low, the melting point of polyethylene and polypropylene are 130 ℃ and 150 ℃, more than the temperature of the diaphragm will melt lead to short circuit in the battery, the actual application, the battery may quickly heat up to 200 ℃ , Some lithium-ion battery combustion explosion is precisely because the diaphragm melted at high temperatures caused. In addition, the power battery needs to undergo a crash test, the traditional polyolefin diaphragm in the battery collision prone to be punctured, the diaphragm rupture led to short circuit. In order to improve the safety of the battery, the nano-materials such as ceramic are coated on the polyolefin diaphragm or the new base material is used as the future technology development trend.
      Compared with the ordinary polyolefin membrane, the wet coated membrane has the advantages of high thermal stability, low heat shrinkage and high wettability of the electrolyte, and can improve the safety and power of the battery. Ceramic coated diaphragm is the use of adhesive in the polyolefin-based film coated PVDF and other adhesives or ceramic alumina, the technology is mainly used in the wet process. Since the thermal conductivity of the coating material is low, it is possible to prevent the whole heat of the diaphragm from being runaway and to withstand a high temperature of 240 ° C, more than about 100 ° C of a conventional polyolefin separator. At a temperature of 130 ° C, the shrinkage of the film is not more than 10%, and the heat shrinkage of the separator may cause the positive and negative materials to come into contact with each other, resulting in a short circuit of the battery, and the addition of the film after shrinkage 2%, and the coating material also greatly improved the anti-piercing ability of the diaphragm, and further improve the safety of the battery. In addition, the inorganic particles have a high surface hydrophilicity, so that the membrane can maintain a higher wettability with the electrolytic solution, thereby reducing the internal resistance of the battery and increasing the discharge power of the battery.


      The wet-coated membrane has been promoted in the high-end consumer electronics sector and is expected to challenge the monopoly of dry membrane in the field of power batteries. Wet coating diaphragm in 2012 in the field of high-end consumer electronics began to promote the current high-end digital products such as Apple batteries have been widely used. China's vast majority of power batteries are used in dry one-way stretch diaphragm, but in the battery crash test, the fire rate of more than 80%, safety is still a big problem, coated wet diaphragm with thermal stability High heat shrinkage, low solubility with electrolyte, improved battery safety and power, and has great potential in the field of power battery applications. Samsung, LG and Panasonic Japan and South Korea lithium giant has begun to try to promote the power battery in the wet coating diaphragm, the source material is China's dry one-way stretch diaphragm of the leading enterprises, is the only domestic LG into the supply chain Diaphragm manufacturer. In 2014, the source material increased the wet diaphragm production line and diaphragm coating production line, and in March 2015 by the LG Chemical authorized a ceramic coated membrane core technology patents. In the field of power batteries, in addition to the technology is not yet fully mature, the cost has to be continued to reduce, according to high-performance lithium data, 2015 double-way stretch double-sided diaphragm price of less than 4 yuan / square meter, dry one- Yuan / square meters around the wet diaphragm about 5 yuan, ceramic coated diaphragm are generally 6 yuan / square meters above. With the wet coating technology to further mature and cost reduction, market share is expected to significantly increase.


     Non-woven diaphragms are widely used in lead-acid batteries, nickel-metal hydride batteries and other fields, but there are no large-scale commercial cases in the field of lithium-ion batteries. In the direction of improving the safety of the diaphragm, one is based on polyolefin-based membrane, coated with PVDF or ceramic materials; the other is to change the matrix material. Nonwoven fabric mainly used PET (polyethylene terephthalate) or PI (polyimide) and other fiber materials as the matrix material, the use of dry drawing, hot melt spinning or wet drawing, etc. Made of the diaphragm. Since the melting points of PET and PI reached 225 ° C and 500 ° C, respectively, the heat resistance was much higher than that of the polyolefin-based separator, and its woven structure was able to substantially improve the puncture resistance of the separator, and the nonwoven sheet had a higher Porosity and electrolyte infiltration. At present, the non-woven membrane has been widely used in the fields of lead acid, alkaline batteries, nickel hydrogen and supercapacitors. However, when the lithium ion battery is used, the non-woven membrane has a large pore size, which leads to the self- Too large, and non-woven moisture content is relatively high, likely to cause high battery short circuit. In addition, the process of non-woven diaphragms and traditional diaphragm vary greatly, high conversion costs, there is no successful commercial case.
     Domestic enterprises to develop non-woven diaphragms less, and the high cost of short-term difficult to shake the status of polyolefin diaphragm. The United States and Japan in the non-woven fabric research and development is more leading, in 2010, the United States DuPont announced the development of PI diaphragm, can be used in automotive power batteries, mass production in 2011; 2012, Japan Hirose Paper announced the development of A lithium ion battery separator made of electroless polypropylene fiber nanofibers. Domestic enterprises, only Shenzhen Hui Cheng and Ningbo Aite Mick and other companies R & D efforts, including Ningbo Aite Mick is expected in the second half of 2015 to achieve an annual output of 4 million square meters of nanofiber membrane test line production. However, non-woven membrane in the lithium-ion battery technology bottlenecks have not yet overcome, and the high cost, the price of 10 yuan / square meters above, far more than polyolefin diaphragm. As a result, polyolefin separators will remain the dominant product in the membrane area before the nonwovens diaphragm does not achieve a technical bottleneck breakthrough and a significant reduction in cost.