Process technology for producing 1.5V rechargeable battery separators—dry and wet separators

　　Process technology for producing 1.5V rechargeable battery separators—dry and wet separators. The production process of 1.5V rechargeable battery separators is complex. The many characteristics of 1.5V rechargeable battery separators and the difficulty in taking into account their performance indicators determine that the technical barriers to its production process are high and its research and development is difficult. 1.5V rechargeable battery separators are the components with the highest technical barriers among the four key components of lithium batteries. The current production processes on the market are mainly dry uniaxial stretching, dry biaxial stretching and wet stretching.

　　Process technology for producing 1.5V rechargeable battery separators

　　As the world's largest 1.5V rechargeable battery manufacturing base and the second largest lithium-ion battery producer and exporter, China's demand for separators is increasing day by day. In 2013, China's domestic diaphragm market capacity was 538 million square meters, a year-on-year increase of 40.40%. In 2013, the output of domestic diaphragms accounted for about 50% of the domestic diaphragm market capacity, but the year-on-year growth rate maintained 54.31%.

　　It is expected that price competition in the domestic 1.5V rechargeable battery separator industry will become increasingly fierce in the next few years, ushering in a major reshuffle of the industry. Those who lack technology, few brands, and short funds will be eliminated, especially small and medium-sized enterprises. The situation is not optimistic. The market characteristics will show the trend that the strong will stay strong and the weak will be eliminated.

　　The many characteristics that lithium-ion battery separators need to possess put forward special requirements for its production process, which includes raw material formula and rapid formula adjustment, micropore preparation technology, and independent design of complete sets of equipment. Among them, micropore preparation technology is the core of the 1.5V rechargeable battery separator preparation process. According to the difference in micropore formation mechanism, the separator process can be divided into two types: dry method and wet method.

　　Introduction to 1.5V rechargeable battery dry separator process

　　1.5V rechargeable battery dry separators can be subdivided into uniaxial stretching processes and biaxial stretching processes. The dry uniaxial stretching process is a method of producing hard elastic fibers to prepare highly oriented polypropylene or polyethylene films with low crystallinity. During the high-temperature annealing process, a film with high crystallinity is obtained. This film is first stretched at low temperatures to form micro-defects, and then at high temperatures the defects are pulled apart to form micropores. At present, more than one-third of China's production capacity uses the dry double drawing process, and its products occupy a large proportion of the mid- to low-end market.

　　The trend of wet separators replacing dry separators for lithium batteries has formed

　　The wet production process can not only prepare interconnected microporous membrane materials, but also produce 1.5V rechargeable battery separators with high longitudinal and transverse strength. At present, the wet production process is mainly used to produce single-layer 1.5V rechargeable battery separators.

　　Compared with dry separators, wet separators are thinner, more precise, have more ideal tensile strength, higher porosity, better air permeability, more uniform pore sizes and higher transverse shrinkage. The puncture strength of the wet separator is higher, which is more conducive to extending battery life, reflecting obvious performance advantages.

　　Compared with the dry method, the wet separator has better performance and can better adapt to the development trend of high energy density of lithium batteries, but the cost is higher. As the subsidy policy for new energy vehicles puts forward higher requirements for battery energy density, the dominance of ternary batteries has led to an increasing demand for wet separators.

　　1.5V rechargeable battery wet separators have significant advantages over dry processes in terms of performance and safety, and can better adapt to the current trend of new energy vehicle batteries developing towards high energy density.

　　The difference between wet separator and dry separator for 1.5V rechargeable battery

　　a. Due to the simple process, the fixed asset investment of dry process separators is smaller than that of wet process; however, it is difficult to control the temperature and other indicators of the dry process of processing technology, and the process of wet process is simpler;

　　b. The dry method can make a three-layer film, while the 1.5V rechargeable battery wet method can only make a single-layer film; (the advantage of the three-layer film is that the thermal shutdown temperature is 135 degrees, but the thermal stable temperature is 160 degrees, which can prevent thermal inertia and has 25 degrees space, safer)

　　c. In addition to different processing techniques, dry and wet 1.5V rechargeable battery separators also use different raw materials. The dry method uses raw materials with good fluidity and low molecular weight, so the high temperature can only reach 135 degrees and will shrink when exposed to heat. It is not safe and suitable for high-power and high-capacity batteries. The wet method uses raw materials that are not fluid and have high molecular weight. The thermal shutdown temperature can reach 180 degrees, which can ensure the safety of high-power lithium batteries;

　　d. In terms of producing general lithium batteries, dry process separators have advantages, such as low cost, less pollution, and more uniform pores; in terms of high-power batteries, wet processes have advantages, mainly in terms of safety and low heat shrinkage.

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