12V27A battery

Analysis of the testing principles and detection methods of 12V27A battery diaphragm technology

What are the testing principles and detection methods of 12V27A battery diaphragm technology? At present, almost all 12V27A battery diaphragm thickness measuring equipment in China only has the detection function, and few can achieve closed-loop control of diaphragm thickness. In this article, the editor will start with the testing principles and methods of diaphragms to have a deep and simple understanding of lithium-ion battery diaphragms. Current status of 12V27A battery diaphragm technology 12V27A battery diaphragm technology is a pain point in my country's power battery industry. Among lithium-ion battery materials, positive and negative electrode materials and electrolytes have basically been domestically produced, while diaphragms started late and domestic enterprises have low technical maturity. Although the localization rate of 12V27A battery diaphragms in my country has been increasing in recent years, it mainly occupies the low-end 3C battery diaphragm market, and the localization rate of high-end diaphragms is still very low. High-end 3C batteries and power battery diaphragms still rely heavily on imports. It is reported that the diaphragm is a high-value-added material with the highest technical barriers among 12V27A battery materials, accounting for about 15% of the cost of lithium batteries. Its technical difficulty lies in the engineering technology of pore making, matrix materials, and manufacturing equipment. The common problem of domestic 12V27A battery diaphragms is low consistency, which is mainly manifested in irregular defects, substandard porosity, uneven thickness, pore distribution and pore size distribution. The porosity and pore size distribution of domestic PP diaphragms stretched in one direction are close to those of foreign products; the porosity of PE diaphragms stretched in two directions and in steps is usually lower than that of foreign products, and the pore size distribution is also not ideal. In the field of wet-process diaphragms, domestic diaphragm companies are limited by many factors such as process and technology, and the product level is still low, and production equipment relies heavily on imports. Like chips, high-end diaphragm technology has a very high threshold. Not only does it require huge investments, but it also requires a strong R&D and production team, sophisticated process technology and high-level production lines, and it is not possible to break through in a short time. 12V27A battery diaphragm technology testing principle The principle of online diaphragm thickness detection is mainly to convert the attenuation of the ray after passing through the diaphragm into the diaphragm thickness. This means that the accuracy and stability of the detection must be guaranteed during the detection process. With the increase of 12V27A battery energy density, the battery diaphragm is getting thinner and thinner, and the measurement accuracy is also required to be higher and higher. Generally, enterprises use micrometers for measurement, and there is also a standard measurement method "GB/T6672-2001 Determination of Thickness of Plastic Film and Thin Sheet_Mechanical Measurement Method". There are also corresponding standards for measurement in the world, but these standards are not formulated for diaphragms, so there are problems such as wide test range and low accuracy. Therefore, enterprises that require accuracy generally use precision thickness gauges for measurement. However, due to the soft material of the diaphragm, excessive pressure during measurement will lead to inaccurate measurement data, so some companies also use non-contact thickness gauges for measurement, but the diaphragm has a porous structure, and non-contact measurement will also lead to inconsistent thickness measurement problems, so in the actual measurement process, different test methods need to be selected according to the type of diaphragm. What are the technical detection methods for 12V27A battery diaphragms? 1. Thickness There are two main online control technologies for 12V27A battery diaphragm thickness, one is MD (longitudinal) control and CD (transverse) control; the other is diaphragm online machine vision detection technology. The so-called MD control and CD control refer to the closed-loop control of the thickness in the MD direction by controlling the speed of the feeding screw or the pulling speed; and the data measurement by the scanning frame, and finally the closed-loop control of the data in the CD direction. 2. Curvature Some companies also call it arch degree, which refers to the arc produced after the 12V27A battery diaphragm is cut. When the arc is obvious, it will cause uneven stacking and vortex when winding, causing the pole piece to be exposed and short-circuited. The test method is to lay the diaphragm strip flat on the table, and compare the parallelism with the edge of the steel ruler to get the curvature of the diaphragm. 3. Air permeability The time required for a certain volume of air to pass through the diaphragm under certain conditions is also called the Gurley value. Its size has a certain influence on the performance of the 12V27A battery. The ASTM test method is generally used. 4. Porosity refers to the ratio of the volume of voids to the total volume. The test methods include liquid absorption calculation method and test method. The liquid absorption calculation method is to immerse the 12V27A battery diaphragm in a known solvent, and calculate the void volume of the diaphragm occupied by the liquid by measuring the mass difference before and after the diaphragm is immersed. The mercury injection test method is to use external force to apply pressure to the diaphragm to press mercury into the pores of the diaphragm, and then calculate the porosity of the diaphragm by measuring the volume of the pressed mercury. The average value is taken after multiple measurements. 5. The pore size distribution can also be measured by a mercury injection instrument. The mercury injection method is to measure the pressure applied by the mercury into the hole to calculate the pore size parameters. However, it should be noted that the results measured by the mercury injection instrument include through holes and non-through holes, and the dry 12V27A battery diaphragm will produce stress to destroy the microporous structure of the diaphragm when mercury is immersed. Therefore, the capillary flow analyzer is also used for actual testing. Inert gas is used to break through the wetted diaphragm, and the pressure value of the gas outflow is measured to obtain the pore size parameters through calculation. 6. Wettability is generally measured by contact angle measurement. Its principle has been introduced in detail in the introduction of negative electrode related knowledge, so it will not be repeated here. 7. Electrical performance The 12V27A battery diaphragm, positive and negative electrodes, and electrolyte are assembled together to conduct rate, high and low temperature, storage, cycle, internal resistance, safety and other tests to compare the performance of different diaphragms. As one of the four main materials, the 12V27A battery diaphragm has a relatively simple composition, but there are still many test items. With the development of technology, ceramic diaphragms have been widely used, and new diaphragms such as glue-coated diaphragms, functional coating diaphragms, and non-woven diaphragms have also been gradually applied to lithium-ion batteries. I believe that in the near future, more high-safety and high-mechanical performance diaphragms will gradually enter the lithium-ion battery industry. In recent years, the development of lithium batteries has been rapid, and the society has paid more attention to its safety issues. Therefore, while ensuring the electrical performance of lithium batteries, more attention should be paid to the safety performance testing of 12V27A battery diaphragms.

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