Aluminum plastic film is a multilayer film composed of outer nylon layer, adhesive, middle layer aluminum foil, adhesive, and inner heat-seal layer. It is a packaging material for soft-packed lithium batteries. At present, there is still a big gap between my country's aluminum-plastic film products and foreign countries.

　　Compared with other batteries, soft-packed lithium batteries are widely used in consumer electronics, automobiles, military, medical, power tools and other industries due to their advantages of good safety performance, light weight, large capacity, low internal resistance, and flexible design.

　　The essence of 　　 soft-pack lithium battery is actually just a layer of polymer casing for liquid lithium ion battery, and its performance is so excellent, of which the aluminum-plastic film in the polymer casing is indispensable. Then the author will analyze the magical aluminum plastic film for everyone.

　　One. Introduction to Aluminum Plastic Film

　　Aluminum plastic film is a multilayer film composed of outer nylon layer, adhesive, middle layer aluminum foil, adhesive, and inner heat-seal layer. It is a packaging material for soft-packed lithium batteries. Compared with other commonly used plastic films, aluminum plastic film has the following advantages:

　　1) Aluminum-plastic film has extremely high barrier properties: 10,000 times higher than ordinary aluminum-plastic composite film barrier properties;

　　2) Good cold stamping formability: It can fit new battery cell models according to customer product requirements.

　　3) Good puncture resistance: due to the copper and aluminum mesh burrs surrounding the polymer lithium battery core, pitting corrosion will accelerate the electrification. When vacuuming and gathering, the burrs will pierce the inner membrane violently, and may pierce the inner membrane until Aluminum foil, the hydrofluoric acid in the battery cell will directly corrode the aluminum foil and change the electrolyte composition. In severe cases, the aluminum foil will corrode and leak, and it will cause a short circuit and cause the battery to be scrapped. Therefore, the puncture resistance is particularly important.

　　4) Good stability against electrolyte: a variety of organic solvents usually swell, dissolve, and absorb flexible packaging materials. They are good solvents for adhesives, which will destroy the bonding effect of the composite layer and change the concentration of the components in the electrolyte. , Which in turn affects the electrical performance of the battery. The presence of strong corrosive hydrofluoric acid will severely corrode the aluminum foil, separate the inner film from the aluminum foil, and then corrode and perforate the aluminum foil, thereby destroying the entire package. The aluminum-plastic film has good electrolyte stability, ensuring the entire battery’s stability. Safety

　　5) The aluminum-plastic film is resistant to high temperatures and has strong insulation: the thickness of the metal electrode sheet is about 100u. When heat-sealed at 170°C and a pressure of about 3kg/cm2, if there is no high temperature resistant insulating layer in the inner film, the metal electrode is often Overwhelm the packaging aluminum foil, causing a short circuit, making the battery scrap, and reducing the yield. Therefore, high temperature resistance and insulation resistance are essential attributes of the shell.

　　2. The structure and classification of aluminum plastic film

　　The main component of the aluminum plastic film is composed of a total of three layers of ON/ALCPP materials. The surface ON layer (nylon layer) is a decorative ON layer, which also protects the AL layer from scratches; the middle is the AL which is shaped and prevents moisture intrusion. Layer; The inner CPP (polypropylene) layer is an electrolyte resistant layer.

　　According to different preparation processes, aluminum-plastic films can be divided into the following two categories. The following is a schematic diagram of typical DNP and Showa Denko aluminum-plastic films:

　　The dry method is widely used. 95% of the Showa ALF output is the dry method, which is mainly used in high-energy and heavy batteries such as mobile phone batteries, MP3, and MP4. In addition, it is also widely used in electric vehicles, model airplanes, and other large-rate, high-capacity power batteries; the thermal method can only be applied to batteries that do not require high capacity.

　　3. The preparation process of aluminum-plastic film　　 Generally speaking, the preparation methods of aluminum-plastic film are divided into two types: dry method and heat sealing:

　　Dry method: After the AL and CPP are bonded with an adhesive, they are directly pressed together. The advantage is to reiterate the molding performance, short-circuit resistance performance, appearance (less impurities, pinholes, fish eyes), and cutting performance. In addition, it has good resistance to electrolyte and water resistance.

　　Heat bonding: MPP is used to connect between AL and CPP, and then thermally synthesized under the conditions of slow temperature increase and pressure increase, the production process is longer. And due to the long-term high-temperature baking effect, the ALF is embrittled, which leads to the deterioration of the drawing performance. The advantage lies only in electrolyte resistance and water resistance, but its deep drawing performance, short-circuit resistance, appearance, and cutting performance are all unsatisfactory.

　　Fourth, the dilemma faced by domestic aluminum-plastic film manufacturers

　　At present, the performance of aluminum-plastic film products in my country only has a few technical indicators of a few companies that can reach the level of Japanese companies. The main problem is that the electrolyte resistance and drawing depth are not good. The drawing depth of domestic aluminum-plastic film is about 5mm. Foreign products are at 8mm or even up to 15mm, and there is still a certain gap between foreign products. Especially the reaction conditions and precision control. In the manufacturing process of this kind of high-precision material, the difference is often very small, and the difficulty of process control is reflected in the minute. At present, domestic aluminum-plastic film manufacturers have the following five major dilemmas:

　　1) The surface treatment process of aluminum foil is backward and pollution is large: due to the use of water to wash out the oil and "chromic anhydride" passivation treatment, the pollution is large. At the same time, due to the surface tension of the water, the oil in the micropores of the aluminum foil cannot be cleaned, resulting in defects in the subsequent process;

　　2) The water treatment process of aluminum foil will produce "hydrogen embrittlement", so the domestic aluminum plastic film has poor resistance to disassembly;

　　3) The surface of the aluminum foil is coated with a UV layer, the stiffness of the aluminum foil is not enough, it is easy to wrinkle when the dry method is compounded, and the wide product cannot be produced and the yield is poor;

　　4) For CPP, the main domestic use of laminating machine coating, when combined with the surface of high thermal conductivity aluminum foil, it is easy to curl and produce layered crystals;

　　5) Due to the technical reasons of the domestic adhesive formulation, the product is prone to delamination and peeling.

　　Domestic lithium battery manufacturers are facing huge cost pressures and urgently demand to reduce the cost of lithium battery raw materials. Therefore, the demand for import substitution and localization of aluminum-plastic film has become increasingly prominent.