Aluminum-plastic film was jointly developed by Japan's Showa and SONY in 1999. It is a packaging material for soft-pack lithium batteries. It is a high-strength, high-barrier multi-layer composite composed of a variety of plastics, aluminum foil and adhesives. Aluminum plastic film has a high technical threshold. In order to ensure the long-term stable operation of the battery, the aluminum plastic film needs to have extremely high barrier properties, good cold stamping formability, puncture resistance, stability and insulation.

　　The main structure of the aluminum-plastic film: ON (surface layer)/AL (aluminum layer)/CPP (resin layer) is composed of three layers of materials, of which the outermost nylon layer mainly plays a protective role; aluminum is the base material, which plays a waterproof and barrier role; Polypropylene separates the aluminum from the battery core to prevent leaked liquid from corroding the aluminum. The adhesive bonds the nylon layer to the aluminum layer on the one hand and the aluminum layer to the polypropylene layer on the other hand.

　　The main use of aluminum-plastic film for lithium batteries is as packaging material for battery cells. In terms of name, it is different from hard-shell packaging materials such as steel shells and aluminum shells. Therefore, lithium batteries packaged with aluminum-plastic films are often called soft-pack lithium batteries. .

　　Lithium battery aluminum plastic film stamping process

　　Aluminum-plastic film is a multi-layer film composed of an outer nylon layer (ON), adhesive, middle aluminum foil (Al), adhesive, and inner heat sealing layer (CPP). It is a package for soft-pack lithium batteries. Material. Aluminum-plastic films for batteries are required to have the following characteristics:?

　　(1) It has extremely high barrier properties;?

　　(2) Has good heat sealing performance;?

　　(3) The material is resistant to electrolyte and strong acid corrosion;?

　　(4) It has good ductility, flexibility and mechanical strength. ?

　　The main components of aluminum plastic film are three layers of ON/AL/CPP, and each layer is bonded with an adhesive. According to the different composite processes, aluminum-plastic films can be divided into two types: dry method and thermal method, as shown in Figure 1. The dry process is where aluminum and polypropylene are bonded with an adhesive and then directly pressed together. The thermal process is where aluminum and polypropylene are bonded with MPP and then hot-pressed by slowly increasing the temperature and pressure.

　　The main advantages of dry process aluminum plastic film are good deep forming effect, good appearance consistency, and less prone to pinholes, fish eyes, impurities and other defects, but its electrolyte resistance is poor. The thermal process can improve the adhesion between the Al layer and the PP layer, greatly improving the ability of the inner surface layer to prevent electrolyte swelling and falling off. However, this specially treated MPP requires a higher temperature to melt it to achieve bonding. After cooling, due to the large difference in shrinkage coefficient with PP, it is easy to curl inward.

　　Lithium battery aluminum plastic film stamping process

　　The functions of each part of ON/AL/CPP:

　　Nylon: It can effectively prevent the penetration of air, especially oxygen, maintain the environment inside the battery core, and ensure that the packaging aluminum foil has good deformation ability.

　　Al: It can effectively prevent the penetration of moisture in the air, maintain the environment inside the battery core, and has a certain thickness and strength to prevent external damage to the battery core.

　　PP: It will not be dissolved or swollen by organic solvents in the battery core. It is the most direct packaging protection and insulation for the internal environment of the battery core. It effectively prevents the internal electrolyte from contacting the Allayer and prevents the Allayer from being corroded.

　　Aluminum plastic film stamping forming process

　　At present, the company actually uses the following two stamping processes for production:

　　(1) Scalable punching: The aluminum-plastic film is under greater pressure from the blank holder. The edge of the aluminum-plastic film is fixed and the fixed part does not deform. It is difficult to compensate for the punching depth. The edge part is compensated by the bottom, and the depth is adjustable. It has poor performance and is rarely used by enterprises now;

　　(2) Compensatory punching: The edge pressure of the aluminum-plastic film is adjustable, and the punching part of the aluminum-plastic film can be compensated by the edge and the substrate. The overall movement and deformation of the aluminum-plastic film has uniform thickness and strong punching ability.

　　Aluminum-plastic film is an indispensable packaging material for soft-pack batteries. The continued increase in demand for soft-pack batteries in the 3C, energy storage and power fields may drive the market demand for aluminum-plastic films.

　　Soft-packed batteries can be designed into different sizes according to customer needs. After the outer dimensions are designed, corresponding molds need to be opened to stamp the aluminum-plastic film. The forming process is also called pit punching, which uses a forming mold to punch out a pit on the aluminum-plastic film that can be used to roll the core.

　　Lithium battery aluminum plastic film stamping process

　　After the aluminum plastic film is punched, it is cut and formed, generally called a pocket bag. Generally, when the battery core is thin, you choose to punch a single pit. When the battery core is thick, you choose to punch a double pit. When punching the double pit, it will be due to the deformation of one side. The assembly breaks through the deformation limit of the aluminum-plastic film and causes rupture.

　　Lithium battery aluminum plastic film stamping process

　　Sometimes, according to design requirements, a small pit will be made on one side of the pit to expand the volume of the air bag.

　　4. Packaging side sealing and top sealing process

　　The packaging process includes two processes: top sealing and side sealing. First, place the rolled core into the punched pit, and then fold the unpunched side in half along the punched pit.

　　Lithium battery aluminum plastic film stamping process

　　After the aluminum-plastic film is loaded into the roll core, the locations that need to be sealed include the top sealing area, side sealing area, first sealing area, and second sealing area.

　　Lithium battery aluminum plastic film stamping process

　　After placing the roll core into the aluminum-plastic film, the aluminum-plastic film can be placed in the clamp and sealed in the top sealing and side sealing machines.

　　Lithium battery aluminum plastic film stamping process

　　The top seal is to seal the tabs. The tabs are made of metal (positive aluminum, negative nickel). How can they be packaged together with PP? This is accomplished by a small component on the lug - the lug glue.

　　I'm not very clear about the specific structure of the ear glue, so I hope someone knowledgeable can add to it. I only know that it also has the cost of PP, which means it can melt and bond when heated. The package at the tab position is shown in the circle in the figure below.

　　During packaging, the PP in the tab glue and the PP layer of the aluminum-plastic film melt and bond, forming an effective packaging structure.

　　Lithium battery aluminum plastic film stamping process

　　5. Liquid injection and pre-sealing process

　　After the soft-packed battery core is sealed on the top side, it needs to be x-rayed to check the parallelism of the core, and then it goes into the drying room to remove moisture. After standing in the drying room for a certain period of time, the liquid injection and pre-sealing process begins.

　　Lithium battery aluminum plastic film stamping process

　　After the battery core is sealed on the top side, there is only an opening on the side of the air bag, which is used for liquid injection. After the liquid injection is completed, the air bag side needs to be pre-sealed immediately, also called a seal.

　　After one seal is completed, the inside of the cell is completely isolated from the external environment.

　　6. Resting, forming, and fixture shaping

　　After the liquid injection and sealing are completed, the battery core needs to be left to rest. Depending on the production process, it is divided into high-temperature resting and room-temperature resting. The purpose of resting is to allow the injected electrolyte to fully infiltrate the cell, and then You can use it to make it into a chemical.

　　The formation process is the first charge of the battery cell, but it will not charge to the highest voltage, and the charging current is also very small. The purpose of formation is to form a stable SEI film on the electrode surface, which is also equivalent to a process of activating the battery core.

　　A certain amount of gas will be produced during this process, which is why an air bag is reserved.

　　Some factories will use fixtures to form cells, put the cells in the fixtures and then put them on the forming cabinet. The gas generated in this way will be fully squeezed into the air bag, and the electrode interface after formation will be better.

　　After the formation is completed, some cells, especially thick cells, will deform to a certain extent due to large internal stress. Therefore, some factories will set up a shaping process after formation, also called fixture baking.

　　7. Second sealing process

　　Lithium battery aluminum plastic film stamping process

　　During the second sealing, the air bag is first punctured with a guillotine and vacuumed at the same time, so that the gas and part of the electrolyte in the air bag will be extracted. Then immediately carry out the second sealing to ensure the airtightness of the battery core. Finally, cut off the air bag, and a soft-packed battery core is basically formed.

　　8. Subsequent processes

　　After cutting the air bag for the second seal, you need to trim and fold the edges to ensure that the width of the battery core does not exceed the standard. The folded batteries will enter the capacity classification cabinet for capacity classification, which is actually a capacity test.

　　After the capacity division is completed, cells with qualified capacity will enter subsequent processes, including appearance inspection, yellow glue application, edge voltage detection, tab transfer welding, etc. Several processes can be added or deleted according to customer needs, and finally OQC inspection is performed. Then package and ship.

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