button cell battery cr2025.The importance of aluminum-plastic film from the production and packaging process of soft-packed lithium batteries

　　The soft-packed batteries we have seen so far are all batteries that use aluminum-plastic film as packaging material. Broadly speaking, lithium-ion soft-packed batteries are divided into two categories. One type uses aluminum-plastic film as packaging. Batteries, the other type is metal-cased batteries, and metal-packaged batteries include steel shells, aluminum shells, etc.

　　1. Soft-packed batteries

　　The soft-packed batteries we have seen so far are all batteries that use aluminum-plastic film as packaging material. Broadly speaking, lithium-ion soft-packed batteries are divided into two categories. One type uses aluminum-plastic film as packaging. Batteries, the other type is metal-cased batteries, and metal-packaged batteries include steel shells, aluminum shells, etc.

　　Different outer packaging materials determine the use of different packaging methods. Polymer soft-packed batteries use thermal packaging, while metal-packed batteries use welding methods.

　　2. Packaging soft film-aluminum plastic film

　　The aluminum-plastic composite film can be roughly divided into three layers - the inner layer is an adhesive layer, mostly made of polyethylene or polypropylene, which plays a sealing and bonding role; the middle layer is aluminum foil, which can prevent the penetration of water vapor from the outside of the battery and prevent internal damage. Leakage of electrolyte; the outer layer is a protective layer, which is mostly made of polyester or nylon materials with high melting points. It has strong mechanical properties, prevents damage to the battery from external forces, and plays a role in protecting the battery.

　　The research and development of high-quality aluminum-plastic composite films is the key to the successful development of liquid flexible packaging lithium-ion batteries, a high-tech product. As the outer shell of liquid flexible packaging lithium-ion batteries, the aluminum-plastic composite film is no longer just a simple outer packaging of the battery, but also an indispensable and important component of liquid flexible packaging lithium-ion batteries.

　　If the importance of this flexible packaging material is not fully understood, it will be detrimental to the design and development of flexible packaging batteries. It plays such an important role in the development of liquid flexible packaging lithium-ion batteries, which shows that the product has high technical content and is qualitatively different from ordinary composite packaging materials in terms of design, manufacturing and application.

　　Domestic and foreign manufacturers are working hard to continuously improve their products, and the production technology of aluminum-plastic composite films is also under continuous research and development.

　　3. Aluminum plastic film stamping forming process

　　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.

　　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.

　　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.

　　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.

　　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.

　　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 to form an effective packaging structure.

　　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.

　　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

　　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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