cr2032 button battery.Analysis of soft pack lithium battery assembly process

　　Whether in the digital or power application markets, soft-pack batteries are becoming a very important technical route.

　　Soft-packed batteries are actually batteries that use aluminum-plastic packaging film as packaging material. Relatively speaking, the packaging of lithium-ion batteries is divided into two categories, one is soft-packed cells and the other is metal-cased cells. Metal-cased batteries include steel shells, aluminum shells, etc. In recent years, due to special needs, some batteries use plastic shells, which can also be classified into this category.

　　The difference between the two is not only the shell material, but also the packaging method. Soft-packed batteries use thermal packaging, while metal-cased batteries generally use welding (laser welding). The reason why soft-packed batteries can be thermally sealed is that they use aluminum-plastic packaging film.

　　Aluminum plastic packaging film

　　The composition of aluminum-plastic packaging film (referred to as aluminum-plastic film) is shown in the figure. Its cross-section consists of three layers: nylon layer, Al layer and pp layer.

　　Each of the three layers has its own role. First, the nylon layer ensures the shape of the aluminum-plastic film and ensures that the film will not deform before it is manufactured into a lithium-ion battery.

　　The Al layer is composed of a layer of metal Al, and its function is to prevent water from penetrating. Lithium-ion batteries are very afraid of water, and generally require the moisture content of the pole pieces to be at the ppM level, so the packaging film must be able to block the penetration of water vapor. Nylon is not waterproof and cannot provide protection. Metal Al will react with oxygen in the air at room temperature to form a dense oxide film, which prevents water vapor from penetrating and protects the inside of the battery core. The Al layer also provides the plasticity for punching when the aluminum plastic film is formed. Please see point 3 for details.

　　PP is the abbreviation of polypropylene. The characteristic of this material is that it melts at temperatures of more than 100 degrees Celsius and is sticky. Therefore, the thermal sealing of batteries mainly relies on the pp layer melting and bonding together under the action of heating of the sealing head. Then the sealing head is removed and the temperature is reduced to solidify and bond.

　　Aluminum plastic film looks very simple, but in practice, it is not so easy to combine the three layers of materials evenly and firmly together. Unfortunately, good-quality aluminum-plastic films are basically imported from Japan. Domestic ones are not available, but the quality still needs to be improved.

　　Aluminum plastic film forming process

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