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

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

　　The difference between the two is not only the case material, which determines the packaging method is also different. The soft-packed cells are thermally packaged, while the metal shell cells are generally welded (laser welding). The reason why soft-pack batteries can be thermally packaged is that they use aluminum-plastic packaging film.

　　aluminum plastic packaging film

　　The composition of 　　 aluminum-plastic packaging film (abbreviated as aluminum-plastic film) is shown in the figure, and its cross-section has three layers: nylon layer, Al layer and PP layer.

　　Each of the three layers has its own function. First of all, the nylon layer ensures the shape of the aluminum-plastic film and ensures that the film will not be deformed before being manufactured into a lithium ion battery.

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

　　PP is the abbreviation of polypropylene. The characteristic of this material is that it will melt at a temperature of more than one hundred degrees Celsius, and it is viscous. Therefore, the thermal packaging of the battery mainly relies on the PP layer being melted and bonded together under the action of the heating of the head, and then the head is removed, and the temperature is cooled to solidify and bond.

　　Aluminum plastic film looks very simple. In practice, how to evenly and firmly combine the three layers of materials is not so easy. It is a pity that the good quality aluminum-plastic film is basically imported from Japan, and the domestic ones are not available, but the quality needs to be improved.

　　Aluminum plastic film forming process

　　The soft-packed batteries can be designed into different sizes according to the needs of customers. After the external dimensions are designed, the corresponding molds need to be opened to form the aluminum-plastic film. The forming process is also called a punching hole (in fact, I think it should be a "punch hole", but everyone writes it like that). As the name suggests, it is to use a forming mold to punch out a mold that can be installed on the aluminum plastic film under heating. The pit of the core is shown in the figure below for details.

　　After 　　 aluminum plastic film is punched and cut into shape, it is generally called Pocket bag, as shown in the figure below. Generally, when the battery core is thin, choose to punch a single pit (left in the figure below), and when the battery core is thick, choose to punch a double pit (right in the figure below), because too much deformation on one side will break the deformation limit of the aluminum-plastic film. Cause rupture.

　　top side sealing process

　　has finally come to the topic (how good are you digressing!), the top-side sealing process is the first packaging process of the soft-packed lithium-ion battery. The top side seal actually includes two processes, the top seal and the side seal. First put the wound core into the punched pit, and then fold the packaging film in half along the dotted line.

　　There is not much to say about the side seal (the side voltage is too far to talk about it), mainly talk about the top seal, the schematic diagram of the top seal area is shown in the figure below. The top seal is to seal the tabs. The tabs are made of metal (aluminum anode and nickel cathode). How can they be packaged with PP? This is done by relying on a small part on the lug-lug glue. I am not very clear about the specific structure of the tabular gel. I hope someone who knows how to do it will add 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 circled part in the figure below. During packaging, the PP in the tab glue and the PP layer of the aluminum-plastic film are melted and bonded to form an effective packaging structure.

　　is actually a charging and discharging device. I haven't found a picture of a charged core after searching for a long time. Think about the picture of the battery sandwiched on it. The chemical achievement is the first charging of the battery, but it will not be charged to the highest voltage used, and the charging current is also very small.

　　The purpose of chemical conversion is to form a stable SEI film on the surface of the electrode, which is equivalent to a process of "activating" the cell. In this process, a certain amount of gas will be generated, which is why the aluminum plastic film needs to reserve an air bag. In some factories, the process will use fixture formation, that is, the cell is clamped in the fixture (sometimes the picture is simple and the glass plate is used, and then the steel clamp is installed) and then the cabinet is formed, so that the gas generated will be fully squeezed to the side of the gas. The electrode interface after chemical formation is also better.

　　Some cells, especially thick cells, may undergo certain deformation due to large internal stress after formation. Therefore, some factories will set up a fixture shaping process after the formation, which is also called fixture baking (baking).

　　Second Sealing Process

　　I just said that gas is generated during the formation process, so we have to extract the gas and then perform the second encapsulation. Some companies here have two processes: Degassing (exhaust) and second seal, and the latter process of cutting the air bag. Here I call them the second seal in general.

　　After cutting the air bag with the second seal, it is necessary to trim and fold the edges, that is, cut the one edge and the second seal to the appropriate width, and then fold it to ensure that the width of the battery does not exceed the standard. After folding, the battery cell can be installed in the capacity-dividing cabinet for capacity distribution. In fact, it is a capacity test to see if the capacity of the battery core has reached the specified minimum value. In principle, all batteries need to be tested before leaving the factory to ensure that batteries with unqualified capacity will not be delivered to customers. However, when the production volume of battery cells is large, some companies will make partial capacity, and use statistical probability to judge the qualified rate of the batch of battery cells.

　　After the capacity is divided, the cells with qualified capacity will enter the subsequent processes, including appearance inspection, yellow glue, edge voltage detection, tab transfer welding, etc. Several processes can be added or subtracted according to customer needs. The last is OQC inspection, and then packaged and shipped.

　　Attention, here are only batteries. The cells will be sent to the Pack factory for further processing, including welding circuit boards, packaging, and so on. Downstream of the Pack factory are various manufacturers, such as Apple, Lenovo, and Huawei. They will take the battery pack and install it in the terminal before it comes to our consumers.