Soft package of lithium battery assembly flow chart solution

The soft-packed battery core is a battery core that uses an aluminum-plastic packaging film as a packaging material. Relatively speaking, the packaging of lithium-ion batteries divide into two categories, one is a soft-packed battery core, and the other is a metal-clad battery core. The metal casing core includes a steel shell and an aluminum shell, etc. recent years the special needs of battery core with plastic shell, it can also classified as a metal-clad battery core

The difference between the two, in addition to the different shell materials, determines the way it is packaged. The soft-clad cells are made of thermal packaging, while the metal-clad cells are usually soldered (laser welded). The reason why the soft-packed battery can be thermally packaged is that it uses an aluminum-plastic packaging film.

Aluminum plastic packaging film

The aluminum plastic packaging film (abbreviated as aluminum plastic film) is shown in the figure, and has a three-layer structure in cross section: a nylon layer, an Al layer and a PP layer.

The three layers each have their own functions. First, the nylon layer ensures the shape of the aluminum plastic film, ensuring that the film does not deform before being fabricated into a lithium ion battery.

The Al layer is composed of a layer of metal Al, which serves to prevent water from penetrating. Lithium-ion batteries are very afraid of water. Generally, the water content of the pole pieces is at the PPM level, so the packaging film must be able to block the infiltration of moisture. Nylon is not waterproof and does not provide protection. Metal Al reacts with oxygen in the air at room temperature to form a dense oxide film, which prevents moisture from penetrating and protects the inside of the cell. The Al layer also provides the plasticity of the crater when the aluminum film is formed. See point 3 for details.

PP is an abbreviation for polypropylene, which is characterized by melting at a temperature of more than one hundred degrees Celsius and is viscous. Therefore, the thermal packaging of the battery mainly relies on the PP layer being melted and bonded under the action of the heating of the head, and then the head is removed, and the temperature is solidified and bonded.

The aluminum plastic film looks very simple. Actually, how to combine the three layers of materials evenly and firmly is not so easy. It is a pity that the quality aluminum film is basically imported from Japan. The domestic product is not without, 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 customer's requirements. When the external dimensions are designed, the corresponding molds need to be opened to shape the aluminum plastic film. The molding process is also called the crater (in fact, the individual thinks it should be "squatting", but everyone writes it as usual.) As the name suggests, it is a mold that can be loaded on the aluminum film with heating. The core of the core, see the figure below.

After the aluminum film is punched and cut, it is generally called the Pocket bag, as shown in the figure below. Generally, when the battery core is thin, select a single pit (the left side of the figure below), and when the battery core is thick, select the double pit (the right figure below), because the deformation amount of one side will break the deformation limit of the aluminum plastic film. Causes rupture.

Top side sealing process

Finally, I got to the point (you are awesome!), the top side sealing process is the first packaging process of soft-packed lithium-ion batteries. The top side seal actually contains two processes, a top seal and a side seal. First, put the wound core into the punched hole, and then fold the packaging film in half along the dotted line.

There is not much to say about the side seals (the side voltage is too far away to talk about it), mainly speaking, the top seal, the top seal area is shown below. The top seal is to seal the ear, the ear is metal (positive aluminum, negative nickel), how to package with PP? This is done by a small part of the ear, the ear gel. I don't know the specific structure of the ear gel. I hope someone with knowledge can add it. I only know that it also has the cost of PP, which means that it can melt and bond when heated. The package in the polar ear is shown in the circle in the figure below. When packaged, the PP in the ear gel melts and bonds with the PP layer of the aluminum plastic film to form an effective package structure.

In fact, it is a charging and discharging device. I haven't found a picture of the charged core for a long time. Let's think about the picture of the battery clip on it. The achievement is the first charge of the battery, but it will not charge to the highest voltage used, and the charging current is very small.

The purpose of the formation 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 is generated, which is why an aluminum film is reserved for an air bag. In some factories, the process is formed by using a fixture, that is, the battery is clamped in the fixture (sometimes the glass plate is used, and then the steel clamp is used) and then the cabinet is turned into a cabinet, so that the generated gas is fully squeezed to the side. The bag is also removed, and the electrode interface after the formation is also better.

After the formation, some batteries, especially thick batteries, may have some deformation due to the large internal stress. Therefore, some factories will set up a fixture shaping process after the formation, also known as fixture baking.

Two processes

I just said that gas will be generated during the formation process, so we have to pump out the gas and then carry out the second package. Here, some companies have become two processes: Degassing (exhaust) and two, and the latter process of cutting air bags. Here I will call them two general ones.

After cutting the air bag, the trimming and folding are required. The edge and the second edge are cut to the appropriate width, and then folded to ensure that the width of the battery is not exceeded. After folding the battery, the battery can be divided into sub-combined cabinets. In fact, it is the capacity test to see if the capacity of the battery has reached the specified minimum. In principle, all the batteries need to be tested before they leave the factory, so that the batteries with unqualified capacity will not be sent to the customer. However, when the production capacity of the battery is large, some companies will do partial capacity and judge the qualified rate of the batch capacity by statistical probability.

After the volume is divided, the qualified batteries will enter the post-process, including inspection appearance, yellow glue, side voltage detection, polar ear transfer welding, etc., and can increase or decrease several processes according to customer needs. The last is the OQC check, and then the package is shipped.

Here are just the batteries. The batteries will send to Pack factory for further processing, including soldering of boards, packaging, and other etc... Downstream of the Pack factory are various manufacturers, such as Apple, Lenovo, Huawei, they will pack the battery pack into terminal, and then come to our consumers.

The page contains the contents of the machine translation.