After aluminum-plastic film is punched and cut, it is generally called pocket bag. Generally, a single pit is selected when the battery is thin, and a double pit is selected when the battery is thick, because one side of the battery is deformed too much to break through the deformation limit of aluminum-plastic film, which leads to damage.
Sometimes, according to the design requirements, a small pit is made in the position of the airbag to expand the volume of the airbag.
Top-side sealing process, which is the first packaging process of flexible packaging lithium-ion batteries. Top sealing and side sealing actually include two processes, top sealing and side sealing. First, put the winding core into the perforated pit, and then fold the packaging film in half along the dotted line.
The following figure shows several positions where the aluminum-plastic film needs to be packaged after being put into the winding core, including the top sealing area, the side sealing area, the first sealing area and the second sealing area. The following online applications are analyzed respectively.
After the winding core is placed in the into the pit, the whole aluminum-plastic film can be placed in the fixture and sealed at the top side in the top side sealing machine. The top seal looks like this:
The top side sealing machine of this model in the picture has four clamps, the left station is the top sealing and the right station is the side sealing. Two yellow metal pieces are the top head, and there is a bottom head below. When packaging, both ends have a certain temperature (generally around 180℃). When it is closed, it is pressed on the aluminum-plastic film, and the PP layer of the aluminum-plastic film melts and sticks together, and the packaging is OK.
Let's talk about the top seal. The schematic diagram of the top sealing area is shown in the following figure. The top seal is used to seal the pull ring. The tab is made of metal (anode aluminum, cathode nickel). How to use PP packaging? This is done through a small part of ear glue. The package with the label position is shown in the circled part in the figure below. When packaging, the PP in the pull-tab adhesive and the PP layer of the aluminum-plastic film are fused and bonded to form an effective packaging structure.
In the process of liquid injection and pre-sealing, after the soft package battery core is sealed at the top side, X-ray should be taken to check the parallelism of its winding core, and then it will enter the drying room to remove moisture. After the drying chamber is allowed to stand for a period of time, it enters the processes of liquid injection and pre-sealing.
From the above analysis, we know that after the battery cell is sealed on the top side, there is only one opening on the airbag side, which is used for liquid injection. After the liquid injection is completed, the edge of the airbag should be pre-sealed immediately, which is also called sealing. Theoretically, after packaging, the battery cells are completely isolated from the external environment. The packaging principle of a letter is the same as the top side seal, so I won't go into details here.
In the process of standing, forming and fixture setting, after the completion of liquid injection and sealing, the battery cell should be allowed to stand first, which can be divided into high temperature standing and normal temperature standing according to different processes. The purpose of standing is to make the injected electrolyte fully soak the pole piece. Then you can do it with batteries.
The picture above shows the soft battery melting cabinet. It's actually a charging and discharging device. I haven't found a picture with a battery after looking for it for a long time. Think about the picture of the battery clip on it. The result is that the battery is charged for the first time, but it will not be charged to the highest voltage, and the charging current is very small.
The purpose of formation is to form a stable SEI film on the electrode surface, which is equivalent to a process of activating the battery. In this process, a certain amount of gas will appear, which is why the aluminum-plastic film should reserve airbags. In some factories, the process will adopt fixture molding, that is, the battery core will be clamped in the fixture (sometimes glass plate will be used for simplicity, and then steel clamp will be used), and then it will be molded in the cabinet, so that the gas will be fully squeezed into the adjacent airbag, and the molded electrode interface will be better.
Some batteries, especially thick batteries, may be deformed due to large internal stress after formation. Therefore, some factories will set up a fixture molding process after molding, also called fixture baking.
In the second sealing process, we just said that gas will appear in the molding process, so we have to pump out the gas and then carry out the second packaging. Here, some companies have become two processes: exhaust and two seals, followed by a process of cutting airbags. Here, the painting lines are collectively referred to as two letters.
When sealing for the second time, the straw cutter first pierces the airbag, and at the same time, vacuumizes to extract the gas and a small amount of electrolyte in the airbag. Then, immediately package the two sealing heads in two sealing areas to ensure the airtightness of the battery cell. Finally, the airbag is cut off from the packaged battery, and the soft package battery is basically formed. Secondary sealing is the last packaging process of lithium-ion battery, and the principle is the same as that of the previous thermal packaging, so I won't go into details here.