The basic structure of the soft pack battery is similar to that of a cylinder and a box. They are all positive electrode, negative electrode, diaphragm, insulating material, positive electrode, negative electrode lug and shell, but the main body of the soft pack battery is aluminum plastic film.
The outermost layer is a nylon layer, the middle is an aluminum foil, and the inner layer is a heat-sealing layer, and each layer is bonded with an adhesive.
requires the aluminum plastic film to have the following characteristics: high barrier properties; good heat sealing performance. The material is resistant to electrolyte and strong acid corrosion, and has good ductility, flexibility and mechanical strength.
Soft pack battery lithium battery processing technology
Aluminum-plastic film molding process, flexible packaging batteries can be designed into different sizes according to customer needs. When the designed size is good, you need to open the corresponding mold to form the aluminum-plastic film. The molding process is also called pits. As the name suggests, it uses a molding die to extrude the aluminum-plastic film under heating.
After cutting the aluminum-plastic film into shapes, it is generally called a pocket bag, as shown in the figure below. Generally speaking, when the cell is thin, choose a pit (left), when the cell is thick, choose a double pit (right), because the amount of deformation on one side is too large, breaking the deformation limit of the aluminum plastic film, resulting in rupture.
Sometimes, according to the design, a small hole is made in the position of the airbag to increase the volume of the airbag.
top side sealing process, top side sealing process is the first packaging process for soft packaging lithium battery processing. Top sealing actually includes two processes, top sealing and side sealing. First put the winding core into the hole, and then fold the packaging film in half along the dotted line, as shown in the figure below.
The picture below shows several positions that need to be sealed after the aluminum plastic film is loaded into the roll core, including the top sealing area, side sealing area, letter area and second sealing area. Here are some introductions.
After the roll core is placed in the pit, the entire aluminum plastic film is placed in the clamp, and the top side sealing machine is carried out in the top side sealing machine.
This kind of sealing machine has four clamps, the left one is the top of the sealing machine, the right one is the side of the sealing machine. The two yellow metals are the upper head and the lower one. During packaging, the two heads have a certain temperature (usually around 180°C). When closing, press on the aluminum-plastic film, melt and bond the PP layer of the aluminum-plastic film together, so that the packaging is OK.
Talking about the top seal is still important. The schematic diagram of the top sealing area is shown in the figure below. The upper seal is the sealing tab, and the tab is made of metal (aluminum anode, nickel cathode). How to package with PP? This is done by a small part of the ear glue. I am not very clear about the specific structure of Polar Ear Gel. I hope people who understand this industry can add it. I only know that it also has the cost of PP, which means it can be melted and bonded when heated. The packaging of the tab position is shown in the circled part 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.
liquid injection and pre-sealing process, after the soft core is sealed on the top side, the parallelism of the roll core needs to be checked by x-ray, and then it enters the drying room to remove water and air. When the drying chamber stands up many times, it enters the liquid injection pre-sealing process.
Through the above introduction, we learned that after the top side of the cell is sealed, there is only one opening on the side of the airbag for liquid injection. The edge of the airbag is pre-sealed immediately after the injection, also called an envelope. Once the shell is sealed, in theory, the cell is completely isolated from the external environment.