At present, the packaging forms of lithium batteries on the market are mainly divided into square packaging, cylindrical packaging and aluminum-plastic film packaging. The square package and cylindrical package are mainly made of metal shells, including aluminum shells and steel shells. Aluminum-plastic film packaging is mainly used in the packaging of pouch cell lithium-ion batteries. Pouch cell encapsulated in aluminum-plastic film are mainly used in the 3C field, and have gradually penetrated into the new energy automobile industry in recent years, providing safe and stable power output for various types of automobiles.

1. Introduction to Aluminum Plastic Film

The packaging material used for pouch cell is aluminum-plastic composite film, referred to as aluminum-plastic film. The design and manufacturing technology requirements of aluminum-plastic film are relatively high. The thickness of aluminum-plastic film has different specifications. Its structure is mainly composed of three kinds of materials, which are CPP layer, Al layer and nylon layer from the inside to the outside.

Before encapsulating the bare cell, the aluminum-plastic film should be punched. We can provide pouch cell case forming machine to punched the aluminum-plastic film. After the aluminum-plastic film is punched to the required specifications, the cell is packaged. The inner material of the punching pit is a cast polypropylene film (CPP), which has a certain melting point, and the CPP layer materials on both sides of the encapsulation are relatively melted and bonded together under a certain temperature and pressure during packaging. The CPP layer material has good heat-seal adhesion with metal Ni, Al and tab glue, and has good electrolyte resistance and HF resistance. At the same time, the CPP layer also has good insulation and physical protection properties, which can effectively prevent The short-circuit between the electrode and the lithium-ion battery soft package material causes corrosion of the aluminum-plastic film.

2. Discussion on influencing factors of heat sealing

First of all, it is necessary to understand that the purpose of aluminum-plastic film heat sealing is to isolate the cell from the external environment, that is, all poor packaging that may affect external moisture, air infiltration, and electrolyte leakage should not occur. The packaging of soft-packed cells is mainly divided into top-side sealing and final sealing processes.

The top-sealing process is mainly the direct packaging of aluminum-plastic film, tab glue and copper-nickel tabs, which has a greater possibility of damage. The side seal is the encapsulation between the aluminum-plastic film CPP layer, there are not too many problems, mainly to prevent the appearance of wrinkles and bubbles. The final seal is a vacuum package. As the lithium battery is pre-charged, gas will be generated, and the electrolyte will easily stick to the PP layer of the aluminum plastic film, resulting in poor packaging. ACEY NEW ENERGY provides top&side sealing machine，vacuum sealing machine for pouch cell.

3. Craft

The packaging process is a more critical link. The key factors in the packaging process are temperature, pressure and time. The better state of the package is that after the PP film reaches the melting point, it is bonded together, the package has a good appearance, no bubbles or wrinkles, high package strength, and good airtightness, and it has passed the insulation test.

After selecting an aluminum-plastic film, a three-factor DOE of temperature, pressure and time is required to confirm the best packaging process. The PP melting temperature of aluminum plastic film is generally 180℃~190℃. Several temperature points can be selected within a certain range to perform heat sealing experiments under the same pressure and heat sealing time, and the best packaging temperature can be determined by the heat sealing strength and effect. Pay attention to the flatness and parallelism of the sealing head during the daily use of the packaging equipment, confirm whether the temperature of the sealing head and the temperature sensor are normal, etc., and solve the corresponding problems when the temperature is abnormal.

Cell packaging is a key process that affects the final performance of the cell. The main factors affecting the packaging of aluminum-plastic film are the selection of equipment and molds, and the determination of the packaging process. The packaging temperature and packaging time in the packaging process occupy the main position. The secondary influencing factors are the quality of incoming materials, the capabilities of the operators, and the workshop environment. Only by coordinating all aspects, can the cell packaging work be done well. While preventing the electrolyte from corroding, the inside of the cell is isolated from the external environment to prevent the infiltration of water vapor and ensure the cycle life and use safety of the lithium battery.