Some Things About Lithhium Pouch Cell Battery

The packaging materials and structure of the soft pack battery give it a series of advantages. For example, the safety performance is good. The soft pack battery is structured with aluminum-plastic film packaging. When a safety problem occurs, the soft pack battery will generally burst and crack. It explodes like a steel shell or aluminum shell battery; light weight, the weight of the soft pack battery is 40% lighter than the steel shell Lithium Battery of the same capacity, and 20% lighter than the aluminum shell lithium battery; the internal resistance is small, the internal resistance of the soft pack battery Smaller than lithium batteries, it can greatly reduce the self-consumption of the battery; good cycle performance, longer cycle life of the soft pack battery, 100 cycles attenuation less than 4% to 7% than the aluminum shell; flexible design, variable shape The shape can be thinner, and it can be customized according to customer needs, and new battery cell models can be developed.

With the introduction of the new subsidy policy for new energy vehicles, the system energy density of the battery has become an important assessment indicator. The capacity of the ternary soft pack battery is 10~15% higher than the steel shell lithium battery of the same size and 5~10% higher than the aluminum shell battery, but the weight is lighter than the steel shell battery and aluminum shell battery of the same capacity specification. Therefore, The new subsidy policy is more beneficial to ternary soft-pack batteries. In view of the advantages of soft-pack batteries, industry experts predict that with the development of battery routes, the penetration rate of soft-pack batteries in the new energy vehicle market will continue to increase. In the future, soft-pack batteries will account for more than 50% of all types of batteries.

The materials used in the housing determine their packaging methods. Only the soft package has aluminum plastic film, which needs to be thermally sealed; the metal shell is generally sealed by laser welding. The aluminum-plastic film generally has three layers. The nylon layer ensures the shape of the aluminum-plastic film, reduces damage to the shell, and ensures that the film will not be deformed before being manufactured into a Lithium Ion Battery, preventing the penetration of air, especially oxygen, and maintaining the cell The internal environment also ensures that the packaging aluminum foil has good deformability. The Al layer is composed of a layer of metallic Al, which functions to prevent the penetration of water and maintain a certain thickness and strength inside the cell to prevent damage to the cell from the outside. Lithium-ion batteries are very afraid of water, and generally require the water content of the pole pieces to be PPM level, so the packaging film must be able to block the infiltration of water vapor. 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 punching plasticity when forming the aluminum plastic film. PP is the abbreviation of polypropylene, this material 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 together under the heating of the head, and then the head is removed, and the temperature is cooled to solidify and bond. The PP will not be dissolved or swelled by the organic solvent in the battery, which can effectively prevent it. The internal electrolyte is in contact with the Al layer to prevent the Al layer from being corroded.

The aluminum-plastic film looks very simple. In practice, how to evenly and firmly combine the three layers of materials is not so easy.

The first section is the same as the general battery process, so I won`t repeat it here. The pole piece forming method usually adopts die cutting, and the pole ear adopts laser cutting or die cutting. Pole piece stacking method, lamination generally adopts Z-shaped pole piece and winding type pole piece. The cut pole pieces are stacked and glued into a core and put into the punched aluminum-plastic film. In the pit, let's talk about flushing the pit next.

The soft-pack batteries can be designed into different sizes according to the needs of customers. After the outer dimensions are designed, the corresponding molds need to be opened to form the aluminum-plastic film. The forming process is also called a punching pit. As the name suggests, it uses a forming mold to punch a pit that can accommodate the core of the aluminum-plastic film under heating, as shown in the following figure: