What are the causes of flatulence in soft-packed lithium batteries?

The reason for the flatulence of soft-packed lithium battery The polymer lithium battery core adopts the packaging technology of aluminum-plastic composite film. When gas appears inside the battery core due to the occurrence of abnormal chemical reactions, the pocket will be charged and the battery core swells (with slight Bulging and severe swelling), and regardless of the appearance, the battery cell's performance (Capacity, Cyclelife, C-rate, etc.) will seriously fail, causing the battery cell to be unusable. Flatulence can occur in the processing process and in the hands of customers and even end users. Of course, a certain amount (generally a small amount) of gas will normally appear in the battery cell during the start-up or Baking process. This varies depending on the raw materials used, and this gas will be pumped out during the Degassing process. At present, some models (one-time packaging and molding battery cells) add V18 solvent to eliminate this kind of gas that occurs in the formation of the SEI layer and the stable and on-time interface of the phase interface. However, the gas generated due to abnormal process is very obvious on the front surface of Degassing or cannot be eliminated after Degassing or by adding V18. Here is a brief analysis of the causes of abnormal gas in the process: 1. Poor packaging: The proportion of bloated battery cells caused by poor packaging has been greatly reduced. The causes of poor packaging on the three sides of Topsealing, Sidesealing and Degassing have already been analyzed. Poor packaging on any side will lead to battery cells. Topsealing and Degassing are the most common. Topsealing is mainly due to poor sealing of the tab position. Degassing is mainly due to delamination (including electrolysis). The influence of liquid and gel causes pp to separate from Al). Poor packaging causes moisture in the air to enter the battery core, causing the electrolyte to decompose and produce gas. 2. The surface of the pocket is damaged: the battery cell is abnormally damaged or artificially damaged during the flow process, which causes the pocket to be damaged (such as pinholes) and moisture enters the battery cell. 3. Corner damage: Due to the special deformation of the aluminum at the corners of the flange, the air bag shaking will twist the corner and cause Al damage (the larger the battery cell, the larger the air bag, the easier it is to break) and lose its use as a barrier to water. Wrinkle glue or hot melt glue can be added to the corner to relieve it. In addition, it is forbidden to move the battery cell with an air bag in each process after the top seal. Pay more attention to the operation method to prevent the battery cell from swinging on the aging board. 4. The internal water content of the battery core exceeds the standard: We have already analyzed that there are certain requirements for the water content in the battery core. Once the water content exceeds the standard, the electrolyte will fail and gas will appear after formation or degassing. The main reasons that cause the internal water content of the battery to exceed the standard are: the electrolyte water content exceeds the standard, the water content of the bare cell after Baking exceeds the standard, and the humidity in the drying room exceeds the standard. If it is suspected that excessive water content causes flatulence, a retrospective inspection of the process can be carried out. 5. Abnormal formation process: Wrong formation process will cause flatulence in the battery cell. 6. The SEI film is unstable: the battery cell emits a little flatulence during the charging and discharging process of the capacity test. 7. Overcharge and over-discharge: The battery cell will be overcharged or over-discharged due to the abnormality of the process, the machine or the protection board, and the battery cell will be severely out of air. 8. Short circuit: due to operating errors, the two tabs of the charged battery cells are short-circuited, the battery cells will swell and the voltage will drop rapidly, and the tabs will be burnt black. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: What are the factors that affect the service life of electric vehicle batteries?