Understanding the causes of inflation in soft pack lithium batteries

　　Inflation can occur during the production process and also in the hands of customers and even end users. Of course, the battery cell will normally produce a certain amount (usually very little) of gas during the formation, start-up, or Baking process, depending on the raw material used. This gas will be extracted during the Degassing process.

　　At present, some models (once packaged battery cells) eliminate the gas generated during the formation of SEI layers and the stabilization of phase interfaces by adding V18 solvent. However, the gas generated due to process abnormalities is very obvious on the surface before degassing or cannot be eliminated after degassing, or cannot be eliminated by adding V18. Here is a brief introduction to the reasons for abnormal gas production in the process:

　　1. Poor packaging: The proportion of inflated battery cells caused by poor packaging has greatly decreased. The reasons for the poor three-sided packaging of Topsizing, Sidesealing and Degassing have been described previously. A poor packaging of either side will lead to the battery cell, which is mainly manifested in Topsizing and Degassing. Topsizing is mainly due to poor sealing of the tab position, and Degassing is mainly due to layering (including separation of PP from Al due to the influence of electrolyte and gel). Poor packaging causes moisture in the air to enter the interior of the battery cell, causing electrolyte to decompose and produce gas.

　　2. Pocket surface damage: During the pulling process, the battery cell is abnormally damaged or artificially damaged, resulting in pocket damage (such as pinholes) and allowing water to enter the interior of the battery cell.

　　3. Corner damage: Due to the special deformation of the folded corner aluminum, the shaking of the air bag can distort the corner and cause Al damage (the larger the battery cell, the larger the air bag, the easier it is to be damaged), losing its barrier effect on water. Wrinkle glue or hot melt glue can be added to the corners to alleviate the problem. And it is prohibited to move the battery cells with air bags in various processes after the top sealing, and more attention should be paid to the operation method to prevent the swing of the battery cells on the aging board.

　　4. The water content inside the battery cell exceeds the standard: As we have already introduced, there are certain requirements for the water content inside the battery cell. Once the water content exceeds the standard, the electrolyte will fail and produce gas after formation or degassing. The main reasons for the excessive water content inside the battery are: the excessive water content in the electrolyte, the excessive water content in the bare cell after Baking, and the excessive humidity in the drying room. If it is suspected that the excessive water content may cause bloating, a retrospective inspection of the process can be carried out.

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