Here is a brief introduction to the causes of abnormal gas in the process:
1. Poor packaging, the proportion of inflated battery cells caused by poor packaging has been greatly reduced. Top sealing, Side sealing and Degassing three side packages have been described as bad reasons. Any side of the package will lead to battery core. Top sealing and Degassing are the main components. Top sealing is mainly sealed by Tab position. The main purpose of the Top is to separate layers (including electrolyte and gel, leading to the separation of the cathode and the solder). Poor packaging causes moisture in the air to enter the battery cell, causing electrolyte decomposition to produce gas, etc.
2. The surface of the pocket is damaged. During the flow and pulling process, the battery cell is abnormally damaged or the pocket is damaged (such as pinholes) due to artificial ring breaking, so that water enters the interior of the battery cell.
3. Corner damage: due to the special deformation of aluminum at the folded corner, the shaking of air bag will distort the corner, resulting in Al damage (the larger the battery cell, the larger the air bag, the easier it is to be damaged), and the barrier effect on water will be lost. Wrinkle glue or hot melt glue can be added at the corner to relieve. In addition, it is forbidden to take the air bag to move the battery cell in each process after top sealing, and pay more attention to the operation mode to prevent the swing of the battery cell on the aging plate.
4. The water content in the battery cell exceeds the standard. As we have described earlier, there are certain requirements for the water content in 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 in 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 water content exceeds the standard, resulting in flatulence, the traceability inspection of the process can be carried out.
5. The formation process is abnormal. The wrong formation process will cause the battery cell to swell.
6. SEI film is unstable, and the emission function of battery cell is slightly inflated during charging and discharging of capacity test.
7. Overcharge and over discharge: due to the abnormality of process or machine or protective plate, the battery cell is overcharged or over discharged, and the battery cell will be seriously inflated.
8. Short circuit: due to misoperation, the two tabs of the charged cell will be short circuited, the battery cell will blow up, the voltage will drop rapidly, and the tab will be burned black.
9. Internal short circuit, short circuit between anode and cathode inside the battery cell, resulting in rapid discharge and heating of the battery cell and serious air blowing. There are many reasons for internal short circuit: design problems; Shrink, curl and damage of isolation film; Bi cell dislocation; Burrs pierce the isolation film; Excessive clamp pressure; Excessive extrusion of edge ironing machine, etc. For example, due to insufficient width, the edge ironing machine excessively squeezed the cell entity, resulting in short circuit and gas expansion of the cathode and anode.
10. Corrosion: the battery cell is corroded, the aluminum layer is consumed by reaction, the barrier effect on water is lost, and flatulence occurs.
11. Abnormal vacuum pumping, abnormal vacuum degree caused by system or machine, incomplete degassing; The thermal radiation area of vacuum sealing is too large, resulting in the degassing air extraction bayonet can not effectively pierce the pocket bag, resulting in unclean air extraction.
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