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What is the cause of flatulence in soft-pack lithium-ion batteries

The polymer lithium ion battery cell uses aluminum-plastic composite film packaging technology. When gas is generated inside the battery cell due to the occurrence of abnormal chemical reactions, the Pocket will be charged and the battery cell swells (there are two types: subtle swelling and severe swelling) Circumstances), and regardless of the appearance, the service performance of the battery cell (Capacity, Cyclelife, C-rate, etc.) will experience severe failure, causing the battery cell to be unusable.

Flatulence will occur in the production process and in the hands of customers and even end users. Of course, a certain amount (generally a small amount) of gas will normally be generated in the battery cell during the formation or Baking process. This varies according to the original data used. This gas will be pumped out in the Degassing process.

Now part of the Model (one-time packaging molding battery cell) has been added with V18 solvent to eliminate the gas generated by the formation of the SEI layer and the stable and timely interface. However, the gas generated by the abnormal process is very obvious before Degassing or cannot be eliminated after Degassing or by adding V18. Here is a brief introduction to the cause 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 been introduced above. 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. The influence of electrolyte 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 generate gas.

2. Pocket appearance damage: The battery cell is abnormally damaged or man-made damage caused the Pocket to be damaged (such as pinholes) during the flow process, and moisture enters the battery cell.

3. Corner damage: Due to the special deformation of the aluminum at the corners of the flange, the airbag shaking will twist the corner and cause Al damage (the larger the battery cell, the larger the airbag, the easier it is to break) and lose the water insulation effect. Wrinkle glue or hot melt glue can be added to the corner to relieve it. And in each process after the top seal, stop using the air bag to move the battery cell, and pay more attention to the operation method to prevent the swaying of the battery cell on the aging board.

4. The internal water content of the battery cell is overrun: We have already introduced that there are certain requirements for the water content in the battery cell. Once the water content is overrun, the electrolyte will fail and generate gas after formation or Degassing. The main reasons for the overrun of the internal water content of the battery are: the overrun of the electrolyte water content, the overrun of the water content of the bare cell after Baking, and the overrun of the humidity in the drying room. If it is suspected that the water content overruns causes flatulence, the process can be traced back.

5. Abnormal formation process: Wrong formation process will cause flatulence in battery cells.

6. The SEI film is unstable: the battery cell emits slight 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 outgassed.

8. Short circuit: due to operation 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.

9. Internal short circuit: The internal short circuit of the anode and cathode of the battery core causes the battery core to quickly discharge and generate heat and severe swelling. There are many reasons for the internal short circuit: planning problems; shrinkage, curling, and breakage of the insulating film; Bi-cell misalignment; burrs piercing the insulating film; excessive clamp pressure; excessive squeezing of the edge ironing machine, etc. For example, in the past, because of the insufficient width, the edge ironing machine excessively squeezed the body of the cell, which caused the cathode and anode to short-circuit and swell.

10. Corrosion: The battery core is corroded, the aluminum layer is consumed by the reaction, and the water insulation effect is lost, and flatulence occurs. 11. Abnormal vacuum pumping: The vacuum is abnormal due to the system or the machine. Degassing is not completely pumped; the heat radiation area of VacuumSealing is too large, which causes the Degassing bayonet to not effectively pierce the Pocket bag and cause pumping. Not clean.

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