Overcharging or overdischarge, or discharging at overdischarge rate, will cause flatulence. Polymer lithium-ion battery adopts aluminum-plastic composite film soft packaging technology. When the battery produces gas due to abnormal chemical reaction, the pocket will expand and the battery will expand (slightly and seriously). Regardless of appearance, battery performance (capacity, cycle life, C rate, etc. ) will be seriously reduced and the battery will be unusable. Flatulence will occur in the production process, as well as in the hands of customers and even end users. Of course, in the process of activation or baking, a certain amount of gas (usually very little) will be generated under normal circumstances, which will be pumped out in the degassing process according to the different raw materials used. At present, some models (disposable packaged batteries) eliminate the gas generated by the formation of SEI layer and the stability of phase interface by adding some solvents. However, the gas generated due to abnormal process is very obvious on the surface before degassing or after degassing, and cannot be eliminated or the solvent cannot be eliminated. Briefly introduce the reason of abnormal gas production in process 1. Poor packaging, and the proportion of rechargeable lithium battery cells is greatly reduced due to poor packaging. The causes of poor top sealing, side sealing and degassing packaging are introduced. Poor packaging on any side will lead to batteries, which are mostly manifested in top sealing and degassing. The top sealing is mainly due to the poor sealing of the Tab position, while the degassing is mainly due to delamination (including the separation of PP and Al due to the influence of electrolyte and gel on P2 model). Poor packaging will cause moisture in the air to enter the battery cell, which will lead to the decomposition of electrolyte and the generation of gas. 2. The pocket surface is damaged. In the process of wire drawing, the battery cell is damaged abnormally or artificially (such as pinholes), so that water enters the battery cell. 3. Angular loss, due to the special deformation of aluminum in the corner, the airbag sloshing will distort the angular position and cause al damage (the bigger the battery, the greater the possibility of airbag damage), and it will lose its barrier effect on water. You can add wrinkle-removing glue or hot melt adhesive to the corners to relieve it. Moreover, it is forbidden to move the battery cells with airbags in each process after top sealing, and more attention should be paid to the operation mode to prevent the battery cells from swinging on the aging board. 4. The water content in the battery exceeds the standard. As we have already introduced, the water content in lithium battery cells has certain requirements. Once the water content exceeds the standard, the electrolyte will not be able to produce gas after formation or degassing. The main reasons for the excessive water content of battery are: excessive water content of electrolyte, excessive water content of bare battery after baking and excessive humidity of drying room. If FA suspects that excessive moisture causes flatulence, it can carry out process retrospective inspection. 5. The formation process is abnormal, and the wrong formation process will lead to battery flatulence. 6. The 6.SEI film is unstable, and the emission function of the battery cell is slightly flattened during the charge and discharge of the capacity test. 7. Overcharging and overdischarge. Due to the abnormality of process, equipment or protective plate, the battery cell will be overcharged to 4.5V or overdischarged, and the battery cell will expand seriously. 8. Short circuit, because of misoperation, the two lugs of the rechargeable battery are short-circuited, the charging voltage of the battery will drop rapidly, and the lugs will be burnt black. 9. Internal short circuit. The short circuit between the positive and negative electrodes inside the battery cell leads to the rapid discharge and heating of the battery cell, and at the same time it expands seriously. There are many reasons for internal short circuit: design problems; The isolation membrane shrinks, curls and is damaged; Double cell dislocation; Burrs pierce the isolation membrane; Excessive clamping pressure; Excessive extrusion of the battery core entity by the edge ironing machine leads to short circuit and flatulence of the positive and negative electrodes. 10. Corrosion, the core of lithium battery was corroded, and the aluminum layer was consumed by the reaction, which lost its barrier effect on water and caused flatulence. 1 1. Abnormal vacuum suction caused by system or machine. Exhaust pumping is incomplete; The thermal radiation area of vacuum seal is too large (generally, its thermal radiation width is 8mm), which leads to the degassing suction port can not effectively pierce the pocket bag, resulting in poor suction.

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