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Influence and improvement of burr on performance of soft pack lithium battery
Release time:2022/3/10 10:34:48      Clicks:698

1. Burr formation



In order to meet the needs of various types of batteries, the pole sheet needs to be blanked and formed. The pole sheet may produce too long burrs on the blanking edge of the fluid collection due to unreasonable blanking process parameters. After it is wound or laminated and packaged into a battery, there is a burr puncture diaphragm when the part is subjected to large pressure, causing the risk of short circuit of the battery.


 

2. Burr example


640 (1).png


After the blanking process, the part of the fluid collection blanking edge appears too long burrs (marked in the figure). Long burrs may puncture the diaphragm, resulting in short circuit of the battery and the risk of battery failure, affecting the safety performance of the battery.


 

2.png

a is the negative plate, b is the positive plate

 


Observing the blanking edge section of the lithium battery electrode sheet, it can be seen that the length of the burr part of the fluid collector is significantly longer than the original thickness of the fluid collector, and further observation can be found that the fluid collector seems to have a stretching behavior in a certain direction, so the thickness of the upper and lower battery material layers is inconsistent.


 

3, the impact of burrs on battery performance



The burr defect battery with obvious positive collector, the burr defect battery with obvious negative collector and the normal battery, then the special indenter is pressed into the burr part of the defective battery, the change of load and voltage is recorded, and the change of load and voltage is compared with that of the normal battery, so as to obtain the influence of the burr on the external load failure behavior of the battery and the internal short circuit.



3.png

B Pressing test process; C Embossing test internal diagram

 


Normal cells in the control group (blue solid/dashed line) showed no significant voltage fluctuation after compression. The battery in the experimental group, when the load is still rising, has plunged, and the voltage has plummeted, proving that the battery has an internal short circuit at this time


4.png 



4, burr process improvement


(1) Set the following process parameters to be studied:

The offset gap is 0.0005mm, 0.001mm, 0.003mm, 0.005mm and 0.007mm, and the rounded Angle of the fixed die is 0.001mm;

For the die rounding, take 0.0005mm, 0.001mm, 0.003mm, 0.005mm and 0.007mm, and the fixed blanking clearance is 0.001mm


(2) The general conclusions are as follows:

The burr length of fluid collection increases with the increase of blanking clearance and fillet size.

Under the same scale change, the change of burr length caused by the change of blanking clearance is greater than that caused by the change of die clearance.

Under the same conditions, the burr length of the positive collector is less than that of the negative collector.

Should always pay attention to the loss of the mold, as far as possible to ensure that the blanking clearance and mold rounded Angle to less than 0.001mm, in order to reduce the length of burrs.




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