Lithium-ion batteries
process defects
1. Poor packaging
The proportion of battery cells experiencing gas buildup due to poor encapsulation has been significantly reduced. The causes of topsealing, sidesealing, and degassing have already been discussed. Poor encapsulation on any side can lead to battery cell damage, with topsealing and degassing being the most common. Topsealing primarily involves poor sealing at the tab positions, while degassing is mainly caused by delamination (including the separation of PP and Al due to electrolyte and gel effects). Poor encapsulation allows moisture from the air to enter the battery cell, causing electrolyte decomposition and the release of gas.
2. Pocket surface damaged
During the drawing process, the battery cell may be damaged abnormally or intentionally, causing the Pocket to break (such as with pinholes), allowing moisture to enter the battery cell.
3. Corner damage
Due to the special deformation of the aluminum at the corner of the folded edge, the movement of the air bag can twist the corner, causing Al to break (the larger the battery cell, the larger the air bag, and the more easily it breaks), thus losing its function of blocking water. This can be mitigated by adding wrinkle-reducing adhesive or hot melt adhesive to the corner. Furthermore, it is forbidden to move the battery cell by the air bag in any process after top sealing, and extra care should be taken to prevent the cells from swaying on the aging board.
4. Excessive water content inside the battery cell
If the water content exceeds the standard, the electrolyte will become ineffective, resulting in gas formation or degassing. The main causes of excessive water content inside the battery include: excessive water content in the electrolyte, excessive water content in the bare cells after baking, and excessive humidity in the drying room. If excessive water content is suspected as causing gas expansion, a process traceability inspection can be performed.
5. Abnormal formation process
Incorrect formation processes can cause the battery cells to swell.
6. The SEI film is unstable.
The battery cell exhibited slight gas expansion during the charge and discharge process of the capacity test.
7. Overcharging and over-discharging
Due to abnormalities in the process, machine, or protection board, the battery cell may be overcharged or over-discharged, resulting in severe bulging of the battery cell.
8. Short circuit
If a short circuit occurs due to an operational error that causes the two tabs of a charged battery cell to come into contact, the battery cell will bulge and the voltage will drop rapidly, and the tabs will be burned black.
9. Internal short circuit
Internal short circuits between the anode and cathode of the battery cell cause rapid discharge, heat generation, and severe bulging. There are many causes of internal short circuits: design flaws; shrinkage, curling, or damage to the separator; Bi-cell misalignment; burrs puncturing the separator; excessive clamping pressure; and excessive pressure from the heat-sealing machine. For example, in one instance, insufficient width led to excessive pressure on the battery cell by the heat-sealing machine, resulting in a short circuit and bulging between the anode and cathode.
10. Corrosion
When the battery cell corrodes, the aluminum layer is consumed by the reaction, loses its function of blocking water, and swells.
11. Abnormal vacuum pumping
Abnormal vacuum levels caused by system or machine issues, resulting in incomplete vacuuming; excessive heat radiation zone of VacuumSealing prevents the vacuuming piercer from effectively piercing the pocket bag, leading to incomplete vacuuming.
