1.Poor depth of penetration
Key issue: Insufficient forming depth or structural defects resulting in cracks, wrinkles, etc.
1.1 The influence of mold parameters
1.2 Forming Condition Control
- Controlled surface pressure: 0.3 - 0.5 MPa. Insufficient pressure → wrinkles; excessive pressure → cracks
- Pressing speed: ≤ 5 mm/sec. Rapid speed may cause stress concentration and lead to cracking
- Maintenance time: ≥ 2 sec. Insufficient time affects the rebound rate and results in insufficient depth
1.3 Adverse Countermeasures
Note: The gap between the molds is usually set at 0.25mm (twice the thickness of the aluminum foil), and the R angle is adjusted according to the depth of the punch:
When the depth ≤ 4mm, the R angle = 1.5mm; when the depth > 5mm, the R angle ≥ 2mm.
For small-sized batteries, a balance between appearance and strength needs to be achieved. The R angle can be appropriately reduced.
2. Top Seal Defects
2.1 Causes and Solutions
- Creasing Issues: Inconsistent depth of the die and the thickness of the battery cell → Adjust the die depth
- Rebound Deformation: Excessive static time before the thick battery is sealed → Shorten the process interval
- Fixture Accuracy: Deviation in flatness between the fixture base and the sealing head → Regular calibration
- Equipment Cleaning: Residual PP glue on the sealing head → Clean every shift
- Operational Specifications: Standardize the picking and placing gestures to avoid pulling
2.2 Causes of Leakage
3. Battery corner damage
Common location: The folded edge of the second seal (on the positive/negative electrode tab side)
Cause analysis
Repeated bending of the air bag causes fatigue and damage to the aluminum-plastic film. The injection time for the second seal is too long, and the bending frequency is excessive. Solution
It is prohibited to directly grab the air bag. To reduce the manual bending of the aluminum-plastic film, the pre-sealing process must undergo a 180° bending test with ≥5 bends without any pinholes. The pre-sealing procedure: temperature 150-160℃, time 1s, pressure 0.1-0.2MPa.
4. Two sealing defects
4.1 Causes of leakage / poor soldering
High temperature fluctuations in the sealing head → Calibration of the temperature control system → After filling, the interval between two seals is > 24 hours → Deviation in the flatness of the sealing head during the control process > 0.1mm → Grinding and repair of residual electrolyte → Pre-sealing angle position + inclined baking.
4.2 In-depth analysis
Core issue: Electrolyte contaminates the CPP layer, resulting in a decrease in heat sealing strength
Risk points: Although the secondary heat sealing can vaporize the electrolyte, the residual liquid film may still cause leakage in the later stage
4.3 Optimization measures
Increase the diameter of the filling port opening, reduce electrolyte leakage → The filling needle is close to the battery cell, reducing the aging stage of the sprayed electrode (inclined angle 15-30°) → Promote electrolyte absorption → Use a slanted position during vacuum pumping → Reduce residual
5. Edge Voltage Abnormality
5.1 Definition:
The potential difference between the aluminum layer of the aluminum-plastic film and the positive/negative electrodes, reflecting the insulation performance of the package.
5.2 Standard
Industry threshold: ≤ 1V (for some enterprises such as Guangyu, it is ≤ 0.5V) Measurement method: Use the red probe of the multimeter to connect to the tab, and slide the black probe over the aluminum layer to obtain the maximum value.
5.3 Causes and countermeasures
Packaging defects: Insufficient top sealing / double sealing heat sealing → Control the PP residual rate at 70-90%
Aluminum layer damage: Insufficient sealing edge allowance → The allowance width should be ≥ 3mm
6. Internal corrosion defect (black spot defect)
6.1 Cause
The skew of the end plates causes the aluminum layer to come into contact with the negative plate end, resulting in insufficient sealing of the battery cell, insufficient exposure of the aluminum layer end plate outside the PP layer, and short circuit between the metal end plate and the aluminum layer.
6.2 Control points
The hard sealing process strictly calibrates the position of the end plates (offset ≤ 0.3mm), with the sealing edge reserve ≥ 2mm, the thickness of the PP layer after heat sealing ≥ 20μm, and the coverage of the end plate adhesive on the metal part ≥ 1.5mm.
7. Nylon Layer Stratification
7.1 Phenomenon
After forming, bubbles appear at the corners or folded edges, which are particularly noticeable after heat sealing.
This is not a problem with the non-aluminum plastic film itself (it only occurs locally).
7.2 Reason
During the molding process, the nylon layer was overly stretched. After heat sealing, the contraction force exceeded the bonding force with the aluminum layer
7.3 Countermeasure
8.Comprehensive Analysis of Leakage Abnormalities
8.1 All-stage Risk Points
- Forming Stage: Insufficient R angle at the four corners leads to rupture
- Assembly Stage: Internal force of the cell (T1) exceeds the heat sealing adhesion force (T2)
- Heat Sealing Stage: Damage to the mold's aluminum layer and insufficient reserved space cause delamination, and non-compliance with temperature/pressure/time standards
- Filling Stage: Residual electrolyte at the seal → Decrease in the heat sealing strength of the CPP layer
- Long-term Storage: Electrolyte corrodes the tab (requires surface passivation treatment of the Al layer)
- Post-Processing: Excessive folding edge causes damage to the heat sealing area.
8.2 Key Controls:
Heat Sealing Quality Inspection: Peel Strength ≥ 3N/15mm
Aluminum Plastic Film CPP Thickness ≥ 30μm, Compensation for the Gap of the Tab Adhesive Tape
Summary:
The production process of soft-pack batteries is complex. The matching of parameters in each stage and the detailed control are the core to ensure high yield. From optimizing the R-angle and gap of the mold with poor deepening performance, to precisely controlling the temperature and pressure for top sealing and double sealing, and preventing structural defects such as corner damage and delamination, all require systematic optimization based on material characteristics (such as the ductility of the aluminum-plastic film and the heat sealing strength of the CPP layer) and equipment precision (such as the flatness of the fixture and the temperature control of the sealing head).
The key to solving the process problems lies in:
- Full-process risk prediction: Set error prevention points for each process from molding to packaging, such as reducing electrolyte contamination in the pre-sealing process and promoting infiltration through inclined placement and static standing;
- Dynamic parameter matching: Adjust R-angle, deepening, and heat sealing conditions according to battery size and material system to avoid "one-size-fits-all";
- Dual standardization of equipment and operation: Regularly calibrate fixture accuracy, clean the sealing head, and strengthen the training of employees' hand gestures for removing and placing the battery cells to reduce human damage;
- Material performance verification: Select aluminum-plastic films that have passed bending and peel strength tests to reduce the risks of delamination and leakage from the source.
Through process closed-loop control and continuous iteration, the consistency and reliability of pouch batteries can be effectively enhanced, laying the foundation for the mass production of high energy density and long-cycle products.
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