A. Voltage-related issues
Voltage inconsistency or individual low levels
High self-discharge: Some battery cells exhibit a higher self-discharge rate than others, resulting in faster voltage drop after being left idle.
Uneven charging: During the charging process, differences in contact resistance or inconsistent current detection in the cabinet lead to non-uniform charge states among battery cells, resulting in significant voltage disparities after prolonged storage.
Solution: Store the charged battery for more than 24 hours before measuring the voltage during production, and screen low-voltage cells for recharging or replacement.
Overvoltage or overcharge anomaly
Failure of the protection circuit or malfunction of the detection equipment causes the charging voltage to exceed 5V, leading to electrolyte decomposition, gas emission, and even explosion.
The LMU (Battery Management Unit) balancing function has failed, preventing the adjustment of individual cell voltages, resulting in a continuous rise in the voltage of certain cells.
B. Abnormal internal resistance issue
The internal resistance is higher than normal
Insufficient detection equipment accuracy or failure to eliminate contact resistance results in falsely high measurement values, necessitating the use of an instrument based on the AC bridge principle for testing.
If the battery cell is stored for an extended period, it may experience internal passivation and capacity loss, which can be restored through charge-discharge activation.
The processing causes an increase in internal resistance
Spot welding, ultrasonic processing, and other operations cause abnormal heating of the battery cell, leading to thermal closure of the separator and significantly increasing internal resistance.
C. Mechanical and Structural Issues
Short-circuit risk
Pillar burrs piercing the separator, electrode misalignment, or loose assembly can all lead to internal short circuits, affecting the open-circuit voltage.
Incorrect spot welding positions or poor weldability of nickel strips require high-current welding, which can easily puncture the separator and cause internal short circuits.
Battery swelling
Swelling during charging: Normal charging causes slight swelling (≤0.1mm), but overcharging leads to electrolyte decomposition and internal pressure rise, resulting in noticeable bulging.
Cyclic Swelling: As the number of cycles increases, the thickness gradually rises, particularly noticeable in aluminum shell batteries, with an increase of 0.3 to 0.6mm generally falling within the normal range.
D. Safety and Thermal Runaway Risks
Thermal runaway hazard
Overcharging, over-discharging, short circuits, or mechanical damage may trigger a chain reaction of exothermic processes, leading to battery overheating, fire, or even explosion.
Laboratory tests must be conducted under explosion-proof equipment, such as using thermal runaway pressure vessels for battery cells to ensure safety.
Improper selection of fire extinguishing methods
Although dry powder fire extinguishers can temporarily suppress flames, they cannot prevent the release of energy from within the battery, and the surface temperature may still exceed 190°C.
A more effective method is to soak in water, which can reduce the surface temperature below 60°C within 90 seconds and restore the battery interface impedance.
E. Testing Process and Data Management Issues
Improper temperature control
The performance of lithium batteries is temperature-sensitive, and failure to precisely control the temperature during testing may lead to data distortion.
It is recommended to conduct basic tests in a standard environment of 20±5℃, while extreme condition tests require strict setting of the incubator parameters.
Data Collection and Analysis Challenges
Large-scale testing generates massive amounts of data, requiring efficient data collection systems and analytical tools to extract key trends and anomalies.
Data security must also be prioritized to prevent the leakage of sensitive R&D information.
Insufficient maintenance of testing equipment
Failure to regularly calibrate or maintain the equipment may lead to issues such as current control errors and measurement inaccuracies, compromising the reliability of test results.