Acceptance Quality Limit Sampling Plans for Lithium Cell Receiving Facilities
Enforce ANSI ASQ Z1.4 Level II sampling with AQL 0.010 for critical safety flaws and Kelvin OCV IR screening to reject defective lithium cells at receiving dock.
Pouch Cell Isolation Resistance
Meaning
Electrical isolation testing verifies the integrity of the protective pouch laminate to prevent electrical shorts to the environment. Measuring pouch cell isolation resistance involves applying a high voltage between the internal electrodes and the aluminum barrier layer of the pouch. This measurement confirms that the plastic layers have not been compromised during cell assembly or forming.
Voltage Application
High-potential tests are executed under strict safety and current-limit controls to prevent damaging the cell. To determine pouch cell isolation resistance, the testing system applies a specific direct current voltage for a fixed duration. A flow of leakage current indicates that the internal polymer layer is too thin or has been punctured.
This test is essential to identify early failures before the cells are assembled into modules. If a defect is found, the cell is rejected immediately to avoid the risk of a high-voltage short circuit in the finished vehicle pack.
Moisture Influence
Humidity and temperature in the assembly area can affect the measured resistance values. If moisture penetrates the pouch edges, the measured pouch cell isolation resistance will drop, causing false rejections. Maintaining a controlled dry environment ensures that the test results accurately reflect the physical quality of the cell insulation.
Pack Integrity
High resistance values are required to ensure the safety and longevity of the completed battery pack. A low pouch cell isolation resistance can lead to current leaks that drain individual cells, resulting in state-of-charge imbalances. Over time, these leaks can cause the module to overheat, posing a risk of thermal runaway.