Vacuum loading on battery packs

Air inclusions or air pockets in modern lithium battery packs are a serious and dangerous problem. The isi-sys SE sensor is able to detect small and large defects such as air bubbles, air pockets, cracks and others within a second. The defects can be far below or near to the surface. An example of a battery pack (test sample from the University of Munich, IWB) and the measurement result is shown below.

Test setup:
The test was performed by the SE2 sensor in combination with a glass vacuum chamber for a simple manual test. This is a cost-effective solution for spot NDT by manual service. For automated series tests in production, different setups are required.

Test procedure:
The battery packs are tested using small pressure differences of some mbar, which can be applied within seconds in small chambers. The sensor is monitoring the surface of the battery pack while the pressure is changed, measuring the differential deformation of the surface. Due to the expansion of the air inclusions, their locations can be identified, as shown in the images.
The first image shows the live view of the battery pack from the sensor. The second shows the reconstructed phase, which is corresponding to the local deformation gradient.
The required pressure difference depends on the defect depth, defect size, and the mechanical stiffness of the tested structure. However, due to the high sensitivity of the SE sensor to differential surface deformations, only a small pressure difference is typically sufficient.