Reliable non-contact and non-destructive testings are useful for the verification of quality and safety standards of battery cells. The battery cells are commonly electrically characterized. In this case a possible failure is detected but neither identified nor localized. With non-invasive internal visualization of battery cells detailed information about such failures is obtained.
Scanning Acoustic Microscopy (SAM) in the reflection-mode is a non-destructive ultrasonic tool, with which the interior of battery cells can be visualized with a good resolution. This method is still relatively unknown in the battery community. SAM is suitable for the visualization of defects like electrolyte leakage, faulty electrodes and gas accumulation inside battery cells. These failures are detected through the local atypical reflection of acoustic waves at faulty interfaces.
The transducer with the appropriated frequency is scanned along the x and y directions providing a complete visualization of a battery cell in few minutes. In a so-called C-scan mode, two-dimensional acoustic micrographs are generated from the detected echoes. Individual images are produced from the reflected wavefronts obtained at specific time delays allowing additionally information about the depth of the investigated failures by using the X-scan mode. In this case several micrographs with defined depths are generated, by dividing the reflectogram into gates according to the selected interval of time delay, or time-of-flight (TOF). Acoustic cross-sections, also called B-Scan mode, are obtained by scanning the sample along a defined vertical plane.
This fast and non-destructive visualisation tool can be used for the quality control of battery cells during their production or as end-of-line test. It allows the adjustment of the production in time, decreasing the wastage of resources. The evaluation of used battery cells for a second-life can be a field for this technology. SAM also brings a valuable contribution on the assistance in choosing representative spots of battery cells for post-mortem analyses.