In situ tomography of lithium-ion battery cells enabled by scanning acoustic imaging
David Wasylowski, Sven Neubauer, Matthias Faber, Heinrich Ditler, Morian Sonnet, Alexander Blömeke, Philipp Dechent, Alexander Gitis, Dirk Uwe Sauer
Abstract
Imaging the interior of battery cells provides vital information for battery manufacturing, as well as lifetime and performance prediction. This work demonstrates a scalable and in-situ method to image the structural state of battery cells with layer resolution. Building on our prior publication, we apply ultrasound waves on pouch cells and process the reflected instead of the transmitted wave. This allows us to utilize time-of-flight data to provide depth information for later signal parts. We develop and demonstrate an algorithm that dissects the reflected ultrasound wave and calculates individual reflections from material interfaces within the electrode stack by fitting their estimated envelopes onto the Hilbert transformation of the entire wave. Consecutive individual reflections are used to calculate the reflection coefficient from the material interface, which is then mapped onto a color map. Using this algorithm, we image an aged and pristine pouch cell from the same manufacturing batch. The generated images showed a clear correlation with optical images from a post-mortem analysis. Indications from the ultrasound image were verified as lithium-plating.