Investigation of Acoustic Attenuation and Resonances in Lithium‐Ion Batteries Using Ultrasound Spectroscopy

Ultrasound spectroscopy up to 6 MHz is carried out on a 12 Ah Lithium-ion battery pouch-cell. The analysis revealed that the attenuation behavior can be effectively described as having an absorption component and a resonance component. It was demonstrated that the absorption can be modeled as a second order polynomial. Two distinct resonances were identified at 2.2 MHz and 4.4 MHz. The first of these resonances shows a significant almost linear reduction in magnitude with increasing state of charge. By smartly choosing the ultrasound interrogation frequency to coincide with this resonance, an almost linear increase by a factor of more than five was measured in the signal amplitude between between state of charge levels of 0 and 100. This could provide the basis for a robust and straightforward state of charge determination method.