  Lithium-ion battery degradation estimation using fast and noninvasive
techniques is a crucial issue in the circular economy framework of this
technology. Currently, most of the approaches used to establish the
battery-state (i.e., State of Charge (SoC), State of Health (SoH)) require
time-consuming processes. In the present preliminary study, an ultrasound array
was used to assess the influence of the SoC and SoH on the variations in the
time of flight (TOF) and the speed of sound (SOS) of the ultrasound wave inside
the batteries. Nine aged 18650 Lithium-ion batteries were imaged at 100% and 0%
SoC using a Vantage-256 system (Verasonics, Inc.) equipped with a 64-element
ultrasound array and a center frequency of 5 MHz (Imasonic SAS). It was found
that second-life batteries have a complex ultrasound response due to the
presence of many degradation pathways and, thus, making it harder to analyze
the ultrasound measurements. Although further analysis must be done to
elucidate a clear correlation between changes in the ultrasound wave properties
and the battery state estimation, this approach seems very promising for future
nondestructive evaluation of second-life batteries.
