Ultrasonic guided waves as an indicator for the state-of-charge of Li-ion batteries

Conventional battery management systems rely on cell voltage, current, and temperature to predict the battery state-of-charge and state-of-health, but their accuracy is limited. To overcome this limitation, ultrasonic probing has been proposed as a novel battery monitoring technique. This paper introduces the use of ultrasonic chirp signals for the transfer of ultrasound-based battery monitoring techniques without requiring prior knowledge of the architecture of the cell. To validate this technique, small, lightweight piezoelectric disc transducers that can be easily installed on off-the-shelf battery pouch cells were utilized for large cells with a capacity of 12.5 Ah. Furthermore, the dominant frequency of the response signal to a Hanning-windowed tone burst signal was identified as a quantitative state-of-charge indicator. A predictive model was developed to compare the performance of this indicator with that of previous ultrasound-based state-of-charge prediction methods. The influence of the cell temperature and cycle age on ultrasonic guided wave propagation was also investigated and isolated for analysis.