Assessing spatial non-uniformities in lithium-ion battery state of charge using ultrasound immersion testing

Enhancing the performance, safety and reliability of battery management systems is crucial for advancing the state of the art in battery electric vehicles. Current research explores the potential of ultrasound to monitor state of charge (SoC) changes in individual batteries. Understanding spatial variations in SoC is essential, as non-uniformities could lead to sub-optimal performance, premature aging, and possible safety risks. This study uses ultrasound immersion testing to map wave speed and attenuation at different SoC levels during battery discharging. Results indicate non-uniform wave speed and attenuation suggestive of SoC spatial variations within single cells. Future work will include acoustic measurements under various discharge rates and relaxation periods to provide further insights into SoC inhomogeneities. Potential causes of structure and manufacturing variations of the battery are discussed, highlighting the need to address these issues to prevent over-charging/over-discharging in specific battery areas.