Research on Ultrasonic-Based Measurement of State of Charge in Lithium-ion Batteries

This paper presents a novel approach for estimating the State of Charge (SoC) of batteries using ultrasonic measurements. Traditional SoC estimation methods, such as ampere-hour integration and model-based techniques, often face challenges related to complexity and cost. In contrast, ultrasonic measurements leverage the properties of mechanical waves, which can penetrate opaque materials and provide real-time insights into battery conditions. The study explores the relationship between ultrasonic wave propagation and the internal changes in battery materials during charge and discharge cycles. An experimental setup was developed, incorporating a charge-discharge module, a battery, and piezoelectric transducers to measure the time of flight (ToF) of ultrasonic waves. The results indicate that ToF varies significantly with SoC, with a decrease in ToF observed during charging and an increase during discharging. The correlation between ToF and SoC was analyzed using the Pearson correlation coefficient, signal-to-noise ratio, and various fitting methods, including polynomial fitting and Classification and Regression Trees (CART).