Ultrasonic guided wave measurement and modeling analysis of the state of charge for lithium-ion battery

This work presents the analytical acoustic model to investigate the interaction mechanism between the state of charge (SOC) of lithium-ion battery and the propagation characteristics of ultrasonic guided waves. Meanwhile, the multi-layered porous structure characteristics of lithium-ion batteries are focused on, the Biot theory and transfer matrix method are introduced to construct the analytical acoustic theory model of lithium-ion batteries. The mechanical performance (modulus and density) of the electrode is dynamically changing during cycling, which will influence the dispersion characteristics of ultrasonic guided waves in lithium-ion battery. Based on this, the intrinsic connection between the SOC and the guided wave dispersion curve of lithium-ion battery is numerically analyzed. Moreover, the frequency domain simulation model with equal structural characteristics is established to verify the validity of the above theoretical results. Theoretical results performed on the customized pouch cell show that the changes in time of flight resulting from shifts in the group velocity of guided wave A0 mode correlate strongly with the SOC. An ultrasonic guided wave detection experiment system is built to extract the variations in time of flight and amplitude of the guided wave signal during cycling, which correctly validates the range of theoretical time of flight. Furthermore, the applicability of the proposed method is verified by battery experiments with different temperature and current rate operating conditions. Furthermore, the ultrasonic guided wave detection approach has also been shown to be a sensitive means of determining the SOC of lithium-ion batteries.