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As the demand for reliable and safe operation of lithium-ion batteries (LIBs) increases, the need for accurate and real-time inspection methods has become increasingly crucial. In this study, we investigated the ultrasonic propagation characteristics of LIBs caused by their periodic internal structure. A mechanical model for LIBs is constructed using a transfer matrix method, and the dispersion curves for the longitudinal waves are derived using the Floquet–Bloch theorem. We demonstrated that LIBs exhibit a Bragg bandgap within a specific frequency range. This acoustic characteristic leads to the suppression of ultrasonic wave transmission and wave dispersion due to the slowdown of group velocity. Based on the present study, we evaluated the ultrasonic properties of a commercial battery during a cycling test across different excitation frequencies, showing that the reflection signals associated with the Bragg bandgap exhibit a significant and sensitive correlation with the state of charge of the LIB cell.
Ma et al. (Sat,) studied this question.