To monitor the performance and reliability of a lithium-ion battery during charge/discharge cycles, an ultrasonic time-of-flight (ToF) and attenuation measurement was performed. Ultrasonic ToF of the reflected pulse echo increased with the decrease in the state of charge (SoC) and with the increase in number of cycles (i.e., degradation). A health evaluation map relating SoC with ToF at various cycles was constructed. In this map, ultrasonic hysteresis was reported, of which area reflected the magnitude of irreversible electrochemical damage to the battery material. A linear correlation between the ToF and the number of cycles was observed.
