Acoustic emission characteristics of lithium-ion batteries under low-temperature discharge and their relation to structural degradation processes

The performance degradation and safety risks of lithium-ion batteries under low-temperature conditions are closely related to changes in their electrochemical–mechanical behavior. In this study, acoustic emission (AE) techniques were used to investigate a distinctive class of dual-waveform AE signals observed during low-temperature discharge. Wavelet coherence analysis demonstrated strong time–frequency correlations between the paired waveforms, indicating a common or strongly coupled acoustic source. In addition, the time interval between the two waveforms gradually stabilized during discharge, suggesting systematic changes in the internal conditions affecting acoustic wave propagation. Time–frequency energy analysis revealed that decreasing temperature caused the peak frequency of AE signals to shift from the mid-frequency range (100–200 kHz) toward lower frequencies (<100 kHz). Simultaneously, AE activity evolved from multi-band, multi-scale behavior to a response dominated by low-frequency components associated with larger-scale structural processes. These results demonstrate that low-temperature conditions significantly affect AE characteristics and highlight the sensitivity of AE techniques to temperature-dependent internal responses, providing insights into battery condition assessment under low-temperature operation.