Correlated Acoustic and Synchrotron Based X-ray Radiographic Measurements for Early Warning Detection of Li-Ion Battery Thermal Runaway: Part I. Ultrasonic Spectroscopy Translated from Small to Large Format Pouch Cells

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Abstract
Monitoring the safety state of lithium-ion batteries (LIBs) in real time is critical for improving cell reliability and protecting end users. This study explores the capability of ultrasonic testing (UT) as a diagnostic tool during overcharging of NMC pouch cells. UT measurements are correlated with in-situ high speed synchrotron based X-ray radiography providing complementary insight into the evolution of internal degradation processes. Small 220 mAh cells were tested inside a custom-built chamber, allowing simultaneous ultrasonic and X-ray radiograph measurements. We observed clear links between structural changes captured by radiography and changes in the ultrasonic signals during overcharging. Spectral analysis showed an increase in low-frequency fast Fourier transform (FFT) magnitude, indicating internal cell degradation, while X-ray radiography revealed internal structure changes as cells transitioned from compact interlayer configurations to gas void accumulation. We then extended the ultrasonic monitoring to larger 56.3 Ah electric vehicle pouch cells, where radiographic imaging was not feasible. Similar trends in the ultrasonic data were detected, marking the first time such ultrasonic monitoring during an overcharging test has been demonstrated on EV-scale cells. This shows a potential for non-invasive, real-time monitoring of battery health during abuse.
Funding Information
  • Royal Academy of Engineering (CiET1718/59)
  • Ministry of Trade, Industry and Energy of the Republic of Korea (P0030266)
  • Diamond Light Source (MG30541-2)
  • Faraday Institution (HISTORY)

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