Contactless ultrasound spectroscopy for testing state-of-charge and integrity in lithium-ion batteries

Lithium-ion batteries (LIBs) are playing nowadays a key role in the decarbonization of the economy. However, safety issues and the lack of an accurate performance predictor after manufacturing led to the application of non-destructive methods in this field that can assess their condition. Contact ultrasounds have been successfully applied in recent years in this regard, mainly in research facilities, proving the potential of ultrasonic waves to collect meaningful information. However, some restrictions on their applicability have been identified, compromising their repeatability and stability in operando and in fabrication. Here, we present a contactless ultrasound spectroscopy technique based on the use of air-coupled transducers of high sensitivity and wide frequency band to detect state-of-charge (SOC)-related changes in LIB cells in operando. Additionally, its ability to detect mechanical integrity alterations was also revealed, showing the potential of contactless ultrasound spectroscopy as a powerful tool to test and predict early failures in LIBs.