Investigations into the Dynamic Acoustic Response of Lithium-Ion Batteries During Lifetime Testing

Abstract

Techniques using acoustic waves to interrogate batteries are increasingly investigated in the literature due to the appeal of three main properties: they are non-destructive, relatively low cost and have acquisition rates enabling operando testing. Popular demonstrations attempt to extract degradation markers from acoustic data, by continuous monitoring, and to attribute them to degradation modes. This is founded on the premise that the speed of sound depends on mechanical properties, such as the density and stiffness. Nevertheless, additional sensitivities of an acoustic time-of-flight analysis are often neglected, leading to incomplete experiments that can overstate the capabilities of the technique. In this work, such sensitivities are quantified and the use of pulse tests instead of CCCV protocols is recommended to elucidate the concurrent dynamic evolution of temperature, voltage and acoustic signals. A degradation experiment is performed, with pulse sequences incorporated in periodic reference performance tests. Dynamic parameters are extracted from each pulse; specifically, the dynamic rise of the time-of-flight (ΔToFrise) and temperature (ΔTemprise) signals. Their evolution with degradation is traced and a statistical comparison of the main effects is performed. It is concluded that markers of degradation in the dynamic acoustic response are very subtle, masked by the effects of temperature.