Ultrasonic diagnostics offer a promising method for monitoring lithium-ion batteries by detecting mechanical changes that occur during cycling and aging. While conventional ultrasonic analysis often relies on time-of-flight (ToF) measurements, recent studies show that frequency-domain approaches can provide more robust correlations with battery state.

In this work, ultrasonic spectroscopy is used to investigate acoustic resonances in lithium-ion cells that arise from standing waves within the layered structure. The temperature dependence of these resonances is analyzed to evaluate their suitability for practical battery diagnostics.

The results show that resonance frequency correlates strongly with temperature but only weakly with the state of charge (SoC), whereas resonance amplitude correlates strongly with SoC while remaining largely insensitive to temperature. This complementary sensitivity enables simultaneous determination of temperature and SoC from a single ultrasonic measurement.

Compared to conventional ToF-based methods, resonance analysis therefore provides a more robust approach for battery state monitoring under varying thermal conditions.