Real-time measurement of lithium-ion batteries’ state-of-charge based on air-coupled ultrasound

In order to overcome the drawbacks of the traditional method of measuring a lithium-ion battery’s state-of-charge by charging and discharging its voltage curve, a method based on air-coupled ultrasound is proposed, which slows aging of the battery. Analysis is conducted on the propagation characteristics of ultrasound in the battery using Biot’s fluid-saturated porous media model; the signal is monitored in real time by monitoring ultrasonic waves during charging, and fast-wave and slow-wave signals are obtained. Firstly, the fast-amplitude value of the time domain signal is analyzed, and the near linear relation between the amplitude and lithium-ion battery’s state-of-charge is established. Frequency domain analysis is then carried out to understand the relationship between the phase and phase velocity for different state-of-charge consumptions and spectra. The results from using an air-coupled ultrasonic detection method to obtain the fast-amplitude value of the battery’s time domain signal show that fast-amplitude has an approximately linear relationship with state-of-charge. This verifies the feasibility and accuracy of this method and provides a new theoretical foundation for the real-time monitoring of lithium-ion batteries’ state-of-charge.