Researchers at Liten, a CEA Tech institute, equipped batteries with acoustic sensors to listen to the ultrasound they emit (between 100 kHz and 300 kHz) during operation. Their work involved not only NiMH but also lithium-ion and NiZn batteries.

The researchers discovered that outgassing at the electrodes increased the acoustic emissions of nickel batteries as they reached full charge. This is crucial information that battery management systems (BMS) could use to ensure more effective charging throughout a battery’s lifetime. The technique can also prevent thermal runaway in lithium batteries—a common phenomenon that we can now “hear.” This discovery could help make batteries much safer.

In addition, when charged for the first time, a lithium-ion battery creates a passivation layer, which partly determines the battery’s service life. Until now manufacturers have used empirical techniques for this process as there is no non-destructive way of measuring the layer. This research could soon help manufacturers produce higher quality batteries by using sound to monitor the formation of the passivation layer without altering the battery.