“Through some careful scientific work, our team has managed to decode the acoustic emissions,” says Martin Z. Bazant, a professor of chemical engineering and mathematics. They were able to classify them as coming from gas bubbles generated by side reactions or from fractures caused by expansion and contraction of the active material, two primary mechanisms of degradation and failure.

The team coupled electrochemical testing of working batteries with recordings of their acoustic emissions, using signal processing to correlate sound characteristics with voltage and current. Then they took the batteries apart and studied them under an electron microscope to detect fracturing.

With Oak Ridge National Laboratory researchers, the team has also shown that acoustic emissions can warn of gas generation before thermal runaway, which can lead to fires. As Bazant says, it’s “like seeing the first tiny bubbles in a pot of heated water, long before it boils.”