When lithium-ion batteries degrade, they emit acoustic signals that reveal what’s going wrong inside. Now, MIT researchers say they’ve figured out how to interpret those sounds, and the subtle creaks and pops that come before major failures, to help predict problems before things go up in smoke.

Led by MIT chemical engineering and mathematics professor Martin Bazant, the team’s recently published findings suggest that it doesn’t take much more than listening to the groans of a Li-ion battery to determine precisely what’s going on inside. The “acoustic emissions” of Li-ion batteries aren’t uniform, the team said, but vary based on the specific problem with a damaged or dying cell. 

“We were able to classify [acoustic emissions] as coming from gas bubbles that are generated by side reactions, or by fractures from the expansion and contraction of the active material, and to find signatures of those signals even in noisy data,” Bazant told MIT News. 

In order to determine which sounds indicated what type of failure, Bazant and his team attached microphones to Li-ion batteries and ran them through charge and discharge cycles while also monitoring their electrochemical states. By pairing electrical readings with acoustic data, the researchers were able to correlate particular sounds with specific electrical states and failure conditions like side reactions or fractures. That may sound simple, but according to MIT, no one had done it before.

Prior research, like NIST’s study on detecting battery failure through sound last year, showed that lithium-ion cells emit faint acoustic signals as they approach thermal runaway, and that those signals can be separated from ambient noise. Bazant’s own research, conducted with Oak Ridge National Laboratory, backed up those findings and went further, showing that specific sound patterns emerge well before thermal runaway – the chain reaction that can lead to overheating, fire, or explosion. This outcome, the Professor added, suggests that there’s a relatively simple way to know what might go wrong before it ever happens.

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Small sounds happening prior to a thermal runaway scream are “like seeing the first tiny bubbles in a pot of heated water long before it boils,” Bazant told MIT News. 

The MIT team now intends to figure out how to take their tech from the lab to a practical battery monitoring system that can signal issues before they go critical. MIT noted that they’ve already received a grant from Indian automaker Tata Motors to develop a system to monitor its EV batteries. The team also believes their tech could find a home in grid-level battery systems, which have seen high-profile failures in recent years, such as fires reported at Tesla Megapack installations in California and Australia. 

The acoustic monitoring tech Bazant and his crew developed could also be useful in battery manufacturing, helping to detect defects before batteries leave a factory. 

Whether that tech could appear in future smartphones or other consumer electronics wasn’t mentioned in the paper. We reached out to Bazant with questions, but didn’t hear back. ®