A Warning For When A Lithium-Ion Battery Is About To Explode

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, how to give the gift of scientific curiosity to the kids in your life. We’ve rounded up some of our favorite science books for kids. But first, fascinating new research on how to better predict if a lithium ion battery is going to catch fire. Maybe there’s one or two in some of your gifts that you’re giving.

You know about the dangers in widespread use of lithium ion batteries. They’re used in all sorts of electronics like smartphones, laptops, e-bikes. And this is because they can store a lot of energy in a small package. And unfortunately, this also means that when a battery is damaged, there’s a lot of energy to expel, leading to explosions and fires.

You may have read the headlines about e-bike batteries catching fire. In New York City alone, there have been 733 fires started by lithium ion batteries since 2019. 29 people have been killed, 442 have been injured, and there are no currently available national statistics.

But here’s the possible good news. Researchers have trained AI algorithms to be able to predict when a lithium ion battery is about to explode. And they have documented how the battery gives off a sound some two minutes before the explosion.

Joining me now to talk more about their work on the subject are my guests, Dr. Andy Tam, mechanical engineer in the Fire Research Division at NIST– that’s the National Institute of Standards and Technology, based in Gaithersburg, Maryland– and Dr. Anthony Putorti, fire protection engineer and leader of the Firefighting Technology Group at the NIST in Gaithersburg, Maryland. Welcome, both of you, to Science Friday.

ANDY TAM: Thanks for having us.

ANTHONY PUTORTI: Thank you, Ira.

IRA FLATOW: You’re welcome. Dr. Putorti, let me start with you. Some of the basics– why are lithium ion battery fires more dangerous than other types of residential fires?

ANTHONY PUTORTI: Well, there’s a couple of things that contribute to that. One is rapid growth. So when the batteries are damaged, overheated, there’s an internal fault, they can catch fire and eject toxic combustion products very rapidly. And then that serves as a very good ignition source to ignite other materials that surround it.

The other is that the combustion products that are emitted from the battery are a little bit different than your normal smoke from a fire. They contain a lot of fluorinated compounds, such as hydrogen fluoride. They also result in toxic debris that contain heavy metals and metals such as nickel, cobalt, manganese, and of course, lithium. And so those are the kinds of things that make them more of a challenge as far as a fire hazard is concerned.

IRA FLATOW: And when they get going, I mean, they’re really hot, burning, aren’t they?

ANTHONY PUTORTI: Yes, and typically, in a product, you don’t just have one battery. You have a number of batteries that make up a module. And so if you have one go into thermal runaway, then it tends to overheat the batteries next to it. So you can have multiple of these battery fires.

In addition, fires related to lithium ion batteries are much more difficult to extinguish. So that should be kept in mind as well. And there’s research going on as far as extinguishment and how to deal with these fires.

IRA FLATOW: Right. And Dr. Tam, let’s talk about this sound I mentioned in the introduction. What kind of sound does it make? And what’s going inside the battery that makes it make this sound?

ANDY TAM: So the entire thing is caused by thermal runaway. So basically, it is a self-sustaining destruct process that will occur when the temperature of the battery increases. And when the temperature increases, there will be an internal chemical reaction. And that causes the temperature to further increase.

And during this process, there are three important events when the battery undergoing a thermal runaway due to, let’s say, thermal abuse. First, there will be a safety valve breakage moment with very little amount of gas coming out. There will be a hissing sound.

IRA FLATOW: So there’s a safety valve that breaks, and then there’s a hissing sound?

ANDY TAM: Yep, yep, yep. And then secondly, it will enter to what we call a venting stage. And at that stage, there will be more and more hot toxic gases, just like what Tony mentioned. And then finally, there will be an ignition stage, in which you will see flame jets. And the surface temperature of the battery can be as high as 1,000 degrees C.

IRA FLATOW: Wow.

ANDY TAM: And we were only talking about one single cell. If we have a pack of batteries, this means that the igniter battery will trigger what we called the thermal runaway propagation in which the surrounding batteries will get ignited. And at this point, the fire will become very difficult to put out.

IRA FLATOW: Is there some way for a detector to hear the hissing sound in that two minutes beforehand, the signature that it’s going to explode?

ANDY TAM: Oh, yeah, definitely. And it is exactly what we were doing. And then we want to make use of sound and also machine learning to develop a fast-responding, easy-to-use, and accurate model to detect the safety valve breakage moment, which we consider as one of the earliest stage of the thermal runaway.

IRA FLATOW: So to solve this problem, you developed an algorithm to be able to detect this safety valve explosion sound? Tell me how this works.

ANDY TAM: Oh, we actually do this as a team. And we have collaboration with other institutions. Basically, we conduct a series of experiments with different state of charge, different battery orientation relative to the microphone, collect different sound signature. And then each of the tests lasts about 10 minutes.

And then basically, during the experiment, you will hear some hissing sound, and then you will see some kind of small jets when the safety valve breaks open. And in my opinion, this sound signature is very unique. And we extract this sound signature together with audio data from various human activities to develop an effective early stage thermal runaway detection model.

ANTHONY PUTORTI: You mentioned explosion. What we’re really seeing here is we have this relief valve on these cells. And so what it’s doing is there’s a jet of hot gases and fire and particles that are coming out. So the whole cell isn’t coming apart in a big explosion. Really, what you’re seeing is this jet of flame once this phenomenon occurs.

IRA FLATOW: Wow. And Dr. Putorti, is this something you can take advantage of in a product or safety somehow?

ANTHONY PUTORTI: Typically, when you think about buildings, your home, your office, you’re going to have smoke detectors that are on the ceiling. You could also have sprinklers. And so you have some distance between the battery or the product and the detector.

So you could potentially build this technology into detectors that are located there, but you could also put them, potentially, in a product to also provide detection. And that might be able to be done faster than the more difficult and time consuming process, at least in the near term, for getting these types of capabilities in other kinds of fire detectors.

IRA FLATOW: Right. Could you build it into the battery itself to detect its own hissing sound and put out an alarm somehow?

ANDY TAM: It can be integrated. Certainly, there would be a possibility to do that. But we want to make it in a way that it can be portable.

IRA FLATOW: Ah.

ANDY TAM: Let’s say now you already have your lithium ion battery. You don’t want to buy a new one. So we want to build this technology such that it can be used for any old devices.

IRA FLATOW: And how far or how close are we to be able to do that? Dr. Tam, I know you’ve applied for a patent for this technology. How long would it take for this to be a safety feature that’s available for consumers?

ANDY TAM: First of all, we want it to be safe. So we anticipate to conduct more experiments, to collect data with different types of batteries, because right now, we’re only looking at one battery. And then we will also have to look at different microphone and also different environmental settings.

And at the same time, we will have to deploy our model while we are doing the experiment and see whether or not our model would need further improvement. And then this is something that we’ll be working on in 2025.

IRA FLATOW: Why do we see these e-bikes? I was talking about this in the introduction about how many explosions there have been. Why does that happen?

ANTHONY PUTORTI: I’m not familiar with all the statistics as to how prevalent each cause is, but you do have manufacturing defects in the batteries. And the quality of the batteries can vary, depending on the manufacturer and the origin of the battery. You can also have issues with repairs that can be made to the devices, replacement batteries that were not specifically meant for that device.

You can have chargers that are used that are not the correct charger, especially if you needed a replacement. You can have issues with the device getting wet, with it getting too hot, if you leave it in a place where there’s high temperatures. So there’s a variety of different types of things that can cause the malfunction that leads to the fire.

IRA FLATOW: Well, until we have your product, Dr. Tam, until then, give me a suggestion about how folks can stay as safe as possible if they have e-bikes or other devices with lithium ion batteries.

ANDY TAM: So Tony sort of mentioned it a little bit. So basically, we would encourage using proper charging practices– for example, using right charger. Don’t overcharge the battery, and avoid extreme environment. And then while we are charging the battery, make sure that we are charging it in a safe place.

And then just to anticipate, maybe it’s good practice to think ahead of time. Let’s say if the battery really go wrong, what you would want to do to try to mitigate the process or plan for the exit route. And we believe that this will be helpful, just in case there will be an accident.

ANTHONY PUTORTI: Also, when you’re buying your product, you can make sure it’s listed by a qualified testing and certification lab to make sure that the product is a good product. I’d also like to mention the National Fire Protection Association. On their website, they actually have some good one-page summaries of what you can do to use these products more safely.

And also, as Dr. Tam indicated, especially if you have an e-scooter or something like that, you definitely don’t want to store it or charge it in an exit route. That’s a really bad place to do it because if something goes wrong, that can block your exit.

IRA FLATOW: Those are good tips for everybody who’s got them and who will be getting them for the holidays. Thank you both for taking time to be with us today.

ANDY TAM: Thank you.

ANTHONY PUTORTI: Thank you very much, Ira.

IRA FLATOW: You’re welcome. Dr. Andy Tam, mechanical engineer in the Fire Research Division at the NIST, and Dr. Anthony Putorti, fire protection engineer, leader of the Firefighting Technology Group at the NIST in Gaithersburg, Maryland.

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