Here's Why Podcast Series
November 1, 2023

Airlines Ask You About Lithium-Ion Batteries … Here’s Why


On this episode of Here’s Why, we’re talking about lithium-ion batteries and why the airlines care about you bringing them on airplanes. Lithium-ion batteries are used in products that we see every day, including our smartphones, activity trackers, flashlights, laptops, tablets, and more. 

We'll talk with experts about why you're asked about them at the airport, the risks they pose, safety precautions you can take, and how current safety science research around lithium-ion batteries can impact your everyday lives.



  • Kristen Delphos, vice president of communications and public relations, UL Research Institutes (ULRI)


  • Judy Jeevarajan, vice president and executive director, Electrochemical Safety Research Institute (ESRI)
  • Dr. Ya-Ting Liao, associate professor, Department of Mechanical & Aerospace Engineering, Case Western Reserve University
  • Pushkal Kannan, Ph.D. student, Case Western Reserve University


Kristen: Hi, and welcome to Here's Why, brought to you by UL Research Institutes. I'm your host, Kristen Delphos, and today we're talking about lithium-ion batteries and why the airlines care about you bringing them on airplanes.

Lithium-ion batteries are used in products that we see every day, including our smartphones, activity trackers, flashlights, laptops, tablets, and more. We'll talk with experts about why you're asked about them at the airport, the risks they pose, and how current safety science research around lithium-ion batteries can impact your everyday lives.

Today, we have three great guests joining me:

Judy Jeevarajan, vice president and executive director of UL Research Institute's Electrochemical Safety Research Institute, or as we call it, ESRI. Dr. Jeevarajan oversees ESRI's research into safer energy storage, but she also has experience working with NASA to review and approve all the batteries that flew for human space flight. Dr. Ya-Ting Liao, associate professor in the Department of Mechanical and Aerospace Engineering at Case Western Reserve University. And Pushkal Kannan, a Ph.D. student at Case Western Reserve University. Thank you all for joining me today.

We're going to get right into the questions. So, Ya-Ting, let's start with you. For our listeners who might not be familiar, can you explain what are lithium-ion batteries?

Ya-Ting: So lithium-ion battery is a type of rechargeable battery. Lithium-ion move between positive and negative electrodes through electrolyte inside the cell. So, many characteristics set them apart from other type of batteries. The most important one would be high-energy density. By that I mean they can store more energy in a smaller and lighter package, so that really makes them appealing for products where size and weight are crucial factors; for example, portable electronic devices or even electric vehicles. There are many other advantages of them. 

Kristen: Perfect. So, all kinds of products use lithium-ion batteries. Pushkal, we've covered a couple of them, but give us a sense for the range.

Pushkal: Yeah, so many portable products that are [out] there, where it can be from the headphones you're wearing to the laptops to your phones. And it's also there in e-cigarettes and vapes, and it can even be as small as the ones in our car keys where it's a small coin cell. So, it comes in all sizes. So, anything that's portable and electronic most probably has a lithium-ion battery in it.

Kristen: Okay. Some people might not even realize that they have these batteries with them.

So, Judy, every time I check a bag on a flight, especially now that I work at UL Research Institutes, when I hear the airline staff ask me if I have a lithium-ion battery in my luggage, I think about it. But why are they asking that? So, why do they want us to move them from our checked baggage into our carry-ons?

Judy: Sure. About eight years ago, there were several catastrophic events that happened in the cargo compartment of cargo aircraft, and that actually brought planes down and people died because of that. And so [the airlines] prevent us from keeping lithium-ion batteries in the cargo compartment, whether it's a passenger aircraft or a cargo aircraft. And it's not that they prevent [it], they want us to have a lower state of charge when we store them in the cargo compartment. It's because if there is a fire, it's very difficult to find out where exactly the fire is in the cargo compartment and put it out. And usually, lithium-ion batteries give out some kind of pressure because of the venting, and that can bring down the panels in an aircraft, in the cargo compartment, and that brings down the plane itself. So, as an additional warning, [the airlines] let us know that they prefer that we don't keep those batteries in case something happens to them inadvertently and causes a fire in the cargo compartment.

Kristen: Okay. Because there's no one down there to take of it?

Judy: Yes, to take care of it immediately.

Kristen: But what about in the airplane itself?

Judy: Yes.

Kristen: How do they deal with that if the thing that I'm actually carrying caught fire?

Judy: So, in the airplane itself, the flight attendants are actually trained to take care of fires. So, they have fire containment bags. They also have buckets which they can use, and they've been taught to pour either water or even soda on it to put out a lithium-ion battery fire. So, they have been trained.

But there are certain things that you will also hear on the plane whereby they tell you if you drop your phone on the side of your seat, don't try to move your seat to retrieve your phone. It's mainly because most of our cell phones have pouch format lithium-ion cells in them, and if you crush them, they can actually cause a fire. So, the flight attendants don't want you to move your seat and crush the battery because that can then take your battery into a fire. So, they know ways of doing it more safely. So, they give the warning that you shouldn't do that. But in general, they've been taught how to deal with lithium-ion fires in the cabin environment.

Kristen: Okay. Well, the fire itself is different than a normal fire.

So, maybe Ya-Ting, can you explain to us what's the difference in how they would have to be trained or what's the difference in this kind of fire?

Ya-Ting: Right. So, when you compare battery fire to conventional fire, for a fire to occur, you always need to have something called [a] fire triangle: You need to have fuel, you need to have oxidizer, [and] you need to have heat. So, [for] other conventional fires, you just need the suppression works when you remove one of the three out of the triangle. So, for example, if you use an extinguisher, you use CO2 to push away the fuel or to separate the fuel oxidize or even to use water to cool down things, then you remove elements from the fire triangle.

The tricky thing about battery fire is [that the] battery itself contains all three components. You have a fuel vapor released even inside the battery during thermal runaway, the undesired process when the battery is not properly handled, [and] thermal runaway process can release oxygen. So, it's almost impossible to remove the fuel and oxidizer in the battery fire scenario. And then the third component: heat. Thermal runaway process keeps generating heat. So, you suppress it, but you don't wait long enough, you leave, you can reignite it again. So, it's really tricky and it's really hard to be suppressed.

Another thing I would like to point out is the gas coming out from the battery cell during thermal runaway [is] not only highly flammable but also very toxic. So, that toxicity itself is another concern, in addition to the fire concern. So, it is really dangerous. We really need to be really careful about lithium-ion batteries.

Kristen: So, we hear this term thermal runaway. Can you explain what that is?

Pushkal: Yeah, sure. So, during thermal runaway, [the] battery internally keeps generating heat and it's usually not a problem because heat is being dissipated all the time. But the challenge that comes during thermal runaway is that it's heating up so fast that the dissipation that normally happens is not enough to catch up and so there's more and more heat building up, but it's not dissipating and therefore, it would eventually lead to a fire starting from the battery.

Kristen: Okay. So, that makes me think that we're all just carrying around these little nuclear reactors in our pockets. Tell me why I'm wrong.

Judy: Well, any energetic device, any energy source, has energy and has the propensity to have a failure that can result in fire or what we call thermal runaway. But if you design it and use it correctly, and you build it correctly, then we can reduce the risk. That's why we are very confident with most of what we carry around, that they're safe enough for us to carry around, because a lot of work goes into certifying and understanding and characterizing the safety and making sure that the safety controls that are set in the batteries actually work, and that's why we are more confident about carrying most of these around. And that's another reason why we also need to make sure that we buy high-quality products so all the controls and the safeties and the certifications are in place.

Kristen: That makes sense. So, when I think about now, I'm on the plane and people get very fearful, they don't want to get in trouble. So, someone realizes something's going wrong with their device and they don't want something to happen, so they go into the restroom and think they're going to take care of it. Why shouldn't they do that?

Pushkal: That would be a very bad idea because... That would be [an] extremely bad idea.

So, even as researchers, we have been spending so much time in understanding what's happening, what are the reactions that are going on in the battery, and why is it catching on fire. There are a multitude of reasons why things can happen and for so many years we have been coming up with multiple different strategies to suppress this fire so it's not just one single solution that works, and a common consumer might not really have all this knowledge to address the issue.

It's not like a normal fire where you just put water on it and then it gets suppressed. And that's why there's been a lot of efforts going on in training the flight attendants to handle such situations. So, for example, especially let's say you have a battery bank or maybe an e-cigarette or something, and these are things that have been known to catch on fire pretty easily with their lithium-ion batteries, and you decide to go to the restroom and then maybe use the toilet... I'm not sure how you would save it. But stopping the event from happening earlier in the process where you see some smoke or something starting up, rather than waiting all the way until there's fire, can save human lives, where if you wait [until it's] too late, the damage would be more catastrophic. Maybe if you start much earlier in the process, you can suppress it and then all it ends up [being] is a simple flight landing immediately and everyone's life is not jeopardized because of that.

Kristen: Okay. So, listen to our flight attendants.

Judy: Yes.

Kristen: That's basically what we want to say.

Ya-Ting: Yes.

Kristen: They are trained in this safety more than we are.

Judy: Yes, exactly.

Kristen: We don't want to actually scare all of our listeners. So, ground us in how big of a problem is this? How many incidents are we seeing out there with these batteries? How dangerous are they?

Pushkal: Yeah, so a small statistic is that just in 2022, there were 74 fire incidents that happened in airplanes because of lithium-ion batteries. So, that's more than one a week. And some of the major recalls or issues that we have seen, like the Boeing 787 Dreamliners, and then the Samsung Galaxy Note 7, and recently many of the power banks being recalled. All these have had issues because it was not even at the operating conditions where the manufacturer specified that it will work safely, it did not happen. So, they had to recall these batteries back.

So, the onus is not just on the consumers, but it's also on the manufacturers to ensure that the batteries that they're making in the operating conditions, it's being used, it's absolutely safe.

Kristen: So why is lithium-ion battery safety important for our listeners?

Ya-Ting: Right. The battery safety precaution is really important because it's not just about personal safety, it's really about also protecting others around you.

So, we have heard so many electric bike fires in major U.S. city now. In many of these incidents, the owner of the bike often accidentally charged a damaged battery or did not use the proper charger. And when that happened, not only the owner of the bike but also their neighbors were injured or even killed in many incidents.

Judy: So, it's very important, as Ya-Ting pointed out, that they are used in the right manner, they're charged with the right chargers, they are built with high quality products and also used in the right manner. People should not try to push the limits of either charging or using them. And mainly because when you go off nominal or subject them to off-nominal conditions, then you're going to start degrading some of the components and also cause site reactions to happen that can eventually lead into a fire and thermal runaway.

So, people should understand the value of this particular battery chemistry and the benefits that it gives them and make sure that they do not use it beyond what the manufacturer specifies.

Kristen: That's great. I have one little bonus question for you because it's not just the batteries when you're on a plane, it's in your whole lives. But also, when you're done using this device or you have something that you're not using anymore, you can't just put it in a drawer. We're going to have another episode on this, but tell people why it's important to dispose of these batteries correctly.

Judy: So, one of the things with lithium-ion batteries is that the materials that go into making up the electrodes are actually expensive. And so to have a circular economy, it is best if we actually recycle and regenerate the expensive metals that go into building the battery, and that has to be done safely. Recycling has to be done safely because recycling different battery chemistries requires different processes.

For instance, if you take lead acid batteries and combine them with lithium-ion batteries, then in a lead acid recycling facility, they crush the battery as a first step in the recycling process. But if you crush a lithium-ion, it is going to go into a fire and thermal runaway. So, that needs to be avoided. Lead acid recycling facilities have had fires and been destroyed completely, so people need to keep that in mind.

So, it's not only beneficial to recycle them so you can reuse the expensive metal components, but it also needs to be done safely.

Kristen: So, where should people go for more information?

Judy: So, just go to and you should be able to find a lot of information on safe recycling of lithium-ion batteries.

Kristen: Great.

Judy: Yes.

Kristen: Easy to remember. Thank you. Great. So Judy, Ya-Ting and Pushkal, thank you for your time. By all accounts, lithium-ion batteries are here to stay in our lives. Hopefully, you learned something about them today to help keep you and your family safe. 

Judy: Thank you.

Pushkal: Thank you.


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