By Sharon Adarlo

When Samsung’s latest smartphone, the Galaxy Note 7, was released in August, it came with one unexpected flaw. There were news reports of the phone bursting into flames. In one case, a Florida man’s Jeep combusted into a fiery heap while the phone was charging inside the vehicle. The incidents prompted the Federal Aviation Administration to send out a warning against use of the phone on aircraft while Samsung started a massive recall.

What was the culprit behind these fires? Lithium ion batteries, which are ubiquitous in many of the modern electronic devices we use today, were identified as the cause. To understand some of the science behind the battery explosions and how we can make these batteries safer, we discussed these issues with battery expert Daniel Steingart, assistant professor of mechanical and aerospace engineering and the Andlinger Center for Energy and the Environment at Princeton University. In his lab at the Andlinger Center, Steingart tests, analyzes, and develops batteries for different applications and scale – from the electric grid to the phone in your hand.

What made the Samsung lithium ion batteries explode?

Batteries can explode for a number of reasons. From what I had read in the news, there were two parts of the battery inside that had touched when they were not supposed to touch. Imagine a layer cake or the very fine layers of a croissant or phyllo dough. Imagine phyllo dough where the layers should not touch. The inside of a lithium ion battery is like that. If the layers touch just a little bit, you can have a reaction where part of the battery just dies, but the rest of it is okay. In some instances when the layers do touch, that could be the start of a chain reaction that consumes the whole battery in a blaze.

One of the theories – I am sure Samsung is testing this out right now – is that some of the batteries had a manufacturing defect where the anode and cathode, two battery parts that are supposed to be separated, were touching enough to cause this event.  What is challenging about these short circuits is that they can exist when the battery is manufactured, or they can evolve as the battery is operated, likely during charging. From what I understand, Samsung recently applied a software patch to limit the extent to which the batteries can be charged until the full recall can be executed.  If this is the case, it might indicate that either lithium plating, or electrode swelling during charging is leading to the short circuit events, which can cause the fire.  My colleague Craig Arnold, professor of mechanical and aerospace engineering and the director of the Princeton Institute for the Science and Technology of Materials (PRISM), has done considerable work exploring this exact behavior.

How often do lithium ion batteries explode?

Lithium ion batteries have been in production for the past 25 years. There have been fires in the past, and this won’t be the last. But the amount of battery fires has been shockingly small given the amount of batteries produced to date. It’s pretty low.

We think of batteries as this black box where magic happens. The truth is they are made up of very well structured layers that change over time. They can be safe one day, but the next day they can rearrange and the layers could touch each other. If you think of all the countless batteries manufactured and how rarely these events occur, it’s a testament to how very careful the engineering is, which enables this.

We are demanding more and more from batteries: to store more energy, take up less space, charge more quickly, and to be cheaper. Pushing those demands to their limits has the unfortunate physical consequence of increased fires or explosion risk.

So the question among battery engineers, who are currently debating this, can we make batteries that store a large amount of energy, but can we make these batteries in the billions and minimize the amount of fires or keep the amount of fires the same?

Are there tests to make sure batteries are safe and effective?

There are different failure mechanisms that can lead to a fire in a battery. There are existing tests to see whether a battery’s layers are touching. You can use certain tools to measure a battery’s resistance for instance. You can use x-rays, such as the powerful x-rays at national labs, to examine batteries. But it is difficult to test every battery because of the cost and time it takes. You usually test one battery out of a whole batch in order to make sure that batch is safe.

What is your lab doing to help assess the safety and effectiveness of batteries?

In my lab, we have developed acoustic investigation tools – basically using sound waves – that are low cost and fast so you can test every battery in a batch. Maybe we can see the problems that Samsung experienced. We have strong data that indicates we can see these problems by using these newly developed acoustic tools. This method is non-invasive and scalable. You can learn the health, the charge, and physical structure of the battery without taking it apart.

Where is this technology now?

This technology has been spun off into a start-up company called Feasible. Two former postdoctoral research associates of the lab, Andrew Hsieh and Barry Van Tassell, spun off the company, and they were tapped to join Cyclotron Road, an energy technology incubator, which is sponsored by the Lawrence Berkeley National Laboratory and U.S. Department of Energy.  Shaurjo Biswas, a current postdoctoral research associate in the lab, and I are also co-founders of the company.

The Andlinger Center Speaks is a Q/A series that features experts from the center addressing topical and timely energy and environmental issues.

For more information on the Andlinger Center for Energy and the Environment at Princeton University, contact Sharon Adarlo, communications specialist, at sadarlo@princeton.edu or (609) 258-9979.