The Risk of Thermal Runaway: Managing Safety with Lithium-Ion Batteries

A lightweight battery that lasts for years: what more could you want? Developed in the 1970s, the lithium-ion battery has made the world rechargeable. You can now find the battery in mobile phones, laptops, toothbrushes, razors, music boxes, flashlights, e-steps, e-bikes, e-scooters, hoverboards. And under the hood of electric cars: six to seven thousand units in one battery pack.

The lithium-ion battery is a great invention because of its favorable energy-to-weight ratio, with one drawback: the risk of a thermal runaway. Under certain conditions, the battery can become unstable and heat up, causing a chemical-electric reaction that can turn into a fire beyond your control. In the event of a car fire, says Nils Rosmuller, professor of energy and transport safety at the Netherlands Institute for Public Safety (NIPV), all those six to seven thousand battery cells ignite and that goes on and on, “until they are all burnt out. ”

This can take days.

On the Fremantle Highway, the freighter that has been burning in the North Sea since Tuesday night, an electric car was probably the cause – the investigation is still ongoing. On board are just under 4,000 cars, 25 of which are electric. The extinguishing work can take days, also because the fire brigade cannot come on board.

Manage your own batteries

Extinguishing is one of the major challenges, the NIPV wrote a month ago in a report titled Incident response electric vehicles on ships. This came after the fire on the car transporter Felicity Ace near the Azores in 2022, loaded with thousands of electric cars, and the ban imposed by a Scandinavian ferry company on electric cars on board last year. According to the report, hardly any preventive measures have been taken to prevent a thermal runaway of electric cars on transport ships.

And that is why legislation and regulations are always a bit behind the times, sees Nils Rosmuller. The energy transition rages on and “we usually only learn the real lessons about safety after an incident”. Rosmuller saw the same in the development of safety measures for solar panels and the charging of electric cars. “At first we did all this with a plug in the socket, but there are now safer systems.”

Thinking about safety is all the more important now that more and more citizens manage their own batteries. You used to have one large power plant with a fence around it, “now we are all our own energy company,” says Rosmuller. People charge their phones and their laptops, but also their bicycles and cars, and they store excess solar energy at home. In some neighborhoods there are sea containers with rechargeable lithium-ion batteries – ‘the neighborhood battery’.

Read also: Bite, swallow… and the battery burns a hole in the esophagus

It often goes wrong. According to the NIPV annual report, there were a total of 117 fires involving electrically powered vehicles last year. The year before there were still 62. Not that electric cars catch fire more often than cars that run on diesel or petrol, but they are rapidly increasing in number – more than one in twelve cars is now (partly) electric.

According to a spokesman for the National Police, putting out the fire is quite a job. Especially because there is a sturdy box around the battery that protects the batteries against rain and dust, but also against fire extinguishing water. “A car with an unstable battery has to be towed away and then there is always a risk that it will burn again.” Salvage companies are now placing the car in an immersion bath to prevent it from igniting later due to thermal runaway.

E-bikes catch fire

It also regularly goes wrong with e-bikes. The examples from New York are well known, where people often charge their electric bicycle in their apartment high up in a flat and have to be rescued by the fire brigade along the facade. E-bikes also regularly catch fire in the Netherlands, Rosmuller knows. “But then they are usually in a shed and the consequences are minor.” Particularly electric shared scooters are notorious. “Something that is not your own, you are often less careful with. Those scooters are knocked down and sometimes a passer-by kicks them. That can damage the battery, which increases the risk of fire.”

Thinking about safety is all the more important now that more and more citizens manage their own batteries

He also has concerns about batteries that people use at home to store the energy from their solar panels. “Some use simple batteries from the do-it-yourself store or from Marktplaats, from second-hand cars. They can still work fine in themselves, but there is little regulation for them and as a user you have to know what you are doing.” Even then: you don’t know what the quality of such a battery is exactly.

And that’s the point of a thermal runaway: the reaction in such a lithium-ion battery is often a slow, dormant process. A battery can heat up slowly due to an error in the manufacturing process. Or because a car has had a crash before. It can take days before the battery gets so hot that it catches fire and the heat transfers to another battery cell. And then again on the next. And the car next to it catches fire. Etcetera.

Until, like on the Fremantle Highway, the entire ship ends up as one giant thermal runaway.

With the cooperation of Kees Versteegh

A version of this article also appeared in the newspaper on July 28, 2023.
2023-07-27 19:17:09


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