All About Battery Energy

Contributing towards global net zero

Why do Li-ion batteries explode or catch fire?

22 June, 2023

Why do Li-ion batteries explode or catch fire?

Hey, a quick heads up: this page may include affiliate links.

If you click and purchase from these links, we may receive a small commission at no extra cost to you.

Read more here.

We all know it: Lithium batteries can catch fire and explode. But why?

To understand the reasons, we need to go back to battery basics. It’s not too complex, just bear with us.

As mentioned in our article “What is a battery?”, a cell consists of 3 main parts: An anode, a cathode and the electrolyte. The electrolyte can either be a liquid, or a solid (gel or other). Here’s a simplified drawing to show these:

Battery Anatomy

Battery Anatomy

As the positive ions move from the cathode to the anode, electricity is produced. This electricity powers anything connected to the circuit, such as the light bulb. This is all achieved with the help of the electrolyte. The electrolyte is a special liquid, gel or solid, that helps ions move freely from one end of the battery to the other. Without the electrolyte, the ions wouldn’t have a way to move, and the battery wouldn’t be able to produce electricity.

What is the electrolyte of Li-ion batteries made of?

The specific composition of the electrolyte can vary, but for Li-ion batteries it usually consists of a lithium salt dissolved in an organic solvent. The lithium salt provides the lithium ions necessary for the battery’s operation. The organic solvent in the electrolyte serves as a medium for the lithium ions to move between the electrodes.

So why do Li-ion batteries explode or catch fire?

Because their electrolyte is reactive and flammable.

Let’s break these two properties down:

Being reactive means exposure of the electrolyte to moisture or air can trigger unwanted chemical reactions, leading to the degradation of the electrolyte and reducing the battery’s performance or safety. Such chemical reactions may even lead to combustion, which means the electrolyte can ignite. Have a look at the video below to see how reactive the electrolyte in Li-ion batteries is:

Being flammable means that the electrolyte can catch fire if exposed to a spark, high temperature or come in contact with an ignition source. Should any of these happen, the battery may quickly enter into a state of what is called a thermal runaway reaction.

What happens to a battery when it undergoes a thermal runaway reaction?

A thermal runaway reaction is a chemical reaction in batteries. It typically starts with an increase in temperature. So, for example, if a battery is exposed to high heat or is overcharged, this may start a thermal runaway reaction. This can also happen for other reasons, such as manufacturing defects or damage to the battery due to mishandling, puncture or shock.

Here you can see different Lithium batteries and how they react to puncture. It’s a very interesting video explaining thermal runaway reaction in detail:

As you can see, the problem with this process is that, as the temperature rises, it accelerates the chemical reactions within the battery, leading to a self-sustaining process that generates even more heat. Essentially, if a thermal runaway reaction starts, it is practically almost impossible to stop it until the source of heat and the materials that cause the chemical reactions get depleted.

The thermal runaway reaction involves the following stages:

Stage 1: The heat generated from an external or internal source causes the temperature of the battery to rise. At a certain threshold, the battery materials begin to decompose, releasing gases.

Stage 2: As the temperature increases, the electrolyte in the battery starts to break down, producing flammable gases and causing a further rise in temperature. The decomposition of the electrolyte can release gases such as carbon dioxide, carbon monoxide, and various hydrocarbons.

Stage 3: The decomposition of the electrolyte and other battery components generates a significant amount of gas. The pressure inside the battery can increase rapidly due to the build-up of gas.

Stage 4: The increasing temperature and pressure can cause a rupture to the battery’s casing, leading to the release of hot gas and electrolyte. This can result in a violent reaction, with flames, explosions, and the ejection of burning materials.

If this happens to a cell that is part of a large battery with adjacent cells, it can lead to a cascading effect significantly increasing the severity of the incident. The video below shows several different types of batteries, from smaller to larger, and the results of them going into a thermal runaway reaction:

The main characteristic of thermal runaway reactions is that a potential fire can escalate very quickly. The more cells are packed in a battery, the bigger the fire or explosion. For example, here is an Electric Bus in Paris, catching fire after its battery went through a thermal runaway reaction:

In the incident below, we can also see how cells from one bus ignited and caused a significant increase in the outside temperature of the cells in nearby buses:

Notice the speed with which the fire grows and the amount of fumes coming out of the batteries. This can be deadly in enclosed spaces such as houses, flats or offices, or even airplanes. Considering how many lithium batteries our everyday appliances use, it is clear that the danger is present almost anywhere.

How can I stop a thermal runaway reaction?

In essence, you cannot, especially if we are talking about electric vehicles. Here’s a video explaining why:

What you can do is take some measures to mitigate the risk and minimize the potential consequences:

Isolate the battery: If a thermal runaway reaction starts, it is crucial to isolate the affected battery from other batteries or flammable materials. Removing the heat source and preventing the spread of the reaction can help contain the incident.

Ventilate the area: Ventilation will help dissipate the heat and reduces the build-up of potentially dangerous gases.

Cool the battery: Use water or a fire-suppressing foam to cool the battery and surrounding area.

Suppress the fire: If a thermal runaway event leads to flames or a fire, fire extinguishers suitable for lithium-ion battery fires, such as Class D fire extinguishers or specialized battery fire suppression systems, can help control the fire.

Evacuate and seek professional assistance: In case of a severe thermal runaway event or if there is a risk to personal safety, it is essential to evacuate the area and contact emergency services for professional assistance.

As is clear, your priority should be to prevent the thermal runaway reaction from happening in the first place, instead of trying to control it after it does. Avoiding extreme temperatures, not overcharging or over-discharging the battery, and using reputable battery products with built-in safety mechanisms can significantly reduce the risks involved.

You mentioned above that I need to ventilate the area. Won’t this feed the fire with more oxygen?

This is correct; a fire will grow bigger when fed with more oxygen. The step of ventilating the area is not intended to put the fire out though. The idea is to remove the toxic gases produced during a thermal runaway reaction by the decomposition of battery materials, to minimise the risk of inhalation.

Furthermore, as thermal runaway generates a significant amount of heat, ventilation helps dissipate the heat, preventing further temperature escalation and reducing the likelihood of an explosion or fire.

Does thermal runaway reaction happen only to Li-ion batteries?

No, it can happen to any battery but it is most usual in Lithium batteries. A well known example was the infamous Galaxy Note 7 smartphone by Samsung, which caused two battery recalls and the company to stop production back in October 2017. In the case of the first battery, Samsung said there was a design flaw that in some cases caused the positive and negative tabs to come in touch, resulting in a short circuit. During the first recall, these were exchanged for batteries from a different manufacturer. The second battery was also faulty, as it had a welding defect that was also causing batteries to catch fire. Several injuries and burns were reported worldwide.

Why do Li-ion batteries explode or catch fire - Samsung Note 7 mobile phone catching fire

Samsung Note 7 mobile phone catching fire

How dangerous is the storage and transportation of Li-ion batteries?

There have been several reported accidents, some even fatal.

On September 3rd 2010, a UPS Boeing 747 in the United Arab Emirates was destroyed by a fire that started in the lithium batteries it was carrying in the cargo hold. The excessive heat from the fire disabled the crew’s oxygen system and very dense smoke filled the cockpit within three minutes of the first warning, obscuring the pilots’ view. Both crew members were killed. (Source).

On August 1st 2018, a Ryanair Boeing 737 flight was preparing to depart from Barcelona for a short flight to Ibiza. One of the passengers was charging their mobile phone using a Li-ion battery pack. The battery pack caught fire and caused an urgent evacuation of the plain. Luckily, the plane was still on the ground, but the panic that ensued was quite clear in the video recorded by another passenger:

On February 3rd 2018, Frontier Airlines flight 1883 departed from Orlando, Florida to Phoenix, Arizona. During the climb, the battery of a passenger’s smartphone caught fire. He threw it on the floor and another passenger picked it up and took it to the bathroom to place it in the sink, burning his hand in the process. The pilots immediately diverted the flight to Tampa and landed the Airbus A320 safely about 40 minutes after take-off. The two injured passengers were give treatment for their burns.

These were just a few of several examples of accidents or incidents caused by Li-ion batteries. From January 23, 2006 to June 30, 2021, there had been 322 thermal incidents involving lithium batteries as air cargo or baggage. Many of the batteries were in personal electronic devices such as mobile phones, laptops and e-cigarettes.

With so many appliances around using Li-ion batteries, such incidents will keep increasing in numbers. There is talk about introducing legislation to limit the number of Li-ion battery powered devices on each flight, as well as to enforce containment bags as a first measure to combat fires.

Due to the risks mentioned above, the International Air Transport Association (IATA) and the United Nations have been forced to create strict regulations on the storage, packaging and shipping of Li-ion batteries. They are classified as Class 9 “miscellaneous dangerous goods” and there are four UN regulations describing the shipment requirements:

  • UN 3090, for Lithium metal batteries when shipped by themselves
  • UN 3480, for Lithium ion batteries shipped by themselves
  • UN 3091, for Lithium metal batteries contained in equipment or packed with equipment, and
  • UN 3481, for Lithium ion batteries contained in equipment or packed with equipment

If Li-ion batteries are so dangerous, why don’t we use different chemistry batteries?

Because Li-ion batteries are not the only ones who can catch fire or explode. Several other chemistries are susceptible to thermal runaway reaction and incidents have been recorded for many of them. The ongoing research on new battery chemistries and technologies aims to eliminate, or at least minimise, these risks by making use of different materials for the anodes, cathodes and electrolyte. Scientists are in constant search for materials that are less reactive and flammable, easier and cheaper to source, and cause the least harm possible to humans and the environment.

As mentioned earlier, it’s not just manufacturing errors that cause Li-ion batteries to catch fire. It’s also bad practices in storage and transport. A recent example is the 20 June 2023 fire that took the lives of 4 people in New York at an e-bike store in lower Manhattan. The city’s fire commissioner said that the shop had been known for several fire safety violations in the past. From the beginning of 2023, there have been 108 fires that caused 13 fatalities related to lithium-ion batteries just in New York City alone.

Why do Li-ion batteries explode or catch fire - The New York fire that took 4 lives

Why do Li-ion batteries explode or catch fire – The New York fire that took 4 lives Luiz C. Ribeiro/New York Daily News/Tribune News Service/Getty Images

If Li-ion batteries that catch fire are so hard to control or put out, what can someone use to prevent further damage once a fire has started?

The most useful tool is called a containment bag. They look like simple bags but it can withstand high temperatures and contain the smoke. Here’s what they look like:

Why do Li-ion batteries explode or catch fire - Containment bag for Li-ion batteries that catch fire

Containment bag for Li-ion batteries that catch fire

And here’s a video showing how they work:

Brimstone Preventer Plus Fire and Smoke Containment System Introduction and Training_ from Brimstone Fire Protection on Vimeo.

There are other products in the market that can be used both in domestic and commercial environments.