Written by T-admin

March 12, 2021

EV Powertrain

Are you afraid of Li-Ion fires? The Li-Ion batteries are lightweight, inexpensive, powerful, and more ecological power-storage devices than most alternatives. This is why they are vastly used in appliances, and in the last decade also in our vehicles. We had all heard of the fire in 2019 that destroyed a fleet of electric motorcycles and made a stop to the first MotoE World Cup – the electric spin-off of MotoGP. Events like this add to the skepticism of electric vehicles, which is nothing new when it comes to new technology. For instance, when the first cars appeared in the early 1900s there was a heated debate about the highly flammable gasoline that runs the ICE cars.

But are Li-Ion batteries, that power EVs really a fire hazard?

When you think about it, Li-ion batteries are everywhere: they power our mobile phones, home appliances, laptops,… and even though these batteries are so prevalent, there are actually really few accidents. By comparison: Your chance of being struck by lightning in the course of a lifetime is about 1 in 13,000. Lithium-ion batteries have a failure rate that is less than one in a million. The failure rate of a quality Li-ion cell is better than 1 in 10 million. When comparing EVs with ICEs, it is worth noting that EVs produce fewer fires per billion kilometers driven than ICEs. The most notorious EV manufacturer Tesla for instance reported only two fires per one billion kilometers driven.

The manufacturers put a special emphasis on quality production of the Li-Ion cells. To verify the safety of a new cell, a manufacturer may release 1 million samples into a workforce on observation. The cell is approved for the use of critical missions, such as medical, if no failure occurs in one year that could compromise safety.

So how come the batteries catch fire, if all these tests are done?

Almost all fire incidents in the Li-Ion batteries were caused by non-certified battery cells. The other causes for Li-Ion battery fires are excessive vibration, electrical shorting, elevated heat, rapid discharge, overcharging, poor design, or mechanical damage.

Li-Ion batteries should never be fully discharged. Their charge should never drop below 2V per cell. If this happens, when re-charged, these cells can become unstable, causing excessive heat, resulting in combustion.

Li-Ion batteries should also always be kept away from heat sources and direct sunlight, especially when fully charged. They should always be stored in a cool and dry place, partially charged. Overheating results in a process called thermal runaway, when the internal temperature and pressure of the battery rise faster than it can be spent, causing the battery to combust. The heat of one cell then affects the neighboring cells and causes a chain reaction.

Often usage of quick-chargers can additionally damage the cells, making them more prone to catching fires.

How to react if the Li-Ion battery catches fire?

If the battery overheats, hisses, bulges, exhumes smoke, or catches fire, you should immediately remove it from your e-bike (if possible), and move it away from flammable materials. Try to bring the battery outside and let it burn out. If the battery starts burning while charging, disconnect it, but this will unfortunately not stop it from further destruction.

If the fire is small, you can use a foam extinguisher, CO2, ABC dry chemical, powdered graphite, copper powder or soda (sodium carbonate). You can also use water, which will not extinguish the fire itself, but it will prevent it from spreading, by cooling down the affected area. If the Li-Ion battery catches fire, you will have to let it burn out and make sure the fire does not spread to other materials. The Li-Ion fire can’t be extinguished. If the cause of fire is a cell in a battery pack, leave a whole pack outdoors or in the area that you can control for a while, since the affected cell could destabilize the rest of the cells, causing them to ignite.

When burning, Li-Ion batteries produce CO2, vaporized electrolyte consisting of hydrogen fluoride (HF) and phosphoryl fluoride (POF3). There are also organic solvents and combustion products in the gases. In case the fire happens indoors, you should ventilate and vacate the area.

To sum it up…

The fires in Li-Ion batteries are pretty rare, but if they happen, stay calm, take the battery outside and keep it cool, so the fire doesn’t spread. Ventilate the room where the fire started, and keep an eye on the battery pack after the fire burned out. And most of all, if building your own battery pack, always purchase the cells from certified manufacturers.

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