Going to car shows I am often asked this question and I wanted to put some facts on some of the myths surrounding the battery packs that we use. Before I start into some facts, I find this fear somewhat funny coming from people who have been sitting on top of a 10-20 gallon tank of liquid gasoline most of their lives as they travel at high speeds down the road. Though gasoline is not quite as explosive as in the movies, it is highly flammable and can explode if the conditions are right. If your gas tank is punctured it is sure to spill all over the ground and create an even bigger hazard. In a report from 2005 over 266,000 gasoline related car fires killed over 566 people.1 So with that said, I will begin to approach the subject of the dangers of lithium ion fires.
The metal lithium is highly flammable and burns very hot. It also reacts with water. But lithium ion cells like those use in most electric cars these days do not actually contain metallic lithium. Rechargeable, lithium ion cells utilize lithium ions that are intercalated into graphite, lithium metal oxides and/or lithium salts. There is no metallic lithium in a lithium ion battery. This means that they are much more stable than many of the earlier non-rechargeable lithium batteries which did contain metallic lithium. One big safety factor in this is that you can use standard ABC fire extinguishers or water to put out a lithium ion battery fire.2 You do not need to use a Class D fire extinguisher which is used on metal fires and are also quite expensive and rare.
So what can cause a lithium ion battery to catch fire? It is in the charging process that they are most vulnerable. If you over charge a lithium ion cell the cells will expand and become very hot. If over charged to much, this heat will build up and cause the cell to ignite. During the normal charging process the cells should not become hot. This is why it is very important to have some kind of monitoring system hooked up to the cells while they are being charged to make sure that the charger shuts off automatically when they reach a fully charged state or if the cells become hot. This is standard gear in a modern electric car. If the cells are over charged, care should be taken and the cells should be removed from the pack and slowly discharged. Leaving them in this engorged state full of energy has been know to cause them to ignite even days afterward.
Most of the lithium battery fires posted on Youtube of laptops afire were caused by earlier more lithium laptop batteries which had a different chemistry which was more unstable. Many of the laptops also did not have adequate monitoring circuits for charging the cells. Todays modern electric cars use cells which are much more stable and the charging systems usually have multiple means of measuring the packs state of charge to cut off the current once the pack is fully charged.
The other way that the cells can ignite is if one of the terminals is loose and a plasma event, or arc of electricity develops across the small gap. This can again produce high amounts of heat which can cause them to ignite. This is why it is extremely important that all of the connection are tightened properly and the use of lock washers is important.
Another thing that needs to be mentioned is that lithium ion cells do not contain any liquid battery acid like the old acid cells you use as your cars starter battery. There isn’t any harmful chemicals in them that can be splashed on you should you get in an accident in your car. The cells can be turned upside down or even ruptured and nothing will splash out of them to corrode your skin.
But a Chevy Volt caught on fire! Well yes it did, three weeks after being in a crash test and left to sit outside in the rain with liquid coolant leaking all over the batteries which hadn’t been disconnected. That’s kind of like crashing a gas car, not emptying the gas tank, leaving it outside to let the gas spill all over the ground and then wondering why it ignited when someone flicked a cigarette at it. Personally if it takes my car 3 weeks to ignite after I was in a horrible crash in it, I am ok with that. I won’t be in it. Oh and that fire could have been easily avoided if the batteries had been properly disconnected and taken out of the car after the crash.
The cells that we use in our cars are lithium polymer cells which are even safer. This newer technology from CALB is even more resistant to fire.
Are they dangerous? Well any kind of energy product has a certain amount of danger involved simple because it does contain stored energy. This means that they should be treated with respect. But they are by leaps and bounds safer than fossil fuel products such as gasoline, diesel fuel, or natural gas. If I had to be in a wreck I would much prefer having a pack of lithium ion cells behind me than a gas tank.