Why Do Batteries Catch Fire Or Explode?

Batteries have been in the news in the last few years with instances of cell phones and laptops catching fire and sometimes even exploding. The most infamous example is Samsung's Galaxy Note 7 which was so bad that it was literally banned from being taken aboard airplanes.

This raises the question: why do batteries catch fire and sometimes even explode?

I spent some time researching the causes for battery failures and found that there were apparently many different reasons for the failures. I felt that the real reason was not actually these very many failure modes but one simple fact of physics. In essence it all boils down to one thing:

Whenever you pack a lot of energy into either a small volume or a short amount of time, or both, bad things can happen.

Battery technology has progressed a lot in the last decade with energy densities steadily creeping up to satisfy consumer demand for either longer life or smaller and lighter devices. This all comes at a cost. Whenever you pack a lot of energy into a small volume the safety margins are always reduced.

High Energy Density

For example, look at the gas tank in your car. There is a lot of energy in a gallon of gas as demonstrated daily by fast moving cars on our roads, highways and freeways. Care must be taken to manage the hazards of this energy dense material and yet even to this day many cars burn to the ground each when mistakes are made.

Another example of high energy density is the spring that lifts your garage door. These powerful springs make it possible to easily lift your garage door but they are strong and tightly coiled. Trying to remove one of these springs is a hazardous task because of all the energy stored in the spring (it is usually best to leave that job to a professional).

Energy in A Short Time Frame

Examples of energy being expended in a short amount of time are obvious: explosives and rockets (sometimes they are even the same thing).

The energy released in a gram of TNT is defined to be 4184 joules which is not a huge amount of energy but it is powerful because it is released in fraction of a second when detonated.

Rockets as well release massive amounts of energy in a short, usually controlled, manner. The launch thrust of the Saturn V rocket engines was 7.9 million pounds.

Whenever a launch goes badly though it is quite obvious what having a small margin to failure can mean when you are trying to control large amounts of energy.

Back To Batteries

So that device that you are carrying in your pocket is carrying a lot of energy and the probability that it will fail and catch fire is quite low. Even so, it still needs to be taken care of and not allowed to overheat or get damaged.

If a battery is ever damaged then there is a chance of an internal short happening which will cause the battery to heat up, the compounds inside will catch fire and then it will heat up even more causing a positive feedback loop called a thermal run-away. This means that it is always prudent to replace any damaged batteries.

Closing Words

Batteries are continuing to get more powerful but this means ever increasing energy densities and ever tighter safety margins. It is always wise to buy batteries from reputable manufacturers and to take good care of them while you own them.

Having said that, storing lots of energy in a small space means we will no doubt continue to hear of battery issues making it into the news well into the future.

Thank you for reading my post.

Post Sources

Why phone batteries like the Note 7's explode - YouTube
Why Are Smartphone Batteries Combusting? - YouTube
Understanding how Lithium-ion batteries fail - YouTube
Lithium Ion Batteries: Why They Explode - YouTube
https://en.wikipedia.org/wiki/Samsung_Galaxy_Note_7
https://en.wikipedia.org/wiki/TNT_equivalent
https://en.wikipedia.org/wiki/Saturn_V
https://en.wikipedia.org/wiki/Thermal_runaway