May 29, 2012
(note: This blog post has been edited from its initial form, and will likely continue to be edited in the near future. This editing is in response to the correct summary that it was originally too alarmist, and that’s not a tone that I like or support. So I’m trying to improve the flow of the entry. If you have suggestions or factual corrections, please comment below)
In a real way, lithium batteries make modern life possible. They’re in everything that needs extended battery power, like cellphones, laptops, tablets, and so on. They are largely very safe devices (if they weren’t, you’d be able to tell since practically everyone carries a lot of them, and you don’t notice people catching on fire everywhere), but under certain conditions, they can fail, and when they do fail, it’s in a spectacular fashion.
Battery technology hasn’t made any revolutionary changes in the past couple of decades, but has been more of a constant stream of improvements from the typical zinc-carbon battery that were (and still are) commonly found on the shelf, to the “alkaline” batteries (so called because it uses an alkaline electrolyte), on up to the current crop of higher performance batteries.
Depending on the use case, these high performance batteries today are typically Nickel/Cadmium (Ni-Cd), Nickel Metal-Hydride (NiMH), or Lithium Ion (Li-ion), although relatively recently, we’ve managed to produce Lithium Gel or Lithium polymer batteries (which are kind of like Li-ion, but
designed to be safer, although they’re still subject to the same kinds of problems I’ll be describing. For the sake of laziness, I’ll refer to all relevant types of Lithium batteries as Li-ion).
The use case for these batteries varies depending on the application, because the key differences are power density (NiMH and Li-ion are both comparatively good), the power curve during discharge, and well, cadmium is like, really, really bad for you.
Because it is so very energy-dense, we use Li-ion batteries for most modern computing hardware. Your mobile phone almost certainly has a Li-ion battery in it, as does your laptop computer. Any other fun gadgets that don’t take off the shelf AA or AAA batteries probably do as well.
You may already know this, but although your laptop might have a single monolithic battery that you plug into it, contained within that single battery is very likely a series of smaller “cells”, seen above.
Most of the cells are wired together in series so that they can push enough voltage to power the equipment, and a couple more are put together in parallel to boost the amperage. Chances are good that you have either a 6-cell or a 9-cell battery in your laptop. The more cells, the more electricity your computer stores, obviously. Also, the more lithium you have, but we’ll get to that shortly.
As it turns out, there are some problems with Li-ion batteries (and really, all of the batteries listed above, but we don’t keep half a dozen cells of the others on our laps at all times). It seems that they’re only stable up to around 60 degrees Celsius (140 degrees Fahrenheit). Much above that and they have a tendency to…well, explode. Violently.
On September 3rd, 2010, a UPS cargo flight crashed outside of Dubai. A large portion of its cargo consisted of Li-ion batteries (and devices with them). It’s not conclusive what caught on fire originally, but for our purposes, it doesn’t matter a lot. Raising the temperature of a Li-ion battery above the 140F mark leads to a compromised cell which causes an explosion and a resulting fire.
So what is it about 60C that causes the problem? At that temperature, lithium undergoes what’s called “thermal runaway“. The lithium begins to outgas, trying to lose heat, but when it can’t, either because the outgassing is blocked, the source of heat is external, or it is gaining heat more rapidly than it can lose it, the heat builds up. In any of these cases, the runaway feeds back on itself, causing more heat, more pressure, etc, until an explosion occurs.
Now, one of the important considerations here is that this happens per cell. Remember how we have 6 or 9 of them in our laptops? Yeah, exactly. One cell can overheat, start a thermal runaway, explode, and in the process, catch the device itself on fire. Which, of course, applies heat to the other cells. And repeat.
These kinds of events aren’t all that rare. These are the reason that every once in a while a laptop manufacturer will issue a battery recall. It’s because one (or more likely several) batteries exploded, and the company’s insurance underwriters deemed it cheaper to replace a bunch of faulty batteries than pay the likely lawsuits from the people hurt or killed by the explosions.
When I asked what it acted like, he said…
It wasn’t so much a fire per say. More like one of those little jumping jack fireworks you get on the 4th. It did poof a flame about a foot high and than just sizzled mostly…
So I became curious, and after researching, I found a very sobering video.
If you’ve traveled on a plane, you know that you have several Li-ion batteries with you at all times, and so does everyone else. That’s several hundred potential bombs on every flight, so it figures that the FAA would have spent some time dealing with the ramifications.
Here’s a 10 minute video that they produced to help train on-flight staff to deal with the eventuality of a lithium battery fire while in the air:
(if you can’t see that video, you can get to it here)
Before watching that video, I was under the impression that the best defense against a laptop fire was a Class D Type 2, copper powder fire extinguisher. I was wrong.
The real problem isn’t the burning lithium (although that’s certainly bad); it’s the potential of one explosion to cause a thermal runaway in the other cells. For that reason, liquids like water are very useful in preventing the reaction.
The flames that you see are almost certainly not the lithium burning, but the casing and materials of the laptop. Those can be dealt with using a regular ABC extinguisher. Once the fire is out, cool down the battery as quickly as possible.
Also of interest might be a great entry that I ran into while researching this blog post: Bob Burtis’s Six Deadly Myths of Lithium Batteries. I can’t honestly say that I have fact-checked every line item, but the ones that I knew and came across were all right. Here’s an informative tidbit:
What is the real culprit with Lithium Polymer Batteries? As a battery ages or is abused, its chemistry changes. Lithium Batteries develop Lithium Salts, which raises the internal resistance of the cell much like the sulfating of a Lead/Acid battery. When you pass a current through a resistance you develop heat and as I’ve already pointed out several times, it is heat that triggers the chemical reaction within the cell.
So remember, if you’re faced with a situation like this, try to stop the runaway. You saw the FAA video above; the most effective defense against the fire was a pure water extinguisher, but barring that, just pour as much water on as you can to get the cells cooled to below 60C.
I hope you enjoyed learning this as much as I did while I was researching this entry. I was genuinely surprised to see that water was the best defense, but it is something that I’ll keep in mind. You should too. Just file it away with the other information that you hope you never need.