Why the Boeing Dreamliner’s batteries burst into flames

Boeing’s Dreamliner is currently grounded due to two of their Li-Ion batteries having burst into flames, one in flight, and another on the ground. Two accidents of the same type in a small fleet is no little matter as an airplane fire can be deadly on the ground or at 50,000 feet.

The fires are particularly bad on the Dreamliner because these lithium batteries control virtually everything that goes on aboard the plane. Even without a fire, when they go out so does virtually every control and sensor. So why did they burn and what has Boeing done to take care of it? The simple reason for the fires is that management chose to use Li-Cobalt oxide batteries, the same Li-battery design that every laptop computer maker had already rejected ten years earlier when laptops using them started busting into flames. This is the battery design that caused Dell and HP to recall every computer with it. Boeing decided that they should use a massive version to control everything on their flagship airplane because it has the highest energy density see graphic below. They figured that operational management would insure safety even without the need to install any cooling or sufficient shielding.

All lithium batteries have a negative electrode (anode) that is mostly lithium. The usual chemistry is lithium metal in a graphite matrix. Lithium metal is light and readily gives off electrons; the graphite makes is somewhat less reactive. The positive electrode (cathode) is typically an oxide of some sort, and here there are options. Most current cell-phone and laptop batteries use some version of manganese nickel oxide as the anode. Lithium atoms in the anode give off electrons, become lithium ions and then travel across to the oxide making a mixed ion oxide that absorbs the electron. The process provides about 4 volts of energy differential per electron transferred. With cobalt oxide, the cathode reaction is more or less CoO2 + Li+ e– —> LiCoO2. Sorry to say this chemistry is very unstable; the oxide itself is unstable, more unstable than MnNi or iron oxide, especially when it is fully charged, and especially when it is warm (40 degrees or warmer) 2CoO2 –> Co2O+1/2O2. Boeing’s safety idea was to control the charge rate in a way that overheating was not supposed to occur.

Despite the controls, it didn’t work for the two Boeing batteries that burst into flames. Perhaps it would have helped to add cooling to reduce the temperature — that’s what’s done in lap-tops and plug-in automobiles — but even with cooling the batteries might have self-destructed due to local heating effects. These batteries were massive, and there is plenty of room for one spot to get hotter than the rest; this seems to have happened in both fires, either as a cause or result. Once the cobalt oxide gets hot and oxygen is released a lithium-oxygen fire can spread to the whole battery, even if the majority is held at a low temperature. If local heating were the cause, no amount of external cooling would have helped.

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Something that would have helped was a polymer interlayer separator to keep the unstable cobalt oxide from fueling the fire; there was none. Another option is to use a more-stable cathode like iron phosphate or lithium manganese nickel. As shown in the graphic above, these stable oxides do not have the high power density of Li-cobalt oxide. When the unstable cobalt oxide decomposed there was oxygen, lithium, and heat in one space and none of the fire extinguishers on the planes could put out the fires.

The solution that Boeing has proposed and that Washington is reviewing is to leave the batteries unchanged, but to shield them in a massive titanium shield with the vapors formed on burning vented outside the airplane. The claim is that this shield will protect the passengers from the fire, if not from the loss of electricity. This does not appear to be the best solution. Airbus had planned to use the same batteries on their newest planes, but has now gone retro and plans to use Ni-Cad batteries. I don’t think that’s the best solution either. Better options, I think, are nickel metal hydride or the very stable Lithium Iron Phosphate batteries that Segway uses. Better yet would be to use fuel cells, an option that appears to be better than even the best batteries. Fuel cells are what the navy uses on submarines and what NASA uses in space. They are both more energy dense and safer than batteries. As a disclaimer, REB Research makes hydrogen generators and purifiers that are used with fuel-cell power.

More on the chemistry of Boeing’s batteries and their problems can be found on Wikipedia. You can also read an interview with the head of Tesla motors regarding his suggestions and offer of help.

 

13 thoughts on “Why the Boeing Dreamliner’s batteries burst into flames

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    1. R.E. Buxbaum Post author

      Thanks. My son is the company web-master. He’s 21 now and does all the code-magic. I taught him to code when he was 8 or 9, and now he’s far better at it than me. If you want to contact him, he’s admin at rebresearch. He’s also the writer and chief doom at a site called “halocustoms.com.” I’m pretty proud of him.

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  9. YetAnotherGeekGuy

    Hmmmm …. I don’t see anywhere in here WHY they burst into flames as promised by the headline. Only anecdotal reasons why they shouldn’t have tried Li-Cobalt. Up until the Wright Brothers, folks used to give reasons why should event try to fly either, starting with Icarus. But at some point folks actually figure technology out and we all move on despite the naysayers.

    We saw this when airships transitioned from hot air to lighter than air. They all blamed the hydrogen for the Hindenburg when the real primary root cause was the rocket fuel that they used to waterproof the skin.This transition in battery technology really isn’t much different from when airplanes moved from Lead-Acid to NiCad. Progress will, again, be in fits and starts.

    I guess I shouldn’t have really expected an answer; root cause can only be validated when you can make the problem repeat at will. We aren’t there yet. But I also didn’t expect wild speculation with no basis in the facts of the case.

    Maybe we could all back off the rhetoric and stick to the facts first. Perhaps if they had with the Hindenburg, we wouldn’t have such an acceptance problem with hydrogen fuel cells today.

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    1. R.E. Buxbaum Post author

      Sorry, I guess that point wasn’t as clear as I’d hoped. Local heating. Any large battery will have some, most chemistries have a lot less than this one, and most large batteries include a mechanism to minimize the damage when it starts (like a membrane for instance); these did not. On cutting up the batteries, there’s evidence of hot spots that set everything else ablaze.

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