Lithium-ion batteries and the Boeing 787 Dreamliner

The Boeing 787 Dreamliner is the most recent major new aircraft design from Boeing, and the manufacturer’s most fuel-efficient plane. I have never had the pleasure of being passenger on one of these, but the design is certainly very modern. Composite materials are widely used in the aircraft, which is key to the plane’s fuel efficiency and explains the popularity of the plane. With more than 800 orders in the books, Boeing was also on a good track to break even commercially.

Then, on January 16 the FAA grounded all 787, following a number of technical problems. Earlier, the Japanese airlines ANA and JAL had already suspended all 787 flights, which was a significant signal because combined these two airlines operate almost half of the 787 delivered to date. Aside from a number of other technical issues such as a fuel leak, a key reason to ground the entire fleet has been two incidences where the back-up batteries overcharged and overheated such that there was the danger of fire on board. But how big a deal are these battery incidents?

A Boeing 787 Dreamliner. Photo by Spaceaero2 via Wikimedia.

The batteries used in the plane are common ones, using lithium cobalt oxide. They are rechargeable batteries, where the lithium ions are used for charge storage and transportation. Lithium-ion batteries are widely used for all sorts of electronic devices such as laptops or mobile phones. In principle, this type of batteries is safe, although the 787 is the first large aircraft to heavily rely on such batteries.

Although the battery technology is well-known, designing an aircraft is complex, and if not done properly can lead to unexpected situations where the batteries are operated outside their specifications. In the case of the Dreamliner, overcharging the batteries has been suspected to be the cause of the plane’s battery problem.

That overcharged batteries are a hazard should not come as that much a surprise. In a lithium ion battery, the lithium atoms need to move through the crystal. Of course, this is no different from electrons moving through an electrical cable when you turn on the lights. But even though lithium is only the third element in the periodic table these ions are a lot larger than electrons, so that this movement is not that easy. To stay vaguely on topic, it is the same as squeezing an oversized passenger into a tiny air plane seat. It creates friction, and in case of the batteries this is the cause of heating – in particularly when charging the batteries, or when discharging them too fast.

For gadgets such as phones there will never be that much of a problem, the maximum power the batteries need to supply to the gadget is in no comparison to the power an aircraft needs for its back-up systems. Moreover, trying to push the lithium ions fast through the battery is far more problematic than taking it slow. That’s why the lithium-ion batteries on the Dreamliner are made of lithium cobalt oxide, which is more suited to heavy loads than lithium iron phosphate and other compounds used in consumer devices. The drawback is only that overcharging lithium cobalt oxide is more of an issue… as we have seen.

On the other hand, lithium ion batteries have been successfully used in demanding applications, for example to power electric sports cars such as the Tesla Roadster. Indeed, Elon Musk, a co-founder of Tesla Motors, has offered their help to Boeing in a tweet:

Maybe already under control, but Tesla & SpaceX are happy to help with the 787 lithium ion batteries.

— Elon Musk (@elonmusk) January 18, 2013

To me, the problem also looks solvable. If indeed overcharging is the issue here, this might even point more towards a design flaw in the electrical system of the plane, rather than the battery design itself. But this is pure speculation on my part.

The bigger issue in the long-term might be how much rechargeable batteries might be able to replace crucial systems on air planes, to achieve more fuel-efficient aircraft designs. Storing a huge amount of energy in the confined space of a battery will always create safety issues, in particularly if the charging and release of the energy need to occur at very short time scales. There might always be a delicate balance between operational demands and safety, and further research in new batteries is crucially needed. But we should not forget that regardless of the use of such batteries, passenger jets always carry around materials storing high levels of energy. By this I mean the jet fuel. What happens in the jet engines is not much different nothing but a controlled explosion and burning of that fuel.

For my part, I am confident that Boeing’s engineers will eventually find a solution. Fuel-efficient, light-weight aircraft designs are urgently needed and planes such as the 787 do point towards the future in passenger transportation. For this reason, the lessons learned here for the battery systems will be very valuable in future.

Update – 20 January 2013: The US National Transportation Safety Board has now ruled out excessive voltage applied to the batteries as a cause for their failure.