Questions about the cooling of the Boeing 787's batteries came up again this week, as Tesla Motors CEO Elon Musk publicly stated that the plane's large pack design is a risky one.
"Unfortunately, the pack architecture supplied to Boeing is inherently unsafe," he wrote in an email to Flightglobal.com. "Large cells without enough space between them to isolate against the cell-to-cell thermal domino effect means it is simply a matter of time before there are more incidents of this nature."
Tesla uses lithium-ion battery packs in its Tesla Roadster and Tesla Model S vehicles. Its design involves 6,000-7,000 small lithium-ion cells. Musk told Flightglobal that the cells are separated in a way that makes them less likely than large cells to suffer from thermal runaway events.
Elon Musk of Tesla and SpaceX: "Unfortunately, the pack architecture supplied to Boeing is inherently unsafe." (Source: revengeoftheelectriccar.com)
Musk has tweeted his desire to help Boeing with its battery problems, which included incidents in two Japan Airlines flights and a United flight this month. On Jan. 18, he wrote, "Maybe already under control, but Tesla and SpaceX are happy to help with the 787 lithium ion batteries." A few days ago, he followed up: "Desire to help Boeing is real & am corresponding w 787 chief engineer." Shanna Hendriks, a spokeswoman for Tesla Motors, confirmed to us that Musk made the comments on his Twitter account and by email to Flightglobal.
Marc Birtel, a Boeing spokesman, would not verify whether his company's chief engineer has been in contact with Musk. "We're engaged with a number of experts both inside and outside the company," he told us, but Boeing is "not identifying them by name publicly."
The issue of battery cooling has been at the forefront of the Boeing story for a week. Donald Sadoway, the John F. Elliott professor of materials chemistry at MIT who is involved in a battery startup with Bill Gates, told us last week that a forced air cooling system and sensors may be needed to monitor and cool the battery in the event of overheating. Elton Cairns, a professor of chemical and biomolecular engineering at the University of California, Berkeley, and a fuel cell designer for NASA's Gemini spaceflights, also suggested that an air- or liquid-cooled system would be necessary.
Even at low temperatures, the Boeing system could still have been at risk, according to Cairns. "When the plane is at altitude, the air is less dense," he told us. "So even if it's cooler, the less dense air may not have adequate heating capacity to provide enough cooling for the battery. If they don't have active cooling, then I question the adequacy of the cooling arrangement."
Boeing uses eight lithium cobalt oxide cells in its battery packs. According to experts, the cobalt oxide chemistry is known to have higher energy densities than other forms of lithium-ion, so it needs an active cooling system.
Boeing representatives told us that they are not aware of an active cooling system for the 787 batteries. "Obviously, there were multiple backups associated with the battery to ensure the system was safe against overcharging and overdischarging," Birtel said. "But there was not a specific cooling system associated with the battery."
Cairns called battery management ICs (to monitor voltage and current) an important part of a safe pack, but he also said energetic batteries often need more than that.
"The electrical system that manages the battery is not a complete battery management system," he said. "In my view, a complete battery management system includes the dispersion of any heat that is generated by the operation of the battery. Just having protective circuits is fine, but it is absolutely insufficient."
Wow. Thanks for this, Chuck. Definitely a developing story. I'm delighted to hear that there is collaboration (or at least a coalition) of lithium-ion battery users that are willing to swap experience with these systems. I'm sure this type of information sharing between CEOs has happened since the dawn of time, but I'm encouraged that it can be facilitated by social networking such as twitter and not left to chance meetings on the putting green at the club. I'm sure networking at the Engineer level is still best found at the Dearborn Heights Applebee's, but online story swapping is another emerging development that helps to accelerate the exponential technology development curve...
Chuck, Outstanding coverage. It's amazing how all of this is playing out in the online media. But it's also obvious there is engineering and science behind the comments. Keep up the good work.
Great that you're keeping on top of this story, Charles. I guess now what we're waiting for is Boeing to admit what it has done wrong and then come up with a plan to fix the problem. I was sort of defending them at first but it actually seems like a fairly major oversight to not proivide a proper cooling system...but maybe they thought they did and it was just an honest mistake. I will continue reading your coverage to see how this unfolds! Let's hope it's a good ending for everyone and Boeing sorts this out.
As an alternative to overcharging and heat dissipation how about over discharging? Over discharge damage is the reason many RC enthuiasists charge their lithium ion batteries outside.
Boeing has recieved 100 batteries back from the airlines as defective. It appears the majority have been inadvertently discharged until the battery low voltage cutoff tripped, disabling the battery. In ANA's case 5 of 10 returns were disabled by the low voltage cutoff. Once a lithuim ion battery has gone below the low voltage limit it is very hazardous to charge. It seems risky procedure for the user to bang up against only battery safety stop during routine ground maintenance. Maybe some batteries have very nearly tripped but were unknowingly flown.
Anticipating the question of why don't the battery electronics cut off discharge at a higher voltage, I don't know. It might have something to do with the fact the batteries are also a last ditch power source to keep flying. I can imagine a situation where you would want every joule you could get out of the battery and willingly scrap it later.
I would discount poor high altitude cooling. The batteries are in the pressurized part of the plane, an equivalent to an altitude of 6000 feet so you still have good heat transfer.
Regarding the issue of whether a battery management IC, by itself, was sufficient protection for the Boeing batteries: We asked Donald Sadoway of MIT that question by e-mail, and his response came in after the story deadline. So here's his response, which arrived late yesterday: "We have evidence that whatever the electrical demands are in the 787, the IC alone doesn't prevent fire. So perhaps the IC isn't right, perhaps the IC is right but the execution is flawed, or perhaps there is some other factor like decompression/compression, which is the result of ascent and descent."
You raise a really good point about the reasons for Musk's collaboration, Nadine. Obviously, no one but Musk knows the full reason, but I imagine there is an element of self-preservation in this. Lithium-ion batteries are getting a going-over in the popular press right now, and some news stories have wondered aloud if lithium-ion is appropriate for electric vehicles. Whether those questions are fair or not, I would imagine that Musk wants people to know that Tesla's battery configuration works safely because the design allegedly makes better allowances for heat dissipation. It's hard to blame him for that.
It is pretty amazing how much media is giving time to the Boeing battery issues. You do not often hear scientific discussion in mainstream media, but the Boeing story has brought out a lot of experts.
Here is a low brainier- GET ALL THE HELP YOU CAN, BOEING!
Tesla has experience with these batteries. Boeing's future rides on a solution to this problem. We all need counselors. Boeing would do well to bring others to the engineering table and utilize their experience.
I hope they already are. Pride has brought down companies and countries. I hope Boeing doesn't let pride get in the way of their future!
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