The Boeing 787's high-profile battery fire may have been the result of an engineering double-whammy: an energetic battery chemistry combined with a possibly inadequate cooling system.
Battery experts who spoke to Design News this week said that the 787's lithium-ion batteries employed a cobalt oxide cathode, which is known to be more prone to overheating than other lithium battery chemistries. If that chemistry was used without extra measures to draw heat away from the pack, it could be a problem, experts said.
"It's a no-brainer," Elton Cairns, a professor of chemical engineering at the University of California and a nationally known battery expert, told us. "If they used a cobalt oxide chemistry, then the battery should use a cooling system."
An NTSB engineer examines the casing from the battery involved in the JAL Boeing 787 flight in Boston. (Source: NTSB)
Although Boeing has not said whether the 787's lithium-ion battery packs use any kind of active cooling system, experts who saw photos of the packs said it looked unlikely. "The images I saw indicated that there was no active cooling system and this battery pack has many cells stacked close together," Donald Sadoway, the John F. Elliot Professor of Materials Chemistry at the Massachusetts Institute of Technology, wrote in an email to Design News. "So you need active thermal management."
Boeing representatives told Design News that their lithium-ion battery pack used specific measures to prevent overcharging. "There are multiple back-ups to ensure the battery system is safe," a Boeing spokesman told us. "That includes protection against over-charging and over-discharging."
Boeing representatives did not know whether the battery packs included cooling, however. And cooling was not mentioned in a five-page transcription of a Boeing media call explaining the incidents.
The 787's use of lithium-ion batteries for the auxiliary power unit is said to be a first, which is one of the reasons why the batteries are being scrutinized so heavily. The National Transportation Safety Board (NTSB) X-rayed batteries from a January 7 fire aboard a Japan Airlines Boeing 787 at Logan International Airport in Boston. The NTSB team also did CT scans, disassembled the battery, and examined flight data recorders to determine if it exceeded its design voltage of 32V.
On January 20, investigators said that the battery did not exceed its prescribed voltage. Since then, the agency has continued to look for the root cause of the problems, which have occurred on two Japan Airlines flights and one United flight.
It would seem that not enough is known about the characteristics of this chemistry when used in aircraft systems where high altitudes are encountered. If a cooling system is deemed necessary, it will require redundancy for safety purposes. This of course will require futher testing and approval by the FAA for airworthyness. Perhaps a step back to a known and proven battery technology could be used temporarily at the cost of reduced capacity, but at least it will get the aircraft flying once again until a new, improved battery design can be readied.
There is someting fishy,for decades I have used embedded temperature sensors in all batteries, it is a part of my designed cell balancing and battery management systems, surely sudden temperature surges would be recorded -of course it will not prevent explosion due to O2 accumulation. I have seen cost saving measures causing accidents -but in aerospace!!
Many Lithium ion batteries are not actively cooled but do manage not to burst into flames. Most laptop batteries, camcorder batteries, etc., manage to function without active cooling.
Looking at the photos of the Boeing 787 battery pack I can only make out a single pair of high current output pins that ties the battery to the aircraft's power bus. If so, then all charging and discharging is going through that single pair of contacts, which means the cell monitoring and charging circuitry must live inside the battery. So, if the battery got too hot, possible runaway condition, it could have fried the controller thus disabling any chance of shut down or external alarm.
It would be foolish to not have additional wiring to enable external monitoring and control of the pack. Virtually every Lithium ion camcorder battery communicates with its host as do many other consumer and professional battery packs.
Not having active cooling and external monitoring of system temperature for an aircraft battery system would seem foolhardy.
Battar, your principle is sound but the article suggests that the cooling system may have been inadequate. Seems to me they might not have asked the question properly...and in a critical application safety margins for proper operation would be pretty important.
This was a massive integration effort with literally thousands of verification tests. Notwithstanding it's relative criticality, if this is the biggest issue Boeing can pat themselves on the back, but (as previously mentioned) they must move expeditiously to arrest the problem, accept full culpability, and implement a lasting fix before their market share begins to suffer. The Defense industry has thought me that these post-production woes are intrinsic in a project of this magnitude; thank God the problem was discovered without catastrophic consequences.
It looks like control electronics reside inside the battery pack, so yes they would be subject to rising temperatures AND if electrolyte sprays on the control board all bets are off. This does not appear to be an intrinsically safe design.
The litium battery must be observed in its used enviroment. We are talking low atmospheric pressure and the batteries could be outgassing causing a rupture between layers. Include with that plane vibration from jet engines could play in deterioating loose layers within the battery. The colder temperature at that altitude could have cause contractions the batteries should not have seen. As I remember the batteries should have thermal monitoring device and balance circuits to prevent heavy discharge and charge. So Rapid short within the batteries due to enviromental such as atmospheric condition not designed into the battery compartment would give a clue why the thermal sensing did not have time to respond and shut down.
You cannot analyze this by the damaged batteries alone. And new set for enviromental testing needs to be done to characterize the destruction.
If this is true, then it's a bit scary to think this could happen again. Let's hope engineers get the battery chemistry right next time so something like this doesn't happen again and cause an even more dangerous situation.
They will get it right eventually, Liz. But it could take a while. Over the weekend, CNET published a story in which they, too, interviewed Donald Sadoway of MIT. Sadoway told them that the problems could keep the 787 fleet grounded until 2014.
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