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Microscopic Crystals Studied by NTSB in 787 Battery Probe

February 12, 2013

Microscopic Crystals Probed by U.S. NTSB in 787 Battery Fire

The so-called dendrites, which can impede electrical flow and cause overheating, are a known cause of battery failure, according to a 2010 article in the magazine Nature. Photographer: Andrew Harrer/Bloomberg

Tiny crystals that can cause lithium-ion batteries to short-circuit and fail are among areas under investigation in Boeing Co. (BA:US) 787 fire and smoke incidents, according to a U.S. agency conducting the probe.

“It’s definitely something we’re looking at,” Kelly Nantel, spokeswoman for the U.S. National Transportation Safety Board, said in an interview.

The crystals known as dendrites aren’t a central focus of the investigation and the safety board hasn’t found evidence of them in the battery that burned Jan. 7 aboard a Boeing 787 operated by Japan Airlines Co. that had just landed in Boston, Nantel said. Nantel also said investigators haven’t seen evidence of the crystals in other batteries they have examined.

Dendrites, which can impede electrical flow and cause overheating, are a known cause of battery failure, according to a 2010 article in the magazine Nature.

The particles are among several areas under investigation that could have caused one of eight cells within the battery to short-circuit and burn, igniting adjacent cells, Nantel said.

The NTSB is looking into whether a manufacturing defect, the charging process or the battery design could have led to the fire, NTSB Chairman Debbie Hersman said Feb. 7 in a news conference.

The 787 has been grounded by the U.S. Federal Aviation Administration since Jan. 16 after a battery aboard another of the planes, this one operated by All Nippon Airways Co., smoldered and emitted smoke in Japan.

Fire, Explosion

The formation of dendrites, also known as “moss,” can occur after rapid charging and discharging of batteries, according to the Nature article. The formations can render batteries “potentially unsafe and unusable owing to the risk of fire and explosion,” it said.

They consist of lithium metal particles that form, particularly after rapid charging, said Clare Grey, a chemistry professor at England’s University of Cambridge who has studied the issue.

“It is a possible mechanism to cause catastrophic failure,” Grey said in an interview

Lithium-ion batteries were developed in the 1990s to limit the formation of dendrites because they were so dangerous in rechargeable lithium-metal batteries, she said.

Dendrites are difficult to detect in batteries because they react in air and have to be examined in an environment of inert argon gas, she said. It would be impossible to detect them in a battery that had already burned, she said.

Test Flights

Because the phenomenon is well-known, battery manufacturers take precautions with recharging circuitry to prevent dendrites from forming, she said. Other issues, such as manufacturing defects, can lead to battery fires, she said.

Transportation Secretary Ray LaHood today said Boeing’s test flights on the 787, which the FAA allowed last week, were part of the agency’s review of the plane’s safety.

“They made the case that it has to be part of the overall review,” LaHood said, speaking to reporters at a U.S. High Speed Rail Association meeting in Washington. “We’ve said all along we’ve got to get this right.”

Boeing test pilots completed the first round of battery- monitoring flights yesterday with a flight the company described in a release as “uneventful.”

To contact the reporter on this story: Alan Levin in Washington at alevin24@bloomberg.net

To contact the editor responsible for this story: Bernard Kohn at bkohn2@bloomberg.net


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