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Can Signal Processing Stop Battery Fires?

Burned Out Batteries: The auxiliary power unit from a Japan Airlines Boeing 787 Dreamliner jet burned up on 7 January 2013. Could subtle signal processing have found a problem with the lithium-ion batteries sooner?

The 787 Dreamliner’s battery problems have been a nightmare for Boeing and a reminder that bigger batteries require more-extensive safety measures. Technologies that use new battery chemistries and cooling techniques to prevent lithium-ion battery fires are in the works, but systems that monitor the batteries’ electrical behavior offer particular promise to catch future catastrophic conflagrations long before they happen.

Lithium-ion batteries can experience what’s called thermal runaway, in which some event leads to heating, which in turn leads to more heating, and so on. Part of the lithium-ion safety problem, says Elton Cairns, a faculty senior scientist at Lawrence Berkeley National Laboratory, in California, involves the electrolytes in the batteries. “We’re using mixtures of organic solvents that are quite flammable and quite volatile,” he says of today’s lithium-ion electrolytes. “In my view, that’s just asking for trouble.” And with enough heat, oxygen gets liberated from a battery’s metal-oxide anode. “There you’ve got all the makings of a fire,” he says. And a flame front that doesn’t need anything outside the battery to sustain itself is very hard to extinguish. That’s why lithium-ion battery fires can get so big (like the one that knocked out a U.S. Navy minisub in 2008), he says.

Nonflammable electrolytes are in the works. Cairns’s group has, in fact, patented one that it has successfully tested on prototype lithium-ion cells since 2006, he says. Cooling systems, such as the Chevy Volt’s dedicated battery radiator, can help prevent thermal runaway too, says Donald Sadoway, a professor of materials chemistry at MIT.

But cooling and chemistry will work a lot better if they’re combined with sensing and circuitry, according to Michael Pecht, director of the University of Maryland’s Center for Advanced Life Cycle Engineering. He says engineers need to work harder on smarter battery-management systems. Many such systems monitor only a battery’s current flow over time, he says. “It’s like the doctor just measuring your pulse and saying you’re healthy.”

Pecht says his group is developing battery-management systems that track current, voltage, mechanical strain, temperature, and other operating parameters. And once a battery’s use and performance run too far astray, the system warns that the battery needs servicing.

Sensing systems may, in fact, be able to detect bad batteries that have already passed factory tests. These parts suffer from an internal short circuit, a defect that is difficult to identify. As a private consultant to lithium-ion battery manufacturers and device makers that use those batteries, Brian Barnett, vice president of the Lexington, Mass.–based technology-development company TIAX, has examined many case studies of lithium-ion problems. “Frequently, the level of destruction was too great to determine what transpired,” he says. “However, when you could find a cause, overwhelmingly we discovered proof that there had been a foreign metal particle that had got into the cell.” What was particularly worrisome was that in “a couple hundred incidents, it showed that none of them occurred in the first three months,” he says. Many internal short circuits, in other words, cannot be detected at the factory.
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