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The Science Behind Dreamliner’s Batteries

Lithium-ion batteries became crucial to the design of Boeing Co.’s BA -1.17% new Dreamliner jet because they offered a combination of high power and low weight.

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The distorted main lithium-ion battery, left, and an undamaged auxiliary battery of the All Nippon Airways’ Boeing 787 which made an emergency landing on Jan. 16.

Yet the very chemistry that makes these high-tech batteries so attractive to designers may increase their risk of overheating and catching fire, a situation that has contributed to the global grounding of about 50 Dreamliners in use and a halt to new deliveries after two onboard fires.

Investigators aren’t just looking at the batteries. Safety experts are combing over the jet’s wiring, circuit boards and other battery-related external components as they probe the incidents.

Batteries convert stored chemical energy into usable, electrical energy. A lithium ion battery consists of a negative electrode and a positive electrode that are linked by an electrolyte, such as an organic solvent.

When the battery is being used, the electrolyte transports ions between the electrodes; electrons flow along a separate wire circuit and that electrical current is used to start an auxiliary power unit and for emergency power.

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By mixing and matching different metals and chemistries, scientists have created a range of different battery types that differ in terms of voltage, service life, size and cost. Low-power devices such as those in a TV remote are usually powered by inexpensive alkaline batteries.

The challenge for battery makers has been to boost the amount of energy that can be stored in a given volume—and that is where lithium-ion technology shines. A lithium-ion power-pack can deliver more energy than a similar-size battery based on another metal, a measure known as energy density.

That is why lithium batteries were compelling to the 787’s designers. The Dreamliner was crafted to allow for big fuel savings and weight reductions, some of which are enabled by the small but powerful lithium-ion batteries Boeing is using.
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Lithium is the least dense of all metals and highly electropositive, which means it delivers a high voltage. Lithium-ion batteries pack twice as much energy density as nickel-metal-hydride versions, and four to six times as much energy density of the lead-acid battery found in many cars, according to Stanley Whittingham, a professor of chemistry and expert on lithium-ion batteries at Binghamton University in Binghamton, N.Y.

Lithium also is the third-smallest element after hydrogen and helium. “Because it is small, you can pull it in and out of materials easily” compared with other elements that are bigger and can’t be moved so easily, said Clare Grey, professor of materials chemistry at the University of Cambridge, England.


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