The Boeing 787 Dreamliner was supposed to be the company's bold entry into the future of air travel—an environmentally friendly, fuel-efficient world traveler. Using 20 percent less fuel than Boeing's similarly sized 767, it was the most heavily pre-ordered widebody aircraft ever.

But now, the entire fleet of 787s has been grounded because of a series of mishaps involving the plane's batteries. On January 7, a Japan Airlines 787 just in from Tokyo caught fire at Boston's Logan International Airport when the batteries in the aircraft's auxiliary power unit ignited; eight days later, a battery scare forced an All Nippon Airways 787 flying from Yamaguchi, Japan to make an emergency landing and evacuate.

The batteries at the heart of the problem, manufactured by the Japanese firm GS Yuasa Corporation, are essentially giant versions of the lithium-ion batteries used in cell phones and laptops. Like those batteries, the Dreamliner's use a lithium-cobalt oxide cathode, which is "an inherently unsafe cathode," said Mark Allen, assistant professor of chemistry and biochemistry at the University of Maryland, Baltimore County. And in the larger form used by Boeing, they pose an even larger risk. When overcharged or damaged, they can become essentially a firebomb inside the airplane—one that burns without air and can't be put out by usual aircraft fire suppression systems.

The batteries are an essential part of the Dreamliner's core innovation—using electricity in place of jet engine "bleed air" and hydraulic energy to power the aircraft's controls. They help start up the plane's onboard power plant, which generates 5 megawatts of electricity—five times more than any other aircraft.

But the electrical system's complexity has been a particular stumbling block for the plane model in the past. And with the whole plane being essentially a flying network (the plane's avionics are wired together with a derivative of 100 megabit Ethernet to reduce the amount of wiring and corresponding weight) and the controls entirely dependent on electrical power, any problem with electrical systems can become a disaster.

Where there's smoke

Six hours into a test flight in November of 2010, in the skies over Texas just after 2:30 in the afternoon Central Time, the pilot of a Boeing 787 Dreamliner Number 2 declared an emergency. There was smoke in the cabin, and the airplane's "glass cockpit"—its computerized displays and controls—had partially failed, its primary flight displays and automatic throttle controls gone.

As he touched down at Laredo International Airport and brought the plane to a halt, the crew and passengers—Boeing company execs and technicians monitoring flight data—evacuated the plane, jumping down the emergency slides. The cause of the emergency was an electrical fire that took out the aircraft's primary and auxiliary power units. The Dreamliner would have become a nightmare without the emergency power source—a Ram Air Turbine, which dropped down from the fuselage to convert airflow past the plane into power for essential controls. The incident led to further delays for the Dreamliner, as Boeing went back to redesign the entire electrical distribution system of the aircraft. But the redesign didn't eliminate the hazard of the batteries themselves.

Batteries using lithium-cobalt oxide of any size are prone to overheating when they're charging because of their small electrical resistance. But because the batteries in phones and computers are relatively small, they can usually shed the heat unless they're charged too quickly or past their designed capacity.

The Dreamliner's batteries, however are not your garden-variety laptop battery. Manufacturer GS Yuasa started in the business making motorcycle batteries and now makes large-scale specialty batteries for all sorts of power applications—including powering satellites. The batteries selected for the Dreamliner "were very large scale—65 amp-hour batteries which is very, very large," said Allen. "They are very high power batteries, and they charge them to 90 percent (of capacity) in about 70 minutes. That's a very fast charge for any lithium battery of this size. And that's a problem when there isn't a cooling system incorporated."

The problem escalates as the battery gets hotter. "When these batteries reach a certain temperature—about 140 degrees Celsius—they reach a thermal runaway where they basically go out of control," Allen said. And that can turn the battery—the one in a plane, or the one in your cell phone—into a firebomb.

"The cobalt in the cathode is in a plus-four oxidation state, which is very unstable," he explained, "and it's sitting in an electrolyte which is organic and very combustible. It's a highly oxidized system with a fuel, so it becomes a combustible system very quickly."

When a battery overheats, the electrolytes in it can start to leak. "As long as it's away from some sort of oxidant, (the chemicals) are very safe," said University of Michigan Chemical Engineering Professor Levi Thompson. But once they're exposed to an oxidant, they can catch fire quickly, as he explained in this video on the subject:

Normally, the only time when there's a risk of battery combustion is during charging. The batteries are discharged during the plane's startup, when the Auxiliary Power Unit—essentially a jet-powered generator for the aircraft's electrical systems—is first started. In the Boston incident, the batteries were likely being recharged when they caught fire; in the airborne incident, they may have entered thermal runaway while on the ground, or they may have been taking a charge from the APU itself after take-off and continued to overheat.

Safer alternatives

There are a number of fixes Boeing could make to reduce the risk from the batteries. One is to use batteries with a cooling system—either water or air cooling.

But there are also much safer choices for the cathode material in large lithium batteries that can reduce the risk of explosive combustion. Allen hopes that the Dreamliner issues will lead to wider adoption of safer battery technology.

"They are available and becoming more popular," Allen said. "Lithium nickel manganese oxide cathodes are safer, and iron phosphate ones are much safer because they don't actually release oxygen when you arc it or when it's damaged."

Dr. Ann Marie Sastry, President and CEO of battery technology company Sakti3, said her company is developing a solid-state lithium-ion battery that would address many of these issues. "To eliminate risk in energy storage systems, the best thing to do is to eliminate the liquid electrolyte in favor of solid materials that are not combustible," she said. Solid state lithium-ion batteries could improve both safety and performance of batteries, but she added that they'll "add substantial cost."

Whatever the solution, there are larger engineering concerns about the Dreamliner to be addressed as the aircraft experiences what some have called "teething pains." And Boeing isn't the only aircraft manufacturer that should be concerned—Airbus also uses lithium-ion batteries for its newest APUs.