MAY 1, 2015
WASHINGTON, DC (AP)
International aviation officials are trying to quickly come
up with safer packaging for cargo shipments of lithium-ion batteries on
passenger planes, after U.S. testing confirmed that aircraft fire suppression
systems can't prevent overheated batteries from causing a powerful explosion.
The International Civil Aviation Organization's committee on
hazardous cargo met this week in Montreal. Officials familiar with the discussions
say the panel heard a detailed presentation by aircraft manufacturers and pilot
unions on the potential for the batteries to cause an explosion and fire
capable of destroying a plane.
If a working group cannot come up with packaging capable of containing
an explosion or fire, union officials said they will consider offering a formal
proposal at a meeting in October to ban bulk battery shipments.
The batteries are used in devices from cellphones to
electric cars. It's not unusual for as many as 80,000 batteries to be carried
on board a plane.
Federal Aviation Administration tests over the past year and
a half show that a single short-circuiting battery in a large shipment of
batteries can cause overheating to spread to other batteries. Fire suppression
systems have been able to put out the flames, but do not stop the spread of
continually increasing temperatures known as thermal runaway.
The overheated batteries emit a mixture of explosive gases,
of which hydrogen is the most abundant. As the gases build up, they eventually
explode and ignite a fire.
An FAA test in February resulted in a powerful explosion
despite an atmosphere of 5 percent halon, the main gas used to suppress fires
in passenger aircraft.
//---------------------///
WHY SOME LITHIUM-ION
BATTERIES EXPLODE
Real-time images have captured the chain reaction that
causes lithium-ion batteries to explode
The process can occur in just milliseconds: Overheated
battery modules create a domino effect, producing more and more heat, and the
battery explodes. But it turns out that not all batteries are equally likely to
fail, according to a new study published today (April 28) in the journal Nature
Communications.
"The presence of certain safety features can mitigate
against the spread of some of this thermal runaway process," said study
co-author Paul Shearing, a chemical engineer at the University College London
in the United Kingdom. Those features include mechanical supports inside the
battery, Shearing said.
The results suggest some ways to make rechargeable
lithium-ion batteries safer, the researchers wrote in the paper.
Rechargeable batteries
Lithium-ion batteries are the workhorses of modern-day
gadgets; they're found in everything from smartphones to jumbo jets to the Tesla
Model S. They are typically made with two layers of material, called the
anode and the cathode, separated by an electrically conducting fluid. Lithium ions start off
in the cathode, a layer of material that, in laptop and cellphone batteries,
typically includes cobalt, manganese, nickel and oxygen.
When the batteries are
charged, electricity drives the lithium ions from the cathode, across an
ion-filled electrolyte fluid, and into the anode, which is made of stacks of
graphite. As the battery drains, the lithium ions return from the anode back
into the cathode. The batteries typically come in cells; a laptop battery may
have three or four cells, whereas a Tesla Model S may have thousands, Shearing
said.
Chain reaction
Hundreds of millions of lithium-ion batteries are produced
every year, and catastrophic failure, such as explosion or melting, is rare, Shearing
said. Still, there have been 43 product
recalls for defective lithium-ion batteries since 2002, according to the
U.S. Consumer Product Safety Commission.
Batteries can blow up or melt when internal electrical
components short-circuit, when mechanical problems crop up after a fall or an
accident, or when they are installed incorrectly, Shearing said. But at the
heart, all of these failures occur because one portion of the battery gets too
hot and can't cool down quickly enough, creating a chain reaction that
generates more and more heat.
"It's kind of this snowball process that we call
thermal runaway," Shearing told Live Science.
During thermal runaway, the miniature battery modules can
melt, giving off heat, and the electrolyte material between the anode and the
cathode may even boil, Shearing said.
To understand more about this dangerous chain reaction,
Shearing and his colleagues heated commercial lithium-ion batteries to 482
degrees Fahrenheit (250 degrees Celsius). Using a high-speed 3D camera and a
particle collider, which bombarded the batteries with synchrotron X-rays, the
team captured thermal images of the batteries as they underwent the flash
transition to overheating and thermal runaway.
Safer batteries
Even at high temperatures, not all of the batteries failed —
some had internal safety features that prevented the dangerous reaction. Of
those that did fail, the batteries with internal supports stayed intact until
the internal temperature reached a scorching 1,830 F (1,000 C). At that point,
the internal copper materials melted, leading to the runaway chain reaction.
But the batteries
without these internal supports exploded, likely because their internal cores
collapsed, which could have short-circuited the internal electrical components,
the study showed.
The new technique provides a way to systematically test
safety features in batteries in the future, Shearing said.
Even though exploding
batteries sound frightening, they're actually quite rare, Shearing said.
After all, most people don't bake their iPhones during daily use, he said.
"We had to push these into really extreme conditions,
which [you] are very unlikely to see in your normal day-to-day operations,"
Shearing said.