www.sciencenews.org/aaas2011
new batteries
heal themselves
self-repairing versions last
longer, less likely to catch fire
by devin Powell
A newly created lithium-ion battery
that can heal itself may improve the life
span and safety of today’s energy-storage
technologies.
Rechargeable lithium-ion batteries
power cell phones, laptops and other
portable electronics. But, like any batteries, they tend to break down over time.
“There are many different types of
degradation that happen, and fixing this
degradation could help us make longer-lasting batteries,” said Scott White, a
materials engineer at the University
of Illinois at Urbana-Champaign who
described the innovation February 20.
One vulnerable site is the anode, a battery’s negatively charged terminal. As a
battery charges and discharges, the anode
swells and shrinks. Over time, this cycling
causes damage, creating cracks that can
interfere with the flow of current.
To counteract this cracking, White
and his colleagues embedded tiny microspheres inside an anode. As cracks formed
they tore open the plastic shells, releasing the contents within: a material called
gallium indium. This liquid metal alloy
seeped out of the spheres and filled the
cracks, restoring the flow of electricity.
Damage to a battery or a short circuit
between its components can cause problems beyond a shorter life span. Out-of-control currents are known to create hot
spots that can grow into raging fires.
“It’s not a common occurrence, but
when it happens, the consequences are
severe,” White said. Battery fires have
prompted laptop recalls by Dell and
minuscule microcapsules like the ones
shown here could be used to make safer
and longer-lasting lithium-ion batteries.
200 μm
Hewlett-Packard; the U.S. Department
of Transportation has proposed stricter
rules for cargo planes that transport
large quantities of lithium-ion batteries.
To safeguard against this type of failure, White developed a second kind of
microsphere made of solid polyethylene,
an inexpensive plastic. Small spheres
embedded in the anode and other battery components can function as a safety
cutoff switch. If the temperature inside
the battery rises above 105° Celsius, the
spheres melt into a thin layer of insulating material that shuts off the flow of
electricity, preventing a conflagration.
“We’ve tested this in real batteries,”
said White, whose lab is a partner of
the U.S. Department of Energy’s Center
for Electrical Energy Storage. “It works
beautifully.” This safety feature, he said,
could be useful for electric cars emerging
on the market.
“Lithium-ion batteries will continue
to be the technology used for the next 10
to 15 years in electric cars,” said Kristin
Persson of Lawrence Berkeley National
Laboratory in California, who is looking for new materials that store energy
better and avoid some of the pitfalls of
existing batteries. s
model tackles logistics nightmares
Computer program could help deliver relief after disasters
by rachel ehrenberg
Getting blood or other perishable supplies to an area that’s been struck by an
earthquake or hurricane isn’t as simple
as asking what brown can do for you.
But a new model quickly determines
the best routes and means for delivering humanitarian aid, even in situations
where bridges are out or airport tarmacs
are clogged with planes.
The research, presented February 18,
could help get supplies to areas hit by
natural disasters or help distribute vaccines when a flu epidemic strikes.
Efficient supply chains have long been
a goal of manufacturers, but transport
in fragile networks— where supply,
demand and delivery routes may be in
flux— requires a different approach,
said Anna Nagurney of the University of
Massachusetts Amherst, who presented
the new work. Rather than considering the shortest path from one place to
another to maximize profit, her system
aims for the cleanest path at minimum
cost, while capturing factors such as
the perishability of the product and the
uncertainty of supply routes. “You don’t
know where demand is, so it’s tricky,”
said Nagurney. “It’s a multicriteria
decision-making problem.”
By calculating the total cost associated
with each link in a network, accounting
for congestion and incorporating penal-
ties for time and products that are lost,
the computer model calculates the best
supply chain in situations where stan-
dard routes may be disrupted.
“Mathematical tools are essential to
develop formal means to predict, and to
respond to, such critical perturbations,”
said Iain Couzin of Princeton University,
who uses similar tools to study collective
animal behavior. “This is particularly
important where response must be rapid
and effective, such as during disaster
scenarios … or during epidemics or
breaches of national security.”
marta baginska
www.sciencenews.org
