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These microcapsules, filled with liquid metal, sit on a gold conductive layer. If the circuit is mechanically damaged, the capsules burst to restore the conductive pathway. Each is just 10 um across; 10 could fit side by side in a human hair. Image: Amanda Jones and Ben Blaiszik.
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Imagine
dropping your phone on the hard concrete sidewalk—but when you pick it up, you
find its battery has already healed itself.
A team of
researchers from the University
of Illinois at
Urbana-Champaign (UIUC) and the U.S. Department of Energy's (DOE) Argonne
National Laboratory are exploring ways to design batteries that heal themselves
when damaged.
"This
would help electronics survive daily use—both the long-term damage caused by
charging over and over again, and also the inevitable physical damage of
everyday life," said Jeff Moore, a UIUC scientist on the team.
Scientists
think that loss of electrical conductivity is what causes a battery to fade and
die. Theories abound on the specific molecular failures; perhaps chemicals
build up on electrodes, or the electrodes themselves pull away. Perhaps it's
simply the inevitable stress fractures in materials forced to expand and
contract repeatedly as the battery is charged and used.
In any
case, the battery's storage capacity drops due to loss of electrical
conductivity. This is what the team wants to address.
The idea
is to station a team of "emergency repairmen" already contained in
the battery. These are tiny microspheres, each smaller than a single red blood
cell, and containing liquid metal inside. Added along with the battery
components, they lie dormant for most of the battery's lifetime.
But if the
battery is damaged, the capsules burst open and release their liquid metal into
the battery. The metal fills in the gaps in the electrical circuit, connecting
the broken lines, and power is restored.
Capsules
could be designed to be triggered by different events—some that respond to
physical damage and others that respond to overheating, for example. This would
allow scientists to tailor the contents of the different capsules to repair
specific situations.
Microcapsules
have been manufactured in large scale since the 1950s. When you press your
pencil down on carbonless copy paper, microcapsules full of ink burst open to
leave an imprint on the paper layers beneath. Microcapsules full of perfume
burst when you rub a scratch-and-stiff sticker.
"We
hope that using microcapsules, which are a well-known technology, could make
this technology easy to scale up for commercial use," Moore said.
The team's
first step was to test the system in a simple system, connecting an electrode
with a wire to see if the capsules could "heal" the circuit if cut.
"Our
new self-healing materials can completely repair the circuit in less than a
millisecond," Moore
said.
The next
step, which the researchers are beginning, is to test the capsules in a
prototype battery. Argonne materials scientist
and battery expert Khalil Amine is helping the team adapt the capsules for
lithium-ion batteries.
The
results have been published in a paper, "Autonomic Restoration of
Electrical Conductivity", in Advanced
Materials.
SOURCE
