battery research
a series of image slices over time to capture changes
“One possible explanation for the fading is that
In a working lithium-ion battery, the lithium
in moving tissue, such as the inflation of a lung while
lithium is becoming trapped inside the electrodes, and
must flow through a liquid electrolyte that fills the
a person is breathing, NDP can measure how the
NDP would be an ideal method to see and quantify
space between the cathode and anode - and that
composition of a slice of material changes over time.
trapped lithium,” Co said.
fact alone created the experiment’s main challenge.
But whereas an MRI subjects materials to a
The researchers measured the concentration of
NDP only works inside a vacuum chamber, and
magnetic field and measures how the polarity of the
lithium in the battery anode - the negative electrode
vacuums vaporise liquids. That’s why another group
atoms in that material change, NDP hits materials with
where positively charged lithium flows in as the battery
of researchers in a 2011 study used a solid-state
a low-energy neutron beam and counts the different
charges and out as the battery discharges. Normally,
battery - that is, one in which the electrolyte was
kinds of charged particles that are created when an
anodes in lithium-ion batteries are made of graphite,
made from solid material.
individual neutron happens to collide with one of the
but for this experiment, the researchers replaced the
atoms in the test material and annihilates it.
graphite with a tin alloy.
The researchers got around the problem by sealing their test battery in a special holding cell designed and
“Just like an MRI is the best way of seeing inside
Key to the experiment, said L Raymond Cao,
tested by Danny Liu, a doctoral student in chemistry
the human body without cutting it open, we believe
assistant professor of nuclear engineering, is that it was
and biochemistry at Ohio State. That’s how they were
that NDP is the best - and one of only a few - techniques
non-invasive, so researchers could get a true picture
able to measure lithium concentration in a truly typical
capable of taking a non-invasive look inside a lithium-
of battery function. Though NDP’s annihilation of
lithium-ion battery, containing electrolyte and all.
ion battery,” said Anne Co, assistant professor of
lithium atoms doesn’t sound very non-invasive, Cao
In the future, the team will try to identify the
chemistry and biochemistry and associate fellow at
explained that these low-energy neutron collisions
factors that cause lithium to become trapped in anodes
Ohio State’s Center for Automotive Research. The
very rarely happen and therefore couldn’t interfere
and investigate new materials that might lessen the
images they’ve obtained thus far are two-dimensional,
with the normal performance of the battery.
effect. Along the way, they hope to find ways to boost
but with further development, 3D imaging might be possible, she added.
“We could hit it with a trillion neutrons per square
overall charge capacity. Aside from battery studies,
centimetre and the beam would still only consume
the researchers say that NDP also holds promise for
Lithium-ion batteries are popular in cars and
one in a billion lithium atoms inside the battery,”
examining certain materials for solar cells and catalysts,
handheld electronics because they are light and
Cao said. “However, it is the capture of that one-in-
including materials that are used to treat nuclear waste.
powerful, though their charge capacity still fades
a-billion reaction that tells us where the lithium ions
over time.
are and how many.”
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The research has been published in the journal Angewandte Chemie International Edition.
LAB+LIFE SCIENTIST - October 2014 | 51