Lab+Life Scientist Oct 2014

Page 51

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.” |

The research has been published in the journal Angewandte Chemie International Edition.

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