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Jason Graetz, left, and Jiajun Chen at NSLS beamline X14 A. Photo: Brookhaven National Laboratory.
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A team of Brookhaven National Laboratory researchers has
fabricated a new transparent chemical reactor vessel that may give scientists
in many fields a window into real-time chemistry. Scientists in the Lab's
Energy Storage Group recently used the transparent reactor to study the
synthesis of lithium iron phosphate for rechargeable batteries. The technique,
described in a paper published in the Journal of Physical Chemistry Letters,
allowed them to monitor the reactions in real time and pinpoint the conditions
for producing a defect-free material.
Eliminating defects from materials used in lithium-ion batteries
is essential to making them attractive for applications such as electric
vehicles capable of driving hundreds of miles on a single charge. They are
already favored compared to other rechargeables for portable electronics
because they are lightweight, can store more energy for longer periods of time,
and can handle more cycles of use and recharge without deteriorating.
A stumbling block for their use in larger applications like
electric vehicles has been cost. A big part of that cost comes from processing
the lithium iron phosphate material to produce a suitable, defect-free material
using the conventional synthesis method.
"We wanted to identify the mildest conditions necessary to make
defect-free lithium ion phosphate," says Brookhaven Materials Scientist Jason
Graetz, leader of the Energy Storage Group.
"Generally we make battery materials in a stainless steel
reactor. There's no window, no way to see the reaction—we just see what goes in
and what comes out. So we designed a reactor made out of a glass capillary and,
using synchrotron X-ray diffraction, we can not only probe the precursors—the initial
parts of the reaction—but we can also track what happens as the reaction takes
place."
The scientists started with a slurry of both solid and liquid
precursors, placed them in the glass capillary reaction vessel, and placed the
whole setup in beamline X14A at the National Synchrotron Light Source (NSLS), a
source of extremely bright X-rays and other forms of light for probing
materials' structure and properties. NSLS researchers Haiyan Chen and Jianming
Bai helped to fabricate the novel reactor. As the X-rays pass through the
transparent reaction vessel, they bounce off, or get diffracted by, the atoms
in the reactor, producing a pattern that reveals the atomic structure of the
various materials in the reactor and how they change as the reaction takes
place.
"Because we're getting the diffraction pattern, we can learn
something about the structure," Graetz says. "By analyzing these diffraction
patterns, we can also learn about the defect concentration in the material and
can track the defects in real time as a function of temperature or time in the
reaction."
By doing a series of experiments at different temperatures and
different lengths of time, the scientists can identify where the defects are
and where they start to disappear, allowing them to pinpoint the lowest
temperature and the simplest reaction to produce a defect-free material.
"This method has proven to be a cost-effective and industrial
viable method for manufacturing battery materials," says Brookhaven Materials
Scientist and lead (corresponding) author on the paper, Jiajun Chen. "We're
trying to find the relationship between the synthesis conditions—pressure,
temperature, time, concentration of solution—and how that relates to the
material morphology, the defect concentration, and the structure. Establishing
those relationships often can take a very long time. But with this type of
technique we can establish those very quickly."
By identifying the ideal conditions for producing defect-free
lithium iron phosphate, this research should eliminate the need for further
processing, thus reducing the cost of the most expensive part of lithium-ion
batteries.
This battery research is just one example of a problem that can
be tackled with the new transparent reactor. Other candidate materials for
batteries as well as for other applications can be made and tested more quickly
than by conventional methods. When reactions can be observed in real time,
researchers can save both time and money while developing needed 21st century
technologies in energy and other important fields.
SOURCE
