There
is an ever-increasing need for advanced batteries for portable
electronics, such as phones, cameras, and music players, but also to
power electric vehicles and to facilitate the distribution and storage
of energy derived from renewable energy sources. But, once a battery
fails, there are no corrective measures—how do you look inside a battery
without destroying it?
Now,
researchers at Cambridge University, Stony Brook University, and New
York University have developed methodology, based on magnetic resonance
imaging (MRI), to do just that. Their technique, which is described in
the journal Nature Materials, also creates the possibility of improving
battery performance and safety by serving as a diagnostic of its
internal workings.
MRI
has been extremely successful in the medical field for visualizing
disorders and assessing the body’s response to therapy. However, MRI is
not typically used in the presence of a lot of metal, a primary
component in many batteries. This is because conducting surfaces
effectively block the radio frequency fields that are used in MRI to see
beneath surfaces or inside the human body.
The
researchers, however, turned this limitation into a virtue. Because
radio frequency fields do not penetrate metals, one can actually perform
very sensitive measurements on the surfaces of the conductors. In the
case of the popular lithium-ion batteries, for example, the team was
able to directly visualize the build-up of lithium metal deposits on the
electrodes after charging the battery. Such deposits can also detach
from the surface, eventually leading to overheating, battery failure,
and—in some cases—to fire or explosion.
Visualizing
small changes on the surface of the batteries’ electrodes allows, in
principle, for the testing of many different battery designs and
materials under normal operating conditions.
The
work is the result of a collaboration between Clare Grey, associate
director of the Northeastern Center for Chemical Energy Storage and a
professor at Cambridge and Stony Brook universities, and Alexej
Jerschow, a professor in the Department of Chemistry at New York
University who heads a multi-disciplinary MRI research laboratory.
“New
electrode and electrolyte materials are constantly being developed, and
this non-invasive MRI technology could provide insights into the
microscopic processes inside batteries, which hold the key to eventually
making batteries lighter, safer, and more versatile,” said Jerschow.
“Both electrolyte and electrode surfaces can be visualized with this
technique, thus providing a comprehensive picture of the batteries’
performance-limiting processes.”
“MRI
is exciting because we are able to identify where the chemical species
inside the battery are located without having to take the battery apart,
a procedure which to some degree defeats the purpose,” added Grey. “The
work clearly shows how we can use the method to identify where lithium
deposits form on metal electrodes. The resolution is not yet where we
want it to be and we would like to extend the method to much larger
batteries, but the information that we were able to get from these
measurements is unprecedented.”
The
project’s other researchers were: S. Chandrashekar, a postdoctoral
fellow at both Stony Brook and New York Universities, Nicole Trease, a
postdoctoral fellow at Stony Brook University, and Hee Jung Chang, a
Stony Brook University graduate student.
“We
still have some way to go to make the images better resolved, and make
imaging time shorter,” Chandrashekar noted, “We feel that with this
work, we have made the field wide open for interesting applications.”
The
research team also envisions that the method could lead to the study of
irregularities and cracks on conducting surfaces in the materials
sciences field. In addition, they add, the methods developed here could
be highly valuable in the quest for enhanced battery performance and in
the evaluation of other electrochemical devices, such as fuel cells.
The research was supported by grants from the U.S. Department of Energy and the National Science Foundation