In a Fluid
Interface Reactions, Structures and Transport Center project to probe a
battery’s
atomic activity
during its first charging cycle, Robert Sacci and colleagues used the
Spallation Neutron
Source’s vibrational spectrometer to gain chemical information.
Image credit: Oak
Ridge National Laboratory, U.S. Dept. of Energy; photographer Genevieve Martin.
(January 20, 2016) Rechargeable
batteries power everything from electric vehicles to wearable gadgets, but
obstacles limit the creation of sleeker, longer-lasting and more efficient
power sources. Batteries produce electricity when charged atoms, known as ions,
move in a circuit from a positive end (anode) to a negative end (cathode)
through a facilitating mix of molecules called an electrolyte.
Scientists at the Department of Energy’s Oak Ridge National
Laboratory are improving the lifetimes of rechargeable batteries that run on
lithium, a small atom that can pack tightly into graphite anode materials. The
valuable ions are depleted as a battery charges, and they are also lost to the
formation of a thin coating on a battery’s anode during initial charging. ORNL
researchers used two of the most powerful neutron science facilities in the
world to try to understand the dynamics behind this phenomenon.
In a paper published in the Journal of Physical Chemistry C,
the ORNL researchers focused on the spontaneous growth of the thin coating,
called the solid-electrolyte interphase (SEI). This nanoscale coating protects
and stabilizes the new battery, but it comes at a cost. The electrolyte, a
mixture of molecules composed of hydrogen, carbon, lithium and oxygen, is
forced to break down to form this film.
“The big picture is to increase the amount of lithium we can
put into a battery,” said Robert Sacci, lead author and Materials Science and
Technology Division scientist. “When you develop a battery, you put in excess
lithium because a lot of that lithium gets eaten up or taken away from
usability to form this thin film.”
Sacci and colleagues used beams of subatomic particles
called neutrons to delve into a battery’s atomic reactivity during its first
charging cycle. Neutrons were necessary because they can easily enter
three-dimensional structures and are sensitive to changes in hydrogen
concentration, a major component of electrolytes.