Molecular paddlewheels propel sodium ions through next-generation
batteries
Insights into the atomistic dynamics of emerging solid-state batteries
will help speed their evolution

Date:
January 11, 2022
Source:
Duke University
Summary:
Materials scientists have revealed paddlewheel-like molecular
dynamics that help push sodium ions through a quickly evolving class
of solid- state batteries. The insights should guide researchers
in their pursuit of a new generation of sodium-ion batteries to
replace lithium-ion technology in a wide range of applications
such as data centers and home energy storage.



FULL STORY ========================================================================== Materials scientists at Duke University have revealed paddlewheel-like molecular dynamics that help push sodium ions through a quickly evolving
class of solid-state batteries. The insights should guide researchers
in their pursuit of a new generation of sodium-ion batteries to replace lithium-ion technology in a wide range of applications such as data
centers and home energy storage.


==========================================================================
The results appeared online November 10 in the journal Energy &
Environmental Science.

In general, rechargeable batteries work by moving electrons through
external wires from one side to the other and back again. To balance
this transfer of energy, atoms with an electric charge called ions, such
as lithium ions, move within the battery through a chemical substance
called an electrolyte. How quickly and easily these ions can make their
journey plays a key role in how fast a battery can charge and how much
energy it can provide in a given amount of time.

"Most researchers still tend to focus on how the crystalline framework of
a solid electrolyte might allow ions to quickly pass through an all-solid battery," said Olivier Delaire, associate professor of mechanical
engineering and materials science at Duke. "In the last few years, the
field has begun to realize that the molecular dynamics of how the atoms
can jump around are important as well." Lithium ion batteries have long
been the dominant technology used for most all commercial applications requiring energy storage, from tiny smart watches to gigantic data
centers. While they have been extremely successful, lithium ion batteries
have several drawbacks that make new technologies more attractive for
certain applications.

For example, lithium ion batteries have a liquid electrolyte inside that,
while extremely efficient at allowing lithium ions to travel quickly
through, is also extremely flammable. As the market continues to grow exponentially, there are worries about being able to mine enough lithium
from the relatively limited global deposits. And some of the rare earth elements used in their construction -- such as cobalt and manganese --
are even rarer and are only mined in a few locations around the world.



==========================================================================
Many researchers believe that alternative technologies are necessary to supplement the skyrocketing demand for energy storage, and one of the
leading candidates is sodium-ion batteries. While not as energetically
dense or fast as their lithium-ion batteries, the technology has many
potential advantages.

Sodium is much cheaper and more abundant than lithium. The materials
required for their constituent parts are also much more commonly
available. And by replacing the liquid electrolyte with a solid-state electrolyte material instead, researchers can build all-solid batteries
that promise to be more energy dense, more stable and less likely to
ignite than currently available rechargeable batteries.

These advantages lead researchers to consider sodium-ion batteries a potentially viable replacement for lithium-ion batteries in applications
that are not as constrained by space and speed requirements as thin smart phones or light electric vehicles. For example, large data centers or
other buildings that require large amounts of energy over a long period
of time are good candidates.

"This is generally a very active area of research where people are racing toward the next generation of batteries," said Delaire. "However, there
is not a sufficiently strong fundamental understanding of what materials
work well at room temperature or why. We're providing insights into the atomistic dynamics that allow one popular candidate to transport its
sodium ions quickly and efficiently." The material studied in these experiments is a sodium thiophosphate, Na3PS4.

Researchers already knew that the crystalline structure of the phosphorus
and sulfur atoms creates a one-dimensional tunnel for sodium ions to
travel through. But as Delaire explains, nobody had looked to see whether
the movement of neighboring atoms also plays an important role.

To find out, Delaire and his colleagues took samples of the material
to Oak Ridge National Laboratory. By bouncing neutrons off the atoms
at extremely fast rates, researchers captured a series of snapshots of
the atoms' precise motions. The results showed that the pyramid-shaped phosphorus-sulfur PS4 units that frame the tunnels twist and turn in place
and almost act as paddlewheels that help the sodium ions move through.



========================================================================== "This process has been theorized before, but the arguments are usually
made in a cartoonish way," said Delaire. "Here we show what the atoms
are actually doing and show that, while there's a bit of truth to this
cartoon, it's also much more complex." The researchers confirmed the neutron-scattering results by computationally modeling the atomic dynamics
at the National Energy Research Scientific Computing Center. The team
used a machine learning approach to capture the potential energy surface
in which the atoms vibrate and move. By not needing to recalculate the
quantum mechanical forces at every point in time, the approach sped up
the calculations by several orders of magnitude.

With the new insights into the atomistic dynamics of one sodium-ion
electrolyte and the new approach to quickly modeling their behavior,
Delaire hopes the results will help push the field forward more quickly,
from Na3PS4 and beyond.

"Even though this is one of the leading materials because of its high
ionic conductivity, there's already a slightly different version being
pursued that uses antimony instead of phosphorus," Delaire said. "But
despite the speed at which the field is moving, the insights and tools
we present in this paper should help researchers make better decisions
about where to go next." This research was supported by the Department
of Energy (DE-SC0019978, DE-AC02- 05CH11231, DE-AC02-06CH11357) and the National Science Foundation EPSCOR RII Track 4 award (No. 2033397).

========================================================================== Story Source: Materials provided by Duke_University. Original written
by Ken Kingery. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mayanak K. Gupta, Jingxuan Ding, Naresh C. Osti, Douglas
L. Abernathy,
William Arnold, Hui Wang, Zachary Hood, Olivier Delaire. Fast
Na diffusion and anharmonic phonon dynamics in superionic
Na3PS4. Energy & Environmental Science, 2021; 14 (12): 6554 DOI:
10.1039/D1EE01509E ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220111193040.htm

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