Flexing crystalline structures provide path to a solid energy future
Machine learning approach opens insights into an entire class of
materials being pursued for solid-state batteries

Date:
May 23, 2023
Source:
Duke University
Summary:
Researchers have uncovered the atomic mechanisms that make a
class of compounds called argyrodites attractive candidates for
both solid-state battery electrolytes and thermoelectric energy
converters. The discoveries -- and the machine learning approach
used to make them - - could help usher in a new era of energy
storage for applications such as household battery walls and
fast-charging electric vehicles.


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FULL STORY ==========================================================================
A team of researchers at Duke University and their collaborators
have uncovered the atomic mechanisms that make a class of compounds
called argyrodites attractive candidates for both solid-state battery electrolytes and thermoelectric energy converters.

The discoveries -- and the machine learning approach used to make them --
could help usher in a new era of energy storage for applications such
as household battery walls and fast-charging electric vehicles.

The results appeared online May 18 in the journal Nature Materials.

"This is a puzzle that has not been cracked before because of how big and complex each building block of the material is," said Olivier Delaire, associate professor of mechanical engineering and materials science
at Duke.

"We've teased out the mechanisms at the atomic level that are causing
this entire class of materials to be a hot topic in the field of
solid-state battery innovation." As the world moves toward a future
built on renewable energy, researchers must develop new technologies for storing and distributing energy to homes and electric vehicles. While
the standard bearer to this point has been the lithium-ion battery
containing liquid electrolytes, it is far from an ideal solution given
its relatively low efficiency and the liquid electrolyte's affinity for occasionally catching fire and exploding.

These limitations stem primarily from the chemically reactive liquid electrolytes inside Li-ion batteries that allow lithium ions to move
relatively unencumbered between electrodes. While great for moving
electric charges, the liquid component makes them sensitive to high temperatures that can cause degradation and, eventually, a runaway
thermal catastrophe.

Many public and private research labs are spending a lot of time and
money to develop alternative solid-state batteries out of a variety of materials. If engineered correctly, this approach offers a much safer
and more stable device with a higher energy density -- at least in theory.

While nobody has yet discovered a commercially viable approach to
solid-state batteries, one of the leading contenders relies on a
class of compounds called argyrodites, named after a silver containing
mineral. These compounds are built from specific, stable crystalline
frameworks made of two elements with a third free to move about the
chemical structure. While some recipes such as silver, germanium and
sulfur are naturally occurring, the general framework is flexible enough
for researchers to create a wide array of combinations.

"Every electric vehicle manufacturer is trying to move to new solid-state battery designs, but none of them are disclosing which compositions
they're betting on," Delaire said. "Winning that race would be a game
changer because cars could charge faster, last longer and be safer all
at once." In the new paper, Delaire and his colleagues look at one
promising candidate made of silver, tin and selenium (Ag8SnSe6). Using
a combination of neutrons and x-rays, the researchers bounced these
extremely fast-moving particles off atoms within samples of Ag8SnSe6to
reveal its molecular behavior in real-time.

Team member Mayanak Gupta, a former postdoc in Delaire's lab who is now a researcher at the Bhabha Atomic Research Center in India, also developed
a machine learning approach to make sense of the data and created a computational model to match the observations using first-principles
quantum mechanical simulations.

The results showed that while the tin and selenium atoms created a
relatively stable scaffolding, it was far from static. The crystalline structure constantly flexes to create windows and channels for the
charged silver ions to move freely through the material. The system,
Delaire said, is like the tin and selenium lattices remain solid while
the silver is in an almost liquid-like state.

"It's sort of like the silver atoms are marbles rattling around about
the bottom of a very shallow well, moving about like the crystalline
scaffold isn't solid," Delaire said. "That duality of a material living
between both a liquid and solid state is what I found most surprising."
The results and, perhaps more importantly, the approach combining
advanced experimental spectroscopy with machine learning, should help researchers make faster progress toward replacing lithium-ion batteries
in many crucial applications. According to Delaire, this study is just
one of a suite of projects aimed at a variety of promising argyrodite
compounds comprising different recipes. One combination that replaces
the silver with lithium is of particular interest to the group, given
its potential for EV batteries.

"Many of these materials offer very fast conduction for batteries while
being good heat insulators for thermoelectric converters, so we're systematically looking at the entire family of compounds," Delaire
said. "This study serves to benchmark our machine learning approach
that has enabled tremendous advances in our ability to simulate these
materials in only a couple of years. I believe this will allow us to
quickly simulate new compounds virtually to find the best recipes these compounds have to offer." This work was supported by the Guangdong Basic
and Applied Basic Research Foundation (2021B1515140014), the National
Natural Science Foundation of China (52101236, U1732154, T2125008,
52272006), the Institute of High Energy Physics, Chinese Academy of
Science (E15154U110), the Open project of Key Laboratory of Artificial Structures and Quantum Control (2021-05), the U.S. National Science
Foundation (DMR-2119273), the "Shuguang Program" from the Shanghai
Education Development Foundation and Shanghai Municipal Education
Commission, the Australia Research Council (DP210101436).

* RELATED_TOPICS
o Matter_&_Energy
# Batteries # Physics # Spintronics # Materials_Science
# Energy_and_Resources # Civil_Engineering #
Engineering_and_Construction # Energy_Technology
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o Battery_electric_vehicle o Fuel_cell o Energy o Wind_turbine
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========================================================================== Story Source: Materials provided by Duke_University. Original written
by Ken Kingery. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Qingyong Ren, Mayanak K. Gupta, Min Jin, Jingxuan Ding, Jiangtao Wu,
Zhiwei Chen, Siqi Lin, Oscar Fabelo, Jose Alberto
Rodri'guez-Velamaza'n, Maiko Kofu, Kenji Nakajima, Marcell
Wolf, Fengfeng Zhu, Jianli Wang, Zhenxiang Cheng, Guohua Wang,
Xin Tong, Yanzhong Pei, Olivier Delaire, Jie Ma. Extreme phonon
anharmonicity underpins superionic diffusion and ultralow thermal
conductivity in argyrodite Ag8SnSe6. Nature Materials, 2023; DOI:
10.1038/s41563-023-01560-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230523123807.htm

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