Molecular paddlewheels propel sodium ions through next-generation batteries – BIOENGINEER.ORG

DURHAM, NC – Materials scientists at Duke University have unveiled paddle wheel-like molecular dynamics that help push sodium ions through a class of fast-developing solid state batteries. The insights should guide researchers as they seek 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.

DURHAM, NC – Materials scientists at Duke University have unveiled paddle wheel-like molecular dynamics that help push sodium ions through a class of fast-developing solid state batteries. The insights should guide researchers as they seek 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 Nov. 10 in the journal Energy and Environmental Science.

Rechargeable batteries generally work by moving electrons through external wires from one side to the other and back again. To balance this transfer of energy, electrically charged atoms called ions, such as lithium ions, move within the battery via a chemical substance called electrolyte. How fast and easy these ions can make their trip plays a key role in how fast a battery can charge and how much energy it can provide in a given period of time.

“Most researchers still tend to focus on how a solid electrolyte crystalline framework could allow ions to pass quickly through a solid battery,” said Olivier Delaire, associate professor of mechanical engineering and materials science at Duke. “In recent years, the field has begun to realize that the molecular dynamics of how the atoms can jump around are important too.”

Lithium ion batteries have long been the dominant technology used for most commercial applications that require energy storage, from small smart watches to huge data centers. Although they have been very successful, lithium ion batteries have several disadvantages which make new technologies more attractive for some applications.

For example, lithium ion batteries have a liquid electrolyte inside which, while extremely efficient in allowing lithium ions to travel quickly through it, is also highly flammable. As the market continues to grow exponentially, there are concerns about being able to extract 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 support the huge demand for energy storage, and one of the leading candidates is sodium-ion batteries. Although not as dense or fast as their lithium-ion batteries, the technology has many potential benefits. Sodium is much cheaper and more abundant than lithium. The materials needed for their constituent parts are also much more commonly available. And by replacing the liquid electrolyte with a solid state electrolyte instead, researchers can build all-solid batteries that promise to be more energy-intensive, more stable and less likely to ignite than the rechargeable batteries is currently available.

These advantages lead researchers to consider sodium-ion batteries instead of potential lithium-ion batteries in applications that are not limited by space and speed requirements as thin smartphones or light electric vehicles. For example, big data centers or other buildings that require large amounts of energy over a long period of time are good candidates.

“Overall, this is a very active area of ​​research where people are racing towards the next generation of batteries,” said Delaire. “However, there is not a strong enough basic understanding of what materials work well at room temperature or why. We provide insights into the atomistic dynamics that allow one popular candidate to transport his / her sodium ions quickly and efficiently. ”

The material studied in these experiments is sodium thiophosphate, No3PS4. Researchers already knew that the crystalline structure of the phosphorus and sulfur atoms creates a one-dimensional tunnel for sodium ions to pass through. But as Delaire explains, no one had looked at whether the movement of nearby atoms also played 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 precise movements of the atoms. The results showed that the pyramid-shaped phosphorus-sulfur PS4 units that frame the tunnels twist and turn in place and almost act as paddle wheels 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 really do and show that, while this cartoon has some truth, it is also much more complex.”

The researchers confirmed the neutron scattering results by computationally modeling the atomic dynamics at the National Scientific Computing Center for Energy Research. The team used an engineering learning method to capture the potential energy surface where the atoms vibrate and move. Because the quantum mechanical forces did not need to be recalculated at each point in time, the method accelerated the calculations to several orders of magnitude.

With the new insights into the atomic dynamics of a single sodium-ion electrolyte and the new approach to rapidly model their behavior, Delaire hopes the results will help push the field forward faster, as No3PS4 and beyond.

“Although it is one of the leading materials due to its high ionic conductivity, a slightly different version is already being followed that uses antimony instead of phosphorus,” said Delaire. “But despite how fast 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’s EPSCOR RII Track 4 award (No. 2033397).

AWARD: “Dynamics of No Fast and Anharmonic Diffusion Phones in Superionic Na3PS4.” Mayanak K. Gupta, Jingxuan Ding, Naresh C. Osti, Douglas L. Abernathy, William Arnold, Hui Wang, Zachary Hood and Olivier Delaire. Energy Science and the Environment, November 10, 2021. DOI: 10.1039 / D1EE01509E


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