Engineering Tomorrow’s Batteries Through Molecular Modeling

Duke Engineering launched the Beyond the Horizon initiative to provide interdisciplinary teams with substantial investment to begin pursuing extremely high-risk, high-reward projects that have the potential for deep, transformative societal impact. Three proposals were selected for an initial round of funding that will play key roles in shaping Duke Engineering’s future research and teaching profile. Each play to the school’s unique strengths and hold the promise of helping to define the future of their respective fields.

Lithium-ion batteries have become so commonplace in today’s society that the two terms are practically synonymous. While a few people were already using rechargeable AA and AAA batteries in the 80s and 90s, it wasn’t until lithium-ion’s unrivaled efficiency began powering laptops and cell phones that simply recharging devices became the norm rather than the exception.

But the technology does have its drawbacks. The term lithium-ion refers to the batteries’ electrolyte—the inner substance that allows charged atoms called ions to easily travel from one end to the other. In this case, that electrolyte is a liquid mixture of lithium salts and organic solvents. While effective, the electrolyte is also extremely flammable and has been known to catch fire and endanger lives. Lithium is also a rare metal, making its few sources a point of global contention and uncertainty.

Many researchers around the world are working to engineer a new type of electrolyte that is just as efficient and powerful as lithium-ion technology but is also much more stable and abundant. One such approach is solid-state sodium-ion batteries.

While not as energetically dense as its lithium-ion counterpart, sodium-ion 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, researchers can build all-solid sodium batteries that promise to be more energy dense, more stable and less likely to ignite.

“This is generally a very active area of research where people are racing toward the next generation of batteries,” said Olivier Delaire, associate professor of mechanical engineering and materials science at Duke. “However, there is not a sufficiently strong fundamental understanding of what materials work well at room temperature or why.”

Delaire is leading a new “Beyond the Horizon” project that seeks to bridge that gap in understanding and make sodium-ion batteries a reality. By better understanding how these materials transport ions at a molecular level, he hopes to enable the control and optimization of their thermodynamic and transport properties.

To do this, Delaire is teaming with Johann Guilleminot, the Paul Ruffin Scarborough Associate Professor of Mechanical Engineering and Materials Science at Duke, who is a leading expert in developing computational models that incorporate random effects into their calculations. His expertise will help sodium-ion simulations become more predictive while characterizing the battery materials’ inner workings to solve current roadblocks.

“Such materials present numerous challenges in terms of multiscale modeling and characterization, with many unknowns – such as grain interfaces – impacting the overall performance of the system. This constitutes the perfect playground for the uncertainty quantification methods we are developing at Duke”, said Guilleminot. “By quantifying errors and uncertainties, we aim to advance new predictive tools supporting robust analysis and design.”

These inner workings will also be investigated and tested with the help of Miaofang Chi, professor of mechanical engineering and materials science at Duke, who is a world leader in probing delicate next-generation energy materials at the atomic level through innovative cryo-electron microscopy techniques.

The team will also rely on collaborators at Oak Ridge National Laboratory, which houses one of the world’s most powerful neutron sources capable of capturing the details of atomic phenomena in action.

To date, there have been no reported nanoscopic studies of these sodium-conducting materials. Better understanding and predictions of sodium solid-state behaviors, bridging the atomic scale to the battery pack, are critically required to make these dream batteries a reality.

“We are working with material compositions that are the current best candidates for ‘real world’ sodium solid-state batteries, and some of our samples are from our collaborators who launched battery startups using this technology,” Delaire said. “We are working on improving the materials to make these solid-state sodium batteries competitive.”

If successful, the project will then use the ingenuity of Duke undergraduate students to engineer a prototype electric vehicle with the new sodium-ion technology as a demonstration of its potential.