Tracking Hidden Highways to Build Better Batteries
Anyone who’s ever used a battery-powered device in Chicago (or anywhere else with a similar climate) is all too familiar with one particular problem: batteries slow down in the cold.
A new study published in Science by a group of American and Canadian researchers describes a new material that could help solve the battery problem.
Illinois Tech Research Professor of Chemistry James Kaduk played a key role in this discovery by answering a specific question: where are the lithium atoms?
Published in October, the paper, titled “Anion Sublattice Design Enables Superionic Conductivity in Crystalline Oxyhalides,” introduces a new solid electrolyte material called lithium tantalum oxychloride that shows promise for the next generation of lithium batteries. Lithium is the lightest metal, favored for use in batteries because its ions move easily, allowing energy to be stored and released efficiently.
Understanding how lithium moves through the material turned out to be essential to why it performs so well.
“My contribution is small but ends up being useful,” says Kaduk. “What really gets me excited is finding out where the atoms are.”
Kaduk’s task wasn’t straightforward. The primary tool he often uses to map atomic structures—X-ray diffraction—has trouble detecting lighter elements such as hydrogen and lithium, especially when they are surrounded by heavier elements including tantalum.
“Since X-rays scatter off electrons, lithium having only three electrons can be especially hard to find,” says Kaduk.
Instead of trying to find the lithium atoms directly, Kaduk used an indirect approach by looking for empty spaces where those atoms could exist. Since atoms can’t overlap, once the positions of the heavier atoms were known, Kaduk could then find small gaps between them that were large enough to accommodate lithium ions.
By gradually narrowing the size of his search, Kaduk identified a set of sites—open positions within the crystal structure where small particles can fit and move through—that could host lithium. Those sites sit close enough together to allow lithium ions to “hop” easily from one site to the next.
That detail proved to be critical. The structure revealed long, rigid chains of tantalum, oxygen, and chlorine that create open channels between them. Lithium ions diffuse through those channels, moving more efficiently than in current batteries along the length of the material. This process helps create better batteries because the more freely lithium ions can move through a structure, the better a battery performs.
With the lithium positions identified, the team then tested the structure using quantum mechanical calculations to confirm that the structure would remain stable.
“We apply what are called ‘density functional quantum mechanical techniques’ to optimize the structure,” Kaduk says. “In this case, the structure stayed very nearly the way it refined, so that provided some extra evidence for the correctness of the structure.”
The open pathways revealed by the structure help explain one of the material’s most promising properties: it conducts lithium ions well even at low temperatures. This property makes it especially valuable for applications ranging from electric vehicles to energy storage in cold climates.
While his role is just one part of a much larger international collaboration, Kaduk’s contribution helped turn an intriguing observation into a clearer understanding of how the material works, bringing researchers one step closer to designing better batteries.
For Kaduk, the reward comes from having solved that molecular puzzle.
“Being able to complete the job just based on some pretty simple ideas, that’s very satisfying,” says Kaduk. “Especially when you do the quantum mechanics calculations and see that they’re pretty happy with where these lithiums were, it gives you extra confidence.”
