A team led by UChicago Pritzker Molecular Engineering has discovered materials that defy convention, shrinking when heated and expanding under pressure, marking a breakthrough in fundamental science.

What expands when crushed, shrinks when heated, and could both transform scientists’ fundamental understanding of materials and restore old EV batteries to like-new performance?

This isn’t a riddle—it’s a remarkable new class of materials discovered by battery researchers at the University of Chicago’s Pritzker School of Molecular Engineering (UChicago PME) in collaboration with visiting scientists from the University of California, San Diego. Through their ongoing research partnership, the team uncovered materials exhibiting negative thermal expansion properties in metastable, oxygen-redox active states.

In simpler terms, these researchers developed materials that appear to defy traditional expectations based on thermodynamics. Typically, stable materials respond predictably to heat, pressure, or electricity. However, in the newly identified metastable states, these reactions become inverted, behaving exactly opposite to conventional norms.

“When you heat the materials, there’s no volume change. When heated, the material shrinks instead of expanding,” said UChicago PME Liew Family Professor in Molecular Engineering Shirley Meng, who also serves as the faculty director for Energy Technology Initiative of the newly launched Institute for Climate and Sustainable Growth. “We think we can tune these materials’ properties through redox chemistry. That can lead to very exciting applications.”

Their results were published in Nature.

“One of the goals is bringing these materials from research to industry, possibly developing new batteries with higher specific energy,” said co-first author Bao Qiu, a visiting scholar at UC San Diego from the Ningbo Institute of Materials Technology & Engineering (NIMTE).

Beyond the myriad new technologies enabled by this discovery, the research represents an advance in pure science. To Meng, that is even more exciting.

“This changes our understanding of fundamental science,” Meng said. “Our work has been guided by UChicago’s model, a model that promotes inquiry and knowledge for its own sake.”

Buildings, batteries, and “wild ideas”

By finely tuning the ways these materials react to heat and other forms of energy, researchers could create materials with zero thermal expansion. This could revolutionize areas such as construction.

“Zero-thermal-expansion materials are the dream, I would say,” said UChicago PME Research Assoc. Prof. Minghao Zhang, a co-corresponding author of the work. “Take every single building, for example. You don’t want the materials making up different components to change volume that often.”

But heat is only one form of energy. To test how the materials react to mechanical energy, they compressed it on the gigapascal level – a pressure level so high it is usually reserved for discussing tectonic plate activity. They found what they call “negative compressibility.”

“Negative compressibility is just like negative thermal expansion,” Zhang said. “If you compress a particle of the material in every direction, you will imagine, naturally, it will shrink. But this material, it will expand.”

A material tuned to resist heat or pressure could enable some previously theoretical “wild ideas,” Zhang said. He gave the example of structural batteries where an EV airplane’s walls double as the battery walls, helping create lighter, more efficient aircraft. These new materials could keep the battery components safe from the changes in temperature and pressure seen at different altitudes, making the sky no longer the limit for this new technology.

Making old EVs like new

As with heat and pressure, the metastable materials’ reaction to electrochemical energy – voltage – is also flipped.

“This is important not only as a scientific discovery, but very applicable for battery research,” Zhang said. “When we use the voltage, we drive the material back to its pristine state. We recover the battery.”

To understand metastability, picture a ball on a hill. The ball is unstable at the top of the hill. It will roll down. It’s stable at the bottom of the hill. It won’t roll up. Metastable is in between, a ball near the top of the hill, but nestled in a divot. That metastable state can be quite durable – diamonds are a metastable form of graphite, for example. But energy is needed to push a metastable material out of its “divot” so it can roll back to its stable state.

“To drive the materials back from the metastable state to a stable state, you don’t have to always use heat energy,” Zhang said. “You can use any sort of energy to drive the system back.”

This sets a path toward resetting aging EV batteries. After years on the road, an electric car that once got, for example, 400 miles to a charge, will drive only 300 or 200 miles before needing to plug in. Using the electrochemical driving force to push the materials into their stable states would return the car to the mileage it saw when new.

“You don’t have to send the battery back to the manufacturer or to any vendors. You just do this voltage activation,” Zhang said. “Then, your car will be a new car. Your battery will be a new battery.”

Bao said the next steps are to continue to use redox chemistry to examine the materials and “pull out the key points,” exploring the boundaries of this new area of fundamental research.

Reference: “Negative thermal expansion and oxygen-redox electrochemistry” by Bao Qiu, Yuhuan Zhou, Haoyan Liang, Minghao Zhang, Kexin Gu, Tao Zeng, Zhou Zhou, Wen Wen, Ping Miao, Lunhua He, Yinguo Xiao, Sven Burke, Zhaoping Liu and Ying Shirley Meng, 16 April 2025, Nature.
DOI: 10.1038/s41586-025-08765-x