A team led by the University of Chicago's Pritzker School of Molecular Engineering has discovered a breakthrough in basic science by discovering a material that shrinks when heated and expands under pressure.

What expands when squeezed and shrinks when heated, both to change scientists' basic understanding of materials and to restore old EV batteries to new performance?

It's not a mystery – it's a remarkable new material 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 collaboration, the team has discovered materials that exhibit negative thermal expansion properties in a metastable, oxygen-redox active state.

To put it simply, the materials developed by these researchers seem to go against traditional expectations based on thermodynamics. In general, the reaction of stable materials to heat, pressure, or electricity is predictable. However, in the newly discovered metastability, these reactions become reversed, behaving in complete opposition to traditional norms.

"When you heat the material, the volume doesn't change. When heated, the material shrinks rather than expands," said Shirley Meng, a professor of molecular engineering at the PME Liew Family at the University of Chicago and director of the Energy Technology Initiative at the newly formed Institute for Climate and Sustainable Growth. "We believe that we can adjust the properties of these materials through redox chemistry. This can lead to very exciting applications. ”

Their findings were published in the journal Nature.

"One of the goals is to bring these materials from research to industry, potentially developing new batteries with higher specific energies," said Bao Qiu, a visiting scholar at the University of California, San Diego, from the Ningbo Institute of Materials Technology and Engineering (NIMTE).

In addition to the myriad new technologies that this discovery has brought about, this research represents a progress in pure science. For Shirley Meng, it's even more exciting.

"This has changed our understanding of basic science," Shirley Meng said. "Our work has been guided by the University of Chicago model, which fosters inquiry and the development of knowledge."

Buildings, batteries, and "crazy ideas"

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

"I would say that zero thermal expansion materials are a dream," said the University of Chicago PME Research Associate. Prof. Minghao Zhang is the co-corresponding author of this paper. "Take each building as an example. You don't want the materials that make up the different components to change volume too often. ”

But heat is just one form of energy. To test how these materials react to mechanical energy, they compressed them to the level of gigapascals – a pressure level so high that it is usually only used when discussing tectonic plate activity. They found the so-called "negative compressibility".

"Negative compressibility is like negative thermal expansion," says Professor Zhang. "If you compress a material particle from all directions, as you can imagine, it will naturally shrink. But this material expands. ”

Professor Zhang said that a material that can resist high temperatures or pressure could realize some previously theoretical "crazy ideas". He gave the example of a structural battery, where the bulkhead of an all-electric aircraft doubles as a battery wall, helping to create a lighter, more efficient aircraft. These new materials can protect battery cells from temperature and pressure changes at different altitudes, making the sky no longer the limit of this new technology.

Give your old electric car a new look

As with heat and pressure, the response of metastable materials to electrochemical energy (voltage) is reversed.

"This is not only an important scientific discovery, but also very applicable to battery research," Professor Zhang said. "When we use voltage, we drive the material back to its original state. We recycle the batteries. ”

To understand metastability, imagine a ball on a mountain. The ball is unstable at the top of the hill. It will roll down. It is stable at the foot of the mountain. It doesn't roll. Metastability is in between, a ball near the top of a hill but perched on a piece of turf. This metastability can be quite persistent – diamond, for example, is the metastable form of graphite. But energy is needed to push the metastable substance out of its "turf" so that it can roll back to a steady state.

"In order to get a material back to a steady state from metastability, you don't always have to use thermal energy," says Prof. Zhang. "You can use any kind of energy to drive the system."

This opens the way for resetting aging EV batteries. For example, an electric car that can run 200 miles on a single charge can only travel 0 or 0 miles before charging after years of driving. Using electrochemical drive to push these materials back to their stable state can restore the car to the range it had when it was new.

"You don't have to send the battery back to the manufacturer or any supplier. You just have to do this voltage start-up," Professor Zhang said. "Well, your car will be a new car. Your battery will be a new one. ”

The next step, the researchers say, is to continue using redox chemistry to examine materials and "extract critical points", exploring the boundaries of this new frontier of basic research.