A phase-change material, or PCM, releases or absorbs significant energy when it changes states, such as from solid to liquid or gas — like an ice cube melting. Phase-change materials are gaining traction in the cleantech space as components of energy-efficient heating and cooling technologies. But common technical challenges have held back their widespread use so far.

Scientists at the University of Illinois Urbana-Champaign say they have overcome a major hurdle: most systems either have high energy density but low power density, or high power density but low energy density. 

“Classically, the way people have been handling this — for well over thirty, forty years — is they mix the two. What they do is create composites where some fraction of the volume is metal, or a metal matrix, to help conduct heat and achieve good power density,” Nenad Miljkovic, a UIUC associate professor, said in a news release. “But the trade-off is they are losing storage material, and so they sacrifice energy density in the process.”

The researchers found a way to decouple the two factors by using a simple method: pressure. 

Previously, solid phase-change materials were melted by putting them next to a stationary heat source. But as the material melts, the side closest to the heat recedes and the remaining material’s distance from the heat grows. The system therefore becomes less efficient as the PCM melts and power density degrades.

The UIUC team’s approach applies pressure to keep the PCM close to the heat source as it melts. They liken this method to pressing on a stick of butter in a hot pan to help it melt.

The researchers say the beauty of their contribution is the simplicity and ease of the pressure approach. They believe it will make thermal energy storage more viable for a variety of everyday applications.

“Our work makes it possible to achieve thermal storage at a high power not previously possible,” said study co-author William King. “We really need high power to make it really compelling and useful for demanding applications like electric vehicles, power generation, and data centers.”