Adding salt to a road before a winter storm changes when ice will form. Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have applied this basic concept to develop a new method of heating and cooling. The technique, which they have named “ionocaloric cooling,” is described in a paper published in the journal, Science.
Ionocaloric cooling takes advantage of how energy, or heat, is stored or released when a material changes phase – such as changing from solid ice to liquid water. Melting a material absorbs heat from the surroundings, while solidifying it releases heat. The ionocaloric cycle causes this phase and temperature change through the flow of ions (electrically charged atoms or molecules), which come from a salt.
Researchers hope that the method could one day provide efficient heating and cooling, which accounts for more than half of the energy used in homes, and help phase out current vapor compression systems, which use high-GWP refrigerants. Ionocaloric refrigeration would eliminate the risk of such gases escaping into the atmosphere by replacing them with solid and liquid components.
“The landscape of refrigerants is an unsolved problem: No one has successfully developed an alternative solution that makes stuff cold, works efficiently, is safe, and doesn’t hurt the environment,” said Drew Lilley, a graduate research assistant at Berkeley Lab and PhD candidate at UC Berkeley who led the study. “We think the ionocaloric cycle has the potential to meet all those goals if realized appropriately.”
The new ionocaloric cycle joins several other kinds of “caloric” cooling in development. Those techniques use different methods – including magnetism, pressure, stretching, and electric fields – to manipulate solid materials so that they absorb or release heat. Ionocaloric cooling differs by using ions to drive solid-to-liquid phase changes. Using a liquid has the added benefit of making the material pumpable, making it easier to get heat in or out of the system – something solid-state cooling has struggled with.
In demonstrating the technique experimentally, Lilley used a salt made with iodine and sodium, alongside ethylene carbonate, a common organic solvent used in lithium-ion batteries. Running current through the system moves the ions, changing the material’s melting point. When it melts, the material absorbs heat from the surroundings, and when the ions are removed and the material solidifies, it gives heat back. The first experiment showed a temperature change of 25°C using less than one volt, a greater temperature lift than demonstrated by other caloric technologies.
The ionocaloric team is continuing work on prototypes to determine how the technique might scale to support large amounts of cooling, improve the amount of temperature change the system can support, and improve the efficiency.
