Cracking the code of ice batteries: A high-tech spin on an old cooling method

By Rob | September 15, 2025 |

Freezing liquids at night and then using it to cool homes and buildings during the day could reduce the carbon burden of air-conditioning

By Anthropocene Team

September 4, 2025

Before refrigerators were invented, people used ice boxes to keep food cold. A large block of ice in a top compartment of the box—typically made of wood and packed with insulating straw or sawdust—would slowly melt, sending cool air to the shelves below.

Just like ice has for decades kept food and drinks cold, it could also help to cool down buildings. And in a new paper published in The Journal of Physical Chemistry C, researchers advance the concept of such “ice batteries.” Their research could help to improve the materials used in such systems, making them more efficient and long-lasting.

Ice batteries use energy to freeze water or other liquid at times when electricity demand is low, or when there is excess electricity being produced. The ice is then melted to bring down building temperatures during peak hours. This takes some of the burden off energy-intensive air conditioning during the day, lowering energy use and costs.

“The ice battery technology has been around for a while,” Patrick Shamberger, a professor of materials science and engineering at Texas A&M University, said in a press release. “But there are problems on the material side that I’m interested in: what’s the right material at the right temperature? Can we make it reversible? Can we make it last for 30 years?”

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Ice battery systems typically convert liquids into ice with the help of chemicals called salt hydrates: salts that naturally contain water molecules in their crystal structures.

In an ice battery, salt hydrates interact with small solid particles called nucleation particles to freeze liquids. The type of salt hydrates, nucleation particles, and the temperatures at which they interact all affect the efficiency and stability of ice battery systems.

Shamberger and colleagues are developing and testing new salt hydrates that work best at temperatures suitable for real-world cooling systems. One issue with salt hydrates is that the material separates into solid and liquid phases that have different densities and compositions. This phase separation degrades the system after several freeze-thaw cycles.

In the new study, the researchers set out to find salt hydrate materials that avoid this separation. They used the salt hydrate calcium chloride hexahydrate, which is a promising compound for near room temperature ice battery systems. By analyzing the thermodynamics of phase changes, they found that nucleation particles with the element barium were better at triggering the freezing in the system.

Source: Denali Ibbotson et al, Mutability of Nucleation Particles in Reactive Salt Hydrate Phase Change Materials, The Journal of Physical Chemistry C, 2024.

Abstract

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Nucleation particles, solid phases dispersed throughout a medium to decrease the energy barrier for solidification or other reversible phase transitions, are generally selected on the basis of structural or interfacial energy considerations between the host phase and the solid phase that is crystallizing. However, the existence of chemical reactions between the nucleation particles and the host phase can obscure these underlying relationships, thereby complicating the process of selection of active nucleation particle phases. Here, we reveal the origin of nucleation activity of barium-based nucleation particles in the salt hydrate calcium chloride hexahydrate (CCH), a candidate for near room temperature thermal energy storage. We demonstrate that these compounds undergo a series of cation exchange and secondary precipitation reactions, resulting in an assemblage of solid precipitates with some degree of limited solid solution, which collectively dramatically reduce undercooling in CCH, but which obscure the identification of a single crystalline phase primarily responsible for the nucleation of crystalline CCH from the liquid. Importantly, this result illustrates a pathway to harness in situ chemical reactions to generate stable active nucleation particles in reactive phase change materials, which may not be readily synthesized by alternative methods, or which may not be active or remain stable when added in isolation.

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