Thermochemical Salt Hydrates—Structural Dynamics and Kinetic Insights for High-Density and Sustainable Energy Storage

Thermochemical (TCM) salt hydrates represent a promising class of thermal energy storage materials, leveraging reversible solid-gas reactions—specifically hydration and dehydration—to store and release energy. This energy is stored through chemisorption reactions between inorganic salts and water molecules, forming and breaking covalent bonds. Due to the high enthalpy associated with these reactions, TCMs offer superior energy density compared to other thermal storage methods, such as phase change materials or sensible and latent heat storage. However, TCMs face significant challenges in material stability at the particle level, leading to poor multi-cycle efficiency and high levelized cost of storage.
The repeated hydration and dehydration cycles cause substantial structural and mass changes in the salt hydrates, which can alter interplanar distances due to the incorporation or loss of water molecules. These atomic-scale shifts can degrade the material’s overall behavior and kinetics, often resulting in increased porosity and compromised performance. In this study, we investigate the microscale structural evolution of salt hydrates during dehydration and hydration cycles to better understand how these changes affect bulk energy density and long-term performance. Our findings provide critical insights into the particle size optimization, kinetic behavior of salt hydrates and offer pathways for optimizing their use in high-efficiency, durable thermal energy storage systems.