Investigating structural and morphological transformations of strontium chloride for thermochemical energy storage

Abstract

Thermochemical materials (TCMs) offer a sustainable solution for long-duration thermal energy storage due to their near-lossless energy retention by separating the solid and gas phases. Salt hydrates, which undergo de(hydration) reactions with high reaction enthalpies and low operating temperatures (<100 °C), are particularly promising for applications such as space conditioning and domestic hot water in buildings. However, mechanical degradation of TCMs during (dis)charge cycling is not well understood and limits storage performance. Here, we investigate the structural and morphological changes that occur during (de)hydration cycling of SrCl₂, a high-capacity TCM with multiple stable hydrates. In situ optical microscopy is used to observe morphological changes and fracture processes in SrCl₂ pellets undergoing hydration and dehydration reactions. In situ X-ray diffraction and calorimetry/thermogravimetric analysis further elucidate the distinct kinetics governing various SrCl₂·xH₂O phase transformations, revealing asymmetry during hydration/dehydration and rate limiting transformations. This study provides valuable insight into the phase transformations and mechanical degradation mechanisms of salt hydrate TCMs in pellet form to guide the optimal (dis)charge cycling conditions for stable energy storage performance.