Discovery of Salt Hydrates for Thermal Energy Storage

Abstract

Thermal energy storage (TES) has the potential to improve the efficiency of many applications but has not been widely deployed. The viability of a TES system depends upon the performance of its underlying storage material; improving the energy density of TES materials is an important step in accelerating the adoption of TES systems. For applications in thermochemical energy storage, salt hydrates are a promising class of materials due to their relatively high energy densities and their reversibility. Despite their promise, relatively few salt hydrates have been characterized, presenting the possibility that new hydrate compositions with superior properties may exist. Here, the energy densities, turning temperatures, and thermodynamic stabilities of 5292 hypothetical salt hydrates are predicted using highthroughput density functional theory calculations. The hydrates of several metal fluorides, including CaF 2 , VF 2 , and CoF 3 , are identified as stable TES materials with class-leading energy densities and operating temperatures suitable for use in domestic heating and intermediate-temperature applications. The promising performance of these materials is demonstrated at the system level by parameterizing an operating model of a solar thermal TES system with data from the new hydrates. Finally, machine learning models for salt hydrate thermodynamics are developed and used to identify design guidelines for maximizing the energy density. In total, the new materials and design rules reported here are expected to nurture the implementation of TES systems.

Computational Discovery of Thermochemical Heat Storage Materials Based on Chalcogenide and Complex Anion Salt Hydrates

“…The computational protocol of Kiyabu et al 22 for screening hypothetical salt hydrates for TES was adapted for salt hydrates containing chalcogenides and complex anions. The main components of the protocol are summarized below.…”

Enhanced Thermal Conductivity of Phase Change Microcapsules Based on Boron Nitride/Graphene Oxide Composite Sheets

“…As one of the most widely used TES materials, latent heat storage materials, namely, phase change materials (PCMs), have attracted intensive interest, thanks to their unique high energy storage and thermostatic capacities . The PCMs are often divided into organic PCMs, inorganic PCMs, and eutectics. , Compared to inorganic PCMs, organic PCMs hold more advantages, including high latent heat, narrow phase transition temperature range, good chemical stability, and low corrosiveness. However, organic PCMs, like paraffin, are often hampered by leakage problems when they are undergoing solid to liquid phase transition.…”

“…12−14 In fact, the encapsulation of inorganic PCMs like ionic liquids and salt hydrates via a variety of polymer materials has also been adopted to improve the cycling phase change capability. 11,15,16 Generally, high-performance phase change microcapsules (PCMCs) shall have the attributes including high thermal conductivity (TC), high thermal-energy storage capacity, and good thermal stability. 9,17,18 Limited by the intrinsically low TC values of common polymers and organic PCMs, the thermal conduction ability of polymeric PCMCs is relatively poor.…”

“…However, organic PCMs, like paraffin, are often hampered by leakage problems when they are undergoing solid to liquid phase transition. Encapsulation of PCMs through polymeric, inorganic, or hybrid shells (SiO 2 , polystyrene, poly­(methyl methacrylate), polyurethane, polyurea, urea–formaldehyde resins, melamine–formaldehyde (MF) resins, and biodegradable polymers) to form nanocapsules or microcapsules has been widely used to solve the leakage problem of organic PCMs. − In fact, the encapsulation of inorganic PCMs like ionic liquids and salt hydrates via a variety of polymer materials has also been adopted to improve the cycling phase change capability. ,, …”

“…3 The PCMs are often divided into organic PCMs, inorganic PCMs, and eutectics. 3,11 Compared to inorganic PCMs, organic PCMs hold more advantages, including high latent heat, narrow phase transition temperature range, good chemical stability, and low corrosiveness. However, organic PCMs, like paraffin, are often hampered by leakage problems when they are undergoing solid to liquid phase transition.…”