Core-Shell Encapsulation of Salt Hydrates into Mesoporous Silica Shells for Thermochemical Energy Storage

Abstract

The advent of thermochemical energy storage (TcES), that is, storage of thermal energy by means of reversible chemical reactions, incites finding pathways of stabilization of thermochemical materials for thermal batteries of the future. Currently, salt hydrates such as LiCl·H2O, CaCl2·6H2O, and SrBr2·6H2O are being actively studied for TcES in buildings due to both high energy storage density (1-2.5 GJ/m3) and high storage duration. In this work, we report the core-shell composites "salt in hollow SiO2 spheres with mesopores"(salt = LiCl·H2O, CaCl2·6H2O, SrBr2·6H2O) for domestic TcES. The salt hydrates were encapsulated into submicrometer-sized hollow SiO2 (HS) capsules as confirmed by transmission electron microscopy (TEM) and N2 sorption analyses. High sorption/desorption rates due to mesopores of the shells were shown by thermogravimetric analysis (TGA). The sorption equilibrium for salt@HS was reported, and the applicability of the materials for domestic heat batteries was analyzed. As a result of almost the densest packing of salt@HS, the composites were shown to provide a state-of-the-art energy storage density up to 0.86 GJ/m3 on the bed level for the high-temperature lift of 32-47 °C, showing high energy storage capacity. The stability in at least 50 charging/discharging cycles was confirmed by TGA and TEM.