Critical review of CaO/Ca(OH)2 thermochemical energy storage material

CaO/Ca(OH)2 is considered as one of the most promising thermochemical thermal storage materials, due to its high thermal density and theoretically unlimited storage duration. However, there are few specialized reviews on the material. The solutions to key challenges were not reviewed, such as material sintering, poor thermal conductivity, and high dehydration temperature. The potential application of the industrial reactors was not explored. To fill these gaps, the latest research findings on the material have been summarized and categorized, including physical properties, chemical characteristics, cyclic stability, and state-of-the-art applications. Thermal conductivity, specific heat capacity, and energy density have been reviewed. Reaction kinetics, reaction temperature and pressure, reaction enthalpy, and reaction equilibrium have been analyzed. Issues such as sintering and cracking of the material have been investigated. Reactors have been classified and discussed. Research results indicate that the preparation of composite materials and the application of granulation techniques are key methods to improve its thermal conductivity, reduce dehydration temperature, and mitigate agglomeration. The concept of energy density should be used as an essential indicator for evaluating composite materials. Fluidized bed reactors are considered the most promising reactor type for industrial applications.