Development of dense Ca-based, Al-stabilized composites with high volumetric energy density for thermochemical energy storage of concentrated solar power

Thermochemical energy storage based on the Calcium-Looping process characterized high energy density, low cost, and scalability, which is an advantageous candidate for the heat storage systems of Concentrated Solar Power plants. The main disadvantage of Calcium-Looping technology is the rapid decrease in the reactivity of CaO during cycling due to sintering. Many methods have been developed to synthesize high-cycling-behavior CaO-based materials. However, the state-of-the-art synthesized CaO-based materials remain far from the requirements due to the lack of consideration from an application perspective, which not only demands high-cycling-behavior but also needs to consider volumetric energy density. In this work, dense CaO/Al 2 O 3 composites were fabricated using the space-confined chemical vapor deposition method and considering both stability and volumetric energy density. Among different Ca-precursors, calcium formate does not expand during calcination, thus possesses a relatively dense structure, and taken together with the deposition of Al 2 O 3 on the surface of CaO grains obtained composites possessing high density and excellent stability. The optimized composite with 10 mol.% Al achieves a high volumetric energy density of 2.07 GJ/m 3 after 20 cycles, which is 1.58, 4.31, and 6.68 times of the capacity of limestone-derived CaO, sol–gel based CaO/Al 2 O 3 composites, and wet-mixing based CaO/Al 2 O 3 composites, respectively. This study presents a design principle for CaO-based heat storage materials, which are becoming denser and more stable.