Core@shell design for enhanced cyclic stability of Ca-based thermochemical energy storage materials

Ca-based thermochemical energy storage (TCES) systems are critical for large-scale green energy utilization, as they bridge the gap between intermittent solar supply and stable energy demand, and stand out for their high energy density and economic advantages. However, their practical application is limited by persistent challenges, including CaO sintering and weak solar absorption. In this study, Fe/Mn co-doped CaCO₃ microspheres were synthesized by co-precipitation method, followed by coating with SiO₂ or TiO₂ shells to construct two core@shell composites, namely CaCO₃(Fe, Mn)@SiO₂ and CaCO₃(Fe, Mn)@TiO₂. The introduction of Fe/Mn doping markedly improved the solar absorption capacity of the CaCO₃ matrix. High temperature cyclic tests (800 °C, 100 calcination/carbonation cycles) further demonstrated that the core@shell structure significantly improved the cyclic stability. Notably, CaCO₃(Fe, Mn)@TiO₂ maintained 96.2% of its initial energy storage density (1046.1 kJ kg^-1) after 100 cycles, corresponding to a final density of approximately 1006.1 kJ kg^-1. In contrast, CaCO₃(Fe, Mn)@SiO₂ retained 752.4 kJ kg^-1 (from an initial 1178.7 kJ kg^-1) after 100 cycles, while uncoated CaCO₃(Fe, Mn) dropped to 481.1 kJ kg^-1 (from an initial 1817.9 kJ kg^-1). This superiority is attributed to the higher Tammann temperature and stronger TiO bond dissociation energy of TiO₂, which endow the TiO₂ shell with robust thermal stability and structural integrity, effectively suppressing particle sintering and pore collapse. The results validate that the core@shell protection strategy provides a viable design paradigm for developing high performance TCES materials, thereby promoting progress in the field of TCES.