Study on the thermal cycling performance of calcium-based thermal storage materials doped with Al ₂ O ₃

Abstract Calcium-based thermochemical thermal energy storage, based on the reversible CaCO 3 /CaO reaction, features high energy density, low cost, and long storage duration, making it one of the thermal storage solutions for next-generation concentrated solar thermal power generation technologies. During charge-discharge cycles, the reactivity of calcium-based materials rapidly declines, limiting their further application. To address this issue, this study systematically investigates the effect of Al 2 O 3 doping on the cycle stability of calcium-based thermal storage and the reaction performance during heat storage/release. Results demonstrate that Al 2 O 3 doping significantly enhances the stability of the CaCO 3 /CaO cycle, achieving a heat release efficiency exceeding 84% after 20 cycles. Notably, the modified material exhibits optimal stability at a doping molar ratio of 100:12 (Ca:Al). The modified material exhibits optimal stability with a heat release efficiency of 87.5% after 20 cycles, compared to only 55.4% for the unmodified material—a 1.6-fold increase. During cycles involving calcination at 900°C and carbonation at 750°C, Al 2 O 3 doping accelerates reaction rates, initiating carbonation earlier and reducing overall reaction time. Based on characterization results, this paper proposes the reaction mechanism by which Al 2 O 3 doping improves calcium-based cycle stability. Al 2 O 3 uniformly disperses as nanoparticles on the surface and interstitial spaces of calcium-based materials, forming a physical barrier that effectively inhibits calcium migration and agglomeration, thereby enhancing the reaction performance of CaCO 3 /CaO during heat storage and release cycles.