Boosting the thermochemical energy storage performance of Limestone by adding Mayenite

Long-duration energy storage (LDES) systems play a critical role in the integration of intermittent renewable energy sources into the grid. Thermochemical energy storage (TCES) systems, particularly Limestone ones, offer promising solutions due Limestone's high energy storage density and cost-effectiveness. However, the cycling performance of Limestone is hindered by sintering phenomena and pore plugging. This paper explores the enhancement of Limestone's TCES performance by incorporating Mayenite, a mesoporous ternary oxide, as an additive. Mayenite can improve the cycling performance of Limestone by enhancing: (1) the Ca²⁺ ion migration at high temperatures promoting the carbonation reaction and (2) the CO₂ diffusion as shown by the carbonation reaction rate analysis of the mixture samples. In detail, three different Mayenite samples with unique Ca to Al ratios were synthesized and added to Limestone in varying concentrations. The mixture sample containing 5 % Mayenite (with a lower Ca to Al ratio) enhanced 2.5 times Limestone's energy storage performance after 40 cycles, boosting it from 455 kJ/kg to 1137 kJ/kg. Characterization techniques including X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis provide insights into the structural and kinetic changes induced by Mayenite addition. On the other hand, Density Functional Theory Calculations showed that migration of Ca²⁺ ions is promoted at high temperatures, improving the carbonation reaction of Limestone. The results demonstrate the potential of Mayenite as an effective additive for improving the performance of Limestone TCES systems, paving the way for more efficient and reliable long-duration energy storage solutions.