The effect of SiC additives on the cycling performance of CaCO3 when used as a high-temperature thermal battery

Calcium carbonate (CaCO3) is considered an ideal candidate for large scale energy storage systems due to its high energy density, high operating temperature and low cost. Its degrading performance over consecutive energy storage/release cycles is the main inhibiting factor from utilizing such material as a high-temperature thermal battery for concentrated solar power (CSP) systems. In this study, silicon carbide (SiC) was added to calcium carbonate in three different weight concentrations (5, 10 and 20 wt% of SiC) as to improve the cycling stability of CaCO3 over 40 cycles. SiC is an excellent additive since it is a chemically inert ceramic which possesses high heat conductivity, oxidation resistance, and temperature stability. Most importantly it does not chemically react with CaCO3 upon cycling to form a ternary oxide, retaining the initial CaCO3 energy storage density. The system which demonstrated the greatest improvement in cycling efficiency utilized 5 wt% SiC, which increased the cycling performance of pure CaCO3 by a factor of 1.32. In order to further enhance the performance of this system, 300 and 100 nm polystyrene (PS) spheres were added to the SiC/CaCO3 mixture respectively. The PS spheres were then removed by thermal treatment, creating a porous SiC/CaCO3 structure with higher specific surface area in comparison to their bulk counterpart. Both porous mixtures showed an increase in their cycling stability for the first 20 cycles in relation to the bulk sample, allowing the CO2 gas to travel through their porous structure, and effectively hasten the carbonation reaction. •The cycling performance of CaCO3 was improved with the addition of SiC.•SiC did not react with CaCO3 upon cycling.•Polystyrene spheres in 300 and 100 nm were used to create a porous structure.•The SiC/CaCO3 porous structure exhibited higher performance to the bulk.