Calcium-Based Pellets Bonded with Calcium Aluminate Cement for Direct Solar Absorbing Thermochemical Energy Storage

Thermochemical heat storage (TCHS) materials have been found to be promising in the field of solar energy conversion and storage. However, the energy storage density and cyclic stability of TCHS materials remain to be further improved. In this study, high-performance CaCO3 pellets with enhanced light absorption, cycling stability, mechanical strength, and energy storage density were prepared via granulation using scallop shells as the calcium source, Ca2MnO4 as the light-absorbing component, and aluminate cement as the binder. The microstructure, phase composition, and pore structure of the pellets were characterized, and the effects of the Ca2MnO4 content and aluminate cement content on the light absorption, heat storage reaction rate, cycling stability, and mechanical strength of the pellets were studied. Results revealed that sample (A10M8) with 8 wt % Ca2MnO4 and 10 wt % aluminate cement achieved a solar weighted average absorptance of 85.1% (348% higher than that of raw scallop shell powder). Under 108 kW/m2 simulated sunlight, A10M8 reached decomposition temperature in ∼110 s, achieved a relative conversion rate of 0.966 at 50 min, and exhibited a final energy storage density of 2172 kJ/kg with a crush strength of 3.02 N. After 100 cycles, the final energy storage density was 1958 kJ/kg (90.14% retention), and the crush strength remained at 2.82 N. The aluminate cement-formed skeleton provided mechanical strength, improved cycling stability, and created a porous network structure that facilitated rapid CO2 release, enhancing heat storage/release rates. The composite pellets exhibited excellent flowability, meeting the industrial requirements for CaCO3/CaO thermochemical energy storage materials.