Synergy of Li2CO3 promoters and Al-Mn-Fe stabilizers in CaCO3 pellets enables efficient direct solar-driven thermochemical energy storage

Calcium carbonate (CaCO 3 ) pellets are suitable for scalable solar thermochemical energy storage but suffer from low solar absorptance, poor stability, and slow reaction kinetics, which lead to low solar energy storage efficiency. Here, for the first time, we successfully achieve fast and efficient solar thermochemical energy storage via synergistically employing Al, Mn, and Fe stabilizers for improving both cyclic stability and solar absorptance, and Li 2 CO 3 promoters for accelerating decomposition of CaCO 3 pellets. The average solar absorptance is 1500% higher than that of pure CaCO 3 pellets. After 60 cycles, the energy storage density is still as high as 1671 kJ/kg with a decay rate of only 4.14%, in stark contrast to energy density of 1121 kJ/kg and decay rate of 56.73% for pure CaCO 3 pellets. The average decomposition rate is about twice as fast as that of pure CaCO 3 pellets due to enhanced Ca 2+ diffusion by doped Li 2 CO 3 . Under direct light irradiation, novel CaCO 3 pellets demonstrate high energy storage rate due to both high solar absorptance and fast decomposition rate, while pure CaCO 3 pellets cannot even reach the decomposition temperature. This work opens new opportunities for scalable deployment of direct solar-driven thermochemical energy storage techniques based on Li 2 CO 3 -doped dark CaCO 3 pellets.