Calcium-based materials for thermochemical energy storage: Advances in synthesis, granulation and lab-scale reactor validation

The rapid growth of renewable energy technologies has driven demand for high-density and long-duration energy storage systems. Thermochemical energy storage (TCES) stands out owing to its high energy storage density, minimal self-discharge loss, and wide operating temperature ranges. Calcium looping (CaL) represents one of the most competitive TCES routes, benefiting from abundant low-cost feedstock, large reaction enthalpy and compatibility with high-temperature solar utilization. However, the practical application of CaL-TCES remains constrained by severe cyclic degradation, intrinsic trade-offs between solar absorptance and energy density, and poor engineering feasibility of raw powdered materials. This review consolidates recent progress on Ca-based TCES materials across three interrelated research directions: material synthesis, granulation modification, and lab-scale reactor development. Key advances include multiscale strategies for enhanced cyclic stability, feasible granulation methods for raw powders, trade-off optimization between solar light absorption and heat storage capacity, and the advancement of lab-scale reactor platforms toward realistic solar-driven CaL-TCES evaluation. Future research directions are outlined, including the development of durable, transportable Ca-based TCES materials for long-duration energy storage, alongside solar-driven Ca-based thermochemical conversion into fuels. This review elucidates the design principles of high-performance Ca-based TCES materials, providing theoretical insights and practical guidance toward stable, efficient, and scalable solar TCES systems.