Progress in multiscale research on calcium-looping for thermochemical energy storage: From materials to systems

Thermochemical energy storage (TCES) based on calcium-looping (CaL) has great potential to mitigate the intermittency and instability problems of solar energy harvesting, especially for high-temperature solar thermal utilization. The CaCO3/CaO TCES system has been the focus of intense research over the past few decades for its advantages of high energy storage density, natural abundance of raw materials, low cost, and environmentally benign nature, simultaneously. Although some properties of the CaCO3/CaO TCES system have been concluded, few of them consider the relationships between structures and performances at multiple time and length scales. Herein, we summarize the multiscale developments of the CaCO3/CaO-based TCES systematically, including atomic-scale mechanisms, reaction thermodynamics, cyclic stabilities, energy storage/release properties in reactors, operations, and efficiency optimizations at a system level. This review aims to broaden research interests in multiscale structure-function relationships in the field of TCES and provide constructive references for exploring advanced methods and mature technologies for material development, reactor upgradation, and system optimization. Finally, it will promote the large-scale industrial applications of calcium-looping for thermochemical energy storage. •Calcium-looping thermochemical energy storage has great potential in the solar energy utilization.•Multiscale developments of the CaCO3/CaO system are discussed and summarized systematically.•Multiscale models should work together to build a unified description of the material properties.•Cost-effective rejuvenation methods should be used to recover the material performances.•Reactor integration and multi-objective optimizations of systems are promising to improve overall efficiency.