Recent Advances in CaO/Ca(OH) ₂ Thermochemical Energy Storage: Materials, Reactors, and System Integration

Thermochemical energy storage technology is one of the most widely studied methods of energy storage, offering a high capacity and enabling energy storage across seasons. The CaO/Ca(OH)2 system, in particular, offers high energy density and uses low-cost, abundant raw materials, making it a potential thermochemical energy-storage medium. This paper summarizes the key progress and future challenges of the system, from materials to system integration. At the material level, remarkable progress has been made in improving cycle stability through chemical doping, microstructure regulation, encapsulation, and surface modification. However, intrinsic sintering, volume strain, and dynamic attenuation remain the primary bottlenecks. Notably, machine learning is accelerating the rational design and optimization of system operations for high-performance materials. By constructing an intelligent “composition-structure-process-performance” mapping, it provides a new paradigm for solving the aforementioned multiscale, complex problems. At the reactor level, the focus is on structural strengthening and configuration innovation. New configurations such as fin-embedded channels are adopted to enhance heat transfer. Fluidized and moving beds are used to enable continuous and efficient regulation. At the system level, a multienergy complementary coupling mode is developed and energy efficiency is improved through calcium-based medium coordination and heat exchange optimization. Multiscale modeling promotes megawatt demonstration and industrial integration.