Slag-based hydrated salt composites for thermochemical energy storage: Preparation, characterization and performance

Bulk solid waste recycling and reuse, as well as new and cheap energy storage materials, have become the research hotspots in recent years. In this study, a scheme for the preparation of medium-temperature energy storage materials using industrial solid waste slag was proposed, and its energy storage performance was experimentally investigated. In this study, a porous matrix - slag powder-cement paste (SP-CP) was prepared from industrial solid waste, Yunnan iron ore slag as the main raw material. This matrix was further integrated with CaCl₂/MgCl₂ hydrated salts. By controlling the salt impregnation concentration and combining characterization techniques such as Scanning Electron Microscopy (SEM), Dynamic Vapor Sorption analysis (DVS), and Simultaneous Thermal Analysis (STA), and the influence of the porous structure on moisture adsorption characteristics and energy storage density was investigated. The experimental results showed that: In terms of adsorption capacity, the pore structure of SP-CP significantly contributed to the loading capacity of the hydrated salt, in which the adsorption of MgCl₂ composite (SP-CP35/Mg) reached 0.323 g/g, which was 30.8% higher than that of the same concentration CaCl₂ system. Compared with the conventional zeolite/MgCl₂ thermal storage solution, the adsorption capacity of SP-CP35/Mg is increased by about 1.34 times. The energy storage density of SP-CP35/Mg reaches 764.35 J/g, which is 18% higher than that of conventional zeolite/MgCl₂, and the raw material cost is only 42.2% of the latter. In addition, after 10 adsorption/desorption cycles, the normalized energy storage density of SP-CP/35 Mg remains around 0.8, showing excellent stability. This industrial byproduct-based design establishes an economically superior thermochemical energy storage (TCES) system with validated stability.