Enhanced thermochemical energy storage performance of SrCl₂–MgCl₂ composites hosted by expanded graphite: Synthesis and experimental study

Efficient energy storage is essential for integrating renewable energy and managing fluctuating energy demand. Thermochemical energy storage technology offers high energy density and long-term storage potential. However, the performance of this technology strongly depends on the properties of the active storage materials, and challenges remain in optimizing material performance, stability, and kinetics. In this work, a novel composite based on SrCl₂–MgCl₂ binary salts supported in expanded graphite (EG) is experimentally investigated. SrCl₂ was selected as the primary salt, MgCl₂ was added to enhance water uptake, and EG was used to improve thermal conductivity and provide structural support. Nine samples with varying salt ratios and EG contents were synthesized and evaluated through characterization, water uptake, and cycling tests. According to the results, at 50% relative humidity, the addition of MgCl₂ significantly improved hydration: SM1EG10 and SM2EG10 reached 0.56–0.59 g/g, compared to 0.46 g/g for pure SrEG10, representing a nearly 20% improvement. Additionally, the reaction exhibits fast kinetics, reaching equilibrium in approximately 2 h. However, Further increase in relative humidity to 60% produced no significant performance improvement. Thermal conductivity increased from 0.6 to 0.7 W/m.K for pure salts to 2.4–3.2 W/m.K for EG-containing composites. SM1EG10 achieved an energy storage density of 853 kJ/kg and retained ~91% of its water uptake after 15 cycles, demonstrating good stability. Overall, the proposed composites provide a balanced combination of water uptake, kinetics, thermal performance, and proper stability.