Thermal properties of eutectic salts/ceramics/expanded graphite composite phase change materials for high-temperature thermal energy storage

Eutectic chloride salts are a new and novel type of thermal energy storage (TES) material for high-temperature solar TES systems. Their thermal properties and stability are key factors in determining their application in TES systems. In this study, we prepared and characterized eutectic NaCl–KCl–MgCl2/α-alumina/expanded graphite (EG) composite phase change materials (PCMs). The results show that eutectic salts, α-alumina and EG have good crystalline properties and chemical compatibility. The elements are relatively uniform in distribution within the pores and channels. Moreover, the Na, K, and Mg distributions occupy the same locations, indicating the excellent eutectic properties of the salts. The latent heat of composite PCMs decreases with the increase in α-alumina and EG percentage, while the addition of EG to the eutectic salts/α-alumina composite PCM improves the thermal conductivity of the composite PCMs by more than 6 times, from 0.85 to 5.10 W/(m·K). Moreover, after 50, 100, and 300 heating–cooling cycles at 550 °C, the composite PCMs demonstrate enhanced thermal and physical properties at high temperatures. The improved thermal characteristics of composite PCMs with α-alumina and EG allow for promising applications of high-temperature solar TES systems.