Preparation and thermal properties of LiNO3-NaNO3-NaCl/EG composite heat storage material

•A novel ternary nitrate-chloride phase change material was prepared.•PCM has good heat storage performance.•Composite phase change material was prepared with EG as adsorption material.•Composite phase change material still has good thermal properties. Nitrate phase change materials (PCM) have important applications in the field of thermal energy storage, but their latent heat value is relatively low. A novel LiNO3-NaNO3-NaCl ternary molten salt with high latent heat was prepared and studied. LiNO3-NaNO3-NaCl/expanded graphite (EG) composite phase change material (CPCM) was prepared by using high thermal conductivity EG as the carrier adsorption material. The performance of PCM and CPCM were tested and analyzed. Compared with LiNO3-NaNO3, the newly prepared ternary nitrate-chloride mixed molten salt has a lower phase change temperature, a higher latent heat value, and a higher thermal decomposition temperature. At the same time, the supercooling degree of LiNO3-NaNO3-NaCl is about half lower than that of LiNO3-NaNO3. There is no chemical reaction between different molten salts or between mixed molten salts and EG. The mixed molten salt is uniformly dispersed into the pore structure of EG, and no agglomeration occurs. Both LiNO3-NaNO3-NaCl and LiNO3-NaNO3-NaCl/EG have good cyclic thermal stability. The addition of EG greatly improves the thermal conductivity of LiNO3-NaNO3-NaCl. When the addition ratio of EG is 20%, the thermal conductivity of ternary molten salt increases from 1.378 to 5.453 W/m·K. The phase change materials added with EG still have high latent heat of phase change. The results show that LiNO3-NaNO3-NaCl/EG has broad application prospects in medium temperature heat storage.