Preparation and thermal characterization of LiNO3–NaNO3–KCl ternary mixture and LiNO3–NaNO3–KCl/EG composites

Phase change material (PCM) has important applications in the field of thermal energy storage due to its characteristic that the temperature is basically unchanged during the endothermic and exothermic processes. At the same time, it helps to achieve heat supply/demand balance and reasonable energy distribution. Nitrates are widely used as mid-temperature phase change material, but they have relatively low phase change latent heat than chlorine salt. In order to get a kind of material with high phase change latent heat, 50 wt% LiNO3–45 wt% NaNO3–5 wt% KCl (LNK) ternary mixed molten salt is prepared with static mixing melting method. Meanwhile, LNK/expanded graphite (EG) composite phase change materials are prepared with ultrasound smashing method. The experimental results show that the addition of KCl changes the performance. The melting temperature of LNK reduces 20.6 °C and its phase change latent heat increases 19.9 J/g, compared with 43 wt% NaNO3–57 wt% LiNO3 binary nitrate mixture. The thermal properties and thermal stability of the materials are tested and analyzed. The experimental results show that both the ternary phase change material and the composite phase change materials have high phase change latent heat and chemical stability. EG has greatly increased the heat conductivity of the composite phase change materials. The thermal conductivity of 85 wt% LNK/15 wt% EG composite phase change material increases by 778% compared to LNK at 20 MPa forming pressure.