Dual-strategy design of high-latent heat NaNO3–LiNO3–LiCl eutectics for Medium–Low temperature thermal energy storage

Medium-low temperature molten salt phase change materials (MSPCMs) face challenges such as mismatches between phase change and working temperatures, and low latent heat. To address these issues, this paper developed a high-latent heat (100–300 °C) NaNO3–LiNO3–LiCl ternary MSPCM using two strategies (LiCl gradient doping and ternary eutectic design), based on calculations and experiments. Characterization results showed that the melting point of NLL20 % (NaNO3–LiNO3 gradient-doped with 20 mol% LiCl) was 190.8 °C, and its phase change latent heat reached 312.0 J/g. Although the melting point of NLL (ternary eutectic composition NaNO3–LiNO3–LiCl) increased to 225.3 °C, its latent heat reached as high as 397.0 J/g. In addition, their thermal conductivities (solid, NLL20 %: 1.54 W/(m·K); NLL: 1.44 W/(m·K)) and specific heat capacities (liquid, NLL20 %: 2.69 J/(g·°C); NLL: 2.56 J/(g·°C)) are also relatively high among MSPCMs. The changes in melting point and latent heat of both salts after 500 cycles were below 2 % and 6 %, respectively, showing good cyclic stability. This novel high-latent heat nitrate-based MSPCM shows promising potential for medium-low temperature solar thermal energy storage and industrial waste heat recovery, providing a foundation for the development of next-generation MSPCMs.