Preparation of energy storage materials working at 20–25 °C as a cold source for long-term stable operation

•The melting temperature of the composited PCM could be reached around 23 °C.•The phase change latent heat was kept as high as 130 J/g.•The degree of supercooling of the composited PCM was less than 1 °C.•The recovery latent heat of the composited PCM kept high degree after 100 cycles. As an inorganic phase change material (PCM), CaCl2·6H2O is an effective energy storage material because its energy can be transformed around 30 °C through the melting and crystallization. The different compositions of PCM were prepared in order to decrease the phase transition temperature to 20–25 °C and to improve its capability of heat storage and release. MgCl2·6H2O was added as a nucleating agent and the composite PCMs (CPCMs) of CaCl2·6H2O/MgCl2·6H2O binary salt system was prepared. At the same time, SrCl2·6H2O was added to reduce the supercooling degree of inorganic PCM. As a thickener, hydroxyethyl cellulose (HEC) was also included to improve the recycling ability. With the application of thermogravimetric analysis and differential scanning calorimeter, the phase transition temperature, thermal properties of CPCMs, supercooling degree and thermal cycle performance were studied by changing the content of each component in the CPCMs. The results demonstrated that the phase transition temperature of PCM with 35% MgCl2·6H2O, 5% SrCl2·6H2O, 0.5% HEC balanced by CaCl2·6H2O was reached to 23 °C. The phase change latent heat of PCM was kept at 130 J/g. The degree of supercooling was kept within 0.7 °C and the recyclability was greatly improved after 100 cycles.