A SrBr2/SrCl2-expanded graphite composite material for low temperature thermochemical energy storage

Thermochemical energy storage (TCES) based on salt hydrate stands out as an important method for long-term energy storage. However, the low energy storage density (ESD) at low temperature and poor cycle stability of the materials limit the practical application. In this work, new composites for thermochemical heat storage at low temperature (about 100 °C) are synthesized, consisting of SrBr₂ and SrCl₂ with various mass ratios and expanded graphite (EG). The material properties are characterized and measured using scanning electron microscope (SEM), X-ray diffraction (XRD), thermal constant analyzer and simultaneous thermal analyzer (STA). The results demonstrate that the composites display excellent thermal conductivity, ESD and cycling performance. The composites exhibit an improvement in thermal conductivity by almost eightfold when compared with pure SrBr₂. In comparison with SrCl₂, the composites demonstrate a reduction in hydration time by approximately 3/5. The ESD of the composites at 100 °C surpasses 800 kJ kg⁻¹, and the ESD of SrBr5Cl5@EG reaches 918.66 kJ kg⁻¹, representing an 18.23 % enhancement compared with pure SrBr₂. Furthermore, it is revealed that reducing the adsorption temperature, raising the heat source temperature and evaporation temperature are conducive to enhancing the heat storage performance of the composite. The cycling test results indicate that the SrBr5Cl5@EG composite retains 94.44 % of the initial ESD after 14 cycles, affirming its good stability. This work provides a new avenue for the development of advanced thermal energy storage materials and demonstrates great potential for long-term thermochemical energy storage applications at low temperature.