Volume 55

Performance Study of Na3PO4-Expanded Graphite Composites for Low-Temperature Thermochemical Heat Storage Junfeng Zhou, Shusen Lin, Lisheng Deng, Jun Li, Tao Zeng, Zhen Huang, Hongyu Huang

Abstract

Salt hydrate-based thermochemical heat storage is a crucial technology for long-term heat storage. Sodium phosphate stands out due to its high energy storage density, lower dehydration temperature, and low cost. However, its practical application is limited by issues such as deliquescence and agglomeration. In this study, expanded graphite, known for its high thermal conductivity and rich microstructure, was used as the primary matrix. Composites with mass contents of 80%, 60%, and 40% were prepared using the impregnation method. Hydration tests were conducted at 30°C and RH 80% to examine the microstructure, thermal storage properties, and cycling stability of the pure salt and the composites. The results demonstrated that the incorporation of expanded graphite improved the adsorption kinetics of the composites and thermal conductivity mitigated the deliquescent agglomeration of pure salt, and reduced the dehydration temperature. EG80 has a maximum water absorption of 1.24 g/g, an energy storage density of 1081.8 kJ/kg and a thermal conductivity of 2.98 W/(m-K). After 10 storage discharge cycles, the thermal storage density remained above 1000 kJ/kg, indicating good stability.

Keywords thermochemical energy storage, Na3PO4·12H2O, energy storage density, cycle stability