Thermal energy storage technology depending upon phase change is the hot spot in the field of heat storage research, which has a significant effect on improving energy utilization efficiency. As one of the high-efficiency thermal energy storage technologies, solid-solid phase change thermal energy storage mainly realizes the absorption and release of heat through solid phase transformation process. Compared with the solid-liquid phase change thermal energy storage, the volume change of solid-solid phase change is smaller, and there is no obvious phase separation and leakage phenomenon. It has attractive development potential in many fields such as energy conservation, environmental protection and new energy. The organic materials in solid-solid phase change thermal energy storage field mainly include polymer, polyhydric alcohols and layered perovskite. Among them, polymeric phase change materials are mainly formed by the 'soft phase' macromolecules connected with the 'hard phase' polymer skeleton by means of chemical bonds. The 'soft phase' is the main part of the phase transformation process, and the solid-liquid transition occurs when the temperature rises to the transition temperature. The'hard phase' skeleton restricts its macro flow and plays an important role in maintaining the solid morphology. At low temperature, polyhydric alcohols present a layered crystal structure. The interlayer molecules are connected by hydrogen bonds, and part of the hydrogen bonds break during the solid phase transition, and the molecules change to face centered cubic crystal structure. Layered perovskite is an intercalated crystal structure composed of long chain alkanes in organic layer and metal coordination tetrahedron [MX42-]in inorganic layer. Its solid-solid phase transition mechanism is similar to that of polymer, that is, the long alkyl chain of organic layer undergoes order-disorder transformation, while the inorganic layer structure remains unchanged. At present, in the preparation technology of organic solid-solid phase change thermal energy storage materials, polymer materials are mainly formed by grafting copolymerization, block copolymerization and other methods, using polyethylene glycol as phase change medium and combining with polymer skeleton by means of chemical bond; polyhydric alcohols are suitable for medium and high temperature working conditions, and their phase transition temperature and enthalpy are related to the number of hydrogen bonds contained, and their thermophysical properties can be adjusted by multi-component composite ratio. The thermophysical properties of layered perovskite depend on the length of alkyl chain, which can be used to prepare the pluralistic system to widen the range of phase transition temperature. In recent years, in order to meet the requirements of high thermal energy storage power in practice, in addition to the development of new phase change materials, the heat conduction enhancement technology of phase change materials is also constantly improved. Based on current researches published in the opened literatures, the solid-solid thermal energy storage technology was analyzed and summarized in detail from various aspects including the characteristics of phase change behavior, material preparation, performance optimization techno-logy and application, etc. On this basis, from the perspective of material preparation and phase change mechanism control, the technical barriers and future research directions of solid-solid phase change thermal energy storage materials are prospected. The content of this review can provide valuable professional reference for further research in exploring new thermal energy storage materials, especially for the development of medium and high temperature solid-solid phase change thermal energy storage materials. © 2022, Materials Review Magazine. All right reserved.
