Review on solid-solid phase change materials for thermal energy storage: Molecular structure and thermal properties

Solid-solid phase change materials (SS-PCMs) for thermal energy storage have received increasing interest because of their high energy-storage density and inherent advantages over solid-liquid counterparts (e.g., leakage free, no need for encapsulation, less phase segregation and smaller volume variation). Four main SS-PCMs for thermal energy storage are reviewed, with a focus on their thermal properties and the relationship between molecular structure, processes involved during phase transition, and thermal properties. This review aims to provide guidance for selecting appropriate SS-PCMs for various applications and tailoring the synthesis of SS-PCMs with desired thermal, physical and mechanical properties. Challenges and opportunities to use of SS-PCMs for thermal storage and other applications are also discussed.