Research Progress of Sandwich-structured Flexible Energy Storage Dielectric Materials

Polymer dielectric materials show wide applications in smart power grids, new energy vehicles, aerospace, and national defense technologies due to the ultra-high power density, large breakdown strength, flexibility, easy processing, and self-healing characteristics. With the rapid development of integration, miniaturization and lightweight production of electronic devices, it is required to develop such storage and transportation dielectric system with larger energy storage density, higher charge and discharge efficiency, good thermostability and environmental friendly. However, the contradiction between dielectric constant and breakdown strength of dielectric materials are the key factors and bottleneck to obtain high performance dielectric materials. It is accepted that controlling charge distribution and inhibiting charge carrier injection are important to improve the energy storage characteristics of polymer dielectrics. In recent years, designing sandwich or stacking structured materials exhibits outstanding advantages in inhibiting charge injection and promoting polarization, thereby the permittivity and breakdown strength of polymer dielectrics can be simultaneously enhanced. Accordingly, this paper reviews the research progress of sandwich-structured polymer dielectric films in improving the energy storage performances from the perspectives of materials composition, structural design, and preparation methods. The influence of dielectric polarization, charge distribution, charge injection, interfacial barrier and electrical dendrite growth on the energy storage performance and the synergistic enhancement mechanisms in such sandwich-structured dielectric materials are systematically summarized, implying good development and vast application prospects. In brief, introducing easy polarization, wide-gap and deep-trap nanofillers has greater designability and regulation in the dielectric and breakdown properties. In addition, using the hard layer as the outer layer can reduce charge injection more effectively, achieving high breakdown resistance performance easily. Sandwich structure design also possesses advantages over other methods in maintaining good flexibility and dielectric stability of dielectric materials, thus becoming a hot-topic research area in recent years. In the future, it is necessary to combine low conductivity and high thermal conductivity of dielectric polymers to achieve high temperature energy storage and efficiency. Research on recyclable, self-repairing sandwich insulating films is good for the service life and safety of electronic components and will further expand the application of dielectric polymers. Finally, effective evaluation of sandwich-structured dielectric and energy storage performances through simulation and theoretical modeling is very helpful to reveal the breakdown and thermal failure mechanisms, and theoretically guide the design of polymer dielectric materials.