Research progress of flexible energy storage dielectric materials with sandwiched structure

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 a storage and transportation dielectric system with larger energy storage density, higher charge and discharge efficiency, good thermostability and being environmentally friendly. However, the contradiction between dielectric constant and breakdown strength of dielectric materials is the key factor and bottleneck to obtain a high performance dielectric material. 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, the materials with sandwiched or stacking structures have demonstrated outstanding advantages in inhibiting charge injection and promoting polarization, allowing polymer dielectrics to have increased permittivity and breakdown strength at the same time. Therefore, from the perspectives of material composition, structural design, and preparation methods, this study reviews the research progress of polymer dielectric films with sandwiched structure in improving the energy storage performance. 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, showing 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, resulting in a high breakdown resistance performance that is easy to achieve. The sandwiched structure design also possesses advantages over other methods in maintaining good flexibility and dielectric stability of dielectric materials, thus having become 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 realize high temperature energy storage and efficiency. Researches on recyclable, self-repairing sandwiched insulating films are good for the service life and safety of electronic components and will further expand the application scope of dielectric polymers. Finally, effective evaluation of dielectric with sandwiched structure and energy storage performances through simulation and theoretical modeling is very helpful in revealing the breakdown mechanism and thermal failure mechanism, and also in theoretically guiding the design of polymer dielectric materials.