Achieving low dielectric loss and high energy density of polyimide composite dielectric film: inhibiting the formation of conductive path in both macro–microscales

Polyimide (PI) possesses high heat resistance and low dielectric loss, but exhibits low dielectric constant (k) and energy storage density, which constrains its further application in the field of high-temperature energy storage dielectric. The compounding of high-k filler and PI can greatly improve the dielectric constant of polymer-based dielectric composites, but it is often accompanied by the increase of dielectric loss and deterioration of breakdown strength. This issue can be effectively solved by the fabrication of dielectric filler with core–shell structure and construction of a layered structure. Therefore, in this research, a new SiC@polydopamine (PDA)@Ag nanoparticles (AgNPs)/PI flexible composite film with a sandwich structure (SSP) was prepared by a step-by-step casting method, in which the insulating layer (pristine PI) was intercalated between two polarization layers (SiC@PDA@Ag/PI composites). Pristine PI in the middle layer effectively hinders the transmission of carriers in the middle layer of the composite multilayer film. The SSP shows the highest energy storage density (1.35 J cm−3 under 273.4 kV mm−1), and the tanδ is as low as 0.0057. Additionally, SSP also shows excellent thermal stability and moisture resistance.Graphical abstract