Preparation of All-Organic Sandwich-Structured PI-ANFm-PI films and Their Dielectric Properties

For breaking the endowed paradox between dielectric constant and breakdown strength of polymer dielectric films and optimizing the dielectric properties and breakdown strength at high temperatures under electric field. polyimide (PI) solution and aramid nanofiber film (ANFm) were utilized to construct all-organic sandwich-structured PI-ANF-PI (P-A-P) dielectric films via “dipping and pulling” process. Due to the top and bottom PI layers reduced the surface roughness of ANFm as well as the formation of electron-hole pairs, the leakage current density of the P-A-P film was effectively suppressed. When the concentration of PI solution was 7 wt%, the breakdown strength of P-A-P-7 film reached 411.6 MV/m and 350.7 MV/m at 25℃ and 150℃, respectively, which was 58.4% and 44.7% higher than that of single-layer ANFm. Moreover, on account of the reduction of space-charge polarization, the dielectric stability and insulating performance of P-A-P film significantly improved. The obtained results demonstrate that the insulating layers on both surfaces of ANFm contribute to improving the breakdown strength and decreasing the leakage current density. Hence, this work provides a novel approach and a new idea for the development of all-organic high-temperature dielectric films.