High Electric Field Conduction and Polarization in Polymer Dielectrics

Polymer dielectrics with high energy density are essential elements to fulfill the future needs on pulse power, power conditioning, and electrification applications. The energy density is determined by the breakdown strength and dielectric constant of the polymer dielectrics, essentially controlled by conduction and polarization processes. However, the high field conduction and polarization phenomena of polymer dielectrics with a lack of fundamental understanding are extremely complex involving electronic and conformational structure of polymer, multi-factor interactions from electrical, thermal, mechanical and chemical properties. Thus, the basic experimental and theoretical research on conduction and polarization phenomena of polymer dielectrics under high electric field is a critical enabler to meet the ever-increasing need for high energy density capacitors. In this comprehensive study, the overarching goal is to come up with a satisfactory understanding of high electric field (high field) conduction and polarization phenomena in polymer dielectrics. Characterizations of the conduction and polarization processes in polymer dielectric thin films are presented with a special focus on the relationship between energy storage properties and physical morphology/chemical structures. A novel high electric field conduction measurement system is developed, making prebreakdown conduction measurement through polymer dielectric thin films possible. High field phenomena involving charge instability and charge induced aging are observed for the first. The analysis of the temperature dependent prebreakdown conduction result allows the reconstruction of the defect density of states in the electronic band structures of polymer dielectrics. The result suggests that semi-crystalline polymer films have fundamental advantages over amorphous polymer films with less defect states and shallower trap depth, resulting in a higher breakdown strength. A systematic broadband dielectric spectroscopy measurement is performed with a detailed analysis of individual polarization processes. A design methodology by combining flexible and rigid segments to enhance the sub-glass transition dipolar relaxation is presented for the exploration of novel high energy density polymers. These findings are very insightful for the understanding of high field phenomena in polymers and the essential structure-property relationship to enhance the energy density of polymer dielectrics. This study paves a way to design and optimize polymer dielectrics with high energy density for future pulse power applications