Enhanced Discharged Efficiency and High Energy Density at Elevated Temperature in Polymer Dielectric via Manipulating Relaxation Behavior

Polymer dielectrics with excellent dielectric properties and energy storage performance under elevated temperature are urgently needed in electrical power systems.Polyetherimide(PEI),which is supposed to be the most promising candidate among polymer dielectric materials,has a limitation for high-temperature dielectric applications especially at high electric field owing to secondary relaxation.Herein,a series of self-cross-linkable oligomers are prepared by combining the advantages of PEI and phenylethynyl groups.Cross-linked polymer dielectric films with enhanced voltage resistance and low leakage current density are obtained by cross-linking under oxygen.The occurrence ofβ-relaxation is diminished by cross-linking,which makes polymer dielectrics exhibit desirable dielectric stability over a broad temperature and frequency range.Particularly,the dielectric loss of c-10%PEPA-PEI at 1000 Hz is 0.0037 and 0.0043 at room temperature and 150℃,respectively.Simultaneously,the polymer dielectric maintains a still low dielectric loss(<0.010)between 10^(2)and 10^(6)Hz.Furthermore,c-10%PEPA-PEI possesses excellent hightemperature energy storage performance owing to much interchain reaction originating from proper chain length,and exhibits ultrahigh charge–discharge efficiency(>95.0%)and improved energy density(3.6 J/cm^(3))at 150℃.The authors believe that these cross-linked films showing excellent dielectric performance have a promising future in high-temperature applications.