Research On Energy Storage Characteristics Of Polyetherimide Composite Dielectric Based On Gradient Structure Design

For polymer-based composite dielectrics widely used in modern power electronic devices,it is still a common phenomenon to pay more attention to its energy storage density while ignoring charge/discharge efficiency.How to prepare two important properties-energy storage density and charge/discharge efficiency are both excellent dielectric materials has become our research direction.Breakdown strength and polarization strength are the two most important indicators for judging the performance of energy storage dielectrics.Unfortunately,usually the two are a pair of contradictory characteristics.In order to solve this problem,this paper designs a model of composite dielectric with double gradient structure based on polyetherimide(PEI).Among them,two-dimensional(2D)hexagonal boron nitride nanosheets(BNNS)with reverse gradient distribution are used to improve the breakdown strength of the composite dielectric,and one-dimensional(1D)barium zirconium titanate calcium nanofibers(BZCT NFs)with a normal gradient distribution are used to enhance the polarization strength of the composite dielectric.And 3D phase field simulation results preliminarily verified the correctness of the design route.This novel method effectively solves the dilemma of this major research on the mutual restriction of energy storage density and efficiency.In order to improve the interfacial compatibility between the matrix PEI and the ceramic fiber BZCT,a"core-shell"structure nanofibers of barium calcium zirconate titanate nanofibers modified with SiO₂(BZCT@SiO₂)were prepared as a one-dimensional filler.In order to explore the effect of gradient concentration on energy storage characteristics,a series of nano-composites with double gradient structures with different gradient concentrations were prepared by alternately and directionally filling one-dimensional and two-dimensional fillers into the matrix PEI.The double gradient composite dielectrics obtain extremely high breakdown strength and energy storage density at the same time,and maintain extremely low dielectric loss.Through the optimized topology and the synergy of the two filled phases,a certain composite dielectric achieves excellent energy density(15.2 J/cm³)and extremely high charge/discharge efficiency(82.6%)at a field strength of 580 k V/mm.This work provides a new design strategy for the preparation of high-performance energy storage composite dielectrics.