Research On Preparation And Energy Storage Performance Of Polyethersulfone Dielectric Composite

As energy storage device,dielectric capacitors have the advantages of long service life,good temperature stability,and higher power density.They play a crucial role in hybrid vehicles,filters and inverters.Polymers with excellent flexibility are the materials of choice for dielectric capacitors.Polymer polyethersulfone（PESU）has the advantages of high breakdown strength and low dielectric loss.However,the energy storage density and polarization strength of PESU are not ideal,which can limit practical applications.Therefore,the starting point of this research is to improve the polarization strength under the premise of increasing the breakdown strength of PESU polymer,and the energy storage density of PESU-based polymers is effectively elevated.The specific research mainly focuses on three parts: heat treatment,introduction of inorganic filler phase and core-shell structure.It is well known that different heat treatment temperatures can affect the evaporation rate and molecular structure of the solvent.Simultaneously,the morphology and structure of the material can be greatly transformed in the microscopic aspect.Consequently,this thesis firstly researches the effects of five different heat treatment temperatures on the microstructure and electrical properties of PESU dielectric materials,and determines 140 ℃ as the relative optimum heat treatment temperature.Energy storage density and efficiency of PESU reaches up 7.0J/cm³ and 85% at 390 kV/mm,respectively.On this basis,high dielectric constant barium calcium zirconate titanate nanofibers(0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ NFs,BZCT NFs)are prepared as the fillers by electrospinning technology,then BZCT NFs be doped into PESU matrix.It can enhance the energy storage performance of dielectric composite by adjusting the content of BZCT NFs.The results illustrate that the 3 wt.%BZCT/PESU dielectric composite has discharge energy density of 8.4 J/cm³ and efficiency of 72% at 420 kV/mm.COMSOL simulation results demonstrate that the local electric field distortion of the composite dielectric is severe after the introduction of BZCT NFs,and lead to reduced charge-discharge efficiency.It is necessary to ensure high energy storage density while still maintaining high efficiency by alleviating the local electric field distortion.In this thesis,inorganic filled phases with core-shell structure are prepared by water bath method and hydrothermal method,respectively.BZCT NFs are wrapped with Zn O to prepare BZCT@ZnO NFs and composited with PESU.When the filling content is 1 wt.%,the discharge energy density of BZCT@Zn O/PESU dielectric composite can obtain 7.8 J/cm³,meanwhile,the efficiency is 82% at 400 kV/mm.BZCT NFs are wrapped with bismuth ferrite-strontium titanate（0.25BiFeO₃-0.75 SrTiO₃,BFSTO）as a buffer layer to alleviate the dielectric property difference.The discharge energy density of 2wt.%BZCT@BFSTO/PESU dielectric composite can acquire 10.5 J/cm³,at the same time,charge-discharge efficiency is 84% at 500 kV/mm.Compared with pure PESU,the discharge energy density is increased by 50%.in the meantime,it can maintain high efficiency.This experiment conducted in-depth research on PESU-based dielectric composite,laying an experimental foundation for improving breakdown strength and energy storage performance of dielectric composite,providing new ideas for promoting the development of new dielectrics.