| Dielectric capacitors,as one of the essential components in energy system,are widely used in the field of electronic and electrical engineering.With the advantages of high working voltage,good flexibility,easy processing and low cost,dielectric composites meet the development trend of miniaturization,lightweight and high integration of electronic components,and stand out among numerous dielectric materials,becoming one of the current research hotspots.However,there are still some problems in the preparation of high-performance polymer based dielectric composites.For example,the type of filling component and polymer matrix,the dispersion and compatibility of fillers in polymer matrix and the issue of interface in composite.According to the problems,dielectric composite films with various low volume fraction dielectric ceramics were prepared in this paper based on the polyvinylidene fluoride?PVDF?.The problem of interface,dielectric properties and energy storage properties of the composite films were disscussed.The main research contents are as follows:?1?Bismuth sodium titanate nanoparticles were synthesized by hydrothermal method,and there were used as fillers to fabricate the BNT/PVDF composite films.The maximum dielectric constant of composite films was 14.8.And the maximum discharged energy density of composites films with 3 vol%BNT nanoparticles reached 6.91 J/cm3 at 330 kV/mm,which was 1.4 times than that of the pure PVDF films.Dopamine was used to modify the surface of BNT nanoparticles to improve the dispersion and compatibility of BNT nanoparticles in PVDF.In addition,due to the insulating effect of dopamine layer and its ability to surpress the movement of polymer chains in the matrix,the dielectric loss of the composite film was reduced,and the breakdown strength improved significantly,so the composite films exhibited the excellent dielectric and energy storage properties.The maximum discharged energy density of 3 vol%BNT@Dopa/PVDF composite film was 13.09 J/cm3,which was 89.43%higher than that of BNT/PVDF composite film.Besides,the composite films performed stable energy storage performance under 80?.In order to further improve the breakdown strength of the composite film,the BNT@TiO2@Dopa nanofibers were prepared by coating the BNT nanofibers with titanium dioxide.Owing to the characteristics of titanium dioxide and dopamine layers,the accumulation and migration of space charge were reduced,and there were less conductive path.So the breakdown strength of the composite film was improved significantly.The highest breakdown strength reached 480 kV/mm,and the maximum discharged energy density was 14.28J/cm3.?2?PMN-PT particles prepared by the method of molten salt and then modified with dopamine.Because of the super high dielectric constant of PMN-PT,the dielectric constant of 15 vol%PMN-PT@Dopa/PVDF composite film reached 19.25,and the minimum dielectric loss was only 0.012 at 1 kHz.The maximum discharged energy density of 3 vol%PMN-PT@Dopa composite film at 370 kV/mm was 11.01J/cm3,which was 2.29 times of that of pure PVDF film.?3?FTN ceramic particles were prepared by the solid-state method and then were modified with dopamine.The dielectric properties of the FTN@Dopa/PVDF composite films were similar to those of BNT based films.The FTN@Dopa/PVDF composites exhibited low electrical conductivity and leakage current.The conductivity of the FTN@Dopa/PVDF films was 6.60×10-66 S/m at 100 Hz,and the leakage current density of FTN@Dopa/PVDF film was in the range of 10-8-10-4A/cm2 at 100 kV/mm electric field.The maximum discharged energy density of FTN@Dopa/PVDF film was 8.12 J/cm3 at applied electric field of 370 kV/mm. |
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