Preparation And Dielectric Properties Of Magnetically Oriented ZnFe₂O₄ Core-shell Particles/PVDF Composite

Energy storage capacitors have great potential for application in the fields of electronics and advanced technology due to their high energy storage efficiency and high breakdown voltage.However,due to the relatively low energy storage density of common energy storage capacitor materials,most energy storage materials are often bulky in practical use,making it difficult to adapt to the requirements of today’s society for lightweight and miniaturization of energy storage materials.Among all kinds of capacitor materials,polymer matrix composites are the most promising to achieve this goal.For polymer matrix composites,the distribution of functional fillers in the matrix has an important impact on the dielectric properties of the materials.However,under natural conditions,most of the functional fillers are disorderly distributed in the polymerization system.It is found that the dispersion of functional fillers can be effectively improved and the orientation of functional fillers can be induced by applying external physical field in the process of material preparation,which endows polymer matrix composites with excellent properties.In this paper,core-shell particles with BaTiO₃as shell and Zn Fe₂O₄as core were prepared by sol-gel method;The core-shell particles with amorphous carbon（C）as shell and magnetic rod-shaped zinc ferrite（Zn Fe₂O₄）as core were prepared by freeze drying method.These two kinds of core-shell particles were doped into polyvinylidene fluoride-co hexafluoropropene P（VDF-HFP）to prepare composite materials.On this basis,by introducing a vertical parallel magnetic field during the curing process,Zn Fe₂O₄@BaTiO₃/P（VDF-HFP）and Zn Fe₂O₄@C/P（VDF-HFP）composite film with orderly arrangement of particles was successfully obtained.The morphology,dielectric properties and energy storage properties of the two kinds of composite films were tested.The effects of different arrangement of rod fillers in the matrix on the polarization,electric field distribution and energy storage properties of the composite films were analyzed by finite element simulation.The test results show that the core-shell particles prepared in this experiment are composed of magnetic core and dielectric shell.The core-shell particles can rotate under the action of magnetic field,thus forming an orientation structure parallel to the electric field in the composite film.When the Zn Fe₂O₄@BaTiO₃and Zn Fe₂O₄@C oriented parallel to the test electric field,the maximum permittivity of the oriented composite is 27.76 and 40.11,which is 28%and33%higher than that of the unoriented composite,113%and 208%higher than that of the pure polyme;When the filling ratio of Zn Fe₂O₄@BaTiO₃/P（VDF-HFP）composite and Zn Fe₂O₄@C/P（VDF-HFP）composite is 40 Vol.%,the energy storage density of the oriented composite film is 18%and 22%higher than that of the unoriented composite material,32%and 53%higher than that of the polymer pure film.The finite element simulation results show that the polarization degree and energy density of the composite film with the orientation structure parallel to the electric field direction is significantly higher than that of the composite film without orientation,which further verifies and explains the internal mechanism of the performance improvement of the oriented composite film in the experimental results.Therefore,the structure of orientation that one-dimensional fillers parallel to the electric field can effectively improve the dielectric properties and energy storage properties of the composite by using the external magnetic field.