Research On The Preperation And Dielectric Properties Of Calcium Copper Titanate/Polyvinylidene Fluoride Composites

The materials with the high dielectric property have very broad application prospects in electrical and electronic engineering fields,such as energy storage capacitors for pulse power sources and embedded capacitors.In the field of energy utilization in the new era,the needs for achieving lightweight,miniaturized and special applications of energy storage devices has placed higher demands on the dielectric property of the materials.It is hoped to obtain the dielectric material system with good comprehensive properties including high permittivity,low dielectric loss,high breakdown strength and easy processing.Therefore,the high dielectric ceramic-polymer composite has attracted more and more attention with the development of nanocomposite technology.In this paper,the structural design of copper calcium titanate(CaCu₃Ti₄O₁₂)inorganic ceramic filler was carried out to improve the dielectric and energy storage properties of polyvinylidene fluoride?PVDF?-based composites.In the study of micro-/nano-CaCu₃Ti₄O₁₂/PVDF composites,micro-sized CaCu₃Ti₄O₁₂?CCTO?particles were prepared by the sol-gel and combustion method,and nano-sized CCTO particles were prepared by a hydrothermal synthesis method.And micro-or nano-CCTO can increase the relative permittivity of PVDF-based composites.The CCTO@Ni microparticle filling phase was synthesized by electroless nickel plating,and the CCTO@Ni/PVDF composite film with a high relative permittivity was obtained by applying magnetic field treatment in the solution coating method.Research shows that the surface nickel plating modification of CCTO particles can reduce the amount of filling phase.Using magnetic field treatment can promote interfacial polarization and further increase the relative permittivity of PVDF.The copper calcium titanate fiber was prepared by electrospinning method,and the spinning and annealing parameters were controlled to obtain CCTO fiber filling phase with different size and surface morphology.It was comparatively studied that effects of morphology and size of the CCTO fiber on microstructure and dielectric property of PVDF.Controlling parameters such as the amount of polyvinylpyrrolidone?PVP?,spinning speed,sintering temperature and sintering time can regulat the surface morphology and size of CCTO fibers.Compared with microparticles,copper titanate nanofibers?CCTO NFs?are randomly distributed in the PVDF matrix,which are less prone to appearing agglomeration and pore defects.And it has stronger interfacial polarization with the matrix,which more effectively improve the dielectric properties of PVDF.In this paper,the surface electroless nickel plating and process control of CCTO NFs was carried out,and the CCTO@Ni NFs filling phase with controlled morphology was obtained,and the CCTO@Ni NFs/PVDF composite film with a higher relative permittivity was prepared.The CCTO@Ni NFs maintained good dispersion in the PVDF matrix;Introduction of Ni nanoparticles significantly increased electron concentration in the interface region,while the magnetic field induced strengthening of interfacial polarization,resulting in significantly increasing relative permittivity of the PVDF-based composites.Methods of surface electroless nickel plating and magnetic field treatment can significantly improve relative permittivity of PVDF-based composites,accompanied by an increase in the loss factor,which affects the breakdown and energy storage characteristics of the material.In order to overcome the above problems,the CCTO@Al₂O₃ NFs filling phase with a core-shell structure was designed.And the Al₂O₃NFs/PVDF,CCTONFs/PVDFandCCTO@Al₂O₃NFs/PVDF nanocomposites have been prepared after filling phases were treated by the dopamine.Effects of filling phase type,volume fraction and core-shell structure design on microstructure,dielectric properties,breakdown properties and energy storage characteristics of PVDF composites were studied.Research shows that the intrinsic high dielectric property of the CCTO core can maintain a high relative permittivity of the composite??_r¹8.4?.Insulated Al₂O₃ shell can not only suppress carrier migration to reduce inherent conductivity,resulting in reducing loss factor?tan?⁰.13?,but also improve dielectric variability to alleviate electric field distortion,resulting in enhancing the breakdown strength?E_b³53.77kV/mm?.At an electric field strength of 340kV/mm,the maximum of energy storage density of 4vol.%CCTO@Al₂O₃NFs/PVDF nanocomposite film is 8.46J/cm³,which is 1.3 times higher than that of PVDF.