Preparation And Properties Of Polyvinylidene Fluoride Based Composites With High Dielectric Performance And Energy

With the development of electron-electrical systems,the research of thin-film capacitors become more and more important.Polymer dielectrics are the preferred materials for high-energy density capacitors,owing to their high breakdown strength,mechanical flexibility as well as light weight.However,their applicability is largely impeded by their intrinsic low dielectric permittivity.As compared with polymers,inorganic materials,such as ferroelectric ceramics,have relatively higher permittivity.However,dielectric ceramics are limited by their much smaller breakdown strength,harsh processing conditions and poor scalability.Hence,it is difficult to find a single dielectric material with all the desired properties.Introduction of ceramic fillers with high dielectric constant into polymer matrix with high breakdown strength is a promising method and has been widely studied.However,the dispersion of nanoparticles,as well as the compatibility between polymer and nanoparticles,become giant challenges in the method of nanocomposites.In order to avoid the weak compatibility and agglomerated nanoparticles,surfactants are usually employed.The distribution of physical fields in multi-component composite materials can be well adjusted by rearranging the organization of the constituents to obtain the optimized overall performance.In this contribution,the network of MPMS@BaTiO3/P(VDF-TrFE)nanocomposites,the heterogeneous PMMA/(VDF-TrFE)sandwich structure films,the five layers structure BaTiO3/P(VDF-HFP)films and the TiO2@PDA@Ag/PVDF nanocomposites are prepared:1.The methods of nanocomposite and cross-linking are combined to create amorphous regions nearby crystalline regions,leading to the improvements of energy density and efficiency.In addition,the preparation was easier than sandwich structures and significantly improved energy density and efficiency compared to the nanocomposites.In this work,firstly γ-methacryloyl-propyltrimethoxysilane(MPMS)was used as a coupling agent to modify BaTiO3 nanoparticles(BT NPs),leading to the double bonds onto the surface of the nanoparticles,then breaking into free radicals initiating the reaction of cross-linking by irradiation.Then the MPMS@BT NPs were added into the P(VDF-TrFE)matrix.Finally,MPMS@BT/P(VDF-TrFE)ferroelectric nanocomposite network occurred by irradiation.The hierarchical interface is controlled to get a high energy density(9.52 J/cm3)in 100 kGy irradiated nanocomposite.It is 1.34 times larger than unirradiated samples and ≈476%times over than biaxially oriented polypropylenes.2.Antiferroelectric-like behavior is achieved by building dipoles along antiparallel directions in ferroelectric layer.In this contribution,P(VDF-TrFE)inner layer with PMMA outer layer is manufactured through layer-by-layer stacking with easily obtained raw materials(PMMA,P(VDF-TrFE),showing more functional and accessible for tuning ferroelectric response.With the increasing thickness of outer layer,the resulting ferroelectric responses from normal ferroelectric to antiferroelectric-like to line behavior occur.To explore the influence of polarization of outer layer on ferroelectric response,the PMMA outer layers are substituted by PMMA and P(VDFTrFE)mixture.The film with lowest polarization of outer layer shows antiferroelectriclike behavior.Hence,we conclude that decreasing the polarizability and thickness of outer layer lead to antiferroelectric-like behavior.More,the highest discharge energy density is 11.72 J/cm3 at 3300 kV/cm with the charge-discharge efficiency of 50.4%in PV0.05PM1.75.3.Five layers films is prepared by tuning multi-layer structure.Firstly,the sandwich structure films were fabricated by spin-coating and drying.Then,the five layers films are prepared by the same way.There are 5-A,10-B,15-C BT/P(VDF-HFP)nanocomposites.The dielectric constant of five layers films increases steadily with the BT content of outer and inner layers.The energy density of five layers films first increases and then decreases with the increased BT content of outer and inner layers.The highest discharge energy density is 11.65 J/cm3 in 10-B five layers BT/P(VDFHFP)nanocomposites.4.TiO2 nanofibers with single atomic in the surface is prepared,resulting in charge restriction effect and outstanding energy storge density.Anatase TiO2 nanofibers with high aspect ratio is synthesized by hydrothermal method and modified by dopamine.Then,the TiO2 nanofibers were thermal treated at reducing atmosphere to achieve defective supports with surface oxygen vacancies.TiO2 nanofibers with surface oxygen vacancies and TiO2@DPA nanofibers can catch the isolated Ag single atomic,forming TiO2@Ag and TiO2@DPA@Ag.Finally,the different kinds of nanofibers filled PVDF based nanocomposite films were prepared by solution blending.Interesting,the highest discharge energy density is 10.43 J/cm3 in TiO2@DPA@Ag/PVDF nanocomposites.