Preparation And Energy Storage Property Of Barium Zirconate Titanate-Barium Calcium Titanate Fiber-Poly (Vinylidene Fluoride) Dielectric Composite

In the context of the development of emerging energy,the researches of dielectric materials are of great significance for the miniaturization and light-weight of the integrated and intelligent electrical energy storage and conversion devices.The dielectric energy storage becomes an important part of pulse power capacitors due to its high power density,which plays a critical role in the application of high-efficiency pulsed power capacitors.And the polarization and the depolarization behaviors of ferroelectric polymers under the electric field correspond to the charging and discharging processes of dielectric capacitors,respectively.Recently,the researches of ferroelectric polymer as dielectric capacitor material with high energy storage density attract the attention of many researchers.Although the researches on the energy storage and conversion for ferroelectric polymer dielectrics are widely studied,there are still the following problems.For instance,it is difficult to obtain a high energy storage density of dielectrics because the polarization and breakdown field strength of dielectrics are limitedly improved.And,the inelastic polarization and energy loss under the applied electric field are induced to reduce the energy storage efficiency of dielectrics.In view of above problems,this thesis systematically studies the composition of dielectric composites,which mainly includes three aspects:the matrix,the filler and the organic-inorganic interface.In addition,the morphology and the distribution state of the filler in the matrix are regulated during the preparation of the composites.For the regulation of matrix,the all-organic ferroelectric polymer-based composites with the linear dielectric polymethyl methacrylate?PMMA?are prepared in this thesis.The PMMA is used to mitigate the relaxation phenomenon of ferroelectric polymer,and to reduce the energy loss and to improve the energy storage efficiency.The effects of PMMA on the crystallinity,dielectric properties,breakdown strength,polarization behavior and energy storage properties of ferroelectric polymer-based all-organic composites are investigated and analyzed systematically.When the weight content of PMMA is 7 wt.%,the P?VDF-TrFE-CFE??PVTC?+7 wt.%PMMA all-organic composite is obtained with the discharged energy density of around 7.0 J/cm³ and the charge and discharge efficiency of around 71.9%under the electric field strength of 330kV/mm.For the regulation of filler,the 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃inorganic nanofibers?BZCT NFs?are introduced into the ferroelectric polymer PVDF matrix.And the PVDF-based dielectric composites with different BZCT NFs composition gradient structures are prepared by adjusting the layer cycle of concentration gradient and the electrospinning sequence of precursor suspension.The 0-10-0 BZCT-PVDF composite with BZCT NFs composition gradient structure possesses the excellent polarization,breakdown strength and energy storage property,such as the discharged energy density is about 9.8 J/cm³ and the charge and discharge efficiency is about 52.0%at the electric field strength of310 kV/mm.For the regulation of filler orientation,the Unaligned BZCT-PVDF and Aligned BZCT-PVDF dielectric composites are prepared by adjusting the arrangement of nanofibers in polymer.The 3 vol.%Aligned BZCT-PVDF dielectric composite is obtained with the good discharged energy density of around 8.9 J/cm³ and efficiency of around 57.6%under 400 kV/mm.For the regulation of organic-inorganic interface,the hybrid inorganic nanofibers of BZCT@SiO₂ NFs with core-shell structure are synthesized.And the highly aligned BZCT@SiO₂-PVDF composite is prepared by electrospinning.The influences of content and distribution of hybrid BZCT@SiO₂ nanofibers on the microstructure and electrical properties of dielectric composites are studied systematically.Meanwhile,the mechanisms of influences of SiO₂ insulating shell on electrical conductivity,tan?,breakdown strength and leakage current behavior of composite are investigated in detail.The 3 vol.%Aligned BZCT@SiO₂-PVDF composite has the better discharged energy density of about 18.9 J/cm³ and efficiency of about 53.3%at 560 kV/mm.And the in-plane thermal conductivity of 3 vol.%Aligned BZCT@SiO₂-PVDF composite is as high as 0.29 W/?m·K?.Referring to the process parameters,the ferroelectric polymer PVTC blending with linear dielectric PMMA is used as matrix,and the hybrid inorganic BZCT@Al₂O₃@SiO₂ NFs work as fillers,and the double shells of Al₂O₃ and SiO₂serve as transition layers at the interface.The PVTC+PMMA composites with the three-dimensional?parallel or orthogonal?distribution of double-shell hybrid BZCT@Al₂O₃@SiO₂ NFs are obtained.It is found that the Orthogonal BZCT@Al₂O₃@SiO₂?PVTC+PMMA dielectric composite with 3 vol.%BZCT@Al₂O₃@SiO₂ NFs possesses the excellent discharged energy density of about 20.1 J/cm³,and the efficiency of about 58.6%at 440 kV/mm.The in-plane thermal conductivity of composite with 3 vol.%double-shell nanofibers exhibiting three-dimensional distribution in polymer can reach 0.33 W/?m·K?.The inorganic nanofiber-ferroelectric polymer composites with excellent energy storage performances are investigated.The factors for storage energy density and efficiency of composites are studied,and the influence mechanism of regulation factors on performance of composite is clarified.The researches in this thesis promote the application of ferroelectric polymer-based dielectric composite in the new energy field.