Preparation And Properties Of BN And Al₂O₃@BaTiO₃ Fibers Co-doped PVDF Dielectric Composite Films

For dielectric energy storage materials,the research of high dielectric,high breakdown and high thermal conductivity has attracted much attention.The combination of multiple fillers with morphological structure design is an effective strategy to obtain dielectric energy storage materials with excellent overall performance.In this paper,polyvinylidene fluoride（PVDF）is used as the matrix,and multi-dimensional fillers such as aluminum oxide particles（Al₂O₃）,barium titanate fibers（BT）and boron nitride nano sheets（BN）are used to build a thermal conduction path and inhibit carrier migration,so as to synergistically improve the dielectric constant,breakdown field strength and thermal conductivity of PVDF based composite films.Firstly,BT fibers and BT fibers loaded with Al₂O₃ particles（Al₂O₃@BT）were prepared by electrospinning,then use Al₂O₃ particles and BT fibers blend（Al₂O₃-b-BT）,and Al₂O₃@BT fibers were used to fill PVDF,Al₂O₃-b-BT/PVDF and Al₂O₃@BT/PVDF composites were obtained by casting and hot-pressing.Compared with Al₂O₃-b-BT,Al₂O₃@BT has better dispersion in the polymer matrix,Al₂O₃@BT/PVDF composite films show better breakdown strength,energy storage,thermal conductivity and mechanical properties,and the dielectric constant is slightly lower than that of Al₂O₃-b-BT/PVDF composite films with the same filler content.When the filler content is 5 wt%,The dielectric constant of Al₂O₃@BT/PVDF composite film is 14.1@1 k Hz,The breakdown strength and energy storage density are the highest,reaching 236.5 k V/mm and 6.09 J/cm³ respectively,which are 32.6%and 36.5%higher than Al₂O₃-b-BT/PVDF,2.3 times and 1.9 times higher than pure PVDF.In addition,the thermal conductivity and tensile strength were increased to0.234 W/（m·K）and 47.3 MPa,respectively.Hydroxylated BN nano sheets prepared by high temperature calcinationand and Al₂O₃@BT fibers are filled with PVDF to obtain BN-Al₂O₃@BT/PVDF composite films.The bridging of a proper amount of Al₂O₃@BT fibers and BN nano sheets is conducive to the formation of heat conduction paths and the inhibition of carrier migration,which further improves the breakdown field strength,energy storage performance and thermal conductivity of the BN-Al₂O₃@BT/PVDF composite films.When the content of BN and Al₂O₃@BT are all 5 wt%,BN-Al₂O₃@BT/PVDF composite films show the highest breakdown field strength and the maximum energy storage density,which are 253.9 k V/mm and 7.51 J/cm³,respectively,2.4 times and2.3 times of pure PVDF.At the same time,the thermal conductivity is also greatly increased to 0.508 W/（m·K）,which is 220.8%higher than that of pure PVDF,and the tensile strength is increased to 41.23 MPa.