Preparation And Research Energy Storage Properties Of BiFeO₃ Fiber/PVDF Composite Films

With the development of modern society,energy issues are concerned.Among many energy storage technologies,dielectric energy storage technology is favored because of its low cost,simple manufacturing,high integration,low energy consumption,fast response and other advantages.Dielectric material is the focus of dielectric energy storage technology.Ceramic/polymer composite has the characteristics of high breakdown field strength,high polarization strength,excellent flexibility and good processability,which has become a research hot spot.In this paper,a polymer matrix composite with high energy density is prepared,by changing the preparation process,which bismuth ferrite?BiFeO₃?was used as filler and poly?vinylidene fluoride??PVDF?as polymer matrix.BiFeO₃ powder with different micromorphology is prepared by the solid-state method,hydrothermal method and electrospinning method.The BiFeO₃/PDVF composite films were prepared by the tape casting method.The results show that the fiber filler has the largest specific surface area,and the fiber BiFeO₃ has a more significant impact on the dielectric properties and magnetic stability of BiFeO₃/PDVF composite films.In low electric field,the fiber BiFeO₃/PDVF composite films have excellent magnetic dielectric properties and energy storage properties in low electric field,due to the large dipole moment of the fiber.The BiFeO₃ fiber/PVDF composite films with different filler content were prepared by tape casting.The results show that the chain movement of polymer is changed,and promoted the transformation of a phase to ? phase in composite films by adding to BiFeO₃ filler.It increases the dielectric constant of the composite.By theoretical model calculation,the contribution of interface to the polarization strength of composite is revealed,and the positive correlation between the interface area and the permittivity,polarizability of the composite film is pointed out.When the filler content is 1 vol.%,the composite films has the largest energy storage density,which is 4.9 J/cm3.The BiFeO₃/PVDF textile films were prepared by electrospinning,hot pressing and heat treatment.The contact between the fibers is suppressed in the polymer matrix and the breakdown field strength is increased by this process.The interface model is proposed and the distribution of electric charge on the fiber interface is revealed.The migration path of electron in polymer under the action of external electric field is reasonably explained.Both ends of the fiber have greater conductivity than the polymer matrix,because the charge is gathered at both ends of the fiber.It means that electrons are more likely to migrate from both ends of the fiber than in the polymer matrix.The breakdown path in the composite is discussed,and the reason why the composite has high breakdown field strength under the low filler content is explained.By the ferroelectric test,the energy storage density of 0.5 vol.%BiFeO₃/PVDF textile film under the electric field of 3800 kV/cm is 9.6 J/cm3.The BiFeO₃/PVDF directional textile film was prepared by electrospinning,hot pressing and heat treatment,and by improving the process,adding parts.By the directional arrangement of the fibers,the stress in the polymer matrix is dispersed,the breakdown path of the composite is extended,and the polarization is enhanced.The energy density of pulse discharge reaches 4.03 J/cm3,and the discharge efficiency reaches 90%within 8 ns by charge discharge test.