| Fossil fuel reserves are limited and energy consumption is rapid,spurring the exploration of renewable energy and high energy density storage.Compared with other energy storage technologies such as batteries,fuel cells and super capacitors,electrostatic capacitors are the only energy storage devices that can provide higher power density,and are widely used in electronic and electrical equipment such as circuits and high-frequency inverters And hybrid cars.With the increasing demand for compact,miniaturized and high-efficiency electronic equipment,people have higher requirements for energy storage medium materials with high energy density.The combination of high dielectric constant of ceramics and high breakdown strength of polymers is of great significance for improving the energy storage performance of composite materials.In this paper,Na0.5Bi4.5Ti4O15(NBT4)is used as the ceramic filler,and polyvinylidene fluoride(PVDF)is used as the polymer matrix.By changing the morphology of the NBT4 ceramic particles,and designing the electric field distribution and"sandwich" of the multilayer composite material structural design to improve the dielectric properties and energy storage properties of composite materials.The research content of this paper is as follows:NBT4 sheets and NBT4 particles were prepared by molten salt method and traditional solid phase method,and NBT4 sheets/PVDF composite material and NBT4 particles/PVDF composite material were prepared by casting method.Since two parallel NBT4 sheets can be regarded as a microcapacitor,the capacitance value of the entire composite material can be regarded as a microcapacitor connected in parallel,and an increase in capacitance can increase the dielectric constant of the composite material.The NBT4 sheets can also serve as a barrier layer inside the composite material,which makes it difficult to form a conductive path under the action of an external electric field,which ultimately increases the breakdown strength of the composite material.Since the dielectric constant and breakdown strength of the NBT4 sheets/PVDF composite material have been improved,the energy storage performance of the NBT4 sheets/PVDF composite material is better than that of the NBT4 particle/PVDF composite material.When the volume fraction of the NBT4 sheet is 1%,its energy storage density reaches 9,45 J/cm3 at 300 kV/mm electric field,and the energy storage efficiency of the composite material is 52.28%.Using NBT4 as a filler,a three-layer gradient structure is designed.The volume fraction of NBT4 is gradually reduced from the top layer to the bottom layer to construct a gradient electric field.Under the applied electric field,the gradient electric field will have a buffering effect that makes the material difficult to break down,thereby increasing Breakdown strength of large composite materials.The larger interface polarization between the layers increases the dielectric constant of the composite.The sample 0.5-2-5 gradient-textured composite material obtained an ultra-high energy storage density of 16.41 J/cm3 under an electric field of 350 kV/mm,at which time the energy storage efficiency of the composite material was 53.3%.By adding NBT4 sheets on both sides to ensure high breakdown strength of the composite,the intermediate layer(BaTi03)BT/PVDF layer provides a high dielectric constant for the composite,the purpose is to add more BT nanometers while maintaining high breakdown strength The ceramic particles thus increase the dielectric constant of the composite material.The sample 0.5-1.0-0.5 composite material obtained an ultra-high energy storage density of 16.9 J/cm 3 at an electric field of 460 kV/mm,and the energy storage efficiency of the composite material was 62%. |
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