Preparation Of PVDF-based Organic/Inorganic Composites And Investigation Of Their Dielectric And Energy Storage Properties

With the development of technology and the exhaustion of fossil energy resources,the search for sustainable energy has always been a hotspot of current research.Polymer film capacitors are widely used in the field of power electronics because of their fast charge and discharge speed,low cost,and excellent processing performance.However,due to the limitation of the covalent bond,the dielectric constant of the polymer is relatively low,resulting in a low energy storage density of the material,which severely limits the application of the current dielectric polymer.Even the most common commercial Biaxial ly Oriented Polypropylene(BOPP)at present has an energy density of only 2-3 J/cm3 under an electric field of up to 600 MV/m,which is difficult to meet the current increasing performance of high-performance energy storage equipment Demand.To this end,scholars have conducted a lot of experimental research,and found that adding inorganic fillers to polymers is an effective method.On this basis,reasonable structural design,such as micro-structure control,is to achieve the coordination of various components Function,and then prepare a high-performance dielectric energy storage composite material.At present,the most common method is to add a high content of inorganic filler to the polymer,but the introduction of a large amount of inorganic filler will inevitably bring about the problem of a decrease in the mechanical properties of the composite materials.Based on the above problems,this paper prepared sandwich-like h-BN/PVDF/BT ternary composite dielectric materials on the basis of adding low content(<1 wt%)inorganic fillers,and studied their properties.In this paper,polyvinylidene fluoride(PVDF)is selected as the polymer matrix.In addition to its advantages of light weight and easy processing,the dielectric constant of PVDF(about 8-13)is also relatively high among the polymers.Barium titanate(BT)and hexagonal boron nitride(h-BN)are chosen as inorganic fillers,the choice of barium titanate(BT)is due to its large dielectric constant,and h-BN,which has always been known as "white graphene",it has excellent performance,and compared with graphene,its insulating advantages make it applicable to insulating materials.In this thesis,bulk h-BN is exfoliated by tip ultrasonic-assisted stripping method to obtain several layers of Boron Nitride Nanosheets(BNNSs),then BNNSs and BT are separately compounded with PVDF by solution blending method,using adjustable film applicator to scrape film to prepare binary composite film,and finally a sandwich-like ternary composite material is prepared by hot pressing method.Different from the reports in the literature,the composite material prepared in this experiment showed good dielectric properties when the low content of inorganic filler was added.After adding BNNSs and BT,the dielectric constant of the composite material has been significantly improved.In particular,the enhancement of dielectric constant of the ternary h-BN/PVDF/BT composite is more obvious.When the BNNSs content is 0.9 wt%,the dielectric constant of the ternary composite can reach 13.5,which is about 1.5 times of pristine PVDF.At the same time,through the comparison of the breakdown strength of several composite materials,it is found that the breakdown strength of the binary composite film is significantly higher than that of the pure PVDF,which is about 1.7 times of pure PVDF.At the same time,the D-E diagram of the composite films is integrated to obtain the discharge energy density and charge-discharge efficiency of the composite films.It was found that the discharge energy density of the ternary composite film was higher than that of the addition of the binary composite film and pure PVDF.Under the electric field of 150 MV/m and the BNNSs content of 0.1 wt%,the energy density of the ternary composite film reached a maximum of 1.25 J/cm3.