The Preparation Of Two-dimensional Nanosheets And Application Research In Composites

In this paper,nanosheet-like magnesium oxide(MgO NSs)and hexagonal boron nitride(h-BN NSs)powders were prepared,the two kinds of two-dimensional fillers were combined with PVDF to form MgO NSs/PVDF composites and h-BN NSs/PVDF composites by solution casting method.The effect of the addition amount of fillers on the properties of dielectric composites was studied,it was helpful to obtain the PVDF-based composites with high stored energy density,and the mechanism of improving compisites dielectric properties by two-dimensional fillers was discussed.MgO NSs with about 400 nm lateral sizes and 30 nm thickness were synthesized by hydrothermal reacting 24 h at 180?,in which,MgCl2 as the magnesium source and NaOH concentration was 2 mol/L.The morphology of MgO NSs was uniform and the main crystal was cubic phase.The effect of MgO NSs addition on the properties of MgO NSs/PVDF composites was investigated.The results showed that the introduction of MgO NSs could improve the dielectric properties of PVDF material,and the properties of composites with 3wt%MgO NSs was best,its dielectric constant was 9.2,the breakdown strength was up to 404 kV/mm,the stored energy density was up to 7.81 J/cm3 and 92%higher than that of the pure PVDF material.The breakdown strength and stored energy density of 3wt%MgO NSs/PVDF composites were also 10%and 21%higher than MgO NPs/PVDF composite with the same amount of spherical nano-magnesia(MgO NPs).The results showed that the addition of two-dimensional fillers had an advantage in improving the breakdown trength and stored energy density of composites.Ultrathin hexagonal boron nitride nanosheets(h-BN NSs)were prepared by aqueous solvent ultrasonic stripping method with lateral sizes and thicknesses of 200-400 nm and 2 nm,respectively.The effect of the addition amount of h-BN NSs on the properties of h-BN NSs/PVDF composites was investigated.The results showed that the dielectric properties of composites with h-BN NSs were higher than composites with MgO NSs.When 8wt%h-BN NSs were added,the composite reached a maximum breakdown strength and stored energy density to 486 kV/mm and 10.25 J/cm3,respectively,which led to 20%and 31%increasement compared with 3wt%MgO NSs/PVDF composites.Theoretical analysis showed that the two-dimensional fillers in this study had a significant effect on improving the breakdown strength and stored energy density of dielectric composites.On the one hand,the fillers itself was high insulation material,on the other hand,the two-dimensional fillers have a high aspect ratio which made it tend to be perpendicular to the electric field distribution in the PVDF matrix,and acted as insulating barriers to impede the direct extension of the electronic tree,the electron tree would spread along the surface of the two-dimensional sheet,which made the breakdown path of the material more tortuous.As a result,the breakdown strength of the composites was significantly increased,and the high breakdown strength resulted in a higher stored energy density of the composites.