Research On Structural Design And Energy Storage Property Of PVDF-based Composite Films

Polymer-based composites with high discharged energy density and energy efficiency are tremendous desired for modern electronic systems.In recent year,PVDF polymer have drawn increasing attentions owing to their intrinsic advantages of high breakdown strength and excellent flexibility.Yet,the low discharged energy density of PVDF polymer restricts their further applications.Although the researches on the improve energy storage performance of PVDF polymer are extensively studied,such as ceramic fillers with high dielectric constant have been filled into the PVDF matrix,there are still following problems.There seem to be a contradiction between dielectric constant increase and breakdown strength decrease in the monolayer inorganic/organic composites,leading to a limited discharged energy density.In order to overcome the above problems,this paper studies the construction of multilayer composites and regulates each individual-layer properties.Besides,the all-organic composites construct by blending different polymers was also studied.First,in order to the improve dielectric constant and breakdown field simultaneously,a sandwich-structured composite was constructed.x TBT(where x is the TO nw fractions,T and B are the TO nws and BT nps filled layers respectively)sandwich-structured composite with excellent energy storage performance have been realized though regulating each individual-layer properties,including the dielectric properties,polarization,leakage current and breakdown strength and so on.Notably,the maximum discharged energy density of the 2TBT composite film reaches up to 13.7J/cm~3 at 400 MV/m,and maintains a relatively high energy efficiency of 65%.Subsequently,in order to further study the effect of the property difference between two layers on the energy storage performance of multilayer composites,a bilayer heterostructural composite(named as THV/x BT)with excellent energy storage performances was constructed by one layer of a Ba Ti O3 nanoparticles(BT nps)-filled P(VDF-HFP)composite and another layer of a pure P(TFE-HFP-VDF)(THV)polymer with a moderate dielectric constant and high breakdown strength.The experimental and finite element simulation results indicate that regulation of dielectric contrast between these two adjacent layers improves not only the interfacial polarization but also the breakdown strength and limits the leakage current density of THV/x BT composites.As a result,the THV/5BT composite delivers the best energy storage performance with the discharged energy density of 22.7 J/cm~3,and an energy efficiency of 79.0%is achieved.Finally,P(VDF-HFP)is blended with P(VDF-Tr FE-CFE)(VTC)with a high dielectric constant.The experimental results indicate that the all-organic composites(named as x VTC)exhibit improved dielectric constant and breakdown strength due to excellent compatibility between organic polymer.As a result,the 20 VTC composite delivers the best energy storage performance with the discharged energy density of 25.8 J/cm~3,and an energy efficiency of 75.4%is achieved.Subsequently,the sandwich-structured dielectric(named as x VTC-S)was constructed with 20VTC as the outer layer and x VTC(x=30,40,50 and 60)as the inner layer.Ultimately,the discharged energy density of 50VTC-S composites is further increased to 29.2 J/cm~3.