Synthesis Of Core-shell Nanoparticles And Their Application As Fillers In Polymer Energy Storage Dielectric

Dielectric materials have a wide range of applications in the electronics and electrical industry,including portable electronic equipment,biomedical equipment and hybrid electric vehicles.With the development of electronic power system integration and miniaturization,the dielectric materials are required to have high energy storage density,and the dielectric constant and breakdown strength of the dielectric are positively correlated with the energy storage density.Traditional ceramic has high dielectric constant,but it has some disadvantages,such as low breakdown strength,complex preparation process.The breakdown strength of polymer is high but the dielectric constant is low.Excellent dielectric materials can be obtained by combining ceramics with high dielectric constant and polymers with high breakdown strength.Through the design of nano-filler,the properties of dielectric composites can be well adjusted to meet the needs of the rapid development of high-end technologies.The main research contents of thesis are as follows:In the second chapter,the traditional ferroelectric material barium titanate(BT)was selected as the filler,and polyvinylidene fluoride(PVDF)with good breakdown resistance and chemical stability was used as the substrate to prepare the dielectric composite.The experimental results show that 1 wt%BT/PVDF has excellent performance,the highest breakdown strength is 4096k V/cm,and the highest energy storage density is 6.9 J/cm~3 under the external electric field.In order to improve the energy storage density of dielectric composites,In the thrid chapter,the amorphous barium strontium titanate coated crystal barium titanate(c-BT@a-BST)was selected as filler and PVDF as polymer substrate to explore the properties of its dielectric composites.It is found that the breakdown strength of c-BT@a-BST/PVDF composite filled with 1 wt%of c-BT@a-BST is 14%higher than that of BT/PVDF composite,and the highest energy storage density can be 11.6 J/cm~3,which is much higher than that of the pure PVDF and biaxially oriented polypropylene film(BOPP).Then the current density and space charge distribution of polymer composites in the external electric field were simulated and analyzed by COMSOL software,and the mechanism of improving dielectric and breakdown strength was clarified.In the fourth chapter,polyimide(PI)with good dielectric properties,thermal stability and high resistivity was selected as polymer substrate.The filler c-BT@a-BST was dispersed in PI polymer matrix and the composites were obtained by roller coating.The thickness of the composites was measured by optical microscope,and the dielectric,breakdown strength,and energy storage properties were tested.The experimental results show that the dielectric property is stable and the breakdown strength is improved compared with the energy storage property of pure PI.