The Design Of Ceramics Fillers And Properties Study In Polymer-based Nanocomposite Dielectrics For Energy Storage

Due to the advantages of high power density,high operating voltage,and high cycle lifetime,the dielectric capacitor is widely used in pulse power sources,inverters and so on.However,the current mainstream dielectric materials suffer from the disadvantage of low energy storage density thus cannot adapt to the development trend of miniaturization of energy storage devices.Therefore,the development of dielectric materials with high energy storage density becomes one of the hot spots in the scientific and industrial circles.Combining the high dielectric constant of ceramic materials and the high breakdown strength of polymer materials,polymer-based nanocomposite dielectric materials has become one of the most significant choice for next-generation dielectric capacitors.In view of the insufficient understanding of the interface polarization and dielectric theory of nanowire filled composites in the current research,different types of nano-fillers were fabricated,mixed with P（VDF-CTFE）polymer matrix,and prepared their composites films by solution casting.As a result,the following three aspects were explored:Firstly,a highly insulating SiO₂ layer was coated on the surface of high dielectric constant BaTiO₃ nanoparticles to construct a core-shell structured filler.Comparing the energy storage performance of pure BaTiO₃ nanoparticles filled composites,it is found that although SiO₂ coating reduces the electrical displacement of the composite,the breakdown strength is significantly improved and the remnant polarization is reduced due to the decrease of interfacial polarization,which ultimately leads to a significantly improved discharged energy storage density and charge-discharge efficiency.Secondly,on the basis of SiO₂ coated BaTiO₃ nanoparticles,the paraelectrical SrTiO₃ with lower dielectric constant was selected to construct SiO₂@SrTiO₃ core-shell nano-filler.The effect of volume fraction of the filler on the energy storage properties was studied systematically.Then the energy storage performance of SiO₂@SrTiO₃ and SiO₂@BaTiO₃ filled nanocomposite were compared,it is found that the low dielectric difference between filler and polymer matrix can effectively reduce the distortion of the electric field distribution,so that the ceramics filler can bear a larger electric field.Therefore,high polarization of the ceramic filler can be obtained,resulting in a relatively high electrical displacement of the composite.More importantly,the smaller difference in dielectric constant further reduces the interfacial polarization,resulting in greatly improved charge-discharge efficiency.Finally,a dielectric model of one-dimensional nanowire-filled nanocomposites was constructed based on Maxwell-Garnet model.The theoretical model showed that the dielectric constant of the composites increased with the increase of the aspect ratio.The dielectric constant is saturated when the aspect ratio reaches 100.Subsequently,SrTiO₃nanowires with different aspect ratios were prepared by hydrothermal method.The effect of aspect ratio on the dielectric constant of the composites was confirmed by experiments.It was also found that increasing the aspect ratio of nanowires can improve the breakdown strength.Therefore,both theory and experiment have proved that increasing the aspect ratio of nanowires can improve the energy storage performance of composites.