Research On Energy Storage Properties Of Low-loss PVDF-based Dielectric Films

As a commonly used energy storage element,organic film capacitors have the characteristics of ultra-high releasable power density,high breakdown voltage and fast charge and discharge rates,and have become a research hotspot in the field of energy storage capacitors.However,the dielectric films prepared by academia still have problems such as high dielectric loss and low charge-discharge efficiency.In this paper,poly（vinylidene fluoride-hexafluoropropylene）（Polyvinylidene fluoride-hexafluoropropylene,abbreviated as P（VDF-HFP））and thermoplastic-polyimide（Thermoplastic-Polyimide,abbreviated as TPI）are selected as the main materials.On the premise of ensuring its high dielectric constant,it can effectively reduce the dielectric loss of thin-film materials and improve the energy storage properties of thin-film materials and thin-film capacitors.In this paper,a variety of dielectric film samples with different structures were prepared,and various analytical methods were used to test the dielectric properties and microstructure of the dielectric film samples,and discussed the related energy storage mechanism.The main work is as follows:1.The effects of different flooding temperatures on the dielectric properties of P（VDF-HFP）dielectric films were systematically studied.Through various characterizations,it is found that the leaf-like crystals on the surface of the dielectric film are enhanced with the increase of the flooding temperature.Further research shows that there is a certain relationship between the expulsion temperature and the crystallinity of the dielectric film.When the expulsion temperature is higher,the dielectric film shows higher crystallinity;and the dielectric loss increases with the increase of crystallinity;when the flooding temperature is 120℃,the dielectric loss is as high as 0.0313;according to this conclusion,different flooding temperatures（60℃-120℃-60℃）were prepared)of P（VDF-HFP）multilayer films with a high dielectric constant of 9.45 and a dielectric loss as low as 0.0278.2.The effect of flooding temperature on the dielectric properties of TPI dielectric films was systematically studied.The experimental results show that the crystallinity of the TPI dielectric film increases with the increase of the flooding temperature,and the dielectric constant and dielectric loss are positively correlated with it.When the flooding temperature is 120℃,the dielectric constant is 4.38,the loss is 0.0096.The paper further discusses the influence of the bulk composite structure of TPI material and P（VDF-HFP）material on the dielectric properties.The composite of TPI material with low polarization strength and P（VDF-HFP）can effectively reduce the thermal conductivity of the blended system.Dielectric loss.With the increase of TPI doping ratio,both the dielectric constant and dielectric loss of the composites decreased.When the mass fraction ratio of TPI and P（VDF-HFP）was 1:1,the dielectric loss could be reduced to 0.0179.3.The P（VDF-HFP）/TPI sandwich structure composite film was also prepared in this paper,and the effect of flooding temperature on the dielectric properties and energy storage properties of the interlayer composite film was systematically studied.By adjusting the crystallinity,the prepared sandwich structure composite film at 60°C（TPI）-120°C（P（VDF-HFP））-60°C（TPI）has the best dielectric energy storage properties,and the dielectric loss is further lower.At the same time,the composite film has a breakdown field strength of 473 k V/mm,and the energy storage density reaches 4.89 J/cm~3.