| Dielectric capacitors are received widespread attention with its'very stable performance,excellent cycle life and high power density.However,its application is limited by the low discharge energy density of dielectric materials in capacitors.Therefore,improving its discharge energy density is one of the research hotspots in the field of high-performance thin film capacitors.Polyvinylidene fluoride(PVDF)has good dielectric constant and breakdown strength,but its energy storage density can not meet the current development.In order to improve the dielectric constant and e nergy storage density,polypyrrole(PPy)with two different doping states was selected as filler to improve the dielectric constant and energy storage density of composite films.Firstly,PPy-Ti O2/PVDF composite film and PPy-C/PVDF composite film were successfully prepared by electrostatic spinning and hot pressing.The microstructures of two kinds of the monolayer composite film were characterized,and the effects of PPy-Ti O2 and PPy-C on their mechanical properties were explored.The dielectric and breakdown properties were tested as the research objectives.Infrared spectrum and XRD analysis show that the addition of PPy-Ti O2 and PPy-C can promote the formation of?phase of two kinds of composite films.SEM diagram shows that the two particles are well embedded in PVDF fiber,respectively.The dispers ion of the two composite films at different concentrations can be observed.The experimental results show that the energy storage modulus of PPy-Ti O2/PVDF composite film reaches 1125 Mpa,which is 2.13 times of that of pure PVDF at the same temperature.Th e energy storage modulus of PPy-C/PVDF composite film is 1.5 times that of pure PVDF at the same temperature.40 wt.%of PPy-Ti O2/PVDF composite film and 7 wt.%of PPy-C/PVDF composite film have the highest dielectric constants,which are28.5@1000 Hz and 32.9@1000 Hz,respectively,212%and 265%higher than that of pure PVDF.10 wt.%PPy-Ti O2/PVDF composite film and 1 wt.%PPy-C/PVDF composite film have the highes t breakdown strength,reaching 44k V/mm and 45.2 k V/mm,respectively.In order to improve the energy storage density of the composite films,In further study,PVDF||PPy-Ti O2/PVDF||PVDF composite films and PVDF||PPy-C/PVDF||PVDF composite films is successfully prepared by electrostatic spinning and hot pressing process.The microstructure analysis shows that the boundary line between the layers of the two composite films is relatively obvious.And there are no obvious defects at the interface.The performance test results show that the construction of the three-layer structure composite films can still increase the dielectric constant of the composite films.When PPy-Ti O2 content is 40 wt.%,the dielectric constant of PVDF||PPy-Ti O2/PVDF||PVDF composite films was the highest,reaching 20.4@1000 Hz,119%higher than PVDF film(9.3@1000 Hz).When the content of PPy-C is 5wt.%,the dielectric constant of PVDF||PPy-C/PVDF||PVDF composite films was the highest,reaching 17@1000 Hz,85%higher than the PVDF film(9.3@1000 Hz).The breakdown strength of PVDF||PPy-Ti O2/PVDF||PVDF composite films with 10 wt.%was the highest,reaching 161 k V/mm.The breakdown strength of PVDF||PPy-C/PVDF||PVDF composite films with 1wt.%is the highest,reaching 118.2 k V/mm.When the filling amount is 30wt.%,under the breakdown strength of 1700 k V/cm,PVDF||PPy-Ti O2/PVDF||PVDF composite films of energy storage density is 2.68 J/cm~3.When PPy-C content is 5 wt.%,under 1000 k V/cm PVDF||PPy-C/PVDF||PVDF composite films energy storage dens ity is 1.22 J/cm~3.This is because the presence of filler can improve the polarity of PVDF,coupled with the interface effect,the shape of D-E curve is relatively elongated.It is proved that PVDF matrix composite films have good dielectric properties by adding doped conductive polymer. |
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