Novel Nanoparticle-filled Organic-inorganic Composite Films With High Energy Density

Dielectric capacitors have the advantages of high power density,fast charge and discharge speed,safety and reliability,high voltage resistance,and long service life,so they are widely used in electrical energy storage,medical,electric vehicles,and military fields.With the development of power electronic devices and systems toward miniaturization,light weight,and integration,dielectric capacitors with low energy density will gradually fail to meet the requirements.Therefore,it is of great significance to develop new dielectric capacitors with high energy storage density.Polymer-based nanocomposites combine the advantages of polymers with high breakdown field strength and inorganic nanoparticles with high dielectric constant,which is one of the hot topics in the field of high energy storage dielectrics.To this end,this paper uses PVDF or its copolymer as the polymer matrix to composite with new-type nanoparticles,and explores the effects of filled particles on the dielectric,breakdown,and energy storage properties of composite films.Firstly,in improving the energy discharged efficiency,poly vinylidene fluoride-hexafluoropropylene film blended with poly(methylmethacrylate)is employed as the polymer matrix.Highly dispersive Ba0.6Sr0.4TiO3 nanoparticles with an average particle size of 12.1 nm are utilised to improve the polarisation of the blend film without sacrificing the dielectric strength.Uniform nanocomposite films with high flexibility and excellent energy-storage performance are obtained.Especially,due to the optimisation of both polymer matrix and fillers,the Ba0.6Sr0.4TiO3 modified P(VDF-HFP)/PMMA blend films show improved breakdown strength and depressed energy loss,which leads to an enhanced energy density of 10.3 J/cm3 at 378 kV/mm.Secondly,topological insulator two-dimensional Bi2Se3 hexagonal nanoplates,which are highly insulating in the bulk and have a conductive topological surface state,have been prepared via an "EG-sol" method and characterized by transmission electron microscopy,X-ray diffraction,and scanning electron microscopy.Bi2Se3/PVDF nanocomposites with various Bi2Se3 contents have been fabricated by a tape-casting method.The microstructure and dielectric performance of the Bi2Se3/PVDF nanocomposites are studied.The dielectric constant of the dense nanocomposite films keeps a relatively low value of about 16 when the Bi2Se3 content is lower than 12 vol.%,then suddenly increases to 36 with a critical Bi2Se3 content of 13 vol.%.The study of the Bi2Se3/PVDF nanocomposite system is conducive to the exploration of high-performance dielectrics.Lastly,compact nanocomposite films comprising PVDF polymer and core-shell BaTiO3@TiO2 nanoparticles are prepared,in which the BaTiO3(d?8 nm)nanoparticles are encapsulated by the amorphous TiO2 shell layer.Compared to the conventional BaTiO3/PVDF nanocomposite,the BaTiO3@TiO2/PVDF nanocomposite takes advantage of the small particle size and the gradient dielectric design of the interface,which enhances the electric displacement as high as 65%and the breakdown strength of 20%simultaneously.A maximal discharged energy density of 11.34 J·cm-3 is achieved under an electric field of 420 kV·mm-1 in the nanocomposite film containing 5 vol.%BaTiO3?10 wt.%TiO2.Therefore,the gradient design of ultrasmall dielectric nanofillers shows high potential in fabrication of high energy-density nanocomposite.