Ke Yu's research while affiliated with Xi'an Jiaotong University and other places

A series of composites comprising of poly(vinylidene fluoride) (PVDF) as matrix and calcium copper titanate (CCTO) particles as fillers were prepared and investigated. The dielectric displacement and energy density of the composites are enhanced and an energy density of 8.64 J/cm3 has been obtained under an electric field of 310 MV/m with the CCTO concentration of 3 vol.%. The results indicate that the introduced low volume fraction of CCTO fillers contribute to the enhancement of the dielectric responses and energy storage properties of the composites.

Surface modification on ceramic fillers is of interest to help improving their compatibility in ceramic/polymer nanocomposites, and if possible, to control the influence of modifiers on the performance of the nanocomposites. In this paper, four kinds of small-molecule modifiers were chosen to treat the surface of BT nanoparticles, and the PVDF-based nanocomposites filled with the modified BT nanoparticles were prepared. The influences of modifiers on compatibility, permittivity, breakdown strength and polarization have been systematically investigated, in order to identify the optimal surface modifier to enhance the energy density of the nanocomposites. Due to different structures (including types, number and position of functional groups in molecules), the modifiers show different effects on the permittivity of the nanocomposites, while the breakdown strengths are all significantly improved. Consequently, the discharged energy densities of nanocomposites modified by 2,3,4,5-tetrafluorobenzoic acid and phthalic acid increase 35.7% and 37.7% respectively compared to BT/PVDF, indicating their potential as high energy density capacitors.

Ceramic/polymer composites combining high permittivity fillers and high breakdown strength matrix have shown great potential applications in power system. However, the compatibility between the two phases in composite is always a key factor influencing its dielectric performance. Surface modification on fillers using traditional modifiers can improve the breakdown strength of the composites but also increase the dielectric loss at the same time, which reduces the energy efficiency of the material. In this work, we report a modifier for the surface modification of barium titanate (BT) nanoparticles, which as modifier for nanoparticles has not been demonstrated before. The poly(vinylidene fluoride) (PVDF) composites filled with the modified BT have good compatibility, high breakdown strength and low dielectric loss. Especially, the breakdown strength is much higher than that of the composites filled with unmodified BT nanoparticles. When filler volume fraction is 40%, the increase of the breakdown strength can reach 81.3%. A high energy density of 9.4 J/cm3 is achieved at 400 MV/m when the volume fraction is 10%, which is two times higher than that of the unmodified BT/PVDF composites.The abstract should be a single paragraph which summarises the content of the article.two times higher than that of the unmodified BT/PVDF composites.

Ceramic-polymer composites have attracted extensive attention in electrical applications due to their high permittivity and low loss. In this work, we report the studies on the preparation and properties of barium titanate (BT)/ poly(vinylidenefluoride) (PVDF) composite thin films. The composite film was prepared by a modified process rather than the conventional method. The modified process adopted ballmilling technique instead of the stirring method to disperse BT nanoparticles into PVDF solution. Scanning electron microscopy images of the obtained composites show that the BT nanoparticles are incorporated into the PVDF network and are well dispersed in the matrix. When the BT volume fraction is 30%, the permittivity and breakdown strength of the composites reach their optimal values and the energy density reaches maximum value (5.3 J/cm3), an increase of 80% compared with that of the composites prepared using the stirring method. Another modification is the use of acetone and butanone mixed solution instead of N,N-dimethylformamide to dissolve the PVDF, which is beneficial to form pure α-PVDF composite films on the polyethylene terephthalate substrate by tape casting. The composites prepared by the modified process, with high permittivity and significantly enhanced breakdown strength, are useful candidates for energy storage applications.

Polyacrylate elastomers were introduced into poly(vinylidene fluoride) polymer-based nanocomposites filled with BaTiO3 nanoparticles and the three-phase nanocomposite films were prepared. The energy discharged of the nanocomposite with 3 vol. % polyacrylate elastomers is 8.8 J/cm3, approximately 11% higher compared to that of the nanocomposite without adding polyacrylate elastomers. Large elastic deformation of the polyacrylate elastomers increases Maxwell–Wagner–Sillars interfacial polarization and space charge polarization of the nanocomposites with the electric field increasing, which results in increased maximum polarization and energy discharged of the nanocomposites.

We report improved electric breakdown strength, high energy density, and low dielectric loss of nanocomposites using surface modified BaTiO3 (BT) nanoparticles filling in poly(vinylidene fluoride) polymer matrix. Dielectric and electric breakdown properties of the nanocomposites have been investigated as a function of BT content. The electric breakdown strength of 285 MV/m has been achieved at the nanocomposite with 10 vol. % BT nanoparticles. The results indicate that functionalized and produced passivation layers on the surface of ceramic fillers can improve the homogeneity of the nanocomposites, promote space charge and interface effects, and significantly enhance electric breakdown strength of the nanocomposites.

The Ag@SiO2 core–shell structure nanoparticles prepared by chemical method were dispersed into epoxy matrix. By comparing with the epoxy-based composites filled with the mixed Ag and SiO2 nanoparticles (Ag + SiO2), it is found that the Ag@SiO2 core–shell structure fillers had important effects on the improved dielectric properties of the Ag@SiO2/epoxy composites. The core–shell structure fillers introduce a duplex interfacial polarization and a small number of free charge carriers, which enhance the dielectric permittivity of the composites. At the same time, the insulating SiO2 shell layer changes the interfacial interaction between the Ag filler and the epoxy matrix, not only avoiding Ag particles to connect directly and aggregate together but also providing a rough surface to contact with the epoxy host, which enhances the compatibility between the Ag@SiO2 fillers and the epoxy matrix. As the Ag@SiO2 packing ratio increases, the permittivity of the composites straightly increases and the loss tangent decreases, reaching the maximum and minimum respectively with the filler loading up to 60%.

We report nanocomposites of increased dielectric permittivity, enhanced electric breakdown strength and high‐energy density based on surface‐modified BaTiO3 (BT) nanoparticles filled poly(vinylidene fluoride) polymer. Polyvinylprrolidone (PVP) is used as the surface modification agent and homogeneous nanocomposite films have been prepared by solution casting processing. The dielectric permittivity of the nanocomposite with treated BT is higher than those with untreated BT and reaches the maximum value of 77 (1 kHz) at BT concentration of 55 vol%. The electric breakdown strength of the nanocomposite is greatly enhanced to 336 MV/m at BT concentration of 10 vol% and the calculated energy density is 6.8 J/cm3. The results indicate that using PVP as surface modification agent can greatly enhance the dielectric permittivity and electric breakdown strength of the ceramic–polymer nanocomposite and achieve high‐energy density for energy storage and power capacitor applications.

A polymer based composite was prepared by using modified aluminum fibers and aluminum nanoparticles as fillers in polyimide matrix that resulted in the high thermal conductivity and low relative permittivity. It was found that silica coated aluminum fibers with the multilayer coating structures can significantly reduce the relative permittivity (about 19.6 at 1 MHz) of the composite while keeping lower dielectric loss (0.024 at 1 MHz). The thermal conductivity of composites was significantly increased to 15.2 W/m K. This work shows a useful way to choose proper modifier fillers to improve the composite properties for electronic packaging composite materials.

Homogeneous ceramics-polymer nanocomposites comprising core-shell structured BaTiO3/SiO2 nanoparticles and a poly(vinylidene fluoride) polymer matrix have been prepared. The nanocomposite of 2 vol. % BaTiO3/SiO2 nanoparticles exhibits 46% reduced energy loss compared to that of BaTiO3 nanoparticles, and an energy density of 6.28 J/cm3, under an applied electric field of 340 MV/m. Coating SiO2 layers on the surface of BaTiO3 nanoparticles significantly reduces the energy loss of the nanocomposites under high applied electric field via reducing the Maxwell–Wagner–Sillars interfacial polarization and space charge polarization.