Yujuan Niu

Significantly Enhanced Breakdown Strength and Energy Density in Sandwich‐Structured Barium Titanate/Poly(vinylidene fluoride) Nanocomposites

Sandwich-structured BaTiO3 /poly(vinylidene fluoride) (PVDF) nanocomposites are successfully prepared by the solution-casting method layer by layer. They possess both high breakdown strength and large dielectric polarization simultaneously. An ultra-high energy-storage density of 18.8 J cm(-3) can be achieved by adjusting the volume fraction of ceramic fillers: this is almost three times larger than that of pure PVDF.

Enhanced dielectric properties of BaTiO3/poly(vinylidene fluoride) nanocomposites for energy storage applications

In this work, homogeneous ceramics-polymer nanocomposites consisting of surface treated BaTiO3 (BT) particles as fillers and poly(vinylidene fluoride) polymer as matrix have been prepared using a solution casting process. The nanocomposites exhibit enhanced dielectric permittivity and reduced loss tangent. The frequency and temperature dependencies of the dielectric permittivity and loss tangent of the nanocomposites suggest that the introduced BT phase and interface areas contribute to the improvement of the dielectric responses. Meanwhile, the X-ray diffraction patterns and Differential Scanning Calorimetry (DSC) curves indicate that the incorporation of ceramic particles contributes to the decrease of the crystallite size, the increase of the crystallinity, and the shift of the crystallization temperature of the polymer matrix. Furthermore, the dielectric displacement and energy density of the nanocomposites are significantly enhanced and an energy density of 3.54 J/cm3 was obtained under an electric f...

Poly(vinylidene fluoride) polymer based nanocomposites with significantly reduced energy loss by filling with core-shell structured BaTiO3/SiO2 nanoparticles

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.

Enhanced high thermal conductivity and low permittivity of polyimide based composites by core-shell Ag@SiO2 nanoparticle fillers

A kind of polymer based composites was prepared by embedding the fillers of core-shell Ag@SiO2 nanoparticles into the polyimide (PI) matrix. The obtained Ag@SiO2/PI (50% vf of fillers) composites show remarkably improved high thermal conductivity and low relative permittivity. The maximum value of the thermal conductivity of composites is 7.88 W/(mK) and the relative permittivity and dielectric loss are about 11.7 and 0.015 at 1 MHz, respectively. Compared with self-passivated nanometer Al* particles composites, core-shell Ag@SiO2 nano-composite is beneficial to increase the thermal conductivity and reduce the permittivity of the composites. The relative mechanism was studied and discussed.

Effect of the Modifier Structure on the Performance of Barium Titanate/Poly(vinylidene fluoride) Nanocomposites for Energy Storage Applications

Surface modification on ceramic fillers is of interest to help improve 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 type, 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.

Compositional tailoring effect on electric field distribution for significantly enhanced breakdown strength and restrained conductive loss in sandwich-structured ceramic/polymer nanocomposites

Compared to conventional single-layered thin films, spatial organization of the polymer matrix and ceramic nanofillers into three-dimensional sandwich structures is a promising route to dielectric materials for enhanced energy storage properties (ESPs) that enable the dielectric capacitors for a number of applications in advanced electronic and electrical power systems. In this study, a systematic study of the sandwich-structured ceramic/polymer nanocomposites composed of pristine poly(vinylidene fluoride) (PVDF) as the middle layer and barium titanate (BT)/PVDF nanocomposites as two outer layers has been presented. Experimental results indicate that the ESP of the sandwich BT/PVDF composites, including breakdown strength, discharge efficiency, and energy density, can be significantly improved by tailoring the BT content. As verified by finite element simulations, the ESP of sandwich films is mainly governed by the electric field distribution owing to the introduction of high-dielectric-constant BT into the layered structures. The rational design of BT content leads to the electric field distribution capable of enhancing the dielectric strength and reducing the electrical conductivity for high energy density and improved discharge efficiency. An ultrahigh energy density of 16.2 J cm−3 has been achieved at the breakdown strength of 410 MV m−1 in the optimized sandwich-structured nanocomposites. The understanding of the influence of filler content on electric field distribution achieved in this work provides a viable way for exploiting novel layered dielectrics with exceptional ESPs for energy storage devices.

Enhanced electric breakdown strength and high energy density of barium titanate filled polymer 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.

Ultrahigh electric displacement and energy density in gradient layer-structured BaTiO3/PVDF nanocomposites with an interfacial barrier effect

Negative environmental consequences of non-renewable energy resources and limited reserves of fossil fuel supplies have spurred the development of renewable and environmentally friendly energies as well as advanced energy conversion and storage technologies. Among the currently available electrical energy storage devices, electrostatic capacitors possess highest power density because of their fast charge–discharge capability. However, their low energy densities limit their applications. Herein, we demonstrated a remarkable improvement in the breakdown strength and energy density of a group of three-tiered ferroelectric polyvinylidene fluoride (PVDF) films with the content of barium titanate (BT) nanoparticle fillers gradually increasing layer by layer. It was found that a weak electric field region could be formed as an efficient insulating barrier to hamper the development of electrical trees via tailoring of the gradient of filler contents. Optimization of the composite compositions guided by simulation studies resulted in a greatly enhanced breakdown strength of 390 MV m−1 with an ultrahigh maximum polarization of 12.5 μC cm−2, and thus, an impressive discharged energy density of 16.5 J cm−3 was achieved. This successful structural design provides a new paradigm to explore polymer nanocomposites having excellent dielectric and capacitive properties, which can also be applied to other materials in electric and electrical applications.

Poly(vinylidene fluoride) polymer based nanocomposites with enhanced energy density by filling with polyacrylate elastomers and BaTiO3 nanoparticles

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.

Enhanced dielectric performance of BaTiO 3 /PVDF composites prepared by modified process for energy storage applications

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.