Dielectric breakdown model for composite materials

Recent Advances in Multilayer-Structure Dielectrics for Energy Storage Application

An electrostatic capacitor has been widely used in many fields (such as high pulsed power technology, new energy vehicles, etc.) due to its ultrahigh discharge power density. Remarkable progress has been made over the past 10 years by doping ferroelectric ceramics into polymers because the dielectric constant is positively correlated with the energy storage density. However, this method often leads to an increase in dielectric loss and a decrease in energy storage efficiency. Therefore, the way of using a multilayer structure to improve the energy storage density of the dielectric has attracted the attention of researchers. Although research on energy storage properties using multilayer dielectric is just beginning, it shows the excellent effect and huge potential. In this review, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multilayer structure dielectrics are mainly described. This article covers not only an overview of the state-of-the-art advances of multilayer structure energy storage dielectric but also the prospects that may open another window to tune the electrical performance of the electrostatic capacitor via designing a multilayer structure.

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 performance of BaTiO3/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.

Fluorocarboxylic acid-modified barium titanate/poly(vinylidene fluoride) composite with significantly enhanced breakdown strength and high energy density

Fluorocarboxylic acid, as a novel surface modifier for BT nanoparticles, has significantly improved the performance of the BT/PVDF composites.

Nanostructural anisotropy underlies anisotropic electrical bistability

Regular arrays of nanorods having asymmetric cross-sections are fabricated by a combination of electrodeposition and glancing-angle deposition (GLAD). When these nanorods are embedded in a polymer matrix, they give rise to composite materials in which the structural anisotropy at the nanoscale translates into functional anisotropy in the form of direction-dependent electrical bistability. The degree of this directional bistability depends on and can be controlled by the spacing between the nearby nanorods.

Field fluctuations and fractality in electrical breakdown trees

In the present paper, the discharge avalanche model, initially proposed by Dissado and co-workers, is modified to explore (by correlating its results with experimental information) the role of the space-charge characteristics in the fractal nature of electric trees. Stochastic fluctuations of the local electrical field in each site of the polymer sample (E(loc)) around the Laplacian field (E(lap)) are allowed and limited to intermediate values of E(lap). The major achievements of the modified model are the prediction of a nonmonotonic behavior in both the average time to failure and the average fractal dimension of the electrical trees, and the prediction of a transition from branched to runaway trees as the applied voltage is increased.

Dielectric breakdown model for conductor-loaded and insulator-loaded composite materials

In the present work we generalize the dielectric breakdown model to describe dielectric breakdown patterns in both conductor-loaded and insulator-loaded composites. The present model is an extension of a previous one [F. Peruani et al., Phys. Rev. E 67, 066121 (2003)] presented by the authors to describe dielectric breakdown patterns in conductor-loaded composites. Particles are distributed at random in a matrix with a variable concentration p. The generalized model assigns different probabilities P(i,k-->i('),k(')) to breakdown channel formation according to particle characteristics. Dielectric breakdown patterns are characterized by their fractal dimension D and the parameters of the Weibull distribution. Studies are carried out as a function of the fraction of inhomogeneities, p.