Enhanced Breakdown Strength Research Articles

Effect of BaTiO3Nanofillers on the Energy Storage Performance of Polymer Nanocomposites

AbstractPolymer nanocomposite is a promising substitute for the charge‐storage dielectric material in capacitors. Barium titanate/polycarbonate (BT/PC) nanocomposite is one of the system due to its comprehensive excellent dielectric properties. As the dielectric response of nanocomposite depends strongly on the size of the fillers, concentration of fillers in the composite system. In this study, BT/PC nanocomposites (BT = 1‐5%) with thickness of 100 µm were fabricated to reveal the effect of the fillers on the energy storage performance of the polymer nanocomposites. Owing to the variable concentration and good dispersibility of the nanofillers, the nanocomposites with small concentration of BT particles show more uniform and denser microstructures. Moreover, with the increase of filler concentration, dielectric results indicate a breakdown strength enhancement in the nanocomposites with BT fillers, which is quite different from the nanocomposites with normal fillers, and therefore leads to the superior energy storage performance. This study demonstrates a strategy of obtaining large dielectric constants and energy densities in ceramic/polymer composites for energy storage device applications.

Simultaneous Realization of Significantly Enhanced Breakdown Strength and Moderately Enhanced Permittivity in Layered PMMA/P(VDF–HFP) Nanocomposites via Inserting an Al2O3/P(VDF–HFP) Layer

Simultaneous Realization of Significantly Enhanced Breakdown Strength and Moderately Enhanced Permittivity in Layered PMMA/P(VDF–HFP) Nanocomposites via Inserting an Al₂O₃/P(VDF–HFP) Layer

A novel intrinsic semi-aromatic polyamide dielectric toward excellent thermal stability, mechanical robustness and dielectric performance

The development of aliphatic polyamide as dielectric polymer is limited due to relatively high dielectric loss, low breakdown strength and low servicing temperature. Different from the traditional ways for enhancing the dielectric properties of aliphatic polyamides by compositing with inorganic materials, here an alternative strategy is reported via random copolymerizing aliphatic polyamide with semi aromatic polyamides as functional segments. The designed co-polyamide shows decreased dielectric loss of 0.04 and enhanced breakdown strength of 319 MV/m with a low content of semi aromatic polyamides. Moreover, taking advantage of the inherent rigid benzene ring and flexible aliphatic chain, high glass transition temperature and great toughness are achieved simultaneously in the prepared semi aromatic polyamides. The introduction of aromatic segments has also improved dielectric and mechanical properties of co-polyamide at elevated temperature (150 °C), which is desirable and crucial for polymer dielectrics. The strategy provides new possibilities for the development of high-performance intrinsic polymer dielectrics.

Metal-organic Framework/Polyimide composite with enhanced breakdown strength for flexible capacitor

Metal-organic frameworks (MOFs), as new-generation of “star” materials, are widely applied in electrochemistry, pharmaceutical biology, energy storage and other emerging fields. However, there are few reports about strengthening mechanical and insulation properties of polymer-based dielectric materials by using 3D topological framework of MOFs. Here, we found that the Polyimide (PI)-based composites dielectrics using ZIF-8 nanoparticles (a typical MOFs) as fillers exhibit significantly enhanced Young's modulus and breakdown strength. The DC breakdown strength of the composites as high as 516.3 kV/mm with only loading 1 wt% ZIF-8, which is about 85% higher than those of PI (279.8 kV/mm). In-situ synchrotron radiation characterizations revealed that the unsaturated active sites of ZIF-8 could bind to PI molecules, via thermal activation, inducing 3D multi-site bonding networks, which improves the Young's modulus and reduces the dielectric loss of the composite, and further enhances the breakdown strength of the composite. Molecular dynamics (MD) calculations show that the multi-site bonding networks can effectively capture charges and raise the ionization threshold at high field. The discharge energy densities (Ue) of composites are significantly superior to that of PI and the state-of-the-art commercial biaxially oriented polypropylene BOPP (about 5 times of the latter), meanwhile the charge–discharge efficiencies (η) of all composites are maintained above 90%. This breakdown strength enhancement effect also exists in PI-based composites loaded with UiO-66 nanoparticles (another typical MOFs). We believe that this study would further broaden the flexible dielectric application opportunities of MOFs, as well as develop into a new pathway for structural designs of flexible thin-film capacitors.

Tuning Surface States of Metal/Polymer Contacts Toward Highly Insulating Polymer-Based Dielectrics.

Metal-polymer interface plays a crucial role in controlling the dielectric performance in all flexible electronics. Ideally, the formation of the Schottky barrier due to the large band offset of the electron affinity of the polymer over the work function of the electrode should sufficiently impede the charge injection. Arguably, however, such an injection barrier has hardly been indisputably verified in polymer-metal junctions due to the ever-existing surface states, which dramatically compromise the barrier thus leading to undesired high electrical conduction. Here, we demonstrate experimentally a clear negative correlation between the breakdown strength and the density of surface states in polymer dielectrics. The existence of surface states reduces the effective barrier height for charge injection, as further revealed by density functional theory calculations and photoinjection current measurements. Based on these findings, we present a surface engineering method to enhance the breakdown strength with the application of nanocoatings on polymer films to eliminate surface states. The density of surface states is reduced by 2 orders of magnitude when the polymer is coated with a layer of two-dimensional hexagonal boron nitride nanosheets, leading to about 100% enhancement of breakdown strength. This work reveals the critical role played by surface states on electrical breakdown and provides a versatile surface engineering strategy to curtail surface states, broadly applicable for all polymer dielectrics.

(Bi0.5Na0.5)TiO3-based relaxor ferroelectrics with medium permittivity featuring enhanced energy-storage density and excellent thermal stability

High energy density, efficiency and thermal stability of energy-storage properties are extremely pivotal for the application of dielectric ceramics in advanced pulsed power systems. In this work, we utilize a composition-driven strategy to induce polar nanoregions, refine grain size and adjust permittivity of (1-x)Bi0.5(Na0.9Li0.1)0.5TiO3-xSr(Al0.5Nb0.25Ta0.25)O3 ceramics. As a result, an extraordinary Wrec of 6.43 J/cm3 and high η of 88% are simultaneously obtained in the x = 0.16 composition. Meanwhile, the x = 0.16 sample also shows good frequency stability (5–100 Hz), cycle stability (105 cycles) and superior thermal stability (-55 ~ 225 ℃). The enhanced breakdown strength is analyzed by Weibull distribution and mainly attributed to the decreased average grain size. The typical relaxor behavior is reflected by the broadened and diffused Raman spectra as well as the dispersive and temperature-stable dielectric curves. The existence of dynamic polar nanoregions as confirmed by piezoresponse force microscopy measurements enables the nearly hysteresis-free polarization–electric field response and the related frequency and cycle stability. The mitigated polarization saturation is related to the field-insensitive moderate permittivity and will be conducive to the energy-storage properties at elevated electric field. In addition, the temperature-dependent Raman spectra and the slightly fluctuated ΔP (Pm - Pr) value over the whole temperature range reflect the temperature-stable energy-storage properties. Hence, the current work may provide some novel perspectives for designing dielectric ceramics with enhanced energy-storage properties.

Enhanced breakdown strength and energy density of multilayered P(VDF-HFP)/Nd-doped BaTiO3 nanofibers composites

Flexible dielectric materials with benign energy storage performance are highly desirable for the miniaturization, portability and integration of modern electronics. However, the limited energy storage density seriously restricts their practical applications. Herein, multilayered composite films composed of the P(VDF-HFP) matrix and Nd doped BaTiO3 nanofibers with various filling ratios, layer numbers and topological structures were systematically designed and constructed via the layer-by-layer non-equilibrium process. The 3-layered composite films (3.0 wt% filling ratio) with the pure P(VDF-HFP) layer adjacent to the electrodes revealed good mechanical behavior, greatly enhanced captured ions at interfacial regions and suppressed injected charges from electrodes, which facilitated the improvement of the breakdown strength and discharged energy density. And a maximum Ue of 25.5 J/cm3 with a Eb of 719.9 MV/m was achieved, which was not only 1.4 times more than the pure P(VDF-HFP) via the same process, but also behaved better than counterparts with the similar filling ratios and was among the top Ue values of related P(VDF-HFP)-based nanocomposites.

Improvement of dielectric properties and energy storage performance in sandwich-structured P(VDF-CTFE) composites with low content of GO nanosheets

Polymer-based dielectric capacitors play a notable part in the practical application of energy storage devices. Graphene oxide (GO) nanosheets can improve the dielectric properties of polymer-based composites. However, the breakdown strength will greatly reduce with the increase of GO content. Hence, the construction of sandwich structure can enhance the breakdown strength without reducing the dielectric constant. Herein, single-layered and sandwich-structured poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposites with low content of GO nanosheets (<1.0 wt%) are prepared via employing a straightforward casting method. Compared with the single-layered composites and pure P(VDF-CTFE), the sandwich-structured composites exhibit comprehensively better performance compared. The sandwich-structured composite with 0.4 wt% GO nanosheets show an excellent dielectric constant of 13.6 (at 1 kHz) and an outstanding discharged energy density of 8.25 J cm−3 at 3400 kV cm−1. These results demonstrate that the growth of the dielectric properties is owing to 2D GO nanosheets and the enhancement of breakdown strength due to the sandwich structure. The results from finite element simulation provide theoretical support for the design of high energy density composites.

Vinylsilane-rich silicone filled by polydimethylsiloxane encapsulated carbon black particles for dielectric elastomer actuator with enhanced out-of-plane actuations

Due to an extremely low permittivity, silicone based dielectric elastomer actuator (DEA) needs to be triggered by a very high voltage, thus endures the risks of electrical breakdown and creep rupture. To address this problem, polydimethylsiloxane (PDMS) encapsulated carbon black (PCB) particles are filled in a vinylsilane-rich silicone (VRS) to obtain a hybrid PCB/VRS film with enhanced mechanical and insulation properties. The detected Young’s modulus and dielectric permittivity of the hybrid film containing 5.82 vol% PCB increase by 613 and 244% compared to the pure film, respectively. PDMS’ encapsulation effectively prevents the adjacent PCB particles forming conductive networks, thus the resultant PCB/VRS composite presents an enhanced breakdown strength of 63.31 V/μm and an attenuated dielectric loss of 0.078, which benefit DEA working. Triggered by a relatively low electrical field of 7.14 V/μm, the hybrid DEA exhibits better out-of-plane actuations compared to the pure DEA: 1.91-fold in flection amplitude, 2.79-fold in arealstrain, and 4.35-fold in force output.

Flexible dielectric nanocomposite films based on chitin/boron nitride/copper calcium titanate with high energy density

The increasing environmental pollution produced by synthetic polymer stimulates a huge demand for new biodegradable dielectric materials stemming from bioresources. Herein, regenerated chitin (RCH)/boron nitride nanosheets (BNNS)/copper calcium titanate nanofiber (CCTO) composite films were fabricated by simple mixing in aqueous KOH/urea solution. The two-dimensional BNNS possess wide bandgap and excellent intrinsic insulating properties to reduce the dielectric loss, thus exhibiting a greatly enhanced breakdown strength. Simultaneously, CCTO with ultrahigh dielectric constant significantly improved the dielectric constant of these ternary composite films. Accordingly, an extremely high energy storage density of 9.27 J cm−3 was obtained when loaded with 6 wt% BNNS and 5 wt% CCTO. Moreover, a superhigh charge-discharge efficiency of about 80% was well-maintained even when the applied electric field reaches 440 MV m−1. Furthermore, the ternary composite films also possessed much better thermal and mechanical properties.

Enhanced breakdown strength of multilayer polypropylene film with structured interface

Extensive research has been carried out to improve the breakdown strength (BDS) of polymer materials used in high-voltage power equipment. However, almost all the modifications, including nanocomposites, polymer blends, and multilayer films have enhanced the BDS by introducing alien material, which inevitably resulted in an increase in the dielectric losses. Therefore, we propose a multilayer structured film simplex composed of polypropylene (PP) to simultaneously achieve high BDS and low losses. By including virgin and fluorinated bi-axially oriented PP (BOPP) films, three different interface structures were constructed. All the multilayer PP films showed DC BDSs that were improved by varying degrees, compared to the single-layer film. In particular, owing to the enhanced electron trap depth and density caused by fluorination, the DC BDSs of multilayer films with fluorinated BOPP reached 458.7 kV mm−1, which was 20% higher than that of a single-layer PP film of the same thickness, while their dielectric loss was even lower than that of the single-layer film.

Breakdown strength and energy density enhancement in polymer-ceramic nanocomposites: Role of particle size distribution

Polymer-ceramic nanocomposites play a very promising role for energy-storage in high power electronics and advanced pulsed power systems, due to their extremely fast charge-discharge capability. The low energy density is the key factor hindering their application, for which large endeavors have been made in the modulation of the fraction, morphology, size, and dispersion of the particle fillers but small in that of the size distribution, which is critical for energy-storage performance. We first investigated the role of this based on simulated nanocomposites with controlled lognormal distributions via a generation algorithm devised in this work. Dielectric response, breakdown behavior and energy-storage performance were explored for distributions with different standard deviations (SD) and mean values (MV), which were solved with the energy equivalence basis and a phase-field dielectric breakdown model. With the decrease of SD and MV, the effective permittivity declines slightly with enhanced permittivity change, which was related with the enhanced local electric field with intensified fluctuation and should be originated from the major contribution of the polymer matrix from the local energy perspective; whereas improved nominal breakdown strength was achieved owing to the weakened local maximum electric field, which leads to distinctly increased nominal energy density despite the slight decline of the permittivity. Keeping the fillers within a narrow disperse outperforms employing super fine particles. This work demonstrates that enhancement in breakdown strength and energy density can be attained via particle size distribution modulation, paving a new way for the further improvement of the energy-storage performance of polymer-ceramic nanocomposites.

Sandwich-Structured Polymer Composites with Core–Shell Structure BaTiO3@SiO2@PDA Significantly Enhanced Breakdown Strength and Energy Density for a High-Power Capacitor

Sandwich-Structured Polymer Composites with Core–Shell Structure BaTiO₃@SiO₂@PDA Significantly Enhanced Breakdown Strength and Energy Density for a High-Power Capacitor

Simultaneous enhancement of breakdown strength and discharged energy efficiency of tri-layered polymer nanocomposite films by incorporating modified graphene oxide nanosheets

Developing high dielectric performance of polymer nanocomposites is still a long-standing issue to simultaneously inherit the high dielectric constant of nanofillers and maintain the high breakdown strength of polymer matrix. In the current study, a tri-layered nanocomposite film is fabricated by a simple and effective solution-casting and dip-coating method, where graphene oxide nanosheets (GONSs) were modified by insulating SiO2 layer (SiO2@GONSs) and polyvinylidene fluoride (PVDF)/SiO2@GONS nanocomposite inner layer was sandwiched by polycarbonate (PC) layers. The surface modification could minimize the local electric field concentration and block conductive path. Furthermore, the sandwich or tri-layered structure inhibited the relaxation and migration of space charge or impurity ions and suppressed the charge injection, thus achieving enhanced breakdown strength and discharged energy efficiency. As a result, the as-prepared tri-layered nanocomposite film exhibited a dielectric constant of 5.2 and a low dielectric loss (tanδ) of 0.013 at 1 kHz, and breakdown strength of 219 MV m−1, which was significantly higher than single-layered nanocomposite films and its counterpart without SiO2 modification. The corresponding discharged energy density was 1.20 J cm−3 with an excellent efficiency of 86.2% at 200 MV m−1. More interestingly, the insulating SiO2 modification layer and PC outer layers could also effectively restrict the relaxation or migration of impurity ions at a high temperature of 120 °C, endowing excellent high-temperature dielectric performance to the as-prepared tri-layered nanocomposite film. The combination of surface modification and sandwich structure opens up an avenue to fabricate GONS-based dielectric nanocomposites with low dielectric loss, high breakdown strength, high efficiency and high temperature tolerance.

Greatly enhanced breakdown strength and energy density in ultraviolet‐irradiated polypropylene

Polymer dielectrics have drawn great attentions for applications in advanced electronic devices and power grids because of their high breakdown strength, low dielectric loss, and excellent flexibility. However, the low energy density in polymer dielectric capacitors will hinder the continuous miniaturization of electrical systems. In this work, ultraviolet irradiation is demonstrated to greatly enhance the breakdown strength and energy density of polypropylene. Dramatically improved breakdown strength of 867 MV/m and discharged energy density of 8.0 J/cm3, together with the high energy efficiency of >90%, were simultaneously achieved in polypropylene after ultraviolet irradiation. Our research shows that proper ultraviolet irradiation can effectively improve the energy density of polypropylene without sacrificing its high charge-discharge efficiency, being potential for applications in power electronics and pulse electric systems.

Enhanced Breakdown Strength of BN/ER by the 2D Ordinal Tiled Structure of Fillers

The objective of this paper is to propose constructing a 2D ordinal fillers structure to improve the breakdown strength of BN/ER. By loading ferrite on the fillers and applying a rotating magnetic field during curing process, epoxy composites with tiled structure of plate-type BN are obtained. Considering the side effect of ferrite on the insulation properties, its minimum load under the premise of implementing the tiled structure is determined, accordingly the composite materials with breakdown strength about 30% higher than that of traditional BN/ER is obtained. Furthermore, the technological parameters of magnetic treatment is analyzed quantitatively, and a meso-scopic finite element model of BN/ER is built to further discuss the enhancing mechanism of breakdown strength brought by the filler tiled structure.

Bi0.5Na0.5TiO3-based lead-free ceramics with superior energy storage properties at high temperatures

Dielectric capacitors with high energy storage and dielectric properties at high temperatures have significantly practical application in many fields. Lead-free ceramics of (1-x)(0.65Bi0.5Na0.5TiO3-0.35Bi0.2Sr0.7TiO3)-xBaSnO3 were prepared by a solid-state reaction method. It was found that the 0.8(0.65Bi0.5Na0.5TiO3-0.35Bi0.2Sr0.7TiO3)-0.2BaSnO3 ceramic shows a large recoverable energy storage density (Wr) of 3.75 J/cm3 and efficiency (η) of 84.8% under 380 kV/cm along with outstanding power density of 38.73 MW/cm3 under 130 kV/cm at room temperature. Additionally, a high Wr of 3.21 J/cm3 and η of 77% are achieved under a high electric field of 300 kV/cm at 100 °C. When the temperature reaches 140 °C, it still has a high Wr of 3.1 J/cm3 and η of 72%. The outstanding energy storage performance at high temperatures can be explained by the enhancement of breakdown strength and the constructing of polar phase stability caused by the introduction of BaSnO3.

Superior energy storage performance of PVDF-based composites induced by a novel nanotube structural BST@SiO2 filler

Polymer-based composites act as film capacitors are an ideal candidate, but further applications are limited by the conflict between energy density and efficiency. Herein, a novel one-dimensional core–shell tubular structure of nanofillers is proposed, SiO2 surface-modified Ba0.6Sr0.4TiO3 nanotubes (BST@SiO2 NTs) are prepared by improved electrospinning and then wet chemical method. Notably, both improved dielectric properties and enhanced breakdown strength could be obtained by incorporating moderate BST@SiO2 NTs. Consequently, the 2 vol% BST@SiO2 NT/PVDF composites achieve an ultra-high Ud (discharged energy density) of ~ 18.08 J/cm3,and it is quite larger than 11.25 J/cm3 of neat PVDF. More importantly, compared to pure PVDF (59.87%), an excellent efficiency of 70.06% is also maintained. This work opens up a novel and unique sight for the structural designing of inorganic nanofillers, which is the ideal strategy to obtain high-performance dielectric composites and related potential applications.

Enhanced breakdown strength and energy storage density of lead-free Bi0.5Na0.5TiO3-based ceramic by reducing the oxygen vacancy concentration

Lead-free 0.9(Na0.4Bi0.4Ba0.06Sr0.14Ti(1−x)TaxO3)-0.1NaNbO3 ceramics with x = 0 ~ 0.05 were synthesized via solid-state reaction method. Raman spectra and X-ray diffraction confirmed the perovskite structure of ceramics. The generation of oxygen vacancy was effectively inhibited after substitution of Ta for Ti. Leakage current density and average grain size decreased because of the reduction of oxygen vacancies, which subsequently contributed to the improvement of breakdown strength from 180 to 270 kV/cm. The ceramic with x = 0.01 exhibited an excellent recoverable energy storage density of 3.12 J/cm3 and an efficiency of 87.86% at 270 kV/cm. The power density of 79.98 MW/cm3 with a short time around 350 ns for releasing 90% of the discharge energy density was obtained. The superior cycling reliability with less than 7% degradation over 105 cycles and the excellent thermal stability with a variation of discharged energy density less than 5% from 25 to 150 °C guarantee the promising prospects of application.

Breakdown-Strength Enhancement of Coaxial-to-Waveguide Adapters

An improved structure of a high-power adapter is proposed for broadband matching of coaxial transmission lines and rectangular waveguides with a narrow side wall that are network used in space communication systems. Numerical simulation and optimization of such a microwave two-port are performed with the aid of the finite-element method in a frequency interval of 2.5–4.9 GHz. The sizes of a modified coaxial-to-waveguide adapter that provide the desired electrodynamic characteristics in the specified frequency interval are determined.