Improved Breakdown Strength Research Articles

Enabling High‐Energy‐Density High‐Efficiency Ferroelectric Polymer Nanocomposites with Rationally Designed Nanofillers

AbstractFerroelectric polymers have been regarded as the preferred matrix for high‐energy‐density dielectric polymer nanocomposites because of their highest dielectric constants among the known polymers. Despite a library of ferroelectric polymer‐based composites having been demonstrated as highly efficient in enhancing the energy density, the charge–discharge efficiency remains moderate because of the high intrinsic loss of ferroelectric polymers. Herein, a systematic study of the oxide nanofillers is presented with varied dielectric constants and the vital role of the dielectric match between the filler and the polymer matrix on the capacitive performance of the ferroelectric polymer composites is revealed. A combined experimental and simulation study is further performed to specifically investigate the effect of the nanofiller morphology on the electrica properties of the polymer nanocomposites. The solution‐processed ferroelectric polymer nanocomposite embedded with Al2O3 nanoplates exhibits markedly improved breakdown strength and discharged energy density along with an exceptional charge–discharge efficiency of 83.4% at 700 MV m−1, which outperforms the ferroelectric polymers and nanocomposites reported to date. This work establishes a facile approach to high‐performance ferroelectric polymer composites through capitalizing on the synergistic effect of the dielectric properties and morphology of the oxide fillers.

High energy storage and ultrafast discharge in NaNbO3-based lead-free dielectric capacitors via a relaxor strategy

Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO3-xBi(Ni2/3Nb1/3)O3(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni0·5Nb0.5)O3 boosts the insulation ability, thus obtaining a high breakdown strength (Eb) of 440 kV/cm in xBNN ceramics. A high energy storage density (Wtotal) of 4.09 J/cm3, recoverable energy storage density (Wrec) of 3.31 J/cm3, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of Wrec ≤ 0.4% over 5–100 Hz and Wrec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm3) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.

Ultrahigh energy density and thermal stability in sandwich-structured nanocomposites with dopamine@Ag@BaTiO3

The progress in advanced dielectrics by tremendously enhancing the discharge energy densities is of great importance for the current electronic power systems. Herein, we report heterogeneous sandwich-structured nanocomposites with low nanofillers content, which offered the ultrahigh discharge energy density (Ue) of 21.03 ​J/cm3 at 592.1 ​MV/m. This energy density is the highest reported until now, with similar nanoparticle content and equivalent electric field. We used linear-type polyetherimide as the outer two layers, which offered insulation of charge injection from electrodes, reduced polymer free-volume, improved breakdown strength, and enhanced the overall thermo-mechanical stability. Besides, dopamine@Ag@BaTiO3 nanoparticles (DA@Ag@BT NPs)-modified ferroelectric-type polyvinylidene fluoride is employed as the middle layer for rendering higher polarizability and additionally increased breakdown strength due to well-known Coulomb blockade effect. Finite element simulations showed reduced local electric field in the outer, as well as middle layer matrixes, indicating higher breakdown strength and consequently higher energy storage prospects of heterogeneous sandwich-structured nanocomposites. The energy storage results at high temperatures demonstrated its significant thermal stability until 170 ​°C. Overall, this contribution not only paves the new way for developing industrially viable low nanofillers-concentrated flexible dielectric films but also provides the insight of polarization mechanism and electric breakdown in heterogeneous sandwich-structured dielectric materials.

High discharge efficiency and energy density for polymer composites filled with S-doped zinc oxide nanoparticles

Inorganic-polymer nanocomposites consisting of sulfur doped zinc oxide nanoparticles (ZOS_nps) as fillers and poly(vinylidene fluoride) (PVDF) as the polymer matrix were prepared via the solution casting method. The energy storage behaviors of PVDF/ZOS nanocomposites were studied. The results indicated that the incorporation of ZOS_nps in the polymer matrix could effectively improve breakdown strength (Eb), resulting in greatly enhanced energy density (Ue) and discharge efficiency (η). The nanocomposite with 1 vol% of ZOS_nps shows an outstanding discharge energy density of 11.5 J cm−3 and maintains a high discharge efficiency of 68.7% at 4800 kV cm−1. This reason is that S-doped zinc oxide nanoparticles with isoelectronic hope traps suppress the interfacial polarization. The present work may offer a novel way to confine the movement of charges by introducing isoelectronic impurities in polymer nanocomposites.

Realization of temperature insensitive high energy storage performance via introducing NaNbO3 into NBT-KBT system

The development of lead-free dielectric ceramics with temperature insensitive high discharge energy density (Wdis) and high energy efficiency (η) are highly demanded for the practical applications in energy storage capacitors. In this work, we have designed and fabricated the NaNbO3 modified Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT-KBT-xNN) relaxor ferroelectrics. The addition of metastable antiferroelectric NN into the NBT-KBT matrix leads to enhanced relaxor behavior and improved breakdown strength. As a result, the x = 0.4NN specimen not only showed optimal integrated energy storage properties with a large Wdis of 1.7 J/cm3 and η of 90% under a moderate electric field of 150 kV/cm, but also exhibited superior temperature stability with the variation of Wdis within ±15% and η more than 80% from −50 °C to 150 °C. All these properties indicate that NN modified NBT-KBT ceramic was a promising candidate for the practical application of energy storage capacitors.

Recent progress in polymer dielectrics containing boron nitride nanosheets for high energy density capacitors

Hexagonal boron nitride nanosheets (BNNSs) are two-dimensional nanomaterials with graphitic-like layered nanostructures, high surface areas, and large aspect ratios. Owing to their excellent thermal conductivity, electrical and mechanical strengths, BNNSs are emerging as multifunctional fillers in polymer dielectrics. In this article, the authors review the recent progress in the BN-containing polymer nanocomposites designed for high-performance film capacitors. While general synthetic approaches to BNNSs and polymer/BNNS nanocomposites are summarized, particular attention is placed on structure-property correlation and rational structural design of the composites with optimized dielectric properties and capacitive performances. In stark contrast to the polymer composites employing high dielectric constant fillers to enhance the electric displacement, a new design concept based on the utilization of BNNSs with a wide bandgap to impede electrical conduction and consequently improve breakdown strength and charge-discharge efficiency of the polymer composites, is highlighted. The significance of developing dielectric capacitors with desirable thermal conductivity and thermal stability to ensure their robust and efficient operation is emphasized. The merits and challenges regarding the existing polymer dielectrics containing BNNSs for energy storage are identified. An outlook for future research opportunities and engineering applications is also presented in this review.

Ni(OH)2 as an novel shell layer material for core-shell dielectric filler based on barium titanate and their dielectric polymer composites in P(VDF-HFP) matrix

Dielectric capacitors with high dielectric constant and energy density are of great importance for electronic devices. Barium titanate(BaTiO3) have been widely explored for polymer-based dielectric composites owning to its ultrahigh dielectric constant and commercial availability. However, due to the large difference of dielectric constant between BaTiO3 and polymer matrix, the interface becomes fragile under electric field, which is not conducive for the improvement in breakdown strength and energy storage density. Herein, a flower like barium titanate/nickel hydroxide(BTO/Ni(OH)2) core-shell structured filler has been fabricated to provide a novel approach to modify the interface between BTO and P(VDF-HFP) matrix for dielectric polymer composites. Ni(OH)2 nanoflakes have grown in-situ on the surface of hydroxylated BaTiO3 particles to form the flower like core-shell assemblies via hydrothermal reaction. Then, these synthetic BTO/Ni(OH)2 particles with specific flower-like core-shell structure can be uniformly dispersed in P(VDF-HFP) without any additional surface modification due to their surface –OH groups. Meanwhile, Ni(OH)2 shell triggered beta phase of P(VDF-HFP) near core-shell filler based on the interfacial interaction between Ni(OH)2 and P(VDF-HFP). Thus, the intensity of the local electric field can be gradually reduced due to the formation of a dielectric constant gradient. Besides, these Ni(OH)2 nanoflakes shell are able to cut down the local electric field and prevent the growth of electrical trees on the surface of BaTiO3 during breakdown process. When the composite filler content is 10 wt%, the dielectric constant and breakdown strength increases to 14.8 and 330 kV/mm from 11 to 260 kV/mm, respectively. And the calculated energy density is 7.13 J/cm3, which is 1.5 times that of 10 wt% BTO/P(VDF-HFP) composite film. This study provides a novel shell material Ni(OH)2 for the preparation of BTO core-shell structure filler, which has good compatibility with polymer substrates.

Enhanced energy storage performance in a PVDF/PMMA/TiO2 blending nanodielectric material

The growing demand for miniaturization of electrical and electronic system poses a great challenge on energy storage capacitors, which requires associated dielectric materials exhibiting high energy density. In ferroelectric polymer dielectrics, it is one of the key issues to achieve both high dielectric permittivity and high breakdown strength. In this paper, we propose a method on improving the dielectric permittivity and breakdown strength concurrently taking the advantage of nanocomposite and blending. Our results show that PVDF/PMMA/TiO2 blending nanodielectric material presents improved relative dielectric permittivity of 12 and breakdown strength of 387 kV/mm compared with pristine PVDF, leading to an enhanced energy density about 5.8 J/cm3 and an efficiency of 77%. Further electric properties measurements and structure characterizations indicate that the moderate enhancement of permittivity can be ascribed to the doping of TiO2 nanoparticles, and the improved breakdown strength is caused by blending of PMMA with good insulating properties. Our results might provide a promising approach to develop high-performance energy-storage dielectric materials concerning the synergistic effect of blending and nanocomposite.

Interface-Strengthened Polymer Nanocomposites with Reduced Dielectric Relaxation Exhibit High Energy Density at Elevated Temperatures Utilizing a Facile Dual Crosslinked Network.

High-temperature ceramic/polymer nanocomposites with large energy density as the reinforcement exhibit great potential for energy storage applications in modern electronic and electrical power systems. Yet, a general drawback is that the increased dielectric constant is usually achieved at the cost of decreased breakdown strength, thus leading to moderate improvement of energy density and even displaying a marked deterioration under high temperatures and high electric fields. Herein, a new strategy is reported to simultaneously improve breakdown strength and discharged energy density by a step-by-step, controllable dual crosslinking process, which constructs a strengthened interface as well as reduces molecular chains relaxation under elevated temperatures. Great breakdown strength and discharged energy density is achieved in the dual crosslinked network BT-BCB@DPAES nanocomposites at elevated temperatures when compared to noninterfacial-strengthened, BT/DPAES composites, i.e., an enhanced breakdown strength and a discharged energy density of 442 MV m-1 and 3.1 J cm-3 , increasing by 66% and 162%, and a stable cyclic performance over 10 000 cycles is demonstrated at 150 °C. Moreover, the enhancement through the synergy of two crosslinked networks is rationalized via a comprehensive phase-field model for the composites. This work offers a strategy to enhance the electric storage performances of composites at high temperatures.

Critical role of CuO doping on energy storage performance and electromechanical properties of Ba0.8Sr0.1Ca0.1Ti0.9Zr0.1O3 ceramics

CuO doped Ba0.8Sr0.1Ca0.1Ti0.95Zr0.05O3 (BSCTZ) ceramics were prepared by a modified mechano-chemical activation technique with the aim of improving energy storage properties for ceramic capacitor applications. CuO can effectively improve the microstructural characteristics along with a transformation of BSCTZ from classical ferroelectric to relaxor, which is the prime requirement for obtaining high discharge energy density and energy efficiency. The effect of CuO doping on the microstructural, ferroelectric, dielectric, and piezoelectric properties have been systematically studied. The study reveals that an appropriate amount of CuO doping can significantly enhance the morphological properties along with improvement in material density, which is very beneficial in a material for attaining improved energy storage performance. The BSCTZ sample with 3 mol% CuO doping has shown a highly dense microstructure, high saturation polarization (33.01 μC/cm2), low remnant polarization (6.74 μC/cm2), ultrahigh discharge energy density (1.81 J/cm3) and high energy efficiency (81.9%). The CuO doping in BSCTZ has also led to a slight improvement in breakdown strength and electromechanical properties compared to pure BSCTZ ceramics, which is mainly attributed to excellent density and optimum grain size of the material.

Modulation of individual-layer properties results in excellent discharged energy density of sandwich-structured composite films

Sandwich-structured composite films have been regarded as an effective route to resolve the paradox between polarization increase and breakdown strength decrease, and achieve the excellent energy storage performances. However, there are few studies focused on optimizing the individual-layer properties and obtaining satisfactory energy storage performances in the sandwich-structured composite films. In this study, the xTBT (where x is the TO nw fractions, T and B are the TO nws and BT nps filled layers, respectively) sandwich-structured composite films with excellent energy storage performance have been realized though regulating each individual-layer properties, including the dielectric properties, polarization, leakage current and breakdown strength and so on. Notably, the maximum discharged energy density of the 2TBT composite film reaches up to 13.7 J/cm3 at 400 MV/m, and maintains a relatively high energy efficiency of 65%. The enhanced discharged energy density of 2TBT composite film represents a great improvement of 137% higher than that of the neat PVDF (5.8 J/cm3 at 345 MV/m) due to the simultaneously improved breakdown strength and polarization. The preliminary results might pave the way for future designing and optimizing discharged energy density and energy efficiency of sandwich-structured films.

Polyimide films coated by magnetron sputtered boron nitride for high-temperature capacitor dielectrics

Polymers are widely used as dielectric materials in dielectric capacitors, which are the key component of various circuits in power electronic devices. The sharply increased conduction loss at elevated temperatures limits their high-temperature applications. To address this issue, here in this study boron nitride (BN)/polyimide (PI)/BN sandwich-structured films were developed by depositing BN of optimal thickness onto both sides of PI films using magnetron sputtering. Dielectric, insulating and energy-storage performance at 150 °C of the resultant composite films were investigated. The experimental results showed that a dense layer of hexagonal boron nitride (h-BN) was formed on the surface of the polyimide and the coating layer could effectively suppress the charge injection at the electrode/dielectric interfaces by improving the barrier height. Consequently, the sandwiched film of optimal BN thickness exhibited a declined leakage current of about one order of magnitude lower and an improved breakdown strength by 12% in comparison to the neat PI. The sandwiched film could discharge an energy density of 0.493 J/cm3 with charge-discharge efficiency of over 90% under an electric field of 200 MV/m at 150 °C, while the neat PI only possesses an efficiency of 72% and a much lower discharged energy density.

Energy storage property of (Pb0.97La0.02)(Zr0.5Sn0.4Ti0.1)O3-(Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics: Effects of antiferroelectric-relaxor transition and improved breakdown strength

(1-x)(Pb0.97La0.02)(Zr0.5Sn0.4Ti0.1)O3-x(Na0.5Bi0.5)0.94Ba0.06TiO3 (x = 0 ∼ 0.4) ceramics have been prepared and investigated. The ceramics consist of perovskite solid solution matrix and precipitated, isolated SnO2 particle, resulting in 0–3 type composite structure. With increasing x value, the room temperature crystal structure of perovskite solid solution transforms from tetragonal to pseudocubic, therefore, the electrical property evaluates form robust antiferroelectric at x = 0, metastable antiferroelectric at x = 0.1, and then relaxor ferroelectric at x > 0.1. Moreover, the breakdown strength is enhanced due to the composite structure and reaches maximum value of 190 kV/cm at x = 0.2. Both the phase transition and enhanced breakdown strength are helpful to improve energy storage property, the x = 0.2 ceramic shows largest recoverable energy density wrec of 1.84 J/cm3, discharge efficiency η of 86.6 %. Especially, both wrec and η illustrates significantly improved thermal stability within 25−125 °C.

Magneto-fibrillation augments the breakdown strength of ferrofluid dielectrics

The present article reports experimental evidence with a theoretical formalism on the enhancement of the dielectric breakdown strength of ferrofluids by inducing magneto-fibrillation with an external magnetic field. The dielectric breakdown strengths of oil based ferrofluids are determined, and it is further shown that the strength enhances due to the presence of a localized magnetic field in the streamer development zones. The improvement in breakdown strength is also supplemented by improvement in the reliability of the liquid dielectrics, which is established by a two parameter Weibull analysis. It is also noted that a horizontal magnetic field is more potent toward improved breakdown strength than an equivalent vertical field. The enhanced scavenging of electrons from the streamer development zones due to localized magnetic fibrillation by the nanoparticles is proposed as the crux mechanism. Microscopy studies are conducted to provide visual evidence of the fibrillation process in the ferrofluids due to the local magnetic field. A theoretical formalism is proposed to predict the ferrohydrodynamics of fibrillation, and this is further used to develop a model to predict the increment in breakdown strengths. The proposed model predictions are noted to agree well with the experimental observations. The study may find strong implications in design and development of high voltage liquid dielectrics with tunable electrical stress bearing caliber.

Core-satellite ultra-small hybrid Ni@BT nanoparticles: A new route to enhanced energy storage capability of PVDF based nanocomposites

Polymer-based composites comprising of high dielectric constant ceramic nanoparticles are widely used in dielectric capacitors due to their excellent energy storage and processing properties. In this study, ultra-small Ni nanoparticles were used to fabricate core-satellite structured hybrid Ni@BT nanoparticles. Compared with BT/PVDF composites, the Ni@BT/PVDF nanocomposites exhibited the enhanced energy storage properties due to the low electric conductivity, small dielectric loss and improved breakdown strength. The maximum discharged energy density reached 9.55 J/cm3 for nanocomposites with 3 vol% Ni@BT at the electric field of 350 kV/mm, which was nearly eight times of commercial BOPP (1.2 J/cm3 at 640 kV/mm) and was around 208% compared to the pristine PVDF (4.58 J/cm3 at 340 kV/mm). The improved energy density of the nanocomposites could be attributed to the Coulomb-blockade effect of the introduced ultra-small Ni nanoparticles exactly. This work provides an effective approach to improve the energy storage property of dielectric nanocomposites.

Novel nanostructure composite dielectric with high insulation performance: Silica-based nanometer-sized porous composite insulating paper reinforced by ceramic fibers

Nano-dielectrics, which were discovered more than 20 years ago, were once considered as promising insulators. Adding or hybridizing inorganic oxides into polymer matrices inevitably results in poor compatibility between multiphase materials and thus results in limited breakdown strength improvement (generally lower than 20%). Therefore, we bypassed the traditional nano-doping method and proposed the direct construction of matrix materials on nanostructures, that is, a ceramic fiber-porous silica composite insulating paper. The breakdown strength of prepared dielectric was remarkably improved by 120.5%. To the best of our knowledge, such a high improvement in electrical performance has not been reported in previous studies.

Large enhancement of discharge energy density of polymer nanocomposites filled with one-dimension core-shell structured NaNbO3@SiO2 nanowires

Design an architecture with the ability to improve breakdown strength has critical role to play for performance enhancement in energy storage capability. In this work, we report that the composite films with loaded with one dimension (1D) core-shell structured NaNbO3@SiO2 nanowires (NN@SiO2 NWs) are prepared and achieved significantly performance improvement in energy storage capability. The finite element simulation and experiment results both confirm the superiority of the 1D core-shell structured NN@SiO2 NWs in improving the energy density of the nanocomposite films. Especially, the nanocomposite films filled with 3 vol% NN@SiO2 NWs show a large discharged energy density of 12.1 J cm−3, which is ≈ 243% over the bare PVDF (4.98 J cm−3) and ≈ 1008% greater than biaxially oriented polypropylenes (BOPP) (≈ 1.2 J cm−3 at 640 MV m−1). Therefore, this nanocomposite film can be considered as potential high-performance dielectric materials for next-generation pulsed power capacitor applications.

Simultaneously realizing ultra-high energy density and discharge efficiency in PVDF composites loaded with highly aligned hollow MnO2 microspheres

Enhancing the energy density and discharge efficiency of dielectric poly(vinylidene fluoride) (PVDF) has long been a challenging task to realize their practical application as advanced electrostatic capacitors. Herein, in this work, we demonstrated a facile yet effective approach to simultaneously strengthen the energy density and discharge efficiency of PVDF through the synergy of optimized fabrication process and introduction of aligned MnO2 hollow spheres. First, using a nonequilibrium manufacturing approach involving electrospinning, hot-pressing and hot-rolling, reduced ferroelectric loss and improved breakdown strength was achieved in PVDF, which were advantageous to enhance the energy density and discharge efficiency. By further introducing oriented MnO2 microspheres, one could boost the discharge energy density up to 36 J/cm3 while maintain the high discharge efficiency of 73% (500MV/m) due to the enhanced interfacial coupling effect and suppressed conduction loss. This work provides a new paradigm to explore high performance PVDF based composites as viable dielectrics for electrostatic capacitors.

Improved breakdown strength of Poly(vinylidene Fluoride)-based composites by using all ball-milled hexagonal boron nitride sheets without centrifugation

Hexagonal boron nitride (h-BN) is an ideal candidate to endow ferroelectric polymers with high energy density (Ue) due to its intrinsic high breakdown strength (Eb) of 800 kV/mm. Generally, it is believed that only boron nitride nanosheets (BNNSs) could remarkably improve Eb of composite. Nevertheless, low-yield and time-consuming preparation procedures of BNNSs greatly limits the application of h-BN. To overcome this challenge, in this study, all ball-milled h-BN (B-BN) sheets were entirely used to enhance Eb of poly (vinylidene fluoride) (PVDF) without any further centrifugation. Eb of composites increased as ball-milling time increases at filler content of 8 wt%. Remarkably, PVDF with h-BN ball-milled for 16 h (B16-BN) possesses an impressive Eb value of 506.8 kV/mm, which is 2.86 times that of neat PVDF (272.4 kV/mm) and even 1.33 times higher than that of PVDF/h-BN composites (380.6 kV/mm). Eb of PVDF/B16-BN composites is close to that of PVDF/OH-BNNSs composites at same filler content, suggesting that the centrifugation is not a necessary procedure. Besides, improved dielectric loss, calculated Ue, mechanical properties and in-plane thermal conductivity can also be achieved for PVDF/B16-BN composites. These improved properties of PVDF/B16-BN composites indicate that the employment of B16-BN can avoid the weakness of low-yield and time-consuming preparation procedure of BNNSs and broaden its applications in the field of energy storage. Finally, the improved dispersion of OH-BN as well as synergy effect (f) on Eb between OH-BN and OH-BNNSs were discussed to better understand these improved properties of PVDF/B16-BN composites.

Experimental and Modeling Studies of 2D Clay/PE Nanocomposites for High Voltage Applications

The exceptional properties of two-dimensional (2D) nanoclay fillers can alter the dielectric and thermo-mechanical properties of the thermoplastic materials and consequently extend its engineering applications. In this work, polyethylene (PE) was filled with 2D organo-modified montmorillonite nanolcay (O-MMT) to fabricate polyethylene/clay nanocomposites. The dielectric properties of neat PE and its nanocomposites were investigated. The results indicated that the dielectric permittivity and breakdown strength were increased by the incorporation of the 2D nanoclay filler. Based on the achieved experimental results, 2D finite element model (FEM) was performed to explain the physical mechanisms behind the improved breakdown strength of the nanocomposites.