High Dielectric and Mechanical Properties Achieved in Cross-Linked PVDF/α-SiC Nanocomposites with Elevated Compatibility and Induced Polarization at the Interface

Remarkable Dielectric Breakdown Strength of Printable Polyelectrolyte Photopolymer Complexes

Polymer-based dielectrics are struggling to keep pace with the increasing demands of modern electronics. This lag in dielectric performance has spurred significant interest in the production of advanced dielectrics via novel chemistries and processing techniques. Polyelectrolyte complexes (PECs) have recently shown great promise as dielectric insulation, but processing challenges presented by these ionically bound networks limit their use to conformal thin films. Recent advances have enabled the additive manufacturing of PECs with vat photopolymerization, allowing the creation of a polyelectrolyte complex of arbitrary shape. Herein, multiple polyelectrolyte resin formulations, comprised of polyethylenimine and methacrylic acid (with varying amounts of 2-hydroxyethyl methacrylate and/or N,N-dimethylacrylamide), are investigated for the production of additively manufactured dielectric insulators. These dielectrics not only possess high dielectric breakdown strengths (>300 kV/mm), but their dielectric behavior can also be readily tailored through resin formulation and post-processing conditions. The presented vat photopolymerization of PECs allows for the creation of bulk dielectrics with arbitrary geometry, while the novel chemistry provides a practical route forward to produce dielectrics with precisely tailored properties for specific applications.

Hybrid Core-Shell TiCN@SiO2 Nanoparticles in Percolation-Based Polyvinylidene Fluoride Dielectrics for Improved High-Voltage Capacitive Energy Storage

Solid-state polymer dielectrics offer an exceptional dielectric breakdown, but require an enhanced energy density to be competitive with alternative electrolyte-based energy storage technologies. Therefore, this research introduces conductive titanium carbonitride (TiCN) nanoparticles in a polyvinylidene fluoride (PVDF) matrix to obtain flexible percolation-based nanodielectrics by ultrasonication-based suspension processing and hot pressing. Well-dispersed TiCN nanoparticles in PVDF were obtained for a wide range of filler volume fractions, and an exceptional peak in the dielectric constant equal to 1130 (0.1 Hz) and 29 (10 kHz) was observed near the percolation threshold (9.2 vol %). The enhanced dielectric constant was ascribed to massive interfacial polarization occurring, resulting from Maxwell-Wagner-Sillars (MWS) polarization and a nanocapacitor mechanism that are dominant at low and high frequencies, respectively. An improvement by 30% in the energy density (0.042 Wh kg-1) compared with the neat PVDF matrix was achieved for the PVDF/TiCN nanodielectrics. The first successful uniform deposition of a nanometer-thin (3 nm) silica (SiO2) shell via the Stöber process on TiCN nanoparticles significantly suppressed the dielectric losses near percolation for the PVDF/TiCN@SiO2 nanodielectrics by more than 1 order of magnitude while offering dielectric constants of 34 (0.1 Hz) and 10 (10 kHz). This study demonstrates the potential of hybrid (core-shell) percolation-based dielectrics for an improved capacitive dielectric performance by an integrated dielectric characterization approach that simultaneously optimizes the dielectric constant, loss tangent, breakdown strength, and energy density.

High energy capability in poly(vinylidene fluoride-co-chlorotrifluoroethylene) nanocomposite incorporated with Ag@polyaniline@covalent organic framework core-shell nanowire

The development of polymer film with large electrical displacement is essential for the applications of lightweight and compact energy storage. The dielectric diversity at interface of polymer composite should be addressed to realize the film capacitor with high energy density and dielectric reliability. In this work, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite was incorporated by core-shell nanowire with covalent organic framework (COF) outer coating to alleviate the dielectric mismatch at interface. After the preparation of Ag nanowire through polyol reduction, polyaniline (PANI) and COF layers were sequentially deposited to construct core-shell Ag@polyaniline@covalent organic framework (Ag@PANI@COF) nanowire. According to the unique core-shell architecture, the COF framework is utilized to suppress the remanent polarization while high electrical displacement is preserved by the center Ag nanowire. The maximum energy density of 25.0 J/cm3 at 425 MV/m is obtained in 0.1 wt% stretched Ag@PANI@COF/P(VDF-CTFE) nanocomposite. The presence of core-shell nanowire depresses the distribution distortion of electric field and the diffusion of charge carriers under high field. This work demonstrates an effective method to develop the polymer film with large electrical displacement, and sheds a light on insightful exploration of interfacial polarized mechanism in polymer dielectric composite.

Perspective on interface engineering for capacitive energy storage polymer nanodielectrics

Polymer nanodielectrics with high breakdown strength (E_b), high energy density (U_e) and low energy loss have great potential to be used as capacitive energy storage materials of high-voltage film capacitors in modern electrical and electronic equipment, such as smart grids, new energy vehicles and pulse powered weapons. Usually, inorganic nanoparticles with high dielectric constant (ε_r) are added into a high E_b polymer matrix to achieve simultaneously enhanced ε_r and E_b, thus leading to nanodielectrics with high U_e. However, this strategy was seriously hampered by the uneven distribution of electric fields and inhomogeneous microstructures of the multi-phased nanodielectrics until increasing research work was focused on interface engineering. Recent progress in nanocomposites suggests that interface engineering plays a critical role in regulating the polarization and breakdown behaviors of the nanodielectrics, such as balancing ε_r and E_b, enhancing U_e and energy discharge efficiency (η). This article highlights the recent advances in the interface engineering of polymer nanodielectrics, including theoretical models, interface engineering strategies, and the latest characterization and fabrication techniques of high performance nanodielectrics. Finally, the challenges and opportunities in the interface engineering of the nanodielectrics in film capacitors are discussed and predicted from a practical point of view.

Synchronously improved thermal conductivity and dielectric constant for epoxy composites by introducing functionalized silicon carbide nanoparticles and boron nitride microspheres

Polymer-based dielectrics with high thermal conductivity and superb dielectric properties hold great promising for advanced electronic packaging and thermal management application. However, integrating these properties into a single material remains challenging due to their mutually exclusive physical connotations. Here, an ideal dielectric thermally conductive epoxy composite is successfully prepared by incorporating multiscale hybrid fillers of boron nitride microsphere (BNMS) and silicon dioxide coated silicon carbide nanoparticles (SiC@SiO₂). In the resultant composites, the microscale BNMS serve as the principal building blocks to establish the thermally conductive network, while the nanoscale SiC@SiO₂ as bridges to optimize the heat transfer and suppress the interfacial phonon scattering. In addition, the special core-shell nanoarchitecture of SiC@SiO₂ can significantly impede the leakage current and generate a great deal of minicapacitors in the composites. Consequently, favorable thermal conductivity (0.76 W/mK) and dielectric constant (∼8.19) are simultaneously achieved in the BNMS/SiC@SiO₂/Epoxy composites without compromising the dielectric loss (∼0.022). The strategy described in this study provides important insights into the design of high-performance dielectric composites by capitalizing on the merits of different particles.

PI-based composites with high dielectric constant and low loss by filling with self-derived carbon

In this work, we prepared polyimide (PI) composite films by directly filling the matrix with self-derived carbon particles. Without any surface modification layer, these specially made particles were compatible with their parent matrix quite well. For the composite film with 25 wt% filler content, the dielectric constant was 72.5 at 1 MHz at room temperature, and the dielectric loss was only 0.069. The conductivity of the corresponding composite was measured to be below 10−6 Sm−1, and the breakdown strength was 165 MVm−1. In addition, the tensile strength of the composite film was measured to be 73 MPa. These results indicate that carbonized PI can be used as an excellent filler to prepare PI-based composite films with high dielectric constant.

Improving the Energy Density and Efficiency of the Linear Polymer PMMA with a Double-Bond Fluoropolymer at Elevated Temperatures

A variety of applications can be found for high-temperature film capacitors, including energy storage components and pulsed power sources. In this work, in order to increase the energy density (U _e), poly(vinylidene fluoride-chlorotrifluoroethylene-double bond) (P-DB) is introduced into poly(methyl methacrylate) (PMMA) to manufacture composite films by a solution casting process. In the case of the pure PMMA film, there is significant improvement in the polarization (P _max) and breakdown field (E _b) of the composite film. These improvements can effectively increase the U _e of the composite film at room temperature and the elevated temperature. The results show that at an elevated temperature of 90 °C and at 350 MV/m, the U _e of 40 vol % P-DB reaches 8.7 J/cm³, and the efficiency (η) of 77% is also considerable. Compared with biaxially oriented polypropylene (2.0 J/cm³), the proposed film exhibits 4 times enhancement in the energy storage density, meaning that it can be an energy storage capacitor with huge potential at high temperatures.

PVDF promotes TiO2 dispersion to obtain composite films with high dielectric constant and low loss

A series of three-phase composite films with different filler contents were prepared by in-situ polymerization. The composite films comprise polyimide (PI), poly (vinylidene fluoride) (PVDF), and titanium dioxide (TiO2). Compared with PI/TiO2 composite films, the PI/TiO2-PVDF composite films not only get a significant increase in dielectric constant, but also own better mechanical properties. Our results show that with the loading of 50wt% PVDF particles, the dielectric constant of PI/TiO2-PVDF composite films increased from 6.5 to 18.14 at 1 MHz and room temperature, while the tensile strength of PI/TiO2-PVDF composite films increased from 45 to 72 MPa. In addition, the films maintain a low loss tangent of about 0.02. PI/PVDF composite films were also prepared. It was found that dielectric constant of PI/PVDF composite was significantly lower than that of PI/TiO2-PVDF composite films when the loading of PVDF is 50wt%.

Enhanced energy storage density of all-organic fluoropolymer composite dielectric via introducing crosslinked structure

Polymer-based dielectrics have been attracted much attention to flexible energy storage devices due to their rapid charge–discharge rate, flexibility, lightness and compactness. Nevertheless, the energy storage performance of these dielectric polymers was limited by the weak dielectric breakdown properties. Crosslinked structure has been proven efficient to enhance breakdown strength (E_b) and charge–discharge efficiency (η) of polymer film capacitors. However, crosslinked networks usually lead to low electric displacement of dielectric capacitors, which greatly restrict their energy storage density (U_d). In this work, we present a tri-layered composite via layer-by-layer casting technology, where crosslinked polyvinylidene fluoride (c-PVDF) was used as the inter-layer to offer high breakdown strength, and the outer ternary fluoropolymer layers with high dielectric constant could provide high electric displacement. The optimal tri-layered composites exhibit an ultrahigh discharge energy density of 18.3 J cm⁻³ and a discharge efficiency of 60.6% at 550 kV mm⁻¹. This energy density is much higher than that of the PVDF terpolymer and commercially biaxially oriented polypropylene (BOPP, 1–2 J cm⁻³). The simulation results prove that the enhanced energy density originates from the effectively depressed charge transport in crosslinked structure at high applied electric field. Moreover, this work provides a feasible method for developing flexible all-organic high-energy-density composites for polymer capacitors.

High energy density is achieved for all-organic composites by introducing crosslinked structure.

Microcellular structure assisted phase transformation of polyvinylidene fluoride/titanium dioxide nanocomposites

A novel nanocomposite foam with microcellular structures based on poly(vinylidene fluoride) (PVDF) and titanium dioxide (TiO2) was fabricated by the combination of melt compounding and supercritical carbon dioxide (scCO2) foaming. To improve its dielectric performance, silane modified and unmodified titanium dioxide nanoparticles were added as reinforcing fillers at low weight percentages (0.5, 1, and 5 wt%) during the melt blending process. It was found that the incorporation of nanoparticles had a strong influence on cell morphology. As a result, the foaming process significantly altered the dielectric, and mechanical properties of the composite foams. The dielectric constants of the composite foams were no longer frequency dependent while tan delta was lowered at least by a factor of 10. Furthermore, the porous structure generated by foaming also assisted the α-to-β phase transformation of the PVDF matrix in a way similar to mechanical stretching. Such method is superior to other phase transformation techniques since β-phase PVDF can be produced in bulk geometries instead of a thin film configuration.

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.

Achieving high performance poly(vinylidene fluoride) dielectric composites via in situ polymerization of polypyrrole nanoparticles on hydroxylated BaTiO3 particles

PPy@BTOH composite particles with a ‘mulberry-like’ structure are fabricated to prepare dielectric composites with excellent comprehensive dielectric properties.

Polymer dielectric composites have widespread applications in many fields ranging from energy storage, microelectronic devices, and sensors to power driven systems, etc. and attract much attention of researchers. However, it is still challenging to prepare advanced polymer dielectric composites with a high dielectric constant (ε′), low dielectric loss (tan δ) and simultaneously high breakdown strength (E_bd). In this work, conductive polypyrrole (PPy) nanoparticles were in situ synthesized in a reaction system containing the common barium titanate (BaTiO₃, BT) or hydroxylated BaTiO₃ (BTOH) particles, and then the PPy@BT and PPy@BTOH composite particles were incorporated into poly(vinylidene fluoride) (PVDF) to prepare the composites. The morphologies and microstructures of the PPy@BT and PPy@BTOH composite particles and the corresponding PVDF composites were comparatively investigated. The results showed that the PPy@BTOH composite particles had a ‘mulberry’-like morphology with a rough surface and the self-assembled structure could be maintained in the PVDF composites, which was apparently different from the PVDF/PPy@BT composites, in which most of the PPy nanoparticles dissociatively dispersed in the PVDF matrix. Electrical conductivity measurements showed that at high particle content (≥20 wt%), the PPy@BTOH composite particles endowed the composites with lower electrical conductivity compared with the PPy@BT composite particles. Dielectric property measurements showed that the ‘mulberry’-like PPy@BTOH composite particles endowed the PVDF composites with extremely high ε′, ultralow tan δ and high E_bd compared with the PVDF/PPy@BT composites with dissociatively dispersed PPy nanoparticles and BaTiO₃ particles. The polarization and loss mechanisms of the composites were then proposed based on the morphologies and the microstructures of the composites. This work provides an alternative way to fabricate functional dielectric particles through trace functional groups inducing in situ polymerization of conductive polymers, and these particles can be used to fabricate advanced dielectric composites.

Optimizing sandwich-structured composites based on the structure of the filler and the polymer matrix: toward high energy storage properties

Polymer-based energy storage materials have been widely applied in the energy storage industry, such as in the hybrid electric vehicle and power-conditioning equipment, due to their moderate energy density and ultrafast charging/discharging speed. Accordingly, the improvement of the energy storage density of polymer matrix composites has become the focus of current research. In this study, different fillers (e.g., 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ nanofibers (BCZT NFs), BCZT + Ag NFs and BCZT + Ag@Al₂O₃ NFs) were synthesized via electrospinning and were added to the poly(vinylidene fluoride) (PVDF) matrix as a middle layer in sandwich-structure composites. The PVDF polymer-containing PMMA was prepared as the outer layer in the sandwich structure composites. These sandwich-structured composites have low loss, low current density, better breakdown strength and higher efficiency. In particular, 40% PMMA/PVDF/3 vol% BCZT + Ag@Al₂O₃/PVDF/40% PMMA/PVDF composites have an energy density of 7.23 J cm⁻³ and efficiency above 75.8% at 370 kV mm⁻¹. This article could open up a convenient and effective means for the practical application of power-pulsed capacitors by tuning the filler nanostructure and polymer nanocomposites.

Inorganic composite fillers and sandwich-structured composite films have been designed for further increasing the energy storage density.

Improved Energy Storage Performance of Linear Dielectric Polymer Nanodielectrics with Polydopamine coated BN Nanosheets

Polymer-based nanodielectrics have been intensively investigated for their potential application as energy storage capacitors. However, their relatively low energy density (U_e) and discharging efficiency (η) may greatly limit their practical usage. In present work, high insulating two-dimensional boron nitride nanosheets (BNNS), were introduced into a linear dielectric polymer (P(VDF-TrFE-CTFE)-g-PMMA) matrix to enhance the energy storage performance of the composite. Thanks to the surface coating of polydopamine (PDA) on BN nanosheets, the composite filled with 6 wt% coated BNNS (mBNNS) exhibits significantly improved breakdown strength (E_b) of 540 MV/m and an energy density (U_e) of 11 J/cm³, which are increased by 23% and 100%, respectively as compared with the composite filled with the same content of pristine BNNS. Meanwhile, η of both composites is well retained at around 70% even under a high voltage of 400 MV/m, which is superior to most of the reported composites. This work suggests that complexing polymer matrix with linear dielectric properties with surface coated BNNS fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency.

In-depth understanding of interfacial crystallization via Flash DSC and enhanced energy storage density in ferroelectric P(VDF-CTFE)/Au NRs nanocomposites for capacitor application

High-capacity or high-power-density capacitors are being actively investigated for portable electronics, electric vehicles, and electric power systems. We describe the filler system in dielectric nanocomposites with a small loading of Au nanorods [NRs] to elucidate the mechanism of interfacial crystallization behavior including the crystallization kinetics, and crystalline morphology and structure, and to investigate the intrinsic causes for concurrent great improvements in the dielectric constant and energy density in the nanocomposite system. Remarkly, at high crystallization temperature, the addition of Au NRs, which are used as heterogeneous nucleators, can reduce the nucleation barrier, resulting in accelerating the crystallization rate. However, the crystallization rate slows down at low temperatures because the addition of Au NRs limited the mobility of poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] chains, and thus enhanced the diffusion barrier. Furthermore, the addition of NRs has a huge impact on the crystalline morphology and structure which changes from large paraelectric α-phase spherulites with TGTG' conformations into minor ferroelectric γ-phase spherulites with T3GT3G' conformations, and also produces more exogenous interfaces between the lamellar crystals and amorphous regions, resulting in a higher dielectric constant and higher electric energy density in P(VDF-CTFE)/Au NRs nanocomposites. Our approach provides a facile and straightforward way to design or understand PVDF-based polymers for their practical applications in high-energy-density capacitors.

Enhancing High-Frequency Dielectric Properties of Beta-SiC Filled Nanocomposites from Synergy between Percolation and Polarization

Promising comprehensive properties, including high permittivity, low dielectric loss, high breakdown strength, low electrical conductivity, and high thermal conductivity, are very hard to simultaneously obtain in high-frequency applicable polymer nanocomposite dielectrics. Instead of traditional electric percolation, in this work, a novel route based on a synergy between electric percolation and induced polarization has been raised to prepare 0⁻3 type nanocomposites with an enhanced high permittivity (high-k) property and low loss at high frequency. This work aimed at optimizing that synergy to achieve the favorable properties mentioned above in composite dielectrics used at high frequencies such as 1 MHz and 1 GHz. Conductive beta-SiC nanoparticles with a particle size of ~30 nm were employed as filler and both insulating poly(vinyl alcohol) and polyvinyl chloride were employed as polymer matrices to construct two composite systems. Utilizing polyvinyl chloride rather than poly(vinyl alcohol) realizes higher comprehensive electrical properties in composites, ascribed to optimization of that synergy. The optimization was achieved based on a combination of mild induced polarization and polarization-assisted electric percolation. Therefore, this work might open the way for large-scale production of high-frequency applicable composite dielectrics with competitive comprehensive electrical properties.

Achieving High Energy Density and Low Loss in PVDF/BST Nanodielectrics with Enhanced Structural Homogeneity

Poor compatibility of polymer/ceramic composites used as high-pulse capacitors with high permittivity suffers from the reduced breakdown strength ( E_b) and lowered energy density ( U_e). Herein, mussel-inspired poly(dopamine) (PDA)-modified BaSrTiO₃ (mBST) nanoparticle and poly(vinylidene fluoride) (PVDF) matrix are bonded together to fabricate nanocomposites with a cross-linked network and enhanced compatibility. The significantly improved E_b of 466 MV/m and the highest U_e of 11.0 J/cm³ for PVDF-based polymer/BST composites have been obtained. By comparing the properties of the three series of composites with different structures, the contribution of ferroelectric relaxation, interface polarization, and leakage conduction to the dielectric loss has been well addressed. Notably, the surface modification of BST with PDA could remarkably enhance the compatibility of the two components and the structural homogeneity of the composite. The improved bonding between the polymer matrix and the filler chemically or physically is responsible for the reduced dielectric loss from both conduction loss and interfacial polarization, which is the key to improve the E_b, U_e, and η of the composite. It has been revealed that enhancing the homogeneity of the composites by modifying ceramics and constructing cross-linked networks between the polymer matrix and the filler might be a facile strategy to achieve high energy storage performance in polymer composites.

Significantly Enhanced Electromechanical Performance of PDMS Crosslinked PVDF Hybrids

Poly(vinylidene fluoride)-based ferroelectric polymers have large and tunable dielectric permittivity (εr), but rather high Young's modulus (Y), which limits its electromechanical response when used as actuators. In this work, a silicone oligomer involving amino groups is employed to crosslink a non-crystallized poly(vinylidene fluoride-chlorotrifluoroethylene) matrix bearing double bonds (P(VDF-CTFE-DB)) via addition reaction. Thanks to the flexible silicone molecules, the modulus of the hybrids is reduced over 30% when compared with the pristine matrix. Most interestingly, the εr of the hybrids is improved to nearly 100% higher than that of the matrix when the silicone content reaches 30 wt %. This may be due to the dilution effect of silicone molecules, which favors macromolecular chain rearrangement and dipole orientation of the hybrids under an applied electric field. As a result, electric-field activated displacements of the above hybrid increases to 0.73 mm from 0.48 mm of the matrix under 60 MV/m. The maximum electric field-induced thickness strain increases from 1% of the matrix to nearly 3% of the crosslinked hybrid. This work may provide a facile strategy to fabricate PVDF-based hybrids with enhanced electromechanical performance under low activating voltage.

Enhanced Dielectric and Mechanical Properties of Ternary Composites via Plasticizer-Induced Dense Interfaces

High overall performance, including high dielectric constant, low loss, high breakdown strength, fine flexibility, and strong tensile properties, is difficult to achieve simultaneously in polymer nanocomposites. In our prior work, we modified the surfaces of alpha-SiC nanoparticles and chemically cross-linked the polymeric matrix to simultaneously promote the dielectric and mechanical properties of composites. In this work, a novel strategy of high-temperature plastification towards a polymeric matrix has been proposed to fabricate ternary nanocomposites with balanced dielectric and mechanical characteristics by the solution cast method in order to reduce costs and simplify steps during large-scale preparation. Poly(vinylidene fluoride-chlorotrifluoroethylene) with inner double bonds as matrix, unfunctionalized alpha-SiC nanoparticles (NPs) as filler, and dibutyl phthalate (DBP) as plasticizer were employed. By introducing DBP and high-temperature treatment, the dispersion of NPs and the degree of compactness of the interface regions were both improved due to the reduced cohesion of the fluoropolymer, resulting in an increase in the dielectric constant (by 30%) and breakdown strength (by 57%) as well as the lowering of loss (by 30%) and conductivity (by 16%) in nanocomposites. Moreover, high-temperature plastification contributed to the promotion of flexible and tensile properties. This work might open the door to large-scale fabrication of nanocomposite dielectrics with high overall properties through the cooperation of the plasticizer and high temperature.

Enhanced energy density and thermal conductivity in poly(fluorovinylidene-co-hexafluoropropylene) nanocomposites incorporated with boron nitride nanosheets exfoliated under assistance of hyperbranched polyethylene

Polymer dielectric film with a large dielectric constant, high energy density and enhanced thermal conductivity are of significance for the development of impulse capacitors. However, the fabrication of polymer dielectrics combining high energy density and thermal conductivity is still a challenge at the moment. Here we demonstrate the facile exfoliation of hexagonal boron nitride nanosheets (BNNSs) in common organic solvents under sonication with the assistance of hyperbranched polyethylene (HBPE). The noncovalent CH-π interactions between the nanosheets and HBPE ensure the dispersion of BNNSs in organic solvents with high concentrations, because of the highly branched chain structure of HBPE. Subsequently, the resultant BNNSs with a few defects are distributed uniformly in the poly(fluorovinylidene-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposite films prepared via simple solution casting. The BNNS/P(VDF-HFP) nanocomposite exhibits outstanding dielectric properties, high energy density and high thermal conductivity. The dielectric constant of the 0.5 wt% nanocomposite film is 35.5 at 100 Hz with an energy density of 5.6 J cm^-3 at 325 MV m^-1 and a high charge-discharge efficiency of 79% due to the depression of the charge injection and chemical species ionization in a high field. Moreover, a thermal conductivity of 1.0 wt% nanocomposite film reaches 0.91 W·m^-1 · K^-1, which is 3.13 times higher than that of the fluoropolymer matrix. With dipole accumulation and orientation in the interfacial zone, lightweight, flexible BNNS/P(VDF-HFP) nanocomposite films with high charge-discharge performance and thermal conductivity, exhibit promising applications in relatively high-temperature electronics and energy storage devices.

Fabrication of Stretchable Nanocomposites with High Energy Density and Low Loss from Cross-Linked PVDF Filled with Poly(dopamine) Encapsulated BaTiO3

In this report, a simple solution-cast method was employed to prepare poly(dopamine) (PDA) encapsulated BaTiO₃ (BT) nanoparticle (PDA@BT) filled composites using PVDF matrix cross-linked by the free radical initiator. The effects of both the particle encapsulation and matrix cross-linking on the mechanical and dielectric properties of the composites were carefully investigated. The results suggested that the introduction of BT particles improved permittivity of the composites to ∼30 at 100 Hz when particle contents of only 7 wt % were utilized. This was attributed to the enhanced polarization, which was induced by high permittivity ceramic particles. Compared to bare BT, PDA@BT particles could be dispersed more homogeneously in the matrix, and the catechol groups of PDA layer might form chelation with free ions present in the matrix. The latter might depress the ion conduction loss in the composites. Other results revealed that the formation of hydrogen-bonding between the PDA layer and the polymer, especially the chemical cross-linking across the matrix, resulted in increased Young' modulus by ∼25%, improved breakdown strength by ∼40%, and declined conductivity by nearly 1 order of magnitude when compared to BT filled composites. The composite films filled with PDA@BTs indicated greater energy storage capacities by nearly 190% when compared to the pristine matrix. More importantly, the excellent mechanical performance allowed the composite films to adopt uni- or biaxially stretching, a crucial feature required for the realization of high breakdown strength. This work provided a facile strategy for fabrication of flexible and stretchable dielectric composites with depressed dielectric loss and enhanced energy storage capacity at low filler loadings (<10 wt %).