Vinylidene Fluoride-hexafluoropropylene) [P Research Articles

Tailorable high-k and negative-k percolation behaviors in PPy/P(VDF-HFP) composites

Polymer-based composites with high permittivity and low loss are highly desirable for many applications such as embedded capacitors and pulse-power. In the meantime, percolating composites with negative permittivity can be promising candidates for metamaterials. In this paper, nanocomposites using conductive polypyrrole nanowires as fillers and poly(vinylidenefluoride-hexafluoropropylene) (P(VDF-HFP)) as matrix were prepared by a solution-casting method. The electrical properties were investigated in detail. Two types of percolation behavior were observed in the composites with increasing PPy content. The permittivity significantly enhanced when the PPy content exceeded high-dielectric percolation threshold (i.e. fhigh-k) due to the large number of microcapacitors formed by PPy fillers and P(VDF-HFP) matrix. With further increasing PPy content, tunable negative permittivity behavior was achieved due to the formation of conductive networks, this phenomenon can be regarded as a negative-dielectric percolation (i.e. negative-k percolation), which can be well described by Drude-Lorentz model. The realization of high permittivity and tunable negative permittivity in PPy/P(VDF-HFP) nanocomposites gives a new and efficient strategy toward high-k materials and random metamaterials.

Interfacial and Bulk Polarization of P(VDF-HFP) Investigated by Dielectric Spectroscopy

Capacitors in electrical and electronic systems composed of thin film dielectrics operate under extremely high electric fields. Dynamics of charge transport and relaxation are closely correlated to the energy storage properties and electrical degradation of thin film dielectrics for capacitive applications. In this paper, the dielectric relaxation properties of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films are investigated over a broad frequency range from 10 mHz to 10 MHz and temperature range from -130 °C to 130 °C. The dielectric responses correlated to bulk and interfacial processes are clarified by varying the thickness and interfacial contact status of P(VDF-HFP) films. A low frequency process originating from the quasi-DC (QDC) process and a dielectric dispersion process correlated to the interfacial polarization are identified based on the Dissado-Hill dielectric response model and the equivalent circuit analysis. The high permittivity and high operation electric field of P(VDF-HFP) for capacitive energy storage give rise to improved blocking capacitance associated with the interface, suggesting the enhanced interfacial polarization. This work provides insights into the bulk and interface charge dynamics of polymer thin film dielectrics.

Significantly enhanced energy density and breakdown strength of polymer nanocomposites using highly textured [111]c BaTiO3 platelets

Polymer-based dielectric films are considered as most promising materials for pulsed power capacitors due to their ultra-high power density and current density, fast discharging speed, excellent cycle lifetime and so on. However, the relatively low energy density and efficiency limit their applications in modern electronics and electrical power systems. Here we demonstrate a remarkable improvement in the breakdown strength and energy density of [111]c-BaTiO3 (BT) textured ceramic platelets synthesized in a poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) matrix. The breakdown strength of 1.0 wt% BT/P(VDF-HFP) composite films is 130 MV/m higher than that of pristine poly(vinylidene fluoride-hexafluoropropylene) films. The highest energy density of 19.5 J/cm³ and discharged energy density of 10.6 J/cm³ are achieved under an electric field of 480 MV/m in the 1.0 wt% BT/P(VDF-HFP) composite films. Fatigue experimental results show that the energy density and efficiency enhanced with the increase of cycles. This study provides a new paradigm to develop the polymer composites with high breakdown strength and energy density, which has great potential for flexible electrical energy storage applications.

Temperature dependence and correlation of polarization processes in P(VDF-HFP) films

Polymer dielectrics are indispensable in electrical and electronic systems, being used as insulation, capacitors, gate dielectric, etc. However, a lot of polymer materials show unsatisfactory efficiency at high temperature and low frequencies, which has been found to be closely related to polarization processes. In this paper, the dielectric spectroscopy of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) films is investigated over a broad frequency range from 10 mHz to 1 MHz and temperature range from −130 °C to 130 °C based on the Dissado-Hill model. The processes in the entire response are identified and characterized quantitatively. The temperature dependence of major processes contributing to energy storage and dielectric loss are revealed. It is found that the variations of both β polarization and DC conductance coincide with Arrhenius equation, while both α polarization and quasi-DC polarization show Vogel−Fulcher−Tammann (VFT) features. Moreover, α polarization and quasi-DC polarization share the same form parameter of VFT equation, indicating that they have a common origin of microstructure. The origin and correlation of polarization processes could be used to develop a paradigm for rational design of polymer dielectrics to enhance or suppress specific processes for certain purposes.

Enhanced energy density in sandwich-structured P(VDF-HFP) nanocomposites containing Hf0.5Zr0.5O2 nanofibers

Ceramic/polymer composites with high energy density attract great interest due to their application in micro-electric power systems. However, the large permittivity mismatch between ceramic fillers and polymer matrix will largely decrease the breakdown strength and energy density of nanocomposites. Herein, one-dimensional Hf0.5Zr0.5O2 nanofibers (HZO-NFs) with very low permittivity were proposed as the loading fillers in poly (vinylidene fluoride - hexafluoro propylene) (P(VDF-HFP)) copolymer for energy-storage applications for the first time via a simple scalable method of electrospinning technique. P(VDF-HFP) nanocomposites with 3 wt% HZO-NFs (3 wt% HZO/P) showed a high discharged energy density (Ud) of 13.68 J/cm3 with a high breakdown strength (Eb) of 508.66 kV/mm. Sandwich-structured P-3 wt% HZO/P-P nanocomposite achieved an excellent Ud of 21.63 J/cm3 and a high η of ∼ 65.68% at ultrahigh Eb of 706.71 kV/mm, which are much higher than those of the commercial BOPP, i.e. 2 J/cm3 at 640 kV/mm. Moreover, the COMSOL simulations revealed that the introduction of 1D nanofibers and charge traps could effectively improve the local distribution of electric field, and finally increased the breakdown strength. The major contribution to the improved Ud originates from the large breakdown strength (4 ∼ 8 MV/cm), because of the large band width of HZO and the existence of multi-interfaces. This work can provide a new perspective for promoting the performance of polymer nanocomposites.

Achieving Concurrent High Energy Density and Efficiency in All-Polymer Layered Paraelectric/Ferroelectric Composites via Introducing a Moderate Layer.

Dielectric polymer capacitors are extensively applied in advanced electronics by virtue of their extremely high power density. However, it remains a challenge to concurrently realize high energy density and high discharge efficiency. In order to solve this conundrum, we herein design a novel all-polymer trilayer structure, where the paraelectric poly(methyl methacrylate) (PMMA) is used as the top layer to obtain a high discharge efficiency, and ferroelectric P(VDF-HFP) is employed as the bottom layer to obtain a high energy density. Particularly, the PMMA/poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) blend composite is used as the middle layer to homogenize the electric field inside the trilayer composites, turning out an obviously boosted breakdown strength and elevated energy density. Consequently, an efficiency as high as 85% and an energy density up to 7.5 J/cm3 along with excellent cycling stability are simultaneously realized at an ultrahigh electric field of 490 kV/mm. These attractive characteristics of the all-polymer trilayer structure suggest that the feasible pathway presented herein is significant to realize concurrently a high energy density and discharge efficiency.

Enhanced Energy Storage Performance of Polymer/Ceramic/Metal Composites by Increase of Thermal Conductivity and Coulomb-Blockade Effect.

Polymer-based dielectrics have attracted considerable attention for a wide range of applications as energy storage devices with high power. However, high loss from low thermal conductivity (K) and leaky current may limit their practical utilization greatly. To overcome these issues, two-dimensional hexagonal boron nitride (h-BN) modified with polydopamine (PDA) and metal palladium nanoparticles (h-BN@PDA@Pd NPs) are introduced into a poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) copolymer matrix. The PDA coating improves the compatibility between the ceramic h-BN filler and the polymer matrix. Contrary to the general idea, the metallic Pd NPs enhance the breakdown strength of the polymer nanocomposites through the Coulomb-blockade effect. The nanocomposite film filled with 6 vol % h-BN@PDA@Pd NPs exhibits significantly improved recoverable energy density (Urec) of 58.6 J cm-3, which is increasedby 496% compared to pure P(VDF-HFP) film, maintaining an efficiency of 65%, even under a high voltage of 500 MV m-1. The in-plane thermal conductivity of the nanocomposites was improved from 0.21 to 1.02 W m-1 K-1 with increasing ceramic h-BN content. This study suggests that a dielectric polymer with surface-engineered ceramic h-BN fillers through a Coulomb-blockade effect of metal Pd NPs might be a promising strategy for high energy storage devices.

Grafting modification of poly(vinylidene fluoride-hexafluoropropylene) via Cu(0) mediated controlled radical polymerization

In the present work, diverse vinyl monomers were successfully grafted onto poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) via direct activation of CF bonds using Cu(0)/4,4′-dimethyl-2,2′-bipyridyl (DMDP) as catalyst under mild conditions. The structure of the graft copolymer was carefully characterized, and the initiating site was confirmed at the same time. Moreover, the kinetic results indicated the controlled behavior of the graft polymerization, and the composition of the graft copolymer can be regulated by changing the reaction conditions. This work may provide a facile strategy to endow P(VDF-HFP) copolymer with new functions via directly activating CF bonds.

Relaxation behavior of sandwich-structured fluorinated graphene/poly(vinylidene fluoride-hexafluoropropylene) composites by dielectric relaxation spectroscopy

The sandwich-structured fluorinated graphene (FGN)/poly(vinylidene fluoride-hexafluoro- propylene) [P(VDF-HFP)] composites with various FGN constituents were fabricated via a layer-by-layer solution casting technique, and their dielectric relaxation phenomenons of the trilayered composites were studied in a systematic way by dielectric relaxation spectroscopy (DRS) at various temperatures (25°C–200 °C) in the range of 20 Hz to 5 M Hz. The variations in dielectric parameters (ε′and ε") with frequency at each studied temperature show that ε′and ε" increase with the rise of temperature and ε" significantly decreases with the addition of FGN. Moreover, the asymmetric shapes of electric modulus spectra (M″) and Cole-Cole plots exhibit the relaxation process of non-Debye, especially in trilayered FGN/P(VDF-HFP) composites. AC conductivity is irrelevant to frequency and temperature under low frequency-high temperature, but frequency sensitive under high frequency region. Furthermore, the two activation energies (Eτ and Eσ) gradually increased with the addition of FGN, showing that the mobility of charge carriers is suppressed, thus they are unable to overcome the relaxing and conducing barrier.

Design on orientation of one-dimensional ZnO/P(VDF-HFP) nanocomposites for significant enhanced electromechanical conversion

Flexible piezoelectric generators (PEGs) are receiving considerable attention due to the increasing demands on lightweight and sustainable power supply for wearable electronics. Combing piezoelectric nanofillers with polymers have been extensively investigated as a promising strategy. Here, piezotronic ZnO nanorods are introduced into poly (vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] considering that piezoelectric functions of both components can be united for high performance PEGs. ZnO/P(VDF-HFP) nanocomposites were designed with fillers distribution controlled via different processing, and the relationship between the filler orientation and the crystallization behaviors, dielectric and electromechanical conversion performances with respect to filler content were studied. The microcapacitor model and percolation theory were employed to understand the dielectric anisotropy in oriented nanocomposites, and furthermore, finite element analyses were utilized to reveal the distribution of local electric field. Finally, a maximum output voltage 11.8 V has been achieved in oriented ZnO/P(VDF-HFP) film, which is 2.3 times and 7.9 times the value of random nanocomposites (5.1 V) and pure P(VDF-HFP) film (1.5 V), respectively. With the piezoelectric responses obtained from piezoelectric force microscopy, significant enhancement in electromechanical conversion performance has been thoroughly discussed. The results thus demonstrate a promising strategy towards high-performance flexible piezoelectric generator.

Improving Dielectric Properties in Novel P(VDF-HFP)/V2AlC MAX/Montmorillonite Composite Films via Interfacial Electric-Leakage Depressing Strategy

Dielectric constants of polymer/conductor composites are often high, owing to strong interface interaction in those composites. They can be used for dielectric energy storage, but they usually have high dielectric loss and conductivity. In order to reduce the dielectric loss and conductivity in poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP))/V2AlC MAX composites, in this study, we explored the novel P(VDF-HFP)/V2AlC MAX/montmorillonite (MMT) ternary composites. Compared with binary composites, the ternary composites showed the mildly reduced dielectric constant, significantly decreased dielectric loss and conductivity. Using highly-conductive V2AlC MAX filler aimed at taking advantage of the polymer/MAX interface polarization to increase the dielectric response of composites. Employing well-insulating MMT filler aimed at reducing the interface electric leakage conduction. At 1 kHz, the outstanding ternary composite with 2 wt% MMT and 20 wt% MAX could exhibit a high dielectric constant of ca. 27 and low dielectric loss of ca. 0.21. This work might offer a new research idea for the construction of high-performance composite dielectric films containing modern MAX ceramic fillers.

Sandwich-structured Co3[Co(CN)6]2/P(VDF-HFP) piezoelectric composites with superior electromechanical activity

The development of piezoelectric polymers with superior electromechanical performance is a demand in the areas of flexible sensors, actuators and tissue engineering, among others. In this work, we reported a novel sandwich-structured piezoelectric composites comprising of poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] and Prussian blue analogs Co3[Co(CN)6]2 with excellent electromechanical activities. The large specific surface area, unique three-dimensional porous nanostructure and redox behavior of Co3[Co(CN)6]2 appeared to significantly promote the interfacial coupling effect within P(VDF-HFP), resulting in enhanced electromechanical response. Moreover, the sandwich structure topological design would enlarge the interfacial coupling effect, strengthen the breakdown strength and consequently raise the electromechanical performance. For instance, a maximum piezoelectric coefficient d33 of ~ 41 pC/N can be achieved in the sandwiched composites at a loading of 0.8 wt%, which is 1.78 times that of pure P(VDF-HFP). Furthermore, the sandwiched composites possess superior electromechanical coupling factor k33 up to 0.215, while that of pure P(VDF-HFP) is only 0.134.

Study of electrical and electrochemical properties of P(VdF-HFP)-MMT based nanocomposite gel polymer electrolytes for application in energy storage devices

The present study reports synthesis and analysis of different characteristics of montmorillonite (MMT) clay loaded nanocomposite gel polymer electrolytes (NCGPEs) based on poly (vinylidene fluoride hexafluoropropylene) [(P(VdF-HFP)] as host matrix and LiPF6 as salt. AC impedance analysis shows that the ionic conductivity of NCGPEs increases first with the increase of clay content and attains a maximum value of 9 X10-3 Scm−1 at 5 wt% of clay content, and then it decreases. TEM result shows a clear intercalation of polymer into the galleries of MMT clay. The variation of pore size in NCGPEs upon addition of MMT has been studied by SEM. XRD patterns show that MMT clay reduce the crystallinity of NCGPEs. The interaction among the various components of NCGPEs and its effect on ionic conductivity has been studied by FTIR. The interfacial and electrochemical stabilities are also found to be enhanced upon the addition of clay in P(VdF-HFP) matrix.

Three-dimensional structured asymmetric electrolytes for high interface stability and fast Li-ion transport in solid-state Li-metal batteries

Replacing flammable liquid electrolytes with solid polymer electrolytes is a promising route to improve safety of lithium (Li)-metal batteries. However, developing a suitable high-performance electrolyte with both high ionic conductivity and interface stability against electrodes remains as a challenge. Herein, we design a poly(propylene carbonate) (PPC)/poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)]–based asymmetric solid electrolyte with a 3D blow-spun Li7La3Zr2O12 (LLZO) framework. The controllable degradation of PPC facilitates the wettability and stability between the electrolyte and Li metal. The P(VDF-HFP) with good electrochemical stability is used to match with cathode. With the support of the 3D LLZO Li-ion conductor, the electrolyte displays high ionic conductivity (4.9 × 10−4 S cm−1 at room temperature). The Li||Li symmetric cells assembled with this electrolyte show a long cycling life of more than 2700 h at 100 μA cm−2. The electrolyte also delivers an excellent cycling performance in solid-state LiFePO4||Li batteries (300 cycles with a capacity retention of 91.3%).

Electron-Beam Irradiation for Boosting Storage Energy Density of Tuned Poly(vinylidene fluoride-hexafluoropropylene)/Graphene Nanoplatelet Polymer Composites

In current, the energy storage materials based on electrets and ferroelectric polymers are urgently demanded for electric power supply and renewable energy applications. The high energy storage density can be enhanced by conducting or inorganic fillers to ferroelectric polymer matrix. However, agglomeration, phase separation of fillers, interfacial phase regions and crystallinity of matrix remain the main factors for the improvement of energy storage density in those composites. Poly(vinylidene fluoride-hexafluoropropylene) was modified with graphene nanoplatelets for enhanced the dielectric properties and energy storage density, which combines the irradiated by electron beam. Tuning effect of the crystalline regions and polar phases with graphene nanoplatelets and electron irradiation on its surface, structure, electrical and energy storage properties were observed. The film homogeneity was increased by reducing the pores, along with the improvement of surface roughness and hydrophobicity, which related with the dielectric properties and energy storage density. The β-phase fraction and crystallinity improvement significantly affect electrical properties by improving polarization and dielectric constant. As a core, electron beam dramatically reduce the crystals size by two times. Hence, energy storage density of composites was enhanced, while energy loss was reduced under operating conditions. Results on the improvement of energy efficiency were from 68.11 to 74.66% for neat poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)), much higher than previously reported of 58%, and doubled for P(VDF-HFP)/GNPs composites which will be discussed and evaluated for the practical energy storage materials.

Influence of nano SrTiO3 and ultrasonic irradiation on the properties of polymer blend electrolytes

ABSTRACT Lithium (Li+) ion conducting nanocomposite polymer blend electrolytes (NCPBEs) based on poly(ethylene oxide) (PEO), poly(vinylidene fluoride hexafluoropropylene) (P(VdF-HFP)) as polymer hosts, lithium perchlorate (LiClO4) as an electrolyte and strontium titanate (SrTiO3) as a nanofiller have been prepared by both the conventional stirring and ultrasonic irradiation methods. Complex formation and hence the structural changes of the prepared samples have been confirmed by X-ray diffraction analysis. Conductivity studies have been carried out by means of AC impedance spectroscopy. In order to highlight the role of ultrasonic irradiation, conductivity values have been compared with the values obtained through conventional mechanical stirring method. It has been found that the system with 15 minutes of ultrasonic irradiation resulted in better homogenous dispersion of SrTiO3 in PEO/P(VDF-HFP)/LiClO4 matrix. Maximum ionic conductivity of 2.519 × 10−4 Scm−1 has been obtained for 6 wt% of SrTiO3 system which is a magnitude higher than the ionic conductivity value, 2.031 × 10−5 Scm−1 obtained for the original NCPBE prepared using conventional mechanical stirring at room temperature. Further, ionic conductivity value increases with the increase of temperature and it exhibit the Arrhenius relation. Higher degree of free ionic motion in the samples has been proven by the increase in intensity of photoluminescence spectra peaks. The dielectric properties of the prepared samples have also been studied using the complex dielectric permittivity spectra and complex electric modulus spectra. The morphology and hence the surface roughness of the samples have been depicted through AFM study.

Preparation and Storage Energy Density Base on Dielectric Properties of P(VDF-HFP)/PU/BNKT Thin Films

Novel electrical devices based on energy storage capacitor and energy conversion, have developed to advanced dielectric properties including electrical performance.In this work, three phases composite of poly(vinylidene fluoride hexafluoropropylene) (P(VDF-HFP)) blended with polyurethane (PU) and filled with Bi0.5(Na0.8 -K0.2)0.5TiO3 (BNKT) ceramic was studied on the on the dielectric, electrical properties and a storage energy density. All composite thin films are fabricated by the tape casting method in solution. Polarization-Electrical (P-E) loop of all composite thin films were also investigated relaxor-ferroelectric characteristic with the various electric fields. The recoverable energy density and energy efficiency from the loop were then analysed. As a result, the three phases composite of P(VDF-HFP)/PU/BNKT composites produce the highest dielectric constant as well as conductivity; however, they produce the lowest energy efficiency in this work. It seems that the interfacial polarization is easy switchable dipole moment in three phases more than one phase, resulting in high dielectric constant as well as conductivity. However, the larger conductivity seemly generates larger dielectric loss, resulting in lower energy efficiency. Therefore, the comparison based on three and two phases can be used to predict in capability of electric capacitor devices in the future.

High-performance gel polymer electrolytes using P(VDF-HFP) doped with appropriate porous carbon powders as the matrix for lithium-ion batteries

Porous carbon powders are prepared from raw material camellia oleifera shells by ball milling and pyrolysis processes. Poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)-based gel polymer electrolytes (GPEs) doped with different proportions of porous carbon powders are successfully fabricated using a classical inverse phase method, which is confirmed by X-ray diffraction, thermo-gravimetric analysis, and field emission scanning electron microscope. The results show that the porous GPE-3 membrane has a high liquid uptake ratio of about 104.3%, a high decomposition temperature of 435 °C, a rapidly stabilized interface impedance to 517.6 Ω after 5 days storage time, and a high ionic conductivity of 3.921 mS cm−1 at room temperature when the doping amount of porous carbon powders is 3.0 wt%. Furthermore, the assembled LiCoO2/GPE-3/Li coin cells can deliver a high initial discharge specific capacity of 152.7 mAh g−1 and an excellent initial coulombic efficiency of 97.27% at 0.1 C. These good properties indicate that the as-prepared GPE-3 can be used as a potential polymer electrolyte for lithium-ion batteries.

Effect of solvent on the energy storage property of poly(vinylidene fluoride-hexafluoropropylene)

The application prospects of dielectric materials such as poly(vinylidene fluoride) (PVDF) based polymers in the field of energy storage have stimulated extensive research. In this study, the energy storage characteristics of poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) films crystallized from several solvents with different vapor pressure were investigated. The charge-discharge efficiency of the P (VDF-HFP) film crystallized from N, N-dimethylformamide (DMF) demonstrates an efficiency of 85% under an electric field of 1000 kV cm−1, which is 1.42 times of the film crystallized from dimethyl sulfoxide (DMSO). Meanwhile, the insulation resistivity of the film crystallized from DMF is also higher than other films, and the energy storage characteristics are optimal in this study. This work provides guidance for the preparation of PVDF-based polymer films using the solution method.

High Electromechanical Deformation Based on Structural Beta-Phase Content and Electrostrictive Properties of Electrospun Poly(vinylidene fluoride- hexafluoropropylene) Nanofibers.

The poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) polymer based on electrostrictive polymers is essential in smart materials applications such as actuators, transducers, microelectromechanical systems, storage memory devices, energy harvesting, and biomedical sensors. The key factors for increasing the capability of electrostrictive materials are stronger dielectric properties and an increased electroactive β-phase and crystallinity of the material. In this work, the dielectric properties and microstructural β-phase in the P(VDF-HFP) polymer were improved by electrospinning conditions and thermal compression. The P(VDF-HFP) fibers from the single-step electrospinning process had a self-induced orientation and electrical poling which increased both the electroactive β-crystal phase and the spontaneous dipolar orientation simultaneously. Moreover, the P(VDF-HFP) fibers from the combined electrospinning and thermal compression achieved significantly enhanced dielectric properties and microstructural β-phase. Thermal compression clearly induced interfacial polarization by the accumulation of interfacial surface charges among two β-phase regions in the P(VDF-HFP) fibers. The grain boundaries of nanofibers frequently have high interfacial polarization, as they can trap charges migrating in an applied field. This work showed that the combination of electrospinning and thermal compression for electrostrictive P(VDF-HFP) polymers can potentially offer improved electrostriction behavior based on the dielectric permittivity and interfacial surface charge distributions for application in actuator devices, textile sensors, and nanogenerators.