Vinylidene Fluoride-hexafluoropropylene) [P Research Articles

Highly conductive and nonflammable boron-based gel type single ion conducting electrolyte membranes toward high-safety and dendrite-free lithium metal batteries

Single-ion conducting polymer electrolytes (SIPEs), having a high Li-ion transference number (tLi+) close to unity, hold great promise for circumventing the lithium dendrite growth of lithium metal batteries (LMBs). However, SIPEs synthesized by a simple method that also simultaneously fulfill the requirements of high ionic conductivity, good thermal stability, and remarkable fire resistance are still quite rare. Herein, a novel single-ion conducting fibrous membrane (es-DDBSB-Li) based on borate anions of single-ion conductors (denoted as DDBSB-Li) and poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) as a binder was prepared via facile electrospinning technology. The introduction of borate anions promotes the homogeneous distribution of highly concentrated Li-ions and accelerates the ionic migration, leading to an enhanced ionic conductivity of 3.75 × 10−4 S cm−1 at 25 °C for DDBSB-Li saturated with organic solvents. Additionally, the thermally stable and nonflammable DDBSB-Li endows the resultant fibrous membranes to possess good high-temperature stability and fire-resistance properties. The Li||Li cell using this electrolyte displays a high tLi+ of 0.91 and effectively mitigates concentration polarization, thereby enabling a remarkably stable cyclic performance over 2000 h at 2.5 mA cm−2 at 25 °C. Also, this gel SIPE-based Li||LiFePO4 battery demonstrates superior rate performances up to 3C and delivers long-term cycling durability over 600 cycles under 1C at 25 °C. We believe this novel gel SIPE-based fibrous membrane has great potential for practical application in high-safety and dendrite-proof LMBs.

Excellent energy storage and discharge performances realized in polymer nanocomposites by introducing core-shell antiferroelectric fillers and constructing bilayer interfaces

Polymer composites filled with one or two-dimensional ferroelectrics possess large discharged energy density (Ue), but deliver low efficiency (η) by reason of their high remnant electric displacement (Dr), and require demanding process conditions. To solve these issues, we have proposed Pb,La(Zr,Sn,Ti)O3 (PLZST)@Al2O3 nanoparticles (NPs)/polyimide (PI)-PLZST@Al2O3 NPs/poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) bilayer nanocomposites. PLZST antiferroelectrics exhibit small Dr and high maximum electric displacement (Dmax), and the Al2O3 shell possesses near dielectric constant with P(VDF-HFP) and PI, which can improve the Dmax, increase the breakdown strength (Eb), and refine D-E loops, and simple preparation method of the NPs is beneficial for the industrial production. The bilayer structure combines advantages of PLZST@Al2O3 NPs/PI with slim D-E loops and small Dr, and PLZST@Al2O3/P(VDF-HFP) possessing high Dmax. Besides, large dielectric differences between adjacent layers inhibit electrical tree growth, thus further causing improved Eb, which is confirmed by electrical tree evolving simulations. Consequently, the bilayer nanocomposites display an ultrahigh Ue of 21.89 J/cm3, which surpasses those of currently reported polymer nanocomposites filled with NPs, and large η of 78.2%. More encouragingly, it manifests ultrafast discharge time of 18.8 ns and ultrahigh power density of 28.3 MW/cm3, meaning its great application prospect in pulse power systems.

Highly conductive and mechanically robust single-ion conducting polymer electrolyte membranes with a high concentration of charge carriers for dendrite-proof lithium metal batteries

Single-ion polymer electrolytes (SIPEs) with high Li-ion transference number (tLi+≈1) are promising candidates for inhibiting the growth of lithium dendrites in lithium metal batteries (LMBs). However, it remains challenging to develop SIPEs applicable to high-performance LMBs due to their relatively low ionic conductivity and poor mechanical strength. Herein, an aromatic single-ion conductor (LiPSBI) with high Li-ion concentration is elaborately designed, yielding porous and mechanically robust SIPE membranes (NSIPM) when mixed with aliphatic poly (vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) binder via “structural self-assembly” method. As expected, the as-prepared NSIPM porous membranes can simultaneously exhibit a high porosity of 41.4%, a considerable organic solvent uptake of 181.0%, and excellent mechanical strength of 20.5 MPa. Notably, the LiPSBI-based gel NSIPM demonstrates an ionic conductivity of 8.15 × 10−5 S cm−1 at 25 °C, which is almost twice that of the single-ion electrolyte with low Li-ion concentration (4.74 × 10−5 S cm−1). Consequently, the Li||LiFePO4 cells using the gel NSIPM display remarkable cycling durability for several hundred cycles while delivering high discharge specific capacities of 148.4 mA h g−1 and 122.9 mA h g−1 at 0.2C and 1 C, respectively. In addition, the Li/Li symmetric cells assembling the gel NSIPM can effectively alleviate concentration polarization and inhibit the lithium dendrites growth, which is responsible for an exceptionally steady striping/plating process with a low overpotential over 1300 h at 2.5 mA cm−1 at 25 °C. This work provides a new strategy to prepare high-performance SIPEs by increasing the concentration of charge carriers.

In Situ Construction Channels of Lithium-Ion Fast Transport and Uniform Deposition to Ensure Safe High-Performance Solid Batteries.

Solid-state lithium-ion batteries (SLIBs) are the promising development direction for future power sources because of their high energy density and reliable safety. To optimize the ionic conductivity at room temperature (RT) and charge/discharge performance to obtain reusable polymer electrolytes (PEs), polyvinylidene fluoride (PVDF), and poly(vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) copolymer combined with polymerized methylmethacrylate (MMA) monomers are used as substrates to prepare PE (LiTFSI/OMMT/PVDF/P(VDF-HFP)/PMMA [LOPPM]). LOPPM has interconnected lithium-ion 3D network channels. The organic-modified montmorillonite (OMMT) is rich in the Lewis acid centers, which promoted lithium salt dissociation. LOPPM PE possessed high ionic conductivity of 1.1 × 10-3 S cm-1 and a lithium-ion transference number of 0.54. The capacity retention of the battery remained 100% after 100 cycles at RT and 0.5 C. The initial capacity of one with the second-recycled LOPPM PE is 123.9 mAh g-1 . This work offered a feasible pathway for developing high-performance and reusable LIBs.

The simple synthesis of all‐organic polymer bilayer films: Achieving simultaneous enhancements in energy storage density and efficiency

AbstractAll‐organic dielectric polymers with excellent capacitive energy storage capabilities have great potential applications in the fields of modern electronics and power systems. However, it is still challenging to achieve simultaneous improvements in both energy density and efficiency in these all‐organic dielectric polymers. This work proposes the all‐organic bilayer composite films with ferroelectric polymer poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF‐HFP)) and linear polymer fluorene polyester (FPE) as the energy storage dielectrics for film capacitors. Compared with pure FPE films, the bilayer composite films exhibit improved dielectric constant. What is more outstanding is that the bilayer composite films has higher energy storage density and energy storage efficiency under the same electric field compared with the pure P(VDF‐HFP) film. Particularly, an outstanding Ud of 7.00 J/cm3 accompanied with great η of 95.9% has been delivered in the resulting bilayer composite films via optimizing the P(VDF‐HFP) content (22.2 vol%) at 520 kV/mm. The compatibility of the two polymers was discussed by simulating the potential distribution of the two polymer molecular chains. This work opens up a new way to prepare compatible polymer flexible capacitor films on a large scale.

Low‐fuel‐permeation thermoplastic vulcanizates prepared from mutually miscible fluoroelastomer and poly(vinylidene fluoride–hexafluoropropylene)

AbstractAn oleophobic barrier material is imperative for automotive fuel hose applications to reduce permeation of air‐polluting hydrocarbons. With the increasingly strict exhaust emission regulations, the development of new fluoroelastomer (FKM) materials with enhanced fuel permeation resistance is highly desirable. Herein, we successfully developed a class of all‐fluorinated thermoplastic vulcanizates (TPVs) by dynamic vulcanization from FKM and poly(vinylidene fluoride–hexafluoropropylene) (P(VDF‐HFP)). The mechanical properties, recyclability and fuel resistance of the FKM/P(VDF‐HFP) TPVs were examined. The results show that the FKM/P(VDF‐HFP) blends present high mechanical performance with tensile strength up to 26.3 MPa and strain at break of more than 600% at a high rubber/plastic ratio of 7:3 by weight. Moreover, our FKM/P(VDF‐HFP) TPVs show excellent fuel resistance and recyclability. Such high mechanical properties, recyclability and fuel resistance are correlated with the good miscibility between FKM and P(VDF‐HFP), the strong FKM rubber network and the fine phase morphology of TPVs. This work provides a guidance for the preparation of new TPVs through selecting mutually miscible polymers without any compatibilizer, and demonstrates that these new TPVs can be a good alternative option to replace the traditional thermosetting fluororubbers in the automotive industry as barrier layers for fuel hoses. © 2023 Society of Industrial Chemistry.

The interface effects on the breakdown strength of multilayer PVDF-based capacitors

Exploring polymer-based films with high energy density and low cost is important, because they have potential applications in flexible electronic equipment. In this paper, we investigated the evidence of structure changes in multilayer films and elaborated on the part of interface effects on dielectric properties. Polyvinylidene fluoride (PVDF) and poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) were spun-coated to form multilayer polymer films. The PVDF/P(VDF-HFP)/PVDF multilayer film has an improved breakdown strength of 4492 kV cm−1 and a discharged energy density of 6.24 J cm−3. According to experimental results, an increase in breakdown strength is caused by an improvement in leakage current and a reduction in ferroelectric β-phase. The high breakdown strength of multilayer films contributes to the improvement of energy storage density. This work will provide a process method for creating low cost, defect-free, high energy density polymer capacitors.

A P(VDF-HFP) and nonwoven-fabric based composite as high-performance gel polymer electrolyte for fast-charging sodium metal batteries

Although sodium metal batteries (SMBs) have drawn numerous attentions as the promising candidate for the next-generation rechargeable batteries, various issues hinder their practical applications, e.g., the growth of dendrites and large volume change of Na metal during cycling, etc.. The adoption of gel polymer electrolyte (GPE) is an effective solution to address the safety issues and increase the lifetime of SMBs. In this study, a novel composite membrane consisting of nonwoven fabric as the supporting matrix and poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) as the Na+ transmission medium is easily fabricated via non-solvent induced phase inversion method. After plasticized by NaClO4-based liquid electrolyte, the obtained composite membrane exhibits an enhanced mechanical strength, high uptake to organic liquid electrolyte (115%), high thermal and electrochemical stability, superior ionic conductivity (1.38 mS cm−1) and remarkable Na ion transference number (0.47), which has been demonstrated to effectively suppress the growth of sodium dendrite, improve the fast-charging performance and cycling stability of the corresponding SMBs. This work paves a way for the commercialization of GPE in the fast-charging SMBs.

Dielectric loss reduction and validation of P(VDF-HFP) films via sandwiching film fabrication for capacitive energy storage

Poly(vinylidene fluoride) (PVDF) series polymers have a high dielectric constant (k) among polymer families but a high intrinsic loss tangent disqualifying their capacitor application. In this work, Poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer as the high-k dielectric layer is sandwiched between two low-k polyetherimide (PEI and PEI/BaTiO3) layers to construct the composite films with tunable dielectric responses. By changing the low-k layer thickness in the PEI/P(VDF-HFP)/PEI tri-layer structure, its characteristic of capacitors in series results in the moderate dielectric constant and dramatic reduction of loss tangent to a meaningful level for capacitor design. The loss tangent can be dramatically reduced to below 0.005 at 1 kHz using the thickness ratio of 1:1:1 from about 0.03 for P(VDF-HFP) film alone. The extraordinary dielectric response of the tri-layer structure is also accompanied by more than 2 times the higher energy density than that of the PEI film under the same electric field. The ingenious design of the low-k/high-k/low-k sandwiched polymers synergizes the high-k advantage of P(VDF-HFP) and low tangent loss of the low-k layer as well as their high dielectric strength. This work provides a meaningful and effective method for realizing PVDF-based polymers with reduced loss tangent for actual capacitor application.

Enhancement of electrical and electrochemical properties of sodium bromide incorporated with poly (ethylene oxide)/poly (vinylidene fluoride-hexafluoropropylene) solid blend polymer electrolytes for electrochemical double layer capacitors

Sodium-ion conducting solid blend polymer electrolytes are prepared with Poly (ethylene oxide) (PEO)/Poly (vinylidene fluoride-hexafluoropropylene) P(VdF-HFP)/Sodium Bromide (NaBr) by solution casting technique. Different analysis such as structural, vibrational, electrical and electrochemical studies reveal promising properties of the prepared solid polymer electrolytes (SPE). The XRD analysis illustrates the increase in amorphous nature of the sample up to 8 wt% NaBr salt concentration. The complexation between polymers and salt has been examined by FTIR analysis. To examine the electrical conductivity, AC impedance analysis was performed in the temperature range of 303–373 K. The higher ionic conductivity (σ) of 1.10 × 10−3 S cm−1 was found for the solid polymer electrolyte (SPE) containing 8 wt% NaBr at room temperature. The temperature dependence of ionic conductivity resembles Arrhenius behavior. The dielectric behavior has been analyzed using dielectric permittivity (ε*) and the relaxation frequency (τ) has been calculated from the loss tangent spectra (tan δ). The modulus spectra indicate the non-Debye nature of the material. Wagner's DC polarization technique was used to compute the transference number. According to the LSV analysis, the solid blend polymer electrolytes have the suitable electrochemical potential window to be used in electrochemical devices. The cyclic voltammetry (CV) and charge-discharge studies (GCD) of the assembled electrochemical double-layer capacitor (EDLC) show specific capacitance (Csp) values of 12.9 F/g and 10.4 F/g respectively. Further the better performance of EDLC is confirmed with its energy density (3.25 to 2.12 Wh/kg), power density (750 to 2623 W/kg) as well as coulombic efficiency (98.2 %) after 1500 cycles.

Magnetoelectric behavior and magnetic field-tuned energy storage capacity of SrFe12O19 nanofiber reinforced P(VDF-HFP) composite films

• Fabrication of flexible magnetoelectric (ME) P(VDF-HFP)/SrFe 12 O 19 composite films. • Inclusion of SrFe 12 O 19 nanofiber enhances the polar β-phase in P(VDF-HFP) matrix. • P(VDF-HFP)/SrFe 12 O 19 films exhibit enhanced dielectric and ferroelectric properties . • A strong strain mediated ME coupling exists in the P(VDF-HFP)/SrFe 12 O 19 films. • P(VDF-HFP)/SrFe 12 O 19 films' energy storage capacity is tuned by magnetic fields. Flexible, self-standing magnetoelectric (ME) polymer composite films were prepared using the solution casting method by reinforcing one-dimensional ferromagnetic strontium ferrite (SrFe 12 O 19 ) nanofibers, synthesized using the electrospinning method, into poly(vinylidene fluoride–hexafluoropropylene) (P(VDF-HFP)) matrix. The effects of loading of SrFe 12 O 19 nanofibers on the functional, structural, magnetic, dielectric, and ferroelectric properties of P(VDF-HFP) were investigated. The loading enhanced the electroactive β-phase of the films, as confirmed by XRD and FTIR analyses. The ME coupling that existed in the composite films was confirmed by the changes in ferroelectric parameters under various magnetic fields. The energy storage capacity and dielectric constant of the composite films were enhanced with the addition of SrFe 12 O 19 nanofibers, with the maximum values of 56 at 100 Hz and 1678 mJ/cm 3 at 444 kV/cm, respectively, in the composite film with 20 wt% SrFe 12 O 19 nanofibers. The energy storage capacity was further enhanced and tuned by applying an external magnetic field. Thus, this work reports an innovative approach to tuning the energy storage capacity of ME polymer composite films through a magnetic field and also describes use of these films for a wide range of applications, such as energy storage and memory devices and magnetic sensors.

Enhanced energy storage density in poly(vinylidene fluoride-hexafluoropropylene) nanocomposites by filling with core-shell structured BaTiO3@MgO nanoparticals

Filling with high dielectric constant inorganic nanoparticles is an effective approach to enhance the energy storage performance of an organic dielectric. However, the dielectric mismatch between ceramic and polymer causes early breakdown, which limits the storage density of ceramic/polymer nanocomposites in the application of dielectric capacitors. Herein, we employed MgO as a buffer barrier to mitigate the mismatched dielectric characteristics among BaTiO3 (BT) nanoparticles and poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) substrate considering its high insulation and medium dielectric constant. The alien oxide was coated on the spherical BT by a simple chemical precipitation process, forming a BaTiO3@MgO (BT@MgO) core-shell nanostructure, which has been carefully examined by TEM and EDS. The BT-MgO heterogeneous interfacial region provides channels for carriers and promotes charge movement, and therefore the dielectric constant and potential shift have been significantly enhanced. The BT@MgO/P(VDF-HFP) nanocomposite with 1 vol% filling ratio delivered a maximum energy density Ud, and the value reaches up to 5.6 J/cm3 that is 40.0 % and 55.6 % greater than that of the host matrix and BT-filled counterpart with the same filler amount. The BT@MgO core-shell nanostructure demonstrates an alternative way to effectively heighten the energy storage performance of ceramic/polymer composite dielectrics.

Improved Electroactive β Phase Nucleation and Dielectric Properties of P(VDF-HFP) Composite with Al(NO3)3·9H2O Fillers

In this study, the poly (vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) film is facilely prepared by the solution casting technique. The effect of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) on the crystalline phase and dielectric behavior of P(VDF-HFP) composite films is systematically investigated. Experimental results founded that the P(VDF-HFP) composite films exhibit the micro-pores structure on the top surface. Addition of the Al(NO3)3·9H2O filler is found to enhance the electroactive β phase by about 20%. Furthermore, the dielectric constants of pure P(VDF-HFP) and P(VDF-HFP)/1.5 wt.% Al(NO3)3·9H2O films are derived as 8 and 28, respectively. These results indicate that the Al(NO3)3·9H2O hydrated salt acts as the nucleation agent to produce the crystallization of the β phase resulted in improved dielectric constant in P(VDF-HFP) composite films.

Three-dimensional polypyrrole induced high-performance flexible piezoelectric nanogenerators for mechanical energy harvesting

Flexible piezoelectric nanogenerators (FPNGs) have received tremendous attention in terms of harvesting mechanical energy and driving portable devices. However, the weak interactions and interfacial defects between the fillers and matrix hinder from improving the flexibility and electromechanical properties of the composites, which limits the practical applications of nanogenerators. In this work, high-performance FPNGs based on all-organic composite thin films comprising of three-dimensional polypyrrole (3D PPy) and poly(vinylidene fluoride -hexafluoropropylene) [P(VDF-HFP)] are fabricated for the first time. The composite films exhibit excellent ferroelectric and piezoelectric properties, mainly resulting from the strong interfacial bonding between 3D PPy and the P(VDF-HFP) matrix. As a result, the FPNG prepared from the composites loaded with 5 wt% 3D PPy achieve considerable piezoelectric outputs (average power density of 5.52 μW/cm2 and peak power density of 10.84 μW/cm2). Meanwhile, the FPNGs can effectively obtain mechanical energy from human activities and still show a stable output after continuous operation over 3000 cycles. This work provides a novel idea to design and fabricate high-performance FPNGs through introducing conductive polymers into the matrix.

Preparation and characterization of hydrophobic P(VDF-HFP) flat sheet membranes using Tamisolve® NxG solvent for the treatment of saline water by direct contact membrane distillation and membrane crystallization

• Tamisolve® was used as a non-toxic solvent for P(VDF-HFP) membranes preparation. • The prepared porous P(VDF-HFP) membranes were fully characterized. • The membranes were tested in membrane distillation and membrane crystallization. • Membrane crystallization allowed achieving crystals with rejection greater than 99%. The replacement of the toxic solvents with non-toxic equivalents attracts a great attention in membrane preparation and application processes. The purpose of this work is to study the preparation of poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) flat sheet membranes by non-solvent induced phase separation (NIPS) using Tamisolve® as a non-toxic solvent, for membrane distillation (MD) and membrane crystallization (MCr) applications. The prepared porous P(VDF-HFP) membranes were fully characterized in terms of morphology, porosity, thickness, pore-size, contact angle and pure water permeability (PWP). The effect of additive(s) and polymer content were investigated. Moreover, preliminary DCMD and MCr tests were carried out and the achieved results indicate the good performance of the prepared flat sheet membranes in terms of permeate flux and salt rejection in comparison to a commercial PVDF membrane. The obtained results confirmed the ability of the eco-friendly Tamisolve® NxG to compete with the highly toxic diluents usually used in membrane fabrication by phase inversion method.

Electrostrictive and Structural Properties of Poly(Vinylidene Fluoride-Hexafluoropropylene) Composite Nanofibers Filled with Polyaniline (Emeraldine Base).

Previous studies have reported that poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymers can exhibit large electrostrictive strains depending on the filler. This work examines the electrostrictive and structural properties of P(VDF-HFP) nanofibers modified with conductive polymer polyaniline (PANI). The P(VDF-HFP)/PANI composite nanofibers were prepared by an electrospinning method with different PANI concentrations (0, 0.5, 1, 1.5, 3 and 5 wt.%). The average diameter, water contact angle and element were analyzed by SEM, WCA and EDX, respectively. The crystalline, phase structure and mechanical properties were investigated by XRD, FTIR and DMA, respectively. The dielectric properties and electrostrictive behavior were also studied. The results demonstrated that the composite nanofibers exhibited uniform fibers without any bead formation, and the WCA decreased with increasing amount of PANI. However, a high dielectric constant and electromechanical response were obtained. The electrostrictive coefficient, crystalline, phase structure, dielectric properties and interfacial charge distributions increased in relation to the PANI content. Moreover, this study indicates that P(VDF-HFP)/PANI composite nanofibers may represent a promising route for obtaining electrostrictive composite nanofibers for actuation applications, microelectromechanical systems and sensors based on electrostrictive phenomena.

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.