Vinylidene Fluoride-hexafluoropropylene) [P Research Articles

A High‐Performance Graphene Oxide‐Doped Ion Gel as Gel Polymer Electrolyte for All‐Solid‐State Supercapacitor Applications

AbstractA high‐performance graphene oxide (GO)‐doped ion gel (P(VDF‐HFP)‐EMIMBF4‐GO gel) is prepared by exploiting copolymer (poly(vinylidene fluoride‐hexafluoro propylene), P(VDF‐HFP)) as the polymer matrix, ionic liquid (1‐ethyl‐3‐methylimidazolium tetrafluoroborate, EMIMBF4) as the supporting electrolyte, and GO as the ionic conducting promoter. This GO‐doped ion gel demonstrates significantly improved ionic conductivity compared with that of pure ion gel without the addition of GO, due to the homogeneously distributed GO as a 3D network throughout the GO‐doped ion gel by acting like a ion “highway” to facilitate the ion transport. With the incorporation of only a small amount of GO (1 wt%) in ion gel, there has been a dramatic improvement in ionic conductivity of about 260% compared with that of pure ion gel. In addition, the all‐solid‐state supercapacitor is fabricated and measured at room temperature using the GO‐doped ion gel as gel polymer electrolyte, which demonstrates more superior electrochemical performance than the all‐solid‐state supercapacitor with pure ion gel and the conventional supercapacitor with neat EMIMBF4, in the aspect of smaller internal resistance, higher capacitance performance, and better cycle stability. These excellent performances are due to the high ionic conductivity, excellent compatibility with carbon electrodes, and long‐term stability of the GO‐doped ion gel.

Electrochemical performance of lithium/sulfur batteries using perfluorinated ionomer electrolyte with lithium sulfonyl dicyanomethide functional groups as functional separator

Lithium/sulfur (Li/S) batteries using the novel perfluorinated ionomer electrolyte with lithium sulfonyl dicyanomethide functional groups as both separator and electrolyte are demonstrated. Comparison was made with the Li/S batteries with the conventional liquid electrolyte, poly(vinylidenefluoride-hexafluoropropylene) [P(VDF-HFP)] gel polymer electrolyte, the lithiated Nafion ionomer electrolyte, and the novel perfluorinated ionomer electrolyte. The battery with novel perfluorinated ionomer electrolyte shows stable capacity retention compared with the batteries with the conventional liquid electrolyte and the gel electrolyte, and good rate performance compared with the battery with the lithiated Nafion ionomer electrolyte.

Towards magnesium ion conducting poly(vinylidenefluoride-hexafluoropropylene)-based solid polymer electrolytes with great prospects: Ionic conductivity and dielectric behaviours

A simple solid polymer electrolyte (SPE) system based purely on poly(vinylidenefluoride-hexafluoropropylene) [P(VdF-HFP)] and magnesium trifluoromethanesulfonate (MgTf) is synthesised via solution casting technique with acetone as solvent. The SPEs produced exhibit high ionic conductivity of ∼10−3S/cm at ambient temperature when 40wt.% of MgTf is incorporated. The major focus of this work is on ionic conductivity and dielectric behaviours. Three dissimilar types of impedance spectra have been identified and differentiated by magnitude of ionic conductivity. The trend of ionic conductivity increases almost proportionally to the content of magnesium salt and can be related to an increase of amorphous phase at high level of dopant salt. This SPE system has also been found to possess Arrhenius temperature dependence. This study discusses three samples with 10, 25 and 40wt.% of magnesium salt, representing low, intermediate and high concentrations of magnesium salt which are examined in frequency-dependence conductivity, dielectric permittivity and dielectric modulus studies.

Gel polymer electrolyte with ionic liquid for high performance lithium sulfur battery

Poly(vinylidenefluoride-hexafluoropropylene)[P(VDF-HFP)] membrane with porous structure was prepared by a simple phase separation process. The gel polymer electrolyte (GPE) prepared by combining the porous membrane with N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid shows good thermal stability, high anodic oxidation potential (>5.0V vs. Li/Li+) and good interfacial stability with lithium electrode. The lithium sulfur battery with the GPE delivers an initial discharge capacity 1217.7mAhg−1 and maintains a reversible capacity of 818mAhg−1 after 20cycles at a current density of 50mAg−1.

Concentration effect of BMIMTf on P(VdF-HFP)/MgTf-based solid polymer electrolyte system

Abstract

Relaxation processes and structural transitions in stretched films of polyvinylidene fluoride and its copolymer with hexafluoropropylene

Relaxation processes and structural transitions in nonstretched and uniaxially stretched films of poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) and its homopolymer polyvinylidene fluoride (PVDF) for comparison were investigated with the aim of understanding the electromechanical properties of this lower-modulus ferroelectric copolymer. The mechanical and the dielectric response at the glass transition (αa relaxation) exhibit similar temperature dependence of the relaxation time, whereas mechanical and dielectric processes above the glass transition are not related. They represent a continuous softening process within the amorphous phase and the dielectric αc relaxation, respectively. The latter is attributed to conformational changes of VDF segments in lamellae of spherulites constituting the nonpolar crystalline α phase. Furthermore, there is a contribution from melting of secondary crystallites formed in the amorphous phase during annealing or storage. Mechanically, this transition appears in nonstretched and stretched films as an accelerated decrease of the elastic modulus that terminates the rubber plateau. Dielectrically, this transition becomes visible as a frequency-independent loss peak only in stretched films, because stretching removes the αc relaxation, which superimposes the transition in nonstretched films. Melting of secondary crystallites is shown to appear in the homopolymer, too, though less pronounced because of more complete primary crystallisation.

Large magnetoelectric coupling coefficient in poly(vinylidene fluoride-hexafluoropropylene)/Metglas laminates

Poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] 90/10 wt% copolymers were fabricated by extrusion-blown and hot press-quench methods. The electric field induced phase transition was observed starting from 79 MV/m, and completing at 216 MV/m, in these copolymers. The transition was manifested by a change from a double hysteresis loop to a single hysteresis loop and supported by the x-ray diffraction measurement. Linear relationships between the magnetoelectric coupling coefficient and the in situ poling electric field, the remanent polarization and the field, were observed at electric fields less than 300 MV/m. A magnetoelectric coupling coefficient as large as 12 V/cm·Oe was obtained.

Atypical behaviors of BMIMTf ionic liquid present in ionic conductivity, SEM, and TG/DTG analyses of P(VdF-HFP)/LiTf-based solid polymer electrolyte system

Abstract

High field properties and energy storage in nanocomposite dielectrics of poly(vinylidene fluoride-hexafluoropropylene)

Poly(vinylidene fluoride) (PVDF) has generated interest for use in electrical energy storage, mostly due to its high dielectric constant compared to other polymers. There still exist challenges, such as its high energy losses, that have prevented large scale commercialization of PVDF-based capacitors, but progress is continuously being made. In this paper we explore a promising route to improve the energy storage performance of PVDF, through a synergy of HFP comonomers and of kaolinite clay nanofillers. This study shows that the addition of these high aspect ratio fillers to poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] copolymers does not increase the polar phase and, consequently, these composites exhibit markedly enhanced dielectric properties at high electric fields. Specifically, strained films of these composites exhibit reduced high field losses, markedly increased breakdown strength and, thus, large recoverable energy density values, in the range of 19 J/cm3.

A Theoretical and Experimental Study of the Mass Transport in Gel Electrolytes II. Experimental Characterization of LiPF6-EC-PC-P(VdF-HFP)

The mass transport in a gel consisting of LiPF6 dissolved in ethylene carbonate (EC), propylene carbonate (PC) and poly(vinylidenefluoride-hexafluoropropylene) (P(VdF-HFP)) was characterized at 25°C. Four diffusion coefficients, two transport numbers, one conductivity and two parameters describing the relationship between a concentration and a potential gradient were obtained in the characterization. The transport properties were obtained by optimizing a Maxwell-Stefan based transport model to data from four types of experiments. The transport model and the characterization method were analyzed in Part I. In order to give the results a comprehensible interpretation and to present a way of benchmarking electrolytes, we introduce the concept of a normalized potential gradient for gel electrolytes. The optimum composition range of the gel in terms of mass transport was found to lie between 5 and 7 wt % LiPF6 and as little polymer as possible without compromising the mechanical stability. It is suggested that measuring the normalized potential gradient can be used as a screening method when benchmarking electrolytes.

A Theoretical and Experimental Study of the Mass Transport in Gel Electrolytes I. Mathematical Analysis of Characterization Method

Mass transport of lithium ions is one of the major limitations to the performance of high-rate lithium-ion batteries. This paper presents an analysis of a mass transport characterization method for gel electrolytes. The method is based on a Maxwell–Stefan transport model, which takes into account the polymer as an active specie in the transport. Nine apparent transport properties aredefined from the model and their dependence on the Maxwell–Stefan diffusivities and the thermodynamic enhancement factors are presented. The characterization method is analyzed by finding analytical expressions that describe the characterization experiments. From the expressions it can be seen how the nine apparent transport properties influence the experimental response. The conclusions ofthe analysis will be used later in a characterization of the gel electrolyte: LiPF6 –ethylene carbonate (EC)–propylene carbonate (PC)–poly(vinylidenefluoride-hexafluoropropylene) P(VdF-HFP).

Polar-fluoropolymer Blends for High Energy Density Low Loss Capacitor Applications

ABSTRACTBesides energy density, the electric loss at high electric fields is another major concern for many capacitor applications. This paper presents recent works in developing high energy density low loss polymer capacitors. In order to reduce the dielectric loss while maintaining high energy density in poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) and P(VDF-CTFE) (CTFE: Chlorotrifluoroethylene) based polymers, a polymer blend approach was investigated. We show that by blending P(VDF-CTFE) with a proper low loss polymer such as poly(ethylene- chlorotrifluoroethylene) (ECTFE) can lead to marked improvement in the loss of dielectric films. In this study, P(VDF-CTFE) blends films with different wt% of ECTFE have been examined to find a balance between dielectric constant and the loss. In addition, crosslink in the blends has been employed to further improve the dielectric performance of the blends. The results indicate that these blends exhibit an excellent performance: relatively high dielectric constant (~ 6~7) and low loss (~ 0.01) at 1 kHz. For the crosslink blend films, the high field loss is reduced to below 5% with a discharged energy density 4.3 J/cm3 under a field of 300 MV/m.

PEO/P(VdF-HFP) blend based Li+ ion-conducting composite polymer electrolytes dispersed with dedoped (insulating) polyaniline nanofibers

Composite polymer electrolyte membranes composed of poly(ethylene oxide) (PEO), poly(vinylidene fluoride-hexafluoropropylene) {P(VdF-HFP)} blends, dedoped (insulating) polyaniline (PAni) nanofibers, and LiClO4 as salt have been synthesized with varying fraction of dedoped PAni nanofibers (from 2 to 10 wt.%). The ionic conductivity of PEO–P(VdF-HFP)–LiClO4 electrolyte system increases with increase in the fraction of dedoped polyaniline nanofibers. This could be attributed to the incorporation of nanofibers (aspect ratio >50), which may provide high ion conducting path along the interface due to Lewis acid–base interactions between Li+ ions and lone pair of electrons of nitrogen atom of polyaniline. However, at higher fraction (>6 wt.%), the nanofibers get phase separated from the polymer matrix and form domain-like structures, which may act as physical barrier to the conduction of Li+ ions resulting in decreased ionic conductivity. Electrochemical potential window and interfacial stability of nanofibers dispersed polymer electrolyte membranes are also better than that of nanofibers free membranes.

Polypropylene-supported and nano-Al 2O 3 doped poly(ethylene oxide)- poly(vinylidene fluoride-hexafluoropropylene)-based gel electrolyte for lithium ion batteries

A new gel polymer electrolyte (GPE) is reported in this paper. In this GPE, blending polymer of poly(ethylene oxide) (PEO) with poly(vinylidene fluoride-hexafluoropropylene) (P(VdF-HFP)), doped with nano-Al 2O 3 and supported by polypropylene (PP), is used as polymer matrix, namely PEO-P(VdF-HFP)-Al 2O 3/PP. The performances of the PEO-P(VdF-HFP)-Al 2O 3/PP membrane and the corresponding GPE are characterized with mechanical test, CA, EIS, TGA and charge-discharge test. It is found that the performances of the membrane and the GPE depend to a great extent on the content of doped nano-Al 2O 3. With doping 10 wt.% nano-Al 2O 3 in PEO-P(VdF-HFP), the mechanical strength from 9.3 MPa to 14.3 MPa, the porosity of the membrane increases from 42% to 49%, the electrolyte uptake from 176% to 273%, the thermal decomposition temperature from 225 oC to 355 oC, and the ionic conductivity of corresponding GPE is improved from 2.7 × 10 −3 S.cm −1 to 3.8 × 10 −3 S.cm −1. The lithium ion battery using this GPE exhibits good rate and cycle performances.

Enhanced polarization in melt-quenched and stretched poly(vinylidene fluoride-hexafluoropropylene) films

β-phase poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films were prepared by uniaxially stretching solution-cast or melt-quenched samples. Different preparation routes lead to different amounts of the crystalline α and β phases in the films, as detected by means of Fourier-transform infrared spectroscopy and X-ray diffractometry. The β phase is significantly enhanced in melt-quenched and stretched films in comparison to solution-cast and stretched films. This is particularly true for copolymer samples with higher HFP content. The β-phase enhancement is also observed in ferroelectric-hysteresis experiments where a rather high polarization of 58 mC/m2 was found on melt-quenched and stretched samples after poling at electric fields of 140 MV/m. After poling at 160 MV/m, one of these samples exhibited a piezoelectric d33 coefficient as high as 21 pC/N. An electric-field-induced partial transition from the α to the β phase was also observed on the melt-quenched and stretched samples. This effect leads to a further increase in the applications-relevant dipole polarization. Uniaxially stretched ferroelectric-polymer films are highly anisotropic. Dielectric resonance spectroscopy reveals a strong increase of the transverse piezoelectric d32 coefficient and a strong decrease of the transverse elastic modulus c32 upon heating from 20 to 50°C.

Structural, morphological, thermal, and conductivity studies of magnesium ion conducting P(VdF‐HFP)‐based solid polymer electrolytes with good prospects

AbstractSolid polymer electrolyte (SPE) system purely based on poly(vinylidenefluoride‐hexafluoropropylene) [P(VdF‐HFP)] and magnesium trifluoromethanesulfonate (MgTf) has been synthesized via solution‐casting technique with acetone as solvent. Various instruments have been used to examine the structural, morphological, and thermal behaviors of the samples. X‐ray diffraction (XRD), horizontal attenuated total reflectance‐Fourier transform infrared spectroscopy (HATR‐FTIR) and differential scanning calorimetry (DSC) are utilized to study the conversion of crystalline to amorphous nature in the copolymer. The crystallinity of copolymer matrix has been shown to be greatly affected by incorporation of MgTf, even with low concentration and absence of plasticisers. Scanning electron microscopy (SEM), photoluminescence spectroscopy (PL), and AC impedance spectroscopy further corroborate the findings. FTIR spectra suggest complexation has occurred between the constituents in these SPEs. Thermogravimetric analysis (TGA) and DSC thermograms show some improvements in thermal behaviors upon the addition of MgTf. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Field-induced phase transition and its impact on the magnetoelectric effect in P(VDF-HFP)/Metglas laminates

AbstractThe field-induced phase transition driven by electric field was observed in poly(vinylidene fluoride – hexafluoropropylene) (P(VDF-HFP)) 90/10 wt% copolymers. Experimental results indicated that the electric field may remarkably affect the remanent polarization in terms of changing the D-E loop forms from double loops to single loop, starting from 68 MV/m, and completing at 216 MV/m. It was found that the remanent polarization as well as the piezoelectric constant d31 had a linear relationship with the poling electric field in above electric field range. Thus the magnetoelectric (ME) coupling coefficient ME in P(VDF-HFP)/Metglas laminates increased with the poling electric field. Moreover, the cyclic poled ME device demonstrated different peak d.c. magnetic bias field HDC on the ME - HDC curves from conventional room temperature poled ones. The peak ME coefficient obtained was 4 V/cm Oe.

PZT/P(VDF-HFP) 0–3 composites as solvent-cast thin films: preparation, structure and piezoelectric properties

Composite films of lead zirconate titanate (PZT) and poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) were prepared as 100 µm thin films by solvent casting. Within the 0–3 composites, the ceramic-volume fraction was varied between 0.19 and 0.65, which yielded films with different structural and dielectric properties. These influenced the piezoelectric properties of the composite films found after electric poling, which was performed here at room temperature. The piezoelectric activity, with a maximum piezoelectric coefficient of 11 pC N−1 in the film-thickness direction, originates from the polarization of the embedded ceramic particles as proved by poling experiments in corona discharges as well as in direct contact.

Influence of polymer concentration and dyes on photovoltaic performance of dye-sensitized solar cell with P(VdF-HFP)-based gel polymer electrolyte

A series of gel polymer electrolytes (GPEs) is synthesized using Poly(vinylidenefluoride-hexafluoropropylene) P(VdF-HFP) as the host matrix and propylene carbonate (PC)–diethyl carbonate (DEC) as plasticizers to fabricate dye-sensitized solar cells. Equal amounts of PC and DEC are used to comprehend high dielectric constant and low viscosity of the electrolyte. The as-prepared GPEs are characterized by XRD, FTIR and SEM. Their thermal properties and ionic conductivities are investigated by TGA/DSC analyses and AC impedance measurements, respectively. The optimized gel polymer electrolyte gives a maximum ionic conductivity of 5.25 × 10 −3 S cm −1 at room temperature. The formation of porous structure in the electrolyte film supports the entrapment of large volumes of liquid electrolyte inside its cavities. The role of N3 and N719 dyes are also investigated for better photovoltaic performance of DSSC. The overall light-to-electrical-energy conversion efficiencies of 3.95% and 4.41% are obtained for N3 and N719 dyes, respectively, under 100 mW cm −2 irradiation, which are comparable to those obtained from the corresponding liquid electrolyte cell.

Piezoelectric responses in poly(vinylidene fluoride/hexafluoropropylene) copolymers

The authors show that a high transverse piezoelectric response with both high piezoelectric d31 (d31=43.1pm∕V) and electromechanical coupling k31 coefficients (k31=0.187), much higher than those in the piezoelectric poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) copolymers, can be obtained in poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] 10wt% copolymers under quasistatic condition. Furthermore, the copolymers also display a higher d31 coefficient compared to the d33 coefficient, which seems to be unusual compared with most other piezopolymers. The experimental data suggest that the origin of the unusual piezoelectric response in these P(VDF-HFP) copolymers originates from a reversible change between a poled α-like structure and β-like structure. The phase change nature also results in a large frequency dispersion of the piezoelectric response and a smaller d31 (=20.5pm∕V) at 50kHz.