PVDF-HFP Copolymer Research Articles

Application of Surface-Modified Nanoclay in a Hybrid Adsorption-Ultrafiltration Process for Enhanced Nitrite Ions Removal: Chemometric Approach vs. Machine Learning

Herein, we report the results of a study on combining adsorption and ultrafiltration in a single-stage process to remove nitrite ions from contaminated water. As adsorbent, a surface-modified nanoclay was employed (i.e., Nanomer® I.28E, containing 25-30 wt. % trimethyl stearyl ammonium). Ultrafiltration experiments were conducted using porous polymeric membranes (Ultracel® 10 kDa). The hybrid process of adsorption-ultrafiltration was modeled and optimized using three computational tools: (1) response surface methodology (RSM), (2) artificial neural network (ANN), and (3) support vector machine (SVM). The optimal conditions provided by machine learning (SVM) were found to be the best, revealing a rejection efficiency of 86.3% and an initial flux of permeate of 185 LMH for a moderate dose of the nanoclay (0.674% w/v). Likewise, a new and more retentive membrane (based on PVDF-HFP copolymer and halloysite (HS) inorganic nanotubes) was produced by the phase-inversion method, characterized by SEM, EDX, AFM, and FTIR techniques, and then tested under optimal conditions. This new composite membrane (PVDF-HFP/HS) with a thickness of 112 μm and a porosity of 75.32% unveiled an enhanced rejection efficiency (95.0%) and a lower initial flux of permeate (28 LMH). Moreover, molecular docking simulations disclosed the intermolecular interactions between nitrite ions and the functional moiety of the organonanoclay.

Membranes Based on PVdF–HFP and Alkylammonium Protic Ionic Liquids: Thermal and Transport Properties

Casting from a solution is used to obtain proton-conducting membranes based on a poly(vinylidenefluoride-co-hexafluoropropylene) copolymer doped with diethylammonium hydrogen sulfate and diethylammonium mesylate with different levels of doping. An IR spectroscopic study is performed, and the phase behavior of the obtained membranes, their thermal and electrochemical stability, and specific electrical conductivity are investigated. It is established that doping protic ionic liquids into PVdF-HFP copolymer reduces the degree of its crystallinity. It has been shown that all membranes are thermally stable up to 290–300°C, and their conductivity at 145°C varies from 1.6 to 10.4 mS cm–1, depending on the level of doping.

Metal–organic framework for dendrite-free anodes in aqueous rechargeable zinc batteries

Aqueous rechargeable zinc batteries (ZBs) have many advantages, such as eco-friendliness, low cost, and high-rate performance. However, the Zn dendrite growth on the Zn metal anode of ZBs causes a short-circuit problem between the cathode and anode of the battery, resulting in the degradation of the cell performance. In this study, we employed a Zr-based metal–organic framework (Zr-MOF; UiO-66(Zr)-(COOH)2) with a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) copolymer binder as a composite protective layer (CPL) to inhibit dendrite formation. The highly stable and porous metal–organic framework (MOF) in the CPL acted as a sieve allowing Znions to be uniformly deposited on the Zn anode. It effectively controlled the Zn dendrite formation during cycling. In addition, compared to a polyvinylidene fluoride (PVDF) homopolymer binder, the PVDF-HFP copolymer binder has a higher ionic conductivity and binding affinity with the Zr-MOF in the CPL, thus reducing the overpotential of the Zn symmetric cell and further improving its cyclability. As a result, the Zn symmetric cell, coated with the CPL composed of Zr-MOF and PVDF-HFP copolymer binder, exhibited stable operation for 2400 cycles at a high current density of 10 mA/cm2 without a short circuit. This result suggests that the combination of MOF materials and copolymer binders to design a CPL is efficient in suppressing Zn dendrites.

Enhancing functional properties of PVDF-HFP/BZT-BCT polymer-ceramic composites by surface hydroxylation of ceramic fillers

We report the mechanism to enhance the dielectric and ferroelectric behavior of polymer-ceramic composites through surface hydroxylation of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) ceramic filler-particles embedded in PVDF-HFP copolymer matrix. Varying the hydroxylated h-(BZT-BCT) filler particle-content (φ = 0–40 wt%) in PVDF-HFP copolymer matrix, composite films (of ~75 μm thickness) were prepared. We observed that, with an increase in filler content up to an optimum concentration of 15 wt%, a microstructure with gradually denser particle-arrangement and enhanced particles-polymer surface interaction is exhibited, which leads to improved dielectric and ferroelectric behavior. The energy storage density (728 mJ/cm3 at an electric field of 750 kV/cm) of the composite with 15 wt% of h-(BZT-BCT) is found to be much higher than those of the pure BZT-BCT sample, pure PVDF-HFP copolymer and their composites. Our work demonstrates the method of enhancing the functional properties through a suitable microstructure of composite materials with surface-hydroxylation of filler particles.

Boosted energy-storage efficiency by controlling conduction loss of multilayered polymeric capacitors

Among the organic dielectrics, polyvinylidene fluoride PVDF-based polymers present the highest level of polarizability with permittivity >35. Nonetheless, their applications in advanced electronics and industrial uses are limited by significant leakage current under high voltage, which is considered the principal cause of device energy consumption and short lifetime. Therefore, the main objective of this paper was to focus on alternative capacitor structure-based polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene (PVDF-TrFE-CTFE) terpolymers to efficiently limit the leakage current and lead to enhanced electrical breakdown with negligible degradation of polarization level. The novel bilayer capacitor was constructed by depositing a thin barrier layer of high polar PVDF-HFP copolymer on the terpolymer via a rapid solution-casting technique. The relationship between leakage current, dielectric strength and conduction mechanisms was investigated. Implementation of such a barrier layer led to a significant reduction (70%) in leakage current and ferroelectric losses (approximately 90%), thus boosting the performance of multilayered material up to 50% of enhanced energy-storage efficiency. Experimental results are very promising, allowing to confirm that combining both terpolymer and copolymer in a hybrid multilayer design makes a possibility to achieve the best compromise in terms of energy efficiency, dielectric properties, and breakdown strength.

Preparation of hydrophobic flat sheet membranes from PVDF-HFP copolymer for enhancing the oxygen permeance in nitrogen/oxygen gas mixture

In this study, poly(vinilydene fluoride-co-hexafluoropropylene) (PVDF-HFP) was used for preparation of hydrophobic membranes using non-solvent induced phase inversion (NIPS) technique. PVDF-HFP copolymer with concentrations of 10 wt% and 12 wt% was prepared to investigate the effect of polymer concentration on pore structure, morphology, hydrophobicity and performance of prepared membranes. Besides, the use of two coagulation baths with the effects of parameters such as coagulant time, polymer type and concentration, and the amount of non-solvent were studied. The performance of prepared membranes was evaluated based on the permeability and selectivity of oxygen and nitrogen from a gas mixture of nitrogen/oxygen under operating conditions of feed flow rate (1–5 L·min−1), inlet pressure to membrane module (0.1–0.5 MPa) and temperatures between 25 and 45 °C. The results showed that the use of two coagulation baths with different compositions of distillated water and isopropanol, coagulant time, polymer type and concentration, and the amount of non-solvent additive have the most effect on pore structure, morphology, thickness, roughness and crystallinity of fabricated membranes. Porosity ranges for the three fabricated membranes were determined, where the maximum porosity was 73.889% and the minimum value was 56.837%. Also, the maximum and minimum average thicknesses of membrane were 320.85 μm and 115 μm. Besides, the values of 4.7504 × 10−7 mol· m−2· s−1· Pa−1, 0.525 and 902.126 nm were achieved for maximum oxygen permeance, O2/N2 selectivity and roughness, respectively.

Enhanced interfacial dielectric polarization in PVDF-HFP copolymer with treating PPy by using silane coupling agent

Dielectric materials are polar materials for energy storage applications such as capacitors, transformer, and other electrical devices. The great dielectric properties generally depend on easily switchable polarization and higher-order structure in a material. Filler composite in the flexible dielectric polymer is then considered to rearrange polymer chain. However, the filler becomes agglomeration easily at high loading content in polymer, resulting in high energy loss and low electrical breakdown. This work presents the treated Polypyrrole (PPy) filler by 3-Aminopropyltriethoxysilane for avoiding agglomeration in PVDF-HFP thin film. These 30 μm PVDF-HFP film thickness is fabricated by tape casting method with N, N-dimethylformamide (DMF) solvent. The distributions of PPy filler on PVDF-HFP are observed by SEM image. Dielectric constant, dielectric loss, and conductivity are analyzed. As a result, the maximum silane content was found on 1 wt% for 1 wt% PPy/PVDF-HFP to maximized dielectric constant and reduce dielectric loss and conductivity. The conductive of PPy filler was lowered by covering with electrical insulating silane, resulting in decreased dielectric loss and conductivity. Then, polymer chain with silane bonding easily polarized under the electric field, resulting in an intensification of dielectric constant around 2.5 times compared with non-silane. Afterward, this dielectric constant clearly decreased when it reached to exceeded silane content as 5-20 wt%. Treated PPy with the suitable silane content in PVDF-HFP performs good dielectric properties for advanced energy storage in this work.

Nitric oxide releasing poly(vinylidene fluoride-co-hexafluoropropylene) films using a fluorinated nitric oxide donor to greatly decrease chemical leaching

Nitric oxide (NO) releasing polymers have been widely applied as biomaterials for a variety of biomedical implants and devices. However, the chemical leaching of NO donors and their byproduct species is almost always observed during the application of polymers doped with NO donors, unless the donor is covalently linked to the polymer. Herein, we report the first NO releasing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fluorinated copolymer prepared by incorporating a fluorinated S-nitrosothiol as the NO donor. Under physiological conditions, the resulting polymeric films can release NO for 16 days. Importantly, due to both fluorine-fluorine and electrostatic charge interactions between the fluorinated NO donor and the PVDF-HFP copolymer, the total chemical leaching of the fluorinated NO donor and its disulfide product after 9 day was only 0.6% (mol%) of the initial amount of NO donor loaded into the film. These new NO release PVDF-HFP films exhibit antimicrobial and anti-biofilm activities against both Gram positive S. aureus and Gram negative P. aeruginosa strains. The NO-releasing PVDF-HFP polymer can also be coated on Teflon tubing to release NO under physiological conditions for extended time periods. This NO-releasing PVDF-HFP copolymer with greatly reduced chemical leaching could help enhance the biocompatibility and antimicrobial activity of various biomedical devices. Statement of SignificanceFluoropolymers have been widely used in creating various biomedical implants and devices. However, nitric oxide (NO) release fluoropolymers have not been well studied to date. Additionally, in the application of biomaterials doped with NO donors, a significant amount of NO donors and their byproducts almost always leach into aqueous environment.We now report an NO releasing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fluoropolymer by incorporating a new fluorinated S-nitrosothiol. The NO release can last for 16 days under physiological conditions. The total chemical leaching was determined to be only 0.6 mol% of the initial S-nitrosothiol loaded. As expected, significant antimicrobial/anti-biofilm activities of the NO release PVDF-HFP film were observed against Gram positive S. aureus and Gram negative P. aeruginosa bacterial strains.

Polymer electrolytes based on PVdF-HFP doped with protic ionic liquids containing different cations

Several protic ionic liquids based on trifluoroacetate anion and different alkylammonium (diethyl-, dimethylethyl-, tributyl-, diisopropylethyl-) cations have been synthesized and investigated by different methods. Based on the results obtained earlier for triethylammonium and triethanolammonium trifluoroacetates, the influence of the cations structure on the thermal (phase transition and decomposition temperatures) and electrochemical (conductivity, electrochemical window, ionicity) properties of the PILs has been studied. For the investigated salts, the specific conductivity within the cation series DMEA > DEA > TEA > TBA decreases. These PILs have been used as dopants to prepare membranes based on (poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)) whose electrochemical and thermal properties have also been investigated. The electric conductivity of these membranes was lower than that of the PILs themselves because of the confined mobility of the ions. However, the conductivity decrease was not too significant and did not exceed one order of magnitude. Doping PILs into the PVdF-HFP copolymer lowered the polymer crystallinity degree. The values of the electrochemical window of the studied PILs and PVdF-HFP–PILs membranes ranged from 0.9 to 1.3 V and from 6 to 7 V, respectively.

Electrochemical Characteristics of the Na-Ion Hybrid Capacitors Assembled with Fibrous Composite Separator Containing Core-Shell Structured SiO2 Nanoparticles

Sodium is currently being investigated as efficient energy storage due to its abundance in nature. Na-ion hybrid capacitors (NHCs) exhibit the characteristics of high power density as well as high specific energy. The need for development on the NHCs arises as they incorporate the advantages of capacitors and rechargeable batteries as well as cost-effectiveness. As one of the main components in NHCs, an electrolyte plays an essential role in several aspects such as safety, electrochemical characteristics and cycling performance. Conventional liquid electrolytes provide high ionic conductivity and good electrochemical properties, however, they raise safety concerns. A gel polymer electrolyte (GPE) is a promising alternative for liquid electrolyte, as it possesses great safety features and mechanical properties, but suffers from low ionic conductivity due to poor ion transport. In this study, to develop a gel polymer electrolyte with high ionic conductivity and enhanced safety, PVdF-HFP copolymer was electrospun with core-shell structured SiO2(Na+) particles. Core-shell structured SiO2(Na+) nanoparticles were synthesized and utilized as fillers to increase ionic conductivity by releasing Na+ ions into gel polymer electrolyte. Incorporation of core-shell structured nanoparticle fillers can also improve mechanical properties as well as thermal stability. Composition of the composite separators was optimized in consideration of ionic conductivity and mechanical property. Finally, the electrochemical performance of the Na-ion hybrid capacitors employing optimized gel polymer electrolyte was evaluated. References S. H. Ju, Y.-S. Lee, Y.-K. Sun, and D.-W. Kim, J. Mater. Chem. A, 1 (2013) 395-401.S.-R. Park, Y.-C. Jung, W.-K. Shin, K. H. Ahn, C. H. Lee, and D.-W. Kim, J. Membr. Sci., 527 (2017) 129-136.

Microporous ceramic coated separators with superior wettability for enhancing the electrochemical performance of sodium-ion batteries

Finding an alternative to glass fiber (GF) separators is a crucial factor for the fast commercialization of sodium-ion batteries (SIBs), because GF separators are too thick for use in SIBs, thereby decreasing the volumetric and gravimetric energy density. Here we propose a microporous composite separator prepared by introducing a polymeric coating layer of polyvinylidene fluoride–hexafluoropropylene (PVdF-HFP co-polymer) with ZrO2 nanoparticles to a polyethylene (PE) separator. The coated separator efficiently enhances the cell performance of SIBs. The ZrO2 nanoparticles, finely dispersed on the polymeric coating layer, induce the formation of many micropores on the polymeric coating layer, suggesting that micropore formation on the coating layer renders the composite separator more open in structure. An ethylene carbonate/propylene carbonate liquid electrolyte for SIBs is not absorbed by PE separators even after 1 h of electrolyte droplet testing, while the proposed separator with many micropores is completely wetted by the electrolyte. Sodium ion migration across the composite separator is therefore effectively enhanced by the formation of ion transfer pathways, which improve ionic conductivity. As a result, the microporous composite separator affords stable cycle performances and excellent specific capacity retention (95.8%) after 50 cycles, comparable to those offered by a SIB with a GF separator.

Electrochemical Performance of Activated Carbon Based Electric Double Layer Capacitors Using 1-Ethyl-3-Methylimidazolium Dicyanamide Ionic Liquid and Its Gel Polymer Electrolyte

The supercapacitors have emerged as an important energy storage device as they can deliver a high specific power, long cycle life, and much higher charge-discharge rates than a battery. In particular, solid-state supercapacitors have gained worldwide attention as an emerging candidate for smart and efficient energy storage devices due to the increasing demand for miniaturized electronics. Electric double layer capacitors (EDLCs) are the most widely studied class of supercapacitors which physically stores charge by forming an electric double layer at the interfaces between the high surface area carbon electrode and the electrolyte. The conventional EDLCs using high surface area activated carbon electrodes and non-aqueous liquid electrolytes represent the current state of the art. The most common cause of failure of such devices is related to the electrolyte leakage. Most of the past work on EDLCs have been carried out using the liquid electrolytes (aqueous, organic and pure ionic liquid). The gel polymer electrolytes with high ionic mobility and good dimensional/mechanical stability, offer a viable substitute for the liquid electrolytes and they are being used for flexible and solid-state electrochemical energy storage devices. Here, we report the electrochemical performance of high surface area activated carbon based EDLCs using 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA) ionic liquid and its poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) gel counterpart as electrolytes. The gel electrolyte films were prepared by immobilizing the EMImDCA ionic liquid in PVdF-HFP copolymer matrix by solution casting method. The activated carbon electrodes were prepared by mixing the activated carbon powder with conductive additive (Super C65) and PVdF-HFP binder in a ratio of 8:1:1 (w/w/w), and then the mixture was drop-casted onto a flexible thin graphite sheet which serves as current collector. The solid-state EDLC cells were fabricated by sandwiching the gel electrolyte film between two identical activated carbon electrodes whereas EDLC cells with pure IL were fabricated by using fiberglass separator soaked with IL. The EDLC cells show highly capacitive behavior as evident from the cyclic voltammogram of the cells measured at a scan rate of 20 mV s-1 which is rectangular in shape (Fig 1a). However, gel electrolyte based solid-state cell shows slightly higher resistance, obvious from slight deviation from rectangular shape at both turning potential. Typical galvanostatic charge-discharge characteristic of the EDLC cells at current density of 5 mA cm-2is shown in Fig. 1b. The linear discharge characteristics of the cell further confirms the capacitive behavior of the cells due to formation of an electric double layer at the interfaces. The EDLC cell with pure IL shows specific capacitance of ~98 F g-1 whereas IL-gel based EDLC cell shows specific capacitance of ~86 F g-1, derived from charge-discharge curves at 5 mA cm-2. A comparative performance of the EDLC cells was carried our using the impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. This paper discusses the results of these comparative studies with pure IL and its PVdF-HFP gel electrolytes. Figure 1

Fabrication of protein-resistant blend based on PVDF-HFP and amphiphilic brush copolymer made from PMMA and PEGMA

Polymeric blends provide a facile route to obtaining materials with various synergistic properties arising from the individual components. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a hydrophobic polymer, is finding new applications in polymer electrolytes, membranes, and heat-resistant structural materials owing to its high thermal stability, mechanical strength, and weatherability. In this report, blends of PVDF-HFP and polymer brush were prepared with enhanced water uptake and protein resistance, which are important requirements for membranes used in food and biological applications. Polymer brush is composed of poly(methyl methacrylate) main chains, which are miscible with PVDF-HFP, and hydrophilic poly(ethylene glycol) (PEG) brush chains. Incorporation of PEG chains through the polymer brush structure not only enhanced water uptake and protein adsorption resistance but also produced a well-distributed morphology of the blending components through the matrix as evidenced by observation of the morphology after selective extraction of polymer brush from the matrix.

Highly conductive and electrochemically stable plasticized blend polymer electrolytes based on PVdF-HFP and triblock copolymer PPG-PEG-PPG diamine for Li-ion batteries

A new plasticized poly(vinylidene fluoride-co-hexafluoropropylene (PVdF-HFP)/PPG-PEG-PPG diamine/organosilane blend-based polymer electrolyte system has been synthesized and characterized. The structural and electrochemical properties of the electrolytes thus obtained were systematically investigated by a variety of techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile test, Fourier transform infrared spectroscopy (FTIR), 13C and 29Si solid-state NMR, AC impedance, linear sweep voltammetry (LSV) and charge–discharge measurements. The FTIR and NMR results provided the information about the interaction among the constituents in the blend polymer membrane. The present blend polymer electrolyte exhibits several advantageous electrochemical properties such as ionic conductivity up to 1.3×10−2Scm−1 at room temperature, high value of Li+ transference number (t+=0.82), electrochemical stability up to 6.4V vs. Li/Li+ with the platinum electrode, and stable charge–discharge cycles for lithium-ion batteries.

Water desalination by membrane distillation using PVDF-HFP hollow fiber membranes

Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique using different polyethylene glycol (PEG) concentrations as non-solvent additive in the dope solution. Two different PEG concentrations (3 and 5 wt.%). The morphology and structural characteristics of the hollow fiber membranes were studied by means of optical microscopy, scanning electron microscopy, atomic force microscopy (AFM) and void volume fraction. The experimental permeate flux and the salt (NaCl) rejection factor were determined using direct contact membrane distillation (DCMD) process. An increase of the PEG content in the spinning solution resulted in a faster coagulation of the PVDF-HFP copolymer and a transition of the cross-section internal layer structure from a sponge-type structure to a finger-type structure. Pore size, nodule size and roughness parameters of both the internal and external hollow fiber surfaces were determined by AFM. It was observed that both the pore size and roughness of the internal surface of the hollow fibers enhanced with increasing the PEG concentration, whereas no change was observed at the outer surface. The void volume fraction increased with the increase of the PEG content in the spinning solution resulting in a higher DCMD flux and a smaller salt rejection factor.

Effect of the rheology of poly(vinylidene fluoride- co-hexafluropropylene) (PVDF–HFP) dope solutions on the formation of microporous hollow fibers used as membrane contactors

The rheological properties of polymer dope solutions influence the membrane structure and performance. In the present work, the effect of shear rate on the fabrication of poly(vinylidene fluoride- co-hexafluropropylene) (PVDF–HFP) asymmetric microporous hollow fiber membranes has been studied in terms of membrane morphology, pure water flux, filtration rejection, mechanic strength and the performance of the membrane contactors made by as-spun hollow fibers for CO 2 capture. The PVDF–HFP copolymer possesses strong viscoelasticity, which is believed to be associated with the occurrence of an irregular morphology in the PVDF–HFP hollow fibers made at a high dope extrusion rate. For the first time, the viscoelastic Mach number was applied to elaborate the deformation of the inner contour of the membranes by means of characterizing the delayed die swell in the process of hollow fiber fabrication. Based on the Mach number, several batches of PVDF–HFP dope solutions with an appropriate viscosity were adopted for hollow fiber fabrication at given dope extrusion rates. The effects of the shear rate on the permeation flux and molecular weight cutoff (MWCO) of the membranes made by Batch III-2L.5T dope solution (2 wt.% LiCl and 0.5% Tween 80 as the additive) presented a V shape curve; while for the polymer dope of Batch V-2P9G (2 wt.% PVP and 9 wt.% glycerol as the additive), the effect of the shear rate on the resultant membranes showed a different pattern: increasing the shear rate resulted in smaller MWCOs, enhanced water permeation flux and higher elongation strength. These behaviors have been discussed thoroughly based on the shear-induced macromolecular chain orientation and close packing, variation of the porosity with the shear rate and shear-thinning rheological property of the dope solution under a high shear stress.

Preparation and characterization of PVDF–HFP copolymer hollow fiber membranes for membrane distillation

Poly(vinylidene fluoride- co-hexafluoropropylene) (PVDF–HFP) hollow fiber membranes were prepared by the dry/wet spinning technique at different copolymer concentrations from 17 to 24 wt%. All the spinning parameters were kept constant except the copolymer concentration. The temperature of both the internal and external coagulants was maintained at 40ºC. The effects of the copolymer concentration on the morphological properties of the hollow fibers were studied in terms of external and internal diameter and scanning electron microscopy (SEM). It was found that the thickness of all tested hollow fibers did not change significantly. An evolution of the cross-section structure with the increase of the copolymer concentration was detected. The cross-section of the hollow fiber prepared with the lowest copolymer concentration exhibited a finger-like structure in both the external and internal layers disappearing in the internal layer as the copolymer concentration increases. Finally, a sponge-like structure is formed through all cross-section of the hollow fiber prepared with the highest concentration. This may be explained based on the decrease of the coagulation rate with the increase of the copolymer concentration in the dope solution.

Polymer Electrolytes Based on Ionic Liquids and Their Application to Solid-state Thin-film Li-Oxygen Batteries

Ionic liquids that are non-volatile, non-flammable, and stable with Li metal and exhibit wide electrochemical stability window are promising for application to lithium batteries, including Li/air cells. 1-Methyl-3-Propylpyrrolidinium bis (trifluoromethanesulfonyl)imide (P13TFSI) is identified to be such an ionic liquid. Dimensionally stable, elastic polymer electrolyte membranes with high thermal and electrochemical stability, high ionic conductivity and other desirable properties are synthesized by blending P13TFSI with lithium imide salt dissolved in it and the PVDF-HFP co-polymer. Preliminary solid-state, thin-film Li-oxygen cells are constructed using the polymer electrolyte membranes and their performance analyzed.

Influence of extrusion, stretching and poling on the structural and piezoelectric properties of poly (vinylidene fluoride‐hexafluoropropylene) copolymer films

AbstractThree types of poly (vinylidene fluoride‐hexafluoropropylene) (PVDF–HFP) copolymer films were prepared by extrusion, stretching as well as simultaneously stretching and static electric field poling (SSSEP), respectively, and measured by the differential scanning calorimetric, wide angle X‐ray diffraction, fourier transformation infrared‐attenuated total reflection, and Dynamic mechanical analysis. The experimental results showed that the films prepared by stretching and SSSEP have higher crystallinity and β phase than by extrusion. SSSEP improved the chain orientation enormously both in crystalline and amorphous regions, resulting in the highest storage modulus. Because of the lower β phase content, the extruded films exhibited the lowest piezoelectric coefficient d33. For the stretched and SSSEP films, although the β phase content was similar, the d33 was distinct because of the different potential energy for the rotation of the dipoles. In addition, the SSSEP films gave the maximum d33 (24 pC/N), higher than the other PVDF–HFP copolymer films that have been reported. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 858–862, 2007

Structure and ionic conductivity of porous polymer electrolytes based on PVDF-HFP copolymer membranes

The porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes were prepared by solvent evaporation method using dibutyl phthalate (DBP), polyvinylpyrrolidone (PVP-k30), polyethylene glycol 200 (PEG200) as additives. The influence of additives on morphology and structure, electrolyte uptake of porous membranes and lithium ionic conductivity of the activated membranes were investigated. The properties of the PVDF-HFP microporous membranes, such as crystallinity, thermal characterization, conductivity and mechanical strength were characterized. The PVDF-HFP gel electrolytes were formed by microporous PVDF-HFP membranes filled and swollen by a liquid electrolyte. The lithium ionic conductivity of polymer electrolytes at 25 °C was measured by ac impendence technique. The membrane took on asymmetric structure and relatively small pore size when DBP and PEG200 were used as additives, whereas nearly symmetric and microporous structure when PVP was used as an additive. Moreover, the average pore size and porosity was about 0.3 μm and 48.7%, respectively. The crystallinity of the membranes was smaller than that of pure PVDF-HFP and decreased in the sequence of PVP, PEG200 and DBP as additives. The maximum electrolyte uptake is 124.6 wt.% and the conductivity is 0.49 mS/cm when PVP as an additive.