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Lithium bis(perfluoroethanesulfonyl)imide (BETI; guest species)-based polyvinylidenefluoride-hexafluoropropylene (PVDF-HFP) (host matrix) polymer nanocomposites (PNC) films by loading barium titanate (BaTiO) as a filler in ascending proportions with plasticizer (mixture of EC + DMC) while keeping host and guest content as constants has been investigated by employing AC impedance, thermal, X-ray diffraction (XRD), phase morphology, and Fourier transform infrared (FTIR) studies. The ionic conductivity measurements on these PNC show that 2.5% BaTiO-loaded polymer nanocomposites (PNC) showed mitigation in magnitude of the conductivity compared with that of 0 wt.% loaded PNC; but increase in conductivity is noted thereafter with increase in filler content of up to 7.5 wt.%. The higher conductivity is observed for 7.5% filler-loaded membrane. The XRD study identifies suppression of polymer phase associated with (200) plane. The SEM image illustrates inhomogeneity in surface morphologies for PNCs with the filler dispersed. The thermal profile registers the endothermic changes associated with polymer host indicating a varying heat of fusion ∆Hm with filler increase. FTIR studies confirm possible interaction between various constituents of the PNCs. [ABSTRACT FROM AUTHOR]

Abstract: Room temperature ionic liquid (IL): 1-methyl-3-hexylimidazolium imide (HxMImTFSI) has been synthesized showing a high conductivity value of 4.3mS/cm at room temperature. Polymer electrolytes (PEs) have been developed by impregnating the RTIL in poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) matrix with different binary compositions which have different molecular weights. PE''s that are synthesized with the polymer having an average molecular weight of 400,000 shows highest room temperature conductivity of 4.86×10−4 S/cm at room temperature for (3:7 weight ratio). The nano-composite polymer electrolytes (NCPEs) were prepared by dispersing nano-tubular titania in the PE. Thermal stability of the IL and NCPEs was investigated using TGA (Thermogravimetric Analysis) and DSC (Differential Scanning Calorimetric) studies showing the stability of these electrolytes in excess of 250°C. High ionic conductivity has been observed of the order of 10−4 S/cm at RT and 10−3 S/cm at 120°C for NCPE having composition 3:7 ratio of polymer and IL and containing 2wt% nano-tubular titania. SEM studies show that there is an improvement in the morphology of the NCPEs with the addition of nano-tubular titania. [Copyright &y& Elsevier]

Abstract: This paper describes, nanocomposite polymer electrolyte (NCPE) based on polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP), which comprises the novel lithium difluoro(oxalato)borate (LiDFOB). Ehtylene carbonate (EC) and diethyl carbonate (DEC) mixture was used as gelling agent and nanoparticulate TiO2 used as filler. The NCPE membranes were subjected to a.c. impedance, tensile strength, Raman studies, TG/DTA and morphological studies. 5wt% TiO2 comprising membranes exhibited enhanced conductivity of 0.56mScm−1and the Young’s modulus was increased from 1.32 to 2.74MPa. The structural change of α to β phase was confirmed by Raman studies. The thermal stability of the NCPE membrane is found to be 130°C. Calculation of activation energy and synthesis of LiDFOB has also been presented. [Copyright &y& Elsevier]

Abstract: Sodium ion conducting composite polymer electrolytes (CPE) have been prepared by solution casting technique in the skeleton of polyvinylidenefluoride-co-hexafluoropropylene/poly ethylmethacrylate blend. The binary mixture of diethyl carbonate and ethylene carbonate were used as plasticizer, and nanosized Sb2O3 as filler. The sodium trifluoromethanesulfonate (NaCF3SO3) was used as an ionic conducting source. The a.c. impedance study shows that 10wt% Sb2O3 containing CPE exhibits the maximum conductivity 0.569mScm−1 at ambient temperature. Molecular interactions of the constituents were analyzed by Fourier transform infra red spectroscopy. X-ray diffractogram reveals the amorphous nature of the CPE. A surface morphological feature was studied through scanning electron microscope. The activation energy and coherence length calculated were in support of the ionic transport. [Copyright &y& Elsevier]

Abstract: Polymer electrolyte membranes consisting of a novel hyperbranched polyether PHEMO (poly(3-{2-[2-(2-hydroxyethoxy) ethoxy] ethoxy}methyl-3′-methyloxetane)), PVDF-HFP (poly(vinylidene fluoride-hexafluoropropylene)) and LiTFSI have been prepared by solution casting technique. X-ray diffraction of the PHEMO/PVDF-HFP polymer matrix and pure PVDF-HFP revealed the difference in crystallinity between them. The effect of different amounts of PVDF-HFP and lithium salts on the conductivity of the polymer electrolytes was studied. The ionic conductivity of the prepared polymer electrolytes can reach 1.64×10−4 S·cm−1 at 30 °C and 1.75×10−3 S·cm−1 at 80 °C. Thermogravimetric analysis informed that the PHEMO/PVDF-HFP matrix exhibited good thermal stability with a decomposition temperature higher than 400 °C. The electrochemical experiments showed that the electrochemical window of the polymer electrolyte was around 4.2 V vs. Li+/Li. The PHEMO/PVDF-HFP polymer electrolyte, which has good electrochemical stability and thermal stability, could be a promising solid polymer electrolyte for polymer lithium ion batteries. [Copyright &y& Elsevier]

Abstract: This paper describes the preparation and characterization of polyvinylidene fluoride–hexafluoropropylene (PVdF–HFP) based nanocomposite polymer electrolyte (NCPE). For the first of its kind lithium fluoroalkylphosphate (LiPF3(CF3CF2)3) was incorporated as electrolyte salt in the polymer skeleton. Ethylene carbonate and diethyl carbonate mixture (1:1, wt/wt) was used as a plasticizing agent and SiO2 nanoparticle as filler. The NCPE membranes were characterized by a.c. impedance, Scanning electron microscope, Differential scanning calorimetry, Fourier transform infrared and fluorescence studies. An electrolyte with 2.5wt% SiO2 exhibited a conductivity of 1.16mScm−1 at ambient temperature. It was found that filler contents above 2.5wt% rendered the membranes less conducting. Activation energy and percentage of crystallinity has also been calculated. [Copyright &y& Elsevier]

• Surfaces with micropillar structures developed using nanoimprint lithography. • Presence of micropillars enhanced the hydrophobicity of the films. • Superhydrophobic films obtained using combination of low surface energy materials and micropillar structures. Nanoimprint lithography was employed in this study to fabricate superhydrophobic polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) films. The nanoimprinted PVDF-HFP films exhibited uniform micropillar arrays on their surfaces. The difference in water contact angle between nanoimprinted and neat PVDF-HFP films indicated the involvement of surface micropillars in increasing the hydrophobicity of PVDF-HFP. After coating the nanoimprinted PVDF-HFP films with the self-assembled monolayer of silane, the surface free energy of the films further reduced. This surface treatment improved the hydrophobicity of the imprinted PVDF-HFP films and helped them to exhibit superhydrophobic behavior. [ABSTRACT FROM AUTHOR]

We prepared side-chain grafted functional groups poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) fluorinated membranes to fine control hydrophobic and anti-fouling nature of membrane for desalination of high saline water by vacuum membrane distillation (VMD) process. Different functional groups viz. tri-methoxy silane, 4-methyl styrene, and 2, 3, 4, 5, 6-penta fluoro styrene were explored for side-chain grafting with PVDF-HFP matrix to improve the hydrophobic nature. Successful grafting of functional groups was confirmed by spectral analysis, while surface morphology of different membranes was assessed by scanning electron and atomic force microscopy. Membrane performance was assessed by permeate flux, fouling resistant nature, water contact angle and long-term performance. Among different prepared membranes, 2, 3, 4, 5, 6-penta fluoro styrene grafted PVDF-HFP membrane (M-PFS) was assessed suitable for VMD with permeate water flux (36% increase compared to the pristine membrane), salt rejection (99.99%), rechargeable (anti-fouling) nature by simple water washing, and longevity. The reported M-PFS membrane with novel architecture is a promising contender for desalination of high saline water by the VMD process. • Side-chain grafted functional groups PVDF-HFP to fine control membrane hydrophobicity. • Tri-methoxy silane, methyl styrene, and penta fluoro styrene functional groups were explored. • Membrane performance assessed by water flux, salt rejection and fouling resistance. • M-PFS membrane is promising for desalination of high saline water by VMD process. [ABSTRACT FROM AUTHOR]

[Display omitted] • PVDF-HFP based polymer films possess good wettability and liquid retention ability. • GPEs present a high ionic conductivity of 1.82×10−3 S·cm−1 at 25 °C. • The lithium ions transference number of GPEs is up to 0.513 at 25 °C. • LFP|GPEs|Li cell displays the capacity retention of 92% after 1000 cycles at 1 C. Lithium metal batteries are confronted with safety issues in liquid electrolyte systems owing to rapid growth of lithium dendrite and uneven lithium deposition. Exploration of gel polymer electrolytes (GPEs) with excellent ionic conductivity and high Li+ migration number is a possible strategy to replace liquid electrolyte. Herein, a high-powered GPEs relied on poly (vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) modified by polymer polyethylene glycol (PEG) and lithium montmorillonite (LiMNT) via bond interactions is reported. The prepared porous polymer electrolyte presents a captivating ionic conductivity of 1.82 × 10−3 S·cm−1 and lithium ions transference number up to 0.513 at 25 °C. In view of the eminent ionic conductivity and efficient migration number of Li+, the three-dimensional porous polymer electrolyte is very conducive to the fast transport and stable deposition of lithium ions, restraining the occurrence and growth rate of lithium dendrites, which improves the cycle performance and rate capability of lithium battery. LiFePO 4 | PPL122 electrolyte |Li battery delivers a desired cycling performance with a capacity retention of 92% after 1000 cycles at 1 C. [ABSTRACT FROM AUTHOR]

Solid-state batteries (SSBs) are gaining attention as they promise to provide better safety and a higher energy density than conventional liquid electrolyte batteries. Solid polymer electrolytes (SPEs) are promising candidates due to their flexibility providing better interfacial contact between electrodes and the electrolyte. However, SPEs exhibit very low ionic conductivity at ambient temperatures, which prevents their practical use in batteries. Herein, a simple and effective technique of hot press rolling is demonstrated to improve ionic conductivity and, hence, the performance of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)-based solid polymer electrolyte. Applying hot press rolling to the electrolyte membrane induced structural changes in the grain boundaries, which resulted in a reduction in the crystallinity of the material and, hence, an increase in the amorphous phase of the material, which eased the movement of the lithium ions within the material. This technique also improved the surface of the membrane, making it homogeneous and smoother, which resulted in better interfacial contact between the electrodes and electrolyte. Electrochemical tests were carried out on electrolyte membranes treated with and without hot press rolling to evaluate the effect of the treatment. The hot pressed electrolyte membrane showed significant improvements in its ionic conductivity and transference number. The cycling performance of the LFP/Li batteries using a hot press rolled electrolyte was also evaluated, which gave a specific discharge capacity of 134 mAh/g at 0.1 C. These results demonstrate that hot press rolling can have a significant effect on the electrochemical performance of solid polymer electrolytes. [ABSTRACT FROM AUTHOR]

Developing superhydrophobic/icephobic coatings is of significance in limiting ice formation, and is an ideal selection to solve the icing issues faced by daily life and industrial production. Recent investigations are mainly focused on scientific research but not practical application. Here, nanocomposite based superhydrophobic PVDF-HFP/SiO 2 /CNTs coatings were designed and fabricated. Large-area nanocomposite coatings have been fabricated, which are robust and adhesive to many substrates. As-synthesized coatings exhibited exceptional water repellency with a contact angle up to 168° and slide angle lower than 2°. Anti-icing performance of the resultant coatings is excellent. Ice formation process on aluminum film was delayed by more than 300 s at −19 °C. A purpose-built equipment was designed to investigate the placement orientation of coated samples on anti-icing performance. It has proved that a small angle of inclination had great benefits to the anti-icing performance of the superhydrophobic coating. Moreover, the nanocomposite coating has its superior deicing characteristic. Ice adhesion strength tested is lower than 10 kPa, denoting ice can be detached naturally by the action of the wind or its own weight. The anti-icing mechanism was proposed based on nucleation theory and heat transfer physics, which will give further guideline for developing superior anti-icing coatings. [Display omitted] • Robust superhydrophobic coating (>160°) was prepared with excellent icephobicity. • Icing time on the nanocomposite coating was delayed more than 300 s at −19 °C. • Fabricated coating with extremely low ice adhesion strength can be used repeatedly. • Superhydrophobicity maintains in many substrates with various preparation methods. [ABSTRACT FROM AUTHOR]

• Hierarchical BNdT microspheres can enhance the formation of β − phase of PVDF-HFP. • The special 3D interconnected architecture greatly enhances the piezoelectric outputs of the nanocomposite PEHs. • The flexible PEHs can harvest the biomechanical energy of human movements with high durability. [Display omitted] The inclusion of inorganic piezoelectric fillers in the polymeric matrix of flexible ferroelectric polymer synergies the piezoelectricity for wearable electronics. Herein, hierarchical Bi 3.15 Nd 0.85 Ti 3 O 12 microspheres (H-BNdT MPs) embedded in the polymeric matrix of polyvinylidene fluoride–hexafluoropropylene (PVDF-HFP) based piezoelectric thin films are fabricated by using a facile and cost-effective film-forming method, drop-casting. The composites possess improved dielectric and ferroelectric properties comparing with that of the pure PVDF-HFP film without any electrical poling treatment. More importantly, the highest outputs of an open-circuit voltage of 20 V and a short-circuit current of 1.9 μA under the repeated mechanical force of 10 N at the frequency of 2 Hz were successfully achieved. The maximum power of the optimal PEH can reach as high as 4.6 mW, corresponding to a power density of 938 μW/cm2, and the output electricity can light up 10 LEDs with a full-wave rectifier circuit. The enhanced output performance is attributed to the high local stress around the H-BNdT MPs arising from the hollow hierarchical architecture of the inorganic fillers. The lead-free flexible PEH is also proved to have the ability to harvest the biomechanical energy of human movements, such as finger pinching, finger tapping, and fist punching. In particular, a PEH shoe is made to harvest energy from walking and running. This PEH is confirmed to be a potential energy harvester and effective self-powered generator to drive wearable devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel PDA coated WO 3 @PVDF-HFP electrospun nanofiber membranes were synthesized. • PDA coating/WO 3 blending changed the hydrophobic membranes to superhydrophilic. • PDA/WO 3 @PVDF-HFP nanofiber membranes were oleophobic due to the hydration layer. • Nanofiber membranes exhibited excellent water flux and oil rejection. • Nanofiber membranes showed potential in water evaporation applications. In this work, electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membranes were loaded with tungsten oxide (WO 3) nanoparticles, surface coated with polydopamine (PDA) hierarchical structures, and tested in oil/water separation, photothermal water evaporation, and degradation of ampicillin. The electrospun nanofiber membranes (ENMs) consisted of three layers and the WO 3 nanoparticles were incorporated into the top layer to increase their surface exposure. These layers were then heat-pressed for dimensional stability and surface coated with PDA hierarchical structures. Characterization was conducted using microscopic, goniometric, gravimetric, and spectroscopic methods. All ENMs displayed randomly oriented, smooth microporous structure and EDS mapping revealed a uniform distribution of WO 3 nanoparticles on the nanofiber matrix. WO 3 -blended ENMs showed improved mechanical strength, higher UV/Vis absorption, and similar thickness as pristine ENM. PDA deposition has reduced the water contact angle of pristine PVDF-HFP membrane from 130.3 to 0°, whereas, the underwater oil contact angle has increased from 55.8 to 159.7°. The PDA-coated ENMs exhibited enhanced oil/water separation with 384.3 L m−2h−1 (LMH) of flux and 97.6% oil rejection when filtered under gravity. Photothermal interfacial evaporation and ampicillin degradation tests also demonstrated the multifunctionality and exciting features of the fabricated membranes for a wide range of applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multifunctional UiO-66 modified PVDF-HFP separator is presented. • UiO-66 significantly improves the dimensional thermal stability of the separator. • UiO-66 selectively transports Na-ion inducing a high ionic conductivity. • A quasi-solid-state Na-ion hybrid capacitor based on the separator is fabricated. • The device demonstrates excellent electrochemical performance. The practical application of sodium-ion hybrid capacitors is limited by their low energy densities resulted from the kinetics mismatch between cathodes and anodes, and the fire safety related to the flammable electrolyte-separator system. Hence, we report a rational design of metal–organic frameworks (MOFs, UiO-66) modified PVDF-HFP separator. High tensile strength and dimensional thermal stability of the separator reduce the risk of electrode short circuit caused by the separator deformation. MCC test demonstrates a reduction of 75% in peak heat release rate (pHRR), indicating an enhanced fire-resistant property of the separator. This is due to the transformation of UiO-66 into ZrO 2 accompanied by the consumption of oxygen and the formation of the barrier char that suppresses further heat release. Quasi-solid-state electrolyte prepared based on this separator presents an enhanced ionic conductivity of 2.44 mS cm−1 and Na-ion transference number of 0.55, which are related to the high porosity (>70%) and electrolyte uptake (~320%) of the separator. Moreover, the open metal sites of UiO-66 can capture PF 6 –and consequently liberate the Na+ for faster migration, thus reducing the kinetics mismatch between cathodes and anodes. Such multifunctional separator enables the quasi-solid-state Na-ion hybrid capacitor to achieve high energy density (182 Wh kg−1 @31 W kg−1) and power density (5280 W kg−1 @22 Wh kg−1), as well as excellent cyclic stability (10,000 cycles @1000 mA g−1). [ABSTRACT FROM AUTHOR]

The thermally induced phase separation (TIPS) process was employed to prepare poly (vinylidene fluoride-co-hexafluoropropylene; PVDF-HFP) microporous membranes using sulfolane as the diluent. The phase diagram of the PVDF-HFP/sulfolane system was drawn and analyzed. The effects of polymer content in casting solution and cooling rate on the cross-sectional morphology, crystallinity, crystal structure, and porous structure of the resulting membranes were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and a mercury porosimeter, respectively. The mechanical properties of the membranes were evaluated by tensile tests. It was found that a solid-liquid phase separation occurred in the PVDF-HFP/sulfolane system. Spherulites and “net-shaped” structures coexisted in the obtained membranes. Polymer content and cooling rates had some influences on the crystallinity, porous structure, and mechanical properties of the membranes, but no influence on the polymer crystal structure of the membranes. [ABSTRACT FROM AUTHOR]

Abstract: Quasi-solid state dye-sensitized solar cells (DSSCs) were fabricated with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) in methoxy propionitrile (MPN) as gel polymer electrolyte (GPE), tetrabutylammonium iodide (TBAI)/iodine (I2) as redox couple, 4-tertiary butyl pyridine (TBP) as additive and silica nanoparticles as fillers. The energy conversion efficiency of the cell with 5wt% PVDF-HFP is comparable to that one obtained in liquid electrolyte system. Solar cell containing PVDF-HFP with 0.8M of TBAI and 0.12M of I2 shows maximum short-circuit current density (J SC). Further, tertiary butyl pyridine (TBP) has little effect in improving the performance of the solar cell. Moreover, the addition of 1wt% silica nanoparticles is found to improve the at-rest durability and the performance of the solar cell. The transient photovoltage and photocurrent measurements were employed to find out the electron lifetimes in TiO2 electrode with different weight percentages of PVDF-HFP, various concentrations of I2 and durability of the cell storage at 70°C. A photocurrent density of 14.04mAcm−2, an open-circuit voltage of 0.71V, a fill factor of 0.598 and an overall conversion efficiency of 5.97% under 100mWcm−2 was observed for the best performance of a solar cell in this work. [Copyright &y& Elsevier]

Abstract: In the present work, novel gel-based composite polymer electrolytes for lithium batteries were prepared by introducing a hierarchical mesoporous silica network to the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-based gel electrolytes. As compared with the PVDF-HFP-based gel electrolytes with/without conventional nano-sized silica fillers, the novel electrolytes have shown more homogeneous microstructure, higher ionic conductivity and better mechanical stability, which could be caused by the strong silica network and the effective interactions among the polymer, the liquid electrolytes and the silica. Moreover, the cell with this kind of electrolytes could achieve a discharge capacity as much as 150mAhg−1 at room temperature (LiCoO2 as the cathode active material), with high Coulomb efficiency. [Copyright &y& Elsevier]

Abstract: In order to improve the discharge capacity in lithium ion microbatteries, a thick-film cathode was fabricated by a screen printing using LiCoO2 pastes. The printed cathode showed a different discharge curves when the cell was tested using various (liquid, gel and solid-state) electrolytes. When a cell test was performed with organic liquid electrolyte, the maximum discharge capacity was 200μAhcm−2, which corresponded to approximately 133mAhg−1 when the loading weight of LiCoO2 was calculated. An all-solid-state microbattery could be assembled using sputtered LiPON electrolyte, an evaporated Li anode, and printed LiCoO2 cathode films without delamination or electrical problems. However, the highest discharge capacity showed a very small value (7μAhcm−2). This problem could be improved using a poly(vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) gel electrolyte, which enhanced the contact area and adhesion force between cathode and electrolyte. The discharge value of this cell was measured as approximately 164μAhcm−2 (≈110mAhg−1). As the PVDF-HFP electrolyte had a relatively soft contact property with higher ionic conductance, the cell performance was improved. In addition, the cell can be fabricated in a leakage-free process, which can resolve many safety problems. According to these results, there is a significant possibility that a film prepared using the aforementioned paste with screen printing and PVDF-HFP gel electrolyte is feasible for a microbattery. [Copyright &y& Elsevier]

Abstract: The effects of two typical additives, lithium chloride (LiCl) and glycerol, on the fabrication of poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) asymmetric microporous hollow fiber membranes were investigated in terms of membrane morphology, structure, permeation performance, hydrophobicity and mechanical property. The addition of the additives into the dope solution altered the morphology and structure of the resultant membranes, which was believed to be associated with the change of the thermodynamic and kinetic properties of the system in the phase inversion process. The membranes with improved pure water permeability (PWP) from 6.908×10−5 (7) to 4.835×10−4 (49), 3.256×10−4 (33) and 5.003×10−4 L/hm2 Pa (51L/hm2 atm) were obtained when 2wt.% LiCl, 4wt.% LiCl and 10wt.% glycerol was used as the additive, respectively. Among these, the membrane made from the dope containing 4wt.% LiCl possessed the highest retention capability of 40kDa molecular weight cut-off (MWCO). The LiCl or glycerol addition into the polymer dope also made the membranes exhibit a narrow pore size distribution. Moreover, the membrane hydrophobicity was affected less by LiCl and glycerol than by poly(vinyl pyrrolidone) (PVP). The addition of 4wt.% LiCl into the dope could form the membrane with four times stronger strain strength than the poly(vinylidene fluoride) (PVDF) commercial membrane while keeping similar rigidity. [Copyright &y& Elsevier]

In this study, poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) with low crystallinity was applied as the membrane material for pervaporative separating ethyl acetate (EtAc) from its aqueous solutions. The drying conditions during membrane fabrication by means of casting the PVDF-HFP solution dominated the obtained membrane morphologies when the polar solvents such as dimethylacetamide (DMAc) and acetone were used. It was demonstrated that both the DMAc-cast and acetone-cast PVDF-HFP membranes vacuum-dried at 60°C were dense but had different crystalline structures. Predominantly α and γ crystalline phases were found in the acetone-cast and DMAc-cast PVDF-HFP membranes, respectively. And the different pervaporative separating performances of the two solvent-cast PVDF-HFP membranes were well explained in terms of different solution-diffusion properties which were induced from the permeants/polymer interactions on the base of the polarity differences between permeants and the two solvent-cast PVDF-HFP membranes. [Copyright &y& Elsevier]

Abstract: In the present work, poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) asymmetric microporous hollow fiber membranes were successfully fabricated using nonsolvent-induced phase inversion method which has not been reported previously. Analyses of thermodynamic characteristics of the PVDF-HFP/NMP/water system without/with PVP as an additive and the rheological property of the spinning dopes were carried out as a first step. Subsequently, the effects of spinning conditions (wet spinning, air gap, bore fluid composition), dope concentration and PVP addition on the resultant hollow fiber membranes were studied in terms of membrane morphology, structure, pure water flux and molecular weight cut-off (MWCO) as well as their hydrophobicity and mechanical properties. It was found that the wet spinning process produced hollow fibers with irregular inner contour under present experimental conditions. The strong viscoelastic property of PVDF-HFP material was thought to be associated with this phenomenon. A partial release of accumulated back stress in the nascent fibers might have caused the macromolecules to move inward in the transverse direction. Increasing the air gap could eliminate this inner contour deformation, as the outer surface of the nascent fiber was not vitrified prior to entering the water bath, thus allowing the orientated macromolecules to be relaxed. In addition, the nascent fiber is generally expected to experience an elongational stretch over the distance of the air gap, which might help to smooth the inner surface. Membranes made from the PVDF-HFP/NMP dopes were found to have small pure water fluxes no matter what the polymer concentration, the bore fluid composition and the air gap were used in the spinning processes. The pure water flux can be increased by adding PVP into the dope solution, up to 5wt.% PVP in the dope can promote the formation of macrovoids in the membrane. When the PVP content was increased to 10wt.%, the macrovoids were suppressed, but the membrane still presented a higher porosity, which was reflected from the significant increase in the pure water flux from 60 to 107L/(hm2 atm). In addition, PDVF-HFP hollow fiber membranes were more hydrophobic than those membranes made from pure PVDF, the former also exhibited pronounced ductile behavior when compared with the latter. [Copyright &y& Elsevier]

Abstract: We have built TiO2 Dye sensitized solar cells (DSSCs) that combined flexible TiO2 photoanodes coated on ITO/PET substrates with a gel electrolyte based on PVDF–HFP–SiO2 films. Titanium isopropoxide (TiP4) was used as additive to TiO2 nanoparticles for increasing power conversion efficiency in Dye sensitized solar cell electrodes prepared at low-temperature (130°C). An efficiency η AM1.5G =3.55% on ITO/PET substrates is obtained at 48mW/cm2 illumination with a standard liquid electrolyte based on methoxypropionitrile. Among several solvents forming gels with PVDF–HFP–SiO2, N-methyl (pyrrolidone) (NMP) was found to enable the most stable devices. A power conversion efficiency η AM1.5G =2% was obtained under 10mW/cm2 with flexible TiO2–ITO–PET photoanodes and the PVDF–HFP–SiO2 +NMP gel electrolyte. [Copyright &y& Elsevier]

Abstract: The photoelectrochemical characteristics of titanium dioxide (TiO2)-based dye-sensitized solar cells (DSSCs) containing gel polymer electrolyte (GPE) and organic liquid electrolyte (OLE) were studied in detail. GPE was prepared by adding poly(vinyidene fluoride-co-hexafluoro propylene) (PVDF-HFP) to imidazolinium ionic liquids (IILs) of the type, 1-methyl-3-alkyl imidazolinium iodides (alkyl is C n H2 n +1, where n=3–10) in methoxy propionitrile (MPN) and the OLE contained the above molten salt in MPN. The IILs were synthesized in the laboratory and characterized by 1H nuclear magnetic resonance spectroscopy (NMR). The conductivities (σ) of both GPE and OLE decrease with increase in chain length (n) of the alkyl group of IILs; however, the effect is more drastic in the former case. The performance of the DSSCs containing OLE increases with the increase in alkyl chain length of IIL from C3 to C7, whereas, there is a linear decrease in the efficiency of the DSSCs incorporated with GPE containing IIL of alkyl chain length from C3 to C10. The change in short circuit current density (J SC) determines the cell efficiency as the V OC of the DSSCs remains almost the same with increase of alkyl chain length of IILs for both the electrolytes. The change in J SC values and the consistency of the V OC of the DSSCs for both the electrolytes may be explained on the basis of increase in viscosity of IILs from C3 to C10 and the dominating role of the 4-tertiary butyl pyridine (TBP), respectively, on the phenomenon of charge recombination. [Copyright &y& Elsevier]

Abstract: Molecular sieves of NaY, MCM-41, and SBA-15 were used as fillers in a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer matrix to prepare microporous composite polymer electrolyte. The SBA-15-based composite polymer film was found to show rich pores that account for an ionic conductivity of 0.50mScm−1. However, the MCM-41 and NaY composite polymer films exhibited compact structure without any pores, and the addition of MCM-41 even resulted in aggregation of fillers in the polymer matrix. These differences were investigated and interpreted by their different compatibility with DMF solvent and PVdF-HFP matrix. Results of linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) have revealed that the addition of SBA-15 has extended the electrochemical stability window of polymer electrolyte, enhanced the interfacial stability of polymer electrolyte with lithium electrode, and inhibited also the crystallization of PVdF-HFP matrix. Half-cell of Li/SBA-15-based polymer electrolyte/MCF was assembled and tested. The results have demonstrated that the coulombic efficiency of the first cycle was around 87.0% and the cell remains 94.0% of the initial capacity after 20 cycles, which showed the potential application of the composite polymer electrolyte in lithium ion batteries. [Copyright &y& Elsevier]

Abstract: A novel process was proposed for preparation of microporous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) membranes by phase inversion techniques using water as the non-solvent. Being prepared by dissolving the polymer (PVDF–HFP) in the acetone/water solution with mechanical stirring, the homogenous casting solution was cast onto a clean glass plate. The microporous membranes were directly obtained after the evaporation of the solvent. Their porosities reached 70–90%. The test cells with the gel electrolytes prepared from as-prepared microporous membranes showed stable cycling capacities, indicating that the microporous membrane can be used for the gel electrolyte of lithium batteries. [Copyright &y& Elsevier]

Abstract: A micro-porous polymer blend electrolyte based on polyvinylidene fluoride-co-hexa fluoropropylene (PVdF-co-HFP) and polyacrylonitrile (PAN) was prepared by phase inversion technique with different compositions. The ionic conductivity of micro-porous polymer blend electrolyte films were studied by varying the PAN content in the (PVdF-co-HFP) matrix. It was observed that the ionic conductivity of micro-porous polymer blend electrolyte increases with increase in PAN content. The effect of lithium salt concentrations was studied for the micro-porous polymer blend electrolyte by measuring the conductivity at different temperatures in the range of 301–353K. The micro-porous polymer blend electrolyte was subjected to XRD, SEM and TG/DTA analysis to determine the amorphosity nature, surface morphology and thermal stability of the polymer electrolyte, respectively. Linear sweep voltammetry and dc-polarization studies were also performed to find the stability and lithium transference number of micro-porous polymer blend electrolyte, respectively. Finally, charge–discharge studies were carried out in an assembled cell with carbon anode and LiSr0.25Mn1.75O4 cathode and micro-porous polymer blend electrolyte in between the above electrodes. [Copyright &y& Elsevier]

Abstract: Composition of polyacene (PAS)-based negative electrode has been optimized to be suitable for rechargeable battery systems with polymeric gel electrolytes. The gel electrolytes consisted of poly(vinylidenefluoride-co-hexafluoropropylrne) (PVdF-HFP) as a host polymer, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) as a plasticizer, and LiX (X=ClO4 or (C2F5SO2)2N) as a carrier salt. Three types of composite PAS electrodes were prepared and their compatibility with the polymeric gel electrolytes was examined. A half cell assembled with the composite PAS electrode containing proper amounts of polymeric gel and the electrolyte film with the same gel composition showed good cycling characteristics. The gel composition containing 1.0moldm−3 (M) Li(C2F5SO2)2N/(EC+DEC) gave discharge capacity of about 600Ahkg−1 (with respect to the mass of PAS) with high rechargeability. [Copyright &y& Elsevier]

A novel composite microporous polymer electrolyte composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and mesoporous SBA-15 was pre- pared. The composite solid polymer electrolyte (CSPE) exhibits ionic conductivity as high as 0.30 mS·cm-1 with a composition of SBA-15 : PVdF-HFP=3 : 8 at room temperature. Infrared transmission spectroscopic results suggested that the mechanism of micropore formation is similar to that of the phase inversion. X-ray diffraction (XRD) results demonstrated that the addition of SBA-15 inhibits the crystallization of PVdF-HFP, while the SBA-15 preserves well its ordered mesoporous structure during the course of preparation. The Li/CSPE/MCF of half-cell was assembled, and it showed a good electrochemical and cyclability performance during charge-discharge cycles. [ABSTRACT FROM AUTHOR]

A novel solid polymer electrolyte (pore-gel SPE) has been found to provide superior SPE having a high conductivity, good mechanical strength and low solution leakage. This pore-gel SPE was prepared from gelation in pores of polymer membrane with electrolyte solution including solvent. The conductivity of pore-gel type PVDF-HFP/ TEABF4 (Tetraethylammomium tetrafluoroborate) membrane can reach 1.6×10-1 Scm-1. The tensile strength of this membrane was 4,000 kPa, which is about 23 times larger than that of gel-type SPE with the same composition. Poregel SPE reduced solution leakage to 0%, compared with 2% of hybrid-type SPE after 2.0 hr leakage test in PVDFHFP/ TEABF4 membrane. [ABSTRACT FROM AUTHOR]

Solvent evaporation rate, ionic conductivity, and photovoltaic response were used to compare a traditional organic liquid electrolyte to a gel electrolyte and a nanocomposite gel electrolyte consisting of poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) and 12.5 wt.% synthetic layered silicate particles. The addition of layered silicate nanoparticles to the pure gel electrolyte markedly increased solvent retention and improved mechanical strength. The nanocomposite gel electrolyte had a conductivity of 2.6 × 10-3 S/cm and a power conversion efficiency matching that of the liquid electrolyte. [Copyright &y& Elsevier]

A novel polymer electrolyte composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(vinyl pyrrolidone) (PVP), ethylene carbonate (EC), dimethyl carbonate (DMC), and LiBF4 salts has been prepared. The transport properties were measured including the conductivity, the salt diffusion coefficient, and the lithium ion transference number. The polymer electrolyte based on the blend of PVDF-HFP and PVP exhibited ionic conductivity of 0.4 mS cm−1 at room temperature when PVP:PVDF-HFP:liquid electrolyte was about 1:10:18 by weight. The salt diffusion coefficient, cation transference number, and electrochemical window were determined by restricted diffusion experiment, steady state polarization, and linear sweep voltammetry method, respectively. The lithium ion battery with the polymer electrolyte based on the blend of PVDF-HFP and PVP was assembled and the initial coulombic efficiency was about 90%. [Copyright &y& Elsevier]

γ-LiAlO2, Al2O3 and MgO were used as fillers in a PVdF-HFP polymer matrix to form self-standing, intrinsically porous separators for lithium-ion batteries. These separators can be hot-laminated onto the electrodes without losing their ability to adsorb liquid electrolyte. The electrochemical stability of the separators was tested by constructing half-cells with the configuration: Li/fibre-glass/filler-based separator/electrode. MgO-based separators were found to work well with both positive and negative electrodes. An ionic conductivity of about 4×10−4 S cm−1 was calculated for the MgO-based separator containing 40% 1 M solution of LiPF6 in an EC/DMC 1:1 solvent. Self-standing, lithium-ion cells were constructed using the MgO-based separator and the resulting battery performance evaluated in terms of cyclability, power and energy density. [Copyright &y& Elsevier]

Poly (vinylidene fluoride) (PVDF) and its copolymers have piqued a substantial amount of research interest for its use in modern flexible electronics. The piezoelectric β -phase of the polymers can be augmented with the addition of suitable fillers that promote β -phase nucleation. In this work, we report an improved output voltage response of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with the incorporation of 10 wt.% Titanium (IV) oxide nanoparticles into the polymer matrix. The nano-filler was dispersed in the polymer matrix to form nanocomposite films via the solution casting technique. X-ray Diffraction and Scanning Electron Microscopy measurements were performed to verify the structure and morphology of the films. Fourier Transform Infrared Spectroscopy revealed enhancement in the β -phase nucleation from ∼15% to ∼36% with the addition of 10 wt.% titania nanoparticles. Thermogravimetric analysis and Differential Scanning Calorimetry results show improved thermal stability of the nanocomposite film, up to 345 °C, as compared to pristine PVDF-HFP. We also demonstrate a facile method for the fabrication of a piezoelectric nanogenerator with β -PVDF-HFP/TiO 2 nanocomposite as an active layer. The outputs from the fabricated nanogenerator reached up to 8.89 V through human finger tapping motions, paving way for its potential use in the field of sensors, actuators, and self-sustaining flexible devices., (© 2022 IOP Publishing Ltd.)

Anti-icing or passive strategies have undergone a remarkable growth in importance as a complement for the de-icing approaches or active methods. As a result, many efforts for developing icephobic surfaces have been mostly dedicated to apply superhydrophobic coatings. Recently, a different type of ice-repellent structure based on slippery liquid-infused porous surfaces (SLIPS) has attracted increasing attention for being a simple and effective passive ice protection in a wide range of application areas, especially for the prevention of ice formation on aircrafts. In this work, the electrospinning technique has been used for the deposition of PVDF-HFP coatings on samples of the aeronautical alloy AA7075 by using a thickness control system based on the identification of the proper combination of process parameters such as the flow rate and applied voltage. In addition, the influence of the experimental conditions on the nanofiber properties is evaluated in terms of surface morphology, wettability, corrosion resistance, and optical transmittance. The experimental results showed an improvement in the micro/nanoscale structure, which optimizes the superhydrophobic and anticorrosive behavior due to the air trapped inside the nanotextured surface. In addition, once the best coating was selected, centrifugal ice adhesion tests (CAT) were carried out for two types of icing conditions (glaze and rime) simulated in an ice wind tunnel (IWT) on both as-deposited and liquid-infused coatings (SLIPs). The liquid-infused coatings showed a low water adhesion (low contact angle hysteresis) and low ice adhesion strength, reducing the ice adhesion four times with respect to PTFE (a well-known low-ice-adhesion material used as a reference). [ABSTRACT FROM AUTHOR]

ZnS is one of the typical representative materials of II-VI direct bandgap semiconductors, and its photoluminescence (PL), mechanoluminescence (ML), and electroluminescence (EL) have already been extensively studied. Herein, ZFP + PU/PVDF composite fibers based on ZnS:Cu phosphors were fabricated for low-temperature lighting monitoring sensor devices, whose long-afterglow luminescent light-emitting process went from slowly brighter to slowly dim as the temperature changed. Impressively, the shell-core structure of ZnS doped with PVDF-HFP particles (ZFP particles) can enhance the light intensity duration by up to 100 s. Different from the pure ZnS:Cu phosphors, the luminescence mechanism of ZFP particles was the synergy of the piezoelectric effect in addition to the stimulating effect of temperature. Otherwise, using PU/PVDF as a substrate can endow the fiber with good flexibility, elasticity, and mechanical properties. Then, to confirm whether the shape changes affect the luminescence, the device of the ropes and fabrics woven by the fibers were further characterized. The results suggested that the tightness of the devices was an extrinsic factor influencing luminous intensity. In summary, this study presents a new luminescence concept with profound research prospects. [Display omitted] • A novel long-afterglow luminescence composite fiber was fabricated. • The fiber with long-afterglow luminescence happened in ultra-low temperature. • The fiber has good flexibility, elasticity and mechanical properties. • Various light-emitting devices were woven by the fiber. [ABSTRACT FROM AUTHOR]

CQDs doped PVDF-HFP film with porous structure was firstly fabricated for self-powered flexible piezoelectric sensors. [Display omitted] • Carbon quantum dots (CQDs) doped PVDF-HFP film was firstly fabricated for self-powered flexible piezoelectric sensors (FPS). • The content of β phase in the PVDF-HFP/CQDs film is improved by 14.4 % compared with that in the PVDF-HFP film. • PVDF-HFP/CQDs based FPS exhibit better sensitivity (36.6 mV/g) than PVDF-HFP (25.7 mV/g) with good linearity (R2 > 99 %). • The FPS show excellent mechanical stability under repeated dynamic loading. • Some potential applications of the PVDF-HFP/CQDs based self-powered FPS were explored. Flexible piezoelectric sensors (FPS) have been widely applied to intelligent robot, human/machine interaction and human health measurement system, etc. To improve the piezoelectric performance of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), carbon quantum dots (CQDs) were introduced to form PVDF-HFP/CQDs piezoelectric film. Owing to their large specific surface area (96.3 m²/g) and abundant surface defects, CQDs provide mass potential induced active points for the formation of β phase in PVDF-HFP, and rich surface functional groups (COOH, OH and NH 2 , etc) which could promote chemical bond with PVDF-HFP. The content of β phase in the PVDF-HFP/CQDs film is increased by 14.4 % compared with that in the PVDF-HFP film. Thereby, PVDF-HFP/CQDs based FPS exhibit better sensitivity (36.6 mV/g) than PVDF-HFP based FPS (25.7 mV/g) with good linearity (R2 > 99 %). Besides, the FPS show excellent mechanical stability under repeated dynamic loading. On this basis, some potential applications of the PVDF-HFP/CQDs based self-powered FPS were explored, including anti-touch alarm system, finger bending detection, voice recognition and vibration monitoring. [ABSTRACT FROM AUTHOR]

Solid polymer electrolytes are potential replacement of liquid electrolytes due to their much less flammability and leakage. Among them, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based electrolytes have several advantages including improved processability and electrochemical stability. Unfortunately, poor ionic conductivity and mechanical properties due to high plasticizer concentration hinder their practical applications. Herein, we address these issues by exploiting the solvation effect in the electrolyte through tuning the amount of residual N-methyl-2-pyrrolidone (NMP) and lithium salts. Moreover, by blending with porous carbon (PC) the mechanical integrity of the PVDF-HFP electrolytes is substantially enhanced due to improved interfacial bonding and specific surface area. The appropriate value of electrical conductivity and highly porous morphology of PC also meet the ionic transport and electronic insulation requirements. With the absorbed residual NMP as plasticizer and complexed with Li ions to form L i [ N M P ] 3 + , ionic conductivity and amorphicity are improved. By elucidating the solvent and salt concentration interplay, Li-ion conductivity of up to 0.56 mS cm−1, wide electrochemical window of 5 V versus Li/Li+ and 1000 h of cycling stability (versus Li, 0.2 mA/cm2) are obtained. These findings afford a novel electrolyte design guideline for enhancing interfacial compatibility and cycling through hybridization and ion solvation to develop practical lithium batteries. [Display omitted] • Solvation and plasticizer effect of NMP improve electrochemical performance. • Better performance is achieved due to the synergistic effect with porous carbon. • Composite polymer electrolyte with high ionic conductivity of 0.56 mS cm−1 at RT. • Symmetric lithium system shows good cycling stability and long life (over 1000 h). • Transfer number measured accurately via regulating the interfacial impedance. [ABSTRACT FROM AUTHOR]

The demand for more efficient energy storage devices has led to the exponential growth of lithium-ion batteries. To overcome the limitations of these systems in terms of safety and to reduce environmental impact, solid-state technology emerges as a suitable approach. This work reports on a three-component solid polymer electrolyte system based on poly(vinylidene fluoride- co -hexafluoropropylene) (PVDF-HFP), the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), and clinoptilolite zeolite (CPT). The influences of the preparation method and of the dopants on the electrolyte stability, ionic conductivity, and battery performance were studied. The developed electrolytes show an improved room temperature ionic conductivity (1.9 × 10 -4 S cm -1 ), thermal stability (up to 300 °C), and mechanical stability. The corresponding batteries exhibit an outstanding room temperature performance of 160.3 mAh g -1 at a C/15-rate, with a capacity retention of 76% after 50 cycles. These results represent a step forward in a promising technology aiming the widespread implementation of solid-state batteries.