Poly Vinilydene Fluoride Research Articles

New Formulations of High-Voltage Cathodes for Li-Ion Batteries with Water-Processable Binders

While not electrochemically active, the binder still remains a component of great importance in the electrodes for lithium-ion batteries, as it has a strong influence on their performance. Polyvinilydene fluoride (PVdF) is the most employed binder, thanks to its electrochemical stability and good adhesive properties. However, PVdF is expensive, not readily disposable, and requires the use of organic solvents, such as N-methyl-2-pyrrolidone (NMP), which is also very expensive as well as harmful to health and environment [1]. The use of water-soluble binders could lower production costs and grant an easier and more environment-friendly processing. Although carboxy-methyl-cellulose (CMC) is the most investigated aqueous binder for lithium-ion batteries, many other promising materials are under study [2]. This work investigates the use of two water-soluble binders, namely poly vinyl acetate (PVAc) and sodium alginate, for high-voltage cathode electrodes in Li-ion batteries. PVAc, commercially available under the Vinavil trademark, is an inexpensive synthetic polymer, employed in a wide variety of industrial applications [3]; it was previously investigated by P. Prosini et al. as binder for Li-ion batteries [4, 5], and the published results encouraged further studies. Sodium alginate is a high-modulus, natural polysaccharide commonly extracted from brown algae. It has a peculiar composition since it contains carboxylic groups in each polymer’s monomeric unit. It was also extensively studied as binder for both anodes and cathodes with very promising results [6, 7]. We focused our work on the use of sustainable binders for cathodes based on LiNi0.5Mn1.5O4 (LNMO), a commercially available material with a very high Li+ deinsertion/insertion potential of 4.7-4.75 V versus Li+/Li and a theoretical specific capacity of 147 mAh/g. These properties account for the highest energy density of any material currently available on the market [8]. The present study reports the morphological and structural characterizations carried out on the LNMO-based composite materials and the electrochemical tests at 30°C on the corresponding electrodes assembled in half-cells versus Li/Li+ in conventional electrolyte (EC/DMC – LiPF6). The electrochemical performance of cathodes with PVAc and alginate binders are compared with those obtained with PVdF-based electrodes. While the results obtained for PVAc-based composite material should be improved, the alginate-based material shows very promising electrochemical results, comparable or even better than those of PVdF-based materials. Acknowledgements The authors wish to thank ENEA and Italy’s Ministero dello Sviluppo Economico for financial support under the Program “Electric System Research”, Cathode Materials for High Energy Lithium Ion Batteries.

Concentration of olive mill wastewater by membrane distillation for polyphenols recovery

The possibility of olive mill wastewaters (OMW) treatment and concentration by membrane distillation has been investigated. The objective is to obtain pure water and a concentrate containing high amounts of polyphenols, which can be extracted later. Two types of commercial membranes, polytetrafluoroethylene (TF200) and polyvinilydene fluoride (GVHP), were tested and the effects of membrane parameters on direct contact membrane distillation (DCMD) performance (i.e. permeate flux and polyphenols retention) were studied. The effects of different DCMD operating parameters were also investigated. The obtained results demonstrated the efficiency of DCMD for OMW treatment and concentration. The membrane TF200 showed a better separation coefficient (99%) after 9 h of DCMD operation than the membrane GVHP (89%) and the corresponding OMW concentration factor was found to be 1.72 for the membrane TF200, whereas it was only 1.4 for the GVHP membrane after 9 h operating time.

Combined Emulsion and Phase Inversion Techniques for the Preparation of Catalytic PVDF Microcapsules

In this work, polyvinilydene fluoride (PVDF) microcapsules were prepared by using combined emulsion and phase inversion techniques. With this method, microcapsules with different diameters and porosities have been obtained by just controlling the diameter of the membrane used during the preparation. Using a PVDF solution containing the oxidation catalyst ammonium molybdate (20 wt %), catalytic polymeric microcapsules with diameters ranging from 600 to 1,200 microm have been obtained. Characterization of catalytic microcapsules by means of SEM, BSE, and EDX analyses showed a uniform ammonium molybdate dispersion in the polymeric matrix. Catalytic microcapsules have been tested in the oxidation of aromatic primary alcohols to corresponding aldehydes. In the range 600-1,200 microm, the microcapsule diameter influences the formation of oxidation products: in particular, microcapsule diameters >900 microm slightly diminish the formation of aldehyde due to a beginning diffusion limitation. An interesting structure-reactivity behavior, induced by the interaction between the polymeric membrane and the substituted aromatic alcohol, has been observed.

Characterization of pyroelectric detectors between 170 and 300 K using the photopyroelectric technique

In this article, we perform a full characterization of the thermal properties of photopyroelectric detectors in a wide temperature range. Within the experimental uncertainties, the results on lithium tantalate are consistent with results from literature. The thermal properties of polyvinilydene fluoride have a complex behavior.

Fouling and protein adsorption effect of low-temperature plasma treatment of membrane surfaces

Adsorption of proteins and the effect of the chemical nature of membrane surfaces on protein adsorption were investigated using 14C-tagged albumin and several microporous membranes (polyvinilydene fluoride, PVDF; nylon; polypropylene, PP; and polycarbonate, PC). The membrane surfaces were modified by exposing them to low-temperature plasma of several different monomers (n-butane, oxygen, nitrogen alone or as mixtures) in a radiofrequency plasma reactor. Transients in the permeability of albumin solutions through the membranes and changes in flux of distilled water through the membranes before and after adsorption of albumin were used to investigate the role of protein adsorption on membrane fouling. The results show that the extent of adsorption of albumin on hydrophobic membranes was considerably more than that on hydrophilic membranes. The hydrophilic membranes were susceptible to electrostatic interactions and less prone to fouling. A pore-blocking model was successfully used to correlate the loss of water flux through pores of defined geometry.

Radiation effects of keV-MeV ion irradiated PVDF

Polyvinilydene fluoride (PVDF) is a fluoropolymer very useful in the manufacture of synthetic bio-membranes through processes of ion energy deposition. Semicrystalline PVDF, irradiated with different ions in the range 100 keV-100 MeV, exhibits a strong change of crystalline structure, as detected by X-ray diffraction measurements as well as calorimetric analysis. PVDF ion irradiation produces a strong molecular emission for masses 2, 19 and 20, as detected “in situ” by a mass quadrupole spectrometer. At low ion doses, in the range 100–300 kGy, the diffraction analyses show a structure reordering along the (020) atomic plane. At high ion doses, the fluoropolymer shows a degradation of the crystalline structure which consists in radiation damage, reduction of hydrogen and fluorine concentration and formation of carbon reticulation. A phenomenological model, based on the ion track picture, is proposed to explain the experimental data.

Shock profile induced by short laser pulses

Standard 25-μm-thick polyvinilydene fluoride (PVDF) piezoelectric gauges and new 450-μm-thick P(VDF 70%, TrFE 30%) piezoelectric copolymer have been used to record shock profiles at the back face of metallic targets irradiated by laser pulses of 2.5 and 0.6 ns duration at a 1.06 μm wavelength. The records are fully explained with simplified space–time diagram analysis. The pressure profile applied at the front face of the target has been determined from these records combined with numerical simulations of wave propagation through the target. A numerical code describing the interaction of laser with matter (FILM) has also been used for computing the applied pressure. Both methods lead to very close results. The peak pressure dependence on incident laser intensity is determined up to 30 GPa at 1012 W/cm2.

Vibration of symmetrically layered discs having layer dependent in-plane rotations

In recent work on layered discs either constant in-plane rotations or an inner layer that can only support shear and outer layers that cannot support shear have been considered. This paper is concerned with the case of layer dependent in-plane rotations for discs having three symmetrical layers. Two substantially different materials are considered, steel and the polymer PVDF (polyvinilydene fluoride). By using Galerkin's method, results are obtained for natural frequencies and for the in-plane rotations.