Poly Vinylidene Fluoride-hexafluoropropylene Copolymer Research Articles

Synthesis and Properties of Polyvinylidene Fluoride-Hexafluoropropylene Copolymer/Li6PS5Cl Gel Composite Electrolyte for Lithium Solid-State Batteries.

Gel electrolytes for lithium-ion batteries continue to replace the organic liquid electrolytes in conventional batteries due to their advantages of being less prone to leakage and non-explosive and possessing a high modulus of elasticity. However, the development of gel electrolytes has been hindered by their generally low ionic conductivity at room temperature and high interfacial impedance with electrodes. In this paper, a poly (vinylidene fluoride)-hexafluoropropylene copolymer (PVdF-HFP) with a flexible structure, Li6PS5Cl (LPSCl) powder of the sulfur-silver-germanium ore type, and lithium perchlorate salt (LiClO4) were prepared into sulfide gel composite electrolyte films (GCEs) via a thermosetting process. The experimental results showed that the gel composite electrolyte with 1% LPSCl in the PVdF-HFP matrix exhibited an ionic conductivity as high as 1.27 × 10-3 S·cm-1 at 25 °C and a lithium ion transference number of 0.63. The assembled LiFePO4||GCEs||Li batteries have excellent rate (130 mAh·g-1 at 1 C and 54 mAh·g-1 at 5 C) and cycling (capacity retention was 93% after 100 cycles at 0.1 C and 80% after 150 cycles at 0.2 C) performance. This work provides new methods and strategies for the design and fabrication of solid-state batteries with high ionic conductivity and high specific energy.

Designing a multi-stage MoS2 fiber membrane for photothermal membrane distillation

Among the various desalination technologies, membrane distillation (MD) stands out for its high salt rejection, low operating temperature and operating pressure. Photothermal membrane distillation (PMD) represents an innovative approach to membrane distillation (MD), wherein the process harnesses plentiful and renewable solar energy to achieve localized heating at the interface between the membrane and the feed solution. This is achieved by employing photothermal materials, eliminating the need for heating a substantial volume of the feed solution. This study has prepared membranes with micro/nano fiber interwoven structure based on polystyrene (PS) and polyvinylidene fluoride hexafluoropropylene copolymer (PVDF-HFP) by electrospinning technology, and constructed multi-stage MoS2 photothermal fiber membranes by hydrothermal growth process. The PS/PVDF-HFP micro/nano fiber membrane possesses a spacious pore structure and high porosity, serving as a robust framework that facilitates swift transport of water vapor. The MoS2 nanoflowers uniformly grown on the micro/nano fibers have both metal 1T and semiconductor 2H phases, which facilitate the absorption of sunlight, reaching an average absorbance of 90.9 % in the240-2600 nm wavelength range. Under 1 kW m−2 solar illumination, the surface temperature of the PS/PVDF-HFP/MoS2 membrane could be raised to 74.2 °C after 120 s. The permeate flux was stable at 1.21 ± 0.02 L m−2 h−1 within 20 h PMD. The membrane showcased a salt rejection rate of 99.96 % and achieved an energy efficiency of 72.08 %. This suggests that the multi-stage MoS2 photothermal fiber membrane, characterized by remarkable stability and high photothermal conversion efficiency, lays a solid foundation for advancing research in the field of PMD applications.

Fabrication of PS/PVDF-HFP Multi-Level Structured Micro/Nano Fiber Membranes by One-Step Electrospinning.

Recently, the multi-level interwoven structured micro/nano fiber membranes with coarse and fine overlaps have attracted lots of attention due to their advantages of high surface roughness, high porosity, good mechanical strength, etc., but their simple and direct preparation methods still need to be developed. Herein, the multi-level structured micro/nano fiber membranes were prepared novelly and directly by a one-step electrospinning technique based on the principle of micro-phase separation caused by polymer incompatibility using polystyrene (PS) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) as raw materials. It was found that different spinning fluid parameters and various spinning process parameters will have a significant impact on its morphology and structures. Under certain conditions (the concentration of spinning solution is 18 wt%, the mass ratio of PS to PVDF-HFP is 1:7, the spinning voltage is 30 kV, and the spinning receiving distance is 18 cm), the PS/PVDF-HFP membrane with optimal multi-level structured micro/nano fiber membranes could be obtained, which present an average pore size of 4.38 ± 0.10 μm, a porosity of 78.9 ± 3.5%, and a water contact angle of 145.84 ± 1.70°. The formation mechanism of micro/nano fiber interwoven structures was proposed through conductivity and viscosity tests. In addition, it was initially used as a separation membrane material in membrane distillation, and its performance was preliminarily explored. This paper provides a theoretical and experimental basis for the research and development of an efficient and feasible method for the preparation of multi-level micro/nano fiber membranes.

Optimization of cathode microporous layer materials for proton exchange membrane fuel cell

The microporous layer (MPL) of diffusion medium has an important impact on the water management ability of proton exchange membrane fuel cells. In this study, six kinds of carbon black were used to prepare the cathode MPL. The thickness, conductivity, pore structure, hydrophobicity, and surface microstructure of MPL were characterized. The single cell was prepared and electrochemical tests were performed. The results showed that the single cell prepared by Acetylene black (ACET) and Vulcan XC-72R has a considerable power generation performance. In addition, polyvinylidene fluoride hexafluoropropylene copolymer P(VDF-HFP) was used to replace Polytetrafluoroethylene (PTFE) as hydrophobic binder. MPL with different P(VDF-HFP) contents were prepared, and the single cell performance was investigated. The results showed that all the single cells prepared by P(VDF-HFP) were worse than that of PTFE. This study provides an important reference for further improving the performance of fuel cells from the perspective of material optimization with MPL.

A design of Nafion-coated bilayered quasi-solid electrolyte for lithium-O2 batteries with high performance

In this paper, a novel bilayer-structured quasi-solid polymer electrolyte (NSPE) has been designed with separate catholyte and anolyte, which compose of P(VDF-HFP)/Li-Nafion solid polymer electrolyte and TEMPO as cathodic additives. The SEM images shows that the surface morphology of NSPE is smoother and more uniform than that of SPE. The Li-O2 battery using NSPE showed high ionic conductivity, low interface impedance, good rate performance, and higher security and good cycling stability while reducing polarization. Lithium-air (also known as lithium-oxygen) batteries have attracted considerable global attention in recent years due to their extremely high energy density (11,140 W·h·kg −1 ). The electrolyte is a key element in lithium-air batteries and the traditional organic electrolyte has great safety risk due to leakage. On the contrary, the polymer electrolyte has the advantages of high safety, high stability and easy processing comparing with the organic liquid electrolytes. In this paper, a new idea was proposed to coat the Nafion membrane on a layer of polymer for blocking the oxidation reduction electric (RM) and Li based on the selective permeability on lithium ion of the Nafion membrane. Self-made thickness-controllable Nafion membrane, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and 2,2,6,6-tetramethylpiperidinooxy (TEMPO) were used to prepare a quasi solid polymer electrolyte (NSPE). Electrochemical workstation and LAND battery testing system were used to perform a galvanostatic charge/discharge test on Li-O 2 . The ionic conductivity of NSPE was 4.3 × 10 −4 S·cm −1 at room temperature and the discharge platform was 2.6 V and the charging voltage was 3.7 V after 50 cycles with the cut-off capacity of 500 mA·h·g −1 .

Hybrid membranes based on sulfated titania nanoparticles as low-cost proton conductors

This work reports on a novel, hybrid solid-state membrane based on sulfated titania nanoparticles stabilized by a polyvinylidene fluoride–hexafluoropropylene copolymer. A fast solvent-casting technique was adopted as a valid alternative to a fully dry, hot-pressing preparation procedure. Self-standing, flexible membranes with high proton conductivity were obtained.

New, ionic liquid-based membranes for lithium battery application

New types of dimensionally stable, flexible gel-type electrolyte membranes with a relatively wide electrochemical stability, high lithium ion conductivity and other desirable properties have been prepared by immobilizing N- n-butyl- N-ethylpyrrolidinium N, N-bis(trifluoromethane)sulfonimide-lithium N, N-bis(trifluoromethane)sulfonimide (Py 24TFSI-LiTFSI), ionic liquid, IL, solutions in a poly(vinylidene fluoride)-hexafluoropropylene copolymer (PVdF-HFP) matrix. The addition of a discrete amount of ethylene and propylene carbonate (EC–PC), solvent mixture to the membranes resulted in an improvement of the ionic conductivity and in a stabilization of the interface with the lithium electrode. These IL-based gel type membranes can operate without degradation up to a temperature of 110 °C where they reach conductivity values of the order of 10 −2 S cm −1. All these properties make these polymer electrolyte membranes of interest for applications as separators in advanced lithium batteries.

Novel Microporous Poly(vinylidene fluoride) Blend Electrolytes for Lithium‐Ion Batteries

In the present paper, novel microporous poly(vinylidene fluoride)‐hexafluoropropylene copolymer (PVDF-HFP) blend electrolyte/electrode films were obtained as the result of phase separation between PVDF-HFP and polyethylene oxide (PEO) oligomer additives, which were cast from a common solvent. Upon solvent evaporation and removal of the additives, an interconnected microporous morphology was formed. The additives can either be removed from the films by vacuum evaporation or methanol extraction. The conductivities of the methanol extracted microporous (pore sizes range from 1 to 5 μm) films formed from PVDF-HFP/PEO oligomer blends after electrolyte activation are more than 70% higher than those of the methanol extracted nanoporous (pore size in range from 10 to 100 nm) films prepared from PVDF-HFP/dibutyl phthalate blends. Microporous films formed by vacuum evaporation had conductivities similar to solvent extracted nanoporous separators. Battery performance tests were carried out using lithium cobalt dioxide as the cathode and mesocarbon microbeads as the anode. The cells prepared using extracted microporous PVDF-HFP/PEO oligomer blend films as separators show more than 40% higher specific discharge capacity at the C/2 rate, and 70% higher rate capability than those using extracted nanoporous separators. © 2000 The Electrochemical Society. All rights reserved.