A novel high-performance gel polymer electrolyte membrane basing on electrospinning technique for lithium rechargeable batteries

Nonwoven films of composites of thermoplastic polyurethane (TPU) with different proportion of poly(vinylidene fluoride) (PVdF) (80, 50 and 20%, w/w) are prepared by electrospinning 9 wt% polymer solution at room temperature. Then the gel polymer electrolytes (GPEs) are prepared by soaking the electrospun TPU-PVdF blending membranes in 1 M LiClO₄/ethylene carbonate (EC)/propylene carbonate (PC) for 1 h. The gel polymer electrolyte (GPE) shows a maximum ionic conductivity of 3.2 × 10⁻³ S cm⁻¹ at room temperature and electrochemical stability up to 5.0 V versus Li⁺/Li for the 50:50 blend ratio of TPU:PVdF system. At the first cycle, it shows a first charge-discharge capacity of 168.9 mAh g⁻¹ when the gel polymer electrolyte (GPE) is evaluated in a Li/PE/lithium iron phosphate (LiFePO₄) cell at 0.1 C-rate at 25 °C. TPU-PVdF (50:50, w/w) based gel polymer electrolyte is observed much more suitable than the composite films with other ratios for high-performance lithium rechargeable batteries.     

Preparation and characterization of electrospun poly(acrylonitrile) fibrous membrane based gel polymer electrolytes for lithium-ion batteries

Electrospun, non-woven membrane of high molecular weight poly(acrylonitrile) (PAN) is demonstrated as an efficient host matrix for the preparation of gel polymer electrolytes for lithium-ion batteries. Electrospinning process parameters are optimized to get a fibrous membrane of PAN consisting of bead-free, uniformly dispersed thin fibers with diameter in the range 880-1260 nm. The membrane with good mechanical strength and porosity exhibits high uptake when activated with the liquid electrolyte of 1 M LiPF₆ in a mixture of organic solvents and the gel polymer electrolyte shows ionic conductivity of 1.7 × 10⁻⁵ S cm⁻¹ at 20 °C. Electrochemical performance of the gel polymer electrolyte at 20 °C is evaluated in lithium-ion cell with lithium cobalt oxide cathode and graphite anode. Good performance with a low capacity fading on charge-discharge cycling is demonstrated.     

Electrical and electrochemical studies of poly(vinylidene fluoride)-clay nanocomposite gel polymer electrolytes for Li-ion batteries

A study is conducted on the electrical and electrochemical properties of nanocomposite polymer electrolytes based on intercalation of poly(vinylidene fluoride) (PVdF) polymer into the galleries of organically modified montmorillonite (MMT) clay. A solution intercalation technique is employed for nanocomposite formation with varying clay loading from 0 to 4 wt.%. X-ray diffraction results show the β phase formation of PVdF on intercalation. Transmission electron microscopy reveals the formation of partially exfoliated nanocomposites. The nanocomposites are soaked with 1 M LiClO₄ in a 1:1 (v/v) solution of propylene carbonate (PC) and diethyl carbonate (DEC) to obtain the required gel electrolytes. The structural conformation of the nanocomposite electrolytes is examined by Fourier transform infrared spectroscopy analysis. Examination with a.c. impedance spectroscopy reveals that the ionic conductivity of the nanocomposite gel polymer electrolytes increases with increase in clay loading and attains a maximum value of 2.3 × 10⁻³ S cm⁻¹ for a 4 wt.% clay loading at room temperature. The same composition exhibits enhancement in the electrochemical and interfacial properties as compared with that of a clay-free electrolyte system.     

Polymer electrolytes based on an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) membrane for lithium batteries

Electrospinning parameters are optimized for the preparation of fibrous membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} that consist of layers of uniform fibres of average diameter 1 μm. Electrospinning of a 16 wt.% solution of the polymer in acetone/N,N-dimethylacetamide (DMAc) (7/3, w/w) at an applied voltage of 18 kV results in obtaining membranes with uniform morphology. Polymer electrolytes (PEs) are prepared by activating the membrane with liquid electrolytes. The fully interconnected porous structure of the host polymer membrane enables high electrolyte uptake and ionic conductivities of 10⁻³ S cm⁻¹ order at 20 °C. The PEs have electrochemical stability at potentials higher than 4.5 V versus Li/Li⁺. A PE based on a membrane with 1 M LiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC), which exhibits a low and stable interfacial resistance on lithium metal, is evaluated for discharge capacity and cycle properties in Li/LiFePO₄ cells at room temperature and different current densities. A remarkably good performance with a high initial discharge capacity and low capacity fading on cycling is obtained.     

Novel polymer electrolytes based on thermoplastic polyurethane and ionic liquid/lithium bis(trifluoromethanesulfonyl)imide/propylene carbonate salt system

Polymer electrolytes were prepared from thermoplastic polyurethane with addition of mixture of ionic liquid N-ethyl(methylether)-N-methylpyrrolidinium trifluoromethanesulfonimmide (PYRA_12O1TFSI), lithium bis(trifluoromethanesulfoneimide) salt and propylene carbonate. The electrolytes characterization was performed by thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy. The electrical properties were investigated in detail by impedance spectroscopy with the aid of equivalent circuit fitting of the impedance spectra. A model describing temperature evolution of ionic conductivity and the properties of electrolyte/blocking electrode interface was developed. The electrochemical stability of the electrolytes was studied by linear voltammetry. Our results indicate that the studied electrolytes have good self-standing characteristics, and also a sufficient level of thermal stability and a fairly good electrochemical window. The ionic conductivity increases with increasing amount of mixture, and the character of temperature dependence of conductivity indicates decoupling of ion transport from polymer matrix. For studied system, the highest value of ionic conductivity measured at room temperature was 10⁻⁴ S cm⁻¹.     

Preparation and electrochemical characterization of polymer electrolytes based on electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/polyacrylonitrile blend/composite membranes for lithium batteries

Apart from PEO based solid polymer electrolytes, tailor-made gel polymer electrolytes based on blend/composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) and polyacrylonitrile are prepared by electrospinning using 14 wt% polymer solution in dimethylformamide. The membranes show uniform morphology with an average fiber diameter of 320-490 nm, high porosity and electrolyte uptake. Polymer electrolytes are prepared by soaking the electrospun membranes in 1 M lithium hexafluorophosphate in ethylene carbonate/dimethyl carbonate. Temperature dependent ionic conductivity and their electrochemical performance are studied. The blend/composite polymer electrolytes show good ionic conductivity in the range of 10⁻³ S cm⁻¹ at ambient temperature and good electrochemical performance. All the Polymer electrolytes show an anodic stability >4.6 V with stable interfacial resistance with storage time. The prototype cell shows good charge-discharge properties and stable cycle performance with comparable capacity fade compared to liquid electrolyte under the test conditions.     

Polypropylene-supported and nano-Al2O3 doped poly(ethylene oxide)-poly(vinylidene fluoride-hexafluoropropylene)-based gel electrolyte for lithium ion batteries

A new gel polymer electrolyte (GPE) is reported in this paper. In this GPE, blending polymer of poly(ethylene oxide) (PEO) with poly(vinylidene fluoride-hexafluoropropylene) (P(VdF-HFP)), doped with nano-Al₂O₃ and supported by polypropylene (PP), is used as polymer matrix, namely PEO-P(VdF-HFP)-Al₂O₃/PP. The performances of the PEO-P(VdF-HFP)-Al₂O₃/PP membrane and the corresponding GPE are characterized with mechanical test, CA, EIS, TGA and charge-discharge test. It is found that the performances of the membrane and the GPE depend to a great extent on the content of doped nano-Al₂O₃. With doping 10 wt.% nano-Al₂O₃ in PEO-P(VdF-HFP), the mechanical strength from 9.3 MPa to 14.3 MPa, the porosity of the membrane increases from 42% to 49%, the electrolyte uptake from 176% to 273%, the thermal decomposition temperature from 225 °C to 355 °C, and the ionic conductivity of corresponding GPE is improved from 2.7 × 10⁻³ S cm⁻¹ to 3.8 × 10⁻³ S cm⁻¹. The lithium ion battery using this GPE exhibits good rate and cycle performances.     

Preparation and electrochemical characterization of electrospun,microporous membrane-based composite polymer electrolytes for lithium batteries

Poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} membranes incorporating 0, 6 and 10 wt.% of nano-meter sized particles of SiO₂ were prepared by electrospinning. These membranes served as host matrix for the preparation of polymer electrolytes (PEs) by activating with the non-volatile and safe room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (BMITFSI). The membranes consisted of layers of fibers with average fiber diameter of 2–5 μm and had a porosity of ∼87%. PEs with SiO₂ exhibited higher ionic conductivity with a maximum of 4.3 × 10⁻³ S cm⁻¹ at 25 °C obtained with 6% SiO₂. The optimum PE based on the membrane with 6% SiO₂ exhibited better compatibility with lithium metal electrode on storage and resulted in enhanced charge–discharge performance in Li/LiFePO₄ cells at room temperature, delivering the theoretical specific capacity of 170 mAh g⁻¹ at 0.1 C-rate. The PEs exhibited a very stable cycle property as well, demonstrating their suitability for lithium battery applications.     

Preparation and electrochemical characterization of gel polymer electrolyte based on electrospun polyacrylonitrile nonwoven membranes for lithium batteries

Electrospun membranes of polyacrylonitrile are prepared, and the electrospinning parameters are optimized to get fibrous membranes with uniform bead-free morphology. The polymer solution of 16 wt.% in N,N-dimethylformamide at an applied voltage of 20 kV results in the nanofibrous membrane with average fiber diameter of 350 nm and narrow fiber diameter distribution. Gel polymer electrolytes are prepared by activating the nonwoven membranes with different liquid electrolytes. The nanometer level fiber diameter and fully interconnected pore structure of the host polymer membranes facilitate easy penetration of the liquid electrolyte. The gel polymer electrolytes show high electrolyte uptake (>390%) and high ionic conductivity (>2 × 10⁻³ S cm⁻¹). The cell fabricated with the gel polymer electrolytes shows good interfacial stability and oxidation stability >4.7 V. Prototype coin cells with gel polymer electrolytes based on a membrane activated with 1 M LiPF₆ in ethylene carbonate/dimethyl carbonate or propylene carbonate are evaluated for discharge capacity and cycle property in Li/LiFePO₄ cells at room temperature. The cells show remarkably good cycle performance with high initial discharge properties and low capacity fade under continuous cycling.     

Boosting the performance of poly(ethylene oxide)-based solid polymer electrolytes by blending with poly(vinylidene fluoride-co-hexafluoropropylene) for solid-state lithium-ion batteries

To seek a solid polymer electrolyte (SPE) with excellent performance, a novel poly(ethylene oxide) (PEO) based SPE is prepared by blending an appropriate amount of microcrystalline poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with PEO using a universal solution casting method. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) are utilized to analyse the samples. The crystallinity of the blend solid polymer electrolyte is significantly lower than that of the neat PEO-based SPE. The addition of the PVDF-HFP disrupts the segment structure of the PEO crystal region and increases the proportion of the amorphous region, thus boosting the migration of lithium ions. The results show that the electrochemical stability window of the blend solid polymer electrolyte reaches as high as 4.8 V. The initial discharge specific capacity of the solid-state LiFePO₄/SPE/Li battery is 131 mAh g⁻¹ at 0.5 C and 60°C, and the discharge specific capacity is still 110.5 mAh g⁻¹ after 100 cycles. On the basis of the results, the novel SPE has a widespread application prospects in solid-state lithium-ion batteries.     

In situ proton exchange membrane fuel cell durability of poly(vinylidene fluoride)/polyelectrolyte blend Arkema M43 membrane

A typical perfluorosulfonic acid (PFSA) polymer electrolyte membrane is composed of a single type of polymer in order to meet the strict requirements for a fuel cell membrane. The Arkema Inc. membrane technology provides a simple and lower cost route to the design of durable membrane materials. The membrane employs two intimately mixed polymers: Kynar^® PVDF, which provides excellent mechanical characteristics, barrier properties and chemical stability, and a hydrocarbon polyelectrolyte for high proton conductivity and water transport. This work reports in-cell accelerated durability results of Arkema M43 membranes. Arkema M43 membranes demonstrated operation times that are 8-10 times longer than two other types of PFSA membranes under open-circuit voltage (OCV)-hold and voltage-cycle tests; these materials also exhibited significantly better durability than Nafion^® NRE211 under relative humidity (RH)-cycle tests. Unlike PFSAs, the membrane-electrode assemblies (MEAs) constructed using Arkema M43 membranes did not fail with catastrophic gas crossover in OCV-hold tests.     

Inorganic-organic polymer electrolytes based on poly(vinyl alcohol) and borane/poly(ethylene glycol) monomethyl ether for Li-ion batteries

In this study, poly(vinyl alcohol) (PVA) was modified with poly(ethylene glycol) monomethyl ether (PEGME) using borane-tetrahydrofuran (BH₃/THF) complex. Molecular weights of both PVA and PEGME were varied prior to reaction. Boron containing comb-branched copolymers were produced and abbreviated as PVA1PEGMEX and PVA2PEGMEX. Then polymer electrolytes were successfully prepared by doping of the host matrix with CF₃SO₃Li at several stoichiomeric ratios with respect to EO to Li. The materials were characterized via nuclear magnetic resonance (¹H NMR and ¹¹B NMR), Fourier transform infrared spectroscopy (FT-IR), Thermogravimetry (TG) and differential scanning calorimeter (DSC). The ionic conductivity of these novel polymer electrolytes were studied by dielectric-impedance spectroscopy. Li-ion conductivity of these polymer electrolytes depends on the length of the side units as well as the doping ratio. Such electrolytes possess satisfactory ambient temperature ionic conductivity (>10⁻⁴ S cm⁻¹). Cyclic voltammetry results illustrated that the electrochemical stability domain extends over 4 V.     

Proton exchange membranes based on semi-interpenetrating polymer networks of Nafion and poly(vinylidene fluoride) via radiation crosslinking

A new method to prepare proton exchange membranes based on semi-interpenetrating polymer networks (semi-IPN) of Nafion^® and poly(vinylidene fluoride) (PVDF) via radiation crosslinking was proposed. The tensile strength, degree of crosslinking, water uptake, and swelling ratio of the composite membranes were studied. Compared to the recast Nafion^®212 membrane, the composite membranes show much better mechanical properties and improved dimensional stability. The tensile strength of the composite membranes ranges from 34.3 MPa to 53.4 MPa, which is higher than that of the recast Nafion^®212 membrane (23.9 MPa). The dimensional stability of the composite membranes also increases with increasing PVDF content in the membranes. The composite membranes show considerable proton conductivity even at 100-120 °C. The membrane containing 40% PVDF shows the highest proton conductivity of 3.37 × 10⁻² S/cm at 115 °C. These properties make them a great potential in polymer electrolyte membrane fuel cells (PEMFC).     

Quasi-solid state dye-sensitized solar cells based on gel polymer electrolyte with poly(acrylonitrile-co-styrene)/NaI+I2

Gel polymer electrolyte based on poly(acrylonitrile-co-styrene)/NaI+I₂ and binary solvent mixture was prepared. When the system contains 0.5 M NaI and 0.05 M I₂, the maximum ionic conductivity (at 30 °C) of 2.37 mS cm⁻¹ was achieved. Based on a gel polymer electrolyte with 0.5 M NaI, 0.05 M I₂ and 0.5 M 4-tert-butylpyridine, a quasi-solid state dye-sensitized solar cell was fabricated and its overall energy conversion efficiency of light-to-electricity of 2.75% was achieved under irradiation of 60 mW cm⁻².     

Investigation on the corrosion resistance of carbon black-graphite-poly(vinylidene fluoride) composite bipolar plates for polymer electrolyte membrane fuel cells

The goal of the present work was to evaluate the corrosion resistance of carbon black (CB)-synthetic graphite (SG)-poly(vinylidene fluoride) (PVDF) composites using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The tests were conducted in 0.5 M H₂SO₄ + 2 ppm HF solution at 70 °C to simulate the typical environment of polymer electrolyte membrane fuel cells. The fracture surface of the specimens was characterized by scanning electron microscopy. The through-plane electrical conductivity was also determined. The corrosion resistance decreased as the carbon black content increased up to 5 wt.%. The highest electrical conductivity was achieved for the composition CB = 5 wt.%, PVDF = 15 wt.%, SG = 80 wt.%. A detailed discussion of the EIS data is given. This approach is unprecedented in the current literature. EIS has proven to be a valuable tool to the design of electrically efficient bipolar plates.     

Ion transport and ion-filler-polymer interaction in poly(methyl methacrylate)-based, sodium ion conducting, gel polymer electrolytes dispersed with silica nanoparticles

Experimental studies are carried out on novel sodium ion conducting, gel polymer electrolyte nanocomposites based on poly(methyl methacrylate) (PMMA) and dispersed with silica nanoparticles. The nanocomposites are obtained in the form of free-standing transparent films.A gel electrolyte with ∼4 wt.% SiO₂ offers the maximum electrical conductivity of ∼3.4 × 10⁻³ S cm⁻¹ at ∼20 °C with good mechanical, thermal and electrochemical stability. Physical characterization by X-ray diffraction, Fourier transformed infra-red and scanning electron microscopy is performed to examine ion/filler-polymer interaction and the possible changes in the texture of the host polymer due to liquid electrolyte entrapment and the dispersion of SiO₂ nanoparticles. The temperature dependence of the electrical conductivity is consistent with an Arrhenius-type relationship in the temperature range from 25 to 75 °C. Sodium ion conduction in the gel electrolyte film is confirmed from cyclic voltammetry and transport number measurements. The value of the sodium ion transport number (tNa⁺) of the undispersed gel electrolyte is ∼0.23 and it is almost unaffected due to the dispersion of SiO₂ nanoparticles. The effect of SiO₂ dispersion on ionic conduction is described in terms of anion-filler surface interaction.     

Poly(vinylidene fluoride) based anion conductive ionomer as a catalyst binder for application in anion exchange membrane fuel cell

An anion conductive polymeric ionomer incorporated into the electrodes of an anion exchange membrane fuel cell (AEMFC) can help to enhance anion transport in the catalyst layer of electrode, and thus improve the catalyst efficiency and performance of AEMFC. In this work, we report the synthesis and properties of a new type of anion conductive ionomer, which is synthesized by grafting of poly(vinylidene fluoride), or PVDF with poly(vinylbenzyltrimethylammonium chloride) via atom transfer radical polymerization. The ionomer obtained shows improved hydrophilicity relative to pristine PVDF, and exhibits an ion exchange capacity of 1.59 mmol g⁻¹. When used in a direct hydrazine hydrate fuel cell (DHFC) as a catalyst binder, the synthesized ionomer imparts the DHFC a significantly improved power density, which is 5-10 fold as much as that of the cells without using such ionomer. The method developed here for anion exchange ionomer synthesis is facile, green and does not involve the use of carcinogenic chemicals such as chloromethylmethylether and trimethylamine, which are often used for conventional anion exchange membrane or ionomer synthesis.     

Performance improvement of polyethylene-supported poly(methyl methacrylate-vinyl acetate)-co-poly(ethylene glycol) diacrylate based gel polymer electrolyte by doping nano-Al2O3

Polyethylene (PE)-supported poly(methyl methacrylate-vinyl acetate)-co-poly(ethylene glycol) diacrylate with and without doping nano-Al₂O₃, namely P(MMA-VAc)-co-PEGDA/PE and P(MMA-VAc)-co-PEGDA/Al₂O₃/PE, are prepared and their performances as gel polymer electrolytes (GPEs) for lithium ion battery are studied by mechanical test, scanning electron microscopy, thermogravimetric analyzer, electrochemical impedance spectroscopy, cyclic voltammetry, and charge/discharge test. It is found that the doping of nano-Al₂O₃ in the P(MMA-VAc)-co-PEGDA/PE improves the comprehensive performances of the GPE and thus the rate performance and cyclic stability of the battery. With doping nano-Al₂O₃, the mechanical and thermal stability of the polymer and the ionic conductivity of the corresponding GPE increases slightly, while the battery exhibits better cyclic stability. The mechanical strength and the decomposition temperature of the polymer increase from 15.9 MPa to 16.2 MPa and from 410 °C to 420 °C, respectively. The ionic conductivity of the GPE is from 3.4 × 10⁻³ S cm⁻¹ to 3.8 × 10⁻³ S cm⁻¹. The discharge capacity of the battery using the GPE with doping nano-Al₂O₃ keeps 90.9% of its initial capacity after 100 cycles and shows good C-rate performance.     

Effect of salt concentration on poly (vinyl chloride)/poly (acrylonitrile) based hybrid polymer electrolytes

Hybrid, solid polymer electrolyte films consisting of poly (vinyl chloride) (PVC), poly (acrylonitrile) (PAN) and, propylene carbonate (PC) with different concentrations of LiClO₄ are prepared by means of a using solvent-casting technique. The structure and complex formation are studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The temperature dependence of the ionic conductivities of the polymer films is explained in terms of a free volume model. The conductivities of PVC–PAN–LiClO₄–PC complexes are determined at different salt concentrations. The highest ionic conductivity (8.35 × 10⁻⁵ S cm⁻¹) is obtained for 8 wt.% LiClO₄ in the polymer complex at 304 K. The thermal stability of the electrolyte is examined by thermogravimetric/differential thermal analysis (TG/DTA).