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.     

Sulfonated poly(ether sulfone) electrolytes structured with mesonaphthobifluorene graphene moiety for PEMFC

Sulfonated poly(ether sulfone)s containing a mixture of cis and trans mesonaphthobifluorene moiety were synthesized, and their properties were characterized. The mesonaphthobifluorene graphene moiety contained 6 phenyl rings and was conjugated together to form planar sheets of sp²-bonded carbon. Poly(arylene ether sulfone)s containing a mixture of cis and trans tetraphenyl ethylene units were synthesized by polycondensation, and converted into graphene by intramolecular Friedel–Craft cyclization with Lewis acid (FeCl₃). The sulfonation was taken selectively on mesonaphthobifluorene units with concentrated sulfuric acid. The structural properties of the sulfonated polymers were investigated by ¹H NMR spectroscopy. The membranes were studied with regard to ion exchange capacity (IEC), water uptake, and proton conductivity.     

Two distinct lithium diffusive species for polymer gel electrolytes containing LiBF4, propylene carbonate (PC) and PVDF

Polymer gel electrolytes have been prepared using lithium tetrafluoroborate (LiBF₄), propylene carbonate (PC) and polyvinylidene fluoride (PVDF) at 20% and 30% concentration by mass. Self diffusion coefficients have been measured using pulse field gradient nuclear magnetic resonance (PFG-NMR) for the cation and anion using ⁷Li and ¹⁹F resonant frequencies respectively. It was found that lithium ion diffusion was slow compared to the much larger fluorine anion likely resulting from a large solvation shell of the lithium. Lithium ion diffusion measurements exhibited two distinct diffusive species, whereas the fluorine ions exhibited only a single diffusive species.     

Spectroscopic and electrochemical characterization of the passive layer formed on lithium in gel polymer electrolytes containing propylene carbonate

The passive layer formed on lithium in a PEO₂₀–LiTFSI–5%PC gel polymer electrolyte after different electrochemical processes was characterized using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS). EIS indicates that the interface resistance of lithium electrodes increases with time after fresh lithium deposition, whereas the interfacial resistance has no change with time after lithium deposition/dissolution process. The XPS analysis as well as FTIR data show that the main compositions of the passive layer are ROCO₂Li, Li₂CO₃, LiOH, LiX (X = F, S, N, SO₂CF₃) and Li oxides, mostly due to the reactions occurred between lithium and PC, LiTFSI, and trace impurities (H₂O, O₂), and the lithium dissolution process has no distinctive effect on the composition of passive layer. XPS depth profile of the passive film detected by XPS and sputtering experiments further demonstrates that the presence of Li₂CO₃/LiOH is in the outer layer and Li₂O, LiF mainly in the inner part of the passive layer.     

Ionic conduction in poly(vinyl chloride)/poly(ethyl methacrylate)-based polymer blend electrolytes complexed with different lithium salts

Poly(vinyl chloride)/poly(ethyl methacrylate)-based polymer blend electrolytes comprising propylene carbonate as a plasticizer and a lithium salt LiX (X = BF₄⁻, ClO₄⁻, CF₃SO₃⁻) are prepared by a solvent casting technique. The electrolytes are subjected to characterization by ionic conductivity, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetic/differential thermal analysis. The electrolytes that contain LiBF₄ exhibit maximum conductivity and are thermally stable up to 254 °C.     

Long-term stable dye-sensitized solar cells based on UV photo-crosslinkable poly(ethylene glycol) and poly(ethylene glycol) diacrylate based electrolytes

UV photo-crosslinkable polymer electrolytes based on poly(ethylene glycol) (PEG) and poly(ethylene glycol) diacrylate (PEGDA) were used in dye-sensitized solar cells (DSSCs). PEG and bifunctional PEGDA formed a crosslinked structure upon UV light illumination, confirmed by the solubility test and FTIR spectroscopy. The polymeric electrolyte was prepared by photo-polymerization after injecting the monomer electrolyte solution into the porous film in order to make close contact with the TiO₂ porous film. Under AM 1.5 (100 mW/cm²) light irradiation for up to 20 min, a maximum 62% increase in the photo-conversion efficiency (η%) was observed. The DSSCs with the crosslinkable PEG/PEGDA based polymer electrolyte showed improved long-term stability in comparison to those with electrolytes containing only PEG. Also, the effects of solvent on stability of the DSSCs were investigated.     

Characterization of polymer electrolytes based on poly(dimethyl siloxane-co-ethylene oxide)

The usefulness of poly(dimethyl siloxane-co-ethylene oxide) (P(DMS-co-EO)) copolymer as an ion conducting matrix was investigated. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The glass transition temperature (T_g) and degree of crystallization as a function of salt concentration were examined by differential scanning calorimetry. Ionic conductivities as high as 2.6×10⁻⁴ S cm⁻¹ were determined at 25 °C for copolymers films with 5 wt.% LiClO₄. These same films had an electrochemical stability window of 5 V. The pseudo-activation energy as a function of salt concentration was obtained using the Vogel–Tamman–Fulcher (VTF) equation.     

Novel polymer electrolytes based on triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with ionically active SiO2

A novel polymer electrolyte based on triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with ionically active SiO₂ inclusions has been designed. The electrolyte shows favorable features for ion migration such as low glass transition temperature and high concentration of amorphous phase. Combined with the effect of active SiO₂, its ionic conductivity is about 8.0 × 10⁻⁵ S cm⁻¹ at 30 °C, which exceeds that for the PEO-based systems. As applying them to cells with LiFePO₄-type cathodes, a capacity of about 147.0 mAh g⁻¹ is obtained at 60 °C, which is retained by more than 90% after 40 charge/discharge cycles. Moreover, about 100 mAh g⁻¹ could still be delivered as temperature decreases to 30 °C.     

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.     

Quaternary ammonium-functionalized poly(ether sulfone ketone) anion exchange membranes: The effect of block ratios

Anion exchange membranes based on quaternary ammonium-functionalized poly(ether sulfone ketone) block copolymers (QA-PESK) with various hydrophilic–hydrophobic oligomer block ratios (10:7, 10:18, and 10:26) were synthesized, and the block length effect on the membranes' physicochemical and electrical properties were systematically investigated. The QA-PESK-10-18 membrane, prepared using a hydrophilic and hydrophobic block ratio of 10:18, displayed well-balanced hydrophilic/hydrophobic phase separation, the highest conductivity of 23.19 mS cm⁻¹ at 20 °C and 57.84 mS cm⁻¹ at 80 °C, and the highest alkaline stability among the three block ratios tested, indicating that the membranes' properties were closely related to their morphologies, which were determined by the hydrophilic/hydrophobic ratio of the block copolymer. The H₂/O₂ single cell performance using the QA-PESK-10-18 revealed a maximum power density of 235 mW cm⁻².     

Confinement of functionalized graphene oxide in sulfonated poly (ether ether ketone) nanofibers by coaxial electrospinning for polymer electrolyte membranes

A novel cambiform-like core-shell nanofiber containing sulfonated graphene oxide core is fabricated through coaxial electrospinning method to improve proton conductivity, fuel blocking and inorganics/polymer compatibility for fuel cell applications. As induced by the strong electrostatic force, the sulfonated organosilane functionalized graphene oxide nanosheet is axially elongated to form a unique cambiform-like and highly wrinkled morphology in the core of the sulfonated poly (ether ether ketone) nanofiber, which is evidenced by the transmission electron microscopy images. It provides a forced contact and good dispersion of graphene oxide in the polymer to improve the tensile strength (approximately 2.6 and 1.8 folds of that of the blend monoaxial electrospun and cast membranes, respectively). The wrinkled graphene oxide core contains the sulfonated functional groups and micro-voids which are favorable for water uptake, making the co-spinning membrane exhibit approximately 43.2% and 33.0% increase of water uptake compared with that of the blend monoaxial electrospun and cast membranes, respectively, and thus facilitate the formation of hydrogen bond networks for proton hopping but tortuous pathways for fuel permeation. Accordingly, both lower hydrogen permeation and much higher methanol selectivity (11 folds of that of Nafion 115) are achieved in the co-spinning membrane.     

Block copolymers combining semi-fluorinated poly(arylene ether) and sulfonated poly(arylene ether sulfone) segments for proton exchange membranes

A series of aromatic multiblock copolymers based on alternating segments of hydrophilic sulfonated polysulfone (PSU) and hydrophobic polyfluoroether (PFE) were prepared and characterized as proton exchange membranes. PSU precursor blocks were synthesized by polycondensation of dichlorodiphenylsulfone and resorcinol, and PFE precursor blocks were prepared by combining decafluorobiphenyl and isopropylidenediphenol. After preparation of the multiblock copolymers via a mild coupling reaction of the precursor blocks, the resorcinol units of the PSU blocks were selectively and almost completely sulfonated under mild reaction conditions using trimethylsilylchlorosulfonate. Transparent and robust membranes with different PSU-PFE copolymer compositions and ion-exchange capacities were cast from solution. Atomic force microscopy of the membranes revealed a distinct nanophase separated morphology. At 80 °C, the proton conductivity reached 10 mS cm⁻¹ under 65% relative humidity and 100 mS cm⁻¹ under fully hydrated conditions.     

Semi-interpenetrating polymer network electrolyte membranes composed of sulfonated poly(ether ether ketone) and organosiloxane-based hybrid network

A semi-interpenetrating polymer network (semi-IPN) proton exchange membrane is prepared from the sulfonated poly(ether ether ketone) (sPEEK) and organosiloxane-based organic/inorganic hybrid network (organosiloxane network). The organosiloxane network is synthesized from 3-glycidyloxypropyltrimethoxysiane and 1-hydroxyethane-1,1-diphosphonic acid. The semi-IPN membranes prepared were stable up to 300 °C without any degradation. The methanol permeability is much lower than Nafion^® 117 under addition of the organosiloxane network. The proton conductivity of semi-IPN membranes increases with an increase the organosiloxane network content; the membrane containing the 20-24 wt% organosiloxane network shows higher conductivity than Nafion^® 117. The power density of the MEA fabricated with the semi-IPN membrane with 24 wt% organosiloxane network is 135 mW cm⁻², much better than that of the pristine sPEEK membrane, 85 mW cm⁻². Chemical synthesis of the semi-IPN membranes is identified using FTIR, and its ion cluster dimension examined using SAXS. The dimensional stability associated with water swelling and dissolution is investigated at different temperatures, and the semi IPN membranes dimensionally stable in water at elevated temperature.     

Preparation and characterization of fluorinated poly(aryl ether oxadiazole)s anion exchange membranes based on imidazolium salts

A series of fluorinated poly(aryl ether oxadiazole)s ionomers based on imidazolium salts (FPAEO-xMIM) were synthesized by quaternization of bromomethylated poly(aryl ether oxadiazole)s (FPAEO-xBrTM) with 1-methyl imidazole as aminating reagent. The anion exchange membranes (AEMs) were prepared by casting method and then immerged in aqueous sodium hydroxide for hydroxide ion exchanging. The structure of the obtained ionomers was characterized by ¹H-NMR and FT-IR measurements. The physical and electrochemical properties of the membranes were also investigated. The hydroxide conductivity of FPAEO-xMIM membranes was higher than 10⁻² S cm⁻¹ at room temperature, while the water uptake and swelling ratio was moderate even at elevated temperature. TGA analysis revealed that the membranes based on imidazolium salts had good thermal stability.     

High performance blend membranes based on densely sulfonated poly(fluorenyl ether sulfone) block copolymer and imidazolium-functionalized poly(ether sulfone)

Abstract

Novel physically crosslinked polymer membranes were prepared by simply blending densely sulfonated poly(fluorenyl ether sulfone) with imidazolium-functionalized poly(ether sulfone). The blend showed well-defined ionic channels originating from the densely sulfonated structure and was physically crosslinked by ionic interactions. These two factors combined to enhance the physical stability and chemical stability of the prepared membranes while offering a conductivity over 0.24 S/cm at 80 °C for various amounts of crosslinker in the blend. The influence of this crosslinker amount on the chemophysical properties of the blend membranes was studied in a systematic way.     

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.     

Involvement of ethylene carbonate on the enhancement H+ carriers in structural and ionic conduction performance on alginate bio-based polymer electrolytes

This study investigates the structural and ionic conduction performance with the involvement of ethylene carbonate (EC) in a bio-based polymer electrolytes (BBPEs) system, based on alginate doped glycolic acid (GA). The solution casting technique was used to successfully prepare the BBPEs which were characterized with various approaches to evaluate their ionic conduction performance. It was revealed that at ambient temperature, an optimum ionic conductivity of 9.06 × 10^?4 S cm^?1 was achieved after the addition of 6 wt% EC, with an observed improvement of the amorphous phase and thermal stability. The enhancement of ionic conduction properties is believed to be due to the protonation (H⁺) enhancement, as proven by FTIR and TNM studies. The findings show that the developed alginate-GA-EC is a promising candidate for use as electrolytes in electrochemical devices that are based on H⁺ carriers.     

Discharge properties of all-solid sodium–sulfur battery using poly (ethylene oxide) electrolyte

An all-solid sodium/sulfur battery using poly (ethylene oxide) (PEO) polymer electrolyte are prepared and tested at 90 °C. Each battery is composed of a solid sulfur electrode, a sodium metal electrode, and a solid PEO polymer electrolyte. During the first discharge, the battery shows plateau potentials at 2.27 and at 1.76 V. The first discharge capacity is 505 mAh g⁻¹ sulfur at 90 °C. The capacity drastically decreases by repeated on charge–discharge cycling but remains at 166 mAh g⁻¹ sulfur after 10 cycles. The latter value is higher than that reported for a Na/poly (vinylidene difluoride)/S battery at room temperature.     

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).