Preparation and characterization of solid polymer electrolytes based on PHEMO and PVDF-HFP

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.     

Solid electrolyte membranes from semi-interpenetrating polymer networks of PEG-grafted polymethacrylates and poly(methyl methacrylate)

Solid polymer electrolyte membranes were prepared as semi-interpenetrating networks by photo-induced polymerization of mixtures of poly(ethylene glycol) (PEG) methacrylate macromonomers in the presence of poly(methyl methacrylate) (PMMA) and lithium bis(trifluoromethanesulfonyl)imide salt. The composition of the membranes was varied with respect to the PMMA content, the degree of cross-linking, and the salt concentration. Infrared analysis of the membranes indicated that the lithium ions were coordinated by the PEG side chains. Calorimetry results showed a single glass transition for the blend membranes. However, dynamic mechanical measurements, as well as a closer analysis of the calorimetry data, revealed that the blends were heterogeneous systems. The ionic conductivity of the membranes increased with the content of PEG-grafted polymethacrylate, and was found to exceed 10^− 5 S cm^− 1 at 30 °C for membranes containing more than 85 wt.% of this component in the polymer blend.     

Organic dopant added polyvinylidene fluoride based solid polymer electrolytes for dye-sensitized solar cells

The effect of phenothiazine (PTZ) as dopant on PVDF/KI/I₂ electrolyte was studied for the fabrication of efficient dye-sensitized solar cell (DSSC). The different weight percentage (wt%) ratios (0, 20, 30, 40 and 50%) of PTZ doped PVDF/KI/I₂ electrolyte films were prepared by solution casting method using DMF as a solvent. The following techniques such as Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffractometer (XRD) and AC-impedance analysis have been employed to characterize the prepared polymer electrolyte films. The FT-IR studies revealed the complex formation between PVDF/KI/I₂ and PTZ. The crystalline and amorphous nature of polymer electrolytes were confirmed by DSC and XRD analysis respectively. The ionic conductivities of polymer electrolyte films were calculated from the AC-impedance analysis. The undoped PVDF/KI/I₂ electrolyte exhibited the ionic conductivity of 4.68×10⁻⁶ S cm⁻¹ and this value was increased to 7.43×10⁻⁵ S cm⁻¹ when PTZ was added to PVDF/KI/I₂ electrolyte. On comparison with different wt% ratios, the maximum ionic conductivity was observed for 20% PTZ-PVDF/KI/I₂ electrolyte. A DSSC assembled with the optimized wt % of PTZ doped PVDF/KI/I₂ electrolyte exhibited a power conversion efficiency of 2.92%, than the undoped PVDF/KI/I₂ electrolyte (1.41%) at similar conditions. Hence, the 20% PTZ-PVDF/KI/I₂ electrolyte was found to be optimal for DSSC applications.     

Study on ionic conductivity of polymer electrolyte plasticized with PEG–aluminate ester for rechargeable lithium ion battery

We have synthesized poly(ethylene glycol) (PEG)-aluminate ester as a plasticizer for solid polymer electrolytes. The thermal stability, ionic conductivity and electrochemical stability of the polymer electrolyte which consist of poly(ethylene oxide) (PEO)-based copolymer, PEG–aluminate ester and lithium bis-trifluoromethanesulfonimide (LiTFSI) were investigated. Addition of PEG–aluminate ester increased the ionic conductivity of the polymer electrolyte, showing greater than 10^− 4 S cm^− 1 at 30 °C. The polymer electrolyte containing PEG–aluminate ester retained thermal stability of the non-additive polymer electrolyte and exhibited electrochemical stability up to 4.5 V vs. Li⁺/Li at 30 °C.     

Conductivity and thermal studies of blend polymer electrolytes based on PVAc–PMMA

The polymer electrolytes comprising blend of poly(vinyl acetate) (PVAc) and poly(methylmethacrylate) (PMMA) as a host polymer and LiClO₄ as a dopant are prepared by solution casting technique. The amorphous nature of the polymer–salt complex has been confirmed by XRD analysis. The DSC thermograms show two T_g's for PVAc–PMMA blend. A decrease in T_g with the LiClO₄ content reveals the increase of segmental motion. Conductance spectra results are found to obey the Jonscher's power law and the maximum dc conductivity value is found to be 1.76 × 10^− 3 S cm^− 1 at 303 K for the blend polymer complex with 20 wt.% LiClO₄, which is suitable for the Li rechargeable batteries. The conductivity–temperature plots are found to follow an Arrhenius nature. The dc conductivity is found to increase with increase of salt concentration in the blend polymer complexes.     

Li3+ ion irradiation effects on ionic conduction in P(VDF–HFP)–(PC + DEC)–LiClO4 gel polymer electrolyte system

Swift heavy ion irradiation of P(VDF–HFP)–(PC + DEC)–LiClO₄ gel polymer electrolyte system with 48 MeV Li³⁺ ions having five different fluences was investigated with a view to increase the Li⁺ ion diffusivity in the electrolyte. Irradiation with swift heavy ion (SHI) shows enhancement of conductivity at lower fluences and decrease in conductivity at higher fluences with respect to unirradiated polymer electrolyte films. Maximum room temperature (303 K) ionic conductivity is found to be 2.2 × 10^− 2 S/cm after irradiation with fluence of 10¹¹ ions/cm². This interesting result could be ascribed to the fluence-dependent change in porosity and to the fact that for a particular ion beam with a given energy higher fluence provides critical activation energy for cross-linking and crystallization to occur, which results in the decrease in ionic conductivity. The XRD results show decrease in the degree of crystallinity upon ion irradiation at low fluences (≤ 10¹¹ ions/cm²) and increase in crystallinity at high fluences (> 10¹¹ ions/cm²). The scanning electron micrographs (SEM) exhibit increased porosity of the polymer electrolyte films after low fluence ion irradiation.     

Study of EVOH based single ion polymer electrolyte: Composition and microstructure effects on the proton conductivity

A comb-like EVOH based single ion polymer electrolyte (EVOH-g-SPEG) was synthesized by sulfonification of EVOH grafts 2-(2-chloroethoxy) ethanol (C₄H₉O₂Cl)/2-[2-(2-chloroethxy) ethoxy] ethanol (C₆H₁₃O₃Cl) with 1, 3-propane sultone. The main chain of the comb-like polymer is hydrophobic polyethylene segments; the side chain is hydrophilic poly (ethylene glycol) (PEG) segment, which can solubilize large amounts of inorganic salts. The sulfonic acid group was introduced onto the end of the PEG side chain. The acid form of SPE was successfully obtained by being dialyzed from the products with acid solution. The saturation water sorption of EVOH-g-SPEG membrane increased with the side chain length and the immersion time. The XRD results indicate that the water in SPE membrane region can destroy the membrane crystalline structure and the water absorption membranes are nearly amorphous. AFM phase images of the hydration membranes clearly show the hydrophilic domains, with sizes increasing from 10 to 35 nm as a function of the side chain length. A phase inversion could be observed when n ≥ 5, which was consistent with a rapid increase in water absorption. And the ion conductivity is also measured by AC impedance. The conductivity is greatly influenced by ion exchange capacity and water sorption. The comb-like EVOH-g-SPEG polymer electrolyte grafts with 2 PEG side chain provides the highest ionic conductivity (1.65 × 10^− 3 S cm^− 1). The comb-like polymer could be a candidate as new polymeric electrolyte material for fuel cells and other electrochemical devices.     

Polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) with crosslinked poly(ethylene glycol) for lithium batteries

The combination of a poly(ethylene glycol) (PEG) network and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) copolymer chains is one of the most efficient means for modifying PVDF-HFP gel electrolytes. Previous preparations tend to introduce contamination into the polymer gel electrolyte because of irradiation, high temperature or the initiator needed for crosslinking which might result in the electrochemical degradation. In order to overcome the above disadvantages, a new method has been developed to successfully prepare the semi-interpenetrating polymer networks of PVDF-HFP based electrolytes with crosslinked diepoxy polyethylene glycol (DIEPEG). In this process, impurities are avoided because of a moderate reaction temperature at 50 °C and poly(ethylenimine) (PEI) as the crosslinking agent. Microporous films with various compositions are prepared and characterized. Thermal, mechanical, swelling and electrochemical properties, as well as microstructures of the prepared polymer electrolytes have been investigated using thermogravimetric analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and scanning electron microscopy. The results show that the blend polymer electrolyte with PVDF-HFP/PEI + DIEPEG (60:40 w/w) has an ionic conductivity of 2.3 mS cm^? 1 at room temperature in the presence of 1 M LiPF₆ in EC and DMC (1:1 w/w). All the blend electrolytes are electrochemically stable up to 4.8 V versus Li/Li⁺. The results reveal that this new method may be very promising for improving PVDF-HFP based electrolytes.     

Polyphosphazene based composite polymer electrolytes

Composite salt-in-polymer electrolyte membranes were prepared from poly[(bis(2-methoxyethyl)amino)_1−x(n-propylamino)_x-phosphazene] (BMEAP) with dissolved LiCF₃SO₃ and dispersed Al₂O₃ nanoparticles (40 nm). Membranes with good mechanical stability were obtained. Low ionic conductivities were found in particle free membranes with maximum conductivities at 10 wt.% LiCF₃SO₃ ranging from 3.1 × 10^− 7 S/cm at 30 °C to 1.8 × 10^− 5 S/cm at 90 °C. For the composite membranes, addition of 2 wt.% Al₂O₃ nanoparticles leads to a steep increase of the conductivity by almost two orders of magnitude as compared to the homogeneous membranes. The highest room temperature conductivity for the investigated BMEAP–LiCF₃SO₃–Al₂O₃ composite systems was 10^− 5 S/cm.     

Effects of compositions on properties of PEO–KI–I2 salts polymer electrolytes for DSSC

The effects of compositions on properties of PEO/KI/I₂ salts polymer electrolytes were investigated to optimize the photovoltaic performance of solid state DSSCs. XRD pattern for the mole ratio 12:1 of [EO:KI] was showed the formation of complete amorphous complex. DSC results also confirmed the amorphous nature of the polymer electrolyte. The highest value of ionic conductivity is 8.36 × 10^− 5 S/cm at 303 K (ambient temperature) and 2.32 × 10^− 4 S/cm at 333 K (moderate temperature) for the mole ratio 12:1 of EO:KI complex. The effect of contribution of [I⁻] and [I₃⁻] concentration with conductivity were also evaluated. FTIR spectrum reveals that the alkali metal cations were co-ordinated to ether oxygen of PEO. The formation of polyiodide ions, such as symmetric I₃⁻ (114 cm^− 1) and I₅⁻ (145 cm^− 1) caused by the addition of iodine was confirmed by FT Raman spectroscopic measurements. The optimum composition of PEO–KI–I₂ polymer electrolyte system for higher conductivity at ambient and moderate temperatures was reported. A linear Arrhenius type behaviour was observed for all the PEO–KI polymer complexes. Transport number measurements were carried out for several polymer electrolyte compositions. Dye-sensitized solar cells were fabricated by using higher conductivity polymer electrolyte compositions and its photoelectrochemical performance was investigated. The fill factor, short-circuit current, photovoltage and energy conversion efficiency of the DSSC assembled with optimized electrolyte composition were calculated to be 0.563, 6.124 mA/cm², 593 mV and 2.044% respectively.     

Synthesis and ionic conductivity of polymeric ion gel containing room temperature ionic liquid and phosphotungstic acid

Composite electrolyte comprising phosphotungstic acid (PWA) filler and 1-butyl-3-methyl-imidazolium-tetrafluoroborate (BMImBF₄) room temperature ionic liquid (RTIL) in poly(2-hydroxyethyl methacrylate) (PHEMA) matrix has been prepared. The polymer matrix was formed by free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) monomers. BMImBF₄ was used as both ionic source and plasticizer, and PWA filler provided the proton conductivity in this system. The interactions and structure changes of the PHEMA-RTIL-PWA composites were investigated by Fourier transform infrared spectra, differential scanning calorimetry, and X-ray diffraction. PWA fillers maintained their Keggin structure within a limited range and enhanced the ionic conductivity of the composite electrolyte. The electrolyte with PWA at the 2 wt.% showed the highest ionic conductivity of 8 × 10^− 4 S cm^− 1 at room temperature and 96% relative humidity.     

Investigation of ionic conduction and mechanical properties of PMMA–PVdF blend-based polymer electrolytes

Polymeric gel electrolytes, based on a blend of poly(methylmethacrylate)/poly(vinylidene fluoride) (PMMA/PVdF), ethylene carbonate/propylene carbonate (EC/PC) as plasticizer and lithium perchlorate as electrolyte, have been studied as a function of the different polymeric ratios to obtain the best compromise between ionic conduction and mechanical properties of the systems involved. Ionic conductivity and the lithium self-diffusion coefficient were measured by the PFG–NMR method, which revealed a maximum of lithium mobility for the composition PMMA 60%–PVdF 40%. The Raman spectroscopic study revealed a change of the interaction between that of the lithium cations and the plasticizer molecules for different PMMA / PVdF ratios. Oscillatory rheological tests have shown better mechanical properties for the intermediate compositions of the blend.     

Effect of thermal history and characterization of plasticized,composite polymer electrolyte based on PEO and tetrapropylammonium iodide salt (Pr4N+I-)

The search for anionic conductors based on solid polymer electrolytes is important for the development of photo-electrochemical (PEC) solar cells due to their many favourable chemical and physical properties. Although solid polymer electrolytes have been extensively studied as cation, mainly lithium ion, conductors for applications in secondary batteries, their use as anionic conductors have not been studied in greater detail. In a previous paper we reported the application of a PEO based iodide ion conducting electrolyte in a PEC solar cell. This electrolyte had the composition PEO: Pr₄N⁺I^? = 9:1 with 50 wt.% ethylene carbonate (EC). In this work we have studied the effect of incorporating alumina filler on the properties of this electrolyte. The investigation was extended to electrical and dielectric measurements including high frequency impedance spectroscopy and thermal analysis.In the DSC themograms two endothermic peaks have been observed on heating, one of these peaks is attributed with the melting of the PEO crystallites, while the other peak with a melting temperature ~ 30 °C is attributed to the melting of the EC rich phase. The melting temperature of both these peaks shows a marked variation with alumina content in the electrolyte. The temperature dependence of the conductivity shows that there is an abrupt conductivity increase in the first heating run evidently due to the melting of the EC rich phase. High conductivity values are retained at lower temperatures in the second heating. Conductivity isotherms show the existence of two maxima, one at ~ 5% Al₂O₃ content and the other at ~ 15%. The occurrence of these two maxima has been explained in terms of the interactions caused by alumina grains, the crystallinity and melting of the PEO rich phase. As seen from latent heat of melting, the crystallinity of the electrolyte has reduced considerably during the first heating run. In contrast to the conductivity enhancement caused by ceramic fillers in PEO-based cation containing electrolytes, no conductivity enhancement has been observed in the present PEO based anionic conducting materials by adding alumina except at low temperatures.     

Preparation of poly(vinyl phosphate-b-styrene) copolymers and its blend with PPO as proton exchange membrane for DMFC applications

Poly(vinyl phosphate-b-styrene) (poly(VPP-b-St)) block copolymers were prepared via consecutive telomerization of vinyl acetate (VAc), atom transfer radical polymerization (ATRP) with styrene, saponification, and phosphorylation with phosphorus oxychloride. The resulting block copolymers were characterized by FT-IR and pH titration. Then, the block copolymers were blended with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to prepare direct methanol fuel cell (DMFC) membrane. The performance of poly(VPP-b-St)/PPO blend membranes was measured in terms of proton conductivity, methanol permeability, thermal and hydrolytic stability. The proton conductivities were in the range of 10^− 4 to 10^− 2 S/cm (60 °C, RH = 95%); the methanol permeabilities were in the range of 4.14 × 10^− 8 to 9.62 × 10^− 8 cm²/s (25 °C), and quite lower than that of Nafion® 117. Also, the thermal stability of the blend membranes was characterized by TGA, and was stable up to 400 °C; the blend membranes had better hydrolytic stability.     

Development of dry polymer electrolyte based on polyethylene oxide with co-bridging agent crosslinked by electron beam

Polyethylene oxide (PEO)-based electrolytes were crosslinked using electron beam (EB) irradiation. The gel contents of a polymer film were increased after irradiation doses of 0, 140, 280, and 420 kGy, with ionic conductivities of 0.831, 1.55, 6.08, and 7.95 (× 10^? 5) S cm^? 1 at 40 °C, respectively. The slight decrease in conductivity at higher temperatures after irradiation is due to the retardation of polymer motion by crosslinking. The electrolyte with higher EB dose amount exhibits higher conductivity due to stabilization of the amorphous state. The EB crosslinking with a co-bridging agent shows enhanced conductivities of 4.71, 6.59, and 7.18 (× 10^? 5) S cm^? 1 at 40 °C, after irradiation with 140, 280, and 420 kGy. Addition of the co-bridging agent is effective for developing a crosslinked structure with a smaller EB dose. Tensile strength becomes two to three times higher with irradiation compared to the non-treated polymer. Combination of the EB technique with a co-bridging agent is a simple and effective method to prepare strong dry polymer electrolyte films with improved room temperature conductivity.     

Structure,dielectric and optical properties of p-type (PVA/CuI) nanocomposite polymer electrolyte for photovoltaic cells

A novel PVA/CuI nanocomposite polymer electrolyte layer synthesized via the reduction of CuCl₂ by NaI in an aqueous PVA solution. The as-prepared films were characterized by X-ray diffraction, scanning electron microscope, as well as impedance spectroscopy. The obtained results indicated the formation of hexagonal CuI nano particles of ≈55 nm sizes embedded in the PVA matrix. In addition, the study of dielectric parameters and conductivity of PVA/CuI nanocomposite in wide range of temperature and frequency are given and discussed. The frequency dependence of ac-conductivity suggests power law with an exponent 0.026 < s < 0.73 which predicts hopping of charge carriers. The bulk conductivity showed activation with temperature, significant values of activation energy are deduced and discussed. An average value of the energy gap width, 2.05 eV obtained using optical absorption in UV–visible spectra for PVA/CuI nanocomposite polymer electrolyte.     

Investigations on electrical properties of (PVA:NaF) polymer electrolytes for electrochemical cell applications

Solid polymer electrolytes based on poly (vinyl alcohol) (PVA) complexed with sodium fluoride (NaF) at different weight percent ratios were prepared using solution cast technique. The structural properties of these electrolyte films were examined by XRD studies. The XRD data revealed that the amorphous domains of PVA polymer matrix increased with increase of NaF salt concentration. The complexation of the salt with the polymer was confirmed by FT-IR studies. Electrical conductivity was measured in the temperature range of 303–373 K and the conductivity was found to increase with the increase of dopant concentration as well as temperature. The dielectric constant (ε′) increased with the increase in temperature and decreased with the increase in frequency. A loss peak was identified at 365 K in the dielectric loss spectra and is attributed to the orientation of polar groups. Measurement of transference number was carried out to investigate the nature of charge transport in these polymer electrolyte films using Wagner’s polarization technique and Watanabe technique. Transport number data showed that the charge transport in these polymer electrolyte systems was predominantly due to ions and in particular due to anions. Using these polymer electrolytes, solid state electrochemical cells were fabricated. Various cell parameters like open circuit voltage (OCV), short circuit current (SCC), power density and energy density were determined.     

Investigations on Na+ ion conducting polyvinylidenefluoride-co-hexafluoropropylene/poly ethylmethacrylate blend polymer electrolytes

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 10 wt% Sb₂O₃ containing CPE exhibits the maximum conductivity 0.569 mS cm⁻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.     

Effects of dissolution conditions on the properties of PVDF ultrafiltration membranes

Poly (vinylidene fluoride) (PVDF) is an important membrane forming material for water treatment. Earlier works have shown that major morphological changes can be achieved when PVDF is dissolved under different conditions with practical applications in membrane distillation and protein attachment. However, no previous report has discussed the effects of dissolution conditions on the performance of PVDF under ultrafiltration, which is one of the most important applications of the polymer. In this work, four different PVDF ultrafiltration membranes were produced from dopes dissolved either by stirring at 24 °C, 90 °C, 120 °C or by sonication. It is shown that dope sonication results in membrane with enhanced thermal and mechanical stability, improved permeate flux during oil emulsion filtration and high flux recovery of ∼63% after cleaning. As a comparison, flux recovery of only ∼26% was obtained for the membrane produced from dope dissolved at 24 °C. The outstanding performance of the dope-sonicated membrane was linked to its slightly lower porosity, narrow distribution of small pores and relatively smooth skin layer. Performance parameters for all membranes showed good correlation to porosity suggesting a tool for membrane design achievable by simple variation in the mode of polymer dissolution. The polymer dissolution effect was related to the degree of unfolding of the polymer molecular chains and their entanglements.     

Ac and Dc conductivities of polyaniline/poly vinyl formal blend films

The synthesis and characterization of polyaniline (PANI)/poly vinyl formal (PVF) blend films were carried out in this work. Polyaniline base was doped using dodecylbenzene sulfonic acid (DBSA). These blend films were characterized by UV–Visible, FTIR spectra and scanning electron microscopy (SEM) to investigate their optical, structural and morphological properties. It was found that the percolation threshold of these blends is 4.4 wt% of PANI. The dc and ac conductivities of these blend films have been measured at a temperature range from 300 to 100 K in the frequency range of 10 kHz to 1 MHz. The electrical conductivity of the blend films enhanced with the increase of polyaniline amount up to a value of 2.5 × 10⁻⁴ S cm⁻¹ at 65 wt% of polyaniline. The dc conductivity of the PANI/PVF blend films follows the three-dimension variable range hopping. Temperature variation of frequency exponents in this blend suggests that ac conduction is attributed to be correlated barrier hopping.