Lithium ion conducting PVA:PVdF polymer electrolytes doped with nano SiO2 and TiO2 filler

The effect of nano SiO₂ and TiO₂ fillers on the thermal, mechanical and electrochemical properties of PVA:PVdF:LiCF₃SO₃ have been investigated by three optimized systems of SPE (80PVA:20PVdF:15LiCF₃SO₃), CPE-I (SPE:8SiO₂) and CPE-II (SPE:4TiO₂). From the TGA curve least weight loss has been observed for CPE-II indicating high thermal stability compared to other systems. Stress–strain curve of the prepared samples confirm the enhancement of tensile strength in CPE-II compared to CPE-I and SPE. Conductivity studies show that addition of TiO₂ filler slightly enhances ionic conductivity 3.7×10⁻³ S cm⁻¹ compared to filler free system at 303 K. Dielectric plots have been analyzed and CPE-II possesses higher dielectric constant compared to CPE-I and filler free system. Temperature dependence of modulus plots has been studied for highest conductivity possessing sample. Wider electrochemical stability has been obtained for nano-composite polymer electrolytes. The results conclude that the prepared CPE-II shows the best performance and it will be well suited for lithium ion batteries.     

New polymer electrolyte based on (PVA–PAN) blend for Li-ion battery applications

A polymer blend electrolyte based on polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) was prepared by a simple solvent casting technique in different compositions. The ionic conductivity of polymer blend electrolytes was investigated by varying the PAN content in the PVA matrix. The ionic conductivity of polymer blend electrolyte increased with the increase of PAN content. The effect of lithium salt concentrations was also studied for the polymer blend electrolyte of high ionic conductivity system. A maximum ionic conductivity of 3.76×10⁻³ S/cm was obtained in 3 M LiClO₄ electrolyte solution. The effect of ionic conductivity of polymer blend electrolyte was measured by varying the temperature ranging from 298 to 353 K. Linear sweep voltammetry and DC polarization studies were carried out to find out the stability and lithium transference number of the polymer blend electrolyte. Finally, a prototype cell was assembled with graphite as anode, LiMn₂O₄ as cathode, and polymer blend electrolyte as the electrolyte as well as separator, which showed good compatibility and electrochemical stability up to 4.7 V.     

Preparation and Characterization of Nafion/Sulfonated SiO2 Molecular Sieve Composite Membranes

A Nafion/sulfonated SiO₂ molecular sieve composite membrane was prepared by solution casting with sulfonated SiO₂ molecular sieve as the modifier. The ATR/FT-IR results showed that sulfonated SiO₂ molecular sieve did not change the structure of the membrane. The SEM and XRD results showed that the molecular sieve was distributed uniformly in the membrane. The proton conductivity, methanol permeability, water content, and swelling degree were measured. Compared with Nafion membrane, the composite membrane had higher water content and proton conductivity and lower methanol permeability. The overall performance was the best when the content of sulfonated SiO₂ molecular sieve was 5 wt%. These results indicated that Nafion/sulfonated SiO₂ molecular sieve composite membranes would be excellent candidate membrane materials for direct methanol fuel cell (DMFC) applications.     

Electrical characterization of nano-composite polymer gel electrolytes containing NH4BF4 and SiO2: role of donor number of solvent and fumed silica

Nano-composite polymer gel electrolytes were synthesized by using polyethylene oxide (PEO), ammonium tetrafluoroborate (NH₄BF₄), fumed silica (SiO₂), dimethylacetamide (DMA), ethylene carbonate (EC), and propylene carbonate (PC) and characterized by conductivity studies. The effect of donor number of solvent on ionic conductivity of polymer gel electrolytes has been studied. The mechanical strength of the gel electrolytes has been increased with the addition of nano-sized fumed silica along with an enhancement in conductivity. Maximum room temperature ionic conductivity of 2.63 × 10⁻³ and 2.92 × 10⁻³ S/cm has been observed for nano-composite gel electrolytes containing 0.1 and 0.5 wt% SiO₂ in DMA+1 M NH₄BF₄+10 wt% PEO, respectively. Nano-composite polymer gel electrolytes having DMA have been found to be thermally and electrically stable over 0 to 90 °C temperature range. Also, the change in conductivity with the passage of time is very small, which may be desirable to make applicable for various smart devices.

     

Study on performance of a novel P(VDF-HFP)/SiO2 composite polymer electrolyte using urea as pore-forming agent

Novel poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))-based composite polymer electrolyte (CPE) membranes doped with different contents of nano-SiO₂ using urea as a pore-forming agent were prepared by phase inversion method, and the desired CPEs were obtained by being immersed into 1.0 M LiPF₆-EC/DMC/EMC electrolytes for 0.5 h. The physicochemical properties of the CPEs were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). The results show that the CPEs doped with 10 % nano-SiO₂ exhibit the best performance, in which the SEM images of the as-prepared polymer membranes present homogeneous surface and abundant micropores; the uptake ratio is up to 107.4 %; EIS and LSV analysis also show that the ionic conductivity at room temperature and electrochemical stability window of the modified membrane can reach 3.652 mS cm^?1 and 5.0 V, respectively; the interfacial resistance R _i is 380 Ω cm^?2 in the first day,then increases rapidly to a stable value about 500 Ω cm^?2 in a 5-day storage at room temperature. The Li/As-fabricated CPEs/LiCoO₂ cell also shows excellent charge-discharge performance, which suggests that it can be a potential electrolyte for the lithium-ion battery.     

Experimental investigations on plasticized PMMA/PVA polymer blend electrolytes

Blend based polymer electrolytes composed of poly (methyl methacrylate) (PMMA), poly(vinylalcohol) (PVA) and LiClO₄ are prepared using solvent casting technique. The polymer films are characterized by XRD and FTIR studies to determine the molecular environment for the conducting ions. These polymer films have been investigated in terms of ionic conductivity using the results of impedance studies. The influence of the blend composition on the electrochemical behaviour is also discussed. The highest room temperature conductivity obtained for the film consisting of PMMA, PVA, LiClO₄ and DMP is 0.06×10⁻³ S/cm at 303 K. The PMMA-PVA blend based polymer electrolytes look very desirable and promising for lithium battery applications.     

High molecular weight PVA-modified PVA/PAMPS proton-conducting membranes with increased stability and their application in DMFCs

A series of proton-conducting composites has been synthesized from PVA/PAMPS [poly(vinyl alcohol)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid)] using high molecular weight PVA (HMw-PVA). By applying high molecular weight PVA as a polymer matrix, a greater hydrophobicity of the membranes emerged, which endows them with reduced water uptake (70-90%) but high proton conductivity (0.06-0.1 S cm^- 1), low methanol permeability (1/3 to 1/5 that of Nafion 117), and excellent oxidative stability towards Fenton's reagent. A DMFC fabricated with the above membrane showed a high power density of 15.8 mW cm^- 2 at 30 °C, which reached 42.9 mW cm^- 2 at 80 °C. An initial lifetime performance assessment in DMFC mode yielded a value of 70 h for stable cell operation.     

Characterization of a solid state battery based on polyblend of (PVP+PVA+KBrO3) electrolyte

A potassium ion conducting polyblend electrolyte based on polyvinyl pyrrolidone (PVP) + polyvinyl alcohol (PVA) complexed with KBrO₃ was prepared using solution-cast technique. The electrical conductivity and transference number measurements were performed to characterize the polyblend electrolyte for battery applications. These measurements have shown that the electrolyte is a mixed (ionic + electronic) conductor, the charge transport being mainly ionic (t_ion=0.97). Using the electrolyte, electrochemical cells with configurations K / (PVP+PVA+KBrO₃)/(I₂), K / (PVP+PVA+KBrO₃)/(I₂+C) and K/(PVP+PVA+KBrO₃) / (I₂+C+electrolyte) were fabricated and their discharge characteristics studied. The cell with configuration K / (PVP+PVA+KBrO₃) / (I₂+C+electrolyte) exhibited better discharge characteristics than the other configurations. The other cell parameters like open circuit voltage (OCV), short circuit current (SCC) etc. were evaluated and are reported. Paper presented at the 2nd International Conference of Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Ionic conductivity in nanoporous composites SiO2/AgI

In this work, porous silicate glasses were mixed with an ionic conductor AgI to obtain SiO₂/AgI composites. The porous glasses were either commercial Vycor glass (VPG) from Corning or synthesised from phase separated SiO₂–B₂O₃–Na₂O glasses. Depending upon the elaboration process, glasses with different pore sizes were obtained (4, 20 and 40 nm). Composites comprising different amounts of AgI were prepared by heating above the melting point of AgI. SEM characterisation of the obtained composites indicated that heat treatment induced an increase in the pore sizes. The conductivity of the composites was measured by impedance spectroscopy. The maximum conductivity, twice as large as that of pure AgI, was obtained for the 50AgI/50VPG composite, i.e. that comprising the glasses with the smallest pores.     

Structural, vibrational, thermal, and electrical properties of PVA/PVP biodegradable polymer blend electrolyte with CH3COONH4

A biodegradable solid polymer blend electrolyte was prepared by using polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) polymers with different molecular weight percentages (wt.%) of ammonium acetate, and its structural, thermal, vibrational, and electrical properties were evaluated. The polymer blend electrolyte is prepared using solution casting technique, with water as a solvent. X-ray diffraction shows that the incorporation of ammonium acetate into the polymeric matrix causes decrease in the crystallinity degree of the samples. The Fourier transform infrared spectroscopy and laser Raman studies confirm the complex formation between the polymer and salt. Differential scanning calorimerty shows that the thermal stability of the polymer blend electrolyte and the glass transition temperature decreased as the concentration of ammonium acetate increased. The ionic conductivity of the prepared polymer electrolyte was found by AC impedance spectroscopic analysis. A maximum conductivity of 8.12?×?10^?5 Scm^?1 was observed for the composition of 50 PVA/50 PVP/30 wt.% of CH₃COONH₄.     

Preparation of mesoporous poly (acrylic acid)/SiO2 composite nanofiber membranes having adsorption capacity for indigo carmine dye

Mesoporous poly (acrylic acid)/SiO₂ (PAA/SiO₂) composite nanofiber membranes functionalized with mercapto groups were fabricated by a sol-gel electrospinning method, and their adsorption capacity for indigo carmine was investigated. The membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray powder diffraction (XRD), and nitrogen adsorption–desorption measurement. SEM and TEM observation results showed that the PAA/SiO₂ fibers had diameters between 400–800 nm and mesopores with an average pore size of 3.88 nm. The specific surface area of the mesoporous nanofiber membranes was 514.89 m²/g. The characteristic peaks for mercapto group vibration in FTIR and Raman spectra demonstrated that the mercapto groups have been incorporated into the silica skeleton. The adsorption isotherm data of indigo carmine on the membranes fit well with Redlich–Peterson model, and the maximum adsorption capacity calculated was 523.11 mg/g. It was found that the removal rate of indigo carmine by the membranes reached a maximum of 98% in 90 min and the adsorption kinetics followed a pseudo-second-order model. The high adsorption capacity of PAA/SiO₂ nanofiber membrane makes it a promising adsorbent for indigo carmine removal from the wastewater.     

Preparation and characterization of proton exchange membranes with through-membrane proton conducting channels

The primary goal of this study is to develop a novel PEMs with unique surface structure utilizing the high viscosity of the impregnation solution. SiO₂ nanofiber mats were prepared via the electrospinning method and introduced into sulfonated poly(ether sulfone) (SPES) matrix to prepare hybrid membrane. The effect of concentration of impregnation solution on the morphology and properties of the proton exchange membranes (PEMs), including thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeability were investigated. SEM results showed that a unique surface structure was prepared due to the high solution concentration. Moreover, the hydrophilic nanofibers on the surface constructed continuous proton pathways, which can enhance the proton conductivity of the membranes, a maximum proton conductivity of 0.125 S/cm was obtained when the SPES concentration was 40 wt% at 80 °C, and the conductivity was improved about 1.95 times compared to that of pure SPES membrane. The SiO₂ nanofiber mat-supported hybrid membrane could be used as PEMs for fuel cell applications.     

Structural and thermal studies of PVA:NH4I

Proton-conducting polymer electrolytes based on poly vinyl alcohol (PVA; 88% hydrolyzed) and ammonium iodide (NH₄I) has been prepared by solution casting method with different molar ratios of polymer and salt using DMSO as solvent. DMSO has been chosen as a solvent due its high dielectric constant and also its plasticizing nature. The ionic conductivity has been found to increase with increasing salt concentration up to 25 mol% beyond which the conductivity decreases and the highest ambient temperature conductivity has been found to be 2.5×10⁻³ S cm⁻¹. The conductivity enhancement with addition of NH₄I has been well correlated with the increase in amorphous nature of the films confirmed from XRD and differential scanning calorimetry (DSC) analyses. The temperature-dependent conductivity follows the Arrhenius relation. The polymer-proton interactions have been analyzed by FTIR spectroscopy.     

Composite polymeric electrolytes based on PMMA-LiCF3SO3-SiO2

Preliminary results on the mechanical, optical and electrical properties of composite gel electrolytes (CGEs) with fumed silica (SiO₂) as a filler added to gel polymeric electrolyte (GPE) based on PMMA, LiCF₃SO₃ and PC are presented in this paper. Added fumed silica is seen to enhance the mechanical properties of the GPE without changing the conductivity significantly. The high ionic conductivity (×10⁻³ S/cm), high transmission in the visible region and nominal variance of conductivity and viscosity over a wide temperature window show that these CGEs are potential electrolytes for electrochromic windows (ECWs).     

Study of microstructure and properties of HEC-g-AA/SiO2 organic-inorganic hybrid materials

HEC-g-AA/SiO₂ hybrid materials are prepared through a graft copolymerization reaction between acrylic acid (AA) monomer and hydroxyethyl cellulose (HEC), in the presence of a silica sol. The microstructure and properties of the hybrid materials are characterized by Fourier transform infrared spectra (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. The results show that a rigid inorganic phase SiO₂ is dispersed in flexible organic continuous phase uniformly. HEC-g-AA/SiO₂ hybrid material has no obvious phase separation in the presence of the crosslinking agent. The thermal performances of HEC-g-AA/SiO₂ are excellent, and the glass transition temperature (T _g) increases with the increased amount of the crosslinking agent.     

Investigation on the effects of addition of SiO<Subscript>2</Subscript> nanoparticles on ionic conductivity,FTIR, and thermal properties of nanocomposite PMMA–LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>

Composite polymer electrolyte systems composed of poly(methyl methacrylate) (PMMA) as the host polymer, lithium trifluoromethanesulphonate (also known as lithium triflate; LiCF₃SO₃) as dopant salt, and a variety of different concentrations of nano-sized fumed silica (SiO₂) as inorganic filler were studied. The effect upon addition of SiO₂ on the ionic conductivity of the composite polymer electrolytes was investigated, and it was proven that the ionic conductivity had been enhanced. In addition, the interfacial stability also showed improvement. Maximum conductivity was obtained upon addition of 2 wt.% SiO₂. The complexation of PMMA and LiCF₃SO₃ was verified through Fourier transform infrared studies. The thermal stability of the polymer electrolytes was also found to improve after dispersion of inorganic filler. This was proven in the thermogravimetric studies.     

MgAl2SiO6-incorporated poly(ethylene oxide)-based electrolytes for all-solid-state lithium batteries

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs), comprising various concentrations of lithium hexafluorophosphate and magnesium aluminium silicate, were prepared by hot-press technique. The membranes were characterised by scanning electron microscopy, tensile and thermal analyses. It has been demonstrated that the incorporation of the ceramic filler in the polymeric matrix has significantly enhanced the ionic conductivity, thermal stability and mechanical integrity of the membrane. It also improved the interfacial properties with lithium electrode. Finally, an all-solid-state lithium cell composed of Li/CPE/LiFePO₄ has been assembled and its cycling performance was analysed at 70 °C. The cell delivered a discharge capacity of 115 mAh g^?1 at 1 °C rate and is found to be higher than previous reports.     

Polyvinyl pyrrolidone/Mg(ClO4)2 solid polymer electrolyte: structural and electrical studies

Polymer electrolytes comprising polyvinyl pyrrolidone (PVP) as host polymer and Mg(ClO₄)₂ as dopant salt have been prepared by solution casting technique using double-distilled water as solvent. The changes in the structural properties on the incorporation of dopant were investigated by XRD and FTIR analysis. The ionic conductivity and dielectric behavior were explored using AC impedance spectroscopy. The ionic conductivity increases with increasing dopant concentration. The conductivity enhancement with the increasing salt concentration is correlated with the increase in amorphous nature of the electrolytes. The frequency dependence of electrical conductivity obeys the universal Jonscher power law. The electrical modulus representation shows a loss feature in the imaginary component. The distribution of relaxation times was indicated by a deformed arc form of the Argand plot. The relative dielectric constant (ε _r ) decreases with increase in frequency in the low frequency region whereas a frequency-independent behavior is observed in the high frequency region. The total ionic transference number studies have confirmed that the mobile charge carriers are ions. Results obtained by cyclic voltammetry on SS/60 mol% PVP/40 mol% Mg(ClO₄)₂ SPE/SS symmetrical cell show evidence for reversibility.

     

Proton conducting interpenetrating polymer networks

In order to improve stability and performance of the polymer electrolyte-based hydrogen sensor developed for on-line analysis, modifications to the PVA/H₃PO₄ proton conducting polymer blend were made. Water insoluble, increased bulk modulus, and higher conductivity polymer membranes have been fabricated by development of interpenetrating polymer networks that incorporate the PVA/H₃PO₄ (host) blend. The guest polymer is a three dimensional polymer network composed of methacrylic acid and methylenebisacrylamide. High protonic conductivity results from the phosphoric acid and water, the poly (methaacrylic acid-methylenebisacrylamide) contributes to the increased modulus water insolubility. Hydrogen sensors have been demonstrated using these membranes.     

Electrical conductivity studies on PVA/PVP-KOH alkaline solid polymer blend electrolyte

A series of conducting thin-film solid electrolytes based on poly (vinyl alcohol)/ poly (vinyl pyrrolidone) (PVA/PVP) polymer blend was prepared by the solution casting technique. PVA and PVP were mixed in various weight percent ratios and dissolved in 20 ml of distilled water. The samples were analyzed by using impedance spectroscopy in the frequency range between 100 Hz and 1 MHz. The PVA/PVP system with a composition of 80% PVA and 20 wt.% PVP exhibits the highest conductivity of (2.2±1.4) × 10⁻⁷ Scm⁻¹. The highest conducting PVA/PVP blend was then further studied by adding different amounts of potassium hydroxide (KOH) ionic dopant. Water has been used as solvent to prepare PVA/PVP-KOH based alkaline solid polymer blend electrolyte films. The conductivity was enhanced to (1.5 ± 1.1) × 10⁻⁴ Scm⁻¹ when 40 wt.% KOH was added. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.