Effects of ionic liquid on the hydroxylpropylmethyl cellulose (HPMC) solid polymer electrolyte

Biodegradable solid polymer electrolyte (SPE) is prepared by solution-casting technique using low-cost cellulose derivative, hydroxypropylmethyl cellulose (HPMC) as a host polymer. Owing to the hydrophobic nature of this polymer, it is predicted to exhibit low ionic conductivity upon addition of magnesium trifluoromethanesulfonate (MgTf₂) salt. Therefore, ionic liquid (IL), 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIMTf), is added in order to enhance its ionic conductivity. Based on the findings, the ionic conductivity at room temperature and the dielectric behaviors of the SPE complex improved upon incorporation of 40 wt.% IL. On top of that, addition of IL reduces the degree of crystallinity and the glass transition temperature (T _g ) of the SPE. The conductivity-temperature plot revealed that the transportation of ions in these films obey Arrhenius theory. The interaction between SPE complex, MgTf₂ salt, and BMIMTf is investigated by means of Fourier transform infrared (FTIR) spectroscopy through the change in peak intensity around 3413, 1570, and 1060 cm^?1, which are responsible for –OH stretching band, C–C and C–N bending modes of cyclic BMIM⁺, and C–O–C stretching band, respectively.     

Structural and ionic conductivity of PEO blend PEG solid polymer electrolyte

Structural and ionic conductivity of PEO blend PEG with KI solid polymer electrolyte system is presented. The polymer PEG showed miscible with the high molecular weight polymer PEO. The X-ray diffraction patterns of PEO/PEG with KI salt indicated the decrease in the degree of crystallinity with increasing concentration of the salt. The DSC measurements of PEO/PEG:KI polymer electrolyte system showed that the melting temperature is shifted towards the lower temperature with increase of the salt concentration. Optical micrographs demonstrated that the spherulites of different sizes are present along with dark regions between the spherulites for lower salt compositions. With increase of salt concentration more amorphous regions are observed. The significance of blend is the increase of one order in ionic conductivity when compared to without blend PEO electrolyte.     

Polyethylene oxide and ionic liquid-based solid polymer electrolyte for rechargeable magnesium batteries

Solid polymer electrolytes (SPEs) based on polyethylene oxide (PEO) complexed with magnesium triflate Mg(Tf)₂ or Mg(CF₃SO₃)₂) and incorporating the ionic liquid (IL) (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI)) were prepared by solution cast technique. The electrolyte was optimized and characterized using electrical conductivity, cationic transport number measurements, and cyclic voltammetry. The highest conductivity of the PEO/Mg(Tf)₂, 15:1 (molar ratio), electrolyte at room temperature was 1.19 × 10⁻⁴ S cm⁻¹ and this was increased to 3.66 × 10⁻⁴ S cm⁻¹ with the addition of 10 wt.% ionic liquid. A significant increase in the Mg²⁺ ion transport number was observed with increasing content of the ionic liquid in the PEO-Mg(Tf)₂ electrolyte. The maximum Mg²⁺ ion transport number obtained was 0.40 at the optimized electrolyte composition. A battery of the configuration Mg/ and [(PEO)₁₅:Mg(Tf)₂+10%IL]/TiO₂-C was assembled and characterized. Preliminary studies showed that the discharge capacity of the battery was 45 mA h g⁻¹.

     

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10^?4 S cm^?1), lithium ion conductivity (1.40?×?10^?4 S cm^?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li⁺ at 30 °C). Furthermore, the surface of LiFePO₄ cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO₄ cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO₄. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g^?1 for graphene oxide-coated LiFePO₄ and without coated LiFePO₄ at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO₄ cathode after coating with graphene oxide.     

Lithium ion transport and ion-polymer interaction in PEO based polymer electrolyte plasticized with ionic liquid

The polyethylene oxide (PEO) based lithium ion conducting polymer electrolytes complexed with lithium trifluoromethanesulfonate (LiCF₃SO₃ or LiTf) plasticized with an ionic liquid 1-ethyl 3-methyl imidazolium trifluoromethanesulfonate (EMITf) have been reported. Morphological, spectroscopic, thermal and electrochemical investigations demonstrate promising characteristics of the polymer films, suitable as electrolyte in various energy storage/conversion devices. Significant structural changes have been observed in the polymer electrolyte due to the ionic liquid addition, investigated by X-ray diffraction (XRD) and optical microscopy. The ion-polymer interaction, particularly the interaction of imidazolium cation with PEO chains, has been evidenced by IR and Raman spectroscopic studies. The optimized composition of the polymer electrolyte i.e. PEO_25.LiTf + 40 wt.% EMITf offer room temperature ionic conductivity of ~ 3 × 10^− 4 S cm^− 1 with wide electrochemical stability window and excellent thermal stability. The ‘σ versus 1/T’ curves show apparent Arrhenius behavior below and above melting temperature. The ionic conductivity has been observed due to Li⁺ ions, as confirmed from ⁷Li-NMR studies, though the component ions of ionic liquid and anions also contribute significantly to the overall conductivity.     

Nano-composite solid polymer electrolytes for solid state ionic devices

Recent research efforts to improve the ambient temperature conductivity in polyethylene oxide (PEO) based solid polymer electrolytes have been directed towards the incorporation of ultra-fine nano-sized particles of ceramic fillers such as Al₂O₃, γ-LiAlO₂, SiO₂ and TiO₂ into the polymer electrolyte. In these PEO based nano-composite polymer electrolytes, conductivity enhancements of up to two orders of magnitude have been achieved. Thermal, electrical conductivity and dielectric relaxation measurements performed on several nano-composite polymer electrolyte systems have shown that the degree of enhancement depends primarily on the grain size. In this paper, results of three nano-composite polymer electrolyte systems, PEO:LiTFSI:Al₂O₃, PEO:LiTf:Al₂O₃ and PEO:LiTf: SiO₂ are discussed as representative examples. It is suggested that the conductivity enhancement is due to the creation of additional sites and favourable conduction pathways for ionic transport through Lewis acidbase type interactions between the filler surface groups (H/OH) and the ionic species. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Channai, India, Nov. 28–30, 2003.     

A novel and shortcut method to prepare ionic liquid gel polymer electrolyte membranes for lithium-ion battery

The ionic liquid polymer electrolyte (IL-PE) membrane is prepared by ultraviolet (UV) cross-linking technology with polyurethane acrylate (PUA), methyl methacrylate (MMA), ionic liquid (Py₁₃TFSI), lithium salt (LiTFSI), ethylene glycol dimethacrylate (EGDMA), and benzoyl peroxide (BPO). N-methyl-N-propyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py₁₃TFSI) ionic liquid is synthesized by mixing N-methyl-N-propyl pyrrolidinium bromide (Py₁₃Br) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The addition of Py₁₃TFSI to polymer electrolyte membranes leads to network structures by the chain cross-linking. The resultant electrolyte membranes display the room temperature ionic conductivity of 1.37 × 10^?3 S cm^?1 and the lithium ions transference number of 0.22. The electrochemical stability window of IL-PE is about 4.8 V (vs. Li⁺/Li), indicating sufficient electrochemical stability. The interfacial resistances between the IL-PE and the electrodes have the less change after 10 cycles than before 10 cycles. IL-PE has better compatibility with the LiFePO₄ electrode and the Li electrode after 10 cycles. The first discharge performance of Li/IL-PE/LiFePO₄ half-cell shows a capacity of 151.9 mAh g^?1 and coulombic efficiency of 87.9%. The discharge capacity is 131.9 mAh g^?1 with 95.5% coulombic efficiency after 80 cycles. Therefore, the battery using the IL-PE exhibits a good cycle and rate performance.     

Radiotracer diffusion and ionic conduction in a PEO-NaI polymer electrolyte

We studied ion transport in amorphous PEO30NaI consisting of poly(ethylene oxide) and sodium iodide in a Na-to-O ratio of 30. Diffusion coefficients of the radiotracers 22Na and 125I were measured for temperatures between 67 and 180 degrees C and compared with the overall charge diffusivity deduced from dc conductivity data. To explain the observed discrepancy between the sum of the tracer diffusivities and the charge diffusivity we propose a detailed model which is based on the formation of neutral ion pairs. Evaluating simultaneously all experimental data within this model yields not only the true diffusion coefficient of all individual species but also the ion-pairing reaction constant as a function of temperature.     

Proton-conducting polymer electrolyte based on PVA-PAN blend doped with ammonium thiocyanate

Blending of polymers is one of the most useful methods for modulating the conductivity of solid polymer electrolytes. Blend polymer electrolytes have been prepared with polyvinyl alcohol (PVA)-polyacrylonitrile (PAN) blend doped with ammonium thiocyanate with different concentrations by solution casting technique, using dimethyl formamide (DMF) as the solvent. The prepared electrolytes are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), ultraviolet (UV), and ac impedance measurement techniques. The increase in amorphous nature of the blend polymer electrolyte by the addition of salt is confirmed by XRD analysis. The complex formation between the polymers and the salt has been confirmed by FTIR analysis. The thermal behavior has been examined using DSC and TGA. The maximum conductivity has been found to be 2.4?×?10^?3 S cm^?1 for 92.5PVA/7.5PAN/25 % NH₄SCN sample at room temperature. The temperature dependence of conductivity has been studied with the help of Arrhenius plot, and the activation energies are calculated. The proton conductivity is confirmed by dc polarization measurement technique. ¹H NMR studies reveal the presence of protons in the sample. A proton battery is constructed with the highest conducting sample, and its open circuit voltage is measured to be 1.2 V     

Impedance of nonuniform distributed solid protonic electrolyte - polymer systems

The conductivity of mixtures of the solid electrolytes H₃[PMo₁₂O₄₀]·13H₂O and Cs₂H[PW₁₂O₄₀] · 13H₂O follows the predictions of the percolation theory, whereas the electrode impedance in the high frequency range fits well the model of double layer adsorption relaxation. It is concluded that both the adsorption relaxation and the reversibility of the electrodes are related to oxygen transfer, the oxygen ions being the minority charge carriers. Fast oxygen dispersion may occur at the polymer-solid electrolyte interface. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Impedance spectroscopy of carbon nanotube/solid polymer electrolyte composites

New composite polymer electrolytes (CPE) have been prepared by a solution-casting technique, using polyethylene oxide, lithium hexafluorate (LiPF₆) as the doping salt, ethylene carbonate (EC) as the plasticizer and amorphous carbon nanotubes (αCNTs) as the filler. The crystallinity and ionic conductivity of the CPE are examined. Differential scanning calorimetry shows a decrease in melting temperature and crystallinity upon the addition of LiPF₆, EC and αCNTs to the polymer electrolyte system. The addition of salt increases the conductivity up to 10⁻⁵ S cm⁻¹. The incorporation of EC and αCNTs into the salted polymer shows a significant conductivity increase of 10⁻⁴ and 10⁻³ S cm⁻¹. The complexation process is examined using Fourier transform infrared spectroscopy. The Vogel-Tamman-Fulcher (VTF) plots suggest that the temperature dependence of conductivity is a thermally activated process.     

Conductivity studies of plasticized anhydrous PEO-KOH alkaline solid polymer electrolyte

Polyethylene oxide (PEO)–potassium hydroxide (KOH)-based alkaline solid polymer electrolyte films have been prepared by using methanol as solvent. The highest room temperature ionic conductivity of (2.1 ± 0.5) × 10⁻⁸ S cm⁻¹ was achieved for the composition of 70 wt% PEO:30 wt% KOH. The addition of plasticizer, ethylene carbonate, propylene carbonate, or polyethylene glycol to the highest conductivity of PEO–KOH system helps to increase the ambient ionic conductivity to the order of 10⁻⁶–10⁻⁴ S cm⁻¹. The log σ vs 1/T plot of PEO–KOH showed a small conductivity decrease at 50–60 °C range. The small decrease and the hysteresis that occur during the heating–cooling cycle was overcome by the presence of the plasticizer. X-ray diffraction observation supports the conductivity results.     

Impedance spectroscopy investigation of liquid crystals doped with ionic surfactants

The effect of a direct-current (dc) electric field on the electrophysical characteristics of nematic liquid crystals of the alkyl cyanobiphenyl series nCB (n = 6–8) and the multicomponent liquid-crystal mixture MB-1, which are doped with ionic surfactants, has been investigated using impedance spectroscopy. It has been found that the impedance spectra depend substantially on the dc bias voltage applied to the sample. The approximation of the measured spectra with specially developed equivalent circuits of the measuring cell with a sample has made it possible to determine the capacitance of the electric double layer and the electrical conductivity of the samples, as well as the mobility, concentration, and diffusion coefficient of the ions. It has been shown that a region of the space charge is formed in the frequency range f < 100 Hz near the electrodes of the measuring cell with a liquid-crystal sample, which leads to an increase in the active (resistive) and reactive (capacitive) components of the impedance.     

Study of the ionic transport in polymer electrolyte using positron lifetime distribution method

Positron annihilation spectroscopy has been applied to measure the free-volume hole distribution in poly(ether urethane) as a function of temperature. The hole radius distribution determined from orthopositronium lifetime distribution is found to shift to a larger values with increasing temperature. This result, combined with the variation of ionic conductivity, suggests that carrier ions do not migrate naked but are bound to polymer segments through ion-dipole interaction forces, and the ion migration is controlled primarily by segmental motion of the polymer.     

Holographic grating formation in dye doped polymer dispersed liquid crystals

We report a detailed investigation on holographic grating formation in dye-doped polymer dispersed liquid crystals. Both optical and scanning electron microscope measurements have been carried out. All the experimental data support the idea that a photorefractive-like effect is the basic mechanism of the optical storage effect, while it is demonstrated that neither droplets' size or shape effects, nor dye or polymer reorientation are involved in the process.     

Electrical studies on ionic liquid-based gel polymer electrolyte for its application in EDLCs

Ionic liquid-based gel polymer electrolyte (GPE) has been synthesized using standard solution cast technique. Different weight percent of ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl) and liquid electrolyte, ethylene carbonate (EC)–propylene carbonate (PC)–tetra ethyl ammonium tetra fluoro borate (TEABF₄) was incorporated in polymer, poly(vinylidene fluoride-co-hexafluoro propylene (PVdF-HFP) to obtain mechanically stable gel polymer electrolyte film (GPE) having maximum conductivity of ~10⁻³ S cm⁻¹ at room temperature, which is acceptable from device fabrication point of view. Potential window and ionic transference number has been obtained to examine the potential limit and ionic characteristics of optimized GPE system. Temperature dependence behavior of electrical conductivity curve follows Arrhenius nature in the temperature range of 303–373 K. Pattern of dielectric constant and its loss as a function of frequency and temperature have been studied and is being explained on the basis of electrode interfacial polarization effect. Frequency-dependent conductivity spectra obey the Jonscher’s power law. Further, optimized composition of GPE has been tested successfully for its application in supercapacitor fabrication with activated charcoal as an electrode material. Maximum specific capacitance of 118.6 mF cm⁻² equivalent to single electrode specific capacitance of 61.7 F g⁻¹ have been observed for the optimized GPE film.

     

Study on the effect of PEG in ionic transport for CMC-NH<Subscript>4</Subscript>Br-based solid polymer electrolyte

The present study investigates the ion transport properties and structural analysis of plasticized solid polymer electrolytes (SPEs) based on carboxymethyl cellulose (CMC)-NH₄Br-PEG. The SPE system was successfully prepared via solution casting and has been characterized by using electrical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD) technique. The highest conductivity of the SPE system at ambient temperature (303 K) was found to be 1.12?×?10^?4 S/cm for un-plasticized sample and 2.48?×?10^?3 S cm^?1 when the sample is plasticized with 8 wt% PEG. Based on FTIR analysis, it shows that interaction had occurred at O–H, C=O, and C–O moiety from CMC when PEG content was added. The ionic conductivity tabulation of SPE system was found to be influenced by transport properties and amorphous characteristics as revealed by IR deconvolution method and XRD analysis.     

Characterization of solid electrolytes prepared from ionic glass and ionic liquid for all-solid-state lithium batteries

Glassy solid electrolytes were prepared by combining the 50Li₂SO₄·50Li₃BO₃ (mol%) ionic glass and the 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMI]BF₄) ionic liquid. High-energy ball milling was carried out for the mixture of the inorganic ionic glass and the organic ionic liquid. The ambient temperature conductivity of the glass electrolyte with 10 mol% [EMI]BF₄ was 10⁻⁴ S cm⁻¹, which was three orders of magnitude higher than that of the 50Li₂SO₄·50Li₃BO₃ glass. The addition of [EMI]BF₄ to the ionic glass decreased glass transition temperature (T_g) of the glass and the decrease of T_g is closely related to the enhancement of conductivity of the glass. Morphology and local structure of the glass electrolyte was characterized. The dissolution of an ionic liquid in an ionic glass with Li⁺ ion conductivity is a novel way to developing glass electrolytes for all-solid-state lithium secondary batteries.     

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.