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.     

Synthesis of Al2TiO5 and its effect on the properties of chitosan–NH4SCN polymer electrolytes

In this paper, Al₂TiO₅ ceramic material has been synthesised and used as filler in polymer electrolyte system to enhance the conductivity. The precursor sintered at 1,050 °C and contained 0.08 mole of aluminium nitrate gives the best and complete formation of Al₂TiO₅. Composite polymer electrolytes of chitosan–NH₄SCN containing different amount of home-made Al₂TiO₅ were prepared by solution casting. The addition of filler has enhanced the conductivity of polymer electrolyte. The sample 57 wt% chitosan–38 wt% NH₄SCN–5 wt% Al₂TiO₅ exhibited the highest electrical conductivity of 2.10?×?10^?4 S cm^?1 at room temperature. The presence of the Al₂TiO₅ creates favourable pathways for ionic conduction through Lewis acid–base type interactions between ionic species and O/OH surface groups on alumina filler grains. In addition, the space charge region created by the presence of Al³⁺ could attract SCN^?1 ions, thus immobilise it and increase the transport number of the cation. Degree of crystallinity is calculated from the deconvoluted X-ray diffraction patterns and it shows that the lowest degree of crystallinity is achieved when 5 wt% of filler is added. In Fourier transform infrared study, the carboxamide band of the polymer is observed to shift to higher wave number from 1,629 to 1,634 cm^?1, confirming the formation of chitosan–NH₄SCN–Al₂TiO₅ complexes. The morphology of composite polymer electrolyte has been studied using scanning electron microscopy at room temperature.     

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.     

Effect of ethylene carbonate plasticizer and TiO<Subscript>2</Subscript> nanoparticles on 49% poly(methyl methacrylate) grafted natural rubber-based polymer electrolyte

The effect of plasticizer and TiO₂ nanoparticles on the conductivity, chemical interaction and surface morphology of polymer electrolyte of MG49–EC–LiClO₄–TiO₂ has been investigated. The electrolyte films were successfully prepared by solution casting technique. The ceramic filler, TiO₂, was synthesized in situ by sol-gel process and was added into the MG49–EC–LiClO₄ electrolyte system. Alternating current electrochemical impedance spectroscopy was employed to investigate the ionic conductivity of the electrolyte films at 25 °C, and the analysis showed that the addition of TiO₂ filler and ethylene carbonate (EC) plasticizer has increased the ionic conductivity of the electrolyte up to its optimum level. The highest conductivity of 1.1 × 10⁻³ Scm⁻¹ was obtained at 30 wt.% of EC. Fourier transform infrared spectroscopy measurement was employed to study the interactions between lithium ions and oxygen atoms that occurred at carbonyl (C=O) and ether (C-O-C) groups. The scanning electron microscopy micrograph shows that the electrolyte with 30 wt.% EC posses the smoothest surface for which the highest conductivity was obtained.     

Influence of solid electrolyte particles size on ionic transport in model composite system (PVdF-HFP–Li1.3Al0.3Ti1.7(PO4)3)

The influence of filler particles size on lithium ion conductivity of composite polymer electrolytes was issued on model system vinylidenefluoride with hexafluoropropylene (PVdF-HFP)–Li_1.3Al_0.3Ti_1.7(PO₄)₃. Model electrolyte objects with filler grains of different sizes were prepared using a modified solvent casting method from a mixture of PVdF-HFP solution in dimethylformamide and Li_1.3Al_0.3Ti_1.7(PO₄)₃ solid electrolyte particles. The percolation threshold was defined and the transport properties of composite polymer electrolytes at different volume concentrations of the solid electrolyte investigated. A significant decrease in conductivity compared to that of ceramic solid electrolytes was observed. The size of the filler particles was found to affect the structure and transport properties of the prepared composite polymer electrolytes. The conductivity of the composite polymer electrolyte at 100 °C was found to increase by two orders of magnitude with the tenfold increase of the size of the filler particles.     

Poly (ethylene oxide) (PEO)-based,sodium ion-conducting‚ solid polymer electrolyte films,dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> filler,for applications in sodium ion cells

The studies on solid polymer electrolyte (SPE) films with high ionic conductivity suitable for the realization of all solid-state Na-ion cells? form the focal theme of the work presented in this paper. The SPE films are obtained by the solution casting technique using the blend solution of poly (ethylene oxide) (PEO) with ethylene carbonate (EC) and propylene carbonate (PC) and complexed with sodium nitrate. Structural and thermal studies of SPE films are done by XRD, FTIR spectroscopy, and TGA techniques. Surface morphology of the films is studied using the FESEM. The ionic conductivity of SPE films is determined from the electrochemical impedance spectroscopy studies. For the SPE film with 16 wt% of NaNO₃ used for reacting with the polymer blend of PEO with EC and PC, the ionic conductivity obtained is around 1.08 × 10^?5 S cm^?1. Addition of the Al₂O₃ as the filler material is found to enhance the ionic conductivity of the SPE films. The studies on the Al₂O₃ modified SPE film show an ionic conductivity of 1.86 × 10^–4 S cm^?1, which is one order higher than that of the SPE films without the filler content. For the SPE film dispersed with 8 wt% of Al₂O₃, the total ion transport number observed is around 0.9895, which is quite impressive from the perspective of the applications in electrochemical energy storage devices. From the cyclic voltammetry studies, a wide electrochemical stability window up to 4 V is observed, which further emphasizes the commendable electrochemical behavior of these SPE films.     

Enhanced electrical transport in LiBrLiI mixed crystals and LiBrAl2O3 composites

LiBrLiI mixed crystals and LiBrAl₂O₃ composites have been studied by means of complex impedance analysis an conductivity, X-ray diffraction, DTA and SEM techniques. The substitution of wrong size I⁻ ions in LiBr increases the conductivity and decreases the migration energy of Li-ion vacancies. These results are consistent with those of the KBr-KI system and earlier predictions. LiBrAl₂O₃ composites exhibit a sharp increase in the conductivity. The highest conductivity obtained was ≈10⁻³ Ω⁻¹ cm⁻¹ at 302°C for LiBr + 10 m/o Al₂O₃.     

Stability of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al in ionic liquid BMI.BF<Subscript>4</Subscript>/γ-butyrolactone electrolytes for use in electrolytic capacitors

The stability of aluminium oxide has been investigated in mixtures of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄) and γ-butyrolactone (GBL) for application as the impregnation electrolyte of aluminium electrolytic capacitors. Ionic conductivity measurements of BMI.BF₄/GBL electrolytes at different temperatures were performed, as well as electrochemical impedance spectroscopy and cyclic voltammetry experiments. The results show that the highest ionic conductivity value of 40 mS cm^?1 (70 °C) is achieved in electrolyte x _BMI.BF4 = 0.2. The total capacitance values, associated with the dielectric oxides, vary between 1 and 8 μF cm^?2 for all studied electrolytes after 30 days of immersion. The polarization resistance and total capacitance of the electrolyte/Al₂O₃/Al system decrease slightly with immersion time, showing the stability of Al₂O₃/Al in ionic liquid BMI.BF₄/GBL electrolytes.     

AC impedance studies on proton-conducting PAN : NH4SCN polymer electrolytes

Solid polymer electrolytes based on polyacrylonitrile (PAN) doped with ammonium thiocyanate (NH₄SCN) in different molar ratios of polymer and salt have been prepared by solution-casting method using DMF as solvent. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. A shift in glass transition temperature (T _g) of the PAN?:?NH₄SCN electrolytes has been observed from the DSC thermograms which indicates the interaction between the polymer and the salt. From the AC impedance spectroscopic analysis, the ionic conductivity has been found to increase with increasing salt concentration up to 30 mol% of NH₄SCN beyond which the conductivity decreases and the highest ambient temperature conductivity has been found to be 5.79?×?10^?3 S cm^?1. The temperature-dependent conductivity of the polymer electrolyte follows an Arrhenius relationship which shows hopping of ions in the polymer matrix. The dielectric loss curves for the sample 70 mol% PAN?:?30 mol% NH₄SCN reveal the low-frequency β-relaxation peak pronounced at high temperature, and it may be caused by side group dipoles. The ionic transference number of polymer electrolyte has been estimated by Wagner’s polarization method, and the results reveal that the conductivity species are predominantly ions.     

Preparation and characterizations of PMMA-PVDF based polymer composite electrolyte materials for dye sensitized solar cell

Blend polymer composite gel electrolytesare prepared using thepoly vinyledene fluoride (PVDF), polymethyl methacrylate (PMMA) with alumina (Al₂O₃) in variance of alkali metal iodide saltsystem. The alumina doped blend polymer electrolytes characterized by the XRD diffraction and FT-IR spectra. This is supportive to the conformation of the crystallinity behaviour and the composite formation.The high-resolution scanning electron microscopy (HR-SEM) have used to find the composite electrolyte membrane porous size (10 μm) and it has support to understand the morphological structure of the membrane. To analyze the ionic conductivity of the potassium iodide based composite polymer electrolyte by the impedance measurements, which is 4.62 × 10⁻³ Scm⁻¹ at room temperature. Finally, different alkali metal iodide based dye-sensitized solar cells (DSSCs) fabricated and monitored an energy conversion efficiency.     

Quasi-solid state polymer electrolytes for dye-sensitized solar cells: Effect of the electrolyte components variation on the triiodide ion diffusion properties and charge-transfer resistance at platinum electrode

Quasi-solid state polymer electrolytes have been prepared from poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) as gelator for 1-ethyl-3-methylimidazolium based ionic liquids (with anions like trifluoromethanesulfonate [EMIM][TfO], bis(trifluoromethanesulfonyl)imide [EMIM][Tf₂N]) and polyacrylonitrile (PAN) for gelation of 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA] as well as I⁻/I₃⁻ as the redox couple. All electrolytes exhibit high ionic conductivity in the range of 10^− 3 S/cm. The effect of gelation, redox couple concentration, I⁻/I₃⁻ ratio, choice of cations and additives on the triiodide diffusion and charge-transfer resistance of the platinum/electrolyte interface (R_ct) were studied. The apparent diffusion coefficient of triiodide ion (D(I₃⁻)) at various iodide/triiodide ratios in liquid and gelified electrolytes has been calculated from measurements of the diffusion limited current (I_lim) in electrochemical cell resembling the set-up of a dye-sensitized solar cell. The charge-transfer resistance of the platinum/electrolyte interface as well as the capacitance of the electrical double layer (C_dl) have been calculated from impedance measurements. Electrolytes with reduced content of polymer (2.5 wt.%) were doped with Al₂O₃ particles of different sizes (50 nm, 300 nm, 1 μm). The dispersion of the particles proceeds by speedy stirring of the hot electrolyte and the addition of PAN provides a homogeneous suspension. The addition of Al₂O₃ particles causes a slight increase of the triiodide diffusion constants. Furthermore the suggested enhancement of the charge transfer rate shows a dependence on the size of the particles.     

Electrical properties of a solid polymeric electrolyte of PVC–ZnO–LiClO4

The ZnO filler has been introduced into a solid polymeric electrolyte of polyvinyl chloride (PVC)–ZnO–LiClO₄, replacing costly organic filler for conductivity improvement. Ionic conductivity of PVC–ZnO–LiClO₄ as a function of ZnO concentration and temperature has been studied. The electrolyte samples were prepared by solution casting technique. The ionic conductivity was measured using impedance spectroscopy technique. It was observed that the conductivity of the electrolyte varies with ZnO concentration and temperature. The temperature dependence on the conductivity of electrolyte was modelled by Arrhenius and Vogel–Tammann–Fulcher equations, respectively. The temperature dependence on the conductivity does not fit in both models. The highest room temperature conductivity of the electrolyte of 3.7 × 10⁻⁷ Scm⁻¹ was obtained at 20% by weight of ZnO and that without ZnO filler was found to be 8.8 × 10⁻¹⁰ Scm⁻¹. The conductivity has been improved by 420 times when the ZnO filler was introduced into the PVC–LiClO₄ electrolyte system. It was also found that the glass transition temperature of the electrolyte PVC–ZnO–LiClO₄ is about the same as PVC–LiClO₄. The increase in conductivity of the electrolyte with the ZnO filler was explained in terms of its surface morphology.     

The effects of ceramic fillers on the PMMA-based polymer electrolyte systems

The effects of ceramics fillers on the polymethylmethacrylate (PMMA)-based solid polymer electrolytes have been studied using ac impedance spectroscopy and infrared spectroscopy. The polymer film samples were prepared using solution cast technique, tetrahydrofuran (THF) used as a solvent, and ethylene carbonate (EC) has been used as plasticizer. Lithium triflate salt (LiCF₃SO₃) has been incorporated into the polymer electrolyte systems. Two types of ceramic fillers, i.e., SiO₂ and Al₂O₃, were then implemented into the polymer electrolyte systems. The solutions were stirred for several hours before it is poured into petri dishes for drying under ambient air. After the film has formed, it was transferred into desiccator for further drying before the test. From the observation done by impedance spectroscopy, the room temperature conductivity for the highest conducting film from the (PMMA–EC–LiCF₃SO₃) system is 1.36 × 10⁻⁵ S cm⁻¹. On addition of the SiO₂ filler and Al₂O₃ filler, the conductivity are expected to increase in the order of ∼10⁻⁴ S cm⁻¹. Infrared spectroscopy indicates complexation between the polymer and the plasticizer, the polymer and the salts, the plasticizer and the salts, and the polymer and the fillers. The interactions have been observed in the C=O band, C–O–C band, and the O–CH₃ band. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7-9, 2006.     

Effects of Al2O3 nanofiller and EC plasticizer on the ionic conductivity enhancement of solid PEO-LiCF3SO3 solid polymer electrolyte

A solid polymer electrolyte (SPE) is synthesized by solution casting technique. The SPE uses poly(ethylene oxide) PEO as a host matrix doped with lithium triflate (LiCF₃SO₃), ethylene carbonate (EC) as plasticizer and nano alumina (Al₂O₃) as filler. The polymer electrolytes are characterized by Impedance Spectroscopy (IS) to determine the composition of the additive which gives the highest conductivity for each system. At room temperature, the highest conductivity is obtained for the composition PEO-LiCF₃SO₃-EC-15%Al₂O₃ with a value of 5.07 10^− 4 S/cm. The ionic conductivity of the polymer electrolytes increases with temperature and obeys the Arrhenius law. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) studies indicate that the conductivity increase is due to an increase in amorphous content which enhances the segmental flexibility of polymeric chains and the disordered structure of the electrolyte. Fourier transform infrared spectroscopy (FTIR) spectra show the occurrence of complexation and interaction among the components. Scanning electron microscopy (SEM) images show the changes morphology of solid polymer electrolyte.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanofiller on the electrical,thermal and structural properties of PEO:PPG based nanocomposite polymer electrolyte

A new series of nanocomposite polymer electrolyte (NCPE) system comprising of polyethylene oxide (PEO) and polypropylene glycol (PPG) as blended polymer host, zinc trifluoromethanesulfonate [Zn(CF₃SO₃)₂] as dopant salt and nanocrystalline alumina [Al₂O₃] as filler was prepared by solution casting technique. The present system consisting of five different compositions of 87.5 wt% (PEO:PPG)–12.5 wt% Zn(CF₃SO₃)₂ + x wt% Al₂O₃ [where x = 1, 3, 5, 7 and 9, respectively] has been thoroughly characterized by various analytical techniques such as electrical impedance spectroscopy, X-ray diffraction (XRD) studies, differential scanning calorimetry (DSC), scanning electron microscopic (SEM) analysis and linear sweep voltammetry (LSV). The maximum room temperature ionic conductivity exhibited by the NCPE was found to be 2.1 × 10^?4 S cm^?1 for 3 wt% loading of Al₂O₃ which is an order higher than that of the optimized filler-free zinc salt doped polymer electrolyte system at 298 K. The evidence of a decrease in the degree of crystallinity responsible for the enhanced conductivity was revealed by the XRD data and further confirmed by DSC and SEM results. Moreover, the electrochemical stability window of the highly conducting electrolyte matrix has been experimentally determined by linear sweep voltammetry and found to be 3.6 V which is fairly adequate for the construction of zinc primary batteries as well as zinc-based rechargeable batteries at ambient conditions.     

Effect of alumina addition on the microstructure and grain boundary resistance of magnesia partially-stabilized zirconia

The electrical properties of 9 mol% MgO–ZrO₂ (Mg-PSZ) with 1 mol% Al₂O₃ and the mechanisms for electrical degradation were investigated using structural, morphological, and electrochemical analyses. The addition of Al₂O₃ caused an increase in both the monoclinic and the Mg-rich phases at the grain boundaries in the Mg-PSZ. Coarse grains larger than 20 μm and an intergranular layer composed of the Mg-rich phase were identified in a specimen sintered at 1600 °C. This specimen exhibited a minimum of ionic conductivity (4.98 × 10⁻⁴ S cm⁻¹ at 700 °C) due to the grain boundary resistance (245 Ω cm²), which dominated the overall resistance. A similar trend was observed over the entire temperature range (600–1500 °C). An intergranular siliceous impurity (SiO₂) was present in conjunction with the Mg-rich phase. This impurity and the Mg-rich phase acted as a barrier layer for oxygen ion diffusion. The presence of the intergranular phases (i.e. the monoclinic and Mg-rich phases) contributed to the degradation of the ionic conductivity in Mg-PSZ with an Al₂O₃ addition.     

Development of proton conducting biopolymer membrane based on agar–agar for fuel cell

A proton-conducting polymer electrolyte based on agar and ammonium nitrate (NH₄NO₃) has been prepared through solution casting technique. The prepared polymer electrolytes were characterized by impedance spectroscopy, X-ray diffraction, and Fourier transform infra-red spectroscopy. Impedance analysis shows that sample with 60 wt.% NH₄NO₃ has the highest ionic conductivity of 6.57 × 10⁻⁴ S cm⁻¹ at room temperature. As a function of temperature, the ionic conductivity exhibits an Arrhenius behaviour increasing from 6.57 × 10⁻⁴ S cm⁻¹ at room temperature to 1.09 × 10⁻³ S cm⁻¹ at 70 °C. Transport parameters of the samples were calculated using Wagner’s polarization method and thus shows that the increase in conductivity is due to the increase in the number of mobile ions. Fuel cell has been constructed with the highest proton conductivity polymer 40agar/60NH₄NO₃ and the open circuit voltage is found to be 558 mV.

     

Grain size effects on dynamics of Li-ions in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites

Li₃V₂(PO₄)₃ glass-ceramic nanocomposites, based on 37.5Li₂O-25V₂O₅-37.5P₂O₅ mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li⁺ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li⁺ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li⁺ ions/electrons and higher surface area of contact between cathode and electrolyte.     

Effects of MnO<Subscript>2</Subscript> nano-particles on the conductivity of PMMA-PEO-LiClO<Subscript>4</Subscript>-EC polymer electrolytes

Li-ion rechargeable batteries based on polymer electrolytes are of great interest for solid state electrochemical devices nowadays. Many studies have been carried out to improve the ionic conductivity of polymer electrolytes, which include polymer blending, incorporating plasticizers and filler additives in the electrolyte systems. This paper describes the effects of incorporating nano-sized MnO₂ filler on the ionic conductivity enhancement of a plasticized polymer blend PMMA–PEO–LiClO₄–EC electrolyte system. The maximum conductivity achieved is within the range of 10⁻³ S cm⁻¹ by optimizing the composition of the polymers, salts, plasticizer, and filler. The temperature dependence of the polymer conductivity obeys the VTF relationship. DSC and XRD studies are carried out to clarify the complex formation between the polymers, salts, and plasticizer.     

New nanocomposite polymer electrolyte comprising nanosized ZnAl2O4 with a mesopore network and PEO-LiClO4

A novel poly(ethylene oxide) (PEO)-based nanocomposite polymer electrolyte (NCPE) has been developed by using nanosized, high surface area ZnAl₂O₄ with a mesopore network as the filler. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and field emission scanning electron microscopy (FESEM) were used to characterize the NCPE. The results showed that the presence of the nanosized ZnAl₂O₄ powder leads to a reduction in the crystallinity of the PEO phase. The ionic conductivity and lithium ion transference number of the PEO-based polymer electrolyte were enhanced by the addition of the nanosized ZnAl₂O₄ powder. A broad electrochemical stability window suggests that the PEO-LiClO₄-ZnAl₂O₄ NCPE is a viable candidate for the electrolyte material in lithium polymer batteries.