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.

     

Electrical conductivity relaxation in PVOH+LiH2PO4+Al2O3 polymer composites

Low-frequency conductivity measurements have been performed in solid polymer electrolyte composites based on the anhydrous PVOH–LiH₂PO₄–Al₂O₃ system. A typical power law dependency in the real part of the conductivity, at higher frequencies, of the form ω ⁿ is observed, with an exponent n that depends on the alumina content and nearly independent of temperature. An analysis of the frequency dependence of the electrical susceptibility is conducted to obtain relaxation functions of the form exp[?(t/τ) ^β ], with an exponent β?≈?n???1. Correlation times, τ, and parameters characterizing the electrical relaxation in time and frequency domains are compared to show the equivalence of these representations. The anhydrous dc conductivity of the electrolytes increases with increasing lithium salt content, becoming of the order of 10^?5 S/cm for a salt molar fraction of x?=?0.14. This conductivity value increased by about one order of magnitude by addition of nanoporous particles of Al₂O₃. The temperature dependence of the samples conductivity was well described by the Vogel–Tammann–Fulcher’s equation indicating the effect of the polymer chains flexibility on ion migration. Although all membranes exhibited a “universal dynamic response” associated to the random hopping of the mobile carriers, variations in the measured relaxation parameters with alumina content indicate an increase of ionic correlations when adding the nonporous particles to the polyelectrolyte.     

Spectroscopic studies on ion dynamics of PVP–NH4SCN polymer electrolytes

Proton-conducting polymer electrolyte comprising of poly(N-vinyl pyrrolidone) (PVP) and ammonium thiocyanate (NH₄SCN) are prepared by solvent casting method with different polymer–salt concentrations. The changes in the Raman spectra with increasing NH₄SCN concentration state that the free ion concentration is maximum for 20 mol% NH₄SCN concentrated system. At higher salt concentrations (25 mol%), the effective number of charge carriers decreases due to the formation of ion aggregates as confirmed by the Raman analysis. Solid-state NMR and MAS NMR studies are performed to obtain the information about the ionic structure, mobility of the charge carriers, and also to gain insight into the polymer–salt interactions in the polymer electrolytes. The results of ionic transference number show that the charge transport in these polymer electrolytes is mainly due to ions.     

On dielectrics of polymer electrolytes studied by impedance spectroscopy

We present a phenomenological view on dielectric relaxation in polymer electrolytes in the frequency range where conductivity is independent of frequency. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The discussion applies also to ionic liquids. The following is based on systems with poly(ethylene oxide) (PEO) comprising the lithium perchlorate salt (LiClO₄) and also pure low-molecular PEO. In those systems, dipole-dipole interactions form an association/dissociation equilibrium which rules properties of the system in the low-frequency region. It turns out that effective concentration, c _S, of relaxing species provides a suitable variable for discussing electrochemical behavior of the electrolytes. Quantity c _S is proportional to the ratio of DC conductivity and mobility. Polymer salt mixtures form weak electrolytes. However, diffusion coefficient and corresponding molar conductivity display the typical (c _S)^1/2 dependence as well known from strong electrolytes, due to the low effective concentration c _S.     

Study on ionic conductivity and dielectric properties of PEO-based solid nanocomposite polymer electrolytes

The ionic conductivity and dielectric properties of the solid nanocomposite polymer electrolytes formed by dispersing a low particle-sized TiO₂ ceramic filler in a poly (ethylene oxide) (PEO)-AgNO₃ matrix are presented and discussed. The solid nanocomposite polymer electrolytes are prepared by hot press method. The optimum conducting solid polymer electrolyte of polymer PEO and salt AgNO₃ is used as host matrix and TiO₂ as filler. From the filler concentration-dependent conductivity study, the maximum ionic conductivity at room temperature is obtained for 10 wt% of TiO₂. The real part of impedance (Z′) and imaginary part of impedance (Z″) are analyzed using an LCR meter. The dielectric properties of the highest conducting solid polymer electrolyte are analyzed using dielectric permittivity (ε′), dielectric loss (ε″), loss tangent (tan δ), real part of the electric modulus (M′), and imaginary part of the electric modulus (M″). It is observed that the dielectric constant (ε′) increases sharply towards the lower frequencies due to the electrode polarization effect. The maxima of the loss tangent (tan δ) shift towards higher frequencies with increasing temperature. The peaks observed in the imaginary part of the electric modulus (M″) due to conductivity relaxation shows that the material is ionic conductor. The enhancement in ionic conductivity is observed when nanosized TiO₂ is added into the solid polymer electrolyte.     

Conductivity and dielectric relaxation of Li salt in poly(ethylene oxide) and epoxidized natural rubber polymer electrolytes

Two types of polymer electrolytes were studied: poly(ethylene oxide) (PEO) and epoxidized natural rubber (ENR) both filled with lithium perchlorate. Universal dielectric behavior and impedance relaxation were investigated at room temperature over a wide range of salt concentration. Complex impedance plots exhibit one semicircle in some cases (PEO polymer electrolytes) with an extended spike at low frequencies. This implies a double layer capacity strongly influences conductivity at low frequencies. In the ENR–salt system, semicircles can be obtained only at very high concentrations. This points towards stable resistor dominated networks only develop at very high salt concentrations for this system. Centers of the semicircles lie below real axis indicating non-Debye dielectric relaxation. The relaxation peak broadens and shifts to higher frequencies with increasing salt content. It indicates that the relaxation time of polarization relaxations decreases with ascending salt content. Relaxations occur at extremely low salt concentrations in PEO and only at very high salt concentrations in ENR. Hence, conductivity of ENR–salt is one to two orders of magnitude lower as for PEO–salt.     

Dielectric relaxation spectroscopy of phlogopite mica

An in-depth investigation of the dielectric characteristics of annealed phlogopite mica has been conducted in the frequency range 0.1 Hz–10 MHz and over the temperature range 653–873 K through the framework of dielectric permittivity, electric modulus and conductivity formalisms. These formalisms show qualitative similarities in relaxation processes. The frequency dependence of the M″ and dc conductivity is found to obey an Arrhenius law and the activation energy of the phlogopite mica calculated both from dc conductivity and the modulus spectrum is similar, indicating that same type of charge carriers are involved in the relaxation phenomena. The electric modulus and conductivity data have been fitted with the Havriliak–Negami function. Scaling of M′, M″, ac conductivity has also been performed in order to obtain insight into the relaxation mechanisms. The scaling behaviour indicates that the relaxation describes the same mechanism at different temperatures. The relaxation mechanism was also examined using the Cole–Cole approach. The study elaborates that the investigation regarding the temperature and frequency dependence of dielectric relaxation in the phlogopite mica will be helpful for various cutting edge applications of this material in electrical engineering.     

Dielectric properties and fluctuating relaxation processes of poly(methyl methacrylate) based polymeric nanocomposite electrolytes

Solid polymer nanocomposite electrolytes (SPNEs) consisted of poly(methyl methacrylate) (PMMA) and lithium perchlorate (LiClO₄) of molar ratio C=O:Li⁺=4:1 with varying concentration of montmorillonite (MMT) clay as nanofiller have been prepared by classical solution casting and high intensity ultrasonic assisted solution casting methods. The dielectric/electrical dispersion behaviour of these electrolytes was studied by dielectric relaxation spectroscopy at ambient temperature. The dielectric loss tangent and electric modulus spectra have been analyzed for relaxation processes corresponding to the side groups rotation and the segmental motion of PMMA chain, which confirm their fluctuating behaviour with the sample preparation methods and also with change of MMT concentration. The feasibility of these relaxation fluctuations has been explained using a transient complex structural model based on Lewis acid–base interactions. The low permittivity and moderate dc ionic conductivity at ambient temperature suggest the suitability of these electrolytes in fabrication of ion conducting electrochromic devices and lithium ion batteries. The amorphous behaviour and the exfoliated/intercalated MMT structures of these nanocomposite electrolytes were confirmed by X-ray diffraction measurements.     

An insight into the interactions between LiN(CF3SO2)2 - γBL/DMF — PMMA by FTIR spectroscopy

FTIR spectroscopic analysis has been carried out for liquid electrolytes containing lithium —(trifluormethanesulfonimide or imide) salt as the ion source, a binary solvent composed of γBL and DMF and gel electrolytes containing PMMA. These studies illustrate that for all electrolytes, the cation (Li⁺) — solvent interaction is predominant and occurs through the carbonyl oxygen and the electron rich nitrogen atom of the solvating medium i.e., the binary solvent. Ionic conductivity trends upon varying lithium imide concentration, exhibit a single maximum in both liquid and gel polymeric electrolytes. The conductivity at 25 °C (σ₂₅) decline at high salt concentrations attributable to ion aggregation or cation-anion association, has been explained on the basis of detailed spectral analysis. Addition of PMMA as a gelatinizing agent to liquid electrolytes does not affect the conduction mechanism drastically, which is evident from conductivity measurements and is supplemented by spectral studies.     

Impedance spectra of polymer electrolytes

The authors present a phenomenological view on dielectric relaxation in polymer electrolytes. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The following is based on systems with high molar mass poly(ethylene oxide) (PEO) and epoxidized natural rubber with 25 mol% of epoxide content (ENR-25) filled with lithium perchlorate (LiClO₄). Dielectric properties of these systems have been studied as a function of salt content at room temperature. Additionally, properties of neat low molar mass PEO were studied as function of temperature. Relaxation-coined dielectric behavior rules the system with PEO in the frequency that ranged up to 10⁶ Hz. Imaginary parts of impedance, tangent loss, and electric modulus spectra show distribution of relaxation times. Comparison of tangent loss (tan δ) spectra and imaginary part of electric modulus (M″) spectra reveals that localized motion dominates long-range motion of dipoles in the low-frequency range. However, discrepancy between them decreases with growing salt content. Scaling of tan δ spectra demonstrates that distribution of relaxation times does not depend on salt content in the range of low frequencies. The ENR-25 system exhibits solely relaxation like a macroscopic dipole. In conclusion, the system with PEO is characterized by individual relaxation of well-interacting dipoles, whereas the system based on ENR-25 is coined by immobilized dipoles that lead in the state of high-salt content to the relaxation behavior of a macroscopic dipole.     

Structural, vibrational, thermal, and conductivity studies on proton-conducting polymer electrolyte based on poly (N-vinylpyrrolidone)

The proton-conducting polymer electrolytes based on poly (N-vinylpyrrolidone) (PVP), doped with ammonium chloride (NH₄Cl) in different molar ratios, have been prepared by solution-casting technique using distilled water as solvent. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis confirms the complex formation of the polymer with the salt. A shift in glass transition temperature (T _g) of the PVP/NH₄Cl 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 of 15?mol% NH₄Cl-doped PVP polymer complex has been found to be maximum of the order of 2.51?×?10^?5?Scm^?1 at room temperature. The dependence of T _g and conductivity upon salt concentration has been discussed. The linear variation of the proton conductivity of the polymer electrolytes with increasing temperature suggests the Arrhenius type thermally activated process. The activation energy calculated from the Arrhenius plot for all compositions of PVP doped with NH₄Cl has been found to vary from 0.49 to 0.92?eV. The dielectric loss curves for the sample 85?mol% PVP:15?mol% NH₄Cl reveal the low-frequency ?? relaxation peak pronounced at high temperature, and it may be caused by side group dipoles. The relaxation parameters of the electrolytes have been obtained by the study of Tan?? as a function of frequency.     

Dielectric loss,conductivity relaxation process and magnetic properties of Mg substituted Ni–Cu ferrites

The dielectric properties, dc and ac electrical resistivities of Mg substituted Ni–Cu ferrites with general formula Ni_0.5Cu_0.5−xMg_xFe₂O₄ (0.0≤x≤0.5) have been investigated as a function of frequency, temperature and composition. ac resistivity of all the samples decreases with increase in the frequency exhibiting normal ferrimagnetic behavior. The frequency dependence of dielectric loss tangent showed a maximum in between 10 Hz and 1 kHz in all the ferrites. The conductivity relaxation of the charge carriers was examined using the electrical modulus formulism, and the results indicate the presence of the non-Debye type of relaxation in the prepared ferrites. Similar values of activation energies for dc conduction and for conductivity relaxation reveal that the mechanism of electrical conduction and dielectric polarization is the same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the distribution of relaxation time is temperature independent. The saturation magnetization and coercivity as calculated from the hysteresis loop measurement show striking dependence on composition.     

Studies on the structure and transport properties of hexanoyl chitosan-based polymer electrolytes

Polymer electrolytes composed of hexanoyl chitosan as the host polymer, lithium trifluoromethanesulfonate (LiCF₃SO₃) as the salt, diethyl carbonate (DEC)/ethylene carbonate (EC) as the plasticizers were prepared and characterized by X-ray diffraction and impedance spectroscopy. The X-ray diffraction results reveal the variation in conductivity from structural aspect. This is reflected in terms of amorphous content. Sample with higher amorphous content exhibits higher conductivity. In order to further understand the source of the conductivity variation with varying plasticizers compositions as well as temperatures, the ionic charge carrier concentration and their mobility in polymer electrolyte were determined. The Rice and Roth model was proposed to be used to estimate the ionic charge carrier concentration, n. Knowing n and combining the result with dc conductivity, the mobility of the ionic charge carrier can be calculated. It is found that the conductivity change with DEC/EC composition is due mainly to the change in ionic charge carrier concentration while the conductivity change with temperature is due primarily to the change in mobility.     

Plasticized single conductung polyelectrolytes based on poly (AMPS)

Poly(2-acrylamido-2-methyl-propane-1-sulphonic acid), poly(AMPS), has been ion exchanged with lithium and sodium to form alkali metal ion conducting polyelectrolytes. In the pure form these materials are rigid and would thus show limited conductivity. However addition of water or dimethylsulphoxide, as plasticizers, increases the conductivity by several orders or magnitude. The thermal analysis and NMR relaxation studies of these systems suggest that the increase in conductivity is as a direct result of increased ion mobility although the FTIR evidence still suggests significant ion association consistent with weak electrolytes. Although the T_g's of the sodium form of the polymer were higher, this system displayed higher conductivities than lithium which can be explained by a greater degree of ion dissociation and hence a larger number of charge carriers in the case of sodium poly(AMPS).     

Influence of dispersed alumina particles on the transport characteristics of mechanochemically synthesized NaSn2F5

The composite solid electrolytes, NaSn₂F₅, dispersed with submicron size Al₂O₃ fillers of various concentrations and particle sizes have been synthesized through mechanochemical milling technique. X-ray diffraction and microstructure results indicate the biphasic nature of the composite materials. The transport properties of the present composite materials have been investigated by means of impedance spectroscopy, and the results show that the improvement in conductivity increases with decrease in the particle size of the filler. An enhancement in conductivity of two orders in magnitude is obtained for NaSn₂F₅ with Al₂O₃ dopant concentration of 10 mol%. The activation energy responsible for conductivity relaxation, calculated from the modulus spectra, is found to be almost the same as the value obtained from temperature variation of dc conductivity. The scaling result of the imaginary part of the modulus shows the temperature-independent relaxation behavior.     

Solid polymer electrolytes in a poly(butadiene-acrylonitrile)–LiBr system

Poly(nitriles) are among the polymer matrices providing high salt solubility and, in some cases, superionic lithium conductivity at ambient temperatures observed in highly concentrated solvent-free polymer electrolytes. However, the properties of these electrolytes in which ionic aggregation prevails remain difficult to reproduce and predict, as current theories do not adequately model their attributes. The development of new concepts for ion transport in highly concentrated solid polymer electrolytes (SPEs) requires a better understanding of the fundamentals of structure formation in a polymer–salt system over a wide concentration range including salt precipitation. In an attempt to approach this goal, a series of fundamental studies was carried out on the systems based on a rubbery random copolymer of butadiene and acrylonitrile (abbreviated as PBAN). In the present work, LiBr with monatomic halide anion was used as a lithium salt. The effect of LiBr concentration (0.05 to 3.35 mol kg^?1) on phase composition, ion–molecular interactions, glass transition temperature, and ionic conductivity was studied by optical microscopy, FTIR, X-ray diffraction, DSC, and impedance measurements. The results were compared with those of PBAN–LiClO₄ and PBAN–LiAsF₆ studied previously. Low salt solubility and separation of a metastable cubic CsCl-type polymorph of LiBr were established. The highest conductivity of ～10^?4 S cm^?1 at >50 °C was observed for heterogeneous samples comprising this phase. While the conductivity of PBAN–LiBr was lower than that of PBAN–LiClO₄ and PBAN–LiAsF₆, this study provides a new insight into the nature of polymer electrolyte systems.     

Ionic conductivity,ionic transport and electrochemical characterizations of plastic crystal polymer electrolytes

In this work, the plastic crystal polymer electrolytes (PCPEs), composed of polyacrylonitrile (PAN), succinonitrile (SN) and lithium bis(trifluoromethane)sulfonimide (LiTFSI) were prepared. The concentrations of lithium salt were varied by weight percentage from 10 wt% to 50 wt%. The ionic conductivity of the PCPE films increases with the increase of lithium salt, where the highest value recorded is in the order of ~10^?2 S cm^?1. The temperature-dependence conductivity analysis shows that the PCPE films exhibit Arrhenius behaviour when subjected to the temperature range from 303 K to 343 K. The decrease in crystallinity was confirmed by X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC) analyses. The cationic transport number also increases with the increase of salt which corresponds well to their conductivity values. It is found that the films are electrochemically stable up to ~3.6 V as revealed by the linear sweep voltammetry (LSV) analysis. The cyclic voltammetry (CV) plots of the films shown no substantial change in the redox peaks which mean that the charge transfer reaction is reversible.     

Ion dynamics in NaBF<Subscript>4</Subscript> salt-complexed PVC–PEO blend polymer electrolytes: correlation between average ion hopping length and network structure

Electrical transport properties of a series of NaBF₄ salt-doped PVC–polyethylene oxide blend polymer electrolytes are studied using impedance spectroscopy. X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry are implemented to characterize the structural properties of the electrolytes. The characterization data clearly indicate that the interaction between the dopant salt and the polymer host substantially influences the overall crystallinity of the electrolytes. Experimental frequency-dependent complex conductivity and loss tangent data are analyzed using a physical model to extract separately the mobile ion concentration and ion mobility of the charge carriers and the type of their thermal activation. The average hopping length of free ions, which essentially controls the macroscopic ion transport within the electrolytes, is found to be strongly correlated to the network structure of the electrolytes. Both the dc conductivity and free ion mobility are observed to be strongly coupled with the segmental dynamics of blend polymer host over the entire range of ion content studied.     

Enhancement of the electrochemical properties with the effect of alkali metal systems on PEO/PVdF-HFP complex polymer electrolytes

Polymer blend electrolytes based on poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) were prepared by using different lithium salts LiX (X = ClO₄, BF₄, CF₃SO₃, and N [CF₃SO₂]₂) using solution casting technique. To confirm the structure and complexation of the electrolyte films, the prepared electrolytes were subjected to X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. Alternating current (AC) impedance analysis was performed for all the electrolyte samples at various temperatures from 303 to 343 K. The result suggests that among the various lithium salts, LiN[CF₃SO₂]₂-based electrolytes exhibited the highest ionic conductivity at 8.20 × 10^?4 S/cm. The linear variation of the ionic conductivity of the polymer electrolytes with increasing temperature suggests the Arrhenius-type thermally activated process. Activation energies were found to decrease when doping with lithium imide salt. The dielectric behavior has been analyzed using dielectric permittivity (ε*), electric modulus (M*), and dissipation factor (tanδ) of the samples. Cyclic voltammetry has been performed for the electrolyte films to study their cyclability and reversibility. Thermogravimetric and differential thermal analysis (TG/DTA) was used to ascertain the thermal stability of the electrolytes, and the porous nature of the electrolytes was identified using scanning electron microscopy via ion hopping conduction. Surface morphology of the sample having maximum conductivity was studied by an atomic force microscope (AFM).