Conductivity, dielectric behaviour and thermal stability studies of lithium ion dissociation in poly(methyl methacrylate)-based gel polymer electrolytes

Thin films of poly(methyl methacrylate) (PMMA) with lithium triflate (LiCF₃SO₃) were prepared by using the solution-casting method with PMMA as the host polymer. Ionic conductivity and dielectric measurements were carried out on these films. The highest conductivity for polymer electrolyte with a ratio of 65:35 was found to be 9.88 × 10⁻⁵ S cm⁻¹, which is suitable for the production of mobile phone battery. Thermal gravimetric analysis was carried out to evaluate the thermal stability of the polymer electrolyte. The addition of salts will increase thermal stability of the polymer electrolyte.     

EXAFS and thermal studies on zinc polymeric electrolytes

(PEO) _n :ZnX ₂ (X = I, Br) complexes were formed at room temperature with values ofn ranging from 8 to 30. Differential scanning calorimetry (DSC) results indicate that none of them contained any crystalline phases that can be associated with the formation of a complex (i.e. it can be assumed that all the salt is in the amorphous phase). EXAFS studies carried out on these samples suggest that the zinc cation is co-ordinated to two of the halide ions and, in addition, to 4 oxygen atoms whereX = I and 6 oxygen atoms whereX = Br. The DSC results confirm that the zinc cation is in an environment independent of overall stoichiometry, as the glass transition temperatures of the samples were found to be similar throughout. By comparing these with those of annealed samples (made by heating the above samples to 150°C and cooling to –80°C at 320°C min^–1) it was found that the stoichiometry of the amorphous phase was roughly 61 forX=I and 81 forX = Br.     

Conductivity, FTIR studies, and thermal behavior of PMMA-based proton conducting polymer gel electrolytes containing triflic acid

The addition of polymer to liquid electrolytes containing trifluoromethanesulfonic acid (HCF₃SO₃) in propylene carbonate (PC) has been found to result in an increase in conductivity of gel electrolytes. The increase in conductivity has been observed to be due to the dissociation of ion aggregates present in the electrolytes which has also been supported by Fourier transform infrared studies. The maximum ionic conductivity (at 25 °C) of 7.55?×?10^?3 S/cm has been observed for polymer gel electrolytes containing 1.5 wt% polymethylmethacrylate in 0.5 M solution of HCF₃SO₃ in PC. Polymer gel electrolytes have been found to be thermally stable up to a temperature of 125 °C by simultaneous differential scanning calorimetry/thermogravimetric analysis studies. The conductivity of polymer gel electrolytes does not show any appreciable change over a limited period of time.     

Effect of donor number of solvent on the conductivity behaviour of nonaqueous proton-conducting polymer gel electrolytes

The effect of donor number of solvent on the conductivity behaviour of gel electrolytes has been studied. Liquid electrolytes were prepared by dissolving salicylic acid in solvents based on ethylene carbonate (EC), propylene carbonate (PC) and dimethylformamide (DMF) with different donor number and dielectric constant values. Three different polymers, polymethylmethacrylate (PMMA), polyacrylonitrile (PAN) and polyethylene oxide (PEO), were used as the gelling polymer. The conductivity of polymer gel electrolytes has been found to be higher than the corresponding liquid electrolytes, i.e. σ (gel)>σ (liquid). This has been explained to be due to an increase in carrier concentration by the dissociation of undissociated salicylic acid/ion aggregates present in the electrolytes with the addition of polymer. However, the relative increase in conductivity observed with the addition of different gelling polymers has been found to depend upon the donor number of the solvent used.     

Electrical behavior of proton-conducting chitosan-phosphoric acid-based electrolytes

Dielectric and AC conductivity studies have been carried out for chitosan-based proton-conducting electrolytes. Chitosan-phosphoric acid (CP) and chitosan composite (CPS) electrolytes were prepared using the solution cast method. In both systems, the frequency dependence of ε_r, M_i and tanδ is non-Debye type. The AC conductivity in both electrolytes follows the Jonscher power law. Conduction mechanism studies show that the CP sample follows the quantum mechanical tunneling (QMT) model and the CPS electrolyte follows the overlapping large polaron-tunneling (OLPT) model.     

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

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

Conductivity studies of starch-based polymer electrolytes

A proton-conducting polymer electrolyte based on starch and ammonium nitrate (NH₄NO₃) has been prepared through solution casting method. Ionic conductivity for the system was conducted over a wide range of frequency between 50 Hz and 1 MHz and at temperatures between 303 K and 373 K. Impedance analysis shows that sample with 25 wt.% NH₄NO₃ has a smaller bulk resistance (R _b) compared to that of the pure sample. The amount of NH₄NO₃ was found to influence the proton conduction; the highest obtainable room temperature conductivity was 2.83 × 10⁻⁵ S cm⁻¹, while at 100 °C, the conductivity in found to be 2.09 × 10⁻⁴ S cm⁻¹. The dielectric analysis demonstrates a non-Debye behavior. Transport parameters of the samples were calculated using the Rice and Roth model and thus shows that the increase in conductivity is due to the increase in the number of mobile ions.     

Dynamics of argon in confined geometry

The role of geometrical confinement on the dynamics of argon is studied. We have investigated ³⁶Argon adsorbed in nanoporous Gelsil glass by inelastic neutron scattering. By fractional filling the `dimensionality' of the system is tuned from a two-dimensional towards the bulk state. Ab-initio calculations of plane sheets of Ar atoms and of bulk Ar are compared to the experimental results. A shift of various phonon modes to lower energies with decreasing dimensionality is observed in the results of both methods.     

Ion transport mechanism in proton-conducting gel-type electrolytes: solvent and polymer effects

The development and characterization of proton-conducting gel-type electrolytes containing simple aliphatic dicarboxylic acids gelled with poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) has been investigated in the present work. The relation between the various properties and the composition of the electrolyte constituents with different electrical/physical properties has been investigated and established. Electrical properties for the developed gel-type electrolytes were found to depend upon the acidity and concentration of acid and the amount of polymer present. This dependence is explained due to the combined effect of change in ion concentration, viscosity, and physical interactions taking place between the constituents of electrolytes. Maximum conductivity of 1.59 × 10⁻³ S/cm is observed at room temperature for electrolytes containing 1 M oxalic acid. The interactions and behavior of the electrolytes are supported by Fourier transform infrared, nuclear magnetic resonance, viscosity, and pH studies.     

Peculiarities of gallium crystallization in confined geometry

The freezing and melting phase transitions for gallium embedded into a porous glass with a pore size of about 8 nm were studied using acoustic, NMR, and x-ray techniques. It was shown that the broadened solidification and melting transitions upon deep cooling up to complete freezing at 165 K were due to the formation of β-Ga within pores. The offset of confined β-Ga melting was lowered by about 21 K compared to the bulk β-Ga melting point. Both melting and freezing in pores were irreversible. The fulfillment of some special thermal conditions led to gallium crystallization into other modifications. The role of heterogeneous crystallization in freezing of confined gallium is discussed.     

Properties of gel polymer electrolytes based on poly(butyl acrylate) semi-interpenetrating polymeric networks toward Li-ion batteries

A new type of gel polymer electrolyte (GPE) based on poly(butyl acrylate) (PBA) semi-interpenetrating polymer networks (IPNs) and polyvinylidene fluoride (PVDF) was prepared in different molar ratios ranging from 1:0.5 to 1:1. A series of structure characterizations of PBA/PVDF had been measured using FTIR, XRD, and SEM. The electrolyte uptake test revealed that when the semi-IPNs were swollen with the commercial liquid electrolyte solutions, they showed an outstanding electrolyte uptake of 120% with a chemically cross-linked structure. All results indicated that the GPE exhibited the best performance when the molar ratio of BA and PVDF was 1:0.5. The prototype cell assembled with LiFePO₄ as cathode, lithium metal as anode, and GPE as the electrolyte as well as separator retained 94% of its initial specific capacity after 100 charge-discharge cycles, showing an excellent cycling stability and a high electrochemical window (up to 4.5 V against Li⁺/Li) at room temperature. Compared with the liquid electrolyte, the GPE exhibited a similar stable cycling performance and was suitable for practical application in Li-ion batteries.     

Dynamics and phase behaviour of materials in confined geometry

Phase transitions and dynamics of the liquid crystal MBBA [N-( p-methoxybenzylidene)-p-n-butylaniline] microconfined within porous glasses of average pore diameters: 82 and 337 Å were investigated by ¹H Nuclear Magnetic Resonance (NMR). Confinement is found to favour the depression of phase transition temperatures below the corresponding transitions of bulk MBBA. Confinement induces further effects for the molecular dynamics related to the phase investigated. The correlation times of the molecular motions were obtained and the results are discussed by making comparison with the bulk analysis.     

Conductivity cell for temperature cycling of polymer electrolytes

A cell design suitable for conductivity measurements over a temperature cycle on polymer electrolyte films is described. It has been used to investigate LiCF₃SO₃-PEO films.     

Development and characterizations of PVdF-PEMA gel polymer electrolytes

A new class of gel polymer electrolytes comprising the blend of poly(ethyl methacrylate) (PEMA) and poly(vinylidene fluoride), the mixture of ethylene carbonate and propylene carbonate as a plasticizer, and lithium perchlorate (LiClO₄) as a salt was prepared using solvent casting technique. The formation of polymer–salt complexes has been confirmed by XRD analysis. Morphological and thermal studies have been performed using SEM and DMA analyses. A comparative look between PEMA and poly(methyl methacrylate) (PMMA) electrolytes has showed that PEMA electrolytes exhibited better electrochemical performances than PMMA electrolytes, despites its lower conductivity.     

Performance evaluation of PVdF gel polymer electrolytes

A series of gel polymer electrolytes containing PVdF as homo polymer, a mixture of 1:1 Ethylene Carbonate (EC) : Propylene Carbonate (PC) as plasticizer and lithium-bistrifluoromethane sulphone imide [imide — LiN (CF₃SO₂)₂] has been developed. Amounts of polymer (PVdF), plasticizer and the imide lithium salt have been varied as a function of their weight ratio composition in this regard. Dimensionally stable films possessing appreciable room temperature conductivity values have been obtained with respect to certain weight ratio compositions. However, conductivity data have been recorded at different possible temperatures, i.e., from 20 °C to 65 °C. XRD and DSC studies were carried out to characterize the polymer films for better amorphicity and reduced glass transition temperature, respectively. The electrochemical interface stability of the PVdF based gel polymer electrolytes over a range of storage period (24 h – 10 days) have been investigated using A.C. impedance studies. Test cells containing Li/gel polymer electrolyte (GPE)/Li have been subjected to undergo 50 charge-discharge cycles in order to understand the electrochemical performance behaviour of the dimensionally stable films of superior conductivity. The observed capacity fade of less than 20% even after 50 cycles is in favour of the electrochemical stability of the gel polymer electrolyte containing 27.5% PVdF −67.5 % EC+PC −5% imide salt. Cyclic voltammetry studies establish the possibility of a reversible intercalation — deintercalation process involving Li⁺ ions through the gel polymer electrolyte.     

Crystal structure of indium and lead under confined geometry conditions

The crystal structure of lead and indium nanoparticles produced by the introduction of lead and indium into porous glasses with an average pore diameter of 7 nm at a high pressure is studied by X-ray diffraction. In contrast to the lead nanoparticles, the indium nanoparticles exhibit pronounced anomalous asymmetry of their elastic peaks, which can be explained by the fact that the tetragonal body-centered phase in the “core” of a particle transforms gradually into a face-centered cubic phase near the surface.     

Conductivity study of some polymer electrolytes based on polyacrylonitrile

The present paper deals with the room temperature conductivity study of some polymer electrolytes based on polyacrylonitrile, ammonium tetraflouroborate as dopant, and propylene carbonate (PC) and polyethylene glycols (PEG300 and PEG600) as plasticizers. The additions of plasticizers having different dielectric constant have been found to modify the conductivity of polymer electrolytes. The increase in room temperature conductivity with plasticizer addition has been found to depend upon (1) the amount of salt present and (2) amount of plasticizers added. The polymer electrolytes prepared were characterized by X-ray diffraction, scanning electron micrographs, infrared, thermogravimetric, and AC impedance measurements. The highest room temperature conductivity observed in case of these polymer electrolytes was ∼10–13 s/cm.     

Magnetic susceptibility of noninteracting fermions in a confined geometry

A model system of an ideal gas of neutral fermions in a confined geometry of different symmetry and size is theoretically examined. The behavior of these systems is found to exhibit qualitatively new features such as the oscillations in magnetic susceptibility with changing geometry size and particle density, indicating that the geometric confinement substantially affects the thermodynamic properties of the system.     

Critical conditions of hydrogen-air detonation in partially confined geometry

This work presents the results of the large scale experiments with detonation propagating in hydrogen–air mixtures in partially confined geometries. The main aim of the work was to find the critical conditions for detonation propagation in semi-confined geometries with uniform and non-uniform hydrogen–air mixtures. The experimental facility consisted of rectangular 9 × 3 × 0.6 m channel open from the bottom, acceleration section and test section, safety vessel, gas injection and data acquisition system. Sooted plates technique was used as a witness of the detonation. The rectangular channel was placed in a 100 m³ safety vessel. For uniform hydrogen–air mixtures experiments with four different channel heights h were performed: 8, 5, 3 and 2 cm. The critical hydrogen–air mixture height h* for which the detonation may propagate in a layer is close to the 3 cm which corresponds to approximately three detonation cell sizes. For non-uniform hydrogen–air mixture with hydrogen concentration slope equal approximately ?1.1%H₂/cm the critical hydrogen concentration at the top of the layer is approximately equal 26% and the mean detonation layer height is close to the 8.5 cm corresponding to the hydrogen concentration at the bottom of the layer approximately equal 16–17%.