Hybrid film electrolytes with high room temperature conductivity have been prepared by casting solutions of PVDF-HFP copolymers with PEO-PPO block copolymers and PEO oligomers followed by activation of the polymer blend films in electrolyte solutions. The morphology and conductivity of these solid electrolytes were studied as a function of concentration, molecular weight and sequence order (in the case of PPO-co-PEO-co-PPO or PEO-co-PPO-co-PEO) of the PEO and PEO-PPO copolymers, and also of the casting solvent and evaporation rate of the casting solvent. Structural studies of PVDF-HFP/PEO and PVDF- HFP/PPO-co-PEO blend films (SEM, DSC) before activation with lithium salt electrolyte may indicate the occurrence of spinodal decomposition in the films during slow evaporation of the casting solvent. As a result of spinodal decomposition, an interpenetrating bi-continuous phase may evolve with microphase separation between PVDF-HFP and PPO-PEO phases, in which the PVDF phase provides mechanical support and the PPO-PEO phase pfovides a conductive path.

Thin films (0.3μm to 11.2 μm) of Polyethylene Oxide (PEO) with molecular weights from 6 × 103 to 4 × 105 were prepared from aqueous solutions by a spin technique as AI-PEO-AI structures, or as AI-PEO-Si structures. Dielectric measurements (capacitance and loss angle) were carried out in a frequency range 3 mHz ≤ f ≤ 1 MHz in atmospheres of different relative humidity (0% r.h. to 75% r.h.) and at different temperatures (293 K to 323 K). The nominal dielectric permittivity exhibits a remarkable dependence on the sample thickness and the relative humidity. We find a true volume polarization in the high frequency range and a thermally activated relaxation process in the low frequency range, whose time constant is shifted towards high frequencies with increasing r.h.. It is considered that due to the absorbed dipolar water molecules chemical bonds within the sample are broken and quasi-free ions are generated. These ions move through the sample to the electrode interfaces and form an ionic space charge. We assume that at the PEO-Al interface an oxide layer is formed, which is impermeable for these ions. The transit times and the drift velocities of the ions are almost independent of the electric field strength in the low-field limit. Therefore we conclude that the movement of the ions can be described by a multiwell potential model, where the transition probability between neighbored wells is thermally activated.

We have demonstrated that PEO-based polymer electrolytes prepared by solvent-free procedures and with the addition of particle-size ceramic powder have very stable lithium interface properties—a very important feature for the development of successful lithium metal polymer batteries (LPBs). The results of cyclability tests at different charge-discharge rates carried out on prototypes of LPBs assembled with the dry prepared PEO20-LiCF3SO3-20%w/w λLiAlO2 composite electrolyte and with a composite cathode based on LiMn204 spinel operating at 3V are reported and discussed.

The synthesis, spectroscopic and electrochemical characterization of a series of hybrid organic-inorganic materials are reported. The hybrids are formed by conducting organic polymers (polyaniline, polypyrrole) and electroactive inorganic species. The latter can be either molecular anions (polyoxometalates, hexacyanoferrates) or extended oxide (V205), leading to different host-guest combinations. We have carried out a systematic study of the synthesis of the hybrids and determined key parameters for the reproducibility of the materials obtained. We have determined under what conditions the molecular species stay anchored in the polymer contributing to the overall electrochemical activity of these materials and turning the polymers from anion-insertion electrodes into cation-insertion electrodes. In the PAni/V2O5 system we have established the existence of two phases corresponding to the intercalation of one and two monolayers of PAni into V2O5 and have carried out their electrochemical characterization and their optimization as insertion cathodes in reversible lithium cells.

High temperature protonic conducting polymer membrane provides new technological applications in the electrochemical devices including electrochromic displays, chemical sensors, fuel cells and others. Organic/inorganiaianocomposites membrane consists of SiO2/PEO (Polyethylene Oxides) hybrid are remarkable family of isotropic, amorphous polymer materials, which has been synthesized through sol-gel processes. The hybrid membrane doped with acidic surfactant molecules shows good protonic conductivities at high temperatures above 100C. The membrane was found to be thermally stable at high temperatures because of the inorganic SiO2 framework in the composites matrix.

Composites of alumina ceramic powders prepared by co-precipitation and sol-gel methods with Lithium Iodide based polymer electrolytes are described. The polyether matrices Poly(ethylene oxide) (PEO) and block copolymer Poly(propylene glycol-ethylene glycolpropylene glycol) (Triblock) with Lil in a ratio [O]:[Li] = 20:1 are used with up to 17 wt% of α-A1203 (medium grain size). Differential Scanning Calorimetry (DSC) studies show that Tg values for PEO based composites are higher whereas those for Triblock based composites are lower than the Tg value of the polymer/salt system.

Conductivity measurements as a function of temperature show that there is no significant change in conductivity above the melting points for the electrolytes after α-A1203 powder addition (σ approximately 10−3 S.cm−l at 100°C), whereas better mechanical properties are observed for the ceramic reinforced samples. An increase in conductivity is obtained for the Triblock based composites near room temperature as a consequence of the lower melting point of these materials (26°C) in comparison to the PEO based composites (54°C).

Electrolyte solutions formed by the addition of lithium hexafluorophosphate (LiPF6) and lithium perchlorate (LiC104) to solvents obtained by mixing ethylene carbonate (EC) with propylene carbonate (PC) and dimethyl carbonate (DMC) were studied. The temperature dependence of conductivity, infrared and Raman spectra of the EC-DMC and PC-EC-DMC solvent electrolytes are discussed. The experimental and theoretical studies of characteristic vibrations of DMC are reported.

Ion mobility in mixed alkali glass is discussed in the context of the recent experimental observation that oxygen diffusion from molten salt into glass accompanies the replacement of smaller alkali ions for larger alkali ions during ion exchange. The assumption is made that simultaneous migration of two unlike monovalent cations induces, among other things, oxygenexchange diffusion between sites. Diffusing oxygen molecules form additional fluctuating sites or traps lying along the ion pathways between regular ionic sites. Instead of jumping directly to the regular ionic site, mobile ions are forced to execute several additional hops between fluctuating sites, and this results in significant reduction in ion mobility.

Crystalline ion conductors like RbAg4I5 and others display a characteristic shape of their dispersive conductivities at frequencies below the microwave regime. As the temperature is decreased, the onset of the dispersion is shifted to lower frequencies and thus the characteristic shape of the dispersion becomes visible in an increasingly broad frequency range. In a log-log plot of the frequency-dependent conductivity, the slope is found to increase continuously, but not to surpass unity. For the first time, this behavior is now consistently explained. The particular shape of the dispersion is shown to be equivalent to a proportionality of the rates of relaxation via the singleand many-particle routes. This is the essence of the concept of mismatch and relaxation (CMR). Model conductivity spectra based on the CMR include the UDR (universal dynamic response) as well as the NCL (nearly constant loss) behavior. Both universalities are thus traced back to a common dynamic origin.

A brief excerpt of a more comprehensive quantitative theoretical analysis on the role of effective rate constants in interfacial processes is given (in particular [1], see also [2,3]). Chemical incorporation, tracer incorporation and steady state electrical experiments are considered. It is shown that besides experimental differences there are mechanistic and conceptual differences between the three effective rate constants (kδ, k*, Qq). The treatment based on irreversible thermodynamics and chemical kinetics shows similarities and differences with respect to the analogous situation in the bulk. As special cases adsorption and transfer limited kinetics are considered. Having related the k-values to the exchange rates of the rate determining step and to the chemical capacitance outside the boundary zone, the characteristic dependencies on controlling parameters and also the correlation with diffusion coefficients can be derived. This is done for electron-rich materials such as SOFC cathodes. A further point which is briefly mentioned in this context is the fact that flux constriction effects may lead to apparent surface rate constants. The role of space charges is briefly discussed for the case of grain boundary kinetics [4]. In electron-poor materials such as SrTiO3(Fe2O3) or Zr02(Y203) additional mechanistic differences should occur, since in the tracer case mechanisms are possible at the surfaces which do not have to involve electrons directly. Here also discrepancies with respect to electrical experiments are predicted (leading to a surface analogue of a Haven ratio). Some experimental results obtained with SrTiO3 are discussed in this context.

A literature overview on microstructural and electrical properties of nanocrystalline ceramics is given. Space charge effects in nanosystems, especially thin-films and colloidal particles, are discussed from a theoretical point of view. Some common features of nanocrystalline ceramics are pointed out: nanoparticles present few extended lattice imperfections and the densification process begins at distinctly lower temperatures than that of coarse-grained ceramics. A significant decrease of grain boundary resistance occurs due to grain-size dependent dopant segregation, which leads also to an important increase of the apparent solubility of dopants in nanocrystalline materials. A number of studies confirm the theoretically expected reduction of the point defect formation enthalpy at interface sites, giving rise to significantly larger nonstoichiometry and electronic conductivity of nanocrystalline materials. Increased ionic conductivity has been found only in a limited number of cases, some of which remain controversial.

We studied the drift of Cd interstitials in CdS single crystals at an electric field applied to the crystal. These atoms are totally ionized at moderate temperatures of the investigation (300 - 400 K). Mobile Cd ions drift from the anode to the cathode. A time-dependence was studied experimentally for the voltage dropped on the crystal at the constant value of the current passed through the sample. A non-stationary problem developed for the transient process allowed to derive the ion mobility in such a process from the experimental data. Concentration profiles and their time history were investigated in detail for the ions and free carriers.

An analysis is presented that allows calculating properties of primary solid solutions in ionic crystals. These properties are expressed in terms of properties of the undoped host material and the impurity.

One can calculate the solubilities of the impurities with a knowledge of the concentration of what is defined as the “corresponding native species”, the standard chemical potential of the materials involved and the local shear modulus of the host material.

The changes in concentrations of ionic point defects as well as electron/hole concentrations due to doping are also calculated. In order to do so one has to know the concentrations of the native point defects in the undoped host material and the concentration of the dopant. It is shown that in a native p-type semiconductor (e.g., Cu20) extrinsic donors are mainly self-compensated by ionic defects, while extrinsic acceptors are compensated significantly by holes.

Lanthanum silver oxysulfide, (LaO)AgS, exhibits a predominantly ionic conductivity of 10−3 to 10−1 S/cm between 300 K and 770 K. The tetragonal structure consists of alternating (LaO) and (AgS) sheets, their sequence being O-La-S-Ag-S-La-O. The structure suggests that ionic transport arises from migration of silver ions within the AgS layers analogous to sodium ion transport in Na-β-alumina.

Neutron powder diffraction data measured at five temperatures between 300 K and 770 K are analysed using the Rietveld method to determine the distribution and thermal vibration parameters of the mobile silver ions. The structural investigation is accompanied by measurements of the total conductivity in the same temperature range in order to resolve severe discrepancies in the literature data.

Oxide glasses had receive a great deal of attention on the last couple of years because of their potentially high cationic transport. Interesting features have been found on Li20-V205-TeO2 glassy system. Such materials were prepared under open air at 800°C and traditional quenching. Glass formation was been found up to 45% alkali concentration on the V205-TeO2 binary system. Upon addition of Li20 the glass transition temperature lowered systematically up to values near 175°C. Structural correlation between glass transition and structure are made. Those materials show high promise as electrolytes for solid-state batteries applications.

Temperature dependence of 7Li NMR was measured in 50Li20-50B203 glasses. A new method for the analysis of motional narrowing of the line width (MNLW) incorporating Kohlrasuch-Williams-Watt (KWW) function, exp(-(t/τ)β) is presented. The obtained activation parameters are compared with that from conductivity. It was shown that MNLW can be explained by the same activation energy from conductivity. It was found that electrical relaxation time was an order of magnitude smaller than that from those from NMR line width. At high temperature region, where the line is well narrowed, a residual line width was observed. It is as large as 1 kHz, and gradually decreases with the increase in temperature. It was explained that there is a mobility difference in lithium ions in this glass. These results suggest that some fraction of ions are highly mobilized in the glass.

Electrochemical cation doping into the YBCO ceramics has been carried out using SOED 2 method (electro-bi-injection). The SOED 2 method consists of the Anode/M-β”-A1203/Ceramics/YSZ/Cathode electrolysis system, where the metal cation M and oxygen anion are simultaneously injected into the oxide ceramics so that electrical neutrality is maintained in the ceramics. YBa2Cu3Oy superconductor was used as the ceramics to be doped. In general, graded doping occurred at a relatively high temperature, because the migration rate of the oxygen anion is close to that of the metal cation in the grain boundaries of the ceramics at high temperature. As a result, the metal cation was graded on the anode side of the YBCO ceramics. The doping situation depended on the electrolysis temperature, the valence of the doped cation. The mechanism of the electro-bi-injection is discussed.

The electrical conductivity of two-phase mixtures of an ionic conductor with dispersed insulator particles is described using a percolative transport model. The difference of grain sizes, the existence and anisotropy of confined high conductivity paths near the grain interfaces are implemented by simple rules. The model is capable of simulating the two cases of ionic conductor/insulator composites : those with and those without strong interfacial interactions. The discussed experimental examples are LiI-A1203, CuBr-A1203 and CuBr-TiO2.

PbSnF4 is the highest performance fluoride ion conductor. A fast amperometric response oxygen sensor based on PbSnF4 has been constructed and tested. A long life device with time independent response and reliable performance requires the materials used for its construction be stable over the life time of the device in the operating conditions. Since ionic conductivity is thermally activated, possible use at high temperature can be envisaged. Therefore, it is of prime importance to know in details the behavior of the material versus time in the expected temperature range of use and of storage. PbSnF4 can be prepared by many methods that we have investigated, and each method gives a material that is different from the others in one way or another (symmetry, strain, particle rendomization, particle dimensions, temperature range of stability). In addition, we have shown that several phase transitions take place versus temperature or when some other treatments are applied. Many of these transitions are very sluggish, and therefore give a false impression of stability, when the phases are actually metastable, and thus changes take place slowly over time. We have studied the stability of tetragonal α-PbSnF4 and o-PbSnF4 by use of X-ray diffraction, in the most probable conditions of use (ambient temperature to 200°C in air). Changes were found to take place, which should be taken into account in the design of devices and when establishing their optimum temperature of use and storage.

Mössbauer spectroscopy has been seldom used for the characterization of ionic conductors. However, since the introduction of divalent tin in MF2 fluorites (M = Sr, Pb and Ba) to form MSnF4, PbSn4F10 or the Pb1−xSnxF2 solid solution, all of which have structures closely related to the fluorite type, results in an enhancement of the fluoride ion conductivity by up to three orders of magnitude, and since 119 Sn is the second best Mössbauer nuclide, it seems that the Mössbauer technique could provide useful information about how tin(II) modifies the fluorite structure and leads to such a tremendous enhancement of the fluoride ion mobility. The MF2/SnF2 systems contain some number of materials that show order/disorder phenomena (between M and Sn, and also between different fluorine atoms) which make it difficult to understand them from diffraction data only. Mössbauer spectroscopy has been invaluable in helping understand the local structure at tin. By probing the valence electronic structure of tin, we can also make predictions on the possible long range mobility of the tin(II) non-bonded electron pair, which would make the material an electronic conductor or a mixed conductor.