Solid vitreous electrolytes based on the system Li2O-Li2SO4-B2O3-MoO3 for rechargeable lithium power sources

In the given work with the purpose of improvement of moistening ability of sulfoborate solid vitreous electrolyte (SVE) in their structure entered molybdenum oxide (VI). Reduction of wetting angle, i.e. improvement of electrode wetting by a SVE-melt, accompanied by better electrode (aluminium) /SVE interface contact formation. Accordingly, the interface impedance is reduced. As a result of the carried out experiments is established, that the modifying SVE by molybdenum oxide (VI) renders complex positive influence on its physical-chemical properties, namely: improves X-ray-amorphism, raises ionic conductivity, reduces electronic conductivity and effective energy of ion conductivity activation. At comparison of properties modified SVE and "LiPON", it is visible, that the ratio between ionic and electronic conductivity for modified SVE approximately on the order is higher, than for "LiPON". Ionic conductivity of the modified SVE higher than conductivity of "LiPON". The low value of electronic conductivity investigated SVE on a background ionic is the positive factor from the point of view of their use in lithium power sources. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Synthesis and characterisation of new nanostructured manganese oxides for lithium batteries

A variety of new Co-substituted and Al-substituted manganese dioxide materials, having various structures, and various morphologies with nanosize crystals have been prepared by the electrochemical-hydrothermal method. The results of structural and physico-chemical characterizations are presented by comparison to non substituted MnO₂ compounds. The substitution leads to nanostructured deposits with different morphologies and much larger surface areas. Intrinsic electrochemical Li insertion properties of these new substituted γ-MnO₂ materials are also reported. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Improvement of lithium battery performance through composite electrode microstructure optimization

The lithium trivanadate Li_1.2V₃O₈ has been investigated during the past decade as a very promising positive electrode material for lithium batteries due to its high theoretical capacity of 360 mAh/g. However, the experimental capacity remains generally much lower than (about half) the theoretical value. To increase electrode cycling performance in batteries, most researchers generally focus their work on the active material optimisation. Here we show that the polymeric binder of the composite electrode may have an important role on the electrode performance. We describe a new tailored polymeric binder combination with controlled polymer-filler (carbon black) interactions that allows the preparation of new and more efficient electrode architecture. Using this polymeric binder, composite electrodes based on Li_1.2V₃O₈ display a room-temperature cycling capacity of 280 mAh/g (C/5 rate, 3.3-2V) instead of 180 mAh/g using a Bellcore-type composite electrode (PLIon^TM technology). We have coupled SEM observations, galvanostatic cycling and electrochemical impedance spectroscopy in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors that provide efficient charge carrier collection within the composite electrode complex medium will be discussed. Present findings open up new and attractive prospects for electrode performance optimisation. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Electronic structure and covalency in superionic conductors

The electronic states of noble metal halides and alkali halides are calculated by the DVXα cluster method to get more microscopic evidence for the p — d hybridization and the covalency in noble metal halides. It is found that both components of anti-bonding and bonding exist in the diagram of overlap population (DOP) for AgX (X=halogen) and these two components are made up of the 4d band of Ag ion and the p band of halogen ion, which form the p — d hybridization. The covalency of noble metal halides is in the border between that of the fourfold coordinated compounds such as AgI and that of the sixfold coordinated compounds such as AgCl. These calculation results on the covalency are compared with the Phillips's ionicity. Paper presented at the Patras Conference on Solid State Ionics, Patras, Greece, Sept. 14 – 18, 2004.     

Ionic conductivity in hydrogels for contact lens applications

Biphasic hydrogel polymers are in the forefront of new extended wear contact lens development. In the biphasic hydrogel the objective is to produce co-continuous domains of siloxane units for high oxygen permeability, coupled with hydrophilic units forming aqueous channels for hydraulic and ion mobility. These are distributed in phase separated nano-scale regions such that the material is optically clear while achieving the required properties to maintain corneal health and lens movement. This paper describes how Impedance Spectroscopy permits a rapid measurement of ion conductivity in a range of silicone and non-silicone hydrogel materials with water contents ranging from 18% to 75% equilibrium water content. For non-silicone hydrogels relative sodium ion conductivity follows a typical percolation curve. However, for silicone hydrogels ion mobility is three orders of magnitude higher than conventional hydrogels of the same equilibrium water content. The influence of electrolyte concentration, interfacial electrode sample contact pressure and temperature are also reported. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Development of oxygen ion conductors: One relevant tendency

In the past ten years a series of developments in the field of materials with dominant oxygen ion conduction introduced a variety of new systems. The most relevant aspect is a shift from ionic transport mechanisms based on the motion of oxygen vacancies, to mechanisms based on mobile oxygen interstitials. In parallel, structures identified with dominant oxygen ion conduction moved from the relatively simple fluorite related ones to more complex materials, namely with the apatite-type and related structures, including coexistence of ionic and covalent bonding. This shift is understood as a major development, opening a wide range of alternative solutions for further exploitation. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Anode materials for lithium ion batteries in the Li-Zn-P system

This paper presents an exhaustive study of the Li-Zn-P system through the synthesis and electrochemical characterisation of several binary and ternary phases: Li₉ZnP₄, LiZnP, Zn₃P₂ (α and β), ZnP₂ (α and β), LiZn, and LiZn₄. Three synthetic routes have been used to prepare these materials: ceramic synthesis and ball milling without and with annealing. Li-Zn-P system phases have been evaluated through X-ray diffraction and electrochemical reactivity towards lithium. Exhibiting high specific capacities at potentials close to 0.7 V vs. Li⁺/Li, some of these materials are promising as negative electrode materials for lithium ion battery. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

The nature of conduction pathways in mixed alkali phosphate glasses

In this paper we discuss the nature of the ion conduction pathways in Li_xRb_1−xPO₃ glasses. Our investigations are based on a bond valence analysis of reverse Monte Carlo (RMC) produced structural models in quantitative agreement with neutron and X-ray diffraction data. In a previous letter [11] we have shown that this approach enables us to reproduce and understand the mixed alkali effect (MAE) directly from the structural models. The results have shown that the drastic drop of the conductivity for an intermediate composition (x ≈ 0.5) is mainly caused due to the blocking by immobile unlike cations, which is highly effective since the two types of alkali ions are randomly mixed and have distinctly different conduction pathways of low dimensionality. Here, we explore the local dimensionality of the pathways and discuss its implications for the network of pathways and the related ionic conductivity. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Oxide solid electrolytes under non-equilibrium conditions — Interfaces and ageing

This paper gives an overview of the materials transport processes which occur in oxide solid electrolytes subjected to a generalized thermodynamical potential gradient. The general equations allowing to describe the transport processes on the anionic and cationic sublattices are given. Kinetic demixing processes and microstructural changes leading to surface instabilities are analysed. Experimental results obtained with yttria-doped zirconia and gadolinium doped ceria illustrate the importance of these phenomena on the transport properties of the materials but also on their long term stability in operating conditions. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Direct methanol fuel cells: The influence of methanol on the reduction of oxygen over Pt/C catalysts with different particle sizes

Two Pt/C catalysts with different particle sizes (Pt/C: 2.5 nm, Pt/C-700Ar: 5.1 nm) were investigated by applying a half-cell configuration —rotating disk electrode (RDE) technique in H₂SO₄ aqueous solutions in the absence of or in the presence of methanol with different concentrations. Pt/C catalyst exhibited higher mass activity in H₂SO₄ aqueous solution without methanol and slightly lower mass activity in H₂SO₄ plus 0.1 mol/L CH₃OH in comparison with that of Pt/C-700Ar catalyst. On the contrary,single direct methanol fuel cell (DMFC) tests showed that Pt/C exhibited higheroxygen reduction reaction (ORR) activity and better cell performance, mainly due to the different kinds of electrolyte properties. Furthermore, it suggested that a better single DMFC performance could be obtained with a smaller particle size Pt-based cathode catalyst. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 — 18, 2004.     

D.C. conductivity of transparent conductive ZnO:Al films in the temperature range 80–360 K

An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range from 80–360 K on nanocrystalline ZnO:Al films (Al³⁺ 2%) of thickness 500 nm prepared on glass microscope slides by a dip — coating method is presented. The electrical conductivity σ, which at room temperature varied between 0.1 to 2.7 S/cm, increased almost linearly with T for all the samples. Measurements of the Hall coefficient at room temperature and in a magnetic field of 1.2 T, gave R_H=0.53 cm³C⁻¹, from which a carrier concentration of n=1.18×10¹⁹ cm⁻³ and a carrier mobility of μ=1.40 cm²/Vs were deduced. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Rheological properties and impedance spectroscopy of PMMA-PVdF blend and PMMA gel polymer electrolytes for advanced lithium batteries

In the present study, blend ionic conducting membranes formed by poly(methylmethacrylate (PMMA) / poly(vinilydenefluoride) (PVDF) (blend ratio PMMA/PVdF=80/20), lithium perchlorate (LiClO₄) as a salt and a mixture of ethylene carbonate (EC)-propylene carbonate (PC) as plasticizer are prepared and characterized by impedance spectroscopy and dynamic rheological experiments. We compared the results obtained on the blends with those on PMMA gel-based polymer electrolytes incorporating the same EC/PC mixture of plasticizer and the same quantities of salt. The main focus of this study is to illustrate the rheological data of the gels and blends electrolytes to point up their mechanical stability with the temperature in sight of the technological application. The conductivity values are reported in the 20–100 °C temperature range for different lithium salt contents, while the rheological behaviour has been recorded up to 140 °C. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Thin porous anodic alumina films: Interface trap density determination

The electrical properties of thin porous alumina films in the form of MOS structures were studied with dielectric spectroscopy at room temperature. The thickness of the samples was found to be approximately 95 nm with a cross section area of 1.6×10⁻³ cm².C-V andG-V measurements were performed by applying a loop sweep voltage 2.0 V to −5.0 V. Correction to the measurements were performed by considering a series resistanceR _S and leakage currentI _DC. TheC-V results show hysteresis effects due to the presence of positive charges in porous alumina. These charges may be are attributed to the residual electrolyte during the anodization process in the sample preparation. Three distinct regions in theC-V results are observed, namely the inversion, the depletion and the accumulation regions. In the voltage region, where depletion of carriers is observed,C-f andG-f measurements were recorded in the frequency range 1 Hz to 10⁶ Hz. The conductance method was applied for the calculation of the density D_it of carriers, trapped in the interface between insulator and semiconductor, and of the response time τ_it as a function of the applied bias voltage were performed. The values obtained for D_it and τ_it are of the order of 3×10¹² eV⁻¹ cm⁻² and 10⁻³ s, respectively, and they are voltage dependent. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Charge transfer in mixed proton, oxygen ion and electron solid oxide conductor

Analysis of the equivalent scheme of the mixed proton-oxygen ion-electron conductor (MPOEC) allowed to obtain relationships between parameters of the membrane (total conductivity and transfer numbers) and parameters of the charge and mass transfer through the membrane (partial ion and electron currents, the specific flux of hydrogen at the cathode membrane surface) under regime of electrochemical reforming. It was stated that presence of proton conductivity in addition to oxygen ion conductivity led to increase of total flux of produced hydrogen. However, under conditions typical for the electrochemical reforming of methane into hydrogen, the specific hydrogen flux is about four times lower in the case when the membrane has proton-electron conductivity than in the case when the membrane has oxygen ion-electron conductivity. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

IS α-Al2O3/ La0.8Sr0.2Ga0.8Mg0.2O3–δ really a new ionic conductor composite?really a new ionic conductor composite?

The recent interest in the (Sr, Mg) doped LaGaO₃ family compounds as electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs) has suggested the study of the system α-Al₂O₃/La_0.8Sr_0.2Ga_0.8Mg_0.2O_3–δ as a possible new ionic conductor composite. The studies concerning the electrical and microstructural characterization of the system α-Al₂O₃/La_0.8Sr_0.2Ga_0.8Mg_0.2O_3–δ, in a wide compositions range, are reported and discussed. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

An automated setup for impedance and electrochemical measurements of NOX sensors

An automated setup for impedance measurements of NO_X sensors and sensor elements has been assembled. The NO_X atmosphere is generated using NO and NO₂ calibration mixtures and N₂. The mixture is passed to the measurement chamber, where impedance measurements are performed. The sample can be subjected to temperature between 50 and 800 °C. The gas mixture is passed to the chemiluminescence analyser, where NO_X and NO amount is determined. The automation is based on National Instruments LabView programming language. Gas flow control, impedance measurement and NO_X level analysis can be simultaneously performed using a single PC computer. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Phosphate materials for cathodes in lithium ion secondary batteries

Olivine phosphates of general formula LiMPO₄ (M=Fe, Co, Ni) were prepared and characterised in order to evaluate new potential cathode materials for secondary lithium ion batteries. The synthesis was performed by soft chemistry methods to avoid problematical and energetic expensive solid state reactions. In all the compounds no secondary phase was detected and the powder morphology was found to be suitable for cathode layers preparation. Only LiFePO₄ and LiCoPO₄ showed reversible lithium deintercalation-intercalation at 3.5 and 4.8 V vs. Li⁺/Li, respectively. The LiCoPO₄ high potential makes this compound very attractive for high energy batteries, but unfortunately its lifetime appears to be too poor. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Organic-inorganic nanocomposite materials prepared by the sol-gel route as new ionic conductors in quasi solid state electrolytes

Nanocomposite organic/inorganic materials made through sol-gel method exhibit high values of ionic conductivity when they were impregnated with the redox couple I ₃ ⁻ /I⁻ Two different kinds of nanocomposite materials, depending on the different interactions between silica and poly(ethylene)oxide or poly(propylene)oxide blends, were prepared by the sol-gel technique in room temperature. Gels, for both nanocomposite materials, were obtained by acetic acid catalyzed solvolysis and were regulated by formation of intermediate products, such as silicon ester and -Si-O-Si-oligomers. Time-resolved fluorescence techniques and conductivity measurements were performed in order to define the parameters which allow maximum probe mobility and minimum confinement conditions with the aim to apply these materials in quasi solid state electrolytes. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Sodium superionic conductor sputter-deposited coatings

Thin sodium superionic conductor (Nasicon) coatings are deposited on rotating substrates by co-sputtering in the reactive mode of a Zr-Si and a Na₃PO₄ target. The influence of the discharge current and of the target-to-substrate distance is investigated owing to the targeted Na₃Zr₂Si₂PO₁₂ stoichiometry. A thermo-structural analysis shows that the amorphous as-deposited coating of convenient composition crystallises around 700 °C in the monoclinic structure. Electrical measurements performed at room temperature after various annealing treatments indicate a ionic conductivity of about 2·10⁻³ S·cm⁻¹, consistent with that of bulk Nasicon. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Electrochemical promotion of environmental catalysis

Electrochemical catalysts were used for environmental applications, such as the clean production of energy from propane and propene combustion, the elimination of VOC's like propene and the NOx abatement All the selected electrochemical catalysts were composed of a Pt film deposited on YSZ, NASICON or CGO. It was found that all these chemical reactions can be electropromoted. Moreover, the reaction rates can be in-situ tuned by applying a polarisation. Furthermore, the selectivity of Pt-based electrochemical catalysts can be modified in order to avoid the formation of pollutant. Finally, EPOC can improve the lifetime of a catalyst by inhibiting its poisoning by carbonaceous species. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.