Solid State Ionics (v.178, #19-20)

Solid solubility and electrical conduction mechanisms in 3-layer Aurivillius ceramics by E.I. Henriques; H.J. Kim; M.S. Haluska; D.D. Edwards; S.T. Misture (1175-1179).
The Aurivillius ceramics Bi(2−y)Pb y Sr2Nb2TiO(12−δ) and Bi2Sr2Nb2Ti(1−x)M x O(12−δ) (M = Fe, Cr, Mn) were successfully prepared and the solid solubility limits were determined to be y  = 0.2 and x  = 0.2. The solubility limits for the phases are limited by the oxygen vacancy concentration. The electrical conductivity was measured as a function of temperature and oxygen activity, and showed that undoped Bi2Sr2Nb2TiO12 is an electronic conductor at high oxygen activity, while acceptor doping with Pb or Fe results in ionic conduction. The total conductivity increases with dopant concentration to a maximum at the solubility limits of 7.5 × 10− 4 to 10 × 10− 4 S/cm at 800 °C for Pb, Fe, and Mn dopants.
Keywords: Aurivillius; Conductivity; pO2; Solubility;

Effects of gold nanoparticles and lithium hexafluorophosphate on the electrical conductivity of PMMA by Soumen Jana; Amin Salehi-Khojin; Wei-Hong Zhong; Hui Chen; Xiong Liu; Qun Huo (1180-1186).
An increase in electrical conductivity of a polymeric system can be realized by adding conductive fillers and/or dissolving a salt in a suitable solvent or polymer through formation of ionic conduction. An appropriate solvent that can form complexes with alkali metal cations is critical to providing electrical conductivity enhancements to a wide variety of polymers. In this study, we investigated the effects on electrical conductivity of lithium hexafluorophosphate (LiF6P) through the use of butyl glycidyl ether (BGE) as the solvent for dissolving the alkali metal compound LiF6P. Additionally we examined the effects of gold nanoparticles (AuNPs) alone and with the LiF6P/BGE for possible synergistic effects on electrical conductivity. Thin films of poly (methyl methacrylate) (PMMA) blended with LiF6P salt and AuNPs separately and together, were prepared. The electrical conductivity measurements were carried out on these films as a function of the salt and/or AuNP contents. PMMA with only 0.75 wt.% LiF6P decreased the resistivity by 3 orders of magnitude compared to PMMA, which showed the optimum conductivity value for this system. Formation of BGE–LiF6P complexes were studied by FTIR spectra. XRD studies confirmed the formation of complexes in thin film specimens. It was also found that the conductivity of PMMA with AuNPs is dependent on the size of the AuNPs.
Keywords: Nanoparticles; Composites; Conductivity; XRD; FTIR;

Prediction and evaluation of sintering aids for Cerium Gadolinium Oxide by Jason D. Nicholas; Lutgard C. De Jonghe (1187-1194).
This paper presents dilatometry results for Ce0.9Gd0.1O1.95, a common intermediate temperature solid oxide fuel cell electrolyte material, doped at the 1, 3, and 5 mol% level using nitrates. The results indicate that across all dopant nitrate levels, Cu, Co, Fe, Mn, Li, and Zn reduce the Ce0.9Gd0.1O1.95 sintering temperature, while Ca, Mg, and Ni have little effect, and Al and K increase the sintering temperature. These results can be interpreted in terms of a Vegard's Slope quality factor analysis which uses a dopant's charge and size to rank its propensity to heterogeneous dope the material and/or segregate to the grain boundary as a separate phase. Further, this work shows that Ce0.9Gd0.1O1.95 can be sintered to 99% density at a record-low temperature of 800 °C, using as little as 3 mol% lithium as a dopant.
Keywords: Sintering; Low temperature; Densification; Dopant; Undersized; Liquid phase sintering; Vegard's Slope; Grain boundary engineering; CGO; GDC; Ceria; CeO2; Fuel cell; Electrolyte; Heterogeneous doping;

Modified Pechini synthesis and characterization of Y-doped strontium titanate perovskite by Xinyu Lu; Tom S. Pine; Daniel R. Mumm; Jacob Brouwer (1195-1199).
This work reports the modified Pechini preparation and properties of an A-site deficient perovskite Sr0.86Y0.08TiO3−δ (SYT). Good chemical homogeneity and electrical conductivity were determined, making SYT a potential conductive component material in a composite anode for solid oxide fuel cells. As an oxide with inherent resistance to oxidation and hydroxylation, SYT could be a substitute for the metallic Ni component in composite anodes for solid oxide fuel cells, particularly for reversible solid oxide fuel cells with attendant high steam concentrations.
Keywords: Modified Pechini process; Doped strontium titanate; Perovskite; Conductivity; Solid oxide fuel cell;

Oxygen permeation fluxes through La2Cu0.5Ni0.5O4+δ dense ceramics: Comparison with oxygen diffusion coefficients by F. Mauvy; E. Boehm; J.M. Bassat; J.C. Grenier; J. Fouletier (1200-1204).
The copper-substituted lanthanum nickelate (La2Ni0.5Cu0.5O4+δ ) was investigated as possible cathode material for intermediate temperature solid oxide fuel cells because of its mixed ionic and electronic conducting properties (MIEC oxide). The La2Ni0.5Cu0.5O4+δ compound was prepared using the “nitrate–citrate” route. Oxygen permeation fluxes through dense membranes have been measured under various oxygen partial pressure gradients in the 850–1200 K temperature range. The oxygen transport properties are compared with the previous measurements using isotopic exchange depth profile experiments and conductivity relaxation method: all of them show a very good agreement.
Keywords: Lanthanum nickelate; Oxygen permeation; IT-SOFC cathode; Oxygen diffusion coefficient;

Oxygen permeability, thermal expansion and stability of SrCo0.8Fe0.2O3−δ –SrAl2O4 composites by A.A. Yaremchenko; V.V. Kharton; M. Avdeev; A.L. Shaula; F.M.B. Marques (1205-1217).
Additions of SrAl2O4 phase to mixed-conducting SrCo0.8Fe0.2O3−δ promote oxygen-vacancy ordering and brownmillerite formation at temperatures below 1050 K due to Al3+ incorporation, but also decrease thermal expansion coefficients (TECs) and improve thermal shock stability. The SrCo0.8Fe0.2O3−δ –SrAl2O4 composite membranes exhibit also a relatively high stability with respect to interaction with CO2 due to A-site deficiency of the perovskite-related phase, caused by partial SrAl2O4 dissolution. The oxygen permeability and electronic conductivity of (SrCo0.8Fe0.2O3−δ )1−x (SrAl2O4) x (x  = 0.3–0.7) composites are determined by the perovskite component and decrease with increasing x. Despite minor diffusion of the transition metal cations into SrAl2O4, hexagonal above 940 K and monoclinic in the low-temperature range, this phase has insulating properties. Nonetheless, at x  = 0.3 the oxygen permeation fluxes at 1073–1173 are similar to those through single-phase SrCo0.8Fe0.2O3−δ membranes. The average TECs of the composite materials, calculated from dilatometric data in air, vary in the ranges (10.0–11.3) × 10− 6 K− 1 at 300–900 K and (14.7–21.1) × 10− 6 K− 1 at 900–1100 K. The low-p(O2) stability limit and electronic transport properties of SrCo0.8Fe0.2O3−δ are briefly discussed.
Keywords: Ceramic membrane; Mixed conductor; Perovskite; Composite; Oxygen permeability; Thermal expansion; Stability;

Kinetics investigation of a preferential (104) plane oriented LiCoO2 thin film prepared by RF magnetron sputtering by J. Xie; N. Imanishi; A. Hirano; M. Matsumura; Y. Takeda; O. Yamamoto (1218-1224).
LiCoO2 thin films with a preferential (104) orientation were prepared on Au substrates by radio frequency magnetron sputtering. The Li–ion chemical diffusion coefficients Li were measured by cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). The Li values depended on the content of Li in Li1−δ CoO2. The Li values by GITT and PITT were in the range of 10− 10–10− 12 cm2 s− 1 and 10− 11–10− 12 cm2 s− 1, respectively, and those by EIS varied over a more wide rang of from 10− 9 to 10− 12 cm2 s− 1. It was found that the Li values from different methods showed thickness independent. The Li values from different methods were compared with those reported previously.
Keywords: LiCoO2; Thin film batteries; Chemical diffusion coefficient; GITT; PITT; EIS;

Preparation of Cu coating on graphite electrode foil and its suppressive effect on PC decomposition by J. Gao; H.P. Zhang; T. Zhang; Y.P. Wu; R. Holze (1225-1229).
Cu-coated graphite electrode foil was prepared by an improved electroless plating method. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were used to study the surface morphology and composition of Cu-coated graphite electrode foil. Tests of discharge and charge and cyclic voltammograms suggest that the decomposition of propylene carbonate and exfoliation of graphite are greatly suppressed, and lithium ions can reversibly intercalate into and de-intercalate from the Cu-coated graphite electrode. Results from electrochemical impedance spectroscopy show that the Cu-coated graphite electrode has lower charge-transfer resistance and higher diffusion coefficient of lithium ions in comparison with the original graphite.
Keywords: Lithium ion battery; Electroless plating; Low temperature; Propylene carbonate; Cu coating;

Substituting mechanical stirring by ultrasonic irradiation in co-precipitation method, cathode material LiNi0.5Mn0.5O2 for lithium batteries with better layered structure and crystallinity has been successfully synthesized. The physicochemical and electrochemical properties of ultrasonic co-precipitation (UCP) prepared material were compared with those of the mechanical stirring co-precipitation (MSCP) prepared material by thermogravimetery analysis (TGA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and galvanostatic charge–discharge testing in detail. UCP prepared LiNi0.5Mn0.5O2 presents better rate discharge capability, cyclic stability and reversibility, resulting from smaller electrochemical polarization during electrode reaction and easier lithium ion insertion/desertion. Application of ultrasonic irradiation during the co-precipitation preparation process is beneficial to produce samples with better physicochemical and electrochemical properties.
Keywords: LiNi0.5Mn0.5O2; Lithium battery; Layered structure; Ultrasonic irradiation; Cathode material;

Poly(ethylene oxide)-based polymer electrolyte incorporating room-temperature ionic liquid for lithium batteries by Jae-Won Choi; Gouri Cheruvally; Yeon-Hwa Kim; Jae-Kwang Kim; James Manuel; Prasanth Raghavan; Jou-Hyeon Ahn; Ki-Won Kim; Hyo-Jun Ahn; Doo Seong Choi; Choong Eui Song (1235-1241).
The effect of incorporating a room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI), in the polymer electrolyte (PE) based on poly(ethylene oxide)-(lithium bis(trifluoromethanesulfonyl) imide) [PEO-LiTFSI] was investigated. BMITFSI content was varied between 20 and 80 parts by weight (pbw) in 100 pbw of PEO-LiTFSI and the influence on ionic conductivity, electrochemical stability and interfacial properties on lithium electrode was studied. A remarkable increase in ionic conductivity was achieved with BMITFSI addition, the effect being most pronounced at lower temperatures. Compared to PEO-LiTFSI, the PEs containing BMITFSI exhibited well-defined redox peaks corresponding to stripping and deposition of lithium. The PEs containing BMITFSI exhibited good electrochemical stability and significantly low interfacial resistance with the lithium electrode. Good discharge performance with 82% active material utilization and stable cycling property was achieved when the PE containing 60 pbw of BMITFSI was evaluated in Li/LiFePO4 cells at 40 °C.
Keywords: Room temperature ionic liquid; Polymer electrolyte; Lithium battery; Ionic conductivity; Imidazolium salts;

The long-term stability of composite electrodes consisting of silver and yttrium-stabilized bismuth oxide (Ag–YSB) or silver and erbium-stabilized bismuth oxide (Ag–ESB) has been examined in order to evaluate the potential of such systems for use as cathodes in low-temperature solid oxide fuel cells (SOFCs). The performance of these electrodes at 650 °C is initially among the best reported to date. However, the polarization resistance isothermally increases by more than 70% for Ag–YSB and nearly 70% for Ag–ESB, from 0.04 Ω cm to 0.07 Ω cm2 and from 0.06 Ω cm2 to 0.10 Ω cm2, respectively, after 100 h at 650 °C. X-ray diffraction (XRD) and electron probe microanalysis (EPMA) reveal no evidence of reactivity or interdiffusion between the silver and bismuth oxide phases. A pure silver electrode tested under the same conditions showed a near fourfold increase in ASR (from 0.92 Ω cm2 to 3.55 Ω cm2). Scanning electron microscopy (SEM) analysis reveals that the silver phase microstructure undergoes dramatic growth during this timeframe. This microstructural growth and consequent reduction in porosity is believed to diminish the cathodic reaction zone size and inhibit gas transport, thus resulting in the observed rise in polarization.
Keywords: SOFC cathodes; Cathode stability; Silver; Bismuth oxide; ESB; IT-SOFC; Composite cathodes;

Functionalized zeolite A–nafion composite membranes for direct methanol fuel cells by Xiao Li; Edward P.L. Roberts; Stuart M. Holmes; Vladimir Zholobenko (1248-1255).
A series of composite membranes based on zeolite A and Nafion 117 have been fabricated for direct methanol fuel cells. The external surface of zeolite A has been modified to enhance the interface bonding between inorganic zeolite crystals and Nafion ionomer. The modified zeolite samples have been characterised using a combination of thermal analysis and spectroscopic techniques. Methanol permeability of Nafion 117 could be reduced by as much as 86% by incorporating functionalised zeolite NaA crystals into the membrane. The effect of different functionalisation level is discussed.
Keywords: Zeolite NaA; Nafion; Composite membrane; Functionalisation; FTIR spectroscopy; Thermal analysis; Proton conductivity; Methanol permeability; Direct methanol fuel cell;