1999 MRS Spring Meeting & Exhibit

Chairs

Masayasu Arakawa
Nippon Telegraph & Telephone Corp
Integrated Info & Energy Sys Labs
Tokyo, 180-8585 JAPAN
81-422-593883

Hans-Peter Brac
Electrochemistry Section
Paul Scherer Inst
Villigen PSI, CH-5232
SWITZERLAND
41-56-310-2410

Daniel Doughty
Li Battery R&D
Sandia National Labs
MS 0613
Albuquerque, NM 87185
505-845-8105

Katsuhiko Naoi
Dept of Applied Chemistry
Tokyo Univ of Agriculture & Tech
Koganei, Tokyo, 184-8588 JAPAN
81-42-388-7174

Linda Nazar
Dept of Chemistry & Physics
Univ of Waterloo
Waterloo, ON N2L 3G1 CANADA
519-888-4637

Symposium Support

• Sulzer Innotec

Proceedings published as Volume 575
of the Materials Research Society
Symposium Proceedings Series. * Invited paper

SESSION CC1: CATHODES I
Chairs: Daniel H. Doughty and Linda F. Nazar
Monday Morning, April 5, 1999
Metropolitan II (A)

8:30 AM *CC1.1 FIRST-PRINCIPLES STUDY OF PHASE STABILITY AND ELECTROCHEMICAL PROPERTIES IN LITHIUM-METAL OXIDES. Gerbrand Ceder , Anton Van der Ven, Massachusetts Institute of Technology, Department of Materials Science and Engineering, Cambridge, MA.

Many of the properties of insertion electrodes can be directly computed with first-principles methods. Such computations are solely based on the basic laws of Physics and therefore require no experimental data. This makes them particularly suitable for predicting the properties of novel or incompletely characterized materials. We have recently demonstrated the applicability of first-principles methods to predict the Li-insertion potential and the phase stability in lithium-metal oxides. This has already been used to predict the insertion behavior of previously untested compounds. We present first-principles results for the phase stability in the Li_xCoO₂ and Li_xMnO₂ systems. In Li_xCoO₂ we predict the occurence of staging at low Li concentrations. In LiMnO₂ we find that anti-ferromagnetism plays an important role in stabilizing the orthorhombic structure. Calculations are also highly effective instyding the electronic changes that occur in the material upon lithiation. While Li insertion in Li_xCoO₂ transfer an extra electron to the t2g band of the material we find that the net-electron increase is largely located around the oxygen ions. This is due to the increased ionicity of the cobalt-oxygen bond upon lithiation. We demonstrate how this effect relates to important cathode properties such as the average lithiation voltage and the variation of lattice constant with Li content.

9:00 AM *CC1.2
LITHIUM NICKELATE ELECTRODES FOR LITHIUM BATTERIES. Hajime Arai , Yoji Sakurai, NTT Integrated Information and Energy Systems Laboratories, Tokai, Ibaraki, JAPAN.

Lithium nickelate is a promising electrode material for secondary lithium batteries (especially for portable applications) because of its high oxidation power of about 4 V vs. Li/Li⁺ and large capacity of more than 150 mAh g^-1. However, several problems have to be solved before use in commercial systems, such as synthesis difficulties and low thermal stability. This study aims at finding keys to solving these problems, and we demonstrate the importance of structural information of the material. Stoichiometry of the sample (x in Li_1-xNi_1+xO₂) greatly affects its electrode performance and phase transition during lithium extraction. The best composition LiNiO₂ is difficult to attain and several methods for minimizing x value are shown. The excess lithium method is particularly of interest because it offers almost stoichiometric materials by calcination in air. Thus obtained material shows a large capacity of over 200 mAh g^-1 with a good cycle stability.
The thermal stability of Li_1-yNiO₂ is relatively lower than that of Li_1-yCoO₂ because much lithium can be easily extracted from LiNiO₂. We use both electrochemically and chemically delithiated samples for examining the mechanism of the thermal decomposition at around 200C and discuss the instability of Ni³⁺ compared to Co³⁺.
The characteristics of lithium nickelate drastically changes upon substitution of the third metal element (cobalt, manganese, etc.) for nickel. This substitution technique is used to overcome the shortcomings of LiNiO₂ described above, especially the thermal stability. Several examples, in which both large capacity and high thermal stability are attained, are shown and discussed.

9:30 AM CC1.3
PREPARATION AND ELECTROCHEMICAL CHARACTERIZATION OF LiCoO₂ SINGLE CRYSTAL PARTICLES PREPARED BY SUPER CRITICAL WATER SYNTHESIS (SCSW). Kiyoshi Kanamura , Tokyo Metropolitan Univ, Dept of Applied Chemistry, Tokyo, JAPAN; Katsunori Toyoshima, Yukiya Hataku, Tadafumi Adschiri, Kunio Arai, Tohoku Univ, Dept of Chemical Engineering, Sendai, JAPAN.

Various kinds of transition metal oxides have been utilized in rechargeable lithium batteries as both cathode and anode materials. Most of oxides have been prepared by heating a mixture of transition metal nitrates, carbonates, and hydroxides under 500-800C. Such oxides have a lot of defects, crystal grain boundaries, aggregation and so on. In this study, we prepared single crystal particles of transition metal oxides by using supercritical water synthesis (SCWS) and investigated their electrochemical behaviors in nonaqueous electrolytes in order to realize ideal cathode and anode materials for rechargeable lithium batteries. LiCoO₂ is used as a cathode material of recently commercialized ``Lithium Ion Batteries'' Firstly, we prepared LiCoO₂ single crystal particles using SCWS method. Aqueous solutions of CoNO₃ and LiOH were used as starting materials. NO₃^- ions work as oxidant reagent to produce Co³+ from Co²+. The synthesis was performed under various conditions. The best conditions for well-developed single crystal particles were Li / Co mole ratio of 15.0 at 400C in 30MPa. Scanning electron microscopic observation showed a formation of single crystal particles of LiCoO₂ with a hexagonal symmetry. The electrochemical characteristics of the LiCoO₂ were analyzed by cyclic voltammetry. Well-defined anodic and cathodic current peaks were observed, indicating that the prepared single crystal LiCoO₂ has an adequate performance as cathode materials of rechargeable lithium batteries. Moreover, the discharge and charge cycle test was conducted using coin-type cell. The prepared LiCoO₂ showed more excellent cycleability than any other polycrystalline particles. This means that imperfect existing in polycrystalline particles cause failures of active materials (transition metal oxides).

10:15 AM *CC1.4
SYNTHESIS AND CHARACTERIZATION OF LITHIATED NICKEL BASED METAL DIOXIDES AS POSITIVE ELECTRODE MATERIALS FOR LITHIUM ION BATTERIES. Koji Nishio , Toshiyuki Nohma, Shin Fujitani, Sanyo Electric Co. Ltd., New Materials Research Center, Hirakata, Osaka, JAPAN.

Lithium secondary batteries using carbon as a negative active material and LiCoO₂ as a positive active material have attracted a considerable interest as a power source for portable appliances including notebook PCs, cellular phones and VCRs. One key toward higher performance with larger capacity, longer cycle life and lower cost is alternation of the positive active material. From this point of view, lithiated nickel based metal oxides [Li (Ni_1-x-yCO_xMn_y) O₂] were investigated as a positive active material. They were synthesized by sintering a mixture of nickel based hydroxide containing cobalt and/or manganese and lithium hydroxide in an oxygen atmosphere at a temperature between 750C and 900C, and the electrochemical characteristics and thermal stability were examined. Li(Ni_0.7Co_0.3)O₂ sintered at 850C exhibited a highly crystallized phase structure and the largest electrochemical discharge capacity of 165mAh/g at the charging up to 4.3V vs. Li/Li⁺. Capacity decrease was observed for Li(Ni_0.7Co_0.3O₂ sintered at a higher temperature of 900C. Rietveld analysis of X-ray diffraction profiles indicated that the capacity decrease can be attributed to occupation of lithium site by Co and or Ni. Thermal stability of the active materials charged up to 4.5V vs. Li/Li⁺ was characterized by measuring decomposition temperature by TG analysis. Introducing manganese into Li(Ni_0.7Co_0.3)O₂ to form Li(Ni_0.6Co_0.3Mn_0.1)O₂ elevated the decomposition temperature from 208C to 220C without capacity reduction. A cylindrical test cell (diameter:18mm, height:65mm) using Li(Ni_0.6Co_0.3Mn_0.1)O₂ as a positive active material was fabricated and its charge/discharge characteristics were examined. The test cell showed an initial discharge capacity of 1700mAh and the capacity retention was larger than 80 at 300 cycles, which is competitive to the conventional cells using LiCoO₂ in charge/discharge cycle performance.

10:45 AM *CC1.5
SHORT-RANGE STRUCTURAL ASPECTS OF LITHIUM ION BATTERY ELECTRODES DERIVED FROM NUCLEAR MAGNETIC RESONANCE AND X-RAY ABSORPTION SPECTROSCOPIES. S.G. Greenbaum , Y. Wang, S. Kostov, S.H. Chung, S. Calvin, S.A. Bajue, M.L. denBoer and P.E. Stallworth, Physics Dept., Hunter College of CUNY, New York, NY.

Structural studies of materials utilized in lithium battery technology are often hampered by the lack of long-range order found only in well-defined crystalline phases. Powder x-ray diffraction, while being an indispensable technique in the characterization of cathode materials, yields only structural parameters that have been averaged over hundreds of lattice sites. Our laboratory utilizes synchrotron x-ray absorption (EXAFS and NEXAFS) and solid state nuclear magnetic resonance (NMR) methods to investigate structural and chemical aspects of lithium ion cathodes and anodes. Both spectroscopic methods are element- (or nuclear-) specific and both are sensitive to small variations in the immediate environment of the ions being probed. In the case of cathode materials, EXAFS is utilized to study the transition metal ion, while NMR, with a few notable exceptions such as vanadium, is generally applicable to the local surroundings of the Li⁺ ions. NMR and EXAFS methods have been applied to studies of Li insertion mechanisms and solid electrolyte interface formation in carbonaceous and SnO-based anodes, and in several classes of cathode materials. Among the latter are Li_1-xCoO₂, Li_1-xNiO₂ with various levels of metal substitution for Ni, and Li_xV₂O₅ in both crystalline and amorphous forms.

11:15 AM CC1.6
IN-SITU X-RAY DIFFRACTION STUDIES ON Li ION BATTERY CATHODES. Daniel H. Doughty , David Ingersoll, Mark A. Rodriguez and Timothy Boyle, Sandia National Laboratories Albuquerque, NM.

There is high interest in Li based oxides such as LiMn₂O₄, LiCoO₂, and LiNiO₂ for use as cathode materials in secondary battery cells. The dynamic behavior of these materials within the confines of the battery cell is of great importance in determining failure mechanisms as well as in providing possible avenues for modification and improvement in capacity. Structural behavior of the crystalline lattice can significantly affect the electrochemical potential (as in voltage) has great potential for leading to an understanding and improved performance of Li-ion cells. We report a simple technique for XRD measurements on Li-ion cathodes using an electrochemical cell designed for in-situ x-ray analysis. Cells prepared using this cell design allow investigation of the changes in anode and cathode structure during charge and discharge. We will describe the variation in lattice parameters along voltage plateaus and consider the structural changes in terms of the electrochemical results on each cell. In-situ analysis of a variety of cathode materials as well as our chemically synthesized powders will be compared using the in-situ cell. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4-94AL85000.

11:30 AM CC1.7
IN-SITU RAMAN SCATTERING STUDIES OF Li INTERCALATION IN TRANSITION METAL OXIDE CATHODES. J.D. Perkins ¹, C.S. Bahn¹, J.M. McGraw², P.A. Parilla¹, H. Yu¹ and D.S. Ginley¹, ¹National Renewable Energy Laboratory, Golden, CO; ²Colorado School of Mines, Golden, CO.

We report here the application of in-situ Raman scattering for monitoring transition metal oxide electrodes during charge and discharge cycling. Using a LN₂ cooled CCD array detector, a useable Raman scattering spectrum can be measured in a minute whereas the typical electrochemical cycling time is an hour or so. Hence, an in-situ diagnostic permits essentially continuous measurements of the Raman scattering spectrum during cycling to provide insight into the cycling induced structural and electronic changes. The system employs an air cooled Ar-ion laser operating at 488 nm along with a single grating spectrometer equipped with a cooled CCD detector. An 180 degree back-scattering geometry is used with a holographic notch filter to reject the scattered laser light. V₂O₅ and Li_1-xCoO₂ thin films grown by pulsed laser deposition have been examined. As Li is intercalated into V₂O₅ during discharge to 2 volts, there is a general, but not concurrent, decrease in the intensity of the multi-line V₂O₅ Raman spectrum. In addition, at intermediate voltages, new lines appear in the spectrum. In LiCoO₂, as Li is extracted during charging, the spectrum decreases about 60% in intensity but with no spectral change until x = 0.25, at which point the spectrum abruptly vanishes. This may be due to a metal-insulator transition associated with the end of the 3.9 volt two-phase charging plateau. This work was supported by U. S. Department of Energy, office of Basic Sciences contract #DE-AC36-83CH10093.

11:45 AM CC1.8
LITHIUM DIFFUSION MEASUREMENTS IN HIGH QUALITY LiCoO₂ THIN FILMS. C.S. Bahn , J.D. Perkins, D.S. Ginley, National Renewable Energy Laboratory, Golden, CO.

Chronoamperometry measurements have been performed on high quality, textured LiCoO₂ films deposited by pulsed laser ablation. We have examined the rate of lithium diffusion as a function of Li content. Data was taken using a computerized potentiostat/galvanostat with a sealed teflon cell employing an EC-DC electrolyte with lithium perchlorate. For the undoped LiCoO₂ diffusion measurements were taken between 3.8 - 4.2 V for both the charge and discharge cycles allowing the cell to reach electrochemical equilibrium between measurements and with the cell held at potential between the experiments. We will report the dependence of the diffusion constant across this whole range. The data was highly reproducible as a function of potential cycle for a number of cycles. We could distinguish a number of regions in the diffusion data as a function of potential. Of key interest is that when the potential stepped across regions where theory predicts cation ordering we saw inflection points in the diffusion data. For some of these ordering transitions this may be the first direct experimental evidence for the predicted transitions. In the region near 3.95 V vs. Li we observe very complicated behavior. This is expected as this is a two phase region where most of the Li extraction and doping occurs. While most of the potential range shows extremely high reversibility in this region it appears that there is irreversible behavior which may be associated with capacity loss. This work is supported by U.S. Department of Energy, Office of Basic Sciences contract #DE-AC36-83CH10093
 
 
 
 

SESSION CC2: CATHODES II
Chairs: Brett Ammundsen and M. Stanley Whittingham
Monday Afternoon, April 5, 1999
Metropolitan II (A)

1:30 PM *CC2.1
ELECTROCHEMICAL LITHIUM INTERCALATION INTO Nb₂O₅ CATHODE FOR 2 V CLASS-SECONDARY LITHIUM BATTERIES. Naoaki Kumagai , Nobuko Kumagai and Shinichi Komaba, Dept. of Applied Chemistry and Molecular Science, Faculty of Engineering, Iwate University, Morioka, JAPAN.

Niobium pentoxide was synthesized by heating niobium hydroxide in the temperature range from 600 to 1100C. The crystal system of Nb2O5 compounds depended on the heating temperatures, i.e., hexagonal, orthorhombic and monoclinic Nb₂O₅ compounds were obtained at ca. 600, 800 and >1000C, respectively. Electrochemical lithium intercalation into the three Nb₂O₅ compounds was investigated in an lithium perchlorate-propylene carbonate electrolytic solution for the application as lithium battery cathodes. As a result, they displayed good charge-discharge performance as the cathode of 2 V class-lithium battery, which will play important role in power supply for IC memory backup developed recently. The thermodynamics and kinetics of the lithium intercalation into the Nb₂O₅ cathode and their characteristics have been investigated. The thermodynamic parameters, such as interaction energies between ions, the crystal lattice parameters and the kinetic parameters, such as chemical and self diffusion constants, have been deduced as a function of x-value in the Li_xNb₂O₅. These results were compared to those of the Nb₂O₅ thin film electrode prepared by r.f. sputtering method, which has high potential for fabricating thin micro-batteries.

2:00 PM *CC2.2
SOLUTION-BASED SYNTHESIS OF MANGANESE OXIDE CATHODES FOR LITHIUM BATTERIES. Arumugam Manthiram , Jaekook Kim, Texas Materials Institute, Univ of Texas at Austin, TX.

The high cost and toxicity of cobalt demand the development of alternate cathode hosts for rechargeable lithium batteries. Manganese oxides are attractive in this regard as manganese is inexpensive and environmentally benign. But the spinel lithium manganese oxide that has been pursued intensively over the years tends to lose capacity on cycling due to the lattice deformation caused by Jahn-Teller distortion. Our laboratory is involved in utilizing solution-based, low-temperature synthesis procedures to obtain manganese oxide electrode hosts that can overcome some of the difficulties encountered. The low-temperature approach accesses metastable phases that are otherwise inaccessible by conventional procedures and offers smaller particle size with unique microstructures that give better electrochemical cyclability. The reduction of alkali metal permanganates with alkali metal iodides in both aqueous and nonaqueous media as well as oxidation of manganese acetate with lithium peroxide in aqueous medium to obtain amorphous and crystalline manganese oxides will be presented. The amorphous manganese oxides obtained in nonaqueous medium exhibit capacity over 300 mAh/g in the range 4.3 - 1.5 V with excellent capacity retention. Unlike several crystalline manganese oxides, the amorphous manganese oxides do not transform to the spinel phase on cycling. The manganese oxide obtained in aqueous medium gives a nanocomposite on firing at moderate temperatures, which exhibits a capacity of about 200 mAh/g in the range 4.3 - 2.3 V with good cyclability. The oxidation reactions with lithium peroxide offer 3 V spinel manganese oxides, which exhibit capacity over 150 mAh/g with excellent cyclability.

2:30 PM CC2.3
THE STABILIZATION OF LAYERED MANGANESE OXIDES FOR USE IN RECHARGEABLE LITHIUM BATTERIES. M. Stanley Whittingham , Peter Zavalij and Fan Zhang, Materials Research Center and Chemistry Department, State University of New York at Binghamton, NY.

Layered manganese oxides have been extensively studied by many groups because they have the same structure as lithium titanium disulfide and lithium cobalt dioxide, and readily undergo redox reactions with lithium. They also offer the possibility of cycling close to one lithium ion per manganese, thus increasing the available storage capacity by over 50% relative to the manganese oxide spinel or cobalt oxide. However, on extensive cycling the manganese and lithium ions slowly rearrange from their ordered configuration becoming more spinel-like. We have shown that insertion of potassium or other large cations between the manganese dioxide blocks slows the capacity fade on cycling. Manganese oxide tunnel structures have been shown to reversibly cycle lithium well, but at a rather low capacity so inherently stabilization is feasible. A number of approaches are being used to stabilize the layered structure, including placing atomic pillars between the oxide sheets, modifying the electronic structure of the manganese oxide, and the use of crystalline intergrowths. The results of these different approaches will be discussed. Supported by the Departemtn of Energy through the Office of Transportation Technology.

3:15 PM *CC2.4
ELECTROLYTIC V₂O₅: SYNTHESIS, CHARACTERIZATION AND LI INSERTION BEHAVIOR. D. Guyomard , E. Potiron, A. Le Gal La Salle, Y. Piffard and A. Verbaere.

The purpose of this study is to identify possible relationships between the synthesis conditions, the material parameters and the Li insertion properties of electrolytic V₂O₅ compounds, called e-V₂O₅. e-V₂O₅ compounds are prepared by oxidation of an aqueous vanadyl sulfate solution at an inert electrode, such as Pt or Au. Many experimental parameters, such as bath temperature, pH, VOSO₄ concentration, nature of electrode substrate, oxidation conditions, have been changed in order to prepare different materials. A quartz microbalance enables to understand the electrodeposition mechanism by following the mass growth at the electrode as a function of the various parameters. Subsequent annealing under air at temperatures below 200C has been performed. The compounds have been characterized by various complementary techniques, such as XRD, TGA, DSC, redox titration, XAS and Li insertion electrochemical measurements. e-V₂O₅ are layered, poorly crystallized materials, with a structure closely related to that of V₂O₅ xerogels. Their physico-chemical and structural parameters depend on the experimental synthesis conditions. The Li insertion properties (reversible capacity, average voltage and cyclability) of e-V₂O₅ have been studied and related to the material characteristics. The reversible capacity is slightly influenced by the V^IV content of the compounds and their crystallinity. The cyclability, which is excellent, has been compared to that of the standard -Li₃-xV₂O₅. e-V₂O₅ appears as a promising electrode material for lithium batteries.

3:45 PM CC2.5
VOPO₄ A NEW 4 V MATERIAL FOR LITHIUM BATTERIES. J. Gaubicher , T. Le Mercier, J. Angenault, M. Quarton, Univ Pierre et Marie Curie, URA-CNRS 1388, Paris, FRANCE; Y. Chabre, Univ Joseph Fourier, Grenoble, FRANCE.

In search of new positive electrode materials for lithium batteries we investigated the electrochemical behavior of the  forms of the Li_xVOXO4 compounds (X=S, P, As).-VOPO_4appears particularly interesting as it undergoes a first order transition upon the redox process, at high potential 3.98 V. But from stepwise potentiodynamic cycling and ex-situ XRD, we found that it presents a specific behavior on first reduction which is characterized by an extremelylowkinetics. This result has been attributed to the creation of structural or electronic defects upon the first cycle which would allow a faster kinetics upon the next intercalation. Owing to this forming process upon cycling the capacity increases but still is less than 50 mAh/g after 25 cycles at a nominal C/50 regime, and the kinetics rather low. In fact the first reduction concerns only a small part of the grains. This part presents a faster kinetics upon the next reduction which leads to the intercalation of a virgin part of the grains and then induces the increasing of the capacity. Thus, in order to restrain the forming process to the first oxidation, the idea was to perform a complete first reduction before cycling experiments. On this basis, we synthesized the isotypic-Li_0.92VOPO_4by chemical lithiation of-VOPO_4. The Li / -Li_0.92VOPO_4system then shows interesting cycling properties (90 mAh/gat C/50at 4V vs. Li^+/Li0) Its electrochemical behavior is compared to the ones obtained for the Li /-LiVOAsO_4(110 mAh/g at C/50at 4V vs. Li^+/Li0)and Li /-VOSO_4(close to 80 mAh/gat C/2) CATHODE MATERIALS. Brett Ammundsen, David Hassell, Paul Pickering, Rudolf Steiner , Pacific Lithium Ltd, Auckland, NEW ZEALAND; Zhen Liu, Jim Metson, University of Auckland, Auckland, NEW ZEALAND.

The layered lithium manganese (III) oxide LiMnO₂ offers high capacity as an active cathode material in lithium-ion batteries. We have developed solid state reaction routes to prepare both orthorhombic and monoclinic modifications of LiMnO₂. In the case of monoclinic LiMnO₂, which has a structure analogous to layered LiCoO₂, previously reported synthetic routes have involved a wet chemistry step. As far as we are aware this is the first example of a monoclinic product prepared directly by a solid state reaction. The electrochemical characteristics of these materials have been investigated under different current and voltage conditions. Both orthorhombic and monoclinic phases show stabilised high capacities at room and elevated temperatures. The voltage vs. capacity profiles in the first cycles are characteristic of the different crystal modifications of the materials. After continued cycling the discharge profiles in both cases evolve to give 4V and 3V plateaus. These plateaus show different performance characteristics with respect to temperature and current rate. The origins of these different behaviours have been investigated in detail to provide a basis for applications of these materials in lithium-ion batteries.

4:30 PM CC2.7
PULSED LASER DEPOSITION AND CHARACTERIZATION OF LiMn₂O₄ THIN FILMS FOR APPLICATIONS IN LITHIUM BATTERIES. Deepika B. Singh , R. Houriet, H. Hofmann, Swiss Federal Institute of Technology, Department of Materials, Lausanne, SWITZERLAND; Y. Akin, D. Kumar and Rajiv K. Singh, Department of Materials Science and Engineering, University of Florida, Gainesville, FL.

Most studies focussed on fundamental and developmental aspects of cathode materials for lithium ion batteries employ porous electrodes which are made of polymer bonded transition metal oxide powders mixed with conductors such as carbon. The physical, chemical and electrochemical behavior of these materials in these studies are affected significantly by the powder morphology and the presence of carbon and polymeric binders. Therefore transition metal oxide powders in thin film form, which are dense and contain no additivies, are promising alternatives to study fundamental characterisitics of materials for its application in batteries. In this study, we report the pulsed laser assisted deposition, structural characterization and electrochemical analysis of LiMn₂O₄ films grown on silicon and sapphire, and perovskite based substrates with appropriate metallic interlayers such as platinum and conducting oxides such as lanthanum nickel oxide. By choosing the appropriate substrate/buffer layer combination and varying the deposition conditions, the microstructure of the films can be varied from amorphous to randomly polycrystalline to a textured high oriented form. The electrochemical measurments were carried out in a glove box using cyclic voltametry and AC impedance spectroscopy in a half cell configuration with lithium metal as an anode and reference electrode and LiMn₂O₄/LaNiO₃/Si(or sapphire) as a cathode. LaNiO₃ films were deposited insitu on silicon and other substrates prior to deposition of LiMn₂O₄ films. The microstructural studies were carried out using x-ray diffraction, SEM, and AFM measurements. The electrochemical properties have been correlated with the microstructure.

4:45 PM CC2.8
GROWTH AND CHARACTERIZATION OF LiCoO₂ THIN FILM CATHODES USING PULSED LASER DEPOSITION. C.S. Bahn, D.S. Ginley , J.D. Perkins, P.A. Parilla and H. Yu, National Renewable Energy Laboratory, Golden, CO.

LiCoO₂ and LiCo_0.5Al_0.5O₂ thin films have been grown by pulsed laser ablation on SnO₂ coated glass substrates. For both compositions, the resultant films are fully dense and uniaxially textured with the Li and Co layers parallel to the substrate. As a general rule, the growth rate for the and LiCo_0.5Al_0.5O₂ films is roughly four times lower than that for the LiCoO₂ films and the growth temperature on the substrate T_s must be roughly 100C higher to achieve a similar grain size. LiCoO₂ films have been at grown up to T_s = 700C and pO₂ = 2000 mTorr. These films have a typical grain size of 250nm. For constant current cycling between 3.8 and 4.2 volts at 5A, the LiCoO₂ films have an initial discharge capacity of 0.48 Li per LiCoO₂ unit cell (131 mAh/g) decreasing to (0.33 Li /LiCoO₂ (90 mAh/g) after 100 cycles. We have also studied the growth phase space with a substrate temperature of 300C - 700C and an oxygen partial pressure of 50 mTorr - 2000 mTorr. As a general rule, as both T_s and pO₂ increase, the crystallinity and grain size of the films increase as well. This is seen quite clearly in SEM micrographs and is reflected in the Raman scattering signal as well as electrochemical reversibility. The LiCo_0.5Al_0.5O₂ films grown to date have roughly 3 times less capacity than the LiCoO₂ films as well as a more rapid capacity loss. This work is supported by U.S. Department of Energy, Office of Basic Sciences contract #DE-AC36-83CH10093
 

SESSION CC3: PEM FUEL CELLS
Chairs: Hans-Peter Brack and Elton J. Cairns
Tuesday Morning, April 6, 1999
Metropolitan II (A)

8:30 AM *CC3.1
RECENT PROGRESS IN MATERIALS TECHNOLOGY FOR PROTON EXCHANGE MEMBRANE (PEM) FUEL CELLS. Swathy Swathirajan , General Motors Global R&D Center, Global Alternative Propulsion Center, Warren, MI.

Most major automotive manufacturers have recently enhanced their development efforts in PEM fuel cells because of the need to dramatically increase energy efficiency and reduce regulated emissions. Major breakthroughs, needed for achieving techno-economic feasibility of PEM fuel cells for automotive applications, can be realized mainly through developing novel materials and processing methods. Material needs in the PEM fuel cell system consisting of the fuel processor, fuel cell stack, and air, water, thermal and electrical management subsystems will be briefly discussed. Materials and catalysis issues for the hydrogen-rich reformate/air and methanol/air fuel cell systems will be described along with an assessment of the current state of progress in meeting the challenges of cost, performance and reliability for automotive applications.

9:00 AM CC3.2
SYNTHESIS OF NEW PROTONIC CONDUCTING POLYMER ELECTROLYTE FOR EFFICIENT FUEL CELLS. Itaru Honma ¹, J.M. Bae², M. Murata³, T. Yamamoto³, M. Rikukawa⁴, N. Ogata⁴, ¹Electrotechnical Laboratory, Umezono, Tsukuba, Ibaraki, JAPAN; ²NEDO, ³Hoechst, JAPAN; ⁴Sophia University, Chiyoda-ku, Tokyo, JAPAN.

Fuel cells are extremely attractive for use in future transportation owing to their inherently higher efficiency when compared to that of internal combustion engines. However, the current PEM fuel cells are also shackled by elaborate water management. At the same time, a major limitation of the cell comes from the Pt anode electrocatalysts which are extremely CO intolerant down to the 5 to 10 ppm level. Higher temperature PEMFC operation reduces CO poisoning of the Pt electrocatalysts by other condensable species. In this paper, the synthesis of new protonic polymer electrolyte is reported and the conductive properties at the elevated temperature with various humidities have been investigated. S-PPBP (Sulphonated Poly(4-phenoxybenzoyl-1, 4-phenylene)) are a remarkable family of isotropic, amorphous, rigid-rod, poly-para-phenylenes featuring benzenes in the polymer backbone with side chain substituents. The rigid polymer backbone results in exceptionally high modulus and strength while the side chain substituents serve to provide solubility and melt processibility. The protonic conductivities of the membrane are measured at the temperature range from 50C to 110C with humidity controlled conditions. The conductive property is almost same as that of Nafion; the conductivity of 0.001 S/cm was obtained. The Power output measurement was carried out for MEA of S-PPBP membrane with Pt/C electorodes and 0.5 W/cm2 was obtained at cell temperature of 70C.

9:15 AM *CC3.3
EFFECTIVE SELECTION AND USE OF ADVANCED MEMBRANE ELECTRODE POWER ASSEMBLIES. Bamdad Bahar, Carlos Cavalca, Simon Cleghorn, Jeff Kolde , David Lane, Mahesh Murthy, Greg Rusch, W. L. Gore & Associates Inc., Elkton, MD.

PRIMEA(r) membrane electrode power assemblies have been available from W. L. Gore & Associates, Inc. (Gore) since 1995, when Gore introduced the 5000 series based on the GORE-SELECT(r) composite membranes. In order to provide the highest power density power assembly, a second generation PRIMEA* membrane electrode power assembly (series 5510) was introduced in 1997. Both series 5000 and 5510 power assemblies were designed for hydrogen/air applications. A third generation of PRIMEA membrane electrode power assemblies is now available for operation with reformate fuel streams. All Gore MEAs have been made available with complementary components such as integral gasketing and gas diffusion media, to maximize product performance and durability. In this publication, we explore the selection of MEA characteristics required in common applications. Performance data will be provided on a range of PRIMEA power assemblies under conditions which should be relevant to selection and design criteria typically encountered in fuel cell stack and system development. In addition, examples of successful field demonstrations of PRIMEA Power Assemblies will be shown in various applications, demonstrating the scope for system differentiation utilizing one family of MEA products. This paper is divided into four sections; the first three exploring specific requirements of portable, stationary and transportation applications and the fourth section discusses general product issues, such as quality assurance and manufacturing requirements, as well as ancillary components and associated technical support.

9:45 AM CC3.4
Abstract Withdrawn

10:30 AM *CC3.5
CHEMICAL INTERACTIONS IN IONOMERS AND IONOMER MEMBRANES CONTAINING METAL PARTICLES AND IONS. William M. Risen , Brown Univ, Dept of Chemistry, Providence, RI.

Chemical reactions involving oxygen, hydrogen, carbon monoxide or methanol with metal particles or ions in ionomers based on perfluorocarbonsulfonic acid ionomers (PFSA), such as Nafion(TM), or sulfonated styrene-containing ionomers, such as PSSA, will be discussed. Understanding and exploring these interactions are of particular interest in the design of new materials for fuel cells containing polymer electrolyte membranes, especially with regard to the formation and gas-metal reactions in the membrane-catalyst zone and the issues of crossover, diffusion, and hydration of the membranes. Reactions of Pt, Rh and Ru particles and ions in Nafion with CO, of Rh in PSSA with CO, hydrogen and water, and of Ru in PSSA with CO, hydrogen, oxygen and alcohols will be considered in terms of their relationships to analogous reactions carried out under other conditions. The relationship of the information from such gas-ionomer studies to fuel cell problems and new material design will be discussed.

11:00 AM *CC3.6
NMR AND ELECTROCHEMICAL STUDIES OF CO ON PT AND PT ALLOY ELECTROCATALYSTS. Elton J. Cairns , Benjamin M. Rush, and Jeffrey A. Reimer, Lawrence Berkeley National Laboratory and Department of Chemical Engineering, University of California, Berkeley, CA.

The behavior of CO on fuel cell electrocatalysts is important in connection with the use of reformed organic fuels in fuel cells. CO is strongly adsorbed on the electrocatalyst, interfering with the adsorption and oxidation of the hydrogen fuel, resulting in greatly reduced performance. The design and development of electrocatalysts that tolerate and/or readily oxidize CO is essential to achieving high performance under mild conditions. This work reports on investigations of the adsorption and oxidation of CO on carbon-supported fuel cell electrocatalyts in 2 M sulfuric acid at ambient temperature, employing recently developed techniques for the application of NMR to electrochemical systems. The NMR and electrochemical behavior of Pt/C, Pt-Sn/C and Pt-Ru/C in the adsorption and anodic oxidation of CO will be reported and discussed in terms of the surface species formed, their coverages, and the electrocatalyst composition.

11:30 AM CC3.7
PLATINUM-CATALYZED POLYMER ELECTROLYTE MEMBRANE FOR FUEL CELLS. T. Jan Hwang , Hong Shao, J. Eric McEntyre, Wen-yi Lin, Jerome J. Schmitt and Andrew T. Hunt, MicroCoating Technologies Inc., Chamblee, GA.

Catalytic layers composed of precious metal nanoparticles ( 3 nm) were deposited directly on NafionTM membranes by Combustion Chemical Vapor Deposition (CCVD), a novel, open-air thin film process, well suited for manufacturing. These layers were intended to serve as electrochemical catalysts in proton-exchange membrane fuel cells (PEMFC). Activity of trial catalysts was measured in a small PEMFC cell. Cell performance was studied as a function of catalyst loading, composition and microstructure, and compared with state-of-the-art catalyzed membranes available commercially. An optimal catalyst composition and microstructure was determined that minimized platinum content and related cost. The potential of the CCVD process to enable high-volume, low-cost, mass production of PEMFC catalytic layers will be presented.

11:45 AM CC3.8 DEVELOPMENT OF COMPOSITE MATERIALS FOR PEFC BIPOLAR PLATES. Deanna Busick and Mahlon Wilson, Los Alamos National Laboratory, Los Alamos, NM.

Fuel cells are attractive alternatives to traditional energy sources for both stationary and transportation applications, provided they can be manufactured at a reasonable cost. The most costly and problematic components of fuel cell stacks may be bipolar plates. Besides meeting economic constraints, bipolar plates must possess a host of other properties including low gas permeability, corrosion resistance, low weight, high strength, and manufacturability. While we have developed a composite material that meets these requirements, we recognize a need for further understanding and development in two areas: mechanical properties and corrosion resistance. Our baseline bipolar plate material consists of graphite powder embedded in a thermosetting resin matrix. As such, both corrosion resistance and mechanical properties are dominated by the matrix, so the choice of resin in critical. Certain matrix materials are clearly superior to others from a corrosion standpoint. Most of these matrices provide adequate strength for stack assembly to unreinforced formulations, but improved strength and/or rigidity can be achieved, if desired, with fiber reinforcement. The need to mold flow field channels directly into bipolar plates precludes the use of continuous fibers. However, certain types of milled microfibers that are significantly shorter than the flow-field features that must be resolved can still provide substantial improvements in composite strength. These fibers do not have nearly the intrinsic strength of traditional reinforcement fibers such as graphite and glass, yet they are better able to increase the strength of the composite. Presumably, the improvement arises from more effective fiber adhesion to the resin binder, but further characterization of the strengthening mechanism is needed. Additionally, since some of these fibers are composed of organic material, their effect on corrosion resistance warrants investigation. With increased understanding of fiber and resin effects on strength and corrosion resistance, we anticipate continued improvements in bipolar plate materials.
 
 
 

SESSION CC4: PEM FUEL CELLS/POLYMER ELECTROLYTES
Tuesday Afternoon, April 6, 1999
Metropolitan II (A)

1:30 PM *CC4.1
PEMFC DEVELOPMENT AT ASAHI GLASS CO., LTD. M. Yoshitake , E. Yanagisawa, T. Naganuma and Y. Kunisa, Asahi Glass Co., Ltd., Chemistry Research Laboratory, Yokohama, JAPAN.

Asahi Glass Co., Ltd.(AGC) had commercialized chlor-alkali electrolysis process using perfluorinated ion exchange membranes(Flemion). AGC participated in the PEMFC program of NEDO(New Energy and Industrial Technology Development Organization) which started in the fiscal year 1992. Perfluorinated ion exchange membranes were studied and has been developing the membrane technology for PEMFC. In this program, AGC selected FlemionR(50m), S(80m) and T(120m) as candidates membranes for PEMFC. Thermal stability, mechanical strength, water content, AC specific resistance and gas permeability were measured. In this study a standard conditions of membrane pretreatment were proposed and new measurement methods such as evaluation system for gas permeation were designed. The area resistance of FlemionS is about 43 of that of Nafion117 and thermal stability, mechanical properties and gas permeability of FlemionS are almost equivalent to those of Nafion117. FlemionR-electrode assembly showed to maintain stable performance for 2,300hr. In order to obtain high performance MEA (membrane-electrode-assembly), a new binding technology, ``adhesion method'' was developed, in which special adhesives by AGC were used and the assemblage was carried out by pressing by weak force and at room temperature. It was examined that the adhesion method used in this study can afford smaller decrease in pore volume of gas diffusion electrode than hot pressing in the assemblage process of the electrodes and the membrane. Furthermore, better performance was obtained by using FlemionHR (50m) with higher ion-exchange capacity than FlemionR. Reinforcement technology for perfluorinated membranes has been started to be developed. It was found that FlemionMc (PTFE-yarn embedded type) and FlemionUf (PTFE-fibril dispersed type) can afford improvement in mechanical strength at moist and high temperature atmosphere. FlemionMc (100m) was examined to give high cell performance of 0.65V at 0.5A/cm2, 70C, 1 ata. FlemionMc electrode assembly showed stable performance during the life test of 1,500hr.

2:00 PM *CC4.2
LOW-COST PEMFC DEVELOPMENT AT SIEMENS - MATERIAL ASPECTS. Manfred Waidhas , Armin Datz, Ulrich Gebhardt, Rittmar V. Helmolt, Regina Hornung, Guenther Luft, Siemens AG, Corporate Technology, Erlangen, GERMANY.

Proton Exchange Membran Fuel Cells (PEMFC) in combination with an electric drive system are being more and more discussed as a potential solution for a clean and energy-efficient transportation. Exceeding academic visions car manufacturers meanwhile already demonstrated the technical feasibility of a corresponding propulsion concept by fuel cell driven prototypes. Main obstacle for a fast market penetration are the system costs which currently exceed 10⁴ USD/kW. In order to get any acceptance among the endbuyer, the highest challenge in the future will lie in the realisation of costs which will be comparable to ICEs. Diminishing the material costs plays an important role in the list of potential issues. Currently used materials have to be replaced by low-cost substitutes. If this cannot be done, the amount has to be lowered to the required minimum. For instance, the Pt loading has to be lowered to about 0.2 mg/cm², expensive membrane electrolytes have to be substituted by low cost alternatives and last not least cheapest possible construction materials such as stainless steel shall be used. In addition, all manufacturing procedures have to be capable for an automised mass production. For instance, the bipolar plates will be made by a stamping and punching process, the electrodes by spraying or screen printing. As a third attempt to realise a commercially viable SPFC the periphery has to be simplified as far as possible. By realising corresponding concepts stack costs in the range of 30 USD/kW are conceivable. Results on the described issues will be shown and discussed. For instance, the Pt loading of the electrodes could be lowered from 4 mg/cm² to 0.07 mg/cm² and an air cooled stack was operated reliably even under extreme conditions. The bipolar plates in this case were made of thin sheet stainless steel.

2:30 PM CC4.3
ORGANIC-INORGANIC HYBRID PROTONIC POLYMERIC ELECTROLYTES GRAFTED BY SULFON-SULFOAMID MOIETIES. Laurent Depre, Christiane Poinsignon LEPMI-INPG-CNRS Grenoble, FRANCE; Michael Popall, Fraunhofer Institut for Silicatforschung, Wurzburg, GERMANY.

Thin proton conducting membranes are gained by shaping an organic-inorganic polymer electrolyte bearing sulfonamide and sulfonic groups prepared by sol-gel processing and organic crosslinking reactions. The polycondensation of alkoxysilanes provides the inorganic silica backbone whereas the organic network is formed from reactive functional groups R' of alkoxysilanes of R'Si(OR3) type. Sulfon and sulfonamide functionalities are grafted by cocondensation with alkoxysilanes with corresponding functionality. Protonic conductivity was measured in the dry and wet state under controlled temperature and relative humidity: the conductivity increases from 10-4 S.cm-1 in the dry to 6.10-2 S.cm-1 in the wet state at 70°C. The conductivity dependence on temperature and the associated mechanisms will be discussed in both states.

2:45 PM CC4.4
CHARACTERIZATION AND FUEL CELL TESTING OF RADIATION-GRAFTED PSI MEMBRANES. Hans-Peter Brack , Akinori Tsukada, Joerg Huslage, Felix Buechi, Guenther G. Scherer, Paul Scherrer Institute, Electrochemistry Dept., Villigen PSI, SWITZERLAND.

We demonstrated earlier that the current-voltage characteristics of our 30 cm² active area fuel cells containing our PSI radiation-grafted membranes are comparable or better than those of these same cells containing Nafion membranes of similar thickness and operating under the same test conditions (humidified H₂ and O₂ gases at 1 atm, Nafion-impregnated E-TEK electrodes having 0.8 mg Pt/cm²). Long-term testing of PSI radiation-grafted membranes over periods of up to 5,000 h at 60C and 1,000 h at 80°C in these 30 cm² active area cells will be discussed. We have most recently begun testing our PSI membranes in single cells and two cell stacks based on components of a 100W PSI power pack that we developed for educational purposes at Swiss universities and technical colleges. PSI membranes have been tested to date for up to approximately 1,000 h in stacks consisting of two 100 cm² active area graphite cells operating on H₂/O₂ at 60C. Membrane properties have been characterized by means of titration measurements and infrared and Raman spectroscopy both before and after testing in fuel cells. A comparison of these membrane properties to date indicates that little membrane degradation occurs over this period of testing in the graphite cells. Membrane failure in these 100 cm² active area graphite cells has been primarily a result of membrane rupture, probably due to swelling stresses near the active area (swollen membrane)/gasket (non-swollen) border. It is noteworthy that thinner Nafion membranes (less than 100 um thick) can have similar problems in these cells. Efforts are being undertaken to overcome these problems by both further improving the mechanical properties of our PSI radiation-grafted membranes and further refinement of our cell design. Results of our membrane optimization and characterization research and testing of these membranes in fuel cells and fuel cell stacks will be reported.

3:00 PM CC4.5
DEVELOPMENT OF NEW IONOMER MEMBRANE FOR FUEL CELLS APPLICATIONS. Didier Marsacq , Franck Jousse, CEA-DAM, Dept of Materials, FRANCE; Regis Mercier, Lyon Univ, Dept of Organic Materials, Lyon, FRANCE; Gerard Gebel, CEA-DSM, Grenoble, FRANCE; Michel Pineri, CEA-DTA, Grenoble, FRANCE.

Among the different power sources, fuel cell based on proton exchange membrane appears to be one of the interesting power generating device. As it was demonstrated for perfluorinated ionomer membrane, sulfonated polyimides can be used as proton exchange membranes for H₂/O₂ fuel cells and other selective applications such as ions separation. Polyimides based on 4,4'-diaminobiphenyl 2,2'-disulfonic acid (BDSA), 1,4,5,8 naphthalene tetracarboxylic (DNTA) and various diamines were synthesized in order to find out relationships between solubility in common organic solvents and polyimide architecture, i.e., chemical nature and arrangement of monomers. Sulfonated polyimides exhibiting a good solubility in metacresol are obtained and can be processed by hand-coating. By controlling both the viscosity of polymer solution and the casting conditions homogeneous membranes with controlled thickness are prepared. Swelling measurement, ion exchange capacity and ionic conductivity are examined as regard to the sulfonated polyimide composition.

3:30 PM *CC4.6
POLYMER ELECTROLYTES: ALIVE AND WELL FOR 2000. M. Armand , D. Baril, N. Ravet, J.Y. Bergeron, S. Beranger, Dept. de Chimie, Universite de Montreal, Quebec, CANADA; C. Michot, Rhone-Poulenc, Lyon, FRANCE.

As the solvent-free polymer electrolytes battery program (ACEP®) goes towards commercialization for large batteries destined to telecommunications and electric vehicles for the turn of the millennium, it rallies a growing interest at corporate RD centers worldwide. Though this system was at some time hastily deemed unpractical when considering the immediate success and performances of the Li-ion (rocking-chair) batteries for consumer electronics, the safety and cost issues of the latter system are yet unsolved. Poly(ethylene oxide) based polymers remain the workhorse of solid electrolytes. The main points which have been addressed include:  identification of cross-linkable materials via fast processes without introducing chemicals adversely affecting the electrochemistry.  design of a polymer architecture in which a high crosslink density is attainable without affecting the conductivity and improving the mechanical properties.  identification of new salts. The best solute today, in terms of electrochemical performances, is lithium the fluorinated sulfonimide Li(CF₃SO₂)₂N. An extensive research program has allowed to identify a complete panoply of new salts whose properties can be fine-tuned to specific applications and meet the cost requirements imposed for mass production. Also, new anhydrous proton conductors allow to reconsider the dye-based electrochromic devices. Today's ``dry'' polymer electrolytes lithium batteries have energy densities in excess of 150 Wh/Kg for completely equipped systems and power to energy ratios ranging from one to 12 depending on the temperature of operation (40 to 80C) and the system design. The high power system are viable contenders for hybrid vehicles. The different options in terms of polymer science and electrochemistry offered by these systems will be discussed.

4:00 PM *CC4.7
POLMER ELECTROLYTES AND THEIR ELECTROCHEMICAL INTERFACES. Masayoshi Watanabe , Yokohama National Univ, Dept of Chemistry & Biotechnology, Yokohama, JAPAN.

In order to realize all solid high energy density batteries, polymer electrolytes have received much attention. Especially, it is expected that application of the polymer electrolytes to lithium batteries could overcome problems concerned with safety. We have studied to attain highly ionically conducting polymer electrolytes and developed new network polymer electrolytes having many chains ends. However, charge transfer resistance (R_ct) between a highly conductive polymer electrolyte and lithium electrodes is much higher than the polymer electrolyte bulk resistance, especially at low temperatures. In this study we will discuss the factors dominating R_ct between polymer electrolytes and lithium electrodes, especially the relationship between the density of free chain ends in network polymer electrolytes and R_ct. Polymer electrolytes having different densities of free chain ends were synthesized by photo cross-linking reaction of the mixtures of mono-acrylated poly(ethylene oxide-co-propylene oxide) (P(EO/PO)) and tri-acrylated P(EO/PO) in the presence of a lithium salt. Ionic conductivity for the polymer electrolytes is different, depending on the density of free chain ends in the network polymer electrolytes, namely the polymer electrolytes having the largest number of ether side chains show the highest ionic conductivity although glass transition temperature is not so much deiffenrent. On the other hand, it is clearly indicated that R_ct decreases with increasing the ionic conductivity. The big difference of R_ct between LiBF₄ and the other salts is observed even if the same matrix polymer is used. On the other hand, in terms of the density of ether side chains, the polymer electrolytes having the largest number of ether side chains show much lower R_ct. It is suggested that R_ct correlates with the density of ether side chains in the polymer electrolytes.

4:30 PM CC4.8
A NEW FAMILY OF SALTS FOR LITHIUM SECONDARY BATTERIES. D. Baril , N. Ravet, M. Armand, Dépt. de Chimie, Université de Montréal, Québec, CANADA; C. Michot, Rhône-Poulenc, Lyon, FRANCE.

The ideal lithium salt is highly conductive, safe, inexpensive and easy to make. Furthermore, for a solid polymer electrolyte application (SPE), the salt is also required to have a plasticizing effect (lowering effect on T_g and T_m). The choice of available salts for lithium batteries based on a SPE technology is quite limited. Lithium bis-trifluoromethanesulfonimide or LiTFSI has already proven to be successful in this field. Its physical properties and extensive electrochemical stability show performances that outrun any other lithium salt. Also, the plasticizing effect of the salt eases the electrolyte processing when polyethylene oxide (PEO) is used. The price of LiTFSI may however be of concern for very large scale utilization. We have undertaken an extensive study of delocalized anions belonging to different chemical families, in order to understand the charge separation and identify viable alternatives. This work deals with the synthesis and characterization of a new salt, lithium N-(3-trifluoromethyl)phenyl-trifluoromethane sulfonamide. Li-TFPTS is a large delocalized anion whose charge is spread over a single SO₂ and a phenyl ring, and its synthesis is relatively straightforward. Li-TFPTS shows a high degree of solvation in solid PEO which is characteristic of a low lattice energy salt. Preliminary results show that ionic conductivity is similar to that of LiCIO₄ which derives from an acid 10¹⁰ times stronger in water. Also, thermocalorimetric analysis confirms, as expected, that the TFPTS anion hinders the PEO + salt mixture crystallization. Physical properties and electrochemical performances of this salt in solid polymer electrolyte (PEO) will be discussed.

4:45 PM CC4.9
ENHANCED ION MOBILITY IN ALUMINOSILICATE/ POLYSILOXANE NETWORK POLYELECTROLYTES. David P. Siska , Duward F. Shriver, Northwestern University, Department of Chemistry, Materials Research Center, Evanston, IL.

A series of novel polysiloxane-based single-ion conductors containing solvating oligoether sidechains and covalently linked aluminosilicate or alkoxy/siloxyaluminate anions were prepared and characterized. Our previous research shows that the weak basicity of the aluminosilicate anion is conducive to high conductivity. In the present work, we explore the incorporation of aluminosilicates into a low-T_g polysiloxane framework to produce high ionic conductivity with t₊ = 1. Of the two types of systems created, those networks containing the aluminosilicate [(SiO)₄Al]^- anions show higher room temperature conductivities (10^-6 S/cm) than those with alkoxy/siloxyaluminate [(SiO)₂(CH₂O)₂Al]^- anions (10^-7 S/cm), owing to the decreased basicity and increased flexibility provided by the additional Si-O linkages surrounding Al. Lengthening the covalent tethers binding the anions to the polymer backbone results in enhanced room temperature conductivities in the alkoxy/siloxyaluminate systems, particularly at high ion loadings. The differential scanning calorimetry data for the two different types of network polyelectrolytes and their less-constrained counterparts provide a rationale for the improved conductivity.

SESSION CC5: POSTER SESSION
Chairs: Hans-Peter Brack and Linda F. Nazar
Tuesday Evening, April 6, 1999
8:00 P.M.
Metropolitan Ballroom (A)

CC5.1
SYNTHESIS AND ELECTROCHEMISTRY OF LAYERED LITHIUM MANGANESE OXIDES AS CATHODE MATERIALS FOR RECHARGEABLE LITHIUM BATTERIES. Fan Zhang , Peter Zavalij, and M. Stanley Whittingham, Materials Research Center and Chemistry Department, State University of New York at Binghamton, NY.

Lithium ion rechargeable batteries with lithium cobalt oxide cathode have high energy density and excellent cycle life. But this cathode is very expensive. There has been much interest in manganese oxides as cathode candidates for rechargeable lithium batteries. Manganese oxides, particularly the spinel form, are of particular interest because they readily intercalate lithium into their structures. However, only 0.5 lithium can be cycled per manganese atom so that their energy densities are not sufficiently high. We have synthesized potassium manganese dioxide, both with only manganese and with 10 or 33% of the manganese substituted by iron, cobalt or nickel to stabilize the layer structure. Our earlier work showed that the pure layered phase slowly reverted to a spinel-like phase. These compounds were then converted to the lithium form either in an electrochemical cell or by ion exchange. Both the potassium and lithium forms he compounds were characterized by XRD, Electron microprobe, FTIR, and electrochemistry. Electrochemical properties and rate capabilities of the materials used as cathodes for lithium cells will be presented. This work was supported by the Department of Energy.

CC5.2
SYNTHESIS AND PROPERTIES OF A VANADIUM OXIDE BASED LITHIUM ION CATHODE. Benjamin Chaloner-Gill and Dale R. Shackle, Rentech Inc., San Jose, CA.

The development of high capacity cathode materials for lithium ion batteries has uncovered three major players, lithiated manganese, cobalt and nickel oxides and mixtures thereof. In the search for greater energy storage, we have examined a number of vanadium oxides. Comparing the ratio of lithium to metal atom in the three compounds listed above allows for the extraction of 0.5 lithium atoms or less. In other words, you can extract one lithium atom per two metal atoms. If the cathode is vanadium based, the number of cycleable lithiums increases to a value closer to 0.75 - 1.00. Despite the fact that vanadium oxides operate at lower voltages, a net gain in energy is observed from the use of Li_xV_yO_z over the currently available materials. Lithiation of LiV₃O₇.9 for use in a lithium ion cell is the focus of this talk. Chemical lithiation by reducing lithium salt will be described along with analysis, rate data and electrolyte stability.

CC5.3
MECHANOCHEMICAL SYNTHESIS OF CATHODE MATERIALS FOR LITHIUM BATTERIES. Nina V. Kosova , Evgeniya T. Devyatkina, Evgenii G. Avvakumov, Nikolai F. Uvarov, Nikolai Z. Lyakhov, Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, RUSSIA; Igor P. Asanov, Svetlana G. Kozlova, Svyatoslav P. Gabuda, Institute of Inorganic Chemistry, Novosibirsk, RUSSIA.

Complex oxides of lithium and transitional metals (manganese, titanium, vanadium, cobalt, nickel) are perspective cathode materials for lithium batteries. Usually they are prepared by thermal synthesis. In this case final products are characterized by small specific surface and unsufficient electrochemical activity. A new perspective mechanochemical method of synthesis of these compounds is worked out. The different compounds of lithium (hydroxide, carbonate and others) and transitional metals (oxides, hydroxides, carbonates) were used as the initial reagents. The method allows to get high-dispersed, homogeneous compounds either in the process o f activation or as a result of preliminary activation and following thermal treatment. The influence of different factors (chemical, phisical and mechanical) on the process of synthesis and properties of final products has been investidated. The changes of lattice parameters, specific resistance, valence state of surface atoms, lithium position in the lattice and others have been studied by X-ray analysis, complex impedance method, IR, XPS and NMR spectroscopy. It has been stated that the intermediate states, arising under the process of mechanical activation, influenced on the properties of final products. Materials, prepared by mechanochemical method, exibit high specific surface and conductivity and are promising for using as a cathode materials in lithium batteries.

CC5.4
HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF delta-TYPE VANADIUM PENTOXIDE STRUCTURES FOR RECHARGEABLE LITHIUM BATTERIES. Fan Zhang , Peter Zavalij, and M. Stanley Whittingham, Materials Research Center and Chemistry Department, State University of New York at Binghamton, NY.

Recently, soft chemistry has been shown to be an effective method for the preparation of high surface area transition metal oxides, which offer many advantages as cathodes in rechargeable lithium batteries. The goal of this research project concentrates on the development of layered vanadium oxides with new structures. The purpose of developing these new compounds is to apply them as cathode materials in lithium rechargeable batteries. The high free energy of reaction with lithium and their low cost makes vanadium oxides attractive materials to replace the expensive lithium cobalt oxide cathode in commercial lithium batteries. Several synthetic routes aimed at the formation of delta-type vanadium oxides been examined. The compounds were synthesized by the reaction of vanadium (V) oxide, tetramethyl ammonium hydroxide or tetraethyl ammonium hydroxide and transition metal salt at 165 °C for 60 hours. The manganese was incorporated using TMA permanganate as the manganese source. The stoichiometry, phase, and structure of the compounds have been examined as a function of deposition conditions using XRD, DCP, TGA, FTIR, SEM and EDS. In these double sheet oxides, organic species do not appear to impede the incorporation of lithium. They readily react with butyl-lithium solutions. Galvanostatic cycling of composite electrodes based on these compounds revealed a high charge capacity and promising cyclability. Electrochemical properties and rate capabilities of the materials used as cathodes for lithium cells well be presented. Supported by the National Science Foundation.

CC5.5
CHARACTERIZATION OF ELECTROCHEMICALLY SYNTHESIZED V₂O₅ FOR LITHIUM BATTERIES. E. Potiron, A. Le Gal La Salle, A. Verbaere, D. Guyomard and Y. Piffard.

Electrolytic V₂O₅ materials, called e-V₂O₅, are prepared by oxidative electrodeposition from an aqueous vanadyl sulfate solution. These poorly crystallized materials exhibit a layered structure showing many stacking faults. The layers are built up from fragments similar to those observed in the -V₂O₅ structure. They could be bilayers similar to those observed in -Ag_xV₂O₅. e-V2O5 are mixed valence, hydrated vanadium oxides, containing exchangeable protons. Their chemical formula can then be written: H_xV₂O.nH₂O with x0.4, 0<<0.4 and 0<n<1.8. Their water content and interlayer distance (which are related) depend on the relative humidity. The dehydration process occurs in three steps. The last one, between 200 and 260C, coincides with a slow phase transformation leading to -V₂O₅. By varying the electrodeposition current density and the duration of subsequent thermal treatments below 200C, materials with various V⁴⁺/V_total ratios can be prepared. A small part of V⁴⁺ cations are vanadyl pentahydrated ions situated within the interlayer space. The majority part occupies sites within the anionic layers; they are preferentially oxidized upon a thermal treatment in air. Prior to electrochemical tests in Li batteries, e-V₂O₅ are dehydrated at 100C under vacuum for one hour. Upon this treatment the water content decreases down to 0.4 mole per formula unit for all e-V₂O₅ materials, leading to an interlayer distance of 9.8A; their original V⁴⁺ content is maintained.

CC5.6
LITHIUM INSERTION BEHAVIOR OF ELECTROCHEMICALLY SYNTHESIZED V₂O₅. Emmanuel Potiron, Annie Le Gal la salle, Yves Piffard and Dominique Guyomard .

Electrolytic V₂O₅ have been prepared by anodic oxidation of VOSO₄ solutions. In the 4-2V/Li range, it is possible to insert 1.5 Li in these compounds in two reversible steps situated at 2.55 and 3.1 V/Li. Lithium compositions (x) higher than 1.5 are obtained at a lower apparent potential of 1.7 V with a corresponding equilibrium potential situated in the continuation of the 2.55 V phenomenon, in accordance with a prolongation of the corresponding solid solution. The intercalation mechanism was studied by several techniques. X-ray absorption spectroscopy has shown that lithium intercalation is accompanied by a reversible increase of the average vanadium-oxygen distance and of the symmetry around vanadium atoms, correlated to the reduction of V(V) into V(IV). Chemical diffusion coefficient increases when x is comprised between 0 and 0.6, stabilizes when x is comprised between 0.6 and 1.2 then decreases when x is comprised between 1.2 and 1.5, probably in correlation with the steric hindrance in the interlayer space. The important decrease of the diffusion coefficient when x is comprised between 1.5 and 1.8 explains the important polarization observed on the 1.7 V intercalation step. The intercalation capacity at 2.55V is strongly modified by external parameters such as the carbon quantity or the intercalation duration in accordance with a smaller electronic conduction at this voltage. This phenomenon is responsible for the capacity losses that are observed during cycling. e-V₂O₅ materials that were studied exhibit the same interlayer distance and the same water content, and differ only by their V(IV) content. The best results were finally obtained with samples electrodeposited at 100C, having the highest V(V) content, and that were not heat treated. They present good cycling properties, and compete favorably with other vanadium oxides as cathode materials for lithium batteries.

CC5.7
DEGRADATION REACTIONS IN SONY-TYPE Li-ION BATTERIES. E. Peter Roth , Ganesan Nagasubramanian, Sandia National Laboratories, Albuquerque, NM.

Thermal instabilities were identified in SONY-type Li-ion cells and correlated with interactions of cell constituents and reaction products. Three temperature regions of interaction were identified and associated with the state of charge of the cell. Anodes were shown to undergo exothermic reactions as low as 100°C involving the solid electrolyte interface (SEI) layer and the LiPF6 salt in the electrolyte. These reactions could account for the thermal runaway observed in these cells beginning at 100°C. Exothermic reactions were also observed in the anodes in the 200°C - 300°C region between the intercalated lithium and the LiPF6 salt, followed by a high-temperature reaction region, 300°C - 400°C, involving the PVDF binder and the intercalated lithium. Cathode exothermic reactions with the PVDF binder were observed above 200°C and increased with the state of charge (decreasing Li content). This offers an explanation for the observed lower thermal runaway temperatures for charged cells. The stability of the PVDF binder as a function of electrochemical cycling has also been studied using FTIR. We have identified a possible dehyrofluorination reaction at both the anode and cathode which results in a more hydrocarbon like polymer. Decomposition of the electrolyte and subsequent attack of the PVDF has been identified as a possible mechanism for this observed change.

CC5.8
SYNTHESIS AND ELECTROCHEMICAL CHARACTERIZATION OF LiNi_xCo_1-xO₂ POWDERS OBTAINED BY COMPLEX SOL-GEL PROCESS. F. Croce, F. Ronci, University `La Sapienza', Department of Chemistry, Roma, ITALY; A. Deptula , W. Lada, T. Olczak, Institute of Nuclear Chemistry and Technology, Warsaw, POLAND; A. Ciancia, A. Di Bartolomeo.

The layered oxides, among the wide family of intercalation compounds, have received considerable attention as positive electrode materials in high-energy density lithium and lithium ion batteries. Within this frame LiNiO₂ and LiCoO₂ oxides and their solid solutions have been extensively studied as they (and the LiMn₂O₄ spinels) are the only known materials able to intercalate reversibly lithium at high cell voltage (3.5-4 V). Recently, solid solutions such as LiNi_xCo_1-xO₂ have attracted the attention as alternative cathodes to the state of art LiCoO₂ in commercial rechargeable Li-ion batteries¹. These solid solutions LiNi_xCo_1-xO₂ can be successfully prepared using various synthesis ways: mainly by solid state reactions involving the mechanical mixing of precursors salts and/or oxides followed by high temperature firing and extended grinding. Nevertheless the preparation of high `battery quality' material is not easy as the stoichiometry, the oxygen deficiency, but also grain size and the morphology² can have great influence on the cell reversibilty and capacity: they both largely depend upon sample treatment. Low temperature synthesis techniques have specifically been developed for their ability to produce materials with different structure, powder morphology, bulk density and stoichiometry. Therefore we have used the Complex Sol-Gel Process (CSGP)3 (CSGP) to prepare LiNi_1-xCo_xO₂ (x= 0, 0.25, 0.5, 0.75, 1). Starting sols were prepared from Li+-(1-x)Ni2+-xCo2+ acetate aqueous solution in two different routes. Route-I: aqueous ammonia was added to a starting solution containing 0.2 ascorbic acid (ASC) M on 1M SMe. Route-II: the starting acetate solutions were alkalised by ammonia following by addition of ascorbic acid. Regular sols were concentrated 3 times and dried slowly up to 200C. After 200h of heating at 170C monolithic gels are formed. Intensive foaming was observed for samples prepared by variant I during further heating. In both cases self-ignition (SIT) takes place at temperatures 380-460C. It can be noticed that there is no simple relationship between the carbon content and SIT. Thermal transformation of the gel to solid was studied by TG, DTA, XRD and IR. The electrochemical properties of some compounds prepared by the Route-I were evaluated and reported. References 1) C. Delmas and I. Saadoune, Solid State Ionics, 53-56, 370 (1992) 2) A. Yamada et al., J. Electrochem. Soc., 142 (1995) 2149 3) A. Deptula et al., J. Material Res., 11, 1 (1996)

CC5.9
Li DIFFUSION RATES IN AS-DEPOSITED AND CYCLED, CRYSTALLINE AND AMORPHOUS, V₂O₅ THIN-FILM CATHODES. J.M. McGraw , D.W. Readey, Colorado School of Mines, Golden, CO; P.A. Parilla, J.D. Perkins, D.S. Ginley, National Renewable Energy Laboratory, Golden, CO.

V₂O₅ exhibits good charge capacities in both crystalline and amorphous thin films. The open-channeled structure of crystalline V₂O₅ and the evolution of its crystal structure upon Li intercalation are well documented in the literature. Conversely, amorphous V₂O₅ has not been studied as thoroughly. We have measured diffusion rates in amorphous and crystalline V₂O₅ films synthesized by pulsed laser deposition. We have employed chronoamperometric techniques in both as-deposited and cycled films to evaluate the diffusion constants as a function of Li content while also evaluating the structural changes in the crystalline and amorphous films by XRD and Raman spectroscopy. Crystalline films retain their structure and hold a steady charge capacity when cycled above 2.3 V; however when cycled below this threshold, the crystalline order quickly deteriorates as evidenced by XRD and Raman spectroscopy with a concurrent decrease in charge capacity. In contrast, amorphous films demonstrate little capacity loss with a very steady charge capacity, losing only 2 of the original capacity over 100 cycles, even with deeper cycles to 1.8 V vs. Li. The diffusion data for both crystalline and amorphous films are well behaved. Preliminary results indicate that there is a significant decrease in the Li diffusion rate in crystalline films as Li concentration increases. In amorphous films, initial experiments indicate that the decrease in diffusion rates is smaller. We will report the diffusion rates for this on-going study. This work was supported by U. S. Department of Energy, office of Basic Sciences contract #DE-AC36-83CH10093.

CC5.10
SURFACE-MODIFIED MANGANESE DIOXIDE FOR ALKALINE-MANGANESE BATTERY. Jun Nunome , Takuya Nakashima, Hiroshi Yoshizawa, Yoshiaki Nitta, Matsushita Battery Industrial Co., Ltd., Technology Laboratory, Osaka, JAPAN.

Manganese dioxide for positive active material of Alkaline manganese battery is low-priced and show excellent performance. In order to achieve higher capacity of Alkaline manganese battery, many researchers have studied about characterization of manganese dioxide, electron conductive agents, and some additives. One of the causes to be a lesser discharge capacity of manganese dioxide in Alkaline-manganese battery was considered to be a polarization due to the formation of Hetaerolite which was produced at near the end of discharge. The object of the present study is to achieve higher capacity of alkaline-manganese battery by employing positive active material which has been applied with surface modification by doping Titanium element to manganese dioxide. The synthesis of the surface-modified manganese dioxide was obtained by introducing electrolytic manganese dioxide into the solution which consists of H₂SO₄ and Ti(SO₄)₂, stirring for a few hours at 70C. In order to investigate the characteristics of specimen, the characterization was performed by using EXAFS(extended X-ray absorption fine structure), Raman spectroscopy and ESR. The analysis data suggest the following results. In Ti-doped manganese dioxide obtained by surface modification, some of the doped Ti can be displaced partly by Mn, forming M-O bonding in a solid structure. The electrochemical behavior in the alkaline solution of the material above mentioned by using the half-cell have shown a less polarization at near the end of discharge. The result of XRD measurement of the discharged product has shown a lesser production of Spinel-like composite as ZnOMn₂O₃ or Mn₃O₄ in comparison with that of non-modified case. It was suggested that the suppression of producing by-product such as Hetaerolite improves the polarization at near the end of discharge.

CC5.11
STRUCTURAL STUDY OF LITHIUM INSERTION IN VANADIUM OXIDES USED AS CATHODE MATERIALS. Patrick Rozier , Jean-Michel Savariault and Jean Galy CEMES/CNRS, BP, Toulouse, FRANCE.

Combined soft and solid state chemistry followed by precise XRD investigations allow us to determine the Li-V-O phase diagram as well as the structural modifications induced by the insertion of lithium in silver vanadates. These studies drive to propose an interpretation of the electrochemical behavior of both LiV₂O₅ and Li Ag₂V₄O₁₁ batteries. The  and -Li_xV₂O₅ phases and -Li_xV₂O₅ for x>1 are not confirmed. In the 1<x<3 domain, disproportionation of V⁴⁺, following the reaction 2V⁴⁺ V⁵⁺ + V³⁺, occurs as confirmed by the formation of lithium vanadates and vanadium oxides with an ending mixture, for x=3, constituted with Li_xVO₂ and Li₃VO₄. The different domains are directly related to the different steps observed in the discharge curve of the LiV₂O₅ battery. It is also demonstrated that the loss of oxygen occurring in the Ag₂V₄O₁₁ vanadate drives to the formation of a new phase Ag_1+xV₃O₈ instead of an oxygen deficient form Ag₂V₄O_11-y. Single crystal XRD structural determination shows that this phase is isostructural with Li_1+xV₃O₈. Electrochemical lithium insertion starts with the reduction of Ag⁺ driving to the lithiated phase. Comparison with electrochemical behavior of Ag₂V₄O₁₁ suggests that there is an identical mechanism meaning that whatever the starting phase used, the main insertion process occurs in Li_1+xV₃O₈ phase.

CC5.12
LONG RANGE AND LOCAL STRUCTURE IN TRANSITION METAL (Ti, Cr, Co)-DOPED LITHIUM MANGANATE SPINELS. Phillip B. Aitchison, Brett Ammundsen, Deborah J. Jones , Jacques Roziere, Laboratoire des Agregats Moleculaires et Materiaux Inorganiques, Universitaet Montpellier II, FRANCE; Gary R. Burns, School of Physical and Chemical Sciences, Victoria University of Wellington, NEW ZEALAND.

Lithium manganates can accommodate large amounts of substitutional ions as well as changes in the lithium and oxygen stoichiometry whilst retaining the spinel crystal structure. Depending on their nature and concentration, substitutional ions can influence the overall energy of the lattice and hence the redox potentials of electron transfer processes that occur during lithium extraction and insertion. They also strongly influence both the local lattice structure and long range crystalline order, as well as the structural changes which take place as a result of lithium extraction and insertion. A range of substituted lithium manganate spinels are known and many of the relationships between structure and property in these compounds have been clarified by means of X-ray and neutron diffraction, spectroscopic and electrochemical methods of characterisation. However, most of these techniques provide information mainly on the bulk properties and long range structures, rather than probing the localised effects on electronic and atomic structure associated with the sites occupied by the substituent ions. In combination with chemical analyses, and powder X-ray and neutron diffraction methods to determine the average atomic structure and identify eventual ordering in the cation sublattice, we have used EXAFS and XANES spectroscopies to probe the local environment around metal ions in LiMn₂O₄ substituted with Cr(III), Co(III), Ti(IV) and Ga(III). Using EXAFS, local relaxation around a substitutional ion not detected by diffraction methods can readily be identified in materials having a low level of dopant. XANES allows changes in oxidation state of each metal to be followed as lithium is extracted and reinserted. Such local structural and electronic modifications, and changes in symmetry around both substituent and manganese ions, will be described in relation to bulk chemical and electrochemical properties.

CC5.13
SAFETY AND REACTIVITY OF CARBONACEOUS ANODES FOR LITHIUM-ION BATTERY. G.Abbas Nazri , Bouziane Yebka, Maryam Nazri, M. David Curtis, University of Michigan, Department of Chemistry, Ann Arbor, MI; Kim Kinoshita, Lawrence Berkeley Laboratory, University of California, Berkeley, CA; David Derwin, Superior Graphite Company, Chicago, IL.

Safety and reactivity of various carbonaceous anodes have been studied in different combinations of nonaqueous electrolytes. The electrochemical performance of the anode materials during lithium insertion-extraction process has been correlated to the structural parameters of the various natural and synthetic graphites. The long range order of graphitic materials have been studied using x-ray diffraction, and the local disorder has been studied using vibrational spectroscopy. The nature of the gel-type film formed on carbonaceous anodes during initial charge-discharge cycling was studied using thermal analysis and vibrational spectroscopy. We report composition and morphology of the gel-type films and effect of various combinations of solvents and salts on the chemical nature of the film.

CC5.14
Abstract Withdrawn

CC5.15
TRANSFORMATION OF COBALT HYDROXYDE ADDITIVES DURING THE REDOX CYCLING OF THE NICKEL HYDROXIDE ELECTRODE. V. Pralong , A. Delahaye-Vidal, B. Beaudoin, B. Gerand and J.M. Tarascon, Laboratoire de Reactivite et de Chimie des Solides, UPRES-A, Universite de Picardie Jules Verne, rue Saint-Leu, Amiens, FRANCE.

Although cobalt hydroxide is currently added to the Ni(OH)₂ paste to prepare nickel composite electrode used in Ni-based rechargeable alkaline batteries, its redox chemistry in alkaline medium is still poorly documented. As an attempt to better understand how such additives improve the nickel electrode performances, the Co(OH)₂/CoOOH/Co₃O₄ has been further investigated through 1) simulations of redox reaction by using chemical oxidizing and reducing agents and 2) electrochemical cycling of the cobalted phases. The structural features of the reaction products were found to be strongly dependent upon the reaction kinetics, which is controlled by the experimental conditions, namely, temperature, oxidizing agent and reaction time for chemical simulations and charge-discharge rate for electrochemical reactions. For instance, starting from Co(OH)₂, a non-stoechiometric CoOOH highly conductive phase can be obtained either chemically by means of a strong oxidizing agent (NaClO) or electrochemically using relative high charging rates (>C/5). Special experimental cases leading to the formation of the Co₃O₄ phase to the expense of the b-CoOOH phase will also be described. Finally, the electrochemical signatures vs. Cd of the differently made CoOOH phases will be reported and the impact of these findings in optimizing the formation of the Ni-based cells containing Co(OH)₂ additives discussed as well.

CC5.16
TEM INVESTIGATION OF A ZR-BASED BATTERY MATERIAL. Scott Chumbley , Zhan Shi, Iver Anderson, Ames Laboratory USDOE, Ames, IA; Leonard Cantrell, Ovonic Battery Company, Troy, MI.

A Zr-based alloys have been developed by Ovonic Battery Company as a high performance nickel metal hybride negtive electrode material. Currently High Pressure Gas Atomization (HPGA) is being investigated as a way to reduce processing costs. This powder has been examined using transmission electron microscopy (TEM). The TEM investigation showed that the microstructure consisted of regions of large grains separated by an intergranular phase and interspersed with regions of extremely fine grain material. The large grains were found to be FCC cubic with lattice parameter a=7.03 with the intergranular regions being hexagonal with lattice parameter a=4.97, c=8.11. These findings agree with results obtained by X-ray powder diffraction. The fine grains remain to be identified at the time of this writing. The compositions of the large grains and intergranular regions were also analyzed using EDS. The results indicate that segregation of Zr, Ti, V, Mn, Cr occurs, with the intergranular phase being depleted in V, Cr and Mn and enriched in Ti and possibly Zr. The amount of Ni remains approximately the same in both phases. The microstructure and composition of as-received HPGA powder will be compared to that of heat treated HPGA powder and as-received hydrided-dehyrided powder obtained from bulk ingot.

CC5.17
PHASE STABILITY AND HYDROGEN STORAGE CAPACITY OF MULTI-COMPONENT LAVES PHASE ALLOYS BASED ON ZrNi₂. E.P. George , C.T. Liu, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN; B.S. Chao, R.C. Young, S.R. Ovshinsky, Energy Conversion Devices, Inc., Troy, MI.

Multi-component Laves phase (AB₂) alloys based on ZrNi₂ are currently under development as battery materials for electric vehicles. Based on Ovonic's pioneering design principle of multi-component alloying on the A and B sites, we report here the effects of substituting Ti and Nb on the A-sites (Zr-sites) and V, Cr, Mn, and Fe on the B-sites (Ni-sites). Alloys were arc melted and drop cast starting with commercially pure elemental metals. Dendritic segregation was observed in the as-cast condition, which can be reduced substantially after a 1-day anneal in vacuum at 950C. Wavelength-dispersive spectroscopy was used to study the changes in the chemical composition as a function of heat treatment. All the alloys investigated were multi-phase, with the majority phases having the C14 and C15 crystal structures as determined by X-ray diffraction. Hydrogen storage capacity was measured electrolytically in a wet cell and capacities ranging from 380 to 420 mAh/g were obtained depending on the alloying additions. Higher discharge capacities result when the hydrogen storage sites are controlled using Ovonic's design principle. Although the microstructure became homogenized after heat treatment, it did not significantly improve the wet cell capacities. The observed effects of alloying additions will be discussed in terms of atomic size, electronegativity, and hydride formation energy. Research sponsored by the IPP program and the ATP/AMAPP program under subcontract DOE Project No. ERD-96-XJ010 to Lockheed Martin Energy Research Corp. from Ovonic Battery Company/ECD, Troy, MI.

CC5.18
DENSIFICATON AND MICROSTRUCTURE OF La_1-xSr_xFeO_3-d. Lise T. Sagdahl , Mari-Ann Einarsrud and Tor Grande, Department of Inorganic Chemistry, Norwegian University of Science and Technology, Trondheim, NORWAY.

The sintering behavior of La_1-xSr_xFeO_3-d, (x = 0, 0.1, 0.25) has been carefully investigated in order to obtain high quality target material for sputtering of epitaxial thin films. Densification has been studied as a function of temperature and partial pressure of oxygen, and the microstructure and phase composition of the ceramics have been characterized by SEM and XRD. The temperature width of the optimum sintering interval decreases with increasing Sr content. Considerable desintering is observed in the Sr substituted samples above the narrow optimum sintering temperature interval. Possible transport mechanisms are discussed in the relation to the densification and the observed desintering.

CC5.19
DIELECTRIC PROPERTIES OF Pd/Y8Z COMPOSITES. M.G.H.M. Hendriks, H. Verweij, M.P. Timmerman-Oude Wolbers , Inorganic Materials Science, University of Twente, Enschede, NETHERLANDS.

Dense homogeneous dual-phase composites of an oxygen-conducting cubic zirconia and a near percolative palladium phase are prepared by conventional ceramic processing. Such composites are expected to behave as supercapacitors, due to the large interfacial area between electrodes and electrolyte and due to the possibility to store additional charge in the electric double layer. It is expected that in the composites capacitance values of 1 F/cm³ can be achieved. From electrical impedance measurements of the first samples made, it is found that the capacity of these compacts increases with an increasing palladium content. In addition, it is observed that at higher frequencies the composites behave like a true capacitor.

CC5.20
DYNAMIC MECHANICAL SPECTROSCOPY AND IONIC CONDUCTIVITY STUDIES OF GEL ELECTROLYTES BASED ON STEREOCOMPLEXED POLY(METHYL METHACRYLATE). Yury K. Yarovoy , Hong Peng Wang, and Stephanie L. Wunder, Department of Chemistry, Temple University, Philadelphia, PA.

Thermally reversible conducting gel electrolytes, comprising blends of atactic and isotactic poly(methyl methacrylate) (PMMA), lithium salt and an organic solvent, have been prepared and characterized. Due to association between isotactic PMMA (i-PMMA) and syndiotactic sequences of atactic PMMA (a-PMMA), strong gels are formed in solvents which ordinarily do not form gels with high molecular weight a- PMMA, namely dimethyl carbonate (DMC) and diethyl carbonate (DEC). The plot of the dependence of elastic moduli on the fraction of i-PMMA passes through a maximum at  1:1 molar ratio between isotactic PMMA and syndiotactic fractions of a-PMMA. However, the conductivity of the gels is invariant to the ratio of i-PMMA and a-PMMA. Thus, gels with a typical polymer content of 15-20, 1M lithium salt, and a ratio of i-PMMA to a-PMMA of about 1:3 has an ionic conductivity in the range of 1x10^-3 - 4x10^-3 S cm^-1 and possesses a dynamic elastic modulus one order of magniture higher than the electrolytes containing only atactic PMMA. This modulus is obtained at values of the frequency between 0.01 to 100 radians, so that even under static conditions the gels do not flow and exibit reversible elasticity to high degree of elongation. Thermal mechanical analysis and calorimetry of these gels show that the physical crosslinks formed by stereocomplexed syndiotactic and isotactic triads melt in the range of 65-85C depending on the nature of the solvent and lithium salt. The fact that these gel electrolytes are thermoreversible makes them readily processable. After melt casting they form transparent dimensionally stable, self supporting films.

CC5.21
RELATIONSHIP BETWEEN CRYSTAL STRUCTURE AND Li⁺-CONDUCTIVITY IN La_0.5Li_0.5TiO₃ PEROVSKITE. J.A. Alonso , J. Ibarra, M.A. Paris, J. Sanz, Inst. Ciencia de Materiales de Madrid, SPAIN; J. Santamaría, C. León, F.C. Físicas, U. Compl. Madrid, SPAIN; A. Várez, E.P.S., U. Carlos III, Madrid, SPAIN; M.T. Fernández, Inst. Laue-Langevin, Grenoble, SPAIN.

Ionic conductivity of Li_xLa_2/3-x/3TiO₃ perovskites is one of the highest reported values in lithium crystalline conductors (10^-3-1 cm^-1 at T= 300K), making these compounds good candidates for solid electrolites in lithium batteries. The location of Li in the crystal structure of this family had not been possible up to date from X-ray diffraction (XRD) data. A neutron powder diffraction (NPD) study on the material with maximum Li content, Li_0.5La_0.5TiO₃ allowed us to find out some interesting features of this perovskite. In spite of the previous cubic description (from XRD data), the neutron patterns at room temperature show superstructure reflections due to the tilting of the TiO₆ octahedra, corresponding to an orthorhombic symmetry. The refinement in the Pbnm space group shows that Li cations are asymmetrically located at A positions of the perovskite, occupying tetrahedral voids, with Li-O bondlengths between 1.85 and 2.12 A, and large thermal B factors ( 4 A²). The temperature dependence of ⁷Li NMR spectra shows that below 75C the experimental line-width can be explained on the basis of lithium location in a single A site. At higher temperatures the line-width strongly decreases as a consequence of the Li motion, consistent with the large observed thermal factors. The dc-conductivty displays a complex non-Arrhenius behaviour (1) with a progressive change of activation energy from 0.40 to 0.26 eV, from -100 to 200C. The dependence of ⁷Li spin-lattice relaxation time shows the same non-Arrhenius behavior. We suggest that both unusual findings are associated to the observed tilting of the TiO₆ octahedra, which diminishes as temperature increases and leads to the opening of the bottleneck through which the lithium transport takes place.
1. C. León, J. Santamaría, M.A. Paris, J. Sanz, J. Ibarra, L.M. Torres, Phys. Rev. B56(9), 5302 (1997).

CC5.22
PHASE RELATIONS AND CONDUCTIVITY IN Ba₂(In_2-xM_x)O₅ SYSTEM. Akihiko Yamaji and Kazuya Kawakami, Department of Mechanical Engineering, Tokyo Institute of Technology, Tokyo, JAPAN.

Brownmillerite(Ca₂Al₂O₅-Ca₂Fe₂O₅ solid solution) structure can be regarded as an oxygen-ion deficient perovskite structure. Because of high proportion of the oxygen vacancies in the structure, this material could be a candidate of fast oxide ion conductor. Goodenough et al. indeed observed a fast-order transition to a fast oxide-ion conductor at 930C for Ba₂In₂O₅ which adapts brownmillerite structure at ambient temperature. The high temperature cubic phase shows large ion conductivity. It is of interest to examine whether or not the cubic phase stabilizes in the low temperature region by making solid solution of another element. In the present study, we investigated the ion conductivity and the crystal structure of Ba₂(In_2-xM_x)O₅ system by substituting In site for element M such as Sc,Y,La,Ce,Nb,Ta etc. By substituting 3 mole  Nb for In, the transition temperature decreased by about 300C. High temperature X-ray diffraction analysis shows the crystal structure changes from orthorhombic to cubic at this transition temperature. The most effective element which decreased the transition temperature was pentavalent element such as Nb or Ta. The substitution In site for 20 mole  Nb stabilizes the cubic structure down to room temperature. The ion conductivity of Nb 20 mole  substituted ceramics at 500C reached to about 2x10^-1 s/m. This value is a little larger than that of Sc and La co-doped ZrO₂ ceramics.

CC5.23
NEW PROTON CONDUCTING POLYMERS BUFFERED AT NEUTRAL PH. Stéphane Béranger , Nathalie Ravet, Daniel Baril, Michel Armand, Département de Chimie, Université de Montréal, QC, CANADA; Christophe Michot, Rhône-Poulenc, Lyon, FRANCE.

Poly(ethylene-oxide) (POE)_n/histamine-(HTFSI)_x, (8  n  20; 1  x  2) salts complexes are good candidates for the preparation of electrolytes buffered at a neutral pH close to 7 Histamine, which is this new family of proton conductor, contains the imidazole ring which is known to form strong intermolecular hydrogen bonds leading to a Grotthus mechanism. In this study, conductivities, electrochemical and thermal data have been investigated for different proton-vacancy concentrations. These materials show a good thermal behavior, with the formation of amorphous complexes and the electrochemical stability window expected for a proton conductor. Then we suggest their use in dye-based electrochromic cells where the electrochromic materials are dissolved in the electrolyte.

CC5.24
IONIC CONDUCTIVITY IN LITHIUM DOPED POLYSULFONE POLYMER FILMS. A.K. Sharma , Y.R.V. Naidu, D.S. Sagar and V.V.R.N. Rao, S.V. University, Department of Physics, Tirupati, INDIA.

Polymers offer a new range of materials which exhibit high ionic conductivity comparable to that of liquid electrolytes. The technological importance of these materials is exemplified by their use as solid state batteries, fuel cells, sensors etc. It has been shown that complexes between polymers and lithium salts may be used as ionic conductivity media in rechargeable lithium containing batteries. In this paper, we report a new lithium ion conducting polymer based on polysulfone complexed with lithium salt and characterized using I-R and electrical conductivity data. The measurements show that the electrolyte is a mixed (ionic+electronic) conductor, the charge transport being mainly ionic (activation energy 0.8 ev). It was found that room temperature conductivities increased by several orders of magnitude upon doping with lithium and the samples showed better charge-discharge properties. The temperature dependence of conductivities for differently doped samples showed a peculiar behaviour attributable to dopant kinetics.

CC5.25
CHARACTERIZATION OF CREEP BEHAVIOR OF SrCo_0.8Fe_0.2O_3-x. G. Majkic , L. Wheeler and K. Salama, Materials Research Science and Engineering Center, University of Houston, Houston, TX.

In order to achieve commercial utilization, oxygen separation membranes and solid oxide fuel cells must be able to keep their mechanical integrity over acceptable life-time periods. This imposes a need for characterization of mechanical behavior of this class of materials under typical creep operating conditions, in order to identify mechanisms that lead to mechanical degradation during operation. It this study, a series of compressive creep tests on cylindrical specimens is performed, covering a wide range of operating parameters (temperature and stress). The influence of grain size and intergranular glassy phase on controlling mechanisms is also addressed. The material response is interpreted by identifying the relevant parameters such as stress exponent, activation energy and Monkman-Grant relation parameters. The identification of dominant creep mechanisms is obtained by microstructural studies of crept samples. The microstructural observations reveal the mechanisms of microstructural accommodation of macroscopic strains, namely, the relative contribution of intergranular cavitation, grain deformation and grain boundary sliding. The grain-size effect on the relative contribution of these mechanisms to creep deformation is addressed in order to obtain an indication of the relative influence of grain boundary and lattice diffusion. * This work is sponsored by the National Science Foundation through the MRSEC program under Award Number DMR-9632667.

CC5.26
INORGANIC MEMBRANES WITH HIGH PROTON CONDUCTIVITY. Flavio Maron Vichi , Maria Teresa Colomer, Marc A. Anderson, Water Chemistry Program, University of Wisconsin, Madison, WI.

Glass-supported titania and alumina membranes were prepared via the sol-gel method. The proton conductivities of the membranes were determined by impedance spectroscopy for temperatures ranging from 25 to 90C and 100% relative humidity, and the results were compared to those obtained for Nafion film measured under the same conditions. The impedance spectra were obtained using a 2-point configuration, with the conductivity being measured along the surface of the membranes. At 25C, the proton conductivities were 6.84  10^-3, 8.75  10^-3 and 1.99  10^-2 S.cm^-1 for alumina, titania and Nafion, respectively. When the temperature was raised to 90C, the conductivities increased to 2.39  10^-2, 7.39  10^-2 and 2.89  10^-2 for alumina, titania and Nafion, respectively. Thermogravimmetric analysis shows that the water content is higher in the ceramic membranes at temperatures above 60C and, at temperatures above 90C, the water content in the ceramic membranes is 2 to 4 times higher than that of Nafion. The higher water content in these hydrophilic membranes at higher temperatures is the key factor in their maintaining a high protonic conductivity.

CC5.27
Abstract Withdrawn
 
 

CC5.28
NEUTRON VIBRATIONAL SPECTROSCOPY OF WATER AND SOLVATED PROTONS IN HETEROPOLYACID HYDRATES. Terrence J. Udovic , Taner Yildirim, Nicholas C. Maliszewskyj, NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD.

Heteropolyacid hydrates have been of interest in low-temperature fuel-cell research due to their relatively high protonic conductivities. To help elucidate the dynamics of the water and solvated protons which surround the large Keggin polyanions in these structures, we have performed neutron vibrational spectroscopic measurements for a variety of hydration levels in H₃PM₁₂OnH₂O (where M = W, Mo and  30). Moreover, both deuterium isotopic substitution and first-principles total-energy calculations were employed to characterize the vibrational density of states of the novel H₅O₂⁺ dioxonium cation which is stabilized in phosphotungstic acid hexahydrate (H₃PW₁₂O6H₂O).

CC5.29
LARGE QUANTITY OF HYDROGEN UPTAKE BY A LITHIUM MODIFIED CARBON NANOTUBES. Ping Chen , Jianyi Lin, Xiaobin Wu, Kuang Lee Tan, National University of Singapore, Physics Department, SINGAPORE.

The development of high-capacity hydrogen storage system is a long-sought goal of the automobile industry. Recently, large quantity of hydrogen (30 wt) stored in a Lithium modified carbon nanotubes at atmospheric pressure and 623K was found. The amount of hydrgen uptake by carbon nanotubes is compared with that by Li modified activated carbon and graphite, which can absorb hydrogen less than 10 wt under the same conditions. The absorbed hydrogen is stable at room temperature, but released from carbon sorbent at temperature above 573K. All the sorbents can be reused, and was tested for several cycles. It is also found that, the increase in the hydrogen pressure during the uptake process could dramatically accelerate the rate of absorption especially in the case of carbon nanotubes. XRD, TEM, FTIR, XPS and SIMS were applied to investigate the changes in the structure and composition of carbon sorbents after Li modified and hydrogen uptake. It is suggested that the intercalation of Li in the layers of carbon sheets may occur, which may build suitable sites for hydrogen storage. The difference in the amount of hydrogen uptake amonge carbon nanotubes, activated carbon and graphite may mainly related with the material size and number of edges exposed to the hydrgen atmosphere.

CC5.30
SILVER BASED GLASSY ELECTROLYTE FOR SOLID STATE BATTERY APPLICATIONS. M. Venkateswarlu , ¹Pondicherry University, Department of Physics, Pondicherry, INDIA; N. Satyanarayana¹ and B. Rambabu, Southern University and A&M College, Surface Science, Spectroscopy and Solid State Ionics Laboratory, Department of Physics, Baton Rouge, LA.

In the recent past, considerable efforts are made to characterize the high ionic conducting (HIC) materials because of their importance in various device applications including solid state batteries. In view of the potentiality of these HIC materials, efforts are made to improve the conductivity by mixing of various combinations of oxides in the form of binary, pseudo binary, ternary and quaternary compounds for better device applications. Hence, in our paper, we present the preparation, characterization, electrical conductivity and battery applications of AgI-Ag₂O (SeO₂+As₂O₅) (SSA) glassy system. The SSA system was prepared by melt quenching technique and characterized by XRD, DSC & IR. Electrical conductivity studies were made in a wide frequency range (5Hz to 13MHz) using HP 4192 A LF impedance analyzer.
The best conducting SSA glass composition was taken and the different configurations of batteries were fabricated with various cathode materials to improve the performance. All the batteries were characterized by measuring the open circuit voltage, polarization and discharge characteristics data. Complete results will be presented and discussed.
Acknowledgement: MV grateful to CSIR for awarding RA. NS acknowledges UGC & DST, Govt. of India, for granting research projects. B.Rambabu acknowledges RCS program at LLNL and DOE for supporting this work.

CC5.31
Abstract Withdrawn.

CC5.32
CONTROL OF A RUNNING H₂/O₂ FUEL CELL WITH FILLED IONOMERIC MEMBRANES. Bernard LE Gorrec, Claude Montella, Jean-Paul Diard, Gerard Vitter, Christiane Poinsignon , LEPMI-INPG-CNRS Ecole Nationale d'Electrochimie et d'Electrometallurgie Saint Martin d'Heres FRANCE.

Performances of a H₂/O₂ polymeric electrolyte fuel cell running at 70C under 3 bars gas pressure and using a new filled ionomeric membrane are analysed with a recent experimental method established for impedance measurements of electrochemical batteries during discharge. A classical impedance-measurement set controls under sinusoidal current perturbation a battery connected in parallel to the load into which it discharges. The results demonstrate the possibility to study with classical equipment the impedance of high-capacity and low-impedance batteries during their discharge through a constant load. The impedance of the PEMFC connected to a constant load (R = 0.180 ohm) was measured. The impedance diagrams present at high frequencies, an inductive behaviour analogous to that observed for batteries, one capacitive arc and a small straight line. The internal resistance of the PEMFC can be estimated.

CC5.33
NANO COMPOSITE BASED ELECTROLYTES FOR LITHIUM-ION BATTERIES. Michael W. Riley, Peter S. Fedkiw, Saad A. Khan , Dept of Chemical Engineering, North Carolina State University, Raleigh, NC.

Electrolytes for lithium ion batteries must possess high conductivity (>10^-3 S/cm @ 25C), low-interfacial impedance, a high-potential window (>5 V), and mechanical stability. The lithium ion transference number is also an important property, as larger values lower concentration polarization. A transference number of unity can potentially offset a decrease in conductivity by up to an order of magnitude, particularly for high-discharge rate systems. Nano composites of hectorite and other 2:1 layered clays (smectites) are characterized by a negatively charged plate-like structure with exchangeable associated cations sandwiched between the plate-like layers. They offer the ability to act as single ion conductors with potential for exhibiting transference numbers approaching unity. They also possess the ability to provide mechanically stable electrolytes through formation of strong physical gels via assembling into three-dimenional networks. These features make investigation of nanostructured, clay-based electrolytes desirable, even though conductivities of both native dry and organic intercalated forms of the smectites may fall short of magnitude required for lithium batteries. This study involves development of composite electrolytes based on lithium-hectorite clay dispersed in high dielectric organic solvents such as ethylene carbonate (EC) and propylene carbonate (PC), and investigating its electrochemical and rheological behavior. Our initial studies show the LiHectorite/carbonate composites to exhibit room temperature conductivities of 10^-4 S/cm, approximately 20 times lower than that of a Li+ molar equivalent LiPF₆ electrolyte. However, unlike the LiPF₆ electrolyte, the LiHectorite based composites reveal lithium ion transference numbers of 0.8. In addition, dynamic rheological techniques reveal this system to be extremely stable mechanically, with the elastic modulus G' exceeding 10⁷ dynes/cm² and yield stress exceeding 10⁴ dynes/cm². These results will be interpreted in terms of the prevailing structure of the system.
 

SESSION CC6: ANODES & NiMH
Chairs: Daniel H. Doughty and Linda F. Nazar
Wednesday Morning, April 7, 1999
Metropolitan II (A)

8:30 AM *CC6.1
DEVELOPMENT OF A NOVEL COMPOSITE ANODE FOR HIGH-ENERGY AND HIGH-POWER LITHIUM-ION BATTERIES. G. Abbas Nazri , Bouziane Yebka, Maryam Nazri, University of Michigan, Department of Chemistry, Ann Arbor, MI.

Carbonaceous anodes are the most practical elecrode for application in lithium-ion battery, mainly due to their low cost, flexibility for modification to achieve high-energy capacity and high-rate capability, abundance and environmentally uniquencess. In this work we have deveoped a novel composite carbonaceous anode for application in lithium ion batteries. The energy capacity and rate capability of the electrode have been tailored to satisfy the requirments of high-energy and high-power applications. Performance of the composite electrode under continuoes charge-discharge cycling and application of various current pulses will be reported. The safety aaspect of carbonaceous anodes and reactivity of the lithiated anode in contact with cyclic and linear carbonate based electrolytes have been studied using reat-time electrochemical- mass spectrometry and gas chromatography. The nature of gaceous species generated on various carbonaceous anodes and the film formed on electrode surface during initial charge-discharge cycling have been studied. We report the correlation between structural parameters of carbonaceous materials and their irreversible capacity. Structural parameters have been studied using x-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy. We have found a direct correlation between crystal morphology, degree of disorder, degree of graphitisation and the irreversible capacity loss and volume of generated gases during initial charge-disharge cycling. Results also show the importance of removing adsorbed and trapped impurities, in addition to removal of bonded functional groups. Thermal analysis of different graphitic samples at various stages of charge discharge cycling and degree of lithium intercation have ben investigated, and results are correlated to the structural parameters of electrode materials. We have applied TGA and DSC analysis, to clarify how each factors and parameters contributes to the thermal stability of the different intercalated graphite materials.

9:00 AM *CC6.2
DEVELOPMENT AND CHARACTERIZATION OF NANOSTRUCTURE TIN ALLOYS AS ANODES IN LITHIUM-ION BATTERIES. E. Peled and A. Ulus, School of Chemistry, Tel-Aviv University, Tel Aviv, ISRAEL.

Two important properties make tin alloys promising candidates for anodes in lithium-ion batteries: high reversible capacity and high melting point of the LixSn phases. Recently, Besenhard's group showed that reducing the size of the alloy particles resulted in a longer cycle life. In this work we prepared and evaluated nanostructure tin-antimony alloys containing Sn:Sb 9:1 to 1.4:1 atomic ratio and other elements including carbon, oxygen and copper. XRD measurements showed only one antimony phase - the SnSb phase. Fractal-like morphology was obtained. The particles are generally smaller than 100 nm. Anodes made from these alloys were cycled versus lithium between 0 to 1.0V at current densities from 0.02 to 4 mA per square cm in 1M lithium hexafluoroarsenate PC or EC/DEC solutions. For tin rich alloys the insertion curve (at 0.02 mA/ square cm) has three voltage plateaus: at 685 mV, 570 mV, and 440 mV. Antimony rich alloys have another two plateaus at 820 and 850 mV. The de-insertion curves (at 0.2mA/ square cm) have less definite plateaus, about 100 to 200 mV higher than those of the insertion curves, indicating that the overpotential of the de-insertion process is higher than that of insertion. The maximum reversible capacity was 700 mAh/g ( based on the total electrode mass excluding the current collector ) and the minimum irreversible capacity was 15%. The reversible capacity and the rate capability decrease with increasing antimony content of the alloy. Cycle life was found to increase with the content of antimony and copper and up to 40 stable 100% charge-discharge cycles were demonstrated. SEM photographs show evidence for disintegration of the alloys after cycling. The correlation among capacity, cycle life, alloy composition and morphology will be addressed.

9:30 AM CC6.3
EFFECT ON PERFORMANCE OF COMPOSITION OF Li-ION CARBON ANODES DERIVED FROM PMAN/DVB COPOLYMERS. Ronald A. Guidotti , Sandia National Laboratories, Albuquerque, NM; William R. Even, Jr., Sandia National Laboratories, Livermore, CA.

Soft, ordered graphites typically have low first-cycle capacity losses associated with solvent/salt reduction processes. These materials have capacities limited by the composition LiC6, or 372 mAh/g. Hard, disordered or turbostratic carbons, on the other hand, have shown to have capacities well in excess of 372 mAh. The composition of disordered carbons has an impact on its electrochemical performance. The H/C atomic ratio, for example, was found to correlate to the reversible capacity for some specific materials (1). Incorporation of Si into the carbon lattice has also been reported to enhance the reversible capacity (2). Doping with N, however, resulted in degradation of performance, due to an increase in the irreversible capacity (3). We have previously reported on the performance of carbons derived from polymethacrylonitrile (PMAN)/divinyl benzene (DVB) copolymers. In that work, a molar PMAN/DVB ratio of 3:1 was used. In this paper, we present the results of electrochemical characterization of carbons derived from similar precursors but where the PMAN/DVB ratio was varied, to encompass zero-N material to low-N and high-N carbons. Contrary to what others have reported, we find that a high-N material performs better than the low-N counterpart in galvanostatic cycling tests in 1M LiPF6/ethylene carbonate-dimethyl carbonate (1:1 v/v) solution. The pyrolysis temperature affects the performance by changing the bulk composition.
1. T. Zheng, Y. Liu, E.W. Fuller, S. Tseng, U. von Sacken, and J.R. Dahn, J. Electrochem. Soc., 142 (8), p. 2581 (1995).
2. A.M. Wilson and J.R. Dahn, J. Electrochem. Soc., 142 (2), 326 (1995).
3. J.R. Dahn, A.K. Sleigh, H. Shi, B.M. Way, W.J. Weydanz, J.N. Reimers, Q. Zhong, and U. von Sacken, Lithium Batteries - New Materials, Development and Perspectives, G. Pistoia, ed., Elsevier, New York, 1994, p. 1.
This work was supported by the United States Department of Energy under Contract DE-AC04-94AL85000.

9:45 AM CC6.4
SYNTHESIS OF NOVEL HYDRATES VANADATES: THE ROLE OF WATER WITH RESPECT TO THEIR POTENTIAL USE IN RECHARGEABLE Li-ION BATTERIES. P. Poizot, E. Baudrin, S. Denis, S. Laruelle, M. Touboul and J.M. Tarascon , Laboratoire de Reactivite et de Chimie des Solides, Universite de Picardie Jules Verne, Amiens, FRANCE.

Rechargeable Li-ion cells have become key components of the portable, entertainment, computing and telecommunications equipment. However, consumers are in constant demand of batteries with larger autonomy (e.g. greater capacity). In searching for alternative materials to substitute for the carbonaceous negative electrode in Li-ion cells, we expanded on Yoshio's work dealing with lithiated vanadium oxide-based electrodes. We have synthesized, by means of a chimie douce method a large variety of new hydrated vanadates RVO4.nH2O (R= In, Co, Ni, Fe ..) that can be either amorphous or crystallized. Most of these hydrated vanadates are shown to reversibly intercalate large amounts of Li leading to capacities as high as 1000mAh/g, with however a large irreversible loss between the first discharge/charge and a large capacity fading upon cycling. Could such poor performance be linked to the presence of water in these compounds? We capitalized in our advantage of being able to synthesize a serie of materials containing various amounts of either adsorbed or structural H₂O to address the water issue within the field of Li intercalation chemistry, that has long been very controversial. A strong dependence of the electrochemical performance of these hydrated vanadates with respect to the nature of water as well as of its bonding to the lattice was observed. The room temperature and 55C ageing of these as-made materials in various non-aqueous electrolytes, both at room temperature and at 55C, have also revealed, depending again on the material water content, a partial decomposition. An attempt to reconvey all the results, on the basis of the interplay between the electrochemical performance of these materials and their crystal/chemical aspects will be presented and a tentative to generalize these findings to other materials discussed.

10:00 AM CC6.5
THE ROLE OF OXYGEN IN THE REVERSIBILTY OF LITHIUM INSERTION IN METAL OXIDE ANODE MATERIALS. Linda Nazar, University of Waterloo, CANADA; Fabrice Leroux , Universite Blaise-Pascal, FRANCE; Gillian Goward, University of Waterloo, CANADA; Guy Ouvrard, Institut des Materiaux de Nantes, FRANCE.

Considerable attention has been devoted towards developing new negative electrode materials for Li-ion batteries in the past few years. Although graphitic materials that form the basis of current commercial negative electrodes meet many of these demands, they also suffer from some drawbacks, including limited Li insertion capacity poor volumetric energy density. The discovery of promising Li insertion properties of various new materials in recent years has led to exploration of systems other than graphite, including amorphous nanocomposites, and crystalline materials such as metal oxides. Numerous transition metal oxides, in addition to the better known tin oxides, have been shown to offer very good capacities and cyclability. The mechanism of insertion in these materials is not well understood, however. Lithium-7 NMR and XAS have been used to demonstrate that in crystalline oxides containing Mo, Sn and/or Fe, low potential Li insertion is associated with the formation of a complex amorphous nanocomposite, in which the oxygen remains in close association with the metal centers to varying degrees depending on the material. On Li de-insertion, Li migration from within the particle leads to surprisingly ready re-formation of the metal oxygen interaction. The effect of cut-off voltage and the role of the matrix in stabilizing the electrochemical behavior will be discussed.

10:30 AM *CC6.6
MECHANICAL MILLING: AN APPROACH FOR BETTER ELECTRODE MATERIALS WHATEVER THE BATTERY TECHNOLOGY CONSIDERED. L. Aymard, C. Lenain, L. Courvoisier, F. Salver-Disma and J.M. Tarascon , Laboratoire de Chimie et de Reactivite des Solides, UPRESS-A, Universite Picardie Jules Verne, rue Saint-Leu, Amiens, FRANCE.

In the intense search for high capacity electrode materials, the effect of mechanical milling (MM) using either shearing- or shock-type interactions was investigated. Non-reactive mechanical milling that results in the formation of very reactive carbon-edge atoms has, for instance, enabled the preparation of carbonaceous materials able to reversibly accept 2 lithiums per six carbons Li2C6. Separately, reactive room temperature mechanical milling produces highly strained and divided electrochemically active hydride-forming alloys with, therefore, a limited capacity because of oxygen contamination associated to their high division state. It was then interesting to find out whether during a mechanical alloying experiment the carbon-edge atoms could serve as oxygen scavengers in presence of hydride-forming materials in order to restore the theoretical electrochemical capacity of the AB5 alloys. The effect of mechanical milling on powders mixtures consisting of graphite and AB5 alloys, prepared either by mechanical alloying or by a high temperature melting process, was then investigated. The resulting materials were characterized for their structure, composition, morphology, surface area and electrochemical performance. Among the most prominent results are the hydride-forming composite electrodes showing a 10 and 40% capacity enhancement when the AB5 precursor alloy was arch-melted or mechanically prepared, respectively. Such an increase in capacity will be explained as the result of several cumulative effects that are 1) a mechanically induced reducing role of graphite that eliminates the AB5 particles of oxide coatings, 2) the appearance of an increasingly important double layer capacitance on each particle upon increasing milling and 3) the improved electronic conductivity between the active AB5 material and the graphite, which allows a better use of the alloy.

11:00 AM *CC6.7
SURFACE STRUCTURE AND ELECTROCHEMICAL CHARACTERISTICS OF Ti-V-Cr BCC-TYPE SOLID SOLUTION ALLOYS SINTERED WITH Ni. Yoichiro Tsuji , Osamu Yamamoto, Hiromu Matsuda, Yoshinori Toyoguchi, Central Research Laboratory, Matsushita Electric Industrial Co., Ltd., Osaka, JAPAN.

Ti-V-Cr bcc-type solid solution alloys can absorb a large amount of hydrogen and be applied to active materials of Ni-MH batteries. However, because of the insolubility of Ni into these alloys, the electrochemical characteristics like discharge capacity and cycle life were poor. In order to increase the discharge capacity, Ti-V-Cr alloy powders were sintered with Ni to form Ni contained surface layer around the Ni free alloy particle. This structure supplies a high electrochemical activity with the minimum loss of hydrogen absorbing ability. The Ti-V-Cr alloy particles were covered with Ni by mixing Ni and alloy powders or electroless plating, and sintered at various temperatures. As sintering temperature went up, the surface composition changed from TiNi to Ti₂Ni. TiNi surface layer showed better electrochemical characteristics and the best sintering condition was at 600C for 6 hours. Ni electroless plating was preferred because of good adhesion, and the optimum amount of Ni was 7wt%. Discharge capacity of 570 mAhg^-1, which was about twice as large as that of AB₅ alloys, was obtained by optimizing Ni amount and sintering condition as mentioned above.

11:30 AM CC6.8
HIGH PERFORMANCE Zr-BASED METAL HYDRIDE ALLOYS. R.C. Young , B. Huang, Y. Li, B.S. Chao, S.R. Ovshinsky, Energy Conversion Devices, Inc. Troy, MI; E.P. George, C.T. Liu, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN.

Based upon Ovonic's multi-element disorder principle, two families of alloys are being used in commercial NiMH rechargeable battery, i.e. the misch metal (Mm) based and the Zr-based alloys. It is generally recognized that the Mm based alloys is easy to activate, however, is limited by its discharge capacity of 350 mAh/g. On the other hand, the Zr based alloys, which usually takes a little longer to activate, has a higher discharge capacity. In this paper, we demonstrated that the Zr-based multi-element alloys with the discharge capacities well above 450 mAh/g have been achieved. The aspect of the high discharge capacity of the metal hydride alloys is particularly important for the electric vehicle applications because of its stringent requirement on the high specific energy of the battery pack. We would like to emphasize that the high discharge capacity of the alloys not only increases the energy density of the battery, equally important, it also reduces its cost. We have carried out a comprehensive study of the Zr based multi-element alloys, especially, on the effect of stoichiometry, electron concentrations, structures and processing parameters to the electrochemical discharge capacities and kinetics. Within the multi-element disordered transition metal alloys, it is found that a decrease of the electron concentration factor of the alloys, which shifts the structure from diamond cubic(C15) to hexagonal(C14), increases the hydrogen storage capacity. However, it only increases the electrochemical discharge capacity to a certain extent because the hydrogen trapping phenomenon starts to occur.

11:45 AM CC6.9 EFFECT OF ALLOY COMPOSITION TO THE STRUCTURE OF Zr BASED METAL ALLOYS. B.S. Chao , R.C. Young, D.A. Pawlik, J.S. Im, B. Husang, S.R. Ovshinsky, Energy Conversion Devices, Inc., Troy, MI; B.C. Chakoumakos, Neutron Scattering Section, Oak Ridge National Laboratory, Oak Ridge, TN.

The structures of Ovonic multi-element Zr base transition metal alloys for hydrogen storage are studied. It is found that the alloys are multi-phase materials. The hexagonal and diamond cubic structures, known as C14 and C15 structures respectively, are the two major hydrogen storing phases in the alloys. In both hexagonal and diamond cubic structures, Zr and Ti are the elements typically occupying the hydride former (A) sites and V, Cr, Mn, Fe, Co and Ni the catalytic (B) sites. Based on the designed principle for the disordered materials, both sites are compositionally disordered by the corresponding elements in cubic (C15) structure. The hexagonal (C14) structure in the AB2 formulation has two distinct B sites, B(I) and B(II) with a 1:3 ratio. Preliminary neutron diffraction studies indicate that the B(I) sites are predominantly occupied by Ni and the B(II) sites are randomly mixed with V, Cr, Mn, Fe, and Ni. It is then proposed that the formula of the hexagonal structure should become A2B(I)1B(II)3 in the current multi-element Zr alloys. Minor phases close to the structures of Zr7Ni10, Zr9Ni11, and ZrO2 are also present in some alloys. The average electron concentration factor (e/a) derived from the alloy composition dictates the alloy structures. The alloys with higher electron concentration factor (> 7.0) favors the diamond cubic structure. On the other hand, the hexagonal structure is associated with the alloys with lower electron concentration factor (< 6.4). The alloys having electron concentration factors in between are mixtures of the diamond cubic and hexagonal structures. Good kinetics are observed in the alloys containing higher Ni content, closely associated with the diamond cubic structure. Higher discharge capacity is mostly observed in the hexagonal dominant alloys.
 
 
 

SESSION CC7: SUPERCAPACITORS
Chairs: Artur Braun and Katsuhiko Naoi
Wednesday Afternoon, April 7, 1999
Metropolitan II (A)

1:30 PM *CC7.1
PERFORMANCE OF LARGE SIZE ELECTRIC DOUBLE-LAYER CAPACITOR USING ORGANIC ELECTROLYTE. T. Morimoto , M. Tsushima, K. Hiratsuka, M. Suhara, Y. Sanada, T. Kawasato, Asahi Glass Co, Ltd., Research Center, Yokohama, JAPAN.

Electric double-layer capacitors using an organic electrolyte solution have been developed and are widely used as maintenance-free power sources for IC memories and microcomputers. One of the newly proposed applications for large size electric double-layer capacitors is pulse power sources in electric and hybrid vehicles.
The excellent performance of power capacitors is attained by a new electrolyte of high conductivity and high decomposition voltage and an electrode fabricated with high surface area activated carbon. An electrolyte obtained by dissolving 1.1M triethylmethyl ammonium tetrafluoroborate in propylene carbonate having the specific conductivity and the decomposition voltage of 0.018S/cm and 3.0V, respectively, were used. Furthermore, activated carbon of low oxygen content having the specific surface area of 2000m2/g was used as the electrode material. Rectangular power capacitors having the capacitance of 1300F and internal resistance of 3mwere developed using the material mentioned. After charging to 2.5V, the cell voltage of the capacitor decreases linearly under constant discharge current of 50A from 2.5V to 1.0V in 40 seconds. The cycle life test of the capacitor at 45 degrees in centigrade show that the deterioration in capacitance is less than 15% after 400,000 times charge and discharge cycles under constant charge and discharge current of 50A between the cell voltage of 2.5V and 1.25V.

2:00 PM CC7.2
RECENT DOE SPONSORED ELECTROCHEMICAL CAPACITOR TEST RESULTS. Randy B. Wright , Tim C. Murphy, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID; Susan A. Rogers, U.S. Department of Energy, Washington, DC.

Electrochemical capacitors (ultracapacitors) are being developed for hybrid vehicles as candidate power assist devices for the fast response engine and for other energy storage applications. Ultracapacitors show promise towards being able to accept high regenerative pulses and high power delivery capabilites while exhibiting very high cycle life. This paper will present test data from selected U.S. Department of Energy (DOE) supported ultracapacitor projects designed to meet the fast response engine requirements.
Constant-current, constant-power, leakage-current and self-discharge test results will be presented and discussed that have been acquired from prototype capacitors supplied by Maxwell Energy Products, Inc., SAFT America, Inc., and the YUNK-Bureau Ltd, in Kiev, Ukraine. The Maxwell capacitors consisted of individual capacitor cells rated at 2.3 V and 101.4 F, and an integrated capacitor bank consisting of thirty-three of the series connected cells that is rated at 75 V and 2.9 F. SAFT capacitors rated at 3 V and 135 F to 138 F were also evaluated. The Ukrainian capacitor consisted of five series connected cells with individual ratings of 3 V and 2500 F, giving rise to a capacitor bank rated at 15 V and 500 F. All of these capacitors used a non-aqueous electrolyte in there design. The testing results from these devices will be compared to other capacitors that have been previously tested at the INEEL.

2:15 PM *CC7.3
A STUDY ON OXIDIZED GLASSY CARBON SHEETS FOR SUPERCAPACITOR ELECTRODES. Artur Braun , Martin Bartsch, Friederike Geiger, Bernhard Schnyder, Rudiger Kotz, Paul Scherrer Institute, General Energy Research, Villigen PSI, SWITZERLAND.

Electrochemical double layer capacitors for high energy and power density applications, based on glassy carbon (GC) electrodes, are developed in our laboratory [Ref.1]. GC has closed pores, but open porosity is mandatory to achieve a high double layer capacitance (DLC). The pores can be opened by a thermal or electrochemical oxidation process (activation). Results concerning thermally activated thin GC sheets are presented here in terms of the DLC, as measured in sulfuric acid with electrochemical impedance spectroscopy, and on the internal surface area, as obtained by gas adsorption (N₂) and small angle x-ray scattering (SAXS). During long term activation, the volumetric internal surface area decreases to 50% of its maximum value. However, the volumetric capacitance increases for around 10% during activation. The contradictory result of decreasing surface area, but increasing capacitance can be explained as follows: The high internal surface area at the initial stage of oxidation is due to micropores, of which not all are accessible for electrolyte. Upon activation, smaller pores coalesce to larger pores and the internal surface area decreases. But the larger pores are then accessible for the electrolyte, and additional double layer capacitance occurs. Financial support by the Board of the Swiss Federal Institute of Technology, SAXS beamtime from Dr. H.-G. Haubold, Dr. G. Goerigk (HASYLAB Hamburg and Forschungszentrum Jülich, Germany), R. Saliger and A. Emmerling (Universität Würzburg, Germany) is gratefully acknowledged.
[Ref.1] M. Bartsch, R. Kotz, A. Braun, O. Haas, Proceedings of the 38th Power Sources Conference, 8-11 June, p. 17, Cherry Hill, NJ (1998).

2:45 PM CC7.4
NEW CONDUCTING POLYMERS FOR ELECTROCHEMICAL ULTRACAPACITORS. Katsuhiko Naoi , Shunzo Suematsu, Tokyo Univ. A & T, Dept of Applied Chemistry, Koganei, Tokyo, JAPAN.

New conducting polymers based on pai-conjugated system hybridized with other redox systems such as disulfide or quinone. The authors will talk about the electrochmical properties and the characteristics as the electrochemical capacitors or batteries. The results for two polymer materials, viz., poly(dithiodianiline) and poly(1,5-diaminoanthraquinone) will be presented. The poly(1,5-diaminoanthraquinone) [poly(DAAQ)] film showed two redox couples at negative and positive potentials which correspond to the two redox systems; one is for the quinone and the other is for the pai-conjugated polymer system. The electrochemical window of the poly(DAAQ) was as wide as ca. 2.5V. The electrochemical capacitor utilizing the poly(DAAQ) films for both positive and negative electrodes exhibited higher specific energy (30 Wh / kg) and power (13.5 kW / kg) than those for other conducting polythiophene materials. It is proposed here a novel energy storage material of poly (DAAQ) which can be utilized as an electrochemical ultracapacito

3:30 PM CC7.5
A NOVEL CONDUCTING POLYMER WITH 0-S-S-O BONDS FOR POSITIVE MATERIAL: POLY(2,2'-DIAMINOBENZYLOXY- DISULFIDE). Yuzhi Su, Kecheng Gong , South China University of Technology, Polymer Structure & Modification Res. Lab., Guangzhou, CHINA.

Organic disulfide compounds has been proposed as a new class of high energy storage material^[1,2]. Poly(2,2'-diaminobenzyloxydisulfide) (poly(DABO)), a novel conducting polymer having O-S-S-O bond joined two moieties of anilines, is synthesized chemically as a new positive storage material. It exhibits conductivity in the region of 10^-3 S/cm by the four-probe method and the O-S-S-O bonds in it are confirmed by Fourie Transform Raman Spectroscopy (FT-RS) and Fourie Transform Infrared Spectroscopy(FT-IR). The poly(DABO) films are formed by electropolymerization from the DABO monomer solution in 1mol/dm³ H₂SO₄ supporting electrolyte on Pt electrode under continuous cycling between -0.20v and 1.20v vs SCE at scanning rate 100mv/s. The cyclic voltammetry studies show that its electrochemical behaviour is similar to polyanilineÕs. The oxidative peak current of the cyclic voltammograms increase and the starting peak potential negative a little with increasing of the cyclic numbers.
^[1] Gong Kecheng, MaWenshi, Mat Res. Symp. Proc., 461, 87(1995).
^[2] K. Naoi, K. Kawase, M. Mori and M. Komiyama, Mat Res. Symp. Proc., 496, 309(1998).

3:45 PM CC7.6
NANOSTRUCTURE MATERIAL FOR SUPERCAPACITOR APPLICATION. Yuhong Huang , C.T. Chu, Qiang Wei, Haixing Zheng, Chemat Technology, Inc., Northridge, CA.

Capacitive energy storage devices based on double-layer capacitance or pseudocapacitance have a wide range of potential applications. Currently, these capacitors are being used as power back-up for memory devices in electronic equipment or for electrical actuators. Because of their high energy and power densities and long cycle life, their potential applications include pulse power, bridge power, load leveling, and stand-by power. Terms such as supercapacitors, ultracapacitors, double layer capacitors, pseudocapacitors, and electrochemical capacitors have been used interchangeably for these devices. Electrochemical capacitor possesses electrode, electrolyte, seperator. Electrode material is a key element in electrochemical capacitor. The requirement of high energy and power density electrochemical capacitor intrigues development on miniaturization and weight reduction of electrochemical capacitor. A route to increase energy and power density is to increase assessable surface area of electrode. The pore size must be large enough to let electrolyte assess into the pore, and smaller enough to have high surface area per volume or per weight of electrode material. The cohesion of electrode and adhesion to the current collector is a key point to realize high conductivity and power density of electrode materials, such as nitride. Contacting resistance can increase the resistance of the capacitor. In present research, a composite coating technology has been developed and high energy density and power density has been achieved. Electrode material fabricated in Chemat showed same order of energy density and power density with ruthenium oxide crystalline materials. Furthermore, the potential cost is much lower than that of ruthenium oxide.

4:00 PM CC7.7
FABRICATION OF ULTRA THIN-FILM ELECTRODES FOR CHARGE STORAGE DEVICES BY SOL-GEL PROCESS. Suh-Cem Pang , Marc A. Anderson, Water Chemistry Program, University of Wisconsin, Madison, WI; Thomas W. Chapman, Department of Chemical Engineering, University of Wisconsin, Madison, WI.

Ultra thin-film electrodes comprising active materials of lithiated manganese oxides on conducting supporting substrates were fabricated by the sol-gel process. Aqueous polymeric sols were prepared by dissolving both stoichiometric and non-stoichiometric amounts of lithium and manganese salts, together with appropriate amounts of hydroxycarboxylic acids in water. Both amorphous and nanocrystalline thin-film electrodes were fabricated by dip-coating directly onto metal supporting substrates followed by calcination at controlled conditions. Material characterization and electrochemical performance evaluations indicated that these thin-film electrodes have good potential for use in charge storage devices such as batteries and supercapacitors. Cyclic voltammograms of thin-film electrodes gave a characteristic rectangular shape of an ideal supercapacitor with specific capacitance of more than 472 Farads per gram of active material over a voltage window of -0.3V to +0.9V. Thin-film electrodes fabricated at lower temperatures appeared to yield substantially higher specific capacitance, probably attributed to higher specific surface area and lower degree of crystallinity. We speculate that the large specific surface area of sol-gel derived manganese oxide nanoparticulates (double-layer capacitance) coupled with the faradaic charge transfer involving lithium ion intercalation processes (pseudo-capacitance) are the principle means of storing energy. The apparent transition between supercapacitor and battery-like behavior has been attributed to the quasi-two-dimensional processes of Li intercalation into 3-D host lattice of -MnO₂. Such supercapacitor behavior is evidenced from the shape of the 3-D sorption isotherm of the Li intercalation process, which exhibited a continuous decline of potential against extent of 3-D sorption of the sorbate into the host. In this study, we have focused on investigating the microstructural effect on the transition between the supercapacitor and battery-like behavior of these thin-film electrodes. The effect of precursor stoichiometry, complexing agents, supporting substrates and calcination conditions on the final microstructure and phase of active material of thin-film electrodes have been investigated.

4:15 PM CC7.8
PERFORMANCE OF ELECTRIC DOUBLE LAYER CAPACITORS WITH POLYMER GEL ELECTROLYTES. Masashi Ishikawa , Takahiro Kishino, Naoji Katada, Masayuki Morita, Yamaguchi Univ, Dept of Applied Chem & Chem Eng, Ube, JAPAN.

Polymer gel electrolytes consisting of poly(vinylidene fluoride) (PVdF), tetraethylammonium tetrafluoroborate, and propylene carbonate (PC) as a plasticizer have been investigated for electric double layer capacitors. The PVdF gel electrolytes showed high ionic conductivity (ca. 6 mS/cm at 298 K) and had good stability over a wide potential range (ca. 5 V). To assemble model capacitors with the PVdF gel electrolytes and activated carbon fiber cloth electrodes, a pair of the fixed electrodes was soaked in a precursor solution containing PC, PVdF, and tetraethylammonium tetrafluoroborate, followed by evaporating the PC solvent in a vacuum oven. The resulting gel electrolyte was in good contact with the electrodes; the good-contact interface between the activated carbon electrode and the gel electrolyte was found to be crucial for realizing high performance of the gel capacitors. The model capacitors with the PVdF gel electrolytes showed large values of capacitance and high coulombic efficiency in the operation voltage ranges of 1-2 and 1-3 V. It is worth notable that the capacitors with the PVdF electrolytes showed low leakage current and long voltage retention in self-discharge tests. These good characteristics of our gel capacitors are comparable to those of typical double layer capacitors with a liquid organic electrolyte containing PC and tetraethylammonium tetrafluoroborate; rather, the voltage retentivity of the PVdF gel capacitors is superior to that of the capacitors with the organic electrolyte.
 

SESSION CC8: SOLID OXIDE CONDUCTORS
AND SOFCs
Chairs: Hans-Peter Brack and Allan J. Jacobson
Thursday Morning, April 8, 1999
Metropolitan II (A)

8:30 AM *CC8.1
TRANSITION METAL DOPED LaGaO₃ PEROVSKITE FAST OXIDE ION CONDUCTOR AND INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELL. Tatsumi Ishihara , Takaaki Shibayama, Miho Honda, Hiroyasu Nishiguchi and Yusaku Takita, Oita University, Faculty of Engineering, Oita, JAPAN.

Effects of doping Fe, Co, Ni for the Ga site on the oxide ion conductivity of La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ have been investigated in detail. It was found that doping these transiton metals is effective for enhancing the oxide ion conductivity. In particular, a significant increase in the low temperature range was observed. Electrical conductivity was monotonously increased, however, transport number of oxide ion was decreased with increasing amount of transition metal dopant. Considering the transport number and electrical conductivity, the optimized amount of Fe, Co, and Ni doping seems to exist at 8.5, 3, and 5 mol for Ga site, respectively. In agreement with the improved oxide ion conductivity, power density of solid oxide fuel cell was also improved by using transition metal doped LaGaO₃ based oxide as an electrolyte. In particular, it was found that notably large power density was obtained by using Co doped LaGaO₃, and the power density of the cell was attained to 250 mW/cm² at 873 K in spitc of the 0.5mm thickness of electrolyte. Current interuption method suggest that main internal registance of the present cell is electrical registance of the used electrolyte. Therefore, the maximum power density was increased with decreasing the thickness of electrolyte. The power density of ca500 mW/cm² was attained at 873K @ when thickness of electrolyte was 0.2mm. The durability of the cell was also investigated on this thin electrolyte plate cells and it was confirmed that the notably high power density was stably sustained over 350 h. Therefore, this study made clear that transition metal doping LaGaO₃, in particular, Co doped LaGaO₃ perovskite oxide is promising as an electrolyte of intermediate temperature solid oxide fuel cell.

9:00 AM CC8.2
DEVELOPMENT OF ZIRCONIA ELECTROLYTE FILMS ON POROUS LSM CATHODES BY ELECTROPHORETIC DEPOSITION. Rajendra N. Basu , Clive A. Randall, Merrilea J. Mayo, The Pennsylvania State University, Dept of Materials Science and Engineering, University Park.

In this study electrophoretic deposition (EPD) is explored as an inexpensive route for fabricating the zirconia electrolyte in solid oxide fuel cells (SOFCs). Normally, deposition of particulate ceramic powders by EPD onto a porous surface yields a non uniform coating which, after sintering, results in porosity and surface roughness in the coating. To overcome this problem, the present study uses a fugitive coating as an interlayer between the porous substrate (a lanthanum strontium manganite tube) and the deposited zirconia. By this method, a fairly dense green coating (around 60%) is obtained, which yields a smooth surface and pore-free microstructure after sintering. The fugitive interlayer process appears to work for two reasons: (1) the interlayer helps to (temporarily) fill pores in the underlying substrate, thereby making a smooth surface for deposition and (2) the burnout of the interlayer allows the zirconia coating to become largely detached from the underlying substrate during early sintering, thereby eliminating the cracking conventionally associated with constrained sintering.

9:15 AM CC8.3
ANIONIC CONDUCTORS IN THE SYSTEMS (Bi, Sb, Te)-(Mo, W, V)-O. Pascale Begue^a,b, Renee Enjalbert^a, Alicia Castro^b, Patrice Millet^a and Jean Galy ^a, ^aCentre d'Elaboration de Matériaux et d'Etudes Structurales/CNRS, Toulouse, FRANCE; ^bInstituto de Ciencia de Materiales de Madrid/CSIC Cantoblanco, Madrid, SPAIN.

Oxide ion conducting solid electrolytes are of main interest for several applications like gas monitoring, metallurgy, chemical kinetics, solid oxide electrolyte fuel cells.... The well known yttria stabilized zirconia phase Zr_1-xY_xO_2-x/2 exhibits high oxide ion conduction at elevated temperatures, i.e. above 800K. Its advantages, low dissociation pressure and non-corrosive behavior are balanced by the requirement of high temperatures for its sintering (above 2000K) and its low conductivity below 800K. New oxide families based on Bi III and transition elements like Mo, W and V exhibiting particular atomic organization, i.e. ­ layered Aurivillius, and, - columnar structure types, will be presented with the aim to underline their chemical sensing potentialities. To enhance the physical properties of such phases the substitution of lone pair ns² elements, like Sb III, Te IV, Pb II, Bi III has been systematically used to design new multicomponent oxide structures. The syntheses of the Aurivillius phases Sb₂MoO₆, Sb₂WO₆ , Sb₂W_1-xV_xO₆ as well as the columnar ones (Pb,Bi)(Bi₁₂O₁₄)((Mo,V)O₄)₅ are realized via solid state chemistry syntheses at temperatures lower than 800^oC. Their original atomic structures determined by X-ray powder and single crystal analyses will be depicted. It will be shown how some special doping, chosen from detailed structural features, have been used to increase the conductivity of such phases ; the resistivity measurements have been realized by impedance spectroscopy. For example, the conductivity determined for the Bi(Bi_12-xTe_xO₁₄)Mo_4-xV_1+xO₂₀ material amounts 8x10^-3-1cm^-1 at 750^oC (for x=1).

9:30 AM CC8.4
IMPROVING GD-DOPED CERIA ELECTROLYTES FOR LOW TEMPERATURE SOLID OXIDE FUEL CELLS. James M. Ralph , Argonne National Laboratory, Electrochemical Technology Program, Argonne, IL; John A. Kilner, Department of Materials, Imperial College, London, UNITED KINGDOM.

Doped ceria electrolytes continue to be studied because of their high conductivity in the temperature range 500-650C. This high conductivity in the low temperature range makes them candidate electrolyte materials for use in low temperature solid oxide fuel cells (SOFC). At higher temperatures and low oxygen partial pressures, the reduction of ceria introduces substantial electronic conductivity, but below 650C this effect diminishes considerably, permitting ceria based electrolytes to be used in SOFC without a large loss in cell efficiency. Contrary to this trend, as the temperature of operation is lowered to 500C, the contribution from the grain boundaries to the total resistivity becomes significant. Thus the largest scope for reduction in the total resistivity of Gd-doped ceria (CGO) electrolytes in the temperature range of interest, must therefore come from reducing the resistance of the grain boundaries. In most polycrystalline ceramics it is found that impurities present within the materials tend to segregate to high energy surfaces such as the grain boundaries and sintered surfaces. In doped polycrystalline ceria, these impurities are thought to form an insulating phase at the grain boundaries, producing a high resistance layer. It is likely that precursor materials with high proportions of impurities will be used in the large scale production of doped ceria electrolytes, to reduce the overall costs. It is therefore necessary to develop a better understanding of the interplay between impurities and the changing dopant concentrations in ceria, to enable the conductivity in the electrolytes to be optimised. This paper will focus in detail on the electrical properties of Gd-doped ceria electrolytes at low temperatures and the trends observed with increasing dopant concentration. The potential of high Gd concentrations in ceria for SOFCs operating at 500C will also be explored and the effects of impurities, especially silica will be discussed.

9:45 AM CC8.5
Abstract Withdrawn

10:30 AM *CC8.6
DIFFUSION AND SURFACE EXCHANGE IN HIGH TEMPERATURE OXIDE ION TRANSPORT MEMBRANES AND FUEL CELL ELECTRODES. Allan J. Jacobson , Department of Chemistry, University of Houston, Houston, TX.

Membrane reactors that use dense mixed electronic-ionic conducting oxide membranes for oxygen separation and for the production of syn gas from natural gas (methane) have received much recent attention. The oxygen flux achievable in these oxide membranes depends on a combination of the bulk diffusion rate for oxygen transport and the surface reaction rates for oxygen activation or reaction with methane. I will describe some recent measurements of oxygen permeation and carbon monoxide oxidation on several perovskite oxide membranes with different compositions. We have developed a transport model to describe the data and to determine oxygen diffusion coefficients and surface reaction rates. Results form other techniques that also give information about the interplay between surface reactivity and bulk transport in oxides, including isotope exchange, conductivity relaxation and the use of ac impedance measurements on oxygen electrodes will be discussed.

11:00 AM *CC8.7
DEVELOPMENT OF A HEAT-RESISTANT, ELECTRICALLY CONDUCTING JOINT BETWEEN CERAMIC SOFC END PLATES AND METALLIC FE- OR NI-BASED CONDUCTORS. Rolf Wilkenhoener , Argonne National Laboratory, Electrochemical Technology Program, Argonne, IL; H.P. Buchkremer, D. Stoever, D. Stolten, Forschungszentrum Juelich GmbH, Institut fuer Werkstoffe und Verfahren der Energietechnik, Juelich, GERMANY; A. Koch, Dornier GmbH, Friedrichshafen, GERMANY.

Ceramic parts made of doped lanthanum chromite are used as interconnects and end plates in stacks for several SOFC (Solid Oxide Fuel Cell) designs. Metallic conductors have to be attached to enable a low-resistance connection between individual stacks in each SOFC unit, and to permit power to be drawn from the SOFC. The resistances of the metal-ceramic bond and the metallic conductors have to be stable under operating conditions, i.e. 1000C in air. Consequently, heat-resistant materials have to be used. A two-step process to connect commercially available, Ni- or Fe-based metallic conductors to ceramic SOFC end plates by vacuum furnace brazing has been developed. A metallic sheet, which acts as the current collector, is brazed on the ceramic end plate. Thereby, the much lower electrical conductivity of the ceramic part is compensated by that of the metal. Chromium alloys such as Cr₅Fe₁Y₂O₃ are suitable because they offer heat resistance, and their thermal expansion coefficient is close to that of lanthanum chromite. Metallic wires or strips are brazed on the current collector. Since this joint area is significantly smaller than that of the first joint, materials with a different thermal expansion coefficient can be used, such as conventional heat-resistant nickel alloys (Inconel 617) and ferritic stainless steels (Fe₂₂Cr_5.5Al). Filler alloys for both brazing steps with matching melting points have been found. Hence, both brazing steps can be performed cost-effectively in one heating step. Suitable parameters for vacuum furnace brazing of both joints are presented, and the composition of the filler alloys is given. Data concerning the long-term behavior of the joint resistances in air at 1000C are discussed.

11:30 AM CC8.8
EFFECTS OF MICROSTRUCTURE ON THE ELECTRONIC CONDUCTIVITY IN SrCo_0.8Fe_0.2O_3.8. K. Zhang , M. Miranova, Y.L. Yang, A.J. Jacobson and K. Salama, Materials Research Science and Engineering Center, University of Houston, Houston, TX.

Perovskite oxides, such as La_xSr_1-xMnO₃, La_1-xSr_xCo_1-yFe_yO₃, have high electronic and ionic conductivities at elevated temperatures. Extensive studies have been conducted to select the proper perovskite oxides for applications in oxygen separation membranes, solid oxide fuel cells and electrocatalytic reactors. Most of the studies have been focused on the characterization of the electrochemical properties, particularly the oxygen permeability and the elctron conductivity. Little, however, is known about the effects of microstructure on the electrochemical properties of these materials. In a previous study (1), the effect of microstructure on the oxygen permeation in SrCo_0.8Fe_0.2O (SCFO) was investigated, and it was found that the change in grain size has strong effect on the oxygen permeation in this material. In this investigation, the effect of the microstructure of SCFO on the electronic conductivity is studied at elevated temperatures using a four-point dc method. The electronic conductivity of this material was observed to increase with the increase of the average grain size. The grain size effect seems to be more significant in the lower temperature region where the electronic conductivity of this material increases with the increase of the temperature. When the temperature is further increased, the electronic conductivity decreases with the increase of the temperature, and the grain size effect becomes less significant. In order to determine the responsible mechanisms of these effects, effort is being made to investigate the grain boundaries structure using TEM.
(1) K. Zhang, Y.L. Yang, D. Ponnusamy, A.J. Jacobson and K. Salama: ``Effect of microstructure on oxygen permeation in SrCo_0.8Fe_0.2O'' Journal of Materials Science , in press, 19997.
*This work is sponsored by the National Science Foundation through the MRSEC program under Award Number DMR-9632667.

11:45 AM CC8.9
POROUS THIN-FILM ANODE MATERIALS FOR SOLID-OXIDE FUEL CELLS. J.D. Morse , R.T. Graff, J.P. Hayes and A.F. Jankowski, University of California, Lawrence Livermore National Laboratory, Livermore, CA.

Methods to synthesize anodes for thin film solid-oxide fuel cells (TFSOFCs) from the electrolyte and a conductive material are developed using photolithographic patterning and physical vapor deposition. The anode layer must enable combination of the reactive gases, be conductive to pass the electric current, and provide mechanical support to the electrolyte and cathode layers. The microstructure and morphology desired for the anode layer should facilitate generation of maximum current density from the fuel cell. For these purposes, the parameters of the deposition process and post-deposition patterning are developed to optimize a continuous porosity in the anode layer. The fuel cell microstructure is examined using scanning electron microscopy and the power ouput generated is characterized through current-voltage measurement. This work was performed under the auspices of the United States. Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-Eng-48.
 

SESSION CC9: SOLID OXIDE FUEL CELLS
Chair: Masayasu Arakawa
Thursday Afternoon, April 8, 1999
Metropolitan II (A)

1:30 PM *CC9.1
MATERIALS DEVELOPMENT IN SOFC FOR DOMESTIC APPLICATION. Kaspar Honegger , Sulzer Innotec, Roland Diethelm, Sulzer HEXIS, Winterthur, SWITZERLAND.

Several small scale cogeneration demonstration units for the domestic market have been operated successfully using planar SOFC for more then 5000h. Experimental stacks based on selfsupported yttria stabilised zirconia (YSZ) electrolytes, perovskite cathodes and Ni/YSZ anodes have been operated for more than 15,000 hours with stable performance at operating temperatures of 900 to 1000C. Cost analysis of this standard technology showed the dominante influence of the alloy used as interconnector and its protective coating against chromium species evaporation. A reduction of the operating temperature from 1000C to below 800C showed a high potential to lower the stack costs. Commercially available ferritc stainless steels have been examined. Low electrical resistance characteristics have been obtained in air as well as in fuel environements in long-term exposures at 700C. Lightweight bipolar plates were manufactered by brazing pressed thin sheet interconnector structures. Stable performance was obtained at temperatures up to 800C in stacks based on ceria-gadolinium electrolytes or on anode supported thin film YSZ electrolytes cells interconnected with the novel bipolar plates.

2:00 PM CC9.2
NEW ANODE AND CATHODE MATERIALS FOR HIGHLY EFFICIENT SOFCS. Masayasu Arakawa , Reiichi Chiba, Naoki Kato, Yoji Sakurai, Toshiro Hirai and Ichiro Yamada, NTT Integrated Information and Energy Systems Labs., Tokyo, JAPAN.

Energy consumption of Nippon Telegraph and Telephone Corporation (NTT) is expected to greatly increase as we expand the multimedia services. In order to reduce the energy consumption and accompanying environmental pollution, NTT has been conducting researches on clean power generation systems. Among others, we believe that solid oxide fuel cell (SOFC) is most promising energy source because of its high energy conversion efficiency. We have been working on cell structure and materials of SOFC. In this paper, we report the researches on anode and cathode materials of SOFCs. It is very important to keep an SOFC's anode overpotential low. In general, sintering an anode at high temperature reduces the overpotential. However, SOFC composed of a La(Sr)MnO₃ cathode and Zr(Y)O₂ electrolyte should not be sintered at a temperature higher than 1300C, since high-resistance inter-layer is formed at that high temperature due to the reaction between the cathode and electrolyte. In order to overcome this problem, we propose a new anode preparation method where Zr(Y)O₂ are covered with nano-sized Ni particles and the structure is formulated at 1300C. This new anode has the electronic conductivity two or three times higher than the conventional one with the same Ni content. Recently, many studies on SOFC materials have been conducted for reducing the operation temperature of SOFC, since lower operating temperature reduces production cost and improves long-term reliability of the SOFC systems. We have discovered a new cathode material, LaNi(Fe)O₃, for this purpose. LaNi_1-xFe_xO₃ (0.3x0.4) has a rhombohedral structure, whose electronic conductivity is about twice as high as La(Sr)MnO₃ at 800C. The thermal expansion coefficient of LaNi_0.6Fe_0.4O₃ is 11.1x10^-6cm/(cm K), which matches well that of Zr(Y)O₂.

2:15 PM CC9.3
INVESTIGATIIONS OF Fe-Cr FERRITIC STEELS AS SOFC INTERCONNECT MATERIAL. Soren Linderoth , Peter Halvor Larsen, Riso National Laboratory, DENMARK.

There are several demands to a metallic material for use as interconnect in Solid Oxide Fuel Cells (SOFC), e.g. low corrosion rate, the scale must be well adhering to the metal and must possess a good electrical conductivity, and a thermal expansion coefficient (TEC) close to that of the remaining SOFC materials. These requirements have pointed towards the use of a ceramic interconnect based on lanthanum chromite or a Cr-rich alloy. The latter is produced by Metallwerk Plansee. Both of these materials cause problems; the ceramic interconnect is subject to bending (and sometimes cracking) due to dimensional changes upon reduction, and the metallic interconnet is difficult to machine. Both materials makes up a substantial part of the materials costs in the flat plate design. The recent trend for SOFC developers is the use of thin electrolytes supported by the anode or cathode material, thereby enabling SOFC operation at lower temperatures. The lower temperatures promotes the use of metals as interconnect material, i.e. the corrosion and Cr-oxide evaporation are reduced. The effective TEC of the SOFC is in this case typically in the 11-13 10^-6 K^-1 range. As will be reported, the properties of ferritic steels fits well this TEC requirement. We report on studies of TEC and corrosion properties as a function of Fe/Cr ratio, atmosphere and temperature. The corrosion performance is also shown to be improved significantly by a proper surface coating. The thickness of the scale is reduced and the buckling of the scale is minimized. The quality of the electrical contact between the interconnect and the SOFC is also of great importance. Different contact experiments using an Al-free ferritic steel will be presented.

2:30 PM CC9.4
MODELLING STUDY OF THE YSZ-BASED COMPOSITES ELECTRICAL BEHAVIOUR. Giovanni Dotelli , Fabio Casartelli, Polytechnic of Milan, Dept. of Industrial Chemistry and Chemical Engineering, Milan, ITALY; Isabella Natali Sora, University of Brescia, Dept. of Chemistry and Physics for Engineering and Materials, Brescia, ITALY; Chiara Schmid, University of Trieste, Dept. of Materials Engineering and Applied Chemistry, Trieste, ITALY; Claudio M. Mari, University of Milan, Dept. of Materials Science, Milan, ITALY.

Electrical properties of yttria-stabilised zirconia/alumina (YSZ/Al₂O₃) composites were tentatively foreseen by simulating their complex impedance spectra. A digital image-based model was developed to describe the electrical conduction process in polycrystalline mono- or multi-phase materials. The microstructure of each polycrystalline sample was reconstructed using the Voronoi tessellation technique (in fact, ad hoc modifications with respect to the original algorithm were introduced) and it was then converted into a three-dimensional electrical network according to a set of well-defined rules. The network was solved (via a transfer-matrix procedure) for different frequency values and successively the Nyquist plot generated. The alumina content was considered as a parameter and thus the complex impedance spectra of different composites at different temperatures were simulated. Both the bulk and grain boundary electrical conductivity were calculated and the Arrhenius plots obtained. Experimental and simulated results were compared and discussed.