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fall 1997 logo1997 MRS Fall Meeting & Exhibit

December 1 - 5, 1997 | Boston
Meeting Chairs:
 Harry A. Atwater, Peter F. Green, Dean W. Face, A. Lindsay Greer 

Symposium Y—Materials for Electrochemical Energy Storage and Conversion II-Batteries, Capacitors and Fuel Cells


Daniel Doughty, National Renewable Energy Lab
David Ginley, Sandia National Laboratories
Bruno Scrosati, Univ ``La Sapienza'' Roma
Tsutomu Takamura, Petoca Ltd
Z. (John) Zhang, SKC Am

Symposium Support

  • NREL 
  • Sandia National Laboratories 
  • SKC America, Inc.

* Invited paper

Chairs: Daniel H. Doughty and David S. Ginley 
Monday Morning, December 1, 1997 
America Center (W)

8:30 AM *Y1.1 
ADVANCES IN BATTERY TECHNOLOGIES AND MARKETS - MATERIAL SCIENCE ASPECTS. Alvin J. Salkind, Rutgers University, College of Engineering and UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ.

Advances in materials innovation, availability, processing, and volumetric and gravimetric utilization, have lead to dramatic changes in the technology and markets for batteries and other electrochemical storage devices, in recent years. The increased cyclability of the new materials and preparations has also resulted in a more dominant proportion of secondary batteries in the market. The growth of the various technology sectors of the battery and energy storage device industry will be compared to the relevant improvements in materials science. The developments needed in materials, composites, and processing techniques will be discussed, to match the ongoing changes in electronic circuits, power devices, transportation, and the growth of portable appliances. An analysis of the technical/market segments of the battery industry will be presented.

9:00 AM *Y1.2 
APPLICATION OF AB INITIO METHODS TO SECONDARY LITHIUM BATTERIES. M.K. Aydinol and G. Ceder, Massachusetts Institute of Technology, Dept of Mat Sci and Eng, Cambridge, MA.

Ab initio methods have started to be widely used in materials science for the prediction of properties of metals, alloys and compounds. These methods basically require only the atomic numbers of the constituent species. Such methods not only provide us with predictions of the desired properties (even before synthesizing the material) but also help us understanding the nature underlying those properties. The use of these methods in the field of electrochemistry is, however, quite recent and rare. In this study, we demonstrate how ab initio methods can be used to investigate the properties of secondary lithium batteries. Particular examples will be given in predicting average insertion voltages in spinel Li-Mn and Li-Co oxides and in layered LiMO2 (M=Ti, V, Mn, Co and Ni) compounds, stability of these compounds against metal reduction and structural stability of LiCoO2 upon lithium removal. The results of the study on predicting the average voltages showed that the amount of electron transfer to oxygen occuring upon lithium intercalation has the prime importance in obtaining high cell voltages. The more electron transfer to oxygen than to metal yields higher open circuit voltages.

9:30 AM Y1.3 
REACTIONS OF LITHIUM WITH SMALL GRAPHENE FRAGMENTS. SEMI-EMPIRICAL QUANTUM CHEMICAL CALCULATIONS. Marko Radosavljevic, Peter Papanek and John E. Fischer, Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, PA.

Semi-empirical and ab initio calculations [1], as well as inelastic neutron spectroscopy [2], demonstrate that Li can bind to protonated ''edge carbons'' to create a moiety analogous to the organolithium monomer C2H2Li2. This provides a possible additional channel for Li uptake in high capacity Li-ion battery anodes based on low-T pyrolyzed soft carbons. Here we show that similar reactivity is exhibited by polyaromatic hydrocarbons with the protons removed (taken as surrogates for the structural units in hard carbons). In the de-protonated PAH'es the Li serves to saturate dangling bonds, maintaining sp2 hybridization, whereas Li added to PAH'es creates sp3 carbons at the edges. In both cases this extra reactivity occurs in parallel with the usual intercalation. These findings have implications for futher development in Li-ion rechargeable battery technology.

9:45 AM Y1.4 
COMPUTATIONAL ELECTROCHEMICAL AND NMR STUDIES OF DISORDERED CARBONS USED AS ANODES IN LITHIUM ION CELLS. Giselle Sandi,Rex Gerald II, Lawrence G. Scanlon, Kathleen A. Carrado, and Randall E. Winans, Chemistry and Chemical Technology Divisions, Argonne National Laboratory, Argonne, Il; Aero Propulsion and Power Directorate, Wright Laboratory, Wright-Patterson Air Force Base, OH.

Disordered carbons that deliver high reversible capacity have been synthesized by using inorganic clays as templates to control the pore size and the surface area. Several organic precursors were incorporated within the clay structure and pyrolyzed at 700C. The capacities obtained were much higher than those calculated if the resultant carbon has a graphitic-like structure. To explain why these carbons deliver such a high capacity, a theoretical study was conducted in which C60 simulates a disordered carbon system. Computational chemistry has been used to investigate the nature of lithium bonding within a C60, carbon lattice. Two lithium C60, systems were investigated: a dilithium-C60 system with a charge and multiplicity of (0,1) and a trilithium-C60, system with a charge and multiplicity of (0,4). Optimized geometries for these systems suggest two types of lithium within the 60 lattice. An ionic lithium is obtained for the dilithium-C60 system and a lithium with covalent character is obtained for the trilithium-C60 system. In both cases, the lithium-lithium separation of 2.96 Åor less is consistent with that required in order to achieve specific capacities greater than that obtained in a stage 1 lithium intercalated graphite. Diffusion of lithium ion during the intercalation process has been also investigated. An operational electrochemical cell has been incorporated into a toroid cavity nuclear magnetic resonance (NNIR) imager. With this device it is possible to measure the transport properties of ions (e.g., Li+, CF3SO-3,...) in situ. Furthermore, the central conductor of the toroid imaged which also serves as the working electrode, can be coated with a thin layer of a novel ion intercalation material. Therefore, the penetration depth of the Li+ ions into the cathode material can be imaged at different times in the charge/discharge cycle of the battery.

10:00 AM Y1.5 
SIMULATION STUDIES OF POLYMER ELECTROLYTES FOR BATTERY APPLICATIONS. J.W. Halley, Bin Lin and P. T. Boinske, University of Minnesota, Minneapolis, MN.

We present simulation studies of amorphous polyethylene oxide and of solvation and transport of lithium and various anions in it. We address the following issues: 1) The amorphous regions are not in equilibrium in the relevant cases and an experimental criterion for selection of the appropriate model of amorphousness is required. We will describe progress of our program to compare our simulation studies with neutron scattering studies by Argonne coworkers to meet this need. 2) The interaction between the lithium ion and the polymer is strong, resulting in hopping processes too slow to be followed by simple molecular dynamics simulation. We will present evidence that the strong interaction also results in effects of the ion on the polymer matrix out to very substantial length scales (of the order of 10 angstroms) so that simulation models need to be spatially large as well. We present results in which we partially deal with these problems by direct calculation of the frequency dependent conductivity and by improved simulation algorithms. There will be some discussion of possible implications for electrolyte materials design.

10:30 AM *Y1.6 
FIRST-PRINCIPLES THEORY OF CATION- AND VACANCY-ORDERING IN LixCoO2. C. Wolverton and Alex Zunger, National Renewable Energy Laboratory, Golden, CO.

Several types of cation- and vacancy-ordering exist in the LixCoO2 battery materials. The ordering patterns are of interest due to the fact that they can control the voltage in rechargeable Li batteries. We present a first-principles total energy theory which can predict both cation- and vacancy-ordering patterns at both zero and finite temperatures. Also, by calculating the heat of the Li intercalation reaction, this theory can provide first-principles predictions of battery voltages of LixCoO2/Li cells. Our calculations allow us to search the entire configurational space to predict the lowest-energy ground state structures, search for large voltage cathodes, explore low-energy but metastable states, and extend our calculations to finite temperatures, thereby searching for order-disorder transitions and states of partial disorder. The classes of ordering problems that we study are the following: (i) The LiMO2 oxides form a series of structures based on an octahedrally-coordinated network with anions (O) on one fcc sublattice and cations (Li and M) on the other, leading to Li/Co ordering in LiCoO2 (x=1). (ii) In battery applications, Li is (de)intercalated from the compound, creating a vacancy (denoted ) that can be positioned in lattice locations; Thus, /Co ordering in CoO2 is also of interest. (iii) The vacancies left behind by Li extraction can form ordered vacancy compounds in partially de-lithiated LixCoO2, leading to a /Li ordering problem (0x1). Our technique uses a combination of first-principles total energies, a cluster expansion technique, and Monte Carlo simulations to study ordering in these octahedral systems. Supported by BES/OER under contract no. DE-AC02-83CH10093.

11:00 AM Y1.7 
MOLECULAR DYNAMICS STUDY OF LITHIUM DIFFUSION IN LITHIUM-MANGANESE SPINEL CATHODE MATERIALS*. Randall T. Cygan, Henry R. Westrich, and Daniel H. Doughty, Sandia National Laboratories, Albuquerque, NM.

We have completed a series of molecular dynamics (MD) computer simulations of the self-diffusion of lithium in a variety of doped Li-Mn spinel materials. This theoretical approach is part of an effort to understand the mechanisms and rates of lithium diffusion, and to evaluate the structural control of the cathode materials upon the Li+ intercalation (discharge-charge) process. Our MD approach employs a fully ionic forcefield that accounts for electrostatic (Coulombic), repulsive, and dispersion (van der Waals) interactions among all ions. A reference unit cell comprised of 56 ions (Li8Mn3+8Mn4+8O32), each having a full formal charge, is used to perform the MD simulations under constant pressure constraints. All atomic positions and cell parameters are allowed to vary throughout the simulation. Simulations were completed for the undoped and doped LiMn2O4 at various levels of lithium content (based on the number of lithium ions per unit cell and Mn oxidation state). Dopant metals were selected based on our previous energy-optimized calculations using an ionic shell model. The MD results indicate an activation energy of approximately 97 kJ/mole for self-diffusion of lithium in the undoped material. Lithium ion trajectories from the simulations provide diffusion coefficients that decrease by a factor of ten as the cathode accumulates lithium ions during discharge.

11:15 AM Y1.8 
STRUCTURE AND ELECTROCHEMICAL POTENTIAL SIMULATION FOR THE CATHODE MATERIAL Li1+xV3O8. R. Benedek, M.M. Thackeray, Argonne National Laboratory, Argonne, IL; L.H. Yang, Lawrence Livermore National Laboratory, Livermore, CA.

The trivanadate Li1+xV3O8 is of interest as a potential cathode material in rechargeable lithium batteries. Ab initio local density functional theory (LDFT) calculations within the plane wave pseudopotential framework are performed as a function of x to gain insight into the structure, particularly the configurations of Li, and electrochemical potential curves in this system. Existing x-ray diffraction measurements for the special compositions x=0.2 and x=3.0 showed different monoclinic structures with relatively well-ordered Li configurations. We have investigated both structures as a function of x by adding Li to the low-Li structure and removing Li from the high-Li structure. Our calculations show the low-Li structure, which contains tetrahedrally as well as octahedrally coordinated Li, to be energetically favored over the high-Li (defect-rocksalt) structure, in which all Li are octahedrally coordinated, for x less than about 1.5; the defect rocksalt structure is favored at higher Li concentrations. In the case of Li4V3O8, all three Li sites identified by x-ray diffraction (the location of the fourth Li was not resolved) are predicted by our LDFT calculations to be occupied, and our calculations also predict the favored site of the fourth Li.

11:30 AM Y1.9 
AB INITIO CALCULATION OF THE LITHIUM COBALT OXIDE PHASE DIAGRAM. Anton Van der Ven, Mehmet K Aydinol, Gerbrand Ceder, Massachusetts Institute of Technology, Cambridge, MA.

The electrochemical properties of the layered intercalation compound LixCoO2 used as a cathode in Li batteries have been investigated extensively in the past 15 years. Despite this research, very little is known about Li ordering as the lithium concentration is changed. Ordering of Li can cause abrupt changes in lattice parameters which can be detrimental to the cycling properties of the cathode. In this work, the phase diagram of LixCoO2 is calculated ab initio for x ranging from 0 to 1. We find that Li ions order for x=1/6, 2/5, 1/2 and 2/3. The order-disorder transition temperatures for x=1/2 and 2/3 are slightly above room temperature whereas those for x=1/6 and 2/5 occur around 300C. At x=1/6 the most stable Li arrangement is a staged configuration in which every other Li plane is completely vacant. This has as a consequence that the c-lattice parameter of LixCoO2 suddenly drops as the lithium composition is reduced to x=1/6, a result which is observed experimentally. We also calculated the voltage and lattice parameters versus composition and find the predictions to be in good agreement with experiment.

11:45 AM Y1.10 
RELATION BETWEEN NON-STOICHIOMETRY AND Li CELL CAPACITY OF LiMn2O4 SPINEL STRUCTURES. Masaki Yoshio,Yongyao.Xia and Hideyuki Noguchi, Dept. of Appl. Chem., Saga Univ, Saga, JAPAN.

The increasing importance of Li-ion battery cells has prompted a desire to prepare cathode materials more able to reversibly intercalate and deintercalate lithium ions at greater voltage. We will first report on the classification of spinel structures such as lithium ion rich and oxygen rich spinels and the initial charge capacities can be calculated from chemical formula based on the existence of excess Li ion, vacancy and Mn(III) content in 16d site. The capacity of various metal-ion doped spinels can be calculated based on the non-stoichiometry depending on the state of the doped metal ion, namely when (1) a doped metal ion does not participate in the charge/discharge reaction, (2) metal ions doped in the 16d site participate in the charge/discharge reaction. Secondly we will discuss the relationship between the capacity of the spinel structures with doped metal ion and non-stoichiometry of the spinel structure.

Chairs: Douglas J. Wheeler and Thomas A. Zawodzinski 
Monday Afternoon, December 1, 1997 
America Center (W)

1:30 PM *Y2.1 
FABRICATION AND PERFORMANCE OF THIN CERAMIC FILMS ON POROUS ELECTRODES. Steven J. Visco, Craig P. Jacobson, and Lutgard C. De Jonghe, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA.

The motivation to fabricate thin film ceramic electrolytes derives from the benefits associated with lowering of ohmic losses across ionic and mixed ionic-electronic conducting materials as membrane thickness is reduced. For electrolytes based on rare earth oxides there is an additional advantage of cost reduction assuming fabrication costs are not unfavorably increased relative to conventional electrolyte processing. In our laboratory we have focused on the use of wet chemical techniques such as colloidal deposition in an effort to develop technologies that are highly flexible, low-cost, and scaleable. The technical challenge involves depositing a pinhole and crack free dense layer of electrolyte of 5 to 40 microns in thickness on electrode substrates of high porosity and suitable microstructure to ensure low overpotential during device operation. The following paper describes the preparation and characterization of a variety of ceramic membranes having application in solid oxide fuel cells and related electrochemical devices. Work in our laboratory has led to techniques for deposition of fully dense ceramic films on a variety of porous and continuous substrates. Typically, green films of the desired oxide are colloidally deposited onto green or partially fired substrates. The bilayer is then cofired to yield a pinhole free, dense film that is well bonded to the porous structure. The process is inexpensive and scaleable, and can produce devices with high performance at reduced temperatures. This technique has been used with great success to produce yttria stabilized zirconia (YSZ) based solid oxide fuel cells (SOFCs). In this case the YSZ film is cofired onto a NiO/YSZ substrate. The thickness of the YSZ film deposited onto the porous substrate is approximately 10 mm after sintering, and is well bonded to the NiO/YSZ electrode. Ni-YSZ/YSZ/LSM cells built with this method have exhibited theoretical open circuit potentials (OCPs), high current densities and exceptionally good power densities of over 1900 mW/cm2 at 800 oC. Electrochemical characterization of the cells indicates negligible losses across the Ni-YSZ/YSZ interface and minor polarization of the fuel electrode. Thin-film cells have been tested for long periods of time (over 700 hours) and have been thermally cycled from 650 to 800 oC while demonstrating excellent stability over time. Colloidal deposition techniques have been used successfully to fabricate thin-film ceria based SOFCs. Thin, fully dense ceria electrolytes of 12 to 15 microns in thickness were deposited onto porous nickel cermets; porous cathodes were then painted onto the thin-film bilayers and the devices were tested in an H2-H2O/air environment. The electrochemical performance of these devices was quite good. At 750 oC, the peak power density for the Ni-CGO/CGO/LSCN fuel cell was over 650 mW/cm2. At 600 oC the thin-film cells achieved peak power densities of close to 300 mW/cm2. Fuel cell internal resistance as measured by current interrupts was as low as 50 m at 800 oC and 200 m at 600 oC. As expected the open circuit potential of the ceria based SOFCs was depressed by several hundred mV due to electronic conductivity in the electrolyte. In addition to oxygen-ion conducting ceria and zirconia films, our group has deposited thin, dense, SrZr.95Y.05O_3proton conducting films on NiO-CGO porous substrates. These bilayers have demonstrated high open circuit potentials in fuel cell environments. In an effort to explore other oxide systems, thin films of mixed ionic-electronic conductor La_1-zSr_zCo_1-yFe_yO_3have recently been deposited onto porous Ce_0.8Sm_0.2O_1.9 substrates; these materials are being pursued for oxygen separation applications.

2:00 PM Y2.2 
HYDROTHERMAL SYNTHESIS AND PROPERTIES OF CERIA SOLID ELECTROLYTES. Martha Greenblatt, Wensheng Huang, Pavel Shuk, Dept. of Chemistry, Rutgers University, Piscataway, NJ.

Doped ceria is the most promising high-conducting solid electrolyte for solid oxide fuel cell (SOFC) applications in the intermediate temperature range (500-700C). A systematic study of the structure, ionic conductivity and thermophysical properties of hydrothermally prepared samarium and calcium doped ceria solid electrolytes as well as of the influence of terbium or praseodymium substitution on electrolytic domain and electrical properties was carried out. Ce1-xSmxO2-x/2 (x-0-0.30), Ce1-xCaxO2-x (x=0-0.17) and (Ce0.83Sm0.17)1-yTb(Pr)yO1.915-z (y=0-0.10) solid solutions with the fluorite structure were prepared in < 2 h at 260C by the hydrothermal method. Ultrafine particles of uniform crystallite dimension 20-68 nm formed. Because of the small particle size of the ceria, the sintering temperature needed to obtain a dense ceramic pellet was reduced substantially from 1650C, that required for the corresponding materials prepared by conventional solid state methods, to 1400C. The maximum ionic conductivity was found for the X- 0.17 Sm and X= 0.09 Ca substituted ceria (5.7x10-3, Ea 0.9 eV and 2.1x10-3 S/cm, Ea 0.8 eV respectively). The thermal expansion coefficients, determined from high-temperature X-ray data, are 8.6x10-6 and 9.4x10-6 K-1 for the best conducting Ce0.83Sm0.17O1.915 and Ce0.91Ca0.09O1.91 solid electrolytes respectively. Experiments to clarify the electrolytic domain region as well as electronic and ionic contribution to conductivity depending on Tb or Pr contents are in progress.

2:15 PM Y2.3 
THIN FILM SYNTHESIS OF NOVEL ELECTRODE MATERIALS FOR SOLID-OXIDE FUEL CELLS. A.F. Jankowski, University of California, Lawrence Livermore National Laboratory, Chemistry and Materials Science, Livermore, CA.

The development of electrode materials for solid-oxide fuel cells (SOFCs) is approached using sputter deposition. The use of thin-film electrolytes provides a path to lower temperatures for SOFC operation. As such, anodes, for a yttria-stabilized zirconia (YSZ) electrolyte are synthesized as thin waters and thin films. The anode wafers are, sintered compacts of Ni-coated zirzirconia powder. Metal coating the zirconia powders allows for sulfficient conduction while minimizing the volume percent metal thereby ensuring a coefficient of thermal expansion match to the electrolyte. The thin film anodes are co-deposits of Ni and YSZ with optional composition grading hence provision for a mixed-conducting interfacial layer to the electrolyte. Similar synthesis of cathode wafers and thin films proceeds using Ag and YSZ. The novel electrodes are characterized for comparison to conventionally-processed cermet electrodes.

2:30 PM Y2.4 
ENHANCED IONIC CONDUCTIVITY IN CERIUM OXIDE-BASED COMPOSITE MATERIALS THROUGH SOL-GEL PROCESSING. Jeffrey Peterson, Vasantha Amarakoon, New York State College of Ceramics at Alfred University, Alfred, NY.

The usefulness of CeO2-based ionic conductors for applications such as fuel cells and oxygen sensors is severely limited by the formation of electronic charge carriers under low PO2 atmospheres. This limitation may be overcome by using a CeO2/Al2O3 composite material with unique microstructural features that remove free electronic carriers without diminishing the ionic conductivity. Sol-gel synthesis techniques were used to engineer the composite microstructure and provide a homogeneous and reproducible material. The composite was tested for its ionic transference number, and microstructural analysis (SEM/EDS) was carried out to determine the optimum conditions for processing.

3:00 PM *Y2.5 
MIXED IONIC-ELECTRONIC CONDUCTION IN NI DOPED LANTHANUM GALLATE PEROVSKITES. Nick Long1 and Harry L. Tuller2; 1The New Zealand Inst. for Industrial Research and Development, Lower Hutt, NEW ZEALAND; 2Dept. of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA.

Lanthanum gallate is promising as a material for a monolithic fuel cell or oxygen pump, i.e. one in which the electrolyte and electrodes are formed from the same basic material. We have investigated La1-xSrxGa1-yNiyO3 (LSGNx-y) with x=0-0.2 and y=0.1-0.5 as a potential cathode material for such an electrochemical device. The (PO2,T) data suggest that the materials have a p-type electronic conductivity at high PO2 and that the conductivity at low PO2 is largely ionic. AC impedance spectroscopy on an electron blocking cell of the form Pt/LSG/LSGN/LSG/Pt was used to measure the ionic conductivity in the Ni doped material. The ionic conductivity in LSGN10-20 was found to have a similar magnitude and activation energy to that in the undoped LSG material with i=0.12 S/cm at 800C and EA=1.00.1 eV. Thermal expansion measurements show that the Ni doped materials have expansion coefficients similar to the Mg doped electrolyte material.This suggests that this electrode/electrolyte combination should be mechanically stable.

3:30 PM Y2.6 
SOLID OXIDE FUEL CELLS (SOFCs) WITH PEROVSKITE ELECTROLYTES AND ELECTRODES, PART I. OXYGEN REDUCTION PROCESSES. Weitung Wang* and Eric E. Hellstrom, Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI; *Current address: Pacific Northwest National Laboratory, Richland, WA.

Oxygen reduction processes at interfaces between a doped LaGaO3 (LSGM) electrolyte and (La0.6Sr0.4)CoO3 (LSC) or (La0.6Sr0.4)(Co0.9Ni0.1)O3 (LSCN) cathode have been studied by AC impedance and DC overpotential measurements. Both AC impedance and DC overpotential results indicate that charge transfer process is the rate-determining step for oxygen reduction process at the LSC/LSGM interface. Oxygen dissociation and charge transfer processes appear to be approximately equivalent to the overall oxygen reduction processes at the LSCN/LSGM interface. AC impedance results of LSC/LSGM and LSCN/LSGM cells indicate that both electrode conductivity (1/Rel ) and its activation energy increase with increasing oxygen partial pressure. DC overpotential results of LSC/LSGM cell show that the electrode overpotential increases with decreasing oxygen partial pressure and temperature. The higher electrode resistance of LSCN/LSGM cell than that of LSC/LSGM cell may be due to the decomposition of the LSCN electrode in the low oxygen partial pressure.

3:45 PM Y2.7 

Gamma lithium aluminate is a ceramic powder which is used as the porous solid support for the electrolyte in molten carbonate fuel cells. We have previously reported(1) that gamma lithium aluminate will convert to lithium aluminum carbonate hydroxide hydrate and lithium carbonate when exposed to water vapor and carbon dioxide. In this paper, we compare three techniques, weight gain, carbonate content and x-ray diffraction to measure the amount of conversion. The reaction may involve amorphous intermediates and no one technique by itself is satisfactory to study the conversion.

4:00 PM Y2.8 
PHASE STABILITY OF THE MIXED-CONDUCTING Sr-Fe-Co-O SYSTEM. B. Ma, U. Balachandran, Energy Technology Division; J.P. Hodges, J.D. Jorgensen, D.J. Miller, Materials Science Division; J.W. Richardson, Jr., Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL.

Mixed-conducting ceramic oxides have potential uses for high- temperature electrochemical applications, such as solid-oxide fuel cells, batteries, sensors, and oxygen- permeable membranes. The Sr-Fe-Co-O system has not only high electrical conductivity but also appreciable oxygen permeability at elevated temperature. For example, dense ceramic membranes made of this material can be used to separate oxygen from air without the need for external electrical circuitry. The separated high-purity oxygen can be used for partial oxidation of methane to produce syngas. Methane conversion efficiencies of were demonstrated by Balachandran et al., (Am. Ceram. Soc. Bull., 74 [1995]71). Use of this material would greatly improve the economics of fuel production. To study the phase stability of the Sr-Fe-Co-O system, samples were prepared in atmospheres with various oxygen partial pressures. The Sr-Fe-Co-O samples were characterized by X-ray powder diffraction, scanning electron microscopy, and electrical- conductivity testing. Details of the experimental results will be presented.

4:15 PM Y2.9 
CRYSTAL STRUCTURE OF MIXED-CONDUCTING OXIDES PRESENT IN THE Sr-Fe-Co-O SYSTEM. J.P. Hodges, J.D. Jorgensen, D.J. Miller, Materials Science Division, B. Ma, U. Balachandran, Energy Technology Division, J.W. Richardson, Jr., Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL.

The potential applications of mixed-conducting ceramic oxides include solid-oxide fuels cells, rechargeable batteries, gas sensors and oxygen permeable membranes. Several perovskite-derived mixed Sr-Fe-Co oxides show not only high electrical-conductivity but also appreciable oxygen permeability at elevated temperatures. For example, dense ceramic membranes of Sr4Fe4Co2Ol3 can be used to separate oxygen from air without the need for external electrical circuitry. The separated oxygen can be directly used for the partial oxidation of methane to produce syngas. The crystal structures of Sr4Fe4Co2Ol3 and related phases have been studied using a combination of high-resolution powder neutron and X-ray diffraction. Sr4Fe4Co2Ol3 (space group Iba2, a = 11.03 A, b = 19.03 and c = 5.54 ) has a layered crystal structure isostructural to the prototype Sr4Fe6Ol3. The crystal structure of these materials are particularly interesting since the Fe/Co is present in three different coordinations, octahedral, trigonal bipyramidal and square pyramidal. This notable feature may in part be mechanistically responsible for the high oxide-ion conductivity's observed.

4:30 PM Y2.10 
APPLICATION OF EUTECTIC CERAMIC MIXTURES FOR THE FUNCTIONAL COMPONENTS OF HIGH TEMPERATURE SOFC's. Ch. Gerk, M. Willert-Porada, University of Dortmund, Dept. Chem. Engineering, Div. Mater. Sci., Dortmund, GERMANY.

Different geometrical concepts of high temperature Solid Oxide Fuel Cells (SOFC) based on ZrO2-electrolytes were tested over the last decade. In planar as well as tubular arrangements the improvement of mechanical stability was achieved by implementation of thicker supporting elements or by increasing the dimensions of the electrodes. However, the materials concept underlying the modern SOFC is still based on separate electrode-electrolyte materials, with only small areas of ``overlapping'' functionality. In order to insure short transport paths for the electrochemical reaction and a sufficient mechanical stability by increasing the thickness of the cell, eutectic mixtures in the system ZrO2-NiO-(R2O33) and ZrO2-MnO-(R2O3) are of particular interest. Solid samples obtained from partially melted polycrystalline green parts reveal a very fine lamella microstructure, composed of ZrO2-NiO and ZrO2-MnO needles of 1-5 m thickness and extending vertically over several 100m. By careful adjustment of the green composition and microwave sintering in a temperature gradient, functional gradient materials (abbr. FGM) representing a ``cofired'' Anode-Electrolyte-Cathode SOFC element can be obtained. 
The paper presents details of the processing procedure as well as results of impedance measurements on the composites.

4:45 PM Y2.11 
OXYGEN NONSTOICHIOMETRY AND ELECTRICAL CONDUCTIVITY OF SOME NICKELATES. V.V. Vashook, S.P. Tolochko, I.I. Yushkevich, M.V. Zinkevich, L.V. Makhnach, I.F. Kononyuk, Institute of General and Inorganic Chemistry, Academy of Sciences of Belarus, Minsk, BELARUS; H.Altenburg, Fachhochschule Muenster, Steinfurt, GERMANY; J. Hauck, Institute of Festkoerperforschung, Juelich, GERMANY.

Equilibrium oxygen nonstoichiometry (y) and specific electrical conductivity () of the members of solid solution La2-xSrxNiOy (x=0, 0.2, 0.5) at temperatures 20-1060 C and oxygen partial pressures 1-286 Pa were determined. The stronger dependencies of y and r versus •‘2 at constant temperatures were found for La2NiOy. At experiment conditions all nickelates have the hole type of electrical conductivity at the range between 100 and 25 Ohm-1*cm-1. Decrease of pO2 at constant temperature results in the reduction of Ni3+-ions concentration, which are responsible apparent for a hole conductivity. The changing interval of electrical conductivity and oxygen stoichiometry index of nickelates become smaller with the increase of strontium concentration. Preliminary researches show the high oxygen diffusivity in these nickelates too (chemical diffusion coefficients are around 10-6-10-7 cm2*c-1 at 500-1050 C and pO2=1-300 Pa). The obtained results indicate a promise of using these materials to produce of electrode materials for high-temperature solid-electrolyte devices and selective ceramic membranes for oxygen separation from the gaseous mixtures.

Chairs: Masaki Yoshio and Z. (John) Zhang 
Tuesday Morning, December 2, 1997 
America Center (W)

8:00 AM *Y3.1 
PHASE EQUILIBRIA AND THE ELECTROCHEMICAL PROPERTIES OF LiCoO2 FOR Li SECONDARY BATTERIES. Glenn Amatucci, Trevor Bowmer, Bellcore, Energy Storage Research Group, Red Bank, NJ; Dominique Larcher, Jean-Marie Tarascon, Universitie de Picardie, Amiens, FRANCE; Lisa Klein, Rutgers University, Piscataway, NJ.

In the past several years, LiCoO2 has become one of the most celebrated intercalation materials for Li-ion batteries. While having an immense 274 mAhr/g theoretical capacity, only 50% of this capacity may be used for commercial applications due to rapid fade in capacity with cycle number. This is in contrast to the isostructural LiNiO2 based materials where reversible capacities approaching 80% of theoretical have been achieved. In light of this disparity in performance, a study has been initiated on the optimization of the cycling characteristics of LiCoO2 at higher capacities. Third in a series of investigations, this study has focused on the phase equilibria of LiCoO2 and its impact on the electrochemical properties of this material. In this paper possible failure mechanisms responsible for the subtheoretical performance will be presented, with supporting data from in-situ x-ray diffraction, electrochemical investigations, high resolution microscopy, and thermal analysis. Knowledge of these failure mechanisms has enabled the fabrication of LiCoO2 material with performance improvements approaching that of LiNiO2. Electrochemical performance data will be discussed and related to observed changes in physical properties.

8:30 AM Y3.2 
STRUCTURAL PROPERTIES OF THE SPINEL LiMn2-zAlzO4-d WITH . Tatsuya Hatanaka, Jun Sugiyama, Akihiko Koiwai, Jiro Mizuno, Tatsumi Hioki and Shoji Noda; Toyota Central R&D Labs., Inc, Aichi, JAPAN.

In order to investigate the effects of substitution of Al for Mn in the spinel LiMn2-zAlzO4, samples with have been prepared in the temperature range between 700 and 900C (Ts) using a solid state reaction technique. According to a powder X-ray diffraction analysis,the samples with z< 0.2 were assigned to be a single phase of the cubic spinel structure (C-I), though the samples with were found to be a mixture of C-I and another cubic spinel phase (C-II). For the sample with z=0.2, the length of the a-axis of C-I was estimated to be 0.822nm, while that of C-II 0.818nm; in addition, the length of the a-axes for both phases decreased in proportion to z. Furthermore, the volume fraction of C-II in the samples with increased with increasing Ts; and the sample with z=0.5 obtained at C seemed to be of a near single phase of C-II. An ESR measurement indicated that the amount of Mn2+ ions in the sample increased with increasing Ts and/or z; the intensity of the ESR signal of Mn2+ ions for C-II were found to be larger by one order of magnitude than that for C-I. Moreover, a 27Al-NMR measurement suggested that the local symmetry at the Al-site lowered with increasing the volume fraction of C-II, whereas such decrease in the symmetry at the Al-site was not observed for C-I. These implied that oxygen ions coordinating with Al3+ ions were partially lost for C-II; in other words, oxygen vacancies were bound to Al3+ ions; thus, C-II was assigned to be an oxygen-deficient spinel, LiMn2-zAlzO4-d, though, the composition of C-I was considered to be LiMn2-zAlzO4.

8:45 AM Y3.3 
PHASE TRANSITION OF LiMn2O4 SPINEL AND ITS APPLICATION FOR LITHIUM ION SECONDARY BATTERY. Junji Tabuchi, Tatsuji Numata, Material Development Center, NEC Corporation, Kawasaki, JAPAN; Yuichi Shimakawa, Fundamental Research Laboratories, NEC Corporation, Tsukuba, JAPAN; Masato Shirakata, Nippon Moli Energy Corporation, Toyama, JAPAN.

LiMn2O4 is the most promising cathode material for lithium ion secondary battery, because of its advantages such as low cost and non-toxicity. Recently, it has been reported that LiMn2O4 shows a phase transition at room temperature, which is due to the Jahn-Teller effect, however, Mn spinel with excess lithium does not show such a transition.1), 2) In order to make clear the effect of the transition on cell performance, LiMn2O4 and various Mn spinel with excess lithium are synthesized and evaluated, using conductivity measurement, x-ray diffraction and coin cell. The x-ray diffraction pattern at low temperature reveals that LiMn2O4 is cubic at higher temperature and orthorombic at lower temperature than room temperature. The electrical conductivity is changed one order magnitude at the transition temperature. On the other hand, Mn spinel with excess lithium does not show such a transition, which is reported to show good cycle performance.3) The effect of the phase transition on cycle performance is still unclear, however, the fabricated wound cell using Mn spinel cathode shows the same energy density and the same cycle performance as the lithium ion secondary battery in market using LiCoO2 cathode.

9:00 AM Y3.4 
LITHIUM COBALT DIOXIDE THIN FILMS GROWN BY PULSED LASER DEPOSITION (PLD) ON VARIOUS LOW COST SUBSTRATES. M.L. Fu, C.T. Rogers, University of Colorado, Boulder, CO; J.M. McGraw, D.M. Trickett, Colorado School of Mines, Golden, CO; J.D. Perkins, P.A. Parilla, J.G. Zhang, J.A. Turner, T.F. Ciszek, D.S. Ginley, National Renewable Energy Laboratory, Golden, CO..

Lithium transition metal dioxides (LiTmO(2), Tm=Co, Ni, Mn) are excellent candidates for cathode materials in high energy density Li-ion secondary batteries due to their high charge capacity, structural tolerance to repeated electrochemical Li intercalation, and large potentials versus lithium. Li(x)CoO(2) thin films have been grown by pulsed laser deposition (PLD) from a sintered LiCoO(2) target at substrate temperatures of 60-500C with background oxygen pressures ranging from 10mTorr to 2000mTorr. The films have been grown on a variety of low-cost substrates including SnO(2)-coated glass, stainless steel, and polyimide coated with a transparent conductor. The stoichiometry, phase, and structure of the films have been examined as a function of deposition conditions using ICP, X-ray diffraction, FTIR reflectance spectroscopy, and Raman scattering. In addition, electrochemical Li-cycling measurements have been made both to determine the films' potential applications as cathodes in secondary Li-ion batteries, and, in conjunction with the above spectroscopies, to investigate the structural changes in the metal oxide host lattice due to variations in Li content and repeated electrochemical intercalation.

9:15 AM Y3.5 
STRUCTURAL AND ELECTROCHEMICAL FEATURES OF LOW-TEMPERATURE LiCoO2. Y. Shao-Horn, S.A. Hackney, Department of Metallurgical & Materials Engineering, Michigan Technological University, Houghton, MI; C.S. Johnson, A.J. Kahaian and M.M. Thackeray, Electrochemical Technology Program, Chemical Technology Division, Argonne, National Laboratory, Argonne, IL.

Considerable efforts have been made previously to evaluate a low-temperature LiCoO2 (LT-LiCoO2) synthesized at 400C as a positive electrode material for lithium batteries. It has been proposed from the analysis of neutron diffraction data that the averaged LT-LiCoO2 structure, which has a cubic-close packed oxygen array, can be regarded as one which is intermediate between a layered Li2 CoO2 structure and a lithiated-spinel Li2[Co2]O4 structure. Other research groups have concluded from electrochemical studies and vibrational spectroscopy that LT-LiCoO2 has only the lithiated-spinel structure, Li2 [Co2]O4. The similarity between the X-ray/neutron diffraction patterns of an ideal layered LiCuO2 structure and an ideal lithiated-spinel phase Li2[Co2]O4 structure makes it difficult to distinguish the layered phase from the lithiated-spinel phase if the oxygen arrays are ideally cubic-close-packed. We have, therefore, undertaken analyses of LT-LiCoO2 materials by transmission electron microscopy (TEM) coupled with X-ray diffraction and electrochemical measurements in an attempt to reconcile the conflicting reports on the structures of these materials. In this study, the LT-LiCoO2 materials were prepared by the solid state reaction and the sol-gel process as described in the literature, respectively. The LT-LiCoO2 materials were compared by using X-ray and electron diffraction. Single-crystal electron diffraction analysis indicated that even though both LT-LiCoO2 materials had the lithiated-spinel as the major phase, cation distribution between the lithiated-spinel and layered structure, with ideally cubic-closed-packed oxygen arrays, was also found. Moreover, electron diffraction analysis suggested that some cobalt atoms on the tetrahedral sites were found in the LT-LiCoO2 prepared by the sol-gel process but not in that prepared by the solid state reaction. Comparison between the galvanostatic cycling data of the high-temperature LiCoO2 and LT-LiCoO2 also suggested that LT-LiCoO2 electrodes had structural features that corresponded to domains with intermediate layered/spinel character, which were consistent with electron diffraction results.

9:30 AM Y3.6 
ATOMIC AND ELECTRONIC STRUCTURAL CONSEQUENCES OF MN-SUBSTITUTION IN LiMn2-yM2-yO4 FOR Li RECHARGEABLE BATTERIES INVESTIGATED BY X-RAY ABSORPTION AND FTIR SPECTROSCOPIES. Craig R. Horne, Kathryn A. Striebel, Elton J. Cairns, Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA; Melissa M. Grush, Physics Dept., University of Tennesse, Knoxville, TN; Uwe Bergmann, Stephen P. Cramer, Structural Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA.

LiMn2O4 is a low cost, low toxicity alternative to Co or Ni oxides for positive electrodes in Li rechargeable batteries. However, capacity fading is one property which has limited widespread use of LiMn2O4. Partial substitution for Mn in LiMn2O4 by another metal (giving LiMn2-yM2-yO4) has been one method to improve this materialís cyclability. Although the effect has been shown in many studies, there has not yet been a satisfactory explanation of the variant effects observed among the different substituents. The changes in local atomic and electronic structure for substitutions of (M =) Li, Cr, Co, and Ni at various concentrations (y) as determined by X-ray absorption and FTIR spectroscopies will be presented along with the electrochemical consequences to elucidate the structure-property-performance interrelationship for this material system.

10:00 AM *Y3.7 
Mn DISSOLUTION AND CAPACITY LOSSES OF LiMn2O4/C Li-ION CELLS UPON STORAGE AT 55. A. Blyr, D. Larcher, J-M. Tarascon, LRCS UPRES-A 6007, Universite de Picardie Jules Verne, Amiens, FRANCE; G. Amatucci, Bellcore, NJ.

Liquid Li-ion batteries, initially commercialized by Sony, are presently accepted in the portable electronics market. Driven by the foreseen industry demand, researchers have developed a rechargeable Li-ion cell based on the LiMn2O4/C redox system that exhibits excellent room temperature performances. However, occasionally some of these batteries showed limited electrochemical performances, namely short cycle life, poor rate capability and poor storage performance at 55C. This paper discusses the origin of this limited 55C performance and means to alleviate it. From a variety of chemical and three electrodes electrochemical experiments coupled with x-ray diffraction, scanning electron microscopy characterization techniques and x-ray absorption analysis taken as a function of temperature, Mn dissolution induced by HF impurities was shown to be the primary reason for the poor storage performance of LiMn2O4/C Li-ion cells in their discharge state. A mechanism, based on an ion-exchange reaction will be proposed to describe how the Mn dissolution proceeds. Finally, a surface chemistry approach consisting in modifying the LiMn2O4/electrolyte interface that has allowed for an enhancement of the 55C performance will be presented.

10:30 AM *Y3.8 
AMORPHOUS MANGANESE DIOXIDE: A PROMISING CATHODE MATERIAL FOR RECHARGEABLE LITHIUM BATTERIES. Jun John Xu, Boone B. Owens, and William H. Smyrl, Corrosion Research Center, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN.

There has been much interest in manganese oxides as cathode candidates for rechargeable lithium or lithium-ion batteries, due to their low cost and relative non-toxicity. Research reported in the literature has so far focused on lithium manganese oxides of different crystalline structures, such a s the spinel or layered structure. While these crystalline materials offer certain attractive features such as high voltages, problems such as phase transitions and structural irreversibility during lithium intercalation have limited their charge capacity and therefore energy density. We have synthesized manganese dioxide of amorphous structure using sol-gel methods. The entire synthesis process was carried out at room temperature to ensure an amorphous structure, which was confirmed by x-ray powder diffraction of the synthesized material. SEM images and BET analysis showed that the synthesized material has a highly porous morphology and very high internal surface area. Chemical lithiation of the material was carried out with butyllithium In hexanes. Close to two moles of lithium per mole of Mn can be inserted into the amorphous structure , giving rise to the highest lithium intercalation capacity among all manganese oxide materials reported. Galvanostatic cycling of composite electrodes based on the amorphous manganese dioxide also revealed an extremely high charge capacity and promising cyclability. Electrochemical properties and rate capabilities of the material used as cathodes for lithium cells will be presented.

11:00 AM Y3.9 
AMORPHOUS LixMn2-yO4 CATHODES FOR THIN-FILM BATTERIES. N. J. Dudney, J. B. Bates, and R. A. Zuhr, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN; and J. D. Robertson, Dept. of Chemistry, University of Kentucky, Lexington, KY.

Thin-film cathodes fabricated by sputter deposition from sintered or hot-pressed disks (targets) of LiMn2O4 have consistently high specific capacities and long cycle life. These cathodes have a dense columnar microstructure, are amorphous by x-ray diffraction, and adhere tightly with both the Ni current collector and the thin-film Lipon electrolyte of our thin-film Li batteries. Recent work has focused on the 6X film-to-film variation in the cathode resistivity which, along with the initial open circuit voltage of the battery, has been found to correlate roughly with the sputter history of the target. Analytical (RBS, PIGE, and ICP) results of films deposited from targets with extreme differences in their sputter history give atomic ratios for O/Mn of 1.9-2.6 and Li/Mn of 0.5-1.25. The tendency for the film composition to vary with the sputter history, often resulting in a Mn deficient film, may be due to the Li redistribution within the LiMn2O4 sputter target. The wide variation in composition is consistent with cycling results if the discharge behavior between 4.5 and 1.8 V reflects the Mn valence change from +4 to +3 regardless of the Li concentration. Although the film compositions may differ greatly, e.g. LixMn2O4 (03.7 V, which indicates that the Mn in these as-deposited films has a valence near +4.

11:15 AM Y3.10 
NOVEL SYNTHESIS PROCESS AND CHARACTERIZATION OF Li-Mn-O SPINELS FOR RECHARGEABLE LITHIUM BATTERIES. Toshimi Takada, Toshihiro Enoki, Etsuo Akiba, National Institute of Materials and Chemical Research, Ibaraki, JAPAN; Takenori Ishizu, Tatsuo Horiba, Shin-Kobe Electric Machinery Ltd, Saitama, JAPAN.

A new process was developed for synthesis of well-crystallized Li-Mn-O spinels with homogeneous composition, by using the eutectic mixtures of Lithium acetate and Manganese nitrate as starting materials. The crystal structure and thermal stability of these compounds were studied using X-ray and neutron diffraction, and TG-DTA analysis. The lattice parameter and thermal stability of the spinels show a strong dependence on the composition and manganese oxidation states. SEM micrographs indicate that the crystallites are appeared as single crystals. The size of the crystallites were found to be in the range of 0.1 - 2 m depending on the synthesis conditions. The cyclic voltammogram, charge-discharge capacity, and cycleability of these samples were examined to evaluate the possibility of using Li-Mn-O spinels as cathode active material for lithium rechargeable batteries operating at 3V or 4V.

11:30 AM Y3.11 

Lithiated nickel oxide (LiNiO2) is an attractive cathode material for Li-ion rechargeable batteries due to low cost, high working voltage, and high capacity. Extensive studies on LiNiO2 have, however, shown that its electrochemical performance is strongly dependent on the stoichiometry of the material. Stoichiometric LiNiO2 consists of a cubic close-packed oxygen array with lithium and nickel ions occupying the octahedral sites. Depending on the method of preparation, it is very easy to obtain a non-stoichiometric material, Li1-zNi1+zO2, with extra nickel ions within the lithium site. Even a small amount of structural disorder due to the displacement of nickel and lithium ions from their respective sites can affect the working voltage and reversible capacity of the cathode material. In this paper, the optimum conditions for preparing LiNiO2 with high power and good rechargeability are presented. Three different methods were investigated: € LiOH and NiO at 700C in air (Batch A), € LiOH and NiO between 150 and 750C in oxygen (Batch B), and € LiNO3 and NiC03 between 600 and 750C in oxygen (Batch C). Batch C exhibited the highest first discharge capacity of about 150 mAh/g between 2.0 and 4.0V in a solid state Li/LiNiO2 cell containing a PAN based polymer electrolyte. A relationship was observed between the X-ray diffraction patterns of the LiNiO2 and their electrochemical behavior. Solid state carbon//PAN electrolytes//LiNiO2 cells and two-cell bipolar batteries demonstrated high rate capabilities at room temperature with an ability to sustain pulsed discharge currents as high as 50 mA/cm2. Approximately 25,000, 13,000, and 1,000 pulses were obtained at culTent densities of 10, 20, and 50 rnA/cm2, respectively, between 2 and 4V. Each pulse involved a pulse width of 10 ms followed by a rest period of 50 ms.

11:45 AM Y3.12

The synthesis and electrochemical characteristics of LiMn2O4 and Li(MnM)2O4 (M = Co, Ni) spinel as the cathode materials for rechargeable lithium batteries were investigated. Lithium manganese oxide spinel is an attractive materials in rechargeable lithium secondary batteries because of its low cost and less toxicity. However, highly lithium intercalation / de-intercalation(Li2Mn2O4/Mn2O4) lead to a decrease in cycle capacity. We studied the electrochemical properties of LiMn2O4 from the point of view of crystal structure, stoichiometry(Li/Mn/O ratio) and charge/discharge properties as a cathode for lithium batteries. It was found that the capacity fading of LiMn2O4 in the region of 2.0 - 4.2V was suppressed by the control of crystal structure, and the crystal structure was controlled by the replacement of a part of Mn with another metal as well. LiMn2O4 and LiMn1.9Ni_0.1%%O4 showed a good cycling performance and good cycle capacity about 190mAh g-1 and 200mAh g-1, respectively, at 50 cycles in the region of 2.0-4.2V.

Chairs: Ken-ichiro Ota and Steven J. Visco 
Tuesday Afternoon, December 2, 1997 
America Center (W)

1:30 PM *Y4.1 
STRUCTURE-CONDUCTIVITY CORRELATIONS FOR PYROCHLORE FUEL-CELL MATERIALS AS A FUNCTION OF TEMPERATURE AND COMPOSITION. Kevin Eberman, Per Önnerud, Bernhardt J. Wuensch, Department of Materials Science and Engineering, MIT, Cambridge, MA; James D. Jorgensen, IPNS, Argonne National Laboratory, Argonne, IL; Judith Stalick, Reactor Radiation Division, NIST, Gaithersburg, MD.

Pyrochlore oxides (A3+)2(B4+)2O7 are mixed ionic/electronic conductors in which the ionic portion of the conductivity is contributed by oxygen ions. This provides opportunity for design of a fuel cell in which chemically and thermally compatible pyrochlore oxides of appropriate composition and doping serve as the electrodes as well as the electrolyte of the device. The pyrochlore structure type is a cubic superstructure derived from the atomic arrangement of fluorite. The A3+ and B4+ cations order in alternating <110> rows. Two crystallographically distinct oxygen ions order among seven-eighths of the available anion sites in a fluorite like array. Elevated temperature or substitution of a third cation of different radius in solid solution drives both the anion and cation arrays to partial or complete disorder, in some systems, with an accompanying increase in ionic conductivity, , by a factor of up to 103. Rietveld analysis of x-ray and neutron powder diffraction data has been used to determine the slate of disorder in several (A1-zAz)2(B1-yBy)2O7 systems as a function of composition to correlate structure with measured conductivities. For A2(Ti1-yZry)2O7 (A = Y or Gd) the anion and cation arrays were earlier found to disorder with increasing y (but, remarkably, at distinct and independent rates). The structural results explain a measured sigmoidal increase of with y. For A2(Ti1-ySny)2O7 (A = Y or Gd) substitution of Sn creates no measurable disorder in the anion arrangement despite the fact that the average radius of the ions occupying the B site overlaps with the Zr phases over a considerable range of composition. Structures have been determined as a function of temperature up to 1500C to confirm that the distribution of mobile oxygen ions in quenched material is the same as in specimens equilibrated at temperature. Similar analyses have been performed for the related systems Y2(Zr1-ySny)2O7 and (SczYb1-z)2Ti2O7.

2:00 PM Y4.2 
A COMPOSITE ELECTROLYTE FOR AN SOFC CONSISTING OF A CERIA SHEET AND A ZIRCONIA FILM DEPOSITED BY THE SOL-GEL METHOD. Reiichi Chiba, Fumikatsu Yoshimura, Jun-ichi Yamaki, Nippon Telegraph and Telephone Corporation, Naka-Gun, Ibaraki-Ken, JAPAN.

We investigated a composite electrolyte for a solid oxide fuel cell prepared by coating a ceria sheet (0.9(Ce0.8Gd0.2O)-0.1MgO) with a scandia alumina doped zirconia (0.86ZrO2-0.10Sc2O3-0.04Al2O3) film using the sol-gel method. The sol-gel films were annealed at C after which X-ray diffraction analysis showed them to be in cubic phase at room temperature. The ionic conductivity of these films was 0.076 S/cm at C, which is comparable to the value of 0.090 S/cm for bulk sample prepared by solid state reaction between ZrO2, Sc2O3, Al2O3 powders at C. We observed a cross-section of the composite electrolyte with a scanning electron microscope. The sol-gel films (0.8 m thick) covered the undulations on the as-sintered ceria sheet. The film sintered well and formed a good interface with the ceria sheet, while the annealing temperature was as low as C. A single cell was fabricated which consisted of the composite electrolyte, La0.8Sr0.2MnO3 cathode and a Ni-YSZ anode. The composite electrolyte comprised a 0.2 mm thick ceria sheet and zirconia film about 0.8 m thick deposited by the sol-gel method. O2 gas and H2 gas (moistened with H2O) was supplied to the cathode and anode of the cell, respectively. The cell yielded an open circuit voltage of 1.0 V at C. This is much closer to the value of 1.1 V expected from the Nernst equation, than the value of 0.76V for a cell containing a ceria sheet without the sol-gel film.

2:15 PM Y4.3 
MOLECULAR DYNAMICS SIMULATION AND ELECTRICAL PROPERTIES OF Ba2In2O5. Masami Kanzaki, 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 first-order transition to a fast oxide-ion conductor at 930 C for Ba2In2O5 which adapts brownmllerite structure at ambient temperature. Molecular dynamics simulation was employed to study oxygen ion diffusion and phase transition of Ba2In2O5. The structure was well simulated at 300 K. When the system was heated, the original orthogonal cell transformed to a tetragonal cell at 2300 K. Inspection of the structure revealed that oxygen ions started to migrate from their original sites to nearest vacant oxygen sites at this temperature. The diffusion was restricted for the oxygen sites around In tetrahedron, resulting highly anisotropic diffusion on the ac plane. At 4600 K it further transformed to an oxygen vacancies-disordered cubic perovskite structure. Although predicated transition temperatures were apparently overestimated, the transition phenomena to the phases with high oxygen ion diffusivity is consistent with the experimental results from electrical conductivity measurements. 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 with another elements. We found that the cubic phase is stabilized below 500 C without any loss of conductivity in Ba2In1 .9Ce0.1Oy.

2:30 PM Y4.4 
NEUTRON VIBRATIONAL SPECTROSCOPY OF THE HIGH TEMPERATURE PROTONIC CONDUCTOR SrCe0.95M0.05HxO. C. Karmonik1, T.J. Udovic1, T. Yildirim1, J.J. Rush1, R. Hempelmann2, 1 National Institute of Standards and Technology (NIST), Gaithersburg, MD; 2 Physikalische Chemie, Universitaet Saarbruecken, GERMANY.

The fundamental scientific interest in solid-state high-temperature protonic conductors (HTPC) has increased significantly in recent years mainly because of potential applications in certain types of fuel cells, e.g. in solid oxide fuel cells (SOFC) operating at elevated temperatures. With decreasing operating temperature - a main aim of current studies - proton conducting oxides become competitive with commerically available oxygen conducting yttrium-stabilized zirconia. A model substance for the doped HTPC is SrCe0.95M0.05HxO, where M denotes different trivalent cations. Using neutron vibrational spectroscopy (NVS), we elucidated the influence of dopants with different radii (i.e. Sc3+ (0.73Å), Ho3+ (0.89 Å) and Nd3+ (1.00 Å)) on the hydrogen vibrational modes in the lower energy regime (<130 meV). The results suggest that a large number of protons are associated with locations near the dopants; the attributed modes exhibit a strong temperature dependence. This observed behaviour is in qualitative agreement with the hydrogen dynamics derived from quasielastic neutron scattering (QENS) results of previous experiments carried out on the Yb3+-doped substance and confirm the influence and the importance of the dopant ions for conductivity properties of these materials. We will also discuss first results of first principle calculations.

2:45 PM Y4.5 
THE SOLID ELECTROLYTES BASED ON THE SYSTEMS Li2O-ZnO-SnO2. N.G. Chaban, V. V. Safonov, V.V. Kireyev, Moscow Academy of Fine Chemical Technology name by Lomonosov M.V., RUSSIA.

The systems Li2O-MgO-SnO2) and Li20-ZnO-SnO2 are investigated by physicochemical analysis methods. The new phases with compositions Li4Mg2SnO6 and Li4Zn3Sn5O15 and theirs fields of existence are found out. According to results of vibrational spectroscopy, obtained substances characterized by close packed tetrahedrally coordinated tin polyhedral and highly coordinated (with coordination number is 6) lithium polyhedral, which result in electron density shifting from lithium to tin polyhedron and hence lead to Li-O bond weakening and Li-ion's mobility increasing. The solid electrolytes based on these substances make it possible to create new electrochemical devices with high current densities amounting to 1 mA/cm2, with electromotive force in the system Li; Al/solid electrolyte/PbO2 amounting to 2,2 V. Working temperature of devices of that kind is 500-600C.

3:15 PM *Y4.6 
DHD-001 CARBON AND FLUORINATED CARBON MATERIALS IN FUEL CELLS. Douglas J. Wheeler, International Fuel Cells, South Windsor, CT.

Abstract Not Available

3:45 PM Y4.7 
NEW INTERCONNECTIONS FOR PLANAR ALLOY - SEPARATOR SOFC STACKS. Yohtaro Yamazaki, Takeshi Ide, Naoki Oishi, Osamu Suzuki, Department of Innovative and Engineering Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama, JAPAN.

Solid oxide fuel cells have potential for creating advanced energy conservation systems, however, because of the insufficient durability for thermal cycles, applications of SOFCs are considerably limited. The durability of planar SOFC stacks against thermal cycles increases by adopting alloy separators with sliding seals and flexible interconnections. The use of alloy separators in planar stacks bring about corrosion problems which lower the quality of the electric connections between air electrodes and separators. In this study, a new idea of flexible interconnections between air electrodes and alloy separators in AES planar SOFC stacks is presented. In a cell stack, the edges of thick air electrodes are connected with LaCrO3 rings which are sandwiched with the edges of adjacent alloy separators. The electric currents in the cells flow radially in the LSM supports(air electrodes) and collected to the LaCrO3 rings which are connected to the alloy separators with nickel leads in fuel gas atmosphere. By using the proposed interconnections, the difficulties in the junctions between air electrodes and alloy separators can be diminished in the RD of planar SOFC stacks.

4:00 PM Y4.8 
DEVELOPMENT OF ELECTROLYTE PLATE FOR MOLTEN CARBONATE FUEL CELL. Chieko Shoji, Takahiro Matsuo, Akira Suzuki, Yoshikazu Yamamasu, Research Institute, Ishikawajima-Harima Heavy Industries Co, Ltd, Tokyo, JAPAN.

It is important for the commercialization of molten carbonate fuel cell(MCFC) to improve the endurance and the reliability of the electrolyte plate. The electrolyte-loss in the electrolyte plate increases the cell resistance and deteriorates the cell voltage. The formation of cracks in the electrolyte plate causes the gas cross leakage between the fuel gas and the oxidizer gas. The pore structure of the electrolyte plate must be stable and fine to support liquid electrolyte under MCFC operation. It is necessary to prevent the formation of cracks in the electrolyte plate in thermal cycling. We have improved the stability of electrolyte plate using advanced LiAlO2 powder and the durability of electrolyte plate for thermal cycling by the addition of the ceramic fiber . The initial cell voltage using electrolyte plate with advanced LiAlO2 powder was 820mV at current density 150mA/cm2 and the decay rate of cell voltage was under 0.5%/1000h for 8,800h. According to the post analyses, the pore structure of the electrolyte plate did not change. The stability of advanced LiAlO2 powder was confirmed. It was proved that the electrolyte plate reinforced with ceramic fiber is effective for thermal cycling.

4:15 PM Y4.9 
NOVEL PROTON EXCHANGE MEMBRANE FOR HIGH TEMPERATURE FUEL CELLS. M. Bhamidipati, E.D. Lazaro, F. Lyons and R. S. Morris, Cape Cod Research Inc., Falmouth, MA.

This initial effort sought to demonstrate that combining select phosphonic acid additives with NafionÆ could improve Nafion's high temperature electrochemical performance. A 1:1 mixture of the additive with NafionÆ, resulted in a film that demonstrated 30 higher conductivity than a phosphoric acid equilibrated-NafionÆ control at 175C. This improvement to the high temperature conductivity of the proton exchange membrane NafionÆ is without precedent. In addition, thermal analysis of the test films suggested that the additive did not compromise the thermal stability of NafionÆ . These results would suggest that the test films could offer electrochemical performance superior to NafionÆ, but would retain the same degree of thermal stability as NafionÆ. This could eventually lead to portable fuel cells that could oxidize unrefined hydrocarbon fuels, resulting in wider proliferation of fuel cells for portable power. As a result, the automotive industry could give serious consideration to using fuel cells as a safe, high density alternative to batteries for electric vehicles.

4:30 PM Y4.10 
PULSED FIELD GRADIENT NMR INVESTIGATION OF MOLECULAR MOBILITY OF TRIMETHOXYMETHANE IN MEMBRANES. Y. Wu and T.A. Zawodzinski, Electronic Materials Division, Los Alamos National Laboratory, Los Alamos, NM; M.A. Smart, NASA Jet Propulsion Laboratory, Pasadena, CA; S.G. Greenbaum, Physics Dept., Hunter College of CUNY, New York, NY.

Direct methanol oxidation fuel cells are hampered by high methanol crossover rates, which has led to consideration of alternative fuels, one of which is trimethoxymethane (TMM). In order to assess the microscopic basis of molecular crossover, we have undertaken TMM permeation and self diffusion measurements, the latter by pulsed field gradient (PFG) NMR techniques, in membranes. Two different equivalent weights (ew) of were investigated, , With ew = 1100, and an ew = 1500 sample. Self-diffusion coefficients were determined from the methyl proton NMR signal in saturated samples containing various concentrations of TMM in water, from 0.5 to 14 M, and at temperatures varying from 30C to 80C. Diffusion of molecular species containing methyl protons is more than a factor of two slower in the 1500 ew membrane than the 1100 ew membrane at 30C and 1 M concentration; the difference rises to about a factor of four at 80C and 14 M concentration. These differences are attributed mainly to the greater effective distance between acid functional groups in the higher ew material. Measurements of methanol permeation and diffusivity in the two ew membranes were also conducted for comparison with the TMM results. The methanol self diffusion coefficients were found to be quite similar to those determined for TMM-containing membranes. Because the PFG technique cannot distinguish between methyl protons in TMM or methanol, the possibility exists that the TMM is hydrolyzed to methanol in the acidic membrane. The permeation behavior, as characterized by gas chromatographic methods, show that in fact, a major fraction (more than half) of the TMM is transformed to methanol as it passes through the membrane. The implications of these findings for alternative fuels in direct oxidation fuel cells shall be discussed.

4:45 PM Y4.11 
THERMOSTABLE IONOMERIC FILLED MEMBRANE FOR H2/O2 FUEL CELL. B. Baradie1, C. Poinsignon1, J.Y. Sanchez1, Y. Piffard2, G. Vitter1, LEPMI-ENSEEG Domaine Universitaire, St Martin D'Hères, FRANCE.

Dispersion of submicronic particles of phosphatoantimonic acid fillers (H3) in a sulfonated polysulfone (PSSH) gives viscous suspension allowing the ``filled'' material to be shaped in thin films. Conductivity values close to those of the Nafion 117 have been determined in the same experimental conditions, i.e. 96% relative humidity at 80C. The inorganic filler improves both the mechanical strength and the gas impermeability of the filled membrane. Performances in a H2/O2 fuel cell are exemplified at 80C and 4 bar pressure of H2 and O2, Cross linking of the polymeric phase inhibits methanol swelling.

Chairs: Morinobu Endo and T. R. Jow 
Wednesday Morning, December 3, 1997 
America Center (W)

8:00 AM *Y5.1 
PROPERTIES AND PERFORMANCE OF ELECTRIC DOUBLE LAYER CAPACITOR USING ORGANIC ELECTROLYTE. Takeshi Morimoto, Manabu Tsushima, Kazuya Hiratsuka, Manabu Suahra, Research Center of Asahi Glass Co. Ltd., Yokohama, JAPAN.

Electric double layer capacitor based n the charge storage at the interface between a high surface area activated carbon electrode and an electrolyte solution is an energy storage device having many outstanding features compared with batteries. Although, the capacitor can provide short tern high power pulses, it has low energy density compared with batteries. To enhance energy density a new capacitor has been developed that has higher energy density than standard electric double layer capacitor. The capacitor is comprised of activated carbon electrodes and an organic electrolyte. Electrical characteristics of 100F capacitor are reported. The data include charge-discharge characteristics, charge-discharge cycle life performance, retained voltage and temperature dependence of the performance.

8:30 AM *Y5.2 
STRONTIUM RUTHENATE PEROVSKITES WITH HIGH SPECIFIC CAPACITANCE FOR USE IN ELECTROCHEMICAL CAPACITORS. Peter Wilde, Thomas Guther, Ruediger Oesten, Juergen Garche, ZSW Center for Solar Energy and Hydrogen Research Baden Wuerttemberg Division 3, Energy Storage and Conversion, Ulm, GERMANY.

Strontium ruthenates with the perovskite type structure ABO3 have been shown to exhibit attractive capacitive properties [1], [2]. The capacitance values are strongly dependent on the size and valance of the A-cation. Doping SrRuO3 by 20% Lanthanum increases the capacitance by a factor of three. Typical capacitance values of La doped ruthenates are in the range of 25 F/g. Most of the capacitance is delivered by redox processes (pseudocapacitance). In this paper the influence of doping the B site by the transition metals iron, cobalt and manganese on capacitance and electrochemical behavior will be discussed as well as the proposed charge storage mechanism. All the perovskite materials were synthesized by coprecipitating metal hydroxides from a stoichiometric salt solution and subsequent firing at 800C in air [2]. X-ray diffraction experiments revealed phase purity. The electrochemical characterization was done by cyclic voltammetric measurements and carried out in a three electrode arrangement using an Hg/HgO reference electrode in 6molar KOH as electrolyte. Capacitance values were calculated by integrating the cyclic voltammetric curves. Cobalt and iron doping only has a minor effect on the capacitance whereas manganese containing samples show increasing capacitance with the amount of manganese due to an additional redox process. Mn doped material.s show only a marginal influence on the electrochemical stability window. With increasing dopant concentration of Fe and Co the stability window is reduced. In these case.s the onset of hydrogen evolution is shifted towards more anodic potentials and a catalytic effect for hydrogen evolution can be observed. Experimental results and a model for charge storage mechanism will be discussed in detail.

9:00 AM Y5.3 
ELECTROCHEMICAL PROPERTIES OF CRYSTALLINE RuO2 AND AMORPHOUS RuO2-xH2O ELECTRODES. J.P. Zheng, S.P. Ding, and T.R. Jow, Army Research Laboratory, Sensors and Electron Devices Directorate, Adelphi, MD.

Crystalline RuO2 is one of the most promising electrode material for electrochemical capacitors due to its high specific capacitance (380 F/g), low electrical resistivity, and fast reaction between Ru ions on electrode surface and the H ions in electrolyte. Recently, we have demonstrated that in amorphous RuOxH2O materials a specific capacitance at least twice as large as that of RuO2, and attributed this effect to the bulk involvement in the redox reaction of Ru ions in RuOxH20 electrode with H ions in electrolyte. In this work, we further studied these two materials by using cyclic voltammetry (CV) and chronoamperometry to determined their electrochemical stability windows, potential dependence of capacitance reversibility and charge discharge rates. From CV studies, it was found that in 5 M H2SO4 electrolyte the stability windows for RuO2 and RuOXH20 were about 1.0 and 1.4 volts, respectively Hydrogen evolution occurred on RuO2 electrodes at potential below 0.1 volt vs. SCE; while for RuOxH20 electrodes, it was not observed above -0.3 volt vs. SEC it was also found that anodic and cathodic currents were quite symmetrical for RuOxH20 electrodes; while for RuO2 electrodes, a large portion of reductive charges at low potentials could only be recovered at much higher potentials in subsequent oxidative scan From chronoamperometry, it was found that charge/discharge rates for both RuO2 and RuOxH20 were limited by the RC time constants. This indicates that the diffusion of H ions in the bulk of RuOxH20 was a fast process. Based on the above, we concluded that as the electrode material for electrochemical capacitors, amorphous RuOxH2O is superior than crystalline RuO2.

9:15 AM Y5.4 
ELECTRODE OPTIMIZATION FOR HIGH POWER DOUBLE LAYER CAPACITORS. John Dispennette, C. J. Farahmandi, Maxwell Technologies, Energy Products Division, San Diego, CA.

Ultracapacitor performance depends on complex interactions between the electrode, electrolyte, separator and packaging. Development of high power double layer capacitors relies heavily on optimization of all these key areas. Electrode optimization is the most significant area in developing ultracapacitors for high specific power. A discussion of ideal electrode structures based on carbonaceous materials follows.

9:30 AM Y5.5 
MODIFICATION OF A CARBON ELECTRODE SURFACE BY COLD PLASMA TREATMENT FOR ELECTRIC DOUBLE LAYER CAPACITORS. Masashi Ishikawa, Atsushi Sakamoto, Masayuki Morita, Yamaguchi Univ, Dept of Applied Chem & Chem Engr, Ube, JAPAN; Yoshiharu Matsuda, Kansai Univ, Dept of Applied Chem, Suita, JAPAN; Koichi Ishida, Industrial Tech Inst Yamaguchi Prefectural Gov, Yamaguchi, JAPAN.

Recently we reported that electric double layer capacitors (EDLCs) with activated carbon electrodes treated with "cold plasma", plasma generated at low temperature, showed enhanced capacitance. The cold plasma treatment can modify the surface properties of carbon materials without changing the chemical and physical properties of material bulk. The present study reports the origin of EDLC capacitance enhancement with the cold plasma treatment. The cold plasma treatment was performed in a plasma chemical vapor deposition apparatus. This apparatus has two types of high-frequency power supply (13.65 MHz); one generates pulsed electric power (max. power: 50 kW) and the other gives continuous electric power (max. power: 500 W). Argon-oxygen mixed gas was introduced to a chamber of the apparatus for the plasma treatment. A model capacitor was fabricated with a Teflon cell case (inner size: 13 mm diameter, 15 mm height), activated carbon electrodes, and propylene carbonate containing tetraethylammonium tetrafluoroborate (0.8 M). For charge-discharge tests of the capacitors, charge-discharge current and operation voltage were 1.0 mA and between 1 and 2 V, respectively. We found that the treatment with the cold plasma generated by the pulsed electric power increased the capacitance of the electrode where cation adsorption/desorption occurred, while no obvious increase was observed in the capacitance of the other electrode where anion adsorption/desorption occurred . We also found that the overall capacitance of the present EDLC was governed by the electrode involving cation transfer. Thus the increase in the overall capacitance of our EDLC with the cold plasma treatment should be ascribed to cation transfer facilitated by the treatment.

9:45 AM Y5.6 
EXPERIMENTAL ELECTROCHEMICAL CAPACITOR TEST RESULTS. Randy B. Wright, Timothy C. Murphy, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID; Susan Rogers, Raymond A. Sutula, U.S. Department of Energy, Washington, DC.

Various electrochemical capacitors (ultracapacitors) are being developed for hybrid vehicles as candidate power assist devices for the fast response engine. The primary functions of the ultracapacitor are to level the dynamic power loads on the primary propulsion device and recover available energy from regenerative breaking during off-peak power periods. 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. Testing data obtained from recent prototype capacitors supplied by Maxwell Energy Products, Inc., SAFT America, Inc., Federal Fabrics-Fibers and the University of Wisconsin Madison will be discussed. Constant-current, constant-power, leakage current, self-discharge and cycle-life testing as a function of temperature of these various capacitors have been conducted. From these tests were determined the capacitance, equivalent series and parallel resistances, specific energy and power densities, and the self-discharge energy loss factor as a function of the device operating temperature. Three non-aqueous electrolyte, carbon-based 3 V, nominally rated 155 F to 165 F cells, (25.4 cm x 7.6 cm x 0.13 cm; 193 cm2) with 0.0251 liter volume, weighing on average 0.0328 kg were fabricated by Maxwell Energy Products, Inc. Also delivered and tested were three carbon-based, non aqueous devices rated at 2300 F at 2.3 V with an average weight of 0.63 kg and dimensions of 13.5 cm x 6 cm x 5.7 cm (461.7 cm3). All of these cells displayed near-ideal behavior during constant-current discharge tests in that the voltage decreased in a linear fashion with discharge time during constant-current discharges. The self-discharge data will be interpreted using various proposed mechanisms for non-ideal energy storage/transfer mechanisms. The other capacitors that were tested and which will be described are ten SAFT America, Inc. non-aqueous, carbon based, non-aqueous electrolyte capacitors rated from 40 F to 62 F at 3 V weighing approximately 0.030 kg (1.83 cm dia. x 6.5 cm high; 0.017 liter volume). Three prototype 1 V, carbon-based/aqueous capacitors rated at 26.0 F, 14 F and 7.7 F prepared by Federal Fabrics-Fibers that were 9.5 cm in diameter and had a projected cross sectional area of 70 cm2 and weighed approximately 0.038 kg were also studied. Two experimental aqueous, NiO/Ni composite-thin-film capacitors prepared at the University of Wisconsin-Madison were also received and tested. These capacitors are single cell aqueous-based devices rated at 1.2 V and I F, with dimensions of approximately 25 cm x 7 cm (175 cm2) and weighted approximately 0.007 kg and 0.0.014 kg, respectively. Results of the complete series of tests conducted on all of these devices will be presented and discussed.

10:30 AM *Y5.7 
HIGH SURFACE AREA METAL CARBIDE AND METAL NITRIDE ELECTRODES. J.Q. Lee, L. Owens, M.R. Wixom, T/J Technologies, Inc., Ann Arbor, MI; L.T. Thompson, University of Michigan, Department of Chemical Engineering, Ann Arbor, MI.

T/J Technologies, in collaboration with the University of Michigan, has developed processes for fabricating new high surface area ceramic electrode materials. These electrode materials have beneficial properties for application in electrochemical capacitors and related energy storage and conversion devices. Sol-gel methods are used to fabricate xerogel and aerogel precursor materials. These precursors are converted into carbide or nitride active materials. The fabrication methods provide the capability to vary the composition and microstructure of the electrode material. A number of new candidate high surface area electrode materials have been synthesized and screened. Compositional and microstructural information is presented and related to general trends in the processing conditions. Electrodes have been prepared and evaluated by cyclic voltammetry, chronopotentiometry, and impedance spectroscopy in both aqueous and organic electrolyte systems. Single electrode and single cell performance data are presented. Intrinsic properties such as open circuit potential, electrochemical stability and specific capacitance are related to electrode composition. The influence on performance of extrinsic factors such as electrode thickness, particle size, and pore structure is also be discussed. The performance of these new materials is compared to carbon, with emphasis on potential advantages with respect to volumetric energy and power density.

11:00 AM Y5.8 
GROWTH OF MoxN AND FexN FILMS FOR AQUEOUS AND NON-AQUEOUS ELECTROCHEMICAL DOUBLE LAYER CAPACITOR ELECTRODES. S.L. Roberson*, D. Finello*, R.F. Davis, North Carolina State University, Department of Materials Science & Engineering, Raleigh, NC. * USAF Palace Knight student attending North Carolina State University; **USAF Wright Labs, Armament Directorate, WL/MNMF.

The electrochemical stability and capacitance of polycrystalline MoxN (x= 1 or 2) and FexN (x=2 or 3) thin film electrodes deposited on Ti substrates in H2SO4, KOH, and ethylene glycol based electrolytes has been investigated. The films were prepared by chemical vapor deposition of either MoCl5 or MoCO6 and NH3 or Iron Acetylacetonate and NH3 at 100 Torr and various deposition temperatures. Cyclic voltammetry referenced to a standard Ag/AgCl electrode indicated that both materials had higher voltage stability limits in H2SO4 than KOH. MoxN films had a voltage stability of -0.6 to + 0.8 V and -0.6 to + 0.2 V in 4.4 M H2SO4 and 7.6 M KOH, respectively. FexN films had a voltage stability of -1.0 to + 0.6 V and -0.8 to + 0.1 V in 4.4 M H2SO4 and 7.6 M KOH, respectively. Both MoxN and FexN had a higher voltage stability in the ethylene glycol based electrolyte. Both cyclic voltammetry and AC impedance spectroscopy indicated that these materials were capacitive with MoxN and FexN possessing 0.2 F/cm2 and 0.08 F/cm2, respectively in both H2SO4 and KOH electrolytes. Both MoxN and FexN had a capacitance of 0.02 F/cm2 in the glycol based electrolyte.

11:15 AM Y5.9 
ELECTROCHEMICAL PROPERTIES OF EARLY TRANSITION METAL NITRIDES. James R. Waldecker, Levi T. Thompson, Univ. of Michigan, Dept. of Chemical Engineering, Ann Arbor, MI.

High surface area early transition metal nitrides and carbides have recently emerged as promising candidates for use in electrochemical capacitor electrodes and as fuel cell catalysts. These interstitial compounds possess high thermal and chemical stabilities as well as high electronic conductivities. Because the energy stored in an electrochemical capacitor is proportional to the square of the voltage, it is desirable for the potential window overwhich the electrode material is stable to be 1 V (in aqueous electrolytes) and the electrode rest potiential to be at the center of this window. Very little has been reported with respect to the practical electrochemical properties of metal nitrides and carbides. In this paper we describe the electrochemical properties of Group IV, V and VI metal nitrides. Thin film electrodes containing these materials were fabricated using a Teflon binder. The electrochemical properties were determined in acidic and alkaline electrolyte solutions using cyclic voltammetry and chronoamperometry. The double-layer capacitances were determined by measuring the charging current at different scan rates. 
With the exception of HfN, all the materials demonstrated at least a 1 V stability window. Furthermore, we were able to isolate regions where the electrodes were stable within 500 mV of their rest potentials. There appeared to be a periodic trend between the nitrides and their rest potentials. The rest potential increased on moving from Group IV to VI and on moving up a period. This trend is similar to that known for the electronegativities of the parent metals. Several of the materials exhibited irreversible surface reactions within the stability window. These reactions did not change the electrode material and the voltammograms were reproducible for many cycles. From a stability, rest potential and electronic conductivity perspective, Ti, Zr and Nb nitrides appear to be the most promising materials for further development. These and other conclusions will be discussed.

11:30 AM Y5.10 
NOVEL SOLID STATE HYDROGEN ION CHEMISTRY FOR ULTRA-THIN RECHARGEABLE POWER SOURCES. Niles A. Fleischer, Joost Manassen, Joel Lang, Eli Rosh Chodesh, Maya Shalom and Moshe Homyonfer, E.C.R. - Electro-Chemical Research, Ltd., Rehovot, ISRAEL.

Energy storage and conversion has long been a subject of study and development. Of special importance, now that electronic devices are shrinking in size, is the storage of electrical energy in a compact, thin, lightweight, safe and environmentally friendly form which can be readily charged and discharged. The use of solid electrolytes for power sources enables the construction of very thin bipolar batteries and capacitors which have the advantages of increased energy and power density, higher reliability and cost effective manufacturing. Several solid state proton conductors are noted for their relatively high current capabillity but some have disadvantages of high temperature operation or excessive cost. A high rate, room temperature solid state proton conducting electrolyte and new proton reaction electrode materials for ultra-thin batteries and electrochemical capacitors will be discussed. Power sources as thin as 60 microns can be made by printing (via simple, ambient techniques)the electrodes onto the solid electrolyte. The electrolyte enables a high form factor for shapeable and flexible power sources. The system can provide currents of at least 400 mA per square cm of electrode area at room temperature. Batteries based on this technology have theoretical energy densitites significantly greater than convernional secondary batteries. So far, double layer capacitors have been cycled at high rates for about 100,000 cycles and pseudo-caps for around 10,000 cycles without significant degradation. The pseudo-caps provide high energy densitites at charge-discharge rates of 100 to 400 mA per square cm. Analytical investigations, structural analyses and electrochemical properties of the electrolyte and electrode materials will be presented and detailed performance data of batteries and capacitors will also be provided.

11:45 AM Y5.11 
HIGH ENERGY ELECTRIC DOUBLE-LAYER CAPACITOR WITH AQUAS ELECTROLYTE USING NEW CARBON ELECTROD. M. Endo*, S.Ishibe, M. Ueda, A. Miyashita and T. Takeda, Faculty of Engineering, Shinshu University, Nagano-city, JAPAN; *Isuzu Advanced Engineering Center, Ltd., Fujisawa-city, Kanagawa, JAPAN.

Various kind of activated carbons have been used for the polarized electrodes of electric double-layer capacitor having aqueous or organic electrolyte. High specific surface area and electric conductivity of the activated carbons have been recognized to be important feature for high performance capacitors. In the present paper, carbonized materials beside of activated carbons have been prepared as the capacitor electrode without any activation process. High performance polarized electrode has been successfully prepared by only carbonization of the polymers, which works well in low as well as high out put current conditions. As the starting polymers of carbonization, polyvinylidene chloride (PVdC) has been used, and the heat treatment temperature as well as the treatment conditions was studied with the pore structure as studied by high-resolution electron microscopy combined with image analysis. The specific capacitances (F/cc,F/g) of the carbonized PVdC are very much related with the pore structure as well as the width. On the plates obtained from the carbonized powder, as the polarized electrode for aqueous solution of sulfuric acid, specific capacitance of 7080F/cc has been obtained under low output current(1mA/cm2) (The specific capacitance as well as the pore structure of the present samples is characterized in comparison with conventional activated carbons. Present electrode is suggested to have a high potential for practical applications.

Wednesday Afternoon, December 3, 1997 
America Center (W)

1:30 PM *Y6.1 
POLYACENE (PAS) BATTERIES. Shizukuni Yata, Kanebo, Ltd, Battery Business Promotion, Osaka, JAPAN; Kazuyoshi Tanaka, Tokio Yamabe, Kyoto Univ, Graduate School of Engineering, Dept of Molecular Engineering, Kyoto, JAPAN.

Polyacenic semi-conductor (PAS) material, which we have been originally developing, prepared from pyrolytic treatment of phenolic resin, is chemically stable and essentially amorphous with a rather loose structure. It enables PAS to be doped with both p- and n- type doping, and to store much larger amount of dopant than conventional carbonaceous materials with high stability. PAS can be doped with Li up to C2Li stage (1100mAh/g) without deposition of Li metal, and the amount of Li doped to PAS is three times as much as that of graphite. Such deeply Li-doped PAS has almost the same energy density as Li metal itself from volumetric comparison. In safety, Li-doped PAS also shows the higher thermal stability than other Li-doped carbonaceous materials. We have fabricated two types of cylindrical cells, employing PAS material. One is a cylindrical-type battery (18650-type) which is constructed with LiCoO2 cathode and PAS anode. It has an excellent energy density of 450Wh/l, which is 1.5 time as high as that of other conventional lithium-ion batteries. It also has the good characteristics about rate capability, low temperature dependence, cycle life, and especially safety. It is suitable for main power source of portable electronic equipment such as note-type computers and cellular phones. Another is a cylindrical-type capacitor (18650-type), in which PAS is employed for both the cathode and anode. It shows a capacitance of 140F and can be discharged at the extremely high power over 100C. It can also be charged and discharged within a minute, and maintain a capacity of more than 90% of its initial value after 10,000 cycles. It is considered to be favorable for the use of high power back-up for starting drive parts of a variety of electric equipment such as solenoids and motors, and to be suitable for solar back-up use.

2:00 PM *Y6.2 
MECHANISMS CAUSING CAPACITY LOSS ON LONG TERM STORAGE IN NiMH SYSTEM. Deepika Singh, Tony Wu, Matt Wendling, Priya Bendale, Joe Ware, Dale Ritter, Lian Zhang, Energizer Power Systems, Gainesville, FL.

Capacity recovery after long term storage and loaded storage is a cntical issue with the NiMH system since its inception. A permanent loss in capacity is observed when cells are stored for long periods of time or discharged deeply to zero volts. The different mechanisms that are known to cause self discharge and capacity loss after storage and deep discharge will be the focus of this paper. Permanent loss in capacity after long term storage involves two main events. One is self discharge which causes the open circuit voltage(OCV) of the cell to drop. Self discharge is caused by decomposition of NiOOH, migration of metal ions and possible degradation of separator. Self discharge can be prevented by reducing contaminants such as nitrates and carbonates. Various separator types and treatment can play an important role in inhibiting metal ions from migrating and thus reducing self discharge. The second cause for capacity loss is the breakdown of the cobalt conductive network in the nickel electrode. This breakdown in conductivity results from the nickel electrode being in a highly discharged state for long time periods. Loss in conductivity negatively effects charge and discharge efficiency of the cell. This leads to permanent capacity loss after storage. Capacity loss can be prevented by adding higher amounts of conductive material in the nickel electrode and thus reducing capacity loss after long term storage.

2:30 PM Y6.3 
EVALUATION OF ELECTROCHEMICAL CAPACITY OF HYDROGEN STORAGE ALLOY. Nobuhiro Kuriyama, Tetsuo Sakai, Hideaki Tanaka, Hiroyuki T. Takeshita and Itsuki Uehara, Osaka National Research Institure, AIST, MITI, Dept. of Energy and the Environment, Osaka, JAPAN.

Evaluation of electrochemical capacity of an metal-hydride electrode is the first step of development of hydrogen storage alloys for metal hydride batteries. In the experiment, accuracy and reproducibility of capacity and dischargeability are required in order to evaluate potential of alloys properly and to use the results for one's business and research papers. In this paper, preparation technique and condition of a metal hydride electrode will be presented to attain good accuracy and reproducibility in electrochemical capacity of an hydrogen storage alloy. An AB2.2 type alloy, Ti0.5Zr0.5Ni1.3V0.7Mn0.1Cr0.1, was used, because observed electrochemical capacity is affected by preparation condition of electrodes. The alloy was pulverized by hydrogenation, and sieved under 75 m. Mixture of alloy powder and fine Cu powder (2.3 m in diameter) was pressed into an tablet. This tablet electrode without binder preserves its shape over 100 electrochemical cycles. Electrochemical capacity, dischargeability and activation characteristics of the electrodes containing 3 or more parts of Cu powder to 1 of alloy in weight coincided with each other. The pressure between 3-10 tons/cm2 in tablet preparation was suitable for the test. Too high pressure led to slow activation and low dischargeability, and too low pressure caused low reproducibility. In addition, impregnation of electrolyte into the tablet in vacuo is appreciably effective to improve electrochemical capacity, dischargeability and activation, and their reproducibility. Based on this study, the average electrochemical capacity for the 6 electrodes was evaluated as (333.12.0) mAh/g at 100 mA/g at 10th cycle.

2:45 PM Y6.4 
BENEFITS OF RAPID SOLIDIFICATION PROCESSING OF MODIFIED LaNi5 ALLOYS BY HIGH PRESSURE GAS ATOMIZATION FOR BATTERY APPLICATIONS. I.E. Anderson, V.K. Pecharsky, J. Ting, Ames Laboratory (USDOE), Iowa State University, Ames, IA; R. Bowman, Jet Propulsion Laboratories (NASA), Pasadena, CA.

A high pressure gas atomization approach to rapid solidification has been employed to investigate simplified processing of Sn modified LaNi5 powders that can be used for advanced Ni/metal hydride (Ni/MH) batteries. The current industrial practice involves considerable post-solidification processing and utilizes a complex and costly alloy design. This investigation is an attempt to produce powder for battery cathode fabrication that can be used in an as-atomized condition without annealing or grinding. Both Ar and He atomization gas were tried and sufficient Sn was added to promote subambient pressure hydrogen absorption/desorption behavior at ambient temperature. The resulting fine, spherical powders were subject to microstructural analysis, hydrogen charging/discharging cycles, and electrochemical cell testing to evaluate suitability for Ni/MH battery applications. Funding from DOE-BES-DMS and DCS under contract no. W-7405-Eng-82 is gratefully acknowledged.

3:00 PM Y6.5 

An important life limiting process in rechargeable metal air batteries is the carbonation of the electrolyte. The major source of carbon dioxide is from the oxidation of the carbon substrate of the bifunctional air electrode. During the charge process (i.e. oxygen evolution process) the electrode is held at potentials well above the oxidation potential of the carbon substrate. In the O2 rich environment of the air electrode (during charge), it is reasonable to expect that some of the O2, or precursors to O2 can oxidize the carbon. This corrosion process and the effect it has on zinc air cell life was investigated. Several commercially available carbons including Shawinigan Black (SAB), Vulcan XC-72, heat treated Vulcan (GV), Ketjen Black (KB), and mixtures of SAB and KB were studied. Various aspects of the corrosion of these carbons were studied including the relative corrosion currents, TGA of the carbons in air, and cell cycling. Based on both electrochemical and physical testing, it was found that there is a relation between both the surface properties and structural properties of the carbon and the rate of corrosion. Also the corrosion reaction generates both CO2 and CO, though the latter is produced in much lower quantities. A closer examination of the chemical processes in SAB and GV electrodes and pure powders was made. The effect of adding porphyrin O2 reduction catalysts are discussed and conclusions are drawn based on the results of these studies and the physical and electrochemical surface properties of the carbons.

Chair: W. F. (Rick) Howard 
Wednesday Afternoon, December 3, 1997 
America Center (W)

3:45 PM *Y7.1 
NOVEL CATHODE MATERIALS BASED ON ORGANIC COUPLES FOR LITHIUM BATTERIES. N. Raveta, C. Michotb, M. Armanda, aDépartement de Chimie Université de Montréal, QC, CANADA; bLaboratoire d'Electrochimie et de physicochimie des matériaux et des interfaces (UMR 5631 INPG-CNRS), Institut National Polytechnique de Grenoble, Saint Marint d'Héres, FRANCE.

In aqueous electrolytes the monocyclic oxocarbon(1)rhodizonic acid can be reduced reversibly in a two steps sequence:(2). Each step involves the transfer of two electrons. The complete delocalization of the electronic charges around the ring stabilizes anionic and radical structures(3). We have studied the electrochemical behavior of some rhodizonate salts as candidates for active material in lithium batteries cathodes. Composite cathodes were made from rhodizonate salts, electrolyte and carbon and were electrochemically tested using slow scan voltammetry (MacPileR) in polymer electrolyte batteries of the type: + rhodizonate composite / PEO20LiTFSI / Li- Indeed, lithium rhodizonate, for instance, could insert 4 lithium equivalents with a capacity of 590 mAhg-1, in the voltage range 3 to 1.6+V vs. Li+/Li to be compared with 300 mAhg 1 for V2O5. Interestingly, the first two electrons injection occurs close to 3V. These materials are thus viable alternatives to metal oxides as electrode materials. We will present our results in terms of capacities and reversibilities for lithium and copper rhodizonate. Preliminary results for the latter show that this material can exchange at least 5 electrons above 1.5 vs. Li+/Li.

4:15 PM Y7.2 
NEW ORGANOSULFUR MATERIALS FOR LITHIUM BATTERIES-POLY(DI-, TRI-, TETRA-SULFIDE) AND POLY(2,2'-DITHIODIANILINE). Katsuhiko Naoi, Tokyo University of Agriculture & Technology, Cooperative Research Center, Koganei, Tokyo, JAPAN.

Recently, disulfide compounds have been introduced as new organic cathodes in lithium batteries. To obtain better charge-discharge performance or even higher energy density out of the materials, the authors propose two new kinds of Organosulfur Compounds, namely, Poly(Tri-, Tetra-sulfide) and Poly(2, 2'-Dithiodianiline). Polysulfides contain multiple sulfur atoms-(S)n- in their molecules, the energy density(1500-3500 Wh/Kg) of which are even higher than those of organodisulfides. 2, 2'-Dithiodianiline(DTDA), a conducting polymer having disulfide bond in it, is proposed here as a new class of high energy storage material. DTDA has one S-S bond interconnected between two moieties of anilines. DTDA was electrochemically polymerized to form an electroactive thin film. Li/SPE/poly(DTDA) cell delivered more than 675 Wh/kg-cathode which is more than 81% of cathode utilization.

4:30 PM Y7.3 
LiCuyIICu2yIIIMn0.84-3yIIIMn1.16IVO4: FIVE VOLT CATHODE MATERIALS. Yair Ein-Eli and W.F. Howard, Jr., Covalent Associates, Inc., Woburn, MA; James McBreen, Department of Applied Science, Brookhaven National Laboratory, Upton, NY.

A series of electroactive compounds, LiCuxMn2x04 (0.1 x 0.5), that contain two valence disordered elements was studied by spectroscopic (XAS), morphologic (SEM), and electrochemical methods. The existence of Cu(II)/Cu(III) and Mn(III)/Mn(IV) in the prepared materials was indicated by electrochemical evidence and confirmed by EXAFS. These CuMn spinels are nearly identical in structure to cubic LiMn204 and successfully undergo reversible Li intercalation. Cyclic voltammetry shows a +175 mV shift in the 4.1 V Mn plateau and the appearance of a 4.9 V Cu plateau, indicating that Li binding energy increases due to Cu(II) in the lattice and a higher potential is necessary to extract electrons from Cu 3d eg levels compared to Mn 3d eg levels.

4:45 PM Y7.4 

Production of batteries and their wastage have increased with development of portable electrical equipment. Usual secondary batteries, such as lead-acid or nickel-cadmium cell, use heavy metals which are expected to pollute our environment. Biodegradability of active materials, electrodes, and/or electrolytes is one of key properties for future batteries. Potentially biodegradable polyamides and polyesters were prepared by condensation between diacid (for example, 3,3'-dithiodipropionic acid) containing disulfide bond and alkyldiamine (cystamine) or diol (p-xylylene glycol). Electrochemical behavior of the polymers was investigated in various organic electrolytes. Polyamide (PIDI) showed an electrochemical response due to reduction of disulfide bonds in the polymer chain and re-oxidation of the produced thiolate anions. Polyester(PODOM) was soluble in usual organic electrolytes, such as acetonitrile, propylene carbonate. Therefore, crosslinked PODOM (c-PODOM) was prepared with 1,3,5-benzenetricarbonyl chloride as crosslinking reagent and used for electrochemical studies. Apparent capacity of the PIDI electrode was 44.1 Ah/kg and c-PODOM electrode was 48.1 Ah/kg estimated from CV peak area. Degradability of the polymers was also investigated in various pH buffer solutions. Weight loss of PIDI was about 10 % for 10 days and 40 % for 90 days in pH 5 buffer solution at 37 C. In this condition simple hydrolysis of the PIDI to diacid and diamine was observed. Weight loss of PODOM was about 10 % for 60 days in same condition.

Wednesday Evening, December 3, 1997 
8:00 P.M. 
America Ballroom (W)

ACCELERATED CORROSION OF STAINLESS STEEL BELOW 923 K WITH THE PRESENCE OF MOLTEN CARBONATE. Ken-ichiro Ota, Katsuya Toda, Naobumi Motohira, Nobuyuki Kamiya, Yokohama National University, Dept of Energy Engineering, Yokohama, JAPAN.

The molten carbonate fuel cell (MCFC) is developing since it has high conversion efficiency and it can use wide variety of fuels. However, the MCFC has technical problems concerning the durability of materials. The corrosion of separator (stainless steel) is one of them. In this paper the high temperature corrosions of stainless steels (SUS316L and SUS310S) have been studied with the presence of molten carbonate film coating (Li/K eutectic carbonate and Li/Na eutectic carbonate) in oxygen containing atmosphere by measuring the weight gain and the weight loss of specimens. Generally, the corrosion rate of SUS310S is smaller than that of SUS316L. The corrosion behavior of SUS316L depends significantly on the reaction conditions;atmosphere, temperature, amount of the carbonate melt, etc. For SUS316L, two types of accelerated corrosions were observed around 823 K that is lower than 923 K (the operating temperature of a MCFC) with Li/Na eutectic carbonate melt coating. One is the severe corrosion at the initial stage of the reaction in carbon dioxide-oxygen atmosphere. The corrosion was a local corrosion and several through holes were observed at the specimens after corrosion tests of 60 h. The corrosion was suppressed at higher temperatures. The other severe corrosion took place in pure carbon dioxide atmosphere. The corrosion was a general corrosion and the reaction followed the linear rate law. The corrosion was suppressed with the presence of oxygen in the atmosphere. These accelerated corrosions should be taken into account to decide the start up conditions of a MCFC.

SYNTHESIS AND ELECTROCHEMICAL STUDIES OF LiMn2O4 PREPARED BY HYDROTHERMAL SYNTHESIS. Sang-Mock Lee, Sylvie Bourderau and Donald M. Schleich, ISITEM, Laboratoire de Genie des Materiaux, Nantes, FRANCE..

There is a great deal of attention on lithium metal oxides as a cathode materials for lithium rechargeable batteries. Among the proposed candidates as the cathode, LiCoO2, LiNiO2 and LiMn2O4 show particular interests because they intercalate Li reversibly at high voltages. Lithium cobalt dioxide is used commercially as a cathode material. Even though LiCoO2 is a successful cathode and currently used extensively, considerable work has focused on lithiated maganese oxides as alternative cathode materials because of the high cost and toxicity of cobalt compounds. Lithium manganes oxides, LiMn2O4 and LiMnO2 have been synthesized by hydrothermal reactions in the temperature range between 200 C and 400 C. This synthesis technique creates a homogeneous environment in solution to avoid various nonstoichiometric compounds. LiMn2O4 and LiMnO2 were characterized by using X-ray diffraction (XRD), Scanning electronmicroscopy (SEM) and Thermogravimetric analyses (TGA). The purity and structure of both lithium manganates were confirmed by XRD. The powder x-ray diffraction patterns and SEM observation of all the samples indicates that the hydrothermal reactions yield good crystalline products. Thin films (3 5 m) of LiMn2O4 with polymeric binder and carbons were prepared by spraying on to an aluminum substrate and tested in the system LiMn2O4/LiPF6/Li. Although the cathode conditions were not optimized for electrochemical behavior, electrochemical performance of the cathode prepared by spraying LiMn2O4 on the aluminum substrate shows that specific capacities over 100 mAh/g (theoretical capacity of LiMn2O4, 148 mAh/g) can be obtained based on the active lithium manganese oxide mass as cathode. Less than 5 capacity drop in the first charge-discharge-recharge cycle was observed. Similar cathodes were prepared from LiMnO2 indicating a transformation to the spinel phase upon cycling.

EFFECTS OF MICROSTRUCTURE ON THE ELECTROCHEMICAL PROPERTIES OF SOME PEROVSKITE OXIDES. K. Zhang, Y.L. Yang, A.J. Jacobson, and K. Salama, Materials Research Science and Engineering Center, University of Houston, Houston, TX.

Mixed type conducting materials have attracted much attention in recent years because of their potential applications in oxygen separation membranes, solid oxide fuel cells and electrocatalytic reactors. One group of these materials, the perovskite oxides have been extensively investigated due to their high electronic and ionic conductivities at elevated temperatures. The primary studies of these materials have been focused on the characterization of the electrochemical properties, particularly the oxygen permeability. Little is known about the effects of microstructure on the electrochemical properties. Furthermore, the results reported are found to vary considerably, and the reasons for these variations are not yet completely understood. In this investigation, a systematic study was performed to understand the effects of microstructure on the electrochemical properties of some perovskite oxides. The results show that the difference in microstructure, especially the grain size, has strong influence on the electrochemical properties of the materials investigated. In particular, the measured oxygen permeation flux increased as the average grain size of the sample is decreased indicating that the grain boundaries provide a faster path for oxygen penetration in perovskite oxides. Detailed analysis of the microstructure are conducted in order to determine the responsible mechanism.

ON THE PECULIAR LOW TEMPERATURE EPR IN ELECTROLYTIC MANGANESE DIOXIDES FOR BATTERY APPLICATIONS. M.V. Ananth and K. Dakshinamurthi, Central Electrochemical Research Institute - Madras Unit, C.S.I.R. Complex, Madras, INDIA.

Electron paramagnetic resonance [EPR] investigations have been made on four practical electrolytic manganese dioxides used for battery assembly. Measurements have been made both at room temperature [RT] and liquid nitrogen temperature [LNT]. At RT, except for a sample which displayed a doublet in the major portion of the spectra, mostly a singlet is seen. The signal width varies from 1000 to 2375 Gauss. The signals occur mostly at around 2700 Gauss. But in one case the shift was as high as to 3300 Gauss. The asymmetry factor varies from 0.84 to 2.0. In two cases , in the major singlet, development of six line pattern characteristic of Mn2+ could be seen within a signal width of 550 Gauss. But when one or more lines are not prominent, the signal width exceeds the stipulated value of 550 Gauss for Mn2+. In other two lines, the presence of Mn2+ could not be detected. In one case, the spectrum was elongated in HF regions. At LNT, the observed extension of the spectrum in LF regions indicated some interesting physical phenomenon. In samples displaying the presence of Mn2+ at RT, Mn2+ could be detected again at LNT. In one sample, which did not indicate the presence of Mn2+ at RT, Mn2+ did not get developed at LNT also. But in other such sample development of Mn2+ can be seen at LNT. Amongst the various EPR parameters at LNT, the peculiar development of the multiple line pattern corresponding to Mn2+ [present as minority species] assumes much importance as it reveals the magnetic transitions taking place and is useful in understanding the physics of materials responsible for the variations in alkaline battery activity of the samples.

MONOLITHIC DOUBLE-CELL THIN-FILM LITHIUM ION RECHARGEABLE BATTERIES. T.Y. Liu, M.A. Goldner, R.B. Goldner, A. Gerouki, T.E. Haas, P. Zerigian, Tufts University Electro-Optics Technology Center, Medford, MA; S. Jones, Eveready Battery Company, Westlake, OH.

One appealing property of thin-film rechargeable batteries is their ''stackability'' for a multi-cell series configuration without any external wiring and assemblies. To our knowledge, this property had not been demonstrated previously. We have successfully fabricated double-cell batteries with a carbon anode and a lithium cobalt oxide cathode, using rf-sputtering, electron-beam, and ion-assisted thermal evaporation processes. The double-cell rechargeable battery consists of eleven thin-film layers with following configurations: Al2O3 substrate/Cu/TiN/C/LiPON/LiCoO2/TiN/C/LiPON/LiCoO2/TiN/Al. It has total thickness of 6um and a charged-state voltage close to 7V. With a footprint of a single-cell battery, an optimized double-cell battery is expected to have a charged-state voltage of more than 8V.


In this study, the evolution of the stress-states in ReNi5 particles, where Re denotes the rare earths La, Ce, and Misch-metals, during hydrogen charging and discharging cycles were investigated using coupled diffusion/deformation FEM analyses. The results indicate that large tensile stresses, on the order of 20-30% of the modulus of elasticity, develop in the particles even in the absence of both internal and external crack-like defects. The internal and external cracks behave differently from each other during hydrogen charging and discharging cycles. Therefore, the fracture resistance of the particles containing external cracks will be different than the particles having internal cracks. The disk shaped particles, in addition to having faster charging/discharging cycles, may offer better resistance to fracture than the spherical particles.

THE CORROSION PHENOMENA IN THE COIN CELL BR2325 BY THE "SUPERSTOICHIOMETRIC FLUOROCARBON-LITHIUM" SYSTEM. Valentin N. Mitkin, P.S. Galkin, T.N. Denisova, O.V. Koreneva, S.V. Filatov, Institute of Inorganic Chemistry, Novosibirsh, RUSSIA; A.B. Alexandrov, V.L. Afanasiev, A.A. Enin, V.V. Moukhin, V.V. Rozhkov, V.V. Telezhkin, Joint Stock Novosibirsk Chemical Concentrates Plant, Novosibirsk, RUSSIA.

There were assembled an experienced series over 8000 coin lithium cells BR2325 with cathodes based on superstoichiometric CF1.25. Electrolyte is 1Ì LiClO4 in mix PC+DME. In cathodes are randomly distributed traces of HF and H2O but also given metal additives- Fe, Cu, Ni, Pb and Cd in a range 0.1-5.0%. Some details of BR2325 construction and the modes of cell's technology were also varied. Effects of corrosion and the discharge properties in specified experienced set after 1 year storage were studied. It has been shown that the composition of body and film covers of cathodes strongly influences to stability of BR2325 through the contaminations of HF. It has been established that in all case of HF traces absence the appreciable corrosion is not observed and discharge capacity BR2325 does not undergo of essential decreasing. The presence into cathodes of BR2325 of 0.0N 0.N% HF and of 0.2-5.0% Cu leads to increasing of related metal content in separator and anode and also steady decreasing of cell capacity under storage. Distribution histogram of pilot series after one year storage has shown unequivocal correlation between the short circuit current, open circuit voltage, depth of corrosion processes and proton concentration in cathodes. On the basis of the physical-chemical methods it is supposed the autocathalytic mechanism of corrosion of the cell's materials and anode, connected with slow C-F bond's hydrolysis by traces of a moisure, accumulation of HF and metal transferring to anode as a coordination compounds with their sequent reduction by lithium.

AER ENERGY'S OXYGEN SELECTIVE MEMBRANE PROGRAM FOR ZINC AIR CELL ENVIRONMENTAL CONTROL. M.Neal Golovin, V.Roger Shepard, AER Energy Resources, Inc., Smyrna, GA; Daniel J. Brose, Chemica Technologies, Inc., Bend, OR; Thomas A. Reynolds, ReyTech, Bend, OR.

Because of the intrinsic need for oxygen, zinc air cells and batteries are designed to be exposed to the environment. This exposure can be a source of shortened life in electrically rechargeable zinc air systems due to water loss/gain. AER Energy has undertaken a program, over the past four years, to develop a membrane system that will allow the permeation of O2 relative to water vapor. Several classes of gas permeable systems that can be formed into membranes and can easily be incorporated into the standard AER cell construction have been investigated. In this paper, the theoretical background to the AER approach of supported liquid membranes will be discussed. The mechanism of gas permeation through the membranes will be discussed, as well as how these mechanisms affect the desired permeation rate (Pi) and permselectivity ( defined below) of oxygen over water vapor. Data will be presented for fluorocarbon based PO2 / PH<<619>>2O membranes that show l along with systems that show 1. Systems that have l include standard polymer membrane systems such as poly(dimethylsiloxane), microporous Teflon, as well as sputtered SnO films (with and without co-sputtered carbon). O2 permeation will be presented in terms of both gas permeation and half cell polarization measurements.


We carried out photon correlation spectroscopy measurements of molten poly(ethylene oxide) (PEO), a model compound for solid polymer electrolytes (SPE), with and without added lithium perchlorate to imporove the understanding of ion trasport in these systems. The moloecular weights of the two polymer samples studied (M = 50,600 and 1060) were chosen to compare highly entangled and non-entangled bulk polymer systems. For both molecular weights, we observed a very slow relaxation process with charactgeristic times of the order ms - s which clearly exhibited single exponential behavior. This behavior is very different from that of poly(propylene oxide), another SPE polymer. The slow process resembles the so-called ultra-slow mode or cluster mode which has recently been found, for example, in certain glass forming liquids and diblock copolymers, and which has been tentatively interpreted as due to long-ranged density fluctuations. In addition to the temperature dependence of the observed process, the influence of added lithium perchlorate on the behavior of these polymer melts as well as the presence of large scale heterogeneities will be discussed.

ON OXIDE ION CONDUCTIVITY OF PEROVSKITE OXIDES LaGaO3 AND LaYO3. G.V.M. Kiruthika and U.V. Varadaraju, Materials Science Research Centre, Indian Institute of Technology, Chennai, INDIA.

Solid oxide fuel cells (SOFC) are found to be ideal candidates for the electrochemical generation of electricity with high efficiency (l ,2). A typical SOFC utilizes yttria-*stabilized zirconia with a fluorite structure as the electrolyte having an oxide ion conductivity of about 0.1 cm-1 at 1000C. Oxide ion conductors operating at lower temperatures with high efficiency increase the life and reduce the cost of the cell. Higher oxide ion conductivity has been discovered in the doped perovskite LaGaO3(3). Aliovalent substitution of Sr at the La site and Mg at the Ga site has given a remarkable conductivity of 0.11 cm-1 at 800C(4). A systematic study on the oxide ion conductivity in the perovskite family of compounds LaGaO3 - LaYO3 with Sr arid Mg substitution at the A and B sites has been undertaken. Apart from high concentrations of oxide ion vacancies, it is necessary to reduce the activation energy of the oxide ion movement for a better conductivity. This may be achieved by providing a strain free pathway for oxide ion motion. Attempts have been made to substitute (10-20%) Y (ionic radius = 0.90A) at the Ga (0.62A) site. This may be thought of to increase the size of the unit cell and hence provide an optimal bottle-neck size for oxide ion migration. Compositions of the formula La0.9)<<1533>>0.9)%%0.9)Sr_0.1Y_1-zMg_zO_3(z=0-0.3), La_0.9)Sr_0.1(Y_x,Ga_1-x)_0.8Mg_0.2O_3Sr0.1)(Ga0.8Mg0.2)O3 (LSGM) electrolyte has a higher maximum power density (MPD) at 800ƒC than cells with Y0.16Zr0.84O2 (YSZ), (La0.8Sr0.2)(Ga0.85Mg0.15)O3 (LSGM2) or ((La0.9Nd0.1)0.9Sr0.1)(Ga0.8Mg0.2)O3 (LNSGM) electrolytes. The LSGM cell had a lower open circuit voltage (OCV) than the YSZ cell, which is believed to be due to the small amount of p-type electronic conduction in the LSGM electrolyte. The higher OCV of the LNSGM cell than that of LSGM cell confirmed that the addition of a small amount of Nd for La site in LSGM suppressed the p-type electronic conduction at high oxygen partial pressure (10-5 to 1 atm). La0.6Sr0.4CoO3 (LSC) and La0.6Sr0.4MnO3 (LSM) perovskite cathode materials increase the oxygen reduction rate at three-phase boundaries and result in the lower cathodic polarization and higher maximum power density, which compared to the Pt cathode material. The LSC/LSGM cell had the highest maximum power density of all the systems tested.

PREPARATION OF Pt/WO3 POWDERS AND THIN COATINGS BY THE COMPLEX SOL-GEL PROCESS (CSGP). A. Deptua, W. ada, T. Olczak, B. Sartowska, Institute of Nuclear Chemistry and Technology, Warsaw, POLAND; A. Ciancia, L. Giorgi, A. DiBartolomeo, ENEA-CRE-Casaccia, ITALY.

Pt/W03 electrodes are used as catalyst for direct methanol fuel cells. Generally they are prepared by mechanical mixing of Pt and W03 followed by Teflon bonding or electrodeposition from Pt-W-CI aqueous solution. In this work the CSGP was applied. Saturated tungsten ascorbate aqueous sol (0.15M) was prepared by dissolving ammonium tungstate in saturated ascorbic acid solution. To this solution H2PtCl6 (30%) was added to obtain the molar ratio Pt:W=1. After evaporation and heating at 700C for 2h homogeneous yellow-green powders were obtained. Another parts of this solution was diluted with ethanol and after ultrasonic mixing used for preparation of coating on Ag substrate by the immersion technique. Gel layers were dried at 200C for 20h and then calcined at 700C for 2h. The resulting white colored layers were very adherent. Their thickness varied from 40 to several m depending on dilution and withdrawal rate. The thermal evolution of the gels into final products was examined by TG, DTA, SEM, EDS and XRD. Those latter studies confirmed the relatively homogeneous distribution on crystalline W03. The catalytic activity toward methanol oxidation is under study. For comparison a sample of the catalyst was prepared by impregnation of commercial W03 with solution H2PtCI6 (30%) and similar thermal treatment.

SYNTHESIS AND PRELIMINARY ELECTROCHEMICAL CHARACTERIZATION OF LINI0.5CO0.5O2 POWDERS OBTAINED BY THE COMPLEX SOL GEL PROCESS (CSGP). A. Deptua, W. ada, T. Olczak, Institute of Nuclear Chemistry and Technology, Warsaw, POLAND; F. Croce, G.B. Appetecchi Dipartimento di Chimica, University ''La Sapienza'', Roma, ITALY; A. Ciancia, L. Giorgi, A. Brignocchi and A. DiBartolomeo, ENEA-CRE- Casaccia, ITALY.

LiNi0.5Co0.5O2 is one of most promising compounds for positive electrode for Li rechargeable batteries. According to the best author's knowledge it has never been synthesized by the sol-gel process. In this work a very efficient Complex Sol- Gel Process (CSGP) for the preparation of LiNi0.5Co0.5O2 was applied. Starting sol-solutions were prepared in two different ways, namely: I, in which aqueous ammonia was added to a starting solution of Li+ Ni2+-Co2+ acetate-ascorbate, and II in which LiOH was added to a solution of Ni2+- Co2+ and NH4+ acetate-ascorbate. The synthesis reaction was studied potentiometrically. It was found that in the absence of ascorbic acid, or at its lower content (0.2 M on 1M Li+Ni2+- Co2+) precipitation of hydroxides, prevalently of Co occurred in both cases. Regular sols were concentrated 3 times and dried slowly up to 200C. After 200h of heating at 200C monolithic gels are formed. Intensive foaming was observed for samples prepared by variant I during further heating. In both cases self-ignition takes place at 350C. Thermal transformation of the gel to solid was studied by TG, DTA, XRD and IR. The main feature of this step is carbonate formation. The content of carbonate in the temperature range 300-600C varied from 50 to 75% of stoichiometric quantity calculated on the basis of the formula LiNi0.5Co0.5 (CO3)1.5 Further heating results in intensive decomposition of carbonates. The final structure LiNi0.5Co0.5O2 is observed after heating for lh at 800C or for 1Oh at 700C. Electrochemical properties, of the LiNi0.5Co0.5O2 compound, prepared by both the variant of the CSGP were evaluated and considered satisfactory.

STRUCTURAL CHARACTERIZATION OF HYDROTHERMALLY SYNTHESIZED POTASSIUM BIRNESSITE, KxMnO2yD2O. Dianna M. Young and Arthur J. Schultz, Argonne National Laboratory, Intense Pulsed Neutron Source, Argonne, IL.

Natural and synthetic manganese oxides have recently received much attention for their technological applications in the areas of secondary batteries, catalysis, and environmental remediation. We have hydrothermally synthesized potassium birnessite, Kx,MnO2 yD2O (x= 0.33-67; y = 0.25-0.47) from KMnO4 Kx,MnO2yD2O is hexagonal, space group = R.

8:00 AM *Y9.1 
IN-SITU X-RAY CHARACTERIZATION OF LiMn2O4: A COMPARISON OF STRUCTURAL AND ELECTROCHEMICAL BEHAVIOR*. Mark A. Rodriguez, David Ingersoll, Daniel H. Doughty, Sandia National Laboratories, Albuquerque, NM.

LixMn2O4 materials are of considerable interest in battery research and development, and the crystal structure of this material can significantly affect the electrochemical performance. The spinel polymorph of LiMn2O4 exhibits both a 3V and a 4V plateau. However, presumably as a result of a lattice expansion resulting from a Jahn-Teller distortion of the initial cubic lattice, the 3V plateau of the compound does not appear stable. The ability to monitor the changes of the crystal structure during use, that is during electrochemical cycling, would prove useful to verify these types of structural changes. We report in-situ XRD measurements of LiMn2O4 cathodes with the use of an electrochemical cell designed for in-situ x-ray analysis. Cells prepared using this cell design allow investigation of the changes in LiMn2O4 structure during charge and discharge. We will describe the variation in lattice parameters along the voltage plateaus and consider the structural changes in terms of the electrochemical results on each cell. Kinetic effects of LiMn2O4 phase changes and their resultant effects on performance will also be addressed. We will discuss the behaviors of LiMn2O4 materials from differing commercially available sources as well as our own chemically prepared powders and compare and contrast the materials based on the observed in-situ diffraction data.

8:30 AM Y9.2 
IN-SITU RAMAN SCATTERING TO STUDY Li CYCLING INDUCED STRUCTURAL CHANGES IN TRANSITION METAL OXIDE CATHODES. J.D. Perkins1, C.W. Teplin2, J.M. McGraw3, M.L. Fu2, D.M. Trickett3, J.-G. Zhang1, P.A. Parilla1, T.F. Ciszek1, C.T. Rogers2, and D.S. Ginley1, 1National Renewable Energy Laboratory, Golden, CO; 2University of Colorado, Boulder, CO; 3Colorado School of Mines, Golden, CO.

Transition metal oxides are promising cathode materials for Li-ion rechargeable batteries, in part, due to their large capacity for electrochemically intercalated Li. However, deep and repeated cycling often results in structural changes and degraded battery performance. For example, crystalline V2O5 films show a steady decrease in capacity and crystallinity when repeatedly cycled between 4.1 and 2.0 volts vs. Li. To date, we have studied this effect via electrochemical cycling experiments coupled with x-ray diffraction and Raman scattering measurements. We report here the development of an Raman spectrometer 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 diagnostic will permit essentially continuous measurements of the Raman scattering spectrum during cycling to provide insight into the cycling induced structural changes. We have constructed a fiber optically coupled Raman scattering diagnostic using 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 LiCoO2 thin films grown by pulsed laser deposition along with LiCoO2 single crystals have been examined.

8:45 AM Y9.3 
MAGNETIC AND TRANSPORT PROPERTIES OF HEAT-TREATED POLYPARAPHENYLENE-BASED CARBONS. M.J. Matthewsa, N. Kobayashid, M.S. Dresselhausa,b, M. Endoc, T. Enokid, T. Hiraokac, T. Karakic, aDepartment of Physics, Massachusetts Institute of Technology, Cambridge, MA; b Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA; c Faculty of Engineering, Shinshu University, Nagan, JAPAN; dDepartment of Chemistry, Tokyo Institute of Technology, Tokyo, JAPAN.

Electron spin resonance (ESR), magnetic susceptibility and transport measurements were recently performed on a set of heat-treated polyparaphenylene (PPP)-based carbon samples, which are of significant interest as novel carbon-based anode electrodes in Li-ion batteries. Attention is focused on the evolution of the carbonaceous structures formed at low heat-treatment temperatures (THT) in the regime of 600C HTT 800C, where percolative transport behavior is observed. At the percolation threshold, T 700C a coexistence of two spin centers with peak-to-peak Lorentzian linewidths of (300K) = 0.5, 5.0 G is observed. The relatively high ratio of hydrogen:carbon (H/C) is believed to influence the ESR results through an unresolved hyperfine interaction. , where Ipp is the peak-to-peak lineheight, is plotted versus T, yielding Weiss temperatures that are in agreement with static susceptibility, , measurements. At low THT, PPP-based materials exhibit a high amount of disorder and this is evidenced by the high density of localized spins, NC, which is obtained from a Curie-Weiss fit to assuming a spin quantum number of . A model is given for the microstructure and high electrochemical doping capacity of PPP samples heat-treated to 700C which can be related to Li-ion battery performance.

9:00 AM Y9.4 

The potentiometric titration method is useful and powerful for studying reactions at the interface between particle and solution, because the titration curves obtained for aqueous suspensions will clearly reflect even small difference in the surface characteristics of powders prepared in the same way, but each having different history. The method was applied to evaluate the surface characteristics of electrolytic manganese dioxide powders (EMD) prepared at several electrolysis temperatures. Titration curves were obtained for the dioxides in solutions containing Li+ and K+ ions. Comparison of the curves provided useful informations on the pore size distributions of the EMDs having water in the pores and showed that the electrolysis temperatures affect the distributions significantly. The pores, which permit penetration for Li+ ions, but do not for K+ ions, should contain only water in KOH solution. The water supports H2O as a reactant of the following reaction MnO2 + H2O + e- MnOOH + OH-. Thus the characteristics evaluated by the titration method could be correlated to the discharge performance as an alkaline EMD battery active material. Such useful informations can not be obtained from the nitrogen adsorption-desorption isotherms and by using a mercury porosimeter. The titration technique was also applied to evaluation of LiCoO2 as an active material of lithium ion secondary battery. The titration procedures and the results will be presented.

9:30 AM Y9.6 
NR MEASUREMENTS TO STUDY THE REVERSIBLE TRANSFER OF LITHIUM ION IN LITHIUM TITANIUM OXIDE. Takao Esaka, Shigeomi Takai, Dept of Materials Science, Tottori Univ, Tottori, JAPAN; Masahiro Kamata, Dept of Scientific Education, Tokyo Gakugei Univ, Tokyo, JAPAN.

The present authors have previously reported that the neutron radiography (NR) is helpful to visualize the lithium ion distribution in Li-conducting oxide, Li1.33Ti1.67O4 or Ca0.95Li0.10WO4. In this study, Neutron radiography has been also applied in order to investigate the reversible transfer of lithium ions in Li1.33Ti1.67O4. The pellet-type sintered samples with different isotope ratios (smpA with 100% 7Li and smpB with 92.5% 7Li) were at first prepared by the ordinary solid state reaction at high temperatures. Dc current was passed through the stack of smpA and smpB for Li+ to be transferred from smpB to smpA at the first step, and the polarity of dc current was changed assuming the once transferred Li+'s go back to the initial positions at the second step. On each step, a set of NR images was obtained. The same experiment was carried out only in smpB with 92.5% 7Li in order to obtain the numerical data of the transferred lithium contents. The magnitude of interaction between neutron and each lithium isotope is so different that, before passing current, smpA looks black and smpB whitish on the radiograms (negative films). After passing current, the white region moved from smpB to smpA. When the polarity changed, the white region goes bach to the initial condition. These illustrated the lithium ion transfer in the oxide according to the direction of dc current. The numeric data profile obtained from the NR images showed that the region having rich Li contents (about 200 % of the initial one) was present on one way charging, which means that the lithium ions are not only transferred by electric field but also accumulated in the sample under a special condition. X-ray diffraction showed that almost pure TiO2 remained in the Li-extracted sample. On reverse charging, the region containing the rich Li content was shifted toward TiO2 keeping its Li content of 200 %. This illustrates visually that TiO2 works as a lithium ion insertion material. These results will be discussed in detail together with the principle and another application of NR.

9:45 AM Y9.7 
INFLUENCE OF WATER AND OTHER CONTAMINANTS ON LITHIUM ELECTRODEPOSITION. Takuya Fujieda, Shinji Koike and Shunichi Higuchi, Osaka National Reserach Institute, AIST, Osaka, JAPAN.

Electrochemistry of nickel and lithium electrodes in propylene carbonate (PC) etc. containing LiCI04, LiCF3SO3, LiPF6 was studied through microelectrode technique. The solvents and electrolytes used for the experiments were cautiously purified in a glove box filled with purified Ar gas and their stability were estimated under various contaminants, potential etc. Three cathodic peaks were observed at the potentials prior to lithium electrodeposition on nickel in linear sweep voltammogram. This process was common to all electrolytes examined and attributed to the reactions related to contaminants. The cathodic decomposition of the electrolytes on a nickel electrode did not show any clear peaks in the voltammogram. The decomposition of PC would occur in the background of the cathodic current which rose with the addition of a small amount of proton or purification of the electrolytes. In contrast the addition of alkaline such as LiOH had Iittle influence on lithium electrodeposition.

10:15 AM *Y9.8 
HIGH RESOLUTION LITHIUM-7 NMR STUDIES OF LITHIUM INSERTION IN HARD CARBON ANODES. V. Eshkenazi and E. Peled, School of Chemistry, Tel Aviv University, Ramat Aviv, ISRAEL; Y. Dai, Y. Wang and S.G. Greenbaum, Physics Dept., Hunter College of CUNY, New York, NY.

Lithium battery anodes based on hard carbon exhibit high reversible capacity ( 500 mAh/g) compared to graphite. Hard carbon samples were prepared by pyrolysis of cotton cloth at 1000C in several heating steps. Samples were lithiated in an electrochemical cell with a lithium counter electrode and EC/DEC:LiAsF6 electrolyte. The intercalation (voltage vs. capacity) curve exhibits two different regions: a sloping one, from l. l to 0.1 volts (vs. Li/Li+) denoted as the high voltage region (HVR), and a plateau between 0. l and zero volts, denoted as the low voltage plateau (LVP). Lithium-7 high resolution (magic angle spinning) NMR measurements in fully lithiated samples reveal three main features: a broad line at ca. 50 ppm, a relatively sharp line at 17 ppm, with a ''shoulder¹¹ at about zero ppm (all shifts relative to aqueous LiCI) The 50 ppm component is attributed to a disordered (as reflected in the NMR line width) graphite-like LiC6 phase and is associated with the LVP part of the voltage curve. The 17 ppm signal arises from a Li site which resides in hydrogen-containing regions of the carbon, as verified by proton decoupling measurements, and is correlated with the HVR part of the curve. The zero ppm component is attributed to the irreversible portion of the Li (up to 20% of the total) which constitutes the solid electrolyte interface (SEI) on the surface of the carbon grains formed by electrochemical reduction of the electrolyte. These spectral assignments were verified by running several samples which were electrochemically delithiated to varying degrees. Further information on the composition of the SEI was obtained by XPS measurements.

10:45 AM Y9.9 
LITHIUM-7 NMR STUDIES OF CONCENTRATED LiI/PEO-BASED SOLID ELECTROLYTES. Y. Dai and S. Greenbaum, Department of Physics, Hunter College of CUNY, New York, NY; S.A. Bajue, Department of Physical Sciences, Medgar Evers College of CUNY, Brooklyn, NY; D. Golodnitsky, G. Ardel, E. Strauss and E. Peled, School of Chemistry, Tel Aviv University, Tel Aviv, ISRAEL.

Highly concentrated polymer electrolytes based on poly(ethylene oxide) LEO) md Ld, with EO/Li ratio 3, were investigated by differential scanning calorimetry (DSC), powder x-ray diffraction (MD) and 7Li solid state nuclear magnetic resonance (NMR) methods. The effect of 15 nm particle size Al203 additives and in several cases, other constituents ethylene carbonate and poly(methylmethacrylate) on structure and Li+ ion environment was explored. The addition of Al203 suppresses the formation of crystalline phases, including free LiI, which is present in EO/Li = 1.5 samples without Al203. The conductivity jump observed in these concentrated electrolytes at around 80C is correlated with an NMR-observed transition to a Li+ environment which is similar to that of free ions in a molten phase.

11:00 AM Y9.10 
ELECTROCHEMICAL AND SPECTROSCOPIC EVALUATION OF LITHIUM INTERCALATION IN TAILORED POLYMETHACRYLONITRILE CARBONS. Kevin R. Zavadil and Ronald A. Guidotti, Sandia National Laboratories, Albuququerque, NM; and William R. Even, Sandia National Laboratories, Livermore, CA.

One of the challenges of tailored carbon development for lithium ion battery applications is minimization of the irreversible loss of lithium. Losses occur because electrolyte decomposition and subsequent passive layer formation, along with metallic lithium phase formation, can occur at intercalation potentials. Successful design of a carbon electrode requires relating these losses to the surface activity and bulk structure of the carbon. The establishment of such a relationship requires the use of monolithic carbon electrodes and contiguous processing/characterization methods to eliminate concerns of electrode additive effects and secondary chemistry unrelated to electrochemical events. A method has been developed to allow for both electrochemical and spectroscopic evaluation of tailored carbon monoliths in a contiguous fashion by coupling solution and vacuum environments. Polymethacrylonitrile-divinylbenzene (PMAN) derived carbon electrodes have been evaluated in a 1M lithium hexafluorophosphate, ethylene carbonate, dimethylcarbonate electrolyte. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) have been used to examine the extent of passive layer formation at the surface and the degree of lithium intercalation into the bulk. Cyclic voltammetry shows that lithium deposition/intercalation begins at an overpotential several hundred millivolts negative of the reversible lithium couple. This behavior is similar to lithium deposition on highly oriented pyrolytic graphite (HOPG) and glassy carbon. Spectroscopy shows that sigificant electrolyte decomposition occurs along with passive layer formation and provides insight to the decomposition mechanism. Comparison of data obtained from PMAN-derived carbons, HOPG and glassy carbon allows a distinction between deposited and intercalated lithium and an estimation of the irreversible lithium loss. The relationship between the surface activity and the structure of these carbons to the efficiency of intercalation and the extent of lithium loss will be presented.

11:15 AM Y9.11 
STUDIES ON LITHIUM INSERTION INTO NON-GRAPHITIZABLE CARBON FIBERS AS ANODES OF RECHARGEABLE LITHIUM-ION BATTERIES. Toshifumi Kawamura, Tomoji Hosotubo, Hideyuki Nakajima, Advanced Materials Division, Petoca, Ltd., Kamisumachi, Ibaraki, JAPAN; Kuniaki Tatsumi, Yoshihiro Sawada, Hiroshi Ishikawa, Osaka National Research Institute, Ikeda, Osaka, JAPAN.

Several non-graphitizable carbons heat-treated at ca. 1200C give capacity higher than that of LiC6 with a significant capacity showing a plateau in the charge-discharge curves below 0.1 V (the plateau capacity). We found that non-graphitizable carbon fibers heat-treated between 1000 and 1200C also display capacity higher than the capacity of LiC6 (372 mAh g-1) with a significant value of the plateau capacity below 0.1 V. Furthermore, 7Li-NMR analysis showed that the plateau capacity below 0.1 V corresponds to the formation of a new species of lithium. In this paper, the Li insertion into several types of non-graphitizable carbon fibers were examined with galvanostatic charge-discharge cycling test in EC/DEC mixed electrolyte containing 1 mol dm-3 LiClO4. In addition, chronopotentiograms of charge-discharge curves were recorded in order to evaluate the plateau capacity below 0.1 V. Although each non-graphitizable carbon fiber clearly gave the plateau capacity below 0.1 V, the carbon heat-treated between 1000 and 1200C showed a maximum of the plateau capacity in each type of non-graphitizable carbon fiber, respectively. The relationship linking the plateau capacity and the structural change of the carbon fibers during heat-treatment will be discussed.

11:30 AM Y9.12 
X-RAY ABSORPTION INVESTIGATIONS OF THE ATOMIC AND ELECTRONIC STRUCTURE OF LixMn2O4 FOR Li RECHARGEABLE BATTERIES.. Craig R. Horne, Elton J. Cairns, Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA; Uwe Bergmann, Stephen P. Cramer, Structural Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA; Brenda J. R. Weiss, Physics Dept., University of California, Davis, Davis, CA; and Melissa M. Grush, Physics Dept., University of Tennesse, Knoxville, TN.

Li insertion involves transport and accomodation of a Li cation and an electron, therefore both atomic and electronic structure play a role in the insertion reaction. The changes in local atomic and electronic structure resulting from Li insertion of LiMn2O4 was characterized by an array of X-ray absorption spectroscopy (XAS) techniques to explore the structure-property interrelationship of LixMn2O4. The XAS techniques employed include XANES (Mn K-edge, Mn L2,3-edge, and oxygen K-edge), and EXAFS (Mn K-edge). Among the findings are the presence of a dynamic Jahn-Teller effect at the Mn(III) site of LiMn2O4 and evidence that the degree of covalency increases in LixMn2O4, x>1.8.

11:45 AM Y9.13 
OPTICAL EXCITATIONS OF LiCoO2 SINGLE CRYSTALS. J.D. Perkins1, D.M. Trickett2, T.F. Ciszek1, M.L. Fu3, C.T. Rogers3, J.M. McGraw2, J.-G. Zhang1, P.A. Parilla1 and D.S. Ginley1, 1National Renewable Energy Laboratory, Golden, CO; 2Colorado School of Mines, Golden, CO; 3University of Colorado, Boulder, CO.

While LiCoO2 is one of the most promising cathode materials for rechargeable Li-ion batteries, many open questions persist regarding the interrelationship of the electronic, structural and battery properties. To better understand the basic electronic structure of LiCoO2, we are conducting visible and infra-red optical transmission and reflection measurements on LiCoO2 single crystals. The plate-like single crystals, grown via solution growth using a Li2O flux, have lateral dimensions up to 1.5 cm with the thickness ranging from 5 - 400 m. As-grown or cleaved surfaces can be shiny and optically smooth. Thin crystals are partially transparent in the visible. Optical reflection and transmission spectra of as-grown crystals have been measured from 300 nm to 25 m at temperatures ranging from 10 to 300 K. Work is underway to electrochemically extract Li from the crystals, and, if successful, will enable measurements of the optical spectra as a function of Li content.

Chairs: Bruno Scrosati and Kuniaki Tatsumi 
Thursday Afternoon, December 4, 1997 
America Center (W)

1:30 PM *Y10.1 
TIN-BASED ALLOYS AS ANODE MATERIAL FOR SECONDARY LITHIUM-ION BATTERIES. O. Mao and J. Dahn, Departments of Physics and Chemistry, Dalhousie University, Halifax, CANADA.

A recent breakthrough in anode materials for secondary Li-ion batteries was to use tin oxide composites[l,2], which have a much higher capacity compared to the conventional anode material (graphite). In this contribution, tin alloys are evaluated as anode materials. Alloys and intermetallic phases were prepared from tin and powders of other metals. We report our results on a variety of systems.

2:00 PM *Y10.2 
COMPARISON OF CARBON AND METAL OXIDE ANODE MATERIALS FOR RECHARGEABLE LI-ION CELLS. C.-K. Huang1, J. S. Sakamoto2, M. C. Smart1, S. Surampudi1, and J. Wolfenstine2, 1Jet Propulsion Lab., California Institute of Technology, Pasadena, CA; 2University of California, Irvine, Dept. of Chemical and Biochemical Engineering, Irvine, CA.

Carbon materials are widely used as anodes in Li-ion rechargeable batteries. Recent developments suggest that certain metals oxides can also be used as anodes in Li-ion cells. At JPL, we are currently investigating the use of tin oxides (SnO and SnO2) as anodes. Preliminary results revealed that the initial amount of Li that can react with 1 mole of SnO and SnO2 is 6.25 and 8.2 moles, respectively. This leads to the following possible reactions: 6.4 Li + SnO=Li2O + Li4.4Sn and 8.4 Li + SnO2 =2Li2O + Li4.4Sn. As a result, it seems that Li insertion into tin oxides forms Li-Sn alloys surrounded by Li2O. The irreversible Li capacities are 2.2 moles of Li per mole of SnO and 5.3 moles per mole of SnO2. Consequently, SnO (4 moles of Li per mole of SnO) has a higher reversible specific capacity than SnO2 (3 moles of Li per mole of SnO2). Preliminary data reveals that SnO has a reversible capacity exceeding 600 mAh/g at potentials between 0 and 0.6 volts versus Li. This is twice the capacity obtained with carbon anodes (300 mAh/g). Some potential reasons for the large irreversible Li loss in SnO and SnO2 are: 1) the formation of Li2O and 2) the loss of some of the anode material as a result of the volume change when Li reacts with the Sn. The irreversible Li capacity of tin oxide anode materials was found to be insensitive to electrolyte composition but is highly dependent on electrolyte type. In the case of Li-ion cells containing carbon anode materials, the irreversible capacity during the first cycle is due to electrolyte decomposition, which results in the formation of a film on the carbon surface. This irreversible capacity is highly dependent on the electrolyte type and composition. In this paper, the Li reaction mechanism, effect of electrolyte type and composition, effect of particle size, effect of binder amount on the capacity, and cycle life performance of tin oxide and carbon anode materials will be compared and discussed in depth.

2:30 PM Y10.3 
NEW7Li-NMR EVIDENCE FOR LITHIUM INSERTION IN DISORDERED CARBON. Shenglong Wang, Hisaji Matsui, Yuji Matsumura, Fundamental Research Laboratories, Osaka Gas Co., Ltd., Osaka, JAPAN; Tokio Yamabe, Division of Molecular Engineering, Faculty of Engineering, Kyoto University, Kyoto, JAPAN.

7Li-NMR spectroscopy can provide meaningful information for the nature of lithium species in lithiated carbon anode and especially for the equilibrium arrangements of littium species at low temperature. We try to measure the Li Knight shift by the solid-state magic-angle spinning 7Li-NMR at various temperatures and to disclose equilibrium arrangements of lithium species in the carbon. For lithium intercalated graphite only one band at 45.6ppm was observed at room temperature and even at 100°C. However, one broad band at 81.0 ppm for lithiated disordered carbon was observed at room temperature while three bands at 18.7 ppm, 71.5 ppm and 148.5 ppm were clearly observed at 100C. The results of theoretical calculations show that lithium species located between graphitic layers are most stable and fully ionized, and lithium species located at the edge of the graphitic layers are less positive than those located on the surface of a crystallite. The band at 18.7 ppm is assigned to lithium species located between graphitic layers. The bands at 71.5 and 148.5 ppm may be assigned to the lithium species located on the surface of a crystallite and at the edge of the graphitic layers, respectively. The result gives direct evidence for the model which explain why the discharge capacity of the carbon electrode with a disordered structure as an anode can exceed the theoretical capacity of graphite anode in lithium ion rechargeable batteries.

2:45 PM Y10.4 
INVESTIGATION OF LITHIUM INTERCALATION INTO MICROPOROUS CARBONS BY SOLID STATE NMR. Sophia E. Hayes, Hellmut Eckert, Dept. of Chemistry, Univ. of California, Santa Barbara, CA 93106; William R. Even, Robert W. Crocker, Sandia National Laboratories, P.O. Box 969, Livermore, CA 94550; Ronald Guidotti, Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185; Zhengming (John) Zhang, Eveready Battery Co., P.O. Box 45077, Westlake, OH 44145.

7Li Solid state nuclear magnetic resonance (NMR) has been utilized to probe the structure of carbon-based materials for lithium-ion electrodes. Disordered and turbostratic carbon materials have become a focus of interest because they appear to allow for significantly higher intercalation levels. Previous studies have shown that emulsion-derived copolymers of poly-methacrylonitrile/divinylbenzene are stable, highly crosslinked systems and can serve as suitable polymeric precursors for the disordered carbon materials used as electrodes. Lithium is electrochemically intercalated into these materials, with the carbon electrodes being cycled by constant current lithiation and delithiation, achieving different levels of intercalation (generally greater than 450 mAh/g). We are investigating the effect of the microstructure of these carbons on the intercalation process, the role of matrix atoms other than carbon, and the local environments and spatial organization of the lithium ions. Our study focuses on the relationship between microstructure and performance of these materials. NMR is an ideal structural tool for addressing these questions, being an element-selective, inherently quantitative method, sensitive to local environments. 7Li magic-angle spinning (MAS) NMR studies carried out in this context are able to distinguish clearly between those lithium atoms that are reversibly intercalated and those that are unable to participate in the intercalation due to parasitic processes. The preliminary results obtained here so far suggest that beyond its utility for quantitatively discriminating between reversibly and irreversibly intercalated lithium species, 7Li NMR might become a very useful tool for assessing and differentiating between various types of charging states in lithium insertion compounds of amorphous carbon materials. Further NMR studies are in progress, which will address the spatial distribution of the intercalated lithium species, and specific interactions between the lithium atoms and defect states arising from the presence of hydrogen or nitrogen species in the amorphous carbon materials.

3:00 PM Y10.5 
HYSTERESIS OF VOLTAGE AND HEAT GENERATION BEHAVIOR IN LITHIUM-ION BATTERIES. Yoshiyasu Saito, Kiyonami Takano, Katsuhiko Kanari, Ken Nozaki, Electrotechnical Laboratory, Tsukuba, JAPAN.

Thermal safety is one of important issues on lithium-ion batteries. In order to characterize heat generation behavior of a lithium-ion cell during charge and discharge, calorimetry was applied. A twin-type calorimeter, C-80 (SETARAM), was used, and commercial cell, US14500 (SONY Energytec. Inc.), was charged and discharged in the sample holder. During charge and discharge cycling under constant condition, reproducible results were obtained in calorimetry. The heat was consisted of mainly two factors. One of them was the electrochemical polarization at the interface between electrolyte and electrodes, and the other was the electrochemical reactions, especially entropy change of the reactions. However, when the cell was charged and discharged under various conditions, the influence of the history was observed in heat generation behavior. The test cell showed hysteresis during charge and discharge in its voltage, and the heat generation had relation to this hysteresis. We have discussed the experimental results of the calorimetry and other electrochemical measurements, and conclude that the thermal behavior correlated with the voltage hysteresis is caused by the reaction in the negative electrode. A hard carbon is used in the test cell, and we are going to discuss the heat generation mechanism in the lithium-ion cell considering the reaction in the hard carbon electrode.

3:15 PM Y10.6 
A NOVEL METHOD FOR OBTAINING A HIGH PERFORMANCE CARBON ANODE FOR Li-ION SECONDARY BATTERIES. Tsutomu Takamura, Petoca, Ltd. Advanced Material Div, Tokyo, JAPAN; Koji Sumiya, Yoichiro Nishijima, Junji Suzuki, Kyoichi Sekine, Rikkyo Univ, Dept of Chemistry, Tokyo, JAPAN.

In an attempt to provide a carbon anode for Li-ion batteries whose high rate performance is greatly improved we examined the effect of evaporated film of chemically stable metals which can afford to absorb Li atom. The surface of carbon fibers prepared from mesophase pitch at 3100C was covered with an evaporated film of Au, Sn, Ag, etc. The entire surface of the fiber could be covered by the metal film by which almost of the chemical entities originally present on the surface could be masked. The film thickness was controlled by monitoring with a quartz vibrating micro-balance. The Li dope/undope performances were evaluated with cyclic voltammery (CV) and constant current test mainly in EC/DMC mixed electrolyte containing 1 M LiClO4 Pristine sample gave a sharp cathodic and anodic current peaks on the CV diagram, the latter being located at around 250mV, which is attributed to the undoping of intercalated Li in the spacing of inter-graphen planes. Repeated CV diagrams showed a gradual deterioration of the cycle performances. In contrast, when we covered the surface of carbon fiber with an evaporated film of metal such as Au, Sn. Ag, etc. the cycleability as well as the reaction rate were markedly improved. These features were dependent on the film thickness whose preferable value was around 200-400 Åin the most enhanced case the deintercalation peak was splitted into two sub-peaks showing a stepwise deintercalation beginning with the stage 1 followed by that of stage 2. Mechanism of the process will be discussed in detail.

3:45 PM Y10.7 
LOCAL STRUCTURE AND MORPHOLOGY OF DISORDERED CARBONS. A. Claye, Y. Sorek, P. Zhou and J. E. Fischer, Department of Materials Science and Engineering and Laboratory for Research and Structure of Matter, University of Pennsylvania, Philadelphia, PA.

Some disordered carbon materials exhibit Li capacities superior to graphite. We used x-ray and neutron diffraction, small angle neutron scattering, transmission electron microscopy and electron spin resonance to try to understand the origin of the high capacity. Neutron radial distribution function analysis and TEM reveal a universal building block consisting of small flat graphene monolayer regions whose size and shape correlate with ball milling parameters. In materials with low residual H and low spin density, we infer that these fragments must be edge-connected to form a ribbon-like or potato-chip structure. The size and connectivity of the fragments play a major role in controlling the pore size and density, which in turn correlates positively with capacity in oxidized materials derived from coal-tar pitch, and in ball-milled graphite. On the other hand, SANS data rule out the hypothesis that Li fills the pores. RDF analysis of lithiated samples suggests that the crystal compound LiC6 may not be a valid model for any of the Li uptake channels in disordered carbons. Supported by Mitsubishi and Hughes Aircraft Co.; work done in collaboration with the groups of J.-M. Tarascon and J. R. Dahn.

4:00 PM Y10.8 
STRUCTURES AND ELECTRONIC PROPERTIES OF LITHIUM-DOPED CARBON MATERIALS. Tokio Yamabe, Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, JAPAN, Institute for Fundamental Chemistry, Takano, Sakyo-ku, Kyoto, JAPAN.

Amorphous carbon materials have been highlighted as an anode material of the Li rechargeable battery. In spite of a number of research efforts, the Li storage mechanisms of these carbon materials are still unclear due to their disordered structure. We have investigated the carbon material prepared at relatively low temperature (hydrogen-containing carbon) with various experimental methods. For further understanding of the Li storage mechanism, we analyze the relationship between the microscopic Li configuration and the electronic structure based on molecular orbital calculations. Review of the representative Li storage models proposed and our calculational results will be presented. The discussion concerns: (i)effect of the edgestructure of a carbon plane, (ii)difference in stability and ionicity of Li ions located at the carbon plane and those located in-between the carbon planes, (iii)effect of covalent-bond nature through the 2p atomic orbital of a Li dopant, and (iv)interpretation of the low-temperature 7Li NMR spectra.

4:15 PM Y10.9 

Mesophase pitch-based Carbon Fibers(MPCF) have been investigated as anode materials for lithium secondary cells by examining their physical and electrochemical properties. Discharge capacity and initial charge-discharge efficiency of the materials were studied in relation to the heat treatment temperatures of MPCF. MPCF heat treated at about 3000C gave high discharge capacity over 310mAh/g, good efficiency (93%) and superior current capability of 600 mA/g (6mA/cm2). On the other hand, to improve the battery capacity, Boron was doped to the fiber about several % by adding B4C to the pre-carbonized milled fibers and then heat-treated up to 3000C in Ar. The structure of Boron-doped fibers was characterized and compared with that of non-doped standard fibers, and also Li ion battery performances are evaluated. The Boron-doped MCF indicated improvement in crystallite thickness and increased discharge capacity as high as 350mAh/g. The voltammograms of both fibers are different from each other. The cell mechanism is discussed based on the unique structure of Boron-doping to the MPCF is very effective for the battery performance.

4:30 PM Y10.10 
COMMERCIAL COKES AND GRAPHITES AS ANODE MATERIALS FOR LITHIUM-ION CELLS. D.J. Derwina, P. Zaleskia, Kim Kinoshitab and Tri D. Tranc, aSuperior Graphite Co., Chicago, IL; bEnergy and Environmental Division, Lawrence Berkeley National Laboratory, Berkeley, CA; cChemistry & Materials Science Department, Lawrence Livermore National Laboratory, Livermore, CA.

Commercially-available cokes and graphics were examined as lithium intercalation compounds for use in lithium-ion rechargeable cells. The coke; materials were investigated in propylene carbonate-based electrolytes and the graphitic materials were studied in ethylene carbonate/dimethyl carbonate based solutions to prevent exfoliation. The reversible capacities of disorder cokes are below 230 mAh/g and those for many highly-ordered synthetic and natural graphites approached 372 mAh/g (LiC6). The irreversible capacity losses vary between 15 to as much as 200% of reversible capacities for various types of carbons. Heat-treated petroleum cokes with average particle size of 10 m showed marked improvements in reversible capacity for lithium intercalation. The electrochemical characteristics are correlated with data obtained from scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface area analyses. The electrochemical performance, cost, availability and manufacturability of a number of these commercial carbons will be discussed.

4:45 PM Y10.11 
ELECTROCHEMICAL PROPERTIES OF NITROGEN-SUBSTITUTED CARBON AND ORGANOFLUORINE COMPOUNDS. Tsuyoshi Nakajima, Meiten Koh and Koichi Dan, Division of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, JAPAN.

Nitrogen-substituted carbon CxN was synthesized by CVD using acetonitrile with nickel catalyst at 800-1100C. CxN-coated graphite was also prepared by CVD using surface-oxidized natural graphite powder. Li+ ion intercalation and deintercaletion reactions were examined of these materials in 1 M LiC104 EC/DEC(1:1) at 25C with metallic lithium as the counter and reference electrodes. The discharge and charge curves gradually decreased and increased with lithium ion intercalation and deintercalation. As the nitrogen content in CxN decreased, the profiles of charge-discharge curves approached that of natural graphite. The CxN-coated graphite demonstrated a low and nearly constant potential in the similar manner to that of natural graphite in the lithium ion deintercalation reaction and the gradual increase in the potential at the end of the process, having a higher charge capacity than natural graphite and comparable cycleability to that of natural graphite. The effect of organofluorine compounds was investigated at 0C and -5C by adding some fluoroesters to 1 M EC/DEC by 5-10 volt. Cyclic volammetry and constant current charge-discharge cycling showed that the low temperature characteristics were significantly improved by addition of the small amounts of fluoroesters, which may be due mainly to decrease in the viscosity by addition of fluorocompounds. Small currents due to the reduction of fluoroesters were observed at around 1 V at first cycle.

Chair: Daniel H. Doughty 
Friday Morning, December 5, 1997 
America Center (W)

8:00 AM *Y11.1 
THERMAL STABILITY OF LITHIUM ION ELECTRODE MATERIALS IN ORGANIC SOLVENTS. M.N. Richard and J.R. Dahn, Departments of Physics and Chemistry, Dalhousie University, Halifax, Nova Scotia, CANADA.

The possibility of future large scale applications for lithium ion batteries requires that the thermal stability of these batteries be determined. This knowledge becomes necessary in order to predict the behaviour of the batteries when they achieve high temperatures as would be attained in large systems where heat dissipation for the material in the center of the system is a problem. Information on the thermal stability of MCMB materials, LiCoO2 and Conoco XP Coke, as a function of lithium content and electrolyte type, has been reported previously by Moli Energy(1,2). Their data was obtained using an Accelerated Rate Calorimeter (ARC) from Columbia Scientific Instrumentation. They also proposed a simple model for the self heating rate observed in the materials(1). Using an ARC, we've collected data similar to that of the MCMB in (2), however, we've observed that the data in (2) is incomplete and hence that the proposed model is incomplete We propose an alternate model, consisting of a two step reaction, to explain the observed self heating rate.

8:30 AM *Y11.2 
EFFECT OF HF IN LiPF6 BASED ELECTROLYTES ON THE PROPERTIES OF SURFACE PASSIVATION FILMS FORMED ON GRAPHITE ELECTRODES IN Li SECONDARY BATTERIES. Tomohiro Sato, Marc Deschamps, Hitoshi Suzuki, Hitoshi Asahina and Shoichiro Mori Mitsubishi Chemical Co, Tsukuba Research Center, Ibaraki, JAPAN.

Interest in the formation of the solid electrolyte interphase (SEI) on graphite electrode has recently increased to improve the performance of lithium ion batteries. It is well known that surface passivating films play a key role in the cycling of lithium ion cells. We examined the effect of HF in conventional LiPF6/EC+DEC electrolyte on the cell cyclabilities and properties of surface films formed on synthetic graphite as an anode. The contents of LiF in SEI were affected by the HF concentration in the electrolyte. Higher F content in the SEI was observed in the case high HF electrolyte was used, although the irreversible capacitiy were nearly the same.The cell ciclability was significantly improved when SEI contained larger amount of LiF. These results indicate that HF content in LiPF6 based electrolyte strongly influences not only the property of SEI but also the performance of graphite electrode.Characterization of SEI formed in different HF content electrolytes and charge-discharge performance of synthetic graphite will be discussed in detail.

9:00 AM Y11.3 
SUBSTRATE EFFECTS ON PASSIVE-FILM FORMATION IN 1M LiPF6/EC-DMC SOLUTION. Ronald Guidotti, Gerry Nelson, and David Ingersoll, Sandia National Laboratories, Albuquerque, NM.

There is currently considerable worldwide effort aimed at development of carbon materials suitable for Li-ion anodes in rechargeable batteries for consumer products, such as cellular telephones. These materials have intrinsic advantages over elemental Li as anodes in that they have a longer cycle life and they do not suffer from dendrite formation on recharge which can lead to cell shorting. These materials are used in electrolytes composed of aprotic organic solvents, typically cyclic ethers such as ethylene carbonate (EC), propylene carbonate (PC), and dimethylcarbonate (DMC) with various dissolved Li-salts. During the first intercalation of Li ions into the carbon, irreversible reduction processes are observed which give rise to passive film formation. These initial losses can account for more than half of the initial charge passed in the first cycle. To obtain a better understanding of the role that the passive film plays in Li-ion cells, the reduction processes were studied using a number of metal and carbon materials as substrates. These included Cu, Ni, Mo, 304 stainless steel, glassy carbons, and highly oriented pyrolytic graphic (HOPG) in 1M LiPF6/EC-DMC (1:1 v/v). The Cu and stainless steel were of particular interest since Cu is used in most commercial cells and both metals are used in test-cell configurations for characterization of carbon. Film formation was examined as a function of applied potential, down to voltages where Li deposition was observed. The films were then examined ex situ using secondary ion mass spectroscopy (SIMS) and Fourier-transform infrared spectroscopy (FTIR), for correlation to the electrochemical properties. Complex-impedance spectroscopy was used as a complementary analytical technique. Atomic force microscopy (AFM) was used to study in-situ film formation in real time. The results of electrochemical characterization and spectroscopic examination will be presented and the significance of film formation discussed.

9:15 AM Y11.4 
APPLICATION TO LITHIUM BATTERIES OF TERNARY SOLVENT ELECTROLYTES WITH ETHYLENE CARBONATE-1.2-DIMETHOXYETHANE MIXTURE. Yukio Sasaki, Nobuyuki Yamazaki and Minoru Handa, Department of Industrial Chemistry, Faculty of Engineering, Tokyo Institute of Polytechnics, Atsugi, Kanagawa, JAPAN.

The electrolytic conductivity and the lithium cycling efficiency of lithium electrode were examined in ternary solvent electrolytes containing LiClO4, LiCF3SO2 and LiPF4 with ethylene carbonate (EC) - 1,2-dimethoxyethane (DME) equimolar binary mixture at 25C. The solvents applied to EC-DME mixture are dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,3-dimethyl-2-imidazolidinone (DMI), 1-methyl-2-pyrrolidinone (NMP), 1,3-dioxolane (DOL) and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL). The molar conductivities in these electrolytes appeared to be mainly influenced by the dielectric constants of mixed solvents. The lithium cycling efficiences in ternary electrolytes containing LiPF4 became higher than those in ternary electrolytes containing LiClO4 and LiCF3SO2. For example, the efficiences in DMI and TFDOL systems containing LiPF4 were about 75% at more than 30 cycle numbers. In addition, the efficiencies in ternary solvent electrolytes containing mixed electrolyte were liable to become higher compared with those in ternary electrolytes containing a kind of electrolyte. The efficiency in LiPF6 + LiCF3SO2/ EC-DME-DEC electrolyte was beyond 75% over the wide cycle range. The efficiency in LiPF4 + LiClO4 / EC-DME-DMC electrolyte was about 80% at the 40th cycle. The lithium electrodeposition on the Ni (working) electrode surface in binary and ternary solvent electrolytes by cyclic voltammetry was observed by atomic force microscopy (AFM). The formation of dendrite lithium after several cycle numbers in these solvent electrolytes containing LiPF4 become much higher than that in electrolytes containing LiClO4 and LiCF3SO2. This means that the lithium cycling efficiency at lower cycle numbers was dependent on the morphology and composition of films formed on electrode rather than the formation of dendrite lithium.

9:30 AM Y11.5 
PYRROLE COPOLYMERS WITH ENHANCED ION DIFFUSION RATES FOR LITHIUM BATTERIES. Paul Calvert, Zack Gardlund, Trey Huntoon, Department of Materials Science and Engineering, H.K. Hall and Anne Padias, Department of Chemistry, University of Arizona, Tucson, AZ.

Copolymers of pyrrole and polyether-substituted pyrroles have been tested as cathodes for lithium batteries. Electrodes were tested in a propylene carbonate/lithium perchlorate electrolyte with lithium anode and reference electrodes. Constant-current and constant-voltage charge and discharge cycles showed that the copolymers sustained higher charge and discharge rates. This can be attributed to a higher diffusion rate of perchlorate ions within the cathode. Potential decay measurments indicate a diffusion coefficient one order of magnitude higher than for the same ion in polypyrrole. Compared to polypyrrole, the copolymers show a higher potential at a given ion concentration and a higher threshold for degradation. In consequence the energy density associated with the copolymer electrodes is about 75% higher than for polypyrrole.

9:45 AM Y11.6 
LITHIUM ION DIFFUSION THROUGH GLASSY CARBON PLATE. Minoru Inaba, Syunsuke Nohmi, Atsushi Funabiki, Takeshi Abe and Zempachi Ogumi, Dept. of Energy and Hydrocarbon Chem., Grad. Sci. of Eng., Kyoto University, Kyoto, JAPAN.

The diffusion coefficient of lithium ion in carbonaceous anode is one of the important parameters that determine the performance of lithium-ion cells. In this presentation, we report a novel method called the electrochemical permeation method to measure the diffusion coefficient of lithium ion in carbonaceous materials. As a test electrode, we used a glassy carbon plate (Tokai Carbon, HTT = 2000C, thickness = 1 mm), which is a typical hard carbon. The cell was composed of two compartments, which were filled with 1 M LiC104/EC + DEC. The electrode separated the two compartments and was used as a bipolar electrode. The potential at one surface was stepped from 1 V to a lower potential, while that at the other surface was kept at I V where no lithium insertion occurs. Lithium ion was inserted from the stepped face, and extracted from the other face. The current transient for lithium-ion permeation was monitored. The insertion potential was successively lowered to 0 V (build-up curves), and then stepped back in the reversed direction (decay curves). The diffusion coefficient was determined by fitting the transient curves with theoretical curves. When the potential was stepped from between 0 and 0.5 V, transient curves were well fitted with the theoretical ones. The diffusion coefficient was of the order of 10-8 cm2 s-1. In contrast, when the insertion potential was stepped across 0.5 V, significant deviations were observed in both build-up and decay curves. The deviations were considered to be due to the presence of tap sites of lithium ion in the carbon.

10:15 AM Y11.7 
NOVEL APPROACH TO ANODE MATERIALS: THE POLYMER-OXIDE COMPOSITE ALTERNATIVE. T.A. Kerr, F. Leroux, and L.F. Nazar, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Ontario, CANADA.

Molybdenum trioxide provides a flexible layer structure for the insertion of conductive polymers. Recently, nanocomposites of the type [poly(aniline)]MoO3 and [poly(pyrrole)]MoO3 have been studied for their application as the cathode material in lithium rechargeable batteries. The results suggest that the polymer enhances Li diffusion giving rise to a smaller polarization and better kinetics from that of the pristine transition metal oxide. We have applied this approach lo anode materials using {poly(para-phenylene) (PPP)MoO3} composite of which both components, individually, can intercalate Li at low voltage. From the inorganic component consideration, metal oxide-based anodes are able to accommodate large amounts of lithium, presenting reversible capacities of >700 mAh/g. These large capacities are associated with polarization problems at low potential, which restrict their applicability as Li ion battery electrodes. In order to enhance the poor electronic conductivity of the metal oxide upon charging, PPP is introduced to the MoO3 material by a ``chimie douce'' route. Herein we present the results of the first polymer-oxide composite, [PPP]MoOx, to be used as the anode material in a lithium battery. The electrochemical response will be described by the cycling performance of the electrodes (reversibility and cyclability) as well as the influences of polymer content, and its polymer derivative forms within the composite.

10:30 AM Y11.8 

Conventional lead-acid batteries contain separators derived from the extrusion processing of polyethylene/oil/silica mixtures. After extraction of the oil phase (i.e.,diluent), a porous polyethylene/silica separator is formed. In this study, we have produced polyethylene/silica separators using different types of precipitated silica and examined their pore size, mechanical properties, and electrical performance.

10:45 AM Y11.9 
IONICALLY CONDUCTING GLASSES WITH SUBAMBIENT GLASS TRANSITION TEMPERATURES. Rensl E. A. Dillon, Duward F. Shriver, Department of Chemistry and Materials Research Center, Northwestern University, Evanston, IL.

Cryptands and crown ethers were employed to form ionic glassy electrolytes. These cation encapsulating macrocycles were added to the Li(+), Na(+) and K(+) salts of N-(3-Methoxypropyl)trifluoromethanesulfonamide (MPSA) in a 1:1 ratio. An amorphous complex was formed when there was a mismatch in size between the cavity of the macrocycle and that of the cation. For example, the 1:1 complex of LiMPSA (lithium cation radius0.78 ) and 2.2.2 Cryptand (2.2.2 Cryptand cavity radius1.44 ) has a low glass transition temperature (T(g)= -50C) and no apparent melting point. The properties of this complex are remarkable given the relatively high melting points (T(m)) of the individual components, LiMPSA (T(m)= 256C) and 2.2.2 Cryptand (T(m)= 73C). The introduction of a small amount of a polar polymer (poly(bis[methoxyethoxyethoxide]phosphazene)) or polyelectrolyte (poly(sodium-4-styrenesulfonate) into this ionic glass imparts improved viscoelastic properties resulting in a rubbery electrolyte. The room temperature (25C) ionic conductivity (1x10(-5) S cm(-1)) of the electrolyte is maintained over the range of 10 to at least 30 mol% of the polymer or polyelectrolyte.