Nippon Telegraph & Telephone Corp
Integrated Info & Energy Sys Labs
Tokyo, 180-8585 JAPAN
Paul Scherer Inst
Villigen PSI, CH-5232
Li Battery R&D
Sandia National Labs
Albuquerque, NM 87185
Dept of Applied Chemistry
Tokyo Univ of Agriculture & Tech
Koganei, Tokyo, 184-8588 JAPAN
Dept of Chemistry & Physics
Univ of Waterloo
Waterloo, ON N2L 3G1 CANADA
Proceedings published as Volume 575
of the Materials Research Society
Symposium Proceedings Series.
* Invited paper
SESSION CC1: CATHODES I
8:30 AM *CC1.1
FIRST-PRINCIPLES STUDY OF PHASE STABILITY AND ELECTROCHEMICAL
PROPERTIES IN LITHIUM-METAL OXIDES. Gerbrand Ceder , Anton Van der Ven,
Massachusetts Institute of Technology, Department of Materials Science
and Engineering, Cambridge, MA.
Chairs: Daniel H. Doughty and Linda F. Nazar
Monday Morning, April 5, 1999
Metropolitan II (A)
Many of the properties of insertion electrodes can be
directly computed with first-principles methods. Such computations are
solely based on the basic laws of Physics and therefore require no experimental
data. This makes them particularly suitable for predicting the properties
of novel or incompletely characterized materials. We have recently demonstrated
the applicability of first-principles methods to predict the Li-insertion
potential and the phase stability in lithium-metal oxides. This has already
been used to predict the insertion behavior of previously untested compounds.
We present first-principles results for the phase stability in the LixCoO2
and LixMnO2 systems. In LixCoO2
we predict the occurence of staging at low Li concentrations. In LiMnO2
we find that anti-ferromagnetism plays an important role in stabilizing
the orthorhombic structure. Calculations are also highly effective instyding
the electronic changes that occur in the material upon lithiation. While
Li insertion in LixCoO2 transfer an extra
electron to the t2g band of the material we find that the net-electron
increase is largely located around the oxygen ions. This is due to the
increased ionicity of the cobalt-oxygen bond upon lithiation. We demonstrate
how this effect relates to important cathode properties such as the average
lithiation voltage and the variation of lattice constant with Li content.
9:00 AM *CC1.2
LITHIUM NICKELATE ELECTRODES FOR LITHIUM BATTERIES. Hajime
Arai , Yoji Sakurai, NTT Integrated Information and Energy Systems Laboratories,
Tokai, Ibaraki, JAPAN.
Lithium nickelate is a promising electrode material for
secondary lithium batteries (especially for portable applications) because
of its high oxidation power of about 4 V vs. Li/Li+ and large
capacity of more than 150 mAh g-1. However, several problems
have to be solved before use in commercial systems, such as synthesis difficulties
and low thermal stability. This study aims at finding keys to solving these
problems, and we demonstrate the importance of structural information of
the material. Stoichiometry of the sample (x in Li1-xNi1+xO2)
greatly affects its electrode performance and phase transition during lithium
extraction. The best composition LiNiO2 is difficult to attain
and several methods for minimizing x value are shown. The excess lithium
method is particularly of interest because it offers almost stoichiometric
materials by calcination in air. Thus obtained material shows a large capacity
of over 200 mAh g-1 with a good cycle stability.
The thermal stability of Li1-yNiO2
is relatively lower than that of Li1-yCoO2
because much lithium can be easily extracted from LiNiO2. We
use both electrochemically and chemically delithiated samples for examining
the mechanism of the thermal decomposition at around 200C
and discuss the instability of Ni3+ compared to Co3+.
The characteristics of lithium nickelate drastically
changes upon substitution of the third metal element (cobalt, manganese,
etc.) for nickel. This substitution technique is used to overcome the shortcomings
of LiNiO2 described above, especially the thermal stability.
Several examples, in which both large capacity and high thermal stability
are attained, are shown and discussed.
9:30 AM CC1.3
PREPARATION AND ELECTROCHEMICAL CHARACTERIZATION OF LiCoO2
SINGLE CRYSTAL PARTICLES PREPARED BY SUPER CRITICAL WATER SYNTHESIS (SCSW).
Kiyoshi Kanamura , Tokyo Metropolitan Univ, Dept of Applied Chemistry,
Tokyo, JAPAN; Katsunori Toyoshima, Yukiya Hataku, Tadafumi Adschiri, Kunio
Arai, Tohoku Univ, Dept of Chemical Engineering, Sendai, JAPAN.
Various kinds of transition metal oxides have been utilized
in rechargeable lithium batteries as both cathode and anode materials.
Most of oxides have been prepared by heating a mixture of transition metal
nitrates, carbonates, and hydroxides under 500-800C.
Such oxides have a lot of defects, crystal grain boundaries, aggregation
and so on. In this study, we prepared single crystal particles of transition
metal oxides by using supercritical water synthesis (SCWS) and investigated
their electrochemical behaviors in nonaqueous electrolytes in order to
realize ideal cathode and anode materials for rechargeable lithium batteries.
LiCoO2 is used as a cathode material of recently commercialized
``Lithium Ion Batteries'' Firstly, we prepared LiCoO2 single
crystal particles using SCWS method. Aqueous solutions of CoNO3
and LiOH were used as starting materials. NO3- ions
work as oxidant reagent to produce Co3+ from Co2+.
The synthesis was performed under various conditions. The best conditions
for well-developed single crystal particles were Li / Co mole ratio of
15.0 at 400C in 30MPa. Scanning
electron microscopic observation showed a formation of single crystal particles
of LiCoO2 with a hexagonal symmetry. The electrochemical characteristics
of the LiCoO2 were analyzed by cyclic voltammetry. Well-defined
anodic and cathodic current peaks were observed, indicating that the prepared
single crystal LiCoO2 has an adequate performance as cathode
materials of rechargeable lithium batteries. Moreover, the discharge and
charge cycle test was conducted using coin-type cell. The prepared LiCoO2
showed more excellent cycleability than any other polycrystalline particles.
This means that imperfect existing in polycrystalline particles cause failures
of active materials (transition metal oxides).
10:15 AM *CC1.4
SYNTHESIS AND CHARACTERIZATION OF LITHIATED NICKEL BASED
METAL DIOXIDES AS POSITIVE ELECTRODE MATERIALS FOR LITHIUM ION BATTERIES.
Koji Nishio , Toshiyuki Nohma, Shin Fujitani, Sanyo Electric Co. Ltd.,
New Materials Research Center, Hirakata, Osaka, JAPAN.
Lithium secondary batteries using carbon as a negative
active material and LiCoO2 as a positive active material have
attracted a considerable interest as a power source for portable appliances
including notebook PCs, cellular phones and VCRs. One key toward higher
performance with larger capacity, longer cycle life and lower cost is alternation
of the positive active material. From this point of view, lithiated nickel
based metal oxides [Li (Ni1-x-yCOxMny)
O2] were investigated as a positive active material. They were
synthesized by sintering a mixture of nickel based hydroxide containing
cobalt and/or manganese and lithium hydroxide in an oxygen atmosphere at
a temperature between 750C and
900C, and the electrochemical
characteristics and thermal stability were examined. Li(Ni0.7Co0.3)O2
sintered at 850C exhibited a highly
crystallized phase structure and the largest electrochemical discharge
capacity of 165mAh/g at the charging up to 4.3V vs. Li/Li+.
Capacity decrease was observed for Li(Ni0.7Co0.3O2
sintered at a higher temperature of 900C.
Rietveld analysis of X-ray diffraction profiles indicated that the capacity
decrease can be attributed to occupation of lithium site by Co and or Ni.
Thermal stability of the active materials charged up to 4.5V vs. Li/Li+
was characterized by measuring decomposition temperature by TG analysis.
Introducing manganese into Li(Ni0.7Co0.3)O2
to form Li(Ni0.6Co0.3Mn0.1)O2
elevated the decomposition temperature from 208C
to 220C without capacity reduction.
A cylindrical test cell (diameter:18mm, height:65mm) using Li(Ni0.6Co0.3Mn0.1)O2
as a positive active material was fabricated and its charge/discharge characteristics
were examined. The test cell showed an initial discharge capacity of 1700mAh
and the capacity retention was larger than 80
at 300 cycles, which is competitive to the conventional cells using LiCoO2
in charge/discharge cycle performance.
10:45 AM *CC1.5
SHORT-RANGE STRUCTURAL ASPECTS OF LITHIUM ION BATTERY
ELECTRODES DERIVED FROM NUCLEAR MAGNETIC RESONANCE AND X-RAY ABSORPTION
SPECTROSCOPIES. S.G. Greenbaum , Y. Wang, S. Kostov, S.H. Chung, S. Calvin,
S.A. Bajue, M.L. denBoer and P.E. Stallworth, Physics Dept., Hunter College
of CUNY, New York, NY.
Structural studies of materials utilized in lithium battery
technology are often hampered by the lack of long-range order found only
in well-defined crystalline phases. Powder x-ray diffraction, while being
an indispensable technique in the characterization of cathode materials,
yields only structural parameters that have been averaged over hundreds
of lattice sites. Our laboratory utilizes synchrotron x-ray absorption
(EXAFS and NEXAFS) and solid state nuclear magnetic resonance (NMR) methods
to investigate structural and chemical aspects of lithium ion cathodes
and anodes. Both spectroscopic methods are element- (or nuclear-) specific
and both are sensitive to small variations in the immediate environment
of the ions being probed. In the case of cathode materials, EXAFS is utilized
to study the transition metal ion, while NMR, with a few notable exceptions
such as vanadium, is generally applicable to the local surroundings of
the Li+ ions. NMR and EXAFS methods have been applied to studies
of Li insertion mechanisms and solid electrolyte interface formation in
carbonaceous and SnO-based anodes, and in several classes of cathode materials.
Among the latter are Li1-xCoO2, Li1-xNiO2
with various levels of metal substitution for Ni, and LixV2O5
in both crystalline and amorphous forms.
11:15 AM CC1.6
IN-SITU X-RAY DIFFRACTION STUDIES ON Li ION BATTERY CATHODES.
Daniel H. Doughty , David Ingersoll, Mark A. Rodriguez and Timothy Boyle,
Sandia National Laboratories Albuquerque, NM.
There is high interest in Li based oxides such as LiMn2O4,
LiCoO2, and LiNiO2 for use as cathode materials in
secondary battery cells. The dynamic behavior of these materials within
the confines of the battery cell is of great importance in determining
failure mechanisms as well as in providing possible avenues for modification
and improvement in capacity. Structural behavior of the crystalline lattice
can significantly affect the electrochemical potential (as in voltage)
has great potential for leading to an understanding and improved performance
of Li-ion cells. We report a simple technique for XRD measurements on Li-ion
cathodes using an electrochemical cell designed for in-situ x-ray analysis.
Cells prepared using this cell design allow investigation of the changes
in anode and cathode structure during charge and discharge. We will describe
the variation in lattice parameters along voltage plateaus and consider
the structural changes in terms of the electrochemical results on each
cell. In-situ analysis of a variety of cathode materials as well as our
chemically synthesized powders will be compared using the in-situ cell.
*Sandia is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin Company, for the United States Department of Energy under
11:30 AM CC1.7
IN-SITU RAMAN SCATTERING STUDIES OF Li INTERCALATION
IN TRANSITION METAL OXIDE CATHODES. J.D. Perkins 1, C.S. Bahn1,
J.M. McGraw2, P.A. Parilla1, H. Yu1 and
D.S. Ginley1, 1National Renewable Energy Laboratory,
Golden, CO; 2Colorado School of Mines, Golden, CO.
We report here the application of in-situ Raman scattering
for monitoring transition metal oxide electrodes during charge and discharge
cycling. Using a LN2 cooled CCD array detector, a useable Raman
scattering spectrum can be measured in a minute whereas the typical electrochemical
cycling time is an hour or so. Hence, an in-situ diagnostic permits essentially
continuous measurements of the Raman scattering spectrum during cycling
to provide insight into the cycling induced structural and electronic changes.
The system employs an air cooled Ar-ion laser operating at 488 nm along
with a single grating spectrometer equipped with a cooled CCD detector.
An 180 degree back-scattering geometry is used with a holographic notch
filter to reject the scattered laser light. V2O5
and Li1-xCoO2 thin films grown by pulsed laser
deposition have been examined. As Li is intercalated into V2O5
during discharge to 2 volts, there is a general, but not concurrent, decrease
in the intensity of the multi-line V2O5 Raman spectrum.
In addition, at intermediate voltages, new lines appear in the spectrum.
In LiCoO2, as Li is extracted during charging, the spectrum
decreases about 60% in intensity but with no spectral change until x =
0.25, at which point the spectrum abruptly vanishes. This may be due to
a metal-insulator transition associated with the end of the 3.9
volt two-phase charging plateau. This work was supported by U. S. Department
of Energy, office of Basic Sciences contract #DE-AC36-83CH10093.
11:45 AM CC1.8
LITHIUM DIFFUSION MEASUREMENTS IN HIGH QUALITY LiCoO2
THIN FILMS. C.S. Bahn , J.D. Perkins, D.S. Ginley, National Renewable Energy
Laboratory, Golden, CO.
Chronoamperometry measurements have been performed on
high quality, textured LiCoO2 films deposited by pulsed laser
ablation. We have examined the rate of lithium diffusion as a function
of Li content. Data was taken using a computerized potentiostat/galvanostat
with a sealed teflon cell employing an EC-DC electrolyte with lithium perchlorate.
For the undoped LiCoO2 diffusion measurements were taken between
3.8 - 4.2 V for both the charge and discharge cycles allowing the cell
to reach electrochemical equilibrium between measurements and with the
cell held at potential between the experiments. We will report the dependence
of the diffusion constant across this whole range. The data was highly
reproducible as a function of potential cycle for a number of cycles. We
could distinguish a number of regions in the diffusion data as a function
of potential. Of key interest is that when the potential stepped across
regions where theory predicts cation ordering we saw inflection points
in the diffusion data. For some of these ordering transitions this may
be the first direct experimental evidence for the predicted transitions.
In the region near 3.95 V vs. Li we observe very complicated behavior.
This is expected as this is a two phase region where most of the Li extraction
and doping occurs. While most of the potential range shows extremely high
reversibility in this region it appears that there is irreversible behavior
which may be associated with capacity loss. This work is supported by U.S.
Department of Energy, Office of Basic Sciences contract #DE-AC36-83CH10093
SESSION CC2: CATHODES II
1:30 PM *CC2.1
ELECTROCHEMICAL LITHIUM INTERCALATION INTO Nb2O5
CATHODE FOR 2 V CLASS-SECONDARY LITHIUM BATTERIES. Naoaki Kumagai , Nobuko
Kumagai and Shinichi Komaba, Dept. of Applied Chemistry and Molecular Science,
Faculty of Engineering, Iwate University, Morioka, JAPAN.
Chairs: Brett Ammundsen and M. Stanley Whittingham
Monday Afternoon, April 5, 1999
Metropolitan II (A)
Niobium pentoxide was synthesized by heating niobium hydroxide
in the temperature range from 600 to 1100C.
The crystal system of Nb2O5 compounds depended on the heating temperatures,
i.e., hexagonal, orthorhombic and monoclinic Nb2O5
compounds were obtained at ca. 600, 800 and >1000C,
respectively. Electrochemical lithium intercalation into the three Nb2O5
compounds was investigated in an lithium perchlorate-propylene carbonate
electrolytic solution for the application as lithium battery cathodes.
As a result, they displayed good charge-discharge performance as the cathode
of 2 V class-lithium battery, which will play important role in power supply
for IC memory backup developed recently. The thermodynamics and kinetics
of the lithium intercalation into the Nb2O5 cathode
and their characteristics have been investigated. The thermodynamic parameters,
such as interaction energies between ions, the crystal lattice parameters
and the kinetic parameters, such as chemical and self diffusion constants,
have been deduced as a function of x-value in the LixNb2O5.
These results were compared to those of the Nb2O5
thin film electrode prepared by r.f. sputtering method, which has high
potential for fabricating thin micro-batteries.
2:00 PM *CC2.2
SOLUTION-BASED SYNTHESIS OF MANGANESE OXIDE CATHODES
FOR LITHIUM BATTERIES. Arumugam Manthiram , Jaekook Kim, Texas Materials
Institute, Univ of Texas at Austin, TX.
The high cost and toxicity of cobalt demand the development
of alternate cathode hosts for rechargeable lithium batteries. Manganese
oxides are attractive in this regard as manganese is inexpensive and environmentally
benign. But the spinel lithium manganese oxide that has been pursued intensively
over the years tends to lose capacity on cycling due to the lattice deformation
caused by Jahn-Teller distortion. Our laboratory is involved in utilizing
solution-based, low-temperature synthesis procedures to obtain manganese
oxide electrode hosts that can overcome some of the difficulties encountered.
The low-temperature approach accesses metastable phases that are otherwise
inaccessible by conventional procedures and offers smaller particle size
with unique microstructures that give better electrochemical cyclability.
The reduction of alkali metal permanganates with alkali metal iodides in
both aqueous and nonaqueous media as well as oxidation of manganese acetate
with lithium peroxide in aqueous medium to obtain amorphous and crystalline
manganese oxides will be presented. The amorphous manganese oxides obtained
in nonaqueous medium exhibit capacity over 300 mAh/g in the range 4.3 -
1.5 V with excellent capacity retention. Unlike several crystalline manganese
oxides, the amorphous manganese oxides do not transform to the spinel phase
on cycling. The manganese oxide obtained in aqueous medium gives a nanocomposite
on firing at moderate temperatures, which exhibits a capacity of about
200 mAh/g in the range 4.3 - 2.3 V with good cyclability. The oxidation
reactions with lithium peroxide offer 3 V spinel manganese oxides, which
exhibit capacity over 150 mAh/g with excellent cyclability.
2:30 PM CC2.3
THE STABILIZATION OF LAYERED MANGANESE OXIDES FOR USE
IN RECHARGEABLE LITHIUM BATTERIES. M. Stanley Whittingham , Peter Zavalij
and Fan Zhang, Materials Research Center and Chemistry Department, State
University of New York at Binghamton, NY.
Layered manganese oxides have been extensively studied
by many groups because they have the same structure as lithium titanium
disulfide and lithium cobalt dioxide, and readily undergo redox reactions
with lithium. They also offer the possibility of cycling close to one lithium
ion per manganese, thus increasing the available storage capacity by over
50% relative to the manganese oxide spinel or cobalt oxide. However, on
extensive cycling the manganese and lithium ions slowly rearrange from
their ordered configuration becoming more spinel-like. We have shown that
insertion of potassium or other large cations between the manganese dioxide
blocks slows the capacity fade on cycling. Manganese oxide tunnel structures
have been shown to reversibly cycle lithium well, but at a rather low capacity
so inherently stabilization is feasible. A number of approaches are being
used to stabilize the layered structure, including placing atomic pillars
between the oxide sheets, modifying the electronic structure of the manganese
oxide, and the use of crystalline intergrowths. The results of these different
approaches will be discussed. Supported by the Departemtn of Energy through
the Office of Transportation Technology.
3:15 PM *CC2.4
ELECTROLYTIC V2O5: SYNTHESIS, CHARACTERIZATION
AND LI INSERTION BEHAVIOR. D. Guyomard , E. Potiron, A. Le Gal La Salle,
Y. Piffard and A. Verbaere.
The purpose of this study is to identify possible relationships
between the synthesis conditions, the material parameters and the Li insertion
properties of electrolytic V2O5 compounds, called
e-V2O5. e-V2O5 compounds are
prepared by oxidation of an aqueous vanadyl sulfate solution at an inert
electrode, such as Pt or Au. Many experimental parameters, such as bath
temperature, pH, VOSO4 concentration, nature of electrode substrate,
oxidation conditions, have been changed in order to prepare different materials.
A quartz microbalance enables to understand the electrodeposition mechanism
by following the mass growth at the electrode as a function of the various
parameters. Subsequent annealing under air at temperatures below 200C
has been performed. The compounds have been characterized by various complementary
techniques, such as XRD, TGA, DSC, redox titration, XAS and Li insertion
electrochemical measurements. e-V2O5 are layered,
poorly crystallized materials, with a structure closely related to that
of V2O5 xerogels. Their physico-chemical and structural
parameters depend on the experimental synthesis conditions. The Li insertion
properties (reversible capacity, average voltage and cyclability) of e-V2O5
have been studied and related to the material characteristics. The reversible
capacity is slightly influenced by the VIV content of
the compounds and their crystallinity. The cyclability, which is excellent,
has been compared to that of the standard -Li3-xV2O5.
e-V2O5 appears as a promising electrode material
for lithium batteries.
3:45 PM CC2.5
A NEW 4 V MATERIAL FOR LITHIUM BATTERIES. J. Gaubicher , T. Le Mercier,
J. Angenault, M. Quarton, Univ Pierre et Marie Curie, URA-CNRS 1388, Paris,
FRANCE; Y. Chabre, Univ Joseph Fourier, Grenoble, FRANCE.
In search of new positive electrode materials for lithium
batteries we investigated the electrochemical behavior of the
forms of the LixVOXO4 compounds (X=S, P,
As).-VOPO_4appears particularly interesting as it undergoes a
first order transition upon the redox process, at high potential
3.98 V. But from stepwise potentiodynamic cycling and
ex-situ XRD, we found that it presents a specific
behavior on first reduction which is characterized by an extremelylowkinetics.
This result has been attributed to the creation of structural
or electronic defects upon the first cycle which would allow a faster
kinetics upon the next intercalation. Owing to this forming
process upon cycling the capacity increases but still is less than
50 mAh/g after 25 cycles at a nominal C/50
regime, and the kinetics rather low. In fact the first
reduction concerns only a small part of the grains. This part
presents a faster kinetics upon the next reduction which leads to the
intercalation of a virgin part of the grains and then induces the
increasing of the capacity. Thus, in order to restrain
the forming process to the first oxidation, the idea was
to perform a complete first reduction before cycling experiments.
On this basis, we synthesized the isotypic-Li_0.92VOPO_4by
chemical lithiation of-VOPO_4. The Li / -Li_0.92VOPO_4system
then shows interesting cycling properties (90 mAh/gat
C/50at 4V vs. Li^+/Li0) Its electrochemical
behavior is compared to the ones obtained for the Li /-LiVOAsO_4(110
mAh/g at C/50at 4V vs. Li^+/Li0)and
Li /-VOSO_4(close to 80 mAh/gat C/2)
CATHODE MATERIALS. Brett Ammundsen, David Hassell, Paul Pickering, Rudolf
Steiner , Pacific Lithium Ltd, Auckland, NEW ZEALAND; Zhen Liu, Jim Metson,
University of Auckland, Auckland, NEW ZEALAND.
The layered lithium manganese (III) oxide LiMnO2
offers high capacity as an active cathode material in lithium-ion batteries.
We have developed solid state reaction routes to prepare both orthorhombic
and monoclinic modifications of LiMnO2. In the case of monoclinic
LiMnO2, which has a structure analogous to layered LiCoO2,
previously reported synthetic routes have involved a wet chemistry step.
As far as we are aware this is the first example of a monoclinic product
prepared directly by a solid state reaction. The electrochemical characteristics
of these materials have been investigated under different current and voltage
conditions. Both orthorhombic and monoclinic phases show stabilised high
capacities at room and elevated temperatures. The voltage vs. capacity
profiles in the first cycles are characteristic of the different crystal
modifications of the materials. After continued cycling the discharge profiles
in both cases evolve to give 4V and 3V plateaus. These plateaus show different
performance characteristics with respect to temperature and current rate.
The origins of these different behaviours have been investigated in detail
to provide a basis for applications of these materials in lithium-ion batteries.
4:30 PM CC2.7
PULSED LASER DEPOSITION AND CHARACTERIZATION OF LiMn2O4
THIN FILMS FOR APPLICATIONS IN LITHIUM BATTERIES. Deepika B. Singh , R.
Houriet, H. Hofmann, Swiss Federal Institute of Technology, Department
of Materials, Lausanne, SWITZERLAND; Y. Akin, D. Kumar and Rajiv K. Singh,
Department of Materials Science and Engineering, University of Florida,
Most studies focussed on fundamental and developmental
aspects of cathode materials for lithium ion batteries employ porous electrodes
which are made of polymer bonded transition metal oxide powders mixed with
conductors such as carbon. The physical, chemical and electrochemical behavior
of these materials in these studies are affected significantly by the powder
morphology and the presence of carbon and polymeric binders. Therefore
transition metal oxide powders in thin film form, which are dense and contain
no additivies, are promising alternatives to study fundamental characterisitics
of materials for its application in batteries. In this study, we report
the pulsed laser assisted deposition, structural characterization and electrochemical
analysis of LiMn2O4 films grown on silicon and sapphire,
and perovskite based substrates with appropriate metallic interlayers such
as platinum and conducting oxides such as lanthanum nickel oxide. By choosing
the appropriate substrate/buffer layer combination and varying the deposition
conditions, the microstructure of the films can be varied from amorphous
to randomly polycrystalline to a textured high oriented form. The electrochemical
measurments were carried out in a glove box using cyclic voltametry and
AC impedance spectroscopy in a half cell configuration with lithium metal
as an anode and reference electrode and LiMn2O4/LaNiO3/Si(or
sapphire) as a cathode. LaNiO3 films were deposited insitu on
silicon and other substrates prior to deposition of LiMn2O4
films. The microstructural studies were carried out using x-ray diffraction,
SEM, and AFM measurements. The electrochemical properties have been correlated
with the microstructure.
4:45 PM CC2.8
GROWTH AND CHARACTERIZATION OF LiCoO2 THIN
FILM CATHODES USING PULSED LASER DEPOSITION. C.S. Bahn, D.S. Ginley , J.D.
Perkins, P.A. Parilla and H. Yu, National Renewable Energy Laboratory,
LiCoO2 and LiCo0.5Al0.5O2
thin films have been grown by pulsed laser ablation on SnO2
coated glass substrates. For both compositions, the resultant films are
fully dense and uniaxially textured with the Li and Co layers parallel
to the substrate. As a general rule, the growth rate for the and LiCo0.5Al0.5O2
films is roughly four times lower than that for the LiCoO2 films
and the growth temperature on the substrate Ts must be
roughly 100C higher to achieve
a similar grain size. LiCoO2 films have been at grown up to
Ts = 700C and
pO2 = 2000 mTorr. These films have a typical grain size of 250nm.
For constant current cycling between 3.8 and 4.2 volts at 5A,
the LiCoO2 films have an initial discharge capacity of 0.48
Li per LiCoO2 unit cell (131 mAh/g) decreasing to (0.33 Li /LiCoO2
(90 mAh/g) after 100 cycles. We have also studied the growth phase space
with a substrate temperature of 300C
- 700C and an oxygen partial pressure
of 50 mTorr - 2000 mTorr. As a general rule, as both Ts
and pO2 increase, the crystallinity and grain size of the films
increase as well. This is seen quite clearly in SEM micrographs and is
reflected in the Raman scattering signal as well as electrochemical reversibility.
The LiCo0.5Al0.5O2 films grown to date
have roughly 3 times less capacity than the LiCoO2 films as
well as a more rapid capacity loss. This work is supported by U.S. Department
of Energy, Office of Basic Sciences contract #DE-AC36-83CH10093
SESSION CC3: PEM FUEL CELLS
8:30 AM *CC3.1
RECENT PROGRESS IN MATERIALS TECHNOLOGY FOR PROTON EXCHANGE
MEMBRANE (PEM) FUEL CELLS. Swathy Swathirajan , General Motors Global R&D
Center, Global Alternative Propulsion Center, Warren, MI.
Chairs: Hans-Peter Brack and Elton J. Cairns
Tuesday Morning, April 6, 1999
Metropolitan II (A)
Most major automotive manufacturers have recently enhanced
their development efforts in PEM fuel cells because of the need to dramatically
increase energy efficiency and reduce regulated emissions. Major breakthroughs,
needed for achieving techno-economic feasibility of PEM fuel cells for
automotive applications, can be realized mainly through developing novel
materials and processing methods. Material needs in the PEM fuel cell system
consisting of the fuel processor, fuel cell stack, and air, water, thermal
and electrical management subsystems will be briefly discussed. Materials
and catalysis issues for the hydrogen-rich reformate/air and methanol/air
fuel cell systems will be described along with an assessment of the current
state of progress in meeting the challenges of cost, performance and reliability
for automotive applications.
9:00 AM CC3.2
SYNTHESIS OF NEW PROTONIC CONDUCTING POLYMER ELECTROLYTE
FOR EFFICIENT FUEL CELLS. Itaru Honma 1, J.M. Bae2,
M. Murata3, T. Yamamoto3, M. Rikukawa4,
N. Ogata4, 1Electrotechnical Laboratory, Umezono,
Tsukuba, Ibaraki, JAPAN; 2NEDO, 3Hoechst, JAPAN;
4Sophia University, Chiyoda-ku, Tokyo, JAPAN.
Fuel cells are extremely attractive for use in future
transportation owing to their inherently higher efficiency when compared
to that of internal combustion engines. However, the current PEM fuel cells
are also shackled by elaborate water management. At the same time, a major
limitation of the cell comes from the Pt anode electrocatalysts which are
extremely CO intolerant down to the 5 to 10 ppm level. Higher temperature
PEMFC operation reduces CO poisoning of the Pt electrocatalysts by other
condensable species. In this paper, the synthesis of new protonic polymer
electrolyte is reported and the conductive properties at the elevated temperature
with various humidities have been investigated. S-PPBP (Sulphonated Poly(4-phenoxybenzoyl-1,
4-phenylene)) are a remarkable family of isotropic, amorphous, rigid-rod,
poly-para-phenylenes featuring benzenes in the polymer backbone with side
chain substituents. The rigid polymer backbone results in exceptionally
high modulus and strength while the side chain substituents serve to provide
solubility and melt processibility. The protonic conductivities of the
membrane are measured at the temperature range from 50C to 110C with humidity
controlled conditions. The conductive property is almost same as that of
Nafion; the conductivity of 0.001 S/cm was obtained. The Power output measurement
was carried out for MEA of S-PPBP membrane with Pt/C electorodes and 0.5
W/cm2 was obtained at cell temperature of 70C.
9:15 AM *CC3.3
EFFECTIVE SELECTION AND USE OF ADVANCED MEMBRANE ELECTRODE
POWER ASSEMBLIES. Bamdad Bahar, Carlos Cavalca, Simon Cleghorn, Jeff Kolde
, David Lane, Mahesh Murthy, Greg Rusch, W. L. Gore & Associates Inc.,
PRIMEA(r) membrane electrode power assemblies have been
available from W. L. Gore & Associates, Inc. (Gore) since 1995, when
Gore introduced the 5000 series based on the GORE-SELECT(r) composite membranes.
In order to provide the highest power density power assembly, a second
generation PRIMEA* membrane electrode power assembly (series 5510) was
introduced in 1997. Both series 5000 and 5510 power assemblies were designed
for hydrogen/air applications. A third generation of PRIMEA membrane electrode
power assemblies is now available for operation with reformate fuel streams.
All Gore MEAs have been made available with complementary components such
as integral gasketing and gas diffusion media, to maximize product performance
and durability. In this publication, we explore the selection of MEA characteristics
required in common applications. Performance data will be provided on a
range of PRIMEA power assemblies under conditions which should be relevant
to selection and design criteria typically encountered in fuel cell stack
and system development. In addition, examples of successful field demonstrations
of PRIMEA Power Assemblies will be shown in various applications, demonstrating
the scope for system differentiation utilizing one family of MEA products.
This paper is divided into four sections; the first three exploring specific
requirements of portable, stationary and transportation applications and
the fourth section discusses general product issues, such as quality assurance
and manufacturing requirements, as well as ancillary components and associated
9:45 AM CC3.4
10:30 AM *CC3.5
CHEMICAL INTERACTIONS IN IONOMERS AND IONOMER MEMBRANES
CONTAINING METAL PARTICLES AND IONS. William M. Risen , Brown Univ, Dept
of Chemistry, Providence, RI.
Chemical reactions involving oxygen, hydrogen, carbon
monoxide or methanol with metal particles or ions in ionomers based on
perfluorocarbonsulfonic acid ionomers (PFSA), such as Nafion(TM), or sulfonated
styrene-containing ionomers, such as PSSA, will be discussed. Understanding
and exploring these interactions are of particular interest in the design
of new materials for fuel cells containing polymer electrolyte membranes,
especially with regard to the formation and gas-metal reactions in the
membrane-catalyst zone and the issues of crossover, diffusion, and hydration
of the membranes. Reactions of Pt, Rh and Ru particles and ions in Nafion
with CO, of Rh in PSSA with CO, hydrogen and water, and of Ru in PSSA with
CO, hydrogen, oxygen and alcohols will be considered in terms of their
relationships to analogous reactions carried out under other conditions.
The relationship of the information from such gas-ionomer studies to fuel
cell problems and new material design will be discussed.
11:00 AM *CC3.6
NMR AND ELECTROCHEMICAL STUDIES OF CO ON PT AND PT ALLOY
ELECTROCATALYSTS. Elton J. Cairns , Benjamin M. Rush, and Jeffrey A. Reimer,
Lawrence Berkeley National Laboratory and Department of Chemical Engineering,
University of California, Berkeley, CA.
The behavior of CO on fuel cell electrocatalysts is important
in connection with the use of reformed organic fuels in fuel cells. CO
is strongly adsorbed on the electrocatalyst, interfering with the adsorption
and oxidation of the hydrogen fuel, resulting in greatly reduced performance.
The design and development of electrocatalysts that tolerate and/or readily
oxidize CO is essential to achieving high performance under mild conditions.
This work reports on investigations of the adsorption and oxidation of
CO on carbon-supported fuel cell electrocatalyts in 2 M sulfuric acid at
ambient temperature, employing recently developed techniques for the application
of NMR to electrochemical systems. The NMR and electrochemical behavior
of Pt/C, Pt-Sn/C and Pt-Ru/C in the adsorption and anodic oxidation of
CO will be reported and discussed in terms of the surface species formed,
their coverages, and the electrocatalyst composition.
11:30 AM CC3.7
PLATINUM-CATALYZED POLYMER ELECTROLYTE MEMBRANE FOR FUEL
CELLS. T. Jan Hwang , Hong Shao, J. Eric McEntyre, Wen-yi Lin, Jerome J.
Schmitt and Andrew T. Hunt, MicroCoating Technologies Inc., Chamblee, GA.
Catalytic layers composed of precious metal nanoparticles
( 3 nm) were deposited directly on NafionTM membranes by Combustion Chemical
Vapor Deposition (CCVD), a novel, open-air thin film process, well suited
for manufacturing. These layers were intended to serve as electrochemical
catalysts in proton-exchange membrane fuel cells (PEMFC). Activity of trial
catalysts was measured in a small PEMFC cell. Cell performance was studied
as a function of catalyst loading, composition and microstructure, and
compared with state-of-the-art catalyzed membranes available commercially.
An optimal catalyst composition and microstructure was determined that
minimized platinum content and related cost. The potential of the CCVD
process to enable high-volume, low-cost, mass production of PEMFC catalytic
layers will be presented.
11:45 AM CC3.8 DEVELOPMENT OF COMPOSITE MATERIALS
FOR PEFC BIPOLAR PLATES. Deanna Busick and Mahlon Wilson, Los Alamos National
Laboratory, Los Alamos, NM.
Fuel cells are attractive alternatives to traditional
energy sources for both stationary and transportation applications, provided
they can be manufactured at a reasonable cost. The most costly and problematic
components of fuel cell stacks may be bipolar plates. Besides meeting economic
constraints, bipolar plates must possess a host of other properties including
low gas permeability, corrosion resistance, low weight, high strength,
and manufacturability. While we have developed a composite material that
meets these requirements, we recognize a need for further understanding
and development in two areas: mechanical properties and corrosion resistance.
Our baseline bipolar plate material consists of graphite powder embedded
in a thermosetting resin matrix. As such, both corrosion resistance and
mechanical properties are dominated by the matrix, so the choice of resin
in critical. Certain matrix materials are clearly superior to others from
a corrosion standpoint. Most of these matrices provide adequate strength
for stack assembly to unreinforced formulations, but improved strength
and/or rigidity can be achieved, if desired, with fiber reinforcement.
The need to mold flow field channels directly into bipolar plates precludes
the use of continuous fibers. However, certain types of milled microfibers
that are significantly shorter than the flow-field features that must be
resolved can still provide substantial improvements in composite strength.
These fibers do not have nearly the intrinsic strength of traditional reinforcement
fibers such as graphite and glass, yet they are better able to increase
the strength of the composite. Presumably, the improvement arises from
more effective fiber adhesion to the resin binder, but further characterization
of the strengthening mechanism is needed. Additionally, since some of these
fibers are composed of organic material, their effect on corrosion resistance
warrants investigation. With increased understanding of fiber and resin
effects on strength and corrosion resistance, we anticipate continued improvements
in bipolar plate materials.
SESSION CC4: PEM FUEL CELLS/POLYMER ELECTROLYTES
1:30 PM *CC4.1
PEMFC DEVELOPMENT AT ASAHI GLASS CO., LTD. M. Yoshitake
, E. Yanagisawa, T. Naganuma and Y. Kunisa, Asahi Glass Co., Ltd., Chemistry
Research Laboratory, Yokohama, JAPAN.
Tuesday Afternoon, April 6, 1999
Metropolitan II (A)
Asahi Glass Co., Ltd.(AGC) had commercialized chlor-alkali
electrolysis process using perfluorinated ion exchange membranes(Flemion).
AGC participated in the PEMFC program of NEDO(New Energy and Industrial
Technology Development Organization) which started in the fiscal year 1992.
Perfluorinated ion exchange membranes were studied and has been developing
the membrane technology for PEMFC. In this program, AGC selected FlemionR(50m),
S(80m) and T(120m)
as candidates membranes for PEMFC. Thermal stability, mechanical strength,
water content, AC specific resistance and gas permeability were measured.
In this study a standard conditions of membrane pretreatment were proposed
and new measurement methods such as evaluation system for gas permeation
were designed. The area resistance of FlemionS
is about 43 of that of Nafion117
and thermal stability, mechanical properties and gas permeability of FlemionS
are almost equivalent to those of Nafion117.
assembly showed to maintain stable performance for 2,300hr. In order to
obtain high performance MEA (membrane-electrode-assembly), a new binding
technology, ``adhesion method'' was developed, in which special adhesives
by AGC were used and the assemblage was carried out by pressing by weak
force and at room temperature. It was examined that the adhesion method
used in this study can afford smaller decrease in pore volume of gas diffusion
electrode than hot pressing in the assemblage process of the electrodes
and the membrane. Furthermore, better performance was obtained by using
(50m) with higher ion-exchange capacity
Reinforcement technology for perfluorinated membranes has been started
to be developed. It was found that FlemionMc
(PTFE-yarn embedded type) and FlemionUf
(PTFE-fibril dispersed type) can afford improvement in mechanical strength
at moist and high temperature atmosphere. FlemionMc
(100m) was examined to give high cell
performance of 0.65V at 0.5A/cm2, 70C,
1 ata. FlemionMc
electrode assembly showed stable performance during the life test of 1,500hr.
2:00 PM *CC4.2
LOW-COST PEMFC DEVELOPMENT AT SIEMENS - MATERIAL ASPECTS.
Manfred Waidhas , Armin Datz, Ulrich Gebhardt, Rittmar V. Helmolt, Regina
Hornung, Guenther Luft, Siemens AG, Corporate Technology, Erlangen, GERMANY.
Proton Exchange Membran Fuel Cells (PEMFC) in combination
with an electric drive system are being more and more discussed as a potential
solution for a clean and energy-efficient transportation. Exceeding academic
visions car manufacturers meanwhile already demonstrated the technical
feasibility of a corresponding propulsion concept by fuel cell driven prototypes.
Main obstacle for a fast market penetration are the system costs which
currently exceed 104 USD/kW. In order to get any acceptance
among the endbuyer, the highest challenge in the future will lie in the
realisation of costs which will be comparable to ICEs. Diminishing the
material costs plays an important role in the list of potential issues.
Currently used materials have to be replaced by low-cost substitutes. If
this cannot be done, the amount has to be lowered to the required minimum.
For instance, the Pt loading has to be lowered to about 0.2 mg/cm2,
expensive membrane electrolytes have to be substituted by low cost alternatives
and last not least cheapest possible construction materials such as stainless
steel shall be used. In addition, all manufacturing procedures have to
be capable for an automised mass production. For instance, the bipolar
plates will be made by a stamping and punching process, the electrodes
by spraying or screen printing. As a third attempt to realise a commercially
viable SPFC the periphery has to be simplified as far as possible. By realising
corresponding concepts stack costs in the range of 30 USD/kW are conceivable.
Results on the described issues will be shown and discussed. For instance,
the Pt loading of the electrodes could be lowered from 4 mg/cm2
to 0.07 mg/cm2 and an air cooled stack was operated reliably
even under extreme conditions. The bipolar plates in this case were made
of thin sheet stainless steel.
2:30 PM CC4.3
ORGANIC-INORGANIC HYBRID PROTONIC POLYMERIC ELECTROLYTES
GRAFTED BY SULFON-SULFOAMID MOIETIES. Laurent Depre, Christiane Poinsignon
LEPMI-INPG-CNRS Grenoble, FRANCE; Michael Popall, Fraunhofer Institut for
Silicatforschung, Wurzburg, GERMANY.
Thin proton conducting membranes are gained by shaping
an organic-inorganic polymer electrolyte bearing sulfonamide and sulfonic
groups prepared by sol-gel processing and organic crosslinking reactions.
The polycondensation of alkoxysilanes provides the inorganic silica backbone
whereas the organic network is formed from reactive functional groups R'
of alkoxysilanes of R'Si(OR3) type. Sulfon and sulfonamide functionalities
are grafted by cocondensation with alkoxysilanes with corresponding functionality.
Protonic conductivity was measured in the dry and wet state under controlled
temperature and relative humidity: the conductivity increases from 10-4
S.cm-1 in the dry to 6.10-2 S.cm-1 in the wet state at 70°C. The conductivity
dependence on temperature and the associated mechanisms will be discussed
in both states.
2:45 PM CC4.4
CHARACTERIZATION AND FUEL CELL TESTING OF RADIATION-GRAFTED
PSI MEMBRANES. Hans-Peter Brack , Akinori Tsukada, Joerg Huslage, Felix
Buechi, Guenther G. Scherer, Paul Scherrer Institute, Electrochemistry
Dept., Villigen PSI, SWITZERLAND.
We demonstrated earlier that the current-voltage characteristics
of our 30 cm2 active area fuel cells containing our PSI radiation-grafted
membranes are comparable or better than those of these same cells containing
Nafion membranes of similar thickness and operating under the same test
conditions (humidified H2 and O2 gases at 1 atm,
Nafion-impregnated E-TEK electrodes having 0.8 mg Pt/cm2). Long-term
testing of PSI radiation-grafted membranes over periods of up to 5,000
h at 60C and 1,000 h at 80°C
in these 30 cm2 active area cells will be discussed. We have
most recently begun testing our PSI membranes in single cells and two cell
stacks based on components of a 100W PSI power pack that we developed for
educational purposes at Swiss universities and technical colleges. PSI
membranes have been tested to date for up to approximately 1,000 h in stacks
consisting of two 100 cm2 active area graphite cells operating
on H2/O2 at 60C.
Membrane properties have been characterized by means of titration measurements
and infrared and Raman spectroscopy both before and after testing in fuel
cells. A comparison of these membrane properties to date indicates that
little membrane degradation occurs over this period of testing in the graphite
cells. Membrane failure in these 100 cm2 active area graphite
cells has been primarily a result of membrane rupture, probably due to
swelling stresses near the active area (swollen membrane)/gasket (non-swollen)
border. It is noteworthy that thinner Nafion membranes (less than 100 um
thick) can have similar problems in these cells. Efforts are being undertaken
to overcome these problems by both further improving the mechanical properties
of our PSI radiation-grafted membranes and further refinement of our cell
design. Results of our membrane optimization and characterization research
and testing of these membranes in fuel cells and fuel cell stacks will
3:00 PM CC4.5
DEVELOPMENT OF NEW IONOMER MEMBRANE FOR FUEL CELLS APPLICATIONS.
Didier Marsacq , Franck Jousse, CEA-DAM, Dept of Materials, FRANCE; Regis
Mercier, Lyon Univ, Dept of Organic Materials, Lyon, FRANCE; Gerard Gebel,
CEA-DSM, Grenoble, FRANCE; Michel Pineri, CEA-DTA, Grenoble, FRANCE.
Among the different power sources, fuel cell based on
proton exchange membrane appears to be one of the interesting power generating
device. As it was demonstrated for perfluorinated ionomer membrane, sulfonated
polyimides can be used as proton exchange membranes for H2/O2
fuel cells and other selective applications such as ions separation. Polyimides
based on 4,4'-diaminobiphenyl 2,2'-disulfonic acid (BDSA), 1,4,5,8 naphthalene
tetracarboxylic (DNTA) and various diamines were synthesized in order to
find out relationships between solubility in common organic solvents and
polyimide architecture, i.e., chemical nature and arrangement of monomers.
Sulfonated polyimides exhibiting a good solubility in metacresol are obtained
and can be processed by hand-coating. By controlling both the viscosity
of polymer solution and the casting conditions homogeneous membranes with
controlled thickness are prepared. Swelling measurement, ion exchange capacity
and ionic conductivity are examined as regard to the sulfonated polyimide
3:30 PM *CC4.6
POLYMER ELECTROLYTES: ALIVE AND WELL FOR 2000. M. Armand
, D. Baril, N. Ravet, J.Y. Bergeron, S. Beranger, Dept. de Chimie, Universite
de Montreal, Quebec, CANADA; C. Michot, Rhone-Poulenc, Lyon, FRANCE.
As the solvent-free polymer electrolytes battery program
(ACEP®) goes towards commercialization for large batteries destined
to telecommunications and electric vehicles for the turn of the millennium,
it rallies a growing interest at corporate RD
centers worldwide. Though this system was at some time hastily deemed unpractical
when considering the immediate success and performances of the Li-ion (rocking-chair)
batteries for consumer electronics, the safety and cost issues of the latter
system are yet unsolved. Poly(ethylene oxide) based polymers remain the
workhorse of solid electrolytes. The main points which have been addressed
include: identification of
cross-linkable materials via fast processes without introducing chemicals
adversely affecting the electrochemistry.
design of a polymer architecture in which a high crosslink density is attainable
without affecting the conductivity and improving the mechanical properties.
identification of new salts. The best solute today, in terms of electrochemical
performances, is lithium the fluorinated sulfonimide Li(CF3SO2)2N.
An extensive research program has allowed to identify a complete panoply
of new salts whose properties can be fine-tuned to specific applications
and meet the cost requirements imposed for mass production. Also, new anhydrous
proton conductors allow to reconsider the dye-based electrochromic devices.
Today's ``dry'' polymer electrolytes lithium batteries have energy densities
in excess of 150 Wh/Kg for completely equipped systems and power to energy
ratios ranging from one to 12 depending on the temperature of operation
(40 to 80C) and the system design.
The high power system are viable contenders for hybrid vehicles. The different
options in terms of polymer science and electrochemistry offered by these
systems will be discussed.
4:00 PM *CC4.7
POLMER ELECTROLYTES AND THEIR ELECTROCHEMICAL INTERFACES.
Masayoshi Watanabe , Yokohama National Univ, Dept of Chemistry & Biotechnology,
In order to realize all solid high energy density batteries,
polymer electrolytes have received much attention. Especially, it is expected
that application of the polymer electrolytes to lithium batteries could
overcome problems concerned with safety. We have studied to attain highly
ionically conducting polymer electrolytes and developed new network polymer
electrolytes having many chains ends. However, charge transfer resistance
(Rct) between a highly conductive polymer electrolyte
and lithium electrodes is much higher than the polymer electrolyte bulk
resistance, especially at low temperatures. In this study we will discuss
the factors dominating Rct between polymer electrolytes
and lithium electrodes, especially the relationship between the density
of free chain ends in network polymer electrolytes and Rct.
Polymer electrolytes having different densities of free chain ends were
synthesized by photo cross-linking reaction of the mixtures of mono-acrylated
poly(ethylene oxide-co-propylene oxide) (P(EO/PO)) and tri-acrylated P(EO/PO)
in the presence of a lithium salt. Ionic conductivity for the polymer electrolytes
is different, depending on the density of free chain ends in the network
polymer electrolytes, namely the polymer electrolytes having the largest
number of ether side chains show the highest ionic conductivity although
glass transition temperature is not so much deiffenrent. On the other hand,
it is clearly indicated that Rct decreases with increasing
the ionic conductivity. The big difference of Rct between
LiBF4 and the other salts is observed even if the same matrix
polymer is used. On the other hand, in terms of the density of ether side
chains, the polymer electrolytes having the largest number of ether side
chains show much lower Rct. It is suggested that Rct
correlates with the density of ether side chains in the polymer electrolytes.
4:30 PM CC4.8
A NEW FAMILY OF SALTS FOR LITHIUM SECONDARY BATTERIES.
D. Baril , N. Ravet, M. Armand, Dépt. de Chimie, Université
de Montréal, Québec, CANADA; C. Michot, Rhône-Poulenc,
The ideal lithium salt is highly conductive, safe, inexpensive
and easy to make. Furthermore, for a solid polymer electrolyte application
(SPE), the salt is also required to have a plasticizing effect (lowering
effect on Tg and Tm). The choice of
available salts for lithium batteries based on a SPE technology is quite
limited. Lithium bis-trifluoromethanesulfonimide or LiTFSI has already
proven to be successful in this field. Its physical properties and extensive
electrochemical stability show performances that outrun any other lithium
salt. Also, the plasticizing effect of the salt eases the electrolyte processing
when polyethylene oxide (PEO) is used. The price of LiTFSI may however
be of concern for very large scale utilization. We have undertaken an extensive
study of delocalized anions belonging to different chemical families, in
order to understand the charge separation and identify viable alternatives.
This work deals with the synthesis and characterization of a new salt,
lithium N-(3-trifluoromethyl)phenyl-trifluoromethane sulfonamide. Li-TFPTS
is a large delocalized anion whose charge is spread over a single SO2
and a phenyl ring, and its synthesis is relatively straightforward. Li-TFPTS
shows a high degree of solvation in solid PEO which is characteristic of
a low lattice energy salt. Preliminary results show that ionic conductivity
is similar to that of LiCIO4 which derives from an acid 1010
times stronger in water. Also, thermocalorimetric analysis confirms, as
expected, that the TFPTS anion hinders the PEO + salt mixture crystallization.
Physical properties and electrochemical performances of this salt in solid
polymer electrolyte (PEO) will be discussed.
4:45 PM CC4.9
ENHANCED ION MOBILITY IN ALUMINOSILICATE/ POLYSILOXANE
NETWORK POLYELECTROLYTES. David P. Siska , Duward F. Shriver, Northwestern
University, Department of Chemistry, Materials Research Center, Evanston,
A series of novel polysiloxane-based single-ion conductors
containing solvating oligoether sidechains and covalently linked aluminosilicate
or alkoxy/siloxyaluminate anions were prepared and characterized. Our previous
research shows that the weak basicity of the aluminosilicate anion is conducive
to high conductivity. In the present work, we explore the incorporation
of aluminosilicates into a low-Tg polysiloxane framework
to produce high ionic conductivity with t+ = 1. Of the two types
of systems created, those networks containing the aluminosilicate [(SiO)4Al]-
anions show higher room temperature conductivities (10-6 S/cm)
than those with alkoxy/siloxyaluminate [(SiO)2(CH2O)2Al]-
anions (10-7 S/cm), owing to the decreased basicity and increased
flexibility provided by the additional Si-O linkages surrounding Al. Lengthening
the covalent tethers binding the anions to the polymer backbone results
in enhanced room temperature conductivities in the alkoxy/siloxyaluminate
systems, particularly at high ion loadings. The differential scanning calorimetry
data for the two different types of network polyelectrolytes and their
less-constrained counterparts provide a rationale for the improved conductivity.
SESSION CC5: POSTER SESSION
SYNTHESIS AND ELECTROCHEMISTRY OF LAYERED LITHIUM MANGANESE
OXIDES AS CATHODE MATERIALS FOR RECHARGEABLE LITHIUM BATTERIES. Fan Zhang
, Peter Zavalij, and M. Stanley Whittingham, Materials Research Center
and Chemistry Department, State University of New York at Binghamton, NY.
Chairs: Hans-Peter Brack and Linda F. Nazar
Tuesday Evening, April 6, 1999
Metropolitan Ballroom (A)
Lithium ion rechargeable batteries with lithium cobalt
oxide cathode have high energy density and excellent cycle life. But this
cathode is very expensive. There has been much interest in manganese oxides
as cathode candidates for rechargeable lithium batteries. Manganese oxides,
particularly the spinel form, are of particular interest because they readily
intercalate lithium into their structures. However, only 0.5 lithium can
be cycled per manganese atom so that their energy densities are not sufficiently
high. We have synthesized potassium manganese dioxide, both with only manganese
and with 10 or 33% of the manganese substituted by iron, cobalt or nickel
to stabilize the layer structure. Our earlier work showed that the pure
layered phase slowly reverted to a spinel-like phase. These compounds were
then converted to the lithium form either in an electrochemical cell or
by ion exchange. Both the potassium and lithium forms he compounds were
characterized by XRD, Electron microprobe, FTIR, and electrochemistry.
Electrochemical properties and rate capabilities of the materials used
as cathodes for lithium cells will be presented. This work was supported
by the Department of Energy.
SYNTHESIS AND PROPERTIES OF A VANADIUM OXIDE BASED LITHIUM
ION CATHODE. Benjamin Chaloner-Gill and Dale R. Shackle, Rentech Inc.,
San Jose, CA.
The development of high capacity cathode materials for
lithium ion batteries has uncovered three major players, lithiated manganese,
cobalt and nickel oxides and mixtures thereof. In the search for greater
energy storage, we have examined a number of vanadium oxides. Comparing
the ratio of lithium to metal atom in the three compounds listed above
allows for the extraction of 0.5 lithium atoms or less. In other words,
you can extract one lithium atom per two metal atoms. If the cathode is
vanadium based, the number of cycleable lithiums increases to a value closer
to 0.75 - 1.00. Despite the fact that vanadium oxides operate at lower
voltages, a net gain in energy is observed from the use of LixVyOz
over the currently available materials. Lithiation of LiV3O7.9
for use in a lithium ion cell is the focus of this talk. Chemical lithiation
by reducing lithium salt will be described along with analysis, rate data
and electrolyte stability.
MECHANOCHEMICAL SYNTHESIS OF CATHODE MATERIALS FOR LITHIUM
BATTERIES. Nina V. Kosova , Evgeniya T. Devyatkina, Evgenii G. Avvakumov,
Nikolai F. Uvarov, Nikolai Z. Lyakhov, Institute of Solid State Chemistry
and Mechanochemistry, Novosibirsk, RUSSIA; Igor P. Asanov, Svetlana G.
Kozlova, Svyatoslav P. Gabuda, Institute of Inorganic Chemistry, Novosibirsk,
Complex oxides of lithium and transitional metals (manganese,
titanium, vanadium, cobalt, nickel) are perspective cathode materials for
lithium batteries. Usually they are prepared by thermal synthesis. In this
case final products are characterized by small specific surface and unsufficient
electrochemical activity. A new perspective mechanochemical method of synthesis
of these compounds is worked out. The different compounds of lithium (hydroxide,
carbonate and others) and transitional metals (oxides, hydroxides, carbonates)
were used as the initial reagents. The method allows to get high-dispersed,
homogeneous compounds either in the process o f activation or as a result
of preliminary activation and following thermal treatment. The influence
of different factors (chemical, phisical and mechanical) on the process
of synthesis and properties of final products has been investidated. The
changes of lattice parameters, specific resistance, valence state of surface
atoms, lithium position in the lattice and others have been studied by
X-ray analysis, complex impedance method, IR, XPS and NMR spectroscopy.
It has been stated that the intermediate states, arising under the process
of mechanical activation, influenced on the properties of final products.
Materials, prepared by mechanochemical method, exibit high specific surface
and conductivity and are promising for using as a cathode materials in
HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF delta-TYPE
VANADIUM PENTOXIDE STRUCTURES FOR RECHARGEABLE LITHIUM BATTERIES. Fan Zhang
, Peter Zavalij, and M. Stanley Whittingham, Materials Research Center
and Chemistry Department, State University of New York at Binghamton, NY.
Recently, soft chemistry has been shown to be an effective
method for the preparation of high surface area transition metal oxides,
which offer many advantages as cathodes in rechargeable lithium batteries.
The goal of this research project concentrates on the development of layered
vanadium oxides with new structures. The purpose of developing these new
compounds is to apply them as cathode materials in lithium rechargeable
batteries. The high free energy of reaction with lithium and their low
cost makes vanadium oxides attractive materials to replace the expensive
lithium cobalt oxide cathode in commercial lithium batteries. Several synthetic
routes aimed at the formation of delta-type vanadium oxides been examined.
The compounds were synthesized by the reaction of vanadium (V) oxide, tetramethyl
ammonium hydroxide or tetraethyl ammonium hydroxide and transition metal
salt at 165 °C for 60 hours. The manganese was incorporated using TMA
permanganate as the manganese source. The stoichiometry, phase, and structure
of the compounds have been examined as a function of deposition conditions
using XRD, DCP, TGA, FTIR, SEM and EDS. In these double sheet oxides, organic
species do not appear to impede the incorporation of lithium. They readily
react with butyl-lithium solutions. Galvanostatic cycling of composite
electrodes based on these compounds revealed a high charge capacity and
promising cyclability. Electrochemical properties and rate capabilities
of the materials used as cathodes for lithium cells well be presented.
Supported by the National Science Foundation.
CHARACTERIZATION OF ELECTROCHEMICALLY SYNTHESIZED V2O5
FOR LITHIUM BATTERIES. E. Potiron, A. Le Gal La Salle, A. Verbaere, D.
Guyomard and Y. Piffard.
Electrolytic V2O5 materials, called
e-V2O5, are prepared by oxidative electrodeposition
from an aqueous vanadyl sulfate solution. These poorly crystallized materials
exhibit a layered structure showing many stacking faults. The layers are
built up from fragments similar to those observed in the -V2O5
structure. They could be bilayers similar to those observed in -AgxV2O5.
e-V2O5 are mixed valence, hydrated vanadium oxides, containing exchangeable
protons. Their chemical formula can then be written: HxV2O.nH2O
with x0.4, 0<<0.4
and 0<n<1.8. Their water content and interlayer distance (which are
related) depend on the relative humidity. The dehydration process occurs
in three steps. The last one, between 200 and 260C,
coincides with a slow phase transformation leading to -V2O5.
By varying the electrodeposition current density and the duration of subsequent
thermal treatments below 200C,
materials with various V4+/Vtotal ratios can
be prepared. A small part of V4+ cations are vanadyl pentahydrated
ions situated within the interlayer space. The majority part occupies sites
within the anionic layers; they are preferentially oxidized upon a thermal
treatment in air. Prior to electrochemical tests in Li batteries, e-V2O5
are dehydrated at 100C under vacuum
for one hour. Upon this treatment the water content decreases down to 0.4
mole per formula unit for all e-V2O5 materials, leading
to an interlayer distance of 9.8A;
their original V4+ content is maintained.
LITHIUM INSERTION BEHAVIOR OF ELECTROCHEMICALLY SYNTHESIZED
V2O5. Emmanuel Potiron, Annie Le Gal la salle, Yves
Piffard and Dominique Guyomard .
Electrolytic V2O5 have been prepared
by anodic oxidation of VOSO4 solutions. In the 4-2V/Li range,
it is possible to insert 1.5 Li in these compounds in two reversible steps
situated at 2.55 and 3.1 V/Li. Lithium compositions (x) higher than 1.5
are obtained at a lower apparent potential of 1.7 V with a corresponding
equilibrium potential situated in the continuation of the 2.55 V phenomenon,
in accordance with a prolongation of the corresponding solid solution.
The intercalation mechanism was studied by several techniques. X-ray absorption
spectroscopy has shown that lithium intercalation is accompanied by a reversible
increase of the average vanadium-oxygen distance and of the symmetry around
vanadium atoms, correlated to the reduction of V(V) into V(IV). Chemical
diffusion coefficient increases when x is comprised between 0 and 0.6,
stabilizes when x is comprised between 0.6 and 1.2 then decreases when
x is comprised between 1.2 and 1.5, probably in correlation with the steric
hindrance in the interlayer space. The important decrease of the diffusion
coefficient when x is comprised between 1.5 and 1.8 explains the important
polarization observed on the 1.7 V intercalation step. The intercalation
capacity at 2.55V is strongly modified by external parameters such as the
carbon quantity or the intercalation duration in accordance with a smaller
electronic conduction at this voltage. This phenomenon is responsible for
the capacity losses that are observed during cycling. e-V2O5
materials that were studied exhibit the same interlayer distance and the
same water content, and differ only by their V(IV) content. The best results
were finally obtained with samples electrodeposited at 100C,
having the highest V(V) content, and that were not heat treated. They present
good cycling properties, and compete favorably with other vanadium oxides
as cathode materials for lithium batteries.
DEGRADATION REACTIONS IN SONY-TYPE Li-ION BATTERIES.
E. Peter Roth , Ganesan Nagasubramanian, Sandia National Laboratories,
Thermal instabilities were identified in SONY-type Li-ion
cells and correlated with interactions of cell constituents and reaction
products. Three temperature regions of interaction were identified and
associated with the state of charge of the cell. Anodes were shown to undergo
exothermic reactions as low as 100°C involving the solid electrolyte
interface (SEI) layer and the LiPF6 salt in the electrolyte. These reactions
could account for the thermal runaway observed in these cells beginning
at 100°C. Exothermic reactions were also observed in the anodes in
the 200°C - 300°C region between the intercalated lithium and the
LiPF6 salt, followed by a high-temperature reaction region, 300°C -
400°C, involving the PVDF binder and the intercalated lithium. Cathode
exothermic reactions with the PVDF binder were observed above 200°C
and increased with the state of charge (decreasing Li content). This offers
an explanation for the observed lower thermal runaway temperatures for
charged cells. The stability of the PVDF binder as a function of electrochemical
cycling has also been studied using FTIR. We have identified a possible
dehyrofluorination reaction at both the anode and cathode which results
in a more hydrocarbon like polymer. Decomposition of the electrolyte and
subsequent attack of the PVDF has been identified as a possible mechanism
for this observed change.
SYNTHESIS AND ELECTROCHEMICAL CHARACTERIZATION OF LiNixCo1-xO2
POWDERS OBTAINED BY COMPLEX SOL-GEL PROCESS. F. Croce, F. Ronci, University
`La Sapienza', Department of Chemistry, Roma, ITALY; A. Deptula , W. Lada,
T. Olczak, Institute of Nuclear Chemistry and Technology, Warsaw, POLAND;
A. Ciancia, A. Di Bartolomeo.
The layered oxides, among the wide family of intercalation
compounds, have received considerable attention as positive electrode materials
in high-energy density lithium and lithium ion batteries. Within this frame
LiNiO2 and LiCoO2 oxides and their solid solutions
have been extensively studied as they (and the LiMn2O4
spinels) are the only known materials able to intercalate reversibly lithium
at high cell voltage (3.5-4 V). Recently, solid solutions such as LiNixCo1-xO2
have attracted the attention as alternative cathodes to the state of art
LiCoO2 in commercial rechargeable Li-ion batteries1.
These solid solutions LiNixCo1-xO2
can be successfully prepared using various synthesis ways: mainly by solid
state reactions involving the mechanical mixing of precursors salts and/or
oxides followed by high temperature firing and extended grinding. Nevertheless
the preparation of high `battery quality' material is not easy as the stoichiometry,
the oxygen deficiency, but also grain size and the morphology2
can have great influence on the cell reversibilty and capacity: they both
largely depend upon sample treatment. Low temperature synthesis techniques
have specifically been developed for their ability to produce materials
with different structure, powder morphology, bulk density and stoichiometry.
Therefore we have used the Complex Sol-Gel Process (CSGP)3 (CSGP) to prepare
LiNi1-xCoxO2 (x= 0, 0.25,
0.5, 0.75, 1). Starting sols were prepared from Li+-(1-x)Ni2+-xCo2+ acetate
aqueous solution in two different routes. Route-I: aqueous ammonia was
added to a starting solution containing 0.2 ascorbic acid (ASC) M on 1M
SMe. Route-II: the starting acetate solutions were alkalised by ammonia
following by addition of ascorbic acid. Regular sols were concentrated
3 times and dried slowly up to 200C.
After 200h of heating at 170C
monolithic gels are formed. Intensive foaming was observed for samples
prepared by variant I during further heating. In both cases self-ignition
(SIT) takes place at temperatures 380-460C.
It can be noticed that there is no simple relationship between the carbon
content and SIT. Thermal transformation of the gel to solid was studied
by TG, DTA, XRD and IR. The electrochemical properties of some compounds
prepared by the Route-I were evaluated and reported. References 1) C. Delmas
and I. Saadoune, Solid State Ionics, 53-56, 370 (1992) 2) A. Yamada et
al., J. Electrochem. Soc., 142 (1995) 2149 3) A. Deptula et al., J. Material
Res., 11, 1 (1996)
Li DIFFUSION RATES IN AS-DEPOSITED AND CYCLED, CRYSTALLINE
AND AMORPHOUS, V2O5 THIN-FILM CATHODES. J.M. McGraw
, D.W. Readey, Colorado School of Mines, Golden, CO; P.A. Parilla, J.D.
Perkins, D.S. Ginley, National Renewable Energy Laboratory, Golden, CO.
V2O5 exhibits good charge capacities
in both crystalline and amorphous thin films. The open-channeled structure
of crystalline V2O5 and the evolution of its crystal
structure upon Li intercalation are well documented in the literature.
Conversely, amorphous V2O5 has not been studied as
thoroughly. We have measured diffusion rates in amorphous and crystalline
V2O5 films synthesized by pulsed laser deposition.
We have employed chronoamperometric techniques in both as-deposited and
cycled films to evaluate the diffusion constants as a function of Li content
while also evaluating the structural changes in the crystalline and amorphous
films by XRD and Raman spectroscopy. Crystalline films retain their structure
and hold a steady charge capacity when cycled above 2.3 V; however when
cycled below this threshold, the crystalline order quickly deteriorates
as evidenced by XRD and Raman spectroscopy with a concurrent decrease in
charge capacity. In contrast, amorphous films demonstrate little capacity
loss with a very steady charge capacity, losing only 2
of the original capacity over 100 cycles, even with deeper cycles to 1.8
V vs. Li. The diffusion data for both crystalline and amorphous films are
well behaved. Preliminary results indicate that there is a significant
decrease in the Li diffusion rate in crystalline films as Li concentration
increases. In amorphous films, initial experiments indicate that the decrease
in diffusion rates is smaller. We will report the diffusion rates for this
on-going study. This work was supported by U. S. Department of Energy,
office of Basic Sciences contract #DE-AC36-83CH10093.
SURFACE-MODIFIED MANGANESE DIOXIDE FOR ALKALINE-MANGANESE
BATTERY. Jun Nunome , Takuya Nakashima, Hiroshi Yoshizawa, Yoshiaki Nitta,
Matsushita Battery Industrial Co., Ltd., Technology Laboratory, Osaka,
Manganese dioxide for positive active material of Alkaline
manganese battery is low-priced and show excellent performance. In order
to achieve higher capacity of Alkaline manganese battery, many researchers
have studied about characterization of manganese dioxide, electron conductive
agents, and some additives. One of the causes to be a lesser discharge
capacity of manganese dioxide in Alkaline-manganese battery was considered
to be a polarization due to the formation of Hetaerolite which was produced
at near the end of discharge. The object of the present study is to achieve
higher capacity of alkaline-manganese battery by employing positive active
material which has been applied with surface modification by doping Titanium
element to manganese dioxide. The synthesis of the surface-modified manganese
dioxide was obtained by introducing electrolytic manganese dioxide into
the solution which consists of H2SO4 and Ti(SO4)2,
stirring for a few hours at 70C.
In order to investigate the characteristics of specimen, the characterization
was performed by using EXAFS(extended X-ray absorption fine structure),
Raman spectroscopy and ESR. The analysis data suggest the following results.
In Ti-doped manganese dioxide obtained by surface modification, some of
the doped Ti can be displaced partly by Mn, forming M-O bonding in a solid
structure. The electrochemical behavior in the alkaline solution of the
material above mentioned by using the half-cell have shown a less polarization
at near the end of discharge. The result of XRD measurement of the discharged
product has shown a lesser production of Spinel-like composite as ZnOMn2O3
or Mn3O4 in comparison with that of non-modified
case. It was suggested that the suppression of producing by-product such
as Hetaerolite improves the polarization at near the end of discharge.
STRUCTURAL STUDY OF LITHIUM INSERTION IN VANADIUM OXIDES
USED AS CATHODE MATERIALS. Patrick Rozier , Jean-Michel Savariault and
Jean Galy CEMES/CNRS, BP, Toulouse, FRANCE.
Combined soft and solid state chemistry followed by precise
XRD investigations allow us to determine the Li-V-O phase diagram as well
as the structural modifications induced by the insertion of lithium in
silver vanadates. These studies drive to propose an interpretation of the
electrochemical behavior of both LiV2O5
and Li Ag2V4O11
batteries. The and -LixV2O5
phases and -LixV2O5
for x>1 are not confirmed. In the 1<x<3 domain, disproportionation
of V4+, following the reaction 2V4+
V5+ + V3+, occurs as confirmed by the formation of
lithium vanadates and vanadium oxides with an ending mixture, for x=3,
constituted with LixVO2 and Li3VO4.
The different domains are directly related to the different steps observed
in the discharge curve of the LiV2O5
battery. It is also demonstrated that the loss of oxygen occurring in the
Ag2V4O11 vanadate drives to the formation
of a new phase Ag1+xV3O8 instead
of an oxygen deficient form Ag2V4O11-y.
Single crystal XRD structural determination shows that this phase is isostructural
with Li1+xV3O8. Electrochemical
lithium insertion starts with the reduction of Ag+ driving to
the lithiated phase. Comparison with electrochemical behavior of Ag2V4O11
suggests that there is an identical mechanism meaning that whatever the
starting phase used, the main insertion process occurs in Li1+xV3O8
LONG RANGE AND LOCAL STRUCTURE IN TRANSITION METAL (Ti,
Cr, Co)-DOPED LITHIUM MANGANATE SPINELS. Phillip B. Aitchison, Brett Ammundsen,
Deborah J. Jones , Jacques Roziere, Laboratoire des Agregats Moleculaires
et Materiaux Inorganiques, Universitaet Montpellier II, FRANCE; Gary R.
Burns, School of Physical and Chemical Sciences, Victoria University of
Wellington, NEW ZEALAND.
Lithium manganates can accommodate large amounts of substitutional
ions as well as changes in the lithium and oxygen stoichiometry whilst
retaining the spinel crystal structure. Depending on their nature and concentration,
substitutional ions can influence the overall energy of the lattice and
hence the redox potentials of electron transfer processes that occur during
lithium extraction and insertion. They also strongly influence both the
local lattice structure and long range crystalline order, as well as the
structural changes which take place as a result of lithium extraction and
insertion. A range of substituted lithium manganate spinels are known and
many of the relationships between structure and property in these compounds
have been clarified by means of X-ray and neutron diffraction, spectroscopic
and electrochemical methods of characterisation. However, most of these
techniques provide information mainly on the bulk properties and long range
structures, rather than probing the localised effects on electronic and
atomic structure associated with the sites occupied by the substituent
ions. In combination with chemical analyses, and powder X-ray and neutron
diffraction methods to determine the average atomic structure and identify
eventual ordering in the cation sublattice, we have used EXAFS and XANES
spectroscopies to probe the local environment around metal ions in LiMn2O4
substituted with Cr(III), Co(III), Ti(IV) and Ga(III). Using EXAFS, local
relaxation around a substitutional ion not detected by diffraction methods
can readily be identified in materials having a low level of dopant. XANES
allows changes in oxidation state of each metal to be followed as lithium
is extracted and reinserted. Such local structural and electronic modifications,
and changes in symmetry around both substituent and manganese ions, will
be described in relation to bulk chemical and electrochemical properties.
SAFETY AND REACTIVITY OF CARBONACEOUS ANODES FOR LITHIUM-ION
BATTERY. G.Abbas Nazri , Bouziane Yebka, Maryam Nazri, M. David Curtis,
University of Michigan, Department of Chemistry, Ann Arbor, MI; Kim Kinoshita,
Lawrence Berkeley Laboratory, University of California, Berkeley, CA; David
Derwin, Superior Graphite Company, Chicago, IL.
Safety and reactivity of various carbonaceous anodes have
been studied in different combinations of nonaqueous electrolytes. The
electrochemical performance of the anode materials during lithium insertion-extraction
process has been correlated to the structural parameters of the various
natural and synthetic graphites. The long range order of graphitic materials
have been studied using x-ray diffraction, and the local disorder has been
studied using vibrational spectroscopy. The nature of the gel-type film
formed on carbonaceous anodes during initial charge-discharge cycling was
studied using thermal analysis and vibrational spectroscopy. We report
composition and morphology of the gel-type films and effect of various
combinations of solvents and salts on the chemical nature of the film.
TRANSFORMATION OF COBALT HYDROXYDE ADDITIVES DURING THE
REDOX CYCLING OF THE NICKEL HYDROXIDE ELECTRODE. V. Pralong , A. Delahaye-Vidal,
B. Beaudoin, B. Gerand and J.M. Tarascon, Laboratoire de Reactivite et
de Chimie des Solides, UPRES-A, Universite de Picardie Jules Verne, rue
Saint-Leu, Amiens, FRANCE.
Although cobalt hydroxide is currently added to the Ni(OH)2
paste to prepare nickel composite electrode used in Ni-based rechargeable
alkaline batteries, its redox chemistry in alkaline medium is still poorly
documented. As an attempt to better understand how such additives improve
the nickel electrode performances, the Co(OH)2/CoOOH/Co3O4
has been further investigated through 1) simulations of redox reaction
by using chemical oxidizing and reducing agents and 2) electrochemical
cycling of the cobalted phases. The structural features of the reaction
products were found to be strongly dependent upon the reaction kinetics,
which is controlled by the experimental conditions, namely, temperature,
oxidizing agent and reaction time for chemical simulations and charge-discharge
rate for electrochemical reactions. For instance, starting from Co(OH)2,
a non-stoechiometric CoOOH highly conductive phase can be obtained either
chemically by means of a strong oxidizing agent (NaClO) or electrochemically
using relative high charging rates (>C/5). Special experimental cases leading
to the formation of the Co3O4 phase to the expense
of the b-CoOOH phase will also be described. Finally, the electrochemical
signatures vs. Cd of the differently made CoOOH phases will be reported
and the impact of these findings in optimizing the formation of the Ni-based
cells containing Co(OH)2 additives discussed as well.
TEM INVESTIGATION OF A ZR-BASED BATTERY MATERIAL. Scott
Chumbley , Zhan Shi, Iver Anderson, Ames Laboratory USDOE, Ames, IA; Leonard
Cantrell, Ovonic Battery Company, Troy, MI.
A Zr-based alloys have been developed by Ovonic Battery
Company as a high performance nickel metal hybride negtive electrode material.
Currently High Pressure Gas Atomization (HPGA) is being investigated as
a way to reduce processing costs. This powder has been examined using transmission
electron microscopy (TEM). The TEM investigation showed that the microstructure
consisted of regions of large grains separated by an intergranular phase
and interspersed with regions of extremely fine grain material. The large
grains were found to be FCC cubic with lattice parameter a=7.03
with the intergranular regions being hexagonal with lattice parameter a=4.97,
c=8.11. These findings agree with results
obtained by X-ray powder diffraction. The fine grains remain to be identified
at the time of this writing. The compositions of the large grains and intergranular
regions were also analyzed using EDS. The results indicate that segregation
of Zr, Ti, V, Mn, Cr occurs, with the intergranular phase being depleted
in V, Cr and Mn and enriched in Ti and possibly Zr. The amount of Ni remains
approximately the same in both phases. The microstructure and composition
of as-received HPGA powder will be compared to that of heat treated HPGA
powder and as-received hydrided-dehyrided powder obtained from bulk ingot.
PHASE STABILITY AND HYDROGEN STORAGE CAPACITY OF MULTI-COMPONENT
LAVES PHASE ALLOYS BASED ON ZrNi2. E.P. George , C.T. Liu, Metals
and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN; B.S.
Chao, R.C. Young, S.R. Ovshinsky, Energy Conversion Devices, Inc., Troy,
Multi-component Laves phase (AB2) alloys based
on ZrNi2 are currently under development as battery materials
for electric vehicles. Based on Ovonic's pioneering design principle of
multi-component alloying on the A and B sites, we report here the effects
of substituting Ti and Nb on the A-sites (Zr-sites) and V, Cr, Mn, and
Fe on the B-sites (Ni-sites). Alloys were arc melted and drop cast starting
with commercially pure elemental metals. Dendritic segregation was observed
in the as-cast condition, which can be reduced substantially after a 1-day
anneal in vacuum at 950C. Wavelength-dispersive
spectroscopy was used to study the changes in the chemical composition
as a function of heat treatment. All the alloys investigated were multi-phase,
with the majority phases having the C14 and C15 crystal structures as determined
by X-ray diffraction. Hydrogen storage capacity was measured electrolytically
in a wet cell and capacities ranging from 380 to 420 mAh/g were obtained
depending on the alloying additions. Higher discharge capacities result
when the hydrogen storage sites are controlled using Ovonic's design principle.
Although the microstructure became homogenized after heat treatment, it
did not significantly improve the wet cell capacities. The observed effects
of alloying additions will be discussed in terms of atomic size, electronegativity,
and hydride formation energy. Research sponsored by the IPP program and
the ATP/AMAPP program under subcontract DOE Project No. ERD-96-XJ010 to
Lockheed Martin Energy Research Corp. from Ovonic Battery Company/ECD,
DENSIFICATON AND MICROSTRUCTURE OF La1-xSrxFeO3-d.
Lise T. Sagdahl , Mari-Ann Einarsrud and Tor Grande, Department of Inorganic
Chemistry, Norwegian University of Science and Technology, Trondheim, NORWAY.
The sintering behavior of La1-xSrxFeO3-d,
(x = 0, 0.1, 0.25) has been carefully investigated in order to obtain high
quality target material for sputtering of epitaxial thin films. Densification
has been studied as a function of temperature and partial pressure of oxygen,
and the microstructure and phase composition of the ceramics have been
characterized by SEM and XRD. The temperature width of the optimum sintering
interval decreases with increasing Sr content. Considerable desintering
is observed in the Sr substituted samples above the narrow optimum sintering
temperature interval. Possible transport mechanisms are discussed in the
relation to the densification and the observed desintering.
DIELECTRIC PROPERTIES OF Pd/Y8Z COMPOSITES. M.G.H.M.
Hendriks, H. Verweij, M.P. Timmerman-Oude Wolbers , Inorganic Materials
Science, University of Twente, Enschede, NETHERLANDS.
Dense homogeneous dual-phase composites of an oxygen-conducting
cubic zirconia and a near percolative palladium phase are prepared by conventional
ceramic processing. Such composites are expected to behave as supercapacitors,
due to the large interfacial area between electrodes and electrolyte and
due to the possibility to store additional charge in the electric double
layer. It is expected that in the composites capacitance values of 1 F/cm3
can be achieved. From electrical impedance measurements of the first samples
made, it is found that the capacity of these compacts increases with an
increasing palladium content. In addition, it is observed that at higher
frequencies the composites behave like a true capacitor.
DYNAMIC MECHANICAL SPECTROSCOPY AND IONIC CONDUCTIVITY
STUDIES OF GEL ELECTROLYTES BASED ON STEREOCOMPLEXED POLY(METHYL METHACRYLATE).
Yury K. Yarovoy , Hong Peng Wang, and Stephanie L. Wunder, Department of
Chemistry, Temple University, Philadelphia, PA.
Thermally reversible conducting gel electrolytes, comprising
blends of atactic and isotactic poly(methyl methacrylate) (PMMA), lithium
salt and an organic solvent, have been prepared and characterized. Due
to association between isotactic PMMA (i-PMMA) and syndiotactic sequences
of atactic PMMA (a-PMMA), strong gels are formed in solvents which ordinarily
do not form gels with high molecular weight a- PMMA, namely dimethyl carbonate
(DMC) and diethyl carbonate (DEC). The plot of the dependence of elastic
moduli on the fraction of i-PMMA passes through a maximum at
1:1 molar ratio between isotactic PMMA and syndiotactic fractions of a-PMMA.
However, the conductivity of the gels is invariant to the ratio of i-PMMA
and a-PMMA. Thus, gels with a typical polymer content of 15-20,
1M lithium salt, and a ratio of i-PMMA to a-PMMA of about 1:3 has an ionic
conductivity in the range of 1x10-3 - 4x10-3 S cm-1
and possesses a dynamic elastic modulus one order of magniture higher than
the electrolytes containing only atactic PMMA. This modulus is obtained
at values of the frequency between 0.01 to 100 radians, so that even under
static conditions the gels do not flow and exibit reversible elasticity
to high degree of elongation. Thermal mechanical analysis and calorimetry
of these gels show that the physical crosslinks formed by stereocomplexed
syndiotactic and isotactic triads melt in the range of 65-85C
depending on the nature of the solvent and lithium salt. The fact that
these gel electrolytes are thermoreversible makes them readily processable.
After melt casting they form transparent dimensionally stable, self supporting
RELATIONSHIP BETWEEN CRYSTAL STRUCTURE AND Li+-CONDUCTIVITY
IN La0.5Li0.5TiO3 PEROVSKITE. J.A. Alonso
, J. Ibarra, M.A. Paris, J. Sanz, Inst. Ciencia de Materiales de Madrid,
SPAIN; J. Santamaría, C. León, F.C. Físicas, U. Compl.
Madrid, SPAIN; A. Várez, E.P.S., U. Carlos III, Madrid, SPAIN; M.T.
Fernández, Inst. Laue-Langevin, Grenoble, SPAIN.
Ionic conductivity of LixLa2/3-x/3TiO3
perovskites is one of the highest reported values in lithium crystalline
cm-1 at T= 300K), making these compounds good candidates for
solid electrolites in lithium batteries. The location of Li in the crystal
structure of this family had not been possible up to date from X-ray diffraction
(XRD) data. A neutron powder diffraction (NPD) study on the material with
maximum Li content, Li0.5La0.5TiO3 allowed
us to find out some interesting features of this perovskite. In spite of
the previous cubic description (from XRD data), the neutron patterns at
room temperature show superstructure reflections due to the tilting of
the TiO6 octahedra, corresponding to an orthorhombic symmetry.
The refinement in the Pbnm space group shows that Li cations are asymmetrically
located at A positions of the perovskite, occupying tetrahedral voids,
with Li-O bondlengths between 1.85 and 2.12 A, and large thermal B factors
( 4 A2). The temperature
dependence of 7Li NMR spectra shows that below 75C
the experimental line-width can be explained on the basis of lithium location
in a single A site. At higher temperatures the line-width strongly decreases
as a consequence of the Li motion, consistent with the large observed thermal
factors. The dc-conductivty displays a complex non-Arrhenius behaviour
(1) with a progressive change of activation energy from 0.40 to 0.26 eV,
from -100 to 200C. The dependence
of 7Li spin-lattice relaxation time shows the same non-Arrhenius
behavior. We suggest that both unusual findings are associated to the observed
tilting of the TiO6 octahedra, which diminishes as temperature
increases and leads to the opening of the bottleneck through which the
lithium transport takes place.
1. C. León, J. Santamaría, M.A. Paris,
J. Sanz, J. Ibarra, L.M. Torres, Phys. Rev. B56(9), 5302 (1997).
PHASE RELATIONS AND CONDUCTIVITY IN Ba2(In2-xMx)O5
SYSTEM. Akihiko Yamaji and Kazuya Kawakami, Department of Mechanical Engineering,
Tokyo Institute of Technology, Tokyo, JAPAN.
solid solution) structure can be regarded as an oxygen-ion deficient perovskite
structure. Because of high proportion of the oxygen vacancies in the structure,
this material could be a candidate of fast oxide ion conductor. Goodenough
et al. indeed observed a fast-order transition to a fast oxide-ion conductor
at 930C for Ba2In2O5
which adapts brownmillerite structure at ambient temperature. The high
temperature cubic phase shows large ion conductivity. It is of interest
to examine whether or not the cubic phase stabilizes in the low temperature
region by making solid solution of another element. In the present study,
we investigated the ion conductivity and the crystal structure of Ba2(In2-xMx)O5
system by substituting In site for element M such as Sc,Y,La,Ce,Nb,Ta etc.
By substituting 3 mole Nb for
In, the transition temperature decreased by about 300C.
High temperature X-ray diffraction analysis shows the crystal structure
changes from orthorhombic to cubic at this transition temperature. The
most effective element which decreased the transition temperature was pentavalent
element such as Nb or Ta. The substitution In site for 20 mole
Nb stabilizes the cubic structure down to room temperature. The ion conductivity
of Nb 20 mole substituted ceramics
at 500C reached to about 2x10-1
s/m. This value is a little larger than that of Sc and La co-doped ZrO2
NEW PROTON CONDUCTING POLYMERS BUFFERED AT NEUTRAL PH.
Stéphane Béranger , Nathalie Ravet, Daniel Baril, Michel
Armand, Département de Chimie, Université de Montréal,
QC, CANADA; Christophe Michot, Rhône-Poulenc, Lyon, FRANCE.
20; 1 x
2) salts complexes are good candidates for the preparation of electrolytes
buffered at a neutral pH close to 7 Histamine, which is this new family
of proton conductor, contains the imidazole ring which is known to form
strong intermolecular hydrogen bonds leading to a Grotthus mechanism. In
this study, conductivities, electrochemical and thermal data have been
investigated for different proton-vacancy concentrations. These materials
show a good thermal behavior, with the formation of amorphous complexes
and the electrochemical stability window expected for a proton conductor.
Then we suggest their use in dye-based electrochromic cells where the electrochromic
materials are dissolved in the electrolyte.
IONIC CONDUCTIVITY IN LITHIUM DOPED POLYSULFONE POLYMER
FILMS. A.K. Sharma , Y.R.V. Naidu, D.S. Sagar and V.V.R.N. Rao, S.V. University,
Department of Physics, Tirupati, INDIA.
Polymers offer a new range of materials which exhibit
high ionic conductivity comparable to that of liquid electrolytes. The
technological importance of these materials is exemplified by their use
as solid state batteries, fuel cells, sensors etc. It has been shown that
complexes between polymers and lithium salts may be used as ionic conductivity
media in rechargeable lithium containing batteries. In this paper, we report
a new lithium ion conducting polymer based on polysulfone complexed with
lithium salt and characterized using I-R and electrical conductivity data.
The measurements show that the electrolyte is a mixed (ionic+electronic)
conductor, the charge transport being mainly ionic (activation energy 0.8
ev). It was found that room temperature conductivities increased by several
orders of magnitude upon doping with lithium and the samples showed better
charge-discharge properties. The temperature dependence of conductivities
for differently doped samples showed a peculiar behaviour attributable
to dopant kinetics.
CHARACTERIZATION OF CREEP BEHAVIOR OF SrCo0.8Fe0.2O3-x.
G. Majkic , L. Wheeler and K. Salama, Materials Research Science and Engineering
Center, University of Houston, Houston, TX.
In order to achieve commercial utilization, oxygen separation
membranes and solid oxide fuel cells must be able to keep their mechanical
integrity over acceptable life-time periods. This imposes a need for characterization
of mechanical behavior of this class of materials under typical creep operating
conditions, in order to identify mechanisms that lead to mechanical degradation
during operation. It this study, a series of compressive creep tests on
cylindrical specimens is performed, covering a wide range of operating
parameters (temperature and stress). The influence of grain size and intergranular
glassy phase on controlling mechanisms is also addressed. The material
response is interpreted by identifying the relevant parameters such as
stress exponent, activation energy and Monkman-Grant relation parameters.
The identification of dominant creep mechanisms is obtained by microstructural
studies of crept samples. The microstructural observations reveal the mechanisms
of microstructural accommodation of macroscopic strains, namely, the relative
contribution of intergranular cavitation, grain deformation and grain boundary
sliding. The grain-size effect on the relative contribution of these mechanisms
to creep deformation is addressed in order to obtain an indication of the
relative influence of grain boundary and lattice diffusion. * This work
is sponsored by the National Science Foundation through the MRSEC program
under Award Number DMR-9632667.
INORGANIC MEMBRANES WITH HIGH PROTON CONDUCTIVITY. Flavio
Maron Vichi , Maria Teresa Colomer, Marc A. Anderson, Water Chemistry Program,
University of Wisconsin, Madison, WI.
Glass-supported titania and alumina membranes were prepared
via the sol-gel method. The proton conductivities of the membranes were
determined by impedance spectroscopy for temperatures ranging from 25 to
90C and 100% relative humidity,
and the results were compared to those obtained for Nafion
film measured under the same conditions. The impedance spectra were obtained
using a 2-point configuration, with the conductivity being measured along
the surface of the membranes. At 25C,
the proton conductivities were 6.84
10-3, 8.75 10-3
and 1.99 10-2 S.cm-1
for alumina, titania and Nafion, respectively. When the temperature was
raised to 90C, the conductivities
increased to 2.39 10-2,
7.39 10-2 and 2.89
10-2 for alumina, titania and Nafion, respectively. Thermogravimmetric
analysis shows that the water content is higher in the ceramic membranes
at temperatures above 60C and,
at temperatures above 90C, the
water content in the ceramic membranes is 2 to 4 times higher than that
of Nafion. The higher water content in these hydrophilic membranes at higher
temperatures is the key factor in their maintaining a high protonic conductivity.
NEUTRON VIBRATIONAL SPECTROSCOPY OF WATER AND SOLVATED
PROTONS IN HETEROPOLYACID HYDRATES. Terrence J. Udovic , Taner Yildirim,
Nicholas C. Maliszewskyj, NIST Center for Neutron Research, National Institute
of Standards and Technology, Gaithersburg, MD.
Heteropolyacid hydrates have been of interest in low-temperature
fuel-cell research due to their relatively high protonic conductivities.
To help elucidate the dynamics of the water and solvated protons which
surround the large Keggin polyanions in these structures, we have performed
neutron vibrational spectroscopic measurements for a variety of hydration
levels in H3PM12OnH2O
(where M = W, Mo and 30). Moreover,
both deuterium isotopic substitution and first-principles total-energy
calculations were employed to characterize the vibrational density of states
of the novel H5O2+ dioxonium cation which
is stabilized in phosphotungstic acid hexahydrate (H3PW12O6H2O).
LARGE QUANTITY OF HYDROGEN UPTAKE BY A LITHIUM MODIFIED
CARBON NANOTUBES. Ping Chen , Jianyi Lin, Xiaobin Wu, Kuang Lee Tan, National
University of Singapore, Physics Department, SINGAPORE.
The development of high-capacity hydrogen storage system
is a long-sought goal of the automobile industry. Recently, large quantity
of hydrogen (30 wt) stored in a Lithium
modified carbon nanotubes at atmospheric pressure and 623K was found. The
amount of hydrgen uptake by carbon nanotubes is compared with that by Li
modified activated carbon and graphite, which can absorb hydrogen less
than 10 wt under the same conditions.
The absorbed hydrogen is stable at room temperature, but released from
carbon sorbent at temperature above 573K. All the sorbents can be reused,
and was tested for several cycles. It is also found that, the increase
in the hydrogen pressure during the uptake process could dramatically accelerate
the rate of absorption especially in the case of carbon nanotubes. XRD,
TEM, FTIR, XPS and SIMS were applied to investigate the changes in the
structure and composition of carbon sorbents after Li modified and hydrogen
uptake. It is suggested that the intercalation of Li in the layers of carbon
sheets may occur, which may build suitable sites for hydrogen storage.
The difference in the amount of hydrogen uptake amonge carbon nanotubes,
activated carbon and graphite may mainly related with the material size
and number of edges exposed to the hydrgen atmosphere.
SILVER BASED GLASSY ELECTROLYTE FOR SOLID STATE BATTERY
APPLICATIONS. M. Venkateswarlu , 1Pondicherry University, Department
of Physics, Pondicherry, INDIA; N. Satyanarayana1 and B. Rambabu,
Southern University and A&M College, Surface Science, Spectroscopy
and Solid State Ionics Laboratory, Department of Physics, Baton Rouge,
In the recent past, considerable efforts are made to characterize
the high ionic conducting (HIC) materials because of their importance in
various device applications including solid state batteries. In view of
the potentiality of these HIC materials, efforts are made to improve the
conductivity by mixing of various combinations of oxides in the form of
binary, pseudo binary, ternary and quaternary compounds for better device
applications. Hence, in our paper, we present the preparation, characterization,
electrical conductivity and battery applications of AgI-Ag2O
(SeO2+As2O5) (SSA) glassy system. The
SSA system was prepared by melt quenching technique and characterized by
XRD, DSC & IR. Electrical conductivity studies were made in a wide
frequency range (5Hz to 13MHz) using HP 4192 A LF impedance analyzer.
The best conducting SSA glass composition was taken and
the different configurations of batteries were fabricated with various
cathode materials to improve the performance. All the batteries were characterized
by measuring the open circuit voltage, polarization and discharge characteristics
data. Complete results will be presented and discussed.
Acknowledgement: MV grateful to CSIR for awarding RA.
NS acknowledges UGC & DST, Govt. of India, for granting research projects.
B.Rambabu acknowledges RCS program at LLNL and DOE for supporting this
CONTROL OF A RUNNING H2/O2 FUEL
CELL WITH FILLED IONOMERIC MEMBRANES. Bernard LE Gorrec, Claude Montella,
Jean-Paul Diard, Gerard Vitter, Christiane Poinsignon , LEPMI-INPG-CNRS
Ecole Nationale d'Electrochimie et d'Electrometallurgie Saint Martin d'Heres
Performances of a H2/O2 polymeric
electrolyte fuel cell running at 70C
under 3 bars gas pressure and using a new filled ionomeric membrane are
analysed with a recent experimental method established for impedance measurements
of electrochemical batteries during discharge. A classical impedance-measurement
set controls under sinusoidal current perturbation a battery connected
in parallel to the load into which it discharges. The results demonstrate
the possibility to study with classical equipment the impedance of high-capacity
and low-impedance batteries during their discharge through a constant load.
The impedance of the PEMFC connected to a constant load (R = 0.180 ohm)
was measured. The impedance diagrams present at high frequencies, an inductive
behaviour analogous to that observed for batteries, one capacitive arc
and a small straight line. The internal resistance of the PEMFC can be
NANO COMPOSITE BASED ELECTROLYTES FOR LITHIUM-ION BATTERIES.
Michael W. Riley, Peter S. Fedkiw, Saad A. Khan , Dept of Chemical Engineering,
North Carolina State University, Raleigh, NC.
Electrolytes for lithium ion batteries must possess high
conductivity (>10-3 S/cm @ 25C),
low-interfacial impedance, a high-potential window (>5 V), and mechanical
stability. The lithium ion transference number is also an important property,
as larger values lower concentration polarization. A transference number
of unity can potentially offset a decrease in conductivity by up to an
order of magnitude, particularly for high-discharge rate systems. Nano
composites of hectorite and other 2:1 layered clays (smectites) are characterized
by a negatively charged plate-like structure with exchangeable associated
cations sandwiched between the plate-like layers. They offer the ability
to act as single ion conductors with potential for exhibiting transference
numbers approaching unity. They also possess the ability to provide mechanically
stable electrolytes through formation of strong physical gels via assembling
into three-dimenional networks. These features make investigation of nanostructured,
clay-based electrolytes desirable, even though conductivities of both native
dry and organic intercalated forms of the smectites may fall short of magnitude
required for lithium batteries. This study involves development of composite
electrolytes based on lithium-hectorite clay dispersed in high dielectric
organic solvents such as ethylene carbonate (EC) and propylene carbonate
(PC), and investigating its electrochemical and rheological behavior. Our
initial studies show the LiHectorite/carbonate composites to exhibit room
temperature conductivities of 10-4
S/cm, approximately 20 times lower than that of a Li+ molar equivalent
LiPF6 electrolyte. However, unlike the LiPF6 electrolyte,
the LiHectorite based composites reveal lithium ion transference numbers
of 0.8. In addition, dynamic
rheological techniques reveal this system to be extremely stable mechanically,
with the elastic modulus G' exceeding 107 dynes/cm2
and yield stress exceeding 104 dynes/cm2. These results
will be interpreted in terms of the prevailing structure of the system.
SESSION CC6: ANODES & NiMH
8:30 AM *CC6.1
DEVELOPMENT OF A NOVEL COMPOSITE ANODE FOR HIGH-ENERGY
AND HIGH-POWER LITHIUM-ION BATTERIES. G. Abbas Nazri , Bouziane Yebka,
Maryam Nazri, University of Michigan, Department of Chemistry, Ann Arbor,
Chairs: Daniel H. Doughty and Linda F. Nazar
Wednesday Morning, April 7, 1999
Metropolitan II (A)
Carbonaceous anodes are the most practical elecrode for
application in lithium-ion battery, mainly due to their low cost, flexibility
for modification to achieve high-energy capacity and high-rate capability,
abundance and environmentally uniquencess. In this work we have deveoped
a novel composite carbonaceous anode for application in lithium ion batteries.
The energy capacity and rate capability of the electrode have been tailored
to satisfy the requirments of high-energy and high-power applications.
Performance of the composite electrode under continuoes charge-discharge
cycling and application of various current pulses will be reported. The
safety aaspect of carbonaceous anodes and reactivity of the lithiated anode
in contact with cyclic and linear carbonate based electrolytes have been
studied using reat-time electrochemical- mass spectrometry and gas chromatography.
The nature of gaceous species generated on various carbonaceous anodes
and the film formed on electrode surface during initial charge-discharge
cycling have been studied. We report the correlation between structural
parameters of carbonaceous materials and their irreversible capacity. Structural
parameters have been studied using x-ray diffraction, Raman spectroscopy,
scanning and transmission electron microscopy. We have found a direct correlation
between crystal morphology, degree of disorder, degree of graphitisation
and the irreversible capacity loss and volume of generated gases during
initial charge-disharge cycling. Results also show the importance of removing
adsorbed and trapped impurities, in addition to removal of bonded functional
groups. Thermal analysis of different graphitic samples at various stages
of charge discharge cycling and degree of lithium intercation have ben
investigated, and results are correlated to the structural parameters of
electrode materials. We have applied TGA and DSC analysis, to clarify how
each factors and parameters contributes to the thermal stability of the
different intercalated graphite materials.
9:00 AM *CC6.2
DEVELOPMENT AND CHARACTERIZATION OF NANOSTRUCTURE TIN
ALLOYS AS ANODES IN LITHIUM-ION BATTERIES. E. Peled and A. Ulus, School
of Chemistry, Tel-Aviv University, Tel Aviv, ISRAEL.
Two important properties make tin alloys promising candidates
for anodes in lithium-ion batteries: high reversible capacity and high
melting point of the LixSn phases. Recently, Besenhard's group showed that
reducing the size of the alloy particles resulted in a longer cycle life.
In this work we prepared and evaluated nanostructure tin-antimony alloys
containing Sn:Sb 9:1 to 1.4:1 atomic ratio and other elements including
carbon, oxygen and copper. XRD measurements showed only one antimony phase
- the SnSb phase. Fractal-like morphology was obtained. The particles are
generally smaller than 100 nm. Anodes made from these alloys were cycled
versus lithium between 0 to 1.0V at current densities from 0.02 to 4 mA
per square cm in 1M lithium hexafluoroarsenate PC or EC/DEC solutions.
For tin rich alloys the insertion curve (at 0.02 mA/ square cm) has three
voltage plateaus: at 685 mV, 570 mV, and 440 mV. Antimony rich alloys have
another two plateaus at 820 and 850 mV. The de-insertion curves (at 0.2mA/
square cm) have less definite plateaus, about 100 to 200 mV higher than
those of the insertion curves, indicating that the overpotential of the
de-insertion process is higher than that of insertion. The maximum reversible
capacity was 700 mAh/g ( based on the total electrode mass excluding the
current collector ) and the minimum irreversible capacity was 15%. The
reversible capacity and the rate capability decrease with increasing antimony
content of the alloy. Cycle life was found to increase with the content
of antimony and copper and up to 40 stable 100% charge-discharge cycles
were demonstrated. SEM photographs show evidence for disintegration of
the alloys after cycling. The correlation among capacity, cycle life, alloy
composition and morphology will be addressed.
9:30 AM CC6.3
EFFECT ON PERFORMANCE OF COMPOSITION OF Li-ION CARBON
ANODES DERIVED FROM PMAN/DVB COPOLYMERS. Ronald A. Guidotti , Sandia National
Laboratories, Albuquerque, NM; William R. Even, Jr., Sandia National Laboratories,
Soft, ordered graphites typically have low first-cycle
capacity losses associated with solvent/salt reduction processes. These
materials have capacities limited by the composition LiC6, or 372 mAh/g.
Hard, disordered or turbostratic carbons, on the other hand, have shown
to have capacities well in excess of 372 mAh. The composition of disordered
carbons has an impact on its electrochemical performance. The H/C atomic
ratio, for example, was found to correlate to the reversible capacity for
some specific materials (1). Incorporation of Si into the carbon lattice
has also been reported to enhance the reversible capacity (2). Doping with
N, however, resulted in degradation of performance, due to an increase
in the irreversible capacity (3). We have previously reported on the performance
of carbons derived from polymethacrylonitrile (PMAN)/divinyl benzene (DVB)
copolymers. In that work, a molar PMAN/DVB ratio of 3:1 was used. In this
paper, we present the results of electrochemical characterization of carbons
derived from similar precursors but where the PMAN/DVB ratio was varied,
to encompass zero-N material to low-N and high-N carbons. Contrary to what
others have reported, we find that a high-N material performs better than
the low-N counterpart in galvanostatic cycling tests in 1M LiPF6/ethylene
carbonate-dimethyl carbonate (1:1 v/v) solution. The pyrolysis temperature
affects the performance by changing the bulk composition.
1. T. Zheng, Y. Liu, E.W. Fuller, S. Tseng, U. von Sacken,
and J.R. Dahn, J. Electrochem. Soc., 142 (8), p. 2581 (1995).
2. A.M. Wilson and J.R. Dahn, J. Electrochem. Soc., 142
(2), 326 (1995).
3. J.R. Dahn, A.K. Sleigh, H. Shi, B.M. Way, W.J. Weydanz,
J.N. Reimers, Q. Zhong, and U. von Sacken, Lithium Batteries - New Materials,
Development and Perspectives, G. Pistoia, ed., Elsevier, New York, 1994,
This work was supported by the United States Department
of Energy under Contract DE-AC04-94AL85000.
9:45 AM CC6.4
SYNTHESIS OF NOVEL HYDRATES VANADATES: THE ROLE OF WATER
WITH RESPECT TO THEIR POTENTIAL USE IN RECHARGEABLE Li-ION BATTERIES. P.
Poizot, E. Baudrin, S. Denis, S. Laruelle, M. Touboul and J.M. Tarascon
, Laboratoire de Reactivite et de Chimie des Solides, Universite de Picardie
Jules Verne, Amiens, FRANCE.
Rechargeable Li-ion cells have become key components of
the portable, entertainment, computing and telecommunications equipment.
However, consumers are in constant demand of batteries with larger autonomy
(e.g. greater capacity). In searching for alternative materials to substitute
for the carbonaceous negative electrode in Li-ion cells, we expanded on
Yoshio's work dealing with lithiated vanadium oxide-based electrodes. We
have synthesized, by means of a chimie douce method a large variety of
new hydrated vanadates RVO4.nH2O (R= In, Co, Ni, Fe ..) that can be either
amorphous or crystallized. Most of these hydrated vanadates are shown to
reversibly intercalate large amounts of Li leading to capacities as high
as 1000mAh/g, with however a large irreversible loss between the first
discharge/charge and a large capacity fading upon cycling. Could such poor
performance be linked to the presence of water in these compounds? We capitalized
in our advantage of being able to synthesize a serie of materials containing
various amounts of either adsorbed or structural H2O to address
the water issue within the field of Li intercalation chemistry, that has
long been very controversial. A strong dependence of the electrochemical
performance of these hydrated vanadates with respect to the nature of water
as well as of its bonding to the lattice was observed. The room temperature
and 55C ageing of these as-made
materials in various non-aqueous electrolytes, both at room temperature
and at 55C, have also revealed,
depending again on the material water content, a partial decomposition.
An attempt to reconvey all the results, on the basis of the interplay between
the electrochemical performance of these materials and their crystal/chemical
aspects will be presented and a tentative to generalize these findings
to other materials discussed.
10:00 AM CC6.5
THE ROLE OF OXYGEN IN THE REVERSIBILTY OF LITHIUM INSERTION
IN METAL OXIDE ANODE MATERIALS. Linda Nazar, University of Waterloo, CANADA;
Fabrice Leroux , Universite Blaise-Pascal, FRANCE; Gillian Goward, University
of Waterloo, CANADA; Guy Ouvrard, Institut des Materiaux de Nantes, FRANCE.
Considerable attention has been devoted towards developing
new negative electrode materials for Li-ion batteries in the past few years.
Although graphitic materials that form the basis of current commercial
negative electrodes meet many of these demands, they also suffer from some
drawbacks, including limited Li insertion capacity poor volumetric energy
density. The discovery of promising Li insertion properties of various
new materials in recent years has led to exploration of systems other than
graphite, including amorphous nanocomposites, and crystalline materials
such as metal oxides. Numerous transition metal oxides, in addition to
the better known tin oxides, have been shown to offer very good capacities
and cyclability. The mechanism of insertion in these materials is not well
understood, however. Lithium-7 NMR and XAS have been used to demonstrate
that in crystalline oxides containing Mo, Sn and/or Fe, low potential Li
insertion is associated with the formation of a complex amorphous nanocomposite,
in which the oxygen remains in close association with the metal centers
to varying degrees depending on the material. On Li de-insertion, Li migration
from within the particle leads to surprisingly ready re-formation of the
metal oxygen interaction. The effect of cut-off voltage and the role of
the matrix in stabilizing the electrochemical behavior will be discussed.
10:30 AM *CC6.6
MECHANICAL MILLING: AN APPROACH FOR BETTER ELECTRODE
MATERIALS WHATEVER THE BATTERY TECHNOLOGY CONSIDERED. L. Aymard, C. Lenain,
L. Courvoisier, F. Salver-Disma and J.M. Tarascon , Laboratoire de Chimie
et de Reactivite des Solides, UPRESS-A, Universite Picardie Jules Verne,
rue Saint-Leu, Amiens, FRANCE.
In the intense search for high capacity electrode materials,
the effect of mechanical milling (MM) using either shearing- or shock-type
interactions was investigated. Non-reactive mechanical milling that results
in the formation of very reactive carbon-edge atoms has, for instance,
enabled the preparation of carbonaceous materials able to reversibly accept
2 lithiums per six carbons Li2C6. Separately, reactive room temperature
mechanical milling produces highly strained and divided electrochemically
active hydride-forming alloys with, therefore, a limited capacity because
of oxygen contamination associated to their high division state. It was
then interesting to find out whether during a mechanical alloying experiment
the carbon-edge atoms could serve as oxygen scavengers in presence of hydride-forming
materials in order to restore the theoretical electrochemical capacity
of the AB5 alloys. The effect of mechanical milling on powders mixtures
consisting of graphite and AB5 alloys, prepared either by mechanical alloying
or by a high temperature melting process, was then investigated. The resulting
materials were characterized for their structure, composition, morphology,
surface area and electrochemical performance. Among the most prominent
results are the hydride-forming composite electrodes showing a 10 and 40%
capacity enhancement when the AB5 precursor alloy was arch-melted or mechanically
prepared, respectively. Such an increase in capacity will be explained
as the result of several cumulative effects that are 1) a mechanically
induced reducing role of graphite that eliminates the AB5 particles of
oxide coatings, 2) the appearance of an increasingly important double layer
capacitance on each particle upon increasing milling and 3) the improved
electronic conductivity between the active AB5 material and the graphite,
which allows a better use of the alloy.
11:00 AM *CC6.7
SURFACE STRUCTURE AND ELECTROCHEMICAL CHARACTERISTICS
OF Ti-V-Cr BCC-TYPE SOLID SOLUTION ALLOYS SINTERED WITH Ni. Yoichiro Tsuji
, Osamu Yamamoto, Hiromu Matsuda, Yoshinori Toyoguchi, Central Research
Laboratory, Matsushita Electric Industrial Co., Ltd., Osaka, JAPAN.
Ti-V-Cr bcc-type solid solution alloys can absorb a large
amount of hydrogen and be applied to active materials of Ni-MH batteries.
However, because of the insolubility of Ni into these alloys, the electrochemical
characteristics like discharge capacity and cycle life were poor. In order
to increase the discharge capacity, Ti-V-Cr alloy powders were sintered
with Ni to form Ni contained surface layer around the Ni free alloy particle.
This structure supplies a high electrochemical activity with the minimum
loss of hydrogen absorbing ability. The Ti-V-Cr alloy particles were covered
with Ni by mixing Ni and alloy powders or electroless plating, and sintered
at various temperatures. As sintering temperature went up, the surface
composition changed from TiNi to Ti2Ni. TiNi surface layer showed
better electrochemical characteristics and the best sintering condition
was at 600C for 6 hours. Ni electroless
plating was preferred because of good adhesion, and the optimum amount
of Ni was 7wt%. Discharge capacity of 570 mAhg-1, which was
about twice as large as that of AB5 alloys, was obtained by
optimizing Ni amount and sintering condition as mentioned above.
11:30 AM CC6.8
HIGH PERFORMANCE Zr-BASED METAL HYDRIDE ALLOYS. R.C.
Young , B. Huang, Y. Li, B.S. Chao, S.R. Ovshinsky, Energy Conversion Devices,
Inc. Troy, MI; E.P. George, C.T. Liu, Metals and Ceramics Division, Oak
Ridge National Laboratory, Oak Ridge, TN.
Based upon Ovonic's multi-element disorder principle,
two families of alloys are being used in commercial NiMH rechargeable battery,
i.e. the misch metal (Mm) based and the Zr-based alloys. It is generally
recognized that the Mm based alloys is easy to activate, however, is limited
by its discharge capacity of 350 mAh/g. On the other hand, the Zr based
alloys, which usually takes a little longer to activate, has a higher discharge
capacity. In this paper, we demonstrated that the Zr-based multi-element
alloys with the discharge capacities well above 450 mAh/g have been achieved.
The aspect of the high discharge capacity of the metal hydride alloys is
particularly important for the electric vehicle applications because of
its stringent requirement on the high specific energy of the battery pack.
We would like to emphasize that the high discharge capacity of the alloys
not only increases the energy density of the battery, equally important,
it also reduces its cost. We have carried out a comprehensive study of
the Zr based multi-element alloys, especially, on the effect of stoichiometry,
electron concentrations, structures and processing parameters to the electrochemical
discharge capacities and kinetics. Within the multi-element disordered
transition metal alloys, it is found that a decrease of the electron concentration
factor of the alloys, which shifts the structure from diamond cubic(C15)
to hexagonal(C14), increases the hydrogen storage capacity. However, it
only increases the electrochemical discharge capacity to a certain extent
because the hydrogen trapping phenomenon starts to occur.
11:45 AM CC6.9 EFFECT OF ALLOY COMPOSITION TO THE
STRUCTURE OF Zr BASED METAL ALLOYS. B.S. Chao , R.C. Young, D.A. Pawlik,
J.S. Im, B. Husang, S.R. Ovshinsky, Energy Conversion Devices, Inc., Troy,
MI; B.C. Chakoumakos, Neutron Scattering Section, Oak Ridge National Laboratory,
Oak Ridge, TN.
The structures of Ovonic multi-element Zr base transition
metal alloys for hydrogen storage are studied. It is found that the alloys
are multi-phase materials. The hexagonal and diamond cubic structures,
known as C14 and C15 structures respectively, are the two major hydrogen
storing phases in the alloys. In both hexagonal and diamond cubic structures,
Zr and Ti are the elements typically occupying the hydride former (A) sites
and V, Cr, Mn, Fe, Co and Ni the catalytic (B) sites. Based on the designed
principle for the disordered materials, both sites are compositionally
disordered by the corresponding elements in cubic (C15) structure. The
hexagonal (C14) structure in the AB2 formulation has two distinct B sites,
B(I) and B(II) with a 1:3 ratio. Preliminary neutron diffraction studies
indicate that the B(I) sites are predominantly occupied by Ni and the B(II)
sites are randomly mixed with V, Cr, Mn, Fe, and Ni. It is then proposed
that the formula of the hexagonal structure should become A2B(I)1B(II)3
in the current multi-element Zr alloys. Minor phases close to the structures
of Zr7Ni10, Zr9Ni11, and ZrO2 are also present in some alloys. The average
electron concentration factor (e/a) derived from the alloy composition
dictates the alloy structures. The alloys with higher electron concentration
factor (> 7.0) favors the diamond cubic structure. On the other hand, the
hexagonal structure is associated with the alloys with lower electron concentration
factor (< 6.4). The alloys having electron concentration factors in
between are mixtures of the diamond cubic and hexagonal structures. Good
kinetics are observed in the alloys containing higher Ni content, closely
associated with the diamond cubic structure. Higher discharge capacity
is mostly observed in the hexagonal dominant alloys.
SESSION CC7: SUPERCAPACITORS
1:30 PM *CC7.1
PERFORMANCE OF LARGE SIZE ELECTRIC DOUBLE-LAYER CAPACITOR
USING ORGANIC ELECTROLYTE. T. Morimoto , M. Tsushima, K. Hiratsuka, M.
Suhara, Y. Sanada, T. Kawasato, Asahi Glass Co, Ltd., Research Center,
Chairs: Artur Braun and Katsuhiko Naoi
Wednesday Afternoon, April 7, 1999
Metropolitan II (A)
Electric double-layer capacitors using an organic electrolyte
solution have been developed and are widely used as maintenance-free power
sources for IC memories and microcomputers. One of the newly proposed applications
for large size electric double-layer capacitors is pulse power sources
in electric and hybrid vehicles.
The excellent performance of power capacitors is attained
by a new electrolyte of high conductivity and high decomposition voltage
and an electrode fabricated with high surface area activated carbon. An
electrolyte obtained by dissolving 1.1M triethylmethyl ammonium tetrafluoroborate
in propylene carbonate having the specific conductivity and the decomposition
voltage of 0.018S/cm and 3.0V, respectively, were used. Furthermore, activated
carbon of low oxygen content having the specific surface area of 2000m2/g
was used as the electrode material. Rectangular power capacitors having
the capacitance of 1300F and internal resistance of 3mwere
developed using the material mentioned. After charging to 2.5V, the cell
voltage of the capacitor decreases linearly under constant discharge current
of 50A from 2.5V to 1.0V in 40 seconds. The cycle life test of the capacitor
at 45 degrees in centigrade show that the deterioration in capacitance
is less than 15% after 400,000 times charge and discharge cycles under
constant charge and discharge current of 50A between the cell voltage of
2.5V and 1.25V.
2:00 PM CC7.2
RECENT DOE SPONSORED ELECTROCHEMICAL CAPACITOR TEST RESULTS.
Randy B. Wright , Tim C. Murphy, Idaho National Engineering and Environmental
Laboratory, Idaho Falls, ID; Susan A. Rogers, U.S. Department of Energy,
Electrochemical capacitors (ultracapacitors) are being
developed for hybrid vehicles as candidate power assist devices for the
fast response engine and for other energy storage applications. Ultracapacitors
show promise towards being able to accept high regenerative pulses and
high power delivery capabilites while exhibiting very high cycle life.
This paper will present test data from selected U.S. Department of Energy
(DOE) supported ultracapacitor projects designed to meet the fast response
Constant-current, constant-power, leakage-current and
self-discharge test results will be presented and discussed that have been
acquired from prototype capacitors supplied by Maxwell Energy Products,
Inc., SAFT America, Inc., and the YUNK-Bureau Ltd, in Kiev, Ukraine. The
Maxwell capacitors consisted of individual capacitor cells rated at 2.3
V and 101.4 F, and an integrated capacitor bank consisting of thirty-three
of the series connected cells that is rated at 75 V and 2.9 F. SAFT capacitors
rated at 3 V and 135 F to 138 F were also evaluated. The Ukrainian capacitor
consisted of five series connected cells with individual ratings of 3 V
and 2500 F, giving rise to a capacitor bank rated at 15 V and 500 F. All
of these capacitors used a non-aqueous electrolyte in there design. The
testing results from these devices will be compared to other capacitors
that have been previously tested at the INEEL.
2:15 PM *CC7.3
A STUDY ON OXIDIZED GLASSY CARBON SHEETS FOR SUPERCAPACITOR
ELECTRODES. Artur Braun , Martin Bartsch, Friederike Geiger, Bernhard Schnyder,
Rudiger Kotz, Paul Scherrer Institute, General Energy Research, Villigen
Electrochemical double layer capacitors for high energy
and power density applications, based on glassy carbon (GC) electrodes,
are developed in our laboratory [Ref.1]. GC has closed pores, but open
porosity is mandatory to achieve a high double layer capacitance (DLC).
The pores can be opened by a thermal or electrochemical oxidation process
(activation). Results concerning thermally activated thin GC sheets are
presented here in terms of the DLC, as measured in sulfuric acid with electrochemical
impedance spectroscopy, and on the internal surface area, as obtained by
gas adsorption (N2) and small angle x-ray scattering (SAXS).
During long term activation, the volumetric internal surface area decreases
to 50% of its maximum value. However, the volumetric capacitance increases
for around 10% during activation. The contradictory result of decreasing
surface area, but increasing capacitance can be explained as follows: The
high internal surface area at the initial stage of oxidation is due to
micropores, of which not all are accessible for electrolyte. Upon activation,
smaller pores coalesce to larger pores and the internal surface area decreases.
But the larger pores are then accessible for the electrolyte, and additional
double layer capacitance occurs. Financial support by the Board of the
Swiss Federal Institute of Technology, SAXS beamtime from Dr. H.-G. Haubold,
Dr. G. Goerigk (HASYLAB Hamburg and Forschungszentrum Jülich, Germany),
R. Saliger and A. Emmerling (Universität Würzburg, Germany) is
[Ref.1] M. Bartsch, R. Kotz, A. Braun, O. Haas, Proceedings
of the 38th Power Sources Conference, 8-11 June, p. 17, Cherry Hill, NJ
2:45 PM CC7.4
NEW CONDUCTING POLYMERS FOR ELECTROCHEMICAL ULTRACAPACITORS.
Katsuhiko Naoi , Shunzo Suematsu, Tokyo Univ. A & T, Dept of Applied
Chemistry, Koganei, Tokyo, JAPAN.
New conducting polymers based on pai-conjugated system
hybridized with other redox systems such as disulfide or quinone. The authors
will talk about the electrochmical properties and the characteristics as
the electrochemical capacitors or batteries. The results for two polymer
materials, viz., poly(dithiodianiline) and poly(1,5-diaminoanthraquinone)
will be presented. The poly(1,5-diaminoanthraquinone) [poly(DAAQ)] film
showed two redox couples at negative and positive potentials which correspond
to the two redox systems; one is for the quinone and the other is for the
pai-conjugated polymer system. The electrochemical window of the poly(DAAQ)
was as wide as ca. 2.5V. The electrochemical capacitor utilizing the poly(DAAQ)
films for both positive and negative electrodes exhibited higher specific
energy (30 Wh / kg) and power (13.5 kW / kg) than those for other conducting
polythiophene materials. It is proposed here a novel energy storage material
of poly (DAAQ) which can be utilized as an electrochemical ultracapacito
3:30 PM CC7.5
A NOVEL CONDUCTING POLYMER WITH 0-S-S-O BONDS FOR POSITIVE
MATERIAL: POLY(2,2'-DIAMINOBENZYLOXY- DISULFIDE). Yuzhi Su, Kecheng Gong
, South China University of Technology, Polymer Structure & Modification
Res. Lab., Guangzhou, CHINA.
Organic disulfide compounds has been proposed as a new
class of high energy storage material[1,2]. Poly(2,2'-diaminobenzyloxydisulfide)
(poly(DABO)), a novel conducting polymer having O-S-S-O bond joined two
moieties of anilines, is synthesized chemically as a new positive storage
material. It exhibits conductivity in the region of 10-3 S/cm
by the four-probe method and the O-S-S-O bonds in it are confirmed by Fourie
Transform Raman Spectroscopy (FT-RS) and Fourie Transform Infrared Spectroscopy(FT-IR).
The poly(DABO) films are formed by electropolymerization from the DABO
monomer solution in 1mol/dm3 H2SO4 supporting
electrolyte on Pt electrode under continuous cycling between -0.20v and
1.20v vs SCE at scanning rate 100mv/s. The cyclic voltammetry studies show
that its electrochemical behaviour is similar to polyanilineÕs.
The oxidative peak current of the cyclic voltammograms increase and the
starting peak potential negative a little with increasing of the cyclic
 Gong Kecheng, MaWenshi, Mat Res. Symp.
Proc., 461, 87(1995).
 K. Naoi, K. Kawase, M. Mori and M. Komiyama,
Mat Res. Symp. Proc., 496, 309(1998).
3:45 PM CC7.6
NANOSTRUCTURE MATERIAL FOR SUPERCAPACITOR APPLICATION.
Yuhong Huang , C.T. Chu, Qiang Wei, Haixing Zheng, Chemat Technology, Inc.,
Capacitive energy storage devices based on double-layer
capacitance or pseudocapacitance have a wide range of potential applications.
Currently, these capacitors are being used as power back-up for memory
devices in electronic equipment or for electrical actuators. Because of
their high energy and power densities and long cycle life, their potential
applications include pulse power, bridge power, load leveling, and stand-by
power. Terms such as supercapacitors, ultracapacitors, double layer capacitors,
pseudocapacitors, and electrochemical capacitors have been used interchangeably
for these devices. Electrochemical capacitor possesses electrode, electrolyte,
seperator. Electrode material is a key element in electrochemical capacitor.
The requirement of high energy and power density electrochemical capacitor
intrigues development on miniaturization and weight reduction of electrochemical
capacitor. A route to increase energy and power density is to increase
assessable surface area of electrode. The pore size must be large enough
to let electrolyte assess into the pore, and smaller enough to have high
surface area per volume or per weight of electrode material. The cohesion
of electrode and adhesion to the current collector is a key point to realize
high conductivity and power density of electrode materials, such as nitride.
Contacting resistance can increase the resistance of the capacitor. In
present research, a composite coating technology has been developed and
high energy density and power density has been achieved. Electrode material
fabricated in Chemat showed same order of energy density and power density
with ruthenium oxide crystalline materials. Furthermore, the potential
cost is much lower than that of ruthenium oxide.
4:00 PM CC7.7
FABRICATION OF ULTRA THIN-FILM ELECTRODES FOR CHARGE
STORAGE DEVICES BY SOL-GEL PROCESS. Suh-Cem Pang , Marc A. Anderson, Water
Chemistry Program, University of Wisconsin, Madison, WI; Thomas W. Chapman,
Department of Chemical Engineering, University of Wisconsin, Madison, WI.
Ultra thin-film electrodes comprising active materials
of lithiated manganese oxides on conducting supporting substrates were
fabricated by the sol-gel process. Aqueous polymeric sols were prepared
by dissolving both stoichiometric and non-stoichiometric amounts of lithium
and manganese salts, together with appropriate amounts of hydroxycarboxylic
acids in water. Both amorphous and nanocrystalline thin-film electrodes
were fabricated by dip-coating directly onto metal supporting substrates
followed by calcination at controlled conditions. Material characterization
and electrochemical performance evaluations indicated that these thin-film
electrodes have good potential for use in charge storage devices such as
batteries and supercapacitors. Cyclic voltammograms of thin-film electrodes
gave a characteristic rectangular shape of an ideal supercapacitor with
specific capacitance of more than 472 Farads per gram of active material
over a voltage window of -0.3V to +0.9V. Thin-film electrodes fabricated
at lower temperatures appeared to yield substantially higher specific capacitance,
probably attributed to higher specific surface area and lower degree of
crystallinity. We speculate that the large specific surface area of sol-gel
derived manganese oxide nanoparticulates (double-layer capacitance) coupled
with the faradaic charge transfer involving lithium ion intercalation processes
(pseudo-capacitance) are the principle means of storing energy. The apparent
transition between supercapacitor and battery-like behavior has been attributed
to the quasi-two-dimensional processes of Li intercalation into 3-D host
lattice of -MnO2.
Such supercapacitor behavior is evidenced from the shape of the 3-D sorption
isotherm of the Li intercalation process, which exhibited a continuous
decline of potential against extent of 3-D sorption of the sorbate into
the host. In this study, we have focused on investigating the microstructural
effect on the transition between the supercapacitor and battery-like behavior
of these thin-film electrodes. The effect of precursor stoichiometry, complexing
agents, supporting substrates and calcination conditions on the final microstructure
and phase of active material of thin-film electrodes have been investigated.
4:15 PM CC7.8
PERFORMANCE OF ELECTRIC DOUBLE LAYER CAPACITORS WITH
POLYMER GEL ELECTROLYTES. Masashi Ishikawa , Takahiro Kishino, Naoji Katada,
Masayuki Morita, Yamaguchi Univ, Dept of Applied Chem & Chem Eng, Ube,
Polymer gel electrolytes consisting of poly(vinylidene
fluoride) (PVdF), tetraethylammonium tetrafluoroborate, and propylene carbonate
(PC) as a plasticizer have been investigated for electric double layer
capacitors. The PVdF gel electrolytes showed high ionic conductivity (ca.
6 mS/cm at 298 K) and had good stability over a wide potential range (ca.
5 V). To assemble model capacitors with the PVdF gel electrolytes and activated
carbon fiber cloth electrodes, a pair of the fixed electrodes was soaked
in a precursor solution containing PC, PVdF, and tetraethylammonium tetrafluoroborate,
followed by evaporating the PC solvent in a vacuum oven. The resulting
gel electrolyte was in good contact with the electrodes; the good-contact
interface between the activated carbon electrode and the gel electrolyte
was found to be crucial for realizing high performance of the gel capacitors.
The model capacitors with the PVdF gel electrolytes showed large values
of capacitance and high coulombic efficiency in the operation voltage ranges
of 1-2 and 1-3 V. It is worth notable that the capacitors with the PVdF
electrolytes showed low leakage current and long voltage retention in self-discharge
tests. These good characteristics of our gel capacitors are comparable
to those of typical double layer capacitors with a liquid organic electrolyte
containing PC and tetraethylammonium tetrafluoroborate; rather, the voltage
retentivity of the PVdF gel capacitors is superior to that of the capacitors
with the organic electrolyte.
SESSION CC8: SOLID OXIDE CONDUCTORS
8:30 AM *CC8.1
TRANSITION METAL DOPED LaGaO3 PEROVSKITE FAST
OXIDE ION CONDUCTOR AND INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELL.
Tatsumi Ishihara , Takaaki Shibayama, Miho Honda, Hiroyasu Nishiguchi and
Yusaku Takita, Oita University, Faculty of Engineering, Oita, JAPAN.
Chairs: Hans-Peter Brack and Allan J. Jacobson
Thursday Morning, April 8, 1999
Metropolitan II (A)
Effects of doping Fe, Co, Ni for the Ga site on the oxide
ion conductivity of La0.8Sr0.2Ga0.8Mg0.2O3
have been investigated in detail. It was found that doping these transiton
metals is effective for enhancing the oxide ion conductivity. In particular,
a significant increase in the low temperature range was observed. Electrical
conductivity was monotonously increased, however, transport number of oxide
ion was decreased with increasing amount of transition metal dopant. Considering
the transport number and electrical conductivity, the optimized amount
of Fe, Co, and Ni doping seems to exist at 8.5, 3, and 5 mol
for Ga site, respectively. In agreement with the improved oxide ion conductivity,
power density of solid oxide fuel cell was also improved by using transition
metal doped LaGaO3 based oxide as an electrolyte. In particular,
it was found that notably large power density was obtained by using Co
doped LaGaO3, and the power density of the cell was attained
to 250 mW/cm2 at 873 K in spitc of the 0.5mm thickness of electrolyte.
Current interuption method suggest that main internal registance of the
present cell is electrical registance of the used electrolyte. Therefore,
the maximum power density was increased with decreasing the thickness of
electrolyte. The power density of ca500 mW/cm2 was attained
at 873K @ when thickness of electrolyte
was 0.2mm. The durability of the cell was also investigated on this thin
electrolyte plate cells and it was confirmed that the notably high power
density was stably sustained over 350 h. Therefore, this study made clear
that transition metal doping LaGaO3, in particular, Co doped
LaGaO3 perovskite oxide is promising as an electrolyte of intermediate
temperature solid oxide fuel cell.
9:00 AM CC8.2
DEVELOPMENT OF ZIRCONIA ELECTROLYTE FILMS ON POROUS LSM
CATHODES BY ELECTROPHORETIC DEPOSITION. Rajendra N. Basu , Clive A. Randall,
Merrilea J. Mayo, The Pennsylvania State University, Dept of Materials
Science and Engineering, University Park.
In this study electrophoretic deposition (EPD) is explored
as an inexpensive route for fabricating the zirconia electrolyte in solid
oxide fuel cells (SOFCs). Normally, deposition of particulate ceramic powders
by EPD onto a porous surface yields a non uniform coating which, after
sintering, results in porosity and surface roughness in the coating. To
overcome this problem, the present study uses a fugitive coating as an
interlayer between the porous substrate (a lanthanum strontium manganite
tube) and the deposited zirconia. By this method, a fairly dense green
coating (around 60%) is obtained, which yields a smooth surface and pore-free
microstructure after sintering. The fugitive interlayer process appears
to work for two reasons: (1) the interlayer helps to (temporarily) fill
pores in the underlying substrate, thereby making a smooth surface for
deposition and (2) the burnout of the interlayer allows the zirconia coating
to become largely detached from the underlying substrate during early sintering,
thereby eliminating the cracking conventionally associated with constrained
9:15 AM CC8.3
ANIONIC CONDUCTORS IN THE SYSTEMS (Bi, Sb, Te)-(Mo, W,
V)-O. Pascale Beguea,b, Renee Enjalberta,
Alicia Castrob, Patrice Milleta and
Jean Galy a, aCentre d'Elaboration
de Matériaux et d'Etudes Structurales/CNRS, Toulouse, FRANCE; bInstituto
de Ciencia de Materiales de Madrid/CSIC Cantoblanco, Madrid, SPAIN.
Oxide ion conducting solid electrolytes are of main interest
for several applications like gas monitoring, metallurgy, chemical kinetics,
solid oxide electrolyte fuel cells.... The well known yttria stabilized
zirconia phase Zr1-xYxO2-x/2
exhibits high oxide ion conduction at elevated temperatures, i.e. above
800K. Its advantages, low dissociation pressure and non-corrosive behavior
are balanced by the requirement of high temperatures for its sintering
(above 2000K) and its low conductivity below 800K. New oxide families based
on Bi III and transition elements like Mo, W and V exhibiting particular
atomic organization, i.e. layered Aurivillius, and, - columnar structure
types, will be presented with the aim to underline their chemical sensing
potentialities. To enhance the physical properties of such phases the substitution
of lone pair ns2 elements, like Sb III, Te IV, Pb II, Bi III
has been systematically used to design new multicomponent oxide structures.
The syntheses of the Aurivillius phases Sb2MoO6,
Sb2WO6 , Sb2W1-xVxO6
as well as the columnar ones (Pb,Bi)(Bi12O14)((Mo,V)O4)5
are realized via solid state chemistry syntheses at temperatures lower
than 800oC. Their original atomic structures determined
by X-ray powder and single crystal analyses will be depicted. It will be
shown how some special doping, chosen from detailed structural features,
have been used to increase the conductivity of such phases ; the resistivity
measurements have been realized by impedance spectroscopy. For example,
the conductivity determined for the Bi(Bi12-xTexO14)Mo4-xV1+xO20
material amounts 8x10-3-1cm-1 at 750oC
9:30 AM CC8.4
IMPROVING GD-DOPED CERIA ELECTROLYTES FOR LOW TEMPERATURE
SOLID OXIDE FUEL CELLS. James M. Ralph , Argonne National Laboratory, Electrochemical
Technology Program, Argonne, IL; John A. Kilner, Department of Materials,
Imperial College, London, UNITED KINGDOM.
Doped ceria electrolytes continue to be studied because
of their high conductivity in the temperature range 500-650C.
This high conductivity in the low temperature range makes them candidate
electrolyte materials for use in low temperature solid oxide fuel cells
(SOFC). At higher temperatures and low oxygen partial pressures, the reduction
of ceria introduces substantial electronic conductivity, but below 650C
this effect diminishes considerably, permitting ceria based electrolytes
to be used in SOFC without a large loss in cell efficiency. Contrary to
this trend, as the temperature of operation is lowered to 500C,
the contribution from the grain boundaries to the total resistivity becomes
significant. Thus the largest scope for reduction in the total resistivity
of Gd-doped ceria (CGO) electrolytes in the temperature range of interest,
must therefore come from reducing the resistance of the grain boundaries.
In most polycrystalline ceramics it is found that impurities present within
the materials tend to segregate to high energy surfaces such as the grain
boundaries and sintered surfaces. In doped polycrystalline ceria, these
impurities are thought to form an insulating phase at the grain boundaries,
producing a high resistance layer. It is likely that precursor materials
with high proportions of impurities will be used in the large scale production
of doped ceria electrolytes, to reduce the overall costs. It is therefore
necessary to develop a better understanding of the interplay between impurities
and the changing dopant concentrations in ceria, to enable the conductivity
in the electrolytes to be optimised. This paper will focus in detail on
the electrical properties of Gd-doped ceria electrolytes at low temperatures
and the trends observed with increasing dopant concentration. The potential
of high Gd concentrations in ceria for SOFCs operating at 500C
will also be explored and the effects of impurities, especially silica
will be discussed.
9:45 AM CC8.5
10:30 AM *CC8.6
DIFFUSION AND SURFACE EXCHANGE IN HIGH TEMPERATURE OXIDE
ION TRANSPORT MEMBRANES AND FUEL CELL ELECTRODES. Allan J. Jacobson , Department
of Chemistry, University of Houston, Houston, TX.
Membrane reactors that use dense mixed electronic-ionic
conducting oxide membranes for oxygen separation and for the production
of syn gas from natural gas (methane) have received much recent attention.
The oxygen flux achievable in these oxide membranes depends on a combination
of the bulk diffusion rate for oxygen transport and the surface reaction
rates for oxygen activation or reaction with methane. I will describe some
recent measurements of oxygen permeation and carbon monoxide oxidation
on several perovskite oxide membranes with different compositions. We have
developed a transport model to describe the data and to determine oxygen
diffusion coefficients and surface reaction rates. Results form other techniques
that also give information about the interplay between surface reactivity
and bulk transport in oxides, including isotope exchange, conductivity
relaxation and the use of ac impedance measurements on oxygen electrodes
will be discussed.
11:00 AM *CC8.7
DEVELOPMENT OF A HEAT-RESISTANT, ELECTRICALLY CONDUCTING
JOINT BETWEEN CERAMIC SOFC END PLATES AND METALLIC FE- OR NI-BASED CONDUCTORS.
Rolf Wilkenhoener , Argonne National Laboratory, Electrochemical Technology
Program, Argonne, IL; H.P. Buchkremer, D. Stoever, D. Stolten, Forschungszentrum
Juelich GmbH, Institut fuer Werkstoffe und Verfahren der Energietechnik,
Juelich, GERMANY; A. Koch, Dornier GmbH, Friedrichshafen, GERMANY.
Ceramic parts made of doped lanthanum chromite are used
as interconnects and end plates in stacks for several SOFC (Solid Oxide
Fuel Cell) designs. Metallic conductors have to be attached to enable a
low-resistance connection between individual stacks in each SOFC unit,
and to permit power to be drawn from the SOFC. The resistances of the metal-ceramic
bond and the metallic conductors have to be stable under operating conditions,
i.e. 1000C in air. Consequently,
heat-resistant materials have to be used. A two-step process to connect
commercially available, Ni- or Fe-based metallic conductors to ceramic
SOFC end plates by vacuum furnace brazing has been developed. A metallic
sheet, which acts as the current collector, is brazed on the ceramic end
plate. Thereby, the much lower electrical conductivity of the ceramic part
is compensated by that of the metal. Chromium alloys such as Cr5Fe1Y2O3
are suitable because they offer heat resistance, and their thermal expansion
coefficient is close to that of lanthanum chromite. Metallic wires or strips
are brazed on the current collector. Since this joint area is significantly
smaller than that of the first joint, materials with a different thermal
expansion coefficient can be used, such as conventional heat-resistant
nickel alloys (Inconel 617) and ferritic stainless steels (Fe22Cr5.5Al).
Filler alloys for both brazing steps with matching melting points have
been found. Hence, both brazing steps can be performed cost-effectively
in one heating step. Suitable parameters for vacuum furnace brazing of
both joints are presented, and the composition of the filler alloys is
given. Data concerning the long-term behavior of the joint resistances
in air at 1000C are discussed.
11:30 AM CC8.8
EFFECTS OF MICROSTRUCTURE ON THE ELECTRONIC CONDUCTIVITY
IN SrCo0.8Fe0.2O3.8. K. Zhang , M. Miranova,
Y.L. Yang, A.J. Jacobson and K. Salama, Materials Research Science and
Engineering Center, University of Houston, Houston, TX.
Perovskite oxides, such as LaxSr1-xMnO3,
have high electronic and ionic conductivities at elevated temperatures.
Extensive studies have been conducted to select the proper perovskite oxides
for applications in oxygen separation membranes, solid oxide fuel cells
and electrocatalytic reactors. Most of the studies have been focused on
the characterization of the electrochemical properties, particularly the
oxygen permeability and the elctron conductivity. Little, however, is known
about the effects of microstructure on the electrochemical properties of
these materials. In a previous study (1), the effect of microstructure
on the oxygen permeation in SrCo0.8Fe0.2O
(SCFO) was investigated, and it was found that the change in grain size
has strong effect on the oxygen permeation in this material. In this investigation,
the effect of the microstructure of SCFO on the electronic conductivity
is studied at elevated temperatures using a four-point dc method. The electronic
conductivity of this material was observed to increase with the increase
of the average grain size. The grain size effect seems to be more significant
in the lower temperature region where the electronic conductivity of this
material increases with the increase of the temperature. When the temperature
is further increased, the electronic conductivity decreases with the increase
of the temperature, and the grain size effect becomes less significant.
In order to determine the responsible mechanisms of these effects, effort
is being made to investigate the grain boundaries structure using TEM.
(1) K. Zhang, Y.L. Yang, D. Ponnusamy, A.J. Jacobson
and K. Salama: ``Effect of microstructure on oxygen permeation in SrCo0.8Fe0.2O''
Journal of Materials Science , in press, 19997.
*This work is sponsored by the National Science Foundation
through the MRSEC program under Award Number DMR-9632667.
11:45 AM CC8.9
POROUS THIN-FILM ANODE MATERIALS FOR SOLID-OXIDE FUEL
CELLS. J.D. Morse , R.T. Graff, J.P. Hayes and A.F. Jankowski, University
of California, Lawrence Livermore National Laboratory, Livermore, CA.
Methods to synthesize anodes for thin film solid-oxide
fuel cells (TFSOFCs) from the electrolyte and a conductive material are
developed using photolithographic patterning and physical vapor deposition.
The anode layer must enable combination of the reactive gases, be conductive
to pass the electric current, and provide mechanical support to the electrolyte
and cathode layers. The microstructure and morphology desired for the anode
layer should facilitate generation of maximum current density from the
fuel cell. For these purposes, the parameters of the deposition process
and post-deposition patterning are developed to optimize a continuous porosity
in the anode layer. The fuel cell microstructure is examined using scanning
electron microscopy and the power ouput generated is characterized through
current-voltage measurement. This work was performed under the auspices
of the United States. Department of Energy by Lawrence Livermore National
Laboratory under contract W-7405-Eng-48.
SESSION CC9: SOLID OXIDE FUEL CELLS
1:30 PM *CC9.1
MATERIALS DEVELOPMENT IN SOFC FOR DOMESTIC APPLICATION.
Kaspar Honegger , Sulzer Innotec, Roland Diethelm, Sulzer HEXIS, Winterthur,
Chair: Masayasu Arakawa
Thursday Afternoon, April 8, 1999
Metropolitan II (A)
Several small scale cogeneration demonstration units for
the domestic market have been operated successfully using planar SOFC for
more then 5000h. Experimental stacks based on selfsupported yttria stabilised
zirconia (YSZ) electrolytes, perovskite cathodes and Ni/YSZ anodes have
been operated for more than 15,000 hours with stable performance at operating
temperatures of 900 to 1000C.
Cost analysis of this standard technology showed the dominante influence
of the alloy used as interconnector and its protective coating against
chromium species evaporation. A reduction of the operating temperature
from 1000C to below 800C
showed a high potential to lower the stack costs. Commercially available
ferritc stainless steels have been examined. Low electrical resistance
characteristics have been obtained in air as well as in fuel environements
in long-term exposures at 700C.
Lightweight bipolar plates were manufactered by brazing pressed thin sheet
interconnector structures. Stable performance was obtained at temperatures
up to 800C in stacks based on
ceria-gadolinium electrolytes or on anode supported thin film YSZ electrolytes
cells interconnected with the novel bipolar plates.
2:00 PM CC9.2
NEW ANODE AND CATHODE MATERIALS FOR HIGHLY EFFICIENT
SOFCS. Masayasu Arakawa , Reiichi Chiba, Naoki Kato, Yoji Sakurai, Toshiro
Hirai and Ichiro Yamada, NTT Integrated Information and Energy Systems
Labs., Tokyo, JAPAN.
Energy consumption of Nippon Telegraph and Telephone Corporation
(NTT) is expected to greatly increase as we expand the multimedia services.
In order to reduce the energy consumption and accompanying environmental
pollution, NTT has been conducting researches on clean power generation
systems. Among others, we believe that solid oxide fuel cell (SOFC) is
most promising energy source because of its high energy conversion efficiency.
We have been working on cell structure and materials of SOFC. In this paper,
we report the researches on anode and cathode materials of SOFCs. It is
very important to keep an SOFC's anode overpotential low. In general, sintering
an anode at high temperature reduces the overpotential. However, SOFC composed
of a La(Sr)MnO3 cathode and Zr(Y)O2 electrolyte should
not be sintered at a temperature higher than 1300C,
since high-resistance inter-layer is formed at that high temperature due
to the reaction between the cathode and electrolyte. In order to overcome
this problem, we propose a new anode preparation method where Zr(Y)O2
are covered with nano-sized Ni particles and the structure is formulated
at 1300C. This new anode has the
electronic conductivity two or three times higher than the conventional
one with the same Ni content. Recently, many studies on SOFC materials
have been conducted for reducing the operation temperature of SOFC, since
lower operating temperature reduces production cost and improves long-term
reliability of the SOFC systems. We have discovered a new cathode material,
LaNi(Fe)O3, for this purpose. LaNi1-xFexO3
has a rhombohedral structure, whose electronic conductivity is about twice
as high as La(Sr)MnO3 at 800C.
The thermal expansion coefficient of LaNi0.6Fe0.4O3
is 11.1x10-6cm/(cm K), which matches well that of Zr(Y)O2.
2:15 PM CC9.3
INVESTIGATIIONS OF Fe-Cr FERRITIC STEELS AS SOFC INTERCONNECT
MATERIAL. Soren Linderoth , Peter Halvor Larsen, Riso National Laboratory,
There are several demands to a metallic material for use
as interconnect in Solid Oxide Fuel Cells (SOFC), e.g. low corrosion rate,
the scale must be well adhering to the metal and must possess a good electrical
conductivity, and a thermal expansion coefficient (TEC) close to that of
the remaining SOFC materials. These requirements have pointed towards the
use of a ceramic interconnect based on lanthanum chromite or a Cr-rich
alloy. The latter is produced by Metallwerk Plansee. Both of these materials
cause problems; the ceramic interconnect is subject to bending (and sometimes
cracking) due to dimensional changes upon reduction, and the metallic interconnet
is difficult to machine. Both materials makes up a substantial part of
the materials costs in the flat plate design. The recent trend for SOFC
developers is the use of thin electrolytes supported by the anode or cathode
material, thereby enabling SOFC operation at lower temperatures. The lower
temperatures promotes the use of metals as interconnect material, i.e.
the corrosion and Cr-oxide evaporation are reduced. The effective TEC of
the SOFC is in this case typically in the 11-13 10-6 K-1
range. As will be reported, the properties of ferritic steels fits well
this TEC requirement. We report on studies of TEC and corrosion properties
as a function of Fe/Cr ratio, atmosphere and temperature. The corrosion
performance is also shown to be improved significantly by a proper surface
coating. The thickness of the scale is reduced and the buckling of the
scale is minimized. The quality of the electrical contact between the interconnect
and the SOFC is also of great importance. Different contact experiments
using an Al-free ferritic steel will be presented.
2:30 PM CC9.4
MODELLING STUDY OF THE YSZ-BASED COMPOSITES ELECTRICAL
BEHAVIOUR. Giovanni Dotelli , Fabio Casartelli, Polytechnic of Milan, Dept.
of Industrial Chemistry and Chemical Engineering, Milan, ITALY; Isabella
Natali Sora, University of Brescia, Dept. of Chemistry and Physics for
Engineering and Materials, Brescia, ITALY; Chiara Schmid, University of
Trieste, Dept. of Materials Engineering and Applied Chemistry, Trieste,
ITALY; Claudio M. Mari, University of Milan, Dept. of Materials Science,
Electrical properties of yttria-stabilised zirconia/alumina
(YSZ/Al2O3) composites were tentatively foreseen
by simulating their complex impedance spectra. A digital image-based model
was developed to describe the electrical conduction process in polycrystalline
mono- or multi-phase materials. The microstructure of each polycrystalline
sample was reconstructed using the Voronoi tessellation technique (in fact,
ad hoc modifications with respect to the original algorithm were introduced)
and it was then converted into a three-dimensional electrical network according
to a set of well-defined rules. The network was solved (via a transfer-matrix
procedure) for different frequency values and successively the Nyquist
plot generated. The alumina content was considered as a parameter and thus
the complex impedance spectra of different composites at different temperatures
were simulated. Both the bulk and grain boundary electrical conductivity
were calculated and the Arrhenius plots obtained. Experimental and simulated
results were compared and discussed.