Table Of ContentINTERNATIONAL CONFERENCE
ON
ADVANCED AAATERIALS
-ICAM91-
Organised by the European Materials Research Society
Under the auspices of the
International Union of Materials Research Societies
Part of the
EMRS 1991 Spring Meeting
SOLID STATE OINCI S
Proceedings of Symposium A2 on
Solid State Ionics
of the International Conference on Advanced Materials - ICAM 91
Strasbourg, France, 27-31 May, 1991
Edited by:
M. BALKANSKI
Laboratoire de Physique des Solides
Universite Pierre et Marie Curie
Paris, France
T. TAKAHASHI
Nagoya University
Nagoya, Japan
H.L TULLER
Department of Materials Science and Engineering
Massachusetts Institute of Technology
Cambridge, MA, USA
1992
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Library of Congress Catalog1ng-in-Publ1cat1on Data
Symposium A2 on Solid State Ionics (1991 : Strasbourg , France)
Solid state ionics : Proceeding s of Symposium A2 on Solid State
Ionics of the Internationa l Conference on Advanced Materials(cid:151)ICAM
91, Strasbourg , France, 27-31 May, 1991 / edited by M. Balkanski, T.
Takahash i, H. Tu1ler.
æ. cm.
Includes bibliographica l reference s and index.
ISBN 0-444-89354-7
1. Solid state electronics(cid:151)Congresses . 2. Semiconductors -
-Congresses. 3. Ions(cid:151)Congresses . I. Balkanski, Minko, 1927-
II. Takahashi, Takehiko. III. Tuller, Harry L. IV. Internationa l
Conference on Advanced Materials(cid:151)ICAM 91 (1991 : Strasbourg ,
France) V. Title.
TK7871.85.S953 1991
621.381(cid:151)dc20 91-42719
CIP
ISBN 0 444 89354 7
© 1992 Elsevier Science Publishers B.V. All rights reserved.
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ν
PREFACE
The Series of International Conferences on Advanced Materials (ICAM)
is an initiative of the International Federation of Materials Research
Societies. The 1991 Meeting was organized jointly by the Ε-MRS: the
European Materials Research Society, and the International Materials
Research Committee.
Professor R.P.H. Chang was efficient in pressing Professor M.
Balkanski to accept the coordination of the different symposia forming
the Conference.
The Conference which was held in Strasbourg, May 27-31, 1991
consisted of the following symposia :
Symposium Al: High Temperature Superconductor Thin Films
Chairmen: L. Correra (Italy), Τ Kawai (Japan),
Τ Venkatesan (USA)
Symposium A2: Solid State Ionics
Chairmen: M. Balkanski (France), T. Takahashi
(Japan), H.L. Tuller (USA)
Symposium A3: Non-Stoichiometry in Semiconductors
Chairmen: K.J. Bachmann (USA), H.-L. Hwang
(Taiwan, R.O. China), C. Schwab (France)
Symposium A4: Composite Materials
Chairmen: A.T. Di Benedetto (USA), L. Nicolais
(Italy), E. Yasuda (Japan)
This volume assembles the communications presented in Symposium
A2: Solid State Ionics. Emphasis was put on theory as well as
experiments and possible applications were reviewed.
vi Preface
Sessions were held on:
Session I: Applications
Chairmen: J.B. Goodenough, W. Weppner
Session II: New Materials
Chairman: B.C.H. Steele
Session III: Insertion Compounds
Chairmen: C.RA. Catlow
Session IV: Transport
Chairmen: H.L. Tuller, Takehiko Takahashi
Session V: Structure
Chairman: D. Shriver
Session VI: Polymeric Electrolytes
Chairmen: F.G.K. Baucke, B. Scrosati
Session VII: Mixed Conductors
Chairmen: B.J. Wuensch
Session VIII: Protonic and Oxygen Conductors
Chairmen: G. Livage, I. Riess
Session IX: Electrochromics
Chairman: Tomonori Takahashi
Oral presentations and posters were selected out of a large flux of
abstracts. All papers published here were directly refereed according
to the standards of International Journals.
Symposium chairmen, M. Balkanski, T. Takahashi and H.L. Tuller,
appreciate the help of the Program Committee and particularly
acknowledge the efficient involvement in handling all kinds of practical
tasks related to the processing of the papers by young scientists of the
Laboratoire de Physique des Solides de TUniversite Pierre et Marie
Curie, J. Deppe, M. Eddrief, D. Ivanov, M. Hussain, C. Julien,
I. Kosacki and M. Massot.
The key role of holding together the whole structure of the Symposium
up to assembling and sending the manuscripts for publication was
filled by Mrs. M. Massetti to whom the chairmen express their deep
gratitude.
The Symposium largely benefitted from the generous help and devotion
of M.P. Siffert and Mrs. M. Adloff as well as Mrs. M. Cobut.
M. Balkanski
T. Takahashi
H.L. Tuller
vii
SYMPOSIUM INFORMATION
This Conference was held under the auspices of:
- The Council of Europe
- The Commission of the European Communities
It is our pleasure to acknowledge with gratitude the financial
assistance provided by:
- Ε-MRS (European Materials Research Society)
- Banque Populaire (France)
- Centre de Recherches Nucleaires (France)
- Centre National de la Recherche Scientifique (France)
- Service de Documentation Touristique du Palais des Congres de
Strasbourg (France)
- The Commission of the European Communities
- The Council of Europe
- The European Parliament
- The Brewery Kronenbourg (France)
and in particularly with respect to Symposium A2:
- Japan Storage Battery Company Ltd. (Japan)
- Mitsubishi Electric Corporation (Japan)
- Mitsubishi Heavy Industries (Japan)
- Sanyo Electric Company Ltd. (Japan)
- Toho Gas Company Ltd. (Japan)
- Yuasa Battery Company Ltd. (Japan)
Solid State Ionics
M. Balkanski, T. Takahashi and H.L. Tuller (Editors)
© 1992 Elsevier Science Publishers B.V. All rights reserved. 3
Development and Status of Sodium Sulfur Batteries
S. Menmcke
ABB Hochenerqiebatterie GmbH, Eppelheimer Strasse 82,
D-6900 Heidelberg 1, Germany
1. INTRODUCTION
Electric enercjy is a secondary energy but it is the most important form
of energy for an advanced industrial society. Reason for the importance of
electric energy is the fact that it can be converted with high efficiency
to many other forms of energy like radiation, heat or mechanical energy.
Historically primary and secondary batteries were the first sources of
eiectric energy. With the industrial use of generators and the development
of electric grids the scientific and technological interest in secondary
batteries grew rapidly as it. is shown by the development of the nickel iron
battery by Edison.
investigating the fields of technical use of the storage of electric
energy it can be seen very clearly, that the most important uses of elec
tric energy storage emerging are load levelling in eiectric grids, uninter-
ruptabie power supplies, and road traffic (Tab. 1).
Possible electrochemical devices to be used in these energy storage tasks
are primary batteries, combinations of fuel cells and electrolysers, and
secondary batteries. Since primary batteries and the combination of fuel
cells and electrolysers need a developed technology for transport and re
cycling of the energy carriers, hydrogen and electrode materials, their
application cannot bet expected in the near future. So secondary batteries
seem to be the devices most useful for electric energy storage now and in
the next years.
2. SECONDARY BATTERIES
The essential components of secondary batteries are electrodes which are
able to store and to release energy by a reversible chemical reaction, an
electrolyte which transports ions from one electrode to the other and a
separator which prevents direct chemical reaction of the electrodes
(Fig. 1). To assess secondary batteries it is necessary to develop criteria
of the fitness for purpose of these devices. The criteria depend to a
certain extend on the special application of the battery. Nevertheless,
some criteria are of common importance.
Common criteria are: Cycle life. Calendar life. Cost, Efficiency, Safety.
Specific criteria are: Energy density. Power density. Maintenance.
Ordering batteries by the time elapsed since the beginning of the deve
lopment it can be seen that the oldest systems are the best with respect to
4 S Mennicke
cycle life, calendar life, and cost. More recently developed systems are
advantageous with respect to energy density and efficiency (Tab. 2). Since
a system is improved more and more during the time of development there is
also necessary a consideration of the potentials of emerging systems
(Tab. 3).
So it can be shown that concepts as solid electrolytes and liquid elect
rodes used in emerging battery systems have the potential for tetter
performance than known, fully developed systems. Commercial success will be
determined, safety and reliability assumed to be given, by the cost per
energy unit stored mainly.
3. SODIUM BATTERIES WITH BETA-ALUMINA ELECTROLYTE
The discovery of beta alumina to be a solid electrolyte stimulated the
invention of the sodium-sulfur battery by Rummer and Weber [1] 1966· Since
the sulfur electrode has some difficulties some other systems were deve
loped replacing the sulfur electrode by different materials. The test known
approaches are the sodium antimony chloride battery of Werth and coworkers
[2] and the sodium nickel chloride battery invented by Coetze r[3 J.
The sodium antimony chloride battery uses SbCls dissolved in NaAiCU as
cathode material. The battery is discharged to SbCl3 and 2NaCl. To avoid
precipitation of NaCl there is an excess of AICI3 in the liquid electrolyte
at the cathode side. This electrolyte is a strong Lewis acid and causes
severe corrosion problems. This was the reason to stop the development of
tins system.
To overcome this problem Coetzer used a chlorine carrier which is insolu
ble in NaAiCJ.4. Doing this, precipitation of NaCl can be allowed. So it is
possible to work with an NaAlCl.4 composition which is rich in NaCl. This
electrolyte is a Lewis base with much lower corrosion problems. Besides
N1CI2 FeCl2r C0CI2τ and MnCl2 can be used as cathode materials. Other
systems with sodium anode and teta-al ununa solid electrolyte proposed in
the literature were not developed to technical cells.
3.1 Sodium Sulfur Technology
3.1.1 Cells
The chemical nature of teth electrode material demands for a ceil with
hermetic seals between the two electrodes and the ambient and between each
other. Additionally the key component of a sodium sulfur cell, the beta-
alumina electrolyte, can be manufacture:! without major problems to the
shape of plates or tubes. Using a tube, the length of the necessary seals
for a cell with given capacity and resistance is much lower than using a
plate. So all groups developing sodium sulfur batteries are using teta-
al umina tubes as solid electrolytes. Also the question whether to place the
sodium electrode inside or outside the solid electrolyte was decided
unanimously to the favour of the sodium inside technique, further common
decisions are to use a glass seal to join the solid electrolyte to an
insulating header and to use a hot pressing technique to join this header
to metal parts which are used to close the cell by a weld after assembling
the electrodes. This allows for explaining the function of a sodium sulfur
cell using a basic cell design which is common to ail developers (Fig. 2).
Development and status of sodium sulfur batteries 5
Discharging the cell sodium is transported as sodium ion through the
beta-alumina electrolyte to the cathode compartment. Here it reacts with
sulfur and forms sodium polysulfides. Because sulfur is an insulator it is
absorbed in a porous graphite materia] which carries the electronic current
in the electrode and at whose surface the electron exchange reaction takes
place. The porous graphite material, usually a graphite felt, contacts the
ceil casing which serves as the cathodic current collector. During discha
rge the sodium level in the anode compartment falls. To keep a large area
of the solid electrolyte wetted by sodium a wick or a separate sodium
container with a pressurized gas volume above the sodium discharging
through a hole in the bottom is used. In this case the sodium cartridge nay
serve as a current collector. Otherwise a special current collector has to
be placed into the sodium electrode.
The phase diagram (Fig. 3) of the sodium sulfur system shows that the
melting points of the sodium polysulf ides down to the composition Na2S:< lie
below 300 °C. This means that the battery must be operated above this
temperature to avoid freezing of the reaction products.
In addition it can be seen from the phase diagram too that there is a two
phase liquid in the composition range Na2Ss.2 to pure sulfur. In this
region there is a constant EMF of 2.08 V at 300 °C is established. In the
one phase region the EMF drops linearly to 1.78 V at the composition
Na2S2.7. The theoretical energy density for this composition range is 790
Wh/kg. Practical cells have an energy density of 200 Wh/kg.
3.1.2 Batteries
Necessary components of Na-S batteries are the cells, a heat insulation,
and feedthroughs for current and sensor leads (Fig. 4). For a safe opera
tion of a Na-S battery there is also a battery controller necessary. Since
the electrolyte ceramics cannot be manufactured in many different sizes
economically the capacity of a battery is adjusted to the requirements by
parallel connection of strings of ceils. Rules to be obeyed designing the
interconnection of a battery are derived from the behaviour of failed
cells. These have a low resistance in charging direction but they adopt
high resistance after loading by a discharge current. This means that it is
a good strategy not to connect single cells in parallel but strings of
cells. Doing so, it is possible to operate batteries with several failed
cells without severe loss of capacity and power if the number of strings
and the number of groups formed by the connections in parallel are suf
ficiently high. This will be the case for large stationary batteries. In
small batteries it is advantageous to bridge failed cells automatically by
appropriate switches.
The properties of the heat insulation depend on the size of the battery.
In large 'hatteries the heat loss is very low compared to the energy stored
in the battery. So an insulation using a conventional material will be
sufficient. For small batteries in electric vehicles there is a high demand
to keep heat losses low and to minimize the volume of the heat insulation.
Therefore, for such batteries evacuated heat insulations are used contai
ning insulation materials bearing the atmospheric pressure. Heat conducti
vities down to 2*10"3 W/m*K can be reached. For small batteries designed to
high power capability heat loss along the current leads is a problem which
demands for a proper design.
6 S. Mennicke
4. ISSUES OF THE SODIUM SULFUR BATTERY
Since the sodium sulfur battery is the first high temperature battery
system with a solid electrolyte this development opens a new field of
technology. So many problems were to be solved to proof the technical
feasibility of the system. Other problems are still to be solved to cross
the threshold to a successful commercialization of the system.
4.1 The Beta-Alumina Electrolyte
The β"-alumina tube used as both separator and solid electrolyte in
sodium sulfur cells has electrochemical and structural functions. There
fore, its electric and mechanical properties have to be optimized at the
same time. Furthermore, under operational conditions it is in contact with
two different highly corrosive liquids.
Mechanical properties: The beta-alumina tube is stressed in sodium sulfur
cells mechanically by freeze-thaw cycling mainly. The reason is the large
mismatch of thermal expansion coefficients of (Na) β"-alumina (7*10"6) and
Na-polysulfides (25*1U'6). Since sodium polysuifides are materials of low
strength the problem does not seem to be very serious at the first glance.
But in the sulfur electrode of a sodium sulfur cell the sodium polysuifide
is reinforced by the graphite felt acting as electron conductor in the
sulfur electrode. Though the sodium polysulfide-graphite felt-composite is
weakened by suitable methods a minimum strength of 100 MPa of the electro
lyte tubes is necessary. This means that crack initiating flaws larger than
300 μπι have to be avoided reliably. A second source for mechanical stress
is the overheating of spots of the solid electrolyte by inhomogeneous
operation of the electrodes [43. The reasons for these inhomogeneities,
insulating layers on the solid electrolyte and inhomogeneous distribution
of reactands in the sulfur electrode cannot be avoided totally. So it is
necessary to avoid surface flaws in the solid electrolyte as far a spos
sible.
Electrochemical properties: Since the transfer of sodium ions from the
(Na)β"-alumina to the electrodes does not need any significant activation
energy good sodium ion conductivity is the single electrochemical require
ment to the solid electrolyte. It is well known that th eβ"-phase contai
ning two mobile Na4-ions per conduction slab is more conductive than the
β-phase. Harbach [5] pointed out that the conductivity of th eβ"-phase
depends only on the composition of the material but not on the kind of the
dopant used for the stabilization of the β''-phase. Difficulties to reach
good mechanical properties with materials optimized for conductivity forced
several developers to choose compositions with a somewhat lower content of
stabilizing dopant.
Corrosion: Thermodynamic stability of β- and β"-alumina in sodium, sulfur
and sodium polysuifides at elevated temperatures was discussed in many
papers [6,7,8]. It may be concluded from these papers that pseudo-binary
β"-alumina is thermodynamically instable in sodium under the operational
conditions of the sodium sulfur battery. For lithia or magnesia stabilized
material no reliable thermodynami.c data are available. The experimental
evidence favours kinetic stability of the technical β"-alumina consisting
of a mixture of NaAl02, β-alumina, partially stabilized β"-alumina and
fully stabilized β"-alumina in sodium over several years. No change of the
phase content and no corrosional attack from the sodium side have been
found after several thousands of cycles of operation. Sodium dendrite
