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New Trends in Intercalation Compounds for Energy Storage
NATO Science Series A Series presenting the results of scientific
meetings supported under the NATO Science Programme.
The Series is published by lOS Press, Amsterdam, and Kluwer
Academic Publishers in conjunction with the NATO Scientific Affairs
Division
Sub-Series
I. Life and Behavioural Sciences II. Mathematics, Physics and
Chemistry III. Computer and Systems Science IV. Earth and
Environmental Sciences V. Science and Technology Policy
lOS Press Kluwer Academic Publishers lOS Press Kluwer Academic
Publishers lOS Press
The NATO Science Series continues the series of books published
formerly as the NATO ASI Series.
The NATO Science Programme offers support for collaboration in
civil science between scientists of countries of the Euro-Atlantic
Partnership Council. The types of scientific meeting generally
supported are "Advanced Study Institutes" and "Advanced Research
Workshops", although other types of meeting are supported from time
to time. The NATO Science Series collects together the results of
these meetings. The meetings are co-organized bij scientists from
NATO countries and scientists from NATO's Partner countries -
countries of the CIS and Central and Eastern Europe. .
Advanced Study Institutes are high-level tutorial courses offering
in-depth study of latest advances in a field. Advanced Research
Workshops are expert meetings aimed at critical assessment of a
field, and identification of directions for future action.
As a consequence of the restructuring of the NATO Science Programme
in 1999, the NATO Science Series has been re-organised and there
are currently Five Sub-series as noted above. Please consult the
following web sites for information on previous volumes published
in the Series, as well as details of earlier Sub-series.
http://www.nato.inVscience http://www.wkap.nl
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New Trends in Intercalation Compounds for Energy Storage edited
by
C.Julien Universite Pierre el Marie Curie, Laboratoire des Milieux
Desordonnes el Heterogenes, Paris, France
J.P. Pereira-Ramos CNAS/LESCQ, Thiais, France
aod
.....
" Springer-Science+Business Media, B.V.
Proceedings of the NATO Advanced Study Institute on New Trends in
Intercalation Compounds for Energy Storage Sozopol, Bulgaria 22
September-2 October 2001
A C.I. P. Catalogue record for this book is available from the
Library of Congress.
ISBN 978-1-4020-0595-4 ISBN 978-94-010-0389-6 (eBook) DOI
10.1007/978-94-010-0389-6
Printed on acid-free paper
AII Rights Reserved © 2002 Springer Science+Business Media
Dordrecht Originally published by Kluwer Academic Publishers in
2002 Softcover reprint of the hardcover 1st edition 2002 No part of
this work may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical,
photocopying, microfilming, recording or otherwise, without written
permission from the Publisher, with the exception of any material
supplied specifically for the purpose of being entered and executed
on a computer system, for exclusive use by the purchaser of the
work.
TABLE OF CONTENTS
Part 1. Lectures
Intercalation compounds for energy storage C. Julien, J.P.
Pereira-Ramos and A. Momchilov
.................................................. 1
Lithium intercalation compounds - The reliability of the rigid-band
model C. Julien
.................................................................................................................
9
Overview of carbon anodes for lithium-ion batteries K. Zaghib and
K. Kinoshita
....................................................................................
27
Electronic structure of various forms of solid state carbons -
Graphite intercalation compounds
J. Conard
................................................................................................................
39
From intercalation compounds to inserted clusters Li in carbon
superanodes for secondary batteries
J. Conard
................................................................................................................
63
Lithium NMR in lithium-carbon solid state compounds J. Conard and
P. Lauginie .. ....... ................... .........
.................. ...................... ........ 77
Critical review of HlCarbon literature and ab-initio research for a
chemical site between two coroners
F. Marinelli, R.J.-M. Pellenq and J. Conard
.......................................................... 95
Carbon-based negative electrodes of lithium-ion batteries obtained
from residua of the petroleum industry
R. Alcantara, R1 Fernandez-Madrigal, P. Lavela, 1L. Tirado, 1M
Jimenez- Mateos, C. Gomez de Salazar, R. Stoyanova and E. Zhecheva
.............................. 101
Hydrogen in metals J. Huot
....................................................................................................................
109
vi
Effects of composition in LalNi-based intermetallic compounds used
as negative electrodes in Ni-MH batteries
R. Baddour-Hadjean, J.P. Pereira-Ramos, M. Latroche and A.
Percheron-Guegan
.............................................................................................
145
Lithium insertion compounds for energy storage A. Manthiram
...........................................................................................................
157
Chemical and structural stabilities of layered oxide cathodes A.
Manthiram
..........................................................................................................
177
In situ preparation of composite electrodes : antimony alloys and
compounds R. Alcantara, F.J. Fernandez-Madrigal, P. Lavela, C.
Perez-Vicente and J.L Tirado
.......................................................................................................
193
On the use of in-situ generated tin-based composite materials in
lithium-ion cells R. Alcantara, F.J. Fernandez-Madrigal, P. Lavela,
C. perez-Vicente and J.L Tirado
.......................................................................................................
201
Physical chemistry of lithium intercalation compounds c. Julien
.................................................................................................................
209
Lattice dynamics of manganese oxides and their intercalated
compounds c. Julien and M. Massot
.........................................................................................
235
Physical chemistry and electrochemistry of intercalation in
disordered compounds C. Julien and B. Yebka
...........................................................................................
253
Modified host lattices for Li intercalation with improved
electrochemical properties J.P. Pereira-Ramos, S. Bach, S. Franger,
P. Soudan and N. Baffier ..................... 269
Surface science investigations of intercalation reactions with
layered metal dichalcogenides
W. Jaegermann and D. Tonti
..................................................................................
289
Conductive polymers and hybrid materials as insertion electrodes
for energy storage applications
P. Gomez-Romero
..................................................................................................
355
An electrochemical point of view on the intercalation compounds A.
Momchilov
.........................................................................................................
377
Manganese dioxides promising cathode materials for lithium
batteries B. Banov ...... .......... .... .... .............. ....
... ......... .... ... ......... ......... .... ..... ...... .....
...... ....... 393
vii
Part 2. Seminars
Impedance of diffusion of inserted ions. Simple and advanced models
J. Bisquert
...............................................................................................................
405
Dielectric relaxation spectroscopy for probing ion/network
interactions in solids F. Henn, S. Devautour and J. e. Giuntini
...............................................................
413
Cations mobility and water adsorption in zeolites G. Maurin, S.
Devautour, P. Senet, J.e. Giuntini and F. Henn
............................ 421
Strategies to improve the cycling performance of lithium storage
alloys M Wachtler, M. Winter and J.O. Besenhard
......................................................... 429
Nanoscaled containers for hydrogen J.D. Dragieva, Ch.D. Deleva, MA.
Mladenov and P.P. Zlatilova ......................... 433
Nanocrystalline materials for lithium batteries e. W Kwon, S.J.
Hwang, A. Poquet, N. Treuil, G. Campet, J. Portier and J.H. Choy
.........................................................................................................
439
Study of fluorinated graphite intercalation compounds J.P. Asanov,
P.P. Semyannikov and V.M Paasonen
.............................................. 447
Insertion of rare-earth metals into AgI-based compounds - First
evidence of disordering and strong modification of 13- and y-AgI
crystal structures
A.L. Despotuli ...
.......................................................................................................
455
Electronic structure of oxygen in delitiated LiTM02 studied by
electron energy-loss spectrometry
J. Graetz, R. Yazami, e.e. Ahn, P. Rez and B. Fultz
.............................................. 469
Short-range ColMn ordering and electrochemical intercalation of Li
into Li[Mn2_yCOy]04 spinels. O<y:s;; 1
E. Zhecheva, R. Stoyanova, P. Lavela and l.-L. Tirado
........................................ .475
Limitation of cathode electrolyte reaction in lithium ion batteries
H. Omanda, T. Brousse and D.M Schleich
.............................................................
483
The nature of the phase transition in LixMn204 J. Marzec, M. Marzec
and J. Molenda
...................................................................
489
viii
Morphology control of electrode materials for Li batteries through
sol-gel technique S. V. Pouchko, AK. Ivanov-Schitz, T.L. Kulova,
A.M. Skundin and E.P. Turevskaya
......................................................................................................
493
Cryochemical processing of cathode materials for lithium-ion
batteries O.A. Brylev, O.A. Shlyakhtin, A V Egorov, T.L. Kulova,
AM. Skundin and S. V. Pouchko
..........................................................................................................
497
Amorphous and active carbon: the quantum chemistry view on the
structure V.D. Khavryutchenko, A V. Khavryutchenko and V V Strelko
.............................. 501
Mechanochemical synthesis of intercalation lithium transition-metal
oxide compounds: some aspects of mechanism
N. V. Kosova
............................................................................................................
507
Electronic state of ions in mechanochemically prepared
intercalation lithium-transition metal oxide compounds
N V. Kosova, E. T. Devyatkina, VF. Anufrienko, V. V. Kaichev, V.!.
Buhktiyarov, S. V. Vosel, NT. Vasenin and T.V Larina
...............................................................
515
Part 3. Posters
A. Castro-Couceiro, S. Castro-Garcia, M.A. Sefiaris-Rodriguez, C.
Rey-Cabezudo and C. Julien
..............................................................................
523
Structural and electrochemical properties of V 205 thin films
obtained by atomic layer chemical vapor deposition (ALCVD)
A. Mantoux, J.e. Badot, N Baffier, J. Farcy, J.P. Pereira-Ramos, D.
Lincot and H. Groult ............ _
............................................................................................
531
Influence of thermal treatment and atmospheres on the
electrochemistry of V 205 as lithium insertion cathode
A.K. Cuentas-Gallegos and P Gomez-Romero
...................................................... 535
Dielectric dispersion and kinetics properties of Bi2Se3
intercalated by molecular iodine 1.1. Grygorchak and N.K. Tovstyuk
.........................................................................
539
High-frequency capacitor nanostructure formation by intercalation
l.l. Grygorchak, B.a. Seredyuk, K.D. Tovstyuk and B.P. Bakhmatyuk
.................. 543
Method of synthesis of electrode materials with controlled particle
size for lithium batteries
S. Uzunova, B. Banov and A. Momchilov
...............................................................
545
IX
Synthesis of cobalt substituted Li nickelates from a high
dispersity mixed oxide precursor R. Moshtev, P. Zlatilova, I.
Bakalova and S. Vassilev
........................................... 551
Application of the current interruption method for the measurement
of the ohmic resistivity of LiNi1_yCoy0 2 cathodes as a function of
the state of discharge
R. Moshtev, P. Zlatilova, I. Bakalova and S. Vassilev
........................................... 557
Pulsed microplasma cluster source technique for synthesis of
nanostructured carbon films P. Milani, P. Piseri, E. Barborini and
I.N. Kholmanov .......................................... 561
Oxygen intercalation in strontium ferrite: evolution of
thermodynamics and electron transport properties
M. V. Patrakeev, J.A. Shilova, E.B. Mitberg, A.A. Lakhtin, I.A.
Leonidov and V.L. Kozhevnikov
.............................................................................................
565
Insertion of aluminium into a boron icosahedral hollows as the
first step of nanofilaments
crystals formation A.!. Kharlamov, Ch. Trapalis, N. V. Kirillova,
S. V. Loytchenko, V. V. Fomenko and A.A. Kharlamova
.............................................................................................
573
Structure, microstructure and magneto-transport properties of
Prl_xBxC003_11(B2+=Ba2+, Ca2+) perovskite materials
B. Rivas-Murias, M. Simchez-Andujar, J. Rivas, A. Fondado, J. Mira
and M.A. Seiiaris-Rodriguez
..................................................................................
577
Electronic structure of LiMn204 Q.-H. Wu, A. ThifJen and W
Jaegermann
..............................................................
585
Electrochemical behaviour of manganese spinel obtained by a
controlled particle size method at low temperature
B. Banov, S. Uzunova, A. Momchilov and l. Uzunov
............................................. 591
Li-Si system studies as possible anode for Li-ion batteries I.
Samaras, L. Tsiakiris, S. Kokkou, O. Valassiades and Th. Karakostas
.............. 597
Synthesis. structural and thermodynamical characterization of
Mm(NiCo )5_xAlx alloys S. Bliznakov, E. Lefterova, M. Mitov, L.
Bozukov, A. Popov and I. Dragieva ....... 601
Structural and electrochemical studies of Li-Co-Cr-O oxides
prepared by wet chemistry N. Amdouni, C. Julien and H. Zarrouk
...................................................................
607
Influence on physico-chemical properties of LiFexMn2_x04 upon iron
doping K. Swierczek.1. Marzec, M. Marzec and J. Molenda
............................................. 613
Phase transition disappearance in Li1+liMn2_804 depended on lithium
excess M. Molenda and R. Dziembaj
.................................................................................
615
x
Processes of deintercalation of lithium fluoride out of exhausted
cathode materials of lithium batteries
A.A. Evtukh, v.N. Plakotnik and I. V. Goncharova
............................................... 619
Electrochemical properties of nanoparticies produced by borohydride
reduction M. Mitov, S. Bliznakov, A. Popov, l. Dragieva and l.
Markova ............................. 623
Problems of the intercalated layer structures C.D. Tovstyuk and
C.C. Tovstyuk
...........................................................................
629
Cryochemically processed Li2Cu02 for lithium-ion batteries A. V.
Egorov, O.A. Brylev, a.A. Shlyakhtin, T.L. Kulova, A.M. Skundin and
Yu. D. Tretyakov
.....................................................................................................
633
Investigation of charge carrying in Li-intercalated ordinary and
oxidized graphite-like materials
V.S. Kuts and V. V. Strelko
......................................................................................
635
Thermodynamics and kinetics of lattice gases: statistical mechanics
perspective V.S. Vikhrenko, G. S. Bokun and Y.G. Groda
......................................................... 641
Electrical and electrochemical properties of LiNi1•yCOy0 2 prepared
by sol-gel method L. EI-Farh, S. Ziolkiewicz, M. Benkaddour and C.
Julien ..................................... 643
Author index
...............................................................................................................
645
Subject index
..............................................................................................................
649
PREFACE
This volume is based on the lectures at the NATO Advanced Study
Institute, entitled 'New Trends in Intercalation Compounds for
Energy StorageN
, held at Sozopol, Bulgaria, from September 22 till October 2,
2001. It attracted almost 82 participants from 18 different
countries. A total of 38 lectures has been provided during this
AS!.
The meeting combined different types of scientists from advanced
experts to aspiring young researchers. It aimed at stimulating
future developments by providing across
borders-cross-fertilisation and exchange between previously
unconnected groups. This is reflected in the contents of the volume
which covers the lectures given. The book also contains in a second
and third parts seminar and poster presentations mostly from
younger participants with valuable complementation and
specifications to the lectures. The subject of intercalation
compounds is a major development in high technology which bears
considerable industrial potential. It is important to give the
opportunity to young scientists and engineers to be rapidly updated
by the best experts in the field. Meeting of western world
specialists with scientists from the newly freed eastern countries
is considered as an eminent priority because it concerns the basic
training of future engineers and the modern industrial development
of these countries. The selection of the participants was carefully
planned with these perspectives in mind.
With its topics the Advanced Study Institute constitutes an attempt
to bring together in an organised manner the areas work on new
technologies for uniting materials scientists with chemists,
electrochemists and physicists with the hope of increasing
communication and understanding of various aspects of sophisticated
materials. Recent advances in electrochemistry and materials
science have opened the way for the evolution of entirely new types
of systems for energy storage, the rechargeable lithium-ion
batteries, the electrochroms, the hydrogen containers, etc. with
greatly improved electrical performance and other desirable
characteristics.
The book encompasses all the branches linked in the progress from
fundamentals to applications: from description and modelling of
different materials to technological use, from general diagnostics
to methods related to technological control and operation of
intercalation compounds. Designing devices with higher specific
energy and power will require a deeper understanding of materials
properties and performance. In this way the status of materials and
advanced efforts based the development of new substances for energy
storage are covered.
The main topics developed of this book are as follows. Two brief
reviews presented here introduce the field of intercalation
compounds
with special emphasis to energy storage. Engineering design and
optimisation of materials are summarised.
The following six lectures concern the principles and technological
developments of carbon-based materials; carbon anodes have been
treated in all forms: amorphous carbons, graphite and GICs, hard
carbons, fibres, nanotubes, fullerenes, etc. Parameters determining
the potentials and capacities of electrochemical cells, thtO
fundamental aspects of intercalation reactions linked to battery
operation are reported. Materials
xi
xii
obtained from residua of the petroleum industry find also some
special emphasis. By a number of lectures great weight is also
given to recent work concerning the synthesis and structural
characteristics of new compounds. Application of alternative
anodes. in particular oxides and antimony alloys for lithium
batteries, are extensively discussed.
The excellent examples of intercalation compounds for energy
storage are. of course. metal hydrides. Hydrogen insertion is
experimentally evidenced in metals. alloys and nanocomposites. The
discussion on the structural modifications occurring in various
insertion compounds is presented in a systematic way, where the
interplay between theory and empirical data are emphasised. One
lecture on new compositions aOO structures of Ni-based
intermetallic compounds covers the fundamental background on which
Ni-MH batteries optimisation is envisaged. Several lectures on the
present status and progress in the field of conductive polymers and
hybrid materials as insertion electrodes for energy storage
applications are combined in this volume to an extensive
review.
In addition to structural and physico-chemical properties of
intercalation materials. in which ions and electrons are exchanged
along the charge transfer cycles, synthesis processes are widely
evoked. Here. we have complementary sets of lectures which covered
all aspects of material growth. Low-temperature route. mechanical
milling. etc. are evoked. One of these sets dealt with
transition-metal oxides prepared via wet chemistry method, namely
sol-gel process. Specific modem developments aOO openings to
applications for modified electrodes. i.e.. doped and substituted
materials. are discussed with a luxury of precision and details.
The discussion around these sets of lectures gave the prospective
for todais batteries and projected tomorrow's power sources.
A set of surface science investigations such as XPS, LEEDS. EELS.
etc .• which are probes for electronic structure, are also treated.
It is high vacuum physics aOO technology that allows in-situ
intercalation of alkali metals in layered frameworks. An extensive
discussion on the present status of research in advanced diagnostic
techniques for investigation of the charge transfer was presented
at the Institute.
It was also important to consider the practical ways in which the
intercalation compounds are applied in devices such as lithium-ion
batteries. The present status of the technology. difficulties
encountered. and advances to be expected are widely examined. These
aspects were covered in a set of lectures addressing the
fundamental reactivity arxl safety of advanced lithium batteries.
The effects of growth characteristics and preparation techniques on
the performance of materials. were examined in detail.
By the structure of the program and the quality of the lectures
this Institute constitutes an excellent basis for further
development of scientists and engineers in this rapidly growing new
field of intercalation compounds applications.
December 2001
ACKNOWLEDGEMENTS
It is a pleasure to acknowledge with gratitude the award from NATO
Assistant Secretary General for Scientific and Environmental
Affairs which was possible the Advanced Study Institute on "New
Trends in Intercalation Compounds for Energy Storage" within a
partnership programme on high technology. We are grateful to the
NATO Science Committee and the Scientific and Environmental Affairs
Division for their interest and helpful attitude to arrange the
meeting.
The help given by NATO to participants from Greece and by NSF to
students from USA is also appreciated for the preparation and
planning of the Institute.
Our thanks for financial and organisational support are also
directed to the Institut des Hautes Etudes pour Ie Developpement de
la Culture, de la Science et de la Technologie en Bulgarie, Paris,
and its director Professor Minko Balkanski (Universite Pierre et
Marie Curie, Paris).
We are indebted to our colleagues, lecturers and members of the ASI
Scientific Committee, for their valuable advise. We want to address
our special thank to our colleagues coming from North America,
Prof. Jacques Huot and Dr. Karim Zaghib who, despite a very
difficult situation following the appalling events of September 11
th, reached to Sozopol on time.
Of great value for the present success of this Institute and the
future development of the Centre for Scientific Culture in Bulgaria
is the personal involvement of Dichko Fotev, administrator of the
Sozopol Pochivna Basa of Bulbank.
We also wish to thank Miss Delphine Julien for giving so much of
her energy and helping the organisation of the Institute.
Finally, sincere thanks must go to the authors of the papers.
Without their timely submission of their manuscripts of high
quality, publication of these proceedings would not have been
possible.
xiii
C. JULIEN i , J.P. PEREIRA-RAMOS2 and A. MOMCHILOV3
J LMDH, UMR 7603, Universite Pierre et Marie Curie 4 place Jussieu,
case 86, 75252 Paris cedex 05, France 2 LESCO-CNRS, 2 rue
Henri-Dunant, 94232 Thiais, France 3CLEPS, Bulgarian Academy of
Sciences Acad. G. Bonchev Bl. 10, Sofia 1113, Bulgaria
As society becomes increasingly more dependent on electricity, the
development of systems capable of storing directly or indirectly
this secondary energy form will be a crucial issue for the 21st
century. Batteries, which are devices converting the energy
released by spontaneous chemical reactions to electricity work,
have some extraordinary properties in these regards. They store and
release electrical energy; they are portable and can be used
flexibly with a short lead time in manufacture. In this brief
introduction, we show the important functions of intercalation
compounds used in advanced systems for energy storage.
1. Energy Storage Ability
Energy storage (ES) can be obtained through various ways depending
on the stored energy:
- mechanical, like water stored behind a dam (potential energy) or
like high speed heavy wheel used to start marine engines (kinetic
energy),
- electrical in capacities (voltage is equivalent to potential
energy) or in superconductive coils with high values current
(equivalent to kinetic energy),
- chemical by storing separately two chemical elements like Li and
F, or molecules like H2S04 and H20 able to react when in contact,
producing a high value bonding energy. Also, ES in explosives where
the energy is obtained by chemical reorganisation pertains to this
class. Both use some kind of stored potential energy, differences
of the chemical potential.
- electrochemical storage is a variant of the chemical one where
the stored energy depends on the difference of bonding energy
between two different compounds of the same element, or ion, one
used as anode, the other one as a cathode. Classical example is the
lead battery where the oxidation degree of lead changes from one
electrode to the other one. Now a new very important component
appears in the form of the electrolyte able to transport the ion,
i.e. in that case sol. Two configurations exist for this ES: either
the chemical components are compressed together, with a mechanical
separator, between the electrodes able to give only one discharge
and then we speak of primary battery. or the system is reversible
(secondary) and able to be recharged electrically, as we do pump
water at the top of a dam. Another application is to use the high
surface area
C. Julien et al. (eds.), New Trends in Intercalation Compounds for
Energy Storage, 1-8. © 2002 Kluwer Academic Publishers.
2
of nano-structures with possibly intercalation compounds to produce
thanks to thin layers of charged species high value capacities.
Values such as Fig are now easily produced with the constraints due
to double-layer formation and potential stability (the earth
capacity in space is -1 F !).
The purpose of these lectures is to study in details the electronic
structure and the new bonding modes present in intercalation
compounds of various morphologies, and with intercalated species,
to satisfy the storage properties.
2. The Sustained Energy
It is well kwon that the present production on use of energy
displays serious problems to the global environment, particularly
in relation to greenhouse gas emission such as carbon dioxide which
provokes climate modification [1]. The challenge in moving towards
global energy sustainability can be assessed by the trends in the
use of fuels for primary energy supplies. Table 1 gives statistics
reported by the International Energy Agency (lEA). The total
primary energy supply in the world, in megatons oil equivalent
(Mtoe), was 5096 Mtoe in 1998 [2]. The lEA's forecast of the world
demand is 13,700 Mtoe in 2020.
TABLE 1. Total primary energy supply by fuel (in % terms) for the
world and forecast (lEA data [I]).
Energy supply 1973 1998 2010 2020
Oil 44.9 53.2 38.8 3~.3
Coal, biomass and waste 36.1 24.4 28.4 28.7
Gas 16.3 18.8 23.6 25.2
Nuclear 0.9 1.3 5.8 4.4
Hydroelectric power 1.8 2.1 2.6 2.6
Geothermal, wind, solar and heat 0.1 0.2 0.7 0.8
The goal of global energy sustainability implies the replacement of
all fossil fuels (oil, coal, natural gas) by renewable energy
sources (geothermal, biomass, hydrogen, batteries, etc.). The large
explosion of systems able to store energy may be considered to be
due to influences related to economy and connected to basic
problems in industrialised countries from the economical,
environmental, technological and political points of view. Many
technologies were recently developed for producing, storing and
saving electricity; they include lithium and lithium-ion batteries,
fuel cells, electrochromics, supercapacitors, etc. To reach the
goal of a high specific energy and energy density, two fundamental
requirements must be met by electrode materials: a high specific
charge, in mAhlg and a large difference between standard redox
potential of the respective electrode reaction leading to a high
cell voltage. These preconditions are usually achieved by reactions
of insertion electrode materials [3-4].
As electrical energy storage is required to power microelectronics,
i.e. cell phones and pagers, stand-by power systems, it is obvious
to consider the recent tendency of the technology. Figure 1 shows
the evolution of voltage at which the semiconductor devices operate
in a cellular phone. The voltage decrease is related to the
thickness of integrated circuits. This picture demonstrates that
the powering voltage could reach the range 2-3 V for integrated
circuit with a thickness of -0.2 mm. Of course, this issue led to
the design of batteries for telecommunication devices.
8.0 .............. ..,....., .......
,....,...,....,.....-r"T"T""'r'..,....,,....,...r"T""'I"'"T......,r-T""1
Year 96 98 00
Figure 1. The evolution of the voltage at which the semiconductor
devices operate in a cellular phone.
3. Intercalation Compounds
3
In intercalation systems such as Li in graphite, hydrogen in
metals, and alkali metals in transition-metal dichalcogenides [5],
the guest atom occupies certain host sites preferentially at low
temperatures while others remain empty. Because of this specificity
of the interactions between the guest atoms and the intercalation
lattice sites, a wide variety of intercalated structures can form,
including ordered vacancy compounds. This topotactic intercalation
mechanism is the basic concept for the material's application as an
electrode in rechargeable batteries, electrochromic displays, smart
windows, etc. The topotactic insertion-extraction reactions occur
by diffusion in one-dimensional (ID) channels, by 2D diffusion or
by 3D diffusion. Typical examples are given in Table 2.
Low dimensional materials are particularly susceptible to
intercalation reactions due to the presence of the weak van der
Waals forces between either strongly bonded chains or layers, but
three dimensional materials can also be host to intercalation
provided that interstitial sites exist and that these are
accessible to the incoming guest. This usually implies the presence
of channels which will aid diffusion. Further, some amorphous
substances can be used and this area is receiving increasing
attention. An intercalation reaction is topotactic in nature; the
reaction does not involve diffusive rearrangement of the host
atoms. Moreover, the guest species in such reaction may be neutral,
an electron donor, or an electron acceptor. For instance, water is
neutral guest as interlayer species in clays; oxygen is an electron
acceptor into the intergrowth structure of Ba2 YCU306, which
converts to superconductor; lithium is an electron donor in
secondary-batteries electrodes such as LixTiS2, LixV20 s, or
Li\.xMn204' In addition to the intrinsic properties of the
intercalation compounds itself, the geometric design of an
insertion-compound electrode is critically important [6]. The
principle of the geometric design is similar for every application.
An important strategy in the design and optimisation of an
electrode is the use of smaller intercalation-compound particles.
The smaller the particle size, the shorter is the distance a guest
species must diffuse in the solid electrode and the smaller the
change of the volume to surface area of the individual particles
during a discharge/Charge cycle (intercalationldeintercalation
process). Nevertheless, a compromise has to be found to balance the
particle size and the grain boundaries.
4
Dimension
Na,W03. Li,KFeSz graphite. coke. hard carbon (LiC6) Li. TiSz.
Li.MoSz intergrowth Baz YCu306+d Lij.xCoOz. Lij .• NiOz Hz.MgzNi.
LaNisH6 LixVzOs. Lij.,V30S. H,MnOz. LixMnOz Lij.,Mnz04.
Li,Fez(S04)3. Li4l3Tis1304
4. Systems and Cell Development
The reason of the widespread application of intercalation compounds
is their electrochemical insertion ability (electroinsertion) which
is intrinsically simple and reversible. The term electroinsertion
refers to solid-state redox reaction involving electrochemical
charge transfer coupled with introduction of mobile guest ions into
the lattice of the solid host.
4.1. LITHIUM-ION BATTERIES
Intercalation compounds appear mainly as a help for electrochemical
storage. The idea of using materials that undergo insertion
reactions as the electrochemically active components of batteries
began to be explored and accepted in the early 1970s [7]. Two
approaches consist in designing rechargeable lithium batteries with
the use of insertion compounds. The first system utilises an
insertion material as a lithium-ion accepting cathode material and
a lithium metal as the negative electrode, the so-called lithium
metal battery, i.e. LilffiS2 and LilN60 13 cells. The second system
consists in using two open-structured materials as electrodes
(Table 3), in which the lithium ions can be shuttled from one
intercalation compound acting as lithium-ion source to another
lithium ion accepting material. This type of battery is commonly
known as a lithium-ion (Li-ion) battery, i.e. LixCJILiCo02 and
LixCJILiMn204 cells.
A good reversibility is frequently obtained and the voltage, up to
4 volts, depends on the chosen intercalation compounds, mainly the
oxide in that case. But a good knowledge of the sites where the
active species is stored, is useful because we need to keep almost
constant the potential energy of the free element (e.g. the
potential energy of Li between graphene sheets is practically the
same as that of free metal). Basically, the charge-discharge
reactions of lithium batteries involve the generation of lithium
ions and their migration across the electrolyte and insertion into
the crystal lattice of the host electrode materials (Fig. 2). For
instance, lithium reacts with LiCo02 according to the
reaction
(1)
in which 0 represents the vacant octahedral sites. We need also to
keep attention to the mobility of the working species, related to
the diffusion through the potential barriers around the sites (e.g.
frozen Li in Li-batteries stops their efficiency at -30°C), and to
the parasitic reactions with the electrolyte. the mechanical
barrier, etc.
5
Any liquid or solid lithium-ion conductor may be used as a suitable
electrolyte. Solutions of lithium salts in aprotic organic solvent
or solvent mixtures are examples of liquid electrolytes, while
lithium ion conducting polymer membranes are examples of solid
electrolytes.
Positive electrode Electrolyte Negative electrode
Figure 2. The principle of lithium-ion battery.
Figure 3 shows the cell voltage vs. capacity for various
intercalation compounds used in lithium batteries. In the past few
years, Li-ion batteries have been introduced into the consumer
market, particularly the cellular phone and camcorder segments [8].
Li-ion batteries excel through their high cell voltage, low weight
and volume for given stored energy, favourable power output and
long cycle life. These outstanding features have led to considering
Li-ion batteries for electric vehicle (EV) applications [9].
5.0
LiCoQ,
> a-MnO z. MO~ •• V02 • '-' LiV3 0s 11.} TiS z 00 ~
f- • .CrO z ...... 2.0 M'i '0 > MoQ, • • TiOz
1.0 f- .WQ.
I I I
100 200 300 400 500 Capacity (mAh/g)
Figure 3. Cell voltage versus capacity for various intercalation
compounds used in lithium batteries.
6
TABLE 3. Electrochemical equivalents of negative and positive
electrodes used in lithium-ion batteries.
Materials Molar weight Density Reversible Specific capacity
(glcm3) range (Ox) (mAhlg) Negative electrodes U.C6(C) 72.06 2.0
0.5 186
U.~(g) 72.06 2.25 1.0 372
Wch 215.8 12.11 1.0 124
MoCh 127.9 6.47 0.5 105
U413 Tis1304 153.1 1.0 ISS
Positive electrodes UMn204 180.8 S.16 1.0 148
UCOO2 97.9 4.28 0.5 137
UNiCh 97.6 4.78 0.7 192
4.2. Ni-MH BATTERIES AND HYDROGEN STORAGE
Intermetallic compounds can store reversibly large quantities of
hydrogen through solid gas reactions to form intermetallic
hydrides, which has prompted their application in the field of the
electrochemical and chemical storage.
The battery application concerns the use of intermetallic hydrides
as negative· electrodes in the nickel-metal hydride battery to
replace the toxic heavy metal Cd electrode in Ni-cadmium batteries.
Major activities in the direction of developing commercial Ni-MH
rechargeable battery for portable devices concern the study of
ABn-
type intermetallic compounds (A: rare earth; B: transition metal;
2~n~5). More particularly, two classes of binary or pseudo-binary
intermetallic compounds are currently being developed: AB2-type
alloys (Laves type) are largely investigated due to their inherent
high hydrogen absorption capacity, but they suffer from
passivation, slow activation and corrosion. On the other hand multi
component ABs-type alloys (Haucke phase CaCus) are now widely used
in commercial batteries, despite some improvements are still needed
from kinetics and cycle life behavior. Electrodes made from ABs
compounds and AB2 Laves phases type alloys allow to reach electrode
capacities between 200 and 350 mAhlg and energy densities which are
30% higher and more than those of conventional Ni-Cd cells.
In addition to their application as rechargeable battery
electrodes, metallic hydrides may be used for chemical storage as
they can store hydrogen at low pressure while having volumetric
densities comparable to liquid hydrogen. In addition to their
utilisation as rechargeable-battery electrodes, insertion compounds
may be used for chemical storage. Metal hydrides are considered a
promising means of hydrogen storage mainly because they store
hydrogen at low pressure while having volumetric densities
comparable to liquid hydrogen. These systems are inherently safe
because the release of hydrogen in metal hydrides being an
endothermic process [10]. Furthermore, the concept of
nano-crystallinity is a new issue for hydrogen storage. Table 4
lists the density and hydrogen storage capacity in various
systems.
For instance, hydrogen may be stored more densely and conveniently
in a hydride such as H2xMg2Ni than as a liquid. It can be retrieved
from the hydride by modest heating in the thermally controlled
reversible reaction
(2)
7
TABLE 4. The density and hydrogen storage capacity in various
systems.
System Density (mol H:z/dm3) Storage capacity H2 wt. %
MgH2 55 7.7
LaNisH6 52 1.4
gas (275 K, 1 bar) 0.045 100 Iiquid(20K) 35 100
Hydrogen storage in porous carbon structures near the normal
conditions of temperature and pressure has triggered a great deal
of research in order to provide storage facility for transportation
systems [11]. The case of hydrogen insertion in carbon is specific,
quite different from light alkaline metals. It has not been
proposed for energy-chemical storage, but the hydrogen storage
itself in dense forms is problematic and if carbon succeeds in this
task, it should be considered as a chemical storage.
4.3. ELECTROCHROMICS
Reduction or oxidation of a transparent, i.e. white-powder, host
changes its colour, which makes possible an electrochromic displays
or a smart window. For example, white W03
film associated with an acidic electrolyte can be used in an
electrochromic display since the reversible reaction
(3)
products a dark blue tungsten bronze, Hx W03• Paired electrochromic
reactions have been used to construct a smart window [12].
4.4. ULTRACAPACITORS
For applications in which significant energy is needed in pulse
form, traditional capacitors as used in electronic circuits cannot
store enough energy in the volume and weight available. For these
applications, the development of high energy density capacitors has
been undertaken by various groups around the world [13]. The
simplest capacitors store energy by charge separation in a thin
layer of dielectric material that is supported by metal plates that
act as the terminals for the device. The energy stored in a
capacitor is given by 1I2CY2, where C is its capacitance and Y is
the voltage between the plates. In an ultracapacitor, the
electrodes are fabricated from high surface area, porous material
having pores of diameter in the nanometer range. There are carbon
black, aerogel carbon, anhydrous RU02 or doped conducting polymers
providing capacitance in the range 100-1300 F/cm3• Projections of
future developments using carbon indicate that energy densities of
10 mWh/g or higher are likely with power densities of 1-2
Wig.
s. Concluding Remarks
Investigations on intercalation compounds constitute a
multidisciplinary research of modem material science and
technology. There is also considerable global activity in wider
applications on insertion reactions that constitute a breakthrough
with these multi component materials in the development of storage
energy. The fascination with electrical energy storage is driven by
the potential superior performance of materials, by environmental
necessity, and by the fundamental challenges these technologies
present.
8
The most advanced technology using intercalation compounds concerns
the search of high performing systems for energy storage such as
metal-hydride batteries, lithium ion batteries, electrochromics,
etc. All these systems need optimised intercalation compounds.
Recently, new applications for nano-structured intercalation
compounds have been proposed in thin-films micro-batteries for
powering sensors, biomedical devices, credit cards, etc.
The aim of this NATO-ASI is to stimulate an intense discussion on
the fundamental and technological properties and prospects of a
large variety of intercalation materials such as graphite,
carbonaceous compounds, oxides, chalcogenides, clays, metal
hydrides and other related materials.
References
1. NOAA (2001) Washington, USA
(http://w.w.w.al.noaa.gov).ThegreenhousegasesincludeC02.CA4. 03,
N20 and CFC. In 2000, the atmospheric concenttation of CD2 was 368
ppm against 280 ppm in 1750. Each year, 5 metric tons of carbon
dioxide are added to the atmosphere for each person in the
USA.
2. International Energy Agency (2000) Key World Energy
statisticsjrom the lEA, 2000 Edition, Paris, France. 3. Winter, M.,
Besenhard, J.O., Spahr, M.E., and Novak, P. (198) Adv. Mater,
10,725. 4. Julien, C. and Nazri, G.A. (2001) in U.S. Nalwa (ed.)
Handbook of Advanced Electronic and Photonic
Materials, Academic Press, San Diego, vol. 10, 99. 5. Whittingham,
M.S. (1978) Prog. Solid State Chem. 12,41. 6. Julien, C. and Nazri,
G.A. (1994) Solid State Batteries: Materials Design and
Optimization, Kluwer,
Boston. 7. Armand, M. (1980) in D.W. Murphy, 1. Broadhead and
B.C.U. Steele (eds.), Materialsfor Advanced
Batteries, Plenum Press, New York, p. 145. 8. Nagaura, T. (1991)
Prog. Batteries Solar Cells 10, 218. 9. The following
considerations are based on the performance of the General Motors
Impact EV with a curb
weight of 1,350 kg. The car would achieve a range of -150 miles on
the highway and -120 miles in city driving using a 24-kWh Li
battery weighting -160 kg.
10. Uuot, 1. (2001) in this Book. II. Marelli, F., Pellenq, RJ.M,
and Conard, J. (2001) in this Book. 12. Campet, G., Portier, J.,
Wen, SJ., Morel, B., Bourrel, M., and Chabagno, J.M. (1992) Active
Passive Elec.
Compo 14, 225. 13. Burke, A. (2000) J. Power Sources 91,37.
LITmUM INTERCALATION COMPOUNDS. THE RELIABILITY OF THE RIGID-BAND
MODEL
C.JULIEN Laboratoire des Milieux Desordonnes et Heterogenes, UMR
7603 Universite Pierre et Marie Curie 4 place Jussieu, case 86,
75252 PARIS cedex 05, France
Numerous layered structured compounds are interesting materials in
which lithium intercalation occurs primarily without destruction of
the host lattice. In many cases a rigid band model is a useful
first approximation for describing the changes in electronic
properties of the host material with intercalation [W.Y. Liang,
Mater. Sci. Eng. B 3 (1989) 139]. This review paper presents
results obtained on transition-metal chalcogeoide compounds and
effects of lithium intercalation on transition-metal oxides as
well. We observed, nevertheless, that the rigid-band model is not
applicable to all of the layered intercalation materials. One may
argue that the applicability of the rigid-band model may be taken
as a test for the properties most desirable in a good intercalation
material. This needs yet to be more extensively documented for
their promising applications as insertion electrode in solid state
batteries.
1. Introduction
Layered compounds, in particular the transition-metal
dichalcogenies (TMDs) arxl transition-metal oxides (TMOs), can be
intercalated with a wide range of both organic and inorganic
materials which may have a profound influence on the physical
properties of the host compound. The intercalation reaction in
these compounds is driven by charge transfer from the intercalant
to the host layered compound conduction band and thus
electron-donating species can take place in such a reaction. The
reversible ion-electron transfer reaction is classically
represented by the scheme
(1)
in the usual case where (H) is the host material, A an alkali metal
and x the molar intercalation fraction. The electronic transport
plays an important role in such reaction toward the formation of
intercalation compounds. It also governs the phase transitions as
the parameter expansion of the host structure has an electronic
component. Consequently, it is possible to consider three classes
of intercalation reaction that correspond to the different steps in
the delocalisation of the transferred electrons. The level of
acceptance can be either a discrete atomic state, or a molecular
level of a discrete polyatomic entity existing in the structure, or
part of a conduction band.
The rigid-band model (RBM) is a useful approximation for describing
the changes in electronic properties of the host material with
intercalation. Sellmyer [1] distinguishes two versions of the
rigid-band model for dilute solid solutions which might be called
the
9
C. Julien et al. (eds.), New Trends in Intercalation Compounds for
Energy Storage, 9-26. © 2002 Kluwer Academic Publishers.
10
electron-gas RBM and the screened-impurity RBM. In the former, due
mainly to Jones [2], the valence electrons are regarded essentially
as in plane wave states and the only effect of alloying with an
element having a valence difference tlZ, is to change the free
electron density to a new value, that obtained simply by scaling
the valences of the solvent and solute according to their atomic
fractions in the alloy. In the screened impurity RBM of Friedel
[3], it is recognised that the electron gas cannot support an
electric field at long distances from the charge impurity. It can
be shown with a dielectric-screening or Thomas-Fermi level that the
conduction electron will redistribute themselves to screen out the
Coulomb field. In this case, any charged impurity added to a solid
will polarise the solid, and attract to itself.
EA
c e I. ca e U.
Figure I. The fundamental question concerning the evolution of the
Fermi level.
The concept of rigid-bands implies chemical stability of the
system. From the energetic point of view, this means the total
energy of the substance is little affected by the addition of
intercalant electrons. The consequence is that the structure too is
stable, and the only energy band involved in intercalation is the
narrow "d" conduction band in TMD materials for instance. These are
precisely the properties most desirable in a good cathode material
which provide features such as stable voltage against ageing and
mechanical durability [4]. It is most important, therefore, to
investigate theoretically and experimentally how well the
approximation can apply in a system employed for the lithium
battery cathode. In this paper the validity of the rigid-band model
is demonstrated by optical experiments and band structure
examination.
2. Lesson I. Lithium Intercalation in TiS2
Electronic band structure ofTMD materials have been generally
calculated using simplest molecular-orbital arguments [5]. The
schematic band structure of the MX2 compounds with octahedral and
trigonal prismatic co-ordination are shown in Fig. 2. In the simple
picture, during intercalation, the donating-electrons will occupied
one of the empty d bands. The simplest approximation to the band
structure of an intercalation compound is just that of the parent
host compound with the Fermi level moved up to accommodate the
extra electrons.
In LixTiS2 the magnitude of the Hall coefficient decreases with
increasing lithium content, confirming the occurrence of electron
transfer from the intercalate to the host [6- 8]. The electron
concentration is TiS2 before intercalation is 3. Ix 1020 cm·3
indicating that
11
this material is of stoichiometry Til.0044S2 [8]. Upon lithium
intercalation we observe a large decrease of the resistivity as
well as of the Hall coefficient. The carrier concentration in
electrointercalated samples increases to 5x1021 and 9.6x1021 cm-3
for x=0.25 and x=O.5, respectively. The Hall coefficient RH of all
the samples is nearly temperature independent, as would be expected
for a normal metal.
octahedral trigonal prismatic (a) (b) (a) (b)
Density of states N(E)
Figure 2_ Schematic band structures for all the TMDs compounds with
octahedral and trigonal prismatic co ordination. Sketches show the
electronic structures before (a) and after (b) lithium
intercalation with the respective position of the Fermi
level.
Klipstein et al. [6] explain this behaviour by a model involving
the interplay between inter-pocket and intra-pocket scattering of
electrons by longitudinal acoustic phonons, whereby the increase in
Fermi surface dimensions reduces the restriction on the wave-vector
of phonons that may take part in the scattering process, implying
that, as the carrier concentration increases, a should tend towards
unity and, simultaneously, the temperature T min' below which the
In(p-po) versus In(T) curve starts deviating from linearity, should
increase. This model, which was originally based on studies in
pristine TiS2 with a varying degree of stoichiometry, was later
verified to remain valid for higher carrier concentrations, such as
in TiS2 intercalated with lithium via the BuLi technique [7] or
intercalated with hydrazine [9].
Electron transfer is also apparent in the optical properties of
this system. Fig. 3 shows the absorption spectra, in the energy
range 0.5-6.0 eV of pure and Li-intercalated TiS2 [10]. In the
spectrum of the intercalation complex it is clearly seen that it
shows free carrier absorption below 1 eV for LiTiS2• We also
observe interband transitions which are the first direct allowed
transitions from the p valence to the d conduction band at the L
point of the Brillouin zone. Moving into the spectrum of Lix TiS2,
the onset of inter-band transitions is seen to have shifted to
higher energies and the oscillator strength under the absorption
band is roughly halved. Beal and Nulsen [10] argue that this is
exactly that one would expect if the dz band is now half-full
following saturation of the intercalation complexes.
12
Energy (eV)
Figure 3. Room-temperature absorption spectra of TiS2 and LiTiS2
(after [10]). The schematic band structure shows that the
rigid-band model may be used for the intercalation complexes.
Another optical experiment is the infrared reflectivity carried out
on Li-electro intercalated TiS2 [8]. Fig. 4 shows the temperature
dependence of the reflectivity spectra of pure TiS2 and Li
intercalated TiS2 single crystals. We observe a large shift in the
plasma edge for Li1.0TiS2 with respect to pure TiS2. According to
the single carrier Drude model, the analysis of the dielectric
function gives the values as follows. In TiS2• the plasma edge lies
around 1200 cm-1, whereas in LiTiS2 the plasma edge occurs at about
4000 cm-1 giving plasma frequencies of 1360 and 4100 cm-1,
respectively, if we take into account that the high-frequency
dielectric constant remains similar to that of the pristine
material and if we consider the electron effective mass as obtained
by Isomaki et al. [11]. At the L-point of the Brillouin zone,
Isomaki et al. estimate m.=O.4mo along the a-axis. This assumption
implies that the optical effective mass mopt has a value higher
than 1.3ffio. In the present studies, the Drude analysis gives a
carrier concentration of 1.7x1022 cm-3 for complete intercalation
of TiS2 at x=l. This is in excellent agreement with the
theoretically expected value of 1.75x1022 cm-3 and very close to
the value of 2.2x1022 cm-3 determined from Hall measurements.
We assume in the spirit of the rigid-band model [4] that
intercalation does not change appreciably the conduction band
effective mass, nor the high-frequency dielectric constant of the
host material. The charge transfer dn from the alkali-metal atoms
to the d-conduction band of the host compound can be directly
calculated from the difference between 00/ before and after
intercalation. Here dn is expressed in terms of the number of
electrons transferred per Ti atoms. Using this method we have
dn=0.9±0.1 electrons. The uncertainty of 0.1 electrons is thought
to be a reasonable estimate in view of the
13
assumptions made. It is interesting to note the large increase of
the plasma damping factor from 310 to 2160 cm-l in Til.oosS2 and
Li1.0Ti1.00sS2' respectively_ This increase is observed in the
energy-loss function by the broadening of the plasmon peak The
damping factor can be expressed as follows
r = lit = q/m*~H' (2)
where ~H is the Hall mobility of free carriers_ The observed
increase of r suggests a decrease of the Hall mobility or a
modification of the effective mass tin the intercalated sample_ In
Li!.OTi1.00SS2 the electron mobility measured by Hall effect has a
value of 1.9 cm2V-ls-l at room temperature [8]_ This value can be
related with those given in the literature of 13_5 and 035
cm2y-ls-l for TiS2 and LiTiS2, respectively [71-
100 100
.... • u u
50 50
.. -. 0 0 500 1000 1500 2000 2500 1000 2000 3000 4000 5000
Wavenumber (em-I) Wavenumber (em-I)
(a) (b) Figure 4. IR reflectivity spectra of (a) TiS2 and (b)
LiTiS2 as a function of temperature.
IR reflectivity spectra of the Li1.oTiLoosS2 sample shows
surprising departure from ordinary Drude behaviour, and there is
not a strong change in the IR spectra as a function of the sample
temperature in comparison with that in pure material [12]. The dip
in the reflectivity is close to the plasma frequency rop=4180 cm:l
extracted from analysis of the data using a Drude-like model with a
frequency dependent relaxation time, as
lIt(x,T,ro) = xto + a[(pT)2 +ro2]. (3)
A good fit to the optical data is achieved with the scattering rate
given by Eqn_ (3) which reduces to the ideal electron-electron
scattering behaviour in the isotropic three-
14
dimensional effective mass model [13]. For Li intercalated TiS2
sample, the temperature and frequency components of Eqn. (2) are
strongly screened by the first term (x'to) as shown in Fig. 5. This
may be due to the complete filling of the d-band associated with a
very low Hall mobility. In this case, it is difficult to evaluate
the optical mobility because the quantity o.>'t» 1 is no more
valid. Considering that Hall measurements on the LiJ.oTiJ.oosS2
sample give NH=1.8x1022 cm-3 and that the Fermi energy obtained by
optical reflectivity measurements is Ep=4180 cm-1=0.52 eV, we may
estimate the electron effective mass m*=0.49 mo. This value is very
close of that in pure material reported by Isomaki et al. [11]. In
conclusion, it can be seen from the electrical and optical
properties of the Li- intercalated TiS2 presented above that,
s-bands aside, they can all be explained in terms of the rigid-band
model. It is worth mentioning here that optical absorption results
by Scholz and Frindt [14] on Ag-intercalated TiS2 also agree with
this model.
Lo ~ 900 'l--
g' ·50 E to
o 100 200 300 Temperature (K)
Figure 5. Temperature dependence of the damping factor (inverse
relaxation time) for (a) TiS2 and (b) LiTiS2•
3. Lesson II. Lithium Intercalation in TaSz
Among the group-V TMDs, TaS2 has perhaps been the subject of
greatest interest, because of the fascination range of structural
and electronic properties that this material exhibits. Due to
valence electron occupying their di band, this metallic compound
can exist in either 1 T-, 2H-, or 4H-structure [15]. As a
consequence of the switching from octahedral (Oh) to trigonal
prismatic (TP) co-ordination, the shift of the dz2 band to lower
energies occurs gradually. The absorption spectrum of pure 2H-TaS2
shows a Drude edge below 1 e V associated with the free-carrier
absorption in this material owing to the half filled dz2 band.
After intercalation, the Drude edge disappears and the first dz2-1d
transition shifts toward lower energy. These changes are attributed
to the gradual filling of the dz2 band by electron transferred from
lithium.
The absorption spectrum of IT-TaS2 is shown in Fig. 6. Above 1.5
eV, the absorption bands are associated with the dZ\---7dz22 and
dz\---7d transitions, whereas the band above -3.5 eV owing to
p---7di2 transition. Charge transfer from Li to the host
15
lattice increases the population of the dz2 band and raise the
Fermi level Ep to a new energy, E' p. The displacement of the
strong absorption edge around -3 eV indicates a considerable
lowering of the dz2 band with respect to its position in the
pristine material. The lowering of the dz2 band is attributed to
the filling with electrons donated by Li, as well as the
modification of the crystal structure, e.g. an increase of the cIa
ratio after intercalation [16]. These results provide further
support to the argument that, upon lithium intercalation the
rigid-band model is not entirely applicable in 1 T -TaS2.
c ..J6 I ..... c z4 e Q
~2 < ,----- ........ _----,' -- O~1~--2~--3~--4~--~5--~6
Energy (eV)
Figure 6. Absorption spectra of pure IT-TaS2 and IT-LixTaS2• The
schematic band structure shows the lowering of the dz band upon Li
intercalation (after [15]).
4. Lesson III. Lithium Intercalation in 2H-MoS2
Among the group-VI TMD, MoS2 is one of the materials where
intercalation reactions induce a transition of the host related to
local ligand field modification. In that particular case,
molybdenum presents a trigonal prismatic sulphur co-ordination
which changes to the octahedral one (TP~Oh transition) [17-19]. The
structure modification is accompanied by an increase of the M-X
band ionicity in agreement with the respective stability of the new
atomic arrangement, the Coulomb repulsion between partially charged
ligands favouring the octahedral form. Also, comparison of the
d-band density cf states for 2H-MoS2 and hypothetical I T-LiMoS2
show that the occupied bands which contain six states are lower in
the case of the Oh phase corresponding to the glide
16
process between Mo and S atoms. This is a fine example of
destabilisation through lithium reduction.
The transformation from (TP) to (Oh) co-ordination is attributed to
a process which is driven by a lowering of the electronic energy
for the octahedral structure when electrons are donated from Li to
the MoS2 layer upon intercalation [4]. The octahedral
transformation starting at x=<O.l completes around x=1.0 and is
preserved on subsequent cycling. Cell discharge-charge occurs in
the range 2.2-1.3 V with a mid-discharge voltage of -1.7 V.
Electron diffraction studies on the Li-MoS2 system have shown that
this transformation is accompanied by a 2aox2ao superlattice
formation [20].
:t:' S ...l ,,; > (: Gl
!. r-: .' . , t:rN: : ~ .
0.0 0.5 1.0 1.5 2.0 2.5 x(Li) in Lix MoS2
Figure 7. (a) Discharge curve of LilILixMoS1 and (b) related
incremental capacity, -rJxjaV.
Fig. 7a-b shows the cell voltage vs. composition of Li/ILixMoS2 and
the related variation in the inverse derivative voltage, -ax/iN, at
ambient temperature [19]. The natural sample has a 2H-MoS2
structure and upon Li intercalation behaves as a two-phase system.
The first phase is the initial material and the second one is the 1
T -structure of Lil.()MoS2 which appears at x=1 [17]. The
incremental capacity (Fig. 7b) that the cathode material exhibits a
complex intermediate behaviour; at least four states can be
observed up to Li\.oMoS2' but the analysis of such a feature is
very difficult because the validity of the Fick law requires that
the host material remains single phased. However, it is interesting
to note that, in this case, the cathode is highly strained and each
of the above states can be described approximately with an
interaction energy, UO,!' of the intercalant. At room temperature
the difference in standard potential UO,! of the successive states
is very small.
17
The structure observed at x::0.25 in the incremental capacity (Fig.
7b) may be related with the superlattice formation identified in
the Raman scattering measurements of LiO.3MoS2 by Sekine et al.
[21-22] and in the electronic microscopy diffraction mode by
Chrissafis et al. [20] corresponding to a 2aox2a., superlattice
which is interpreted as a pseudo-staging on the basal hexagonal
lattice (Fig. 8). However, we do expect that LixMoS2 is accompanied
by the raising of the Fermi level due to the charge transfer from
Li intercalation. This is depicted in Fig. 9 where the temperature
dependence of the electrical conductivity of lithium intercalated
MoS2. Undoped MoS2 is an-type semiconductor with o-exp(-E/kBT),
where E.=0.05 eV, and Lio.3MoS2 is a highly degenerate
semiconductor with 0-rIA. Here, we must be aware of the limitations
of the rigid band model. It is probably non appropriate for LixMoS2
because the fully occupied di states in the pristine material imply
new electrons to enter the next higher "d" band with a change of
the cIa ratio associated with the destabilisation of the host
lattice.
Figure 8. Li intercalation of MoS2 in n-butyllithium. (a) After to
min. defects are created near the edges and in the steps of the
specimen denoted by arrows. (b) After 2 h intercalation.
superlattice spots appear (denoted by the letter s). which are
indexed as (11201120). Notice also the splitting of the main spots
(denoted by the letter M). (c) A microcrograph taken from the same
area reveals that the specimen is heavily defected owing to
intercalation. (d) Distribution of lithium vs. Distance from the
edges of the specimen as revealed by SSNTD images.
Following the above structural transformation, phonon spectroscopy
offers an excellent way of quantifying the degree of anisotropy not
only by distinguishing inter-
18
and intra-layer normal modes but also determining the shear moduli
in different directions. The Raman spectrum of 2H-MoS2 at room
temperature is shown in Fig. 10. It exhibits four Raman-active
bands that are the intra-layer A!g mode at 407 cm·! involving
motion along the c-axis, the intra-layer ~g mode at 382 cm·!
involving motion in the based plane, the E!g mode at 286 cm·! and
the rigid-layer (RL) mode at 32 cm-! of ~g symmetry. This last mode
is of interlayer type involving rigid motion of neighbouring
sandwiches in opposite phase.
1000
Temperature (K)
Figure 9. Temperature dependence of the electrical conductivity of
lithium intercalated MoSz.
5 D
100 200 300 400 Raman shift (cm-I)
Figure 10. Raman spectra of 2H-MoSz natural crystal as a function
of Li content lithium.
The Raman spectra of LixMoS2 with x=O.1 and x=O.3 (Fig. 10) display
the structural changes from the B-phase (2H structure) to a
a.-phase (IT structure) upon Li
19
intercalation [21-22]. This transformation from trigonal prismatic
to octahedral c0-
ordination has been attributed to a process which is driven by a
lowering of the electronic energy for the octahedral structure when
electrons are donated from Li to the MoS2 layer on intercalation
[7.1]. The octahedral transformation in LixMoS2 starts at x=O.l
arxl completes around x=l. For a degree of intercalation x:::::O.l,
the Raman intensity is considerably reduced (by a factor 5) and we
observe two new bands: a broad peak located at 153 cm-' (A-line)
and a weak peak situated at 205 em-' (B-line) and the intensity of
the RL mode is reduced. The two pristine intra-layer modes can
still be observed, with little shift in frequency, but both are
split to give weak additional side bands towards lower energies (C-
and D-line). These band are attributed to the Davydov pairs of the
optical phonon branches. For x=O.3, the spectrum of LixMoSz is
modified compared with the former ones. The RL mode is not longer
recorded. All other lines are still observed. We remark the small
shift in frequency of the lattice modes of MoS2 [22].
A simple model has been used to calculate the frequencies of the
new modes appearing after Li intercalation. The intercalation mode
is given by
(4)
where m, and m2 are the masses of the MoS2 molecule and of the Li
atom, respectively, and k is the force constant between the Sand Li
atoms. We estimate k=8.23x103 dynlcm, which is much smaller than
the intra-layer force constants.
For a degree of intercalation x=0.3, we assume that LixMoS2 is a
two-phase system. The following changes on the lattice dynamics can
be expected. The RL mode disappears because the elementary cell of
the IT-structure contains only one molecular unit (3 atoms per
sandwich). The symmetry changes from D6h to D3d and the new
symmetry allows only the two Raman active AlB and Eg modes which
are representative of the intra layer atomic motions. The weak
spacing expansh.>n observed upon Li intercalation arxl the
difference of the molybdenum co-ordination do not modify
significantly the frequency of these modes. A simplest calculation
gives a change of about 6% in frequency. Thus, we can trust the
validity of the lattice dynamics model using a 2H-structure
[22].
5. Lesson IV. Lithium Intercalation in Mo03
The molybdenum oxides display a varieties of structural types
involving linked Mo06
octahedra whose arrangements are favourable for intercalation
process. These materials offer high voltages and composition
intervals accessible for lithium intercalation are wide. The
interest of a-Mo03 arises from its layered structure presenting
open channels for fast Li-ions diffusion, a higher electrochemical
activity vs. LilLi+ than that of chalcogenides and the highest
chemical stability among the oxide lattices [23]. Fig. 11 shows the
first discharge charge curves of a LiJ/Mo03 cell using a
well-crystallised film. This film grown by sputtering technique on
nickel substrate in oxygen partial pressure of 100 mTorr displays
the electrochemical features of the a-Mo03 phase [24].
Fig. 12 shows the temperature dependence of electrical conductivity
of LixMo03 (O.O=:;x::S;O.3) intercalated by electrochemical
titration. One observes a clear departure from semiconducting
behaviour of pure Mo03 material to degenerate semiconductor of Li
intercalated Mo03 even at low Li content The metallic features are
also observed in the temperature dependence of the Hall
coefficient. The observation of plasma absorption in this material
implies carrier concentration of at least 10'8 electrons/cm3
indicating a weak variation of the free-electron effective mass and
of the high-frequency permittivity. In
20
Mo03, the bonding framework is composed of five O(p ) and three
MO(~g) orbitals which interact to form nand n* bands [25]. As the
antibon~ing n* states hold the extra electrons supplied by the
inserted lithium, Lio.3Mo03 may be expected to exhibit two
dimensional electronic conductivity. The narrowing of the
conduction band is expected to lead to an increase in the effective
electron mass which can affect the position of the Drude edge in
LixMo03 phases. The conductivity of Mo03 is believed to exist
because of the electron hopping between MoM and Mos+ sites. The
nature of the conductivity variation observed in Fig. 11
corresponds to a steadily decrease with the addition of
intercalants. Intercalation of lithium ions in the Mo03 structure
is believed to lower the valency state of molybdenum ions by
transfer of electrons from lithium to molybdenum. The relative
concentration of MoM and Mos+ ions results in the lowering of the
conductivity towards a insulator behaviour. Further experiments are
needed to elucidate the mechanism of the charge transfer occurring
in transition-metal oxide compounds but the rigid-band model seems
adequate in LixMo03 which found technological application in
electrochromic rear mirror in automotive industry.
.-., 3.5 +
~ 3.0 o-l ...; > 2.5 :> '-" cu bIl :I 2.0 '0 > ~ 1.5
U
1.0 0 0.3
1.5
Figure 11. First discharge charge curves of a LilIMo03 cell using a
well-crystallised film grown by sputtering technique Ni substrate
(after [24)).
10-1 I
LixMoOs '0 '. c:: 0 10-4 r '. u '. ", .. . . , . x=O.OO r . .. . '
. ..
10-5 • I I I I I
2 4 6 8 10 12 14 IOOOff (K-I)
Figure 12. Arrhenius plot of the electrical conductivity of a.-Mo03
and LixMo03•
21
Infrared absorption studies of LixMo03 compounds revealed a
transition from metallic to small-polaron features [26]. After
intercalation the lattice vibration spectrum is completely screened
by the free electrons in the host material. The Drude edge
contribution, i.e. plasmon feature, is responsible of the metallic
absorption due to high electron density in Lio.3Mo03 as shown in
Fig. 13. The free-carrier absorption coefficient can be expressed
by
a = wp2 't' [n c (l+Clh2)], (5)
where wp is the plasma frequency, 't' is the relaxation time of the
free carrier, n is the refractive index and c the light velocity.
Using Eqn. (5), the fit of experimental data gives a carrier
concentration of 5xlO16 cm-3 in Lio.3Mo03. This value is in good
agreement with the Hall measurements. The temperature dependence of
the absorption coefficient shows a small increase of a with
temperature, which can be attributed to the fact that Li
intercalated Mo03 is a degenerate semiconductor for x=O.3.
1.6
1.4
-e 0 0.6 ell
Wavenumber (em-I)
Figure 13. IR absorption spectra of a-Mo03 and Lio,Mo03.
Nadkarni and Simmons [27] studied the electrical properties of Mo03
and reported that there is a donor band between the conduction and
the valence bands due to oxygen vacancies. Mo03 has the outer
electron configuration 4s5 5s1. If Mo03 is considered to be ionic,
i.e. composed only of Mo(VI) and 0 2- ions, the valence band would
be composed of oxygen 2p states and the conduction band of empty 4
d and 5s states [28]. Upon Li intercalation the electrical
conductivity of LixMo03 increases by two orders of magnitude and
the temperature dependence of 0' shows important changes in the
conduction mechanism. The semiconducting character of Mo03
gradually disappears and, for a degree of intercalation of x = 0.3,
the material exhibits a metallic behaviour.
6. Lesson V. Lithium Intercalation in V60 13
V 6013 is a black material which derives from the Re03 structure
and is intermediate in composition between V02 and V20 5• In this
family, V30 7 and V40 9 appear to have an intermediate structure
between that of V60 13 and V20 5• The monoclinic structure of V60
13
22
contains edge-shared distorted Y06 octahedra forming single and
double zig-zag chains linked together by further edge sharing
comer-shared. The resulting sheets (single am double) are
interconnected by comer sharing, thus giving a tridimensional
framework [29]. This structure contains tri-capped cavities joined
through shared square faces. The three open faces of the cavity
should permit lithium-ion diffusion along (010) with the
possibility of exchange between pairs of adjacent channels.
Stoichiometric Y 6013 can be written as (y4i-Mys+MQ2-)13 as far as
the valency state of the vanadium ions are concerned.
The structure of Y 6013 is interesting from an electrochemical
viewpoint due to the theoretical maximum limit of lithium uptake
giving a energy density of 890 mWh/g. The stoichiometric Y 6013
structure is believed to accommodate 8 Li per formula unit as
determined by the available electronic sites rather than the
structural cavities [30]. The limit corresponds to a situation when
all the vanadium ions are present in the trivalent y3+ state. As a
function of the stoichiometry, the maximum uptake goes to 1.35 Li
for Y02.18 oxide. Reversible chemical and electrochemical insertion
of lithium into Y60 13
was first demonstrated by Murphy et al. [31-32], and its potential
as an active cathode material in practical batteries has since been
more fully investigated [30]. The discharge curve exhibits three
distinct plateaus, reflecting the sequential ftlling of
unequivalent sites in the host structure_
,......., -S ~ en '-' t:l
2.0
0.0
-2.0
-4.0
-6.0
-8.0
lOOOff (1(-1)
Figure 14. Arrhenius plot of the electrical conductivity of V 6013
and Li. V 6013 (OS;xS;6).
Fig. 14 shows the Arrhenius plot of the electrical conductivity of
Y60 13 and Li,V6013 (0~x~6). The pure material has a conductivity
of lxlO-2 S/cm at room temperature and exhibits a semiconductor
behaviour. The electronic conduction in Y60 13
is due to the electron hopping between y4i- and Vs+ states. The
nature of the conductivity observed in Fig. 14 corresponds to a
steadily decrease with addition of Li-ions in the Li.V60 13
framework. Intercalation of Li-ions is believed to lower the
valence state of vanadium ions by transfer of electrons. The
relative concentration of reduced cations results 10 the lowering
of the conductivity towards a poor electronic semiconductor.
23
Electronic conductivity of pressed V 6013 powders indicates a sharp
fall in two steps with increasing Li content [33-34]. For lithiated
V60 13, we observe a continuous decrease of the electrical
conductivity. Lowest conductivity of 5xlO-4 S cm-l has been
measured in Li6V60 13. This is also accompanied by an increase in
activation energy, a general phenomenon observed in any oxide with
small-polaron conduction.
Infrared studies of Li. V 6013 compounds revealed the transition
from metal-like to small-polaron features (Fig. 15). In pure V
6013' one has a Drude edge around 200 cm- l
which is the contribution of the free charge-carriers. For
lithiated V 6013' we observe a continuous decrease of the
electrical conductivity which is also recorded in the far-infrared
spectrum by the disappearance of the Drude absorption [26].
1.0
~ 0.2
Wavenumber (em-!)
7. Lesson VI. Lithium Intercalation in LiCo02
Lithiated transition metal oxides with a layered, a-NaFeOrtype,
structure such as LiMe02 (Me=Ni, Co) have been a great interest as
positive electrode materials tor rechargeable lithium batteries.
LiCoOz has been proposed as cathode for lithium battery by
Mizushima et al. in 1980 [35] and currently it is being used in
commercial rechargeable Li-ion batteries by Sony [36]. Fig. 16
shows the potential curve of LiCo02
during the first charge in the potential range 2.5-4.2 V vs.
LilLi+. The charged capacity was 155 mAhig for the cathode and
matched well with published data [37].
Fig. 17 displays the FTIR absorption spectra of LixCo02
cathode-active materials as a function of the lithium content. As
predicted from the factor group analysis, one observes four
distinct bands in the FTIR absorption spectrum of pristine LiCo02•
They are located at 269, 420, 539, and 602 cm- l . The spectrum of
LiCo02 matches well with those reported previously [38-40]. A
closer examination of the shape of the high vavenumber band at 602
cm- l indicates that a shoulder exists at 646 cm- I . We remark the
shape of the IR band at 269 cm- l which corresponds to an
oscillator with a great strength. The infrared-active bands shown
in Fig. 17 are generally broader that those observed in Raman
spectroscopy [41]. The broadening of IR bands is attributed to the
average oxidation state of Co, which are oxidised into the COIV
state during charge of the cell, and to the random distribution of
Li+ ions in the interlayer space.
24
~ ;:: 0 LiCo02 > 3.0 --CI)
2.5 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x(Li) in LixCo~ Figure 16. The potential curve of LiCo02 during the
first charge in the potential range 2.5-4.2 V vs. LilLi' (0.1
mAlcm2 current density).
tI) ..... ..... s:: ::s Q) (.)
100 200 300 400 500 600 700 Wavenumber (em-I)
Figure 17. FfIR absorption spectra of LiCo02 as a function of the
Li concentration.
To get a better understanding of the vibrational spectra of the
layered LiCo02 with R-3m space group, we consider a structure which
consists of compressed Co06 and
25
elongated Li06 octahedra that yields distinct vibrations in two
different frequency regions, i.e. at 400-650 cm-! there are bands
due to Co06 vibrations, while the Li06 vibrations are within the
region 200-400 cm-!. Infrared bands located in the high-frequency
region, i.e. at 602 and 539 cm-!, are attributed to Co-O stretching
and O-Co-O bending motion, respectively. The low-frequency band
situated at 269 cm-! involves the motion of Li atoms against their
oxygen neighbours in an octahedral environment. This peak is
related to an asymmetric stretching vibration of Li06 units
[40].
There are obvious modifications of the FfIR spectrum of LiCoOz upon
lithium 00- intercalation (Fig. 17) as follows. (a) We observed a
decrease of the oscillator strength and a broadening of all the
IR-bands which can be associated to a disorder induces by the
departure of Li-ions located between two CoOz blocks. The
broadening of the low frequency band can be also attributed to the
random distribution of the Li-ions remaining in the host matrix.
(b) No frequency change is observed for the high-wavenumber bands
which are assigned to the Co06 vibrations. Thus, as expected, we
can conclude that the CoOz layers are not affected significantly by
the lithium de-intercalation process. (c) A significant shift of
the low-frequency band is recorded. This band shifts toward the
low energy side from 269 to 258 cm-! in Lio.sCoOz. The frequency
shift corresponds to the increase in the interlayer spacing due to
an increase of the repulsive interactions between two adjacent
negatively charged CoOz layers upon de-lithiation. Thus, the
interlayer force constant is reduced by about 8%.(d) The increase
of the far-infrared absorption of Lio.4CoOz sample is attributed to
the Drude edge due to the change in the electrical conductivity of
the material. This suggests the existence of collective delocalised
electrons. These results agree well with the data of electrical
measurements which show that LiCoOz has a semiconductor-like
conductivity while Li,CoOz exhibits almost a
temperature-independent conductivity [42].
LiCoOz is a p-type semiconductor (band gap Eg=2.7 eV) [43] while
Li,CoOz for x$0.75 has a metal-like behaviour. Li,CoOz is predicted
to have partially filled valence bands for x lower than 1.0 [44].
For every Li removed from LiCoOz lattice, an electron hole is
created within the valence band. For x<0.75, we expect that
there are sufficient holes to allow for a sign:ficant degree of
screening, and in this regime, the hole states in the valence bands
are likely to be delocalised such that Li,CoOz exhibits metallic
electronic properties. This behaviour is clearly observed in the
FTIR absorption spectra where absorption by holes are observed in
the low-wavenumber region. As pointed out by Van der Ven et al.
[44] the occurrence of delocaIised holes contribute to the free
energy of the electrode, influencing both the energetic and
entropic terms. This could be at the origin of the two-phase region
observed in the potebtial curves of the Li/lLiCoOz cells.
From the infrared data, it is also interesting to remark that
LiCoOz is less sensitive to lithium content due to the higher bond
covalency in the CoOz slabs than LiNiOz does. Consequently, the
strong bond covalency in LiCoOz, with reduced Co-O bond distance,
results in stabilisation of CoIII in low-spin ground state, and
reduces the electronic conductivity of the compound. By
de-intercalating lithium into materials, the repulsion of the
negatively charged CoOzlayers increases and the Co4+/C03+ redox
couple offers the possibility of electronic transfer. This cation
oxidation results in an increase of the conductivity due to the
decrease of the covalent character of the CoOz slabs. XRD and FfIR
data seem to be in good accordance with such a structural
model.
Acknowledgments
The author wishes to thank Dr. Bouziane Yebka for his assistance in
experimental works
26
on lithium intercalation in oxides. Dr. Michel Massot is gratefully
acknowledged for his contribution in Raman scattering
measurements.
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OVERVIEW OF CARBON ANODES FOR LITHIUM-ION BATTERIES
Karim ZAGHIBa and Kim KINOSHIT Ab a Institut de Recherche d'
Hydro-Quebec, 1800 boul, Lionel-Boulet Varennes, Quebec, Canada,
J3X 1 S1 bEnvironmental Energy Technologies Division Lawrence
Berkeley National Laboratory 1 Cyclotron Road, Berkeley, CA 94720
USA
Commercial lithium-ion batteries utilize metal oxide (lithiated Co
oxide) pOSItive electrodes, non-aqueous solvent containing LiPF6 as
the electrolyte and carbon negative electrodes. There has been
extensive research to identify the optimum carbon to meet
requirements such as high capacity, low irreversible capacity loss,
long cycle life, low co