Nonaqueous Electrochemistry

593 Pages·1999·14.371 MB·English

by  Doron Aurbach

N O N A Q U E O US
ELECTROCHEMISTRY
ghEDITED BY
DORON AURBACH
Bar-llan University
Ramat-Gan, Israel
m
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Preface
Nonaqueoussystemsarebecomingimportantinmodernelectrochemistryforthe
following reasons:
1. Highenergydensitybatteriesareacrucialneedasmodernelectronics
progresses and moves more and more toward miniaturization. Many
novel battery systems require the use of nonaqueous electrolyte sys-
tems because important new developments in this field are based on
active metal electrodes (eg, Li and Li-C intercalation compounds).
2. Theuseofnonaqueoussystemsincreasestherangeofapplicabilityof
electrochemicaltechniquestomanyorganicandinorganiccompounds
thatareeitherunstableorinsolubleinwater.Theelectrochemicalwin-
dow of many nonaqueous systems is much wider than that of water.
Intheliteratureofrecentyears,weindeedseemoreandmorepublications
on the study and development of novel nonaqueous high energy density battery
systems,nonaqueouselectro-organicsynthesis,andmechanisticstudies.Thispar-
allelsworldwideeffortstocommercializenonaqueouslithiumandlithium-carbon
batteries.Hence,itisimportanttogatherfromtimetotimetheknowledgeaccu-
mulatedintheseareas,toupdatetheliteratureandprovidetheincreasingnumber
ofpeopleworkinginthisfieldwithacomprehensivecompendiumonthepractical
and theoretical aspects of nonaqueous electrochemistry.
This book focuses on three types ofnonaqueous systems—liquid electro-
lyte solutions, ionically conducting polymers, and molten salts—with emphasis
on the more commonly used liquid systems. It provides a review of a variety
iv Preface
of important and useful nonaqueous systems in terms of properties, purification
procedures, and handling.
Theintrinsicreactionsofmanyimportantsolvents,salts,andcommoncon-
taminants on both active and nonactive electrodes are described and discussed.
This providesthereaderwith acomprehensive viewofthetrue electrochemical
windowofthesesystems.Thespectroelectrochemicaltoolsthatcanbeappliedto
thestudyofthesesystems(withtheemphasisoninsitutechniques)arereviewed.
Importantapplicationsofnonaqueoussystemsinthefieldsofelectrosynthe-
sis, mechanistic research by electrochemical techniques, and batteries are de-
scribed and demonstrated.
Thisbookisdirectedatnotonlyelectrochemistsbutalsoscientistsinother
discipines who need to work with nonaqueous systems, including organic and
inorganicchemists(intheaspectsofsynthesisandmechanisticresearch),energy
physicists,andmaterialscientists.Inadditiontofundamentalaspectsthatremain
invariant,greatefforthasbeenmadeinthisbooktocoverthemostrecentaccu-
mulated knowledge.
Doron Aurbach
Contents
Preface
Contributors
1. Nonaqueous Electrochemistry: An Overview
Doron Aurbach and Idit Weissman
2. Physical and Chemical Properties of Nonaqueous Electrolyte
Solutions
George E. Blomgren
3. Experimental Considerations Regarding the Use and Study
of Nonaqueous Electrochemical Systems
Doron Aurbach and Arie Zaban
4. The Electrochemical Window of Nonaqueous Electrolyte
Solutions
Doron Aurbach and Yosef Gofer
5. The Chemical and Electrochemical Reactivity of Nonaqueous
Solvents Toward Metallic Lithium
Daniel A. Scherson
6. The Electrochemical Behavior of Active Metal Electrodes
in Nonaqueous Solutions
Doron Aurbach
7. Ionic Conducting Polymers for Applications in Batteries
and Capacitors
Tetsuya Osaka, Shinichi Komaba, and Xingjiang Liu
8. Nonaqueous Batteries
Larry A. Dominey
9. Electrochemistry of Molten Salts
Ioan Galasiu, Rodica Galasiu, and Jomar Thonstad
Contributors
Doron Aurbach Department of Chemistry, Bar-Ilan University, Ramat-Gan,
Israel
George E. Blomgren Energizer, Westlake, Ohio
Larry A. Dominey, Ph.D. Vice President, Research and Development, OMG
Americas, Inc., Cleveland, Ohio
Ioan Galasiu Roumanian Academy, Institute of Physical Chemistry, Bucha-
rest, Roumania
RodicaGalasiu RoumanianAcademy,InstituteofPhysicalChemistry,Bucha-
rest, Roumania
YosefGofer DepartmentofChemistry,Bar-IlanUniversity,Ramat-Gan,Israel
ShinichiKomaba* DepartmentofAppliedChemistry,SchoolofScience and
Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan
*Current affiliation: Department of Applied Chemistry and Molecular Science, Faculty of Engi-
neering,IwateUniversity,Morioka,Japan
viii Contributors
XingjiangLiu DepartmentofAppliedChemistry,SchoolofScienceandEngi-
neering, Waseda University, Shinjuku-ku, Tokyo, Japan
TetsuyaOsaka DepartmentofAppliedChemistry,SchoolofScienceandEn-
gineering, Waseda University, Shinjuku-ku, Tokyo, Japan
DanielA.Scherson DepartmentofChemistry,CaseWesternReserveUniver-
sity, Cleveland, Ohio
Jomar Thonstad Norwegian University of Science and Technology, Trond-
heim, Norway
Idit Weissman Department of Chemistry, Bar-Ilan University, Ramat-Gan,
Israel
ArieZaban DepartmentofChemistry,Bar-IlanUniversity,Ramat-Gan,Israel
1
Nonaqueous Electrochemistry: An
Overview
Doron Aurbach and Idit Weissman
Bar-IlanUniversity,Ramat-Gan,Israel
I. INTRODUCTORY REMARKS
Defining and describing nonaqueous electrochemistry as a specific, separated
branchin modernelectrochemistrymeans thatwe takeaqueouselectrochemical
systemsasthereferencearea.Sincetheessenceofelectrochemistryisthepassage
ofelectriccurrentinchemicalsystems,atleastinpartbyiontransportandmigra-
tion, electrolyte solutions based on water are ideal media for electrochemical
reactions. The highly polar water (dielectric constant of about 78 at 25°C) dis-
solvesalargevarietyofsaltsandthusformshighlyionicallyconductingsolutions
of low resistivity. However, water solutions have several limitations as electro-
chemical media:
1. Therearetoomanychemicalsubstancesofpotentiallyimportantelec-
trochemical reactivity which are insoluble in water (mostly organic
compounds).
2. Waterasaproticsolventishighlyreactivewithavarietyofelectrode
materials and compounds of interest, such as active metal (alkaline,
alkaline earth), organic salts which undergo fast hydrolysis, basic or
acidic compounds, complexes, etc.
3. The applicability of aqueous solutions is limited to temperatures in
which these media are in the liquid state. Hence, their temperature
windowisabout100°C,whichmaybetoonarrowformanyuses,espe-
ciallyinareasrelatedtoenergystorageandconversion(batteries,fuel
cells).
4. The electrochemical window of water is too narrow. On a thermody-
namic basis the potential difference between the cathodic (H(cid:1) (cid:1)
e(cid:2) 1/2H2)andtheanodic(1/2O2(cid:1)2H(cid:1)(cid:1)2e(cid:2) H2O)limiting
reactionsisonly1.299volts.Thispotentialwindowmaybeextendedby
akineticcontrol,suchashighovervoltageforthecathodicreaction,using
certainelectrodematerials(e.g.,mercury,lead).However,toomanyim-
portantcompoundsandsubstancesarereducedoroxidizedatpotentials
farbeyondthepotentialsinwhichwateriselectrolyzed.
Consequently, there is an increasing interest in alternative (or additional)
electrolyte systems in which the above limitations can be removed. Providing
theanswerstotheabovelimitationsofaqueoussolutionsandthestudy,matching,
and classification of alternative/additional electrolyte systems is the essence of
nonaqueous chemistry. An overview of this branch of modern electrochemistry
should include the presentation and classification of the important nonaqueous
electrolyte systems, indicating their basic features, advantages, and limitations,
as well as a short review of their typical applications.
The important nonaqueous electrolyte systems may be divided into five
groups:
1. Liquid solutions based on organic and inorganic solvents
2. Liquid systems based on molten salts (high temperature and ambient
temperature)
3. Ionically and electronically conducting polymers
4. Solutions based on liquefied gases (inorganic, compressed liquids at
ambient temperatures)
5. Conducting solids (doped oxides and glass)
These fivetypesofelectrolytesystems aredescribed brieflyin thischapter. The
first three groups of systems, which are the most common and important, are
treated in detail in this book.
II. LIQUID ELECTROLYTE SOLUTIONS
A. General
Nonaqueousliquidelectrolytesolutionsmaybedividedintosubgroupsaccording
to several criteria based on the differences among the various polar aprotic sol-
vents. The first division can be between protic or polar aprotic nonaqueoussol-
vents and nonpolar solvents. In polar aprotic and protic nonaqueous systems,
conductivityisachievedbythedissolutionoftheelectrolytesandtheappropriate
chargeseparationofthedissolvedspecies,allowingfortheirfreemigrationunder
theelectricalfield.Innonpolarsystemstheconductancemechanismmaybemore