U.S. patent application number 11/101724 was filed with the patent office on 2005-08-18 for polymer electrolyte, intercalation compounds and electrodes for batteries.
This patent application is currently assigned to Massachusetts Institute of Technology. Invention is credited to Aydinol, Mehmet K., Ceder, Gerbrand, Chiang, Yet-Ming, Huang, Biying, Jang, Young-Il, Sadoway, Donald R..
Application Number | 20050181280 11/101724 |
Document ID | / |
Family ID | 27487657 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050181280 |
Kind Code |
A1 |
Ceder, Gerbrand ; et
al. |
August 18, 2005 |
Polymer electrolyte, intercalation compounds and electrodes for
batteries
Abstract
Solid battery components are provided. A block copolymeric
electrolyte is non-crosslinked and non-glassy through the entire
range of typical battery service temperatures, that is, through the
entire range of at least from about 0.degree. C. to about
70.degree. C. The chains of which the copolymer is made each
include at least one ionically-conductive block and at least one
second block immiscible with the ionically-conductive block. The
chains form an amorphous association and are arranged in an ordered
nanostructure including a continuous matrix of amorphous
ionically-conductive domains and amorphous second domains that are
immiscible with the ionically-conductive domains. A compound is
provided that has a formula of Li.sub.xM.sub.yN.sub.zO.sub.2. M and
N are each metal atoms or a main group elements, and x, y and z are
each numbers from about 0 to about 1. y and z are chosen such that
a formal charge on the M.sub.yN.sub.z portion of the compound is
(4-x). In certain embodiments, these compounds are used in the
cathodes of rechargeable batteries. The present invention also
includes methods of predicting the potential utility of metal
dichalgogenide compounds for use in lithium intercalation
compounds. It also provides methods for processing lithium
intercalation oxides with the structure and compositional
homogeneity necessary to realize the increased formation energies
of said compounds. An article is made of a dimensionally-stable,
interpenetrating microstructure of a first phase including a first
component and a second phase, immiscible with the first phase,
including a second component. The first and second phases define
interphase boundaries between them, and at least one particle is
positioned between a first phase and a second phase at an
interphase boundary. When the first and second phases are
electronically-conductive and ionically-conductive polymers,
respectively, and the particles are ion host particles, the
arrangement is an electrode of a battery.
Inventors: |
Ceder, Gerbrand; (Wellesley,
MA) ; Chiang, Yet-Ming; (Framingham, MA) ;
Sadoway, Donald R.; (Watertown, MA) ; Aydinol, Mehmet
K.; (Isci Bloklari Mah, TR) ; Jang, Young-Il;
(Sugar Hill, GA) ; Huang, Biying; (Las Vegas,
NV) |
Correspondence
Address: |
WOLF GREENFIELD & SACKS, PC
FEDERAL RESERVE PLAZA
600 ATLANTIC AVENUE
BOSTON
MA
02210-2211
US
|
Assignee: |
Massachusetts Institute of
Technology
77 Massachusetts Avenue
Cambridge
MA
02139
|
Family ID: |
27487657 |
Appl. No.: |
11/101724 |
Filed: |
April 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11101724 |
Apr 8, 2005 |
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09862916 |
May 22, 2001 |
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09862916 |
May 22, 2001 |
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09284447 |
Jun 24, 1999 |
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09284447 |
Jun 24, 1999 |
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PCT/US97/18839 |
Oct 10, 1997 |
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60028342 |
Oct 11, 1996 |
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60028341 |
Oct 11, 1996 |
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60028278 |
Oct 11, 1996 |
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60053876 |
Jul 28, 1997 |
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Current U.S.
Class: |
429/231.1 ;
429/223; 429/224; 429/229; 429/231.5; 429/231.6; 429/232 |
Current CPC
Class: |
C01G 53/42 20130101;
H01M 4/525 20130101; C01B 13/14 20130101; C01P 2002/08 20130101;
H01M 4/382 20130101; H01M 4/133 20130101; H01M 10/052 20130101;
H01M 10/0525 20130101; H01M 2300/0085 20130101; C01P 2002/20
20130101; Y02E 60/10 20130101; C01P 2006/40 20130101; C01G 45/1228
20130101; C01P 2004/04 20130101; Y10T 428/31935 20150401; C01P
2006/80 20130101; H01B 1/122 20130101; C01P 2002/02 20130101; C01P
2002/30 20130101; C01P 2002/52 20130101; C01P 2002/54 20130101;
H01M 10/0565 20130101; C01P 2002/72 20130101; H01M 4/13 20130101;
H01M 4/485 20130101; H01M 4/505 20130101; H01M 4/624 20130101; H01M
2300/0091 20130101; Y10T 428/31 20150115; C01G 51/42 20130101; H01M
4/131 20130101; H01M 4/362 20130101; C01D 15/02 20130101 |
Class at
Publication: |
429/231.1 ;
429/231.6; 429/229; 429/231.5; 429/224; 429/223; 429/232 |
International
Class: |
H01M 004/48; H01M
004/50; H01M 004/62; H01M 004/52 |
Goverment Interests
[0002] This invention was made with government support under
Contract Number DEFC07-941D13223 awarded by the U.S. Department of
Energy and Grant Number NIH-5P30-ES02109 awarded by the National
Institutes of Health. The government has certain rights in the
invention.
Claims
What is claimed is:
1. An electrochemical device comprising: a first component
comprising a composition having a formula
Li.sub.xM.sub.yN.sub.zO.sub.2, wherein M is a metal atom or a main
group element, N is a metal atom or a main group element, x, y and
z are all numbers in the range of >0 to about 1, and y and z are
such that a formal charge on a M.sub.yN.sub.z portion of the
compound is (4-x), provided that where one of M or N is Ni the
other may not be Al, B or Sn, and further provided that where one
of M or N is Co the other may not be Al, B, Sn, In, Si, Mg, Mn, Cu,
Zn, Ti or P; an electrically conductive material in electrical
communication with the first component; and a lithium ion
conductive, dimensionally supportive matrix positioned to allow
lithium ion communication with the first component.
2. An electrochemical device as in claim 1, wherein the composition
has a formula LiNi.sub.yMn.sub.zO.sub.2.
3. An electrochemical device of manufacture according to claim 1,
the composition Li.sub.xM.sub.yN.sub.zO.sub.2 having a charging
voltage of at least 2.5 V.
4. An electrochemical device of manufacture according to claim 1,
the composition Li.sub.xM.sub.yN.sub.zO.sub.2 crystallizing in an
.alpha.-NaFeO.sub.2, orthorhombic LiMnO.sub.2 or tetragonal spinel
Li.sub.2Mn.sub.2O.sub.4 structure.
5. An electrochemical device of manufacture according to 1, wherein
the first component is a cathode.
6. An electrochemical device of manufacture according to 1, wherein
the electrically conductive material is carbon black.
7. An electrochemical device of manufacture according to 1, wherein
the lithium ion conductive, dimensionally supportive matrix is a
lithium ion conductive polymer.
8. An electrochemical device as in 1, having a charging voltage of
at least about 3.9 V.
9. An electrochemical device as in 1, having a charging voltage of
at least about 4.0 V.
10. An electrochemical device as in 1, having an energy density of
at least 100 Whr/kg.
11. An electrochemical device as in 1, wherein at least one of the
electrically conductive material and the lithium ion conductive
matrix is polymeric.
12. An electrochemical device as in claim 11, wherein each of the
electrically conductive material and the lithium ion conductive
matrix is polymeric.
13. An electrochemical device as in claim 1, wherein ion host
material comprises an ion host particle, the article including a
plurality of ion host particles in electronic communication with
the electronically-conductive polymer and in ionic communication
with the ionically-conductive polymer.
14. An electrochemical device, comprising: a first component
comprising a mixed transition metal or main group lithium
intercalation oxide comprising lithium, manganese, nickel, and
cobalt; an electrically conductive material in electrical
communication with the first component; and a lithium ion
conductive, dimensionally supportive matrix positioned to allow
lithium ion communication with the first component.
15. The electrochemical device of claim 14, wherein the first
component further comprises aluminum.
16. An electrochemical device, comprising: a first component
comprising a lithium intercalation compound having a formula
Li.sub.xM.sub.yN.sub.zO.s- ub.2, wherein M is Ni and N is Co,
wherein the lithium intercalation compound is doped with Mn; an
electrically conductive material in electrical communication with
the first component; and a lithium ion conductive, dimensionally
supportive matrix positioned to allow lithium ion communication
with the first component.
17. The electrochemical device of claim 16, wherein the first
component further comprises aluminum.
Description
RELATED APPLICATIONS
[0001] This is a continuation application of U.S. patent
application Ser. No. 09/862,916, filed May 22, 2001, which is a
divisional of U.S. patent application Ser. No. 09/284,447, filed
Jun. 24, 1999 which is a national stage of and claims priority to
International Application No. PCT/US97/18839 filed Oct. 10, 1997,
which claims priority to U.S. Provisional Application No.
60/028,342, filed Oct. 11, 1996; U.S. Provisional Application No.
60/028,341, filed Oct. 11, 1996; U.S. Provisional Application No.
60/028,278, filed Oct. 11, 1996; and U.S. Provisional Application
No. 60/053,876, filed Jul. 28, 1997.
FIELD OF THE INVENTION
[0003] The present invention relates generally to batteries, and
more particularly to batteries that can include one or more of a
block copolymeric electrolyte, lithium dichalcogenide compounds
having a substantial amount of oxygen p-level characteristic at the
Fermi energy level, and an electrode, one or more of which can be
used with a lithium solid polymer electrolyte battery.
BACKGROUND OF THE INVENTION
[0004] Rechargeable batteries enjoy an enormous and constantly
growing global market due to their implementation in, for example,
cellular phones, laptop computers and other consumer electronic
products. In addition, the development of electrically-powered
vehicles represents an immense potential market for these
batteries. The increased interest in lithium intercalation
compounds stems from their use in rechargeable batteries and, in
particular, lithium solid state batteries.
[0005] Intercalation refers to a reaction in which ions, atoms or
molecules penetrate between the layers of a solid material to form
intercalation compounds. For example, alkali metal ions are known
to insert between graphite layers to form intercalation compounds.
Recently, dichalcogenides, such as dioxides and disulfides, have
become increasingly popular for use in the intercalation of lithium
ions. When dioxides are used, the overall reaction occurs as
follows:
(x.sub.2-x.sub.1)Li+(x.sub.2-x.sub.1)e.sup.-+Li.sub.x1MO.sub.2.fwdarw.Li.s-
ub.x2MO.sub.2 (1)
[0006] where M represents a metal or main group element and
x.sub.2>x.sub.1.gtoreq.0.
[0007] In this reaction, lithium is placed in the structure of the
dioxide without major changes to the structure.
[0008] The lithium solid polymer electrolyte rechargeable battery
is an attractive technology for rechargeable battery applications
due to its high predicted energy density, freedom in battery
configuration, minimal potential for environmental and safety
hazard, and low associated materials and processing costs. The
lithium battery is charged by applying a voltage between the
battery's electrodes, which causes lithium ions and electrons to be
withdrawn from lithium hosts at the battery's cathode. Lithium ions
flow from the cathode to the battery's anode through a polymer
electrolyte to be reduced at the anode, the overall process
requiring energy. Upon discharge, the reverse occurs; lithium ions
and electrons are allowed to re-enter lithium hosts at the cathode
while lithium is oxidized to lithium ions at the anode, an
energetically favorable process that drives electrons through an
external circuit, thereby supplying electrical power to a device to
which the battery is connected.
[0009] The dioxide serves as lithium hosts in rechargeable
batteries by intercalating lithium. The battery voltage derived
from such an intercalation reaction depends on the difference in
the chemical potential for lithium between the anode and cathode
material: 1 V ( x ) = - Li cathode ( x ) - Li anode zF ( 2 )
[0010] where z is the electron transfer associated with Li
intercalation, usually assumed to be equal to 1, and F is the
Faraday constant. By integrating equation (2) between charged and
discharged limit one obtains the average battery voltage arising
from the intercalation reaction 2 V average = - 1 x 2 - x 1 [ E Li
x2 MO 2 - E Li x1 MO 1 - ( x 2 - x 1 ) E Li ( 3 )
[0011] The right-hand side of equation (3) is the energy associated
with the formation of the discharged compound (Li.sub.x2MO.sub.2)
from the charged compound (Li.sub.x1MO.sub.2). Hereafter x.sub.2 is
set to 1, x.sub.1 is set to 0, and the right hand side of equation
(3) is referred to as the "formation energy" of the intercalation
compound LiMO.sub.2. The anode reference state is taken to be
metallic Li although this has no significance for the results.
[0012] Currently known compounds such as LiCoO.sub.2 and
LiMn.sub.2O.sub.4 have formation energies between 3 and 4eV. For
many applications a high voltage and low weight are desirable for
the cathode as this leads to high specific energy. For example, for
electrical vehicle applications the energy-to-weight ratio of the
battery determines the ultimate driving distance between
recharging.
[0013] With this goal in mind, the research into lithium
intercalation compounds that has been conducted thus far has
focused primarily on the synthesis and subsequent testing of
various dioxide compounds. In preparing these compounds, workers
have been guided by the conventional belief that, during
intercalation of the lithium ion, the electron is transferred to
the metal or main group atom of the dioxide. These efforts have led
to the development of a variety of compounds, including
Li.sub.xCoO.sub.2, Li.sub.xNiO.sub.2, Li.sub.xMn.sub.2O.sub.4, and
Li.sub.xV.sub.3O.sub.13. In addition, Li.sub.xTiS.sub.2 and other
disulfides have been investigated for use in lithium intercalation.
However, each of these compounds suffers from at least one
shortcoming. For example, Li.sub.xCoO.sub.2,
Li.sub.xV.sub.3O.sub.13 and Li.sub.xTiS.sub.2 are relatively
expensive to prepare. Moreover, Li.sub.xNiO.sub.2 is comparatively
difficult to process. Furthermore, Li.sub.xMn.sub.2O.sub.4
possesses a limited capacity for providing energy.
[0014] Systems with multiple metals have been described in several
patents and publications. Ohzuku, et al., "Synthesis and
Characterization of LiAl.sub.1/4Ni.sub.3/4O.sub.2 for Lithium-Ion
(Schuttle Cock) Batteries," J. Electrochem. Soc., vol. 142, p. 4033
(1995), describe the mixed-metal composition of the title and
report electrochemical properties thereof. The purpose of the
preparation of the material, according to the authors, is to
prevent overcharging-related degradation of a cathode.
[0015] Nazri, et al., in "Synthesis, Characterization, and
Electrochemical Performances of Substituted Layered Transition
Metal Oxides, LiM.sub.1-yM'.sub.yO.sub.2 (M=Ni and Co, M'=B and
Al)," Mat. Res. Soc. Symp. Proc., vol. 453, p. 635 (1997), describe
addition of Al at various levels to LiNiO.sub.2 and LiCoO.sub.2 and
investigation of related voltage change.
[0016] While the above and other reports represent, in some cases,
interesting lithium compounds for electrochemical devices, on the
whole the prior art is directed towards relatively high-temperature
firing of compounds resulting in generally low-energy state
products. For example, the above-cited reports do not appear to
reflect the recognition or realization that LiAlO.sub.2 of the
.alpha.-NaFeO.sub.2 structure has a higher formation energy than
previously studied oxides such as LiCoO.sub.2 and LiNiO.sub.2, or
that additions of LiAlO.sub.2 to another oxide of the
.alpha.-NaFeO.sub.2 structure will raise the formation energy of
said oxide. Instead, the results of Ohzuku et al. and Nazri et al.
appear to show no significant voltage increase in batteries based
on such compositions, which would discourage aspects of the present
invention.
[0017] In general, many prior art mixed-metal compositions exhibit
phase separation, and there is a general lack of appreciation that
intercalation compounds of the present invention, described below,
can play a role in high-energy electrochemical devices. Hence, it
remains a challenge in the art to provide dichalcogenide compounds
for use as lithium intercalation compounds that are relatively
light-weight, inexpensive and easy to process and that have
comparatively large formation energies. In addition, it is
desirable to provide methods of predicting which dichalcogenide
compounds may be most useful in lithium intercalation in order to
reduce the time, effort and cost associated with the development of
these compounds. Furthermore, methods must be provided for the
synthesis and processing of these predicted compounds in the
desired structure and with the desired homogeneity necessary to
realize the predicted formation energies.
[0018] Development of commercially-viable lithium solid polymer
electrolyte batteries has been hindered by complications, in
particular complications involving the electrolyte. An inherent
inverse relationship between ionic conductivity and dimensional
stability exists in most known polymer electrolytes. That is, prior
art electrolytes typically demonstrate good ionic conductivity, or
good dimensional stability, but not both. Dimensional stability can
be achieved by crosslinking, crystallization, glassification, or
the like, but these arrangements generally impede ionic
conductivity since conductivity requires a significant degree of
polymer chain mobility.
[0019] For example, in linear chain polyethylene oxide (PEO)
lithium salt electrolytes, crystallinity can severely hinder the
mobility of the polymer chains, compromising room temperature ionic
conductivities. Above the melting point of this system
(T.sub.m=65.degree. C.), ionic conductivity increases
significantly, but at these temperatures PEO behaves Theologically
as a viscous fluid, losing its dimensional stability and hence its
distinct advantage over liquid electrolytes that display much
higher conductivities.
[0020] Since high ionic conductivity in PEO is characteristic of an
amorphous state, most prior developmental efforts have concentrated
on reducing crystallinity through the addition of plasticizers or
modification of the polymer architecture through random
copolymerization or the use of electrolytic pendant groups.
However, these strategies generally have yielded materials with
poor mechanical properties, i.e., materials that behave more like
liquids than solids since, as crystallinity in PEO is reduced via
these techniques, dimensional stability necessary for application
in solid state batteries is compromised.
[0021] Crosslinking has been used as a technique for imparting
mechanical rigidity to polymeric electrolytes, a common synthetic
approach being to prepare network-type structures via irradiation
or chemical crosslinking. The ionic conductivity of crosslinked
systems is, however, inherently hindered by the presence of the
crosslinks, as the crosslinks suppress chain mobility. Furthermore,
crosslinked networks of solid polymer electrolyte materials do not
flow and are insoluble, therefore multiple processing steps are
required for preparation of electrolytes and arrangement of the
electrolytes in batteries. Additionally, crosslinked materials tend
to be non-recyclable.
[0022] Cathodes in state-of-the-art lithium solid polymer
electrolyte batteries contain lithium ion host materials,
electronically conductive particles to electronically connect the
lithium ion hosts to a current collector (i.e., a battery
terminal), and ionically-conductive particles to ionically connect
the lithium ion hosts to a lithium-conducting polymer electrolyte.
The lithium ion host particles typically are particles of lithium
intercalation compounds. Typically, the electronically conductive
particles are made of a substance such as carbon black or graphite,
and the ionically conductive material is a polymer such as
polyethylene oxide. The resulting cathode includes a mixture of
particles of average size typically on the order of no less than
about 100 microns.
[0023] For reliable operation, good contact between particles must
be maintained to ensure an electronically-conductive pathway
between lithium host particles and the external circuit, and a
lithium-ion-conductive pathway between lithium host particles and
the polymer electrolyte. In typical prior art arrangements,
however, expansion and contraction of the mixture of particles
occurring naturally during the course of charging and discharging,
and due to temperature change of the environment in which the
cathode is used, can result in loss of inter-particle contact, in
particular, disconnection of the lithium host
particle/electronically conductive particle interface. Moreover,
repeated cycling often results in increased electrical resistance
within the cathode due to passivation of the intercalation compound
surface.
[0024] The available literature contains descriptions of a variety
of solid polymer electrolytes. For example, Nagaoka, et al., in an
article entitled, "A High Ionic Conductivity in Poly(dimethyl
siloxane-co-ethylene oxide) Dissolving Lithium Perchlorate,"
Journal of Polymer Science: Polymer Letters Edition, Vol. 22,
659-663 (1984), describe ionic conductivity in poly(dimethyl
siloxane-co-ethylene oxide) doped with LiClO.sub.4. Bouridah, et
al., in an article entitled, "a
Poly(dimethylsiloxane)-Poly(ethylene- oxide) Based Polyurethane
Networks Used as Electrolytes in Lithium Electrochemical Solid
State Batteries," Solid State Ionics, 15, 233-240 (1985) describe
crosslinked polyether-grafted PDMS filled with 10 wt % LiClO.sub.4,
and its ionic conductivity and thermal stability. Matsumoto, et
al., in an article entitled, "Ionic Conductivity of Dual-Phase
Polymer Electrolytes Comprised of NBR-SBR Latex Films Swollen with
Lithium Salt Solutions," J. Electrochem. Soc., 141, 8 (August,
1994) describe a technique involving swelling
poly(acrylonitrile-co-butadiene) rubber and
poly(styrene-co-butadiene) rubber mixed latex films with lithium
salt solutions resulting in dual-phase polymer electrolytes.
[0025] The patent and academic literature contains descriptions of
a variety of electrodes for polymer batteries. For example, Minett,
et al. in "polymeric insertion electrodes, Solid State Ionics,
28-30, 1192-1196 (1988)" describe a mixed ionic/electronic
conducting polymer matrix formed by exposing a film of polyethylene
oxide soaked in pyrrole to aqueous FeCl.sub.3 solution or by
exposing a film of FeCl.sub.3-impregnated polyethylene oxide to
pyrrole vapor. Films were assembled into all-solid-state
electrochemical cells using lithium as the anode and
PEO.sub.8LiClO.sub.4 as electrolyte. U.S. Pat. No. 4,758,483
(Armand) describes a solid polymeric electrolyte that can be used
in a composite electrode. The electrolyte is reported to include an
ionic compound in solution in a copolymer of ethylene oxide and a
second unit that is preferably an ethylene polyoxide structure
including side-group radicals that introduce structural
irregularities into the system reducing or eliminating
crystallinity. A lithium salt, such as lithium perchlorate, is
dissolved in the polymer system. Li and Khan, in an article
entitled "Synthesis and properties of poly(2,5,8,11,14,17,20,23-o-
ctaoxapentacosyl methacrylate)-block-poly(4-vinylpyridine)",
Makromol. Chem. 192, 3043-3050 (1991) describe block copolymers of
a soft, oxyethylene phase doped with LiClO.sub.4 and a hard,
4-vinylpyridine phase doped with a tetracyanoquinodimethane. The
soft phase is rendered ionically conductive and the hard phase is
rendered electronically conductive, and the copolymer can serve as
a polymer electrode. The block copolymer shows microphase
separation as indicated by the presence of two glass transition
temperatures.
[0026] Significant effort has been directed toward viable solid
polymer electrolytes, electrodes, and improved ion host particles,
yet improvements are greatly needed. Therefore, it is an object of
the present invention to provide lithium intercalation compounds
that have reduced costs associated with their preparation and
processing and that possess increased formation energies and
lighter weight.
[0027] It is a further object of the present invention to provide
methods of predicting which lithium intercalation compounds may be
most useful in lithium batteries to decrease the effort and expense
associated with the development of these compounds.
[0028] It is still another object of the invention to provide
methods of processing lithium intercalation oxides with a high
level of compositional homogeneity, as this is necessary to realize
the increased formation energies of said compounds.
[0029] It is still another object of the invention to provide an
electrolyte for batteries that exhibits good ionic conductivity,
good dimensional stability, and that is easily processed.
[0030] It is still another object of the invention to provide an
improved electrode for batteries that is dimensionally-stable,
robust, that maintains good ionic conduction between the ion host
and electrolyte and good electronic connection between the ion host
and current collector after repeated cycling, and that is easily
and economically manufactured.
SUMMARY OF THE INVENTION
[0031] The present invention provides improved ion host particles,
polymer electrolytes, and electrodes for lithium batteries. Each is
useful separately in a battery, and any combination of these
improved products is embraced by the invention. That is, one aspect
involves improved host particles that can be used in a variety of
batteries, one aspect involves an improved electrode, another
aspect involves the improved ion host particles of the invention
incorporated into an improved cathode of the invention, another
aspect involves the improved electrolyte of the invention, another
aspect involves the electrolyte in combination with an electrode of
the invention that may or may not include the ion host particles of
the invention, another aspect involves the electrolyte with any
electrode incorporating the ion host particles of the invention,
and another aspect involves a combination of host particles,
electrolyte, and electrode of the invention.
[0032] In one aspect, the present invention provides a compound
having a formula of Li.sub.xM.sub.yN.sub.zO.sub.2. M and N are each
metal atoms or main group elements, and x, y and z are each numbers
from about 0 to about 1. y and z are chosen such that a formal
charge on the M.sub.yN.sub.z portion of the compound is (4-x). In
one embodiment each oxygen atom of the compound has at least about
20% p-level characteristic at the Fermi energy of the compound as
measured according to a pseudo potential technique. In another
embodiment, the composition has a charging voltage of at least
about 2.5 volts. In yet another embodiment the composition which
crystallizes in the .alpha.-NaFeO.sub.2, the orthorhombic
LiMnO.sub.2 or the tetragonal spinel Li.sub.2Mn.sub.2O.sub.4
structure.
[0033] In another embodiment, the present invention provides a
composition having a formula LiAl.sub.yM.sub.1-yO.sub.2, where M is
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn. This compound, as well as
other compounds of the invention, is not phase separated, but is
homogeneous at scale measurable by x-ray crystallography.
[0034] In a further illustrative embodiment, the present invention
provides a method of making this compound. In certain embodiments,
the method includes calculating the p-level characteristic of each
oxygen atom of the compound using a first principles method of
solving a Schrodinger equation, such as the pseudo potential
method.
[0035] A variety of methods of making compositions of the invention
are provided according to another aspect, including dispersing
precursor powders, drying the suspension, and heating the powder to
cause crystallization, and other precipitation and co-precipitation
techniques as described herein.
[0036] In another aspect the composition of the invention can
define an ion host component of a combination of an ion host
component, an electrically conductive material in electrical
communication with the host component, and a lithium conductive,
dimensionally-supportive matrix positioned to allow lithium ion
communication with the host component.
[0037] In another aspect, the present invention provides a polymer
electrolyte including a non-crosslinked association of a plurality
of block copolymer chains. Each of the chains includes at least one
ionically-conductive block and at least one second block immiscible
with the ionically-conductive block. The association is amorphous
and non-glassy through the entire range of typical battery service
temperatures, that is, through the entire range of at least from
about 0.degree. C. to about 70.degree. C., preferably from about
-25.degree. C. to about 80.degree. C., more preferably from about
-40.degree. C. to about 100.degree. C. The chains are arranged in
an ordered nanostructure including a continuous matrix of amorphous
ionically-conductive domains defined by association of
ionically-conductive blocks, and amorphous second domains,
immiscible with the ionically-conductive domains, defined by
association of second blocks.
[0038] Another aspect involves the polymer electrolyte of the
invention constructed and arranged as an electrolyte in a battery.
The battery can be an ionic solid state battery such as a lithium
solid battery. In this arrangement the electrolyte will be in ionic
communication with both a cathode and an anode which are each in
electric communication with an external circuit.
[0039] In a further aspect, the present invention provides an
article including a dimensionally-stable, interpenetrating
microstructure of a first phase including a first component and a
second phase, immiscible with the first phase, including a second
component. The first and second phases define interphase boundaries
between them, and at least one particle is positioned between a
first phase and a second phase at an interphase boundary. In one
embodiment, the first phase is made of an electronically-conductive
polymer, the second phase is an ionically-conductive polymer, and
the particle is an ion host particle. This arrangement can define
an electrode in a battery. The ionically-conductive polymer can be
the polymer electrolyte of one aspect of the invention. The ion
host particle can be made of a composition according to one aspect
of the invention.
[0040] In a further aspect, the present invention provides an
electronically-conductive polymer, an ion host material in
electronic communication with the electronically-conductive
polymer, and an ionically-conductive polymer in ionic communication
with the ion host material. The ion host material can be an ion
host particle, the article including a plurality of ion host
particles each in electronic communication with the
electronically-conductive polymer and in ionic communication with
the ionically-conductive polymer. This arrangement, in one aspect,
can define an electrode material for a battery.
[0041] In a further aspect, the present invention provides a method
of making an article. The method involves creating a melt of
components, including a first component and a second component and
at least one particle. The system can be formed by a reduction of
temperature of a disordered melt, e.g. the melt can be allowed to
solidify and the first component to phase separate from the second
component to form an interpenetrating microstructure of a first
phase including the first component and a second phase, immiscible
with the first phase, including the second component. The particle
migrates to and is positioned at an interphase boundary defined
between the first and second phases. The first and second phases
are, according to one embodiment of the invention, electronically
and ionically-conductive polymers, respectively. The
ionically-conductive phase can be the polymer electrolyte according
to one aspect of the invention, and the particle can be a
composition according to that aspect of the invention.
[0042] In a further aspect, the present invention provides a method
involving withdrawing, from an ion host material, an ion into an
ionically-conductive polymer and an electron into an
electronically-conductive polymer. In one embodiment, the method
involves simultaneously withdrawing a plurality of ions and
electrons from a plurality of ion host particles. The ion host
particles can be made of the composition of the invention, and the
ionically-conductive polymer can be the polymer electrolyte of the
invention.
[0043] In another aspect, the present invention provides a system
including a first ion host material having a first potential
associated with withdrawal of an ion from the first material, a
second ion host material having a second potential associated with
withdrawal of an ion from the second material, and an
ionically-conductive material in ionic communication with each of
the first and second ion host materials. The first and second ion
host materials can be made of the composition of the invention, and
the ionically-conductive material can be the polymer electrolyte of
the invention.
[0044] The invention also provides a solid state polymer
electrolyte battery assembly. The assembly includes an anode, a
cathode, a first electrolyte in ionic communication with each of
the anode and cathode, and an external circuit in electronic
communication with each of the anode and cathode. At least one of
the anodes or cathodes is defined by a bicontinuous,
interpenetrating microstructure of a first,
electronically-conductive component, a second, ionically-conductive
component immiscible with and phase-separated from the
electronically-conductive component at typical battery surface
temperatures, and ion host particles positioned at interphase
boundaries between the electronically-conductive and
ionically-conductive components.
[0045] Other advantages, novel features, and objects of the
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings. In the drawings, components that can be
common to various figures are represented by common numerical
designations.
BRIEF DESCRIPTION OF THE FIGURES
[0046] FIG. 1 is a schematic representation of a rechargeable
battery including lithium dichalcogenide intercalation compounds in
accordance with the prior art;
[0047] FIG. 2 illustrates schematically a polymer electrolyte in
accordance with the invention;
[0048] FIG. 3 illustrates schematically a portion of an
interpenetrating microstructure including the polymer electrolyte
of the invention and an immiscible, electronically conductive
polymer, with particles pinned at interface boundaries between the
polymer electrolyte and electronically conductive polymer;
[0049] FIG. 4 illustrates schematically a lithium solid polymer
electrolyte battery in accordance with the invention including a
cathode and an anode each composed of an interpenetrating polymeric
microstructure as illustrated in FIG. 3 including the polymer
electrolyte of the invention, with lithium intercalation compounds
positioned at interface boundaries, the anode and cathode connected
by the polymer electrolyte of the invention;
[0050] FIG. 5 is a powder X-ray diffraction pattern of LiCoO.sub.2
forming the .alpha.-NaFeO.sub.2 structure, prepared by mixing
Co(OH).sub.2 and LiOH.H.sub.2O powders and heating to 600.degree.
C. in air for 8 hours;
[0051] FIG. 6 shows powder X-ray diffraction patterns for a
freeze-dried hydroxide precursor to LiCoO.sub.2, after
freeze-drying, and after heating in air for 2 hours at
100-500.degree. C.;
[0052] FIG. 7 shows powder X-ray diffraction patterns of a
composition Li(Al.sub.1/4CO.sub.3/4)O.sub.2 prepared by
co-precipitation and freeze-drying, and fired in air for 2 hours at
temperatures 400.degree. C. to 700.degree. C., in each instance
forming the .alpha.-NaFeO.sub.2 crystal structure;
[0053] FIG. 8 shows charging curves for compositions LiCoO.sub.2,
Li(Al.sub.1/4Co.sub.3/4)O.sub.2, and
Li(Al.sub.1/2Co.sub.1/2)O.sub.2 prepared according to Examples 3
and 4, and tested as a cathode material against a Li metal anode in
a coin-type Li battery where the charging current is 0.2 mA per
cm.sup.2 of cathode area, and each composition was charged to a
nominal composition of Li.sub.0.6Al.sub.yCo.sub.zO.sub.2;
[0054] FIG. 9 shows discharging curves for compositions
LiCoO.sub.2, Li(Al.sub.1/4Co.sub.3/4)O.sub.2, and
Li(Al.sub.1/2Co.sub.1/2)O.sub.2, prepared according to Examples 3
and 4, and tested as a cathode material against a Li metal anode in
a coin-type Li battery, the discharging current being 0.2 mA per
cm.sup.2 of cathode area, and each composition was first charged to
a nominal composition of Li.sub.0.6Al.sub.yCo.sub.zO- .sub.2;
[0055] FIG. 10 shows the open-circuit voltage as a function of time
for two coin cell type Li batteries, containing LiCoO.sub.2 and
Li(Al.sub.1/4Co.sub.3/4)O.sub.2, prepared according to Examples 3
and 4, as the cathode materials respectively and Li metal as the
anode material, after first charging to a nominal composition of
Li.sub.0.6Al.sub.yCo.sub- .zO.sub.2 at a current density of 0.2
mA/cm.sup.2;
[0056] FIG. 11 shows charge-discharge curves over two cycles for a
compound (LiAl.sub.1/4Co.sub.3/4)O.sub.2, prepared according to
Example 2.
[0057] FIG. 12 shows the powder X-ray diffraction pattern for a
composition Li(Al.sub.0.25Mn.sub.0.75)O.sub.2 prepared according to
Example 6, and which is crystallized in the monoclinic variant of
the .alpha.-NaFeO.sub.2 structure type;
[0058] FIG. 13 shows the first charge-discharge curve for a coin
cell type Li battery containing Li(Al.sub.0.25Mn.sub.0.75)O.sub.2
prepared according to Example 6 as the cathode and Li metal as the
anode, showing the existence of two voltage plateaus upon discharge
indicating a transformation to spinel-like cation ordering in the
intercalation compound;
[0059] FIG. 14 shows the capacity vs. cycle number for a coin cell
type Li battery containing Li(Al.sub.0.25Mn.sub.0.75)O.sub.2
prepared according to Example 6 as the cathode and Li metal as the
anode, showing an initial decrease in capacity followed by an
increase and stabilization of the capacity at about 150 mAh/g;
[0060] FIG. 15 shows storage (G') and loss (G") moduli for
PLMA-b-PMnG (47:53) as a function of reduced frequency, and G" of
PMnG homopolymer prepared according to Example 7, in which the
reference temperature is 45.degree. C.;
[0061] FIG. 16 shows the electrical conductivity of
PEO(.quadrature.) PLMA-b-PMnG (0) and PLMA-b-PMnG/PEGDME blend
(.smallcircle.) systems doped with LiCF.sub.3SO.sub.3
([EO]:Li.sup.+=20:1)prepared according to Example 7;
[0062] FIG. 17 shows (a) a battery cycle test of Li/BCE/LiCoO.sub.2
cell at T=20.degree. C. for the first seven charge/discharge
cycles; and (b) first charge/discharge cycle of Li/BCE/LiCoO.sub.2
cell at T=-20.degree. C.;
[0063] FIG. 18 is a photocopy of an optical micrograph, at
magnification 640.times., of a phase-separated interpenetrating
microstructure of ionically-conductive block copolymeric
poly(lauryl methacrylate)-b-PMnG and electronically-conductive
poly(p-phenylene-vinylene);
[0064] FIG. 19 is a photocopy of an optical micrograph of an
interpenetrating phase separated microstructure of sulfonated
polyaniline (SPAn; an electrically-conductive polymer),
P(MMA-r-MnG) (a random copolymer electrolyte), with fine particles
of Al.sub.2O.sub.3 (.apprxeq.5 .mu.m in diameter) located at the
phase boundary;
[0065] FIG. 20 is a photocopy of a transmission electron micrograph
(TEM) of PLMA-b-PMnG (47:53) showing a defect lamellar
structure.
DETAILED DESCRIPTION
[0066] The following co-pending, commonly-owned, United States
Patent Applications are incorporated herein by reference: Ser. No.
60/028,342, filed Oct. 11, 1996 by Mayes, et al., entitled
ELECTRODE FOR SOLID POLYMER ELECTROLYTE BATTERIES; Ser. No.
60/028,341, filed Oct. 11, 1996 by Mayes, et al., entitled POLYMER
ELECTROLYTE FOR BATTERIES; Ser. No. 60/053,876, filed Jul. 28, 1997
by Ceder, et al., entitled INTERCALATION COMPOUNDS AND METHODS OF
THEIR MANUFACTURE AND USE.
[0067] The present invention provides improved battery components,
combinations of these components, and methods of their manufacture
and use.
[0068] The invention provides significant improvement as compared
to prior art lithium polymer electrolyte batteries, for example the
battery illustrated schematically in FIG. 1. The prior art battery
10 of FIG. 1 includes a cathode 12, an anode 14, a solid polymer
electrolyte 16 in ionic communication with cathode 12 and anode 14,
and an external electrical circuit 18 in electronic communication
with cathode 12 and anode 14 via terminals 13 and 15, respectively.
As used herein "ionic communication" and "electronic communication"
is meant to define a relationship between components in which ions
or electrons, respectively, can be made to flow through a battery
with minimal resistance, that is, with low enough resistance that
the battery is operable. For example, when cathode 12 and anode 14
are in contact with solid polymer electrolyte 16, cathode 12 and
anode 14 are in ionic communication with the solid polymer
electrolyte, and in ionic communication with each other.
[0069] Cathode 12 includes ionically-conductive material 26 and
electronically-conductive particles 28 admixed with lithium
intercalation compound particles 24. For fabrication of such a
cathode, lithium intercalation compound particles 24,
ionically-conductive material 26, and electronically-conductive
particles 28 are provided in a random mixture in the cathode. The
particles tend to have a size in the 10 to 100 micron range.
[0070] Battery 10 is illustrated in a charging mode, that is, a
mode in which energy is introduced into the battery and stored
therein by applying an electrical potential across terminals 13 and
15. This results in a reaction within the battery that proceeds in
an energetically uphill direction. In particular, in the charging
mode electrons are driven into anode 14 from terminal 15 and
combined with lithium ions 20 to produce lithium or Li in anode 14.
For this reaction to occur, electrons are drawn from cathode 12 via
terminal 13 into the external circuit and lithium ions 20 are drawn
from cathode 12 into electrolyte 16 and are made to flow through
polymer electrolyte 16 in a direction from the cathode toward the
anode. Within cathode 12, electrons and lithium ions are drawn from
lithium intercalation compound particles 24 and flow to terminal 13
and polymer electrolyte 16, respectively.
[0071] The chemical/physical process occurring within the battery
during charging is energetically disfavored, that is, energetically
uphill, since net energy is required to remove a lithium ion and
electron from lithium intercalation compound particles 24 and
simultaneously to reduce a lithium ion 20 to lithium at the
interface between anode 14 and polymer electrolyte 16. In
particular, while reduction of lithium ion to lithium releases
energy, removal of a lithium ion and electron from a lithium host
particle 24 requires significantly more energy. During discharge
(use of the battery to power a device connected to external circuit
18) the reverse reaction occurs, and net energy is released.
[0072] FIG. 2 is a schematic drawing of a block copolymeric
electrolyte 34 of the invention (which can be a diblock copolymer,
triblock copolymer, or the like). Polymer electrolyte 34 is a block
copolymer composition that is non-crosslinked, non-crystalline, and
non-glassy at typical battery service temperatures (i.e., through
the entire range of typical battery service temperatures, that is,
through the entire range of at least from about 0.degree. C. to
about 70.degree. C., preferably from about -25.degree. C. to about
80.degree. C., more preferably from about -40.degree. C. to about
100.degree. C.). The electrolyte is formed by block copolymer
chains each including at least one ionically-conductive block 47
and at least one second block 49 immiscible with the
ionically-conductive block, the second block typically being
non-ionically-conductive. The blocks are selected such that, at an
elevated temperature above typical battery service temperatures, or
in solution in a suitable solvent, the blocks are segmentally mixed
and, upon reducing temperature or precipitation from solution or
evaporation of solvent from the solution, an ordered nanostructure
(domain cross-section of less than about 200 microns, typically) is
formed which includes a continuous matrix of amorphous
ionically-conductive domains (doped with an appropriate salt) that
are defined by association of the ionically-conductive blocks, and
amorphous second domains, immiscible with the ionically-conductive
domains, that are defined by association of second blocks.
[0073] Species for forming the ionically-conductive copolymer 34
should be selected according to the following criteria: Both
blocks, at service temperatures, are amorphous, Theologically in a
rubbery or melt state (well above Tg), and non-crystalline; the
ionically-conductive blocks form continuous, ionically-conducting
domains (when doped with an appropriate salt), upon microphase
separation occurring from precipitation, or decrease in
temperature, or evaporation of a solvent; and components used in
the block copolymer form the ordered structure in a manner such
that global dimensional stability of the copolymer exists in the
absence of crosslinking, crystallization, or glassification, while
chain mobility that provides high ionic conductivity remains high.
As used herein, "microphase separation" means a process in which
blocks of the copolymer are locally segregated to form ordered
domains. Continuous, ionically-conductive pathways may be inherent
to the equilibrium ordered morphology, or may result from defects
in the ordered structure.
[0074] That is, the ionically-conductive polymer 34, according to
preferred embodiments, is an association of block copolymer chains
in which inter-block, non-covalent chemical attraction such as
polar/polar or polar/induced polar interactions, including hydrogen
bonding, or nonpolar/nonpolar interactions including van der Waals
interactions, create association between the chains that allows for
mobility required for good ionic conductivity, while maintaining
dimensional stability required for a solid polymer electrolyte
battery. This non-covalent, chemical attraction of like blocks to
each other results in unique thermodynamic and rheological
behavior. At high temperatures, or in solution, the block
copolymers form isotropic phases in which the different blocks are
segmentally mixed. Upon lowering the temperature or evaporating
away the solvent, or upon precipitation from solution, the
repulsion between unlike segments increases, causing the copolymer
to phase separate locally into regions each composed of one of the
two block copolymer components. These segregated regions organize
into ordered nanostructures, the morphology of which is governed by
the relative volume fractions of the different blocks. Global
dimensional stability is imparted to the material.
[0075] The following discussion on miscibility will aid those of
ordinary skill in the art in selecting suitable
ionically-conductive and second blocks for ionically-conductive
block copolymer 34. For a diblock copolymer of N total statistical
segments, with a 50:50 volume composition, .chi.N>10.5 for block
segregation, where .chi. is the Flory-Huggins interaction
parameter, well known to one skilled in the art. The critical value
of .chi.N is larger if the volume composition is different from
50:50. For asymmetric A-B diblock copolymer compositions, the value
of .chi. required for block segregation can be calculated from a
formula by L. Leibler (Macromolecules 13, 1602 (1980)), while for
A-B-A triblock copolymers, a similar formula by A. M. Mayes and M.
Olvera de la Cruz (J. Chem. Phys. 91, 7228 (1989)) can be employed
to calculate values of X required for phase separation for any
composition and molecular weight. Those of ordinary skill in the
art can carry out this determination technique, and can determine
the critical composition for a given diblock or triblock copolymer
of any N and composition.
[0076] The block copolymer preferred for the ionically-conductive
polymer 34 offers unique processing advantages. The isotropic melt
or solution can be processed into thin films as in traditional
thermoplastic processing, and the required processing temperatures
are tunable through variation of molecular weight and composition.
Furthermore, such block copolymers can be made inexpensively, and
have excellent recycling potential since the order-disorder
transition is thermally reversible.
[0077] The molecular weight of the block copolymer chains of the
ionically-conductive polymer should be selected to be high enough
so that a segregated morphology in the service temperature range of
battery operation is maintained. Specifically, the molecular weight
is at least about 10,000, preferably at least about 15,000, more
preferably at least about 25,000 Daltons, more preferably at least
about 50,000 Daltons, more preferably still at least about 100,000
Daltons. Block copolymeric electrolyte 34 can include
ionically-conductive blocks 47 and second blocks 49 (which can be
non-conductive or preferably ionically conductive) as a minor
phase, possessing high room-temperature mobility. The second blocks
can be selected among non-ionically-conductive acrylates such as
polydecyl methacrylate, polylauryl methacrylate, and the like
(where decyl and lauryl can be replaced with moieties having a
number of carbon atoms high enough that the glass transition
temperature of the block is less than service temperature, and
selected such that crystallization does not occur), polyalkyl
acrylates, polydimethyl siloxane, polybutadiene, polyisoprene, and
saturated polymers or copolymers derived from polybutadiene and
polyisoprene such as polyethylethylene and polyethylenepropylene
and copolymers thereof, and modified polystyrenes with flexible
side chains (e.g., alkyl fluorocarbon or siloxane side chains)
attached through the phenyl group. Species with Tg less than about
0.degree. C. are preferred, more preferably less than about
-10.degree. C., more preferably less than about -25.degree. C., and
more preferably still less than about -40.degree. C.
[0078] The ionically-conductive block can be defined by a
polyethylene oxide (PEO) derivative material, in particular a PEO
derivative that meets the criteria of Tg, lack of crystallinity and
glassification as discussed above. The ionically-conductive block
can be selected among species such as methoxy polyethylene glycol
(PEG) methacrylate (referred to herein as MnG), methoxy PEG
acrylate, and other acrylate and methacrylate polymers modified
via, for example, a transesterfication reaction to include short
polyethylene oxide (PEO) or polyethylene glycol (PEG) side chains,
polybutadiene modified so as to include short PEO or PEG side
chains, polystyrene similarly modified via a phenyl group reaction
to include a PEO or PEG side groups, and the like. The
ionically-conductive block also can be defined by an
ionically-conductive polymeric material such as described by Ward,
et al. in U.S. Pat. No. 5,051,211, incorporated herein by
reference. Ionically-conductive polymeric material includes those
materials made ionically-conductive via doping with an appropriate
salt.
[0079] Each of the ionically-conductive and non-ionically
conductive blocks can be a mixture of components, that is, each
block can be, for example, a random copolymer of different
components so long as one block is sufficiently
ionically-conductive, and so long as the criteria herein including
lack of crystallization and lack of glassy domains, and sufficient
dimensional stability, at service temperatures, is achieved. In
some instances, a block copolymer in which one block (or both
blocks) is itself a copolymer such as a random copolymer, can
result in a non-crystalline block copolymer that, with a more
regular sequence of the same components along the chain backbone,
would be crystalline. The ionically-conductive polymer domains can
include, in addition to the ionically-conductive polymer block, a
lower molecular weight, ionically-conductive species that
segregates to the ionically-conductive domain of the block
copolymer, thereby improving the ionic conductivity of the
copolymer. Examples include polyethylene glycol dimethyl ether.
[0080] Block copolymeric electrolyte 34 includes, as described
above, a continuous matrix of amorphous ionically-conductive
domains defined by association of ionically-conductive blocks and
an amorphous second domain, immiscible with the first domains
defined by association of a second block that can be non-conductive
or ionically-conductive. The continuous ionically-conductive
domains define at least a continuous ionically-conducive pathway
when the block copolymer is ordered due either to defects in the
association, or inherent micro-phase separations. That is, the
electrolyte makes use of self-assembling polymeric systems that are
block copolymeric systems or blends of polymers, and that can
include block copolymers, to form 1, 2 or 3-dimensional structures
that are topologically connected to form at least a continuous
ionic pathway. For example, lamellar self-assembled structures
suitable for use in the invention are those constructed of a block
copolymeric species that self-assembles to a lamellar structure
including defects providing an topologically connected continuous
ionically-conductive pathway. An ordered cylinder or sphere
morphology columnar structure, self-assembled, is suitable where
the continuous matrix phase is ionically-conductive. Bicontinuous
periodic block copolymer morphologies such as a double gyroid
arrangement, double diamond configuration, or the like, can be
used. These structures are known to those of ordinary skill in the
art.
[0081] Anionic synthesis is well-suited for the preparation of
block copolymeric electrolyte 34 with well-defined molecular
weights and compositions. For example, methoxy-polyethyleneglycol
methacrylate (MnG; available from Polysciences) can be initiated
anionically to yield an amorphous polymer with a Tg of -60.degree.
C., and room temperature conductivities when doped with a Li salt
near 10.sup.-5 S/cm, and diblock copolymers of MnG and lauryl
methacrylate can be prepared by sequential addition of lauryl
methacrylate to living MnG homopolymer. Alternatively, block
copolymers can be prepared by the reaction of end-functionalized
homopolymers, by addition polymerization of one block component
onto an end-functionalized homopolymer, or by sequential addition
of two monomer species in a living free radical polymerization.
When doped with appropriate lithium salts, which are known in the
art, the block copolymer can be rendered ionically-conductive,
i.e., electrolytic. The block copolymeric electrolyte 34 can be
prepared by melt processing such as melt pressing, or solvent
casting techniques such as spin coating or evaporation.
Technologies for synthesizing and processing such block copolymeric
species are well-known to those of ordinary skill in the art.
[0082] Planning and simple screening tests can be used to select
suitable components for use in block copolymeric electrolyte 34.
First, the ionically-conductive and second blocks should be made of
materials that are immiscible. Once a particular block copolymer is
synthesized, it can be screened for suitability for use in the
invention by analysis via differential scanning calorimetry. If two
glass transition temperatures are observed, then the
ionically-conductive and second blocks are immiscible, that is, the
desired microphase separation has taken place. If only one glass
transition temperature is observed, then the block components are
miscible and microphase separation has not occurred, or the glass
transition temperatures of the differing blocks are coincidentally
similar. If one glass transition temperature is observed, another
screening test involving small angle scattering or rheology
measurements can determine whether phase separation has occurred.
See Bates, F. Macromolecules 1984, 17, 2607; Rosedale, J. H.; Bates
F. S. Macromolecules 1990, 23, 2329; Almdal, K; Rosedale, J. H.;
Bates, F. S. Macromolecules 1990, 23, 4336. The existence of
crystallinity is readily determined by thermal analysis techniques
such as DSC or DTA, or by X-ray diffraction.
[0083] Another test involves subjecting the block copolymer to heat
to determine its resistance to flow. If the material flows easily,
microphase separation and resulting dimensional stability at the
test temperature does not exist.
[0084] Described above is a copolymeric electrolyte useful in a
battery. It is to be understood that the electrolyte can serve as
an electrolyte in any kind of battery, preferably in a lithium (or
other ion) solid state battery or in another device such as a fuel
cell. In addition, the electrolyte of the invention finds use as a
component of an electrode as described below with reference to FIG.
3.
[0085] Referring now to FIG. 3, another aspect of the invention is
illustrated schematically. The arrangement of FIG. 3 can serve as
an electrode in a solid battery, and can include as one component
the electrolyte described immediately above. FIG. 3 illustrates the
arrangement in general, as it can be applied to any arrangement of
any combination of species that meet certain criteria, so as to
clarify the physical parameters involved. Arrangement 30 of FIG. 3
includes particulate material 31 positioned at interface
(interphase) boundaries 36 of a bicontinuous, interpenetrating
microstructure (component dimension typically less than about 100
microns) formed of a first component 33 and a second component 35
phase-separated from component 33. Components 33 and 35 are
immiscible, that is, the two species are mutually repulsive to the
extent that they are not miscible. For example, polar species
typically are immiscible with non-polar species and will coexist in
an immiscible admixture including interphase boundaries between the
two species. Oil-in-water emulsions and water-in-oil emulsions are
examples of mixtures of immiscible species. Components 33 and 35
differ in chemical functionality (generally differing with respect
to polarity) to the extent that they coexist as interpenetrating
polymer phases that meet at interphase boundaries 36.
"Interpenetrating" is meant herein to define an arrangement in
which portions of different phases co-mingle to create a structure
in which separate portions of each phase have cross-sectional
dimensions on the micron scale. The length scale of FIG. 3, which
is representative, is on the order of 1 micron. Separate portions
of components 33 and 35 have cross-sectional dimensions, according
to this arrangement, of from about 0.05 micron to about 200
microns. More typically, the interpenetrating structure will
include portions having cross-sectional dimensions of from about
0.1 micron to about 100 microns.
[0086] Positioned between component phases 33 and 35 are particles
31. Particles 31 are made to segregate at interphase boundaries 36
by tailoring the interfacial tensions of the three species 33, 35,
and 31. That is, when the interfacial tensions are selected
appropriately, the selection of component 33 in conjunction with
component 35 can be made on the basis of immiscibility
(incompatibility), which can be predicted by referring to
solubility parameters that are readily available, or otherwise by
performing simple experiments. The two components should be
selected so as to be able to form an interpenetrating structure
induced by spinodal decomposition resulting from quenching of a
melt or evaporation of a solvent from a solution of the two
components. That is, above a certain temperature the two polymers
should be miscible, and should thermodynamically favor phase
separation to a bicontinuous interpenetrating structure upon
lowering the temperature to a point below the spinodal temperature.
Alternatively, the two components should be soluble in a solvent
that, when evaporated, induces phase separation to form a
bicontinuous interpenetrating structure. In either case, the
bicontinuous interpenetrating structure should be most favored
energetically, resulting in the bicontinuous interpenetrating
structure as illustrated, with particulate material at interphase
boundaries 36. This self-organization will occur when the following
conditions (equation 4) are approximately met:
.gamma..sub.AB>2.gamma..sub.BC-2.gamma..sub.AC (4)
[0087] where .gamma..sub.ij represents interfacial tension between
species i and j, A and B represent the immiscible interpenetrating
component, C represents the particulate material, and
.gamma..sub.BC is greater than .gamma..sub.AC. The arrangement is
very robust owing to the fact that the particulate material 31 will
not lose contact with either component 33 or 35.
[0088] A simple screening test to determine whether a set of
species meets these criteria is to dissolve species A and B in a
solvent in which C is suspended or dissolved, place the
solution/suspension on a glass slide, and allow the solvent to
evaporate, optionally with the aid of applied heat, and to observe
the resultant solid microscopically. Alternatively, a melt of the
above can be cooled and solidified and then observed
microscopically.
[0089] In a preferred embodiment the two interpenetrating phases
are polymers. A required condition for phase separation of two
polymer phases by a spinodal decomposition mechanism is:
2.chi..sub.AB>1/N.sub.A.phi.+1/N.sub.B(1-.phi.) (5)
[0090] where .chi..sub.AB is the well-known, temperature-dependent
Flory interaction parameter that quantifies the repulsion between A
and B components, N.sub.i is the average number of segments per
chain of component i, and .phi. is the volume fraction of the A
component in a blend of the two polymers. Equation 5 defines the
instability threshold of the polymer blend. At temperatures where
this equation is satisfied, the system will break spontaneously
into two phases forming an interpenetrating, bicontinuous structure
for systems with sizable fractions of both components. The
interaction parameter can be estimated from:
.chi..sub.AB=.nu.(.delta..sub.A-.delta..sub.B).sup.2/kT (6)
[0091] where .delta..sub.i is the Hildebrand solubility parameter
of component i, v is the average segmental volume, k is the
Boltzmann constant and T is the temperature in degrees Kelvin. The
solubility parameters of numerous polymers are available in
standard tables, can be calculated by group contribution methods or
can be obtained by performing a series of solubility tests in
various solvents with known solubility parameters. Alternatively,
the miscibility of two polymers can be tested by casting a film of
the two polymers from a mutual solvent, and subjecting the film to
microscopic inspection or thermal analysis. Specifically, if a
glass or melt transition specific to one of the components is
detected by differential scanning calorimetry or differential
thermal analysis, the blend is likely to be phase separated.
[0092] In a preferred embodiment, particles are arranged at
interphase boundaries between two polymer phases where all
components satisfy the interfacial tension criteria of equation 4.
Interfacial tension between A and B polymer phases is related to
the interaction parameter through: 3 AB = ( AB / 6 ) 1 / 2 b v kT (
7 )
[0093] where b is the average segment length. The interfacial
tension between any two components can alternatively be determined
directly from contact angle measurements (e.g., by measuring the
contact angle of a molten polymer component on the particulate
material) if the surface tensions of each component are known.
Surface tension data can be obtained from the literature or
calculated from multiple contact angle measurements using different
liquids of known surface tension.
[0094] The arrangement of FIG. 3 in which particles 31 are
positioned at interphase boundaries 36 finds particularly
advantageous application as an electrode in a battery in accordance
with the invention, in particular a solid polymer electrolyte
battery. In the arrangement, the different components 33 and 35 are
defined by an electronically-conductive polymer and an electrolyte
34 (such as the electrolyte of the invention), respectively, and
particles 31 are defined by ion host particles (such as those of
the invention). This arrangement is particularly robust in that the
ion host particles cannot lose contact with either the
electronically-conductive polymer or the electrolyte, hence failure
by loss of electrical contact with the lithium host particles is
prevented.
[0095] An arrangement of one such embodiment of the invention is
shown in FIG. 4, in which a lithium solid polymer electrolyte
battery assembly 50 is illustrated schematically and includes an
anode 52, cathode 42, and an external circuit 18 including
terminals 13 and 15 as in the arrangement 10 of FIG. 1. Each of
anode 52 and cathode 42 of battery 50 provided in accordance with
this aspect of the invention is defined by a bicontinuous,
interpenetrating polymeric structure of polymers immiscible at
typical battery service temperatures, with particles positioned at
polymer interphase boundaries as discussed with reference to FIG.
3. Each of the electrodes includes, specifically, a bicontinuous,
interpenetrating structure of an electronically-conductive polymer
32 and block copolymeric electrolyte 34, with ion host particles 37
(cathode 42) and particles 54 (anode 52) positioned at interphase
boundaries 36 of the interpenetrating structure. Block copolymeric
electrolyte 34 also is in contact with and provides ionic
communication between anode 52 and cathode 42.
[0096] As used herein, the term "bicontinuous" used in connection
with an interpenetrating polymer structure including ion host
particles positioned at polymer interphase boundaries, means at
least two polymeric species that interpenetrate and in which a
continuous conductive pathway, within each polymeric species, can
be followed from any one ion host particle to at least two other
ion host particles or to at least one ion host particle and a
terminal or polymer electrolyte 34. That is, an arrangement exists
in which most or all of the ion host particles are in electronic
communication with a terminal of external circuit 18 via
electronically-conductive polymer 32 and in ionic communication
with polymer electrolyte 34. Interpenetrating polymeric structures
of the invention are to be distinguished from interpenetrating
polymeric networks described in common literature that are
interpenetrating on the molecular scale. In a particularly
preferred embodiment, the bicontinuous, interpenetrating structure
self-organizes such that a continuous conductive pathway can be
followed from any one ion host particle via
electronically-conductive polymer 32, to a terminal and via
electrolyte 34 of the interpenetrating structure to polymer
electrolyte 34 of the region separating the anode 52 from the
cathode 42.
[0097] Electrolyte 34 in this arrangement (including polymers that
can be made ionically-conductive upon appropriate doping) and
electronically-conductive polymer 32 (including polymers that can
be made electronically-conductive upon appropriate doping) should
be selected to form a bicontinuous interpenetrating structure, with
lithium host particles 37 positioned at interphase boundaries, as
discussed above with reference to the arrangement of FIG. 2.
Additionally, the ionically-conductive polymer should be amorphous
and non-glassy at typical battery service temperatures.
[0098] The electronically-conductive polymer of the invention
should be selected to meet the above criteria among those that are
known, for example, polyacetylene, poly(1,4-phenylenevinylene),
polyaniline, sulphonated polyaniline, trans-polyacetylene,
polypyrrole, polyisothianaphthalene, poly(p-phenylene),
poly(p-phenylenevinylene), polythiophene, and
poly(3-alkyl-thiophene). In some cases, an appropriate surfactant
might be used to improve the solubility of an
electronically-conducting polymer in common organic solvents. For
example, camphor sulfonic acid can be used to render polyaniline
soluble in meta-cresol or CH.sub.3Cl (Y. Cao et al., Appl. Phys.
Lett. 60, 2711 (1992)). In other cases, heat treatment may be
required to convert a precursor polymer into the conjugated polymer
after processing the blend into a bicontinuous microstructure. For
example, films of poly(p-phenylene vinylene) can be prepared by
solution casting of a polymer precursor followed by heating to
above 200.degree. C. whereupon the polymer is converted to its
conducting form. In some cases, doping of the polymer by an
appropriate agent may be required to achieve sufficient levels of
electronic conductivity.
[0099] All that is required for battery 50 to be operative is that
the chemical potential of lithium is low at the cathode as compared
with the anode. Therefore, selection of different lithium host
particles for the cathode and anode would suit the necessary
criteria. Lithium host particles 37 and 54 can be any lithium host
particle, including lithium intercalation compounds as described
herein, when overall withdrawal of lithium ions and electrons from
lithium host particle 37 and insertion of lithium ions and
electrons into lithium host particles 54 is energetically uphill.
When the opposite is the case, that is, when withdrawal of lithium
and electrons from particles 37 and insertion of lithium and
electrons into particles 54 is energetically downhill, the battery
is operative with electrode 42 defining the anode and electrode 52
defining the cathode.
[0100] In other aspects of the invention, only cathode 42 or anode
52, respectively, is an electrode of the invention as illustrated
in FIGS. 3 and 4, and the other electrode is conventional.
[0101] It is to be understood that block copolymeric electrolyte 34
can be used with any battery, including a typical prior art
arrangement as illustrated in FIG. 1, the arrangement of FIG. 3, or
other battery. For example, a battery including a cathode 42 as
illustrated in FIG. 4, and a standard anode composed of lithium
metal is embraced by the invention, as well as any other
arrangement in which block copolymeric electrolyte 34 is useful in
transporting ions. The particular ionic species used for ion
conduction is not important to the embodiment embraced by the
electrode structure of the invention. For example, alkali metal
ions such as Na.sup.+ and K.sup.+ would be suitable as ionic
species, also alkaline earth metals such as Ca.sup.++ and
Mg.sup.++. Preferred for all embodiments is a lithium-doped
polymer.
[0102] Ion host particles for use with an electrode of the
invention can be selected from among many species. "Ion host
particle" as used herein is meant to define a material that can
reversibly accept an ion. A particle of material that participates
in an ion metathetical reaction is suitable, for example
Ag.sub.2WO.sub.3. In this arrangement, lithium can displace silver
reversibly according to equation 8.
2Li+Ag.sub.2WO.sub.3Li.sub.2 WO.sub.3+2Ag (8)
[0103] Ion intercalation compounds also are suitable and, in
preferred embodiments, a lithium intercalation compound such as
LiCoO.sub.2 is used. In another set of embodiments, an ion
intercalation compound such as a metal dichalcogenide compound or
compounds having a substantial amount of oxygen p-band
characteristic at the Fermi energy level, as described below, and
other embodiments of the invention involving improved ion host
particles, can be used.
[0104] One advantage of the battery arrangement of the invention as
illustrated in FIG. 4 (or any arrangement in which at least one
anode includes the described and illustrated microstructure) is
that, due to the inherent connectivity of the self-organized
microstructure, it is possible to use smaller ion host particles
than those used in conventional cathode designs. In particular,
particles of size on the order of less than 80 microns, and
preferably particles in the nanometer size range can be used. The
use of finer particles, that is, those of smaller maximum
cross-sectional dimensions, minimizes the detrimental effects of
volume change occurring naturally during charging and discharging
of the battery, and enhances overall lithium ion transport rate.
From the perspective of current-carrying capacity, an ion needs to
diffuse a shorter distance within a smaller particle. That is, as
the ratio of surface area to volume is minimized (with small
particles) the amount of diffusion of lithium within each particle
is minimized. Small particles are better able to withstand size
changes upon intercalation and de-intercalation, reducing the
potential of the particles to crack and/or to lose contact with
electronically-or ionically-conductive materials. One embodiment of
the invention provides, therefore, ion host particles, preferably
lithium host particles, less than about 80 microns in maximum
cross-sectional dimension, preferably less than about 20 microns,
more preferably less than about 1 micron, more preferably less than
about 500 nm, more preferably less than about 100 nm, and more
preferably still less than about 10 nm.
[0105] The present invention also provides a series of ion host
particles, preferably lithium dichalcogenide compounds that are
prepared for use in lithium intercalation reactions, particularly
lithium metal or main group dioxides. These compounds are prepared
based upon their predicted utility for intercalation as calculated
using computer modeling techniques. Surprisingly, this approach has
demonstrated that, in sharp contrast to the aforementioned
conventional belief, during intercalation of a lithium ion into a
metal or main group dioxide, the electron density may be
transferred to electron bands which have states with a significant
portion of charge density on the oxygen atoms.
[0106] Methods of the invention used to model intercalation
reactions by computer include first principles methods of solving
the Schrodinger equation. Such methods include, but are not limited
to, the pseudo potential technique, the LMTO technique, the FLAPW
technique and the Hartree-Fock technique. Other such first
principles methods are known to those skilled in the art and are
intended to be within the scope of the present invention.
[0107] Using these methods, the invention involves the discovery
that, for lithium intercalation compounds with optimal formation
energies, a significant amount of electron density is transferred
to the oxygen atom p-level energy states of these compounds. In
particular, as the amount of electron density transferred to the
p-level energy states of the oxygen atoms increases monotonically,
the formation energy of the lithium intercalation compound also
increases monotonically.
[0108] In one embodiment, the amount of electron density
transferred to the p-level energy states associated with the oxygen
atoms was calculated using the pseudo potential method, such as
described in: Computer Physics Reports 9, 115 (1989); Rep. Prog.
Phys. 51, 105 (1988); Rev. Mod. Phys. 64, 1045 (1992); and/or Phys.
Rev. B23, 5048 (1981). In this embodiment, the charge densities of
the MO.sub.2 and LiMO.sub.2 compounds were calculated assuming
these compounds had the same geometry. The difference in the charge
densities of these two compounds were then calculated
point-by-point on a grid of 40.times.40.times.40 points per unit
cell. This difference was then integrated in a sphere of radius
about 1.15 .ANG. centered on an oxygen atom. This method provides
the electron density transferred to a single oxygen atom during
intercalation compound synthesis. Thus, since there are two oxygen
atoms per intercalation compound, to calculate the total amount of
electron density transferred to the p-level energy states of the
oxygen atoms of the intercalation compound, this number is
doubled.
[0109] Table I shows the fraction of electron charge transferred to
each oxygen atom during intercalation compound synthesis as
calculated using this pseudo potential approach, assuming both the
MO.sub.2 and LiMO.sub.2 compounds were in the .alpha.-NaFeO.sub.2
crystal structure. The electron charge transfer values are
calculated with the optimized pseudopotential method as described
in Payne, M. C., M. P. Teter, et al. (1992). "Iterative
Minimization Techniques for Ab-Initio Total Energy Calculations:
Molecular Dynamics and Conjugate Gradients." Rev. Mod. Phys. 64:
1045. The formation energies are calculated with the soft
pseudopotential technique as described by Kresse G. and J.
Furthmuller (1996). Comput Mat Sci, 6:15. Kresse, G. And J. Hafner
(1993); Phys Rev B, 47: 558. Kresse, G. and J. Hafner (1994); Phys
Rev B, 49: 14, 251 and as implemented in the Vienna ab-initio
Simulation Package (VASP) version 3.2. This table demonstrates
that, as the amount of charge transferred to the oxygen atoms of
the intercalation compound increases, the formation energy of the
intercalation compound also increases.
1 TABLE I intercalation compound LiTiO.sub.2 LiVO.sub.2 LiCoO.sub.2
LiZnO.sub.2 LiAlO.sub.2 fraction of electron 0.21 0.24 0.25 0.27
0.32 charge transferred to each O atom formation energy 2.36 3.05
3.73 4.79 5.37 of intercalation compound (eV)
[0110] Accordingly, in one embodiment the invention provides
lithium intercalation compounds having at least about 20% of the
electron density transferred to each oxygen atom during lithium
intercalation compound synthesis as defined by the above-noted
pseudo potential technique, more preferably at least about 25% and
most preferably at least about 30%.
[0111] While an emphasis has been placed herein on the calculation
of appropriate dioxides for use as lithium intercalation compounds,
it is to be appreciated that the present invention is not limited
to such methods or compounds. For example, the methods of the
present invention may be readily used to calculate formation
energies for other dichalcogenide compounds that may be used in
lithium intercalation. In this regard, the formation energies for
LiCoO.sub.2, LiCoS.sub.2 and LiCoSe.sub.2 have been calculated as
3.97 eV, 2.36 eV and 1.68 eV, respectively. As known to those
skilled in the art, for such calculations, the energies and other
appropriate parameters associated with the atomic species in these
other chalcogenide systems should be substituted for those of
oxygen.
[0112] Furthermore, the intercalation compounds of the present
invention may be used with ions other than lithium ions. For
example, alkali atoms and ions other than lithium may be used.
Other such molecules, atoms and ions are known to those skilled in
the art and are intended to be within the scope of the present
invention.
[0113] While shown in Table I as being fully intercalated, lithium
intercalation compounds in accordance with the present invention
need not be fully intercalated. Instead, lithium intercalation
compounds may be represented by the empirical formula
Li.sub.xM.sub.yN.sub.zO.sub.2. In this formula, M and N represent
metal atoms or main group elements. x, y and z may each have any
value between 0 and about 1, but y and z should be selected such
that the formal charge on the M.sub.yN.sub.z portion of the
compound is (4-x). x is between 0 and 1.
[0114] Metals and main group elements appropriate for use as M or N
include, but are not limited to, the 3d series of transition metals
(i.e., Sc, Ti, V, Cr, Fe, Co, Ni, Cu and Zn), Cd, Al and B.
Preferably one of M or N are Zn or Al. Other metals or main group
elements may also be used as M or N, but some of these atoms may
have particular disadvantages. For example, certain metals or main
group elements may result in lithium intercalation compounds that
are relatively heavy or expensive. Moreover, some metals or main
group elements are comparatively rare or difficult to process.
[0115] In certain embodiments, the lithium intercalation compounds
of the present invention are mixed metal or main group element
compounds (i.e., y and z are each greater than zero) since these
compounds can offer good formation energies while allowing other
desirable features to be tailored to a particular purpose. For
example, under certain circumstances, it may be desirable to
prepare Li.sub.xZnO.sub.2 or Li.sub.xAlO.sub.2 with the crystal
structure of Li.sub.xCoO.sub.2 (i.e., the .alpha.-NaFeO.sub.2
crystal structure). However, it may be difficult to prepare
Li.sub.xZnO.sub.2 or Li.sub.xAlO.sub.2 in this structure.
Therefore, a Li.sub.xZn.sub.yCo.sub.zO.sub.2 or
Li.sub.xAl.sub.yCo.sub.zO.sub.2 compound may be prepared that has
the crystal structure of Li.sub.xCoO.sub.2 and a formation energy
close to that predicted for Li.sub.xZnO.sub.2 or Li.sub.xAlO.sub.2
in this structure.
[0116] In another example, while LiAlO.sub.2 is predicted to have a
very high energy density, it may be difficult to prepare in the
.alpha.-NaFeO.sub.2 structure or may have low electronic
conductivity. Therefore a mixed-metal
Li.sub.x(M.sub.yAl.sub.z)O.sub.2 compound may be prepared that
still has high energy density but with better electronic
conductivity and that can be made in a crystal structure that
allows for lithium (de-)intercalation. Table II shows the predicted
formation energies for Li.sub.x(M.sub.yAl.sub.z)O.sub.2 compounds
with M=Ti, V, Mn, Fe, and Co and y equal to 1/3 and 2/3 while z is
equal to 2/3 and 1/3. The energies are calculated with the VASP 3.2
program. This table demonstrates that a significant formation
energy increase is retained for Al even when mixed with other
metals.
2 TABLE II Metal Li(M.sub.1/3Al.sub.2/3)O.sub.2
Li(M.sub.2/3Al.sub.1/3)O.sub.2 Ti 4.06 3.13 V 3.58 2.97 Mn 4.02
3.67 Fe 4.35 3.88 Co 4.66 4.20
[0117] In other embodiments, it may be advantageous to prepare
lithium intercalation compounds from only one metal or main group
element to reduce the cost and/or time associated with preparation
of these compounds. For these embodiments, z should be 0 such that
the empirical formula of the lithium metal or main group element
dioxide is Li.sub.xMO.sub.2.
[0118] In one particular set of embodiments, the invention reflects
the discovery that addition of Al, in a homogeneous manner, into a
lithium oxide compound can result in a high-energy compound, in
particular a compound having a raised voltage relative to the
lithium oxide without aluminum. The invention involves substitution
of Al for M, to some extent, in the compound LiMO.sub.2, where M is
a metal as described herein. This aspect of the invention is a
significant departure from the teachings of the prior art, as a
whole, which do not involve recognition of any possibility of
increasing the voltage of a lithium intercalation compound by
incorporation of Al. The compound of the present invention is
homogeneous, rather than being phase separated, and as a result
exhibits advantageous electrical properties. Formation of a
homogeneous compound is achieved by generally lower-temperature
synthesis techniques that retain a higher-energy state in the
compound. General prior art synthetic techniques for mixed-metal
compounds of this type typically result in phase separation to a
low-energy state. The incorporation of Al into compounds of this
type, and the discovery of a technique for incorporation resulting
in a high-voltage compound, is a significant advantage since Al is
very light weight and inexpensive relative to most other metals
that would be candidates for use in such compounds. Indeed, even if
an increase in voltage in the compounds of this aspect of the
invention had not been realized, but voltage had remained
essentially identical, a significant advantage would have been
realized due to the relatively low expense of Al. An additional
benefit is the low toxicity of Al.
[0119] In another set of embodiments, the invention reflects the
discovery that addition of Al to form an intercalation compound
LiAl.sub.yM.sub.1-yO.sub.2 allows the stabilization of the
.alpha.-NaFeO.sub.2 structure type for a compound which as pure
LiMO.sub.2 is not easily formed in this structure. Here M can be
but is not limited to Mn, Fe, and Ti. For instance, LiMnO.sub.2 can
be crystallized in the orthorhombic symmetry phase (T. Ohzuku, A.
Ueda, T. Hirai, Chemistry Express, Vol. 7, No. 3, pp. 193-196,
1992) as a pure compound, or as the tetragonal spinel
Li.sub.2Mn.sub.2O.sub.4 by electrochemical or chemical insertion of
Li into the spinel LiMn.sub.2O.sub.4, but has only been formed in
the .alpha.-NaFeO.sub.2 structure type (which in this composition
has monoclinic symmetry, space group C2/m) by the ionic exchange of
Li.sup.+ for Na.sup.+ in NaMnO.sub.2 (A. R. Armstrong and P. G.
Bruce, Nature, Vol. 381, p. 499, 1996). As we show in Example 6, a
solid solution Li(Al, Mn)O.sub.2 can be readily crystallized in the
monoclinic variant of the a-NaFeO.sub.2 structure type by using a
mixed hydroxide precursor and heating in a reducing gas
environment.
[0120] Still another set of embodiments reflects the discovery that
an intercalation compound LiAl.sub.yMn.sub.1-yO.sub.2 which is
crystallized in the, .alpha.-NaFeO.sub.2 structure type, forms upon
electrochemical cycling an intercalation compound with two
characteristic voltages of intercalation, a high energy density,
and excellent cycling performance. In particular, this
intercalation compound can be cycled over voltage and capacity
ranges which include both a 4V and 3V plateau (against a Li metal
anode), similar to that of Li--Mn--O spinels, but without the loss
of capacity upon cycling that is characteristic of previous
spinels. This allows practical utilization of both voltage regimes,
and consequently results in a higher practical energy density.
[0121] Those of ordinary skill in the art also typically would not
have expected to have achieved success by incorporating Al into
compounds of this sort since Al is not a 3d metal, and is fixed in
valence. In oxide systems, Al is a metal or Al.sup.3+. Thus, those
of ordinary skill would not have expected Al to be a useful
participant in a system of this type which typically is thought to
involve a reaction such as M.sup.4++e.sup.-.fwdarw.M.sup.3+.
However, the present invention involves the recognition that oxygen
is electrochemically active in the compounds disclosed, thus the
fixed-valence nature of Al is not problematic.
[0122] The compound LiAl.sub.yM.sub.1-yO.sub.2 preferably includes
Ti, V, Mn, Fe, Co, Ni, Cr, Co or Mn, and in a particularly
preferred embodiment M=Co. In this formula, 0<y<0.75 in
preferred embodiments, and in a particularly preferred embodiment
0.15<y<0.5. The compound has an .alpha.-NaFeO.sub.2
structure, or a spinel structure.
[0123] Lithium intercalation compounds are commonly prepared by the
physical mixing of powders of salts of each of the metals. For
example, in order to prepare LiCoO.sub.2, Li.sub.2CO.sub.3 or LiOH
may be used as a source of Li, and CoO or Co(NO.sub.3).sub.2 used
as the source of Co. A mixture of such powders typically must be
fired at temperatures of about 800.degree. C. or higher in order to
crystallize a well-ordered LiCoO.sub.2 The extent of ordering can
be determined by X-ray crystallography, and it is recognized in the
art that the highly ordered, so-called "high temperature (HT)"
LiCoO.sub.2 has superior electrochemical properties compared to the
so-called "low-temperature (LT)" LiCoO.sub.2, as explained by R. J.
Gummow et al., Mat. Res. Bull., Vol. 28, pp. 1177-1184 (1983), and
Garcia et al., J. Electrochem Soc., Vol. 144, pp.
1179-1184(1997).
[0124] While the nominal compositions of the present invention may
also be prepared by such methods, the increased formation energy of
the subject compounds may not be realized in such a preparation due
to a lack of sufficient homogeneity. For example, Ohzuku et al.
have tested LiAl.sub.1/4Co.sub.3/4O.sub.2 prepared by mixing
together LiNO.sub.3, NiCO.sub.3, and Al(OH).sub.3 and firing at
750.degree. C. in oxygen for 20 h, and report no increase in
voltage compared to LiCoO.sub.2. Thus they teach against the
present invention. As another example, Nazri et al. have tested
LiAl.sub.yCO.sub.1-yO.sub.2 and LiAl.sub.yNi.sub.1-yO.sub- .2
prepared by mixing powders of LiOH and CoO, Co.sub.3O.sub.4, or
NiO, and firing at 750.degree. C. for a total of 45 h, and also
show no increase in voltage compared to LiCoO.sub.2 and
LiNiO.sub.2. They also teach against the present invention.
[0125] According to the present invention, a preferred method of
preparing the subject compounds utilizes hydroxides of each of the
metals in the compound. Hydroxides of the constituent metals
firstly decompose to the oxides without melting, unlike most metal
nitrate salts, secondly decompose typically at lower temperatures
upon firing than do other metal salts such as carbonates or
sulfates, and thirdly, yield primarily water vapor as a
decomposition product, rather than undesirable or toxic gases. For
the compounds LiCoO.sub.2 and LiNiO.sub.2, or solid solutions
containing Co or Ni, the use of the hydroxides Co(OH).sub.2, CoOOH,
Ni(OH).sub.2 or NiOOH has a particular advantage. These hydroxides
are structurally closely related to the desired .alpha.-NaFeO.sub.2
structure. Co(OH).sub.2 and Ni(OH).sub.2 tend to form CoOOH and
NiOOH upon decomposition, and the latter are nearly identical in
structure to LiCoO.sub.2 and LiNiO.sub.2, differing primarily in
the substitution of Li.sup.+ and H.sup.+ within the structure.
Furthermore, Li.sup.+ and H.sup.+ both have high diffusion
coefficients in these structures, and can be readily exchanged for
one another. Thus by using hydroxide precursors, it is possible to
obtain the ordered "HT" structure of these compounds at markedly
reduced firing temperatures compared to conventional
preparation.
[0126] In another, particularly preferred synthesis technique, a
still greater level of homogeneity is achieved in a
precipitation/freeze-drying process. The hydroxides of the metals M
and N are first simultaneously precipitated from an aqueous
solution containing water-soluble salts of these metals, such as an
aqueous nitrate solution. This can be accomplished by determining a
relatively narrow pH range within which hydroxides of M and N are
simultaneously insoluble. The hydroxide or mixed hydroxides are
then separated from the solution in which they were precipitated,
for example by filtering or centrifugation, so that the origin
salts are not reformed upon firing. As all of the well-known Li
salts are soluble in water, Li is not easily co-precipitated with
the M,N hydroxides. In order to obtain a highly homogeneous mixture
of Li, M, and N, the precipitated hydroxides or mixed hydroxides
are then dispersed in an aqueous solution containing a
water-soluble Li salt such as LiOH. This suspension of solid
hydroxide particulates in the Li containing solution is then dried
so as to prevent compositional segregation. A preferred method of
drying is freeze-drying, wherein the suspension is atomized or
sprayed into liquid nitrogen, and then frozen droplets freeze-dried
so as to achieve a microscopically homogeneous mixture of LiOH and
the hydroxides of M and N. The dried hydroxide mixture is then
heated in air or oxygen at temperatures of 200-800.degree. C. to
obtain the mixed oxide compound.
[0127] According to the present invention, lithium intercalation
compounds preferably have a formation energy of at least about 3
eV, more preferably at least about 4 eV and most preferably at
least about 4.5 eV as measured according to the above-described
pseudo potential technique. The energy densities of lithium
intercalation compounds of the present invention preferably are at
least 100 W.multidot.hr/kg, preferably at least about 150
W.multidot.hr/kg, more preferably at least about 180
W.multidot.hr/kg.
[0128] Lithium intercalation compounds in accordance with the
present invention should be electrical conductors. As used herein,
the term "electrical conductor" refers to a compound having an
electrical conductivity of at least about 1.times.10.sup.-5
Siemen/cm as measured by the four-point DC technique or by AC
impedance spectroscopy. However, some lithium intercalation
compounds with formation energies within the above-noted ranges are
electrical insulators. By "electrical insulator," it is herein
meant to refer to a compound with an electrical conductivity of
less than about 1.times.10.sup.-5 Siemen/cm as measured by the
four-point DC technique or by AC impedance spectroscopy. For
example, LiAlO.sub.2 has a formation energy of higher than 5V, but
this compound is an electrical insulator.
[0129] According to the present invention, electrically insulating,
lithium intercalation compounds that have a formation energy within
the above-noted ranges may be doped with atoms such that the
resulting intercalation compound is electrically conductive and has
a formation energy in accordance with the present invention.
Dopants appropriate for use in the present invention include, but
are not limited to, Ti, Mn, Fe and Cr. Methods of doping such
lithium metal or main group element dioxide intercalation compounds
include, for example, firing a mixture of the oxide, along with the
dopant oxide and lithium oxide or lithium hydroxide under
appropriate conditions of temperature and oxygen pressure.
[0130] The intercalation compounds of the present invention can be
used as lithium intercalation compound 24 in a cathode for a
rechargeable battery such as cathode 12 of battery 10 as depicted
in FIG. 1 which includes electrically conductive particles 28
(formed, for example, from a substance such as carbon black),
ionically conductive material 26 (for example, doped polyethylene
oxide). Ion host particles of the invention also can be used in an
electrode of the invention as illustrated in FIGS. 3 and 4. In an
arrangement such as that of FIG. 4 in which cathode 42 and anode 52
are each formed from interpenetrating polymer microstructures, the
formation energy of the ion host particles of the anode should be
less than that of the ion host particles of the cathode.
[0131] For battery 10 to function effectively, there must be
electronic communication between lithium intercalation compound
particles 24 and terminal 13 of cathode 12 and ionic communication
between lithium intercalation compound particles 24 and polymer
electrolyte 16. This requires good contact between components 24,
26 and 28. That is, for electrons to flow from each lithium
intercalation compound particle 24 to terminal 13, a well-connected
network of electronically-conductive particles 28 (and lithium
intercalation compound particles where they are
electronically-conductive) must exist between each intercalation
compound particle and terminal 13, and a well-connected pathway of
ionically-conductive material 26 (and lithium intercalation
compound particles where they are ionically-conductive) must exist
between lithium intercalation compound particles 24 and the polymer
electrolyte 16. One significant problem with prior art cathode
designs is that repeated charge/discharge cycling typically leads
to increased electrical resistance across the cathode. The effect
is thought to be due to passivation of the intercalation particle
surface. This leads to a decrease in battery performance, for
example, peak current falls.
[0132] Another problem of the arrangement of FIG. 1 is that, even
assuming good electrical or ionic contact between adjacent
components, the arrangement of cathode 12 does not guarantee that
each lithium intercalation particle 24 will be in ionic
communication with electrolyte 16 and in electronic communication
with terminal 13. Since the arrangement of cathode 12 is simply a
mixture of three different components, a lithium intercalation
particle 24 can become either isolated electronically from terminal
13, or isolated ionically from polymer electrolyte 16, or both. For
example, a lithium intercalation particle 25, as illustrated, is in
ionic communication with polymer electrolyte 16 via an
ionically-conductive material 26 contacting both particle 25 and
electrolyte 16, but is not in electronic communication with
terminal 13 since it is not in contact with any
electronically-conductive material that is in electronic
communication with terminal 13 or with another lithium
intercalation particle that is in electronic communication with
terminal 13. Accordingly, particle 25 is effectively isolated and
can play no part in charging and discharging of battery 10. This
leads to a loss of capacity in the battery.
[0133] According to a particularly preferred embodiment of the
invention as illustrated in FIG. 4, ionically-conductive polymer 34
of cathode 42 and the solid polymer electrolyte of the battery are
defined by the same material (although, as discussed above, any
electrolyte can be used in the invention). Use of a solid polymer
electrolyte, as opposed to a liquid electrolyte, offers many
advantages, as is known. Use of the same material for
ionically-conductive polymer 34 and the solid polymer electrolyte
of the battery minimizes an energy barrier associated with ion
transfer across the electrode/electrolyte interface.
[0134] Described above is a cathode suitable for use in a lithium
solid polymer electrolyte battery. However, the invention provides
an arrangement suitable for use as a cathode or anode, or both, in
a solid battery. For example, a battery having a cathode as
illustrated in FIG. 4, and an anode including a similar
bicontinuous, interpenetrating polymer microstructure of an
electronically-conductive polymer and an ionically-conductive
polymer, with a different lithium host particle, could be used.
[0135] The function and advantage of these and other embodiments of
the present invention will be more fully understood from the
examples below. The following examples are intended to illustrate
the benefits of the present invention, but do not exemplify the
full scope of the invention.
EXAMPLE 1
Synthesis of LiCoO.sub.2 from Mixed Hydroxides
[0136] LiCoO.sub.2 crystallized in the .alpha.-NaFeO.sub.2
structure was prepared. 23.70 g of Co(OH).sub.2 powder (formula
weight 92.95, from Aldrich Chemical Company, Milwaukee, Wis.) and
11.23 g of LiOH.H.sub.2O powder (formula weight 41.96, from Aldrich
Chemical Company), were mixed by ball-milling with aluminum oxide
milling balls in a polypropylene jar at 120 rpm for 18 hours. The
mixed hydroxide powders were heated to 600.degree. C. in air in an
alumina crucible and held for 8 hours, then cooled. Powder X-ray
diffraction, FIG. 5, showed that the resulting powder had the
highly-ordered .alpha.-NaFeO.sub.2 structure, indicated by the
clear separation between the closely spaced diffraction peaks
labeled (006)/(012) and (108)/(110).
EXAMPLE 2
Synthesis of LiAl.sub.0.25Co.sub.0.75O.sub.2 from Mixed
Hydroxides
[0137] The compound LiAl.sub.0.25Co.sub.0.75O.sub.2, crystallized
in the .alpha.-NaFeO.sub.2 structure, was prepared. 10.49 g of
LiOH.H.sub.2O powder (formula weight 41.96, from Aldrich Chemical
Company), 17.43 g of Co(OH).sub.2 powder (formula weight 92.95,
from Aldrich Chemical Company, Milwaukee, Wis.) and 4.88 g of
Al(OH).sub.3 (formula weight 78.00, from Aldrich Chemical Company,
Milwaukee, Wis.) were mixed by ball-milling with aluminum oxide
milling balls in a polypropylene jar at 120 rpm for 18 hours. The
mixed hydroxide powders were heated to 850.degree. C. in air in an
alumina crucible and held for 3.5 hours, then cooled. Powder X-ray
diffraction showed that the resulting powder had the highly-ordered
.alpha.-NaFeO.sub.2 structure.
EXAMPLE 3
Synthesis of LiCoO by Hydroxide Precipitation and Freeze-Drying
[0138] LiCoO.sub.2 of the "HT" structure, i.e., the
.alpha.-NaFeO.sub.2 structure, was prepared. Co(OH).sub.2 was
precipitated by adding 0.1 M solution of Co(NO.sub.3).sub.2 (Alfa
Aesar, Ward Hill, Mass.) in deionized water to a continuously
stirred solution of LiOH.H.sub.2O in deionized water kept at pH=11,
near the minimum solubility pH for Co(OH).sub.2. The precipitate
was allowed to digest for 12 h, then settled by centrifugation.
Nitrate ions, which otherwise re-form into low-melting nitrate
compounds upon drying which can melt and cause compositional
segregation upon subsequent firing, were removed in a rinsing
procedure. The supernatant liquid from precipitation was decanted,
and the Co(OH).sub.2 ultrasonically dispersed in a buffer solution
of LiOH.H.sub.2O in deionized water at pH=11. The precipitate was
settled by centrifugation, and the supernatant again decanted. This
cycle of dispersion in a buffer solution, settling by
centrifugation, and decanting was conducted a total of 5 times. The
rinsed precipitate was dispersed a final time in an aqueous
solution containing dissolved LiOH.H.sub.2O at a concentration
which yielded an overall composition with a Li to Co ratio of
approximately one. This suspension was then atomized into liquid
nitrogen, and the frozen droplets freeze-dried (Consol 12LL, the
Virtis Company, Gardiner, N.Y.), to obtain a uniform and fine
dispersion of crystalline Co(OH).sub.2 and amorphous lithium
hydroxide (partially hydrated). The freeze-dried precursor powder
was then heated in air to temperatures from 100-850.degree. C. for
2 hours. FIG. 6 shows X-ray diffraction (XRD) scans of the
as-freeze-dried powder, and after firing in air for 2 hours at
temperatures from 100-600.degree. C. The precursor contains
Co(OH).sub.2 as the predominant crystalline phase; the lithium
hydroxide is amorphous to X-rays. Upon firing at 100.degree. C. for
2 h, the strongest lines for Co(OH).sub.2 ((100), (101), and (102))
are already greatly diminished, whereas those for LiCoO.sub.2 are
appearing. With increasing firing temperature, the increasingly
sharper lines indicate a well-crystallized product, in which the
peak positions and relative intensities indicate "HT" LiCoO.sub.2 ,
of the .alpha.-NaFeO.sub.2 structure.
EXAMPLE 4
Synthesis of LiAl.sub.yCo.sub.1-yO.sub.2 by Hydroxide Precipitation
and Freeze-Drying
[0139] LiAl.sub.yCo.sub.1-yO.sub.2 of compositions y=0.25, 0.50 and
0.75 were prepared. The compositions y=0.25 and 0.50 were
crystallized in the .alpha.-NaFeO.sub.2 structure, while the
composition y=0.75 showed a majority of the .alpha.-NaFeO.sub.2
structure and a minority crystallized in the tetragonal polymorph
of LiAlO.sub.2. Cobalt and aluminum hydroxide were simultaneously
co-precipitated by preparing a 0.2 M solution containing
Co(NO.sub.3).sub.2 and Al(NO.sub.3).sub.3 (Alfa Aesar, Ward Hill,
Mass.) in the desired Al/Co molar ratio, dissolved in deionized
water. The mixed hydroxide was precipitated by adding this solution
to a continuously stirred solution of LiOH.H.sub.2O in deionized
water kept at pH=10.5. The precipitate was allowed to digest for 12
h, then settled by centrifugation. The rinsing and settling
procedure described in Example 3 was used in order to remove
residual nitrate ions. The rinsed precipitate was dispersed a final
time in an aqueous solution containing dissolved LiOH.H.sub.2O at a
concentration which yielded an overall composition with a Li to
Co+Al molar ratio of approximately one. This suspension was then
atomized into liquid nitrogen, and the frozen droplets
freeze-dried, then heated in air to temperatures from
400-850.degree. C. for 2 hours. FIG. 7 shows X-ray diffraction
scans for the LiAl.sub.0.25Co.sub.0.75O.su- b.2 powder after firing
at temperatures from 400-700.degree. C. With increasing
temperature, the X-ray diffraction lines are increasingly sharper,
and show a well-crystallized powder of the .alpha.-NaFeO.sub.2
structure, while the compound LiAl.sub.0.75Co.sub.0.25O.sub.2
showed a minor amount of the tetragonal polymorph of LiAlO.sub.2
after calcining for 2 hours in air at 200-700.degree. C.
EXAMPLE 5
Electrochemical Testing
[0140] The compounds of Examples 1-4 were tested in a standard test
cell configuration: Li metal/1.0M LiPF.sub.6 in (50% EC+50% DEC)
oxide+carbon+PVDF. Approximately 30 mg of oxide powder were used in
each cell. The cells were charged and discharged at constant
current densities from 0.05 to 0.4 mA per cm.sup.2 of electrode
area.
[0141] FIG. 8 shows charging curves for the compounds LiCoO.sub.2,
Li(Al.sub.1/4Co.sub.3/4)O.sub.2, and
Li(Al.sub.1/2Co.sub.1/2)O.sub.2, prepared according to Examples 3
and 4. The charging current is 0.2 mA per cm.sup.2 of cathode area,
and each composition was charged to a nominal lithium concentration
of Li.sub.0.6Al.sub.yCo.sub.zO.sub.2. The systematic increase in
the voltage with Al concentration indicates that the Al addition
has the predicted effect of increasing formation energy of the
compound. FIG. 9 shows discharging curves 0.2 mA/cm.sup.2 for the
same samples after charging to a nominal composition of
Li.sub.0.6Al.sub.yCo.sub.zO.sub.2. The initial discharge voltage is
higher for both of the Al containing compositions than for
LiCoO.sub.2. The discharge voltage for
Li(Al.sub.1/4Co.sub.3/4)O.sub.2 remains higher out to a discharged
Li concentration beyond Li.sub.0.8Al.sub.yCo.sub.zO.s- ub.2.
[0142] FIG. 10 shows the open-circuit voltage as a function of time
for two cells containing LiCoO.sub.2 and
Li(Al.sub.1/4CO.sub.3/4)O.sub.2 respectively, prepared according to
Examples 3 and 4. The cells were charged to a nominal lithium
concentration of Li.sub.0.6Al.sub.yCo.sub.zO- .sub.2 at a current
density of 0.2 mA/cm.sup.2. Then the cells were disconnected from
the charging current and the open circuit voltage measured over
time. The voltage of the Al-containing compound remains higher
throughout this measurement, to 24 hours. Further testing showed
that the higher voltage is retained over several days. The result
shows that the increase in voltage is a true equilibrium
voltage.
[0143] FIG. 11 shows charge-discharge curves over two cycles for a
compound Li(Al.sub.1/4Co.sub.3/4)O.sub.2, prepared according to
Example 2, and charged/discharged at 0.4 mA/cm.sup.2. Here, as in
FIGS. 8-10, the charge and discharge voltages are respectively
higher than those for LiCoO.sub.2.
EXAMPLE 6
Synthesis of LiAl.sub.0.25Mn.sub.0.75O.sub.2 by Hydroxide
Precipitation and Freeze-Drying, and Firing in a Reducing Gas
Atmosphere, and Electrochemical Testing of Same
[0144] LiAl.sub.0.25Mn.sub.0.75O.sub.2 was prepared by a similar
process to Example 4. Aluminum and manganese hydroxide were
simultaneously co-precipitated by adding a 0.2 M solution
containing Al(NO.sub.3).sub.3 and Mn(NO.sub.3).sub.2 (Alfa Aesar,
Ward Hill, Mass.) dissolved in deionized water in a 1:3 molar ratio
to a continuously stirred solution of LiOH.H.sub.2O in deionized
water kept at pH=10.5. The precipitate was allowed to digest for
12h, was settled by centrifugation, and the rinsing and settling
procedure described in Example 3 was used in order to remove
residual nitrate ions. The rinsed precipitate was dispersed a final
time in an aqueous solution containing dissolved LiOH.H.sub.2O at a
concentration which yielded an overall composition with a Li to
Al+Mn ratio of approximately one, and freeze-dried according to the
procedure described in Example 4. The freeze-dried precursor was
then heated in air and in argon at temperatures of 400-900.degree.
C. for 2 h. When the precursor was fired in air, X-ray diffraction
showed that the phases formed were LiMn.sub.2O.sub.4 spinel and
Li.sub.2MnO.sub.3. However, when the precursor was fired in argon,
X-ray diffraction, FIG. 12, shows that the phase which is formed is
the monoclinic variant of .alpha.-NaFeO.sub.2 isomorphous with pure
LiMnO.sub.2 formed in this structure by the Li ion exchange of
NaMnO.sub.2 (A. R. Armstrong and P. G. Bruce, Nature, Vol. 381, p.
499, 1996). The monoclinic phase is distinguished from the
tetragonal lithiated spinel phase Li.sub.2Mn.sub.2O.sub.4 by the
appearance of two peaks in the 2q range 64-68.degree. (F.
Capitaine, P. Gravereau, C. Delmas, Solid State Ionics, Vol. 89,
pp. 197-202, 1996). This result therefore shows that the
a-NaFeO.sub.2 structure type is stabilized by the addition of Al to
LiMnO.sub.2.
[0145] FIG. 13 shows the first charge and discharge cycle for a
battery prepared according to Example 5, using said
LiAl.sub.0.25Mn.sub.0.75O.sub- .2 as the cathode. The charging
curve shows a voltage exceeding 4V, which is higher than the
voltage realized by Armstrong and Bruce (Nature, Vol. 381, p. 499,
1996) for LiMnO.sub.2 of this structure prepared by ion exchange.
The first discharge curve shows two voltage plateaus, at
approximately 4V and 3V respectively. The appearance of similar
plateaus has been observed in the spinel LiMn.sub.2O.sub.4, the
higher voltage plateau being associated with intercalation of Li
over concentrations between 0<x<1 in Li.sub.xMn.sub.2O.sub.4,
and the lower voltage plateau being associated with 1<x<2 in
Li.sub.xMn.sub.2O.sub.4, the higher Li concentration being
accomplished typically by using a Li metal anode. The appearance of
two voltage plateaus upon discharge has also been reported for
orthorhombic LiMnO.sub.2 (R. J. Gummow, D. C. Liles, and M. M.
Thackeray, Mat. Res. Bull., Vol. 28, pp. 1249-1256, 1993) and for
monoclinic LiMnO.sub.2 prepared by ion exchange (G. Vitins and K.
West, J. Electrochem. Soc., Vol. 144, No. 8, pp. 2587-2592, 1997),
and has been attributed to a change in the cation ordering of the
respective structures to that of the spinel LiMn.sub.2O.sub.4 and
lithiated spinel Li.sub.2Mn.sub.2O.sub.4.
[0146] FIG. 14 shows the charge capacity of the battery prepared
according to Example 5, using LiAl.sub.0.25Mn.sub.0.75O.sub.2
prepared according to this Example as the cathode, as a function of
the cycle number. The battery is cycled over the voltage range 2.0V
to 4.4V, thereby encompassing both voltage plateaus. It is seen
that the charge capacity initially decreases over the first 5
cycles, but then increases again and remains constant at about 150
cycles. This capacity is retained to over 40 cycles. The
corresponding energy density is about 290 mAh/g of cathode
material.
[0147] The cycling stability of this intercalation compound is
superior to other Li--Mn--O based compounds. It is well-known in
the art that when LiMn.sub.2O.sub.4 spinel is cycled over both
voltage plateaus, the capacity fades rapidly. This effect has been
attributed to a collective Jahn-Teller distortion due to the
presence of sufficient Mn.sup.3+ ions. In addition, both
orthorhombic and monoclinic LiMnO.sub.2 have been shown to lose
capacity rapidly when cycled over both voltage plateaus (I.
Koetschau, M. N. Richard, J. R. Dahn, J. B. Soupart, and J. C.
Rousche, J. Electrochem. Soc., Vol. 142, No. 9, pp. 2906-2910,
1995, and G. Vitins and K. West, J. Electrochem. Soc., Vol. 144,
No. 8, pp. 2587-2592, 1997). The stability of the present
intercalation compounds when cycled over both voltage plateaus
increases the practical capacity and energy density of the compound
compared to other Li--Mn--O compounds which can only be repeatedly
cycled over one voltage plateau without incurring significant
capacity loss.
[0148] The fact that Al additions to a lithium manganese oxide will
result in such improvements is unexpected to those skilled in the
art. In fact, F. Le Cras et al. (Solid State Ionics, Vol. 89, pp.
203-213, 1996) report that a spinel of composition LiAlMnO.sub.4
exhibits rapid capacity loss upon cycling over a similar voltage
range, thereby teaching away from the present invention. However,
the present results do indicate that an intercalation compound of
composition LiAl.sub.yMn.sub.1-yO.sub.2 which is prepared in a
phase isostructural with orthorhombic LiMnO.sub.2 or
Li.sub.2Mn.sub.2O.sub.4 spinel will also exhibit good cycling
behavior over both voltage plateaus and high energy density.
[0149] These results show that by using mixed hydroxide powders as
described in Example 2, or by using co-precipitated and
freeze-dried powders as in Examples 4 and 6, the predictions of the
invention can be realized.
EXAMPLE 7
Preparation of Microphase-Separated, Amorphous Non-Glassy
Nanostructured Block Copolymeric Electrolyte
[0150] Microphase-separated, amorphous, non-glassy nanostructured
block copolymeric electrolyte, in particular a copolymer of lauryl
methacrylate with methoxy polyethylene glycol methacrylate
(PLMA-b-PMnG) was made by an anionic synthetic route using
monofunctional diphenyl methyl potassium as initiator and THF as a
solvent. Diphenyl methyl potassium was prepared by first reacting
naphthalene and an excess of potassium metal in THF to produce
potassium napthalide, then adding a stoichiometric equivalent of
diphenyl methane at room temperature. In the copolymerization
procedure, an initiator solution was prepared in freshly distilled
THF under an inert gas atmosphere, the solution was cooled to
-40.degree. C., then the distilled monomers were slowly titrated
in. Lauryl methacrylate was injected first, followed 30 minutes
later by injection of an equal mass of MnG macromonomer. Each MnG
macromonomer contained about 9 ethylene oxide units, below the
limit for crystallinity. Upon termination of the reaction with
degassed methanol, the copolymer solution was concentrated on a
rotary evaporator, precipitated from 10:1 (v/v) hexane:THF, and
finally centrifuged to isolate the colorless polymer. The molecular
weight of the resulting diblock copolymer was determined by size
exclusion chromatography/light scattering to be approximately
MW=170,000 Daltons. For comparison purposes, PMnG homopolymer was
also anionically synthesized following a similar procedure.
Molecular weights and compositional characteristics of the polymers
are given in Table III. This system is particularly advantageous
due to the high mobility of both blocks at room temperature. The
material was structurally characterized by FTIR, NMR and GPC.
Additionally, microphase separation was determined in the
(PLMA-b-PMnG) system. Simple heating of the sample to above
200.degree. C. using a heat gun failed to induce flow in the
sample, providing strong evidence of block segregation.
3 TABLE III Molecular Ionic conductivity Composition weight at
25.degree. C. PLMA:PMnG, v:v) (g/mol) (10.sup.-6 S/cm) PLMA-b-PMnG
47:53 64,700 2.54 PLMA-b-PMnG 32:68 77,800 4.44 PLMA-b-PMnG 23:77
62,900 6.13 PMnG 0:100 100,000 9.57
[0151] Rheological characterization of this system was performed
using a Rheometrics ARES rheometer with a parallel plate fixture.
The polymer was pressed to a gap width below 1 mm and a stable
normal force of approximately I 000 g. The complex shear modulus,
G=G'+iG", was then measured as a function of frequency by
dynamically shearing the polymer at a fixed strain of 1.5% over the
frequency range of 0.1 to 250 rad s.sup.-1 at temperatures from
25.degree. C. to 90.degree. C. The rheological behavior of block
copolymer melts varies dramatically depending on whether the
material resides in the ordered or disordered state. FIG. 15
presents typical results for the storage (G') and loss (G") moduli
of the PLMA-b-PMnG block copolymers. At low frequencies the storage
modulus reaches a plateau value while the loss modulus assumes a
limiting power law in which G".about..omega..sup.0.5. This
low-frequency scaling behavior is characteristic of a
microphase-separated system and verifies its solid-like nature
(Karis, Russell, et al., Macromolecules, 1995, 28, 1129). Even with
the addition of significant amounts (23 wt %) of poly(ethylene
glycol) dimethyl ether, PEGDME (Polysciences, M=430 g mol.sup.-1),
the low-frequency scaling behavior observed in FIG. 15 is
preserved, indicating that these short PEO chains stay confined to
the PMnG domains of the copolymer morphology. The formation of
nanoscale domains was further verified by direct imaging with
transmission electron microscopy (FIG. 20). By contrast, the PMnG
homopolymer exhibits the low frequency scaling behavior
G".about..omega., indicative of a polymer in its molten state.
[0152] The electrolyte was doped with a lithium salt ( a variety of
salts are known and are suitable). Concentration was
EO:Li.sup.+=20:1. For all EO:Li.sup.+ compositions of the diblock
and LiCF.sub.3SO.sub.3 between 4:1 and 87:1 there was no apparent
crystallization as shown by DSC; the polymer flowed only when
pressure was applied at temperatures to 110.degree. C.
[0153] Conductivity measurements were performed on PEO (Polymer
Laboratories, M=448,000 g mol.sup.-1), the PMnG homopolymer, and
the PLMA-b-PMnG block copolymers at fixed salt concentration
[EO]:Li.sup.+=20:1. Specimens for conductivity measurements were
initially dried in a vacuum oven at 70.degree. C. for 24 hours.
LiCF.sub.3SO.sub.3 (lithium triflate) was dried in vacuo at
130.degree. C. for 24 hours. The materials were then transferred
into an inert atmosphere, dissolved in dry THF or acetonitrile, and
solution cast on a glass die. The polymer/salt complex was then
annealed in vacuo for 48 hours at 70.degree. C. Under argon, the
polymer electrolyte was loaded between a pair of blocking
electrodes made of type 316 stainless steel, pressed to a thickness
of about 250 .mu.m, and annealed in situ at 70.degree. C. for 24
hours. On the temperature interval spanning 20.degree. C. to
90.degree. C. electrical conductivity was measured by impedance
spectroscopy using a Solartron 1260 Impedance Gain/Phase
Analyser.
[0154] FIG. 16 shows that at room temperature the doped 47:53
PLMA-b-PMnG block copolymer displayed ionic conductivities about
two orders of magnitude higher than that of doped PEO, and similar
to that of pure PMnG. As expected, increasing the PMnG content of
the copolymer had the effect of increasing conductivity (Table
III). Significantly higher conductivities were achieved by blending
the block polymer with PEGDME, resulting in a values approaching
10.sup.-4 S cm.sup.-1 at room temperature.
[0155] Cyclic voltammetry was performed on a block copolymer
electrolyte (BCE) composed of 87 wt % 47:53 PLMA-b-PMnG and 23 wt %
PEGDME at a salt concentration [EO]:Li.sup.+=20:1 to investigate
the range of electrochemical stability. The BCE was sandwiched
between a counter electrode of lithium and a working electrode of
aluminum, and pressed to a thickness of approximately 150 .mu.m. A
lithium reference electrode was extruded into the cell through the
side and positioned near the working electrode. Potential was
scanned from -0.3 to +6.0 V vs. Li/Li.sup.+ at a sweep rate of 5 mV
s.sup.-1. Current levels well below 10 .mu.A cm.sup.-2 were
measured between 2.0 and 5.3 V, indicating that the material is
electrochemically stable on this voltage interval, which brackets
that used in commercial lithium-ion batteries, namely 2.5 to 4.2
V.
[0156] The BCE was subjected to charge/discharge testing in a
battery fitted with a lithium-foil anode and a composite cathode of
LiCoO.sub.2 (57 wt %), carbon black (7 wt%), graphite (6 wt %), and
polyacrylonitrile (9 wt %), plasticized with butyrolactone and
ethylene carbonate doped with LiClO.sub.4 (21 wt %). Electrolyte
films were prepared in a dry box by casting the doped block
copolymer directly onto lithium foil from 15 wt % dry THF solution.
The resulting copolymer films were placed under vacuum at room
temperature overnight to remove excess solvent, and pressed to a
thickness of approximately 150 .mu.m. Cycle testing was conducted
between 2.0 and 4.4 V with a MACCOR Series 4000 Automated Test
System over the temperature range from +20 to -20.degree. C. As
shown in FIG. 17(a), at room temperature the battery exhibits
excellent reversibility and a reversible capacity of about 100 mAh
g.sup.-1. At -20.degree. C. the battery remains fully functional,
i.e., it can be discharged and charged, although the capacity is
reduced from that measured at room temperature, as shown in FIG.
17(b).
[0157] Attempts to take data at lower temperatures (below
-20.degree. C.) were frustrated by suspected cathode failure. To
further assess the electrical performance of the BCE, a second test
cell was constructed in which both electrodes were made of lithium.
The Li/BCE/Li cell was subjected to d.c. polarization at an applied
potential of 50 mV; and the current response was measured.
Isothermal experiments were conducted at 10.degree. intervals from
+20.degree. C. to -50.degree. C. While the BCE conductivity
decreased with temperature, the material demonstrated its ability
to pass current down to -40.degree. C. At a room temperature
between -40.degree. C. and -46.degree. C., the PLMA block of the
copolymer undergoes its glass transition with the apparent result
that the lithium ion mobility drops precipitously. This experiment
also allowed us to determine the transference number of Li.sup.+
from the ratio of the steady-state current to the initial current.
At room temperature t.sub.Li+.apprxeq.0.5.
EXAMPLE 8
Preparation of a Bicontinuous, Interpenetrating Microstructure of
an Electronically-Conductive Polymer and an Ionically-conductive
Polymer
[0158] An electronically-conductive polymer,
poly(p-phenylene-vinylene) (PPV) was prepared following a precursor
route (P. L. Burn, et al. J. Chem. Soc. Perkin. Trans., 1, 1992,
3225). The intermediate non-conjugated polymer has good stability
and processing properties and can be readily converted into the
conjugated PPV by a simple heat treatment. The polymer precursor
was blended with an ionically conductive diblock copolymer of
example 7 and samples of bicontinuous, interpenetrating
microstructures of the electronically-conductive polymer and
ionically-conductive polymer were prepared by solvent casting or
spin coating this mixture onto glass slides and heating the
resulting film under vacuum at 210 C. Optical microscopy showed
phase separation of the two polymers into the bicontinuous,
interpenetrating microstructure. A photocopy of an optical
micrograph of the phase-separated structure is shown in FIG. 18, at
magnification 640.times..
EXAMPLE 9
Preparation of Bicontinuous, Interpenetrating Microstructures of
Electronically-Conductive Polymers and Ionically-conductive
Polymers
[0159] Sulfonated polyaniline was synthesized according to a
reported method (J. Yue, et al., J. Am. Chem. Soc., 112, 2800
(1990)). A random copolymer of methylmethacrylate (MMA) and MnG was
synthesized anionically in a manner similar to the method of
example 7, but with simultaneous addition of both monomers to form
a random copolymer architecture. Mixtures of SPAn and P(MMA-r-MnG)
were cast from solution in methanol or m-cresol. The resulting
interpenetrating microstructures were structurally characterized by
optical and transmission electron microscopy. The characteristic
length of the phase separation can be varied between 0.01 and 10
microns, depending upon the processing conditions (i.e., solvent
selected, concentration in solvent, etc.).
EXAMPLE 10
Preparation of Bicontinuous, Interpenetrating Microstructures of
Electronically-Conductive Polymers and Ionically-Conductive
Polymers with Particles Positioned at Interphase Boundaries
[0160] Sulfonated polyaniline (SPAn; an electrically-conductive
polymer), P(MMA-r-MnG) (random copolymer electrolyte), and fine
particles of Al.sub.2O.sub.3 (.apprxeq.5 .mu.m in diameter) were
cast from methanol or m-cresol solution. FIG. 19 is a photocopy of
an optical micrograph of a the resulting interpenetrating
microstructure. The Al.sub.2O.sub.3 phase appears as dark particles
outlining the interface between the polymer electrolyte-rich
regions (light phase) and the SPAn-rich regions (dark phase).
[0161] SPAn and P(MMA-r-MnG) and TiO.sub.2 particles of about 0.1
micron diameter were cast from a similar solution. Phase separation
of the polymers occurred and TiO.sub.2 was observed by TEM to
segregate to interphase boundaries.
[0162] Those skilled in the art would readily appreciate that all
parameters listed herein are meant to be exemplary and that actual
parameters will depend upon the specific application for which the
methods and apparatus of the present invention are used. It is,
therefore, to be understood that the foregoing embodiments are
presented by way of example only and that, within the scope of the
appended claims and equivalents thereto, the invention may be
practiced otherwise than as specifically described.
[0163] Having thus described certain embodiments of the present
invention, various alterations, modifications and improvements will
be apparent to those skilled in the art. Such alterations,
modifications and improvements are intended to be part of this
disclosure and are intended to be within the scope of the present
invention. Accordingly, the foregoing description is by way of
example only and not intended as limiting. The present invention is
limited only as defined by the following claims and equivalents
thereto.
* * * * *