U.S. patent application number 11/823847 was filed with the patent office on 2008-03-06 for ionically conductive composites for protection of active metal anodes.
This patent application is currently assigned to PolyPlus Battery Company. Invention is credited to Bruce D. Katz, Yevgeniy S. Nimon, Steven J. Visco.
Application Number | 20080057399 11/823847 |
Document ID | / |
Family ID | 32107991 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080057399 |
Kind Code |
A1 |
Visco; Steven J. ; et
al. |
March 6, 2008 |
Ionically conductive composites for protection of active metal
anodes
Abstract
Disclosed are ionically conductive composites for protection of
active metal anodes and methods for their fabrication. The
composites may be incorporated in active metal negative electrode
(anode) structures and battery cells. In accordance with the
invention, the properties of different ionic conductors are
combined in a composite material that has the desired properties of
high overall ionic conductivity and chemical stability towards the
anode, the cathode and ambient conditions encountered in battery
manufacturing. The composite is capable of protecting an active
metal anode from deleterious reaction with other battery components
or ambient conditions while providing a high level of ionic
conductivity to facilitate manufacture and/or enhance performance
of a battery cell in which the composite is incorporated.
Inventors: |
Visco; Steven J.; (Berkeley,
CA) ; Nimon; Yevgeniy S.; (Danville, CA) ;
Katz; Bruce D.; (Berkeley, CA) |
Correspondence
Address: |
BEYER WEAVER LLP
P.O. BOX 70250
OAKLAND
CA
94612-0250
US
|
Assignee: |
PolyPlus Battery Company
|
Family ID: |
32107991 |
Appl. No.: |
11/823847 |
Filed: |
June 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10686189 |
Oct 14, 2003 |
7282296 |
|
|
11823847 |
Jun 27, 2007 |
|
|
|
60418899 |
Oct 15, 2002 |
|
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|
Current U.S.
Class: |
429/246 |
Current CPC
Class: |
C03C 10/00 20130101;
H01M 4/381 20130101; Y10T 29/49112 20150115; H01M 4/382 20130101;
H01M 2004/021 20130101; C03C 4/18 20130101; H01M 4/134 20130101;
Y10T 29/49115 20150115; H01M 4/405 20130101; H01M 10/0583 20130101;
H01M 4/40 20130101; H01M 10/052 20130101; H01M 10/0562 20130101;
Y02E 60/10 20130101; H01M 4/366 20130101; H01M 2300/0094
20130101 |
Class at
Publication: |
429/246 |
International
Class: |
H01M 2/16 20060101
H01M002/16 |
Claims
1. An electrochemical device component, comprising: an active metal
electrode having a first surface and a second surface; a protective
composite separator on the first surface of the electrode, the
composite comprising, a first material layer in contact with the
electrode, the first material being ionically conductive and
chemically compatible with the active metal; and a second material
layer in contact with the first layer, the second material being
substantially impervious, ionically conductive and chemically
compatible with the first material; wherein the ionic conductivity
of the composite is at least 10.sup.-7 S/cm.
2-72. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. patent application
Ser. No. 10/686,189 filed Oct. 14, 2003, titled IONICALLY
CONDUCTIVE COMPOSITES FOR PROTECTION OF ACTIVE METAL ANODES, now
pending, which in turn claims priority to U.S. Provisional Patent
Application No. 60/418,899 filed Oct. 15, 2002, titled IONICALLY
CONDUCTIVE COMPOSITES FOR PROTECTION OF ANODES AND ELECTROLYTES.
These patent applications are incorporated herein by reference in
its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to separators and
electrode structures for use in batteries. More particularly, this
invention relates composites for protection of active metal anodes
from deleterious reaction with air, moisture and other battery
components and methods for their fabrication.
[0004] 2. Description of Related Art
[0005] The low equivalent weight of alkali metals, such as lithium,
render them particularly attractive as a battery electrode
component. Lithium provides greater energy per volume than the
traditional battery standards, nickel and cadmium. Unfortunately,
no rechargeable lithium metal batteries have yet succeeded in the
market place.
[0006] The failure of rechargeable lithium metal batteries is
largely due to cell cycling problems. On repeated charge and
discharge cycles, lithium "dendrites" gradually grow out from the
lithium metal electrode, through the electrolyte, and ultimately
contact the positive electrode. This causes an internal short
circuit in the battery, rendering the battery unusable after a
relatively few cycles. While cycling, lithium electrodes may also
grow "mossy" deposits which can dislodge from the negative
electrode and thereby reduce the battery's capacity.
[0007] To address lithium's poor cycling behavior in liquid
electrolyte systems, some researchers have proposed coating the
electrolyte facing side of the lithium negative electrode with a
"protective layer." Such protective layer must conduct lithium
ions, but at the same time prevent contact between the lithium
electrode surface and the bulk electrolyte. Many techniques for
applying protective layers have not succeeded.
[0008] Some contemplated lithium metal protective layers are formed
in situ by reaction between lithium metal and compounds in the
cell's electrolyte which contact the lithium. Most of these in situ
films are grown by a controlled chemical reaction after the battery
is assembled. Generally, such films have a porous morphology
allowing some electrolyte to penetrate to the bare lithium metal
surface. Thus, they fail to adequately protect the lithium
electrode.
[0009] Various pre-formed lithium protective layers have been
contemplated. For example, U.S. Pat. No. 5,314,765 (issued to Bates
on May 24, 1994) describes an ex situ technique for fabricating a
lithium electrode containing a thin layer of sputtered lithium
phosphorus oxynitride ("LiPON") or related material. LiPON is a
glassy single ion conductor (conducts lithium ion) which has been
studied as a potential electrolyte for solid state lithium
microbatteries that are fabricated on silicon and used to power
integrated circuits (See U.S. Pat. Nos. 5,597,660, 5,567,210,
5,338,625, and 5,512,147, all issued to Bates et al.).
[0010] Work in the present applicants' laboratories has developed
technology for the use of glassy or amorphous protective layers,
such as LiPON, in active metal battery electrodes. (See, for
example, U.S. Pat. No. 6,025,094, issued Feb. 15, 2000, U.S. Pat.
No. 6,402,795, issued Jun. 11, 2002, U.S. Pat. No. 6,214,061,
issued Apr. 10, 2001 and U.S. Pat. No.6,413,284, issued Jul. 2,
2002, all issued to Visco, et al. and assigned to at PolyPlus
Battery Company). Despite this progress, alternative protective
layers and structures that could also enhance active metal,
particularly lithium metal, battery performance continue to be
sought. In particular, protective layers that combine the
characteristics of high ionic conductivity and chemical stability
to materials and conditions on either side of the protective layer
are desired.
SUMMARY OF THE INVENTION
[0011] The present invention provides ionically conductive
composites for protection of anodes and electrolytes and methods
for their fabrication. The composites may be incorporated in active
metal negative electrode (anode) structures and battery cells. In
accordance with the invention, the properties of different ionic
conductors are combined in a composite material that has the
desired properties of high overall ionic conductivity and chemical
stability towards the anode, the cathode and ambient conditions
encountered in battery manufacturing. The composite is capable of
protecting an active metal anode from deleterious reaction with
other battery components or ambient conditions while providing a
high level of ionic conductivity to facilitate manufacture and/or
enhance performance of a battery cell in which the composite is
incorporated.
[0012] The composite is composed of at least two layers of
different materials having different chemical compatibility
requirements. By "chemical compatibility" (or "chemically
compatible") it is meant that the referenced material does not
react to form a product that is deleterious to battery cell
operation when contacted with one or more other referenced battery
cell components or manufacturing, handling or storage conditions. A
first material layer (or first layer material) of the composite is
ionically conductive, and chemically compatible with an active
metal electrode material. Chemical compatibility in this aspect of
the invention refers both to a material that is chemically stable
and therefore substantially unreactive when contacted with an
active metal electrode material. It may also refer to a material
that is chemically stable with air, to facilitate storage and
handling, and reactive when contacted with an active metal
electrode material to produce a product that is chemically stable
against the active metal electrode material and has the desirable
ionic conductivity (i.e., a first layer material). Such a reactive
material is sometimes referred to as a "precursor" material. A
second material layer of the composite is substantially impervious,
ionically conductive and chemically compatible with the first
material. Additional layers are possible to achieve these aims, or
otherwise enhance electrode stability or performance. All layers of
the composite have high ionic conductivity, at least 10.sup.-7
S/cm, generally at least 10.sup.-6 S/cm, for example at least
10.sup.-5 S/cm to 10.sup.-4 S/cm, and as high as 10.sup.-3 S/cm or
higher so that the overall ionic conductivity of the multi-layer
protective structure is at least 10.sup.-7 S/cm and as high as
10.sup.-3 S/cm or higher.
[0013] A wide variety of materials may be used in fabricating
protective composites in accordance with the present invention,
consistent with the principles described above. For example, the
first layer, in contact with the active metal, may be composed, in
whole or in part, of active metal nitrides, active metal
phosphides, active metal halides or active metal phosphorus
oxynitride-based glass. Specific examples include Li.sub.3N,
Li.sub.3P, LiI, LiBr, LiCl, LiF and LiPON. These materials may be
applied to the active metal electrode, or they may be formed in
situ by application of precursors such as metal nitrides, metal
phosphides, metal halides, red phosphorus, iodine, nitrogen or
phosphorus containing organics and polymers, and the like. The in
situ formation of the first layer may result from an incomplete
conversion of the precursors to their lithiated analog.
Nevertheless, such incomplete conversions meet the requirements of
a first layer material for a protective composite in accordance
with the present invention and are therefore within the scope of
the invention.
[0014] A second layer of the protective composite may be composed
of a substantially impervious glassy or amorphous ionic conductor,
such as a phosphorus-based glass, oxide-based glass,
phosphorus-oxynitride-based glass, sulpher-based glass,
oxide/sulfide based glass, selenide based glass, gallium based
glass, germanium-based glass, glass-ceramic active metal ion
conductor, lithium beta-alumina, sodium beta-alumina, Li superionic
conductor (LISICON), Na superionic conductor (NASICON), and the
like. Specific examples include LiPON,
Li.sub.3PO.sub.4.Li.sub.2S.SiS.sub.2,
Li.sub.2S.GeS.sub.2.Ga.sub.2S.sub.3, Li.sub.2O.11Al.sub.2O.sub.3,
Na.sub.2O.11Al.sub.2O.sub.3, (Na,
Li).sub.1+xTi.sub.2-xAl.sub.x(PO.sub.4).sub.3
(0.6.ltoreq.x.ltoreq.0.9) and crystallographically related
structures, Na.sub.3Zr.sub.2Si.sub.2PO.sub.12,
Li.sub.3Zr.sub.2Si.sub.2PO.sub.12, Na.sub.5ZrP.sub.3O.sub.12,
Na.sub.5TiP.sub.3O.sub.12, Na.sub.3Fe.sub.2P.sub.3O.sub.12,
Na.sub.4NbP.sub.3O.sub.12, Li.sub.5ZrP.sub.3O.sub.12,
Li.sub.5TiP.sub.3O.sub.12, Li.sub.3Fe.sub.2P.sub.3O.sub.12 and
Li.sub.4NbP.sub.3O.sub.12.
[0015] A particularly suitable glass-ceramic material for the
second layer of the protective composite is a lithium ion
conductive glass-ceramic having the following composition:
TABLE-US-00001 Composition mol % P.sub.2O.sub.5 26-55% SiO.sub.2
0-15% GeO.sub.2 + TiO.sub.2 25-50% in which GeO.sub.2 0-50%
TiO.sub.2 0-50% ZrO.sub.2 0-10% M.sub.2O.sub.3 0 < 10%
Al.sub.2O.sub.3 0-15% Ga.sub.2O.sub.3 0-15% Li.sub.2O 3-25%
and containing a predominant crystalline phase composed of
Li.sub.1+x(M,Al,Ga),(Ge.sub.1-yTi.sub.y).sub.2-x(PO.sub.4).sub.3
where X.ltoreq.0.8 and 0.ltoreq.B.ltoreq.1.0, and where M is an
element selected from the group consisting of Nd, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm and Yb and/or and
Li.sub.1+x+yQ.sub.xTi.sub.2-xSi.sub.yP.sub.3-yO.sub.12 where
0.ltoreq.X.ltoreq.0.4 and 0.ltoreq.Y.ltoreq.0.6, and where Q is Al
or Ga. The glass-ceramics are obtained by melting raw materials to
a melt, casting the melt to a glass and subjecting the glass to a
heat treatment. Such materials are available from OHARA
Corporation, Japan and are further described in U.S. Pat. Nos.
5,702,995, 6,030,909, 6,315,881 and 6,485,622, incorporated herein
by reference.
[0016] Either layer may also include additional components. For
instance, a suitable active metal compatible layer (first layer)
may include a polymer component to enhance its properties. For
example, polymer-iodine complexes like poly(2-vinylpyridine)-iodine
(P2VP-I.sub.2), polyethylene-iodine, or with
tetraalkylammonium-iodine complexes can react with Li to form a
LiI-based film having significantly higher ionic conductivity than
that for pure LiI. Also, a suitable first layer may include a
material used to facilitate its use, for example, the residue of a
wetting layer (e.g., Ag) used to prevent reaction between vapor
phase lithium (during deposition) and LiPON when LiPON is used as a
first layer material.
[0017] A suitable second layer may include a polymer component to
enhance its properties. For example, a glass-ceramic active metal
ion conductor, like the glass-ceramic materials described above,
may also be combined with polymer electrolytes to form flexible
composite sheets of material which may be used as second layer of
the protective composite. One important example of such a flexible
composite material has been developed by OHARA Corp. (Japan). It is
composed of particles of a Li-ion conducting glass-ceramic
material, such as described above, and a solid polymer electrolyte
based on PEO-Li salt complexes. OHARA Corp. manufactures this
material in the form of sheet with a thickness of about 50 microns
that renders it flexible while maintaining its high ionic
conductivity. Because of its relatively high ionic conductivity
(better than 4*10.sup.-5 S/cm at room temperature in the case of
the OHARA product) and stability toward metallic Li, this type of
composite electrolyte can be used at room temperature or elevated
temperatures in fully solid-state cells.
[0018] In addition, the layers may be formed using a variety of
techniques. These include deposition or evaporation (including
e-beam evaporation) of layers of material, such as LiN.sub.3 or an
ionically conductive glass. Also, as noted above, the active metal
electrode adjacent layer may be formed in situ from the
non-deleterious reaction of one or more precursors with the active
metal electrode. For example, a LiN.sub.3 layer may be formed on a
Li anode by contacting CuN.sub.3 with the Li anode surface, or
LiP.sub.3 may be formed on a Li anode by contacting red phosphorus
with the Li anode surface.
[0019] The invention encompasses protected anode structures with
fully-formed protective layers and battery separators incorporating
ambient stable precursors, each of which may be handled or stored
in normal ambient atmospheric conditions without degradation prior
to incorporation into a battery cell. Battery cells and methods for
making composites and battery cells are also provided.
[0020] These and other features of the invention will be further
described and exemplified in the detailed description below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic illustration of an active metal
battery cell incorporating an ionically conductive protective
composite in accordance with the present invention.
[0022] FIG. 2 is a schematic illustration of a protective composite
battery separator in accordance with the present invention.
[0023] FIG. 3 is a schematic illustration of an active metal anode
structure incorporating an ionically conductive protective
composite in accordance with the present invention.
[0024] FIGS. 4A-B, 5 and 6A-B are schematic illustrations of
alternative methods of making an electrochemical device structure
incorporating an ionically conductive protective composite in
accordance with the present invention.
[0025] FIGS. 7A-B and 8A-D are plots of data illustrating the
performance benefits of ionically conductive protective composites
in accordance with the present invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0026] Reference will now be made in detail to specific embodiments
of the invention. Examples of the specific embodiments are
illustrated in the accompanying drawings. While the invention will
be described in conjunction with these specific embodiments, it
will be understood that it is not intended to limit the invention
to such specific embodiments. On the contrary, it is intended to
cover alternatives, modifications, and equivalents as may be
included within the spirit and scope of the invention as defined by
the appended claims. In the following description, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. The present invention may
be practiced without some or all of these specific details. In
other instances, well known process operations have not been
described in detail in order not to unnecessarily obscure the
present invention.
[0027] When used in combination with "comprising," "a method
comprising," "a device comprising" or similar language in this
specification and the appended claims, the singular forms "a,"
"an," and "the" include plural reference unless the context clearly
dictates otherwise. Unless defined otherwise, all technical and
scientific terms used herein have the same meaning as commonly
understood to one of ordinary skill in the art to which this
invention belongs.
[0028] Introduction
[0029] Ionically conductive composites for protection of anodes and
electrolytes and methods for their fabrication. The composites may
be incorporated in active metal negative electrode (anode)
structures and battery cells. In accordance with the invention, the
properties of different ionic conductors are combined in a
composite material that has the desired properties of high overall
ionic conductivity and chemical stability towards the anode, the
cathode and ambient conditions encountered in battery
manufacturing. The composite is capable of protecting an active
metal anode from deleterious reaction with other battery components
or ambient conditions while providing a high level of ionic
conductivity to facilitate manufacture and/or enhance performance
of a battery cell in which the composite is incorporated.
[0030] The composite is composed of at least two layers of
different materials having different chemical compatibility
requirements. By "chemical compatibility" (or "chemically
compatible") it is meant that the referenced material does not
react to form a product that is deleterious to battery cell
operation when contacted with one or more other referenced battery
cell components or manufacturing, handling or storage conditions. A
first material layer of the composite is both ionically conductive
and chemically compatible with an active metal electrode material.
Chemical compatibility in this aspect of the invention refers to a
material that is chemically stable and therefore substantially
unreactive when contacted with an active metal electrode material.
Active metals are highly reactive in ambient conditions and can
benefit from a barrier layer when used as electrodes. They are
generally alkali metals such (e.g., lithium, sodium or potassium),
alkaline earth metals (e.g., calcium or magnesium), and/or certain
transitional metals (e.g., zinc), and/or alloys of two or more of
these. The following active metals may be used: alkali metals
(e.g., Li, Na, K), alkaline earth metals (e.g., Ca, Mg, Ba), or
binary or ternary alkali metal alloys with Ca, Mg, Sn, Ag, Zn, Bi,
Al, Cd, Ga, In. Preferred alloys include lithium aluminum alloys,
lithium silicon alloys, lithium tin alloys, lithium silver alloys,
and sodium lead alloys (e.g., Na.sub.4Pb). A preferred active metal
electrode is composed of lithium. Chemical compatibility also
refers to a material that may be chemically stable with oxidizing
materials and reactive when contacted with an active metal
electrode material to produce a product that is chemically stable
against the active metal electrode material and has the desirable
ionic conductivity (i.e., a first layer material). Such a reactive
material is sometimes referred to as a "precursor" material.
[0031] A second material layer of the composite is substantially
impervious, ionically conductive and chemically compatible with the
first material. By substantially impervious it is meant that the
material provides a sufficient barrier to battery electrolytes and
solvents and other battery component materials that would be
damaging to the electrode material to prevent any such damage that
would degrade electrode performance from occurring. Thus, it should
be non-swellable and free of pores, defects, and any pathways
allowing air, moisture, electrolyte, etc. to penetrate though it to
the first material. Preferably, the second material layer is so
impervious to ambient moisture, carbon dioxide, oxygen, etc. that
an encapsulated lithium alloy electrode can be handled under
ambient conditions without the need for elaborate dry box
conditions as typically employed to process other lithium
electrodes. Because the composite protective layer described herein
provides such good protection for the lithium (or other active
metal), it is contemplated that electrodes and
electrode/electrolyte composites of this invention may have a quite
long shelf life outside of a battery. Thus, the invention
contemplates not only batteries containing a negative electrode,
but unused negative electrodes and electrode/electrolyte laminates
themselves. Such negative electrodes and electrode/electrolyte
laminates may be provided in the form of sheets, rolls, stacks,
etc. Ultimately, they are integrated with other battery components
to fabricate a battery. The enhanced stability of the batteries of
this invention will greatly simplify this fabrication
procedure.
[0032] It should be noted that the first and second materials are
inherently ionically conductive. That is, they do not depend on the
presence of a liquid electrolyte or other agent for their ionically
conductive properties.
[0033] Additional layers are possible to achieve these aims, or
otherwise enhance electrode stability or performance. All layers of
the composite have high ionic conductivity, at least 10.sup.-7
S/cm, generally at least 10.sup.-6 S/cm, for example at least
10.sup.-5 S/cm to 10.sup.-4 S/cm, and as high as 10.sup.-3 S/cm or
higher so that the overall ionic conductivity of the multi-layer
protective structure is at least 10.sup.-7 S/cm and as high as
10.sup.-3 S/cm or higher.
[0034] Protective Composites and Structures
[0035] FIG. 1 illustrates an ionically conductive protective
composite in accordance with the present invention in context as it
would be used in an active metal battery cell 120, such as a
lithium-sulfur battery, in accordance with the present invention.
The composite 100 is composed of a first layer 102 of a material
that is both ionically conductive and chemically compatible with an
active metal electrode material. The composite also includes second
layer 104 of a material that is substantially impervious, ionically
conductive and chemically compatible with the first material. The
ionic conductivity of the composite is at least 10.sup.-7 S/cm,
generally at least 10.sup.-6 S/cm, for example at least 10.sup.-5
S/cm to 10.sup.-4 S/cm, and as high as 10.sup.-3 S/cm or higher.
The first layer 102 is adjacent to an active metal (e.g., lithium)
anode 106. The active metal cathode 106 is connected with a current
collector 108, composed of a conductive metal such as copper. On
the other side of the composite 100, the second layer 104 is
(optionally) in contact with an electrolyte 110. Alternatively, in
some embodiments, the second layer 104 may itself be the sole
electrolyte of the battery cell. Adjacent to the electrolyte is the
cathode 112 with its current collector 114.
[0036] FIG. 2 illustrates a protective composite battery separator
in accordance with the present invention. The separator 200
includes a layer of a first material or precursor 202 that is
ionically conductive and chemically compatible with an active
metal. In most cases, the first material is not chemically
compatible with oxidizing materials (e.g., air, moisture, etc). The
first layer, in contact with the active metal, may be composed, in
whole or in part, of active metal nitrides, active metal
phosphides, active metal halides or active metal phosphorus
oxynitride-based glasses. Specific examples include Li.sub.3N,
Li.sub.3P, LiI, LiBr, LiCl and LiF. In at least one instance,
LiPON, the first material is chemically compatible with oxidizing
materials. The thickness of the first material layer is preferably
about 0.1 to 5 microns, or 0.2 to 1 micron, for example about 0.25
micron.
[0037] As noted above, the first material may also be a precursor
material which is chemically compatible with an active metal and
reactive when contacted with an active metal electrode material to
produce a product that is chemically stable against the active
metal electrode material and has the desirable ionic conductivity
(i.e., a first layer material). Examples of suitable precursor
materials include metal nitrides, red phosphorus, nitrogen and
phosphorus containing organics (e.g., amines, phosphines, borazine
(B.sub.3N.sub.3H.sub.6), triazine (C.sub.3N.sub.3H.sub.3)) and
halides. Some specific examples include P (red phosphorus),
Cu.sub.3N, SnN.sub.x, Zn.sub.3N.sub.2, FeN.sub.x, CoN.sub.x,
aluminum nitride (AlN), silicon nitride (Si.sub.3N.sub.4) and
I.sub.2, Br.sub.2, Cl.sub.2 and F.sub.2. Such precursor materials
can subsequently react with active metal (e.g., Li) to form a Li
metal salts, such as the lithium nitrides, phosphides and halides
described above. In some instances, these first layer material
precursors may also be chemically stable in air (including moisture
and other materials normally present in ambient atmosphere), thus
facilitating handling and fabrication. Examples include metal
nitrides, for example Cu.sub.3N.
[0038] Also, a suitable active metal compatible layer may include a
polymer component to enhance its properties. For example,
polymer-iodine complexes like poly(2-vinylpyridine)-iodine
(P2VP-I.sub.2), polyethylene-iodine, or with
tetraalkylammonium-iodine complexes can react with Li to form a
LiI-based film having significantly higher ionic conductivity than
that for pure LiI.
[0039] The ionic conductivity of the first material is high, at
least 10.sup.-7 S/cm, generally at least about 10.sup.-5 S/cm, and
may be as high as 10.sup.-3 S/cm or higher.
[0040] Adjacent to the first material or precursor layer 202 is a
second layer 204 that is substantially impervious, ionically
conductive and chemically compatible with the first material or
precursor, such as a phosphorus-based glass, oxide-based glass,
phosphorus-oxynitride-based glass, sulpher-based glass,
oxide/sulfide based glass, selenide based glass, gallium based
glass, germanium-based glass, glass-ceramic active metal ion
conductor, lithium beta-alumina, sodium beta-alumina, Li superionic
conductor (LISICON), Na superionic conductor (NASICON), and the
like. Specific examples include LiPON,
Li.sub.3PO.sub.4.Li.sub.2S.SiS.sub.2,
Li.sub.2S.GeS.sub.2.Ga.sub.2S.sub.3, Li.sub.2O.11Al.sub.2O.sub.3,
Na.sub.2O.11Al.sub.2O.sub.3, (Na,
Li).sub.1+xTi.sub.2-xAl.sub.x(PO.sub.4).sub.3
(0.6.ltoreq.x.ltoreq.0.9) and crystallographic related structures,
Na.sub.3Zr.sub.2Si.sub.2PO.sub.12,
Li.sub.3Zr.sub.2Si.sub.2PO.sub.12, Na.sub.5ZrP.sub.3O.sub.12,
Na.sub.5TiP.sub.3O.sub.12, Na.sub.3Fe.sub.2P.sub.3O.sub.12,
Na.sub.4NbP.sub.3O.sub.12, Li.sub.5ZrP.sub.3O.sub.12,
Li.sub.5TiP.sub.3O.sub.12, Li.sub.3Fe.sub.2P.sub.3O.sub.12 and
Li.sub.4NbP.sub.3O.sub.12.
[0041] A particularly suitable glass-ceramic material for the
second layer of the protective composite is a lithium ion
conductive glass-ceramic having the following composition:
TABLE-US-00002 Composition mol % P.sub.2O.sub.5 26-55% SiO.sub.2
0-15% GeO.sub.2 + TiO.sub.2 25-50% in which GeO.sub.2 0-50%
TiO.sub.2 0-50% ZrO.sub.2 0-10% M.sub.2O.sub.3 0 < 10%
Al.sub.2O.sub.3 0-15% Ga.sub.2O.sub.3 0-15% Li.sub.2O 3-25%
and containing a predominant crystalline phase composed of
Li.sub.1+x(M,Al,Ga).sub.x(Ge.sub.1-yTi.sub.y).sub.2-x(PO.sub.4).sub.3
where X.ltoreq.0.8 and 0.ltoreq.Y.ltoreq.1.0, and where M is an
element selected from the group consisting of Nd, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm and Yb and/or and
Li.sub.1+x+yQ.sub.xTi.sub.2-xSi.sub.yP.sub.3-yO.sub.12 where
0<X.ltoreq.0.4 and 0<Y.ltoreq.0.6, and where Q is Al or Ga.
The glass-ceramics are obtained by melting raw materials to a melt,
casting the melt to a glass and subjecting the glass to a heat
treatment. Such materials are available from OHARA Corporation,
Japan and are further described in U.S. Pat. Nos. 5,702,995,
6,030,909, 6,315,881 and 6,485,622, incorporated herein by
reference.
[0042] The high conductivity of some of these glasses and
glass-ceramics (ionic conductivity in the range of about 10.sup.-5
to 10.sup.-3 S/cm or greater) may enhance performance of the
protected lithium anode, and allow relatively thick films to be
deposited without a large penalty in terms of ohmic resistance.
[0043] Also, a suitable second layer may include a polymer
component to enhance its properties. For example, a glass-ceramic
active metal ion conductor, like the glass-ceramic materials
described above, may also be combined with polymer electrolytes to
form flexible composite sheets of material which may be used as
second layer of the protective composite. One important example of
such a flexible composite material has been developed by OHARA
Corp. (Japan). It is composed of particles of a Li-ion conducting
glass-ceramic material, such as described above, and a solid
polymer electrolyte based on PEO-Li salt complexes. OHARA Corp.
manufactures this material in the form of sheet with a thickness of
about 50 microns that renders it flexible while maintaining its
high ionic conductivity. Because of its relatively high ionic
conductivity (better than 4*10.sup.-5 S/cm at room temperature in
the case of the OHARA product) and stability toward metallic Li,
this type of composite electrolyte can be used at room temperature
or elevated temperatures in fully solid-state cells.
[0044] The composite barrier layer should have an inherently high
ionic conductivity. In general, the ionic conductivity of the
composite is at least 10.sup.-7 S/cm, generally at least about
10.sup.-6 to 10.sup.-5 S/cm, and may be as high as 10.sup.-4 to
10.sup.-3 S/cm or higher. The thickness of the first precursor
material layer should be enough to prevent contact between the
second material layer and adjacent materials or layers, in
particular, the active metal of the anode with which the separator
is to be used. For example, the first material layer may have a
thickness of about 0.1 to 5 microns; 0.2 to 1 micron; or about 0.25
micron.
[0045] The thickness of the second material layer is preferably
about 0.1 to 1000 microns, or, where the ionic conductivity of the
second material layer is about 10.sup.-7 S/cm, about 0.25 to 1
micron, or, where the ionic conductivity of the second material
layer is between about 10.sup.-4 about 10.sup.-3 S/cm, about 10 to
1000 microns, preferably between 1 and 500 microns, and more
preferably between 10 and 100 microns, for example 20 microns.
[0046] When the first material layer is a precursor material
chemically stable in air, for example Cu.sub.3N or LiPON, the
protective composite battery separator may be handled or stored in
normal ambient atmospheric conditions without degradation prior to
incorporation into a battery cell. When the separator is
incorporated into a battery cell, the precursor layer 202 is
contacted with an active metal (e.g., lithium) electrode. The
precursor reacts with the active metal to form an ionically
conductive material that is chemically compatible with the active
metal electrode material. The second layer is contacted with an
electrolyte to which a cathode and current collector is or has been
applied. Alternatively, the second layer acts as the sole
electrolyte in the battery cell. In either case, the combination of
the two layers in the protective composite protects the active
metal electrode and the electrolyte and/or cathode from deleterious
reaction with one another.
[0047] FIG. 3 illustrates an encapsulated anode structure
incorporating a protective composite in accordance with the present
invention. The structure 300 includes an active metal electrode
308, e.g., lithium, bonded with a current collector 310, e.g.,
copper, and a protective composite 302. The protective composite
302 is composed of a first layer 304 of a material that is both
ionically conductive and chemically compatible with an active metal
electrode material, but not chemically compatible with oxidizing
materials (e.g., air). For example, the first layer, in contact
with the active metal, may be composed, in whole or in part, of
active metal nitrides, active metal phosphides or active metal
halides. Specific examples include Li.sub.3N, Li.sub.3P, LiI, LiBr,
LiCl and LiF. The thickness of the first material layer is
preferably about 0.1 to 5 microns, or 0.2 to 1 micron, for example
about 0.25 micron.
[0048] These first layer materials may be applied to the active
metal electrode, or they may be formed in situ by application of
precursors such as metal nitrides, metal phosphides, metal halides,
red phosphorus, iodine and the like. The in situ formation of the
first layer may be by way of conversion of the precursors to a
lithiated analog, for example, according to reactions of the
following type (using P, CuN.sub.3, and PbI.sub.2 precursors as
examples):
[0049] 1. 3Li+P=Li.sub.3P (reaction of the precursor to form Li-ion
conductor);
[0050] 2(a). 3Li+Cu.sub.3N=Li.sub.3N+3 Cu (reaction to form Li-ion
conductor/metal composite);
[0051] 2(b). 2Li+PbI.sub.2=2 LiI+Pb (reaction to form Li-ion
conductor/metal composite).
[0052] First layer composites, which may include electronically
conductive metal particles, formed as a result of in situ
conversions meet the requirements of a first layer material for a
protective composite in accordance with the present invention and
are therefore within the scope of the invention.
[0053] A second layer 306 of the protective composite is composed
of a substantially impervious glassy or amorphous ionic conductor,
such as a phosphorus-based glass, oxide-based glass,
phosphorus-oxynitride-based glass, sulpher-based glass,
oxide/sulfide based glass, selenide based glass, gallium based
glass, germanium-based glass, glass-ceramic active metal ion
conductor, lithium beta-alumina, sodium beta-alumina, Li superionic
conductor (LISICON), Na superionic conductor (NASICON), and the
like. Specific examples include LiPON,
Li.sub.3PO.sub.4.Li.sub.2S.SiS.sub.2,
Li.sub.2S.GeS.sub.2.Ga.sub.2S.sub.3,
Li.sub.1-x-yAl.sub.xTi.sub.2-xSi.sub.yP.sub.3-yO.sub.12 (available
from OHARA Corporation, Japan; further described in U.S. Pat. Nos.
5,702,995, 6,030,909, 6,315,881, incorporated herein by reference),
Li.sub.2O.11Al.sub.2O.sub.3, Na.sub.2O.11Al.sub.2O.sub.3, (Na,
Li).sub.1+xTi.sub.2-xAl.sub.x(PO.sub.4).sub.3
(0.6.ltoreq.x.ltoreq.0.9) and crystallographically related
structures, Na.sub.3Zr.sub.2Si.sub.2PO.sub.12,
Li.sub.3Zr.sub.2Si.sub.2PO.sub.12, Na.sub.5ZrP.sub.12,
Na.sub.5TiP.sub.3O.sub.12, Na.sub.3Fe.sub.2P.sub.3O.sub.12,
Na.sub.4NbP.sub.3O.sub.12, Li.sub.5ZrP.sub.3O.sub.12,
Li.sub.3Fe.sub.2P.sub.3O.sub.12, Li.sub.3Fe.sub.2P.sub.3O.sub.12
and Li.sub.4NbP.sub.3O.sub.12.
[0054] The ionic conductivity of the composite is at least
10.sup.-7 S/cm, generally at least 10.sup.-6 S/cm, for example at
least 10.sup.-5 S/cm to 10.sup.-4 S/cm, and as high as 10.sup.-3
S/cm or higher. The thickness of the second material layer is
preferably about 0.1 to 1000 microns, or, where the ionic
conductivity of the second material layer is about 10.sup.-7 S/cm,
about 0.25 to 1 micron, or, where the ionic conductivity of the
second material layer is between about 10.sup.-4 about 10.sup.-3
S/cm, 10 to 1000 microns, preferably between 1 and 500 micron, and
more preferably between 10 and 100 microns, for example 20
microns.
[0055] When the anode structure is incorporated in a battery cell,
the first layer 304 is adjacent to an active metal (e.g., lithium)
anode and the second layer 306 is adjacent to an electrolyte or,
where the second layer is the sole electrolyte in the battery cell,
a cathode.
[0056] Either layer may also include additional components. For
instance, a suitable first active metal compatible layer 304 may
include a polymer component to enhance its properties. For example,
polymer-iodine complexes like poly(2-vinylpyridine)-iodine
(P2VP-I.sub.2), polyethylene-iodine, or with
tetraalkylammonium-iodine can react with Li to form a Liu-based
film having significantly higher ionic conductivity than that for
pure LiI. Also, a suitable second layer 306 may include a polymer
component to enhance its properties. For example, a glass-ceramic
active metal ion conductor like that available from OHARA
Corporation, described above, may be fabricated within a polymer
matrix that renders it flexible while maintaining its high ionic
conductivity (available from OHARA Corporation, Japan).
[0057] In addition, the layers may be formed using a variety of
techniques. These include deposition or evaporation (including
e-beam evaporation) of layers of material, such as LiN.sub.3 or an
ionically conductive glass. Also, as noted above, the active metal
electrode adjacent layer may be formed in situ from the
non-deleterious reaction of one or more precursors with the active
metal electrode. For example, a LiN.sub.3 layer may be formed on a
Li anode by contacting CuN.sub.3 with the Li anode surface, or
LiP.sub.3 may be formed on a Li anode by contacting red phosphorus
with the Li anode surface.
[0058] Also, an approach may be used where a first material and
second material are coated with another material such as a
transient and/or wetting layer. For example, an OHARA glass ceramic
plate is coated with a LiPON layer, followed by a thin silver (Ag)
coating. When lithium is evaporated onto this structure, the Ag is
converted to Ag--Li and diffuses, at least in part, into the
greater mass of deposited lithium, and a protected lithium
electrode is created. The thin Ag coating prevents the hot (vapor
phase) lithium from contacting and adversely reaction with the
LiPON first material layer. After deposition, the solid phase
lithium is stable against the LiPON. A multitude of such
transient/wetting (e.g., Sn) and first layer material combinations
can be used to achieve the desired result.
[0059] Thus, the invention encompasses protected anode structures
with fully-formed protective layers and battery separators
incorporating ambient stable precursors, each of which may be
handled or stored in normal ambient atmospheric conditions without
degradation prior to incorporation into a battery cell. Battery
cells and methods for making separators, anode structures and
battery cells are also provided.
[0060] Fabrication Techniques
[0061] Materials and techniques for fabrication of active metal
battery cells are described, for example, in U.S. Pat. No.
5,686,201 issued to Chu on Nov. 11, 1997. Further description of
materials and techniques for fabrication of active metal battery
cells having anode protective layers are described, for example, in
U.S. patent application Ser. No. 09/139,601, filed Aug. 25, 1998
(now U.S. Pat. No. 6,214,061, issued Apr. 10, 2001), titled
ENCAPSULATED LITHIUM ALLOY ELECTRODES HAVING BARRIER LAYERS, and
naming May-Ying Chu, Steven J. Visco and Lutgard C. DeJonge as
inventors; U.S. patent application Ser. No. 09/086,665 filed May
29, 1998 (now U.S. Pat. No. 6,025,094, issued May 15, 2000), titled
PROTECTIVE COATINGS FOR NEGATIVE ELECTRODES, and naming Steven J.
Visco and May-Ying Chu as inventors; U.S. patent application Ser.
No. 09/139,603 filed Aug. 25, 1998 (now U.S. Pat. No. 6,402,795,
issued Jun. 11, 2002), titled "PLATING METAL NEGATIVE ELECTRODES
UNDER PROTECTIVE COATINGS," and naming May-Ying Chu, Steven J.
Visco and Lutgard C. DeJonghe as inventors; U.S. patent application
Ser. No. 09/139,601 filed Aug. 25, 1998 (now U.S. Pat. No.
6,214,061, issued Apr. 10, 2001), titled "METHOD FOR FORMING
ENCAPSULATED LITHIUM ELECTRODES HAVING GLASS PROTECTIVE LAYERS,"
and naming Steven J. Visco and Floris Y. Tsang as inventors. The
active metal electrode may also be an active metal alloy electrode,
as further described in U.S. patent application Ser. No. 10/189,908
filed Jul. 3, 2002, titled "ENCAPSULATED ALLOY ELECTRODES," and
naming Steven J. Visco, Yevgeniy S. Nimon and Bruce D. Katz as
inventors. The battery component materials, including anodes,
cathodes, separators, protective layers, etc., and techniques
disclosed therein are generally applicable to the present invention
and each of these patent applications is incorporated herein by
reference in its entirety for all purposes.
[0062] In particular, a protective composite in accordance with the
present invention may be formed using a variety of methods. These
include deposition or evaporation (including e-beam evaporation) of
the first layer of material or precursor on the second layer of
material. Also, as noted above and described further below, the
first layer may be formed in situ from the non-deleterious reaction
of one or more precursors with an active metal electrode or
material, by deposition or evaporation of lithium on the precursor,
by direct contact of the precursor with a lithium metal (e.g.,
foil), or by plating of the precursor with lithium through a second
layer material. In some embodiments, the second layer material may
also be formed on the first layer material, as described further
below.
[0063] Referring to FIG. 4A, a first method for forming a
protective composite in accordance with the present invention is
shown. A first layer, that is a highly ionically conductive active
metal chemically compatible material, is directly deposited onto a
second layer material, that is a substantially impervious,
ionically conductive material, for example, a highly ionically
conductive glass or glass-ceramic material such as LiPON or an
OHARA glass-ceramic material described above. This can be done by a
variety of techniques including RF sputtering, e-beam evaporation,
thermal evaporation, or reactive thermal or e-beam evaporation, for
example. In the particular example illustrated in the figure,
lithium is evaporated in a nitrogen plasma to form a lithium
nitride (Li.sub.3N) layer on the surface of a glass-ceramic
material such as the OHARA material described above. This is
followed by evaporation of lithium metal onto the Li.sub.3N film.
The Li.sub.3N layer separates the lithium metal electrode from the
second material layer, but allows Li ions to pass from the Li
electrode through the glass. Of course, other active metal, and
first and second layer materials, as described herein, may be used
as well.
[0064] Alternatively, referring to FIG. 4B, a second method for
forming a protective composite in accordance with the present
invention is shown. The ionically conductive chemically compatible
first layer material is formed in situ following formation of a
precursor layer on the second layer material. In the particular
example illustrated in the figure, a surface of a glass-ceramic
layer, for example one composed of the OHARA material described
above, is coated with red phosphorus, a precursor for an active
metal (in this case lithium) phosphide. Then a layer of lithium
metal is deposited onto the phosphorus. The reaction of lithium and
phosphorus forms Li.sub.3P according to the following reaction:
3Li+P=Li.sub.3P. Li.sub.3P is an ionically conductive material that
is chemically compatible with both the lithium anode and the
glass-ceramic material. In this way, the glass-ceramic (or other
second layer material) is not in direct contact with the lithium
electrode. Of course, other active metal, first layer precursor and
second layer materials, as described herein, may be used as well.
Alternative precursor examples include CuN.sub.3, which may be
formed as a thin layer on a second layer material (e.g.,
glass-ceramic) and contacted with a Li anode in a similar manner
according to the following reaction: 3Li+Cu.sub.3N=Li.sub.3N+3 Cu;
or lead iodide which may be formed as a thin layer on a polymer
electrolyte and contacted with a Li anode in a similar manner
according to the following reaction: 2Li+PbI.sub.2=2 LiI+Pb.
[0065] In either of the forgoing methods, rather than forming a
lithium (or other active metal) layer on the first layer material
or precursor, the first layer material or precursor of the
protective composite may be contacted with the lithium by bonding
metallic lithium to the protective interlayer material or
precursor, for example by direct contact with extruded lithium
metal foil. One embodiment of this alternative is illustrated for
either of the FIG. 4A or FIG. 4B methods in FIG. 5.
[0066] In a further embodiment, a suitable substrate, e.g., having
a wetting layer, such as a film of tin on copper, may be coated
with a first layer material precursor, e.g., Cu.sub.3N. This may
then be coated with a second layer material, e.g., a (ionically)
conductive glass. An active metal electrode may then be formed by
plating the tin electrode with lithium (or other active metal),
through the first and second layer materials. The Cu.sub.3N
precursor is also converted to Li.sub.3N by this operation to
complete the protective composite in accordance with the present
invention on a lithium metal electrode. Details of an active metal
plating process are described in commonly assigned U.S. Pat. No.
6,402,795, previously incorporated by reference.
[0067] Also, in either of the methods illustrated in FIGS. 4A or
4B, rather than forming a lithium (or other active metal) layer on
the first layer material or precursor, the first layer material or
precursor of the protective composite may be deposited (or
otherwise formed) on lithium or other active metal material. Then,
a second later material may be formed, for example by evaporation
of a high conductivity glass, on the first layer material. One
embodiment of this alternative is illustrated in FIG. 5 in which
the active metal electrode is formed by evaporating lithium onto a
pre-formed copper-tin (Cu--Sn) alloy to form a pre-expanded
Li--Cu--Sn alloy anode as a substrate for the first and second
layer materials forming the protective composite.
[0068] Also as noted above, in an alternative embodiment of the
invention the first layer may include additional components. For
instance, a suitable first layer may include a polymer component to
enhance its properties. For example, polymer-iodine complexes like
poly(2-vinylpyridine)-iodine (P2VP-I.sub.2), polyethylene-iodine,
or tetraalkylammonium-iodine can react with Li to form an ionically
conductive LiI-based film that is chemically compatible with both
an active metal and a second layer material as described herein.
Without intending to be bound by theory, it is expected that the
use of polymer-iodine charge transfer complexes can lead to
formation of composites containing LiI and polymer and having
significantly higher ionic conductivity than that for pure LiI.
Other halogens may also be used in this manner, for example in
bromine complexes.
[0069] Referring to FIG. 6A, a first embodiment of this aspect of
the present invention is shown. A polymer layer and a layer of
iodine are coated on a second layer material surface and allowed to
react forming polymer-iodine complex.
[0070] According to this method, a thin layer of polymer may be
applied to the second material layer (e.g., conductive glass) using
brushing, dipping, or spraying. For example, a conductive glass
layer may be coated with a thin (e.g., 0.5 to 2.0 micron,
preferably 0.1 to 0.5 micron) layer of P2VP in this way.
[0071] One technique for applying an iodine coating is sublimation
of crystalline iodine that can be achieved at room temperature
(e.g., about 20 to 25.degree. C.) in a reactor placed in the dry
box or in a dry room. A sublimed layer of iodine can be made very
thin (e.g., 0.05 to 1.0 microns and the rate of sublimation can be
adjusted by varying the temperature or distance between the
substrate and source of iodine.
[0072] Alternatively, high concentrations (e.g., 50 to 100 g/liter
of iodine can be dissolved in an organic solvent, such as
acetonitrile and n-heptane. Dissolved iodine can be coated on the
conductive glass surface by such methods as dip coating, spraying
or brushing, among others. In this case, treatment conditions can
be easily changed by varying the length of coating treatment and
iodine concentrations. Examples of iodine sources for this
technique include metal iodides are AgI and PbI.sub.2, which are
known to be used as the cathode materials in solid-state batteries
with Li anode and LiI-based solid electrolyte.
[0073] Then, lithium (or other active metal) is contacted with the
polymer-iodine complex on the conductive glass (or other second
layer material), for example by evaporation or pressing onto the
glass coated with this complex. The result is a LiI-containing
composite protective barrier layer on the Li anode.
[0074] Referring to FIG. 6B, an alternative embodiment of this
aspect of the present invention is shown. A conductive glass (or
other second layer material) surface is coated with a thin layer of
iodine, such as by a technique described above, that can react with
Li forming LiI layer (A).
[0075] Active metal, for example lithium foil, can be coated with a
thin layer of polymer (B), for example as described above, and then
contacted with the iodine layer on the glass. After assembly,
iodine reacts with the polymer layer and, as a result,
LiI-containing composite protective barrier layer with reduced
impedance is formed.
EXAMPLES
[0076] The following examples provide details illustrating
advantageous properties, in particular very low impedance, of
composite protective structures in accordance with the present
invention on lithium electrodes. These examples are provided to
exemplify and more clearly illustrate aspects of the present
invention and are in no way intended to be limiting.
Example 1
Impedance Measurements using LIPON in Composite Protective
Layer
[0077] Approximately 0.75 microns of LiPON was RF sputter-deposited
onto copper foil samples in a MRC 8671 Sputter Deposition system.
Some of the copper foil samples were coated with an additional
layer of Cu.sub.3N (approximately 0.9 microns) by RF Magnetron
sputtering of a copper target in a nitrogen environment. One
LiPON/Cu sample was transferred to a vacuum evaporator, and
approximately 3 to 7 microns of lithium metal was evaporated
directly onto the LiPON surface. Another Cu.sub.3N/LiPON/Cu sample
was coated with a similar thickness of lithium. The impedance for
the unprotected LiPON/Cu sample is shown in FIG. 7A; the
evaporation of lithium onto the LiPON surface led to a dramatic
rise in the resistance of the sample, which is undesirable for
electrochemical devices. The beneficial effects of the protective
Cu.sub.3N film is seen in FIG. 7B; the impedance is dramatically
lower in this case.
Example 2
Impedance Measurements using Glass-Ceramic Active Metal Ion
Conductor (OHARA) in Composite Protective Layer
[0078] Samples of Li.sup.+ conductive glass-ceramic plates were
received from OHARA Corporation. Approximately 3 to 7 microns of
lithium was evaporated directly onto the OHARA glass-ceramic plate.
The deleterious reaction of lithium with the electrolyte is seen in
FIG. 8A; the impedance of the sample is quite large, approximately
40,000 Wcm.sup.2. Onto a second sample of glass-ceramic plate was
RF Magnetron sputter-deposited a film of Cu.sub.3N (.about.0.9
microns thick), with subsequent evaporation of about 3 to 7 microns
of lithium. The beneficial effect of the Cu.sub.3N film can be seen
in FIG. 8B; the impedance of the glass-ceramic is dramatically
improved relative to the plate without the Cu.sub.3N film.
Superimposition of FIGS. 8A and 8B in FIG. 8C further illustrates
the dramatic improvement in performance for the Cu.sub.3N protected
plate. The ionically conductive nature of the protective film is
seen in 8D, where lithium is moved across the Li/Cu.sub.3N/glass
interface; this is presumably due to conversion of the ionically
insulating Cu.sub.3N film to highly conductive Li.sub.3N+Cu.
CONCLUSION
[0079] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications may be practiced
within the scope of the appended claims. It should be noted that
there are many alternative ways of implementing both the process
and compositions of the present invention. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein.
[0080] All references cited herein are incorporated by reference
for all purposes.
* * * * *