U.S. patent application number 17/344128 was filed with the patent office on 2021-12-30 for protective layers in lithium-ion electrochemical cells and associated electrodes and methods.
This patent application is currently assigned to Sion Power Corporation. The applicant listed for this patent is Sion Power Corporation. Invention is credited to Tracy Earl Kelley, Michael G. Laramie, Zhaohui Liao, Yuriy V. Mikhaylik, Chariclea Scordilis-Kelley.
Application Number | 20210408550 17/344128 |
Document ID | / |
Family ID | 1000005840003 |
Filed Date | 2021-12-30 |
United States Patent
Application |
20210408550 |
Kind Code |
A1 |
Liao; Zhaohui ; et
al. |
December 30, 2021 |
PROTECTIVE LAYERS IN LITHIUM-ION ELECTROCHEMICAL CELLS AND
ASSOCIATED ELECTRODES AND METHODS
Abstract
Protective layers in lithium-ion electrochemical cells, and
associated electrodes and methods, are generally described. The
protective layers may comprise lithium-ion-conductive inorganic
ceramic materials, such as lithium oxide, lithium nitride, and/or
lithium oxysulfide. The resulting lithium-ion electrochemical cells
may exhibit enhanced performance, including reduced capacity fade
rates and reduced self-discharge rates.
Inventors: |
Liao; Zhaohui; (Tucson,
AZ) ; Scordilis-Kelley; Chariclea; (Tucson, AZ)
; Kelley; Tracy Earl; (Tucson, AZ) ; Laramie;
Michael G.; (Tucson, AZ) ; Mikhaylik; Yuriy V.;
(Tucson, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sion Power Corporation |
Tucson |
AZ |
US |
|
|
Assignee: |
Sion Power Corporation
Tucson
AZ
|
Family ID: |
1000005840003 |
Appl. No.: |
17/344128 |
Filed: |
June 10, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14848659 |
Sep 9, 2015 |
11038178 |
|
|
17344128 |
|
|
|
|
62048228 |
Sep 9, 2014 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/628 20130101;
H01M 4/0426 20130101; H01M 4/525 20130101; H01M 4/0428 20130101;
H01M 4/5825 20130101; H01M 4/0423 20130101; H01M 4/505 20130101;
H01M 4/1391 20130101; H01M 4/131 20130101; H01M 4/485 20130101;
H01M 10/0525 20130101 |
International
Class: |
H01M 4/62 20060101
H01M004/62; H01M 4/485 20060101 H01M004/485; H01M 4/58 20060101
H01M004/58; H01M 4/525 20060101 H01M004/525; H01M 4/505 20060101
H01M004/505; H01M 4/131 20060101 H01M004/131; H01M 4/1391 20060101
H01M004/1391 |
Claims
1. (canceled)
2. An electrochemical cell, comprising: a first electrode, wherein
the first electrode is a lithium intercalation electrode, and
wherein the first electrode comprises: a layer comprising a first
electroactive material, wherein the first electroactive material is
a lithium intercalation compound; and an inorganic
lithium-ion-conductive layer disposed on a surface of the layer
comprising the first electroactive material, wherein the inorganic
lithium-ion-conductive layer comprises particles that are
substantially aligned; a liquid electrolyte, wherein the liquid
electrolyte is an organic electrolyte; and a second electrode.
3. A method of fabricating an electrochemical cell, comprising:
depositing an inorganic lithium-ion-conductive layer on a layer
comprising a first electroactive material to form a first
electrode, wherein the first electroactive material is a lithium
intercalation compound, wherein the inorganic
lithium-ion-conductive layer comprises particles that are
substantially aligned; and assembling the first electrode with a
liquid electrolyte and a second electrode.
4. The electrochemical cell of claim 2, wherein at least a portion
of the first electroactive material is in direct contact with the
liquid electrolyte.
5. The method of claim 3, wherein at least a portion of the first
electroactive material is in direct contact with the liquid
electrolyte.
6. The electrochemical cell of claim 2, wherein: the inorganic
lithium-ion-conductive layer comprises lithium; and at least a
portion of the first electrode is in contact with the
electrolyte.
7. A method, comprising: cycling the electrochemical cell of claim
3, wherein the inorganic lithium-ion-conductive layer comprises
lithium; and substantially inhibiting a species decomposed from the
first electrode and/or a species decomposed from the electrolyte
from residing at the second electrode.
8. The electrochemical cell of claim 2, wherein the inorganic
lithium-ion-conductive layer has a thickness of at least 0.1
microns and at most 10 microns.
9. The electrochemical cell of claim 2, wherein the layer
comprising the first electroactive material comprises a plurality
of particles of the first electroactive material.
10. The electrochemical cell of claim 9, wherein at least a portion
of the plurality of particles of the first electroactive material
have a coating.
11. The electrochemical cell of claim 2, wherein the inorganic
lithium-ion-conductive layer comprises a ceramic material.
12. The electrochemical cell of claim 11, wherein the ceramic
material comprises lithium oxide, lithium nitride, lithium
oxysulfide, Li.sub.10GeP.sub.2S.sub.12, and/or
Li.sub.7La.sub.3Zr.sub.2O.sub.12.
13. The electrochemical cell of claim 2, wherein the inorganic
lithium-ion-conductive layer has a surface roughness Rz of between
10 nm and 20 .mu.m.
14. The electrochemical cell of claim 9, wherein the plurality of
particles of the layer comprising the first electroactive material
has a mean maximum cross-sectional dimension of between 1 nm and 15
.mu.m.
15. The electrochemical cell of claim 2, wherein the layer
comprising the first electroactive material has a porosity at least
10% by volume and less than 70% by volume.
16. The electrochemical cell of claim 2, wherein the first
electrode is a cathode.
17. The electrochemical cell of claim 2, wherein the first
electroactive material is a layered oxide, a transition metal
polyanion oxide, and/or a spinel.
18. The electrochemical cell of claim 2, wherein the first
electroactive material is lithium titanate, lithium cobalt oxide,
lithium iron phosphate, lithium nickel oxide, lithium manganese
oxide, lithium nickel cobalt aluminum oxide, and/or lithium nickel
cobalt manganese oxide.
19. The electrochemical cell of claim 2, wherein a porosity of the
inorganic lithium-ion-conductive layer is greater than or equal to
10% by volume and less than 30% by volume.
20. The electrochemical cell of claim 2, wherein the inorganic
lithium-ion-conductive layer is a unitary material.
21. The electrochemical cell of claim 2, wherein a porosity of the
inorganic lithium-ion-conductive layer is less than 5% by volume.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/848,659, filed Sep. 9, 2015, which claims priority under 35
U.S.C. .sctn. 119(e) to U.S. Provisional Application Ser. No.
62/048,228, filed Sep. 9, 2014, each of which is incorporated
herein by reference in its entirety for all purposes.
TECHNICAL FIELD
[0002] Protective layers in lithium-ion electrochemical cells, and
associated electrodes and methods, are generally described.
BACKGROUND
[0003] Lithium-ion electrochemical cells (also sometimes referred
to as lithium-ion batteries) are a family of electrochemical cells
in which lithium ions are transported between an anode and a
cathode during charge and discharge. Typical lithium-ion
electrochemical cells include a lithium intercalation
compound-based cathode paired with a carbon-comprising anode such
as graphite. There has been considerable interest in recent years
in developing high-energy-density lithium-ion electrochemical
cells, especially in consumer electronics, vehicle, and aerospace
applications. However, the performance of lithium-ion
electrochemical cells can be inhibited due to adverse interactions
between battery components such as the electrodes and the
electrolyte.
[0004] Accordingly, improved lithium-ion electrochemical cells are
desirable.
SUMMARY
[0005] Protective layers in lithium-ion electrochemical cells, and
associated electrodes and methods, are generally described. The
subject matter of the present invention involves, in some cases,
interrelated products, alternative solutions to a particular
problem, and/or a plurality of different uses of one or more
systems and/or articles.
[0006] In one aspect, a lithium intercalation electrode is
described. According to some embodiments, the lithium intercalation
electrode comprises a layer comprising an electroactive material
(i.e., an electroactive layer), wherein the electroactive material
is a lithium intercalation compound. The electrode also includes an
inorganic lithium-ion-conductive layer disposed on a surface of the
layer comprising the electroactive material.
[0007] According to some embodiments, the lithium intercalation
electrode comprises a layer comprising an electroactive material.
In certain embodiments, the electroactive material is a lithium
intercalation compound. In some embodiments, an inorganic
lithium-ion-conductive layer is integrated with the layer
comprising the electroactive material. The lithium-ion-conductive
layer has a thickness of at least 0.1 microns.
[0008] In another aspect, a method of fabricating a lithium
intercalation electrode is described. In some embodiments, the
method comprises depositing an inorganic lithium-ion-conductive
layer on a layer comprising an electroactive material. In certain
cases, the electroactive material is a lithium intercalation
compound.
[0009] In another aspect, an electrochemical cell is provided. In
some embodiments, the electrochemical cell comprises a first,
lithium intercalation electrode including a layer comprising an
electroactive material, and an inorganic lithium-ion-conductive
layer integrated with the layer comprising the electroactive
material. The inorganic lithium-ion-conductive layer may comprise
lithium. The electrochemical cell also includes a second electrode
and an electrolyte. At least a portion of the first lithium
intercalation electrode is in contact with the electrolyte.
[0010] In another aspect, a method is provided. The method
comprises cycling an electrochemical cell comprising a first,
lithium intercalation electrode including a layer comprising an
electroactive material, and an inorganic lithium-ion-conductive
layer integrated with the layer comprising the electroactive
material. The inorganic lithium-ion-conductive layer may comprise
lithium. The electrochemical cell also includes a second electrode.
The method involves substantially inhibiting a species decomposed
from the first, lithium intercalation electrode, or a species
decomposed from the electrolyte, from residing at the second
electrode.
[0011] In another aspect, an electrode is described. In some
embodiments, the electrode comprises a layer comprising an
electroactive material. In certain cases, at least a portion of the
electroactive material is in direct contact with an electrolyte
and/or the layer is porous and/or the layer comprises a plurality
of particles of the electroactive material. In some embodiments,
the first electrode comprises an inorganic lithium-ion-conductive
layer integrated with the layer comprising the electroactive
material.
[0012] In another aspect, a method of fabricating an electrode is
described. In some embodiments, the method comprises depositing an
inorganic lithium-ion-conductive layer on a layer comprising an
electroactive material. In certain cases, the layer comprising the
electroactive material is porous and/or comprises a plurality of
particles. In some embodiments, the inorganic
lithium-ion-conductive layer comprises lithium.
[0013] Other advantages and novel features of the present invention
will become apparent from the following detailed description of
various non-limiting embodiments of the invention when considered
in conjunction with the accompanying figures. In cases where the
present specification and a document incorporated by reference
include conflicting and/or inconsistent disclosure, the present
specification shall control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Non-limiting embodiments of the present invention will be
described by way of example with reference to the accompanying
figures, which are schematic and are not intended to be drawn to
scale. In the figures, each identical or nearly identical component
illustrated is typically represented by a single numeral. For
purposes of clarity, not every component is labeled in every
figure, nor is every component of each embodiment of the invention
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the invention. In the
figures:
[0015] FIG. 1 is a cross-sectional schematic illustration of an
electrode, according to some embodiments;
[0016] FIG. 2 is a cross-sectional schematic illustration of an
electrode, according to some embodiments;
[0017] FIGS. 3A-3B are cross-sectional schematic illustrations of
an electrochemical cell, according to some embodiments, comprising:
(A) a lithium-ion-conductive layer integrated with a first
electroactive-material-containing layer; and (B) a
lithium-ion-conductive layer integrated with a second, different
electroactive-material-containing layer;
[0018] FIG. 4 is a cross-sectional schematic illustration of an
electrochemical cell comprising a first lithium-ion-conductive
layer integrated with a first electroactive-material-containing
layer and a second lithium-ion-conductive layer integrated with a
second electroactive-material-containing layer, according to some
embodiments;
[0019] FIG. 5 is a cross-sectional schematic illustration of an
electrochemical cell comprising first and second
electroactive-material-containing layers, a lithium-ion-conductive
layer, a separator, and first and second substrates, according to
some embodiments;
[0020] FIG. 6 is a cross-sectional schematic illustration of an
electrochemical cell comprising first and second
electroactive-material-containing layers, first and second
lithium-ion-conductive layers, a separator, and first and second
substrates, according to some embodiments;
[0021] FIG. 7 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a graphite
anode and a lithium oxide-coated lithium iron phosphate (LFP)
cathode, according to some embodiments;
[0022] FIGS. 8A-8B are scanning electron microscope (SEM) images of
a cross-sectional view of a lithium oxide-coated LFP cathode,
according to some embodiments: (A) before cycling; and (B) after 70
cycles (initial 5 cycles at room temperature, then at 50.degree.
C.);
[0023] FIGS. 9A-B are energy-dispersive spectroscopy (EDS) spectra
of a graphite anode after 70 cycles in: (A) a graphite/LFP control
cell; and (B) a graphite/Li.sub.2O-coated LFP cell;
[0024] FIG. 10 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a graphite
anode and an LFP cathode with a 0.5 .mu.m-thick lithium oxysulfide
coating, according to some embodiments; where the electrochemical
cells were cycled at room temperature for the first 5 cycles, then
cycled at 50.degree. C.
[0025] FIG. 11 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a graphite
anode and an LFP cathode with a 0.5 .mu.m-thick lithium oxysulfide
coating, according to some embodiments, where the electrochemical
cells were cycled at room temperature for the first 5 cycles,
stored at full charge in a 60.degree. C. oven for 1 week, then
cycled at room temperature for an additional 5 cycles;
[0026] FIG. 12 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a 2
.mu.m-thick lithium oxide layer on a graphite anode, according to
some embodiments, where the electrochemical cells were cycled at
room temperature for the first 5 cycles, stored at full charge in a
60.degree. C. oven for 1 week, then cycled at room temperature for
an additional 5 cycles;
[0027] FIG. 13 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising, according
to some embodiments, a 2 .mu.m-thick lithium oxide layer on a
graphite anode and a 2 .mu.m-thick lithium oxide layer on an LFP
cathode, according to some embodiments, where the electrochemical
cells were cycled at room temperature for the first 5 cycles,
stored at full charge in a 60.degree. C. oven for 1 week, then
cycled at room temperature for an additional 5 cycles;
[0028] FIG. 14 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a 2
.mu.m-thick lithium oxide layer on a graphite anode and a 2
.mu.m-thick lithium oxide layer on a lithium nickel manganese
cobalt oxide ("NMC" or "NCM") cathode, according to some
embodiments, where the electrochemical cells were cycled at room
temperature for the first 5 cycles, stored at full charge in a
60.degree. C. oven for 1 week, then cycled at room temperature for
an additional 5 cycles;
[0029] FIG. 15 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a graphite
anode and an LFP cathode, a graphite anode and an LFP cathode
coated with a 0.5 .mu.m-thick layer of lithium oxysulfide, and a
graphite anode and an LFP cathode coated with a 1 .mu.m-thick layer
of lithium oxysulfide, according to some embodiments, where the
electrochemical cells were cycled at room temperature for the first
5 cycles, then cycled at 50.degree. C.
[0030] FIG. 16 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a graphite
anode and an LFP cathode coated with a 1 .mu.m-thick layer of
lithium oxysulfide, according to some embodiments, where the
electrochemical cells were cycled at room temperature for the first
5 cycles, stored at full charge in a 60.degree. C. oven for 1 week,
then cycled at room temperature for an additional 5 cycles;
[0031] FIG. 17 is an exemplary plot of discharge capacity as a
function of cycle for electrochemical cells comprising a graphite
anode coated with a 1 .mu.m-thick layer of lithium oxysulfide and
an LFP cathode, according to some embodiments, where the
electrochemical cells were cycled at room temperature for the first
5 cycles, stored at full charge in a 60.degree. C. oven for 1 week,
then cycled at room temperature for an additional 5 cycles
[0032] FIG. 18A is an SEM image of an uncoated NCM cathode,
according to some embodiments;
[0033] FIG. 18B is an SEM image of an NCM cathode coated with a 1
.mu.m-thick layer of lithium oxide, according to some
embodiments;
[0034] FIG. 19 is, according to some embodiments, an exemplary plot
of discharge capacity as a function of cycle for electrochemical
cells comprising a graphite anode and an NCM cathode coated with a
1 .mu.m-thick layer of lithium oxide, where the electrochemical
cells were cycled at room temperature for the first 5 cycles, then
cycled at 50.degree. C. FIG. 20A is an EDS spectrum and SEM image
(inset) of a graphite anode from an electrochemical cell comprising
an uncoated NCM cathode after 179 cycles (initial 5 cycles at room
temperature, then at 50.degree. C.), according to some
embodiments;
[0035] FIG. 20B is an EDS spectrum and SEM image (inset) of a
graphite anode from an electrochemical cell comprising a
lithium-oxide-coated NCM cathode after 191 cycles (initial 5 cycles
at room temperature, then at 50.degree. C.), according to some
embodiments;
[0036] FIG. 21A is, according to some embodiments, an SEM image of
a top-down view of a substantially continuous
lithium-ion-conductive layer; and
[0037] FIG. 21B is, according to some embodiments, an SEM image of
a top-down view of a substantially porous lithium-ion-conductive
layer.
DETAILED DESCRIPTION
[0038] Lithium-ion electrochemical cells, and associated electrodes
and methods, are generally described. Certain embodiments are
related to the recognition that a protective lithium-ion-conductive
layer can be positioned between a positive electrode (e.g., a
cathode) and a negative electrode (e.g., an anode) within a
lithium-ion electrochemical cell to inhibit the transportation of
electrochemical byproducts (e.g., side reaction byproducts,
dissolution/leaching products) between the positive electrode and
the negative electrode.
[0039] The performance of lithium-ion electrochemical cells can be
inhibited by a number of mechanisms. For example, in certain
lithium-ion electrochemical cells, active lithium can be lost due
to side reactions of the lithium with the electrolyte. In some
cases, the electrolyte can decompose at the cathode and/or anode of
the electrochemical cell, which can lead to increased cell
impedance. In certain cases, electrolyte decomposition can result
in deleterious acidic byproducts, such as hydrofluoric acid (HF).
In some instances, non-lithium metal cations within the lithium-ion
cathode can be dissolved and subsequently reduced to metallic
clusters at the anode, which can degrade the passivation layer on
the anode and further lead to detrimental side reactions of lithium
with the electrolyte. Loss of non-lithium metal cations can also
lead to changes in the lithium-ion cathode structure and/or loss of
active material in the cathode.
[0040] It has been discovered, according to certain embodiments of
the present invention, that positioning a lithium-ion-conductive
material (e.g., an inorganic lithium-ion-conductive material such
as a lithium-ion-conductive ceramic) between the anode and the
cathode of a lithium-ion electrochemical cell can reduce the degree
to which electrochemical cell byproducts or other undesirable
species are transported between the electrodes of the lithium-ion
electrochemical cell. It is believed that, by inhibiting the
transport of such byproducts or species between the electrodes of
the electrochemical cell, the structures of the electrodes are
better maintained, less electrolyte is lost or decomposed, and/or
less active lithium is lost within the electrochemical cell, thus
enhancing cell performance (e.g., increasing cycle life).
[0041] According to some embodiments, a lithium-ion-conductive
layer may inhibit transport of certain deleterious electrochemical
cell byproducts or species between electrodes by, for example,
neutralizing and/or mitigating the byproducts or species. For
example, in some electrochemical cells, hydrolysis of certain
lithium salts (e.g., LiPF.sub.6) in an electrolyte may result in
hydrofluoric acid (HF) production. The presence of a
lithium-ion-conductive material in the electrochemical cell may act
as an acid trap, neutralizing the HF, and/or may act as a water
vapor trap, mitigating hydrolysis by reacting with water and
reducing the amount of water available for hydrolysis of lithium
salts. In some embodiments, a lithium-ion-conductive layer may
inhibit transport of certain deleterious electrochemical cell
byproducts or species between electrodes by physically impeding
transport of the byproducts. For example, in some electrochemical
cells, a lithium-ion-conductive layer may provide a physical
barrier that is impermeable to certain electrochemical cell
byproducts (e.g., non-lithium metal cations). Other mechanisms for
inhibiting transport of certain deleterious electrochemical cell
byproducts or species are also possible.
[0042] According to certain embodiments, the lithium-ion-conductive
layer can be integrated with a porous and/or particulate
electroactive material-containing layer. The lithium-ion-conductive
layers incorporated into such electrodes can, in some embodiments,
be made sufficiently thin, yet effective for inhibiting or reducing
the rate of transport of byproducts or species, and with sufficient
ion conductivity to effectively transport lithium ions across the
layer.
[0043] FIG. 1 is an exemplary cross-sectional schematic
illustration of electrode 100, according to certain embodiments. In
FIG. 1, electrode 100 comprises electroactive-material-containing
layer (also referred to as "electroactive material layer") 102 and
lithium-ion-conductive layer 104. In some embodiments,
lithium-ion-conductive layer 104 is integrated with
electroactive-material-containing layer 102. As used herein,
lithium-ion-conductive layer 104 is "integrated with"
electroactive-material-containing layer 102 if the two layers are
coupled (directly or indirectly) such that they cannot be separated
without damaging at least one of the two layers or damaging one or
more intervening layers positioned between the two layers. In some
embodiments, electroactive-material-containing layer 102 is
positioned adjacent lithium-ion-conductive layer 104. In certain
cases, such as the embodiment illustrated in FIG. 1,
electroactive-material-containing layer 102 is in direct physical
contact with lithium-ion-conductive layer 104. However, in certain
other embodiments, one or more intervening layers (not shown in
FIG. 1) are positioned between electroactive-material-containing
layer 102 and lithium-ion-conductive layer 104. For example, an
intervening layer positioned between
electroactive-material-containing layer 102 and
lithium-ion-conductive layer 104 may provide a surface that is
relatively smoother than the surface of
electroactive-material-containing layer 102. It has been recognized
that it may be advantageous, in certain embodiments, to provide a
smoother surface in order to enhance deposition of
lithium-ion-conductive layer 104 on
electroactive-material-containing layer 102 (e.g., a smoother
surface may allow lithium-ion-conductive layer 104 to be deposited
in a more continuous manner, potentially increasing the smoothness
and/or reducing the number of defects in lithium-ion-conductive
layer 104). A non-limiting example of an intervening layer that may
be appropriate for providing a smoother surface for deposition of
lithium-ion-conductive layer 104 is a polymer layer. Suitable
polymers include, but are not limited to, polyvinylidene fluoride,
polyvinylidene fluoride-hexafluropropylene copolymer, polyethers,
polyethylene oxides, polypropylene oxides, polyimides,
polyphosphazenes, polyacrylonitriles, polysiloxanes, derivatives of
the foregoing, copolymers of the foregoing, crosslinked and network
structures of the foregoing, and blends of the foregoing. Another
non-limiting example of an intervening layer that may be used to
provide a smoother surface is a layer comprising particles (e.g.,
nanoparticles) of the electroactive material and/or additives of
electroactive-material-containing layer 102, where the particles of
the intervening layer have a mean maximum cross-sectional dimension
that is smaller than the particles of
electroactive-material-containing layer 102. Additionally,
non-planar arrangements, arrangements with proportions of materials
different than those shown, and other alternative arrangements are
useful in connection with the present invention.
[0044] As used herein, when a layer is referred to as being (e.g.,
disposed) "on," "on top of," or "adjacent" another layer, it can be
directly on, on top of, or adjacent the layer, or an intervening
layer may also be present. A layer that is "directly on," "directly
adjacent," or "in contact with" another layer means that no
intervening layer is present. Likewise, a layer that is positioned
"between" two layers may be directly between the two layers such
that no intervening layer is present, or an intervening layer may
be present.
[0045] In some embodiments, the lithium-ion-conductive layer
comprises an inorganic material. For example, in certain cases, the
lithium-ion-conductive layer comprises a ceramic material. The
ceramic material may have a crystalline, polycrystalline, partially
crystalline, or amorphous structure. Suitable ceramic materials
include, but are not limited to, oxides, carbonates, nitrides,
carbides, sulfides, oxysulfides, and/or oxynitrides of metals
and/or metalloids. In some cases, the ceramic material comprises
lithium. Non-limiting examples of suitable ceramic materials
comprising lithium include lithium oxides (e.g., Li.sub.2O, LiO,
LiO.sub.2, LiRO.sub.2, where R is scandium, yttrium, lanthanum,
cerium, praseodymium, neodymium, promethium, samarium, europium,
gadolinium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium, and/or lutetium), lithium carbonate (Li.sub.2CO.sub.3),
lithium nitrides (e.g., Li.sub.3N), lithium oxysulfide, lithium
oxynitride, lithium garnet-type oxides (e.g.,
Li.sub.7La.sub.3Zr.sub.2O.sub.12), Li.sub.10GeP.sub.2S.sub.12,
lithium phosphorus oxynitride, lithium silicosulfide, lithium
germanosulfide, lithium lanthanum oxides, lithium titanium oxides,
lithium borosulfide, lithium aluminosulfide, lithium
phosphosulfide, lithium silicate, lithium borate, lithium
aluminate, lithium phosphate, lithium halides, and combinations of
the above. In certain cases, the ceramic material comprises a
lithium oxide, a lithium nitride, or a lithium oxysulfide. In some
embodiments, the ceramic includes a carbonate and/or a carbide. In
some particular embodiments, the lithium-ion-conductive layer
comprises or is formed of a mixture of an oxide, a carbonate, and
in some cases, a carbide. For instance, the material may include
lithium oxide, lithium carbonate, and/or lithium carbide. Other
materials are also possible.
[0046] In many embodiments described herein, the
lithium-ion-conductive layer is selected to be non-electroactive
(e.g., the layer does not participate in lithium intercalation
processes or lithium conversion reactions). Additionally, in some
embodiments, the lithium-ion-conductive layer is selected to
substantially impede the passage of certain species such as certain
non-lithium ions. For example, the lithium-ion-conductive layer may
provide a physical barrier that is impermeable to certain
non-lithium ions, neutralize and/or mitigate the ions, or otherwise
prevent or reduce the rate of passage of the ions through the
lithium-ion-conductive layer. In certain embodiments, the
lithium-ion-conductive layer may substantially impede or reduce the
rate of passage, from the cathode to the anode and/or across the
lithium-ion-conductive layer, of certain ions such as certain
non-lithium metal cations (e.g., metal cations that do not include
Lit) resulting from dissolution and/or leaching of the cathode.
However, the lithium-ion-conductive layer is generally selected to
be conductive to lithium ions (e.g., the lithium-ion-conductive
layer allows passage of lithium ions between the anode and the
cathode, permitting the lithium-ion electrochemical cell to
function).
[0047] One method of determining lithium ion conductivity is
electrochemical impedance spectroscopy (EIS). For example, the
lithium-ion-conductive layer may be placed between two electrodes,
and resistance may be measured over a range of frequencies from
100,000 Hz to 0.01 Hz at an amplitude of 5 mV. The lithium ion
conductivity of the lithium-ion-conductive layer may then be
calculated from the measured resistance values. In some
embodiments, the lithium-ion-conductive layer has a lithium ion
conductivity greater than or equal to about 10.sup.-8 S/cm, greater
than or equal to about 10.sup.-7 S/cm, greater than or equal to
about 10.sup.-6 S/cm, greater than or equal to about 10.sup.-5
S/cm, greater than or equal to about 10.sup.-4 S/cm, greater than
or equal to about 10.sup.-3 S/cm, greater than or equal to about
10.sup.-2 S/cm, greater than or equal to about 10.sup.-1 S/cm, or
greater than or equal to about 1 S/cm. In some embodiments, the
lithium-ion-conductive layer has a lithium ion conductivity of less
than or equal to about 1 S/cm, less than or equal to about
10.sup.-1 S/cm, less than or equal to about 10.sup.-2 S/cm, less
than or equal to about 10.sup.-3 S/cm, less than or equal to about
10.sup.-4 S/cm, less than or equal to about 10.sup.-5 S/cm, less
than or equal to about 10.sup.-6 S/cm, less than or equal to about
10.sup.-7 S/cm, or less than or equal to about 10.sup.-8 S/cm.
Combinations of the above-referenced ranges are also possible.
[0048] In some embodiments, the lithium-ion-conductive layer is
substantially continuous. For instance, the lithium-ion-conductive
layer may be substantially free of pores, gaps, defects, or
discontinuities, e.g., across the thickness of the layer. FIG. 21A
shows a scanning electron microscope (SEM) image of a top-down view
of an exemplary substantially continuous lithium-ion-conductive
layer. In some cases, the lithium-ion-conductive layer is
substantially free of discontinuities (e.g., holes, pores or
defects) that are larger than about 1000 nm, about 500 nm, about
100 nm, about 50 nm, about 10 nm, about 5 nm, about 1 nm, about 0.5
nm, about 0.1 nm, about 0.05 nm, or about 0.01 nm. In certain
embodiments, discontinuities within the lithium-ion-conductive
layer (such as those within one or more of the size ranges noted
above) occupy less than about 5%, less than about 1%, or less than
about 0.1% of the external geometric surface area of the
lithium-ion-conductive layer. As used herein, the "external
geometric surface area" refers to the surface area of the external
geometric surface of the lithium-ion-conductive layer. The
"external geometric surface" of the lithium-ion-conductive layer
refers to the surface defining the outer boundaries of the layer
when analyzed at substantially the same scale as the maximum
cross-sectional dimension of the layer. Generally, the external
geometric surface of a layer does not include the internal
surfaces, such as the surfaces defined by pores within a porous
layer.
[0049] In some embodiments, the lithium-ion-conductive layer is
substantially porous (e.g., the layer comprises a plurality of
pores). The term "pore" generally refers to a conduit, void, or
passageway, at least a portion of which is surrounded by the medium
in which the pore is formed. Generally, voids within a material
that are completely surrounded by the material (and, thus, not
accessible from outside the material, e.g., closed cells) are not
considered pores within the context herein.
[0050] In certain embodiments, the porous lithium-ion-conductive
layer comprises a plurality of particles. In cases where the
lithium-ion-conductive layer comprises a plurality of particles,
pores may include both interparticle pores (i.e., those pores
defined between particles when they are packed together, e.g.,
interstices) and intraparticle pores (i.e., those pores lying
within the envelopes of individual particles).
[0051] In embodiments in which the lithium-ion-conductive layer
comprises particles (e.g., particles of lithium-ion-conductive
material), the particles may have any suitable shape. In some
embodiments, at least a portion of the particles may have a
substantially elongated (e.g., columnar) shape. In some cases, the
columnar structures have a shape and/or configuration resembling
the structures shown in Thornton et al, "Influence of apparatus
geometry and deposition conditions on the structure and topography
of thick sputtered coatings", Journal of Vacuum Science &
Technology 11, 666 (1974), which is incorporated herein by
reference in its entirety for all purposes. In cases where the
plurality of particles comprises a plurality of columnar
structures, pores may include both intercolumnar pores and
intracolumnar pores. In some embodiments, at least about 10%, at
least about 20%, at least about 30%, at least about 40%, at least
about 50%, at least about 60%, at least about 70%, at least about
80%, at least about 90%, at least about 95%, at least about 99%, or
about 100% of the particles of the porous lithium-ion-conductive
layer are columnar structures. In certain embodiments, less than
about 100%, less than or equal to about 90%, less than or equal to
about 80%, less than or equal to about 70%, less than or equal to
60%, less than or equal to about 50%, less than or equal to 40%,
less than or equal to about 30%, less than or equal to 20%, or less
than or equal to about 10% of the particles are columnar
structures. Combinations of the above-referenced ranges are also
possible.
[0052] FIG. 21B shows an SEM image of a top-down view of an
exemplary substantially porous lithium-ion-conductive layer
comprising a plurality of columnar structures. It should be
appreciated, however, that the particles of a layer may also have
any other suitable shape (e.g., substantially spherical,
substantially elliptical, irregular). The particles may have any
suitable cross-sectional shape, such as, for example, circular,
elliptical, polygonal (e.g., triangular, rectangular, etc.),
irregular, and the like.
[0053] In embodiments in which the lithium-ion-conductive layer
comprises particles (e.g., particles of lithium-ion-conductive
material), the particles may have any suitable size. In some
embodiments, the particles have a mean maximum dimension (e.g.,
length) of about 10 micrometers (.mu.m) or less, about 5 .mu.m or
less, about 2 .mu.m or less, about 1.5 .mu.m or less, about 1 .mu.m
or less, about 500 nanometers (nm) or less, about 100 nm or less,
about 50 nm or less, about 20 nm or less, or about 10 nm or less.
In some embodiments, the particles have a mean maximum dimension of
at least about 10 nm, at least about 20 nm, at least about 50 nm,
at least about 100 nm, at least about 500 nm, at least about 1
.mu.m, at least about 1.5 .mu.m, at least about 2 .mu.m, at least
about 5 .mu.m, or at least about 10 .mu.m. Combinations of the
above-noted ranges are also possible. As used herein, the "maximum
dimension" of a particle refers to the largest distance between two
opposed boundaries of an individual particle that can be measured
(e.g., length, diameter). The "mean maximum dimension" of a
plurality of particles refers to the number average of the maximum
dimensions of the plurality of particles (e.g., where n is at least
20).
[0054] In some embodiments, the particles (e.g., particles of
lithium-ion-conductive material) can be at least partially fused
together with other particles. Fused particles generally refers to
the physical joining of two or more particles such that they form a
single particle. For example, in some cases, the volume occupied by
a single particle (e.g., the entire volume within the outer surface
of the particle) prior to fusion is substantially equal to half the
volume occupied by two fused particles. Those skilled in the art
would understand that the term "fused" does not refer to particles
that simply contact one another at one or more surfaces, but
particles wherein at least a portion of the original surface of
each individual particle can no longer be discerned from the other
particle.
[0055] In some cases, the particles are fused such that at least a
portion of the plurality of particles form a continuous pathway
across the layer (e.g., between a first surface of the layer and a
second surface of the layer). A continuous pathway may include, for
example, an ionically-conductive pathway from a first surface to a
second, opposing surface of the layer in which there are
substantially no gaps, breakages, or discontinuities in the
pathway. Whereas fused particles across a layer may form a
continuous pathway, a pathway including packed, unfused particles
would have gaps or discontinuities between the particles that would
not render the pathway continuous. In certain aspects, the layer
includes a plurality of such continuous pathways across the layer.
In some aspects, at least 10 vol %, at least 30 vol %, at least 50
vol %, or at least 70 vol % of the layer comprises one or more
continuous pathways comprising fused particles (e.g., which may
comprise an ionically conductive material). In certain aspects,
less than or equal to about 100 vol %, less than or equal to about
90 vol %, less than or equal to about 70 vol %, less than or equal
to about 50 vol %, less than or equal to about 30 vol %, less than
or equal to about 10 vol %, or less than or equal to about 5 vol %
of the second layer comprises one or more continuous pathways
comprising fused particles. Combinations of the above-referenced
ranges are also possible (e.g., at least about 10 vol % and less
than or equal to about 100 vol %). In some cases, 100 vol % of the
layer comprises one or more continuous pathways comprising fused
particles. In some aspects, the layer consists essentially of fused
particles (e.g., the layer comprises substantially no unfused
particles). In other aspects, substantially all of the particles
are unfused.
[0056] In some embodiments, the particles of the
lithium-ion-conductive layer have a mean maximum cross-sectional
dimension (e.g., diameter, width) of about 5 .mu.m or less, about 2
.mu.m or less, about 1.5 .mu.m or less, about 1 .mu.m or less,
about 500 nm or less, about 100 nm or less, about 50 nm or less,
about 20 nm or less, about 10 nm or less, about 5 nm or less, about
2 nm or less, or about 1 nm or less. In some embodiments, the
particles of the lithium-ion-conductive layer have a mean maximum
cross-sectional dimension (e.g., diameter, width) of at least about
1 nm, at least about 2 nm, at least about 5 nm, at least about 10
nm, at least about 20 nm, at least about 50 nm, at least about 100
nm, at least about 500 nm, at least about 1 .mu.m, at least about
1.5 .mu.m, at least about 2 .mu.m, at least about 5 .mu.m, or at
least about 10 .mu.m. Combinations of the above-noted ranges are
also possible. As used herein, the "maximum cross-sectional
dimension" of a particle refers to the largest distance between two
opposed boundaries of an individual particle that can be measured
in a plane orthogonal to the axis along which the maximum dimension
of the particle can be measured. The "mean maximum cross-sectional
dimension" of a plurality of particles refers to the number average
of the maximum cross-sectional dimensions of the plurality of
particles (e.g., where n is at least 20).
[0057] One of ordinary skill in the art would be capable of
calculating the mean maximum dimension and/or mean maximum
cross-sectional dimension of the plurality of particles. For
example, the maximum dimensions and/or maximum cross-sectional
dimensions of individual particles may be determined through
analysis of scanning electron microscope (SEM) images of the
particles. In a non-limiting, illustrative example, a first
cross-sectional plane of an electrochemical cell at a depth halfway
through the thickness of the electrochemical cell may be imaged
using SEM. Through analysis of the resultant images, the mean
maximum cross-sectional dimension of the particles may be
determined. In certain cases, a backscatter detector and/or an
energy-dispersive spectroscopy (EDS) detector may be used to
facilitate identification of lithium-ion-conductive material
particles (e.g., as distinguished from particles of additives that
may be present). In embodiments comprising agglomerated particles,
the particles should be considered separately when determining the
maximum cross-sectional dimensions. The measurement could be
performed by establishing boundaries between each of the
agglomerated particles, and measuring the maximum cross-sectional
dimension of the hypothetical, individuated particles that result
from establishing such boundaries. The distribution of maximum
cross-sectional dimensions and particle volumes could also be
determined by one of ordinary skill in the art using SEM analysis.
The mean maximum cross-sectional dimension of the plurality of
particles may be obtained by calculating the arithmetic mean of the
maximum cross-sectional dimensions of the particles. In another
non-limiting, illustrative example, a second cross-sectional plane
that is orthogonal to the first cross-sectional plane and is
halfway through the length or width of the electrochemical cell may
be imaged using SEM. In some cases, the mean maximum dimension of
the particles may be determined through analysis of the resultant
images. In some embodiments, at least 20 measurements may be used
to calculate an average value.
[0058] In some cases, at least a portion of the particles (e.g.,
columnar structures) of the lithium-ion-conductive layer may be
substantially aligned. For example, in embodiments in which the
plurality of particles comprises a plurality of columnar
structures, at least a portion of the columnar structures may be
substantially vertically aligned. As used herein, a columnar
structure of a lithium-ion-conductive layer in an electrochemical
cell comprising an anode and a cathode is "vertically aligned" if
an angle between the axis along which the maximum dimension (e.g.,
length) of the columnar structure can be measured (e.g., a
longitudinal axis) and the axis running from the anode to the
cathode is about 45.degree. or less. The angle may be determined,
for example, through SEM image analysis. In some embodiments, at
least about 10%, at least about 20%, at least about 30%, at least
about 40%, at least about 50%, at least about 60%, at least about
70%, at least about 80%, at least about 90%, at least about 95%, at
least about 99%, or about 100% of the particles of the
lithium-ion-conductive layer are substantially aligned. In certain
embodiments, less than about 100%, less than or equal to about 90%,
less than or equal to about 80%, less than or equal to about 70%,
less than or equal to about 60%, less than or equal to about 50%,
less than or equal to about 40%, less than or equal to about 30%,
less than or equal to about 20%, or less than or equal to about 10%
of the particles of the lithium-ion-conductive layer are
substantially aligned.
[0059] Combinations of the above-referenced ranges are also
possible. In certain embodiments, at least about 10%, at least
about 20%, at least about 30%, at least about 40%, at least about
50%, at least about 60%, at least about 70%, at least about 80%, at
least about 90%, at least about 95%, at least about 99%, or about
100% of the particles of the lithium-ion-conductive layer are
substantially vertically aligned. In certain embodiments, less than
about 100%, less than or equal to about 90%, less than or equal to
about 80%, less than or equal to about 70%, less than or equal to
about 60%, less than or equal to about 50%, less than or equal to
about 40%, less than or equal to about 30%, less than or equal to
about 20%, or less than or equal to about 10% of the particles of
the lithium-ion-conductive layer are substantially vertically
aligned.
[0060] In some embodiments in which the lithium-ion-conductive
layer comprises pores, some or all of the pores of a porous
lithium-ion-conductive layer can be filled by a fluid (e.g., an
electrolyte). In certain cases, at least some of the pores of the
lithium-ion-conductive layer are filled with an electrolyte that is
a liquid, a gel, a solid polymer, and/or a solid inorganic
compound. According to certain embodiments, at least a portion of
the porous lithium-ion-conductive layer is permeable to a fluid
(e.g., an electrolyte).
[0061] The porous lithium-ion-conductive layer may have any
suitable porosity. For example, the porous lithium-ion-conductive
layer may have a porosity of up to about 1%, up to about 2%, up to
about 5%, up to about 10%, up to about 15%, up to about 20%, up to
about 25%, up to about 30%, up to about 40%, up to about 50%, up to
about 60%, or up to about 70% (where the percentages indicate void
volume within the porous lithium-ion-conductive layer). In some
embodiments, the porous lithium-ion-conductive layer has a porosity
of at least about 1% by volume, at least about 2% by volume, at
least about 5% by volume, at least about 10% by volume, at least
about 15% by volume, at least about 20% by volume, at least about
25% by volume, at least about 30% by volume, at least about 40% by
volume, at least about 50% by volume, at least about 60% by volume,
or at least about 70% by volume. Combinations of the above-noted
ranges are also possible.
[0062] The pores of the lithium-ion-conductive layer may have any
suitable size and shape. The pores may comprise any suitable
cross-sectional shape such as, for example, circular, elliptical,
polygonal (e.g., rectangular, triangular, etc.), irregular, and the
like. In some cases, the porous lithium-ion-conductive layer has an
average pore size of about 1 .mu.m or less, about 500 nm or less,
about 200 nm or less, about 100 nm or less, about 50 nm or less,
about 20 nm or less, about 10 nm or less, about 5 nm or less, about
2 nm or less, or about 1 nm or less. In some cases, the porous
lithium-ion-conductive layer has an average pore size of at least
about 1 nm, at least about 2 nm, at least about 5 nm, at least
about 10 nm, at least about 20 nm, at least about 50 nm, at least
about 100 nm, at least about 200 nm, at least about 500 nm, or at
least about 1 .mu.m. Combinations of the above-noted ranges are
also possible.
[0063] One of ordinary skill in the art would be capable of
calculating the porosity, pore size distribution and the average
pore size of the plurality of pores within a layer using mercury
intrusion porosimetry, as described in ASTM standard D4284-92,
which is incorporated herein by reference in its entirety. For
example, the methods described in ASTM standard D4284-92 can be
used to produce a distribution of pore sizes plotted as the
cumulative intruded pore volume as a function of pore diameter. To
calculate the percentage of the total pore volume within the sample
that is occupied by pores within a given range of pore diameters,
one would: (1) calculate the area under the curve that spans the
given range over the x-axis, (2) divide the area calculated in step
(1) by the total area under the curve, and (3) multiply by 100%.
Average pore size can then be calculated from this information.
Optionally, in cases where the layer includes pore sizes that lie
outside the range of pore sizes that can be accurately measured
using ASTM standard D4284-92, porosimetry measurements may be
supplemented using BET surface analysis, as described, for example,
in S. Brunauer, P. H. Emmett, and E. Teller, J. Am. Chem. Soc.,
1938, 60, 309, which is incorporated herein by reference in its
entirety.
[0064] In some embodiments, the porous lithium-ion-conductive layer
may comprise pores with relatively uniform maximum cross-sectional
dimensions. Without wishing to be bound by any theory, such
uniformity may be useful in maintaining relatively consistent
structural stability throughout the bulk of the porous
lithium-ion-conductive layer. In addition, the ability to control
the pore size to within a relatively narrow range can allow one to
incorporate a large number of pores that are large enough to allow
for fluid penetration (e.g., electrolyte penetration) while
maintaining sufficiently small pores to preserve structural
stability of the porous lithium-ion-conductive layer. In some
embodiments, the distribution of pore sizes within the porous
lithium-ion-conductive layer can have a standard deviation of less
than about 50%, less than about 25%, less than about 20%, less than
about 10%, less than about 5%, less than about 2%, or less than
about 1% of the mean maximum cross-sectional dimension of the
plurality of pores. In some embodiments, the distribution of pore
sizes within the porous lithium-ion-conductive layer can have a
standard deviation of at least about 1%, at least about 2%, at
least about 5%, at least about 10%, at least about 20%, at least
about 25%, or at least about 50% of the mean maximum
cross-sectional dimension of the plurality of pores. Combinations
of the above-referenced ranges are also possible. Standard
deviation (lower-case sigma) is given its normal meaning in the
art, and can be calculated as:
.sigma. = i = 1 n .times. .times. ( D i - D avg ) 2 n - 1 ( 1 )
##EQU00001##
wherein D.sub.i is the maximum cross-sectional dimension of pore i,
D.sub.avg is the number average of the maximum cross-sectional
dimensions of the plurality of pores, and n is the number of pores.
The percentage comparisons between the standard deviation and the
average pore size outlined above can be obtained by dividing the
standard deviation by the average and multiplying by 100%.
[0065] In some cases, the lithium-ion-conductive layer is formed
from a unitary material. A unitary material may refer to one that
is processed such that any individual particles used to form the
material cease to be readily separable as individual particles. For
example, a unitary material may be formed through a vapor
deposition process and/or an aerosol deposition process in some
embodiments under certain deposition conditions.
[0066] In embodiments described herein, the lithium-ion-conductive
layer (e.g., a substantially continuous lithium-ion-conductive
layer or a substantially porous lithium-ion-conductive layer) may
be deposited by any suitable method, including, but not limited to,
sputtering (e.g., diode sputtering, direct current (DC) magnetron
sputtering, radio frequency (RF) sputtering, RF magnetron
sputtering, pulsed sputtering, dual magnetron sputtering,
alternating current (AC) sputtering, mid frequency (MF) sputtering,
reactive sputtering), electron beam evaporation, vacuum thermal
evaporation, laser ablation, chemical vapor deposition (CVD),
thermal evaporation (e.g., resistive, inductive, radiation, and
electron beam heating), plasma-enhanced chemical vacuum deposition
(PECVD), laser-enhanced chemical vapor deposition, aerosol
deposition, ion plating, cathodic arc, and jet vapor deposition.
The technique used may depend on a variety of factors, including
the type of material being deposited, the thickness of the layer,
and the underlying layer on which the lithium-ion-conductive layer
is deposited.
[0067] In some embodiments, the lithium-ion-conductive layer may be
substantially smooth. In certain embodiments, increased smoothness
of the lithium-ion-conductive layer may result in enhanced
performance of the lithium-ion electrochemical cell, e.g., under
certain operating conditions. Accordingly, the
lithium-ion-conductive layer may have a relatively low surface
roughness. In other embodiments, however, the
lithium-ion-conductive layer may be substantially rough.
Accordingly, the lithium-ion-conductive layer may have a relatively
high surface roughness.
[0068] Surface roughness may be quantified using any appropriate
method. For example, in some cases, a surface roughness profile of
the lithium-ion-conductive layer may be obtained using a
profilometer (e.g., a contact profilometer, an optical
profilometer). From the surface roughness profile, certain measures
of surface roughness, including R.sub.z (e.g., the average of the
ten lowest valleys subtracted from the average of the ten highest
peaks), R.sub.a (e.g., arithmetic mean surface roughness), and
R.sub.q (e.g., root mean square surface roughness), may be
obtained. Generally, the surface roughness of the
lithium-ion-conductive layer is determined by examining the layer
at a 5.times. magnification.
[0069] Surface roughness R.sub.z may be calculated as follows:
1 10 .times. i = 1 10 .times. .times. R pi - R vi ( 2 )
##EQU00002##
[0070] where R.sub.pi is the height of the i.sup.th highest peak
and R.sub.vi is the height of the i.sup.th lowest valley in a
surface roughness profile. In some cases, the
lithium-ion-conductive layer has a surface roughness R.sub.z of
about 20 .mu.m or less, about 15 .mu.m or less, about 10 .mu.m or
less, about 5 .mu.m or less, about 2 .mu.m or less, about 1 .mu.m
or less, about 500 nm or less, about 200 nm or less, about 100 nm
or less, about 50 nm or less, about 20 nm or less, or about 10 nm
or less. In some embodiments, the lithium-ion-conductive layer has
a surface roughness R.sub.z of about 10 nm or more, about 20 nm or
more, about 50 nm or more, about 100 nm or more, about 200 nm or
more, about 500 nm or more, about 1 .mu.m or more, about 2 .mu.m or
more, about 5 .mu.m or more, about 10 .mu.m or more, about 15 .mu.m
or more, or about 20 .mu.m or more. Combinations of the above-noted
ranges are also possible.
[0071] Arithmetic mean surface roughness R.sub.a may be calculated
as follows:
1 N .times. i = 1 N .times. .times. R i ( 3 ) ##EQU00003##
where R.sub.i is the height at the i.sup.th point in a surface
roughness profile and N is the number of points that were measured.
In some cases, the lithium-ion-conductive layer has an arithmetic
mean surface roughness R.sub.a of about 20 .mu.m or less, about 15
.mu.m or less, about 10 .mu.m or less, about 5 .mu.m or less, about
2 .mu.m or less, about 1 .mu.m or less, about 500 nm or less, about
200 nm or less, about 100 nm or less, about 50 nm or less, about 20
nm or less, or about 10 nm or less. In certain embodiments, the
lithium-ion-conductive layer has an arithmetic mean surface
roughness R.sub.a of about 10 nm or more, about 20 nm or more,
about 50 nm or more, about 100 nm or more, about 200 nm or more,
about 500 nm or more, about 1 .mu.m or more, about 2 .mu.m or more,
about 5 .mu.m or more, about 10 .mu.m or more, about 15 .mu.m or
more, or about 20 .mu.m or more. Combinations of the above-noted
ranges are also possible.
[0072] RMS surface roughness R.sub.q may be calculated as
follows:
1 N .times. i = 1 N .times. .times. R i 2 ( 4 ) ##EQU00004##
where R.sub.i is the height at the i.sup.th point in a surface
roughness profile and N is the number of points that were measured.
In some cases, the lithium-ion-conductive layer has a root mean
square surface roughness R.sub.q of about 20 .mu.m or less, about
15 .mu.m or less, about 10 .mu.m or less, about 5 .mu.m or less,
about 2 .mu.m or less, about 1 .mu.m or less, about 500 nm or less,
about 200 nm or less, about 100 nm or less, about 50 nm or less,
about 20 nm or less, or about 10 nm or less. In certain
embodiments, the lithium-ion-conductive layer has a root mean
square surface roughness R.sub.q of about 10 nm or more, about 20
nm or more, about 50 nm or more, about 100 nm or more, about 200 nm
or more, about 500 nm or more, about 1 .mu.m or more, about 2 .mu.m
or more, about 5 .mu.m or more, about 10 .mu.m or more, about 15
.mu.m or more, or about 20 .mu.m or more. Combinations of the
above-noted ranges are also possible.
[0073] In some embodiments, the lithium-ion-conductive layer may be
characterized by a thickness (e.g., a largest dimension measured
from a first end of the layer to a second end of the layer in a
direction parallel to the axis running from the anode to the
cathode). In some cases, the lithium-ion-conductive layer may be
relatively thin (e.g., the thickness may be relatively small
compared to the other two dimensions of the layer). In some cases,
the lithium-ion-conductive layer has a thickness of about 10 .mu.m
or less, about 5 .mu.m or less, about 2 .mu.m or less, about 1.5
.mu.m or less, about 1 .mu.m or less, about 0.5 .mu.m or less, or
about 0.1 .mu.m. Correspondingly, in certain embodiments, the
lithium-ion-conductive layer has a thickness of about 0.1 .mu.m or
more, about 0.2 .mu.m or more, about 0.3 .mu.m or more, about 0.5
.mu.m or more, about 0.7 .mu.m or more, about 1 .mu.m or more,
about 1.5 .mu.m or more, about 2 .mu.m or more, about 5 .mu.m or
more, or about 10 .mu.m. Combinations of the above-noted ranges are
also possible. In certain cases, the lithium-ion-conductive layer
is substantially uniform in thickness. For example, the percent
difference between the largest and smallest measurements of
thickness of the lithium-ion-conductive layer may be less than
about 80%, less than about 50%, less than about 20%, less than
about 10%, less than about 5%, or less than about 1%.
[0074] In some embodiments, the lithium-ion-conductive layer is
relatively basic. For example, the lithium-ion-conductive layer may
comprise a material that is selected from species that can donate
electron pairs (e.g., a Lewis base). Examples of suitable
electron-donating materials include, but are not limited to,
lithium oxides (e.g., Li.sub.2O, LiO, LiO.sub.2, LiRO.sub.2, where
R is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium,
promethium, samarium, europium, gadolinium, terbium, dysprosium,
holmium, erbium, thulium, ytterbium, and/or lutetium), lithium
carbonate (Li.sub.2CO.sub.3), lithium nitrides (e.g., Li.sub.3N),
lithium oxysulfide, lithium oxynitride, lithium garnet-type oxides
(e.g., Li.sub.7La.sub.3Zr.sub.2O.sub.12),
Li.sub.10GeP.sub.2S.sub.12, lithium phosphorus oxynitride, lithium
silicosulfide, lithium germanosulfide, lithium lanthanum oxides,
lithium titanium oxides, lithium borosulfide, lithium
aluminosulfide, lithium phosphosulfide, lithium silicate, lithium
borate, lithium aluminate, lithium phosphate, lithium halides, and
combinations of the above. For example, in some embodiments, 1 mole
of a material of the lithium-ion-conductive layer (e.g., Li.sub.2O)
may neutralize 1 mole of an acid (e.g., HF). It has been recognized
that it may be advantageous for the lithium-ion-conductive layer to
be relatively basic (e.g., comprising a Lewis base), in some
embodiments, because a basic material may be capable of at least
partially neutralizing deleterious acidic byproducts that result
from certain side reactions. For example, hydrolysis of certain
components of an electrolyte such as lithium salts (e.g.,
LiPF.sub.6) in a lithium-ion electrochemical cell may result in
acidic byproducts, such as HF. The presence of a
lithium-ion-conductive layer in the electrochemical cell may, in
certain embodiments, neutralize at least a portion of any HF that
may form.
[0075] As shown in FIG. 1, the electrode may further comprise a
layer comprising an electroactive material, such as a material that
is capable of participating in a lithium intercalation process
(e.g., a material in which lithium ions can reversibly be inserted
and extracted) and/or a material that is capable of chemically
reacting with lithium (e.g., a material that can participate in a
lithium conversion reaction). An electrode comprising an
electroactive material that is capable of participating in a
lithium intercalation process is referred to as a "lithium
intercalation electrode." An electrode comprising an electroactive
material that is capable of participating in a lithium conversion
reaction is referred to as a "lithium conversion electrode." In
some embodiments, the electrode comprising the
lithium-ion-conductive layer integrated with the electroactive
material layer is a cathode. A cathode for use in a lithium-ion
electrochemical cell generally refers to an electrode from which a
lithium ion is liberated during charge and into which the lithium
ion is integrated (e.g., intercalated, chemically bonded) during
discharge.
[0076] In some embodiments, the electroactive material of the
cathode comprises a lithium intercalation compound (e.g., a
compound that is capable of reversibly inserting lithium ions at
lattice sites and/or interstitial sites). In certain cases, the
electroactive material of the cathode comprises a layered oxide. A
layered oxide generally refers to an oxide having a lamellar
structure (e.g., a plurality of sheets, or layers, stacked upon
each other). Non-limiting examples of suitable layered oxides
include lithium cobalt oxide (LiCoO.sub.2), lithium nickel oxide
(LiNiO.sub.2), and lithium manganese oxide (LiMnO.sub.2). In some
embodiments, the layered oxide is lithium nickel manganese cobalt
oxide (LiNi.sub.xMn.sub.yCo.sub.zO.sub.2, also referred to as "NMC"
or "NCM"). In some such embodiments, the sum of x, y, and z is 1.
For example, a non-limiting example of a suitable NMC compound is
LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2. In some embodiments, the
layered oxide is lithium nickel cobalt aluminum oxide
(LiNi.sub.xCo.sub.yAl.sub.zO.sub.2, also referred to as "NCA"). In
some such embodiments, the sum of x, y, and z is 1. For example, a
non-limiting example of a suitable NCA compound is
LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2. In certain embodiments,
the electroactive material of the cathode is a transition metal
polyanion oxide (e.g., a compound comprising a transition metal, an
oxygen, and/or an anion having a charge with an absolute value
greater than 1). A non-limiting example of a suitable transition
metal polyanion oxide is lithium iron phosphate (LiFePO.sub.4, also
referred to as "LFP"). Another non-limiting example of a suitable
transition metal polyanion oxide is lithium manganese iron
phosphate (LiMn.sub.xFe.sub.1-xPO.sub.4, also referred to as
"LMFP"). A non-limiting example of a suitable LMFP compound is
LiMn.sub.0.8Fe.sub.0.2PO.sub.4. In some embodiments, the
electroactive material of the cathode is a spinel (e.g., a compound
having the structure AB.sub.2O.sub.4, where A can be Li, Mg, Fe,
Mn, Zn, Cu, Ni, Ti, or Si, and B can be Al, Fe, Cr, Mn, or V). A
non-limiting example of a suitable spinel is lithium manganese
oxide (LiMn.sub.2O.sub.4, also referred to as "LMO"). Another
non-limiting example is lithium manganese nickel oxide
(LiNi.sub.xM.sub.2-xO.sub.4, also referred to as "LMNO"). A
non-limiting example of a suitable LMNO compound is
LiNi.sub.0.5Mn.sub.1.5O.sub.4. In certain cases, the electroactive
material of the cathode comprises
Li.sub.1.14Mn.sub.0.42Ni.sub.0.25Co.sub.0.29O.sub.2 ("HC-MNC"),
lithium carbonate (Li.sub.2CO.sub.3), lithium carbides (e.g.,
Li.sub.2C.sub.2, Li.sub.4C, Li.sub.6C.sub.2, Li.sub.8C.sub.3,
Li.sub.6C.sub.3, Li.sub.4C.sub.3, Li.sub.4C.sub.5), vanadium oxides
(e.g., V.sub.2O.sub.5, V.sub.2O.sub.3, V.sub.6O.sub.13), and/or
vanadium phosphates (e.g., lithium vanadium phosphates, such as
Li.sub.3V.sub.2(PO.sub.4).sub.3), or any combination thereof.
[0077] In some embodiments, the electroactive material of the
cathode comprises a conversion compound. For instance, the cathode
may be a lithium conversion electrode/cathode. It has been
recognized that a cathode comprising a conversion compound may have
a relatively large specific capacity. Without wishing to be bound
by a particular theory, a relatively large specific capacity may be
achieved by utilizing all possible oxidation states of a compound
through a conversion reaction in which more than one electron
transfer takes place per transition metal (e.g., compared to 0.1-1
electron transfer in intercalation compounds). Suitable conversion
compounds include, but are not limited to, transition metal oxides
(e.g., Co.sub.3O.sub.4), transition metal hydrides, transition
metal sulfides, transition metal nitrides, and transition metal
fluorides (e.g., CuF.sub.2, FeF.sub.2, FeF.sub.3). A transition
metal generally refers to an element whose atom has a partially
filled d sub-shell (e.g., Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y,
Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au,
Hg, Rf, Db, Sg, Bh, Hs).
[0078] In some cases, the electroactive material of the cathode may
be doped with one or more dopants to alter the electrical
properties (e.g., electrical conductivity) of the electroactive
material. Non-limiting examples of suitable dopants include
aluminum, niobium, silver, and zirconium.
[0079] In some embodiments, the electrode comprising the
lithium-ion-conductive layer integrated with the electroactive
material layer is an anode.
[0080] In some cases, the electroactive-material-containing layer,
which may have a lithium-ion-conductive layer associated therewith,
may comprise a plurality of particles of the electroactive
material. FIG. 2 is a cross-sectional schematic illustration of
exemplary electrode 200, according to certain embodiments. In FIG.
2, electrode 200 comprises lithium-ion-conductive layer 206 and
plurality of particles 202 comprising an electroactive material. In
certain embodiments, such as the embodiment illustrated in FIG. 2,
pores 204 may form in the interstices between particles 202. In
some embodiments, at least a portion of the plurality of particles
have a coating (e.g., to prevent dissolution of the active
material). The coating may be electronically conductive.
Non-limiting examples of suitable materials for the coating include
carbon and carbon-containing materials. To form the electrode, the
plurality of particles comprising the electroactive material may be
combined with a binder and one or more additives to form a mixture
(e.g., a slurry). The mixture may then be coated on a substrate
and/or a current collector and subsequently dried. In certain
embodiments, the binder comprises one or more polymers (e.g.,
styrene butadiene copolymer, polyvinylidene fluoride (PVDF)). In
some cases, additives may be selected to enhance the performance of
the electrode. For example, an additive may increase electronic
conductivity. Examples of suitable additives include, but are not
limited to, carbon-containing materials such as carbon black.
[0081] In one particular set of embodiments, and as shown
illustratively in FIG. 2, lithium-ion-conductive layer 206 forms a
layer on one side or surface (e.g., a single side or surface) of
the layer comprising the particles of electroactive material (i.e.,
the electroactive layer). That is, the inorganic
lithium-ion-conductive layer may be disposed on a side or surface
of the layer comprising the electroactive material. The
lithium-ion-conductive layer may coat (form a coating) a side or
surface of the electroactive layer. In some such embodiments, the
lithium-ion-conductive layer may be integrated with a side or
surface of the electroactive layer. The lithium-ion-conductive
material may be absent from the solid interior portions and/or the
opposing side/surface of the electroactive layer. In such
embodiments, a portion (e.g., the portion of the particles of the
electroactive material at the surface of the layer), but not all of
the particles of the electroactive material, are coated with the
lithium-ion-conductive material/layer. For example, in some cases,
at least a portion (e.g., at least 10%, at least 20%, at least 30%,
at least 40%, at least 50%, at least 60%, at least 70%, at least
80%, at least 90%, and/or less than 100%, less than or equal to
95%, less than or equal to 90%, e.g., by weight) of the particles
of electroactive material in the electroactive layer (e.g., the
particles on the opposing side/surface of the electroactive layer
and/or the particles in the interior of the layer) are uncoated
with the lithium-ion-conductive material (a coating of
lithium-ion-conductive material may be absent from such particles).
In other embodiments, a second lithium-ion-conductive layer may be
formed on the opposing side or surface of the layer comprising the
particles of electroactive material. Similar to the embodiment
involving a single layer of lithium-ion-conductive material, the
lithium-ion-conductive material may be absent from the solid,
interior portions of the electroactive layer. These embodiments may
be formed by, for example, forming the electroactive layer (e.g.,
from a slurry of the electroactive particles or by another suitable
process), followed by depositing the lithium-ion-conductive layer
on the electroactive layer after the electroactive layer has been
formed. Such a method contrasts with coating individual
electroactive particles of electroactive material prior to the
particles forming the electroactive layer.
[0082] The particles comprising the electroactive material may be
of any suitable shape or size. For example, the particles may be
spherical, ellipsoidal, cylindrical, or prismatic (e.g., a
triangular prism, a rectangular prism, etc.), or may have an
irregular shape. In some embodiments, the plurality of particles
has a mean maximum cross-sectional dimension of about 50 .mu.m or
less, about 25 .mu.m or less, about 20 .mu.m or less, about 15
.mu.m or less, about 10 .mu.m or less, about 5 .mu.m or less, about
1 .mu.m or less, about 500 nm or less, about 200 nm or less, about
100 nm or less, about 90 nm or less, about 80 nm or less, about 70
nm or less, about 60 nm or less, about 50 nm or less, about 40 nm
or less, about 30 nm or less, about 20 nm or less, about 10 nm or
less, about 5 nm or less, or about 1 nm. In some embodiments, the
plurality of particles has a mean maximum cross-sectional dimension
of at least about 1 nm, at least about 5 nm, at least about 10 nm,
at least about 20 nm, at least about 30 nm, at least about 40 nm,
at least about 50 nm, at least about 60 nm, at least about 70 nm,
at least about 80 nm, at least about 90 nm, at least about 100 nm,
at least about 200 nm, at least about 500 nm, at least about 1
.mu.m, at least about 5 .mu.m, at least about 10 .mu.m, at least
about 15 .mu.m, at least about 20 .mu.m, at least about 25 .mu.m,
or at least about 50 .mu.m. Combinations of the above-noted ranges
are also possible. The mean maximum cross-sectional dimension may
be determined using SEM and/or EDS analysis, as described
above.
[0083] In some cases, the layer comprising the electroactive
material may be porous (e.g., the layer may comprise a plurality of
pores). It should be understood that, in cases where the
electroactive-material-containing layer comprises an agglomeration
of particles, pores include both the interparticle pores (i.e.,
those pores defined between particles when they are packed
together, e.g. interstices) and intraparticle pores (i.e., those
pores lying within the envelopes of the individual particles).
[0084] The porous electroactive-material-containing layer may have
any suitable porosity. For example, the porous
electroactive-material-containing layer may have a porosity of up
to about 10%, up to about 15%, up to about 20%, up to about 25%, up
to about 30%, up to about 40%, up to about 50%, up to about 60%, or
up to about 70% (where the percentages indicate void volume within
the porous electroactive-material-containing layer). In some
embodiments, the porous electroactive-material-containing layer has
a porosity of at least about 10% by volume, at least about 15% by
volume, at least about 20% by volume, at least about 25% by volume,
at least about 30% by volume, at least about 40% by volume, at
least about 50% by volume, at least about 60% by volume, or at
least about 70% by volume. Combinations of the above-noted ranges
are also possible.
[0085] The pores of the electroactive-material-containing layer may
have any suitable size and shape. The pores may comprise any
suitable cross-sectional shape such as, for example, circular,
elliptical, polygonal (e.g., rectangular, triangular, etc.),
irregular, and the like. In some cases, the porous
electroactive-material-containing layer may have an average pore
size of less than about 300 micrometers, for example, less than
about 100 micrometers, between about 0.5 micrometer and about 300
micrometers, between about 50 micrometers and about 200
micrometers, or between about 100 micrometers and about 200
micrometers. In some embodiments, some or all of the porosity can
be filled by electrolyte. In some cases, at least some of the pores
of the electroactive-material-containing layer are filled with an
electrolyte that is a liquid, a gel, a solid polymer, and/or a
solid inorganic compound. As described above, one of ordinary skill
in the art would be capable of calculating the pore size
distribution and the average pore size of the plurality of pores
within a layer using mercury intrusion porosimetry and/or BET
surface analysis.
[0086] In some embodiments, the porous
electroactive-material-containing layer may comprise pores with
relatively uniform maximum cross-sectional dimensions (e.g.,
diameters). Not wishing to be bound by any theory, such uniformity
may be useful in maintaining relatively consistent structural
stability throughout the bulk of the porous layer. In addition, the
ability to control the pore size to within a relatively narrow
range can allow one to incorporate a large number of pores that are
large enough to allow for fluid penetration (e.g., electrolyte
penetration) while maintaining sufficiently small pores to preserve
structural stability of the porous
electroactive-material-containing layer. In some embodiments, the
distribution of pore sizes within the porous
electroactive-material-containing layer can have a standard
deviation of less than about 50%, less than about 25%, less than
about 10%, less than about 5%, less than about 2%, or less than
about 1% of the mean maximum cross-sectional dimension of the
plurality of pores.
[0087] In other embodiments, an electroactive material layer
described herein, which may have a lithium-ion-conductive layer
associated therewith, is substantially non-porous.
[0088] Certain embodiments are directed to an electrochemical cell.
FIG. 3A shows an exemplary cross-sectional schematic illustration
of electrochemical cell 300 comprising cathode 102, anode 106,
separator 108 positioned between cathode 102 and anode 106, and
lithium-ion-conductive layer 104 positioned between cathode 102 and
separator 108. In certain cases, lithium-ion-conductive layer 104
is positioned adjacent cathode 102. As shown in FIG. 3A,
lithium-ion-conductive layer 104 may be in direct physical contact
with cathode 102. In some cases, lithium-ion-conductive layer 104
is integrated with cathode 102.
[0089] In some embodiments, the lithium-ion-conductive layer can be
positioned adjacent the anode. For example, in certain cases,
including the embodiment illustrated in FIG. 3B,
lithium-ion-conductive layer 104 is positioned adjacent anode 106.
As shown in FIG. 3B, lithium-ion-conductive layer 104 may be in
direct physical contact with anode 106. In some embodiments,
lithium-ion-conductive layer 104 is integrated with anode 106.
[0090] In some embodiments, an electrochemical cell may comprise a
first lithium-ion-conductive layer integrated with a cathode and a
second lithium-ion-conductive layer integrated with an anode. FIG.
4 shows an exemplary cross-sectional schematic illustration of
electrochemical cell 400 comprising cathode 102 integrated with
first lithium-ion-conductive layer 104 and anode 106 integrated
with second lithium-ion-conductive layer 110. As shown in FIG. 4,
separator layer 108 is positioned between first
lithium-ion-conductive layer 104 and second lithium-ion-conductive
layer 110. In certain embodiments, first lithium-ion-conductive
layer 104 and second lithium-ion-conductive layer 110 may comprise
the same material (e.g., ceramic material). In some cases, first
lithium-ion-conductive layer 104 and second lithium-ion-conductive
layer 110 may comprise different materials (e.g., a first ceramic
material and a second, different ceramic material).
[0091] In some embodiments, the electrochemical cell further
comprises additional components, such as an electrolyte, one or
more substrates, and/or one or more current collectors. FIG. 5
shows an exemplary cross-sectional schematic illustration of
electrochemical cell 500 comprising cathode 102,
lithium-ion-conductive layer 104, anode 106, separator 108, first
substrate and/or current collector 112, and second substrate and/or
current collector 114. As shown in FIG. 5, electrochemical cell 500
may comprise a separator 108 positioned between cathode 102 and
anode 106. In some cases, separator 108 may comprise an
electrolyte, as discussed in further detail below. As shown in FIG.
5, in some cases, lithium-ion-conductive layer 104 is positioned
between cathode 102 and separator/electrolyte 108. In some cases,
lithium-ion-conductive layer 104 is positioned between anode 102
and separator/electrolyte 108. In some cases, electrochemical cell
500 further comprises first substrate 112. First substrate 112 may
be positioned adjacent to cathode 102. As shown in FIG. 5, in some
embodiments, substrate 112 is in direct physical contact with
cathode 102. In some embodiments, one or more intervening layers
may be positioned between substrate 112 and cathode 102. In certain
cases, substrate 112 may comprise a metal (e.g., aluminum), and
substrate 112 may act as a current collector for cathode 102. In
some embodiments, electrochemical cell further comprises second
substrate 114. As shown in FIG. 5, in some embodiments, second
substrate 114 is in direct physical contact with anode 106. In
certain cases, second substrate 114 may comprise a metal (e.g.,
copper), and second substrate 114 may act as a current collector
for anode 106. In some embodiments, one or more intervening layers
may be positioned between second substrate 114 and anode 106.
[0092] In some embodiments, an electrochemical cell comprises an
electrolyte, a separator, first and second substrates and/or
current collectors, a first lithium-ion-conductive layer integrated
with a cathode, and a second lithium-ion-conductive layer
integrated with an anode. FIG. 6 shows an exemplary cross-sectional
schematic illustration of electrochemical cell 600 comprising
cathode 102, first lithium-ion-conductive layer 104, anode 106,
second lithium-ion-conductive layer 110, separator 108, first
substrate and/or current collector 112, and second substrate and/or
current collector 114. As shown in FIG. 6, second
lithium-ion-conductive layer 110, which is integrated with anode
106, is positioned between anode 106 and separator 108.
[0093] The electrolyte of an electrochemical cell is generally
positioned between the anode and the cathode, providing an ionic
path between the anode and the cathode (e.g., the electrolyte is
generally capable of conducting lithium ions). The electrolyte may
comprise any liquid, solid, or gel material capable of storing and
transporting lithium ions. Generally, the electrolyte is
electronically non-conductive to prevent short circuiting between
the anode and the cathode.
[0094] Any suitable anode can be included in an electrochemical
cell described herein. In some embodiments, the anode is an
electrode from which a lithium ion is liberated during discharge
and into which the lithium ion is integrated (e.g., intercalated)
during charge. In some embodiments, the electroactive material of
the anode is a lithium intercalation compound (e.g., a compound
that is capable of reversibly inserting lithium ions at lattice
sites and/or interstitial sites). In some embodiments, the
electroactive material of the anode comprises carbon. In certain
cases, the electroactive material of the anode is or comprises a
graphitic material (e.g., graphite). A graphitic material generally
refers to a material that comprises a plurality of layers of
graphene (e.g., layers comprising carbon atoms arranged in a
hexagonal lattice). Adjacent graphene layers are typically
attracted to each other via van der Waals forces, although covalent
bonds may be present between one or more sheets in some cases. In
some cases, the carbon-comprising electroactive material of the
anode is or comprises coke (e.g., petroleum coke). In certain
embodiments, the electrochemical material of the anode comprises
silicon, lithium, and/or any alloys of combinations thereof. In
certain embodiments, the electroactive material of the anode
comprises lithium titanate (Li.sub.4Ti.sub.5O.sub.12, also referred
to as "LTO"), tin-cobalt oxide, or any combinations thereof.
[0095] In some embodiments, the anode (e.g., a first electrode, a
second electrode) comprises lithium (e.g., lithium metal), such as
lithium foil, lithium deposited onto a conductive substrate, and
lithium alloys (e.g., lithium-aluminum alloys and lithium-tin
alloys). Lithium can be contained as one film or as several films,
optionally separated by a protective structure/material such as a
ceramic material or an ion conductive material described herein.
Suitable lithium alloys for use in the aspects described herein can
include alloys of lithium and aluminum, magnesium, silicium
(silicon), indium, and/or tin.
[0096] A protective structure (e.g., for anode) may include a
protective layer such as an ion conductive layer, which may help to
inhibit a species in the electrolyte from contacting the
electroactive material of the anode. In some embodiments, the
ion-conductive material may be selected to be conductive to
particular ions such as metal ions. The ion-conductive material may
be conductive to lithium ions or other alkali metal ions, according
to some embodiments. In some cases, the ion-conductive material may
comprise an inorganic material such as a ceramic and/or a glass
conductive to metal ions. Suitable glasses include, but are not
limited to, those that may be characterized as containing a
"modifier" portion and a "network" portion, as known in the art.
The modifier may include a metal oxide of the metal ion conductive
in the glass. The network portion may include a metal chalcogenide
such as, for example, a metal oxide or sulfide. In other cases, the
ion-conductive material may comprise or be a polymeric material.
Combinations of ion conductive materials and ion conductive
material layers within a protective structure are also possible
(e.g., a first ion conductive layer that comprises a ceramic and a
second ion conductive layer that comprises a polymer). The
protective layer for the anode may be substantially impermeable
(e.g., to the electrolyte used with the electrochemical cell
including the anode).
[0097] In some embodiments, the ion-conductive material may
comprise a material selected from the group consisting of lithium
nitrides, lithium silicates, lithium borates, lithium aluminates,
lithium phosphates, lithium phosphorus oxynitrides, lithium
silicosulfides, lithium germanosulfides, lithium oxides (e.g.,
Li.sub.2O, LiO, LiO.sub.2, LiRO.sub.2, where R is a rare earth
metal), lithium lanthanum oxides, lithium titanium oxides, lithium
borosulfides, lithium aluminosulfides, and lithium phosphosulfides,
oxysulfides, and combinations thereof. In some embodiments, the
ion-conductive material may comprise Al.sub.2O.sub.3, ZrO.sub.2,
SiO.sub.2, CeO.sub.2, and/or Al.sub.2TiO.sub.5. The selection of
the ion-conductive material will be dependent on a number of
factors including, but not limited to, the properties of
electrolyte and the anode and cathode used in the cell.
[0098] Examples of classes of polymers that may be suitable for use
in a protective structure (e.g., as a polymer layer) include, but
are not limited to, polyamines (e.g., poly(ethylene imine) and
polypropylene imine (PPI)); polyamides (e.g., polyamide (Nylon),
poly( -caprolactam) (Nylon 6), poly(hexamethylene adipamide) (Nylon
66)), polyimides (e.g., polyimide, polynitrile, and
poly(pyromellitimide-1,4-diphenyl ether) (Kapton)); vinyl polymers
(e.g., polyacrylamide, poly(2-vinyl pyridine),
poly(N-vinylpyrrolidone), poly(methylcyanoacrylate),
poly(ethylcyanoacrylate), poly(butylcyanoacrylate),
poly(isobutylcyanoacrylate), poly(vinyl acetate), poly (vinyl
alcohol), poly(vinyl chloride), poly(vinyl fluoride), poly(2-vinyl
pyridine), vinyl polymer, polychlorotrifluoro ethylene, and
poly(isohexylcynaoacrylate)); polyacetals; polyolefins (e.g.,
poly(butene-1), poly(n-pentene-2), polypropylene,
polytetrafluoroethylene); polyesters (e.g., polycarbonate,
polybutylene terephthalate, polyhydroxybutyrate); polyethers
(poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO),
poly(tetramethylene oxide) (PTMO)); vinylidene polymers (e.g.,
polyisobutylene, poly(methyl styrene), poly(methylmethacrylate)
(PMMA), poly(vinylidene chloride), and poly(vinylidene fluoride));
polyaramides (e.g., poly(imino-1,3-phenylene iminoisophthaloyl) and
poly(imino-1,4-phenylene iminoterephthaloyl)); polyheteroaromatic
compounds (e.g., polybenzimidazole (PBI), polybenzobisoxazole (PBO)
and polybenzobisthiazole (PBT)); polyheterocyclic compounds (e.g.,
polypyrrole); polyurethanes; phenolic polymers (e.g.,
phenol-formaldehyde); polyalkynes (e.g., polyacetylene); polydienes
(e.g., 1,2-polybutadiene, cis or trans-1,4-polybutadiene);
polysiloxanes (e.g., poly(dimethylsiloxane) (PDMS),
poly(diethylsiloxane) (PDES), polydiphenylsiloxane (PDPS), and
polymethylphenylsiloxane (PMPS)); and inorganic polymers (e.g.,
polyphosphazene, polyphosphonate, polysilanes, polysilazanes). In
some embodiments, the polymer may be selected from the group
consisting of polyvinyl alcohol, polyisobutylene, epoxy,
polyethylene, polypropylene, polytetrafluoroethylene, and
combinations thereof. The mechanical and electronic properties
(e.g., conductivity, resistivity) of these polymers are known.
[0099] Other suitable materials and/or properties of the protective
layer are described in U.S. Patent Publication No. 2010/0327811,
filed Jul. 1, 2010 and published Dec. 30, 2010, entitled "Electrode
Protection in Both Aqueous and Non-Aqueous Electromechanical Cells,
Including Rechargeable Lithium Batteries," which is incorporated
herein by reference in its entirety for all purposes.
[0100] In certain embodiments, at least a portion of the anode
and/or a portion of the cathode are in direct physical contact with
the electrolyte. In certain embodiments, at least a portion of the
electroactive material of the anode and/or a portion of the
electroactive material of the cathode are in direct physical
contact with the electrolyte. For example, the electrolyte may be
in contact with the electroactive material of the anode and/or the
electroactive material of the cathode to facilitate transport of Li
ions across the electrode in the electrochemical cell. For example,
in some embodiments the electrolyte resides in pores or interstices
of the electrode. In some embodiments, the electrolyte can be in
direct physical contact with a lithium species of an electrode. In
some embodiments, the electrolyte is in contact (e.g., direct
physical contact) with two or more sides of the anode and/or the
cathode. According to certain embodiments, for example, the
electrolyte may be a liquid that surrounds two or more sides of the
anode and/or the cathode. In some embodiments, the electrochemical
cell is a pouch cell, and the anode and cathode are positioned
within a pouch filled with an electrolyte (e.g., a liquid
electrolyte) that surrounds two or more sides of the anode and/or
cathode.
[0101] In certain embodiments, at least a portion of one electrode
(e.g., a cathode) but not a second electrode (e.g., an anode) is in
direct physical contact with the electrolyte. For example, the
second electrode (e.g., anode) may include a protective layer (e.g.
a substantially impermeable layer) that substantially inhibits
direct contact of the electrode with the electrolyte. The
protective layer may be in direct physical contact with the
electrolyte instead of the electroactive material of the electrode,
though minor imperfections (e.g., defects) in the protective layer
may cause indirect contact of the electrolyte with the
electroactive material (e.g., via the protective layer) in some
embodiments.
[0102] In certain embodiments, the electrolyte comprises an organic
solvent. Examples of suitable organic solvents include, but are not
limited to, dimethyl carbonate, diethyl carbonate, ethyl-methyl
carbonate, ethylene carbonate, and propylene carbonate. In some
embodiments, the electrolyte comprises one or more solid polymers.
Examples of useful gel polymer electrolytes include, but are not
limited to, those comprising one or more polymers selected from the
group consisting of polyethylene oxides, polypropylene oxides,
polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes,
polyethers, sulfonated polyimides, perfluorinated membranes (NAFION
resins), polydivinyl polyethylene glycols, polyethylene glycol
diacrylates, polyethylene glycol dimethacrylates, derivatives of
the foregoing, copolymers of the foregoing, crosslinked and network
structures of the foregoing, and blends of the foregoing, and
optionally, one or more plasticizers. Examples of useful solid
polymer electrolytes include, but are not limited to, those
comprising one or more polymers selected from the group consisting
of polyethers, polyethylene oxides, polypropylene oxides,
polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,
derivatives of the foregoing, copolymers of the foregoing,
crosslinked and network structures of the foregoing, and blends of
the foregoing. In some cases, the electrolyte further comprises a
lithium salt. Non-limiting examples of suitable lithium salts
include lithium hexafluorophosphate (LiPF.sub.6), lithium
tetrafluoroborate (LiBF.sub.4), lithium perchlorate (LiClO.sub.4),
lithium hexafluoroarsenate monohydrate (LiAsF.sub.6), lithium
triflate (LiCF.sub.3SO.sub.3), LiN(SO.sub.2CF.sub.3).sub.2, and
LiC(SO.sub.2(CF.sub.3).sub.3.
[0103] In some embodiments, the electrolyte has a relatively high
lithium ion conductivity. In some embodiments, the electrolyte has
a lithium ion conductivity of at least about 10.sup.-5 S/cm, at
least about 10.sup.-4 S/cm, at least about 10.sup.-3 S/cm, at least
about 10.sup.-2 S/cm, at least about 10.sup.-1 S/cm, or at least
about 1 S/cm. In some embodiments, the electrolyte has a lithium
ion conductivity in the range of about 10.sup.-5 S/cm to about
10.sup.4 S/cm, about 10.sup.-5 S/cm to about 10.sup.-3 S/cm, about
10.sup.-5 S/cm to about 10.sup.-2 S/cm, about 10.sup.-5 S/cm to
about 10.sup.-1 S/cm, about 10.sup.-5 S/cm to about 1 S/cm, about
10.sup.4 S/cm to about 10.sup.-3 S/cm, about 10.sup.4 S/cm to about
10.sup.-2 S/cm, about 10.sup.-4 S/cm to about 10.sup.-1 S/cm, about
10.sup.-4 S/cm to about 1 S/cm, about 10.sup.-3 S/cm to about
10.sup.-2 S/cm, about 10.sup.-3 S/cm to about 10.sup.-1 S/cm, about
10.sup.-3 S/cm to about 1 S/cm, or about 10.sup.-2 S/cm to about 1
S/cm. The lithium ion conductivity of the electrolyte may be
measured using EIS, as described above.
[0104] In certain cases, the electrolyte may optionally further
comprise additives. The additives may, for example, reduce
impedance of the anode and/or cathode, and/or promote the formation
of films. Non-limiting examples of suitable additives include
vinylene carbonate, vinyl ethylene carbonate, CO.sub.2, SO.sub.2,
ethylene sulfite, and any combination thereof.
[0105] The separator of an electrochemical cell (e.g., separator
108 of electrochemical cell 400 in FIG. 4) is generally positioned
between the anode and the cathode. The separator may be a solid
non-electronically conductive or electrically insulating material.
In some cases, the separator may separate or insulate the anode and
the cathode from each other, preventing short circuiting, while
permitting the transport of ions between the anode and the cathode.
In some embodiments, the separator may be porous (e.g., the
separator may comprise a plurality of pores). In certain cases, the
porous separator may be permeable to the electrolyte.
[0106] The pores of the separator may be partially or substantially
filled with electrolyte. Separators may be supplied as porous free
standing films which are interleaved with the anodes and the
cathodes during the fabrication of cells. Alternatively, the porous
separator layer may be applied directly to the surface of one of
the electrodes, for example, as described in PCT Publication No. WO
99/33125 to Carlson et al. and in U.S. Pat. No. 5,194,341 to Bagley
et al.
[0107] A variety of separator materials are known in the art.
Examples of suitable solid porous separator materials include, but
are not limited to, polyolefins, such as, for example,
polyethylenes (e.g., SETELA.TM. made by Tonen Chemical Corp) and
polypropylenes, glass fiber filter papers, and ceramic materials.
For example, in some embodiments, the separator comprises a
microporous polyethylene film. Further examples of separators and
separator materials suitable for use in this invention are those
comprising a microporous xerogel layer, for example, a microporous
pseudo-boehmite layer, which may be provided either as a free
standing film or by a direct coating application on one of the
electrodes, as described in U.S. Pat. Nos. 6,153,337 and 6,306,545
by Carlson et al. of the common assignee. Solid electrolytes and
gel electrolytes may also function as a separator in addition to
their electrolyte function.
[0108] Examples of suitable separator materials include, but are
not limited to, polyolefins (e.g., polyethylenes, poly(butene-1),
poly(n-pentene-2), polypropylene, polytetrafluoroethylene),
polyamines (e.g., poly(ethylene imine) and polypropylene imine
(PPI)); polyamides (e.g., polyamide (Nylon), poly( -caprolactam)
(Nylon 6), poly(hexamethylene adipamide) (Nylon 66)), polyimides
(e.g., polyimide, polynitrile, and
poly(pyromellitimide-1,4-diphenyl ether) (Kapton.RTM.) (NOMEX.RTM.)
(KEVLAR.RTM.)); polyether ether ketone (PEEK); vinyl polymers
(e.g., polyacrylamide, poly(2-vinyl pyridine),
poly(N-vinylpyrrolidone), poly(methylcyanoacrylate),
poly(ethylcyanoacrylate), poly(butylcyanoacrylate),
poly(isobutylcyanoacrylate), poly(vinyl acetate), poly (vinyl
alcohol), poly(vinyl chloride), poly(vinyl fluoride), poly(2-vinyl
pyridine), vinyl polymer, polychlorotrifluoro ethylene, and
poly(isohexylcynaoacrylate)); polyacetals; polyesters (e.g.,
polycarbonate, polybutylene terephthalate, polyhydroxybutyrate);
polyethers (poly(ethylene oxide) (PEO), poly(propylene oxide)
(PPO), poly(tetramethylene oxide) (PTMO)); vinylidene polymers
(e.g., polyisobutylene, poly(methyl styrene),
poly(methylmethacrylate) (PMMA), poly(vinylidene chloride), and
poly(vinylidene fluoride)); polyaramides (e.g.,
poly(imino-1,3-phenylene iminoisophthaloyl) and
poly(imino-1,4-phenylene iminoterephthaloyl)); polyheteroaromatic
compounds (e.g., polybenzimidazole (PBI), polybenzobisoxazole (PBO)
and polybenzobisthiazole (PBT)); polyheterocyclic compounds (e.g.,
polypyrrole); polyurethanes; phenolic polymers (e.g.,
phenol-formaldehyde); polyalkynes (e.g., polyacetylene); polydienes
(e.g., 1,2-polybutadiene, cis or trans-1,4-polybutadiene);
polysiloxanes (e.g., poly(dimethylsiloxane) (PDMS),
poly(diethylsiloxane) (PDES), polydiphenylsiloxane (PDPS), and
polymethylphenylsiloxane (PMPS)); and inorganic polymers (e.g.,
polyphosphazene, polyphosphonate, polysilanes, polysilazanes). In
some embodiments, the polymer may be selected from
poly(n-pentene-2), polypropylene, polytetrafluoroethylene,
polyamides (e.g., polyamide (Nylon), poly( -caprolactam) (Nylon 6),
poly(hexamethylene adipamide) (Nylon 66)), polyimides (e.g.,
polynitrile, and poly(pyromellitimide-1,4-diphenyl ether)
(Kapton.RTM.) (NOMEX.RTM.) (KEVLAR.RTM.)), polyether ether ketone
(PEEK), and combinations thereof.
[0109] The electrochemical cell may have any suitable shape. In
some cases, the electrochemical cell is cylindrical (e.g., a
sandwich of cathode, separator, and anode rolled into a single
spool). In certain cases, the electrochemical cell is prismatic. In
some embodiments, the electrochemical cell is a pouch cell. For
example, the anode and cathode of the electrochemical cell may be
sealed within a pouch formed from a polymer film, and the pouch may
be filled with an electrolyte (e.g., a liquid electrolyte). Metal
tabs (e.g., Ni, Al) may be attached to the anode and cathode for
electrical connection to an external electrical circuit.
[0110] A typical electrochemical cell also would include, of
course, current collectors, external circuitry, a housing
structure, and the like. Those of ordinary skill in the art are
well aware of the many arrangements that can be utilized with the
general schematic arrangement as shown in the figures and described
herein.
[0111] As noted elsewhere, the energy storage devices described
herein may be capable of achieving enhanced performance. For
example, certain of the electrochemical cells incorporating
lithium-ion-conductive layers may have reduced capacity fade rate
(e.g., loss of capacity per cycle) relative to electrochemical
cells lacking such lithium-ion-conductive layers but otherwise
including the same components. In some embodiments, the
electrochemical cell capacity decreases by less than about 5% per
charge and discharge cycle, less than about 2% per charge and
discharge cycle, less than about 1% per charge and discharge cycle,
less than about 0.8% per charge and discharge cycle, less than
about 0.6% per charge and discharge cycle, less than about 0.4% per
charge and discharge cycle, less than about 0.2% per charge and
discharge cycle, or less than about 0.1% per charge and discharge
cycle over at least about 2, at least about 10, at least about 20,
at least about 30, at least about 50, at least about 75, at least
about 100, at least about 125, or at least about 135 cycles
subsequent to a first charge and discharge cycle at a temperature
of at least about 25.degree. C., at least about 40.degree. C., or
at least about 60.degree. C. In some embodiments, the
electrochemical cell capacity decreases by more than about 0.1% per
charge and discharge cycle, more than about 0.2% per charge and
discharge cycle, more than about 0.4% per charge and discharge
cycle, more than about 0.6% per charge and discharge cycle, more
than about 0.8% per charge and discharge cycle, more than about 1%
per charge and discharge cycle, more than about 2% per charge and
discharge cycle, or more than about 5% per charge and discharge
cycle. Combinations of the above-noted ranges are also possible.
Capacity fade rate may be determined by measuring capacity during
each cycle of charge and discharge.
[0112] In some embodiments, an electrochemical cell comprising a
lithium-ion-conductive layer may exhibit a capacity fade rate that
is at least about 1%, at least about 5%, at least about 10%, at
least about 20%, at least about 50%, at least about 75%, or at
least about 100% lower than the capacity fade rate of an equivalent
electrochemical cell that does not comprise a
lithium-ion-conductive layer but otherwise includes the same
components.
[0113] In some embodiments, the electrochemical cells described
herein may exhibit relatively high capacities after repeated
cycling of the cell. For example, in some embodiments, after
alternately discharging and charging the cell five times, the cell
exhibits at least about 50%, at least about 80%, at least about
90%, or at least about 95% of the cell's initial capacity at the
end of the fifth cycle. In some cases, after alternately
discharging and charging the cell ten times, the cell exhibits at
least about 50%, at least about 80%, at least about 90%, or at
least about 95% of the cell's initial capacity at the end of the
tenth cycle. In still further cases, after alternately discharging
and charging the cell twenty-five times, the cell exhibits at least
about 50%, at least about 80%, at least about 90%, or at least
about 95% of the cell's initial capacity at the end of the
twenty-fifth cycle.
[0114] Some lithium-ion electrochemical cells may be susceptible to
self-discharge (e.g., discharge of the electrochemical cell (e.g.,
loss of capacity during storage of the electrochemical cell). In
some cases, the rate of self-discharge of certain of the
electrochemical cells described herein may be reduced relative to
electrochemical cells lacking lithium-ion-conductive layers but
otherwise including the same components. In certain cases, the
self-discharge rate of the electrochemical cell may be about 90% or
less, about 80% or less, about 70% or less, about 60% or less,
about 50% or less, about 40% or less, about 30% or less, about 20%
or less, or about 10% or less per week at 60.degree. C. In certain
embodiments, the self-discharge rate of the electrochemical cell
may be about 10% or more, about 20% or more, about 30% or more,
about 40% or more, about 50% or more, about 60% or more, about 70%
or more, about 80% or more, or about 90% or more per week at
60.degree. C. In some embodiments, the self-discharge rate of the
electrochemical cell may be about 90% or less, about 80% or less,
about 70% or less, about 60% or less, about 50% or less, about 40%
or less, about 30% or less, about 20% or less, or about 10% or less
per week at room temperature (e.g., about 25.degree. C.). In some
cases, the self-discharge rate of the electrochemical cell may be
about 10% or more, about 20% or more, about 30% or more, about 40%
or more, about 50% or more, about 60% or more, about 70% or more,
about 80% or more, or about 90% or more per week at room
temperature (e.g., about 25.degree. C.). Combinations of the
above-noted ranges are also possible.
[0115] In some embodiments, an electrochemical cell comprising a
lithium-ion-conductive layer may exhibit a self-discharge rate that
is at least about 1%, at least about 5%, at least about 10%, at
least about 20%, at least about 50%, at least about 75%, or at
least about 100% lower than the self-discharge rate of an
equivalent electrochemical cell that does not comprise a
lithium-ion-conductive layer but otherwise includes the same
components. Correspondingly, in certain cases, an electrochemical
cell comprising a lithium-ion-conductive layer may exhibit a
self-discharge rate that is less than about 100%, less than about
75%, less than about 50%, less than about 20%, less than about 20%,
less than about 10%, less than about 5%, or less than about 1%
lower than the self-discharge rate of an equivalent electrochemical
cell that does not comprise a lithium-ion-conductive layer but
otherwise includes the same components. Combinations of the
above-noted ranges are also possible.
[0116] In certain embodiments, an electrochemical cell comprising a
lithium-ion-conductive layer may experience a reduction in
irreversible capacity loss during storage and/or after the initial
discharge after storage. In some embodiments, the electrochemical
cell may experience a reduction in irreversible capacity loss upon
subsequent discharges as well (e.g., after recharging at room
temperature or elevated temperatures such as 50 degrees Celsius, or
other elevated temperatures described herein). For example, the
electrochemical cell may experience a reduction in irreversible
capacity loss or at least 5%, at least 10%, at least 20%, at least
30%, at least 40%, or at least 50% during storage, after initial
discharge, or after the 2.sup.nd, 3.sup.rd, 4.sup.th, 5.sup.th,
6.sup.th, 7.sup.th, 8.sup.th, 9.sup.th, or 10.sup.th discharge of
the electrochemical cell compared to that performed using a similar
electrochemical cell including similar components and amounts, but
without the lithium-ion-conductive layer (i.e., all other factors
being equal). In some embodiments, the reduction in irreversible
capacity loss may be less than or equal to 80%, less than or equal
to 60%, less than or equal to 40%, less than or equal to 20%, or
less than or equal to 10% during storage, after initial discharge,
or after the 2.sup.nd, 3.sup.rd, 4.sup.th, 5.sup.th, 6.sup.th,
7.sup.th, 8.sup.th, 9.sup.th, or 10.sup.th discharge of the
electrochemical cell compared to that performed using a similar
electrochemical cell but without the lithium-ion-conductive layer,
all other factors being equal. Combinations of the above-referenced
ranges are also possible.
[0117] In certain embodiments, an electrochemical cell comprising a
lithium-ion-conductive layer may experience a reduced rate of
impedance increase relative to electrochemical cells that do not
comprise a lithium-ion-conductive layer but otherwise include the
same components in the same amounts (i.e., all other factors being
equal). In some embodiments, an electrochemical cell comprising a
lithium-ion-conductive layer may have a rate of impedance increase
that is at least about 1%, at least about 5%, at least about 10%,
at least about 20%, at least about 50%, at least about 75%, or at
least about 100% lower than the rate of impedance increase of an
equivalent electrochemical cell that does not comprise a
lithium-ion-conductive layer but otherwise includes the same
components. In certain cases, an electrochemical cell comprising a
lithium-ion-conductive layer may have a rate of impedance increase
that is less than about 100%, less than about 75%, less than about
50%, less than about 20%, less than about 20%, less than about 10%,
less than about 5%, or less than about 1% lower than the rate of
impedance increase of an equivalent electrochemical cell that does
not comprise a lithium-ion-conductive layer but otherwise includes
the same components. Combinations of the above-noted ranges are
also possible.
[0118] In certain embodiments in which an electrochemical cell
comprises a first electrode (e.g., a lithium-intercalation
electrode) comprising a lithium-ion-conductive layer, a second
electrode (e.g., an intercalation electrode, a lithium metal
electrode), and an electrolyte, no species decomposed from the
first electrode or the electrolyte resides at the second electrode
after the electrochemical cell has undergone at least about 10
cycles, at least about 25 cycles, at least about 50 cycles, at
least about 75 cycles, at least about 100 cycles, at least about
125 cycles, at least about 150 cycles, at least about 175 cycles,
at least about 200 cycles, at least about 250 cycles, or at least
about 300 cycles. In some embodiments, no species decomposed from
the first electrode or the electrolyte resides at the second
electrode after the electrochemical cell has undergone less than or
equal to about 300 cycles, less than or equal to about 250 cycles,
less than or equal to about 200 cycles, less than or equal to about
175 cycles, less than or equal to about 150 cycles, less than or
equal to about 125 cycles, less than or equal to about 100 cycles,
less than or equal to about 75 cycles, less than or equal to about
50 cycles, less than or equal to about 25 cycles, or less than or
equal to about 10 cycles. Combinations of the above-noted ranges
are also possible. Species residing at the second electrode may be
detected, for example, through energy dispersive spectroscopy
(EDS).
[0119] Some embodiments may include electrochemical devices in
which the application of an anisotropic force is used to enhance
the performance of the device. Application of force to the
electrochemical cell may improve the cycling lifetime and
performance of the cell. Any of the electrode properties (e.g.,
porosities, average pore size, etc.) and/or performance metrics
outlined above may be achieved, alone or in combination with each
other, while an anisotropic force is applied to the electrochemical
cell (e.g., during charge and/or discharge of the cell). The
magnitude of the anisotropic force may lie within any of the ranges
mentioned below.
[0120] In some embodiments, the anisotropic force applied to the
energy storage device comprises a component normal to the active
surface of an electrode of the energy storage device (e.g., the
anode of a lithium-ion electrochemical cell). In the case of a
planar surface, the force may comprise an anisotropic force with a
component normal to the surface at the point at which the force is
applied. In the case of a curved surface, for example, a concave
surface or a convex surface, the force may comprise an anisotropic
force with a component normal to a plane that is tangent to the
curved surface at the point at which the force is applied. In some
embodiments, an anisotropic force with a component normal to the
active surface of the anode is applied during at least one period
of time during charge and/or discharge of the electrochemical cell.
In some embodiments, the force may be applied continuously, over
one period of time, or over multiple periods of time that may vary
in duration and/or frequency. The anisotropic force may be applied,
in some cases, at one or more pre-determined locations, optionally
distributed over the active surface of one or both electrodes. In
some embodiments, the anisotropic force is applied uniformly over
the active surface of an electrode.
[0121] An "anisotropic force" is given its ordinary meaning in the
art and means a force that is not equal in all directions. A force
equal in all directions is, for example, internal pressure of a
fluid or material within the fluid or material, such as internal
gas pressure of an object. Examples of forces not equal in all
directions include forces directed in a particular direction, such
as the force on a table applied by an object on the table via
gravity. Another example of an anisotropic force includes a force
applied by a band arranged around a perimeter of an object. For
example, a rubber band or turnbuckle can apply forces around a
perimeter of an object around which it is wrapped. However, the
band may not apply any direct force on any part of the exterior
surface of the object not in contact with the band. In addition,
when the band is expanded along a first axis to a greater extent
than a second axis, the band can apply a larger force in the
direction parallel to the first axis than the force applied
parallel to the second axis. A force with a "component normal" to a
surface, for example an active surface of an electrode, is given
its ordinary meaning as would be understood by those of ordinary
skill in the art and includes, for example, a force which at least
in part exerts itself in a direction substantially perpendicular to
the surface.
[0122] In some embodiments, an anisotropic force with a component
normal to the active surface of an electrode (e.g., a cathode) is
applied, during at least one period of time during charge and/or
discharge of the electrochemical cell. The component of the
anisotropic force normal to the electrode active surface may, for
example, define a pressure of at least about 5, at least about 10,
at least about 25, at least about 50, at least about 75, at least
about 100, at least about 120, at least about 150, at least about
175, at least about 200, at least about 225, or at least about 250
Newtons per square centimeter. In some embodiments, the component
of the anisotropic force normal to the electrode active surface
may, for example, define a pressure of less than about 250, less
than about 225, less than about 200, less than about 150, less than
about 120, less than about 100, less than about 50, less than about
25, or less than about 10 Newtons per square centimeter. In some
cases, the component of the anisotropic force normal to the anode
active surface is may define a pressure of between about 5 and
about 150 Newtons per square centimeter, between about 50 and about
120 Newtons per square centimeter, between about 70 and about 100
Newtons per square centimeter, between about 80 and about 110
Newtons per square centimeter, between about 5 and about 250
Newtons per square centimeter, between about 50 and about 250
Newtons per square centimeter, between about 80 and about 250
Newtons per square centimeter, between about 90 and about 250
Newtons per square centimeter, or between about 100 and about 250
Newtons per square centimeter. While forces and pressures are
generally described herein in units of Newtons and Newtons per unit
area, respectively, forces and pressures can also be expressed in
units of kilograms-force and kilograms-force per unit area,
respectively. One of ordinary skill in the art will be familiar
with kilogram-force-based units, and will understand that 1
kilogram-force (kgf) is equivalent to about 9.8 Newtons.
[0123] Some embodiments relate to methods involving one or more
components described herein. In some embodiments, a method
comprises cycling an electrochemical cell comprising a first
electrode (e.g., a lithium intercalation electrode, a lithium
conversion electrode), a second electrode, and an electrolyte.
According to certain embodiments, the first electrode comprises a
layer comprising an electroactive material integrated with an
inorganic lithium-ion-conductive layer. Certain advantages
described herein (e.g., increased cycle life, reducing electrolyte
loss, inhibition of certain species from residing at an electrode)
may be achieved during such cycling.
[0124] In some embodiments, the method comprises cycling the
electrochemical cell at a temperature of at least about 20 degrees
Celsius, at least about 25 degrees Celsius, at least about 30
degrees Celsius, at least about 35 degrees Celsius, at least about
40 degrees Celsius, at least about 45 degrees Celsius, at least
about 50 degrees Celsius, at least about 55 degrees Celsius, or at
least about 60 degrees Celsius, at least 65 degrees Celsius. In
some embodiments, the method comprises cycling the electrochemical
cell at a temperature of less than or equal to about 70 degrees
Celsius, less than or equal to about 65 degrees Celsius, less than
or equal to about 60 degrees Celsius, less than or equal to about
55 degrees Celsius, less than or equal to about 50 degrees Celsius,
less than or equal to about 45 degrees Celsius, less than or equal
to about 40 degrees Celsius, less than or equal to about 35 degrees
Celsius, less than or equal to about 30 degrees Celsius, less than
or equal to about 25 degrees Celsius, or less than or equal to
about 20 degrees Celsius. Combinations of the above-referenced
ranges are also possible.
[0125] In some embodiments, the method comprises cycling the
electrochemical cell with an end-of-charge voltage of at least
about 4.2 V, at least about 4.3 V, at least about 4.4 V, or at
least about 4.5 V, at least about 4.6 V, at least about 4.7 V, at
least about 4.8 V, or at least about 4.9 V. In some embodiments,
the method comprises cycling the electrochemical cell with an
end-of-charge voltage of about 5.0 V or less, about 4.9 V or less,
about 4.8 V or less, about 4.7 V or less, about 4.6 V or less,
about 4.5 V or less, about 4.4 V or less, about 4.3 V or less, or
about 4.2 V or less. Combinations of the above-referenced ranges
are also possible.
[0126] In certain embodiments, the electrochemical cell is cycled
for at least about 10 cycles, at least about 25 cycles, at least
about 50 cycles, at least about 75 cycles, at least about 100
cycles, at least about 125 cycles, at least about 150 cycles, at
least about 175 cycles, at least about 200 cycles, at least about
250 cycles, or at least about 300 cycles. In some embodiments, the
electrochemical cell is cycled for less than or equal to about 300
cycles, less than or equal to about 250 cycles, less than or equal
to about 200 cycles, less than or equal to about 175 cycles, less
than or equal to about 150 cycles, less than or equal to about 125
cycles, less than or equal to about 100 cycles, less than or equal
to about 75 cycles, less than or equal to about 50 cycles, less
than or equal to about 25 cycles, or less than or equal to about 10
cycles. Combinations of the above-noted ranges are also
possible.
[0127] In some embodiments, a method comprises substantially
inhibiting a species decomposed from the first electrode, or a
species decomposed from the electrolyte, from residing at the
second electrode. In some embodiments, the method comprises
substantially inhibiting the species from depositing on the second
electrode.
[0128] According to some embodiments, the method comprises
inhibiting a species decomposed from the first electrode or from
the electrolyte from residing at the second electrode at a
temperature of at least about 20 degrees Celsius, at least about 25
degrees Celsius, at least about 30 degrees Celsius, at least about
35 degrees Celsius, at least about 40 degrees Celsius, at least
about 45 degrees Celsius, or at least about 50 degrees Celsius. In
some embodiments, the method comprises inhibiting a species
decomposed from the first electrode or from the electrolyte from
residing at the second electrode at a temperature of less than or
equal to about 50 degrees Celsius, less than or equal to about 45
degrees Celsius, less than or equal to about 40 degrees Celsius,
less than or equal to about 35 degrees Celsius, less than or equal
to about 30 degrees Celsius, less than or equal to about 25 degrees
Celsius, or less than or equal to about 20 degrees Celsius.
Combinations of the above-noted ranges are also possible.
[0129] Some embodiments are directed to methods of fabricating
electrodes and/or electrochemical cells. In some embodiments, the
method comprises the step of depositing a lithium-ion-conductive
layer on an electroactive-material-containing layer. The depositing
step may be performed using any suitable method, including, but not
limited to, electron beam evaporation, chemical vapor deposition
(CVD), plasma-enhanced chemical vapor deposition (PECVD),
laser-enhanced chemical vapor deposition, thermal evaporation
(including, but not limited to, resistive, inductive, radiation,
and electron beam heating), aerosol deposition, sputtering
(including, but not limited to, diode, DC magnetron, RF, RF
magnetron, pulsed, dual magnetron, AC, MF, and reactive), laser
ablation, ion plating, cathodic arc, and jet vapor deposition. The
technique used may depend on a variety of factors, including the
type of material being deposited, the thickness of the layer, and
the underlying layer on which the lithium-ion-conductive layer is
deposited. For example, aerosol deposition may be utilized to
deposit a lithium-ion-conductive layer comprising ceramics having a
crystalline structure, such as Li.sub.10GeP.sub.2S.sub.12 and/or
Li.sub.7La.sub.3Zr.sub.2O.sub.12.
[0130] In some embodiments, methods described herein further
comprise exposing at least a portion of the anode and/or the
cathode to the electrolyte. In some embodiments, methods described
herein further comprise exposing at least a portion of the
electroactive material of the anode and/or the electroactive
material of the cathode to the electrolyte.
[0131] The following documents are incorporated herein by reference
in their entireties for all purposes: U.S. Pat. No. 7,247,408,
filed May 23, 2001, entitled "Lithium Anodes for Electrochemical
Cells"; U.S. Pat. No. 5,648,187, filed Mar. 19, 1996, entitled
"Stabilized Anode for Lithium-Polymer Batteries"; U.S. Pat. No.
5,961,672, filed Jul. 7, 1997, entitled "Stabilized Anode for
Lithium-Polymer Batteries"; U.S. Pat. No. 5,919,587, filed May 21,
1997, entitled "Novel Composite Cathodes, Electrochemical Cells
Comprising Novel Composite Cathodes, and Processes for Fabricating
Same"; U.S. patent application Ser. No. 11/400,781, filed Apr. 6,
2006, published as U. S. Pub. No. 2007-0221265, and entitled
"Rechargeable Lithium/Water, Lithium/Air Batteries"; International
Patent Apl. Serial No.: PCT/US2008/009158, filed Jul. 29, 2008,
published as International Pub. No. WO/2009017726, and entitled
"Swelling Inhibition in Lithium Batteries"; U.S. patent application
Ser. No. 12/312,764, filed May 26, 2009, published as U.S. Pub. No.
2010-0129699, and entitled "Separation of Electrolytes";
International Patent Apl. Serial No.: PCT/US2008/012042, filed Oct.
23, 2008, published as International Pub. No. WO/2009054987, and
entitled "Primer for Battery Electrode"; U.S. patent application
Ser. No. 12/069,335, filed Feb. 8, 2008, published as U.S. Pub. No.
2009-0200986, and entitled "Protective Circuit for Energy-Storage
Device"; U.S. patent application Ser. No. 11/400,025, filed Apr. 6,
2006, published as U.S. Pub. No. 2007-0224502, and entitled
"Electrode Protection in both Aqueous and Non-Aqueous
Electrochemical Cells, including Rechargeable Lithium Batteries";
U.S. patent application Ser. No. 11/821,576, filed Jun. 22, 2007,
published as U.S. Pub. No. 2008/0318128, and entitled "Lithium
Alloy/Sulfur Batteries"; patent application Ser. No. 11/111,262,
filed Apr. 20, 2005, published as U.S. Pub. No. 2006-0238203, and
entitled "Lithium Sulfur Rechargeable Battery Fuel Gauge Systems
and Methods"; U.S. patent application Ser. No. 11/728,197, filed
Mar. 23, 2007, published as U.S. Pub. No. 2008-0187663, and
entitled "Co-Flash Evaporation of Polymerizable Monomers and
Non-Polymerizable Carrier Solvent/Salt Mixtures/Solutions";
International Patent Apl. Serial No.: PCT/US2008/010894, filed Sep.
19, 2008, published as International Pub. No. WO/2009042071, and
entitled "Electrolyte Additives for Lithium Batteries and Related
Methods"; International Patent Apl. Serial No.: PCT/US2009/000090,
filed Jan. 8, 2009, published as International Pub. No.
WO/2009/089018, and entitled "Porous Electrodes and Associated
Methods"; U.S. patent application Ser. No. 12/535,328, filed Aug.
4, 2009, published as U.S. Pub. No. 2010/0035128, and entitled
"Application of Force In Electrochemical Cells"; U.S. patent
application Ser. No. 12/727,862, filed Mar. 19, 2010, entitled
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12/471,095, filed May 22, 2009, entitled "Hermetic Sample Holder
and Method for Performing Microanalysis Under Controlled Atmosphere
Environment"; U.S. patent application Ser. No. 12/862,513, filed on
Aug. 24, 2010, entitled "Release System for Electrochemical cells
(which claims priority to Provisional Patent Apl. Ser. No.
61/236,322, filed Aug. 24, 2009, entitled "Release System for
Electrochemical Cells"); U.S. patent application Ser. No.
13/216,559, filed on Aug. 24, 2011, published as U.S. Patent
Publication No. 2012/0048729, entitled "Electrically Non-Conductive
Materials for Electrochemical Cells;" U.S. Provisional Patent Apl.
Ser. No. 61/376,554, filed on Aug. 24, 2010, entitled "Electrically
Non-Conductive Materials for Electrochemical Cells;" U.S. patent
application Ser. No. 12/862,528, filed on Aug. 24, 2010, published
as U.S. Patent Publication No. 2011/0177398, entitled
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12/862,563, filed on Aug. 24, 2010, published as U.S. Pub. No.
2011/0070494, entitled "Electrochemical Cells Comprising Porous
Structures Comprising Sulfur" [S1583.70029US00]; U.S. patent
application Ser. No. 12/862,551, filed on Aug. 24, 2010, published
as U.S. Pub. No. 2011/0070491, entitled "Electrochemical Cells
Comprising Porous Structures Comprising Sulfur" [51583.70030US00];
U.S. patent application Ser. No. 12/862,576, filed on Aug. 24,
2010, published as U.S. Pub. No. 2011/0059361, entitled
"Electrochemical Cells Comprising Porous Structures Comprising
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12/862,581, filed on Aug. 24, 2010, published as U.S. Pub. No.
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application Ser. No. 13/240,113, filed on Sep. 22, 2011, published
as U.S. Patent Pub. No. 2012/0070746, entitled "Low Electrolyte
Electrochemical Cells"; U.S. Patent Apl. Ser. No. 61/385,343, filed
on Sep. 22, 2010, entitled "Low Electrolyte Electrochemical Cells";
and U.S. patent application Ser. No. 13/033,419, filed Feb. 23,
2011, published as U.S. Patent Pub. No. 2011/0206992, entitled
"Porous Structures for Energy Storage Devices" [51583.70034US00];
U.S. patent application Ser. No. 13/789,783, filed Mar. 9, 2012,
published as U.S. Patent Pub. No. 2013/0252103, and entitled
"Porous Support Structures, Electrodes Containing Same, and
Associated Methods"; U.S. patent Pub. Ser. No. 13/644,933, filed
Oct. 4, 2012, published as U.S. Patent Pub. No. 2013/0095380, and
entitled "Electrode Structure and Method for Making the Same"
[51583.70044US01]; U.S. patent application Ser. No. 14/150,156,
filed Jan. 8, 2014, and entitled "Conductivity Control in
Electrochemical Cells" [51583.70049US01]; U.S. patent application
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Structures for Electrodes" [51583.70051US00]; U.S. patent
application Ser. No. 14/209,274, filed Mar. 13, 2014, published as
U.S. Patent Pub. No. 2014/0272597 and entitled "Protected Electrode
Structures and Methods" [S1583.70052US01]; U.S. patent application
Ser. No. 14/150,196, published as U.S. Patent Pub. No.
2014/0193713, filed Jan. 8, 2014, entitled, "Passivation of
Electrodes in Electrochemical Cells" [51583.70058US01]; U.S. patent
application Ser. No. 14/552,608, published as U.S. Patent Apl. No.:
2015/0086837, filed Nov. 25, 2014, entitled "Ceramic/Polymer Matrix
for Electrode Protection in Electrochemical Cells, including
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application Ser. No. 14/455,230, published as U.S. Patent Pub. No.
2015/0044517, filed Aug. 8, 2014, and entitled "Self-Healing
Electrode Protection in Electrochemical Cells" [51583.70064US01];
U.S. patent application Ser. No. 14/184,037, published as U.S.
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"Electrode Protection Using Electrolyte-Inhibiting Ion Conductor"
[S1583.70065US01]. All other patents and patent applications
disclosed herein are also incorporated by reference in their
entirety for all purposes.
[0132] The following examples are intended to illustrate certain
embodiments of the present invention, but do not exemplify the full
scope of the invention.
Example 1
[0133] This example describes the fabrication and testing of
electrochemical cells comprising an anode, a cathode coated with a
lithium-ion-conductive ceramic, and a porous separator positioned
between the anode and the cathode.
[0134] In the electrochemical cell, the anode was graphite, and a
10 .mu.m Cu foil acted as a substrate and current collector. The
porous separator was a 25 .mu.m-thick layer of polyolefin (Celgard
2325). The cathode was lithium iron phosphate (LFP) coated on an
aluminum substrate. The cathode had a capacity of about 1.21
mAh/cm.sup.2. Lithium oxide was coated on the LFP cathode by vacuum
deposition, in which oxygen-containing gas was reacted with lithium
vapor. In both the anode and the cathode, PVDF was used as a
binder.
[0135] The above components were assembled in a single-layer cell,
with the separator positioned between the anode and the cathode,
and the cell components were placed in a foil pouch. The total
active cathode surface area was 16.574 cm.sup.2. 0.3 mL of LP30
electrolyte (44.1% dimethyl carbonate, 44.1% ethylene carbonate,
11.8% lithium hexafluorophosphate) was added to the foil pouch, and
the cell package was then vacuum sealed. The cell was allowed to
soak with the electrolyte for 24 hours unrestrained, and then 10
kg/cm.sup.2 pressure was applied. The cell was cycled under the 10
kg/cm.sup.2 pressure.
[0136] Charge and discharge cycling was performed at standard C/8
(2.5 mA) and C/5 rates (4 mA), respectively, with a charge cutoff
voltage of 4.2 V followed by taper at 4.2 V to 0.5 mA, and a
discharge cutoff voltage of 2.5 V. The cell was cycled at room
temperature for 5 cycles. From the 6.sup.th cycle, the cell was
cycled at 50.degree. C.
[0137] FIG. 8A shows an SEM image of the cross-sectional view of
the lithium oxide-coated LFP cathode before cycling, and FIG. 8B
shows an SEM image of the cathode after approximately 70 cycles.
From FIGS. 8A-8B, it appears that the lithium oxide ceramic coating
remained intact after approximately 70 cycles.
Comparative Example 1
[0138] This comparative example describes the fabrication and
testing of control cells comprising an uncoated graphite anode and
an uncoated LFP cathode. The materials and procedures presented in
Example 1 were used and followed, except the LFP cathode was not
coated with a lithium-ion-conductive ceramic material.
[0139] FIG. 7 shows that the discharge capacity fade rate at
50.degree. C. cycling temperature for the electrochemical cells
from Example 1 (702) was considerably improved compared to the rate
for the electrochemical cells from Comparative Example 1 (704).
FIGS. 9A-9B show energy-dispersive spectroscopy (EDS) spectra of
the graphite anode from an electrochemical cell of Comparative
Example 1 (9A) and an electrochemical cell of Example 1 (9B).
Although there was no notable difference in morphology between the
control cell and ceramic-coated LFP cell, as indicated by SEM (FIG.
8), EDS detected Fe on the graphite anode of the control cell,
while Fe was absent on the graphite anode from the ceramic-coated
LFP cell. This result suggests lithium oxide inhibited the Fe
dissolution from LFP and subsequent reduction on the graphite
anode, and therefore improved the capacity fade rate.
Example 2
[0140] This example describes the fabrication and testing of
electrochemical cells comprising an oxysulfide-coated LFP
cathode.
[0141] The materials and procedures presented in Example 1 were
used and followed, except the LFP cathode was coated with
oxysulfide instead of lithium oxide. A 0.5 .mu.m-thick coating of
oxysulfide ceramic was sputtered on LFP electrodes. FIG. 10 shows
improved discharge capacity fade rate in the cells containing
oxysulfide-coated LFP (1000) relative to the control cells of
Comparative Example 1 (1020).
Example 3
[0142] This example describes the fabrication and testing of
electrochemical cells comprising a lithium oxide-coated LFP
cathode.
[0143] A 2 .mu.m-thick lithium oxide layer was vacuum deposited on
LFP electrodes. The cells were built in the same manner as in
Example 1 and cycled at room temperature for 5 cycles. The fully
charged cells were stored at 60.degree. C. for a week and then
cycled at room temperature. The control cells with regular LFP
cathodes were built and cycled/stored the same way. As shown in
FIG. 11, 100% self-discharge was observed from the control cells of
Comparative Example 1 (1120). In the presence of lithium oxide
ceramic coating on the LFP cathodes, cell self-discharge was
reduced to 56% (1100).
Example 4
[0144] This example describes the fabrication and testing of
electrochemical cells comprising a lithium oxide-coated anode.
[0145] A 2 .mu.m-thick lithium oxide layer was vacuum deposited on
graphite electrodes. The cells were built in the same manner as in
Example 1 and cycled at room temperature for 5 cycles. The fully
charged cells were stored at 60.degree. C. for a week and then
further cycled at room temperature. As shown in FIG. 12, 100%
self-discharge was observed from the control cells of Comparative
Example 1 (1220). In the presence of lithium oxide ceramic coating
on the graphite anode, cell self-discharge was reduced to 91%
(1200).
Example 5
[0146] This example describes the fabrication and testing of
electrochemical cells comprising a lithium oxide-coated graphite
anode and a lithium oxide-coated LFP cathode.
[0147] A 2 .mu.m layer of lithium oxide was vacuum deposited on
graphite electrodes and on LFP electrodes. The cells using
oxide-coated graphite and oxide-coated LFP were built in the same
manner as in Example 1 and cycled at room temperature for 5 cycles.
The fully charged cells were then stored at 60.degree. C. for a
week and then further cycled at room temperature. As shown in FIG.
13, 100% self-discharge was observed from the control cells of
Comparative Example 1 (1320). In the presence of lithium oxide
ceramic coating on both the graphite and LFP electrodes, cell
self-discharge was reduced to 55% (1300).
Example 6
[0148] This example describes the fabrication and testing of
electrochemical cells comprising a lithium oxide-coated anode and a
lithium oxide-coated NMC cathode.
[0149] A 2 .mu.m layer of lithium oxide was vacuum deposited on
graphite electrodes and on NMC electrodes. The cells using
oxide-coated graphite and oxide-coated NMC were built in the same
manner as in Example 1. Charge and discharge cycling was performed
at standard C/8 (3.3 mA) and C/5 rates (5.2 mA), respectively, with
a charge cutoff voltage of 4.2 V and a discharge cutoff voltage of
3.2 V. The cells were cycled at room temperature for 5 cycles. The
fully charged cells were stored at 60.degree. C. for a week and
then further cycled at room temperature. Control cells with regular
graphite and NMC electrodes were built and cycled/stored the same
way. As shown in FIG. 14, 41% self-discharge was observed from the
control cells (1420). In the presence of lithium oxide ceramic
coating on both graphite and NMC, cell self-discharge was reduced
to 30% (1400).
Example 7
[0150] This example describes the fabrication and testing of
electrochemical cells comprising an oxysulfide-coated LFP
cathode.
[0151] A 1 .mu.m layer of electron-beamed oxysulfide ceramic was
coated on LFP electrodes as the protective Li-ion conducting
ceramic. FIG. 15 shows improved discharge capacity fade rate in the
cells containing oxysulfide-coated LFP relative to the control
cells with uncoated LFP. Furthermore, from FIG. 15, it can be seen
that a 1 .mu.m oxysulfide coating (1500) improved the capacity fade
rate more than those containing a 0.5 .mu.m oxysulfide coating
(1520) or those not containing a coating (1540).
Example 8
[0152] This example describes the fabrication and testing of
electrochemical cells comprising an oxysulfide-coated LFP
cathode.
[0153] A 1 .mu.m layer of electron-beamed oxysulfide ceramic was
coated on LFP electrodes as the protective Li-ion conducting
ceramic. The cells were built in the same manner and cycled at room
temperature for 5 cycles. The fully charged cells were stored at
60.degree. C. for a week and then further cycled at room
temperature. The control cells with regular graphite and LFP
electrodes were built and cycled/stored the same way. As shown in
FIG. 16, 100% self-discharge was observed from the control cells
(1620). In the presence of a 1 .mu.m lithium oxysulfide ceramic
coating on LFP, cell self-discharge was reduced to 78% (1600).
Example 9
[0154] This example describes the fabrication and testing of
electrochemical cells comprising an oxysulfide-coated graphite
anode.
[0155] A 1 .mu.m layer of electron-beamed lithium oxysulfide was
vacuum deposited on graphite electrodes. The cells were built in
the same manner and cycled at room temperature for 5 cycles. The
fully charged cells were stored at 60.degree. C. for a week and
then further cycled at room temperature. The control cells with
regular graphite and LFP electrodes were built and cycled/stored
the same way. As shown in FIG. 17, 100% self-discharge was observed
from the control cells (1720). In the presence of lithium
oxysulfide ceramic coating on graphite, cell self-discharge was
reduced to 84% (1700).
Example 10
[0156] This example describes the fabrication and testing of
electrochemical cells comprising a graphite anode and an NCM
cathode coated with a substantially porous lithium oxide layer.
[0157] FIG. 18A shows an SEM image of an uncoated NCM cathode. A 1
.mu.m-thick lithium oxide layer was coated on the NCM cathode by
vacuum deposition as a protective lithium-ion-conductive ceramic
layer. FIG. 18B shows an SEM image of the NCM cathode with the
lithium oxide ceramic coating. From FIG. 18B, it can be seen that
the lithium oxide ceramic coating is porous.
[0158] The electrochemical cells included an LP30 electrolyte
composed of 44.1% dimethyl carbonate, 44.1% ethylene carbonate,
11.8% lithium hexafluorophosphate.
[0159] The electrochemical cells were cycled at room temperature
for 5 cycles and at 50.degree. C. starting from the 6.sup.th cycle.
FIG. 19 shows improved discharge capacity fade rate in the
electrochemical cells comprising the lithium-oxide-coated NCM
cathode (1900) relative to control electrochemical cells with the
uncoated NCM cathode (1910).
[0160] FIGS. 20A-20B show EDS spectra and SEM images (inset) of the
graphite anode from an electrochemical cell with an uncoated NCM
electrode after 179 cycles (FIG. 20A) and an electrochemical cell
with a lithium-oxide-coated NCM electrode after 191 cycles (FIG.
20B). From the EDS spectra in FIGS. 20A-20B, it can be seen that
EDS detected Mn on the graphite anode of the cell with the uncoated
NCM electrode but not on the graphite anode of the cell with the
lithium-oxide-coated NCM electrode. This result suggests that the
porous lithium oxide coating on the NCM cathode inhibited Mn
corrosion from the NCM cathode and its subsequent reduction on the
graphite anode. This may also have improved the capacity fade rate
of the electrochemical cell with the lithium-oxide-coated NCM
cathode.
[0161] While several embodiments of the present invention have been
described and illustrated herein, those of ordinary skill in the
art will readily envision a variety of other means and/or
structures for performing the functions and/or obtaining the
results and/or one or more of the advantages described herein, and
each of such variations and/or modifications is deemed to be within
the scope of the present invention. More generally, those skilled
in the art will readily appreciate that all parameters, dimensions,
materials, and configurations described herein are meant to be
exemplary and that the actual parameters, dimensions, materials,
and/or configurations will depend upon the specific application or
applications for which the teachings of the present invention
is/are used. Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. 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
and claimed. The present invention is directed to each individual
feature, system, article, material, and/or method described herein.
In addition, any combination of two or more such features, systems,
articles, materials, and/or methods, if such features, systems,
articles, materials, and/or methods are not mutually inconsistent,
is included within the scope of the present invention.
[0162] The indefinite articles "a" and "an," as used herein in the
specification and in the claims, unless clearly indicated to the
contrary, should be understood to mean "at least one."
[0163] The phrase "and/or," as used herein in the specification and
in the claims, should be understood to mean "either or both" of the
elements so conjoined, i.e., elements that are conjunctively
present in some cases and disjunctively present in other cases.
Other elements may optionally be present other than the elements
specifically identified by the "and/or" clause, whether related or
unrelated to those elements specifically identified unless clearly
indicated to the contrary. Thus, as a non-limiting example, a
reference to "A and/or B," when used in conjunction with open-ended
language such as "comprising" can refer, in one embodiment, to A
without B (optionally including elements other than B); in another
embodiment, to B without A (optionally including elements other
than A); in yet another embodiment, to both A and B (optionally
including other elements); etc.
[0164] As used herein in the specification and in the claims, "or"
should be understood to have the same meaning as "and/or" as
defined above. For example, when separating items in a list, "or"
or "and/or" shall be interpreted as being inclusive, i.e., the
inclusion of at least one, but also including more than one, of a
number or list of elements, and, optionally, additional unlisted
items. Only terms clearly indicated to the contrary, such as "only
one of" or "exactly one of," or, when used in the claims,
"consisting of," will refer to the inclusion of exactly one element
of a number or list of elements. In general, the term "or" as used
herein shall only be interpreted as indicating exclusive
alternatives (i.e. "one or the other but not both") when preceded
by terms of exclusivity, such as "either," "one of," "only one of,"
or "exactly one of." "Consisting essentially of," when used in the
claims, shall have its ordinary meaning as used in the field of
patent law.
[0165] As used herein in the specification and in the claims, the
phrase "at least one," in reference to a list of one or more
elements, should be understood to mean at least one element
selected from any one or more of the elements in the list of
elements, but not necessarily including at least one of each and
every element specifically listed within the list of elements and
not excluding any combinations of elements in the list of elements.
This definition also allows that elements may optionally be present
other than the elements specifically identified within the list of
elements to which the phrase "at least one" refers, whether related
or unrelated to those elements specifically identified. Thus, as a
non-limiting example, "at least one of A and B" (or, equivalently,
"at least one of A or B," or, equivalently "at least one of A
and/or B") can refer, in one embodiment, to at least one,
optionally including more than one, A, with no B present (and
optionally including elements other than B); in another embodiment,
to at least one, optionally including more than one, B, with no A
present (and optionally including elements other than A); in yet
another embodiment, to at least one, optionally including more than
one, A, and at least one, optionally including more than one, B
(and optionally including other elements); etc.
[0166] In the claims, as well as in the specification above, all
transitional phrases such as "comprising," "including," "carrying,"
"having," "containing," "involving," "holding," and the like are to
be understood to be open-ended, i.e., to mean including but not
limited to. Only the transitional phrases "consisting of" and
"consisting essentially of" shall be closed or semi-closed
transitional phrases, respectively, as set forth in the United
States Patent Office Manual of Patent Examining Procedures, Section
2111.03.
* * * * *