U.S. patent application number 16/563791 was filed with the patent office on 2020-03-12 for electrode with conductive interlayer and method thereof.
The applicant listed for this patent is Sila Nanotechnologies, Inc.. Invention is credited to Mareva FEVRE, Adam KAJDOS, Jens STEIGER, Weimin WANG, Justin YEN, Gleb YUSHIN, Eniko ZSOLDOS.
Application Number | 20200083542 16/563791 |
Document ID | / |
Family ID | 69720077 |
Filed Date | 2020-03-12 |
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United States Patent
Application |
20200083542 |
Kind Code |
A1 |
YUSHIN; Gleb ; et
al. |
March 12, 2020 |
ELECTRODE WITH CONDUCTIVE INTERLAYER AND METHOD THEREOF
Abstract
In an embodiment, a Li-ion battery electrode comprises a
conductive interlayer arranged between a current collector and an
electrode active material layer. The conductive interlayer
comprises first conductive additives and a first polymer binder,
and the electrode active material layer comprises a plurality of
active material particles mixed with a second polymer binder (which
may be the same as or different from the first polymer binder) and
second conductive additives (which may be the same as or different
from the first conductive additives). In a further embodiment, the
Li-ion battery electrode may be fabricated via application of
successive slurry formulations onto the current collector, with the
resultant product then being calendared (or densified).
Inventors: |
YUSHIN; Gleb; (Atlanta,
GA) ; YEN; Justin; (Alameda, CA) ; STEIGER;
Jens; (Alameda, CA) ; ZSOLDOS; Eniko;
(Waterloo, CA) ; FEVRE; Mareva; (Oakland, CA)
; KAJDOS; Adam; (Alameda, CA) ; WANG; Weimin;
(San Mateo, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sila Nanotechnologies, Inc. |
Alameda |
CA |
US |
|
|
Family ID: |
69720077 |
Appl. No.: |
16/563791 |
Filed: |
September 6, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62728025 |
Sep 6, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/386 20130101;
H01M 4/661 20130101; H01M 4/8828 20130101; H01M 4/1395 20130101;
H01M 10/0525 20130101; H01M 4/625 20130101; H01M 4/668 20130101;
H01M 4/622 20130101; H01M 4/663 20130101; H01M 4/667 20130101; H01M
4/134 20130101 |
International
Class: |
H01M 4/88 20060101
H01M004/88; H01M 10/0525 20060101 H01M010/0525; H01M 4/62 20060101
H01M004/62; H01M 4/38 20060101 H01M004/38 |
Claims
1. A Li-ion battery electrode, comprising: a current collector; a
conductive interlayer arranged on the current collector, the
conductive interlayer including first conductive additives and a
first polymer binder; and an electrode active material layer
arranged on the conductive interlayer, the electrode active
material layer including a plurality of active material particles
mixed with a second polymer binder and second conductive additives,
the plurality of active material particles exhibiting an average
particle size in the range from about 0.2 microns to about 10
microns, an average volume expansion in the range of about 8 vol. %
to about 180 vol. % during one or more charge-discharge cycles of
the Li-ion battery cell, and an average areal capacity loading in
the range of about 3 mAh/cm.sup.2 to about 12 mAh/cm.sup.2.
2. The battery electrode of claim 1, wherein the first polymer
binder comprises at least one component of the second polymer
binder.
3. The battery electrode of claim 1, wherein the first conductive
additives comprise at least one component of the second conductive
additives.
4. The battery electrode of claim 1, wherein the plurality of
active material particles comprise Si.
5. The battery electrode of claim 1, wherein the electrode active
material layer comprises water-soluble or water-dispersible
binders.
6. The battery electrode of claim 1, wherein the electrode active
material layer comprises a plurality of binder components.
7. The battery electrode of claim 5, wherein at least one of the
plurality of binder components comprises particles or fibers of an
elastomeric material with a maximum elongation in the range from
about 50% to about 5,000%.
8. The battery electrode of claim 7, wherein the particles or
fibers of the elastomeric material comprise around 60 wt. % to
around 95 wt. % of all binder in the electrode active material
layer.
9. The battery electrode of claim 7, wherein a smallest average
dimension of the particles or fibers of the elastomeric material
ranges from around 30 nm to around 600 nm.
10. The battery electrode of claim 1, wherein the second conductive
additives comprise single walled, double-walled and/or multi-walled
carbon nanotubes.
11. The battery electrode of claim 10, wherein a weight fraction of
all carbon nanotubes of the second conductive additives ranges from
around 0.1 wt. % to around 5 wt. % of the electrode active material
layer.
12. The battery electrode of claim 1, wherein the first conductive
additives single walled, double-walled and/or multi-walled carbon
nanotubes.
13. The battery electrode of claim 12, wherein a weight fraction of
all carbon nanotubes of the first conductive additives ranges from
around 0.1 wt. % to around 5 wt. %.
14. The battery electrode of claim 1, wherein a first weight
fraction of the first conductive additives in the conductive
interlayer exceeds a second weight fraction of the second
conductive additives in the electrode active material layer by at
least about 2 times.
15. The battery electrode of claim 1, wherein, upon separation of
the current collector from the conductive interlayer, Raman
spectroscopy mapping detects at least about 2 times more conductive
additives on an exposed surface of the separated current collector
or an exposed surface of the separated conductive interlayer than a
top surface of the electrode active material layer.
16. The battery electrode of claim 1, wherein an average thickness
of the conductive interlayer ranges from around 25 nm to around 500
nm.
17. The battery electrode of claim 1, wherein a current collector
is a metal foil with a thickness in the range from around 4 micron
to around 15 micron.
18. A Li-ion battery comprising the battery electrode of claim
1.
19. A process of manufacturing of a Li-ion battery electrode,
comprising: mixing a first polymer binder, a first solvent and
first conductive additives to form a first uniform conductive
interlayer slurry; coating a current collector with the first
slurry at a first thickness to form a conductive interlayer; drying
the first slurry coating to attain a conductive interlayer on the
current collector; mixing a second polymer binder, a second
solvent, second conductive additives and active material particles
to form a second uniform active material slurry; coating the
conductive interlayer with the second slurry at a second thickness;
drying the second slurry coating to attain an electrode active
material layer; and calendaring the conductive interlayer and/or
the electrode active material layer until a desired density is
achieved.
20. The method of claim 19, wherein the first polymer binder
comprises at least one component of the second polymer binder.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn. 119
[0001] The present application for patent claims the benefit of
U.S. Provisional Application No. 62/728,025, entitled
"HIGH-CAPACITY BATTERY ELECTRODES WITH IMPROVED BINDERS,
CONSTRUCTION, AND PERFORMANCE," filed Sep. 6, 2018, which is
expressly incorporated herein by reference in its entirety.
BACKGROUND
Field
[0002] The present disclosure relates generally to energy storage
devices, and more particularly to battery technology and the
like.
Background
[0003] Owing in part to their relatively high energy densities,
relatively high specific energy, light weight, and potential for
long lifetimes, advanced rechargeable batteries are desirable for a
wide range of consumer electronics, electric vehicle, grid storage
and other important applications.
[0004] However, despite the increasing commercial prevalence of
batteries, further development of these batteries is needed,
particularly for potential applications in low- or zero-emission,
hybrid-electrical or fully-electrical vehicles, consumer
electronics, energy-efficient cargo ships and locomotives,
aerospace applications, and power grids. In particular, further
improvements are desired for various rechargeable batteries, such
as rechargeable metal and metal-ion batteries (such as rechargeable
Li and Li-ion batteries, rechargeable Na and Na-ion batteries,
rechargeable Mg and Mg-ion batteries, etc.), rechargeable aqueous
batteries, rechargeable alkaline batteries, rechargeable metal
hydride batteries, and lead acid batteries, to name a few.
[0005] A broad range of active (charge-storing) materials, a broad
range of polymer binders, a broad range of conductive additives and
various mixing recipes may be utilized in the construction of
battery electrodes. However, for improved electrode performance
(low and stable resistance, high cycling stability, high rate
capability, etc.), the optimal choice of binders, additives, and
mixing protocols needs to be determined for specific types and
specific sizes of active particles. In many cases, these choices
are not trivial and can be counter-intuitive.
[0006] In many different types of rechargeable batteries, charge
storing materials may be produced as high-capacity (nano)composite
powders, which exhibit moderately high volume changes (8-160 vol.
%) during the first cycle and moderate volume changes (5-50 vol. %)
FIG. 4idual particle level during the subsequent charge-discharge
cycles. A subset of such charge-storing particles includes
particles with an average size in the range from around 0.2 to
around 20 microns. Such a class of charge-storing particles offers
great promises for scalable manufacturing and achieving high
cell-level energy density and other performance characteristics.
Unfortunately, such particles are relatively new and their
formation into electrodes typically results in poor performance
characteristics and limited cycle stability. The performance often
becomes particularly poor when the electrode capacity loading
becomes moderate (2-4 mAh/cm.sup.2) or even more so when it becomes
high (e.g., 4-12 mAh/cm.sup.2). Higher capacity loading, however,
is advantageous for increasing cell energy density and reducing
cell manufacturing costs.
[0007] Examples of materials that exhibit moderately high volume
changes (8-160 vol. %) during the first cycle and moderate volume
changes (5-50 vol. %) during the subsequent charge-discharge cycles
include (nano)composites comprising so-called alloying-type active
electrode materials. In the case of metal-ion batteries (such as
Li-ion batteries), examples of such alloying-type active electrode
materials include, but are not limited to, silicon, germanium,
antimony, aluminum, magnesium, zinc, gallium, arsenic, phosphorous,
silver, cadmium, indium, tin, lead, bismuth, their alloys, and
others. Silicon-based electrodes are particularly attractive for
most applications due to their very high gravimetric and volumetric
capacities and moderate cost. Alloying-type electrode materials
typically offer higher gravimetric and volumetric capacity than
so-called intercalation-type electrodes used in commercial Li-ion
batteries, such as graphite.
[0008] Accordingly, there remains a need for improved batteries,
components, and other related materials and manufacturing
processes.
SUMMARY
[0009] An embodiment is directed to a Li-ion battery electrode,
comprising a current collector, a conductive interlayer arranged on
the current collector, the conductive interlayer including first
conductive additives and a first polymer binder, and an electrode
active material layer arranged on the conductive interlayer, the
electrode active material layer including a plurality of active
material particles mixed with a second polymer binder and second
conductive additives, the plurality of active material particles
exhibiting an average particle size in the range from about 0.2
microns to about 10 microns, an average volume expansion in the
range of about 8 vol. % to about 180 vol. % during one or more
charge-discharge cycles of the Li-ion battery cell, and an average
areal capacity loading in the range of about 3 mAh/cm.sup.2 to
about 12 mAh/cm.sup.2.
[0010] Another embodiment is directed to a process of manufacturing
of a Li-ion battery electrode, comprising mixing a first polymer
binder, a first solvent and first conductive additives to form a
first uniform conductive interlayer slurry, coating a current
collector with the first slurry at a first thickness to form a
conductive interlayer, drying the first slurry coating to attain a
conductive interlayer on the current collector, mixing a second
polymer binder, a second solvent, second conductive additives and
active material particles to form a second uniform active material
slurry, coating the conductive interlayer with the second slurry at
a second thickness, drying the second slurry coating to attain an
electrode active material layer, and calendaring the conductive
interlayer and/or the electrode active material layer until a
desired density is achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings are presented to aid in the
description of embodiments of the disclosure and are provided
solely for illustration of the embodiments and not limitation
thereof. Unless otherwise stated or implied by context, different
hatchings, shadings, and/or fill patterns in the drawings are meant
only to draw contrast between different components, elements,
features, etc., and are not meant to convey the use of particular
materials, colors, or other properties that may be defined outside
of the present disclosure for the specific pattern employed.
[0012] FIG. 1 illustrates an example (e.g., Li-ion) battery in
which the components, materials, methods, and other techniques
described herein, or combinations thereof, may be applied according
to various embodiments.
[0013] FIGS. 2A and 2B illustrate example (e.g., Li-ion)
electrodes, in which the interlayer (or a buffer layer) exists
between the composite anode particles and an example Cu current
collector.
[0014] FIG. 3 illustrates scanning electron microscopy (SEM) images
of the top and bottom electrode surfaces after the separation from
the current collector copper foil, showing significantly higher
fraction of the binder left from an interlayer left on the bottom
surface in accordance with an embodiment of the present
disclosure.
[0015] FIGS. 4A and 4B illustrate Raman mappings of the top of the
electrode surface and that of the current collector copper foil
separated from the bottom of the electrode, showing a significantly
higher fraction of carbon nanotubes on the copper foil left from
the interlayer, in accordance with embodiments of the present
disclosure.
[0016] FIGS. 5A, 5B, 5C and 5D illustrate Raman mapping of the
electrode surface with increasing content of carbon nanotube
conductive additives in accordance with an embodiment of the
present disclosure.
[0017] FIG. 6 illustrates Raman spectra taken from different areas
of an example carbon nanotube-comprising interlayer (buffer layer),
showing a very strong G band, in accordance with an embodiment of
the present disclosure.
[0018] FIG. 7 illustrates a process of Li-ion electrode fabrication
in accordance with an embodiment of the disclosure.
[0019] FIGS. 8-10 illustrate example processes, in which the
interlayer (or a buffer layer) is produced between the electrode
coating and the surface of the current collector foil in accordance
with embodiments of the present disclosure.
DETAILED DESCRIPTION
[0020] Aspects of the present invention are disclosed in the
following description and related drawings directed to specific
embodiments of the invention. The term "embodiments of the
invention" does not require that all embodiments of the invention
include the discussed feature, advantage, process, or mode of
operation, and alternate embodiments may be devised without
departing from the scope of the invention. Additionally, well-known
elements of the invention may not be described in detail or may be
omitted so as not to obscure other, more relevant details.
[0021] Any numerical range described herein with respect to any
embodiment of the present invention is intended not only to define
the upper and lower bounds of the associated numerical range, but
also as an implicit disclosure of each discrete value within that
range in units or increments that are consistent with the level of
precision by which the upper and lower bounds are characterized.
For example, a numerical distance range from 50 .mu.m to 1200 .mu.m
(i.e., a level of precision in units or increments of ones)
encompasses (in .mu.m) a set of [50, 51, 52, 43, . . . , 1199,
1200], as if the intervening numbers 51 through 1199 in units or
increments of ones were expressly disclosed. In another example, a
numerical percentage range from 0.01% to 10.00% (i.e., a level of
precision in units or increments of hundredths) encompasses (in %)
a set of [0.01, 0.02, 0.03, . . . , 9.99, 10.00], as if the
intervening numbers between 0.02 and 9.99 in units or increments of
hundredths were expressly disclosed. Hence, any of the intervening
numbers encompassed by any disclosed numerical range are intended
to be interpreted as if those intervening numbers had been
disclosed expressly, and any such intervening number may thereby
constitute its own upper and/or lower bound of a sub-range that
falls inside of the broader range. Each sub-range (e.g., each range
that includes at least one intervening number from the broader
range as an upper and/or lower bound) is thereby intended to be
interpreted as being implicitly disclosed by virtue of the express
disclosure of the broader range.
[0022] While the description below may describe certain examples in
the context of Li and Li-ion batteries (for brevity and
convenience, and because of the current popularity of Li
technology), it will be appreciated that various aspects may be
applicable to other rechargeable and primary batteries (such as
Na-ion, Mg-ion, K-ion, Ca-ion and other metal-ion batteries,
alkaline batteries, etc.). Further, while the description below may
also describe certain examples of the material formulations in a
Li-free state (for example, as in silicon-comprising nanocomposite
anodes) during electrode assembling, it will be appreciated that
various aspects may be applicable to Li-containing electrodes (for
example, lithiated Si anodes, Li-containing cathodes including but
not limited to various types of conversion-type cathodes,
etc.).
[0023] While the description below may describe certain examples in
the context of electrodes (or, more generally, batteries) filled
with liquid electrolytes, it will be appreciated that various
aspects may be applicable to solid electrolyte-comprising electrode
(or, more generally, battery) compositions. Examples of such solid
electrolytes may include, but are not limited to, gel polymer
electrolytes, solid polymer electrolytes, single ion conducing
polymer electrolytes (where, for example, anions are chemically
attached to the polymer framework), inorganic solid electrolytes
(including the ones introduced via a melt-infiltration technology
into the electrodes or cells), composite solid electrolytes
(including the ones comprising both inorganic and polymer
components), among others. While the description below may describe
certain examples in the context of electrodes (or, more generally,
batteries) filled with liquid electrolytes based on single salts
(e.g., LiPF.sub.6 or others for Li-ion batteries) dissolved in the
mixture of organic solvents, it will be appreciated that various
aspects may be applicable to liquid electrolytes comprising two or
more salts (e.g., two, three or more Li salts or mixtures of Li and
non-Li salts) as well as to liquid electrolytes comprising ionic
liquids or inorganic solvents. The combination of such "unusual"
for Li-ion battery electrolytes (various solid electrolytes or
composite electrolytes or liquid electrolytes comprising more than
one salts or ionic liquids or inorganic solvents) with conductive
interlayer between the electrode or current collectors (or, more
generally, attaining substantially higher volume fraction of
conductive additives or polymer binder or both near the current
collectors) may be particularly advantageous for attaining enhanced
stability or rate performance or safety or other attractive cell
characteristics.
[0024] While the description below may describe certain examples in
the context of some specific silicon-comprising anodes (such as
silicon-comprising composite particles with specific dimensions,
surface area and volume changes during cycling), it will be
appreciated that various aspects may be applicable to other types
of silicon-comprising anodes, such as silicon-comprising anodes
with silicon content in the range from around 2.0 at. % to around
93.0 at. % (in some designs, from around 10 at. % to around 85 at.
%) as atomic fraction of the total dry anode coating composition,
including all active materials, all conductive additives, all other
additives and all binder(s), but not including the current
collectors).
[0025] While the description below may describe certain examples in
the context of some specific alloying-type chemistries of anode
active materials for Li-ion batteries (such as silicon-comprising
anodes), it will be appreciated that various aspects may be
applicable to other chemistries for Li-ion batteries
(conversion-type anodes and cathodes, other alloying-type
electrodes, mixed anodes or cathodes comprising both intercalation
and conversion or alloying type active materials, anodes or
cathodes comprising intercalation-type active materials, including
(but not limited to) cathodes with gravimetric capacity in excess
of about 200 mAh/g (e.g., in a fully lithiated stage) not counting
the weight of the current collectors and anodes with the
gravimetric capacity in excess of about 400 mAh/g (e.g., in a fully
lithiated stage) not counting the weight of the current collectors,
lithium metal anodes, etc.) as well as to other battery
chemistries. In the case of metal-ion batteries (such as Li-ion
batteries), examples of other suitable conversion-type active
materials for electrodes include, but are not limited to, various
metal fluorides and oxyfluorides (including, but not limited to
those comprising lithium fluoride (LiF) mixed with metals (e.g.,
nickel (Ni), iron (Fe), copper (Cu), bismuth (Bi), silver (Ag) and
others and their various alloys), FeF.sub.3, FeF.sub.2, Fe--F--O,
CuF.sub.2, BiF.sub.3, BiF.sub.5, Cu--Fe--F.sub.x,
Cu--Fe--F.sub.x--O.sub.y, NiF.sub.2, Cu--Fe--Ni--F.sub.x,
Cu--Fe--Ni--F.sub.x--O.sub.y, and many others and their various
mixtures and alloys), sulfur and metal sulfides (including, but not
limited to Li.sub.2S), selenium and metal selenides (including, but
not limited to Li.sub.2Se), various selenium-sulfur mixed
electrodes (including, but not limited to Li.sub.2S--Li.sub.2Se
solid solutions, line compounds or mixtures), metal oxides, metal
nitrides, metal phosphides, metal hydrides, and others, as well as
their various alloys (incl. solid solutions), mixtures and
combinations.
[0026] While the description below may describe certain examples in
the context of some specific pre-fabrication of conductive
interlayer(s) between the bulk of the electrode and current
collectors (or, more generally, in the context of attaining
substantially higher volume fraction of conductive additives or
polymer binder or both near the current collectors by depositing a
coating on the current collector prior to depositing active
material or active material slurry), it would be appreciated that
such an interlayer (or, more generally, attaining substantially
higher volume fraction of conductive additives or polymer binder or
both near the current collectors) may be attained during or after
the electrode preparation (e.g., during deposition of the
interlayer and active material layer, or during drying and
preferential (enhanced) sedimentation of conductive additives or
polymers on the current collector (compared to the active particle
surface), or during electrode densification (e.g., when conductive
additives and polymer binders deform more readily during
calendaring/densification) or at other stages of the electrode
fabrication).
[0027] While the description below may describe certain examples in
the context of wet slurry-based electrode fabrication, it would be
appreciated that various aspects may be applicable to dry electrode
fabrications.
[0028] While the description below may describe certain examples in
the context of some specific electrode compositions, specific
slurry compositions, specific slurry mixing procedures, specific
calendaring procedures, specific current collectors, specific
distribution of binder or conductive additives in the electrodes,
specific polymer binder compositions, specific conductive additive
compositions, specific electrode loadings, specific electrolytes
and other specific battery cell manufacturing, composition or
architectural features, it will be appreciated that various aspects
may be advantageously applicable to combinations of two, three or
more of such features.
[0029] During battery (such as a Li-ion battery) operation,
so-called conversion materials change (convert) from one crystal
structure to another (hence the name "conversion"-type). During
(e.g., Li-ion) battery operation, Li ions may be inserted into
so-called alloying type materials forming lithium alloys (hence the
name "alloying"-type). Sometimes, "alloying"-type electrode
materials are considered to be a sub-class of "conversion"-type
electrode materials.
[0030] While the description below may describe certain examples in
the context of primary or rechargeable metal or metal-ion batteries
(such as nonchargeable or rechargeable Li metal or Li-ion batteries
or nonchargeable or rechargeable Na metal or Na-ion batteries,
among others), other conversion-type or alloying-type electrodes
that may benefit from various aspects of the present disclosure
include: various chemistries used in a broad range of aqueous
batteries, such as alkaline batteries, metal hydride batteries,
lead acid batteries, etc. These include, but are not limited to,
various metals (such as iron, zinc, cadmium, lead, indium, etc.)
and metal alloys, metal oxides, metal hydroxides, metal
oxyhydroxides, and metal hydrides, to name a few.
[0031] FIG. 1 illustrates an example metal-ion (e.g., Li-ion)
battery in which the components, materials, methods, and other
techniques described herein, or combinations thereof, may be
applied according to various embodiments. A cylindrical battery is
shown here for illustration purposes, but other types of
arrangements, including prismatic or pouch (laminate-type)
batteries, may also be used as desired. The example battery 100
includes a negative anode 102, a positive cathode 103, a separator
104 interposed between the anode 102 and the cathode 103, an
electrolyte (not shown) impregnating the separator 104, a battery
case 105, and a sealing member 106 sealing the battery case
105.
[0032] Both liquid and solid electrolytes may be used for the
designs herein. Conventional electrolytes for Li- or Na-based
batteries of this type are generally composed of a single Li or Na
salt (such as LiPF.sub.6 for Li-ion batteries and NaPF.sub.6 or
NaClO.sub.4 salts for Na-ion batteries) in a mixture of organic
solvents (such as a mixture of carbonates). Other common organic
solvents include nitriles, esters, sulfones, sulfoxides,
phosphorous-based solvents, silicon-based solvents, ethers, and
others. Such solvents may be modified (e.g., be sulfonated or
fluorinated). The electrolytes may also comprise ionic liquids (in
some designs, neutral ionic liquids; in other designs, acidic and
basic ionic liquids). The electrolytes may also comprise mixtures
of various salts (e.g., mixtures of several Li salts or mixtures of
Li and non-Li salts for rechargeable Li and Li-ion batteries).
[0033] In the case of aqueous Li-ion (or aqueous Na-ion, K-ion,
Ca-ion, etc.) batteries, electrolytes may include a solution (e.g.,
aqueous solution or mixed aqueous-organic solution) of inorganic Li
(or Na, K, Ca, etc.) salt(s) (such as Li.sub.2SO.sub.4, LiNO.sub.3,
LiCl, LiBr, Li.sub.3PO.sub.4, H.sub.2LiO.sub.4P,
C.sub.2F.sub.3LiO.sub.2, C.sub.2F.sub.3LiO.sub.3S,
Na.sub.2O.sub.3Se, Na.sub.2SO.sub.4, Na.sub.2O.sub.7Si.sub.3,
Na.sub.3O.sub.9P.sub.3, C.sub.2F.sub.3NaO.sub.2-, etc.). These
electrolytes may also comprise solutions of organic Li (or Na, K,
Ca, etc.) salts, such as (listed with respect to Li for brevity)
metal salts of carboxylic acids (such as HCOOLi, CH.sub.3COOLi,
CH.sub.3CH.sub.2COOLi, CH.sub.3(CH.sub.2).sub.2COOLi,
CH.sub.3(CH.sub.2).sub.3COOLi, CH.sub.3(CH.sub.2).sub.4COOLi,
CH.sub.3(CH.sub.2).sub.5COOLi, CH.sub.3(CH.sub.2).sub.6COOLi,
CH.sub.3(CH.sub.2).sub.7COOLi, CH.sub.3(CH.sub.2).sub.8COOLi,
CH.sub.3(CH.sub.2).sub.9COOLi, CH.sub.3(CH.sub.2).sub.10COOLi,
CH.sub.3(CH.sub.2).sub.11COOLi, CH.sub.3(CH.sub.2).sub.12COOLi,
CH.sub.3(CH.sub.2).sub.13COOLi, CH.sub.3(CH.sub.2).sub.14COOLi,
CH.sub.3(CH.sub.2).sub.15COOLi, CH.sub.3(CH.sub.2).sub.16COOLi,
CH.sub.3(CH.sub.2).sub.17COOLi, CH.sub.3(CH.sub.2).sub.18COOLi and
others with the formula CH.sub.3(CH.sub.2)xCOOLi, where x ranges up
to 50); metal salts of sulfonic acids (e.g., RS(.dbd.O).sub.2--OH,
where R is a metal salt of an organic radical, such as a
CH.sub.3SO.sub.3Li, CH.sub.3CH.sub.2SO.sub.3Li,
C.sub.6H.sub.5SO.sub.3Li, CH.sub.3C.sub.6H.sub.4SO.sub.3Li,
CF.sub.3SO.sub.3Li, [CH.sub.2CH(C.sub.6H.sub.4)SO.sub.3Li].sub.n
and others) and various other organometalic reagents (such as
various organilithium reagents), to name a few. Such solutions may
also comprise mixtures of inorganic and organic salts, various
other salt mixtures (for example, a mixture of a Li salt and a salt
of non-Li metals and semimetals), and, in some cases, hydroxide(s)
(such as LiOH, NaOH, KOH, Ca(OH).sub.2, etc.), and, in some cases,
acids (including organic acids). In some designs, such aqueous
electrolytes may also comprise neutral or acidic or basic ionic
liquids (from approximately 0.00001 wt. % to approximately 40 wt. %
relative to the total weight of electrolyte). In some designs, such
"aqueous" (or water containing) electrolytes may also comprise
organic solvents (from approximately 0.00001 wt. % to approximately
40 wt. % relative to the total weight of electrolyte), in addition
to water. Illustrative examples of suitable organic solvents may
include carbonates (e.g., propylene carbonate, ethylene carbonate,
diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate,
fluoriethylene carbonate, vinylene carbonate, and others), various
nitriles (e.g., acetonitrile, etc.), various esters, various
sulfones (e.g., propane sulfone, etc.), various sultones, various
sulfoxides, various phosphorous-based solvents, various
silicon-based solvents, various ethers, and others.
[0034] The most common salt used in a Li-ion battery electrolyte,
for example, is LiPF.sub.6, while less common salts include lithium
tetrafluoroborate (LiBF.sub.4), lithium perchlorate (LiClO.sub.4),
lithium bis(oxalato)borate (LiB(C.sub.2O.sub.4).sub.2), lithium
difluoro(oxalate)borate (LiBF.sub.2(C.sub.2O.sub.4)), various
lithium imides (such as SO.sub.2FN.sup.-(Li.sup.+)SO.sub.2F,
CF.sub.3SO.sub.2N.sup.-(Li.sup.+)SO.sub.2CF.sub.3,
CF.sub.3CF.sub.2SO.sub.2N.sup.-(Li.sup.+)SO.sub.2CF.sub.3,
CF.sub.3CF.sub.2SO.sub.2N.sup.-(Li.sup.+)SO.sub.2CF.sub.2CF.sub.3,
CF.sub.3SO.sub.2N.sup.-(Li.sup.+)SO.sub.2CF.sub.2OCF.sub.3,
CF.sub.3OCF.sub.2SO.sub.2N.sup.-(Li.sup.+)SO.sub.2CF.sub.2OCF.sub.3,
C.sub.6F.sub.5SO.sub.2N.sup.-(Li.sup.+) SO.sub.2CF.sub.3,
C.sub.6F.sub.5SO.sub.2N.sup.-(Li.sup.+)SO.sub.2C.sub.6F.sub.5 or
CF.sub.3SO.sub.2N.sup.-(Li.sup.+)SO.sub.2PhCF.sub.3, and others),
and many others. Electrolytes for Na-ion, Mg-ion, K-ion, Ca-ion,
and Al-ion batteries are often more exotic as these batteries are
in earlier stages of development. They may comprise different salts
and solvents (in some cases, ionic liquids may replace organic
solvents for certain applications).
[0035] Conventional electrodes utilized in Li-ion batteries are
typically produced by (i) formation of a slurry comprising active
materials, conductive additives, binder solutions and, in some
cases, surfactant or other functional additives; (ii) casting a
slurry onto a metal foil (e.g., Cu foil for most anodes and Al foil
for most cathodes); and (iii) drying the casted electrodes to
completely evaporate the solvent.
[0036] Conventional anode materials utilized in Li-ion batteries
are of an intercalation-type. Examples of these include but are not
limited to lithium titanate, synthetic and natural graphite, hard
carbons and others. Metal ions are intercalated into and occupy the
interstitial positions of such materials during the charge or
discharge of a battery. Such anodes experience very small volume
changes when used in electrodes. However, such anodes exhibit
relatively small gravimetric and volumetric capacities (typically
less than 370 mAh/g rechargeable specific capacity in the case of
graphite- or hard carbon-based anodes and less than 600
mAh/cm.sup.3 rechargeable volumetric capacity).
[0037] Conventional cathode materials utilized in Li-ion batteries
are also of an intercalation-type. Examples of these include but
are not limited to lithium cobalt oxide (LCO), lithium manganese
oxide (LMO), lithium nickel cobalt aluminum oxide (NCA), lithium
nickel oxide (LNO), lithium nickel manganese oxide (LNM), lithium
nickel cobalt manganese oxide (NCM), various other layered lithium
and nickel comprising oxides (some comprising Mn, Cr, Al, Mg and
other metals), lithium iron phosphate (LFP) and other olivine type
cathodes, among others. Metal ions are intercalated into and occupy
the interstitial positions of such materials during the charge or
discharge of a battery.
[0038] Polyvinylidene fluoride, or polyvinylidene difluoride
(PVDF), and carboxymethyl cellulose (CMC) (typically as a mixture
of CMC and styrene butadiene rubber (SBR)) are the two most common
binders used in intercalation-type electrodes (CMC is most commonly
used in the intercalation-type anodes and PVDF is most commonly
used in the intercalation-type cathodes).
[0039] However, many other binders and their mixtures may be
effectively used in the context of one or more embodiments of the
present invention for intercalation-type, alloying-type,
conversion-type and mixed-type anodes and cathodes. These include,
but are not limited to, polyacrylic acid (PAA) and various salts of
PAA (Na-PAA, K-PAA, Li-PAA and many others and their various
mixtures), (poly)alginic acid and various salts of (poly)alginic
acid (Na-alginate, Li-alginate, Ca-alginate, K-alginate and many
others and their various mixtures), maleic acid and their various
salts, various (poly)acrylates (including, but not limited to
dimethylaminoethyl acrylate and many others), various
(poly)acrylamides, various polyesters, styrene butadiene rubber
(SBR), (poly)ethylene oxide (PEO), (poly)vinyl alcohol (PVA),
cyclodextrin, maleic anhydride, methacrylic acid and its various
salts (Li, Na, K, etc.), various (poly)ethylenimines (PEI), various
(poly)amide imides (PAI), various (poly)amide amines, various other
polyamine-based polymers, various (poly)ethyleneimines, sulfonic
acid and their various salts, various catechol group-comprising
polymers, various lignin-comprising or lignin-derived polymers,
various epoxies, various cellulose-derived polymers (including, but
not limited to nanocellulose fibers and nanocrystals, carboxyethyl
cellulose, etc.), chitosan, other polymers (e.g., preferably
water-soluble polymers) and their various co-polymers and mixtures.
A particular polymer binder choice for battery electrode in a given
cell design may depend on various parameters, including the voltage
range electrodes are exposed to, volume changes during
electrochemical cycling, operational temperature range, electrolyte
used and others. In some designs, a suitable molecular weight (MW)
of such polymer binders may generally range from as low as about 50
to as much as about 50,000,000. In some designs, it may be
advantageous to use aqueous solutions of water-soluble polymers as
binders. Carbon black is the most common conductive additive used
in battery electrodes.
[0040] Alloying-type anode materials for use in Li-ion batteries
offer higher gravimetric and volumetric capacities compared to
intercalation-type anodes. For example, silicon (Si) offers
approximately 10 times higher gravimetric capacity and
approximately 3 times higher volumetric capacity compared to an
intercalation-type graphite (or graphite-like) anode. However, Si
suffers from significant volume expansion during Li insertion (up
to approximately 300 vol. %) and thus may induce thickness changes
and mechanical failure of Si-comprising anodes. In addition, Si
(and some Li--Si alloy compounds that may form during lithiation of
Si) suffer from relatively low electrical conductivity and
relatively low ionic (Li-ion) conductivity. Electronic and ionic
conductivity of Si is lower than that of graphite. Formation of
(nano)composite Si-comprising particles (including, but not limited
to Si--C composites, Si-metal composites, Si-polymer composites,
Si-ceramic composites, Si--C-polymer composites or other types of
porous composites comprising nanostructured Si or nanostructured or
nano-sized Si particles of various shapes and forms and preferably
comprising carbon) may reduce volume changes during Li-ion
insertion and extraction, which, in turn, may lead to better cycle
stability in rechargeable Li-ion cells.
[0041] In addition to Si-comprising (nano)composite anodes, other
examples of such nanocomposite anodes comprising alloying-type
active materials include, but are not limited to, those that
comprise germanium, antimony, aluminum, magnesium, zinc, gallium,
arsenic, phosphorous, silver, cadmium, indium, tin, lead, bismuth,
their alloys, and others.
[0042] In addition to (nano)composite anodes comprising
alloying-type active materials, other interesting types of high
capacity (nano)composite anodes may comprise metal oxides
(including silicon oxide including partially oxidized silicon,
lithium oxide, etc.), metal nitrides, metal phosphides, metal
sulfides, metal hydrides, and others.
[0043] In particular, high-capacity (nano)composite anode powders,
which exhibit moderately high volume changes (e.g., about 8-160
vol. %) during the first cycle, moderate volume changes (e.g.,
about 4-50 vol. %) during the subsequent charge-discharge cycles
and an average size in the range from around 0.2 to around 40
microns (more preferably from around 0.4 to around 20 microns) may
be particularly attractive for battery applications in terms of
manufacturability and performance characteristics. In case of
Si-comprising (nano)composite anode powders, it may be particularly
useful for the battery designs to use those with the specific
capacity in the range from about 500 mAh/g to about 3000 mAh/g. In
some designs, the specific capacity of such powders may range from
about 600 mAh/g to about 2000 mAh/g. The Si-containing
(nano)composite powders that additionally comprise conductive
(e.g., primarily sp.sup.2-bonded) carbon may be particularly
attractive for some applications. In some designs, an anode coating
layer may advantageously exhibit volumetric capacity (after
lithiation and the resulting expansion) in the range from about 600
mAh/cc to about 1800 mAh/cc (in some designs, from about 700 mAh/cc
to about 1400 mAh/cc). In some designs, electrodes with electrode
capacity loading from moderate (e.g., about 2-4 mAh/cm.sup.2) to
high (e.g., about 4-10 mAh/cm.sup.2) are also particularly
attractive for use in cells. Furthermore, in some designs,
electrodes with a majority of near-spherically
(spheroidally)-shaped composite particles may additionally be very
attractive for optimizing rate performance and volumetric capacity
of the electrodes.
[0044] In spite of some improvements that may be achieved with the
formation and utilization of such alloying-type or conversion-type
nanocomposite anode materials, however, substantial additional
improvements in cell performance characteristics may be achieved
with the improved composition and preparation of electrodes, beyond
what is known or shown by the conventional state-of-the-art. The
relatively low density of such composite anode materials (e.g.,
about 0.5-2.5 g/cc) may make uniform slurry mixing, coating
deposition, and calendaring (electrode densification) more
challenging and require special methodologies for optimal
performance. In addition, such nanocomposites may be coated with a
carbon outer layer, which is less polar compared to conventional
intercalation-type cathodes and thus may make such nanocomposite
particles more difficult to disperse in some solvents. The volume
changes accompanying electrochemical cycling of high-capacity
(nano)composite anodes may induce stresses within electrodes that
may lead to delamination from the current collector, formation of
cracks and eventual cell failure.
[0045] Unfortunately, high-capacity (nano)composite anode or
cathode powders (including those that comprise Si and C), which
exhibit moderately high volume changes (e.g., about 8-160 vol. %)
during the first cycle, moderate volume changes (e.g., about 4-50
vol. %) during the subsequent charge-discharge cycles, an average
size in the range from around 0.2 to around 20 microns and
relatively low density (e.g., about 0.5-3.8 g/cc), are relatively
new and their formation into electrodes using conventional binders,
conductive additives, mixing and calendaring (densification)
protocols typically result in unfavorable morphology and mechanical
properties and relatively poor performance characteristics and
limited cycle stability, particularly if electrode capacity loading
is moderate (e.g., about 2-4 mAh/cm.sup.2) and even more so if it
is high (e.g., about 4-10 mAh/cm.sup.2). Substantial volume changes
(particularly during the initial cycles) typically lead to inferior
performance.
[0046] One or more embodiments of the present disclosure are
directed to overcoming at least some of the above-discussed
challenges of various types of nanocomposite electrode materials
(for example, those that comprise alloying-type active materials,
such as Si, as well as carbon) that experience certain volume
changes during cycling (for example, moderately high volume changes
(e.g., about 8-160 vol. %) during the first cycle and moderate
volume changes (e.g., about 4-50 vol. %) during the subsequent
charge-discharge cycles) and an average size in the range from
around 0.2 to around 20 microns for a broad range of batteries. It
also allows one to formulate substantially more stable electrodes
in moderate (e.g., about 2-4 mAh/cm.sup.2) and, very importantly,
high capacity loadings (e.g., about 4-10 mAh/cm.sup.2).
[0047] In one or more embodiments, electrodes based on high
capacity nanocomposite powders (e.g., comprising conversion- or
alloying-type active materials and including elements such as Si
and C) that experience certain volume changes during cycling
(moderately high volume changes (e.g., an increase by about 8-160
vol. % or a reduction by about 8-70 vol. %) during the first cycle
and moderate volume changes (e.g., about 4-50 vol. %) during the
subsequent charge-discharge cycles) and an average size in the
range from around 0.2 to around 20 micron (such as Si-based
nanocomposite anode powders, among many others) may require very
specific types of binders for significantly improved performance
(particularly for high capacity loadings), as well as a very
specific range of most favorable binder content, a specific type of
carbon additives and specific amount of carbon additives and
finally an interlayer between a Cu current collector and
electrode.
[0048] For example, (i) continuous volume changes in high capacity
nanocomposite particles during cycling in combination with (ii)
electrolyte decomposition on the electrically conductive electrode
surface at electrode operating potentials (e.g., mostly
electrochemical electrolyte reduction in case of Si-based anodes)
may lead to a continuous (even if relatively slow) growth of a
solid electrolyte interphase (SEI) layer on the surface of the
nanocomposite particles. If binders are used that swell
substantially (e.g., by around 5-100 vol. % or reduce their modulus
by over around 15-20%) in electrolytes (e.g., PVDF binders and the
like), the interface between the nanocomposite particles and
conductive carbon additives becomes filled with an SEI (electrolyte
decomposition products) even if the binder coats and separates this
interface from direct access of electrolyte. This is because
electrolyte slowly permeates/penetrates through such "swellable"
binders. The SEI growth at the composite electrode
particles/conductive additive(s) interface leads to a gradual
increase in the separation distance between the surface of the
composite electrode particle and the attached conductive additive
particle(s). In some designs, a higher degree of swelling in
electrolyte (stronger reduction in modulus) may typically lead to
faster separation for high capacity volume-changing nanocomposite
particles. This increase in separation distance may undesirably
increase the composite electrode particle/conductive additive
particle(s) contact resistance. More importantly, at some point the
separation may reach a critical value that corresponds to the
situation when a conductive additive particle(s) and composite
electrode particle become effectively electrically separated (e.g.,
when the separation distance exceeds substantially a distance that
typically provides at least a moderate (e.g., greater than about
0.1%) probability for "quantum tunneling" of electrons between the
separated particles). A similar phenomenon may happen at the
particle-to-particle interfaces as well as the
particle-to-current-collector interface in the electrode. Once an
electrode particle becomes electrically separated from other
particles and the current collector of the electrode, it
effectively stops being able to accept or donate electrons and thus
cannot participate in electrochemical reactions (which are required
for charge storage in a battery). As such, the electrode capacity
becomes reduced by the capacity of this separated particle. The
gradual electrical (or electrochemical) separation of the various
active composite electrode particles within the electrode leads to
undesirable irreversible losses of electrode (and thus battery)
capacity and eventual cell "end of life". Higher binder swelling in
electrolytes may lead to faster cell degradation and shorter cycle
stability. Because higher temperatures typically increase SEI
growth rate and electrolyte diffusion through the binders, stable
cell operation at above around 40-50.degree. C. (often required for
commercial cells) becomes particularly challenging to achieve. In
contrast, conventional (intercalation-type) electrode materials
exhibit a stable SEI and thus could be used with a broad range of
binders, including those that exhibit substantial swelling in
battery electrolytes.
[0049] Swelling of binders in electrolytes depends on both the
binder and electrolyte compositions. Furthermore, such swelling
(and the resulting performance reduction) often correlates with the
reduction in elastic modulus upon exposure of binders to
electrolytes. In this sense, the smaller the reduction in modulus,
the more stable the binder-linked (protected) composite active
particles/conductive additives interface becomes. The reduction in
binder modulus by over about 15-20% may typically result in a
noticeable reduction in performance in some applications. For
example, the reduction in the binder modulus by two times
(2.times.) may typically result in a substantial performance
reduction. In a further example, a reduction in modulus by five or
more times (e.g. 5.times.-500.times.) may result in a very
significant performance reduction. Such "swellable in electrolyte"
binders may exhibit either higher or (more often) lower maximum
elongations (maximum strain) when exposed to electrolyte (reduction
of maximum elongation may be undesirable). Exposure of electrodes
with such binders to electrolyte may also weaken the interfaces
between these binders and (nano)composite electrode particles,
conductive additives and current collectors, which may be
undesirable in some designs.
[0050] On the other hand, "swellable in electrolytes" binders may
typically undergo substantial (e.g., about 5-200 vol. %) expansion
(either in a dry state or when exposed to electrolyte) before
failure (e.g. in a tensile test), which can be important in one or
more embodiments because certain electrodes of interest exhibit a
moderate (but substantial) change in volume during cycling.
[0051] As a compromise, in some designs, the use of binders that
are slightly (e.g., about 2-25 vol. %) swellable in electrolytes
(e.g., polyvinyl alcohol (PVA)) may offer reasonable performance.
In some designs, such binders (including PVA) may work particularly
well, if such binders are used in combination with other binders
(or as co-polymers) and/or more effective conductive additives,
such as carbon nanofibers and carbon nanotubes or metal nanowires;
if the size of the high capacity particles is not too large (e.g.,
< about 6 micron); if carbon nanotubes (e.g., single-walled
carbon nanotubes, double-walled carbon nanotubes or multiwalled
carbon nanotubes) or carbon nanofibers or their various
combinations (including those that may additionally comprise carbon
black, exfoliated graphite, carbon ribbons or graphene) in the
amount of about 0.1-15 wt. %, if the capacity loading is within
about 3-8 mAh/cm.sup.2 and, preferably, if an interlayer exists
between the electrode and a metal (e.g., Cu) coated current
collector.
[0052] Binders that exhibit no or small (e.g., about 0.001-2 vol.
%) swelling upon exposure to electrolytes (such as various salts of
Carboxymethyl cellulose (CMC) including, but not limited to Na-CMC,
Li-CMC, K-CMC, etc., poliacrylic acid (PAA) and their various salts
(Na-PAA, Li-PAA, K-PAA, etc.), various acrylic binders, various
alginates (alginic acid and various salts of alginic acids) and
most of other water-dissolvable binders in case of Li-ion batteries
based on organic electrolytes) may also be used in some designs.
However, such binders may be very brittle (even when exposed to
electrolyte) and, in some designs, electrodes with the described
alloying-type composite materials may be carefully optimized in
terms of the binder amount, porosity, bonding between the binder
and the particle surface, the amount and type of elongated
particles (such as nanotubes, nanofibers and other fiber-shaped
conductive particles as well as flake-like particles) and their
mixtures, the amount and type of secondary (e.g., more elastic)
binders, and the presence of an interlayer that may exist between
the electrode and a metal (e.g., Cu) coated current collector. In
some designs, such binders also tend to work better with a smaller
size of composite particles (e.g., about 100 nm-4 micron, on
average). Larger particles, on the other hand, exhibit a smaller
specific surface area in contact with electrolyte and thus offer a
lower rate of undesirable side reactions in some designs (e.g., a
smaller volume fraction of the SEI or other types of surface
layers, less electrolyte decomposition, less dissolution of
electrode materials, etc.). In addition, larger particles are
easier to handle and process into electrodes. Finally, larger
particles may typically require less binder and conductive
additives for sufficiently stable performance, which may be
advantageous in terms of maximizing gravimetric electrode
capacitance, rate performance and, in some cases, cell stability.
Therefore, the use of large particles may be preferable, although
these may not perform well with some of the binders, particularly
if no interlayer exists between the Cu current collectors and the
electrode.
[0053] In some designs, it may be advantageous for the binder for
volume-changing electrode particles in the active material layer to
comprise two or more distinct components with substantially
different shape, substantially different solubility in a slurry
solvent (by 2 or more times; in some designs, one component may not
be soluble at all), substantially different (by 2 or more times)
swelling in electrolyte and/or substantially different mechanical
properties (e.g., elastic modulus, elasticity, etc. differing by 2
or more times). In some designs, it may be advantageous to use
elastic nanoparticles (e.g., with an average size in the range from
around 10 nm to around 500 nm) in combination with more brittle
and/or water-soluble binders (e.g., including those described
above--CMC, Na-CMC, Li-CMC, K-CMC, alginic acid, Na-alginate,
Li-alginate, PAA, Na-PAA, Li-PAA, various acrylic binders, various
alginates, etc.) to overcome their brittle nature and be
effectively utilized with both small and large (e.g.,
Si-containing) composite particles. In some designs, elastic
nanofibers or nanoribbons (e.g., with an average diameter in the
range from around 2 nm to around 500 nm, an average length in the
range from around 10.0 nm to around 500,000.0 nm and an average
aspect ratio in the range from around 3:1 to around 10,000:1) or
elastic flakes (e.g., with an average thickness in the range from
around 1 nm to around 500 nm, an average length in the range from
around 10.0 nm to around 500,000.0 nm and an average aspect ratio
in the range from around 3:1 to around 10,000:1; in some designs
with holes) may be advantageously used instead of or in addition to
conventional elastic nanoparticles. Suitable examples of
composition of such particles include but are not limited to SBR,
polybutadiene, polyethylene, polyethylene propylene, styrene
ethylene butylene, ethyelene vinyl acetate,
polytetrafluoroethylene, perfluoroalkoxyethylene, isoprene, butyl
rubber, nitril rubber, ethylene propylene rubber, polyacrylic
rubber, silicone rubber, fluorosilicone rubber, polyether block
amide, polysiloxanes and their various copolymers (such as
polydimethylsiloxane), chlorosulfonated polyethylene,
ethylene-vinyl acetate, their various mixtures and copolymers,
among other suitable elastomers. In some designs, a suitable mass
fraction of such elastic nanoparticles (or nanofibers or
nanoflakes) may range from around 5 wt. % to around 99 wt. % (as a
fraction of the total binder content in the electrode). While some
conventional electrodes (e.g., graphite anodes) may comprise
spherical SBR particles (which may be made elastic, in some
designs), these commonly comprise only from around 15% to around 50
wt. % of the total weight fraction of the binder. In contrast, in
the context of the present disclosure for larger volume-changing
particles it may be highly advantageous to use a substantially
larger fraction of elastic particles. In some designs it may be
advantageous for the weight fraction of the elastic nanoparticles
(or nanofibers or nanoflakes) (made of SBR or other elastic
materials, including those described above) to range from around 50
wt. % to around 97 wt. % (in some designs, from around 70 wt. % to
around 95 wt. %; including, for example, about 75 wt. % to about 90
wt. %). The size of the volume-changing nanocomposite particles,
the value of the volume changes and their shape impact the optimal
fraction of elastic particles. Typically, larger volume changes,
larger particles and more spherical particles (in contrast, for
example, to flake-shaped or random shaped particles) require larger
fraction of elastic particles in the binder.
[0054] In some designs, it may be advantageous for such elastic
particles to exhibit certain mechanical properties. In some
designs, maximum elongation (elongation at break) of elastic
nanoparticles (or nanofibers or nanoflakes) may preferably range
from around 20.0% to around 10,000.0% (in some designs, from around
50.0% to around 5000.0%). In some designs, a strain at yield of
elastic nanoparticles (or nanofibers or nanoflakes) may preferably
exceed about 20% (in some design, the strain at yield of the
elastic nanoparticles may exceed about 100%). In some designs, it
may be advantageous to use a smaller fraction of conductive
additives in an electrode because conductive additives occupy space
(and thus reduce volumetric and gravimetric capacity of electrodes)
and may induce undesirable side reactions (e.g., SEI formation,
electrolyte decomposition, etc.) on their surface. Therefore, the
use of small (e.g., below about 5 wt. %, even more preferably below
about 2 wt. %, and even more preferably below about 1 wt. %)
amounts of conductive additives may be preferable for cell
operation, although electrodes with a smaller fraction of
conductive additives may not perform well with some of the brittle
(in electrolyte) binders in combination with high-capacity
volume-changing composite electrode particles, especially for high
capacity loadings.
[0055] In some applications, a (e.g., aqueous) binder suspension
may include surfactant in order to achieve a uniform binder
distribution in a slurry. In some cell designs, however, surfactant
may at least partially dissolve during cycling or weaken adhesion
of the solid electrolyte interphase (SEI) layer and thus induce
undesirable cell degradation. In this case, the amount of the
surfactant may be kept below a threshold (e.g., to below about 5
wt. % of all the binder in the electrode; in some designs--to below
about 1 wt. %. of all the binder in the electrode).
[0056] In some designs, it may be advantageous for volume-changing
(nano)composite electrodes to utilize polymer binders that exhibit
a relatively low glass transition temperature (e.g., below around
70.degree. C.; in some designs--below around 20.degree. C.) to
accommodate the mechanical stresses during calendaring
(densification) and electrochemical cycling.
[0057] In some designs, the use of polyacrylates and
polymethacrylates (and their derivatives and co-polymers) as
binders for (nano)composite electrode materials may be
advantageous. Such polymers are available with various side chain
lengths and functionalities and may be tuned to achieve a desired
solubility, mechanical properties, adhesion and stability.
[0058] In some designs, it may be advantageous to add conductive
additives (for example, conductive additives comprising one
dimensional (1D) conductive particles, such as conductive
nanotubes, conductive ribbons, conductive fibers, conductive
nanowires, etc.) in several stages during the electrode slurry
mixing. In one illustrative example, it may be advantageous to (i)
mix some conductive additives and active (nano)composite materials
(and optionally some binder) in a solvent in a first stage and (ii)
add binder (or binder solution or binder suspension) and
(optionally) additional conductive additives (or suspension of
conductive additives) and (optionally) additional solvent in the
second or other stage. In another illustrative example, it may be
advantageous to (i) mix some conductive additives with a binder (or
a binder solution or suspension) in a first stage, (ii) add active
(nano)composite materials (and, in some process designs, additional
solvent) and more conductive additives in the second or other stage
and (iii) (optionally) add more solvent in the final stage (e.g.,
in order to reduce viscosity and make the slurry easier to
process). In some designs, it may be advantageous to have
substantially (e.g., by about 2-10,000 times) higher viscosity of
the mix in the first stage (or at least one of the initial stages)
than in the subsequent (or the final) slurry mix. In some designs,
regulating the viscosity in this manner may result in improved
performance due to the achievement of a higher effective shear rate
needed to break up any agglomerates and more uniformly distributed
slurry ingredients.
[0059] In some designs, it may be advantageous to have a
substantially (e.g., by about 1.2-100 times) higher fraction of
solids in the first stage (or at least one of the initial stages)
of the mixing than in the subsequent (or the final) slurry mix.
Such procedures may lead to improved performance, which may be
related to better slurry dispersion.
[0060] In some designs, when more than one binder is used, it may
be advantageous to add binders (or binder suspension(s) or
solution(s)) in several stages during the electrode slurry mixing.
In one illustrative example, it may be advantageous to (i) mix all
or some conductive additives (or conductive additive suspension in
a solvent) and a first binder (or first binder solution or first
binder suspension) in a first stage, (ii) add active
(nano)composite materials (and optionally more conductive
additives) in a second stage or other stage, (iii) add the second
binder (or second binder solution or second binder suspension) and
possibly additional conductive additives (or suspension of
conductive additives) in the third or other subsequent stage, (iv)
(optionally) add more solvent in the fourth or other subsequent
stage. In some designs, when gradual (or step-wise) binder addition
is utilized, it may be important that binder(s) do not adsorb onto
electrode particles or conductive additives (from a binder solution
or slurry) during slurry mixing to the level when they link
particles together and form aggregates during the slurry mixing
stage. At the same time, in some designs (for example, when more
than one binder is used and when one binder may preferably be
located at the surface of electrode particles or when one binder
may help one to achieve more uniform dispersion of particles in a
solution, acting similar to a surfactant), it may be advantageous
to achieve at least partial (e.g., about 20-100%) surface
adsorption of one binder during the slurry mixing stage. However,
in some designs, it may be desired to configure the slurry
composition, surface chemistry of the electrode particles and
conductive additives, slurry solvent and mixing protocols in such a
way as to reduce or avoid formation of agglomerates during the
slurry mixing (while preferably achieving improved mixing).
[0061] In some designs, it may also be further advantageous to use
different types of conductive additives in different stages
(particularly in aqueous slurries). In some designs, it may be
advantageous to mix conductive additives (for example, 1D additives
or a mixture of 1D additives and near-spherical nanoparticles, such
as carbon black nanoparticles) in a solution before adding the
binder (or binder solution or suspension) or the active
(nano)composite materials (particularly in aqueous slurries). In
some designs, it may be further advantageous to use surfactant(s)
during the conductive additives (for example, 1D additives or a
mixture of 1D additives and near-spherical nanoparticles, such as
carbon black nanoparticles) mixing or dispersing in a solution. In
some designs, it may be further advantageous to functionalize the
surface of conductive additives with functional groups or small
molecules or polymers to improve (or to better control) their
dispersion (distribution) in a slurry (during the electrode slurry
mixing) and the final (casted) electrode.
[0062] In some designs, it may be advantageous to have some (or
all) the binder and some (or all) conductive additives premixed
before adding active (nano)composite materials into a slurry.
[0063] In some designs, it may be advantageous to add binder (or
binder solution or suspension) in several stages during the
electrode slurry mixing. In some designs, it may also be further
advantageous to use different types of binders in different
stages.
[0064] In some designs, it may be advantageous to have active
material, some (or all) the binder and some (or all) conductive
additives premixed and dried (e.g., to form a powder, including
granulated powder) before adding a solvent or solvent mixture (and
optionally some additional conductive additives and/or optionally
some additional binder) into a slurry. In this case, improved
uniformity or performance or smaller performance variation may be
attained in cell designs.
[0065] In some designs, it may be further advantageous to add a
solvent (e.g., water) in several stages during the electrode slurry
mixing. In some designs, it may also be further advantageous to use
different types of solvents (e.g., water and an alcohol or water
and alcohol-containing water) in different mixing stages.
[0066] In some designs, it may be advantageous for the aqueous
(water-based) slurries to additionally comprise an alcohol (e.g.,
ethanol, methanol, isopropanol, etc.) in the amount from around 2
vol. % to around 20 vol. % (relative to the total water-alcohol
volume mixture) in order to achieve a high performing electrode
coating (e.g., with a reduced content of defects, with higher
degree of uniformity, with a more favorable distribution of
conductive additives, etc.).
[0067] In some designs, it may be particularly advantageous to
arrange a conductive interlayer between the electrode with at least
moderate volume changing particles (such as those comprising Si and
carbon, among others) and the current collector foil (such as Cu or
Ni or stainless steel or Ti or another suitable metal or alloy
metal foil, including but not limited to electrodeposited or rolled
or layered or porous or fiber-comprising foils, in case of a
Si-comprising anode). For example, not only such a conductive
interlayer may enhance rate performance of the electrode with
volume-changing (nano)composite electrode particles, but most
importantly it may significantly enhance electrode mechanical
stability and adhesion to the current collector (e.g., by reducing
stress concentration near this area). In some designs, such an
interlayer may also protect a metal current collector foil from
undesirable reactions with electrolyte. In some designs, such an
interlayer may become particularly advantageous for electrodes
comprising (nano)composite particles exhibiting larger volume
changes (particularly those that comprise Si). In some designs,
such an interlayer may further be particularly advantageous for
such electrodes produced at medium-to-high capacity loading (e.g.,
about 3-12 mAh/cm.sup.2). In some designs, such an interlayer may
also be particularly advantageous for relatively thin current
collector foils (e.g., foils with an average thickness from around
4 .mu.m to around 15 .mu.m). In some designs, the use of both
higher capacity loadings and thinner foils may be advantageous
because such design approaches maximize energy density of the
cells.
[0068] The volume changes in the electrode (at both the first cycle
and subsequent cycling) may induce significant stresses within the
foils, which may eventually lead to its mechanical failure.
Similarly, such volume changes may also lead to separation of at
least portions of the electrodes from the current collector foils.
Unfortunately, higher capacity loadings may induce larger stresses
at both the electrode/foil interface and, in some cases, within the
foil and, thus, lead to mechanical failure(s). If such stresses
exceed some critical value related to the electrode/foil adhesion
strength, the electrode may delaminate from the foil after a
certain number of charge-discharge cycles. In some designs, the use
of a conductive interlayer may significantly reduce stress
concentration and additionally improve electrode adhesion.
Therefore, in some designs, the conductive interlayer may
effectively reduce or prevent the delamination and improve cell
cycle stability to acceptable values. In some designs, the strain
and stresses within the electrode may effectively translate into
the (cycling) strain and stresses within the current collector
foils. In some designs, thinner foils may not exhibit sufficiently
high strength, sufficiently high maximum strain or sufficiently
good fatigue resistance and, thus, form cracks and fractures during
cycling, leading to premature cell failure. In some designs, the
use of a conductive interlayer between the electrode and current
collector foils may absorb some of the stresses, thereby reducing
stresses within the foil and effectively prevent (or significantly
delay to an acceptable value) foil failure.
[0069] In some designs, this conductive interlayer (which may
alternatively be called "a buffer layer") may be deposited on the
surface of the current collector prior to electrode slurry coatings
(or, more generally, prior to electrode coating deposition since
the electrode coatings may also be deposited dry). In some designs,
this interlayer (buffer layer) may be deposited on the metal
current collector (e.g., metal current collector foils) by tape
casting (slurry casting) or by spraying or by electrophoretic
deposition or by electrostatic deposition (electrostatic painting)
or by other suitable techniques or their various combinations.
[0070] In some designs, such an interlayer may comprise solid
particles, polymeric binder and pores. In some designs, the
polymeric binder may be electrically conductive or electrically
insulative. In some designs, mechanical properties of the
interlayer may be optimized for a particular electrode design. In
some designs, a suitable fraction of electronically conductive
materials within the interlayer may range from around 0.05 wt. % to
around 100 wt. % (in some designs, from around 1 wt. % to around 30
wt. %). In some designs, the interlayer may be configured so as to
remain electrically conductive even when a small fraction of
conductive materials is utilized (e.g., so that electrical
percolation of conductive particles is achieved within the
interlayer).
[0071] In some designs, solid particles in the interlayer may
exhibit a near-spherical or elliptical shape, irregular shape, be
planar (two dimensional, 2D) or be elongated (one dimensional, 1D).
In some designs, the average smallest dimension of the solid
particles (diameter or thickness) may range from around 0.3 nm to
around 5 microns (in some designs, from around 1 nm to around 300
nm). In the case of 1D and 2D solid particles, the average largest
dimension of the solid particles (average length of the
(nano)fibers, (nano)wires, (nano)tubes, or average diameter of
planar particles) may range from around 10 nm to around 5,000 .mu.m
(e.g., more preferably from around 500 nm to around 30 .mu.m). In
some designs, planar or elongated (2D or 1D) particles with larger
length may be challenging to coat/deposit on a foil.
[0072] In some designs, the use of mechanically strong 2D and 1D
nanomaterials within this interlayer improves its mechanical
properties and thus may be particularly effective for cell
stability improvements. In some designs, 1D materials may
additionally provide simplicity for the interlayer fabrication
because they may be easier to disperse or intermix with other
components of the interlayer. In some designs, a suitable fraction
of such 1D nanomaterials in the interlayer may depend on the
particular electrode design and may range from around 0 wt. % to
around 100 wt. %. Suitable examples of 1D materials include, but
are not limited to single walled carbon nanotubes (SWCNTs),
double-walled carbon nanotubes (DWCNTs), multi-walled carbon
nanotubes (MWCNTs), carbon (nano)fibers, graphite ribbons, suitable
(compatible with the electrode) metal (nano)wires, (nano)tubes and
(nano)fibers (for example, copper, iron, nickel, or titanium or
their alloys for Li ion battery anodes; aluminum or nickel for
Li-ion battery cathodes), suitable (compatible with the electrode)
ceramic nanowires or nanofibers (for example, nanowire or nanotube
or nanofibers comprising aluminum oxide, zirconium oxide, magnesium
oxide, and other oxides; titanium nitride, boron nitride, various
other nitrides; various other suitable ceramic materials), suitable
polymer or organic (nano)fibers, various structural composite and
core-shell (nano)fibers, (nano)wires and nanotubes, etc. In some
designs, these 1D materials may be conductive or may be insulative.
In some designs, higher electrical conductivity may be advantageous
for achieving higher power performance and better electrical
connectivity between the electrode and the current collector foil.
In some designs, it may be advantageous for at least one type of
the solid particles to exhibit a 1D shape.
[0073] In some designs, it may be particularly advantageous for the
interlayer to comprise a polymer binder that comprises the same
functional groups as the binder used in the electrode formulation.
In some designs, it may be advantageous for the interlayer to
comprise a polymer binder with the same (or similar, within about
10-20%) degree of hydrolysis as the binder used in the electrode
formulation. In some designs, it may be advantageous for the
interlayer to comprise the same or similar polymer binder as the
one used in the electrode formulation. In some designs, it may be
advantageous for both the interlayer and the electrode formulation
to comprise SWCNTs or DWCNTs or MWCNTs or their combinations.
[0074] FIG. 2A and FIG. 2B illustrate a schematic example of one
side of an electrode 201 comprising (nano)composite particles 203,
a current collector 204 and a conductive interlayer 202 in between.
The interlayer 202 in this example comprises suitable conductive
additives 205 (e.g., carbon black or carbon nanotubes or carbon
fibers or nanowires or other suitable conductive additives) and a
polymer 206. The interlayer 202 electrically connects the current
collector and active (ion storing) portion of the electrode and
improves adhesion and mechanical robustness of the electrode (and
may also reduce electrode resistance). In FIG. 2A all or nearly all
(nano)composite particles 203 do not have a direct contact with a
current collector 204 (e.g., the electrical interconnection between
the (nano)composite particles 203 and the current collector 204 is
instead facilitated via the conductive additives 205 of the
conductive interlayer 202). In FIG. 2B some of the (nano)composite
particles 203 may have a direct contact with a current collector
204 (e.g., by virtue of a thinner conductive interlayer 202 on at
least part of the current collector 204 relative to the conductive
interlayer 202 depicted in FIG. 2A).
[0075] In some designs, it may be advantageous for the conductive
interlayer 202 between the electrode 201 and current collector
foils 204 to be composed of several sub-layers of distinct
compositions or to exhibit a gradual change in composition. In one
example, the type of the binder or the amount of the binder may be
different at the interface with the metal foil (or current
collector 204) and at the surface or top coating of the conductive
interlayer 202. In another example, the type of the conductive
additive(s) or the amount of conductive additives may be different
at the interface with the metal foil (or current collector 204) and
at the surface or top layer of the conductive interlayer 202. In
some designs, when more than one sub-layer is used for the
conductive interlayer formation, different solvents may be utilized
for the deposition of each sub-layer. In some designs, it may be
advantageous for the sub-layers to be of different thickness for
optimal performance.
[0076] In some designs, it may be advantageous to add functional
groups (or a substantially thin, e.g., about 1-5 nm in average
thickness, layer of an organic component, such as a polymer) onto
the surface of metal foil current collectors 204 in order to: (i)
improve adhesion of the electrode (or the conductive interlayer
202), (ii) improve electrode slurry wetting (or wetting of the
pre-deposited conductive interlayer slurry), or (iii) achieve
preferential adsorption of the components of the slurry (or
components of the conductive interlayer slurry) at the interface
with the metal for improved electrode performance (improved
stability, improved rate, etc.). An example of such a functional
group is depicted in FIGS. 2A-2B as a portion of the polymer layer
206. In some designs, such functional groups (or a thin polymer
layer) may be used to chemically bond the (electrode or interlayer)
binder or the conductive additives or the active particles to the
current collector foils. In some designs, such functional groups
may be added by using solution-based chemistry or by using dry
chemistry techniques (such as plasma, ultraviolet (UV)-treatment,
ozone treatment, exposure to one or more reactive gases, etc.).
[0077] It will be appreciated that, in the forgoing discussion, the
"electrode" layer is separately described from the interlayer and
the metal foil current collector. However, in some other examples,
the electrode may be understood as a combination of all the
components, including the foil and the interlayer.
[0078] In some designs, a suitable thickness of the interlayer may
range from around 1 nm to around 10 .mu.m. In some designs, a
suitable thickness of the interlayer may range even more preferably
from around 5 nm to around 1 .mu.m (in some designs, from around 10
nm to around 200 nm). In some designs, larger than optimal
thickness may reduce the energy density of the cell to an
undesirably low level and, in some cases, may increase first cycle
losses. On the other hand, in some designs, lower than optimal
thickness may be insufficient for providing the desired enhancement
in performance. In some designs, an optimal thickness of the
interlayer may also depend on the particular electrode and cell
designs as well as the interlayer composition and properties.
[0079] In some applications, two or more conductive additives in
the electrode (or in the interlayer or in both) may be selected to
achieve different functions. In one example, one type of additive
(e.g., with larger dimensions or higher conductivity) may be
selected to provide higher electrical conductivity within the
electrode as a whole, while the second type of conductive additive
may be selected to ensure that each individual electrode particle
is effectively electrically connected to multiple neighboring
electrode particles and the first type of additive, thereby forming
an efficient conductive network that results in high capacity
utilization of the electrode material. In another example, one type
of additive may be selected to perform multiple functions (e.g., to
enhance both electrical conductivity and mechanical stability of
the electrodes or to enhance electrical conductivity of the
electrode and provide faster ionic pathways (e.g., if it is porous
or if it prevents electrode pore closing)). In another example, one
type of conductive additive may also assist in better dispersing
the second type during the slurry mixing. In particular, in some
designs, it may be advantageous to use a mixture of two of the
following types of conductive additives in the same slurry: (i)
various types of single walled carbon nanotubes (SWCNTs) (with or
without surface coatings); (ii) various types of double-walled and
multiwalled carbon nanotubes (MWCNTs) (with or without surface
coatings); (iii) various types of carbon black (including those
that are annealed at above 1000.degree. C. in an inert
environment); (iv) various types of carbon fibers (including those
that are annealed at above 1000.degree. C. in an inert
environment); (v) various types of carbon nanofibers; (vi) various
types of metal nanowires (without or with protective or functional
surface coating layers) (e.g., Cu, Fe, Ti, or Ni nanowires for low
potential anodes in Li-ion batteries, such as Si comprising anodes;
Al nanowires for cathodes or high voltage anodes in Li-ion
batteries, or other nanowires (e.g., Ni or Ti nanowires) for
various aqueous batteries, etc.); (vii) various types of
carbon-coated or metal- (e.g., Cu, Fe, Ni, Ti or Al, etc.) coated
ceramic nanowires or fibers (e.g., Al.sub.2O.sub.3 nanowires or
fibers); (viii) various types of carbon onions; (ix) various types
of graphite ribbons (including metal-coated graphite ribbons); (x)
various types of metal (e.g., Cu, Fe, Ni, Ti or Al, etc.)
nanoparticles (with or without coatings by a protective or
functional surface layer); and (xi) various types of metal (e.g.,
Cu, Fe, Ni, Ti or Al, etc.) (nano)flakes (with or without coatings
by a protective or functional surface layer), (xii) conductive
metal oxides (e.g., suboxides of titanium oxide) provided these
remain electrochemically stable within the electrode operating
potential (often more suitable for conversion-type cathodes), to
name a few examples. In some designs, the surface chemistry of each
type of such additive could be individually optimized for optimum
performance in cells.
[0080] In some applications, it may be advantageous to restrict the
overall volume fraction of all conductive additive particles within
the electrode to less than about 5 vol. % (e.g., in some designs,
even more preferably below about 2 vol. %). By mass, the fraction
of all conductive additive particles within the electrode may
preferably be less than about 7 wt. % in some designs (e.g., in
some designs, even more preferably below about 3 wt. %) if only
carbon materials are used as conductive additives and less than
about 10 wt. % (e.g., in some designs, even more preferably below
about 5 wt. %) if some of the conductive additives comprise
suitable metals or metal oxides. In some designs, a higher volume
fraction of conductive additives may reduce ionic transport and
volumetric capacity of electrodes and may increase the extent of
undesirable side reactions. In some designs, a higher gravimetric
(mass) fraction of conductive additives may reduce the specific
capacity of the electrodes.
[0081] In some designs, the volume fraction of conductive additives
in an interlayer may exceed the average volume (or weight) fraction
of conductive additives in the bulk of the electrode by two times
or more (in some designs by about 2-100 times). For example, if the
bulk of the electrode comprises about 0.2 wt. % of conductive
additives, the interlayer may comprise from about 0.4 wt. % to
about 20.0 wt. % of conductive additives. In some advantageous
designs, the volume fraction of conductive additives in such an
interlayer may exceed the average volume (or weight) fraction of
conductive additives on the top surface of the electrode by two
times or more (in some designs by about 2-100 times). One way to
discover such differences in carbon additive content within a
battery electrode is to separate an electrode from a current
collector and image the top surface of the electrode (that used to
contact a separator member) and the bottom surface of the electrode
(that used to contact a current collector foil) or the current
collector. If either the separated bottom surface of the electrode
or the current collector comprises significantly (by about 2 times
or more) larger fraction of conductive additives, it means that the
interlayer was present and comprised significantly larger fraction
of conductive additives. Examples of suitable imaging or
characterization techniques (that may be capable of detecting such
differences in conductive additives) may include, but not limited
to, Raman microscopy (Raman mapping), secondary electron microscopy
(SEM), energy dispersive x-ray spectroscopy mapping (often called
EDS or EDX or EDXA mapping), optical microscopy, X-ray
photoelectron spectroscopy (XPS) and related techniques, secondary
ion mass spectrometry (SIMS) and related techniques, Auger
spectroscopy and related techniques, and other suitable techniques.
Another way to discover such differences in carbon additive content
within a battery electrode is to separate an electrode from a
current collector and image the cross-section of the electrode and
the bottom surface of the electrode (that contacted a current
collector foil prior to the separation) or the current collector.
If either the separated bottom surface of the electrode or the
current collector comprises significantly (by about 2 times or
more) larger fraction of conductive additives than the
cross-section of the electrode, then the presence of an interlayer
comprised of a significantly larger fraction of conductive
additives is indicated.
[0082] In some designs, the volume fraction of polymer binders in
such an interlayer may exceed the average volume (or weight)
fraction of conductive additives in the bulk of the electrode by
two times or more (in some designs by about 2-50 times). For
example, if the bulk of the electrode comprises about 8 wt. % of
the binder, the interlayer may comprise about 16 wt. % to about
99.0 wt. % of conductive additives. In another example, if the bulk
of the electrode comprises about 10 vol. % of the binder (e.g., the
rest being occupied by the pores, active material and conductive
additives), the interlayer may comprise about 20 vol. % to about
99.0 vol. % of binder (e.g., the rest being occupied by the pores
and the conductive additives or the active material, the pores and
the conductive additives).
[0083] In some advantageous designs, the volume fraction of
conductive additives in such an interlayer may exceed the average
volume (or weight) fraction of conductive additives on the top
surface of the electrode by two times or more (in some designs by
about 2-100 times).
[0084] Referring to FIGS. 2A-2B, in some designs, an Li-ion
electrode may comprise a current collector (e.g., current collector
204), a conductive interlayer (e.g., the interlayer 202) arranged
on the current collector, and an electrode active material layer
(e.g., the electrode 201) arranged on the conductive interlayer. In
some designs, the conductive interlayer may comprise first
conductive additives (e.g., conductive additives 205) and a first
polymer binder (e.g., polymer 206). In some designs, the electrode
active material layer comprises a plurality of active material
particles (e.g., (nano)composite particles 203) mixed with a second
polymer binder and second conductive additives, the plurality of
active material particles exhibiting an average particle size in
the range from about 0.2 microns to about 10 microns, an average
volume expansion in the range of about 8 vol. % to about 180 vol. %
during one or more charge-discharge cycles of the Li-ion battery
cell, and an average areal capacity loading in the range of about 3
mAh/cm.sup.2 to about 12 mAh/cm.sup.2.
[0085] In some designs, the first polymer binder comprises at least
one component of the second polymer binder. However, in other
designs, the first and second polymer binders may be different in
composition. In some designs, the first and second polymer binders
may also different in terms of concentration irrespective of
whether the first and second polymer binders are the same or
different in terms of composition.
[0086] In some designs, the first conductive additives comprise at
least one component of the second conductive additives. However, in
other designs, the first and second conductive additives may be
different in composition. In some designs, the first and second
conductive additives may also different in terms of concentration
irrespective of whether the first and second conductive additives
are the same or different in terms of composition.
[0087] In some designs, the first conductive additives comprise at
least one component of the second conductive additives. However, in
other designs, the first and second conductive additives may be
different in composition. In some designs, the first and second
conductive additives may also different in terms of concentration
irrespective of whether the first and second conductive additives
are the same or different in terms of composition.
[0088] In some designs, the plurality of active material particles
comprise Si. In some designs, the electrode active material layer
comprises water-soluble or water-dispersible binders. The
water-soluble or water-dispersible binders may be part of (e.g., at
least one component of) the second polymer binder, or alternatively
may be separate from the second polymer binder. In an example, the
second polymer binder may comprise at least one component that is
water soluble and at least one component that is water-dispersible.
In some designs, the electrode active material layer comprises a
plurality of binder components (e.g., the second polymer binder and
at least one other binder component, or multiple polymer binder
components). In some designs, at least one of the plurality of
binder components comprises particles or (nano)fibers or
(nano)ribbons of an elastomeric material with a maximum elongation
(or maximum strain) in the range from about 50% to about 5,000%. In
some designs, the particles or fibers of the elastomeric material
comprise around 60 to 95 wt. % of all binder in the electrode
active material layer. In some designs, a smallest average
dimension of the particles or fibers of the elastomeric material
(diameter for spherical particles or fiber-shaped particles) ranges
from around 30 nm to around 600 nm. In some designs, particles of
elastomeric materials may exhibit two or more distinct sizes or a
broad particle size distribution with a coefficient of variation
larger than around two.
[0089] In some designs, the second conductive additives comprise
single walled, double-walled and/or multi-walled carbon nanotubes.
In some designs, a weight fraction of all carbon nanotubes of the
second conductive additives ranges from around 0.05 wt. % to around
5 wt. % of the electrode active material layer. In some designs,
the first conductive additives single walled, double-walled and/or
multi-walled carbon nanotubes. In some designs, a weight fraction
of all carbon nanotubes of the first conductive additives ranges
from around 0.1 wt. % to around 20 wt. %. In some designs, a first
weight fraction of the first conductive additives in the conductive
interlayer exceeds a second weight fraction of the second
conductive additives in the electrode active material layer by at
least about 2 times.
[0090] In some designs, as will be described in more detail with
respect to FIGS. 4A-6 below in more detail, upon separation of the
current collector from the conductive interlayer, Raman
spectroscopy mapping detects at least about 2 times more conductive
additives on an exposed surface of the separated current collector
or an exposed surface of the separated conductive interlayer than a
top surface of the electrode active material layer. In some
designs, an average thickness of the conductive interlayer ranges
from around 25 nm to around 500 nm. In some designs, a Li-ion
battery electrode as described above may be incorporated into a
Li-ion battery.
[0091] FIG. 3 shows SEM images of the top (left) and the bottom
(right) of a high capacity anode 301 comprising near-spherical
volume-changing Si-containing (nano)composite particles 303 and
initially comprising a conductive interlayer (in turn, comprising a
polymer binder-conductive carbon nanotube mix) between the
electrode layer and the copper current collector foil. In
particular, FIG. 3 illustrates a significant difference in the
amount of binder mixed with conductive additives 302 clearly
visible between the two images: e.g., on the left side of FIG. 3,
hardly any binder-rich regions could be clearly distinguished at
the top of the electrode 301, while on the right side of FIG. 3,
nearly half of the bottom of the electrode 301 (e.g., positioned
near the current collector foil before the foil was detached from
the electrode) comprises binder-rich regions.
[0092] Note that in some designs when spherical or near-spherical
active (nano)composite particles are used, it may be advantageous
for at least a portion (e.g., from around 0.1 wt. % to around 20
wt. % or from around 0.1 vol. % to around 20 vol. %) of such
spherical particles to be broken into smaller fractions of the
initial spheres in order to attain higher electrode density or
higher electrode stability. In some designs, at least a portion of
such particle breakage may take place during particle synthesis and
before electrode casting. In some designs, at least a portion of
such particle breakage may take place during slurry mixing. In some
designs, at least a portion of such particle breakage may take
place during electrode densification (e.g., by pressure
calendaring).
[0093] FIG. 4A illustrates Raman mappings of the G/D band ratio at
a top surface of a high capacity anode (e.g., such as the electrode
301 of FIG. 3) comprising volume-changing Si-containing
(nano)composite particles, SWCNTs (as conductive additives, e.g.,
at about 0.13 wt. % relative to all solids in the anode), other
conductive carbon and a polymer binder. FIG. 4B illustrates Raman
mappings of the G/D band ratio at a surface of a copper current
collector foil separated from the anode (e.g., the electrode 301 of
FIG. 3). SWCNTs exhibit a very strong Raman signal and high ratio
of the integrated intensities of so-called G band (typically
centered around 1580 cm.sup.-1) and so-called D band (typically
centered around 1360 cm.sup.-1), as known in the state of the art.
By plotting a map of either the G/D ratio or just an intensity of
the G band one may visualize the relative difference in the SWCNT
distribution on various surfaces because the absence or small
amount of SWCNTs gives very weak (or no) signal of the G band.
These Raman mappings in FIGS. 4A-4B show that the top of the anode
(FIG. 4A) comprises a dramatically smaller fraction of SWCNTs (or
SWCNT agglomerates) compared to the Cu foil separated from the
bottom of the electrodes (FIG. 4B), thus indicating the presence of
the SWCNT-comprising interlayer between the Cu current collector
foil and the anode prior to their separation.
[0094] FIGS. 5A-5D illustrate Raman mappings of the G/D ratios
collected from the top of 4 different anodes comprising the
volume-changing Si-containing (nano)composite particles, different
amounts of SWCNTs (as conductive additives), other conductive
carbon and a polymer binder. In particular, FIG. 5A depicts a Raman
mapping for an anode with an SWCNT content in the bulk of the
electrode at about 0.13 wt. %, FIG. 5B depicts a Raman mapping for
an anode with an SWCNT content in the bulk of the electrode at
about 0.27 wt. %, FIG. 5C depicts a Raman mapping for an anode with
an SWCNT content in the bulk of the electrode at about 0.40 wt. %,
and FIG. 5D depicts a Raman mapping for an anode with an SWCNT
content in the bulk of the electrode at about 0.54 wt. %. As shown
with respect to FIGS. 5A-5D, an increase in the surface fraction of
the map with high G/D ratio correlates well with higher fraction of
SWCNTs in the bulk of the electrode.
[0095] FIG. 6 illustrates several Raman spectra taken from
different areas of an example carbon nanotube-comprising interlayer
(buffer layer), comprising SWCNTs in accordance with an embodiment
of the present disclosure. As shown in FIG. 6, there is a
significant difference in the intensities of D and G bands in all
spectra (G band is much stronger).
[0096] In some designs, the interlayer may be deposited on the
current collector from a slurry.
[0097] FIG. 7 illustrates a process 700 of Li-ion electrode
fabrication in accordance with an embodiment of the disclosure. For
example, one or more of the electrodes described above (e.g., such
as the electrode described with respect to FIGS. 2A-2B, etc.) may
be produced in accordance with the process 700 of FIG. 7.
[0098] Referring to FIG. 7, at 701, a first polymer binder, a first
solvent and first conductive additives are mixed to form a first
uniform conductive interlayer slurry. At 702, a current collector
is coated with the first slurry at a first thickness to form a
conductive interlayer. At 703, the first slurry coating is dried to
attain a conductive interlayer on the current collector. At 704, a
second polymer binder, a second solvent, second conductive
additives and active material particles (for example,
(nano)composite particles, which may comprise Si, among others) are
mixed to form a second uniform active material slurry. At 705, the
conductive interlayer is coated with the second slurry at a second
thickness. At 706, the second slurry coating is dried to attain an
electrode active material layer. At 707, the conductive interlayer
and/or the electrode active material layer are calendared until a
desired density is achieved.
[0099] Referring to FIG. 7, in some designs, alternative to
depositing the wet coating (702) and drying it (703) to form an
interlayer, dry coating methods could be utilized (e.g. by
electrostatic coatings or other techniques). In such case, stage
701 would include mixing first polymer binder and first conductive
additives (without a solvent). Similarly, in some designs,
alternative to depositing the wet coating (705) and drying it (706)
to form electrode active material layer, dry coating methods could
be utilized (e.g. by electrostatic coatings or other techniques).
In such case, stage 704 would include mixing a second polymer
binder, second conductive additives and active material particles
(without a solvent).
[0100] Referring to FIG. 7, in some designs, the coating (702) and
the drying (703) of the first slurry may repeat a plurality of
times (e.g., so as to produce multiple conductive interlayer
sub-layers which may be the same or different in terms of
composition) to attain the conductive interlayer. Further, in some
designs, the coating (705) and the drying (706) of the second
slurry may repeat a plurality of times (e.g., so as to produce
multiple electrode active material sub-layers which may be the same
or different in terms of composition) to attain the electrode
active material layer.
[0101] FIGS. 8-10 collectively illustrate one example
implementation of the process 700 of FIG. 7.
[0102] FIG. 8 illustrates a process of interlayer fabrication in
accordance with an embodiment of the disclosure. At 801, a polymer
binder, a solvent, and conductive additives are mixed at a given
ratio. At 802, the mixing of 801 eventually results in a uniform
slurry being obtained. At 803, the uniform slurry is then applied
to (or deposited as one or more coatings on) the current collector
(e.g., a metal (e.g., Cu) foil). For example, the uniform slurry
may be tape cast, sprayed onto the current collector,
electro-sprayed onto the current collector, or alternatively may be
applied via electrophoretic deposition, until the cast slurry
reaches a desired average thickness. At 804, the deposited
coating(s) are then dried to remove the solvent and provide
sufficient adhesion to the current collector. In some designs, the
interlayer may be deposited by a dry coating technique (without
solvents), such as electrostatic coatings (e.g., electrostatic
painting), among others. In this case, the solvent being added to
the mixture at 801 can be omitted, and likewise the evaporation
stage at 804 can be omitted.
[0103] Referring to FIG. 8, in some designs, the slurry for the
interlayer formulation may comprise about 0.5-20 wt. % solids and
about 80-99.5% solvent. In some designs, a solvent for the slurry
may be water or be water miscible. In some designs, the density of
the solvent may range from around 0.9 to around 1.15 gcm.sup.-3. In
some designs, the melting point of the solvent may range from
around -50.degree. C. to around +10.degree. C. In some designs, a
solvent for the slurry may be N-methyl-2-pyrrolidone (NMP). In some
designs, the solids may comprise one or more polymer binder and one
or more conductive carbon additive. In some designs, the polymer
binder(s) comprise about 70 to about 99.95 wt. % of the solids. In
some designs, the polymer binder is water soluble. In some designs,
the molecular weight of such a polymer binder may range from around
10,000 to around 2,500,000 gmol.sup.-1. In some designs, the
density of such a polymer may range from around 1.1 to around 1.7
gcm.sup.-3. In some designs, the melting point of such a polymer
may preferably range from around 100.degree. C. to around
300.degree. C. In some designs, the slurry for the interlayer
formulation may also comprise a surfactant/dispersant. In some
designs, the surfactant/dispersant may contribute from around 0.001
wt. % to around 20.000 wt. % of all the solids in the slurry. In
some designs, the wt. fraction of the surfactant may advantageously
range from around 0.1 wt. % to around 9 wt. %. In some designs,
another (polar) polymer may serve as a surfactant/dispersant. In
some designs, the molecular weight of such a polymer may range from
around 500 to around 2,500,000 gmol.sup.-1. In some designs, the
density of such a polymer may range from around 0.9 to around 1.4
gcm.sup.-3. In some designs, the melting point of such a polymer
may preferably range from around 100.degree. C. to around
300.degree. C. In some designs, such a dispersant polymer may be
polyvinylpyrrolidone (PVP). In some designs, the conductive
additives in the slurry may comprise carbon nanotubes (such as
SWCNTs, DWCNTs, MWCNTs or their combination). In some designs, the
conductive additives may contribute to range of about 0.1 wt. % to
about 30 wt. % of all the solids in the slurry. In some designs
(e.g., when SWCNTs are used), the conductive additives may
contribute to range of 0.15% to 5 wt. % of all the solids in the
slurry. In some designs, a viscosity of the slurry may preferably
range from around 10 to around 30,000 cp (in some designs, from
around 500 to around 3000 cp). In some designs, during mixing the
slurry from individual components at 301, a power of the mixing may
be in the range from around 0.1 kW/L to around 30 kW/L may be
applied.
[0104] In one example (for exemplary illustrative purpose), the
slurry exhibits the following composition: around 3 wt. % solids in
NMP solvent. In this example, the solids comprise around 92 wt. %
PVA, around 6 wt. % PVP and around 2 wt. % SWCNT composition (e.g.,
note SWCNT composition may comprise some amount of amorphous carbon
or DWCNTs or MWCNTs, but typically no more than about 75 wt. %). In
this example, the viscosity of the slurry may be in the range from
around 700 to 2,000 cp at room temperature (depending on the shear
rate). In case of using a small batch and a centrifugal mixer, the
mixing speed in this example is about 2,000 RPM (although the
optimal speed may vary from application to application). In this
example, a mixing time ranges from around 0.5 to around 20 minutes
(e.g., preferably, from around 5 to around 10 minutes). In case of
using an overhead mixer, in some designs, a mixing time may range
from around 0.5 minute to around 180 minutes (e.g., preferably,
from around 5 to around 60 minutes). In case of using an overhead
mixer with a planetary blade, in some designs, the mixing speed may
range from around 2 to around 1000 RPM (e.g., preferably, from
around 20 to around 100 RPM). In case of using an overhead mixer
with a high-shear blade, in some designs, the tip speed may range
from around 50 to around 5,000 m/s (e.g., preferably, from around
200 to around 500 m/s) and (in some designs, for example with blade
size in the range from around 20 to around 40 mm) the mixing speed
may range from around 2 to around 1000 RPM (e.g., preferably, from
around 20 to around 100 RPM).
[0105] Referring to FIG. 8, once a uniform slurry is prepared at
802, the uniform slurry may be coated on a metal current collector
(such as a Cu foil) at 803 using a draw-down coater or a spray
deposition or another suitable technique. In case of a draw-down
coater, a Gavure-type coater may be advantageously used in some
designs. In some designs, the coating speed may range from 0.01 m/s
to around 10 m/s (e.g., preferably, from around 0.03 to around 0.1
m/s). In one illustrative example, the coating speed is about 0.038
m/s. In some designs, the as-deposited (wet) coating thickness may
range from around 0.5 to around 50 micron (e.g., preferably, from
around 2 to around 20 micron). In one illustrative example, the
coating thickness (gap in a small draw-down coater) is about 13
micron. In some designs, after drying the coating at 804, a
thickness of the dried coating may range from around 0.02 micron to
around 5 micron (e.g., preferably, from around 0.05 to around 1
micron).
[0106] In some designs, an interlayer may be formed during or after
the coating (or slurry) deposition on the (e.g., metal) current
collector (such as a Cu foil, in some designs). In some designs,
the slurry may exhibit sufficient mobility of the binder or
conductive additive or both that during drying a larger portion of
the binder (or binder/conductive additive mix) is deposited on the
surface of the metal current collector compared to the binder or
conductive additive deposition on the surface of active
(nanocomposite) particles. This may take place, in some examples,
due to stronger affinity of the binder to the current collector
surface or, in some examples, due to the more stable suspension of
the active particles in a slurry compared to that of the binder or
conductive additives or, in some examples, due to the application
of the electric field and the resulting electrophoretic forces or
due to other mechanisms. The precise conditions of the slurry
processing may be fine-tuned or optimized (which may include, for
example, adjusting the slurry viscosity, adjusting the charges on
the surface of conductive additives, active particles or the
binder, adjusting the molecular weight (MW) of the binder,
adjusting the size of the active particles and conductive
additives, adjusting the dielectric constant of the solvent,
adjusting the surface tension of the solvent, adjusting the surface
chemistry of the conductive additives and active particles, among
others) in order to attain the formation of the interlayer of a
desired thickness, composition, porosity and/or other
properties.
[0107] FIG. 9 illustrates another process of interlayer fabrication
in accordance with an embodiment of the disclosure. At 901, a
polymer binder, a solvent, active (e.g., nanocomposite) particles
and conductive additives of suitable properties are mixed at a
given ratio. At 902, the mixing of 901 eventually results in a
uniform slurry being obtained. At 903, the uniform slurry is then
applied to (e.g., deposited as one or more coatings on) a current
collector (e.g., a metal (e.g., Cu in case of Si-comprising anode)
foil). For example, the uniform slurry may be tape cast, sprayed
onto the current collector, electro-sprayed onto the current
collector, or alternatively may be applied via electrophoretic
deposition, until the cast slurry reaches a desired average
thickness. At 904, the deposited coating(s) are then dried at the
suitable temperature and at suitable rate to remove the solvent and
facilitate migration of at least a small portion of the binder and
conductive additives (e.g., from around 0.001 wt. % to around 5.000
wt. % relative to the total amount of binder or the total amount of
conductive additives in the slurry) onto the surface of the current
collector. In this case, the interlayer of suitable thickness and
properties is formed during drying, providing enough adhesion to
the current collector and various performance advantages to the
electrode, as previously described. At 905, an optional electrode
densification (calendaring) is conducted to increase density of the
electrode (and thus volumetric capacity of the electrode), to
improve uniformity of the electrode thickness and, in some cases,
increase adhesion to the current collector and improve mechanical
properties of the electrode.
[0108] In some designs, the interlayer may be deposited by a dry
coating technique (without solvents), such as electrostatic
coatings (electrostatic painting), among others. In some designs,
the rest of the electrode coating may be deposited by a dry coating
technique, such as electrostatic coatings (electrostatic painting),
among others. In some designs, both the interlayer and the rest of
the coatings may be deposited by a dry coating technique. In this
case, the solvent being added to the mixture at 901 can be omitted,
and likewise the evaporation stage at 904 can be omitted.
[0109] In some designs, the interlayer may be formed from the (at
least partially) dried and deposited coatings during calendaring
(densification). In some designs, a gradient in temperature or a
remaining solvent content or binder mechanical properties is
achieved through the electrode thickness in such a way as to make
the binder near the current collector foil more deformable. For
example, the bottom of the electrode may be hotter or may comprise
a larger fraction of the remaining solvent or may comprise a binder
with lower glass transition temperature or lower yield strength,
etc. In this case, electrode densification will induce
significantly stronger deformation in the electrode binder closer
to the current collector, where a relatively soft binder (with
conductive additives) would flow, thus forming an interlayer. The
hotter temperature of the bottom of the electrode (near the current
collector) may be attained, for example, by pre-heating the
electrode and using a colder calendaring press (e.g., to maintain
the electrode top-layer or electrode surface at a lower relative
temperature than the bottom-layer near the current collector).
Alternatively, the current collector may be heated in a targeted
manner (e.g., by passing electrical current through the current
collector) such that the electrode is heated specifically near the
current collector.
[0110] FIG. 10 illustrates another process of interlayer
fabrication in accordance with an embodiment of the disclosure. At
1001, an electrode coating comprising a polymer binder, active
(e.g., nanocomposite) particles and conductive additives of
suitable properties and compositions is deposited onto one or both
sides of a suitable current collector foil by a suitable mechanism.
At 1002, a gradient in binder mechanical properties is attained by
a suitable mechanism (e.g., stronger heating the electrode near the
current collector, cooling the electrode surface, introducing
larger amount of binder-swelling solvent in the top portion of the
electrode, etc.) so that the binder near the top of the electrode
remains more rigid than the binder near the bottom of the electrode
(near a metal current collector) and so that the binder near the
current collector becomes relatively softer (e.g., hardness lower
by 1.5-1000 times) and more deformable. At 1003, a pressure is
applied to the electrode by suitable means (e.g. calendaring or
pressure rolling) inducing a stronger deformation in the electrode
near the current collector foils, thus forming an interlayer. At
1004, the pressure is released. In some designs where the pressure
at 1004 is applied via calendaring, the calendaring may be applied
concurrently to electrode coatings arranged on both sides of the
current collectors (e.g., via rollers).
[0111] In some designs, the binder in the interlayer (or electrode
material layer or both) may comprise a copolymer. In some designs,
this copolymer binder may be water-soluble. In some designs, a
water-soluble copolymer in the interlayer (or the electrode
material layer or both) may comprise at least one of the following
components: vinyl (or butyl or methyl or propyl, etc.) acetate,
vinyl (or butyl or methyl or propyl, etc.) acrylic, vinyl (or butyl
or methyl or propyl, etc.) alcohol, vinyl (or butyl or methyl or
propyl, etc.) acetate-acrylic, vinyl (or butyl or methyl or propyl,
etc.) acrylate, styrene-acrylic, alginic acid, acrylic acid, vinyl
(or butyl or methyl or propyl, etc.) siloxane (or other siloxanes),
pyrrolidone, sterene, various sulfonates (e.g., styrene sulfonate,
among others), various amines (incl. quaternary amines), various
dicyandiamide resins, amide-amine, ethyleneimine, diallyldimethyl
ammonium chloride. In some designs, copolymer binders may comprise
poly(acrylamide) (that is comprise acrylamide
(--CH.sub.2CHCONH.sub.2--) subunits). In some designs, such
poly(acrylamide)-comprising copolymer binders may be water soluble.
In some designs, such poly(acrylamide)-comprising copolymer binders
may also comprise acrylic acid, carboxylic acid, alginic acid or
metal salt(s) thereof (e.g., Na, K, Ca, Mg, Li, Sr, Cs, Ba, La and
other salts of such acids). In some designs, such and other
additions may be utilized to tune the ionic character of the
polymer, its solubility and interactions with both the solvents and
active (electrode) particles (e.g., to achieve stability of a
slurry, etc.).
[0112] In some designs, anion conducting heterogeneous polymers
(such as alkoxysilane/acrylate or epoxy alkoxysilane, etc.),
various anion conducting interpenetrating polymer networks, various
anion conducting poly (ionic liquids) (cross-linked ionic liquids)
or poly(acrylonitriles), various anion conducting polyquaterniums,
various anion conducting comprising quaternary ammonium salts
(e.g., benzyltrialkylammonium tetraalkylammonium, trimethyl
ammonium, dimethyl ammonium, diallyldimethylammonium, etc.),
various anion conducting copolymers comprising ammonium groups,
various anion conducting copolymers comprising norbornene, various
anion conducting copolymers comprising cycloalkenes (e.g.,
cyclooctene), methacrylates, butyl acrylate, vinyl benzyl or
poly(phenylene), various anion conducting copolymers comprising
organochlorine compounds (e.g., epichlorohydrin, etc.), various
anion conducting copolymers comprising ethers, bicyclic amines
(e.g., quinuclidine), various anion conducting poly (ionic liquids)
(cross-linked ionic liquids), various anion conducting copolymers
comprising other amines (e.g., diamines such as ethylene diamine,
monoamines, etc.), various anion conducting copolymers comprising
poly(ether imides), various polysaccharides (e.g., chitosan, etc.),
xylylene, guanidine, pyrodinium, among other units, may be
advantageously used as copolymer binders (or components of the
polymer/copolymer binder mixture) in the interlayer (or electrode
layer or both) in the context of one or more embodiments of the
present disclosure. In some designs, a copolymer binder may be
cationic and highly charged.
[0113] In some designs, various cation conducting polymers
(including interpenetrating polymer networks) and cross-linked
ionic liquids (e.g., with cation conductivity above around
10.sup.-10 S sm.sup.-1) may be advantageously used in the
interlayer (or electrode layer or both) as binders or components of
binders in the context of one or more embodiments of the present
disclosure. In some designs, such polymers may advantageously
exhibit medium-to-high conductivity (e.g., above around 10.sup.-10
S sm.sup.-1, or more preferably above around 10.sup.-6 S sm.sup.-1)
for Li ions (in the case of Li or Li-ion batteries).
[0114] In some designs, various electrically conductive polymers or
copolymers (e.g., preferably with electrical conductivity above
around 10.sup.-2 S sm.sup.-1), particularly those soluble in water
(or at least processable in water-based electrode slurries) may be
advantageously used as binders or components of binders (e.g.,
components of the binder mixtures or components of co-polymer
binders) in the interlayer (or in the electrode or in both) in the
context of one or more embodiments of this disclosure. In
particular, sulfur (S) containing polymers/co-polymers, also
comprising aromatic cycles, may be advantageously utilized. In some
examples, S may be in the aromatic cycle (e.g., as in
poly(thiophene)s (PT) or as in poly(3,4-ethylenedioxythiophene)
(PEDOT)), while in other examples, S may be outside the aromatic
cycle (e.g., as in poly(p-phenylene sulfide) (PPS)). In some
designs, suitable conductive polymers/co-polymers may also comprise
nitrogen (N) as a heteroatom. In some designs, the N atoms may, for
example, be in the aromatic cycle (as in poly(pyrrole)s (PPY),
polycarbazoles, polyindoles or polyazepines, etc.) or may be
outside the aromatic cycle (e.g., as in polyanilines (PANI)). In
some designs, some conductive polymers may have no heteroatoms
(e.g., as in poly(fluorene)s, polyphenylenes, polypyrenes,
polyazulenes, polynaphthalenes, etc.). In some designs, the main
chain may comprise double bonds (e.g., as in poly(acetylene)s (PAC)
or poly(p-phenylene vinylene) (PPV), etc.). In some designs, it may
be advantageous for the polymer/copolymer binders to comprise
ionomers (e.g., as in polyelectrolytes where ionic groups are
covalently bonded to the polymer backbone or as in ionenes, where
ionic group is a part of the actual polymer backbone). In some
designs, it may be advantageous to use a polymer mixture of two or
more ionomers. In some designs, such ionomers may carry the
opposite charges (e.g., one negative and one positive). Examples of
ionomers that may carry a negative charge include, but are not
limited to, various deprotonated compounds (e.g., if parts of the
sulfonyl group are deprotonated as in sulfonated polystyrene).
Examples of ionomers that may carry a positive charge include, but
are not limited to, various conjugated polymers, such as PEDOT,
among others. An example of a suitable polymer mixture of two
ionomers with the opposite charge is
poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. In some
designs, it may be advantageous to use polymer binders that
comprise both conductive polymers and another polymer, that
provides another functionality (e.g., serve as an elastomer to
significantly increase maximum binder elongation or serve to
enhance bonding to active materials or current collector, or serve
to enhance solubility in water or other slurry solvents, etc.).
[0115] In some designs, copolymer binders in the interlayer (or in
the electrode active material layer or both) may advantageously
comprise halide anions (e.g., chloride anions, fluoride anions,
bromide anions, etc.). In some designs, copolymer binders may
advantageously comprise ammonium cations (e.g., in addition to
halide anion, as, for example, in ammonium chloride). In some
designs, copolymer binders may advantageously comprise sulfur (S).
In some designs, copolymer binders may advantageously comprise an
allyl group (e.g., in addition to ammonium cations). For example,
such copolymer binders may advantageously comprise
diallyldimethylammonium chloride (DADMAC) or diallyldiethylammonium
chloride (DADEAC). In some designs, other suitable examples of such
copolymer binder components may include (but are not limited to):
methylammonium chloride, N,N-diallyl-N-propylammonium chloride,
methylammonium bromide, ethylammonium bromide, propylammonium
bromide, butylammonium bromide, methylammonium fluoride,
ethylammonium fluoride, propylammonium fluoride, butylammonium
fluoride, to name a few.
[0116] In some designs, copolymer binders in the interlayer (or in
the electrode active material layer or both) may comprise both
poly(acrylamide) and ammonium halides (e.g, ammonium chloride) in
their structure. As one suitable example,
poly(acrylamide-co-diallyldimethylammonium chloride) (PAMAC) may be
advantageously used as a copolymer binder in the context of the
present disclosure. In some designs, such PAMAC copolymer binders
may additionally comprise minor (e.g., less than around 5-10 wt. %)
amounts of acrylic acid, carboxylic acid or alginic acid or metal
salt(s) thereof (e.g., Na, K, Ca, Mg, Li, Sr, Cs, Ba, La and other
salts of such acids).
[0117] In some designs, when forming a polymer binder-comprising
interlayer between the polymer binder-comprising electrode and the
current collector it may be important to make sure that the binder
in the interlayer and the binder in the electrode are compatible
with each other. For example, if the selected binders are
incompatible with each other, the electrode may de-wet from the
interlayer surface (e.g., after coating), form bubbles, reduce
(instead of improving) adhesion or induce formation of species that
may harm cell performance. In some designs, it may be advantageous
for the polymer binders in the interlayer and the electrode to
comprise the same functional groups. In some designs, it may be
advantageous for the polymer binders in the interlayer and the
electrode to comprise the same or approximately the same fractions
of the same functional groups (e.g., within about 10% or less or,
in some designs, within about 4% or less or, in some designs within
about 2% or less). In some designs (particularly in case of aqueous
slurries) it may be advantageous for the polymer binders in the
interlayer and the electrode to exhibit the same or similar degree
of hydrolysis (e.g. within about 10% or less or, in some designs,
within about 4% or less or, in some designs within about 2% or
less). In some designs, it may be advantageous for the polymer
binders in the interlayer and the electrode to be of the same or
approximately the same (e.g., within about 10% or less or, in some
designs, within about 4% or less or, in some designs within about
2% or less) composition. In some designs, it may be advantageous
for the polymer binders in the interlayer and the electrode to
exhibit the same or similar molecular weight (e.g., within one
order of magnitude). In some designs, it may be advantageous for
the polymer binders in the interlayer and the electrode to comprise
the same polymer or copolymer. In some designs, it may be
advantageous for the polymer binders in the interlayer and the
electrode to be exactly the same.
[0118] The nanocomposite particles described with respect to
various embodiments of the present disclosure may generally be of
any shape (e.g., near-spherical, cylindrical, plate-like, have a
random shape, etc.) and of any size. In some designs, a maximum
size of the particle may depend on the rate performance
requirements, on the rate of the ion diffusion into the partially
filled particles, and on other parameters.
[0119] This description is provided to enable any person skilled in
the art to make or use embodiments of the present invention. It
will be appreciated, however, that the present invention is not
limited to the particular formulations, process steps, and
materials disclosed herein, as various modifications to these
embodiments will be readily apparent to those skilled in the art.
That is, the generic principles defined herein may be applied to
other embodiments without departing from the spirit or scope of the
invention.
* * * * *