U.S. patent application number 13/744509 was filed with the patent office on 2013-07-18 for compositions, layerings, electrodes and methods for making.
This patent application is currently assigned to E I DU PONT DE NEMOURS AND COMPANY. The applicant listed for this patent is E I DU PONT DE NEMOURS AND COMPANY. Invention is credited to Kostantinos Kourtakis.
Application Number | 20130183550 13/744509 |
Document ID | / |
Family ID | 48780178 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130183550 |
Kind Code |
A1 |
Kourtakis; Kostantinos |
July 18, 2013 |
COMPOSITIONS, LAYERINGS, ELECTRODES AND METHODS FOR MAKING
Abstract
There is a cell comprising an article comprising a hydrocarbon
ionomer. The article may be any element in the cell, such as an
interior wall, or a modification to an element, such as a film, a
membrane, and a coating. The hydrocarbon ionomer is any polymer
with ionic functionality, such as a polymeric (methacrylate)
neutralized with lithium, and not containing halogen or
halogen-containing substituents. The hydrocarbon ionomer may also
be included in a composition within an element of the cell, such as
a porous separator. The cell also comprises a positive electrode
including sulfur compound, a negative electrode, a circuit coupling
the positive electrode with the negative electrode, an electrolyte
medium and an interior wall of the cell. In addition, there are
methods of making the cell and methods of using the cell.
Inventors: |
Kourtakis; Kostantinos;
(Media, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E I DU PONT DE NEMOURS AND COMPANY; |
Wilmington |
DE |
US |
|
|
Assignee: |
E I DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
48780178 |
Appl. No.: |
13/744509 |
Filed: |
January 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61587849 |
Jan 18, 2012 |
|
|
|
Current U.S.
Class: |
429/50 ;
29/623.1; 429/144; 429/161 |
Current CPC
Class: |
H01M 10/058 20130101;
H01M 4/366 20130101; H01M 2/1686 20130101; H01M 4/382 20130101;
H01M 10/04 20130101; H01M 4/38 20130101; H01M 4/134 20130101; Y02P
70/50 20151101; H01M 4/622 20130101; H01M 10/052 20130101; Y02T
10/70 20130101; Y10T 29/49108 20150115; H01M 2/1653 20130101; H01M
4/62 20130101; H01M 10/02 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
429/50 ; 429/161;
429/144; 29/623.1 |
International
Class: |
H01M 10/02 20060101
H01M010/02; H01M 10/04 20060101 H01M010/04 |
Claims
1. A cell, comprising: a positive electrode comprising sulfur
compound; a negative electrode; a circuit coupling the positive
electrode with the negative electrode; an electrolyte medium; an
interior wall of the cell; and an article comprising a hydrocarbon
ionomer.
2. The cell of claim 1, wherein the article is a porous separator
comprising at least one of polyimide, polyethylene and
polypropylene.
3. The cell of claim 1, wherein the hydrocarbon ionomer is
incorporated as a surface coating on a surface of the article in an
amount of about 0.0001 to 100 mg/cm.sup.2.
4. The cell of claim 2, wherein the hydrocarbon ionomer is located
in a pore wall of a pore in the porous separator and exposed to
electrolyte medium in a pore volume in the pore.
5. The cell of claim 1, wherein the electrolyte medium is a
lithium-containing cell solution comprising solvent and
electrolyte.
6. The cell of claim 1, wherein the article is a coating located on
a surface of at least one of a porous separator, the negative
electrode, the circuit, and the interior wall of the cell.
7. The cell of claim 1, wherein the hydrocarbon ionomer comprises
at least one ionic group selected from carboxylate ionic
groups.
8. The cell of claim 1, wherein the hydrocarbon ionomer is a random
copolymer of poly(ethylene-co-(meth)acrylic) acid, and wherein the
copolymer is at least partially neutralized and comprises
(meth)acrylic acid comonomer that is one of acrylic acid comonomer,
methacrylic acid comonomer, and a combination of acrylic acid and
methacrylic acid comonomers.
9. A method for making a cell, comprising: fabricating a plurality
of components to form the cell, wherein the plurality comprises a
positive electrode comprising sulfur compound, a negative
electrode, a circuit coupling the positive electrode with the
negative electrode, an electrolyte medium, an interior wall of the
cell, and an article comprising a hydrocarbon ionomer.
10. The method of claim 9, wherein the article is a porous
separator comprising at least one of polyimide, polyethylene and
polypropylene.
11. The method of claim 9, wherein the hydrocarbon ionomer
comprises at least one ionic group selected from carboxylate ionic
groups.
12. A method for using a cell, comprising at least one step from
the plurality of steps comprising converting chemical energy stored
in the cell into electrical energy; and converting electrical
energy into chemical energy stored in the cell, wherein the cell
comprises a positive electrode comprising sulfur compound, a
negative electrode, a circuit coupling the positive electrode with
the negative electrode, an electrolyte medium, an interior wall of
the cell, and an article comprising hydrocarbon ionomer.
13. The method of claim 12, wherein the cell is associated with at
least one of a portable battery, a power source for an electrified
vehicle, a power source for an ignition system of a vehicle and a
power source for a mobile device.
14. The method of claim 12, wherein the article is a porous
separator comprising at least one of polyimide, polyethylene and
polypropylene.
15. The method of claim 12, wherein the hydrocarbon ionomer
comprises at least one ionic group selected from carboxylate ionic
groups.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority on and the benefit of the
filing date of U.S. Provisional Application Nos. 61/587,849, filed
on Jan. 18, 2012, and U.S. Provisional Application Nos. 61/602,180,
filed on Feb. 23, 2012, the entirety of which is herein
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] There is significant interest in lithium sulfur (i.e.,
"Li--S") batteries as potential portable power sources for their
applicability in different areas. These areas include emerging
areas, such as electrically powered automobiles and portable
electronic devices, and traditional areas, such as car ignition
batteries. Li--S batteries offer great promise in terms of cost,
safety and capacity, especially compared with lithium ion battery
technologies not based on sulfur. For example, elemental sulfur is
often used as a source of electroactive sulfur in a Li--S cell of a
Li--S battery. The theoretical charge capacity associated with
electroactive sulfur in a Li--S cell based on elemental sulfur is
about 1,672 mAh/g S. In comparison, a theoretical charge capacity
in a lithium ion battery based on a metal oxide is often less than
250 mAh/g metal oxide. For example, the theoretical charge capacity
in a lithium ion battery based on the metal oxide species
LiFePO.sub.4 is 176 mAh/g.
[0003] A Li--S battery includes one or more electrochemical voltaic
Li--S cells which derive electrical energy from chemical reactions
occurring in the cells. A cell includes at least one positive
electrode. When a new positive electrode is initially incorporated
into a Li--S cell, the electrode includes an amount of sulfur
compound incorporated within its structure. The sulfur compound
includes potentially electroactive sulfur which can be utilized in
operating the cell. A negative electrode in a Li--S cell commonly
includes lithium metal. In general, the cell includes a cell
solution with one or more solvents and electrolytes. The cell also
includes one or more porous separators for separating and
electrically isolating the positive electrode from the negative
electrode, but permitting diffusion to occur between them in the
cell solution. Generally, the positive electrode is coupled to at
least one negative electrode in the same cell. The coupling is
commonly through a conductive metallic circuit.
[0004] Li--S cell configurations also include, but are not limited
to, those having a negative electrode which initially does not
include lithium metal, but includes another material. Examples of
these materials are graphite, silicon-alloy and other metal alloys.
Other Li--S cell configurations include those with a positive
electrode incorporating a lithiated sulfur compound, such as
lithium sulfide (i.e., Li.sub.2S).
[0005] The sulfur chemistry in a Li--S cell involves a related
series of sulfur compounds. During a discharge phase in a Li--S
cell, lithium is oxidized to form lithium ions. At the same time
larger or longer chain sulfur compounds in the cell, such as
S.sub.8 and Li.sub.2S.sub.8, are electrochemically reduced and
converted to smaller or shorter chain sulfur compounds. In general,
the reactions occurring during discharge may be represented by the
following theoretical discharging sequence of the electrochemical
reduction of elemental sulfur to form lithium polysulfides and
lithium sulfide:
[0006]
S.sub.8.fwdarw.Li.sub.2S.sub.8.fwdarw.Li.sub.2S.sub.6.fwdarw.Li.sub-
.2S.sub.4.fwdarw.Li.sub.2S.sub.3.fwdarw.Li.sub.2S.sub.2.fwdarw.Li.sub.2S
[0007] During a charge phase in a Li--S cell, a reverse process
occurs. The lithium ions are drawn out of the cell solution. These
ions may be plated out of the solution and back to a metallic
lithium negative electrode. The reactions may be represented,
generally, by the following theoretical charging sequence
representing the electrooxidation of the various sulfides to
elemental sulfur:
[0008]
Li.sub.2S.fwdarw.Li.sub.2S.sub.2.fwdarw.Li.sub.2S.sub.3.fwdarw.Li.s-
ub.2S.sub.4.fwdarw.Li.sub.2S.sub.6.fwdarw.Li.sub.2S.sub.8.fwdarw.S.sub.8
[0009] A common limitation of previously-developed Li--S cells and
batteries is capacity degradation or capacity "fade". Capacity fade
is associated with coulombic efficiency, the fraction or percentage
of the electrical charge stored by charging that is recoverable
during discharge. It is generally believed that capacity fade and
coulombic efficiency are due, in part, to sulfur loss through the
formation of certain soluble sulfur compounds which "shuttle"
between electrodes in a Li--S cell and react to deposit on the
surface of a negative electrode. It is believed that these
deposited sulfides can obstruct and otherwise foul the surface of
the negative electrode and may also result in sulfur loss from the
total electroactive sulfur in the cell. The formation of
anode-deposited sulfur compounds involves complex chemistry which
is not completely understood.
[0010] In addition, low coulombic efficiency is another common
limitation of Li--S cells and batteries. A low coulombic efficiency
can be accompanied by a high self-discharge rate. It is believed
that low coulombic efficiency is also a consequence, in part, of
the formation of the soluble sulfur compounds which shuttle between
electrodes during charge and discharge processes in a Li--S
cell.
[0011] Some previously-developed Li--S cells and batteries have
utilized high loadings of sulfur compound in their positive
electrodes in attempting to address the drawbacks associated with
capacity degradation and anode-deposited sulfur compounds. However,
simply utilizing a higher loading of sulfur compound presents other
difficulties, including a lack of adequate containment for the
entire amount of sulfur compound in the high loading. Furthermore,
positive electrodes formed using these compositions tend to crack
or break. Another difficulty may be due, in part, to the insulating
effect of the higher loading of sulfur compound. The insulating
effect may contribute to difficulties in realizing the full
capacity associated with all the potentially electroactive sulfur
in the high loading of sulfur compound in a positive electrode of
these previously-developed Li--S cell and batteries.
[0012] Conventionally, the lack of adequate containment for a high
loading of sulfur compound has been addressed by utilizing higher
amounts of binder in compositions incorporated into these positive
electrodes. However, a positive electrode incorporating a high
binder amount tends to have a lower sulfur utilization which, in
turn, lowers the effective maximum discharge capacity of the Li--S
cells with these electrodes.
[0013] Li--S cells and batteries are desirable based on the high
theoretical capacities and high theoretical energy densities of the
electroactive sulfur in their positive electrodes. However,
attaining the full theoretical capacities and energy densities
remains elusive. Furthermore, as mentioned above, the sulfide
shuttling phenomena present in Li--S cells (i.e., the movement of
polysulfides between the electrodes) can result in relatively low
coulombic efficiencies for these electrochemical cells; and this is
typically accompanied by undesirably high self-discharge rates. In
addition, the concomitant limitations associated with capacity
degradation, anode-deposited sulfur compounds and the poor
conductivities intrinsic to sulfur compound itself, all of which
are associated with previously-developed Li--S cells and batteries,
limits the application and commercial acceptance of Li--S batteries
as power sources.
[0014] Given the foregoing, what is needed are Li--S cells and
batteries without the above-identified limitations of
previously-developed Li--S cells and batteries.
BRIEF SUMMARY OF THE INVENTION
[0015] This summary is provided to introduce a selection of
concepts. These concepts are further described below in the
Detailed Description. This summary is not intended to identify key
features or essential features of the claimed subject matter, nor
is this summary intended as an aid in determining the scope of the
claimed subject matter.
[0016] The present invention meets the above-identified needs by
providing Li--S cells incorporating hydrocarbon ionomer articles,
such as coatings, membranes, films and other articles incorporating
hydrocarbon ionomer. Examples of various types and combinations of
hydrocarbon ionomer articles which may be utilized are described
below in the Detailed Description. The hydrocarbon ionomer articles
provide Li--S cells with high coulombic efficiencies. In some
embodiments, the hydrocarbon ionomer articles also provide Li--S
cells with high maximum discharge capacities as well as high
coulombic efficiencies, and without the above-identified
limitations of previously-developed Li--S cells and batteries.
[0017] Hydrocarbon ionomer articles, according to the principles of
the invention, provide Li--S cells with surprisingly high coulombic
efficiencies and very high ratios of discharge to charge capacity.
While not being bound by any particular theory, it is believed that
the hydrocarbon ionomer in the hydrocarbon ionomer articles
suppresses the shuttling of soluble sulfur compounds and their
arrival at negative electrodes in the Li--S cells. This reduces
capacity fade through sulfur loss in the cells. Furthermore, low
sulfur utilization and high discharge capacity degradation are
avoided in these cells.
[0018] These and other objects are accomplished by the hydrocarbon
ionomer articles, methods for making such and methods for using
such, in accordance with the principles of the invention.
[0019] According to a first principle of the invention, there is a
cell. The cell comprises an article comprising a hydrocarbon
ionomer. The cell may also comprise one or more of a positive
electrode comprising sulfur compound, a negative electrode, a
circuit coupling the positive electrode with the negative
electrode, an electrolyte medium, and an interior wall of the cell.
The article may be a porous separator. The porous separator may
comprise one or more of polyimide, polyethylene and polypropylene.
The hydrocarbon ionomer may be incorporated as a surface coating on
a surface of the article in an amount of about 0.0001 to 100
mg/cm.sup.2. The surface coating may be applied by a process
comprising a calendaring step. The hydrocarbon ionomer may be a
component in a polymer blend incorporated within the porous
separator. The hydrocarbon ionomer may be located in a pore wall of
a pore in the porous separator and exposed to electrolyte medium in
a pore volume in the pore. The electrolyte medium may be a
lithium-containing cell solution comprising solvent and
electrolyte. The article may be a coating located on a surface of
one or more of a porous substrate, the negative electrode, the
circuit, and the interior wall of the cell. The coating may have
characteristics of a film and be located on a surface of one or
more of the circuit, and the interior wall of the cell. The coating
may have characteristics of a membrane and be located on a surface
of one or more at least one of the negative electrode, the circuit,
and the interior wall of the cell. The article may be situated in
the electrolyte medium and be one of a film, a membrane and a
combination comprising characteristics of a film and a membrane in
different parts of the combination. The hydrocarbon ionomer may
comprise one or more ionic group selected from sulfonate,
phosphate, phosphonate and carboxylate ionic groups. The
hydrocarbon ionomer may be a copolymer comprising about 5 to 25% by
weight ionic comonomer. The hydrocarbon ionomer may have a
neutralization ratio of greater than about 10%. The hydrocarbon
ionomer may be at least partially neutralized with lithium. The
hydrocarbon ionomer may be a random copolymer of
poly(ethylene-co-(meth)acrylic) acid. The copolymer may be at least
partially neutralized. The copolymer may comprise (meth)acrylic
acid comonomer that is acrylic acid comonomer, methacrylic acid
comonomer or a combination of acrylic acid and methacrylic acid
comonomers. The poly(ethylene-co-(meth)acrylic) acid copolymer may
incorporate the (meth)acrylic acid comonomer in an incorporation
ratio of less than 20% per mole. The hydrocarbon ionomer may be a
neutralized polyvinyl sulfonic acid. The hydrocarbon ionomer may be
a neutralized sulfonated derivative of a poly(ether ether-ketone).
The article may comprise a plurality of different types of
hydrocarbon ionomer.
[0020] According to a second principle of the invention, there is a
method for making a cell. The method comprises fabricating a
plurality of components to form the cell. The plurality comprises
an article comprising a hydrocarbon ionomer. The plurality may also
comprise one or more of a positive electrode comprising sulfur
compound, a negative electrode, a circuit coupling the positive
electrode with the negative electrode, an electrolyte medium, and
an interior wall of the cell. The article may be a porous
separator. The porous separator may comprise one or more of
polyimide, polyethylene and polypropylene. The hydrocarbon ionomer
may be incorporated as a surface coating on a surface of the
article in an amount of about 0.0001 to 100 mg/cm.sup.2. The
surface coating may be applied by a process comprising a
calendaring step. The hydrocarbon ionomer may be a component in a
polymer blend incorporated within the porous separator. The
hydrocarbon ionomer may be located in a pore wall of a pore in the
porous separator and exposed to electrolyte medium in a pore volume
in the pore. The electrolyte medium may be a lithium-containing
cell solution comprising solvent and electrolyte. The article may
be a coating located on a surface of one or more of a porous
substrate, the negative electrode, the circuit, and the interior
wall of the cell. The coating may have characteristics of a film
and be located on a surface of one or more of the circuit, and the
interior wall of the cell. The coating may have characteristics of
a membrane and be located on a surface of one or more at least one
of the negative electrode, the circuit, and the interior wall of
the cell. The article may be situated in the electrolyte medium and
be one of a film, a membrane and a combination comprising
characteristics of a film and a membrane in different parts of the
combination. The hydrocarbon ionomer may comprise one or more ionic
group selected from sulfonate, phosphate, phosphonate and
carboxylate ionic groups. The hydrocarbon ionomer may be a
copolymer comprising about 5 to 25% by weight ionic comonomer. The
hydrocarbon ionomer may have a neutralization ratio of greater than
about 10%. The hydrocarbon ionomer may be at least partially
neutralized with lithium. The hydrocarbon ionomer may be a random
copolymer of poly(ethylene-co-(meth)acrylic) acid. The copolymer
may be at least partially neutralized. The copolymer may comprise
(meth)acrylic acid comonomer that is acrylic acid comonomer,
methacrylic acid comonomer or a combination of acrylic acid and
methacrylic acid comonomers. The poly(ethylene-co-(meth)acrylic)
acid copolymer may incorporate the (meth)acrylic acid comonomer in
an incorporation ratio of less than 20% per mole. The hydrocarbon
ionomer may be a neutralized polyvinyl sulfonic acid. The
hydrocarbon ionomer may be a neutralized sulfonated derivative of a
poly(ether ether-ketone). The article may comprise a plurality of
different types of hydrocarbon ionomer.
[0021] According to a third principle of the invention, there is a
method for using a cell. The method comprises one or more steps
from the plurality of steps comprising converting chemical energy
stored in the cell into electrical energy, and converting
electrical energy into chemical energy stored in the cell. The cell
comprises an article comprising a hydrocarbon ionomer. The cell may
also comprise one or more of a positive electrode comprising sulfur
compound, a negative electrode, a circuit coupling the positive
electrode with the negative electrode, an electrolyte medium, and
an interior wall of the cell. The porous separator may comprise one
or more of polyimide, polyethylene and polypropylene. The
hydrocarbon ionomer may be incorporated as a surface coating on a
surface of the article in an amount of about 0.0001 to 100
mg/cm.sup.2. The surface coating may be applied by a process
comprising a calendaring step. The hydrocarbon ionomer may be a
component in a polymer blend incorporated within the porous
separator. The hydrocarbon ionomer may be located in a pore wall of
a pore in the porous separator and exposed to electrolyte medium in
a pore volume in the pore. The electrolyte medium may be a
lithium-containing cell solution comprising solvent and
electrolyte. The article may be a coating located on a surface of
one or more of a porous substrate, the negative electrode, the
circuit, and the interior wall of the cell. The coating may have
characteristics of a film and be located on a surface of one or
more of the circuit, and the interior wall of the cell. The coating
may have characteristics of a membrane and be located on a surface
of one or more at least one of the negative electrode, the circuit,
and the interior wall of the cell. The article may be situated in
the electrolyte medium and be one of a film, a membrane and a
combination comprising characteristics of a film and a membrane in
different parts of the combination. The hydrocarbon ionomer may
comprise one or more ionic group selected from sulfonate,
phosphate, phosphonate and carboxylate ionic groups. The
hydrocarbon ionomer may be a copolymer comprising about 5 to 25% by
weight ionic comonomer. The hydrocarbon ionomer may have a
neutralization ratio of greater than about 10%. The hydrocarbon
ionomer may be at least partially neutralized with lithium. The
hydrocarbon ionomer may be a random copolymer of
poly(ethylene-co-(meth)acrylic) acid. The copolymer may be at least
partially neutralized. The copolymer may comprise (meth)acrylic
acid comonomer that is acrylic acid comonomer, methacrylic acid
comonomer or a combination of acrylic acid and methacrylic acid
comonomers. The poly(ethylene-co-(meth)acrylic) acid copolymer may
incorporate the (meth)acrylic acid comonomer in an incorporation
ratio of less than 20% per mole. The hydrocarbon ionomer may be a
neutralized polyvinyl sulfonic acid. The hydrocarbon ionomer may be
a neutralized sulfonated derivative of a poly(ether ether-ketone).
The article may comprise a plurality of different types of
hydrocarbon ionomer.
[0022] The above summary is not intended to describe each
embodiment or every implementation of the present invention.
Further features, their nature and various advantages will be more
apparent from the accompanying drawings and the following detailed
description of the examples and embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The features and advantages of the present invention become
more apparent from the detailed description set forth below when
taken in conjunction with the drawings in which like reference
numbers indicate identical or functionally similar elements.
Additionally, the left-most digit of a reference number identifies
the drawing in which the reference number first appears.
[0024] In addition, it should be understood that the drawings in
the figures, which highlight the aspects, methodology,
functionality and advantages of the present invention, are
presented for example purposes only. The present invention is
sufficiently flexible, such that it may be implemented in ways
other than that shown in the accompanying figures.
[0025] FIG. 1 is a two-dimensional perspective of a Li--S cell
incorporating several hydrocarbon ionomer articles, according to an
example;
[0026] FIG. 2 is a context diagram illustrating properties of a
Li--S battery including a Li--S cell incorporating a hydrocarbon
ionomer article, according to an example; and
[0027] FIG. 3 is a two-dimensional perspective of a Li--S coin cell
incorporating a hydrocarbon ionomer article, according to different
examples.
DETAILED DESCRIPTION
[0028] The present invention is useful for certain energy storage
applications, and has been found to be particularly advantageous
for high maximum discharge capacity batteries which operate with
high coulombic efficiency utilizing electrochemical voltaic cells
which derive electrical energy from chemical reactions involving
sulfur compounds. While the present invention is not necessarily
limited to such applications, various aspects of the invention are
appreciated through a discussion of various examples using this
context.
[0029] For simplicity and illustrative purposes, the present
invention is described by referring mainly to embodiments,
principles and examples thereof. In the following description,
numerous specific details are set forth in order to provide a
thorough understanding of the examples. It is readily apparent
however, that the embodiments may be practiced without limitation
to these specific details. In other instances, some embodiments
have not been described in detail so as not to unnecessarily
obscure the description. Furthermore, different embodiments are
described below. The embodiments may be used or performed together
in different combinations.
[0030] The operation and effects of certain embodiments can be more
fully appreciated from a series of examples, as described below.
The embodiments on which these examples are based are
representative only. The selection of those embodiments to
illustrate the principles of the invention does not indicate that
materials, components, reactants, conditions, techniques,
configurations and designs, etc. which are not described in the
examples are not suitable for use, or that subject matter not
described in the examples is excluded from the scope of the
appended claims and their equivalents. The significance of the
examples can be better understood by comparing the results obtained
therefrom with potential results which can be obtained from tests
or trials that may be or may have been designed to serve as
controlled experiments and provide a basis for comparison.
[0031] As used herein, the terms "based on", "comprises",
"comprising", "includes", "including", "has", "having" or any other
variation thereof, are intended to cover a non-exclusive inclusion.
For example, a process, method, article, or apparatus that
comprises a list of elements is not necessarily limited to only
those elements but may include other elements not expressly listed
or inherent to such process, method, article, or apparatus.
Further, unless expressly stated to the contrary, "or" refers to an
inclusive or and not to an exclusive or. For example, a condition A
or B is satisfied by any one of the following: A is true (or
present) and B is false (or not present), A is false (or not
present) and B is true (or present), and both A and B are true (or
present). Also, use of the "a" or "an" is employed to describe
elements and components. This is done merely for convenience and to
give a general sense of the description. This description should be
read to include one or at least one and the singular also includes
the plural unless it is obvious that it is meant otherwise.
[0032] The meaning of abbreviations and certain terms used herein
is as follows: ".ANG." means angstrom(s), "g" means gram(s), "mg"
means milligram(s), ".mu.g" means microgram(s), "L" means liter(s),
"mL" means milliliter(s), "cc" means cubic centimeter(s), "cc/g"
means cubic centimeters per gram, "mol" means mole(s), "mmol" means
millimole(s), "M" means molar concentration, "wt. %" means percent
by weight, "Hz" means hertz, "mS" means millisiemen(s), "mA" mean
milliamp(s), "mAh/g" mean milliamp hour(s) per gram, "mAh/g S" mean
milliamp hour(s) per gram sulfur based on the weight of sulfur
atoms in a sulfur compound, "V" means volt(s), "x C" refers to a
constant current that may fully charge/discharge an electrode in
1/x hours, "SOC" means state of charge, "SEI" means solid
electrolyte interface formed on the surface of an electrode
material, "kPa" means kilopascal(s), "rpm" means revolutions per
minute, "psi" means pounds per square inch, "maximum discharge
capacity" is the maximum milliamp hour(s) per gram of a positive
electrode in a Li--S cell at the beginning of a discharge phase
(i.e., maximum charge capacity on discharge), "coulombic
efficiency" is the fraction or percentage of the electrical charge
stored in a rechargeable battery by charging and is recoverable
during discharging and is expressed as 100 times the ratio of the
charge capacity on discharge to the charge capacity on charging,
"pore volume" (i.e., Vp) is the sum of the volumes of all the pores
in one gram of a substance and may be expressed as cc/g, "porosity"
(i.e., "void fraction") is either the fraction (0-1) or the
percentage (0-100%) expressed by the ratio: (volume of voids in a
substance)/(total volume of the substance).
[0033] As used herein and unless otherwise stated the term
"cathode" is used to identify a positive electrode and "anode" to
identify the negative electrode of a battery or cell. The term
"battery" is used to denote a collection of one or more cells
arranged to provide electrical energy. The cells of a battery can
be arranged in various configurations (e.g., series, parallel and
combinations thereof).
[0034] The term "sulfur compound" as used herein refers to any
compound that includes at least one sulfur atom, such as elemental
sulfur and other sulfur compounds, such as lithiated sulfur
compounds including disulfide compounds and polysulfide compounds.
For further details on examples of sulfur compounds particularly
suited for lithium batteries, reference is made to "A New Entergy
Storage Material: Organosulfur Compounds Based on Multiple
Sulfur-Sulfur Bonds", by Naoi et al., J. Electrochem. Soc., Vol.
144, No. 6, pp. L170-L172 (June 1997), which is incorporated herein
by reference in its entirety.
[0035] The term "ionomer", as used herein, refers to any polymer
including an ionized functional group (e.g., sulfonic acid,
phosphonic acid, phosphoric acid or carboxylic acid, such as
acrylic or methacrylic acid (i.e., "(meth)acrylic acid") in which
the acid group is neutralized with a base including an alkali
metal, such as lithium, to form an ionized functionality, such as
lithium methacrylate). An ionomer may be made by various methods
including polymerizing ionic monomers and by chemically modifying
ionogenic polymers. The term "hydrocarbon ionomer", as used herein,
refers to any ionomer not including any halogen atoms incorporated
by a covalent bond into a site (e.g., the polymer backbone or
branching) on the ionomer.
[0036] According to the principles of the invention, as
demonstrated in the following examples and embodiments, there are
Li--S cells incorporating hydrocarbon ionomer articles, such as
coatings, films, and membranes. The hydrocarbon ionomer articles
may be associated with various elements in a Li--S cell, such as a
hydrocarbon ionomer coating on a porous separator or an interior
wall of the cell. According to various embodiments, different types
of hydrocarbon ionomers may be used in forming one or more of the
articles in a cell, such as an ionomer containing acrylate groups
based on ionized acrylic acid, methacrylate groups based on ionized
methacrylic acid or a combination of both acrylate and methacrylate
(i.e., (meth)acrylate) groups.
[0037] Examples of hydrocarbon ionomers include SURLYN.RTM. and
derivatives of SURLYN.RTM., a copolymer of ethylene and
(meth)acrylic acid. Depending upon the commercially available grade
of SURLYN.RTM. that is used, an amount of the ionizable
(meth)acrylic acid groups in the SURLYN.RTM. can be neutralized to
their ionic (meth)acrylate salt. Other examples of hydrocarbon
ionomers include sulfonated polyacrylamide and sulfonated
polystyrene. Other hydrocarbon ionomers may also be utilized, such
as ionomers having ionomer functional groups based on neutralized
carboxylic acids, phosphonic acids, phosphoric acids and/or other
ionomer functional groups.
[0038] Different types of copolymers may be hydrocarbon ionomers,
such as copolymers with different non-ionic monomers or multiple
types of ionic monomers. Other hydrocarbon ionomers may also be
utilized or combined in a hydrocarbon ionomer article, such as
different hydrocarbon ionomers with different structures and/or
different substituents which may be the same or different ionomer
functional groups. As noted above, hydrocarbon ionomers never
contain halogen or halogen-containing substituents, but may include
other substituents. In an embodiment, a hydrocarbon ionomer may
include alcohol and alkyl substituents. For example, a hydrocarbon
ionomer may include unsaturated branches with or without any
functional groups or substituents. The substituent sites on a
hydrocarbon ionomer may be located anywhere in the polymer, such as
along the backbone and along any branching which may be
present.
[0039] Hydrocarbon ionomer may be combined with other components to
form hydrocarbon ionomer articles which can be incorporated into a
Li--S cell, according to various embodiments. The hydrocarbon
ionomer may be identified or quantified with respect to other
components in different ways within the article. For example, in a
hydrocarbon ionomer article which is a coated porous separator, the
separator itself may be made from polyimide, such as a mat or other
article made from polyimide fiber, or a polyethylene/polypropylene
laminate which is then coated with a hydrocarbon ionomer. In
another variant, a hydrocarbon ionomer composition may be prepared
which is a blend, such as a combination including hydrocarbon
ionomer and a modified polyethylene which is modified to enhance
its miscibility with the hydrocarbon ionomer. Additives may also be
included, such as a polymer compatibilizer that is combined with
the components to stabilize the blend including hydrocarbon
ionomer. A composition comprising hydrocarbon ionomer may be molded
or press-formed to produce a hydrocarbon ionomer article, such as a
porous separator, constituted by the hydrocarbon ionomer alone or a
blend containing hydrocarbon ionomer. Hydrocarbon ionomer may also
be present as a function of a structure associated with these
embodiments, such as a weight measure of hydrocarbon ionomer per
surface area of an article, such as a porous separator, or as a
weight percentage of the porous separator constituted by a
hydrocarbon ionomer blend.
[0040] An amount of hydrocarbon ionomer in an article may be
quantified in terms of an amount of hydrocarbon ionomer associated
with a volume of material in a coating or a membrane, or below an
area on the surface of an element in an Li--S cell, such as a
porous separator, an interior wall of the cell, a positive
electrode, a negative electrode, a circuit coupling electrodes or
another cell element exposed to electrolyte medium in the cell.
According to an embodiment, a suitable amount of hydrocarbon
ionomer in a coating is about 0.0001 to 100 mg/cm.sup.2. In other
embodiments, a suitable amount of hydrocarbon ionomer in a coating
is about 0.001 to 75 mg/cm.sup.2, about 0.001 to 50 mg/cm.sup.2,
about 0.001 to 35 mg/cm.sup.2, about 0.01 to 20 mg/cm.sup.2, about
0.01 to 15 mg/cm.sup.2, about 0.1 to 10 mg/cm.sup.2 and about 0.3
to 5 mg/cm.sup.2.
[0041] An amount of hydrocarbon ionomer may be expressed as a
weight percentage present in an article, such a membrane or a film.
In this example, the membrane or film may be an element in another
article, such as porous separator. The hydrocarbon ionomer may also
be part of more than one article, such as a porous separator made
from a hydrocarbon ionomer blend and coated with a pure hydrocarbon
ionomer coating. The hydrocarbon ionomer loading in an element may
be varied as desired. According to an embodiment, a suitable amount
of hydrocarbon ionomer in an article is about 0.0001 to 100 wt. %.
According to other embodiments, a suitable amount of hydrocarbon
ionomer in an article is about 0.0001 wt. % to about 99 wt. %, 98
wt. %, 95 wt. %, 90 wt. %, 85 wt. %, 80 wt. %, 75 wt. %, 70 wt. %,
65 wt. %, 60 wt. %, 55 wt. %, 50 wt. %, 45 wt. %, 40 wt. %, 35 wt.
%, 30 wt. %, 25 wt. %, 20 wt. %, 15 wt. %, 10 wt. %, 5 wt. %, 2 wt.
%, 1 wt. %, 0.1 wt. %, 0.01 wt. % and 0.001 wt. %.
[0042] In an embodiment, a hydrocarbon ionomer article may modify
another element in a cell, such as a hydrocarbon ionomer coating on
a porous separator. In another embodiment, a hydrocarbon ionomer
article may form a separate element in a cell, such as a
hydrocarbon ionomer film or a membrane which is situated in the
cell solution, separate from other elements in the cell. Such an
article may float freely in the cell solution or be secured, such
as affixed to a cell wall. In this circumstance, the hydrocarbon
ionomer film or membrane, may be fully or partially situated within
the electrolyte medium, such as a cell solution in a Li--S cell,
and may be secured by fastening an edge of the film or membrane to
the interior wall of the cell or affixing it to another element or
part in the cell.
[0043] Referring to FIG. 1, depicted is a cell 100, such as a Li--S
cell in a Li--S battery. Cell 100 includes a lithium containing
negative electrode 101, a sulfur-containing positive electrode 102,
a circuit 106 and a porous separator 105. A cell container wall 107
contains the elements in the cell 100 with an electrolyte medium,
such as a cell solution comprising solvent and electrolyte. The
positive electrode 102 includes a circuit contact 104. The circuit
contact 104 provides a conductive conduit through a metallic
circuit 106 coupling the negative electrode 101 and the positive
electrode 102. The positive electrode 102 is operable in
conjunction with the negative electrode 101 in the cell 100 to
store electrochemical voltaic energy and release electrochemical
voltaic energy, this converting chemical and electrical energy from
one form to the other, depending upon the whether the cell 100 is
in the charge phase or discharge phase. A porous carbon material,
such as a carbon powder, having a high surface area and a high pore
volume, may be utilized in the making the positive electrode 102.
According to an embodiment, sulfur compound, such as elemental
sulfur, lithium sulfide, and combinations of such, may be
introduced to the porous regions within the carbon powder to make a
carbon-sulfur (C--S) composite which is incorporated into a cathode
composition in the positive electrode 102. A polymeric binder may
also be incorporated into the cathode composition with the C--S
composite in the positive electrode 102. In addition, other
materials may be utilized in the positive electrode 102 to host the
sulfur compound as an alternative to the carbon powder, such as
graphite, graphene and carbon fibers. The construction of the
positive electrode 102 may be varied as desired.
[0044] The porous separator 105 in cell 100 incorporates a
composition 103, and is a hydrocarbon ionomer article. The
composition 103 comprises hydrocarbon ionomer, optionally in a
blend including other components such as additives and/or other
polymers which are miscible with the hydrocarbon ionomer. An
example of such a miscible polymer is an ethylene copolymer with
polar functional groups grafted to promote miscibility with the
hydrocarbon ionomer in the composition 103. When situated in the
cell 100, the composition 103 within the porous separator 105 may
be exposed to an amount of the cell solution contained inside or
passing through a pore volume within the porous separator 105. The
exposed areas of the composition 103 within the porous separator
105 appears to function as a barrier to limit the passage of
soluble sulfur compounds "shuttling" through the cell solution
within the pore volume from reaching the negative electrode 101.
The composition 103 may also function as a reservoir through
adsorption of the sulfur compounds from the cell solution in the
pore volume, thus withdrawing these sulfur compounds temporarily
from the cell solution in the pore volume of the porous separator
105. However, the composition 103 in the porous separator 105 still
permits diffusion of lithium ions through the pore volume to and
from the negative electrode 101 during charge and discharge phases
in the cell 100.
[0045] Cell 100 also includes membranes 111, 112 and 115, coatings
113 and 114 and films 110 and 116, all of which are hydrocarbon
ionomer articles. These elements of cell 100 incorporate
compositions comprising hydrocarbon ionomer. The compositions may
be the same or different from each other and composition 103.
[0046] Membrane 111 is an anodic-membrane as it is affixed or in
close proximity to a surface of the negative electrode 101.
Membrane 111 comprises hydrocarbon ionomer. In an embodiment,
membrane 111 includes a protective layer, separating lithium metal
in the negative electrode 101 from the hydrocarbon ionomer in
membrane 111. The protective layer comprises a permeable substance
which is substantially inert to lithium metal in the negative
electrode 101. Suitable inert substances include porous films
containing polypropylene and polyethylene. According to an
embodiment, the hydrocarbon ionomer in membrane 111 is a derivative
of SURLYN.RTM. in which the SURLYN.RTM. is partially neutralized
with a lithium ion source. In other embodiments, membrane 111 may
comprise other hydrocarbon ionomers, as alternatives or in addition
to the SURLYN.RTM. derivative in the anodic-membrane. The membrane
111 is permeable, but functions in the cell 100 as a barrier to
limit the passage of soluble sulfur compounds in the cell solution
from reaching the negative electrode 101. Membrane 111 may also
function as a reservoir through adsorption of soluble sulfur
compounds from the cell solution or by otherwise limiting their
passage through a pore structure in the membrane 111. However,
membrane 111 permits diffusion of lithium ions to and from the
negative electrode 101 during charge-discharge cycles in the cell
100.
[0047] Coatings 113 and 114 are applied to respective separate
surfaces of the porous separator 105. The coatings 113 and 114 may
be applied through various well-known techniques such as spray
coating, dip coating and the like. Coatings 113 and 114 comprise
hydrocarbon ionomer, such as a hydrocarbon ionomer with
carboxylate, sulfonate, phosphate, and/or phosphonate groups, or
may comprise a plurality of different types of hydrocarbon ionomer.
Like the membrane 111, the coatings 113 and 114 are permeable, but
appear to function as a barrier to soluble sulfur compounds from
reaching the negative electrode 101 by limiting their passage by
diffusion through the cell solution. The coatings 113 and 114 may
also function as reservoirs for the sulfur compounds, possibly
through adsorption or by otherwise limiting the passage of soluble
sulfur compounds through pores in coatings 113 and 114. While the
coatings 113 and 114 appear to act as barriers and/or reservoirs
for soluble sulfur compounds in the cell solution, they permit the
diffusion of lithium ions to and from the negative electrode 101
during charge-discharge cycles in the cell 100.
[0048] Membranes 112 and 115 are fully situated within the cell
solution of the cell 100. Both membranes 112 and 115 are located
between positive electrode 102 and the negative electrode 101.
However, the respective membranes are on different respective sides
of the porous separator 105. Membranes 112 and 115 may be secured
within cell 100 by being affixed to another object in the cell 100,
such as the cell container wall 107. Membranes 112 and 115 comprise
hydrocarbon ionomer with ionic functional groups, such as
carboxylate, sulfonate, phosphate and/or phosphonate groups and may
comprise a plurality of different types of hydrocarbon ionomer.
Membranes 112 and 115 are permeable, but they function to limit the
passage of soluble sulfur compounds in the cell solution from
reaching the negative electrode 101 by acting as barriers to the
sulfur compounds. Membranes 112 and 115 may also act as reservoirs
through adsorption of the sulfur compounds. However, the membranes
112 and 115 permit the diffusion of lithium ions through their
respective pores to pass between the positive electrode 102 and the
negative electrode 101 during charge-discharge cycles in the cell
100.
[0049] Films 110 and 116 are situated in the cell 100 so as to be
partially exposed to the cell solution. Films 110 and 116 do not
separate the positive electrode 102 and negative electrode 101.
Therefore, films 110 and 116 may be permeable or impermeable. Films
110 and 116 are secured within cell 100 by being affixed to the
cell container wall 107. The respective films 110 and 116 comprise
respective hydrocarbon ionomer that may be the same or different,
such as a hydrocarbon ionomer with carboxylate, sulfonate,
phosphate, and/or phosphonate groups and may comprise a plurality
of different types of hydrocarbon ionomer. Although the films 110
and 116 may not be permeable, they appear to function as reservoirs
to soluble sulfur compounds, and limit the passage of sulfur
compounds in the cell solution from reaching the negative electrode
101. Without being bound by any particular theory, they appear to
accomplish this through the adsorption of sulfur compounds from the
electrolyte solution during charge-discharge cycles in the cell
100.
[0050] According to the principles of the invention, a Li--S cell,
such as cell 100, incorporates at least one hydrocarbon ionomer
article and may incorporate multiple hydrocarbon ionomer articles
as demonstrated in cell 100, and in various other combinations and
configurations. In one embodiment, the hydrocarbon ionomer articles
comprise a polymeric sulfonate. In another embodiment, the
hydrocarbon ionomer articles comprise a polymeric carboxylate. In
yet another embodiment the hydrocarbon ionomer articles comprise a
polymeric phosphate. In yet another embodiment the hydrocarbon
ionomer articles comprise a polymeric phosphonate. In still another
embodiment, the hydrocarbon ionomer articles comprise a copolymer
including at least two types of ionic functionality. In still yet
another embodiment, the hydrocarbon ionomer articles comprise at
least two different types of hydrocarbon ionomer with different
ionic functionality in the different types of hydrocarbon
ionomers.
[0051] Hydrocarbon ionomers which are suitable for use herein,
include ionomers which include pendant negatively charged
functional groups which are neutralized. The negatively charged
functional groups, such as an acid (e.g., carboxylic acid,
phosphonic acid and sulfonic acid) or an amide (e.g., acrylamide).
These negatively charged functional groups are neutralized, fully
or partially with a metal ion, preferably with an alkali metal.
Lithium is preferred for utilization in a Li--S cell. The
hydrocarbon ionomers may contain negatively-charged functional
groups, exclusively (i.e., anionomers) or may contain a combination
of negatively-charged functional groups with some
positively-charged functional groups (i.e., ampholytes).
[0052] The hydrocarbon ionomers may include ionic monomer units
copolymerized with nonionic (i.e., electrically neutral) monomer
units. The hydrocarbon ionomers can be prepared by polymerization
of ionic monomers, such as ethylenically unsaturated carboxylic
acid comonomers. Other hydrocarbon ionomers which are suitable for
making the articles are ionically modified "ionogenic" polymers
which made ionomers by chemical modification of negatively charged
functional groups on the ionogenic polymer (i.e., chemical
modification after polymerization), such as by treatment of a
polymer having carboxylic acid functionality which is chemically
modified by neutralizing to form ester-containing carboxylate
functional groups which are ionized with an alkali metal, thus
forming negatively charged ionic functionality. The ionic
functional groups may be randomly distributed or regularly located
in the hydrocarbon ionomers.
[0053] The hydrocarbon ionomers may be polymers including ionic and
non-ionic monomeric units in a saturated or unsaturated backbone,
optionally including branching, which is carbon based and may
include other elements, such as oxygen or silicon. The negatively
charged functional groups may be any species capable of forming an
ion with an alkali metal. These include, but are not limited to,
sulfonic acids, carboxylic acids and phosphonic acids. According to
an embodiment, the polymer backbone or branches in the hydrocarbon
ionomer may include comonomers such as alkyls. Alkyls which are
.alpha.-olefins are preferred. Suitable .alpha.-olefin comonomers
include, but are not limited to, ethylene, propylene, 1-butene,
1-pentene, 1-hexene, 1-heptene, 3 methyl-1-butene,
4-methyl-1-pentene, styrene and the like and mixtures of two or
more of these .alpha.-olefins.
[0054] According to an embodiment, hydrocarbon ionomers are
ionogenic acid copolymers which are neutralized with a base so that
the acid groups in the precursor acid copolymer form ester salts,
such as carboxylate or sulfonate groups. The precursor acid
copolymer groups may be fully neutralized or partially neutralized
to a "neutralization ratio" based on the amount neutralized of all
the negatively charged functional groups that may be neutralized in
the ionomer. According to an embodiment, the neutralization ratio
is 0% to about 1%. In other embodiments, the neutralization ratio
is about 5%, about 10%, about 20%, about 30%, about 40%, about 50%,
about 60%, about 70%, about 80%, about 90%, about 95%, or about
100%. According to an embodiment, the neutralization ratio is about
0% to 90%. In other embodiments, the neutralization ratio is about
20% to 80%, about 30% to 70%, about 40% to 60% or about 50%.
[0055] The neutralization ratio may be selected for different
properties, such as to promote conductivity in the ionomer, to
promote the dispersability of the hydrocarbon ionomer in a
particular solvent or to promote miscibility with another polymer
in a blend. Methods of changing the neutralization ratio include
increasing the neutralization, such as by introducing basic ion
sources to promote a greater degree of ionization among the monomer
units. Methods of changing the neutralization ratio also include
those for decreasing neutralization, such as by introducing a
highly neutralized ionomer to strong acids so as to convert some or
all of an ionic functionality (e.g., (meth)acrylate) to an acid
(e.g., (meth)acrylic acid).
[0056] Although any stable cation is believed to be suitable as a
counter-ion to the negatively charged functional groups in a
hydrocarbon ionomer, monovalent cations, such as cations of alkali
metals, are preferred. Still more preferably, the base is a lithium
ion-containing base, to provide a lithiated hydrocarbon ionomer
wherein part or all of the precursor groups are replaced by lithium
salts. To obtain the hydrocarbon ionomers, the precursor polymers
may be neutralized by any conventional procedure with an ion
source. Typical ion sources include sodium hydroxide, sodium
carbonate, zinc oxide, zinc acetate, magnesium hydroxide, and
lithium hydroxide. Other ion sources are well known and a lithium
ion source is preferred.
[0057] According to an embodiment, a a suitable hydrocarbon ionomer
includes ethylene-(meth)acrylic acid copolymer having about 5 to 25
wt. % (meth)acrylic acid monomer units based on the weight of the
ethylene-(meth)acrylic acid copolymer; and more particularly, the
ethylene-(meth)acrylic acid copolymer has a neutralization ratio of
0.40 to about 0.70. Hydrocarbon ionomers suitable for use herein
are available from various commercial sources or they can be
prepared by synthesis.
[0058] SURLYN.RTM. is an example of a carboxylate hydrocarbon
ionomer which is a random copolymer-poly(ethylene-co-(meth)acrylic
acid). E.I. du Pont de Nemours and Co., Wilmington, Del., provides
the SURLYN.RTM. resin brand, a copolymer of ethylene and
(meth)acrylic acid. It is produced through the copolymerization of
ethylene and (meth)acrylic acid via a high pressure free radical
reaction, similar to that for the production of low density
polyethylene and has an incorporation ratio of (meth)acrylic
comonomer that is relatively low and is typically less than 20% per
mole and often less than 15% per mole of the copolymer. Variants of
the SURLYN.RTM. resin brand are disclosed in U.S. Pat. No.
6,518,365 which is incorporated by reference herein in its
entirety. According to an embodiment, particularly useful
hydrocarbon ionomers include SURLYN.RTM. and variants of
SURLYN.RTM. which are derivatives of commercially available forms
of SURLYN.RTM.. One SURLYN.RTM. variant may be made by treating
SURLYN.RTM. with a strong acid to reduce the overall neutralization
ratio to promote its dispersability in aqueous solution. According
to another variant, SURLYN.RTM. is ion-exchanged to increase the
lithium ion content.
[0059] The hydrocarbon ionomer may be neutralized. Neutralization
of the hydrocarbon ionomer may be with a neutralization agent that
may be represented by the formulas MA where M is a metal ion and A
is the co-agent moiety such as an acid or base. Metal ions suitable
as the metal ion include monovalent, divalent, trivalent and
tetravalent metals. Metal ions suitable for use herein include, but
are not limited to, ions of Groups IA, IB, IIA, IIB, IIIA, IVA,
IVB, VB, VIIB, VIIB and VIII metals of the Periodic Table. Examples
of such metals include Na.sup.+, Li.sup.+, K.sup.+ and Sn.sup.4+.
Li.sup.+ is preferred for uses of the hydrocarbon ionomer in a
Li--S cell.
[0060] Neutralization agents suitable for use herein include any
metal moiety which would be sufficiently basic to form a salt with
a low molecular weight organic acid, such as benzoic acid or
p-toluene sulfonic acid. One suitable neutralization agent is
lithium hydroxide distributed by Sigma Aldrich (Sigma Aldrich,
545856). Other neutralization agents and neutralization processes
to form hydrocarbon ionomers are described in U.S. Pat. No.
5,003,012 which is incorporated by reference herein in its
entirety.
[0061] Other hydrocarbon ionomers which are suitable include block
copolymers such as those derived from the sulphonation of
polystyrene-b-polybutadiene-b-polystyrene. Sulfonated polysulphones
and sulfonated polyether ether ketones are also suitable.
Phosphonate hydrocarbon ionomers may also be used, as well as
copolymers with more than one ionic functionality. For example,
direct co-polymerization of dibutyl vinylphosphonate with acrylic
acid yields a mixed carboxylate-phosphonate ionomer. Copolymers
derived from vinyl phosphonates with styrene, methyl methacrylate,
and acrylamide may also be used. Phosphorus containing polymers can
also be made after polymerization by phosphonylation reactions,
typically with POCl.sub.3. For example, phosphonylation of
polyethylene can produce a polyethylene-phosphonic acid
copolymer.
[0062] Hydrocarbon ionomers which are suitable for use include
carboxylate, sulfonate and phosphonate hydrocarbon ionomers. Others
are also suitable, such as styrene alkoxide hydrocarbon ionomers
such as those derived from polystyrene-co-4-methoxy styrene. A
hydrocarbon ionomer may have a polyvinyl or a polydiene backbone.
Different hydrocarbon ionomers may differ in properties, partly due
to differences in the strength of the ionic interactions and
structure. Carboxylate hydrocarbon ionomers, sulfonate hydrocarbon
ionomers, and their mixtures are preferred. Also hydrocarbon
ionomers in which the negatively charged ionic functional groups
are neutralized with a lithium ion source to form a salt with
lithium are preferred.
[0063] The positive electrode 102 in cell 100 may be made by
incorporating a cathode composition comprising carbon-sulfur (C--S)
composite made from sulfur compound and carbon powder. The cathode
composition may also include a non-ionomeric polymeric binder, a
carbon black and a hydrocarbon ionomer.
[0064] A representative carbon powder for making the C--S composite
is KETJENBLACK EC-600JD, distributed by Akzo Nobel having an
approximate surface area of 1400 m.sup.2/g BET (Product Data Sheet
for KETJENBLACK EC-600JD, Akzo Nobel) and an approximate pore
volume of 4.07 cc/gram, as determined according to the BJH method,
based on a cumulative pore volume for pores ranging from 17-3000
angstroms. In the BJH method, nitrogen adsorption/desorption
measurements were performed on ASAP model 2400/2405 porosimeters
(Micrometrics, Inc., No. 30093-1877). Samples were degassed at
150.degree. C. overnight prior to data collection. Surface area
measurements utilized a five-point adsorption isotherm collected
over 0.05 to 0.20 p/p.sub.0 and were analyzed via the BET method,
described in Brunauer et al., J. Amer. Chem. Soc., v. 60, no. 309
(1938), and incorporated by reference herein in its entirety. Pore
volume distributions utilized a 27 point desorption isotherm and
were analyzed via the BJH method, described in Barret, et al., J.
Amer. Chem. Soc., v. 73, no. 373 (1951), and incorporated by
reference herein in its entirety.
[0065] Additional commercially available carbon powders which may
be utilized include KETJEN 300: approximate pore volume 1.08 cc/g
(Akzo Nobel) CABOT BLACK PEARLS: approximate pore volume 2.55 cc/g,
(Cabot), PRINTEX XE-2B: approximate pore volume 2.08 cc/g (Orion
Carbon Blacks, The Cary Company). Other sources of such carbon
powders are known to those having ordinary skill in the art.
[0066] Other porous carbon materials suitable for use herein may be
manufactured or synthesized using known processes, as desired, for
their pore volume, surface area and other features. Porous carbon
materials suitable for use herein include templated carbons.
Templated carbon has a synthesized carbon microstructure which is
complementary to an inorganic template used in making the templated
carbon. Templated carbon materials are demonstrated in co-assigned
and co-pending U.S. Patent Application Ser. No. 61/587,805, filed
on Jan. 18, 2013, based on Attorney Docket No.: CL-5409, which is
incorporated by reference herein in its entirety.
[0067] Carbon powders which are suitable for making the C--S
composite include those having a surface area of about 100 to 4,000
square meters per gram carbon powder, about 200 to 3,000 square
meters per gram, about 300 to 2,500 square meters per gram carbon
powder, about 500 to 2,200 square meters per gram, about 700 to
2,000 square meters per gram, about 900 to 1,900 square meters per
gram, about 1,100 to 1,700 square meters per gram and about 1,300
to 1,500 square meters per gram carbon powder.
[0068] Carbon powders which are suitable for making the C--S
composite also include those having a pore volume ranging from
about 0.25 to 10 cc per gram carbon powder, from about 0.7 to 7 cc
per gram, from about 0.8 to 6 cc per gram, from about 0.9 to 5.5 cc
per gram, from about 1 to 5.2 cc per gram, from about 1.1 to 5.1 cc
per gram, from about 1.2 to 5 cc per gram, from about 1.4 to 4 cc
per gram, and from about 2 to 3 cc per gram. A particularly useful
carbon powder is one having a pore volume that is greater than 1.2
cc per gram and less than 5 cc per gram carbon powder.
[0069] Sulfur compounds which are suitable for making the C--S
composite include molecular sulfur in its various allotropic forms
and combinations thereof, such as "elemental sulfur". Elemental
sulfur is a common name for a combination of sulfur allotropes
including puckered S.sub.8 rings, and often including smaller
puckered rings of sulfur. Other sulfur compounds which are suitable
are compounds containing sulfur and one or more other elements.
These include lithiated sulfur compounds, such as for example,
Li.sub.2S or Li.sub.2S.sub.2. A representative sulfur compound is
elemental sulfur distributed by Sigma Aldrich as "Sulfur", (Sigma
Aldrich, 84683). Other sources of such sulfur compounds are known
to those having ordinary skill in the art.
[0070] A non-ionomer polymeric binder which may be utilized for
making the cathode composition includes polymers exhibiting
chemical resistance, heat resistance as well as binding properties,
such as polymers based on alkylenes, oxides and/or fluoropolymers.
Examples of these polymers include polyethylene oxide (PEO),
polyisobutylene (PIB), and polyvinylidene fluoride (PVDF). A
representative polymeric binder is polyethylene oxide (PEO) with an
average M.sub.w of 600,000 distributed by Sigma Aldrich as
"Poly(ethylene oxide)", (Sigma Aldrich, 182028). Another
representative polymeric binder is polyisobutylene (PIB) with an
average M.sub.w of 4,200,000 distributed by Sigma Aldrich as
"Poly(isobutylene)", (Sigma Aldrich, 181498). Polymeric binders
which are suitable for use herein are also described in U.S.
Published Patent Application No. US2010/0068622, which is
incorporated by reference herein in its entirety. Other sources of
polymeric binders are known to those having ordinary skill in the
art.
[0071] Carbon blacks which are suitable for making the cathode
composition include carbon substances exhibiting electrical
conductivity and generally having a lower surface area and lower
pore volume relative to the carbon powder described above. Carbon
blacks typically are colloidal particles of elemental carbon
produced through incomplete combustion or thermal decomposition of
gaseous or liquid hydrocarbons under controlled conditions. Other
conductive carbons which are also suitable are based on graphite.
Suitable carbon blacks include acetylene carbon blacks which are
preferred. A representative carbon black is SUPER C65 distributed
by Timcal Ltd. and having BET nitrogen surface area of 62 m.sup.2/g
carbon black measured by ASTM D3037-89. Other commercial sources of
carbon black, and methods of manufacturing or synthesizing them,
are known to those having ordinary skill in the art.
[0072] Carbon blacks which are suitable for use herein include
those having a surface area ranging from about 10 to 250 square
meters per gram carbon black, about 30 to 200 square meters per
gram, about 40 to 150 square meters per gram, about 50 to 100
square meters per gram and about 60 to 80 square meters per gram
carbon black.
[0073] The C--S composite includes a porous carbon material, such
as carbon powder, containing the sulfur compound situated in the
carbon microstructure of the porous carbon material. The amount of
sulfur compound which may be contained in the C--S composite (i.e.,
the sulfur loading in terms of the weight percentage of sulfur
compound, based on the total weight of the C--S composite, is
dependent to an extent on the pore volume of the carbon powder.
Accordingly, as the pore volume of the carbon powder increases,
higher sulfur loading with more sulfur compound is possible. Thus,
a sulfur compound loading of, for example, about 5 wt. %, 10 wt. %,
15 wt. %, 20 wt. %, 25 wt. %, 30 wt. %, 35 wt. %, 40 wt. %, 45 wt.
%, 50 wt. %, 55 wt. %, 60 wt. %, 65 wt. %, 70 wt. %, 75 wt. %, 80
wt. %, 85 wt. %, 85 wt. %, 90 wt. % or 95 wt. % may be used. Ranges
among these amounts define embodiments which may be used.
[0074] The cathode composition may include various weight
percentages of C--S composite. The cathode composition may
optionally include non-ionomer polymeric binder, hydrocarbon
ionomer, and carbon black in addition to the C--S composite.
Exclusive of the amount of hydrocarbon ionomer present, C--S
composite is generally present in the cathode composition in an
amount which is greater than 50 wt. % of the remainder (i.e.,
excluding hydrocarbon ionomer) of the cathode composition. Higher
loading with more C--S composite is possible. Thus, exclusive of
the amount of hydrocarbon ionomer present, a C--S composite loading
of, for example, about 55 wt. %, 60 wt. %, 65 wt. %, 70 wt. %, 75
wt. %, 80 wt. %, 85 wt. %, 90 wt. %, 95 wt. %, 98 wt. %, or 99 wt.
% may be used. According to an embodiment, exclusive of the amount
of hydrocarbon ionomer present, about 50 to 99 wt. % C--S composite
may be used. In another embodiment, exclusive of the amount of
hydrocarbon ionomer present, about 70 to 95 wt. % C--S composite
may be used. Ranges among these amounts define embodiments which
may be used.
[0075] Exclusive of the amount of hydrocarbon ionomer present,
polymeric binder (i.e., non-ionomer polymeric binder) may be
present in the cathode composition in an amount which is greater
than 1 wt. %. Higher loading with more polymeric binder is
possible. Thus, a polymeric binder loading of, for example, about 2
wt. %, 3 wt. %, 4 wt. %, 5 wt. %, 6 wt. %, 7 wt. %, 8 wt. %, 9 wt.
%, 10 wt. %, 12 wt. %, 14 wt. %, 16 wt. %, or 17.5 wt. % may be
used exclusive of the amount of hydrocarbon ionomer present.
According to an embodiment, about 1 to 17.5 wt. % polymeric binder
may be used exclusive of the amount of hydrocarbon ionomer present.
In another embodiment, about 1 to 12 wt. % polymeric binder may be
used exclusive of the amount of hydrocarbon ionomer present. In
another embodiment, about 1 to 9 wt. % polymeric binder may be used
exclusive of the amount of hydrocarbon ionomer present. Ranges
among these amounts define embodiments which may be used.
[0076] According to an embodiment, the carbon black may optionally
be present in the cathode composition in an amount which is greater
than 0.01 wt. %. Higher loading with more carbon black is possible.
Thus, a carbon black loading, exclusive of the amount of
hydrocarbon ionomer present, of about 0.1 wt. %, about 1 wt. %,
about 2 wt. %, 3 wt. %, 4 wt. %, 5 wt. %, 6 wt. %, 8 wt. %, 10 wt.
%, 12 wt. %, 14 wt. %, 15 wt. %, or 20 wt. % may be used. According
to an embodiment, about 0.01 to 15 wt. % carbon black may be used,
exclusive of the amount of hydrocarbon ionomer present. In another
embodiment, about 5 to 10 wt. % carbon black may be used, exclusive
of the amount of hydrocarbon ionomer present. Ranges among these
amounts define embodiments which may be used.
[0077] The C--S composite may made by various methods, including
simply mixing, such as by dry grinding, the carbon powder with the
sulfur compound. C--S composite may also be made by introducing the
sulfur compound into the microstructure of the carbon powder
utilizing such vehicles as heat, pressure, liquid (e.g., a
dissolution of sulfur compound in carbon disulfide and impregnation
by contacting the solution with the carbon powder), etc.
[0078] Useful methods for introducing sulfur compound into the
carbon powder include melt imbibement and vapor imbibement. These
are compositing processes for introducing the sulfur compound into
the microstructure of the carbon powder utilizing such vehicles as
heat, pressure, liquid, etc.
[0079] In melt imbibement, a sulfur compound, such as elemental
sulfur can be heated above its melting point (about 113.degree. C.)
while in contact with the carbon powder to impregnate it. The
impregnation may be accomplished through a direct process, such as
a melt imbibement of elemental sulfur, at a raised temperature, by
contacting the sulfur compound and carbon at a temperature above
100.degree. C., such as 160.degree. C. A useful temperature range
is 120.degree. C. to 170.degree. C.
[0080] Another imbibement process which may be used for making the
C--S composite is vapor imbibement which involves the deposition of
sulfur vapor. The sulfur compound may be raised to a temperature
above 200.degree. C., such as 300.degree. C. At this temperature,
the sulfur compound is vaporized and placed in proximity to, but
not necessarily in direct contact with, the carbon powder.
[0081] These processes may be combined. For example, melt
imbibement process can be followed by a higher temperature process.
Alternatively, the sulfur compound can be dissolved in carbon
disulfide to form a solution and the C--S composite can be formed
by contacting this solution with the carbon powder. The C--S
composite is prepared by dissolving sulfur compound in non-polar
solvent such as toluene or carbon disulfide and contacted with the
carbon powder. The solution or dispersion can be contacted,
optionally, at incipient wetness to promote an even deposition of
the sulfide compound into the pores of the carbon powder. Incipient
wetness is a process in which the total liquid volume exposed to
the carbon powder does not exceed the volume of the pores of that
porous carbon material. The contacting process can involve
sequential contacting and drying steps to increase the weight %
loading of the sulfur compound.
[0082] Sulfur compound may also be introduced to the carbon powder
by other methods. For example, sodium sulfide (Na.sub.2S) can be
dissolved in an aqueous solution to form sodium polysulfide. The
sodium polysulfide can be acidified to precipitate the sulfur
compound in the carbon powder. In this process, the C--S composite
may require thorough washing to remove salt byproducts.
[0083] Suitable introducing methods include melt imbibement and
vapor imbibement. One method of melt imbibement includes heating
elemental sulfur (Li.sub.2S will not melt under these conditions)
and carbon powder at about 120.degree. C. to about 170.degree. C.
in an inert gas, such as nitrogen. A vapor imbibement method may
also be utilized. In the vapor imbibement method, sulfur vapor may
be generated by heating a sulfur compound, such as elemental
sulfur, to between the temperatures of about 120.degree. C. and
400.degree. C. for a period of time, such as about 6 to 72 hours in
the presence of the carbon powder. Other examples of melt
imbibement and vapor imbibement are shown in co-assigned and
co-pending U.S. Patent Application Ser. No. 61/587,805, filed on
Jan. 18, 2013, based on Attorney Docket No.: CL-5409, which is
incorporated by reference above.
[0084] According to an embodiment, a C--S composite formed by a
compositing process may be combined with hydrocarbon ionomer and,
optionally, polymeric binder and carbon black by conventional
mixing or grinding processes. A solvent, preferably an organic
solvent, such as toluene, alcohol, or n-methylpyrrolidone (NMP) may
optionally be utilized. The solvent should preferably not react
with the hydrocarbon ionomer or polymeric binder, if any, so as to
break these down, or significantly alter them. Conventional mixing
and grinding processes are known to those having ordinary skill in
the art. The ground or mixed components may form a composition 103,
according to an embodiment, which may be processed or incorporated
and/or formed into an electrode.
[0085] According to another embodiment, a layering or an electrode
incorporating a cathode composition may be made through a layering
process to form the layering and the electrode. The layering
process may utilize, for example, a porous carbon material, such as
carbon powder, having a pore volume greater than 1.2 cc/g in a C--S
composite. The layering and the electrode may be formed through the
application of one or several individual layers on a surface of a
detachable substrate. The hydrocarbon ionomer may be incorporated
into the layering in a variety of ways, including simply mixing the
hydrocarbon ionomer in a composition with the C--S composite and
optionally, a polymeric binder and any other components.
[0086] The hydrocarbon ionomer may also be incorporated by applying
separate coats including a hydrocarbon ionomer in a composition
with a lesser amount or excluding the C--S composite and/or other
components such as polymeric binder and carbon black. In one
example, after a composition including the C--S composite is
applied to form a layering/electrode, the hydrocarbon ionomer may
be applied in a separate layer above the base composition with the
C--S composite. In another example, the hydrocarbon ionomer may be
applied as a dispersion which is interleaved or applied in
alternate coating applications along with a base composition
including C--S composite.
[0087] The individual layers in a spray coated layering or
electrode may have the same or different proportions of different
components. For example, different sets of materials with different
components and different proportions of components may be prepared
and applied in combination to form a layering or electrode. One or
more components may be completely absent from any one material
applied this way. The different materials may be applied using
different coating apparatuses and different application
techniques.
[0088] For example, two cathode compositions with different C--S
components may be prepared with different C--S composites or
different amounts of C--S composites. In this example, the
respective C--S composites in the two different C--S components may
have respective porous carbon materials with differing physical
properties, respective sulfur loadings, etc. The two cathode
compositions may be applied in alternate passes of spray coating
for a layering in an electrode with an average amount of the two
compositions throughout or with localized concentrations of one or
the other of the two compositions. The components in the different
sets of compositions may vary according to multiple parameters,
such as respective hydrocarbon ionomers, respective weight
percentages hydrocarbon ionomer, respective polymeric binders,
respective weight percentages polymeric binder, respective C--S
composites, respective weight percentages C--S composite,
respective carbon powders and respective weight percentages sulfur
in the respective C--S composites of the different
compositions.
[0089] Also, a porogen (i.e., a void or pore generator) may be
included within the layers themselves in the positive electrode. A
porogen is any additive which can be removed by a chemical or
thermal process to leave behind a void, changing the pore structure
of the layering or electrode. This level of porosity control may be
utilized in terms of managing mass transfer in a laying or
electrode layer. For example, a porogen may be a carbonate, such as
calcium carbonate powder, which is added to an ink slurry and then
coated in combination with other components in the ink slurry, such
as C--S composite, polymeric binder and an optional conductive
carbon, onto an aluminum foil current collector to form a layering
or electrode. A porogen may also be added in intervening layers and
between layers containing the C--S composite. It may be desirable
to add the porogen in higher concentrations closer to the current
collector to create a gradient in the direction of the thickness of
the layering or electrode. Once the porogen is in place in the
formed layering or electrode, it may then be removed from by
washing with dilute acid to leave a void or pore. The type of
porogen and the amount can be varied in each layer to control the
porosity of the layering or electrode.
[0090] Referring again to FIG. 1, depicted is the positive
electrode 102, that may be formed incorporating a cathode
composition as described above. The formed positive electrode 102
may be utilized in the cell 100 in conjunction with a negative
electrode, such as the lithium-containing negative electrode 101
described above. According to different embodiments, the negative
electrode 101 may contain lithium metal or a lithium alloy. In
another embodiment, the negative electrode 101 may contain graphite
or some other non-lithium material. According to this embodiment,
the positive electrode 102 is formed to include some form of
lithium, such as lithium sulfide (Li.sub.2S), and according to this
embodiment, the C--S composite may be lithiated utilizing lithium
sulfide which is incorporated into the powdered carbon to form the
C--S composite, instead of elemental sulfur.
[0091] A porous separator, such as porous separator 105, may be
constructed from various materials. As an example, a mat or other
porous article made from fibers, such as polyimide fibers, which
may be used as a porous separator. In another example, using porous
laminates made from polymers such as polyvinylidene fluoride
(PVDF), polyvinylidene fluoride co-hexafluoropropylene (PVDF-HFP),
polyethylene (PE), polypropylene (PP), and polyimide. In addition,
polymers with sufficient functionality or modifications to promote
miscibility with a hydrocarbon ionomer in a polymer blend may also
be used in a blend with a hydrocarbon ionomer.
[0092] Positive electrode 102, negative electrode 101 and porous
separator 105 are in contact with a lithium-containing electrolyte
medium in the cell 100, such as a cell solution with solvent and
electrolyte. In this embodiment, the lithium-containing electrolyte
medium is a liquid. In another embodiment, the lithium-containing
electrolyte medium is a solid. In yet another embodiment, the
lithium-containing electrolyte medium is a gel.
[0093] Referring to FIG. 2, depicted is a context diagram
illustrating properties 200 of a Li--S battery 201 including a
Li--S cell, such as cell 100, having a positive electrode including
sulfur, such as electrode 102. The Li--S cell in Li--S battery 201
incorporates one or more hydrocarbon ionomer articles such as
films, membranes, coatings and compositions, such as described
above with respect to cell 100. The context diagram of FIG. 2
demonstrates the properties 200 of the Li--S battery 201, having a
high coulombic efficiency and high maximum discharge capacity
associated with its discharge. The high coulombic efficiency
appears to be directly attributable to the presence of the
hydrocarbon ionomer articles in the Li--S cell of Li--S battery
201. FIG. 2 also depicts a graph 202 demonstrating maximum
discharge capacity per cycle of Li--S battery 201 with respect to a
number of charge-discharge cycles. The Li--S battery 201 also
exhibits high lifetime recharge stability and a high maximum
discharge capacity per charge-discharge cycle. All these properties
200 of the Li--S battery 201 are demonstrated in greater detail
below through the specific examples.
[0094] Referring to FIG. 3, depicted is a coin cell 300 which is
operable as an electrochemical measuring device for testing various
configurations and types of hydrocarbon ionomer articles. The
function and structure of the coin cell 300 are analogous to those
of the cell 100 depicted in FIG. 1. The coin cell 300, like the
cell 100, utilizes a lithium-containing electrolyte medium. The
lithium-containing electrolyte medium is in contact with the
negative electrode and the positive electrode and may be a liquid
containing solvent and lithium ion electrolyte.
[0095] The lithium ion electrolyte may be non-carbon-containing For
example, the lithium ion electrolyte may be a lithium salt of such
counter ions as hexachlorophosphate (PF.sub.6.sup.-), perchlorate,
chlorate, chlorite, perbromate, bromate, bromite, periodiate,
iodate, aluminum fluorides (e.g., AlF.sub.4.sup.-), aluminum
chlorides (e.g. Al.sub.2Cl.sub.7.sup.-, and AlCl.sub.4.sup.-),
aluminum bromides (e.g., AlBr.sub.4.sup.-), nitrate, nitrite,
sulfate, sulfites, permanganate, ruthenate, perruthenate and the
polyoxometallates.
[0096] In another embodiment, the lithium ion electrolyte may be
carbon containing. For example, the lithium ion salt may contain
organic counter ions such as carbonate, the carboxylates (e.g.,
formate, acetate, propionate, butyrate, valerate, lactacte,
pyruvate, oxalate, malonate, glutarate, adipate, deconoate and the
like), the sulfonates (e.g., CH.sub.3SO.sub.3.sup.-,
CH.sub.3CH.sub.2SO.sub.3.sup.-,
CH.sub.3(CH.sub.2).sub.2SO.sub.3.sup.- benzene sulfonate,
toluenesulfonate, dodecylbenzene sulfonate and the like. The
organic counter ion may include fluorine atoms. For example, the
lithium ion electrolyte may be a lithium ion salt of such counter
anions as the fluorosulfonates (e.g., CF.sub.3SO.sub.3.sup.-,
CF.sub.3CF.sub.2SO.sub.3.sup.-,
CF.sub.3(CF.sub.2).sub.2SO.sub.3.sup.-,
CHF.sub.2CF.sub.2SO.sub.3.sup.- and the like), the fluoroalkoxides
(e.g., CF.sub.3O--, CF.sub.3CH.sub.2O.sup.-,
CF.sub.3CF.sub.2O.sup.- and pentafluorophenolate), the fluoro
carboxylates (e.g. trifluoroacetate and pentafluoropropionate) and
fluorosulfonimides (e.g., (CF.sub.3SO.sub.2).sub.2N.sup.-). Other
electrolytes which are suitable for use herein are disclosed in
U.S. Published Patent Applications 2010/0035162 and 2011/00052998
both of which are incorporated herein by reference in their
entireties.
[0097] The electrolyte medium may exclude a protic solvent, since
protic liquids are generally reactive with the lithium anode.
Solvents are preferable which may dissolve the electrolyte salt.
For instance, the solvent may include an organic solvent such as
polycarbonate, an ether or mixtures thereof. In other embodiments,
the electrolyte medium may include a non-polar liquid. Some
examples of non-polar liquids include the liquid hydrocarbons, such
as pentane, hexane and the like.
[0098] Electrolyte preparations suitable for use in the cell
solution may include one or more electrolyte salts in a nonaqueous
electrolyte composition. Suitable electrolyte salts include without
limitation: lithium hexafluorophosphate, Li
PF.sub.3(CF.sub.2CF.sub.3).sub.3, lithium
bis(trifluoromethanesulfonyl)imide, lithium
bis(perfluoroethanesulfonyl)imide, lithium(fluorosulfonyl)
(nonafluoro-butanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,
lithium tetrafluoroborate, lithium perchlorate, lithium
hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium
tris(trifluoromethanesulfonyl)methide, lithium bis(oxalato)borate,
lithium difluoro(oxalato)borate, Li.sub.2B.sub.12F.sub.12-xH.sub.x
where x is equal to 0 to 8, and mixtures of lithium fluoride and
anion receptors such as B(OC.sub.6F.sub.5).sub.3. Mixtures of two
or more of these or comparable electrolyte salts can also be used.
In one embodiment, the electrolyte salt is lithium
bis(trifluoromethanesulfonyl)imide). The electrolyte salt may be
present in the nonaqueous electrolyte composition in an amount of
about 0.2 to about 2.0 M, more particularly about 0.3 to about 1.5
M, and more particularly about 0.5 to about 1.2 M.
EXAMPLES
[0099] The following examples demonstrate sample cells with porous
separators coated with hydrocarbon ionomer as porous separator 306
of coin cell 300. Comparative examples A and B demonstrate cells
without any articles incorporating hydrocarbon ionomer. Reference
is made to the specific examples below.
Example 1
[0100] Example 1 describes the preparation and electrochemical
evaluation of a Li--S cell incorporating a porous separator coated
with hydrocarbon ionomer which is a lithium exchanged derivative of
SURLYN.RTM., a copolymer of ethylene and methacrylate partially
neutralized with zinc, sodium, lithium or other metals. The porous
separator was coated by spraying it with SURLYN.RTM. and the coated
porous separator was immersed in a bath containing a lithium ion
source for lithium exchange to increase the lithium neutralization
in the SURLYN.RTM..
[0101] Preparation of C--S Composite:
[0102] Approximately 1.0 g of carbon powder (KETJENBLACK EC-600JD,
Akzo Nobel) having a surface area of approximately 1400 m.sup.2/g
BET (Product Data Sheet for KETJENBLACK EC-600JD, Akzo Nobel) and a
pore volume of 4.07 cc/g (as measured by the BJH method) was placed
in a 30 ml glass vial and loaded into an autoclave which was
charged with approximately 100 grams of elemental sulfur (Sigma
Aldrich 84683). The carbon powder was prevented from being in
physical contact with the elemental sulfur but the carbon powder
had access to sulfur vapor. The autoclave was closed, purged with
nitrogen, and then heated to 300.degree. C. for 24 hours under a
static atmosphere to develop sulfur vapor. The final sulfur content
of the C--S composite was 51 wt. % sulfur.
[0103] Jar Milling of C--S Composite:
[0104] 1.52 g of the C--S composite described above, 43.2 g of
ethanol (Sigma Aldrich 459836) and 125 g of 5 mm diameter zirconia
media were weighed into a 125 mL polyethylene bottle. The bottle
was sealed, and tumbled end-over-end inside a larger jar on jar
mill for 15 hours.
[0105] Preparation of Electrode Composition (C--S
Composite/Binder/Carbon Black Formulation):
[0106] Polyethylene oxide with average M.sub.w of 600,000 (Sigma
Aldrich 182028) was dissolved in acetonitrile (Sigma Aldrich
271004) to produce a 5.0 wt. % polymer solution. 121 mg of
conductive carbon black SUPER C65 (Timcal Ltd.) (BET nitrogen
surface area of 62 m.sup.2/g measured by ASTM D3037-89) (Technical
Data Sheet for SUPER C65, Timcal Ltd.) was dispersed in 3.65 g of
the 5.0 wt. % PEO solution, 6.8 g of deionized water and 2 g of
ethanol. The slurry was mixed with a magnetic stir bar for 15
minutes to form a SUPER C65/PEO slurry. 36 g of the jar milled
suspension of C--S composite described above was added to the SUPER
C65/PIB slurry along with 24 g of deionized water. The solid
loading in this mixture has an approximate % PEO in the PEO &
C--S of 0.1304 (i.e., 13.04% by weight PEO). This formulation was
stirred for 90 minutes, then mixed for 30 minutes in an ultrasonic
bath, and stirred again for 60 minutes.
[0107] Spray Coating to Form Layering/Electrode:
[0108] A layering/electrode was formed by spraying the formulated
ink slurry mixture onto one side of double-sided carbon coated
aluminum foil (1 mil, Exopac Advanced Coatings) as a substrate for
the layering/electrode. The dimensions of the coated area on the
substrate was approximately 10 cm.times.10 cm. The ink slurry
mixture was sprayed through an air brush (PATRIOT 105, Badger
Air-Brush Co.) onto the substrate in a layer by layer pattern. The
substrate was heated on a 70.degree. C. hotplate for about 10
seconds following the application of every 4 layers to the
substrate surface. Once all of the ink slurry mixture was sprayed
onto the substrate, the layering/electrode was placed in a vacuum
at a temperature of 70.degree. C. for a period of 5 minutes. The
dried layering/electrode was calendared between two steel rollers
on a custom built device to a final thickness of about 1 mil.
[0109] Preparation of Hydrocarbon Ionomer (SURLYN.RTM.) Coated
Porous Separator:
[0110] A piece of CELGARD 2325 separator (Celgard, LLC) with
dimensions 6 cm by 11.6 cm was taped to a glass plate and heated to
70.degree. C. on a hot plate. The separator was then sprayed, using
the air brush, with an aqueous dispersion of SURLYN.RTM. ionomer,
6.4 wt. % loading. When the Surlyn.RTM. loading on the separator
reached 0.3 mg per cm.sup.2, the sample was dried in a vacuum oven
at 70.degree. C. for 15 minutes. The coated separator was then ion
exchanged by immersing it in a bath of aqueous 2M LiOH solution
overnight. It was rinsed with deionized water and dried under
vacuum at 70.degree. C. for 2 hours.
[0111] Preparation of Electrolyte:
[0112] 2.87 grams of lithium bis(trifluoro-methane sulfonyl)imide
(LiTFSI, Novolyte) was combined with 10 milliters of 1,2
dimethoxyethane (glyme, Sigma Aldrich, 259527) to create a 0.9 M
electrolyte solution.
[0113] Preparation of Coin Cell:
[0114] A 14.29 mm diameter circular disk was punched from the
layering/electrode and used as the positive electrode 307. The
final weight of the electrode (14.29 mm in diameter, subtracting
the weight of the aluminum current collector) was 4.3 mg. This
corresponds to a calculated weight of 1.76 mg of elemental sulfur
on the electrode.
[0115] The coin cell 300 included the positive electrode 307, a 19
mm diameter circular disk was punched from Surlyn.RTM.-coated
separator sheet described in the previous section. This disk was
soaked overnight in glyme (Sigma Aldrich, 259527). The soaked disk
was used as the porous separator 306 in the coin cell 300 with the
coated side of the separator facing the positive electrode. The
positive electrode 307, the separator 306, a lithium foil negative
electrode 304 (Chemetall Foote Corp.) and a few electrolyte drops
305 of the nonaqueous electrolyte was sandwiched in a Hohsen 2032
stainless steel coin cell can with a 1 mil thick stainless steel
spacer disk and wave spring (Hohsen Corp.). The construction
involved the following sequence as shown in FIG. 3: bottom cap 308,
positive electrode 307, electrolyte drops 305, porous separator
306, electrolyte drops 305, negative electrode 304, spacer disk
303, wave spring 302 and top cap 301. The final assembly was
crimped with an MTI crimper (MTI).
[0116] Electrochemical Testing Conditions:
[0117] The positive electrode 307 was cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0118] Electrochemical evaluation: The maximum charge capacity
measured on discharge at cycle 10 was 827 mAh/g S with a coulombic
efficiency of 80.2%.
Example 2
[0119] The materials in example 2 were prepared as identical to
those in example 1, except the hydrocarbon ionomer coated porous
separator was calendared at a higher temperature before the cell
was assembled.
[0120] Preparation of Hydrocarbon Ionomer (SURLYN.RTM.) Coated
Porous Separator:
[0121] A strip of the lithium ion exchanged SURLYN.RTM. coated
separator, 6 cm.times.3 cm, was cut from the separator in Example 1
and calendared between two steel rollers on a custom-built
calendaring device. The separator was sandwiched between pieces of
KAPTON film. The temperature of the rollers was maintained at
70.degree. C.
[0122] Preparation of Coin Cell:
[0123] A coin cell and electrolyte were prepared and cycled using
the same procedures as example 1. The final weight of the electrode
(14.29 mm in diameter, subtracting the weight of the aluminum
current collector) was 4.1 mg. This corresponds to a calculated
weight of 1.68 mg of elemental sulfur on the electrode.
[0124] Electrochemical Testing Conditions:
[0125] The positive electrode 307 was cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0126] Electrochemical Evaluation:
[0127] The maximum charge capacity measured on discharge at cycle
10 was 855 mAh/g S with a coulombic efficiency of 90%.
Comparative Example A
[0128] Comparative example A describes the preparation and
electrochemical evaluation of a Li--S cell with a porous separator
not coated with any hydrocarbon ionomer for comparison with
examples 1 and 2 above. The Li--S cell in comparative example A
utilizes a porous separator that is not coated with any hydrocarbon
ionomer or calendared at any temperature, but was otherwise
prepared in a manner similar to the preparation described in
examples 1 and 2 above.
[0129] Preparation of Coin Cell:
[0130] A coin cell was prepared and cycled using the same
procedures as examples 1 and 2. The positive electrode 307 used in
comparative example A was identical to the electrodes in examples 1
and 2. The final weight of the electrode (14.29 mm in diameter,
subtracting the weight of the aluminum current collector) was 4.8
mg. This corresponds to a calculated weight of 2.0 mg of sulfur on
the electrode. The porous separator was made from CELGARD 2325,
which was used as received. The porous separator was not soaked in
glyme prior to assembling the coin cell.
[0131] Electrochemical Testing Conditions:
[0132] The positive electrode 307 was cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0133] Electrochemical Evaluation:
[0134] The maximum charge capacity measured on discharge at cycle
10 was 1,056 mAh/g S with a coulombic efficiency of 51.3%.
Example 3
[0135] Example 3 describes the preparation and electrochemical
evaluation of a Li--S cell including a porous separator coated with
a hydrocarbon ionomer that is a lithium exchanged derivative of a
sodium salt of polyvinyl sulfonic acid (PVSA) (Sigma Aldrich,
278424).
[0136] Preparation of C--S Composite:
[0137] Approximately 1.0 g of carbon powder (KETJENBLACK EC-600JD,
Akzo Nobel) having a surface area of approximately 1400 m.sup.2/g
BET (Product Data Sheet for KETJENBLACK EC-600JD, Akzo Nobel) and a
pore volume of 4.07 cc/g (as measured by the BJH method) was placed
in a 30 ml glass vial and loaded into an autoclave which was
charged with approximately 100 grams of elemental sulfur (Sigma
Aldrich 84683). The carbon powder was prevented from being in
physical contact with the elemental sulfur but the carbon powder
had access to sulfur vapor. The autoclave was closed, purged with
nitrogen, and then heated to 300.degree. C. for 24 hours under a
static atmosphere to develop sulfur vapor. The final sulfur content
of the C--S composite was 51 wt. % sulfur.
[0138] Jar Milling of C--S Composite:
[0139] 1.8 g of the C--S composite described above, 51 g of toluene
(EMD Chemicals) and 120 g of 5 mm diameter zirconia media was
weighted into a 125 mL polyethylene bottle. The bottle was sealed,
and tumbled end-over-end inside a larger jar on jar mill for 15
hours.
[0140] Preparation of Base Composition (C--S
Composite/Binder/Carbon Black Formulation):
[0141] Polyisobutylene with average M.sub.w of 4,200,000 (Sigma
Aldrich 181498) was dissolved in toluene to produce a 2.0 wt. %
polymer solution. 153 mg of conductive carbon black SUPER C65
(Timcal Ltd.) (BET nitrogen surface area of 62 m.sup.2/g measured
by ASTM D3037-89) (Technical Data Sheet for SUPER C65, Timcal Ltd.)
was dispersed in 11.4 g of the 2.0 wt. % PIB solution. 45 g of the
jar milled suspension of C--S composite described above was added
to the SUPER C65/PIB slurry along with 27 g of toluene to form an
ink slurry with about 2 wt. % solid loading. This ink was stirred
for 3 hours.
[0142] Spray Coating to Form Layering/Electrode:
[0143] A layering/electrode was formed by spraying the formulated
ink slurry onto one side of double-sided carbon coated aluminum
foil (1 mil, Exopac Advanced Coatings) as a substrate for the base
layering/electrode. The dimensions of the coated area on the
substrate was approximately 10 cm.times.10 cm. The ink slurry was
sprayed through an air brush (PATRIOT 105, Badger Air-Brush Co.)
onto the substrate in a layer by layer pattern. The substrate was
heated on a 70.degree. C. hotplate for about 10 seconds following
the application of every 4 layers to the substrate surface. Once
all of the ink slurry was sprayed onto the substrate, the base
layering/electrode was placed in a vacuum at a temperature of
70.degree. C. for a period of 5 minutes.
[0144] Preparation of Hydrocarbon Ionomer (PVSA) Solution:
[0145] A 25 wt. % dispersion of polyvinylsulfonic acid (PVSA)
sodium salt (Sigma Aldrich, 278424) was passed through a column of
DOWEX.RTM. (Dow 50WX8-200) ion exchange resin which had been
exchanged with lithium ions. The polymer concentration in the
eluate solution was 2.5 wt. %.
[0146] Hydrocarbon Ionomer (PVSA) Spray Coating of Porous
Separator:
[0147] A piece of CELGARD 2325 separator (Celgard, LLC) with
dimensions 6 cm by 9 cm was taped to a glass plate and heated to
70.degree. C. on a hot plate. The porous separator was then sprayed
using the air brush with the PVSA solution prepared in the previous
section. When the PVSA loading on the separator reached about 0.7
mg per square cm, the sample was dried in a vacuum oven at
70.degree. C. overnight. The coated separator was transferred to a
nitrogen dry box.
[0148] Preparation of Electrolyte:
[0149] 2.87 grams of lithium bis(trifluoro-methane sulfonyl)imide
(LiTFSI, Novolyte) was combined with 10 milliters of 1,2
dimethoxyethane (glyme, Sigma Aldrich, 259527) to create a 0.9 M
electrolyte solution.
[0150] Preparation of Coin Cell:
[0151] A coin cell 300 was prepared using electrode and the coated
porous separator described above for testing. A 14.29 mm diameter
circular disk was punched from the final layering/electrode and
used as the positive electrode 307. The final weight of the
electrode (14.29 mm in diameter, subtracting the weight of the
aluminum current collector) was 5.7 mg. This corresponds to a
calculated weight of 2.34 mg of elemental sulfur on the
electrode.
[0152] A 19 mm diameter circular disk was punched from the
PVSA-coated separator sheet described in the previous section. This
disk was soaked overnight in glyme (Sigma Aldrich, 259527). It was
then used as the porous separator 306 in the coin cell 300 with the
coated side of the separator facing the positive electrode 307.
[0153] The positive electrode 307, the separator 306, a lithium
foil negative electrode 304 (Chemetall Foote Corp.) and a few
electrolyte drops 305 of the nonaqueous electrolyte were sandwiched
in a Hohsen 2032 stainless steel coin cell can with a 1 mil thick
stainless steel spacer disk and wave spring (Hohsen Corp.). The
construction involved the following sequence as shown in FIG. 3:
bottom cap 308, positive electrode 307, electrolyte drops 305,
porous separator 306, electrolyte drops 305, negative electrode
304, spacer disk 303, wave spring 302 and top cap 301. The final
assembly was crimped with an MTI crimper (MTI).
[0154] Electrochemical Testing Conditions:
[0155] The positive electrode 307 was cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0156] Electrochemical Evaluation:
[0157] The maximum charge capacity measured on discharge at cycle
10 was 1,002 mAh/g S with a coulombic efficiency of 83.6%.
Example 4
[0158] Example 4 describes the preparation and electrochemical
evaluation of a Li--S cell including a porous separator coated with
hydrocarbon ionomer which was a lithium exchanged sulfonated
derivative (SPEEK) of a poly(ether ether-ketone) PEEK (Victrex,
150P). The positive electrode in this example was identical to the
electrode used in example 3. The separator in this example was
coated with sulfonated poly(ether ether ketone) (SPEEK) ionomer
instead of PVSA.
[0159] Sulfonation of PEEK with Lithium Ion Exchange Forming
SPEEK:
[0160] 5.0 g of PEEK (Victrex, 150P, Lancashire, UK) was dissolved
in 176 g of concentrated sulfuric acid, and stirred rapidly for six
days at room temperature. The polymer was precipitated from
solution in ice water, then filtered and rinsed with deionized
water until the filtrate pH reached 4. The polymer was exchanged
with lithium ions by stirring in a bath of 2 M lithium hydroxide.
The solution was filtered and the polymer was rinsed with deionized
water until the filtrate was pH neutral. Finally the polymer was
dried in a 70.degree. C. vacuum oven overnight.
[0161] Hydrocarbon Ionomer (SPEEK) Spray Coating of Porous
Separator:
[0162] Lithium-exchanged SPEEK was dissolved in dimethylacetimide
(DMAc) (Sigma Aldrich, 271012) at a 5 wt. % concentration. A piece
of CELGARD 2325 porous separator (Celgard, LLC) with dimensions 6
cm by 6 cm was taped to glass plate and heated to 70.degree. C. on
a hot plate. The porous separator was then spray coated, using the
air brush, with the lithium-exchanged SPEEK solution. When the
ionomer loading on the separator reached about 0.2 mg per square
cm, the sample was transferred to a 70.degree. C. vacuum oven for 8
hours. The coated separator was transferred to a nitrogen dry
box.
[0163] Preparation of Electrolyte:
[0164] 2.87 grams of lithium bis(trifluoro-methane sulfonyl)imide
(LiTFSI, Novolyte) is combined with 10 milliters of 1,2
dimethoxyethane (glyme, Sigma Aldrich, 259527) to create a 0.9 M
electrolyte solution.
[0165] Preparation of Coin Cell:
[0166] Coin cells were prepared and cycled using the same
procedures as example 1. The final weight of the electrode (14.29
mm in diameter, subtracting the weight of the aluminum current
collector) was 4.9 mg. This corresponds to a calculated weight of
2.01 mg of sulfur on the electrode.
[0167] Electrochemical Testing Conditions:
[0168] The positive electrode 307 is cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0169] Electrochemical Evaluation:
[0170] The maximum charge capacity measured on discharge at cycle
10 was 945 mAh/g S with a coulombic efficiency of 92.3%.
Comparative Example B
[0171] Comparative example B describes the preparation and
electrochemical evaluation of a Li--S cell with a porous separator
not coated with any hydrocarbon ionomer for comparison with
examples 3 and 4 above. The Li--S cell in comparative example B
utilizes a porous separator that is not coated with any hydrocarbon
ionomer.
[0172] Preparation of Coin Cell:
[0173] A coin cell was prepared and cycled using the same
procedures as examples 3 and 4. The positive electrode 307 used in
comparative example B was identical to the electrode in examples 3
and 4. The final weight of the electrode (14.29 mm in diameter,
subtracting the weight of the aluminum current collector) was 5.2
mg. This corresponds to a calculated weight of 2.09 mg of sulfur on
the electrode. The porous separator was made from CELGARD 2325,
which was used as received. The porous separator was not soaked in
glyme prior to assembling the coin cell.
[0174] Electrochemical Testing Conditions:
[0175] The positive electrode 307 was cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0176] Electrochemical Evaluation:
[0177] The maximum charge capacity measured on discharge at cycle
10 was 1,023 mAh/g S with a coulombic efficiency of 56.5%.
Example 5
[0178] Example 5 describes the preparation and electrochemical
evaluation of a Li--S cell incorporating a porous separator coated
with hydrocarbon ionomer which is a lithium exchanged derivative of
SURLYN.RTM., a copolymer of ethylene and methacrylate partially
neutralized with zinc, sodium, lithium or other metals. The porous
separator was coated by spraying it with SURLYN.RTM. and the coated
porous separator was immersed in a bath containing a lithium ion
source for lithium exchange to increase the lithium neutralization
in the SURLYN.RTM..
[0179] Preparation of C--S Composite:
[0180] Approximately 1.0 g of carbon powder (KETJENBLACK EC-600JD,
Akzo Nobel) having a surface area of approximately 1400 m2/g BET
(Product Data Sheet for KETJENBLACK EC-600JD, Akzo Nobel) and a
pore volume of 4.07 cc/g (as measured by the BJH method) was placed
in a 30 ml glass vial and loaded into an autoclave which was
charged with approximately 100 grams of elemental sulfur (Sigma
Aldrich 84683). The carbon powder was prevented from being in
physical contact with the elemental sulfur but the carbon powder
had access to sulfur vapor. The autoclave was closed, purged with
nitrogen, and then heated to 300.degree. C. for 24 hours under a
static atmosphere to develop sulfur vapor. The final sulfur content
of the C--S composite was 53.3 wt. % sulfur.
[0181] Jar Milling of C--S Composite:
[0182] 1.85 g of the C--S composite described above, 53.15 g of
toluene (EMD Chemicals) and 115 g of 5 mm diameter zirconia media
were weighed into a 125 mL polyethylene bottle. The bottle was
sealed, and tumbled end-over-end inside a larger jar on jar mill
for 15 hours.
[0183] Preparation of (80/12/8) Electrode Composition (C--S
Composite/Binder/Carbon Black Formulation):
[0184] Polyisobutylene with average Mw of 4,200,000 (Sigma Aldrich
1814980 was dissolved in toluene to produce a 2.0 wt. % polymer
solution. 290 mg of conductive carbon black SUPER C65 (Timcal Ltd.)
(BET nitrogen surface area of 62 m.sup.2/g measured by ASTM
D3037-89) (Technical Data Sheet for SUPER C65, Timcal Ltd.) was
dispersed in 21.65 g of the 2.0 wt. % PIB solution along with 21 g
of toluene. The slurry was mixed with a magnetic stir bar for 5
minutes to form a SUPER C65/PIB slurry. 2.912 g of the jar milled
suspension of C--S composite described above was added to the SUPER
C65/PIB slurry along with an additional 44 g of toluene. This ink,
with a 2.10 wt. % solid loading, was stirred for 3 hours.
[0185] Spray Coating to Form Layering/Electrode:
[0186] A layering/electrode was formed by spraying the formulated
ink slurry mixture onto one side of double-sided carbon coated
aluminum foil (1 mil, Exopac Advanced Coatings) as a substrate for
the layering/electrode. The dimensions of the coated area on the
substrate was approximately 5 cm.times.5 cm. The ink slurry mixture
was sprayed through an air brush (PATRIOT 105, Badger Air-Brush
Co.) onto the substrate in a layer by layer pattern. The substrate
was heated on a 70.degree. C. hotplate for about 10 seconds
following the application of every 4 layers to the substrate
surface. Once all of the ink slurry mixture was sprayed onto the
substrate, the layering/electrode was placed in a vacuum at a
temperature of 70.degree. C. for a period of 5 minutes. The dried
layering/electrode was calendared between two steel rollers on a
custom built device to a final thickness of about 1 mil.
[0187] Preparation of Hydrocarbon Ionomer (SURLYN.RTM.) Coated
Energain.RTM. Polyimide Battery Separator:
[0188] A piece of Energain.RTM. Polyimide Battery Separator (DuPont
Company) with dimensions 10.7 cm by 6.7 cm was taped to a glass
plate and heated to 70.degree. C. on a hot plate. The separator was
then sprayed, using the air brush, with an aqueous dispersion of
SURLYN.RTM. ionomer, 6.4 wt. % loading. When the Surlyn.RTM.
loading on the separator reached 0.4 mg per cm.sup.2, the sample
was dried in a vacuum oven at 70.degree. C. for 15 minutes. The
coated separator was then ion exchanged by immersing it in a bath
of aqueous 2M LiOH solution overnight. It was rinsed with deionized
water and dried under vacuum at 70.degree. C. for 2 hours. After
drying overnight at 70 C, a 2.25''.times.2.15'' piece of the
Surlyn.RTM./Energain.RTM. composite was hot pressed on a Carver
hyraulic press. The hydraulic press was preheated to 70 C. The
composite was sandwiched between two PFA (perfluoroalkyl) sheets
and then sandwiched between two pieces of 4''.times.4'' glass
plate. 1000 pounds force was applied for 10 minutes to create the
final composite structure.
[0189] Scanning electron micrographs of the polymer composite were
obtained by first cutting approximately 0.5 cm.times.1.0 cm section
film and mounting it on sticky carbon tape on an Si wafer. The
mounted films were coated with 2 nm Os metal using the OPC-80
Osmium Plasma Coater. The films were examined in the Hitachi 54000
FE-SEM at 2.5 keV accelerating voltage at a 10 mm working distance.
Images were taken at very low magnifications (100.times.) to
moderately high magnification (10,000.times.) to compare surface
features.
[0190] Preparation of Electrolyte:
[0191] 3.59 grams of lithium bis(trifluoro-methane sulfonyl)imide
(LiTFSI, Novolyte) was combined with 20.32 grams (23.40 ml) of 1,2
dimethoxyethane (glyme, Sigma Aldrich, 259527) to create a 0.5 M
electrolyte solution.
[0192] Preparation of Coin Cell:
[0193] A 14.29 mm diameter circular disk was punched from the
layering/electrode and used as the positive electrode 307. The
final weight of the electrode (14.29 mm in diameter, subtracting
the weight of the aluminum current collector) was 4.71 mg. This
corresponds to a calculated weight of 2.01 mg of elemental sulfur
on the electrode.
[0194] The coin cell 300 includes the positive electrode 307, the
19 mm diameter circular disk punched from the
Surlyn.RTM./Energain.RTM. composite described in the previous
section and two 19 mm piece of Celgard 2500 polyolefin separator
(Celgard, LLC). The two Celgard 2500 diskes were used to sandwich
the Surlyn.RTM./Energain.RTM. compous, and were used together as
the final separator 306 in the coin cell 300 with the lithium
exchanged The Surlyn.RTM./Energain.RTM.composite was assembled so
the "Surlyn" side of the separator faced the positive electrode.
The positive electrode 307, the separator 306, a lithium foil
negative electrode 304 (3 mils thickness, Chemetall Foote Corp.)
and a few electrolyte drops 305 of the nonaqueous electrolyte was
sandwiched in a MTI stainless steel coin cell can with a 1 mil
thick stainless steel spacer disk and wave spring (Hohsen Corp.).
The construction involved the following sequence as shown in FIG.
3: bottom cap 308, positive electrode 307, electrolyte drops 305,
separator 306, electrolyte drops 305, negative electrode 304,
spacer disk 303, wave spring 302 and top cap 301. The final
assembly was crimped with an MTI crimper (MTI).
[0195] Electrochemical Testing Conditions:
[0196] The positive electrode 307 was cycled at room temperature
between 1.5 and 3.0 V (vs. Li/Li.sup.0) at C/5 (based on 1675 mAh/g
S for the charge capacity of elemental sulfur). This is equivalent
to a current of 335 mAh/g S in the positive electrode 307.
[0197] Electrochemical Evaluation:
[0198] The maximum charge capacity measured on discharge at cycle
10 was 1013 mAh/g S with a coulombic efficiency of 90%.
[0199] Utilizing a Li--S cell incorporating hydrocarbon ionomer
articles, such as coatings, membranes, films and other articles
incorporating hydrocarbon ionomer provides a high maximum charge
capacity Li--S battery with high coulombic efficiency. Li--S cells
incorporating hydrocarbon ionomer articles may be utilized in a
broad range of Li--S battery applications in providing a source of
potential power for many household and industrial applications. The
Li--S batteries incorporating these hydrocarbon ionomer articles
are especially useful as power sources for small electrical devices
such as cellular phones, cameras and portable computing devices and
may also be used as power sources for car ignition batteries and
for electrified cars.
[0200] Although described specifically throughout the entirety of
the disclosure, the representative examples have utility over a
wide range of applications, and the above discussion is not
intended and should not be construed to be limiting. The terms,
descriptions and figures used herein are set forth by way of
illustration only and are not meant as limitations. Those skilled
in the art recognize that many variations are possible within the
spirit and scope of the principles of the invention. While the
examples have been described with reference to the figures, those
skilled in the art are able to make various modifications to the
described examples without departing from the scope of the
following claims, and their equivalents.
[0201] Further, the purpose of the foregoing Abstract is to enable
the U.S. Patent and Trademark Office and the public generally and
especially the scientists, engineers and practitioners in the
relevant art who are not familiar with patent or legal terms or
phraseology, to determine quickly from a cursory inspection the
nature and essence of this technical disclosure. The Abstract is
not intended to be limiting as to the scope of the present
invention in any way.
* * * * *