U.S. patent application number 14/676173 was filed with the patent office on 2021-08-19 for high capacity polymer cathode and high energy density rechargeable cell comprising the cathode.
The applicant listed for this patent is IONIC MATERIALS, INC.. Invention is credited to Alexei B. Gavrilov, Randy Leising, Keith Smith, Andy Teoli, Michael A. Zimmerman.
Application Number | 20210257609 14/676173 |
Document ID | / |
Family ID | 1000005750097 |
Filed Date | 2021-08-19 |
United States Patent
Application |
20210257609 |
Kind Code |
A9 |
Zimmerman; Michael A. ; et
al. |
August 19, 2021 |
HIGH CAPACITY POLYMER CATHODE AND HIGH ENERGY DENSITY RECHARGEABLE
CELL COMPRISING THE CATHODE
Abstract
The invention features a rechargeable cathode and a battery
comprising the cathode. The cathode includes a solid, ionically
conducting polymer material and electroactive sulfur. The battery
contains a lithium anode; the cathode; and an electrolyte; wherein
at least one of anode, the cathode and the electrolyte, include the
solid, ionically conducting polymer material.
Inventors: |
Zimmerman; Michael A.; (No.
Andover, MA) ; Leising; Randy; (No. Andover, MA)
; Gavrilov; Alexei B.; (Woburn, MA) ; Smith;
Keith; (Methuen, MA) ; Teoli; Andy;
(Wilmington, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IONIC MATERIALS, INC. |
Woburn |
MA |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150280218 A1 |
October 1, 2015 |
|
|
Family ID: |
1000005750097 |
Appl. No.: |
14/676173 |
Filed: |
April 1, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14559430 |
Dec 3, 2014 |
9742008 |
|
|
14676173 |
|
|
|
|
13861170 |
Apr 11, 2013 |
9819053 |
|
|
14559430 |
|
|
|
|
61973325 |
Apr 1, 2014 |
|
|
|
61911049 |
Dec 3, 2013 |
|
|
|
61622705 |
Apr 11, 2012 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/38 20130101; H01M
4/625 20130101; H01M 2004/028 20130101; H01M 4/602 20130101; H01M
4/364 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/38 20060101 H01M004/38; H01M 4/60 20060101
H01M004/60; H01M 4/62 20060101 H01M004/62 |
Claims
1. A cathode electrode comprising sulfur as the active material,
and an ionically conductive polymer.
2. The cathode of claim 1 where the polymer has an ionic
conductivity of greater than 1.times.10.sup.-4 S/cm at room
temperature.
3. The cathode of claim 1 wherein the polymer is electrically
insulative.
4. The cathode of claim 1 wherein the polymer has Lithium cation
diffusivity greater than 1.times.10.sup.-11 meters squared per
second at room temperature.
5. The cathode of claim 1 further comprising electrically
conductive fillers are used to add electrical conductivity.
6. The cathode of claim 1 wherein the solid, ionically conductive
polymer material encapsulates at least one particle of the active
material
7. The cathode of claim 1 wherein the solid, ionically conducting
polymer material is formed from a reactant product of a base
polymer, an electron acceptor, and a compound including a source of
ions.
8. The cathode of claim 1 wherein the solid, ionically conducting
polymer material contains a base polymer which is oxidatively doped
in the presence of Li+ groups.
9. The cathode of claim 7 where the compound including an ion
source is either LiOH, L.sub.2O or a mixture of the two.
10. The cathode of claim of claim 8 where the base polymer is one
that can be "oxidized", and wherein the base polymer is a
conjugated polymer.
11. The cathode of claim 7 where the base polymer is selected from
a group comprising polyphenylene sulfide, liquid crystal polymer, a
polyether ether ketone (PEEK) or a semicrystalline polymer with a
crystallinity index of greater than 30%, and combinations
thereof.
12. The cathode of claim 7 where the electron acceptor is selected
from a group comprising Dichloro Dicyano Quinone
(C.sub.8Cl.sub.2N.sub.2O.sub.2), TCNE (C.sub.6N.sub.6), Sulfur
Trioxide (SO.sub.3) or chloranil and combinations thereof.
13. An electrochemical cell comprising, an anode, and a cathode,
said cathode comprising sulfur as the active material, and an
ionically conductive polymer.
14. The electrochemical cell of claim 13, wherein the cathode
specific capacity is greater than 500 mAh/g.
15. The electrochemical cell of claim 13, wherein the cathode
specific capacity is greater than 1000 mAh/g.
16. The electrochemical cell of claim 13, wherein the cathode
specific capacity is greater than 1500 mAh/g.
17. The electrochemical cell of claim 13, wherein the voltage of
cell is greater than 1.0 volts.
18. The electrochemical cell of claim 13, wherein the anode is
selected from a group comprising Lithium, Tin, Silicon, graphite,
or any alloy or mixture thereof.
19. The electrochemical cell of claim 13, wherein the cell is a
secondary cell.
20. The electrochemical cell of claim 19, wherein the cathode
specific capacity is greater than 1000 mAh/g.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] N/A
BACKGROUND OF THE INVENTION
[0002] Batteries have become increasingly important in modern
society, both in powering a multitude of portable electronic
devices, as well as being key components in new green technologies.
These new technologies offer the promise of removing the dependence
on current energy sources such as coal, petroleum products, and
natural gas which contribute to the production of by-product
green-house gases. Furthermore, the ability to store energy in both
stationary and mobile applications is critical to the success of
new energy sources, and is likely to sharply increase the demand
for all sizes of advanced batteries. Especially for batteries for
large applications, a low base cost of the battery will be key to
the introduction and overall success of these applications.
[0003] Conventional batteries have limitations, however. For
example, lithium ion and other batteries generally employ a liquid
electrolyte which is hazardous to humans and to the environment and
which can be subject to fire or explosion. Liquid electrolyte
batteries are hermetically sealed in a steel or other strong
packaging material which adds to the weight and bulk of the
packaged battery. Conventional liquid electrolyte suffers from the
build-up of a solid interface layer at the electrode/electrolyte
interface which causes eventual failure of the battery.
Conventional lithium ion batteries also exhibit slow charge times
and suffer from a limited number of recharges since the chemical
reaction within the battery reaches completion and limits the
re-chargeability because of corrosion and dendrite formation. The
liquid electrolyte also limits the maximum energy density which
starts to break down at about 4.2 volts while often 4.8 volts and
higher are required in the new industry applications. Conventional
lithium ion batteries require a liquid electrolyte separator to
allow ion flow but block electron flow, a vent to relieve pressure
in the housing, and in addition, safety circuitry to minimize
potentially dangerous over-currents and over-temperatures.
[0004] While the battery technology for many advanced applications
is Lithium Ion (Li-ion), increased demands for higher energy
density, both in terms of volumetric (Wh/L) for portable devices,
and gravimetric (Wh/kg) for electric vehicles and other large
applications have shown the necessity for accessing technologies
well beyond the current capabilities of Li-ion cells. One such
promising technology is Li/sulfur batteries. A sulfur based cathode
is enticing because of the high theoretical energy density (1672
mAh/g) which is .about.10.times. better than the current Li-ion
metal oxide cathode active materials. Sulfur is also exciting
because it is a very abundant, low cost, environmentally friendly
material, unlike many current Li-ion battery materials, such as
LiCoO.sub.2.
[0005] Recently, there has been a great amount of activity in
Li/sulfur battery research, with advances in the capacity and cycle
life of rechargeable Li/sulfur cells. Activity has included
modifications to the cathode, anode, electrolyte and separator, all
with the goal of reducing the polysulfide shuttle and thereby
improving cell performance. Applications of this research to sulfur
cathodes has focused in two main areas: 1) the use of engineered
materials to surround and contain the sulfur and soluble lithiated
products, for example see: U.S. Patent Application 2013/0065128,
and 2) the use of conductive polymers which react with sulfur to
produce a "sulfurized" composite cathode material. Examples of
"sulfurized-polymer" include reaction products from high
temperature exposure of sulfur with polyacrylonitrile (PAN) [see:
Jeddi, K., et. al. J. Power Sources 2014, 245, 656-662 and Li, L.,
et. al. J. Power Sources 2014, 252, 107-112]. Other conductive
polymer systems used in sulfur cathodes include
polyvinylpyrrolidone (PVP) [see: Zheng, G., et. al. Nano Lett.
2013, 13, 1265-1270] and polypyrrole (PPY) [see: Ma, G., et. al. J.
Power Sources 2014, 254, 353-359]. While these methods have met
with various degrees of success in limiting the polysulfide shuttle
mechanism, they all rely on the use of expensive materials which
are not well suited to large scale manufacturing.
BRIEF SUMMARY OF THE INVENTION
[0006] A solid, ionically conducting polymer material is provided
having very high ionic diffusivity and conductivity at both room
temperature and over a wide temperature range. The solid ionic
polymer material is useful as a solid electrolyte for batteries and
is also is useful as a component to make battery electrodes. The
material is not limited to battery applications but is more broadly
applicable for other purposes such as alkaline fuel cells,
supercapacitors, electrochromic devices, sensors and the like. The
polymer material is non-flammable and self-extinguishes, which is
especially attractive for applications which otherwise might be
flammable. In addition the material is mechanically strong and can
be manufactured using high volume polymer processing techniques and
equipment which themselves are known in the art.
[0007] The solid, ionically conducting polymer material includes a
base polymer, a dopant and at least one compound including an ion
source. The dopant includes an electron donor, an electron acceptor
or an oxidant. In one embodiment, the base polymer can be a
polyphenylene sulfide, a polyether ether ketone also known as PEEK,
or a liquid crystal polymer. In this embodiment, the dopant is an
electron acceptor such as, for non-limiting examples, 2,3,
dicloro-5,6-dicyano-1,4-benzoquinone, TCNE, sulfur trioxide or
chloranil. Other dopants acting as electron acceptors or containing
functional groups capable to accept electrons can be employed. The
compound including an ion source includes compounds containing ions
or materials chemically convertible to compounds containing a
desired ion including, but not limited to, hydroxides, oxides,
salts or mixtures thereof, and more specifically Li.sub.2O, Na2O,
MgO, CaO, ZnO, LiOH, KOH, NaOH, CaCl2, AlCl3, MgCl2, LiTFSI
(lithium bis-trifluoromethanesulfonimide), LiBOB (Lithium
bis(oxalate)borate) or a mixture of the preceding two
components.
[0008] The solid ionically conducting polymer material exhibits
carbon 13 NMR (detection at 500 MHz) chemical shift peaks at about
172.5 ppm, 143.6 ppm, 127.7 ppm, and 115.3 ppm. A similar carbon 13
NMR scan of the electron acceptor shows chemical shift peaks at
about 195 ppm, and 107.6 ppm in addition to the chemical shift
peaks at about 172.5 ppm, 143.6 ppm, 127.7 ppm, and 115.3 ppm. In
other words, the reaction between the base polymer and the electron
acceptor appears to eliminate the chemical shift peaks at about 195
ppm, and 107.6 ppm. In addition, the .sup.13C NMR spectrum of the
solid ionically conducting polymer movement in the main peak
(dominated by the aromatic carbon) in going from the base polymer
to the solid ionically conducting polymer. The chemical shift of
the dominant peak in the solid ionically conducting polymer is
greater than the chemical shift of the dominant peak in the base
polymer.
[0009] The solid ionically conductive material has crystallinity
index of at least or greater than about 30%, and can include the
ion source is in a range of 10 wt. % to 60 wt. %. The dopant molar
ratio is preferably in the range of about 1-16 relative the base
polymer. Further the material has an ionic conductivity of at least
1.times.10.sup.-4 S/cm at room temperature of between 20.degree. C.
to 26.degree. C., a tensile strength in the range of 5-100 MPa, a
Modulus of Elasticity in the range of 0.5-3.0 GPa, and Elongation
in the range of 0.5-30%.
[0010] In one embodiment of said battery, the battery comprises an
anode; a cathode; and wherein at least one of the anode, and the
cathode comprise a solid, ionically conducting polymer material.
The battery can be rechargeable or primary. The battery further
comprises an electrolyte, and the electrolyte can comprise the
solid, ionically conducting polymer material in whole or in part.
The battery can alternatively or additionally further comprise an
electrolyte.
[0011] The solid, ionically conducting polymer material is formed
from a reactant product comprising a base polymer, an electron
acceptor, and a compound including a source of ions. The solid,
ionically conducting polymer material can be used as an electrolyte
in either the anode or cathode. If used in a battery the cathode of
said battery can comprise an active material selected from the
group comprising ferrate, iron oxide, cuprous oxide, iodate, cupric
oxide, mercuric oxide, cobaltic oxide, manganese oxide, lead
dioxide, silver oxide, oxygen, nickel oxyhydroxide, nickel dioxide,
silver peroxide, permanganate, bromate, silver vanadium oxide,
carbon monofluoride, iron disulfide, iodine, vanadium oxide, copper
sulfide, sulfur or carbon and combinations thereof. The anode of
said battery can comprise an active material selected from the
group comprising lithium, magnesium, aluminum, zinc, chromium,
iron, nickel, tin, lead, hydrogen, copper, silver, palladium,
mercury, platinum or gold, and combinations thereof, and alloyed
materials thereof.
[0012] The battery can alternatively further comprise an
electrically conductive additive and/or a functional additive in
either the anode or cathode. The electrically conductive additive
can be selected from the group comprising a carbon black, a natural
graphite, a synthetic graphite, a graphene, a conductive polymer, a
metal particle, and a combination of at least two of the preceding
components.
[0013] The battery electrodes (anode or cathode) can composite
structure which can be formed by a process such as injection
molding, tube extrusion and compression molding. In a preferred
embodiment, a cathode electrode is made including sulfur as the
active material, which also includes an ionically conductive
polymer. Sulfur as used herein is intended to mean any source of
electroactive sulfur such as elemental sulfur, polymeric sulfur,
pyrite and other materials that can act to supply sulfur to the
electrochemical reaction of the cathode.
[0014] The ionically conductive polymer has an ionic conductivity
of greater than 1.times.10.sup.-4 S/cm at room temperature, has
Lithium cation diffusivity greater than 1.times.10.sup.-11 meters
squared per second at room temperature and is electrically
insulative.
[0015] The cathode can further include electrically conductive
fillers in order to add electrical conductivity, and the solid,
ionically conductive polymer material can encapsulate at least one
particle of the active material or other components of the
cathode.
[0016] The solid, ionically conducting polymer material is formed
from a reactant product of a base polymer, an electron acceptor,
and a compound including a source of ions. The base polymer is
selected from a group comprising conjugated polymers, polyphenylene
sulfide, liquid crystal polymer, a polyether ether ketone (PEEK) or
a semicrystalline polymer with a crystallinity index of greater
than 30%, and combinations thereof, and can be is oxidatively doped
in the presence of Li+ cations. The electron acceptor is selected
from a group comprising Dichloro Dicyano Quinone
(C.sub.8Cl.sub.2N.sub.2O.sub.2), TCNE (C.sub.6N.sub.6), Sulfur
Trioxide (SO.sub.3) or chloranil and combinations thereof. The
compound including an ion source is preferably LiOH, L.sub.2O or a
mixture of the two.
[0017] The cathode including sulfur as the active material, and an
ionically conductive polymer is preferably incorporated into an
electrochemical cell which further includes an anode. The anode
active material is preferably lithium but can be alternatively
selected from a group comprising Lithium, Tin, Silicon, graphite,
or any alloy or mixture thereof.
[0018] The demonstrated voltage of the electrochemical cell is
greater than 1.0 volts, and the the cathode specific capacity is
greater than 500 mAh/g, preferably the cathode specific capacity is
greater than 1000 mAh/g, and most preferably the cathode specific
capacity is greater than 1500 mAh/g, while demonstrating
rechargeable behavior over two thousand cycles.
[0019] The solid, ionically conductive polymer material can also be
useful as a separator film, as it is electrically non-conductive,
and ionically conductive. Therefore the solid, ionically conductive
polymer material cast or otherwise rendered as a film can be used
as a separator positioned between an anode and cathode. In
addition, the solid, ionically conductive polymer material can be
coated onto an electrode to function as a separator or
alternatively to isolate the electrode or an electrode component
from another battery component such as an aqueous electrolyte. The
solid, ionically conductive polymer material enables ionic
communication between such an isolated component despite it being
physically separated, and electrically segmented from the rest of
the battery component. The material can also comprise an aggregated
or cast agglomeration of small particles of the solid, ionically
conductive polymer material. Such an aggregation can take any shape
but include an engineered porosity while possessing an engineered
surface area. Fillers, such as hydrophobic materials can be mixed
in the material to provide desirable physical properties such as
low effective aqueous porosity. Thus the solid, ionically
conductive polymer material can include a low or very high surface
area, and or a low or very high porosity. Shapes such as an annulus
and other moldable shapes can be engineering with desired physical
properties with the ionic conductivity of the solid, ionically
conductive polymer material are enabled by the invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0020] FIG. 1 exemplarily shows a resulting formula for the
crystalline polymer of the present invention.
[0021] FIG. 2 exemplarily illustrates a dynamic scanning
calorimeter curve of a semicrystalline polymer.
[0022] FIG. 3 exemplarily illustrates formulations which were
investigated for use with the invention.
[0023] FIG. 4 shows a schematic illustration of amorphous and
crystalline polymers.
[0024] FIG. 5 exemplarily illustrates a chemical diagram of
2,3-dicyano-5,6-dichlorodicyanoquinone (DDQ) as a typical electron
acceptor dopant for use in the invention.
[0025] FIG. 6 exemplarily illustrates a plot of the conductivity of
the ionically conductive polymer according to the invention in
comparison with a liquid electrolyte and a polyethylene oxide
lithium salt compound.
[0026] FIG. 7 exemplarily illustrates the mechanical properties of
the ionically conducting film according to the invention.
[0027] FIG. 8 exemplarily illustrates possible mechanisms of
conduction of the solid electrolyte polymer according to the
invention.
[0028] FIG. 9 exemplarily shows a UL94 flammability test conducted
on a polymer according to the invention.
[0029] FIG. 10 exemplarily shows a plot of volts versus current of
an ionically conductive polymer according to the invention versus
lithium metal.
[0030] FIG. 11 exemplarily illustrates a schematic of extruded
ionically conductive electrolyte and electrode components according
to the invention.
[0031] FIG. 12 exemplarily illustrates the solid state battery
according to the invention where electrode and electrolyte are
bonded together.
[0032] FIG. 13 exemplarily illustrates a final solid state battery
according to the invention having a new and flexible form.
[0033] FIG. 14 exemplarily illustrates a method of the invention
including steps for manufacturing a solid state battery using an
extruded polymer.
[0034] FIG. 15 exemplarily illustrates the extrusion process
according to the invention.
[0035] FIG. 16 exemplarily illustrates a schematic representation
of an embodiment according to the invention.
[0036] FIG. 17 exemplarily illustrates a comparison of process
steps for standard Li-ion cathode manufacturing with those for
extrusion of the composite polymer-sulfur cathode of the
invention.
[0037] FIG. 18 exemplarily illustrates lithium diffusivity at room
temperature in a solid polymer electrolyte of the invention.
[0038] FIG. 19 exemplarily illustrates a first discharge voltage
curve for Li/Ionic polymer-sulfur cell of the present
invention.
[0039] FIG. 20 exemplarily illustrates a discharge capacity curve
plotted as a function of cycle number for Li/Ionic polymer-sulfur
cell of the present invention.
[0040] FIG. 21 exemplarily illustrates the discharge capacity curve
as a function of cycle number for the lithium-sulfur cell of the
present invention.
[0041] FIG. 22 exemplarily illustrates the first discharge voltage
curve for the lithium-sulfur cell of the present invention with a
slurry cast cathode.
[0042] FIG. 23 exemplarily illustrates a comparison of first
discharge for literature example Li/Sulfur-CMK-3 with Li/Ionic
polymer-sulfur of present invention.
[0043] FIG. 24 illustrates a charge/discharge voltage curves for a
Li/sulfur-poly(pyridinopyridine) cell from the prior art.
[0044] FIG. 25 shows the cycle life curves for a literature example
Li-Sulfur battery with the Li-solid ionically conductive
polymer-sulfur battery of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0045] This application claims priority to U.S. patent application
Ser. No. 14/559,430, filed Dec. 3, 2014 and U.S. Provisional
Application No. 61/973,325, filed Apr. 1, 2014 each of which is
incorporated herein by reference in its entirety for all
purposes.
[0046] The invention comprises a cathode containing a solid,
ionically conductive polymer material and a battery including the
cathode. The solid ionically conductive polymer material includes a
base polymer, a dopant, and at least one compound including an ion
source. The polymer material has a capacity for ionic conduction
over a wide temperature range including room temperature. It is
believed that ion "hopping" occurs from a high density of atomic
sites. Thus, the solid, ionically conductive polymer material can
function as a means for conducting and supplying ions and while
retaining the significant material strength of the base
polymer.
[0047] For the purposes of this application, the term "polymer" is
known in the art and refers to a macromolecule composed of many
repeating subunits or monomers, and preferably the based polymer is
a crystalline or semi-crystalline polymer. The base polymer can be
selected depending upon the desired properties of the composition
in relation to the desired application. For example, the
thermoplastic, solid, ionically conductive polymer material can be
molded into shapes thus allowing for desired electrode or battery
component forms.
[0048] For purposes of the application, the term "dopant" refers to
electron acceptors or oxidants or electron donors. The dopant is
selected depending upon the desired properties of the composition
in relation to the desired application. Similarly, the compound
including an ion source is selected depending upon the desired
properties of the composition in relation to the desired
application.
[0049] I. Solid, Ionically Conductive Polymer Material for Li.sup.+
Chemistries
[0050] In one aspect, the invention relates to the solid, ionically
conductive polymer material used in a battery to conduct lithium
ions.
[0051] In this aspect, the base polymer is characterized as having
a crystallinity value of between 30% and 100%, and preferably
between 50% and 100%. The base polymer has a glass transition
temperature of above 80.degree. C., and preferably above
120.degree. C., and more preferably above 150.degree. C., and most
preferably above 200.degree. C. The base polymer has a melting
temperature of above 250.degree. C., and preferably above
280.degree. C., and more preferably above 320.degree. C. The
molecular weight of the monomeric unit of the base polymer of the
invention is in the 100-200 gm/mol range and can be greater than
200 gm/mol. FIG. 1 shows the molecular structure of an exemplary
base polymer, wherein the monomeric unit of the base polymer has a
molecular weight of 108.16 g/mol. FIG. 2 exemplarily illustrates a
dynamic scanning calorimeter curve of an exemplary semicrystalline
base polymer. FIG. 3 illustrates exemplary formulations for the
solid, ionically conducting polymer material in this aspect of the
invention where DDQ is the dopant. Typical materials that can be
used for the base polymer include liquid crystal polymers and
polyphenylene sulfide also known as PPS, or any semi-crystalline
polymer with a crystallinity index greater than 30%, and preferably
greater than 50%. In one embodiment, the invention uses a
"crystalline or semi-crystalline polymer", exemplarily illustrated
in FIG. 4, which typically is above a crystallinity value of 30%,
and has a glass transition temperature above 200.degree. C., and a
melting temperature above 250.degree. C.
[0052] In this aspect, the dopant is an electron acceptor, such as,
for non-limiting examples, 2,3-dicyano-5,6-dichlorodicyanoquinone
(C.sub.8Cl.sub.2N.sub.2O.sub.2) also known as DDQ,
Tetracyanoethylene(C.sub.6N.sub.4) known as TCNE, chloranil and
sulfur trioxide (SO.sub.3). A preferred dopant is DDQ. FIG. 5
provides a chemical diagram of this preferred dopant. It is
believed that the purpose of the electron acceptor is two-fold: to
release ions for transport mobility, and to create polar high
density sites within the polymer to allow for ionic conductivity.
The electron acceptor can be "pre-mixed" with the initial
ingredients and extruded without post-processing or alternatively,
a doping procedure such as vapor doping can be used to add the
electron acceptor to the composition after the material is
created.
[0053] Typical compounds including an ion source for use in this
aspect of the invention include, but are not limited to, Li.sub.2O,
LiOH, ZnO, TiO.sub.2, Al.sub.2O.sub.3, and the like. The compounds
containing appropriate ions which are in stable form can be
modified after creation of the solid, polymer electrolytic
film.
[0054] Other additives, such as carbon particles nanotubes and the
like, can be added to the solid, polymer electrolyte including the
solid, ionically conducting material to further enhance electrical
conductivity or current density.
[0055] The novel solid polymer electrolyte enables a lighter weight
and much safer architecture by eliminating the need for heavy and
bulky metal hermetic packaging and protection circuitry. A novel
solid polymer battery including the solid polymer electrolyte can
be of smaller size, lighter weight and higher energy density than
liquid electrolyte batteries of the same capacity. The novel solid
polymer battery also benefits from less complex manufacturing
processes, lower cost and reduced safety hazard, as the electrolyte
material is non-flammable. The novel solid polymer battery is
capable of cell voltages greater than 4.2 volts and is stable
against higher and lower voltages. The novel solid polymer
electrolyte can be formed into various shapes by extrusion (and
co-extrusion), molding and other techniques such that different
form factors can be provided for the battery. Particular shapes can
be made to fit into differently shaped enclosures in devices or
equipment being powered. In addition, the novel solid polymer
battery does not require a separator, as with liquid electrolyte
batteries, between the electrolyte and electrodes.
[0056] In another aspect of the invention, a solid polymer
electrolyte including the solid, ionically conducting polymer
material is in the form of an ionic polymer film. An electrode
material is directly applied to each surface of the ionic polymer
film and a foil charge collector or terminal is applied over each
electrode surface. A light weight protective polymer covering can
be applied over the terminals to complete the film based structure.
The film based structure forms a thin film battery which is
flexible and can be rolled or folded into intended shapes to suit
installation requirements.
[0057] In yet another aspect of the invention, a solid polymer
electrolyte including the solid, ionically conducting polymer
material is in the form of an ionic polymer hollow monofilament.
Electrode materials and charge collectors are directly applied
(co-extruded) to each surface of the solid, ionically conductive
polymer material and a terminal is applied at each electrode
surface. A light weight protective polymer covering can be applied
over the terminals to complete the structure. The structure forms a
battery which is thin, flexible, and can be coiled into intended
shapes to suit installation requirements, including very small
applications.
[0058] In still another aspect of the invention, a solid polymer
electrolyte including the solid, ionically conducting polymer
material has a desired molded shape. Anode and cathode electrode
materials can be disposed on respective opposite surfaces of the
solid polymer electrolyte to form a cell unit. Electrical terminals
can be provided on the anode and cathode electrodes of each cell
unit for interconnection with other cell units to provide a multi
cell battery or for connection to a utilization device.
[0059] In aspects of the invention relating to batteries, the
electrode materials (cathode and anode) can be combined with a form
of the novel solid, ionically conductive polymer material to
further facilitate ionic movement between the two electrodes. This
is analogous to a conventional liquid electrolyte soaked into each
electrode material in a convention lithium battery.
[0060] Films of solid, ionically conducting polymer materials of
the present invention have been extruded in thickness ranging
upwards from 0.0003 inches. The ionic surface conductivity of the
films has been measured using a standard test of AC-Electrochemical
Impedance Spectroscopy (EIS) known to those of ordinary skill in
the art. Samples of the solid, ionically conducting polymer
material film were sandwiched between stainless steel blocking
electrodes and placed in a test fixture. AC-impedance was recorded
in the range from 800 KHz to 100 Hz using a Biologic VSP test
system to determine the electrolyte conductivity. The results of
the surface conductivity measurements are illustrated in FIG. 6.
The conductivity of solid, ionically conductive polymer material
film according to the invention (A) is compared with that of
trifluoromethane sulfonate PEO ( ) and a liquid electrolyte made up
of a Li salt solute and a EC:PC combination solvent using a Celgard
separator (O). The conductivity of the solid, ionically conducting
polymer material film according to the invention tracks the
conductivity of the liquid electrolyte and far surpasses that of
trifluoromethane sulfonate PEO at the lower temperatures. Further,
unlike PEO electrolytes, the temperature dependence of the
conductivity for inventive polymer material does not display a
sharp increase above its glass transition temperature, associated
with chain mobility, as described by Vogel-Tamman-Fulcher behavior
activated by temperature. Therefore, segmental movement as the
ion-conduction mechanism in the inventive polymer material is
unlikely. Furthermore, this demonstrates that the inventive polymer
material has similar ionic conductivity to liquid electrolytes.
[0061] FIG. 7 shows the mechanical properties of the solid,
ionically conductive polymer material films of the invention. The
mechanical properties were evaluated using the Institute for
Interconnecting and Packaging Electronic Circuits IPC-TM-650 Test
Methods Manual 2.4.18.3. In the tensile strength versus elongation
curve of FIG. 7, the "ductile failure" mode indicates that the
material can be very robust.
[0062] The solid, ionically conductive polymer material of the
invention offers three key advantages in its polymer performance
characteristics: (1) It has an expansive temperature range. In
lab-scale testing, the crystalline polymer has shown high ionic
conductivity both at room temperature and over a wide temperature
range. (2) It is non-flammable. The polymer self-extinguishes,
passing the UL-V0 Flammability Test. The ability to operate at room
temperature and the non-flammable characteristics demonstrate a
transformative safety improvement that eliminates expensive thermal
management systems. (3) It offers low-cost bulk manufacturing.
Rather than spraying the polymer onto electrodes, the polymer
material can be extruded into a thin film via a roll-to-roll
process, an industry standard for plastics manufacturing. After the
film is extruded, it can be coated with the electrode and charge
collector materials to build a battery "from the inside out." This
enables thin, flexible form factors without the need for hermetic
packaging, resulting in easy integration into vehicle and storage
applications at low cost.
[0063] It is believed that the solid, ionically conducting polymer
material of the present invention creates a new ionic conduction
mechanism that provides a higher density of sites for ionic
transport and allows the conducting material to maintain higher
voltages without risk of thermal runaway or damage to ion transport
sites from, for example, lithiation. This characteristic enables
the solid, ionically conducting polymer material to be durable for
anode materials and higher voltage cathode thin-film applications,
resulting in higher energy densities for batteries which may be
used in vehicle and stationary storage applications. The ability to
maintain high voltages within a solid, ionically conductive polymer
material which is mechanically robust, chemical and moisture
resistant, and nonflammable not only at room temperature, but over
a wide range of temperatures, allows integration with high
performance electrodes without costly thermal and safety mechanisms
employed by the industry today.
[0064] FIG. 8 shows possible mechanisms of conduction of the solid,
ionically conducting polymer material in a solid polymer
electrolyte aspect of the invention. Charge carrier complexes are
set up in the polymer as a result of the doping process.
[0065] Flammability of the solid polymer electrolyte including the
solid, ionically conductive polymer material of the invention was
tested using a UL94 flame test. For a polymer to be rated UL94-V0,
it must "self-extinguish" within 10 seconds and `not drip". The
solid polymer electrolyte was tested for this property and it was
determined that it self-extinguished with 2 seconds, did not drip,
and therefore easily passed the V0 rating. FIG. 9 shows pictures of
the result.
[0066] In addition to the properties of ionic conductivity, flame
resistance, high temperature behavior, and good mechanical
properties, it is preferable that the solid polymer electrolyte
including the solid, ionically conductive polymer material of the
invention is electrochemically stable at low and high potentials.
The traditional test for the electrochemical stability is cyclic
voltammetry, when working electrode potential is ramped linearly
versus time. In this test, the polymer is sandwiched between a
lithium metal anode and blocking stainless steel electrode. A
voltage is applied and it is swept positively to a high value
(greater than 4 volts vs. Li) for stability towards oxidation and
negatively to a low value (0V vs. Li or less) for stability towards
reduction. The current output is measured to determine if any
significant reaction occurs at the electrode interface. High
current output at high positive potential would signify oxidation
reaction taking place, suggesting instability with cathode
materials operating at these or more positive potentials (such as
many metal oxides). High current output at low potentials would
signify that a reduction reaction takes place, suggesting
instability with anodes operating at these or more negative
potentials (such as metal Li or lithiated carbon). FIG. 10 shows a
plot of voltage versus current for a solid polymer electrolyte
including the solid, ionically conductive polymer material
according to the invention versus lithium metal. The study shows
that the solid polymer electrolyte is stable up to about 4.6 volts.
These results indicate that the solid polymer electrolyte could be
stable with cathodes including LCO, LMO, NMC and similar cathodes,
along with low voltage cathodes such as, for non-limiting examples
iron phosphate and sulfur cathodes.
[0067] The solid polymer electrolyte including the solid, ionically
conductive polymer material of the invention is able to achieve the
following properties: A) high ionic conductivity at room
temperature and over a wide temperature range (at least -10.degree.
C. to +60.degree. C.); B) non-flammability; C) extrudability into
thin films allowing for reel-reel processing and a new way of
manufacturing; D) compatibility with Lithium metal and other active
materials. Accordingly, this invention allows for the fabrication
of a true solid state battery. The invention allows for a new
generation of batteries having the following properties: no safety
issues; new form factors; large increases in energy density; and
large improvements in cost of energy storage.
[0068] FIGS. 11, 12 and 13 show several elements of the solid state
battery including the solid, ionically conductive polymer material
of the invention which are, respectively: A) an extruded
electrolyte; B) extruded anodes and cathodes; and C) a final solid
state battery allowing for new form factors and flexibility.
[0069] In other aspects, the invention provides methods for making
Li batteries including the solid, ionically conducting polymer
material of the invention. FIG. 14 shows a method of manufacturing
a solid state lithium ion battery using an extruded solid,
ionically conducting polymer material according to the invention.
The material is compounded into pellets, and then extruded through
a die to make films of variable thicknesses. The electrodes can be
applied to the film using several techniques, such as sputtering or
conventional casting in a slurry.
[0070] In yet another aspect, the invention provides a method of
manufacturing of an ionic polymer film including the solid,
ionically conductive polymer material of the invention which
involves heating the film to a temperature around 295.degree. C.,
and then casting the film onto a chill roll which solidifies the
plastic. This extrusion method is shown in FIG. 15. The resulting
film can be very thin, in the range of 10 microns thick or less.
FIG. 16 shows a schematic representation of the architecture of an
embodiment according to the invention.
[0071] II. Polymer-Sulfur Cathode
[0072] In addition, the invention relates to a composite
polymer-sulfur cathode. The composite polymer-sulfur cathode
includes a sulfur component and a solid, ionically conducting
polymer material including a base polymer, a dopant and a compound
including a source of ions. The composite polymer-sulfur cathode is
characterized as having a high specific capacity and a high
capacity retention when employed in a secondary lithium or Li-ion
sulfur cell. The composite cathode is characterized as having a
specific capacity of greater than 200 milliamp-hr/gm, and
preferably greater than 500 milliamp-hr/gm, and more preferably
greater than 750 milliamp-hr/gm, and most preferably greater than
1000 milliamp-hr/gm. The composite cathode is characterized as
having a retention of least 50% and preferably at least 80% for
over 500 recharge/discharge cycles. The composite polymer-sulfur
cathode of the present invention has direct application to
low-cost, large-scale manufacturing enabled by the unique polymer
used in this composite electrode. The composite polymer-sulfur
cathode of the invention can provide high performance while
simultaneously meeting the requirements for producing low-cost
batteries.
[0073] Notably, sulfur cathodes reduce during discharge to create
sequentially lower order polysulfides through the sequence
illustrated in the following equation:
S.sub.8.fwdarw.Li.sub.2S.sub.8.fwdarw.Li.sub.2S.sub.4.fwdarw.Li.sub.2S.s-
ub.2.fwdarw.Li.sub.2S
[0074] The intermediate polysulfides between Li.sub.2S.sub.8 and
Li.sub.2S.sub.4 are soluble in liquid electrolytes. Thus, dissolved
polysulfide particles are able to migrate (or "shuttle") across
porous separators and react directly with the anode and cathode
during cycling. The polysulfide shuttle produces parasitic
reactions with the lithium anode and re-oxidation at the cathode,
all causing capacity loss. Furthermore, aspects of this shuttle
reaction are irreversible, leading to self-discharge and low cycle
life that has, until now, plagued lithium sulfur batteries.
[0075] The present invention demonstrates a composite
polymer-sulfur cathode including a sulfur component and a solid,
ionically conducting polymer material. This cathode can be extruded
into a flexible, thin film via a roll-to-roll process. Such thin
films enable thin, flexible form factors which can be incorporated
into novel flexible battery designs. As shown in the examples which
follow, this composite polymer-sulfur cathode can include an
electrically conductive additive such as, for example, an
inexpensive carbon black component, such as Timcal C45, which is
already in use for many commercial battery products. In addition to
the exemplary carbon black component, the composite polymer-sulfur
cathode can include other electrically conductive additives such
as, for non-limiting examples, a carbon component including but not
limited to carbon fibers, a graphene component, a graphite
component, metallic particles or other metal additives, and an
electrically conductive polymer.
[0076] The engineering properties of the composite polymer-sulfur
cathode allow the extrusion of the cathode into a wide range of
possible thicknesses, which in turn provides important advantages
in terms of flexibility in design in large-scale cathode
manufacturing. The composite polymer-sulfur cathode can be extruded
as thin as 5 microns and up to thicknesses greater than several 100
microns.
[0077] A comparison of the process steps necessary for producing
standard lithium ion cathodes with those necessary to produce the
inventive composite polymer-sulfur cathode is instructive relative
to the inherent lower cost of the composite polymer-sulfur cathode
manufacturing. FIG. 17 illustrates the process steps needed to
manufacture a standard lithium ion cathode compared with the much
simpler manufacturing of an extruded composite polymer-sulfur
cathode of the invention. The extrusion process for the composite
polymer-sulfur cathode is easily scaled-up to high volume
manufacturing which provides a significant advantage over existing
lithium ion battery, as well as a much lower capital expenditure
for factory equipment.
[0078] In addition to extrusion, the composite polymer-sulfur
cathode can be formed by injection molding, compression molding, or
any other process involving heat, or other techniques known by
those skilled in the art for engineering plastics.
[0079] The composite polymer-sulfur cathode includes a sulfur
component and a solid, ionically conducting polymer material
including a base polymer, a dopant and a compound including a
source of ions, as discussed above.
[0080] The sulfur component can include non-reduced and/or reduced
forms of sulfur including elemental sulfur. In particular, the
composite polymer-sulfur cathode includes a sulfur component
including the fully lithiated form of sulfur (Li.sub.2S), wherein
the Li.sub.2S, is a solid. The composite polymer-sulfur cathode can
also include a carbon component. The advantage to using the fully
lithiated form of sulfur is that it provides a lithium source for a
sulfur battery with a Li Ion anode, which, unlike metal Li, must by
lithiated during initial charge. Combination of a sulfur cathode
with a Li-ion anode provides benefit in preventing the formation of
lithium dendrites which can be formed after cycling lithium anodes.
Dendrites are caused by a non-uniform plating of lithium onto the
lithium metal anode during charging. These dendrites can grow
through separator materials and cause internal short circuits
between cathode and anode, often leading to high temperatures and
compromised safety of the battery. Materials that reversibly
incorporate lithium, either through intercalation or alloying,
lessen the chance for dendrite formation and have been proposed for
use in high safety lithium/sulfur cells. The composite
polymer-sulfur cathode can be used with an anode material such as,
for example, a carbon-based (petroleum coke, amorphous carbon,
graphite, carbon nano tubes, graphene, etc.) material, Sn, SnO,
SnO.sub.2 and Sn-based composite oxides, including composites with
transition metals, such as Co, Cu, Fe, Mn, Ni, etc. Furthermore,
silicon has shown promise as a lithium ion anode material, in the
elemental form, or as an oxide or composite material, as described
for tin. Other lithium alloying materials (for example, Ge, Pb, B,
etc.) could also be used for this purpose. Oxides of iron, such as
Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4 and various vanadium oxide
materials have also been shown to reversibly incorporate lithium as
a Li-ion anode material. Anode materials may be considered in
different forms, including amorphous and crystalline, and
nano-sized particles as well as nano-tubes.
[0081] The composite polymer-sulfur cathode can be combined with a
standard liquid electrolyte, a standard nonwoven separator, and/or
an electrolyte including a solid, ionically conducting polymer
material with no liquid electrolyte. An example of a standard
organic electrolyte solution includes a lithium salt, such as
lithium bis(trifluoromethane sulfonyl)imide (LiTFSI), dissolved in
a mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME).
Additives, such as LiNO.sub.3, can be added to the electrolyte to
improve cell performance. Other lithium salts can be utilized in
organic liquid electrolyte, including: LiPF.sub.6, LiBF.sub.4,
LiAsF.sub.6, lithium triflate, among others. Additionally, other
organic solvents can be used, such as propylene carbonate (PC),
ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl
carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene
carbonate (FEC), as a few examples, either alone or as mixtures
together or with DOL and DME. Examples of standard nonwoven
separators include polypropylene (PP), polyethylene (PE), and
combinations of PP/PE films. Other separator materials include
polyimide, PTFE, ceramic coated films and glass-mat separators. All
of the above materials can be used with the composite
polymer-sulfur cathode. Further, the composite polymer-sulfur
cathode could also be utilized in a gel-polymer system, where for
example, a PVDF-based polymer is swelled with an organic
electrolyte.
[0082] It is believed that the ability of the composite
polymer-sulfur cathode to provide lithium ionic conductivity
improves the performance of the cell by limiting the polysulfide
shuttle mechanism, while simultaneously providing a sulfur cathode
with high voltage. Furthermore, this unique engineering composite
polymer-sulfur cathode allows for the large scale, low cost
manufacturing necessary for commercial viability of the
cathode.
[0083] Thus, the unique composite polymer-sulfur cathode has
numerous potential benefits to batteries, including those
illustrated and described in the following examples.
Example 1
[0084] Solid polymer electrolyte was made by mixing PPS base
polymer and ion source compound LiOH monohydrate in the proportion
of 67% to 33% (by wt.), respectively, and mixed using jet milling.
DDQ dopant was added to the resulting mixture in the amount of 1
mole of DDQ per 4.2 moles of PPS. The mixture was heat treated at
325/250.degree. C. for 30 minutes under moderate pressure (500-1000
PSI). After cooling, the resulting material was grinded and placed
into NMR fixture.
[0085] Self-diffusion coefficients were determined by using pulsed
field gradient solid state NMR technique. The results shown in FIG.
20 indicates, that Li.sup.+ diffusivity in the solid polymer
electrolyte is the highest of any known solid, and over an order of
magnitude higher at room temperature compared to recently developed
Li.sub.10GeP.sub.2S.sub.12 ceramic at much higher temperatures
(140.degree. C.) or the best PEO formulation at 90.degree. C.
Example 2
[0086] PPS base polymer and ion source compound LiOH monohydrate
were added together in the proportion of 67% to 33% (wt/wt),
respectively, and were mixed using jet milling. DDQ dopant was
added to the resulting mixture in the amount of 1 mole of DDQ per
4.2 moles of PPS. The mixture was compression molded at 325.degree.
C./250.degree. C. for 30 minutes under low pressure. The
polymer-sulfur composite cathode was prepared by additionally
mixing from 25% to 50% of sulfur powder, 5% to 15% of C45 carbon
black, and 0% to 10% LiNO.sub.3 with the solid, ionically
conducting polymer material. The materials were compression molded
onto stainless steel mesh (Dexmet) at 120.degree. C. for 30
minutes, yielding a cathode disc 15 mm in diameter and 0.3 to 0.4
mm thick.
[0087] The resulting cathodes were used to assemble test cells in
2035 coin cell hardware. Polypropylene separator (Celgard) 25
microns thick and 19 mm in diameter was used along with lithium
foil anode material, 15 mm in diameter. A liquid electrolyte of 1M
LiTFSI salt dissolved in a 50/50 (vol/vol) mixture of DOL/DME was
used, with 0.5M LiNO.sub.3 additive. The cells were assembled in an
argon gas filled glove box, with low oxygen and water levels.
[0088] Cells were discharged under constant current conditions (1
mA) using a Maccor 4600 battery test system. Discharge was
terminated at a voltage of 1.75 V.
[0089] FIG. 19 shows a first cycle discharge voltage curve for a
Li/composite polymer-sulfur cathode in a cell of the present
invention. The composite polymer-sulfur cathode provides a high
initial capacity of greater than 1300 mAh/g, based on the amount of
sulfur in the cathode. The FIG. 19 discharge voltage curve displays
two plateaus, at .about.2.3V and .about.2.1V. This shows that the
composite polymer-sulfur system enables high capacity, while
producing the expected voltage curve for a lithium/sulfur system,
consistent with a stable electrochemical couple.
Example 3
[0090] Composite polymer-sulfur cathodes were manufactured as
described in Example 16. These cathodes were assembled into coin
cells using lithium metal anodes, polypropylene separator, and 1M
LiTFSI in DOL/DME electrolyte with 0.5M LiNO.sub.3 additive.
[0091] Cells were discharged under constant current conditions (1
mA) using a Maccor 4600 battery test system. Discharge was
terminated at a voltage of 1.75 V. Charge was accomplished in two
steps, the first at a lower charge rate of 0.2 mA current to a
maximum voltage of 2.3 V, and the second charge step at a higher
rate of 1 mA current to a maximum voltage of 2.45 V. The overall
charge capacity was limited for these test cells. These cells were
allowed to cycle several times at room temperature.
[0092] FIG. 20 shows the discharge capacity curve plotted as a
function of cycle number for Li/composite polymer-sulfur cell of
the present invention. The capacity curve graph shows that the
composite polymer-sulfur cathode will support reversible
charge/discharge, with high reversible capacity of at least 1000
mAh/g based on the amount of sulfur in the cathode.
Example 4
[0093] As an alternative preparation of a polymer-sulfur cathode, a
mixture of PPS polymer, LiOH monohydrate filler, sulfur powder, C45
carbon black and polyvinylidene fluoride (PVDF) binder were slurry
coated onto a conductive foil substrate. The PVDF was added to
provide adhesion to the foil, and was pre-dissolved in N-methyl
pyrrolidone (NMP) solvent. The materials were mixed to provide a
slurry, which was cast onto the foil and then dried to remove the
NMP. The slurry-cast polymer-sulfur composite cathode contained
from 25% to 50% by weight of sulfur powder, 5% to 35% of C45 carbon
black, with the solid, ionically conducting polymer material,
filler and PVDF binder constituting the reminder of the cathode
coating. The cathode was compressed and cut to a disk, 15 mm in
diameter, to fit the test cell.
[0094] The slurry-cast cathodes were used to assemble test cells in
2035 coin cell hardware. Polypropylene separator (Celgard) 25
microns thick and 19 mm in diameter was used along with lithium
foil anode material, 15 mm in diameter. A liquid electrolyte of 1M
LiTFSI salt dissolved in a 50/50 (vol/vol) mixture of DOL/DME was
used, with 0.5M LiNO.sub.3 additive. The cells were assembled in an
argon gas filled glovebox, with low oxygen and water levels.
[0095] Cells were discharged under constant current conditions (1.5
mA) using a Maccor 4600 battery test system. Discharge was
terminated at a voltage of 1.75 V. Charge was accomplished in two
steps, the first at a lower charge rate of 0.2 mA current to a
maximum voltage of 2.3 V, and the second charge step at a higher
rate of 1 mA current to a maximum voltage of 2.45 V. The overall
charge capacity was limited for these test cells. These cells were
allowed to cycle several hundreds of times at room temperature.
FIG. 21 shows the discharge capacity for a cell to .about.2000
cycles. This graph shows that the Ionic polymer-sulfur cathode will
support reversible charge/discharge for many cycles with no
evidence of short circuits due to lithium dendrites.
Example 5
[0096] Slurry-cast polymer-sulfur cathodes were manufactured as
described in Example 2, except that the cathodes were cut into
larger 4.9.times.8.1 cm rectangular electrodes. The cathodes were
coated with the electro-active solid, ionically conducting polymer
material-sulfur mixture on both sides of the conductive foil
substrate to form a polymer-sulfur cathode. These cathodes were
assembled into pouch cells using lithium metal anodes
(4.9.times.8.1 cm), polypropylene separator, and 1M LiTFSI in
DOL/DME electrolyte with 0.5M LiNO.sub.3 additive. The cells were
vacuum sealed inside an inert atmosphere glove box which was low in
water and oxygen.
[0097] The pouch cells were discharged under constant current
conditions (9 mA) using a Maccor 4600 battery test system.
Discharge was terminated at a voltage of 1.75 V. The discharge
voltage profile for the first cycle is displayed in FIG. 22. It can
be seen that the polymer-sulfur cathode provides a high initial
capacity of greater than 1300 mAh/g, based on the amount of sulfur
in the cathode. The cell in FIG. 22 also displays a discharge
voltage curve with two plateaus, at .about.2.3V and .about.2.1V,
identical to that found for coin cells, as displayed in Example 2
(FIG. 19). This shows that the slurry-cast Ionic polymer-sulfur
system enables high capacity, and this technology is scalable to
larger pouch cells that have relevance to many commercial
applications.
Comparative Example 6
[0098] A noteworthy example of a highly ordered interwoven
composite electrode is presented in the literature [Ji, X.; Lee, K.
T.; Nazar, L. F. Nature Materials 2009, 8, 500-506]. This composite
cathode utilized CMK-3 mesoporous carbon with sulfur entrenched in
the pores through heat treatment at 155.degree. C. FIG. 23 compares
the first discharge for literature example Li/Sulfur-CMK-3 with
Li/composite polymer-sulfur of present invention.
[0099] The composite cathode in this example was slurry-cast from
cyclopentanone onto a carbon coated aluminum current collector. The
cathode utilized 84 wt % CMK-3/S composite, 8 wt % Super-S carbon
and 8 wt % PVDF binder. The electrolyte was composed of 1.2 M
LiPF.sub.6 in ethyl methyl sulphone, and Li metal was used as the
anode. In comparison, the results for the composite polymer-sulfur
cathode of the invention, as described in Example 2, are plotted on
the same graph. It is apparent that the composite polymer-sulfur
cathode of the invention gives as good, or better, results than
literature examples of composite sulfur cathodes.
Comparative Example 7
[0100] The use of sulfur-conductive polymer composites as cathodes
for lithium batteries has been demonstrated. In one case,
polyacrylonitrile (PAN) is sulfurized to form a conductive and
chemically active cathode material. The sulfurization of the
polymer takes place at a relatively high temperature of
.about.300.degree. C. An example of the discharge curve for this
material is shown in FIG. 24, which was displayed in U.S. Patent
Application 2014/0045059 [He, X.-M., et. al.]. FIG. 37 shows the
typical voltage signature seen for Li/Sulfur-Polyacrylonitrile
(S/PAN) cells. These cells are typified by a single sloping voltage
plateau, with an average voltage below 2.0 V. In comparison to the
voltage curve observed in FIG. 19 for the Li/composite
polymer-sulfur cathode in a cell of the invention, it can be seen
that the S/PAN cells display significantly lower voltage throughout
discharge, which results in a lower energy density, based on
Watt-hours. Thus, the voltage behavior displayed by the composite
polymer polymer-sulfur cathode of the invention is superior to that
of the sulfurized PAN-based cathodes.
Comparative Example 8
[0101] An example of a Lithium/Sulfur coin cell cycle test is
provided in the literature [Urbonaite, S.; Novak, P. J. Power
Sources 2014, 249, 497-502]. The sulfur cathode utilized a standard
carbon black material, comparable to the carbon used in the
cathodes of the present invention. The electrolyte, separator and
lithium anode in the J. Power Sources paper were all identical to
the materials used in the cells of the present invention. The
difference is that the cathode in the J. Power Sources paper did
not contain the solid ionically conducting polymer material of the
present invention. Thus, this literature example provides a good
comparison to the cells using the cathodes incorporating
polymer-electrolyte of the present invention. The cycle life curve
for the comparison Li/sulfur coin cell is displayed in FIG. 25.
Notably, the literature cell provided only about 500 cycles to the
same capacity as the invention cell at over 1000 cycles. Therefore,
the cell of the present invention provided approximately twice the
cycle life of the literature example.
[0102] While the present invention has been described in
conjunction with preferred embodiments, one of ordinary skill,
after reading the foregoing specification, will be able to effect
various changes, substitutions of equivalents, and other
alterations to that set forth herein. It is therefore intended that
the protection granted by Letters Patent hereon be limited only by
the definitions contained in the appended claims and equivalents
thereof.
* * * * *