U.S. patent application number 13/949732 was filed with the patent office on 2014-05-22 for graphene electrode, energy storage device employing the same, and method for fabricating the same.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. The applicant listed for this patent is INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Ping-Chen CHEN, Hsiao-Feng HUANG, Wei-Jen LIU, Chun-Hsiang WEN.
Application Number | 20140141355 13/949732 |
Document ID | / |
Family ID | 50728260 |
Filed Date | 2014-05-22 |
United States Patent
Application |
20140141355 |
Kind Code |
A1 |
HUANG; Hsiao-Feng ; et
al. |
May 22, 2014 |
GRAPHENE ELECTRODE, ENERGY STORAGE DEVICE EMPLOYING THE SAME, AND
METHOD FOR FABRICATING THE SAME
Abstract
The disclosure provides a graphene electrode, an energy storage
device employing the same, and a method for fabricating the same.
The graphene electrode includes a metal foil, a non-doped graphene
layer, and a hetero-atom doped graphene layer. Particularly, the
hetero-atom doped graphene layer is separated from the metal foil
by the non-doped graphene layer.
Inventors: |
HUANG; Hsiao-Feng; (Taoyuan
City, TW) ; CHEN; Ping-Chen; (Taipei City, TW)
; WEN; Chun-Hsiang; (Hsinchu City, TW) ; LIU;
Wei-Jen; (Hsinchu City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE |
Chutung |
|
TW |
|
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
Chutung
TW
|
Family ID: |
50728260 |
Appl. No.: |
13/949732 |
Filed: |
July 24, 2013 |
Current U.S.
Class: |
429/482 ;
361/502; 427/115; 427/122; 427/535; 427/79; 429/231.8; 429/523 |
Current CPC
Class: |
Y02T 10/70 20130101;
Y02E 60/13 20130101; B05D 1/42 20130101; H01M 4/1393 20130101; H01G
11/36 20130101; H01G 11/38 20130101; H01G 11/86 20130101; H01M
4/0402 20130101; H01M 4/0404 20130101; Y02E 60/10 20130101; H01M
4/583 20130101; H01M 4/621 20130101; H01M 4/624 20130101; H01M
10/0525 20130101; H01M 4/0471 20130101; B05D 3/148 20130101; H01M
4/0409 20130101; H01M 4/133 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
429/482 ;
361/502; 427/122; 427/79; 427/115; 427/535; 429/231.8; 429/523 |
International
Class: |
H01G 11/38 20060101
H01G011/38; H01M 4/96 20060101 H01M004/96; H01M 4/133 20060101
H01M004/133; H01G 11/32 20060101 H01G011/32; H01M 4/04 20060101
H01M004/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2012 |
TW |
101143373 |
Claims
1. A graphene electrode, comprising: a metal foil; a non-doped
graphene layer; and a hetero-atom doped graphene layer, wherein the
hetero-atom doped graphene layer is separated from the metal foil
by the non-doped graphene layer.
2. The graphene electrode as claimed in claim 1, wherein the
hetero-atoms doped in the hetero-atom doped graphene layer comprise
nitrogen atoms, phosphorous atoms, boron atoms, or combinations
thereof.
3. The graphene electrode as claimed in claim 1, wherein the doped
amount of hetero-atoms in the hetero-atom doped graphene layer is
from 0.1 to 3 atom %, based on the total atomic amount of the
hetero-atom doped graphene layer.
4. The graphene electrode as claimed in claim 1, wherein the
non-doped graphene layer is a single-layer graphene, or graphene
nanosheets.
5. The graphene electrode as claimed in claim 1, wherein the
hetero-atom doped graphene layer is a single-layer hetero-atom
doped graphene, or hetero-atom doped graphene nanosheets.
6. A method for fabricating a graphene electrode, comprising:
providing the metal foil; forming the graphene layer on the metal
foil; and subjecting the graphene layer to a dry-process surface
modification treatment, thereby doping the hetero-atoms into the
graphene layer surface.
7. The method as claimed in claim 6, wherein the hetero-atoms
comprise nitrogen atoms, phosphorous atoms, boron atoms, or
combinations thereof.
8. The method as claimed in claim 6, wherein the hetero-atoms are
doped into the surface of the graphene layer, forming the
hetero-atom doped graphene layer.
9. The method as claimed in claim 6, wherein the graphene layer has
a portion which is not doped with the hetero-atoms.
10. The method as claimed in claim 9, wherein the portion, which is
not doped with the hetero-atoms, of the graphene layer is defined
as the non-doped graphene layer.
11. The method as claimed in claim 6, wherein the steps for forming
the graphene layer comprise: forming the coating on the metal foil,
wherein the coating is formed from a graphene-containing
composition; and subjecting the coating to a drying process,
obtaining the graphene layer.
12. The method as claimed in claim 11, wherein the
graphene-containing composition comprises: a graphene; and a
binder.
13. The method as claimed in claim 12, wherein the binder comprises
an aqueous-based binder, an organic-based binder, or combinations
thereof.
14. The method as claimed in claim 12, wherein the
graphene-containing composition further comprises a conducting
agent.
15. The method as claimed in claim 14, wherein the conducting agent
comprises graphite, carbon black, or combinations thereof.
16. The method as claimed in claim 6, wherein the dry-process
surface modification treatment comprises a plasma modification
process.
17. The method as claimed in claim 16, wherein a reactive gas is
introduced during the plasma modification process, and the reactive
gas comprises nitrogen gas, ammonia gas, air, or combinations
thereof.
18. The method as claimed in claim 17, wherein the reactive gas
further comprises argon gas, hydrogen gas, oxygen gas, or
combinations thereof.
19. The method as claimed in claim 17, wherein a carrier gas is
introduced during the plasma modification process, and the carrier
gas comprises helium gas, argon gas, nitrogen gas, neon gas, or
combinations thereof.
20. An energy storage device, comprising: a first electrode,
wherein the first electrode is the graphene electrode as claimed in
claim 1; a second electrode; and an isolation membrane disposed
between the first electrode and the second electrode.
21. The energy storage device as claimed in claim 20, wherein the
energy storage device is a lithium ion battery, supercapacitor or a
fuel cell.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is based on, and claims priority
from, Taiwan (International) Application Serial Number 101143373,
filed Nov. 21, 2012, the disclosure of which is hereby incorporated
by reference herein in its entirety.
TECHNICAL FIELD
[0002] The disclosure relates to a graphene electrode and, more
particularly, to a graphene electrode used in an energy storage
device.
BACKGROUND
[0003] Due to rising concerns for environmental issues and higher
gasoline prices, research and development of electric vehicles have
received increased attention.
[0004] Conventional lithium ion batteries, however, cannot meet the
requirements of high capacity, high power, and fast charging. In
order to improve the properties of conventional lithium ion
batteries, novel anode materials for replacing graphite material
are desired.
[0005] Due to the superior electronic conductivity and the porous
structure, electrons and lithium ion have high transport/diffusion
mobility within a graphene layer. Further, due to the irregular
structure of the graphene, the graphene has a higher capacity in
comparison with the graphite. Due to the high irreversible capacity
and low conductivity, the commercialization of lithium ion
batteries employing the graphene electrode, however, cannot be
achieved.
SUMMARY
[0006] One embodiment of the disclosure provides a graphene
electrode and a method for fabricating the same. Since the
hetero-atom is doped into the surface of a graphene at a low
temperature by a dry-process surface modification treatment, the
obtained graphene electrode can have high capacity and low
irreversible capacity. On the other hand, the graphene electrode of
the disclosure is suitable for being used in energy storage
devices.
[0007] The graphene electrode of the disclosure includes: a metal
foil, a non-doped graphene layer, and a hetero-atom doped graphene
layer, wherein the hetero-atom doped graphene layer is separated
from the metal foil by the non-doped graphene layer.
[0008] The disclosure also provides a method for fabricating the
aforementioned graphene electrode. The method includes: providing
the metal foil; forming the graphene layer on the metal foil; and
subjecting the graphene layer to a dry-process surface modification
treatment, thereby doping the hetero-atoms into the graphene layer
surface.
[0009] According to an embodiment of the disclosure, the disclosure
further provides an energy storage device, wherein the energy
storage device includes the aforementioned graphene electrode
serving as a first electrode, a second electrode, and an isolation
membrane disposed between the first electrode and the second
electrode.
[0010] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The disclosure can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0012] FIG. 1 is a cross-section of a graphene electrode according
to an exemplary embodiment.
[0013] FIG. 2 is a flow chart illustrating the method for
fabricating the aforementioned graphene electrode according to an
exemplary embodiment.
[0014] FIG. 3 is a cross-section of an energy storage device
according to an exemplary embodiment.
[0015] FIG. 4 shows a graph plotting the nitrogen-atom doping
amount of the graphene electrodes (II)-(IV).
[0016] FIG. 5 shows a graph plotting the charge-discharge curves of
the batteries (I) and (II).
[0017] FIG. 6 shows a graph plotting discharge capacity against
C-rates of the batteries (I) and (II).
[0018] FIG. 7 shows a graph plotting charge-discharge cycles
against discharge capacity of the batteries (I), (III), and
(IV).
DETAILED DESCRIPTION
[0019] In the following detailed description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of the disclosed embodiments. It
will be apparent, however, that one or more embodiments may be
practiced without these specific details. In other instances,
well-known structures and devices are schematically shown in order
to simplify the drawing.
[0020] As shown in FIG. 1, the graphene electrode of the disclosure
100 can include a metal foil 10, wherein a graphene layer 20 is
disposed on the metal foil 10. Particularly, the graphene layer 20
includes a non-doped graphene layer 24, and a hetero-atom doped
graphene layer 22. It should be noted that, the hetero-atom doped
graphene layer 22 and the metal foil 10 are separated by the
non-doped graphene layer 24. Suitable materials of the metal foil
10 can be a conductive metal, such as a copper foil. The thickness
of the metal foil 10 is unlimited and can be between 0.1 and 200
.mu.. The hetero-atom doped graphene layer 22 includes the surface
21 of the portion of the graphene layer 20 which is doped with the
hetero-atoms 23. Further, the portion, which is not doped with the
hetero-atom 23 of the graphene layer 20, is defined as the
non-doped graphene layer 24. The hetero-atoms 23 can be nitrogen
atoms, phosphorous atoms, boron atoms, or combinations thereof. The
hetero-atom doped graphene layer 22 can have a hetero-atom doping
dosage of 0.1-3 atom %, based on the total atomic amount of the
hetero-atom doped graphene layer 22. The non-doped graphene layer
24 can be a single-layer graphene, or graphene nanosheets or
combinations thereof. The hetero-atom doped graphene layer 22 can
be a single-layer hetero-atom doped graphene, or hetero-atom doped
graphene nanosheets, or combinations thereof.
[0021] The disclosure also provides a method for fabricating the
aforementioned graphene electrode. FIG. 2 is a flow chart
illustrating the method for fabricating the aforementioned graphene
electrode according to an embodiment of the disclosure. First, a
metal foil is provided (step 101), wherein the metal foil can be a
copper foil. Next, a graphene layer is formed on the metal foil
(step 102). Finally, the graphene layer is subjected to a
dry-process surface modification treatment for doping the
hetero-atoms into the surface of the graphene layer (step 103). In
the dry-process surface modification treatment, the hetero-atoms
are doped into a part of the graphene layer (i.e. the surface of
the graphene layer), to form a hetero-atom doped graphene layer and
a non-doped graphene layer (the portion of the graphene layer which
is not doped with the hetero-atom).
[0022] The dry-process surface modification treatment, for example,
can be a plasma modification process. It should be noted that,
since the hetero-atoms have to be confined within the surface of
the graphene layer rather than the whole graphene layer, the
graphene layer or metal foil must not be heated during the
dry-process surface modification treatment. Further, a reactive gas
is introduced into the reactor of the plasma modification process
to dope the hetero-atoms into the graphene layer.
[0023] For example, the reactive gas includes a gas containing the
hetero-atoms (such as nitrogen gas, ammonia gas, air, or
combinations thereof), or a mixture of the gas containing the
hetero-atoms (such as nitrogen gas, ammonia gas, air, or
combinations thereof) and other gas (such as hydrogen gas, argon
gas, oxygen gas, or combinations thereof). According to another
embodiment of the disclosure, a carrier gas can be introduced into
the reactor of the plasma modification process, in order to
stabilize the plasma modification process. The carrier gas can
include helium gas, argon gas, nitrogen gas, neon gas, or
combinations thereof. The reactor of the plasma modification
process can be a low pressure plasma reactor or an atmospheric
pressure plasma reactor. In the plasma modification process, the
parameters (such as the reactive gas flow, the carrier gas flow,
the reaction pressure, the power, the reaction time, and the
distances between the graphene layer and electrodes of the reactor)
can be optionally adjusted, assuming that the doped amount of
hetero-atoms in the hetero-atom doped graphene layer is from 0.1 to
3 atom %, based on the total atomic amount of the hetero-atom doped
graphene layer.
[0024] According to an embodiment of the disclosure, the method for
forming the graphene layer includes the following steps. First, a
coating prepared from a graphene-containing composition is formed
on the metal foil, wherein the method for forming the coating on
the metal foil can be a screen printing, spin coating, bar coating,
blade coating, roller coating, or dip coating method.
[0025] Next, the coating is subjected to a drying process,
obtaining the graphene layer. The drying process can be performed
at 40-150.degree. C. for a period of time from 1 min to 10 hrs.
Herein, the graphene-containing composition can include a graphene,
and a binder. According to other embodiments of the disclosure, the
graphene-containing composition can further include a conducting
agent. The binder can be an aqueous-based binder, an organic-based
binder, such as carboxymethyl cellulose (CMC), styrene butadiene
rubber (SBR), or polyvinylidene difluoride (PVdF), or combinations
thereof. The conducting agent can be, for example, graphite, carbon
black, or combinations thereof.
[0026] As shown in FIG. 3, the disclosure also provides an energy
storage device (such as a lithium ion battery, supercapacitor or
fuel cell) 200, including the aforementioned graphene electrode
100. The energy storage device 200 can include a graphene electrode
serving as a first electrode 202 (such as anode), a second
electrode 206 (such as cathode), and an isolation membrane 204
disposed between the first electrode 202 and the second electrode
206. It should be noted that the hetero-atom doped graphene layer
of the graphene electrode directly contacts to the isolation
membrane. Suitable materials of the second electrode 206 can be
lithium or lithium-containing oxide such as Li, LiCoO.sub.2,
LiFePO.sub.4, LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2,
LiMn.sub.2O.sub.4 or combinations thereof. Suitable materials of
the isolation membrane can be polymer, such as polyethylene,
polypropylene, or combinations thereof. Further, the isolation
membrane can have a plurality of pores. The energy storage device
can further include an electrolysis (not shown) within the
isolation membrane 204, such as ethylene carbonate (EC), propylene
carbonate (PC), gamma-butyrolactone (GBL), diethyl carbonate (DEC),
dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl
propyl carbonate (MPC), vinylene carbonate (VC), lithium salt, or
combinations thereof.
[0027] Below, exemplary embodiments will be described in detail
with reference to accompanying drawings so as to be easily realized
by a person having ordinary knowledge in the art. The inventive
concept may be embodied in various forms without being limited to
the exemplary embodiments set forth herein. Descriptions of
well-known parts are omitted for clarity, and like reference
numerals refer to like elements throughout.
EXAMPLES
[0028] Preparation of the Graphene Electrode
Example 1
[0029] First, 5.3571 g of DI water, and 0.0337 g of carboxymethyl
cellulose (CMC, serving as a binder) were added into a reaction
bottle, and stirred by a homogenizer (with a spinning rate of 2000
rpm) for 20 min. Next, 0.0056 g of acetylene black (sold and
manufactured by Timcal with a trade number of Super P, serving as a
conducting agent), and 0.5 g of graphene were added into the
reaction bottle. After stirring for 20 min, 0.0562 g of styrene
butadiene rubber (SBR, serving as binder) was added into the
reaction bottle. After stirring for 20 min, a graphene-containing
slurry was obtained.
[0030] Next, the above graphene-containing slurry was coated on a
copper foil by blade coating (using the doctor blade (150 .mu.m) to
form a coating. After drying at 120.degree. C., a graphene
electrode (I) having the graphene layer was obtained. It should be
noted that the graphene layer of the graphene electrode (I) was not
doped with any hetero-atom.
Example 2
[0031] The graphene electrode (I) was disposed into a plasma
reactor, wherein the copper foil of the graphene electrode (I)
directly contacted with a support substrate of the plasma reactor,
and the distance between the graphene layer and the electrode of
the plasma reactor was 2.2 mm. Next, a nitrogen gas (with a flow of
5 sccm) and a helium gas (with a flow of 5.88 L/min) were
introduced into the plasma reactor. Next, the surface of the
graphene layer was subjected to a plasma modification process under
a pressure of 1 atm, and a RF power of 65W, in order to dope
nitrogen atoms into the surface of the graphene layer. It should be
noted that no heating process was performed during the plasma
modification process. After reacting for 6 sec, a graphene
electrode (II) was obtained.
[0032] Next, the surface of the graphene electrode (II) was
analyzed by an X-ray Photoelectron Spectrometer (XPS) to measure
the doping amount of nitrogen atoms of the hetero-atom doped
graphene layer of the graphene electrode (II). The results are as
shown in FIG. 4.
Example 3
[0033] Example 3 was performed as Example 2 except that the flow
rate of the nitrogen gas was increased to 30 sccm instead of 5
sccm. The graphene electrode (III) was obtained.
[0034] Next, the surface of the graphene electrode (III) was
analyzed by an X-ray Photoelectron Spectrometer (XPS) to measure
the doping amount of nitrogen atoms of the hetero-atom doped
graphene layer of the graphene electrode (III). The results are
shown in FIG. 4.
Example 4
[0035] Example 4 was performed as Example 1 except that the
reaction time was changed to 18 sec instead of 6 sec. The graphene
electrode (IV) was obtained.
[0036] Next, the surface of the graphene electrode (IV) was
analyzed by an X-ray Photoelectron Spectrometer (XPS) to measure
the doping amount of nitrogen atoms of the hetero-atom doped
graphene layer of the graphene electrode (IV). The results are
shown in FIG. 4.
[0037] According to FIG. 4, the nitrogen atoms were observed as the
impurities in the surface of the graphene electrodes (II)-(IV) of
the disclosure. Therefore, the nitrogen atoms were indeed doped
into the surface of the graphene layer via the plasma modification
process.
Example 5
[0038] Example 5 was performed as Example 2 except that the flow
rate of nitrogen gas was changed to 15 sccm and the reaction time
was 18 sec instead of the flow rate of 5 sccm and the reaction time
of 6 sec. The graphene electrode (V) was obtained.
Example 6
[0039] Example 6 was performed as Example 2 except that the flow
rate of nitrogen gas was adjusted at 30 sccm and the reaction time
was 18 sec. The graphene electrode (VI) was obtained. Table 1
showed the parameters of the plasma modification process employed
in Example 2-6.
TABLE-US-00001 TABLE 1 flow rate of flow rate of RF reaction
nitrogen gas helium gas power time (sccm) (L/cm) (W) (sec) Example
2 5 5.88 65 6 Example 3 30 5.88 65 6 Example 4 5 5.88 65 18 Example
5 15 5.88 65 18 Example 6 30 5.88 65 18
[0040] Fabrications of the Battery Having the Graphene
Electrode
Example 7
[0041] The graphene electrode (I) of Example 1 was cut to form an
anode (with a diameter of 13 mm) Next, the anode, an isolation
membrane (a polyethylene/polypropylene composite film with a
thickness of 20 .mu.m), and a lithium layer (serving as a cathode)
were assembled. Next, an electrolyte (including ethylene carbonate
(EC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and 1M
of LiPF.sub.6) was injected into the isolation membrane, and a
button-type lithium ion battery (I) was obtained.
Example 8
[0042] The graphene electrode (IV) of Example 1 was cut to form an
anode (with a diameter of 13 mm). Next, the anode, an isolation
membrane (a polyethylene/polypropylene composite film with a
thickness of 20 .mu.m), and a lithium layer (serving as a cathode)
were assembled. Next, an electrolyte (including ethylene carbonate
(EC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and 1M
of LiPF.sub.6) was injected into the isolation membrane, and a
button-type lithium ion battery (II) was obtained.
Example 9
[0043] The graphene electrode (V) of Example 1 was cut to form an
anode (with a diameter of 13 mm). Next, the anode, an isolation
membrane (a polyethylene/polypropylene composite film with a
thickness of 20 .mu.m), and a lithium layer (serving as a cathode)
were assembled. Next, an electrolyte (including ethylene carbonate
(EC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and 1M
of LiPF.sub.6) was injected into the isolation membrane, and a
button-type lithium ion battery (III) was obtained.
Example 10
[0044] The graphene electrode (VI) of Example 1 was cut to form an
anode (with a diameter of 13 mm). Next, the anode, an isolation
membrane (a polyethylene/polypropylene composite film with a
thickness of 20 .mu.m), and a lithium layer (serving as a cathode)
were assembled. Next, an electrolyte (including ethylene carbonate
(EC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and 1M
of LiPF.sub.6) was injected into the isolation membrane, and a
button-type lithium ion battery (IV) was obtained.
[0045] Electrical Test
[0046] The batteries (I) and (II) of Examples 7-8 were subjected to
a charge-discharge test respectively, and the results are shown in
FIG. 5.
[0047] Next, the discharge capacities of the batteries (I) and (II)
were evaluated under various C-rates at room temperature, and the
results are shown in FIG. 6. In FIG. 6, the battery (II) (having
the nitrogen-atom doped grapheme layer) had higher discharge
capacities in comparison with those of the battery (I) under
various C-rates.
[0048] Next, the batteries (I), (III), and (IV) were subjected to a
cycle life test, and the results are shown in FIG. 7. In FIG. 7,
the batteries (III) and (IV) (having the nitrogen-atom doped
grapheme layer) had a higher capacities in comparison with those of
the battery (I) under various cycles. Particularly, the batteries
had more than double the capacities as compared to that of the
battery (I). Further, as shown in FIG. 7, the performances of the
batteries (III) and (IV) were maintained over multiple cycles.
[0049] The batteries (I), (II), and (III) were subjected to a
charging and discharging cycle tests and measured for evaluating
the irreversible capacity loss and Coulombic efficiencies thereof.
The results are shown in Table 2.
TABLE-US-00002 TABLE 2 first first irreversible second second
irreversible cycle cycle Coulombic capacity cycle cycle Coulombic
capacity (charge) (discharge) efficiency loss (charge) (discharge)
efficiency loss mAh/g mAh/g (%) (%) mAh/g mAh/g (%) (%) Battery
1079.78 666.29 61.71 38.29 951.69 886.29 93.13 6.87 (I) Battery
1178.37 964.89 81.88 18.12 835.67 820.22 98.15 1.85 II) Battery
1103.93 838.48 75.95 24.05 849.72 827.25 97.36 2.64 (III)
[0050] As shown in Table 2, the batteries (II) and (III) having the
graphene electrode of the disclosure had an increased Coulombic
efficiency and a reduced irreversible capacities in comparison with
the battery (I) in both the first cycle and second cycle. This
means that the graphene electrode subjected to the plasma
modification process had stable electrical characteristics.
[0051] Accordingly, since the surface of the graphene layer was
subjected to a dry-process surface modification treatment, the
graphene electrode of the disclosure exhibited improved electrical
characteristics (such as high capacity, high carrier mobility, and
low irreversible capacity). Therefore, the graphene electrode of
the disclosure is suitable for being used in an energy storage
device.
[0052] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed methods
and materials. It is intended that the specification and examples
be considered as exemplary only, with a true scope of the
disclosure being indicated by the following claims and their
equivalents.
* * * * *