U.S. patent application number 14/270561 was filed with the patent office on 2014-10-02 for graphene-based battery electrodes having continuous flow paths.
This patent application is currently assigned to BATTELLE MEMORIAL INSTITUTE. The applicant listed for this patent is BATTELLE MEMORIAL INSTITUTE. Invention is credited to Xiaolin Li, Jun Liu, Deyu Wang, Jie Xiao, Wu Xu, Jiguang Zhang.
Application Number | 20140295298 14/270561 |
Document ID | / |
Family ID | 46455514 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140295298 |
Kind Code |
A1 |
Zhang; Jiguang ; et
al. |
October 2, 2014 |
Graphene-based Battery Electrodes Having Continuous Flow Paths
Abstract
Some batteries can exhibit greatly improved performance by
utilizing electrodes having randomly arranged graphene nanosheets
forming a network of channels defining continuous flow paths
through the electrode. The network of channels can provide a
diffusion pathway for the liquid electrolyte and/or for reactant
gases. Metal-air batteries can benefit from such electrodes. In
particular Li-air batteries show extremely high capacities, wherein
the network of channels allow oxygen to diffuse through the
electrode and mesopores in the electrode can store discharge
products.
Inventors: |
Zhang; Jiguang; (Richland,
WA) ; Xiao; Jie; (Richland, WA) ; Liu;
Jun; (Richland, WA) ; Xu; Wu; (Richland,
WA) ; Li; Xiaolin; (Richland, WA) ; Wang;
Deyu; (Nihgho, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BATTELLE MEMORIAL INSTITUTE |
Richland |
WA |
US |
|
|
Assignee: |
BATTELLE MEMORIAL INSTITUTE
Richland
WA
|
Family ID: |
46455514 |
Appl. No.: |
14/270561 |
Filed: |
May 6, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13004138 |
Jan 11, 2011 |
8758947 |
|
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14270561 |
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Current U.S.
Class: |
429/406 ;
429/188; 429/199; 429/200; 429/231.4; 429/231.5; 429/231.7;
429/231.8; 429/338; 429/341; 429/342; 429/405 |
Current CPC
Class: |
H01M 4/5835 20130101;
H01M 4/96 20130101; H01M 4/587 20130101; Y02E 60/128 20130101; H01M
12/00 20130101; H01M 4/133 20130101; H01M 10/052 20130101; Y02E
60/10 20130101; H01M 4/382 20130101; H01M 6/16 20130101; H01M 4/583
20130101; H01M 12/08 20130101; H01M 2004/021 20130101 |
Class at
Publication: |
429/406 ;
429/405; 429/231.8; 429/231.7; 429/231.4; 429/231.5; 429/200;
429/188; 429/199; 429/338; 429/341; 429/342 |
International
Class: |
H01M 4/583 20060101
H01M004/583; H01M 10/052 20060101 H01M010/052; H01M 12/00 20060101
H01M012/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with Government support under
Contract DE-AC0576RL01830 awarded by the U.S. Department of Energy.
The Government has certain rights in the invention.
Claims
1. A metal-air battery having an air electrode comprising graphene,
the air electrode characterized by randomly arranged graphene
nanosheets forming a network of channels defining continuous flow
paths through the air electrode and by oxygen diffusing through the
channels.
2. The metal-air battery of claim 1, further comprising a carbon
material mixed with the graphene nanosheets, the carbon material
having a mesopore volume greater than 1 cc/g.
3. The metal -air battery of claim 1, wherein at least a portion of
the air electrode comprises fluorinated graphene nanosheets
(CF.sub.x, where 0.5 <x<1.5).
4. The metal-air battery of claim 1, wherein the air electrode
further comprises a catalyst deposited on surfaces of the
electrode, the catalyst comprising a transition metal or transition
metal oxide.
5. The metal-air battery of claim 1, wherein the channels have
average diameters between 0.1 and 10 .mu.m.
6. The metal-air battery of claim 1, wherein the metal comprises
Zn, Na, Mg, Fe, Ca, or Al.
7. The metal-air battery of claim 1, wherein the metal comprises
Li.
8. The metal-air battery of claim 1, having a specific capacity
greater than or equal to 5000 mAh/g graphene/carbon.
9. The metal-air battery of claim 1, further comprising an
electrolyte comprising ethers, glymes, or combinations thereof.
10. The metal-air battery of claim 9, wherein the electrolyte
comprises lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in
tri(ethylene glycol) dimethyl ether (triglyme).
11. The metal-air battery of claim 9, wherein the electrolyte
comprises LiTFSI in di(ethylene glycol) dibutyl ether (or butyl
diglyme).
12. The metal-air battery of claim 1, further comprising discharge
product stored in mesopores adjacent to the channels.
13. A battery having a cathode comprising graphene, the cathode
characterized by randomly arranged graphene nanosheets forming a
network of channels defining continuous flow paths through the
cathode and by liquid electrolyte diffusing through the
channels.
14. The battery of claim 13, wherein the graphene nanosheets are on
average less than 1 .mu.m in length, width, or both.
15. The battery of claim 13, wherein the graphene nanosheets are on
average less than 30 nm in length, width, or both.
16. The battery of claim 13, wherein at least a portion of the
cathode comprises fluorinated graphene nanosheets (CF.sub.x, where
0.5<x<1.5).
17. The battery of claim 13, further comprising an anode comprising
lithium.
18. The battery of claim 17, further comprising a lithium
intercalation anode selected from the group consisting of
LiC.sub.6, Li.sub.xSi (x=0.5 to 4.4), Li.sub.xSn (x=0.5 to 4.4),
Li.sub.xSnO.sub.2, and Li.sub.xTiO.sub.y.
19. The battery of claim 17, wherein the battery is a primary
lithium battery.
20. The battery of claim 17, wherein the battery is a rechargeable
lithium battery.
21. The battery of claim 20, wherein the liquid electrolyte
comprises a compound selected from the group consisting of lithium
bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium
bis(oxalate)borate (LiBOB), LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6,
and combinations thereof.
22. The battery of claim 21, wherein the liquid electrolyte
comprises a solvent selected from the group consisting of ethylene
carbonate (EC), propylene carbonate (PC), dimethyl ether (DME)
solvent, diethylene carbonate (DEC), ethyl methyl carbonate (EMC),
triglyme, butyl diglyme, tetraglyme, diglyme, and combinations of
thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to, and is a continuation
of, currently pending U.S. patent application Ser. No. 13/004,138,
filed on Jan. 11, 2011. The earlier application is incorporated
herein by reference.
BACKGROUND
[0003] Among all of the different electrochemical couples upon
which energy storage devices can be based, metal-air systems can
exhibit the largest theoretical specific energies. For example, a
lithium-air system can exhibit a theoretical specific energy of
11,972 Wh/kg. However, electrochemical performance of metal-air
batteries can depend greatly on many factors including the
properties of the carbon-based air electrode. While various
nanostructured carbon materials have been explored in attempts to
improve metal-air energy storage devices, the practical capacity,
specific energy and rate performance of such devices has not been
sufficient for most energy storage applications. Accordingly, an
improved metal-air energy storage device is needed.
SUMMARY
[0004] The present invention includes batteries having electrodes
comprising graphene nanosheets and methods for forming such
electrodes. In one embodiment, the air electrode of a metal-air
battery is characterized by randomly arranged graphene nanosheets
forming a network of channels defining continuous flow paths
through the air electrode and by oxygen diffusing through the
channels. Exemplary metals in the metal-air batteries can include,
but are not limited to Zn, Na, Mg, Fe, Ca, or Al. Preferably, the
metal comprises Li. The graphene nanosheets can on average be less
than 1 .mu.m in length, width, or both. In particular examples, the
graphene nanosheets on average are less than 30 nm in length, width
or both.
[0005] The air electrode can further comprise mesopores adjacent to
the channels, wherein discharge product is stored in the mesopores.
In some embodiments, the mesopore volume can be enhanced by mixing
a highly mesoporous carbon material with the graphene nanosheets.
Preferably, the carbon material itself has a mesopore volume
greater than 1 cc/g. Storage of discharge products in the mesopores
can minimize blockage of the channels to maintain flow paths for
oxygen. Preferably, the channels can have an average diameter
between 0.1 and 10 .mu.m. In some instances, the graphene
nanosheets can be modified to improve performance. For example, in
one embodiment, the graphene nanosheets can be fluorinated and at
least a portion of the electrode can comprise fluorinated graphene
nanosheets (CF.sub.x). In particular examples, x can be between 0.5
and 1.5. In another embodiment, a catalyst comprising a transition
metal or a transition metal oxide can be deposited on surfaces of
the electrode such as on the graphene nanosheets and/or on the
mesopores.
[0006] Embodiments of the metal-air batteries described above and
elsewhere herein can have a specific capacity greater than or equal
to 5000 mAh/g active material (i.e., graphene/carbon).
[0007] In a particular embodiment of the present invention, a
lithium-air battery has a specific capacity greater than or equal
to 5000 mAh/g active material and has an air electrode comprising
graphene. The air electrode comprises randomly arranged graphene
nanosheets forming a network of channels defining continuous flow
paths through the air electrode in which oxygen diffuses. The air
electrode further comprises a carbon material mixed with the
graphene nanosheets, wherein the carbon material has a mesopore
volume greater than 1 cc/g. The air electrode can further comprise
a transition metal or a transition metal oxide deposited as a
catalyst on surfaces of the electrode, such as on the graphene
nanosheets and/or on the mesopores. In preferred embodiments, the
channels have an average diameter between 0.1 and 10 .mu.m.
Furthermore, at least a portion of the electrode can comprise
fluorinated graphene nanosheets (CF.sub.x).
[0008] While some aspects of the present invention are particularly
applicable to metal-air batteries, the present invention is not
necessarily limited to metal-air batteries. For example, some
embodiments encompass metal batteries or metal-ion batteries. Other
embodiments encompass batteries having a cathode comprising
graphene and a liquid electrolyte. Similar to embodiments described
elsewhere herein, the cathode is characterized by randomly arranged
graphene nanosheets forming a network of channels. In the context
of liquid electrolytes, the channels define continuous flow paths
through the cathode for the liquid electrolyte. In one instance,
the battery can have an anode comprising lithium. The anode can
comprise lithium metal or lithium-based compounds. Exemplary
lithium-based anodes can include, but are not limited to LiC.sub.6,
Li.sub.xSi (x=0.5 to 4.4), Li.sub.xSn (x=0.5 to 4.4),
Li.sub.xSnO.sub.2, and Li.sub.xTiO.sub.y, and
Li.sub.5Ti.sub.4O.sub.12. In another example, the battery is an
aqueous Li-air battery. In some embodiments, the graphene
nanosheets can be less than 1 .mu.m in length, width, or both. More
particularly, the graphene nanosheets are less than 30 nm in
length, width or both. In other embodiments, the graphene
nanosheets are fluorinated and at least a portion of the electrode
comprises fluorinated graphene (CF.sub.x). In some instances, x can
be between 0.5 and 1.5 and/or the batteries can be configured
either as primary lithium batteries or as rechargeable lithium
batteries.
[0009] In any of the embodiments utilizing liquid electrolytes, the
electrolyte preferably comprises glymes, ethers, or both. Exemplary
ethers and glymes include, but are not limited to, Triglyme, butyl
glyme, tetra(ethylene glycol) dimethyl ether (i.e Tetraglyme),
di(ethylene glycol) dimethyl ether (i.e. Diglyme), and di(propylene
glycol) dimethyl ether (i.e. diproglyme). Particular examples of
electrolytes include Lithium bis(trifluoromethylsulfonyl)imide
(LiTFSI) in tri(ethylene glycol) dimethyl ether (Triglyme) and
LiTFSI in di(ethylene glycol) dibutyl ether (or Butyl diglyme).
Most preferably, the electrolytes comprise solvents that form
Li.sub.2O.sub.2 discharge products.
[0010] In a particular embodiment of the present invention, a
lithium-based battery having a specific capacity greater than or
equal to 8000 mAh/g graphene/carbon, comprises an electrode in
which graphene nanosheets are randomly arranged to form a network
of channels that define a continuous flow path for fluids through
the electrode. A carbon material is mixed with the graphene
nanosheets, wherein the carbon material has a mespore volume
greater than 1 cc/g. An electrolyte in the battery comprises
glymes, ethers, or both. While reaction products can often contain
mixtures of compounds, in some preferred embodiments, a discharge
product comprises Li.sub.2O.sub.2.
[0011] A method for forming the electrodes described herein can
comprise the steps of dispersing graphene in water or other
solvents and adding a binder to the dispersed graphene to form a
mixture. The weight ratio of the graphene to the binder can range
from 25:75 to 95:5. The mixture is then dried to remove the water
or the other solvents and is formed under pressure into a desired
shape. The final graphene loading is between 1 and 20 mg/cm.sup.2.
A conductive support is embedded into the electrode before, during,
or after formation into the desired shape. In preferred
embodiments, the final graphene loading is approximately 2
mg/cm.sup.2.
[0012] Exemplary binders can include, but are not limited to,
polytetrafluoroethylene (PTFE) in an emulsion or polyvinylidene
fluoride (PVDF) dissolved in a solvent. Preferably, the ratio of
the graphene to the binder is approximately 75:25.
[0013] Forming under pressure can comprise feeding the mixture into
a roller, wherein the roller pressure ranges from 10 to 120
psi.
[0014] In some embodiments, a carbon material having a mesopore
volume larger than 1 cc/g is added to the mixture. The ratio of
graphene to carbon material can range from 100:0 to 5:95.
Preferably, the ratio of graphene to carbon material is
approximately 50:50. In other embodiments, a catalyst comprising
transition metals or transition metal oxides can be deposited on
surfaces or pores of carbon materials in the electrode.
[0015] The purpose of the foregoing abstract is to enable the
United States Patent and Trademark Office and the public generally,
especially the scientists, engineers, and practitioners in the art
who are not familiar with patent or legal terms or phraseology, to
determine quickly from a cursory inspection the nature and essence
of the technical disclosure of the application. The abstract is
neither intended to define the invention of the application, which
is measured by the claims, nor is it intended to be limiting as to
the scope of the invention in any way.
[0016] Various advantages and novel features of the present
invention are described herein and will become further readily
apparent to those skilled in this art from the following detailed
description. In the preceding and following descriptions, the
various embodiments, including the preferred embodiments, have been
shown and described. Included herein is a description of the best
mode contemplated for carrying out the invention. As will be
realized, the invention is capable of modification in various
respects without departing from the invention. Accordingly, the
drawings and description of the preferred embodiments set forth
hereafter are to be regarded as illustrative in nature, and not as
restrictive.
DESCRIPTION OF DRAWINGS
[0017] Embodiments of the invention are described below with
reference to the following accompanying drawings.
[0018] FIG. 1 contains scanning electron microscope (SEM)
micrographs of a graphene-based electrode encompassed by
embodiments of the present invention.
[0019] FIGS. 2a and 2b compare pore size distributions of
as-received graphene and a graphene-based electrode encompassed by
embodiments of the present invention.
[0020] FIG. 3 presents a discharge curve of a Li-air cell utilizing
a graphene-based air electrode encompassed by embodiments of the
present invention.
[0021] FIGS. 4a and 4b present and compare cycling data for one
embodiment of a graphene-based Li-air battery and a
Ketjenblack-based Li-air battery.
[0022] FIGS. 5a and 5b include a photograph of a Li-air pouch cell
used for testing as well as the voltage profile of the pouch cell,
respectively.
[0023] FIG. 6 includes a graph showing specific capacity of a
Li-air cell using an electrolyte comprising LiTFSI in Triglyme.
DETAILED DESCRIPTION
[0024] The following description includes the preferred best mode
of one embodiment of the present invention. It will be clear from
this description of the invention that the invention is not limited
to these illustrated embodiments but that the invention also
includes a variety of modifications and embodiments thereto.
Therefore the present description should be seen as illustrative
and not limiting. While the invention is susceptible of various
modifications and alternative constructions, it should be
understood, that there is no intention to limit the invention to
the specific form disclosed, but, on the contrary, the invention is
to cover all modifications, alternative constructions, and
equivalents falling within the spirit and scope of the invention as
defined in the claims.
[0025] FIGS. 1-6 show a variety of aspects and embodiments of the
present invention. Referring first to FIG. 1, scanning electron
microscope (SEM) micrographs of an electrode comprising randomly
arranged graphene nanosheets are shown at two different
magnifications 100 and 101. The random distribution of graphene
nanosheets, according to embodiments of the present invention,
leads to the formation of a significant network of channels 102.
The channels define continuous flow paths through the
electrode.
[0026] In one example, wherein the battery is a metal-air battery,
the network of channels formed by the random distribution of
graphene nanosheets can continuously supply oxygen to the interior
of air electrode during the discharge process. Unlike the
engineered holes or pores in other carbon-based air electrodes,
which can expand back after being wetted by an electrolyte, the
channels formed by the graphene nanosheets in embodiments of the
present invention maintain their structure.
[0027] Graphene, as used herein, can refer to a material comprising
stacks of single-atom-thick sheets of conjugated sp.sup.2 carbon
atoms typically having a wide open double-sided surface. However,
traditional graphene does not have intrinsic pores and has a
relatively low surface area. It has, therefore, not been considered
to be a good candidate for use in various applications including
air electrodes. The random arrangement of graphene nanosheets
utilized by embodiments of the present invention forms a network of
channels providing continuous flow paths for oxygen and/or liquid
electrolyte. Furthermore, discharge products can be stored in the
channels and/or in the mesopores adjacent to the channels.
[0028] Referring to FIGS. 2a and 2b, pore size distributions are
provided for the graphene-based electrodes formed according to
embodiments of the present invention and for as-received graphene,
respectively. There are no peaks in either figure, which can
indicate that neither the as-received graphene nor the graphene air
electrode have substantial porous structures. The average "pore"
sizes (shown in Table 1) calculated from FIGS. 2a and 2b are 27.1
nm and 18.1 nm for the as-received graphene and the graphene-based
air electrode, respectively.
TABLE-US-00001 TABLE 1 Comparison of the physical properties for
as-received graphene and graphene electrode BET Surface Area Pore
Volume Average Pore (m.sup.2/g) (cc/g) Size (nm) As-received 590.3
4.0 27.1 graphene Graphene-based 186.2 0.84 18.1 air Electrode
The pore volume and surface area decrease significantly after being
made into an electrode according to methods of the present
invention. In part, this is probably due to the addition of a
binder.
[0029] Comparing the physical properties summarized in Table 1 and
in FIG. 2 with the micrographs in FIG. 1, it is most likely that
the pore size, pore volume, and surface area data represents the
average size of the open channels which are residing in the
mesopore range suitable for the formation of tri-phase regions.
Since there appear to be fewer and smaller pores in the
graphene-based air electrode (relative to as-received graphene),
the improvement in performance is most likely explained by the
formation of the network of channels through the random arrangement
of graphene nanosheets, which define flow paths through the
electrode. The natural folding areas and the inter-layer spaces
between the graphene nanosheets as shown in FIG. 1 result in
externally formed channels that can be utilized as flow paths
and/or as storage places for discharge products.
[0030] FIG. 3 is a graph of the discharge curve for a Li-air
battery using a graphene-based air electrode according to
embodiments of the present invention. The cell was tested in pure
oxygen (.about.2 atm) at a current density of 0.1 mA/cm.sup.2. A
very high capacity of greater than 8000 mAh/g is achieved when
discharged to 2.6 V. A relatively flat plateau is observed at
around 2.8 V similar with other air electrodes using different
carbons.
[0031] The recharge-ability of the Li-air battery using a
graphene-based air electrode is plotted in FIG. 4a. The data shown
in FIG. 4a indicates that the graphene-based air electrode is
rechargeable. Other carbon-based air electrodes with highly porous
structures usually have a high surface area (2672 m.sup.2/g for
Ketjenblack as an example) which can lead to significant
decomposition of the organic electrolyte during the charge process.
For comparison with FIG. 4a, the rechargeability of a common Li-air
battery using Ketjenblack-based air electrode is plotted in FIG.
4b. After 5 cycles the voltage of the Ketjenblack-based Li-air cell
shows unstable fluctuation related to electrolyte decomposition. In
contrast, the embodiments of the graphene-based air electrodes
described herein exhibit a relatively low surface area of 590.3
m.sup.2/g (Table 1). The limited surface area appears to result in
reduced electrolyte decomposition on the surface of graphene
nanosheets at voltages higher than 4.2 V. In some embodiments, a
transition metal or transition metal catalyst deposited on the
graphene nanosheets can further improve the cycling stability and
to reduce the over potential during charge processes.
[0032] The tests described above were performed in a pure oxygen
atmosphere. In order to evaluate the performance of the embodiments
of the graphene-based air electrode in an ambient environment, a
pouch-type cell was prepared as illustrated in FIG. 5a. The size of
the air electrode was 2.times.2 cm.sup.2 with a carbon loading of 4
mg/cm.sup.2. FIG. 5b shows the discharge curve of the pouch-type
Li-air battery using graphene-based air electrodes when operated in
ambient conditions. A stable plateau is observed between 2.7-2.8 V
and the discharge capacity was 5093 mAh/g carbon at 0.1 mA/cm.sup.2
in the ambient environment.
[0033] Referring to FIG. 6, embodiments of the present invention
utilizing electrolytes comprising glymes, ethers, or both can
result in specific capacities exceeding approximately 15,000 mAh/g.
The data provided in FIG. 6 was acquired on a Li-air cell having an
electrode with randomly arranged graphene nanosheets, as described
elsewhere herein, in conjunction with an electrolyte comprising
lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in tri(ethylene
glycol) dimethyl ether (Triglyme). Alternative electrolytes can
include those that comprise Triglyme, butyl glyme, tetra(ethylene
glycol) dimethyl ether (i.e Tetraglyme), di(ethylene glycol)
dimethyl ether (i.e. Diglyme), and di(propylene glycol) dimethyl
ether (i.e. diproglyme). Another particular example of an
electrolyte includes LiTFSI in di(ethylene glycol) dibutyl ether
(or Butyl diglyme). Generally speaking, it is preferable to utilize
an electrolyte that is stable and yields Li.sub.2O.sub.2 during the
discharge process of Li-air batteries X-Ray Diffraction (XRD)
patterns (data not shown) indicate that both LiTFSI in Triglyme and
LiTFSI in butyl diglyme can result in discharge products comprising
Li.sub.2O.sub.2. Further still, the liquid electrolyte can comprise
compounds such as Lithium bis(trifluoromethylsulfonyl)imide
(LiTFSI), lithium bis(oxalate)borate (LiBOB), LiPF.sub.6,
LiBF.sub.4, LiAsF.sub.6. Exemplary solvents in addition to those
listed elsewhere herein, can include, but are not limited to,
ethylene carbonate (EC), propylene carbonate (PC), dimethyl ether
(DME) solvent, diethylene carbonate (DEC), ethyl methyl carbonate
(EMC), and combinations thereof.
[0034] One of several available methods for making the
graphene-based electrodes described elsewhere herein includes
mixing dispersed graphene nanosheets with a binder and then forming
them into electrodes. For example, as-received graphene can be
dispersed in de-ionized water or other organic solvent and stirred.
A PTFE emulsion (60% solids) can be added drop by drop into the
graphene dispersion while stirring. The weight ratio of graphene to
PTFE can be between 25:75 and 95:5. Preferably, the ratio is
approximately 75:25.
[0035] The graphene and PTFE mixture can be stirred for an
additional two hours and then dried in air at 80.degree. C.
overnight. The resultant powder mixture can be fed into a roller
having a roller pressure between 10 and 120 psi. Preferably, the
pressure is approximately 80 psi. The final loading in the rolled
powder can be between 1 and 10 mg graphene/cm.sup.2. Preferably,
the loading is approximately 2 mg graphene/cm.sup.2.
[0036] A conductive support, which can include, but is not limited
to a nickel mesh or aluminum mesh can be embedded into the rolled
graphene. The electrode can then be punched directly from rolled
graphene into a desired shape and size.
[0037] In some embodiments, the graphene can be mixed with other
mesoporous carbons such as Ketjenblack to improve the mesopore
volume of the whole electrode. Preferably, the mesoporous carbons
have a mesopore volume larger than 1 cc/cm.sup.3. The mixture of
the randomly arranged graphene with the mesoporous carbon can
provide both the network of channels as well as increased porosity
for improved storage of reaction products. Exemplary reaction
products in Li-air batteries can include Li.sub.2O.sub.2 and
Li.sub.2O. The ratio of graphene to other mesoporous carbons can
vary from 100:0 to 5:95, preferably 50:50.
[0038] Furthermore, different catalysts such as Pt, Pd, Au, Cu, Ag,
V.sub.2O.sub.5, Fe.sub.3O.sub.4, Cr.sub.2O.sub.3, MnO.sub.2,
Co.sub.3O.sub.4, NiO can be deposited on the graphene nanosheets
homogeneously to promote oxidation reactions such as
Li.sub.2O.sub.2 in Li-air batteries or ZnO in Zinc-air batteries.
One method for catalyst deposition includes self-assembly.
[0039] While a number of embodiments of the present invention have
been shown and described, it will be apparent to those skilled in
the art that many changes and modifications may be made without
departing from the invention in its broader aspects. The appended
claims, therefore, are intended to cover all such changes and
modifications as they fall within the true spirit and scope of the
invention.
* * * * *