U.S. patent application number 13/448197 was filed with the patent office on 2012-10-18 for flow ultracapacitor.
This patent application is currently assigned to EnerG2 Technologies, Inc.. Invention is credited to Aaron Feaver, Chad Goodwin, Richard Varjian.
Application Number | 20120262127 13/448197 |
Document ID | / |
Family ID | 47005939 |
Filed Date | 2012-10-18 |
United States Patent
Application |
20120262127 |
Kind Code |
A1 |
Feaver; Aaron ; et
al. |
October 18, 2012 |
FLOW ULTRACAPACITOR
Abstract
The present application is generally directed towards
electrochemical energy storage devices. The devices comprise
electrode material suspended in an appropriate electrolyte. Such
devices are capable of achieving economical $/kWh(cycle) values and
will enable much higher power and cycle life than currently used
devices.
Inventors: |
Feaver; Aaron; (Seattle,
WA) ; Varjian; Richard; (Kirkland, WA) ;
Goodwin; Chad; (Seattle, WA) |
Assignee: |
EnerG2 Technologies, Inc.
Seattle
WA
|
Family ID: |
47005939 |
Appl. No.: |
13/448197 |
Filed: |
April 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61476136 |
Apr 15, 2011 |
|
|
|
Current U.S.
Class: |
320/167 ;
320/166; 361/502; 361/503; 361/523; 977/773; 977/948 |
Current CPC
Class: |
H01G 9/155 20130101;
Y02E 60/13 20130101; H01G 9/042 20130101; H01G 9/145 20130101; H01G
11/58 20130101; H01G 11/30 20130101 |
Class at
Publication: |
320/167 ;
361/502; 361/503; 361/523; 320/166; 977/948; 977/773 |
International
Class: |
H01G 9/042 20060101
H01G009/042; H01G 9/145 20060101 H01G009/145; H02J 7/00 20060101
H02J007/00; H01G 9/155 20060101 H01G009/155; H01G 9/15 20060101
H01G009/15 |
Claims
1. An electrochemical energy storage device comprising: (a)
electrode material; (b) electrolyte; (c) an electrochemical cell;
and (d) first and second charge storage tanks in fluid connection
with the electrochemical cell; wherein the electrode material is
suspended in the electrolyte, and wherein the electrochemical
energy storage device is configured to allow the suspended
electrode material to flow through the electrochemical cell to the
first and second charge storage tanks in the presence of a voltage
applied to the electrochemical cell.
2. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises carbon.
3. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a metal oxide.
4. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a silicon alloy, titania,
transition metal oxides, NMC, NMA, LiCoO.sub.2, LiFePO.sub.4, metal
phosphates, MoS.sub.2, lithium/aluminum alloys, FeS, sodium,
sulfur, a carbon material, zinc, bromine, lithium, magnesium,
aluminum, iron, calcium, cadmium, iron oxide, silver oxide, nickel
oxide, cadmium hydroxide, zinc oxide, nickel hydroxide, nickel
oxyhydroxide, metallic iron, silver oxide, lead, lead oxide, water,
air or combinations thereof.
5. The electrochemical energy storage device of claim 1, wherein
the device comprises two different electrode materials.
6. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a carbon material having a total
impurity content of less than 500 ppm of elements having atomic
numbers ranging from 11 to 92 as measured by proton induced x-ray
emission.
7. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a carbon material comprising
micropores, mesopores and a total pore volume, wherein from 40% to
90% of the total pore volume resides in micropores, from 10% to 60%
of the total pore volume resides in mesopores and less than 10% of
the total pore volume resides in pores greater than 20 nm.
8. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a carbon material comprising at
least 1000 ppm of a bi-functional catalyst and a pore structure
comprising pores, the pore structure comprising a total pore volume
of at least 1 cc/g, wherein at least 50% of the total pore volume
resides in pores having a pore size ranging from 2 nm to 50 nm as
determined from N.sub.2 sorption derived DFT
9. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a carbon material comprising at
least 1,000 ppm of an electrochemical modifier, wherein the
electrochemical modifier comprises lead, tin, antimony, bismuth,
arsenic, tungsten, silver, zinc, cadmium, indium, sulfur, silicon
or combinations thereof, and wherein the carbon material comprises
a total of less than 500 ppm of all other elements having atomic
numbers ranging from 11 to 92, as measured by proton induced x-ray
emission.
10. The device of claim 1, wherein the electrode material comprise
a carbon material and the carbon material further comprises a
material selected from a silicon alloy, titania, transition metal
oxides, NMC, NMA, LiCoO.sub.2, LiFePO.sub.4, metal phosphates,
MoS.sub.2, lithium/aluminum alloys, FeS, sodium, sulfur, a
different type of carbon material, zinc, bromine, lithium,
magnesium, aluminum, iron, calcium, cadmium, iron oxide, silver
oxide, nickel oxide, cadmium hydroxide, zinc oxide, nickel
hydroxide, nickel oxyhydroxide, metallic iron, silver oxide, lead
and lead oxide.
11. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises particles having an average
diameter ranging from 1 .mu.m to 20 .mu.m.
12. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises particles having an average
diameter ranging from 10 nm to 1 .mu.m.
13. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises particles having an average
diameter ranging from 20 .mu.m to 500 .mu.m.
14. The electrochemical energy storage device of claim 1, wherein
the electrochemical cell comprises a positive current collector and
a negative current collector.
15. The electrochemical energy storage device of claim 1, wherein
the electrochemical cell comprises an inert porous separator
interposed between a positive current collector and a negative
current collector.
16. The electrochemical energy storage device of claim 15, wherein
the electrochemical cell comprises first and second flow channels
defined by the volume occupied between the positive current
collector and the inert porous separator and the negative current
collector and the inert porous separator, respectively.
17. The electrochemical energy storage device of claim 16, wherein
the first and second flow channels have hydraulic radii ranging
from about 100 nanometers to about 500 micrometers.
18. The device of claim 1, wherein the dimensions of the
electrochemical cell are sized to enable laminar flow of a first
lamella containing a suspension of positively charged electrode
material and electrolyte and a second lamella comprising a
suspension of negatively charged electrode material and
electrolyte, wherein the first and second lamellae flow in contact
with one another without substantial mixing of the two
lamellae.
19. The device of claim 18, wherein the device does not comprise an
inert porous separator within the electrochemical cell.
20. The electrochemical energy storage device of claim 1, wherein
the electrochemical energy storage device comprises a plurality of
electrochemical cells.
21. The electrochemical energy storage device of claim 20, wherein
the plurality of electrochemical cells are connected in
parallel.
22. The electrochemical energy storage device of claim 20, wherein
the plurality of electrochemical cells are connected in series.
23. The electrochemical energy storage device of claim 1, wherein
the electrical energy storage device further comprises an outer
structure which is electrically insulating.
24. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises a solute dissolved in an aqueous
solvent.
25. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises a solute dissolved in an non-aqueous
solvent.
26. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises an ionic liquid.
27. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises carbon and silicon.
28. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises a viscosity of 100 cp or less.
29. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises a viscosity of 10 cp or less.
30. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises a viscosity of 1 cp or less.
31. The electrochemical energy storage device of claim 1, wherein
the electrolyte comprises a solvent having thixotropic
properties.
32. The electrochemical energy storage device of claim 1, wherein
the electrode material comprises a battery electrode material.
33. An electrochemical energy storage device comprising: (a)
electrode material; (b) electrolyte; and (c) an electrochemical
cell, wherein the electrode material is suspended in the
electrolyte.
34. The electrochemical energy storage device of claim 33, wherein
the electrode material comprises carbon.
35. A method for storing electrochemical energy, the method
comprising: (a) providing a device comprising: (i) electrode
material; (ii) electrolyte; (iii) an electrochemical cell; and (iv)
first and second charge storage tanks in fluid connection with the
electrochemical cell; (b) applying a voltage to the electrochemical
cell; and (c) flowing a suspension of the electrode material in the
electrolyte through the electrochemical cell and into the first and
second charge storage tanks.
36. The method of claim 35, further comprising discharging the
device by flowing the suspension of electrode material from the
first and second charge storage tanks through the electrochemical
cell.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Patent Application No. 61/476,136
filed on Apr. 15, 2011; which application is incorporated herein by
reference in its entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention generally relates to electrochemical
energy storage devices and, in particular, to flow
ultracapacitors.
[0004] 2. Description of the Related Art
[0005] Ultracapacitors have advantages in electrical grid
applications because of their extraordinary cycle life and
longevity, but using existing commercial ultracapacitors would cost
$14,800/kWh (not counting module and system integration cost);
which is not economically feasible. There are major efforts
underway to reduce cost, but ultracapacitors will continue to be
designed for high volumetric energy and power density making them
most useful for portable applications.
[0006] Flow batteries are designed for the grid and have large
electrolyte storage tanks with relatively small cells. Sodium
sulfur batteries using molten sodium as an electrode are another
high energy density device with relevance at grid scale.
Unfortunately these systems cost in the $300-500/kWh range. Most
are capable of longer cycle lives than lead acid batteries, perhaps
reaching 2000-3000 deep discharge cycles. Vanadium and zinc bromide
systems operate at room temperature, but sodium sulfur batteries
operate at high temperatures .about.300.degree. C.--requiring
vacuum insulation. Sodium sulfur batteries have high efficiency at
90%, while vanadium flow batteries only reach 65-75% round trip
efficiency. Generally, flow batteries or molten metal batteries are
still too expensive and have substantial operating drawbacks such
as poor cycle life, low efficiency, and high operating
temperature.
[0007] Ultracapacitors solve problems associated with batteries but
are far too expensive for bulk storage grid applications.
Accordingly, there is a need in the art for energy and cost
efficient electrochemical energy storage devices having fast
response, high power, and excellent cycle life. The present
invention provides these and other related benefits.
BRIEF SUMMARY
[0008] In general terms, the present invention is directed to
electrochemical energy storage devices. The devices are well suited
for any number of applications, and can be scaled for use in bulk
electrical storage and distribution grids (e.g., greater than 10
MW). Due to their increased efficiency, the devices are expected to
provide an economical solution to bulk electrical energy storage
(e.g., about 500 ($/kWh). The disclosed devices include
electrochemical cells comprising electrode material which is
suspended in an appropriate electrolyte to form an
electrode/electrolyte suspension. Electrochemical energy is stored
within the device in the form of charged electrode material. In
some embodiments, the charged electrode material remains within the
electrochemical cell, while in other embodiments the charged
electrode material flows through the device into external storage
containers where it is stored until used.
[0009] Accordingly, one embodiment of the present invention is an
electrochemical energy storage device, wherein the electrochemical
energy storage device comprises:
[0010] (a) electrode material;
[0011] (b) electrolyte;
[0012] (c) an electrochemical cell; and
[0013] (d) first and second charge storage tanks in fluid
connection with the electrochemical cell;
[0014] wherein the electrode material is suspended in the
electrolyte, and wherein the electrochemical energy storage device
is configured to allow the suspended electrode material to flow
through the electrochemical cell to the first and second charge
storage tanks in the presence of a voltage applied to the
electrochemical cell.
[0015] In other embodiments, the electrochemical energy storage
device is a static device and the charged electrode material
remains within the electrochemical cell. In such embodiments, the
electrochemical energy storage device comprises:
[0016] (a) electrode material;
[0017] (b) electrolyte; and
[0018] (c) an electrochemical cell,
[0019] wherein the electrode material is suspended in the
electrolyte.
[0020] Methods for use of the disclosed devices in electrical
energy storage and distribution applications are also provided.
[0021] These and other aspects of the invention will be apparent
upon reference to the attached drawings and following detailed
description. To this end, various references are set forth herein
which describe in more detail certain procedures, compounds and/or
compositions, and are hereby incorporated by reference in their
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In the figures, identical reference numbers identify similar
elements. The sizes and relative positions of elements in the
figures are not necessarily drawn to scale and some of these
elements are arbitrarily enlarged and positioned to improve figure
legibility. Further, the particular shapes of the elements as drawn
are not intended to convey any information regarding the actual
shape of the particular elements, and have been solely selected for
ease of recognition in the figures.
[0023] FIG. 1 shows a schematic of a representative flow
device.
[0024] FIG. 2 depicts a representative static device.
[0025] FIG. 3 shows carbon pore width vs. volume for various carbon
materials.
[0026] FIG. 4 shows charge/discharge curve showing voltage--state
of charge, and current applied in a representative device.
[0027] FIG. 5 depicts an exemplary flow device.
[0028] FIG. 6 presents charge current in different zones of an
exemplary device.
DETAILED DESCRIPTION
[0029] In the following description, certain specific details are
set forth in order to provide a thorough understanding of various
embodiments. However, one skilled in the art will understand that
the invention may be practiced without these details. In other
instances, well-known structures have not been shown or described
in detail to avoid unnecessarily obscuring descriptions of the
embodiments. Unless the context requires otherwise, throughout the
specification and claims which follow, the word "comprise" and
variations thereof, such as, "comprises" and "comprising" are to be
construed in an open, inclusive sense, that is, as "including, but
not limited to." Further, headings provided herein are for
convenience only and do not interpret the scope or meaning of the
claimed invention.
[0030] Reference throughout this specification to "one embodiment"
or "an embodiment" means that a particular feature, structure or
characteristic described in connection with the embodiment is
included in at least one embodiment. Thus, the appearances of the
phrases "in one embodiment" or "in an embodiment" in various places
throughout this specification are not necessarily all referring to
the same embodiment. Furthermore, the particular features,
structures, or characteristics may be combined in any suitable
manner in one or more embodiments. Also, as used in this
specification and the appended claims, the singular forms "a,"
"an," and "the" include plural referents unless the content clearly
dictates otherwise. It should also be noted that the term "or" is
generally employed in its sense including "and/or" unless the
content clearly dictates otherwise.
Definitions
[0031] "Electrochemical cell" refers to a device used for
generating an electromotive force (voltage) and current from
chemical reactions, or inducing a chemical reaction by a flow of
current. Electrochemical cells generally comprise a first and
second current collector (e.g., electrode) and an electrolyte.
Electrochemical cells may comprise two half-cells, each half cell
containing a current collector and the same or different
electrolyte. The two half cells may separated by an inert porous
separator (e.g., salt bridge). Upon application of a voltage to the
current collectors, ions, atoms, or molecules from one half-cell
lose electrons (oxidation) to the current collector while ions,
atoms, or molecules from the other half-cell gain electrons
(reduction) from the electrode. The stored electrical energy may be
released through the current collectors upon discharge.
[0032] "Suspension" refers to a heterogeneous mixture of a solid
(e.g., electrode material) and a liquid (e.g., electrolyte).
Generally the suspensions described herein are fluid and can be
moved through a device by means of gravity and/or pumping means.
Suspensions include "colloids."
[0033] A "colloid" is a suspension in which the solid component
does not separate out from the liquid component upon standing.
[0034] "Electrode material" refers to a material capable of
conducting, holding, acquiring and/or releasing an electrical
charge (i.e., electron(s)). Electrode materials include metals and
non-metals. Non-limiting examples of electrode materials are
provided below. Other electrode materials are well known to one of
ordinary skill in the art.
[0035] "Hydraulic radius" is calculated from the following
formula:
R h = A P ##EQU00001##
where R.sub.h is the hydraulic radius, A is the cross sectional
area of flow (e.g., of a flow channel) and P is the wetted
perimeter (the portion of the cross-section's perimeter that is
wet)
[0036] "Aspect ratio" refers to the ratio of the width of a shape
(e.g., a flow channel or charge channel) to its height.
[0037] "Electrolyte" means a substance containing free ions such
that the substance is electrically conductive.
[0038] "Thixotropic" refers the property of certain gels or fluids
(e.g., electrolytes) that are thick (viscous) under normal
conditions, but flow (become thin, less viscous) over time when
shaken, agitated, or otherwise stressed. Generally, a thixotropic
fluid will return to a more viscous state upon standing.
[0039] "Carbon material" refers to a material or substance
comprised substantially of carbon. Carbon materials include
amorphous and crystalline carbon materials. Examples of carbon
materials include, but are not limited to, activated carbon, carbon
black, graphite, graphene, hard carbon, carbon nanotubes,
buckyballs, pyrolyzed dried polymer gels, pyrolyzed polymer
cryogels, pyrolyzed polymer xerogels, pyrolyzed polymer aerogels,
activated dried polymer gels, activated polymer cryogels, activated
polymer xerogels, activated polymer aerogels and the like.
[0040] "Amorphous" refers to a material, for example an amorphous
carbon material, whose constituent atoms, molecules, or ions are
arranged randomly without a regular repeating pattern. Amorphous
materials may have some localized crystallinity (i.e., regularity)
but lack long-range order of the positions of the atoms. Pyrolyzed
and/or activated carbon materials are generally amorphous.
[0041] "Crystalline" refers to a material whose constituent atoms,
molecules, or ions are arranged in an orderly repeating pattern.
Examples of crystalline carbon materials include, but are not
limited to, diamond and graphite.
[0042] "Cryogel" refers to a dried gel that has been dried by
freeze drying.
[0043] "Pyrolyzed cryogel" is a cryogel that has been pyrolyzed but
not yet activated.
[0044] "Activated cryogel" is a cryogel which has been activated to
obtain activated carbon material.
[0045] "Xerogel" refers to a dried gel that has been dried by air
drying, for example, at or below atmospheric pressure.
[0046] "Pyrolyzed xerogel" is a xerogel that has been pyrolyzed but
not yet activated.
[0047] "Activated xerogel" is a xerogel which has been activated to
obtain activated carbon material.
[0048] "Aerogel" refers to a dried gel that has been dried by
supercritical drying, for example, using supercritical carbon
dioxide.
[0049] "Pyrolyzed aerogel" is an aerogel that has been pyrolyzed
but not yet activated.
[0050] "Activated aerogel" is an aerogel which has been activated
to obtain activated carbon material.
[0051] "Activate" and "activation" each refer to the process of
heating a raw material or carbonized/pyrolyzed substance at an
activation dwell temperature during exposure to oxidizing
atmospheres (e.g., carbon dioxide, oxygen, steam or combinations
thereof) to produce an "activated" substance (e.g., activated
cryogel or activated carbon material). The activation process
generally results in a stripping away of the surface of the
particles, resulting in an increased surface area. Alternatively,
activation can be accomplished by chemical means, for example, by
impregnation of carbon-containing precursor materials with
chemicals such as acids like phosphoric acid or bases like
potassium hydroxide, sodium hydroxide or salts like zinc chloride,
followed by carbonization. "Activated" refers to a material or
substance, for example a carbon material, which has undergone the
process of activation.
[0052] "Carbonizing", "pyrolyzing", "carbonization" and "pyrolysis"
each refer to the process of heating a carbon-containing substance
at a pyrolysis dwell temperature in an inert atmosphere (e.g.,
argon, nitrogen or combinations thereof) or in a vacuum such that
the targeted material collected at the end of the process is
primarily carbon. "Pyrolyzed" refers to a material or substance,
for example a carbon material, which has undergone the process of
pyrolysis.
[0053] A "bi-functional catalyst" refers to a material which acts
as a catalyst in both oxidation and reduction reactions.
Bi-functional catalysts may be comprised of a single component or
of several phases for example in the case where one component is
catalytic for oxidation and the other is catalytic for reduction.
Bi-functional catalysts within the context of the present
disclosure include metals such as: iron, nickel, cobalt, manganese,
copper, ruthenium, rhodium, palladium, osmium, iridium, gold,
halfnium, platinum, titanium, rhenium, tantalum, thallium,
vanadium, niobium, scandium, chromium, gallium, zirconium,
molybdenum and oxides thereof (e.g., nickel oxide, iron oxide,
etc.) as well as alloys thereof. Bi-functional catalysts also
include carbides such as lithium carbide, magnesium carbide, sodium
carbide, calcium carbide, boron carbide, silicon carbide, titanium
carbide, zirconium carbide, hafnium carbide, vanadium carbide,
niobium carbide, tantalum carbide, chromium carbide, molybdenum
carbide, tungsten carbide, iron carbide, manganese carbide, cobalt
carbide, nickel carbide and the like. Bi-functional catalysts may
be present in elemental form, oxidized form (e.g., metal oxides,
metal salts, etc.) or as part of a chemical compound.
[0054] "Electrochemical modifier" refers to any chemical element,
compound comprising a chemical element or any combination of
different chemical elements and compounds which enhances the
electrochemical performance of a carbon material. Electrochemical
modifiers can change (increase or decrease) the resistance,
capacity, power performance, stability and other properties of a
carbon material. Electrochemical modifiers generally impart a
desired electrochemical effect. In contrast, an impurity in a
carbon material is generally undesired and tends to degrade, rather
than enhance, the electrochemical performance of the carbon
material. Examples of electrochemical modifiers within the context
of the present disclosure include, but are not limited to,
elements, and compounds or oxides comprising elements, in groups
12-15 of the periodic table, other elements such as sulfur,
tungsten and silver and combinations thereof. For example,
electrochemical modifiers include, but are not limited to, lead,
tin, antimony, bismuth, arsenic, tungsten, silver, zinc, cadmium,
indium, silicon and combinations thereof as well as oxides of the
same and compounds comprising the same.
[0055] "Pore" refers to an opening or depression in the surface, or
a tunnel in a carbon material, such as for example activated
carbon, pyrolyzed dried polymer gels, pyrolyzed polymer cryogels,
pyrolyzed polymer xerogels, pyrolyzed polymer aerogels, activated
dried polymer gels, activated polymer cryogels, activated polymer
xerogels, activated polymer aerogels and the like. A pore can be a
single tunnel or connected to other tunnels in a continuous network
throughout the structure.
[0056] "Pore structure" refers to the layout of the surface of the
internal pores within a carbon material, such as an activated
carbon material. Components of the pore structure include pore
size, pore volume, surface area, density, pore size distribution
and pore length. Generally the pore structure of an activated
carbon material comprises micropores and mesopores. For example, in
certain embodiments the ratio of micropores to mesopores is
optimized for enhanced electrochemical performance.
[0057] "Mesopore" generally refers to a pore having a diameter
ranging from 2 nanometers to 50 nanometers while the term
"micropore" refers to a pore having a diameter less than 2
nanometers.
Electrochemical Energy Storage Devices
[0058] As noted above, the present invention generally relates to
devices and methods having utility in any number of electrical
energy storage and distribution applications, including bulk
electrical energy storage and distribution grids. In one embodiment
the present invention is directed to an electrochemical energy
storage device having high energy density and power capabilities as
well as increased cycle life compared to other known electrical
energy storage and distribution devices. In one embodiment,
operation of the device includes flowing a suspension of electrode
material in electrolyte through an electrochemical cell having a
voltage applied thereto, and subsequently directing the electrode
suspension into charge storage tanks. The device is discharged by
reversing the flow of the electrode material. Such devices are
generally referred to as flow devices herein. In a representative
embodiment, the electrochemical energy storage device
comprises:
[0059] (a) electrode material;
[0060] (b) electrolyte;
[0061] (c) an electrochemical cell; and
[0062] (d) first and second charge storage tanks in fluid
connection with the electrochemical cell;
[0063] wherein the electrode material is suspended in the
electrolyte, and wherein the electrochemical energy storage device
is configured to allow the suspended electrode material to flow
through the electrochemical cell to the first and second charge
storage tanks in the presence of a voltage applied to the
electrochemical cell.
[0064] FIG. 1 depicts an exemplary device according to one
embodiment of the present invention. Referring to FIG. 1, electrode
material is suspended in an electrolyte to form a suspension. The
electrode material and electrolyte are selected from any of the
electrode materials and electrolytes known in the art, including
those described below. The illustrated device includes storage
containers 101, 102 for storage of uncharged suspended electrode
material. Storage containers 101 and 102 are in fluid connection
with an electrochemical cell 109. The electrochemical cell
generally comprises a first and second current collector 105, 106.
The current collectors may serve as a means for applying a voltage
across the electrochemical cell to charge the electrode material
and for distribution of electrical energy upon discharge of the
electrode material. Current collectors may be prepared from any
number of materials known in the art. In certain embodiments the
current collectors comprise aluminum, copper, stainless steel,
carbon, graphite, nickel or any other electrically conductive
material that is compatible with the electrode/electrolyte
suspension.
[0065] In some embodiments, the electrochemical cell comprises an
inert porous separator 104 (e.g., porous polymer, porous glass or
ceramic) interposed between the first and second current
collectors. The separator serves to isolate negatively charged
electrode material from positively charged electrode material,
while allowing electrolyte to flow through the separator. The
volume occupied between the first current collector 105 and the
porous separator 104 defines a first flow channel, and the volume
occupied between the second current collector 106 and the porous
separator 104 defines a second flow channel. The dimensions of the
first and second flow channels range from the macro down to
microfluidic ranges (e.g., hydraulic radii ranging from about 100
nanometers to about 500 micrometers). This dimension can be
optimized for a desired flow rate or charge time. Flow channels
having various aspect ratios (e.g., from about 1 to about 100) and
various sizes and shapes are also included.
[0066] FIG. 1 further illustrates first and second charge storage
tanks 107, 108, which are in fluid connection with an end of the
electrochemical cell. The charge storage tanks serve to store
charged electrode material until discharge is desired. For example,
the charged electrode material may be discharged through the
current collectors by flowing the charged suspended electrode
material back through the electrochemical cell as described in more
detail below.
[0067] In other variations, the electrical energy stored in the
charged electrode material/electrolyte suspension is not released
through the same electrochemical cell in which it was charged. For
example, in some embodiments the charged electrode/electrolyte
suspension is injected into another system as a source of
electrical energy. For example, the charged electrode/electrolyte
suspension may be used to inject in any number of devices which use
electricity as a power source. One non-limiting example of these
embodiments includes use of the charged electrode/electrolyte
suspension for powering an electric car, for example by pumping the
charged electrode/electrolyte suspension through the car's
electrical cell.
[0068] Other related embodiments include examples where the device
comprises an electrode/electrolyte suspension and an
electrochemical cell, but the device optionally does not include
charge storage tanks. Instead, operation of the device includes
flowing the electrode/electrolyte suspension through the
electrochemical cell and then using the charged
electrode/electrolyte suspension as a source of electrical energy
in another device (electric car, etc.). The charged suspension may
be stored prior to use or injected directly from the
electrochemical cell into another device for use.
[0069] The charge storage tanks may optionally comprise an
electrical insulation (e.g., glass or plastic) to reduce loss of
electrical energy to the environment through static or atmospheric
self-discharge. In some embodiments, charge storage tanks are
equipped with a charging apparatus to maintain a trickle charge so
that the charge storage tanks' charge is not depleted by self
discharge. Furthermore, the charge storage tanks may be sized for
the desired application. Thus, one advantage of the flow devices
described herein is that the charge storage capacity is limited
only by the physical size of the charge storage containers and not
by the size of the electrochemical cell.
[0070] The embodiment depicted in FIG. 1 comprises a single
electrochemical cell. It should be noted that alternative
embodiments include devices having a plurality (i.e., more than 1)
of electrochemical cells. The plurality of electrochemical cells
can be connected in parallel or in series depending on the desired
application. One of ordinary skill in the art will recognize the
appropriate configuration for various applications. In some
embodiments, the plurality of electrochemical cells are each
fluidly connected to the same first and second charge storage tanks
and/or the same uncharged suspended electrode storage tanks. In
these embodiments, the flow of electrode material is diverted from
the uncharged suspended electrode material storage tanks through
the plurality of electrochemical cells. The suspended electrode
material is then recombined into first and second charge storage
tanks at an exit end of the plurality of electrochemical cells.
[0071] In other related embodiments, each of the plurality of
electrochemical cells is connected to unique first and second
uncharged suspended electrode storage tanks and/or unique first and
second charge storage tanks. Such devices may also be connected in
series or in parallel depending on the desired application.
[0072] Operation of certain embodiments of the device can be
understood in general terms by referring again to FIG. 1. The
electrical energy storage device generally operates by applying a
voltage to the current collectors and initiating a flow of
electrode material through the electrochemical cell and into the
first and second charge storage tanks. Discharge of the device
includes flowing the charged electrode material from the first and
second charge tanks through the electrochemical cell where the
charged electrode material is discharged through the current
collectors. In some embodiments, flow of the electrode material
through the device is controlled by gravity and/or a pump connected
to the device.
[0073] As neutral particles of electrode material flow through the
electrochemical cell, they become charged 103 when they come in
contact with the current collectors. The fast Electric Double Layer
Capacitance (EDLC) charging mechanism that operates within the
devices can respond in the short time that an electrode particle
may be in electrical contact with a current collector or other
electrode particles. As the flow continues, the slurry gradually
picks up substantial double layer capacitance from contact with the
current collectors and also reaches equilibrium with itself through
particle-to-particle interaction. As the electrode suspension
reaches full charge passing through the electrochemical cell, it
exits the cell and is deposited in the charge storage tanks.
Altering the flow rate of the suspension as well as modifying the
design of the channels to increase the surface area of the current
collector can modify charging rates. Charging can also be altered
by fluid dynamics which are controlled using the characteristics of
the channel to increase or decrease the amount of time that
particles are in contact with the surface of the current
collector.
[0074] Discharge occurs through a similar mechanism by reversing
the flow and flowing charged electrode material back through the
cell where the electrode material is discharged through the current
collectors.
[0075] Methods for use of the device, which may include the above
steps, are contemplated within the scope of the present invention.
For example, in some embodiments the disclosure provides a method
for storing electrochemical energy, the method comprising:
[0076] (a) providing a device comprising: [0077] (i) electrode
material; [0078] (ii) electrolyte; [0079] (iii) an electrochemical
cell; and [0080] (iv) first and second charge storage tanks in
fluid connection with the electrochemical cell;
[0081] (b) applying a voltage to the electrochemical cell; and
[0082] (c) flowing a suspension of the electrode material in the
electrolyte through the electrochemical cell and into the first and
second charge storage tanks.
[0083] Other embodiments of the method include discharging the
device by flowing the suspension of electrode material from the
first and second charge storage tanks through the electrochemical
cell.
[0084] In another embodiment, the present invention is directed to
a static device. Accordingly, one embodiment is directed to an
electrochemical energy storage device comprising:
[0085] (a) electrode material;
[0086] (b) electrolyte; and
[0087] (c) an electrochemical cell,
[0088] wherein the electrode material is suspended in the
electrolyte.
[0089] Embodiments of the static devices have many features in
common with the flow devices described above, except the electrode
suspension does not flow through the device and leave the
electrochemical cell, for example into charge storage containers.
Instead, the charged electrode suspension remains in the
electrochemical cell. For example, in some embodiments the
electrochemical cell comprises an inert porous separator interposed
between first and second current collectors. The volume occupied
between the first or second current collector and the inert porous
separator defines the dimensions of first and second charge
channels, respectively. The dimensions of such charge channels can
be varied as described above with respect to the flow channels of a
flow device. Current collectors, electrode materials and
electrolytes can also be selected based on the desired application
from materials known in the art and as described herein with
respect to other devices.
[0090] The static devices can be understood by reference to an
exemplary embodiment depicted in FIG. 2. Referring to FIG. 2, the
illustrated embodiment includes electrode material suspended in
electrolyte (not depicted in FIG. 2) and first and second current
collectors 201. Interposed between the current collectors is an
inert porous separator 202. The volumes between the first current
collector and the inert porous separator and the second current
collector and the inert porous separator define first and second
charge channels, respectively 203. The device includes an outer
structure 204 for encasing the current collectors, electrode
material and other internal components of the device. The outer
structure is made from insulating materials commonly used for
encasing electrical energy storage devices (e.g., glass, plastic
and the like). Some embodiments also include gaskets 205 (e.g.,
Teflon.TM. and the like) to prevent leakage of electrolyte and
electrode material from the device.
[0091] Methods for use of the static device are also included. One
embodiment of the method comprises:
[0092] (a) providing an electrochemical energy storage device
comprising: [0093] (i) electrode material suspended in electrolyte;
and [0094] (ii) an electrochemical cell, and
[0095] (b) applying a voltage to the electrochemical cell.
[0096] Certain features of the above devices can be varied to
optimize their performance for the desired application. Key
parameters used to optimize the above embodiments include
optimization of flow channel (and charge channel) dimensions and
aspect ratios from the macro down to microfluidic ranges. In
certain embodiments, microfluidically sized flow channels (e.g.,
from about 100 nm to about 500 micrometers) obviate the need for a
separator membrane. If a membrane is required, porous glasses or
ceramics may be used. In addition, the energy and power density of
the devices can be optimized by adjusting electrode flow rates,
pump pressures and device configurations.
[0097] A number of parameters are amendable to optimization. For
example, methods for optimizing charge retention in storage tanks
are included in the scope of the invention. These methods include,
for example, controlling the atmosphere, trickle charging the tanks
to counter self-discharge, and optimizing tank materials. Also,
improving the cell configuration will allow control over the power.
Experiments performed in support of the present invention have
demonstrated that a suspended electrode material can be passed
through a hypodermic needle; however, sedimentation and pumpability
issues require optimization such as using coulombic charges, for
example, as used in the polystyrene dispersion art.
[0098] In certain embodiments, the flow channels have microfluidic
dimensions (e.g., hydraulic radii ranging from about 100 nanometers
to about 500 micrometers) such that the negatively charged and
positively charged electrode suspension can flow through the device
without mixing with one another in the absence of a porous
separator. For example, in some embodiments the dimensions of the
electrochemical cell are sized to enable laminar flow of a first
lamella containing a suspension of positively charged electrode
material and electrolyte and a second lamella comprising a
suspension of negatively charged electrode material and
electrolyte, wherein the first and second lamellae flow in contact
with one another without substantial mixing of the two
lamellae.
[0099] In some embodiments, the device operating time is readily
controlled by the size of the charge storage tanks. In some
embodiments, the charge storage tanks range in size from less than
1 L to millions of liters or more. Accordingly, devices having
various sizes of charge storage tanks are included within the scope
of the invention. As noted above, various embodiments are provided
having a plurality of electrochemical cells. Such devices can be
designed (e.g., connected in parallel or series, etc.) to obtain an
optimal power output, for example greater than 100 kW.
[0100] The devices are also capable of responding in the
millisecond timeframe. Furthermore, since the devices include
features similar to EDLC electrodes, and EDLC electrodes are known
for their long calendar life (often multiple decades), the
disclosed devices are expected to maintain their efficiency for
long periods of time, for example more than 100,000 cycles.
Mechanical accessories and cells may need to periodically be
maintained or replaced.
[0101] In other embodiments, the devices have high efficiency
(i.e., ratio of power release versus power needed to charge). In
some embodiments, the device has an efficiency greater than 90%,
greater than 95%, greater than 97% or even greater than 99%.
Efficiency can be increased (and self discharge reduced) through
proper electrode design, insulation, and atmosphere control in the
head space of the charge storage tanks. Furthermore, in certain
embodiments the devices are capable of less than 10%, less than 5%
or even less than 3% loss in 24 hours (i.e., loss of charge upon
standing). In some embodiments, electrical isolation of tubing and
charge storage tanks is employed to reduce losses.
[0102] In other embodiments, the devices are capable of charging
and discharging on second time scales (e.g., about 1 to 10
seconds). Accordingly, the devices are well suited for use in
applications requiring fast charge and discharge cycles.
[0103] The power capacity of the devices can be varied according to
the desired application. In some embodiments, the power capacity
ranges from about 0.01 kW to about 1 kW, for example about 0.1
kW.
[0104] The voltage of the devices can be tailored to the desired
application. Voltage is generally governed by the selection of
electrolyte and in certain embodiments ranges from about 1V to
about 9V. Aqueous electrolytes are generally employed at the lower
voltage range, while ionic liquid electrolytes may be useful for
the higher voltage range. In some typical embodiments, the voltage
of the devices ranges from about 2.5V to about 4.5V.
Electrode Materials and Electrolytes
[0105] The composition of the electrode material is not
particularly limited. In this regard, any electrode material can be
used. In some embodiments, the electrode material comprises carbon,
for example an activated or unactivated carbon material. Other
types of carbon useful as electrode material include graphite, hard
carbon and coke.
[0106] In certain embodiments, the device comprises a battery
electrode material. A battery electrode material is a material
which stores energy electrochemically (in the form of electrons),
and releases stored energy directly as electric current. The
storage of energy may or may not be repeatable or reversible.
Battery electrode materials are well known to those of ordinary
skill in the art. In other embodiments, any of the materials known
in the art for use as capacitor or EDLC electrodes may be used.
[0107] In certain other embodiments, the electrode material
comprises a material selected from silicon alloys, titania,
transition metal oxides, mixtures of nickel, manganese and aluminum
(NMC), mixtures of nickel, cobalt and aluminum (NMA), LiCoO.sub.2,
LiFePO.sub.4, metal phosphates and MoS.sub.2.
[0108] Other embodiments include devices comprising electrode
materials comprise a material selected from lithium/aluminum alloys
and FeS. In other embodiments, the electrode material comprises a
material selected from sodium and sulfur. In still other
embodiments, the electrode material comprises lithium and/or
lithium oxide. In still other embodiments, the electrode material
comprises zinc, blends of high surface area carbon and zinc, or
blends of high surface are carbon and bromine.
[0109] Still other embodiments include electrode materials selected
from lithium, zinc, magnesium, aluminum, iron and calcium.
Furthermore, owing to its particular oxidation/reduction
properties, air may be used as an electrode in certain embodiments.
Accordingly, some embodiments include device wherein at least a
portion (e.g., a flow channel or charge channel) of the
electrochemical device is open to air and the electrode material
comprises air.
[0110] In particular embodiments include device comprising
electrode materials selected from zinc, cadmium, iron oxide and
silver oxide. In other embodiments, the electrode material
comprises water or nickel oxide. Still other examples of electrode
materials include zinc, cadmium hydroxide, zinc oxide, nickel
hydroxide and nickel oxyhydroxide.
[0111] In yet other embodiments, the devices comprise electrode
materials comprising metallic iron, nickel oxide, silver oxide,
lead or lead oxide.
[0112] Furthermore, in some embodiments the device comprises two or
more different electrode materials. For example, the device may
comprise a first electrode material in a first flow or charge
channel (i.e., the "anode material") and a second, different
electrode material in a second flow or charge channel (i.e., the
"cathode material"). Examples of devices comprising two different
electrode materials include devices comprising a different type of
carbon electrode material for the anode material and the cathode
material. Other various exemplary embodiments of devices and their
respective anode and cathode material are provided in Table 1.
TABLE-US-00001 TABLE 1 Exemplary Devices Device Type Anode Material
Cathode Material Ultracapacitor Carbon A Carbon A Asymmetric Carbon
A Carbon B capacitor Lithium ion Graphite NMC battery Hard carbon
NMA Coke LiCoO.sub.2 Silicon alloys LiFePO.sub.4 Titania Metal
phosphates Transition-metal oxides MoS.sub.2 Bipolar lithium Li--Al
FeS ion sulfide Sodium/Sulfur Sodium Sulfur Zinc/Bromine Zinc/high
surface area Bromine/high surface area Flow (already carbon carbon
in flow design) Metal/Air Lithium Air (i.e., electrochemical (open
to air) Zinc cell is open to air) Magnesium Aluminum Iron Calcium
Silver Oxide Zinc Silver oxide Cadmium Iron oxide Nickel-Hydrogen
Water (hydrogen) Nickel oxide Nickel-Zinc Zinc/zinc oxide
Nickel-hydroxide/nickel oxyhydroxide Nickel-Cadmium Cadmium
hydroxide Nickel hydroxide Iron Metal Metallic iron Nickel oxide
Air (cell open to air) Silver oxide Lead Acid Lead Lead oxide
[0113] As noted above, some embodiments include electrode materials
comprising carbon. Carbon materials may be engineered with
controlled pore size distribution, surface area, surface chemistry,
density, and particle size at low cost. This enables optimization
for different characteristics such as energy vs. power. The ability
to produce a wide variety of carbons is critical to engineering a
carbon for a flow ultracapacitor. Carbon materials useful as
electrode material in the disclosed devices include the carbon
materials described herein, carbon materials known in the art,
commercially available carbon materials and the carbon materials
described in U.S. Pat. Nos. 7,723,262 and 7,835,136; co-pending
U.S. application Ser. No. 12/829,282 (U.S. Pub. No. 2011/002086);
Ser. No. 13/046,572 (U.S. Pub. No. 2011/0223494); Ser. No.
12/965,709 (U.S. Pub. No. 2011/0159375); Ser. No. 13/336,975 and
co-pending U.S. Provisional App. No. 61/613,790, which applications
are hereby incorporated by reference in their entireties for all
purposes.
[0114] FIG. 3 demonstrates carbon materials having various pore
size distributions (each line indicates a different carbon
material). Using the proven ability to control the pore size
distribution and particle size, a variety of carbons can be used to
optimize the efficacy of the devices. AC impedance spectroscopy and
carbons with varying pore size distributions may be used to study
which pores are effective in the devices during a variety of time
constants. The particle size distribution of carbon suspended in
electrolyte also drives the efficacy of the electrode material and
is optimized in various embodiments as described below. The primary
metric used in evaluating carbon for use in the devices is energy
stored per dollar of carbon.
[0115] Carbon materials for use in the present device include
activated and unactivated carbon materials, including carbon
cryogels, carbon xerogels and carbon aerogels. In some embodiments,
the carbon electrode material comprises a surface area ranging from
1500 m.sup.2/g to 3000 m.sup.2/g, and a pore size distribution
comprising:
[0116] a) pores having a diameter less than 2 nm;
[0117] b) pores having a diameter of 3 nm; and
[0118] c) pores having a diameter between 7 and 8 nm.
[0119] In some other embodiments, the carbon electrode material
comprises a peak pore volume greater than 0.1 cm.sup.3/g for pores
comprising a diameter less than 2 nm and a peak pore volume greater
than 0.1 cm.sup.3/g for pores comprising a diameter ranging from 5
nm to 12 nm.
[0120] In some other embodiments, the carbon electrode material is
an ultrapure synthetic carbon material comprising a total impurity
content of less than 500 ppm of elements having atomic numbers
ranging from 11 to 92 as measured by proton induced x-ray emission.
The high purity of such carbon materials may increase the
electrical performance of the device and/or reduce self discharge
of the electrode/electrolyte suspension. In other embodiments, the
carbon electrode material comprises less than 200 ppm, less than
100 ppm, less than 50 ppm or even less than 10 ppm of elements
having atomic numbers ranging from 11 to 92 as measured by proton
induced x-ray emission.
[0121] The carbon electrode materials may comprise a high surface
area. While not wishing to be bound by theory, it is thought that
such high surface area may contribute to the high energy density
obtained from devices comprising the carbon electrode material.
Accordingly, in some embodiments, the carbon electrode material
comprises a BET specific surface area of at least 1000 m.sup.2/g,
at least 1500 m.sup.2/g, at least 2000 m.sup.2/g, at least 2400
m.sup.2/g, at least 2500 m.sup.2/g, at least 2750 m.sup.2/g or at
least 3000 m.sup.2/g.
[0122] In still other embodiments, the carbon electrode material
comprises a bi-functional catalyst (e.g., at least 1000 ppm of a
bi-functional catalyst). For example, in some embodiments the
carbon electrode material comprises at least 1000 ppm of a
bi-functional catalyst and a pore structure comprising pores, the
pore structure comprising a total pore volume of at least 1 cc/g,
wherein at least 50% of the total pore volume resides in pores
having a pore size ranging from 2 nm to 50 nm as determined from
N.sub.2 sorption derived DFT. The bifunctional catalysts (as
defined above) are selected to optimize electrochemcial performance
of the device for the desired application.
[0123] In other embodiments, the carbon electrode material
comprises an electrochemical modifier (e.g., at least 1,000 ppm of
an electrochemical modifier). For example, in some embodiments the
carbon electrode material comprises at least 1,000 ppm of an
electrochemical modifier, wherein the electrochemical modifier
comprises lead, tin, antimony, bismuth, arsenic, tungsten, silver,
zinc, cadmium, indium, sulfur, silicon or combinations thereof, and
wherein the carbon electrode material comprises a total of less
than 500 ppm of all other elements having atomic numbers ranging
from 11 to 92, as measured by proton induced x-ray emission.
Electrochemical modifiers are selected to enhance the
electrochemical performance of the device.
[0124] In still other embodiments, the carbon electrode material
may comprise a battery electrode material within the same particle.
This may allow for an EDLC mechanism to be activated when the
particle contacts the current collector which can then charge a
battery material within the same particle while the particle is no
longer in contact with the current collector. In such a way, the
energy storing capability of the particle may be increased by the
usage of higher energy density but lower power battery
materials.
[0125] Accordingly, certain embodiments are directed to devices
comprising a carbon electrode material, wherein the carbon
electrode material further comprises an electrode material selected
from silicon alloys, titania, transition metal oxides, NMC, NMA,
LiCoO.sub.2, LiFePO.sub.4, metal phosphates, MoS.sub.2,
lithium/aluminum alloys, FeS, sodium, sulfur, a different type of
carbon material, zinc, bromine, lithium, magnesium, aluminum, iron,
calcium, cadmium, iron oxide, silver oxide, nickel oxide, cadmium
hydroxide, zinc oxide, nickel hydroxide, nickel oxyhydroxide,
metallic iron, silver oxide, lead and lead oxide.
[0126] In still other embodiments, the carbon electrode material
comprises a pore structure optimized to enhance the electrochemical
performance (e.g., power) of the device. In some embodiments, the
carbon electrode material comprises a pore structure, the pore
structure comprising micropores, mesopores and a total pore volume,
wherein from 40% to 90% of the total pore volume resides in
micropores, from 10% to 60% of the total pore volume resides in
mesopores and less than 10% of the total pore volume resides in
pores greater than 20 nm.
[0127] In certain embodiments, the electrode material is in the
form of particles. The size of the particles is not particularly
limited. For example, in some embodiments the electrode material
comprises particles having average diameters ranging from about 1
nm to about 100 .mu.m. In other embodiments, the electrode material
comprises particles having average diameters ranging from about 10
nm to about 1 .mu.m. In other embodiments, the electrode material
comprises particles having average diameters ranging from about 10
nm to about 100 .mu.m. In other embodiments, the electrode material
comprises particles having average diameters ranging from about 100
nm to about 100 .mu.m. In some other embodiments, the electrode
material comprises particles having average diameters ranging from
about 1 .mu.m to about 100 .mu.m, for example from about 1 .mu.m to
about 20 .mu.m or from about 20 .mu.m to about 500 .mu.m.
[0128] The electrolyte may be selected from any electrolyte known
in the art or disclosed in U.S. Patent Nos. 7,723,262 and 7,835,136
and co-pending U.S. application Ser. No. 12/829,282 (U.S. Pub. No.
2011/002086); Ser. No. 13/046,572 (U.S. Pub. No. 2011/0223494);
Ser. No. 12/965,709 (U.S. Pub. No. 2011/0159375); Ser. No.
13/336,975 and co-pending U.S. Provisional App. No. 61/613,790,
which applications were incorporated by reference above. In some
embodiments, the electrolyte in the device is capable of suspending
carbon particles for long periods of time (greater than the 24 hour
requirement for <5% loss). This may require surface chemistry
modification of the electrode materials (e.g., carbon) to enable a
good interface between the electrode material and electrolyte. The
electrolyte conductivity will have a strong impact on power
performance during fast discharge events and energy density as the
electrolyte can maximize particle charging. The combination of
electrolyte and electrode material drives features such as
viscosity and charge retention, which have an impact on the device
characteristics.
[0129] Useful electrolytes for the present invention include
solutes (e.g., salts) dissolved in aqueous solvent, salts dissolved
in non-aqueous solvents, and ionic liquids. Examples of
electrolytes useful in various embodiments of the present invention
include, but are not limited to, solvents such as propylene
carbonate, ethylene carbonate, butylene carbonate, dimethyl
carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane,
methylsulfolane, acetonitrile or mixtures thereof in combination
with solutes such as tetralkylammonium salts such as TEA TFB
(tetraethylammonium tetrafluoroborate), MTEATFB
(methyltriethylammonium tetrafluoroborate), EMITFB (1
ethyl-3-methylimidazolium tetrafluoroborate), tetraethylammonium,
triethylammonium based salts or mixtures thereof.
[0130] Typical aqueous electrolytes useful in the various
embodiments are selected from HCl, NaOH, KOH, H.sub.2SO.sub.4,
Ni/Caustic and NaCl. Aside from cost, aqueous systems may have
advantages over other electrolytes because higher capacitance is
often observed, conductivity can be very high, and the system-level
cost advantages are substantial. Much of the cost associated with
commercial Electric Double Layer Capacitors (EDLCs) is due to their
anhydrous nature. Water based systems result in lower operating
voltage, but in this case that lower potential may reduce
self-discharge. While not practical in systems that require high
gravimetric or volumetric performance, an aqueous system is ideal
for grid level $/kWh metrics.
[0131] In other embodiments, the electrolyte comprises an ionic
liquid. A wide variety of ionic liquids are known to one skilled in
the art including, but not limited to, imidazolium salts, such as
ethylmethylimidazolium hexafluorophosphate (EMIPF6) and
1,2-dimethyl-3-propyl imidazolium [(DMPIX)Im]. See, for example,
McEwen et al., "Nonaqueous Electrolytes and Novel Packaging
Concepts for Electrochemical Capacitors," The 7th International
Seminar on Double Layer Capacitors and Similar Energy Storage
Devices, Deerfield Beach, Fla. (Dec. 8-10, 1997), which reference
is hereby incorporated by reference in its entirety.
[0132] The viscosity of the electrolyte medium can be in the range
of 100 cp or less. In additional embodiments, the viscosity of the
electrolyte medium can be in the range of 10 cp or less. In yet
additional embodiments, the viscosity of electrolyte medium can be
about 1 cp or less. In other embodiments, the electrolyte solvent
can be thixotropic.
EXAMPLES
Example 1
Static Device
[0133] A static device as generally depicted in FIG. 2 was
prepared. The device measured approximately 10 cm.times.10 cm and
was about 1.6 mm deep. Electrode material was carbon and the
electrolyte was TEA TFB. This device was capable of easily charging
and discharging at about 10 mA constant current. A charge/discharge
curve for the device is shown in FIG. 4. The observed
charge/discharge imbalance is likely due to self-discharge caused
by the presence of air, water and/or lack of electrical contact
optimization. Such charge imbalance can be corrected by
optimization of the parameters described herein.
Example 2
Flow Device
[0134] A flow device was prepared as illustrated in FIG. 5. The
device comprised a carbon electrode material, electrolyte (TEA
TFB), current collectors 501, an inert porous separator 502, charge
channels 503, an outer structure 504 and gaskets 505. Studies
conducted with this device indicate that the electrode material
becomes charged as it flows through the device. During operation of
the device, the electrode suspension moved from an inlet 506 in
zone 1 507 through zone 2 508 to an outlet 510 in zone 3 509.
Measurements were taken in each zone as the electrode suspension
flowed through the electrochemical cell. The voltage was held at 2V
with a relatively steady current and electrode flow was initiated
at .about.940 seconds. FIG. 6 shows that the current requirement of
Zone 1 increased immediately with zones 2 and 3 lagging in current
accepting capability until fresh--uncharged--electrode material
arrived in the respective zones. The charged electrode suspension
was captured into charge storage containers upon exiting the
electrochemical cell. Even on a bench top in air, an average
voltage at .about.0.8V across the two charge storage containers was
observed. The results indicate that that charge can be stored in
the charge storage tanks outside the cell for future use.
[0135] The various embodiments described above can be combined to
provide further embodiments. All of the U.S. patents, U.S. patent
application publications, U.S. patent applications, foreign
patents, foreign patent applications and non-patent publications
referred to in this specification and/or listed in the Application
Data Sheet, are incorporated herein by reference, in their
entirety. Aspects of the embodiments can be modified, if necessary
to employ concepts of the various patents, applications and
publications to provide yet further embodiments. These and other
changes can be made to the embodiments in light of the
above-detailed description. In general, in the following claims,
the terms used should not be construed to limit the claims to the
specific embodiments disclosed in the specification and the claims,
but should be construed to include all possible embodiments along
with the full scope of equivalents to which such claims are
entitled. Accordingly, the claims are not limited by the
disclosure.
* * * * *