U.S. patent application number 12/694641 was filed with the patent office on 2010-08-12 for electrode folds for energy storage devices.
This patent application is currently assigned to G4 Synergetics, Inc.. Invention is credited to Kenneth Cherisol, Myles Citta, Nelson Citta, Anthony George, Eileen Higgins, Martin Patrick Higgins, Allen Michael, Barbara Patterson, Julius Regalado, Daniel J. West, Jon Kenneth West, Xin Zhou.
Application Number | 20100203384 12/694641 |
Document ID | / |
Family ID | 42102329 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100203384 |
Kind Code |
A1 |
West; Jon Kenneth ; et
al. |
August 12, 2010 |
ELECTRODE FOLDS FOR ENERGY STORAGE DEVICES
Abstract
A stacked energy storage device (ESD) has at least two
conductive substrates arranged in a stack. Each cell segment may
have a first electrode unit having a first active material
electrode, a second electrode unit having a second active material
electrode, and an electrolyte layer between the active material
electrodes. Each active material electrode may have a plurality of
folded sections and planar sections to increase the ESD capacity,
for example, by increasing number of interfaces within each cell
segment.
Inventors: |
West; Jon Kenneth;
(Gainesville, FL) ; Higgins; Martin Patrick; (Old
Field, NY) ; Higgins; Eileen; (Old Field, NY)
; Regalado; Julius; (Gainesville, FL) ; George;
Anthony; (Coventry, RI) ; Zhou; Xin;
(Gainesville, FL) ; Citta; Nelson; (Lake City,
FL) ; Citta; Myles; (Lake City, FL) ; Michael;
Allen; (Gainesville, FL) ; Cherisol; Kenneth;
(Mt. Laurel, NJ) ; West; Daniel J.; (Gainesville,
FL) ; Patterson; Barbara; (Lake City, FL) |
Correspondence
Address: |
ROPES & GRAY LLP
PATENT DOCKETING 39/361, 1211 AVENUE OF THE AMERICAS
NEW YORK
NY
10036-8704
US
|
Assignee: |
G4 Synergetics, Inc.
Roslyn
NY
|
Family ID: |
42102329 |
Appl. No.: |
12/694641 |
Filed: |
January 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61147725 |
Jan 27, 2009 |
|
|
|
61181194 |
May 26, 2009 |
|
|
|
Current U.S.
Class: |
429/209 ;
264/128; 361/523 |
Current CPC
Class: |
H01M 10/0418 20130101;
H01M 10/28 20130101; H01M 10/286 20130101; H01M 10/044 20130101;
H01M 10/4214 20130101; Y02E 60/50 20130101; H01M 4/70 20130101;
H01M 8/02 20130101; H01M 50/172 20210101; H01M 10/0468 20130101;
H01M 10/0477 20130101; H01M 10/282 20130101; H01M 10/4235 20130101;
H01M 6/48 20130101; H01M 8/04 20130101; H01M 2004/029 20130101;
H01M 10/0413 20130101; H01M 50/463 20210101; H01M 50/183 20210101;
Y02E 60/10 20130101; H01M 10/045 20130101 |
Class at
Publication: |
429/209 ;
361/523; 264/128 |
International
Class: |
H01M 4/02 20060101
H01M004/02; H01G 9/00 20060101 H01G009/00; H01M 4/04 20060101
H01M004/04 |
Claims
1. An energy storage device (ESD) comprising: a first conductive
substrate; a second conductive substrate provided in a stacking
direction; a first active material provided between the first
conductive substrate and the second conductive substrate; and a
second active material provided between the first conductive
substrate and the second conductive substrate, wherein each of the
first and second active materials is folded and comprises: a
plurality of planar sections orthogonal to the stacking direction,
wherein each planar section is coupled to an adjoining planar
section by a folded section, and wherein each respective planar
section of the first active material interfaces with a respective
planar section of the second active material.
2. The ESD of claim 1 wherein the first active material is
positively charged and the second active material is negatively
charged.
3. The ESD of claim 1 wherein the first active material is coupled
to the first conductive substrate and the second active material is
coupled to the second conductive substrate.
4. The ESD of claim 1 wherein the first active material and the
second active material comprise a flexible conductive matrix as the
support structure for the respective first and second active
materials.
5. The ESD of claim 4 wherein the flexible conductive matrix is
nickel-metal foam.
6. The ESD of claim 1 further comprising a first pressure contact
to connect the first active material to the first conductive
substrate and a second pressure contact to connect the second
active material to the second conductive substrate.
7. The ESD of claim 1 wherein at least one of the first active
material and the second active material is sleeved within a
respective separator prior to being folded.
8. The ESD of claim 1 further comprising: an electrolyte layer at
each interface of the first active material and the second active
material, wherein the electrolyte layer comprises a separator and
an electrolyte.
9. The ESD of claim 1 further comprising an electrode segment
provided at each of the plurality of planar sections for the first
and second active materials.
10. The ESD of claim 9 wherein the electrode segment has circular
cross-sectional area.
11. The ESD of claim 9 wherein the electrode segment has a
rectangular cross-sectional area.
12. The ESD of claim 1 wherein the plurality of planar sections and
folded portions for the respective first and second active
materials combine to form a respective electronic raceway that
serves as an electron transfer path.
13. A method for powder packing electrodes for an energy storage
device, the method comprising: dry packing active powders into a
substrate; wetting the active powders with a wetting agent to
ensure an even distribution and surface gradient of the substrate;
and over-coating the active powders with a binder layer on the
surface of the substrate.
14. The method of claim 13 wherein the chemical resistance of the
binder layer holds the active powders in place while allowing the
transportation of electrolyte ions to and from the substrate.
15. The method of claim 13 wherein wetting the dry packed powders
allows transport of active materials from the surface of the
substrate into the bulk of the substrate.
16. The method of claim 13, further comprising: dissolving the
wetting agent off of the active powders wherein the wetting agent
leaves no residuals in the active powders.
17. The method of claim 13, further comprising: dissolving the
wetting agent off of the active powders; and leaving a residual
element in the active powders, wherein the residual element
contributes to the electrical properties of the electrode.
18. The method of claim 17 wherein the residual elements increase
the capacity of the ESD.
19. The method of claim 13 further comprising providing a common
collector and coupling the substrate to the common collector.
20. The method of claim 19 wherein the common collector is folded
to form a folded electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/147,725, filed Jan. 27, 2009, and U.S.
Provisional Application No. 61/181,194, filed May 26, 2009, both of
which are hereby incorporated by reference herein in their
entireties.
FIELD OF THE INVENTION
[0002] This invention relates generally to energy storage devices
(ESDs) and, more particularly, this invention relates to stacked
ESDs with electrode folds.
BACKGROUND OF THE INVENTION
[0003] Bi-polar ESDs may provide an increased discharge rate and a
higher voltage potential between their external connectors than
standard wound or prismatic cells, and are therefore in high demand
for certain applications. Conventional ESDs have been manufactured
as either a wound cell structure that has only two electrodes or a
standard prismatic cell structure that has many plate sets in
parallel. In both of these types, the electrolyte is shared
everywhere within the ESD. The wound cell structure and prismatic
cell structure both suffer from high electrical resistances due to
their electrical paths having to cross multiple connections and
span significantly long distances to cover the complete circuit
from one cell to the next in a series arrangement.
[0004] In addition, both the wound cell and prismatic cell
structures require electrodes having relatively high mechanical
stability for assembly, processing, and packaging of the electrodes
into the cell. The wound cell electrode must be sufficiently
resilient to avoid the stress-related defects associated with
winding, as it is bent to a range of curvatures during the winding
and packaging process, which can impart structural damage and
negatively affect ESD performance. Prismatic electrodes are
typically flat and are generally not subjected to the stresses
imparted by the winding process of the wound cell structure.
Prismatic electrodes, however, require additional connection
components between plates having the same polarity within a
cell.
[0005] Accordingly, it would be desirable to provide an ESD that
avoids the process of winding and thereby the stress-related
defects of winding. Further, it would be desirable to provide an
ESD having electrodes along a folded mechanical compliment common
collector, or electron transfer path, to eliminate the need for
additional connection components as in the prismatic cell
structure.
[0006] With the increasing use of ESDs for various applications,
the capacity of these devices has become an important factor. ESD
capacity is a measure of the charge stored by the ESD and is a
component of the maximum amount of energy that can be extracted
from the ESD. An ESD's capacity may be related to the mass of
active materials contained in the ESD and by the number of
interfaces between the electrodes in the ESD. In conventional wound
cell and prismatic cell structures, the capacity is increased by
adding more material (e.g., by adding more electrodes or increasing
the size of the electrodes). This increases the size of the ESD and
may add a considerable amount of mass to the ESD relative to the
resulting increase in the capacity.
[0007] Accordingly, it would be desirable to provide a stacked
bi-polar ESD having cells with increased capacity while minimizing
the mass and volume of the ESD. Further, it would be desirable to
provide a stacked bi-polar ESD having cells with an increased
number of interfaces between electrodes.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing, apparatus and methods are provided
for stacked ESDs having increased capacity and folded
electrodes.
[0009] In accordance with an embodiment, there is provided an ESD
having a first conductive substrate and a second conductive
substrate provided in a stacking direction. A first active material
may be provided between the first conductive substrate and the
second conductive substrate, and a second active material may be
provided between the first conductive substrate and the second
conductive substrate. Each of the first and second active materials
may be folded and may have a plurality of planar sections
orthogonal to the stacking direction, where each planar section may
be coupled to an adjoining planar section by a folded section, and
where each respective planar section of the first active material
may interface with a respective planar section of the second active
material.
[0010] In some embodiments of the present invention powder packed
electrodes for an energy storage device may be provided. Active
powders may be dry-packed into a substrate, and the active powders
may be wetted with a wetting agent to ensure an even distribution
and surface gradient of the substrate. The active powders may be
over-coated with a binder layer on the surface of the substrate.
The chemical resistance of the binder layer may hold the active
powders in place while allowing the transportation of electrolyte
ions to and from the substrate. In some embodiments, the substrate
may be coupled to a common collector that may be folded to form a
folded electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The above and other objects and advantages of the invention
will be apparent upon consideration of the following detailed
description, taken in conjunction with the accompanying drawings,
in which like reference characters refer to like parts throughout,
and in which:
[0012] FIG. 1 shows a schematic cross-sectional view of a structure
of a bi-polar electrode unit (BPU) according to an embodiment of
the invention;
[0013] FIG. 2 shows a schematic cross-sectional view of a structure
of a stack of BPUs of FIG. 1 according to an embodiment of the
invention;
[0014] FIG. 3 shows a schematic cross-sectional view of a structure
of a stacked bi-polar ESD according to an embodiment of the
invention;
[0015] FIG. 4 shows a schematic cross-sectional view of a structure
of a stack of BPUs having thickened electrodes according to an
embodiment of the invention;
[0016] FIG. 5 shows a schematic cross-sectional view of a structure
of a stack of BPUs having electrode folds according to an
embodiment of the invention;
[0017] FIG. 6 shows a schematic cross-sectional view of a structure
of a stack of BPUs having electrode folds according to an
embodiment of the invention;
[0018] FIG. 7 shows a perspective view of an origami electrode fold
according to an embodiment of the present invention;
[0019] FIG. 8 shows a side elevation view of the origami electrode
fold of FIG. 7 according to an embodiment of the invention;
[0020] FIGS. 9A and 9B show a top plan view and a side elevation
view, respectively, of a structure of an active material electrode
layer according to an embodiment of the invention;
[0021] FIG. 9C shows a side elevation view of the active material
electrode layer of FIGS. 9A-9B that has been folded according to an
embodiment of the invention;
[0022] FIGS. 10A and 10B show a top plan view and a side elevation
view, respectively, of a structure of an active material electrode
layer according to an embodiment of the invention;
[0023] FIG. 10C shows a side elevation view of the active material
electrode layer of FIGS. 10A-10B that has been folded according to
an embodiment of the invention; and
[0024] FIG. 11 shows an illustrative flow diagram for powder
packing an electrode according to an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Apparatus and methods are provided for stacked energy
storage devices (ESDs) with increased capacity, and are described
below with reference to FIGS. 1-11. The present invention relates
to ESDs such as, for example, batteries, capacitors, or any other
suitable electrochemical energy or power storage devices which may
store and/or provide electrical energy or current. It will be
understood that while the present invention is described herein in
the context of a stacked bi-polar ESD, the concepts discussed are
applicable to any intercellular electrode configuration including,
but not limited to, parallel plate, prismatic, folded, wound and/or
bi-polar configurations, any other suitable configuration, or any
combinations thereof.
[0026] Various types of ESDs with sealed cells in a stacked
formation have been developed that are able to provide higher
discharge rates and higher voltage potentials between external
connectors than that of standard wound or prismatic ESDs, and are
therefore in high demand for certain applications. Certain types of
these ESDs with sealed cells in a stacked formation have been
developed to generally include a stack of independently sealed
pairs of mono-polar electrode units (MPUs). Each of these MPUs is
provided with either a positive active material electrode layer or
a negative active material electrode layer coated on a first side
of a current collector. An MPU with a positive active material
electrode layer (i.e., a positive MPU) and an MPU with a negative
active material electrode layer (i.e., a negative MPU) has an
electrolyte layer therebetween for electrically isolating the
current collectors of those two MPUs. The current collectors of
this pair of positive and negative MPUs, along with the active
material electrode layers and electrolyte therebetween, are sealed
as a single cell or cell segment. An ESD that includes a stack of
such cells, each having a positive MPU and a negative MPU, shall be
referred to herein as a "stacked mono-polar" ESD.
[0027] The side of the current collector of the positive MPU not
coated with an electrode layer in a first cell is electrically
coupled to the side of the current collector of the negative MPU
not coated with an electrode layer in a second cell, such that the
first and second cells are in a stacked formation. The series
configuration of these cell segments in a stack may cause the
voltage potential to be different between current collectors.
However, if the current collectors of a particular cell contact
each other or if the common electrolyte of the two MPUs in a
particular cell is shared with any additional MPU in the stack, the
voltage and energy of the ESD would fade (i.e., discharge) quickly
to zero. Therefore, a stacked mono-polar ESD independently seals
the electrolyte of each of its cells from each of its other
cells.
[0028] Other types of ESDs with sealed cells in a stacked formation
have been developed to generally include a series of stacked
bi-polar electrode units (BPUs). Each of these BPUs is provided
with a positive active material electrode layer and a negative
active material electrode layer coated on opposite sides of a
current collector. Any two BPUs can be stacked on top of one
another with an electrolyte layer provided between the positive
active material electrode layer of one of the BPUs and the negative
active material electrode layer of the other one of the BPUs for
electrically isolating the current collectors of those two BPUs.
The current collectors of any two adjacent BPUs, along with the
active material electrode layers and electrolyte therebetween, may
also be a sealed single cell or cell segment. An ESD that includes
a stack of such cells, each having a portion of a first BPU and a
portion of a second BPU, shall be referred to herein as a "stacked
bi-polar" ESD.
[0029] While the positive side of a first BPU and the negative side
of a second BPU may form a first cell, the positive side of the
second BPU may likewise form a second cell with the negative side
of a third BPU or the negative side of a negative MPU, for example.
Therefore, an individual BPU may be included in two different cells
of a stacked bi-polar ESD. The series configuration of these cells
in a stack may cause the voltage potential to be different between
current collectors. However, if the current collectors of a
particular cell contact each other or if the common electrolyte of
the two BPUs in a first cell is shared with any other cell in the
stack, the voltage and energy of the ESD would fade (i.e.,
discharge) quickly to zero.
[0030] Conventional stacked bi-polar ESDs use flat electrode
plates. By using flat plates and isolating them by use of an edge
seal, cells in a stacked electrochemical ESD may operate
substantially independently. As the independent cells are charged
and discharged, slight pressure differences may develop between
adjacent cells. If the pressure difference between the adjacent
cells exceeds a few pounds per square inch, then the flat electrode
may deflect from the first cell towards the second cell. This
deflection may strain the separator material of the second cell,
creating a "hot spot" where a short circuit may develop. Because
the physical components and the chemistry of individual cells will
generally be slightly different from one another, pressure
differentials between cells will generally exist.
[0031] FIG. 1 shows an illustrative "flat plate" bi-polar electrode
unit or BPU 102, in accordance with an embodiment of the present
invention. Flat plate structures for use in stacked cell ESDs are
discussed in more detail in Ogg et al. U.S. patent application Ser.
No. 11/417,489, and Ogg et al. U.S. patent application Ser. No.
12/069,793, both of which are hereby incorporated by reference
herein in their entireties. BPU 102 may include a positive active
material electrode layer 104 that may be provided on a first side
of an impermeable conductive substrate or current collector 106,
and a negative active material electrode layer 108 that may be
provided on the other side of impermeable conductive substrate 106
(see, e.g., Fukuzawa et al., U.S. Pat. No. 7,279,248, issued Oct.
9, 2007, which is hereby incorporated by reference herein in its
entirety).
[0032] It will be understood that the bi-polar electrode may have
any suitable shape or geometry. For example, in some embodiments of
the present invention, the "flat plate" BPU may alternatively, or
additionally, be a "dish-shaped" electrode. This may reduce
pressures that may develop during operation of a bi-polar ESD.
Dish-shaped and pressure equalizing electrodes are discussed in
more detail in West et al. U.S. patent application Ser. No.
12/258,854, which is hereby incorporated by reference herein in its
entirety.
[0033] FIG. 2 shows a schematic cross-sectional view of a structure
of a stack of BPUs (see, e.g., BPU 102 of FIG. 1) in accordance
with an embodiment of the present invention. For example, multiple
BPUs 202 may be stacked substantially vertically into a stack 220,
with an electrolyte layer 210 that may be provided between two
adjacent BPUs 202, such that positive electrode layer 204 of one
BPU 202 may be opposed to negative electrode layer 208 of an
adjacent BPU 202 via electrolyte layer 210. Each electrolyte layer
210 may include a separator (not shown) that may hold an
electrolyte. The separator may electrically separate the positive
electrode layer 204 and negative electrode layer 208 adjacent
thereto, while allowing ionic transfer between the electrode units,
as described in more detail below.
[0034] With continued reference to the stacked state of BPUs 202 in
FIG. 2, for example, the components included in positive electrode
layer 204 and substrate 206 of a first BPU 202, the negative
electrode layer 208 and substrate 206 of a second BPU 202 adjacent
to the first BPU 202, and the electrolyte layer 210 between the
first and second BPUs 202 shall be referred to herein as a single
"cell" or "cell segment" 222. Each impermeable substrate 206 of
each cell segment 222 may be shared by the applicable adjacent cell
segment 222.
[0035] As shown in FIG. 3, for example, positive and negative
terminals may be provided along with stack 20 of one or more BPUs
2a-d to constitute a stacked bi-polar ESD 50 in accordance with an
embodiment of the invention. A positive mono-polar electrode unit
or MPU 12, that may include a positive active material electrode
layer 14 provided on one side of an impermeable conductive
substrate 16, may be positioned at a first end of stack 20 with an
electrolyte layer provided (i.e., electrolyte layer 10e), such that
positive electrode layer 14 of positive MPU 12 may be opposed to a
negative electrode layer (i.e., layer 8d) of the BPU (i.e., BPU 2d)
at that first end of stack 20 via the electrolyte layer 10e. A
negative mono-polar electrode unit or MPU 32, that may include a
negative active material electrode layer 38 provided on one side of
an impermeable conductive substrate 36, may be positioned at the
second end of stack 20 with an electrolyte layer provided (i.e.,
electrolyte layer 10a), such that negative electrode layer 38 of
negative MPU 32 may be opposed to a positive electrode layer (i.e.,
layer 4a) of the BPU (i.e., BPU 2a) at that second end of stack 20
via the electrolyte layer 10a. MPUs 12 and 32 may be provided with
corresponding positive and negative electrode leads 13 and 33,
respectively.
[0036] It should be noted that the substrate and electrode layer of
each MPU may form a cell segment with the substrate and electrode
layer of its adjacent BPU 2a/2d, and the electrolyte layer 10a/10e
therebetween, as shown in FIG. 3, for example (see, e.g., segments
22a and 22e). The number of stacked BPUs 2a-d in stack 20 may be
one or more, and may be appropriately determined in order to
correspond, for example, to a desired voltage for ESD 50. Each BPU
2a-d may provide any desired potential, such that a desired voltage
for ESD 50 may be achieved by effectively adding the potentials
provided by each component BPU 2a-d. It will be understood that
each BPU 2a-d need not provide identical potentials.
[0037] In some embodiments, bi-polar ESD 50 may be structured so
that BPU stack 20 and its respective positive and negative MPUs 12
and 32 may be at least partially encapsulated (e.g., hermetically
sealed) into an ESD case or wrapper 40 under reduced pressure. MPU
conductive substrates 16 and 36 (or at least their respective
electrode leads 13 and 33) may be drawn out of ESD case 40, so as
to mitigate impacts from the exterior upon usage and to prevent
environmental degradation, for example.
[0038] In order to prevent electrolyte of a first cell segment
(see, e.g., electrolyte layer 10a of cell segment 22a) from
combining with the electrolyte of another cell segment (see, e.g.,
electrolyte layer 10b of cell segment 22b), gaskets or sealants may
be stacked with the electrolyte layers between adjacent electrode
units to seal electrolyte within its particular cell segment. A
gasket or sealant may be any suitable compressible or
incompressible solid or viscous material, any other suitable
material, or combinations thereof, for example, that may interact
with adjacent electrode units of a particular cell to seal
electrolyte therebetween. In one suitable arrangement, as shown in
FIG. 3, for example, the bi-polar ESD of the invention may include
gaskets or seals 60a-e that may be positioned as a barrier about
electrolyte layers 10a-e and active material electrode layers
4a-d/14 and 8a-d/38 of each cell segment 22a-e. The gasket or
sealant may be continuous and closed and may seal electrolyte
between the gasket and the adjacent electrode units of that cell
(i.e., the BPUs or the BPU and MPU adjacent to that gasket or
seal). The gasket or sealant may provide appropriate spacing
between the adjacent electrode units of that cell, for example.
[0039] In sealing the cell segments of stacked bi-polar ESD 50 to
prevent electrolyte of a first cell segment (see, e.g., electrolyte
layer 10a of cell segment 22a) from combining with the electrolyte
of another cell segment (see, e.g., electrolyte layer 10b of cell
segment 22b), cell segments may produce a pressure differential
between adjacent cells (e.g., cells 22a/22b) as the cells are
charged and discharged. Equalization valves may be provided to
substantially decrease the pressure differences thus arising.
Equalization valves may operate as a semi-permeable membrane or
rupture disk, either mechanically or chemically, to allow the
transfer of a gas and to substantially prevent the transfer of
electrolyte. An ESD may have BPUs having any combination of
equalization valves. Pressure equalization valves are discussed in
more detail in West et. al U.S. patent application Ser. No.
12/258,854, which is hereby incorporated by reference herein in its
entirety.
[0040] FIGS. 4-6 show various embodiments of the present invention
that may be used, for example, to increase the capacity of an
ESD.
[0041] FIG. 4 shows a schematic cross-sectional view of a structure
of a stack 420 of two cell segments 422a-b according to an
embodiment of the invention. As shown in FIG. 4, for example, each
cell segment 422a-b may include a positive active material
electrode layer 404 and a negative active material electrode layer
408 with an electrolyte layer provided therebetween. Impermeable
conductive substrate or current collector 406c may be at a first
end of stack 420, and conductive substrate 406a may be at a second
end of stack 420. A stacking direction may be defined, using
conductive substrates 406c and 406a, as the direction from the
first end of stack 420 to the second end of stack 420. With
continued reference to the stacked state of FIG. 4, for example,
the components between and including conductive substrate 406a and
conductive substrate 406b may be included in cell segment 422a.
Similarly, the components between and including conductive
substrate 406b and conductive substrate 406c may be included in
cell segment 422b.
[0042] In the stack of FIG. 4, for example, positive electrode
layer 404 and negative electrode layer 408 may be separated by a
gap distance 415. Gap distance 415 may be any suitable distance.
For example, gap distance 415 may be any suitable distance that
minimizes internal resistance while restricting electron transport
between electrode surfaces. For example, suitable gap distances may
be design specific and may be 0 mils, 5 mils, 10 mils, or greater.
Gap distances may be related, for example, to the closing force of
the ESD assembly, the electrode thickness, and the electrode
loading of active materials. Gap distances may be optimized, for
example, to minimize electrode separation without causing excess
force on the electrodes, or the separator, during charge and
discharge cycling. An ESD incorporating variable volume containment
may independently adjust cells to set a respective gap distance to
compensate for the volumetric changes of electrodes during cycling.
Variable volume containment is described in more detail in West et
al. U.S. patent application Ser. No. ______ (Attorney Docket No.
106210-0005-101), filed Jan. 27, 2010, which is hereby incorporated
by reference herein in its entirety.
[0043] In some embodiments, for example, to increase the ESD
capacity of stack 420, positive electrode layer 404 and negative
electrode layer 408 may be thickened by increasing height 404h or
height 408h, or both, so that gap distance 415 may be relatively
small, for example, compared to the gap distance between positive
electrode layer 204 and negative electrode layer 208 of FIG. 2.
[0044] Thickening positive electrode layer 404 and/or negative
electrode layer 408 may yield a loss in conductivity, however,
because the anode and cathode interfacial area may not
substantially change (i.e., the interfacial surface area of
positive electrode layer 404 and negative electrode layer 408 may
not substantially change when either or both electrode layers are
thickened), yet the thickened electrodes may lead to longer paths
for ion and electron flow, thereby increasing the internal
resistance.
[0045] FIG. 5 shows a schematic cross-sectional view of a structure
of a stack 520 of two cell segments 522a-b according to an
embodiment of the invention. FIG. 5 illustrates another approach
for increasing the capacity of an ESD by providing, for example,
what shall be referred to herein as a "z-fold" electrode. As shown
in FIG. 5, for example, each cell segment 522a-b may include a
positive active material electrode layer 504 and a negative active
material electrode layer 508 with an electrolyte layer provided
between each interface of the active materials (see, e.g.,
interfaces 517, 518, and 519). Impermeable conductive substrate or
current collector 506c may be at a first end of stack 520, and
conductive substrate 506a may be at a second end of stack 520. A
stacking direction may be defined, using conductive substrates 506c
and 506a, as the direction from the first end of stack 520 to the
second end of stack 520. With continued reference to the stacked
state of FIG. 5, for example, the components between and including
conductive substrate 506a and conductive substrate 506b may be
included in cell segment 522a. Similarly, the components between
and including conductive substrate 506b and conductive substrate
506c may be included in cell segment 522b.
[0046] Providing a z-fold electrode may substantially increase the
number of interfaces between positive electrode layer 504 and
negative electrode layer 508 (e.g., interface 518) in a given cell
segment 522a-b. For example, there may be a greater number of
interfaces between positive electrode layer 504 and negative
electrode layer 508 in cell segment 522a than the number of
interfaces in a cell segment in FIG. 4, which shows only a single
interface in each cell segment (see, e.g., cell segment 422a). The
interfaces of the z-fold electrode may increase the surface area
where electrodes contact each other and the current collectors,
thereby decreasing the internal resistance of the ESD since the
resistance is inversely proportional to surface area.
[0047] As illustrated in FIG. 5, interfaces between positive
electrode layer 504 and negative electrode layer 508 may be
provided that may not be balanced, or may be unused, within a cell
segment. For example, interface 517 and interface 519 may be
between electrode layers having the same polarity. In particular,
interface 517 may be between two planar surfaces of positive
electrode layer 504, and interface 519 may be between two planar
surfaces of negative electrode layer 508.
[0048] The edges of the individual electrodes may be relatively
sharp and may pierce the separator if not preferably sealed by an
insulating material. The edges of the electrodes may also be
insulated by an insulating material so as not to touch the inside
edges of the substrates. As number of folds increases, quality
control becomes more important as individual cells are preferably
matched in weight, thickness, and packing uniformity, for example,
in order to limit dense spots.
[0049] FIG. 6 shows a cross-sectional segment view of a structure
of a stack 620 of two cell segments 622a-b according to an
embodiment of the invention. FIG. 6 illustrates another approach
for increasing the capacity of an ESD by providing, for example, an
"origami" electrode fold. As shown in FIG. 6, for example, cell
segments 622a-b may include a positive active material electrode
layer 604 and a negative active material electrode layer 608 with
an electrolyte layer provided between each interface of the active
materials (see, e.g., interface 621). Impermeable conductive
substrate or current collector 606c may be at a first end of stack
620, and conductive substrate 606a may be at a second end of stack
620. A stacking direction may be defined, using conductive
substrates 606c and 606a, as the direction from the first end of
stack 620 to the second end of stack 620. With continued reference
to the stacked state of FIG. 6, for example, the components between
and including conductive substrate 606a and conductive substrate
606b may be included in cell segment 622a. Similarly, the
components between and including conductive substrate 606b and
conductive substrate 606c may be included in cell segment 622b.
[0050] Providing an origami electrode may substantially increase
the number of interfaces (e.g., interface 621) between positive
electrode layer 604 and negative electrode layer 608 in a given
cell segment 622a-b. For example, there may be a greater number of
interfaces between positive electrode layer 604 and negative
electrode layer 608 in cell segment 622a than the number of
interfaces in a cell segment in FIG. 4, which shows only a single
interface in each cell segment (see, e.g., cell segment 422a of
FIG. 4). Further, there may be a greater number of interfaces
between electrode layers of opposite polarity than that of FIG. 5,
at least because some of the interfaces of FIG. 5 are between
electrode layers having the same polarity (see, e.g., interfaces
517 and 519 of FIG. 5).
[0051] As shown in FIG. 6, for example, interface 621 may be
between positive electrode layer 604 and negative electrode layer
608. An advantage of the origami electrode embodiment may be that
each and every interface within a cell may be between electrode
layers of opposite polarity (i.e., there may be no interfaces
between electrode layers having the same polarity, unlike
interfaces 517 and 519 of FIG. 5). ESD capacity and electrochemical
transport properties may be dependent, for example, on the number
of interfaces between electrodes of opposite polarity. Because the
origami electrode may increase the number of interfaces between
electrodes of opposite polarity in a given cell, this configuration
may substantially increase the capacity of the ESD. This may allow
the origami electrode fold to increase the ESD capacity by
increasing the anode to cathode interfacial area within a cell
segment.
[0052] FIG. 7 shows a perspective view of an origami electrode fold
700 according to an embodiment of the present invention. For
example, FIG. 7 may be a more detailed perspective view of various
segments of the origami electrode fold of FIG. 6. As shown in FIG.
7, for example, positive active material electrode layer 704 and
negative active material electrode layer 708 may include a
plurality of planar sections and folded portions. Origami
electrodes 700 of FIG. 7 may be provided, for example, in a cell
segment of an ESD (e.g., cell segment 22b of FIG. 3).
[0053] FIG. 8 shows a side elevation view of the origami electrode
fold of FIG. 7 according to an embodiment of the invention. A first
planar section 751a of negative electrode layer 708 may include a
top planar surface 742 and a bottom planar surface 744. First
planar section 751a may be coupled to a second planar section 751b
by a first folded portion 752a. Similarly, second planar section
751b may be coupled to a third planar section 751c by a second
folded portion 752b. There may be a similar number of planar
sections and folded portions in the corresponding positive
electrode layer 704. Although only three planar sections and two
folded portions are shown for each of positive electrode layer 704
and negative electrode layer 708, it will be understood that any
suitable number of planar sections coupled to folded portions may
be provided. For example, in order to provide an ESD with a desired
capacity there may be a preferred number of interfaces within some
cells of the ESD.
[0054] The planar sections of each electrode layer may be provided
in a plane that is substantially orthogonal to a stacking direction
of the ESD. For example, each planar section 751a-c of FIG. 7 may
lie in a plane that is orthogonal to a stacking direction of the
ESD defined by axis 741.
[0055] In some embodiments, planar sections may be provided in any
other suitable direction. For example, planar sections may be
provided in a plane that faces radially outwardly from the stacking
direction defined by axis 741 (i.e., the planar sections may lie
substantially parallel to the stacking direction). It will be
understood that there may be any suitable number of possible shapes
of electrode layers 704 and 708 provided where each and every
interface may be between electrode layers having opposite polarity.
For example, although the cross-sectional areas of the planar
sections of FIGS. 7 and 8 are shown as being substantially
rectangular, the planar sections may be circular, triangular,
hexagonal, or any other desired shape or combinations thereof.
[0056] Top planar surface 742 of negative electrode layer 708 may
be coupled to a first conductive substrate located within a cell
segment (see, e.g., conductive substrate 606a of FIG. 6) and bottom
planar surface 748 of positive electrode layer 704 may be coupled
to a second conductive substrate located within the same cell
segment (see, e.g., conductive substrate 606b of FIG. 6). An
electrode may be connected to a conductive substrate using various
approaches. In an embodiment, an electrode layer may be coupled to
a conductive substrate using a pressure contact. For example,
spring contacts may allow for an electrical contact without
soldering. By avoiding solder fatigue, spring contacts may be
resistant against shock, vibration, and corrosion, for example, and
may provide relatively high temperature cycling. By omitting solder
layers, for example, there may be a relatively lower resistance
compared to leaded connections. In other embodiments, an electrode
layer may be spot welded or sintered to a conductive substrate.
[0057] As discussed above in connection with FIGS. 6-8, an origami
electrode may provide a plurality of interfaces between the
positive and negative electrode layers within a cell segment. For
example, bottom planar surface 744 of negative electrode layer 708
and top planar surface 746 of positive electrode layer 704 may be
one of five interfaces of the origami electrodes of FIG. 8. It will
be understood that there may be any suitable number of interfaces
provided in a cell segment.
[0058] In an embodiment of the present invention, the positive
active material electrode layer (see, e.g., positive electrode
layer 704) and/or negative active material electrode layer (see,
e.g., negative electrode layer 708) may include a single active
material electrode sheet, respectively, that is folded at a
plurality of folded portions in order to make the structure of the
origami electrode. A similar approach may be used to make the
structure of the z-fold electrode or any other suitable folded
electrode configuration. Alternatively, in some embodiments the
positive electrode layer and/or negative electrode layer may
include one or more electrodes provided along a common collector or
what shall be referred to herein as an "electronic raceway," that
may provide an electron transfer path.
[0059] FIGS. 9A and 9B show a top plan view and a side elevation
view, respectively, of a structure of an active material electrode
layer according to an embodiment of the invention. As shown in
FIGS. 9A and 9B, for example, active material electrode layer 904
may include electrode segments 905a-c coupled to a common collector
or electronic raceway 901, which may serve as an electron transfer
path. Although three exemplary electrode segments are shown (i.e.,
electrode segments 905a-c), it will be understood that any suitable
number of electrode segments may be provided along electronic
raceway 901. For example, active material electrode layer 904 may
include one more electrode segments according to any preferred
design criteria for the ESD.
[0060] The portions of electronic raceway 901 that are not coupled
to electrode segments 905a-c may be folded into folded portions
952a and 952b as shown in FIG. 9C to make a folded electrode. Each
electrode segment 905a-c may correspond to a respective planar
section of the active material electrode when it is folded, for
example, into the origami or z-fold configuration. For example,
electrode segment 905a may correspond to planar section 951a,
electrode segment 905b may correspond to planar section 951b, and
electrode segment 905c may correspond to planar section 951c.
[0061] In some embodiments, a separator may be provided in the
electrolyte layer between the active material electrode layers. For
example, the separator may electrically separate the positive
active material electrode layer (see, e.g., positive electrode
layer 204) and negative active material electrode layer adjacent
thereto (see, e.g., negative electrode layer 208), while allowing
ionic transfer between the electrode units. In some embodiments a
separator may alternatively, or additionally, be provided around
each electrode segment (e.g., electrode segments 905a-c). For
example, a separator sleeve may be ultrasonically welded around
electrode segment 905a. Any other suitable technique, or
combination of techniques, may be used to fit and/or fasten the
separator sleeve around electrode segment 905a.
[0062] As shown, each of electrode segments 905a-c may be of the
same polarity (i.e., positive or negative) and may have a
substantially rectangular cross-section. It will be understood that
there may be any suitable number of possible shapes of electrode
segments 905a-c provided on electronic raceway 901. For example,
although the cross-sectional areas of the electrode segments of
FIGS. 9A-9C are shown as being substantially rectangular, the
electrode segments may be circular, triangular, hexagonal, or any
other desired shape or combinations thereof.
[0063] FIGS. 10A-10C show a structure of an active material
electrode layer having circular electrode segments according to an
embodiment of the invention. As shown in FIGS. 10A-10C, for
example, active material electrode layer 1004 may include electrode
segments 1005a-c coupled to a common collector or electronic
raceway 1001, which may serve as an electron transfer path. Active
material electrode layer 1004 may be folded, where each electrode
segment 1005a-c may correspond to a respective planar section
1051a-c of the folded electrode, and the portions of electronic
raceway 1001 that are not coupled to electrode segments 1005a-c may
be folded into folded portions 1052a and 1052b as shown in FIG. 10C
to make a folded electrode.
[0064] The origami electrodes of the present invention may help
maintain the inter-electrode spacing of the ESD. As defined herein,
"inter-electrode spacing" is the distance between active material
electrode layers in a stacked bi-polar ESD. This may be applied,
for example, to the distance between a positive and negative
electrode in a cell that only contains one positive and one
negative electrode. In some embodiments, this may be applied to a
cell with multiple electrode sets or segments within the same cell.
For cells with multiple electrodes or electrode segments, there may
be multiple inter-electrode spacings.
[0065] When an ESD having origami electrodes expands or contracts
along a stacking direction or axis (see, e.g., axis 741 of FIG. 8),
the displacement of a given planar electrode section (e.g., planar
section 751b of FIG. 8) may relate to the total distance moved
divided by the total number of folds, such that changes in the
inter-electrode spacing of the ESD may be relatively minimal in the
case of expansion and/or contraction of the electrodes along the
stacking axis during operation of the ESD. Maintaining
inter-electrode spacing in ESDs using variable volume containment
is discussed in more detail in West et al. U.S. patent application
Ser. No. ______ (Attorney Docket No. 106210-0005-101), filed Jan.
27, 2010, which is hereby incorporated by reference herein in its
entirety.
[0066] It will be understood that the cell segments of a given ESD
of the present invention may include positive and negative active
material electrode layers of any of the configurations as discussed
above in connection with FIGS. 1-10, or any other suitable
configurations, or combinations thereof. For example, cell segment
22a of FIG. 3 may include a thickened electrode configuration, cell
segment 22b may include a z-fold electrode configuration, and cell
segment 22c may include an origami electrode fold
configuration.
[0067] In accordance with embodiments of the present invention, any
suitable technique for producing any of the active material
electrode layers as discussed above in connection with FIGS. 1-10
may be used.
[0068] FIG. 11 shows illustrative flow diagram 1100 for a process
according to an embodiment of the present invention for powder
packing an active material electrode layer. This generally may
involve the steps of dry packing active powders into a substrate,
wetting the dry packed powders with a wetting agent, and
over-coating the dry packed powders with a binder layer.
[0069] In dry packing step 1102, the active material electrode
powders may be dry packed into a substrate or conductive matrix.
The substrate may be any electrically conductive matrix that may
hold active materials. For example, the substrate may be nickel
foam.
[0070] In wetting step 1104, the dry packed powders may be wetted
with a wetting agent to reduce viscosity and ensure a substantially
even distribution and surface gradient, which may allow relatively
uniform transport of the active materials from the surface of the
conductive matrix into the bulk of the conductive matrix. This step
may reduce the surface gradient, for example, to allow relatively
easier impregnation of the active material into the conductive
matrix. It will be understood that the active material electrode
powder may be wetted with a wetting agent before it is packed into
the conductive matrix, or after, or both. Further, it will be
understood that the active material electrode powders may be wetted
using any suitable wetting agent, such as distilled water, alcohol,
or any other suitable agent, or any combination thereof.
[0071] In some embodiments, a wetting agent may be used that may
substantially dissolve off of the conductive matrix. This may
ensure that particulates that may be non-reactive (e.g., that do
not contribute to the electrical performance of the ESD), and/or
particulates that may degrade the performance of the ESD, are not
left as a by-product in the substrate mix. Alternatively, or
additionally, the wetting agent may be baked off. For example,
solvents such as water, ispropyl alcohol, ethanol, and
N-Methylpyrroliodone (NMP), or any other suitable agent, or
combinations thereof, may be evaporated or baked off in order to
leave few or substantially no residuals.
[0072] In some embodiments, it may be desirable to leave a residual
element after dissolving or baking off most of the wetting agent if
the residual element enhances the performance of the conductive
matrix. This may be useful, for example, when preparing electrodes
using a slurry impregnation process, where a relatively low
viscosity slurry that includes a hydrophilic binder (e.g., PVA) may
be used to increase the surface gradient and help impregnation of
the electrodes. The binder may primarily consist of water, which
when dissolved or baked off after impregnation, may leave a small
amount of binder material that helps enhance the mechanical
properties of active materials in the electrode matrix. For
example, the binder material may help keep the active materials in
place within the electrode matrix. During cycling, the active
materials may change in volume, and the binder material may help to
prevent the active materials from being pushed out of the electrode
matrix, causing early failure modes of the ESD.
[0073] In over-coating step 1106, the dry packed active material
electrode powders may be over-coated with a binder layer on the
surface of the conductive matrix. The chemical resistance of the
binder layer may hold the dry packed powders in place while
substantially allowing the transportation of electrolyte ions to
and from the active materials of the conductive matrix.
[0074] A binder may be used, for example, to bind separate
particles together or facilitate adhesion to a surface. If a binder
is mixed with active material electrode powders before the powders
are pasted onto a substrate or conductive matrix, the active
surfaces may be coated with a substantially non-conducting
material. This may potentially reduce conductivity and may reduce
the chemical kinetics of the ESD, and a given cell segment and/or
the ESD may have reduced electrical and chemical performance. If no
binder is used then the active material electrode powders may be
free to move throughout the cell and across the separator, and may
form hard shorts and/or soft shorts which may hinder ESD
performance or even destroy the cell.
[0075] In some embodiments, nickel foam may be used as a conductive
matrix for both the positive electrode layer and the negative
electrode layer (see, e.g., positive electrode layer 704 and
negative electrode layer 708 of FIG. 7). Traditionally, nickel foam
has been used in positive nickel hydroxide Ni(OH).sub.2 electrodes
for nickel-metal hydride (NiMH) ESDs. This is due to the relatively
low conductivity of the positive material. However, nickel foam may
be used for both the positive and negative electrodes. This may
enhance the interfaces in the respective conductive matrices.
[0076] It should be understood that the steps of flow diagram 1100
are merely illustrative. Any of the steps of flow diagram 1100 may
be modified, omitted, or rearranged, two or more of the steps may
be combined, or any additional steps may be added, without
departing from the scope of the present invention.
[0077] Producing the origami electrode of the present invention may
generally involve the steps of providing an active material
electrode layer and folding the layer.
[0078] When an origami electrode fold is employed (e.g., origami
electrode 700 of FIGS. 7 and 8), the positive and negative active
material electrode layers may include a flexible substrate or
conductive matrix as the support structure for the active
materials. In some embodiments, the conductive matrix may be nickel
foam, however, any other suitable flexible and/or perforated
metallic conductive matrix, or combinations thereof, may also be
used as the active material host material. The foam matrix may be
sized at the folded portions prior to impregnating and folding the
foam. This may substantially prevent the nickel foam from breaking
due to the relatively brittle material properties of the nickel
foam.
[0079] Inserting tabs and/or attaching the electronic raceway to
the electrode segments (see, e.g., electrode segments 905a-c of
FIG. 9B) may create relatively sharp edges, which may in turn
penetrate the insulating separator, as previously discussed. A
conductive material resistant to the electrolyte in the cell
including, for example, nickel, nickel-plated copper, stainless
steel, nickel-plated steel, or any other suitable material, or
combinations thereof, may be used to attach the electrode segments
of the continuous electronic raceway strip, which may then be
folded to make up the folded electrode stack. The material between
the individual electrode segments (e.g., electronic raceway 901)
may be sized to contact separate electrode segments and/or to
minimize internal resistance between electrodes of the same
potential (i.e., positive or negative). The material connecting
electrode segments of the same potential may have a relatively
greater mechanical strength than the electrode segments, for
example, in order to be less susceptible to breaking due to
folding, thereby substantially preventing potential creep stresses
at the edges of the material.
[0080] The substrates used to form the electrode units of the
invention (e.g., substrates 6a-d, 16, and 36) may be formed of any
suitable conductive and impermeable or substantially impermeable
material, including, but not limited to, a non-perforated metal
foil, aluminum foil, stainless steel foil, cladding material
including nickel and aluminum, cladding material including copper
and aluminum, nickel plated steel, nickel plated copper, nickel
plated aluminum, gold, silver, any other suitable material, or
combinations thereof, for example. Each substrate may be made of
two or more sheets of metal foils adhered to one another, in
certain embodiments. The substrate of each BPU may typically be
between 0.025 and 5 millimeters thick, while the substrate of each
MPU may be between 0.025 and 10 millimeters thick and act as
terminals to the ESD, for example. Metalized foam, for example, may
be combined with any suitable substrate material in a flat metal
film or foil, for example, such that resistance between active
materials of a cell segment may be reduced by expanding the
conductive matrix throughout the electrode.
[0081] The positive electrode layers provided on these substrates
to form the electrode units of the invention (e.g., positive
electrode layers 4a-d and 14) may be formed of any suitable active
material, including, but not limited to, nickel hydroxide
(Ni(OH).sub.2), zinc (Zn), any other suitable material, or
combinations thereof, for example. The positive active material may
be sintered and impregnated, coated with an aqueous binder and
pressed, coated with an organic binder and pressed, or contained by
any other suitable technique for containing the positive active
material with other supporting chemicals in a conductive matrix.
The positive electrode layer of the electrode unit may have
particles, including, but not limited to, metal hydride (MH),
palladium (Pd), silver (Ag), any other suitable material, or
combinations thereof, infused in its matrix to reduce swelling, for
example. This may increase cycle life, improve recombination, and
reduce pressure within the cell segment, for example. These
particles, such as MH, may also be in a bonding of the active
material paste, such as Ni(OH).sub.2, to improve the electrical
conductivity within the electrode and to support recombination.
[0082] The negative electrode layers provided on these substrates
to form the electrode units of the invention (e.g., negative
electrode layers 8a-d and 38) may be formed of any suitable active
material, including, but not limited to, MH, Cd, Mn, Ag, any other
suitable material, or combinations thereof, for example. The
negative active material may be sintered, coated with an aqueous
binder and pressed, coated with an organic binder and pressed, or
contained by any other suitable technique for containing the
negative active material with other supporting chemicals in a
conductive matrix, for example. The negative electrode side may
have chemicals including, but not limited to, Ni, Zn, Al, any other
suitable material, or combinations thereof, infused within the
negative electrode material matrix to stabilize the structure,
reduce oxidation, and extend cycle life, for example.
[0083] Various suitable binders, including, but not limited to,
organic carboxymethylcellulose (CMC) binder, Creyton rubber, PTFE
(Teflon), any other suitable material, or combinations thereof, for
example, may be mixed with the active material layers to hold the
layers to their substrates. Ultra-still binders, such as 200 ppi
metal foam, may also be used with the stacked ESD constructions of
the invention.
[0084] The common collector or electronic raceway used to form the
active material electrode layers in some embodiments of the
invention (e.g., electronic raceway 901a) may be formed of any
suitable conductive and impermeable or substantially impermeable
material, including, but not limited to, a non-perforated metal
foil, aluminum foil, stainless steel foil, cladding material
including nickel and aluminum, cladding material including copper
and aluminum, nickel plated steel, nickel plated copper, nickel
plated aluminum, gold, silver, any other suitable conductive and/or
mechanically durable material, or combinations thereof, for
example. In some embodiments, each electronic raceway may be made
of two or more sheets of metal foils adhered to one another. As
discussed above, the electronic raceway may have a relatively high
mechanical strength in order to resist potentially negative
stress-effects from folding.
[0085] The separator of each electrolyte layer of the ESD of the
invention may be formed of any suitable material that electrically
isolates its two adjacent electrode units while allowing ionic
transfer between those electrode units. The separator may contain
cellulose super absorbers to improve filling and act as an
electrolyte reservoir to increase cycle life, wherein the separator
may be made of a polyabsorb diaper material, for example. The
separator may, thereby, release previously absorbed electrolyte
when charge is applied to the ESD. In certain embodiments, the
separator may be of a lower density and thicker than normal cells
so that the inter-electrode spacing (IES) may start higher than
normal and be continually reduced to maintain the capacity (or
C-rate) of the ESD over its life as well as to extend the life of
the ESD.
[0086] The separator may be a relatively thin material bonded to
the surface of the active material on the electrode units to reduce
shorting and improve recombination. This separator material may be
sprayed on, coated on, pressed on, or combinations thereof, for
example. The separator may have a recombination agent attached
thereto, in certain embodiments. This agent may be infused within
the structure of the separator (e.g., this may be done by
physically trapping the agent in a wet process using a polyvinyl
alcohol (PVA or PVOH) to bind the agent to the separator fibers, or
the agent may be put therein by electro-deposition), or it may be
layered on the surface by vapor deposition, for example. The
separator may be made of any suitable material or agent that
effectively supports recombination, including, but not limited to,
Pb, Ag, any other suitable material, or combinations thereof, for
example. While the separator may present a resistance if the
substrates of a cell move toward each other, a separator may not be
provided in certain embodiments of the invention that may utilize
substrates stiff enough not to deflect.
[0087] The electrolyte of each electrolyte layer of the ESD of the
invention may be formed of any suitable chemical compound that may
ionize when dissolved or molten to produce an electrically
conductive medium. The electrolyte may be a standard electrolyte of
any suitable chemical, including, but not limited to, NiMH, for
example. The electrolyte may contain additional chemicals,
including, but not limited to, lithium hydroxide (LiOH), sodium
hydroxide (NaOH), calcium hydroxide (CaOH), potassium hydroxide
(KOH), any other suitable material, or combinations thereof, for
example. The electrolyte may also contain additives to improve
recombination, such as, but not limited to, Ag(OH).sub.2, for
example. The electrolyte may also contain rubidium hydroxide
(RbOH), for example, to improve low temperature performance. In
some embodiments of the invention, the electrolyte may be frozen
within the separator and then thawed after the ESD is completely
assembled. This may allow for particularly viscous electrolytes to
be inserted into the electrode unit stack of the ESD before the
gaskets have formed substantially fluid tight seals with the
electrode units adjacent thereto.
[0088] The seals or gaskets of the ESD of the invention (e.g.,
gaskets 60a-e) may be formed of any suitable material or
combination of materials that may effectively seal an electrolyte
within the space defined by the gasket and the electrode units
adjacent thereto. In certain embodiments, the gasket may be formed
from a solid seal barrier or loop, or multiple loop portions
capable of forming a solid seal loop, that may be made of any
suitable nonconductive material, including, but not limited to,
nylon, polypropylene, cell gard, rubber, PVOH, any other suitable
material, or combinations thereof, for example. A gasket formed
from a solid seal barrier may contact a portion of an adjacent
electrode to create a seal therebetween.
[0089] Alternatively, the gasket may be formed from any suitable
viscous material or paste, including, but not limited to, epoxy,
brea tar, electrolyte (e.g., KOH) impervious glue, compressible
adhesives (e.g., two-part polymers, such as Loctite.RTM. brand
adhesives made available by the Henkel Corporation, that may be
formed from silicon, acrylic, and/or fiber reinforced plastics
(FRPs) and that may be impervious to electrolytes), any other
suitable material, or combinations thereof, for example. A gasket
formed from a viscous material may contact a portion of an adjacent
electrode to create a seal therebetween. In yet other embodiments,
a gasket may be formed by a combination of a solid seal loop and a
viscous material, such that the viscous material may improve
sealing between the solid seal loop and an adjacent electrode unit.
Alternatively or additionally, an electrode unit itself may be
treated with viscous material before a solid seal loop, a solid
seal loop treated with additional viscous material, an adjacent
electrode unit, or an adjacent electrode unit treated with
additional viscous material, is sealed thereto, for example.
[0090] Moreover, in certain embodiments, a gasket or sealant
between adjacent electrode units may be provided with one or more
weak points that may allow certain types of fluids (i.e., certain
liquids or gasses) to escape therethrough (e.g., if the internal
pressures in the cell segment defined by that gasket increases past
a certain threshold). Once a certain amount of fluid escapes or the
internal pressure decreases, the weak point may reseal. A gasket
formed at least partially by certain types of suitable viscous
material or paste, such as brai, may be configured or prepared to
allow certain fluids to pass therethrough and configured or
prepared to prevent other certain fluids to pass therethrough. Such
a gasket may prevent any electrolyte from being shared between two
cell segments that may cause the voltage and energy of the ESD to
fade (i.e., discharge) quickly to zero.
[0091] As mentioned above, one benefit of utilizing ESDs designed
with sealed cells in a stacked formation (e.g., bi-polar ESD 50)
may be an increased discharge rate of the ESD. This increased
discharge rate may allow for the use of certain less-corrosive
electrolytes (e.g., by removing or reducing the whetting,
conductivity enhancing, and/or chemically reactive component or
components of the electrolyte) that otherwise might not be feasible
in prismatic or wound ESD designs. This leeway that may be provided
by the stacked ESD design to use less-corrosive electrolytes may
allow for certain epoxies (e.g., J-B Weld epoxy) to be utilized
when forming a seal with gaskets that may otherwise be corroded by
more-corrosive electrolytes.
[0092] The case or wrapper of the ESD of the invention (e.g., case
40) may be formed of any suitable nonconductive material that may
seal to the terminal electrode units (e.g., MPUs 12 and 32) for
exposing their conductive substrates (e.g., substrates 16 and 36)
or their associated leads (i.e., leads 13 and 33). The wrapper may
also be formed to create, support, and/or maintain the seals
between the gaskets and the electrode units adjacent thereto for
isolating the electrolytes within their respective cell segments.
The wrapper may create and/or maintain the support required for
these seals such that the seals may resist expansion of the ESD as
the internal pressures in the cell segments increase. The wrapper
may be made of any suitable material, including, but not limited
to, nylon, any other polymer or elastic material, including
reinforced composites, nitrile rubber, or polysulfone, or shrink
wrap material, or any rigid material, such as enamel coated steel
or any other metal, or any insulating material, any other suitable
material, or combinations thereof, for example. In certain
embodiments, the wrapper may be formed by an exoskeleton of tension
clips, for example, that may maintain continuous pressure on the
seals of the stacked cells. A non-conductive barrier may be
provided between the stack and wrapper to prevent the ESD from
shorting.
[0093] With continued reference to FIG. 3, for example, bi-polar
ESD 50 of the invention may include a plurality of cell segments
(e.g., cell segments 22a-e) formed by MPUs 12 and 32, and the stack
of one or more BPUs 2a-d therebetween. In accordance with an
embodiment of the invention, the thicknesses and materials of each
one of the substrates (e.g., substrates 6a-d, 16, and 36), the
electrode layers (e.g., positive layers 4a-d and 14, and negative
layers 8a-d and 38), the electrolyte layers (e.g., layers 10a-e),
and the gaskets (e.g., gaskets 60a-e) may differ from one another,
not only from cell segment to cell segment, but also within a
particular cell segment. This variation of geometries and
chemistries, not only at the stack level, but also at the
individual cell level, may create ESDs with various benefits and
performance characteristics.
[0094] Additionally, the materials and geometries of the
substrates, electrode layers, electrolyte layers, and gaskets may
vary along the height of the stack from cell segment to cell
segment. With further reference to FIG. 3, for example, the
electrolyte used in each of the electrolyte layers 10a-e of ESD 50
may vary based upon how close its respective cell segment 22a-e is
to the middle of the stack of cell segments. For example, innermost
cell segment 22c (i.e., the middle cell segment of the five (5)
segments 22 in ESD 50) may include an electrolyte layer (i.e.,
electrolyte layer 10c) that is formed of a first electrolyte, while
middle cell segments 22b and 22d (i.e., the cell segments adjacent
the terminal cell segments in ESD 50) may include electrolyte
layers (i.e., electrolyte layers 10b and 10d, respectively) that
are each formed of a second electrolyte, while outermost cell
segments 22a and 22e (i.e., the outermost cell segments in ESD 50)
may include electrolyte layers (i.e., electrolyte layers 10a and
10e, respectively) that are each formed of a third electrolyte. By
using higher conductivity electrolytes in the internal stacks, the
resistance may be lower such that the heat generated may be less.
This may provide thermal control to the ESD by design instead of by
external cooling techniques.
[0095] As another example, the active materials used as electrode
layers in each of the cell segments of ESD 50 may also vary based
upon how close its respective cell segment 22a-e is to the middle
of the stack of cell segments. For example, innermost cell segment
22c may include electrode layers (i.e., layers 8b and 4c) formed of
a first type of active materials having a first temperature and/or
rate performance, while middle cell segments 22b and 22d may
include electrode layers (i.e., layers 8a/4b and layers 8c/4d)
formed of a second type of active materials having a second
temperature and/or rate performance, while outermost cell segments
22a and 22e may include electrode layers (i.e., layers 38/4a and
layers 8d/14) formed of a third type of active materials having a
third temperature and/or rate performance. As an example, an ESD
stack may be thermally managed by constructing the innermost cell
segments with electrodes of nickel cadmium, which may better absorb
heat, while the outermost cell segments may be provided with
electrodes of nickel metal hydride, which may need to be cooler,
for example. Alternatively, the chemistries or geometries of the
ESD may be asymmetric, where the cell segments at one end of the
stack may be made of a first active material and a first height,
while the cell segments at the other end of the stack may be of a
second active material and a second height.
[0096] Moreover, the geometries of each of the cell segments of ESD
50 may also vary along the stack of cell segments. Besides varying
the distance between active materials within a particular cell
segment, certain cell segments 22a-e may have a first distance
between the active materials of those segments, while other cell
segments may have a second distance between the active materials of
those segments. In any event, the cell segments or portions thereof
having smaller distances between active material electrode layers
may have higher power, for example, while the cell segments or
portions thereof having larger distances between active material
electrode layers may have more room for dendrite growth, longer
cycle life, and/or more electrolyte reserve, for example. These
portions with larger distances between active material electrode
layers may regulate the charge acceptance of the ESD to ensure that
the portions with smaller distances between active material
electrode layers may charge first, for example.
[0097] In an embodiment, the geometries of the electrode layers
(e.g., positive layers 4a-d and 14, and negative layers 8a-8d and
38 of FIG. 3) of ESD 50 may vary along the radial length of
substrates 6a-d. With respect to FIG. 3, the electrode layers are
of uniform thickness and are symmetric about the electrode shape.
In an embodiment, the electrode layers may be non-uniform. For
example, the positive active material electrode layer and negative
active material electrode layer thicknesses may vary with radial
position on the surface of the conductive substrate. Non-uniform
electrode layers are discussed in more detail in West et al. U.S.
patent application Ser. No. 12/258,854, which is hereby
incorporated by reference herein in its entirety.
[0098] Although each of the above described and illustrated
embodiments of a stacked ESD show a cell segment including a gasket
sealed to each of a first and second electrode unit for sealing an
electrolyte therein, it should be noted that each electrode unit of
a cell segment may be sealed to its own gasket, and the gaskets of
two adjacent electrodes may then be sealed to each other for
creating the sealed cell segment.
[0099] In certain embodiments, a gasket may be injection molded to
an electrode unit or another gasket such that they may be fused
together to create a seal.
[0100] In certain embodiments, a gasket may be ultrasonically
welded to an electrode unit or another gasket such that they may
together form a seal. In other embodiments, a gasket may be
thermally fused to an electrode unit or another gasket, or through
heat flow, whereby a gasket or electrode unit may be heated to melt
into an other gasket or electrode unit. Moreover, in certain
embodiments, instead of or in addition to creating groove shaped
portions in surfaces of gaskets and/or electrode units to create a
seal, a gasket and/or electrode unit may be perforated or have one
or more holes running through one or more portions thereof.
Alternatively, a hole or passageway or perforation may be provided
through a portion of a gasket such that a portion of an electrode
unit (e.g., a substrate) may mold to and through the gasket. In yet
other embodiments, holes may be made through both the gasket and
electrode unit, such that each of the gasket and electrode unit may
mold to and through the other of the gasket and electrode unit, for
example.
[0101] Although each of the above described and illustrated
embodiments of the stacked ESD show an ESD formed by stacking
substrates having substantially round cross-sections into a
cylindrical ESD, it should be noted that any of a wide variety of
shapes may be utilized to form the substrates of the stacked ESD of
the invention. For example, the stacked ESD of the invention may be
formed by stacking electrode units having substrates with
cross-sectional areas that are rectangular, triangular, hexagonal,
or any other desired shape or combination thereof.
[0102] It will be understood that the foregoing is only
illustrative of the principles of the invention, and that various
modifications may be made by those skilled in the art without
departing from the scope and spirit of the invention. It will also
be understood that various directional and orientational terms such
as "horizontal" and "vertical," "top" and "bottom" and "side,"
"length" and "width" and "height" and "thickness," "inner" and
"outer," "internal" and "external," and the like are used herein
only for convenience, and that no fixed or absolute directional or
orientational limitations are intended by the use of these words.
For example, the devices of this invention, as well as their
individual components, may have any desired orientation. If
reoriented, different directional or orientational terms may need
to be used in their description, but that will not alter their
fundamental nature as within the scope and spirit of this
invention. Those skilled in the art will appreciate that the
invention may be practiced by other than the described embodiments,
which are presented for purposes of illustration rather than of
limitation, and the invention is limited only by the claims that
follow.
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