U.S. patent application number 10/693789 was filed with the patent office on 2004-05-06 for multi-cell battery.
Invention is credited to Corrigan, Dennis A., Higley, Lin R., Muller, Marshall D..
Application Number | 20040086779 10/693789 |
Document ID | / |
Family ID | 24839993 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040086779 |
Kind Code |
A1 |
Higley, Lin R. ; et
al. |
May 6, 2004 |
Multi-cell battery
Abstract
A rechargeable multi-cell battery including a plurality of
electrochemical cells. Each of the cells includes a gas port that
allows passage of cell gases into and out of the cell but prevent
passage of cell electrolyte out of the cell. The gas port may be a
gas permeable membrane. The multi-cell batter may be a bipolar
battery.
Inventors: |
Higley, Lin R.; (Troy,
MI) ; Muller, Marshall D.; (Farmington, MI) ;
Corrigan, Dennis A.; (Troy, MI) |
Correspondence
Address: |
Philip H. Schlazer
Energy Conversion Devices, Inc.
2956 Waterview Drive
Rochester Hills
MI
48309
US
|
Family ID: |
24839993 |
Appl. No.: |
10/693789 |
Filed: |
October 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10693789 |
Oct 24, 2003 |
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09707009 |
Nov 6, 2000 |
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09707009 |
Nov 6, 2000 |
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09139384 |
Aug 23, 1998 |
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6255015 |
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Current U.S.
Class: |
429/86 ; 429/152;
429/185; 429/210; 429/218.2; 429/223; 429/88 |
Current CPC
Class: |
H01M 6/48 20130101; H01M
10/52 20130101; H01M 10/281 20130101; H01M 6/46 20130101; H01M
6/485 20130101; H01M 10/282 20130101; Y02E 60/10 20130101; H01M
50/24 20210101; H01M 50/30 20210101; Y02P 70/50 20151101; H01M
10/0418 20130101 |
Class at
Publication: |
429/086 ;
429/152; 429/223; 429/218.2; 429/088; 429/210; 429/185 |
International
Class: |
H01M 002/12; H01M
002/08; H01M 004/32; H01M 010/30; H01M 004/58 |
Claims
We claim:
1. A multi-cell battery, comprising: a battery case; and a
plurality of electrochemical cells housed in said battery case,
each of said cells including: at least one positive electrode, at
least one negative electrode and an electrolyte; and an enclosure
housing said at least one positive electrode, said at least one
negative electrode and said electrolyte, said enclosure including a
gas port allowing passage of cell gases into and out of said cell
but preventing passage of said electrolyte out of said cell.
2. The battery of claim 1, wherein said gas port comprises a gas
permeable material.
3. The battery of claim 1, wherein gas port comprises a hydrophobic
material.
4. The battery of claim 1, wherein said electrolyte comprises an
alkaline material.
5. The battery of claim 1, wherein said battery is a nickel-metal
hydride battery.
6. The battery of claim 1, wherein said battery is a bipolar
battery.
7. A multi-cell battery, comprising: a battery case; and a
plurality of electrochemical cells housed in said battery case,
each of said cells including: at least one positive electrode, at
least one negative electrode and an electrolyte; and an enclosure
housing said at least one positive electrode, said at least one
negative electrode and said electrolyte, said enclosure including a
gas permeable membrane allowing passage of cell gases into and out
of said cell but preventing passage of said electrolyte out of said
cell.
8. The battery of claim 7, wherein said gas permeable membrane
comprises a polymeric material.
9. The battery of claim 7, wherein said polymeric membrane
comprises a hydrophobic material.
10. The battery of claim 7, wherein said membrane comprises at
least one layer of a membrane material.
11. The battery of claim 7, wherein said membrane protrudes
outwardly from said cell.
12. The battery of claim 7, wherein said membrane comprises at
least one corrugated layer of a membrane material.
13. The battery of claim 7, wherein said plurality of cells are
electrically coupled in series.
14. The battery of claim 7, wherein said at least one negative
electrode comprises a hydrogen storage alloy.
15. The battery of claim 7, wherein said at least one positive
electrode comprises a nickel hydroxide material.
16. The battery of claim 7, wherein electrolyte comprises an
alkaline material.
17. The battery of claim 7, wherein said battery case is a common
pressure vessel for each of said electrochemical cells.
18. The battery of claim 7, wherein battery operates at a peak
pressure of at least 10 psi.
19. The battery of claim 7, wherein said enclosure is formed from
an electrically nonconductive material.
20. The battery of claim 7, wherein said enclosure comprises a
polymeric material.
21. The battery of claim 7, wherein each of said electrochemical
cells is a bipolar cell.
22. A multi-cell battery, comprising: a battery case; and a
plurality of electrochemical cells housed in said battery case,
each of said cells including: at least one positive electrode, at
least one negative electrode and an electrolyte; an enclosure
housing said at least one positive electrode, said at least one
negative electrode and said electrolyte, said enclosure having an
opening allowing passage of cell gases into and out of said cell;
and a hydrophobic material positioned relative to said opening so
as to prevent passage of said electrolyte out of said cell.
23. The battery of claim 22, wherein said hydrophobic material is
disposed along the periphery of said opening.
24. The battery of claim 22, wherein said hydrophobic material at
least partially seals said opening.
25. The battery of claim 22, wherein said opening is a circuitous
pathway formed by said hydrophobic material.
26. The battery of claim 22, wherein said hydrophobic material is
gas permeable.
27. The battery of claim 22, wherein said hydrophobic material
comprises at least one hydrophobic layer.
28. The battery of claim 22, wherein said plurality of cells are
electrically coupled in series.
29. The battery of claim 22, wherein said at least one negative
electrode comprises a hydrogen storage alloy.
30. The battery of claim 22, wherein said at least one positive
electrode comprises a nickel hydroxide material.
31. The battery of claim 22, wherein said electrolyte comprises an
alkaline material.
32. The battery of claim 22, wherein said battery case is a common
pressure vessel for each of said electrochemical cells.
33. The battery of claim 22, wherein said battery operates at a
peak pressure of at least 10 psi.
34. The battery of claim 22, wherein said enclosure is formed from
an electrically nonconductive material.
35. The battery of claim 22, wherein said enclosure comprises a
polymeric material.
36. The battery of claim 22, wherein each of said electrochemical
cells is a bipolar cell.
37. A bipolar electrochemical battery, comprising: a battery case;
and a stack of at least two serially coupled electrochemical cells
housed within said case, each of said cells comprising: a positive
electrode, a negative electrode, and an electrolyte; and an
enclosure housing said positive electrode, said negative electrode
and said electrolyte, said enclosure including a gas permeable
membrane allowing passage of cell gases into and out of said cell
but preventing passage of said electrolyte out of said cell.
38. The battery of claim 37, wherein said membrane comprises a
polymeric material.
39. The battery of claim 37, wherein said membrane comprises a
hydrophobic material.
40. The battery of claim 37, wherein said membrane comprises at
least one layer of a membrane material.
41. The battery of claim 37, wherein said membrane protrudes
outwardly from said cell.
42. The battery of claim 37, wherein said membrane comprises at
least one corrugated layer of a membrane material.
43. The battery of claim 37, wherein said at least one negative
electrode comprises a hydrogen storage alloy.
44. The battery of claim 37, wherein said at least one positive
electrode comprises a nickel hydroxide material.
45. The battery of claim 37, wherein said electrolyte comprises an
alkaline material.
46. The battery of claim 37, wherein said battery case is a common
pressure vessel for each of said electrochemical cells.
47. The battery of claim 37, wherein said battery operates at a
peak pressure of at least 10 psi.
48. The battery of claim 37, wherein said enclosure comprises a
first electrically conductive portion electrically coupled to said
at least one positive electrode and a second electrically
conductive portion electrically coupled to said at least one
negative electrode, said first conductive portion electrically
isolated from said second conductive portion.
49. The battery of claim 48, wherein said first conductive portion
and said second conductive portion comprise a polymeric
material.
50. The battery of claim 48, wherein said first and second
conductive portions comprise a carbon-filled polymeric
material.
51. The battery of claim 48, wherein adjacent cells have said first
conductive portion of one cell contacting said second conductive
portion of an adjacent cell.
52. The battery of claim 48, wherein said enclosure further
includes an electrically nonconductive polymeric material sealed
peripherally to said first and second conductive portions, said gas
permeable membrane being at least a portion of said nonconductive
material.
53. A bipolar electrochemical battery, comprising: a battery case;
and a stack of at least two serially coupled electrochemical cells
housed within said case, each of said cells comprising: at least
one positive electrode, at least one negative electrode, and an
electrolyte; and an enclosure housing said at least one positive
electrode, said at least one negative electrode and said
electrolyte, said enclosure having an opening allowing passage of
cell gases into and out of said cell; and a hydrophobic material
positioned relative to said opening so as to prevent passage of
said electrolyte out of said cell.
54. The battery of claim 1, wherein said hydrophobic material is
disposed along the periphery of said opening.
55. The battery of claim 1, wherein said hydrophobic material at
least partially seals said opening.
56. The battery of claim 1, wherein said opening is a circuitous
pathway formed by said hydrophobic material.
57. The battery of claim 1, wherein said hydrophobic material
comprises at least one hydrophobic layer.
58. The battery of claim 1, wherein said at least one negative
electrode comprises a hydrogen storage alloy.
59. The battery of claim 1, wherein said at least one positive
electrode comprises a nickel hydroxide material.
60. The battery of claim 1, wherein said battery comprises an
alkaline electrolyte.
61. The battery of claim 1, wherein said battery case is a common
pressure vessel for each of said electrochemical cells.
62. The battery of claim 1, wherein said battery operates at a peak
pressure of at least 10 psi.
63. The battery of claim 1, wherein said enclosure comprises a
first electrically conductive portion electrically coupled to said
positive electrode and a second electrically conductive portion
coupled to said negative electrode, said first conductive portion
electrically isolated from said second conductive portion.
64. The battery of claim 63, wherein said first conductive portion
and said second conductive portion comprise a polymeric
material.
65. The battery of claim 63, wherein said first conductive portion
and said second conductive portion comprise a carbon-filled
polymeric material.
66. The battery of claim 63, wherein adjacent cells have said first
conductive portion of one cell contacting said second conductive
portion of an adjacent cell.
67. The battery of claim 63, wherein said opening extends about the
entire periphery of said first and second conductive portions.
68. The battery of claim 63, wherein said hydrophobic material is
disposed along the periphery of said first and second conductive
portions.
69. The battery of claim 63, wherein said enclosure further
comprises a nonconductive polymeric portion sealed peripherally to
said first and second conductive portions.
Description
RELATED APPLICATION INFORMATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/707,009, filed on Nov. 6, 2000, which is a
continuation-in-part of U.S. patent application Ser. No.
09/139,384, filed on Aug. 8, 1998. U.S. patent application Ser. No.
09/707,009 is hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates to rechargeable
electrochemical cells. In particular, the present invention relates
to rechargeable alkaline electrochemical cells.
BACKGROUND OF THE INVENTION
[0003] Multi-cell, rechargeable batteries are used in a variety of
industrial and commercial applications such as fork lifts, golf
carts, uninterruptable power supplies, and electric vehicles.
[0004] Rechargeable lead-acid batteries are a useful power source
for starter motors for internal combustion engines. However, their
low energy density (about 30 Wh/kg) and their inability to reject
heat adequately, makes them an impractical power source for an
electric vehicles (EV), hybrid electric vehicles (HEV) and 2-3
wheel scooters/motorcycles. Electric vehicles using lead-acid
batteries have a short range before requiring recharge, require
about 6 to 12 hours to recharge and contain toxic materials. In
addition, electric vehicles using lead-acid batteries have sluggish
acceleration, poor tolerance to deep discharge, and a battery
lifetime of only about 20,000 miles.
[0005] Nickel-metal hydride batteries ("Ni--MH batteries") are
superior to lead-acid batteries and are the ideal battery available
for electric vehicles, hybrid vehicles and other forms of vehicular
propulsion. For example, Ni--MH batteries, such as those described
in U.S. Pat. No. 5,277,999, the disclosure of which is incorporated
herein by reference, have a much higher energy density than
lead-acid batteries, can power an electric vehicle over 250 miles
before requiring recharge, can be recharged in 15 minutes, and
contain no toxic materials.
[0006] Extensive research has been conducted in the past into
improving the electrochemical aspects of the power and charge
capacity of nickel-metal hydride batteries. This is discussed in
detail in U.S. Pat. Nos. 5,096,667, 5,104,617, 5,238,756 and
5,277,999, the contents of which are all incorporated by reference
herein.
[0007] Multi-cell nickel-metal hydride batteries may be packaged in
a variety of configurations. For example, individual cells may
simply be secured together with the use of end plates and a strap
to form a "bundle" of individual cells. Alternatively, the
individual cells may be all be housed within a common outer battery
case. Examples of multi-cell batteries are provided in U.S. patent
application Ser. No. 09/139,384, the disclosure of which is
incorporated herein by reference.
[0008] The electrochemical cells of multi-cell batteries may be
electrically coupled in series by conductive links, or they may be
formed in a bipolar configuration where an electrically conductive
bipolar layer serves as the electrical interconnection between
adjacent cells as well as a partition between the cells. To be
successfully utilized, the bipolar layer must be sufficiently
conductive to transmit current from cell to cell, chemically stable
in the cell's environment, capable of making and maintaining good
electrical contact to the electrodes and capable of being
electrically insulated and sealable around the boundaries of the
cell so as to contain electrolyte in the cell. Examples of bipolar
batteries are provided in U.S. Pat. Nos. 5,393,617, 5,478,363,
5,552,243, and 5,618,641, the disclosures of which are all
incorporated by reference herein.
[0009] The requirements for making high quality multi-cell
rechargeable batteries become more difficult to achieve in the case
of nickel-metal hydride batteries due to the charging potential of
the cells which can accelerate corrosion of battery components, to
the creep nature of the alkaline electrolyte that can cause
self-discharge between cells, and to the higher cell pressures
which can deform and damage the cell enclosures. The present
invention provides an improved design for rechargeable multi-cell
batteries applicable to all battery chemistries and, in particular,
to the rechargeable nickel-metal hydride chemistry.
SUMMARY OF THE INVENTION
[0010] Disclosed herein is a multi-cell battery, comprising:
[0011] a battery case; and
[0012] a plurality of electrochemical cells housed in the battery
case, each of the cells including:
[0013] at least one positive electrode, at least one negative
electrode and an electrolyte; and
[0014] an enclosure housing the at least one positive electrode,
the at least one negative electrode and the electrolyte, the
enclosure including a gas port allowing passage of cell gases into
and out of the cell but preventing passage of the electrolyte out
of the cell.
[0015] Disclosed herein is a multi-cell battery, comprising:
[0016] a battery case; and
[0017] a plurality of electrochemical cells housed in the battery
case, each of the cells including:
[0018] at least one positive electrode, at least one negative
electrode and an electrolyte; and
[0019] an enclosure housing the at least one positive electrode,
the at least one negative electrode and the electrolyte, the
enclosure including a gas permeable membrane allowing passage of
cell gases into and out of the cell but preventing passage of the
electrolyte out of the cell.
[0020] Also disclosed herein is a multi-cell battery,
comprising:
[0021] a battery case; and
[0022] a plurality of electrochemical cells housed in the battery
case, each of the cells including:
[0023] at least one positive electrode, at least one negative
electrode and an electrolyte;
[0024] an enclosure housing the at least one positive electrode,
the at least one negative electrode and the electrolyte, the
enclosure having an opening allowing passage of cell gases into and
out of the cell; and
[0025] a hydrophobic material positioned relative to the opening so
as to prevent passage of the electrolyte out of the cell.
[0026] Also disclosed herein is a bipolar electrochemical battery,
comprising:
[0027] a battery case; and
[0028] a stack of at least two serially coupled electrochemical
cells housed within the case, each of the cells comprising:
[0029] at least one positive electrode, at least one negative
electrode, and an electrolyte; and
[0030] an enclosure housing the at least one positive electrode,
the at least one negative electrode and the electrolyte, the
enclosure including a gas permeable membrane allowing passage of
cell gases into and out of the cell but preventing passage of the
electrolyte out of the cell.
[0031] Also disclosed herein is a bipolar electrochemical battery,
comprising:
[0032] a battery case; and
[0033] a stack of at least two serially coupled electrochemical
cells housed within the case, each of the cells comprising:
[0034] at least one positive electrode, at least one negative
electrode, and an electrolyte; and
[0035] an enclosure housing the at least one positive electrode,
the at least one negative electrode and the electrolyte, the
enclosure having an opening allowing passage of cell gases into and
out of the cell; and
[0036] a hydrophobic material positioned relative to the opening so
as to prevent passage of the electrolyte out of the cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 shows a multi-cell bipolar battery of the present
invention;
[0038] FIG. 2A shows a cross-sectional view, parallel to the width,
of a bipolar wafer cell of the present invention;
[0039] FIG. 2B shows a cross-sectional view, parallel to the
length, of a bipolar wafer cell of the present invention;
[0040] FIG. 2C shows a three-dimensional view of a bipolar wafer
cell of the present invention;
[0041] FIG. 3 shows a cross-section view of a bipolar wafer cell
with a double-layer gas permeable membrane;
[0042] FIG. 4 shows a cross-section view of a bipolar wafer cell
with a gas permeable membrane that protrudes outwardly from the
cell;
[0043] FIG. 5 shows a cross-sectional view of a bipolar wafer cell
with a corrugated gas permeable membrane;
[0044] FIG. 6 shows a three-dimensional view of a cell enclosure
having an opening with a hydrophobic border;
[0045] FIG. 7 shows a cross-sectional view of a bipolar wafer cell
wherein a hydrophobic material is arranged so that there is an
opened circuitous pathway between the interior and exterior of the
wafer cell;
[0046] FIG. 8 shows a three-dimensional view of a bipolar cell
having a hydrophobic material around the perimeter of the bipolar
plates; and
[0047] FIG. 9 shows a cross-sectional view of a multi-cell battery
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The present invention is directed to an electrochemical
battery comprising a plurality of electrochemical cells disposed in
a common pressure vessel. Each electrochemical cell includes a
specially designed gas port which permits the passage of the cell
gases into and out of the cell but which prevents the passage of
cell electrolyte out of the cell. In one embodiment, this gas port
is in the form of a gas permeable membrane that allows the cell
gases to pass into and out of the cell but which prevents passage
the cell electrolyte out of the cell.
[0049] In one embodiment of the present invention, the
electrochemical battery is a bipolar battery. FIG. 1 shows a
bipolar battery 30 of the present invention. The bipolar battery
comprises a plurality of serially coupled electrochemical cells 1
all housed within a common battery case 20. Each of the
electrochemical cells 1 shown in FIG. 1 is referred to herein as a
"wafer cell". The wafer cell 1 is specially designed so that the
plurality of such cells can be easily "stacked" together
side-by-side in a bipolar configuration. The battery case 20 serves
as a common pressure vessel for each of the electrochemical cells 1
wherein gases from each of the individual wafer cells 1 are
released by each of the cells by way of the gas permeable membrane
9 and are shared within the case 20.
[0050] The battery case 20 may be sealed to avoid the loss of cell
gases from the interior of the case 20. A resealable vent 18, set
to release gases above a maximum operating pressure, may be used to
safely deal with any excessive gas generation during operation.
[0051] FIG. 2A is a two-dimensional, cross-sectional view of an
embodiment of single wafer cell 1 through the width "W" of the
cell. The width "W" of the cell is parallel to the plane of the
illustration. The length "L" of the cell is perpenducular to the
plane of the illustration. FIG. 2B is a two-dimensional,
cross-section view of the same wafer cell through the length "L" of
the cell. That is, the length "L" is parallel to the plane of the
illustration of FIG. 2B. FIG. 2C is a three-dimensional view of the
same wafer cell 1. The wafer cell 1 includes a positive electrode 4
and a negative electrode 5. The positive and negative electrodes 4,
5 are prevented from making direct physical contact by a separator
6 which is disposed between the electrodes 4,5. The electrochemical
cell further includes an electrolyte which wets the electrodes 4, 5
and the separator 6. The separator 6 may be porous so as to absorb
the electrolyte. The separator material may be formed of synthetic
resin fibers (such as polyamide), polypropylene fibers or a
combination thereof. The separator between the electrodes typically
has a porous structure capable of absorbing and holding the
electrolyte within the cell. In one embodiment of the invention the
separator includes two layers of non-woven polypropylene.
[0052] Generally, the electrolyte may be an aqueous or a nonaqueous
electrolyte. An example of a nonaqueous electrochemical cell is a
lithium-ion cell which uses intercalation compounds for both anode
and cathode and a liquid organic or polymer electrolyte. Aqueous
electrochemical cells may be classified as either "acidic" or
"alkaline". An example of an acidic electrochemical cell is a
lead-acid cell which uses lead dioxide as the active material of
the positive electrode and metallic lead, in a high-surface area
porous structure, as the negative active material. Examples of
alkaline electrochemical cells are nickel cadmium (Ni--Cd) cells
and nickel-metal (Ni--MH) hydride cells.
[0053] Preferably, the electrochemical cells of the present
invention are alkaline electrochemical cells. The alkaline
electrolyte may be an aqueous solution of an alkali hydroxide.
Preferably, the alkaline electrolyte includes an aqueous solution
of potassium hydroxide, sodium hydroxide, lithium hydroxide or
mixtures thereof. The alkaline electrolyte may be a mixed hydroxide
of potassium and lithium hydroxide. In the one embodiment of the
present invention, the alkaline electrochemical cell is a
nickel-metal hydride cell (Ni--MH) having a negative electrode 5
comprising a hydrogen storage material that can electrochemically
and reversibly store hydrogen and a positive electrode 4 comprising
a nickel hydroxide active material. Various active materials for
the positive and the negative electrodes are discussed in more
detail below.
[0054] The positive and negative electrodes are contained between a
first electrically conductive outer layer 2 and a second
electrically conductive outer layer 3. The first conductive outer
layer 2 is a "first conductive portion" of the enclosure of the
wafer cell. Likewise, the second conductive outer layer 3 is "a
second conductive portion" of the enclosure of the wafer cell. The
first and second conductive portions of the enclosure are
electrically isolated from one another.
[0055] Generally, the conductive outer layers 2 and 3 may be formed
of any conductive material including, but not limited to, metals
(for example, nickel or a nickel alloy) and conductive polymers.
Preferably, the conductive outer layers 2 and 3 are each formed of
a conductive polymer. The conductive polymer may be a carbon-filled
polymeric material. An example of a carbon-filled plastic is
provided in U.S. Pat. No. 4,098,976, the disclosure of which is
incorporated by reference herein. The plastic material may be
filled with a finely divided carbon (such as a vitreous carbon,
carbon black or carbon in graphite form) to form a non-corrosive,
liquid-impervious, conductive layer. It is also possible to form
the conductive polymeric material by filling a plastic material
with a finely divided metal such a nickel. The materials chosen for
the conductive outer layers are impermeable to the cell electrolyte
so as to prevent the electrolyte that is within each cell from
leaving the cell.
[0056] The conductive outer layers 2 and 3 make electrical contact
to the positive and negative electrodes 4 and 5, respectively. The
conductive outer layer 2 is preferably adjacent to (and most
preferably adjoins) the positive electrode 4 and the conductive
outer layer 3 is preferably adjacent to (and most preferably
adjoins) the negative electrode 5. In order to enhance the
electrical contact between the electrodes and the outer layers, a
conductive paste or cement may be used between each of the
conductive polymeric outer layers and the respective electrode with
which it is in electrical contact. The conductive outer layer 2 is
also referred to as the "positive face" of the wafer cell 1 and the
conductive outer layer 3 is also referred to as the "negative face"
of the wafer cell 1.
[0057] In the embodiment of the wafer cell shown in FIG. 2A, the
positive electrode 4, the negative electrode 5, the separator 6,
and the two outer layers 2, 3 are all substantially flat and are
preferably in tight physical and electrical contact with the
adjacent components. The design illustrated in FIG. 2A permits
construction of a wafer cell which is relatively thin.
[0058] Furthermore, in the embodiment of the wafer cell shown in
FIG. 2A, the wafer cell 1 comprises a single positive electrode 4
and a single negative electrode 5. However, other configurations
are possible wherein a wafer cell comprises a plurality of positive
and a plurality of negative electrodes to increase cell capacity
and/or electrode area. In this case the positive and negative
electrodes may include tabs or current collectors which
electrically connect all of the negative electrodes together and
which electrically connect all of the positive electrodes
together.
[0059] In order for the electrodes, the separator and the
electrolyte to be contained within an enclosed wafer cell, the
conductive polymeric outer layers 2 and 3 preferably have a
physical area which is larger than the area of the electrodes 4 and
5. That is, the perimeter of the outer layers 2, 3 preferably
extends beyond the perimeter of the respective adjacent electrode
4, 5. This is shown in FIG. 2B. Also, in the embodiment of the cell
shown in FIG. 2B, the perimeter of the separator 6 also extends
beyond the perimeter of the electrodes 4, 5.
[0060] Referring to FIGS. 2A-C, it is seen that the enclosure of
the wafer cell 1 includes a nonconductive polymeric material 7
which is sealed peripherally to the conductive outer layers 2 and 3
to form a nonconductive border 7 around at least a portion of the
perimeter of the wafer cell. In the embodiment shown in FIGS. 2A-C,
the nonconductive border 7 is formed around the bottom and the
sides of the perimeter of the wafer cell. The nonconductive border
7 physically separates and electrically isolates the two conductive
outer layers 2 and 3.
[0061] Generally, the nonconductive border 7 may be formed of any
nonconductive material which is inert to the electrochemical
environment of the cell and which is also impermeable to the cell
electrolyte. Preferably, the nonconductive material is a
nonconductive polymer. The nonconductive polymer may include
polypropylene and/or a vinyl polymer. It may further include a
strength enhancing filler material. The nonconductive border
material 7 may be sealed to the conductive outer layers 2, 3 via
adhesive. Alternately, the nonconductive polymer 7 may be a
thermoplastic which can be heat sealed to the perimeter of the
conductive outer layers 2 and 3.
[0062] As discussed, in the embodiment of the wafer cell shown in
FIGS. 2A-C, the nonconductive border material 7 is sealed around at
least a portion of the perimeter of the wafer cell. In the
particular embodiment shown, the nonconductive material 7 is sealed
around the bottom portion and the side portions of the perimeter of
the wafer cell. The remaining portion of the perimeter of the wafer
cell (i.e., the portion of the perimeter not covered by the
nonconductive material 7) is sealed by a gas permeable material 9
which allows passage of the cell gases out of and into the wafer
cell but which prevents the passage of the cell electrolyte. This
gas permeable region of the enclosure forms a gas port for the cell
which allows the gases to freely flow into and out of the cell but
which prevents the cell electrolyte from leaving the cell. In one
embodiment of the invention, the gas permeable material is in the
form of a gas permeable membrane.
[0063] The membrane material 9 is formed from a material which is
permeable to the cell gases so as to allow the cell gases to go out
of and into the wafer cell. However, the membrane material is also
preferably impermeable to the cell electrolyte thereby preventing
the electrolyte from leaving the cell. More preferably, the
membrane material is a hydrophobic material.
[0064] As discussed, the electrolyte used is preferably an alkaline
electrolyte. Hence, the membrane material is preferably one which
is impermeable to an alkaline electrolyte. The hydrophobic nature
of the material used is preferably "electrolyte-phobic" and more
preferably "alkaline-phobic". Hence, the material is preferably one
which is not readily wetted by the electrolyte and is more
preferably one which is not readily wetted by an alkaline
electrolyte. In one embodiment, the wetting or contact angle of the
membrane material is preferably greater than about 90.degree..
Furthermore, the membrane material is also preferably a
nonconductive material. Hence, the membrane material may form all
or a portion of the nonconductive border around the perimeter of
the wafer cell.
[0065] Preferably, the membrane material comprises a polymeric
material. In particular, the material may comprise a polymeric
material that is modified with the addition of an inorganic salt
such as a calcium carbonate. An example of a material which may be
used is the breathable type XBF-100W EXXAIRE film that is supplied
by Tridegar products. This film is a polyethylene film that has
been mixed with fine calcium carbonate particles and then further
stretched to make it porous. In one embodiment, the layer is chosen
to have a thickness of about 0.25 gauge (0.25 g per square meters),
which corresponds to about 0.001 inch. The Gurley porosity of the
material is chosen to be about 360 (360 seconds for 100 cc of gas
to pass per square inch with a gas pressure of 4.9 inches of
water). The hydrophobic nature of this film is demonstrated by a
very high contact angle in 30% KOH electrolyte of about 120
degrees.
[0066] It is noted that it is also possible to form the gas
permeable membrane from a material which is not polymeric. For
example, the membrane may be formed from an inorganic salt such as
calcium carbonate or calcium fluoride. The salt may be made into a
particulate and the particles may be pressed together to form a
porous body. This porous body can serve as the gas permeable
membrane.
[0067] As noted, in addition to being gas permeable, the material
used for the membrane 9 is preferably nonconductive so as to insure
electrical isolation between the first conductive layer 2 and
second conductive layer 3. Hence, the gas exchange membrane may
comprise a nonconductive polymer.
[0068] In the embodiments shown in FIGS. 2A-C, the membrane
material 9 is sealed across a top portion of the wafer cell 1. The
membrane material 9 is sealed to the nonconductive border material
7 as well as to the conductive polymeric outer layers 2, 3. Sealing
is preferably accomplished by heat sealing, although other means
(such as adhesive) is also possible. The membrane material 9, the
nonconductive border material 7, and the first and second
conductive outer layers 2 and 3 form an enclosure for the wafer
cell 1 that houses the pair of electrodes, the separator and the
electrolyte. The first conductive outer layer 2 forms a first
conductive portion of this enclosure. Likewise, the second
conductive outer layer 3 forms a second conductive portion of this
enclosure. The first and the second conductive portions are
electrically isolated from each other by the nonconductive border
material 7 and by the membrane material 9. The enclosure shown in
FIGS. 2A-C completely surrounds the electrodes 4,5, the separator 6
and the electrolyte.
[0069] In the embodiment of the wafer shell shown in FIGS. 2A-C,
the membrane material 9 is positioned on a top portion of the
border around the perimeter of the wafer cell. However, the
membrane material 9 may be positioned anywhere on the border along
the perimeter of the cell between the first and second conductive
portions. In an alternate embodiment, the wafer cell may include a
plurality of separate membranes positioned various places around
the border of the wafer cell. In yet another embodiment of the
invention, the entire border of the wafer cell may be formed of the
membrane material 9. In still another embodiment of the invention,
it is possible that one or more openings may be placed in the
conductive outer layers 2, 3 and these openings may be at least
partially covered by the membrane material 9.
[0070] In the embodiment of the wafer cell shown in FIGS. 2A-C, the
gas permeable membrane 9 is formed as a single layer of membrane
material. Generally, the thickness of the layer is not limited to
any particular dimension. Moreover, other configurations for the
gas permeable membrane are also possible. For example, as shown in
FIG. 3, to provide additional reliability the gas port membrane 9
comprises a plurality of layers of membrane material. In another
embodiment, as shown in FIG. 4, the gas port membrane 9 is formed
as one or more layers of membrane material that are shaped to
protrude outwardly from the opening of the cell so as to provide
additional surface area. In still another embodiment, as shown in
FIG. 5, the membrane 9 is formed as one or more corrugated layers
of membrane material. The corrugated shape also provides for
additional surface area. Generally, the gas permeable membrane is
not limited to any particular size or shape.
[0071] In addition to functioning as a gas port for the wafer cell,
the gas permeable membrane also provides for a convenient means of
filling the wafer cell with electrolyte. For example, the wafer
cell may be filled with electrolyte via a syringe inserted through
the membrane material. As noted, the membrane material is
preferably hydrophobic and the hydrophobic nature of the material
will prevent electrolyte from flowing through the small holes or
openings produced by the insertion of the syringe needle. Hence,
holes or openings (even those large enough to allow gases as well
as electrolyte to pass) may be poked into the membrane and the
hydrophobic nature of the membrane material will still break the
wicking path of the electrolyte so as to prevent the electrolyte
from passing through.
[0072] An alternate embodiment of the wafer cell 1 of the present
invention is shown in FIG. 6 (note that for simplicity, the
electrodes and separator are not shown). In this embodiment, like
those shown in FIGS. 2A-C, 3, 4, 5, the nonconductive border
material 7 is sealed peripherally to the conductive outer layers 2
and 3 to form a nonconductive border 7 around a portion of the
perimeter of the cell (and, in the particular embodiment, around
the bottom and the sides of the perimeter of the wafer cell). The
nonconductive border portion 7 and the conductive outer layers 2, 3
form a cell enclosure with an opening 10. The opening 10 is sized
to allow the passage of the cell gases into and out of the
enclosure, and it may also be sized to allow passage of the
electrolyte as well. In this embodiment, a hydrophobic material 11
is placed around the inside perimeter of the opening 10 to form a
hydrophobic border around the perimeter of opening 10. As discussed
above, an electrolyte path between individual wafer cells may occur
by electrolyte "wicking" or "creep" along the first and second
conductive portions 2 and 3, thereby causing self-discharge by the
ion transfer through the electrolyte path. The hydrophobic border
11 is used to break the wicking path of the electrolyte, thereby
preventing the electrolyte from leaving the cell. In the embodiment
shown in FIG. 6, the cell gases are free to flow into and out of
the wafer cell through the opening 10. More generally, a
hydrophobic material may be positioned relative to the opening in
the enclosure so as to prevent passage of the electrolyte while
still allowing the passage of gases into and out of the enclosure
through the opening. The hydrophobic material may partially or
totally cover the opening. If the hydrophobic material totally
covers the opening, then it should also be gas permeable in order
to allow the cell gases to exit and enter the cell.
[0073] As another example, the hydrophobic material 11 may be
arranged as shown in FIG. 7 so that the opening 10 takes the form
of a circuitous or labyrinthine pathway between the interior and
the exterior of the enclosure of wafer cell 1. This may be
accomplished in many different ways. An example of one possible way
is by rolling together layers of hydrophobic material (such as
rolling up the opened end of a bag).
[0074] Yet another embodiment of the invention is shown in FIG. 8.
In this embodiment, the bipolar electrochemical cell 1 comprises a
first conductive outer layer 2 and the second outer conductive
layer 3. Disposed between the two outer conductive layers is the
positive electrode 4, the electrolyte filled separator 6 and the
negative electrode 5. In this embodiment, the enclosure for the
cell consists of the first and second conductive outer layers 2, 3
while the entire periphery around the bipolar cell is an opening
that permits the cell gases to freely leave and enter the cell. It
is noted that in this case, the enclosure formed by the first and
second outer layers 2, 3 does not completely surround the cell. A
hydrophobic material 11 is disposed around the periphery of the
first and second outer layers 2, 3 (i.e., preferably around the
periphery on the side of the conductive outer layers 2,3 facing the
electrodes 4,5) so as to form a hydrophobic border around each of
the conductive outer layers 2, 3. The hydrophobic border placed
around entire perimeter of each of the conductive outer layers 2, 3
breaks the wicking path of the electrolyte and prevents the
electrolyte from leaving the interior of the cell.
[0075] It is again noted that, in a preferred embodiment of the
present invention, the electrolyte used is an alkaline electrolyte.
Hence, the hydrophobic material used to break the wicking path of
the electrolyte is thus preferably one that is capable of breaking
the wicking path of an alkaline material.
[0076] Referring again to FIG. 1, shown is a multi-cell bipolar
battery 20 made by stacking several wafer cells 1. The wafer cells
are electrically arranged in series with the positive face of each
cell (that is, outer layer 2) contacting the negative face of the
adjacent cell (that is, outer layer 3). Hence, electrical current
is carried between the adjacent wafer cells though the outer layers
2 and 3. The end cells have metal foil contacts, 14 and 15 which
conduct the electric current from the battery stack to the positive
battery terminal 24 and negative battery terminal 25, respectively.
The cell-to-cell contact or the contact between the end cells and
the metal foil contacts may be enhanced by use of a conductive
paste or cement. The bipolar battery stack assembly may be held in
compression to insure uniform physical contact between the adjacent
cells and between the respective layers within each cell.
[0077] In the embodiment shown in FIG. 1, the electrical current is
carried between the adjacent cells through the outer layer 2 and 3
without the use of additional tabs or current collectors that add
additional weight, complexity and resistance to the cell. However,
it is within the scope of the present invention that external tabs
or current collectors could be used in addition to or instead of
the conductive outer layers 2, 3 to electrically couple one cell to
the next. An embodiment of the present invention which uses
electrode tabs and interconnects to electrically connect individual
cells is provided below.
[0078] As shown in FIG. 1, the stack of wafer cells is housed in an
outer battery case 20. The battery case 20 is preferably sealed to
avoid the loss of gases from the case. A resealable vent 18, set to
release gases above a maximum operating pressure, may be used to
safety vent internal gases. Each of the electrochemical cells is in
gaseous communication with a common region 22 which is exterior to
each of the cells but interior to the battery case. Hence, gas
generated by each of the electrochemical cells 1 exits the interior
of the cell through the gas port membrane 9 and is free to
circulate within the common region 22. The cell gases are also free
to re-enter the interior of the cells from the common region 22
(also through the gas port polymeric membrane 9). Hence, the single
battery case 20 forms a common pressure vessel for all of the
electrochemical cells.
[0079] Hence, the membrane 9 serves as a gas port for the wafer
cell, allowing passage of cell gases into and out of the cell but
preventing passage of the cell electrolyte. The membrane gas port 9
is important for equalizing the pressures between the regions
inside the cell enclosures and the region 22 within battery case 20
that is outside of the cell enclosures. To avoid mechanical
stresses within the battery, an equalization of pressure is also
sought within all cell gas cavities within battery case 20. The
membrane gas port 9 allows cell gases to flow out of the cell
enclosures as cell gases are generated during battery operation,
especially during charge at high states of charge. In addition, the
membrane gas port allows cell gases to pass into the cell as cell
gases are consumed from recombination processes, especially during
battery operation after completion of charge. Additionally, the
membrane gas port 9 is highly reliable against electrolyte leakage
between the wafer cells so as to avoid the formation of
electrolytic shorting paths between cells.
[0080] The necessary functions of a gas port for the wafer cell 1
are better achieved by the gas permeable membrane 9 of the present
invention than by a conventional resealable mechanical vent that is
typically used in the battery industry. The gas permeable membrane
9 of the present invention does not prevent the cell from venting
below a given maximum operating pressure. This is neither necessary
nor desirable in the present invention. The membrane gas port is
simpler and less expensive than a mechanical vent. It also has a
smaller size (i.e., the membrane may be made extremely narrow)
thereby enabling the stacking of very thin wafer cells into a
battery case without interference by mechanical vents. Furthermore,
the membrane gas port is more reliable that a conventional
mechanical vent. Mechanical vents are prone to electrolyte leakage
and as well as to failure during repeated use. Additionally,
mechanical vents tend to be "one-way" valves so that it may be
necessary to install two vents on each wafer cell in order to allow
passage of cell gases both into and out of the cells.
[0081] As noted, battery case 20 serves as a common pressure vessel
for each of the individual cells. The operating pressure within the
battery case 20 may be maintained below a maximum operating
pressure by a resealable pressure vent 18. This greatly reduces the
mechanical strength requirements for the cell enclosures and
enables the use of lightweight and inexpensive components that do
not need to withstand significant pressures. The pressure of the
common pressure vessel is contained by battery case 20, which does
need to be constructed with sufficient mechanical strength in order
to withstand the maximum operation pressure of the battery. In one
embodiment of the invention, the battery may operate at a peak
pressure of at least 10 psi, preferably at a peak pressure of at
least 25 psi and more preferably at a peak pressure of at least 50
psi. In another embodiment of the invention, the battery may
operate at peak pressures up to about 140 psi. Hence, it is
preferable that an embodiment of the multi-cell battery case should
be able to withstand peak operating pressures from about 10 psi to
about 140 psi. Of course, the multi-cell battery and the battery
case of the present invention are not limited to such operating
pressures.
[0082] The battery case 20 is preferably formed of a nonconductive
material. Examples of nonconductive materials include plastics and
ceramics. Alternately, it is possible that the battery case be
formed from a metal such as from a stainless steel (however, in
this case, the battery terminals 25, 25 should be electrically
insulated from the steel case). The battery case 20 may comprise a
container, a lid, and battery terminals. The battery terminals 24,
25 provide electrical connection to the electrically interconnected
cells within the case. The battery terminals may comprise a metal
foil material electrically connected to the interconnected
electrochemical cells within the case. The metal foil material may
comprise a copper and/or nickel laminated foil material. The
battery case lid may include a nonconductive material to isolate
the battery terminals from a stainless steel case. This
nonconductive material may be a phenolic glass material which can
be attached to the case lid by an adhesive.
[0083] In the embodiment of the battery 30 shown in FIG. 1, the
battery is a bipolar battery. In particular, the electrochemical
cells are wafer cells 1 that are arranged in a bipolar
configuration. The cells are arranged in electrical series such
that the positive face (conductive outer layer 2) of each cell
contacts the negative face (conductive outer layer 3) of an
adjacent cell. The adjacent outer layers 2, 3 form the bipolar
plates of the bipolar battery. The electrical current is carried
between the adjacent cells though the conductive outer layers 2 and
3 without the use of additional tabs or current collectors that add
additional weight, complexity and resistance to the cell. However,
it is within the scope of the present invention that external tabs
or current collected could be used in addition to or instead of the
conductive outer layers 2, 3 or instead of the conductive outer
layers 2, 3. It is also noted that it is possible that other forms
of bipolar cells may be used to form the bipolar battery. (For
example, it is possible that adjacent first and second conductive
outer layers 2, 3 be replaced by a single bipolar plate. The
bipolar plate could be a single layer of conductive polymer.)
[0084] An embodiment of the present invention which uses electrode
tabs and interconnects to connect individual cells is shown in FIG.
9. FIG. 9 shows an electrochemical battery 40 comprising a
plurality of serially coupled electrochemical cells 101 housed
within a battery case 20. Each of the electrochemical cells
includes at least one positive electrode 4, at least one negative
electrode 5, and electrolyte. Each cell also preferably includes
separators 6 disposed between the positive electrodes 4 and the
negative electrodes 5.
[0085] A cell enclosure 27 accommodates the positive electrodes 4,
the negative electrodes 5, the electrolyte and the separators 6 of
each of the electrochemical cells. Generally, the cell enclosure 27
may be formed any material which will not be corroded by the
electrolyte. Examples of materials include, not are not limited to,
plastics, ceramics and metals (such as stainless steel) . If a
metal is used, the metal should be electrically insulated from the
cell interconnects 37. Preferably, the enclosure is formed from a
nonconductive material such as a nonconductive polymer or
ceramic.
[0086] In one embodiment, the cell enclosure 27 is formed from a
nonconductive polymeric material. Preferably, the polymeric
material is impermeable to the passage of the cell electrolyte;
however, it may be permeable to the cell gases. An example of a
nonconductive polymeric material which may be used is a
polypropylene. In one example, the cell enclosure 27 is formed from
a polypropylene bag.
[0087] The cell enclosure 27 includes the gas port of the present
invention which allows passages of the cell gases into and out of
the cell but which prevent passage of the cell electrolyte out of
the cell. In the embodiment shown in FIG. 9, the gas port is the
gas permeable membrane 9. Alternately, as described above, the gas
port may be formed as an opening in the enclosure which allows
passage of the cell gases into and out of the enclosure. A
hydrophobic material is positioned relative to the opening so as to
prevent passage of the electrolyte out of the cell. The entire
discussion of the gas port, as well as the configurations of the
membrane and hydrophobic materials shown in FIGS. 2A-C, 3-7 are, of
course, all applicable to the multi-cell battery, such as the one
shown in FIG. 9.
[0088] FIG. 9 also shows current collection tabs 30a and 30b
connected to each of the positive and negative electrodes. In FIG.
9, the tabs 30a are connected to each of the positive electrodes,
and the tabs 30b are connected to each of the negative electrodes.
All of the current collection tabs 30a are joined together to form
a "positive interconnect" 35a. As well, all of the negative tabs
30b are joined together to form a "negative interconnect" 35b.
Preferably, the tabs are mechanically joined together by welding.
As noted, the individual electrochemical cells are electrically
interconnected. Each cell may be electrically connected to another
cell either in series or in parallel. Preferably, all of the cells
are serially electrically connected together. The electrochemical
cells may be electrically connected in series through the
enclosures by electrically connecting the positive interconnect of
one cell to the negative interconnect of the next cell. A serial
interconnection between cells is shown in FIG. 9. FIG. 9 shows 3
electrochemical cells 101A, 101B, and 101C that have been serially
coupled together. As serial interconnection is achieved by
connecting the negative interconnect 35b of the cell 101A to the
positive interconnect 35a of the next adjacent cell 101B. The
negative interconnect of the cell 101B is electrically connected to
the positive interconnect of the cell 101C.
[0089] Preferably, the positive and negative interconnects 35a and
35b are electrically connected by welding the interconnect
together. A "connection spacer" 37 may be welded between the
interconnects to provide distance between adjacent electrochemical
cells. The connection spacer 37 may comprise nickel, copper, a
nickel alloy, a copper alloy, a nickel-copper alloy, a
copper-nickel alloy. Further the connection spacer may comprise
both copper and nickel. For example, the connection spacer may
comprise nickel-plated copper, or the connection spacer may
comprise a copper control portion surrounded by nickel.
Alternatively, the connector may comprise a copper cylinder which
is wrapped with a nickel wire. The electrical connection is
accomplished through the cell enclosures. The region where the
interconnects are joined together is called the "interconnection
region". It is possible that electrolyte can escape from each cell
enclosure at the interconnection region. To prevent the escape of
electrolyte, each cell enclosure is sealed at the interconnection
region by an "interconnection region seal". The interconnection
region seal may include a polymer gasket such as an EDPM rubber
gasket. Furthermore, the interconnection region seal may be
selected from the group consisting of a hot melt adhesive, and an
epoxy adhesive.
[0090] The electrochemical cells 101A,B,C are housed in a battery
case 20 having positive and negative electrode 24, 25. The battery
case 20 preferably also has a resealable vent 18. The battery case
20 was described above and that discussion is, of course,
applicable to the embodiment shown in FIG. 9.
[0091] In the electrochemical cells of the present invention, the
positive electrode may comprise any active positive electrode
material. Likewise, the negative electrode may comprise any active
negative electrode material. Examples of positive electrode
materials are powders of lead oxide, lithium cobalt dioxide,
lithium nickel dioxide, lithium nickel dioxide, lithium manganese
oxide compounds, lithium vanadium oxide compounds, lithium iron
oxide, lithium compounds, i.e., complex oxides of these compounds
and transition metal oxides, manganese dioxide, nickel oxide,
nickel hydroxide, manganese hydroxide, copper oxide, molybdenum
oxide, carbon fluoride, etc. Preferably, the positive active
material is a nickel hydroxide material. Examples of negative
electrode materials include metallic lithium and like alkali
metals, alloys thereof, alkali metal absorbing carbon materials,
zinc, cadmium hydroxide, hydrogen storage alloys, etc. Preferably,
the active negative electrode material is a hydrogen storage alloy.
It is within the spirit and intent of this invention that any
hydrogen storage alloy can be used. It is noted that as used
herein, the terminology "hydrogen storage alloy" and "hydrogen
absorbing alloy" may be used interchangeably.
[0092] Some extremely efficient electrochemical hydrogen storage
alloys were formulated, based on the disordered materials described
above. These are the Ti--V--Zr--Ni type active materials such as
disclosed in U.S. Pat. No. 4,551,400 ("the '400 Patent") the
disclosure of which is incorporated herein by reference. These
materials reversibly form hydrides in order to store hydrogen. All
the materials used in the '400 Patent utilize a generic Ti--V--Ni
composition, where at least Ti, V, and Ni are present and may be
modified with Cr, Zr, and Al. The materials of the '400 Patent are
multiphase materials, which may contain, but are not limited to,
one or more phases with C.sub.14 and C.sub.15 type crystal
structures.
[0093] Other Ti--V--Zr--Ni alloys, also used for rechargeable
hydrogen storage negative electrodes, are described in U.S. Pat.
No. 4,728,586 ("the '586 Patent"), the contents of which is
incorporated herein by reference. The '586 Patent describes a
specific sub-class of Ti--V--Ni--Zr alloys comprising Ti, V, Zr,
Ni, and a fifth component, Cr. The '586 Patent, mentions the
possibility of additives and modifiers beyond the Ti, V, Zr, Ni,
and Cr components of the alloys, and generally discusses specific
additives and modifiers, the amounts and interactions of these
modifiers, and the particular benefits that could be expected from
them. Other hydrogen absorbing alloy materials are discussed in
U.S. Pat. Nos. 5,096,667, 5,135,589, 5,277,999, 5,238,756,
5,407,761, and 5,536,591, the contents of which are incorporated
herein by reference.
[0094] Both the positive and negative electrodes may be either
non-paste type or a paste-type electrodes. The positive and
negative electrodes may be fabricated as paste-type electrodes by
mixing the active materials with a binder. The mixing may be done
with a liquid (i.e., wet mixing) or without a liquid (i.e., dry
mixing) to form a cohesive structure in which the active particles
are embedded.
[0095] The active materials may be applied to conductive substrates
to form the electrodes. It is possible to apply the active mixture
to a separate conductive support structure (such as a conductive
foam, mesh, expanded metal, perforated metal, etc).
[0096] Alternatively, referring again to the embodiment the bipolar
battery wafer cell shown in FIG. 2A, it is noted that the positive
electrode 4 may simply be a positive active material which is
affixed to the inner surface of the first conductive outer layer 2.
Likewise, the negative electrode 5 may simply be a negative active
material which is affixed to the inner surface of the second
conductive outer layer 3. The conductive outer layers 2, 3 may be
textured to provide appropriate support for the active
material.
[0097] As noted above, in one embodiment of the present invention,
each electrochemical cell is a nickel-metal hydride cell comprising
negative electrodes including hydrogen storage materials as the
active material, and positive electrodes including nickel hydroxide
active material.
[0098] Hence, in an embodiment of the present invention, the
multi-cell battery is a nickel-metal hydride multi-cell battery.
The multi-cell battery of the present invention may thus operate at
pressures of at least the standard operating pressures of a sealed
nickel-metal hydride battery. This may vary depending upon the
actual hydrogen storage alloys, nickel hydroxide materials used as
the active materials. In one embodiment of the invention, the
multi-cell battery may operate at a peak pressure of at least 10
psi, preferably at a peak pressure of at least 25 psi and more
preferably at a peak pressure of at least 50 psi. In another
embodiment of the invention, the multi-cell battery may operate at
peak pressures up to about 140 psi. Hence, it is preferable that an
embodiment of the multi-cell base case (such as the case 20 shown
in FIGS. 1 and 9) should be able to withstand peak operating
pressures from about 10 psi to about 140 psi. Of course, the
multi-cell battery and multi-cell case of the present invention are
not limited to such operating pressures.
[0099] While the invention has been described in connection with
preferred embodiments and procedures, it is to be understood that
it is not intended to limit the invention to the preferred
embodiments and procedures. On the contrary, it is intended to
cover all alternatives, modifications and equivalence which may be
included within the spirit and scope of the invention as defined by
the claims appended hereinafter.
* * * * *