U.S. patent application number 11/367331 was filed with the patent office on 2006-07-13 for composite material and current collector for battery.
This patent application is currently assigned to Firefly Energy Inc.. Invention is credited to Kurtis C. Kelley, Matthew J. Maroon, Charles F. Ostermeier.
Application Number | 20060151756 11/367331 |
Document ID | / |
Family ID | 32593343 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151756 |
Kind Code |
A1 |
Kelley; Kurtis C. ; et
al. |
July 13, 2006 |
Composite material and current collector for battery
Abstract
A composite material including a first carbon foam structure
including a network of pores and a second carbon foam structure
including a network of pores. An intermediate bonding structure is
disposed at least in part between the first and second carbon foam
structures.
Inventors: |
Kelley; Kurtis C.;
(Washington, IL) ; Ostermeier; Charles F.; (Ames,
IA) ; Maroon; Matthew J.; (Grayslake, IL) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Firefly Energy Inc.
|
Family ID: |
32593343 |
Appl. No.: |
11/367331 |
Filed: |
March 6, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10324068 |
Dec 20, 2002 |
7033703 |
|
|
11367331 |
Mar 6, 2006 |
|
|
|
Current U.S.
Class: |
252/502 ;
252/511; 429/245 |
Current CPC
Class: |
H01M 4/663 20130101;
H01M 4/667 20130101; Y02E 60/10 20130101; Y10T 29/10 20150115 |
Class at
Publication: |
252/502 ;
252/511; 429/245 |
International
Class: |
H01B 1/04 20060101
H01B001/04; H01B 1/24 20060101 H01B001/24; H01M 4/66 20060101
H01M004/66; H01M 4/68 20060101 H01M004/68 |
Claims
1. A composite material, comprising: a first carbon foam structure
including a network of pores; a second carbon foam structure
including a network of pores; and an intermediate bonding structure
disposed at least in part between the first and second carbon foam
structures.
2. The composite material of claim 1, wherein the intermediate
bonding structure permeates at least some of the pores of the first
carbon foam structure and at least some of the pores of the second
carbon foam structure.
3. The composite material of claim 2, wherein the intermediate
bonding structure permeates the pores of the first carbon foam
structure by a depth equal to or greater than an average pore size
of the first carbon foam structure.
4. The composite material of claim 2, wherein the intermediate
bonding structure permeates the pores of the second carbon foam
structure by a depth equal to or greater than an average pore size
of the second carbon foam structure.
5. The composite material of claim 1, wherein the intermediate
bonding structure comprises a polymer.
6. The composite material of claim 5, wherein the intermediate
bonding structure comprises polypropylene.
7. The composite material of claim 1, wherein the intermediate
bonding structure comprises a metal.
8. The composite material of claim 1, wherein the intermediate
bonding structure comprises an electrically conductive
material.
9. The composite material of claim 1, wherein at least one of the
first and second carbon foam structures is graphite foam.
10. The composite material of claim 1, wherein at least one of the
first and second carbon foam structures has a total porosity value
of at least about 60%.
11. The composite material of claim 1, wherein at least one of the
first and second carbon foam structures has an open porosity value
of at least about 90%.
12. The composite material of claim 1, wherein each of the first
and second carbon foam structures has an average pore size of
between about 0.25 mm and about 2.0 mm.
13. A method of making a composite material, comprising: providing
a first carbon foam element including a network of pores; applying
bonding material to the first carbon foam element; and placing a
second carbon foam element, which includes a network of pores, on
the bonding material.
14. The method of claim 13, wherein applying the bonding material
and placing the second carbon foam element forms a stacked
structure, and wherein the method further comprises applying heat
to the stacked structure.
15. The method of claim 14 further comprising applying pressure to
the stacked structure.
16. The method of claim 15, wherein the steps of applying pressure
and applying heat are at least in part performed substantially
simultaneously.
17. The method of claim 13, further including forming a current
collector for a battery by coupling a first electrical connection
element with the first carbon foam element.
18. The method of claim 17, wherein the layer of bonding material
comprises an insulating material.
19. The method of claim 18, further comprising coupling a second
electrical connection element with the bonding material.
20-40. (canceled)
Description
TECHNICAL FIELD
[0001] This invention relates generally to a composite material
and, more particularly, to a composite material current collector
for an energy storage device.
BACKGROUND
[0002] Lead acid batteries are known to include at least one
positive current collector, at least one negative current
collector, and an electrolytic solution including, for example,
sulfuric acid (H.sub.2SO.sub.4) and distilled water. Ordinarily,
both the positive and negative current collectors in a lead acid
battery are constructed from lead. The role of these lead current
collectors is to transfer electric current to and from the battery
terminals during the discharge and charging processes. Storage and
release of electrical energy in lead acid batteries is enabled by
chemical reactions that occur in a paste disposed on the current
collectors. The positive and negative current collectors, once
coated with this paste, are referred to as positive and negative
plates, respectively. A notable limitation on the durability of
lead acid batteries is corrosion of the lead current collector of
the positive plate.
[0003] The rate of corrosion of the lead current collector is a
major factor in determining the life of the lead acid battery. Once
the sulfuric acid electrolyte is added to the battery and the
battery is charged, the current collector of each positive plate is
continually subjected to corrosion due to its exposure to sulfuric
acid and to the anodic potentials of the positive plate. One of the
most damaging effects of this corrosion of the positive plate
current collector is volume expansion. Particularly, as the lead
current collector corrodes, lead dioxide is formed from the lead
source metal of the current collector. This lead dioxide corrosion
product has a greater volume than the lead source material consumed
to create the lead dioxide. Corrosion of the lead source material
and the ensuing increase in volume of the lead dioxide corrosion
product is known as volume expansion.
[0004] Volume expansion induces mechanical stresses on the current
collector that deform and stretch the current collector. At a total
volume increase of the current collector of approximately 4% to 7%,
the current collector may fracture. As a result, battery capacity
drops, and eventually, the battery will reach the end of its
service life. Additionally, at advanced stages of corrosion,
internal shorting within the current collector and rupture of the
cell case can occur. Both of these corrosion effects may lead to
failure of one or more of the cells within the battery.
[0005] One method of extending the service life of a lead acid
battery is to increase the corrosion resistance of the current
collector of the positive plate. Several methods have been proposed
for inhibiting the corrosion process in lead acid batteries.
Because carbon does not oxidize at the temperatures at which lead
acid batteries generally operate, some of these methods have
involved using carbon in various forms to slow or prevent the
detrimental corrosion process in lead acid batteries. For example,
U.S. Pat. No. 5,512,390 (hereinafter the '390 patent) discloses a
lead acid battery that includes current collectors made from
graphite plates instead of lead. The graphite plates have
sufficient conductivity to function as current collectors, and they
are more corrosion resistant than lead. Substituting graphite
plates for the lead current collectors may, therefore, lengthen the
life of a lead acid battery.
[0006] While the battery of the '390 patent may potentially offer a
lengthened service life as a result of reduced corrosion at the
positive plate, the graphite plates of the '390 patent are
problematic. For example, the graphite plates of the '390 patent
are dense, flat sheets of material each having a relatively small
amount of surface area. Unlike lead electrode plates of a
conventional lead acid battery, which are generally patterned into
a grid-like structure to increase the available surface area of the
plates, the graphite plates of the '390 patent are smooth sheets
with no patterning. In lead acid batteries, an increase in surface
area of the current collector may increase the specific energy of
the battery and, therefore, may translate into improved battery
performance. More surface area on the current collectors may also
lead to a reduction in the time required for charging and
discharging of the battery. The relatively small surface area of
the graphite plates of the '390 patent results in poorly performing
batteries that have slow charging speeds.
[0007] Additionally, the graphite plates of the '390 patent lack
the toughness of lead current collectors. The dense graphite plates
of the '390 patent are brittle and may fracture when subjected to
physical shock or vibration. Such physical shock and vibration
commonly occur in vehicular applications, for example. Any
fracturing of the graphite plates would lead to the same problems
caused by volume expansion of ordinary lead current collectors.
Therefore, despite offering an increased resistance to corrosion
compared to conventional lead current collectors, the brittle
nature of the graphite plates of the '390 patent could actually
result in battery service lives shorter than those possible through
use of ordinary lead current collectors.
SUMMARY OF THE INVENTION
[0008] One aspect of the present invention includes a composite
material. The composite material includes a first carbon foam
structure including a network of pores and a second carbon foam
structure including a network of pores. An intermediate bonding
structure is disposed at least in part between the first and second
carbon foam structures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate exemplary
embodiments of the invention and, together with the written
description, serve to explain the principles of the invention. In
the drawings:
[0010] FIG. 1 is a cross-sectional view of a composite material in
accordance with an exemplary embodiment of the present
invention;
[0011] FIG. 2A is a plan view of a current collector in accordance
with an exemplary embodiment of the present invention;
[0012] FIG. 2B is a cross-sectional view of the current collector
of FIG. 2A taken along the line 2A;
[0013] FIG. 3A is a plan view of another current collector in
accordance with an exemplary embodiment of the present
invention;
[0014] FIG. 3B is a cross-sectional view of the current collector
of FIG. 3A taken along the line 3B;
[0015] FIG. 4 is a diagrammatic cut-away representation of a
battery in accordance with an exemplary embodiment of the present
invention.
DETAILED DESCRIPTION
[0016] In the following description, reference is made to the
accompanying drawings that form a part thereof, and in which is
shown by way of illustration specific exemplary embodiments in
which the invention may be practiced. These embodiments are
described in sufficient detail to enable those skilled in the art
to practice the invention, and it is to be understood that other
embodiments may be utilized and that changes may be made without
departing from the scope of the present invention. The following
description is, therefore, not to be taken in a limited sense.
Wherever possible, the same reference numbers are used throughout
the drawings to refer to the same or like parts.
[0017] As shown in FIG. 1, according to one embodiment of the
invention, composite material 10 includes two layers of porous
carbon foam 11, 13. A intermediate bonding material 12 is disposed
between carbon foam layers 11 and 13. Bonding material 12 attaches
carbon foam layers 11 and 13 together and provides structural
support for composite material 10.
[0018] The carbon foam used to form carbon foam layers 11 and 13 of
composite material 10 is electrically conductive. In certain forms,
the carbon foam may offer sheet resistivity values of less than
about 1 ohm/cm. In still other forms, the carbon foam may have
sheet resistivity values of less than about 0.75 ohm/cm. The
electrical conductivity of carbon foam layers 11 and 13 allows
composite material 10 to be used in a variety of applications such
as, for example, current collectors in batteries.
[0019] The carbon foam used to form carbon foam layers 11 and 13 of
composite material 10 is also resistant to corrosion. In general,
carbon oxidizes only at very high temperatures and will resist
corrosion even in corrosive environments. The carbon foam used in
composite material 10 retains this corrosion resistance, and
therefore, composite material 10 may be used, for example, in the
corrosive environment of a lead acid battery.
[0020] Additionally, carbon foam layers 11 and 13 are lightweight
due to the presence of a network of pores 14. In one embodiment of
the invention, for example, the carbon foam may include a total
porosity value of at least about 60%. In other words, at least 60%
of the volume of carbon foam layers 11 and 13 is included within
pores 14. Moreover, the carbon foam may have an open porosity value
of at least about 90%. In other words, at least 90% of pores 14 are
open to adjacent pores such that the network of pores 14 forms a
substantially open network. This open network of pores 14 may
result in a density of less than about 0.6 gm/cm3 for each of
carbon foam layers 11 and 13. Further, the average pore size of the
carbon foam may be between about 0.25 mm and about 2.0 mm, although
other sizes may also be possible.
[0021] In addition to carbon foam, graphite foam may also be used
to form composite material 10. One such graphite foam, under the
trade name PocoFoam.TM., is available from Poco Graphite, Inc. The
density and pore structure of graphite foam may be similar to
carbon foam. A primary difference between graphite foam and carbon
foam is the orientation of the carbon atoms that make up the
structural elements of the foam. For example, in carbon foam, the
carbon may be primarily amorphous. In graphite foam, however, much
of the carbon is ordered into a graphite, layered structure.
Because of the ordered nature of the graphite structure, graphite
foam offers higher conductivity than carbon foam. PocoFoam.TM.
graphite foam exhibits electrical resistivity values of between
about 100 .mu..OMEGA./cm and about 400 .mu..OMEGA./cm.
[0022] In composite material 10, bonding material 12 is disposed
between carbon foam layers 11 and 13. Bonding material 12 attaches
carbon foam layers 11 and 13 together by permeating at least some
of pores 14 of carbon foam layer 11 and at least some of pores 14
of carbon foam layer 13. In an exemplary embodiment, bonding
material 12 permeates the pores of carbon foam layer 11 by a depth
equal to or greater than an average pore size of layer 11.
Similarly, in the exemplary embodiment, bonding material 12 may
permeate the pores of carbon foam layer 13 by a depth equal to or
greater than an average pore size of layer 13. The depth of
permeation of bonding material 12 into carbon foam layers 11 and 13
is not limited to depths of at least the average pore size of
layers 11 and 13. Rather, a suitable bond may be created with a
penetration depth sufficient to include at least one carbon
structure (e.g., elements bordering a pore) within foam layers 11
and 13. The permeation of bonding material 12 into carbon foam
layers 11 and 13 is represented in FIG. 1 by permeation zones 15
and 16, respectively.
[0023] A variety of materials may be used as bonding material 12.
Bonding material 12 may include an electrically insulating material
including a polymer. For example, in one embodiment, bonding
material 12 may include polypropylene. In yet another embodiment,
bonding material 12 may include any of a wide range of epoxies. In
still another embodiment, an electrically conductive material may
be used as bonding material 12. Such electrically conductive
materials may include, for example, various metals and electrically
conductive polymers.
[0024] To make the composite material of one embodiment of the
present invention, a bonding material may be applied to a sheet of
carbon foam material. Next, a second sheet of carbon foam material
may be placed on the bonding material to form a stacked structure.
If the bonding material is applied as a solid, such as in the case
of most polymers and metals, then heat may be applied to the
stacked structure to soften and/or melt the bonding material.
Softening and/or melting of the bonding material encourages
permeation of the bonding material into the pores of the carbon
foam. In addition to heat, pressure can also be applied to the
stacked structure. The application of external pressure may aid in
forcing the bonding material to permeate the pores of the carbon
foam. In an exemplary embodiment of the present invention, heat and
pressure are applied simultaneously. In certain situations,
however, heat may be applied exclusive of pressure. In still other
situations, the application of heat may occur separate from the
application of pressure.
[0025] In instances where the bonding material is applied as a
liquid, such as an epoxy, for example, the bonding material may
permeate the pores of each of the two sheets of carbon foam without
the need for applying heat or pressure. Nevertheless, even in the
case of bonding materials applied as a liquid, the application of
heat and/or pressure, either together or individually, may
facilitate permeation of the bonding material into the pores of the
carbon foam by reducing the viscosity of the bonding material.
[0026] FIGS. 2A and 2B illustrate a current collector 20 that
includes the composite material of one embodiment of the present
invention. As shown in FIGS. 2A and 2B, current collector 20
includes carbon foam layers 11 and 13 bonded together by a
conductive bonding material 22. Bonding material 22 permeates at
least some of the pores of the carbon foam layers 11 and 13.
Further, bonding material 22 may permeate the pores of carbon foam
layers 11 and 13 by a depth equal to or greater than an average
pore size of layers 11 and 13, respectively.
[0027] An electrical connection element 21 is disposed within
bonding material 22 and provides an external, electrical connection
for current collector 20. Electrical connection element 21 includes
a tab 31 that extends beyond an edge of either or both of carbon
foam layers 11 and 13. Electrical connection element 21 also
includes at least one electrically conductive portion (not shown)
that extends within current collector 20. Electrical connection
element 21 may be formed using various different conductive
materials, such as but not limited to metals, suitable for
providing an electrical connection to either or both of carbon foam
layers 11 and 13.
[0028] In the exemplary embodiment shown in FIGS. 2A and 2B,
bonding material 22 of current collector 20 is an electrically
conductive material. For example, bonding material 22 may include a
metal or an electrically conductive polymer. Because bonding
material 22 is electrically conductive, an external electrical
connection to current collector 20 may be made using only one
electrical connection element 21. Particularly, tab 31 can make
electrical contact to both carbon foam layers 11 and 13 through
bonding material 22.
[0029] FIGS. 3A and 3B illustrate another current collector 40
including the composite material of the present invention. As shown
in FIGS. 3A and 3B, current collector 40 includes carbon foam
layers 11 and 13 bonded together by a bonding material 42. Similar
to the bonding material of composite material 10, bonding material
42 permeates at least some of the pores of the carbon foam layers
11 and 13. Further, bonding material 42 may permeate the pores of
carbon foam layers 11 and 13 by a depth equal to or greater than an
average pore size of layers 11 and 13, respectively.
[0030] In the exemplary embodiment shown in FIGS. 3A and 3B,
bonding material 42 is an electrically insulating material. Because
bonding material 42 is electrically insulating, an external
electrical connection to current collector 40 may be made using two
electrical connection elements 21. Particularly, when making
current collector 40, a first electrical connection element 21 may
be disposed on, for example, carbon foam layer 11. Then, bonding
material 42 is applied to both the first electrical connection
element and to carbon foam layer 11. Because electrically
insulating bonding material 42 coats the first electrical
connection element 21, an additional electrical connection element
may be required to make contact with carbon foam layer 13, which is
applied to the bonding material 42 to create a stacked structure.
Therefore, prior to placing carbon foam layer 13 on bonding
material 42, a second electrical connection element 21 may be
placed on bonding material 42. The second electrical connection
element 21 provides an external electrical contact with carbon foam
layer 13.
[0031] Accordingly, two electrical connection elements 21 are shown
in FIG. 3B. Each resides at an interface between bonding material
42 and carbon foam layers 11 and 13, respectively. Electrical
connection elements 21 may be configured with some open space or
porosity so as not interfere with permeation of bonding material 42
into the pores of the respective carbon foam layers.
[0032] While the exemplary embodiment of the present invention
illustrated in FIG. 3B includes two electrical connection elements
21, electrical connections to the carbon foam layers 11 and 13 may
be accomplished through alternative configurations. For example, a
single electrical connection element 21 may be configured such that
electrically conductive portions 33 make electrical contact to both
carbon foam layers 11 and 13. For example, conductive portions 33
may be arranged such that some of the conductive portions contact
foam layer 11 and other conductive portions contact foam layer 13.
Alternatively, electrical connection element 21 may be sized with a
sufficient thickness relative to the thickness of bonding material
42 such that a single connection element 21 may contact both foam
layers 11 and 13. In these exemplary instances, one electrical
connection element 21 would be sufficient.
[0033] FIG. 4 illustrates a battery 100 in accordance with an
exemplary embodiment of the present invention. Battery 100 includes
a housing 110 and terminals 120, which are external to housing 110.
At least one cell 130 is disposed within housing 110. While only
one cell 130 is necessary, multiple cells may be connected in
series to provide a desired total potential of battery 100.
[0034] Each cell 130 may be composed of alternating positive and
negative plates immersed in an electrolytic solution including, for
example, sulfuric acid and distilled water. Both the positive and
negative plates include a current collector packed with a paste
material, including, for example, an oxide of lead. As noted above,
FIGS. 2A, 2B, 3A, and 3B illustrate current collectors 20 and 40
according to exemplary embodiments of the present invention that
may be used to form the positive and/or negative plates of battery
100. Chemical reactions in the paste disposed on the current
collectors of the battery enable storage and release of energy. The
composition of this paste, and not the material selected for the
current collector, determines whether a given current collector
functions as either a positive or a negative plate.
[0035] To create the positive and negative plates of battery 100, a
chemically active paste is applied to current collectors 20, 40
such that the chemically active paste penetrates the network of
pores in the carbon foam of the current collector. Initially, the
chemically active paste that is applied to the current collectors
20, 40 of both the positive and negative plates may be
substantially the same in terms of chemical composition. For
example, the paste may include lead oxide (PbO). Other oxides of
lead may also be suitable. The paste may also include various
additives including, for example, varying percentages of free lead,
structural fibers, conductive materials, carbon, and extenders to
accommodate volume changes over the life of the battery. In
practice, the constituents of the chemically active paste may be
mixed with a small amount of sulfuric acid and water to form a
paste that may be disposed within pores 14 of the current
collectors 20, 40.
[0036] Once the paste has been deposited on current collectors 20,
40 the positive and negative plates are formed. To create a
positive plate, current collectors 20, 40 including lead oxide
paste, for example, are subjected to a curing process. This curing
process may include exposing the pasted current collectors 20, 40
to elevated temperature and humidity to encourage growth of lead
sulfate crystals within the paste. To create the negative plate,
current collectors 20, 40 including the lead oxide paste may be
left "as is", with the exception of an optional step of drying.
[0037] When the positive and negative plates have been assembled
together to form the cells of a battery 100 (shown in FIG. 4),
battery 100 is subjected to a charging (i.e., formation) process.
During this charging process, the cured paste of the positive plate
is electrically driven to lead dioxide (PbO2), and the paste of the
negative plate is converted to sponge lead. Conversely, during
subsequent discharge of the battery 100, the pastes of both
positive and negative plates convert toward lead sulfate.
INDUSTRIAL APPLICABILITY
[0038] The composite material of the present invention is useful in
any of a wide variety of applications where materials with
corrosion resistance, high surface area, electrical conductivity,
or low weight would be desirable. In one possible application, the
composite material of the present invention may serve as a current
collector in a battery, such as a lead acid battery, for example.
Current collectors may support the chemically active components of
the battery and promote the flow of current between terminals of
the battery.
[0039] Because current collectors 20, 40 include carbon foam, these
current collectors resist corrosion even when exposed to sulfuric
acid and to the anodic potentials of the positive plate in a lead
acid battery. As a result, the battery may offer a significantly
longer service life as compared to batteries without carbon foam
current collectors.
[0040] The carbon foam includes a network of pores, which provides
a large amount of surface area for each current collector 20, 40.
Current collectors composed of carbon foam may exhibit more than
2000 times the amount of surface area provided by conventional lead
current collectors. The large amount of surface area associated
with current collectors 20, 40 translates into batteries having
large specific energy values. For example, because of the open
cell, porous network and relatively small pore size of the carbon
foam materials, the chemically active paste of the positive and
negative plates is intimately integrated with the conductive carbon
material of current collectors 20, 40. Therefore, electrons
produced in the chemically active paste at a particular reaction
site must travel only a short distance through the paste before
encountering the conductive carbon foam of current collectors 20,
40. This current may then be carried by the electrically conductive
portion 33 of the electrical connection element 21, for
example.
[0041] As a result, batteries with carbon foam current collectors
20, 40 may offer improved specific energy and power values. In
other words, these batteries, when placed under a load, may sustain
their voltage above a predetermined threshold value for a longer
time than some conventional batteries, including those having
either lead current collectors or graphite plate current
collectors. Also, these batteries may discharge more quickly than
batteries including either lead current collectors or graphite
plate current collectors.
[0042] The increased specific power values offered by batteries of
the present invention may also translate into reduced charging
times. Therefore, the batteries may be suitable for applications in
which charging energy is available for only a limited amount of
time. For instance, in vehicles, a great deal of energy is lost
during ordinary braking. This braking energy may be recaptured and
used to charge a battery of, for example, a hybrid vehicle. The
braking energy, however, is available only for a short period of
time (i.e., while braking is occurring). In view of their reduced
charging times, the batteries of the present invention may provide
an efficient means for storing such braking energy.
[0043] The porous nature of the carbon foam current collectors also
creates an improved substrate for retaining the chemically active
paste of the energy storage device. By impregnating the paste into
pores of the carbon foam current collectors, the paste is less
likely to separate from the current collectors. This property is
important in vehicle and other applications where vibration is
common.
[0044] Further, by including carbon foam current collectors having
a density of less than about 0.6 g/cm3, a battery may weigh
substantially less that batteries including either lead current
collectors or graphite plate current collectors. Other aspects and
features of the present invention can be obtained from a study of
the drawings, the disclosure, and the appended claims.
* * * * *