U.S. patent application number 12/819342 was filed with the patent office on 2010-10-07 for electrochemical cell stack assembly.
Invention is credited to Craig P. JACOBSON, Lutgard C. De Jonghe, Steven J. Visco.
Application Number | 20100255398 12/819342 |
Document ID | / |
Family ID | 29420425 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100255398 |
Kind Code |
A1 |
JACOBSON; Craig P. ; et
al. |
October 7, 2010 |
ELECTROCHEMICAL CELL STACK ASSEMBLY
Abstract
Multiple stacks of tubular electrochemical cells having a dense
electrolyte disposed between an anode and a cathode preferably
deposited as thin films arranged in parallel on stamped conductive
interconnect sheets or ferrules. The stack allows one or more
electrochemical cell to malfunction without disabling the entire
stack. Stack efficiency is enhanced through simplified gas
manifolding, gas recycling, reduced operating temperature and
improved heat distribution.
Inventors: |
JACOBSON; Craig P.;
(Lafayette, CA) ; Visco; Steven J.; (Berkeley,
CA) ; Jonghe; Lutgard C. De; (Lafayette, CA) |
Correspondence
Address: |
JOHN P. O'BANION;O'BANION & RITCHEY LLP
400 CAPITOL MALL SUITE 1550
SACRAMENTO
CA
95814
US
|
Family ID: |
29420425 |
Appl. No.: |
12/819342 |
Filed: |
June 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11512521 |
Aug 30, 2006 |
7740966 |
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12819342 |
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10434403 |
May 7, 2003 |
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11512521 |
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60378701 |
May 7, 2002 |
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Current U.S.
Class: |
429/452 |
Current CPC
Class: |
H01M 8/04097 20130101;
H01M 8/2415 20130101; H01M 8/0206 20130101; H01M 8/0232 20130101;
Y02E 60/50 20130101; H01M 8/0271 20130101; H01M 8/2484 20160201;
H01M 4/8621 20130101; H01M 8/0247 20130101; Y02P 70/50 20151101;
H01M 8/0273 20130101; H01M 8/025 20130101; H01M 4/8885 20130101;
H01M 8/243 20130101; H01M 8/1007 20160201; H01M 2008/1293
20130101 |
Class at
Publication: |
429/452 |
International
Class: |
H01M 8/24 20060101
H01M008/24 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under Grant
(Contract) No. DE-AC03-76F00098 awarded by The United States
Department of Energy. The government has certain rights to this
invention.
Claims
1-85. (canceled)
86. An electrochemical cell stack assembly, comprising: a plurality
of conductive interconnect plates; each said interconnect plate
having a plurality of apertures; and a plurality of tubular
electrochemical cells disposed and sealed between said interconnect
plates; wherein a said tubular electrochemical cell is oriented
over a corresponding said aperture to form a gas passageway.
87. A module for a modular assembly of electrochemical cells,
comprising: a first set of tubular electrochemical cells, each said
cell having an anode contact end and a cathode contact end; a
second set of tubular electrochemical cells, each said cell having
an anode contact end and a cathode contact end; and an electrically
conductive interconnect sheet with a plurality of apertures and top
and bottom sides, said top side of said interconnect sheet
configured to electrically couple with said anode contact ends of
said first set of electrochemical cells, said bottom side of said
interconnect sheet configured to electrically couple with said
cathode contact ends of said second set of electrochemical cells;
wherein said first and second set of electrochemical cells are
aligned over the apertures of the interconnect sheet forming gas
passageways through said electrochemical cells and said
interconnect sheet.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. provisional
application Ser. No. 60/378,701 filed on May 7, 2002, incorporated
herein by reference.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT
DISC
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention pertains generally to solid-state
electrochemical device assemblies, and more particularly to a
modular parallel electrochemical cell in series stack.
[0006] 2. Description of Related Art
[0007] Steadily increasing demand for power and the atmospheric
build up of greenhouse and other combustion gases has spurred the
development of alternative energy sources for the production of
electricity. Fuel cells, for example, hold the promise of an
efficient, low pollution technology for generating electricity.
Because there is no combustion of fuel involved in the process,
fuel cells do not create any of the pollutants that are commonly
produced in the conventional generation of electricity by boilers
or furnaces and steam driven turbines.
[0008] Unfortunately, the present cost of electrical energy
production from fuel cells is several times higher than the cost of
the same electrical production from fossil fuels. The high cost of
capitalization and operation per kilowatt of electricity produced
has delayed the commercial introduction of fuel cell generation
systems.
[0009] A conventional fuel cell is an electrochemical device that
converts chemical energy from a chemical reaction with the fuel
directly into electrical energy. Electricity is generated in a fuel
cell through the electrochemical reaction that occurs between a
fuel (typically hydrogen produced from reformed methane) and an
oxidant (typically oxygen in air). This net electrochemical
reaction involves charge transfer steps that occur at the interface
between the ionically-conductive electrolyte membrane, the
electronically-conductive electrode and the vapor phase of the fuel
or oxygen. Water, heat and electricity are the only products of one
type of fuel cell system designed to use hydrogen gas as fuel.
Other types of fuel cells that have been developed include molten
carbonate fuel cells; phosphoric acid fuel cells, alkaline fuel
cells, proton exchange membrane fuel cells. Because fuel cells rely
on electrochemical rather than thermo-mechanical processes in the
conversion of fuel into electricity, the fuel cell is not limited
by the Carnot efficiency experienced by conventional mechanical
generators.
[0010] Solid-state electrochemical devices are normally cells that
include two porous electrodes, the anode and the cathode, and a
dense solid electrolyte membrane disposed between the electrodes.
In the case of a typical solid oxide fuel cell, the anode is
exposed to fuel and the cathode is exposed to an oxidant in
separate closed systems to avoid any mixing of the fuel and
oxidants due to the exothermic reactions that can take place with
hydrogen fuel.
[0011] The electrolyte membrane is normally composed of a ceramic
oxygen ion conductor in solid oxide fuel cell applications. In
other implementations, such as gas separation devices, the solid
membrane may be composed of a mixed ionic electronic conducting
material ("MIEC"). The porous anode may be a layer of a ceramic, a
metal or, most commonly, a ceramic-metal composite ("cermet") that
is in contact with the electrolyte membrane on the fuel side of the
cell. The porous cathode is typically a layer of a mixed ionically
and electronically-conductive (MIEC) metal oxide or a mixture of an
electronically conductive metal oxide (or MIEC metal oxide) and an
ionically conductive metal oxide.
[0012] Solid oxide fuel cells normally operate at temperatures
between about 900.degree. C. and about 1000.degree. C. to maximize
the ionic conductivity of the electrolyte membrane. At appropriate
temperatures the oxygen ions easily migrate through the crystal
lattice of the electrolyte. However, most metals are not stable at
the high operating temperatures and oxidizing environment of
conventional fuel cells and become converted to brittle metal
oxides. Accordingly, solid-state electrochemical devices have
conventionally been constructed of heat-tolerant ceramic materials.
However, these materials tend to be expensive and still have a
limited life in high temperature and high oxidation conditions. In
addition, the materials used must have certain chemical, thermal
and physical characteristics to avoid delamination due to thermal
stresses, fuel or oxidant infiltration across the electrolyte and
similar problems during the production and operation of the
cells.
[0013] Since each fuel cell generates a relatively small voltage,
several fuel cells may be associated to increase the capacity of
the system. Such arrays or stacks generally have a tubular or
planar design. Planar designs typically have a planar
anode-electrolyte-cathode deposited on a conductive interconnect
and stacked in series. However, planar designs are generally
recognized as having significant safety and reliability concerns
due to the complexity of sealing of the units and manifolding a
planar stack.
[0014] In addition, conventional stacks of planar fuel cells
operated at the higher temperature of approximately 1000.degree. C.
have relatively thick electrolyte layers compared to the porous
anode and cathode layers applied to either side of the electrolyte
and provides structural support to the cell. However, in order to
reduce the operating temperature to less than 800.degree. C., the
thickness of the electrolyte layer has been reduced from more than
50-500 microns to approximately 5-50 microns. The thin electrolyte
layer in this configuration is not a load bearing layer. Rather,
the relatively weak porous anode and cathode layers must bear the
load for the cell. Stacks of planar fuel cells supported by weak
anodes or cathodes may be prone to collapse under the load.
[0015] Tubular designs utilizing long porous support tubes with
electrodes and electrolyte layers disposed on the support tube
reduce the number of seals that are required in the system. Fuel or
oxidants are directed through the channels in the tube or around
the exterior of the tube. However, tubular designs provide less
power density because of the relatively long current path on the
electrodes since the current collection for the entire tube occurs
on only a small area on the circumference of the tube. This
contributes to internal resistive losses thereby limiting power
density.
[0016] In addition, the concentration of the reactants often
diminishes as gas flows through the channels along the length of
the tubes if an insufficient volume of reactants is directed
through the apparatus. Decreased gas concentration at the anode,
for example, will result in a reduction in the electrical output of
the cell depending on the position of the cell in the stack.
Increasing the volume of fuel or oxidants flowing through the
apparatus may result in excess reactants exhausting the system
along with the reaction products of the electrochemical device.
Excess reactants are typically burned to provide operating heat for
the solid fuel cells in conventional devices. Excess reactants that
exhaust the system and are burned further reduce the efficiency of
the apparatus.
[0017] Another significant problem encountered with planar stacks
with repeating cell elements is that the failure of one cell may
result in the failure of the entire stack. Malfunctioning cells in
present designs may require cooling the stack and taking it off
line to replace a single cell.
[0018] Thus, present solid-state electrochemical devices
incorporating conventional designs are expensive to manufacture and
may suffer from safety, reliability, and/or efficiency
concerns.
[0019] Accordingly, there is a need to provide a stack or array of
electrochemical devices, such as solid oxide fuel cells, that are
capable of operating efficiently at lower temperatures and use less
expensive materials and production techniques. Stack designs that
reduce the cost of materials and manufacturing while increasing the
reliability of fuel cells and other solid state electrochemical
devices, may allow for the commercialization of such devices that
have been previously too expensive, inefficient or unreliable to
exploit. The present invention satisfies these needs, as well as
others, and generally overcomes the deficiencies in conventional
devices.
BRIEF SUMMARY OF THE INVENTION
[0020] An apparatus is provided for a stack of tubular
electrochemical cells that can operate at lower operating
temperatures and has improved fuel efficiency and electricity
production over the art. By way of example, and not of limitation,
in accordance with one aspect of the invention a stack of arrays of
tubular solid-state electrochemical cells connected in parallel to
interconnect plates is provided and the arrays are connected in
series.
[0021] According to another aspect of the invention, the
electrochemical devices are either anode, cathode or electrolyte
supported tubes preferably oriented perpendicularly to the
interconnect plates.
[0022] According to another aspect of the invention, interconnect
plates are provided that are connected to the anode of one set of
tubular cells and the cathodes of a second set of tubular
cells.
[0023] In accordance with yet another aspect of the invention, top
and bottom electrochemical cells are sealed to a ferrule, which may
be attached to an interconnect plate or to stack electrochemical
cells within a row.
[0024] According to one embodiment of the invention, the
electrochemical cell layer has a first electrode layer that is
formed into a tube by any number of methods such as extrusion,
injection molding, deposition on a mandrel, pressing, tape casting
and the like. The first electrode can be made of material to
provide either an anode or a cathode. A preferably thin film
electrolyte layer of ion conducting material is applied to the
tubular electrode that is essentially gas impermeable. A second
electrode layer is then applied to the exterior surface of the
electrolyte.
[0025] In another embodiment of the invention, the electrolyte
layer is dimensioned to be a support layer and a first electrode
layer is applied to the interior of the tube and a second electrode
is applied to the exterior of the electrolyte tube.
[0026] In one embodiment of the invention, a number of holes and
formed joints are punched into a metallic interconnect plate. The
tubular electrochemical devices are attached and sealed to both
sides of the interconnect holes to form a continuous preferably gas
tight passageway through the center of the tubes. The interconnect
plate is in electrical contact with the anode of one tubular cell
and the cathode of the other tubular cell.
[0027] An object of the invention is to provide parallel arrays of
tubular electrochemical devices with thin films of electrolyte and
electrode layers that can be organized in stacks of parallel arrays
and connected in series.
[0028] Another object of the invention is to provide an array of
electrochemical devices that is configured to avoid a failure of
the array upon failure of a single electrochemical device in the
array.
[0029] Another object of the invention is to provide a solid oxide
fuel cell that has an operating temperature of less than
approximately 800.degree. C.
[0030] Another object of the invention is to provide an
electrochemical cell that is durable, reliable and is easy to
manufacture.
[0031] Another object of the invention is to provide a stack of
electrochemical cells that have long term stability with reduced
cost.
[0032] Still another object of the invention is to provide a stack
of electrochemical cells that is resistant to thermal shock.
[0033] Further aspects and objects of the invention will be brought
out in the following portions of the specification, wherein the
detailed description is for the purpose of fully disclosing
preferred embodiments of the invention without placing limitations
thereon.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0034] The invention will be more fully understood by reference to
the following drawings which are for illustrative purposes
only:
[0035] FIG. 1 is a side view of an stack of electrochemical cells
according to the present invention.
[0036] FIG. 2 is a side detailed view of one tubular
electrochemical cell of one embodiment of a stack of
electrochemical cells according to the invention shown in FIG.
1.
[0037] FIG. 3 is a top plan view of one metallic interconnect plate
of the embodiment of a stack of electrochemical cells shown in FIG.
1.
[0038] FIG. 4 is a perspective view of one tubular electrochemical
cell according to the present invention.
[0039] FIG. 5 is a cross sectional view of one embodiment of a
tubular fuel cell taken along the lines 5-5 of FIG. 4.
[0040] FIG. 6 is a side cross sectional view of one embodiment of a
junction between a top electrochemical cell and a bottom
electrochemical cell with the metallic interconnect plate according
to the present invention.
[0041] FIG. 7 is a side cross sectional view of an alternative
embodiment of a junction between top and bottom electrochemical
cells with the metallic interconnect plate according to the present
invention.
[0042] FIG. 8 is a side cross sectional view of an alternative
embodiment of a junction between top and bottom electrochemical
cells with the metallic interconnect plate according to the present
invention.
[0043] FIG. 9 is a side cross sectional view of an alternative
embodiment of a junction between top and bottom electrochemical
cells with the metallic interconnect plate according to the present
invention.
[0044] FIG. 10 is a side cross sectional view of an alternative
embodiment of a junction between top and bottom electrochemical
cells with the metallic interconnect plate according to the present
invention.
[0045] FIG. 11 is a perspective view of a ferrule used in an
alternative embodiment of the invention as a junction between top
and bottom electrochemical cells.
[0046] FIG. 12 is a cross section of the ferrule of FIG. 11 taken
along the lines 12-12 in FIG. 11.
[0047] FIG. 13 is a detailed sectional view of a ferrule junction
between top and bottom electrochemical cells.
[0048] FIG. 14 is detailed sectional view of an alternative
embodiment of the sealing of a ferrule junction between top and
bottom electrochemical cells.
[0049] FIG. 15 is an alternative embodiment of an electrochemical
stack according to the present invention using ferrules and
interconnect plates.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Referring more specifically to the drawings, for
illustrative purposes the present invention is embodied in the
apparatus generally shown in FIG. 1 through FIG. 15. It will be
appreciated that the apparatus may vary as to configuration and as
to details of the parts without departing from the basic concepts
as disclosed herein.
[0051] Turning now to FIG. 1, one embodiment of a stack 10 of
parallel arrays of electrochemical cells 18 with planar
interconnect sheets is shown. In the embodiment shown in FIG. 1,
arrays of fifty tubular cells are stacked ten high. It will be
apparent that the invention can be configured to use virtually any
number of tubes and those tubes can be stacked to virtually any
number of levels. Although a tubular electrochemical cell is shown
as a cylindrical cell for illustration, it will be understood that
the tubular electrochemical cell can have any shaped cross section
that will preferably maximize the packing density and efficiency of
the stack. For example, the electrochemical cells may have a
square, octagonal, oval or preferably rectangular cross sections
and may have one or more channels running axially through the
cell.
[0052] Referring also FIG. 2 and FIG. 3, the electrochemical cell
stack 10 has rows 12 of tubular electrochemical cells that are
mounted to interconnect plates 14. The interconnect sheets or
plates 14 are preferably between approximately 50 .mu.m and
approximately 5000 .mu.m thick, and more preferably between
approximately 100 .mu.m and approximately 1000 .mu.m thick (0.1 to
1.0 mm).
[0053] The interconnect plates 14 are preferably made of metal and
have a plurality of holes 16. The circumference of the holes 16 is
preferably configured with a rim that will orient the individual
electrochemical cells 18 and hold the cells in place so that they
can be sealed from leaking. Elongate tubes 20 of essentially gas
tight electrochemical cells are formed, as the rows 12 of the array
of electrochemical cells 18 are stacked upon each other as seen in
FIG. 1. The resulting tubes 20 can be connected to manifolds 22, 24
that are connected to a source of gas. The source of gas can either
be fuel or oxidants depending on the configuration of the
electrochemical cells.
[0054] Manifolds 22, 24 allow fuel or oxidants to be recycled so
that the threshold concentration of fuel can be maximized so that
optimum concentrations of fuel are present at the anodes. Likewise,
oxidants can be recycled to optimize concentrations at the cathode
and improve the efficiency of the system. In one embodiment, the
water, contaminants, partially reacted fuel, and other reaction
products are separated from the excess fuel exhausting from the
stack and the fuel is returned to the supply side of the apparatus.
Thus, the efficiency of the system can be increased by fully
utilizing the fuel that is produced for the electrochemical device
for the production of electricity, for example, rather than losing
the fuel to combustion as occurs in conventional fuel cell
stacks.
[0055] It will be seen that the array of rows 12 of electrochemical
cells are connected in parallel to the conductive metallic
interconnect plate 14. The interconnect plates 14 are connected in
series to increase the capacity of the apparatus. The series array
design has been shown to improve stack efficiency by producing a
power output that is 10% greater than the output of a single cell
with the same active area.
[0056] Metals used for interconnecting sheets 14 include but are
not limited to: Ni, Cu, alloys containing Ni, Ni based superalloys,
alloys containing Cu, alloys containing Fe, stainless steel, Fe
based alloys containing Cr, Fe--Cr alloys containing a reactive
element such as Y or La, austenitic steels such as AISI 304 or 316,
terrific steels such as AISI 430 or 446, Al containing alloys,
Fe--Cr alloys containing Al and a reactive element such as Y,
Fe--Cr alloys containing 0.1 to 3.0 wt % Mn, Fe--Cr alloys
containing 12-30 wt % Cr, Fe--Cr alloys containing 16-26 wt % Cr,
Fe based alloys containing 18 to 22 wt % Cr with 0.5 to 2.0 wt % Mn
and 0.1 to 1.0 wt % Y. Surface modification of part or all of the
metal by sol-gel deposition, vapor deposition, plasma spray,
plating, or any other means know in the art is also suitable.
Coating part or the entire metal surface of the interconnect 14
with a catalyst, such as a reforming catalyst used for reforming
hydrocarbon containing fuels, is also contemplated.
[0057] The parallel connections of each of the electrochemical
cells 18 with plate 14 will also increase the reliability of the
stack. One deficiency that is observed in conventional fuel cell
stack designs is that defects in individual fuel cells that occur
during manufacture or damage to cells that occurs during
transportation and handling may not become apparent until all of
the cells are installed in a unitary stack and the apparatus is
activated. Defects in an individual cell may be seen as poor
electrical production from the stack. Defective cells may also
affect the performance of adjacent cells. Furthermore, the physical
stacking of multiple fuel cells in series will not allow the
replacement of a single defective cell with a new cell in
conventional stacks. Consequently, the entire stack may need to be
replaced due to defects or failure of a single cell.
[0058] The tubular electrochemical cell design of the present
invention will not lead to the catastrophic failure of the stack
with defects or failure of one electrochemical cell 18.
Inefficiencies or failure of one cell may slightly reduce the
overall output of the row 12 of cells but should not affect the
production of neighboring electrochemical cells 18 in the row or
adjacent rows of cells. The redundancy via the interconnect plate
allows current to be conducted through one of the many other
parallel cells in the row 12.
[0059] In addition, because the small tubular cells are independent
of each other, the apparatus 10 can accommodate large thermal
gradients without placing the individual cells 18 in danger of
failure. One of the products of the chemical reactions of the fuel
cell may be heat creating thermal gradients through the stack.
Excess heat may be removed by blowing air through the stacks or
other methods of regulating temperature. Heat from the stack can be
removed through the flat metal interconnects 14 that can act as
cooling fins in one embodiment of the invention where the
interconnect plates extend beyond the area containing the row 12 of
cylindrical fuel cells as seen in FIG. 2. This embodiment reduces
the amount of excess air that may be required to be blown through
the stacks to remove the excess heat. It can also be seen that the
presence of multiple metallic heat conducting sheets will help
equalize the heat distribution within the stack. Local cooling of
some plates can normalize the overall operating temperature of the
stack.
[0060] As shown generally in FIG. 2, the stack 10 of
electrochemical cells 18 is preferably contained in an insulated
gas tight housing 26 that can contain fuel or oxidants depending on
the configuration of the electrochemical cells 18. In the
embodiment shown in FIG. 2, heat from the metal interconnect plates
14 is used in a heat exchanger 28 that is used to pre-heat fuel gas
or oxidants before introduction into the stack to improve
efficiency.
[0061] Additionally, ceramics are capable of carrying far greater
compressive forces than tensile forces. Uneven plates and tensile
forces applied during use or during cooling periods in conventional
fuel cell stacks can lead to cracks and breaks in the electrolyte
and ultimately to the destruction of the individual cells.
Accordingly, uneven or excessive loads applied to thin electrolyte
electrochemical cells can cause the cells to delaminate or break
even when the plates are constructed under very tight tolerances.
It will be appreciated that the tubular electrochemical cells 18
are of uniform size and experience primarily compressive forces
from the adjacent rows of cells and interconnect plates.
Consequently, the tubular electrochemical cells 18 are durable and
resistant to thermal shock.
[0062] It will also be seen that the distribution of
electrochemical cells 18 within the stack 10 can vary to optimize
the efficiency of the stack and account for thermal differences
that may be in the stack. Unit cells 18 in the rows 12 of the stack
need not be the same size or contain the same electrolyte, cathode,
anode, and/or support materials. For example, in a fuel cell stack,
ceria based electrolyte cells can be used for lower temperature
regions or regions near the fuel inlet or exit in the stack and/or
proton conducting electrolyte cells (such as doped SrCeO.sub.3 or
SaZrO.sub.3) could be used in the interior region, and/or doped
zirconia based electrolyte cells could be used near the high
temperature anode gas exit. Such designs improve the performance of
the stack by improving the performance near the inlet by utilizing
a higher conductivity electrolyte, reducing the steam requirements
near the inlet, and by removing H.sub.2 from the anode chamber and
thereby reducing the partial pressure of water on the fuel side
thus increasing the fuel utilization. The optimum distribution of
each cell 18 would be determined by the particular fuel choice and
stack configuration. Accordingly, the electrochemical cell stack
assembly of the present invention has great flexibility in design
configuration.
[0063] Turning now to FIG. 4 and FIG. 5, a single electrochemical
cell 18 according to one embodiment of the invention is shown.
Electrochemical cells 18 generally comprise an ion-conducting
electrolyte 30 sandwiched between a porous anode 32 and cathode 34
in fuel cell applications. Although a fuel cell is used as an
example of an electrochemical cell for purposes of illustration, it
will be understood that the electrochemical cell may be an oxygen
generator, syn-gas generator or hydrogen gas separator and similar
devices.
[0064] Electrochemical cells 18 can be either anode supported,
cathode supported or electrolyte supported. Electrode supported
electrochemical cells 18 can have electrode supports that are a
ceramic, a ceramic metal composite (cermet) or an alloy. In one
embodiment, the cells are manufactured as bilayers such as
Ni--YSZ/YSZ or LSM/YSZ and the counter electrode is applied after
the high temperature sintering of the bi-layer. In another
embodiment, all three layers are applied and sintered in one high
temperature step. For example, LSM/YSZ/LSM or LSMNSZ/Ni--YSZ
tri-layers can be sintered in one step.
[0065] Additionally, I will be understood that the electrode
supported structures can also be multi-layered or graded structures
composed of different materials and/or microstructures and not
simply a homogeneous electrode. For example, a cathode supported
design could consist of an extruded or injected molded porous LSM
support to which is applied a layer of porous LSM+YSZ and onto this
is applied the YSZ electrolyte film and the counter electrode.
Alternatively a porous catalytic layer, such as Ni--YSZ, can be
positioned between a porous alloy layer, such as a ferritic steel,
and the electrolyte layer, such as YSZ.
[0066] The embodiment illustrated in FIG. 4 and FIG. 5 is a cathode
supported electrochemical cell 18. In this embodiment, the cathode
material is formed into a thin tube by injection molding,
centrifugal casting, slip-casting, tape-casting, extrusion,
co-extrusion, isostatic pressing, eletrophoretic deposition, dip
coating, aerosol spray, and many other methods know in the art of
ceramics processing and powder metallurgy are possible for
producing porous substrates suitable for thin film deposition.
Extrusion or injection molding are the preferred methods of support
structure production. Anode supported electrochemical cells 18 are
formed in similar fashion. In another embodiment, the anode,
electrolyte, and cathode are disposed on a tubular porous support,
preferably made of powdered metal or cermet. The anode, electrolyte
and cathode are preferably disposed on the porous metal support as
thin films.
[0067] The preferred height of the electrochemical cell 18 is
determined by the conductivity of the electrode layers. For ceramic
supported structures the electrochemical cell 18 is preferably
between approximately 1 cm to approximately 5 cm in height. For
metal supported electrochemical cell structures the cells 18 are
preferably between approximately 2 cm and approximately 10 cm in
height.
[0068] The cathode electrode 34 is preferably a cylindrical or
rectangular tube ranging in thickness from approximately 100 .mu.m
to approximately 3000 .mu.m in cathode supported embodiments.
However, cathode layers ranging in thickness of between
approximately 150 .mu.m to approximately 2000 .mu.m are especially
preferred. In anode supported electrochemical cells, the cathode 34
is preferably applied as a thin film to one surface of the
electrolyte 30 and bonded to provide a cathode electrode 34 ranging
in thickness of between approximately 50 .mu.m to approximately
1500 .mu.m. It will be understood that the selected thickness of
the electrode tubes and electrolyte can vary depending on the
thermal expansion, electronic conductivity and ionic conductivity
characteristics of the electrode and electrolyte materials.
[0069] Suitable cathode electrode 30 materials in accordance with
the present invention include cermets and ceramics. For example,
other suitable ceramic components include:
La.sub.1-xSr.sub.xMn.sub.yO.sub.3-.delta. (1.gtoreq.X.gtoreq.0.05)
(0.95.gtoreq.y.ltoreq.1.15) ("LSM") (.delta. is defined as that
value signifying a small deviation from perfect stoichiometry),
La.sub.1-xSr.sub.xCoO.sub.3-.delta. (1.gtoreq.X.gtoreq.0.10)
("LSC"), La.sub.1-xSr.sub.xFe.sub.yO.sub.3-.delta.
(1.gtoreq.X.gtoreq.0.05) (0.95.ltoreq.y.ltoreq.1.15) ("LSF"),
SrCo.sub.1-xFe.sub.xO.sub.3-.delta. (0.30.gtoreq.X.gtoreq.0.20),
La.sub.0.6Sr.sub.0.4Co.sub.0.6Fe.sub.0.4O.sub.3-.delta.,
Sr.sub.0.7Ce.sub.0.3MnO.sub.3-.delta.,
LaNi.sub.0.6Fe.sub.0.4O.sub.3-.delta.,
Sm.sub.0.5Sr.sub.0.5CoO.sub.3-.delta., yttria stabilized zirconia
(YSZ), scandia stabilized zirconia (SSZ),
(CeO.sub.2).sub.0.8(Gd.sub.2O.sub.3).sub.0.2(CGO),
La.sub.0.8Sr.sub.0.2Ga.sub.0.85Mg.sub.0.15O.sub.2.825 (LSGM20-15),
(Bi.sub.2O.sub.3).sub.0.75(Y.sub.2O.sub.3).sub.0.25 and
alumina.
[0070] Preferred LSM materials include
La.sub.0.8Sr.sub.0.2MnO.sub.3,
La.sub.0.65Sr.sub.0.30MnO.sub.3-.delta., and
La.sub.0.45Sr.sub.0.55MnO.sub.3-.delta.. Suitable metal components
for the cermets are transition metals, Cr, Fe, Ag and/or alloys
such as low-chromium ferritic steels, such as type 405 and 409
(11-15% Cr), intermediate-chromium ferritic steels, such as type
430 and 434, (16-18% Cr), high-chromium ferritic steels, such as
type 442, 446 and E-Brite (19-30% Cr), chrome-based alloys such as
Cr5Fe1Y and chrome-containing nickel-based alloys such as Ni20Cr
and Inconel alloys including Inconel 600 (Ni 76%, Cr 15.5%, Fe 8%,
Cu 0.2%, Si 0.2%, Mn 0.5%, and C 0.08%).
[0071] A very thin layer of electrolyte 30 is preferably applied to
the cathode tube 34. It has been shown that the operating
temperature of an electrochemical cell can be reduced with the use
of thin film ceramic electrolytes and electrodes because of the
reduction of ohmic losses across ionic and ionic-electric
conducting materials deposited as thin films. The bi-layer is then
co-fired to yield a pinhole free, dense film of electrolyte that is
well bonded to the porous structure of the electrode in one
embodiment. The sintering behavior of both film and substrate
materials should also be considered in the selection of electrolyte
and electrode materials. For example, it may be necessary to fire
the second electrode at a different temperature than used to give
the electrolyte sufficient density to prevent gases from crossing
the electrolyte layers or the temperature used to process the first
electrode depending on the nature of the selected electrode
material.
[0072] Several approaches to thin film fabrication are known in the
art including physical vapor deposition techniques, tape
calendaring, sol-gel deposition, sputtering, colloidal deposition,
centrifugal casting, slip-casting, tape-casting, extrusion, screen
printing, brushing, tape transfer, co-extrusion, electrophoretic
deposition, dip coating, aerosol spray, vacuum infiltration, plasma
deposition, electrochemical deposition, and many other methods know
in the art. Dip coating, aerosol spray, and screen printing are
preferred. Heating the layers to a sufficient temperature to ensure
bonding of the porous support and densification of the electrolyte
is typically required.
[0073] While there are many methods of creating thin films, it is
preferred that the films be deposited using a colloidal deposition
method. In this embodiment, the electrolyte material is generally
prepared as a suspension of the powder material in a liquid media,
such as water, isopropanol, and other suitable organic solvents.
The suspension may be applied to a surface of an electrode layer by
a variety of methods; for example, by aerosol spray, dip coating,
electrophoretic deposition, vacuum infiltration, or tape casting.
Typically, green films of the desired oxide are colloidally
deposited onto green or partially fired substrates. In addition,
the film should be well bonded to the surface of the substrate
without excessive infiltration into the porosity of the electrode
and there should be minimal polarization at the interface between
the electrolyte and electrode.
[0074] The colloidal process is preferred because it is inexpensive
and scaleable, and can produce devices with high performance at
reduced temperatures. However, colloidal deposition of dense
electrolyte layers on porous substrates requires that the materials
be chemically compatible at the processing temperature and there
must be an adequate thermal expansion match between the layers.
[0075] A pinhole and crack free dense layer of electrolyte 30
ranging from approximately 1 .mu.m to approximately 50 .mu.m in
thickness on electrode substrates of high porosity and suitable
microstructure to ensure low overpotential during device operation
are generally preferred. For typical fuel cell applications, an
electrolyte layer ranging from approximately 10 .mu.m to
approximately 30 .mu.m in thickness is preferred.
[0076] The electrolyte material is preferably composed of a thin
layer of a metal oxide (ceramic) powder, such as yttria stabilized
zirconia (YSZ) (e.g., (ZrO.sub.2).sub.x(Y.sub.2O.sub.3).sub.y where
(0.88.gtoreq.X.gtoreq.0.97) and (0.03.ltoreq.y.ltoreq.0.12). The
preferred material is (ZrO.sub.2).sub.0.92(Y.sub.2O.sub.3).sub.0.08
or (ZrO.sub.2).sub.0.90(Y.sub.2O.sub.3).sub.0.10 that are available
commercially. Other possible electrolyte materials include
(ZrO.sub.2).sub.0.9(Sc.sub.2O.sub.3).sub.0.1 scandia stabilized
zirconia (SSZ), (CeO.sub.2).sub.0.8(Gd.sub.2O.sub.3).sub.0.2 (CGO),
La.sub.0.8Sr.sub.0.2Ga.sub.0.85Mg.sub.0.15O.sub.2.825 (LSGM20-15)
and (Bi.sub.2O.sub.3).sub.0.75(Y.sub.2O.sub.3).sub.0.25.
Alternatively, the electrolyte material may be a mixed ionic
electronic conductor, for example
SrCo.sub.1-xFe.sub.xO.sub.3-.delta. (0.30.gtoreq.X.gtoreq.0.20),
La.sub.0.6Sr.sub.0.4Co.sub.0.6Fe.sub.0.4O.sub.3-.delta.,
Sm.sub.0.5Sr.sub.0.5CoO.sub.3 and
La.sub.1-xSr.sub.xCoO.sub.3-.delta.. Such structures may also find
use in oxygen separation devices, for example.
[0077] The anode electrode 32 on the cathode supported
electrochemical cell 18 is preferably a thin film ranging in
thickness from approximately 50 .mu.m to 500 .mu.m. However,
electrode layers ranging in thickness of between approximately 150
.mu.m to approximately 300 .mu.m are preferred. In anode supported
electrochemical cells 18, an anode tube ranging in thickness from
between approximately 250 .mu.m to approximately 2500 .mu.m is
preferred.
[0078] Electrode and electrolyte materials are preferably matched
and the thickness of the applied materials may be selected based on
the thermal expansion, electronic conductivity and ionic
conductivity characteristics of the electrode and electrolyte
materials as well as the interconnect materials. In addition, the
thickness of the film of electrolyte 30 may depend the ability of
the electrolyte material to be gas impermeable and maintain its
mechanical integrity e.g. resist cracking when exposed to a range
of operating and rest temperatures.
[0079] The interconnect plates 14 can be made of inexpensive
ferritic steel materials which have a thermal expansion which match
the typical electrode and electrolyte materials. It will be
appreciated that the metallic interconnect plates 14 can be punched
and stamped using low cost technology to provide a fitted junction
between top and bottom rows 12 of electrochemical cells 18 and the
interconnect plate 14.
[0080] Referring also to FIG. 6 through FIG. 10, several
embodiments of stamped interconnect designs are shown in cross
section with a top electrochemical cell 36 and a bottom
electrochemical cell 38 and one stamped hole 16 design in
interconnect plate 14. In FIG. 6, it can be seen that interconnect
plate 14 has been punched and stamped to provide a seat for the top
and bottom electrochemical cells 36, 38. In the embodiment shown,
the electrochemical cells 36, 38 are cathode 34 supported with a
thin electrolyte 30 and exterior anode 32. The top electrochemical
cell 36 preferably has a metal to electrode pressure contact from
the top vertical collar 44 of interconnect plate 14 to the anode 32
of the cell 36 and provides an electrical contact from the cell 18
to the plate 14. In one embodiment, the collar 40 is sealed to the
anode electrode with a sealing material 42.
[0081] The interior of the tubular bottom electrochemical cell 34
receives a vertical ring 40 of plate 14 and the ring is in contact
with the cathode 30 in the embodiment shown in FIG. 6. The top end
of the bottom electrochemical cell 34 is preferably sealed with the
interconnect plate with metal, glass or ceramic seals 42.
[0082] Sealing the individual electrochemical cell 18 to the
preferably metal interconnect sheet 14 may be accomplished with
ceramic, glass, glass-ceramic, cermet, alloy brazes, or welds. The
electronically insulating seals are preferably alumina, silica, or
titania containing ceramic pastes or cermets. The electronically
conductive seals are preferably brazes based on Ag, Cu, or Ni
alloys, or brazing alloys mixed with ceramics such as alumina,
silica, or titania. Brazes can be applied as foils or paints.
Paints are typically applied by spray, brush, roller, or screen
printing.
[0083] Note that the anode 32 or the electrolyte 30 of the bottom
electrochemical cell 38 is not in contact with the interconnect
plate 14. The only contact that the bottom electrochemical cell 38
has with the interconnect plate 14 is the contact ring 44 has with
the cathode 34. Note also that it is preferred that the only
contact that the top electrochemical cell 36 has with the
interconnect plate 14 is with the anode 32. The cathode 34 and the
electrolyte 30 of the bottom electrochemical cell 38 are preferably
sealed to the interconnect plate 14 with a glass or ceramic seal
48.
[0084] FIG. 7 and FIG. 8 are alternative embodiments of stamped
interconnect plate 14 providing an electrical contact with the
anode on the side of the tubular electrochemical cells 36, 38.
Anode-interconnect seams may be sealed with a sealing material as
described above.
[0085] FIG. 9 and FIG. 10 are alternative embodiments of stamped
interconnects 14 that utilize spring seal edges. In these
embodiments the stamped edges of the perforations 16 are biased to
seat and seal the top and bottom electrochemical cells 36, 38. If
the compression seals are insufficient, then sealing material can
be applied at the anode interconnect seam in the embodiments shown
in FIG. 9 and FIG. 10 as described previously.
[0086] Turning now to FIG. 11 through FIG. 15, an alternative
embodiment of an interconnect-electrochemical cell junction is
generally shown. In this embodiment, the top and bottom
electrochemical cells 50, 52 may be inserted into top and bottom
annular grooves 54, 56 respectively of ferrule 58 and sealed. The
unit of ferrule 58, top electrochemical cell 50 and bottom
electrochemical cell 52 is then inserted into a holes 16 the
interconnect sheet 14 and attached to the sheet 14 with a planar
lip 60 around the periphery of the ferrule 58. The outer lip 60 of
the ferrule 58 may not only be used to bond to the metal sheet but
to provide a parallel connection within the stack.
[0087] Turning now to FIG. 13, the details of one embodiment of a
junction of the ferrule 58 and the top and bottom electrochemical
cells 50, 52 are shown. In this embodiment, the cathode 64 of the
bottom electrochemical cell 52 is sealed in groove 56 of ferrule 58
with an electronically conductive sealant 62. Neither the anode 68
nor the electrolyte 66 are in contact with the ferrule 58 in this
embodiment. The top electrochemical cell 50 is inserted into top
groove 54 of ferrule 58 with the bottom and side of cathode 64
sealed to the groove with a non-conducting sealant 70. The anode 68
of electrochemical cell 50 is bonded to the wall of groove 54 of
ferrule 58 with an electrically conductive sealant 72 in the
embodiment shown in FIG. 13.
[0088] An alternative embodiment of a junction showing the sealing
of top and bottom electrochemical cells 50, 52 to ferrule 58 is
seen. In this embodiment, the bottom edge of the top
electrochemical cell 50 is disposed in groove 54 of ferrule 58 and
sealed with an electrically non-conductive sealant 74. Similarly,
bottom electrochemical cell 52 is placed in groove 56 of ferrule 58
and sealed with an electrically non-conductive sealant 74.
[0089] The anode 68 of the top electrochemical cell 50 is further
joined and sealed to the ferrule 58 with an electronically
conductive paste 78 or similar conductive sealant or connective
material. The conductive paste 76 preferably provides a good
contact for the movement of electrons from the anode 68. Likewise,
the cathode 64 of the bottom electrochemical cell 52 has an
electronically conductive paste 78 or the like that brings the
cathode 64 in contact with the ferrule 58.
[0090] Turning now to FIG. 15, an alternative embodiment of the
invention with a paired multiple cell stack using ferrules and
interconnect plates 14 is seen. In this embodiment a single
electrochemical cell can be connected in series with N cells
between the parallel connecting plates where N=1-100, preferably
N=2-10. Shown in the FIG. 15 are two parallel rows of tubes, each
containing three electrochemical cells in series (N=3).
[0091] It has been seen that devices that carry current can fail
either in the open condition or in a shorted condition. Information
about the failure mode of a device can be used to further optimize
the stack design. Failure of one cell by shorting will not short
all of the cells positioned between the parallel plates.
[0092] In this embodiment, a bottom electrochemical cell 80 is
mounted and sealed to a ferrule 58 which is then sealed to a base
interconnect plate 14 as described previously. A second ferrule 58
is sealed to the distal end of electrochemical cell 80. A middle
electrochemical cell 82 is sealed with the second ferrule 58 and
with a third ferrule at the distal end of the cell 82. A third cell
84 is sealed to the third ferrule at one end and a fourth ferrule
at the other. The fourth ferrule is mounted to an interconnect
plate 14.
[0093] Accordingly, the electrochemical cells may be sealed
directly to the interconnect plate 14 or the cell may first be
attached to a ferrule 58 and then inserted into the plate 14. A
ferrule 58 can be applied to one or both ends of the
electrochemical device repeat unit (single cell). In another
embodiment, one ferrule 58 may be designed such that it will fit
into a second ferrule or into the metal sheet with male/female
connections (not shown).
[0094] With the use of a module of a ferrule 58 and mounted
electrochemical cells, the composition of the ferrule 58 can be
different from the composition of the interconnect plate 14 and the
manufacturing conditions can be varied. For example, brazing or
bonding the ferrule 58 to the tubular electrochemical cells 50, 52
can be separate from bonding or connecting the ferrule 58 to the
interconnect plate 14 and allows the use of alumina or silica
forming alloys as the interconnect sheet 14 without forming highly
resistive interfaces.
[0095] Individual tubular cells or a series of electrochemical
cells as seen in FIG. 15 can be brazed to a Ni or Cu or stainless
steel ferrule 58 using, for example a AgCuTi braze for the
electronically conductive seal between the ferrule and the support
electrode of the cell. Pastes, sealants and brazes may be applied
to the interconnect sheet 14 or to the ferrule 58 or to the
electrochemical cells 80,82 or 84 as well as to a combination of
these components depending on the deposition technology used (i.e.
dip coating, screen printing, roll, brush, etc).
[0096] In the embodiment shown in FIG. 15, alumina paste may be
used for the non-conducting seal between the second ferrule and the
cell; and a AgCuTi braze could then be used to electronically
connect the second ferrule to the counter electrode so that an
electrical path would be created through the first ferrule to the
support electrode, through the electrolyte to the second counter
electrode, and then to the second ferrule.
[0097] The ferrule in this structure can then be spot welded to an
alumina forming alloy interconnect sheet 14 (typically an Fe based
alloy containing Cr Al and Y and commonly designated as FeCrAlY).
It will be appreciated that the inner part of the weld would not be
subject to oxidation and so would maintain electrical contact
between the metal interconnect sheet 14 and the ferrule 58. This
allows a high temperature alloy that forms an electronically
insulating scale to be bonded electrically to the cell or cell
series via a weld or similar method.
[0098] Similarly an alumina forming alloy (such as FeCrAlY) can
have metal gaskets, for example of Ni or Cu rings, located around
the opening for the gas flow to the tubular cell, that are welded
to the FeCrAlY sheet. The ferrule or cell is bonded or brazed to
this metal rather than the FeCrAlY. This again allows the use of an
alloy that forms a highly adherent though electronically
non-conductive scale to be used as the interconnect plate.
[0099] Although the description above contains many details, these
should not be construed as limiting the scope of the invention but
as merely providing illustrations of some of the presently
preferred embodiments of this invention. Therefore, it will be
appreciated that the scope of the present invention fully
encompasses other embodiments which may become obvious to those
skilled in the art, and that the scope of the present invention is
accordingly to be limited by nothing other than the appended
claims, in which reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated,
but rather "one or more." All structural, chemical, and functional
equivalents to the elements of the above-described preferred
embodiment that are known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the present claims. Moreover, it is not necessary
for a device or method to address each and every problem sought to
be solved by the present invention, for it to be encompassed by the
present claims. Furthermore, no element, component, or method step
in the present disclosure is intended to be dedicated to the public
regardless of whether the element, component, or method step is
explicitly recited in the claims. No claim element herein is to be
construed under the provisions of 35 U.S.C. 112, sixth paragraph,
unless the element is expressly recited using the phrase "means
for."
* * * * *