Abstract:
An ROB stack ( 10′ ) contains a plurality of stacked ROB cells ( 10 ) made from: thin metal bipolar housings ( 13 ) having air inlets and exits and horizontal channels for feeding air between the inlets ( 16 ) and exits ( 17 ), the channel having top ridges and also grooves ( 25 ) for containing active material ( 34 ); a porous air electrode ( 21/39 ) next to the air channels allowing air contact; a metal electrode ( 36 ); and an oxygen ion transfer membrane ( 37 ) acting as electrolyte; wherein the plurality of all the assemblies form vertical air inlet and outlet plenums.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This present invention relates to engineering methods for constructing rechargeable oxide-ion battery ROB cells (hereinafter “ROB cells and stacks”) which include oxygen/air plenums. More specifically, the invention details low cost fabrication methods and oxygen and auxiliary gas feed flows for practical low weight compact ROB cells and stacks. 
         [0003]    2. Description of Related Art 
         [0004]    Electrical energy storage is crucial for the effective proliferation of an electrical economy and for the implementation of many renewable energy technologies. During the past two decades, the demand for the storage of electrical energy has increased significantly in the areas of portable, transportation, load-leveling and central backup applications. The present electrochemical energy storage systems are simply too costly to penetrate major new markets. Higher performance is required, and environmentally acceptable materials are preferred. Transformational changes in electrical energy storage science and technology are in great demand to allow higher and faster energy storage at lower costs and longer lifetimes necessary for major market enlargement. Most of these changes require new materials and/or innovative concepts, with demonstration of larger redox capacities that react more rapidly and reversibly with cations and/or anions. 
         [0005]    Batteries are by far the most common form of storing electrical energy, ranging from: standard every day lead—acid cells, nickel-metal hydride (NiMH) batteries taught by Kitayama in U.S. Pat. No. 6,399,247 B1, metal-air cells taught by Isenberg in U.S. Pat. No. 4,054,729, and to the lithium-ion battery taught by Ohata in U.S. Pat. No. 7,396,612 B2. These latter metal-air, nickel-metal hydride and lithium-ion battery cells require liquid electrolyte systems. 
         [0006]    Batteries range in size from button cells used in watches, to megawatt load leveling applications. They are, in general, efficient storage devices, with output energy typically exceeding 90% of input energy, except at the highest power densities. 
         [0007]    Rechargeable batteries have evolved over the years from lead-acid through nickel-cadmium and nickel-metal hydride (NiMH) to lithium-ion batteries. NiMH batteries were the initial workhorse for electronic devices such as computers and cell phones, but they have almost been completely displaced from that market by lithium-ion batteries because of the latter&#39;s higher energy storage capacity. Today, NiMH technology is the principal battery used in hybrid electric vehicles, but it is likely to be displaced by the higher power energy and now lower cost lithium batteries, if the latter&#39;s safety and lifetime can be improved. Of the advanced batteries, lithium-ion is the dominant power source for most rechargeable electronic devices. 
         [0008]    What is needed is a dramatically new electrical energy storage device that can easily discharge and charge a high capacity of energy quickly and reversibly, as needed. What is also needed is a device that can operate for years without major maintenance. What is also needed is a device that does not need to operate on natural gas, hydrocarbon fuel or its reformed by-products such as H 2 . One possibility is a rechargeable oxide-ion battery (ROB), as set out, for example, in application Ser. No. 12/695,386, filed on Jan. 28, 2010, now U.S. Patent Publication No. 2011/0033769, and application Ser. No. 13/167,900 filed on Jun. 24, 2011 (ESCM 283139-01297; Docket 2010P18820US, entitled “Construction of Planar Rechargeable Oxide-Ion Battery Cells and Stacks Using Stainless Steel Housing Structures.”) 
         [0009]    A ROB comprises a metal electrode, an oxide-ion conductive electrolyte, and a cathode. The metal electrode undergoes reduction-oxidation cycles during charge and discharge processes for energy storage. The working principles of a rechargeable oxide-ion battery ROB cell  1  are schematically shown in  FIG. 1 . In discharge mode, oxide-ion anions migrate from high partial pressure of the oxygen side (air electrode-2) to low partial pressure of the oxygen side (metal electrode-4) under the driving force of the gradient oxygen chemical potential. Electrolyte is shown as 3. There exist two possible reaction mechanisms to oxidize the metal. One of them, solid-state diffusion reaction as designated as Path 1, is that oxide ion can directly electrochemically oxidize metal to form metal oxide. The other, gas-phase transport reaction designated as Path 2, involves generation and consumption of gaseous phase oxygen. The oxide ion can be initially converted to a gaseous oxygen molecule on a metal electrode, and then further reacts with metal via solid-gas phase mechanism to faun metal oxide. In charge mode, the oxygen species, released by reducing metal oxide to metal via electrochemical Path 1 or solid-gas mechanism Path 2, are transported from a metal electrode back to an air electrode. 
         [0010]    During discharge/charge cycles metal redox reactions induce significant volume variation, for instance, if iron (Fe) metal is used, the volume change associated with the reaction of Fe+½O 2 =FeO is 1.78 times. Therefore, the metal electrode must be appropriately designed so that the drastic volume variation can be properly accommodated. For energy storage application, oxide ion must be transported across the electrolyte between a metal electrode and a cathode to carry electrical charge. Therefore, the metal electrode must be hermetically sealed to prevent direct contact with an oxygen-containing environment (for example, air). Otherwise, oxygen in air will directly consume the metal without involving charge transfer between electrodes, which will lead to self discharge. 
         [0011]    The cell voltage for each individual ROB cell is limited in most cases, for practical applications where certain voltage output is demanded, ROB cells must be connected together to fowl a stack to raise the voltage of a ROB device. Means must be also found to provide oxygen and steam or hydrogen to the stack cells via gas plenums. Additionally, weight must be lowered to make the ROB stacks practical. Thus, there is a need of engineering methods to construct an ROB stack using single ROB cells containing various gas plenums. 
         [0012]    It is a main object of this invention to provide ROB cell and stack designs that supply the above needs by using cost-effective materials and processing techniques. 
       SUMMARY OF THE INVENTION 
       [0013]    The above needs for producing a ROB cell and stack are supplied and object accomplished by utilizing an ROB stack comprising: 1) a plurality of stacked ROB cells each ROB cell comprising an electrically conducting thin metal bipolar housing having a very thin thickness of from about 0.1 cm to 0.75 cm, each bipolar housing having openings for vertical air inlets, vertical air exhaust inlets and interiors of horizontal channels for feeding air between the vertical air inlets and exhaust inlets, where said interiors of channels have top ridges; and grooves between the top ridges for containing active material; 2) a porous air electrode disposed next to the interior of the horizontal air channels allowing air contact; 3) a metal electrode; 4) an oxygen ion transfer cell membrane acting as electrolyte, allowing oxygen ion transfer, disposed on top of the metal electrode; and 5) dielectric perimeter seal disposed between the bipolar housings; where, in the plurality of ROB cells, the vertical air inlets and air exhaust inlets form air inlet plenums and air exhaust plenums which allow air contact with adjacent cells and where the horizontal channel ridges and grooves prevent air contact with any active material. Dielectric contacts can be disposed at far edges between the bipolar housings. Preferably, the very thin bipolar housing can be hydro-formed, electroformed or, most preferably, stamped, rather than milled or cast, saving substantial costs and manufacturing time, making the ROB stack more commercially viable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a better understanding of the invention, reference may be made to the preferred embodiments exemplary of this invention, shown in the accompanying drawings in which: 
           [0015]      FIG. 1  is a cross-sectional view that illustrates the known working principals of a rechargeable oxide-ion battery (ROB) cell; 
           [0016]      FIG. 2  is a simplified three-dimensional stacked view that generally illustrates a metal framed ROB cell; 
           [0017]      FIG. 3 , which best describes the invention, is a three-dimensional view that illustrates one preferred embodiment of a complete ROB cell showing vertical gas flow and horizontal gas flow; 
           [0018]      FIG. 4  is one embodiment of a three-dimensional partial view showing horizontal flow paths of gases in a metal bipolar housing structure of the ROB; 
           [0019]      FIG. 5  is a three-dimensional stacked view that illustrates two ROB assemblies stacked on top of each other; 
           [0020]      FIG. 6  illustrates a top view of a single metal bipolar housing; 
           [0021]      FIG. 7  is a cross-sectional view of section  7 - 7  shown in  FIG. 6 ; 
           [0022]      FIG. 8  is one embodiment of a cross-sectional view of section  8 - 8  shown in  FIG. 6  showing auxiliary gas flow; and 
           [0023]      FIG. 9  is one embodiment of a cross-sectional view of section  9 - 9  shown in  FIG. 6  showing air or oxygen gas flow. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]    The requirements of a practical, commercial ROB cell include:
       a) an air electrode for reversible conversion of oxygen into an oxide ion (O 2 ) that carries/has two electrical charges;   b) an oxide-ion conductive electrolyte for transporting electrical charge in the form of O 2− ;   c) a metal electrode where electrical charge associated with the oxide-ion is stored or released by an active metal component(s), and for accommodating the volume change associated with a metal redox reaction;   d) a reliable seal separating direct contact between air and active metal;   e) air and H 2  or steam plenums and distribution means;   f) light weight from use of thin components; and   g) cost effectiveness.       
 
         [0032]    The present invention relates to a low cost method for constructing rechargeable oxide-ion battery (ROB) cells and stacks with emphasis on the geometry of a thin metal bipolar housing that lends itself equally to existing low-cost stamping, hydro-forming, or electroforming fabrication methods, and use of gas feed plenums geometry therein. This metal bipolar housing  13  has a thickness of from about 0.1 cm to 0.75 cm, preferably from about 0.2 cm to 0.5 cm. These novel ROB cells  10 , best shown in  FIG. 3 , have a total thickness 10″ each of from about 0.3 cm to 2.5 cm, with a cost savings in materials and processing over cast, milled/machined, or powder formed of from 50% to 200%. A plurality of these ROB cells  10  form a ROB stack  10 ′, having interior air inlet and exhaust plenums, formed by openings for air inlet  16  and air exhaust outlet inlets  17 . As shown in  FIG. 5 , these inlets when combined in stacked relationship form stacked plenum openings as shown by arrows  16 ,  17  and  18 . All components, the metal bipolar housing, air electrode, metal electrode, cell membrane are generally the same thickness described above for the bipolar housing, that is, 0.1 cm to 0.75 cm. 
         [0033]    In general, the construction of a planar ROB cell  10  requires a metal bipolar housing  13 , shown in  FIG. 4 , with an included plurality of cavities in the form of channels/grooves between ridges, which grooves provide containment for an active metal. This bipolar housing  13  must also serve as an electrical conductor while providing a means to permit air-flow to come into contact with the air electrode cathode of the adjacent ROB cell in a stack array. A ROB cell membrane  37  is attached to a metal frame  5  via a sealed interface  6  as shown in  FIG. 2 . This assembly is then mated and sealed to the metal bipolar housing via edge welds. An optional feature provides a means to feed a supply of auxiliary gas  18  shown in  FIG. 4 , such as steam or hydrogen, to the grooves that contain the active metal. This auxiliary gas-flow is facilitated from opposing openings in the bipolar housing and metal frame. Similar opposing openings in the bipolar housing and metal frame facilitate the flow of air across a separate set of channels. 
         [0034]    Prior embodiments of experimental planar ROB cell assemblies utilized thick bipolar housings formed via a pressed powder metal process. Other past embodiments of planar ROB cell assemblies utilized thick bipolar housings machined from thick stock metal plate providing bipolar housings. Each of the prior approaches requires lengthy, expensive manufacturing processes and consume high amounts of metal raw material. 
         [0035]    This invention provides the functionality to satisfy the aforementioned ROB bipolar housing requirements via a geometry that is intended to be formed from thin metal. The geometry of the metal bipolar housing is intended to be formed by one of several existing low-cost fabrication methods. 
         [0036]    More specifically, referring again to  FIG. 2 , a preferred metal framed ROB cell assembly is generally illustrated. A ROB cell oxygen ion transfer electrolyte cell membrane  37  is attached to a metal frame  5  via a seal  6  interface such as, for example, glass or a metal braze. The metal frame  5  has a plurality of opposing openings  15  that serve, in a stacked relationship, as gas inlet and outlet plenums for both primary and optional auxiliary gas flows. The primary gas is intended to be air and the optional auxiliary gas may be, preferably, steam or hydrogen or their combination. Due to the relative complexity of the ROB assembly, applicants may refer to several figures in the same paragraph in order to try to clarify construction. 
         [0037]    In  FIGS. 3 and 4 , a planar ROB cell  10  is illustrated, having a total thickness of  10 ″. A plurality of preferably, from about 5 to 20 of these cell assemblies  10  are stacked to form a ROB stack  10 ′ in  FIG. 5 . The plurality of components, shown in  FIG. 3 , in combination form inlet and exhaust plenums, such as auxiliary gas  18  plenums  19  and  19 ′ and air plenum generally shown as openings for  16  and  17 . Arrows  16 ,  17  and  18  indicate overall plenum gas flow. The construction of the planar ROB cell assembly includes a metal bipolar housing  13  with a recess  13 ′ having a bottom containing the ROB cell membrane  37 , also shown in  FIG. 2 , which supports an included plurality of interior and exterior cavities in the form of channels  25  and grooves  14 ′ between the channels, shown in  FIG. 4 . These grooves also shown as  14 ′ in  FIG. 4  provide containment for a porous active metal material, while the interior  14  of the channels provide air passage. A number of these grooves may also provide passages for an optional auxiliary gas flow through porous active material. The metal bipolar housing  13  has opposing openings  15 , shown in  FIG. 2 , that serve as air or oxygen gas inlet  16  and exhaust gas inlet  17  for the separate primary and auxiliary gas flows  18 . In  FIGS. 4 and 6 , the steam and/or hydrogen auxiliary gas flow  18  is depicted exiting the small auxiliary inlet  19  and distributing to separate grooves  25  between the channels which grooves and channels span the width of the entire ROB cell membrane  37 , as will be further discussed later. 
         [0038]    The small auxiliary inlet  19  and output  19 ′, which are parts of the auxiliary plenums, shown more clearly in  FIG. 3 , is associated with a recess  13 ′ that is formed into the metal bipolar housing  13 , as shown in  FIG. 3 . The auxiliary gas flow is collected by an identical opposing small auxiliary outlet  19 ′. It is anticipated that the auxiliary gas flow will be relatively small; hence, the auxiliary gas flow pressure drop should aid in provide a uniform distribution of flow. The metal bipolar housing  13  can have four formed rectangular support bosses  100  at each corner. 
         [0039]    These support bosses  100  along with the two central formed bosses  102  at the locations of the auxiliary plenums, shown in  FIG. 5 , provide a defined load path to the adjacent ROB cell when assembled into a stack configuration. Additionally, two formed optional compression spacer bosses  11 , shown in  FIG. 3 , over and around the locations of the auxiliary inlet plenum  19 , provide a flanged seal surface to maintain separate auxiliary and primary gas plenums. 
         [0040]    The metal bipolar housing  13  serves as an electrical conductor. The electrical path is created by the incorporation of a compliant and porous electrical contact. This electrical contact  12  is mated to the tops of the ridges formed by the plurality of channels. The framed ROB cell assembly  10  is then installed by mating it to the flange at the perimeter of the metal bipolar housing. The installation of the framed ROB cell assembly slightly compresses the electrical contact to form continuity with the ROB cell membrane. Finally, this framed ROB cell assembly is then sealed to the metal bipolar housing via edge weld seals  30 , that are depicted in  FIGS. 7 ,  8  and  9 . 
         [0041]    Referring back to  FIGS. 4 and 5 , the ROB stack comprises two or more planar ROB cells  10  stacked atop one another. Two auxiliary flow seals  23  are located between the two flanged seal surfaces located at the auxiliary plenums of the metal bipolar housing  13  of one planar ROB cell and the mating surface of the framed ROB cell assembly  10 , shown in  FIG. 3 , of the mating planar ROB cell assembly to contain the separate auxiliary gas plenums from the primary plenums. A design requirement of the ROB assembly is the prevention of air from coming into contact with the active metal electrode material. 
         [0042]    The two auxiliary flow seals  23  also serve as a dielectric to prevent the current path from shorting across the planar ROB cell assemblies. Four dielectric contacts  20  constructed from the same material used for the flow seals  23  are placed at the four edges shown as  44  between the bipolar housings  13  at the formed support bosses. An additional perimeter seal  22  is be placed between opposing bipolar housings of the planar ROB cell assemblies to prevent air from bypassing from the air inlet plenum to the outlet plenum. This perimeter seal  22  must also serve as a dielectric for the same aforementioned reasons. The perimeter seal  22  can be glass or a compressible porous ceramic material, that permits only a small amount of total air leakage (generally &lt;3 vol. %). Finally, a second compliant and porous electrical contact  12  is inserted between the metal bipolar housing  13  of one planar ROB cell assembly and the mating surface of the ROB cell membrane  37  of the mating planar ROB cell assembly. 
         [0043]      FIGS. 7-9  provide details of a preferred embodiment of the invention and are not meant to be limiting.  FIG. 7  shows the section view  7 - 7  taken from the view in  FIG. 6  and helps understand location of channels and grooves. The construction of the planar ROB cell assembly requires a metal bipolar housing  13  with an included plurality of separate open, unimpeded air/oxidant interior channels  14  and grooves  25 , where the grooves  25  provide containment for a porous active metal  34 , shown in dotted cross-section. The channels  14  permit air flow to come into contact with the porous air electrode cathode  39  of the adjacent cell in a stack array.  FIG. 7  depicts the separate air channels  14 , and also the grooves  25  that house the active metal material  34 . Edge weld seals  30  are located at the interface of the ROB cell membranes  37  and the metal frame  5 . Perimeter seals are shown as  42 . 
         [0044]      FIG. 8  shows the section view  8 - 8  taken from the view in  FIG. 6 . The inlet auxiliary flow plenum is depicted and the flow path auxiliary gas  18  is shown as it feeds into a typical active metal groove  25 , containing porous active material  34 . Several seals are depicted including the seal welds at the outer edge, the auxiliary flow seals  23 , the perimeter seals  42 , and compressed spacer  11 . 
         [0045]      FIG. 9  shows the section view  9 - 9  taken from the view in  FIG. 6 . The inlet air flow plenum is depicted and the flow path is shown as it feeds into a typical air flow  14  as it goes into the interior of the air interior channel  14 . Several seals are depicted including the seal welds at the outer edge and edge of the air plenum. Edge seals  30  are located at the interface of the ROB cell membrane and the metal frame. Perimeter seals are shown as  42 . 
         [0046]    Reiterating; prior embodiments of ROB cells constructed at Siemens utilized bipolar housings formed via a pressed powder metal process or machined from stock metal plate which both inherently consume higher amounts of metal raw material. Each of the prior approaches requires expensive manufacturing processes unsuitable for both high volume and low cost production. This invention provides the functionality to satisfy the aforementioned ROB bipolar housing requirements via a complex geometry that is intended to be formed from thin metal. The final metal bipolar housing will be much lighter than prior embodiments resulting in greater energy storage density. The complex geometry of the metal bipolar housing is intended to be formed by one of several existing well known low-cost fabrication methods including stamping, hydro-forming, or electro-forming. 
         [0047]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.