JP2011510432A - Current collector structure - Google Patents

Abstract

  A current collector structure used to distribute the potential across the electrode layer of an electrochemical cell. This electrochemical cell has an electrolyte layer adjacent to an electrode layer for transporting oxygen ions. The current collector structure has a porous conductive layer placed on the electrode layer. Furthermore, at least one elongated strip of conductive material layer is placed on the porous conductive layer facing the electrode and oriented in the length direction of the electrode layer.

Description

  The present invention relates to a current collector structure for distributing a potential to an electrode layer of an electrochemical cell. More particularly, the present invention provides that a porous conductive layer is placed on the electrode layer and one or more elongated strip layers of conductive material are placed on the porous conductive layer. It relates to such a current collector structure.

  An electrochemical cell is used that separates oxygen from the oxygen-containing feed. The purpose of the separation may be to condense oxygen or to remove oxygen from the feed for purification purposes.

  The current collector structure has an electrolyte layer that conducts oxygen ions that is disposed between two electrode layers to apply a potential between the electrolytes. The electrode layer is porous and can have sublayers, while the electrolyte is an airtight dense layer. The resulting composite structure may be tubular, in which the oxygen-containing feed is fed inside the tube and the separated oxygen is collected outside the tube and then dissipated. The reverse is also possible: oxygen may be supplied to the outside of the tube and oxygen that passes through may be collected inside the tube. For example, other forms of flat plate or honeycomb structure are possible.

  The electrolyte layer is composed of an ion conductor, and can conduct oxygen ions when a potential is applied to the electrode layer at a high temperature. Under such conditions, oxygen ions are ionized on one side of the electrolyte layer and are transported through the electrolyte layer to the opposite side of the electrolyte layer under potential activation, where the oxygen ions recombine and become molecular oxygen. Become. A typical material used for forming the electrolyte layer is ceria doped with yttria-stabilized zirconia and gadolinium. A potential is applied to the electrolyte layer by the cathode electrode and the anode electrode. Oxygen is ionized at the cathode and oxygen ions recombine at the anode. Typically, the electrode may be made of a mixture of an electrolyte material and a conductive metal, metal alloy or conductive perovskite.

  For the purpose of distributing current to the electrodes, a current collector is utilized in layer form on the electrode facing the electrolyte. In some electrochemical cells, a current collector layer is provided only on the cathode electrode layer. In other electrochemical cells, current collectors are provided in both the cathode layer and the anode layer. However, for ionization purposes, it is important that the current collector layer is also porous so that oxygen can be transported through the current collector layer to the electrode layer. In order to minimize the transport resistance, the current collector layer is made as thin as possible. However, this increases the electrical resistance of the current collector layer.

  US Pat. No. 6,457,657 discloses a porous current collector configured such that the current collector is formed from a mixture of ceramic and metal conductive particles to improve the aging characteristics of the current collector. In this regard, when the current collector is made of metal and metal alloy, given the operating temperature of the electrochemical cell, the holes in such a structure tend to close over time and reduce oxygen transport through the current collector. .

  Other current collectors are not composed of layers. For example, US Patent Application Serial No. 2007/0003818 A 1 utilizes a spring loaded wire current collector that contacts the electrode. Singhai et al., “High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications” Elsevier, pp. 219-220 (2004), discloses a wrap wire current collector. Hatchwell et al's “Cathode Current-Collectors for Novel Tubular SOFC Design”, Journal of Power Sources 70, pp. 85-90 (1998) uses silver strips and silver wires to distribute the potential across the electrodes. .

  As discussed, among other advantages, the present invention provides a current collector structure that utilizes a porous conductive layer on the electrode layer so that the potential can be distributed across the surface of the electrode layer. However, it overcomes the shortcomings of such collector structures where the resistance is increased because attempts are made to make such current collectors sufficiently thin to minimize the transport resistance of molecular oxygen through such electrode layers. .

  The present invention provides a current collector structure that distributes potential across an electrode layer of an electrochemical cell having an electrolyte layer adjacent to the electrode layer for oxygen ion transport. The current collector includes a porous conductive layer placed on the electrode layer. At least one elongated strip of conductive material is placed on a porous conductive layer facing the electrode and oriented along the length of the electrode layer.

  The porous conductive layer may be formed of metal alloy particles containing a metal or metal oxide surface deposit. Preferably, the conductive material and the metal or metal alloy are silver and the metal oxide is zirconia. The silver in the at least one elongated strip layer may have a density between about 50% and about 100% of the theoretical density of silver. In other words, the strip-like layer may be porous or non-porous and dense.

  The elongated strip-like layers each preferably have a thickness and width between about 100 microns and about 1000 microns. Preferably, the porous conductive layer has a thickness between about 15 microns and about 25 microns.

  The specification concludes with claims that clearly point out the subject matter that the applicant regards as his invention, but it is believed that the present invention will be better understood when taken together with the accompanying drawings.

1 is a fragmentary schematic cross-sectional view of a tubular electrochemical cell having a current collector structure according to the present invention. It is a cross-sectional view of FIG. 2 is a fragmentary electron micrograph of a current collector according to the present invention applied to an electrode of an electrochemical cell.

  An electrochemical cell incorporating a current collector structure according to the present invention will be described with reference to FIGS.

  The electrochemical cell 1 has an electrolyte layer 10 formed from a ceramic that becomes an ionic conductor at a high temperature, such as between about 400 ° C and 1000 ° C. When the electrochemical cell 1 is heated to a high temperature and a potential is applied to the opposing surface of the electrolyte layer 10, oxygen ions conduct through the electrolyte and create oxygen permeation. Thus, as is well known in the art, the electrochemical cell is placed in an insulated enclosure where the electrochemical cell 1 is heated and fed with an oxygen-containing stream 14 from which an oxygen permeable stream 16 is supplied. Discharged.

  In the illustrated embodiment, the electrochemical cell 1 has a tubular shape. Other configurations such as flat plates are possible as described above. The oxygen-containing stream 14 is in contact with the outside of the electrochemical cell 14. Oxygen ions in the oxygen-containing gas conduct through the electrolyte layer 10. The oxygen ions recombine with each other inside the tube, creating an oxygen permeate stream represented by arrow 16. The potential in the illustrated embodiment is applied to the cathode electrode layer 18 and the anode electrode layer 18 placed on the opposite side of the electrolyte layer 10. The potential 12 applied to the cathode electrode layer 18 and the anode electrode layer 18 serves as a driving force for oxygen ion transport.

  The cathode electrode layer 18 and the anode electrode layer 18 may be formed from a mixture of a metal or a metal alloy and a ceramic used in the electrolyte for the purpose of heat compatibility. For example, the cathode electrode layer 18 and the anode electrode layer 20 may be formed of a mixture of yttria stabilized zirconia and silver particles for an electrolyte formed from yttria stabilized zirconia. In the case of an electrolyte layer 10 formed from gadolinium-doped ceria, the cathode and anode electrode layers 18 and 20 are a mixture containing 65 weight percent lanthanum strontium iron cobalt oxide and the balance gadolinium-doped ceria. What is necessary is just to form. In the illustrated example, the electrolyte layer 10 is formed of scandia-stabilized zirconia, and the cathode and anode electrode layers 18 and 20 are each about 60 weight percent lanthanum strontium manganite and the balance is scandia-stabilized zirconia. It is formed with the mixture containing. The cathode and anode electrode layers 18 and 20 are porous so that oxygen reaches the surface of the electrode 10, with a porosity of about 25 percent to about 40 percent and about 0.1 microns to about 2.0 microns. What is necessary is just to have a hole size up to. The electrolyte 10 is a honey layer with few holes, and any existing holes do not connect so that the electrolyte layer 10 is airtight. However, it is understood that the present invention has application to any type of electrochemical cell of any architecture formed from any suitable material.

  The current collector structure of the present invention has a porous conductive layer 22 disposed on the cathode electrode layer 18, and in the illustrated embodiment, each is opposed to the cathode electrode layer 18. And two strip-like layers 28 and 30 placed on a porous conductive layer 32 placed on the anode electrode layer 20. However, it should be noted that there may be only one strip-like layer associated with each porous conductive layer or more than two such strip-like layers according to the dimensions of the electrochemical cell 1. .

  As can be appreciated, the current collector structure described above need only be provided on the cathode electrode layer 18 for certain applications known in the art. In addition, the illustrated structure may conversely place the cathode layer 20 inside the tube and the anode layer 20 outside the tube. In such a case, the oxygen-containing gas 14 is introduced into the tube.

The porous conductive layers 22 and 32 must be porous so that oxygen can pass through the electrolyte layer 10 through the cathode electrode layer 18. Although the porous conductive layer 22 or 32 may be formed from a metal or metal alloy or a mixture thereof, or a mixture of a metal and a metal oxide such as zirconia, the preferred porous conductive layer 22 or 32 is a metal. It is formed from a metal alloy having a surface deposit of contained powder or metal oxide. Such powders can be made by methods well known in the art, for example by wash coating or mechanical alloy methods. For illustrative purposes, the silver powder expressed as FERRO S11000-02 powder was obtained from Ferro Corporation, Electronic Material Systems, 3900 South Clinton Avenue, South Plainfield, New Jersey 07080 USA. The dimensions of the particles contained in such powders are from about 3 to 10 microns in diameter, and the particles have a low specific surface area of about 0.2 m ² / gram. A zirconia surface deposit was formed on such powder so that zirconia was considered to be about 0.25 weight percent of the coated particles. As will be appreciated, other conductive metals and metal alloys can be used, such as Au, Pd, Pt, Ni, Ru, Rh, Ir, and alloys of two or more such elements. Furthermore, in addition to zirconia, the metal oxide, CeO _2, doped ZrO ₂ (e.g., yttria-stabilized zirconia -YSZ), doped CeO ₂ (e.g., gadolinia-doped ceria _{-CGO), Y 2 O 3,} Al ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ , Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ , SnO ₂ , La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ , La _0.8 Sr _0.2 MnO ₃ , La _0.8 Sr _0.2 It may be FeO ₃ , La _0.8 Sr _0.2 CrO ₃ , or La _0.8 Sr _0.2 CoO ₃ .

  The particle size for the metal or metal alloy may be larger than those described above, but preferably the particle size ranges from about 0.1 microns to about 20 microns. In addition, 0.25 weight percent is a particularly preferred content of the metal oxide, but higher amounts may be used. However, it is assumed that such an amount is not larger than the weight of the metal or metal alloy used in forming the conductive particles. In this regard, the metal oxide content of the conductive particles is preferably from about 0.05 weight percent to 1.0 weight percent. The weight content remains unchanged in the finished current collector layer. This is because after the metal or metal alloy is sintered, the metal oxide utilized in forming such a layer is distributed throughout the layer.

  Such powder may be applied to the cathode electrode layer 18 and the anode electrode layer 20 having a layered structure in a sintered shape by a slurry dip coating technique. The layered structure includes an electrolyte layer 10, a cathode electrode layer 18, and an anode electrode layer 18. Other types of deposition methods include aerosol deposition, screen printing, and tape casting. The slurry content is of course modified by methods well known in the art to suit a particular type of application. Sintered shapes can be generated by various well known techniques in the art such as extrusion, injection molding, isopressing, tape casting, or combinations of such techniques. Note that the layered structure can be in an unsintered or green state. In such a case, after the porous conductive layer 22 is attached to the cathode electrode layer 18 and the porous conductive layer 32 is attached to the anode electrode layer 18, these coating structures are fired together to sinter the composite structure.

  In the case of dip coating, a suitable slurry can be formed by well-known techniques such as mixing conductive particles or powders with solvents, binders and plasticizers. The solvent is ethanol and toluene, the binder is polyvinyl butyral, and the plasticizer is dibutyl phthalate. Dispersants such as menhaden fish oil may optionally be mixed into the slurry. As noted above, in the case of silver coated particles obtained from Ferro Corporation, the slurry may be made as recommended by such manufacturer. That is, the conductive particles are mixed with the FERRO B-73210 Tape Casting Binder System (available from Ferro Corporation above). The particles are about 45 weight percent to about 75 weight percent of the slurry. In addition, the binder system is from about 20 weight percent to about 50 weight percent of the slurry. The balance is equal amounts of ethanol and toluene. A preferred slurry is about 70 weight percent particles, about 20 weight percent binder system and the balance ethanol and toluene. Obviously, the lower the percentage of particles, the more dip time it takes for the shape to obtain the desired thickness. The layered structure may then be dipped into a slurry and then dried and heated to remove the solvent and burn out organic components such as binders and plasticizers. Further heating partially sinters the current collector layer and produces the necessary porous conductive layers 22 and 32. Either of the porous conductive layers 22 and 32 formed by the method described above is preferably about 15 microns to about 25 microns thick and has a porosity of about 30 percent to 50 percent. . Particularly preferred is a pore size ranging from about 1 micron to about 10 microns. The pore size, in particular the average pore diameter, is measured by the known quantitative stereological line intersection analytical technique. Although well known, a specific reference to and explanation of such techniques can be found in E.E. Underwood, Quantitative Stereology, Addison-Wesley Publishing Co., Reading MA, (1970). A conductive particle content of about 45 weight percent to about 75 weight percent of the slurry is necessary to produce the above thickness range of the porous conductive layer 22.

  As will be appreciated, the thickness, porosity and pore size may be varied by changing the slurry making, the number of dip coatings and the particle size. Furthermore, even if the porous conductive layer 22 or 32 is formed from a metal such as silver, or other metal, or metal alloy, or a mixture of other conductive materials, the resulting layer has a thickness as described above. It is only necessary to have porosity and pore size.

  The elongated strip-like layers 24, 26, 28 and 30 each have a thickness and width from about 50 microns to about 2000 microns and can be from about 50 percent to about 100 percent of the theoretical density of silver. That's fine. For a theoretical density of 100 percent, the elongated strip-like layers 14 and 26 are not porous. The layer is formed from a slurry of FERRO SF4MA silver flakes obtained from Ferro Corporation, mixed with 21 grams of binder obtained from Ferro Corporation as binder B73210. The mixture may be rolled for about 8 hours in a 25 gram zirconia milling medium and coated glass jar. The elongated strips 24 and 26 may be deposited along the length of the tube using an injector. The elongated strip layers 28 and 30 may be formed by positioning a tube of PTFE having a small lateral opening of about 1.3 mm within the composite structure forming the electrochemical cell 1. The mixture of silver and binder may then be injected into the composite structure and removed. For example, a length of # 16 PTFE tube (Cole-Parmer) was inserted all the way into an electrolyte tube coated with a single porous electrode and current collector, one end fitted with a 17GA needle and filled with silver paste. Attached to a 30 ml syringe. As the electrolyte tube is drawn linearly at a rate of 18 seconds / ft, silver paste is dispensed into thin silver stripes along the internal length of the tube using a 40 psi extrusion pressure setting device. In a similar manner using a PTFE tube held through a clamped injector needle hole, a silver stripe is applied to the outside of the electrolyte tube coated with the porous electrode and the silver current collector.

  After application, the resulting composite structure containing the resulting strip-like layer is then fired at about 850 ° C. to secure the strip-like layer to the underlying conductive porous layer 22 and the conductive porous layer 32 and strip The layers 24, 26, 28 and 30 are produced.

  Referring to FIG. 3, an electrochemical cell 1 of the above type was formed. There, each of the cathode electrode layer 18 and the anode electrode layer 20 is made from a composite of about 60 weight percent lanthanum, strontium, manganite and the balance scandia stabilized zirconia, and the electrolyte layer 10 is made of scandia stabilized zirconia. was made. In the illustration, electrolyte layer 10 is approximately 500 microns thick, and each of cathode and anode electrode layers 18 and 20 is approximately 40 microns thick. Each of the conductive porous layers 22 and 32 is made of silver particles having a surface deposit of about 0.25 weight percent zirconia, the particles having a size of about 7 microns. Conductive layers 22 and 32 had a thickness of about 20 microns, a pore size of about 12 microns and a porosity of about 50 volume percent. The strip layers 24, 26, 28 and 30 were made of silver as described above and had thicknesses and widths of about 300 microns and about 800 microns, respectively.

  Although the invention has been described with reference to preferred embodiments, it will be appreciated by those skilled in the art that numerous additions, omissions and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims. It can be done.

Claims (6)

A current collector structure for distributing the potential to the electrode layer of an electrochemical cell having an electrolyte layer adjacent to the electrode layer for transport of oxygen ions,
A porous conductive layer placed on the electrode layer;
The current collector structure comprising at least one elongated strip of conductive material placed on a porous conductive layer facing the electrode and oriented in the length direction of the electrode layer.   The current collector structure of claim 1, wherein the porous conductive layer comprises particles of a metal or metal alloy comprising a metal oxide surface deposit.   The current collector structure of claim 2 wherein the conductive material and the metal or metal alloy is silver and the metal oxide is zirconia.   4. The current collector structure of claim 3 wherein the silver in the at least one elongated strip layer comprises from about 50 percent to about 100 percent of the theoretical density of silver.   5. The current collector structure of claim 4, wherein the at least one elongated strip layer is about 50 microns to about 2000 microns in thickness and width each.   The current collector structure of claim 5 wherein the porous conductive layer has a thickness of from about 15 microns to about 25 microns.

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