KR20100106973A - Current collector structure - Google Patents

Abstract

Current collector structure used to distribute the potential to the electrode layer of the electrochemical cell. The electrochemical cell includes an electrolyte layer adjacent to the electrode layer for the movement of oxygen ions. The current collector structure includes a porous electrically conductive layer located on the electrode layer. In addition, at least one elongate strip type layer formed of an electrically conductive material is located on the porous electrically conductive layer, opposite the electrode layer, and oriented in the longitudinal direction of the electrode layer.

Description

Current collector structure {CURRENT COLLECTOR STRUCTURE}

The present invention relates to a current collector structure that distributes a potential to an electrode layer of an electrochemical cell. In particular, the present invention relates to a current collector structure wherein a porous electrically conductive layer is located on an electrode and at least one elongated strip type layer formed of an electrically conductive material is located on the porous electrically conductive layer.

Electrochemical cells are used to separate oxygen from oxygen-containing feeds. The purpose of the separation may be to concentrate oxygen or remove oxygen from the feed for purification purposes.

The electrochemical cell has an electrolyte layer that conducts oxygen ions, positioned between two electrode layers to apply a potential across the electrolyte layer. The electrode layers are porous and may have sublayers, while the electrolyte layer is an air-tight dense layer. The resulting composite structure may be in the form of a tube, in which an oxygen-containing feed is supplied inside the tube, and the separated oxygen is collected outside of the tube and then dispersed. The reverse is possible, where oxygen is supplied to the outside of the tube and permeated oxygen can be collected inside the tube. Other forms are possible, for example flat plates and honeycomb type structures.

The electrolyte layer is formed of an ion conductor capable of conducting oxygen ions when an elevated temperature and a potential are applied to the electrode layer. Under these circumstances, oxygen ions will ionize on one surface of the electrolyte layer and will move through the electrolyte layer to the opposite side under the stimulus of the potential, where the oxygen ions will recombine with molecular oxygen. Common materials used to form the electrolyte layer are yttria stabilized zirconia and gadolinium doped ceria. The potential is applied to the electrolyte layer through the cathode electrode and the anode electrode. Oxygen is ionized at the cathode and oxygen ions are recombined at the anode. In general, the electrodes can be made of a mixture of an electrolyte material and a conductive metal, a metal alloy or an electrically conductive perovskite.

In order to distribute the current to the electrode, the current collector is utilized in layer form on the electrode opposite the electrolyte layer. In some electrochemical cells, only the cathode electrode layer has a current collector layer. In other electrochemical cells, both the cathode and anode electrode layers have a current collector. However, it is important that the current collector layer is also porous to transfer oxygen through the current collector layer to the electrode layer for ionization purposes. The current collector layer is made as thin as possible to minimize the transfer resistance. However, this increases the electrical resistance of the current collector layer.

U. S. Patent No. 6,457, 657 discloses a porous current collector in which the current collector is formed of a mixture of ceramic particles and metal conductive particles to improve the aging characteristics of the current collector. In this regard, when the current collector is made of a metal and a metal alloy, and given the operating temperature of the electrochemical cell, the voids in this structure tend to close over time, reducing the oxygen transport through the current collector.

The other current collector is not formed in layers. For example, US patent application Ser. No. 2007/0003818 A1 uses a spring-loaded wire current collector in contact with an electrode. See, "High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications", Elsevier, pp. 219-220 by Singhal et al. (2004) discloses a wrap wire current collector. "Cathode Current-Collectors for a Novel Tubular SOFC Design", Journal of Power Sources 70, pp. 85-90 by Hatchwell et al. (1998) use silver strips and silver wires to distribute the potential to the electrodes.

As will be discussed, the present invention provides, among other advantages, a current collector structure using a porous electrically conductive layer over the electrode layer to distribute the potential across the surface of the electrode layer. However, the present invention overcomes the disadvantages of structures with increased resistance since the current collector is made sufficiently thin to attempt to minimize the resistance to the movement of molecular oxygen through these layers.

The present invention provides a current collector structure that distributes a potential to an electrode layer of an electrochemical cell having an electrolyte layer adjacent to the electrode layer for the movement of oxygen ions. The current collector structure has a porous electrically conductive layer located on the electrode layer. At least one elongate strip type layer formed of an electrically conductive material is located on the porous electrically conductive layer, opposite the electrode layer, and oriented in the longitudinal direction of the electrode layer.

The porous electrically conductive layer may be formed of particles of a metal or metal alloy containing surface deposits of metal oxides. Preferably, the electrically conductive material and the metal or metal alloy are silver and the metal oxide is zirconia. The silver in the at least one long strip type layer may have a density of about 50% to about 100% of the theoretical silver density. That is, the strip type layer can be porous or void free and dense.

The long strip type layer preferably has a thickness and width of about 100 micrometers to about 1000 micrometers, respectively. Preferably, the thickness of the porous electrically conductive layer is from about 15 micrometers to about 25 micrometers.

Although this specification ends with the claims clearly indicating what the applicant considers to be the invention, it is believed that the present invention will be further understood by reference to the accompanying drawings.
1 is a partial, schematic cross-sectional view of a tubular electrochemical cell having a current collector structure according to the present invention.
2 is a cross-sectional view of FIG. 1.
3 is a partial electron micrograph of a current collector according to the present invention applied to an electrode of an electrochemical cell.

1 and 2, there is shown an electrochemical cell 1 comprising a current collector structure according to the invention.

The electrochemical cell 1 includes an electrolyte layer 10 formed of a ceramic which is an ion conductor at a high temperature such as about 400 ° C to 1000 ° C. When the electrochemical cell 1 is under high temperature and a potential is applied to the opposing surfaces of the electrolyte layer 10, oxygen ions will conduct through the electrolyte layer to provide an oxygen permeate. Thus, as is well known in the art, electrochemical cells are located in an insulated enclosure, in which the electrochemical cells 1 are heated, and oxygen-containing stream 14 is supplied therefrom. The oxygen permeate stream 16 is discharged.

In the illustrated embodiment the electrochemical cell 1 is in the form of a tube. As mentioned above, other forms such as flat plates are possible. The oxygen containing stream 14 is in contact with the exterior of the electrochemical cell 1. Oxygen ions in the oxygen-containing gas are conducted through the electrolyte layer 10. Oxygen ions recombine inside the tube to form an oxygen permeate stream, indicated by arrow 16. In the illustrated embodiment, a potential is applied to the cathode electrode layer 18 and the anode electrode layer 20 located on opposite sides of the electrolyte layer 10. The potential 12 applied to the cathode electrode layer 18 and the anode electrode layer 20 serves as a driving force for the movement of oxygen ions.

The cathode electrode layer 18 and the anode electrode layer 20 may be formed of a mixture of ceramic and metal or metal alloy used in the electrolyte layer for thermal compatibility purposes. 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 when the electrolyte layer 10 is formed of yttria stabilized zirconia. In the case of the electrolyte layer 10 formed of gadolinium doped ceria, the cathode electrode 18 and the anode electrode 20 may be formed of a mixture containing 65% by weight of lanthanum strontium iron cobalt oxide and the remaining gadolinium doped ceria. have. In the example illustrated herein, the electrolyte layer 10 is formed of Scandia stabilized zirconia, and the cathode electrode 18 and the anode electrode 20 are a mixture of about 60% by weight lanthanum strontium manganate and the remaining Scandia stabilized zirconia Form each. In order for oxygen to reach the surface of the electrode 10, the cathode electrode layer 18 and the anode electrode layer 20 are porous and have a porosity of about 25% to about 40% and a pore size of about 0.1 to about 2.0 micrometers. Can be. The electrolyte layer 10 is a dense layer with few voids, and any voids present are not connected, so that the electrolyte layer 10 is an airtight layer. However, it will be understood that the present invention can be applied to any type of electrochemical cell formed of any structure and any suitable material.

The current collector structure of the present invention includes a porous electrically conductive layer 22 positioned on the cathode electrode layer 18, and in the illustrated embodiment each of the two strip type layers 24 and 26 are located opposite each other and the cathode electrode layer 18 Opposing), two strip type layers 28 and 30 are located on the porous electrically conductive layer 32 located on the anode electrode layer 20. However, it should be appreciated that there may be only one strip type layer associated with each porous electrically conductive layer or more than two strip type layers, depending on the size of the electrochemical cell 1.

As will be appreciated, the current collector structure described above may be provided only on the cathode electrode layer 18 in certain applications known in the art. In addition, the illustrated structure may be reversed so that the cathode layer 18 is located inside the tube and the anode layer 20 is located outside the tube. In this case the oxygen containing gas 14 is introduced into the tube.

The porous electrically conductive layers 22 and 32 should be porous so that oxygen passes through the cathode electrode layer 18 and into the electrolyte layer 10. The porous electrically conductive layer 22 or 32 may be formed of a metal or metal alloy or a mixture thereof, or a mixture of metal and metal oxides such as zirconia, but the preferred porous electrically conductive layer 22 or 32 may be a surface of the metal oxide. It is formed from a powder containing a metal or metal alloy with a surface deposit. Such powders may be prepared by methods well known in the art, such as wash-coating or mechanical alloying methods. For illustrative purposes, silver powder, designated FERRO S11000-02 powder, was obtained from Ferro Corporation, Electronic Material Systems, 3900 South Clinton Avenue, South Plainfield, New Jersey 07080 USA. The size of the particles contained in these powders is about 3 to about 10 micrometers in diameter, and the particles have a low specific surface area of about 0.2 m 2 / gram. Zirconia surface deposits were formed on these powders such that zirconia accounted for about 0.25% by weight of the coated particles. As can be appreciated, other electrically conductive metals and metal alloys such as Au, Pd, Pt, Ni, Ru, Rh, Ir and alloys of two or more of these elements can be used. In addition, the metal oxides may include CeO _{2 in} addition to zirconia, doped-ZrO ₂ (eg yttria stabilized zirconia-YSZ), doped CeO ₂ (eg 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 FeO 3,} La 0 .8 Sr 0 .2 may be a CrO _3, or _{La 0 .8 Sr 0 .2 CoO 3} .

The particle size of the metal or metal alloy may be larger than the particle size described above, but preferably the particle size ranges from about 0.1 micrometers to about 20 micrometers. In addition, although 0.25% by weight is a particularly preferred content of the metal oxide, larger amounts may be used provided the amount is less than or equal to the weight of the metal or metal alloy used to form the electrically conductive particles. In this regard, the metal oxide content of the electrically conductive particles is preferably from about 0.05% to about 1.0% by weight. The above weight-based content will remain unchanged in the final current collector layer in that the metal or metal alloy and metal oxide used to form the current collector layer after sintering is distributed throughout the current collector layer.

The powder may be applied to the cathode electrode layer 18 and the anode electrode layer 20 in the sintered form of the layered structure including the electrolyte layer 10, the cathode electrode layer 18, and the anode electrode layer 20 by a slurry immersion application technique. have. Other types of applications such as aerosol applications, screen printing and tape casting can be used. Of course, the slurry content is varied in a manner well known in the art to suit the particular type of application employed. The sintered form can be provided by various well known techniques such as extrusion, injection molding, isopressing and tape casting or a combination of these techniques. It should be noted that the layered structure may be in an unsintered or green state. In this case, the porous conductive layer 22 is applied to the cathode electrode layer 18 and the porous conductive layer 32 is applied to the anode electrode layer 20, and then the coated structures are heat treated together to sinter the composite structure.

In the case of dip coating, suitable slurries can be formed by known techniques such as mixing electrically conductive particles or powders with solvents such as ethanol and toluene, binders such as polyvinyl butyral, and plasticizers such as dibutyl phthalate. Dispersants such as herring fish oil may optionally be mixed into the slurry. In the case of silver coated particles obtained from Ferro Corporation as described above, the slurry is prepared according to the manufacturer's recommendations, ie, the conductive particles may be coated with FERRO B-73210 Tape Casting Binder System (available from Ferro Corporation, above), ethanol and toluene. It can form by mixing. The particles are about 45% to about 75% by weight of the slurry. In addition, the binder system is about 20% to 50% by weight of the slurry, with the remainder being the same amount of ethanol and toluene. Preferred slurries are about 70% by weight particles, 20% by weight binder system and the same amount of ethanol and toluene. Obviously, the lower the proportion of particles, the longer the time to immerse to achieve the desired thickness of shape. The layered structure can then be dipped into the slurry and then dried and heated to remove the solvent and burn organic components such as binders and plasticizers. Further heating partially sinters the current collector layer to provide the required porous electrically conductive layers 22 and 32. The porous electrically conductive layer 22 or 32 formed in the manner described above preferably has a thickness of about 15 micrometers to about 25 micrometers and has a porosity of about 30% to about 50%. Particular preference is given to pore sizes in the range of about 1 micrometer to about 10 micrometers. Pore size or specifically average pore diameter is determined by known quantitative three-dimensional line intersection analysis techniques. Although well known, specific references and descriptions of these techniques are described in Quantitative Stereology, by E.E. Underwood, Addison-Wesley Publishing Co., Reading MA, (1970). It should be noted that a content of electrically conductive particles, from about 45% to about 75% by weight of the slurry, is necessary to provide the above-described thickness range for the porous electrically conductive layer 22.

As can be appreciated, the thickness, porosity and pore size can be varied by changing the slurry composition, the number of dip coatings and the particle size. In addition, even when the porous electrically conductive layers 22 and 32 are formed of a metal such as silver or another metal or metal alloy or other suitable electrically conductive material mixture, the resulting layer has the thickness, porosity and pore size described above. Can have

The long strip type layers 24, 26, 28, and 30 may have a thickness and width that are each about 50 micrometers to about 2000 micrometers, and may be about 50% to 100% of theoretical silver density. For 100% theoretical density, the long strip type layers 24 and 26 are not porous. These layers can be formed from a slurry of FERRO SF4MA silver flakes obtained from Ferro Corporation mixed with 21 grams of binder available as binder B73210 from Ferro Corporation. The mixture can be placed in a coated glass jar containing 25 grams of zirconia milling media and shaken for about 8 hours. The long strip type layers 24 and 26 can be applied along the length of the tube using a syringe. The long strip type layers 28 and 30 can be formed by placing a tube formed of PTFE with a small side opening of about 1.3 mm into the composite structure forming the electrochemical cell 1. The mixture of silver and binder can then be injected into the composite structure and taken out. For example, a 30 ml syringe of predetermined length # 16 PTFE tube (Cole-Parmer) is fully inserted into a single porous electrode and current collector coated electrolyte tube, one end of which is equipped with a 17GA needle and filled with silver paste Is attached to. As the electrolyte tube is pulled linearly at a rate of 18 seconds / feet, the silver paste is dispensed into silver strips along the inner length of the tube using a 40 psi extrusion pressure setting. Using a PTFE tube held through a needle hole of a fixed syringe, the silver strip is applied in the same way to the outside of the electrolyte tube coated with the porous electrode and the silver current collector.

After application, the resulting composite structure comprising the strip-type layers was heat treated at about 850 ° C. to attach the strip-type layers to the underlying electrically conductive porous layer 22 and the electrically conductive porous layer 32 to thereby provide a strip-type layer ( 24, 26, 28 and 30).

Referring to FIG. 3, each of the cathode electrode layer 18 and the anode electrode layer 20 is formed of a composite of about 60 wt% lanthanum strontium manganate and the rest of Scandia stabilized zirconia, and the electrolyte layer 10 is made of Scandia stabilized zirconia. The electrochemical cell 1 of the type mentioned above was formed. In the example, electrolyte layer 10 is about 500 micrometers thick, and each of cathode electrode layer 18 and anode electrode layer 20 is about 40 micrometers thick. Each of the electrically conductive porous layers 22 and 32 is formed of silver particles having a surface deposit of about 0.25% by weight zirconia, the silver particles having a size of about 7 micrometers. The electrically conductive porous layers 22 and 32 had a thickness of about 20 micrometers, a pore size of about 12 micrometers, and a porosity of about 50% by volume. Each of the strip type layers 24, 26, 28 and 30 was formed of silver in the manner described above and had a thickness and width of about 300 micrometers and about 800 micrometers, respectively.

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

Claims (6)

A current collector structure for distributing a potential to an electrode layer of an electrochemical cell having an electrolyte layer adjacent to an electrode layer for movement of oxygen ions,
The current collector structure,
A porous electrically conductive layer located on the electrode layer; And
At least one elongated strip type layer formed of an electrically conductive material, positioned on the porous electrically conductive layer, opposite the electrode layer and oriented in the longitudinal direction of the electrode layer
Current collector structure comprising a. The method of claim 1,
And the porous electrically conductive layer is formed of particles of a metal or metal alloy containing surface deposits of a metal oxide. The method of claim 2,
And the metal or metal alloy is silver and the metal oxide is zirconia. The method of claim 3,
The current collector structure in which the silver in the at least one long strip type layer is about 50% to about 100% of the theoretical silver density. The method of claim 4, wherein
The current collector structure having a thickness and a width wherein the at least one long strip type layer is each from about 50 micrometers to about 2000 micrometers. The method of claim 5,
And the porous electrically conductive layer has a thickness of about 15 micrometers to about 25 micrometers.

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