SEPARATOR FOR ELECTROCHEMICAL DEVICE, ELECTROCHEMICAL DEVICE

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of priority to Korean Patent Application No. 10-2024-0147335 filed on Oct. 25, 2024, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a separator for an electrochemical device, and an electrochemical device.

Electrochemical devices include fuel cells that generate electrical energy by electrochemically reacting fuel (hydrogen) and an oxidizer (pure oxygen, or oxygen in the air), and electrolysis cells that generate hydrogen and oxygen through electrolysis of water.

As examples of such electrochemical devices, a solid oxide fuel cell (SOFC) and a solid oxide electrolysis cell (SOEC) include a cell comprised of an air electrode, a fuel electrode and a solid electrolyte having oxygen ion conductivity, and here, the cell may be referred to as a solid oxide cell. The solid oxide cell generates electrical energy through an electrochemical reaction or produces hydrogen by electrolyzing water through a reverse reaction of a solid oxide fuel cell. In addition thereto, other types of fuel cells or electrolytic cells, such as a phosphoric acid fuel cells (PAFC), an alkaline fuel cell (AFC), a polymer electrolyte fuel cell (PEMFC), and a direct methanol fuel cell (DMFC), are also used as a type of electrochemical device.

When electrochemical devices such as solid oxide cells are operated at high temperatures for long periods of time, the characteristics of the electrochemical device may deteriorate due to the diffusion of unintended substances, such as the diffusion of elements contained in the separator. Accordingly, attempts have been made in the art to reduce deteriorations in the performance of electrochemical devices.

SUMMARY

An aspect of the present disclosure is to provide a separator for an electrochemical device which may reduce performance degradation when applied to an electrochemical device, and an electrochemical device.

As a method to resolve the above-described aspect, provided is a separator for an electrochemical device including: a separator body; and a protective layer coated on a surface of the separator body, wherein the protective layer includes a Mn—Co oxide, and when a region including an inner surface in contact with the surface of the separator body in the protective layer is referred to as an inner region, and a region including an external surface is referred to as an outer region, the Mn—Co oxide has a higher content of Mn in the inner region than a content of Mn in the outer region.

In some example embodiments, the Mn—Co oxide may have a tendency for the content of Mn to decrease from the inner region to the outer region.

In some example embodiments, the Mn—Co oxide may have a tendency for a content of Co to decrease from the outer region to the inner region.

In some example embodiments, a degree to which the content of Mn decreases from the inner region to the outer region in the Mn—Co oxide may be greater than a degree to which the content of Co decreases from the outer region to the inner region.

In some example embodiments, the inner region may include a Mn oxide that substantially does not include Co.

In some example embodiments, the Mn oxide may be formed on the inner surface.

In some example embodiments, the outer region may include a Co oxide that substantially does not include Mn.

In some example embodiments, the Co oxide may be formed on the external surface.

In some example embodiments, a thickness of the protective layer may be 2 μm to 10 μm.

In some example embodiments, a thickness of the inner region may be 1/10 to ⅕ of a thickness of the protective layer, and a thickness of the outer region may be 1/10 to ⅕ of the thickness of the protective layer.

In some example embodiments, the protective layer may be formed on two main surfaces opposing each other in a thickness direction of the separator body and on a side surface connecting the two main surfaces.

In some example embodiments, the protective layer may be formed on one main surface of two main surfaces opposing each other in a thickness direction of the separator body, and may not be formed on a remaining main surface of the two main surfaces and on a side surface connecting the two main surfaces.

In some example embodiment, the protective layer is formed on two main surfaces opposing each other in a thickness direction of the separator body, and may not be formed on a side surface connecting the two main surfaces.

Meanwhile, according to another aspect of the present disclosure, provided is a electrochemical device including: a plurality of separators; and an electrochemical cell disposed between the plurality of separators and including a fuel electrode, an air electrode, and an electrolyte, wherein at least one of the plurality of separators may include a separator body and a protective layer coated on a surface of the separator body, the protective layer may include a Mn—Co oxide, and when a region including an inner surface in contact with a surface of the separator body in the protective layer is referred to as an inner region, and a region including an external surface is referred to as an outer region, the Mn—Co oxide may have a higher content of Mn in the inner region than a content of Mn in the outer region.

In some example embodiments, in a separator disposed adjacently to the air electrode among the plurality of separators, the protective layer may be formed at least on a main surface facing the air electrode, among two main surfaces opposing each other in a thickness direction in the separator body.

In some example embodiments, in a separator disposed adjacently to the air electrode among the plurality of separators, the protective layer may not be formed on a remaining main surface of the two main surfaces of the separator body and on a side surface connecting the two main surfaces.

In the case of a separator for an electrochemical device according to an example embodiment of the present disclosure, high performance thereof may be provided when the separator is applied to an electrochemical device.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the present disclosure will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 schematically illustrate an appearance of a separator for an electrochemical device according to an example embodiment of the present disclosure, and correspond to a perspective view and a cross-sectional view, respectively;

FIG. 3 is an enlarged view of region A in FIG. 2;

FIG. 4 to FIG. 7 are graphs illustration the relative contents of Mn and Co in a Mn—Co oxide of a protective layer according to positions;

FIGS. 8 and 9 illustrate an example of a process of forming a protective layer of a separator for an electrochemical device;

FIGS. 10 to 12 are cross-sectional views illustrating a separator for an electrochemical device according to a modified embodiment; and

FIG. 13 illustrates a water electrolysis device to which a separator according to an example embodiment of the present disclosure is applied.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present disclosure will be described with reference to specific example embodiments and the attached drawings. The example embodiments of the present disclosure may, however, be exemplified in many different forms and should not be construed as being limited to the specific embodiments set forth herein. Furthermore, the example embodiments disclosed herein are provided for those skilled in the art to better explain the present disclosure. Accordingly, in the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements.

Furthermore, in order to clearly describe the present disclosure in the drawings, contents unrelated to the description are omitted, and since sizes and thicknesses of each component illustrated in the drawings are arbitrarily illustrated for convenience of description, the present disclosure is not limited thereto. Furthermore, components with the same function within the same range of ideas are described using the same reference numerals. Throughout the specification, when a certain portion “includes” or “comprises” a certain component, this indicates that other components are not excluded and may be further included unless otherwise noted.

As used herein, the term “substantially” means a small, insignificant amount from absolute or perfect conditions, dimensions, measurements, results, etc., would be expected by one skilled in the art, but which does not significantly affect overall performance and allow for variation. “Substantially” when used for a number or parameter or property that can be expressed as a number means within 10 percent

FIGS. 1 and 2 schematically illustrate an appearance of a separator for an electrochemical device according to an example embodiment of the present disclosure, and correspond to a perspective view and a cross-sectional view, respectively, and FIG. 3 is an enlarged view of region A in FIG. 2. Additionally, FIG. 4 to FIG. 7 are graphs illustration the relative contents of Mn and Co in a Mn—Co oxide of a protective layer according to positions.

First, referring to FIGS. 1 to 3, a separator 100 for an electrochemical device according to an example embodiment of the present disclosure (hereinafter referred to as a “separator for an electrochemical device” or a “separator”) includes a separator body 101 and a protective layer 110, and here, the protective layer 110 has a function of preventing a component (e.g., Cr) included in the separator body 101 from diffusing into the cell and deteriorating the cell when the electrochemical device is driven. To this end, the protective layer 110 includes a Mn-Co oxide, and here, the content of Mn in an inner region 110A of the protective layer 110 is higher than the content of Mn in an outer region 110B. The Mn—Co oxide having such content conditions may be included, so that the protective layer 110 may be implemented to be dense and have a sufficient thickness, and may effectively prevent elements of the separator body 101 from diffusing into the cell side. Additionally, since the protective layer 110 includes the Mn—Co oxide, the protective layer 110 may have excellent electrical conductivity at high temperatures while not having a large difference in thermal expansion coefficient with the separator body 101, and may thus contribute to improving the performance of the electrochemical device.

The separator body 101 may be formed of a conductive material as a component separating each unit cell in the electrochemical device. Specifically, when the separator body 101 is used as an SOEC or SOFC, the separator body 101 may include a metal having a high melting point so that the separator body 101 does not melt or soften at high temperatures. For example, the separator body 101 may use a nickel-based material, an iron-based material, a stainless-based material, or other materials. Additionally, when an operating temperature of the separator body 101 is relatively low, for example, at about 800° C. or lower, copper or copper alloys having good electrical conductivity may also be used. As described above, when a material forming the separator body 101, for example, the Cr component, diffuses outwardly from the separator body 101, the performance of the cell may deteriorate, and in some example embodiments, the protective layer 110 coating the separator body 101 is adopted to reduce such deterioration. Hereinafter, the protective layer 110 will be described in detail.

Referring to FIGS. 4 to 7 together, a change in the contents of Mn and Co in the Mn—Co oxide of the protective layer 110 will be described. The graphs of FIGS. 4 to 7 show that the contents of each of Mn (see a thick line) and Co (see a thin line) tend to change depending on the position of the protective layer 110, and do not show the relationship in magnitude between the contents of Mn and Co. In other words, a left vertical axis indicating the content of Mn and a right vertical axis indicating the content of Co are unrelated to each other.

As described above, the protective layer 110 includes a Mn—Co oxide, and here, the content of Mn in the inner region 110A of the protective layer 110 is higher than the content of Mn in the outer region 110B. Here, the inner region 110A of the protective layer 110 refers to a region including an inner surface S1 coming into contact with the surface of the separator body 101, and the outer region 110B refers to a region including an external surface S2. The Mn-Co oxide of the protective layer 110 may be (Mn, Co)₃O₄, and the content of Mn may be defined as a molar content of Mn in the Mn—Co oxide. In terms of effectively preventing diffusion of Cr, and the like, from the separator body 101, a thickness (t) of the protective layer 110 may be about 2 μm to 10 μm. Additionally, with respect to how deep the inner region 110A and the outer region 110B are defined, for example, a thickness (t1) of the inner region 110A may be 1/10 to ⅕ of the thickness (t) of the protective layer 110, and similarly, a thickness (t2) of the outer region 110B may be 1/10 to ⅕ of the thickness (t) of the protective layer 110. Meanwhile, as illustrated in the form of FIG. 4, the separator body 101 may also include Mn, and in this case, the content of Mn may be lower than that of an adjacent region of the protective layer 110.

As one specific example, the Mn—Co oxide of the protective layer 110 may show a tendency for the content of Mn to decrease from the inner region 110A to the outer region 110B. On the contrary, the Mn—Co oxide of the protective layer 110 may show a tendency for the content of Co to decrease from the outer region 110B to the inner region 110A. This content distribution may be formed in the process in which Mn and Co diffuse toward each other by separately forming a Mn layer and a Co layer and then performing heat treatment when forming the protective layer 110, as described below. Additionally, a degree to which the content of Mn decreases from the inner region 110A to the outer region 110B in the Mn—Co oxide of the protective layer 110 may be greater than a degree to which the content of Co decreases from the outer region 110B to the inner region 110A. In other words, the content of Mn may show a more rapid change pattern than the content of Co. In this case, the degree of decrease of Mn and Co may be defined as a value obtained by dividing contents (absolute value) on the inner surface S1 and the external surface S2 by the thickness (t) of the protective layer 110. Such a tendency of decreasing the contents of Mn and Co may be obtained when the Co layer is formed to be thicker than the Mn layer and then heat-treated.

As a more specific example, as illustrated in the graph of FIG. 5, the inner region 110A may include a Mn oxide that does not substantially include Co, which may occur in a case in which the Mn layer is thick, or in an environment in which Co is difficult to diffuse. In this case, the Mn oxide may be formed on the inner surface S1 of the protective layer 110. Additionally, as illustrated in the graph of FIG. 6, the outer region 110B may include Co oxide that does not substantially include Mn, which is more likely to occur than when Co is not substantially present. As compared to the Co layer, the Mn layer is often difficult to form thickly, and when the Co layer is significantly thicker than the Mn layer, the Mn may not diffuse to the external surface S2. In this case, the Co oxide may be formed on the external surface S2 of the protective layer 110. The graph of FIG. 7 shows a protective layer 110 in which the inner region 110A includes Mn oxide that substantially does not include Co, and the outer region 110B includes Co oxide that substantially does not include Mn.

An example of a process of forming the protective layer 110 will be described with reference to FIGS. 8 and 9. First, as illustrated in FIG. 8, a first layer 111 including Mn is formed on the surface of the separator body 101. In the case of the first layer 111, this may be a Mn single material layer and may be formed using a deposition process, for example, a Physical Vapor Deposition (PVD) process such as sputtering. The first layer 111 for providing a Mn component may be formed with a thinner thickness than the Co layer, and for example, a thickness (t3) of the first layer 111 may be about 0.1 μm to 0.3 μm. Next, as illustrated in FIG. 9, a second layer 112 including Co is formed on the surface of the first layer 111. The second layer 112 may be a Co single material layer and may be formed using electroplating. The second layer 112 may be formed to be thicker than the first layer 111, and a difference in thickness may be significant, such that the second layer 112 is 10 to 30 times thicker than the first layer 111. An electroplating process is suitable for forming the second layer 112 densely and with sufficient thickness. After forming the second layer 112, a heat treatment may be performed so that the Mn of the first layer 111 may diffuse, and during this process, Mn—Co oxide may be formed. When the second layer 112 is significantly thicker than the first layer 111, Mn diffusion from the first layer 111 may be actively performed, but Co diffusion from the second layer 112 to the first layer 111 may also occur.

As described above, the first layer 111 including Mn may be formed to be relatively thin, and the second layer 112 including Co may be formed to be thick, and then, a heat treatment may be performed on the first layer 111 and the second layer 112 so that diffusion thereof occurs, thereby implementing the protective layer 110 to have a dense and sufficient thickness, as well as effectively preventing the elements of the separator body 101 from diffusing toward the cell. Additionally, the protective layer 110 may include the Mn—Co oxide, and thus, while the electrical conductivity at a high temperature is excellent, a difference in a thermal expansion rate from the separator main body 101 is not large, thereby improving the performance of the electrochemical device.

Hereinafter, a separator according to a modified example will be described with reference to FIGS. 10 to 12. First, the separator body 101 may include a flow path F through which a fluid may flow, as in the modified example of FIG. 10, and in this case, the protective layer 110 may be formed along a surface of the flow path F. A stamping process, an etching process, or the like, may be used to form the flow path F in the separator body 101. When the separator 100 is used as a water electrolysis device, water may be injected in the form of water vapor through a fluid inlet and hydrogen gas may be discharged through the fluid outlet, or vice versa when used as a fuel cell.

Next, a modified example of FIGS. 11 and 12 differ in a region in which the protective layer 110 is formed. In the above-described example embodiment, the protective layer 110 shows an example formed on an entire surface of the separator body 101. That is, the protective layer 110 may be formed on two main surfaces (upper and lower surfaces based on the drawing) facing each other in the thickness direction of the separator body 101 and on a side surface connecting the two main surfaces. In contrast, the protective layer 110 may be selectively formed depending on a required region. First, as illustrated in FIG. 11, the protective layer 110 may be formed on one of the two main surfaces opposing each other in the thickness direction of the separator body 101, and may not be formed on the remaining main surfaces of the two main surfaces and on the side surface connecting the two main surfaces.

In FIG. 11, an example is illustrated in which the protective layer 110 is formed only on a lower surface of the separator body 101, but the protective layer 110 may also be formed only on an upper surface of the separator body 101. When the protective layer 110 is selectively formed in a region in which diffusion from the separator body 101 to the protective layer 110 is greatly required to be prevented, there is an advantage in that while maintaining a diffusion function, it may be possible to prevent deterioration of electrical performance of the separator body 101, and to reduce the size of the separator. For example, the influence of Cr diffusion in the separator body 101 may be relatively greater in an air electrode of the solid oxide cell, and in this case, in the stack structure described below, the protective layer 110 may be formed at least on a main surface facing the air electrode, among two main surfaces opposing each other in a thickness direction in the separator body. Additionally, as illustrated in the form of FIG. 12, the protective layer 110 is formed on two main surfaces opposing each other in the thickness direction of the separation plate body 101, and may not be formed on the side surface connecting the two main surfaces.

An example of applying the separator described above to an electrochemical device will be described with reference to FIG. 13. FIG. 13 illustrates a water electrolysis device to which a separator for an electrochemical device according to an example embodiment is applied. However, the separators of the structure described above may be applied to other types of electrochemical devices such as fuel cells, not just water electrolysis devices. Referring to FIG. 13, a water electrolysis device 1000 includes a plurality of separator plates 301 and 302 and an electrochemical cell 310 disposed therebetween. Water in the form of water vapor may be supplied as fuel to the water electrolysis device 1000, and the water may be separated into hydrogen and oxygen through electrolysis. In order to improve the function of the electrolysis device 1000, a plurality of units 300 including the separator 301 and 302 and the electrochemical cell 310 may be provided and may be repeatedly configured to form a stack body 400.

Components of the unit 300 will be described. The unit 300 may include a fuel electrode-side separator 301 and an air electrode-side separator 302. In this case, at least one of the fuel electrode-side separator 301 and the air electrode-side separator 302 includes a separator body 101 and a protective layer 110, and here, the protective layer 110 includes Mn—Co oxide. Additionally, the content of Mn in the inner region 110A of the protective layer 110 may be implemented in a form higher than the content of Mn in the outer region 110B, the performance of the electrolysis device 1000 may be improved. In FIG. 13, an example is shown in which the protective layer 110 is formed on two separators 301 and 302, but the protective layer 110 may be formed on only one of the two separators 301 and 302. For example, the protective layer 110 may be formed on only the air electrode-side separator 302, and as described above, the protective layer 110 may be formed on a main surface facing an air electrode 312, among the two main surfaces opposing each other, in the thickness direction of the separator body 101. Additionally, the protective layer 110 may not be formed on the remaining main surface of the two main surfaces and on a side surface connecting the two main surfaces in the separator body 101, and this structure may be understood as a form in which the separator of FIG. 11 is adopted on the air electrode-side separator 302. Alternatively, the protective layer 110 may be formed only on the fuel electrode side separator 301.

In the case of the electrochemical cell 310, as an example, a solid oxide cell may be used. Specifically, the electrochemical cell 310 may include a fuel electrode 311, an air electrode 312, and an electrolyte 313 disposed therebetween. Here, the fuel electrode 311 may include a cermet layer including a metal-containing phase and a ceramic phase. Here, the metal-containing phase may include at least one metal catalyst selected from the group consisting of such as nickel (Ni), cobalt (Co), copper (Cu), or alloys thereof, which acts as an electron conductor. The metal catalyst may be in a metal state or an oxide state. The ceramic phase of the fuel electrode 311 may include at least one selected from the group consisting of gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), yttria-doped ceria (YDC), scandia-stabilized zirconia (SSZ), and ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ). The air electrode 312 may include at least one electrically conductive material selected from the group consisting of such as an electrically conductive perovskite material, such as lanthanum strontium manganite (LSM). Other conductive perovskites, such as lanthanum strontium cobalt (LSC), lanthanum strontium cobalt manganese (LSCM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium ferrite (LSF), La_0.85Sr_0.15Cr_0.9Ni_0.1O₃ (LSCN), or metals such as Pt may also be used. In some example embodiments, the air electrode 312 may include a mixture of an electrically conductive material and an ionically conductive ceramic material. For example, the air electrode 312 may include about 10 wt % to about 90 wt % of an electrically conductive material (e.g., LSM, etc.) and about 10 wt % to about 90 wt % of an ionically conductive material. The ionically conductive material may include a zirconia-based and/or ceria-based material. The electrolyte 313 may include stabilized zirconia. Specifically, the electrolyte 313 may include at least one selected from the group consisting of scandia-stabilized zirconia (SSZ), yttria-stabilized zirconia (YSZ), scandia-ceria-stabilized zirconia (SCSZ), scania-ceria-yttria-stabilized zirconia (SCYSZ), and scandia-ceria-ytterbia-stabilized zirconia (SCYbSZ).

Meanwhile, the case in which the electrochemical cell 310 is a solid oxide cell was described above, but in the electrochemical cell 310, a polymer electrolyte membrane cell or the like may also be adopted.

Gaskets 321 and 322 for preventing a fluid from leaking out to the outside may be disposed on an outer portion of the electrochemical cell 310 between the separators 301 and 302. Additionally, current collecting layers 323 and 324 may be disposed between the separators 301 and 302 and the electrochemical cell 310. The current collecting layer 323 and 324 may preferably have excellent oxidation resistance so as to maintain excellent electrical conductivity. Additionally, illustrated in as the illustrated form, the current collecting layers 323 and 324 may have a porous structure such as a mesh structure so that a fluid may pass therethrough.

The present disclosure is not limited by the above-described example embodiments and the attached drawings, but is limited by the appended claims. Accordingly, it will be understood by those skilled in the art that various substitutions, modification and changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims, and these replacements, modifications, or changes should be construed as being included in the scope of the present disclosure.