Waveform green sheet for manufacturing large ceramic sheet, related method and use

Abstract

The present invention relates to an unsintered green sheet or tape comprising a corrugated surface having alternating peaks and valleys arranged along both a first direction of the surface and a second direction of the surface, the second direction forming an angle of 60° to 120° with the first direction, and the corrugation period and / or corrugation amplitude in the first direction being different from that in the second direction. The present invention allows for the preparation of reliable large ceramic sheet materials, for example as ceramic electrolyte layers for use in solid oxide cells, as ceramic sheets for filter or membrane applications, or as sintered substrates or setters. Additionally, sintered ceramic sheets and electrolytes, methods of preparation, and solid oxide cells (SOCs) using the unsintered green sheets or tapes are described.

Description

Technical Field

[0001] The present invention relates to a high-reliability large ceramic sheet material that can be used, for example, as a ceramic electrolyte layer used in a solid oxide cell, as a ceramic sheet for use in applications such as filters or membranes, or as a sintered substrate or setter, and enables the preparation of an unsintered green sheet or tape including a wavy surface.

[0002] In addition, the present invention relates to a sintered ceramic sheet and an electrolyte sheet obtained from the green sheet or tape, and a solid oxide cell including them.

Background Art

[0003] In recent years, solid oxide cell (SOC) technology has attracted attention during the development and exploration of sustainable energy sources.

[0004] For example, solid oxide cells, which may include solid oxide fuel cells (SOFCs), solid oxide regenerative fuel cells (SORFCs), and solid oxide electrolysis cells (SOECs), include a high-density solid-oxide-based electrolyte sandwiched between two electrodes, namely, a fuel electrode and an oxygen electrode. The configuration of these components is specifically selected based on electrical and ionic conductivity, reactivity, stability, and mechanical strength. The electrodes must be porous to allow gas diffusion throughout the structure and at the same time exhibit sufficient ionic and electrical conductivity, while the solid electrolyte is characterized by high ionic conductivity, low electrical conductivity, and gas-tight properties. For the efficient and large-scale operation of SOCs, a so-called stack is constructed in which a number of single cells are arranged in series and parallel to achieve the desired voltage and power output. Typically, substantially flat electrodes that support the cathode and anode electrode layers have been proposed for use in several different SOC configurations, including stack designs, where each flat electrode / electrolyte subunit is joined to a framework manifold structure and terminally supported by the framework manifold structure.

[0005] Under the economic aspect, the material costs, especially those related to the interconnectors (ICs), frames, and sealant materials included in each repeating unit in the stack, account for the majority of the expenses in the manufacturing and operation of the SOC stack. Therefore, it is considered desirable to increase the occupied area of the SOC by expanding the sizes of the electrodes and electrolyte layers, and thus reduce the total stack cost per kilowatt.

[0006] However, expanding the cell size is difficult, especially for the electrolyte sheet or layer.

[0007] As an example, a process for preparing a ceramic electrolyte sheet includes a step of preparing a slurry containing a ceramic material powder, a binder, and a dispersion medium, a step of forming the slurry into a sheet (e.g., by a doctor blade, calendar, or extrusion method), a step of drying the formed sheet and removing the dispersion medium through volatilization to obtain a green sheet, a step of punching the green sheet into a predetermined shape, and a step of sintering to produce a ceramic electrolyte sheet. Alternatively, the green electrolyte sheet is stacked in a multilayer structure including one or more electrode layers and then sintered (see, for example, EP1930974A1). However, during sintering, a flat green sheet tends to undergo substantial shrinkage (typically about 70% - 90% in length and about 40% - 80% in area relative to the original size of 100%) and form bulges in the center and end curls. As shown in FIG. 1, typically, the amplitude increases towards the center of the end. The upper figure illustrates the bulge formation area, and the lower line graph illustrates the end of the cell. This effect is presumably more pronounced with a larger cell area based on the adhesion of the green sheet to the substrate (sintered on the substrate). The bulges and burrs at the ends substantially remain in the resulting ceramic sheet, which may lead to defects in the cell and, in the worst case, cracks in the ceramic cell, especially under pressure in a stacked configuration. Moreover, the non-uniform decomposition and dissipation rate of the organic binder within the green sheet surface during sintering lead to uneven shrinkage, which can further contribute to defects and breakage. In addition, since the end curl tends to increase as the sheet area increases, the sintered sheet often has to be cut into a size that exhibits an acceptable flatness, which can overall result in a poor process yield.

[0008] The waveform can improve the mechanical strength in the ceramic sheet of the SOEC cell and reduce the in-plane stress. In this context, US2006 / 0003213A1 and EP1113518A1 propose, for example, an egg tray type waveform. US2004 / 0265663A1 and US2007 / 0273070A1 disclose an electrolyte sheet including indentations formed by embossing a green sheet before sintering to improve mechanical stability at a thin thickness. However, the problem of avoiding the formation of bulges at the ends of large ceramic sheets during sintering has not been addressed at all. US6,620,637A discloses a method for preparing a sintered zirconia body in sheet form, including a step of firing a green sheet of zirconia while applying a load by placing at least one weight on the green sheet. US6,001,761A discloses a method for manufacturing a ceramic sheet including a pre-firing of a green sheet between porous sheets having a bulk density corresponding to 30% to 85% of the theoretical density, wherein the shrinkage rate caused by heating to the pre-firing temperature of the green sheet is 5% or less under the condition that the periphery of the green sheet does not protrude from the porous sheet. However, the flatness obtained by these methods still has room for improvement, especially in the case of large sheets.

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, when subjected to sintering, even when manufactured in large dimensions, a ceramic sheet can be obtained that has no substantial bulges and / or burrs around it, thus increasing the occupied area of the SOC cell and making it possible to suppress the stack cost without the risk of cracks forming in the cell stack. It is still desired to provide a green sheet or tape.

[0010] Moreover, there is still a need to provide a method that enables the production of large ceramic sheets with high yield, low cost, and simplicity.

Means for Solving the Problems

[0011] The present invention solves these objects by the subject matter of the claims defined herein. Further advantages of the present invention will be described in more detail in the following sections.

[0012] In one aspect, the present invention is an unsintered green sheet or tape for preparing a ceramic sheet material, including a wavy surface having alternating ridges and valleys arranged along both a first direction and a second direction of the surface, the second direction forming an angle of 60° to 120° with respect to the first direction, and the waveform period and / or waveform amplitude in the first direction being different from those in the second direction, relating to an unsintered green sheet or tape.

[0013] In another aspect, the present invention is a method for manufacturing the aforementioned unsintered green sheet or tape, including: step a1) of preparing an unsintered green sheet or tape without a waveform; step a2) of corrugating the unsintered green sheet or tape to provide alternating ridges and valleys arranged along a first direction of the surface of the unsintered green sheet or tape; and step a3) of corrugating the unsintered green sheet or tape to provide alternating ridges and valleys arranged along a second direction of the surface of the unsintered green sheet or tape, wherein, to generate the corrugated unsintered green sheet or tape, steps a2) and a3) are carried out by a roll-to-roll method or by matching the unsintered green sheet prepared in step a1) with the surface of one or more ready-made substrates including waveforms, relating to a method.

[0014] In an additional aspect, the present invention is a method for manufacturing a ceramic sheet material, including: step a) of preparing an unsintered green sheet or tape according to the aforementioned method; and step b) of subjecting the unsintered green sheet or tape to a sintering process, relating to a method.

[0015] In a further aspect, the present invention relates to a ceramic sheet material manufactured according to the aforementioned method, an electrolyte sheet including the ceramic sheet material, and a solid oxide cell including the electrolyte sheet.

[0016] In an additional aspect, the present invention relates to the use of the aforementioned unfired green sheet or tape for the preparation of an electrolyte sheet.

[0017] Preferred embodiments and other aspects of the unfired green sheet or tape of the present invention are described in the following description and claims.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0019] To more fully understand the present invention, reference is now made to the following description of its exemplary embodiments.

[0020] Unsintered Green Sheets and Tapes In a first embodiment, the present invention is an unsintered green sheet or tape for the preparation of a ceramic sheet material, comprising a wavy surface having alternating ridges and valleys arranged along both a first direction and a second direction of the surface, the second direction forming an angle between 60° and 120° with respect to the first direction, and the waveform period and / or waveform amplitude in the first direction being different from those in the second direction.

[0021] Advantageously, it has been found that by pre-wavily processing the green sheet, the sheet can be flattened during the sintering process while minimizing the movement of the contact points between the sheet and the substrate and the adhesion between the green sheet and the substrate. A simple two-dimensional explanatory diagram of this effect is illustrated in FIG. 2. As a result, even when manufactured in large dimensions, a conveniently flat ceramic sheet without substantial swelling and / or burrs at the side edges can be obtained. Accordingly, the horizontal shrinkage during the sintering process, which causes friction by the support that results in tensile stress in the cell, is offset, and even large electrolytes can avoid swelling at the edges.

[0022] An exemplary corrugated surface is illustrated in FIG. 3, where both the waveform period and the waveform amplitude in the first direction (y-axis) are different from (or larger than) those in the second direction (x-axis). Generally, both the first and second directions are in the x / y plane, while the z-axis represents the thickness direction of the green sheet. The expression "a second direction forming an angle between 60° and 120° with respect to the first direction" refers herein to the angle between the first and second directions in the x / y plane. The angle does not have to be constant over the entire surface of the green sheet or tape and can vary within a given range in the x / y plane, for example, in the form of a curve. For example, as illustrated in FIG. 4, ridges and grooves may be arranged in the form of a sine wave in the x / y plane. In-plane waves such as those shown in FIG. 4 can be used to avoid straight lines in the sintered body and can advantageously contribute to a reduction in thermochemical and / or thermomechanical stress, thus improving the toughness of the sintered body. In other preferred embodiments, the angle between the first and second directions ranges from 70° to 110°, more preferably from 80° to 100°, still more preferably from 85° to 95°, and particularly preferably about 90°.

[0023] When the waveform period in the second direction is greater than the waveform period in the first direction, from the perspective of improved flattening during sintering, the ratio of the waveform period in the second direction to the waveform period in the first direction is preferably at least 2:1, more preferably 2:1 to 40:1, still more preferably at least 2.2:1, even more preferably 2.2:1 to 30:1, particularly preferably 2.5:1 to 20:1, for example 3:1 to 12:1. The expression "period" in this specification indicates the distance between adjacent peaks and adjacent valleys of the waveform profile.

[0024] In a more preferred embodiment, the waveform period in the second direction is 25 mm or more, preferably 30 mm or more, and / or the waveform period in the first direction is less than 25 mm, preferably less than 20 mm.

[0025] The waveform profiles in the first and second directions are not particularly limited and independently include symmetric periodic waves (e.g., sine waves, square waves, triangular waves, or combinations thereof) and / or asymmetric periodic waves (e.g., sawtooth profiles). The use of a sine wave profile is particularly preferred for the waveforms in both directions.

[0026] When the waveform amplitude in the second direction is greater than the waveform amplitude in the first direction, when the ratio of the waveform amplitude in the second direction to the waveform amplitude in the first direction is at least 1.5:1, more preferably at least 1.8:1, still more preferably at least 2:1, particularly preferably between 2:1 and 100:1, for example between 2:1 and 10:1, further improved flattening is achieved. The expression "amplitude" in this specification is understood to indicate the peak amplitude measured between the peak and the baseline (i.e., half of the total depth of the sheet profile).

[0027] In a more preferred embodiment, the waveform amplitude in the second direction is 5 mm or more, preferably 7 mm or more, and / or the waveform amplitude in the first direction is less than 5 mm, preferably less than 3 mm.

[0028] A particularly advantageous match between planar shrinkage and sintering shrinkage can be achieved when both the waveform period and the waveform amplitude in the first direction are different from those in the second direction, preferably further satisfying the above ranges. The planar shrinkage of the waveform pattern is preferably more than 5%, for example 6% or more, more preferably adjusted between 8% and 40%, particularly preferably between 15% and 38%, for example between 20% and 37%.

[0029] The thickness of the unsintered green sheet or tape (i.e., the material thickness) is preferably substantially constant in order to obtain an ideally flat and uniform ceramic sheet without steps. In a further preferred embodiment, the thickness is in the range of, for example, 10 μm to 1 cm, more preferably 30 μm to 0.7 cm, particularly preferably 50 μm to 0.5 cm, for example 70 to 220 μm.

[0030] The waveform pattern is not necessarily applied over the entire surface of the unsintered green sheet or tape, and may, for example, occupy only 60%, 70%, 80% or 90% of the area, but the advantages of the present invention are most prominent when the above waveform pattern extends over the entire surface.

[0031] Generally, the term "green" describes an unsintered and unfired material in this specification. In a preferred embodiment, the green sheet or tape for preparing the ceramic sheet material according to the present invention has not been subjected to heat treatment at 800 °C or higher, 600 °C or higher, or 400 °C or higher after being supplied in the form of a sheet or tape.

[0032] The composition of the green sheet or tape is not particularly limited as long as the sintering of the green material produces the ceramic sheet material. In a preferred embodiment, the green sheet or tape comprises, in the form of raw material powder, one or more pre-ceramic materials selected from zirconia, zirconates, alumina, aluminates, titania, titanates, silica, silicates, rare earth metals and / or their oxides, alkali metals and / or their oxides, alkaline earth metals and / or their oxides, steel, stainless steel, aluminides, intermetallic compounds, aluminum and its alloys, the first, second and third transition series of metals, their oxides, borides, nitrides, carbides, silicides, and / or combinations thereof. In a more preferred embodiment, the green sheet or tape comprises, as a pre-ceramic material, one or more of zirconia (e.g., monoclinic zirconia (ZrO2), etc.), rare earth metals (e.g., yttrium, cerium, samarium, scandium or gadolinium) and / or their oxides (e.g., Y2O3, etc.). Specific examples having favorable mobility of oxygen vacancies upon heating and excellent stability in both reducing and oxidizing atmospheres include yttrium-stabilized zirconia (e.g., 3YSZ, 8YSZ), scandium-cerium-stabilized zirconia (e.g., 6Sc1CeSZ, 10Sc1CeSZ), and yttrium-scandium-stabilized zirconia (YScSZ). Among them, yttrium-stabilized zirconia is particularly preferred from the viewpoints of the cost and availability of high-quality raw materials. Particularly preferred is zirconium oxide stabilized with 2 to 10 mol% of yttrium oxide and having a tetragonal and / or cubic structure, respectively. If desired, the ceramic sheet can be made tougher by selecting specific toughening agents (e.g., oxides of tantalum and niobium, etc.) known to those skilled in the art.

[0033] In particular, the unsintered green sheet or tape may have a multilayer structure having two or more layers, provided that the materials of the different layers are sufficiently compatible with respect to the adhesion and shrinkage behavior during sintering. In such a configuration, at least one, but not necessarily all, of the sub-layers is required to contain a pre-ceramic material. In other words, it is sufficient for one sub-layer to form a ceramic layer during sintering.

[0034] Depending on the method for preparing the green sheet or tape, optional additives selected from one or more of a sintering aid, a dispersant (e.g., a polymer dispersant such as polyvinylpyrrolidone, a copolymer of butadiene and maleic anhydride, and ammonium salts thereof), a coalescing agent, a binder, a plasticizer (glycols such as propylene glycol and glycol ethers), a curing agent, an antifoaming agent, and a solvent (e.g., an organic solvent) are typically also included.

[0035] There is no particular limitation on the type of binder used in the present invention, and known organic binders can be appropriately selected and used. Examples of organic binders include ethylene copolymers, styrene copolymers, acrylate or methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl butyral resins, vinyl acetal resins, vinyl formal resins, vinyl alcohol resins, waxes, and cellulose such as ethyl cellulose. These organic binders may be used alone or, if necessary, in an appropriate combination of two or more of them. The ratio of the raw material powder to the binder to be used may be a binder in the range of preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, per 100 parts by mass of the raw material powder, which ensures sufficient strength and flexibility of the green sheet and at the same time promotes the adjustment of the viscosity of the slurry.

[0036] The solvent used in the production of the green sheet or tape may be appropriately selected by those skilled in the art. In particular, water; alcohols such as methanol, ethanol, 2-propanol, 1-butanol, and 1-hexanol; ketones such as acetone and 2-butanone; aliphatic hydrocarbons such as pentane, hexane, and butane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and acetate esters such as methyl acetate, ethyl acetate, and butyl acetate can be mentioned. These solvents may be used alone or in an appropriate combination of two or more of them. The amount of the solvent can be appropriately adjusted by those skilled in the art according to the desired viscosity of the green material.

[0037] Method for manufacturing a corrugated green sheet or tape In a second embodiment, the present invention is a method for manufacturing an unsintered green sheet or tape according to the first embodiment, comprising: a1) a step of preparing an uncorrugated unsintered green sheet or tape; a2) a step of corrugating the unsintered green sheet or tape to provide alternating ridges and valleys arranged along a first direction on the surface of the unsintered green sheet or tape; and a3) a step of corrugating the unsintered green sheet or tape to provide alternating ridges and valleys arranged along a second direction on the surface of the unsintered green sheet or tape, wherein steps a2) and a3) are carried out by a roll-to-roll method or by matching the unsintered green sheet prepared in step a1) with the surface of one or more ready-made substrates containing the corrugation in order to produce the corrugated unsintered green sheet or tape. Advantageously, the method enables the rapid, continuous, and inexpensive production of large green sheets or tapes having the desired corrugation characteristics and a thin thickness.

[0038] Regarding step a1), various preparation methods of non-wavy flexible green materials in the form of sheets or tapes are known in the art (e.g., US4,710,227A, EP0302972A1, and EP0317676). Generally, these are not particularly limited and can be adopted as appropriate to produce a substrate for corrugation processing according to the present invention. As an example, the green sheet or tape can be prepared from a slurry containing one or more pre-ceramic materials and optional additives selected from among the sintering aids, dispersants, coalescing agents, binders, plasticizers, curing agents, and solvents according to the description of the first embodiment. As a result, sheet-shaped slurries can be produced by methods including, but not limited to, tape casting, doctor blade method, calendar method, extrusion method, etc. Optionally, a drying process may follow the latter step.

[0039] Subsequently, the corrugation profile described with respect to the first embodiment is provided in steps a2) and a3), which is preferably obtained by a method that requires as little stretching or squeezing as possible, thereby enabling a substantially uniform material thickness across the resulting corrugated sheet. It should be noted that the order of steps a2) and a3) can be interchanged, and steps a2) and a3) can also be performed simultaneously. However, a two-step approach is often preferred to minimize deformation in the tape or sheet during corrugation processing.

[0040] As described above, steps a2) and a3) may be carried out by a roll-to-roll method. As an example, a cast green sheet or tape can be passed between rolls, where at least one of these rolls may be patterned and configured to bend the green sheet or tape to provide alternating ridges and valleys arranged along a first direction on its surface. The ridges and valleys arranged along a second direction on the green sheet surface can be provided by passing the sheet or tape between additional roll sets.

[0041] Alternatively, steps a2) and a3) may be carried out by matching the green sheet obtained in step a1) with the surface of one or more ready-made substrates containing the waveform in order to produce a green sheet or tape with a waveform. In a preferred embodiment, the one or more ready-made substrates are, for example, corrugated plates that can be pre-assembled by means of a 3-D printing method. Advantageously, the green sheet is matched with the surface of a first corrugated plate containing alternating ridges and valleys in a pattern along a first direction (a corrugation profile having a relatively small period and / or amplitude), and subsequently, the green sheet is matched with the surface of a second corrugated plate containing alternating ridges and valleys in a pattern along both the first and second directions (a complete corrugation pattern), thereby achieving a reduction in undesirable plastic deformation. The surface of the green sheet is preferably matched with the surface of the ready-made substrate via a rolling mechanism. An example of the method is illustrated in FIGS. 5 (first corrugated plate) and 6 (second corrugated plate), where, in the final corrugation process step, the roll is patterned to match the corrugation in the first direction (see FIG. 6). Accordingly, undesirable stretching or squeezing and local thinning of the green sheet can be avoided. Accordingly, a high-quality green sheet or tape having a desired corrugation profile can be obtained simply and inexpensively.

[0042] In an embodiment, steps a2) and a3) are carried out at an elevated temperature (for example, between 40°C and 120°C, or between 50°C and 85°C) to enhance the flexibility of the green tape or sheet during the corrugation process, thus enabling improved tracking to the roll and / or corrugated plate.

[0043] Method for manufacturing a ceramic sheet material and an SOC electrolyte sheet In a third embodiment, the present invention relates to a method for manufacturing a ceramic sheet material, comprising: a) preparing an unsintered green sheet or tape according to the second embodiment; and b) subjecting the unsintered green sheet or tape to a sintering process. This method enables the production of large ceramic sheets without the formation of bulges and curled edges that are normally observed upon sintering. Furthermore, since such defects and related scrap are reduced, the manufacturing yield can be substantially improved.

[0044] In general, the sintering conditions in step b) will depend, inter alia, on the composition and structure of the unsintered green sheet and the desired properties of the ceramic sheet. However, when it is intended to use the ceramic sheet as an SOC electrolyte, the duration of the sintering process is preferably appropriately selected by those skilled in the art to achieve a sufficient degree of densification (percentage of theoretical density) that correlates with the overall electrical conductivity and gas tightness of the electrolyte. In this regard, to meet the requirements of a gas-tight electrolyte, the target degree of densification should be 95% or more, and the porosity of the ceramic sheet should be less than 5%.

[0045] However, in general, it is preferable to carry out sintering at a temperature above 800°C, more preferably above 1000°C, still more preferably from 1100°C to 1900°C, particularly preferably from 1250°C to 1850°C, for a duration of more than about 1 hour, preferably at least 3 hours, more preferably between 6 hours and 20 hours, particularly preferably between 8 hours and 16 hours, in an inert, oxidizing or reducing atmosphere, preferably in an oxidizing or reducing atmosphere.

[0046] During sintering, the sheet or tape may preferably be constrained to reduce lateral movement in the width direction of the sintered substrate. For this purpose, weights may be placed on each corner portion of the sheet or tape, and preferably on one or more end portions. Optionally or alternatively, a flat plate (preferably a porous ceramic plate, such as a porous ceramic plate based on alumina, mullite / alumina, zirconia, cordierite or magnesia, etc.) may preferably be placed on the upper surface of the sheet without damaging the wavy surface, thereby conveniently reducing the lateral movement and resulting in an improvement in flatness.

[0047] Optionally, a debinding process may be carried out prior to actual sintering to remove organic binders and volatile components in the green sheet or tape. For this purpose, a separate preheating process (e.g., at about 300 °C to 500 °C for about 30 minutes to 300 minutes) may be carried out in advance, or the ramp heating rate towards the sintering temperature plateau may be appropriately adjusted to ensure the debinder. Without limitation, typical ramp heating rates range from 1 °C / h to 150 °C / h.

[0048] Ceramic sheet material In a fourth embodiment, the present invention relates to a ceramic sheet material manufactured according to the third embodiment.

[0049] As used herein, the expression "ceramic sheet material" is understood to include a multilayer sheet or composite film comprising two or more sublayers, provided that at least one sublayer is a ceramic layer. By way of example, the ceramic sublayer may be combined with sublayers having different compositions or structures.

[0050] As described above, the ceramic sheet material exhibits favorable flatness when manufactured on a large scale. Therefore, in a preferred embodiment, the area of the ceramic sheet material is 50 cm 2 or more, preferably 100 cm 2 or more, more preferably 150 cm 2 or more, for example 160 cm 2 or more, 200 cm2 Above, 300 cm 2 Above, 500 cm 2 Above, 1000 cm 2 Above, 1500 cm 2 Above, or 2000 cm 2 Above.

[0051] Typically, the ceramic sheet material is flattened during the sintering process, but the surface of the ceramic sheet material obtained according to the present invention shows a residual waveform structure with a waveform period in the first and second directions substantially corresponding to that before sintering (defined in conjunction with the above-described first embodiment), but with a relatively small waveform amplitude. Accordingly, while showing favorable flatness, the surface of the ceramic sheet material of the present invention typically shows a fine structure in which residual undulation profiles (extending beyond the surface roughness) in both the first and second directions can be recognized.

[0052] Characteristically, the residual waveforms in the sintered sheet of the present invention have an essentially regular structure over the entire surface, in contrast to the presence of irregular bulges in the central portion or curl formation concentrated at the ends observed in conventional sintered sheets. In addition, the angle between the first and second directions in the x / y plane with respect to the green sheet is preferably in the range of 60° to 120°, more preferably 70° to 110°, still more preferably 80° to 100°, and even more preferably 85° to 95°, and particularly preferably about 90°.

[0053] In particular, the surface shape of the ceramic sheet can be analyzed by a profilometry method known in the art. Specifically, in order to distinguish surface roughness and waviness (i.e., obtained from the waveform), the surface shape of the ceramic sheet can be traced with a profilometer to obtain an unfiltered measurement profile, which is then first filtered by an electronic low-pass filter to obtain a primary profile, and then further filtered in accordance with ISO11562 / ISO16610-21 to generate independent waviness and roughness profiles. The variable λc (i.e., the cut-off wavelength of the profile filter) for determining the boundary between waviness and roughness can be appropriately selected by those skilled in the art according to the valley spacing or the expected value of roughness, typically in the range of 0.5 to 7 μm, for example 5 μm. In the case of a porous surface structure or obvious surface impurities, after subjecting the primary profile to appropriate narrow-band filtering, the waviness profile may be extracted (for example, in accordance with VDA2007 / ISO4288).

[0054] Based on the waviness profile, the residual waveform in the sintered sheet can be analyzed as outlined below.

[0055] Generally, the period of the residual wave (after sintering) in either the first direction or the second direction is related to the period that existed before sintering (in the green sheet) and the sintering shrinkage during sintering by the following relational expression: Period (after sintering) ≥ Period (before sintering) × (100% - Sintering shrinkage [%]) and correlates accordingly.

[0056] "Sintering shrinkage" as defined in this specification corresponds to the estimated material-dependent shrinkage rate. The unsintered green sheet can be subjected to heating and cooling cycles by a process assuming the preparation of a ceramic sheet, and the shrinkage rate can be determined in advance by a method known to those skilled in the art (e.g., dilatometry). From the perspective of obtaining the desired density, the sintering conditions in step b) in the method of manufacturing a sintered ceramic sheet are adjusted to result in a sintering shrinkage of, for example, more than 5%, for example 6% or more, more preferably between 8% and 50%, particularly preferably between 15% and 38%, for example between 20% and 37%.

[0057] In the sintered sheet, the ratio of the waveform period in the second direction to the waveform period in the first direction is preferably at least 2:1, more preferably between 2:1 and 40:1, still more preferably at least 2.2:1, even more preferably between 2.2:1 and 30:1, particularly preferably between 2.5:1 and 20:1, for example between 3:1 and 12:1.

[0058] In a preferred embodiment of the sintered sheet, the waveform period in the second direction may be 23 mm or more, preferably 28 mm or more, and / or the waveform period in the first direction is less than 23 mm, preferably less than 18 mm.

[0059] The amplitude of the residual waveform is not particularly limited and can be determined by the processing conditions during sintering (e.g., planar shrinkage, temperature and pressure conditions). In this regard, the waveform amplitude in the second direction after sintering is preferably 200 μm or less, more preferably less than 100 μm, particularly preferably less than 50 μm. Preferably, the waveform amplitude in the second direction after sintering is 0.5 μm or more, for example 1 μm or more, 2 μm or more, or 5 μm or more. Alternatively, or in combination, the waveform amplitude in the first direction after sintering is preferably 100 μm or less, more preferably less than 50 μm, particularly preferably less than 25 μm. In addition, the waveform amplitude in the first direction after sintering is 0.1 μm or more, for example 0.5 μm or more, 1 μm or more, or 2 μm or more.

[0060] The ceramic sheet material preferably has a surface roughness R of less than 60 μm, more preferably 40 μm or less, particularly preferably 0.01 to 20 μm, for example 0.1 to 10 μm. a Here, R a is measured in accordance with ISO 4287:1997.

[0061] The ceramic sheet material according to the present invention can be used in a number of applications including, but not limited to, chemical and materials processing, dielectrics and electrical insulation, or casting and metalworking. Preferably, the ceramic sheet material is used in the assembly of an electrochemical device (e.g., SOC), a photovoltaic cell (e.g., as a barrier layer in a thin film solar cell), an electronic device, a ceramic filter, a ceramic membrane, a sensor (e.g., as a substrate sheet, protective sheet or membrane), a setter, kiln furniture, a sintered substrate, or a wear protection pad.

[0062] SOC electrolyte sheet In a fifth embodiment, the present invention relates to an electrolyte sheet comprising the ceramic sheet material according to the fourth embodiment.

[0063] In an embodiment, the electrolyte sheet can have various compositions and can have a multilayer structure including an arrangement of the multilayer ceramic sheet material according to the fourth embodiment above.

[0064] The electrolyte sheet is a substantially pore-free (i.e., substantially no isolated pores, porosity less than 5%, preferably less than 3%, more preferably less than 1%) object.

[0065] Solid oxide cell (SOC) In a sixth embodiment, the present invention relates to a solid oxide cell comprising the electrolyte sheet according to the fifth embodiment above.

[0066] The solid oxide cell (SOC) described in this specification may include an electrochemical device that can be used as either a solid oxide electrolysis cell (SOEC) or a solid oxide fuel cell (SOFC) depending on the direction of the current. The solid oxide cell may be capable of reversible operation. Cells may be combined to form a stack to increase the overall output.

[0067] The solid oxide cell (SOC) configuration includes a cathode layer disposed on one side of an electrolyte sheet and an anode layer disposed on the other side of the electrolyte sheet. Otherwise, the specific design of the SOC is not particularly limited, and examples include a segmented series cell design, a monolithic design, and a flat plate design. A corrugated electrolyte sheet can be utilized, for example, in an electrolyte-supported, anode- or cathode-supported, symmetric electrode-supported solid oxide fuel cell and / or a multilayer tape-cast cell.

[0068] An exemplary SOC can be prepared, for example, by tape casting a fuel electrode, an electrolyte layer, and a barrier layer (e.g., a CGO (cerium-gadolinium oxide) layer). This can be done either by multilayer tape casting prior to co-sintering of the entire half-cell or by laminating the layers either through or after tape casting.

[0069] Furthermore, the SOC may be assembled using additional components known in the art, including interconnects, frames, and sealant materials. With respect to the interconnect, most of the two sides of the cell are typically allocated for gas channels and sealant materials. The size of the frame and the amount of glass sealant typically scale approximately with the area of the cell subtracted from the area of the interconnect. By extending the side length, the amount of extra electrolyte and electrode materials, as well as the materials used for the interconnect, end plates, and framing, and the amount of glass sealant, and the costs associated therewith can be reduced. The present invention can increase the side length and the working area of the cell (i.e., 50 cm 2Above, preferably 100 cm 2 Above, more preferably 150 cm 2 Above, for example 160 cm 2 Above, 200 cm 2 Above, 300 cm 2 Above, 500 cm 2 Above, 1000 cm 2 Above, 1500 cm 2 Above, or 2000 cm 2 Above, enables an increase up to the solid electrolyte area of)

[0070] When operating a large stack including such scaled-up cell dimensions, as disclosed in WO2020 / 201485A1, an undesirable increase in the temperature gradient may be observed inside the cell stack, but this can be offset by applying one or more voltage or current fluctuations to the SOC so that a substantially thermally neutral operation at partial load becomes possible by matching the integrated Joule heat generation amount with the integrated reaction heat consumption amount inside the cell.

[0071] It will be understood that the preferred features of the first to sixth embodiments can be freely combined in any combination, except for combinations in which at least some of the features are mutually contradictory.

Example

[0072] Preparation of solid electrolyte sheet The solid electrolyte sheet was prepared based on a corrugated green sheet according to the method described below.

[0073] In each of Examples 1 to 3, a commercially available 159 μm thick 8YSZ-based green ceramic tape (purchased from Kerafol®) was used.

[0074] The corrugation was carried out using a 3D printed corrugated plate manufactured using FDM (fused deposition modeling) printing with a polylactic acid (PLA) wire having a thickness of 0.1 to 0.2 mm.

[0075] To minimize plastic deformation within the tape during corrugation processing, the process was divided into two steps. The first step was to create a corrugation pattern (a corrugation profile with a relatively small period and / or amplitude) for the first direction within the corrugation pattern using the corrugation plate of FIG. 7. Subsequently, the tape was to be slid onto another corrugation plate having a complete corrugation pattern as seen in FIG. 8, which corrugation had a relatively large period and / or amplitude in a second direction perpendicular to the first direction. In both cases, the alternating peaks and valleys arranged along both the first direction of the surface and the second direction of the surface had a sine-wave-like shape. The green sheet surface was made to match the corrugation of the substrate by gently bending the green sheet surface onto the prefabricated substrate by means of a rolling mechanism (illustrated in FIGS. 5 and 6). In this way, unsintered green sheets having three different corrugation patterns according to Table 1 below were prepared (Examples 1 to 3).

[0076]

Table 1

[0077] To obtain the desired properties of the SOC electrolyte, the green sheets of Examples 1 to 3 were subjected to debinding and sintering, and a final area of 13.4×13.4 cm 2 was obtained. The corrugation of the tape withstood the debinding process and the structure remained intact. In the sintering process, a ramp rate of 120 °C / h was used to heat the corrugated tape up to 1450 °C, and this temperature was maintained for 12 hours and then cooled again. The sintered sheets of Examples 1 to 3 showed an average thickness of 75 μm corresponding to a 25% shrinkage in the z-direction.

[0078] As Comparative Example 1, a commercially available 159-μm-thick 8YSZ green sheet (purchased from Kerafol®) cut to a size of 9×9 cm 2 was subjected to the same sintering process. The sintered sheet of Comparative Example 1 showed an average thickness of 138 μm corresponding to a 13% shrinkage in the z-direction.

[0079] Evaluation The sintered electrolyte sheets according to Examples 1 to 3 and Comparative Example 1 were visually inspected for flatness from the viewpoints of bulge formation at the central portion and curl formation at each end. The results are shown in Table 2 below, where "++" indicates excellent, "+" indicates good, and "-" indicates poor flatness of the electrolyte.

[0080]

Table 2

[0081] As shown in the attached photos of FIGS. 9 and 10, the sintering of the non-waveform sample according to Comparative Example 1 shows a substantial bulge increasing towards the center of the end and end curl.

[0082] On the other hand, Examples 1 to 3 according to the present invention show significantly small bulges and end curl formation and excellent flatness despite the considerably large electrolyte dimensions. Photographs of the sintered sheets of Examples 2 and 3 are shown in FIGS. 11 and 12, respectively.

[0083] Furthermore, the sintered sheets of Examples 2 and 3 were subjected to profilometry evaluation using a profilometer. The results shown in FIG. 13 demonstrate that the sheet of Example 3 is flatter when compared with the sheet of Example 2, while Example 3 prepared from a green sheet having a waveform pattern C shows a higher surface roughness when compared with Example 2.

[0084] Overall, the above results indicate that an unsintered green sheet or tape including a wavy surface can be successfully used for the preparation of a large-sized flat electrolyte sheet that maintains its mechanical strength and reduces the risk of cracks due to the bulging phenomenon.

[0085] Surface Structure Analysis of Sintered Sheet As Comparative Example 2, a commercially available 3YSZ-based green ceramic tape was used and subjected to the same sintering process as in Examples 1 to 3. Subsequently, the profiles and surface structures of the sintered sheets of Comparative Example 2 and Example 3 were analyzed with a profilometer. The results of the profilometry analysis are shown in FIGS. 14 to 19.

[0086] Specifically, FIG. 14 shows an upper view of the surface structure of the sintered sheet obtained as Comparative Example 2, while FIG. 15 shows a profile along the cross-section (horizontal line) shown in FIG. 14. FIG. 6 exemplifies a 3D view of the surface structure of Comparative Example 2, showing the presence of irregular bulges across the entire surface.

[0087] An upper view of the surface structure of the sintered sheet obtained as Example 3 is shown in FIG. 17. Different from FIG. 14, residual waveforms are visible in the sintered sheet, and the ridges extend along both the y-direction and the x-direction. FIG. 18 showing the profile along the cross-section shown in FIG. 17 confirms the presence of a regular sine wave pattern. A 3D view of the surface structure of Example 3 is shown in FIG. 19.

[0088] Accordingly, it is shown that the sintered sheet of the present invention can retain a unique residual waveform having an essentially regular structure.

[0089] From the above disclosure, many other features, modifications, and improvements will become apparent to those skilled in the art.

Claims

1. An unsintered green sheet or tape for preparing a ceramic sheet material, comprising a wavy surface having alternating ridges and valleys arranged along both a first direction and a second direction of the surface, wherein the second direction forms an angle between 60° and 120° with respect to the first direction, the waveform period in the second direction is greater than the waveform period in the first direction, the ratio of the waveform period in the second direction to the waveform period in the first direction is at least 2:1, and / or the waveform amplitude in the second direction is greater than the waveform amplitude in the first direction, the ratio of the waveform amplitude in the second direction to the waveform amplitude in the first direction is at least 1.5:1, the unsintered green sheet or tape.

2. the waveform period in the second direction is greater than the waveform period in the first direction, the ratio of the waveform period in the second direction to the waveform period in the first direction is between 2:1 and 40:1, the unsintered green sheet or tape according to claim 1.

3. the waveform amplitude in the second direction is greater than the waveform amplitude in the first direction, the ratio of the waveform amplitude in the second direction to the waveform amplitude in the first direction is between 2:1 and 100:1, the unsintered green sheet or tape according to claim 1.

4. the waveform amplitude in the second direction is 5 mm or more, and / or the waveform amplitude in the first direction is less than 5 mm, the unsintered green sheet or tape according to claim 1.

5. the thickness of the green sheet or tape is substantially constant and in the range of 10 μm to 1 cm, the unsintered green sheet or tape according to claim 1.

6. the wavy surface extends over the entire surface of the unsintered green sheet or tape, the unsintered green sheet or tape according to claim 1.

7. the green sheet or tape is selected from one or more of zirconia, zirconate, alumina, aluminate, titania, titanate, silica, silicate, rare earth metals and / or their oxides, alkali metals and / or their oxides, alkaline earth metals and / or their oxides, steel, stainless steel, aluminide, intermetallic compounds, aluminum and its alloys, the first, second and third transition series of metals, their oxides, borides, nitrides, carbides, silicides, and / or combinations thereof, An optional additive selected from one or more of a sintering aid, a dispersant, a binder, a plasticizer, a hardening agent, a coalescing agent, and a solvent, and comprising the unsintered green sheet or tape according to claim 1.

8. The unsintered green sheet or tape according to claim 1, wherein the alternating ridges and valleys arranged along both the first direction and the second direction of the surface both have a sinusoidal shape.

9. a1) A step of preparing a non-wavy unsintered green sheet or tape; and a2) A step of corrugating the unsintered green sheet or tape to provide alternating ridges and valleys arranged along the first direction of the surface of the unsintered green sheet or tape; and a3) A step of corrugating the unsintered green sheet or tape to provide alternating ridges and valleys arranged along the second direction of the surface of the unsintered green sheet or tape A method for manufacturing the unsintered green sheet or tape according to claims 1 to 8, comprising In order to produce a corrugated unsintered green sheet or tape, steps a2) and a3) are carried out by a roll-to-roll method or by matching the unsintered green sheet prepared in step a1) with the surface of one or more ready-made substrates containing a waveform.

10. a) A step of preparing the unsintered green sheet or tape according to claim 9; and b) A step of subjecting the unsintered green sheet or tape to a sintering process, optionally under a reducing or oxidizing atmosphere A method for manufacturing a ceramic sheet material.

11. A ceramic sheet material including a wavy surface having alternating ridges and valleys arranged along both the first direction and the second direction of the surface, wherein the second direction forms an angle between 60° and 120° with respect to the first direction, the waveform amplitude in the second direction is 0.5 μm or more and 200 μm or less, and the waveform amplitude in the first direction is 0.1 μm or more and 100 μm or less.

12. The area of the ceramic sheet material is 50 cm ２ or more, and / or The ceramic sheet material having a waveform profile, wherein the ceramic sheet material has a waveform amplitude in the second direction of less than 100 μm and / or a waveform amplitude in the first direction of less than 50 μm. The ceramic sheet material according to claim 11.

13. An electrolyte sheet comprising the ceramic sheet material according to claim 11.

14. Use of an unsintered green sheet or tape according to any one of claims 1 to 8 for the preparation of an electrolyte sheet, a solid oxide fuel cell, a ceramic filter or a ceramic membrane.

15. A solid oxide fuel cell comprising an electrolyte sheet according to claim 13, a cathode layer disposed on one side of the electrolyte sheet, and an anode layer disposed on the other side of the electrolyte sheet.

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