Mixed cell unit with support electrode and electrolyte and methods for manufacturing same

Abstract

The invention relates to an electrochemical cell unit comprising the following, in the following order across its thickness: a hydrogen electrode (200) comprising a support electrode layer (203) and a functional electrode layer (204) stacked one on top of the other; a solid electrolyte (300) comprising a thin layer (302) having a first surface (305) and a second surface (306); and an oxygen electrode (400), characterised in that the solid electrolyte (300) comprises a frame (303) which extends from the first face (305) of the thin layer (302) and forms a cavity (304) in which the hydrogen electrode (200) is at least partially arranged. The invention relates to the optimisation of a solid oxide cell, including solid oxide fuel cells and solid oxide electrolyser cells.

Description

[0001] “Mixed cell unit with electrode and electrolyte supports and its manufacturing processes”

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to the optimization of a solid oxide cell called SOC for Solid Oxide Cell in English and in particular its sealing. This type of cell is used in systems for producing electricity from hydrogen and oxygen (solid oxide fuel cell or cell called SOFC for Solid Oxide Fuel Cell) or hydrogen and oxygen from water vapor (solid oxide electrolyzer cell called SOEC for Solid Oxide Electrolysiser Cells).

[0004] STATE OF THE ART

[0005] An SOC electrochemical cell is schematically represented by 3 layers, i.e. 2 electrodes separated by an electrolyte. The electrodes are the site of electrochemical reactions, and are electronically conductive, or even mixed electronic / ionic, while the electrolyte is only ionically conductive.

[0006] SOFC fuel cells are electrochemical cells producing electrical and thermal energy that use chemical energy generated by the reaction of water formation from hydrogen and oxygen.

[0007] The operating principle of a SOFC cell is based on the following mechanism:

[0008] The oxygen in the air, which is supplied to the cathode, is dissociated to give O2- anions. The anions thus formed migrate through the electrolyte until they reach the anode where they oxidize the hydrogen atoms which are supplied by the fuel. This reaction releases electrons and water.

[0009] Cells operating as SOEC (Solid Oxide Electrolysiser Cells) are hydrogen-producing electrochemical cells whose operating principle is strictly the opposite of that of SOFCs. Indeed, in the case of a SOEC cell, water vapor is supplied to the cathode and the water molecules are dissociated into hydrogen and O2 anions. The anions thus formed diffuse through the electrolyte to recombine in the form of oxygen at the anode while the hydrogen remains, with the water vapor, at the cathode. This hydrogen can then be recovered for use as fuel in other applications.

[0010] Hydrogen is thus produced with high efficiency, which makes this technology very relevant in the current energy context. Indeed, the increasing use of renewable energies, often intermittent, requires an efficient means of storage, and the hydrogen vector then takes on its full meaning.

[0011] Historically, the first SOC cells were made from a central element: the thick electrolyte. In this configuration, the thick electrolyte constitutes the initial element on which the other layers (electrodes, barrier layer, contact layers, etc.) are subsequently deposited.

[0012] The main advantages of this cell geometry are the mechanical robustness of the thick dense electrolyte with Young's moduli greater than 100GPa, the sealing of the electrolyte is easy to obtain, thanks to its thickness and the fact that the latter is manufactured and heat treated alone, without risk of mechanical stresses linked to the other layers, and the ease of implementing sealing solutions (such as vitroceramic seals, high temperature glue, etc.) around the edges of the cell in a system, since dense areas of the electrolyte are accessible from both sides (hydrogen and oxygen).

[0013] The main disadvantage of this thick electrolyte cell geometry is the loss of performance linked to this significant thickness of the electrolyte. Indeed, part of the ohmic drop during cell operation is directly linked to the resistance induced by the electrolyte during the migration of the Ch- ions. It is easy to understand that the thicker the electrolyte, the greater this loss will be.

[0014] A second classic cell geometry is the support electrode geometry. In this configuration, the hydrogen electrode support provides mechanical support for the cell. It is the initial element on which the other layers (functional hydrogen electrode, electrolyte, oxygen electrode, barrier layer, contact layers, etc.) are subsequently deposited.

[0015] The main advantage of this cell geometry is the possibility of having a very thin electrolyte, and therefore ultimately a higher cell performance than with the geometry with a supported electrolyte (for the same temperature), by reducing the ohmic drop linked to this layer.

[0016] However, this geometry also has disadvantages, the main ones being: the difficulty in obtaining a perfectly dense and sealed electrolyte, the latter being thin and potentially heat-treated at the same time as the hydrogen electrode side. This single heat treatment for several layers, called co-sintering, can add constraints inherent in accommodating differential shrinkage between the layers. In addition, the greater thickness of the hydrogen electrode, via the support, can generate difficulties for the gas to diffuse into this electrode, and increase diffusion overvoltages (losses linked to the diffusion of gases in the electrode), especially in the case of water vapor electrolysis.

[0017] Finally, with this geometry, it is difficult to seal the cell edges in a system. Indeed, the dense electrolyte is only accessible from the oxygen electrode side to position a sealing solution. Remember that the support is necessarily porous to allow the circulation of gases to the functional electrode.

[0018] In particular, documents US 2018 / 269489, US2023 / 061956, US8921003 and D4 113346118 disclose cell architectures comprising a metal support. This arrangement ensures satisfactory mechanical strength and ease of sealing on this metal support. However, these cells with a metal support have disadvantages in terms of lifetime in electrolyzer-type applications in which the metal support is in almost permanent contact with water, which leads to deterioration of the support and therefore quickly of the cell. In addition, the presence of the metal support in contact with the other layers of the cell leads to deterioration of the cell during heating cycles and successive thermal expansions of the different layers.Finally, a metal-backed cell can be used up to maximum temperatures of 500°C, whereas for an electrolyzer temperatures of at least 800°C must be reached for the reaction to be efficient. These cells are therefore not suitable for many applications.

[0019] Therefore, there is a need for a solution that addresses some or all of the drawbacks of existing cell geometries or takes advantage of the benefits of each of them.

[0020] SUMMARY OF THE INVENTION

[0021] To achieve this objective, according to one embodiment, an electrochemical cell unit is provided comprising, in the order according to its thickness: - a hydrogen electrode comprising a support electrode layer and a functional electrode layer stacked on top of each other, the hydrogen electrode comprising a first surface formed by the support electrode layer and a second surface formed by the functional electrode layer, opposite each other, - a solid electrolyte comprising a thin layer having a first surface and a second surface, opposite each other, the first surface of the thin layer of the solid electrolyte facing the functional electrode layer, i.e. the second surface of the hydrogen electrode, and - an oxygen electrode comprising a first surface and a second surface, opposite each other,the first surface of the oxygen electrode facing the second surface of the thin layer of the solid electrolyte, characterized in that the solid electrolyte comprises a frame extending from the first face of the thin layer and forming a cavity in which the hydrogen electrode is arranged at least in part.,

[0022] The cell unit according to the invention is a mixed cell with a support electrode and a support electrolyte. The cell unit comprises a support electrode arranged in a solid electrolyte frame. This arrangement has the advantage of limiting the ohmic drops linked to the migration of oxide ions in the electrolyte, thanks to an electrolyte comprising a thin layer, advantageously with a thickness less than or equal to 10 μm such as in a cell with a support electrode. This arrangement also makes it possible to have a large bearing surface on a dense and gas-tight surface, on both sides of the cell, such as in a cell with a support electrolyte thanks to the solid electrolyte frame surrounding the support electrode over at least part of its thickness.

[0023] According to the invention, the support electrode is ceramic-based and comprises a variation of the composition configured so that the composition of the support electrode approaches that of the solid electrolyte frame in a horizontal direction, perpendicular to the thickness of the cell unit.

[0024] The ceramic-based support electrode layer ensures longer life and cycling and allows for a higher operating temperature.

[0025] The concentration gradient of the support electrode optimizes the sealing of the support electrode and its junction with the solid electrolyte. According to another aspect, the invention relates to a stack comprising at least one electrochemical cell unit as described above and a first interconnector intended to be arranged facing the first surface of the hydrogen electrode and / or a second interconnector intended to be arranged facing the second surface of the oxygen electrode, the first interconnector comprises a first planar surface intended to be facing the first surface of the hydrogen electrode.

[0026] According to another aspect, the invention relates to a method for manufacturing the cell unit as described above comprising a step I) of preparing a hydrogen electrode comprising the formation of a support electrode layer and a functional electrode layer stacked on top of each other, the hydrogen electrode comprising a first surface formed by the support electrode layer and a second surface formed by the functional electrode layer, opposite each other, a step II) of preparing a solid electrolyte comprising the formation of a thin layer having a first surface and a second surface, opposite each other, the first surface of the thin layer of the solid electrolyte facing the functional electrode layer, i.e. the second surface of the hydrogen electrode, and a step III) of preparing an oxygen electrode comprising a first surface and a second surface,opposite each other, the first surface of the oxygen electrode facing the second surface of the solid electrolyte, characterized in that step II) of preparing the solid electrolyte comprises the preparation of a frame extending from the first face of the thin layer and forming a cavity in which the hydrogen electrode is arranged at least in part.,

[0027] According to the invention, step I) of preparing a hydrogen electrode comprises forming the support electrode layer with a composition variation configured so that the composition of the support electrode approaches that of the solid electrolyte frame in a horizontal direction, perpendicular to the thickness of the cell unit.

[0028] The method according to the invention makes it possible to ensure a chronology and an adjustment of the different layers to maintain satisfactory flatness.

[0029] An advantage of the invention is that it is very easy to offer different cell unit thicknesses, while maintaining all the advantages mentioned.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which: Figure 1 represents a block diagram of the cell unit in cross section according to the invention

[0032] Figure 2 represents a view along section AA of Figure 1.

[0033] Figure 3 represents the steps of a method of manufacturing the cell unit of Figure 1 according to a first embodiment.

[0034] Figure 4 shows the steps of a method of manufacturing the cell unit of Figure 1 according to a second embodiment.

[0035] Figure 5 shows the steps of a method of manufacturing the cell unit of Figure 1 according to a third embodiment.

[0036] Figure 6 shows a schematic diagram of the cell unit in cross section according to one embodiment.

[0037] Figure 7 shows a schematic diagram of the cell unit in cross section according to another embodiment.

[0038] Figure 8 represents a view along section AA of Figure 7.

[0039] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the thicknesses of the layers are not representative of reality.

[0040] DETAILED DESCRIPTION OF THE INVENTION

[0041] Before commencing a detailed review of embodiments of the invention, optional features which may optionally be used in combination or alternatively are set out below:

[0042] - According to one example, the variation in the composition of the support electrode 203 is a continuous gradient of the concentration of the composition towards the frame 303;

[0043] - According to one example, the variation in the composition of the support electrode (203) is a discontinuous gradient of the concentration of the composition towards the frame (303).

[0044] - According to one example, the support electrode (203) comprises an internal zone (203a) and a periphery (203b) ensuring contact with the frame (303) of the solid electrolyte (300), the internal zone (203a) has a first concentration and the periphery (203b) has a second concentration, the first concentration and the second concentration being different.

[0045] - According to one example, the support electrode (203) comprises a mixture of nickel oxide (NiO) and at least one ceramic-based ionic conductor.

[0046] - In one example, the second concentration comprises less nickel oxide (NiO) than the first concentration so as to approximate the composition of the solid electrolyte.

[0047] - According to one example, the frame 303 of the solid electrolyte 300 has a thickness 12 at least equal to the thickness 10 of the hydrogen electrode 200;

[0048] - According to one example, the thin layer 302 of the solid electrolyte 300 has a thickness less than or equal to 10 pm;

[0049] - According to one example, the support electrode layer 203 has a thickness greater than or equal to 260 pm;

[0050] - According to one example, the step of preparing the hydrogen electrode (200) comprises the formation of an internal zone 203a of the support electrode (203) at a first concentration and a periphery 203b of the support electrode (203) ensuring contact with the frame 303 of the solid electrolyte 300 at a second concentration, the first concentration and the second concentration being different;

[0051] - According to one example, the step of preparing the hydrogen electrode 200 is carried out by casting in strips;

[0052] - According to one example, the step of preparing the solid electrolyte 300 is at least partially carried out by casting in strips followed by removal of a central part over the entire thickness so as to form the frame 303 and the cavity 304 advantageously said to be open or bottomless;

[0053] - According to one example, the method comprises a step of positioning the hydrogen electrode 200 in the cavity 304 advantageously called open;

[0054] - According to one example, the method comprises a step of thermocompression of the hydrogen electrode 200 and the frame 303;

[0055] - According to one example, the preparation of the thin layer 302 of solid electrolyte is carried out by thin-layer screen printing on the second surface 202 of the hydrogen electrode 200;

[0056] - According to one example, the preparation of the thin layer 302 of solid electrolyte is carried out by casting in thin strip on the second surface 202 of the hydrogen electrode 200;

[0057] - According to one example, the solid electrolyte 300 is produced at least partially by casting in strips followed by removal of a central part over part of the thickness so as to form the frame 303 and the cavity 304 closed by the thin layer of electrolyte 302;

[0058] - According to one example, the step of preparing the hydrogen electrode 200 is carried out by overcasting a slip into the cavity 304.

[0059] - According to one example, the solid electrolyte 300 is produced at least partially by overcasting around the hydrogen electrode 200 so as to form at least the frame 303;

[0060] - According to one example, the preparation of the thin layer 302 of solid electrolyte is also carried out by overcasting on the second surface 305 of the hydrogen electrode 200;

[0061] - According to one example, the preparation of the thin layer 302 of solid electrolyte is carried out by casting in thin strip on the second surface 202 of the hydrogen electrode 200;

[0062] For the remainder of the description, 'top' and 'bottom', or their derivatives, are understood to mean a quality of relative positioning of a cell unit element or stack as shown in the figures, the 'top' being oriented away from the ground and the 'bottom' being oriented towards the ground. The upper end is at the top and the lower end is at the bottom.

[0063] Vertical means that which is directed according to the thickness of the stack or cell unit, that is to say according to the main direction of extension of the stack or cell unit, and horizontal means that which is perpendicular to the vertical. The top and the bottom are vertically opposed.

[0064] Transverse means a direction perpendicular to a longitudinal direction. The longitudinal direction is understood as a direction perpendicular to the thickness of the stack or cell unit. A transverse section is a section perpendicular to the longitudinal axis. A transverse section is a section along the thickness of the stack or cell unit. A longitudinal section is a section perpendicular to the thickness of the stack or cell unit. The width of the frame or section, or of an area or layer is understood as a dimension extending in the longitudinal direction.

[0065] A parameter "substantially equal / greater / less than" or "of the order of" a given value means that this parameter is equal / greater / less than the given value, to within plus or minus 10%, or even plus or minus 5%, of this value.

[0066] For the purposes of this disclosure, the expression "A and / or B" means (A), (B), or (A and B). For the purposes of this disclosure, the expression "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0067] The terms "first," "second," and "third," "additional," etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0068] The term "upper" used in particular to describe a face of a layer is here only used to designate the first of the two faces of a layer (the other being the lower face), without making any assumptions about the relative position of the faces, in a vertical direction. The upper face could thus also have been called the front face, as opposed to a rear face.

[0069] A layer “based” on a material A is understood to mean a layer comprising this material A and possibly other materials, for example doping elements.

[0070] The shapes or dimensions given for certain components of the present invention are always only indicative and are understood as including substantially equivalent shapes and dimensions.

[0071] It is specified that in the context of the present invention, the term "on", "overcomes", "covers", "above" or "underlying" or "below" or "facing" or their equivalents do not necessarily mean "in contact with". For example, the deposition of a first layer on a second layer does not necessarily mean that the two layers are in direct contact with each other, but it does mean that the first layer at least partially covers the second layer either by being in direct contact with it, or by being separated from it by at least one other layer or at least one other element.

[0072] The present invention relates to an electrochemical cell unit 1. The electrochemical cell unit 1 is intended to be used for forming SOFC type solid oxide fuel cells and SOEC solid oxide electrolysers.

[0073] The cell unit 1 comprises a superposition of layers including an anode, a cathode and a solid electrolyte 300 arranged between the anode and the cathode. More specifically, the cell unit 1 comprises a superposition of layers including a hydrogen electrode 200, an oxygen electrode 400 and a solid electrolyte 300 arranged between the hydrogen electrode 200 and the oxygen electrode 400.

[0074] The cell unit 1 comprises a superposition of layers extending perpendicular to the stacking direction of the layers corresponding to the thickness of the cell unit.

[0075] Target thicknesses of cell unit 1 can vary depending on application and systems from approximately 200 pm to 500 pm.

[0076] The hydrogen electrode 200 is advantageously the seat of the water reduction reactions or alternatively the hydrogen oxidation reactions. The hydrogen electrode 200 is the electrode near which hydrogen and water vapor circulate.

[0077] According to the invention, the electrochemical cell unit 1 is of the support electrode and support electrolyte type.

[0078] The electrochemical cell unit 1 according to the invention comprises a hydrogen electrode 200 which comprises a support electrode 203 and a functional electrode 204 stacked on top of each other.

[0079] The term support electrode 203 is understood to mean an electrode which at least partially ensures the mechanical support of the cell unit. The term support means the electrode on which the weight of the rest of the cell unit is exerted. Preferably, the support electrode 203 is the lower electrode of the cell unit 1.

[0080] The functional electrode 204 is the electrode which ensures the electrochemical operation of the hydrogen electrode 200.

[0081] Advantageously, the hydrogen electrode 200 is a layer with a minimum thickness of the order of 270 pm, preferably 300 pm and for example of the order of 400 pm or even 500 pm. Advantageously, the electronic conductivity of the hydrogen electrode 200 is greater than 1000 S / cm. For example, the functional electrode 204 has a thickness of between 10 and 25 pm, preferably between 15 and 20 pm. The cell unit 1 with support electrode makes it possible to reduce the operating temperature while maintaining an acceptable ohmic drop. The cells with support electrode generally operate between 600°C and 800°C, greatly limiting degradation problems while making it possible to consider interconnection plates made of cheaper metal alloys.

[0082] For example, the hydrogen electrode 200 is a cermet. For example, the hydrogen electrode 200 is composed of a mixture of ionically conductive oxide and a catalyst metal, most often nickel. This metal has a high catalytic activity with respect to the reduction of water and therefore the production of hydrogen. In addition, thanks to its high electronic conductivity (4.5, 10 3 S.cm-1 at 800°C), nickel ensures electronic continuity in the electrode. The ceramic network accommodates thermomechanical constraints linked to a difference in coefficient of thermal expansion (CTE) between that of nickel (16.5 .10 -6 K-1) and that of the electrolyte (10.5, 10' 6 K-1 for 8YSZ). For example, a 40% vol Ni - 60% vol 8YSZ cermet has a CET of approximately 13.10 -6K-1. Finally, thanks to its high ionic conductivity, this ceramic network allows the electrochemical reaction to be delocalized in a volume close to the interface with the solid electrolyte 300.

[0083] The hydrogen electrode 200 comprises a first surface 201 and a second surface 202, opposite each other and preferably parallel. The first surface 201 and the second surface 202 extend along a longitudinal plane, perpendicular to the thickness of the cell unit 1. Preferably, the first surface 201 and the second surface 202 are of identical dimensions. Preferably, the second surface 202 is flat. Preferably, the first surface 201 is formed by the support electrode 203 while the second surface is formed by the functional electrode 204.

[0084] The hydrogen electrode 200, i.e. the functional electrode 204 and the support electrode 203, is ceramic-based, preferably made of a cermet (composite material composed of a ceramic reinforcement and a metal matrix). Advantageously, the hydrogen electrode 200 and in particular the support electrode 203 is not a metal layer.

[0085] The hydrogen electrode 200 comprises a mixture of nickel oxide NiO, and one or more ionic conductive material(s) such as zirconium or cerium based which can be doped. By way of non-limiting example, the hydrogen electrode 200 is made up of a mixture of nickel oxide NiO, and doped zirconium oxide (typically doped with yttrium oxide at a rate of 8 mol%). The mixtures conventionally used have a content of approximately 50 to 70% by mass of NiO. For example, the support electrode 203 is a mixture of NiO and YSZ, the zirconia being stabilized by doping with yttrium oxide (Y2O3) at a level of 3 mol% (3YSZ) and the functional electrode 204 is a mixture of NiO and YSZ, the zirconia being stabilized by doping with yttrium oxide (Y2O3) at a level of 8 mol% with (8YSZ).

[0086] According to one embodiment, the support electrode 203 comprises a variation in composition along a horizontal direction, i.e. perpendicular to the thickness of the stack or the cell unit. The variation in composition is made in the direction of the frame 303 and advantageously from the center of the support electrode 203.

[0087] According to one possibility, the variation in composition is a variation in the concentration of the composition of the support electrode 203.

[0088] The variation is a concentration gradient of the composition. The gradient may be continuous or discontinuous. The concentration gradient is configured so that the composition of the support electrode 203 approaches that of the solid electrolyte 300 and more specifically of the frame 303. By “approaches” is meant that the composition of the support electrode 203 is increasingly close, or identical, to the composition of the frame 303 towards the frame 303. For example, the composition of the support electrode 203 approaches 5% or even 10% of the composition of the frame 303. According to one possibility, a continuous gradient may be obtained by an additive manufacturing process.

[0089] According to one possibility, the support electrode 203 comprises an internal zone 203a and a periphery 203b ensuring contact with the frame 303 of the solid electrolyte 300. The periphery 203b extends along the thickness of the support electrode 203 at the periphery of the support electrode 203 intended to be in contact with the frame 303. The width of the periphery 203b may represent from 1% to 10% or even 20%, or even 30% of the width of the support electrode 203. The internal zone 203a has a first concentration and the periphery 203b has a second concentration, the first concentration and the second concentration being different. For example, the composition of the support electrode 203 comprises a mixture of nickel oxide (NiO) and ceramic-based ionic conductor.Advantageously, the second concentration comprises less catalyst metal, i.e. less metal oxide such as nickel oxide than the first concentration so as to approach the composition of the solid electrolyte.

[0090] According to another possibility, the support electrode 203 comprises a periphery 203b comprising at least two, or even three or a plurality of successive sections parallel to each other and extending along the main shape of the periphery 203b. The successive sections comprise variations in composition and more precisely in successive concentrations from the center of the support electrode 203 towards the frame 303 to approach the composition and more precisely the concentration of the frame 303.

[0091] The cell unit 1 advantageously comprises an oxygen electrode 400. The oxygen electrode 400 is advantageously arranged facing the second surface 306 of the solid electrolyte 300. The oxygen electrode 400 comprises a first surface 401 and a second surface 402 opposite each other and preferably parallel. The first surface 401 and the second surface 402 extend along a longitudinal plane perpendicular to the thickness of the cell unit 1. Preferably, the first surface 401 and the second surface 402 are of identical dimensions. Preferably, the first surface 401 and the second surface 402 of the oxygen electrode 400 are of smaller dimensions than those of the second surface 306 of the thin layer 302 of the solid electrolyte 300. Preferably, the first surface 401 and the second surface 402 of the oxygen electrode 400 are flat.The oxygen electrode corresponds to the electrode where the circulation of air and therefore of oxygen takes place. As a non-limiting example, the oxygen electrode materials are conventionally of perovskite structure (ABO3). One of the materials currently mainly used is the material (LaSr)(CoFe)03. Preferably, the oxygen electrode 400 is configured so as not to cover the entire second surface 306 of the thin layer 302 of the solid electrolyte 300. Preferably, the oxygen electrode 400 leaves the edge of the second surface 306 of the thin layer 302 of the solid electrolyte 300 free so that the solid electrolyte 300 forms a surface surrounding the oxygen electrode 400 devoid of oxygen electrode 400.For example, 5 to 10% of the surface area of ​​the solid electrolyte 300 is left free in order to position the sealing area there to allow direct contact between a sealing material and a dense material such as the solid electrolyte.

[0092] According to one possibility, the cell unit 1 comprises a barrier layer 500 arranged between the solid electrolyte 300 and the oxygen electrode 400. More specifically, the barrier layer 500 is arranged between the second surface 306 of the solid electrolyte 300 and the first surface 401 of the oxygen electrode 400. The barrier layer 500 has a first surface 501 and a second surface 502 opposite each other and preferably parallel. The first surface 501 and the second surface 502 extend along a longitudinal plane perpendicular to the thickness of the cell unit 1. Preferably, the first surface 501 and the second surface 502 are planar. Preferably, the first surface 501 and the second surface 502 are of identical dimensions. Preferably, the first surface 501 and the second surface 502 of the barrier layer 500 are of identical dimensions to the second surface 402 of the oxygen electrode 400.The barrier layer 500 is intended to limit the diffusion of elements and reactivity between the oxygen electrode and the electrolyte material (typically strontium and lanthanum). Indeed, without this barrier layer insulating phases can form during the manufacture of the cell or its operation and harm the initial performance and durability.

[0093] The cell unit 1 comprises a solid electrolyte 300. The solid electrolyte 300 comprises a thin layer 302 comprising a first surface 305 and a second surface 305, opposite each other and preferably parallel. The first surface

[0094] 305 and the second surface 306 extend along a longitudinal plane, perpendicular to the thickness of the cell unit 1. Preferably, the first surface 305 and the second surface 306 are planar. In the cell unit 1, at least, the second surface

[0095] 306 and possibly the first surface 305 of the solid electrolyte 300 are of larger dimensions than the second surface 202 of the hydrogen electrode 200. According to one possibility, the first surface 305 is of smaller dimensions than those of the second surface 306. The first surface 305 is of identical dimensions to those of the second surface 202 of the hydrogen electrode 200. During the manufacturing methods as described below, steps may be provided in which the thin layer 302 overflows from the hydrogen electrode 200. The first surface 305 and the second surface 306 are of identical dimensions. Advantageously, the second surface 202 of the hydrogen electrode 200 is arranged in contact with the first surface 305 of the thin layer 302 of the solid electrolyte 300.

[0096] The thin layer 302 is understood as a layer of material. The layer 302 is characterized as a thin layer in contrast to the frame 303 and the thickness of the hydrogen electrode 200, in particular the support electrode 203. The thin layer 302 advantageously has a conventional thickness for a layer of solid electrolyte not acting as a support electrolyte. For example, the thin layer 302 has a maximum thickness 11 of 10 μm and preferably between 2 and 6 μm.

[0097] Typically, the solid electrolyte 300 comprises a frame 303. The frame

[0098] 303 extends transversely from the periphery of the thin layer 302 and in particular of the first surface 305 to form a cavity 304. The frame 303 is advantageously continuous so as to form a continuous side wall for the cavity 304. The cavity 304 is advantageously closed especially its periphery or side wall by the frame 303. The cavity

[0099] 304 is called a closed cavity 304 when one of these longitudinal sides, i.e. transverse to the frame 303, is closed by the thin layer 302, the second surface 305 of the thin layer 302 forming the bottom of the cavity 304, conversely, the cavity 304 is called an open cavity 304 when none of these longitudinal sides, i.e. transverse to the frame 303, is closed by the thin layer 302. The cavity 304 is advantageously intended to receive at least in part and preferably all of the hydrogen electrode 200.

[0100] The frame 303 advantageously has a thickness 12 at least equal to and preferably greater than the thickness of the functional electrode 204 of the hydrogen electrode. Preferably, the frame 303 has a thickness 12 at least equal to the thickness 10 of the hydrogen electrode 200.

[0101] The frame 303 has, for example, a width 13, a dimension perpendicular to the thickness, of at least 5 mm, preferably between 10 and 20 mm.

[0102] The frame 303 plays a supporting role by stiffening the cell unit 1 and ensuring better sealing of the cell unit on the side of the hydrogen electrode 200 which is surrounded on its lateral sides by a solid electrolyte material which is dense and facilitates sealing of the hydrogen compartment.

[0103] The solid electrolyte 300 is an electrolytic membrane that separates the two compartments of a battery. As such, it must be perfectly dense to be impermeable to gas. As a non-limiting example, conventional electrolyte materials are zirconium oxides, doped with yttrium or scandium oxides at a level of 3 to 10 mol%.

[0104] The invention also relates to an electrochemical half-cell comprising, preferably consisting of, the hydrogen electrode 200 as described above, with the functional electrode 204 and the support electrode 203, and the solid electrolyte 300 as described above, with the thin layer 302 and the frame 303. The half-cell does not comprise the layers on the oxygen compartment side.

[0105] The present invention also relates to a method of manufacturing a cell unit 1 and more precisely an electrochemical half-cell as detailed above. Several embodiments are illustrated in Figures 3 to 5.

[0106] The method according to the invention comprises a step I) of preparing a hydrogen electrode 200. This step of preparing the hydrogen electrode 200 comprises the formation of a support electrode layer 203, the formation of a functional electrode layer 204 and advantageously the stacking of the two layers on top of each other.

[0107] In this step I), the formation of the support electrode layer 203 and the formation of the functional electrode layer 204 are carried out successively one after the other or in parallel.

[0108] According to a first possibility, the hydrogen electrode 200 is formed at least in part by strip casting. Strips of the support electrode material 203 are cast. According to one option, strips of the functional electrode material 204 are cast separately, these strips are then superimposed to form the hydrogen electrode 200. According to another option, strips of the functional electrode material 204 are cast directly onto the support electrode strips 203.

[0109] Strip casting is a known method in which a slip is deposited on a support by the passage of a shoe; the thickness of the deposit is adjusted by a system consisting, for example, of two blades. It conventionally makes it possible to obtain layers with a thickness of between 25 and 200 μm. These layers are quick to produce, however, a drying step is required before a thermocompression step. For example, a temperature of 60°C and a pressure of 2000 PSI can be used within the framework of the invention.

[0110] According to a second possibility, the hydrogen electrode 200 is produced at least in part by screen printing. Preferably, the functional electrode 204 is produced by screen printing on the support electrode 203. The support electrode 203 is preferably produced beforehand by strip casting with thermocompression carried out before the screen printing of the functional electrode 204. According to a third possibility, the hydrogen electrode 200 is produced at least in part by overcasting. The hydrogen electrode 200 is overcast in the cavity 304 already formed from the solid electrolyte 300.

[0111] Overcasting consists of pouring a slip of a material, in this case hydrogen electrode material 200 directly into the cavity 304. Preferably, the support electrode 203 and the functional electrode 204 are overcast successively.

[0112] According to one embodiment, the support electrode 203 is formed by an internal zone 203a and a periphery 203b. The internal zone 203a and the periphery 203b have concentrations of different compositions, in particular of metal oxide. The internal zone 203a and the periphery 203b are successively formed preferably by one of the three possibilities described above.

[0113] The method according to the invention comprises a step II) of preparing a solid electrolyte 300. This step of preparing the solid electrolyte 300 comprises the formation of a thin layer 302 having a first surface 305 and a second surface 306, opposite each other, the first surface 305 of the thin layer 302 of the solid electrolyte 300 being intended to face the functional electrode layer 204, that is to say the second surface 202 of the hydrogen electrode 200.

[0114] Typically, step II) of preparing the solid electrolyte 300 comprises the formation of a frame 303. The frame 303 is intended to be arranged so as to extend from the first face 305 of the thin layer 302 and form a cavity 304 in which the hydrogen electrode 200 is arranged at least in part.

[0115] The formation of the frame 303 and the formation of the thin layer 302 can be carried out at the same time or successively.

[0116] According to a first possibility, the formation of the thin layer 302 is carried out by strip casting. The strip casting of the thin layer 302 is advantageously carried out on the second surface 202 of the hydrogen electrode 200.

[0117] According to a second possibility, the formation of the thin layer 302 is carried out by screen printing, advantageously on the second surface 202 of the hydrogen electrode 200.

[0118] According to a third possibility, the formation of the thin layer 302 is carried out by overcasting onto the hydrogen electrode 200.

[0119] With regard to the formation of the frame 303, according to a first possibility, the frame is produced by strip casting and advantageously with a cutting of a central part over at least a part of the thickness of the frame 303 so as to form a closed or open cavity 304 depending on the thickness removed from the central part. According to a second possibility, the frame 303 is produced by overcasting onto the hydrogen electrode 200.

[0120] The different possibilities of forming the thin layer 302 and the different possibilities of forming the frame 303 are combinable.

[0121] At this stage, the process results in an electrochemical half-cell.

[0122] Advantageously, to obtain an electrochemical cell unit, the method according to the invention comprises a step III) of preparing an oxygen electrode 400, this step is not illustrated in the figures. This step of preparing the oxygen electrode 400 comprises the formation of a hydrogen electrode layer comprising a first surface 401 and a second surface 402, opposite each other, the first surface 401 of the oxygen electrode 400 facing the second surface 402 of the solid electrolyte 300. This step of preparing the oxygen electrode 400 is for example carried out by strip casting or by screen printing. Similarly, in the case where the cell unit comprises a barrier layer 500, this is carried out by strip casting or by screen printing.

[0123] According to different possibilities, steps I, II and III are carried out successively or independently of each other without any precise order and then the whole is assembled.

[0124] A first embodiment is described with reference to Figure 3.

[0125] As illustrated, strips of the solid electrolyte material 300, Figure 3 (a), the support electrode material 203, Figure 3 (d), and the functional electrode material 204, Figure 3 (c), are cast separately. According to a possibility not illustrated, the functional electrode 204 is produced by screen printing. According to a possibility not illustrated, the support electrode 203 is formed either by a gradient as illustrated in Figure 6 or by an inner zone 203a and a periphery 203b as illustrated in Figures 7 and 8, formed separately by strip casting. According to another possibility, the inner zone 203a or the periphery 203b is formed by strip casting and respectively the periphery 203b or the inner zone 203a is formed after step e) described below by overcasting. According to the possibility in which the periphery 203b comprises several successive sections then each successive section is deposited by strip casting.

[0126] To form the solid electrolyte frame 303, a central portion of the strips of solid electrolyte material 300 is cut, for example by laser, to form the frame 303, FIG. 3(b). According to a preferred embodiment, only the frame 303 is formed without the thin layer 302. A cavity 304 is formed, the cavity 304 being, as illustrated, an open cavity, i.e., without a bottom or cover.

[0127] The support electrode strips 203 and the functional electrode strips 204 are positioned inside the frame 303 in a superimposed manner, FIG. 3 (e). Preferably, the strips are positioned before thermocompression.

[0128] At this point, two options are possible for forming the thin layer 302.

[0129] According to a first option, the stack obtained in the previous step, Figure 3 (e), is thermo-compressed, Figure 3 (f). For example, thermocompression at 60°C and 2000 PSI is used. Then, the electrolyte material is deposited by screen printing in a thin layer on the second surface 204 of the hydrogen electrode to form the thin layer 302, Figure 3 (g).

[0130] According to a second option, the thin layer 302 is formed by strip casting on the second surface 204 and preferably on the frame 303, figure 3 (h). The stack obtained is then thermo-compressed to obtain a half-unit of the cell of the invention, figure 3 (g). The oxygen electrode 400 and the optional barrier layer 500 are deposited by screen printing.

[0131] A second embodiment is described with reference to Figure 4

[0132] According to this embodiment, step II) is carried out, the solid electrolyte 300 is formed. Advantageously, an electrolyte material is cast in strip form, figure 4 (a), then the cavity 304 is formed by cutting the cast strips, figure 4 (b) for example by laser. Preferably, the cutting is carried out so as to form the frame 303 and the thin layer 302. The cavity 304 formed is said to be closed in that it comprises a bottom, the thin layer 302.

[0133] The hydrogen electrode 200 is formed by overcasting in the cavity 304, Figure 4 (b). A slip of the support electrode material 203 is first cast in the cavity 304 and then dried. According to a possibility not shown, the support electrode 203 is formed either by a gradient as illustrated in Figure 6 or by an internal zone 203a and a periphery 203b as illustrated in Figures 7 and 8. In this case, before casting, a mask is placed on the frame 303 in order to cast first, for example, the internal zone 203a and then the periphery 203b after removal of the mask. This method applies in the same way in the case where the periphery 203b comprises several successive sections. A slip of the functional electrode material 204 is then cast in the cavity 304 and then dried.

[0134] Throughout the present invention, the removal of the layer or mask is carried out by methods conventionally known to those skilled in the art.

[0135] According to one option, Figure 4 (e), before casting the hydrogen electrode 200, a mask is placed on the frame 303 so that the hydrogen electrode 200 is located only in the cavity 304. For example, the mask is a plastic film.

[0136] The hydrogen electrode 200 is flush with the frame 303 without covering it, figure 4 (c).

[0137] According to one possibility, this embodiment for obtaining a half-cell according to the invention comprises a thermocompression step to obtain figure 4 (d).

[0138] A third embodiment is described with reference to Figure 5.

[0139] According to a first option, the support electrode 203 is formed by strip casting followed by thermocompression, Figure 5 (b). According to a possibility not illustrated, the support electrode 203 is formed either by a gradient as illustrated in Figure 6 or by an internal zone 203a and a periphery 203b as illustrated in Figures 7 and 8, formed separately by strip casting.

[0140] The functional electrode 204 is formed by tape casting, Figure 5 (a) or by screen printing on the support electrode 203 to obtain Figure 5 (c).

[0141] The resulting hydrogen electrode 200, Figure 5 (c), is repositioned in a casting bench. The electrolyte material is overcast, Figure 5 (c). A slip of the electrolyte material is cast onto the hydrogen electrode 200. Upon drying on the hydrogen electrode 200, and having cast a dimension larger than the latter, the electrolyte material forms the frame 303 around the hydrogen electrode.

[0142] According to one option, the thin layer 302 is formed simultaneously during the overcasting, figure 5 (e).

[0143] According to another option, the thin layer 302 is formed subsequently, figure 5 (f). For this, the second surface 204 of the hydrogen electrode 200 is masked, for example by a plastic film, before the overcasting of the electrolyte material. The overcasting is advantageously controlled so as not to cover the mask. Then, the thin layer 302 is deposited by screen printing figure 5 (g). This option makes it possible to deposit a thinner thin layer 302 of electrolyte by screen printing than what is achievable by tape casting.

[0144] Preferably, according to the second and third embodiments, that is to say when an overcasting step is present, the half-cell obtained is heat-treated, for example at 1400°C, after a debinding phase adapted to the composition of the slips used. Once the half-cell has been heat-treated, the layers on the side of the oxygen electrode 400 can also be produced conventionally to complete the electrochemical cell unit which then becomes functional.

[0145] According to one aspect of the invention, the electrochemical cell unit is surrounded by an upper interconnector arranged opposite the oxygen electrode 400 and a lower interconnector arranged opposite the support electrode 203 so as to form an electrochemical stack.

[0146] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

[0147] LIST OF REFERENCES

[0148] I. Electrochemical cell unit

[0149] 10. Thickness of hydrogen electrode

[0150] II. Thickness of the thin layer of solid electrolyte

[0151] 12. Thickness of solid electrolyte frame

[0152] 13. Frame width

[0153] 100. Mask

[0154] 200. Hydrogen electrode

[0155] 201. First surface

[0156] 202. Second surface

[0157] 203. Support electrode

[0158] 203a. internal zone

[0159] 203b. perimeter

[0160] 204. Functional electrode

[0161] 300. Solid electrolyte

[0162] 302. Thin layer

[0163] 303. Frame

[0164] 304. Cavity

[0165] 305. First surface

[0166] 306. Second surface

[0167] 400. Oxygen electrode

[0168] 401. First surface

[0169] 402. Second surface

[0170] 500. Barrier Layer

[0171] 501. First surface

[0172] 502. Second surface

Claims

CLAIMS 1. Electrochemical cell unit (1) comprising in order according to its thickness: • a hydrogen electrode (200) comprising a support electrode layer (203) and a functional electrode layer (204) stacked on top of each other, the hydrogen electrode (200) comprising a first surface (201) formed by the support electrode layer (203) and a second surface (202) formed by the functional electrode layer (204), opposed to each other, • a solid electrolyte (300) comprising a thin layer (302) having a first surface (305) and a second surface (306), opposite each other, the first surface (305) of the thin layer (302) of the solid electrolyte (300) facing the functional electrode layer (204), and • an oxygen electrode (400) comprising a first surface (401) and a second surface (402), opposite each other, the first surface (401) of the oxygen electrode (400) facing the second surface (306) of the thin layer (302) of the solid electrolyte (300), characterized in that the solid electrolyte (300) comprises a frame (303) extending from the first face (305) of the thin layer (302) and forming a cavity (304) in which the hydrogen electrode (200) is arranged at least in part and that the support electrode 203 is ceramic-based and comprises a variation of the composition configured so that the composition of the support electrode 203 approaches that of the frame 303 of the solid electrolyte 300 in a horizontal direction, perpendicular to the thickness of the unit of cell.

2. Electrochemical cell unit (1) according to the preceding claim in which the variation in the composition of the support electrode (203) is a continuous gradient of the concentration of the composition towards the frame (303).

3. Electrochemical cell unit (1) according to claim 1 wherein the variation in the composition of the support electrode (203) is a discontinuous gradient of the concentration of the composition towards the frame (303).

4. Electrochemical cell unit (1) according to the preceding claim in which the support electrode (203) comprises an internal zone (203a) and a periphery (203b) ensuring contact with the frame (303) of the solid electrolyte (300), the internal zone (203a) has a first concentration and the periphery (203b) has a second concentration, the first concentration and the second concentration being different.

5. Electrochemical cell unit (1) according to any one of the preceding claims wherein the support electrode (203) comprises a mixture of nickel oxide (NiO) and at least one ceramic-based ionic conductor.

6. Electrochemical cell unit (1) according to the preceding claim in combination with claim 4 in which the second concentration comprises less nickel oxide (NiO) than the first concentration so as to approach the composition of the solid electrolyte.

7. Electrochemical cell unit (1) according to any one of the preceding claims in which the frame (303) of the solid electrolyte (300) has a thickness (12) at least equal to the thickness (10) of the hydrogen electrode (200).

8. Electrochemical cell unit (1) according to any one of the preceding claims in which the thin layer (302) of the solid electrolyte (300) has a thickness less than or equal to 10 pm.

9. Electrochemical cell unit (1) according to any one of the preceding claims wherein the support electrode layer (203) has a thickness greater than or equal to 260 pm.

10. Stack comprising at least one electrochemical cell unit (1) according to any one of the preceding claims, characterized in that it comprises a first interconnector intended to be arranged facing the first surface (201) of the hydrogen electrode (200) and / or a second interconnector intended to be arranged facing the second surface (402) of the oxygen electrode (400), the first interconnector comprises a first flat surface intended to be facing the first surface (201) of the hydrogen electrode (200).

11. A method of manufacturing an electrochemical cell unit according to any one of claims 1 to 9 comprising a step I) of preparing a hydrogen electrode (200) comprising the formation of a support electrode layer (203) and a functional electrode layer (204) stacked on top of each other, the hydrogen electrode (200) comprising a first surface (201) formed by the support electrode layer (203) and a second surface (202) formed by the functional electrode layer (204), opposite each other, a step II) of preparing a solid electrolyte (300) comprising the formation of a thin layer (302) having a first surface (305) and a second surface (306), opposite each other, the first surface (305) of the thin layer (302) of the solid electrolyte (300) facing the functional electrode layer (204), and a step III) of preparing an oxygen electrode (400) comprising a first surface (401) and a second surface (402), opposite each other, the first surface (401) of the oxygen electrode (400) facing the second surface (302) of the solid electrolyte (300),characterized in that step II) of preparing the solid electrolyte (300) comprises the preparation of a frame (303) extending from the first face (305) of the thin layer (302) and forming a cavity (304) in which the hydrogen electrode (200) is arranged at least in part and that step I) of preparing a hydrogen electrode (200) comprises the formation of the support electrode layer (203) with a variation of the composition configured so that the composition of the support electrode 203 approaches that of the frame 303 of the solid electrolyte 300 in a horizontal direction, perpendicular to the thickness of the cell unit., 12. Method according to the preceding claim in which the step of preparing the hydrogen electrode (200) comprises the formation of an internal zone 203a of the support electrode (203) at a first concentration and a periphery 203b of the support electrode (203) ensuring contact with the frame 303 of the solid electrolyte 300 at a second concentration, the first concentration and the second concentration being different.

13. Method according to any one of the two preceding claims in which the step of preparing the hydrogen electrode (200) is carried out by casting in strips.

14. Method according to any one of the three preceding claims in which the step of preparing the solid electrolyte (300) is at least partially carried out by casting in strips followed by removal of a central part over the entire thickness so as to form the frame (303) and the cavity (304).

15. Method according to the preceding claim comprising a step of positioning the hydrogen electrode (200) in the cavity (304).

16. Method according to the preceding claim comprising a step of thermocompression of the hydrogen electrode (200) and the frame (303).

17. Method according to any one of claims 11 to 16 wherein the preparation of the thin layer (302) of solid electrolyte is carried out by thin-layer screen printing on the second surface (202) of the hydrogen electrode (200).

18. Method according to any one of claims 11 to 16 wherein the preparation of the thin layer (302) of solid electrolyte is carried out by casting in thin strip on the second surface (202) of the hydrogen electrode (200).

19. Method according to claim 11 or 12 in which the solid electrolyte (300) is produced at least partially by casting in strips followed by removal of a central part over part of the thickness so as to form the frame (303), the cavity (304) closed by the thin layer of electrolyte (302).

20. Method according to the preceding claim in which the step of preparing the hydrogen electrode (200) is carried out by overcasting a slip in the cavity (304).

21. Method according to any one of claims 11 to 13 in which the solid electrolyte (300) is produced at least partially by overcasting around the hydrogen electrode (200) so as to form at least the frame (303).

22. Method according to the preceding claim in which the preparation of the thin layer (302) of solid electrolyte is also carried out by overcasting on the second surface (305) of the hydrogen electrode (200).

23. Method according to claim 13 wherein the preparation of the thin layer (302) of solid electrolyte is carried out by casting in thin strip on the second surface (202) of the hydrogen electrode (200).

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