SOEC / SOFC solid oxide cell stack with internal guide elements

Description

TECHNICAL FIELD

[0001] The present invention relates to the general field of high temperature electrolysis (HTE), in particular high temperature steam electrolysis (HTSE), respectively designated by the English terms "High Temperature Electrolysis" (HTE) and "High Temperature Steam Electrolysis" (HTSE), of carbon dioxide (CO2) electrolysis, or even of high temperature co-electrolysis of water vapor and carbon dioxide (CO2).

[0002] More specifically, the invention relates to the field of high-temperature solid oxide electrolyzers, usually designated by the acronym SOEC (for "Solid Oxide Electrolysis Cell" in English).

[0003] It also concerns the field of high-temperature solid oxide fuel cells, usually referred to by the acronym SOFC (for "Solid Oxide Fuel Cells" in English).

[0004] Thus, more generally, the invention relates to the field of SOEC / SOFC type solid oxide stacks operating at high temperature.

[0005] More specifically, the invention relates to a stack of SOEC / SOFC type solid oxide cells comprising internal guiding elements, as well as an associated conditioning method. PREVIOUS STATE OF THE ART

[0006] In a high-temperature solid oxide electrolyzer (SOEC), the process involves converting water vapor (H₂O) into hydrogen (H₂) and oxygen (O₂) via an electric current within the same electrochemical device, and / or converting carbon dioxide (CO₂) into carbon monoxide (CO) and oxygen (O₂). In a high-temperature solid oxide fuel cell (SOFC), the operation is reversed, producing both electricity and heat when fueled by hydrogen (H₂) or other fuels such as methane (CH₄), natural gas, biogas, and oxygen (O₂), for example, oxygen from the air. For the sake of simplicity, the following description focuses on the operation of a high-temperature solid oxide electrolyzer of the SOEC type performing the electrolysis of water vapor.However, this principle is applicable to the electrolysis of carbon dioxide (CO2), and even to the co-electrolysis of high-temperature steam with carbon dioxide (CO2). Furthermore, this principle can be transposed to the case of a high-temperature solid oxide fuel cell (SOFC).

[0007] To carry out the electrolysis of water, it is advantageous to do so at high temperature, typically between 600 and 1000°C, because it is more advantageous to electrolyze water vapor than liquid water and because part of the energy required for the reaction can be supplied by heat, which is cheaper than electricity.

[0008] To implement high-temperature steam electrolysis (HTSE), a high-temperature solid oxide electrolyzer (SOEC) consists of a stack of elementary units, each comprising a solid oxide electrolysis cell, or electrochemical cell, made up of three stacked anode / electrolyte / cathode layers, and interconnecting plates made of metallic alloys, also called bipolar plates or interconnectors. Each electrochemical cell is sandwiched between two interconnecting plates. A high-temperature solid oxide electrolyzer (SOEC) is therefore an alternating stack of electrochemical cells and interconnectors. A high-temperature solid oxide fuel cell (SOFC) is made up of the same type of stack of elementary units.Because this high-temperature technology is reversible, the same stack can operate in electrolysis mode and produce hydrogen and oxygen from water and electricity, or in fuel cell mode and produce electricity from hydrogen and oxygen.

[0009] Each electrochemical cell consists of an electrolyte / electrode assembly, typically a multilayered assembly where the electrolyte is formed by a central ion-conducting layer. This layer is solid, dense, and impermeable, sandwiched between two porous layers that form the electrodes. It should be noted that additional layers may exist, but these serve only to enhance one or more of the layers already described.

[0010] Electrical and fluidic interconnecting devices are electronic conductors that ensure, from an electrical standpoint, the connection of each electrochemical cell of elementary pattern within the stack of elementary patterns, guaranteeing electrical contact between one face and the cathode of one cell and between the other face and the anode of the next cell. From a fluidic standpoint, they ensure the supply of reactants and the removal of products for each cell. The interconnectors thus perform the functions of supplying and collecting electrical current and delineate gas circulation compartments for distribution and / or collection.

[0011] More specifically, the interconnectors have the main function of ensuring the passage of electric current but also the circulation of gases in the vicinity of each cell (namely: injected water vapor, extracted hydrogen and oxygen for EHT electrolysis; air and fuel including injected hydrogen and extracted water for a SOFC), and of separating the anodic and cathodic compartments of two adjacent cells, which are the gas circulation compartments on the anode and cathode sides of the cells respectively.

[0012] In particular, for a high-temperature solid oxide electrolyzer (SOEC), the cathode compartment contains water vapor and hydrogen, products of the electrochemical reaction, while the anode compartment contains a drain gas, if present, and oxygen, another product of the electrochemical reaction. For a high-temperature solid oxide fuel cell (SOFC), the anode compartment contains the fuel, while the cathode compartment contains the propellant.

[0013] To perform high-temperature steam electrolysis (HTE), steam (H₂O) is injected into the cathode compartment. Under the influence of the electric current applied to the cell, the dissociation of water molecules into steam occurs at the interface between the hydrogen electrode (cathode) and the electrolyte. This dissociation produces hydrogen gas (H₂) and oxygen ions (O₂⁻). The hydrogen (H₂) is collected and discharged from the hydrogen compartment. The oxygen ions (O₂⁻) migrate through the electrolyte and recombine into oxygen (O₂) at the interface between the electrolyte and the oxygen electrode (anode). A draining gas, such as air, can circulate at the anode and thus collect the oxygen generated in gaseous form at the anode.

[0014] To operate a solid oxide fuel cell (SOFC), air (oxygen) is injected into the cathode compartment and hydrogen into the anodic compartment. The oxygen in the air dissociates into O2- ions. These ions migrate through the electrolyte from the cathode to the anode to oxidize the hydrogen and form water, simultaneously producing electricity. In an SOFC, as in SOEC electrolysis, water vapor is found in the hydrogen (H2) compartment. Only the polarity is reversed.

[0015] For example, the figure 1 represents a schematic view showing the operating principle of a high-temperature solid oxide electrolyzer of the SOEC type. The function of such an electrolyzer is to transform water vapor into hydrogen and oxygen according to the following electrochemical reaction: 2 H 2 O → 2 H 2 + O 2 .

[0016] This reaction is carried out electrochemically in the cells of the electrolyzer. As shown schematically on the figure 1 Each elementary electrolysis cell 1 consists of a cathode 2 and an anode 4, placed on either side of a solid electrolyte 3. The two electrodes (cathode and anode) 2 and 4 are electronic and / or ionic conductors, made of porous material, and the electrolyte 3 is gas-tight, an electronic insulator, and an ionic conductor. The electrolyte 3 can, in particular, be an anionic conductor, more precisely an anionic conductor of O2- ions, and the electrolyzer is then called an anionic electrolyzer, as opposed to proton electrolytes (H+).

[0017] Electrochemical reactions take place at the interface between each of the electronic conductors and the ionic conductor.

[0018] At cathode 2, the half-reaction is as follows: 2 H 2 O + 4 e -< → 2 H 2 + 2 O 2-< .

[0019] At anode 4, the half-reaction is as follows: 2 O 2-< → O 2 + 4 e -< .

[0020] Electrolyte 3, intercalated between the two electrodes 2 and 4, is the site of migration of O 2- ions under the effect of the electric field created by the potential difference imposed between the anode 4 and the cathode 2.

[0021] As illustrated in parentheses on the figure 1 The water vapor entering the cathode may be accompanied by hydrogen (H₂), and the hydrogen produced and recovered at the outlet may be accompanied by water vapor. Similarly, as illustrated by the dotted line, a draining gas, such as air, can also be injected at the anode inlet to remove the oxygen produced. The injection of a draining gas also serves as a thermal regulator.

[0022] An elementary electrolyzer, or electrolysis reactor, consists of an elementary cell as described above, with a cathode 2, an electrolyte 3, and an anode 4, and two interconnectors which provide the electrical and fluidic distribution functions.

[0023] To increase the flow rates of hydrogen and oxygen produced, it is known to stack several elementary electrolysis cells on top of each other, separated by interconnectors. The assembly is positioned between two end interconnection plates that support the electrical and gas supplies of the electrolyzer (electrolysis reactor).

[0024] A high-temperature solid oxide electrolyzer of the SOEC type thus comprises at least one, usually a plurality of electrolysis cells stacked one on top of the other, each elementary cell being formed of an electrolyte, a cathode and an anode, the electrolyte being intercalated between the anode and the cathode.

[0025] As previously stated, fluid and electrical interconnection devices that are in electrical contact with one or more electrodes generally provide the functions of supplying and collecting electrical current and delimit one or more gas circulation compartments.

[0026] Thus, the so-called cathodic compartment has the function of distributing the electric current and water vapor as well as recovering hydrogen at the cathode in contact.

[0027] The so-called anodic compartment has the function of distributing the electric current as well as recovering the oxygen produced at the anode in contact, possibly with the help of a draining gas.

[0028] There figure 2 represents an exploded view of elementary motifs of a high-temperature solid oxide electrolyzer of the SOEC type according to the prior art. This electrolyzer comprises a plurality of elementary electrolysis cells C1, C2, of the solid oxide cell (SOEC) type, stacked alternately with interconnectors 5. Each cell C1, C2 consists of a cathode 2.1, 2.2 and an anode (only the anode 4.2 of cell C2 is shown), between which is disposed an electrolyte (only the electrolyte 3.2 of cell C2 is shown).

[0029] The interconnector 5 is a metal alloy component that separates the cathode compartment 50 from the anodic compartment 51, defined by the volumes between the interconnector 5 and the adjacent cathode 2.1 and between the interconnector 5 and the adjacent anode 4.2, respectively. It also distributes the gases to the cells. Water vapor is injected into each element in the cathode compartment 50. The hydrogen produced and residual water vapor at cathodes 2.1 and 2.2 are collected in the cathode compartment 50 downstream of cell C1 and C2 after the water vapor has been dissociated by the cell. The oxygen produced at anode 4.2 is collected in the anodic compartment 51 downstream of cell C1 and C2 after the water vapor has been dissociated by the cell.Interconnector 5 ensures the passage of current between cells C1 and C2 by direct contact with adjacent electrodes, i.e. between anode 4.2 and cathode 2.1.

[0030] To ensure good electrical contact between all the interconnectors, the electrochemical cells and the interconnectors are sandwiched between two rigid plates, called the upper terminal plate and the lower terminal plate, which are electrically insulated from the interconnectors. This resulting sandwich is called a "stack," and thus comprises the upper and lower terminal plates, the electrochemical cells, and the interconnectors. This stack must be kept under compressive force to ensure good electrical continuity of the contact planes between the plates.

[0031] During the first phase of manufacturing the stacks, the glass-ceramic seal is formed by subjecting the stack to a thermal cycle while applying a controlled compressive force to the stack. This thermal cycle is called the conditioning cycle.

[0032] Indeed, the various seals between circuits are ensured by fused glass gaskets. This fused glass is obtained by depositing slip, a precursor to glass. The slip is deposited in the form of beads sandwiched between the interconnecting plates (or interconnectors). This slip then dries in place, resulting in a bead made of glass powder mixed with organic binders. Thus, in a cold state, before the heating cycle that will form the glass, the interconnecting plates are separated by beads of dried slip. These beads will melt during the heating cycle, and the contacts will be established at the reactive zones described previously. The melting of the beads can result in a reduction of more than 50% in the thickness of the slip bead. These beads can also be made of already densified glass, sandwiched between two successive interconnectors in the stack.Just as in the conditioning cycle with dried slip cords, the melting of the glass joint will cause the space between the interconnectors to sag, but to a lesser extent than with slip.

[0033] In all cases, it is important to ensure guidance along a direction perpendicular to the plane of the interconnectors, or collinear with the direction of the compressive force exerted by the interconnecting and end plates. Such guidance guarantees that, during the stack's settling, which occurs during glass formation, the stack's constituent parts (particularly interconnectors, insulating plates, and end plates) remain correctly aligned with each other. During this phase, the stack's height decreases by approximately 50%, resulting in significant vertical movement of the stack.

[0034] The development of industrial systems incorporating high-temperature electrolyzers requires an increase in the volume of gas treated (in SOEC or SOFC). To achieve this, an increase in surface area, the number of cells, and the number of interconnectors is necessary. However, a significant increase in the number of plates, and therefore in the stack height, poses numerous technical challenges, particularly during the manufacturing phases. Indeed, the greater the stack height, the greater the sagging during the conditioning phase, and the more critical the control of the stack guidance becomes.

[0035] In current designs, this guidance is provided by cylindrical columns positioned inside the stack structure, passing through the various plates in which cylindrical or oblong holes are machined to match the diameter of the columns. The base of these columns is mechanically secured in the lower end plate.

[0036] This type of system has several limitations due to the small diameters of the guide columns imposed by the internal structure of the interconnectors. Achieving satisfactory guidance of numerous thin plates over considerable heights using these columns requires precise control of the relative clearances between the columns and the diameters of the through holes. This type of assembly, with its tight clearances, exposes the system to the risk of rotational jamming, which can occur during the glass-ceramic sealing cycle, during which the stack exhibits a significant drop in height. It should be noted that the force applied to ensure contact between the different plates is not particularly high, and therefore any accidental jamming of the plates relative to their guide elements is problematic.

[0037] For example, the Figures 3A and 3Brepresent the current guidance solution. Two columns 11 and 12 are used to guide the plates P of the stack 20 (shown here very schematically) as they descend. The plates P can be interconnecting plates, insulating plates, or even the lower and upper end plates. Here, on the figure 3B For example, we consider that two interconnection plates P are represented, the other possible interconnection and insulating plates and the lower and upper terminal plates are therefore not represented.

[0038] On one side, a circular orifice O1 is used, and the fit between plate P and column 11 is very fine, for example, on the order of 0.1 mm of clearance J1. On the other side, the orifice O2 in plate P is oblong in cross-section, allowing a larger clearance J2. Therefore, applying pressure at the center to lower the plates P, as indicated by arrows F, as the glass-ceramic seals melt, can cause a slight deflection of these plates P, thus resulting in a buttressing blockage, represented by AC on the diagram. figure 3B , on the column 11 on which the adjustment is tight. In practice, in order to avoid these risks of AC buttressing, the clearance J1 around the guide column 11 can be drastically increased, which then fundamentally degrades the guiding function and is therefore not at all desirable.

[0039] Document EP 1 826 851 discloses such an example of a cell stacking having internal guiding elements.

[0040] There is therefore a need to offer an effective guidance solution to avoid this buttressing problem while maintaining guidance accuracy during the slump of the plate stack. DESCRIPTION OF THE INVENTION

[0041] The invention aims to remedy at least partially the needs mentioned above and the drawbacks related to prior art achievements.

[0042] The invention thus relates, according to one of its aspects, to a stack of SOEC / SOFC type solid oxide cells operating at high temperature, consisting of a plurality of plates stacked one on top of the other in a vertical direction substantially perpendicular to each horizontal plane of extent of each plate, said plurality of plates comprising at least: a plurality of electrochemical cells, each consisting of a cathode, an anode, and an electrolyte interposed between the cathode and the anode, and a plurality of interconnectors arranged each between two adjacent electrochemical cells, an upper terminal plate and a lower terminal plate, between which the plurality of electrochemical cells and the plurality of interconnectors are enclosed, said stacking further comprising at least two guide elements ensuring the vertical stacking guidance of at least a portion of the plates, each plate of said at least a portion of the plates comprising at least two guide orifices, each opening onto the upper and lower faces of each plate and allowing the passage of said at least two guide elements, characterized in that, by observation in section in a horizontal plane of extent of each plate of said at least a portion of the plates, said at least two guide orifices are aligned along a first horizontal direction and spaced by a smaller inter-orifice distance, said at least two guide elements being spaced by a smaller inter-element distance greater than the smallest inter-orifice distance, the difference between the smallest inter-element distance and the smallest inter-orifice distance, corresponding to the internal clearance,being identical for said at least two guide holes and said at least two guide elements, in that, along the first horizontal direction, said at least two guide holes are spaced at a greater inter-hole distance, said at least two guide elements being spaced at a greater inter-element distance less than the greatest inter-hole distance, the difference between the greatest inter-hole distance and the greatest inter-element distance, corresponding to the external clearance, and in that the external clearance is greater than the internal clearance.

[0043] The stacking according to the invention may further include one or more of the following characteristics taken individually or in any possible technical combinations.

[0044] The internal clearance is advantageously greater than 0, in particular greater than 0.6 µm, and especially between 1 µm and 100 µm.

[0045] The external clearance is advantageously greater than the internal clearance, and in particular between 0.5 mm and 3 mm.

[0046] The ratio between outside play and inside play can be greater than 30, notably between 30 and 500.

[0047] The value of the internal and / or external clearance can depend on the thickness of the plate(s), and also on their possible or tolerated inclination, due to local solid body movement or deformation, particularly bending. The level of compressive force and the rigidity of the plates also play a role in determining this value.

[0048] Furthermore, the external clearance may be identical for said at least two guide holes and said at least two guide elements.

[0049] The said at least two guide holes may have the same shape and dimensions.

[0050] Furthermore, the said at least two guide holes may have, in section, an oblong shape, or a circular shape, or a polygonal shape, in particular a square or rectangular shape, with in particular at least the angle closest to the center of the plate making an angle other than 90°, in particular greater than 90°.

[0051] Furthermore, each plate of said at least a portion of the plates may be square or rectangular in shape. Said at least two guide holes may be diagonally opposite.

[0052] The said at least two guide elements may be guide rods of cylindrical shape, and in particular of circular shape in section.

[0053] Furthermore, by observation in section in a horizontal plane of extent of each plate of said at least a part of the plates, the largest dimension of guide hole of each guide hole, along a second horizontal direction perpendicular to the first horizontal direction, may be greater than the largest dimension of guide element of each guide element, measured along the second horizontal direction.

[0054] Furthermore, the ratio between the largest dimension of the guide hole and the largest dimension of the guide element, measured along the second horizontal direction, can be between 1 and 3. This ratio can be determined based on various parameters such as plate thickness, plate rigidity, and the possible plate inclination, among others. This determination is made through mechanical calculation, with the geometric criterion of ensuring the existence of functional clearance, taking into account the solid body movements of the mechanical elements as well as their potential deformation.

[0055] In addition, the invention also relates, according to another of its aspects, to a method of conditioning a stack of SOEC / SOFC type solid oxide cells operating at high temperature as defined above, characterized in that it comprises the step of guiding in vertical stacking at least a part of the plates constituting the stack by means of said at least two guiding elements.

[0056] The guiding step can be implemented while maintaining a substantially constant gap between said at least two guiding elements and said at least two guiding orifices.

[0057] Furthermore, with said at least two guiding elements fixed in a conditioning base, the process may include the step of using the same coefficients of thermal expansion for the materials of the plates and the conditioning base.

[0058] In particular, the materials used for the plates and the conditioning base can be identical to have the same coefficient of thermal expansion or different but with the same coefficient of thermal expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the schematic and partial figures in the attached drawing, on which: [ Fig. 1 ] is a schematic view showing the operating principle of a high-temperature solid oxide electrolyzer (SOEC), [ Fig. 2 ] is an exploded schematic view of part of a high-temperature solid oxide electrolyzer (SOEC) including interconnectors according to the prior art, [ Fig. 3A] and [Fig. 3B] represent, schematically and partially, respectively from a top view and from a side view, a principle according to the prior art of guiding the plates of a high-temperature SOEC / SOFC type stack, [ Fig. 4A] and [Fig. 4B ] represent, schematically and partially, respectively from a top view and from a side view, an example according to the invention of guiding the plates of a high-temperature SOEC / SOFC type stack, [ Fig. 4C] and [Fig. 4D ] are respectively enlarged views along C and D of [ Fig. 4A ], [ Fig. 5A ] represents, schematically and partially, from a top view, another example according to the invention of guiding the plates of a high-temperature SOEC / SOFC type stack, [ Fig. 5B ] is an enlarged view along B1 of [ Fig. 5A ], [ Fig. 6A] represents, schematically and partially, from a top view, yet another example according to the invention of guiding the plates of a high-temperature SOEC / SOFC type stack, and [ Fig. 6B ] is an enlarged view along B1 of [ Fig. 6A ].

[0060] Throughout these figures, identical references may designate identical or analogous elements.

[0061] Furthermore, the different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0062] THE figures 1 to 3 have already been described previously in the section relating to the prior art and the technical context of the invention. It is specified that, for the figures 1 and 2The symbols and arrows for supplying water vapor H2O, distributing and recovering dihydrogen H2, oxygen O2, air and electric current, are shown for clarity and accuracy, to illustrate the operation of the devices shown.

[0063] Furthermore, it should be noted that all the components (anode / electrolyte / cathode) of a given electrochemical cell are preferentially ceramics. The operating temperature of a high-temperature SOEC / SOFC stack is also typically between 600 and 1000°C.

[0064] Furthermore, the possible terms "upper", "lower", "horizontal" and "vertical" are to be understood here according to the normal orientation of a SOEC / SOFC type stack when in its usage configuration.

[0065] THE Figures 4A to 6B allow us to illustrate the guiding principle according to the invention.

[0066] First of all, the Figures 4A to 4D represent a first possibility of guiding the stacking of the plates P of a stack of 20 of high-temperature SOEC / SOFC type solid oxide cells, the plates P being positioned one on top of the other in a vertical direction substantially perpendicular to each horizontal plane of extent of each plate P.

[0067] It should be noted that, in all the examples described here, a plate P can correspond to, among other things, an electrochemical cell C1, C2, an interconnector 5, an upper terminal plate or a lower terminal plate, or even an insulating plate. Preferably, the plate P will generally be an interconnector 5.

[0068] This vertical stacking guidance is achieved using two guide elements 11 and 12, here in the form of guide rods or columns. These guide columns 11, 12 are diagonally spaced on each square plate P, but this choice is not limiting.

[0069] In addition, each plate P has two guide holes O1 and O2 which each open onto the upper face FS and the lower face FI of each plate P. These guide holes O1, O2 allow the passage of the guide columns 11, 12. They are also diagonally spaced on each plate P, but this choice is not limiting.

[0070] During the stack 20 conditioning process, a vertical compressive force is applied to it. This force is generally located between the guide columns 11 and 12, which can cause the stacked plates P to bend, as shown schematically by the arrows F on the diagram. figure 3Band here on the figure 4B In the event of contact between the plates P and the columns 11, 12, as previously shown schematically on the figure 3B , an undesirable AC buttressing phenomenon may occur.

[0071] The proposed configuration according to the invention on the Figures 4A to 4D is such that, by observation in section in a horizontal plane of extent of each plate P, the guide holes O1, O2 are aligned along a first horizontal direction X and spaced by a small inter-hole distance Do1. In addition, the guide columns 11, 12 are spaced by a small inter-element distance Dt1 which is greater than the smallest inter-hole distance Do1.

[0072] The difference between the smallest inter-element distance Dt1 and the smallest inter-orifice distance Do1 corresponds to the internal clearance Jm1. This internal clearance Jm1 is identical at the level of each pair O1, 11 and O2, 12 of guide orifice and guide column.

[0073] Furthermore, still along the first horizontal direction X, the guide holes O1, O2 are spaced apart by a greater inter-hole distance Do2, and the guide columns 11, 12 are spaced apart by a greater inter-element distance Dt2 which is less than the greatest inter-hole distance Do2.

[0074] The difference between the largest inter-orifice distance Do2 and the largest inter-element distance Dt2 corresponds to the external clearance Jm2. Advantageously, this external clearance Jm2 is greater than the internal clearance Jm1.

[0075] Consequently, the bending of a plate P, as schematically represented by the arrows F on the figure 4BThis facilitates its vertical descent. Indeed, during bending, the smallest inter-orifice distance Do1, measured along the first horizontal direction X, i.e., the distance between points A1 and A1', will decrease due to the deflection of plate P. This will tend to free the vertical movement of plate P because the smallest inter-element distance Dt1, still measured along the first horizontal distance X, between the two columns 11 and 12, remains constant. Thus, the resulting internal clearance Jm1' (see figure 4B ) will increase compared to the Jm1 game.

[0076] Similarly, the largest inter-orifice distance Do2, namely the distance between points A2 and A2', will also decrease during bending, as can be seen on the figure 4BHowever, due to the presence of an external play Jm2 much greater than the internal play Jm1, and because the greatest inter-element distance Dt2 does not vary, there will be no contact between the plate P and the columns 11, 12, and therefore no phenomenon of jamming or buttressing.

[0077] To avoid any blocking of the plate P on the columns 11, 12, the internal clearance Jm1 can be between 1 µm and 100 µm.

[0078] Similarly, the external clearance Jm2 can be between 0.5 mm and 3 mm.

[0079] In particular, for a smaller inter-orifice distance Do1 of the order of 300 mm and a plate height H of the order of 0.6 mm, the clearance Jm1 can be greater than 0.6 µm to avoid any blockage in a local solid body movement of the plate P. This corresponds to a very small clearance value and therefore allows very precise guidance, and thus positioning, of the plate P relative to the guide columns 11, 12.

[0080] Advantageously, it should also be noted that the external clearance Jm2 is identical for both guide ports O1, O2 and both guide columns 11, 12.

[0081] Furthermore, in this example of the Figures 4A to 4BThe guide holes O1, O2 each have an oblong cross-section. In this case, the ratio of the largest dimension of the guide hole do2 of each guide hole O1, O2, along a second horizontal direction Y perpendicular to the first horizontal direction X, is the distance between points B1 and B2 or between points B1' and B2' in the example of Figures 4C and 4D , and the largest dimension of the guide element dt2 of each guide element 11, 12, measured along the second horizontal direction Y, namely here the diameter passing through the center O of the columns 11, 12, as shown on the Figures 5B and 6B for example, may be too close to 1. In other words, the distances B 1 B 2 and B 1 'B 2 ' may be approximately equal to the diameter of the columns 11, 12.

[0082] Therefore, if plate P is rotated along the first horizontal direction X, there may be a buttressing at points B1, B1', B2 and B2' of the oblong shape (see Figures 4C and 4D ). To avoid this phenomenon, another configuration according to the invention may be proposed.

[0083] Thus, in the example of Figures 5A and 5B The guide holes O1, O2 correspond to cylinders whose circular cross-section is larger than that of the columns 11, 12. In other words, the diameter of each guide hole O1, O2 is greater than the diameter of each guide column 11, 12. The guide holes O1, O2 are eccentric with respect to the guide columns 11, 12.

[0084] A tight fit is maintained at points A1 and A1' but the games are now more important at points B1, B2, B1' and B2'.

[0085] Specifically, the largest dimension of the guide hole do2 of each guide hole O1, O2, along the second horizontal direction Y, is different here in the example of Figures 5A and 5b of the distance B 1 B 2 or B 1 'B 2 ', is greater than the largest dimension of guide element dt2 of each guide column 11, 12, namely here its diameter passing through the center O.

[0086] Advantageously, the ratio between the largest dimension of guide orifice do2 and the largest dimension of guide element dt2, measured along the second horizontal direction Y, is between 1 and 3.

[0087] A third possible configuration of the invention, illustrated in the Figures 6A and 6B , consists of the use of guide holes 11, 12 of substantially square shape, wider, and eccentric with respect to the position of the columns 11, 12.

[0088] This configuration describes a principle similar to that of Figures 5A and 5BHowever, here it uses "V"-shaped contacts (A1, O, A2), as seen on the figure 6B .

[0089] This configuration prevents rotation along a third vertical direction Z, and still retains the advantage that the distances A1A1' or A2A2' are reduced, thus avoiding any contact between plate P and column 11, 12 during vertical descent during the stacking process of stack 20. This avoids any buttressing problems. The angle α closest to the center of plate P, namely the angle α between the two contact planes, can be variable. Advantageously, it is chosen to be different from 90°, specifically larger than this value to allow for slightly greater rotational flexibility along the X and Z directions.

[0090] During the conditioning process of such a stack 20, it is important to maintain a substantially constant gap between the guide columns 11, 12 and the guide orifices 01, O2, particularly during the temperature rise. This gap must remain greater than 0. To ensure this, it is necessary to balance the thermal expansions, which govern both the size of the columns 11, 12 and the size of the plates P, notably through a judicious choice of the coefficients of thermal expansion of the materials used, and a temperature field that is as homogeneous as possible across the entire assembly.

[0091] Advantageously, the guide columns 11, 12 will be fixed in a conditioning base and one or more of the same materials will be used for the plates P and for the conditioning base in order to obtain the same coefficients of thermal expansion.

[0092] The invention finds its main application in the assembly of high-temperature SOEC / SOFC type stacks. In particular, the invention is applicable during the conditioning phase, during which the stack decreases significantly in size due to the melting of the glass joints of the assembly, as described previously in the section relating to the prior art and the technical context of the invention.

Claims

1. A stack (20) of SOEC / SOFC- type solid-oxide cells operating at high temperature, consisting of a plurality of plates (P) stacked on top of one another according to a vertical direction substantially perpendicular to each horizontal plane of extent of each plate (P), said plurality of plates (P) including at least: - a plurality of electrochemical cells (C1, C2) each formed of a cathode, an anode and an electrolyte interposed between the cathode and the anode, and a plurality of interconnectors (5) each arranged between two adjacent electrochemical cells (C1, C2), - an upper end plate (P) and a lower end plate (P), between which the plurality of electrochemical cells (C1, C2) and the plurality of interconnectors (5) are sandwiched, said stack (20) further including at least two guiding elements (11, 12) ensuring guidance of at least part of the plates (P) into a vertical stacking, each plate (P) of said at least part of the plates (P) including at least two guiding orifices (O1, O2) each opening onto the upper (FS) and lower (FI) faces of each plate (P) and enabling passage of said at least two guiding elements (11, 12), characterised in that, when observed in section in a horizontal plane of extent of each plate (P) of said at least part of the plates (P), said at least two guiding orifices (O1, O2) are aligned according to a first horizontal direction (X) and spaced apart by a smallest inter-orifice distance (Do1), said at least two guiding elements (11, 12) being spaced apart by a smallest inter-element distance (Dt1) larger than the smallest inter-orifice distance (Do1), the difference between the smallest inter-element distance (Dt1) and the smallest inter-orifice distance (Do1), corresponding to the inner clearance (Jm1), being identical for said at least two guiding orifices (O1, O2) and said at least two guiding elements (11, 12), in that, according to the first horizontal direction (X), said at least two guiding orifices (O1, O2) are spaced apart by a largest inter-orifice distance (Do2), said at least two guiding elements (11, 12) being spaced apart by a largest inter-orifice distance (Dt2) smaller than the largest inter-orifice distance (Do2), the difference between the largest inter-orifice distance (Do2) and the largest inter-element distance (Dt2), corresponding to the outer clearance (Jm2), and in that the outer clearance (Jm2) is larger than the inner clearance (Jm1).

2. The stack according to claim 1, characterised in that the inner clearance (Jm1) is comprised between 1 µm and 100 µm.

3. The stack according to claim 1 or 2, characterised in that the outer clearance (Jm2) is comprised between 0.5 mm and 3 mm.

4. The stack according to one of the preceding claims, characterised in that the outer clearance (Jm2) is identical for said at least two guiding orifices (01, 02) and said at least two guiding elements (11, 12).

5. The stack according to any one of the preceding claims, characterised in that said at least two guiding orifices (O1, O2) have the same shape and the same dimensions.

6. The stack according to claim 5, characterised in that said at least two guiding orifices (O1, O2) have, in section, an oblong shape.

7. The stack according to claim 6, characterised in that said at least two guiding orifices (O1, O2) have, in section, a circular shape.

8. The stack according to claim 6, characterised in that said at least two guiding orifices (O1, O2) have, in section, a polygonal shape, in particular a square or rectangular shape, in particular with at least the angle (α) the closest to the centre of the plate (P) forming an angle different from 90°, in particular larger than 90°.

9. The stack according to any one of the preceding claims, characterised in that each plate (P) of said at least part of the plates (P) is square or rectangular shaped and in that said at least two guiding orifices (O1, O2) are diagonally opposite.

10. The stack according to any one of the preceding claims, characterised in that said at least two guiding elements (11, 12) are guiding rods (11, 12) having a cylindrical shape, and in particular having a circular shape in section.

11. The stack according to any one of the preceding claims, characterised in that, when observed in section in a horizontal plane of extent of each plate (P) of said at least part of the plates (P), the largest guiding orifice dimension (do2) of each guiding orifice (O1, O2), according to a second horizontal direction (Y) perpendicular to the first horizontal direction (X), is larger than the largest guiding element dimension (dt2) of each guiding element (11, 12), measured according to the second horizontal direction (Y).

12. The stack according to claim 11, characterised in that the ratio between the largest guiding orifice dimension (do2) and the largest guiding element dimension (dt2), measured according to the second horizontal direction (Y), is comprised between 1 and 3.

13. A method for packaging a stack (20) of SOEC / SOFC-type solid-oxide cells operating at high temperature according to any one of the preceding claims, characterised in that it includes the step of guiding into a vertical stacking at least part of the plates (P) making up the stack (20) by means of said at least two guiding elements (11, 12).

14. The method according to claim 13, characterised in that the guiding step is implemented while preserving a substantially constant gap between said at least two guiding elements (11, 12) and said at least two guiding orifices (O1, O2).

15. The method according to claim 13 or 14, characterised in that, said at least two guiding elements (11, 12) being fixed in a packaging base, the method includes the step of using the same coefficients of thermal expansion for the materials of the plates (P) and of the conditioning base.