Hybrid seal for stack of electrochemical cells, especially solid electrolyte cells, stack of electrochemical cells and method for manufacturing a stack of electrochemical cells

Abstract

The invention relates to a hybrid seal for a stack of electrochemical cells, especially solid electrolyte cells, comprising a first seal (2) configured to be placed on either an anode current lead (6) or a cathode current lead (7), and a second seal (3) configured to be placed around either a gas inlet opening (9) or a gas outlet opening (10), wherein said second seal (3) comprises a connecting hole (8) which together with either the gas inlet opening (9) or the gas outlet opening (10) form either a gas inlet manifold or a gas outlet manifold, respectively, when a plurality of cells (8) is stacked one on top of the other. The invention also relates to a stack of electrochemical cells and a method for manufacturing thereof.

Description

[0001] Hybrid seal for stack of electrochemical cells, especially solid electrolyte cells, stack of electrochemical cells and method for manufacturing a stack of electrochemical cells

[0002] Technical Field

[0003] The invention generally relates to the field of electrochemical cells intended to convert the chemical energy of a gaseous fuel into electricity or to decompose water under the influence of an external source of electricity. More particularly, the subject-matter of the invention is a hybrid seal for a stack of electrochemical cells, especially solid electrolyte cells, a stack of electrochemical cells and a method for manufacturing of a stack of electrochemical cells. The invention finds particular application in double-sided solid oxide fuel cells.

[0004] Background art

[0005] Electrochemical cells are devices that can operate in two modes, i.e. galvanic (fuel cell) and electrolytic (electrolytic cell) mode. In galvanic mode, the cell acts as a source of electrical energy, converting chemical energy into electricity. In electrolytic mode, the cell uses electrical energy to carry out a chemical reaction, in particular the decomposition of water into hydrogen and oxygen. Selected cell designs can operate alternately in both modes, and we then call them reversible cells. In fuel cells, the reagents are continuously supplied from outside of the cell while the reaction products are removed from the cell. A characteristic feature of the cells is their layered structure, i.e. they consist successively of an anode, electrolyte and cathode layers. The anode and cathode are two electrodes between which there is an ionic conductor, i.e. an electrolyte. The electrical charge is supplied to or received from the cell electrodes. Individual cells can be connected to each other mechanically and electrically to form stacks of cells.

[0006] Fuel cells are known in the prior art that are characterized by the use of a solid oxide material as an electrolyte (Solid Oxide Fuel Cell). Stacks of such fuel cells are capable of directly converting the chemical energy of a fuel such as hydrogen, methane, natural gas or synthesis gas into electricity. The fact that they can operate using various fuels makes them applicable in a wide range of technologies, from green energy sources using renewable raw materials to conventional industrial ones based on hydrocarbon fuels. Their high operating temperature (typically between 600°C and 900°C) enables efficient conversion of energy from fuel to electricity. The advantage of systems using SOFC cells is therefore their high electrical efficiency of up to 60%, compared to 40% for systems based on popular low-temperature PEMFC (Proton Exchange Membrane Fuel Cell). An additional advantage is their low sensitivity to fuel contamination, especially of organic origin, e.g. carbon monoxide. Compared to conventional power generators (e.g. those based on heat engines), they are also characterized by a low environmental impact, both in terms of emissions of harmful substances (NOX, dust, CO2), as well as vibrations or noise.

[0007] One of the basic applications of SOFC fuel cell stacks are power generators operating wherever fast modulation of electrical power at the source and a quick start are not required. Due to heat generation during operation, the most common application of this type of stacks are cogeneration systems, from solutions dedicated to households - with an electric power of 0.5 * 3 kW, through solutions dedicated to small and medium-sized businesses - with a capacity of up to 1 MW and large system units with a capacity of several MW. SOFC stacks are also known to be used as auxiliary or main generators in means of transport, such as ships, locomotives or trucks.

[0008] Another application are electrolysers, where the same SOFC stacks are configured to operate in the SOE (Solid Oxide Electrolyser) mode. In SOE stacks, water is decomposed into hydrogen and oxygen using electrical energy. This process is more effective at high temperatures, in addition, SOE stacks can utilize waste heat from industrial processes, which allows for reduced electricity consumption compared to competitive electrolysis methods using low-temperature technologies.

[0009] A single SOFC fuel cell consists of two electrodes separated by an oxygen ion conducting, gas-tight electrolyte. The electrodes: cathode and anode are connected by an external circuit that receives electrical energy from the cell. Oxygen obtained from the air is reduced at the cathode and transported via the electrolyte to the anode, where it reacts with fuel. In conventional solutions, to obtain useful power, single cells are stacked by means of interconnectors, which additionally ensure a gas-tight separation of the cathode and anode chambers. The interconnectors are made of electrically conductive ceramics or metal alloys. The disadvantage of ceramic interconnectors is their high manufacturing cost. Metallic solutions are susceptible to high-temperature corrosion and differ in their thermal expansion coefficient from other cell elements. The compact structure of a conventional stack makes the heating process difficult, which results in a long start-up time of up to 20 hours, and dynamic power modulation is significantly limited.

[0010] US 4276355A patent application describes a fuel cell system comprising a plurality of electrically connected fuel cells with at least one cooling module disposed between the selected fuel cells, such that the fuel cells together with the cooling module form a stack and have a cross-section of an elongated polygon having pairs of parallel sides such that the pairs of longer sides of the polygon are closer together than the other pairs of sides of the polygon. Each fuel cell has an electrolyte placed between two bipolar plates that define channels for the flow of fuel and oxidant, the inlets and outlets of which are located on pairs of shorter sides of parallel cross-sections of the fuel cell stacks, allowing fuel and oxidant to be transported along the longer sides of cross-sections of these stacks.

[0011] US7531053B2 patent describes a fuel cell and a method for producing thereof; the said cell consists of an electrolyte, electrodes and interconnectors. The interconnector is made of an alloy composed of a suitably selected combination of elements such as iron, silicon, manganese, chromium, molybdenum and niobium. This material provides better resistance of the interconnectors used in the stack to oxidation occurring at high operating temperatures.

[0012] The above documents show the structure of classical stacks, in which flat, single-sided cells are used. Subsequent cells alternately adhere to each other, creating a stack in the form of a compact block, which prevents the free flow of air around individual cells. The cells are connected by interconnectors, which are responsible for the distribution of reagents and the flow of electric charge between subsequent cells in the stack.

[0013] The elimination of the unfavourable features disclosed in the conventional SOFC stack is possible by using double-sided DFC (double-sided cell) fuel cells and connecting them into a stack. Double-sided fuel cells are a specific type of SOFC cells, in which two adjacent cells are connected by a common anode containingfuel channels.

[0014] In order to increase the electrical voltage, DFCs are electrically connected in series into stacks. A stack consists of DFCs (e.g. 30) stacked one on top of the other. Seals are placed between the cells, which seals simultaneously keep them at a distance allowing for free supply of the oxidant (air) and provide electrical insulation. Connecting fuel cells in series forces equal electric current to flow through all cells. An equal current flowing through successive cells requires the same amounts of fuel to be supplied to each cell. At the same time, the flow of fuel through the fuel channel formed by alternately arranged seals and cells causes a pressure drop alongthat channel.

[0015] Polish patent specification PL213349 discloses a DFC type cell. In this patent, a single DFC, unlike conventionalsolutions, has a double-sided active surface, and its supporting structure is made entirely of ceramic materials. The central support with the fuel distribution channels on both its sides is made of anode material. The channels on both sides of the support are covered by the active anode layer, on which the electrolyte and the cathode layer are applied. Within one flat plate, two cells with common anode part are formed. These cells are connected into a stack, while maintaining a distance between subsequent plates, which allows air to flow freely through the stack.

[0016] Polish patent specification PL218785A discloses a fuel cell battery which has flat doublesided cells, wherein each double-sided cell is provided with input-output openings of distribution channels, through which openings draw bolt are passed to ensure the connection with subsequent double-sided cells. The individual double-sided cells are separated from each other by flexible separators.

[0017] Polish patent specification PL220309 discloses a fuel cell battery which is an autonomous power source. The battery comprises at least one stack of interconnected flat double-sided cells arranged inside a thermally insulated chamber. Each doublesided cell is made in the form of a ceramic plate which has its own connections for the supply and discharge of reagents and the discharge of electrical energy, and is equipped with a central ceramic anode structure with high electrical conductivity, which on both sides has fuel distribution channels and operating channels covered with operational anode layers, which are then covered successively with: solid electrolyte layers, cathode layers and cathode conductive layers. Each double-sided cell is in mechanical contact with adjacent double-sided cells via flexible separators that allow the transfer of fuel and catalytic oxidation products.

[0018] The connection of double-sided DFC cells into stacks is disclosed in Polish patents PL 218785 and PL 220309. The invention described in these patents gives a unique property to stacks, consisting in increasing the dynamics of operation by accelerating heating and cooling thereof. The increase in dynamics is possible due to two disclosed innovative design features. First, the use of DFC cells resulted in elimination of differences in the material properties of individual layers (channels, support and anode made of the same material), which minimizes the formation of thermal stresses during heating and cooling. Second, in the disclosed solutions, individual cells are spaced apart, which allows for intensification of heat exchange by significantly exposing the surface washed by the working medium. Both these design features translate into the measurable performance parameters of cell stacks, i.e. start-up and cooling times, which are significantly shortened. In addition, this solution improves the dynamics of stack operation, i.e. their response to variable electrical load, and significantly improves reliability. Noteworthy features of the solutions disclosed in patents PL 218785 and PL 220309 are their gas seals in the mechanical connections between cells and the degradation of current connections. The connections using metal ribbons disclosed in PL220309 lose mechanical contact as a consequence of relaxation, which leads to the interruption of the electrical circuit. An additional problem identified is the degradation of electrical connections on the anode side due to the action of a dual atmosphere, i.e. the reducing one from hydrogen and the oxidizing one from air. The problem of degradation also relates to electrical connections disclosed in PL 218785.

[0019] Summary of the invention

[0020] The objective of the invention is to provide solution that will at least partially eliminate the problems related to the gas-tightness of the connections between cells and the degradation of the current connections. According to the first aspect of the invention, there is provided a hybrid seal for a stack of electrochemical cells, especially solid electrolyte cells, wherein said electrochemical cell comprises an anode, a cathode, a solid electrolyte, an at least one reactant flow channel extending longitudinally, a gas inlet opening and a gas outlet opening in the form of through holes formed in the thickness of the cell and connected to the at least one reactant flow channel, an at least one anode current lead and an at least one cathode current lead. The seal comprises a first seal configured to be placed on either the anode current leads or the cathode current leads, and a second seal configured to be placed around the gas inlet opening or the gas outlet opening, wherein said second seal comprises a connecting hole which together with either the gas inlet opening or the gas outlet opening form either a gas inlet manifold or a gas outlet manifold, respectively, when a plurality of cells is stacked one on top of the other.

[0021] In one preferred embodiment, the first seal is in the form of a plate.

[0022] In one preferred embodiment, the second seal is in the form of a disc.

[0023] In another embodiment, the first seal is made of material with greater deformability than the second seal.

[0024] In yet another embodiment, the first seal is made of material having a greater thickness than the second seal.

[0025] In yet another embodiment, the first seal comprises a connecting hole which, together with the connecting hole of the second seal and either the gas inlet opening or the gas outlet opening, form either the gas inlet manifold or the gas outlet manifold, respectively, when a plurality of cells is stacked one on top of the other.

[0026] In yet another embodiment, the first seal comprises a socket configured to receive the second seal, wherein the dimensions of the socket and the second seal are matched so that when the second seal is placed in the socket and compressed between the two cells, gas-tightness between the first seal and the second seal is achieved.

[0027] In yet another embodiment, the first seal comprises longitudinal openings for the passage of conductive connectors, preferably in the form of a ribbon, wherein said conductive connectors are configured to connect the anode current leads to the cathode current leads of the adjacent cells.

[0028] In yet another embodiment, the seals are made on the basis of vermiculite.

[0029] In yet another embodiment, upon application of stress when the cells are compressed in the stack, the thickness of the seals is reduced by about 10% or by at least the thickness of the current leads.

[0030] According to the second aspect of the invention, there is provided an electrochemical cell stack comprising a plurality of electrochemical cells stacked one on top of the other, wherein each cell comprises an anode, a cathode, a solid electrolyte, an at least one reactant flow channel extending longitudinally, a gas inlet opening and a gas outlet opening in the form of through holes formed in the thickness of the cell and connected to the at least one reactant flow channel, an at least one anode current lead and an at least one cathode current lead, and conductive connectors connecting the anode current leads to the cathode current leads of the adjacent cells. At least one of a first seal and a second seal of a hybrid seal is placed between the adjacent cells, wherein the first seal is placed on either the anode current leads orthe cathode current leads, and the second seal is placed around either the gas inlet openings or the gas outlet openings.

[0031] In one embodiment, each cell is a double-sided electrochemical cell, preferably with solid oxide electrolyte, comprising a central support structure with the at least one reagent flow channel formed in the support structure on each of its sides, wherein an active anode layer, a solid electrolyte layer, a cathode layer and a current collecting layer are arranged on both sides of the support structure, wherein the anode current leads are located on one of the left or right side of the cell on both faces thereof and the cathode current leads are also located on one of the left or right side of the cell on both faces thereof, which side of the cell is opposite the side of the cell on which the anode current leads are located.

[0032] In yet another embodiment, the electrochemical cells in the stack are arranged successively alternately so that the anode current leads and the cathode current leads in the adjacent cells are arranged with respect to each other on the opposite sides of the stack. According to the third aspect of the invention, there is provided a method for manufacturing a stack of electrochemical cells comprising the following steps: arranging a plurality of electrochemical cells one on top of the other in a stack, placing hybrid seals between adjacent electrochemical cells so as to create a gap between the adjacent cells, wherein first seals cover anode current leads and cathode current leads, and second seals surround gas inlet openings and gas outlet openings, compressing the stack so arranged until the first seals are compressed with the second seals to achieve gas-tightness between the seals.

[0033] In one embodiment, during the compression step, under the influence of pressure the thickness of the seals is reduced by about 10% or is reduced by at least the thickness of the current leads.

[0034] Advantageous effects of the invention

[0035] A hybrid seal of the invention performs the functions of a supporting structure for the stack, a gas seal, and a seal for electrical connections of the cells in the stack.

[0036] The first seals ensure that conductive connectors (metal ribbons) are pressed to the current leads of both the anode and the cathode, in order to create the electrical contact and thus continuity of the current circuit.

[0037] The second seals ensure gas-tightness for the reagents fed into and removed from the electrochemical cells. The first seals protect the anode current leads from a double gas atmosphere, i.e. the reducing one on the anode side and the oxidizing (oxygen) one on the cathode side, tightly coveringthe anode current leads.

[0038] Brief description of the drawings

[0039] The object of the invention is shown in the drawings, in which:

[0040] Fig. 1 - schematically shows a stack of electrochemical cells with visible seals according to the first embodiment,

[0041] Fig. 2 - schematically shows an assembled stack of electrochemical cells with a hybrid seal, accordingto the first embodiment, Fig. 3 - shows the diagram of connection of the cells in a stack in a cross-sectional view accordingto the first embodiment,

[0042] Fig. 4 - schematically shows a stack of electrochemical cells according to the second embodiment,

[0043] Fig. 5 - schematically shows a of electrochemical cells according to the third embodiment,

[0044] Fig. 6 - shows the diagram of connections of the cells in a stack in a cross-sectional view accordingto the third embodiment.

[0045] Fig. 7 -schematically shows a stack of electrochemical cells with a hybrid seal according to the first embodiment with the supporting structure,

[0046] Fig. 8 - shows schematically an alternative embodiment of the cell, in exploded view (above) and with stacked cells (below).

[0047] Fig. 9 - shows another variant of the embodiment of the cell from Fig. 8.

[0048] Detailed description of preferred embodiments of the invention

[0049] A hybrid seal made according to the invention comprises at least one first seal 2 and at least one second seal 3. The hybrid seal is intended to connect electrochemical cells in a stack, ensuring gas-tightness of the connections on the gas manifolds and protecting the current connections from degradation. Various variants of the seal will be presented in more detail below with reference to the description of the preferred embodiments of the stack of electrochemical cells according to the invention, as illustrated in Figs. 1 -6.

[0050] The first seal 2 is intended to be placed on anode current leads 6 and cathode current leads 7. It preferably has the form of a plate placed just next to the opposite, usually shorter sides of the electrochemical cell 1 , where the current leads 6, 7 and gas manifold openings are located. The first seal 2 may contain either a socket 12 accordingto the first embodiment (Fig. 1) or a connecting hole 11 according to the second and third embodiment (Fig. 4 and Fig. 5). The dimension of the connecting hole 11 matches either a gas inlet openings or a gas outlet opening 10, and is a part of either a gas inlet manifold or a gas outlet manifold. Preferably, the diameter of the connecting hole 11 is equal to or greater than the diameter of either the gas inlet opening 9 or the gas outlet opening 10. The size of the socket 12 is, in turn, adjusted to the external size of the second seal 3, which is placed in this socket 12.

[0051] The first seal 2 is a gas-tight barrier for the current leads 6, 7 and acts as a spacer and stabilizing element for individual cells 1 in the stack.

[0052] The second seal 3 is preferably in the form of a disc and contains a connecting hole 8 configured to match the dimension of either the gas inlet opening 9 or the gas outlet opening 10. Preferably, the diameter of the connecting hole 8 of the second seal3 is equal to the diameter of either the gas inlet opening 9 or the gas outlet opening 10. The second seal 3, together with either the gas inlet openings 9 or the gas outlet openings 10, and in one of the variants of the hybrid seal also with the connecting hole 11 of the first seal 2, form gas manifolds, either the gas inlet manifold or the gas outlet manifold, respectively. The main task of the second seal 3 is to ensure tightness in the area of the gas openings 9, 10, and thus the gas manifolds.

[0053] The first and second seals 2, 3 are made of material with certain deformability under applied stress. This deformability can be defined as a general measure of elastic deformations and plastic deformations, i.e. the temporary or permanent ability of a material to change dimensions or form. With regard to the present invention, it means the ability of the material to deform under external stresses, i.e. to reduce its thickness by a certain value. In one embodiment, the first seal 2 and the second seal 3 are made of material with the same deformability. In another embodiment, the first seal is made of material with greater deformability, i.e. a more susceptible to deformations, than the second seal 3. In yet another embodiment, the first seal 2 is made of material having greater thickness than the second seal 3. In yet another embodiment, the seals 2, 3 can be made of material of the same thickness but different deformability.

[0054] Preferably, the first seal 2 and the second seal 3 are made on the basis of vermiculite. Examples of such seals are Thermiculite seals from Flexita llic or Planix Megatherm High seals from Carrara.

[0055] Figs. 1 -3 schematically illustrate a stack of electrochemical cells according to the first embodiment of the invention. The stack of electrochemical cells is composed of a plurality of SOFC electrochemical cells 1 made using DFC technology with a solid oxide electrolyte. It is obvious to a person skilled in the art that hybrid seals can be applied to other electrochemical cells, including single-sided ones.

[0056] The said double-sided DFC cell comprises a central support structure, preferably made of a ceramic material. The support structure is also an anode structure. A plurality of longitudinally extending fuel flow channels is made in the support structure. On both sides of the support structure, an active anode layer, a solid electrolyte layer, a cathode layer and a current collecting layer (e.g. a metallic mesh) are placed successively. Each cell 1 comprises a gas inlet opening 9 and a gas outlet opening 10, which are connected by the fuel flow channels. The gas openings 9, 10 are arranged at the opposite sides of the cell 1 .

[0057] Further, the anode current leads 6 and the cathode current leads 7 are placed in the area of the gas inlet opening 9 and the gas outlet opening 10. The anode current leads 6 are located on one of the left or right side of the cell 1 on both faces thereof, and the cathode current leads 7 are located on the other side of the cell 1 , left or right, on both faces thereof, which side of the cell 1 is opposite the side of the cell 1 at which the anode current leads 6 are located. In the embodiment presented, on each side of the cell 1 there are two current leads of the anode and cathode 6, 7. The electrical contact between the individual current leads 6, 7 and the adjacent cells 1 is provided by conductive connectors 4. In the first embodiment illustrated in the drawings, the conductive connectors 4 are made of a metallic ribbon in the shape resemblingthe letter S.

[0058] The gas inlet openings 9 and the gas outlet openings 10, after connecting the cells 1 into the stack, form, together with the second seals 3, the gas inlet manifold 1 and the gas outlet manifold 2, respectively.

[0059] Fig. 2 shows a diagram of the connection of cells 1 in the stack. The individual cells 1 in the stack are arranged alternately in such a way that the anode current leads 6 of two adjacent cells 1 are located on opposite sides of the fuel cell stack. The cathode current leads 7 are arranged analogously, wherein the anode current leads 6 and the cathode current leads 7 on the same side of the cell 1 are placed on opposite sides. The conductive connector 4 connects either the anode current lead 6 or the cathode current lead 7 with either the anode current lead 6 or the cathode current lead 7 of the adjacent fuel cell 1 , respectively.

[0060] In the presented embodiment, each hybrid seal comprises one first seal 2 and one second seal 3. The first seal 2 comprises a socket 12 in which the second seal 3 is placed. The internal dimension of the socket 12 matches the external dimension of the second seal 3. The second seal 3 may be slightly smaller or slightly larger than the socket 12. Preferably, these dimensions are selected so that after the seals have been compressed in the stack, they are compacted and the first seal 2 is tightly connected to the second seal 3. Two hybrid seals are placed between adjacent cells 1 , i.e. one pair of seals 2, 3 on opposite sides of the cells. One of the first seals 2 of the pair contains longitudinal openings 5 for conductive connectors 4 in the form of a ribbon. The purpose of the first seal 2 with longitudinal openings 5, through which the conductive connectors 4 in the form of a ribbon are passed, is to press the ribbons against the surface of the anode current leads 6 and to maintain a gas-tight barrier on these current leads. In addition, the first seal 2 presses the conductive connections 4 in the form of a ribbon to the surface of the cathode current leads 7 of the next cell 1 in the stack. In turn, the first seal 2 of the second pair without longitudinal openings presses the conductive connections 4 in the form of a ribbon to the surface of the cathode current leads 7. The first seals 2 of each of the two pairs act as a spacer for the subsequent cells 1 in the stack, which allows air to flow between the subsequent cells, while the mechanical stabilization of the stack is maintained. The second seal 3 is an element ensuring the gas-tightness around either the gas inlet opening 9 or the gas outlet opening 10. The second seal 3 is made of a material which is less susceptible to deformation than the material from which the first seal 2 is made. In this embodiment, both seals 2, 3 of a given pair have the same thickness, e.g. 1 mm. The seals 2, 3 are characterized by the ability to work at temperatures from 600-850 degrees Celsius. This solution improves the gas-tightness of the stack, while reducing the bending moments on the cells 1 in the stack, if these do not have perfect flatness and parallelism around the gas manifolds.

[0061] Fig. 4 shows a stack of electrochemical cells according to a second embodiment of the invention. The structure of the stack and cells 1 is analogous to that of the first embodiment. In the second embodiment, two hybrid seals are placed between cells 1 , where each seal comprises one first seal 2 and two second seals 3. The first seal 2 is placed between two second seals 3. The first seal 1 comprises a connecting hole 11 , which together with the connecting holes 8 of the second seals 3 and either the gas inlet or outlet openings 9, 10 form a part of either the gas inlet manifold or the gas outlet manifold, respectively. In this embodiment, all seals 2, 3 are made of the same material, but have different thicknesses. The first seal 2 has a thickness of 1 mm, and each of the second seal 3 has a thickness of 0,5 mm. After the cells 1 have been compressed in the stack, the seals 2, 3 are compacted and connected tightly, which further improves the gas-tightness of the connections. As a result of the compression of the seals 2, 3, the second seals 3 adapt to the surface of the cell 1 around the gas manifolds, which ensures the gas-tightness. At the same time, the second seals 3 are also pressed into the first seal 2. Preferably, the compression process is carried out until the second seals 3 are entirely pressed into the first seal 2. Preferably, the compression is carried out until the first seal 2 is compressed by about 10% or its thickness is reduced by at least the thickness of the anode current lead 6, which provides protection of the anode current leads 6 against a double atmosphere.

[0062] The third embodiment of the stack of electrochemical cells according to the invention is shown in Fig. 5 and Fig. 6, which illustrate the stack with the conductive connectors 4 in a trimetric view and in a cross-section, respectively. The structure of the stack and cells 1 is analogoustothat of the first and second embodiments. In the third embodiment, only a single first seal 2 is used, which simultaneously seals the current leads 6, 7 and the gas inlet and outlet openings 9, 10. The first seal 2 comprises the connecting hole 11 , which together with either the gas inlet opening 9 or the gas outlet opening 10 forms the gas inlet manifold or the gas outlet manifold, respectively, when a plurality of cells 1 is stacked one on top of the other. In this embodiment, the conductive connectors 4 made of a metallic ribbon in the form of a lower-case letter h are also used. The diagram of connections of the cells 1 in the stack using the aforementioned conductive connectors 4 is shown in Fig. 6. The conductive connectors 4 in the shape of the lower-case letter h connect the current leads of the same type lying on both sides into one contact surface. The contact surfaces of adjacent cells 1 are then joined in pairs, i.e. the contact surfaces of the anode 6 are connected to the contact surfaces of the cathode 7 between adjacent cells 1 .

[0063] According to the invention, a method for manufacturing a stack of electrochemical cells comprises the following steps: arranging a plurality of electrochemical cells 1 one on top of the other in a stack, placing the hybrid seals 2, 3 between adjacent electrochemical cells 1 so as to create a gap between the adjacent cells, wherein the first seals 2 cover the anode current leads 6 and the cathode current leads 7, and the second seals 3 surround the gas inlet openings 9 and the gas outlet openings 10, compressing the stack so arranged until the first seals 2 are compacted with the second seals 3 and connected tightly.

[0064] For the implementation of the method, an assembly shown schematically in Fig. 7 is preferably used. The assembly comprises two pressure plates, i.e. a base plate 13 and an end plate 14, draw bolts 15 with nuts and guide rods (not shown). The individual cells 1 together with the seal 2, 3 are put on the guide rods, which pass through the gas inlet and outlet openings 9, 10 of each cell 1 , the connecting holes 8 of the second seals 3 and the connecting holes 11 of the first seals 2 in the second embodiment of the hybrid seal. Further, the pressure plates 13, 14 are tightened by means of draw bolt 15 until the seals 2, 3 are compacted and tight connections are created.

[0065] In an alternative embodiment of the invention - the advantages of the present invention can also be observed in electrochemical cells 1 which are single-sided. By such cells 1 , cells 1 are meant in the form of generally plates made of anode material, in which flow channels are made, and which are covered with an electrolyte layer on both sides. On one side of such cells 1 , cathode material is then applied to such electrolyte and metallic paths 21 (e.g. made of silver) are present, acting as surface current collectors.

[0066] In such an embodiment - in order to electrically connect subsequent cells 1 in the stack - it is necessary to create an electrical connection between the anode of one cell and the cathode of the adjacent cell - for this purpose a metallic (e.g. silver) ribbon (metallic connector) 22 is used. However, in orderto avoid corrosion of such metallic ribbon 22, which could occur in the event of contact with a double atmosphere - similarly to the previously described embodiments - a specially shaped seal 23 is used. Such seals 23 also have an additional function, as they help to stabilize subsequent cells 1 in the stack and, due to their elasticity, reduce the risk of stresses that may occur when stacking cells 1 with certain manufacturing defects (i.e. not perfectly flat, having only minor deviations, which, for example, appeared after firing the ceramic material of the cell 1 ).

[0067] A cell 1 of this type is shown, for example, in Fig. 8. The cathode side of the cell is visible there - with visible paths 21 of the current collector marked on it. These paths 21 in the presented embodiment converge at two locations - on the extreme sides of the cell, creating larger contact surfaces 24, which appear on both sides of the visible gas ports (inlet 9 and outlet 10, respectively).

[0068] Also visible in Fig. 8 is the seal 23, in the form of a plate with a through hole 25 in the middle and two slits 26 on both sides of this through hole 25. Through these slits 26 pass the bent side arms of the metallic connector 22 - which in the structure of the cell stack on one side connects the anode (entering into direct contact with it) and on the other side the contact surfaces 24 of the current collector formed on the cathode side of the cell 1 .

[0069] Thanks to such a construction, in the fuel cell stack - the seal 23 on one hand presses the metallic connector 24 (preferably in the form of a silver ribbon) to the parts of the adjacent cells, ensuring a strong connection without any play, and on the other hand - isolates the metallic connector 24 and the current collectors from the area where a dual atmosphere may occur, thus reducing the risk of corrosion.

[0070] Also - connectingsubsequent cells 1 in a stack is simplified, and by providingsupportfor cells 1 only along the line of the inlet ports 9 and the outlet ports 10 and this through the material of the seal 23 - it is easier to stack cells 1 that exhibit certain minor imperfections in their geometry.

[0071] Moreover, when creating current collectors of this type as shown in Fig. 8, i.e. which have contact surfaces 24 on both sides of a given cell 1 - the current path on individual electrodes of cell 1 is shortened. Further, in Fig. 9 another variant of this alternative embodiment of the invention is presented - in which the metallic paths 21 of the current collector on the cathode side of the cell 1 , instead of converging to the contact fields 24 on the extreme sides of the cell - have numerous contact fields 24 formed alongthe centre line of the cell 1 .

[0072] In such a variant -the metallic connector 22 has a different form - similar in shape to the harmonica, and its bent parts are then based on the contact fields of the current collector, while the ends of such connector 22 - again pass through the seal 23 (here - through two slits 26 formed one per a given seal 23) and in the area covered by such seal 23 - are pressed against the anode of the subsequent, adjacent cell 1 .

[0073] This type of variant has similar advantages to the one described above, wherein it additionally provides even greater surface contact with the cathode current collector.

[0074] List of markings in the drawing:

[0075] 1 - electrochemical cell

[0076] 2 - first seal

[0077] 3 -second seal

[0078] 4 - conductive connector

[0079] 5 - longitudinal opening

[0080] 6 - anode current leads

[0081] 7 - cathode current leads

[0082] 8 -connecting hole of the second seal

[0083] 9 -gas inlet opening

[0084] 10 - gas outlet opening

[0085] 11 -connecting hole of the first seal

[0086] 12 -socket of the first seal

[0087] 13 - base plate

[0088] 14 - end plate

[0089] 15 - draw bolts

[0090] 21 - metallic paths

[0091] 22 - metallic connector / metallic ribbon

[0092] 23 -seal

[0093] 24 - contact surfaces

[0094] 25 -through hole

[0095] 26 -slits

Claims

Claims1 . A hybrid seal for a stack of electrochemical cells, especially solid electrolyte cells, wherein said electrochemical cell (1 ) comprises an anode, a cathode, a solid electrolyte, an at least one reactant flow channel extending longitudinally, a gas inlet opening (9) and a gas outlet opening (10) in the form of through holes formed in the thickness of the cell (1 ) and connected to the at least one reactant flow channel, an at least one anode current lead (6) and an at least one cathode current lead (7), characterized in that the hybrid seal further comprises a first seal (2) configured to be placed on either the anode current leads (6) or the cathode current leads (7), and a second seal (3) configured to be placed around either the gas inlet opening (9) or the gas outlet opening (10), wherein said second seal (3) comprises a connecting hole (8) which together with either the gas inlet opening (9) or the gas outlet opening (10) form either a gas inlet manifold or a gas outlet manifold, respectively, when a plurality of cells (8) is stacked one on top of the other.

2. The hybrid seal according to claim 1 , wherein the first seal (2) is in the form of a plate.

3. The hybrid seal according to claim 1 , wherein the second seal (3) is in the form of a disc.

4. The hybrid seal according to any of the preceding claims 1 to 3, wherein the first seal (2) is made of material with greater deformability than the second seal.

5. The hybrid seal according to any of the preceding claims 1 to 4, wherein the first seal (2) is made of material with greater thickness than the second seal.

6. The hybrid seal according to any of the preceding claims 1 to 5, wherein the first seal (2) comprises a connecting hole (11 ) which, together with the connecting hole (8) of the second seal (3) and either the gas inlet opening (9) or the gas outlet opening (10), forms either the gas inlet manifold or the gas outlet manifold, respectively, when a plurality of cells (1 ) is stacked one on top of the other.

7. The hybrid seal according to any of the preceding claims 1 to 5, wherein the first seal (2) comprises a socket (12) configured to receive the second seal (3), wherein the dimensions of the socket (12) and the second seal (3) are matched so that when the second seal (3) is placed in the socket (12) and compressed between the two cells (1 ), gas-tightness between the first seal (2) and the second seal (3) is achieved.

8. The hybrid seal according to any of the preceding claims 1 to 7, wherein the first seal (2) comprises longitudinal openings (5) for the passage of conductive connectors (4), preferably in the form of a ribbon, said conductive connectors (4) are configured to connect the anode current leads (6) to the cathode current leads (7) of adjacent cells (1).

9. The hybrid seal according to any of the preceding claims 1 to 8, wherein the seals (2, 3) are made of vermiculite based material.

10. The hybrid seal according to any of the preceding claims 1 to 9, wherein upon application of stress when the cells are compressed in the stack, the thickness of the seals (2, 3) is reduced by about 10% or by at least the thickness of the current leads (6, 7).

11. An electrochemical cell stack comprising a plurality of electrochemical cells (1 ) stacked one on top of the other, wherein each cell (1 ) comprises an anode, a cathode, a solid electrolyte, an at least one reactant flow channel extending longitudinally, a gas inlet opening (9) and a gas outlet opening (10) in the form of through holes formed in the thickness of the cell (1 ) and connected to the at least one reactant flow channel, an at least one anode current lead (6) and an at least one cathode current lead (7), and conductive connectors (4) connecting the anode current leads (6) to the cathode current leads (7) of adjacent cells (1 ), characterized in that an at least one of a first seal (2) and a second seal (3) of a hybrid seal as defined according to any claim 1 to 10 is placed between the adjacent cells (2), wherein the first seal (2) is placed on either the anode current leads (6) or the cathode current leads (7), and the second seal (3) is placed around either the gas inlet opening (9) or the gas outlet opening (10).

12. The stack according to claim 11 , wherein each cell (1 ) is a double-sided electrochemical cell, preferably with a solid oxide electrolyte, comprising a central support structure with the at least one reagent flow channel formed in the support structure on each of its sides, wherein an active anode layer, a solid electrolyte layer, a cathode layer and a current collecting layer are arranged on both sides of the support structure, wherein the anode current leads (6) are located on one of the left or right side of the cell (1 ) on both faces thereof, and the cathode current leads (7) are also located on one of the left or right side of the cell (1 ) on both faces thereof, whichside of the cell (1 ) is opposite the side of the cell (1 ) on which the anode current leads (6) are located.

13. The stack according to claim 12, wherein the electrochemical cells (1 ) in the stack are arranged successively alternately so that the anode current leads (6) and the cathode current leads (7) in adjacent cells are arranged with respect to each other on the opposite sides of the stack.

14. A method for manufacturing a stack of electrochemical cells as defined in claims 11 to 13, using a hybrid seal as defined in claims 1 to 10, comprising the following steps: arranging a plurality of electrochemical cells (1 ) one on top of the other in a stack, placing hybrid seals (2, 3) between adjacent electrochemical cells (1 ) so as to create a gap between the cells, wherein first seals (2) cover anode current leads (6) and cathode current leads (7), and second seals (3) surround gas inlet openings (9) and the gas outlet openings (10), compressing the stack so arranged until the first seals (2) and the second seals (3) are pressed in.

15. The method according to claim 14, wherein during the compression step, under the influence of pressure the thickness of the seals (2, 3) is reduced by about 10% or is reduced by at least the thickness of the current leads (6, 7).

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