Stack of electrochemical cells, especially solid electrolyte cells, and method for stacking electrochemical cells

Abstract

The subject-matter of the present invention is a stack of electrochemical cells comprising a plurality of electrochemical cells (C) stacked on top of each other, an inlet gas manifold (1) having a supply connector (3), an outlet gas manifold (2) having a discharge connector (4), seals (8), conductive connectors connecting electrically adjacent electrochemical cells (C) in the stack. Accordingto the invention, the electrochemical cells (C) in the stack are arranged in a defined order from a cell (C1 ) with the highest flow resistance through an at least one reactant flow channel to a cell (Cn) with the lowest flow resistance through the at least one reactant flow channel, wherein the cell (C1) with the highest flow resistance is placed closest to the supply connector (3) of the inlet gas manifold (1) while the cell (Cn) with the lowest flow resistance is placed at the location furthest from the supply connector (3) of the inlet gas manifold (1).

Description

[0001] Stack of electrochemical cells, especially solid electrolyte cells, and method for stacking 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 vapour under the influence of an external source of electricity. More particularly, the subjectmatter of the invention is a stack of electrochemical cells, especially solid electrolyte cells, and a method for stacking electrochemical cells.

[0004] Background art

[0005] Fuel cells are electrochemical devices that directly convert the chemical energy of a fuel into electricity and heat. The reagents are continuously supplied from outside of the cell while the reaction products are removed from the cell. The anode and cathode sides of the cells - swept with fuel and oxidizer respectively - are separated by elements enabling the distribution of reagents and the transport of electrical charges between the subsequent cells - called bipolar plates (interconnectors).

[0006] Double-sided fuel cells (DFCs) are a specific type of SOFC (Solid Oxide Fuel Cell) cells, in which two adjacent cells are connected by a common anode containing fuel channels.

[0007] Polish patent specification PL213349 discloses a DFC type cell. In this patent, a single DFC cell, unlike conventional solutions, has a cathode on both sides of the cell, 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 deposited. Within one flat plate, two cells with a 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. Polish patent specification PL218785A discloses a fuel cell battery which has flat doublesided cells, wherein each double-sided cell is provided with input-output ports of distribution channels, through which ports tightening screws are passed to ensure the connection with subsequent double-sided cells. The individual double-sided cells are separated from each other by flexible separators.

[0008] 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 fuel 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 fluids 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 fuel oxidation products.

[0009] The continuous flow of fuel through the internal channels of the fuel cell requires the creation of a gas pressure difference between the inlet port and the outlet channel. The fuel flows simultaneously through all internal channels of the each cells in the stack, evenly washing the electrochemically active surface.

[0010] The DFCs can be characterized with a parameter describing the resistance that a cell puts up to the gas flowing through the internal channels. In the tested range of gas pressure and flow rate, the flow resistance of a cell can be defined as a slope of the straight line fitted to the measured pairs of points - P(F). An example graph showing the determination of the flow resistance for two cells is shown in Fig. 1 . The flow resistance through the second cell is equal to coefficient a2 and is greater than the resistance of the first cell described by flow resistance a1 .

[0011] In order to increase the electrical voltage, known DFCs are electrically connected in series into stacks. A stack consists of a plurality of DFCs stacked one above 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 between adjacent cells. 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 of alternately arranged seals and cells causes a pressure drop along that passage. Thereby, the cell furthest from the front plate operates under conditions of the smallest fuel pressure difference and thus, in the case of using cells with the same resistance to gas flow through the fuel channels, the smallest amount of gas flows through them.

[0012] Summary of the invention

[0013] The objective of the invention is to provide a solution that will at least partially eliminate the disadvantages of the prior art. Another objective of the invention is to provide a solution that will cause a fuel to flow evenly through internal channels of each cell in a stack.

[0014] According to the first aspect of the invention, there is provided a stack of electrochemical cells, especially double-sided solid electrolyte cells, comprising a plurality of electrochemical cells arranged one on top of the other, wherein each 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, seals placed between adjacent electrochemical cells in the area of gas inlet openings and gas outlet openings, wherein each seal has a connecting hole arranged substantially coaxially with the gas inlet opening and the gas outlet opening, respectively, a gas inlet manifold having a supply connector, wherein the gas inlet manifold is formed by coaxially arranged gas inlet openings and the connecting holes of the seals, a gas outlet manifold having a discharge connector, wherein the gas discharge manifold is formed by substantially coaxially arranged gas outlet openings and the connecting holes of the seals, wherein the supply connector and the discharge connector are disposed at the first cell in the stack, conductive connectors electrically connecting adjacent electrochemical cells in the stack, wherein the electrochemical cells in the stack are arranged in an order from a cell with the highest flow resistance through the at least one reactant flow channel to a cell with the lowest flow resistance through the at least one reactant flow channel, wherein the cell with the highest flow resistance is placed closest to the supply connector of the inlet gas manifold while the cell with the lowest flow resistance is placed at the location furthest from the supply connector of the gas inlet manifold and the discharge connector of the outlet gas manifold.

[0015] In one preferred embodiment, each cell is a double-sided fuel cell, preferably with solid oxide electrolyte, comprising a central support structure with an at least one fuel 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 anode current leads are located on one of the sides of the cell on both sides thereof and cathode current leads are also located on one of the sides of the cell on both sides thereof, which side of the cell is opposite the side of the cell on which the anode current leads are located.

[0016] In another preferred embodiment, the fuel cells in the stack are arranged successively alternately so that the anode current leads and the cathode current leads in adjacent cells are arranged with respect to each other on opposite sides of the stack.

[0017] According to the second aspect of the invention, there is provided a method for stacking electrochemical cells, in which method the flow resistance through reactant flow channels of individual electrochemical cells is measured, the electrochemical cells are stacked in an order from a cell with the highest flow resistance to a cell with the lowest flow resistance, wherein the cell with the highest flow resistance is placed closest to ta supply connector of a inlet gas manifold, while the cell with the lowest flow resistance is placed at the location furthest from the supply connector of the inlet gas manifold.

[0018] Brief description of the drawings

[0019] The object of the invention is shown in the drawings in which:

[0020] Fig. 1 - shows a method for determining the flow resistance coefficients through a double-sided electrochemical cell,

[0021] Fig. 2 - shows a comparison of the measured gas flow resistance through the flow channels of three selected DFCs,

[0022] Fig. 3 - shows a schematic structural diagram of a stack of DFC-type cells in cross section.

[0023] Detailed description of an embodiment of the invention

[0024] Fig. 3 illustrates a stack of electrochemical cells in which a plurality of electrochemical cells C1 , C2, C3, Cn-1 , Cn are arranged, where n is an integer greater than 2. In the following part of the description, the electrochemical cell will be generally designated as C. In the embodiment presented herein, the stack comprises a plurality of DCF-type double-sided fuel cells with solid oxide electrolyte. It is obvious to a person skilled in the art that the stack can also be constructed of other electrochemical cells C, including single-sided cells, for example those having fuel channels tightly integrated inside the anode structure, wherein the anode structure is tightly closed on the exposed side - opposite to the electrolyte. Each double-sided 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 thereof. 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 comprises a gas inlet opening and a gas outlet opening, which are connected by fuel flow channels. The gas openings are arranged at opposite sides of the cell. The gas inlet openings and gas outlet openings, after connecting the cells in the stack, form, together with seals 8, the gas inlet manifold 1 and the gas outlet manifold 2, respectively. The gas inlet manifold 1 comprises a supply connector 3, through which the gas fuel is supplied, and the gas outlet manifold 2 comprises a discharge connector 4, which removes the products of the oxidation reaction. The supply connector 3 and the discharge connector 4 are located at the first cell C1 in the stack, counting from a front plate 5. In the embodiment presented herein, the connectors 3, 4 pass through the front plate 5.

[0025] Anode current leads and cathode current leads are located nearby the gas inlet opening and the gas outlet opening. The anode current leads are located on one of the sides of the cell C on both sides thereof, and the cathode current leads are located on the other side of the cell C on both sides thereof, which side of the cell is opposite the side of the cell at which the anode current leads are located. The electrical contact between the individual current leads and the adjacent cells C is provided by conductive connectors. For better readability, the current leads and electrical connectors are not shown in the drawings.

[0026] The individual cells C in the stack are arranged alternately in such a way that the anode current leads of two adjacent cells are located on opposite sides of the fuel cell stack. The cathode current leads are arranged analogously, wherein the anode current leads and the cathode current leads on the same side of the cell are located on opposite sides. The conductive connector connects either the anode or the cathode current lead to the anode or cathode lead of the adjacent cell C, respectively.

[0027] The cells C are separated from each other by the seals 8. The seals 8 separate the individual cells C from each other, creating a space through which the oxidizer flows. In addition, the seals 8 seal the gas inlet openings and the gas outlet openings, and also cover the current leads tightly. Preferably, the seals 8 made of expanded vermiculite are used.

[0028] The cells C in the stack located between the front plate 5 and an end plate 6 are compressed by means of compression screws 7. As a result of the action of the compression forces, the seals 8 are compressed, which ensures the tightness of the connections on the gas manifolds 1 , 2 and the current leads.

[0029] A method of stacking electrochemical cells C in a stack consists in that that first the flow resistance through reactant flow channels of individual electrochemical cells C is measured. Fig. 2 shows a comparison of the measured gas flow resistance through the reactant flow channels of three selected DFCs from the cell with the highest to the cell with the lowest flow resistance. The grey area is the conventional acceptance area for the flow parameters of the cell.

[0030] Then, the electrochemical cells C are stacked in an orderfrom the cell C1 with the highest flow resistance to the cell Cn with the lowest flow resistance. The cell C1 with the highest flow resistance is located closest to the supply connector 3 of the gas inlet manifold 1 , while the cell Cn with the lowest flow resistance is located at the furthest location from the supply connector 3 of the gas inlet manifold 1 .

[0031] The flow resistance parameters of subsequent electrochemical cells C thus decrease as the distance of a given cell from the supply connector 3 and the discharge connector 4 increases. Due to such arrangement of the cells C in the stack, the variance of flow through the individual cells C is minimized, which results in a more even voltage distribution of the cells C in the stack.

Claims

Claims1. A stack of electrochemical cells, especially solid electrolyte cells, comprising a plurality of electrochemical cells (C) arranged one on top of the other, wherein each electrochemical cell (C) 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, seals (8) disposed between adjacent electrochemical cells (C) in the area of the gas inlet openings and the gas outlet openings, wherein each seal (8) has a connecting hole arranged substantially coaxially with the gas inlet opening and the gas outlet opening, respectively, a gas inlet manifold (1 ) having a supply connector (3), wherein the gas inlet manifold (1 ) is formed by coaxially arranged the gas inlet openings and the connecting holes of the seals (8), a gas outlet manifold (2) having a discharge connector (4), wherein the gas discharge manifold (2) is formed by substantially coaxially arranged the gas outlet openings and the connecting holes of the seals (8), wherein the supply connector (3) and the discharge connector (4) are disposed at the first cell (C1 ) in the stack, conductive connectors electrically connecting electrically adjacent electrochemical cells (C) in the stack, characterized in that the electrochemical cells (C) in the stack are arranged in an order from a cell (C 1 ) with the highest flow resistance through the at least one reactant flow channel to a cell (Cn) with the lowest flow resistance through the at least one reactant flow channel, wherein the cell (C1 ) with the highest flow resistance is placed closest to the supply connector (3) of the inlet gas manifold (1 ) while the cell (Cn) withthe lowest flow resistance is placed at the location furthest from the inlet connector (3) of the inlet gas manifold (1 ).

2. Stack of cells according to claim 1 , wherein each electrochemical cell (C) is a doublesided fuel cell, preferably with solid oxide electrolyte, comprising a central support structure with an at least one fuel 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 anode current leads are located on one of the sides of the cell on both sides thereof and cathode current leads are also located on one of the sides of the cell on both sides thereof, which side of the cell is opposite the side of the cell on which the anode current leads are located.

3. Stack according to either claim 1 or 2, wherein the electrochemical fuel cells (C) in the stack are arranged successively alternately so that the anode current leads and the cathode current leads in adjacent cells are arranged with respect to each other on opposite sides of the stack.

4. Method for stacking electrochemical cells (C) in the stack according to any claim 1 to 3, in which method the flow resistance through reactant flow channels of individual electrochemical cells (C) is measured, characterized in that the electrochemical cells (C) are stacked in an order from a cell (C1 ) with the highest flow resistance to a cell (Cn) with the lowest flow resistance, wherein the cell (Cl ) with the highest flow resistance is placed closest to a supply connector (3) of an inlet gas manifold (1 ), while the cell (Cn) with the lowest flow resistance is placed at the location furthest from the supply connector (3) of the inlet gas manifold (1 ).

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