HK1176467B

HK1176467B - Combined flow patterns in a fuel cell stack or an electrolysis cell stack

Info

Publication number: HK1176467B
Application number: HK13103938.4A
Authority: HK
Inventors: Sune Danø; Mads Find Madsen; Jens Ulrik Nielsen; Harald Usterud
Original assignee: Haldor Topsøe A/S
Priority date: 2009-07-06
Filing date: 2010-07-01
Publication date: 2016-01-29

Description

Combined flow patterns in fuel cell stacks or electrolysis cell stacks

The invention relates to a stack (cell stack), in particular a Solid Oxide Fuel Cell (SOFC) stack or a Solid Oxide Electrolysis Cell (SOEC) stack, in which the flow direction of the cathode gas inside each cell relative to the anode gas and the flow direction of the gas between adjacent cells are combined through different cell layers of the stack. In addition, the cathode gas or the anode gas or both may pass through more than one cell before they are exhausted, and multiple gas flows may be split or combined after passing through the primary cell and before passing through the secondary cell. These combinations serve to increase the current density and minimize the thermal gradient across the cell and the entire stack.

Hereinafter, the present invention will be described with respect to SOFC. Therefore, in the SOFC, the cathode gas is an oxidizing gas, and the anode gas is a fuel gas. However, the invention can also be used for other types of cells, such as the SOEC already mentioned or even polymer electrolyte fuel cells (PEM) or Direct Methanol Fuel Cells (DMFC).

An SOFC comprises an oxygen-ion conducting electrolyte, a cathode in which oxygen is reduced, and an anode in which hydrogen is oxidized. The overall reaction in a SOFC is the hydrogen and oxygen electrochemical reaction to produce electricity, heat, and water. The SOFC is operated at temperatures in the range of 650-1000 deg.C, preferably 750-850 deg.C. SOFCs deliver a voltage of about 0.8V in normal operation. To increase the overall voltage output, the fuel cells are assembled into a stack, wherein the fuel cells are electrically connected via an interconnector plate.

To produce the required hydrogen, the anode is typically catalytically active for steam reforming of hydrocarbons (particularly natural gas), thereby producing hydrogen, carbon dioxide and carbon monoxide. Steam reforming of methane (the major component of natural gas) can be described by the following equation:

during operation, an oxide (such as air) is supplied to the solid oxide fuel cell in the cathode region. A fuel (such as hydrogen) is supplied in the anode region of the fuel cell. Alternatively, a hydrocarbon fuel (such as methane) is supplied to the anode zone where it is converted to hydrogen and carbon oxides by the reactions described above. The hydrogen passes through the porous anode and reacts at the anode/electrolyte interface with oxygen ions generated on the cathode side and conducted through the electrolyte. Oxygen ions are generated in the cathode side as a result of accepting electrons from the external circuit of the cell.

Interconnects (interconnects) are used to separate the anode and fuel sides of adjacent cells and simultaneously enable current conduction between the anode and cathode. The interconnect is typically provided with a plurality of channels for passing fuel gas on one side of the interconnect and oxide gas on the other side. The flow direction of the fuel gas is defined as a substantial direction from the fuel inlet portion to the fuel outlet portion of the cell unit. Also, the flow direction of the oxide gas (cathode gas) is defined as a substantial direction from the cathode inlet portion to the cathode outlet portion of the battery cell. Thus, internally, the cell may have co-flow (co-flow) if the fuel gas flow direction is substantially the same as the cathode gas flow direction, or cross-flow (cross-flow) if the fuel gas flow direction is substantially perpendicular to the cathode gas flow direction, or counter-flow if the fuel gas flow direction is substantially opposite to the cathode gas flow direction.

Conventionally, cells are stacked (stack) on top of each other with complete overlap, resulting in a stack with, for example, co-flow, with all fuel and oxidant inlets on one side of the stack and all fuel and oxidant outlets on the opposite side. Due to the exothermicity of the electrochemical process, the outlet gas exits at a higher temperature than the inlet temperature. When combined in a SOFC stack operating at, for example, 750 ℃, a significant temperature gradient is created across the stack. Although the cooling of the stack is required to some extent, since air cooling is proportional to the temperature gradient, large thermal gradients induce thermal stresses in the stack, which are highly undesirable, and they cause differences in current density and resistance. Therefore, there is a problem of heat treatment of the SOFC stack: reducing the thermal gradient is sufficient to avoid unacceptable stresses, but has a sufficiently large thermal gradient: the outlet gas temperature differential compared to the inlet gas temperature enables the use of the gas cooling stack.

US 6,830,844 describes a system for thermal management in a fuel cell assembly, in particular by periodically reversing the direction of air flow across the cathode, thereby alternating the supply and exhaust edges of the cathode, for preventing temperature gradients across the cathode exceeding 200 ℃.

US 6,803,136 describes a fuel cell stack with partial overlap between cells comprising the stack, resulting in an overall spiral configuration of the cells. The cells are angularly offset from each other, which provides for ease of multiplication and heat treatment.

It is an object of the present invention to provide a fuel cell stack, in particular a solid oxide fuel cell stack, with improved heat treatment across the stack.

It is another object of the invention to provide a solid oxide fuel cell stack having a reduced electrical resistance compared to prior art SOFC stacks.

It is a further object of the present invention to provide a SOFC stack having a greater power output over a greater portion of each cell in the stack than conventional SOFCs.

Another object of the present invention is to provide a SOFC group having a higher maximum fuel utilization coefficient than a conventional SOFC group by: by redistributing the fuel flow, the splitting or merging of the fuel gases is or is not performed after the primary fuel cell flow passes to the secondary fuel cell flow pass.

The present invention addresses these and other objectives.

We have found that the spiral stack system of US 6,803,136 is not very effective in reducing the temperature gradient across the stack, apparently because each cell in the stack is only slightly rotated relative to the adjacent cells.

We therefore provide a solid oxide fuel cell stack comprising a plurality of planar cells arranged in layers on top of each other in planes parallel to each other, wherein each cell unit comprises an anode, an electrolyte and a cathode, and wherein the anodes and cathodes of adjacent cells are separated from each other by an interconnect provided with an inlet section and an outlet section for passing fuel gas and oxide gas to each cell, wherein a combination of co-flow and counter-flow patterns of fuel and oxide gas is provided inside each cell and between adjacent cells, and the fuel and cathode gas may flow through only the primary fuel cell before it is depleted from the stack, or may flow through the primary cell before it is depleted and then further through the secondary cells; the fuel and cathode gases may be combined into a single stream from multiple flow streams as they pass through one or more primary cells, or split from one stream into multiple flow streams and then continue to one or more secondary cells in the stack.

In this context, "combining" is understood such that each cell in a group may have any pattern of co-flow, counter-flow, or cross-flow internally, and each cell in a group may be arranged in alternating sequence with respect to its adjacent cells such that adjacent cells experience co-flow, counter-flow, or cross-flow with respect to their adjacent cells. Thus, according to the invention, all the cells in a group may have, for example, a co-flow internally between the fuel and the cathode gas, while each adjacent cell in the group is arranged in alternating order so that the cell undergoes a counter-flow with respect to its adjacent cells.

Thus, the present invention provides a wide range of flow patterns in a SOFC stack. As a result, an improved heat treatment across the stack is obtained.

According to the invention, the combination of flow patterns inside each cell and between adjacent cells, and the combination of single and multiple gas flows passing between one or more cells, plus the combination of splitting and merging of the gas flow streams, offers the possibility of obtaining advantageous temperature and current output distributions across individual cells and across the entire stack. Thus, a low Area Specific Resistance (ASR) is obtained due to the current extraction from a large and relatively hot area, and at the same time, by ensuring a high cathode gas outlet temperature, an efficient cooling using the cathode gas is obtained. Furthermore, some combined flow patterns additionally give improved maximum fuel utilization coefficients by: mixing the fuel gas flow inside the stack, CMR, or distributing the pressure drop variation of each individual cell to two or more cells in series on the fuel gas side.

The co-flow, cross-flow or counter-flow within the fuel cell stack known in the art each have different characteristics and advantages. At a given maximum stack temperature, cross flow has less current density than both co-flow and counter-flow, primarily due to better distribution of temperature and current output across the cell by co-flow and counter-flow. When comparing counter-flow and co-flow, each has its advantages. The counter-flow stack has its current output relatively hot, meaning relatively low internal resistance (ASR-area specific resistance), to a higher degree than the co-flow stack, while the co-flow stack has a higher cathode gas outlet temperature (Δ T), and therefore the most efficient cooling, than the cathode gas inlet temperature, but has a current output relatively cold, meaning greater ASR, to a higher degree.

By combining the flow patterns generally throughout the stack and within the cells in the stack, different advantages can be combined according to the invention as described. Furthermore, the merging or splitting of the gas flow streams discussed and the cell passing of the gas flow streams more than once provides the additional benefit of a higher fuel utilization coefficient. Thus, three main advantages of the invention can be defined:

the method has the advantages that: reduced resistance inside the cell by virtue of the current output from a larger portion of the cell, particularly in the hotter regions (lower resistance in the ceramic conductor and lower polarization resistance in the electrode).

The method has the advantages that: the high cathode outlet gas temperature, Δ T, compared to the cathode inlet gas temperature, results in improved cooling when passing through the cathode gas cooling stack.

The method has the advantages that: a higher maximum fuel utilization factor by redistributing fuel to more than one fuel cell flow pass, possibly including splitting or merging of flow streams between the primary and secondary flow passes.

These advantages conventionally each involve one of the following settings: counter-current, co-current and series groups. The present invention provides a solution whereby all three advantages can be combined and the advantages of counter-flow can be improved, even over the prior art.

As illustrated, the present invention provides any combination of gas flow stream merging, splitting and cell pass times, as well as any combination of gas flow direction patterns (co-flow, cross-flow and counter-flow) within each cell and between adjacent cells in a stack. In the following, a series of embodiments of the present invention are described in the examples, and their advantages are analyzed.

1. A stack comprising a plurality of fuel cells or electrolysis cells arranged in layers on top of each other, each of said cells comprising an anode, an electrolyte and a cathode, each layer of cells being separated by a plurality of interconnects, one interconnect between each cell, said interconnects being provided with gas channels on each side facing the anode or cathode side of an adjacent cell, said gas channels passing from an inlet portion to an outlet portion of said cell, the substantial direction from the anode inlet portion to the anode outlet portion of the anode side of each cell defining the anode gas flow direction of each cell, and the substantial direction from the cathode inlet portion to the cathode outlet portion of the cathode side of each cell defining the cathode gas flow direction of each cell, each cell in the stack having one of:

● internal co-flow with respect to the direction of flow of the cathode gas, the direction of flow of the anode gas, or

● internal cross-flow with respect to the direction of flow of the cathode gas, the direction of flow of the anode gas, or

● are counter-current to the direction of cathode gas flow, internally to the direction of anode gas flow,

on each side of the interconnect, the interface sides of adjacent cells are oriented in any of the following ways:

● interconnection co-flow

● interconnection cross flow

● the interconnection is arranged in a counter-flow manner,

wherein the stacked cells are arranged such that each individual cell and an adjacent cell have a combination of said internal co-flow, internal cross-flow or internal counter-flow of anode gas direction relative to cathode gas flow direction inside each individual cell and said combination of said interconnect co-flow, interconnect cross-flow or interconnect counter-flow between two interfacing sides of adjacent cells.

2. The battery of feature 1, wherein the cell is a solid oxide fuel cell.

3. The battery of feature 1, wherein the battery is a solid oxide electrolysis battery.

4. A battery according to any of the preceding features, the battery comprising at least one set of primary cells and a set of secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas undergoes a second cell flow pass.

5. A battery according to any of features 1-3, the battery comprising at least one set of primary cells and a set of secondary cells, wherein the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one secondary cell whereby the primary cathode outlet gas undergoes a second cell flow pass.

6. A battery according to any of features 1-3, the battery comprising at least one set of primary cells and a set of secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one secondary cell and the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one secondary cell, whereby the primary anode outlet gas and the primary cathode outlet gas undergo a second cell flow pass.

7. The battery of any of features 4-6, wherein the anode outlet gas of all primary cells is collected, mixed and redistributed to the anode inlet gas fraction of all secondary cells, or the cathode outlet gas of all primary cells is collected, mixed and redistributed to the cathode inlet gas fraction of all secondary cells, or the anode outlet gas of all primary cells is collected, mixed and redistributed to both the anode inlet gas fraction of all secondary cells and the cathode outlet gas of all primary cells is collected, mixed and redistributed to the cathode inlet gas fraction of all secondary cells, whereby the primary anode outlet gas or the primary cathode outlet gas or both the primary anode outlet gas and the primary cathode outlet gas pass through the secondary cell.

8. The battery of any of features 4-6, wherein the anode outlet gas of each primary cell is redistributed to the anode inlet gas portion of at least one adjacent secondary cell, or the cathode outlet gas of each primary cell is redistributed to the cathode inlet gas portion of at least one adjacent secondary cell, or both the anode outlet gas of each primary cell is redistributed to the anode inlet gas portion of at least one adjacent secondary cell and the cathode outlet gas of each primary cell is redistributed to the cathode inlet gas portion of at least one adjacent secondary cell, whereby the primary anode outlet gas or the primary cathode outlet gas of each primary cell or both the primary anode outlet gas and the primary cathode outlet gas undergo the second cell flow pass in at least one adjacent secondary cell.

9. The battery of feature 7 or 8, wherein the anode and cathode gas inlet and outlet portions of the at least one primary cell are oriented such that the at least one primary cell has anode gas flow in a first direction and cathode gas flow in a second, substantially opposite direction relative to the anode gas flow direction, such that the primary cell has counter flow inside and the at least two adjacent secondary cells have anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least two adjacent secondary cells have co-flow ("I") inside.

10. The battery of feature 7 or 8, said set comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is directed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas is subjected to a second flow pass through said secondary cells, and whereby at least one primary cell has anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to the anode gas flow direction, such that said primary cell has counter flow inside, and said at least one secondary cell has anode gas flow in said second direction and cathode gas flow in said second direction, such that said at least one secondary cell has co-flow ("H") inside.

11. The battery of any of features 1-3, the stack comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary cell has anode gas flow in a second direction and cathode gas in a first direction that is substantially opposite with respect to the anode gas flow direction such that the primary cell has counter flow inside and the at least one adjacent secondary cell has anode gas flow in the first direction and cathode gas flow in the first direction such that the at least one secondary cell has co-flow ("C") inside.

12. The battery of any of features 1-3, the stack comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary cell has anode gas flow in a first direction and cathode gas in the first direction such that the primary cell has co-flow therein, and the at least one adjacent secondary cell has anode gas flow in a second direction substantially opposite the first direction and cathode gas flow in the second direction such that the at least one secondary cell has co-flow ("A") therein.

13. The battery of any of features 1-3, the stack comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary cell has anode gas flow in a first direction and cathode gas in the first direction such that the primary cells have co-flow internally and the at least one adjacent secondary cell has anode gas flow in the first direction and cathode gas flow in a second direction substantially opposite the first direction such that the at least one secondary cell has counter-flow ("B") internally.

14. The battery of feature 7 or 8, said stack comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gases of at least two primary cells combine into one primary anode outlet gas flow and are directed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas undergoes a second flow pass through said secondary cell, and at least two primary cells have anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to said first direction, such that said primary cells have counter-flow therein, and said at least one secondary cell has anode gas flow in said second direction and cathode gas flow in said second direction, such that said at least one secondary cell has co-flow ("J") therein.

15. The battery pack of any of features 9-14, wherein the battery pack of any of features 9-14 is combined into a group comprising a plurality of combined groups.

16. A fuel cell stack comprising a plurality of fuel cells arranged in layers on top of each other, each of said fuel cells comprising an anode, an electrolyte and a cathode, wherein each layer of fuel cells is separated by a plurality of interconnects, one interconnect between each fuel cell, wherein said interconnects provide electrical contact from one fuel cell to an adjacent cell, and wherein said interconnects are provided with gas channels on each side, anode gas channels on one side of each interconnect and cathode gas channels on the other side of each interconnect, wherein said gas channels lead from an inlet portion to an outlet portion of said interconnect, a substantial direction from an anode inlet portion to an anode outlet portion of each interconnect defines an anode gas flow direction of each interconnect, and a substantial direction from a cathode inlet portion to a cathode outlet portion of each interconnect defines a cathode gas flow direction of each interconnect, wherein each fuel cell in the group has one of:

● co-flow of the direction of flow of the anode gas relative to the direction of flow of the cathode gas, or

● cross-flow of the direction of flow of the anode gas relative to the direction of flow of the cathode gas, or

● counter-current to the direction of flow of the anode gas relative to the direction of flow of the cathode gas,

wherein the interface sides of adjacent fuel cells are oriented in any one of the following ways:

● co-flow

● cross flow

● in the reverse direction of the flow,

wherein the stacked fuel cells are arranged such that each individual cell and adjacent cells have a combination of said co-flow, cross-flow or counter-flow of the anode gas direction relative to the cathode gas flow direction within each individual cell and said combination of co-flow, cross-flow or counter-flow between two interfacing sides of adjacent cells.

17. The fuel cell stack of feature 16, wherein the fuel cells are planar fuel cells and each successive layer of fuel cells is arranged such that the anode side of one fuel cell faces the cathode side of an adjacent fuel cell and the cathode side of one fuel cell faces the anode side of an adjacent cell, the interfacing anode and cathode sides of adjacent fuel cells being oriented in either:

wherein the stacked fuel cells are arranged such that each individual cell and adjacent cells have a combination of said co-flow, cross-flow or counter-flow of the anode gas direction relative to the cathode gas flow direction within each individual cell and between two interfacing sides of adjacent cells.

18. The fuel cell stack of feature 16 or 17, wherein the fuel cell is a solid oxide fuel cell.

19. The fuel cell stack of features 16 or 17 or 18 comprising at least one set of primary cells and a set of secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one secondary cell whereby the primary anode outlet gas undergoes a second fuel cell flow pass.

20. The fuel cell stack of features 16 or 17 or 18 comprising at least one set of primary cells and a set of secondary cells, wherein the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one secondary cell whereby the primary cathode outlet gas undergoes a second fuel cell flow pass.

21. The fuel cell stack of features 16 or 17 or 18 comprising at least one set of primary cells and a set of secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one secondary cell and the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one secondary cell, whereby the primary anode outlet gas and the primary cathode outlet gas undergo a second fuel cell flow pass.

22. The fuel cell stack of any of features 19-21, wherein the anode outlet gas of all primary cells is collected, mixed and redistributed to the anode inlet gas fraction of all secondary cells, or the cathode outlet gas of all primary cells is collected, mixed and redistributed to the cathode inlet gas fraction of all secondary cells, or the anode outlet gas of all primary cells is collected, mixed and redistributed to both the anode inlet gas fraction of all secondary cells and the cathode outlet gas of all primary cells is collected, mixed and redistributed to both the cathode inlet gas fraction of all secondary cells, whereby either the primary anode outlet gas or the primary cathode outlet gas or both the primary anode outlet gas and the primary cathode outlet gas undergo the second fuel cell flow pass.

23. The fuel cell stack of any of features 19-21, wherein the anode outlet gas of each primary cell is redistributed to the anode inlet gas portion of at least one adjacent secondary cell, or the cathode outlet gas of each primary cell is redistributed to the cathode inlet gas portion of at least one adjacent secondary cell, or both the anode outlet gas of each primary cell to the anode inlet gas portion of at least one adjacent secondary cell and the cathode outlet gas of each primary cell to the cathode inlet gas portion of at least one adjacent secondary cell, whereby the primary anode outlet gas or the primary cathode outlet gas or both the primary anode outlet gas and the primary cathode outlet gas of each primary fuel cell undergoes a second fuel cell flow through in at least one adjacent secondary fuel cell.

24. The fuel cell stack of features 16 or 17 or 18 comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one adjacent secondary cell whereby the primary anode outlet gas undergoes a second fuel cell flow pass.

25. The fuel cell stack of feature 24, wherein the anode outlet gas of at least one primary cell is divided and redistributed to the anode inlet portions of at least two adjacent secondary cells.

26. The fuel cell stack of feature 24, wherein the anode outlet gases of at least two primary cells are combined and redistributed to the anode inlet portion of at least one adjacent secondary cell.

27. A fuel cell stack according to any of the preceding features, comprising at least one set of primary cells and adjacent secondary cells, wherein the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one adjacent secondary cell, whereby the primary cathode outlet gas is passed through by the second fuel cell.

28. The fuel cell stack of feature 27, wherein the cathode outlet gas of at least one primary cell is divided and redistributed to the cathode inlet portions of at least two adjacent secondary cells.

29. The fuel cell stack of feature 27, wherein the cathode outlet gases of at least two primary cells are combined and redistributed to the cathode inlet portion of at least one adjacent secondary cell.

30. The fuel cell stack of features 16 or 17 or 18 comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is split into two primary anode outlet gas flows and directed to the anode inlet portions of at least two adjacent secondary cells arranged on each side of said at least one primary cell, whereby the primary anode outlet gas is subjected to a second flow pass through said secondary fuel cells.

31. The fuel cell stack of feature 30, wherein the anode and cathode gas inlet and outlet portions of the at least one primary fuel cell are oriented such that the at least one primary fuel cell has anode gas flow in a first direction and cathode gas flow in a second, substantially opposite direction relative to the anode gas flow direction, such that the primary fuel cell has counter flow inside, and the at least two adjacent secondary fuel cells have anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least two adjacent secondary fuel cells have co-flow ("I") inside.

32. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is directed to the anode inlet portion of at least one adjacent secondary adjacent cell, whereby the primary anode outlet gas is subjected to a second flow pass through said secondary fuel cells, and whereby at least one of the primary fuel cells has an anode gas flow in a first direction, and having a cathode gas flow in a second direction substantially opposite to the anode gas flow direction, such that the main fuel cell has a reverse flow inside, and the at least one adjacent secondary fuel cell has anode gas flow in the second direction and cathode gas flow in the second direction such that the at least one secondary fuel cell has a co-flow ("H") inside.

33. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary fuel cell has anode gas flow in a second direction and cathode gas in a first direction substantially opposite to the direction of anode gas flow, such that said primary fuel cell has counter flow internally, and said at least one adjacent secondary fuel cell has anode gas flow in said first direction and cathode gas flow in said first direction, such that said at least one secondary fuel cell has co-flow ("C") internally.

34. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one set of primary fuel cells and adjacent secondary fuel cells, wherein at least one primary fuel cell has anode gas flow in a first direction and cathode gas flow in said first direction such that said primary fuel cells have co-flow internally, and said at least one adjacent secondary fuel cell has anode gas flow in a second direction substantially opposite to said first direction and cathode gas flow in said second direction such that said at least one secondary fuel cell has co-flow ("a") internally.

35. The fuel cell stack of features 16 or 17 or 18, the stack comprising at least one set of primary fuel cells and adjacent secondary fuel cells, wherein at least one primary fuel cell has anode gas flow in a first direction and cathode gas in the first direction such that the primary fuel cells have co-flow internally and the at least one adjacent secondary fuel cell has anode gas flow in the first direction and cathode gas flow in a second direction substantially opposite the first direction such that the at least one secondary fuel cell has counter-flow ("B") internally.

36. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is directed to the anode inlet portion of at least one adjacent secondary adjacent cell, whereby a primary anode outlet gas is subjected to a second flow pass through the secondary fuel cells and whereby at least one primary fuel cell has an anode gas flow in a first direction and a cathode gas flow in the first direction, such that the primary fuel cells have a co-flow internally, and the at least one adjacent secondary fuel cell has anode gas flow in a second direction substantially opposite to the first direction, and having cathode gas flow in the first direction such that the at least one secondary fuel cell has a counterflow ("D") therein.

37. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one group of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is directed to the anode inlet portion of at least one adjacent secondary cell and the cathode outlet gas of said primary cell is directed to the cathode inlet of said secondary cell, whereby the primary anode and cathode outlet gases are subjected to a second flow pass through said secondary fuel cells and whereby at least one primary fuel cell has an anode gas flow in a first direction and a cathode gas flow in said first direction, such that said primary fuel cells have a co-flow inside and said at least one adjacent secondary fuel cell has an anode gas flow in a second direction substantially opposite with respect to said first direction and a cathode gas flow in said second direction, such that the at least one secondary fuel cell has a co-flow ("E") therein.

38. The fuel cell stack of feature 30, wherein the anode and cathode gas inlet and outlet portions of the at least one primary fuel cell are oriented such that at least one primary fuel cell has anode gas flow in a first direction and cathode gas flow in the first direction such that the primary fuel cell has co-flow therein and the at least two adjacent secondary fuel cells have anode gas flow in a second direction substantially opposite the first direction and cathode gas flow in the first direction such that the at least two adjacent secondary fuel cells have counter-flow ("F") therein.

39. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gases of at least two primary cells are combined into one primary anode outlet gas flow and directed to the anode inlet portion of at least one adjacent secondary cell arranged between said at least two primary cells, whereby the primary anode outlet gas is subjected to a second flow pass through said secondary fuel cells, and at least two primary fuel cells have anode gas flow in a first direction and cathode gas flow in said first direction, such that said primary fuel cells have co-flow internally, and said at least one adjacent secondary fuel cell has anode gas flow in a second direction substantially opposite to said first direction and cathode gas flow in said first direction, such that the at least one adjacent secondary fuel cell has a reverse flow ("G") therein.

40. The fuel cell stack of features 16 or 17 or 18, said stack comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gases of at least two primary cells are combined into one primary anode outlet gas flow and directed to the anode inlet portion of at least one adjacent secondary cell arranged between said at least two primary cells, whereby the primary anode outlet gas is subjected to a second flow passage through said secondary fuel cells, and at least two primary fuel cells have anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to said first direction, such that said primary fuel cells have counter flow inside and said at least one adjacent secondary fuel cell has anode gas flow in said second direction and cathode gas flow in said second direction, such that the at least one adjacent secondary fuel cell has a co-flow ("J") therein.

41. The fuel cell stack of any of features 30-40, wherein the fuel cell stack of any of features 30-40 is combined into a group comprising a plurality of combined groups.

The invention is described in more detail below with reference to the attached drawing, in which

Figure 1 is a schematic diagram showing the gas flow principle of the repeating elements of a prior art internal co-flow fuel cell,

figure 2 shows the gas flow principle of a prior art internal counterflow fuel cell repeating element,

fig. 3-12 show the repeating elements of the different flow pattern combinations of the present invention, combinations "a" through "D" and "F" through "J",

figure 13 shows the power output/cell in a stack with flow pattern combinations "a" to "D" and "F" to "J" and natural gas as fuel,

figure 14 shows the power output/cell in a stack with flow pattern combinations "a" to "D" and "F" to "J" and hydrogen as fuel,

figure 15 shows ASR in a group with flow pattern combinations "a" to "D" and "F" to "J" and natural gas as fuel,

figure 16 shows ASR in a group with flow pattern combinations "a" to "D" and "F" to "J" and hydrogen as fuel,

figure 17 shows the delta T (cathode gas outlet temperature minus cathode gas inlet temperature) of the cathode gas in a stack with flow pattern combinations "a" to "D" and "F" to "J" and natural gas as fuel,

figure 18 shows the delta T of the cathode gas in a set with flow pattern combinations "a" to "D" and "F" to "J" and hydrogen as fuel,

figure 19 shows the average cell voltage in a stack with flow mode combinations "a" to "D" and "F" to "J" and natural gas as fuel,

figure 20 shows the average cell voltage in a stack with flow pattern combinations "a" to "D" and "F" to "J" and hydrogen as fuel,

fig. 21 shows that the natural gas as fuel flow pattern combines "C" cell temperature along the flow direction,

fig. 22 shows that the natural gas as fuel flow pattern combines the current density "C" along the flow direction,

fig. 23 shows that the natural gas as fuel flow pattern combines "H" cell temperature along the flow direction,

fig. 24 shows that the natural gas as fuel flow pattern combines the current density "H" along the flow direction,

fig. 25 shows that the natural gas as fuel flow pattern combines "I" cell temperature along the flow direction,

fig. 26 shows that the natural gas as fuel flow pattern combines the current density "I" along the flow direction,

FIG. 27 shows a schematic diagram of a CMR (Collection, mixing, redistribution) with two primary and two secondary fuel cells, an

Fig. 28 shows a schematic of the series connection of the anode sides of two primary and two secondary cells.

A series of combined flow patterns are presented below: combined cell internal flow patterns, alternating flow patterns between adjacent cells in a stack, and combinations of cathode gas and anode gas flow passes (with or without merging or splitting of gas flows) through only a single cell or a plurality of cells in series before gas is discharged from the stack. While the following embodiments of the invention from modes "a" to "J" are numerous, they are not exhaustive. The invention according to independent claim 1 covers a wide combination of flow patterns and the following examples of embodiments should not be seen as limiting the scope of the invention.

Fig. 1 and 2 show two conventional gas flow principles of a fuel cell: the cathode gas (e.g., air) is shown by solid arrows, while the anode gas (e.g., natural gas or hydrogen) is shown by dashed arrows. A fuel cell comprising an anode, a cathode and an electrolyte is shown with solid lines. As seen in these schematic diagrams, the anode gas and the cathode gas flow on opposite sides of the fuel cell. The anode and cathode gas inlets are not shown as these are not essential parts of the invention. What is important is the substantial flow direction of the anode gas relative to the cathode gas. The substantial flow direction is defined as the substantial direction from the inlet portion to the outlet portion. In this context, when the term "substantially" is used, it is to be understood that the inlet portion and the outlet portion need not be a single point, but may have a certain width, for example when side manifolds are used. The flow direction cannot therefore always be defined as the "substantial" direction from exactly one point to another, but from the mean median point of the inlet to the mean median point of the outlet within the inlet and outlet sections. Nevertheless, a "substantial" flow direction is defined with sufficient accuracy to determine whether the anode gas and the cathode gas flow in generally the same direction, in opposite directions or in a perpendicular direction, which corresponds to a co-flow, counter-flow or cross-flow concept, which is essential to define the invention. Thus, FIG. 1 shows a conventional co-flow fuel cell, while FIG. 2 shows a conventional counter-flow fuel cell, each having inherent characteristics and advantages already described.

When multiple fuel cells are assembled in a stack, each fuel cell is separated by interconnects that serve to, among other things, separate the anode flowing gas of one cell from the cathode flowing gas of its neighboring cell. Stacking a plurality of co-flow cells as shown in fig. 1, as in a conventional fuel cell stack, results in a stack with a co-flow inside each cell and a co-flow on each side of the interconnect for adjacent cells, hereinafter referred to as an "interconnect" co-flow. Accordingly, when multiple reverse flow batteries are stacked according to fig. 2, it results in a stack with internal battery reverse flow and interconnect reverse flow.

Figures 3-12 each show different embodiments of the invention in which co-flow and counter-flow and multiple gas flow passes (redistribution), combination and division of gas flows are combined. In fig. 3, the primary cell and the secondary adjacent cell are shown separated by an interconnect (shown by a narrow dashed line). The primary and secondary batteries have internal co-flow. However, the flow direction of the primary cell is opposite to the flow direction of the adjacent secondary cell. Thus, as seen in the figure, the two cells have an interconnected counterflow. And in general, the flow pattern combination "a" according to fig. 3 has a combination of internal co-flow and interconnecting counter-flow. It is therefore contemplated that flow pattern combination "a" combines advantages 1 and 2, as advantage 1 is particularly directed to counter-flow and advantage 2 is particularly directed to co-flow. Also, one might expect the power output of such a bank to be high, since low ASR results in low power loss in the bank. The low ASR is due to a relatively flat temperature distribution and a high average temperature, which is the result of averaging the temperature distributions of the primary and secondary cells. However, according to the test results, the power output from such a set is relatively low, because the low Δ T of combination "a" results in too little heat being removed by the cathode air. Thus, combination "a" lacks advantage 2, but has significant advantage 1. Thus, the effects and advantages of different possible flow pattern combinations cannot be easily predicted, and only the test results will clarify which combination results in the optimum performance of the fuel cell stack. As seen below, advantages can be optimized even more complexly using more complex combinations of flow patterns.

It should be understood that the principles shown in fig. 3 may be applied to the entire stack such that a plurality of stacked cells (more than two) may have internal co-flow and interconnect counter-flow as the direction of flow on opposite sides of each interconnect in the stack changes. Furthermore, the flow principle of fig. 3 may be combined with any of the flow principles of fig. 1-2 and 4-12.

Fig. 4 shows a flow pattern combination "B" where a primary cell with internal counter flow is adjacent to a secondary cell with internal co-flow, and the flow streams on each side of the separation interconnect flow in the same substantial direction across the two fuel cells shown. However, when more stacks are stacked according to combination "B", some have interconnect co-flow and some have interconnect counter-flow. Thus, flow pattern combination "B" has an internal counter flow in combination with an internal co-flow and in combination with an interconnecting co-flow and an interconnecting counter flow. Also, as with all of the flow pattern combinations shown, the principle shown in fig. 4 for two cells may be repeated throughout a stack containing a plurality of cells, or it may be combined with other flow patterns, such as shown in the preceding and following figures.

In fig. 5, a flow pattern combination "C" is shown, which differs from combination "B" in that "C" has alternating anode flow directions, while "B" has alternating cathode flow directions.

The flow pattern combination "D" shown in fig. 6 includes the principle of having two cells in series on the fuel side. As illustrated, the anode gas is passed through the primary cell for a first pass, followed by a second pass through the adjacent secondary cell, followed by release of the anode gas. In this way, the fuel utilization factor is increased because a higher degree of fuel is oxidized by the fuel cell stack. Thus, "D" has the following combination: internal co-flow, internal counter-flow and anode gas redistribution.

Another embodiment involving "D" is shown in fig. 7, i.e., a flow pattern combination "E" where the cathode gas flow is also redistributed so that the primary cell is connected in series to the secondary cell not only on the anode gas side but also on the cathode gas side. However, in combination "E", both cells have internal co-flow, so that the overall combination "E" has: internal co-flow, interconnect counter-flow, anode gas redistribution and cathode gas redistribution.

Fig. 8 shows a flow pattern combination "F" which takes advantage of another possibility, namely the principle of splitting the primary gas flow stream into two streams after a first flow pass, and then redistributing the two streams for a second flow pass through two adjacent secondary cells. In combination "F", this operation is performed on the anode gas. As can be seen, in summary, "F" includes the following combinations: internal co-flow, internal counter-flow, interconnect co-flow, interconnect counter-flow and anode gas split and redistribute.

Fig. 9 shows an embodiment generally opposite to "F", i.e., a flow pattern combination "G", which combines two primary anode gas streams into one stream after they have been subjected to a first cell flow pass through two primary fuel cells, and then directs the combined anode gas stream to a secondary fuel cell where a second flow pass is performed. As illustrated, the two primary cells have internal co-flow of anode gas and the secondary fuel cell has counter-flow with respect to the cathode gas. Thus, the combination "G" has: internal co-flow and internal counter-flow, interconnect counter-flow and interconnect co-flow, and anode gas are combined and redistributed. When the principle of the combination "G" is applied to an entire group containing a plurality of cells, it is understood that the main pairs of cells are adjacent to each other, separated by interconnects. Depending on the application, these primary cells may have either co-flow or counter-flow of interconnects.

The flow pattern combination "H" is shown in fig. 10. Where the redistribution of anode gas from the primary cell to the secondary cell is combined with internal counter-flow in the primary cell and internal co-flow in the secondary cell.

In fig. 11, a combination "I" is shown in which the primary fuel cell anode gas flow stream is split into two secondary streams after passing through the primary fuel cell. The two secondary anode gas flow streams are then passed through two secondary fuel cells for a second flow pass, and then released. The primary fuel cell has internal counter flow and the secondary fuel cell has internal co-flow. In summary, the combination "I" thus includes: internal counterflow in the primary cell, internal co-flow in the secondary cell, interconnect co-flow, interconnect counterflow and anode gas split and redistribute.

Fig. 12 shows a final illustrated embodiment of the invention. The combination "J" merges the two primary anode gas flow streams into one secondary anode gas flow stream. Further "J" has internal counterflow of the primary fuel cell, internal and interconnect co-flow of the secondary fuel cell and interconnect counterflow.

To be able to compare the performance of the flow pattern combinations "a" to "J", fixed process parameters were selected at fixed fuel utilization and cathode gas utilization coefficients:

cathode gas inlet temperature: t is_in＝700℃

Maximum temperature: t is_max＝827℃

For these fixed operating parameters, the resulting current output I and average cell voltage U are observed for each flow mode combination. The results can also be expressed in terms of average power per cell (P ═ U × I) and ASR (area specific resistance). It is of interest to obtain these results for both reformed and non-reformed fuels. Thus, the results of different combinations of flow patterns were observed for both natural gas and hydrogen as fuel. Note that the test results for combination "E" are not shown, as the Δ T of this combination is too low to give meaningful test results.

An important object of the invention is to enable the highest possible power/fuel cell, whereby less cells are needed per group to obtain a certain power output and, therefore, lower costs. The power output of each flow pattern combination "a" to "J" as well as two conventional art references "RefCof" (reference for co-flow mode) and "RefCou" (reference for counter-flow mode) as bar charts is seen in fig. 13 (for natural gas as anode gas) and fig. 14 (for hydrogen as anode gas). On the Y-axis of the bar graph, power is expressed in watts per fuel cell, W per cell. The combination of flow patterns giving the highest power output is mainly achieved for two reasons: low ASR associated with "advantage 1" and high Δ T (cathode outlet temperature minus cathode inlet temperature) associated with "advantage 2".

In fig. 15-18, ASR and Δ T are shown for different combinations of flow patterns for natural gas and hydrogen, respectively. In FIGS. 15 and 16, ASR is labeled in milliohm-square centimeters on the Y-axis for natural gas "ng" and hydrogen "H2". The flow mode combinations "D" through "J" have the additional advantage of fuel CMR, i.e., "advantage 3".

Fig. 17 and 18 show the difference between the gas outlet temperature and the gas inlet temperature, at, degrees celsius (on the Y-axis) for the different illustrated flow pattern combinations for both natural gas "ng" and hydrogen "H2" as anode gases.

Fig. 19 and 20 show the average cell voltage in volts (on the Y-axis) for the different illustrated flow pattern combinations using natural gas "ng" and hydrogen "H2" as the anode gas.

As seen in fig. 13-20, the flow pattern combinations "C", "H", "I" and "J" have greater power output than conventional flow pattern co-flow and counter-flow. Using natural gas as the anode gas, combination "I" has a power density 15% higher than conventional co-flow and 31% higher than counter-flow. "H", "I" and "J" have the additional advantage that they allow fuel CMR within the stack ("advantage 3").

Examples for understanding these advantages can be seen when comparing the data of fig. 13-20. For example, when looking at combination "C", it is a hybrid between co-flow and counter-flow. The current output is suitably distributed to achieve maximum current output from the hottest region, as is the case with conventional reverse flow. This results in low ASR (less than co-flow, but slightly greater than counter-flow- "advantage 1"). At the same time, the combined flow pattern results in a higher Δ T of the cathode gas, which means more efficient cell cooling ("advantage 2"). More effective cooling means that a fixed T is reached_maxA larger current output before.

For illustration, the temperature and current density profiles of combination "C" are shown in fig. 21 and 22, as compared to conventional co-flow and counter-flow. "advantage 1" is seen by the wide distribution of current output, with good convergence (OutA and OutB for the primary and secondary cells combined "C") of the current output and temperature distribution, the temperature (Kelvin) and current density (amperes per square meter, A/m) being calculated on the Y-axis respectively²)). "advantage 2" is seen by the increased cathode gas outlet temperature compared to the counter flow.

Fig. 23-26 show the same temperature and current density profiles for combinations "H" and "I" only now. Also for these two combinations, a broadly distributed current density is observed, which is distributed with temperature ("advantage 1") and due to the high T_outGood convergence was achieved for effective cooling ("advantage 2"). The combination of both "H" and "I" also has a Fuel CMR ("advantage3"). As can be seen in the figure, combination "I" has slightly better performance than "H". Since "I" and "H" have nearly equal low ASR, the better performance of "I" must be attributed primarily to slightly more efficient cooling.

The flow pattern combinations "C", "H", "I" and "J" using both natural gas and hydrogen as anode gases have the same or higher cell voltage than co-flow. Therefore, lower battery degradation must also be expected compared to the case of co-flow, even though "C", "H", "I", and "J" have higher average power densities. When compared to reverse flow, "C", "H" and "I" have significantly higher average power densities, but also lower cell voltages. This is due to the premise of the comparison, where T_inAnd T_maxConstant, while the voltage and current vary. Thus, the potentially higher degradation rate is also a function of these operating parameters.

A significant disadvantage of the combined flow pattern of the present invention is that the fuel cell stack obviously requires a more complex gas manifold system, which will result in a lower active area of the fuel cell. However, simple geometric considerations show that this reduced efficiency is less than the benefit of increased power density. Further, combinations of "C", "H", "I", and "J" may be achieved using the cathode gas side manifold.

Notably, combining "a" and "B" gives a low ASR ("advantage 1") and the possibility of using non-reformed fuels such as hydrogen. This is due to the opposite cathode flow directions of the primary and secondary cells, which in turn results in a flat temperature distribution. This, combined with cooling by means other than the cathode gas, can result in high electrical efficiency and high yield, particularly with non-reformed fuels.

Fig. 27 and 28 show two embodiments that allow for a higher maximum fuel utilization factor. Fig. 27 shows a CMR (collection, mixing, redistribution) in which the gas outlet flows from multiple cells are collected into a common intermediate gas flow stream, which is then again split into multiple gas flow streams for a second flow pass through multiple secondary fuel cells. This improves stack tolerance to rare but severe faults in the fuel supply for some of the individual cells of the stack.

Fig. 28 shows an embodiment in which gas flows from a single primary cell to a single secondary cell in series, with the gas undergoing a second flow pass across the cells. The fuel supply to two cells in series is therefore dependent on the total pressure loss over the two cells concerned, so that a partial equalization of the pressure loss variations of the individual cells is achieved. This embodiment improves group tolerance to less severe but more frequent failures.

Claims

● internal co-flow of the direction of flow of the anode gas relative to the direction of flow of the cathode gas, or

● internal cross-flow of the direction of flow of the anode gas relative to the direction of flow of the cathode gas, or

● the direction of flow of the anode gas is counter-current to the internal direction of flow of the cathode gas,

on each side of the interconnect, the interfacing sides of adjacent cells are oriented in either of the following orientations:

● interconnection co-flow

● interconnection cross flow

● the interconnection is arranged in a counter-flow manner,

wherein the stack is arranged such that each individual cell and adjacent cells have a combination of said internal co-flow, internal cross-flow or internal counter-flow of anode gas direction relative to cathode gas flow direction inside each individual cell and said combination of said interconnection co-flow, interconnection cross-flow or interconnection counter-flow between two interfacing sides of adjacent cells.

2. The battery of claim 1, wherein the cell is a solid oxide fuel cell.

3. The battery of claim 1, wherein the cell is a solid oxide electrolysis cell.

4. The battery of claim 1, comprising at least one set of primary cells and a set of secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas undergoes a second cell flow pass.

5. The battery of claim 1, comprising at least one set of primary cells and a set of secondary cells, wherein the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one secondary cell, whereby the primary cathode outlet gas undergoes a second cell flow pass.

6. The battery of claim 1, comprising at least one set of primary cells and a set of secondary cells, wherein the anode outlet gas of at least one primary cell is redistributed to the anode inlet portion of at least one secondary cell and the cathode outlet gas of at least one primary cell is redistributed to the cathode inlet portion of at least one secondary cell, whereby the primary anode outlet gas and the primary cathode outlet gas undergo a second cell flow pass.

7. The battery of any of claims 4-6, wherein the anode outlet gas of all primary cells is collected, mixed and redistributed to the anode inlet gas fraction of all secondary cells, or the cathode outlet gas of all primary cells is collected, mixed and redistributed to the cathode inlet gas fraction of all secondary cells, or both the anode outlet gas of all primary cells is collected, mixed and redistributed to the anode inlet gas fraction of all secondary cells and the cathode outlet gas of all primary cells is collected, mixed and redistributed to the cathode inlet gas fraction of all secondary cells, whereby the primary anode outlet gas or the primary cathode outlet gas or both the primary anode outlet gas and the primary cathode outlet gas undergo the secondary cell flow pass.

8. The battery of any of claims 4-6, wherein the anode outlet gas of each primary cell is redistributed to the anode inlet gas portion of at least one adjacent secondary cell, or the cathode outlet gas of each primary cell is redistributed to the cathode inlet gas portion of at least one adjacent secondary cell, or both the anode outlet gas of each primary cell is redistributed to the anode inlet gas portion of at least one adjacent secondary cell and the cathode outlet gas of each primary cell is redistributed to the cathode inlet gas portion of at least one adjacent secondary cell, whereby the primary anode outlet gas or the primary cathode outlet gas or both the primary anode outlet gas and the primary cathode outlet gas of each primary cell undergo the second cell flow pass in at least one adjacent secondary cell.

9. The battery of claim 7, wherein the anode and cathode gas inlet and outlet portions of the at least one primary cell are oriented such that at least one primary cell has anode gas flow in a first direction and cathode gas flow in a second, substantially opposite direction relative to the anode gas flow direction, such that the primary cell has counter flow inside and the at least two adjacent secondary cells have anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least two adjacent secondary cells have co-flow "I" inside.

10. The battery of claim 8, wherein the anode and cathode gas inlet and outlet portions of the at least one primary cell are oriented such that at least one primary cell has anode gas flow in a first direction and cathode gas flow in a second, substantially opposite direction relative to the anode gas flow direction, such that the primary cell has counter flow inside and the at least two adjacent secondary cells have anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least two adjacent secondary cells have co-flow "I" inside.

11. The battery of claim 7 comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is directed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas is subjected to a second flow pass through the secondary cells, and whereby at least one primary cell has anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to the anode gas flow direction, such that the primary cell has counter flow inside, and the at least one secondary cell has anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least one secondary cell has co-flow "H" inside.

12. The battery of claim 8 comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gas of at least one primary cell is directed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas is subjected to a second flow pass through the secondary cells, and whereby at least one primary cell has anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to the anode gas flow direction, such that the primary cell has counter flow inside, and the at least one secondary cell has anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least one secondary cell has co-flow "H" inside.

13. The battery of claim 1, comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary cell has anode gas flow in a second direction and cathode gas flow in a first direction substantially opposite to the anode gas flow direction such that the primary cell has counter flow inside, and the at least one adjacent secondary cell has anode gas flow in the first direction and cathode gas flow in the first direction such that the at least one secondary cell has co-flow "C" inside.

14. The battery of claim 1, comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary cell has anode gas flow in a first direction and cathode gas flow in the first direction such that the primary cell has co-flow therein, and the at least one adjacent secondary cell has anode gas flow in a second direction substantially opposite the first direction and cathode gas flow in the second direction such that the at least one secondary cell has co-flow "a" therein.

15. The battery of claim 1, comprising at least one set of primary cells and adjacent secondary cells, wherein at least one primary cell has anode gas flow in a first direction and cathode gas flow in the first direction such that the primary cells have co-flow therein, and the at least one adjacent secondary cell has anode gas flow in the first direction and cathode gas flow in a second direction substantially opposite the first direction such that the at least one secondary cell has counter-flow "B" therein.

16. The battery of claim 7, comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gases of at least two primary cells are combined into one primary anode outlet gas flow and directed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas is subjected to a second flow pass through the secondary cell, and at least two primary cells have anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to the first direction, such that the primary cells have counter-flow therein, and the at least one secondary cell has anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least one secondary cell has co-flow "J" therein "。

17. The battery of claim 8, comprising at least one set of primary cells and adjacent secondary cells, wherein the anode outlet gases of at least two primary cells are combined into one primary anode outlet gas flow and directed to the anode inlet portion of at least one secondary cell, whereby the primary anode outlet gas is subjected to a second flow pass through the secondary cell, and at least two primary cells have anode gas flow in a first direction and cathode gas flow in a second direction substantially opposite to the first direction, such that the primary cells have counter-flow therein, and the at least one secondary cell has anode gas flow in the second direction and cathode gas flow in the second direction, such that the at least one secondary cell has co-flow "J" therein "。

18. The battery pack according to any one of claims 9 to 17, wherein the battery cases described in any one of claims 9 to 17 are combined into a battery pack comprising a plurality of combined battery cases.