Electrochemical cell assembly and method for preparing an electrochemical cell assembly

Abstract

The invention relates to an electrochemical cell assembly (10) comprising a first end plate assembly (12) having a first end plate (14), a second end plate assembly (16) having a second end plate (18), and a stack (20) of cell units (22) arranged between said first end plate and said second end plate, said first end plate and / or said second end plate comprising at least one through-hole (26) formed therein, said through-hole being associated with a sealing device ( 42 ), said sealing device comprising a sleeve (44) formed from a ceramic material, and a gasket (52, 54) disposed on an end face (48, 50) of said sleeve, said end face being provided with a coating (56) that has an outer layer (58), said outer layer being in contact with the gasket and comprising a cobalt oxide material. The invention also relates to a method for preparing an electrochemical cell assembly.

Description

[0001] Title : Electrochemical cell assembly and method for preparing an electrochemical cell assembly

[0002] Specification

[0003] The invention relates to the field of electrochemical cell stacks , in particular, fuel cell stacks and electrolyser cell stacks . More speci fically, the invention relates to an electrochemical cell assembly .

[0004] Fuel cells and electrolyser cells are examples of electrochemical cells . Fuel cells are energy conversion devices that allow for conversion of electrochemical fuel to electricity . Electrolyser cells are fuel cells running in reverse mode , i . e . using electricity to decompose a compound into its constituent parts , for example H20 into hydrogen and oxygen . Reversible cells are capable of operating in both modes . Such electrochemical cells typically comprise electrochemically active layers that may be configured to allow for conversion of electrochemical fuel to electricity ( fuel cells ) or for decomposing a compound into its constituent parts using electricity ( electrolyser cells ) .

[0005] The present invention speci fically relates to solid oxide cells ( SOCs ) . Such solid oxide cells ( SOCs ) typically comprise an electrolyte layer formed from a solid oxide , e . g . from Yttria-stabilised Zirconia (YSZ ) , Gadolinia-doped Ceria, or Cerium Gadolinium oxide ( CGO) . SOCs can be run as solid oxide fuel cell ( SOFC ) or as solid oxide electrolyser cell ( SOEC ) .

[0006] Typically, multiple of such cell units are stacked upon one another to form a " stack" of cell units , also referred to as ' cell repeat units ' . Said stack may be held in a compressed state between two end plates provided on opposite sides of the stack, thus forming an electrochemical cell assembly . The end plates , in addition to said compression function, typically serve as an access point for supplying the cell stack with fuel . For this , at least one of the end plates may comprise at least one through-hole formed therein to form a fluid port for transporting fluid between the outside of the electrochemical cell assembly and the stack of cell units .

[0007] In such electrochemical cell assemblies , sealing gaskets may be interposed between the end plates and between the individual cell units to achieve a fluid-tight , in particular gas-tight , seal of the cell stack .

[0008] It is an obj ect of the present invention to improve sealing in an electrochemical cell assembly .

[0009] According to the invention, there is provided an electrochemical cell assembly according to claim 1 . The electrochemical cell assembly comprises a first end plate assembly having a first endplate , a second end plate assembly having a second end plate , and a stack of cell units . The stack of cell units comprises a plurality of cell units stacked upon one another along a stacking direction . The stack of cell units is arranged, preferably held in compression, between said first end plate and said second end plate . The first and second end plates are preferably provided on opposite sides of the stack of cell units such that , when seen in the stacking direction, one of the end plates is located in front of the stack of cell units while the other one of the end plates is located behind the stack of cell units .

[0010] The first end plate comprises at least one through-hole formed therein to form a fluid port for transporting fluid between the outside of the electrochemical cell assembly and the stack of cell units . Alternatively or in addition, the second end plate comprises at least one through-hole formed therein to form a fluid port for transporting fluid between the outside of the electrochemical cell assembly and the stack of cell units . In other words , at least one through-hole is provided in the first end plate and / or at least one through-hole is provided in the second end plate , said at least one through-hole forming a fluid port for transporting fluid between the outside of the electrochemical cell assembly and the stack of cell units . Transporting fluid between the outside of the electrochemical cell assembly and the stack of cell units may mean supplying fluid from the outside of the electrochemical cell assembly to the stack of cell units or may mean removing fluid from the stack of cell units to the outside of the electrochemical cell assembly. Preferably, the through-hole extends through the end plate concerned in the stacking direction.

[0011] Said at least one through-hole (that is each of said one or more through-holes) is associated with a sealing device. This, however, does not exclude that the first end plate and / or the second end plate comprise additional through- holes fulfilling different functions (e.g. for mounting) . Said sealing device defines, preferably delimits, a fluid channel, preferably along the stacking direction, for guiding fluid, particularly fuel, from the associated through-hole in the end plate to the stack of cell units. Thus, the sealing device provides a fluid guiding function. Furthermore, the sealing device is configured to prevent loss of fluid between the end plate and the stack of cell units. Thus, the sealing device provides a sealing function. The sealing device is located between the end plate with the associated through-hole and the stack of cell units, preferably at a position locally corresponding to the position of the associated through-hole.

[0012] The sealing device at least comprises a sleeve formed from a ceramic material and a gasket disposed on an end face of said sleeve. Said sleeve formed from a ceramic material may also be denoted as "spacer sleeve". The end face of the sleeve is provided with a coating. The coating has an outer layer. Said outer layer of the coating is in contact with the gasket. Said outer layer comprises a metal oxide material . The proposed configuration allows for improved sealing of the stack of cell units . More speci fically, the outer layer comprising the metal oxide material allows for forming an adhesive bond with the gasket disposed thereon in the presence of a reducing environment , thus reducing the fluid permeability between the end face of the sleeve and the gasket disposed thereon . In particular, it has been found that this is because the reducing environment activates the metal oxide material , which then chemically bonds with the gasket material . Such a reducing environment may be provided during normal use of the cell unit , e . g . due to the presence of the fuel ( e . g . hydrogen) , or during manufacture of the cell unit ( e . g . during certain conditioning steps ) . That is to say, the above-mentioned adhesive bond may form and strengthen during normal use of the cell unit or during conditioning .

[0013] As used herein, a metal oxide material is a material that comprises at least one metal oxide or consists of at least one metal oxide . In case that the metal oxide material comprises at least one metal oxide , further compounds are present in addition to the metal oxide or metal oxides . Speci fically, the metal oxide material may comprise the metal or metals of the metal oxide or metal oxides in its / their non-oxidised form . In case that the metal oxide material consists of at least one metal oxide , further compounds besides metal oxides are present at most in traces . Preferably, said metal oxide material comprises an alkali metal oxide, an alkaline earth metal oxide, a transition metal oxide, a semimetal oxide and / or a basic metal oxide. Metal oxides of those groups proved to strong adhesive bonds with the gasket disposed thereon.

[0014] Preferably, said metal oxide material comprises at least one metal oxide selected from the group consisting of: cobalt oxide, iron oxide, manganese oxide, magnesium oxide, silicon oxide, potassium oxide, aluminium oxide, titanium oxide, chromium oxide and calcium oxide.

[0015] Most preferably, the metal oxide material comprises cobalt oxide. That is to say, the metal oxide material preferably is a cobalt oxide material. Cobalt oxide materials have proven to form a particularly strong adhesive bonding between the outer layer and the gasket, thus improving the sealing effect.

[0016] Preferably, the mass concentration of metal oxide, preferably cobalt oxide, in the outer layer is at least 60%. A mass concentration of at least 60% goes along with an effective improvement of the sealing effect. More preferably, the mass concentration of metal oxide in the outer layer is at least 80%, most preferably at least 90%.

[0017] Preferably, the gasket is adhesively bonded to the sleeve by said coating. As explained above, the adhesive bonding goes along with the intended improvement regarding the sealing effect. Prior to forming said adhesive bond, the gasket and the sleeve may also be non-bonded to each other ( e . g . prior to conditioning of the electrochemical cell assembly) . In this state , the outer layer and the gasket are in direct contact , but not yet adhesively bonded .

[0018] Preferably, the sealing device is located between the end plate with the associated through-hole and the stack of cell units at a position locally corresponding to the position of the associated through-hole .

[0019] Preferably, the fluid channel defined by the sealing device extends in the stacking direction .

[0020] Preferably, the sleeve is a disk having a central ( axial ) opening . Preferably, the sleeve is formed from aluminium oxide ( alumina ) .

[0021] Preferably, the end face of the sleeve extends perpendicular to the stacking direction . The end face may be directed towards the end plate with the associated through-hole formed therein or towards the stack of cell units . In case that the end face is facing towards the end plate with the associated through-hole formed therein, the gasket is preferably in direct contact with the end face of the sleeve and this end plate . In case that the end face is facing towards the stack of cell units , the gasket is preferably in direct contact with the end face of the sleeve and the neighboring cell unit . Preferably, the at least one gasket ( that is the one or more gaskets ) is an annular ring ( sealing ring) , i . e . ringshaped . The gasket preferably comprises a through-hole that is aligned with an opening of the sleeve along the stacking direction . Preferably, the opening of the sleeve and the through-hole of the at least one gasket together form the fluid channel for guiding fluid from the through-hole to the stack of cell units .

[0022] Preferably, the first end plate and the second end plate each comprise at least one , preferably more than one , preferably four, through-holes . Preferably, each through- hole in the first end plate is assigned a corresponding through-hole in the second end plate . Preferably, said associated through-holes are aligned with each other along the stacking direction . In an alternative embodiment , the first end plate or the second end plate is devoid of a through-hole . That is , only the second end plate or the first end plate comprises at least one through-hole formed therein .

[0023] Preferably, in case several sealing devices are provided, said sealing devices are configured identically .

[0024] Preferably, the stack of cell units is held in compression between said first end plate and said second end plate . For this , the electrochemical cell assembly may comprise additional compression means for tensioning said first end plate and said second end plate towards each other along the stacking direction . Such compression means are known in the art , and may e . g . include tension rods , compression springs or bolts , clamps , a welded enclosure ( skirt ) or other means for compression .

[0025] In some embodiments , the sleeve comprises two opposite end faces , wherein a gasket is disposed on each one of said end faces . This allows to ef ficiently prevent loss of fluid between the end plate with the associated through-hole formed therein and the sealing device as well as between the stack of cell units and the sealing device . The two opposite end faces preferably face away from each other . That is to say, one of the end faces is facing the end plate with the associated through-hole formed therein while the other one of the end faces is facing the stack of cell units .

[0026] The coating may be provided on each of said two opposite end faces . Consequently, the fluid permeability of the sealing device is reduced between both of the two end faces and the respective gasket . Alternatively, the coating may be provided on only one of said two opposite end faces , i . e . only on the end face facing towards the end plate with the associated through-hole formed therein or only on the end face facing towards the stack of cell units .

[0027] The coating may completely cover the end face or the end faces . Alternatively, the coating may be provided only in areas of the end face or the end faces . In some preferred embodiments, said coating is provided only on the end face or the end faces of the sleeve. Hence, only the surfaces of the sleeve that are in direct contact with the gasket or one of the gaskets are provided with the coating. Advantageously, this allows to reduce the amount of material required for the coating.

[0028] In an alternative embodiment, the sleeve comprises at least one lateral surface, said lateral surface being provided with the coating. Particularly, each surface of the sleeve may be completely covered by the coating.

[0029] In some embodiments, the outer layer of the coating has a layer thickness of at least 0.2 pm and at most 2.0 pm. Advantageously, this allows for an effective reduction of the fluid permeability of the sealing device and thus, for an effective improvement of the sealing effect. Preferably, the outer layer of the coating has a layer thickness of at least 0.3 pm and at most 1.0 pm, most preferably at least 0.4 pm and at most 0.8 pm.

[0030] As used herein, the term layer thickness particularly refers to an average layer thickness of the respective layer in a direction perpendicular to the end face.

[0031] In some embodiments, the coating consists of the outer layer. That is to say, the expression "outer layer" does not necessarily imply that there is an additional base layer or inner layer. In some embodiments , the coating has a base layer that is disposed between the end face and the outer layer .

[0032] Preferably, the base layer comprises a cerium material . A base layer comprising a cerium material may improve the adhesion of the outer layer to the sleeve . Preferably, the coating comprises a base layer comprising a cerium material and an outer layer comprising cobalt oxide as a metal oxide .

[0033] Preferably, the base layer has a layer thickness of at least 1 . 0 nm and at most 50 . 0 nm . A layer thickness in this range has proven to result in an ef fective improvement of the adhesion of the outer layer to the sleeve . Preferably, the base layer has a layer thickness of at least 2 . 0 nm and at most 70 . 0 nm, most preferably at least 5 . 0 nm and at most 50 . 0 nm .

[0034] Preferably, the gasket or gaskets are formed from an exfoliated vermiculite material . The exfoliated vermiculite material may comprise exfoliated vermiculite or consist of exfoliated vermiculite . Vermiculite is a layered silicate with the chemical sum formula (K, Mg, Fe ) ( Si , Al ) 4O10 (OH) 2 • An exfoliated vermiculite material has proven to form a particularly strong adhesive bond with the metal oxide material of the outer layer . According to a preferred embodiment , the gasket or gaskets are formed from an exfoliated vermiculate material and the metal oxide material of the outer layer comprises cobalt oxide as a metal oxide . The exfoliated vermiculite material may be thermally or chemically exfoliated . The exfoliated vermiculate material may comprise a diluent filler made of steatite and an elastomer added as a binder . Examples for an exfoliated vermiculite material comprising a diluent filler and an elastomer are the materials Thermiculite 815 , Thermiculite 835 and Thermiculite 715 ( registered trademarks of the Flexitallic group ) . An example for an exfoliated vermiculite material comprising steatite is the material Thermiculite 866 ( registered trademark of the Flexitallic group ) .

[0035] The sealing devices described above are applicable to various types of cell units . In some preferred embodiments , the cell units are solid oxide cell units , preferably solid oxide fuel cell units ( SOFC ) or solid oxide electrolyser cell units ( SOEC ) . Preferably, the cell units are metal- supported solid oxide fuel cell units .

[0036] The cell units each may comprise multiple layers , including a mechanical support layer, electrochemically active layers , and, optionally, a spacer or interconnector . The electrochemically active layers may comprise a fuel electrode layer, an electrolyte layer and an air or oxidant electrode layer . The electrochemically active layers may be deposited ( e . g . as thin coatings or films ) on and supported by the mechanical support layer, e . g . by a metal support plate , such as a metal foil . The cell units may comprise each at least one, preferably two or more, through-holes, said through-holes being in fluid communication with the active layers of the cell units allowing for fluid entering and exiting the cell units (e.g. via respective fluid channels) . Thus, the through-holes in the cell units may form fluid ports of the cell units. The stack of cell units may further comprise gaskets, preferably sealing rings, configured to seal said fluid ports of the cell units. In the stack, the column of fluid ports of the stacked cell units and the optional gaskets of the stack of cell units together form a fluid pathway (or chimney) extending along the stacking direction, said fluid pathway serving as an internal manifold for distributing fluid inside the stack of cell units. The stack of cell units, in addition to the cell units, may comprise further components, such as electrical connectors, electrical contact (or current collection) plates (e.g. monopole or endpole plates) or additional sealing gaskets.

[0037] The invention also relates to a method for preparing an electrochemical cell assembly, said method comprising:

[0038] - Providing a first end plate assembly having a first end plate, and a second end plate assembly having a second end plate, wherein said first end plate and / or said second end plate comprises at least one through- hole formed therein. Said through-hole may be used as a fluid port in the assembled electrochemical cell assembly . - Providing said at least one through-hole with a sealing device , comprising providing a sleeve formed from a ceramic material , wherein at least one end face of said sleeve is provided with a coating, said coating having an outer layer that comprises a metal oxide material , and disposing a gasket on said end face that is provided with the coating such that the gasket is in contact with the outer layer of the coating . The metal oxide material may comprise cobalt oxide as a metal oxide . That is to say, the metal oxide material may be a cobalt oxide material .

[0039] - Providing a stack of cell units , comprising a plurality of cell units stacked upon one another along a stacking direction .

[0040] - Arranging said stack of cell units between said first end plate and said second end plate such that said sealing device defines a fluid channel for guiding fluid from the associated through-hole to the stack of cell units . That is to say, the stack and the end plates are arranged in a way that the sealing device is located between the end plate with the associated through-hole formed therein and the stack . Due to the location of the sealing device , the sealing device may prevent loss of fluid between the end plate with the associated through-hole formed therein and the stack of cell units .

[0041] Optionally, the method may comprise compressing said stack of cell units by displacing said first and second end plates towards each other along the stacking direction . This may result in an improved sealing ef fect . Further optionally, the method may comprise providing the end plates with a respective insulation plate and / or providing the electrochemical cell assembly with at least one current collector plate .

[0042] In some embodiments of the method, obtaining the outer layer comprising the metal oxide material comprises providing the end face with a precursor layer comprising a metal material , preferably cobalt metal , and subsequently oxidising said precursor layer . This approach facilitates the provision of a desired outer layer . Preferably, the precursor layer is provided by Physical Vapour Deposition ( PVD) . Oxidising said precursor layer may comprise heat treating of the precursor layer in an oxygen-containing environment .

[0043] Further embodiments are derivable from the following description and the drawings .

[0044] In the drawings :

[0045] Fig . 1 shows a perspective view of an embodiment of an electrochemical cell assembly;

[0046] Fig . 2A shows a cross-sectional view of the electrochemical cell assembly according to Fig . 1 ; and Fig . 2B shows a detail of Fig . 2A; Fig . 3A shows a perspective section of the electrochemical cell assembly according to Fig . 1 ; and Fig . 3B shows a detail of Fig . 3A;

[0047] Fig . 4 shows an exploded view of an end plate assembly according to Fig . 1 ;

[0048] Fig . 5 shows a detail of a sealing device of the electrochemical cell assembly according to Fig . 1 ; and

[0049] Fig . 6 shows a method for preparing an electrochemical cell assembly .

[0050] Repeat use of reference symbols in the present speci fication and drawings is intended to represent the same or analogous features or elements .

[0051] Figure 1 schematically shows an exemplary embodiment of an electrochemical cell assembly 10 . The electrochemical cell assembly 10 comprises a first end plate assembly 12 having a first end plate 14 , a second end plate assembly 16 having a second end plate 18 , and a stack 20 of cell units 22 (herein referred to as ' cell repeat units ' ) . Figure 1 is intended to primarily provide an overview of the electrochemical cell assembly 10 and its components in general by way of example .

[0052] The stack 20 is arranged between the first end plate assembly 12 and the second end plate assembly 16 . In the assembled state , the stack 20 is preferably held in a compressed state between the first end plate assembly 12 and the second end plate assembly 16 . For this , the electrochemical cell assembly 10 may comprise additional compression means known in the art (not shown) , such as tension rods , , a welded enclosure ( skirt ) , compression springs or bolts .

[0053] Referring to Fig . 2 , the stack 20 comprises a plurality of cell repeat units 22 , said cell repeat units 22 being stacked upon each other along a stacking direction 24 . As set out above , the cell repeat units 22 may be fuel cell units , electrolyser cell units or reversible cell units comprising electrochemically active layers (not shown) .

[0054] In the embodiment shown, exemplarily, the first end plate assembly 12 and the second end plate assembly 16 are configured identically . In the following, the structure of the end plate assemblies 12 , 16 is described by way of example using the first end plate assembly 12 .

[0055] Referring to Fig . 4 , the first end plate assembly 12 comprises the first end plate 14 . The first end plate 14 comprises at least one through-hole 26 formed therein, in the example four through-holes 26 . The through-holes 26 extend along the stacking direction 24 and form respective fluid ports 28 for transporting fluid between the outside of the electrochemical cell assembly 10 and the stack 20 of cell repeat units 22 . In the embodiment shown, the first end plate assembly 12 further comprises an optional insulation plate 30 . The first end plate 14 and the insulation plate 30 are stacked upon each other along the stacking direction 24 . In the electrochemical cell assembly 10 , the insulation plate 30 is located between the first end plate 14 and the stack 20 of cell repeat units 22 ( see e . g . Fig . 2A) . Accordingly, an insulation plate 30 of the second end plate assembly 16 is located between the second end plate 18 and the stack 20 of cell repeat units 22 .

[0056] Preferably, the insulation plate 30 is formed from an electrically insulating material , e . g . from mica or alumina .

[0057] As shown in Figure 4 , the insulation plate 30 comprises at least one through-hole 32 extending along the stacking direction 24 , in this example four through-holes 32 . The through-holes 32 are arranged at positions locally corresponding to the positions of the through-holes 26 in the first end plate 14 ( see Fig . 2A and 2B ) . Preferably, the through-holes 32 in the insulation plate 30 are arranged coaxially to the through-holes 26 in the first end plate 14 . Preferably, the diameter of the through-holes 26 in the first end plate 14 is smaller than the diameter of the through-holes 32 in the insulation plate 30 .

[0058] Referring to Fig . 2 and 3 , it can be seen that each cell repeat unit 22 has at least one through-hole 34 , in this example four through-holes 34 , said through-holes 34 being in fluid communication with the active layers of the cell unit 22 , e . g . via respective fluid channels (not shown) . Thus , the through-holes 34 form fluid ports of the respective cell repeat units 22 . In the embodiment shown, the stack 20 of cell repeat units 22 further comprises sealing gaskets 38 located between the individual cell repeat units 22 and surrounding the through-holes 34 . Preferably, the through-holes 34 in the cell repeat units 22 are arranged coaxially to the through-holes 26 in the first end plate 14 and the through-holes 32 in the insulation plate 30 ( see e . g . Fig . 2B ) .

[0059] Referring to Fig . 4 , it can be seen that each through-hole 26 formed in the first end plate 14 is associated with a respective sealing device 42 . In this example , the sealing devices 42 are arranged in a respective through-hole 32 of the optional insulation plate 30 . Each sealing device 42 defines a fluid channel 47 for guiding fluid from the associated through-hole 26 formed in the end plate 14 to the stack 20 of cell repeat units 22 ( further details below) and is configured to prevent loss of fluid between the end plate 14 , 18 with the associated through-hole 26 formed therein and the stack 20 of cell repeat units 22 .

[0060] In the embodiment shown, the sealing devices 42 are configured identically . Referring to Fig . 5 , the structure of the sealing devices 42 is described by way of example using one of the sealing devices 42 . The sealing device 42 comprises a sleeve 44. Said sleeve 44 is formed from a ceramic material, preferably alumina. The sleeve 44 comprises a central opening (through-hole) 43 (see e.g. Fig. 3B) and a closed circumferential wall 45 surrounding the central opening 43 in a circumferential direction .

[0061] The sleeve 44 comprises a first end face 48 and a second end face 50 opposite the first end face 48. In the assembled electrochemical cell assembly 10, the first end face 48 is facing the end plate 14, 18 with the associated through-hole 26 formed therein. The second end face 50 is facing the stack 20 of cell repeat units 22.

[0062] In the embodiment shown, each of the end faces 48, 50 is provided with a respective gasket 52, 54. That is to say, the first end face 48 is provided with a first gasket 52 and the second end face 50 is provided with a second gasket 54. In the embodiment shown, the gaskets 52, 54 are annular sealing rings each having a central opening 55 (see e.g. Fig. 4) . The gaskets 52, 54 are preferably formed from an exfoliated vermiculite material. Said vermiculite material may be thermally or chemically exfoliated.

[0063] As shown in Fig. 2B, the gaskets 52, 54 and the sleeve 44 are arranged coaxially to each other, such that the aligned column of gaskets 52, 54 and sleeve 44 together delimit an inner fluid pathway, i.e. the above-described fluid channel 43. In other words, the central opening 43 of the sleeve 44 and the central openings 55 of the gaskets 52 , 54 together form the fluid channel 43 .

[0064] Referring to Figure 2A, it can be seen that an aligned column of through-holes 26 , fluid channel 43 ( central opening 43 of the sleeve 44 and central openings 55 of the gaskets 52 , 54 ) and through-holes 34 of the cell repeat units 22 forms a fluid pathway or chimney extending throughout the electrochemical cell assembly 10 along the stacking direction 24 .

[0065] Referring to Fig . 5 , both end faces 48 , 50 are provided with a coating 56 . In an alternative embodiment , only the first end face 48 or only the second end face 50 is provided with said coating 56 .

[0066] The coating 56 comprises an outer layer 58 that is in direct contact with the gasket 52 , 54 . That is to say, in the assembled electrochemical cell assembly 10 the outer layer 58 of the coating 56 touches the respective gasket 52 , 54 .

[0067] The outer layer 58 comprises a metal oxide material . A metal oxide material may comprise at least one metal oxide or consist of at least one metal oxide . Preferably, the mass concentration of metal oxide in said metal oxide material is at least 60% , more preferably at least 80% , most preferably at least 90% . Preferably, said metal oxide material comprises cobalt oxide as a metal oxide. That is to say, said metal oxide material is preferably a cobalt oxide material. Further preferred metal oxides are iron oxide, manganese oxide, magnesium oxide, silicon oxide, potassium oxide, aluminium oxide, titanium oxide, chromium oxide and calcium oxide.

[0068] The outer layer 58 has a layer thickness between 0.2 pm and 2.0 pm. Most preferably, the layer thickness is at least 0.4 pm and at most 0.8 pm. The representation of the sealing device 42 in Fig. 5 is schematic. Specifically, the layer thickness of the outer layer 58 is increased compared to the thickness of the gaskets 52, 54.

[0069] Referring to Fig. 6, the coating 56 further comprises an optional base layer 60 that is disposed between the end faces 48, 50 and the respective outer layer 58. The base layer 60 preferably comprises a cerium material, preferably cerium dioxide.

[0070] The base layer 60 preferably has a layer thickness between 1.0 nm and 50.0 nm. Most preferably, the layer thickness is at least 5.0 nm and at most 50.0 nm. The representation of the sealing device 42 in Fig. 5 is schematic. Specifically, the layer thickness of the base layer 60 is increased compared to the thickness of the gaskets 52, 54.

[0071] Referring to Fig. 5, the coating 56 is provided only on the end faces 48, 52 of the sleeve 44. That is to say, e.g. a radially outer lateral face 62 of the sleeve 44 is devoid of the coating 56 .

[0072] Referring to Fig . 6 , a method for preparing the electrochemical cell assembly 10 is described . Fig . 6 displays said method as a flow chart .

[0073] In a first step 101 of said method, the first end plate assembly 12 having the first end plate 14 and the second end plate assembly 16 having the second end plate 18 are provided . As described above , at least one of the end plates 14 , 18 comprises at least one through-hole 26 formed therein .

[0074] In a second step 103 of said method, the through-hole 26 or through-holes 26 formed in the end plates 14 , 18 is / are provided with a sealing device 42 or a respective sealing device 42 . The sealing device 42 or sealing devices 42 are configured as described above . The second step 103 comprises the following substeps :

[0075] In a first substep, the sleeve 44 formed from the ceramic material is provided .

[0076] In a second substep, a precursor coating is provided on the end faces 48 , 50 of the sleeve 44 . The precursor coating comprises an inner precursor layer formed from cerium and an outer precursor layer formed from a metal , preferably cobalt metal . That is to say, the second substep comprises forming a cerium layer directly on the end face 48 , 50 and, subsequently, forming a metal layer, preferably a cobalt metal layer, on the cerium layer . Preferably, the precursor layers are deposited on the end face 48 , 50 via physical vapour deposition ( PVD) .

[0077] In a third substep, the sleeve 44 comprising the precursor coating is subj ected to heat treatment under an oxidising environment . Heat treatment results in the precursor layers being oxidised . That is to say, the outer precursor layer is oxidised to form the outer layer 58 . The inner precursor layer is oxidised to form the base layer 60 .

[0078] In a fourth substep, the sleeve 44 with the coating 56 formed on its end faces 48 , 50 and the gaskets 52 , 54 are arranged on the end plates 14 , 18 in the stacking order as indicated in Fig . 2A and 3A.

[0079] In a third step 105 of said method, the stack 20 of cell repeat units 22 is provided .

[0080] In a fourth step 107 of said method, the stack 20 of cell repeat units 22 is arranged between said first end plate 14 and said second end plate 18 such that the sealing devices 42 define a respective fluid channel for guiding fluid from the associated through-hole 26 to the stack 20 of cell repeat units 22 and prevent loss of fluid between the end plate 14 , 18 and the stack 20 of cell repeat units 22 . Preferably, the electrochemical cell assembly 10 is compressed . For this , the first end plate assembly 12 and the second end plate assembly 16 may be displaced towards each other to pressuri ze the stack 20 of cell repeat units 22 .

[0081] Prior to use , the electrochemical cell assembly 10 may be conditioned in a reducing environment . During conditioning, the outer layer 58 of the coating 56 adhesively bonds to the gaskets 52 , 54 . It is assumed that that this is due to the reducing environment which results in an activation of the metal oxide of said metal oxide material . That is to say, after conditioning the electrochemical cell assembly 10 in said reducing environment , the outer layer 58 is adhesively bonded to the respective gasket 52 , 54 . Said adhesive bond improves the sealing ef fect of the sealing device 42 . Speci fically, the fluid permeability between the end faces 48 , 50 and the respective gasket 52 , 54 arranged thereon is reduced .

[0082] In case that the cell repeat units 22 are fuel cells , a reducing environment is also present in the electrochemical cell assembly 10 during use . Accordingly, the ef fect described above with respect to the conditioning of the cell assembly 10 may also be achieved independent of a conditioning step .

Claims

Claims1. An electrochemical cell assembly (10) comprising a first end plate assembly (12) having a first end plate ( 14 ) , a second end plate assembly (16) having a second end plate (18) , and a stack (20) of cell units (22) , comprising a plurality of cell units (22) stacked upon one another along a stacking direction (24) , said stack (20) of cell units (22) being arranged between said first end plate (14) and said second end plate (18) , said first end plate (14) and / or said second end plate (18) comprising at least one through-hole(26) formed therein to form a fluid port (28) for transporting fluid between the outside of the electrochemical cell assembly (10) and the stack (20) of cell units (22) , said through-hole (26) being associated with a sealing device (42) , said sealing device (42) defining a fluid channel for guiding fluid from the through-hole (26) to the stack (20) of cell units (22) and being configured to prevent loss of fluid between the end plate (14, 18) and the stack (20) of cell units ( 22 ) , said sealing device (42) comprisinga sleeve (44) formed from a ceramic material, and a gasket (52, 54) disposed on an end face (48, 50) of said sleeve (44) , said end face (48, 50) being provided with a coating (56) that has an outer layer (58) , said outer layer (58) being in contact with the gasket (52, 54) and comprising a metal oxide material.

2. The electrochemical cell assembly (10) according to claim 1, wherein said metal oxide material comprises an alkali metal oxide, an alkaline earth metal oxide, a transition metal oxide, a semimetal oxide and / or a basic metal oxide.

3. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein said metal oxide material comprises at least one metal oxide selected from the group consisting of: cobalt oxide, iron oxide, manganese oxide, magnesium oxide, silicon oxide, potassium oxide, aluminium oxide, titanium oxide, chromium oxide and calcium oxide.

4. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein the mass concentration of metal oxide in said outer layer (58) is at least 60%, preferably at least 80%, most preferably at least 90%.

5. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein the gasket(52, 54) is adhesively bonded to the sleeve (44) by said coating (56) .

6. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein the sleeve (44) comprises two opposite end faces (48,50) , and wherein a respective gasket (52, 54) is disposed on each of said end faces (48, 50) .

7. The electrochemical cell assembly (10) according to the preceding claim, wherein said coating (56) is provided on each of said end faces (48, 50) .

8. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein said coating (56) is provided only on the end face (48, 50) or the end faces (48, 50) of the sleeve (44) .

9. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein said outer layer (58) has a layer thickness of at least 0.2 pm and at most 2 pm, preferably at least 0.3 pm and at most 1 pm, most preferably at least 0.4 pm and at most 0.8 pm .

10. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein the coating (56) has a base layer (60) that is disposed between the end face (48, 50) and the outer layer (58) and comprises a cerium material.

11. The electrochemical cell assembly (10) according to the preceding claim, wherein the base layer (60) has alayer thickness of at least 1 nm and at most 50 nm, preferably at least 2 nm and at most 70 nm, most preferably at least 5 nm and at most 50 nm.

12. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein said gasket (52, 54) is formed from an exfoliated vermiculite material .

13. The electrochemical cell assembly (10) according to the preceding claim, wherein said exfoliated vermiculate material is thermally or chemically exfoliated .

14. The electrochemical cell assembly (10) according to any one of claims 12 and 13, wherein said exfoliated vermiculite material comprises a diluent filler, an elastomer and / or steatite as an additive.

15. The electrochemical cell assembly (10) according to any one of the preceding claims, wherein the cell units (22) are solid oxide cell units, preferably solid oxide fuel cell units (SOFC) or solid oxide electrolyser cell units (SOEC) .

16. A method for preparing an electrochemical cell assembly (10) , comprising: a. providing a first end plate assembly (12) having a first end plate (14) , and a second end plate assembly (16) having a second end plate (18) , wherein said first end plate (14) and / or saidsecond end plate (18) comprises at least one through-hole (26) formed therein, b. providing said at least one through-hole (26) with a sealing device (42) , comprising providing a sleeve (44) formed from a ceramic material, wherein at least one end face (48, 50) of said sleeve (44) is provided with a coating (56) , said coating (56) having an outer layer (58) that comprises a metal oxide material, and disposing a gasket (52,54) on said end face (48,50) such that the gasket (52, 54) is in touch-contact with the outer layer (58) of the coating (56) , c. providing a stack (20) of cell units (22) , comprising a plurality of cell units (22) stacked upon one another along a stacking direction (24) , d. arranging said stack (20) of cell units (22) between said first end plate (14) and said second end plate (18) such that said sealing device (42) defines a fluid channel for guiding fluid from the associated through-hole (26) to the stack (20) of cell units (22) .

17. The method according to the preceding claim, wherein the outer layer (58) comprising the metal oxide material is obtained by providing the end face (48, 50) with a precursor layer comprising a metal material and subsequently oxidising said precursor layer.

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