Method for preparing a material to be used as gasket in electrochemical cell assemblies

Abstract

The invention relates to methods for preparing a material to be used as gasket (30) in electrochemical cell assemblies, said methods comprising providing a vermiculite material (300) and performing a preconditioning treatment (102) on said vermiculite material (300), said preconditioning treatment (102) comprising a pressing process and either or both of a humidity control process and a prebaking process. The invention also relates to the use of such a gasket in an electrochemical cell assembly as well as to a method for preparing an electrochemical cell assembly.

Description

[0001] Title: Method for preparing a material to be used as gasket in electrochemical cell assemblies

[0002] Specification

[0003] The invention relates to the field of electrochemical cell stacks, in particular, fuel cell stacks and electrolyser cell stacks. More specifically, the invention relates to methods for preparing a material to be used as gasket in electrochemical cell assemblies, to the use of such a material as gasket in an electrochemical cell assembly, and a method for preparing 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 (e.g. H2) to electricity. Electrolyser cells are fuels cells running in reverse mode, i.e. using electricity to decompose a fuel (e.g. H2O) into its constituent parts (e.g. H2and O2) . 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 fuel into its constituent parts using electricity (electrolyser cells ) . The present invention specifically 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-stabilized 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) .

[0005] 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' . In order to supply fuel to each of the cell units, at least one fluid manifold is commonly provided in the stack, wherein gaskets are provided around said fluid manifold to prevent loss of fluid. Said stack of cell units is commonly arranged between two end plates provided on opposite sides of the stack, thus forming an electrochemical cell assembly. The end plates typically serve as access points for supplying the cell stack with fluid, particular fuel and oxidant.

[0006] In the field of electrochemical cells, gaskets formed from vermiculite-based materials, in particular exfoliated vermiculite materials, have proven advantageous with regards to reliable sealing performance also at elevated temperatures (SOC's operation temperatures may reach up to 1000 °C) . Vermiculite is a hydrous phyllosilicate mineral (sheet silicate) , which is typically processed in the form of a liquid slurry. In order to achieve a fluid-tight seal of the stack, the stack ( comprising the stacked cell units and gaskets ) is typically subj ect to a stack conditioning process , comprising for example a stack compression process and optionally a stack baking process .

[0007] It is an obj ect of the present invention to improve sealing in an electrochemical cell assembly .

[0008] According to a first aspect , there is provided a method for preparing a material to be used as gasket in electrochemical cell assemblies , preferably in a solid oxide fuel cell stack or solid oxide electrolyser cell stack . The method comprises providing a vermiculite material and performing a preconditioning treatment on said vermiculite material . The preconditioning treatment comprises a humidity control process and a subsequent pressing process .

[0009] The humidity control process comprises storing the vermiculite material in a humidity-controlled storage environment for a predetermined humidity control time . The humidity-controlled storage environment has a controlled absolute humidity within a predetermined absolute humidity range . Preferably, the vermiculite material preferably is stored in a humidity- and temperature-controlled environment . The predetermined absolute humidity range has a lower limit of at least 1 , 88 g / m3( corresponding, for example , to 20% relative humidity at 10 ° C ) and an upper limit of at most 24 , 28 g / m3( corresponding, for example , to 80% relative humidity at 30 ° C ) .

[0010] The pressing process comprises pressing the vermiculite material at a preconditioning pressure of at least 5 MPa .

[0011] As used herein, the term "preconditioning process" refers to a process that is performed prior to assembling the components of an electrochemical cell assembly, in particular, prior to stacking the individual components ( i . e . gaskets and cell units ) into a stack . The term "preconditioning process" is particularly used to distinguish this process from processes that are performed on the final stack, i . e . after the cell units and the gasket have been stacked into a stack . The latter processes are referred to as " stack conditioning processes" , such as the above described stack compression process or the stack baking process . As such, the pressing process of the preconditioning process may be referred to as pre-pressing process .

[0012] The proposed method makes it possible to prepare gaskets with improved mechanical behaviour and thus enhanced sealing performance when used in an electrochemical cell stack . Speci fically, pre-pressing the vermiculite material results in a more homogeneous material and, in particular, leads to less shrinkage of the gasket material during a subsequent stack compression process , thus making the stack compression process better controllable . In particular, the proposed pre-pressing process reduces inhomogeneities and defects in the vermiculite material . For example , during the pre-pressing, pores and voids between the layered silicate structures can be closed, thus leading to higher material density . This further reduces the amount of gasket relaxation in the compressed state , e . g . during use in an electrochemical cell assembly, which enhances sealing performance over li fe time . Furthermore , the pre-pressing process may help to align the silicate layers of the vermiculite material , thus leading to improved mechanical behaviour of the gaskets . Overall , pre-compressing the vermiculite material leads to a more homogeneous material , thus reducing potential deviations between di f ferent gaskets in the final stack . The humidity control process improves the above-described ef fects of the pre-pressing . Speci fically, the proposed combination of a pressing process and a humidity control process prior to said prepressing process has surprisingly proven advantageous with regards to improved sealing performance . By storing the vermiculite material in the humidity-controlled environment for a predetermined humidity control time , a water-content of the vermiculite material (water may be embedded within the sheets of silicates ) can be kept in a predefined range . This has shown to have an important ef fect on the pressing behaviour of the vermiculite material during the pressing process , speci fically with regards to reproducible and uni form pressing . Furthermore , controlling the watercontent helps to reduce or eliminate charge-to charge variations , thus leading to less rej ects . As used herein, the term "absolute humidity" (expressed as grams of water vapour per cubic meter volume of air) is to be understood as it is commonly used in various technical fields, i.e. as a measure of the actual amount of water vapour (moisture) in the air, regardless of the air's temperature .

[0013] As used herein, the term "relative humidity" (expressed as a percentage) is to be understood as it is commonly used in various technical fields, i.e. as the ratio of the partial pressure of water vapour in air to the saturation vapour pressure of water at the same temperature. In other words, relative humidity is the ratio of how much water vapour is in the air and how much water vapour the air could potentially contain at a given temperature.

[0014] In preferred embodiments, the humidity-controlled storage environment has an absolute humidity of at least 3.76 g / m3(corresponding, for example, to 40% relative humidity at 10°C) and at most 24.28 g / m3(corresponding, for example, to 80% relative humidity at 30°C) , preferably at least 5 g / m3and at most 20 g / m3, most preferably at least 5 g / m3and at most 15 g / m3. These ranges have proven particularly advantageous with regards to the above-mentioned effects, specifically with regards to reproducible and easy pressing of the vermiculite material.

[0015] Preferably, the humidity-controlled storage environment has a temperature within a predetermined temperature range, said temperature range having a lower limit of at least 10 °C and an upper limit of at most 30 °C, preferably a lower limit of at least 20 °C and an upper limit of at most 25

[0016] °C.

[0017] Preferably, the absolute humidity of the humidity- controlled storage environment is controlled by controlling the relative humidity and the temperature of said humidity- controlled storage environment. Thus, the relative humidity and the temperature of said humidity-controlled storage environment may be controlled such that the humidity- controlled storage environment has an absolute humidity of at least 1.88 g / m3(corresponding, for example, to 20% relative humidity at 10°C) and at most 24.28 g / m3(corresponding, for example, to 80% relative humidity at 30°C) , preferably of at least 3.76 g / m3(corresponding, for example, to 40% relative humidity at 10°C) and at most 24.28 g / m3(corresponding, for example, to 80% relative humidity at 30°C) , more preferably of at least 5 g / m3and at most 20 g / m3, most preferably of at least 5 g / m3and at most 15 g / m3.

[0018] In preferred embodiments, the relative humidity and the temperature of the humidity-controlled storage environment is controlled such that the relative humidity is within a predetermined humidity range having a lower limit of 20% and an upper limit of 80%, preferably a lower limit of 20% and an upper limit of 60%, more preferably a lower limit of 40% and an upper limit of 60%, and the temperature is within a predetermined temperature range having a lower limit of at least 10 °C and an upper limit of at most 30 °C, preferably a lower limit of at least 20 ° C and an upper limit of at most 25 ° C .

[0019] Preferably, the humidity control process comprises measuring the actual temperature of the humidity-controlled environment and maintaining the actual temperature within the predetermined temperature range . As such, the humidity control process may comprise actively controlling the temperature of the humidity-controlled environment . Maintaining the actual temperature within the predetermined temperature range may comprise increasing or reducing the temperature .

[0020] Furthermore , the humidity control process preferably comprises measuring the actual relative humidity of the humidity-controlled environment and maintaining the actual relative humidity within the predetermined humidity range . As such, the humidity control process may comprise actively controlling the relative humidity in the humidity- controlled environment . This allows for a reliable preconditioning process . Maintaining the actual relative humidity within the predetermined humidity range may comprise increasing or reducing the relative humidity such that the actual relative humidity is within the predetermined range .

[0021] Preferably, the predetermined humidity control time is at least 1 h, more preferably at least 2 h, more preferably at least 6 h, most preferably at least 6 h and at most 5 d . It was shown that longer times lead to a more homogenous material .

[0022] The humidity-controlled environment may be provided in an entire room, e . g . in an air-conditioned manufacturing hall . Preferably, the humidity-controlled environment is provided in a closed barrier system, e . g . in a climate cabinet , located within a room, e . g . in a manufacturing hall .

[0023] Pressing the vermiculite material at the preconditioning pressure may be performed uniaxially (uniaxial pressing) or isostatically ( isostatic pressing) . Thus , the pressing may be performed using a uniaxial pressing apparatus or using an isostatic pressing apparatus . Such apparatus are generally known in the art .

[0024] The preconditioning pressure may be higher than a pressure applied during a subsequent stack compression process . Advantageously, the preconditioning pressure is at least 20 MPa, preferably at least 50 MPa, more preferably at least 100 MPa .

[0025] Preferably, the pressing process is performed within a time span of at most 8 hours , preferably at most 6 hours , more preferably at most 5 hours , after finishing the humidity control process , e . g . after removing the vermiculite material from the humidity-controlled storage environment . Thus , preferably the pressing process is performed after finishing the humidity control process within a maximum waiting time of 8 hours, preferably 6 hours, more preferably 5 hours.

[0026] Preferably, also the pressing process is performed within a humidity-controlled environment (hereinafter referred to as humidity-controlled pressing environment) . This has proven particularly advantageous with regards to reproducible and easy pressing of the vermiculite material.

[0027] The humidity-controlled pressing environment may be the humidity-controlled storage environment. Thus, the pressing process may be performed in the humidity-controlled storage environment, e.g. in a climate cabinet.

[0028] The humidity-controlled pressing environment may be different from the humidity-controlled storage environment. Thus, the preconditioning treatment may comprise a handling stage subsequent to storage. Specifically, the preconditioning treatment may comprise, between the humidity control process and the pressing process, a handling process comprising removing the vermiculite material from the humidity-controlled storage environment and transferring the vermiculite material to the humidity- controlled pressing environment.

[0029] The humidity-controlled pressing environment may be provided in an entire room, e.g. in an air-conditioned manufacturing hall, or in a closed barrier system, e.g. in a climate cabinet, located within a room, e.g. in a manufacturing hall. In preferred embodiments, the humidity-controlled pressing environment has an absolute humidity of at least 2,56 g / m3and at most 18,20 g / m3, preferably of at least 5,13 g / m3and at most 18,20 g / m3.

[0030] Preferably, the absolute humidity of said humidity- controlled pressing environment is controlled by controlling the relative humidity and the temperature of said humidity-controlled pressing environment. Thus, the relative humidity and the temperature may be controlled such that an absolute humidity of the humidity-controlled environment is at least 2,56 g / m3(corresponding, for example, to a relative humidity of 20% at 15°C) and at most 18,20 g / m3(corresponding, for example, to a relative humidity of 60% at 30°C) , preferably at least 5.13 g / m3(corresponding, for example, to a relative humidity of 40% at 15°C) and at most 18.2 g / m3(corresponding, for example, to a relative humidity of 60% at 30°C) .

[0031] Preferably, the humidity-controlled pressing environment has a temperature within a predetermined temperature range, said temperature range having a lower limit of at least 10 °C and an upper limit of at most 30 °C, preferably a lower limit of at least 15 °C and an upper limit of at most 30 °C, more preferably a lower limit of at least 20 °C and an upper limit of at most 25 °C.

[0032] In some embodiments of the first aspect, the preconditioning treatment additionally comprises a prebaking process . The prebaking process comprises heating the vermiculite material in a prebaking environment having a predetermined prebaking temperature . Thus , the preconditioning treatment may comprise a step of heat treating the vermiculite material at a predetermined prebaking temperature . Preferably, the prebaking temperature is at least 600 ° C, preferably at least 700 ° C, more preferably at least 750 ° C, most preferably at least 780 ° C . The prebaking process allows to chemically process the vermiculite material such that chemical modi fications , which may lead to shrinkage or inhomogeneous compression behaviour can be reduced or eliminated .

[0033] Thus , the prebaking process may be beneficial for the prepressing process according to the invention . As such, the prebaking process may be performed prior to the pressing process , preferably prior to the humidity control process ( the humidity control process may again adj ust the potentially decreased water content after the prebaking process ) .

[0034] Alternatively or in addition, a prebaking process may be performed after the pressing process of the preconditioning treatment , particularly after the pressing process of the preconditioning treatment and prior to an optional subsequent stack compression process .

[0035] Preferably, the prebaking environment is provided in an oven . According to the invention, there is further provided a method for preparing a material to be used as gasket in electrochemical cell assemblies , said method comprising : a . providing a vermiculite material ) ; b . performing a preconditioning treatment on said vermiculite material , said preconditioning treatment comprising a humidity control process and a subsequent pressing process , i . said humidity control process comprising storing the vermiculite material ( 300 ) in a humidity-controlled environment ( 302 ) for a predetermined humidity control time , said humidity-controlled environment having a relative humidity within a predetermined relative humidity range having a lower limit of at least 40% and an upper limit of at most 80% , and a temperature within a predetermined temperature range having a lower limit of at least 10 ° C and an upper limit of at most 30 ° C, ii . said pressing process comprising pressing the vermiculite material at a preconditioning pressure (p ) of at least 5 MPa .

[0036] According to a second aspect , there is provided a method for preparing a material to be used as gasket in electrochemical cell assemblies , preferably as gasket in a solid oxide fuel cell stack or solid oxide electrolyser cell stack . The method comprises providing a vermiculite material and performing a preconditioning treatment on said vermiculite material . The preconditioning treatment comprises a prebaking process and a subsequent pressing process . The prebaking process comprises heating the vermiculite material in a prebaking environment , preferably in an oven . The prebaking environment has a prebaking temperature of at least 600 ° C, preferably at least 700 ° C, more preferably at least 750 ° C, most preferably at least 780 ° C . Thus , the prebaking process comprises heat treating the vermiculite material , preferably in an oven, at a prebaking temperature of at least 600 ° C, preferably at least 700 ° C, more preferably at least 750 ° C, most preferably at least 780 ° C . The pressing process comprises pressing the vermiculite material at a preconditioning pressure of at least 5 MPa .

[0037] As set out above in connection with the first aspect , by combining a prebaking process with a (pre- ) pressing process , a homogeneous gasket material may be obtained that undergoes only reduced shrinkage during a subsequent stack compression process and is less prone to relaxation over li fetime . Speci fically, the prebaking process allows to chemically process the vermiculite material such that chemical modi fications , which may lead to shrinkage or inhomogeneous compression behaviour can be reduced or eliminate , thus improving the pressing behaviour of the vermiculite material in the pre-pressing process ( and in an optional stack compression process ) . The prebaking process additionally has the ef fect of improving water resistance of the vermiculite material . This is particularly advantageous when the material is used as a gasket in a fuel cell , wherein water may condense at the gasket . The inventors have found that the above-described ef fects are particularly enhanced when the prebaking temperature is at least 750 ° C, more preferably at least 780 ° C .

[0038] As in the first aspect , the preconditioning pressure preferably is at least 20 MPa, preferably at least 50 MPa, more preferably at least 100 MPa .

[0039] The following optional features and advantages are applicable to both aspects :

[0040] The vermiculite material may comprise vermiculite or may consist of vermiculite . The vermiculite material may be an exfoliated vermiculite material . The exfoliated vermiculite material may comprise exfoliated vermiculite or consist of exfoliated vermiculite . The exfoliated vermiculite material may be thermally or chemically exfoliated . The exfoliated vermiculate material may comprise a diluent filler, an elastomer and / or steatite . 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 ) .

[0041] The vermiculite material may be provided in a sheet form .

[0042] Thus , the preconditioning treatment may be performed on the sheet material . In some embodiments of either aspect , the method may comprise forming at least one , preferably ring-shaped, gasket from the vermiculite material . As such, the method according to the first aspect and the method according to the second aspect may be a method for preparing gaskets for use in an electrochemical cell assembly .

[0043] In an example , the least one gasket may be formed by punching the vermiculite material . Alternatively, the at least one gasket may be formed by casting the vermiculite material into gasket-shape .

[0044] The at least one , preferably ring-shaped, gasket may be formed from the vermiculite material prior to performing the preconditioning treatment . As such, the step of providing the vermiculite material may be a step of providing a ring-shaped vermiculite material , preferably a step of providing vermiculite material in form of one or more , preferably a plurality of , annular rings or ringshaped gaskets . Thus , the vermiculite material may already have the shape of a gasket when subj ect to the preconditioning treatment . In other words , the preconditioning treatment may be performed on a ring-shaped vermiculite material .

[0045] Alternatively, the at least one , preferably ring-shaped, gasket may be formed from the vermiculite material after finishing the preconditioning treatment . In an example , the vermiculite material may be provided as a sheet of vermiculite material (e.g. by casting) , said sheet being subject to the preconditioning treatment, wherein after having performed the preconditioning treatment at least one gasket is formed from the sheet of vermiculite material, e.g. by punching the sheet of vermiculite material.

[0046] In embodiments, in which a ring-shaped gasket is provided, it may be advantageous if, preferably only or selectively, a radial inner surface of the ring-shaped gasket is heated, preferably to a temperature of at least 600 °C, preferably at least 700 °C, more preferably at least 750 °C, most preferably at least 780 °C. That is to say, the gasket is heated only locally. As set out above, heating the vermiculite material to this temperature range may lead to chemical modifications that make the material more resistant to water. As such, the radial inner surface of the gaskets may be particularly resistant to condensing water. This is particularly advantageous in electrochemical cell assemblies, where the gaskets surround a fluid manifold for distributing fluid, particular fuel, in the cell assembly, where water condensation may occur.

[0047] Heat treating the radial inner surface of a gasket may be part of or form the prebaking process described above in connection with the first and second aspects. As such, the prebaking process may comprise or consist of heating selectively a radial inner surface of a ring-shaped gasket, preferably to a temperature of at least 600 °C, preferably at least 700 °C, more preferably at least 750 °C, most preferably at least 780 °C. In such embodiments, the methods of the first and second aspect may comprise a step of providing a ring-shaped gasket formed from vermiculite material or a step of forming a ring-shaped gasket from the vermiculite material prior to performing the prebaking process .

[0048] Advantageously, the radial inner surface of the ring-shaped gasket may be heated with a rod-shaped heating element , said heating element having a temperature of at least 600 °C, preferably at least 700 ° C, more preferably at least 750 ° C, most preferably at least 780 ° C .

[0049] The invention also relates to the use of a material prepared according to the method of the first aspect or according to the method of the second aspect as gasket in an electrochemical cell assembly .

[0050] The invention also relates to a method for preparing an electrochemical cell assembly . The method comprises providing a plurality of cell units , preferably solid oxide fuel cell units or solid oxide electrolyser cell units . The method comprises further providing a plurality of , preferably ring-shaped, gaskets formed from a material prepared according to a method of the first aspect or according to a method of the second aspect . Preferably, the gaskets are ring-shaped gaskets ( e . g . annular sealing rings ) . The method comprises further stacking the cell units and the gaskets alternatingly along a stacking direction to form a stack ( also referred to as stack of cell units or stack of cell repeat units ) . In some embodiments , the method for preparing an electrochemical cell assembly comprises further performing a stack conditioning process on the stack ( comprising the stacked cell units and gaskets ) . The stack conditioning process may comprise a stack compression process comprising pressing the stack at a stack compression pressure .

[0051] Preferably, the stack compression pressure is higher than the preconditioning pressure . In an example , the preconditioning pressure is 5 MPa and the stack compression pressure is larger than 12 MPa, preferably 15 MPa .

[0052] The stack conditioning process may comprise performing a stack baking process , comprising heating the stack at a predetermined stack baking temperature . Preferably, the stack baking temperature is at least 550 ° C and at most 650 °C, more preferably 600 ° C .

[0053] In some embodiments , the stack baking process may comprise or consist of heating a radial inner surface of a respective gasket , preferably to a temperature of at least 600 ° C, preferably at least 700 ° C, more preferably at least 750 ° C, most preferably at least 780 ° C . Preferably, the radial inner surface of the gasket is heated with a rod-shaped heating element , said heating element having a temperature of at least 600 ° C, preferably at least 700 ° C, more preferably at least 750 ° C, most preferably at least 780 ° C . This has proven particularly advantageous in embodiments , wherein a fluid mani fold or fluid channel , preferably in the form of a through-hole , is provided in the stack of cell units and the gaskets delimit said fluid mani fold with their radial inner surfaces . Thus , the rodshaped heating element may simply be inserted into the fluid mani fold for heating the radial inner surfaces of the gaskets .

[0054] Further embodiments are derivable from the following description and the drawings .

[0055] In the drawings :

[0056] Fig . 1 shows a perspective view of an embodiment of an electrochemical cell assembly;

[0057] Fig . 2 shows a cross-sectional view of the electrochemical cell assembly according to Fig . 1 , wherein the inserts shows a perspective view of a gasket ;

[0058] Fig . 3 shows a flow diagram illustrating an embodiment of the method for manufacturing an electrochemical according to a first aspect ; and

[0059] Fig . 4 shows a flow diagram illustrating an embodiment of the method for manufacturing an electrochemical according to a second aspect .

[0060] Repeat use of reference symbols in the present speci fication and drawings is intended to represent the same or analogous features or elements . Figures 1 and 2 schematically show an exemplary embodiment of an electrochemical cell assembly 10 . Figures 1 and 2 are primarily intended to provide a better understanding of a potential use of gaskets prepared according to the invention by way of example . The invention, however, is not limited to the speci fic electrochemical cell assembly shown or to a use of a gasket in such an electrochemical cell assembly .

[0061] The electrochemical cell assembly 10 according to Figure 1 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 arranged between the first end plate assembly 12 and the second end plate assembly 16 .

[0062] In the example , the first end second end plate assemblies 12 , 16 each further comprise an insulation plate 24 located between the respective end plate 14 , 18 and the stack 20 of cell units 22 .

[0063] Referring to Fig . 2 , the stack 20 comprises a plurality of cell units 22 , said cell units 22 being stacked upon each other along a stacking direction 26 . These cell units 22 may be termed cell repeat units . The cell units 22 may be fuel cell units , electrolyser cell units or reversible cell units . In the example , the cell units 22 are metal- supported solid oxide fuel cells or solid oxide electrolyser cells ( SOFC or SOEC ) . As shown in Fig. 2, fluid manifolds 28 in the form of through-holes are provided in the stack 20 of cell units 22, each fluid manifold 28 extending along the stacking direction 26, exemplarily along the full height of the cell assembly 10. The fluid manifolds 28 are configured to transport fluid between the outside of the electrochemical cell assembly 10 and each of the cell units 22. For example, two of the fluid manifolds 28 may be fuel inlet manifolds and two of the fluid manifolds 28 may be fuel outlet (exhaust) manifolds.

[0064] Referring to Figure 1, it can be seen that the stack 20 further comprises gaskets 30 that are interposed between the cell units 22 and surrounding the fuel manifolds 28 to prevent loss of fuel. Exemplarily, the gaskets 30 are annular sealing rings each having a central opening (see insert in Fig. 2) .

[0065] In the following, a preferred embodiment of a method for preparing a material to be used as gasket 30 according to a first aspect is described with reference to Figure 3.

[0066] In a first step of the method, illustrated by block 100 in Figure 3, a vermiculite material 300 is provided. Exemplarily, the vermiculite material 300 is provided as a sheet material. As set out above, the vermiculite material 300 may comprise exfoliated vermiculite. In a second step, illustrated by block 102 in Figure 3, a preconditioning treatment is performed on said vermiculite material 300.

[0067] The preconditioning treatment 102 comprises two steps: a humidity control process (illustrated by block 102-1 in Figure 3) and a subsequent pressing process (illustrated by block 102-2 in Figure 3) .

[0068] The humidity control process 102-1 comprises storing the vermiculite material 300 in a humidity-controlled storage environment 302 for a predetermined humidity control time. Advantageously, the humidity-controlled storage environment 302 has an absolute humidity of at least 1,88 g / m3and at most 24,28 g / m3and a temperature of at least 10 °C and at most 30 °C. Preferably, the vermiculite material 300 is kept in the humidity-controlled storage environment 302 for at least Ih, more preferably at least 6h.

[0069] As set out above, preferably the absolute humidity is controlled by controlling the relative humidity and the temperature of said humidity-controlled storage environment 302. For this, a humidity sensor 306 and a temperature sensor 308 are provided, which are connected to a control unit 310 (only schematically shown) .

[0070] The humidity-controlled environment 302 may be provided in a closet cabinet 304, e.g. in a climate cabinet. Thus, preferably an absolute humidity within said cabinet 304 is at least 1,88 g / m3and at most 24,28 g / m3, and a temperature within said cabinet 304 is at least 10 ° C and at most 30 ° C .

[0071] The pressing process 102-2 comprises pressing the vermiculite material 300 at a preconditioning pressing p of at least 5 MPa, preferably at least 50MPa .

[0072] Preferably, the pressing process 102-2 is performed immediately after taking the vermiculite material 300 out of the humidity-controlled storage environment 302 .

[0073] Preferably, the pressing process 102-2 is performed in a humidity-controlled pressing environment 312 . Advantageously, the humidity-controlled pressing environment 302 has an absolute humidity of at least 5 , 13 g / m3and at most 18 , 20 g / m3.

[0074] As for the humidity-controlled storage environment 302 , preferably the absolute humidity of the humidity-controlled pressing environment 312 is controlled by controlling the relative humidity and the temperature of said humidity- controlled pressing environment 312 . For this , a humidity sensor 306 and a temperature sensor 308 are provided, which are connected to a control unit 310 ( only schematically shown) .

[0075] As exemplarily shown in Figure 3 , the pressing process 102- 2 may be a uniaxial pressing process using a uniaxial pressing apparatus 314 . In embodiments not shown, the pressing process 102-2 may be an isostatic pressing process .

[0076] In an optional further step ( illustrated by block 104 in Figure 3 ) , at least one ring-shaped gasket 30 may be formed from the preconditioned vermiculite material 300 ' , e . g . by punching or stamping the preconditioned vermiculite material 300 ' .

[0077] In embodiments not shown, the vermiculite material 300 may already be provided in ring shape in step 100 . That is , the preconditioning treatment 102 may be performed on the ringshaped vermiculite material 300 .

[0078] In the following, a preferred embodiment of a method for preparing a material to be used as gaskets according to a second aspect is described with reference to Figure 4 .

[0079] In a first step, illustrated by block 200 in Figure 4 , a vermiculite material 300 is provided . Exemplarily, the vermiculite material 300 is provided as a sheet material .

[0080] In a second step, illustrated by block 202 in Figure 4 , a preconditioning treatment is performed on said vermiculite material 300 .

[0081] The preconditioning treatment 202 comprises two steps : a prebaking process ( illustrated by block 202- 1 in Figure 4 ) and a subsequent pressing process ( illustrated by block 202-2 in Figure 4 ) . The prebaking process 202-1 comprises heating the vermiculite material 300 in a prebaking environment 316 for a predetermined prebaking time. Advantageously, the temperature in the prebaking environment 316 is at least 750°C, preferably at least 780°C. Preferably, the vermiculite material 300 is kept in the prebaking environment 316 for 30 min..

[0082] The prebaking environment 316 may be provided in a closet cabinet 318, e.g. in an oven.

[0083] The pressing process 202-2 comprises pressing the vermiculite material 300 at a preconditioning pressing p of at least 5 MPa, preferably at least 50MPa. As for the method described in connection with Figure 3, the pressing process 202-2 may be performed in a humidity-controlled pressing environment 312. In the example, the pressing process 202-2 is illustrated as a uniaxial pressing process using a uniaxial pressing apparatus 314. In embodiments not shown, the pressing process may be an isostatic pressing process .

[0084] In an optional further step (illustrated by block 204 in Figure 4) , at least one ring-shaped gasket 30 may be formed from the preconditioned vermiculite material 300', e.g. by punching or stamping the preconditioned vermiculite material 300 ' . In embodiments not shown, the vermiculite material 300 may already be provided in ring shape in step 200 . That is , the preconditioning treatment 202 may be performed on the ringshaped vermiculite material 300 .

[0085] As set out above , in some embodiments , a prebaking process as described in connection with Figure 4 may also be applied as part of the preconditioning process 102 of the method according to the first aspect ( Figure 3 ) . The prebaking process may then preferably be performed prior to the humidity control process 102- 1 .

[0086] The gasket 30 or gaskets 30 produced according to any one of the described methods may be used in an electrochemical cell assembly 10 as described above with respect to Figures 1 and 2 . Speci fically, the gaskets 30 may be interposed between cell units 22 to form a stack 20 . As set out above , after stacking the cell units 22 and the gaskets 30 , the stack 20 may be subj ect to an additional stack conditioning process , comprising e . g . a stack compression process and / or a stack baking process .

Claims

Claims1. A method for preparing a material to be used as gasket(30) in electrochemical cell assemblies (10) , said method comprising: a. providing a vermiculite material (300) ; b. performing a preconditioning treatment (102) on said vermiculite material (300) , said preconditioning treatment (102) comprising a humidity control process (102-1) and a subsequent pressing process (102-2) , i. said humidity control process (102-1) comprising storing the vermiculite material (300) in a humidity-controlled storage environment (302) for a predetermined humidity control time, said humidity- controlled storage environment (302) having an absolute humidity of at least 1,88 g / m3and at most 24,28 g / m3, ii. said pressing process (102-2) comprising pressing the vermiculite material (300) at a preconditioning pressure (p) of at least 5 MPa.

2. The method according to claim 1, said humidity- controlled storage environment (302) having an absolute humidity of at least 1,88 g / m3and at most 20 g / m3, more preferably of at least 1,88 g / m3and at most 15 g / m3., more preferably of at least 3,76 g / m3and at most 24 . 28 g / m3, more preferably of at least 5 g / m3and at most 20 g / m3, more preferably of at least5 g / m3and at most 15 g / m3.3 . The method according to claim 1 or 2 , wherein said humidity-controlled storage environment has a temperature within a predetermined temperature range having a lower limit of at least 10 ° C and an upper limit of at most 30 ° C, preferably a lower limit of at least 20 ° C and an upper limit of at most 25 ° C .4 . The method according to any one of the preceding claims , wherein the absolute humidity of said humidity-controlled storage environment is controlled by controlling the relative humidity and the temperature of said humidity-controlled storage environment .

5. The method according to any one of the preceding claims , wherein the predetermined humidity control time is at least 1 h, more preferably at least 2 h, more preferably at least 6 h, most preferably at least6 h and at most 5 d .

6. The method according to any one of the preceding claims , wherein said pressing process ( 102-2 ) is performed within a time span of at most 8 h, preferably at most 6 h, more preferably at most 5 h, after finishing the humidity control process .

7. The method according to any one of the preceding claims, wherein said pressing process (102-2) is performed in a humidity-controlled pressing environment .

8. The method according to the preceding claim, said humidity-controlled pressing environment having an absolute humidity of at least 2,56 g / m3and at most 18,20 g / m3, preferably of at least 5,13 g / m3and at most 18,20 g / m3.

9. The method according to the preceding claim, wherein said humidity-controlled pressing environment has a temperature within a predetermined temperature range having a lower limit of at least 10 °C and an upper limit of at most 30 °C, preferably a lower limit of at least 20 °C and an upper limit of at most 25 °C.

10. The method according to claim 8 or 9, wherein the absolute humidity of said humidity-controlled pressing environment is controlled by controlling the relative humidity and the temperature of said humidity- controlled pressing environment.

11. The method according to any one of the preceding claims, wherein the preconditioning treatment comprises a prebaking process, said prebaking process comprising heating the vermiculite material (300) for a predetermined prebaking time in a prebaking environment, said prebaking environment having a prebaking temperature of at least 600 °C, preferablyat least 700 °C, more preferably at least 750 °C, most preferably at least 780 °C.

12. The method according to the preceding claim, wherein the predetermined prebaking time is at least 5 min, preferably at least 10 min, more preferably at least 15 min, most preferably 30 min.

13. The method according to claim 11 or 12, wherein the prebaking process is performed prior to the humidity control process (102-1) .

14. The method according to claim 11 or 12, wherein the prebaking process is performed after the pressing process (102-2) .

15. A method for preparing a material to be used as gasket(30) in electrochemical cell assemblies (10) , said method comprising: a. providing a vermiculite material (200) ; b. performing a preconditioning treatment (202) on said vermiculite material (300) , said preconditioning treatment (202) comprising a prebaking process (202-1) and a subsequent pressing process (202-2) , i. said prebaking process (202-1) comprising heating the vermiculite material (300) in a prebaking environment (314) for a predetermined prebaking time, said prebaking environment (314) having a prebakingtemperature of at least 600 °C, preferably at least 700 °C, more preferably at least 750 °C, most preferably at least 780 °C, ii. said pressing process (202-2) comprising pressing the vermiculite material (300) at a preconditioning pressure (p) of at least 5 MPa.

16. The method according to the preceding claim, wherein the predetermined prebaking time is at least 5 min, preferably at least 10 min, more preferably at least 15 min, most preferably 30 min.

17. The method according to any one of the preceding claims, wherein the preconditioning pressure (p) is at least 20 MPa, preferably at least 50 MPa, more preferably at least 100 MPa.

18. The method according to any one of the preceding claims, wherein at least one, preferably ring-shaped, gasket (30) is formed from the vermiculite material (300) .

19. The method according to the preceding claim, wherein the, preferably ring-shaped, gasket (30) is formed from the vermiculite material (300) after the preconditioning treatment (102, 202) .

20. The method according to claim 18 or 19, wherein a radial inner surface of the ring-shaped gasket (30) is heated with a rod-shaped heating element having a temperature of at least 600 °C, preferably at least700 °C, more preferably at least 750 °C, most preferably at least 780 °C.

21. Use of a material prepared according to any one of the preceding claims as gasket (30) in an electrochemical cell assembly (10) .

22. Method for preparing an electrochemical cell assembly, comprising- providing a plurality of cell units (22) , preferably solid oxide fuel cell units or solid oxide electrolyser cell units;- providing a plurality of, preferably ring-shaped, gaskets formed from a material according to any of claims 1 to 20;- stacking the cell units (22) and the gaskets (30) alternatingly along a stacking direction (26) to form a stack (20) .

23. Method according to the preceding claim, further comprising performing a stack conditioning process on the stack (20) , said stack conditioning process preferably comprising either or both of:- a stack compression process, comprising compressing the stack (20) at a stack compression pressure; a stack baking process, comprising heating the stack (20) at a predetermined stack baking temperature .

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