Method for preconditioning a laminate and electrochemical cell assembly comprising a laminate

Abstract

A method for preconditioning a laminate 100 for an electrochemical cell assembly, comprising; providing a laminate comprising a plurality of mica sheets stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral and wherein the laminate comprises a plurality of through-holes 110; and performing a baking treatment on said laminate, said baking treatment comprising heating the laminate in an oven for a baking time at a baking temperature of at least 300°C. An electrochemical cell assembly comprising a stack of electrochemical cell units and at least one plate comprising a formed laminate comprising a plurality of mica sheets stacked upon one another and bonded by a binder, said mica sheets formed from a material comprising at least one mica group mineral, the laminate comprising a plurality of through-holes and preconditioned by baking at a baking temperature of at least 300°C; wherein the stack and at least one plate are held in compression in the electrochemical cell assembly. Use of a laminate preconditioned according to the method in an electrochemical cell assembly and a method for manufacturing an electrochemical cell assembly are further defined.

Description

Field of the Invention The present invention relates to a method for preconditioning a laminate and electrochemical cell assembly comprising a laminate. In particular the laminate is formed from a mica group mineral. The laminate is for use in an electrochemical cell assembly, particularly an electrolyser cell assembly or a fuel cell assembly. The present invention more specifically relates to solid oxide fuel cell (SOFC) and solid oxide electrolyser cell (SOEC) assemblies, alkaline fuel cell assemblies and alkaline electrolyser cell assemblies. These may include metal-supported solid oxide fuel cell (MS-SOFC) or electrolyser cell (MS-SOEC) assemblies. Background to the Invention Laminates made from mica sheets held together by a binder are often used for electrical or thermal insulation. One such use is in electrochemical cell assemblies, for example electrolyser cell assemblies of fuel cell assemblies. An electrochemical cell assembly operated as an electrolyser cell assembly uses electrolysis to separate hydrogen and oxygen from water given a power supply, or carbon monoxide and oxygen from carbon dioxide given a power supply. An electrochemical cell assembly operated as a fuel cell assembly can produce electricity by using an electrochemical conversion process that oxidises fuel to produce electricity. A solid oxide fuel cell (SOFC) assembly that produces electricity is based upon a solid oxide electrolyte that conducts negative oxygen ions from a cathode to an anode located on opposite sides of the electrolyte. For this, a fuel, or reformed fuel, contacts the anode (fuel electrode) and an oxidant, such as air or an oxygen rich fluid, contacts the cathode (air electrode). Conventional ceramic-supported (e.g. anode-supported) SOFCs have low mechanical strength and are vulnerable to fracture. Hence, metal-supported SOFCs have been developed which have the active fuel cell component layer supported on a metal substrate. In these cells, the ceramic layers can be very thin since they only perform an electrochemical function: that is to say, the ceramic layers are not self-supporting but rather are thin coatings / films laid down on and supported by the metal substrate. Such metal supported SOFC stacks are more robust, lower cost, have better thermal properties than ceramic-supported SOFCs and can be manufactured using conventional metal welding techniques. A solid oxide electrolyser cell (SOEC) assembly may have the same structure as an SOFC but is essentially that SOFC operating in reverse, or in a regenerative mode, to achieve the electrolysis of water and / or carbon dioxide by input of electrical energy and using the solid oxide electrolyte to produce hydrogen gas and / or carbon monoxide and oxygen. Abovementioned electrochemical cell assemblies comprise a stack of electrochemical cell units held in compression. Each cell unit may be planar. Planar electrochemical cell units may be arranged overlying one another in a stack arrangement, for example 100-200 electrochemical cell units in a stack, with the individual electrochemical cell units arranged, for example, electrically in series. One or more plates made formed from a laminate is typically used in or to one or both ends of the stack of electrochemical cell units to provide electrical insulation between parts of the stack of electrochemical cell units or between the stack of electrochemical cell units and components external to the stack of electrochemical cell units. When said laminates are used in electrochemical cell assembles (which are exposed to temperatures of 500 °C or more) at least some of the binder may be liberated (e.g., as offgasses) which may undesirably coat the electrochemical cell assemblies in addition to other undesirable effects. The present invention seeks to improve the performance of plates formed by laminates comprising a mica group mineral. SUMMARY OF THE INVENTION According to a first aspect there is provided a method for preconditioning a laminate for an electrochemical cell assembly, preferably an electrolyser cell assembly or a fuel cell assembly. The method includes: a. providing a laminate comprising a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, and wherein the laminate comprises a plurality of through-holes; and b. performing a baking treatment on said laminate, said baking treatment comprising: i. arranging the laminate in an oven, and ii. heating the laminate in the oven at a baking temperature provided in the oven for a baking time (i.e., a dwell time at the baking temperature), said baking temperature being at least 300 °C. The method of preconditioning reduces the amount of binder in the laminate before said laminate is used as a plate in an assembly, for example an electrochemical cell assembly. As such, the method reduces the amount of binder (or decomposition products thereof) which is expelled once the laminate is used as a plate in said assembly which is advantageous for cleanliness of the assembly. The method of preconditioning results in a decrease of a thickness of the laminate due to escape of the binder (and / or decomposition products thereof) during the baking of the laminate. Accordingly, stability (e.g., in response to elevated temperatures) of the laminate when used (as a plate) in an assembly is improved with corresponding improvement to compression systems including the laminate. The plurality of through-holes significantly increase a rate by which the binder (and / or decomposition products thereof) escape from the laminate, thereby reducing the baking time relative to a laminate not provided with such through-holes. As a result, energy usage for baking the laminate is reduced. It has been found that the plurality of through-holes reduce the propensity for such laminates to delaminate during such baking and during use in environments of elevated and variable temperature, further improving performance and stability of the laminate. The laminate may be provided comprising the plurality of through-holes. The step of providing the laminate may include sub-steps of providing a laminate (i.e., without through-holes) and of forming the plurality of through-holes in the laminate. In other words, the laminate may be provided as a plate devoid of holes, and a sub-step of forming the plurality of through-holes in the laminate is carried out prior to baking. The oven may be any type of oven known in the art. For example, the oven may be a static oven in which the laminate may typically be positioned at or near ambient temperature and the temperature within the oven increased. In another example, the oven may be a conveyor oven in which the laminate traverses the oven on a conveyor belt, temperature changes being as a result of the laminate's progression through the oven on the conveyor belt. The baking temperature may be at least 500°C, preferably at least 600°C, more preferably at least 650°C, more preferably at least 700 °C, more preferably at least 750 °C. The baking temperature may be equal to or less than 1000 °C, preferably equal to or less than 900 °C, more preferably equal to or less than 850 °C. Higher baking temperatures increase the proportion of binder removed during the preconditioning and lead to shorter baking times with correspondingly reduced energy usage. The baking time may be at least 1 hour (h), preferably at least 2 h, more preferably at least 3 h. The baking time may be at most 15 h, preferably at most 10 h, more preferably at most 7 h. In some cases the baking time may be at most 4 h. The plurality of through-holes allow removal of sufficient binder during said bake times. The temperature in the oven may be kept constant (e.g., within + / - 30 °C) for the baking time. The laminate may be arranged (e.g., positioned) in the oven at a first temperature, lower than the baking temperature, and the temperature is increased at a temperature ramp rate for at least a portion of the temperature increase. The temperature ramp rate may be at least 2 °C / min, preferably at least 4 °C / min, more preferably at least 5 °C / min. The temperature ramp rate may be at most 15 °C / min, preferably at most 10 °C / min, more preferably at most 8 °C / min. The temperature ramp rate may be between 2 and 15 °C / min, preferably between 4 and 10 °C / min, preferably between 4 and 8 °C / min. The plurality of through-holes in the laminate allow greater temperature ramp rates to be used with reduced probability of delamination (relative to laminates without said plurality of through-holes), which is undesirable in many applications, for example as part of an electrochemical cell assembly. The temperature ramp rate is applied for at least a portion of the temperature increase. The temperature ramp rate may apply for temperatures of greater than 200 °C, preferably for temperatures of greater than 50 °C. In examples where the baking temperature is greater than 600 °C, the temperature ramp rate particularly is applied for temperatures of greater than 600 °C. In examples where the baking temperature is greater than 400 °C, the temperature ramp rate particularly is applied for temperatures of greater than 400 °C. Such relatively high temperature ramp rates applied at elevated temperatures are enabled by the plurality of through-holes. The method may include forming one or more openings (preferably fluid ports) in the laminate for transfer of fluid within the electrochemical cell assembly, wherein the one or more openings are formed prior to performing the baking treatment. In contrast to the one or more openings, the plurality of through-holes are not configured for transfer of fluid in an electrochemical cell assembly (e.g., by not being configured to be aligned with fluid ports through other components in the electrochemical cell assembly, and / or by being positioned in a central area of the laminate). Preferably, the step of providing the laminate comprises forming the plurality of through-holes in the laminate and the one or more openings are formed in the same step as forming the plurality of through-holes. In other words, the laminate may be provided as a plate devoid of holes, and a step of forming the plurality of through-holes in the laminate and the one or more openings is carried out prior to baking. The one or more openings and / or the plurality of through-holes may be formed by machining (e.g., drilling). The plurality of through-holes and the one or more openings may have different sizes (cross-sectional area or characteristic size, e.g., diameter or side length). Preferably, the one or more openings are larger than the plurality of through-holes. Optionally, each of the one or more openings are larger than each of the plurality of through-holes. Preferably, the plurality of through-holes have a circular cross-section. Preferably, some or all of the one or more openings have a circular cross-section. Some or all of the one or more openings may have an open perimeter. For example, that open perimeter may have a partially circular cross section, with one portion missing. The plurality of through-holes may be arranged randomly a plane of the laminate. Alternatively, the plurality of through-holes may arranged in an array (i.e., a repetitive pattern of geometrical shapes) along the plane of the laminate, e.g. in a hexagonal or square array. The plurality of through-holes may comprise at least 10 through holes, preferably at least 15 through-holes, preferably at least 30 through-holes, more preferably at least 50 through-holes, more preferably at least 80 through-holes, even more preferably at least 100 through-holes. The plurality of through-holes may comprise at most 1000 through-holes, preferably at most 500 through-holes. Reduced space between through-holes (e.g., by using larger through-holes or more smaller through-holes) is advantageous for removal of the binder during the bake, while balancing mechanical stability of the preconditioned laminate. The plurality of through-holes may comprise at least 10 through-holes per 100cm2, preferably at least 20 through-holes per 100cm2, preferably at least 30 through holes per 100cm2, preferably at least 40 through-holes per 100cm2, more preferably at least 50 through-holes per 100cm2. A characteristic size (e.g. diameter or side length) of the through-holes may be at most 25%, preferably at most 15%, of a characteristic size (e.g., width) of the laminate. A subset of the plurality of through-holes may be provided in a central area of the laminate, the subset comprising at least 4 through-holes, preferably at least 10 through-holes, more preferably at least 30 through-holes, more preferably at least 50 through-holes, more preferably at least 80 through-holes. In this case the central area may be a central third, preferably half, of the laminate (i.e., a surface asre of the laminate covering a central third, preferably half, of the length &width for a generally rectangular laminate). The central area may be an area aligned with electrochemically active cell layers in an electrochemical cell assembly, in which case the central area may be provided with all (or substantially all, e.g., at least 90%) of the through-holes. The at least one mica group material may comprises at least one of phlogopite and muscovite. The step of baking in the method for preconditioning may reduce the mass of the laminate by at least 0.5%, preferably at least 0.8%, at most 2.5%, preferably at most 2.0%, more preferably at most 1.5%. The mass loss is due to expulsion of binder (including via decomposition and expulsion of the decomposition products) during the step of baking. The binder may comprises a silicone, preferably siloxane, material. The method (particularly the step of providing a laminate) may include forming as a plate for use in an electrochemical cell assembly. When so used, subsequent to the preconditioning, the laminate may be referred to as a plate. The plate is an insulating plate, and may be used as an electrical insulator in the electrochemical cell assembly. According to a second aspect, the laminate preconditioned according to the above method is used in an electrochemical cell assembly. According to a third aspect, there is provided an electrochemical cell assembly. The electrochemical cell assembly comprises: a stack of electrochemical cell units; at least one plate comprising a formed laminate, wherein the laminate comprises a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, the laminate comprising a plurality of through-holes, the laminate preconditioned by baking at a baking temperature of at least 300 °C; and wherein the stack and at least one plate are held in compression in the electrochemcial cell assembly. The plate may be referred to as an insulating plate. The plate is formed from a laminate, which may be preconditioned according to the above method. Such preconditioning is executed before the laminate is held in compression in the electrochemcial cell assembly. The laminate preconditioned by baking at a baking temperature of at least 300 °C to reduce amount of binder therein. Such preconditioning to remove the binder means that release of said binder (or decomposition products thereof) is reduced once the electrochemical cell assembly experiences elevated temperatures (for example in use). Such release of binder may coat other components of the electrochemical cell assembly, reducing their performance. Further, relaxation of the laminate occurs during the preconditioning method so as to reduce relaxation of the laminate once positioned in the electrochemical cell assembly and held in compression therein (any such relaxation may adversely affect the compression force by decrease of thickness of the laminate (or plate formed from the laminate)). The electrochemical cell assembly may be (or may be used as) an electrolyser cell assembly or a fuel cell assembly. The stack of electrochemical cell units may comprise a plurality of electrochemical cell units stacked one upon another, e.g., along a stacking direction, (the plate may be stacked along the same direction) and the stack of electrochemical cell units and the plate held in compression, the compression acting along the stacking direction. Each electrochemical cell unit of the stack of electrochemical cell units may comprise a cell layer and an interconnect (e.g, interconnect plate). The cell layer comprises an electrochemcially active cell area (formed from layers of anode, electrolyte, and cathode, preferably the electrolyte is a solid oxide electrolyte). The cell layer may comprise a metal support plate which supports the electrochemcially active cell area, in other words the electrochemcially active cell area is coated or deposited over the metal support plate. The metal support plate is provided with a porous region to allow fluidic communication between a fluid volume and a layer of the electrochemcially active cell area nearest to the metal support plate. The at least one insulating plate may comprise one or more openings (preferably fluid ports), the one or more openings in fluidic communication with the stack of electrochemical cell units. In this way, the one or more openings are arranged to supply and / or exhaust fuel and / or oxidant volumes in the stack of electrochemical cell units. The one or more openings may be arranged to allow fluidic communication between the stack of electrochemical cell units and respective ports in an end plate of the electrochemical cell assembly. The at least one plate may be stacked upon the stack of stack of electrochemical cell units, or the stack of electrochemical cell units is stacked upon the at least one plate, or the at least one plate is stacked within the stack of electrochemical cell units, or any combination thereof. Typically, there may be a plate disposed to each end of the stack of electrochemical cell units, to electrically insulate the ends of the stack of electrochemcial cell units from the surroundings (typically neighboring components, e.g., a housing or end plates). The electrochemical cell assembly may comprise a first end plate assembly having a first end plate and a second end plate assembly having a second end plate, the stack of electrochemical cell units and the at least one plate (i.e. the preconditioned laminate) disposed between the first end plate and the second end plate, wherein the at least one plate is disposed between the first end plate and the stack of electrochemical cell units and / or between the second end plate and the stack of electrochemical cell units. One or both of the end plates may have one or more fluid ports aligned with respective ones or the one or more openings in the plate for fluid communication between the stack of electrochemical cell units and external to the electrochemical cell assembly. The stack of electrochemical cell units and the at least one plate may be held in compression by the first end plate and the second end plate. The first end plate and the second end plate may be held in position by tie bars or a housing in tension between said end plates. The plate (preconditioned laminate) may further comprise one or more openings as described above. The plurality of through-holes and / or the at least one mica group material may be as described above. According to a fourth aspect there is provided a method of manufacturing an electrochemical cell assembly. The method comprising: providing a stack of electrochemical cell units; providing at least one plate comprising a formed laminate, wherein the laminate comprises a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, the laminate comprising a plurality of through-holes, the laminate preconditioned by baking at a baking temperature of at least 300 °C; and compressing the stack and at least one plate. The method may further comprise holding (and / or fixing) the stack and at least one plate in compression. The electrochemical cell assembly may be in accordance with the electrochemical cell assembly of the third aspect. Brief Description of the Drawings Features of the present invention will now be described in further detail, by way of various embodiments, and just by way of example, with reference to the accompanying drawings (which drawings are not to scale, and in which the height dimensions are generally exaggerated for clarity), in which: Figure 1 is a perspective view of a laminate. Figure 2 is a method of preconditioning a laminate. Figure 3 is a temperature profile for preconditioning a laminate. Figure 4 is a cross-sectional view of an electrochemical cell assembly comprising a plate in the form of a formed preconditioned laminate. Figure 5 is a perspective view of a further laminate. Detailed Description Referring to Fig. 1, a laminate 100 is shown in perspective view. The laminate 100 has a plate-like geometry, formed from a plurality of mica sheets that are stacked upon one another and bonded together by a binder, for example a siloxane-based binder. The mica sheets are formed from a material comprising at least one mica group mineral, for example phlogopite and / or muscovite. The mica sheets typically each comprise or consist of mica paper. In the context of this application, the term "mica paper" is used in its usual sense to refer to a sheet-like aggregate of mica particles. Mica paper is commonly prepared by grinding mica material into fine particles, preparing an aqueous suspension or slurry of said mica particles, and then forming it into paper (e.g., sheet) by conventional papermaking techniques. Typically, the mica paper, in particular each mica layer of the laminate, has a thickness along the stacking direction of at least 10 pm and / or at most 500 pm, more preferably at most 300 pm, and even more preferably at most 200 pm. The laminate 100 is provided with a plurality of through-holes 110 which are continuous from a first face 105 (upward facing in Fig. 1) to a second, opposed, face 106 (downward facing in Fig. 1). The through-holes may be machined in the laminate, for example by drilling. In the context of this application, the term "through-hole" does not include microscopically small defects or holes naturally occurring in the mica material. That is to say, a through-hole is a deliberately introduced hole in the laminate. The laminate 100 is also provided with a plurality of openings 115,116 which are continuous from the first face 105 (upward facing in Fig. 1) to the second, opposed, face 106 (downward facing in Fig. 1). The openings 115, 116 are configured to transfer fluid through the laminate when used as a plate in an electrochemical cell assembly. The openings 115 have an open perimeter whereas the openings 116 have a closed perimeter. The plurality of through-holes 110 are provided in a central area of the laminate 100, with the plurality of openings 115,116 provided in a peripheral area of the laminate 100 (in other words, closer to the edge of the laminate 100 than the plurality of through-holes). In this case, a subset (three) of the plurality of openings 115, 116 are provided towards each short end of the laminate 100 with the plurality of through-holes 110 provided therebetween. The plurality of through-holes 110 and the openings 115,116 have different sizes (cross-sectional area or characteristic size, e.g., diameter or side length). In this case, the openings 115, 116 are larger than the plurality of through-holes 110. The plurality of through-holes 110 have a circular cross-section, but it will be understood that they may have other cross-sections, for example rectangular. In this case, the openings 116 have a circular cross-section whereas the openings 115 have an open perimeter with a semi-circular or rounded rectangular profile. In this case, the plurality of through-holes are arranged in an array (i.e., a repetitive pattern of geometrical shapes) along the plane of the laminate, in this case a square array but it will be understood that other array patterns are possible, such as hexagonal. Alternatively, the plurality of through-holes may be arranged randomly a plane of the laminate. In this case, the plurality of through-holes includes 68 through-holes. It will be understood that more or fewer through-holes may be provided. The plurality of through-holes may comprise at least 10 through holes, preferably at least 15 through-holes, preferably at least 30 through-holes, more preferably at least 50 through-holes, more preferably at least 80 through-holes, even more preferably at least 100 through-holes. The plurality of through-holes may comprise at most 1000 through-holes, preferably at most 500 through-holes. The plurality of through-holes have an areal density (viewed from either the first side 105 or second side 106 of the alminate 100) of at least 10 through-holes per 100cm2, preferably at least 20 through-holes per 100cm2, preferably at least 30 through holes per 100cm2, preferably at least 40 through-holes per 100cm2, more preferably at least 50 through-holes per 100cm2. A characteristic size (i.e., diameter in this case) of the through-holes is be at most 25%, preferably at most 15%, of a characteristic size (e.g., width) of the laminate 100. A subset of the plurality of through-holes may be provided in the central area (or region) of the laminate, the subset comprising at least 4 through-holes, preferably at least 10 through-holes, more preferably at least 30 through-holes, more preferably at least 50 through-holes, more preferably at least 80 through-holes. In this case the central area may be a central third, preferably half, of the laminate (i.e., a surface asre of the laminate covering a central third, preferably half, of the length &width for a generally rectangular laminate). In the case of Fig. 1, the central area is an area aligned with electrochemically active cell layers in an electrochemical cell assembly, in which case the central area is provided with all (or substantially all, e.g., at least 90%) of the through-holes. Referring to Fig. 2, a method 200 for preconditioning a laminate is provided. At step 205 a laminate is provided. The laminate comprising a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, and wherein the laminate comprises a plurality of through-holes. At step 210 a baking treatment on said laminate is preformed. Said baking treatment comprises arranging the laminate in an oven and heating the laminate in the oven at a baking temperature provided in the oven for a baking time. The baking temperature being at least 300 °C. The laminate preconditioned in method 200 may be the laminate 100 of Fig. 1. During the baking step 210 of the preconditioning method, binder is expelled from the laminate 100 due to the applied heat. The binder itself, or products of its thermal decomposition, is expelled. The through-holes 110 in the laminate 100 allow the binder (or products of decomposition thereof) to escape from the laminate 100, and to do so at a lower temperature and greater rate than is typically the case for a laminate without said through-holes 110. The through-holes 110 also reduce the potential for delamination during the baking which can happen at elevated temperatures or high temperature ramp rates for laminates without a plurality of through-holes 110. The baking step 210 may be executed in any oven capable of providing the required baking temperature, for example a static or conveyor oven. The laminate provided at step 205 of method 200 in this case has through-holes and openings provided therein. The method 200 (step 205) may instead include a step of providing a sheet of laminate and forming through-holes 110 and openings 115,116 in the laminate by machining (e.g., drilling). The laminate may also be formed from a planar sheet into the laminate by forming the outer perimeter of the laminate, e.g., by cutting, in this same step. Fig. 3 depicts a temperature profile 300 of an exemplary baking step 210 according to the method 200 of a laminate 100. Temperature 310 is indicated in degrees Centigrade on the y-axis. Time 305 in hours is indicated on the x-axis. In Fig. 3 the laminate is arranged in the oven at a first temperature, an ambient temperature. In a first portion of the temperature profile 300, the temperature is increased at a temperature ramp rate of approximately 8 °C / minute. After approximately 1.6 hours the baking temperature, of approximately 800 °C, is reached and the temperature of the laminate / oven is kept constant at the baking temperature (e.g., within + / - 30 °C thereof) for the baking time. In this case, the baking time is approximately 3 hours. Once the baking time is complete, the laminate / oven is allowed to cool (e.g., to ambient temperature), which may be a natural or forced cooling (e.g., using a fan and / or cool air stream). The plurality of through-holes 110 in the laminate allow a relatively high temperature ramp rate to be used without delamination of the laminate, by providing paths for the binder (or decomposition products thereof) to escape from the laminate during the baking step. The plurality of through-holes also allow a relatively increased rate of escape of the binder (or decomposition products thereof) for a given temperature, thereby allowing shorter baking times. The baking step exemplified in Fig. 3 results in the mass of the laminate decreasing by at least 0.5%. The mass of the laminate may decrease by at least 0.8%, at most 2.5%, at most 2.0%, or at most 1.5%. the mass loss is due to expulsion of binder (including via decomposition and expulsion of the decomposition products) during the step of performing a baking treatment. Baking temperatures, temperature ramp rates, and baking times other than those exemplified in Fig. 3 are also possible. For example, the baking temperature may be at least 300 °C, at least 500°C, at least 600°C, at least 650°C, at least 700 °C, or at least 750 °C. The baking temperature may be equal to or less than 1000 °C, equal to or less than 900 °C, or equal to or less than 850 °C. Higher baking temperatures increase the proportion of binder removed during the preconditioning and lead to shorter baking times with correspondingly reduced energy usage. For example, the baking time may be at least 1 hour (h), at least 2 h, or at least 3 h. The baking time may be at most 15 h, at most 10 h, or at most 7 h. In some cases, the baking time may be at most 4 h (for example for a balking temperature of at least 750 °C and at most 850 °C. The plurality of through-holes allow removal of sufficient binder during said bake times. In a further specific example, a ramp rate of 3 °C / min and a baking temperature of 800 °C for a baking time of 3 hours appreciably removes binder from the laminate. In a further specific example, a ramp rate of 5 °C / min and a baking temperature of 700 °C for a baking time of 4 hours appreciably removes binder from the laminate. In a further specific example, a ramp rate of 6 °C / min and a baking temperature of 600 °C for a baking time of 15 hours appreciably removes binder from the laminate. As a result, a variety of baking times and baking temperatures are envisaged. In general, a lower temperature requires a longer bake time for a given areal coverage of the plurality of through-holes. Nevertheless, the plurality of through-holes decrease the bake time and decrease the potential for delamination (thereby allowing greater ramp rates) for baking temperatures of 300 °C and above. Appreciable amounts of binder (or thermal decomposition products thereof) escape from the laminate when baking at such temperatures, albeit at reduced escape rates compared to higher temperatures, thereby necessitating longer baking times. The plurality of through-holes particularly protect against delamination for relatively high temperature ramp rates and / or baking temperatures of 600 °C and above. It will be understood that the plurality of through-holes protect against delamination for relatively high temperature ramp rates. Such ramp rates may be present in only a portion of the time taken (or temperature range) to warm the laminate / oven from an insertion temperature to the baking temperature. Fig. 4 is a cross-section of an electrochemical cell assembly 400 comprising two insulating plates 100a, 100b (also merely referred to as plates) formed from a laminate 100 preconditioned according to the method described herein. The electrochemical cell assembly 400 comprises a stack 405 of electrochemical cell units 406. A plurality of electrochemical cell units 406 are stacked one upon another, along a stacking direction, to form the stack of cell units. Each electrochemical cell unit 406 comprises a cell layer 406a and an interconnect 406b (also referred to as an interconnect plate or a separator plate, the latter term because it separates fluid volumes in the stack of cell units). The cell layer 406 comprises an electrochemically active cell area 410 formed from layers of anode, electrolyte, and cathode materials. In this case the electrolyte is a solid oxide electrolyte and the cell units 406 are solid oxide electrochemical cell units. In this case the cell layer 406a includes a metal support plate which supports the electrochemcially active cell area 410, which is coated or deposited over the metal support plate. The metal support plate is provided with a porous region to allow fluidic communication between a first fluid volume and a layer of the electrochemcially active cell area 410 nearest to the metal support plate. The interconnect 406b and the cell layer 406a are joined to one another around their periphery, preferably by welding, to form the cell unit 406. The interconnect 406b is provided with a flanged perimeter which separates the central area of the interconnect 406b from the cell layer 406a. Alternatively, the separation may be achieved by a separator plate in the form of a windowframe (e.g., having a periphery and blank central area), said separator plate provided between the cell layer 406a and interconnect 406b, the three plates being joined, preferably being welded together, around their periphery to form the cell unit 406. The interconnect 406b has up and down protrusions to contact the cell layer 406a of the same cell unit 406 and to contact an outermost layer of the electrochemically active cell area 410 of a neighboring cell unit 406. In this way, the protrusions electrically interconnect neighboring cell units 406 in the stack 405 of cell units 406. The protrusions transfer compressive forces through the stack. The also maintain separation of the cell layer 406a and interconnect 406b in a cell unit 406 to provide a first fluid volume for first fluid internal to the cell unit 406. The protrusions also maintain separation of the interconnect 406b of a cell unit 406 and a cell layer 406a (specifically, electrochemically active cell area 410) of a neighboring cell unit 406 to provide a second fluid volume for second fluid external to the cell units 406. Gaskets 415 separate (and may electrically insulate) neighboring cell units 406 in the stack 405. Each cell unit 406 is provided with at least one fluid port (opening through the cell unit - specifically through the cell layer 406a (metal support plate thereof) and interconnect 406b) for supply or exhaust of the first fluid volume. The gaskets 415 surround the fluid ports and are positioned between neighboring cell units 406 (and between other components of the electrochemical cell assembly as dpicted in Fig. 4). The fluid ports and gaskets are aligned along the stacking direction to form chimneys or manifolds in the stack 405. Arrows in Fig. 4 exemplify flow of first fluid through the electrochemical cell assembly 400: through an inlet chimney to an outlet chimney via the first fluid volume enclosed by one of the cell units 406. The electrochemical cell assembly 400 has two insulating plates 100a, 100b (also referred to as (electrically) insulating plates) that were preconditioned according to the abovementioned method prior to use in the electrochemical cell assembly 400. The stack 405 of cell units 406 is stacked upon insulating plate 100a. Insulating plate 100b is stacked upon the stack 405 of cell units 406. A plurality of through-holes 110 (number thereof reduced relative to Fig. 1 for clarity of the figure) are provided in each of the insulating plates 100a, 100b as described above. The insulating plate 100a is stacked upon a first end plate 420 which forms part of a first end plate assembly. A second end plate 421, which forms part of a second end plate assembly, is stacked upon the insulating plate 100b. The end plates 420,421 are held in position relative to one another so as to apply a compressive force to components therebetween, i.e., at least the stack 405 of cell units 406 and the insulating plates 100a7 100b. In this case the end plates are held in compression by a housing or skirt 422, which may be welded to the end plates. The insulating plates 100a, 100b transfer compression force to the stack 405 of cell units 406 and electrically insulate the end plates 420, 421 from the ends of the stack of cell units. The end plates 420, 421 have one or more openings that align with and are in fluidic communication with at least a subset of the one or more openings in the insulating insulating plates 100a, 100b and with at least a subset of the one or more fluid ports in the cell units 406. The arrows in Fig. 4 exemplify a fluid flow path for first fluid entering the electrochemical cell assembly 400 via an opening in the first end plate 420 and exiting the electrochemical cell assembly 400 via an opening in the second end plate 421. It will be understood that the entry and exit for first fluid need not necessarily be through different ones of the end plates, and may instead be through the same end plate or through openings in the housing 422. One or both of the end plates may provided with one or more openings (not shown) in fluidic communication with the second fluid volume to supply and / or exhaust second fluid therefrom, said openings align with the opening 115 in the preconditioned laminate 100 of Fig. 1. The first fluid volume and the second fluid volume may be for fuel and oxidant or vice-versa. Two different variants of the plate 100 are exemplified in the electrochemical cell assembly 400. Insulating plate 100a is configured similarly to plate 100 of Fig. 1. Support layers 401a are positioned to opposing sides of the insulating plate 100a to transfer the compression within the electrochemically active region of the stack. To do this, the support layers 401a are sized to match the height of the gaskets 415 either side of the insulating plate 100a. Said support layers 401a may be made of similar material to the gaskets 415. Alternatively, the support layers 401a may themselves be formed from a laminate, such as one manufactured according to the above described method. Insulating plate 100b is configured in an alternate manner to insulating plate 100a. Instead of support layers 401a associated with insulating plate 100a, the insulating plate 100b is formed from a laminate having a stepped portion 401b forming part of the first side 105a and stepped portion 401b forming part of the second side 105b. The step accounts for the height of the gaskets 415 positioned to each side of the insulating plate 100b. As depicted, the through-holes 110 in the insulating plate 100b traverse from the first side 105a to the second side 105b through the insulating plate 100b (including through the stepped portions 401b). Each of the insulating plates 100a, 100b is provided with openings. In the cross-section of Fig. 4, the openings 116 of Fig. 1 are shown in cross-section. The electrochemical cell assembly 400 further includes a power assembly disposed to each end of the stack 405 of cell units 406. The power assembly may be referred to as a power take off assembly. Its function is to transfer power to the stack 405 of cell units 406 from external to the electrochemical cell assembly 400 (in electrolysis operation) or transfer power from the stack 405 of cell units 406 to external to the electrochemical cell assembly 400 (in fuel cell operation). Each power assembly includes an electrical end plate 425, a electrical stud 426, electrically insulating sleeve 427 and electrically inslating washer 428. The electrical end plate 425 is positined between an end of the stack 405 and the insulating plate 100. The electrical end plate 425 is in electrical contact with the end of the stack 405 and transfers power therefrom to the electrical stud 426. The insulating plate electrcially insulates the end of the stack 405 and electrical end plate 425 from the end plate (420 or 421 depending upon which end of the stack the power assembly is). The electrical stud 426 is in electrical contact with the electrcial end plate 425; it may be integrally formed with the electrical end plate or may be attached thereto, e.g., by welding. The electrical stud 426 protrudes through one of the openings in the insulating plate 100 and through the end plate 420 / 421 to allow elecrical connection external to the electrochemical cell assembly 400. In this case an electrically insulating sleeve 427 (also referred to as a collar) surrounds the electrical stud 426. The sleeve 427 is formed from an (electrically) insulating material, such as mica or ceramic. It provides mechanical stability to the electrical stud 426 during handling of the stack arrangement 500 and during external connection to the stud 426. The sleeve 427 also prevents ingress of foreign material (e.g. dirt) into the electrochemical cell assembly 400 via the opening in the end plates. Further mechanical stability is provided by a washer 428 which surrounds the sleeve 427 (and stud 426) and sits on the outer face of the end plate. The washer 428 may be formed of any suitable (electrically) insulating material, such as ceramic or mica. It will be understood that other arrangements for the power assemblies are possible. For example they may be arranged such that both electrical studs 426 pass through openings at the same end of the assembly. In other words, both pass through one of the insulating insulating plates 100a, 100b, and through one of the end plates 420, 421. Fig. 5 shows a laminate 500 (and configuration of a plate resulting from the preconditioning method) which is a variant of the laminate 100 (and resulting insulating plate) described with reference to Figs. 1 to 4. The laminate 500 is similar to laminate 100 except that the laminate 500 is not provided with any openings 115,116. In other words the plate resulting from laminate 500 is truncated with respect to that of laminate 100. The truncation is such that the extent of insulating plate resulting from laminate 500 is similar to the extent of the electrochemically active cell area 410 of Fig. 4 and so the support layers 401a or stepped portions 401b are not necessary. In this case the plate formed from laminate 500 does not extend to or contact the gaskets 415.

Claims

1. A method for preconditioning a laminate for an electrochemical cell assembly, said method comprising:a. providing a laminate comprising a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, and wherein the laminate comprises a plurality of through-holes; andb. performing a baking treatment on said laminate, said baking treatment comprising:i. arranging the laminate in an oven, andii. heating the laminate in the oven at a baking temperature provided in the oven for a baking time, said baking temperature being at least 300 °C.

2. The method of claim 1, wherein the baking temperature is at least 500°C, preferably at least 600°C, more preferably at least 650°C, more preferably at least 700 °C, more preferably at least 750 °C.

3. The method of claim 1 or 2, wherein the baking temperature is equal to or less than 1000 °C, preferably equal to or less than 900 °C, more preferably equal to or less than 850 °C.

4. The method according to any one of the preceding claims, wherein the baking time is at least 1 h, preferably at least 2 h, more preferably at least 3 h.

5. The method according to any one of the preceding claims, wherein the baking time is at most 15 h, preferably at most 10 h, more preferably at most 7 h.

6. The method according to any one of the preceding claims, wherein the temperature in the oven is kept constant for the baking time.

7. The method according to any one of the preceding claims, wherein the laminate is arranged in the oven at a first temperature, lower than the baking temperature, and the temperature is increased at a temperature ramp rate for at least a portion of the temperature increase.

8. The method according to claim 7, wherein the temperature ramp rate is at least 2 °C / min, preferably at least 4 °C / min, more preferably at least 5 °C / min.

9. The method according to claim 7 or 8, wherein the temperature ramp rate is at most 15 °C / min, preferably at most 10 °C / min, more preferably at most 8 °C / min.

10. The method according to claim 7, wherein the temperature ramp rate is between 2 and 15 °C / min, preferably between 4 and 10 °C / min, preferably between 4 and 8 °C / min.

11. The method according to any one of claims 7 to 10, wherein the temperature ramp rate is applied at a temperature of greater than 200 °C.

12. The method according to any one of the preceding claims, further comprising forming one or more openings in the laminate for transfer of fluid within an electrochemical cell assembly, wherein the one or more openings are formed prior to performing the baking treatment.

13. The method according to claim 12, wherein the step of providing the laminate comprises forming the plurality of through-holes in the laminate and the one or more openings are formed in the same step as forming the plurality of through-holes.

14. The method according to claim 12 or 13, wherein the plurality of through-holes and the one or more openings have different sizes.

15. The method according to anyone of the preceding claims, wherein plurality of through-holes comprise at least 10 through holes, preferably at least 30 through-holes, more preferably at least 50 through-holes, more preferably at least 80 through-holes, even more preferably at least 100 through-holes.

16. The method according to any one of the preceding claims, wherein the plurality of through-holes comprise at least 10 through-holes per 100cm2, preferably at least 20 through-holes per 100cm2, preferably at least 30 through-holes per 100cm2, preferably at least 40 through-holes per 100cm2, preferably at least 50 through-holes per 100cm2.

17. The method according to any one of the preceding claims, wherein a characteristic size of the through-holes is at most 25% of a characteristic size of the laminate.

18. The method according to any one of the preceding claims, wherein a subset of the plurality of through-holes are provided in a central area of the laminate, the subset comprising at least 4 through holes.

19. The method according to any one of the preceding claims, wherein the mass of the laminate is reduced by at least 0.5%, preferably at least 0.8%, at most 2.5%, preferably at most 2.0%, more preferably at most 1.5% as a result of said step of performing a baking treatment on said laminate.

20. Use of a laminate preconditioned according to any preceding claim in an electrochemical cell assembly.

21. An electrochemical cell assembly comprising:a stack of electrochemical cell units;at least one plate comprising a formed laminate, wherein the laminate comprises a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, the laminate comprising a plurality of through-holes, the laminate preconditioned by baking at a baking temperature of at least 300 °C; and whereinthe stack and at least one plate are held in compression in the electrochemcial cell assembly.

22. The electrochemical cell assembly according to claim 21 wherein the laminate was preconditioned according to any one of claims 1 to 19.

23. The electrochemical cell assembly according to claim 21 or 22, wherein the at least one plate comprises one or more openings, the one or more openings in fluidic communication with the stack of electrochemical cell units.

24. The electrochemical cell assembly according to any one of claims 21 to 23, further comprising a first end plate assembly having a first end plate and a second end plate assembly having a second end plate, the stack of electrochemical cell units and the at least one plate disposed between the first end plate and the second end plate, wherein the at least one plate is disposed between the first end plate and the stack of electrochemical cell units and / or between the second end plate and the stack of electrochemical cell units.

25. A method for manufacturing an electrochemical cell assembly, the method comprising: providing a stack of electrochemical cell units;providing at least one plate comprising a formed laminate, wherein the laminate comprises a plurality of mica sheets that are stacked upon one another and bonded together by a binder, said mica sheets formed from a material comprising at least one mica group mineral, the laminate comprising a plurality of through-holes, the laminate preconditioned by baking at a baking temperature of at least 300 °C; andcompressing the stack and at least one plate.

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