A flexible electrical conductor including elements connected to each other by TIG welding, and a method for manufacturing such a flexible electrical conductor

Abstract

The subject matter of the present invention is a flexible electrical conductor (70), which comprises an assembly (72) and a first connection strip (78). The assembly (72) includes a flexible conductive core (74) made of a first metal material and a sheath (79) covering the conductive core (74), the sheath (79) being made of a second metal material having an electrical resistivity higher than that of the first metal material. The first connection strip (78) is at least partially formed by the second metal material and is connected to a first end (72a) of the assembly (72). At the first end (72a) of the assembly (72), the sheath (79) and the first connection strip (78) are joined by TIG welding, and the conductive core (74) and the first connection strip (78) are joined by fillet brazing or soldering.

Description

Technical Field

[0001] The present invention relates to the general field of high-temperature electrolysis (HTE), in particular, high-temperature steam electrolysis (HTSE), carbon dioxide (CO2) electrolysis, and even high-temperature co-electrolysis of steam and carbon dioxide (CO2).

[0002] More specifically, the present invention relates to the field of high-temperature electrochemical devices (such as high-temperature solid oxide electrolysis cells or SOECs for short, and high-temperature solid oxide fuel cells or SOFCs for short), but also to high-temperature co-electrolysis cells for steam and carbon dioxide, reversible fuel cells and high-temperature electrolysis cell systems, or intermediate-temperature cells or electrolyzers on the order of 400 °C (referred to as proton ceramic fuel cells or PCFCs for short).

[0003] Thus, more generally, the present invention refers to the field of stacks of SOEC / SOFC type solid oxide cells operating at high temperatures. The stacks can operate at atmospheric pressure or under pressure.

[0004] In addition to such stacks of SOEC / SOFC type solid oxide cells, the present invention relates to any system where there is a need for electrical conduction in a high-temperature oxidizing environment or under conditions that result in rapid degradation of the conductive material.

[0005] More specifically, the present invention relates to supplying an electric current to a stack of electrochemical cells in a high-temperature area.

Background Art

[0006] In a high-temperature solid oxide electrolysis cell, i.e., an SOEC, among the same electrochemical devices, water vapor (H2O) is converted into hydrogen (H2) or other fuels (such as methane (CH4), natural gas, biogas, and oxygen (O2)), and / or carbon dioxide (CO2) is converted into carbon monoxide (CO) and oxygen (O2) by an electric current. In a high-temperature solid oxide fuel cell, i.e., an SOFC, the operation is reversed to produce an electric current and heat by supplying hydrogen (H2) and oxygen (O2), typically air and natural gas (i.e., methane (CH4)). For simplicity, the following description preferentially shows the operation of a high-temperature solid oxide electrolysis cell, i.e., an SOEC, that performs the electrolysis of water vapor. However, this operation is applicable to the electrolysis of carbon dioxide (CO2), or even further, to the high-temperature co-electrolysis of water vapor (HTSE) and carbon dioxide (CO2). In addition, this operation can be diverted to the case of a high-temperature solid oxide fuel cell, i.e., an SOFC.

[0007] As is known per se, a high-temperature water vapor (H2O) electrolyzer or HTSE includes a stack of a plurality of basic solid oxide electrochemical cells. Referring to FIG. 1, a solid oxide cell 10, i.e., an SOC, includes, among other things, a) a first porous conductive electrode 12, i.e., a "cathode", intended to be supplied with water vapor for the production of hydrogen; b) a second porous conductive electrode 14, i.e., an "anode", through which oxygen (O2) produced by the electrolysis of water injected at the cathode escapes; and c) a solid oxide film (high-density electrolyte) 16 sandwiched between the cathode 12 and the anode 14, and the film 16 is an anion conductor for high temperatures (usually temperatures higher than 600 °C).

[0008] By heating the cell 10 to at least this temperature and injecting an electric current I at the anode 14, the water at the cathode 12 is reduced, hydrogen (H2) is generated at the cathode 12, and oxygen (O2) is generated at the anode 14.

[0009] A stack 20 of such cells having the purpose of producing a large amount of dihydrogen is shown in the schematic diagram of FIG. 2. In particular, the cells 10 are separated by interconnecting plates 18 or interconnects and stacked on top of each other. The function of these plates is to ensure electrical continuity between the various electrodes of the cells 10, thus enabling them to be connected electrically in series, and to distribute the various gases required for the cells to operate and, if necessary, a carrier gas to assist in exhausting the products of the electrolysis, and / or to provide thermal management of the stack.

[0010] To do this, the plate 18 is connected to a steam supply 22 for the injection of this steam at the cathode of the cell 10 based on a constant steam flow rate D set by a controllable valve 24. H2O The plate 18 is also connected to a gas collector 26 for collecting the gases from the electrolysis. Exemplary stack and interconnect plate structures are described, for example, in international application WO2011 / 110676A1.

[0011] To effectively carry out the electrolysis by the stack 20, the stack is heated to a temperature higher than 600 °C (usually a temperature included between 650 °C and 900 °C), the gas supply is switched on at a constant flow rate, and the power supply 28 is connected between the two terminals 30, 32 of the stack 20 and a current I is circulated there.

[0012] The intensity of the current I is usually of the order of several hundred amperes, which generates significant heat losses due to the Joule effect in the electrical conductors. To optimize the energy efficiency of the solid oxide electrochemical system, it is important to limit these thermal losses by developing particular electrical conductors, also known as busbars.

[0013] The busbars in the stack usually take the form of metal rods. Taking a cylindrical rod as an example, the electrical resistance R can be expressed by the following formula.

[0014] [Number]

[0015] Here, ρ is the resistivity of the rod (unit: Ω·m), l is the length of the rod (unit: m), and S is the cross-section of the rod (unit: m 2 ²).

[0016] Since the loss due to the Joule effect is proportional to the resistance R, in order to limit this effect, it is therefore necessary to reduce the electrical resistance of the busbar. Therefore, possible improvement measures include the following. - Limit the length of the rod. - Increase its cross-section. - Find a material with a lower resistivity that is stable at high temperatures.

[0017] The first two options are generally geometric choices that depend on the shape of the electrochemical system. Therefore, there are constraints on them, and / or the rods in the prior art are already optimized for the electrochemical system. The last point relates to the constituent material of the rod that must be selected to have the lowest resistivity in order to reduce resistance losses.

[0018] Improving this last point has not been fully considered. In fact, for all laboratory developments of technology, energy efficiency is not the most important thing. On the other hand, as explained below, the rods are immersed in a highly corrosive environment, and therefore the standard solution used is to use solid stainless alloy rods, which is therefore the reference solution in all international publications. The resistivity of these rods at room temperature (20 °C) is already high (approximately 75×10 -8It should be noted that the resistivity (Ω·m) increases rapidly with temperature.

[0019] Therefore, at 900 °C (which is a high operating temperature for solid oxide fuel cells), the electrical resistance of the stainless - steel rod is equal to 117.10 -8 Ω·m, which results in a very large resistive loss. These aspects are described, among other things, in French patent application FR3036840A1.

[0020] However, when the aim is to optimize the electrical resistivity, the material generally recommended for an electrical conductor exposed to a high - intensity current is copper. Experimental studies carried out by the applicant have determined the resistivity curve of copper as a function of temperature and have also confirmed that the choice of copper makes it possible to reduce the resistive losses by at least a factor of 10 compared to a reference material over the entire range of operating temperatures for a solid - oxide system.

[0021] However, one of the main constraints to be considered is the problem of corrosion associated with the stack environment.

[0022] Referring to FIG. 3, the stack 20 is actually surrounded by a so-called "thermal" enclosure, the temperature of which is maintained between 650° C. and 900° C. by the application of sweep air. A conventional electrochemical system thus includes: - an HTS electrolyzer 20, for example, as described in relation to FIGS. 1 and 2, including a set of conduits 52, 54, 56, 58 for supplying and collecting gases from the anodes and cathodes of the electrochemical cells of the electrolyzer; - an enclosure 60 housing the electrolyzer 20, the conduits 52, 54, 56, 58 passing through the wall of the enclosure 60 for connection to a gas collection and supply circuit (not shown). The enclosure 60 also has an air inlet conduit 62 and an air outlet conduit 64, and the enclosure 60 is sealed, for example, against gases and liquids at any other location. The conduit 62 can be connected to an air supply circuit (not shown) to apply sweep air to the high-temperature area surrounding the electrolyzer 20, the sweep air being discharged through the outlet conduit 64. Two electrical conductors 66, 68 are connected to the terminals 30, 32 of the stack 20 and pass through the enclosure 60 for their connection to the current supply source 28.

[0023] Under these conditions, the two conductors 66, 68 in the form of copper rods (at least a part of which is included in the enclosure 60) will oxidize very rapidly. In addition, copper does not resist oxidation at high temperatures. The reason is that the oxide formed on the surface is not sufficiently dense and adherent to protect the underlying metal. Materials known to resist oxidation at high temperatures are chromium and aluminum, which form alloys (such as stainless steel and stainless nickel alloys). The reason is that they form chromia and / or alumina, which are much more protective oxides. However, as described above, these alloys have a given electrical resistivity, and their use results in a significant energy loss.

[0024] High-temperature solid oxide fuel cells, i.e., SOFCs, encounter similar problems. In fact, HTS electrolyzers and SOFCs have the same structure, and the only difference is their operating modes. The electrolyzer operates in a carbon dioxide (CO2) reduction mode or a co-electrolysis mode (i.e., the gas mixture at the cathode inlet is composed of water vapor (H2O) and carbon dioxide (CO2)). Therefore, the mixture at the cathode outlet is composed of hydrogen (H2), water vapor (H2O), carbon monoxide (CO), and carbon dioxide (CO2). Referring to Figure 4, the electrochemical cell that makes up the SOFC includes the same elements as the electrolysis cell (anode 12, cathode 14, electrolyte 16), but the cell is supplied with dihydrogen at its anode and dioxygen at its cathode at a constant flow rate, and is also connected to a load C to deliver the generated current. For the current produced in the order of several amperes, the cell thus encounters the same problems as the electrolyzer.

[0025] One solution is to protect the copper rod (or any other metal considered suitable from the perspective of electrical resistivity) with a coating (e.g., a chromia coating or an alumina coating) that gives it a good level of resistance to oxidation. This raises several problems. First, it is necessary to ensure that the coating is tight and remains on top of the copper substrate during heating. Since copper has a high coefficient of thermal expansion, it should be emphasized that significant stress due to the thermal expansion difference can occur, which may damage the coating and / or the coating / copper interface. In addition, at the high-temperature end of the rod, the electrical connection needs to be made to the stack without exposing the copper. Therefore, the connection has to be made to the coating without damaging the coating, which is technically difficult.

[0026] Another solution is to place a copper rod inside a sheath made of an oxidation-resistant material. Since the two materials are not integral, this solves the problem of resistance to stress due to the difference in thermal expansion. Such an assembly (copper + stainless steel sheath) is already known from the prior art for other application fields (for example, in a strong acid environment at low temperatures (50 - 80 °C)), and in particular from the Chinese document CN202608143U, which describes a copper bar simply inserted into a steel tube. This type of conductor has been found to be satisfactory at low temperatures but inappropriate for solid oxide systems. In fact, the almost non-existent contact between the conductive core and the sheath results in a deterioration of the electrical contact between the two materials and an increase in resistance losses, given that it is at a high temperature. In other words, an optimized electrical conduction system that is suitable for high currents and can withstand a significant number of thermal cycles in an oxidizing environment does not exist in the prior art.

[0027] Patent application FR3036840A1 discloses an electrical conductor that is suitable for currents of several hundred amperes, resistant to oxidation at high temperatures, and can withstand thermal cycles up to 900 °C. This electrical conductor includes a rod made of a first metallic material and a sheath made of a second metallic material (completely covering the rod), the two of which are welded together by hot isostatic pressing (HIP).

[0028] More specifically, this application proposes forming a rod composed of a copper round core protected by an Inconel® 600 steel tube sheath, which comprises a part called a "whistle" made of Inconel® 600 steel that is a connection terminal, and a closed-end piece also made of Inconel® 600 steel through which a vacuum is drawn. These parts are assembled by TIG (tungsten inert gas) type arc welding. The resulting rod is then subjected to a hot isostatic pressing (HIP) process, which enables various materials to be diffusion welded together without the addition of a filler metal.

[0029] However, this solution has several drawbacks, particularly the use of hot isostatic pressing (HIP), which is a cumbersome method that can only be carried out by certain companies with cycle times of several hours given a temperature of approximately 900 °C and a high-pressure cycle of 1000 bar.

[0030] In addition, the busbar consists of a single high-temperature connection area, which does not allow internal connections to be made in the high-temperature area.

Prior Art Documents

Patent Documents

[0031]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0032] The present invention aims to at least partially address the above-mentioned needs and the drawbacks of the prior art embodiments.

Means for Solving the Problems

[0033] Accordingly, an object of the present invention, according to one of its aspects, is a flexible electrical conductor, - an assembly, - a first connection strip and includes, the assembly includes - a flexible conductive core made of a first metallic material, - a sheath covering the conductive core, made of a second metallic material (especially a stainless metallic material or a refractory metallic material) having an electrical resistivity higher than that of the first metallic material, and includes, in the flexible electrical conductor, the first connection strip is at least partially formed by the second metallic material and is connected to the first end of the assembly, at the first end of the assembly, the sheath and the first connection strip are joined by TIG (tungsten inert gas) welding, especially over the entire peripheral part, and the conductive core and the first connection strip are joined by fillet brazing or soldering (especially high-temperature fillet brazing or soldering).

[0034] The sheath and the first connection strip can preferably be joined by TIG welding with the addition of a material made of the second metallic material. However, materials such as stainless metal or refractory metal, and / or metal alloy or refractory alloy, especially stainless steel or refractory steel, can also be added. The filler material is preferably resistant to oxidation at high temperatures and is compatible with the materials used for the sheath and the connection strip.

[0035] A "flexible" electrical conductor is understood as a conductor used for connection to a stack that can avoid the transmission of vibrations, expansions, and other parasitic movements between the stack and its environment (e.g., the furnace floor, frame, gas pipeline, etc.), enabling possible electrical connections to be established between stacks during assembly without mechanical displacement. It is contrasted with a "rigid" electrical conductor that mechanically acts within the main link and is not directly connected to the stack. The flexibility of the flexible electrical conductor makes wiring easier, especially at the stack level. It also enables adaptation to different shapes. Regarding the flexible electrical conductor, the forming torque is less than 2 N·m, while for the rigid electrical conductor, it is greater than 10 N·m.

[0036] Moreover, the electrical conductor according to the present invention can include one or several of the following characteristics, either alone or according to any possible technical combination.

[0037] The electrical conductor can advantageously have a second connection strip, which is at least partially formed by a second metallic material and is connected to the second end of the assembly. At the second end of the assembly, the sheath and the second connection strip can be joined by TIG welding, especially with the addition of a material made from the second metallic material. The conductive core and the second connection strip can be joined by fillet brazing or soldering. The TIG welds and the sheath at the two ends of the assembly can completely cover the conductive core over its entire length.

[0038] Furthermore, at least one gap can exist between the outer surface of the conductive core and the inner surface of the sheath over at least a part of the length of the conductive core.

[0039] The conductive core (first metal material) can be made of copper, nickel, or silver, and / or a copper alloy, nickel alloy, or silver alloy, or any other metal or alloy having good electrical conductivity. In particular, any other metal or alloy having good electrical conductivity is sensitive to oxidation at high temperatures on the order of 900 °C (such as brass or bronze).

[0040] In addition, the sheath (second metal material) can be made of a stainless metal or refractory metal, and / or a metal alloy or refractory alloy, in particular, made of stainless steel or refractory steel, for example, nickel, chromium, or cobalt, in particular, Inconel®, for example, Inconel® 600 or 625, or any other metal or alloy resistant to oxidation at high temperatures, for example, made of 316L stainless steel.

[0041] The first connection strip and / or the second connection strip can be made entirely of the second metal material.

[0042] Alternatively, in order to limit any electrical losses, the first connection strip and / or the second connection strip can each have a conductive connection core made of the first metal material and a connection sheath, the connection sheath completely covering the connection core over its entire length and being made of the second metal material.

[0043] The connection sheath can be approximately 0.5 mm thick.

[0044] In particular, according to one particular embodiment aimed at obtaining a flexible and electrically insulated power cable, the assembly comprising the conductive core and the sheath can be flexible, in particular, the conductive core and the sheath are made of a flexible material, and the sheath is completely covered by an electrically insulating jacket, or an electrically insulating protection, in particular, a ceramic braided jacket.

[0045] Moreover, according to another aspect of the present invention, there is provided a method for manufacturing an electrical conductor as defined above, comprising: - cleaning the surface, in particular the surface intended to be welded, i.e. the electrical conduction surface and the surface required to seal the electrical conductor, using in particular a cleaning agent and / or a solvent; - inserting the conductive core into the sheath; - joining the conductive core to the first connection strip by fillet welding or soldering; - joining the sheath to the first connection strip by TIG welding; - evacuating the sheath by pumping, if necessary. The method is characterized by the above steps.

[0046] The electrical conductor can have a second connection strip, which is at least partially formed of a second metallic material and is connected to the second end of the assembly. After the step of joining the sheath to the first connection strip by TIG welding, the method can include: - joining the conductive core to the second connection strip by fillet welding or soldering; - joining the sheath to the second connection strip by TIG welding. The method can include the above steps.

[0047] The manufacturing can be carried out in an ambient atmosphere (air) or a neutral atmosphere (such as argon).

[0048] The first connection strip and / or the second connection strip can be formed by assembling a conductive connection core and a connection sheath that completely covers the connection core. The connection core can be manufactured by die forging. However, methods other than die forging (such as machining or forging) can be used. The connection sheath can be manufactured by deep drawing or assembling a plurality of parts made from a second metallic material.

[0049] Moreover, the step of assembling the first connection strip and / or the second connection strip can at least include - cleaning the constituent elements of the connection strip, especially using a cleaning agent or a solvent; - inserting the connection core into the connection sheath; - evacuating the connection strip; - applying a diffusion welding cycle by hot isostatic pressing (HIP). and can be included.

[0050] The diffusion welding cycle by hot isostatic pressing (HIP) can be carried out under the following operating conditions. - Heating the assembly formed by the connection core and the connection sheath to a temperature included between 600°C and 1060°C, preferably to a temperature included between 800°C and 1000°C, especially to a temperature of 920°C. - Applying a pressure included between 500 bar and 1500 bar, preferably a pressure included between 800 bar and 1200 bar, especially a pressure of 1020 bar, to the connection sheath. - Applying a pressure and temperature plateau over a period of 30 minutes to several hours, preferably over a period of 1 hour to 3 hours, especially over a period of 2 hours. - Allowing the assembly to cool and depressurizing.

[0051] In addition, in order to ensure good electrical conductivity, the conductive core and the connection cores of the first connection strip and / or the second connection strip can be connected together by means of high-temperature brazing or soldering methods.

[0052] In addition, another object of the present invention, according to another aspect thereof, is the use of at least one electrical conductor as defined above as an electrical conductor of an electrochemical system, the electrochemical system comprising: - an enclosure for the circulation of air within a volume defined thereby, - an electrochemical device housed within the enclosure and the electrochemical device comprising: - a solid oxide stack of the high-temperature SOEC / SOFC type of basic electrochemical cells each containing an electrolyte, the electrolyte being inserted between the cathode and the anode and being connected in series between two electrical terminals; - said at least one electrical conductor connected to at least one of the two electrical terminals and

[0053] Moreover, another object of the present invention, according to another aspect thereof, is an electrochemical system comprising: - an enclosure for the circulation of air within a volume defined thereby, - an electrochemical device housed within the enclosure and the electrochemical device comprising: - a solid oxide stack of the high-temperature SOEC / SOFC type of basic electrochemical cells each containing an electrolyte, the electrolyte being inserted between the cathode and the anode and being connected in series between two electrical terminals; - at least one electrical conductor as defined above connected to at least one of the two electrical terminals and

[0054] The present invention will be better understood by reading the following detailed description of its non-limiting and exemplary embodiments, and also by considering the schematic and partial views of the accompanying drawings.

Brief Description of the Drawings

[0055]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Modes for Carrying Out the Invention

[0056] In all of these figures, the same reference numerals may refer to the same or similar elements.

[0057] In addition, the various parts shown in the figures are not necessarily to scale in order to make the figures easier to read.

[0058] Figures 1 to 4 have already been described above in the part related to the prior art and in the background art of the present invention.

[0059] Referring to FIGS. 5 to 11, an exemplary flexible electrical conductor 70 in the form of a flexible power cable is shown. Such a flexible connection facilitates wiring, among other things, and absorbs expansion or vibration.

[0060] Referring to FIGS. 5 and 6, an exemplary flexible electrical conductor 70 according to the present invention is described. Thus, it has an assembly 72, which is composed of a conductive core 74 inserted into a sheath 79. The conductive core 74 is made of a first metal material (copper in this case), and the sheath 79 is made of a second metal material (stainless alloy in this case). The second metal material has an electrical resistivity higher than that of the first metal material.

[0061] Although the conductive core 74 is made of copper in this case, it should be noted that the present invention is applicable to other metals that are good electrical conductors but sensitive to oxidation (such as nickel, silver, brass, bronze, and / or copper alloys, such as those hardened by dispersoids, etc.).

[0062] Moreover, the electrical conductor 70 has a first connection strip 78 and a second connection strip 78. The first connection strip 78 is formed of the second metal material and is connected to the first end 72a of the assembly 72. The second connection strip 78 is formed of the second metal material and is connected to the second end 72b of the assembly 72.

[0063] The connection strip 78 or "whistle" (in this case made of Inconel® stainless alloy) seals and closes the ends 72a and 72b of the assembly 72 and thus prevents the passage of gas. They are used to create electrical connection terminals. They have a shape complementary to the plate of the electrolytic cell to which the strip 78 is attached for the electrical connection of the electrolytic cell.

[0064] The shape or geometry of the connection strip 78 can be a normal terminal shape (as shown here) or any other different shape (for example, cylindrical, intended to fit into a bore, or clamped between two half-shells fixed to the device to be powered).

[0065] At the first end 72a of the assembly 72, the sheath 79 and the first connection strip 78 are joined by TIG welding (for example, orbital welding) over the entire perimeter shown by P in FIG. 6, preferably with the addition of a material made of a second metallic material. The conductive core 74 and the first connection strip 78 are joined by fillet brazing or soldering in part of them (shown by B in FIG. 6). The conductive core 74 and the sheath 79 are not welded together.

[0066] Similarly, at the second end 72b of the assembly 72, the sheath 79 and the second connection strip 78 are joined by TIG welding (reference sign P), preferably with the addition of a material made of a second metallic material. The conductive core 74 and the second connection strip 78 are joined by fillet brazing or soldering (reference sign B) with respect to a part thereof. The TIG welds and the sheath 79 at the two ends 72a and 72b of the assembly 72 completely cover the conductive core 74 over its entire length L, as shown in FIG. 6. The conductive core 74 and the sheath 79 are not welded together. The TIG welding protects the conductive core 74 from oxidation. In fact, the welding is carried out to seal the connection between the whistle 78 and the sheath 79.

[0067] As schematically shown in FIG. 6, one or more gaps J can exist between the outer surface of the conductive core 74 and the inner surface of the sheath 79 over at least a part of the length L of the conductive core 74. In particular, for example, an atmosphere such as air or an inert atmosphere (e.g., argon) can be trapped between the conductive core 74 and the sheath 79.

[0068] In the case of air trapped between the sheath 79 and the conductive core 74, during use, especially at high temperatures, this air will be consumed by the oxidation of copper and Inconel®. However, since the volume is small and non-renewable (weld sealing), the oxide layer will remain very thin. The formation of the oxide layer can be avoided if a neutral atmosphere (e.g., with argon sweeping) is present.

[0069] It is also possible to exhaust the assembly 72 through a tube added for this purpose. Thus, a degassing tube is added at one end and the sheath is evacuated by pumping through the tube. Then, a seal weld can be performed to permanently maintain the vacuum and enable sealing and permanently sealing the tube. Such an evacuation step can also be used to check for leaks.

[0070] The stainless alloy of the sheath 79 and the connection strip 78 is selected according to the thermal stress to which the electrical conductor 70 is exposed. In particular, for a temperature range up to 900 °C, the sheath 79 and the strip 78 can be made of Inconel® 600. The conductive core 74 can have a diameter of approximately 10 millimeters. However, the cross-section can be modified according to requirements, for example, from the viewpoints of current, voltage drop, etc. Also, the conductive core 74 can be composed entirely or partially of one or more multi-strand cables, for example, composed of a multi-strand braid.

[0071] Therefore, the present invention proposes to form a core 74 composed of a copper core (or any other metal considered satisfactory from the viewpoint of electrical resistivity) protected by a sheath 79 made of stainless or refractory metal (in particular, stainless steel or stainless nickel alloy), all being welded together by TIG welding with two connection strips 78 present. Therefore, the present invention can be implemented without using the hot isostatic pressing (HIP) method to enable the assembly between the core 74, the sheath 79, and the connection strip 78.

[0072] Therefore, the present invention can advantageously reduce manufacturing costs, is easy to manufacture, and further enables direct shaping and lengthening (shaping, cutting to length, and whistle welding) at the point of use. The electrical conductor 70 can be used throughout the high-temperature area and can also be used as a partition feedthrough to provide a link between the high-temperature area and the room-temperature area.

[0073] A method for manufacturing such an electrical conductor 70 intended to be used as an electrical conductor for supplying current to an electrochemical system (such as those shown in FIGS. 1 to 4) includes, for example, the following steps. - Manufacturing the parts (core, sheath, strip) described above. - Cleaning the parts, and in particular the surfaces intended to be welded, i.e., the electrical conduction surfaces and the surfaces required to seal the electrical conductor, using a cleaning agent and / or solvent, or any other means. - Inserting the conductive core 74 into the sheath 79. - Joining the conductive core 74 to the first connection strip 78 by fillet brazing or soldering. - Joining the sheath 79 to the first connection strip 78 by TIG welding. - Joining the conductive core 74 to the second connection strip 78 by fillet brazing or soldering. - Joining the sheath 79 to the second connection strip 78 by TIG welding. - Evacuating the sheath 79 by pumping, if necessary.

[0074] In addition, the step of X-ray inspecting the welds can be performed to confirm the quality of the welds from a mechanical, electrical, and sealing perspective.

[0075] The end portion with the strip 78 is the high-temperature end portion, and the high-temperature end portion is drilled perpendicular to the axis of the sheath 79 and can be screwed onto the stack as shown in FIGS. 5 and 6.

[0076] The TIG welds are advantageously made by a person skilled in the art, inter alia, for welding between copper and Inconel® to ensure a good electrical connection and for welding between Inconel® and Inconel® to ensure a seal weld.

[0077] In the case of an electrical conductor 70 having a diameter of 12 mm made entirely of Inconel® 600 (prior art design), and in the case of an electrical conductor 70 having a diameter of 12 mm made of a sheath 79 of Inconel® 600 and a copper core 74 (design according to the invention), in Table 1 below, by comparing the resistance obtained for 1 m of the electrical conductor 70, it has been found that the present invention can reduce the electrical losses by a factor of 10 at an operating temperature of 800°C.

[0078]

Table 1

[0079] Regarding this result in Table 1 (Table 1), the resistivity of copper is 17.24·10 -9 Ω·m at low temperature (20°C) and 70·10 -9 Ω·m at 800°C. The resistivity of Inconel® 600 is 1.03·10 -6 Ω·m at low temperature (20°C) and 1.13·10 -6 Ω·m at 800°C.

[0080] Therefore, the electrical conductor 70 obtained according to the principles of the present invention is an electrical conductor suitable for the high temperature and high current of the SOEC / SOFC stack. However, there may be electrical losses in the connection strips 78, and in order to limit these losses, it is possible to modify the design of these connection strips 78.

[0081] Figures 7 to 11 relate to another embodiment of the electrical conductor 70 according to the present invention, in which embodiment the connection strips 78 have a different design, which is referred to as "high conductivity" connection strips 78 or whistles 78.

[0082] Specifically, the first connection strip 78 and the second connection strip 78 each have a conductive connection core 80 and a connection sheath 81. The conductive connection core 80 is made of a first metal material (in this case, copper, but any other metal described above is also possible), and the connection sheath 81 completely covers the connection core 80 over its entire length l, as shown in Figure 10, and is made of a second metal material (in this case, Inconel® 600, but any other metal described above is also possible). The connection sheath 81 advantageously has a thickness e of approximately 0.5 mm as seen in Figure 10. g There is. A small thickness eg Contributes considerably to reducing electrical losses.

[0083] In addition, each connection strip 78 has a tubular sleeve 82 that is inserted into the corresponding holes of the connection core 80 and the connection sheath 81 to enable attachment to the stack, as shown in Figures 10 and 11.

[0084] As shown in FIGS. 10 and 11, the resulting connection strip 78 makes it possible to reduce the electrical losses therein by replacing a portion of the second metal material with a first metal material having a good level of conductivity. In fact, it is possible to reduce the electrical losses of the whistle 78 by holding an Inconel® connection sheath 81 to protect the copper connection core 80 from oxidation. However, since such a whistle 78 is a connection point, electrical continuity across the entire connection surface is required between the connection sheath 81 and the connection core 80. For this purpose, the method for manufacturing such a whistle 78, described below, uses the hot isostatic pressing (HIP) method, which is used in the present invention only for manufacturing such a "high conductivity" whistle 78, in order to ensure welding across the entire connection surface between the connection core 80 and the connection sheath 81.

[0085] Accordingly, the electrical conductor 70 in the embodiments shown in FIGS. 7 and 8 has a better level of conductivity than that described with reference to FIGS. 5 and 6, thanks to the use of the "high conductivity" connection strip 78. Specifically, the "high conductivity" connection strip 78 can have a resistivity that is only about one tenth that of a connection strip 78 made entirely from a second metal material.

[0086] To manufacture the "high conductivity" connection strip 78, the connection core 80 can be obtained by die forging. Die forging involves shaping a raw part made from an alloy (such as aluminum, copper, titanium, nickel, etc.) by plastic deformation after heating. Also, steel die stamping is known as "stamping". Die forging is a forging operation carried out using tools called "dies", especially an upper half die and a lower half die, which are embossed with the shape of the part to be manufactured.

[0087] In addition, the connection sheath 81 can be obtained by deep drawing or assembling a plurality of parts made of a second metal material. This deep drawing technique is used to produce objects from flat metal sheets, and their shape cannot be unfolded. This technique is suitable for mass production.

[0088] Sheath 79 is a flexible sheath and, in this case, is made of, for example, XS range 321 stainless steel in Kenovel's DN16. In addition, the flexible conductive core 74 is, for example, 70 mm 2 multistrand copper.

[0089] In addition, an electrically insulating jacket is preferably added to the assembly 72, which, as described above, is formed, inter alia, from a Nefatex 1390 ceramic braided jacket (an alumina-silica sheath with a standard insulation resistance of 700 V at 1000 °C). Such an electrically insulating jacket is not shown in the examples described.

[0090] It should be noted that FIG. 9 also shows the soldering B between the connection strip 78 and the conductive core 74. The TIG weld (reference symbol P) is made between the whistle 78 and the flexible sheath 79 to ensure a seal.

[0091] Next, a method for assembling the "high conductivity" connection strip 78 or the "high conductivity" whistle includes the following steps. - Cleaning the components of the whistle 78 using, for example, a cleaning agent, a solvent, or any other suitable means. - Inserting the connection core 80 into the connection sheath 81. - Inserting a tubular sleeve 82 made of a first metal material. - A step of joining the connection sheath 81 to the tubular sleeve 82 by TIG welding, optionally, by means of additional material made, inter alia, of stainless steel, to seal the joints on each face. - A step of adding parts 86 and 87 to the connection core 80, wherein part 86 is formed from a first material and provides mechanical retention between the connection sheath 81 and the flexible sheath 79 and also provides protection against oxidation (seal continuity between 81 and 79), and part 87 is formed from a second material and provides an electrical connection between the connection core 80 and the conductive core 74. - A step of adding a sealing cap 85 formed by the closing plate 83 and the sealing tube 84, as shown in FIG. 10. - A step of joining the connection sheath 81 to the sealing cap 85 by TIG welding to seal the joint. - A step of evacuating the whistle 78, wherein a vacuum pump is connected to the tube 84 so as to generate a vacuum inside the connection sheath 81, and then a step of seal welding the tube 84 so as to seal and permanently seal the tube 84.

[0092] Thereafter, a diffusion welding cycle by hot isostatic pressing (HIP) is applied under the following operating conditions. - In particular, heating the assembly 78 formed by the connection core 80 and the connection sheath 81 to a temperature comprised between 600 °C and 1060 °C, preferably between 800 °C and 1000 °C, and in particular to a temperature of 920 °C. - Applying a pressure comprised between 500 bar and 1500 bar, preferably between 800 bar and 1200 bar, and in particular a pressure of 1020 bar, to the connection sheath 81. - Applying a pressure and temperature plateau over a period of between 30 minutes and several hours, preferably between 1 hour and 3 hours, and in particular for a period of 2 hours. - Enable the assembly to cool and depressurize.

[0093] Finally, each "high conductivity" connection strip 78 can be machined to allow for direct connection of the connection core 80, producing a whistle 78 as shown in FIG. 11.

[0094] The resulting "high conductivity" whistles 78 are then connected to the assembly 72 by low resistivity connections. In particular, the conductive core 74 and connection core 80 of each connection strip 78 can be connected by high temperature brazing or soldering. This creates a high conductivity electrical connection. The choice of filler metal can ensure connections up to a maximum operating temperature of approximately 900°C. The assembly can be carried out, for example, using commercially available soldering and brazing alloys of Castolin® 146 and the recommended 146 M flux. This soldering and brazing alloy is composed of 60% copper, 39% zinc, and 1% tin-manganese.

[0095] Then, as described above, mechanical connections and seals are obtained by TIG welding at point P over the entire periphery, preferably with the addition of a material made from a second metallic material, as shown in FIG. 8. A possible evacuation step can be carried out, and the step of X-ray inspecting the welds and brazed joints can be carried out as described above.

[0096] The present invention can be applied, as described above, to high temperature steam electrolyzers, high temperature co-electrolyzers supplied with a mixture of steam (H2O) and carbon dioxide (CO2), high temperature solid oxide fuel cells, reversible high temperature fuel cell and electrolyzer systems, "intermediate temperature" cells or electrolyzers (i.e., 400°C), or proton ceramic fuel cells or PCFCs.

[0097] The present invention can be applied to the systems described above operating at atmospheric pressure, but can also be applied to systems under pressure.

[0098] Outside the technical field of solid oxide electrochemical systems, the present invention is applicable to all fields where there is a need for electrical conduction in a high-temperature oxidation environment or under conditions that result in rapid degradation of conductive materials.

[0099] Naturally, the present invention is not limited to the exemplary embodiments just described. Various changes can be made to it by those skilled in the art.

Explanation of Reference Numerals

[0100] 10 Solid oxide cell 12 First porous conductive electrode, cathode 14 Second porous conductive electrode, anode 16 Solid oxide film (high-density electrolyte) 18 Interconnect plate 20 Stack 22 Water vapor supply section 24 Controllable valve 26 Gas collector 28 Power supply 30 Terminal 32 Terminal 52 Conduit 54 Conduit 56 Conduit 58 Conduit 60 Enclosure 62 Air inlet conduit 64 Air outlet conduit 66 Electrical conductor 68 Electrical conductor 70 Flexible electrical conductor 72 Assembly 72a First end 72b Second end 74 Conductive core 78 First connection strip, second connection strip, whistle 79 Sheath 80 Connection core 81 Connection sheath 82 Tubular sleeve 83 Closing plate 84 Sealing tube 85 Sealing cap 86 Parts 87 Parts B Soldering C Load e g Thickness I Current J Gap L Length l Length P TIG welded part

Claims

1. A flexible electrical conductor (70), - an assembly (72), - a first connection strip (78) comprising, wherein said assembly (72) - a flexible conductive core (74) made of a first metallic material, - a sheath (79) covering said conductive core (74), said sheath (79) being made of a second metallic material having an electrical resistivity higher than that of said first metallic material comprising, wherein said first connection strip (78) is at least partially formed by said second metallic material and is connected to a first end (72a) of said assembly (72). In a flexible electrical conductor (70), at said first end (72a) of said assembly (72), said sheath (79) and said first connection strip (78) are joined by TIG welding, and said conductive core (74) and said first connection strip (78) are joined by fillet brazing or soldering, characterized in that said flexible electrical conductor (70).

2. Said conductor - a second connection strip (78), at least partially formed by said second metallic material and connected to a second end (72b) of said assembly (72) having, at said second end (72b) of said assembly (72), said sheath (79) and said second connection strip (78) are joined by TIG welding, and said conductive core (74) and said second connection strip (78) are joined by fillet brazing or soldering, and the TIG welds and said sheath (79) at said two ends (72a, 72b) of said assembly (72) completely cover said conductive core (74) over its entire length (L), characterized in that the conductor according to claim 1.

3. At least one gap (J) exists between the outer surface of said conductive core (74) and the inner surface of said sheath (79) over at least a part of the length (L) of said conductive core (74), characterized in that the conductor according to claim 1 or 2.

4. The conductor according to any one of claims 1 to 3, wherein the conductive core (74) is made of copper, nickel, or silver, and / or a copper alloy, a nickel alloy, or a silver alloy.

5. The conductor according to any one of claims 1 to 4, wherein the sheath (79) is made of a stainless metal or a refractory metal, and / or a metal alloy or a refractory alloy, especially stainless steel or refractory steel.

6. The conductor according to any one of claims 1 to 5, wherein the first connection strip (78) and / or the second connection strip (78) each has a conductive connection core (80) made of the first metal material and a connection sheath (81), and the connection sheath (81) completely covers the connection core (80) over its entire length (l) and is made of the second metal material.

7. The conductor according to any one of claims 1 to 6, wherein the assembly (72) including the conductive core (74) and the sheath (79) is completely covered by an electrically insulating jacket.

8. A method for manufacturing an electrical conductor (70) according to any one of claims 1 to 7, comprising: - cleaning the surface, especially using a cleaning agent and / or a solvent; - inserting the conductive core (74) into the sheath (79); - joining the conductive core (74) to the first connection strip (78) by corner brazing or soldering; - joining the sheath (79) to the first connection strip (78) by TIG welding; - evacuating the sheath (79) by pumping, if necessary; characterized by having the above steps.

9. The electrical conductor (70) has a second connection strip (78), the second connection strip (78) is at least partially formed by the second metal material, is connected to the second end (72b) of the assembly (72), and after the step of joining the sheath (79) to the first connection strip (78) by TIG welding, the method comprises: - joining the conductive core (74) to the second connection strip (78) by corner soldering or soldering; - joining the sheath (79) to the second connection strip (78) by TIG welding The method according to claim 8, characterized by comprising the above.

10. The first connection strip (78) and / or the second connection strip (78) is formed by assembling a conductive connection core (80) and a connection sheath (81) that completely covers the connection core (80). The connection core (80) is manufactured by die forging, and the connection sheath (81) is manufactured by deep drawing or assembling a plurality of parts made of the second metal material. The method according to claim 8 or 9, characterized by this.

11. The step of assembling the first connection strip (78) and / or the second connection strip (78) includes at least - cleaning the constituent elements of the connection strip (78) using, inter alia, a cleaning agent or solvent; - inserting the connection core (80) into the connection sheath (81); - evacuating the connection strip (78); - applying a diffusion welding cycle by hot isostatic pressing (HIP) The method according to claim 10, characterized by comprising the above.

12. The diffusion welding cycle by hot isostatic pressing (HIP) has the following operating conditions: - heating the assembly formed by the connection core (80) and the connection sheath (81) to a temperature between 600°C and 1060°C, preferably between 800°C and 1000°C, especially to a temperature of 920°C; - applying a pressure between 500 bar and 1500 bar, preferably between 800 bar and 1200 bar, especially a pressure of 1020 bar, to the connection sheath (81); - applying a pressure and temperature plateau for a period between 30 minutes and several hours, preferably between 1 hour and 3 hours, especially for a period of 2 hours; - allowing the assembly to cool and depressurizing The method according to claim 11, characterized by being implemented by the above.

13. The method according to any one of claims 10 to 12, characterized in that the conductive core (74) and the connection core (80) of the first connection strip (78) and / or the second connection strip (78) are connected together by a method of high-temperature brazing or soldering.

14. Use of at least one electrical conductor (70) according to any one of claims 1 to 7 as an electrical conductor of an electrochemical system, wherein the electrochemical system comprises: - an enclosure (60) for the circulation of air in a volume delimited thereby; - an electrochemical device housed in the enclosure (60) and the electrochemical device comprises: - a solid oxide stack (20) of the high-temperature SOEC / SOFC type of basic electrochemical cells (10) each containing an electrolyte (16), the electrolyte (16) being inserted between a cathode (12) and an anode (14) and being connected in series between two electrical terminals (30, 32); - at least one electrical conductor (70) connected to at least one of the two electrical terminals (30, 32) and use.

15. An electrochemical system, comprising: - an enclosure (60) for the circulation of air in a volume delimited thereby; - an electrochemical device housed in the enclosure (60) and the electrochemical device comprises: - a solid oxide stack (20) of the high-temperature SOEC / SOFC type of basic electrochemical cells (10) each containing an electrolyte (16), the electrolyte (16) being inserted between a cathode (12) and an anode (14) and being connected in series between two electrical terminals (30, 32); - at least one electrical conductor (70) according to any one of claims 1 to 7 connected to at least one of the two electrical terminals (30, 32) and an electrochemical system.

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