Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0232—Metals or alloys
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/60—Constructional parts of cells
  • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/66—Current collectors
  • H01G11/70—Current collectors characterised by their structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
  • H01M8/0245—Composites in the form of layered or coated products
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/13—Energy storage using capacitors
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the invention concerns a new current collector for electrochemical cells, particularly useful for electrolytic cells, fuel cells or other types of cells separated into at least two compartments, wherein the separator is an ion exchange membrane or any other type of semi-permeable diaphragm characterised by a limited mechanical resistance.
• the current collector of the invention is useful for ensuring the electrical continuity between two conductive surfaces separated by a gap, which in the case of an electrochemical cell is typically exploited for feeding reactants, discharging products, circulating electrolytes or for the thermo-regulation of fluids, or for a combination of two or more of these functions.
• deformable elastic elements are well known to the experts of the art.
• Typical examples of deformable elastic collector are metal foams and reticulated porous materials in general, as described for example in US 4,657,650.
• Another example, of larger industrial diffusion, is a sandwiched metal wire structure, as described for example in US 4,693,797.
• Deformable structures of this type have the advantage of being capable of transmitting electric current between two conductive surfaces partially compensating for their deviations from planarity, thanks to the different local compression they may undergo. It is therefore advantageous resorting to the same both in terms of mechanical as well as electrical characteristics, to improve the efficiency of the cells where they are utilised.
• the efficiency of removal/transmission of electric current increases as the contact pressure exerted by the collector onto the conductive surfaces increases. Further, said pressure must be preferably exerted making the collector work under an elastic regimen, to compensate for possible dimensional variations due to expansions, vibrations or other phenomena which may vary the geometry of the system in a microscopic range.
• the pressure exerted by the collector however should not exceed, in many practical applications, a limit threshold to avoid mechanical damages.
• a limit threshold to avoid mechanical damages.
• electrochemical cells where one or more compartments use a semi-permeable diaphragm, for example an ion exchange membrane, said separation elements have a very limited mechanical resistance and resist to mechanical loads only below a certain threshold.
• the problem of mechanical resistance however does not affect only the separators, as it is known that electrochemical cells can be provided with deformable electrodes, for example very thin metal meshes, or gas diffusion electrodes comprising carbon materials with limited resilience, such as carbon paper or carbon cloth, which have a scarcely reliable behaviour with loads exceeding for example 0.35-0.4 kg/cm 2 .
• the mattress described in US 4,693,797 has found a remarkable industrial application in view of the fact that, if used under optimum conditions, it grants a suitable contact pressure (indicatively 0.2- 0.35 kg/cm 2 ) also when using ion exchange membranes or gas diffusion electrodes or both said components.
• the contact load exerted by this type of collector is maintained by the deformation caused by the squeezing when clamping the cell; that is the mattress is inserted in an uncompressed condition, thus with the maximum expansion, and then squeezed when clamping the cell, whereby its thickness is decreased even by 50%.
• a mattress with a thickness of 10 mm when uncompressed may reach, under operation, a thickness of 4 or 5 millimeters.
• an object of the present invention to provide an electrochemical cell, for example an electrolytic cell or a fuel cell equipped with a current collector overcoming the inconveniences of the prior art.
• the invention consists of a current collector obtained by sandwiching compressible and resilient layers, each one formed by an arrangement of metal wires.
• the main characteristic of the current collector is its capability of imparting a suitable load for applications in electrochemical cells, indicatively comprised between 0.15 and 0.40 kg/cm 2 , in a wide range of compressions, equal to at least 10% of the uncompressed thickness of the collector itself. In a preferred embodiment, said range is comprised between 20 and 60% of the compression of the collector with respect to its uncompressed state.
• a typical collector having a thickness, before compression, of 10 millimeters may be compressed upon clamping of the cell with tolerances up to about more or less 1 millimeter without risking ruptures of delicate components or insufficient contact, which result cannot be obtained with the collectors of the prior art.
• the ideal operation thickness is comprised between 3 and 6 millimeters.
• the collector of the invention is preferably made by sandwiches of metal wires having a diameter indicatively comprised between 0.1 and 0.35 millimeters; the thickness of the collector resulting from said sandwich is preferably comprised between 5 and 15 millimeters.
• the preferred materials for producing the collector of the invention are all the metallic materials, in particular valve metals, for example titanium and alloys thereof, for the anodic collector, and nickel or alloys thereof for the cathodic collectors.
• the collector of the invention my also be a bipolar collector, for example provided with nickel layers facing the cathodic surface and titanium or other valve metal layers facing the anodic surface.
• it is possible to further coat the collector with materials providing protection against corrosion for example the cathodic collectors with a silver coating and the anodic collectors with a coating of noble metals or alloys thereof or their oxides.
• the most external layer be generally planar in order to distribute the contact as uniformly as possible onto the surface to be contacted, which may be, in the case of electrochemical cells, metal surfaces (for examples electrodes or metal partition sheets) but also surfaces provided with a remarkably lower planar conductivity, (for example gas diffusion electrodes made of carbon material).
• the planar layers of interwoven wires are affected by the inconvenient, typical of the prior art, of a non sufficient deformability to grant an adequate compression load for a sufficiently broad compression range. It is therefore preferable that the collector comprise internal layers of wires having a permanent undulation according to a geometry easily achieved through automatic working of the product.
• the best way to put the invention into practice is providing at least two of these internal layers, sandwiched in order to have the more offset positioning of the undulation direction, for example the direction of the undulations of adjacent layers may be about 90°.
• the various layers of the collectors are held together by a rigid perimetral frame which presents the further advantage of providing the object with a non deformable geometry with respect to the plane.
• the collector may be easily applied into the complex arrangements made of several cells, for example in conventional electrolysers or fuel cell stacks, made of filter- press arrangements of elementary cells, even when an automated assembling
• Figure 1 shows an electrochemical cells containing the collector of the invention.
• Figure 2 shows a filter-press arrangement of electrochemical cells containing the collector of the invention.
• Figure 3 shows a preferred embodiment of the collector of the invention.
• Figure 4 shows the load curves relating to the collector of the invention
• Figure 1 shows a generic electrochemical cell (1) divided by a membrane or
• the cell may generically be an electrolysis cell or a fuel cell or other type of electrochemical reactor.
• the electrodes whereon the anodic and cathodic reactions take place are indicated by (4).
• the electrodes (4) may be any type of electrode generically known for electrochemical applications, for example metal sheets optionally activated by electrocatalytic coatings, gas diffusion electrodes obtained on porous surfaces such as carbon cloth or graphite, sinterized metals, etc.
• the perimetral gaskets (5) are also illustrated, but as it will be obvious for an expert of the art, other hydraulic sealing systems are likewise possible.
• the electric contact transmission between the plate (3) and the adjacent electrode (4) is therefore preferably effected by a compressible resilient material, preferably operating in an elastic mode.
• This material in the case of figure 1, is the current collector (6) of the invention.
• Figure 2 shows the collector of the invention used in similar cells as those of figure 1 in a filter-press arrangement, in the specific bipolar case.
• Figure 3 shows a preferred embodiment of the multi-layered current collector (6), according to the invention.
• the reference numeral (7) indicates the two external layers, and (8) the two internal layers; it is quite evident how the current collector (6) may be produced also with a different number of internal layers.
• the external layers (7) obtained by interwoven metal wires, preferably with a diameter comprised between 0.1 and 0.35 millimeters, generally have a planar profile.
• the external layers (8) are substantially the same as the external ones, likewise made by interwoven metal wires (for simplicity sake not shown in detail in the figure), apart from the fact that they are undulated, by means of a very simple mechanical working, in order to form a regular arrangement of protrusions (9) and depressions (10), preferably regularly spaced apart.
• the direction of one undulation should be off-set with respect to the underlying one; in the case of the two internal layers (8) of figure 3, the undulations are offset by 90°. In this manner, it is nearly completely avoided a reciprocal penetration of two internal layers (8). It has been found that arrangements of this type exhibit extremely gradual load curves as a function of the compression with respect to prior art current collectors, so that a surprisingly broad range is obtained, in terms of compression and thus of operating thickness, whereby the applied mechanical load is sufficient to permit a good electrical contact without damaging the delicate components of the cell.
• Figure 4 shows the load curve (12) of a nickel collector obtained by two external mono-layers (7) made of a wire with a diameter of 0.27 mm, not undulated, and two internal double layers (8) made of a wire with a diameter of 0.16 mm, undulated with a pitch of 8.6 mm, put on top one of the other in order to off-set the undulations by 90° and avoid reciprocal penetrations.
• the four layers have been inserted in a perimetral frame in the form of a casing, not shown in the figures.
• the overall uncompressed thickness was about 10 millimeters.
• the useful compressed thickness range in the elastic mode that is when the resulting load is comprised between 0.15 and 0.40 kg/cm 2 , varies between 3.6 and 5.4 millimeters, with a comprised between 46 and 64% with respect to the uncompressed thickness. It is a wide range, which easily complies with the tolerances of a conventional cell structure construction.
• the load curve (11) regards a mattress, 6 millimeters thick, made by the same nickel wire, according to the teachings of US 4,693,797: it is readily apparent that the useful operating range is extremely reduced, largely below 10% of the uncompressed thickness.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Power Engineering (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Manufacturing & Machinery (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Composite Materials (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Fuel Cell (AREA)
• Cell Electrode Carriers And Collectors (AREA)
• Inert Electrodes (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electric Double-Layer Capacitors Or The Like (AREA)

Priority Applications (9)

Applications Claiming Priority (2)

Publications (2)

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• 2001
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• 2002
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  • 2002-12-03 WO PCT/EP2002/013677 patent/WO2003048422A2/en not_active Ceased
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