How to make a bipolar plate

Abstract

The present invention relates to a method for producing a bipolar plate composition. The present invention also relates to a method for producing a bipolar plate by injection, extrusion or compression starting from said composition, and to the bipolar plates obtained by these methods.

Description

[Technical field]

[0001] The present invention relates to a method for producing a bipolar plate composition. The present invention also relates to a method for producing a bipolar plate by injection, extrusion or compression starting from said composition, and to the bipolar plates obtained by these methods. [Background technology]

[0002] Bipolar plates are used in fuel cells, electrolysers and redox flow batteries. They can be made from a variety of materials, including metal bipolar plates, graphite plates, and carbon-polymer composite plates.

[0003] The principle of bipolar plates based on organic composites is based on the use of conductive fillers (carbon, graphite, etc.) dispersed in a thermoplastic or thermosetting polymer. The fillers provide the bipolar plate with the electrical conductivity necessary to collect the current, while the polymer matrix provides sufficient mechanical strength necessary for the assembly of the various elements.

[0004] Carbon-polymer composite bipolar plates exhibit advantageous properties: high electrical conductivity, good corrosion resistance, good performance qualities at high temperatures and good mechanical properties, as well as relatively low manufacturing costs. These composite bipolar plates use thermosetting or thermoplastic polymers as a matrix for carbon-based fillers selected from graphite, carbon fibers, carbon black, or carbon nanotubes. The electrical performance of the composite bipolar plates is mainly determined by the carbon-based fillers, but the material of the polymer matrix also influences the electrical behavior of the composite.

[0005] Thermosetting polymer-graphite composites are the preferred material for the manufacture of bipolar plates. However, composites based on thermoplastic polymers, especially thermoplastics stable at high temperatures, are already used for the manufacture of bipolar plates due to their ability to be injection molded or extruded, and are more suitable for automated manufacturing. Such composites have been prepared using polyphenylene sulfide (PPS) or polyethersulfone (PES) containing graphite powder, as reported by Radhakrishnan, S. et al. in the publication: "High-temperature, polymer-graphite hybrid composites for bipolar plates: Effect of processing conditions on electrical properties", Journal of Power Sources, 2006, Vol. 163, pages 702-707.

[0006] The publication by Mighri F. et al., “Electrically conductive thermoplastic blends for injection and compression molding of bipolar plates in the fuel cell application”, Polymer Engineering and Science, 2004, Vol. 44, No. 9, describes bipolar plates manufactured by compression and injection processes starting from graphite, carbon black and polypropylene or polyphenylene sulfide.

[0007] The main properties desired for a bipolar plate for a fuel cell are high electronic and thermal conductivity, good mechanical properties such as bending properties, and high gas barrier properties.

[0008] A need exists to provide a method for producing a composition for bipolar plates, which composition exhibits a good compromise between these properties, and which is compatible with manufacturing processes such as injection, thermocompression, or extrusion. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Radhakrishnan, S. et al., "High-temperature, polymer-graphite hybrid composites for bipolar plates: Effect of processing conditions on electrical properties", Journal of Power Sources, 2006, Vol. 163, pages 702-707 [Non-Patent Document 2] Mighri F. et al., “Electrically conductive thermoplastic blends for injection and compression molding of bipolar plates in the fuel cell application”, Polymer Engineering and Science, 2004, Vol. 44, No. 9 Summary of the Invention [Means for solving the problem]

[0010] According to a first aspect, the present invention relates to a method for producing a composition for a bipolar plate, comprising the following steps: Providing a composite mixture based on at least one carbon-based conductive filler and a polymer; incorporating graphite and a polymer binder into said composite mixture; The present invention relates to a method comprising the steps of:

[0011] Characteristically, the composite mixture originates from recycling lithium ion batteries.

[0012] In one embodiment, recycling of lithium ion batteries is carried out by a method selected from physical separation, pyrometallurgy, hydrometallurgy, or a combination thereof.

[0013] Preferably, the various components of the cell (cathode / anode / separator) are disassembled before being crushed.

[0014] According to one embodiment, the at least one carbon-based conductive filler is graphite, used as an active filler in the anode of a lithium-ion battery.

[0015] According to one embodiment, the carbon-based conductive filler is a mixture of graphite and another carbon-based conductive filler such as carbon black or carbon nanotubes present in the anode or cathode formulation of a Li-ion battery.

[0016] According to one embodiment, the polymers involved in the composition of the composite mixture are fluoropolymers, water-soluble thickening polymers (such as, for example, carboxymethylcellulose), polyolefin elastomers (such as, for example, styrene-butadiene rubber), acrylics (such as, for example, carboxylated acrylic polymers), or mixtures of several of these components, including mixtures of different fluoropolymers.

[0017] According to another aspect, the present invention provides a method for manufacturing a bipolar plate, comprising the steps of: preparing a composition according to the method described above, and subjecting the composition to injection molding. The present invention relates to a method comprising the steps of:

[0018] According to another aspect, the present invention provides a method for manufacturing a bipolar plate, comprising the steps of: preparing a composition according to the method described above, and subjecting the composition to compression molding. The present invention relates to a method comprising the steps of:

[0019] According to another aspect, the present invention provides a method for manufacturing a bipolar plate, comprising the steps of: preparing a composition according to the method described above, and subjecting said composition to a continuous extrusion process. The present invention relates to a method comprising the steps of:

[0020] The present invention further relates to a bipolar plate obtainable by the above process or comprising the above composition.

[0021] The present invention makes it possible to overcome the drawbacks of the state of the art, more particularly, it provides a method for producing a composition that can be easily used for the manufacture of bipolar plates.

[0022] The advantage of this approach using composite mixtures resulting from recycling of lithium-ion batteries is that it benefits from the good dispersion of the polymer binder in the recycled carbon-based conductive filler / polymer mixture, which allows to improve the dispersion of the carbon-based filler in the bipolar plates, thereby improving the mechanical strength, gas barrier properties and electrical conductivity.

[0023] When producing bipolar plates by a method (injection) that requires a low viscosity polymer-graphite mixture, another advantage results from the difference in particle size between the graphite used for the bipolar plates and the graphite used for the anodes of Li-ion batteries. The first (which typically has a volume mean diameter (Dv50) in the range of 50-150 μm) is larger than the second (which typically has a Dv50 around 20 μm and less than 40 μm). This difference allows for an improvement in the lateral electrical conductivity while limiting the high viscosity of the mixture, by the smaller graphite particles being inserted into the gaps left by the larger graphite particles, resulting in a good implementation of the bipolar plates in the mixture.

[0024] Furthermore, the fact that the recycled graphite has experienced a first life in the battery has made it possible to cover it with a solid electrolyte interface (SEI). This SEI layer is composed of inorganic elements (LiF, Li2O2, Li2CO3) and polymer fractions resulting from the decomposition of the electrolyte's solvent. As a result, this SEI layer has better flexibility and crack resistance, endowing the recycled graphite with the ability to improve the mechanical properties of the bipolar plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention is described in detail below.

[0026] The percentages given in this text are percentages by weight.

[0027] The subject of the present invention is the use of a conductive filler / polymer mixture resulting from the recycling of lithium-ion batteries for the manufacture of bipolar plates.

[0028] According to a first aspect, the present invention relates to a method for producing a composition for a bipolar plate, comprising the following steps: Providing a composite mixture (component A) based on at least one carbon-based conductive filler and a polymer; incorporating graphite (component B) and a polymer binder (component C) into said composite mixture; Including, The composite mixture originates from recycling lithium ion batteries.

[0029] According to various implementations, the method includes the following features, when appropriately combined:

[0030] Ingredient A According to one embodiment, the composite mixture is prepared by a method for recycling lithium ion batteries selected from pyrometallurgy, hydrometallurgy, physical separation based on material properties such as particle size, density, magnetic or electrical properties such as flotation, or a combination thereof.

[0031] The batteries to be recycled are dismantled to recover the polymers, carbonaceous fillers and precious metals of the electrodes. Advantageously, the batteries to be recycled are batteries with NMC (nickel-manganese-cobalt) or NCA (nickel-cobalt-aluminum) cathodes and graphite anodes.

[0032] According to one embodiment, the components of the lithium ion battery: cathode / separator / anode are physically separated, the cathode and anode are crushed and then a hydrometallurgical step is carried out to selectively recover the materials, in particular the cobalt and nickel. The hydrometallurgical residue consists of carbon-based conductive fillers and polymers such as PVDF, which are resistant to the leaching and reprecipitation steps and can therefore be reused according to the invention.

[0033] According to another embodiment, the components of the lithium ion battery: cathode / separator / anode are physically separated, the cathode and anode are crushed and then subjected to flotation or air jet sieving, allowing the recovery of the carbon-based conductive filler and the low density, hydrophobic polymer binder, and thus separation from the more dense residue of the active metal fillers and metal current collectors. The recycling process results in the recovery of the carbon-based filler in association with the thermoplastic polymer, i.e. the binder of the electrodes.

[0034] Depending on the appearance of the recycled carbon-based conductive filler / polymer composite mixture (flakes, coarse powder), the method according to the invention can include a preliminary step consisting of grinding, redispersing and sieving said mixture in order to obtain a powder with a particle size of up to 500 μm, preferably less than 200 μm.

[0035] According to one embodiment, if a physical disassembly with cathode / separator / anode separation has been carried out beforehand, the recombination of the carbon-based conductive filler / polymer powders resulting from the cathode and anode is carried out by a dry powder mixing process with items of equipment such as ribbon or paddle mixers. It is possible to carry out this recombination in the molten state by an extrusion process that makes it possible to obtain fragile scales or granules that must then be reground.

[0036] According to one embodiment, the cells or modules are crushed without carrying out a prior dismantling. It is then possible to recover the mixture of carbon-based conductive filler and polymer after one or more physical separation steps as described above, or as a hydrometallurgical process residue.

[0037] According to one embodiment, a pyrometallurgical step is carried out to remove any polymers present, after which only the carbon-based conductive filler is recovered for use according to the present invention.

[0038] According to one embodiment, the at least one carbon-based conductive filler is graphite, used as an active filler in the anode of a lithium-ion battery.

[0039] According to one embodiment, the carbon-based conductive filler is a mixture of graphite and another carbon-based conductive filler, such as carbon black, carbon nanotubes, or carbon fibers (e.g., vapor-grown carbon fibers or VGCF) present in the anode or cathode formulation of a Li-ion battery.

[0040] According to one embodiment, the polymers involved in the composition of the composite mixture are fluoropolymers (such as, for example, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE)), water-soluble thickening polymers (such as, for example, carboxymethylcellulose), polyolefin elastomers (such as, for example, styrene-butadiene rubber), acrylic resins, or mixtures of several of these components, including mixtures of different fluoropolymers.

[0041] According to one embodiment, the fluoropolymer present in component A contains in its chain a vinyl group that can open to polymerize and contains, directly bonded to this vinyl group, at least one monomer selected from compounds containing at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

[0042] According to one embodiment, the monomer is selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene; perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether or perfluoro(propyl vinyl) ether; perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole; products of the formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; products of the formula CF2=CFOCF2CF2SO2F; products of the formula F(CF2) n Products of the formula CH2OCF=CF2, where n is 1, 2, 3, 4 or 5; products of the formula R1CH2OCF=CF2, where R1 is hydrogen or F(CF2) m where m is 1, 2, 3 or 4; products of the formula R2OCF=CH2, where R2 is F(CF2) p where p is 1, 2, 3 or 4; perfluorobutylethylene; 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene.

[0043] The fluoropolymer may be a homopolymer or a copolymer. The copolymer may also contain non-fluorinated monomers such as ethylene.

[0044] According to one embodiment, the fluoropolymer is a polymer comprising units deriving from vinylidene fluoride, preferably chosen from polyvinylidene fluoride homopolymers and copolymers comprising vinylidene fluoride units and units deriving from at least one other comonomer capable of copolymerizing with vinylidene fluoride.

[0045] According to one embodiment, the fluoropolymer present in component A is a vinylidene fluoride homopolymer.

[0046] According to one embodiment, the fluoropolymer is a copolymer comprising vinylidene fluoride (VDF) units and units resulting from one or more monomers. These other monomers are selected from the following list: vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene; 1,2-difluoroethylene, tetrafluoroethylene; hexafluoropropylene; perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether or perfluoro(propyl vinyl) ether; perfluoro(1,3-dioxole; perfluoro(2,2-dimethyl-1,3-dioxole); products of formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; products of formula CF2=CFOCF2CF2SO2F; products of formula F(CF2) n Products of formula R'CH2OCF=CF2, where R' is hydrogen or F(CF2) z where z is 1, 2, 3 or 4; products of formula R"OCF=CH2, where R" is F(CF2) z where z is 1, 2, 3 or 4; perfluorobutylethylene; 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene.

[0047] Among these VDF comonomers, hexafluoropropylene is preferred. The VDF copolymer may also contain non-fluorinated monomers such as ethylene.

[0048] In the VDF copolymer, the content by weight of VDF units is at least 50%, preferably at least 60%, more preferably more than 70% and advantageously more than 80%.

[0049] According to one embodiment, the fluoropolymer is fully or partially functionalized, which makes it possible to improve adhesion to metals, in which case the fluoropolymer comprises monomer units carrying at least one carboxylic acid or hydroxyl functional group.

[0050] According to one embodiment, the functional groups carry a carboxylic acid function, in which case the monomer unit carrying at least one carboxylic acid function is chosen from acrylic acid, methacrylic acid and acryloyloxypropyl succinate.

[0051] According to one embodiment, the unit carrying a carboxylic acid function further comprises a heteroatom selected from oxygen, sulfur, nitrogen and phosphorus.

[0052] According to one embodiment, the functional group carries a hydroxyl function, in which case the monomer unit carrying at least one carboxylic acid function is chosen from hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and hydroxyethylhexyl (meth)acrylate.

[0053] According to one embodiment, the functional group content of the fluoropolymer is at least 0.01 mol %, preferably at least 0.1 mol %, and up to 15 mol %, preferably up to 10 mol %.

[0054] The fluoropolymer present in component A may be a mixture of one or more of the above polymers, such as a mixture of a PVDF homopolymer and at least one VDF copolymer, a mixture of at least two VDF copolymers, a mixture of a functionalized PVDF and a PVDF homopolymer, or a mixture of a functionalized PVDF and a VDF copolymer.

[0055] According to a preferred embodiment, component A can also contain silicon, preferably coming from the recycling of the anodes.

[0056] According to one embodiment, the recycled carbon-based conductive filler / polymer mixture has the following composition by weight: 60%~100% graphite, 0% to 20% silicon 0%~10% water-soluble thickener, 0%~10% polyolefin elastomer, 0%~10% acrylic resin, 0%~10% fluoropolymer, 0% to 40% polyolefin (such as polyethylene and / or polypropylene), 0% to 10% of a second carbon-based conductive filler, and the sum of all these percentages equals 100%.

[0057] According to one embodiment, the recycled carbon-based conductive filler / polymer mixture has the following composition by weight: 70%~100% graphite, 0%~10% water-soluble thickener, 0%~10% polyolefin elastomer, 0%~10% acrylic resin, 0%~10% fluoropolymer, 0% to 40% polyolefin (such as polyethylene and / or polypropylene), 0% to 10% of a second carbon-based conductive filler, and the sum of all these percentages equals 100%.

[0058] According to one embodiment, the weight ratio of the water-soluble thickener to the polyolefin elastomer ranges from 1:9 to 9:1, preferably 1:4.

[0059] Advantageously, the graphite present in component A exhibits a particle size, expressed as volume-average diameter (Dv50), ranging from 1 to 40 μm, preferentially from 5 to 30 μm. Dv50 is the particle size at the 50th percentile of the cumulative particle size distribution. This parameter can be measured by laser particle size analysis.

[0060] Preferably, component A comprises graphite having a particle size, expressed as volume average diameter (Dv50), smaller than the volume average diameter (Dv50) of the graphite constituting component B described below.

[0061] Component B The second component of the bipolar plate composition according to the invention is graphite. It is the main component by weight of the composition, being present at more than 50%. Advantageously, the graphite constituting component B has a volume average diameter (Dv50) ranging from 50 to 500 μm, preferentially from 75 to 150 μm.

[0062] Component C The third component of the bipolar plate composition according to the invention is a polymer acting as a binder, which may be a polyolefin (e.g. polyethylene or polypropylene), a fluoropolymer (PVDF), a polyphenylsulfone, a polyethersulfone, a phenolic resin, a vinyl ester resin, an epoxy resin or a liquid crystal polymer.

[0063] According to one embodiment, the fluoropolymer present in component C contains in its chain a vinyl group that can open to polymerize and contains at least one monomer selected from compounds that contain at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group directly bonded to this vinyl group.

[0064] According to one embodiment, the monomer may be vinylidene fluoride.

[0065] The fluoropolymer may be a homopolymer or a copolymer. The copolymer may also contain non-fluorinated monomers such as ethylene.

[0066] According to one embodiment, the fluoropolymer is a polymer comprising units deriving from vinylidene fluoride, preferably chosen from polyvinylidene fluoride homopolymers and copolymers comprising vinylidene fluoride units and units deriving from at least one other comonomer capable of copolymerizing with vinylidene fluoride.

[0067] According to one embodiment, the fluoropolymer present in component C is a vinylidene fluoride homopolymer.

[0068] According to one embodiment, the fluoropolymer is a copolymer comprising vinylidene fluoride (VDF) units and units resulting from one or more monomers. These other monomers are selected from the following list: vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene; 1,2-difluoroethylene, tetrafluoroethylene; hexafluoropropylene; perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether or perfluoro(propyl vinyl) ether; perfluoro(1,3-dioxole; perfluoro(2,2-dimethyl-1,3-dioxole); products of formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; products of formula CF2=CFOCF2CF2SO2F; products of formula F(CF2) n Products of formula R'CH2OCF=CF2, where R' is hydrogen or F(CF2) z where z is 1, 2, 3 or 4; products of formula R"OCF=CH2, where R" is F(CF2) z where z is 1, 2, 3 or 4; perfluorobutylethylene; 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene.

[0069] Among these VDF comonomers, hexafluoropropylene is preferred. The VDF copolymer may also contain non-fluorinated monomers such as ethylene.

[0070] In the VDF copolymer, the content by weight of VDF units is at least 50%, preferably at least 60%, more preferably more than 70% and advantageously more than 80%.

[0071] According to one embodiment, the fluoropolymer is fully or partially functionalized, which allows to improve adhesion to metals, in which case the fluoropolymer comprises monomer units carrying at least one carboxylic acid or carboxylic anhydride functional group.

[0072] The functional groups are introduced onto the fluoropolymer by chemical reaction capable of grafting or copolymerizing the fluoromonomer with a monomer carrying at least one -COOH or carboxylic anhydride group and a vinyl functional group capable of copolymerizing with the fluoromonomer, according to techniques well known to those skilled in the art.

[0073] According to one embodiment, as polar monomers carrying carboxylic acid functions, unsaturated mono- and dicarboxylic acids having 2 to 20 carbon atoms, in particular 4 to 10 carbon atoms, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, allylsuccinic acid, cyclohex-4-ene-1,2-dicarboxylic acid, 4-methylcyclohex-4-ene-1,2-dicarboxylic acid, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, x-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid and undecylenic acid, as well as their anhydrides, are selected.

[0074] According to one embodiment, the unit carrying a carboxylic acid function further comprises a heteroatom selected from oxygen, sulfur, nitrogen and phosphorus.

[0075] According to one embodiment, the functional group content of the fluoropolymer is at least 0.01 mol %, preferably at least 0.1 mol %, and up to 15 mol %, preferably up to 10 mol %.

[0076] The fluoropolymer present in component C may be a mixture of one or more of the polymers mentioned above, for example a mixture of a PVDF homopolymer and at least one VDF copolymer, or a mixture of at least two VDF copolymers.

[0077] According to one embodiment, the bipolar plate composition by weight used in the method according to the invention comprises: Graphite (component B): 50%~85%, Carbon-based conductive filler + polymer mixture (component A) resulting from recycling of lithium-ion batteries: 1%-50%, preferentially 10-25%, Polymer binder (component C): 5%-40%, preferentially 10-20%, The sum of these percentages equals 100%.

[0078] method According to a first aspect, the present invention relates to a method for producing a composition as defined above, comprising the following steps: Providing a composite mixture (component A) based on at least one carbon-based conductive filler and a polymer; incorporating graphite (component B) and a polymer binder (component C) into said composite mixture; Including, The composite mixture originates from recycling lithium ion batteries.

[0079] The process according to the invention comprises a step of mixing component A in the molten state with components C and B. This step makes it possible to compound a homogeneous mixture.

[0080] According to one embodiment, the powders are mixed dry.

[0081] According to one embodiment, the mixing step is carried out in the melt state by extrusion, for example using a kneader or a twin screw extruder.

[0082] The present invention also relates to a bipolar plate composition produced by the above method.

[0083] Bipolar Plates The present invention also relates to a bipolar plate comprising the above composition in the form of weak aggregates. A bipolar plate is a plate that separates the cells of fuel cells, electrolysers and redox flow batteries. Generally, it has a parallelepiped shape with a thickness of a few millimeters (typically 0.2 to 6 mm) and is provided on each side with a network of channels for circulating gases and fluids. Its function is to supply the fuel cell with gaseous fuel, to evacuate the reaction products and to collect the electric current generated by the cell.

[0084] According to another aspect, the present invention provides a method for manufacturing a bipolar plate, comprising the steps of: preparing a composition according to the method described above, and subjecting the composition to injection molding. The present invention relates to a method comprising the steps of:

[0085] Preferably, the bipolar plate composition is subjected to injection molding in powder form.

[0086] The method according to the invention may further comprise the auxiliary step of grinding this powder, for example using a disc mill.

[0087] The compositions of the invention are particularly well suited for the manufacture of composite bipolar plates by the injection molding process. The injection molding process consists of several stages. First, the granules or powder are introduced into the extruder through a feed hopper. Once introduced, the material is transported in a barrel where it is simultaneously heated, sheared and conveyed towards the die by the extrusion screw. The material is momentarily held in the barrel and pressurized before the injection stage. Once the appropriate pressure is reached, the material is injected into a die having the shape and dimensions of the desired final object, and the temperature of the die is adjusted. The duration of the cycle depends on the size of the part and the solidification time of the polymer. Maintaining the material under pressure after being injected into the die limits deformation and shrinkage after removal from the die. To eject the part, the parts of the die are separated, the core is retracted and the ejector is pushed to remove the part from the die surface.

[0088] The injection process has many parameters, such as the temperature of the material during the plasticization stage, the injection speed, the injection pressure of the material, the retention time and pressure in the mold, and the temperature of the mold.

[0089] For injection of the composite bipolar plate of the present invention, the temperature profile applied along the extrusion screw can vary from 100°C to 280°C from the feed zone to the injection head. The temperature of the mold can range from ambient to 280°C. Several processes for cooling the mold can be used. The material can be injected into the mold maintained at a temperature between the melting point and the glass transition temperature of the semi-crystalline polymer.

[0090] Furthermore, there are injection processes in which the temperature of the mold varies during the injection cycle. In this type of process, the material is first injected entirely into a mold, the temperature of which is higher than the melting point of the semi-crystalline thermoplastic polymer. This stage facilitates the filling of the mold. The mold is then cooled to a temperature between the melting point and the glass transition temperature of the semi-crystalline polymer in order to facilitate crystallization. Commercial versions of these variable mold temperature processes exist. For example, Roctool, Variotherm and Variomelt technologies can be mentioned.

[0091] Other injection parameters such as the injection speed of the material, the injection pressure, or the retention time and pressure within the mold depend on the shape of the mold, its dimensions, or the size and location of the gates.

[0092] According to another aspect, the present invention provides a method for manufacturing a bipolar plate, comprising the steps of: preparing a composition according to the method described above, and subjecting the composition to compression molding. The present invention relates to a method comprising the steps of:

[0093] Preferably, the bipolar plate composition is subjected to compression molding in powder form.

[0094] The method according to the invention may further comprise the step of grinding the powder, for example using a disc mill.

[0095] The compression moulding of the composition intended to manufacture the bipolar plates can be carried out by introducing said composition into a mould, for example a stainless steel mould, which is then closed and heated to a temperature ranging from 200° C. to 350° C., preferably from 250° C. to 300° C. A compression force of 300t to 800t, preferably from 400t to 600t, is then applied over a period of 100000 to 150000 mm 2 Typically, the size of the mold is 130,000 mm. 2 When a compressive force of 500t is applied, the size of the mold is 44000mm 2 A compressive force of 300t is applied when the temperature is 50° C. to 120° C., preferably 60° C. to 100° C., and the plate is removed from the mold.

[0096] According to another aspect, the present invention provides a method for manufacturing a bipolar plate, comprising the steps of: preparing a composition according to the method described above, and subjecting said composition to a continuous extrusion process. The present invention relates to a method comprising the steps of:

[0097] The composition is introduced into a single or twin screw type extruder with a flat die in order to obtain a continuous plate which is subsequently etched.

[0098] The invention further relates to a bipolar plate obtainable by the above method.

[0099] Advantageously, the bipolar plate exhibits at least one of the following characteristics, and preferably all of these characteristics: Surface resistivity less than 0.01ohm.cm; ·Volume resistivity less than 0.03ohm.cm; Thermal conductivity of 10 W / m / K or higher; 25N / mm2 More than flexural strength; 25N / mm 2 More than compressive strength.

[0100] The bending strength is measured according to the standard DIN EN ISO 178. The compressive strength is measured according to the standard ISO 604. The thermal conductivity is measured according to the laser flash technique according to the standard DIN EN ISO 821. The surface resistivity is measured by the four-probe method on ground samples with a thickness of 4 mm. The volume resistivity is measured with a two-electrode device at a resistance of 1 N / mm on a surface sample with a diameter of 13 mm and a thickness of 2 mm. 2 The contact pressure is measured.

[0101] According to certain embodiments, the bipolar plate exhibits a surface resistivity of 0.008 ohm.cm or less, or 0.005 ohm.cm or less, or 0.003 ohm.cm or less, or 0.001 ohm.cm or less.

[0102] According to certain embodiments, the bipolar plate exhibits a through-plane resistivity of 0.025 ohm.cm or less, or 0.02 ohm.cm or less, or 0.015 ohm.cm or less.

[0103] According to certain embodiments, the bipolar plate has a thermal conductivity of 15 W / m / K or more, or 20 W / m / K or more.

[0104] According to a particular embodiment, the bipolar plate has a resistance of 30 N / mm 2 or 35 N / mm 2 It has a bending strength of at least 100%.

[0105] According to a preferred embodiment, the bipolar plate comprises: 50% to 85% of component B as defined herein have a volume average diameter (Dv50) in the range of 50 to 500 μm, Component A as defined in the present invention, comprising 1% to 50% of graphite having a particle size, expressed as volume average diameter (Dv50), in the range of 1 to 40 μm, 5% to 40% of component C as defined in the present invention It consists of: These percentages sum to 100%. EXAMPLES

[0106] For the preparation of the bipolar plates, synthetic graphite (Graphite Timrex KS150) with a particle size characterized by a Dv50 of 55 μm and a tem- perature of 232 °C and 100 s -1 A vinylidene difluoride homopolymer having a melt viscosity of 900 Pa.s, measured at 1000.degree. C., was used.

[0107] Composition 1 obtained from recycling lithium-ion battery graphite anodes: Composition 1 originating from a graphite anode was obtained by a recycling process based on the physical separation of the elements. First, the components of the battery (anode / separator / cathode) were physically separated. Then the anode was crushed. Finally, it was subjected to an air jet sieve to separate the copper fragments, the graphite and the polymer binder. At the end of this stage, a powder was recovered consisting of 94.0% by weight of graphite, 3.4% by weight of carboxymethylcellulose (CMC) and 2.6% by weight of styrene-butadiene elastomer (SBR). The graphite in this composition was synthetic graphite with a particle size characterized by a Dv50 of 17 μm.

[0108] Composition 2 obtained from black mass of a lithium-ion battery with graphite anode and NMC cathode: Composition 2 originates from the black mass of a lithium-ion battery. It contains non-metallic and non-inorganic residues, namely graphite, carbon-based conductive fillers of the cathode, polymeric binders (PVDF, CMC, SBR) of the electrodes and polyolefins of the separator. The components of the battery (anode / separator / cathode) were first chopped and then ground. The ground material was subsequently subjected to various stages of a hydrometallurgical process in order to dissolve the metal current collectors and the inorganic fillers of the separator coating, such as NMC and boehmite. The residue of the hydrometallurgical process is composed of: 82.7% by weight of graphite originating from the anode, which has a grain size characterized by a Dv50 of 17 μm.

[0109] 1.8% by weight of carboxymethylcellulose (CMC) 1.4% by weight of styrene-butadiene elastomer (SBR) 4.1% by weight of polyvinylidene fluoride (PVDF) from the cathode 4.1% by weight of cathode-derived carbon black 5.9% by weight of polyolefins from the separator

[0110] Composition of bipolar plates with the same binder content:

[0111] [Table 1]

[0112] Preparation of bipolar plates: Premixing of compositions used in the manufacture of bipolar plates: The components of Example 1, Timrex KS150 graphite, Kynar® 721 PVDF, and a composition resulting from recycling lithium-ion battery anodes were premixed using a twin-screw extruder. At the end of this mixing stage, very brittle granules were obtained. These granules were then milled using a disk mill to obtain a powder with an average size Dv50 of less than 500 μm.

[0113] Comparative examples were prepared according to the same protocol.

[0114] Manufacturing of bipolar plates by thermocompression: The manufacture of the bipolar plates was carried out by thermocompression. To do this, a 30 × 30 cm 2 The composition in powder form was manually filled into a mold having dimensions of 1.5 mm. The powder was manually leveled with a metal blade. The mold was closed and brought to 240° C. under a pressure of 150 bar. The amount of powder was adjusted to obtain a thickness of approximately 3 mm. The mold was cooled under pressure to a temperature of 80° C. Once this temperature was reached, the pressure was removed and the plate was removed from the mold.

[0115] Characterization method: Bending strength The flexural strength was determined according to standard DIN EN ISO 178.

[0116] result:

[0117] [Table 2]

[0118] As the results demonstrate, the bipolar plate according to the present invention exhibits better bending strength compared to the comparative example that does not contain graphite resulting from battery recycling.

Claims

1. 1. A method for producing a composition for a bipolar plate, comprising the steps of: Providing a composite mixture (component A) based on at least one carbon-based conductive filler and a polymer; Incorporating graphite (component B) and a polymer binder (component C) into the composite mixture; Including, The composite mixture is derived from recycling lithium ion batteries. method.

2. 13. The method of claim 1, wherein the recycling of lithium ion batteries is carried out by a method selected from physical separation, hydrometallurgy, or a combination thereof.

3. 10. The method of claim 1, wherein the at least one carbon-based conductive filler is graphite used as an active filler in the anode of the lithium ion battery.

4. 2. The method of claim 1, wherein the carbon-based conductive filler is a mixture of graphite and another carbon-based conductive filler such as carbon black, carbon nanotubes, or carbon fibers present in the Li-ion battery anode or cathode formulation.

5. 2. The method of claim 1, wherein the polymer participating in the composition of component A is a fluoropolymer, a water-soluble thickening polymer, a polyolefin elastomer, an acrylic resin, or a mixture of several of these components, including a mixture of different fluoropolymers.

6. The fluoropolymer may be a vinylidene fluoride homopolymer; a vinylidene fluoride unit and a fluoroalkyl group selected from the list below: vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene; 1,2-difluoroethylene, tetrafluoroethylene; hexafluoropropylene; a perfluoro(alkyl vinyl) ether such as perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether or perfluoro(propyl vinyl) ether; perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole); ２ = CFOCF ２ CF (CF ３ ) O.C.F. ２ CF ２ X (wherein X is SO ２ F, C.O. ２ H, C.H. ２ O.H., C.H. ２ OCN or CH ２ O.P.O. ３ H); the product of formula CF ２ = CFOCF ２ CF ２ SO ２ F product; Formula F(CF ２ ) ｎ CH ２ OCF = CF ２ wherein n is 1, 2, 3, 4 or 5; ２ OCF = CF ２ (Wherein, R' is hydrogen or F(CF ２ ) ｚ and z is 1, 2, 3 or 4; ２ (Wherein, R″ is F(CF ２ ) ｚ and z is 1, 2, 3 or 4; perfluorobutyl ethylene; 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene; a copolymer comprising units resulting from one or more monomers selected from acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, acryloyloxypropyl succinate; and mixtures thereof.

7. Component A has the following composition by weight: - 60% to 100% graphite, 0% to 20% silicon 0% to 10% water-soluble thickener, 0% to 10% polyolefin elastomer, - 0% to 10% acrylic resin, - 0% to 10% fluoropolymer, 0-40% polyolefin, - 0% to 10% of a second carbon-based conductive filler; and the sum of all these percentages is 100%.

8. 2. The method of claim 1, wherein component A comprises graphite having a particle size, expressed as a volume average diameter (Dv50), smaller than the volume average diameter (Dv50) of the graphite constituting component B.

9. 2. The process according to claim 1, wherein the graphite present in component A exhibits a particle size, expressed as volume average diameter (Dv50), ranging from 1 to 40 μm.

10. 2. The method according to claim 1, wherein the graphite constituting component B has a volume average diameter (Dv50) in the range of 50 to 500 μm.

11. 2. The method of claim 1, wherein the polymer binder constituting component C is a polyolefin, a fluoropolymer, a polyphenylsulfone, a polyethersulfone, a phenolic resin, a vinyl ester resin, an epoxy resin, or a liquid crystal polymer.

12. The bipolar plate composition used in the method comprises, by weight: ・Component B: 50% to 85%, Component A: 1% to 50%, ・Component C: 5% to 40%, It consists of: The method of claim 1 , wherein the sum of these percentages is 100%.

13. 1. A method for manufacturing a bipolar plate, comprising the steps of: - preparing a composition according to the method of one of claims 1 to 12, and subjecting said composition to injection molding; A method comprising:

14. 1. A method for manufacturing a bipolar plate, comprising the steps of: - preparing a composition according to the method of one of claims 1 to 12, and subjecting the composition to compression molding; A method comprising:

15. 1. A method for manufacturing a bipolar plate, comprising the steps of: - preparing a composition according to the method of one of claims 1 to 12, and subjecting said composition to a continuous extrusion process; A method comprising:

16. A bipolar plate obtainable by the method according to claim 13.

17. A bipolar plate obtainable by the method according to claim 14.

18. A bipolar plate obtainable by the method according to claim 15.

19. Component B as defined in any one of claims 1 to 12, having from 50% to 85% of the volume average diameter (Dv50) in the range from 50 to 500 μm, Component A as defined in any one of claims 1 to 12, comprising from 1% to 50% of graphite having a particle size, expressed as volume average diameter (Dv50), in the range from 1 to 40 μm; from 5% to 40% of component C as defined in any one of claims 1 to 12 It consists of: The sum of these percentages is 100% for a bipolar plate.