Electrolyte membrane production method and electrolyte membrane

Abstract

This electrolyte membrane production method comprises: a step for preparing a porous base material including a porous membrane and a crosslinking agent held in pores of the porous membrane; an impregnation step for impregnating the porous base material with a solution containing an electrolyte polymer; and a crosslinking step for reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer.

Description

Electrolyte membrane manufacturing method and electrolyte membrane

[0001] The present disclosure relates to a method for manufacturing an electrolyte membrane and an electrolyte membrane.

[0002] Fuel cells are attracting attention as a new energy technology with high energy efficiency. Among them, solid polymer fuel cells using electrolyte polymers are attracting particular attention because they have a high maximum current density and operate at low temperatures, making them suitable for use as a mobile power source for automobiles and small-capacity power sources for portable electronic devices.

[0003] The electrolyte membrane used in polymer electrolyte fuel cells can develop cracks on the surface or inside the membrane due to repeated swelling due to wetting and shrinkage due to drying. For this reason, electrolyte membranes with improved mechanical strength, which are reinforced by providing a porous substrate inside the membrane, are being studied.

[0004] For example, Patent Document 1 discloses an electrolyte membrane comprising a porous substrate and a resin composition filled, fixed, and held in the voids and / or pores of the porous substrate, wherein the resin composition comprises an electrolyte polymer crosslinked with a crosslinking agent.

[0005] JP 2008-117750 A

[0006] The electrolyte membrane described in Patent Document 1 is produced by impregnating a porous substrate with a resin composition in which a crosslinker and an electrolyte polymer are premixed. However, resin compositions in which a crosslinker and an electrolyte polymer are premixed tend to increase in viscosity due to their short pot life (usable time). As a result, such resin compositions are difficult to impregnate into the porous substrate, and as a result, the mechanical strength of the electrolyte membrane may not be sufficiently improved.

[0007] An object of the present disclosure is to provide at least one of an electrolyte membrane having high mechanical strength and a method for producing the same.

[0008] The present disclosure is as set forth in the claims, and the gist of the disclosure is as follows. [1] A method for producing an electrolyte membrane, comprising: a step of preparing a porous substrate including a porous membrane and a crosslinking agent retained in the pores of the porous membrane; an impregnation step of impregnating the porous substrate with a solution containing an electrolyte polymer; and a crosslinking step of reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer. [2] A method for producing an electrolyte membrane according to [1], comprising: a drying step of drying the solution filled in the porous substrate in the impregnation step; a step of applying a solution containing the electrolyte polymer to the surface of the porous substrate after the drying step to form a layer made of the solution on the surface of the porous substrate; and a step of drying the layer made of the solution to form a contact layer made of the electrolyte polymer. [3] A method for producing an electrolyte membrane according to [2], wherein the thickness of the contact layer is 1 μm or more and 15 μm or less. [4] A method for producing an electrolyte membrane according to any of [1] to [3], wherein the number-average molecular weight of the electrolyte polymer is 18,000 or more and 60,000 or less. [5] The amount of the crosslinking agent held in the porous substrate is 3.0 × 10 －８ mol / cm ２ Above 20.0 x 10 －８ mol / cm ２[6] The method for producing an electrolyte membrane according to any one of [1] to [4], wherein the porous substrate further contains, in the pores, a binder that does not react with the crosslinking agent. [7] The method for producing an electrolyte membrane according to [6], wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer. [8] An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, wherein the reinforcing layer comprises a porous membrane and a crosslinked electrolyte polymer that is at least partially crosslinked and is contained in the pores of the porous membrane, and the contact layer comprises an uncrosslinked electrolyte polymer. [9] The electrolyte membrane according to [8], wherein the crosslinked electrolyte polymer is a reaction product of an electrolyte polymer and a crosslinking agent, and wherein the portion of the crosslinked electrolyte polymer derived from the crosslinking agent is unevenly distributed in the vicinity of the wall surface of the pores of the porous membrane rather than in the center of the pores.

[10] The electrolyte membrane according to [8] or [9], wherein the number-average molecular weight of the crosslinked electrolyte polymer is 50,000 or more and 300,000 or less.

[11] The electrolyte membrane according to any one of [8] to

[10] , wherein the number average molecular weight of the non-crosslinked electrolyte polymer is 18,000 or more and 60,000 or less.

[12] The electrolyte membrane according to any one of [8] to

[11] , wherein the thickness of the contact layer is 1 μm or more and 15 μm or less.

[13] The electrolyte membrane according to any one of [8] to

[12] , wherein the reinforcing layer contains a binder that does not react with the crosslinking agent within the pores of the porous membrane.

[14] The electrolyte membrane according to

[13] , wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer.

[15] The electrolyte membrane according to any one of [8] to

[14] , wherein the electrolyte membrane is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis.

[0009] According to the present disclosure, it is possible to provide at least one of an electrolyte membrane having high mechanical strength and a method for producing the same.

[0010] 1 is a schematic diagram showing a cross section of an electrolyte membrane according to an embodiment of the present disclosure.

[0011] An example of an embodiment of the present disclosure will be described below, possibly with reference to the drawings. However, the present disclosure is not limited to the following embodiment. The present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of the upper and lower limits of the values ​​disclosed herein. Furthermore, "A or B" may include either A or B, or both. Furthermore, unless otherwise specified, the materials exemplified below may be used alone or in combination of two or more. Furthermore, the terms "layer" and "film" encompass not only structures that are formed over the entire surface when observed in a plan view, but also structures that are formed only on a portion of the surface. Furthermore, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0012] <Electrolyte Membrane> FIG. 1 is a schematic diagram showing a cross section of an electrolyte membrane of one embodiment. The electrolyte membrane 10 of FIG. 1 has a structure in which a reinforcing layer 4 is sandwiched between contact layers 5. The reinforcing layer 4 includes a porous membrane 1 and an at least partially crosslinked crosslinked electrolyte polymer 3 contained in the pores 2 of the porous membrane 1. The contact layer 5 includes an uncrosslinked electrolyte polymer. The electrolyte membrane 10 of this embodiment may have a structure in which the contact layer 5, the reinforcing layer 4, and the contact layer 5 are stacked in this order and integrated together (i.e., a structure in which the reinforcing layer 4 is sandwiched between the two contact layers 5). Note that although the two contact layers in FIG. 1 are denoted by the same reference numeral (5), the two contact layers may be the same or different. Details of the contact layer 5 in the following description apply to both of the two contact layers.

[0013] (Reinforcing Layer) [Porous Membrane] The porous membrane 1 has a plurality of pores 2. The porous membrane 1 may have pores 2 that are interconnected at least in the thickness direction.

[0014] The porous membrane 1 may be any membrane usable as a reinforcing membrane for a fuel cell, and may be, for example, a membrane formed of a hydrocarbon polymer such as polyethylene or a fluorine-containing polymer such as expanded polytetrafluoroethylene (PTFE). As the porous membrane (for example, a porous membrane formed of the hydrocarbon polymer), one or more sheets selected from the group consisting of nonwoven fabrics, woven fabrics, and porous bodies (sponges, etc.) may be used.

[0015] The average pore diameter of the pores 2 in the porous film 1 may be 0.1 nm or more, 1 nm or more, or 5 nm or more, and may be 200 nm or less, 175 nm or less, or 150 nm or less. The average pore diameter of the pores 2 in the porous film 1 may be 0.1 nm or more and 200 nm or less, or 1 nm or more and 175 nm or less, or 5 nm or more and 150 nm or less.

[0016] The porosity of the porous membrane 1 may be 50% or more, 60% or more, or 70% or more from the viewpoint of easily increasing the filling amount of the cross-linked electrolyte polymer. The porosity of the porous membrane 1 may be 98% or less or 95% or less from the viewpoint of easily maintaining the strength of the porous membrane 1 itself. From the above viewpoint, the porosity of the porous membrane 1 may be 50% or more and 98% or less, 60% or more and 98% or less, or 70% or more and 95% or less.

[0017] The thickness of the porous membrane 1 may be 1 μm or more, 2 μm or more, or 5 μm or more, and may be 50 μm or less, 30 μm or less, or 20 μm or less, from the viewpoint of further increasing the mechanical strength and swelling resistance without impairing the properties as an electrolyte membrane. The thickness of the porous membrane 1 may be 1 μm or more and 50 μm or less, 2 μm or more and 30 μm or less, or 5 μm or more and 20 μm or less.

[0018] [Crosslinked Electrolyte Polymer] The crosslinked electrolyte polymer 3 is an electrolyte polymer that is at least partially crosslinked and has a crosslinked structure within the molecule. The crosslinked electrolyte polymer 3 may be a reaction product of an electrolyte polymer and a crosslinking agent. That is, the crosslinked electrolyte polymer 3 may be an electrolyte polymer having a plurality of polymer units derived from the electrolyte polymer and a site (crosslinking group) derived from the crosslinking agent that bonds to two or more of the polymer units. In such an electrolyte polymer, the site derived from the crosslinking agent of the crosslinked electrolyte polymer 3 may be unevenly distributed more in the vicinity of the wall surface of the pore 2 than in the center of the pore 2 of the porous membrane 1.

[0019] Examples of the electrolyte polymer include hydrocarbon-based or fluorine-based resins having ion-exchange groups. The electrolyte polymer may be a non-crosslinked (uncrosslinked) electrolyte polymer.

[0020] The electrolyte polymer may include an electrolyte polymer having a hydrophilic segment and a hydrophobic segment, and from the viewpoint of increasing the mechanical strength, may include one or more electrolyte polymers selected from the group consisting of electrolyte polymers having structures represented by the following formulas (P1) to (P5). [In formulas (P1) to (P5), n represents the number of repetitions.]

[0021] The number average molecular weight of the electrolyte polymer may be 18,000 or more and 60,000 or less, 30,000 or more and 55,000 or less, or 40,000 or more and 50,000 or less. The number average molecular weight in the present disclosure is a standard polyethylene glycol / oxide (PEG / PEO) equivalent value measured by gel permeation chromatography (GPC).

[0022] The plurality of polymer units derived from the electrolyte polymer may be the same or different from one another.

[0023] The crosslinking agent may be a known crosslinking compound. From the viewpoint of chemical stability, the crosslinking agent may include a crosslinking compound having one or more aromatic rings, or may include a crosslinking compound having one or two aromatic rings. When the crosslinking agent has an aromatic ring, the polymer unit derived from the electrolyte polymer may be directly bonded to the aromatic ring in the crosslinking group, and may be bonded to an aromatic ring by —O—, —S—, or —SO ２ It may be bonded via -.

[0024] The crosslinkable compound having one or two aromatic rings may include one or more compounds selected from the group consisting of decafluorobiphenyl, 4,4'-dicyano-3,3',5,5'-tetrafluorobiphenyl, 3,3',5,5'-tetrachloro-4,4'-dicyanobiphenyl, and pentachlorobenzonitrile. Among these, decafluorobiphenyl has good reactivity with electrolyte polymers having structures represented by formulas (P1) to (P5).

[0025] When a plurality of sites (crosslinking groups) derived from the crosslinking agent are present, they may be the same or different.

[0026] The number average molecular weight (Mn) of the crosslinked electrolyte polymer 3 may be 50,000 or more and 300,000 or less, depending on its molecular structure. When the number average molecular weight of the crosslinked electrolyte polymer 3 is in this range, the mechanical strength tends to be higher and swelling of the electrolyte membrane due to wetting tends to be suppressed. From the same viewpoint, the number average molecular weight of the crosslinked electrolyte polymer 3 may be 60,000 or more and 250,000 or less, 70,000 or more and 250,000 or less, 70,000 or more and 200,000 or less, 80,000 or more and 150,000 or less, or 90,000 or more and 100,000 or less.

[0027] [Others] The reinforcing layer 4 may further contain a binder that does not react with the crosslinking agent in the pores 2 of the porous membrane 1. The binder is not particularly limited as long as it is a resin that does not react with the crosslinking agent, and may be a polymer having the same molecular structure as the main chain of the above-mentioned electrolytic polymer (for example, a polymer whose main chain structure of the polymer molecule is the same as the above-mentioned electrolytic polymer). Examples of such a polymer include a polymer having a structure without the ion exchange groups of the above-mentioned electrolytic polymer, and a polymer in which a metal is bonded to the ion exchange group of the above-mentioned electrolytic polymer to form a salt.

[0028] The binder may be one or more polymers selected from the group consisting of polymers having structures represented by the following formulas (P6) to (P10). [In formulas (P6) to (P10), n represents the number of repetitions.]

[0029] The reinforcing layer 4 may further contain an additive that promotes the reaction between the electrolyte polymer and the crosslinking agent in the pores 2 of the porous membrane 1. The additive may be a known additive used for the above purpose. For example, one or more selected from cesium carbonate and potassium carbonate may be used, or other basic salts may be used.

[0030] The reinforcing layer 4 may contain uncrosslinked electrolyte polymer, unreacted crosslinking agent, other additives, unavoidable impurities, etc. Examples of other additives include water-retentive inorganic substances and radical scavengers, specifically water, silica, cerium oxide, and manganese oxide. These components may be contained in the pores 2 of the porous membrane 1 or may be retained in the pores 2 of the porous membrane 1.

[0031] The thickness of the reinforcing layer 4 may be approximately the same as the thickness of the porous membrane 1. The thickness of the reinforcing layer 4 may be 1 μm or more and 50 μm or less, 2 μm or more and 30 μm or less, or 5 μm or more and 20 μm or less.

[0032] (Contact Layer) The contact layer 5 contains an uncrosslinked electrolyte polymer, and therefore has appropriate flexibility and is easily deformed. As a result, the contact layer 5 can absorb the surface irregularities of the electrode catalyst layer and adhere closely to the catalyst particles, which tends to expand the proton conduction path.

[0033] [Uncrosslinked Electrolyte Polymer] Examples of the uncrosslinked electrolyte polymer are the same as the examples of the electrolyte polymer in the (reinforcing layer) described above. The uncrosslinked electrolyte polymer contained in the contact layer 5 and the electrolyte polymer that is the raw material for the crosslinked electrolyte polymer in the (reinforcing layer) described above may be the same or different. One type of uncrosslinked electrolyte polymer may be used alone, or two or more types may be used in combination. The uncrosslinked electrolyte polymers contained in each contact layer 5 may be the same or different.

[0034] The uncrosslinked electrolyte polymer generally has a lower number-average molecular weight than the crosslinked electrolyte polymer (e.g., the crosslinked electrolyte polymer contained in the reinforcing layer). The number-average molecular weight of the uncrosslinked electrolyte polymer may be 18,000 or more and 60,000 or less, depending on its molecular structure. When the number-average molecular weight of the uncrosslinked electrolyte polymer is within this range, swelling of the contact layer 5 is suppressed, preventing a decrease in the mechanical strength of the electrolyte membrane 10. Furthermore, the flexibility of the contact layer 5 is increased, thereby enhancing the effect of expanding the proton conduction path. From a similar perspective, the number-average molecular weight of the uncrosslinked electrolyte polymer may be 30,000 or more and 55,000 or less, or 40,000 or more and 50,000 or less.

[0035] The contact layer 5 may be a layer essentially consisting of an electrolytic polymer. The electrolytic polymer may be composed only of an uncrosslinked electrolytic polymer and may not contain the crosslinked electrolytic polymer 3. The contact layer 5 may be a layer consisting only of an electrolytic polymer, or may contain other additives, inevitable impurities, etc. Examples of other additives are the same as the examples of other additives in the reinforcing layer 4.

[0036] The contact layer 5 may have a layer containing the crosslinked electrolyte polymer 3 and a layer not containing the crosslinked electrolyte polymer 3. For example, the above-mentioned crosslinked electrolyte polymer 3 may be present so as to cover at least a part of the surface of the porous membrane 1, and may form a part of the contact layer 5 (the layer containing the crosslinked electrolyte polymer).

[0037] The thickness of the contact layer 5 may be 1 μm or more and 15 μm or less. Having a thickness of 1 μm or more prevents the porous membrane 1 from being exposed on the surface of the electrolyte membrane 10 and enhances the effect of expanding the proton conduction path. Having a thickness of 15 μm or less suppresses swelling of the contact layer 5, thereby preventing a decrease in the mechanical strength of the electrolyte membrane 10. From the same viewpoint, the thickness of the contact layer 5 may be 1 μm or more and 10 μm or less. When the contact layer 5 has a layer containing a crosslinked electrolyte polymer 3, the thickness of the layer not containing the crosslinked electrolyte polymer 3 may be, for example, 1 μm or more and 10 μm or less. The thicknesses of the contact layers 5 may be the same or different. From the same viewpoint, the total thickness of the contact layers 5 (the sum of the thicknesses of the contact layers 5) may be 2 μm or more and 30 μm or less, or 2 μm or more and 20 μm or less.

[0038] In one embodiment, the number-average molecular weight of the electrolyte polymer in the contact layer 5 may be 18,000 or more and 60,000 or less, and the thickness of the contact layer 5 may be 1 μm or more and 10 μm or less. When the number-average molecular weight of the electrolyte polymer is 18,000 or more and the thickness of the contact layer 5 is 10 μm or less, swelling of the contact layer 5 is further suppressed, and the mechanical strength of the electrolyte membrane 10 tends to be higher. Furthermore, when the thickness of the contact layer 5 is 1 μm or more, exposure of the porous membrane 1 on the surface of the electrolyte membrane 10 can be prevented, and when the electrolyte polymer in the contact layer 5 is 60,000 or less, the effect of expanding the proton conduction path can be further enhanced.

[0039] The thickness of the electrolyte membrane 10 may be, for example, 3 to 70 μm.

[0040] The electrolyte membrane 10 of this embodiment can be used, for example, as an electrolyte membrane for a fuel cell such as a polymer electrolyte fuel cell, or as an electrolyte membrane for water electrolysis.

[0041] <Method for manufacturing electrolyte membrane> A method for manufacturing an electrolyte membrane according to one embodiment includes the steps of: preparing a porous substrate including a porous membrane and a crosslinking agent held in the pores of the porous membrane (hereinafter also referred to as a "preparation step"); impregnating the porous substrate with a solution containing an electrolyte polymer; and crosslinking the electrolyte polymer with a crosslinking agent to form a crosslinked electrolyte polymer.

[0042] According to the above method, there is no need to add a crosslinking agent to the solution containing the electrolyte polymer in the impregnation step. Therefore, it is possible to fill the pores of the porous substrate (porous membrane) with the crosslinked electrolyte polymer without increasing the viscosity due to the reaction between the electrolyte polymer and the crosslinking agent. Furthermore, unlike conventional techniques, there is no restriction on the amount of crosslinking agent in consideration of the increase in viscosity, making it possible to increase the crosslink density of the crosslinked electrolyte polymer. Therefore, according to the above method, an electrolyte membrane with high mechanical strength can be obtained. Furthermore, for the same reasons as above, the above method tends to produce an electrolyte membrane with excellent swelling resistance. Therefore, there is no need to add another resin to suppress swelling, and a decrease in the mechanical strength of the electrolyte membrane due to the swelling suppression means can be suppressed. Furthermore, according to the above method, the electrolyte membrane 10 of the above embodiment can also be obtained by performing the solution layer formation step and the contact layer formation step described below. That is, the method for producing the electrolyte membrane of the above embodiment can be a method for producing the electrolyte membrane 10 of the above embodiment.

[0043] (Preparation step) The preparation step may be a step of preparing a porous substrate that has been prepared in advance, or may be a step of preparing a porous substrate.In the latter case, the preparation step may include a step of retaining a crosslinking agent in the pores of the porous membrane.Examples of the porous membrane and the crosslinking agent are the same as the examples of the porous membrane and the crosslinking agent in the (reinforcing layer) described above.

[0044] A method for retaining a crosslinking agent in the pores of a porous membrane includes impregnating a porous membrane with a solution containing a crosslinking agent and an organic solvent (hereinafter also referred to as a "crosslinking agent solution") and then drying the porous membrane. That is, the preparation step may include a process of impregnating a porous membrane with a crosslinking agent solution and a process of drying the porous membrane impregnated with the crosslinking agent solution. By impregnating a porous membrane with the crosslinking agent solution, the crosslinking agent adheres to the pores of the porous membrane, and by drying the porous membrane after impregnation, the crosslinking agent can be fixed to the porous membrane. Examples of methods for impregnating a porous membrane with a crosslinking agent solution include a method of dropping the crosslinking agent solution onto a porous membrane, a method of applying the crosslinking agent solution to a porous membrane, and a method of immersing a porous membrane in the crosslinking agent solution.

[0045] The amount of crosslinking agent retained in the porous substrate varies depending on the crosslinking agent and the electrolyte polymer, but is generally 3.0 × 10 －８ mol / cm ２ Above 20.0 x 10 －８ mol / cm ２ The amount of crosslinking agent retained in the porous substrate may be 3.0 × 10 or less. －８ mol / cm ２ When the amount of the crosslinking agent held in the porous substrate is 20.0×10 or more, the crosslink density of the crosslinked electrolyte polymer in the reinforcing layer becomes high, and the mechanical strength of the electrolyte membrane tends to be higher. －８ mol / cm ２ From these viewpoints, the amount of the crosslinking agent held in the porous substrate is set to 5.0 × 10 or less. －８ mol / cm ２ or more or 10.0 x 10 －８ mol / cm ２ or more, 18.0 × 10 －８ mol / cm ２ or less or 15.0 x 10 －８ mol / cm ２ or less, 5.0 × 10 －８ mol / cm ２ Above 18.0 x 10 －８ mol / cm ２ or less or 10.0 x 10 －８ mol / cm ２ Above 15.0 x 10－８ mol / cm ２ The amount of crosslinking agent held in the porous substrate means the amount of crosslinking agent fixed per unit surface area of ​​the porous substrate, and is calculated by dividing the total amount of crosslinking agent (unit: mol) by the surface area of ​​the porous membrane (unit: cm ２ The concentration of the crosslinking agent in the crosslinking agent solution may be adjusted appropriately so that the amount of the crosslinking agent retained in the porous substrate falls within the above range.

[0046] The crosslinking agent may be directly attached to the fibers constituting the porous membrane by van der Waals forces or the like, or may be fixed to the porous membrane via a binder that does not react with the crosslinking agent. That is, the porous substrate may further contain a binder that does not react with the crosslinking agent in the pores in order to make it easier to retain the crosslinking agent. When a binder is used, the binder may be contained in the crosslinking agent solution.

[0047] Examples of the binder are the same as the examples of the binder in the (reinforcing layer) described above. Among these, the binder may be a polymer having the same molecular structure as the main chain of the electrolyte polymer, or may be one or more polymers selected from the group consisting of polymers having structures represented by the above formulas (P6) to (P10). By using a polymer having the same molecular structure as the main chain of the electrolyte polymer as the binder, the affinity between the porous substrate and the electrolyte polymer is improved, making it easier to fill the pores of the porous substrate with the electrolyte polymer. In addition, since a polymer having the same molecular structure as the main chain of the electrolyte polymer is used, there is no need to prepare a resin different from the electrolyte polymer, and the manufacturing costs of the electrolyte membrane can be reduced.

[0048] The preparation step may further include a step of retaining an additive that promotes the reaction between the electrolyte polymer and the crosslinking agent in the pores of the porous membrane. Examples of the additive are the same as the examples of the additive in the (reinforcing layer) described above.

[0049] Methods for retaining the additive in the pores of the porous membrane include a method in which the additive is contained in a crosslinker solution, and a method in which an aqueous solution containing the additive is impregnated into a porous membrane by coating or the like, and then the porous membrane is dried. When the latter method is adopted, the step of retaining the additive in the pores of the porous membrane may be carried out before or after the step of retaining the crosslinker in the pores of the porous membrane.

[0050] (Impregnation step) In the impregnation step, the porous substrate is impregnated with a solution containing an electrolytic polymer, thereby filling the pores of the porous substrate with the solution containing the electrolytic polymer. As a method for impregnating the porous substrate with the solution containing the electrolytic polymer, for example, a solution casting method such as casting coating may be used.

[0051] Examples of the electrolyte polymer are the same as the examples of the electrolyte polymer in the (reinforcing layer) described above. The range of the number average molecular weight of the electrolyte polymer may also be the same as above. When the number average molecular weight of the electrolyte polymer is 18,000 or more, the mechanical strength of the electrolyte membrane tends to be higher. When the number average molecular weight of the electrolyte polymer is 60,000 or less, the viscosity of the solution containing the electrolyte polymer does not become too high, making it easier to fill the pores of the porous substrate with the solution containing the electrolyte polymer and to form a contact layer on the porous substrate. One type of electrolyte polymer may be used alone, or two or more types may be used in combination.

[0052] The solvent used in the solution containing the electrolytic polymer is not particularly limited as long as it is a solvent capable of dissolving the electrolytic polymer, and may be an organic solvent, such as one or more solvents selected from the group consisting of N-methyl-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, and tetramethylurea. One of the above solvents may be used alone, or two or more may be used in combination.

[0053] The content of the electrolytic polymer in the solution containing the electrolytic polymer may be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more, and 30% by mass or less, 20% by mass or less, or 15% by mass or less, or 1% by mass or more and 30% by mass or less, 3% by mass or more and 20% by mass or less, or 5% by mass or more and 15% by mass or less, based on the total mass of the solution.

[0054] The solution containing the electrolytic polymer may contain components other than the electrolytic polymer and the solvent. However, from the viewpoint of making it easier to obtain the effects of the present disclosure, the content of the crosslinking agent may be 0.01 parts by mass or less or 0 parts by mass per 100 parts by mass of the electrolytic polymer.

[0055] (Crosslinking step) In the crosslinking step, the crosslinking agent held in the pores of the porous substrate reacts with the electrolyte polymer filled in the pores to crosslink the electrolyte polymer. The reaction forms a crosslinked electrolyte polymer in which at least a portion is crosslinked in the pores of the porous substrate. The crosslinked electrolyte polymer formed in this way is a reaction product of the electrolyte polymer and the crosslinking agent, and has a plurality of polymer units derived from the electrolyte polymer and a site (crosslinking group) derived from the crosslinking agent that bonds to two or more of the polymer units. The site derived from the crosslinking agent of this crosslinked electrolyte polymer is derived from the crosslinking agent held in the pores of the porous substrate, and therefore tends to be more concentrated near the wall surface of the pores than in the center of the pores of the porous membrane.

[0056] The reaction between the electrolytic polymer and the crosslinking agent in the crosslinking step can be promoted by heating the porous substrate filled with the electrolytic polymer, although it depends on the combination of the electrolytic polymer and the crosslinking agent. The temperature (heating temperature) at which the porous substrate filled with the electrolytic polymer is heated also depends on the type of porous substrate. When the porous substrate has a melting point, if the heating temperature is a temperature below the melting point of the porous substrate, deformation or deterioration of the porous substrate can be prevented and the electrolytic polymer can be crosslinked.

[0057] The heating temperature may be, for example, 40 to 80° C. from the viewpoint of volatilizing the solvent derived from the solution containing the electrolytic polymer and drying the electrolyte membrane, and from the viewpoint of preventing deformation or deterioration of the porous substrate. The time for which the porous substrate filled with the electrolytic polymer is heated (heating time) may be, for example, 1 to 24 hours.

[0058] According to the method described above, an electrolyte membrane having a reinforcing layer can be obtained, in which the reinforcing layer includes a porous membrane and an at least partially cross-linked cross-linked electrolyte polymer contained in the pores of the porous membrane.

[0059] The method for producing an electrolyte membrane according to the above embodiment may include a drying step of drying the solution containing the electrolyte polymer filled in the porous substrate in the impregnation step, although the drying step is not essential because drying can also be performed in the crosslinking step as described above.

[0060] The drying step may be a step of removing at least a part of the solvent from the solution, for example, a step of drying until the surface of the porous substrate becomes dry to the touch.

[0061] After the drying step, the crosslinking step may be carried out directly, or the impregnation step may be carried out again. That is, the method for producing an electrolyte membrane of the above embodiment may have a first impregnation step and a second impregnation step. In this case, the first impregnation step may be a step of impregnating the pores of the porous substrate from one side of the porous substrate with a solution containing an electrolytic polymer, and the second impregnation step may be a step of impregnating the pores of the porous substrate from the other side of the porous substrate (the side opposite to the first impregnation step). The second impregnation step may be a solution layer formation step described later.

[0062] When it is desired to use electrolyte polymers with different molecular structures in the reinforcing layer and the contact layer, or when it is desired to prevent the solvent from remaining in the reinforcing layer even if the electrolyte polymers in the reinforcing layer and the contact layer are the same, it is effective to carry out the impregnation process in two stages as described above (for example, after filling the pores of the porous substrate with a solution containing an electrolyte polymer and drying it, further applying the solution containing the electrolyte polymer to the surface of the porous substrate).

[0063] The method for producing the electrolyte membrane of the above embodiment may include a step of applying a solution containing an electrolyte polymer to a surface of a porous substrate (e.g., one surface, both surfaces, or the entire surface of the porous substrate) to form a layer of the solution (solution layer) on the surface of the porous substrate (hereinafter also referred to as a "solution layer forming step"), and a step of drying the solution layer to form a contact layer containing the electrolyte polymer (hereinafter also referred to as a "contact layer forming step"). These steps may be performed multiple times to form multiple contact layers.

[0064] By carrying out the above-mentioned solution layer forming process and contact layer forming process, a contact layer containing an uncrosslinked electrolyte polymer can be formed on the reinforcing layer, and therefore, for example, the electrolyte membrane 10 of the above-mentioned embodiment can be obtained.

[0065] The solution layer forming step may be performed after the drying step. That is, the porous substrate to which the solution containing the electrolytic polymer is applied may be a porous substrate after the drying step (a porous substrate filled with the electrolytic polymer).

[0066] The solution layer forming step may be a step overlapping with the impregnation step described above. For example, the solution containing the electrolytic polymer may be applied to the surface of the porous substrate, thereby impregnating the porous substrate with the solution containing the electrolytic polymer and forming the solution layer on the surface of the porous substrate.

[0067] In the solution layer forming step, after applying the solution containing the electrolytic polymer, the thickness of the layer made of the solution containing the electrolytic polymer may be adjusted to a desired thickness. For example, the thickness of the solution layer may be adjusted by passing a porous substrate impregnated with the solution containing the electrolytic polymer through a gap adjusted to a desired thickness of the electrolyte membrane (i.e., a thickness obtained by adding the thickness of the porous substrate and the thickness of the desired contact layer).

[0068] The contact layer forming step may be a step overlapping with the drying step or the crosslinking step. For example, after the solution layer forming step, the solution layer may be dried by performing a heat treatment in the drying step or the crosslinking step, thereby forming a contact layer containing the electrolyte polymer.

[0069] In the electrolyte membrane manufacturing method of the above embodiment, the reinforcing layer and the contact layer may be manufactured simultaneously, or the electrolyte membrane may be manufactured by forming the reinforcing layer and then forming the contact layer on the reinforcing layer. It is also possible to manufacture the electrolyte membrane by manufacturing the reinforcing layer and the contact layer separately and then bonding the contact layers to both sides of the reinforcing layer. By manufacturing the reinforcing layer and the contact layer simultaneously, the number of steps required to manufacture the electrolyte membrane can be reduced, and an electrolyte membrane in which the reinforcing layer and the contact layer are continuous can be obtained because no interface is formed between the reinforcing layer and the contact layer.

[0070] When the reinforcing layer and the contact layer are produced simultaneously, for example, as described above, the porous substrate after the solution layer formation step (porous substrate impregnated with a solution containing an electrolyte polymer) may be passed through a gap adjusted to the thickness of the desired electrolyte membrane to adjust the thickness of the solution layer, and the porous substrate may be heated to simultaneously form a crosslinked electrolyte polymer and dry the solution, thereby producing an electrolyte membrane.

[0071] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0072] <Preparation of Electrolyte Polymer> (Synthesis of Hydrophilic Monomer (M1)) A 10 L flask equipped with a dropping funnel, a reflux condenser, and a mechanical stirrer was purged with nitrogen, and 101 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl and 4 L of dehydrated tetrahydrofuran were charged, and stirring was initiated. The flask was cooled to -70°C in a methanol-dry ice bath, and 320 mL of a 2.6 mol / L n-butyllithium-hexane solution was added dropwise. The mixture was stirred for 1 hour while cooled in the bath. 40 mL of sulfur dioxide gas was introduced into the flask using nitrogen gas. The mixture was stirred for 30 minutes while cooled in the bath. The bath was then removed, and the internal temperature was raised to 0°C.

[0073] The precipitated solid was separated by suction filtration and washed with 200 mL of tetrahydrofuran. The recovered solid was dissolved in 2 L of pure water, and 260 mL of 35% hydrogen peroxide solution was added and stirred for 18 hours. 600 g of sodium chloride was added to the filtrate recovered by suction filtration. The precipitated white solid was recovered by suction filtration and purified by recrystallization from water / isopropyl alcohol. The obtained solid was dried under reduced pressure to obtain a hydrophilic monomer represented by the following formula (M1). The yield was 65%.

[0074] (Synthesis of Hydrophobic Monomer (M2)) A 200 mL flask equipped with a stirrer, Dean-Stark tube, reflux condenser, and calcium chloride tube was charged with 4.0 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl, 14.8 g of [1,1'-biphenyl]-4,4'-diol, and 13.2 g of potassium carbonate, and 50 mL of N,N-dimethylacetamide (DMAc) and 50 mL of toluene were added. The temperature was raised to 160°C in an oil bath with stirring, and heating and stirring were continued for 4 hours. The toluene was removed from the Dean-Stark tube, and the temperature was raised to 180°C in an oil bath. After heating, heating and stirring were continued for 8 hours. After allowing the reaction solution to cool to room temperature, the reaction solution was poured into 200 mL of 10% hydrochloric acid, and the precipitated white solid was filtered off.

[0075] The filtered solid was washed with 300 mL of ethanol and dried. The dried solid was purified by recrystallization from NMP / ethanol. The obtained solid was dried under reduced pressure to obtain a hydrophobic monomer (M2) represented by the following formula (M2). The yield was 50%.

[0076] (Synthesis of Electrolyte Polymer (P1)) 0.983 g of the hydrophobic monomer (M2), 1.181 g of the hydrophilic monomer (M1), and 0.507 g of potassium carbonate were added to a 100 mL three-neck flask equipped with a nitrogen inlet tube, a stirrer, and a Dean-Stark tube, and nitrogen substitution was performed. Then, 10 mL of dimethyl sulfoxide (DMSO) and 10 mL of cyclohexane were added. After heating to 130°C and reflux dehydration for 4 hours, the cyclohexane was extracted from the Dean-Stark tube. Polymerization was performed for 150 hours while heating at 130°C. After allowing the reaction solution to cool to room temperature, reprecipitation purification was performed from 300 mL of isopropyl alcohol (IPA), and the solid was collected by suction filtration.

[0077] The obtained solid was immersed in 1M hydrochloric acid for 24 hours to remove metal ions (Na ＋ or K ＋ ) to protons (H ＋ After the protons were substituted with protons, the polymer was thoroughly washed by immersion in pure water and dried under reduced pressure to obtain an electrolyte polymer (P1) (proton-substituted polymer (P1)) having a structure represented by the following formula (P1). The yield was 97%.

[0078] In formula (P1), n ​​represents a positive number. n in the above formula (P1) was approximately 20.

[0079] [Molecular Weight Measurement] The number average molecular weight of the electrolyte polymer (P1) was measured by GPC. The electrolyte polymer (P1) was dissolved in an eluent (N,N-dimethylformamide solvent containing 10 mmol / L of lithium bromide) at a concentration of 1 mg / mL to prepare a sample solution. The HLC-8320GPC manufactured by Tosoh Corporation was used as the apparatus. Two TSKgel SuperAWM-H columns (inner diameter 6.0 mm, length 15 cm) manufactured by Tosoh Corporation were used. A differential refractometer detector was used as the detector. The measurement was performed at a flow rate of 0.6 mL / min and a temperature of 40°C. The number average molecular weight was calculated in terms of standard polyethylene glycol / oxide (PEG / PEO). The number average molecular weight of the electrolyte polymer (P1) was 50,000.

[0080] <Preparation of porous substrate retaining crosslinking agent> A crosslinking agent (decafluorobiphenyl, purity 98%, manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in isopropyl alcohol to a concentration of the crosslinking agent of 3.0 × 10 －４ A mol / L crosslinker solution was prepared.

[0081] The crosslinking agent solution or its diluted solution obtained above was dropped onto a polyethylene porous substrate (manufactured by Hefei Zhaohui New Material Technology Co., Ltd., product name: CW12L1, porosity 72%, thickness 14 μm nonwoven fabric) and dried at 60° C. for 1 hour, whereby the amount of crosslinking agent retained was 3.2×10 －８ mol / cm ２ , 6.5 × 10 －８ mol / cm ２ and 14.9 x 10 －８ mol / cm ２ The amount of the crosslinking agent held was adjusted by the concentration of the crosslinking agent solution and the amount dropped.

[0082] <Preparation of Electrolyte Membrane> (Example 1) The electrolyte polymer (P1) was dissolved in dimethyl sulfoxide (DMSO) to obtain a solution containing 10 mass % of the electrolyte polymer (P1) (hereinafter also referred to as "electrolyte polymer (P1) solution"). The solution was diluted to a concentration of 3.2 × 10 －８ mol / cm ２ The solution was cast onto one side of a 20 μm thick porous substrate, and the porous substrate was passed through a gap between glass rods with a thickness gap of 30 μm. After the porous substrate was dried to the touch, the porous substrate was turned over, and the solution was cast onto the side opposite to the side on which the solution was cast, and the porous substrate was passed through a gap between glass rods with a thickness gap of 40 μm. The porous substrate was then heated at 60° C. for 6 hours to obtain a 40 μm thick electrolyte membrane of Example 1 having a structure in which the reinforcing layer was sandwiched between contact layers. The thickness of the electrolyte membrane in this example is the average thickness of the electrolyte membrane measured at three points in the plane using a micrometer.

[0083] (Example 2) Crosslinker retention amount: 6.5 × 10 －８ mol / cm ２An electrolyte membrane of Example 2 was obtained in the same manner as in Example 1, except that a porous substrate of

[0084] (Example 3) Crosslinker retention amount: 14.9 × 10 －８ mol / cm ２ An electrolyte membrane of Example 3 was obtained in the same manner as in Example 1, except that a porous substrate of

[0085] (Example 4) Before casting the electrolyte polymer (P1) solution onto the porous substrate, an aqueous potassium carbonate solution having a pH of 9.5 was applied to the porous substrate at a rate of 0.1 mL / cm ２ and then dried by heating at 60° C. for 3 hours.

[0086] Comparative Example 1 An electrolyte membrane of Comparative Example 1 was obtained in the same manner as in Example 1, except that a porous substrate (porous substrate made of polyethylene) not carrying a crosslinking agent was used.

[0087] (Number-average molecular weight of electrolyte polymer in reinforcing layer) The number-average molecular weight (Mn) of the electrolyte polymer in the reinforcing layer of the electrolyte membrane of each Example was measured by GPC. The electrolyte polymer in the reinforcing layer was obtained by cutting out the reinforcing layer from the electrolyte membrane of each Example and dissolving it using N,N-dimethylformamide as a solvent. The number-average molecular weight of the obtained electrolyte polymer was measured using the same method as in the above-mentioned [Measurement of molecular weight]. The number-average molecular weights of the electrolyte polymers in the reinforcing layers of the electrolyte membranes of Examples 1 to 4 were 62,000, 78,000, 90,000, and 72,000, respectively. Therefore, it was confirmed that at least a portion of the electrolyte polymer (P1) was crosslinked in the reinforcing layer of the electrolyte membrane of each Example to form a crosslinked electrolyte polymer.

[0088] <Evaluation> (Swelling ratio) The electrolyte membrane was cut into 4 cm x 2 cm rectangles using a punching machine, the size of the electrolyte membrane was measured, the punched electrolyte membrane was sandwiched between 2 mm thick preparation plates and immersed in 100 mL of room temperature pure water for 1 hour, the electrolyte membrane was then removed, droplets on the surface were removed, the size was measured, and the swelling ratio of the electrolyte membrane in the MD direction or TD direction was calculated for each of the longitudinal and transverse directions using the following formula (1): Swelling ratio [%] = (L2 - L1) / L1 x 100 Formula (1) In formula (1), L1 is the side length of the membrane before swelling, and L2 is the side length of the membrane after swelling.

[0089] (Tensile Strength) A test piece was cut out from the electrolyte membrane (5 cm x 1 cm) before swelling, and a tensile test was carried out based on JIS K6251.

[0090] Under the following measurement conditions, the tensile strain was determined from the parallel length of the test piece and the crosshead displacement, and the tensile strength was determined from the resulting tensile stress-tensile strain diagram. Device name: INSTRON Material Testing Machine 5848 Test speed: 1 mm / min Test piece shape: JIS K6251 No. 8 test piece, 40% reduced shape Test room environment: Temperature 23±2°C, humidity 50±5% RH Parallel length: 6.4 mm Chuck distance: 8 mm

[0091]

[0092] From the above results, it was confirmed that even an extremely rigid electrolyte polymer, which is a crosslinked rigid electrolyte polymer having a biphenyl skeleton in the main chain, can be filled into fine pores.

[0093] Furthermore, the electrolyte membranes of the Examples, in which the electrolyte polymer in the reinforcing layer has a crosslinked structure, all had a lower swelling ratio and improved tensile strength than the electrolyte membrane of Comparative Example 1, confirming that the electrolyte membranes of the Examples have high mechanical strength and excellent swelling resistance.

[0094] Furthermore, a comparison between Example 1 and Example 2 confirmed that the swelling ratio was improved more significantly when the number average molecular weight of the electrolyte polymer in the reinforcing layer was 78,000 or more (the apparent molecular weight was 1.56 times that before crosslinking).

[0095] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2024-36172, filed on March 8, 2024, are incorporated herein by reference as the disclosure of the specification of the present disclosure.

[0096] 1... porous membrane, 2... pore, 3... cross-linked electrolyte polymer, 4... reinforcing layer, 5... contact layer, 10... electrolyte membrane

Claims

1. A method for producing an electrolyte membrane, comprising: a step of preparing a porous substrate comprising a porous membrane and a crosslinking agent retained in the pores of the porous membrane; an impregnation step of impregnating the porous substrate with a solution containing an electrolyte polymer; and a crosslinking step of reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer.

2. A method for producing an electrolyte membrane according to claim 1, comprising: a drying step of drying the solution filled in the porous substrate in the impregnation step; a step of applying a solution containing the electrolyte polymer to the surface of the porous substrate after the drying step to form a layer made of the solution on the surface of the porous substrate; and a step of drying the layer made of the solution to form a contact layer containing the electrolyte polymer.

3. The method for producing an electrolyte membrane according to claim 2, wherein the thickness of the contact layer is 1 μm or more and 15 μm or less.

4. The method for producing an electrolyte membrane according to any one of claims 1 to 3, wherein the number average molecular weight of the electrolyte polymer is 18,000 or more and 60,000 or less.

5. The amount of the crosslinking agent retained in the porous substrate is 3.0 × 10 －８ mol / cm ２ Above 20.0 x 10 －８ mol / cm ２ The method for producing an electrolyte membrane according to any one of claims 1 to 4, wherein:

6. The method for producing an electrolyte membrane according to any one of claims 1 to 5, wherein the porous substrate further contains, in the pores, a binder that does not react with the crosslinking agent.

7. The method for producing an electrolyte membrane according to claim 6, wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer.

8. An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, wherein the reinforcing layer comprises a porous membrane and a cross-linked electrolyte polymer, at least a portion of which is cross-linked, contained within the pores of the porous membrane, and the contact layer comprises an uncross-linked electrolyte polymer.

9. The electrolyte membrane according to claim 8, wherein the cross-linked electrolyte polymer is a reaction product of an electrolyte polymer and a cross-linking agent, and the portions of the cross-linked electrolyte polymer derived from the cross-linking agent are unevenly distributed in greater amounts near the wall surfaces of the pores than in the center of the pores of the porous membrane.

10. The electrolyte membrane according to claim 8 or 9, wherein the number average molecular weight of the crosslinked electrolyte polymer is 50,000 or more and 300,000 or less.

11. The electrolyte membrane according to any one of claims 8 to 10, wherein the number average molecular weight of the non-crosslinked electrolyte polymer is 18,000 or more and 60,000 or less.

12. The electrolyte membrane according to any one of claims 8 to 11, wherein the thickness of the contact layer is 1 μm or more and 15 μm or less.

13. An electrolyte membrane according to any one of claims 8 to 12, wherein the reinforcing layer contains, within the pores of the porous membrane, a binder that does not react with the crosslinking agent.

14. The electrolyte membrane according to claim 13, wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer.

15. The electrolyte membrane according to any one of claims 8 to 14, which is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis.

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