Freestanding ion-selective composite membrane

Abstract

The present disclosure relates to a free-standing composite membrane comprising an ion-selective polymer coating covering at least one surface of a polyolefin substrate and partially penetrating its pore structure. Although the composite membrane does not have open interconnected pores connecting each major surface, ion transport can occur through wetting of available pores and swelling of the ion-selective polymer coating, accompanied by ion migration from one membrane surface to the opposite surface. Such composite membranes are useful for separating anolyte and catholyte in flow batteries.

Description

Technical Field

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 125,361, filed December 14, 2020, entitled "ASYMMETRIC, FREE-STANDING, ION-SELECTIVE COMPOSITE MEMBRANE", the entire disclosure of which is hereby incorporated by reference.

[0002] Copyright Notice @2021 Amtek Research International LLC. Portions of the disclosure of this patent document may contain material subject to copyright protection. The copyright owner does not object to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but reserves all copyrights in all other respects. 37 CFR§1.71(d)

[0003] The present disclosure relates to a free-standing composite membrane comprising an ion-selective polymer coating that coats at least one surface of a polyolefin substrate and penetrates partially into its pore structure. Although the composite membrane does not have open connected pores connecting its major surfaces, ion transport can be effected through wetting of available pores and swelling of the ion-selective polymer coating, which involves ion movement from one membrane surface to the opposite surface. Such composite membranes are useful for separating anolyte and catholyte in a flow battery.

Background Art

[0004] Energy storage from renewable resources such as wind and sunlight is becoming increasingly important to the electric utility industry. Applications for large-scale energy storage serve to mitigate climate change and also enable electric utilities to improve system reliability and performance, smooth out power costs, and allow for the continued consumption of renewable energy.

[0005] To achieve the aforementioned objectives, electric power companies are researching various battery technologies. Lead-acid batteries have been commonly used due to their low cost, reasonable energy density, and discharge capacity under high current loads. However, the cycle life of lead-acid batteries is unfavorable compared to the chemical properties of other batteries. Lithium-ion batteries are also used in large-scale storage systems. While such batteries have outstanding energy density and excellent cycle life, they pose safety issues because their organic electrolytes can cause fires and explosions. Sodium-sulfur batteries are also being researched due to their high energy density, but their operating costs are high because they require an operating temperature of 300-350°C.

[0006] More recently, flow batteries have been studied for large-scale renewable energy facilities. Flow batteries store charge in a liquid electrochemical substance located in a storage tank, which is released through cells during charge-discharge cycles. A flow battery consists of two half-cells, which are separated by an ion-selective membrane that isolates and separates each side from the other. Flow batteries are realized with various redox pairs in water-soluble polyvalent vanadium and iron compounds. Aqueous electrolytes are attractive for safety and other reasons. Although all flow batteries have the problem of low energy density due to the large size of their liquid storage tanks, they are an attractive option for wind and solar power farms, typically located in rural areas where land costs are low.

[0007] One of the keys to achieving high efficiency and long cycle life in flow batteries is the ion-selective membrane. Such membranes must possess excellent chemical stability and high durability while preventing cross-contamination. Furthermore, the membrane must have low ionic resistance to transport between half-cells. To prevent cross-contamination and shorten cycle life, it is desirable to have a composite membrane exhibiting excellent mechanical properties, having a porous aqueous wettable bulk substrate coated on one or both sides with an ion-selective polymer-concentrated nonporous layer. In some embodiments, the composite membrane can be bonded to a frame by heat, ultrasound, or adhesive, with only one side coated with the ion-selective polymer-concentrated nonporous layer and the opposite side remaining porous and uncoated, and can be stacked to form multiple cells in series or parallel. In other embodiments, the composite membrane is coated on both sides with an ion-selective polymer-concentrated nonporous layer. The ion-selective polymer-concentrated nonporous layer can be crosslinked, as will be described in more detail later. [Overview of the Initiative] [Means for solving the problem]

[0008] The embodiments disclosed herein are best understood by reading the following description and the accompanying claims together with the accompanying drawings. These drawings show only typical embodiments, which will be described in more detail using the following accompanying drawings. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of an asymmetric composite membrane having an ion-selective nonporous layer on one side of the membrane. [Figure 2] This is a schematic cross-sectional view of a composite membrane having ion-selective nonporous layers on both sides of the membrane. [Figure 3] This is an image of an exemplary composite film with a coating deposited on top of it. [Figure 4] This is a schematic cross-sectional view of an apparatus used to measure the electrical resistance of a composite film sample disclosed in this application. [Figure 5]This is a schematic perspective view of an apparatus used to measure the electrical resistance of a composite film sample disclosed in this application. [Figure 6] This is a scanning electron microscope (SEM) image of the coating surface of a composite film fabricated according to one embodiment of the present disclosure. [Figure 7] This is an SEM image of the uncoated surface of a composite film fabricated according to one embodiment of the present disclosure. [Figure 8] This is an image of the apparatus used to measure the crossover rate of ferric chloride in the composite film sample disclosed in this application. [Figure 9] This graph shows the absorbance versus wavelength used in this application to determine the crossover rate of ferric chloride in composite film samples. [Figure 10] This is a graph of a calibration curve showing absorbance versus ferric chloride concentration used in this application to determine the crossover rate of ferric chloride in composite film samples. [Figure 11] This graph compares the electrical resistance (Ω-cm) of various composite film samples disclosed in this application. [Figure 12] This graph compares the ferric chloride diffusion rates (mol / hr / m2) of various composite membrane samples disclosed in this application. [Modes for carrying out the invention]

[0010] Nafion® and other ion-selective polymers are incorporated into films (also referred to herein as webs or membranes) for fuel cells and other energy storage applications by casting or extrusion, but these materials have the disadvantage of poor mechanical properties, particularly in wet conditions. In addition, ion-selective polymers are expensive, and therefore it is desirable to minimize the thickness of the film or web, but the thinner the film or web, the more difficult it is to handle. Furthermore, bonding polymers such as Nafion® to other surfaces is difficult.

[0011] The advantage of this disclosure is that it can provide a self-supporting ion-selective membrane for use in flow batteries or other energy storage devices. This advantage is achieved by combining a microporous polyolefin substrate with an ion-selective coating to form a composite membrane. In certain embodiments, the present application discloses a composite membrane comprising a self-supporting microporous polyolefin substrate (also called a web) containing a polyolefin and a high specific surface area hydrophobic filler. The microporous polyolefin substrate has a bulk structure extending from a first main surface to a second main surface. This bulk structure has a porosity of 40-75%, is wettable with an aqueous field-effect material, and contains a high specific surface area hydrophobic filler dispersed throughout the bulk structure. In some examples, the volume fraction of the filler divided by the volume fraction of the polyolefin is greater than 0.75 or greater than 1.0, for example, 0.75-1.3. In some embodiments, the first main surface is uncoated and has open pores, allowing water-soluble decomposition materials to easily penetrate the voids of the bulk structure. The second main surface may be provided with a non-porous coating of an ion-selective polymer that reduces air permeability and fluid permeability. In other embodiments, both main surfaces (i.e., the first and second main surfaces) have a non-porous coating of an ion-selective polymer that reduces air permeability and fluid permeability.

[0012] "Self-supporting" means that the web or film has sufficient mechanical properties for use in unwinding, coating, winding, stippling, and other web handling operations. The terms "film," "sheet," "substrate," "web," and "film" are interchangeable.

[0013] The microporous polyolefin substrate is self-supporting, has a porosity of 40 - 75%, and is wettable with aqueous solutions commonly used in electrolytes for flow batteries. To impart such wettability to the polyolefin substrate, it is desirable to include a large amount of hydrophobic fillers with a high specific surface area such as precipitated or fumed silica. Since the volume fraction and orientation of the polymer in the microporous substrate affect the tensile strength and puncture strength, it is desirable to use ultra-high molecular weight polyethylene (UHMWPE) or a mixture containing it as part of the polymer matrix.

[0014] Lead-acid separators are generally made from UHMWPE and precipitated or fumed silica, but these typically contain 10 - 20% residual process oil to enhance the oxidation resistance of the separator. Residual oil is not very desirable in the composite membranes used in flow batteries. Therefore, it is important to carefully select the process oil so that it can be easily extracted and the residual amount remaining in the microporous polyolefin sheet is minimized. In the field of flow batteries, examples of process oils that can be used include, but are not limited to, paraffin oil, naphthenic oil, mineral oil, plant-derived oil, and combinations thereof. In certain embodiments, the process oil contained in the resulting microporous polymer substrate after extraction of the process oil is less than 3%, more preferably less than 2%.

[0015] The ion-selective polymer coating prevents or minimizes the movement of electrochemically active species (e.g., cations) from the anolyte to the catholyte or vice versa. Such movement can cause a loss of current efficiency in the battery and may lead to a shortened operating life. In some embodiments, a coating is selected that does not overly impede the transport of charge carrier ions between the electrodes. The resistance to the flow of these ions causes a reduction in the voltage efficiency of the battery. The polymer coating prevents fouling and maintains integrity during the operating life of the battery.

[0016] The optimization of ion-selective polymer coatings depends on the chemical properties of the flow battery, but generally the polymer swells in water and contains anhydrides, carboxylic acids, and / or sulfonic acid groups. Conventional ion-selective polymers used to date include perfluorosulfonic acid / polytetrafluoroethylene copolymers (Chemours; Nafion®) and tetrafluoroethylene-fluorinated sulfonyl vinyl ether copolymers (Solvay; Aquivion®). Other fluoropolymers and their copolymers, such as polyvinylidene fluoride, can be chemically modified in the ion exchange head group to make them suitable as ion-selective polymers. Non-fluorinated and / or non-halogenated polymers can also be used as ion-selective polymers. Such polymers include, but are not limited to, polymethacrylic acid and methacrylic acid copolymers, polyacrylic acid and acrylic acid copolymers, sulfonated polyethersulfones, sulfonated polystyrene and sulfonated styrene copolymers, maleic anhydride and maleic anhydride copolymers, and sulfonated block copolymers (Kraton; Nexar®). Other non-limiting examples of polymers that can be modified to provide ion selectivity include polyether ketones (PEEK), polyphenylene oxide (PPO), polyimide (PI), polybenzimidazole (PBI), polyarylene ethersulfones (PAES), and combinations thereof. These polymers can be sulfonated, carboxylated, or otherwise modified to become ion-selective polymers.

[0017] The ion-selective polymer can also be crosslinked, for example, through radiation irradiation, free radicals, or chemical crosslinking. Various types of crosslinking substances or crosslinking agents can be used. For example, the crosslinking agent can be activated by functional groups (such as NH2, OH, etc.) on the ion-selective polymer, chemicals, heat, pressure, pH changes, light (such as UV light), or radiation irradiation. In certain embodiments, polyfunctional aziridine is used as the crosslinking substance. Other types of crosslinking agents can also be used, including but not limited to polyfunctional isocyanates, epoxides, amines, phenols, and anhydrides, etc.

[0018] The ion-selective polymer can further include nanoparticle fillers. Examples of ion nanoparticle fillers include metal oxides such as SiO2, TiO2, ZrO2, SnO2, Al2O3, metal phosphides such as zirconium phosphate, titanium phosphate, boron phosphate, phosphosilicates such as P2O5 - SiO2, metal oxide - P2O5 - SiO2, natural (chabazite, clinoptilolite, mordenite) and synthetic zeolites, heteropolyacids such as phosphotungstic acid, phosphomolybdic acid, tungstosilicic acid, carbon materials such as carbon nanotubes, activated carbon, graphene oxide, metal-organic framework structures (MOF’s), and any combination thereof. Many of these fillers can be further modified by sulfonation, carboxylation, phosphonation, amination, hydrolysis / condensation reactions, and reactions with silanes to add functions to improve wettability and / or ion conductivity.

[0019] When nanoparticle fillers are present, an adhesion and / or binder polymer can also be present in the ion-selective coating. Non-limiting examples of the adhesion and / or binder polymer include PVOH, acrylates, SBR emulsions, and combinations thereof.

[0020] As described above, the microporous polymer substrate or web can be wetted in the aqueous field of the energy storage device, enabling proton transport. For example, the microporous polymer substrate can contain high specific surface area hydrophobic fillers dispersed throughout the polymer matrix, so that the volume fraction of the fillers divided by the volume fraction of the polymer is greater than 0.75 or 1.0, for example, 0.75 to 1.3. In some embodiments, the specific surface area of ​​the high specific surface area hydrophobic fillers is 100 m². 2 Greater than / g. Examples of usable hydrophobic fillers include inorganic oxides, carbonates, or hydroxides, such as alumina, silica, zirconia, titania, mica, boehmite, magnesium hydroxide, calcium carbonate, and combinations thereof. Preferred hydrophobic fillers with high specific surface area are precipitated or fumed silica.

[0021] In flow battery applications, ion-selective composite membranes are chemically inert in the flow battery's electrochemical field. Therefore, in some embodiments, the microporous polymer substrate does not contain surfactants to aid in the wetting properties of the polymer substrate. In other embodiments, the microporous polymer substrate contains surfactants. Furthermore, if residual process oil is present, it should not leach out of the substrate over long periods of use.

[0022] In some embodiments, the thickness of the microporous polyolefin substrate is 100 to 350 micrometers. The thickness of the ion-selective coating is 1 to 25 micrometers or 1 to 10 micrometers.

[0023] The composite film disclosed herein may offer higher durability due to the presence of UHMWPE in at least a portion of the self-supporting microporous polyolefin substrate. Therefore, a method for producing a battery separator with higher durability includes the steps of providing or causing to be provided a microporous polyolefin substrate containing ultra-high molecular weight polyethylene having two main surfaces, and coating one or both of the two main surfaces of the microporous polyolefin substrate with an ion-selective polymer material. The coating may be deposited by spray coating, knife over-roll coating, dip coating, rod coating, slot die coating, or gravure coating. Other coating methods may also be used.

[0024] Exemplary composite films that can be fabricated according to this disclosure are shown in Figures 1 and 2. Figure 1 is a schematic cross-sectional view of an asymmetric composite film 100 having an ion-selective nonporous coating layer 112 on one side of the film 100. As shown in Figure 1, the composite film 100 includes a microporous polymer substrate 102 having a first main surface 104 and a second main surface 106. As further shown in Figure 1, the composite film 100 includes a first ion-selective nonporous coating layer 112 deposited on one side of the microporous polymer substrate 102 (e.g., the first main surface 104).

[0025] Figure 2 is a schematic cross-sectional view of a composite film 200 having ion-selective nonporous coating layers 212 and 214 on both sides of the film 200. As shown in Figure 2, the composite film 200 includes a microporous polymer substrate 202 having a first main surface 204 and a second main surface 206. As further shown in Figure 2, the composite film 200 includes a first ion-selective nonporous coating layer 212 deposited on the first surface (e.g., the first main surface 204) of the microporous polymer substrate 202, and a second ion-selective nonporous coating layer 214 deposited on the second surface (e.g., the second main surface 206) of the microporous polymer substrate 202. Therefore, it should be understood that the composite film 200 can coat one or both of the main surfaces 204 and 206 as desired.

[0026] The following embodiments are illustrative and not limiting. [Examples]

[0027] Example 1 ENTEK gray webs were fabricated by feeding a mixture of UHMWPE (KPIC U090), precipitated silica (Solvay 565B), naphthenic process oil (Nytex 820), and small amounts of carbon black, antioxidant, and lubricant into a twin-screw extruder. Additional oil was added to the throat of the extruder, and the mixture was extruded through a sheet die into a calender stack at approximately 225°C. The extruded product contained approximately 65% ​​oil, which was later extracted to obtain a thickness of approximately 204 μm and a basis weight of approximately 95 g / m². 2 A microporous polyolefin web was formed. The SiO2 / PE mass was approximately 2.6 (volume ratio approximately 1.12), and the residual oil content, measured by thermogravimetric analysis, was approximately 2.4%. The Gahl value measured for the web was 749 (secs / 100cc air).

[0028] ENTEK white webs were fabricated by feeding a mixture of ultra-high molecular weight polyethylene (Celanase GUR 4130), precipitated silica (PPG SBG), mineral oil (Tufflo 6056), and a small amount of antioxidant into a twin-screw extruder. Additional oil was added to the throat of the extruder, and the mixture was extruded through a sheet die into a calender stack at approximately 225°C. The extruded product contained approximately 65% ​​oil, which was later extracted to produce a product with a thickness of approximately 195 μm and a basis weight of approximately 106 g / m². 2 A microporous polyolefin sheet was formed. The silica / PE mass was approximately 2.5 (volume ratio approximately 1.08), and the residual oil content, measured by thermogravimetric analysis, was approximately 1.6%. The Gaarle value measured for the web was 1247 (secs / 100cc air), and the porosity, determined by the Hg porosity measurement method, was approximately 65%.

[0029] Each of the ENTEK gray web and ENTEK white web samples was coated with an ion-selective polymer solution (either 12% Kraton Nexar® MD9200 (sulfonated block copolymer) or 12% Kraton Nexar® MD9204 (sulfonated block copolymer)) using the following coating method: A microporous polymer web sample (section) (8 inches x 12 inches) was taped to a glass plate to allow for single-sided coating. A thin layer of the ion-selective polymer solution (12% Kraton Nexar® MD9200 or MD9204) was applied to the sample using different Meyer rod coaters. The coating on the sample was dried for 2 minutes using a handheld heat gun until completely dry. An image of an example of the coated microporous polymer web (i.e., composite film) is shown in Figure 3.

[0030] Once the coating had dried, its weight was determined and the Gaulle value of the sample was measured. A Gaulle value greater than 20,000 indicates that the coating is non-porous.

[0031] The electrical resistance (ER) of the samples was measured as follows: For each sample, three 0.75-inch diameter disks were drilled, and the thickness of each disk was measured. The sample disks were placed in an aluminum pan with a 1.5 M potassium chloride (KCl) solution and vacuumed (29 inHg) for 1 hour. The sample disks were then immersed in 1.5 M KCl overnight. The ER test was performed using the direct contact method with the apparatus shown in Figures 4 and 5. Specifically, saturated disks were placed between two stainless steel electrodes connected to a Gamry potentiostat, and the impedance was measured at a voltage amplitude of 10 mV and 100 kHz. The real component of the impedance at 100 kHz was recorded as the resistance value. The sample disks were tested individually and in combination. The resistances for one disk, two disks, and three disks were plotted. The resistance of each disk was identified using the slope of a line fitted to three data points. Referring to Figures 4 and 5, the schematic diagram of the test apparatus shows the upper electrode 320, the lower electrode 322, the polytetrafluoroethylene (PTFE) insulator 324, the sample 330, and the leads R, W, B, and G.

[0032] The ion exchange capacity (IEC) of the samples was also calculated based on the coating weight and an IEC value of 2.0 meq / g for both MD9200 and MD9204.

[0033] Tables 1-3 show detailed information on the base material coating, ER, and IEC of various samples.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] The composite film of sample 10 was examined using scanning electron microscopy (SEM). Figure 6 is an SEM image of the surface coated with the ion-selective polymer (Nexar MD9204). As shown therein, the coated surface appears smooth and non-porous. Figure 7 is an SEM image of the opposite, uncoated surface and its voids.

[0038] Example 2 ENTEK gray webs and ENTEK white webs were fabricated as described in Example 1. Each sample of ENTEK gray web and ENTEK white web was coated as follows.

[0039] Single-sided coating: In samples 16–17, sections of microporous polymer webs (8 inches × 12 inches) were taped to a glass plate to allow for single-sided coating. A thin layer of ion-selective polymer solution (12% solid Kraton Nexar® MD9200 or MD9204) was applied to the web using a Meyer Rod coater or Doctor Blade. The samples were placed in an 80°C convection oven for 2 minutes to allow the polymer coating on the web to dry completely. In samples 18–30, the coated webs were then immersed for approximately 1 minute in an aqueous solution containing 0.1–10 wt% of a polyfunctional aziridine crosslinking agent to crosslink the completely dried polymer coating. The specific polyfunctional aziridine crosslinking materials used were pentaerythritol tris[3-(1-aziridinyl)propionate] (PTAP), PZ-28, and PZ-33 from PolyAziridin LLC, and curing agent X7 from ICHEMCO srl. To completely dry the webs with the crosslinked polymer coating, the samples were placed in an 80°C convection oven for 2 minutes.

[0040] Double-sided coating: In samples 31-34, rolled microporous polymer webs (150-200 mm wide) were coated on both sides by dip coating in an ion-selective polymer solution (1-2% solid Kraton Nexar® MD9204) as part of a two-step dip coating process on a laboratory-scale continuous coating line, and dried at 80°C. In the second step, the completely dried polymer-coated webs were crosslinked by passing them through an aqueous solution containing 0.1-3 wt% of a polyfunctional aziridine crosslinking material. The webs with the crosslinked polymer coatings were dried at 80°C.

[0041] One-Step Coating Process: In Example 35, a thin layer of ion-selective Nexar® MD9204 was deposited and crosslinked onto a microporous polymer web (8 inches x 12 inches) in a one-step process. This was done by mixing GP® Crosslinking Resin / Kraton Nexar® MD9204 (60 / 40), 20 wt% solid preparation, and applying it to the web using a Meyer Rod coater or Doctor Blade. To dry the polymer coating on the web, the sample was placed in a 100°C convection oven for 2 minutes to completely dry and crosslink the coating.

[0042] Test method for electrical resistance (ER): The ER of the sample was measured as described in Example 1.

[0043] Test method for ferric chloride crossover rate: The crossover rate of ferric chloride (FeCl3) through a microporous polymer web sample was measured using a diffusion cell apparatus. A photograph of the apparatus is shown in Figure 8. As shown therein, the diffusion cell contained 0.5 M FeCl3 + 1.5 M KCl on the high-concentration or "rich" side and 1.5 M KCl (acidified with hydrochloric acid (HCl)) on the low-concentration or "dilute" side. A sample sheet (4 inches x 4 inches) was placed in an aluminum pan with deionized water and vacuum (29 inHg) was applied for 1 hour. The saturated sample was placed between two cell blocks, and 400 ml of each solution was poured simultaneously into both sides of the diffusion cell. 3 ml of sample was periodically taken from the low-concentration side (e.g., after 10, 20, and 30 minutes), injected into a cuvette with a pipette, and the absorbance test was performed. The absorbance at a wavelength of 334 nm was measured using a Thermo-fisher Scientific UV-vis spectrophotometer. In the ideal case, the self-supporting ion-selective composite film is Fe 3+ It shows no crossover at all, and at the same time, the protons (H) between cells + Transportation of ) is possible.

[0044] An example of a graph showing absorbance versus wavelength is shown in Figure 9. Then, the FeCl3 concentration of the sample was determined from the calibration curve showing absorbance versus FeCl3 concentration. An example of a calibration curve graph showing absorbance versus ferric chloride concentration is shown in Figure 10.

[0045] Table 4 shows detailed information on the base material, coating, ER, and ferric chloride diffusion rate of various samples. Samples 12 and 13 were Nafion® films, commercially available from Fuelcallstore.com, and were used as comparative samples. Sample 12 (Nafion® N115) was a 126 μm thick film, and sample 13 (Nafion® NR212) was a 47 μm thick film.

[0046] [Table 4]

[0047] [Table 5]

[0048] The resistances of various samples and the diffusion rates of ferric chloride are also graphically compared in Figures 11 and 12, respectively. As shown therein, the resistance of each sample was lower than that of the Nafion® film used for comparison. Furthermore, the diffusion rate of ferric chloride decreased due to crosslinking. These data are from Fe 3+ Crossover of (or other cations) at 0.1 mol / hr / m 2 This illustrates the advantage of bridged bridging, which is to maintain low electrical resistance (e.g., less than 250 Ω-cm) while reducing it to below a certain level.

[0049] To ensure understanding, this disclosure relates to structures and methods for manufacturing them. Any method disclosed or contemplated in this specification includes one or more steps or actions for carrying out the described method. The method steps or actions may be interchangeable. In other words, the specific order and / or use of the steps and / or actions may be changed unless a particular order of steps or actions is required for the proper operation of the embodiment.

[0050] Throughout this specification, the phrases “a particular embodiment” or “that embodiment” mean that certain features, structures, or characteristics described in relation to that embodiment are included in at least one embodiment. Therefore, not all of the above phrases or variations thereof described throughout this specification necessarily refer to the same embodiment.

[0051] Similarly, in the above-mentioned descriptions relating to embodiments, various features may be grouped together in a single embodiment, drawing, or description in order to make the disclosure more efficient. However, this method of disclosure should not be interpreted as reflecting an intention that any patent claim requires features other than those expressed in that claim. Rather, as the following patent claims show, aspects of the present invention are found in combinations of all the features of any one of the embodiments disclosed above.

[0052] Throughout this specification, references to approximate numbers are made, for example, by the use of the terms “substantially” and “about.” With respect to each such reference, it should be understood that in some embodiments, numerical values, features, or characteristics may be expressed without the use of approximate numbers. For example, where modifiers such as “about” and “substantially” are used, these terms include, within their scope, the modified word as it would be without the modifier.

[0053] Unless otherwise specified, all ranges include both endpoints and all the distances between them.

[0054] The term “first” in a patent claim, relating to a particular feature or element, does not necessarily imply the existence of a second or subsequent such feature or element.

[0055] The claims following this specification are hereby expressly incorporated herein, and each claim is valid individually as a separate embodiment. This disclosure includes all permutations of the independent claims and their dependent claims. Furthermore, additional embodiments that may be derived from the following independent and dependent claims are also expressly incorporated herein.

[0056] Those skilled in the art will likely be able to make the most of the present invention by utilizing the above description without further ingenuity. The claims and embodiments disclosed herein are merely illustrative and should be construed as not limiting the scope of the disclosure in any way. It will be apparent to those skilled in the art that by utilizing the disclosure, modifications may be made to the details of the embodiments described above without departing from the fundamental principles of the disclosure. In other words, various modifications and improvements to the embodiments specifically disclosed herein are included in the accompanying claims. Furthermore, the order of steps or actions of the methods disclosed herein may be modified by those skilled in the art without departing from the scope of the disclosure. In other words, the specific order or use of steps or actions may be modified unless a particular order of steps or actions is required for the proper operation of the embodiments. The scope of the present invention is therefore defined by the following claims and their equivalents.

Claims

1. It is a composite film, A self-supporting microporous polyolefin substrate comprising a polyolefin and a hydrophilic filler, comprising a microporous polyolefin substrate having a porosity of 40-75% extending from a first main surface to a second main surface, The hydrophilic filler is dispersed throughout the substrate, and the volume fraction of the hydrophilic filler divided by the volume fraction of the polyolefin is greater than 0.75, thereby making the substrate wettable. A composite film in which at least one of the first and second main surfaces comprises a non-porous coating of an ion-selective polymer that is selective for cations, the coating being chemically crosslinked with a crosslinking substance comprising a polyfunctional aziridine, a polyfunctional isocyanate, an epoxide, an amine, a phenol, or an anhydride, and the thickness of the ion-selective polymer coating is 1 micrometer to 25 micrometers.

2. The composite film according to claim 1, wherein at least one main surface includes open pores that allow an aqueous solution electric field to easily penetrate into the voids of the substrate.

3. The composite film according to claim 1, wherein both main surfaces are coated with the ion-selective polymer.

4. The diffusion rate of cations through the composite film is 0.1 mol / hr / m ２ The composite film according to claim 1, which is less than [amount missing].

5. The composite film according to claim 4, wherein the electrical resistance of the composite film is less than 250 Ω-cm.

6. The composite film according to any one of claims 1 to 5, wherein the coating of the ion-selective polymer further comprises nanoparticle fillers.

7. The composite film according to any one of claims 1 to 6, wherein the microporous polyolefin substrate further comprises a surfactant.

8. The composite film according to any one of claims 1 to 7, wherein the microporous polyolefin substrate contains less than 3% residual process oil.

9. The composite film according to any one of claims 1 to 8, wherein the thickness of the microporous polyolefin substrate is 100 micrometers to 350 micrometers.

10. The composite film according to any one of claims 1 to 9, wherein the thickness of the coating of the ion-selective polymer is 1 micrometer to 10 micrometers.

11. The composite film according to claim 1, wherein the crosslinking substance comprises a polyfunctional aziridine.

12. The composite film according to any one of claims 1 to 11, wherein the microporous polyolefin substrate contains ultra-high molecular weight polyethylene, providing higher mechanical strength to the composite film.

13. It is a flow battery, It is a composite film, A self-supporting microporous polyolefin substrate comprising a polyolefin and a hydrophilic filler, comprising a microporous polyolefin substrate having a porosity of 40-75% extending from a first main surface to a second main surface, The hydrophilic filler is dispersed throughout the substrate, and the volume fraction of the hydrophilic filler divided by the volume fraction of the polyolefin is greater than 0.75, thereby making the substrate wettable. At least one of the first and second main surfaces comprises a non-porous coating of an ion-selective polymer that is selective for cations, the coating being chemically crosslinked using a crosslinking agent comprising a polyfunctional aziridine, polyfunctional isocyanate, epoxide, amine, phenol, or anhydride, and the thickness of the ion-selective polymer coating is 1 micrometer to 25 micrometers, forming a composite film. A flow battery that includes a flow battery.

14. The flow battery according to claim 13, wherein at least one main surface includes open pores into which an aqueous field of the substrate can easily penetrate.

15. The flow battery according to claim 13, wherein both main surfaces are coated with the ion-selective polymer.

16. The diffusion rate of cations through the composite film is 0.1 mol / hr / m ２ A flow battery according to claim 13, wherein the flow battery is less than [amount missing].

17. The flow battery according to claim 16, wherein the electrical resistance of the composite film is less than 250 Ω-cm.

18. The flow battery according to any one of claims 13 to 17, wherein the coating of the ion-selective polymer further comprises nanoparticle fillers.

19. The flow battery according to any one of claims 13 to 18, wherein the microporous polyolefin substrate further comprises a surfactant.

20. The flow battery according to any one of claims 13 to 19, wherein the microporous polyolefin substrate contains less than 3% residual process oil.

21. The flow battery according to any one of claims 13 to 20, wherein the thickness of the microporous polyolefin substrate is 100 micrometers to 350 micrometers.

22. The flow battery according to any one of claims 13 to 21, wherein the thickness of the coating of the ion-selective polymer is 1 micrometer to 10 micrometers.

23. The flow battery according to claim 13, wherein the crosslinking substance comprises a polyfunctional aziridine.

24. The flow battery according to any one of claims 13 to 23, wherein the microporous polyolefin substrate contains ultra-high molecular weight polyethylene, providing higher mechanical strength to the composite film.

25. A method for manufacturing a separator with improved durability, A step of providing or making available a microporous polyolefin substrate containing ultra-high molecular weight polyethylene having two main surfaces, The steps include: coating at least one main surface of the microporous polyolefin substrate with an ion-selective polymer that is selective for cations, wherein the coating thickness of the ion-selective polymer is 1 micrometer to 25 micrometers; The steps include: chemically crosslinking the ion-selective polymer using a crosslinking substance comprising a polyfunctional aziridine, a polyfunctional isocyanate, an epoxide, an amine, a phenol, or an anhydride; A method that includes this.

26. The method according to claim 25, wherein the coating step includes spray coating, knife over-roll coating, dip coating, rod coating, slot die coating, or gravure coating.

27. The method according to claim 25 or claim 26, wherein at least one main surface includes open pores that allow aqueous electrochemical particles to easily penetrate into the voids of the substrate.

28. The method according to claim 25 or claim 26, wherein both main surfaces are coated with the ion-selective polymer.

29. The diffusion rate of cations through the separator is 0.1 mol / hr / m ２ The method according to claim 25, wherein the result is less than [value missing].

30. The method according to claim 29, wherein the electrical resistance of the separator is less than 250 Ω-cm.

31. The method according to any one of claims 25 to 30, wherein the coating of the ion-selective polymer further comprises nanoparticle fillers.

32. The method according to any one of claims 25 to 31, wherein the microporous polyolefin substrate further comprises a surfactant.

33. The method according to any one of claims 25 to 31, wherein the microporous polyolefin substrate contains less than 3% residual process oil.

34. The method according to any one of claims 25 to 33, wherein the thickness of the microporous polyolefin substrate is 100 micrometers to 350 micrometers.

35. The method according to any one of claims 25 to 34, wherein the thickness of the coating is 1 micrometer to 10 micrometers.

36. The method according to claim 25, wherein the crosslinking substance comprises a polyfunctional aziridine, a polyfunctional isocyanate, an epoxide, an amine, a phenol, or an anhydride.

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