A porous separator and its preparation method and preparation system

Abstract

The present invention discloses a porous separator, a preparation method thereof and a preparation system, belonging to the technical field of separator preparation. In the present invention, a first slurry is covered on one side of a substrate, and / or a second slurry is covered on the other side of the substrate to obtain a coated substrate; the coated substrate passes through a third space formed between a relatively arranged first steam tank and a second steam tank, such that one side of the coated substrate faces the first steam tank and the other side faces the second steam tank; a first non-solvent steam is output from a steam outlet of the first steam tank to contact one side of the coated substrate, and a second non-solvent steam is output from a steam outlet of the second steam tank to contact the other side of the coated substrate, so that the coating in the coated substrate is preliminarily cured to obtain a preliminarily cured film substrate; the preliminarily cured film substrate enters a coagulation bath to be cured into a film to obtain a porous separator. The separator prepared in this way inhibits the formation of finger-like pores, forms an overall uniform sponge-like porous structure, and can be an asymmetric porous separator on both surface sides.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of diaphragms, and in particular to a porous diaphragm, a preparation method thereof, and a preparation system thereof. Background Art

[0002] Alkaline hydrogen production electrolyzers usually use porous diaphragms as key components for isolating hydrogen and oxygen, and require the diaphragms to have good gas barrier properties, strong ion transport capabilities, low resistance, etc. However, in the related art, finger-like pore structures are likely to appear on the surface of the porous diaphragm, and the formation of finger-like pore structures on the diaphragm surface is likely to form gas transmission channels, which may ultimately lead to air leakage. Summary of the Invention

[0003] The main object of the present invention is to provide a porous diaphragm, a preparation method thereof, and a preparation system thereof, so as to solve the technical problem of difficult to control the morphology growth of finger-like pores inside the diaphragm and the surface porous structure during the phase transfer molding process of the diaphragm.

[0004] To achieve the above object, the present invention provides a method for preparing a porous diaphragm, including the following steps:

[0005] Cover a first slurry on one side of a substrate, and / or cover a second slurry on the other side of the substrate to obtain a coated substrate;

[0006] The coated substrate passes through a second space formed between a relatively arranged first steam tank and a second steam tank, so that one side of the coated substrate faces the first steam tank and the other side faces the second steam tank; the steam outlet of the first steam tank outputs a first non-solvent steam to contact one side of the coated substrate, and the steam outlet of the second steam tank outputs a second non-solvent steam to contact the other side of the coated substrate, so that the coating in the coated substrate is preliminarily cured to obtain a preliminarily cured film-forming substrate;

[0007] The preliminarily cured film-forming substrate enters a coagulation bath to be cured into a film to obtain the porous diaphragm.

[0008] In some embodiments of the present invention, the temperature range of the first non-solvent steam and the second non-solvent steam is 100°C to 240°C;

[0009] The first non-solvent steam includes water, a water-N-methylpyrrolidone mixture, a water-N,N-dimethylacetamide mixture, a water-dimethyl sulfoxide mixture, a water-dimethylformamide mixture, ethanol, isopropanol, ethylene glycol;

[0010] The second non-solvent steam includes at least one of water, a mixture of water and N-methylpyrrolidone, a mixture of water and N,N-dimethylacetamide, a mixture of water and dimethyl sulfoxide, a mixture of water and dimethylformamide, ethanol, isopropanol, ethylene glycol;

[0011] Both the first slurry and the second slurry include powder particles, an organic polymer, and an organic solvent.

[0012] In some embodiments of the present invention, the first non-solvent vapor output from the first vapor tank is the ethylene glycol, and the second non-solvent vapor output from the second vapor tank is the water;

[0013] And / or, the powder particles include at least one of zirconia, zirconium hydroxide, magnesia, magnesium hydroxide, yttria, yttrium hydroxide, ceria, cerium hydroxide, titanium oxide, titanium hydroxide, barium sulfate, and carbon;

[0014] And / or, the organic polymer includes at least one of polysulfone, polyethersulfone, polyphenylsulfone, ethylene-vinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polyimide, polyamide, and polyvinylpyrrolidone

[0015] And / or, the organic solvent includes at least one of N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, dimethylacetamide, formylpiperidine, dioxane, and morpholine.

[0016] In some embodiments of the present invention, the organic solvents in the first slurry and / or the second slurry are N-methyl-2-pyrrolidone and dimethylacetamide;

[0017] And / or, the organic solvents in the first slurry and / or the second slurry are N-methyl-2-pyrrolidone and dimethylacetamide, and the mass percentage content of the dimethylacetamide is 30% - 40%.

[0018] In some embodiments of the present invention, the steam amount of the first non-solvent vapor in the first vapor tank is (5 - 100) g / min·m, and the steam amount of the second non-solvent vapor in the second vapor tank is (5 - 100) g / min·m;

[0019] And / or, the time for the coated substrate to pass through the second space is 0.1 s - 10 s.

[0020] And / or, the vertical distance between the steam outlet of the first vapor tank and one side of the coated substrate is 3 mm - 50 mm, and the vertical distance between the steam outlet of the second vapor tank and the other side of the coated substrate is 3 mm - 50 mm.

[0021] And / or, the coagulation bath contains a coagulating liquid, and the coagulating liquid includes at least one of water, a water-N-methyl-2-pyrrolidone mixture, a water-dimethylacetamide mixture, a water-dimethyl sulfoxide mixture, a water-dimethylformamide mixture, ethanol, isopropanol, and ethylene glycol.

[0022] In some embodiments of the present invention, the substrate passes through a first space formed between a relatively arranged first coating die head and a second coating die head. The first coating die head outputs the first slurry to cover one side of the substrate, and the second coating die head outputs the second slurry to cover the other side of the substrate to obtain the coated substrate.

[0023] In some embodiments of the present invention, the first space, the second space, and the coagulation bath are located on the same straight line, and a third space formed between a relatively arranged first air extraction groove and a second air extraction groove is also provided on the same straight line.

[0024] In some embodiments of the present invention, the first air extraction groove and the second air extraction groove adjust the flow directions of the first non-solvent vapor and the second non-solvent vapor by means of negative pressure.

[0025] The present invention also provides a porous separator prepared by the preparation method of the porous separator as described above.

[0026] The present invention also provides a porous separator preparation system for preparing the porous separator as described above. The porous separator preparation system includes a first coating die head, a first steam tank, and a coagulation bath arranged in sequence;

[0027] The first coating die head is relatively arranged with a second coating die head in a first direction,

[0028] The first steam tank is relatively arranged with a second steam tank in the first direction;

[0029] A first space for the substrate to pass through is provided between the first coating die head and the second coating die head,

[0030] A second space for the coated substrate to pass through is provided between the first steam tank and the second steam tank;

[0031] The porous separator preparation system further includes a first air extraction groove. The first air extraction groove is relatively arranged with a second air extraction groove in the first direction, and a third space is provided between the first air extraction groove and the second air extraction groove,

[0032] The first space, the second space, the third space, and the coagulation bath are located on the same straight line in the first direction.

[0033] The beneficial effects that the present invention can achieve:

[0034] In the process of forming a preliminarily cured film substrate, the coating on the coated substrate is brought into contact with non-solvent vapor, which is a countless number of small high-temperature droplets and can help the coating cure better, inhibit the growth of finger-like pore structures on the surface of the separator, and form a uniform sponge-like porous structure on the surface or even throughout the separator. In addition, the present invention can also control the pore structure on the surface of the separator by adjusting the types and temperatures of the vapors output from the first vapor tank and the second vapor tank, enrich the performance of the separator, and further inhibit the growth of finger-like pore structures, so as to form a grid-like porous structure with a firm organic-inorganic combination on the surface of the separator, and obtain a porous structure with a uniform sponge-like shape.

[0035] In an alkaline electrolytic cell, the separator needs to be clamped by the electrodes. The rough structure and catalyst particles on the surface of the electrodes will puncture the surface of the separator, or due to pressure, minute pressure cracks will form on the surface of the separator. These punctured holes and minute pressure cracks will directly connect to the finger-like pore structures, thereby forming gas transmission channels, and ultimately may lead to air leakage. However, the porous separator prepared by the present invention can form a uniform sponge-like porous structure on the surface or even throughout the separator. Even if punctures and micro-cracks occur on the surface, they will not affect the internal structure, increasing the safety of use of the separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0037] Figure 1 It is a schematic diagram of a porous separator preparation system according to an embodiment of the present invention.

[0038] Figure 2 It is a schematic diagram of a porous separator preparation system according to another embodiment of the present invention.

[0039] Figure 3 It is an SEM image of the separator in Embodiment 1 of the present invention.

[0040] Figure 4 It is an SEM image of the separator in Embodiment 2 of the present invention.

[0041] Figure 5 It is an SEM image of the separator in Comparative Example 1 of the present invention.

[0042] Figure 6 It is an SEM image of the separator in Embodiment 3 of the present invention.

[0043] Figure 7 It is an SEM image of the separator in Comparative Example 2 of the present invention.

[0044] Reference numerals in the drawings:

[0045]

[0046] The realization of the object of the present invention, its functional features and advantages will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific embodiments

[0047] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] In the present invention, descriptions such as "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between various embodiments may be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0050] In an alkaline electrolytic cell, the diaphragm needs to be clamped by the electrodes. The rough structure and catalyst particles on the electrode surface will puncture the diaphragm surface, or due to the pressure effect, tiny compression cracks will be formed on the diaphragm surface. These punctured holes and tiny compression cracks will directly communicate with the finger-like pore structure, thereby forming a gas transmission channel, and ultimately may lead to air leakage.

[0051] In view of this, the present invention provides a method for preparing a porous diaphragm, including the following steps:

[0052] S10. Cover a first slurry on one side of a substrate 200, and / or cover a second slurry on the other side of the substrate 200 to obtain a coated substrate 300;

[0053] S20. The coated substrate 300 passes through the second space formed between the relatively arranged first vapor tank 102 and second vapor tank 202, with one side of the coated substrate 300 facing the first vapor tank 102 and the other side facing the second vapor tank 202. The vapor outlet of the first vapor tank 102 outputs a first non-solvent vapor to contact one side of the coated substrate 300, and the vapor outlet of the second vapor tank 202 outputs a second non-solvent vapor to contact the other side of the coated substrate 300, so that the coating on the coated substrate 300 is preliminarily cured to obtain a preliminarily cured film substrate.

[0054] S30. The preliminarily cured film substrate enters the coagulation bath 103 to be cured into a film to obtain a porous separator.

[0055] In step S10, a slurry can be coated on one side of the substrate 200 to form a single-sided coating, or coatings can be coated on both sides of the substrate 200 to form a double-sided coating.

[0056] In some embodiments, the material of the substrate 200 includes at least one of polyphenylene sulfide, polyether ether ketone, and nylon.

[0057] In some embodiments, the thickness range of the substrate 200 is 30 μm to 300 μm.

[0058] In some embodiments, the single-sided coating thickness of the substrate 200 is 30 μm to 200 μm.

[0059] In some embodiments, the slurry can be coated on one side or both sides of the substrate 200 through a slot coating device.

[0060] In some embodiments, the slurry can also be coated on one side or both sides of the substrate 200 by spraying.

[0061] In step S20, referring to Figure 1 and Figure 2 , in the present invention, the coated substrate 300 passes through the second space formed between the relatively arranged first vapor tank 102 and second vapor tank 202, so that the coating on the coated substrate 300 contacts the non-solvent vapor, enabling the coating to be uniformly preliminarily cured. The non-solvent vapor is countless high-temperature small droplets, which can help the coating to be better cured, inhibit the growth of finger-like pore structures on the separator surface, and is conducive to forming a sponge-like porous structure that is even on the surface or even throughout. In addition, the present invention can also control the pore structure on the separator surface by adjusting the types and temperatures of the vapors output by the first vapor tank 102 and the second vapor tank 202, enrich the performance of the separator, and further inhibit the growth of finger-like pore structures, so as to form a grid-like porous structure with a firm organic-inorganic combination on the separator surface, and obtain a porous structure with a uniform sponge-like shape.

[0062] In some embodiments, the temperature range of the first non-solvent vapor is from 100°C to 240°C. For example, it can be any value within the range of 100°C to 240°C such as 100°C, 150°C, 180°C, 200°C, 240°C, etc.; the temperature range of the second non-solvent vapor is from 100°C to 240°C. For example, it can be any value within the range of 100°C to 240°C such as 100°C, 150°C, 180°C, 200°C, 240°C, etc. When the temperature of the non-solvent vapor is within the above range, it is beneficial to inhibit the formation of finger holes in the separator, and a porous separator with a uniform sponge-like porous structure can be obtained.

[0063] In some embodiments, the first non-solvent vapor includes at least one of water, a mixture of water and N-methylpyrrolidone (NMP), a mixture of water and N,N-dimethylacetamide (DMAC), a mixture of water and dimethyl sulfoxide (DMSO), a mixture of water and dimethylformamide (DMF), ethanol, isopropanol, and ethylene glycol. It can be understood that the above are all in a vapor state, and the non-solvent vapor of the above types can preliminarily cure the coating in the coated substrate 300.

[0064] In some embodiments, the second non-solvent vapor includes at least one of water, a mixture of water and N-methylpyrrolidone (NMP), a mixture of water and N,N-dimethylacetamide (DMAC), a mixture of water and dimethyl sulfoxide (DMSO), a mixture of water and dimethylformamide (DMF), ethanol, isopropanol, and ethylene glycol. It can be understood that the above are all in a vapor state, and the non-solvent vapor of the above types can preliminarily cure the coating in the coated substrate 300.

[0065] In some embodiments, the first non-solvent vapor output from the steam outlet of the first steam tank 102 is ethylene glycol, and ethylene glycol is in a vapor state. The second solvent output from the steam outlet of the second steam tank 202 is water, and water is in a steam state. By using non-solvent vapors of different types in the two-side steam tanks in this embodiment, the separator can have two-side film surfaces with different properties. For example, the surface of the film on the side in contact with the water vapor can form a grid-like porous structure with strong hydrophilicity and a low bubble contact angle, while the surface of the film on the side in contact with the ethylene glycol vapor can achieve a generally dense surface structure with weak hydrophilicity and a high bubble contact angle. Moreover, the two-side films as a whole can present a uniform sponge-like porous structure, and finger holes are not likely to appear in its cross-section. The separator obtained in this embodiment can not only form a uniform sponge-like porous structure, but also has hydrophilic and hydrophobic properties on its surface, can be used as a Janus material, and is also convenient for subsequent different modifications on the surface of the separator.

[0066] In some embodiments, the temperature of the ethylene glycol output from the first steam tank 102 is 220°C, and the temperature of the water output from the second steam tank 202 is 180°C.

[0067] In some embodiments, the compositions of the first slurry and the second slurry may be different, thereby forming coatings with different compositions on one side and the other side of the substrate 200, enriching the performance of the separator. The compositions of the first slurry and the second slurry may also be the same, thereby forming coatings with the same composition on one side and the other side of the substrate 200.

[0068] In some embodiments, the first slurry includes powder particles, an organic polymer, and an organic solvent; the second slurry includes powder particles, an organic polymer, and an organic solvent.

[0069] In some embodiments, the powder particles include at least one of zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, yttrium oxide, yttrium hydroxide, cerium oxide, cerium hydroxide, titanium oxide, titanium hydroxide, barium sulfate, and carbon.

[0070] In some embodiments, the organic solvent includes at least one of N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide, tetrahydrofuran, dimethylacetamide (DMAC), formylpiperidine, dioxane, and morpholine.

[0071] In some embodiments, the organic polymer includes at least one of polysulfone, polyethersulfone, polyphenylsulfone, ethylene-vinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polyimide, polyamide, and polyvinylpyrrolidone.

[0072] The present invention does not limit the weight ratios of the organic solvent, powder particles, and organic polymer in the first slurry and the second slurry, and they can be combined according to actual needs.

[0073] In some embodiments, the organic solvent in the first slurry and / or the second slurry is N-methyl-2-pyrrolidone and dimethylacetamide. A mixed solution of N-methyl-2-pyrrolidone and dimethylacetamide is used as the solvent, and when combined with non-solvent vapor, it can reduce the miscibility of the organic solvent and non-solvent vapor system in the slurry. Thereby, the formation of finger-like pores on the surface of the separator is inhibited, and even the formation of finger-like pores can be completely inhibited, forming a sponge-like porous structure on the surface and inside of the separator, with clear grids, reducing or even eliminating the phenomenon of ceramic powder accumulation on the surface.

[0074] In some embodiments, the mass percentage content of dimethylacetamide in the organic solvent formed by mixing N-methyl-2-pyrrolidone and dimethylacetamide is 30% - 40%. This is beneficial for reducing the miscibility of the organic solvent and non-solvent vapor system and inhibiting the formation of finger-like pores on the surface of the separator.

[0075] In some embodiments, the amount of the first non-solvent vapor in the first vapor bath 102 is (5 - 100) g / min·m, and can be 5 g / min·m, 10 g / min·m, 20 g / min·m, 30 g / min·m, 40 g / min·m, 50 g / min·m, 60 g / min·m, 70 g / min·m, 80 g / min·m, 90 g / min·m, 100 g / min m, etc. The amount of the second non-solvent vapor in the second vapor bath 202 is (5 - 100) g / min·m, and can be 5 g / min·m, 10 g / min·m, 20 g / min·m, 30 g / min·m, 40 g / min·m, 50 g / min·m, 60 g / min·m, 70 g / min·m, 80 g / min·m, 90 g / min·m, 100 g / min m, etc. This is beneficial to the preliminary curing of the coating in the coated substrate 300, and is also beneficial to the formation of a uniform sponge-like or grid-like porous structure.

[0076] In some embodiments, the time for the coated substrate 300 to pass through the second space is 0.1 s - 10 s, preferably 0.1 s - 3 s, so that the coating in the coated substrate 300 is in complete contact with the non-solvent vapor, achieving better preliminary curing, facilitating the formation of a uniformly spongy porous structure as a whole, and not easily damaging the above-mentioned spongy porous structure due to too long contact time.

[0077] In some embodiments, the vertical distance between the vapor outlet of the first vapor bath 102 and one side of the coated substrate 300 is 3 mm - 50 mm.

[0078] In some embodiments, the vertical distance between the vapor outlet of the second vapor bath 202 and the other side of the coated substrate 300 is 3 mm - 50 mm.

[0079] In some embodiments, the vertical distance between the vapor outlet of the first vapor bath 102 and one side of the coated substrate 300 is the same as the vertical distance between the vapor outlet of the second vapor bath 202 and the other side of the coated substrate 300, making the forces on both sides of the coated substrate 300 more uniform, being beneficial to achieving better preliminary curing, forming a uniformly grid-like or sponge-like porous structure on the surface of the diaphragm, and suppressing the formation of finger-like pores.

[0080] In step S30, the preliminarily cured film substrate is immersed in the coagulation bath 103, and the coating is completely cured to obtain a porous diaphragm.

[0081] In some embodiments, the coagulation bath 103 contains a coagulating liquid, and the coagulating liquid includes at least one of water, a mixture of water and N-methyl-2-pyrrolidone (NMP), a mixture of water and dimethylacetamide (DMAC), a mixture of water and dimethyl sulfoxide (DMSO), a mixture of water and dimethylformamide (DMF), ethanol, isopropanol, and ethylene glycol.

[0082] In some embodiments, the substrate 200 passes through a first space formed between the relatively arranged first coating die 101 and the second coating die 201. The first coating die 101 outputs the first slurry to cover one side of the substrate 200, and / or the second coating die 201 outputs the second slurry to cover the other side of the substrate 200. In this embodiment, the coating die is used to coat the substrate 200, which can simplify the process and improve production efficiency.

[0083] In some embodiments, the first space, the second space, and the coagulation bath 103 are located on the same straight line, and a third space formed between the relatively arranged first air extraction groove 104 and the second air extraction groove 204 is also provided on the same straight line. The air extraction groove can control the flow direction of the non-solvent vapor output by the vapor groove, prompt the non-solvent vapor to contact the coated substrate 300, and finally extract the non-solvent vapor. In addition, it can also control the contact time between the non-solvent vapor and the coated substrate 300.

[0084] In some embodiments, referring to Figure 1 , the first air extraction groove 104 and the second air extraction groove 204 can be arranged between the first coating die 101, the second coating die 201 and the first vapor groove 102, the second vapor groove 202, that is, on the same straight line, the first coating die 101, the first air extraction groove 104, and the first vapor groove 102 are arranged in sequence, the second coating die 201, the second air extraction groove 204, and the second vapor groove 202 are arranged in sequence, and the first space, the third space, the second space, and the coagulation bath 103 are arranged in sequence. In this embodiment, the substrate 200 passes through the first space between the first coating die 101 and the second coating die 201, and the coating is applied to both sides or one side of the substrate 200 to obtain the coated substrate 300. The coated substrate 300 then continues to pass through the third space formed by the first air extraction groove 104 and the second air extraction groove 204 and the second space formed by the first vapor groove 102 and the second vapor groove 202. The first air extraction groove 104 and the second air extraction groove 204 can control the flow direction of the non-solvent vapor output by the vapor groove, so that the non-solvent vapor moves in the opposite direction to the movement direction of the coated substrate 300 and finally enters the first air extraction groove 104 and the second air extraction groove 204, prompting the non-solvent vapor to contact the coated substrate 300, and can control the contact time between the non-solvent vapor and the coated substrate 300.

[0085] In some embodiments, referring to Figure 2, the first space, the second space, the third space, and the solidification bath 103 on the same straight line can also be arranged in sequence as the first space, the second space, the third space, and the solidification bath 103. That is, on the same straight line, the first coating die head 101, the first steam tank 102, and the first exhaust slot 104 are arranged in sequence, and the second coating die head 201, the second steam tank 202, and the second exhaust slot 204 are arranged in sequence. The substrate 200 passes through the first space formed by the first coating die head 101 and the second coating die head 201 to obtain the coated substrate 300. The coated substrate 300 passes through the second space formed by the first steam tank 102 and the second steam tank 202 in sequence and comes to the third space formed by the first exhaust slot 104 and the second exhaust slot 204. During this process, the first exhaust slot 104 and the second exhaust slot 204 control the flow direction of the non-solvent vapor output by the steam, so that the non-solvent vapor moves in the direction of moving towards the coated substrate 300 and finally enters the exhaust slot, prompting the non-solvent vapor to contact the coated substrate 300, and being able to control the contact time between the non-solvent vapor and the coated substrate 300.

[0086] In some embodiments, the first exhaust slot 104 and the second exhaust slot 204 adjust the flow direction of the first steam and the second steam by means of negative pressure, and control the contact time between them and the coated substrate 300.

[0087] In some embodiments, the time for the coated substrate 300 to pass through the third space formed between the first exhaust slot 104 and the second exhaust slot 204 is 0.1 s to 3 s.

[0088] The present invention also provides a porous separator preparation system 100. Refer to Figure 1 , the porous separator preparation system 100 includes a first coating die head 101, a first steam tank 102, and a solidification bath 103 arranged in sequence. The first coating die head 101 is oppositely provided with a second coating die head 201 in the first direction. The first steam tank 102 is oppositely provided with a second steam tank 202 in the first direction. There is a first space for the substrate 200 to pass through between the first coating die head 101 and the second coating die head 201. There is a second space for the coated substrate 300 to pass through between the first steam tank 102 and the second steam tank 202.

[0089] When preparing a porous separator using this preparation system, a first slurry is loaded into the first coating die head 101, and / or a second slurry is loaded into the second coating die head 201. The substrate 200 passes through the first space, with one side of the substrate 200 facing the first coating die head 101 and the other side facing the second coating die head 201. The first coating die head 101 is used to coat and form a first coating on one side of the substrate 200, and the second coating die head 201 is used to coat and form a second coating on the other side of the substrate 200. It can be understood that a coating can be formed by coating only on one side of the substrate 200, or coatings can be formed on both sides of the substrate 200.

[0090] The coated substrate 200 becomes the coated substrate 300. The coated substrate 300 continues to pass through the second space formed between the first vapor bath 102 and the second vapor bath 202. The first vapor bath 102 outputs a first non-solvent vapor that acts on one side of the coated substrate 300, and the second vapor bath 202 outputs a second non-solvent vapor that acts on the other side of the coated substrate 300. The coated substrate 300 is preliminarily cured by passing through the first vapor bath 102 and the second vapor bath 202 to obtain a preliminarily cured film-forming substrate, and the preliminarily cured film-forming substrate moves into the coagulation bath 103 and is further cured to obtain a porous separator.

[0091] The porous separator preparation system 100 further includes a first air extraction slot 104. A second air extraction slot 204 is disposed opposite to the first air extraction slot 104 in the first direction. There is a third space between the first air extraction slot 104 and the second air extraction slot 204. The first space, the second space, the third space, and the coagulation bath 103 are located on the same straight line in the first direction. The first air extraction slot 104 and the second air extraction slot 204 are used to control the flow of the first vapor and the second vapor, which not only promotes the contact between the non-solvent vapor and the coated substrate 300, but also can adjust the contact time between the first vapor and the second vapor and the coated substrate 300, and affect the formation of the surface porous structure by flexibly controlling the contact time.

[0092] In some embodiments, continue to refer to Figure 1 , in the porous separator preparation system 100, the order of the first space, the second space, the third space, and the coagulation bath 103 in the first direction is the first space formed by the first coating die head 101 and the first vapor bath 102, the third space formed by the first air extraction slot 104 and the second air extraction slot 204, the second space formed by the first vapor bath 102 and the second vapor bath 202, and the coagulation bath 103.

[0093] In some embodiments, refer to Figure 2, in the porous separator preparation system 100, the order of the first space, the second space, the third space and the coagulation bath 103 in the first direction is the first space formed by the first coating die head 101 and the first steam tank 102, the second space formed by the first steam tank 102 and the second steam tank 202, the third space formed by the first air extraction tank 104 and the second air extraction tank 204, and the coagulation bath 103.

[0094] In some embodiments, the vertical distance between the air extraction port of the first air extraction tank 104 and one side of the passing coating substrate 300 is 1 mm to 50 mm, preferably 5 to 15 mm, and the vertical distance between the air extraction port of the second air extraction tank 204 and the other side of the passing coating substrate 300 is 1 mm to 50 mm, preferably 5 mm to 15 mm.

[0095] In some embodiments, the vertical distance between the steam outlet of the first steam tank 102 and one side of the passing coating substrate 300 is 3 mm to 50 mm, preferably 5 mm to 30 mm, and the vertical distance between the steam outlet of the second steam tank 202 and the other side of the passing coating substrate 300 is 3 mm to 50 mm, preferably 5 mm to 30 mm.

[0096] In some embodiments, the vertical distance between the first air extraction tank 104 and the first coating die head 101 is 5 cm to 100 cm, preferably 10 cm to 20 cm, and the vertical distance between the second air extraction tank 204 and the second coating die head 201 is 5 cm to 100 cm, preferably 10 cm to 20 cm.

[0097] In some embodiments, the vertical distance between the first air extraction tank 104 and the first steam tank 102 is 5 cm to 100 cm, preferably 15 cm to 20 cm, and the vertical distance between the second air extraction tank 204 and the second steam tank 202 is 5 cm to 100 cm, preferably 15 cm to 20 cm.

[0098] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and are not used to limit the present invention.

[0099] Example 1

[0100] Example 1 uses the porous separator preparation system as Figure 1 shown to prepare a porous separator.

[0101] (1) Introduction to the porous separator system

[0102] Refer to Figure 1, the porous diaphragm preparation system includes a first coating die head 101, a first air extraction tank 104, a first steam tank 102, and a coagulation bath 103 arranged in sequence. The first coating die head 101 is oppositely arranged with a second coating die head 201 in the first direction, the first air extraction tank 104 is oppositely arranged with a second air extraction tank 204 in the first direction, and the first steam tank 102 is oppositely arranged with a second steam tank 202 in the first direction; there is a first space for the substrate 200 to pass through between the first coating die head 101 and the second coating die head 201, a third space for the coated substrate 300 to pass through between the first air extraction tank 104 and the second air extraction tank 204, and a second space for the coated substrate 300 to pass through between the first steam tank 102 and the second steam tank 202; the first space, the third space, the second space, and the coagulation bath 103 are located on the same straight line in the first direction.

[0103] Among them, the vertical distance between the air extraction port of the first air extraction tank 104 and the side of the passing substrate 200 facing the air extraction port of the first air extraction tank 104 is 15 mm, the distance between the air extraction port of the second air extraction tank 204 and the other side of the passing substrate 200 is 15 mm, the vertical distance between the steam outlet of the first steam tank 102 and the side of the passing substrate 200 facing the steam outlet of the first steam tank 102 is 30 mm, and the vertical distance between the steam outlet of the second steam tank 202 and the other side of the passing substrate 200 is 30 mm. The vertical distance between the first air extraction tank 104 and the first coating die head 101 is 20 cm, the vertical distance between the second air extraction tank 204 and the second coating die head 201 is 20 cm, the vertical distance between the first air extraction tank 104 and the first steam tank 102 is 50 cm, and the vertical distance between the second air extraction tank 204 and the second steam tank 202 is 50 cm.

[0104] The air extraction tanks on both sides of this system use a negative pressure method to promote the non-solvent steam output from the two steam tanks to move in the opposite direction of the first direction and suck away the output non-solvent steam.

[0105] (2) Using the porous diaphragm preparation system to prepare a porous diaphragm

[0106] S10: Ball-mill and mix 100 g of organic solvent N-methyl-2-pyrrolidone (NMP), 20 g of organic polymer polysulfone (PSU), and 114 g of powder particle zirconia evenly, and perform vacuum degassing to obtain a slurry. Fill this slurry into the first coating die head 101 and the second coating die head 201 respectively, make the substrate 200 pass through the first space, and use the first coating die head 101 and the second coating die head 201 to coat the slurry on both sides of the substrate 200 respectively to obtain a coated substrate 300.

[0107] S20. The coated substrate 300 is sequentially passed through the third space and the second space. The steam outlet of the first steam tank 102 outputs ethylene glycol steam at 220 °C as the first non-solvent steam at a steam flow rate of 20 g / min m and slowly sprays it on one side of the coated substrate 300. The steam outlet of the second steam tank 202 outputs water steam at 180 °C as the second non-solvent steam at a steam flow rate of 60 g / min m and slowly sprays it on the other side of the coated substrate 300. The non-solvent steam on both sides rises under the negative pressure of the first air extraction tank 104 and the second air extraction tank 204 and is successively drawn away by the air extraction tank, so that the contact time between the coated substrate 300 and the non-solvent steam is 1 s, thereby initially curing the slurries on both sides to obtain the initially cured substrate 200.

[0108] S30. The initially cured substrate 200 continues to enter the solidification bath 103 with water as the solidifying liquid, and the initially cured substrate 200 is cured by deionized water to obtain a porous separator.

[0109] Comparative Example 1

[0110] Comparative Example 1 prepares a porous separator by referring to the method of Example 1. However, the difference is that the first non-solvent steam output by the first steam tank 102 in Comparative Example 1 is ethylene glycol steam at a temperature of 250 °C, and the second non-solvent steam output by the second steam tank 202 is water steam at 250 °C.

[0111] Example 2

[0112] Example 2 prepares a porous separator by referring to the method of Example 1. However, the difference is that in Example 2, only the second steam tank 202 outputs steam water at 180 °C as the second non-solvent to initially cure the coated layer on the side of the substrate 200 facing the second coating die head 201, and the first steam tank 102 does not output non-solvent steam.

[0113] Example 3

[0114] Example 3 prepares a porous separator by referring to the method of Example 1. The difference is that in Example 3, 70 g of NMP, 30 g of DMAC, 20 g of PSU, and 114 g of zirconia are ball-milled and mixed evenly, and then vacuum degassed to obtain a slurry, where the mass ratio of NMP to DMAC is 7:3, and both the first steam tank 102 and the second steam tank 202 output water steam at 180 °C.

[0115] Comparative Example 2

[0116] Comparative Example 2 prepares a porous separator by referring to the method of Example 3. The difference is that in Comparative Example 2, the organic solvent in the slurry is replaced with 100 g of NMP, DMAC is not added, and both the first steam tank 102 and the second steam tank 202 output water steam at 180 °C, and the steam flow rate is 1 g / min m for both.

[0117] Performance Test

[0118] The porous separators prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were observed with a scanning electron microscope.

[0119] The SEM image of Example 1 is as Figure 3 shown. Figure 3 On the left in [the figure] is the surface formed by preliminary curing with ethylene glycol vapor on one side of the separator, Figure 3 and on the right is the surface formed by preliminary curing with water vapor on the other side of the separator. It can be seen from Figure 3 this that a globally uniform sponge-like porous structure is formed on one side of the separator, and a globally uniform grid-like porous structure is formed on the other side.

[0120] The SEM image of Example 2 is as Figure 4 shown. The separator shows an asymmetric structure. On the side that did not receive the vapor, finger-like pores grew, while on the side that received preliminary curing with the vapor in the vapor groove, finger-like pores did not grow.

[0121] The SEM image of Comparative Example 1 is as Figure 5 shown. No grid-like structure or sponge-like porous structure was formed on the surface of the separator because the temperature of the non-solvent vapor was too high, reaching 250 °C.

[0122] The SEM image of Example 3 is as Figure 6 shown. Figure 6 On the left is the cross-sectional view of the separator, Figure 6 and on the right is the surface view of the separator. There are no finger-like pores in the cross-section, and it is a complete sponge-like structure. The surface shows a grid-like structure, and the grids are clear, and there is no ceramic powder accumulation on the grid surface.

[0123] The SEM image of Comparative Example 2 is as Figure 7 shown. Finger-like pores appeared in the cross-section of the separator. In Comparative Example 2, the vapor amount was 1 g / min·m, and the formation of finger-like pores could not be completely inhibited.

[0124] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a porous diaphragm, characterized in that: The following steps are involved: Covering one side of a substrate with a first slurry and covering the other side of the substrate with a second slurry to obtain a coated substrate; The coated substrate passes through a second space formed between a first steam tank and a second steam tank that are arranged opposite to each other, so that one side of the coated substrate faces the first steam tank and the other side faces the second steam tank; the steam outlet of the first steam tank outputs a first non-solvent steam that contacts one side of the coated substrate, and the steam outlet of the second steam tank outputs a second non-solvent steam that contacts the other side of the coated substrate, so that the coating in the coated substrate is initially cured to obtain a initially cured film-forming substrate; The preliminary cured film-forming substrate enters a coagulation bath to be cured to form a film to obtain the porous diaphragm; The steam volume of the first non-solvent steam in the first steam tank is (5-100) g / min·m, and the steam volume of the second non-solvent steam in the second steam tank is (5-100) g / min·m; The temperature range of the first non-solvent vapor and the second non-solvent vapor is 100° C. to 240° C.; The organic solvent in the first slurry and / or the second slurry is N-methyl-2-pyrrolidone and dimethylacetamide, and the mass percentage of dimethylacetamide in the organic solvent formed by mixing N-methyl-2-pyrrolidone and dimethylacetamide is 30% to 40%; The substrate passes through a first space formed between a first coating die head and a second coating die head that are arranged opposite to each other, the first coating die head outputs the first slurry to cover one side of the substrate, and the second coating die head outputs the second slurry to cover the other side of the substrate to obtain the coated substrate; The first space, the second space and the coagulation bath are located on the same straight line, and a third space formed by the first exhaust slot and the second exhaust slot which are arranged opposite to each other is also provided on the same straight line; The first exhaust slot and the second exhaust slot adjust the flow directions of the first non-solvent vapor and the second non-solvent vapor by means of negative pressure.

2. The method for preparing a porous diaphragm according to claim 1, characterized in that: The first non-solvent vapor includes water, a water-N-methylpyrrolidone mixture, a water-N,N-dimethylacetamide mixture, a water-dimethyl sulfoxide mixture, a water-dimethylformamide mixture, ethanol, isopropanol, and ethylene glycol; The second non-solvent vapor includes at least one of water, a mixture of water and N-methylpyrrolidone, a mixture of water and N,N-dimethylacetamide, a mixture of water and dimethyl sulfoxide, a mixture of water and dimethylformamide, ethanol, isopropanol, and ethylene glycol; The first slurry and the second slurry both include powder particles, an organic polymer and an organic solvent.

3. The method for preparing a porous diaphragm according to claim 2, characterized in that: The first non-solvent vapor outputted by the first steam tank is the ethylene glycol, and the second non-solvent vapor outputted by the second steam tank is the water; And / or, the powder particles include at least one of zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, yttrium oxide, yttrium hydroxide, cerium oxide, cerium hydroxide, titanium oxide, titanium hydroxide, barium sulfate, and carbon; And / or, the organic polymer includes at least one of polysulfone, polyethersulfone, polyphenylsulfone, ethylene vinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polyimide, polyamide, and polyvinylpyrrolidone.

4. The method for preparing the porous membrane according to claim 1, characterized in that: The time for the coated substrate to pass through the second space is 0.1s to 10s; And / or, the vertical distance between the steam outlet of the first steam groove and one side of the coating substrate is 3 mm to 50 mm, and the vertical distance between the steam outlet of the second steam groove and the other side of the coating substrate is 3 mm to 50 mm; And / or, the coagulation bath contains a coagulation liquid, and the coagulation liquid includes at least one of water, a water-N-methyl-2-pyrrolidone mixture, a water-dimethylacetamide mixture, a water-dimethyl sulfoxide mixture, a water-dimethylformamide mixture, ethanol, isopropanol, and ethylene glycol.

5. A porous membrane prepared by the method for preparing a porous membrane according to any one of claims 1 to 4.

6. A porous membrane preparation system for preparing the porous membrane according to claim 5, characterized in that: The porous membrane preparation system comprises a first coating die head, a first steam tank and a coagulation bath which are arranged in sequence; The first coating die head is provided with a second coating die head opposite to the first direction, The first steam groove is provided with a second steam groove opposite to the first direction; There is a first space between the first coating die head and the second coating die head for the substrate to pass through, A second space is provided between the first steam groove and the second steam groove for the coating substrate to pass through; The porous membrane preparation system further includes a first exhaust groove, wherein the first exhaust groove is provided with a second exhaust groove opposite to the first direction, and a third space is provided between the first exhaust groove and the second exhaust groove. The first space, the second space, the third space and the coagulation bath are located on the same straight line in the first direction.

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