Separator, and preparation method therefor and use thereof

Abstract

A separator, and a preparation method therefor and a use thereof. In the separator, by selecting a wetting agent in a coating, defining the amount of the wetting agent, and defining the proportional relationship between the particle size D of PMMA particles and the thickness H of a coating base layer, the breakdown strength of the separator is enhanced, and the influence of the wetting agent on the insulating performance of the separator is avoided. Compared with a conventional separator in which a base film, a heat-resistant coating and an adhesive coating are applied multiple times in a layered manner, by means of mixed application of inorganic particles and large PMMA particles, the coating is simplified, the bonding and heat resistance requirements on the coating are satisfied, the production cost of the separator is reduced, and there is no higher requirement on a production device.

Description

A diaphragm, its preparation method and application

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. CN202411429843.3, filed on October 14, 2024, entitled "A diaphragm and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of secondary battery technology, specifically relating to a separator, its preparation method, and its application. Background Technology

[0004] With the booming development of the new energy industry, the lithium-ion battery manufacturing field has made rapid progress. Improving the yield of battery cell production and reducing costs and increasing efficiency in battery manufacturing are of great practical significance. The lithium-ion battery separator is one of the four main materials of lithium-ion batteries, which plays a role in isolating the positive and negative electrodes and preventing them from contacting each other and causing short circuits.

[0005] During battery cell manufacturing, short circuits are usually caused by the separator being punctured or broken down by voltage. The causes of short circuits in Hipot testing (also known as high-voltage insulation testing or withstand voltage testing) can be divided into two categories: ① The separator itself has weak points that can be punctured by foreign objects, causing contact between the positive and negative electrodes and resulting in a short circuit. Currently, as the thickness of the separator base film is reduced, its resistance to foreign objects decreases, making it easier for the separator to be punctured; ② During the multiple coating processes, the wetting agent used in the coating penetrates into the microporous structure of the base film, causing a significant decrease in the intrinsic insulation performance of the separator and a reduction in its withstand voltage. This makes it easier for short circuits to occur during battery Hipot testing, threatening the safety of the battery cell.

[0006] Existing methods for improving the breakdown resistance of diaphragms, from the perspective of the base membrane, mainly involve optimizing the base membrane manufacturing process, improving the pore size consistency of the base membrane, reducing the formation of larger pores, and lowering the risk of breakdown. This approach places higher demands on the diaphragm stretching equipment, requiring equipment upgrades and iterations. From the coating perspective, the main approach is to use breakdown-resistant coating materials such as aramid fibers to increase the overall breakdown voltage of the diaphragm. However, the coating methods are mostly oil-based and costly, which is not conducive to large-scale application. Conventional layered coating (heat-resistant inorganic coating + adhesive organic coating) schemes require the use of wetting agents in each coating process, increasing the risk of penetration into the micropores of the base membrane and leading to a decrease in the insulation performance of the diaphragm.

[0007] In summary, it is of great significance to provide a method for improving the breakdown strength of a diaphragm that does not require sophisticated equipment, is inexpensive, and does not affect the insulation performance of the diaphragm.

[0008] Application content

[0009] In view of this, the purpose of this application is to provide a diaphragm, its preparation method and application, in order to overcome the defects of existing methods for improving the breakdown strength of diaphragms, such as high equipment requirements, high cost or impact on the insulation performance of the diaphragm.

[0010] In a first aspect, this application provides a diaphragm, comprising: a base membrane and a coating layer located on at least one side surface of the base membrane, the coating layer comprising a coating base layer and PMMA (polymethyl methacrylate) particles dispersed in the coating base layer;

[0011] The coating substrate comprises inorganic particles, butynediol ethoxylate modified polysiloxane, water-based binder, and thickener;

[0012] The particle size D of the PMMA particles and the thickness H of the coating substrate satisfy the following relationship: 6≥D / H≥1.5.

[0013] In this application, the butynediol ethoxylate modified polysiloxane is obtained by carrying out a hydrosilylation reaction of butynediol ethoxylate (CAS No. 1606-85-5) and polysiloxane (number average molecular weight of 900-11000) at 70°C-90°C under an inert atmosphere for 10-14 hours.

[0014] Beneficial Effects: The separator provided in this application, by selecting the wetting agent in the coating layer and limiting the ratio between the PMMA particle size D and the coating base thickness H, improves the separator's breakdown strength and reduces the number of electrical weaknesses. Cells produced using this separator exhibit lower hit-hole short-circuit rates and higher production yields. Furthermore, compared to conventional separators with multiple layers of base film + heat-resistant coating + adhesive coating, the method of forming a mixed coating layer using inorganic particles and large PMMA particles simplifies the coating process while meeting the adhesion and heat resistance requirements of the coating layer, reducing separator production costs and requiring less sophisticated production equipment. Specifically, the large PMMA particles, acting as a bonding agent between the separator and the electrode, need to contact the electrode surface as contact points during hot pressing. Therefore, their particle size needs to be slightly larger than the coating base to better exert their bonding effect during hot pressing. If the PMMA particle size is too large, it is prone to detachment; if the particle size is too small, the PMMA may be completely embedded in the coating base, or too little may be exposed on the coating base surface, thus affecting the bonding effect. By using butynediol ethoxylated modified polysiloxane as a wetting agent, the dispersion and wetting ability of the slurry is improved, the penetration of the wetting agent into the pores of the base membrane is reduced, and its adverse effect on the diaphragm's puncture resistance is avoided.

[0015] In one alternative embodiment, the mass ratio of butynediol ethoxylate to polysiloxane is 1:(5-8).

[0016] In one alternative embodiment, the porosity of the coating layer is 40% to 50%.

[0017] Beneficial effects: By limiting the porosity of the coating layer to a certain range, the breakdown voltage of the coating layer can be further improved. Since the breakdown of the diaphragm is essentially the breakdown of air in the pores of the diaphragm under voltage, excessively high porosity makes it easier to break down, which will lead to a decrease in the voltage withstand performance of the diaphragm; excessively low porosity increases the pore-blocking effect of the coating, and increases the air permeability of the diaphragm (in this application, air permeability refers to the time required for a fixed volume of air to pass through the diaphragm. The value of air permeability is inversely proportional to porosity; low porosity means high air permeability), which may affect the performance of the battery cell and cause an increase in the internal resistance of the battery cell.

[0018] In one optional embodiment, the wetting agent comprises 0.15% to 0.25% by mass of the total mass of the coating layer.

[0019] Beneficial effects: By selecting a wetting agent, this application can further reduce the amount of wetting agent used in the slurry compared to conventional wetting agents, thereby avoiding the increased risk of wetting agent penetrating into the pores of the base membrane due to excessive use of wetting agent, which would adversely affect the diaphragm's puncture resistance.

[0020] In one optional embodiment, the PMMA particles comprise 4% to 8% of the total mass of the coating layer.

[0021] And / or, the inorganic particles have a mass percentage content of 85.5% to 89.5%;

[0022] And / or, the thickener has a mass percentage content of 1% to 1.5%;

[0023] And / or, the water-based adhesive has a mass percentage content of 4.5% to 5.3%.

[0024] In one optional embodiment, the breakdown voltage of the diaphragm is K1, in V; the breakdown voltage of the base film is K2, in V; and the coating layer thickness H, in μm, satisfies the following relationship:

[0025] 100≤(K1-K2) / H≤200.

[0026] In one optional embodiment, the particle size Dv50 of the inorganic particles is below 300 nm;

[0027] And / or, the thickness of the base film is 3 μm to 20 μm;

[0028] And / or, the thickness H of the coating substrate is 1μm to 3μm.

[0029] In one alternative embodiment, the inorganic particles include, but are not limited to, at least one of alumina and boehmite;

[0030] And / or, the water-based adhesive includes, but is not limited to, at least one of acrylic adhesives or styrene-butadiene rubber;

[0031] And / or, the thickener includes, but is not limited to, sodium carboxymethyl cellulose;

[0032] And / or, the base film includes, but is not limited to, at least one of polyethylene base film and polypropylene base film.

[0033] Secondly, this application provides a method for preparing the above-mentioned diaphragm, comprising the following steps:

[0034] S1, Inorganic particles, PMMA particles, thickener, water-based binder, butynediol ethoxylate modified polysiloxane and water are mixed to obtain a slurry;

[0035] S2, the slurry is coated onto at least one side of the base membrane and dried to obtain the diaphragm.

[0036] In this application, the coating method of the slurry is conventional in the art, typically and non-limitingly, the slurry is coated on one or both sides of the base film by gravure roller coating, and then dried at 70°C to 90°C.

[0037] In step S1, the solid content of the slurry is not specifically limited, as long as it is suitable for roller coating operation.

[0038] Thirdly, this application provides a secondary battery, including the above-described separator or the separator prepared by the above-described preparation method.

[0039] Fourthly, this application provides an electrical device including the aforementioned secondary battery.

[0040] The secondary battery provided in this application also includes a positive electrode, a negative electrode, and an electrolyte. This application does not specifically limit the preparation method of the secondary battery; conventional preparation methods in the art can be used to prepare the secondary battery. For example, the positive electrode, separator, and negative electrode are sequentially stacked, with the separator positioned between the positive and negative electrodes. A cell is obtained through a stacking or winding process, and then the secondary battery of this application is obtained through baking, electrolyte injection, formation, and encapsulation.

[0041] Fifthly, this application provides yet another type of electrical device, including the aforementioned secondary battery. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 is a schematic diagram of the structure of the diaphragm provided in an embodiment of this application;

[0044] Reference numerals: 1. Base film; 2. Coating layer; 3. PMMA particles; 4. Coating base layer. Detailed Implementation

[0045] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0046] The following disclosure provides numerous different embodiments or examples for implementing various structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0047] Example 1

[0048] This embodiment provides a diaphragm, the structural schematic of which is shown in Figure 1. The figure only shows the structure of one side of the base membrane 1, including the base membrane 1 and a coating layer 2. The coating layer 2 includes a coating base layer 4 and PMMA particles 3 dispersed in the coating base layer 4. The specific preparation method includes the following steps:

[0049] (1) Inorganic particles (boehmite, particle size D50 = 200 nm), PMMA particles (Shenzhen Haodian, particle size see Table 1), thickener (sodium carboxymethyl cellulose), water-based binder (acrylic binder, brand Haodian SWA610) and butynediol ethoxylate modified polysiloxane (obtained by hydrosilylation reaction of butynediol ethoxylate and polysiloxane (number average molecular weight 2012) at a mass ratio of 1:6 at 80°C under an inert atmosphere for 12 h) were added to deionized water in a mass ratio of 87.5:6:1.3:5:0.2 to prepare a slurry.

[0050] (2) The slurry is coated on both sides of a conventional porosity PE base film (porosity 40%) with a thickness of 9μm by gravure roller coating. The thickness of a single layer is controlled to be 1μm. The film is dried at 80℃ for 3 minutes to obtain the diaphragm. The diaphragm structure is 9+1+1.

[0051] Example 2

[0052] This embodiment provides a diaphragm that differs from Embodiment 1 only in that the single-layer coating thickness is 2μm and the diaphragm structure is 9+2+2.

[0053] Example 3

[0054] This embodiment provides a diaphragm, which differs from Embodiment 1 only in that the single-layer coating thickness is 3μm and the diaphragm structure is 9+3+3.

[0055] Example 4

[0056] This embodiment provides a diaphragm. Compared with embodiment 2, the only difference is that the slurry is coated on one side of a conventional porosity PE base film with a thickness of 9μm using a gravure roller coating method, and the diaphragm structure is 9+2.

[0057] Example 5

[0058] This embodiment provides a diaphragm, which differs from Embodiment 4 only in that, based on the mass ratio of the effective components, the mass ratio of inorganic particles, PMMA particles, thickener, water-based binder, and butynediol ethoxylate modified polysiloxane in the slurry is 87.45:6:1.3:5:0.25.

[0059] Example 6

[0060] This embodiment provides a diaphragm, which differs from Embodiment 4 only in that, based on the mass ratio of the effective components, the mass ratio of inorganic particles, PMMA particles, thickener, water-based binder, and butynediol ethoxylate modified polysiloxane in the slurry is 87.55:6:1.3:5:0.15.

[0061] Comparative Example 1

[0062] This comparative example provides a diaphragm, the specific preparation method of which is as follows:

[0063] The first step involves preparing a diaphragm coating slurry by adding inorganic particles (boehmite, D50 200 nm), thickener, water-based binder, and wetting agent in a mass ratio of 93.5:1:5:0.5 to deionized water. The slurry is then coated onto both sides of a 9 μm conventional porosity PE base film using a gravure roller coating method, with a coating thickness controlled at 2 μm. The film is then dried at 80°C for 3 minutes.

[0064] The second step involves preparing a diaphragm coating slurry by adding PVDF (commercially available: Arkema LBG), thickener, water-based binder, and wetting agent to deionized water at a mass ratio of 93:1:5:1. The slurry is then coated onto the surface of the semi-finished product obtained in the first step using a gravure roller coating method, with a coating thickness controlled at 1 μm. The coating is then dried at 80°C for 3 minutes to obtain the diaphragm described in this invention, with a diaphragm structure of 9+2+2+1+1.

[0065] Comparative Example 2

[0066] This comparative example provides a diaphragm, the specific preparation method of which is as follows:

[0067] The first step involves preparing a diaphragm coating slurry by adding inorganic particles (boehmite, D50 200nm), thickener, water-based binder, and wetting agent to deionized water at a mass ratio of 93.5:1:5:0.5. The slurry is then coated onto one side of a 9μm conventional porosity PE base film using a gravure roller coating method, with a coating thickness controlled at 2μm. The film is then dried at 80℃ for 3 minutes.

[0068] The second step involves preparing a diaphragm coating slurry by adding PVDF, thickener, water-based binder, and wetting agent to deionized water at a mass ratio of 93:1:5:1. The slurry is then coated onto one side of the semi-finished product obtained in the first step using a gravure roller coating method, with a coating thickness controlled at 1 μm. The coating is then dried at 80°C for 3 minutes to obtain the diaphragm described in this invention, which has a 9+2+1 structure.

[0069] Comparative Example 3

[0070] This comparative example provides a diaphragm that differs from Example 1 only in that the D / H ratio is too large, as shown in the table below.

[0071] Comparative Example 4

[0072] This comparative example provides a diaphragm that differs from Example 1 only in that the D / H ratio is too small, as shown in the table below.

[0073] Comparative Example 5

[0074] This comparative example provides a diaphragm that differs from Example 1 only in that it uses an equal mass of conventional wetting agent lauryl alcohol polyether (Tianjin Cyprus E1206) instead of the wetting agent in the above examples.

[0075] Test case

[0076] 1. Short circuit rate test

[0077] Lithium-ion batteries were prepared using the separators provided in the various embodiments and comparative examples, and the preparation methods are as follows:

[0078] First, the preparation of the positive electrode sheet: A slurry made of lithium iron phosphate is prepared and coated onto carbon-coated aluminum foil. The positive electrode sheet is then processed. The lithium iron phosphate content in the coating is 96%, conductive carbon black is 1.5%, PVDF binder is 2%, and dispersant is 0.5%. The single-sided coating surface density is 20 mg / cm². 2 .

[0079] Second, the preparation of the negative electrode sheet: A slurry is prepared using artificial graphite, which is then coated onto copper foil to form the negative electrode sheet. The artificial graphite accounts for 95.5% of the coating, while conductive carbon black and SBR-based binder comprise 1.5% and 3%, respectively. The single-sided coating density is 9 mg / cm³. 2 .

[0080] Preparation of lithium-ion batteries: The prepared negative electrode, positive electrode, separator, and electrolyte (the electrolyte is a conventional electrolyte containing EC / EMC / DMC solvent in a volume ratio of 1:1:1 and 1 mol / L lithium salt LiPF6) are assembled into 4Ah soft-pack cells. 1000 cells are assembled in each group, and the electrode group Hipot test is performed to calculate the short circuit rate.

[0081] 2. Electrical weakness test

[0082] The membranes prepared in each embodiment and comparative example were subjected to membrane electrical weakness tests: test voltage 1500V, test membrane length 50m, test speed 3m / min, the number of breakdown points was counted and the number of electrical weaknesses per square meter was calculated.

[0083] 3. Breakdown strength test

[0084] The diaphragms prepared in each embodiment and comparative example were subjected to diaphragm breakdown strength test, and the test method referred to GB / T36363-2018.

[0085] 4. Coating thickness test

[0086] The membrane cross-section was tested using SEM (Self-Electron Microscopy) to measure the coating thickness.

[0087] 5. Porosity of the coating layer

[0088] The porosity of the coating layer is calculated by using the true density of the inorganic material and the actual areal density and thickness of the coating. The porosity of the coating layer is: 1 - coating areal density / (true density of coating material × coating thickness).

[0089] 6. Insulation resistance

[0090] DC withstand voltage test: The insulation resistance meter starts the test and applies a high voltage (150V) to the test object. Then, it detects the leakage current flowing through the test object. According to Ohm's law: R = U / I, the insulation resistance value is calculated. The table shows the average value of 1000 samples.

[0091] 7. Adhesion

[0092] After the two diaphragms are hot-pressed on a 90°C plate, the adhesion between the diaphragms is tested using a tensile testing machine.

[0093] The specific test results are shown in the table below:

[0094] Table 1

[0095] Table 2

[0096] As can be seen from the data in the table above, the diaphragm provided in this application embodiment has a significantly improved breakdown voltage compared to existing conventional diaphragms, a substantial reduction in the number of electrical weaknesses, a lower hit-short circuit rate during cell production, a higher production yield, and a more cost-effective diaphragm production. Compared to existing water-based layered coating diaphragms, it reduces one coating step, resulting in lower diaphragm costs. It also reduces the amount of wetting agent used in the coating process, minimizing the reduction in diaphragm breakdown voltage caused by wetting agent penetration into the base film. Specifically, a comparison between Example 2 and Comparative Example 1, and between Example 4 and Comparative Example 2, reveals that the coating layer porosity of the diaphragm provided in this application embodiment is 40-50%, and the average breakdown voltage can reach over 1650V, with a maximum of 2354V. Compared to conventional layered coating diaphragms, whose coating porosity is over 50% and average breakdown voltage is around 1500V, the results of testing the electrical weaknesses of the diaphragm using a 1500V voltage demonstrate that the diaphragm provided in this application embodiment has fewer electrical weaknesses, stronger insulation capabilities, and is less prone to breakdown. Comparing the short-circuit rates of the electrode groups after hot pressing of the battery cells prepared in each group, it can be seen that the short-circuit rates of the electrode groups obtained after diaphragm assembly in each embodiment are lower than those of conventionally layered coated diaphragms, resulting in higher production yields. Comparing the data from Examples 1-3, it can be seen that with the increase of the heat-resistant coating thickness, the breakdown voltage increases, the number of electrical weaknesses in the diaphragm decreases, and the insulation capacity is stronger. Comparing Comparative Example 2 and Examples 4-6, it can be seen that compared to the layered coating method, the simplified coating method of mixed coating in these examples reduces one slurry coating step from two to one. Furthermore, the polysiloxane modified with butyrynylene glycol ethoxylate has a better dispersing and wetting effect than conventional wetting agents, and its usage in the coating can be reduced from 0.5% to 0.15%–0.25%, thus reducing the amount of wetting agent used. Within the usage range, the reduction in the amount of wetting agent in the coating reduces the penetration of wetting into the pores of the base membrane, thus reducing the decrease in diaphragm breakdown voltage caused by the penetration of wetting agent into the base membrane. As shown by the data in Comparative Examples 3-4, only by limiting the relationship between PMMA particle size and inorganic coating thickness (D / H) within a specific range can the coating layer and the base film achieve good adhesion and meet application requirements. If the particle size (D) is too large, it is prone to detachment, affecting the adhesion; if the particle size is too small, too much PMMA will be embedded in the coating, leaving too little exposed, thus affecting the adhesion effect. Furthermore, by using a mixed coating method, coating materials that achieve both heat resistance and adhesion are combined in the same coating layer. This not only improves the high-temperature resistance of the diaphragm but also ensures the adhesion between the diaphragm and the electrode, reducing coating steps and potentially lowering manufacturing energy costs, thus reducing material costs.

[0097] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents. Industrial applicability

[0098] The separator provided in this application improves its breakdown strength and reduces the number of electrical weaknesses by selecting the wetting agent in the coating layer and limiting the ratio between the particle size D of PMMA particles and the thickness H of the coating base layer. Cells produced using this separator exhibit lower hit-pot short-circuit rates and higher production yields. Furthermore, compared to conventional separators with multiple layers of base film + heat-resistant coating + adhesive coating, the method of forming a mixed coating layer using inorganic particles and large-particle PMMA simplifies the coating process while meeting the adhesion and heat resistance requirements of the coating layer. This reduces the production cost of the separator and does not place higher demands on production equipment.

Claims

1. A diaphragm, characterized in that, include: A base film and a coating layer located on at least one side surface of the base film, the coating layer comprising a coating base layer and PMMA particles dispersed in the coating base layer; The coating substrate comprises inorganic particles, butynediol ethoxylate modified polysiloxane, water-based binder, and thickener; The particle size D of the PMMA particles and the thickness H of the coating substrate satisfy the following relationship: 6≥D / H≥1.

5.

2. The diaphragm according to claim 1, characterized in that, The porosity of the coating layer is 40% to 50%.

3. The diaphragm according to claim 1, characterized in that, The wetting agent comprises 0.15% to 0.25% by mass of the total mass of the coating layer.

4. The diaphragm according to claim 1, characterized in that, The PMMA particles comprise 4% to 8% of the total mass of the coating layer. And / or, the inorganic particles have a mass percentage content of 85.5% to 89.5%; And / or, the thickener has a mass percentage content of 1% to 1.5%; And / or, the water-based adhesive has a mass percentage content of 4.5% to 5.3%.

5. The diaphragm according to any one of claims 1 to 4, characterized in that, The breakdown voltage of the diaphragm is K1, in V; the breakdown voltage of the base film is K2, in V; and the thickness of the coating layer is H, in μm. They satisfy the following relationship: 100≤(K1-K2) / H≤200.

6. The diaphragm according to claim 5, characterized in that, The particle size Dv50 of the inorganic particles is below 300 nm; And / or, the thickness of the base film is 3 μm to 20 μm; And / or, the thickness H of the coating substrate is 1μm to 3μm.

7. The diaphragm according to any one of claims 1 to 4, characterized in that, The inorganic particles include at least one of alumina and boehmite; And / or, the water-based adhesive includes at least one of acrylic adhesives or styrene-butadiene rubber; And / or, the thickener includes sodium carboxymethyl cellulose; And / or, the base film includes at least one of polyethylene base film and polypropylene base film.

8. A method for preparing a diaphragm according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1, Inorganic particles, PMMA particles, thickener, water-based binder, butynediol ethoxylate modified polysiloxane and water are mixed to obtain a slurry; S2, the slurry is coated onto at least one side of the base membrane and dried to obtain the diaphragm.

9. A secondary battery, characterized in that, The membrane includes the membrane described in any one of claims 1 to 7 or the membrane prepared by the preparation method described in claim 8.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9.

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