Separator, battery, and separator preparation method

Abstract

The present application provides a separator, and also provides a battery comprising the separator and a separator preparation method. The separator comprises a polyolefin separator and a functional layer. The functional layer covers at least one surface of the polyolefin separator in the thickness direction. Based on the mass of the functional layer, the functional layer comprises 0.1%-0.5% of a dispersant, 3%-6% of a binder, 0.1-0.5% of a thickener, 0.1-0.5% of a wetting agent, and 5%-10% of a functional material, wherein the functional material comprises composite particles, and the composite particles comprise nano Al2O3 particles and polydopamine attached to the surface of the nano Al2O3.

Description

Separator, battery, and preparation method of separator

[0001] This application claims priority to Chinese Patent Application No. 202411907229.3, filed on December 23, 2024, entitled "Separator, Battery and Method for Preparing Separator", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more particularly to a separator, a battery, and a method for preparing the separator. Background Technology

[0003] Polyolefin separators are now widely used in battery separators.

[0004] Polyolefin separators have poor puncture resistance, making them prone to causing battery thermal runaway. During battery thermal runaway, due to the low melting point of polyolefin separators, they are easily ruptured, leading to more severe thermal runaway and potentially causing battery combustion or even explosion. Invention Overview

[0005] Given the problem that polyolefin separators can easily cause thermal runaway in batteries, it is necessary to improve polyolefin separators to enhance battery safety performance.

[0006] The purpose of this application is to provide a separator, a battery, and a method for preparing the separator, aiming to solve the problem that polyolefin separators can easily cause thermal runaway in batteries and improve the safety performance of batteries.

[0007] This application provides a separator, including a polyolefin separator and a functional layer. The functional layer is coated on at least one surface of the polyolefin separator along its thickness direction. Based on the mass of the functional layer, the functional layer includes 0.1% to 0.5% dispersant, 3% to 6% binder, 0.1% to 0.5% thickener, 0.1% to 0.5% wetting agent, and 5% to 10% functional material. The functional material includes composite particles, which include nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles.

[0008] The application also provides a battery, which includes a positive electrode, a negative electrode, and a separator as described above, with the separator disposed between the positive electrode and the negative electrode.

[0009] In some embodiments, the battery is a lithium-ion battery.

[0010] This application also provides a method for preparing a diaphragm, wherein the diaphragm is the diaphragm described above, and the method for preparing the diaphragm includes the step of preparing composite particles:

[0011] Take dopamine and an aluminum salt solution. The aluminum salt solution contains Al.3+ Composite particles are obtained by reacting under alkaline conditions. Embodiments of the present invention

[0012] The technical solutions described below in conjunction with the embodiments of this application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0013] This application provides a battery including a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive and negative electrode. The battery can be manufactured by stacking the positive electrode, separator, and negative electrode, followed by winding or laminating.

[0014] Specifically, the positive electrode sheet includes a positive current collector and a positive electrode layer covering the surface of the positive current collector. The positive electrode layer may cover one or both surfaces of the positive current collector along its thickness direction. For example, the positive current collector may be aluminum foil. The positive electrode layer includes a positive electrode active material. In this embodiment, a lithium-ion battery is used as an example, where the positive electrode active material may be selected from lithium cobalt oxide, lithium iron phosphate, and nickel cobalt oxide.

[0015] The negative electrode sheet includes a negative electrode current collector and a negative electrode layer covering the surface of the negative electrode current collector. The negative electrode layer may cover one or both surfaces of the negative electrode current collector along its thickness direction. For example, the negative electrode current collector may be copper foil or carbon-coated aluminum foil. The negative electrode layer includes a negative electrode active material. For example, the negative electrode active material may be graphite, silicon-based materials, etc.

[0016] In this embodiment, the separator includes a polyolefin separator and a functional layer coated on the surface of the polyolefin separator. The functional layer can be coated on one or both surfaces of the polyolefin separator along its thickness direction. Exemplarily, the functional layer can be prepared by coating, screen printing, or other methods. Exemplarily, the polyolefin separator can be a polyethylene (PE) separator, a polypropylene (PP) separator, etc. By weight, the functional layer includes 0.1%–0.5% dispersant, 3%–6% binder, 0.1%–0.5% thickener, 0.1%–0.5% wetting agent, and 5%–10% functional material. It is understood that other major components in the functional layer are solvents. Exemplarily, the solvent is water.

[0017] This application provides a separator by forming a functional layer on the surface of a polyolefin separator. The composite particles in the functional layer contain nano-Al2O3 particles, which are ceramic materials. These nano-Al2O3 particles have high hardness, which improves the mechanical strength of the separator, making it less prone to puncture and thus preventing thermal runaway in the battery. Furthermore, the nano-Al2O3 particles are heat-resistant, enhancing the separator's heat resistance. In the event of thermal runaway, the separator is less likely to rupture, thus preventing battery combustion or explosion due to separator rupture.

[0018] Furthermore, polyolefin membranes have low polarity and poor affinity with highly polar electrolytes, resulting in poor liquid absorption and retention capabilities. In this embodiment, a functional layer is formed on the surface of the polyolefin membrane. The polydopamine adhering to the surface of the nano-Al2O3 particles in the composite particles of the functional layer is hydrophilic, which enhances the affinity between the membrane and the electrolyte, thereby improving the membrane's liquid absorption and retention performance.

[0019] The functional materials comprise 90%–100% composite particles and 0–10% layered materials by mass. In this embodiment, the composite particles include nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles. For example, dopamine can be used to reduce nano-Al2O3 particles. 3+ Composite particles are prepared by means of Al 3+ The dopamine is reduced to form nano-Al2O3 particles, and the excess polydopamine formed by dopamine adheres to the surface of the nano-Al2O3 particles, thus forming composite particles.

[0020] By employing the above-described scheme, nano-Al2O3 particles and layered materials such as layered montmorillonite are simultaneously added to the functional layer of the polyolefin separator. The alternating stacking of nano-Al2O3 particles and layered materials forms a sandwich structure, which reduces the thermal shrinkage of the separator, thereby lowering the risk of battery fire and explosion. For example, the layered material can be layered montmorillonite (MMT). The aspect ratio of MMT is 1~120. In the embodiments of this application, layered montmorillonite can be prepared using either mechanical exfoliation or ion exchange methods. Layered montmorillonite has a high Young's modulus, which can further improve the mechanical strength of the separator. The polydopamine attached to the surface of the nano-Al2O3 particles is hydrophilic, which can further improve the liquid absorption and retention performance of the separator.

[0021] In functional materials, adding montmorillonite alone cannot form a sandwich structure. Furthermore, the unstable surface free energy of montmorillonite leads to dense accumulation of montmorillonite nanosheets, which can easily hinder the diffusion path of lithium ions in lithium-ion batteries, thus affecting battery performance. In this application, polydopamine-reduced nano-Al2O3 particles are mixed with layered montmorillonite. The one-dimensional nano-Al2O3 particles and the two-dimensional layered material, such as layered montmorillonite, can be interleaved to form a sandwich structure, which is beneficial for improving the heat resistance and mechanical strength of the separator, thereby improving battery performance.

[0022] Polyolefin separators have poor puncture resistance, making them prone to puncture and short circuits between the positive and negative electrodes, which can easily lead to thermal runaway in the battery. Furthermore, polyolefin separators typically have a low melting point, making them susceptible to rupture during thermal runaway, potentially exacerbating the situation and leading to battery combustion or even explosion. To address these issues, this application provides a separator with a functional layer on its surface. The composite particles in this functional layer are composed of nano-Al2O3 ceramic materials. The high hardness of nano-Al2O3 particles enhances the mechanical strength of the separator, making it less prone to puncture and thus preventing thermal runaway. Additionally, the high temperature resistance of the nano-Al2O3 particles improves the separator's heat resistance, further reducing the likelihood of rupture during thermal runaway and preventing battery combustion or explosion caused by separator rupture. Furthermore, polyolefin membranes have low polarity and poor affinity with highly polar electrolytes, resulting in poor liquid absorption and retention capabilities. In this embodiment, a functional layer is formed on the surface of the polyolefin membrane. The polydopamine adhering to the surface of the nano-Al2O3 particles in the composite particles of the functional layer has hydrophilic properties, enhancing the affinity between the membrane and the electrolyte, thereby improving the membrane's liquid absorption and retention performance.

[0023] Furthermore, polyolefin separators exhibit significant thermal shrinkage at high temperatures, posing a high risk of battery fire and explosion. This application addresses this issue by simultaneously adding nano-Al2O3 particles and layered materials such as layered montmorillonite to the functional layer of the polyolefin separator. The alternating stacking of nano-Al2O3 particles and layered materials forms a sandwich structure, reducing the thermal shrinkage of the separator and thus lowering the risk of battery fire and explosion.

[0024] This application also provides a method for preparing the above-mentioned diaphragm, including the following steps S1 to S3.

[0025] S1. Prepare composite particles, which include nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles.

[0026] In this embodiment of the application, dopamine reduction of Al is used. 3+The composite particles were prepared in a manner that, on the one hand, allowed dopamine to reduce Al under mild conditions. 3+ This process forms nano-alumina, avoiding potential side effects from strong reducing agents and thus preserving the original structure and properties of the nano-alumina. On the other hand, dopamine can polymerize to form polydopamine, which adheres to the surface of the nano-alumina. Through the functional groups of polydopamine, other functional groups are introduced into the composite particles, thereby expanding the application range of nano-alumina. Specifically, dopamine and an aluminum salt solution are taken, the aluminum salt solution containing Al... 3+ Composite particles were prepared under alkaline conditions. For example, the alkaline conditions were pH 8-10. Dopamine (3,4-dihydroxyphenylethylamine, C8H11NO2) contains catechol and amino functional groups. Dopamine reacts with Al in the aluminum salt solution. 3+ Coordination compounds are formed, and under alkaline conditions, dopamine reduces Al. 3+ Nano-sized Al2O3 particles are generated, and then dopamine is used to form polydopamine (PDA). Excess polydopamine adheres to the surface of the nano-sized Al2O3 particles to enhance the affinity with the electrolyte, thereby improving the liquid absorption and retention rates of the prepared membrane.

[0027] S2. Mix layered materials with composite particles to form functional materials.

[0028] For example, the layered material is layered montmorillonite. In the embodiments of this application, the layered material and composite particles are stacked alternately to form a sandwich structure, which effectively improves the heat resistance, mechanical strength and liquid absorption and retention performance of the diaphragm.

[0029] S3. Take raw materials including dispersant, binder, thickener, wetting agent and functional material, mix them to form a slurry, provide a polyolefin membrane, and prepare a functional layer on the surface of the polyolefin membrane to obtain the membrane.

[0030] For example, the dispersant is an aliphatic amide dispersant, the binder is a polyacrylic acid binder, the thickener is a sodium carboxymethyl cellulose thickener, and the wetting agent is an alkyl sulfate wetting agent. For example, the polyacrylic acid binder can be selected from polyacrylic acid (PAA) and lithium polyacrylate (PAA). Li), potassium polyacrylate (PAA) K), sodium polyacrylate (PAA) At least one of Na). For example, sodium hydroxymethyl cellulose thickeners include at least one of sodium hydroxymethyl cellulose (HMC) and sodium carboxymethyl cellulose (CMC). For example, alkyl sulfate wetting agents include at least one of sodium dodecyl sulfate (SDS) and triethanolamine dodecyl sulfate (TEA-DOS).

[0031] This application provides a method for preparing a diaphragm, using dopamine (3,4-dihydroxyphenylethylamine, C8H12H2O). 11 NO2) contains catechols and amino functional groups, and dopamine reacts with Al in aluminum salt solutions. 3+ A coordination compound is formed under alkaline conditions, and then dopamine forms polydopamine (PDA). Polydopamine reduces Al. 3+ Nano-Al2O3 particles are generated, and excess polydopamine adheres to the surface of the nano-Al2O3 particles to enhance their affinity with the electrolyte, thereby improving the liquid absorption and retention rates of the prepared diaphragm.

[0032] The diaphragm provided in the embodiments of this application will be specifically described below with reference to Comparative Examples 1-2 and Examples 1-2.

[0033] Comparative Example 1 provides a diaphragm, which is a polyethylene (PE) diaphragm. The diaphragm of Comparative Example 1 is denoted as PE.

[0034] Comparative Example 2 provides a separator comprising a polyethylene separator and a coating on the surface of the polyethylene separator, the coating being a coating formed of nano-Al2O3 particles. The separator of Comparative Example 2 is designated Al2O3-PE.

[0035] Example 1 provides a separator comprising a polyethylene separator and a coating on the surface of the polyethylene separator. The coating is formed of composite particles, including nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles. The separator of Example 1 is designated Al2O3@PDA-PE.

[0036] Example 2 provides a diaphragm comprising a polyethylene diaphragm and a coating covering the surface of the polyethylene diaphragm. By weight percentage (dry weight), the coating comprises 0.1-0.5% dispersant, 3%-6% binder, 0.1-0.5% thickener, 0.1-0.5% wetting agent, and 5%-10% functional material. The dispersant is an aliphatic amide dispersant, the binder is a polyacrylic acid binder, the thickener is a sodium hydroxymethyl cellulose thickener, and the wetting agent is an alkyl sulfate wetting agent. By mass of the functional material, the functional material comprises composite particles and layered montmorillonite, with a composite particle:layered montmorillonite mass ratio of 90:10. The composite particles are nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles. The diaphragm of Example 2 is designated Al2O3@PDA / MMT-PE.

[0037] In Comparative Examples 1-2 and Examples 1-2, the thickness of the polyethylene diaphragm was 9 μm to 11 μm. In Comparative Example 2 and Examples 1-2, the D50 of the nano-Al2O3 particles was 0.3 μm, and the aspect ratio of the layered montmorillonite (MMT) used in Example 2 was 1 to 120.

[0038] The PE membrane of Comparative Example 1 and the Al2O3@PDA / MMT-PE membrane of Example 2 were used, and their impedance and ionic conductivity were measured respectively. The experimental results showed that the impedance of the PE membrane of Comparative Example 1 was 0.99 Ω, and the ionic conductivity was 0.57 mS·cm. -1 The Al2O3@PDA / MMT-PE membrane in Example 2 has a impedance of 6.02 Ω and an ionic conductivity of 0.11 mS·cm. -1 The embodiments of this application verify through experiments that the higher the proportion of MMT in the coating of the diaphragm, the greater the impedance of the resulting diaphragm. In the diaphragm of this application embodiment, the mass fraction of layered montmorillonite in the functional layer is ≤10% to avoid excessive impedance of the diaphragm.

[0039] The diaphragms from Comparative Examples 1-2 and Examples 1-2 were used, and their air permeability, heat shrinkage rate at 150°C, needle penetration strength, liquid absorption rate, and liquid retention rate were measured respectively. The results are shown in Table 1. The method for measuring the air permeability of the diaphragms in Table 1 was as follows: the diaphragm was placed on an air permeability tester, and the time required for 100 mL of air to pass through 1 square inch of the diaphragm under a pressure of 1.22 kPa was measured. The diaphragm at 150°C... o The method for determining the heat shrinkage rate of C is as follows: The diaphragm is left to stand at 150°C. o After being dried in a forced-air oven at temperature C for 1 hour, the diaphragm was removed and its thermal shrinkage rate was calculated by measuring the area of ​​the diaphragm before and after heat treatment. Thermal shrinkage rate (%) = (S0 - S1) / S0 × 100%. Where S1 is the area of ​​the diaphragm after heat treatment, and S0 is the area of ​​the diaphragm before heat treatment. In Table 1, MD represents the thermal shrinkage rate of the diaphragm along the longitudinal direction, and TD represents the thermal shrinkage rate of the diaphragm along the transverse direction.

[0040] The method for determining the puncture strength of the diaphragm is as follows: The puncture strength of the diaphragm sample is tested using a compression testing instrument. The method for determining the liquid absorption rate of the diaphragm is as follows: The mass of the dried diaphragm (M0) is pre-weighed. The diaphragm sample is immersed in the electrolyte for 1 hour. After gently wiping away excess electrolyte from the diaphragm surface, it is weighed again (M1). The liquid absorption rate of the diaphragm is calculated as follows: Liquid absorption rate of the diaphragm (%) = (M1 - M0) / M0 × 100%. The method for determining the liquid retention rate of the diaphragm is as follows: The diaphragm sample is immersed in the electrolyte for 1 hour. After gently wiping away excess electrolyte from the diaphragm surface, it is weighed again (M1). The weighed sample is placed in a desiccator and dried until its weight no longer changes. The diaphragm sample is weighed again (M2). The liquid retention rate of the diaphragm is calculated based on the weight difference between the two weighings. The liquid retention rate of the diaphragm (%) = (M2 - M1) / M1 × 100%.

[0041] Table 1 shows the performance test results of the diaphragms in Comparative Examples 1-2 and Examples 1-2.

[0042]

[0043] As can be seen from Table 1, the membranes of Comparative Examples 1-2 and Examples 1-2 all have a certain air permeability value. Although the air permeability value of the membranes of Examples 1-2 is improved to a certain extent, it does not affect the diffusion of electrolyte in the battery.

[0044] In Comparative Example 1, the PE membrane without coating was at 150 o The thermal shrinkage rate of C is >50%, indicating a high risk of battery fire and explosion, necessitating further improvement. Comparing the separators of Examples 1-2 and Comparative Example 1, the separators of Examples 1 and 2 show better performance at 150°C. o The thermal shrinkage rate of C was reduced. Experimental results show that by adding polydopamine-reduced nano-Al2O3 particles (Al2O3@PDA) to the coating of the polyolefin separator, the thermal shrinkage rate of the separator can be reduced, thereby improving the safety performance of the battery. In addition, by comparing the thermal shrinkage rates of the separators of Example 2 and Example 1, it can be seen that the thermal shrinkage rate of the separator of Example 2 is reduced to less than 5% at 150°C (held between A4 paper). Experimental results show that by simultaneously adding polydopamine-reduced nano-Al2O3 particles (Al2O3@PDA) and layered montmorillonite to the coating of the polyolefin separator, the thermal shrinkage rate of the separator can be significantly reduced, thereby further improving the safety performance of the battery.

[0045] By comparing the needle penetration strength of the membranes in Examples 1-2 and Comparative Example 1, the needle penetration strength of the membranes in Examples 1-2 was improved compared to that of the membrane in Comparative Example 1. Experimental results show that adding polydopamine-reduced nano-Al2O3 particles (Al2O3@PDA) to the coating of the polyolefin membrane can improve the needle penetration strength of the membrane, thereby enhancing its puncture resistance. By comparing the needle penetration strength of the membranes in Example 2 and Example 1, layered montmorillonite was also added to the coating of the polyolefin membrane in Example 2. Since layered montmorillonite has a high Young's modulus, it can further improve the needle penetration strength of the membrane, thereby further enhancing its puncture resistance.

[0046] By comparing the liquid absorption rate and liquid retention rate of the separators in Example 1 and Comparative Example 1, it can be seen that the liquid absorption rate and liquid retention rate of the separator in Example 1 are improved. The experimental results show that when polydopamine-reduced nano-Al2O3 particles (Al2O3@PDA) are added to the coating of the polyolefin separator, the liquid absorption rate and liquid retention rate of the separator can be improved because the nano-Al2O3 particles are attached with hydrophilic polydopamine, thereby obtaining a separator with high electrolyte wetting, which is beneficial to improving the rate cycle performance of the battery.

[0047] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A separator, comprising a polyolefin separator and a functional layer, said functional layer being coated on at least one surface of the polyolefin separator along its thickness direction, wherein, by weight of said functional layer, the functional layer comprises 0.1% to 0.5% dispersant, 3% to 6% binder, 0.1% to 0.5% thickener, 0.1% to 0.5% wetting agent, and 5% to 10% functional material, wherein, The functional material includes composite particles, which include nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles.

2. The diaphragm according to claim 1, wherein, Based on the mass of the functional material, the functional material comprises 90% to 100% of the composite particles and 0% to 10% of the layered material.

3. The diaphragm according to claim 2, wherein, The layered material is layered montmorillonite.

4. The diaphragm according to claim 3, wherein, The layered montmorillonite is prepared by either mechanical exfoliation or ion exchange.

5. The diaphragm according to claim 1, wherein, The dispersant is an aliphatic amide dispersant, the binder is a polyacrylic acid binder, the thickener is a sodium hydroxymethyl cellulose thickener, and the wetting agent is an alkyl sulfate wetting agent.

6. The diaphragm according to claim 5, wherein, The polyacrylic adhesive includes at least one of polyacrylic acid, lithium polyacrylate, potassium polyacrylate, and sodium polyacrylate; the sodium hydroxymethyl cellulose thickener includes at least one of sodium hydroxymethyl cellulose and sodium carboxymethyl cellulose; and the alkyl sulfate wetting agent includes at least one of sodium dodecyl sulfate and triethanolamine dodecyl sulfate.

7. The diaphragm according to claim 1, wherein, The thickness of the polyolefin membrane is 9μm~11μm.

8. A battery, the battery comprising a positive electrode, a negative electrode, and a separator, the separator being disposed between the positive electrode and the negative electrode; The separator comprises a polyolefin separator and a functional layer. The functional layer is coated on at least one surface of the polyolefin separator along its thickness direction. Based on the mass of the functional layer, the functional layer comprises 0.1%–0.5% dispersant, 3%–6% binder, 0.1%–0.5% thickener, 0.1%–0.5% wetting agent, and 5%–10% functional material. The functional material includes composite particles, which include nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles.

9. The battery according to claim 8, wherein, Based on the mass of the functional material, the functional material comprises 90% to 100% of the composite particles and 0% to 10% of the layered material.

10. The battery according to claim 9, wherein, The layered material is layered montmorillonite.

11. The battery according to claim 8, wherein, The dispersant is an aliphatic amide dispersant, the binder is a polyacrylic acid binder, the thickener is a sodium hydroxymethyl cellulose thickener, and the wetting agent is an alkyl sulfate wetting agent.

12. The battery according to claim 11, wherein, The polyacrylic adhesive includes at least one of polyacrylic acid, lithium polyacrylate, potassium polyacrylate, and sodium polyacrylate; the sodium hydroxymethyl cellulose thickener includes at least one of sodium hydroxymethyl cellulose and sodium carboxymethyl cellulose; and the alkyl sulfate wetting agent includes at least one of sodium dodecyl sulfate and triethanolamine dodecyl sulfate.

13. The battery according to claim 8, wherein, The thickness of the polyolefin membrane is 9μm~11μm.

14. The battery according to claim 8, wherein, The battery is a lithium-ion battery.

15. A method for preparing a separator, the separator comprising a polyolefin separator and a functional layer, the functional layer being coated on at least one surface of the polyolefin separator along its thickness direction, wherein, by weight of the functional layer, the functional layer comprises 0.1% to 0.5% dispersant, 3% to 6% binder, 0.1% to 0.5% thickener, 0.1% to 0.5% wetting agent, and 5% to 10% functional material, wherein... The functional material includes composite particles, which include nano-Al2O3 particles and polydopamine attached to the surface of the nano-Al2O3 particles. The method for preparing the diaphragm includes the step of preparing the composite particles: Dopamine and an aluminum salt solution containing Al3+ were reacted under alkaline conditions to obtain the composite particles.

16. The method for preparing the diaphragm according to claim 15, wherein, Based on the mass of the functional material, the functional material comprises 90% to 100% of the composite particles and 0% to 10% of the layered material.

17. The method for preparing the diaphragm according to claim 16, wherein, The layered material is layered montmorillonite.

18. The method for preparing the diaphragm according to claim 15, wherein, The dispersant is an aliphatic amide dispersant, the binder is a polyacrylic acid binder, the thickener is a sodium hydroxymethyl cellulose thickener, and the wetting agent is an alkyl sulfate wetting agent.

19. The method for preparing the diaphragm according to claim 15, wherein, The thickness of the polyolefin membrane is 9μm~11μm.

20. The method for preparing the diaphragm according to claim 15, characterized in that, The alkaline conditions are pH=8~10.

Images