Flame-retardant functional diaphragm and preparation method thereof

Abstract

The invention discloses a flame-retardant functional diaphragm and a preparation method thereof, and relates to the technical field of lithium batteries. The flame-retardant functional diaphragm comprises a diaphragm base material and a flame-retardant ceramic coating arranged on one side of the diaphragm base material, the flame-retardant ceramic coating is obtained by coating and drying flame-retardant ceramic slurry, and the thickness of the flame-retardant ceramic coating is 1-20 microns; the flame-retardant ceramic slurry comprises the following raw materials in parts by mass: 20-55 parts of inorganic particles, 5-30 parts of a phosphorus-based flame retardant, 5-30 parts of a nitrogen-based flame retardant, 100 parts of a solvent, 0.1-1 part of a dispersing agent, 0.2-1 part of a thickening agent, 1-3 parts of a binder and 0.1-0.5 part of a wetting agent. The high-phosphorus and high-nitrogen flame retardants are introduced and compounded into a ceramic coating system, so that the problems of rapid carbonization and fragmentation after ignition of the ceramic diaphragm are solved, and meanwhile, the effects of ignition without open fire after ignition and self-extinguishing after being away from the fire can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a flame-retardant functional diaphragm and a preparation method thereof. Background Art

[0002] With the rapid development and widespread application of lithium-ion batteries, their energy density has gradually increased with different demands, which also means that the battery will store more active chemical energy that can be converted into electrical energy. Once the lithium-ion battery is used improperly, the chemical energy in the battery may suddenly be released in the form of fire or explosion, causing a safety accident. Safety issues have always been a key issue that needs to be urgently addressed in lithium-ion batteries, and the diaphragm and electrolyte in the battery assembly are the key to solving the problem. Efficient, flame-retardant, and stable lithium-ion diaphragms have also become an important direction of diaphragm research; The performance of the diaphragm determines the interface structure and internal resistance of the battery, which will directly affect the battery's capacity, cycle and safety performance. Most commercial diaphragms on the market are polyolefin diaphragms made of PP and PE, which have a low melting point and are therefore flammable and have poor thermal stability. During the use of lithium-ion batteries, once the battery temperature gets out of control, it is easy to heat up to the melting point of the polyolefin diaphragm. The size of the diaphragm will shrink due to heat, and even partial or complete rupture may occur, resulting in a short circuit between the positive and negative electrodes, causing battery fire and explosion. Improving the thermal stability of polyolefin diaphragms and giving them flame retardancy while maintaining excellent other physical properties are research hotspots in the diaphragm industry. The industry often adopts the method of physically adding functionalized additives to modify the coating of the diaphragm. The ceramic coated diaphragm has good heat shrinkage resistance at high temperatures and has been commercialized on a large scale. This method solves the problem of poor thermal stability of the diaphragm, but does not introduce the flame retardant mechanism into the diaphragm coating system. Therefore, introducing flame retardant functionalized additives into the coating system to construct the flame retardancy of the diaphragm is still the key research direction of the diaphragm industry; among them, the comparative document CN115395174A discloses a composite diaphragm, in which an NPS flame retardant is introduced into the diaphragm substrate and the surface coating. According to its molecular structure, the content of the flame retardant elements P, N, and S in the flame retardant is relatively low; therefore, the present invention introduces a high-phosphorus content flame retardant and a high-nitrogen content flame retardant to compound, aiming to greatly improve the flame retardant effect of the diaphragm by increasing the flame retardant component. At the same time, with the help of a rigid structure of ceramic materials, the thermal stability problem of the diaphragm is also solved. Summary of the Invention

[0003] The object of the present invention is to provide a flame retardant functional diaphragm and a preparation method thereof, so as to solve the problems raised in the prior art.

[0004] To achieve the above object, the present invention provides the following technical solutions: A flame retardant functional diaphragm, comprising a diaphragm substrate and a flame retardant ceramic coating disposed on one side of the diaphragm substrate; Furthermore, the flame retardant ceramic coating is obtained by coating and drying the flame retardant ceramic slurry, and has a thickness of 1-20 μm; Furthermore, the flame retardant ceramic slurry includes the following raw materials by mass: 20-55 parts of inorganic particles, 5-30 parts of phosphorus flame retardant, 5-30 parts of nitrogen flame retardant, 100 parts of solvent, 0.1-1 part of dispersant, 0.2-1 part of thickener, 1-3 parts of binder, and 0.1-0.5 part of wetting agent; Furthermore, the phosphorus content of the phosphorus-based flame retardant is 25-40%; the nitrogen content of the nitrogen-based flame retardant is 30-50%; Furthermore, the phosphorus-based flame retardant is one or more combinations of ammonium polyphosphate, melamine pyrophosphate, melamine ammonium polyphosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phosphate; Furthermore, the nitrogen-based flame retardant is one or more combinations of melamine hydrouric acid, 5-aminotetrazole, imidazole compounds and sulfonamide compounds; Furthermore, the inorganic particles are any one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, antimony trioxide, silicate, magnesium hydroxide, and aluminum hydroxide; Furthermore, the particle size of the phosphorus-based flame retardant is 1-20 μm; the particle size of the nitrogen-based flame retardant is 0.8-10 μm; and the particle size of the inorganic particles is 200-900 nm. A method for preparing a flame-retardant functional diaphragm comprises the following steps: Step 1: Weigh the raw materials by mass, add inorganic particles, phosphorus flame retardant, nitrogen flame retardant, thickener, binder and dispersant to the solvent in sequence, stir and disperse at high speed, then add wetting agent and stir and disperse at low speed to obtain flame retardant ceramic slurry; Step 2: coating the flame retardant ceramic slurry on one side of the diaphragm substrate by a gravure coating method, and drying to obtain the flame retardant ceramic diaphragm; Furthermore, in step 1, the rotation speed of high-speed stirring and dispersing is 600-700 rpm, and the time of high-speed stirring and dispersing is 3-4 hours; the rotation speed of low-speed stirring and dispersing is 300-400 rpm, and the time of low-speed stirring and dispersing is 30-40 minutes; Furthermore, the drying temperature in step 2 is 40-50°C; Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention selects a phosphorus-based flame retardant and introduces it into the ceramic coating system. The phosphorus-based flame retardant has a dual flame retardant mechanism. After being heated, it releases PO· free radicals in the gas phase to capture combustion free radicals and interrupt the chain reaction. In the condensed phase, it generates substances such as polyphosphoric acid to promote dehydration into carbon, thereby preventing further combustion. At the same time, the nitrogen element, which also has flame retardancy, is introduced into the coating slurry system. A nitrogen-based flame retardant with a high nitrogen content is selected and compounded with the phosphorus-based flame retardant for synergistic flame retardancy. The nitrogen-based flame retardant decomposes upon heating to produce non-combustible gases such as NH3, N2, HN3 and azide compounds, which dilute the combustible gas and oxygen concentrations to below the minimum value for combustion, thereby inhibiting combustion. The combination of phosphorus and nitrogen-based flame retardants and rigid inorganic particles can impart flame retardancy to the diaphragm while maintaining other physical properties of the diaphragm. The combined use of the three improves the flame retardant efficiency. 2. The flame-retardant functional diaphragm prepared by the present invention is different from the traditional polyolefin diaphragm which quickly breaks holes, shrinks and curls after being ignited, and the ceramic diaphragm which can ignite and quickly carbonize into fragments after 3 seconds of ignition. It can achieve the effect of self-extinguishing within 3 seconds after being ignited or even immediately after being removed from the fire. It has excellent self-extinguishing performance and can even self-extinguish immediately within 3 seconds after being ignited for 30 seconds. The LOI value is greater than 40%. At the same time, the flame-retardant functional diaphragm also has excellent air permeability and thermal stability, and can still maintain excellent heat shrinkage performance (MD <1, TD <1) at 130°C. DETAILED DESCRIPTION

[0005] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0006] In the experiment, the average particle size of melamine pyrophosphate was 5 μm, purchased from Zhejiang Xusen Flame Retardant Co., Ltd.; the average particle size of melamine cyanuric acid was 0.8 μm, purchased from Sichuan Jingshida Technology Co., Ltd.; the average particle size of alumina was 500 μm; the polyolefin separator was homemade, reference CN202010339196.2, with a thickness of 6 μm; the thickener was sodium carboxymethyl cellulose, purchased from Jiangsu Duoyang Biological; the binder was a 0.2% PAM resin aqueous solution, PAM purchased from Shanghai Kaiyin Chemical, model AN910SEP; the wetting agent was a mixture of ethoxylated alcohol and acetylene glycol, purchased from ExxonMobil Chemical; the dispersant was hydrolyzed polymaleic anhydride, with a purity of 98%, purchased from Zhengzhou Alpha Chemical; Example 1: This example provides a method for preparing a flame-retardant functional diaphragm, and the specific steps are as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 18 parts of melamine cyanuric acid, 6 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame-retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame-retardant ceramic diaphragm with a 2.72 μm flame-retardant ceramic coating. Example 2: Referring to the process steps of Example 1, the difference is that the ratio of melamine cyanuric acid and melamine pyrophosphate is adjusted to 1:3, and the parameters of other steps remain the same. The specific steps are as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 6 parts of melamine cyanuric acid, 18 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame retardant ceramic diaphragm with a 5.89 μm flame retardant ceramic coating. Example 3: Referring to the process steps of Example 1, the difference is that the ratio of melamine cyanuric acid and melamine pyrophosphate is adjusted to 1:1, and the parameters of other steps remain the same. The specific steps are as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 12 parts of melamine cyanuric acid, 12 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame retardant ceramic diaphragm with a 5.43 μm flame retardant ceramic coating. Example 4: Referring to the process steps of Example 1, the difference is that the ratio of aluminum oxide is adjusted, and the parameters of other steps remain the same. The specific steps are as follows: Step 1: Weigh the raw materials by mass, add 50 parts of aluminum oxide, 18 parts of melamine cyanuric acid, 6 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame retardant ceramic diaphragm with a 5.64 μm flame retardant ceramic coating. Example 5: Referring to the process steps of Example 1, the difference is that the ratio of aluminum oxide is adjusted, and the parameters of other steps remain the same. The specific steps are as follows: Step 1: Weigh the raw materials by mass, add 20 parts of aluminum oxide, 18 parts of melamine cyanuric acid, 6 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame-retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame-retardant ceramic diaphragm with a 2.81 μm flame-retardant ceramic coating. Comparative Example 1: As a control experiment of Example 1, melamine pyrophosphate was not added, and the specific steps were as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 18 parts of melamine cyanuric acid, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame retardant ceramic diaphragm with a 3.67 μm flame retardant ceramic coating. Comparative Example 2: As a control experiment of Example 1, the number of parts of melamine cyanuric acid was adjusted to 23 parts with reference to Comparative Example 1, and the specific steps were as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 23 parts of melamine cyanuric acid, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame-retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame-retardant ceramic diaphragm with a 3.88 μm flame-retardant ceramic coating. Comparative Example 3: As a control experiment of Example 1, the number of parts of melamine cyanuric acid was adjusted to 13 parts with reference to Comparative Example 1, and the specific steps were as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 13 parts of melamine cyanuric acid, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours, then add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame retardant ceramic slurry is coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40-50°C to obtain a flame retardant ceramic diaphragm with a 3.14 μm flame retardant ceramic coating. Comparative Example 4: As a control experiment of Example 1, melamine cyanuric acid was not added, and the specific steps were as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 6 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours. Then, add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame-retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame-retardant ceramic diaphragm with a 2.69 μm flame-retardant ceramic coating. Comparative Example 5: As a control experiment of Example 1, the number of parts of melamine pyrophosphate was adjusted to 9 parts with reference to Comparative Example 4, and the specific steps were as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 9 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours. Then, add 0.3 parts of wetting agent and stir and disperse at 300-400 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame retardant ceramic diaphragm with a 3.76 μm flame retardant ceramic coating. Comparative Example 6: As a control experiment of Example 1, the number of parts of melamine pyrophosphate was adjusted to 3 parts with reference to Comparative Example 4, and the specific steps were as follows: Step 1: Weigh the raw materials by mass, add 35 parts of aluminum oxide, 3 parts of melamine pyrophosphate, 0.6 parts of thickener, 2.5 parts of binder and 1 part of dispersant to 100 parts of deionized water in sequence, and stir and disperse at 600 rpm for 3 hours. Then, add 0.3 parts of wetting agent and stir and disperse at 300 rpm for 30 minutes to obtain a flame retardant ceramic slurry; Step 2: The flame-retardant ceramic slurry was coated on one side of the polyolefin diaphragm substrate by a gravure coating method, and dried in a dry environment at 40° C. to obtain a flame-retardant ceramic diaphragm with a 2.73 μm flame-retardant ceramic coating. The above lists the formulas of the flame retardant ceramic slurries in Examples 1-5 and Comparative Examples 1-6, as shown in Table 1: Table 1

[0007] Detection test 1. Flame retardant functional membrane air permeability test: The air permeability of the diaphragms prepared in Examples 1-5 and Comparative Examples 1-6 was measured with reference to GB / T 36363, and the data are recorded in Table 2; 2. Thermal shrinkage test of flame retardant functional diaphragm: The separators of Examples 1-5 and Comparative Examples 1-6 were cut into a size of 200 mm × 100 mm, sandwiched between two glass plates, and heated in an oven at 130°C for 1 hour. After heating, the separators were removed and their dimensions were measured. The average value of the measurements was taken multiple times, and the thermal shrinkage in the MD and TD directions was calculated. The data are recorded in Table 2. 3. Flame retardant functional membrane limiting oxygen index test: The diaphragms prepared in Examples 1-5 and Comparative Examples 1-6 were cut into 200 mm × 20 mm sizes and calibrated according to ASTM D Wrap 4804 around the specified rod. After wrapping, tape the end of the sample roll firmly. Then pull the rod out of the rolled film and cut off the top 20 cm of the roll. Use a pen to mark lines 10 mm and 60 mm from the ignition end of the sample. Install the sample vertically in the center of the oxygen index instrument combustion tube, so that the top of the sample is 100 mm below the top of the combustion tube. Adjust the gas mixer and flow meter to mix the oxygen / nitrogen gas and the oxygen concentration reaches the set value (that is, the sample remains in a non-combustible state at this oxygen concentration). Pass the combustion tube at a flow rate of 40 mm / s. After flushing the combustion tube with the mixed gas for 30 seconds, lower the igniter and apply a visible flame to the top surface of the sample, to nearly 6 mm from the vertical surface. Apply the flame continuously for 30 seconds, and check the sample for combustion interruption every 5 seconds until the vertical surface is in steady-state combustion or the visible burning part reaches the upper mark of the support frame. The sample is considered to be ignited. Record the oxygen concentration at this time and calculate the oxygen concentration used. The data are expressed as volume fraction and recorded in Table 2. 4. Flame retardant functional diaphragm UL-94VTM grade test: The diaphragm samples of Examples 1-5 and Comparative Examples 1-6 were cut into a size of 200 mm × 100 mm. A mark was drawn at a position 125 mm from one end of the sample. The longitudinal axis of the sample was tightly wrapped around a round rod with a diameter of 10 mm to form a 200 mm long sealed cylinder. The overlapping end of the sample was fixed to the 125 mm mark with tape. The round rod was then removed, the sample was clamped vertically, and a flame was applied from the bottom for 3 seconds. The burning condition of the diaphragm was observed, the flame extinction time was recorded, and the grade was evaluated. The data are recorded in Table 2.

[0008] Table 2

[0009] Conclusion: The flame-retardant functional diaphragm prepared by the present invention quickly breaks the film and shrinks and curls into a ball after being ignited, which is different from the ceramic diaphragms on the market that quickly carbonize and become fragments after being ignited. In the experiment, the flame-retardant diaphragms prepared in the examples can self-extinguish within 3 seconds after being ignited, and even Examples 2 and 4 can achieve the effect of self-extinguishing when away from the fire; Comparative Examples 1-6 fully demonstrate that the phosphorus-based flame retardants and nitrogen-based flame retardants play a synergistic role and are applied to the surface of the functional diaphragm to achieve excellent flame retardant effects.

[0010] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A flame retardant functional diaphragm, characterized in that: The flame-retardant functional diaphragm includes a diaphragm substrate and a flame-retardant ceramic coating arranged on one side of the diaphragm substrate; the flame-retardant ceramic coating is obtained by coating and drying a flame-retardant ceramic slurry, and has a thickness of 1-20 μm; the flame-retardant ceramic slurry includes the following raw materials by mass: 20-55 parts of inorganic particles, 5-30 parts of phosphorus-based flame retardants, 5-30 parts of nitrogen-based flame retardants, 100 parts of solvents, 0.1-1 parts of dispersants, 0.2-1 parts of thickeners, 1-3 parts of binders, and 0.1-0.5 parts of wetting agents.

2. The flame retardant functional diaphragm according to claim 1, characterized in that: The phosphorus content of phosphorus-based flame retardants is 25-40%; the nitrogen content of nitrogen-based flame retardants is 30-50%.

3. The flame retardant functional diaphragm according to claim 1, characterized in that: The phosphorus-based flame retardant is one or more combinations of ammonium polyphosphate, melamine pyrophosphate, melamine ammonium polyphosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phosphate.

4. The flame retardant functional diaphragm according to claim 1, characterized in that: The nitrogen-based flame retardant is one or more combinations of melamine hydrouric acid, 5-aminotetrazole, imidazole compounds and sulfonamide compounds.

5. The flame retardant functional diaphragm according to claim 1, characterized in that: The inorganic particles are any one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, antimony oxide, silicate, magnesium hydroxide, and aluminum hydroxide.

6. The flame retardant functional diaphragm according to claim 1, characterized in that: The particle size of the phosphorus-based flame retardant is 1-20 μm; the particle size of the nitrogen-based flame retardant is 0.8-10 μm; and the particle size of the inorganic particles is 200-900 nm.

7. A method for preparing the flame-retardant functional diaphragm according to any one of claims 1 to 6, characterized in that: The method comprises the following preparation steps: Step 1: Weigh the raw materials by mass, add inorganic particles, phosphorus flame retardant, nitrogen flame retardant, thickener, binder and dispersant to the solvent in sequence, stir and disperse at high speed, then add wetting agent and stir and disperse at low speed to obtain flame retardant ceramic slurry; Step 2: coating the flame-retardant ceramic slurry on one side of the diaphragm substrate by a gravure coating method, and drying the slurry to obtain the flame-retardant ceramic diaphragm.

8. The method for preparing a flame-retardant functional diaphragm according to claim 7, characterized in that: In step 1, the rotation speed of high-speed stirring and dispersing is 600-700 rpm, and the time of high-speed stirring and dispersing is 3-4 hours; the rotation speed of low-speed stirring and dispersing is 300-400 rpm, and the time of low-speed stirring and dispersing is 30-40 minutes.

9. The method for preparing a flame-retardant functional diaphragm according to claim 7, characterized in that: The drying temperature in step 2 is 40-50°C.

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