Polypropylene diaphragm and preparation method thereof
By forming modified alumina particles and a composite aerogel layer on the surface of polypropylene membrane, the problems of easy wrinkling and high thermal shrinkage of polypropylene membrane are solved, thereby improving the mechanical strength and electrochemical performance of the membrane.
Patent Information
- Application Number
- CN202510835550.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-20
- Publication Date
- 2025-10-17
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Polypropylene separators are prone to wrinkling and have a high thermal shrinkage rate in lithium-ion batteries, which affects their electrochemical performance.
By forming a modified alumina particle coating and a composite aerogel layer on the surface of a polypropylene membrane, the modified alumina particles are chemically bonded to the polypropylene membrane, and the composite aerogel provides a porous structure, enhancing mechanical and electrochemical properties.
It improves the tensile strength and thermal stability of polypropylene membranes, prevents wrinkles, and enhances lithium-ion transport and electrochemical performance.
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Figure BDA0005460532200000191
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of battery separators, in particular to a polypropylene separator and a preparation method thereof. BACKGROUND
[0002] In the structure of a lithium ion battery, a separator, as an inner layer component, can separate the positive and negative electrodes of the battery, prevent the two electrodes from contacting and short-circuiting, and allow ions to transmit in the battery, thereby improving the comprehensive performance of the lithium ion battery, such as the capacity, cycle and safety performance of the battery, and the separator used in the lithium ion battery is mainly based on a polyolefin film, such as a polypropylene separator, a polyethylene separator and a polytetrafluoroethylene separator.
[0003] The polypropylene separator has good electrochemical stability and mechanical strength, and can improve the electrochemical performance of the lithium ion battery as the lithium ion battery separator, but the longitudinal tensile strength and the transverse tensile strength of the polypropylene separator have a large difference, the polypropylene separator is prone to shrinkage or deformation under the impact of liquid during liquid injection, wrinkles are generated, the conduction efficiency of lithium ions in the separator is affected, and the polypropylene separator has extremely high thermal shrinkage at high temperatures, internal short-circuiting is caused, and the electrochemical performance of the polypropylene separator is affected. SUMMARY
[0004] The application provides a polypropylene separator and a preparation method thereof, and solves the problems of wrinkles and high thermal shrinkage of the polypropylene separator.
[0005] The technical scheme of the application is as follows:
[0006] A preparation method of a polypropylene separator comprises the following preparation steps:
[0007] S1. The modified alumina particles and the methyl methacrylate solution are uniformly mixed, the polypropylene film is added, and after irradiation grafting, the modified polypropylene film is taken out, washed, and dried to obtain the modified polypropylene film;
[0008] The irradiation can initiate free radicals in the carbon-carbon bond in the polypropylene film, and the generated free radicals can initiate the copolymerization of the double bond of the glycidyl methacrylate in the modified alumina particles and the double bond of the methyl methacrylate, so that the modified alumina particles form a coating on the surface of the polypropylene film to obtain the modified polypropylene film.
[0009] S2. The composite aerogel and the carboxymethyl cellulose solution are uniformly mixed, sprayed onto the surface of the modified polypropylene film, and dried to obtain the polypropylene separator;
[0010] Further, in step S1, the mass ratio of the modified alumina particles, the methyl methacrylate solution and the polypropylene film is (2-5):(50-60):(8-10).
[0011] Further, in step S1, the methyl methacrylate solution is prepared by mixing methyl methacrylate, deionized water and methanol in a mass ratio of (2-3):(45-55):(35-45).
[0012] Further, in step S1, the irradiation grafting is performed in an irradiation tube, the irradiation time is 22-24h, the radiation dose is 18-22kGy, nitrogen is used as the irradiation medium, and the nitrogen flow rate is 15-20L / min.
[0013] Further, in step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed in a mass ratio of 1:(20-30).
[0014] Further, in step S2, the carboxymethyl cellulose solution is prepared by mixing carboxymethyl cellulose and deionized water in a mass ratio of (1.5-2):(45-55).
[0015] Further, in step S2, the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is (8-10)g.
[0016] Further, in step S2, the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 18-22g / m 2 , and the spraying pressure is 0.3-0.5MPa.
[0017] Further, the polypropylene film has a thickness of 10-15μm.
[0018] Further, the modified polypropylene film has a thickness of 20-30μm.
[0019] Further, the polypropylene separator has a thickness of 30-40μm.
[0020] Further, the modified alumina particles are obtained by mixing dimethylol propionic acid and glycidyl methacrylate, and then reacting with the carboxylated alumina particles.
[0021] Further, the modified alumina particles are prepared by the following steps:
[0022] A1. Dimethylol propionic acid, tetrabutylammonium bromide and 2,6-di-tert-butyl-p-cresol are added to N,N-dimethylformamide, stirred uniformly, glycidyl methacrylate is added, and stirred at 80-100℃ for 6-8h, and then separated to obtain a monomer solution;
[0023] A2. Alumina particles are added to ethanol and deionized water, stirred uniformly, carboxylated polyethylene glycol silane is added, stirred and reacted, cooled to room temperature, filtered, washed and dried to obtain carboxylated alumina particles;
[0024] A3. The carboxylated alumina particles were added to the monomer solution, stirred uniformly, hydrochloric acid was added, stirred at 50-60℃ for 1-2h, cooled to room temperature, filtered, washed, dried, to obtain modified alumina particles.
[0025] Further, in the above A1 reaction process, N,N-dimethylformamide was used as the solvent, tetrabutylammonium bromide was used as the catalyst, 2,6-di-tert-butyl-p-cresol was used as the polymerization inhibitor, and the carboxyl group contained in dimethylol propionic acid could react with the epoxy group of glycidyl methacrylate to open the ring, so that dimethylol propionic acid was grafted on glycidyl methacrylate to obtain a monomer solution.
[0026] Further, in the above A2 reaction process, the silicon hydroxyl generated by the hydrolysis of carboxyl polyethylene glycol silane can be combined with the hydroxyl on the surface of the alumina particles through a chemical bond, so that the carboxyl polyethylene glycol silane is grafted on the alumina particles to obtain carboxylated alumina particles.
[0027] Further, in the above A3 reaction process, the hydroxyl of dimethylol propionic acid in the monomer can react with the carboxyl on the surface of the carboxylated alumina particles, so that the monomer is grafted on the surface of the alumina particles, giving reactive double bonds, which is conducive to the formation of an alumina particle coating on the surface of the polypropylene film.
[0028] Further, in step A1, the mass ratio of dimethylol propionic acid, tetrabutylammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is (5-6):(0.04-0.06):(0.1-0.3):(18-22):(6-6.4).
[0029] Further, in step A2, the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane is (1-2):(68-74):(25-35):(0.6-1.2).
[0030] Further, in step A3, the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid is (1.7-1.9):(23-27):(2-3).
[0031] Further, the composite aerogel is obtained by mixing carboxymethyl cellulose and sodium alginate after pectin is coated on the surface of montmorillonite.
[0032] Further, the composite aerogel is prepared by the following steps:
[0033] B1. Pectin and deionized water were mixed and stirred until the pectin was completely dissolved, then montmorillonite was added, stirred at 50-60℃ for 2-3h, cooled to room temperature, filtered, washed, dried, to obtain pectin-modified montmorillonite;
[0034] B2. Sodium alginate and carboxymethyl cellulose are added to deionized water, stirred until completely dissolved, after ultrasonic treatment, pectin modified montmorillonite is added, stirred at 1000-1200 r / min for 5-10 min, placed in ethanol, and the wet gel is obtained by standing, the wet gel is washed, frozen and dried to obtain a composite aerogel.
[0035] Further, in the above B1 reaction process, the oxygen-containing functional groups contained in the pectin can combine with the hydroxyl groups in the montmorillonite, so that the pectin is grafted on the surface of the montmorillonite to obtain pectin modified montmorillonite.
[0036] Further, in the above B1 reaction process, carboxymethyl cellulose and sodium alginate are combined by chemical bonds to form a network structure of aerogel structure, and the oxygen-containing functional groups contained in the pectin modified montmorillonite can react with the carboxymethyl cellulose, so that the pectin modified montmorillonite is embedded in the composite aerogel.
[0037] Further, in step B1, the mass ratio of the pectin, deionized water and montmorillonite is (2.1-2.5):(30-40):(5.5-5.9).
[0038] Further, in step B2, the mass ratio of the sodium alginate, carboxymethyl cellulose, deionized water, pectin modified montmorillonite and ethanol is (1.4-1.6):(1.6-1.8):(90-110):(1.1-1.3):(80-90).
[0039] A polypropylene separator is prepared by the above-mentioned method for preparing a polypropylene separator.
[0040] The present application has the following beneficial effects:
[0041] (1) In the technical scheme of the present application, the modified alumina particles and methyl methacrylate are coated on the polypropylene film by irradiation grafting. On the one hand, the alumina particles are uniformly stacked on the surface of the polypropylene film, and the gaps between the particles form through channels, improving the transmission of lithium ions and enhancing the mobility of lithium ions, thereby improving the electrochemical performance. The coating formed by the alumina particles has high mechanical strength and heat stability, which improves the tensile strength and thermal shrinkage rate of the polypropylene separator, avoids wrinkles on the polypropylene separator, and affects the conduction efficiency of lithium ions.
[0042] On the other hand, the modified alumina particles are copolymerized with glycidyl methacrylate and methyl methacrylate on the surface of the polypropylene film to form a modified polypropylene film. Therefore, the alumina particles and the polypropylene film are combined by chemical bonds, so that the alumina particles and the polypropylene film have high bonding force, avoiding the alumina particles from falling off and causing the mechanical properties and lithium ion transmission properties of the polypropylene separator to decrease.
[0043] In addition, the unspent hydroxyl group in dimethylol propionic acid can be crosslinked with the polymer formed by glycidyl methacrylate and methyl methacrylate, coated on the surface of the polypropylene film, and further improve the binding force of the aluminum oxide particles and the polypropylene film, and the crosslinked polymer forms a dense crosslinked network structure, which enhances the mechanical properties of the polypropylene separator.
[0044] (2) In the technical scheme of the present application, the pectin modified montmorillonite is mixed and reacted with carboxymethyl cellulose and sodium alginate to form a composite aerogel, and then the carboxymethyl cellulose solution is sprayed onto the modified polypropylene film to form a polypropylene separator. On the one hand, pectin is grafted on montmorillonite, and pectin can adsorb and fix metal ions in montmorillonite, avoiding the migration and precipitation of metal ions into lithium ion batteries, which affects the electrochemical performance of lithium ion batteries. In the charge and discharge cycle, the oxygen-containing functional groups contained in pectin can combine with lithium ions, so that lithium ions are uniformly deposited on the polypropylene separator, avoiding the continuous generation of lithium dendrites caused by uneven lithium deposition. On the other hand, the pectin modified montmorillonite is embedded in the carboxymethyl cellulose and sodium alginate aerogel, and its porous structure enhances the migration rate of lithium ions and improves the electrochemical performance.
[0045] In addition, the composite aerogel contains a large number of carboxyl and hydroxyl functional groups, which are coated on the surface of the polypropylene separator to impart hydrophilicity to the polypropylene separator, limit the free migration of anions, improve the number of lithium ion migration, and avoid the hydrophobicity of the polymer on the surface of the modified polypropylene film, resulting in poor wettability of the prepared polypropylene separator.
[0046] (3) In the technical scheme of the present application, the modified aluminum oxide particles and the polypropylene film form a coating on the surface of the polypropylene film by chemical bonding to obtain a modified polypropylene film as the inner layer of the polypropylene separator, and the composite aerogel is adhered to the modified polypropylene film by an adhesive as the outer layer of the polypropylene separator, thereby forming a polypropylene separator with a double-layer structure, which has excellent mechanical properties, thermal shrinkage rate, wettability and electrochemical performance. DETAILED DESCRIPTION
[0047] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.
[0048] The raw materials used in the embodiments of the present application are as follows, and the reagents used are all analytical grade.
[0049] The polypropylene film was purchased from Xinxiang City Zhongke Technology Co., Ltd.
[0050] The particle size of the aluminum oxide particles is 2 microns.
[0051] The montmorillonite is sodium-based montmorillonite with a particle size of 2.5 μm.
[0052] The carboxymethyl cellulose solution is prepared by mixing carboxymethyl cellulose and deionized water at a mass ratio of 1.8:50.
[0053] Example 1
[0054] A preparation method of a polypropylene separator includes the following preparation steps:
[0055] S1. The modified alumina particles and the methyl methacrylate solution are uniformly mixed, and the polypropylene film is added. After irradiation grafting, it is taken out, washed with deionized water for 3 times, and dried at 50℃ for 12h to obtain a modified polypropylene film;
[0056] S2. The composite aerogel and the carboxymethyl cellulose solution are uniformly mixed, sprayed onto the surface of the modified polypropylene film, and dried at 50℃ for 2h to obtain a polypropylene separator.
[0057] In step S1, the mass ratio of the modified alumina particles, the methyl methacrylate solution and the polypropylene film is 2:50:8.
[0058] In step S1, the methyl methacrylate solution is prepared by mixing methyl methacrylate, deionized water and methanol at a mass ratio of 2:45:35.
[0059] In step S1, the irradiation grafting is carried out in an irradiation tube, the irradiation time is 22h, the radiation dose is 18kGy, nitrogen is used as the irradiation medium, and the nitrogen flow is 15L / min.
[0060] In step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed at a mass ratio of 1:20 to obtain a composite aerogel and a carboxymethyl cellulose solution. The spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa.
[0061] The thickness of the polypropylene film is 13μm, the thickness of the modified polypropylene film is 25μm, and the thickness of the polypropylene separator is 35μm.
[0062] The modified alumina particles are prepared by the following steps:
[0063] A1. Dimethylol propionic acid, tetrabutylammonium bromide and 2,6-di-tert-butyl-p-cresol are added to N,N-dimethylformamide, stirred uniformly, and glycidyl methacrylate is added. Stirring is carried out at 80℃ for 6h, and separation is carried out by thin layer chromatography (ethyl acetate as developing agent) to obtain a monomer solution. The mass ratio of dimethylol propionic acid, tetrabutylammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 5:0.04:0.1:18:6.
[0064] A2. The alumina particles were added to ethanol and deionized water, stirred until uniform, carboxyl polyethylene glycol silane was added, stirred at 70°C for 1.5h, cooled to room temperature, filtered, washed with ethanol 3 times, washed with deionized water 3 times, dried in an oven at 70°C for 10min, to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane was 1:68:25:0.6;
[0065] A3. The carboxylated alumina particles were added to the monomer solution, stirred until uniform, 36% mass fraction hydrochloric acid was added, stirred at 50°C for 1h, cooled to room temperature, filtered, washed with deionized water 3 times, dried in an oven at 90°C for 20min, to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid was 1.7:23:2.
[0066] The composite aerogel was prepared by the following steps:
[0067] B1. The pectin and deionized water were mixed, stirred at 55°C until the pectin was completely dissolved, montmorillonite was added, stirred at 50°C for 2h, cooled to room temperature, filtered, washed with deionized water 3 times, dried in an oven at 80°C for 8min, to obtain pectin modified montmorillonite; the mass ratio of pectin, deionized water and montmorillonite was 2.1:30:5.5;
[0068] B2. The sodium alginate and carboxymethyl cellulose were added to deionized water, stirred until completely dissolved, ultrasonically treated at 40KHz for 20min, the pectin modified montmorillonite was added, stirred at 1000r / min for 5min, placed in ethanol, and stood for 3h, to obtain a wet gel, the wet gel was washed with deionized water 3 times, and freeze-dried at -20°C for 24h, to obtain a composite aerogel; the mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, pectin modified montmorillonite and ethanol was 1.4:1.6:90:1.1:80.
[0069] Example 2
[0070] A method for preparing a polypropylene separator, comprising the following preparation steps:
[0071] S1. The modified alumina particles and methyl methacrylate solution were mixed until uniform, a polypropylene film was added, after irradiation grafting, it was taken out, washed with deionized water 3 times, and dried at 50°C for 12h, to obtain a modified polypropylene film.
[0072] S2. The composite aerogel and carboxymethyl cellulose solution were mixed until uniform, sprayed onto the surface of the modified polypropylene film, and dried at 50°C for 2h, to obtain a polypropylene separator.
[0073] In step S1, the mass ratio of modified alumina particles, methyl methacrylate solution and polypropylene film is 3:555:9;
[0074] In step S1, the methyl methacrylate solution is mixed by methyl methacrylate, deionized water and methanol according to the mass ratio of 2.5:50:40;
[0075] In step S1, the irradiation grafting is carried out in the irradiation tube, the irradiation time is 23h, the radiation dose is 20kGy, nitrogen is used as the irradiation medium, and the nitrogen flow is 18L / min;
[0076] In step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed according to the mass ratio of 1:25, and the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa;
[0077] The thickness of the polypropylene film is 13μm, the thickness of the modified polypropylene film is 25μm, and the thickness of the polypropylene diaphragm is 35μm.
[0078] The modified alumina particles are prepared by the following steps:
[0079] A1. Dimethylol propionic acid, tetrabutyl ammonium bromide and 2,6-di-tert-butyl-p-cresol are added to N,N-dimethylformamide, stirred uniformly, glycidyl methacrylate is added, stirred at 90℃ for 7h, separated by thin layer chromatography (ethyl acetate as developing agent) to obtain a monomer solution; the mass ratio of dimethylol propionic acid, tetrabutyl ammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 5.5:0.05:0.2:20:6.2;
[0080] A2. Alumina particles are added to ethanol and deionized water, stirred uniformly, carboxyl polyethylene glycol silane is added, stirred at 70℃ for 1.5h, cooled to room temperature, filtered, washed with ethanol for 3 times, washed with deionized water for 3 times, dried in a 70℃ oven for 10min to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane is 1.5:70:30:1;
[0081] A3. The carboxylated alumina particles are added to the monomer solution, stirred uniformly, 36% hydrochloric acid is added, stirred at 55℃ for 1.5h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in a 90℃ oven for 20min to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid is 1.8:25:2.5.
[0082] The composite aerogel is prepared by the following steps:
[0083] B1. Mix pectin and deionized water, stir at 55℃ until pectin is completely dissolved, add montmorillonite, stir at 55℃ for 2.5h, cool to room temperature, filter, wash with deionized water for 3 times, dry in oven at 80℃ for 8min, get pectin modified montmorillonite; mass ratio of pectin, deionized water and montmorillonite is 2.3:35:5.7;
[0084] B2. Add sodium alginate and carboxymethyl cellulose into deionized water, stir until completely dissolved, ultrasonic treatment at 40KHz for 20min, add pectin modified montmorillonite, stir at 1100r / min for 8min, place in ethanol, stand for 3h, get wet gel, wash the wet gel with deionized water for 3 times, freeze dry at-20℃ for 24h, get composite aerogel; mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, pectin modified montmorillonite and ethanol is 1.5:1.7:100:1.2:85.
[0085] Example 3
[0086] A preparation method of a polypropylene separator, comprising the following preparation steps:
[0087] S1. Mix modified alumina particles and methyl methacrylate solution uniformly, add polypropylene film, after irradiation grafting, take out, wash with deionized water for 3 times, dry at 50℃ for 12h, get modified polypropylene film.
[0088] S2. Mix composite aerogel and carboxymethyl cellulose solution uniformly, spray to the surface of the modified polypropylene film, dry at 50℃ for 2h, get polypropylene separator.
[0089] In step S1, the mass ratio of modified alumina particles, methyl methacrylate solution and polypropylene film is 5:60:10;
[0090] In step S1, the methyl methacrylate solution is mixed by methyl methacrylate, deionized water and methanol according to the mass ratio of 3:55:45;
[0091] In step S1, the irradiation grafting is carried out in an irradiation tube, the irradiation time is 24h, the radiation dose is 22kGy, nitrogen is used as the irradiation medium, and the nitrogen flow is 20L / min;
[0092] In step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed according to the mass ratio of 1:30, and the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa;
[0093] The thickness of the polypropylene film is 13μm, the thickness of the modified polypropylene film is 25μm, and the thickness of the polypropylene separator is 35μm.
[0094] The modified alumina particles are prepared by the following steps:
[0095] A1. Dimethylol propionic acid, tetrabutyl ammonium bromide and 2,6-di-tert-butyl-p-cresol are added into N,N-dimethylformamide, stirred uniformly, glycidyl methacrylate is added, stirred at 100℃ for 8h, separated by thin layer chromatography (ethyl acetate as developing agent) to obtain monomer solution; the mass ratio of dimethylol propionic acid, tetrabutyl ammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 6:0.06:0.3:22:6.4;
[0096] A2. Alumina particles are added into ethanol and deionized water, stirred uniformly, carboxyl polyethylene glycol silane is added, stirred at 70℃ for 1.5h, cooled to room temperature, filtered, washed with ethanol for 3 times, washed with deionized water for 3 times, dried in 70℃ oven for 10min to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane is 2:74:35:1.2;
[0097] A3. Carboxylated alumina particles are added into monomer solution, stirred uniformly, hydrochloric acid with mass fraction of 36% is added, stirred at 60℃ for 2h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in 90℃ oven for 20min to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid is 1.9:27:3.
[0098] The composite aerogel is prepared by the following steps:
[0099] B1. Pectin and deionized water are mixed, stirred at 55℃ until the pectin is completely dissolved, montmorillonite is added, stirred at 60℃ for 3h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in 80℃ oven for 8min to obtain pectin modified montmorillonite; the mass ratio of pectin, deionized water and montmorillonite is 2.5:40:5.9;
[0100] B2. Sodium alginate and carboxymethyl cellulose are added into deionized water, stirred until completely dissolved, ultrasonic treated at 40KHz for 20min, pectin modified montmorillonite is added, stirred at 1200r / min for 10min, placed in ethanol, and stood for 3h to obtain wet gel, the wet gel is washed with deionized water for 3 times, and freeze-dried at -20℃ for 24h to obtain composite aerogel; the mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, pectin modified montmorillonite and ethanol is 1.6:1.8:110:1.3:90.
[0101] Comparative Example 1
[0102] A method for preparing a polypropylene separator, comprising the following preparation steps:
[0103] S1. The modified alumina particles and methyl methacrylate solution are mixed uniformly, and a polypropylene film is added. After irradiation grafting, it is taken out, washed with deionized water for 3 times, and dried at 50℃ for 12h to obtain a modified polypropylene film.
[0104] S2. The composite aerogel and carboxymethyl cellulose solution are mixed uniformly, sprayed onto the surface of the modified polypropylene film, and dried at 50℃ for 2h to obtain a polypropylene separator.
[0105] In step S1, the mass ratio of modified alumina particles, methyl methacrylate solution and polypropylene film is 5:60:10.
[0106] In step S1, the methyl methacrylate solution is mixed by methyl methacrylate, deionized water and methanol according to the mass ratio of 3:55:45.
[0107] In step S1, the irradiation grafting is carried out in an irradiation tube, the irradiation time is 24h, the radiation dose is 22kGy, nitrogen is used as the irradiation medium, and the nitrogen flow is 20L / min.
[0108] In step S2, the composite aerogel and carboxymethyl cellulose solution are mixed according to the mass ratio of 1:30, and the spraying amount of the composite aerogel and carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa.
[0109] The thickness of the polypropylene film is 13μm, the thickness of the modified polypropylene film is 25μm, and the thickness of the polypropylene separator is 35μm.
[0110] The modified alumina particles are prepared by the following steps:
[0111] A1. Dimethylol propionic acid, tetrabutylammonium bromide and 2,6-di-tert-butyl-p-cresol are added to N,N-dimethylformamide, stirred uniformly, and glycidyl methacrylate is added. Stirring reaction at 100℃ for 8h, separation by thin layer chromatography (ethyl acetate as developing agent) to obtain a monomer solution; the mass ratio of dimethylol propionic acid, tetrabutylammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 6:0.06:0.3:22:6.4.
[0112] A2. Alumina particles are added to the monomer solution, stirred uniformly, and 36% hydrochloric acid is added. Stirring reaction at 60℃ for 2h, cooling to room temperature, filtering, washing with deionized water for 3 times, drying in a 90℃ oven for 20min to obtain modified alumina particles; the mass ratio of alumina particles, monomer solution and hydrochloric acid is 1.9:27:3.
[0113] The composite aerogel is prepared by the following steps:
[0114] B1. Mix pectin and deionized water, stir at 55℃ until the pectin is completely dissolved, add montmorillonite, stir at 60℃ for 3h, cool to room temperature, filter, wash with deionized water for 3 times, dry in an oven at 80℃ for 8min, to obtain pectin modified montmorillonite; the mass ratio of pectin, deionized water and montmorillonite is 2.5:40:5.9;
[0115] B2. Add sodium alginate and carboxymethyl cellulose into deionized water, stir until completely dissolved, ultrasonic treatment at 40KHz for 20min, add pectin modified montmorillonite, stir at 1200r / min for 10min, place in ethanol, stand for 3h, to obtain wet gel, wash the wet gel with deionized water for 3 times, freeze dry at-20℃ for 24h, to obtain composite aerogel; the mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, pectin modified montmorillonite and ethanol is 1.6:1.8:110:1.3:90.
[0116] Comparative Example 2
[0117] A preparation method of a polypropylene separator, comprising the following preparation steps:
[0118] S1. Mix modified alumina particles and methyl methacrylate solution uniformly, add polypropylene film, after irradiation grafting, take out, wash with deionized water for 3 times, dry at 50℃ for 12h, to obtain modified polypropylene film;
[0119] S2. Mix composite aerogel and carboxymethyl cellulose solution uniformly, spray on the surface of the modified polypropylene film, dry at 50℃ for 2h, to obtain a polypropylene separator.
[0120] In step S1, the mass ratio of modified alumina particles, methyl methacrylate solution and polypropylene film is 5:60:10;
[0121] In step S1, the methyl methacrylate solution is mixed by methyl methacrylate, deionized water and methanol according to a mass ratio of 3:55:45;
[0122] In step S1, the irradiation grafting is carried out in an irradiation tube, the irradiation time is 24h, the radiation dose is 22kGy, nitrogen is used as the irradiation medium, and the nitrogen flow is 20L / min;
[0123] In step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed according to a mass ratio of 1:30, and the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa;
[0124] The polypropylene film has a thickness of 13 μm, the modified polypropylene film has a thickness of 25 μm, and the polypropylene separator has a thickness of 35 μm.
[0125] A1. Dimethylol propionic acid is added to N,N-dimethylformamide and stirred to obtain a monomer solution; the mass ratio of dimethylol propionic acid to N,N-dimethylformamide is 12.4:22;
[0126] A2. Alumina particles are added to ethanol and deionized water and stirred to obtain a uniform mixture, carboxyl polyethylene glycol silane is added, and the mixture is stirred at 70°C for 1.5 h, cooled to room temperature, filtered, washed with ethanol three times, washed with deionized water three times, and dried in an oven at 70°C for 10 min to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water, and carboxyl polyethylene glycol silane is 2:74:35:1.2;
[0127] A3. The carboxylated alumina particles are added to the monomer solution and stirred to obtain a uniform mixture, hydrochloric acid with a mass fraction of 36% is added, and the mixture is stirred at 60°C for 2 h, cooled to room temperature, filtered, washed with deionized water three times, and dried in an oven at 90°C for 20 min to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution, and hydrochloric acid is 1.9:27:3.
[0128] The composite aerogel is prepared by the following steps:
[0129] B1. Pectin and deionized water are mixed and stirred at 55°C until the pectin is completely dissolved, and then montmorillonite is added and stirred at 60°C for 3 h, cooled to room temperature, filtered, washed with deionized water three times, and dried in an oven at 80°C for 8 min to obtain pectin-modified montmorillonite; the mass ratio of pectin, deionized water, and montmorillonite is 2.5:40:5.9;
[0130] B2. Sodium alginate and carboxymethyl cellulose are added to deionized water and stirred until completely dissolved, and then ultrasonic treatment is performed at 40 KHz for 20 min, pectin-modified montmorillonite is added and stirred at 1200 r / min for 10 min, and then placed in ethanol and allowed to stand for 3 h to obtain a wet gel, which is washed with deionized water three times and freeze-dried at -20°C for 24 h to obtain a composite aerogel; the mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, pectin-modified montmorillonite, and ethanol is 1.6:1.8:110:1.3:90.
[0131] Comparative Example 3
[0132] A method for preparing a polypropylene separator includes the following preparation steps:
[0133] S1. The modified alumina particles and methyl methacrylate solution were mixed uniformly, polypropylene film was added, taken out, washed with deionized water for 3 times, and dried at 50℃ for 12h to obtain a modified polypropylene film.
[0134] S2. The composite aerogel and carboxymethyl cellulose solution were mixed uniformly, sprayed onto the surface of the modified polypropylene film, and dried at 50℃ for 2h to obtain a polypropylene separator.
[0135] In step S1, the mass ratio of the modified alumina particles, the methyl methacrylate solution and the polypropylene film is 5:60:10;
[0136] In step S1, the methyl methacrylate solution is mixed by methyl methacrylate, deionized water and methanol according to a mass ratio of 3:55:45;
[0137] In step S2, the composite aerogel and carboxymethyl cellulose solution are mixed according to a mass ratio of 1:30, and the spraying amount of the composite aerogel and carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa;
[0138] The thickness of the polypropylene film is 13μm, the thickness of the modified polypropylene film is 25μm, and the thickness of the polypropylene separator is 35μm.
[0139] The modified alumina particles are prepared by the following steps:
[0140] A1. Dimethylol propionic acid, tetrabutylammonium bromide and 2,6-di-tert-butyl-p-cresol were added to N,N-dimethylformamide, stirred uniformly, glycidyl methacrylate was added, stirred at 100℃ for 8h, separated by thin layer chromatography (ethyl acetate as developing agent) to obtain a monomer solution; the mass ratio of dimethylol propionic acid, tetrabutylammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 6:0.06:0.3:22:6.4;
[0141] A2. Alumina particles were added to ethanol and deionized water, stirred uniformly, carboxyl polyethylene glycol silane was added, stirred at 70℃ for 1.5h, cooled to room temperature, filtered, washed with ethanol for 3 times, washed with deionized water for 3 times, and dried in a 70℃ oven for 10min to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane is 2:74:35:1.2;
[0142] A3. The carboxylated alumina particles were added to the monomer solution, stirred uniformly, 36% hydrochloric acid was added, stirred at 60℃ for 2h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in an oven at 90℃ for 20min to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid was 1.9:27:3.
[0143] The composite aerogel was prepared by the following steps:
[0144] B1. The pectin and deionized water were mixed, stirred at 55℃ until the pectin was completely dissolved, the montmorillonite was added, stirred at 60℃ for 3h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in an oven at 80℃ for 8min to obtain pectin modified montmorillonite; the mass ratio of pectin, deionized water and montmorillonite was 2.5:40:5.9;
[0145] B2. The sodium alginate and carboxymethyl cellulose were added to deionized water, stirred until completely dissolved, ultrasonically treated at 40KHz for 20min, the pectin modified montmorillonite was added, stirred at 1200r / min for 10min, placed in ethanol, and stood for 3h to obtain a wet gel, the wet gel was washed with deionized water for 3 times, and freeze-dried at-20℃ for 24h to obtain a composite aerogel; the mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, pectin modified montmorillonite and ethanol was 1.6:1.8:110:1.3:90.
[0146] Comparative Example 4
[0147] A preparation method of a polypropylene separator, comprising the following preparation steps:
[0148] S1. The modified alumina particles and methyl methacrylate solution were mixed uniformly, the polypropylene film was added, and after irradiation grafting, it was taken out, washed with deionized water for 3 times, and dried at 50℃ for 12h to obtain a modified polypropylene film.
[0149] S2. The composite aerogel and carboxymethyl cellulose solution were mixed uniformly, sprayed onto the surface of the modified polypropylene film, and dried at 50℃ for 2h to obtain a polypropylene separator.
[0150] In step S1, the mass ratio of modified alumina particles, methyl methacrylate solution and polypropylene film was 5:60:10.
[0151] In step S1, the methyl methacrylate solution was mixed by methyl methacrylate, deionized water and methanol according to a mass ratio of 3:55:45;
[0152] In step S1, the irradiation grafting was carried out in an irradiation tube, the irradiation time was 24h, the radiation dose was 22kGy, nitrogen was used as the irradiation medium, and the nitrogen flow was 20L / min.
[0153] In step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed in a mass ratio of 1:30, and the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 20 g / m 2 , and the spraying pressure is 0.4 MPa.
[0154] The polypropylene film has a thickness of 13 μm, the modified polypropylene film has a thickness of 25 μm, and the polypropylene separator has a thickness of 35 μm.
[0155] The modified alumina particles are prepared by the following steps:
[0156] A1. Dimethylol propionic acid, tetrabutyl ammonium bromide and 2,6-di-tert-butyl-p-cresol are added into N,N-dimethylformamide, stirred uniformly, glycidyl methacrylate is added, stirred at 100°C for 8 h, separated by thin layer chromatography (ethyl acetate as developing agent) to obtain a monomer solution; the mass ratio of dimethylol propionic acid, tetrabutyl ammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 6:0.06:0.3:22:6.4.
[0157] A2. Alumina particles are added into ethanol and deionized water, stirred uniformly, carboxyl polyethylene glycol silane is added, stirred at 70°C for 1.5 h, cooled to room temperature, filtered, washed with ethanol for 3 times, washed with deionized water for 3 times, dried in a 70°C oven for 10 min to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane is 2:74:35:1.2.
[0158] A3. The carboxylated alumina particles are added into the monomer solution, stirred uniformly, hydrochloric acid with a mass fraction of 36% is added, stirred at 60°C for 2 h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in a 90°C oven for 20 min to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid is 1.9:27:3.
[0159] The composite aerogel is prepared by the following steps:
[0160] Sodium alginate and carboxymethyl cellulose are added into deionized water, stirred until completely dissolved, ultrasonically treated at 40 KHz for 20 min, montmorillonite is added, stirred at 1200 r / min for 10 min, placed in ethanol, and allowed to stand for 3 h to obtain a wet gel, the wet gel is washed with deionized water for 3 times, and freeze-dried at -20°C for 24 h to obtain a composite aerogel; the mass ratio of sodium alginate, carboxymethyl cellulose, deionized water, montmorillonite and ethanol is 1.6:1.8:110:1.3:90.
[0161] Comparative Example 5
[0162] A method for preparing a polypropylene separator, comprising the following preparation steps:
[0163] S1. mixing the modified alumina particles and the methyl methacrylate solution uniformly, adding the polypropylene film, after irradiation grafting, taking out, washing with deionized water for 3 times, drying at 50℃ for 12h, to obtain a modified polypropylene film;
[0164] S2. mixing the composite aerogel and the carboxymethyl cellulose solution uniformly, spraying onto the surface of the modified polypropylene film, drying at 50℃ for 2h, to obtain a polypropylene separator.
[0165] In step S1, the mass ratio of the modified alumina particles, the methyl methacrylate solution and the polypropylene film is 5:60:10.
[0166] In step S1, the methyl methacrylate solution is mixed by methyl methacrylate, deionized water and methanol according to a mass ratio of 3:55:45;
[0167] In step S1, the irradiation grafting is carried out in an irradiation tube, the irradiation time is 24h, the radiation dose is 22kGy, nitrogen is used as the irradiation medium, and the nitrogen flow is 20L / min;
[0168] In step S2, the composite aerogel and the carboxymethyl cellulose solution are mixed according to a mass ratio of 1:30, and the spraying amount of the composite aerogel and the carboxymethyl cellulose solution is 20g / m 2 , and the spraying pressure is 0.4MPa;
[0169] The thickness of the polypropylene film is 13μm, the thickness of the modified polypropylene film is 25μm, and the thickness of the polypropylene separator is 35μm.
[0170] The modified alumina particles are prepared by the following steps:
[0171] A1. adding dimethylol propionic acid, tetrabutylammonium bromide and 2,6-di-tert-butyl-p-cresol into N,N-dimethylformamide, stirring uniformly, adding glycidyl methacrylate, stirring and reacting at 100℃ for 8h, separating by thin layer chromatography (ethyl acetate as developing agent) to obtain a monomer solution; the mass ratio of dimethylol propionic acid, tetrabutylammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is 6:0.06:0.3:22:6.4;
[0172] A2. The alumina particles were added into ethanol and deionized water, stirred until uniform, carboxyl polyethylene glycol silane was added, stirred at 70℃ for 1.5h, cooled to room temperature, filtered, washed with ethanol for 3 times, washed with deionized water for 3 times, dried in an oven at 70℃ for 10min, to obtain carboxylated alumina particles; the mass ratio of alumina particles, ethanol, deionized water and carboxyl polyethylene glycol silane was 2:74:35:1.2;
[0173] A3. The carboxylated alumina particles were added into the monomer solution, stirred until uniform, 36% hydrochloric acid was added, stirred at 60℃ for 2h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in an oven at 90℃ for 20min, to obtain modified alumina particles; the mass ratio of carboxylated alumina particles, monomer solution and hydrochloric acid was 1.9:27:3.
[0174] The composite aerogel was prepared by the following steps:
[0175] B1. The pectin and deionized water were mixed, stirred at 55℃ until the pectin was completely dissolved, montmorillonite was added, stirred at 60℃ for 3h, cooled to room temperature, filtered, washed with deionized water for 3 times, dried in an oven at 80℃ for 8min, to obtain pectin modified montmorillonite; the mass ratio of pectin, deionized water and montmorillonite was 2.5:40:5.9;
[0176] B2. The sodium alginate was added into deionized water, stirred until completely dissolved, ultrasonic treated at 40KHz for 20min, the pectin modified montmorillonite was added, stirred at 1200r / min for 10min, placed in ethanol, stood for 3h, to obtain a wet gel, the wet gel was washed with deionized water for 3 times, freeze-dried at-20℃ for 24h, to obtain a composite aerogel; the mass ratio of sodium alginate, deionized water, pectin modified montmorillonite and ethanol was 3.4:110:1.3:90.
[0177] The polypropylene separators prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance testing.
[0178] The width of the polypropylene separator used for testing was 20mm, the length was 40mm, and the thickness was 35μm.
[0179] Mechanical property testing: the strength performance was tested according to GB / T1040.3-2006, the tensile speed was 50mm / min, the longitudinal tensile strength corresponding to the position of 5% longitudinal deformation and the transverse tensile strength corresponding to the position of 5% transverse deformation were tested; the porosity was determined by a pressure pump instrument, and the thermal shrinkage rate was determined by a battery separator thermal shrinkage rate tester.
[0180] Wettability test: use deionized water instead of electrolyte to do contact angle test, drop deionized water slowly on the membrane through the needle tube, camera snapshot the moment when the water droplet falls on the surface of the membrane, use the ruler to mark the angle between the polypropylene membrane and the tangent of the water droplet, the smaller the contact angle, the better the wettability of the polypropylene membrane.
[0181] Electrochemical performance test: lithium iron phosphate: carbon black: polyvinylidene fluoride is mixed in a ratio of 8:1:1 and coated on aluminum foil, dried at 110°C, cut into a 13mm diameter circle as a positive electrode material, the negative electrode material is selected as pure lithium sheet, the separator is selected as the above prepared polypropylene separator, the positive and negative electrode shell is selected as CR2032 type, assembled into a battery;
[0182] The voltage is 3V, the constant current charge and discharge is carried out at 1C rate, the cycle is 100 times, the voltage protection is set between 0-4.25V, and the discharge capacity of the battery is recorded.
[0183] The test results are shown in Table 1.
[0184] Table 1 Performance test of polypropylene separator prepared in examples 1-3 and comparative examples 1-5
[0185]
[0186] From the data in Table 1, it can be seen that the polypropylene separator prepared in examples 1-3 has high mechanical properties, thermal shrinkage, wettability and electrochemical performance.
[0187] Comparative example 1 replaces carboxylated alumina particles with alumina particles to prepare modified alumina particles coated on polypropylene separator, which reduces the mechanical strength and electrochemical performance, proving that the carboxyl group on the surface of carboxylated alumina particles can react with the hydroxyl group of dimethylol propionic acid in the monomer, making the monomer grafted on the surface of alumina particles, giving reactive double bond, which is beneficial to form alumina particle coating on the surface of polypropylene film.
[0188] Comparative example 2 replaces glycidyl methacrylate with dimethylol propionic acid to prepare modified alumina particles coated on polypropylene separator, which reduces the mechanical strength and electrochemical performance, proving that glycidyl methacrylate and methyl methacrylate can copolymerize on the surface of polypropylene film, which is beneficial to form alumina particle coating on the surface of polypropylene film.
[0189] Comparative example 3 does not perform irradiation grafting in step S1 to prepare polypropylene separator, which reduces the mechanical strength and electrochemical performance, proving that modified alumina particles and methyl methacrylate are coated on the surface of polypropylene film by irradiation grafting, and the alumina particles have high bonding force with the polypropylene film, which improves the tensile strength, thermal shrinkage and electrochemical performance of the polypropylene separator.
[0190] In Comparative Example 4, the pectin-modified montmorillonite was replaced with a composite aerogel prepared from montmorillonite and coated on a polypropylene diaphragm. Its electrochemical performance decreased, proving that pectin can adsorb and fix the metal ions in montmorillonite, preventing the metal ions from migrating and precipitating into the lithium-ion battery, affecting the electrochemical performance of the lithium-ion battery, and pectin can combine with lithium ions, so that the lithium ions are evenly deposited on the polypropylene diaphragm, avoiding uneven lithium deposition that easily leads to the continuous generation of lithium dendrites, affecting the electrochemical performance of the lithium-ion battery.
[0191] In Comparative Example 5, the composite aerogel prepared by replacing the mass of carboxymethyl cellulose with sodium alginate is coated on the polypropylene membrane. Its wettability and electrochemical performance decrease, which proves that the formed composite aerogel contains a large number of carboxyl and hydroxyl functional groups, which are coated on the surface of the polypropylene membrane and give the polypropylene membrane lyophilicity.
[0192] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
[0193] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.
Claims
1. A method for preparing a polypropylene diaphragm, characterized in that: The method comprises the following preparation steps: S1. The modified alumina particles and methyl methacrylate solution were mixed uniformly, a polypropylene film was added, and after irradiation grafting, the film was removed, washed, and dried to obtain a modified polypropylene film; S2. The composite aerogel and carboxymethyl cellulose solution are mixed evenly, sprayed onto the surface of the modified polypropylene membrane, and dried to obtain a polypropylene separator.
2. The method for preparing a polypropylene diaphragm according to claim 1, wherein: The modified alumina particles are specifically prepared by the following steps: A1. Add dimethylolpropionic acid, tetrabutylammonium bromide, and 2,6-di-tert-butyl-p-cresol to N,N-dimethylformamide, stir evenly, add glycidyl methacrylate, and stir at 80-100°C for 6-8 hours. After separation, obtain a monomer solution. A2. Alumina particles were added to ethanol and deionized water, stirred, carboxyl polyethylene glycol silane was added, the reaction was stirred, cooled to room temperature, filtered, washed, and dried to obtain carboxylated alumina particles; A3. Add carboxylated alumina particles to the monomer solution, stir evenly, add hydrochloric acid, stir and react at 50-60°C for 1-2 hours, cool to room temperature, filter, wash, and dry to obtain modified alumina particles.
3. The method for preparing a polypropylene diaphragm according to claim 2, wherein: In step A1, the mass ratio of dimethylolpropionic acid, tetrabutylammonium bromide, 2,6-di-tert-butyl-p-cresol, N,N-dimethylformamide and glycidyl methacrylate is (5-6):(0.04-0.06):(0.1-0.3):(18-22):(6-6.4).
4. The method for preparing a polypropylene diaphragm according to claim 2, wherein: In step A2, the mass ratio of the aluminum oxide particles, ethanol, deionized water and carboxyl polyethylene glycol silane is (1-2):(68-74):(25-35):(0.6-1.2).
5. The method for preparing a polypropylene diaphragm according to claim 2, wherein: In step A3, the mass ratio of the carboxylated alumina particles, the monomer solution and the hydrochloric acid is (1.7-1.9):(23-27):(2-3).
6. The method for preparing a polypropylene diaphragm according to claim 1, characterized in that: The composite aerogel is specifically prepared by the following steps: B1. Pectin and deionized water were mixed and stirred until the pectin was completely dissolved. Montmorillonite was added and stirred at 50-60 ° C for 2-3 hours. The mixture was cooled to room temperature, filtered, washed, and dried to obtain pectin-modified montmorillonite. B2. Sodium alginate and carboxymethyl cellulose were added to deionized water and stirred until completely dissolved. After ultrasonic treatment, pectin-modified montmorillonite was added and stirred at 1000-1200 r / min for 5-10 minutes. The mixture was placed in ethanol and allowed to stand to obtain a wet gel. The wet gel was washed and freeze-dried to obtain a composite aerogel.
7. The method for preparing a polypropylene diaphragm according to claim 6, characterized in that: In step B1, the mass ratio of pectin, deionized water and montmorillonite is (2.1-2.5):(30-40):(5.5-5.9).
8. The method for preparing a polypropylene diaphragm according to claim 6, characterized in that: In step B2, the mass ratio of the sodium alginate, carboxymethyl cellulose, deionized water, pectin-modified montmorillonite and ethanol is (1.4-1.6):(1.6-1.8):(90-110):(1.1-1.3):(80-90).
9. A polypropylene diaphragm produced by the method for producing a polypropylene diaphragm according to any one of claims 1 to 8.