Aramid fiber lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses an aramid fiber lithium battery diaphragm and a preparation method thereof, and belongs to the technical field of battery diaphragms. The preparation method of the aramid lithium battery diaphragm comprises the following steps: S1, mixing and stirring para-aramid fibers, DMSO, KOH and deionized water to prepare a para-aramid nanofiber solution; s2, modified silicon dioxide is added into the para-aramid nanofiber solution, then ultrasonic treatment and stirring are carried out, dispersion liquid is obtained, and the modified silicon dioxide is PEI grafted phosphorus-containing metal organic framework coated SiO2; and S3, coating the surface of a polyolefin diaphragm with the dispersion liquid, treating the coated diaphragm in an aqueous solution for 3-4 hours, and then drying to obtain the aramid fiber lithium battery diaphragm. According to the preparation method disclosed by the invention, the modified silicon dioxide is added, and the modified silicon dioxide is PEI grafted phosphorus-containing metal organic framework coated SiO2, so that the problems that in the prior art, the dispersity of inorganic nanoparticles is poor, and the interface bonding between the inorganic nanoparticles and para-aramid nanofibers needs to be improved are solved, and the comprehensive performance of the diaphragm is improved.

Description

Technical Field

[0001] The present invention relates to the field of battery separators, and in particular to an aramid lithium battery separator and a preparation method thereof. Background Art

[0002] The lithium-ion battery industry has experienced rapid growth in recent years. As a mature and common energy source in mobile devices, it boasts high energy density, high operating voltage, no memory effect, and a long cycle life compared to other battery types. A lithium-ion battery typically consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator serves to electrically insulate the positive and negative electrodes while allowing lithium ions to flow. With the rise of electric vehicles and the emergence of high-power batteries, lithium-ion battery safety has been significantly challenged. Currently, common lithium-ion battery separators are made of polyolefins, typically polypropylene, polyethylene, or a polypropylene / polyethylene / polypropylene sandwich structure. These materials have a melting point below 170°C. When the battery heats up due to internal or external factors, the separator melts and contracts, causing direct contact between the positive and negative electrodes, resulting in a short circuit and potentially causing accidents such as battery combustion and explosion.

[0003] Poly(p-phenylene terephthalamide) (PPTA) is a rigid liquid crystal polymer with excellent thermal stability and a thermal decomposition temperature of up to 550°C. Fibers made from oriented PPTA also exhibit excellent mechanical properties, making PPTA an effective material for addressing the potential heat resistance issues of lithium-ion battery separators. However, due to the rigidity of PPTA molecules and the strong hydrogen bonding between molecules, it is difficult to dissolve in ordinary solvents, making it a significant technical challenge to manufacture porous membranes. Despite this, there are reports of compounding PPTA onto the surface of polyolefin separators to improve their heat resistance.

[0004] Patent CN113206345B discloses a para-aramid nanofiber / inorganic nanoparticle composite coating reinforced polyolefin battery separator and its preparation method. This patent combines the excellent film-forming properties and heat stability of para-aramid nanofibers with inorganic alumina or silica nanoparticles to develop and produce a para-aramid nanofiber / inorganic nanoparticle composite coating reinforced polyolefin battery separator with good liquid affinity, excellent high temperature resistance, high ionic conductivity, and excellent electrochemical properties. However, the dispersibility of the inorganic nanoparticles themselves is poor and the interface bonding between them and the para-aramid nanofibers needs to be improved, thereby further improving the overall performance of the separator. Summary of the Invention

[0005] The present invention provides an aramid lithium battery separator and a preparation method thereof, which can solve the problems in the prior art of poor dispersibility of inorganic nanoparticles themselves and the need to improve the interface bonding between inorganic nanoparticles and para-aramid nanofibers.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing an aramid lithium battery separator comprises the following steps:

[0008] S1: para-aramid fiber, DMSO, KOH and deionized water are mixed and stirred to prepare a para-aramid nanofiber solution;

[0009] The dosage ratio of para-aramid fiber, DMSO, KOH and deionized water is 5 g:500 mL:7.5 g:10-25 mL.

[0010] S2: adding modified silica to the para-aramid nanofiber solution, followed by ultrasonication and stirring to obtain a dispersion, wherein the modified silica is PEI-grafted phosphorus-containing metal organic framework@SiO2;

[0011] The mass of the modified silicon dioxide is 0.5%-3% of the mass of the para-aramid fiber.

[0012] S3: The dispersion is coated on the surface of the polyolefin separator, and the coated separator is treated in an aqueous solution for 3-4 hours, and then dried to obtain an aramid lithium battery separator.

[0013] Furthermore, in step S1, the diameter of the para-aramid nanofiber is 8-15 nm and the length is 3-10 μm.

[0014] Furthermore, in step S3, the coating thickness is 3-6 μm.

[0015] Furthermore, in step S3, the drying temperature is 100° C., and the drying time is 1-2 hours.

[0016] Furthermore, in step S2, the preparation method of modified silicon dioxide is:

[0017] A1: Add glutaric anhydride, APTES, and DMF, stir at 30°C for 3-5 hours, then add the silica mixture, continue stirring for 6-8 hours, collect the reaction product, wash with ethanol, and dry in vacuo at room temperature to obtain carboxylated-SiO2;

[0018] The dosage ratio of glutaric anhydride, APTES, DMF and silica mixture is 1.7 g: 3.6 mL: 100-120 mL: 100 mL; the dosage ratio of silica, DMF and deionized water in the silica mixture is 3 g: 100 mL: 8-10 mL.

[0019] A2: Mix the metal salt, DMF, and carboxylated-SiO2 and stir for 1-2 hours. Then, add 2-aminoterephthalic acid, tris(4-carboxyphenyl)phosphine, and formic acid to the reaction solution. Continue stirring for 30-40 minutes, react at 120°C for 24 hours, cool to room temperature, wash, and dry to obtain a phosphorus-containing metal organic framework@SiO2.

[0020] The usage ratio of the metal salt, DMF, carboxylated-SiO2, 2-aminoterephthalic acid, bis(4-carboxyphenyl)phenylphosphine oxide and formic acid is 0.5-0.6 g:80-100 mL:1 g:0.18-0.2 g:0.4 g:80 mL.

[0021] In the above steps, the phosphorus-containing metal organic framework is in situ grown on the carboxylated-SiO2 surface to obtain the phosphorus-containing metal organic framework@SiO2.

[0022] A3: Add the phosphorus-containing metal organic framework @SiO2 and maleic anhydride to DMF, stir and react at room temperature for 12-24 hours to obtain a pretreated product, add the pretreated product and polyethyleneimine to a phosphate buffer solution with a pH value of 7-8, stir and react at 40-50°C for 12-24 hours, then centrifuge and dry to obtain modified silica.

[0023] The usage ratio of phosphorus-containing metal organic framework @SiO2, maleic anhydride, DMF, polyethyleneimine and phosphate buffer solution is 5g:2g:100mL:1-5g:50-70mL.

[0024] The phosphorus-containing metal organic framework @SiO2 prepared in step A2 has amino groups on its surface. Polyethyleneimine is grafted onto the phosphorus-containing metal organic framework @SiO2 using maleic anhydride to obtain modified silica.

[0025] Furthermore, in step A2, the metal salt is one or more of ferric nitrate, zinc nitrate, and molybdenum nitrate.

[0026] An aramid lithium battery separator is made by the preparation method of the aramid lithium battery separator described in any one of the above contents.

[0027] Beneficial effects of the present invention:

[0028] The present invention adds modified silica, which is PEI grafted phosphorus-containing metal organic framework @SiO2, which can further improve the comprehensive performance of the diaphragm, as follows:

[0029] 1. The porous network structure of the phosphorus-containing metal organic framework has a nanoscale size. After in-situ growth, it forms a "rigid spacer layer" on the SiO2 surface. When the particles approach each other, the steric hindrance of the MOF framework prevents direct contact with SiO2, like a "molecular-level gasket" to expand the distance between particles, thereby improving the dispersion of silica and thus improving the overall performance of the diaphragm.

[0030] 2. The phosphorus-containing metal organic framework contains phosphorus elements, and polyethyleneimine contains a large amount of nitrogen elements, which can form a NP synergistic flame retardant system to improve the flame retardant properties of the diaphragm. The metal part (such as iron ions) in the phosphorus-containing metal organic framework has a catalytic effect, which can reduce the smoke and toxic gases generated during the combustion of the polymer, thereby improving the flame retardant properties of the diaphragm.

[0031] 3. The phosphorus-containing metal organic framework contains P=O, and the polyethyleneimine contains amino groups. These two groups can form bonds with lithium ions to form ion transmission channels, reduce the resistance to lithium ion migration, and improve the ion conductivity of the diaphragm. The micro / mesopores of the metal organic framework and the SiO2 macropores form hierarchical channels, shortening the Li + Diffusion path to improve the ionic conductivity of the membrane.

[0032] 4. The amino group of polyethyleneimine (PEI) can react with the amide group of aramid fiber to form covalent bonds or hydrogen bonds, thereby improving the interfacial compatibility between the phosphorus-containing metal organic framework @SiO2 and organic aramid, improving the mechanical properties of the diaphragm, and helping the phosphorus-containing metal organic framework @SiO2 to exert its flame retardant properties and improve the overall performance of the diaphragm. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0034] The sources of some of the raw materials in the examples of the present invention are as follows. Unless otherwise specified, the raw materials used in the examples can be obtained from conventional commercial channels or can be prepared by conventional methods:

[0035] The polyolefin separator adopts the commercial polyolefin single-layer separator Celgard250 with a thickness of 25 μm;

[0036] The silica particle size was 25 μm and was purchased from Tianjin Borui Jianhe Chromatography Technology Co., Ltd.

[0037] Preparation Example 1

[0038] The preparation method of modified silica is:

[0039] A1: Add 1.7 g of glutaric anhydride, 3.6 mL of APTES, and 100 mL of DMF, and stir at 30°C for 5 h. Then add 100 mL of a silica mixture (the ratio of silica, DMF, and deionized water in the silica mixture is 3 g:100 mL:10 mL). Stir for another 6 h, collect the reaction product, wash with ethanol, and dry in vacuo at room temperature to obtain carboxylated-SiO2.

[0040] A2: 0.5 g of ferric nitrate, 100 mL of DMF, and 1 g of carboxylated-SiO2 were mixed and stirred for 1 h. Then, 0.18 g of 2-aminoterephthalic acid, 0.4 g of tris(4-carboxyphenyl)phosphine, and 80 mL of formic acid were added to the reaction solution. Stirring was continued for 30 min, and the mixture was reacted at 120°C for 24 h. The mixture was cooled to room temperature, washed, and dried to obtain a phosphorus-containing metal organic framework@SiO2.

[0041] A3: 5 g of phosphorus-containing metal organic framework @SiO2 and 2 g of maleic anhydride were added to 100 mL of DMF and stirred at room temperature for 12 hours to obtain a pretreated product. The pretreated product and 1 g of polyethyleneimine were added to 50 mL of phosphate buffer solution with a pH value of 7-8. After stirring at 40°C for 12 hours, the mixture was centrifuged and dried to obtain modified silica.

[0042] Preparation Example 2

[0043] The preparation method of modified silica is:

[0044] A1: Add 1.7 g of glutaric anhydride, 3.6 mL of APTES, and 100 mL of DMF, and stir at 30°C for 5 h. Then add 100 mL of a silica mixture (the ratio of silica, DMF, and deionized water in the silica mixture is 3 g:100 mL:10 mL). Stirring is continued for 7 h. The reaction product is collected, washed with ethanol, and dried in vacuo at room temperature to obtain carboxylated-SiO2.

[0045] A2: 0.6 g of ferric nitrate, 100 mL of DMF, and 1 g of carboxylated-SiO2 were mixed and stirred for 1.5 h. Subsequently, 0.2 g of 2-aminoterephthalic acid, 0.4 g of tris(4-carboxyphenyl)phosphine, and 80 mL of formic acid were added to the reaction solution. Stirring was continued for 40 min, and the mixture was reacted at 120°C for 24 h. The mixture was cooled to room temperature, washed, and dried to obtain a phosphorus-containing metal organic framework@SiO2.

[0046] A3: 5 g of phosphorus-containing metal organic framework @SiO2 and 2 g of maleic anhydride were added to 100 mL of DMF and stirred at room temperature for 24 hours to obtain a pretreated product. The pretreated product and 3 g of polyethyleneimine were added to 70 mL of phosphate buffer solution with a pH value of 7-8. After stirring at 50°C for 24 hours, the mixture was centrifuged and dried to obtain modified silica.

[0047] Preparation Example 3

[0048] The preparation method of modified silica is:

[0049] A1: Add 1.7 g of glutaric anhydride, 3.6 mL of APTES, and 100 mL of DMF, and stir at 30°C for 5 h. Then add 100 mL of a silica mixture (the ratio of silica, DMF, and deionized water in the silica mixture is 3 g:100 mL:10 mL). Stirring is continued for 8 h. The reaction product is collected, washed with ethanol, and dried in vacuo at room temperature to obtain carboxylated-SiO2.

[0050] A2: 0.6 g of ferric nitrate, 100 mL of DMF, and 1 g of carboxylated-SiO2 were mixed and stirred for 2 h. Then, 0.2 g of 2-aminoterephthalic acid, 0.4 g of tris(4-carboxyphenyl)phosphine, and 80 mL of formic acid were added to the reaction solution. Stirring was continued for 40 min, and the mixture was reacted at 120°C for 24 h. The mixture was cooled to room temperature, washed, and dried to obtain a phosphorus-containing metal organic framework@SiO2.

[0051] A3: 5 g of phosphorus-containing metal organic framework @SiO2 and 2 g of maleic anhydride were added to 100 mL of DMF and stirred at room temperature for 24 hours to obtain a pretreated product. The pretreated product and 5 g of polyethyleneimine were added to 70 mL of phosphate buffer solution with a pH value of 7-8. After stirring at 50°C for 24 hours, the mixture was centrifuged and dried to obtain modified silica.

[0052] Comparative Example 1

[0053] This comparative example differs from Preparation Example 1 in that tri(4-carboxyphenyl)phosphine is omitted in Step A2, specifically:

[0054] 0.5 g of ferric nitrate, 100 mL of DMF, and 1 g of carboxylated-SiO2 were mixed and stirred for 1 h. Subsequently, 0.18 g of 2-aminoterephthalic acid and 80 mL of formic acid were added to the reaction solution. After further stirring for 30 min, the mixture was reacted at 120°C for 24 h, cooled to room temperature, washed, and dried to obtain a phosphorus-containing metal organic framework@SiO2.

[0055] The remaining materials and steps are the same as those in Preparation Example 1.

[0056] Comparative Example 2

[0057] This comparative example differs from Preparation Example 1 in that polyethyleneimine is omitted. The specific steps are as follows:

[0058] A1: Add 1.7 g of glutaric anhydride, 3.6 mL of APTES, and 100 mL of DMF, and stir at 30°C for 5 h. Then add 100 mL of a silica mixture (the ratio of silica, DMF, and deionized water in the silica mixture is 3 g:100 mL:10 mL). Stir for another 6 h, collect the reaction product, wash with ethanol, and dry in vacuo at room temperature to obtain carboxylated-SiO2.

[0059] A2: 0.5 g of ferric nitrate, 100 mL of DMF, and 1 g of carboxylated-SiO2 were mixed and stirred for 1 h. Subsequently, 0.18 g of 2-aminoterephthalic acid, 0.4 g of tris(4-carboxyphenyl)phosphine, and 80 mL of formic acid were added to the reaction solution. After further stirring for 30 min, the mixture was reacted at 120°C for 24 h. The mixture was cooled to room temperature, washed, and dried to obtain a phosphorus-containing metal organic framework@SiO2. The remaining raw materials and steps were the same as those in Example 1.

[0060] Comparative Example 3

[0061] This comparative example differs from Preparation Example 1 in that polyethyleneimine is omitted and tri(4-carboxyphenyl)phosphine is omitted in Step A2. Specifically,

[0062] A1: Add 1.7 g of glutaric anhydride, 3.6 mL of APTES, and 100 mL of DMF, and stir at 30°C for 5 h. Then add 100 mL of a silica mixture (the ratio of silica, DMF, and deionized water in the silica mixture is 3 g:100 mL:10 mL). Stir for another 6 h, collect the reaction product, wash with ethanol, and dry in vacuo at room temperature to obtain carboxylated-SiO2.

[0063] A2: 0.5 g of ferric nitrate, 100 mL of DMF, and 1 g of carboxylated-SiO2 were mixed and stirred for 1 h. Subsequently, 0.18 g of 2-aminoterephthalic acid and 80 mL of formic acid were added to the reaction solution. After further stirring for 30 min, the mixture was reacted at 120°C for 24 h. The mixture was cooled to room temperature, washed, and dried to obtain a phosphorus-containing metal organic framework@SiO2. The remaining raw materials and steps were the same as those in Preparation Example 1.

[0064] Comparative Example 4

[0065] In this comparative example, modified silica was replaced by silica.

[0066] Example 1

[0067] A method for preparing an aramid lithium battery separator comprises the following steps:

[0068] S1: 5 g of para-aramid fiber (diameter of para-aramid nanofiber is 12 nm and length is 5 μm), 500 mL of DMSO, 7.5 g of KOH and 25 mL of deionized water were mixed to prepare a para-aramid nanofiber solution;

[0069] S2: 0.025 g of the modified silica prepared in Preparation Example 1 was added to the para-aramid nanofiber solution, where the mass of the modified silica was 0.5% of the mass of the para-aramid fiber, and then ultrasonicated and stirred to obtain a dispersion. The modified silica was a PEI-grafted phosphorus-containing metal organic framework@SiO2;

[0070] S3: The dispersion is coated on the surface of the polyolefin separator with a coating thickness of 4 μm. The coated separator is treated in an aqueous solution for 3 hours and then dried at 100° C. for 1 hour to obtain an aramid lithium battery separator.

[0071] Example 2

[0072] A method for preparing an aramid lithium battery separator comprises the following steps:

[0073] S1: 5 g of para-aramid fiber (diameter of para-aramid nanofiber is 12 nm and length is 5 μm), 500 mL of DMSO, 7.5 g of KOH and 25 mL of deionized water were mixed to prepare a para-aramid nanofiber solution;

[0074] S2: 0.05 g of the modified silica prepared in Preparation Example 1 was added to the para-aramid nanofiber solution, where the mass of the modified silica was 1% of the mass of the para-aramid fiber, and then ultrasonicated and stirred to obtain a dispersion. The modified silica was a PEI-grafted phosphorus-containing metal organic framework@SiO2;

[0075] S3: The dispersion is coated on the surface of the polyolefin separator with a coating thickness of 4 μm. The coated separator is treated in an aqueous solution for 3 hours and then dried at 100° C. for 1 hour to obtain an aramid lithium battery separator.

[0076] Example 3

[0077] A method for preparing an aramid lithium battery separator comprises the following steps:

[0078] S1: 5 g of para-aramid fiber (diameter of para-aramid nanofiber is 12 nm and length is 5 μm), 500 mL of DMSO, 7.5 g of KOH and 25 mL of deionized water were mixed to prepare a para-aramid nanofiber solution;

[0079] S2: 0.1 g of the modified silica prepared in Preparation Example 2 was added to the para-aramid nanofiber solution, where the mass of the modified silica was 2% of the mass of the para-aramid fiber, and then ultrasonicated and stirred to obtain a dispersion. The modified silica was a PEI-grafted phosphorus-containing metal organic framework@SiO2;

[0080] S3: The dispersion is coated on the surface of the polyolefin separator with a coating thickness of 4 μm. The coated separator is treated in an aqueous solution for 4 hours and then dried at 100° C. for 2 hours to obtain an aramid lithium battery separator.

[0081] Example 4

[0082] A method for preparing an aramid lithium battery separator comprises the following steps:

[0083] S1: 5 g of para-aramid fiber (diameter of para-aramid nanofiber is 12 nm and length is 5 μm), 500 mL of DMSO, 7.5 g of KOH and 25 mL of deionized water were mixed to prepare a para-aramid nanofiber solution;

[0084] S2: 0.125 g of the modified silica prepared in Preparation Example 3 was added to the para-aramid nanofiber solution, where the mass of the modified silica was 2.5% of the mass of the para-aramid fiber, and then ultrasonicated and stirred to obtain a dispersion. The modified silica was a PEI-grafted phosphorus-containing metal organic framework@SiO2;

[0085] S3: The dispersion is coated on the surface of the polyolefin separator with a coating thickness of 4 μm. The coated separator is treated in an aqueous solution for 4 hours and then dried at 100° C. for 2 hours to obtain an aramid lithium battery separator.

[0086] Example 5

[0087] A method for preparing an aramid lithium battery separator comprises the following steps:

[0088] S1: 5 g of para-aramid fiber (diameter of para-aramid nanofiber is 12 nm and length is 5 μm), 500 mL of DMSO, 7.5 g of KOH, and 25 mL of deionized water were mixed to prepare a para-aramid nanofiber solution;

[0089] S2: 0.15 g of the modified silica prepared in Preparation Example 3 was added to the para-aramid nanofiber solution, where the mass of the modified silica was 3% of the mass of the para-aramid fiber, and then ultrasonicated and stirred to obtain a dispersion. The modified silica was a PEI-grafted phosphorus-containing metal organic framework@SiO2;

[0090] S3: The dispersion is coated on the surface of the polyolefin separator with a coating thickness of 4 μm. The coated separator is treated in an aqueous solution for 4 hours and then dried at 100° C. for 2 hours to obtain an aramid lithium battery separator.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that the modified silicon dioxide in Example 1 is replaced by the product in Control Example 1, and the remaining raw materials and steps are the same as in Example 1.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that the modified silicon dioxide in Example 1 is replaced by the product in Control Example 2, and the remaining raw materials and steps are the same as in Example 1.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that the modified silicon dioxide in Example 1 is replaced by the product in Control Example 3, and the remaining raw materials and steps are the same as in Example 1.

[0097] Comparative Example 4

[0098] The difference between this comparative example and Example 1 is that the modified silicon dioxide in Example 1 is replaced by the product in Control Example 4, and the remaining raw materials and steps are the same as in Example 1.

[0099] The performance tests were conducted on the diaphragms prepared in Examples 1 to 5 and Comparative Examples 1 to 4. The test items are as follows, and the results are shown in Table 1:

[0100] 1. Flame retardant performance: Test the limiting oxygen index in accordance with the GBT / 2406.3-2022 test standard.

[0101] 2. Ionic conductivity: The diaphragm was clamped between two stainless steel electrodes and electrochemical impedance spectroscopy was performed using an electrochemical workstation. The measurement frequency range was 0.1 Hz-0.1 MHz and the amplitude was 10 mV. The ionic conductivity σ was calculated according to the formula σ = d / (Rb*S), where d is the diaphragm thickness, S is the cross-sectional area, and Rb is the resistance obtained at the high-frequency intercept on the real axis of the Nyquist plot.

[0102] 3. Mechanical Properties: The lithium-ion battery separators obtained in each example and the comparative example were cut into strips of 5 mm × 40 mm, and the tensile strength was tested using a universal tester.

[0103] Table 1

[0104]

[0105] It can be seen from Table 1 that the comprehensive performance of the diaphragms prepared in Examples 1 to 5 is better than that in Comparative Examples 1 to 4.

[0106] Compared with Example 1, the limiting oxygen index and ionic conductivity of Comparative Example 1 are significantly reduced, indicating that the phosphorus element has flame retardant properties, and the phosphorus-containing metal organic framework contains P=O, which can form bonds with lithium ions to form ion transmission channels, reduce the resistance to lithium ion migration, and improve the ionic conductivity of the diaphragm.

[0107] Compared with Example 1, the comprehensive performance of Comparative Example 2 is reduced, indicating that polyethyleneimine contains a large amount of nitrogen elements and has flame retardant properties, and polyethyleneimine contains amino groups, which can form bonds with lithium ions to form ion transmission channels, reduce lithium ion migration resistance, and improve the ion conductivity of the diaphragm. The amino groups of polyethyleneimine (PEI) can react with the amide groups of aramid fibers to form covalent bonds or hydrogen bonds, improve the interfacial compatibility between the phosphorus-containing metal organic framework @SiO2 and the organic aramid, improve the mechanical properties of the diaphragm, and are beneficial to the phosphorus-containing metal organic framework @SiO2 to exert its flame retardant properties and improve the comprehensive performance of the diaphragm.

[0108] The performance of Comparative Example 4 is the worst, indicating that the porous network structure of the phosphorus-containing metal organic framework has a nanoscale size. After in situ growth, a "rigid spacer layer" is formed on the SiO2 surface. When the particles approach each other, the steric hindrance of the MOF skeleton prevents direct contact with SiO2, just like a "molecular-level gasket" that stretches the distance between particles, thereby improving the dispersion of silica and thus improving the overall performance of the diaphragm.

[0109] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A method for preparing an aramid lithium battery separator, characterized in that: The following steps are involved: S1: para-aramid fiber, DMSO, KOH and deionized water are mixed and stirred to prepare a para-aramid nanofiber solution; S2: adding modified silica to the para-aramid nanofiber solution, followed by ultrasonication and stirring to obtain a dispersion, wherein the modified silica is PEI-grafted phosphorus-containing metal organic framework@SiO2; S3: The dispersion is coated on the surface of the polyolefin separator, and the coated separator is treated in an aqueous solution for 3-4 hours, and then dried to obtain an aramid lithium battery separator.

2. The method for preparing an aramid lithium battery separator according to claim 1, characterized in that: In step S1, the usage ratio of para-aramid fiber, DMSO, KOH, and deionized water is 5 g:500 mL:7.5 g:10-25 mL.

3. The method for preparing an aramid lithium battery separator according to claim 1, characterized in that: In step S2, the mass of the modified silica is 0.5%-3% of the mass of the para-aramid fiber.

4. The method for preparing an aramid lithium battery separator according to claim 1, characterized in that: In step S1, the diameter of the para-aramid nanofiber is 8-15 nm and the length is 3-10 μm; In step S3, the coating thickness is 3-6 μm; the drying temperature is 100° C., and the drying time is 1-2 hours.

5. The method for preparing an aramid lithium battery separator according to claim 1, characterized in that: In step S2, the preparation method of modified silicon dioxide is: A1: Add glutaric anhydride, APTES, and DMF, stir at 30°C for 3-5 hours, then add the silica mixture, continue stirring for 6-8 hours, collect the reaction product, wash, and dry to obtain carboxylated-SiO2; A2: Mix the metal salt, DMF, and carboxylated-SiO2 and stir for 1-2 hours. Then, add 2-aminoterephthalic acid, tris(4-carboxyphenyl)phosphine, and formic acid to the reaction solution. Continue stirring for 30-40 minutes, react at 120°C for 24 hours, cool to room temperature, wash, and dry to obtain a phosphorus-containing metal organic framework@SiO2. A3: Add the phosphorus-containing metal organic framework @SiO2 and maleic anhydride to DMF, stir and react at room temperature for 12-24 hours to obtain a pretreated product, add the pretreated product and polyethyleneimine to a phosphate buffer solution with a pH value of 7-8, stir and react at 40-50°C for 12-24 hours, then centrifuge and dry to obtain modified silica.

6. The method for preparing an aramid lithium battery separator according to claim 5, characterized in that: In step A1, the ratio of glutaric anhydride, APTES, DMF, and silica mixture is 1.7 g:3.6 mL:100-120 mL:100 mL; and the ratio of silica, DMF, and deionized water in the silica mixture is 3 g:100 mL:8-10 mL.

7. The method for preparing an aramid lithium battery separator according to claim 5, characterized in that: In step A2, the usage ratio of metal salt, DMF, carboxylated-SiO2, 2-aminoterephthalic acid, bis(4-carboxyphenyl)phenylphosphine oxide, and formic acid is 0.5-0.6 g:80-100 mL:1 g:0.18-0.2 g:0.4 g:80 mL.

8. The method for preparing an aramid lithium battery separator according to claim 5, characterized in that: In step A3, the usage ratio of phosphorus-containing metal organic framework@SiO2, maleic anhydride, DMF, polyethyleneimine, and phosphate buffer solution is 5 g:2 g:100 mL:1-5 g:50-70 mL.

9. The method for preparing an aramid lithium battery separator according to claim 5, characterized in that: In step A2, the metal salt is one or more of ferric nitrate, zinc nitrate, and molybdenum nitrate.

10. An aramid lithium battery separator, characterized in that: The aramid lithium battery separator is prepared by the preparation method of any one of claims 1 to 9.

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