A lithium ion battery separator and a method of making the same

Abstract

The application discloses a kind of lithium ion battery separators and preparation methods thereof, it is related to battery separator technical field.The application is prepared when lithium ion battery separator, with dianhydride DOPO, 4,4'-diamino diphenyl ether, 2-vinyl-4,6-diamino-1,3,5-triazine is reacted, and polyamide acid microspheres are prepared by electrostatic spraying;Polyethylene is sequentially reacted with acrylamide, propenyl-1,3-sulfonic acid lactone, and modified polyethylene is prepared;With mercaptopropyl trimethoxysilane, hydroxylated boron nitride is reacted, and modified boron nitride is prepared;With polyvinylpyrrolidone, modified polyethylene, polyamide acid microspheres, modified boron nitride is mixed, and film is hot-pressed, and lithium ion battery separator is prepared.The lithium ion battery separator prepared by the application has excellent ion conductivity, flame retardancy and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a lithium-ion battery separator and its preparation method. Background Technology

[0002] With the global energy crisis and environmental pollution becoming increasingly severe, the development of efficient and clean energy technologies has become a top priority. Against this backdrop, lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have become a core power source for electric vehicles, consumer electronics, and energy storage systems. As a key component of the battery, the separator, although not involved in the electrochemical reaction, plays a crucial role in isolating the positive and negative electrodes to prevent short circuits and providing a pathway for lithium-ion transport.

[0003] While commercially available polyolefin separators offer advantages such as low cost and good chemical stability, their poor electrolyte wettability and flammability pose safety hazards. The frequent occurrence of battery thermal runaway accidents in recent years further underscores the urgency of improving separator performance. Especially with the rapid popularization of new energy vehicles and the continuous expansion of emerging application areas such as energy storage power stations and electric aircraft, developing novel separator materials that combine high safety (flame retardancy) and excellent electrochemical performance (ionic conductivity) is of great significance.

[0004] To address this need and overcome the key shortcomings of traditional separators, thereby promoting the development of clean energy applications, this study innovatively employs modified polyethylene (PVDF) material to successfully prepare a novel battery separator with excellent flame retardant properties, ion conduction efficiency, and mechanical strength. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium-ion battery separator and its preparation method to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A lithium-ion battery separator, characterized in that the lithium-ion battery separator is prepared by reacting dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine, followed by electrostatic spraying to obtain polyamic acid microspheres; reacting aminated polyethylene and propylene-1,3-sulfonyl lactone to obtain modified polyethylene; modifying hydroxylated boron nitride with mercaptopropyltrimethoxysilane to obtain modified boron nitride; and mixing polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, followed by hot pressing to form a film, thereby obtaining the lithium-ion battery separator;

[0008] The dianhydride DOPO is prepared by reacting 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide with trimellitic anhydride chloride.

[0009] The amination polyethylene is prepared by reacting polyethylene initiated by benzoyl peroxide with acrylamine.

[0010] The hydroxylated boron nitride is prepared by high-temperature calcination of nano-hexagonal boron nitride.

[0011] A method for preparing a lithium-ion battery separator, characterized in that the method comprises the following preparation steps:

[0012] (1) Dianidated DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine were mixed in a molar ratio of 1:(0.67~0.69):(0.27~0.29), and N,N-dimethylformamide was added at 10~12 times the mass of dianidated DOPO. The mixture was stirred at 200~300r / min for 6~8h at 0~2℃, and then aged at 50~60℃ for 48~50h to obtain a polyamic acid solution. The polyamic acid solution was then electrostatically sprayed in an electrostatic sprayer to obtain polyamic acid microspheres.

[0013] (2) Mix amination polyethylene and acetonitrile at a mass ratio of 1:(8-10), ultrasonically disperse for 30-40 min, add 2.0-2.2 times the mass of polyethylene of propylene-1,3-sulfonyl lactone, stir at 300-400 r / min for 10-12 h under nitrogen protection at 60-70 °C, cool to room temperature, filter, wash with acetone 3-5 times, and dry at 50-60 °C for 8-10 h under vacuum to obtain modified polyethylene;

[0014] (3) Mix mercaptopropyltrimethoxysilane and deionized water at a mass ratio of 1:(9-10), adjust the pH to 3.6-4.0 with formic acid, stir at 300-400 r / min for 10-12 min at 20-30℃, add hydroxylated boron nitride at 1-1.2 times the mass of mercaptopropyltrimethoxysilane, disperse ultrasonically for 50-60 min, stir at 300-400 r / min for 3-5 h at 80-90℃, filter, wash with deionized water 3-5 times, freeze dry at -30 to -20℃ under vacuum for 48-50 h to obtain modified boron nitride;

[0015] (4) Weigh 100 parts of modified polyethylene, 7-8 parts of polyamic acid microspheres, 3-5 parts of modified boron nitride, 0.5-0.9 parts of azobisisobutyronitrile, and 15-19 parts of polyvinylpyrrolidone by mass fraction. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride. Stir at 50-60℃ and 300-400r / min for 5-7h. Add azobisisobutyronitrile and mix evenly. Place in a hot press and hot press to form an initial separator of 100μm. Take it out and put it in deionized water at 20-24℃ for 20-30min. Dry it under vacuum at 55-65℃ for 8-9h to obtain a lithium-ion battery separator.

[0016] As an optimization, the preparation method of dianhydride DOPO in step (1) is as follows: 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride are added to toluene at a molar ratio of 1:3 to 12-14 times the mass of trimellitic anhydride chloride, and pyridine is added at a molar ratio of 0.1-0.16 times the mass of trimellitic anhydride chloride. The mixture is stirred at 300-400 r / min for 1-2 h at 10-30 °C, heated to 106-110 °C, and refluxed under a nitrogen atmosphere for 6-8 h. After cooling to room temperature, the mixture is filtered, washed 3-5 times with chloroform and ethyl acetate respectively, and dried at 70-80 °C for 8-10 h under vacuum to obtain dianhydride DOPO; the reaction equation is:

[0017]

[0018] As an optimization, the process parameters for electrostatic spraying in step (1) are: positive pressure 20-22kV, negative pressure 3-5kV, and receiving distance from the base 16-18cm.

[0019] As an optimization, the preparation method of the amination polyethylene in step (2) is as follows: Polyethylene and N,N-dimethylformamide are mixed at a mass ratio of 1:(14-16), stirred at 45-55℃ and 100-200 r / min for 20-40 min, and heated to 65-75℃ under nitrogen protection. Benzoyl peroxide is added at 0.04-0.06 times the mass of polyethylene, and stirring is continued for 20-40 min. Acrylamine is added at 0.2-0.4 times the mass of polyethylene, and the reaction is continued for 7-9 h. After cooling to room temperature, anhydrous ethanol at 24-26 times the mass of polyethylene is added, and the mixture is allowed to stand for 5-7 h. After filtration, the mixture is washed 3-5 times with deionized water and dried at 50-60℃ for 8-10 h under vacuum to obtain the amination polyethylene. The type of the polyethylene is HSV900.

[0020] As an optimization, the preparation method of hydroxylated boron nitride in step (3) is as follows: nano-hexagonal boron nitride is placed in the furnace of a high-temperature resistance furnace and calcined at high temperature. The temperature is increased from room temperature to 890-900℃ at a heating rate of 10℃ / min, and calcined at a constant temperature for 30-40min. After cooling to room temperature, it is ultrasonically crushed for 18-22min to obtain hydroxylated boron nitride. The nano-hexagonal boron nitride is of model number 1489-01-5.

[0021] As an optimization, the polyvinylpyrrolidone in step (4) is model PVP-K30.

[0022] As an optimization, the hot pressing process parameters in step (4) are: hot pressing temperature 130~150℃, hot pressing pressure 1~2MPa, and hot pressing time 30~40s.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0024] In preparing a lithium-ion battery separator, this invention modifies 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide with trimellitic anhydride chloride. Then, dianhydride-modified DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine are reacted, followed by electrostatic spraying to obtain polyamic acid microspheres. Modified polyethylene is prepared by reacting polyethylene initiated by benzoyl peroxide with acrylamine and propylene-1,3-sulfonyl lactone sequentially. Hydroxylated boron nitride is then calcined at high temperature. Modified boron nitride is obtained by modifying the hydroxylated boron nitride with mercaptopropyltrimethoxysilane. Finally, polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride are mixed and hot-pressed into a film to obtain the lithium-ion battery separator.

[0025] First, 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide was modified with trimellitic anhydride chloride. Then, dianhydride-modified DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine were reacted. Polyamic acid microspheres were prepared by electrostatic spraying. DOPO, triazine, and carbon-carbon double bonds were introduced onto the polyamic acid microspheres, and carboxyl groups were generated. The resulting polyamic acid microspheres exhibited excellent electrolyte wettability and porosity. The carboxyl structure has strong negative charge, which accelerates the flow of lithium ions and improves the suppression effect of lithium dendrites in the lithium-ion battery separator, thereby improving the ion conductivity of the lithium-ion battery separator. The introduced DOPO has good flame retardant properties, and the phosphorus element can capture free radicals to promote the formation of carbon layers, thereby isolating heat and oxygen and improving the flame retardant effect of the lithium-ion battery separator. The introduced triazine structure can generate non-flammable nitrogen-containing gas, which can absorb heat, dilute oxygen concentration, and reduce combustion temperature, further improving the flame retardant performance of the lithium-ion battery separator.

[0026] Secondly, benzoyl peroxide-initiated polyethylene was reacted with acrylamine to introduce amino groups onto the polyethylene. Amination of polyethylene was then reacted with propylene-1,3-sulfonyl lactone to prepare modified polyethylene, introducing carbon-carbon double bonds and generating sulfonic acid groups. These sulfonic acid groups are highly polar and interact with ions in the electrolyte, improving the fluidity of lithium ions and thus enhancing the ion conductivity of the lithium-ion battery separator. High-temperature calcination of nano-hexagonal boron nitride increased the hydroxyl groups on the boron nitride surface, making it easier to graft mercaptopropyltrimethoxysilane onto the boron nitride. Modification of hydroxylated boron nitride with mercaptopropyltrimethoxysilane introduced a large number of mercapto groups, improving the compatibility between boron nitride and polyethylene, ensuring uniform dispersion of boron nitride in the membrane material, and preventing agglomeration. Addition reactions occurred between the carbon-carbon double bonds on the modified polyethylene, the carbon-carbon double bonds on the polyamic acid microspheres, and the mercapto groups on the modified boron nitride, forming a cross-linked network that inhibited relative movement between molecular chains and improved the mechanical properties of the lithium-ion battery separator.

[0027] Finally, using azobisisobutyronitrile as a catalyst, polyvinylpyrrolidone as a pore-forming agent, and N,N-dimethylformamide as a solvent, modified polyethylene, polyamic acid microspheres, modified boron nitride, azobisisobutyronitrile, and polyvinylpyrrolidone were mixed and hot-pressed to form a film, thus obtaining a lithium-ion battery separator. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1:

[0030] A method for preparing a lithium-ion battery separator, the method comprising the following preparation steps:

[0031] (1) 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride were added to toluene at a molar ratio of 1:3 to 12 times the mass of trimellitic anhydride chloride, and pyridine at a mass of 0.1 times the mass of trimellitic anhydride chloride was added. The mixture was stirred at 300 r / min for 2 h at 10 °C, then heated to 106 °C and refluxed under a nitrogen atmosphere for 8 h. After cooling to room temperature, the mixture was filtered, washed three times with chloroform and ethyl acetate respectively, and dried at 70 °C for 10 h under vacuum to obtain dianhydride DOPO; the dianhydride... DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine were mixed in a molar ratio of 1:0.67:0.27, and N,N-dimethylformamide with a mass of 10 times that of dianhydride-modified DOPO was added. The mixture was stirred at 200 r / min for 6 h at 0 °C, and then aged at 50 °C for 50 h to obtain a polyamic acid solution. The polyamic acid solution was then subjected to electrostatic spraying in an electrostatic sprayer with the process parameters set as positive pressure 20 kV, negative pressure 3 kV, and receiving distance from the substrate 16 cm to obtain polyamic acid microspheres.

[0032] (2) Polyethylene and N,N-dimethylformamide were mixed at a mass ratio of 1:14 and stirred at 100 r / min for 40 min at 45 °C. Under nitrogen protection, the temperature was raised to 65 °C, and 0.04 times the mass of polyethylene was added with benzoyl peroxide. The mixture was stirred for another 40 min, and 0.2 times the mass of polyethylene was added with acrylamine. The mixture was reacted for another 9 h, cooled to room temperature, and 24 times the mass of polyethylene was added with anhydrous ethanol. The mixture was allowed to stand for 5 h, filtered, washed three times with deionized water, and dried at 50 °C for 10 h under vacuum to obtain amination polyethylene. Amination polyethylene and acetonitrile were mixed at a mass ratio of 1:8 and ultrasonically dispersed for 30 min. Acrylonitrile-1,3-sulfonyl lactone was added at 2.0 times the mass of polyethylene. Under nitrogen protection, the mixture was stirred at 300 r / min for 12 h at 60 °C, cooled to room temperature, filtered, washed three times with acetone, and dried at 50 °C for 10 h under vacuum to obtain modified polyethylene.

[0033] (3) Nano-hexagonal boron nitride was placed in the furnace of a high-temperature resistance furnace and calcined at high temperature. The temperature was increased from room temperature to 890℃ at a heating rate of 10℃ / min, and calcined at a constant temperature for 40 min. After cooling to room temperature, it was ultrasonically crushed for 18 min to obtain hydroxylated boron nitride. Mercaptopropyltrimethoxysilane and deionized water were mixed at a mass ratio of 1:9. The pH was adjusted to 3.6 with formic acid. The mixture was stirred at 300 r / min for 12 min at 20℃. Hydroxylated boron nitride with a mass of 1 times that of mercaptopropyltrimethoxysilane was added. The mixture was ultrasonically dispersed for 50 min. The mixture was stirred at 300 r / min for 5 h at 80℃. The mixture was filtered, washed three times with deionized water, and freeze-dried at -30℃ for 48 h under vacuum to obtain modified boron nitride.

[0034] (4) Weigh 100 parts of modified polyethylene, 7 parts of polyamic acid microspheres, 3 parts of modified boron nitride, 0.5 parts of azobisisobutyronitrile, and 15 parts of polyvinylpyrrolidone by mass fraction. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride. Stir at 50°C and 300 r / min for 7 h. Add azobisisobutyronitrile and mix evenly. Place in a hot press and hot press to form an initial separator of 100 μm. Set the hot pressing process parameters as follows: hot pressing temperature 130°C, hot pressing pressure 1 MPa, and hot pressing time 40 s. Take out and place in deionized water at 20°C for 30 min. Dry at 55°C for 9 h under vacuum to obtain the lithium-ion battery separator.

[0035] Example 2:

[0036] A method for preparing a lithium-ion battery separator, the method comprising the following preparation steps:

[0037] (1) 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride were added to toluene at a molar ratio of 1:3 to 13 times the mass of trimellitic anhydride chloride, and pyridine was added at a molar ratio of 0.13 times the mass of trimellitic anhydride chloride. The mixture was stirred at 350 r / min for 1.5 h at 30 °C, heated to 108 °C, and refluxed under a nitrogen atmosphere for 7 h. After cooling to room temperature, the mixture was filtered, washed four times with chloroform and ethyl acetate respectively, and dried at 75 °C for 9 h under vacuum to obtain dianhydride-modified DOPO. DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine were mixed in a molar ratio of 1:0.68:0.28, and N,N-dimethylformamide (11 times the mass of DOPO) was added. The mixture was stirred at 250 r / min for 7 h at 1 °C, and then aged at 55 °C for 49 h to obtain a polyamic acid solution. The polyamic acid solution was then subjected to electrostatic spraying in an electrostatic sprayer with the process parameters set as positive pressure 21 kV, negative pressure 4 kV, and receiving distance from the substrate 17 cm to obtain polyamic acid microspheres.

[0038] (2) Polyethylene and N,N-dimethylformamide were mixed at a mass ratio of 1:15 and stirred at 50°C and 150 r / min for 30 min. Under nitrogen protection, the temperature was raised to 70°C, and 0.05 times the mass of polyethylene was added with benzoyl peroxide. The mixture was stirred for another 30 min, and 0.3 times the mass of polyethylene was added with acrylamine. The mixture was reacted for another 8 h, cooled to room temperature, and 25 times the mass of polyethylene was added with anhydrous ethanol. The mixture was allowed to stand for 6 h, filtered, washed 4 times with deionized water, and dried at 55°C for 9 h under vacuum to obtain amination polyethylene. Amination polyethylene and acetonitrile were mixed at a mass ratio of 1:9 and ultrasonically dispersed for 35 min. 2.1 times the mass of polyethylene was added with propylene-1,3-sulfonyl lactone. Under nitrogen protection, the mixture was stirred at 65°C and 350 r / min for 11 h, cooled to room temperature, filtered, washed 4 times with acetone, and dried at 55°C for 9 h under vacuum to obtain modified polyethylene.

[0039] (3) Nano-hexagonal boron nitride was placed in the furnace of a high-temperature resistance furnace and calcined at high temperature. The temperature was increased from room temperature to 895℃ at a heating rate of 10℃ / min, and calcined at a constant temperature for 35min. After cooling to room temperature, it was ultrasonically crushed for 20min to obtain hydroxylated boron nitride. Mercaptopropyltrimethoxysilane and deionized water were mixed at a mass ratio of 1:9.5. The pH was adjusted to 3.8 with formic acid. The mixture was stirred at 350r / min for 11min at 25℃. 1.1 times the mass of mercaptopropyltrimethoxysilane hydroxylated boron nitride was added. The mixture was ultrasonically dispersed for 55min. The mixture was stirred at 350r / min for 4h at 5℃. The mixture was filtered, washed 4 times with deionized water, and freeze-dried at -25℃ for 49h under vacuum to obtain modified boron nitride.

[0040] (4) Weigh 100 parts of modified polyethylene, 7.5 parts of polyamic acid microspheres, 4 parts of modified boron nitride, 0.7 parts of azobisisobutyronitrile, and 17 parts of polyvinylpyrrolidone by mass fraction. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride. Stir at 55℃ and 350r / min for 6h. Add azobisisobutyronitrile and mix evenly. Place in a hot press and hot press to form an initial separator of 100μm. Set the hot pressing process parameters as follows: hot pressing temperature 140℃, hot pressing pressure 1.5MPa, and hot pressing time 35s. Take out and place in deionized water at 22℃ for 25min. Dry under vacuum at 60℃ for 8.5h to obtain the lithium-ion battery separator.

[0041] Example 3:

[0042] A method for preparing a lithium-ion battery separator, the method comprising the following preparation steps:

[0043] (1) 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride were added to toluene at a molar ratio of 1:3 to 14 times the mass of trimellitic anhydride chloride, and pyridine was added at a molar ratio of 0.16 times the mass of trimellitic anhydride chloride. The mixture was stirred at 400 r / min for 1 h at 30 °C, then heated to 110 °C and refluxed under a nitrogen atmosphere for 6 h. After cooling to room temperature, the mixture was filtered, washed five times each with chloroform and ethyl acetate, and dried at 80 °C for 8 h under vacuum to obtain dianhydride DOPO. DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine were mixed in a molar ratio of 1:0.69:0.29. N,N-dimethylformamide, in an amount 12 times the mass of dianhydride-modified DOPO, was added. The mixture was stirred at 200 r / min for 8 h at 2 °C, then aged at 60 °C for 48 h to obtain a polyamic acid solution. The polyamic acid solution was then subjected to electrostatic spraying in an electrostatic sprayer with the process parameters set as follows: positive pressure 22 kV, negative pressure 5 kV, and a receiving distance of 18 cm from the substrate, to obtain polyamic acid microspheres.

[0044] (2) Polyethylene and N,N-dimethylformamide were mixed at a mass ratio of 1:16 and stirred at 200 r / min for 20 min at 55 °C. Under nitrogen protection, the temperature was raised to 75 °C, and 0.06 times the mass of polyethylene was added with benzoyl peroxide. The mixture was stirred for another 20 min, and 0.4 times the mass of polyethylene was added with acrylamine. The mixture was reacted for another 7 h, cooled to room temperature, and 26 times the mass of polyethylene was added with anhydrous ethanol. The mixture was allowed to stand for 7 h, filtered, washed 5 times with deionized water, and dried at 60 °C for 8 h under vacuum to obtain amination polyethylene. Amination polyethylene and acetonitrile were mixed at a mass ratio of 1:10 and ultrasonically dispersed for 40 min. Acrylonitrile-1,3-sulfonyl lactone was added at 2.2 times the mass of polyethylene. Under nitrogen protection, the mixture was stirred at 400 r / min for 10 h at 70 °C, cooled to room temperature, filtered, washed 5 times with acetone, and dried at 60 °C for 8 h under vacuum to obtain modified polyethylene.

[0045] (3) Nano-hexagonal boron nitride was placed in the furnace of a high-temperature resistance furnace and calcined at high temperature. The temperature was increased from room temperature to 900℃ at a heating rate of 10℃ / min, and calcined at a constant temperature for 30 min. After cooling to room temperature, it was ultrasonically crushed for 22 min to obtain hydroxylated boron nitride. Mercaptopropyltrimethoxysilane and deionized water were mixed at a mass ratio of 1:10. The pH was adjusted to 4.0 with formic acid. The mixture was stirred at 400 r / min for 10 min at 30℃. 1.2 times the mass of mercaptopropyltrimethoxysilane hydroxylated boron nitride was added. The mixture was ultrasonically dispersed for 60 min. The mixture was stirred at 400 r / min for 3 h at 90℃. The mixture was filtered, washed 5 times with deionized water, and freeze-dried at -20℃ for 50 h under vacuum to obtain modified boron nitride.

[0046] (4) Weigh 100 parts of modified polyethylene, 8 parts of polyamic acid microspheres, 5 parts of modified boron nitride, 0.9 parts of azobisisobutyronitrile, and 19 parts of polyvinylpyrrolidone by mass fraction. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride. Stir at 60°C and 400 r / min for 5 h. Add azobisisobutyronitrile and mix evenly. Place in a hot press and hot press to form an initial separator of 100 μm. Set the hot pressing process parameters as follows: hot pressing temperature 150°C, hot pressing pressure 2 MPa, and hot pressing time 30 s. Take out and place in deionized water at 24°C for 20 min. Take out and dry at 65°C for 8 h under vacuum to obtain the lithium-ion battery separator.

[0047] Comparative Example 1:

[0048] The difference between the preparation method of the lithium-ion battery separator in Comparative Example 1 and Example 2 lies only in step (1). Step (1) is modified as follows: pyromellitic anhydride, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine are mixed in a molar ratio of 1:0.68:0.28, and N,N-dimethylformamide (11 times the mass of pyromellitic anhydride) is added. The mixture is stirred at 250 r / min for 7 h at 1 °C, then aged at 55 °C for 49 h to obtain a polyamic acid solution. The polyamic acid solution is then electrostatically sprayed in an electrostatic sprayer with the process parameters set as positive pressure 21 kV, negative pressure 4 kV, and a receiving distance of 17 cm from the substrate to obtain polyamic acid microspheres. The remaining steps are the same as in Example 2.

[0049] Comparative Example 2:

[0050] The preparation method of the lithium-ion battery separator in Comparative Example 2 differs from that in Example 2 only in step (1). Step (1) is modified as follows: 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride are added to toluene at a molar ratio of 1:3 to 13 times the mass of trimellitic anhydride chloride, and pyridine is added at a molar ratio of 0.13 times the mass of trimellitic anhydride chloride. The mixture is stirred at 350 r / min for 1.5 h at 30 °C, heated to 108 °C, and refluxed under a nitrogen atmosphere for 7 h. After cooling to room temperature, the mixture is filtered and then treated with chloroform and ethyl acetate. The esters were washed four times and dried at 75°C for 9 hours under vacuum to obtain dianhydride-modified DOPO. The dianhydride-modified DOPO and 4,4'-diaminodiphenyl ether were mixed at a molar ratio of 1:0.96, and 11 times the mass of N,N-dimethylformamide was added. The mixture was stirred at 250 r / min for 7 hours at 1°C, then aged at 55°C for 49 hours to obtain a polyamic acid solution. The polyamic acid solution was then subjected to electrostatic spraying in an electrostatic sprayer with the process parameters set as follows: positive pressure 21 kV, negative pressure 4 kV, and a receiving distance of 17 cm from the substrate, to obtain polyamic acid microspheres. The remaining steps were the same as in Example 2.

[0051] Comparative Example 3:

[0052] The difference between the preparation method of the lithium-ion battery separator in Comparative Example 3 and Example 2 is that step (2) is omitted, and step (4) is modified as follows: 100 parts of polyethylene, 7.5 parts of polyamic acid microspheres, 4 parts of modified boron nitride, 0.7 parts of azobisisobutyronitrile, and 17 parts of polyvinylpyrrolidone are weighed by mass fraction. Polyvinylpyrrolidone, polyethylene, polyamic acid microspheres, and modified boron nitride are mixed and stirred at 55°C and 350 r / min for 6 h. Azobisisobutyronitrile is added and mixed evenly. The mixture is placed in a hot press and hot-pressed into an initial separator of 100 μm. The hot-pressing process parameters are set as follows: hot-pressing temperature 140°C, hot-pressing pressure 1.5 MPa, and hot-pressing time 35 s. The separator is taken out and placed in deionized water at 22°C for 25 min. Under vacuum conditions, it is dried at 60°C for 8.5 h to obtain the lithium-ion battery separator.

[0053] Comparative Example 4:

[0054] The difference between the preparation method of the lithium-ion battery separator in Comparative Example 4 and Example 2 is that step (3) is omitted, and step (4) is modified as follows: 100 parts of modified polyethylene, 7.5 parts of polyamic acid microspheres, 4 parts of nano-hexagonal boron nitride, 0.7 parts of azobisisobutyronitrile, and 17 parts of polyvinylpyrrolidone are weighed by mass fraction. Polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and nano-hexagonal boron nitride are mixed and stirred at 55°C and 350 r / min for 6 h. Azobisisobutyronitrile is added and mixed evenly. The mixture is placed in a hot press and hot-pressed into an initial separator of 100 μm. The hot-pressing process parameters are set as follows: hot-pressing temperature 140°C, hot-pressing pressure 1.5 MPa, and hot-pressing time 35 s. The separator is taken out and placed in deionized water at 22°C for 25 min. It is then dried at 60°C for 8.5 h under vacuum to obtain the lithium-ion battery separator.

[0055] Comparative Example 5:

[0056] The preparation method of the lithium-ion battery separator in Comparative Example 5 differs from that in Example 2 in that step (1) is omitted, and step (4) is modified as follows: 100 parts of modified polyethylene, 4 parts of modified boron nitride, 0.7 parts of azobisisobutyronitrile, and 17 parts of polyvinylpyrrolidone are weighed by mass fraction. Polyvinylpyrrolidone, modified polyethylene, and modified boron nitride are mixed and stirred at 55°C and 350 r / min for 6 h. Azobisisobutyronitrile is added and mixed evenly. The mixture is placed in a hot press and hot-pressed into an initial separator of 100 μm. The hot-pressing process parameters are set as follows: hot-pressing temperature 140°C, hot-pressing pressure 1.5 MPa, and hot-pressing time 35 s. The separator is then removed, placed in deionized water at 22°C for 25 min, and dried at 60°C for 8.5 h under vacuum to obtain the lithium-ion battery separator.

[0057] Test Example 1

[0058] Ion conductivity test

[0059] Test Method: Assemble a symmetrical battery using a stainless steel sheet / separator / stainless steel sheet. The assembled battery sample was left to stand for 5 hours before testing. The electrochemical impedance spectroscopy (EIS) of the battery sample was measured using an electrochemical workstation. This EIS is related to the solid-state diffusion process of lithium ions within the separator. The intersection of the diagonal line and the horizontal axis in the obtained AC impedance spectrum represents the bulk resistance of the lithium-ion battery separator. The test frequency was 1×10⁻⁶. 6 Hz-1Hz, voltage 10mV. Ionic conductivity was calculated using the formula: Ionic conductivity = diaphragm thickness / (bulk resistance × effective contact area) × 100%. Results are shown in Table 1.

[0060] Table 1

[0061]

[0062] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-5 in Table 1 reveals that the lithium-ion battery separator prepared by this invention has good ion conductivity.

[0063] By comparison, the ionic conductivity of Examples 1-3 is greater than that of Comparative Example 3, indicating that the reaction of aminated polyethylene and propylene-1,3-sulfonyl lactone to prepare modified polyethylene introduces carbon-carbon double bonds into the polyethylene and generates sulfonic acid groups. The sulfonic acid groups have strong polarity and interact with ions in the electrolyte, improving the fluidity of lithium ions and thus improving the ionic conductivity of the lithium-ion battery separator.

[0064] By comparison, the ionic conductivity of Examples 1-3 is greater than that of Comparative Example 5, indicating that the reaction of dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine with electrostatic spraying produces polyamic acid microspheres. Carboxyl groups are generated on the polyamic acid microspheres. The carboxyl group structure has strong negative charge, which accelerates the flow of lithium ions and improves the suppression effect of lithium dendrites on the lithium-ion battery separator, thereby improving the ionic conductivity of the lithium-ion battery separator.

[0065] Test Example 2

[0066] Flame retardant performance testing

[0067] Test method: Standard samples were prepared according to GB / T2406-93 for the examples and comparative examples, and the limiting oxygen index of the standard samples was tested. The results are shown in Table 2.

[0068] Table 2

[0069] Limiting oxygen index (%) Limiting oxygen index (%) Example 1 30.66 Comparative Example 1 25.52 Example 2 30.17 Comparative Example 2 20.61 Example 3 30.85 Comparative Example 3 30.27 Comparative Example 4 30.38 Comparative Example 5 18.84

[0070] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-5 in Table 2 reveals that the lithium-ion battery separator prepared by this invention has good flame-retardant properties.

[0071] By comparison, the limiting oxygen index of Examples 1-3 is greater than that of Comparative Examples 1 and 5, indicating that the reaction of dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine with electrostatic spraying produces polyamic acid microspheres. DOPO is introduced onto the polyamic acid microspheres. DOPO has good flame retardant properties, and phosphorus can capture free radicals to promote the formation of a carbon layer, thereby isolating heat and oxygen and improving the flame retardant effect of the lithium-ion battery separator.

[0072] By comparison, the limiting oxygen index of Examples 1-3 is greater than that of Comparative Examples 2 and 5, indicating that the reaction of dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine with electrostatic spraying produces polyamic acid microspheres. Triazine is introduced onto the polyamic acid microspheres. The triazine structure can generate non-flammable nitrogen-containing gas, which can absorb heat, dilute oxygen concentration, and reduce combustion temperature, thereby further improving the flame retardant performance of lithium-ion battery separators.

[0073] Test Example 3

[0074] Mechanical property testing

[0075] Test method: GB / T1040.3-2006, tensile strength of the examples and comparative examples was tested using an electronic universal testing machine. The results are shown in Table 3.

[0076] Table 3

[0077] Tensile strength (MPa) Tensile strength (MPa) Example 1 62.34 Comparative Example 1 61.53 Example 2 62.13 Comparative Example 2 47.28 Example 3 61.75 Comparative Example 3 46.81 Comparative Example 4 40.37 Comparative Example 5 48.62

[0078] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-5 in Table 1 reveals that the lithium-ion battery separator prepared by this invention has good mechanical properties.

[0079] By comparison, the tensile strength of Examples 1-3 is greater than that of Comparative Examples 2 and 5, indicating that the reaction of dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine with electrostatic spraying to prepare polyamic acid microspheres introduces carbon-carbon double bonds onto the polyamic acid microspheres. The carbon-carbon double bonds on the polyamic acid microspheres and the thiol groups on the modified boron nitride undergo an addition reaction to form a cross-linked network, which inhibits the relative movement between molecular chains and improves the mechanical properties of the lithium-ion battery separator.

[0080] By comparison, the tensile strength of Examples 1-3 is greater than that of Comparative Example 3, indicating that the reaction of aminated polyethylene and propylene-1,3-sulfonyl lactone to prepare modified polyethylene introduces carbon-carbon double bonds into the polyethylene. The carbon-carbon double bonds on the modified polyethylene and the thiol groups on the modified boron nitride undergo an addition reaction to form a cross-linked network, which inhibits the relative movement between molecular chains and improves the mechanical properties of the lithium-ion battery separator.

[0081] By comparison, the tensile strength of Examples 1-3 is greater than that of Comparative Example 4, indicating that the modified boron nitride prepared by reacting mercaptopropyltrimethoxysilane with hydroxylated boron nitride introduces a large number of thiol groups onto the boron nitride, which improves the compatibility between boron nitride and polyethylene, allowing the boron nitride to be uniformly dispersed in the membrane material and avoiding agglomeration. The carbon-carbon double bonds on the modified polyethylene, the carbon-carbon double bonds on the polyamic acid microspheres, and the thiol groups on the modified boron nitride undergo addition reactions to form a cross-linked network, inhibiting the relative movement between molecular chains and improving the mechanical properties of the lithium-ion battery separator.

[0082] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery separator, characterized by, The lithium ion battery separator is prepared by mixing dianhydride DOPO, 4,4'-diamino diphenyl ether and 2-vinyl-4,6-diamino-1,3,5-triazine in a molar ratio of 1: (0.67-0.69) : (0.27-0.29), adding N,N-dimethylformamide in an amount of 10-12 times the mass of dianhydride DOPO, stirring at 200-300 r / min at 0-2 ℃ for 6-8 h, increasing the temperature to 50-60 ℃ for aging for 48-50 h, preparing a polyamide acid solution, and performing electrostatic spraying on the polyamide acid solution in an electrostatic spraying machine to obtain polyamide acid microspheres; reacting aminated polyethylene and propenyl-1,3-sultone to obtain modified polyethylene; reacting mercaptopropyl trimethoxysilane and hydroxylated boron nitride to obtain modified boron nitride; mixing polyvinylpyrrolidone, modified polyethylene, polyamide acid microspheres and modified boron nitride, and hot-pressing to form a film to obtain the lithium ion battery separator. The molar ratio of the dianhydride DOPO, 4,4'-diamino diphenyl ether and 2-vinyl-4,6-diamino-1,3,5-triazine is 1: (0.67-0.69) : (0.27-0.29). The dianhydride DOPO is prepared by reacting 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phospha-phenanthrene-10-oxide and chlorinated trimellitic anhydride. The aminated polyethylene is prepared by reacting polyethylene initiated by dibenzoyl peroxide and propylene amine. The hydroxylated boron nitride is prepared by high-temperature calcination of nano hexagonal boron nitride.

2. A method of producing a lithium ion battery separator, characterized by, The preparation method of the lithium ion battery separator comprises the following preparation steps: (1) mixing dianhydride DOPO, 4,4'-diamino diphenyl ether and 2-vinyl-4,6-diamino-1,3,5-triazine in a molar ratio of 1: (0.67-0.69) : (0.27-0.29), adding N,N-dimethylformamide in an amount of 10-12 times the mass of dianhydride DOPO, stirring at 200-300 r / min at 0-2 ℃ for 6-8 h, increasing the temperature to 50-60 ℃ for aging for 48-50 h, and preparing a polyamide acid solution; and performing electrostatic spraying on the polyamide acid solution in an electrostatic spraying machine to obtain polyamide acid microspheres; (2) mixing aminated polyethylene and acetonitrile in a mass ratio of 1: (8-10), ultrasonic dispersing for 30-40 min, adding propenyl-1,3-sultone in an amount of 2.0-2.2 times the mass of polyethylene, stirring at 300-400 r / min at 60-70 ℃ for 10-12 h under nitrogen protection, cooling to room temperature, filtering, washing with acetone for 3-5 times, and drying at 50-60 ℃ under vacuum for 8-10 h to obtain modified polyethylene; (3) mixing mercaptopropyl trimethoxysilane and deionized water in a mass ratio of 1: (9-10), adjusting the pH to 3.6-4.0 with formic acid, stirring at 300-400 r / min at 20-30 ℃ for 10-12 min, adding hydroxylated boron nitride in an amount of 1-1.2 times the mass of mercaptopropyl trimethoxysilane, ultrasonic dispersing for 50-60 min, stirring at 300-400 r / min at 80-90 ℃ for 3-5 h, filtering, washing with deionized water for 3-5 times, and freeze-drying at -30--20 ℃ under vacuum for 48-50 h to obtain modified boron nitride; (4) by mass fraction, 100 parts of modified polyethylene, 7-8 parts of polyamide acid microspheres, 3-5 parts of modified boron nitride, 0.5-0.9 parts of azobisisobutyronitrile, and 15-19 parts of polyvinylpyrrolidone are weighed, the polyvinylpyrrolidone, modified polyethylene, polyamide acid microspheres, and modified boron nitride are mixed, stirred at 50-60℃ and 300-400r / min for 5-7h, the azobisisobutyronitrile is added and uniformly mixed, placed in a hot press to form an initial separator of 100μm, taken out, placed in deionized water at 20-24℃ for 20-30min, dried at 55-65℃ under vacuum for 8-9h to obtain a lithium ion battery separator.

3. The method of claim 2, wherein the polymeric material is a polyolefin. The preparation method of the dianhydride DOPO in step (1) is as follows: 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and chlorinated trimellitic anhydride are added to toluene with 12-14 times the mass of chlorinated trimellitic anhydride, and pyridine with 0.1-0.16 times the mass of chlorinated trimellitic anhydride is added, stirred at 300-400r / min at 10-30℃ for 1-2h, heated to 106-110℃, stirred under nitrogen atmosphere at reflux for 6-8h, cooled to room temperature, filtered, washed with chloroform and ethyl acetate for 3-5 times, and dried at 70-80℃ under vacuum for 8-10h to obtain the dianhydride DOPO.

4. The method of claim 2, wherein the polymeric material is a polyolefin. The process parameters of the electrostatic spraying in step (1) are as follows: positive pressure 20-22kV, negative pressure 3-5kV, and receiving distance from the base 16-18cm.

5. The method of claim 2, wherein the polymeric material is a polyolefin. The preparation method of the aminated polyethylene in step (2) is as follows: polyethylene and N,N-dimethylformamide are mixed at a mass ratio of 1:(14-16), stirred at 45-55℃ and 100-200r / min for 20-40min, heated to 65-75℃ under nitrogen protection, 0.04-0.06 times the mass of polyethylene of dibenzoyl peroxide is added, and stirred for 20-40min, 0.2-0.4 times the mass of polyethylene of propylene amine is added, and reacted for 7-9h, cooled to room temperature, 24-26 times the mass of polyethylene of anhydrous ethanol is added, and placed for 5-7h, filtered, washed with deionized water for 3-5 times, and dried at 50-60℃ under vacuum for 8-10h to obtain the aminated polyethylene; the type of the polyethylene is LD608.

6. The method for preparing a lithium-ion battery separator according to claim 2, characterized in that, The preparation method of the hydroxylated boron nitride in step (3) is as follows: the nanometer hexagonal boron nitride is calcined at high temperature in the furnace chamber of a high-temperature resistance furnace, heated from room temperature to 890-900℃ at a heating rate of 10℃ / min, and kept at constant temperature for 30-40min, cooled to room temperature, and ultrasonically broken for 18-22min to obtain the hydroxylated boron nitride.

7. The method for preparing a lithium-ion battery separator according to claim 2, characterized in that, The type of the polyvinylpyrrolidone in step (4) is PVP-K30.

8. The method for preparing a lithium-ion battery separator according to claim 2, characterized in that, The process parameters of the hot pressing in step (4) are as follows: hot pressing temperature 130-150℃, hot pressing pressure 1-2MPa, and hot pressing time 30-40s.

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