Lithium ion battery diaphragm and preparation method thereof

Abstract

The invention discloses a lithium ion battery diaphragm and a preparation method thereof, and relates to the technical field of battery diaphragms. When the lithium ion battery diaphragm is prepared, dianhydridized DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), 4, 4 '-diaminodiphenyl ether and 2-vinyl-4, 6-diamino-1, 3, 5-triazine are subjected to a reaction, and polyamide acid microspheres are prepared through electrostatic spraying; the preparation method comprises the following steps: sequentially reacting polyethylene with allylamine and allyl-1, 3-sultone to prepare modified polyethylene; mercaptopropyltrimethoxysilane and hydroxylated boron nitride are subjected to a reaction, and modified boron nitride is prepared; mixing polyvinylpyrrolidone, the modified polyethylene, the polyamide acid microspheres and the modified boron nitride, and performing hot pressing to form a film, so as to prepare the lithium ion battery diaphragm. The lithium ion battery diaphragm prepared by the invention has excellent ionic conductivity, flame retardance and mechanical property.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and specifically to a lithium-ion battery separator and a preparation method thereof. Background Art

[0002] With the increasingly serious global energy crisis and environmental pollution problems, the development of efficient clean energy technologies has become an urgent task. Against this background, lithium-ion batteries have become the core power source in fields such as electric vehicles, consumer electronics, and energy storage systems due to their advantages of high energy density, long cycle life, and environmental friendliness. As a key component of the battery, although the separator does not participate in the electrochemical reaction, it undertakes the important functions of isolating the positive and negative electrodes to prevent short circuits and providing a lithium-ion transmission channel.

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

[0004] To meet this demand and solve the key defects of traditional separators, promoting the development of clean energy applications. In this study, a novel battery separator with excellent flame retardant performance, ion conduction efficiency, and mechanical strength was successfully prepared by innovatively using modified polyethylene (PVDF) material. Summary of the Invention

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

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[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, and preparing polyamic acid microspheres by electrostatic spraying; reacting aminated polyethylene and allyl-1,3-sultone to prepare modified polyethylene; modifying hydroxylated boron nitride with mercaptopropyltrimethoxysilane to prepare modified boron nitride; mixing polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, and hot pressing into a film to obtain the lithium-ion battery separator;

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

[0009] The aminated polyethylene is prepared by reacting polyethylene initiated by benzoyl peroxide with allylamine;

[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 for preparing the lithium-ion battery separator includes the following preparation steps:

[0012] (1) Mix diphthaloyl DOPO, 4,4'-diaminodiphenyl 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), add N,N-dimethylformamide which is 10 - 12 times the mass of diphthaloyl DOPO, stir at 200 - 300 r / min for 6 - 8 h at 0 - 2 °C, raise the temperature to 50 - 60 °C and age for 48 - 50 h to obtain a polyamic acid solution; place the polyamic acid solution in an electrostatic sprayer for electrostatic spraying to obtain polyamic acid microspheres;

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

[0014] (3) Mix mercaptopropyltrimethoxysilane and deionized water in 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 °C, add hydroxylated boron nitride which is 1 - 1.2 times the mass of mercaptopropyltrimethoxysilane, ultrasonically disperse for 50 - 60 min, stir at 300 - 400 r / min for 3 - 5 h at 80 - 90 °C, filter, wash with deionized water 3 - 5 times, and freeze-dry at -30 - -20 °C under vacuum for 48 - 50 h to obtain modified boron nitride;

[0015] (4) By mass fraction, 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. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, and stir at 50 - 60 °C and 300 - 400 r / min for 5 - 7 h. Add azobisisobutyronitrile and mix evenly. Place it in a hot press and hot press it into an initial separator with a thickness of 100 μm. Take it out and put it into deionized water at 20 - 24 °C for 20 - 30 min. Under vacuum conditions, dry it at 55 - 65 °C for 8 - 9 h to obtain a lithium-ion battery separator.

[0016] As an optimization, the preparation method of the dianhydride DOPO in step (1) is as follows: Add 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride in a molar ratio of 1:3 to toluene with a mass 12 - 14 times that of trimellitic anhydride chloride. Add pyridine with a mass 0.1 - 0.16 times that of trimellitic anhydride chloride. Stir at 10 - 30 °C and 300 - 400 r / min for 1 - 2 h, then raise the temperature to 106 - 110 °C. Under a nitrogen atmosphere, stir and reflux for 6 - 8 h. Cool to room temperature, filter, wash with chloroform and ethyl acetate 3 - 5 times respectively, and dry at 70 - 80 °C under vacuum conditions for 8 - 10 h to obtain dianhydride DOPO; the reaction equation is:

[0017]

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

[0019] As an optimization, the preparation method of the aminated polyethylene in step (2) is as follows: Mix polyethylene and N,N-dimethylformamide in a mass ratio of 1:(14 - 16), stir at 45 - 55 °C and 100 - 200 r / min for 20 - 40 min. Under nitrogen protection, raise the temperature to 65 - 75 °C, add benzoyl peroxide with a mass 0.04 - 0.06 times that of polyethylene, continue stirring for 20 - 40 min, add allylamine with a mass 0.2 - 0.4 times that of polyethylene, and continue to react for 7 - 9 h. Cool to room temperature, add absolute ethanol with a mass 24 - 26 times that of polyethylene, let it stand for 5 - 7 h, filter, wash with deionized water 3 - 5 times, and dry at 50 - 60 °C under vacuum conditions for 8 - 10 h to obtain aminated polyethylene; the model of the polyethylene is HSV900.

[0020] As an optimization, the preparation method of the hydroxylated boron nitride in step (3) is as follows: Place the nano hexagonal boron nitride in the hearth of a high-temperature resistance furnace and calcine it at a high temperature. Heat it from room temperature to 890 - 900 °C at a heating rate of 10 °C / min, keep it at a constant temperature for calcination for 30 - 40 min, cool it to room temperature, and ultrasonically crush it for 18 - 22 min to obtain hydroxylated boron nitride; the model of the nano hexagonal boron nitride is 1489 - 01 - 5.

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

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

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

[0024] When preparing the lithium - ion battery separator, the present invention modifies 10 - (2,5 - dihydroxyphenyl) - 10H - 9 - oxa - 10 - phosphaphenanthrene - 10 - oxide with trichlorophthalic anhydride, reacts dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2 - vinyl - 4,6 - diamino - 1,3,5 - triazine, and prepares polyamic acid microspheres through electrostatic spraying; makes modified polyethylene by successively reacting polyethylene after being initiated by benzoyl peroxide with allylamine and allyl - 1,3 - sultone; calcines hydroxylated boron nitride at a high temperature; modifies hydroxylated boron nitride with mercaptopropyltrimethoxysilane to obtain modified boron nitride; mixes polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, and hot presses them into a film to obtain the lithium - ion battery separator.

[0025] First, modifying 10 - (2,5 - dihydroxyphenyl) - 10H - 9 - oxa - 10 - phosphaphenanthrene - 10 - oxide with trichlorophthalic anhydride, reacting dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2 - vinyl - 4,6 - diamino - 1,3,5 - triazine, and preparing polyamic acid microspheres through electrostatic spraying introduce DOPO, triazine, and carbon - carbon double bonds on the polyamic acid microspheres, and generate carboxyl groups. The generated polyamic acid microspheres have excellent electrolyte wettability and porosity. The generated carboxyl structure has strong negative electricity, which accelerates the flow of lithium ions, improves the inhibitory effect of the lithium - ion battery separator on lithium dendrites, thereby improving the ionic 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 a carbon layer to isolate heat and oxygen, improving the flame - retardant effect of the lithium - ion battery separator. The introduced triazine structure can generate non - combustible nitrogen - containing gases, which can absorb heat, dilute the oxygen concentration, and reduce the combustion temperature, further improving the flame - retardant performance of the lithium - ion battery separator.

[0026] Second, the polyethylenes initiated by benzoyl peroxide are reacted with allylamine to introduce amino groups onto the polyethylenes. The aminated polyethylenes are reacted with allyl-1,3-sultone to prepare modified polyethylenes, on which carbon-carbon double bonds are introduced and sulfonic acid groups are generated. The sulfonic acid groups have strong polarity and interact with the ions in the electrolyte, improving the mobility of lithium ions, thereby enhancing the ionic conductivity of the lithium-ion battery separator. High-temperature calcination of nano-hexagonal boron nitride can increase the hydroxyl groups on the surface of boron nitride, making it easier for boron nitride to graft mercaptopropyltrimethoxysilane. The hydroxyl-grouped boron nitride is modified with mercaptopropyltrimethoxysilane to introduce a large number of mercapto groups onto the boron nitride, enhancing the compatibility between boron nitride and polyethylene, enabling 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 mercapto groups on the modified boron nitride undergo an addition reaction to form a crosslinked network, inhibiting the relative movement between molecular chains and enhancing 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, the modified polyethylene, polyamic acid microspheres, modified boron nitride, azobisisobutyronitrile, and polyvinylpyrrolidone are mixed and hot-pressed into a film to obtain the lithium-ion battery separator. Specific Embodiments

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0029] Example 1:

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

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

[0032] (2) Polyethylene and N,N-dimethylformamide were mixed at a mass ratio of 1:14. At 45 °C, it was stirred at 100 r / min for 40 min. Under nitrogen protection, the temperature was raised to 65 °C, and benzoyl peroxide which was 0.04 times the mass of polyethylene was added, and it was stirred for another 40 min. Allylamine which was 0.2 times the mass of polyethylene was added, and the reaction continued for 9 h. After cooling to room temperature, absolute ethanol which was 24 times the mass of polyethylene was added, and it was left standing for 5 h. After filtration, it was washed 3 times with deionized water. Under vacuum conditions, it was dried at 50 °C for 10 h to obtain aminated polyethylene; Aminated polyethylene and acetonitrile were mixed at a mass ratio of 1:8, and ultrasonically dispersed for 30 min. Allyl-1,3-sultone which was 2.0 times the mass of polyethylene was added. Under nitrogen protection, at 60 °C, it was stirred at 300 r / min for 12 h. After cooling to room temperature, it was filtered and washed 3 times with acetone. Under vacuum conditions, it was dried at 50 °C for 10 h to obtain modified polyethylene;

[0033] (3) Nano hexagonal boron nitride was placed in a high-temperature resistance furnace hearth for high-temperature calcination. At a heating rate of 10 °C / min, it was heated from room temperature to 890 °C, and calcined at a constant temperature for 40 min. After cooling to room temperature, it was ultrasonically broken for 18 min to obtain hydroxylated boron nitride; Mercaptopropyltrimethoxysilane and deionized water were mixed at a mass ratio of 1:9, and the pH was adjusted to 3.6 with formic acid. At 20 °C, it was stirred at 300 r / min for 12 min. Hydroxylated boron nitride which was 1 times the mass of mercaptopropyltrimethoxysilane was added, and ultrasonically dispersed for 50 min. At 80 °C, it was stirred at 300 r / min for 5 h. After filtration, it was washed 3 times with deionized water. Under vacuum conditions, it was freeze-dried at -30 °C for 48 h 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 part of azobisisobutyronitrile, and 15 parts of polyvinylpyrrolidone by mass fraction. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, and stir at 50 °C and 300 r / min for 7 h. Add azobisisobutyronitrile and mix evenly. Place it in a hot press and hot press it into an initial diaphragm with a thickness of 100 μm. Set the process parameters for hot pressing into a film as follows: hot pressing temperature 130 °C, hot pressing pressure 1 MPa, hot pressing time 40 s. Take it out and put it into deionized water at 20 °C for 30 min, and dry it at 55 °C for 9 h under vacuum conditions to obtain a lithium-ion battery separator.

[0035] Example 2:

[0036] A preparation method of a lithium-ion battery separator, the preparation method of the lithium-ion battery separator includes the following preparation steps:

[0037] (1) Add 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride in a molar ratio of 1:3 to toluene with a mass 13 times that of trimellitic anhydride chloride. Add pyridine with a mass 0.13 times that of trimellitic anhydride chloride. Stir at 30 °C and 350 r / min for 1.5 h, then raise the temperature to 108 °C, and stir and reflux for 7 h under a nitrogen atmosphere. Cool to room temperature, filter, wash 4 times with chloroform and ethyl acetate respectively, and dry at 75 °C for 9 h under vacuum conditions to obtain dianhydride DOPO; Mix dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine in a molar ratio of 1:0.68:0.28, add N,N-dimethylformamide with a mass 11 times that of dianhydride DOPO, stir at 1 °C and 250 r / min for 7 h, and age at 55 °C for 49 h to obtain a polyamic acid solution; Place the polyamic acid solution in an electrostatic sprayer for electrostatic spraying, and set the process parameters of electrostatic spraying as positive pressure 21 kV, negative pressure 4 kV, and the receiving distance from the base 17 cm to obtain polyamic acid microspheres;

[0038] (2) Mix polyethylene and N,N-dimethylformamide at a mass ratio of 1:15, stir at 50 °C and 150 r / min for 30 min. Under nitrogen protection, heat up to 70 °C, add benzoyl peroxide at 0.05 times the mass of polyethylene, continue stirring for 30 min, add allylamine at 0.3 times the mass of polyethylene, continue reacting for 8 h, cool to room temperature, add absolute ethanol at 25 times the mass of polyethylene, let stand for 6 h, filter, wash 4 times with deionized water, and dry at 55 °C under vacuum for 9 h to obtain aminated polyethylene; Mix aminated polyethylene and acetonitrile at a mass ratio of 1:9, ultrasonically disperse for 35 min, add allyl-1,3-sultone at 2.1 times the mass of polyethylene, under nitrogen protection, stir at 65 °C and 350 r / min for 11 h, cool to room temperature, filter, wash 4 times with acetone, and dry at 55 °C under vacuum for 9 h to obtain modified polyethylene;

[0039] (3) Place nano hexagonal boron nitride in the furnace chamber of a high-temperature resistance furnace for high-temperature calcination. At a heating rate of 10 °C / min, heat up from room temperature to 895 °C, keep the temperature constant for calcination for 35 min, cool to room temperature, and ultrasonically crush for 20 min to obtain hydroxylated boron nitride; Mix 3-mercaptopropyltrimethoxysilane and deionized water at a mass ratio of 1:9.5, adjust the pH to 3.8 with formic acid, stir at 25 °C and 350 r / min for 11 min, add hydroxylated boron nitride at 1.1 times the mass of 3-mercaptopropyltrimethoxysilane, ultrasonically disperse for 55 min, stir at 5 °C and 350 r / min for 4 h, filter, wash 4 times with deionized water, and freeze-dry at -25 °C under vacuum for 49 h to obtain modified boron nitride;

[0040] (4) By mass fraction, weigh 100 parts of modified polyethylene, 7.5 parts of polyamic acid microspheres, 4 parts of modified boron nitride, 0.7 part of azobisisobutyronitrile, and 17 parts of polyvinylpyrrolidone. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, stir at 55 °C and 350 r / min for 6 h, add azobisisobutyronitrile and mix evenly, place it in a hot press, hot-press it into an initial diaphragm with a thickness of 100 μm. Set the process parameters for hot-pressing into a film as follows: hot-pressing temperature 140 °C, hot-pressing pressure 1.5 MPa, hot-pressing time 35 s. Take it out, put it into deionized water at 22 °C for 25 min, and dry at 60 °C under vacuum for 8.5 h to obtain a lithium-ion battery separator.

[0041] Example 3:

[0042] A preparation method of a lithium-ion battery separator, the preparation method of the lithium-ion battery separator includes the following preparation steps:

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

[0044] (2) Polyethylene and N,N-dimethylformamide were mixed at a mass ratio of 1:16, stirred at 55 °C and 200 r / min for 20 min, under nitrogen protection, heated to 75 °C, benzoyl peroxide at 0.06 times the mass of polyethylene was added, and stirring was continued for 20 min. Allylamine at 0.4 times the mass of polyethylene was added, and the reaction was continued for 7 h. It was cooled to room temperature, absolute ethanol at 26 times the mass of polyethylene was added, allowed to stand for 7 h, filtered, washed 5 times with deionized water, and dried at 60 °C for 8 h under vacuum conditions to obtain aminated polyethylene. Aminated polyethylene and acetonitrile were mixed at a mass ratio of 1:10, ultrasonically dispersed for 40 min, allyl-1,3-sultone at 2.2 times the mass of polyethylene was added, and under nitrogen protection, stirred at 70 °C and 400 r / min for 10 h. It was cooled to room temperature, filtered, washed 5 times with acetone, and dried at 60 °C for 8 h under vacuum conditions to obtain modified polyethylene;

[0045] (3) Nano hexagonal boron nitride was placed in the furnace chamber of a high-temperature resistance furnace for high-temperature calcination. It was heated from room temperature to 900 °C at a heating rate of 10 °C / min, calcined at a constant temperature for 30 min, cooled to room temperature, and 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, stirred at 30 °C and 400 r / min for 10 min, hydroxylated boron nitride at 1.2 times the mass of mercaptopropyltrimethoxysilane was added, ultrasonically dispersed for 60 min, stirred at 90 °C and 400 r / min for 3 h, filtered, washed 5 times with deionized water, and freeze-dried at -20 °C for 50 h under vacuum conditions to obtain modified boron nitride;

[0046] (4) By mass fraction, weigh 100 parts of modified polyethylene, 8 parts of polyamic acid microspheres, 5 parts of modified boron nitride, 0.9 part of azobisisobutyronitrile, and 19 parts of polyvinylpyrrolidone. 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 it in a hot press, and hot press it into an initial separator with a thickness of 100 μm. Set the process parameters for hot pressing into a film as follows: hot pressing temperature 150 °C, hot pressing pressure 2 MPa, hot pressing time 30 s. Take it out, put it into deionized water at 24 °C for 20 min, take it out, and dry it at 65 °C for 8 h under vacuum conditions to obtain a lithium-ion battery separator.

[0047] Comparative Example 1:

[0048] The preparation method of the lithium-ion battery separator in Comparative Example 1 is only different from that in Example 2 in step (1). Modify step (1) as follows: Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine in a molar ratio of 1:0.68:0.28, add N,N-dimethylformamide 11 times the mass of pyromellitic dianhydride, stir at 1 °C and 250 r / min for 7 h, raise the temperature to 55 °C and age for 49 h to obtain a polyamic acid solution; place the polyamic acid solution in an electrostatic sprayer for electrostatic spraying, and set the process parameters of electrostatic spraying as positive pressure 21 kV, negative pressure 4 kV, and the receiving distance from the base 17 cm to obtain polyamic acid microspheres. The remaining steps are the same as those in Example 2.

[0049] Comparative Example 2:

[0050] The preparation method of the lithium-ion battery separator of Comparative Example 2 is only different from that of Example 2 in step (1). Modify step (1) as follows: Add 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride in a molar ratio of 1:3 to toluene which is 13 times the mass of trimellitic anhydride chloride. Add pyridine which is 0.13 times the mass of trimellitic anhydride chloride. Stir at 350 r / min for 1.5 h at 30°C, then raise the temperature to 108°C and stir and reflux for 7 h under a nitrogen atmosphere. Cool to room temperature, filter, wash 4 times with chloroform and ethyl acetate respectively, and dry at 75°C for 9 h under vacuum conditions to obtain dianhydride DOPO. Mix dianhydride DOPO and 4,4'-diaminodiphenyl ether in a molar ratio of 1:0.96, add N,N-dimethylformamide which is 11 times the mass of dianhydride DOPO, stir at 250 r / min for 7 h at 1°C, then raise the temperature to 55°C and age for 49 h to obtain a polyamic acid solution. Place the polyamic acid solution in an electrostatic sprayer for electrostatic spraying, and set the process parameters of electrostatic spraying as a positive pressure of 21 kV, a negative pressure of 4 kV, and a receiving distance from the base of 17 cm to obtain polyamic acid microspheres. The remaining steps are the same as those in Example 2.

[0051] Comparative Example 3:

[0052] The preparation method of the lithium-ion battery separator of Comparative Example 3 is different from that of Example 2 in that step (2) is not carried out. Modify step (4) as follows: By mass fraction, weigh 100 parts of polyethylene, 7.5 parts of polyamic acid microspheres, 4 parts of modified boron nitride, 0.7 part of azobisisobutyronitrile, and 17 parts of polyvinylpyrrolidone. Mix polyvinylpyrrolidone, polyethylene, polyamic acid microspheres, and modified boron nitride, stir at 350 r / min for 6 h at 55°C, add azobisisobutyronitrile and mix evenly, place it in a hot press, and hot press it into an initial separator with a thickness of 100 μm. Set the process parameters of hot pressing into a film as follows: hot pressing temperature of 140°C, hot pressing pressure of 1.5 MPa, and hot pressing time of 35 s. Take it out, place it in deionized water at 22°C for 25 min, and dry at 60°C for 8.5 h under vacuum conditions to obtain a lithium-ion battery separator.

[0053] Comparative Example 4:

[0054] The preparation method of the lithium ion battery separator of Comparative Example 4 is different from that of Example 2 in that step (3) is not performed, 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 polyvinyl pyrrolidone are weighed by mass fraction, polyvinyl pyrrolidone, modified polyethylene, polyamic acid microspheres, and nano hexagonal boron nitride are mixed, stirred at 55°C and 350r / min for 6h, azobisisobutyronitrile is added and mixed evenly, placed in a hot press, and hot pressed into an initial separator of 100μm. The process parameters of hot pressing film formation are set as follows: hot pressing temperature 140°C, hot pressing pressure 1.5MPa, hot pressing time 35s, taken out, placed in deionized water at 22°C for 25min, and dried at 60°C under vacuum conditions for 8.5h to obtain a lithium ion battery separator.

[0055] Comparative Example 5:

[0056] The preparation method of the lithium ion battery separator of Comparative Example 5 is different from that of Example 2 in that step (1) is not performed, 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 polyvinyl pyrrolidone are weighed by mass fraction, polyvinyl pyrrolidone, modified polyethylene, and modified boron nitride are mixed, stirred at 55°C and 350r / min for 6h, azobisisobutyronitrile is added and mixed evenly, placed in a hot press, and hot pressed into an initial separator of 100μm. The process parameters for hot pressing film formation are set as follows: hot pressing temperature of 140°C, hot pressing pressure of 1.5MPa, hot pressing time of 35s, taken out, placed in deionized water at 22°C for 25min, and dried at 60°C under vacuum conditions for 8.5h to obtain a lithium ion battery separator.

[0057] Test Example 1

[0058] Ionic conductivity test

[0059] Test method: Assemble a symmetrical battery of stainless steel sheet / diaphragm / stainless steel sheet. The assembled battery sample is placed for 5 hours before testing. The electrochemical impedance spectrum of the battery sample is tested using an electrochemical workstation. The impedance spectrum is related to the solid diffusion process of lithium ions inside the diaphragm. The intersection of the oblique line and the horizontal axis in the AC impedance spectrum is the bulk resistance of the lithium-ion battery diaphragm. The test frequency is 1×10 6 Hz-1Hz, voltage 10mV. Calculate ionic conductivity according to the formula: ionic conductivity = membrane thickness / (bulk resistance × effective contact area) × 100%. The results are shown in Table 1.

[0060] Table 1

[0061]

[0062] From the comparison of the experimental data of Examples 1-3 and Comparative Examples 1-5 in Table 1, it can be found that the lithium-ion battery separator prepared by the present invention has good ionic conductivity.

[0063] By comparison, the ionic conductivity of Examples 1-3 is greater than that of Comparative Example 3, indicating that the aminated polyethylene and allyl-1,3-sultone are reacted to prepare modified polyethylene, introducing carbon-carbon double bonds onto the polyethylene and generating sulfonic acid groups. The sulfonic acid groups have strong polarity and interact with the ions in the electrolyte, improving the mobility of lithium ions, thereby enhancing 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 dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine are reacted and polyamic acid microspheres are prepared by electrospraying. Carboxyl groups are generated on the polyamic acid microspheres. The carboxyl group structure has strong negative electricity, accelerating the flow of lithium ions, improving the inhibitory effect of the lithium-ion battery separator on lithium dendrites, and thus enhancing the ionic conductivity of the lithium-ion battery separator.

[0065] Test Example 2

[0066] Test of flame retardancy

[0067] Test method: The examples and comparative examples were prepared into standard specimens according to GB / T2406-93, and the limiting oxygen index of the standard specimens 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] From the comparison of the experimental data of Examples 1-3 and Comparative Examples 1-5 in Table 2, it can be found that the lithium-ion battery separator prepared by the present invention has good flame retardancy.

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

[0072] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 2 and Comparative Example 5, indicating that the reaction of dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine, followed by electrostatic spraying, yields polyamic acid microspheres. Triazine is introduced onto the polyamic acid microspheres. The triazine structure can generate non-combustible nitrogen-containing gases, which can absorb heat, dilute the oxygen concentration, reduce the combustion temperature, and further improve the flame retardancy of the lithium-ion battery separator.

[0073] Test Example 3

[0074] Testing of Mechanical Properties

[0075] Test method: GB / T1040.3-2006. An electronic universal testing machine was used to detect the tensile strength of the examples and comparative examples. 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] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 1, it can be found that the lithium-ion battery separator prepared by the present invention has good mechanical properties.

[0079] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Example 2 and Comparative Example 5, indicating that the reaction of dianhydride DOPO, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine by electrostatic spraying yields polyamic acid microspheres. Carbon-carbon double bonds are introduced onto the polyamic acid microspheres. The carbon-carbon double bonds on the polyamic acid microspheres and the sulfhydryl groups on the modified boron nitride undergo an addition reaction to form a crosslinked network, inhibiting the relative movement between molecular chains and enhancing the mechanical properties of the lithium-ion battery separator.

[0080] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Example 3, indicating that the reaction of aminated polyethylene and allyl-1,3-sultone yields modified polyethylene. Carbon-carbon double bonds are introduced onto the polyethylene. The carbon-carbon double bonds on the modified polyethylene and the sulfhydryl groups on the modified boron nitride undergo an addition reaction to form a crosslinked network, inhibiting the relative movement between molecular chains and enhancing the mechanical properties of the lithium-ion battery separator.

[0081] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Example 4, indicating that the reaction of mercaptopropyltrimethoxysilane and hydroxylated boron nitride to prepare modified boron nitride and introducing a large number of mercapto groups on boron nitride will improve the compatibility of boron nitride and polyethylene, enabling 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 mercapto groups on the modified boron nitride undergo an addition reaction to form a crosslinked 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 elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and does not limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium-ion battery separator, characterized in that, The lithium-ion battery separator is prepared by reacting diphosphaphenanthrene dioxide (DOPO) dianhydride, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine, and preparing polyamic acid microspheres by electrostatic spraying; reacting aminated polyethylene with allyl-1,3-sultone to prepare modified polyethylene; reacting mercaptopropyltrimethoxysilane with hydroxylated boron nitride to prepare modified boron nitride; mixing polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, and hot-pressing into a film to obtain the lithium-ion battery separator; The diphosphaphenanthrene dioxide (DOPO) dianhydride is prepared by reacting 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide with trimellitic anhydride chloride; The aminated polyethylene is prepared by reacting polyethylene initiated by benzoyl peroxide with allylamine; The hydroxylated boron nitride is prepared by high-temperature calcination of nano-hexagonal boron nitride; 2. A method for preparing a lithium-ion battery separator, characterized in that, The preparation method of the lithium-ion battery separator includes the following preparation steps: (1) Mix diphosphaphenanthrene dioxide (DOPO) dianhydride, 4,4'-diaminodiphenyl ether, and 2-vinyl-4,6-diamino-1,3,5-triazine at a molar ratio of 1:(0.67 - 0.69):(0.27 - 0.29), add N,N-dimethylformamide 10 - 12 times the mass of diphosphaphenanthrene dioxide (DOPO) dianhydride, stir at 200 - 300 r / min at 0 - 2 °C for 6 - 8 h, raise the temperature to 50 - 60 °C and age for 48 - 50 h to obtain a polyamic acid solution; place the polyamic acid solution in an electrostatic spraying machine for electrostatic spraying to obtain polyamic acid microspheres; (2) Mix aminated polyethylene and acetonitrile at a mass ratio of 1:(8 - 10), ultrasonically disperse for 30 - 40 min, add allyl-1,3-sultone 2.0 - 2.2 times the mass of polyethylene, stir at 300 - 400 r / min at 60 - 70 °C for 10 - 12 h under nitrogen protection, cool to room temperature, filter, wash with acetone 3 - 5 times, and dry at 50 - 60 °C under vacuum for 8 - 10 h to obtain modified polyethylene; (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 at 20 - 30 °C for 10 - 12 min, add hydroxylated boron nitride 1 - 1.2 times the mass of mercaptopropyltrimethoxysilane, ultrasonically disperse for 50 - 60 min, stir at 300 - 400 r / min at 80 - 90 °C for 3 - 5 h, filter, wash with deionized water 3 - 5 times, and freeze-dry at -30 - -20 °C under vacuum for 48 - 50 h to obtain modified boron nitride; (4) By mass fraction, weigh 100 parts of modified polyethylene, 7 - 8 parts of polyamic acid microspheres, 3 - 5 parts of modified boron nitride, 0.5 - 0.9 part of azobisisobutyronitrile, and 15 - 19 parts of polyvinylpyrrolidone. Mix polyvinylpyrrolidone, modified polyethylene, polyamic acid microspheres, and modified boron nitride, and stir at 50 - 60 °C and 300 - 400 r / min for 5 - 7 h. Add azobisisobutyronitrile and mix evenly. Place it in a hot press and hot press it into an initial separator with a thickness of 100 μm. Take it out and put it into deionized water at 20 - 24 °C for 20 - 30 min. Under vacuum conditions, dry it at 55 - 65 °C for 8 - 9 h to obtain a lithium-ion battery separator.

3. The preparation method of a lithium-ion battery separator according to claim 2, characterized in that, The preparation method of the dianhydride DOPO described in step (1) is as follows: Add 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide and trimellitic anhydride chloride in a molar ratio of 1:3 to toluene with a mass 12 - 14 times that of trimellitic anhydride chloride. Add pyridine with a mass 0.1 - 0.16 times that of trimellitic anhydride chloride. Stir at 10 - 30 °C and 300 - 400 r / min for 1 - 2 h. Raise the temperature to 106 - 110 °C, and under a nitrogen atmosphere, stir and reflux for 6 - 8 h. Cool to room temperature, filter, wash 3 - 5 times with chloroform and ethyl acetate respectively, and dry at 70 - 80 °C under vacuum conditions for 8 - 10 h to obtain dianhydride DOPO.

4. The preparation method of a lithium-ion battery separator according to claim 2, characterized in that, The process parameters of the electrostatic spraying described in step (1) are: positive pressure 20 - 22 kV, negative pressure 3 - 5 kV, and the receiving distance from the base 16 - 18 cm.

5. The preparation method of a lithium-ion battery separator according to claim 2, characterized in that, The preparation method of the aminated polyethylene described in step (2) is as follows: Mix polyethylene and N,N-dimethylformamide in a mass ratio of 1:(14 - 16), stir at 45 - 55 °C and 100 - 200 r / min for 20 - 40 min. Under nitrogen protection, raise the temperature to 65 - 75 °C, add benzoyl peroxide with a mass 0.04 - 0.06 times that of polyethylene, continue to stir for 20 - 40 min, add allylamine with a mass 0.2 - 0.4 times that of polyethylene, and continue to react for 7 - 9 h. Cool to room temperature, add absolute ethanol with a mass 24 - 26 times that of polyethylene, let it stand for 5 - 7 h, filter, wash 3 - 5 times with deionized water, and dry at 50 - 60 °C under vacuum conditions for 8 - 10 h to obtain aminated polyethylene; the model of the polyethylene is LD608.

6. The preparation method of a lithium-ion battery separator according to claim 2, characterized in that, The preparation method of the hydroxylated boron nitride described in step (3) is as follows: Place nano hexagonal boron nitride in the hearth of a high-temperature resistance furnace for high-temperature calcination. At a heating rate of 10 °C / min, heat from room temperature to 890 - 900 °C, keep it at a constant temperature for calcination for 30 - 40 min, cool to room temperature, and ultrasonically crush for 18 - 22 min to obtain hydroxylated boron nitride.

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

8. The preparation method of a lithium-ion battery separator according to claim 2, wherein The process parameters of the hot pressing described in step (4) are: hot pressing temperature 130 - 150 °C, hot pressing pressure 1 - 2 MPa, and hot pressing time 30 - 40 s.

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