Fireproof flame-retardant lithium battery diaphragm and fireproof flame-retardant lithium battery

Abstract

The invention discloses a fireproof flame-retardant lithium battery diaphragm and a fireproof flame-retardant lithium battery, and relates to the technical field of battery diaphragms. When the fireproof flame-retardant lithium battery diaphragm is prepared, phosphonitrilic chloride trimer, phenol sulfonyl phthalein and 4, 4 '-methylenebis [2-allylphenol] are subjected to a reaction to prepare polyphosphazene microspheres; treating the polyphosphazene microspheres with sodium hydroxide to obtain modified polyphosphazene microspheres; the preparation method comprises the following steps: sequentially reacting polypropylene with 3-butenoic acid and 4-ethynylbenzene-1, 2-diamine to obtain modified polypropylene; the preparation method comprises the following steps: polymerizing ethyl boric acid and 3-mercaptopropyl methyl dimethoxy silane to prepare polyborosiloxane; and uniformly mixing the modified polypropylene, the modified polyphosphazene microspheres, polyborosiloxane and benzoin dimethyl ether, carrying out electrostatic spinning, and carrying out ultraviolet irradiation to prepare the fireproof flame-retardant lithium battery diaphragm. The fireproof flame-retardant lithium battery diaphragm prepared by the invention has excellent flame retardance, ionic conductivity and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, in particular to a fire-proof and flame-retardant lithium battery separator and a fire-proof and flame-retardant lithium battery. Background Art

[0002] Lithium-ion batteries, with their superior high energy density, long life, low self-discharge rate, and environmental friendliness, have become widely used in electronics, new energy vehicles, and other energy storage applications. As a key component within lithium-ion batteries, the battery separator primarily separates the positive and negative electrodes, preventing direct contact and short circuits. Furthermore, the separator serves as an ion transport channel for the stored electrolyte, allowing lithium ions to flow freely through its microporous structure during the battery's charge and discharge processes. To date, porous polyethylene and polypropylene separators remain the predominant commercial battery separators on the market, offering advantages such as low cost and stable chemical properties. As the energy density of lithium-ion batteries continues to increase, the requirements for battery separators are also becoming increasingly stringent. Conventional polyolefin separators suffer from poor electrolyte wettability and flammability, hindering the further development of the lithium-ion battery industry. Therefore, there is a need to improve existing technologies and develop polyolefin separators with excellent flame retardancy and electrolyte wettability to enhance the electrochemical performance and safety of lithium-ion batteries. Summary of the Invention

[0003] The purpose of the present invention is to provide a fire-resistant and flame-retardant lithium battery separator and a fire-resistant and flame-retardant lithium battery to solve the problems existing in the prior art.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A fire-retardant lithium battery separator is prepared by treating polyphosphazene microspheres with sodium hydroxide to obtain modified polyphosphazene microspheres; reacting pre-modified polypropylene and 4-ethynylbenzene-1,2-diamine to obtain modified polypropylene; and uniformly mixing the modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether, electrospinning the mixture, and irradiating the mixture with ultraviolet light.

[0006] The polyphosphazene microspheres are prepared by reacting hexachlorocyclotriphosphazene, phenolsulfonylphthalide and 4,4'-methylenebis[2-allylphenol].

[0007] The pre-modified polypropylene is prepared by reacting polypropylene and 3-butenoic acid;

[0008] The polyborosiloxane is prepared by polymerizing ethylboric acid and 3-mercaptopropylmethyldimethoxysilane.

[0009] As an optimization, the fire-retardant lithium battery separator includes the following preparation steps:

[0010] (1) Polyphosphazene microspheres and sodium hydroxide aqueous solution are mixed uniformly in a mass ratio of 1:(20-22), stirred at 70-80°C and 200-300 r / min for 2-3 h, centrifuged, washed with 1 mol / L hydrochloric acid aqueous solution and deionized water 4-6 times each, and dried at 50-60°C under vacuum conditions for 10-12 h to obtain modified polyphosphazene microspheres;

[0011] (2) Pre-modified polypropylene and N,N-dimethylformamide were mixed uniformly in a mass ratio of 1:(8-10), stirred at 100-104°C and 200-300 r / min for 12-14 min, 0.6-0.8 times the mass of pre-modified polypropylene of 4-ethynylbenzene-1,2-diamine and 2-2.2 times the mass of pre-modified polypropylene of 3 mol / L hydrochloric acid aqueous solution were added, stirred and refluxed at 100-104°C and 200-300 r / min for 3-4 h, cooled to 60-70°C, adjusted to pH 8-9 with a mass fraction of 10% sodium hydroxide aqueous solution, and dried at 70-80°C under vacuum for 8-10 h to obtain modified polypropylene;

[0012] (3) adding ethylboric acid and 3-mercaptopropylmethyldimethoxysilane in a molar ratio of 1:(1.1-1.2) to 12-14 times the mass of 1,4-dioxane by weight of ethylboric acid, stirring and reacting at 84-86°C and 300-400 r / min for 80-90 minutes, adding hexamethyldisiloxane by weight of 0.03-0.05 times the mass of 3-mercaptopropylmethyldimethoxysilane, continuing to stir and react for 20-30 minutes, and drying at 60-70°C under vacuum conditions for 8-10 hours to obtain polyborosiloxane;

[0013] (4) Weigh 98 to 102 parts of modified polypropylene, 7 to 8 parts of modified polyphosphazene microspheres, 8 to 10 parts of polyborosiloxane, and 1 to 1.6 parts of benzoin dimethyl ether by mass; mix the modified polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether evenly, place them in an electrospinning device for melt electrospinning, and deposit them on a collecting drum to form a fiber membrane with a thickness of 28 to 32 μm; irradiate the fiber membrane with ultraviolet light with a maximum wavelength of 365 nm and a power of 100 W for 38 to 42 minutes to obtain a fire-retardant lithium battery separator.

[0014] As an optimization, the preparation method of the polyphosphazene microspheres in step (1) is: hexachlorocyclotriphosphazene, phenolsulfonylphthalein, 4,4'-methylenebis[2-allylphenol], acetonitrile in a mass ratio of

[0015] 1:(1.6-1.8):(2.4-2.6):(90-100) are mixed evenly, stirred at 200-30°C and 200-300 r / min for 18-20 min, triethylamine (3-3.2 times the mass of hexachlorocyclotriphosphazene) is added, stirring is continued for 3-4 h, centrifuged, washed with anhydrous ethanol and deionized water for 3-5 times each, and dried at 50-60°C under vacuum conditions for 10-12 h to obtain polyphosphazene microspheres.

[0016] The CAS number of the 4,4'-methylenebis[2-allylphenol] is 62386-37-2; the structural formula is as follows:

[0017]

[0018] As an optimization, the mass fraction of the sodium hydroxide aqueous solution in step (1) is 3% to 4%.

[0019] As an optimization, the preparation method of the pre-modified polypropylene in step (2) is as follows: polypropylene and o-xylene are mixed uniformly in a mass ratio of 1:(4-5), stirred at 112-114° C. and 200-300 r / min for 18-20 min, 3-butenoic acid in an amount of 0.22-0.24 times the mass of the polypropylene is added, stirring is continued for 18-20 min, and an initiator solution in an amount of 0.18-0.22 times the mass of the polypropylene is added dropwise at a uniform rate within 40 min. After the addition is completed, the temperature is raised to 138-142° C., the stirring reaction is continued for 4-5 h, the temperature is lowered to 49-51° C., acetone in an amount of 5-6 times the mass of the polypropylene is added and mixed uniformly, the mixture is allowed to stand for 2-3 h, filtered, and dried at 70-80° C. under vacuum conditions for 10-12 h to obtain pre-modified polypropylene.

[0020] As an optimization, the preparation method of the initiator solution is: dibenzoyl peroxide and o-xylene are uniformly mixed in a mass ratio of 1:(6-7) to prepare the initiator solution.

[0021] As an optimization, the model of the polypropylene is PP S2040, purchased from Shanghai Nazhou Plastic Technology Co., Ltd.

[0022] As an optimization, the CAS number of the 4-ethynylbenzene-1,2-diamine in step (2) is 58297-31-7; the structural formula is as follows:

[0023]

[0024] As an optimization, the process parameters of the melt electrospinning in step (4) are as follows: the spinneret aperture is set to 0.2-0.3 mm, the spinning temperature is 230-240° C., the spinning distance is 22-24 cm, the spinning voltage is 24-26 kV, and the collection drum speed is 90-100 r / min.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] When preparing a fireproof and flame-retardant lithium battery separator, the present invention comprises the following steps: reacting hexachlorocyclotriphosphazene, phenolsulfonylphthalide, and 4,4'-methylenebis[2-allylphenol] to obtain polyphosphazene microspheres; treating the polyphosphazene microspheres with sodium hydroxide to obtain modified polyphosphazene microspheres; reacting polypropylene and 3-butenoic acid to obtain pre-modified polypropylene; reacting the pre-modified polypropylene and 4-ethynylbenzene-1,2-diamine to obtain modified polypropylene; polymerizing ethylboric acid and 3-mercaptopropylmethyldimethoxysilane to obtain polyborosiloxane; and uniformly mixing the modified polypropylene, the modified polyphosphazene microspheres, the polyborosiloxane, and benzoin dimethyl ether, subjecting the mixture to electrostatic spinning and irradiation with ultraviolet light to obtain the fireproof and flame-retardant lithium battery separator.

[0027] First, the P-Cl bond of hexachlorocyclotriphosphazene reacts with the phenolic hydroxyl groups on phenolsulfonylphthalide and 4,4'-methylenebis[2-allylphenol] to prepare polyphosphazene microspheres, and cyclotriphosphazene, carbon-carbon double bonds, and sultones are introduced into the polyphosphazene microspheres; the polyphosphazene microspheres are treated with sodium hydroxide to open the sultone ring to generate sulfonic acid groups and hydroxyl groups. Both sulfonic acid groups and hydroxyl groups are polar groups that can improve the wettability of the battery separator with the electrolyte, thereby improving the ionic conductivity of the fire-retardant lithium battery separator; the cyclotriphosphazene introduced into the polyphosphazene microspheres can improve the flame retardant properties of the fire-retardant lithium battery separator, and the carbon-carbon double bonds introduced into the polyphosphazene microspheres can undergo an addition reaction with the thiol groups on polyborosiloxane under the action of a photoinitiator and ultraviolet light to form a cross-linked network, thereby improving the mechanical properties of the fire-retardant lithium battery separator.

[0028] Secondly, 3-butenoic acid was grafted onto the side chain of polypropylene molecules by a solution grafting method to obtain pre-modified polypropylene, and carboxyl groups were introduced into the side chains of the pre-modified polypropylene molecules; the carboxyl groups introduced into the side chains of the pre-modified polypropylene molecules were reacted with 4-ethynylbenzene-1,2-diamine to obtain modified polypropylene, a benzimidazole structure was generated on the modified polypropylene, and an alkynyl group was introduced; the NH bond in the benzimidazole structure can produce hydrogen bond complexation with the anions in the electrolyte, promote the formation of the solvation sheath, promote the migration and deintercalation process of lithium ions, thereby improving the ionic conductivity of the fire-retardant lithium battery separator; the alkynyl group introduced into the side chain of the modified polypropylene molecule can undergo an addition reaction with the thiol group on the polyborosiloxane under the action of a photoinitiator and ultraviolet light to form a cross-linked network, thereby improving the mechanical properties of the flame-retardant lithium battery separator.

[0029] Finally, ethylboric acid and 3-mercaptopropylmethyldimethoxysilane were polymerized to prepare polyborosiloxane; and mercapto groups were introduced on the side chains of the polyborosiloxane molecules; the polyborosiloxane structure contains boron elements and Si-O-Si bonds, which can form a dense expanded carbon layer during combustion, preventing heat transfer and the spread of oxygen, further improving the flame retardant properties of the flame-retardant lithium battery separator; the mercapto groups introduced on the side chains of the polyborosiloxane molecules can undergo addition reactions with the acetylenic groups on modified polypropylene and the carbon-carbon double bonds on modified polyphosphazene microspheres under the action of photoinitiators and ultraviolet light to form a cross-linked network structure, thereby improving the mechanical properties of the flame-retardant lithium battery separator. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] The polypropylene used in the following examples and comparative examples is PP S2040, purchased from Shanghai Nazhou Plastic Technology Co., Ltd.

[0032] Example 1:

[0033] A fire-retardant lithium battery separator, comprising the following preparation steps:

[0034] (1) Hexachlorocyclotriphosphazene, phenolsulfonylphthalein, 4,4'-methylenebis[2-allylphenol], and acetonitrile were mixed in a mass ratio of 1:1.6:2.4:90, stirred at 20°C and 200 r / min for 20 min, and triethylamine (3 times the mass of hexachlorocyclotriphosphazene) was added, and the mixture was stirred for 4 h. The mixture was centrifuged, washed with anhydrous ethanol and deionized water 3 times each, and dried at 50°C for 12 h under vacuum conditions to obtain polyphosphazene microspheres; polyphosphazene microspheres and a 3% sodium hydroxide aqueous solution were mixed in a mass ratio of 1:20, stirred at 70°C and 200 r / min for 3 h, centrifuged, washed with a 1 mol / L hydrochloric acid aqueous solution and deionized water 4 times each, and dried at 50°C for 12 h under vacuum conditions to obtain modified polyphosphazene microspheres;

[0035] (2) Benzoyl peroxide and o-xylene were mixed in a mass ratio of 1:6 to prepare an initiator solution; polypropylene and o-xylene were mixed in a mass ratio of 1:4, stirred at 112 ° C, 200 r / min for 20 min, 3-butenoic acid (0.22 times the mass of polypropylene) was added, and stirring was continued for 20 min. Initiator solution (0.18 times the mass of polypropylene) was added dropwise at a constant speed within 40 min. After the addition was completed, the temperature was raised to 138 ° C, and the stirring reaction was continued for 5 h. The temperature was lowered to 49 ° C, and acetone (5 times the mass of polypropylene) was added and mixed evenly. The mixture was allowed to stand for 3 h, filtered, and heated to 70 ℃ and dried for 12 hours to obtain pre-modified polypropylene; pre-modified polypropylene and N,N-dimethylformamide were uniformly mixed in a mass ratio of 1:8, stirred at 100℃ and 200r / min for 14 minutes, 4-ethynylbenzene-1,2-diamine in an amount of 0.6 times the mass of pre-modified polypropylene was added, and a 3 mol / L hydrochloric acid aqueous solution in an amount of 2 times the mass of pre-modified polypropylene was added, and the mixture was stirred and refluxed at 100℃ and 200r / min for 4 hours, cooled to 60℃, and the pH was adjusted to 8 with a 10% mass fraction of sodium hydroxide aqueous solution, and dried at 70℃ under vacuum conditions for 10 hours to obtain modified polypropylene;

[0036] (3) Ethylboric acid and 3-mercaptopropylmethyldimethoxysilane were added to 1,4-dioxane (12 times the mass of ethylboric acid) in a molar ratio of 1:1.1, and the mixture was stirred at 84°C and 300 r / min for 90 minutes. Hexamethyldisiloxane (0.03 times the mass of 3-mercaptopropylmethyldimethoxysilane) was added and the mixture was stirred and reacted for 30 minutes. The mixture was dried at 60°C for 10 hours under vacuum to obtain polyborosiloxane.

[0037] (4) Weigh 98 parts of modified polypropylene, 7 parts of modified polyphosphazene microspheres, 8 parts of polyborosiloxane, and 1 part of benzoin dimethyl ether by mass; mix the modified polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether evenly, place them in an electrospinning device for melt electrospinning, set the spinneret aperture to 0.2 mm, the spinning temperature to 230 ° C, the spinning distance to 22 cm, the spinning voltage to 24 kV, the collecting drum speed to 90 r / min, and accumulate on the collecting drum to form a fiber membrane with a thickness of 28 μm; irradiate the fiber membrane with ultraviolet light with a maximum wavelength of 365 nm and a power of 100 W for 38 minutes to obtain a fire-retardant lithium battery separator.

[0038] Example 2:

[0039] A fire-retardant lithium battery separator, comprising the following preparation steps:

[0040] (1) Hexachlorocyclotriphosphazene, phenolsulfonylphthalide, 4,4'-methylenebis[2-allylphenol], and acetonitrile were mixed in a mass ratio of 1:1.7:2.5:95, stirred at 25°C and 250 r / min for 19 min, triethylamine (3.1 times the mass of hexachlorocyclotriphosphazene) was added, and the mixture was stirred for 3.5 h. The mixture was centrifuged, washed with anhydrous ethanol and deionized water 4 times each, and dried at 55°C for 11 h under vacuum conditions to obtain polyphosphazene microspheres; polyphosphazene microspheres and a 3.5% sodium hydroxide aqueous solution were mixed in a mass ratio of 1:21, stirred at 75°C and 250 r / min for 2.5 h, centrifuged, washed with a 1 mol / L hydrochloric acid aqueous solution and deionized water 5 times each, and dried at 55°C for 11 h under vacuum conditions to obtain modified polyphosphazene microspheres;

[0041] (2) Dibenzoyl peroxide and o-xylene were mixed evenly in a mass ratio of 1:6.5 to prepare an initiator solution; polypropylene and o-xylene were mixed evenly in a mass ratio of 1:4.5, stirred at 113 ° C, 250 r / min for 19 minutes, 3-butenoic acid (0.23 times the mass of polypropylene) was added, and stirring was continued for 19 minutes. Initiator solution (0.20 times the mass of polypropylene) was added dropwise at a uniform speed within 40 minutes. After the addition was completed, the temperature was raised to 140 ° C, and the reaction was continued with stirring for 4.5 hours. The temperature was lowered to 50 ° C, and acetone (5.5 times the mass of polypropylene) was added and mixed evenly. The mixture was allowed to stand for 2.5 hours, filtered, and vacuumed. The pre-modified polypropylene was dried at 75°C for 11 hours to obtain pre-modified polypropylene; the pre-modified polypropylene and N,N-dimethylformamide were uniformly mixed in a mass ratio of 1:9, stirred at 102°C and 250r / min for 13 minutes, 4-ethynylbenzene-1,2-diamine in an amount of 0.7 times the mass of the pre-modified polypropylene was added, and a 3 mol / L hydrochloric acid aqueous solution in an amount of 2.1 times the mass of the pre-modified polypropylene was added, and the mixture was stirred and refluxed at 102°C and 250r / min for 3.5 hours, cooled to 65°C, and the pH was adjusted to 8.5 with a 10% mass fraction of sodium hydroxide aqueous solution, and dried at 75°C under vacuum conditions for 9 hours to obtain modified polypropylene;

[0042] (3) Ethylboric acid and 3-mercaptopropylmethyldimethoxysilane were added to 1,4-dioxane (13 times the mass of ethylboric acid) in a molar ratio of 1:1.15, and the mixture was stirred at 85°C and 350 r / min for 85 minutes. Hexamethyldisiloxane (0.04 times the mass of 3-mercaptopropylmethyldimethoxysilane) was added and the mixture was stirred for 25 minutes. The mixture was dried at 65°C under vacuum for 9 hours to obtain polyborosiloxane.

[0043] (4) Weigh 100 parts of modified polypropylene, 7.5 parts of modified polyphosphazene microspheres, 9 parts of polyborosiloxane, and 1.3 parts of benzoin dimethyl ether by mass; mix the modified polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether evenly, place them in an electrospinning device for melt electrospinning, set the spinneret aperture to 0.25 mm, the spinning temperature to 235 ° C, the spinning distance to 23 cm, the spinning voltage to 25 kV, the collecting drum speed to 95 r / min, and accumulate on the collecting drum to form a fiber membrane with a thickness of 30 μm; irradiate the fiber membrane with ultraviolet light with a maximum wavelength of 365 nm and a power of 100 W for 40 minutes to obtain a fire-retardant lithium battery separator.

[0044] Example 3:

[0045] A fire-retardant lithium battery separator, comprising the following preparation steps:

[0046] (1) Hexachlorocyclotriphosphazene, phenolsulfonylphthalide, 4,4'-methylenebis[2-allylphenol], and acetonitrile were mixed in a mass ratio of 1:1.8:2.6:100, stirred at 30°C and 300 r / min for 18 min, triethylamine (3.2 times the mass of hexachlorocyclotriphosphazene) was added, and stirring was continued for 3 h. The mixture was centrifuged, washed with anhydrous ethanol and deionized water 5 times each, and dried at 60°C for 10 h under vacuum conditions to obtain polyphosphazene microspheres; polyphosphazene microspheres and a 4% sodium hydroxide aqueous solution were mixed in a mass ratio of 1:22, stirred at 80°C and 300 r / min for 2 h, centrifuged, washed with a 1 mol / L hydrochloric acid aqueous solution and deionized water 6 times each, and dried at 60°C for 10 h under vacuum conditions to obtain modified polyphosphazene microspheres;

[0047] (2) Benzoyl peroxide and o-xylene were mixed in a mass ratio of 1:7 to prepare an initiator solution; polypropylene and o-xylene were mixed in a mass ratio of 1:5, stirred at 114 ° C, 300 r / min for 18 minutes, 3-butenoic acid (0.24 times the mass of polypropylene) was added, and stirring was continued for 18 minutes. Initiator solution (0.22 times the mass of polypropylene) was added dropwise at a uniform speed within 40 minutes. After the addition was completed, the temperature was raised to 142 ° C, and the reaction was continued with stirring for 4 hours. The temperature was lowered to 51 ° C, acetone (6 times the mass of polypropylene) was added and mixed evenly, and the mixture was allowed to stand for 2 hours. The mixture was filtered and heated at 80 ° C under vacuum conditions. Dry for 10 hours to obtain pre-modified polypropylene; mix pre-modified polypropylene and N,N-dimethylformamide in a mass ratio of 1:10, stir at 104°C and 300 r / min for 12 minutes, add 0.8 times the mass of pre-modified polypropylene 4-ethynylbenzene-1,2-diamine, add 2.2 times the mass of pre-modified polypropylene and a 3 mol / L hydrochloric acid aqueous solution, stir and reflux at 104°C and 300 r / min for 3 hours, cool to 70°C, adjust the pH to 9 with a 10% mass fraction of sodium hydroxide aqueous solution, and dry at 80°C under vacuum conditions for 8 hours to obtain modified polypropylene;

[0048] (3) Ethylboric acid and 3-mercaptopropylmethyldimethoxysilane were added to 1,4-dioxane (14 times the mass of ethylboric acid) in a molar ratio of 1:1.2, and the mixture was stirred at 86°C and 400 r / min for 80 minutes. Hexamethyldisiloxane (0.05 times the mass of 3-mercaptopropylmethyldimethoxysilane) was added and the mixture was stirred and reacted for 20 minutes. The mixture was dried at 70°C under vacuum for 8 hours to obtain polyborosiloxane.

[0049] (4) Weigh 102 parts of modified polypropylene, 8 parts of modified polyphosphazene microspheres, 10 parts of polyborosiloxane, and 1.6 parts of benzoin dimethyl ether by mass; mix the modified polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether evenly, place them in an electrospinning device for melt electrospinning, set the spinneret aperture to 0.3 mm, the spinning temperature to 240 ° C, the spinning distance to 24 cm, the spinning voltage to 26 kV, the collecting drum speed to 100 r / min, and accumulate on the collecting drum to form a fiber membrane with a thickness of 32 μm; irradiate the fiber membrane with ultraviolet light with a maximum wavelength of 365 nm and a power of 100 W for 42 minutes to obtain a fire-retardant lithium battery separator.

[0050] Comparative Example 1:

[0051] The difference between the fire-retardant lithium battery separator of Comparative Example 1 and Example 2 lies in the difference in step (1). Step (1) is modified as follows: hexachlorocyclotriphosphazene, phenolsulfonylphthalide, 4,4'-methylenediphenol, and acetonitrile are mixed in a mass ratio of 1:1.7:2.5:95, stirred at 25°C and 250r / min for 19min, triethylamine 3.1 times the mass of hexachlorocyclotriphosphazene is added, stirring is continued for 3.5h, centrifuged, washed with anhydrous ethanol and deionized water 4 times each, and dried at 55°C for 11h under vacuum conditions to obtain polyphosphazene microspheres; polyphosphazene microspheres and a sodium hydroxide aqueous solution with a mass fraction of 3.5% are mixed in a mass ratio of 1:21, stirred at 75°C and 250r / min for 2.5h, centrifuged, washed with a 1mol / L hydrochloric acid aqueous solution and deionized water 5 times each, and dried at 55°C for 11h under vacuum conditions to obtain modified polyphosphazene microspheres. The remaining steps are the same as in Example 2.

[0052] Comparative Example 2:

[0053] The difference between the fire-retardant lithium battery separator of Comparative Example 2 and Example 2 lies in the difference in step (1). Step (1) is modified as follows: hexachlorocyclotriphosphazene, phenolsulfonylphthalein, 4,4'-methylenebis[2-allylphenol], and acetonitrile are uniformly mixed in a mass ratio of 1:1.7:2.5:95, stirred at 25°C and 250 r / min for 19 minutes, triethylamine (3.1 times the mass of hexachlorocyclotriphosphazene) is added, stirring is continued for 3.5 hours, centrifuged, washed with anhydrous ethanol and deionized water four times each, and dried at 55°C under vacuum for 11 hours to obtain modified polyphosphazene microspheres. The remaining steps are the same as in Example 2.

[0054] Comparative Example 3:

[0055] The flame-retardant lithium battery separator of Comparative Example 3 differs from that of Example 2 in that step (1) is omitted and step (4) is modified as follows: 100 parts of modified polypropylene, 9 parts of polyborosiloxane, and 1.3 parts of benzoin dimethyl ether are weighed by mass; the modified polypropylene, polyborosiloxane, and benzoin dimethyl ether are uniformly mixed and melt-spinned in an electrospinning apparatus, with the spinneret aperture being 0.25 mm, the spinning temperature being 235° C., the spinning distance being 23 cm, the spinning voltage being 25 kV, and the collection drum speed being 95 r / min. The fibers are deposited on the collection drum to form a fiber membrane having a thickness of 30 μm; the fiber membrane is irradiated with ultraviolet light having a maximum wavelength of 365 nm and a power of 100 W for 40 min to obtain a flame-retardant lithium battery separator. The remaining steps are the same as those of Example 2.

[0056] Comparative Example 4:

[0057] The difference between the fire-retardant lithium battery separator of Comparative Example 4 and Example 2 is that step (2) is different. Step (2) is modified as follows: dibenzoyl peroxide and o-xylene are mixed uniformly in a mass ratio of 1:6.5 to prepare an initiator solution; polypropylene and o-xylene are mixed uniformly in a mass ratio of 1:4.5, stirred at 113°C and 250r / min for 19min, 3-butenoic acid with a mass of 0.23 times that of polypropylene is added, stirring is continued for 19min, and the initiator solution with a mass of 0.20 times that of polypropylene is added dropwise at a uniform speed within 40min. After the addition is completed, the temperature is raised to 140°C, the reaction is continued with stirring for 4.5h, the temperature is lowered to 50°C, and propylene with a mass of 5.5 times that of polypropylene is added. The ketone was mixed evenly, allowed to stand for 2.5 hours, filtered, and dried at 75°C under vacuum for 11 hours to obtain pre-modified polypropylene. The pre-modified polypropylene and N,N-dimethylformamide were mixed evenly in a mass ratio of 1:9, stirred at 102°C and 250 rpm for 13 minutes, 1,2-phenylenediamine (0.7 times the mass of the pre-modified polypropylene) and a 3 mol / L hydrochloric acid aqueous solution (2.1 times the mass of the pre-modified polypropylene) were added, and the mixture was stirred and refluxed at 102°C and 250 rpm for 3.5 hours. The mixture was cooled to 65°C, the pH was adjusted to 8.5 with a 10% mass fraction of sodium hydroxide aqueous solution, and the mixture was dried at 75°C under vacuum for 9 hours to obtain modified polypropylene. The remaining steps were the same as in Example 2.

[0058] Comparative Example 5:

[0059] The flame-retardant lithium battery separator of Comparative Example 5 differs from that of Example 2 in that step (2) is omitted and step (4) is modified as follows: 100 parts of polypropylene, 7.5 parts of modified polyphosphazene microspheres, 9 parts of polyborosiloxane, and 1.3 parts of benzoin dimethyl ether are weighed by mass; the polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether are uniformly mixed and placed in an electrospinning apparatus for melt electrospinning, with the spinneret aperture being 0.25 mm, the spinning temperature being 235° C., the spinning distance being 23 cm, the spinning voltage being 25 kV, and the collection drum speed being 95 r / min. The fibers are deposited on the collection drum to form a fiber membrane with a thickness of 30 μm; the fiber membrane is irradiated with ultraviolet light having a maximum wavelength of 365 nm and a power of 100 W for 40 min to obtain a flame-retardant lithium battery separator. The remaining steps are the same as those of Example 2.

[0060] Comparative Example 6:

[0061] The flame-retardant lithium battery separator of Comparative Example 6 differs from that of Example 2 in that step (3) is omitted and step (4) is modified as follows: 100 parts of modified polypropylene, 7.5 parts of modified polyphosphazene microspheres, and 1.3 parts of benzoin dimethyl ether are weighed by mass; the modified polypropylene, modified polyphosphazene microspheres, and benzoin dimethyl ether are uniformly mixed and placed in an electrospinning apparatus for melt electrospinning, with the spinneret aperture being 0.25 mm, the spinning temperature being 235° C., the spinning distance being 23 cm, the spinning voltage being 25 kV, and the collection drum speed being 95 r / min. The fibers are deposited on the collection drum to form a fiber membrane with a thickness of 30 μm; the fiber membrane is irradiated with ultraviolet light having a maximum wavelength of 365 nm and a power of 100 W for 40 min to obtain a flame-retardant lithium battery separator. The remaining steps are the same as those of Example 2.

[0062] Comparative Example 7:

[0063] The difference between the fire-retardant lithium battery separator of Comparative Example 7 and Example 2 lies in the difference in step (4). Step (4) is modified as follows: 100 parts of modified polypropylene, 7.5 parts of modified polyphosphazene microspheres, 9 parts of polyborosiloxane, and 1.3 parts of benzoin dimethyl ether are weighed by mass; the modified polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether are mixed uniformly, placed in an electrospinning device for melt electrospinning, and the spinneret aperture is set to 0.25 mm, the spinning temperature is 235° C., the spinning distance is 23 cm, the spinning voltage is 25 kV, and the collection drum speed is 95 r / min. The fibers are accumulated on the collection drum to form a fiber membrane with a thickness of 30 μm, thereby preparing a fire-retardant lithium battery separator. The remaining steps are the same as in Example 2.

[0064] Test Example 1

[0065] Ionic conductivity test

[0066] 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.

[0067] Table 1

[0068]

[0069]

[0070] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 7 in Table 1, it can be found that the fire-resistant and flame-retardant lithium battery separator prepared by the present invention has good ionic conductivity.

[0071] By comparison, the ionic conductivities of Examples 1 to 3 are greater than those of Comparative Examples 2 to 3, indicating that the P-Cl bond of hexachlorocyclotriphosphazene reacts with the phenolic hydroxyl groups on phenolsulfonylphthalide and 4,4'-methylenebis[2-allylphenol] to prepare polyphosphazene microspheres, and sultone is introduced into the polyphosphazene microspheres; the polyphosphazene microspheres are treated with sodium hydroxide to cause the sultone ring to open to generate sulfonic acid groups and hydroxyl groups. Both sulfonic acid groups and hydroxyl groups are polar groups and can improve the wettability of the battery separator with the electrolyte, thereby improving the ionic conductivity of the fire-retardant lithium battery separator.

[0072] By comparison, the ionic conductivity of Examples 1 to 3 is greater than that of Comparative Example 5, indicating that 3-butenoic acid is grafted onto the side chain of the polypropylene molecule by a solution grafting method to prepare a pre-modified polypropylene, and a carboxyl group is introduced into the side chain of the pre-modified polypropylene molecule; the carboxyl group introduced into the side chain of the pre-modified polypropylene is reacted with 4-ethynylbenzene-1,2-diamine to prepare a modified polypropylene, and a benzimidazole structure is generated on the modified polypropylene; the NH bond in the benzimidazole structure can produce a hydrogen bond complex with the anion in the electrolyte, promote the formation of a solvation sheath, and promote the migration and deintercalation process of lithium ions, thereby improving the ionic conductivity of the fire-retardant lithium battery separator.

[0073] Test Example 2

[0074] Flame retardant performance test

[0075] 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.

[0076] Table 2

[0077]

[0078]

[0079] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 7 in Table 2, it can be found that the fireproof and flame-retardant lithium battery separator prepared by the present invention has good flame retardant properties.

[0080] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 3, indicating that polyphosphazene microspheres are prepared by reacting the P-Cl bond of hexachlorocyclotriphosphazene with the phenolic hydroxyl groups on phenolsulfonylphthalide and 4,4'-methylenebis[2-allylphenol], and that cyclotriphosphazene is introduced into the polyphosphazene microspheres. The cyclotriphosphazene introduced into the polyphosphazene microspheres can improve the flame retardant properties of the fire-retardant lithium battery separator.

[0081] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 6, indicating that polyborosiloxane is prepared by polymerizing ethylboric acid and 3-mercaptopropylmethyldimethoxysilane; the polyborosiloxane structure contains boron elements and Si-O-Si bonds, and can form a dense expanded carbon layer during combustion, thereby preventing heat transfer and the spread of oxygen, and further improving the flame retardant properties of the flame retardant lithium battery separator.

[0082] Test Example 3

[0083] Mechanical properties testing

[0084] Test method: According to GB / T1040.3-2006, the tensile strength of standard specimens was tested using an electronic universal testing machine. The results are shown in Table 3.

[0085] Table 3

[0086]

[0087]

[0088] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 7 in Table 3, it can be found that the fire-resistant and flame-retardant lithium battery separator prepared by the present invention has good mechanical properties.

[0089] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 1 and 3, indicating that the P-Cl bond of hexachlorocyclotriphosphazene is reacted with the phenolic hydroxyl groups on phenolsulfonylphthalide and 4,4'-methylenebis[2-allylphenol] to prepare polyphosphazene microspheres, and carbon-carbon double bonds are introduced into the polyphosphazene microspheres; the carbon-carbon double bonds introduced into the polyphosphazene microspheres can undergo an addition reaction with the thiol groups on the polyborosiloxane under the action of a photoinitiator and ultraviolet light to form a cross-linked network, thereby improving the mechanical properties of the fire-retardant lithium battery separator.

[0090] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 4 to 5, indicating that 3-butenoic acid is grafted onto the side chain of the polypropylene molecule by a solution grafting method to prepare a pre-modified polypropylene, and a carboxyl group is introduced into the side chain of the pre-modified polypropylene molecule; the carboxyl group introduced into the side chain of the pre-modified polypropylene is reacted with 4-ethynylbenzene-1,2-diamine to prepare a modified polypropylene, and an alkynyl group is introduced into the modified polypropylene; the alkynyl group introduced into the side chain of the modified polypropylene molecule can undergo an addition reaction with the thiol group on the polyborosiloxane under the action of a photoinitiator and ultraviolet light to form a cross-linked network, thereby improving the mechanical properties of the flame-retardant lithium battery separator.

[0091] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 6 to 7, indicating that polyborosiloxane is prepared by polymerizing ethylboric acid and 3-mercaptopropylmethyldimethoxysilane; and a mercapto group is introduced into the side chain of the polyborosiloxane molecule; the mercapto group introduced into the side chain of the polyborosiloxane molecule can undergo addition reaction with the acetylenic group on the modified polypropylene and the carbon-carbon double bond on the modified polyphosphazene microspheres under the action of a photoinitiator and ultraviolet light to form a cross-linked network structure, thereby improving the mechanical properties of the flame-retardant lithium battery separator.

[0092] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method 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 in the scope of protection of the present invention.

Claims

1. A fire-retardant lithium battery separator, characterized in that: The fire-retardant lithium battery separator is prepared by treating polyphosphazene microspheres with sodium hydroxide to obtain modified polyphosphazene microspheres; reacting pre-modified polypropylene and 4-ethynylbenzene-1,2-diamine to obtain modified polypropylene; uniformly mixing the modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether, electrospinning, and then irradiating with ultraviolet light. The polyphosphazene microspheres are prepared by reacting hexachlorocyclotriphosphazene, phenolsulfonylphthalide and 4,4'-methylenebis[2-allylphenol]. The pre-modified polypropylene is prepared by reacting polypropylene and 3-butenoic acid; The polyborosiloxane is prepared by polymerizing ethylboric acid and 3-mercaptopropylmethyldimethoxysilane.

2. The fire-retardant lithium battery separator according to claim 1, characterized in that The fire-retardant lithium battery separator comprises the following preparation steps: (1) Polyphosphazene microspheres and sodium hydroxide aqueous solution are mixed uniformly in a mass ratio of 1:(20-22), stirred at 70-80°C and 200-300 r / min for 2-3 h, centrifuged, washed with 1 mol / L hydrochloric acid aqueous solution and deionized water 4-6 times each, and dried at 50-60°C under vacuum conditions for 10-12 h to obtain modified polyphosphazene microspheres; (2) Pre-modified polypropylene and N,N-dimethylformamide were mixed uniformly in a mass ratio of 1:(8-10), stirred at 100-104°C and 200-300 r / min for 12-14 min, 0.6-0.8 times the mass of pre-modified polypropylene of 4-ethynylbenzene-1,2-diamine and 2-2.2 times the mass of pre-modified polypropylene of 3 mol / L hydrochloric acid aqueous solution were added, stirred and refluxed at 100-104°C and 200-300 r / min for 3-4 h, cooled to 60-70°C, adjusted to pH 8-9 with a mass fraction of 10% sodium hydroxide aqueous solution, and dried at 70-80°C under vacuum for 8-10 h to obtain modified polypropylene; (3) adding ethylboric acid and 3-mercaptopropylmethyldimethoxysilane in a molar ratio of 1:(1.1-1.2) to 12-14 times the mass of 1,4-dioxane by weight of ethylboric acid, stirring and reacting at 84-86°C and 300-400 r / min for 80-90 minutes, adding hexamethyldisiloxane by weight of 0.03-0.05 times the mass of 3-mercaptopropylmethyldimethoxysilane, continuing to stir and react for 20-30 minutes, and drying at 60-70°C under vacuum conditions for 8-10 hours to obtain polyborosiloxane; (4) Weigh 98 to 102 parts of modified polypropylene, 7 to 8 parts of modified polyphosphazene microspheres, 8 to 10 parts of polyborosiloxane, and 1 to 1.6 parts of benzoin dimethyl ether by mass; mix the modified polypropylene, modified polyphosphazene microspheres, polyborosiloxane, and benzoin dimethyl ether evenly, place them in an electrospinning device for melt electrospinning, and deposit them on a collecting drum to form a fiber membrane with a thickness of 28 to 32 μm; irradiate the fiber membrane with ultraviolet light with a maximum wavelength of 365 nm and a power of 100 W for 38 to 42 minutes to obtain a fire-retardant lithium battery separator.

3. The fire-retardant lithium battery separator according to claim 2, characterized in that: The preparation method of the polyphosphazene microspheres in step (1) is as follows: hexachlorocyclotriphosphazene, phenolsulfonylphthalein, 4,4'-methylenebis[2-allylphenol], and acetonitrile are uniformly mixed in a mass ratio of 1:(1.6-1.8):(2.4-2.6):(90-100), stirred at 200-300 r / min for 18-20 min at 20-30° C., triethylamine in an amount of 3-3.2 times the mass of hexachlorocyclotriphosphazene is added, stirring is continued for 3-4 h, centrifuged, washed with anhydrous ethanol and deionized water for 3-5 times each, and dried at 50-60° C. under vacuum conditions for 10-12 h to obtain the polyphosphazene microspheres.

4. The fire-retardant lithium battery separator according to claim 2, characterized in that: The mass fraction of the sodium hydroxide aqueous solution in step (1) is 3% to 4%.

5. The fire-retardant lithium battery separator according to claim 2, characterized in that: The preparation method of the pre-modified polypropylene in step (2) is as follows: polypropylene and o-xylene are mixed uniformly in a mass ratio of 1:(4-5), stirred at 112-114° C. and 200-300 r / min for 18-20 min, 3-butenoic acid in an amount of 0.22-0.24 times the mass of the polypropylene is added, stirring is continued for 18-20 min, an initiator solution in an amount of 0.18-0.22 times the mass of the polypropylene is added dropwise at a uniform rate within 40 min, the temperature is raised to 138-142° C. after the addition is complete, the stirring reaction is continued for 4-5 h, the temperature is lowered to 49-51° C., acetone in an amount of 5-6 times the mass of the polypropylene is added and mixed uniformly, the mixture is allowed to stand for 2-3 h, filtered, and dried at 70-80° C. under vacuum conditions for 10-12 h to obtain the pre-modified polypropylene.

6. The fire-retardant lithium battery separator according to claim 5, characterized in that: The preparation method of the initiator solution is as follows: dibenzoyl peroxide and o-xylene are uniformly mixed in a mass ratio of 1:(6-7) to prepare the initiator solution.

7. The fire-retardant lithium battery separator according to claim 5, characterized in that: The type of the polypropylene is PP S2040.

8. The fire-retardant lithium battery separator according to claim 2, characterized in that: The process parameters of the melt electrospinning in step (4) are as follows: the spinneret aperture is set to 0.2-0.3 mm, the spinning temperature is 230-240° C., the spinning distance is 22-24 cm, the spinning voltage is 24-26 kV, and the collection drum speed is 90-100 r / min.

9. A fire-retardant lithium battery, characterized in that: The battery separator of the fire-proof and flame-retardant lithium battery is the fire-proof and flame-retardant lithium battery separator according to any one of claims 1 to 8.

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