A high ionic conductivity lithium ion battery separator and preparation method thereof

Abstract

The present invention discloses a high-ionic conductivity lithium-ion battery separator and a preparation method thereof, relating to the technical field of battery separators. In preparing the high-ionic conductivity lithium-ion battery separator, the present invention comprises the following steps: reacting chitosan porous microspheres with 1,3-propane sultone to produce functionalized chitosan porous microspheres; polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane to produce functionalized polysiloxane; reacting polypropylene with 1,4-diamino-2-butene to produce pre-modified polypropylene; reacting pre-modified polypropylene with formaldehyde and allyl hypophosphorous acid to produce modified polypropylene; and uniformly mixing the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile, and performing melt electrospinning to produce the high-ionic conductivity lithium-ion battery separator. The high-ionic conductivity lithium-ion battery separator prepared by the present invention has excellent ionic conductivity, flame retardancy, and mechanical properties.

Description

Technical Field

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

[0002] Lithium-ion batteries, with their high specific energy density, excellent cycle performance, and environmental friendliness, have led to their widespread use in electric vehicles, electronics, energy storage, and other fields, making them the most ideal power source and energy storage system. Lithium-ion batteries consist of four main components: a positive electrode, a negative electrode, a battery separator, and an organic electrolyte. The battery separator, located between the positive and negative electrodes, separates them, preventing direct contact that could lead to short circuits and potential safety accidents. It also blocks electrons and absorbs a certain amount of electrolyte, providing a pathway for lithium ions to transfer.

[0003] Polyolefin battery separators are the most prevalent commercial battery separators on the market due to their low cost and stable electrochemical properties. However, they also have significant drawbacks, such as poor wettability with electrolytes and flammability. In recent years, thermal runaway of lithium-ion batteries has led to frequent incidents of spontaneous combustion and explosions in electronic devices, severely damaging property and personal safety. This has led to a growing awareness of the safety of lithium-ion batteries.

[0004] Based on the above problems, it is necessary to improve the existing technology and prepare a lithium-ion battery separator with high flame retardancy and high ion conductivity to improve the electrical performance and safety of lithium-ion batteries. Summary of the Invention

[0005] The object of the present invention is to provide a lithium ion battery separator with high ionic conductivity and a preparation method thereof, so as to solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A high-ion conductivity lithium-ion battery separator is provided. The high-ion conductivity lithium-ion battery separator is prepared by reacting chitosan porous microspheres and 1,3-propane sultone to obtain functionalized chitosan porous microspheres; polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane to obtain functionalized polysiloxane; reacting pre-modified polypropylene and allyl hypophosphorous acid to obtain modified polypropylene; and uniformly mixing the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile, and performing melt electrostatic spinning to obtain the high-ion conductivity lithium-ion battery separator.

[0008] The chitosan porous microspheres are prepared by using chitosan as raw material, 1,4-dichloro-2-butene as crosslinking agent, and melamine as chain extender through a reverse suspension crosslinking method.

[0009] The functionalized dimethoxysilane is prepared by reacting 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde;

[0010] The pre-modified polypropylene is prepared by reacting polypropylene and 1,4-diamino-2-butene.

[0011] A method for preparing a high ionic conductivity lithium ion battery separator, the method comprising the following steps:

[0012] (1) 1,3-propane sultone and acetonitrile were mixed at a mass ratio of 1:(4~5) to prepare a 1,3-propane sultone solution; chitosan porous microspheres and acetonitrile were mixed at a mass ratio of 1:(50~60) to prepare a 1,3-propane sultone solution; chitosan porous microspheres were mixed at a mass ratio of 1:(50~60) to prepare a 1,3-propane sultone solution; chitosan porous microspheres were ultrasonically dispersed for 30~40 min; under nitrogen protection, at 70~72 ° C, 200~300 r / min stirring conditions, 12~14 times the mass of chitosan porous microspheres were added dropwise at a constant speed within 30 min; after the addition was completed, the mixture was stirred for 10~12 h, cooled to room temperature naturally, filtered, washed with acetone 3~5 times, and dried at 50~60 ° C under vacuum conditions for 8~10 h to prepare functionalized chitosan porous microspheres;

[0013] (2) Functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water are mixed in a mass ratio of 1:(1.3~1.5):(40~50), stirred at 0~2°C and 200~300r / min for 20~30min, and dimethyldichlorosilane (4~5 times the mass of mercaptopropylmethyldimethoxysilane) is uniformly added dropwise within 20min. After the addition is completed, stirring is continued for 10~12min, the temperature is raised to 64~66°C, and the stirring reaction is continued for 4~5h. Acidic white clay (0.06~0.08 times the mass of mercaptopropylmethyldimethoxysilane) is added, the temperature is raised to 98~102°C, and the stirring reaction is continued for 3~4h. The acidic white clay is filtered out, and the filtrate is dried at 70~80°C under vacuum conditions for 16~18h to obtain functionalized polysiloxane;

[0014] (3) Pre-modified polypropylene and m-xylene were mixed uniformly in a mass ratio of 1:(7~8), stirred at 100~102℃ and 100~200r / min for 10~12min, added allyl hypophosphorous acid in an amount of 0.2~0.3 times the mass of pre-modified polypropylene, and then added formaldehyde in an amount equivalent to allyl hypophosphorous acid, and continued to stir and react for 70~80min, cooled to 50~52℃, added acetone in an amount of 3~4 times the mass of pre-modified polypropylene, mixed uniformly, allowed to stand for 1~2h, filtered, and dried at 60~70℃ under vacuum conditions for 10~12h to obtain modified polypropylene;

[0015] (4) Weigh 98-102 parts of modified polypropylene, 5-6 parts of functionalized chitosan porous microspheres, 8-10 parts of functionalized polysiloxane, and 1-2 parts of azobisisobutyronitrile by mass; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile 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 26-28 μm; let the fiber membrane stand at 70-80°C for 2-3 hours, and cool to room temperature to obtain a lithium-ion battery separator with high ionic conductivity.

[0016] As an optimization, the preparation method of the chitosan porous microspheres in step (1) is as follows: chitosan solution, melamine, 1,4-dichloro-2-butene, and anhydrous ethanol are mixed uniformly in a mass ratio of 1:(0.2~0.3):(0.6~0.8):(2~3), 0.06~0.08 times the mass of the chitosan solution of Span-60 and 3~4 times the mass of the chitosan solution of liquid paraffin are added, the temperature is raised to 40~42°C, stirring is continued for 10~20min, the pH is adjusted to 9~10 with a 1mol / L sodium hydroxide aqueous solution, the temperature is raised to 70~80°C, stirring is continued for 1~2h, the mixture is naturally cooled to room temperature, filtered, washed with deionized water 3~5 times, and freeze-dried at -10~-8°C for 40~48h to obtain chitosan porous microspheres.

[0017] As an optimization, the preparation method of the chitosan solution is: chitosan and a 0.1 mol / L hydrochloric acid aqueous solution are uniformly mixed in a mass ratio of 1:(4~6), and stirred at 10~30°C and 200~300 r / min for 20~30 minutes to obtain a chitosan solution.

[0018] As an optimization, the chitosan has a deacetylation degree of 95% and a weight average molecular weight of 85 kDa.

[0019] As an optimization, the preparation method of the functionalized dimethoxysilane in step (2) is as follows: 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde are added in a molar ratio of 1:1 to toluene with a mass 10 to 12 times that of 3-aminopropyldimethoxymethylsilane, and the mixture is stirred at 50 to 60°C and 200 to 300 r / min for 5 to 6 hours, and dried at 50 to 60°C under vacuum conditions for 10 to 12 hours to obtain the functionalized dimethoxysilane.

[0020] As an optimization, the CAS number of the allyl hypophosphorous acid in step (3) is 66899-05-6; the structural formula is: .

[0021] As an optimization, the preparation method of the pre-modified polypropylene in step (3) is as follows: polypropylene and m-xylene are mixed uniformly in a mass ratio of 1:(3~4), stirred at 108~110℃ and 100~200r / min for 10~12min, 1,4-diamino-2-butene in an amount of 0.2~0.3 times the mass of polypropylene is added, and stirring is continued for 8~10min. An initiator solution in an amount of 0.1~0.2 times the mass of polypropylene is added dropwise at a uniform rate within 30min. After the addition is completed, the temperature is raised to 130~132℃, and the stirring reaction is continued for 2~3h. The temperature is lowered to 50~52℃, acetone in an amount of 3~4 times the mass of polypropylene is added and mixed uniformly, and the mixture is allowed to stand for 1~2h, filtered, and dried at 60~70℃ under vacuum conditions for 8~10h to obtain pre-modified polypropylene.

[0022] As an optimization, the preparation method of the initiator solution is: dibenzoyl peroxide and m-xylene are uniformly mixed in a mass ratio of 1:(5~6) to prepare an initiator solution.

[0023] As an optimization, the model of the polypropylene is PP N-Z30S.

[0024] As an optimization, the process parameters of the melt electrospinning in step (4) are as follows: the spinneret aperture is set to 0.1-0.2 mm, the spinning temperature is set to 230-240 °C, the spinning distance is set to 18-20 cm, the spinning voltage is set to 19-21 kV, and the collection drum speed is set to 90-100 r / min.

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

[0026] The invention prepares a lithium ion battery separator with high ion conductivity by using chitosan as a raw material, 1,4-dichloro-2-butene as a crosslinking agent, and melamine as a chain extender, and adopts a reverse suspension crosslinking method to prepare chitosan porous microspheres; the chitosan porous microspheres and 1,3-propane sultone are reacted to prepare functionalized chitosan porous microspheres; 3-aminopropyl dimethoxymethylsilane and 4-pyridine formaldehyde are reacted to prepare functionalized dimethoxysilane; the functionalized dimethoxy Functionalized polysiloxane is prepared by condensation of silane, mercaptopropylmethyldimethoxysilane and dimethyldichlorosilane; pre-modified polypropylene is prepared by reacting polypropylene and 1,4-diamino-2-butene; modified polypropylene is prepared by reacting pre-modified polypropylene, formaldehyde and allyl hypophosphorous acid; modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane and azobisisobutyronitrile are uniformly mixed and melt electrospun to obtain a lithium-ion battery separator with high ionic conductivity.

[0027] Firstly, chitosan was used as raw material, 1,4-dichloro-2-butene was used as cross-linking agent, and melamine was used as chain extender. Chitosan porous microspheres were prepared by reverse suspension cross-linking method, and amino groups and carbon-carbon double bonds were introduced into the chitosan porous microspheres. The carbon-carbon double bonds on the chitosan porous microspheres can react with the thiol groups on the functionalized polysiloxane to form a cross-linked network structure, thereby improving the mechanical properties of the high ion conductivity lithium-ion battery separator. The amino groups on the chitosan porous microspheres were reacted with 1,3-propane sultone to prepare the functionalized polysiloxane. Functionalized chitosan porous microspheres; 3-propane sultone undergoes a ring-opening reaction to generate a large number of sulfonic acid groups on the functionalized chitosan porous microspheres. The sulfonic acid groups have strong polarity and interact with the ions in the electrolyte to increase the mobility of lithium ions, thereby improving the ionic conductivity of high ionic conductivity lithium-ion battery separators; chitosan is a natural polysaccharide with a large number of hydroxyl groups in its structure, which can improve the wettability of the battery separator and the electrolyte, thereby improving the ionic conductivity of high ionic conductivity lithium-ion battery separators.

[0028] Secondly, 3-aminopropyldimethoxymethylsilane and 4-pyridine formaldehyde are reacted to obtain functionalized dimethoxysilane; functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane are condensed to obtain functionalized polysiloxane, and pyridine groups and mercapto groups are introduced into the side chains of the functionalized polysiloxane molecules; during the transmission of lithium ions, the reverse moving free anions will also hinder the migration of lithium ions, resulting in uneven lithium ion transmission. The pyridine group is protonated in the electrolyte and carries a positive charge. The positively charged pyridine group can fix the anions in the electrolyte, promote lithium ion transmission, and prevent parasitic reactions caused by acid. , so that the transmission of lithium ions is not interfered with by anions, thereby improving the ionic conductivity of the high ionic conductivity lithium ion battery separator; the thiol group introduced into the side chain of the functionalized polysiloxane can react with the carbon-carbon double bonds introduced into the functionalized chitosan porous microspheres and the modified polypropylene to form a cross-linked network, inhibiting the relative sliding between molecular chains and improving the mechanical properties of the high ionic conductivity lithium ion battery separator; the Si-O-Si bond in the functionalized polysiloxane forms a silicon-containing carbon layer during the combustion process, which can insulate heat and oxygen, thereby preventing further thermal decomposition and combustion of the polymer material, and improving the flame retardant properties of the high ionic conductivity lithium ion battery separator.

[0029] Finally, 1,4-diamino-2-butene was grafted onto the side chain of polypropylene molecules through a solution grafting method to obtain pre-modified polypropylene, and amino groups were introduced into the side chains of the pre-modified polypropylene molecules; the amino groups introduced into the side chains of the pre-modified polypropylene molecules were reacted with formaldehyde and allyl hypophosphorous acid to obtain modified polypropylene, and phosphorus elements and carbon-carbon double bonds were introduced into the side chains of the modified polypropylene molecules; the introduction of phosphorus elements can improve the flame retardant properties of high ion conductivity lithium-ion battery separators; the carbon-carbon double bonds can undergo addition reactions with the thiol groups on the functionalized polysiloxane to form a cross-linked network, inhibiting the relative movement between molecular chains and improving the mechanical properties of high ion conductivity lithium-ion battery separators. 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] Example 1:

[0032] A method for preparing a high ionic conductivity lithium ion battery separator, the method comprising the following steps:

[0033] (1) Chitosan and 0.1 mol / L hydrochloric acid aqueous solution were mixed in a mass ratio of 1:4, and stirred at 10°C and 200 r / min for 30 min to prepare chitosan solution; chitosan solution, melamine, 1,4-dichloro-2-butene, and anhydrous ethanol were mixed in a mass ratio of 1:0.2:0.6:2, and 0.06 times the mass of the chitosan solution of Siban-60 and 3 times the mass of the chitosan solution of liquid paraffin were added, the temperature was raised to 40°C, and the stirring was continued for 20 min. The pH was adjusted to 9 with a 1 mol / L sodium hydroxide aqueous solution, the temperature was raised to 70°C, and the stirring was continued for 2 h. The mixture was naturally cooled to room temperature, filtered, and washed with deionized water for 3 times. , freeze-dried at -10 ° C for 40 hours to obtain chitosan porous microspheres; 1,3-propane sultone and acetonitrile were mixed at a mass ratio of 1:4 to prepare a 1,3-propane sultone solution; chitosan porous microspheres and acetonitrile were mixed at a mass ratio of 1:50, ultrasonically dispersed for 30 minutes, and under nitrogen protection, at 70 ° C, 200 r / min stirring conditions, 12 times the mass of the chitosan porous microspheres 1,3-propane sultone solution was uniformly added dropwise within 30 minutes. After the addition was completed, the reaction was continued with stirring for 12 hours, naturally cooled to room temperature, filtered, washed with acetone 3 times, and dried at 50 ° C under vacuum conditions for 10 hours to obtain functionalized chitosan porous microspheres;

[0034] (2) 3-aminopropyldimethoxymethylsilane and 4-pyridine formaldehyde were added to toluene with a mass ratio of 1:1, stirred at 50 ° C, 200 r / min for 6 h, and dried at 50 ° C for 12 h under vacuum conditions to obtain functionalized dimethoxysilane; functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane and deionized water were mixed at a mass ratio of 1:1.3:40, and dried at 0 ° C, 200 r / min for 12 h. / min and stirred for 30 minutes, and dimethyldichlorosilane (4 times the mass of mercaptopropylmethyldimethoxysilane) was uniformly added dropwise within 20 minutes. After the addition was completed, stirring was continued for 12 minutes, the temperature was raised to 64°C, and the stirring reaction was continued for 5 hours. Acidic white clay (0.06 times the mass of mercaptopropylmethyldimethoxysilane) was added, the temperature was raised to 98°C, and the stirring reaction was continued for 4 hours. The acidic white clay was filtered out, and the filtrate was dried at 70°C under vacuum conditions for 18 hours to obtain functionalized polysiloxane;

[0035] (3) Dibenzoyl peroxide and m-xylene were mixed evenly in a mass ratio of 1:5 to prepare an initiator solution; polypropylene and m-xylene were mixed evenly in a mass ratio of 1:3, stirred at 108°C and 100 r / min for 12 minutes, 1,4-diamino-2-butene (0.2 times the mass of polypropylene) was added, and stirring was continued for 10 minutes. Initiator solution (0.1 times the mass of polypropylene) was added dropwise at a uniform speed within 30 minutes. After the addition was completed, the temperature was raised to 130°C, and the reaction was continued with stirring for 3 hours. The temperature was lowered to 50°C, and acetone (3 times the mass of polypropylene) was added and mixed evenly. The mixture was allowed to stand for 1 hour, filtered, and dried at 60°C for 10 hours under vacuum conditions to obtain pre-modified polypropylene; the pre-modified polypropylene and m-xylene were mixed uniformly in a mass ratio of 1:7, stirred at 100°C and 100 r / min for 12 minutes, allyl hypophosphorous acid in an amount 0.2 times the mass of the pre-modified polypropylene was added, and then formaldehyde in an amount equimolar to the allyl hypophosphorous acid was added, and the mixture was stirred and reacted for 80 minutes, cooled to 50°C, acetone in an amount 3 times the mass of the pre-modified polypropylene was added and mixed uniformly, allowed to stand for 1 hour, filtered, and dried at 60°C for 12 hours under vacuum conditions to obtain modified polypropylene;

[0036] (4) Weigh 98 parts of modified polypropylene, 5 parts of functionalized chitosan porous microspheres, 8 parts of functionalized polysiloxane, and 1 part of azobisisobutyronitrile by mass; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, set the spinneret aperture to 0.1 mm, the spinning temperature to 230 ° C, the spinning distance to 18 cm, the spinning voltage to 19 kV, the collection drum speed to 90 r / min, and accumulate on the collection drum to form a fiber membrane with a thickness of 26 μm; let the fiber membrane stand at 70 ° C for 3 h, and cool to room temperature to obtain a high ion conductivity lithium ion battery separator.

[0037] Example 2:

[0038] A method for preparing a high ionic conductivity lithium ion battery separator, the method comprising the following steps:

[0039] (1) Chitosan and 0.1 mol / L hydrochloric acid aqueous solution were mixed in a mass ratio of 1:5, and stirred at 20°C and 250 r / min for 25 min to prepare chitosan solution; chitosan solution, melamine, 1,4-dichloro-2-butene, and anhydrous ethanol were mixed in a mass ratio of 1:0.25:0.7:2.5, and 0.07 times the mass of the chitosan solution of Siban-60 and 3.5 times the mass of the chitosan solution of liquid paraffin were added, the temperature was raised to 41°C, and the stirring was continued for 15 min. The pH was adjusted to 9.5 with a 1 mol / L sodium hydroxide aqueous solution, the temperature was raised to 75°C, and the stirring was continued for 1.5 h. The mixture was naturally cooled to room temperature, filtered, and washed with deionized water. Wash 4 times, freeze-dry at -9 ° C for 44 hours to prepare chitosan porous microspheres; 1,3-propane sultone and acetonitrile are mixed at a mass ratio of 1:4.5 to prepare 1,3-propane sultone solution; chitosan porous microspheres and acetonitrile are mixed at a mass ratio of 1:55, ultrasonically dispersed for 35 minutes, and under nitrogen protection, at 71 ° C, 250 r / min stirring conditions, 13 times the mass of the chitosan porous microspheres 1,3-propane sultone solution is added dropwise at a constant speed within 30 minutes. After the addition is completed, the reaction is continued with stirring for 11 hours, naturally cooled to room temperature, filtered, washed with acetone 4 times, and dried at 55 ° C under vacuum conditions for 9 hours to prepare functionalized chitosan porous microspheres;

[0040] (2) 3-aminopropyldimethoxymethylsilane and 4-pyridine formaldehyde were added to toluene (11 times the mass of 3-aminopropyldimethoxymethylsilane) in a molar ratio of 1:1, stirred at 55°C, 250 r / min for 5.5 h, and dried at 55°C for 11 h under vacuum conditions to obtain functionalized dimethoxysilane; functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water were mixed in a mass ratio of 1:1.4:45, and stirred at 1°C, 250 r / min for 5.5 h. The mixture was stirred for 25 minutes, and dimethyldichlorosilane (4.5 times the mass of mercaptopropylmethyldimethoxysilane) was added dropwise at a uniform rate within 20 minutes. After the addition was completed, stirring was continued for 11 minutes. The mixture was heated to 65°C and stirred for 4.5 hours. Acidic clay (0.07 times the mass of mercaptopropylmethyldimethoxysilane) was added, the mixture was heated to 100°C, and stirred for 3.5 hours. The acidic clay was filtered out, and the filtrate was dried at 75°C under vacuum for 17 hours to obtain a functionalized polysiloxane.

[0041] (3) Dibenzoyl peroxide and m-xylene were mixed evenly at a mass ratio of 1:5.5 to prepare an initiator solution; polypropylene and m-xylene were mixed evenly at a mass ratio of 1:3.5, stirred at 109°C and 150r / min for 11 minutes, 1,4-diamino-2-butene (0.25 times the mass of polypropylene) was added, and stirring was continued for 9 minutes. Initiator solution (0.15 times the mass of polypropylene) was added dropwise at a constant speed within 30 minutes. After the addition was completed, the temperature was raised to 131°C, and the reaction was continued with stirring for 2.5 hours. The temperature was lowered to 51°C, and acetone (3.5 times the mass of polypropylene) was added and mixed evenly. , let it stand for 1.5 hours, filter, and dry at 65°C under vacuum conditions for 9 hours to obtain pre-modified polypropylene; the pre-modified polypropylene and m-xylene were mixed uniformly in a mass ratio of 1:7.5, stirred at 101°C and 150r / min for 11 minutes, allyl hypophosphorous acid in an amount 0.25 times the mass of the pre-modified polypropylene was added, and then allyl hypophosphorous acid was added in an amount of formaldehyde in an amount equimolar to that of the pre-modified polypropylene, and the stirring reaction was continued for 75 minutes, cooled to 51°C, acetone in an amount 3.5 times the mass of the pre-modified polypropylene was added and mixed uniformly, let it stand for 1.5 hours, filter, and dry at 65°C under vacuum conditions for 11 hours to obtain modified polypropylene;

[0042] (4) Weigh 100 parts of modified polypropylene, 5.5 parts of functionalized chitosan porous microspheres, 9 parts of functionalized polysiloxane, and 1.5 parts of azobisisobutyronitrile by mass; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, set the spinneret aperture to 0.15 mm, the spinning temperature to 235 ° C, the spinning distance to 19 cm, the spinning voltage to 20 kV, the collection drum speed to 95 r / min, and accumulate on the collection drum to form a fiber membrane with a thickness of 27 μm; let the fiber membrane stand at 75 ° C for 2.5 h, and cool to room temperature to obtain a high ionic conductivity lithium ion battery separator.

[0043] Example 3:

[0044] A method for preparing a high ionic conductivity lithium ion battery separator, the method comprising the following steps:

[0045] (1) Chitosan and 0.1 mol / L hydrochloric acid aqueous solution were mixed in a mass ratio of 1:6, and stirred at 30°C and 300 r / min for 20 min to prepare chitosan solution; chitosan solution, melamine, 1,4-dichloro-2-butene, and anhydrous ethanol were mixed in a mass ratio of 1:0.3:0.8:3, and 0.08 times the mass of the chitosan solution of Siban-60 and 4 times the mass of the chitosan solution of liquid paraffin were added, and the mixture was heated to 42°C and stirred for 10 min. The pH was adjusted to 10 with a 1 mol / L sodium hydroxide aqueous solution, and the mixture was heated to 80°C and stirred for 1 h. The mixture was naturally cooled to room temperature, filtered, and washed with deionized water for 5 min. The chitosan porous microspheres were prepared by freeze-drying at -8 ° C for 48 hours; 1,3-propane sultone and acetonitrile were mixed at a mass ratio of 1:5 to prepare a 1,3-propane sultone solution; the chitosan porous microspheres and acetonitrile were mixed at a mass ratio of 1:60, ultrasonically dispersed for 40 minutes, and under nitrogen protection, 14 times the mass of the chitosan porous microspheres was added dropwise at a constant speed within 30 minutes at 72 ° C and 300 r / min stirring conditions. After the addition was completed, the reaction was continued with stirring for 10 hours, and the mixture was naturally cooled to room temperature, filtered, washed with acetone 5 times, and dried at 60 ° C under vacuum conditions for 8 hours to prepare functionalized chitosan porous microspheres;

[0046] (2) 3-aminopropyldimethoxymethylsilane and 4-pyridine formaldehyde were added to toluene (12 times the mass of 3-aminopropyldimethoxymethylsilane) in a molar ratio of 1:1, stirred at 60°C, 300r / min for 5h, and dried at 60°C for 10h under vacuum conditions to obtain functionalized dimethoxysilane; functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane and deionized water were mixed in a mass ratio of 1:1.5:50, and dried at 2°C, 300r / min for 10h. / min and stirred for 20 minutes, and dimethyldichlorosilane (5 times the mass of mercaptopropylmethyldimethoxysilane) was uniformly added dropwise within 20 minutes. After the addition was completed, stirring was continued for 10 minutes, the temperature was raised to 66°C, and the stirring reaction was continued for 4 hours. Acidic white clay (0.08 times the mass of mercaptopropylmethyldimethoxysilane) was added, the temperature was raised to 102°C, and the stirring reaction was continued for 3 hours. The acidic white clay was filtered out, and the filtrate was dried at 80°C under vacuum conditions for 16 hours to obtain functionalized polysiloxane;

[0047] (3) Dibenzoyl peroxide and m-xylene were mixed evenly in a mass ratio of 1:6 to prepare an initiator solution; polypropylene and m-xylene were mixed evenly in a mass ratio of 1:4, stirred at 110°C and 200r / min for 10min, 1,4-diamino-2-butene (0.3 times the mass of polypropylene) was added, and stirring was continued for 8min. Initiator solution (0.2 times the mass of polypropylene) was added dropwise at a constant speed within 30min. After the addition was completed, the temperature was raised to 132°C, and the reaction was continued with stirring for 2h. The temperature was lowered to 52°C, and acetone (4 times the mass of polypropylene) was added and mixed evenly. The mixture was allowed to stand for 2 hours, filtered, and dried at 70°C for 8 hours under vacuum conditions to obtain pre-modified polypropylene; the pre-modified polypropylene and m-xylene were mixed uniformly in a mass ratio of 1:8, stirred at 102°C and 200r / min for 10 minutes, allyl hypophosphorous acid in an amount 0.3 times the mass of the pre-modified polypropylene was added, and then formaldehyde in an amount equimolar to allyl hypophosphorous acid was added, and the mixture was stirred and reacted for 70 minutes, cooled to 52°C, acetone in an amount 4 times the mass of the pre-modified polypropylene was added and mixed uniformly, allowed to stand for 2 hours, filtered, and dried at 70°C for 10 hours under vacuum conditions to obtain modified polypropylene;

[0048] (4) Weigh 102 parts of modified polypropylene, 6 parts of functionalized chitosan porous microspheres, 10 parts of functionalized polysiloxane, and 2 parts of azobisisobutyronitrile by mass; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, set the spinneret aperture to 0.2 mm, the spinning temperature to 240 ° C, the spinning distance to 20 cm, the spinning voltage to 21 kV, the collection drum speed to 100 r / min, and accumulate on the collection drum to form a fiber membrane with a thickness of 28 μm; let the fiber membrane stand at 80 ° C for 2 h, and cool to room temperature to obtain a lithium ion battery separator with high ionic conductivity.

[0049] Comparative Example 1:

[0050] The difference between the preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 1 and Example 2 is that step (1) is different. Step (1) is modified as follows: chitosan and a hydrochloric acid aqueous solution with a concentration of 0.1 mol / L are mixed uniformly in a mass ratio of 1:5, and stirred at 20°C and 250r / min for 25min to prepare a chitosan solution; chitosan solution, melamine, 1,4-dichlorobutane, and anhydrous ethanol are mixed uniformly in a mass ratio of 1:0.25:0.7:2.5, 0.07 times the mass of the chitosan solution of Siban-60 and 3.5 times the mass of the chitosan solution of liquid paraffin are added, the temperature is raised to 41°C, stirring is continued for 15min, the pH is adjusted to 9.5 with a sodium hydroxide aqueous solution with a concentration of 1 mol / L, the temperature is raised to 75°C and the temperature is continued The mixture was stirred for 1.5 hours, cooled naturally to room temperature, filtered, washed four times with deionized water, and freeze-dried at -9°C for 44 hours to produce porous chitosan microspheres. 1,3-Propane Sultone and acetonitrile were mixed in a mass ratio of 1:4.5 to prepare a 1,3-Propane Sultone solution. The porous chitosan microspheres were mixed in a mass ratio of 1:55 with acetonitrile, and ultrasonically dispersed for 35 minutes. Under nitrogen protection, 1,3-Propane Sultone solution (13 times the mass of the porous chitosan microspheres) was added dropwise at a constant rate over 30 minutes at 71°C and stirring at 250 rpm. After the addition was complete, the mixture was stirred for 11 hours, cooled naturally to room temperature, filtered, washed four times with acetone, and dried under vacuum at 55°C for 9 hours to produce functionalized porous chitosan microspheres. The remaining steps were the same as in Example 2.

[0051] Comparative Example 2:

[0052] The method for preparing a high ionic conductivity lithium ion battery separator in Comparative Example 2 differs from that in Example 2 in that step (1) is omitted and step (4) is modified as follows: 100 parts by mass of modified polypropylene, 9 parts by mass of functionalized polysiloxane, and 1.5 parts by mass of azobisisobutyronitrile are weighed; the modified polypropylene, functionalized polysiloxane, and azobisisobutyronitrile are uniformly mixed and placed in an electrospinning apparatus for melt electrospinning, with the spinneret aperture set to 0.15 mm, the spinning temperature to 235° C., the spinning distance to 19 cm, the spinning voltage to 20 kV, and the collection drum speed to 95 r / min. The fibers are deposited on the collection drum to form a fiber membrane with a thickness of 27 μm; the fiber membrane is allowed to stand at 75° C. for 2.5 h and then cooled to room temperature to obtain a high ionic conductivity lithium ion battery separator. The remaining steps are the same as in Example 2.

[0053] Comparative Example 3:

[0054] The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 3 differs from that of Example 2 only in step (2). Step (2) is modified as follows: dimethyldimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water are mixed in a mass ratio of 1:1.4:45, stirred at 1°C and 250 r / min for 25 minutes, and dimethyldichlorosilane (4.5 times the mass of mercaptopropylmethyldimethoxysilane) is added dropwise at a uniform rate over 20 minutes. After the addition is complete, stirring is continued for 11 minutes, the temperature is raised to 65°C, and the stirring reaction is continued for 4.5 hours. Acidic clay (0.07 times the mass of mercaptopropylmethyldimethoxysilane) is added, the temperature is raised to 100°C, and the stirring reaction is continued for 3.5 hours. The acidic clay is filtered out, and the filtrate is dried at 75°C under vacuum conditions for 17 hours to obtain functionalized polysiloxane. The remaining steps are the same as those of Example 2.

[0055] Comparative Example 4:

[0056] The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 4 is different from that of Example 2 only in step (2). Step (2) is modified as follows: 3-aminopropyldimethoxymethylsilane and 4-pyridine formaldehyde are added to toluene with a mass of 11 times that of 3-aminopropyldimethoxymethylsilane in a molar ratio of 1:1, and the mixture is stirred at 55°C and 250r / min for 5.5h, and dried at 55°C for 11h under vacuum to obtain functionalized dimethoxysilane; functionalized dimethoxysilane, dimethyldimethoxysilane, and deionized water are added to the mixture. The mixture was mixed in a mass ratio of 1:1.4:45, stirred at 1°C and 250 rpm for 25 minutes, and dimethyldichlorosilane (4.5 times the mass of dimethyldimethoxysilane) was added dropwise at a constant rate over 20 minutes. After the addition was complete, stirring was continued for 11 minutes. The mixture was heated to 65°C and stirred for 4.5 hours. Acid clay (0.07 times the mass of dimethyldimethoxysilane) was added, the mixture was heated to 100°C, and stirred for 3.5 hours. The acid clay was filtered out, and the filtrate was dried under vacuum at 75°C for 17 hours to produce a functionalized polysiloxane. The remaining steps were the same as in Example 2.

[0057] Comparative Example 5:

[0058] The preparation method of the high ionic conductivity lithium ion battery separator of Comparative Example 5 differs from that of Example 2 only in that step (2) is omitted and step (4) is modified as follows: 100 parts by mass of modified polypropylene, 5.5 parts by mass of functionalized chitosan porous microspheres, and 1.5 parts by mass of azobisisobutyronitrile are weighed; the modified polypropylene, functionalized chitosan porous microspheres, and azobisisobutyronitrile are uniformly mixed and placed in an electrospinning apparatus for melt electrospinning, with the spinneret aperture being 0.15 mm, the spinning temperature being 235° C., the spinning distance being 19 cm, the spinning voltage being 20 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 27 μm; the fiber membrane is allowed to stand at 75° C. for 2.5 h and then cooled to room temperature to obtain a high ionic conductivity lithium ion battery separator. The remaining steps are the same as those of Example 2.

[0059] Comparative Example 6:

[0060] The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 6 differs from that of Example 2 only in that step (3) is not performed and step (4) is modified as follows: 100 parts of polypropylene, 5.5 parts of functionalized chitosan porous microspheres, 9 parts of functionalized polysiloxane, and 1.5 parts of azobisisobutyronitrile are weighed by mass; the polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile are uniformly mixed and placed in an electrospinning apparatus for melt electrospinning, with the spinneret aperture being 0.15 mm, the spinning temperature being 235° C., the spinning distance being 19 cm, the spinning voltage being 20 kV, the collecting drum speed being 95 r / min, and the fibers being deposited on the collecting drum to form a fiber membrane with a thickness of 27 μm; the fiber membrane is allowed to stand at 75° C. for 2.5 h and then cooled to room temperature to obtain a high ion conductivity lithium ion battery separator; the polypropylene model is PP N-Z30S. The remaining steps are the same as those of Example 2.

[0061] Test Example 1

[0062] Ionic conductivity test

[0063] 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.

[0064] Table 1

[0065]

[0066] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 6 in Table 1, it can be found that the high ion conductivity lithium ion battery separator prepared by the present invention has good ion conductivity.

[0067] By comparison, the ionic conductivity of Examples 1 to 3 is greater than that of Comparative Example 2, indicating that chitosan porous microspheres are prepared by a reverse suspension crosslinking method using chitosan as a raw material, 1,4-dichloro-2-butene as a crosslinking agent, and melamine as a chain extender, and amino groups are introduced into the chitosan porous microspheres; the amino groups on the chitosan porous microspheres are reacted with 1,3-propane sultone to prepare functionalized chitosan porous microspheres; 3-propane sultone undergoes a ring-opening reaction to generate a large number of sulfonic acid groups on the functionalized chitosan porous microspheres. The sulfonic acid groups have strong polarity and interact with ions in the electrolyte to increase the mobility of lithium ions, thereby improving the ionic conductivity of the high ionic conductivity lithium ion battery separator; chitosan is a natural polysaccharide containing a large number of hydroxyl groups in its structure, which can improve the wettability of the battery separator with the electrolyte, thereby improving the ionic conductivity of the high ionic conductivity lithium ion battery separator.

[0068] By comparison, the ionic conductivities of Examples 1 to 3 are greater than those of Comparative Examples 3 and 5, indicating that functionalized dimethoxysilane is prepared by reacting 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde; and functionalized polysiloxane is prepared by condensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane, and pyridine groups are introduced into the side chains of the functionalized polysiloxane molecules. During the transmission of lithium ions, the free anions moving in the opposite direction will also hinder the migration of lithium ions, resulting in uneven lithium ion transmission. The pyridine groups are protonated in the electrolyte and carry a positive charge. The positively charged pyridine groups can fix the anions in the electrolyte, promote lithium ion transmission, and prevent parasitic reactions caused by acid, so that the transmission of lithium ions is not interfered with by anions, thereby improving the ionic conductivity of the high ionic conductivity lithium ion battery separator.

[0069] Test Example 2

[0070] Flame retardant performance test

[0071] 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.

[0072] Table 2

[0073]

[0074] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 6 in Table 2, it can be found that the high ion conductivity lithium ion battery separator prepared by the present invention has good flame retardant properties.

[0075] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 5, indicating that the functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane are polycondensed to produce a functionalized polysiloxane, and the Si-O-Si bonds in the functionalized polysiloxane form a silicon-containing carbon layer during the combustion process. The carbon layer can insulate heat and oxygen, thereby preventing further thermal decomposition and combustion of the polymer material, thereby improving the flame retardant properties of the high ionic conductivity lithium-ion battery separator.

[0076] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 6, indicating that 1,4-diamino-2-butene is grafted onto the side chain of the polypropylene molecule by a solution grafting method to prepare a pre-modified polypropylene, and amino groups are introduced into the side chain of the pre-modified polypropylene molecule; the amino groups introduced into the side chain of the pre-modified polypropylene molecule are reacted with formaldehyde and allyl hypophosphorous acid to prepare modified polypropylene, and phosphorus element is introduced into the side chain of the modified polypropylene molecule. The introduction of phosphorus element can improve the flame retardant properties of the high ionic conductivity lithium ion battery separator.

[0077] Test Example 3

[0078] Mechanical properties testing

[0079] Test method: GB / T1040.3-2006, using an electronic universal testing machine to test the tensile strength of the examples and comparative examples. The results are shown in Table 3.

[0080] Table 3

[0081]

[0082] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 6 in Table 3, it can be found that the high ion conductivity lithium ion battery separator prepared by the present invention has good mechanical properties.

[0083] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 1 to 2, indicating that chitosan porous microspheres are prepared by a reverse suspension crosslinking method using chitosan as a raw material, 1,4-dichloro-2-butene as a crosslinking agent, and melamine as a chain extender, and carbon-carbon double bonds are introduced into the chitosan porous microspheres; the carbon-carbon double bonds on the chitosan porous microspheres can undergo an addition reaction with the thiol groups on the functionalized polysiloxane to form a cross-linked network structure, thereby improving the mechanical properties of the high ion conductivity lithium-ion battery separator.

[0084] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 4 to 5, indicating that the functionalized polysiloxane is prepared by condensation polymerization of functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane, and that thiol groups are introduced into the side chains of the functionalized polysiloxane molecules; the thiol groups introduced into the side chains of the functionalized polysiloxane can undergo addition reactions with the carbon-carbon double bonds introduced into the functionalized chitosan porous microspheres and the modified polypropylene to form a cross-linked network, thereby inhibiting the relative sliding between the molecular chains and improving the mechanical properties of the high ionic conductivity lithium-ion battery separator.

[0085] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Example 6, indicating that 1,4-diamino-2-butene is grafted onto the side chain of a polypropylene molecule by a solution grafting method to prepare a pre-modified polypropylene, and an amino group is introduced into the side chain of the pre-modified polypropylene molecule; the amino group introduced into the side chain of the pre-modified polypropylene molecule is reacted with formaldehyde and allyl hypophosphorous acid to prepare a modified polypropylene, and a carbon-carbon double bond is introduced into the side chain of the modified polypropylene molecule; the introduction of phosphorus can improve the flame retardant properties of the high ionic conductivity lithium ion battery separator; the carbon-carbon double bond can undergo an addition reaction with the thiol group on the functionalized polysiloxane to form a cross-linked network, inhibit the relative movement between the molecular chains, and improve the mechanical properties of the high ionic conductivity lithium ion battery separator.

[0086] 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 high ionic conductivity lithium ion battery separator, characterized in that: The high ion conductivity lithium ion battery separator is prepared by reacting chitosan porous microspheres and 1,3-propane sultone to obtain functionalized chitosan porous microspheres; polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane to obtain functionalized polysiloxane; and reacting pre-modified polypropylene, formaldehyde, and allyl hypophosphorous acid to obtain modified polypropylene. Modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile were uniformly mixed and melt electrospun to prepare a lithium-ion battery separator with high ionic conductivity. The chitosan porous microspheres are prepared by using chitosan as raw material, 1,4-dichloro-2-butene as crosslinking agent, and melamine as chain extender through a reverse suspension crosslinking method. The functionalized dimethoxysilane is prepared by reacting 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde; The pre-modified polypropylene is prepared by reacting polypropylene and 1,4-diamino-2-butene.

2. A method for preparing a lithium-ion battery separator with high ionic conductivity, characterized in that: The method for preparing the high ionic conductivity lithium ion battery separator comprises the following steps: (1) 1,3-propane sultone and acetonitrile were mixed at a mass ratio of 1:(4~5) to prepare a 1,3-propane sultone solution; chitosan porous microspheres and acetonitrile were mixed at a mass ratio of 1:(50~60) to prepare a 1,3-propane sultone solution; chitosan porous microspheres were mixed at a mass ratio of 1:(50~60) to prepare a 1,3-propane sultone solution; chitosan porous microspheres were ultrasonically dispersed for 30~40 min; under nitrogen protection, at 70~72 ° C, 200~300 r / min stirring conditions, 12~14 times the mass of chitosan porous microspheres were added dropwise at a constant speed within 30 min; after the addition was completed, the mixture was stirred for 10~12 h, cooled to room temperature naturally, filtered, washed with acetone 3~5 times, and dried at 50~60 ° C under vacuum conditions for 8~10 h to prepare functionalized chitosan porous microspheres; (2) Functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water are mixed in a mass ratio of 1:(1.3~1.5):(40~50), stirred at 0~2°C and 200~300r / min for 20~30min, and dimethyldichlorosilane (4~5 times the mass of mercaptopropylmethyldimethoxysilane) is uniformly added dropwise within 20min. After the addition is completed, stirring is continued for 10~12min, the temperature is raised to 64~66°C, and the stirring reaction is continued for 4~5h. Acidic white clay (0.06~0.08 times the mass of mercaptopropylmethyldimethoxysilane) is added, the temperature is raised to 98~102°C, and the stirring reaction is continued for 3~4h. The acidic white clay is filtered out, and the filtrate is dried at 70~80°C under vacuum conditions for 16~18h to obtain functionalized polysiloxane; (3) Pre-modified polypropylene and m-xylene were mixed uniformly in a mass ratio of 1:(7~8), stirred at 100~102℃ and 100~200r / min for 10~12min, added allyl hypophosphorous acid in an amount of 0.2~0.3 times the mass of pre-modified polypropylene, and then added formaldehyde in an amount equivalent to allyl hypophosphorous acid, and continued to stir and react for 70~80min, cooled to 50~52℃, added acetone in an amount of 3~4 times the mass of pre-modified polypropylene, mixed uniformly, allowed to stand for 1~2h, filtered, and dried at 60~70℃ under vacuum conditions for 10~12h to obtain modified polypropylene; (4) Weigh 98-102 parts of modified polypropylene, 5-6 parts of functionalized chitosan porous microspheres, 8-10 parts of functionalized polysiloxane, and 1-2 parts of azobisisobutyronitrile by mass; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile 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 26-28 μm; let the fiber membrane stand at 70-80°C for 2-3 hours, and cool to room temperature to obtain a lithium-ion battery separator with high ionic conductivity.

3. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 2, characterized in that: The preparation method of the chitosan porous microspheres in step (1) is as follows: chitosan solution, melamine, 1,4-dichloro-2-butene, and anhydrous ethanol are mixed uniformly in a mass ratio of 1:(0.2~0.3):(0.6~0.8):(2~3), 0.06~0.08 times the mass of the chitosan solution of Span-60 and 3~4 times the mass of the chitosan solution of liquid paraffin are added, the temperature is raised to 40~42°C, stirring is continued for 10~20min, the pH is adjusted to 9~10 with a 1mol / L sodium hydroxide aqueous solution, the temperature is raised to 70~80°C, stirring is continued for 1~2h, the mixture is naturally cooled to room temperature, filtered, washed with deionized water 3~5 times, and freeze-dried at -10~-8°C for 40~48h to obtain chitosan porous microspheres.

4. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 3, characterized in that: The chitosan solution is prepared by mixing chitosan and a 0.1 mol / L hydrochloric acid aqueous solution in a mass ratio of 1:(4-6), stirring at 10-30° C. and 200-300 r / min for 20-30 minutes to obtain the chitosan solution.

5. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 4, characterized in that: The chitosan has a deacetylation degree of 95% and a weight-average molecular weight of 85 kDa.

6. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 2, characterized in that: The preparation method of the functionalized dimethoxysilane in step (2) is as follows: 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde are added in a molar ratio of 1:1 to toluene with a mass 10 to 12 times that of 3-aminopropyldimethoxymethylsilane, and the mixture is stirred at 50 to 60°C and 200 to 300 r / min for 5 to 6 hours, and dried at 50 to 60°C under vacuum conditions for 10 to 12 hours to obtain the functionalized dimethoxysilane.

7. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 2, characterized in that: The preparation method of the pre-modified polypropylene in step (3) is as follows: polypropylene and m-xylene are mixed uniformly in a mass ratio of 1:(3~4), stirred at 108~110°C and 100~200r / min for 10~12min, 1,4-diamino-2-butene in an amount of 0.2~0.3 times the mass of polypropylene is added, stirring is continued for 8~10min, and an initiator solution in an amount of 0.1~0.2 times the mass of polypropylene is added dropwise at a uniform rate within 30min. After the addition is completed, the temperature is raised to 130~132°C, the stirring reaction is continued for 2~3h, the temperature is lowered to 50~52°C, acetone in an amount of 3~4 times the mass of polypropylene is added and mixed uniformly, the mixture is allowed to stand for 1~2h, filtered, and dried at 60~70°C under vacuum conditions for 8~10h to obtain pre-modified polypropylene.

8. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 7, characterized in that: The preparation method of the initiator solution is as follows: dibenzoyl peroxide and m-xylene are uniformly mixed in a mass ratio of 1:(5-6) to prepare the initiator solution.

9. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 7, characterized in that: The model of the polypropylene is PP N-Z30S.

10. The method for preparing a high ionic conductivity lithium ion battery separator according to claim 2, characterized in that: The process parameters of the melt electrospinning in step (4) are as follows: setting the spinneret aperture to 0.1-0.2 mm, the spinning temperature to 230-240° C., the spinning distance to 18-20 cm, the spinning voltage to 19-21 kV, and the collection drum speed to 90-100 r / min.

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