High-ionic-conductivity lithium ion battery diaphragm and preparation method thereof

Abstract

The invention discloses a high-ionic-conductivity lithium ion battery diaphragm and a preparation method thereof, and relates to the technical field of battery diaphragms. When the high-ionic-conductivity lithium ion battery diaphragm is prepared, chitosan porous microspheres and 1, 3-propane sultone are subjected to a reaction to prepare functionalized chitosan porous microspheres; the preparation method comprises the following steps: carrying out condensation polymerization on functionalized dimethoxy silane, mercaptopropyl methyl dimethoxy silane and dimethyl dichlorosilane to prepare functionalized polysiloxane; the preparation method comprises the following steps: carrying out a reaction on polypropylene and 1, 4-diamino-2-butene to prepare pre-modified polypropylene; reacting the pre-modified polypropylene, formaldehyde and allyl hypophosphorous acid to obtain modified polypropylene; and uniformly mixing the modified polypropylene, the functional chitosan porous microspheres, the functional polysiloxane and azodiisobutyronitrile, and carrying out melt electrostatic spinning to prepare the high-ionic-conductivity lithium ion battery diaphragm. The high-ionic-conductivity lithium ion battery diaphragm prepared by the invention has excellent ionic conductivity, flame retardance and mechanical properties.

Description

Technical Field

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

[0002] Lithium ion batteries have characteristics such as high specific energy density, good cycle performance, and environmental friendliness, making them widely used in fields such as electric vehicles, electronic products, and energy storage. They are currently the most ideal power source energy storage system. The internal components of a lithium ion battery mainly include a positive electrode, a negative electrode, a battery separator, and an organic electrolyte. Among them, the battery separator is located between the positive and negative electrodes, separating the positive and negative electrodes to prevent direct contact between the positive and negative electrodes from causing a short circuit and resulting in a safety accident, blocking electrons. In addition, it can absorb a certain amount of electrolyte to provide a transfer channel for lithium ions.

[0003] Polyolefin battery separators are inexpensive and have stable electrochemical properties. They are the most main commercial battery separators on the market. However, their disadvantages are also relatively obvious, such as poor wettability to the electrolyte and flammability. In recent years, accidents such as spontaneous combustion and explosion of electronic devices caused by thermal runaway of lithium ion batteries have occurred frequently, seriously damaging people's property and personal safety, making people pay more and more attention to the safety issues 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 purpose of the present invention is to provide a high ion conductivity lithium ion battery separator and a preparation method thereof to solve the problems existing in the prior art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: A high ion conductivity lithium ion battery separator, wherein the high ion conductivity lithium ion battery separator is prepared by reacting chitosan porous microspheres with 1,3 - propane sultone to obtain functionalized chitosan porous microspheres; polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane to obtain functionalized polysiloxane; reacting pre - modified polypropylene with allyl hypophosphorous acid to obtain modified polypropylene; mixing the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile uniformly and performing melt electrospinning to obtain a high ion conductivity lithium ion battery separator; The chitosan porous microspheres are prepared by using chitosan as a raw material, 1,4 - dichloro - 2 - butene as a cross - linker, and melamine as a chain extender, and adopting an inverse phase suspension cross - linking method; The functionalized dimethoxysilane is prepared by reacting 3-aminopropyldimethoxymethylsilane with 4-pyridinecarboxaldehyde; The pre-modified polypropylene is prepared by reacting polypropylene with 1,4-diamino-2-butene.

[0007] A preparation method of a lithium-ion battery separator with high ionic conductivity, the preparation method of the lithium-ion battery separator with high ionic conductivity comprises the following preparation steps: (1) Mix 1,3-propanesultone and acetonitrile evenly according to a mass ratio of 1:(4-5) to prepare a 1,3-propanesultone solution; mix chitosan porous microspheres and acetonitrile evenly according to a mass ratio of 1:(50-60), ultrasonically disperse for 30-40 min, under nitrogen protection, at 70-72 °C, and under stirring conditions of 200-300 r / min, uniformly dropwise add a 1,3-propanesultone solution which is 12-14 times the mass of the chitosan porous microspheres within 30 min. After the dropping is completed, continue stirring and reacting for 10-12 h, naturally cool to room temperature, filter, wash with acetone 3-5 times, and dry at 50-60 °C for 8-10 h under vacuum conditions to obtain functionalized chitosan porous microspheres; (2) Mix the functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water evenly according to a mass ratio of 1:(1.3-1.5):(40-50), stir at 0-2 °C and 200-300 r / min for 20-30 min, uniformly dropwise add dimethyldichlorosilane which is 4-5 times the mass of the mercaptopropylmethyldimethoxysilane within 20 min. After the dropping is completed, continue stirring for 10-12 min, raise the temperature to 64-66 °C, continue stirring and reacting for 4-5 h, add acid clay which is 0.06-0.08 times the mass of the mercaptopropylmethyldimethoxysilane, raise the temperature to 98-102 °C, continue stirring and reacting for 3-4 h, filter off the acid clay, and dry the filtrate at 70-80 °C for 16-18 h under vacuum conditions to obtain functionalized polysiloxane; (3) Mix the pre-modified polypropylene and m-xylene evenly according to a mass ratio of 1:(7-8), stir at 100-102 °C and 100-200 r / min for 10-12 min, add allyl hypophosphorous acid which is 0.2-0.3 times the mass of the pre-modified polypropylene, then add formaldehyde with an equimolar amount of allyl hypophosphorous acid, continue stirring and reacting for 70-80 min, cool down to 50-52 °C, add acetone which is 3-4 times the mass of the pre-modified polypropylene and mix evenly, let stand for 1-2 h, filter with suction, and dry at 60-70 °C for 10-12 h under vacuum conditions to obtain modified polypropylene; (4)Weigh 98 - 102 parts by mass of modified polypropylene, 5 - 6 parts of functionalized chitosan porous microspheres, 8 - 10 parts of functionalized polysiloxane, and 1 - 2 parts of azobisisobutyronitrile; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, and stack 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 h, and then cool it to room temperature to obtain a lithium-ion battery separator with high ionic conductivity.

[0008] As an optimization, the preparation method of the chitosan porous microspheres in step (1) is as follows: Mix chitosan solution, melamine, 1,4 - dichloro - 2 - butene, and absolute ethanol in a mass ratio of 1:(0.2 - 0.3):(0.6 - 0.8):(2 - 3) evenly, add Span - 60 which is 0.06 - 0.08 times the mass of the chitosan solution and liquid paraffin which is 3 - 4 times the mass of the chitosan solution, heat up to 40 - 42 °C, continue stirring for 10 - 20 min, adjust the pH to 9 - 10 with a 1 mol / L sodium hydroxide aqueous solution, heat up to 70 - 80 °C and continue stirring for 1 - 2 h, naturally cool to room temperature, filter, wash with deionized water 3 - 5 times, and freeze-dry at - 10 - - 8 °C for 40 - 48 h to obtain chitosan porous microspheres.

[0009] As an optimization, the preparation method of the chitosan solution is as follows: Mix chitosan and a 0.1 mol / L hydrochloric acid aqueous solution in a mass ratio of 1:(4 - 6) evenly, and stir at 10 - 30 °C and 200 - 300 r / min for 20 - 30 min to obtain a chitosan solution.

[0010] As an optimization, the degree of deacetylation of the chitosan is 95%, and the weight-average molecular weight is 85 kDa.

[0011] As an optimization, the preparation method of the functionalized dimethoxysilane in step (2) is as follows: Add 3 - aminopropyldimethoxymethylsilane and 4 - pyridinecarboxaldehyde in a molar ratio of 1:1 to toluene which is 10 - 12 times the mass of 3 - aminopropyldimethoxymethylsilane, stir and react at 50 - 60 °C and 200 - 300 r / min for 5 - 6 h, and dry at 50 - 60 °C under vacuum conditions for 10 - 12 h to obtain functionalized dimethoxysilane.

[0012] As an optimization, the CAS number of allyl hypophosphite in step (3) is 66899 - 05 - 6; the structural formula is: 。

[0013] As an optimization, the preparation method of the pre-modified polypropylene described in step (3) is as follows: Mix polypropylene and m-xylene evenly at a mass ratio of 1:(3 - 4), stir at 108 - 110 °C and 100 - 200 r / min for 10 - 12 min, add 1,4-diamino-2-butene which is 0.2 - 0.3 times the mass of polypropylene, continue to stir for 8 - 10 min, uniformly dropwise add an initiator solution which is 0.1 - 0.2 times the mass of polypropylene within 30 min. After the dropping is completed, raise the temperature to 130 - 132 °C, continue to stir and react for 2 - 3 h, cool down to 50 - 52 °C, add acetone which is 3 - 4 times the mass of polypropylene and mix evenly, let it stand for 1 - 2 h, filter by suction, and dry at 60 - 70 °C under vacuum conditions for 8 - 10 h to obtain the pre-modified polypropylene.

[0014] As an optimization, the preparation method of the initiator solution is as follows: Mix benzoyl peroxide and m-xylene evenly at a mass ratio of 1:(5 - 6) to prepare the initiator solution.

[0015] As an optimization, the model of the polypropylene is PP N-Z30S.

[0016] As an optimization, the process parameters of the melt electrospinning described in step (4) are as follows: Set the pore diameter of the spinneret plate 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 rotational speed of the collecting roller to 90 - 100 r / min.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: When preparing the lithium-ion battery separator with high ionic conductivity, the present invention uses chitosan as the raw material, 1,4-dichloro-2-butene as the cross-linking agent, and melamine as the chain extender, and prepares chitosan porous microspheres by the inverse suspension cross-linking method; reacts the chitosan porous microspheres with 1,3-propane sultone to obtain functionalized chitosan porous microspheres; reacts 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde to obtain functionalized dimethoxysilane; polycondenses the functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane to obtain functionalized polysiloxane; reacts polypropylene and 1,4-diamino-2-butene to obtain pre-modified polypropylene; reacts the pre-modified polypropylene, formaldehyde, and allyl hypophosphorous acid to obtain modified polypropylene; mixes the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile evenly, and conducts melt electrospinning to obtain the lithium-ion battery separator with high ionic conductivity.

[0018] First, using chitosan as raw material, 1,4-dichloro-2-butene as crosslinking agent, and melamine as chain extender, porous chitosan microspheres are prepared by inverse suspension crosslinking method, and amino groups and carbon-carbon double bonds are introduced onto the porous chitosan microspheres; the carbon-carbon double bonds on the porous chitosan microspheres can undergo addition reaction with the mercapto groups on the functionalized polysiloxane to form a crosslinked network structure, enhancing the mechanical properties of the separator for high ionic conductivity lithium-ion batteries; the amino groups on the porous chitosan microspheres are reacted with 1,3-propane sultone to obtain functionalized porous chitosan microspheres; 1,3-propane sultone undergoes ring-opening reaction to generate a large number of sulfonic acid groups on the functionalized porous chitosan microspheres. The sulfonic acid groups have strong polarity and interact with the ions in the electrolyte, improving the mobility of lithium ions, thereby enhancing the ionic conductivity of the separator for high ionic conductivity lithium-ion batteries; chitosan is a natural polysaccharide and contains a large number of hydroxyl groups in its structure, which can improve the wettability between the battery separator and the electrolyte, thus enhancing the ionic conductivity of the separator for high ionic conductivity lithium-ion batteries.

[0019] Secondly, 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde are reacted to obtain functionalized dimethoxysilane; the functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane are polycondensed to obtain functionalized polysiloxane, and pyridine groups and mercapto groups are introduced onto the side chains of the functionalized polysiloxane molecules; during the transmission process of lithium ions, the freely moving anions moving in the reverse 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 positive charges. The positively charged pyridine groups can fix the anions in the electrolyte, promote the transmission of lithium ions, and at the same time prevent the parasitic reactions caused by acids, so that the transmission of lithium ions is not interfered by anions, enhancing the ionic conductivity of the separator for high ionic conductivity lithium-ion batteries; the mercapto groups introduced on the side chains of the functionalized polysiloxane can undergo addition reaction with the carbon-carbon double bonds introduced on the functionalized porous chitosan microspheres and modified polypropylene to form a crosslinked network, inhibiting the relative sliding between molecular chains, enhancing the mechanical properties of the separator for high ionic conductivity lithium-ion batteries; the Si-O-Si bonds in the functionalized polysiloxane form a silicon-containing carbon layer during the combustion process, and this carbon layer can insulate heat and oxygen, thereby preventing the further thermal decomposition and combustion of the polymer material, enhancing the flame retardant performance of the separator for high ionic conductivity lithium-ion batteries.

[0020] Finally, 1,4-diamino-2-butene was grafted onto the side chain of polypropylene molecules by solution grafting method to obtain pre-modified polypropylene, and amino groups were introduced onto the side chain of pre-modified polypropylene molecules; the amino groups introduced onto the side chain of pre-modified polypropylene molecules were reacted with formaldehyde and allyl hypophosphorous acid to obtain modified polypropylene, and phosphorus element and carbon-carbon double bonds were introduced onto the side chain of modified polypropylene molecules; the introduction of phosphorus element can improve the flame retardancy of the separator for high ionic conductivity lithium-ion batteries; the carbon-carbon double bond can undergo an addition reaction with the mercapto group on functionalized polysiloxane to form a cross-linked network, inhibit the relative movement between molecular chains, and improve the mechanical properties of the separator for high ionic conductivity lithium-ion batteries. Detailed implementation mode

[0021] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0022] Example 1: A preparation method of a separator for high ionic conductivity lithium-ion batteries, the preparation method of the separator for high ionic conductivity lithium-ion batteries includes the following preparation steps: (1) Chitosan and a hydrochloric acid aqueous solution with a concentration of 0.1 mol / L were mixed evenly according to a mass ratio of 1:4, stirred at 10 °C and 200 r / min for 30 min to obtain a chitosan solution; the chitosan solution, melamine, 1,4-dichloro-2-butene, and absolute ethanol were mixed evenly according to a mass ratio of 1:0.2:0.6:2, 0.06 times the mass of the chitosan solution of Span-60 and 3 times the mass of the chitosan solution of liquid paraffin were added, the temperature was raised to 40 °C, and 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 stirring was continued for 2 h, naturally cooled to room temperature, filtered, washed 3 times with deionized water, freeze-dried at -10 °C for 40 h to obtain chitosan porous microspheres; 1,3-propane sultone and acetonitrile were mixed evenly according to a mass ratio of 1:4 to prepare a 1,3-propane sultone solution; the chitosan porous microspheres and acetonitrile were mixed evenly according to a mass ratio of 1:50, ultrasonically dispersed for 30 min, under nitrogen protection, at 70 °C and 200 r / min stirring conditions, a 1,3-propane sultone solution 12 times the mass of the chitosan porous microspheres was added dropwise evenly within 30 min. After the addition was completed, stirring reaction was continued for 12 h, naturally cooled to room temperature, filtered, washed 3 times with acetone, and dried at 50 °C for 10 h under vacuum conditions to obtain functionalized chitosan porous microspheres; (2) 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde were added to toluene which was 10 times the mass of 3-aminopropyldimethoxymethylsilane at a molar ratio of 1:1, and stirred at 50 °C and 200 r / min for 6 h. Under vacuum conditions, it was dried at 50 °C for 12 h to obtain functionalized dimethoxysilane; functionalized dimethoxysilane, mercaptopropyldimethoxymethylsilane, and deionized water were mixed at a mass ratio of 1:1.3:40, stirred at 0 °C and 200 r / min for 30 min, and dimethyldichlorosilane which was 4 times the mass of mercaptopropyldimethoxymethylsilane was added dropwise uniformly within 20 min. After the addition was completed, stirring continued for 12 min, the temperature was raised to 64 °C, and stirring and reaction continued for 5 h. Acidic clay which was 0.06 times the mass of mercaptopropyldimethoxymethylsilane was added, the temperature was raised to 98 °C, and stirring and reaction continued for 4 h. The acidic clay was filtered off, and the filtrate was dried at 70 °C for 18 h under vacuum conditions to obtain functionalized polysiloxane; (3) Benzoyl peroxide and m-xylene were mixed evenly at a mass ratio of 1:5 to prepare an initiator solution; polypropylene and m-xylene were mixed evenly at a mass ratio of 1:3, stirred at 108 °C and 100 r / min for 12 min, 1,4-diamino-2-butene which was 0.2 times the mass of polypropylene was added, and stirring continued for 10 min. The initiator solution which was 0.1 times the mass of polypropylene was added dropwise uniformly within 30 min. After the addition was completed, the temperature was raised to 130 °C, and stirring and reaction continued for 3 h. The temperature was lowered to 50 °C, acetone which was 3 times the mass of polypropylene was added and mixed evenly, allowed to stand for 1 h, filtered by suction, and dried at 60 °C for 10 h under vacuum conditions to obtain pre-modified polypropylene; pre-modified polypropylene and m-xylene were mixed evenly at a mass ratio of 1:7, stirred at 100 °C and 100 r / min for 12 min, allyl hypophosphorous acid which was 0.2 times the mass of pre-modified polypropylene was added, and formaldehyde in an equimolar amount to allyl hypophosphorous acid was added, and stirring and reaction continued for 80 min. The temperature was lowered to 50 °C, acetone which was 3 times the mass of pre-modified polypropylene was added and mixed evenly, allowed to stand for 1 h, filtered by suction, and dried at 60 °C for 12 h under vacuum conditions to obtain modified polypropylene; (4) By mass, 98 parts of modified polypropylene, 5 parts of functionalized chitosan porous microspheres, 8 parts of functionalized polysiloxane, and 1 part of azobisisobutyronitrile were weighed; modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile were mixed evenly and placed in an electrospinning device for melt electrospinning. The aperture of the spinneret was set to 0.1 mm, the spinning temperature was 230 °C, the spinning distance was 18 cm, the spinning voltage was 19 kV, and the rotational speed of the collecting drum was 90 r / min. It was stacked on the collecting drum to form a fiber membrane with a thickness of 26 μm; the fiber membrane was allowed to stand at 70 °C for 3 h and cooled to room temperature to obtain a lithium-ion battery separator with high ionic conductivity.

[0023] Example 2: A preparation method of a lithium-ion battery separator with high ionic conductivity, the preparation method of the lithium-ion battery separator with high ionic conductivity comprising the following preparation steps: (1) Mix chitosan and an aqueous hydrochloric acid solution with a concentration of 0.1 mol / L evenly at a mass ratio of 1:5, stir at 20 °C and 250 r / min for 25 min to obtain a chitosan solution; mix the chitosan solution, melamine, 1,4-dichloro-2-butene, and absolute ethanol evenly at a mass ratio of 1:0.25:0.7:2.5, add Span-60 with a mass 0.07 times that of the chitosan solution and liquid paraffin with a mass 3.5 times that of the chitosan solution, raise the temperature to 41 °C, continue stirring for 15 min, adjust the pH to 9.5 with an aqueous sodium hydroxide solution with a concentration of 1 mol / L, raise the temperature to 75 °C and continue stirring for 1.5 h, naturally cool to room temperature, filter, wash 4 times with deionized water, freeze-dry at -9 °C for 44 h to obtain chitosan porous microspheres; mix 1,3-propane sultone and acetonitrile evenly at a mass ratio of 1:4.5 to prepare a 1,3-propane sultone solution; mix the chitosan porous microspheres and acetonitrile evenly at a mass ratio of 1:55, ultrasonically disperse for 35 min, under nitrogen protection, at 71 °C and under stirring conditions of 250 r / min, uniformly dropwise add a 1,3-propane sultone solution with a mass 13 times that of the chitosan porous microspheres within 30 min, continue stirring and reacting for 11 h after the dropping is completed, naturally cool to room temperature, filter, wash 4 times with acetone, and dry at 55 °C under vacuum conditions for 9 h to obtain functionalized chitosan porous microspheres; (2) Add 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde in a molar ratio of 1:1 to toluene with a mass 11 times that of 3-aminopropyldimethoxymethylsilane, stir and react at 55 °C and 250 r / min for 5.5 h, and dry at 55 °C under vacuum conditions for 11 h to obtain functionalized dimethoxysilane; mix the functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water evenly at a mass ratio of 1:1.4:45, stir at 1 °C and 250 r / min for 25 min, uniformly dropwise add dimethyldichlorosilane with a mass 4.5 times that of mercaptopropylmethyldimethoxysilane within 20 min, continue stirring for 11 min after the dropping is completed, raise the temperature to 65 °C, continue stirring and reacting for 4.5 h, add acidic clay with a mass 0.07 times that of mercaptopropylmethyldimethoxysilane, raise the temperature to 100 °C, continue stirring and reacting for 3.5 h, filter off the acidic clay, and dry the filtrate at 75 °C under vacuum conditions for 17 h to obtain functionalized polysiloxane; (3) Mix benzoyl peroxide and m-xylene evenly at a mass ratio of 1:5.5 to prepare an initiator solution; mix polypropylene and m-xylene evenly at a mass ratio of 1:3.5, stir at 109 °C and 150 r / min for 11 min, add 1,4-diamino-2-butene which is 0.25 times the mass of polypropylene, continue stirring for 9 min, uniformly dropwise add the initiator solution which is 0.15 times the mass of polypropylene within 30 min. After the dropping is completed, raise the temperature to 131 °C, continue stirring and reacting for 2.5 h, cool down to 51 °C, add acetone which is 3.5 times the mass of polypropylene and mix evenly, let stand for 1.5 h, filter by suction, and dry at 65 °C under vacuum conditions for 9 h to obtain pre-modified polypropylene; mix the pre-modified polypropylene and m-xylene evenly at a mass ratio of 1:7.5, stir at 101 °C and 150 r / min for 11 min, add allyl hypophosphorous acid which is 0.25 times the mass of the pre-modified polypropylene, and then add formaldehyde with an equimolar amount of allyl hypophosphorous acid, continue stirring and reacting for 75 min, cool down to 51 °C, add acetone which is 3.5 times the mass of the pre-modified polypropylene and mix evenly, let stand for 1.5 h, filter by suction, and dry at 65 °C under vacuum conditions for 11 h to obtain modified polypropylene; (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 orifice diameter of the spinneret to 0.15 mm, the spinning temperature to 235 °C, the spinning distance to 19 cm, the spinning voltage to 20 kV, and the rotational speed of the collecting roller to 95 r / min, and stack them on the collecting roller 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 lithium-ion battery separator with high ionic conductivity.

[0024] Example 3: A preparation method of a lithium-ion battery separator with high ionic conductivity, the preparation method of the lithium-ion battery separator with high ionic conductivity includes the following preparation steps: (1)Chitosan and a hydrochloric acid aqueous solution with a concentration of 0.1 mol / L were mixed evenly at a mass ratio of 1:6, stirred at 30 °C and 300 r / min for 20 min to obtain a chitosan solution; the chitosan solution, melamine, 1,4-dichloro-2-butene, and absolute ethanol were mixed evenly at a mass ratio of 1:0.3:0.8:3, added with Span-60 at 0.08 times the mass of the chitosan solution and liquid paraffin at 4 times the mass of the chitosan solution, heated to 42 °C, and continuously stirred for 10 min. The pH was adjusted to 10 with a sodium hydroxide aqueous solution with a concentration of 1 mol / L, heated to 80 °C and continuously stirred for 1 h, naturally cooled to room temperature, filtered, washed 5 times with deionized water, and freeze-dried at -8 °C for 48 h to obtain chitosan porous microspheres; 1,3-propane sultone and acetonitrile were mixed evenly at a mass ratio of 1:5 to prepare a 1,3-propane sultone solution; the chitosan porous microspheres and acetonitrile were mixed evenly at a mass ratio of 1:60, ultrasonically dispersed for 40 min, and under nitrogen protection, at 72 °C and under stirring conditions of 300 r / min, a 1,3-propane sultone solution at 14 times the mass of the chitosan porous microspheres was added dropwise evenly within 30 min. After the addition was completed, the reaction was continued by stirring for 10 h, naturally cooled to room temperature, filtered, washed 5 times with acetone, and dried at 60 °C under vacuum conditions for 8 h to obtain functionalized chitosan porous microspheres; (2)3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde were added to toluene at 12 times the mass of 3-aminopropyldimethoxymethylsilane at a molar ratio of 1:1, stirred and reacted at 60 °C and 300 r / min for 5 h, and dried at 60 °C under vacuum conditions for 10 h to obtain functionalized dimethoxysilane; the functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water were mixed at a mass ratio of 1:1.5:50, stirred at 2 °C and 300 r / min for 20 min, and dimethyldichlorosilane at 5 times the mass of mercaptopropylmethyldimethoxysilane was added dropwise evenly within 20 min. After the addition was completed, the reaction was continued by stirring for 10 min, heated to 66 °C, and continuously stirred and reacted for 4 h. Acidic clay at 0.08 times the mass of mercaptopropylmethyldimethoxysilane was added, heated to 102 °C, and continuously stirred and reacted for 3 h. The acidic clay was filtered off, and the filtrate was dried at 80 °C under vacuum conditions for 16 h to obtain functionalized polysiloxane; (3) Mix benzoyl peroxide and m-xylene evenly at a mass ratio of 1:6 to prepare an initiator solution; mix polypropylene and m-xylene evenly at a mass ratio of 1:4, stir at 110 °C and 200 r / min for 10 min, add 1,4-diamino-2-butene which is 0.3 times the mass of polypropylene, continue to stir for 8 min, dropwise add the initiator solution which is 0.2 times the mass of polypropylene evenly within 30 min. After the dropping is completed, raise the temperature to 132 °C, continue to stir and react for 2 h, cool down to 52 °C, add acetone which is 4 times the mass of polypropylene and mix evenly, let stand for 2 h, filter by suction, and dry at 70 °C for 8 h under vacuum conditions to obtain pre-modified polypropylene; mix the pre-modified polypropylene and m-xylene evenly at a mass ratio of 1:8, stir at 102 °C and 200 r / min for 10 min, add allyl hypophosphorous acid which is 0.3 times the mass of the pre-modified polypropylene, then add formaldehyde with an equimolar amount of allyl hypophosphorous acid, continue to stir and react for 70 min, cool down to 52 °C, add acetone which is 4 times the mass of the pre-modified polypropylene and mix evenly, let stand for 2 h, filter by suction, and dry at 70 °C for 10 h under vacuum conditions to obtain modified polypropylene; (4) Weigh 102 parts of modified polypropylene, 6 parts of functionalized chitosan porous microspheres, 10 parts of functionalized polysiloxane, and 2 parts of azodiisobutyronitrile by mass; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azodiisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, set the spinneret pore diameter to 0.2 mm, the spinning temperature to 240 °C, the spinning distance to 20 cm, the spinning voltage to 21 kV, and the collection roller speed to 100 r / min, and stack them on the collection roller 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.

[0025] Comparative Example 1: The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 1 is different from that of Example 2 in step (1). Modify step (1) as follows: Mix chitosan and an aqueous hydrochloric acid solution with a concentration of 0.1 mol / L evenly at a mass ratio of 1:5, stir at 20 °C and 250 r / min for 25 min to obtain a chitosan solution; Mix the chitosan solution, melamine, 1,4-dichlorobutane, and absolute ethanol evenly at a mass ratio of 1:0.25:0.7:2.5, add Span-60 with a mass 0.07 times that of the chitosan solution and liquid paraffin with a mass 3.5 times that of the chitosan solution, heat up to 41 °C, continue stirring for 15 min, adjust the pH to 9.5 with an aqueous sodium hydroxide solution with a concentration of 1 mol / L, heat up to 75 °C and continue stirring for 1.5 h, naturally cool to room temperature, filter, wash 4 times with deionized water, freeze-dry at -9 °C for 44 h to obtain chitosan porous microspheres; Mix 1,3-propane sultone and acetonitrile evenly at a mass ratio of 1:4.5 to prepare a 1,3-propane sultone solution; Mix the chitosan porous microspheres and acetonitrile evenly at a mass ratio of 1:55, ultrasonically disperse for 35 min, under nitrogen protection, at 71 °C and under stirring conditions of 250 r / min, uniformly dropwise add the 1,3-propane sultone solution with a mass 13 times that of the chitosan porous microspheres within 30 min, continue stirring and reacting for 11 h after the dropping is completed, naturally cool to room temperature, filter, wash 4 times with acetone, and dry at 55 °C under vacuum conditions for 9 h to obtain functionalized chitosan porous microspheres. The remaining steps are the same as those in Example 2.

[0026] Comparative Example 2: The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 2 is different from that of Example 2 in that step (1) is not carried out. Modify step (4) as follows: By mass, weigh 100 parts of modified polypropylene, 9 parts of functionalized polysiloxane, and 1.5 parts of azobisisobutyronitrile; Mix the modified polypropylene, functionalized polysiloxane, and azobisisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, set the orifice diameter of the spinneret to 0.15 mm, the spinning temperature to 235 °C, the spinning distance to 19 cm, the spinning voltage to 20 kV, and the rotational speed of the collecting roller to 95 r / min, and stack them on the collecting roller 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 ion conductivity lithium ion battery separator. The remaining steps are the same as those in Example 2.

[0027] Comparative Example 3: The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 3 is only different from that of Example 2 in step (2). Modify step (2) as follows: Mix dimethyldimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water in a mass ratio of 1:1.4:45, stir at 1 °C and 250 r / min for 25 min, and uniformly add dimethyldichlorosilane 4.5 times the mass of mercaptopropylmethyldimethoxysilane within 20 min. After the addition is complete, continue stirring for 11 min, raise the temperature to 65 °C, and continue stirring and reacting for 4.5 h. Add acidic clay 0.07 times the mass of mercaptopropylmethyldimethoxysilane, raise the temperature to 100 °C, and continue stirring and reacting for 3.5 h. Filter off the acidic clay, and dry the filtrate under vacuum conditions at 75 °C for 17 h to obtain functionalized polysiloxane. The remaining steps are the same as those in Example 2.

[0028] Comparative Example 4: The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 4 is only different from that of Example 2 in step (2). Modify step (2) as follows: Add 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde in a molar ratio of 1:1 to toluene 11 times the mass of 3-aminopropyldimethoxymethylsilane, stir and react at 55 °C and 250 r / min for 5.5 h, and dry under vacuum conditions at 55 °C for 11 h to obtain functionalized dimethoxysilane; Mix functionalized dimethoxysilane, dimethyldimethoxysilane, and deionized water in a mass ratio of 1:1.4:45, stir at 1 °C and 250 r / min for 25 min, and uniformly add dimethyldichlorosilane 4.5 times the mass of dimethyldimethoxysilane within 20 min. After the addition is complete, continue stirring for 11 min, raise the temperature to 65 °C, and continue stirring and reacting for 4.5 h. Add acidic clay 0.07 times the mass of dimethyldimethoxysilane, raise the temperature to 100 °C, and continue stirring and reacting for 3.5 h. Filter off the acidic clay, and dry the filtrate under vacuum conditions at 75 °C for 17 h to obtain functionalized polysiloxane. The remaining steps are the same as those in Example 2.

[0029] Comparative Example 5: The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 5 is only different from that of Example 2 in that step (2) is not carried out, and step (4) is modified as follows: by mass, 100 parts of modified polypropylene, 5.5 parts of functionalized chitosan porous microspheres, and 1.5 parts of azobisisobutyronitrile are weighed; the modified polypropylene, functionalized chitosan porous microspheres, and azobisisobutyronitrile are mixed evenly, placed in an electrospinning device for melt electrospinning, the aperture of the spinneret is set to 0.15 mm, the spinning temperature is 235 °C, the spinning distance is 19 cm, the spinning voltage is 20 kV, the rotation speed of the collecting roller is 95 r / min, and it is stacked on the collecting roller to form a fiber membrane with a thickness of 27 μm; the fiber membrane is left standing at 75 °C for 2.5 h and cooled to room temperature to obtain a high ion conductivity lithium ion battery separator. The remaining steps are the same as those in Example 2.

[0030] Comparative Example 6: The preparation method of the high ion conductivity lithium ion battery separator of Comparative Example 6 is only different from that of Example 2 in that step (3) is not carried out, and step (4) is modified as follows: by mass, 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; the polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile are mixed evenly, placed in an electrospinning device for melt electrospinning, the aperture of the spinneret is set to 0.15 mm, the spinning temperature is 235 °C, the spinning distance is 19 cm, the spinning voltage is 20 kV, the rotation speed of the collecting roller is 95 r / min, and it is stacked on the collecting roller to form a fiber membrane with a thickness of 27 μm; the fiber membrane is left standing at 75 °C for 2.5 h and cooled to room temperature to obtain a high ion conductivity lithium ion battery separator; the model of the polypropylene is PP N-Z30S. The remaining steps are the same as those in Example 2.

[0031] Test Example 1 Test of ionic conductivity Test method: Assemble a stainless steel sheet / separator / stainless steel sheet symmetric battery, and the assembled battery sample is placed for 5 h before testing. Use an electrochemical workstation to detect the electrochemical impedance spectrum of the battery sample. This impedance spectrum is related to the process of solid diffusion of lithium ions inside the separator. The intersection of the diagonal line and the abscissa in the obtained alternating current impedance spectrum diagram is the bulk resistance of the lithium ion battery separator. The test frequency is 1×10 6 Hz - 1 Hz, and the voltage is 10 mV. Calculate the ionic conductivity according to the formula. Ionic conductivity = separator thickness / (bulk resistance × effective contact area) × 100%. The results are shown in Table 1.

[0032] Table 1

[0033] 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 ionic conductivity.

[0034] 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 the inverse suspension cross-linking method using chitosan as the raw material, 1,4-dichloro-2-butene as the cross-linking agent, and melamine as the chain extender, and amino groups are introduced onto the chitosan porous microspheres; the amino groups on the chitosan porous microspheres are reacted with 1,3-propane sultone to obtain functionalized chitosan porous microspheres; the 1,3-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 improve the mobility of lithium ions, thereby improving the ionic conductivity of the high ion 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 between the battery separator and the electrolyte, thereby enhancing the ionic conductivity of the high ion conductivity lithium ion battery separator.

[0035] By comparison, the ionic conductivity of Examples 1 to 3 is greater than that of Comparative Examples 3 and 5, indicating that functionalized dimethoxysilane is prepared by reacting 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde; functionalized polysiloxane is prepared by polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane, and pyridine groups are introduced onto the side chains of the functionalized polysiloxane molecules. During the transmission process of lithium ions, the backward moving free anions will also hinder the migration of lithium ions, resulting in uneven lithium ion transmission. The pyridine groups are protonated in the electrolyte and carry positive charges. The positively charged pyridine groups can fix the anions in the electrolyte, promote lithium ion transmission, and prevent parasitic reactions caused by acids, so that the transmission of lithium ions is not interfered by anions, and the ionic conductivity of the high ion conductivity lithium ion battery separator is improved.

[0036] Test Example 2 Test of flame retardant performance Test method: According to GB / T2406-93, the examples and comparative examples are prepared into standard specimens, and the limiting oxygen index of the standard specimens is tested. The results are shown in Table 2.

[0037] Table 2

[0038] 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 performance.

[0039] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 5, indicating that the functionalized polysiloxane is prepared by polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane. The Si-O-Si bonds in the functionalized polysiloxane form a silicon-containing carbon layer during combustion, which can insulate heat and oxygen, thereby preventing the further thermal decomposition and combustion of the polymer material and improving the flame retardancy of the high ionic conductivity lithium-ion battery separator.

[0040] 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 the solution grafting method to obtain pre-modified polypropylene, and amino groups are introduced onto the side chain of the pre-modified polypropylene molecule; the amino groups introduced onto the side chain of the pre-modified polypropylene molecule react with formaldehyde and allyl hypophosphorous acid to obtain modified polypropylene, and phosphorus elements are introduced onto the side chain of the modified polypropylene molecule. The introduction of phosphorus elements can improve the flame retardancy of the high ionic conductivity lithium-ion battery separator.

[0041] Test Example 3 Testing of mechanical properties Test method: GB / T1040.3-2006. The tensile strength of the examples and comparative examples was detected using an electronic universal testing machine. The results are shown in Table 3.

[0042] Table 3

[0043] 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 ionic conductivity lithium-ion battery separator prepared by the present invention has good mechanical properties.

[0044] 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 the inverse suspension cross-linking method using chitosan as the raw material, 1,4-dichloro-2-butene as the cross-linking agent, and melamine as the chain extender, and carbon-carbon double bonds are introduced onto the chitosan porous microspheres; the carbon-carbon double bonds on the chitosan porous microspheres can undergo an addition reaction with the mercapto groups on the functionalized polysiloxane to form a cross-linked network structure, improving the mechanical properties of the high ionic conductivity lithium-ion battery separator.

[0045] By comparison, the tensile strengths of Examples 1 to 3 are greater than those of Comparative Examples 4 to 5, indicating that functionalized polysiloxane is prepared by polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane, and mercapto groups are introduced into the side chains of the functionalized polysiloxane molecules; the mercapto groups introduced into the side chains of the functionalized polysiloxane can undergo an addition reaction with the carbon-carbon double bonds introduced into the functionalized chitosan porous microspheres and modified polypropylene to form a crosslinked network, inhibit the relative sliding between molecular chains, and improve the mechanical properties of the high ionic conductivity lithium-ion battery separator.

[0046] 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 the polypropylene molecule by the solution grafting method to prepare 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 react with formaldehyde and allyl hypophosphorous acid to prepare modified polypropylene, and carbon-carbon double bonds are introduced into the side chain of the modified polypropylene molecule; the introduction of phosphorus elements can improve the flame retardancy of the high ionic conductivity lithium-ion battery separator; the carbon-carbon double bonds can undergo an addition reaction with the mercapto groups on the functionalized polysiloxane to form a crosslinked network, inhibit the relative movement between molecular chains, and improve the mechanical properties of the high ionic conductivity lithium-ion battery separator.

[0047] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and does not limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium-ion battery separator with high ionic conductivity, characterized in that, The high ionic conductivity lithium-ion battery separator is prepared by reacting chitosan porous microspheres with 1,3-propane sultone to obtain functionalized chitosan porous microspheres; polycondensing functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and dimethyldichlorosilane to obtain functionalized polysiloxane; reacting pre-modified polypropylene, formaldehyde, and allyl hypophosphorous acid to obtain modified polypropylene; Mixing the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile uniformly, and performing melt electrospinning to obtain a high ionic conductivity lithium-ion battery separator; The chitosan porous microspheres are prepared by using chitosan as a raw material, 1,4-dichloro-2-butene as a crosslinking agent, and melamine as a chain extender, and adopting an inverse suspension crosslinking method; The functionalized dimethoxysilane is prepared by reacting 3-aminopropyldimethoxymethylsilane with 4-pyridinecarboxaldehyde; The pre-modified polypropylene is prepared by reacting polypropylene with 1,4-diamino-2-butene.

2. A preparation method of a lithium-ion battery separator with high ionic conductivity, characterized in that, The preparation method of the high ionic conductivity lithium-ion battery separator includes the following preparation steps: (1) Mix 1,3-propane sultone and acetonitrile evenly according to a mass ratio of 1:(4-5) to prepare a 1,3-propane sultone solution; mix chitosan porous microspheres and acetonitrile evenly according to a mass ratio of 1:(50-60), ultrasonically disperse for 30-40 min, under nitrogen protection, at 70-72 °C, with a stirring speed of 200-300 r / min, uniformly dropwise add a 1,3-propane sultone solution that is 12-14 times the mass of the chitosan porous microspheres within 30 min, continue stirring and reacting for 10-12 h after the addition is completed, naturally cool to room temperature, filter, wash with acetone 3-5 times, and dry at 50-60 °C under vacuum for 8-10 h to obtain functionalized chitosan porous microspheres; (2) Mix functionalized dimethoxysilane, mercaptopropylmethyldimethoxysilane, and deionized water according to a mass ratio of 1:(1.3-1.5):(40-50), stir at 0-2 °C and 200-300 r / min for 20-30 min, uniformly dropwise add dimethyldichlorosilane that is 4-5 times the mass of mercaptopropylmethyldimethoxysilane within 20 min, continue stirring for 10-12 min after the addition is completed, raise the temperature to 64-66 °C, continue stirring and reacting for 4-5 h, add acid clay that is 0.06-0.08 times the mass of mercaptopropylmethyldimethoxysilane, raise the temperature to 98-102 °C, continue stirring and reacting for 3-4 h, filter off the acid clay, and dry the filtrate at 70-80 °C under vacuum for 16-18 h to obtain functionalized polysiloxane; (3) Mix pre-modified polypropylene and m-xylene evenly at a mass ratio of 1:(7 - 8), stir at 100 - 102 °C and 100 - 200 r / min for 10 - 12 min, add allyl hypophosphorous acid in an amount of 0.2 - 0.3 times the mass of the pre-modified polypropylene, then add formaldehyde in an equimolar amount to the allyl hypophosphorous acid, continue stirring and reacting for 70 - 80 min, cool down to 50 - 52 °C, add acetone in an amount of 3 - 4 times the mass of the pre-modified polypropylene and mix evenly, let stand for 1 - 2 h, filter by suction, and dry under vacuum conditions at 60 - 70 °C for 10 - 12 h to obtain modified polypropylene; (4) By mass, 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; mix the modified polypropylene, functionalized chitosan porous microspheres, functionalized polysiloxane, and azobisisobutyronitrile evenly, place them in an electrospinning device for melt electrospinning, and stack 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 h and cool to room temperature to obtain a lithium-ion battery separator with high ionic conductivity.

3. The preparation method of a high ionic conductivity lithium ion battery separator according to claim 2, characterized in that, The preparation method of the chitosan porous microspheres described in step (1) is as follows: Mix a chitosan solution, melamine, 1,4-dichloro-2-butene, and absolute ethanol evenly at a mass ratio of 1:(0.2 - 0.3):(0.6 - 0.8):(2 - 3), add Span-60 in an amount of 0.06 - 0.08 times the mass of the chitosan solution and liquid paraffin in an amount of 3 - 4 times the mass of the chitosan solution, heat up to 40 - 42 °C, continue stirring for 10 - 20 min, adjust the pH to 9 - 10 with a 1 mol / L sodium hydroxide aqueous solution, heat up to 70 - 80 °C and continue stirring for 1 - 2 h, naturally cool to room temperature, filter, wash with deionized water 3 - 5 times, and freeze-dry at -10 - -8 °C for 40 - 48 h to obtain chitosan porous microspheres.

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

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

6. The preparation method of a high ionic conductivity lithium-ion battery separator according to claim 2, wherein, The preparation method of the functionalized dimethoxysilane described in step (2) is as follows: Add 3-aminopropyldimethoxymethylsilane and 4-pyridinecarboxaldehyde in a molar ratio of 1:1 to toluene in an amount of 10 - 12 times the mass of 3-aminopropyldimethoxymethylsilane, stir and react at 50 - 60 °C and 200 - 300 r / min for 5 - 6 h, and dry at 50 - 60 °C under vacuum conditions for 10 - 12 h to obtain functionalized dimethoxysilane.

7. The preparation method of a high ionic conductivity lithium ion battery separator according to claim 2, characterized in that, The preparation method of the pre-modified polypropylene described in step (3) is as follows: Mix polypropylene and m-xylene evenly at a mass ratio of 1:(3 - 4), stir at 108 - 110 °C and 100 - 200 r / min for 10 - 12 min, add 1,4-diamino-2-butene which is 0.2 - 0.3 times the mass of polypropylene, continue to stir for 8 - 10 min, dropwise add the initiator solution which is 0.1 - 0.2 times the mass of polypropylene uniformly within 30 min, after the dropping is completed, raise the temperature to 130 - 132 °C, continue to stir and react for 2 - 3 h, cool down to 50 - 52 °C, add acetone which is 3 - 4 times the mass of polypropylene and mix evenly, let stand for 1 - 2 h, filter by suction, and dry at 60 - 70 °C under vacuum conditions for 8 - 10 h to obtain the pre-modified polypropylene.

8. The preparation method of 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: Mix benzoyl peroxide and m-xylene evenly at a mass ratio of 1:(5 - 6) to prepare the initiator solution.

9. The preparation method of 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 preparation method of a high ion conductivity lithium ion battery separator according to claim 2, characterized in that, The process parameters of the melt electrospinning described in step (4) are as follows: Set the pore diameter of the spinneret 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 rotational speed of the collecting roller to 90 - 100 r / min.

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