A lithium battery separator and a preparation method thereof

Abstract

The present invention discloses a lithium battery separator and a preparation method thereof, belonging to the technical field of lithium battery separators. The raw materials include the following parts by weight: 40-60 parts of ultra-high molecular weight polyethylene, 20-32 parts of pore-forming agent, 6-10 parts of modified nano silicon nitride, 5-15 parts of modified chitosan, 0.1-0.2 part of initiator, and 1-3 parts of antioxidant. The pore-forming agent is prepared by compounding polyvinyl alcohol and glycerol. The prepared separator has good pore size consistency, high air permeability, and no closed pores; the modified nano silicon nitride has good compatibility with the matrix and can enhance the mechanical strength and heat resistance of the separator; the prepared modified chitosan can significantly enhance the surface wettability, heat resistance, and flame retardancy of the lithium battery separator, and the performance is long-term stable; therefore, the separator prepared by the present invention has good pore size consistency, high air permeability, excellent mechanical strength, and stable and efficient surface wettability, heat resistance, and flame retardancy, and has important application value in the technical field of lithium battery separators.

Description

Technical Field

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

[0002] In recent years, with the rapid development of the electric vehicle industry, the development of high-energy power equipment, especially the lithium battery industry, has been promoted worldwide. Lithium batteries are used as a commonly used energy storage device with broad market prospects and rapid development due to their relatively high working voltage, specific energy, fast charge and discharge, and high safety performance.

[0003] A lithium battery mainly consists of four functional components: a positive electrode, an electrolyte, a separator, and a negative electrode. In the structure of a lithium battery, the separator is one of the key inner components. Although the separator does not participate in the chemical reactions in the lithium-ion battery, it plays a crucial role in the performance and safety of the lithium battery. Its main function is to separate the positive and negative electrodes of the battery to prevent the battery from short-circuiting due to the contact between the positive and negative electrodes, prevent the diffusion of by-products (such as lithium dendrites) from the oxidation-reduction reaction of the positive and negative electrode materials, and at the same time provide a channel for the migration of lithium ions.

[0004] As lithium batteries become more and more complex, the performance requirements for separators are also getting higher and higher. Currently, the most commonly used lithium battery separator materials on the market are polyolefin separators such as polyethylene and polypropylene. However, these materials have low thermal stability themselves, and will deform and shrink in size when heated at high temperatures, resulting in poor safety and easy to cause safety accidents such as short circuits. Polyolefin materials lack polar functional groups, have low compatibility with high-polarity electrolytes, resulting in poor wettability and large impedance during ion migration. In addition, the oxygen index of polyethylene and polypropylene is low, and the flame retardant performance is poor. Once a fire accident occurs, these separators are extremely easy to ignite, and there is a risk of dripping and spreading the fire, which cannot meet the requirements of lithium-ion battery equipment in high-end fields. Therefore, it is urgent to invent a separator with excellent heat resistance, wettability and flame retardant performance to meet the higher requirements in the technical field of lithium battery separators. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a lithium battery separator and a preparation method thereof.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A preparation method of a lithium battery separator includes the following steps:

[0008] After putting ultra-high molecular weight polyethylene into a pulverizer for pulverization, it is mixed with a pore-forming agent at high speed, and then modified nano-silicon nitride, modified chitosan, an initiator, and an antioxidant are added to a twin-screw extruder for melt blending and extrusion, followed by cooling and shaping, and then longitudinal stretching and transverse stretching to obtain a film. After immersing the film in ultrapure water for 1-2 hours, it is taken out, subjected to high-temperature heat setting, and wound up to prepare a lithium battery separator.

[0009] Further, the raw materials are as follows by weight: 40-60 parts of ultra-high molecular weight polyethylene, 20-32 parts of pore-forming agent, 6-10 parts of modified nano-silicon nitride, 5-15 parts of modified chitosan, 0.1-0.2 parts of initiator, and 1-3 parts of antioxidant.

[0010] Further, the pore-forming agent is prepared by compounding polyvinyl alcohol and glycerol in a mass ratio of 1:3.

[0011] Further, the high-speed mixing and stirring time is 10-20 min, and the stirring speed of the mixer is 2000-3000 r / min.

[0012] Further, the heat setting temperature is 120-150 .

[0013] Further, the initiator is one of benzoyl peroxide and lauroyl peroxide.

[0014] Further, the antioxidant is a hindered phenol antioxidant.

[0015] The pore-forming agent is prepared by compounding polyvinyl alcohol and glycerol, which has strong water solubility and can form a microporous structure when dissolved in water. It has the advantages of low cost, high environmental protection, good pore size consistency, high air permeability, and no closed pores.

[0016] Further, the modified nano-silicon nitride is prepared by the following steps:

[0017] At room temperature, nano-silicon nitride and an ethanol aqueous solution are added to a flask and stirred at high speed for 15 min under a high-shear mixing emulsifier. Vinyltrimethoxysilane (silane coupling agent KH-171) is added, and stirring is continued at high speed for 45 min under the high-shear mixing emulsifier. After the reaction is completed, filtration, vacuum drying, and grinding are carried out to obtain modified nano-silicon nitride.

[0018] Further, the dosage ratio of the nano-silicon nitride, ethanol aqueous solution, and vinyltrimethoxysilane is 2 g:100 mL:4.5 g.

[0019] Nano-silicon nitride is a ceramic powder with excellent properties, having good high-temperature resistance and mechanical properties. By modifying nano-silicon nitride, the surface hydrophobicity of nano-silicon nitride is improved, the compatibility between nano-silicon nitride and the polyethylene matrix is enhanced, the agglomeration phenomenon of nano-silicon nitride is alleviated, and the properties of nano-silicon nitride can be fully exerted, greatly enhancing the heat resistance and mechanical properties of the matrix. Moreover, the modified nano-silicon nitride also contains carbon-carbon double bonds and can crosslink with the matrix to further enhance the mechanical strength of the matrix.

[0020] Further, the modified chitosan is prepared by the following steps:

[0021] S1. Mix 4-hydroxystyrene and toluene, and add them into a three-necked round-bottom flask equipped with a thermometer, a magnetic stirring system and a spherical condenser. Under the condition of an ice-water bath, slowly dropwise add a formaldehyde solution (mass fraction 24%), and continuously stir for 30 min. Then add 4,4'-diaminodiphenyl sulfone, and control the reaction temperature at 65 , keep the temperature for reaction for 6 h. After the reaction is completed, cool to room temperature, rotary evaporate to remove the solvent, and then purify by column chromatography (the eluent uses a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two is 3:1). Rotary evaporate to remove the eluent to obtain intermediate 1. The dosage ratio of 4-hydroxystyrene, toluene, formaldehyde solution, and 4,4'-diaminodiphenyl sulfone is 11.9 g:100 mL:30 mL:25.1 g;

[0022] 4-Hydroxystyrene reacts with 4,4'-diaminodiphenyl sulfone to obtain intermediate 1. The specific reaction process is as follows:

[0023]

[0024] S2. In a three-necked flask equipped with a stirring device, mix glutaraldehyde, intermediate 1, piperidine (condensing agent) and toluene and stir evenly. Then control the reaction temperature at 60 , keep the temperature for reaction for 6 h. After the reaction is completed, naturally cool, distill under reduced pressure to remove the solvent, and then purify by column chromatography (the eluent uses a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two is 3:2). Rotary evaporate to remove the eluent to obtain intermediate 2. The dosage ratio of glutaraldehyde, intermediate 1, piperidine, and toluene is 12.2 g:39.2 g:15 mL:120 mL;

[0025] Under the action of the condensing agent, the amino group on intermediate 1 condenses with the aldehyde group on glutaraldehyde to form an imine group (C=N Schiff base structure). By controlling the molar ratio of the two to be close to 1:1 and glutaraldehyde being slightly in excess, only one aldehyde group on glutaraldehyde participates in the reaction to obtain intermediate 2. The specific reaction process is as follows:

[0026]

[0027] S3. Add chitosan to a mixed solution of acetic acid and toluene (the mass fraction of acetic acid is 28%), stir until completely dissolved, then add intermediate 2 and piperidine. After stirring and reacting at room temperature for 1 h, add sodium hydroxide solution (mass fraction 35%) to adjust the pH to 9, and continue to react for 3 h. After the reaction is completed, let it stand for precipitation, filter, wash successively with ethanol and water, and dry in an oven to obtain modified chitosan; the dosage ratio of the mixed solution of acetic acid and toluene, chitosan, intermediate 2, and piperidine is 100 mL:5 g:8.5 g:20 mL;

[0028] Under the action of a condensing agent, the aldehyde group on intermediate 2 condenses with the amino group on chitosan to form an imino group (C=N Schiff base structure), obtaining modified chitosan;

[0029] Chitosan is a polysaccharide. A large number of hydroxyl groups in the molecule can promote the dehydration and carbonization of the polyethylene matrix, convert the matrix into a high-concentration carbon layer, and improve the flame retardancy of the matrix; moreover, a large number of ether groups are contained in the main chain of chitosan, enabling chitosan to adsorb polysulfides, improving the conductivity of the battery, the utilization rate of active substance sulfur, and the rate performance; in addition, by modifying chitosan, the interfacial compatibility between chitosan and polyethylene can be improved, enabling the performance of modified chitosan to be fully exerted; furthermore, the modified chitosan molecule also contains diphenyl sulfone, benzoxazine, Schiff base, and carbon-carbon double bond structures. Among them, diphenyl sulfone has good high-temperature resistance and thermal oxidation resistance, and generates SO2, sulfurous acid, and water by thermal desulfurization, which can promote the Fries rearrangement reaction of the silicone rubber matrix and accelerate the carbonization of the matrix, effectively enhancing the flame retardancy of the matrix; the introduced benzoxazine can further enhance the heat resistance of the matrix; the C=N double bond in the Schiff base structure can generate a carbon-nitrogen six-membered ring at high temperature. This kind of six-membered ring structure enables the matrix to form a stable cross-linked network, which can cooperate with diphenyl sulfone to greatly enhance the flame retardancy of the matrix; finally, introducing carbon-carbon double bonds into the modified chitosan can generate cross-linking with the matrix. Because the modified chitosan molecule contains a large number of hydroxyl groups, it can enhance the hydrophilicity of the matrix, enabling the separator to have good adsorption affinity with the electrolyte, reducing the impedance of ion migration, and improving the long-cycle performance of the battery.

[0030] It should be added that grafting an organic molecular chain onto chitosan can improve the migration resistance and exudation resistance of organic small molecules and improve the stability of the performance of modified chitosan.

[0031] Advantages of the present invention:

[0032] 1. The pore-forming agent for the lithium battery separator prepared by the present invention is prepared by compounding polyvinyl alcohol and glycerol, has strong water solubility, and the obtained separator has good pore size consistency, high air permeability, and no closed pores;

[0033] 2. Modify nano-silicon nitride. Compared with ordinary nano-silicon nitride, it has better compatibility with the matrix, reduces the agglomeration phenomenon, and can significantly enhance the mechanical strength and heat resistance of the separator.

[0034] 3. The prepared modified chitosan can significantly enhance the surface wettability, heat resistance and flame retardancy of the lithium battery separator, and its performance is long-term stable, not easy to fall off, and can also enhance the long-cycle performance of the battery.

[0035] Therefore, the separator prepared by the present invention has good pore size consistency, high air permeability, excellent mechanical strength, and stable and efficient surface wettability, heat resistance and flame retardancy, and has important application value in the technical field of lithium battery separators. Detailed Embodiments

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] Example 1

[0038] Prepare modified chitosan:

[0039] S1. Mix 11.9 g of 4-hydroxystyrene with 100 mL of toluene, add them to a three-necked round-bottom flask equipped with a thermometer, a magnetic stirring system and a spherical condenser. Under the condition of an ice-water bath, gradually add 30 mL of formaldehyde solution (mass fraction 24%), and continue to stir for 30 min. Then add 25.1 g of 4,4'-diaminodiphenyl sulfone, and control the reaction temperature at 65 , keep the temperature for reaction for 6 h. After the reaction is completed, cool to room temperature, rotary evaporate to remove the solvent, and then purify by column chromatography (the eluent uses a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two is 3:1). Rotary evaporate to remove the eluent to obtain intermediate 1.

[0040] S2. In a three-necked flask equipped with a stirring device, mix 12.2 g of glutaraldehyde, 39.2 g of intermediate 1, 15 mL of piperidine and 120 mL of toluene and stir evenly. Then control the reaction temperature at 60 , keep the temperature for reaction for 6 h. After the reaction is completed, cool naturally, distill off the solvent under reduced pressure, and then purify by column chromatography (the eluent uses a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two is 3:2). Rotary evaporate to remove the eluent to obtain intermediate 2.

[0041] S3. Add 5 g of chitosan to a 100 mL mixed solution of acetic acid and toluene (mass fraction of acetic acid is 28%), stir until completely dissolved, then add 8.5 g of Intermediate 2 and 20 mL of piperidine. After stirring at room temperature for 1 h, add sodium hydroxide solution (mass fraction 35%) to adjust the pH to 9, and continue the reaction for 3 h. After the reaction is completed, let it stand for precipitation, filter, wash successively with ethanol and water, and dry in an oven to obtain modified chitosan.

[0042] Example 2

[0043] Preparation of modified chitosan:

[0044] S1. Mix 23.8 g of 4-hydroxystyrene with 200 mL of toluene, add them to a three-necked round-bottom flask equipped with a thermometer, a magnetic stirring system and a spherical condenser. Under the condition of an ice-water bath, dropwise add 30 mL of formaldehyde solution (mass fraction 24%) and continuously stir for 30 min, then add 50.2 g of 4,4'-diaminodiphenyl sulfone, and control the reaction temperature at 65 , keep the temperature for reaction for 6 h. After the reaction is completed, cool to room temperature, rotary evaporate to remove the solvent, and then purify by column chromatography (the eluent is a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two is 3:1). Rotary evaporate to remove the eluent to obtain Intermediate 1;

[0045] S2. In a three-necked flask equipped with a stirring device, mix 24.4 g of glutaraldehyde, 78.4 g of Intermediate 1, 30 mL of piperidine and 240 mL of toluene and stir evenly, then control the reaction temperature at 60 , keep the temperature for reaction for 6 h. After the reaction is completed, cool naturally, distill off the solvent under reduced pressure, and then purify by column chromatography (the eluent is a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two is 3:2). Rotary evaporate to remove the eluent to obtain Intermediate 2;

[0046] S3. Add 10 g of chitosan to a 200 mL mixed solution of acetic acid and toluene (mass fraction of acetic acid is 28%), stir until completely dissolved, then add 17 g of Intermediate 2 and 40 mL of piperidine. After stirring at room temperature for 1 h, add sodium hydroxide solution (mass fraction 35%) to adjust the pH to 9, and continue the reaction for 3 h. After the reaction is completed, let it stand for precipitation, filter, wash successively with ethanol and water, and dry in an oven to obtain modified chitosan.

[0047] Example 3

[0048] Preparation of modified nano-silicon nitride:

[0049] At room temperature, add 2 g of nano-silicon nitride and 100 mL of ethanol aqueous solution into a flask, stir at high speed for 15 min under a high-shear mixing emulsifier, add 4.5 g of vinyltrimethoxysilane, and continue to stir at high speed for 45 min under the high-shear mixing emulsifier. After the reaction is completed, filter, dry under vacuum, and grind to obtain modified nano-silicon nitride.

[0050] Example 4

[0051] Preparation of modified nano-silicon nitride:

[0052] At room temperature, add 4 g of nano-silicon nitride and 200 mL of ethanol aqueous solution into a flask, stir at high speed for 15 min under a high-shear mixing emulsifier, add 9 g of vinyltrimethoxysilane, and continue to stir at high speed for 45 min under the high-shear mixing emulsifier. After the reaction is completed, filter, dry under vacuum, and grind to obtain modified nano-silicon nitride.

[0053] Example 5

[0054] Put 40 g of ultra-high molecular weight polyethylene into a crusher for crushing, then mix and stir it with 20 g of pore-forming agent (prepared by compounding 5 g of polyvinyl alcohol and 15 g of glycerol) at high speed for 10 min. The stirring speed of the mixer is 2000 r / min. Then add 6 g of modified nano-silicon nitride prepared in Example 3, 5 g of modified chitosan prepared in Example 1, 0.1 g of benzoyl peroxide, and 1 g of antioxidant 1010 into a twin-screw extruder, melt and blend and extrude, cool and shape, then conduct longitudinal stretching and transverse stretching to obtain a film. Immerse the film in ultrapure water for 1 h, then take it out and perform high-temperature heat setting at 120 and wind it up to obtain a lithium battery separator with a separator thickness of.

[0055] Example 6

[0056] Put 50 g of ultra-high molecular weight polyethylene into a crusher for crushing, then mix and stir it with 28 g of pore-forming agent (prepared by compounding 7 g of polyvinyl alcohol and 21 g of glycerol) at high speed for 15 min. The stirring speed of the mixer is 2500 r / min. Then add 8 g of modified nano-silicon nitride prepared in Example 4, 10 g of modified chitosan prepared in Example 2, 0.2 g of benzoyl peroxide, and 2 g of antioxidant 1010 into a twin-screw extruder, melt and blend and extrude, cool and shape, then conduct longitudinal stretching and transverse stretching to obtain a film. Immerse the film in ultrapure water for 2 h, then take it out and perform high-temperature heat setting at 130 and wind it up to obtain a lithium battery separator.

[0057] Example 7

[0058] After putting 60 g of ultra-high molecular weight polyethylene into a pulverizer for pulverization, it is mixed and stirred at high speed with 32 g of a pore-forming agent (prepared by compounding 8 g of polyvinyl alcohol and 24 g of glycerol) for 20 min. The stirring speed of the mixer is 3000 r / min. Then, 10 g of modified nano-silicon nitride prepared in Example 4, 15 g of modified chitosan prepared in Example 2, 0.2 g of benzoyl peroxide, and 3 g of antioxidant 1010 are added to a twin-screw extruder for melt blending and extrusion, followed by cooling and shaping. After longitudinal and transverse stretching, a membrane is obtained. The membrane is immersed in ultrapure water for 2 h, taken out, and then subjected to high-temperature heat setting at 150 to obtain a lithium battery separator after winding.

[0059] Comparative Example 1

[0060] The modified chitosan in Example 7 is replaced with ordinary chitosan of the same mass, and the remaining steps are the same as those in Example 7 to obtain a separator.

[0061] Comparative Example 2

[0062] A commercially available polyethylene separator for lithium batteries is used.

[0063] Examples 5 - 7 and Comparative Examples 1 - 2 are subjected to the following performance tests:

[0064] The limiting oxygen index of the specimens before and after being placed at room temperature for 180 days is determined according to the national standard GB / T 2406 - 2008 "Test Method for Flammability of Plastics";

[0065] The tensile strength is determined according to the national standard GB / T 1040.3 - 2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets";

[0066] The thermal shrinkage rate of the specimens is determined according to the national standard GB / T 36363 - 2018 "Polyolefin Separators for Lithium-Ion Batteries";

[0067] The mass of the dry battery separator is denoted as M0, then the separator is completely immersed in the electrolyte, and the surface residual electrolyte is carefully wiped off with filter paper and weighed again. The weight at this time is denoted as M1. The calculation formula for the liquid absorption rate is as follows: (M1 - M0) / M0 × 100%.

[0068] The measured results are shown in Table 1:

[0069] Table 1

[0070]

[0071] The lithium battery separators of Examples 5-7 and Comparative Examples 1-2 were assembled into half-cells with lithium iron phosphate as the positive electrode and graphite as the negative electrode. The specific test method was as follows: the charging current was 2 mA, the charging cut-off voltage was ≥4.3 V, and the discharging cut-off voltage was ≤2.5 V for testing. After 1500 cycles, the capacity retention rate was tested.

[0072] The measured results are shown in Table 2:

[0073] Table 2

[0074]

[0075] As can be seen from the above table, the separator prepared in the embodiment of the present invention has excellent mechanical strength, and has stable and efficient surface wettability, heat resistance and flame retardancy. It can also enhance the long cycle performance of the battery, and has important application value in the technical field of lithium battery separators.

[0076] In the description of the specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0077] The above content is only an example and illustration of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them. As long as they do not deviate from the invention or exceed the scope defined by the claims of this patent, they should fall within the protection scope of the present invention.

Claims

1. A lithium battery separator, characterized in that: The diaphragm is obtained by melt blending and extruding the raw materials, comprising the following raw materials in parts by weight: 40-60 parts of ultra-high molecular weight polyethylene, 20-32 parts of pore-forming agent, 6-10 parts of modified nano silicon nitride, 5-15 parts of modified chitosan, 0.1-0.2 parts of initiator, and 1-3 parts of antioxidant; Wherein, the modified chitosan is prepared by the following steps: S1. Mix 4-hydroxystyrene and toluene, add formaldehyde solution dropwise under ice-water bath, and continue stirring for 30 min, then add 4,4'-diaminodiphenyl sulfone, react at 65°C for 6 h. After the reaction is complete, cool to room temperature, perform rotary evaporation, purify by column chromatography, and perform rotary evaporation to obtain intermediate 1. S2, glutaraldehyde, intermediate 1, piperidine and toluene were mixed and stirred evenly, and reacted at 60° C. for 6 hours. After the reaction was completed, the mixture was naturally cooled, distilled under reduced pressure, purified by column chromatography, and rotary evaporated to obtain intermediate 2; S3. Add chitosan to the mixed solution of acetic acid and toluene, stir until completely dissolved, then add intermediate 2 and piperidine, stir and react at room temperature for 1 hour, adjust the pH to 9, continue the reaction for 3 hours, and after the reaction is completed, let it stand and precipitate, filter, wash and dry to obtain modified chitosan.

2. A lithium battery separator according to claim 1, characterized in that: In step S1, the ratio of the amount of 4-hydroxystyrene, toluene, formaldehyde solution, and 4,4'-diaminodiphenyl sulfone is 11.9 g: 100 mL: 30 mL: 25.1 g.

3. A lithium battery separator according to claim 1, characterized in that: In step S2, the ratio of glutaraldehyde, intermediate 1, piperidine and toluene is 12.2 g:39.2 g:15 mL:120 mL.

4. A lithium battery separator according to claim 1, characterized in that: In step S3, the ratio of the mixed solution of acetic acid and toluene, chitosan, intermediate 2, and piperidine is 100 mL: 5 g: 8.5 g: 20 mL.

5. A lithium battery separator according to claim 1, characterized in that: The pore-forming agent is prepared by compounding polyvinyl alcohol and glycerol in a mass ratio of 1:

3.

6. A lithium battery separator according to claim 1, characterized in that: The initiator is one of benzoyl peroxide and lauroyl peroxide.

7. A lithium battery separator according to claim 1, characterized in that: The antioxidant is a hindered phenol antioxidant.

8. A lithium battery separator according to claim 1, characterized in that: The modified nano silicon nitride is prepared by the following steps: At room temperature, add nano silicon nitride and ethanol aqueous solution into a flask, stir, add vinyltrimethoxysilane, continue stirring, and when the reaction is complete, filter, vacuum dry, and grind to obtain modified nano silicon nitride.

9. The method for preparing a lithium battery separator according to claim 1, characterized in that: The following steps are involved: The ultra-high molecular weight polyethylene is crushed in a pulverizer, mixed with a pore-forming agent at high speed, and then added into a twin-screw extruder with modified nano silicon nitride, modified chitosan, an initiator and an antioxidant, melt-blended and extruded, cooled and shaped, and then longitudinally and transversely stretched to obtain a membrane. The membrane is immersed in ultrapure water, taken out, heat-shaped at high temperature, and rolled up to obtain a lithium battery separator.

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