A highly flame-retardant separator for lithium-ion batteries and its preparation process

Abstract

The present invention relates to the technical field of battery separators, specifically a highly flame-retardant separator for lithium-ion batteries and its preparation process. KHCO3 is introduced into the coating; COPNA resin is prepared using naphthol as a raw material, and through etherification reaction, copolymerization reaction with bis(2-trifluoromethyl-4-aminophenyl)imide and 4,4-diphenylmethane bismaleimide is carried out to prepare a modified COPNA resin with a multi-branched structure as an adhesive in the coating; β-cyclodextrin framework is grafted onto the KHCO3 nanotubes to improve the binding strength between the KHCO3 nanotubes and the separator, thereby enhancing the thermal stability of the separator; N-aminoethyl-γ-aminopropyltrimethoxysilane and sodium dodecylsulfonate are used to carry out amination treatment on the KHCO3 nanotubes grafted with β-cyclodextrin framework, and then 1,3-propane sultone is grafted. Without adding a dispersant, the uniformity of the dispersion of KHCO3 nanotubes in the coating slurry is improved, and at the same time, the safety of the battery separator is synergistically improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and specifically to a highly flame-retardant separator for lithium-ion batteries and its preparation process. Background Art

[0002] With the booming development of the new energy industry, secondary batteries with high energy density represented by lithium-ion batteries have attracted more and more attention. Among them, improving the safety performance of lithium-ion batteries has great practical significance. The separator is one of the main components of lithium-ion batteries. During the charge and discharge process of lithium-ion batteries, the separator plays a role in separating the positive and negative electrodes, avoiding internal short circuits of the battery, and providing a channel for lithium ions to pass through; the performance of the separator determines the safety of lithium-ion batteries.

[0003] The most widely used lithium-ion battery separator in the existing market is the polyolefin separator. However, the polyolefin separator has low mechanical strength and poor puncture resistance. When used as a lithium-ion battery separator, it is easily punctured and causes contact short circuit, resulting in thermal runaway; moreover, most of the polyolefin materials in the existing market have low melting points, low specific surface area and poor liquid absorption and retention ability, and are prone to membrane rupture during thermal runaway, thus aggravating thermal runaway.

[0004] Existing research usually adds a ceramic coating on the polyolefin separator to solve the problems of low mechanical strength, poor liquid absorption and retention ability, and poor heat resistance of the polyolefin separator. However, the ceramic coating can usually only delay the closing of the separator pores to 150 °C, and 150 °C obviously cannot completely avoid problems such as short circuit and spontaneous combustion of the battery at high temperatures. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly flame-retardant separator for lithium-ion batteries and its preparation process to solve the problems in the prior art.

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

[0007] A highly flame-retardant separator for lithium-ion batteries includes a base film and a coating layer. In terms of mass percentage, the raw material composition in the coating layer is: 12-20% KHCO3 nanotubes, 0-0.6% dispersant, 0.4-0.7% thickener, 0.5-1% binder, 0.05-0.2% wetting agent, and the balance is ultrapure water.

[0008] The present invention provides a lithium-ion battery separator with high mechanical strength, high flame retardancy and high electrolyte wettability in view of the technical defects of low liquid absorption and retention ability, poor heat resistance and mechanical properties in the prior art.

[0009] By introducing KHCO₃ nanotubes, while maintaining the excellent properties of the KHCO₃ nanotubes themselves, through the cross-linking between different nanotubes, the mechanical strength and thermal shrinkage performance of the battery separator are greatly improved; and the hollow structure of the KHCO₃ nanotubes will synergistically improve the lithium ion conductivity, and at the same time greatly increase the specific surface area of the material, thereby greatly enhancing the liquid absorption and retention capacity of the battery separator; when the external temperature rises to the decomposition temperature of the KHCO₃ nanotubes, the KHCO₃ nanotubes will decompose to release water vapor and carbon dioxide, absorb latent heat, and greatly reduce the concentration of oxygen and combustible gases; the protective layer formed on the surface prevents the entry of oxygen and heat, and KHCO 3会 decomposes to form potassium carbonate, which has good high-temperature resistance, thereby improving the ability of the separator to resist open flames.

[0010] Furthermore, the dispersant is hydrolyzed polymaleic anhydride dispersant, the thickener is sodium carboxymethyl cellulose, the binder is a COPNA resin binder, and the wetting agent is a silanol non-ionic surfactant.

[0011] Furthermore, the preparation of the KHCO₃ nanotubes includes the following steps:

[0012] Mix hydrophilic silica nanowires and deionized water and stir for 45 - 55 min, then ultrasonically disperse for 1 - 2 h, add potassium carbonate, stir until dissolved, introduce a mixed gas of carbon dioxide and nitrogen, continue to ventilate for 220 - 230 min, filter and wash, vacuum dry at 75 - 80 °C for 24 h, control the vacuum degree of the vacuum drying at 0.08 Mpa, then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h, filter and wash, and dry at 80 - 85 °C for 10 - 12 h to obtain KHCO₃ nanotubes.

[0013] In the present invention, COPNA resin is selected as the binder. The COPNA resin has a multi-core polycyclic aromatic structure, which is formed by connecting polycyclic aromatic hydrocarbons and has better high-temperature resistance than general resins.

[0014] However, there are many carbon ring structures in the COPNA resin, which will still crack and volatilize under high-temperature conditions, thus affecting its bonding performance. Therefore, in the present invention, the COPNA resin is modified to improve its high-temperature stability and make it still maintain excellent bonding performance in a high-temperature environment.

[0015] Furthermore, the binder is a modified COPNA resin, and the preparation includes the following steps:

[0016] (1) Heat 1-naphthol to melting, add benzaldehyde and stir, add a mixed solution of p-toluenesulfonic acid and ethanol, and stop the reaction when the phenomenon of "sticking to the rod" appears in the reaction solution to obtain naphthol-based COPNA resin;

[0017] (2) Mix naphthol - based COPNA resin and n - butanol, keep warm at 50 - 60 °C for 30 - 60 min, add potassium hydroxide powder, cool down to 35 - 40 °C, add allyl chloride, keep warm for 3 - 4 h, add a mixed solution of absolute ethanol and aluminum sulfate, filter to obtain pretreated COPNA resin;

[0018] (3) Under nitrogen protection, mix 4 - nitro - 2(trifluoromethyl)aniline, 2 - fluoro - 5 - nitrobenzotrifluoride, potassium carbonate, and dimethylacetamide, keep at 135 - 140 °C for 22 - 24 h, pour into deionized water, rinse, and dry to obtain bis(2 - methyl - 4 - nitrophenyl)amine; Under nitrogen protection, mix bis(2 - methyl - 4 - nitrophenyl)amine, palladium - carbon, and absolute ethanol, heat up to 80 °C, cool down to 70 °C and add hydrazine hydrate, keep warm for 10 - 12 h, filter, pour into 40 mL of deionized water, wash, and dry to obtain bis(2 - trifluoromethyl - 4 - aminophenyl)imine;

[0019] (4) Mix the pretreated COPNA resin, bis(2 - trifluoromethyl - 4 - aminophenyl)imine, 4,4 - diphenylmethane bismaleimide, ethanol, tetrahydrofuran, and N,N - dimethylformamide, heat to dissolve, keep warm for 20 - 30 min to obtain a prepolymer, and cure to obtain modified COPNA resin.

[0020] Further, the working conditions for curing are: keep warm at 180 °C for 2 h, heat up to 200 °C and keep warm for 2 h, heat up to 220 °C and keep warm for 2 h, heat up to 240 °C and keep warm for 2 h.

[0021] Further, the mass ratio of 1 - naphthol, benzaldehyde, and p - toluenesulfonic acid is 1:1:0.07; the mass ratio of the pretreated COPNA resin, bis(2 - trifluoromethyl - 4 - aminophenyl)imine, and 4,4 - diphenylmethane bismaleimide is 1:0.2:0.8.

[0022] In the present invention, COPNA resin is prepared from naphthol as a raw material, and through etherification reaction and copolymerization reaction with bis(2 - trifluoromethyl - 4 - aminophenyl)imine and 4,4 - diphenylmethane bismaleimide, a modified COPNA resin with a multi - branched structure is prepared; while improving the high - temperature adhesiveness of COPNA resin, the mechanical strength of the battery separator is improved. The introduced imino group can form hydrogen bonds with the sulfonic acid groups grafted on the surface of KHCO3 nanotubes, thereby constructing a complex hydrogen - bond network, effectively promoting the proton - conduction performance of the battery separator, thus improving the wettability of the battery separator and reducing the risk of separator thermal runaway.

[0023] Further, a preparation process for a highly flame - retardant separator for lithium - ion batteries includes the following steps:

[0024] S1: Prepare KHCO3 nanotubes;

[0025] S2: Mix the dispersant, KHCO₃ nanotubes, and ultrapure water for 30 - 110 min at a rotation speed of 200 - 300 rpm; add the thickener and continue stirring for 20 - 60 min at a rotation speed of 200 - 400 rpm; add the binder and stir for 30 - 50 min at a rotation speed of 300 - 500 rpm; add the wetting agent and stir for 20 - 40 min at a rotation speed of 300 - 600 rpm; filter to remove iron to obtain the KHCO₃ nanotube coated slurry.

[0026] S3: Adopt the microgravure roll coating process, and use a coater to stepwise roll coat the prepared KHCO₃ nanotubes on both sides of the polyolefin separator, then wind it up after baking at 65 - 70 °C to obtain a highly flame - retardant separator for lithium - ion batteries.

[0027] Furthermore, perform surface treatment on the KHCO₃ nanotubes:

[0028] ① Mix β - cyclodextrin, potassium hydroxide, and deionized water, then continuously introduce methanol. After 5 - 7 d, centrifuge, wash with methanol 3 - 5 times, and dry to obtain the β - cyclodextrin framework.

[0029] ② Ultrasonically disperse the KHCO₃ nanotubes in potassium hydroxide, dilute with deionized water to a pH of 6.8 - 7.2, perform vacuum filtration, dry and grind, and then perform plasma treatment to obtain the pretreated KHCO₃ nanotubes.

[0030] ③ Mix the β - cyclodextrin framework, pretreated KHCO₃ nanotubes, absolute ethanol, and deionized water, and ultrasonically stir for 20 - 30 min to obtain solution A; mix N - aminoethyl - γ - aminopropyltrimethoxysilane, sodium dodecylsulfonate, absolute ethanol, and deionized water to obtain solution B; mix solution A and solution B, ultrasonically stir at 65 - 70 °C for 20 - 30 min, let it stand for 3 - 4 h, wash with ethanol 3 - 5 times, under nitrogen protection, add a mixture of 1,3 - propane sultone and dimethyl sulfoxide, ultrasonically stir for 20 - 30 min, wash with deionized water, and dry to obtain the modified KHCO₃ nanotubes.

[0031] Furthermore, the working conditions of the plasma treatment are: the flow rate of oxygen is 100 mL / min, the pressure is 18 Pa, the time is 5 min, and the power is 120 W.

[0032] First, perform plasma treatment on the KHCO₃ nanotubes to expose the surface hydroxyl groups, improve the reaction activity of the KHCO₃ nanotubes, treat β - cyclodextrin to obtain an organic - inorganic hybrid β - cyclodextrin framework, and then graft the β - cyclodextrin framework onto the KHCO₃ nanotubes to improve the binding strength between the KHCO₃ nanotubes and the separator, thereby enhancing the thermal stability of the separator.

[0033] The KHCO₃ nanotubes with grafted β-cyclodextrin framework are aminated with N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane and sodium dodecylsulfonate, and then 1,3-propanesultone is grafted. Without adding a dispersant, the uniformity of the dispersion of KHCO₃ nanotubes in the coating slurry is improved. While synergistically enhancing the thermal stability of battery heat insulation, the construction of a multi-dimensional complex network is beneficial to improving the heat conduction ability of the battery separator, thereby enhancing the safety of the battery separator.

[0034] Furthermore, the working conditions of ultrasonic stirring: the ultrasonic intensity is 65 W; the mass ratio of N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane to sodium dodecylsulfonate is 3:1.

[0035] When aminating with N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane, using a lower-intensity ultrasonic wave can effectively promote the grafting of amino silane.

[0036] The beneficial effects of the present invention:

[0037] The present invention provides a highly flame-retardant separator for lithium-ion batteries and its preparation process. By introducing KHCO₃ nanotubes to prepare the coating of the lithium-ion battery separator, a lithium-ion battery separator with high mechanical strength, high flame retardancy, and high electrolyte wettability is obtained.

[0038] Introducing KHCO₃ into the coating, while maintaining the excellent properties of the KHCO₃ nanotubes themselves, the mechanical strength and thermal shrinkage performance of the battery separator are greatly improved through the cross-linking between different nanotubes; and the hollow structure of the KHCO₃ nanotubes will synergistically improve the lithium-ion conductivity, and at the same time greatly increase the specific surface area of the material, thereby greatly enhancing the liquid absorption and liquid retention ability of the battery separator; when the external temperature rises to the decomposition temperature of the KHCO₃ nanotubes, the KHCO₃ nanotubes will decompose to release water vapor and carbon dioxide, absorb latent heat, and greatly reduce the concentration of oxygen and combustible gases; the protective layer formed on the surface prevents the entry of oxygen and heat, and KHCO₃ will decompose to form potassium carbonate, which has good high-temperature resistance, thereby improving the ability of the separator to resist open flames.

[0039] Using naphthol as a raw material to prepare COPNA resin, through etherification reaction, copolymerization reaction with bis(2-trifluoromethyl-4-aminophenyl)imide and 4,4-diphenylmethane bismaleimide to prepare a modified COPNA resin with a multi-branched structure, as an adhesive in the coating, while improving the high-temperature adhesiveness of the COPNA resin, it also improves the mechanical strength of the battery separator. The introduced imino group can form hydrogen bonds with the sulfonic acid groups grafted on the surface of the KHCO₃ nanotubes, thereby constructing a complex hydrogen bond network, effectively promoting the proton conduction performance of the battery separator, thereby improving the wettability of the battery separator and reducing the risk of separator thermal runaway.

[0040] In the present invention, the KHCO₃ nanotubes are subjected to plasma treatment to expose the surface hydroxyl groups, thereby improving the reactivity of the KHCO₃ nanotubes. β-Cyclodextrin is processed to obtain an organic-inorganic hybrid β-cyclodextrin framework, and then the β-cyclodextrin framework is grafted onto the KHCO₃ nanotubes to enhance the binding strength between the KHCO₃ nanotubes and the separator, thereby enhancing the thermal stability of the separator. N-(2-Aminoethyl)-γ-aminopropyltrimethoxysilane and sodium dodecyl sulfate are used to perform amination treatment on the KHCO₃ nanotubes grafted with the β-cyclodextrin framework, and then 1,3-propane sultone is grafted. Without adding a dispersant, the uniformity of the dispersion of the KHCO₃ nanotubes in the coating slurry is improved, and the safety of the battery separator is synergistically improved. Detailed implementation manners

[0041] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0042] It should be noted that if there are directional indications such as up, down, left, right, front, back... in the embodiments of the present invention, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention. The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention. Embodiment

[0043] A preparation process for a highly flame-retardant separator for a lithium-ion battery, comprising the following steps:

[0044] S1: Prepare KHCO₃ nanotubes;

[0045] Mix 1.1752 g of hydrophilic silica nanowires and 78 mL of deionized water, stir for 45 min, then ultrasonically disperse for 1 h. Add 115 g of potassium carbonate and stir until dissolved. Introduce a mixed gas of carbon dioxide and nitrogen (volume ratio of carbon dioxide to nitrogen is 67.5:32.5), and continue to ventilate for 220 min. Filter, wash, and vacuum dry at 75 °C for 24 h, controlling the vacuum degree of vacuum drying at 0.08 Mpa. Then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h. Filter, wash, and dry at 80 °C for 12 h to obtain KHCO₃ nanotubes;

[0046] S2: Mix the dispersant, KHCO₃ nanotubes, and ultrapure water for 30 min at a rotation speed of 300 rpm; add the thickener and continue to stir for 20 min at a rotation speed of 400 rpm; add the binder and stir for 30 min at a rotation speed of 500 rpm; add the wetting agent and stir for 20 min at a rotation speed of 600 rpm; filter to remove iron to obtain the KHCO₃ nanotube coating slurry;

[0047] By mass percentage, the composition of the KHCO₃ nanotube coating slurry is: 12% KHCO₃ nanotubes, 0.34% dispersant, 0.4% thickener, 0.5% binder, 0.05% wetting agent, and the balance is ultrapure water;

[0048] The dispersant is a hydrolyzed polymaleic anhydride dispersant; the thickener is sodium carboxymethyl cellulose; the wetting agent is a silanol-based nonionic surfactant;

[0049] The binder is a COPNA resin-based binder;

[0050] S3: Adopt the microgravure roll coating process, and use a coater to roll coat the prepared KHCO₃ nanotube coating slurry on both sides of a 9-μm polyolefin separator step by step. The single-sided coating thickness is 3 μm, and after baking at 65 °C, it is wound up to obtain a highly flame-retardant separator for lithium-ion batteries.

[0051] Example 2

[0052] A preparation process for a highly flame-retardant separator for lithium-ion batteries, comprising the following steps:

[0053] S1: Prepare KHCO₃ nanotubes;

[0054] Mix 1.1752 g of hydrophilic silicon dioxide nanowires and 78 mL of deionized water, stir for 50 min, then ultrasonically disperse for 1.5 h. Add 115 g of potassium carbonate and stir until dissolved. Introduce a mixed gas of carbon dioxide and nitrogen (volume ratio of carbon dioxide to nitrogen is 67.5:32.5), continue to ventilate for 225 min, filter and wash. Dry in vacuum at 78 °C for 24 h, control the vacuum degree of vacuum drying at 0.08 Mpa, then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h, filter and wash, and dry at 83 °C for 11 h to obtain KHCO₃ nanotubes;

[0055] S2: Mix the dispersant, KHCO₃ nanotubes and ultrapure water for 80 min at a rotation speed of 250 rpm; add the thickener and continue to stir for 40 min at a rotation speed of 300 rpm; add the binder and stir for 40 min at a rotation speed of 400 rpm; add the wetting agent and stir for 30 min at a rotation speed of 400 rpm; filter to remove iron to obtain the KHCO₃ nanotube coating slurry;

[0056] By mass percentage, the composition of the KHCO₃ nanotube coating slurry is: 16% KHCO₃ nanotubes, 0.34% dispersant, 0.65% thickener, 0.88% binder, 0.17% wetting agent, and the balance is ultrapure water;

[0057] The dispersant is a hydrolyzed polymaleic anhydride dispersant; the thickener is sodium carboxymethyl cellulose; the wetting agent is a silanol non-ionic surfactant;

[0058] The binder is a COPNA resin binder;

[0059] S3: Adopt the microgravure roll coating process, and use a coater to roll-coat the prepared KHCO₃ nanotube coating slurry on both sides of a 9-μm polyolefin separator step by step. The thickness of the single-sided coating is 3 μm, and after baking at 68 °C, it is wound up to obtain a highly flame-retardant separator for lithium-ion batteries.

[0060] Example 3

[0061] A preparation process of a highly flame-retardant separator for lithium-ion batteries, comprising the following steps:

[0062] S1: Prepare KHCO₃ nanotubes;

[0063] Mix 1.1752 g of hydrophilic silica nanowires with 78 mL of deionized water and stir for 55 min, then ultrasonically disperse for 2 h. Add 115 g of potassium carbonate and stir until dissolved. Introduce a mixed gas of carbon dioxide and nitrogen (volume ratio of carbon dioxide to nitrogen is 67.5:32.5), and continue to ventilate for 230 min. Filter and wash, then vacuum dry at 80 °C for 24 h, controlling the vacuum degree of vacuum drying at 0.08 Mpa. Then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h. Filter and wash, and dry at 85 °C for 10 h to obtain KHCO3 nanotubes;

[0064] S2: Mix the dispersant, KHCO3 nanotubes, and ultrapure water for 110 min at a rotation speed of 200 rpm; add the thickener and continue to stir for 60 min at a rotation speed of 200 rpm; add the binder and stir for 50 min at a rotation speed of 300 rpm; add the wetting agent and stir for 40 min at a rotation speed of 300 rpm; filter to remove iron to obtain a KHCO3 nanotube coating slurry;

[0065] By mass percentage, the composition of the KHCO3 nanotube coating slurry is: 20% KHCO3 nanotubes, 0.6% dispersant, 0.7% thickener, 1% binder, 0.2% wetting agent, and the balance is ultrapure water;

[0066] The dispersant is a hydrolyzed polymaleic anhydride dispersant; the thickener is sodium carboxymethyl cellulose; the wetting agent is a silanol-based non-ionic surfactant;

[0067] The binder is a COPNA resin-based binder;

[0068] S3: Adopt a microgravure roll coating process. Use a coater to stepwise roll coat the prepared KHCO3 nanotube coating slurry on both sides of a 9-μm polyolefin separator, with a single-sided coating thickness of 3 μm. After baking at 70 °C, wind up to obtain a highly flame-retardant separator for lithium-ion batteries.

[0069] Example 4

[0070] A preparation process of a highly flame-retardant separator for lithium-ion batteries, comprising the following steps:

[0071] S1: Prepare KHCO3 nanotubes;

[0072] Mix 1.1752 g of hydrophilic silica nanowires and 78 mL of deionized water, stir for 45 min, then ultrasonically disperse for 1 h. Add 115 g of potassium carbonate and stir until dissolved. Introduce a mixed gas of carbon dioxide and nitrogen (volume ratio of carbon dioxide to nitrogen is 67.5:32.5), continue to ventilate for 220 min, filter and wash, and vacuum dry at 75 °C for 24 h. Control the vacuum degree of vacuum drying at 0.08 Mpa, then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h. Filter and wash, and dry at 80 °C for 12 h to obtain KHCO₃ nanotubes;

[0073] Perform surface treatment on the KHCO₃ nanotubes:

[0074] ① Mix 2 mmol of β-cyclodextrin, 15 mmol of potassium hydroxide, and 40 mL of deionized water, then continuously introduce methanol. After 5 days, centrifuge, wash 3 times with methanol, and dry to obtain a β-cyclodextrin framework;

[0075] ② Ultrasonically disperse the KHCO₃ nanotubes in potassium hydroxide, dilute with deionized water to a pH of 6.8, perform vacuum filtration, dry and grind, and then perform plasma treatment to obtain pretreated KHCO₃ nanotubes;

[0076] ③ Mix 0.5 g of β-cyclodextrin framework, 1.5 g of pretreated KHCO₃ nanotubes, 15 mL of absolute ethanol, and 2 mL of deionized water, and ultrasonically stir for 20 min to obtain solution A; mix 1.5 g of N-aminoethyl-γ-aminopropyltrimethoxysilane, 0.5 g of sodium dodecylsulfonate, 50 mL of absolute ethanol, and 100 mL of deionized water to obtain solution B; mix solution A and solution B, ultrasonically stir at 65 °C for 30 min, let stand for 3 h, wash 3 times with ethanol, under nitrogen protection, add a mixture of 5 mL of 1,3-propane sultone and 40 mL of dimethyl sulfoxide, ultrasonically stir for 20 min, wash with deionized water, and dry to obtain modified KHCO₃ nanotubes;

[0077] The working conditions of plasma treatment are: the flow rate of oxygen is 100 mL / min, the pressure is 18 Pa, the time is 5 min, and the power is 120 W; the working conditions of ultrasonic stirring: the ultrasonic intensity is 65 W;

[0078] S2: Mix the KHCO₃ nanotubes and ultrapure water for 30 min at a rotation speed of 300 rpm; add a thickener and continue to stir for 20 min at a rotation speed of 400 rpm; add an adhesive and stir for 30 min at a rotation speed of 500 rpm; add a wetting agent and stir for 20 min at a rotation speed of 600 rpm; filter to remove iron to obtain a KHCO₃ nanotube coating slurry;

[0079] In terms of mass percentage, the composition of the KHCO₃ nanotube coating slurry is as follows: 12% KHCO₃ nanotubes, 0.4% thickening agent, 0.5% adhesive, 0.05% wetting agent, and the balance is ultrapure water;

[0080] The thickening agent is sodium carboxymethyl cellulose; the wetting agent is a silanol-based nonionic surfactant;

[0081] The adhesive is a modified COPNA resin, and its preparation includes the following steps:

[0082] (1) Heat 1 g of 1-naphthol to melting, add 1 g of benzaldehyde and stir, then add a mixture of 0.07 g of p-toluenesulfonic acid and 10 mL of ethanol. Stop the reaction when the "stickiness" phenomenon appears in the reaction solution to obtain naphthol-based COPNA resin;

[0083] (2) Mix 1 g of naphthol-based COPNA resin and 15 mL of n-butanol, keep it at 50 °C for 60 min, add 0.01 g of potassium hydroxide powder, cool down to 35 °C, add 0.2 g of allyl chloride, keep it warm for 3 h, add a mixed solution of 20 mL of absolute ethanol and 0.02 g of aluminum sulfate, filter to obtain pretreated COPNA resin;

[0084] (3) Under nitrogen protection, mix 2.1 g of 4-nitro-2-(trifluoromethyl)aniline, 2.1 g of 2-fluoro-5-nitrobenzotrifluoride, 1.9 g of potassium carbonate, and 20 mL of dimethylacetamide, keep it at 135 °C for 24 h, pour it into 100 mL of deionized water, rinse, and dry to obtain bis(2-methyl-4-nitrophenyl)amine; under nitrogen protection, mix 1.5 g of bis(2-methyl-4-nitrophenyl)amine, 0.2 g of palladium-carbon, and 16 mL of absolute ethanol, heat it to 80 °C, cool down to 70 °C and add 4 mL of hydrazine hydrate, keep it warm for 10 h, filter, pour it into 40 mL of deionized water, wash, and dry to obtain bis(2-trifluoromethyl-4-aminophenyl)imine;

[0085] (4) Mix 1 g of pretreated COPNA resin, 0.2 g of bis(2-trifluoromethyl-4-aminophenyl)imine, 0.8 g of 4,4'-diphenylmethane bismaleimide, 30 mL of ethanol, 20 mL of tetrahydrofuran, and 10 mL of N,N-dimethylformamide, heat it to dissolve, keep it warm for 20 min to obtain a prepolymer, and cure it to obtain a modified COPNA resin;

[0086] The working conditions for curing are: keep it at 180 °C for 2 h, heat it to 200 °C and keep it at 200 °C for 2 h, heat it to 220 °C and keep it at 220 °C for 2 h, heat it to 240 °C and keep it at 240 °C for 2 h;

[0087] S3: Adopt the microgravure roll coating process. Use a coater to apply the prepared KHCO₃ nanotube coating slurry on both sides of a 9-μm polyolefin separator by stepwise roll coating. The thickness of the single-sided coating is 3 μm. After baking at 65 °C, wind up to obtain a highly flame-retardant separator for lithium-ion batteries.

[0088] Example 5

[0089] A preparation process for a highly flame-retardant separator for lithium-ion batteries, comprising the following steps:

[0090] S1: Prepare KHCO₃ nanotubes;

[0091] Mix 1.1752 g of hydrophilic silica nanowires and 78 mL of deionized water and stir for 50 min, then ultrasonically disperse for 1.5 h. Add 115 g of potassium carbonate and stir until dissolved. Introduce a mixed gas of carbon dioxide and nitrogen (volume ratio of carbon dioxide to nitrogen is 67.5:32.5), and continue to ventilate for 225 min. Filter, wash, and vacuum dry at 78 °C for 24 h, controlling the vacuum degree of vacuum drying at 0.08 Mpa. Then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h. Filter, wash, and dry at 83 °C for 11 h to obtain KHCO₃ nanotubes;

[0092] Conduct surface treatment on the KHCO₃ nanotubes:

[0093] ① Mix 2 mmol of β-cyclodextrin, 15 mmol of potassium hydroxide, and 40 mL of deionized water, and then continuously introduce methanol. After 6 days, centrifuge, wash 4 times with methanol, and dry to obtain a β-cyclodextrin framework;

[0094] ② Ultrasonically disperse the KHCO₃ nanotubes in potassium hydroxide, dilute with deionized water to pH 7, carry out vacuum filtration, dry and grind, and then perform plasma treatment to obtain pretreated KHCO₃ nanotubes;

[0095] ③ Mix 0.5 g of β-cyclodextrin framework, 1.5 g of pretreated KHCO₃ nanotubes, 15 mL of absolute ethanol, and 2 mL of deionized water, and ultrasonically stir for 25 min to obtain solution A; mix 1.5 g of N-aminoethyl-γ-aminopropyltrimethoxysilane, 0.5 g of sodium dodecyl sulfate, 50 mL of absolute ethanol, and 100 mL of deionized water to obtain solution B; mix solution A and solution B, ultrasonically stir at 68 °C for 25 min, let stand for 3.5 h, wash 4 times with ethanol, and under nitrogen protection, add a mixture of 5 mL of 1,3-propane sultone and 40 mL of dimethyl sulfoxide, ultrasonically stir for 25 min, wash with deionized water, and dry to obtain modified KHCO₃ nanotubes;

[0096] The working conditions for plasma treatment are as follows: the flow rate of oxygen is 100 mL / min, the pressure is 18 Pa, the time is 5 min, and the power is 120 W; the working conditions for ultrasonic stirring are: the ultrasonic intensity is 65 W;

[0097] S2: Mix the KHCO3 nanotubes and ultrapure water for 80 min at a rotation speed of 250 rpm; add a thickening agent and continue stirring for 40 min at a rotation speed of 300 rpm; add an adhesive and stir for 40 min at a rotation speed of 400 rpm; add a wetting agent and stir for 30 min at a rotation speed of 400 rpm; filter to remove iron to obtain the KHCO3 nanotube coating slurry;

[0098] In terms of mass percentage, the composition of the KHCO3 nanotube coating slurry is: 16% KHCO3 nanotubes, 0.65% thickening agent, 0.88% adhesive, 0.17% wetting agent, and the balance is ultrapure water;

[0099] The thickening agent is sodium carboxymethyl cellulose; the wetting agent is a silanol-based nonionic surfactant;

[0100] The adhesive is a modified COPNA resin, and its preparation includes the following steps:

[0101] (1) Heat 1 g of 1-naphthol to melting, add 1 g of benzaldehyde and stir, add a mixture of 0.07 g of p-toluenesulfonic acid and 10 mL of ethanol, and stop the reaction when the reaction solution shows the "stick-wrapping" phenomenon to obtain naphthol-based COPNA resin;

[0102] (2) Mix 1 g of naphthol-based COPNA resin and 15 mL of n-butanol, keep it at 55 °C for 45 min, add 0.01 g of potassium hydroxide powder, cool down to 38 °C, add 0.2 g of allyl chloride, keep it warm for 3.5 h, add a mixed solution of 20 mL of absolute ethanol and 0.02 g of aluminum sulfate, filter to obtain the pretreated COPNA resin;

[0103] (3) Under nitrogen protection, mix 2.1 g of 4-nitro-2-(trifluoromethyl)aniline, 2.1 g of 2-fluoro-5-nitrobenzotrifluoride, 1.9 g of potassium carbonate, and 20 mL of dimethylacetamide, keep it at 138 °C for 23 h, pour it into 100 mL of deionized water, rinse, and dry to obtain bis(2-methyl-4-nitrophenyl)amine; under nitrogen protection, mix 1.5 g of bis(2-methyl-4-nitrophenyl)amine, 0.2 g of palladium-carbon, and 16 mL of absolute ethanol, heat it to 80 °C, cool down to 70 °C and add 4 mL of hydrazine hydrate, keep it warm for 11 h, filter, pour it into 40 mL of deionized water, wash, and dry to obtain bis(2-trifluoromethyl-4-aminophenyl)imine;

[0104] (4) Mix 1 g of pretreated COPNA resin, 0.2 g of bis(2-trifluoromethyl-4-aminophenyl) imine, 0.8 g of 4,4-diphenylmethane bismaleimide, 30 mL of ethanol, 20 mL of tetrahydrofuran, and 10 mL of N,N-dimethylformamide, heat to dissolve, keep warm for 25 min to obtain a prepolymer, and cure to obtain a modified COPNA resin;

[0105] The working conditions for curing are: keep warm at 180 °C for 2 h, raise the temperature to 200 °C and keep warm for 2 h, raise the temperature to 220 °C and keep warm for 2 h, raise the temperature to 240 °C and keep warm for 2 h;

[0106] S3: Adopt the microgravure roll coating process, and use a coater to roll coat the prepared KHCO3 nanotube coating slurry on both sides of a 9-μm polyolefin separator step by step. The thickness of the single-sided coating is 3 μm, and after baking at 68 °C, it is wound up to obtain a highly flame-retardant separator for lithium-ion batteries. Example

[0107] A preparation process for a highly flame-retardant separator for lithium-ion batteries, comprising the following steps:

[0108] S1: Prepare KHCO3 nanotubes;

[0109] Mix 1.1752 g of hydrophilic silica nanowires and 78 mL of deionized water, stir for 55 min, then ultrasonically disperse for 2 h, add 115 g of potassium carbonate, stir until dissolved, introduce a mixed gas of carbon dioxide and nitrogen (volume ratio of carbon dioxide to nitrogen is 67.5:32.5), continue to ventilate for 230 min, filter and wash, vacuum dry at 80 °C for 24 h, control the vacuum degree of the vacuum drying at 0.08 Mpa, then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h, filter and wash, and dry at 85 °C for 10 h to obtain KHCO3 nanotubes;

[0110] Perform surface treatment on the KHCO3 nanotubes:

[0111] ① Mix 2 mmol of β-cyclodextrin, 15 mmol of potassium hydroxide, and 40 mL of deionized water, then continuously introduce methanol. After 7 days, centrifuge, wash 5 times with methanol, and dry to obtain a β-cyclodextrin framework;

[0112] ② Ultrasonically disperse the KHCO3 nanotubes in potassium hydroxide, dilute with deionized water to a pH of 7.2, perform vacuum filtration, dry and grind, and then perform plasma treatment to obtain pretreated KHCO3 nanotubes;

[0113] ③ Mix 0.5 g of β-cyclodextrin framework, 1.5 g of pretreated KHCO₃ nanotubes, 15 mL of absolute ethanol, and 2 mL of deionized water, and stir ultrasonically for 30 min to obtain Solution A; mix 1.5 g of N-aminoethyl-γ-aminopropyltrimethoxysilane, 0.5 g of sodium dodecylsulfonate, 50 mL of absolute ethanol, and 100 mL of deionized water to obtain Solution B; mix Solution A and Solution B, stir ultrasonically at 70 °C for 20 min, let it stand for 4 h, wash it 5 times with ethanol, under nitrogen protection, add a mixture of 5 mL of 1,3-propane sultone and 40 mL of dimethyl sulfoxide, stir ultrasonically for 30 min, wash it with deionized water, and dry it to obtain modified KHCO₃ nanotubes;

[0114] The working conditions for plasma treatment are as follows: the flow rate of oxygen is 100 mL / min, the pressure is 18 Pa, the time is 5 min, and the power is 120 W; the working conditions for ultrasonic stirring: the ultrasonic intensity is 65 W;

[0115] S2: Mix KHCO₃ nanotubes and ultrapure water for 110 min at a rotation speed of 200 rpm; add a thickener and continue stirring for 60 min at a rotation speed of 200 rpm; add an adhesive and stir for 50 min at a rotation speed of 300 rpm; add a wetting agent and stir for 40 min at a rotation speed of 300 rpm; filter to remove iron to obtain KHCO₃ nanotube coating slurry;

[0116] By mass percentage, the composition of the KHCO₃ nanotube coating slurry is: 20% KHCO₃ nanotubes, 0.7% thickener, 1% adhesive, 0.2% wetting agent, and the balance is ultrapure water;

[0117] The dispersant is hydrolyzed polymaleic anhydride dispersant; the thickener is sodium carboxymethyl cellulose; the wetting agent is a silanol-based nonionic surfactant;

[0118] The adhesive is a modified COPNA resin, and its preparation includes the following steps:

[0119] (1) Heat 1 g of 1-naphthol to melting, add 1 g of benzaldehyde and stir, add a mixture of 0.07 g of p-toluenesulfonic acid and 10 mL of ethanol, and stop the reaction when the reaction solution shows the phenomenon of "sticking to the rod" to obtain naphthol-based COPNA resin;

[0120] (2) Mix 1 g of naphthol-based COPNA resin and 15 mL of n-butanol, keep it warm at 60 °C for 30 min, add 0.01 g of potassium hydroxide powder, cool it to 40 °C, add 0.2 g of allyl chloride, keep it warm for 4 h, add a mixed solution of 20 mL of absolute ethanol and 0.02 g of aluminum sulfate, filter to obtain pretreated COPNA resin;

[0121] (3) Under nitrogen protection, 2.1 g of 4-nitro-2-(trifluoromethyl)aniline, 2.1 g of 2-fluoro-5-nitrobenzotrifluoride, 1.9 g of potassium carbonate, and 20 mL of dimethylacetamide were mixed and maintained at 140 °C for 22 h. Then, it was poured into 100 mL of deionized water, rinsed, and dried to obtain bis(2-methyl-4-nitrophenyl)amine. Under nitrogen protection, 1.5 g of bis(2-methyl-4-nitrophenyl)amine, 0.2 g of palladium-carbon, and 16 mL of absolute ethanol were mixed. The temperature was raised to 80 °C, and then 4 mL of hydrazine hydrate was added while cooling to 70 °C. It was kept warm for 12 h, filtered, poured into 40 mL of deionized water, washed, and dried to obtain bis(2-trifluoromethyl-4-aminophenyl)imine;

[0122] (4) 1 g of pretreated COPNA resin, 0.2 g of bis(2-trifluoromethyl-4-aminophenyl)imine, 0.8 g of 4,4-diphenylmethane bismaleimide, 30 mL of ethanol, 20 mL of tetrahydrofuran, and 10 mL of N,N-dimethylformamide were mixed and heated to dissolve. It was kept warm for 30 min to obtain a prepolymer, which was then cured to obtain a modified COPNA resin;

[0123] The working conditions for curing were: keeping warm at 180 °C for 2 h, raising the temperature to 200 °C and keeping warm for 2 h, raising the temperature to 220 °C and keeping warm for 2 h, and raising the temperature to 240 °C and keeping warm for 2 h;

[0124] S3: Using the microgravure roll coating process, the prepared KHCO₃ nanotube coating slurry was stepwise roll-coated on both sides of a 9-μm polyolefin separator through a coater. The thickness of the single-sided coating was 3 μm, and it was wound up after baking at 70 °C to obtain a highly flame-retardant separator for lithium-ion batteries.

[0125] Comparative Example 1

[0126] Taking Example 6 as the control group, 4,4-diphenylmethane bismaleimide was not added during the preparation of the modified COPNA resin, and other processes were normal.

[0127] Comparative Example 2

[0128] Taking Example 6 as the control group, bis(2-trifluoromethyl-4-aminophenyl)imine was not added during the preparation of the modified COPNA resin, and other processes were normal.

[0129] Comparative Example 3

[0130] Taking Example 6 as the control group, 0.3 g of bis(2-trifluoromethyl-4-aminophenyl)imine and 0.7 g of 4,4-diphenylmethane bismaleimide were used during the preparation of the modified COPNA resin, and other processes were normal.

[0131] Comparative Example 4

[0132] Taking Example 6 as the control group, the β-cyclodextrin framework was not prepared, and other processes were normal.

[0133] Comparative Example 5

[0134] Taking Example 3 as the control group, N-(2-Aminoethyl)-γ-aminopropyltrimethoxysilane and 1,3-Propanesultone were not added, and other processes were normal.

[0135] Comparative Example 6

[0136] Taking Example 6 as the control group, the coating was not applied, and other processes were normal.

[0137] The polyolefin separators used above were all polyethylene separators.

[0138] The preparation of the COPNA resin in Examples 1-3 included the following parts: Heating 1 g of 1-naphthol to melting, adding 1 g of benzaldehyde and stirring, adding a mixed solution of 0.07 g of p-toluenesulfonic acid and 10 mL of ethanol, and stopping the reaction when the phenomenon of "sticking to the rod" appeared in the reaction solution to obtain the COPNA resin.

[0139] Sources of raw materials used in the above examples and comparative examples:

[0140] Hydrophilic silica nanowires TSP-H10 (particle size 20 nm): Nanjing Tianxing New Materials Co., Ltd.; β-Cyclodextrin 856088: Sigma-Aldrich (Shanghai) Trading Co., Ltd.; N-(2-Aminoethyl)-γ-aminopropyltrimethoxysilane 1227157492: (Kermel) Shanghai Spectrum Chemical Reagent Co., Ltd.; Sodium dodecyl sulfate S105389, 1,3-Propanesultone P105652, 1-Naphthol N103797, Benzaldehyde B110463, p-Toluenesulfonic acid T305333, Allyl chloride H345219, 4-Nitro-3-(trifluoromethyl)aniline N108019, 2-Fluoro-5-nitrobenzotrifluoride F135502, Hydrazine hydrate H104517, Dimethylacetamide D108096, N,N-Dimethylformamide D111999, Palladium on carbon P116794, 4,4'-Diphenylmethane bismaleimide B152719: Shanghai Aladdin Biochemical Technology Co., Ltd.; Dimethyl sulfoxide, anhydrous ethanol, tetrahydrofuran, methanol, potassium carbonate, sodium hydroxide, potassium hydroxide, aluminum sulfate, n-butanol, analytical pure, N,N-Dimethylformamide: Sinopharm Chemical Reagent Co., Ltd.; The hydrolyzed polymaleic anhydride dispersant was polyisoprene grafted maleic anhydride 460060, sodium carboxymethyl cellulose 419273, 2-(Dodecyltrithiocarbonate)-2-methylpropanoic acid 723010: Merck reagent.

[0141] Performance test:

[0142] Perform performance tests on the battery separators prepared in Examples 1-6 and Comparative Examples 1-6;

[0143] Oxygen index: Refer to IOS4589-2. Pass a laminar upward-flowing oxygen-nitrogen mixed gas into a transparent combustion tube, place the separator in it, and control the temperature of the mixed gas to 25°C; when igniting the top surface, the flame contacts the top surface for less than 30 s and is moved away every 5 s. Observe whether the separator burns. The minimum oxygen concentration required to just maintain combustion is the oxygen index;

[0144] Liquid retention rate: The sample size is 50 mm × 50 mm. Weigh the sample after drying for 24 h and record it as M; immerse the sample in a beaker filled with electrolyte, take it out and suspend it for 3 min after 10 min to allow some electrolyte to drip off naturally, and then weigh it and record it as M2; liquid retention rate = (M2 - M) / M, (accurate to 0.01 g);

[0145] Liquid absorption rate: The sample size is 50 mm × 50 mm. Weigh the sample after drying for 24 h and record it as M; immerse the sample in a beaker filled with electrolyte, take it out and weigh it immediately after 10 min, and record it as M1; liquid absorption rate = (M1 - M) / M, (accurate to 0.01 g); Refer to GB / T36363-2018 to test the thickness, air permeability value, needle punching strength, and thermal shrinkage (130°C). The obtained results are shown in Table 1;

[0146] Table 1

[0147]

[0148] The present invention provides a highly flame-retardant separator for lithium-ion batteries and its preparation process. By introducing KHCO3 nanotubes to prepare the coating of the lithium-ion battery separator, a lithium-ion battery separator with high mechanical strength, high flame retardancy, and high electrolyte wettability is obtained.

[0149] Compare Examples 1, 2, and 3 with Comparative Example 6. Introducing KHCO3 into the coating significantly improves the mechanical strength, thermal shrinkage performance, and liquid absorption and retention ability of the battery separator, making it have good high-temperature resistance, thereby improving the ability of the separator to resist open flames; however, as the mass ratio of KHCO3 nanotubes increases, the air permeability of the separator will become worse.

[0150] Compare Example 5 with Comparative Examples 1, 2, and 3. Use naphthol as a raw material to prepare COPNA resin. Through etherification reaction, by controlling the mass ratio of bis(2-trifluoromethyl-4-aminophenyl)imine and 4,4-diphenylmethane bismaleimide introduced, a modified COPNA resin with a stable multi-branched structure is prepared by copolymerization reaction as the binder in the coating, which improves the high-temperature adhesiveness of COPNA resin and also improves the mechanical strength of the battery separator;

[0151] Comparing Example 5 with Comparative Example 2, the introduced imino group can form hydrogen bonds with the sulfonic acid groups grafted on the surface of the KHCO3 nanotubes, thereby constructing a complex hydrogen bond network, effectively promoting the proton conduction performance of the battery separator, improving the wettability of the battery separator, and reducing the risk of separator thermal runaway.

[0152] Comparing Example 5 with Comparative Example 4, in the present invention, the KHCO3 nanotubes are treated by plasma to expose the surface hydroxyl groups, improving the reaction activity of the KHCO3 nanotubes. The β-cyclodextrin is treated to obtain an organic-inorganic hybrid β-cyclodextrin framework, and then the β-cyclodextrin framework is grafted onto the KHCO3 nanotubes to improve the binding strength between the KHCO3 nanotubes and the separator, thereby enhancing the thermal stability of the separator.

[0153] Comparing Example 5 with Comparative Example 5, the KHCO3 nanotubes grafted with the β-cyclodextrin framework are aminated with N-aminoethyl-γ-aminopropyltrimethoxysilane and sodium dodecylsulfonate, and then 1,3-propane sultone is grafted. Without adding a dispersant, the uniformity of the dispersion of the KHCO3 nanotubes in the coating slurry is improved, synergistically improving the safety of the battery separator.

[0154] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made using the description of the present invention under the inventive concept of the present invention, or directly / indirectly used in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A highly flame-retardant separator for a lithium-ion battery, characterized in that, It includes a base film and a coating layer. In terms of mass percentage, the raw material composition in the coating layer is as follows: 12 - 20% modified KHCO₃ nanotubes, 0 - 0.6% dispersant, 0.4 - 0.7% thickener, 0.5 - 1% binder, 0.05 - 0.2% wetting agent, and the balance is ultrapure water; The binder is a modified COPNA resin, and its preparation includes the following steps: (1) Heat 1-naphthol to melting, add benzaldehyde and stir, then add a mixed solution of p-toluenesulfonic acid and ethanol, and stop the reaction when the "stickiness" phenomenon appears in the reaction solution to obtain naphthol-based COPNA resin; (2) Mix naphthol-based COPNA resin and n-butanol, keep it at 50 - 60 °C for 30 - 60 min, add potassium hydroxide powder, cool down to 35 - 40 °C, add allyl chloride, keep it warm for 3 - 4 h, add a mixed solution of absolute ethanol and aluminum sulfate, filter to obtain pretreated COPNA resin; (3) Under nitrogen protection, mix 4-nitro-2-(trifluoromethyl)aniline, 2-fluoro-5-nitrobenzotrifluoride, potassium carbonate, and dimethylacetamide, keep it at 135 - 140 °C for 22 - 24 h, pour it into deionized water, rinse, and dry to obtain bis(2-methyl-4-nitrophenyl)amine; Under nitrogen protection, mix bis(2-methyl-4-nitrophenyl)amine, palladium-carbon, and absolute ethanol, heat it to 80 °C, cool down to 70 °C and add hydrazine hydrate, keep it warm for 10 - 12 h, filter, pour it into deionized water, wash, and dry to obtain bis(2-trifluoromethyl-4-aminophenyl)imine; (4) Mix pretreated COPNA resin, bis(2-trifluoromethyl-4-aminophenyl)imine, 4,4-diphenylmethane bismaleimide, ethanol, tetrahydrofuran, and N,N-dimethylformamide, heat it to dissolve, keep it warm for 20 - 30 min to obtain a prepolymer, and cure it to obtain a modified COPNA resin; The preparation of modified KHCO₃ nanotubes includes the following steps: ① Mix β-cyclodextrin, potassium hydroxide, and deionized water, then continuously introduce methanol. After 5 - 7 days, centrifuge, wash with methanol 3 - 5 times, and dry to obtain a β-cyclodextrin framework; ② Ultrasonically disperse KHCO₃ nanotubes in potassium hydroxide, dilute it with deionized water to a pH of 6.8 - 7.2, carry out vacuum filtration, dry and grind, and then perform plasma treatment to obtain pretreated KHCO₃ nanotubes; ③ Mix the β-cyclodextrin framework, pretreated KHCO₃ nanotubes, absolute ethanol, and deionized water, and ultrasonically stir for 20 - 30 min to obtain solution A; Mix N-aminoethyl-γ-aminopropyltrimethoxysilane, sodium dodecylsulfonate, absolute ethanol, and deionized water to obtain solution B; Mix solution A and solution B, ultrasonically stir at 65 - 70 °C for 20 - 30 min, let it stand for 3 - 4 h, wash with ethanol 3 - 5 times, under nitrogen protection, add a mixed solution of 1,3-propane sultone and dimethyl sulfoxide, ultrasonically stir for 20 - 30 min, wash with deionized water, and dry to obtain modified KHCO₃ nanotubes.

2. The highly flame-retardant separator for a lithium-ion battery according to claim 1, wherein, The dispersant is a hydrolyzed polymaleic anhydride dispersant; the thickener is sodium carboxymethyl cellulose; the wetting agent is a silanol non-ionic surfactant.

3. The highly flame-retardant separator for a lithium-ion battery according to claim 1, wherein The preparation of the KHCO3 nanotubes includes the following steps: Mix hydrophilic silica nanowires and deionized water and stir for 45 - 55 min, then ultrasonically disperse for 1 - 2 h. Add potassium carbonate and stir until dissolved. Introduce a mixed gas of carbon dioxide and nitrogen and continue ventilation for 220 - 230 min. Filter and wash, then vacuum dry at 75 - 80 °C for 24 h, controlling the vacuum degree of vacuum drying at 0.08 Mpa. Then add it to a 5.0 mol / L sodium hydroxide solution and keep it for 4 h. Filter and wash, and dry at 80 - 85 °C for 10 - 12 h to obtain KHCO3 nanotubes.

4. A highly flame-retardant separator for a lithium-ion battery according to claim 1, wherein, In the preparation of the modified COPNA resin, the curing working conditions are: keep warm at 180 °C for 2 h, raise the temperature to 200 °C and keep warm for 2 h, raise the temperature to 220 °C and keep warm for 2 h, raise the temperature to 240 °C and keep warm for 2 h.

5. A highly flame-retardant separator for a lithium-ion battery according to claim 1, characterized in that, In the preparation of the modified COPNA resin, the mass ratio of 1-naphthol, benzaldehyde, and p-toluenesulfonic acid is 1:1:0.07; the mass ratio of the pretreated COPNA resin, bis(2-trifluoromethyl-4-aminophenyl) imine, and 4,4-diphenylmethane bismaleimide is 1:0.2:0.

8.

6. The highly flame-retardant separator for a lithium-ion battery according to claim 1, wherein, The preparation process includes the following steps: S1: Prepare modified KHCO3 nanotubes; S2: Mix the dispersant, modified KHCO3 nanotubes, and ultrapure water for 30 - 110 min at a rotation speed of 200 - 300 rpm; add the thickener and continue stirring for 20 - 60 min at a rotation speed of 200 - 400 rpm; add the binder and stir for 30 - 50 min at a rotation speed of 300 - 500 rpm; add the wetting agent and stir for 20 - 40 min at a rotation speed of 300 - 600 rpm; filter to remove iron to obtain a modified KHCO3 nanotube coating slurry. S3: Adopt a microgravure roll coating process, and use a coater to roll coat the prepared modified KHCO3 nanotube coating slurry on both sides of a polyolefin separator step by step. After baking at 65 - 70 °C, wind it up to obtain a highly flame-retardant separator for lithium-ion batteries.

7. A highly flame-retardant separator for a lithium-ion battery according to claim 1, wherein, In the preparation of the modified KHCO3 nanotubes, the working conditions of plasma treatment are: the flow rate of oxygen is 100 mL / min, the pressure is 18 Pa, the time is 5 min, and the power is 120 W.

8. A highly flame-retardant separator for a lithium-ion battery according to claim 1, characterized in that, The working conditions of ultrasonic stirring: the ultrasonic intensity is 65 W; the mass ratio of N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane and sodium dodecyl sulfonate is 3:1.

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