Flame-retardant lithium-ion battery separator and method for preparing the same

Abstract

The application discloses a kind of flame-retardant lithium ion battery separators and preparation method thereof in the technical field of battery separator, which is prepared from the following components: flame-retardant filler, deionized water, vinyl trimethoxysilane, anhydrous ethanol, diphenyl phosphate, glycidyl methacrylate, toluene, tetrabutylammonium bromide, methyl methacrylate, azobisdimethylvaleronitrile, N,N-dimethylformamide, polyacrylic acid and octylphenol polyoxyethylene ether.The application proposes to use halloysite nanotubes combined with phytic acid to prepare flame-retardant filler, and at the same time, diphenyl phosphate is immobilized in the separator coating, thereby obtaining a high-temperature-resistant flame-retardant coating, reducing the negative impact of flame retardant on battery performance, and improving the thermal stability of the separator.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically referring to a flame-retardant lithium-ion battery separator and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in various electronic products and electric vehicles due to their high energy density and long cycle life. However, the organic electrolyte and polyolefin separator used inside are prone to combustion or even explosion under high temperature or abuse conditions, and safety issues are becoming increasingly prominent. As a key component of the battery, the separator is responsible for ion conduction and electron isolation to prevent short circuits caused by direct contact between the positive and negative electrodes. Currently, polyolefin separators are commonly used. Although polyolefin separators have good mechanical strength and electrochemical stability, their hydrophobic surface leads to poor electrolyte wettability and easy leakage. At the same time, their thermal stability is insufficient, and they are prone to shrinkage or melting at high temperatures, which may cause short circuits between the positive and negative electrodes, leading to thermal runaway.

[0003] To improve the safety of the separator, existing technologies mainly employ two approaches: one is to add small-molecule flame retardants to the electrolyte, and the other is to coat the surface of the polyolefin-based membrane with an inorganic ceramic coating. However, both methods have significant drawbacks. First, small-molecule flame retardants tend to migrate into the electrolyte and electrode interface during cycling. This not only leads to a decrease in flame retardant effect over time but may also damage the solid electrolyte interface film of the graphite anode and cause side reactions with the lithium metal anode, severely impairing the battery's cycle life and coulombic efficiency. Second, traditional ceramic coatings mainly rely on physical heat insulation and mechanical... While the support is used to improve the thermal dimensional stability of the diaphragm, it does not possess chemical flame-retardant properties and cannot inhibit the combustion chain reaction of the electrolyte in the early stages. Furthermore, under extreme high-temperature conditions (>300℃), the coating and the base film are prone to peeling due to the difference in thermal expansion coefficients, thus losing their protective function. Moreover, the blend system, which is a simple physical mixture of flame retardant powder and ceramic powder, fails to solve the problem of flame retardant migration. In addition, due to the poor interfacial compatibility between the flame retardant and ceramic particles, the coating structure is prone to deterioration after long-term immersion in the electrolyte, thus introducing new reliability risks.

[0004] The existing technologies currently have the following main problems: 1. The thermal stability of the diaphragm is not good; 2. Small molecule flame retardants are prone to migration. Summary of the Invention

[0005] In view of the above situation and to overcome the defects of the prior art, the present invention provides a flame-retardant lithium-ion battery separator and its preparation method. In order to solve the problem of poor thermal stability of the separator, the present invention proposes to use halloysite nanotubes combined with phytic acid to prepare flame-retardant filler, and simultaneously immobilize diphenyl phosphate in the separator coating to obtain a high-temperature resistant flame-retardant coating, while reducing the negative impact of flame retardants on battery performance and improving the thermal stability of the separator.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention proposes a flame-retardant lithium-ion battery separator, which is composed of a base film and a flame-retardant ceramic coating slurry.

[0007] Preferably, the base film is a PP base film or a PE base film with a thickness of 3~16μm;

[0008] Furthermore, the base film is a PE base film with a thickness of 9 μm.

[0009] Preferably, the flame-retardant ceramic coating slurry is prepared from the following components: flame-retardant filler, deionized water, vinyltrimethoxysilane, anhydrous ethanol, diphenyl phosphate, glycidyl methacrylate, toluene, tetrabutylammonium bromide, methyl methacrylate, azobisisobutyronitrile, N,N-dimethylformamide, polyacrylic acid, and octylphenol polyoxyethylene ether.

[0010] Preferably, the preparation method of the flame-retardant filler specifically includes the following steps:

[0011] (1) Halloysite nanotubes were added to a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 at a dosage of 2 g / L, followed by the addition of dopamine hydrochloride, ultrasonic dispersion for 3 min, stirring at room temperature for 24 h, centrifugation at 10000 rpm for 20 min, filtration to collect the precipitate, washing with deionized water and drying to obtain modified halloysite nanotubes.

[0012] (2) Add modified halloysite nanotubes at a dosage of 3 g / L to deionized water, add zinc nitrate hexahydrate, ultrasonically disperse for 3 min, add inositol hexaphosphate, adjust the pH to 7, heat at 70-80℃ for 8-10 h to obtain flame retardant filler.

[0013] Preferably, in step (1), the mass ratio of halloysite nanotubes to dopamine hydrochloride is 1:0.9~1.2.

[0014] Preferably, in step (2), the mass ratio of modified halloysite nanotubes to zinc nitrate hexahydrate is 1:1.9~2.7;

[0015] Preferably, in step (2), the molar ratio of zinc nitrate hexahydrate to inositol hexaphosphate is 1:1.2~1.6.

[0016] Preferably, the preparation method of the flame-retardant ceramic coating slurry specifically includes the following steps:

[0017] S1. Add 13.2~15.7g of flame retardant filler to 31.2~33.6g of deionized water, add 0.37~0.47g of vinyltrimethoxysilane, add 3.4~5.6g of anhydrous ethanol, stir and mix in a water bath to obtain a dispersion;

[0018] S2. Add 1.3~1.7g of diphenyl phosphate and 0.7~1.2g of glycidyl methacrylate to 7.6~9.4g of toluene, add 0.3~0.45g of tetrabutylammonium bromide, heat in an oil bath for 8h, remove the solvent by vacuum distillation, and obtain a pale yellow liquid.

[0019] S3. Add 0.37~0.49g of methyl methacrylate to the pale yellow liquid obtained in S2, add 0.8~1.1g of polyacrylic acid and 0.03~0.05g of azobisisobutyronitrile, add 10~13g of N,N-dimethylformamide, keep warm and stir for 6h to obtain a mixed solution, pour the mixed solution into methanol for precipitation, filter, wash three times with methanol, and dry to obtain flame retardant powder;

[0020] S4. Add 1.1~1.6g of the flame retardant powder obtained in S3 to 12.4~13.6g of the dispersion obtained in S1, add 0.8~1.1g of polyacrylic acid and 0.03~0.05g of octylphenol polyoxyethylene ether, and mix using a double-star mixer to obtain a flame retardant ceramic coating slurry.

[0021] Preferably, in S1, the water bath stirring temperature is 60~70℃, the speed is 190~210rpm, and the time is 115~125min.

[0022] Preferably, in S2, the oil bath heating temperature is 107~113℃.

[0023] Preferably, in S3, the temperature for heat preservation and stirring is 67~73℃, and the speed is 180~220rpm.

[0024] Preferably, in S4, a dual planetary mixer is used for mixing, with a revolution speed of 27~33 rpm and a rotation speed of 970~1030 rpm.

[0025] This invention also provides a method for preparing a flame-retardant lithium-ion battery separator, specifically including the following steps:

[0026] The flame-retardant ceramic coating slurry is applied to the surface of a 9μm thick PE base film using an anilox roller. After coating, the film is dried in a stepped oven with three temperature zones: 50±5℃, 60±5℃, and 50±5℃ from front to back. After drying, the film is wound up normally to obtain a flame-retardant lithium-ion battery separator.

[0027] Preferably, the coating speed is 2~5m / min; the coating thickness is 1~4μm.

[0028] The beneficial effects achieved by this invention are as follows: This invention uses polydopamine to coat halloysite nanotubes, thereby incorporating Zn...+ Organometallic materials adsorbed onto the surface of nanotubes and prepared on the nanotube surface, namely, Zn chelated onto the surface by inositol hexaphosphate. + Ions were used to obtain stable flame-retardant fillers. Simultaneously, glycidyl methacrylate with epoxy groups and polymerizable double bonds was used to modify diphenyl phosphate. Tetrabutylammonium bromide was used to promote epoxy ring opening, reacting with phosphate groups to obtain phosphorus-containing monomers of methacrylate with polymerizable double bonds. These monomers were then polymerized with methyl methacrylate and polyacrylic acid to obtain flame-retardant powder, thus fixing diphenyl phosphate within the polymer backbone and preventing its migration. The flame-retardant filler with an organometallic layer and polyacrylic acid were mixed with the flame-retardant powder and coated onto the base film surface to obtain a flame-retardant ceramic coating containing inositol hexaphosphate, diphenyl phosphate, and halloysite nanotubes. At high temperatures, the framework structure formed by halloysite nanotubes provides support and reduces diaphragm deformation. Simultaneously, the coating containing diphenyl phosphate and inositol hexaphosphate expands upon heating to inhibit ignition and forms a heat-insulating carbon layer on the surface, thereby blocking the spread of fire. Attached Figure Description

[0029] Figure 1 The figures show the results of thermal stability tests for Examples 1-3 and Comparative Examples 1-2 of this invention.

[0030] Figure 2 These are the results of peel strength tests for Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0031] Figure 3 The following are graphs showing the results of limiting oxygen index tests in Examples 1-3 and Comparative Examples 1-2 of this invention;

[0032] Figure 4 The graphs show the results of the residual carbon rate tests in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0033] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0036] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0037] Example 1

[0038] A flame-retardant lithium-ion battery separator is composed of a 9μm thick PE base film and a flame-retardant ceramic coating slurry.

[0039] The flame-retardant ceramic coating slurry is prepared from the following components: flame-retardant filler, deionized water, vinyltrimethoxysilane, anhydrous ethanol, diphenyl phosphate, glycidyl methacrylate, toluene, tetrabutylammonium bromide, methyl methacrylate, azobisisobutyronitrile, N,N-dimethylformamide, polyacrylic acid, and octylphenol polyoxyethylene ether.

[0040] The preparation method of flame-retardant filler includes the following steps:

[0041] (1) Halloysite nanotubes were added to a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 at a dosage of 2 g / L, followed by the addition of dopamine hydrochloride. The mass ratio of halloysite nanotubes to dopamine hydrochloride was 1:0.9. The mixture was ultrasonically dispersed for 3 min, stirred at room temperature for 24 h, centrifuged at 10000 rpm for 20 min, filtered to collect the precipitate, washed with deionized water, and dried to obtain modified halloysite nanotubes.

[0042] (2) Modified halloysite nanotubes were added to deionized water at a dosage of 3 g / L, and zinc nitrate hexahydrate was added. The mass ratio of modified halloysite nanotubes to zinc nitrate hexahydrate was 1:1.9. The mixture was ultrasonically dispersed for 3 min, and inositol hexaphosphate was added. The molar ratio of zinc nitrate hexahydrate to inositol hexaphosphate was 1:1.2. The pH was adjusted to 7, and the mixture was heated at 70℃ for 8 h to obtain the flame-retardant filler.

[0043] The preparation method of flame-retardant ceramic coating slurry specifically includes the following steps:

[0044] S1. Add 13.2g of flame retardant filler to 31.2g of deionized water, add 0.377g of vinyltrimethoxysilane, add 3.4g of anhydrous ethanol, stir and mix in a 60℃ water bath at 190rpm for 115min to obtain a dispersion.

[0045] S2. Add 1.3g of diphenyl phosphate and 0.7g of glycidyl methacrylate to 7.6g of toluene, add 0.3g of tetrabutylammonium bromide, heat in an oil bath at 107℃ for 8h, remove the solvent by vacuum distillation, and obtain a pale yellow liquid.

[0046] S3. Add 0.37g of methyl methacrylate to the pale yellow liquid obtained in S2, add 0.8g of polyacrylic acid and 0.03g of azobisisobutyronitrile, add 10g of N,N-dimethylformamide, keep warm at 67℃ and stir at 180rpm for 6h to obtain a mixed solution, pour the mixed solution into methanol for precipitation, filter, wash with methanol three times, and dry to obtain flame retardant powder;

[0047] S4. Add 1.1g of the flame retardant powder obtained in S3 to 12.4g of the dispersion obtained in S1, add 0.8g of polyacrylic acid and 0.03g of octylphenol polyoxyethylene ether, and mix using a double-star mixer with an orbital speed of 27rpm and a rotational speed of 970rpm to obtain a flame retardant ceramic coating slurry.

[0048] This invention also provides a method for preparing a flame-retardant lithium-ion battery separator, specifically including the following steps:

[0049] The flame-retardant ceramic coating slurry was applied to the surface of a 9μm thick PE base film using an anilox roller at a speed of 2m / min. The coating thickness was 2μm. After coating, the film was dried in a stepped oven with three temperature zones: 45℃, 55℃, and 45℃ from front to back. After drying, the film was wound up normally to obtain the flame-retardant lithium-ion battery separator.

[0050] Example 2

[0051] A flame-retardant lithium-ion battery separator is composed of a 9μm thick PE base film and a flame-retardant ceramic coating slurry.

[0052] The flame-retardant ceramic coating slurry is prepared from the following components: flame-retardant filler, deionized water, vinyltrimethoxysilane, anhydrous ethanol, diphenyl phosphate, glycidyl methacrylate, toluene, tetrabutylammonium bromide, methyl methacrylate, azobisisobutyronitrile, N,N-dimethylformamide, polyacrylic acid, and octylphenol polyoxyethylene ether.

[0053] The preparation method of flame-retardant filler includes the following steps:

[0054] (1) Halloysite nanotubes were added to a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 at a dosage of 2 g / L, followed by the addition of dopamine hydrochloride. The mass ratio of halloysite nanotubes to dopamine hydrochloride was 1:1.1. The mixture was ultrasonically dispersed for 3 min, stirred at room temperature for 24 h, centrifuged at 10000 rpm for 20 min, filtered to collect the precipitate, washed with deionized water, and dried to obtain modified halloysite nanotubes.

[0055] (2) Modified halloysite nanotubes were added to deionized water at a dosage of 3 g / L, and zinc nitrate hexahydrate was added. The mass ratio of modified halloysite nanotubes to zinc nitrate hexahydrate was 1:2.2. The mixture was ultrasonically dispersed for 3 min, and inositol hexaphosphate was added. The molar ratio of zinc nitrate hexahydrate to inositol hexaphosphate was 1:1.4. The pH was adjusted to 7, and the mixture was heated at 75℃ for 9 h to obtain the flame-retardant filler.

[0056] The preparation method of flame-retardant ceramic coating slurry specifically includes the following steps:

[0057] S1. Add 13.4g of flame retardant filler to 32g of deionized water, add 0.4g of vinyltrimethoxysilane, add 4.2g of anhydrous ethanol, stir and mix in a 65℃ water bath at 200rpm for 120min to obtain a dispersion.

[0058] S2. Add 1.5g diphenyl phosphate and 0.9g glycidyl methacrylate to 8g toluene, add 0.4g tetrabutylammonium bromide, heat in an oil bath at 110℃ for 8h, remove the solvent by vacuum distillation, and obtain a pale yellow liquid.

[0059] S3. Add 0.4g of methyl methacrylate to the pale yellow liquid obtained in S2, add 0.1g of polyacrylic acid and 0.04g of azobisisobutyronitrile, add 12g of N,N-dimethylformamide, keep warm at 70℃ and stir at 200rpm for 6h to obtain a mixed solution, pour the mixed solution into methanol for precipitation, filter, wash with methanol three times, and dry to obtain flame retardant powder;

[0060] S4. Add 1.4g of the flame retardant powder obtained in S3 to 13g of the dispersion obtained in S1, add 0.9g of polyacrylic acid and 0.04g of octylphenol polyoxyethylene ether, and mix using a double-star mixer with an orbital speed of 30rpm and a rotational speed of 1000rpm to obtain a flame retardant ceramic coating slurry.

[0061] This invention also provides a method for preparing a flame-retardant lithium-ion battery separator, specifically including the following steps:

[0062] The flame-retardant ceramic coating slurry was applied to the surface of a 9μm thick PE base film using an anilox roller at a speed of 3m / min. The coating thickness was 2.2μm. After coating, the film was dried in a stepped oven with three temperature zones: 50℃, 60℃, and 50℃ from front to back. After drying, the film was wound up normally to obtain the flame-retardant lithium-ion battery separator.

[0063] Example 3

[0064] A flame-retardant lithium-ion battery separator is composed of a 9μm thick PE base film and a flame-retardant ceramic coating slurry.

[0065] The flame-retardant ceramic coating slurry is prepared from the following components: flame-retardant filler, deionized water, vinyltrimethoxysilane, anhydrous ethanol, diphenyl phosphate, glycidyl methacrylate, toluene, tetrabutylammonium bromide, methyl methacrylate, azobisisobutyronitrile, N,N-dimethylformamide, polyacrylic acid, and octylphenol polyoxyethylene ether.

[0066] The preparation method of flame-retardant filler includes the following steps:

[0067] (1) Halloysite nanotubes were added to a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 at a dosage of 2 g / L, followed by the addition of dopamine hydrochloride. The mass ratio of halloysite nanotubes to dopamine hydrochloride was 1:1.2. The mixture was ultrasonically dispersed for 3 min, stirred at room temperature for 24 h, centrifuged at 10000 rpm for 20 min, filtered to collect the precipitate, washed with deionized water, and dried to obtain modified halloysite nanotubes.

[0068] (2) Modified halloysite nanotubes were added to deionized water at a dosage of 3 g / L, and zinc nitrate hexahydrate was added. The mass ratio of modified halloysite nanotubes to zinc nitrate hexahydrate was 1:2.7. The mixture was ultrasonically dispersed for 3 min, and inositol hexaphosphate was added. The molar ratio of zinc nitrate hexahydrate to inositol hexaphosphate was 1:1.6. The pH was adjusted to 7, and the mixture was heated at 80℃ for 10 h to obtain the flame-retardant filler.

[0069] The preparation method of flame-retardant ceramic coating slurry specifically includes the following steps:

[0070] S1. Add 15.7g of flame retardant filler to 33.6g of deionized water, add 0.47g of vinyltrimethoxysilane, add 5.6g of anhydrous ethanol, stir and mix in a 70℃ water bath at 210rpm for 125min to obtain a dispersion.

[0071] S2. Add 1.7g diphenyl phosphate and 1.2g glycidyl methacrylate to 9.4g toluene, add 0.45g tetrabutylammonium bromide, heat in an oil bath at 113℃ for 8h, remove the solvent by vacuum distillation, and obtain a pale yellow liquid.

[0072] S3. Add 0.49g of methyl methacrylate to the pale yellow liquid obtained in S2, add 1.1g of polyacrylic acid and 0.05g of azobisisobutyronitrile, add 13g of N,N-dimethylformamide, keep warm at 73℃ and stir at 220rpm for 6h to obtain a mixed solution, pour the mixed solution into methanol for precipitation, filter, wash three times with methanol, and dry to obtain flame retardant powder;

[0073] S4. Add 1.6g of the flame retardant powder obtained in S3 to 13.6g of the dispersion obtained in S1, add 1.1g of polyacrylic acid and 0.05g of octylphenol polyoxyethylene ether, and mix using a double-star mixer with an orbital speed of 33rpm and a rotational speed of 970~1030rpm to obtain a flame retardant ceramic coating slurry.

[0074] This invention also provides a method for preparing a flame-retardant lithium-ion battery separator, specifically including the following steps:

[0075] The flame-retardant ceramic coating slurry was applied to the surface of a 9μm thick PE base film using an anilox roller at a speed of 5m / min. The coating thickness was 2.4μm. After coating, the film was dried in a stepped oven with three temperature zones: 55℃, 65℃, and 55℃ from front to back. After drying, the film was wound up normally to obtain the flame-retardant lithium-ion battery separator.

[0076] Comparative Example 1

[0077] This comparative example provides a battery separator that differs from Example 5 only in that it does not contain glycidyl methacrylate; the remaining components and their contents are the same as in Example 3.

[0078] Comparative Example 2

[0079] This comparative example provides a battery separator that differs from Example 5 only in that it does not contain dopamine hydrochloride and zinc nitrate hexahydrate in its composition. That is, halloysite nanotubes and inositol hexaphosphate are simply mixed together, while the remaining components and their contents are the same as in Example 3.

[0080] Experimental Example

[0081] 1. Thermal stability test

[0082] The diaphragms obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention were placed in an oven at 150°C and heated for 1 hour. Then, the dimensional changes before and after the heat treatment were compared, and their longitudinal (MD) and transverse (TD) thermal stability were evaluated respectively.

[0083] Figure 1The figures show the results of thermal stability tests for Examples 1-3 and Comparative Examples 1-2 of the present invention. As shown in the figures, the thermal shrinkage rates (MD) of Examples 1-3 and Comparative Examples 1-2 are 1.2%, 0.9%, 0.7%, 13.4%, and 9.8%, respectively, and the thermal shrinkage rates (TD) of Examples 1-3 and Comparative Examples 1-2 are 0.7%, 0.5%, 0.4%, 9.9%, and 7.8%, respectively. The thermal shrinkage rate of Examples 1-3 is significantly better than that of Comparative Examples 1-2. The use of glycidyl methacrylate and the preparation of flame-retardant fillers effectively improve the thermal stability of the diaphragm.

[0084] 2. Peel strength test

[0085] The diaphragms obtained in Examples 1-3 and Comparative Examples 1-2 of this invention were cut into strips 1 cm wide and 15 cm long and fixed on a steel plate. 3M tape was attached to the upper surface of the sample, leaving one end exposed. The coating was forced to separate from the substrate by stretching this end in the opposite direction. The peel strength was measured using a peel strength tester.

[0086] Figure 2 The figures show the results of peel strength tests for Examples 1-3 and Comparative Examples 1-2 of the present invention. As shown in the figures, the peel strengths of Examples 1-3 and Comparative Examples 1-2 are 98 N / m, 97 N / m, 98 N / m, 67 N / m and 76 N / m, respectively. The peel strength of Examples 1-3 is significantly better than that of Comparative Examples 1-2. The use of glycidyl methacrylate and the preparation of flame-retardant fillers effectively improved the peel strength of the diaphragm.

[0087] 3. Limiting Oxygen Index Test

[0088] The diaphragms prepared in Examples 1-3 and Comparative Example-2 of this invention were prepared into samples with a length of 70-150 mm, a width of 6.5 mm, and a thickness of 3 mm. The samples were placed in a glass chimney. After introducing an oxygen-nitrogen mixture, the chimney was cleaned for 30 seconds. The top of the sample was ignited, and the oxygen concentration was gradually reduced until the flame was extinguished. The lowest oxygen concentration was recorded as the limiting oxygen index.

[0089] Figure 3 The results of limiting oxygen index tests for Examples 1-3 and Comparative Examples 1-2 of the present invention are shown in the figure. As shown, the limiting oxygen indices of Examples 1-3 and Comparative Examples 1-2 are 33.4%, 34.2%, 32.8%, 17.3%, and 21.8%, respectively. The limiting oxygen index of Examples 1-3 is significantly higher than that of Comparative Examples 1-2. The use of glycidyl methacrylate and the preparation of flame-retardant fillers effectively improved the flame-retardant performance of the diaphragm.

[0090] 4. Residual carbon rate test

[0091] The diaphragms prepared in Examples 1-3 and Comparative Example-2 of this invention were tested in a thermogravimetric analyzer. The samples were heated from 20°C to 700°C at a heating rate of 20°C / min under a nitrogen atmosphere, and the carbon residue by weight was measured.

[0092] Carbon residue rate = (weight after experiment / weight before experiment) × 100%.

[0093] Figure 4 The figures show the results of the residual carbon rate tests for Examples 1-3 and Comparative Examples 1-2 of the present invention. As shown in the figures, the residual carbon rates of Examples 1-3 and Comparative Examples 1-2 are 28.9%, 27.9%, 30.4%, 14.5%, and 16.7%, respectively. The residual carbon rate of Examples 1-3 is significantly higher than that of Comparative Examples 1-2. The use of glycidyl methacrylate and the preparation of flame-retardant fillers effectively improved the flame-retardant performance of the diaphragm.

[0094] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

[0095] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A flame-retardant lithium-ion battery separator, wherein the flame-retardant lithium-ion battery separator is composed of a base film and a flame-retardant ceramic coating slurry, characterized in that: The base film is a PP or PE base film with a thickness of 3-16 μm; the flame-retardant ceramic coating slurry is prepared from the following components: flame-retardant filler, deionized water, vinyltrimethoxysilane, anhydrous ethanol, diphenyl phosphate, glycidyl methacrylate, toluene, tetrabutylammonium bromide, methyl methacrylate, azobisisobutyronitrile, N,N-dimethylformamide, polyacrylic acid, and octylphenol polyoxyethylene ether. The preparation method of the flame-retardant ceramic coating slurry specifically includes the following steps: S1. Add 13.2~15.7g of flame retardant filler to 31.2~33.6g of deionized water, add 0.37~0.47g of vinyltrimethoxysilane, add 3.4~5.6g of anhydrous ethanol, stir and mix in a water bath to obtain a dispersion; S2. Add 1.3~1.7g of diphenyl phosphate and 0.7~1.2g of glycidyl methacrylate to 7.6~9.4g of toluene, add 0.3~0.45g of tetrabutylammonium bromide, heat in an oil bath for 8h, remove the solvent by vacuum distillation, and obtain a pale yellow liquid. S3. Add 0.37~0.49g of methyl methacrylate to the pale yellow liquid obtained in S2, add 0.8~1.1g of polyacrylic acid and 0.03~0.05g of azobisisobutyronitrile, add 10~13g of N,N-dimethylformamide, keep warm and stir for 6h to obtain a mixed solution, pour the mixed solution into methanol for precipitation, filter, wash three times with methanol, and dry to obtain flame retardant powder; S4. Add 1.1~1.6g of the flame retardant powder obtained in S3 to 12.4~13.6g of the dispersion obtained in S1, add 0.8~1.1g of polyacrylic acid and 0.03~0.05g of octylphenol polyoxyethylene ether, and mix using a double star mixer to obtain a flame retardant ceramic coating slurry. The preparation method of the flame-retardant filler specifically includes the following steps: (1) Halloysite nanotubes were added to a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 at a dosage of 2 g / L, followed by the addition of dopamine hydrochloride, ultrasonic dispersion for 3 min, stirring at room temperature for 24 h, centrifugation at 10000 rpm for 20 min, filtration to collect the precipitate, washing with deionized water and drying to obtain modified halloysite nanotubes. (2) Add modified halloysite nanotubes at a dosage of 3 g / L to deionized water, add zinc nitrate hexahydrate, ultrasonically disperse for 3 min, add inositol hexaphosphate, adjust the pH to 7, heat at 70-80℃ for 8-10 h to obtain flame retardant filler.

2. The flame-retardant lithium-ion battery separator according to claim 1, characterized in that: In S1, the water bath stirring temperature is 60~70℃, the speed is 190~210rpm, and the time is 115~125min.

3. The flame-retardant lithium-ion battery separator according to claim 2, characterized in that: In S2, the oil bath heating temperature is 107~113℃.

4. The flame-retardant lithium-ion battery separator according to claim 3, characterized in that: In S3, the temperature for heat preservation and stirring is 67~73℃, and the speed is 180~220rpm.

5. The flame-retardant lithium-ion battery separator according to claim 4, characterized in that: In S4, a dual planetary mixer is used for mixing, with an orbital speed of 27~33 rpm and a rotational speed of 970~1030 rpm.

6. The flame-retardant lithium-ion battery separator according to claim 1, characterized in that: In step (1), the mass ratio of halloysite nanotubes to dopamine hydrochloride is 1:0.9~1.2; in step (2), the mass ratio of modified halloysite nanotubes to zinc nitrate hexahydrate is 1:1.9~2.7, and the molar ratio of zinc nitrate hexahydrate to inositol hexaphosphate is 1:1.2~1.

6.

7. A method for preparing a flame-retardant lithium-ion battery separator according to claim 1, characterized in that: Specifically, the steps include the following: The flame-retardant ceramic coating slurry is applied to the surface of a 9μm thick PE base film using an anilox roller. After coating, the film is dried in a stepped oven with three temperature zones: 50±5℃, 60±5℃, and 50±5℃ from front to back. After drying, the film is wound up normally to obtain a flame-retardant lithium-ion battery separator.

8. The method for preparing the flame-retardant lithium-ion battery separator according to claim 7, characterized in that: The coating speed is 2~5m / min; the coating thickness is 1-4μm.

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