Preparation method of high-heat-resistance composite inorganic coating lithium battery diaphragm

Abstract

The invention relates to the technical field of lithium battery diaphragms, and provides a preparation method of a high-heat-resistance composite inorganic coating lithium battery diaphragm, which comprises the following steps: S1, mixing a dispersant and water, carrying out primary stirring, adding a composite material, and carrying out secondary stirring to obtain a mixed solution; s2, adding a binding agent and a thickening agent into the mixed solution, uniformly stirring, and sanding to obtain coating slurry; and S3, coating a base membrane with the coating slurry, and drying to obtain the nanometer aluminum oxide and boron nitride coating lithium battery diaphragm, the composite material is a nano aluminum oxide / silicon dioxide / boron nitride composite material; the nano aluminum oxide / silicon dioxide / boron nitride composite material comprises the following raw material components in parts by weight: 20-30 parts of nano aluminum oxide, 5-10 parts of silicon dioxide and 1-5 parts of hexagonal boron nitride. According to the technical scheme, the problems of poor thermal stability and poor puncture resistance of the lithium battery diaphragm in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and specifically, to a preparation method of a high heat-resistant composite inorganic coating lithium battery separator. Background Art

[0002] With the increasingly wide application of lithium-ion batteries in fields such as electric vehicles and new energy energy storage, the market's requirements for their performance and safety are also constantly improving. Traditional lithium battery separators have obvious shortcomings. They are extremely prone to shrinkage or even failure in high-temperature environments, and will also affect the puncture resistance of the separators, thus directly triggering serious problems such as battery short circuits and thermal runaway, greatly threatening the use safety of the batteries.

[0003] To solve the above problems, the industry usually adds inorganic coating components to the separators, which can improve the thermal stability and puncture resistance of the separators to a certain extent. However, there is a poor interfacial compatibility between traditional inorganic coatings, such as conventional alumina, titanium dioxide and other materials, and commonly used polyolefin-based membranes. Under high-temperature conditions, this incompatibility will be further highlighted, resulting in a significant decrease in the bonding force between the inorganic coating and the base membrane, and then problems such as coating peeling will occur, ultimately limiting the improvement of the thermal stability and puncture resistance of the separators.

[0004] Therefore, it is of great significance to develop a lithium battery separator with good thermal stability and puncture resistance. This not only helps to improve the safety of lithium-ion batteries under complex working conditions, but also can effectively extend the service life of the batteries, meeting the growing market demand for high-performance batteries. Summary of the Invention

[0005] The present invention provides a preparation method of a high heat-resistant composite inorganic coating lithium battery separator, which solves the problems of poor thermal stability and poor puncture resistance of lithium battery separators in related technologies.

[0006] The technical solution of the present invention is as follows: The present invention provides a preparation method of a high heat-resistant composite inorganic coating lithium battery separator, comprising the following steps: S1. Mix a dispersant and water, perform a first stirring, add a composite material, and perform a second stirring to obtain a mixed solution; S2. Add a binder and a thickener to the mixed solution, stir evenly, and then perform sanding to obtain a coating slurry; S3. Coat the coating slurry on a base membrane and dry it to obtain a lithium battery separator with a nano-alumina and boron nitride coating; The composite material is a nano-alumina / silica / boron nitride composite material; The raw materials of the nano-alumina / silica / boron nitride composite material include the following components in parts by weight: 20 - 30 parts of nano - alumina, 5 - 10 parts of silica, and 1 - 5 parts of hexagonal boron nitride.

[0007] As a further technical solution, the weight ratio of the nano - alumina, silica, and hexagonal boron nitride is 28:5:1 - 5.

[0008] In the present invention, by adjusting the weight ratio of the nano - alumina, silica, and hexagonal boron nitride, when the weight ratio of the nano - alumina, silica, and hexagonal boron nitride is 28:5:1 - 5, the synergistic effect of the three can be optimized, thereby further improving the thermal stability and puncture resistance of the lithium - ion battery separator.

[0009] As a further technical solution, the particle size of the nano - alumina: D10 is 190 - 200 nm, D50 is 350 - 390 nm, and D90 is 650 - 770 nm; The particle size of the silica: D10 is 0.400 - 0.470 μm, D50 is 0.600 - 0.680 μm, and D90 is 1.100 - 1.290 μm; The particle size of the hexagonal boron nitride: D10 is 0.450 - 0.550 μm, D50 is 1.500 - 1.600 μm, and D90 is 3.000 - 3.200 μm.

[0010] In the present invention, the nano - alumina, silica, and hexagonal boron nitride have a reasonable particle size distribution. Different particle sizes enable the nano - alumina, silica, and hexagonal boron nitride to better play a synergistic role, so that the lithium - ion battery separator with nano - alumina and boron nitride coatings has good thermal stability and puncture resistance.

[0011] As a further technical solution, the preparation method of the composite material includes the following steps: Mix the nano - alumina, silica, and hexagonal boron nitride, then sinter and cool to obtain the composite material.

[0012] As a further technical solution, the mixing is ball - milling mixing. When ball - milling, the rotation speed is 200 - 600 rpm and the ball - milling time is 10 - 20 min; When sintering, under the protection of an inert gas, heat it at a heating rate of 10 - 16 °C / min to 1000 - 1500 °C, and then sinter for 1 - 2 h; The inert gas is one of helium, argon, and neon.

[0013] In the present invention, boron nitride, nano-aluminum oxide, and silicon dioxide are ball-milled and then sintered under anaerobic conditions, which can improve the overall performance of the composite material. First, during the ball-milling process, the particles of the three powders are uniformly dispersed and refined, which helps to enhance the interfacial bonding force between the components. The anaerobic environment during the sintering process can prevent oxidation reactions, protect the layered structure of boron nitride from being damaged, and maintain its excellent thermal conductivity and chemical stability. At high temperatures, the high-temperature stability and heat resistance of nano-aluminum oxide and silicon dioxide can be further enhanced, and at the same time, the two can also have a synergistic effect with boron nitride to form a stronger and more uniform coating.

[0014] As a further technical solution, the dispersant is one or more of ammonium polyacrylate, sodium dodecylbenzenesulfonate, and sodium lauryl polyoxyethylene ether sulfate; and / or The binder is one or two of polyvinylidene fluoride and polyvinyl alcohol; and / or The thickener is one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, and hydroxyethyl cellulose.

[0015] In the present invention, the addition of the dispersant can make nano-aluminum oxide, silicon dioxide, boron nitride, and other components uniformly dispersed in the system, reduce particle agglomeration, and improve the uniformity and stability of the coating slurry.

[0016] The addition of the binder can, to a certain extent, increase the bonding degree between the nano-aluminum oxide / silicon dioxide / boron nitride composite material and other components, help form a stable coating structure, and thus reduce the shedding of the coating during the use of the separator, maintaining the integrity and performance stability of the separator.

[0017] In addition, the thickener can regulate the rheological properties of the slurry during the preparation of the coating slurry, making it have appropriate viscosity and thixotropy, laying a foundation for subsequent coating operations on the surface of the separator to ensure the uniformity and thickness consistency of the coating.

[0018] As a further technical solution, the weight parts of the composite material are 25-35 parts, the weight parts of the dispersant are 0.2-0.5 parts, the weight parts of the binder are 5-10 parts, the weight parts of the thickener are 5-10 parts, and the weight parts of water are 40-50 parts.

[0019] As a further technical solution, in step S1, during the first stirring, the self-rotation speed of the double planetary stirring device is 500-1500 r / min, the revolution speed is 30-50 r / min, and the stirring time is 10-20 min; During the secondary stirring, the self-rotation speed of the double planetary stirring equipment is 1500 - 2500 r / min, the revolution speed is 30 - 50 r / min, the ultrasonic frequency is 5 - 10 kHz, and the stirring time is 10 - 30 min; In step S2, when the stirring is uniform, it is carried out in a vacuum environment. The stirring speed is 30 - 50 r / min, the ultrasonic frequency is 5 - 10 kHz, and the stirring time is 5 - 10 min; During the cyclic sanding, the sanding time is 30 - 50 min.

[0020] As a further technical solution, in step S3, during the coating, the coating method is single-sided coating or double-sided coating, the coating speed is 20 - 50 m / min, and the coating thickness is 3 - 4 μm.

[0021] As a further technical solution, the particle size of the coating slurry: D50 is 1.350 - 1.400 μm, and D90 is 3.400 - 3.450 μm.

[0022] In the present invention, when the particle size of the coating slurry D50 is 1.350 - 1.400 μm and D90 is 3.400 - 3.450 μm, the uniformity and fineness of the coating can be ensured, which is beneficial to improving the overall performance of the separator.

[0023] As a further technical solution, during the drying, the temperature is 40 - 70 °C and the time is 5 - 10 min.

[0024] In the present invention, during the drying process, the drying temperature is accurately controlled within the range of 40 - 70 °C, and the drying time is clearly set to 5 - 10 min. In the established time period, relying on the appropriate temperature environment and good environmental system, the coating on the separator can be gradually dried and cured, and finally a coated separator that meets the requirements is obtained.

[0025] As a further technical solution, the base film is one of a polyethylene-based film and a polypropylene-based film.

[0026] The working principle and beneficial effects of the present invention are as follows: 1. In the present invention, using a nano-aluminum oxide / silicon dioxide / boron nitride composite material as the base material, with the action of a dispersant, a binder, a thickener, and water, a lithium-ion battery separator with good thermal stability and puncture resistance can be prepared.

[0027] 2. The nano-aluminum oxide / silicon dioxide / boron nitride composite material endows the lithium battery separator with good structural stability and thermal stability. Among them, the surface of the nano-aluminum oxide particles is rich in hydroxyl groups, and these hydroxyl groups can interact with the carboxyl groups on the hexagonal boron nitride lamellae through hydrogen bonds, enabling the nano-aluminum oxide particles to be dispersed between the hexagonal boron nitride lamellae, forming stable hydrophilic ion channels. The addition of silicon dioxide can strengthen this hydrogen bond interaction, enhance the interfacial binding force, and form a more compact structure. Moreover, silicon dioxide and hexagonal boron nitride with a smooth layer structure are jointly filled between the nano-aluminum oxide particles, and the formed thermal conduction network can effectively reduce the interfacial resistance of the separator. While optimizing the electron migration path of the battery, it can help to quickly disperse the heat generated during the operation of the lithium-ion battery, avoid local overheating, thereby improving the thermal stability and puncture resistance of the coating, and endowing the lithium battery separator with good thermal stability and puncture resistance. Description of the Drawings

[0028] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0029] Figure 1 It is a composite schematic diagram of nano-aluminum oxide, hexagonal boron nitride and silicon dioxide in Example 3. Specific Embodiments

[0030] The technical solutions in the embodiments of 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of the present invention.

[0031] In the following examples and comparative examples, the dispersant is ammonium polyacrylate, model number 1124; the binder is polyvinyl alcohol, model number PVA 22-99H; the thickener is carboxymethyl cellulose, with a viscosity of 1400 mPa•s; the average particle size of ordinary alumina is 74 μm; the base film is a polyethylene film, and the model of polyethylene is DFDA-7042; the average particle size of cubic boron nitride is 44 μm.

[0032] Example 1 The raw materials of the nano-aluminum oxide / silicon dioxide / boron nitride composite material include the following components in parts by weight: 20 parts of nano-aluminum oxide, 5 parts of silicon dioxide, and 1 part of hexagonal boron nitride; Particle size of nano-aluminum oxide: D10 is 190 nm, D50 is 350 nm, and D90 is 650 nm; Particle size of silicon dioxide: D10 is 0.400 μm, D50 is 0.600 μm, and D90 is 1.10 μm; Particle size of hexagonal boron nitride: D10 is 0.450 μm, D50 is 1.500 μm, D90 is 3.000 μm; The preparation method of the composite material comprises the following steps: After ball-milling and mixing 20 parts of nano-aluminum oxide, 5 parts of silicon dioxide, and 1 part of hexagonal boron nitride at 200 rpm for 20 min, heating to 1000 °C at a heating rate of 10 °C / min under helium, sintering for 2 h, and cooling, a composite material is obtained; A preparation method of a high heat-resistant composite inorganic coating lithium battery separator comprises the following steps: S1. Mix 0.2 part of ammonium polyacrylate and 40 parts of water, stir for 20 min under a double-planet stirring device with a rotation speed of 500 r / min and a revolution speed of 30 r / min, add 25 parts of the composite material, and stir for 30 min under a double-planet stirring device with a rotation speed of 1500 r / min, a revolution speed of 30 r / min, and an ultrasonic frequency of 5 kHz to obtain a mixed solution; S2. Add 5 parts of polyvinyl alcohol and 5 parts of carboxymethyl cellulose to the above mixed solution, stir for 10 min in a vacuum environment with a stirring speed of 30 r / min and an ultrasonic frequency of 5 kHz, stir evenly, and perform circulating sanding for 30 min to obtain a coating slurry with D50 of 1.350 μm and D90 of 3.400 μm; S3. Coat the coating slurry on a polyvinyl film unidirectionally at a coating speed of 20 m / min, bake at 40 °C for 10 min, and dry to obtain a lithium battery separator with a 9-μm-thick polyvinyl film coated with a 3-μm-thick coating.

[0033] Example 2 The raw materials of the nano-aluminum oxide / silicon dioxide / boron nitride composite material comprise the following components in parts by weight: 30 parts of nano-aluminum oxide, 10 parts of silicon dioxide, and 5 parts of hexagonal boron nitride; Particle size of nano-aluminum oxide: D10 is 200 nm, D50 is 390 nm, D90 is 770 nm; Particle size of silicon dioxide: D10 is 0.470 μm, D50 is 0.680 μm, D90 is 1.290 μm; Particle size of hexagonal boron nitride: D10 is 0.550 μm, D50 is 1.600 μm, D90 is 3.200 μm; The preparation method of the composite material comprises the following steps: After ball-milling and mixing 30 parts of nano-aluminum oxide, 10 parts of silicon dioxide, and 5 parts of hexagonal boron nitride at 600 rpm for 10 min, heating to 1500 °C at a heating rate of 16 °C / min under helium, sintering for 1 h, and then cooling, a composite material is obtained; A preparation method of a high heat-resistant composite inorganic coating lithium battery separator includes the following steps: S1. Mix 0.5 part of ammonium polyacrylate and 50 parts of water, stir for 10 min under a double planetary stirring device with a rotation speed of 1500 r / min and a revolution speed of 50 r / min, add the composite material, and then stir for 10 min under a double planetary stirring device with a rotation speed of 2500 r / min, a revolution speed of 50 r / min, and an ultrasonic frequency of 10 kHz to obtain a mixed solution; S2. Add 10 parts of polyvinyl alcohol and 10 parts of carboxymethyl cellulose to the above mixed solution, stir for 5 min in a vacuum environment with a stirring speed of 50 r / min and an ultrasonic frequency of 10 kHz, stir evenly, and then perform circulating sanding for 50 min to obtain a coating slurry with D50 of 1.400 μm and D90 of 3.450 μm; S3. Unidirectionally coat the coating slurry on a polyvinyl film at a coating speed of 50 m / min, dry at 70 °C for 5 min, and then dry to obtain a lithium battery separator with a 4-μm-thick coating on a 9-μm-thick polyvinyl film.

[0034] Example 3 The raw materials of the nano-aluminum oxide / silicon dioxide / boron nitride composite material include the following components in parts by weight: 28 parts of nano-aluminum oxide, 5 parts of silicon dioxide, and 3 parts of hexagonal boron nitride; The particle size of nano-aluminum oxide: D10 is 190 nm, D50 is 378 nm, and D90 is 743 nm; The particle size of silicon dioxide: D10 is 0.445 μm, D50 is 0.634 μm, and D90 is 1.241 μm; The particle size of hexagonal boron nitride: D10 is 0.521 μm, D50 is 1.532 μm, and D90 is 3.126 μm; The preparation method of the composite material includes the following steps: After ball-milling and mixing 28 parts of nano-aluminum oxide, 5 parts of silicon dioxide, and 3 parts of hexagonal boron nitride at 400 rpm for 10 min, heating to 1200 °C at a heating rate of 13 °C / min under helium, sintering for 1 h, and then cooling, a composite material is obtained; A preparation method of a high heat-resistant composite inorganic coating lithium battery separator includes the following steps: S1. Mix 0.5 part of ammonium polyacrylate and 45 parts of water, stir for 10 min under a double-planet stirring device with a rotation speed of 1000 r / min and a revolution speed of 40 r / min, add 34 parts of composite material, and stir for 30 min under a double-planet stirring device with a rotation speed of 2000 r / min, a revolution speed of 40 r / min, and an ultrasonic frequency of 5 kHz to obtain a mixed solution; S2. Add 7.5 parts of polyvinyl alcohol and 6 parts of carboxymethyl cellulose to the above mixed solution, stir for 10 min in a vacuum environment with a stirring speed of 40 r / min and an ultrasonic frequency of 5 kHz, and after stirring evenly, perform cyclic sanding for 40 min to obtain a coating slurry with D50 of 1.379 μm and D90 of 3.428 μm; S3. Coat the coating slurry on a polyvinyl film unidirectionally at a coating speed of 40 m / min, dry it at 60 °C for 10 min to obtain a lithium-ion battery separator with a 3-μm-thick coating on a 9-μm-thick polyvinyl film; The composite schematic diagram of nano-aluminum oxide, hexagonal boron nitride and silicon dioxide is as Figure 1 shown.

[0035] Example 4 The difference between this example and Example 3 is only that in this example, 3 parts of hexagonal boron nitride are replaced by 5 parts of hexagonal boron nitride.

[0036] Example 5 The difference between this example and Example 3 is only that in this example, 3 parts of hexagonal boron nitride are replaced by 1 part of hexagonal boron nitride.

[0037] Example 6 A preparation method of a high heat-resistant composite inorganic coating lithium-ion battery separator, comprising the following steps: S1. Mix 0.5 part of ammonium polyacrylate and 45 parts of water, stir for 10 min under a double-planet stirring device with a rotation speed of 1000 r / min and a revolution speed of 40 r / min, add 28 parts of nano-aluminum oxide, 5 parts of silicon dioxide, and 1 part of hexagonal boron nitride, and stir for 30 min under a double-planet stirring device with a rotation speed of 2000 r / min, a revolution speed of 40 r / min, and an ultrasonic frequency of 5 kHz to obtain a mixed solution; S2. Add 7.5 parts of polyvinyl alcohol and 6 parts of carboxymethyl cellulose to the above mixed solution, stir for 10 min in a vacuum environment with a stirring speed of 40 r / min and an ultrasonic frequency of 5 kHz, and after stirring evenly, perform cyclic sanding for 40 min to obtain a coating slurry with D50 of 1.379 μm and D90 of 3.428 μm; S3. Coating the coating slurry on the polyethylene film unidirectionally at a coating speed of 40 m / min, drying at 60°C for 10 min, and then drying to obtain a lithium-ion battery separator with a 3-μm-thick coating on a 9-μm-thick polyethylene film. Comparative Example 1 The difference between this comparative example and Example 2 is only that in this comparative example, the nano-aluminum oxide is replaced with an equal amount of ordinary aluminum oxide.

[0038] Comparative Example 2 The difference between this comparative example and Example 2 is only that in this comparative example, the hexagonal boron nitride is replaced with an equal amount of cubic boron nitride.

[0039] Comparative Example 3 The difference between this comparative example and Example 2 is only that in this comparative example, no silicon dioxide is added, 33.75 parts of nano-aluminum oxide are added, and 11.25 parts of hexagonal boron nitride are added.

[0040] Comparative Example 4 The difference between this comparative example and Example 2 is only that in this comparative example, the hexagonal boron nitride and silicon dioxide are replaced with an equal amount of nano-aluminum oxide.

[0041] Comparative Example 5 The difference between this comparative example and Example 2 is only that in this comparative example, the nano-aluminum oxide and silicon dioxide are replaced with an equal amount of hexagonal boron nitride.

[0042] Comparative Example 6 The difference between this comparative example and Example 2 is only that in this comparative example, the nano-aluminum oxide and hexagonal boron nitride are replaced with an equal amount of silicon dioxide.

[0043] Comparative Example 7 The difference between this comparative example and Example 2 is only that in this comparative example, the composite material only includes ordinary aluminum oxide.

[0044] Experimental Example 1 Thermal Stability and Puncture Resistance Test ① Based on GB / T 36363-2018 "Polyolefin Separator for Lithium-Ion Batteries", the lithium-ion battery separators prepared in Examples 1-6 and Comparative Examples 1-7 were used to measure the thermal shrinkage rates in the transverse direction (TD) and longitudinal direction (MD). Among them, the size of the lithium-ion battery separator sample was 100 mm × 100 mm, the thickness was 12 μm, and the test results of the thermal shrinkage rates in the transverse and longitudinal directions were the averages of 3 samples. ② Based on GB / T 36363-2018 "Polyolefin Separator for Lithium-Ion Batteries", the lithium-ion battery separators prepared in Examples 1-6 and Comparative Examples 1-7 were used to conduct a puncture strength test. Among them, the thickness of the separator was 12 μm and the puncture rate was 110 mm / min. The test results are shown in Table 1 below: Table 1 Thermal stability test results of Examples 1-6 and Comparative Examples 1-7

[0045] As can be seen from Table 1, compared with Examples 1-7, the thermal shrinkage rate of Examples 1-5 is significantly reduced and the puncture strength is significantly increased, indicating that nano-aluminum oxide / silicon dioxide / boron nitride in the nano-aluminum oxide / silicon dioxide / boron nitride composite has a synergistic effect, and the combination of the three can significantly improve the thermal stability and puncture resistance of the lithium-ion battery separator. Among them, compared with Example 6, the thermal shrinkage rate of Example 5 is reduced and the puncture strength is increased, indicating that the calcination and compounding of nano-aluminum oxide, hexagonal boron nitride and silicon dioxide can further improve the thermal stability and puncture resistance of the lithium-ion battery separator.

[0046] Experimental Example 2 The lithium-ion battery separator prepared in Example 3 was also subjected to the following performance tests, and the test results are shown in Table 2: Table 2 Other performance test results of Example 3

[0047] The test methods are as follows: ① Permeability test: The permeability of the separator was tested according to the method in GB / T 36363-2018 "Polyolefin Separators for Lithium-Ion Batteries". Among them, the size of the separator sample was 100 mm × 100 mm, and the test result was the average value of 3 samples; ② Tensile strength and elongation at break test: The tensile strength and elongation at break of the separator were tested according to the method in GB / T 36363-2018 "Polyolefin Separators for Lithium-Ion Batteries". Among them, the separator sample was a Type 2 sample with a width of 15 mm, and the test speed was 250 mm / min; ③ Ion conductivity test: The ion conductivity of the separator was tested according to the method in GB / T 36363-2018 "Polyolefin Separators for Lithium-Ion Batteries"; ④ Peel strength test: Three samples with a width of 15 mm were cut from the separator along the longitudinal direction. The cut samples were pasted on the glass slide with double-sided tape. After pasting, the free end of the sample was folded 180°, and the bonding surface was peeled off by 15 mm by hand. The peel strength was tested by a tensile testing machine; ⑤ Liquid absorption rate and liquid retention rate test: A separator sample with a size of 50 mm × 50 mm was cut, and the cut sample was weighed and the mass was recorded as m1. The weighed separator was immersed in the electrolyte for 30 min; Lay a layer of clean industrial wiping paper (size > 150mm × 150mm) flat on a flat tabletop. Take out the soaked diaphragm sample piece and quickly place it on the industrial wiping paper. Then, use another piece of industrial wiping paper to gently press and wipe the free electrolyte on the surface of the diaphragm sample piece until no granular electrolyte can be seen with the naked eye. Weigh the dried diaphragm sample and record the mass as m2; let it stand for 1h, weigh it again, and record the mass as m3; calculate the liquid absorption rate and liquid retention rate of the diaphragm according to the following formula: liquid absorption rate (%) = (m2 - m1) / m1 × 100%, liquid retention rate (%) = (m3 - m1) / m1 × 100%. The test results of the liquid absorption rate and liquid retention rate are the average values of 3 parallel diaphragm sample pieces, and the calculation results are retained to one decimal place.

[0048] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a high heat-resistant composite inorganic coating lithium battery separator, characterized in that It includes the following steps: S1. Mix a dispersant and water, conduct primary stirring, add a composite material, and conduct secondary stirring to obtain a mixed solution; S2. Add a binder and a thickener to the mixed solution, stir evenly, and then perform sand grinding to obtain a coating slurry; S3. Coat the coating slurry on a base film and dry it to obtain a lithium-ion battery separator with a nano-aluminum oxide and boron nitride coating; The composite material is a nano-aluminum oxide / silicon dioxide / boron nitride composite material; The raw materials of the nano-aluminum oxide / silicon dioxide / boron nitride composite material include the following components in parts by weight: 20-30 parts of nano-aluminum oxide, 5-10 parts of silicon dioxide, and 1-5 parts of hexagonal boron nitride.

2. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that The weight ratio of the nano-aluminum oxide, silicon dioxide, and hexagonal boron nitride is 28:5:1-5.

3. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that, The particle size of the nano-aluminum oxide: D10 is 190-200 nm, D50 is 350-390 nm, and D90 is 650-770 nm; The particle size of the silicon dioxide: D10 is 0.400-0.470 μm, D50 is 0.600-0.680 μm, and D90 is 1.100-1.290 μm; The particle size of the hexagonal boron nitride: D10 is 0.450-0.550 μm, D50 is 1.500-1.600 μm, and D90 is 3.000-3.200 μm.

4. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that The preparation method of the composite material includes the following steps: Mix the nano-aluminum oxide, silicon dioxide, and hexagonal boron nitride, sinter them, and then cool to obtain a composite material.

5. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 4, characterized in that, The mixing is ball milling mixing. When ball milling, the rotation speed is 200-600 rpm and the ball milling time is 10-20 min; When sintering, under the protection of an inert gas, heat it at a heating rate of 10-16 °C / min to 1000-1500 °C, and then sinter for 1-2 h; The inert gas is one of helium, argon, and neon.

6. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that The dispersant is one or more of ammonium polyacrylate, sodium dodecylbenzenesulfonate, and sodium lauryl polyoxyethylene sulfate; and / or The binder is one or two of polyvinylidene fluoride and polyvinyl alcohol; and / or The thickener is one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, and hydroxyethyl cellulose.

7. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that, The parts by weight of the composite material are 25-35 parts, the parts by weight of the dispersant are 0.2-0.5 parts, the parts by weight of the binder are 5-10 parts, the parts by weight of the thickener are 5-10 parts, and the parts by weight of water are 40-50 parts.

8. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that, In step S3, when coating, the coating method is single-sided coating or double-sided coating, the coating speed is 20-50 m / min, and the coating thickness is 3-4 μm.

9. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, characterized in that, The particle size of the coating slurry: D50 is 1.350-1.400 μm, and D90 is 3.400-3.450 μm.

10. The preparation method of a high heat-resistant composite inorganic coating lithium battery separator according to claim 1, wherein, When drying, the temperature is 40-70 °C and the time is 5-10 min.

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