High-safety graphene composite lithium battery diaphragm and preparation method and application thereof

Abstract

The present application belongs to the technical field of lithium ion battery materials, and provides a high-safety graphene composite lithium battery separator, a preparation method and application thereof.The separator comprises a porous polymer base film, a composite functional coating and a polymer gel electrolyte layer.The composite functional coating is composed of modified graphene oxide, inorganic heat-resistant particles and a binder, wherein the graphene oxide is subjected to surface modification treatment, which effectively improves its dispersibility and interface compatibility in the coating.The polymer gel electrolyte layer is covered on the composite coating, which can effectively infiltrate the separator and promote ion transmission.The preparation method of the separator comprises modification treatment of graphene oxide, preparation and dispersion of a composite slurry, and a multi-layer coating and curing process.The separator makes full use of the excellent properties of graphene materials, realizes a multiple safety protection mechanism through material modification and structure design, and significantly improves the thermal stability and safety performance of lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a high-safety graphene composite lithium battery separator, its preparation method, and its application. Background Technology

[0002] The safety of lithium-ion batteries has always been a key limiting factor for their widespread application, with the thermal stability of the separator being crucial. Traditional polyolefin separators are prone to shrinkage and melting at high temperatures, leading to internal short circuits and a significant risk of thermal runaway. To improve the thermal stability of the separator, the industry commonly uses a method of coating the base film with ceramic particles. While this method improves the heat resistance of the separator to some extent, it is essentially still a passive protection method and cannot effectively intervene in the early stages of thermal runaway. Furthermore, the introduction of ceramic coatings often leads to increased separator thickness and decreased ionic conductivity, and the adhesion between the coating and the base film is insufficient, posing a risk of coating detachment during long-term use.

[0003] In recent years, graphene materials have been introduced into the field of membrane modification due to their unique two-dimensional structure and excellent physicochemical properties. However, graphene materials face many challenges in practical applications. Due to the strong van der Waals forces between its layers, it is prone to aggregation, making it difficult to achieve uniform and stable dispersion in slurries, thus affecting the uniformity and consistency of the coating. Furthermore, how to effectively combine graphene materials with other functional materials to construct a multi-layered synergistic protection system without sacrificing the membrane's pore structure and ion transport performance remains a problem that current technologies have not yet adequately solved.

[0004] Therefore, developing a novel composite separator that can fully utilize the excellent properties of graphene materials and overcome its application bottlenecks through material modification and structural design, thereby achieving a safety protection mechanism that combines active and passive methods, is of great value in promoting the development of high-safety lithium-ion battery technology. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a high-safety graphene composite lithium battery separator, its preparation method, and its applications.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a high-safety graphene composite lithium battery separator, comprising the following steps: S1. Modified graphene oxide is obtained by mixing graphene oxide dispersion with silane coupling agent and then reacting. S2. Modified graphene oxide, inorganic heat-resistant particles, binder, dispersant, carbon nanotubes and solvent are mixed to obtain a composite coating slurry; S3. The composite coating slurry is coated onto a porous polymer base film, and a composite functional coating is formed by gradient drying. S4. Mix monomers, crosslinking agents, initiators, flame retardants and solvents to obtain a prepolymer liquid. Coat the prepolymer liquid onto the composite functional coating and cure it to form a polymer gel electrolyte layer. Then, roll it up to obtain a high-safety graphene composite lithium battery separator.

[0007] Furthermore, in step S1, the mass ratio of graphene oxide dispersion to silane coupling agent is 100:1~10; the concentration of graphene oxide dispersion is 0.01~0.1g / mL. The reaction temperature is 50~80℃, and the reaction time is 1~12h.

[0008] Furthermore, in step S2, the mass ratio of modified graphene oxide, inorganic heat-resistant particles, binder, dispersant, carbon nanotubes and solvent is 5~15:5~20:2~8:0.5~2:0.1~1:60~80.

[0009] Furthermore, in step S2, the inorganic heat-resistant particles are one or more of alumina, boehmite, silicon dioxide, and boron nitride. The adhesive is one or more of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, and polyacrylonitrile; The dispersant is a polyvinylpyrrolidone or polyether dispersant; The solvent is one or more of N-methylpyrrolidone, N,N-dimethylacetamide, acetone, butanone, water, isopropanol, and ethylene glycol.

[0010] Furthermore, in step S3, the coating is performed using a micro-gravure coating or a slot extrusion coating method. The gradient drying process is divided into three stages: the drying temperature of the first stage is 50~70℃, the drying temperature of the second stage is 75~90℃, and the drying temperature of the third stage is 95~110℃. The drying time of each stage is 1~5 minutes.

[0011] Furthermore, in step S3, the porous polymer base membrane is a polypropylene membrane and / or a polyethylene membrane.

[0012] Furthermore, in step S4, the mass ratio of monomer, crosslinking agent, initiator, flame retardant and solvent is 60~90:0.5~5:0.1~3:1~10:10~40.

[0013] Furthermore, in step S4, the monomer is one or more of polyethylene glycol diacrylate, pentaerythritol tetraacrylate, and hydroxyethyl acrylate. The crosslinking agent is pentaerythritol tetraacrylate; The initiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone or ammonium persulfate; The flame retardant is triphenyl phosphate or hexaphenoxycyclotriphosphazene; The solvent is N-methylpyrrolidone, dimethylacetamide, or water.

[0014] This invention provides a high-safety graphene composite lithium battery separator prepared by the above-mentioned method.

[0015] The present invention also provides a lithium-ion battery, including the above-mentioned high-safety graphene composite lithium battery separator.

[0016] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: By employing a composite coating structure of modified graphene oxide and inorganic heat-resistant particles, the dispersion challenge of graphene materials in the slurry is effectively solved, ensuring the uniformity and stability of the coating. The polymer gel electrolyte layer on the surface not only significantly improves the wettability of the separator to the electrolyte but also further enhances ion transport efficiency. This unique multilayer structure works synergistically, enabling the separator to exhibit excellent thermal dimensional stability and mechanical integrity at high temperatures, effectively suppressing thermal runaway. Simultaneously, this design improves safety while also considering the battery's rate performance and cycle life, providing a reliable solution for high-safety lithium-ion batteries. Detailed Implementation

[0017] This invention provides a method for preparing a high-safety graphene composite lithium battery separator, comprising the following steps: S1. Modified graphene oxide is obtained by mixing graphene oxide dispersion with silane coupling agent and then reacting. S2. Modified graphene oxide, inorganic heat-resistant particles, binder, dispersant, carbon nanotubes and solvent are mixed to obtain a composite coating slurry; S3. The composite coating slurry is coated onto a porous polymer base film, and a composite functional coating is formed by gradient drying. S4. Mix monomers, crosslinking agents, initiators, flame retardants and solvents to obtain a prepolymer liquid. Coat the prepolymer liquid onto the composite functional coating and cure it to form a polymer gel electrolyte layer. Then, roll it up to obtain a high-safety graphene composite lithium battery separator.

[0018] In this invention, in step S1, the mass ratio of graphene oxide dispersion to silane coupling agent is 100:1~10, preferably 100:2~8, more preferably 100:4~6; the concentration of graphene oxide dispersion is 0.01~0.1g / mL, preferably 0.02~0.08g / mL, more preferably 0.04~0.06g / mL; The reaction temperature is 50~80℃, preferably 60~70℃; the reaction time is 1~12h, preferably 2~10h, and more preferably 4~6h; Graphene oxide (GO) has a surface rich in oxygen-containing functional groups such as hydroxyl and carboxyl groups. Although hydrophilic, it has poor compatibility with non-polar polymer-based films and organic solvents. One end of a silane coupling agent (e.g., alkoxy group) reacts with the oxygen-containing functional groups of GO, while the other end (e.g., long organic chains) introduces organic functional groups. This significantly improves the dispersion stability of modified GO in subsequent organic solvent-based slurries, prevents agglomeration, and ensures a uniform and dense coating.

[0019] Silane coupling agents act as "molecular bridges," chemically bonding one end to GO and interacting well (physical entanglement or chemical bonding) with the binder (such as PVDF) in step S2 or the polymer base film in step S3, significantly improving the adhesion between the functional coating and the base film and preventing the coating from falling off during use.

[0020] In this invention, in step S2, the mass ratio of modified graphene oxide, inorganic heat-resistant particles, binder, dispersant, carbon nanotubes and solvent is 5~15:5~20:2~8:0.5~2:0.1~1:60~80, preferably 10:8~15:4~6:1:0.2~0.8:65~75, and more preferably 10:10:5:1:0.5:70.

[0021] In this invention, in step S2, the inorganic heat-resistant particles are one or more of alumina, boehmite, silicon dioxide, and boron nitride. The adhesive is one or more of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, and polyacrylonitrile; The dispersant is a polyvinylpyrrolidone or polyether dispersant; The solvent is one or more selected from N-methylpyrrolidone, N,N-dimethylacetamide, acetone, butanone, water, isopropanol, and ethylene glycol; The carbon nanotubes and the modified graphene oxide form a three-dimensional thermally conductive network.

[0022] In this invention, in step S3, the coating is performed using microgravure coating or slot extrusion coating. The gradient drying process consists of three stages. The drying temperature of the first stage is 50-70℃, preferably 55-65℃, and more preferably 60℃; the drying temperature of the second stage is 75-90℃, preferably 80℃; and the drying temperature of the third stage is 95-110℃, preferably 100℃. The drying time for each stage is independent, ranging from 1 to 5 minutes, preferably 2 to 4 minutes, and more preferably 3 minutes. If high-temperature drying is used from the beginning, the solvent on the surface of the slurry will evaporate rapidly, forming a hard shell, making it difficult for the internal solvent to escape, which will eventually lead to bubbles, cracks, or pores in the coating. Gradient drying perfectly solves this problem.

[0023] In this invention, in step S3, the porous polymer base membrane is a polypropylene membrane and / or a polyethylene membrane.

[0024] In this invention, in step S4, the mass ratio of monomer, crosslinking agent, initiator, flame retardant and solvent is 60~90:0.5~5:0.1~3:1~10:10~40, preferably 70~80:2:2:4~8:20~30.

[0025] In this invention, in step S4, the monomer is one or more of polyethylene glycol diacrylate, pentaerythritol tetraacrylate, and hydroxyethyl acrylate. The crosslinking agent is pentaerythritol tetraacrylate; The initiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone or ammonium persulfate; The flame retardant is triphenyl phosphate or hexaphenoxycyclotriphosphazene; The solvent is N-methylpyrrolidone, dimethylacetamide, or water.

[0026] In this invention, in step S4, when the photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone is used, the curing is carried out under an inert atmosphere with a light intensity of 50~500mW / cm. 2 The exposure energy is 500~2000 mJ / cm. 2 The photocuring time is 5~30s; When using ammonium persulfate as a thermal initiator, the curing temperature is 50~85℃ and the curing time is 10~60min.

[0027] This invention provides a high-safety graphene composite lithium battery separator prepared by the above-mentioned method.

[0028] The present invention also provides a lithium-ion battery, including the above-mentioned high-safety graphene composite lithium battery separator.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1 Take 100g of a 0.05g / mL aqueous dispersion of graphene oxide (GO) (i.e., containing 5g of graphene oxide) and place it in a 250mL three-necked flask equipped with a stirrer and a condenser. Heat the water bath to 60℃ and, under uniform stirring, slowly add 0.3g of KH-550 (aminopropyltriethoxysilane) silane coupling agent (GO to silane coupling agent mass ratio of 100:6). Maintain a constant temperature of 60℃ for 5 hours. After the reaction is complete, cool the product to room temperature to obtain the modified graphene oxide dispersion.

[0031] Weigh all of the above modified graphene oxide dispersions, and add 10g boehmite (inorganic heat-resistant particles), 5g polyvinylidene fluoride (PVDF, binder), 1g polyvinylpyrrolidone (PVP, dispersant), 0.5g carboxylated multi-walled carbon nanotubes (CNTs) to it in sequence. Finally, add 70g N-methylpyrrolidone (NMP, solvent). Transfer the mixture to a planetary ball mill and ball mill at 300 rpm for 4 hours to ensure that the components are evenly dispersed and obtain a composite coating slurry with stable viscosity.

[0032] A 12μm thick porous polyethylene (PE) base film was selected as the substrate. A slotted extrusion coating method was used to uniformly coat one side of the PE base film with a composite coating slurry, maintaining a wet film thickness of 50μm. Immediately afterwards, a three-stage gradient drying process was performed: first stage, drying at 60℃ for 3 minutes; second stage, drying at 80℃ for 3 minutes; third stage, drying at 100℃ for 3 minutes. After drying, a dense, crack-free composite functional coating was formed on the base film, which was then wound up for use.

[0033] Under light-protected conditions, 75g of polyethylene glycol diacrylate (PEGDA, monomer), 2g of pentaerythritol tetraacrylate (PETTA, crosslinking agent), 2g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, 6g of hexaphenoxycyclotriphosphazene (flame retardant), and 25g of N-methylpyrrolidone (solvent) were mixed and magnetically stirred until completely dissolved to obtain a transparent prepolymer solution. The prepolymer solution was then uniformly coated onto the surface of the composite functional coating using a microgravure coating method. The diaphragm was subsequently transferred to a nitrogen-filled glove box and cured using a UV curing machine (light intensity 200mW / cm²). 2 Irradiate for 15 seconds (exposure energy is 3000 mJ / cm²). 2 The coating is then fully cured to form a stable polymer gel electrolyte layer. Finally, it is wound up to obtain the high-safety graphene composite lithium battery separator.

[0034] Example 2 Take 100g of a 0.04g / mL graphene oxide (GO) aqueous dispersion (containing 4g of graphene oxide) and place it in a 250mL three-necked flask equipped with a stirrer and a condenser. Heat the water bath to 65℃ and slowly add 0.2g of KH-570 (methacryloyloxypropyltrimethoxysilane) silane coupling agent (GO to silane coupling agent mass ratio 100:5) dropwise while stirring at a constant speed. Maintain the reaction temperature at 65℃ for 4 hours. After the reaction is complete, cool the product to room temperature to obtain the modified graphene oxide dispersion.

[0035] Weigh all of the above modified graphene oxide dispersion, and add 8g of alumina (inorganic heat-resistant particles), 4g of polyacrylate emulsion (binder), 0.8g of polyvinylpyrrolidone (PVP, dispersant), 0.2g of carboxylated multi-walled carbon nanotubes (CNTs) to it in sequence. Finally, add 65g of N,N-dimethylacetamide (solvent). Transfer the mixture to a planetary ball mill and ball mill at 300 rpm for 2 hours to ensure that the components are evenly dispersed and obtain a composite coating slurry with stable viscosity.

[0036] A 12μm thick porous polypropylene (PP) base film was selected as the substrate. A microgravure coating method was used to uniformly coat one side of the PP base film with a composite coating slurry, maintaining a wet film thickness of 40μm. Immediately afterwards, a three-stage gradient drying process was performed: first stage, drying at 55℃ for 4 minutes; second stage, drying at 75℃ for 4 minutes; third stage, drying at 95℃ for 4 minutes. After drying, a dense, crack-free composite functional coating was formed on the base film, which was then wound up for use.

[0037] Under light-protected conditions, 70g of hydroxyethyl acrylate (monomer), 1g of pentaerythritol tetraacrylate (PETTA, crosslinking agent), 1g of ammonium persulfate (thermal initiator), 5g of triphenyl phosphate (flame retardant), and 30g of deionized water were mixed and magnetically stirred until completely dissolved to obtain a transparent prepolymer solution. The prepolymer solution was uniformly coated onto the surface of the composite functional coating using a microgravure coating method. The mixture was then heat-cured in a 60°C oven for 30 minutes to form a polymer gel electrolyte layer. Finally, the mixture was wound up to obtain the high-safety graphene composite lithium battery separator.

[0038] Example 3 Take 100g of a 0.06g / mL aqueous dispersion of graphene oxide (GO) (i.e., containing 6g of graphene oxide) and place it in a 250mL three-necked flask equipped with a stirrer and a condenser. Heat the water bath to 70℃, and slowly add 0.24g of KH-550 (aminopropyltriethoxysilane) silane coupling agent (GO to silane coupling agent mass ratio of 100:4) dropwise while stirring at a constant speed. Maintain the reaction at 70℃ for 6 hours. After the reaction is complete, cool the product to room temperature to obtain the modified graphene oxide dispersion.

[0039] Weigh all of the above modified graphene oxide dispersion, and add 6g boron nitride, 6g silica (inorganic heat-resistant particles), 6g styrene-butadiene rubber (binder), 1.2g polyvinylpyrrolidone (PVP, dispersant), 0.6g carboxylated multi-walled carbon nanotubes (CNTs) to it in sequence. Finally, add 75g N-methylpyrrolidone (NMP, solvent). Transfer the mixture to a planetary ball mill and ball mill at 300 rpm for 5 hours to ensure that the components are evenly dispersed and obtain a composite coating slurry with stable viscosity.

[0040] A 12μm thick porous polyethylene (PE) base film was selected as the substrate. A slot-die extrusion coating method was used to uniformly coat one side of the PE base film with a composite coating slurry, maintaining a wet film thickness of 55μm. Immediately afterwards, a three-stage gradient drying process was performed: first stage, drying at 65℃ for 2 minutes; second stage, drying at 85℃ for 2 minutes; third stage, drying at 105℃ for 2 minutes. After drying, a dense, crack-free composite functional coating was formed on the base film, which was then wound up for use.

[0041] Under light-protected conditions, 80g of pentaerythritol tetraacrylate, 0.5g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, 8g of hexaphenoxycyclotriphosphazene (flame retardant), and 20g of N-methylpyrrolidone (solvent) were mixed and magnetically stirred until completely dissolved to obtain a transparent prepolymer solution. The prepolymer solution was then uniformly coated onto the surface of the composite functional coating using a microgravure coating method. The diaphragm was subsequently transferred to a nitrogen-filled glove box and cured using a UV curing machine (400mW / cm²). 2 Irradiate for 10 seconds (exposure energy is 3000 mJ / cm²). 2 The coating is then fully cured to form a stable polymer gel electrolyte layer. Finally, it is wound up to obtain the high-safety graphene composite lithium battery separator.

[0042] Comparative Example 1 Similar to Example 1, but with the difference that unmodified graphene oxide was used directly. The resulting composite coating slurry exhibited extremely poor stability; even after forced application, the coating surface was rough and had a high degree of particle texture. After drying, the coating showed very poor adhesion to the PE base film, peeling off in large quantities with even slight rubbing. Because the underlying coating had failed, a diaphragm was not fabricated.

[0043] Comparative Example 2 Similar to Example 1, except that a single high-temperature drying (100°C, 9 min) was used instead of gradient drying, a skin was observed to form rapidly on the slurry surface during the drying process. The internal solvent vaporized but could not escape, forming a large number of bubbles. After drying, obvious blistering, cracks, and localized crazing appeared on the coating surface, and the structural density was destroyed.

[0044] Performance testing 1. Heat shrinkage rate: Cut the diaphragm sample into a 10×10 cm square and equilibrate it for 24 hours in an environment of 23℃ and 50% humidity. Measure the initial length L0 accurately with vernier calipers. Place the sample flat on a smooth ceramic plate and put it in a forced-air drying oven. Treat it at 150℃ for 1 hour. Remove the sample, cool it to room temperature, and measure its dimension L1 again.

[0045] Calculate the heat shrinkage rate: Heat shrinkage rate (%) = (L0-L1) / L0×100%.

[0046] The machine direction (MD) and lateral direction (TD) were measured separately, and the results are shown in Table 1.

[0047] Table 1 Results of heat shrinkage test

[0048] As shown in Table 1, the diaphragm prepared by the present invention has a much better thermal dimensional stability than the defective Comparative Example 2 and the traditional commercial ceramic diaphragm due to the presence of a stable heat-resistant coating composed of modified GO and inorganic particles. In particular, it can effectively maintain structural integrity at high temperatures.

[0049] 2. Battery Cycle Performance: A soft-pack lithium-ion battery with a rated capacity of 2Ah was assembled using a separator, NCM622 as the positive electrode, and graphite as the negative electrode. Charge-discharge cycle tests were conducted at 25℃ using a battery testing system: first, three formation cycles were performed at a 0.5C rate; then, the battery was charged at a 1C constant current to 4.2V, switched to constant voltage until the current dropped to 0.05C, and finally discharged at a 1C constant current to 3.0V. The discharge capacity of each cycle was recorded, and the test results are shown in Table 2.

[0050] Table 2 Test results of battery cycle performance

[0051] As shown in Table 2, after 300 cycles, the battery prepared with the separator of this invention exhibits excellent cycle stability. The uniform coating and good interface ensure the uniformity of electrode reactions and structural stability. In contrast, the defective coating in Comparative Example 2 leads to uneven local current density, increased side reactions, and further stress deterioration during cycling, accelerating performance degradation.

[0052] 3. Hot Box Test: A soft-pack lithium-ion battery with a rated capacity of 2Ah was assembled using a separator, NCM622 as the positive electrode, and graphite as the negative electrode. It was placed in a programmable temperature-controlled explosion-proof test chamber and heated from room temperature at a rate of 5℃ / min. The battery surface temperature and voltage were continuously monitored, and the time and maximum temperature at which the battery ignited and exploded were observed and recorded. The results are shown in Table 3.

[0053] Table 3 Hot Box Test Results

[0054] As shown in Table 3, the high-safety separator prepared by this invention can significantly improve the thermal safety boundary of lithium-ion batteries, verifying its design goal of "high safety".

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-safety graphene composite lithium battery separator, characterized in that, Includes the following steps: S1. Modified graphene oxide is obtained by mixing graphene oxide dispersion with silane coupling agent and then reacting. S2. Modified graphene oxide, inorganic heat-resistant particles, binder, dispersant, carbon nanotubes and solvent are mixed to obtain a composite coating slurry; S3. The composite coating slurry is coated onto a porous polymer base film, and a composite functional coating is formed by gradient drying. S4. Mix monomers, crosslinking agents, initiators, flame retardants and solvents to obtain a prepolymer liquid. Coat the prepolymer liquid onto the composite functional coating and cure it to form a polymer gel electrolyte layer. Then, roll it up to obtain a high-safety graphene composite lithium battery separator.

2. The method for preparing the high-safety graphene composite lithium battery separator according to claim 1, characterized in that, In step S1, the mass ratio of graphene oxide dispersion to silane coupling agent is 100:1~10; the concentration of graphene oxide dispersion is 0.01~0.1g / mL. The reaction temperature is 50~80℃, and the reaction time is 1~12h.

3. The method for preparing the high-safety graphene composite lithium battery separator according to claim 2, characterized in that, In step S2, the mass ratio of modified graphene oxide, inorganic heat-resistant particles, binder, dispersant, carbon nanotubes and solvent is 5~15:5~20:2~8:0.5~2:0.1~1:60~80.

4. The method for preparing the high-safety graphene composite lithium battery separator according to claim 3, characterized in that, In step S2, the inorganic heat-resistant particles are one or more of alumina, boehmite, silicon dioxide, and boron nitride. The adhesive is one or more of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, and polyacrylonitrile; The dispersant is a polyvinylpyrrolidone or polyether dispersant; The solvent is one or more of N-methylpyrrolidone, N,N-dimethylacetamide, acetone, butanone, water, isopropanol, and ethylene glycol.

5. The method for preparing the high-safety graphene composite lithium battery separator according to claim 3, characterized in that, In step S3, the coating is performed using micro-gravure coating or slot extrusion coating. The gradient drying process is divided into three stages: the drying temperature of the first stage is 50~70℃, the drying temperature of the second stage is 75~90℃, and the drying temperature of the third stage is 95~110℃. The drying time of each stage is 1~5 minutes.

6. The method for preparing the high-safety graphene composite lithium battery separator according to claim 5, characterized in that, In step S3, the porous polymer base membrane is a polypropylene membrane and / or a polyethylene membrane.

7. The method for preparing the high-safety graphene composite lithium battery separator according to any one of claims 1 to 6, characterized in that, In step S4, the mass ratio of monomer, crosslinking agent, initiator, flame retardant and solvent is 60~90:0.5~5:0.1~3:1~10:10~40.

8. The method for preparing the high-safety graphene composite lithium battery separator according to claim 7, characterized in that, In step S4, the monomer is one or more of polyethylene glycol diacrylate, pentaerythritol tetraacrylate and hydroxyethyl acrylate. The crosslinking agent is pentaerythritol tetraacrylate; The initiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone or ammonium persulfate; The flame retardant is triphenyl phosphate or hexaphenoxycyclotriphosphazene; The solvent is N-methylpyrrolidone, dimethylacetamide, or water.

9. The high-safety graphene composite lithium battery separator prepared by the method of any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, Including the high-safety graphene composite lithium battery separator as described in claim 9.

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