A high-temperature resistant polyarylate-coated lithium-ion battery separator and its preparation process

Abstract

This application relates to the technical field of lithium-ion battery components, and specifically discloses a high-temperature resistant polyarylate-coated lithium-ion battery separator and its preparation process. In this application, a polyarylate composite slurry is used to reinforce the base film. A liquid crystal phase is locally formed through 3,5-dimethoxyphenyl, a xanthene structural unit is introduced, and nano-lignin is added as an auxiliary agent. Both the xanthene structural unit and nano-lignin contain a large number of aromatic ring structures, which can synergistically enhance the mechanical strength of the coating with the liquid crystal phase by means of the π-π stacking effect between aromatic rings, thereby making up for the defect of the low tensile strength of the non-woven fabric separator and fully meeting the requirements of high-end products.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion battery components. More specifically, it relates to a high-temperature resistant polyarylate-coated lithium-ion battery separator and its preparation process. Background Art

[0002] A lithium-ion battery is a secondary battery (rechargeable battery) that mainly operates by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li+ intercalates and deintercalates between the two electrodes: during charging, Li+ deintercalates from the positive electrode and intercalates into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharging, the opposite occurs. Lithium-ion batteries have the advantages of high energy density, high working voltage, long cycle life, etc., and are very suitable for use in various mobile devices and electric vehicles, with broad market prospects.

[0003] A separator is usually provided between the positive and negative electrodes of a lithium-ion battery. The separator is a thin film material with a microporous structure located between the positive and negative electrodes, which ensures the normal transmission of lithium ions and electron insulation while isolating the direct contact between the positive and negative electrodes. Although it does not directly participate in the electrochemical process, the pore structure and surface properties of the separator have a direct impact on the internal resistance, discharge capacity, cycle stability, and safety performance of the battery. Therefore, the separator is also called the "third electrode" in the battery. Although the separator does not participate in the electrochemical reaction, its structure, properties, and surface chemistry are dynamically affected by the mechanical, thermal, and electrochemical effects of the battery, further affecting ion transport and battery safety. For example, the interaction between the polyolefin separator and the electrolyte causes it to mechanically soften and expand, and at the same time, the volume expansion of the active material during the cycle will generate stress on the separator. Therefore, to avoid short circuits in the battery caused by the volume expansion of the positive and negative electrode materials (such as the growth of lithium dendrites) during charging and discharging, the separator should have good tensile and puncture resistance. Currently, the separators on the market usually use olefin polymers as the base material, such as polyethylene separators, polypropylene separators, non-woven fabric separators, etc.

[0004] Regarding the above related technologies, the inventor believes that the polyolefin separators in the related technologies are prone to cause battery explosions due to shrinkage when the battery overheats, and the safety is poor. Although the non-woven fabric separator has good high-temperature resistance, it has more structural voids and lower tensile strength, making it difficult to fully meet the requirements of high-end products. Summary of the Invention

[0005] In the related technologies, the polyolefin separator has poor safety, and the non-woven fabric separator has low tensile strength, making it difficult to fully meet the requirements of high-end products. To improve the above defects, this application provides a high-temperature resistant polyarylate-coated lithium-ion battery separator and its preparation process.

[0006] In the first aspect, this application provides a high-temperature resistant polyarylate-coated lithium-ion battery separator, adopting the following technical solution:

[0007] A high-temperature resistant polyarylate-coated lithium-ion battery separator, comprising a base film and a coating applied on the surface of the base film. The coating is obtained by coating a polyarylate composite slurry, preheating with steam, and drying with hot air. The polyarylate composite slurry comprises the following components by weight percentage: 15-20% of aromatic polyester, 5-8% of adhesive, and the balance being additives and solvents. The aromatic polyester further contains a xanthene structural unit and 3,5-dimethoxyphenyl. The additives include nano-lignin, and the weight of the nano-lignin accounts for 0.8-1.4% of the total weight of the polyarylate composite slurry.

[0008] By adopting the above technical solution, the present application uses a polyarylate composite slurry to strengthen the base film and defines that the aromatic polyester contains 3,5-dimethoxyphenyl. 3,5-Dimethoxyphenyl can cause the molecules of the aromatic polyester to attract each other and be regularly oriented, thereby forming a liquid crystal phase locally, providing a good basis for improving the mechanical properties of the separator. The present application also defines that the aromatic polyester contains a xanthene structural unit and adds nano-lignin as an additive. Both the xanthene structural unit and nano-lignin contain a large number of aromatic ring structures, which can increase the aromatic ring distribution density in the coating and have good compatibility with the polyarylate. With the help of the π-π stacking effect between the aromatic rings, a strong attraction can be formed between the aromatic polyester and nano-lignin. This attraction can synergistically enhance the mechanical strength of the coating with the liquid crystal phase, thus compensating for the defect of low tensile strength of the non-woven fabric separator and fully meeting the requirements of high-end products.

[0009] Preferably, the aromatic polyester is prepared according to the following method:

[0010] (1) Mix (3,5-dimethoxyphenyl)oxy-isophthalic acid, hydroquinone, and xanthene monomers, add a catalyst, and obtain a prepolymer after heating and polymerization. In this step, the xanthene monomers include at least one of xanthene diol monomers and xanthene diacid monomers.

[0011] (2) Heat-treat the prepolymer to obtain the aromatic polyester.

[0012] By adopting the above technical solution, the present application performs co-condensation polymerization using (3,5-dimethoxyphenyl)oxy-isophthalic acid, hydroquinone, and xanthene monomers. 3,5-Dimethoxyphenyl is introduced through (3,5-dimethoxyphenyl)oxy-isophthalic acid, and the xanthene unit is introduced through the xanthene monomers, and finally an aromatic polyester with a liquid crystal effect and containing a xanthene unit is obtained.

[0013] Preferably, the xanthene monomers include 9,9-bis(4-hydroxyphenyl)xanthene.

[0014] By adopting the above technical solution, 9,9-bis(4-hydroxyphenyl)xanthene is a xanthenediol monomer that can react with (3,5-dimethoxyphenyl)oxy-isophthalic acid and can improve the overall tensile strength of the separator by introducing a xanthene structural unit.

[0015] Preferably, the 9,9-bis(4-hydroxyphenyl)xanthene is prepared according to the following method:

[0016] Mix xanthone, thionyl chloride, and DMF and heat under reflux. Distill off the excess thionyl chloride, then cool the reaction system, add a xylene solution of phenol, heat under reflux again, and then perform vacuum distillation to distill off xylene and the excess phenol to obtain a crude product; recrystallize the crude product with toluene to obtain 9,9-bis(4-hydroxyphenyl)xanthene.

[0017] By adopting the above technical solution, in this application, xanthone is used as the starting material. First, xanthone is treated with thionyl chloride to replace the carbonyl group with a dichloromethylene group, and then the dichloromethylene group reacts with phenol to remove a chlorine atom and connect phenol to the xanthene structure, obtaining 9,9-bis(4-hydroxyphenyl)xanthene that can undergo a co-polycondensation reaction with (3,5-dimethoxyphenyl)oxy-isophthalic acid.

[0018] Preferably, the xanthene monomer further includes 9,9-bis(4-carboxyphenoxyphenyl)xanthene.

[0019] By adopting the above technical solution, this application further defines that the xanthene monomer includes 9,9-bis(4-carboxyphenoxyphenyl)xanthene, and 9,9-bis(4-carboxyphenoxyphenyl)xanthene is a xanthenedioic acid monomer. 9,9-bis(4-carboxyphenoxyphenyl)xanthene has two carboxyl groups and can undergo co-polycondensation with 9,9-bis(4-hydroxyphenyl)xanthene or hydroquinone, and can also improve the overall tensile strength of the separator by introducing a xanthene structural unit.

[0020] Preferably, the 9,9-bis(4-carboxyphenoxyphenyl)xanthene is prepared according to the following method:

[0021] Mix 9,9-bis(4-cyanophenoxyphenyl)xanthene, potassium hydroxide, and an ethanol aqueous solution, heat under reflux, filter off the insoluble matter to obtain a clear solution. After the clear solution cools, place the clear solution in an ice bath, add hydrochloric acid for acidification to obtain a precipitate, wash, filter, and dry the precipitate, then recrystallize with absolute ethanol, and perform vacuum drying on the product to obtain 9,9-bis(4-carboxyphenoxyphenyl)xanthene.

[0022] By adopting the above technical solution, the preparation of 9,9-bis(4-carboxyphenoxyphenyl)xanthene is realized in this application.

[0023] Preferably, the auxiliary agent further includes copolymer-modified halloysite nanotubes. The copolymer-modified halloysite nanotubes are halloysite nanotubes grafted with acrylic acid copolymers on the surface, and phenyl groups are carried in the acrylic acid copolymers.

[0024] By adopting the above technical solution, the present application preferably uses copolymer-modified halloysite nanotubes as the auxiliary agent. The copolymer-modified halloysite nanotubes can be entangled with aromatic polyesters through the long chains formed by the acrylic acid copolymers on the surface, and the phenyl groups in the acrylic acid copolymers can also improve the entanglement effect through the π-π stacking effect, so that the coating is not easily broken when subjected to tension, and the overall tensile strength of the separator is improved.

[0025] Preferably, the copolymer-modified halloysite nanotubes are prepared according to the following method:

[0026] (1) Mix halloysite nanotubes, vinyltriethoxysilane, water and ethanol, heat after ultrasonic dispersion, and then filter and wash to obtain vinyl-modified halloysite nanotubes;

[0027] (2) Add glycidyl methacrylate, ethyl 3-phenylacrylate, vinyl-modified halloysite nanotubes, inhibitor and anionic surfactant to deionized water, obtain a raw material solution after ultrasonic dispersion, add an initiator to the raw material solution, carry out suction filtration after heat reaction, crush the filter residue, and obtain copolymer-modified halloysite nanotubes after Soxhlet extraction and vacuum drying.

[0028] By adopting the above technical solution, the present application first grafts a silane segment with a vinyl group on the surface of halloysite nanotubes using vinyltriethoxysilane, and then under the action of an initiator, the vinyl group at the end of the silane segment copolymerizes with two monomers, glycidyl methacrylate and ethyl 3-phenylacrylate, so as to form a long chain of acrylic acid copolymer with phenyl groups on the surface of halloysite nanotubes, and copolymer-modified halloysite nanotubes are obtained. Glycidyl methacrylate endows the polymer with good flexibility and adhesion, which helps to fully improve the overall tensile strength of the separator.

[0029] Preferably, in step (2) of preparing the copolymer-modified halloysite nanotubes, the raw materials for preparing the raw material solution further include linolenic acid.

[0030] By adopting the above technical solution, the molecule of linolenic acid has three unsaturated bonds, which can participate in the copolymerization of acrylic monomers and generate more branched chain structures in the copolymer, promoting the full contact between the acrylic acid copolymer segments and the aromatic polyester, and helping to fully improve the overall tensile strength of the separator.

[0031] In a second aspect, the present application provides a preparation process for a high-temperature resistant polyarylate-coated lithium-ion battery separator, adopting the following technical solutions.

[0032] A preparation process for a high-temperature resistant polyarylate-coated lithium-ion battery separator includes the following steps:

[0033] (1) Mix an aromatic polyester, an adhesive, an auxiliary agent, and a solvent, and stir to obtain a polyarylate composite slurry for standby; perform corona pretreatment on the lithium-ion battery base film for standby;

[0034] (2) Coat the polyarylate composite slurry on the surface of the lithium-ion battery base film to obtain a coating layer;

[0035] (3) Preheat the coating layer, and then perform hot air drying to obtain a high-temperature resistant polyarylate-coated lithium-ion battery separator.

[0036] By adopting the above technical solutions, the present application first prepares a polyarylate composite slurry and pretreats the base film. Then, through steps such as coating, preheating, and drying, the polyarylate composite slurry is cured and formed, and pores are formed through the evaporation of the solvent, thereby obtaining a high-temperature resistant polyarylate-coated lithium-ion battery separator suitable for use in lithium battery products.

[0037] In summary, the present application has the following beneficial effects:

[0038] 1. The present application uses a polyarylate composite slurry to reinforce the base film, locally forms a liquid crystal phase through 3,5-dimethoxyphenyl, introduces a xanthene structural unit, and adds nano-lignin as an auxiliary agent. Both the xanthene structural unit and nano-lignin contain a large number of aromatic ring structures, and can synergistically enhance the mechanical strength of the coating by means of the π-π stacking effect between the aromatic rings and the liquid crystal phase, thereby making up for the defect of the low tensile strength of the non-woven fabric separator and fully meeting the requirements of high-end products.

[0039] 2. The present application selects 9,9-bis(4-hydroxyphenyl)xanthene and 9,9-bis(4-carboxyphenoxyphenyl)xanthene as xanthene monomers, and introduces a xanthene structural unit through these two monomers, improving the aromatic ring distribution density in the coating and contributing to the improvement of the overall tensile strength of the separator.

[0040] 3. The present application also uses copolymer-modified halloysite nanotubes as an auxiliary agent. The copolymer-modified halloysite nanotubes can entangle with the aromatic polyester through the long chains formed by the acrylic copolymer on the surface, and the phenyl groups in the acrylic copolymer can also improve the entanglement effect through the π-π stacking effect, so that the coating is not easily broken when subjected to tension, improving the overall tensile strength of the separator. Specific Embodiments

[0041] The present application will be further described in detail below with reference to examples, preparation examples and comparative examples. The raw materials involved in the present application are all commercially available.

[0042] Preparation Example of Aromatic Polyester

[0043] The following takes Preparation Example 1 as an example for illustration.

[0044] Preparation Example 1

[0045] In this preparation example, the xanthene monomer is 9,9-bis(4-hydroxyphenyl)xanthene, and 9,9-bis(4-hydroxyphenyl)xanthene is prepared according to the following method:

[0046] Weigh xanthone, thionyl chloride, DMF, phenol and xylene in a ratio of 30 g:100 mL:0.2 mL:50 g:100 mL, and set aside; mix xanthone, thionyl chloride and DMF and heat under reflux for 8 h, distill off the excess thionyl chloride, then cool the reaction system to 25 °C, add the xylene solution of phenol, heat under reflux again for 10 h and then perform vacuum distillation to distill off xylene and the excess phenol to obtain a crude product; recrystallize the crude product with toluene to obtain 9,9-bis(4-hydroxyphenyl)xanthene.

[0047] This preparation example provides an aromatic polyester, which is prepared according to the following method:

[0048] (1) Mix 1 mol of (3,5-dimethoxyphenyl)oxy-isophthalic acid, 1 mol of hydroquinone and 0.5 mol of 9,9-bis(4-hydroxyphenyl)xanthene, add 0.1 mol of tetrabutyl titanate as a catalyst, and heat and polymerize at 195 °C under normal pressure for 12 h to obtain a prepolymer;

[0049] (2) Carry out heat treatment on the prepolymer at 225 °C and 0.05 MPa for 16 h to obtain an aromatic polyester.

[0050] Preparation Example 2

[0051] The difference between this preparation example and Preparation Example 1 is that the xanthene monomer also includes 9,9-bis(4-carboxyphenoxyphenyl)xanthene, and in step (1) of preparing the aromatic polyester, 0.8 mol of (3,5-dimethoxyphenyl)oxy-isophthalic acid, 0.2 mol of 9,9-bis(4-carboxyphenoxyphenyl)xanthene, 1 mol of hydroquinone and 0.5 mol of 9,9-bis(4-hydroxyphenyl)xanthene are mixed.

[0052] 9,9-bis(4-carboxyphenoxyphenyl)xanthene is prepared according to the following method:

[0053] Weigh 9,9-bis(4-cyanophenoxyphenyl)xanthene, potassium hydroxide, and an ethanol aqueous solution (the volume ratio of ethanol to water is 1:1) according to the ratio of 0.045 mol:0.45 mol:300 mL. Mix 9,9-bis(4-cyanophenoxyphenyl)xanthene, potassium hydroxide, and the ethanol aqueous solution. After heating under reflux for 48 h, filter off the insoluble matter to obtain a clear solution. After the clear solution is cooled to 25 °C, place the clear solution in an ice bath, add hydrochloric acid to acidify to pH = 2.5 to obtain a precipitate. Wash, filter, and dry the precipitate, then recrystallize with absolute ethanol, and vacuum dry the product to obtain 9,9-bis(4-carboxyphenoxyphenyl)xanthene.

[0054] Preparation Example of Copolymer-Modified Halloysite Nanotubes

[0055] The following takes Preparation Example 3 as an example for illustration.

[0056] Preparation Example 3

[0057] This preparation example provides a copolymer-modified halloysite nanotube, which is prepared according to the following method:

[0058] (1) Mix halloysite nanotubes (CAS No.: 60676-86-0), vinyltriethoxysilane, water, and ethanol according to a weight ratio of 1:0.1:20:10. After ultrasonic dispersion for 1 h, heat at 110 °C for 8 h, and then filter and wash to obtain vinyl-modified halloysite nanotubes;

[0059] (2) Mix glycidyl methacrylate, ethyl 3-phenylacrylate, vinyl-modified halloysite nanotubes, a polymerization inhibitor (copper sulfate pentahydrate), an anionic surfactant (sodium dodecylbenzenesulfonate), and deionized water according to a weight ratio of 0.3:2.7:1:1:10. After ultrasonic dispersion, obtain a raw material solution. Add an initiator (ammonium persulfate, with a dosage of 0.5% of the total weight of the raw material solution) to the raw material solution, heat and react at 70 °C for 4 h, then perform suction filtration, crush the filter residue, and obtain copolymer-modified halloysite nanotubes after Soxhlet extraction and vacuum drying.

[0060] Preparation Example 4

[0061] The difference between this preparation example and Preparation Example 3 is that in step (2) of preparing the copolymer-modified halloysite nanotubes, the raw materials for preparing the raw material solution further include linolenic acid, and the weight ratio of linolenic acid to vinyl-modified halloysite nanotubes is 1:10.

[0062] Preparation Example 5

[0063] The difference between this preparation example and Preparation Example 3 is that glycidyl methacrylate is replaced with the same weight of ethyl 3-phenylacrylate.

[0064] Examples

[0065] Examples 1 - 5

[0066] The following takes Example 1 as an illustration.

[0067] Example 1

[0068] In this example, nano - lignin is used as an additive. The average particle size of nano - lignin is 320 nm and it is made from delignified lignin; the aromatic polyester is prepared according to the method of Preparation Example 1, the adhesive is vinylidene fluoride - trifluoroethylene copolymer, and the solvent is DMF.

[0069] This example provides a high - temperature resistant polyarylate - coated lithium - ion battery separator, which includes a base film and a coating applied on the surface of the base film. The base film is a PET non - woven fabric with a thickness of 20 μm and a porosity of 62%. The coating is obtained by coating, pre - heating with steam, and drying with hot air using a polyarylate composite slurry. The polyarylate composite slurry includes the following components by weight percentage: 15% aromatic polyester, 8% adhesive, 0.8% nano - lignin, and the balance is solvent.

[0070] This example provides a preparation process for a high - temperature resistant polyarylate - coated lithium - ion battery separator, which includes the following steps:

[0071] (1) Mix the aromatic polyester, adhesive, additive, and solvent, stir to obtain a polyarylate composite slurry, and set aside; perform corona pretreatment on the lithium - ion battery base film and set aside;

[0072] (2) Use the gravure coating method to coat the polyarylate composite slurry on both sides of the lithium - ion battery base film at a coating rate of 5 m / min to obtain a coating layer;

[0073] (3) Perform steam pre - heating on the coating layer for 15 s in an environment with 95% humidity, and then perform hot - air drying to cure the coating layer into a 5 - μm - thick coating, obtaining a high - temperature resistant polyarylate - coated lithium - ion battery separator.

[0074] As shown in Table 1, the main difference between Examples 1 - 5 lies in the different raw material ratios of the polyarylate composite slurry.

[0075] Table 1 Raw material ratios of the polyarylate composite slurry

[0076]

[0077] Example 6

[0078] The difference between this example and Example 5 is that the aromatic polyester is prepared according to the method of Preparation Example 2.

[0079] Example 7

[0080] The difference between this example and Example 6 is that nano-lignin and copolymer-modified halloysite nanotubes are used together as additives. The copolymer-modified halloysite nanotubes are prepared according to the method of Preparation Example 3. The mass fractions of nano-lignin and copolymer-modified halloysite nanotubes in the polyarylate composite slurry are 1.4% and 2.5% respectively.

[0081] Example 8

[0082] The difference between this example and Example 7 is that the copolymer-modified halloysite nanotubes are prepared according to the method of Preparation Example 4.

[0083] Example 9

[0084] The difference between this example and Example 7 is that the copolymer-modified halloysite nanotubes are prepared according to the method of Preparation Example 5.

[0085] Comparative Example

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that the aromatic polyester of Preparation Example 1 is replaced with an aromatic polyester (LCP T820) provided by Mitsubishi Engineering Plastics Corporation of Japan.

[0088] Comparative Example 2

[0089] The difference between this comparative example and Example 1 is that the xanthene monomer used in the preparation of the aromatic polyester is replaced with hydroquinone in equimolar amounts.

[0090] Comparative Example 3

[0091] The difference between this comparative example and Example 1 is that the (3,5-dimethoxyphenyl)oxy-isophthalic acid used in the preparation of the aromatic polyester is replaced with isophthalic acid in equimolar amounts.

[0092] Comparative Example 4

[0093] The difference between this comparative example and Example 1 is that the components of the polyarylate composite slurry do not include nano-lignin.

[0094] Performance Detection Test Method

[0095] Use a universal tensile machine (Zwick Z100) to detect the tensile strength of the diaphragms of each example and comparative example. The sample size is 20 mm × 80 mm, and the tensile speed is 10 mm / min. After the detection, based on the tensile strength of Comparative Example 1, calculate the ratio between the tensile strength of each example and comparative example and the tensile strength of Comparative Example 1, and record this ratio as the relative tensile strength. The results are shown in Table 2.

[0096] Table 2 Relative Tensile Strength

[0097] Sample Relative Tensile Strength / % Example 1 126.8 Example 2 127.4 Example 3 128.3 Example 4 128.7 Example 5 129.5 Example 6 134.8 Example 7 138.6 Example 8 140.2 Example 9 136.1 Comparative Example 1 100.0 Comparative Example 2 110.4 Comparative Example 3 106.8 Comparative Example 4 114.7

[0098] Combined with Examples 1-5 and Comparative Example 1 and with reference to Table 2, it can be seen that the relative tensile strengths measured in Examples 1-5 are higher than those in Comparative Example 1. This is because Comparative Example 1 lacks the aromatic polyester containing the xanthene structural unit and 3,5-dimethoxyphenyl. In this case, it is difficult to sufficiently improve the tensile strength of the separator only by nano-lignin. In Examples 1-5, 3,5-dimethoxyphenyl forms a local liquid crystal phase, and at the same time, the xanthene structural unit and nano-lignin can cooperate with the liquid crystal phase to enhance the mechanical strength of the coating by means of the π-π stacking effect between aromatic rings, thus making up for the defect of the low tensile strength of the non-woven separator and being able to fully meet the requirements of high-end products.

[0099] Combined with Example 1 and Comparative Example 2 and with reference to Table 2, it can be seen that the relative tensile strength measured in Example 1 is higher than that in Comparative Example 2. This is because the aromatic polyester in Comparative Example 2 lacks the xanthene structural unit, resulting in the inability to fully exert the π-π stacking effect between aromatic rings, and the synergistic effect between the π-π stacking effect and the liquid crystal phase is affected. Therefore, the tensile strength measured in Comparative Example 2 is relatively low.

[0100] Combined with Example 1 and Comparative Example 3 and with reference to Table 2, it can be seen that the relative tensile strength measured in Example 1 is higher than that in Comparative Example 3. This is because the aromatic polyester in Comparative Example 3 lacks 3,5-dimethoxyphenyl, and it is impossible to improve the tensile strength by forming a liquid crystal phase. At the same time, the synergistic effect between the π-π stacking effect and the liquid crystal phase is also destroyed. Therefore, the tensile strength of Comparative Example 3 is relatively low.

[0101] Combined with Example 1 and Comparative Example 4 and with reference to Table 2, it can be seen that the relative tensile strength measured in Example 1 is higher than that in Comparative Example 4. This is because Comparative Example 4 lacks nano-lignin, which affects the synergistic effect between the π-π stacking effect and the liquid crystal phase. Therefore, the tensile strength of Comparative Example 4 is relatively low.

[0102] Combined with Example 5 and Example 6 and with reference to Table 2, it can be seen that the relative tensile strength measured in Example 6 is relatively high. This is because the aromatic polyester in Example 6 has the 9,9-bis(4-carboxyphenoxyphenyl)xanthene structural unit, and the density of aromatic rings is higher. Therefore, the synergistic effect between the π-π stacking effect and the liquid crystal phase is stronger, and the tensile strength is improved.

[0103] Combining Example 6 and Example 7 and referring to Table 2, it can be seen that the relative tensile strength measured in Example 7 is higher. This is because the copolymer-modified halloysite nanotubes can form long chains through the acrylic copolymer on the surface and entangle with the aromatic polyester. Moreover, the phenyl groups in the acrylic copolymer can also improve the entanglement effect through the π-π stacking effect, so that the coating is not easily broken when subjected to tension, and the overall tensile strength of the separator is improved.

[0104] Combining Example 7 and Example 8 and referring to Table 2, it can be seen that the relative tensile strength measured in Example 8 is higher. This is because the molecule of linolenic acid has three unsaturated bonds, which can participate in the copolymerization of acrylic monomers and generate more branched-chain structures in the copolymer, thereby promoting the full contact between the acrylic copolymer segments and the aromatic polyester, strengthening the binding between molecular chains, and contributing to fully improving the overall tensile strength of the separator.

[0105] Combining Example 7 and Example 9 and referring to Table 2, it can be seen that the relative tensile strength measured in Example 7 is higher. This is because the glycidyl methacrylate in Example 7 endows the polymer with good flexibility and adhesiveness, which helps to fully improve the overall tensile strength of the separator. However, the copolymer on the surface of the copolymer-modified halloysite nanotubes in Example 9 lacks the glycidyl methacrylate structural unit, so the tensile strength of Example 9 is lower.

[0106] The above embodiments are only explanations of the present application, not limitations on the present application. Those skilled in the art can make modifications to the embodiments of the present application without creative contributions according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-temperature resistant polyarylate-coated lithium-ion battery separator, characterized in that, It includes a base film and a coating applied on the surface of the base film. The coating is obtained by coating a polyarylate composite slurry, preheating with steam, and drying with hot air. The polyarylate composite slurry comprises the following components by weight percentage: 15-20% of aromatic polyester, 5-8% of adhesive, and the balance being auxiliaries and solvents. The aromatic polyester also contains a xanthene structural unit and 3,5-dimethoxyphenyl. The auxiliaries include nano-lignin, and the weight of the nano-lignin accounts for 0.8-1.4% of the total weight of the polyarylate composite slurry. The aromatic polyester is prepared according to the following method: (1) Mix (3,5-dimethoxyphenyl)oxy-isophthalic acid, hydroquinone, and xanthene monomers, add a catalyst, and obtain a prepolymer after heating and polymerization. In this step, the xanthene monomers include at least one of xanthene diol monomers and xanthene diacid monomers. (2) Heat-treat the prepolymer to obtain the aromatic polyester.

2. The high-temperature resistant polyarylate-coated lithium-ion battery separator according to claim 1, wherein, The xanthene monomers include 9,9-bis(4-hydroxyphenyl)xanthene.

3. The high-temperature resistant polyarylate-coated lithium-ion battery separator according to claim 2, wherein The 9,9-bis(4-hydroxyphenyl)xanthene is prepared according to the following method: Mix xanthone, thionyl chloride, and DMF and heat under reflux. Distill off the excess thionyl chloride, then cool the reaction system, add a xylene solution of phenol, heat under reflux again, and then perform vacuum distillation to distill off xylene and the excess phenol to obtain a crude product. Recrystallize the crude product with toluene to obtain 9,9-bis(4-hydroxyphenyl)xanthene.

4. The high-temperature resistant polyarylate-coated lithium ion battery separator according to claim 2, wherein The xanthene monomers also include 9,9-bis(4-carboxyphenoxyphenyl)xanthene.

5. The high-temperature resistant polyarylate-coated lithium-ion battery separator according to claim 4, characterized in that The 9,9-bis(4-carboxyphenoxyphenyl)xanthene is prepared according to the following method: Mix 9,9-bis(4-cyanophenoxyphenyl)xanthene, potassium hydroxide, and an ethanol aqueous solution, heat under reflux, filter off the insoluble matter to obtain a clear solution. After the clear solution is cooled, place it in an ice bath, add hydrochloric acid for acidification to obtain a precipitate. Wash, filter, and dry the precipitate, then recrystallize with absolute ethanol, and perform vacuum drying on the product to obtain 9,9-bis(4-carboxyphenoxyphenyl)xanthene.

6. The high-temperature resistant polyarylate-coated lithium-ion battery separator according to claim 1, wherein, The auxiliaries also include copolymer-modified halloysite nanotubes. The copolymer-modified halloysite nanotubes are halloysite nanotubes grafted with an acrylic copolymer on the surface, and the acrylic copolymer has phenyl groups.

7. The high-temperature resistant polyarylate-coated lithium-ion battery separator according to claim 6, wherein The copolymer-modified halloysite nanotubes are prepared according to the following method: (1) Mix halloysite nanotubes, vinyltriethoxysilane, water, and ethanol, perform ultrasonic dispersion, then heat, and then filter and wash to obtain vinyl-modified halloysite nanotubes. (2) Add glycidyl methacrylate, 3-phenyl ethyl acrylate, vinyl-modified halloysite nanotubes, a polymerization inhibitor, and an anionic surfactant to deionized water, perform ultrasonic dispersion to obtain a raw material solution. Add an initiator to the raw material solution, heat and react, then perform suction filtration, crush the filter residue, perform Soxhlet extraction and vacuum drying to obtain copolymer-modified halloysite nanotubes.

8. The high-temperature resistant polyarylate-coated lithium-ion battery separator according to claim 7, wherein, In step (2) of preparing the copolymer-modified halloysite nanotubes, the raw materials for preparing the raw material solution also include linolenic acid.

9. The preparation process of the high-temperature resistant polyarylate-coated lithium-ion battery separator according to any one of claims 1-8, characterized in that, It includes the following steps: (1) Mix an aromatic polyester, an adhesive, an additive and a solvent, and obtain a polyarylate composite slurry after stirring for standby; perform corona pretreatment on the lithium-ion battery base film for standby; (2) Coat the polyarylate composite slurry on the surface of the lithium-ion battery base film to obtain a coating layer; (3) Preheat the coating layer and then perform hot air drying to obtain a high-temperature resistant polyarylate-coated lithium-ion battery separator.

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