High-heat-resistance and high-adhesion lithium battery diaphragm as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a high-heat-resistance and high-adhesion lithium battery diaphragm as well as a preparation method and application thereof. The high-heat-resistance and high-adhesion lithium battery diaphragm comprises a base membrane and a coating arranged on at least one surface of the base membrane, and the coating is prepared from polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, a silane coupling agent, acrylate light-cured resin, a photoinitiator and an organic solvent. According to the technical scheme, the problem that the lithium battery diaphragm in the prior art cannot have high heat resistance and high interface adhesion at the same time is solved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high heat-resistant and high-adhesion lithium battery separator, its preparation method, and its application. Background Technology

[0002] As a core functional component of lithium-ion batteries, the separator plays a crucial role in separating the positive and negative electrodes and allowing lithium ions to pass through. Its heat resistance, interfacial adhesion, and ion transport performance directly determine the safety level, cycle life, and rate discharge capability of the lithium-ion battery. Currently, commercially available lithium-ion battery separators are mainly based on polyolefins such as polypropylene (PP) and polyethylene (PE). Although these separators possess basic mechanical strength and air permeability, their critical heat resistance temperature is only 80~105℃. Under conditions such as fast charging, overcharging of power batteries, or high-temperature operation of energy storage batteries, they are prone to thermal shrinkage or even melting and rupture, causing short circuits between the positive and negative electrodes, leading to safety accidents such as battery fires and explosions. This fails to meet the safety requirements of high-power lithium-ion batteries.

[0003] To improve the heat resistance of the separator, an inorganic particulate coating is usually applied to the surface of the polyolefin substrate. However, this method has the following problems: First, the coating and the substrate are only physically adsorbed, resulting in insufficient interfacial bonding and a peel strength of <1N / cm. During battery cycling, the coating is very easy to fall off, leading to a rapid decline in separator performance. Second, the coating curing relies on traditional thermosetting processes, which require treatment at 100~120℃ for 10~30 minutes. This not only results in high energy consumption and low production efficiency but also easily causes thermal deformation of the polyolefin substrate, leading to a decrease in separator dimensional stability and a yield rate below 85%.

[0004] Photopolymerization technology, with its advantages of fast curing speed, low-temperature operation, and low energy consumption, has become an optimization direction for overcoming the shortcomings of traditional thermosetting processes and is gradually being applied to the curing of lithium battery separator coatings. However, existing photopolymerization systems have poor compatibility with lithium battery separator coatings: the interfacial bonding between inorganic particles and photocurable resin is weak, making it impossible for the resulting lithium battery separator to simultaneously achieve both heat resistance and adhesion. Therefore, there is an urgent need to develop a lithium battery separator that can simultaneously improve heat resistance, interfacial adhesion, and high heat resistance and adhesion. Summary of the Invention

[0005] This invention proposes a high heat resistance and high adhesion lithium battery separator, its preparation method and application, which solves the problem that lithium battery separators in related technologies cannot simultaneously possess high heat resistance and high interfacial adhesion.

[0006] The technical solution of the present invention is as follows: This invention proposes a high heat-resistant and high-adhesion lithium battery separator, comprising a base film and a coating disposed on at least one surface of the base film. The raw materials for the coating include polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, silane coupling agent, acrylate photocurable resin, photoinitiator and organic solvent.

[0007] As a further technical solution, the weight-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 800,000 to 1,000,000.

[0008] As a further technical solution, the inorganic particles include one or more of alumina, silicon dioxide, hydrotalcite, boehmite, and spinel.

[0009] As a further technical solution, the inorganic particles comprise aluminum oxide and silicon dioxide in a mass ratio of 1:5 to 5:1.

[0010] As a further technical solution, the acrylic photocurable resin includes polyurethane acrylate.

[0011] As a further technical solution, the organic solvent includes one or both of ethyl acetate and butyl acetate.

[0012] As a further technical solution, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, silane coupling agent, acrylate photocurable resin, photoinitiator and organic solvent is 35~60:10~50:5~15:1~3:0.5~2:15~69.

[0013] This invention also proposes a method for preparing a high heat-resistant and high-adhesion lithium battery separator, comprising the following steps: S1. Inorganic particles are modified using silane coupling agents to obtain modified inorganic particles; The polyvinylidene fluoride-hexafluoropropylene copolymer was dissolved in an organic solvent to obtain a resin solution; An acrylic photocurable resin is mixed with a photoinitiator to obtain a photocurable system; S2. Add the modified inorganic particles to the resin solution, add the photocuring system, disperse evenly, and obtain a coating liquid with a solid content of 30%~60% and a viscosity of 500~2000Pa. S3. Coat the base film surface with the coating liquid, dry and cure with ultraviolet light to obtain a high heat resistance and high adhesion lithium battery separator.

[0014] As a further technical solution, in step S3, the wavelength of the ultraviolet light curing is 365~405nm, the light intensity is 500~800mW / cm², and the curing time is 30~120s.

[0015] This invention also proposes the application of the high heat resistance and high adhesion lithium battery separator described above for use in lithium batteries.

[0016] The working principle and beneficial effects of this invention are as follows: In this invention, the diaphragm coating uses polyvinylidene fluoride-hexafluoropropylene copolymer as the matrix, combined with inorganic particles and photocurable resin. The introduction of inorganic particles not only improves the heat resistance of the diaphragm, but the hydroxyl groups on their surface can also form hydrogen bonds with the polyvinylidene fluoride-hexafluoropropylene copolymer, enhancing the interfacial bonding between the coating and the substrate and within the coating itself, thus improving interfacial adhesion. The addition of acrylic photocurable resin enables rapid curing and further strengthens the structural stability of the coating, shortening the preparation cycle. The use of silane coupling agent to modify the surface of the inorganic particles improves the interfacial bonding between the inorganic particles and the photocurable resin, thereby making the prepared diaphragm not only highly heat-resistant but also highly adhesive. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a SEM image of Embodiment 1 of the present invention. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be understood that, unless the context clearly indicates otherwise, the terms "comprising," "including," or "having" as used herein refer to the presence of a particular element, but do not exclude the presence or addition of one or more other elements. Furthermore, as used herein, "comprising" and / or "including" specify the presence of shapes, numbers, steps, operations, members, elements, and / or combinations thereof, and do not exclude the presence or addition of one or more other shapes, numbers, operations, elements, and / or combinations thereof.

[0021] In this invention, the numerical range indicated by "~" refers to the range of values ​​specified as the lower and upper limits, respectively, before or after the term. When multiple values ​​for the upper or lower limit of any numerical range are mentioned, the range disclosed herein can be understood as a range with any one of the mentioned upper limits as its upper limit and any one of the mentioned lower limits as its lower limit.

[0022] The following will describe in detail a high heat-resistant and high-adhesion lithium battery separator according to embodiments of the present invention, its preparation method, and its application.

[0023] According to one aspect of the present invention, a high heat-resistant and high-adhesion lithium battery separator is provided, comprising a base film and a coating disposed on at least one surface of the base film. The raw materials for the coating include polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, silane coupling agent, acrylate photocurable resin, photoinitiator and organic solvent.

[0024] In this invention, the base film is made of one or more of the following materials: polyethylene, polypropylene, polyimide, polyvinylidene fluoride-hexafluoroethylene propylene copolymer, polyethylene terephthalate, nonwoven fabric, glass fiber, and cellulose.

[0025] Using polyvinylidene fluoride (PVDF)-hexafluoropropylene (HCF) copolymer as the matrix, its solubility and film-forming properties are optimized by controlling the weight-average molecular weight of PVDF-HCF copolymer to 800,000 to 1,000,000. Combined with phase separation technology, a three-dimensional network structure is constructed, providing abundant microporous channels for lithium-ion transport and electrolyte wetting, while simultaneously dispersing stress and improving the mechanical strength of the membrane. When the weight-average molecular weight of PVDF-HCF copolymer is <800,000 (e.g., 500,000), the molecular chain entanglement density is insufficient, making it impossible to form a stable three-dimensional network framework with the photocurable resin, resulting in a loose coating structure and insufficient mechanical support. When the weight-average molecular weight of PVDF-HCF copolymer is >1,000,000 (e.g., 1,200,000), the viscosity of the coating solution increases, making film thickness control difficult during coating, resulting in insufficient coating density and increased ion transport resistance.

[0026] The introduction of inorganic particles and silane coupling agents significantly improves the heat resistance of the diaphragm due to the melting point of the inorganic particles exceeding 1600℃. The hydroxyl groups on the surface of the inorganic particles allow them to form hydrogen bonds with the polyvinylidene fluoride-hexafluoroethylene copolymer, enhancing the interfacial adhesion between the coating and the substrate, as well as within the coating itself. Modification of the inorganic particles with silane coupling agents further improves the bonding between the inorganic particles and the photocurable resin, thereby enhancing the diaphragm's adhesion.

[0027] Inorganic particles include one or more of alumina, silica, hydrotalcite, boehmite, and spinel.

[0028] Preferably, the inorganic particles comprise alumina and silicon dioxide in a mass ratio of 1:5 to 5:1.

[0029] By using organic solvents to form an oil-based system, oil-based coating is employed during application, avoiding the erosion of the substrate caused by water-based coatings, improving coating uniformity, and allowing for controllable solvent evaporation, which is beneficial for the formation of the three-dimensional network structure of the polyvinylidene fluoride-hexafluoropropylene copolymer. Preferably, the organic solvent includes one or both of ethyl acetate and butyl acetate.

[0030] Adding an acrylic photocurable resin allows for rapid curing and molding, further enhancing the stability of the coating structure and shortening the preparation cycle. Preferably, the acrylic photocurable resin is a polyurethane acrylate.

[0031] As an example, a method for preparing polyurethane acrylate includes the following steps: (1) Raw material pretreatment The raw materials and composition are: isophorone diisocyanate (IPDI), polyester polyol, hydroxyethyl acrylate (HEA), organic bismuth catalyst, polymerization inhibitor 4-methoxyphenol, and diluent monomer trimethylolpropane triacrylate (TMPTA), with a mass ratio of 30~50:40~60:8~15:0.05~0.2:0.1~0.3:10~20.

[0032] The polyester polyol (hydroxyl value 56 mg KOH / g) was placed in a vacuum drying oven at 100~120℃ for 2~3 hours to dehydrate, and the water content was controlled to be ≤0.05%. It was then cooled to room temperature for later use. The isophorone diisocyanate (IPDI) was brought to room temperature in advance to avoid high viscosity at low temperature, which would affect the uniformity of the drop addition. All raw materials must be free of mechanical impurities to prevent affecting the purity of the resin.

[0033] (2) Reaction stage In a four-necked reactor equipped with a nitrogen protection device, stirrer, thermometer, and dropping funnel, pretreated polyol was added. Stirring was started, and the temperature was raised to 60–80°C. Nitrogen gas was introduced to replace the air in the reactor (to prevent oxygen interference with the reaction). Isophorone diisocyanate (IPDI) was added dropwise at a constant rate of 1–2 mL / min through the dropping funnel, maintaining the system temperature stable at 70–85°C to ensure a gentle reaction. After the addition was complete, an organobismuth catalyst was added, and the temperature was raised to 80–90°C with constant stirring for 2–4 hours. During this period, the content of -NCO groups in the reactor was measured every 30 minutes using di-n-butylamine titration until it reached the theoretical design value of 1.8%–2.5%. Heating was then stopped, yielding a polyurethane prepolymer with -NCO end groups.

[0034] The prepolymer in the reactor is cooled to 50-60°C. Hydroxyethyl acrylate (HEA) is then slowly added dropwise through a dropping funnel, controlling the n(-OH) / n(remaining -NCO) molar ratio to be 1.05-1.1 (excess hydroxyl groups ensure complete reaction of -NCO). Continuous stirring is maintained during the addition process, keeping the system temperature below 65°C to prevent self-polymerization of the acrylate monomers. After the addition is complete, the temperature is raised to 70-80°C and the reaction is held at this temperature for 3-5 hours. Real-time monitoring at 2270 cm⁻¹ is performed using an infrared spectrometer. -1 The characteristic absorption peak of the -NCO group is observed until the absorption peak completely disappears, confirming that the end-capping reaction is complete. At this point, the carbon-carbon double bond of the acrylate monomer has been successfully grafted to the end of the polyurethane backbone, and the resin has photocuring activity.

[0035] (3) Post-processing Add the polymerization inhibitor 4-methoxyphenol to the reaction system and stir quickly to inhibit the self-polymerization of carbon-carbon double bonds in subsequent processes; lower the temperature inside the reactor to below 40°C to reduce the viscosity of the resin.

[0036] Slowly add the diluted monomer trimethylolpropane triacrylate (TMPTA) while stirring, and monitor the resin viscosity in real time using a rotational viscometer until the viscosity at 25°C is adjusted to 1000~5000 mPa·s. This viscosity range is suitable for subsequent coating, potting and other applications.

[0037] The resin with adjusted viscosity is filtered under reduced pressure through a 200-mesh filter to remove any trace gel particles and incompletely dispersed impurities that may be present in the system, ensuring that the resin has a uniform texture.

[0038] The filtered resin was placed in a dry, sealed brown reagent bottle and stored in a cool, ventilated place to avoid strong light exposure which could cause premature curing. The final product was a pale yellow, transparent polyurethane acrylate type free of mechanical impurities and with rapid light curing activity.

[0039] In one embodiment of the present invention, the mass ratio of polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, silane coupling agent, acrylate photocurable resin, photoinitiator and organic solvent is 35~60:10~50:5~15:1~3:0.5~2:15~69.

[0040] According to another aspect of the present invention, the present invention also provides a method for preparing the above-mentioned high heat resistance and high adhesion lithium battery separator, comprising the following steps: S1. Inorganic particles are modified using silane coupling agents to obtain modified inorganic particles; The polyvinylidene fluoride-hexafluoropropylene copolymer was dissolved in an organic solvent to obtain a resin solution; An acrylic photocurable resin is mixed with a photoinitiator to obtain a photocurable system; S2. Add the modified inorganic particles to the resin solution, add the photocuring system, disperse evenly, and obtain a coating liquid with a solid content of 30%~60% and a viscosity of 500~2000Pa. S3. Coat the base film surface with the coating liquid, dry and cure with ultraviolet light to obtain a high heat resistance and high adhesion lithium battery separator.

[0041] In this invention, ultraviolet light curing is used, which significantly shortens the curing time compared with traditional thermal curing, reducing the curing time from 10~30min to 30~120s, reducing energy consumption, and low-temperature curing avoids thermal deformation of the base film, further improving the yield and performance stability of the diaphragm.

[0042] As an example, a method for preparing a high-heat-resistant and high-adhesion lithium battery separator includes the following steps: S1. Mix 0.5-2 parts of silane coupling agent with 5-15 parts of anhydrous ethanol, then add 10-25 parts of inorganic particles, stir at 40-60℃ and 600-1000r / min for 40-80min, filter, and place in a vacuum drying oven at 60-80℃ for 5-10h to obtain the modified inorganic particles. 35-60 parts of polyvinylidene fluoride-hexafluoropropylene copolymer were placed in a vacuum drying oven at 50-70℃ and dried for 10-15 hours to remove the adsorbed moisture and residual small molecule impurities of the polyvinylidene fluoride-hexafluoropropylene copolymer. After cooling to room temperature, the copolymer was pulverized to a particle size ≤1mm and added to 15-69 parts of ethyl acetate. The copolymer was stirred at 25-30℃ and 800-1200r / min for 90-150min until completely dissolved to obtain a homogeneous, flocculent resin solution. The viscosity of the solution was tested and controlled at 300-800mPa·s. Mix 5-15 parts of acrylic photocurable resin with 1-3 parts of photoinitiator, and stir at room temperature for 20-40 minutes until completely dissolved to obtain a photocurable system. S2. Add the modified inorganic particles to the resin solution and stir at 300-600 r / min for 20-40 min to initially disperse the inorganic particles. Add the photocuring system and stir at 1200-1800 r / min for 30-60 min. Then, ultrasonically disperse the particles at 600-800 W and 20 kHz for 30-60 min, or shear disperse them at 10000-12000 r / min for 30-60 min to further disperse the inorganic particles. The particles are uniformly dispersed with a particle size distribution D90≤8μm to obtain a slurry. The slurry temperature is adjusted to 25℃, and it is allowed to stand for 30 minutes to degas and release the air bubbles trapped in the slurry. The slurry is then pressure filtered using a 200~300 mesh nylon filter at 0.2MPa to remove undispersed large particles and agglomerates, resulting in a uniform and stable coating liquid. The coating liquid is tested to have a solid content of 30%~60%, a viscosity of 500~2000mPa·s, and a pH value of 6~7. S3. Apply the coating solution to the base film surface using microgravure coating or comma coating, controlling the coating thickness to be 4~20μm; adjust the coating environment temperature to 60~80℃, allowing the solvent to evaporate at a controllable rate for 5~10min, and use phase separation technology to promote the self-assembly of PVDF~HFP molecules to form a three-dimensional network structure; place the coated base film in a drying oven at 60~70℃ for pre-drying for 5~10min to remove most of the residual solvent in the coating; then send it to an ultraviolet curing device, using ultraviolet light with a wavelength of 365~405nm and a light intensity of 500~800mW / cm² for 30~120s to rapidly cross-link and cure the photocurable resin, enhancing the structural stability and interfacial adhesion of the composite coating, and obtaining a high heat-resistant and high-adhesion lithium battery separator.

[0043] Solution viscosity was measured using a digital rotational viscometer. During testing, the solution was preheated to 25°C in a constant-temperature water bath. A suitable rotor (e.g., No. 2 or No. 3) and rotation speed (30 rpm or 60 rpm) were selected based on the solution viscosity, ensuring the pointer reading was between 20% and 80% of the range. The rotor was vertically immersed in the solution until the mark on the rotor was flush with the liquid surface. The instrument was started, and the value was read after the pointer stabilized. Each sample was tested three times, and the average value was taken as the final result.

[0044] As a further technical solution, in step S3, the wavelength of ultraviolet light curing is 365~405nm, the light intensity is 500~800mW / cm², and the curing time is 30~120s.

[0045] This invention also proposes the application of the above-mentioned high heat resistance and high adhesion lithium battery separator for use in lithium batteries.

[0046] In the following embodiments and comparative examples, The base film is a polyethylene film with a thickness of 7μm; The silane coupling agent is KH550; In the polyvinylidene fluoride-hexafluoropropylene copolymer, the molar ratio of repeating structural units vinylidene fluoride to hexafluoropropylene is 2:1; Alumina with a particle size D50 of 0.318~0.524μm; Silica with a particle size D50 of 0.331~0.562μm; The UV-curable resin is polyurethane acrylate; The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0047] Example 1 A method for preparing a high-heat-resistant and high-adhesion lithium battery separator includes the following steps: S1. Mix 0.5 parts of silane coupling agent with 5 parts of anhydrous ethanol, then add 10 parts of silica, stir at 50℃ and 800r / min for 60min, filter, and place in a vacuum drying oven at 80℃ for 8h to obtain modified silica. 35 parts of polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight of 800,000) were placed in a vacuum drying oven at 60℃ and dried for 12 hours. After cooling to room temperature, the copolymer was pulverized to a particle size of ≤1 mm and added to 15 parts of ethyl acetate. The copolymer was stirred at 25℃ and 800 r / min for 120 min until completely dissolved, resulting in a homogeneous, flocculent resin solution. The viscosity of the resin solution was measured to be 415 mPa·s. Mix 5 parts of acrylic photocurable resin with 1 part of photoinitiator and stir at room temperature for 30 minutes until completely dissolved to obtain a photocurable system. S2. The modified silica was added to the resin solution and stirred at 500 r / min for 30 min. The photocuring system was then added and stirred at 1500 r / min for 45 min. The mixture was then ultrasonically dispersed at 600 W and 20 kHz for 30 min to obtain a slurry. The slurry temperature was adjusted to 25℃ and allowed to stand for 30 min to remove bubbles. The slurry was then pressure filtered using a 200-mesh nylon filter at 0.2 MPa to obtain a uniform and stable coating liquid. The coating liquid was tested and found to have a solid content of 40.25% and a viscosity of 1214 mPa·s. S3. The coating solution is applied to the base film surface using a micro-grooving coating method, with a coating thickness of 6 μm. The coating environment temperature is adjusted to 70℃, allowing the solvent to slowly evaporate for 8 minutes. The coated base film is then pre-dried in a drying oven at 60℃ for 5 minutes. Subsequently, it is placed in an ultraviolet curing device and irradiated with ultraviolet light at a wavelength of 365nm and a light intensity of 600mW / cm² for 45 seconds to obtain a high-heat-resistant and high-adhesion lithium battery separator. Its SEM is shown below. Figure 1 As shown.

[0048] Example 2 A method for preparing a high-heat-resistant and high-adhesion lithium battery separator includes the following steps: S1. Mix 2 parts of silane coupling agent with 15 parts of anhydrous ethanol, then add 25 parts of alumina, stir at 50℃ and 800r / min for 60min, filter, and place in a vacuum drying oven at 80℃ for 8h to obtain modified alumina. Sixty parts of polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight of 1 million) were placed in a vacuum drying oven at 60°C and dried for 12 hours. After cooling to room temperature, the copolymer was pulverized to a particle size of ≤1 mm and added to 69 parts of ethyl acetate. The copolymer was stirred at 30°C and 1200 r / min for 120 min until completely dissolved, resulting in a homogeneous, flocculent resin solution. The viscosity of the resin solution was measured to be 318 mPa·s. Mix 15 parts of acrylic photocurable resin with 3 parts of photoinitiator and stir at room temperature for 30 minutes until completely dissolved to obtain a photocurable system. S2. The modified alumina was added to the resin solution and stirred at 500 r / min for 30 min. The photocuring system was then added and stirred at 1500 r / min for 45 min. The mixture was then ultrasonically dispersed at 800 W and 20 kHz for 60 min to obtain a slurry. The slurry temperature was adjusted to 25℃ and allowed to stand for 30 min to remove bubbles. The slurry was then pressure filtered using a 300-mesh nylon filter at 0.2 MPa to obtain a uniform and stable coating liquid. The solid content of the coating liquid was found to be 51.03%, and the viscosity was 1529 mPa·s. S3. Apply the coating solution to the base film surface using a comma coating method, controlling the coating thickness to 8μm; adjust the coating environment temperature to 65℃, allowing the solvent to slowly evaporate for 6 minutes; place the coated base film in a drying oven at 60℃ for pre-drying for 10 minutes; then send it to an ultraviolet curing device and irradiate it with ultraviolet light of 395nm wavelength and 700mW / cm² intensity for 60 seconds to obtain a high heat-resistant and high-adhesion lithium battery separator.

[0049] Example 3 A method for preparing a high-heat-resistant and high-adhesion lithium battery separator includes the following steps: S1. Mix 1 part of silane coupling agent with 10 parts of anhydrous ethanol, then add 15 parts of silica and 15 parts of alumina. Stir at 50°C and 800 r / min for 60 min, filter, and place in a vacuum drying oven at 80°C for 8 h to obtain modified inorganic particles. 50 parts of polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight of 900,000) were placed in a vacuum drying oven at 60℃ and dried for 12 hours. After cooling to room temperature, the copolymer was pulverized to a particle size of ≤1 mm and added to a mixture of 25 parts ethyl acetate and 25 parts butyl acetate. The mixture was stirred at 25℃ and 1000 r / min for 120 min until completely dissolved, resulting in a homogeneous, flocculent resin solution. The viscosity of the resin solution was measured to be 715 mPa·s. Mix 10 parts of acrylic photocurable resin with 2 parts of photoinitiator and stir at room temperature for 30 minutes until completely dissolved to obtain a photocurable system. S2. The modified silica was added to the resin solution and stirred at 500 r / min for 30 min. The photocuring system was then added and stirred at 1500 r / min for 45 min. The mixture was then ultrasonically dispersed at 700 W and 20 kHz for 45 min to obtain a slurry. The slurry temperature was adjusted to 25℃ and allowed to stand for 30 min to remove bubbles. The slurry was then pressure filtered using a 200-mesh nylon filter at 0.2 MPa to obtain a uniform and stable coating liquid. The coating liquid was tested and found to have a solid content of 45.08% and a viscosity of 1331 mPa·s. S3. The coating liquid is coated onto the surface of the base film using a micro-grooving coating method, and the coating thickness is controlled to be 10μm. The coating environment temperature is adjusted to 75℃, and the solvent is allowed to evaporate slowly for 7min. The coated base film is first placed in a drying oven at 70℃ for 6min to pre-dry. Then it is sent to an ultraviolet curing device and irradiated with ultraviolet light with a wavelength of 405nm and a light intensity of 550mW / cm² for 90s to obtain a high heat resistance and high adhesion lithium battery separator.

[0050] Comparative Example 1 The only difference between this embodiment and Embodiment 2 is that the weight-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 500,000.

[0051] Comparative Example 2 A method for preparing a high-heat-resistant and high-adhesion lithium battery separator includes the following steps: S1. Mix 0.5 parts of silane coupling agent with 5 parts of anhydrous ethanol, then add 10 parts of silica, stir at 50℃ and 800r / min for 60min, filter, and place in a vacuum drying oven at 80℃ for 8h to obtain modified silica. 35 parts of polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight of 800,000) were placed in a vacuum drying oven at 60℃ and dried for 12 hours. After cooling to room temperature, the copolymer was pulverized to a particle size of ≤1 mm and added to 15 parts of deionized water. 5 parts of maleic anhydride copolyammonium salt were added and stirred at 25℃ and 800 r / min for 120 min until completely dissolved to obtain a homogeneous, flocculent resin solution. The viscosity of the resin solution was measured to be 550 mPa·s. Mix 5 parts of acrylic photocurable resin with 1 part of photoinitiator and stir at room temperature for 30 minutes until completely dissolved to obtain a photocurable system. S2. The modified silica was added to the resin solution and stirred at 500 r / min for 30 min. The photocuring system was then added and stirred at 1500 r / min for 45 min. The mixture was then ultrasonically dispersed at 600 W and 20 kHz for 30 min to obtain a slurry. The slurry temperature was adjusted to 25℃ and allowed to stand for 30 min to remove bubbles. The slurry was then pressure filtered using a 200-mesh nylon filter at 0.2 MPa to obtain a uniform and stable coating liquid. The coating liquid was tested and found to have a solid content of 40.66% and a viscosity of 1026 mPa·s. S3. The coating liquid is coated onto the surface of the base film using a micro-grooving coating method, with a coating thickness of 6μm. The coating environment temperature is adjusted to 70℃, and the solvent is allowed to evaporate slowly for 8 minutes. The coated base film is first placed in a drying oven at 60℃ for pre-drying for 5 minutes. Then it is sent to an ultraviolet curing device and irradiated with ultraviolet light with a wavelength of 365nm and a light intensity of 600mW / cm² for 45 seconds to obtain a high heat resistance and high adhesion lithium battery separator.

[0052] Comparative Example 3 A method for preparing a high-heat-resistant and high-adhesion lithium battery separator includes the following steps: S1. Place 35 parts of polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight of 800,000) in a vacuum drying oven at 60℃ for 12h, cool to room temperature and then pulverize to a particle size ≤1mm. Add to 15 parts of ethyl acetate and stir at 25℃ and 800r / min for 120min until completely dissolved to obtain a homogeneous, flocculent resin solution. The viscosity of the resin solution was measured to be 400mPa·s. Mix 5 parts of acrylic photocurable resin with 1 part of photoinitiator and stir at room temperature for 30 minutes until completely dissolved to obtain a photocurable system. S2. Add the photocuring system to the resin solution, stir at 1500 r / min for 45 min, then ultrasonically disperse at 600 W and 20 kHz for 30 min to obtain a slurry; adjust the slurry temperature to 25℃, let it stand to degas for 30 min, and then filter the slurry under pressure at 0.2 MPa using a 200-mesh nylon filter to obtain a uniform and stable coating liquid; the solid content of the coating liquid is 40% and the viscosity is 800 mPa·s. S3. The coating liquid is coated onto the surface of the base film using a micro-grooving coating method, with a coating thickness of 6μm. The coating environment temperature is adjusted to 70℃, and the solvent is allowed to evaporate slowly for 8 minutes. The coated base film is first placed in a drying oven at 60℃ for pre-drying for 5 minutes. Then it is sent to an ultraviolet curing device and irradiated with ultraviolet light with a wavelength of 365nm and a light intensity of 600mW / cm² for 45 seconds to obtain a high heat resistance and high adhesion lithium battery separator.

[0053] Comparative Example 4 The only difference between this comparative example and Example 1 is that step S3 is as follows: the coating liquid is coated onto the surface of the base film by micro-grooving, with a coating thickness of 6 μm; the coating environment temperature is adjusted to 70°C, and the solvent is allowed to evaporate slowly for 8 min; the coated base film is first placed in a drying oven at 60°C for 5 min to pre-dry; and then heat-cured at 120°C for 20 min to obtain a high heat-resistant and high-adhesion lithium battery separator.

[0054] Comparative Example 5 The only difference between this comparative example and Example 1 is that step S3 is as follows: the coating liquid is coated onto the surface of the base film by micro-grooving, with a coating thickness of 6 μm; the coating environment temperature is adjusted to 70°C, and the solvent is allowed to evaporate slowly for 8 min; the coated base film is first placed in a drying oven at 60°C for 5 min to pre-dry; then it is sent to an ultraviolet curing device and irradiated with ultraviolet light of 350 nm wavelength and 400 mW / cm² intensity for 200 s to obtain a high heat resistance and high adhesion lithium battery separator.

[0055] Comparative Example 6 The only difference between this comparative example and Example 1 is that the polyvinylidene fluoride-hexafluoropropylene copolymer is replaced with polyvinylidene fluoride (weight average molecular weight of 800,000).

[0056] Comparative Example 7 The only difference between this comparative example and Example 1 is that the weight-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 600,000.

[0057] Comparative Example 8 The only difference between this comparative example and Example 1 is that the weight-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 1.2 million, the ultrasonic dispersion time in step S2 is 40 min, the solid content of the coating liquid is 40%, and the viscosity is 3200 mPa·s.

[0058] Comparative Example 9 The only difference between this comparative example and Example 1 is that the acrylate photocurable resin is replaced with an equal amount of 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0059] Comparative Example 10 The only difference between this comparative example and Example 1 is that the polyvinylidene fluoride-hexafluoropropylene copolymer is replaced with polyvinylidene fluoride-trifluorochloroethylene copolymer (weight-average molecular weight of 800,000, and the molar ratio of repeating structural units vinylidene fluoride and trifluorochloroethylene is 2:1). The heat resistance and adhesion of the diaphragms of Examples 1-3 and Comparative Examples 1-10 were tested using the following methods: (1) Heat resistance: The transverse (TD) and longitudinal (MD) heat shrinkage rates were determined according to the test methods in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries". The size of the lithium battery separator sample was 100mm×100mm, and the test results of the transverse and longitudinal heat shrinkage rates were the average values ​​of 20 samples. (2) Adhesion (hot-pressed electrode adhesion): When testing the adhesion strength of the hot-pressed positive electrode, the diaphragm size is 25mm×150mm, and the positive electrode (ternary lithium nickel cobalt aluminum oxide, chemical formula LiNi) is used. 0.8 Co 0.15 Al 0.05 The O2 size is 25mm×150mm; the temperature of the hot press is adjusted to 80℃ and the pressure to 1000kg. The diaphragm and positive electrode are preheated for 1s and hot-pressed for 1s using the hot press; the bonding strength of the hot-pressed positive electrode is tested using an electronic tensile testing machine. The diaphragm and positive electrode are peeled until the tensile distance of the electronic tensile testing machine is 50mm. The speed of the electronic tensile testing machine is 300mm / min and the peeling degree is 180°. The bonding strength of the hot-pressed positive electrode is calculated based on the data between 10 and 40mm, that is, the ... When testing the bonding strength of the hot-pressed negative electrode sheet, the diaphragm was cut to a size of 25mm×150mm and the negative electrode sheet (carbon-based graphite electrode sheet with a carbon content of 91%) was cut to a size of 25mm×150mm. The bonding strength of the negative electrode sheet was then tested according to the bonding strength test procedure for the positive electrode sheet described above. The test results were the average values ​​of 20 samples. The test results are shown in Table 1 below: Table 1 Results of heat resistance and adhesion tests

[0060] The coating thickness, peel strength, and ionic conductivity of the diaphragms of Examples 1-3 and Comparative Examples 1-10 were tested using the following methods: (1) Coating thickness: The thickness of the battery separator was tested according to GB / T36363-2018 "Polyolefin separator for lithium-ion batteries". The coating thickness was calculated according to the formula: coating thickness = battery separator thickness - base film thickness. (2) Peel strength: The diaphragm was cut into test samples of 3cm*15cm. 3M release tape (2.6cm*15cm) was applied to the center of the diaphragm's coated surface. A 2kg roller was used to press the test sample (pressing forward 4 times to ensure the entire sample was pressed in place, always in the same direction, without back-and-forth pressing). One end of the 3M release tape was torn off by 5cm. The 3M release tape and diaphragm were then clamped flat between the upper and lower fixtures of an intelligent electronic tensile testing machine (maximum load: 100N, test speed: 100mm / min) to test the peel strength. The formula for calculating peel strength is: average force (N) / width of release tape (cm) * 100%. All test results are the average of 20 samples. (3) Ionic conductivity: Ionic conductivity was tested in accordance with GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries", where the temperature was 40℃ and the relative humidity was 50%. The test results are shown in Table 2 below: Table 2. Test results of coating thickness, peel strength and ionic conductivity

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high heat-resistant and high-adhesion lithium battery separator, characterized in that, Includes a base film and a coating disposed on at least one surface of the base film. The raw materials for the coating include polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, silane coupling agent, acrylate photocurable resin, photoinitiator and organic solvent.

2. The high heat resistance and high adhesion lithium battery separator according to claim 1, characterized in that, The weight-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 800,000 to 1,000,000.

3. The high heat resistance and high adhesion lithium battery separator according to claim 1, characterized in that, The inorganic particles include one or more of alumina, silicon dioxide, hydrotalcite, boehmite, and spinel.

4. The high heat resistance and high adhesion lithium battery separator according to claim 3, characterized in that, The inorganic particles comprise aluminum oxide and silicon dioxide in a mass ratio of 1:5 to 5:

1.

5. The high heat resistance and high adhesion lithium battery separator according to claim 1, characterized in that, The acrylic photocurable resin includes polyurethane acrylate.

6. The high heat resistance and high adhesion lithium battery separator according to claim 1, characterized in that, The organic solvent includes one or both of ethyl acetate and butyl acetate.

7. A high heat-resistant and high-adhesion lithium battery separator according to any one of claims 1 to 6, characterized in that, The mass ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic particles, silane coupling agent, acrylate photocurable resin, photoinitiator and organic solvent is 35~60:10~50:5~15:1~3:0.5~2:15~69.

8. A method for preparing a high heat-resistant and high-adhesion lithium battery separator according to claims 1-7, characterized in that, Includes the following steps: S1. Inorganic particles are modified using silane coupling agents to obtain modified inorganic particles; The polyvinylidene fluoride-hexafluoropropylene copolymer was dissolved in an organic solvent to obtain a resin solution; An acrylic photocurable resin is mixed with a photoinitiator to obtain a photocurable system; S2. Add the modified inorganic particles to the resin solution, add the photocuring system, disperse evenly, and obtain a coating liquid with a solid content of 30%~60% and a viscosity of 500~2000Pa. S3. Coat the base film surface with the coating liquid, dry and cure with ultraviolet light to obtain a high heat resistance and high adhesion lithium battery separator.

9. The method for preparing a high heat-resistant and high-adhesion lithium battery separator according to claim 8, characterized in that, In step S3, the wavelength of the ultraviolet light curing is 365~405nm, the light intensity is 500~800mW / cm², and the curing time is 30~120s.

10. The application of a high heat-resistant and high-adhesion lithium battery separator according to any one of claims 1 to 7, or a high heat-resistant and high-adhesion lithium battery separator prepared by the preparation method according to any one of claims 8 to 9, characterized in that, Used in lithium batteries.

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