Lithium battery diaphragm based on pressure-sensitive adhesive composite slurry and preparation method thereof

Abstract

The invention relates to the technical field of lithium battery diaphragms, and provides a lithium battery diaphragm based on pressure-sensitive adhesive composite slurry and a preparation method thereof.The lithium battery diaphragm based on the pressure-sensitive adhesive composite slurry comprises a base film and a coating arranged on one side or two sides of the base film, and the coating is prepared from slurry; the slurry comprises the following raw materials in parts by weight: 30-50 parts of PVDF or a copolymer thereof, 0.5-1 part of a dispersant, 10-20 parts of a styrene-isoprene-styrene block copolymer, 4-5 parts of an inorganic filler and 40-45 parts of a solvent; the raw materials further comprise a chain extender, the chain extender is a compound containing isocyanate, and the adding amount of the chain extender is 20-300 ppm of the mass of the PVDF or the copolymer of the PVDF. According to the technical scheme, the problems of poor electrochemical performance of the lithium battery diaphragm and poor cohesiveness of the lithium battery diaphragm coating in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and in particular to a lithium battery separator based on a pressure-sensitive adhesive composite slurry and a preparation method thereof. Background Art

[0002] The increasing use of lithium-ion batteries in electric vehicles and energy storage has led to higher requirements for the performance of battery separators. Polyvinylidene fluoride (PVDF) has become the mainstream material for separator coating due to its excellent electrochemical stability, chemical corrosion resistance and thermal stability. Traditional PVDF coating technology has obvious defects: (1) PVDF itself has insufficient adhesion and requires the addition of thickeners to improve performance, which increases the complexity of the process; (2) The oil-based coating process uses organic solvents such as acetone, which poses a risk of flammability and explosion. The solvent can easily penetrate the micropores of the base membrane, causing pore blockage and affecting ion conduction. Although the water-based coating process is environmentally friendly, PVDF has poor dispersion stability in the water-based system, which is prone to uneven coating and insufficient adhesion. Pressure-sensitive adhesive (PSA) has dynamic bonding properties, but traditional solvent-based PSA produces volatile organic compounds (VOCs) during production and use, which does not meet the requirements of green manufacturing.

[0003] Therefore, the development of a composite slurry that combines the excellent electrochemical properties of PVDF, good bonding properties and environmental protection, and the lithium battery separator obtained by coating it on the base film has become a key issue that needs to be urgently solved in the current lithium battery separator field. The development of this slurry and lithium battery separator preparation process will improve the safety performance and cycle life of lithium batteries and promote the green and sustainable development of the lithium battery industry. Summary of the Invention

[0004] The present invention provides a lithium battery separator based on a pressure-sensitive adhesive composite slurry and a preparation method thereof, which solves the problems of poor electrochemical performance of lithium battery separators and poor adhesion of lithium battery separator coatings in the related art.

[0005] The technical solutions of the present invention are as follows: The present invention proposes a lithium battery separator based on a pressure-sensitive adhesive composite slurry, comprising a base film and a coating arranged on one side or both sides of the base film, wherein the coating is prepared from a slurry, and the slurry comprises raw materials of the following components in parts by weight: 30 to 50 parts of PVDF or its copolymer, 0.5 to 1 part of a dispersant, 10 to 20 parts of a styrene-isoprene-styrene block copolymer, 4 to 5 parts of an inorganic filler, and 40 to 45 parts of a solvent; the raw materials also include a chain extender, which is an isocyanate-containing compound, and the added amount of the chain extender is 20 to 300 ppm of the mass of the PVDF or its copolymer, preferably 250 to 300 ppm.

[0006] As a further technical solution, the material of the base film includes one of polyimide and polyolefin, preferably polyolefin.

[0007] Polyimides and polyolefins are both commonly used battery separators, but the synthesis and preparation processes for polyimides are relatively complex and costly, which to some extent limits their large-scale application. Polyolefins, on the other hand, have a wide range of raw material sources, mature production processes, and low costs, which is one of the key reasons for their widespread use in lithium-ion battery separators. In addition to their low cost, polyolefins as battery base membrane materials also possess excellent chemical stability and are not easily corroded or chemically reacted with electrolyte solutions, ensuring the safety and reliability of batteries during long-term use. They also possess a certain tensile strength, capable of withstanding the mechanical stresses experienced during assembly and use, thus ensuring the integrity of the battery's internal structure.

[0008] As a further technical solution, the PVD or its copolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoropropylene copolymer, and vinylidene fluoride-hexafluoroethylene copolymer, preferably vinylidene fluoride-hexafluoropropylene copolymer.

[0009] In the present invention, the vinylidene fluoride-hexafluoropropylene copolymer is prepared by introducing hexafluoropropylene units into PVDF, thereby destroying part of the crystalline structure of PVDF and increasing its flexibility. It can form a uniform and continuous covering layer on the surface of the diaphragm and can well adapt to the deformation of the diaphragm during the battery charging and discharging process, reducing the shedding of the coating due to stress concentration, thereby improving the peel strength of the coating.

[0010] As a further technical solution, the dispersant includes one or more of polyacrylamide, sodium hexametaphosphate or polyethylene glycol.

[0011] As a further technical solution, the chain extender includes hexamethylene diisocyanate and diisocyanate containing a conjugated diene structure.

[0012] In the present invention, the hexamethylene segments in the hexamethylene diisocyanate molecules possess a certain degree of flexibility and length. After chain extension of the PVDF copolymer, these segments increase the flexibility and chain length of the PVDF copolymer chains. This enhances the molecular chain's mobility when mixed with SIS (styrene-isoprene-styrene block copolymer), making it easier for the chains to interpenetrate and entangle with SIS chains. The conjugated diene segments introduced by the diisocyanate containing a conjugated diene structure share structural and chemical similarities with the isoprene segments in SIS. Based on the principle of like dissolves like, this facilitates the interaction and mixing of the PVDF copolymer and SIS, improving their compatibility. When used in combination, the flexible segments provided by the hexamethylene diisocyanate improve the overall flexibility of the PVDF copolymer, enabling the molecular chain to better adapt to conformational changes in the SIS chain. Furthermore, the similar segment structure provided by the diisocyanate containing a conjugated diene structure enhances the specific interaction between the PVDF copolymer and SIS. These two effects synergistically promote the compatibility of the PVDF copolymer and SIS from different perspectives, significantly improving the peel strength of the lithium battery separator coating.

[0013] As a further technical solution, the diisocyanate containing a conjugated diene structure includes 1,3-butadiene-1,4-diisocyanate, 2-(1,3-butadienyl)-phenyl-1,4-diisocyanate, and 2-methyl-1,3-butadiene-1,4-diisocyanate, preferably 2-(1,3-butadienyl)-phenyl-1,4-diisocyanate.

[0014] The conjugated diene-containing diisocyanates used in this invention all contain a conjugated diene structure, similar to the double bond structure of the polyisoprene segments in SIS. Based on the principle of like dissolves like, this helps improve compatibility with SIS. This similarity makes the molecular structure of the chain-extended PVDF closer to that of SIS, enhancing intermolecular interactions. 2-(1,3-Butadienyl)-phenyl-1,4-diisocyanate significantly alters the regularity, flexibility, and polarity of the PVDF molecular chain, further aligning the structure and properties of PVDF with SIS, thereby enhancing their compatibility and further improving the peel strength of the lithium battery separator coating.

[0015] As a further technical solution, the mass ratio of hexamethylene diisocyanate to the diisocyanate containing a conjugated diene structure is 1:1-3, for example, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:3, preferably 1:2.

[0016] By defining the mass ratio of hexamethylene diisocyanate to conjugated diene-containing diisocyanates, the molecular structure and polarity of the chain-extended PVDF can be precisely controlled. This allows for a better match between PVDF and SIS in terms of both molecular chain flexibility and polarity, promoting interpenetration and entanglement between the two chains, thereby improving compatibility and laying the foundation for enhancing the peel strength of the slurry. When the ratio of hexamethylene diisocyanate to conjugated diene-containing diisocyanates is appropriate, the chain-extended PVDF exhibits excellent compatibility with SIS, forming a stable bond at the interface, thereby improving the peel strength of the slurry.

[0017] As a further technical solution, the raw materials also include 0.8 to 1.4 parts of polyvinyl alcohol, for example, it can be 0.8, 0.9, 1, 1.2, 1.4, and preferably 1; the polyvinyl alcohol includes a first polyvinyl alcohol and a second polyvinyl alcohol, both of which have a degree of alcoholysis of 98 mol% to 99 mol%, and the difference between the first polyvinyl alcohol and the second polyvinyl alcohol is that the viscosity is different.

[0018] Polyvinyl alcohol (PVA) has excellent film-forming properties. In battery separator slurries, it can be evenly mixed with other ingredients, helping to form a more regular and dense membrane structure during the film-forming process. The PVA is composed of a first PVA and a second PVA, both with alcoholysis degrees of 98-99 mol%. Polyvinyl alcohol with a high alcoholysis degree contains a large number of hydroxyl groups on its molecular chain, which can form hydrogen bonds with polar groups in PVDF or its copolymers, or styrene-isoprene-styrene block copolymer molecules, enhancing intermolecular interactions. Furthermore, the combination of PVA with different viscosities can adjust the slurry's rheological properties, making the coating more uniform and dense, and further improving peel strength.

[0019] As a further technical solution, the viscosity of the first polyvinyl alcohol is 5.2-6.0 cps, and the viscosity of the second polyvinyl alcohol is 25-31 cps.

[0020] As a further technical solution, the mass ratio of the first polyvinyl alcohol to the second polyvinyl alcohol is 4 to 6:1, for example, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, preferably 5:1.

[0021] The viscosity of PVA affects the phase separation behavior of the system. A PVA with the appropriate viscosity can adjust the speed and degree of phase separation, resulting in a more uniform microstructure in the formed film. This allows the film to withstand thermal stress more evenly when heated, reducing localized shrinkage and, consequently, overall thermal shrinkage.

[0022] The hydroxyl groups of PVA can interact with the active groups on the surface of inorganic fillers. PVAs of different viscosities exhibit varying degrees of bonding with inorganic fillers due to differences in molecular chain length and active group distribution. Low-viscosity PVA can more evenly encapsulate the inorganic filler, increasing its dispersion in the slurry and improving the interfacial bonding between the filler and the polymer matrix. High-viscosity PVA, through its stronger entanglement, can more firmly anchor the inorganic filler in the film structure. This good interfacial bonding helps disperse thermal stress and reduce thermal shrinkage caused by debonding at the filler-matrix interface.

[0023] As a further technical solution, the inorganic filler includes one or both of graphene oxide and aluminum oxide.

[0024] Graphene oxide has high thermal conductivity and thermal stability. Adding graphene oxide to the battery separator coating can improve the separator's heat dissipation performance, allowing the heat generated during the battery's charge and discharge process to dissipate more quickly, reducing the temperature gradient within the battery. This improves the separator's thermal stability, reduces thermal shrinkage and deformation, and helps extend the battery's lifespan.

[0025] Alumina has a high melting point and thermal stability, allowing it to withstand the high temperatures during battery charging and discharging, reducing thermal shrinkage and deformation of the separator at high temperatures. Adding an alumina coating can effectively improve the thermal stability of the battery separator, allowing it to maintain its shape and performance in high-temperature environments, thereby improving battery safety and reliability.

[0026] As a further technical solution, the particle size of the inorganic filler is nanometer-scale.

[0027] Nanoscale graphene oxide can further increase the interaction sites with lithium ions, more effectively promote lithium ion conduction, and improve the battery's charge and discharge efficiency and rate performance; on the other hand, it can enhance the interaction with the diaphragm matrix material, making the two more closely combined, thereby better playing the role of enhancing mechanical properties.

[0028] Nano-sized alumina particles can be more finely packed into the micropores of the battery separator, making the pore structure of the battery separator more uniform and dense. This not only enhances the mechanical strength of the separator, but also effectively prevents the active substances inside the battery from migrating through the separator pores, reducing the battery's self-discharge and improving the battery's energy retention rate.

[0029] As a further technical solution, the solvent includes one of water and dimethyl carbonate.

[0030] Using water and dimethyl carbonate as solvents not only reduces production costs and realizes a green and environmentally friendly manufacturing process, but also effectively avoids the use of organic solvents and large-scale VOC emissions. It also solves the serious solvent pollution problem in traditional lithium battery separator coating technology, promotes the lithium battery industry to move in a more economical and environmentally friendly direction, and reduces pressure on the environment.

[0031] The present invention also proposes a method for preparing a lithium battery separator based on a pressure-sensitive adhesive composite slurry, which is used to prepare the lithium battery separator based on the pressure-sensitive adhesive composite slurry, comprising the following steps: S1. Mix PVDF or its copolymer, solvent, and chain extender uniformly, keep the mixture at 75-85°C for 2-2.5 hours, then add the remaining components and mix again to obtain a coating material; S2. Coating the coating material on one side or both sides of the base film, drying and annealing to form a coating, thereby obtaining a lithium battery separator based on a pressure-sensitive adhesive composite slurry.

[0032] In the present invention, drying during the preparation of the lithium battery separator removes the solvent and helps form good adhesion between the coating and the separator substrate. During the drying process, the coating material molecules gradually approach and interact with molecules on the separator surface, forming chemical bonds or physical adsorption, thereby firmly adhering the coating to the separator and reducing the possibility of the coating falling off during subsequent use.

[0033] During the coating preparation process, internal stress is generated within the coating due to factors such as shrinkage of the coating material and solvent volatilization. This internal stress can cause cracking and deformation during use. During the annealing process, heating provides the coating material molecules with sufficient energy to move and rearrange, thereby eliminating internal stress and improving the coating's stability and reliability.

[0034] As a further technical solution, step S1 is: mixing the raw materials of the slurry evenly and then keeping the mixture at 80° C. for 2 hours to obtain a coating material.

[0035] As a further technical solution, in step S2, the annealing temperature is 100-150°C.

[0036] As a further technical solution, in step S2, the coating method includes one of spraying, roller coating, and spray-roller coating composite coating, preferably spray-roller coating composite coating.

[0037] Spray-roller composite coating combines the advantages of spray and roller coating, enabling both high-precision, uniform localized coating via spraying and efficient, large-area coating via roller coating, resulting in a coating with superior performance on battery separators. The process offers significant flexibility, allowing the process parameters and sequence of spray and roller coating to be flexibly combined to meet diverse product needs, tailored to the specific battery separator performance requirements and production process demands.

[0038] As a further technical solution, the thickness of the spray coating is 1-5 μm, preferably 2 μm, and the thickness of the roller coating is 1-3 μm, preferably 1 μm.

[0039] The working principle and beneficial effects of the present invention are: In the present invention, the PVDF copolymer molecular chains contain reactive groups that react with isocyanate groups. The highly reactive isocyanate groups (-NCO) in the chain extender react chemically with the reactive groups at the ends of PVDF or its copolymer molecular chains, forming chemical bonds that connect the different molecular chains, thereby achieving chain extension. As the PVDF copolymer chain segments grow, on the one hand, the flexibility of the molecular chains increases, allowing the PVDF molecular chains to better adapt to the conformational changes of the SIS molecular chains, making them more easily interpenetrating and entangled with the SIS molecular chains, increasing the contact area and interaction opportunities between the two. On the other hand, the chain segment growth changes the intermolecular forces of PVDF, making them more compatible with the intermolecular forces of SIS, thereby improving the compatibility between the two and enhancing the peel strength of the lithium battery separator coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Figure 1 This is an electron microscope image of one side of the lithium battery separator coating prepared in Example 1 of the present invention (magnification 15,000); Figure 2 This is a microscope image of one side of the lithium battery separator coating prepared in Example 1 of the present invention (magnification 200); Figure 3 This is a microscope image (magnification 100) of one side of the lithium battery separator coating prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] In the following examples and comparative examples: Polyvinyl alcohol PVA-105: viscosity 2.5~6.0cps, alcoholysis degree 98~99mol%, pH 5~7; Polyvinyl alcohol PVA-110: viscosity 10.2~11.8cps, alcoholysis degree 98~99mol%, pH 5~7; Polyvinyl alcohol PVA-117: viscosity 25~31cps, alcoholysis degree 98~99mol%, pH 5~7; Vinylidene fluoride-hexafluoropropylene copolymer: Model 21510, Solvay, USA; Ethylene-isoprene-styrene block copolymer: Model 1105, Sinopec; Graphene oxide: particle size 200nm; The base film was a polyolefin film with a thickness of 0.8 μm.

[0044] Example 1 A method for preparing a lithium battery separator based on a pressure-sensitive adhesive composite slurry comprises the following steps: S1. After uniformly mixing 30 parts of vinylidene fluoride-hexafluoropropylene copolymer and 40 parts of water, a chain extender of 250 ppm by mass of the vinylidene fluoride-hexafluoropropylene copolymer was added, and the mixture was kept at 80° C. for 2 h. Then, 10 parts of ethylene-isoprene-styrene block copolymer, 0.5 parts of sodium hexametaphosphate, and 4 parts of graphene oxide were added and uniformly mixed to obtain a coating material; the chain extender was hexamethylene diisocyanate; S2. The coating material is applied to one side of the base film by spraying and roller coating (the spraying thickness is 2 μm and the roller coating thickness is 1 μm), dried at 120°C, and annealed at 150°C to form a coating to obtain a lithium battery separator based on a pressure-sensitive adhesive composite slurry. The coating side of the lithium battery separator is inspected by electron microscopy and microscopy, as shown in FIG. Figures 1-3 shown.

[0045] Example 2 A method for preparing a lithium battery separator based on a pressure-sensitive adhesive composite slurry comprises the following steps: S1. After uniformly mixing 50 parts of vinylidene fluoride-hexafluoropropylene copolymer and 45 parts of water, 300 ppm of chain extender (based on the mass of vinylidene fluoride-hexafluoropropylene copolymer) was added, the mixture was kept at 80° C. for 2 h, and then 20 parts of ethylene-isoprene-styrene block copolymer, 1 part of sodium hexametaphosphate, and 5 parts of graphene oxide were added and uniformly mixed to obtain a coating material; the chain extender was hexamethylene diisocyanate; S2. The coating material is sequentially coated on one side of the base film by a spray-roll coating composite coating method (the spraying thickness is 2 μm, and the roller coating thickness is 1 μm), dried at 120° C., and annealed at 100° C. to form a coating, thereby obtaining a lithium battery separator based on a pressure-sensitive adhesive composite slurry.

[0046] Example 3 Compared with Example 1, the only difference in this example is that the chain extender is 1,3-butadiene-1,4-diisocyanate.

[0047] Example 4 Compared with Example 1, the only difference of this example is that the chain extender consists of hexamethylene diisocyanate and 1,3-butadiene-1,4-diisocyanate in a mass ratio of 1:2.

[0048] Example 5 Compared with Example 1, the only difference of this example is that the chain extender is composed of hexamethylene diisocyanate and 2-methyl-1,3-butadiene-1,4-diisocyanate in a mass ratio of 1:2.

[0049] Example 6 Compared with Example 1, the only difference of this example is that the chain extender is composed of hexamethylene diisocyanate and 2-(1,3-butadienyl)-phenyl-1,4-diisocyanate in a mass ratio of 1:2.

[0050] Example 7 Compared with Example 1, the difference of this embodiment is only step S1. In this embodiment, step S1 is: S1. After uniformly mixing 30 parts of vinylidene fluoride-hexafluoropropylene copolymer and 40 parts of water, 250 ppm of a chain extender based on the mass of the vinylidene fluoride-hexafluoropropylene copolymer was added, and the mixture was kept warm at 80°C for 2 hours. Then, 10 parts of ethylene-isoprene-styrene block copolymer, 0.5 parts of sodium hexametaphosphate, 1 part of polyvinyl alcohol, and 4 parts of graphene oxide were added and uniformly mixed to obtain a coating material; the chain extender was hexamethylene diisocyanate; and the polyvinyl alcohol was polyvinyl alcohol PVA-105.

[0051] Example 8 Compared with Example 7, the only difference in this example is that the polyvinyl alcohol is polyvinyl alcohol PVA-117.

[0052] Example 9 Compared with Example 7, the only difference of this example is that the polyvinyl alcohol consists of polyvinyl alcohol PVA-105 and polyvinyl alcohol PVA-117 in a mass ratio of 5:1.

[0053] Example 10 Compared with Example 7, the only difference in this example is that the polyvinyl alcohol is polyvinyl alcohol PVA-110.

[0054] Comparative Example 1 A method for preparing a lithium battery separator based on a pressure-sensitive adhesive composite slurry comprises the following steps: S1. Mix 30 parts of vinylidene fluoride-hexafluoropropylene copolymer, 40 parts of water, 10 parts of ethylene-isoprene-styrene block copolymer, 0.5 parts of sodium hexametaphosphate, and 4 parts of graphene oxide to obtain a coating material; S2. The coating material is sequentially coated on one side of the base film by a spray-roll coating composite coating method (the spraying thickness is 2 μm, and the roller coating thickness is 1 μm), dried at 120°C, and annealed at 150°C to form a coating to obtain a lithium battery separator based on a pressure-sensitive adhesive composite slurry.

[0055] Comparative Example 2 Compared with Example 1, the only difference of this comparative example is that no vinylidene fluoride-hexafluoropropylene copolymer is added.

[0056] Comparative Example 3 Compared with Example 1, the only difference of this comparative example is that no ethylene-isoprene-styrene block copolymer is added.

[0057] Comparative Example 4 Compared with Example 1, the only difference of this comparative example is that graphene oxide is not added.

[0058] Experimental example The lithium battery separators prepared in Examples 1 to 10 and Comparative Examples 1 to 4 were tested as follows: (1) Peel strength: Cut three samples of 15 mm width along the longitudinal direction of the diaphragm, and stick the cut samples on a glass slide with double-sided tape. After sticking, fold the free end of the sample 180°, peel off the adhesive surface by hand for about 10-20 mm, and test the peel strength using a tensile testing machine.

[0059] (2) Thermal shrinkage: Determine the transverse thermal shrinkage according to the method in GB / T 36363-2018 “Lithium-ion battery separator performance test”.

[0060] (3) Cycle capacity retention rate: The lithium-ion battery separator was encapsulated in a CR2032 button battery, and the electrolyte was 1 mol / LLiPF6 / EC (ethylene carbonate) / DEC (diethyl carbonate) solution. The battery capacity retention rate was measured after 1000 cycles at 0.5C.

[0061] (4) VOC emissions: measured by gas chromatography-mass spectrometry (GC-MS).

[0062] The measurement results are shown in Tables 1 and 2 below.

[0063] Table 1 Measurement results of Examples 1 to 6 and Comparative Examples 1 to 4

[0064] As shown in Table 1, adding a chain extender composed of hexamethylene diisocyanate and a diisocyanate containing a conjugated diene structure to the slurry of the lithium battery separator coating of the present invention can improve the peel strength of the lithium battery separator coating.

[0065] Table 2 Measurement results of Examples 7 to 10

[0066] As shown in Table 2, adding polyvinyl alcohol consisting of polyvinyl alcohol PVA-105 and polyvinyl alcohol PVA-117 to the slurry of the lithium battery separator coating of the present invention can further reduce the thermal shrinkage rate and improve the safety, stability and life of the battery.

[0067] Table 3 Measurement results of Examples 1 and 2

[0068] As shown in Table 3, when the lithium battery separator prepared by the present invention is used in a battery, the cycle capacity retention rate can be as high as 92%, and the VOC emission is low, which can reduce air pollution.

[0069] The above are only 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 in the scope of protection of the present invention.

Claims

1. A lithium battery separator based on a pressure-sensitive adhesive composite slurry, characterized in that: The invention comprises a base film and a coating arranged on one side or both sides of the base film, wherein the coating is prepared from a slurry, and the slurry comprises the following raw materials in parts by weight: 30 to 50 parts of PVDF or its copolymer, 0.5 to 1 part of a dispersant, 10 to 20 parts of a styrene-isoprene-styrene block copolymer, 4 to 5 parts of an inorganic filler, and 40 to 45 parts of a solvent; the raw materials also include a chain extender, which is an isocyanate-containing compound, and the amount of the chain extender added is 20 to 300 ppm of the mass of the PVDF or its copolymer.

2. The lithium battery separator based on a pressure-sensitive adhesive composite slurry according to claim 1, characterized in that: The chain extender includes hexamethylene diisocyanate and diisocyanate containing a conjugated diene structure.

3. The lithium battery separator based on a pressure-sensitive adhesive composite slurry according to claim 2, characterized in that: The diisocyanate containing a conjugated diene structure includes one or more of 1,3-butadiene-1,4-diisocyanate, 2-(1,3-butadienyl)-phenyl-1,4-diisocyanate, and 2-methyl-1,3-butadiene-1,4-diisocyanate.

4. The lithium battery separator based on a pressure-sensitive adhesive composite slurry according to claim 2, characterized in that: The mass ratio of the hexamethylene diisocyanate to the diisocyanate containing a conjugated diene structure is 1:1-3.

5. The lithium battery separator based on a pressure-sensitive adhesive composite slurry according to claim 1, characterized in that: The raw materials further include 0.8 to 1.4 parts of polyvinyl alcohol, wherein the polyvinyl alcohol includes a first polyvinyl alcohol and a second polyvinyl alcohol both having alcoholysis degrees of 98 mol% to 99 mol%. The difference between the first polyvinyl alcohol and the second polyvinyl alcohol lies in their different viscosities.

6. The lithium battery separator based on the pressure-sensitive adhesive composite slurry according to claim 5, characterized in that: The viscosity of the first polyvinyl alcohol is 5.2-6.0 cps, and the viscosity of the second polyvinyl alcohol is 25-31 cps.

7. The lithium battery separator based on the pressure-sensitive adhesive composite slurry according to claim 6, characterized in that: The mass ratio of the first polyvinyl alcohol to the second polyvinyl alcohol is 4-6:

1.

8. The lithium battery separator based on a pressure-sensitive adhesive composite slurry according to claim 1, characterized in that: The inorganic filler includes one or both of graphene oxide and aluminum oxide.

9. The lithium battery separator based on a pressure-sensitive adhesive composite slurry according to claim 1, characterized in that: The solvent includes one of water and dimethyl carbonate.

10. A method for preparing a lithium battery separator based on a pressure-sensitive adhesive composite slurry, for preparing the lithium battery separator based on a pressure-sensitive adhesive composite slurry according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Mix PVDF or its copolymer, solvent, and chain extender uniformly, keep the mixture at 75-85°C for 2-2.5 hours, then add the remaining components and mix again to obtain a coating material; S2. Coating the coating material on one side or both sides of the base film, drying and annealing to form a coating, thereby obtaining a lithium battery separator based on a pressure-sensitive adhesive composite slurry.

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