Diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention provides a diaphragm, a preparation method thereof and a lithium ion battery, and particularly relates to the technical field of battery diaphragms. The diaphragm comprises a base film and a coating layer, wherein the coating layer is arranged on at least one side of the base film; wherein the coating comprises modified glass fibers and an adhesive, and the modified glass fibers and the adhesive are crosslinked to form a network structure. The modified glass fiber is introduced into the diaphragm coating, and the modified glass fiber and the adhesive can be crosslinked to form a network structure, so that the heat resistance of the diaphragm is improved, and the adhesive property of the diaphragm is improved.

Description

Technical Field

[0001] The present invention relates to the field of battery separators, and in particular to a separator, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] As one of the main components of lithium-ion batteries, the separator plays a vital role. It not only prevents short circuits caused by direct contact between the positive and negative electrodes, but also affects the safety, performance and life of the battery.

[0003] The core materials of the separator are mainly polyethylene (PE) and polypropylene (PP). However, the heat resistance of these two polyolefin materials has the following problems: (1) Low melting point characteristics: The melting point of PE is about 130℃, and that of PP is about 160℃. When the battery operating temperature rises or thermal runaway occurs, the separator is prone to melt shrinkage, resulting in failure of micropore closure or structural collapse, causing direct contact and short circuit between the positive and negative electrodes; (2) High thermal shrinkage rate: The thermal shrinkage rate of traditional PE / PP separators at high temperatures (>100℃) can reach more than 10%, seriously damaging the stability of the internal structure of the battery and increasing the risk of thermal runaway; (3) Insufficient mechanical strength: The tensile strength and puncture resistance of the separator decrease significantly at high temperatures, making it difficult to suppress the penetration of lithium dendrites, further causing internal short circuits.

[0004] The current mainstream technology is to coat inorganic materials such as Al2O3 on the surface of PE / PP base film to reduce high-temperature shrinkage through physical support, but it can only improve the temperature resistance to about 150°C, which cannot meet the current development needs of lithium-ion batteries towards high energy density, large capacity and high power.

[0005] Therefore, it is necessary to provide a high-temperature resistant diaphragm and a preparation method thereof and a lithium-ion battery to meet the development demand of lithium-ion batteries towards high energy density, large capacity and high power. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present invention provides a diaphragm and a preparation method thereof and a lithium ion battery to improve the problem of poor heat resistance of the diaphragm.

[0007] To achieve the above-mentioned purpose and other related purposes, the first aspect of the present invention provides a diaphragm, which includes a base membrane and a coating, and the coating is arranged on at least one side of the base membrane, wherein the coating includes modified glass fiber and an adhesive, and the modified glass fiber and the adhesive are cross-linked to form a network structure.

[0008] In one example of the present invention, the modified glass fiber has one or more of an isocyanate group, an amino group, and an epoxy group.

[0009] In one example of the present invention, the adhesive includes at least one of polyacrylate, PMMA microspheres, polyurethane, polyvinyl alcohol, styrene, butadiene copolymer, and polyvinylidene fluoride.

[0010] In one example of the present invention, the adhesive includes PMMA microspheres, which are core-shell structures. The core of the PMMA microspheres includes at least one of styrene, acrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polyacrylamide, and the shell includes an acrylic soft monomer.

[0011] In one example of the present invention, the adhesive has one or more of hydroxyl groups, carboxyl thiol groups, amide groups, amino groups, and epoxy groups.

[0012] In one example of the present invention, the modified glass fiber has a diameter of 0.5-5 μm and a length of 0.5-10 μm.

[0013] In one example of the present invention, the coating comprises the following raw materials in parts by weight: 0.1 to 50 parts of modified glass fiber and 2.5 to 40 parts of adhesive.

[0014] In one example of the present invention, the coating further comprises 80 to 100 parts of a filler, 0.1 to 3 parts of a dispersant, 0.01 to 3 parts of a wetting agent, and 0.5 to 3 parts of a thickener.

[0015] In one example of the present invention, the filler includes one or more of alumina, boehmite, barium titanate, barium sulfate, silicon dioxide, magnesium hydroxide, lithium aluminum titanium phosphate, lithium iron phosphate, and a ternary positive electrode material.

[0016] In one example of the present invention, the dispersant includes one or more of polyphosphate, polycarboxylate, acrylic acid copolymer, and acrylic acid copolymer.

[0017] In one example of the present invention, the wetting agent includes one or more of an organosilicon wetting agent, an acetylene glycol wetting agent, and a non-ionic wetting agent.

[0018] In one example of the present invention, the thickener includes one or more of polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose.

[0019] In an example of the present invention, the thickness of the coating layer is 1-8 μm.

[0020] The present invention also provides a diaphragm, which includes a base membrane, a first coating and a second coating, wherein the first coating is arranged on at least one side of the base membrane, and the first coating includes a filler; the second coating is arranged on the first coating and / or the base membrane, and the second coating includes modified glass fiber and an adhesive, and the modified glass fiber and the adhesive are cross-linked to form a network structure.

[0021] A second aspect of the present invention provides a method for preparing a diaphragm, the method comprising the following steps:

[0022] preparing modified glass fibers;

[0023] Dispersing the modified glass fiber and adhesive in water to prepare a coating slurry;

[0024] applying the coating slurry on at least one side of a base film;

[0025] drying the base film coated with the coating slurry to obtain a diaphragm;

[0026] During the coating process, the modified glass fiber and the adhesive are cross-linked to form a network structure.

[0027] In one example of the present invention, the step of preparing the modified glass fiber includes:

[0028] The glass fibers are ball-milled to obtain ultrafine glass fibers, wherein the diameter of the ball-milled glass fibers is 0.5 to 5 μm and the length is 0.5 to 10 μm;

[0029] Dispersing the ultrafine glass fibers into water, adding a coupling agent and a catalyst, adjusting the pH of the solution to 4-5, and keeping the solution at 40-80° C.;

[0030] After the heat preservation is completed, the modified glass fiber is obtained by filtering and drying.

[0031] In one example of the present invention, in the step of preparing the modified glass fiber, the added amounts of the raw materials are: 100 parts of glass fiber, 0.1 to 50 parts of coupling agent, and 0.1 to 10 parts of catalyst.

[0032] In one example of the present invention, the coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-isocyanatepropyltrimethoxysilane, isocyanate toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0033] In one example of the present invention, the catalyst includes one or more of acetic acid, formic acid, dilute hydrochloric acid, and phosphoric acid.

[0034] A third aspect of the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator is any of the above-mentioned separators or is prepared by the above-mentioned preparation method.

[0035] In summary, the present invention incorporates modified glass fibers into the separator coating. The modified glass fibers' low thermal expansion coefficient and high thermal stability significantly improve the separator's heat resistance. Furthermore, during the coating process, the modified glass fibers crosslink with the adhesive to form a stable three-dimensional network structure. This network structure not only significantly enhances the coating's interfacial bonding and cohesion but also effectively inhibits particle migration and interfacial delamination at high temperatures, imparting the coating with excellent creep resistance.

[0036] Furthermore, the introduction of modified glass fiber significantly improves the coating's mechanical properties, such as tensile strength and impact resistance, while reducing the risk of cracking. Modified glass fiber offers environmental advantages, requiring no highly polluting solvents for production and inherently recyclable. Compared to traditional polymer fibers, it requires less energy and requires a simpler modification process, making it ideal for large-scale industrial applications. It is particularly well-suited for applications with demanding material properties, such as lithium battery separators and high-temperature protective coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 is a schematic structural diagram of a diaphragm according to an embodiment of the present invention;

[0039] Figure 2 is a schematic structural diagram of a diaphragm according to another embodiment of the present invention;

[0040] Figure 3 is a flow chart of a method for preparing a diaphragm according to an embodiment of the present invention;

[0041] Figure 4 FIG1 is a flow chart of the preparation of modified glass fiber in one embodiment of the method for preparing the diaphragm of the present invention.

[0042] Component number description:

[0043] 10. Diaphragm; 11. Base film; 12. Coating; 13. First coating; 14. Second coating. DETAILED DESCRIPTION

[0044] The following describes the embodiments of the present invention by means of specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the features in the following embodiments and examples can be combined with each other unless they conflict. The test methods for which specific conditions are not specified in the following examples are generally based on conventional conditions or the conditions recommended by the manufacturers.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0046] As used herein, "plurality," "multiple," "multiple times," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0047] Herein, “further”, “further”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of the present invention.

[0048] When referring to a numerical range herein, unless otherwise specified, the distribution of the values ​​within the numerical range is considered continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between the two numerical endpoints. When multiple numerical ranges are provided to describe a feature or characteristic, these numerical ranges may be combined.

[0049] As lithium-ion batteries develop towards high energy density, large capacity and high power (such as electric vehicles and energy storage systems), the heat resistance of the separator has become a major issue affecting battery safety and reliability: (1) Thermal runaway risk: More than 80% of battery thermal runaway events (such as fire and explosion) are caused by internal short circuits, and the high-temperature shrinkage of the separator is one of the main causes of short circuits. For example, when electric vehicle power batteries are exposed to high temperatures or overcharge, traditional PE / PP separators may fail due to shrinkage, leading to a thermal runaway chain reaction. (2) High-temperature operating conditions: The internal temperature of power batteries can exceed 100°C under conditions such as fast charging and high-rate discharge, and the thermal shutdown function of traditional separators (such as the PE closed-cell temperature of about 130°C) cannot effectively block the current. A higher temperature resistance threshold (such as >200°C) is required to widen the safety window.

[0050] The current mainstream technology is to coat inorganic materials such as Al2O3 on the surface of PE / PP base membranes to reduce high-temperature shrinkage through physical support, but it can only improve the temperature resistance to about 150°C; for heat resistance above 150°C, some researchers add cellulose nanowhiskers (CNC), cellulose nanofibers (CNF), aramid fibers, PI fibers, PEEK fibers and other polymer heat-resistant fibers to the coating. Although these solutions can improve the heat resistance of the membrane, the improvement effect is limited. In addition, the synthesis process of these polymer fibers involves a large amount of solvent emissions, energy consumption, and complex synthesis processes. The high cost of actual application is not conducive to industrial application.

[0051] Based on this, the present invention provides a diaphragm, a preparation method thereof, and a lithium-ion battery, which can improve the heat resistance of the diaphragm to above 150°C, and the production process has the advantages of being green and environmentally friendly, and is suitable for large-scale industrial applications.

[0052] See also Figure 1 In a first aspect, the present invention provides a diaphragm, which includes a base film 11 and a coating 12. The base film 11, as the matrix of the diaphragm 10, can be made of any porous material in the art that has an insulating isolation function and can provide a channel for lithium ion transmission. As an example, the base film 11 can be a polyethylene (PE) film, a polypropylene (PP) film, a polyethylene / polypropylene / polyethylene three-layer composite film, a polyimide (PI) film, a polyvinylidene fluoride (PVDF) porous film, etc. Furthermore, the thickness of the base film 11 is 3 to 20 mm, for example, 3 mm, 10 mm, 15 mm or 20 mm, and the porosity is 30% to 50%, for example, 30%, 40% or 50%, etc. The specific materials and parameters of the base film 11 can be selected according to actual production and are not limited here. The coating 12 is disposed on at least one side of the base film 11. Specifically, the base film 11 has a first surface and a second surface disposed opposite each other along its thickness. The coating 12 can be disposed on the first surface of the base film 11, the second surface of the base film 11, or both. Preferably, the coating 12 is disposed on both the first and second surfaces of the base film 11. The provision of the coating 12 can improve the heat resistance of the diaphragm.

[0053] The coating 12 of the diaphragm 10 in the present invention includes at least modified glass fiber and adhesive. The modified glass fiber and the adhesive are cross-linked during the coating process to form a network structure. This network structure not only significantly improves the interfacial bonding strength and cohesive force of the coating, but also effectively inhibits particle migration and interfacial peeling at high temperatures, giving the coating excellent creep resistance.

[0054] In some embodiments, the modified glass fiber has one or more of an isocyanate group (-NCO), an amino group (-NH2), and an epoxy group (-CH(O)CH-). Further, the modified glass fiber has an isocyanate group. The adhesive has an active group that undergoes a cross-linking reaction with the active group of the modified glass fiber, such as a hydroxyl group (-OH), a carboxyl group (-COOH), a thiol group (-SH), an amide group (-CONH2), an amino group (-NH2), an epoxy group (-CH(O)CH-), etc. Further, the adhesive has a hydroxyl group and / or a carboxyl group. At high temperatures, the active groups of the modified glass fiber and the active groups on the adhesive undergo cross-linking to form a network structure.

[0055] In one embodiment, the modified glass fiber is formed by grafting a coupling agent onto glass fiber. The glass fiber is ultra-fine alkali-free glass fiber with a softening point of 850-860°C and an expansion coefficient of 5*10 -6 / ℃, the diameter of the glass fiber is 0.5-5μm, such as 0.5μm, 1μm, 3μm or 5μm, and the length is 0.5-10μm, such as 0.5μm, 2μm, 5μm, 8μm or 10μm. The coupling agent is selected from amino-containing silane coupling agents, epoxy-containing silane coupling agents or isocyanate-containing silane coupling agents, wherein the amino-containing silane coupling agent includes but is not limited to γ-aminopropyltriethoxysilane (KH550) and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH792), the epoxy-containing silane coupling agent includes, for example, γ-glycidoxypropyltrimethoxysilane (KH560, A-187), and the isocyanate-containing silane coupling agent includes 3-isocyanatepropyltriethoxysilane (IPTS), 3-isocyanatepropyltrimethoxysilane (IPTMS), isocyanate toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). The coupling agent may be a single type or a combination of two or more types. For example, the coupling agent may be KH550, IPTS, or a combination of IPTS and IPTMS. Preferably, the coupling agent is IPTS.

[0056] The mechanism of coupling agent modification of glass fiber is: the silane coupling agent is first hydrolyzed to form silanol (Si(OH)3), and then the silanol (-Si(OH)3) undergoes condensation reaction with the silanol (Si-OH) on the surface of the alkali-free glass fiber to form a stable Si-O-Si covalent bond, thereby grafting active groups on the surface of the glass fiber.

[0057] Taking IPTS as an example, the modification mechanism of glass fiber is described in detail below:

[0058] 1) Hydrolysis of silane coupling agent: The triethoxysilane group of IPTS is hydrolyzed under the action of water (possibly through ambient humidity or solution) to generate silanol (Si(OH)3), while releasing ethanol (EtOH). During this process, a small amount of acid can be added as a catalyst to provide a weak acid environment, accelerate the hydrolysis of the silane coupling agent, and inhibit the self-polymerization of silanol.

[0059] 2) Condensation reaction and bonding with glass fiber surface:

[0060] Si(OH)3+GF-OH→GF-O-Si-O-(covalent bond)+H2O

[0061] The silanol generated by hydrolysis reacts with the silanol (Si-OH) on the surface of the alkali-free glass fiber to form a stable Si-O-Si covalent bond, fixing the IPTS on the fiber surface. The modification mechanism of the other coupling agents is the same as that of IPTS.

[0062] In some embodiments, the adhesive includes at least one of polyacrylate, PMMA microspheres, polyurethane, polyvinyl alcohol, styrene, butadiene copolymer, and polyvinylidene fluoride. That is, the adhesive can be selected from any one of the materials listed above, such as polyacrylate or PMMA microspheres. The adhesive can also be selected from any two or more of the materials listed above, such as polyacrylate and PMMA microspheres, or a combination of polyacrylate, PMMA microspheres, and polyvinyl alcohol. Furthermore, the adhesive includes polyacrylate and PMMA microspheres, wherein the Tg (glass transition temperature) of the polyacrylate is between -40°C and 200°C, and the polyacrylate has -COOH and -OH groups on its ends or side chains. PMMA microspheres have a core-shell structure, wherein the core can provide cohesive strength and the shell can provide adhesion. The core includes at least one of styrene, acrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polyacrylamide. Furthermore, the core is styrene and the shell is a grafted modified acrylic soft monomer, which can provide adhesion, and the shell has -COOH and -OH modified groups. The Tg of the PMMA microspheres is 20-90°C and the particle size is 0.1-8μm.

[0063] The isocyanate groups, amino groups, or epoxy groups grafted onto the surface of the modified glass fiber can undergo cross-linking reactions with the -COOH and -OH groups at the end or side chains of the polyacrylate, or with the -COOH and -OH groups on the surface of the PMMA microspheres, forming a network structure. The specific process includes the following steps: (1) glass fiber modification, (2) cross-linking reaction with the polyacrylate, and (3) cross-linking reaction with the PMMA microspheres:

[0064]

[0065]

[0066] In one embodiment, the coating 12 further includes a filler. The filler is a high-temperature resistant inorganic material. This filler not only improves the heat resistance of the separator but also forms a rigid skeleton at high temperatures, reducing the thermal shrinkage of the separator 10 at high temperatures. An adhesive can be placed between the filler particles to bond them together to form an inorganic heat-resistant coating. Furthermore, the adhesive provides adhesion between the coating 12 and the base film 11, preventing the coating 12 from falling off the base film 11. Fillers include, but are not limited to, one or more of alumina, boehmite, barium titanate, barium sulfate, silica, magnesium hydroxide, lithium aluminum titanium phosphate, lithium iron phosphate, and ternary positive electrode materials. That is, the filler can be selected from any one of the materials listed above, such as alumina, titanium dioxide, or lithium iron phosphate. The inorganic filler can also be selected from any combination of two or more of the materials listed above, such as a combination of barium sulfate and barium titanate, or a combination of alumina, lithium aluminum titanium phosphate, and magnesium hydroxide, etc. It should be noted that when the filler is a combination of two or more, the ratio of the components within the composition is not limited, and any proportion can be mixed. Furthermore, the Dv50 particle size of the filler is 0.1 to 5 μm, for example, 0.1 μm, 1 μm, 3 μm or 5 μm.

[0067] In some embodiments, the coating comprises the following raw material components in parts by weight: 80-100 parts of filler, 0.1-50 parts of modified glass fiber, and 2.5-40 parts of adhesive. Furthermore, the adhesive comprises 0.5-20 parts of polyacrylate and 2-20 parts of PMMA microspheres. For example, the filler may be 80 parts, 90 parts, or 100 parts, etc., the modified glass fiber may be 0.1 parts, 10 parts, 30 parts, or 50 parts, etc., the polyacrylate may be 0.5 parts, 1 part, 10 parts, 15 parts, or 20 parts, etc., and the PMMA microspheres may be 2 parts, 5 parts, 10 parts, 15 parts, or 20 parts, etc.

[0068] In some embodiments, the coating further comprises a small amount of auxiliary agents, including 0.1 to 3 parts of a dispersant, 0.01 to 3 parts of a wetting agent, and 0.5 to 3 parts of a thickener. For example, the dispersant may be 0.1, 1, 2, or 3 parts, the wetting agent may be 0.01, 1, 2, or 3 parts, and the thickener may be 0.5, 1, 2, or 3 parts. The dispersant comprises one or more of polyphosphate, polycarboxylate, acrylic copolymer, and acrylic copolymer. Further, the dispersant is a polycarboxylate. The wetting agent comprises one or more of an organosilicon wetting agent, an acetylene glycol wetting agent, and a nonionic wetting agent. Further, the wetting agent is an organosilicon wetting agent. The thickener comprises one or more of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and sodium carboxymethyl cellulose (CMC). Further, the thickener is CMC, and the degree of substitution of CMC is 0.6. It should be noted that the CMC substitution degree refers to the average number of hydrogen atoms on the hydroxyl groups on the glucose residue ring of each cellulose macromolecule replaced by carboxymethyl groups.

[0069] The thickness of the coating can be set according to actual needs. In some embodiments, the thickness of the coating is 1 to 8 μm, for example, 1 μm, 3 μm, 5 μm or 8 μm.

[0070] See also Figure 2 In one embodiment of the present invention, a diaphragm is further provided, which includes a base film 11, a first coating layer 13, and a second coating layer 14, wherein the first coating layer 13 is an inorganic coating layer, which is arranged on at least one side of the base film 11, that is, the base film 11 has a first surface and a second surface arranged opposite to each other along its thickness direction, and the first coating layer 13 can be arranged on the first surface of the base film 11, or on the second surface of the base film 11, or on the first surface and the second surface at the same time. The second coating layer 14 includes modified glass fiber and an adhesive, and the modified glass fiber and the adhesive are cross-linked to form a network structure. The second coating layer 14 is arranged on the first coating layer 13 and / or the base film 11, that is, the second coating layer 14 can be arranged only on the first coating layer 13, or only on the base film 11, or on the first coating layer 13 and the base film 11 at the same time. Figure 2 Only the case where the second coating layer 14 is provided on the first coating layer 13 is shown, and the other cases can be adjusted adaptively.

[0071] Specifically, when the first coating 13 is arranged on one of the surfaces of the base film 11, such as the first surface, the second coating 14 can be arranged only on the first coating 13, or only on the second surface of the base film 11, or on both the first coating 13 and the second surface of the base film 11.

[0072] When the first coating layer 13 is provided on both the first and second surfaces of the base film 11 , the second coating layer 14 may be provided on only one side of the first coating layer 13 or on both the first and second surfaces.

[0073] In one embodiment, the first coating 13 includes a filler and an adhesive. The filler can be a high-temperature resistant inorganic material, including but not limited to one or more of alumina, boehmite, barium titanate, barium sulfate, silicon dioxide, magnesium hydroxide, lithium aluminum titanium phosphate, lithium iron phosphate, and a ternary positive electrode material. The adhesive is filled between the filler particles to bond them together to form an inorganic coating, and the inorganic coating is bonded to the base film 11. The adhesive can be a conventional viscous material in the art. For example, the adhesive includes one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyimide, polyvinylpyrrolidone, polymethyl methacrylate, polyacrylic acid, polyacrylate, and polyacrylate. The adhesive can also be made of the materials listed above for the coating 12. The first coating 13 also includes a small amount of additives, such as a dispersant, a wetting agent, and a thickener. The dispersant, wetting agent, and thickener can be made of the materials listed above for the coating 12, or conventional materials in the art not listed above. The ratio of each component in the first coating layer 13 can be set according to a conventional ratio and is not limited here.

[0074] Second coating 14 includes modified glass fibers and an adhesive. The modified glass fibers and adhesive are cross-linked to form a network structure. This network structure not only significantly enhances the coating's interfacial bonding and cohesion but also effectively inhibits particle migration and interfacial delamination at high temperatures, imparting excellent creep resistance to the coating. The modified glass fibers and adhesive in second coating 14 are made of the same material types as those in coating 12.

[0075] In some embodiments, the second coating 14 further includes fillers and a small amount of additives, wherein the fillers are selected from high-temperature resistant inorganic materials, and the additives include dispersants, wetting agents, and thickeners. The selection and proportion of the raw materials in the second coating 14 refer to the above-mentioned coating 12.

[0076] See also Figure 3 The second aspect of the present invention provides a method for preparing a diaphragm, the method comprising the following steps:

[0077] S1. preparing modified glass fiber;

[0078] S2. Dispersing the modified glass fiber and adhesive into water to prepare a coating slurry;

[0079] S3, applying the coating slurry on at least one side of the base film;

[0080] S4. Drying the base film coated with the coating slurry to obtain a separator.

[0081] See also Figure 4 Specifically, in step S1, the modified glass fiber is obtained by grafting the alkali-free glass fiber with a coupling agent. The modification process is as follows:

[0082] S11, ball-milling the glass fiber to obtain ultrafine glass fiber.

[0083] In this step, the glass fiber is commercially available ordinary alkali-free glass fiber, which has a softening point of 850-860°C and an expansion coefficient of 5*10 -6 / °C. Ball milling can be performed using conventional ball milling methods in the art, such as wet or dry ball milling. Ultrafine alkali-free glass fibers with a diameter of 0.5-5 μm and a length of 0.5-10 μm can be obtained through ball milling. Ultrafine alkali-free glass fibers have a large specific surface area, which increases the contact area with other components such as adhesives and fillers. The short fibers are easily dispersed and resist agglomeration, forming a stable slurry.

[0084] S12. Disperse the ultrafine glass fiber into water, add a coupling agent and a catalyst, adjust the pH of the solution to 4-5, and keep the solution warm at 40-80°C.

[0085] Step S12 is the modification process of the glass fiber. First, the ultrafine glass fiber obtained after ball milling in step S11 is dispersed into water, and then a coupling agent and a catalyst are added. The coupling agent is used to graft and modify the glass fiber, and the catalyst is used to provide an acidic environment. The pH value of the solution is adjusted to 4-5 using a catalyst. In a weakly acidic environment, the hydrolysis of the silane coupling agent can be promoted to generate silanols, and the self-condensation of silanols can be inhibited. The solution is kept warm at 40-80°C for a period of time to allow the silanols generated by the hydrolysis of the silane coupling agent to condense with the silanols on the surface of the glass fiber to form stable covalent bonds, thereby fixing the coupling agent on the surface of the glass fiber. The reaction temperature in this step is, for example, 40°C, 60°C or 80°C, and the holding time is, for example, 4-8h, specifically 4h, 6h or 8h.

[0086] In some embodiments, the coupling agent may be a silane coupling agent, including but not limited to KH550, KH792, KH560, IPTS, IPTMS, TDI, MDI, HDI, IPDI, etc. The catalyst may be an acid, including but not limited to one or more of acetic acid (CH3COOH), formic acid (HCOOH), dilute hydrochloric acid (HCl), and phosphoric acid (H3PO4). Acidic conditions can accelerate the hydrolysis of the silane coupling agent, inhibit silanol self-condensation, and form a stable monomer.

[0087] The weight proportions of glass fiber, coupling agent, and catalyst are 100 parts, 0.1 to 50 parts, and 0.1 to 10 parts, respectively. For example, the coupling agent can be 0.1 parts, 10 parts, 20 parts, 30 parts, or 50 parts, and the catalyst can be 0.1 parts, 3 parts, 5 parts, 7 parts, or 10 parts, etc. Too much or too little coupling agent is detrimental to the modification of the glass fiber. Too little coupling agent will result in incomplete modification of the glass fiber, with only a portion of the glass fiber surface being grafted with active groups. Too much coupling agent will result in the inability of the excess coupling agent molecules to fully condense, and the residual silanol groups (-SiOH) will absorb water to form a weak interface layer, affecting the performance of the coating formed subsequently. Similarly, too much or too little catalyst is also detrimental to the modification of glass fiber. Too little catalyst will cause weak acidity, incomplete hydrolysis of the silane coupling agent, and aggravate the self-condensation of the silanols generated by hydrolysis, affecting the polycondensation reaction between the glass fiber and the silanols; too much catalyst will cause excessive acidity, breaking the Si-O-Si bonds on the surface of the glass fiber and affecting its mechanical properties. In this step, the amount of water added is not limited, as long as the glass fiber, coupling agent, and catalyst are fully mixed.

[0088] S13, that is, after step S12 is completed, the glass fiber after the solution is filtered is dried in an environment of 50°C to obtain a modified glass fiber, which has an amino group, epoxy group or isocyanate group that can undergo a cross-linking reaction with the active group of the adhesive. The specific group type is related to the type of coupling agent.

[0089] Please continue reading Figure 2 , step S2 is to prepare the coating slurry. The specific process is as follows: first, the modified glass fiber, filler, dispersant and water obtained in step S1 are evenly dispersed in a high-speed disperser. For example, the high-speed dispersion is performed for 30 to 60 minutes, then the adhesive is added and the stirring is continued for 30 to 60 minutes, and then the thickener is added and the stirring is continued for 30 to 60 minutes. Finally, the wetting agent is added and the stirring is continued for 30 to 60 minutes. There is no specific restriction on the stirring time of each stage. It is only necessary to disperse the raw materials evenly. For example, the dispersion time can be 30 minutes, 40 minutes, 50 minutes or 60 minutes. In this step, the amount of water added is not limited, and the solid content of the slurry is taken as the benchmark. In some embodiments, the solid content of the coating slurry is 20 to 40%, and further, the solid content of the coating slurry is 30%. In this step, the selection of the raw material components is described above and will not be repeated here.

[0090] Step S3, coating, is a process in which the coating slurry prepared in step S2 is applied to the base film. Coating can be performed using a gravure roller or a Meyer rod for double-sided or single-sided coating. The coating thickness is 0.5 to 10 μm, for example, 1 μm, 5 μm, or 10 μm, and the vehicle speed is 10 to 200 m / min, for example, 10 m / min, 50 m / min, 100 m / min, 150 m / min, or 200 m / min.

[0091] Step S4 is to dry the base film coated with the coating slurry at an environment of 40 to 120°C to obtain a diaphragm. The specific drying temperature can be 40°C, 60°C, 80°C, 100°C or 120°C, etc. There is no limit to the drying time, as long as the coating is completely dried, for example, 8 to 24 hours. Furthermore, the drying time can be 8 hours, 12 hours, 16 hours, 20 hours or 24 hours, etc. When the diaphragm includes a base film 11, a first coating layer 13 and a second coating layer 14, its preparation method is different from the above preparation method in that: the configuration of the coating slurry in step S2 includes configuring a first coating layer slurry and a second coating layer slurry, wherein the first coating layer slurry includes a filler, an adhesive and a small amount of additives, and the second coating layer slurry is the same as the above coating layer slurry;

[0092] In step S3, when applying the slurry, the first coating slurry is first applied to the base film 11. After the first coating slurry is dried, the second coating slurry is applied to the first coating 13 and / or the base film 11. The coating method can be conventional in the art and will not be described in detail here.

[0093] A third aspect of the present invention provides a lithium-ion battery comprising the above-mentioned separator.

[0094] Those skilled in the art should know that a lithium-ion battery may also include necessary components such as a positive electrode sheet and a negative electrode sheet, wherein a separator is provided between the positive electrode sheet and the negative electrode sheet to serve as insulation and isolation.

[0095] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector. The positive electrode current collector can adopt the conventional current collector types in the art, such as aluminum foil. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and an adhesive. The positive electrode active material includes, but is not limited to, one or more of lithium nickel cobalt manganese oxide (NCM), lithium nickel oxide (LNO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium cobalt oxide (LCO), or lithium nickel cobalt aluminum oxide (NCA). These materials can be used alone or in combination. For example, the positive electrode active material is NCM, or a composition of NCM and LNO, etc. The conductive agent includes, but is not limited to, one or more of graphite, graphene, carbon black, carbon fiber, and carbon nanotube. The adhesive includes one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyvinylpyrrolidone (PVP). The proportions of the various substances in the positive electrode active material layer can be set according to the conventional proportions in the art and are not limited herein.

[0096] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector. The negative electrode current collector can adopt the conventional current collector types in the art, such as copper foil. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and an adhesive. Among them, the negative electrode active material includes a graphite material and / or a silicon material. The graphite material includes, but is not limited to, artificial graphite, natural graphite, soft carbon, hard carbon, etc.; the silicon material includes silicon oxide SiOx (0 < x < 2), silicon-carbon composite, silicon单质, etc. The conductive agent includes, but is not limited to, one or more of graphite, graphene, carbon black, carbon fiber, and carbon nanotube. The adhesive includes one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyvinylpyrrolidone (PVP). The proportions of the various substances in the negative electrode active material layer can be set according to the conventional proportions in the art and are not limited herein.

[0097] It should be noted that the term "硅单质" in the original Chinese text is translated as "silicon" in the English text. If there is a more accurate term in the context, it can be adjusted accordingly. Also, there may be some inaccuracies in the Chinese text you provided (such as an incomplete or incorrect "硅单质"), and you may want to double-check the original content for more accurate translation.The lithium-ion battery also includes an electrolyte for transmitting lithium ions. The electrolyte includes a lithium salt and an organic solvent. The present application does not limit the specific types of lithium salts and organic solvents, and lithium salts and organic solvents well known in the art can be selected. As an example, the lithium salt is selected from one or more of LiPF6, LiBF4, LiFSI, LiTFSI, LiClO4, LiAsF6, LiBOB, and LiDFOB. The organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Furthermore, some functional additives can be added to the electrolyte according to actual needs, such as ethylene sulfate (DTD), 1,3-propane sultone (PS), vinylene carbonate (VC), or vinyl ethylene carbonate (VEC).

[0098] It should be noted that the structures not described in detail in the above lithium-ion battery can be configured with reference to the existing technology and will not be described in detail here.

[0099] The technical solutions of the present invention are described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art. The instruments used in the examples are all commercially available. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in the art or in accordance with the product instructions shall be followed.

[0100] Example 1

[0101] This embodiment provides a diaphragm, which includes a base film and coatings coated on both sides of the base film, wherein the base film is a 7 μm thick PE film, and the thickness of the coating on one side is 3 μm.

[0102] The preparation process of the diaphragm is as follows:

[0103] Preparation of modified glass fiber: 100 parts by weight of commercially available ordinary alkali-free glass fiber is ball-milled into short fibers with a diameter of 0.5 μm and a length of 3 μm; deionized water, 20 parts by weight of coupling agent IPTS, and 1 part by weight of catalyst CH3COOH are added to the ball-milled glass fiber, the pH of the mixed solution is adjusted to 4-5, and the mixture is kept warm at 60°C for 6 hours; the glass fiber after the solution is filtered is dried at 50°C to obtain the modified glass fiber.

[0104] Coating slurry preparation: 100 parts by weight of alumina (particle size 0.3 μm), 20 parts by weight of modified glass fiber and 1 part by weight of sodium polyacrylate (molecular weight 1000-3000 Mw) are dispersed in water and stirred at 800 rpm for 60 minutes; 8 parts by weight of PMMA microspheres (commercially available from Zhuhai Chenyu, Tg: 60°C, particle size 5 μm) are added and stirred for 50 minutes, and then 1 part by weight of thickener CMC (commercially available, degree of substitution 0.6) is added and stirred for 30 minutes, and then 8 parts by weight of polyacrylate (commercially available from Zhuhai Chenyu, Tg: 180°C) are added and stirred for 30 minutes, and then 1.5 parts by weight of wetting agent (BASF ET-3061) are added and stirred for 30 minutes to obtain a coating slurry with a solid content of 30%.

[0105] Coating: The coating slurry was evenly coated on a 7 μm thick PE base film, and placed in a blast oven at 80°C for drying to obtain a double-sided coated diaphragm, with the thickness of the coating on one side being 3 μm.

[0106] Example 2

[0107] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the amount of modified glass fiber added is 25 parts by weight.

[0108] Example 3

[0109] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the amount of modified glass fiber added is 10 parts by weight.

[0110] Example 4

[0111] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the amount of modified glass fiber added is 1 part by weight.

[0112] Example 5

[0113] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the amount of modified glass fiber added is 50 parts by weight.

[0114] Example 6

[0115] The difference between this embodiment and embodiment 1 is that the amount of coupling agent IPTS added during the preparation of the modified glass fiber is 25 parts by weight.

[0116] Example 7

[0117] The difference between this embodiment and embodiment 1 is that the amount of coupling agent IPTS added during the preparation of the modified glass fiber is 10 parts by weight.

[0118] Example 8

[0119] The difference between this embodiment and embodiment 1 is that the amount of coupling agent IPTS added during the preparation of the modified glass fiber is 0.1 parts by weight.

[0120] Example 9

[0121] The difference between this embodiment and embodiment 1 is that the amount of coupling agent IPTS added during the preparation of the modified glass fiber is 50 parts by weight.

[0122] Example 10

[0123] The difference between this embodiment and embodiment 1 is that the amount of coupling agent IPTS added during the preparation of the modified glass fiber is 25 parts by weight, and the amount of modified glass fiber added during the preparation of the coating slurry is 25 parts by weight.

[0124] Example 11

[0125] The difference between this embodiment and embodiment 1 is that the coupling agent IPTS is replaced by KH550 during the preparation of the modified glass fiber.

[0126] Example 12

[0127] The difference between this embodiment and embodiment 1 is that the coupling agent IPTS is replaced by KH560 during the preparation of the modified glass fiber.

[0128] Example 13

[0129] The difference between this embodiment and embodiment 1 is that the amount of catalyst CH3COOH added during the preparation of the modified glass fiber is 0.1 parts by weight.

[0130] Example 14

[0131] The difference between this embodiment and embodiment 1 is that the amount of catalyst CH3COOH added during the preparation of the modified glass fiber is 10 parts by weight.

[0132] Example 15

[0133] The difference between this embodiment and embodiment 1 is that the catalyst CH3COOH is replaced by HCl during the preparation of the modified glass fiber.

[0134] Example 16

[0135] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the filler alumina is replaced by boehmite.

[0136] Example 17

[0137] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the filler aluminum oxide is replaced by lithium iron phosphate.

[0138] Example 18

[0139] The difference between this embodiment and embodiment 1 is that during the preparation of the coating slurry, the filler aluminum oxide is replaced by barium titanate.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that no re-lined glass fiber is added during the preparation of the coating slurry.

[0142] Comparative Example 2

[0143] The difference between this comparative example and Example 1 is that during the preparation of the coating slurry, the glass fiber is unmodified glass fiber.

[0144] The diaphragms prepared in Examples 1-18 and Comparative Examples 1-2 were tested. The test results are shown in Table 1. The test method is as follows:

[0145] (1) Peel force

[0146] The diaphragm sample was cut into 25 mm × 200 mm strips along the coating direction, and 3M9080A double-sided tape was attached to the steel plate. A 2 kg rubber stick was used to attach the sample at 5 mm / s, and the peel strength test was performed on a universal tensile testing machine.

[0147] (2) Adhesion

[0148] The electrode (double-sided coated positive electrode, ternary material MCN 523, electrode thickness 120μm, aluminum foil thickness 15μm) and the separator sample were stacked together and hot-pressed for 60 seconds at a pressure of 1MPa to 3MPa and a temperature of 60°C to 85°C to bond the separator and electrode together. The bonded sample was cut into 25mm x 200mm strips and then subjected to adhesion testing on a universal tensile testing machine.

[0149] (3) Thermal shrinkage

[0150] The diaphragm of each embodiment / comparative example was cut into 100 mm*100 mm dimensions. The initial dimension l0 was recorded using an imager. The samples were placed in a constant temperature oven at 150°C, 180°C, and 200°C for 1 hour. The post-test dimension l1 of the samples was then recorded. The thermal shrinkage ratio was calculated as (l0-l1) / l0*100%.

[0151] Table 1: Test results of the separators of Examples 1-18 and Comparative Examples 1-2

[0152]

[0153]

[0154] As can be seen from Table 1, compared with Comparative Example 1, Examples 1-5 add modified glass fibers to the diaphragm coating, and the thermal shrinkage, peeling force and bonding force of the diaphragm are significantly improved, especially when the modified glass fiber addition amount is 10 to 25 parts by weight, the thermal shrinkage of the diaphragm at high temperatures of 150°C, 180°C, and 200°C is less than 5%; this shows that the low expansion coefficient and high thermal stability of the modified glass fiber significantly improve the heat resistance of the diaphragm. In addition, the modified glass fiber and the adhesive undergo cross-linking during the coating process to form a stable three-dimensional network structure. This network structure not only significantly improves the interfacial bonding and cohesive force of the coating, but also inhibits particle migration and interfacial peeling at high temperatures. Although glass fiber is added to Comparative Example 2, the glass fiber is not modified by a coupling agent. Based on the low expansion of the glass fiber itself, the heat resistance of the diaphragm is improved, but the improvement effect is not good compared to the modified glass fiber, and the bonding force is not improved. This is because the unmodified glass fiber has no active groups and cannot be cross-linked with the adhesive to form a network structure.

[0155] Comparing Example 1 with Examples 6-10, the amount of coupling agent IPTS added during the glass fiber modification process varied between Examples. When too little IPTS was added, the heat resistance and adhesion of the separator decreased. When too much coupling agent was added, although the heat resistance remained unchanged, the adhesion did not significantly improve. This is because the appropriate amount of coupling agent fully contacted the glass fiber and grafted active groups onto the glass fiber surface. Too little coupling agent did not fully modify the glass fiber, resulting in limited improvement in separator performance. Too much coupling agent completely modified the glass fiber, and the excess coupling agent was filtered out.

[0156] Comparing Example 1, Example 11 and Example 12, the types of coupling agents in each example are different. Although each coupling agent has a significant improvement effect, it is found that IPTS has the best improvement effect.

[0157] Comparing Example 1 and Examples 13-15, the amount of catalyst added or the type of catalyst is different between the examples. The type of catalyst has little effect on the modification results. Insufficient addition of the catalyst will lead to a decrease in the heat resistance and adhesion of the diaphragm. This is because the role of the catalyst in the glass fiber modification process is to provide a weak acid environment. If the addition amount is insufficient, the silane coupling agent is not completely hydrolyzed, and the self-condensation of the silanol generated by hydrolysis is aggravated, affecting the condensation reaction between the glass fiber and the silanol, thereby affecting the heat resistance and adhesion properties of the diaphragm.

[0158] Comparing Example 1 with Examples 16-18, the types of fillers in each example are different. The test results show that the type of filler has little effect on the heat resistance and adhesion of the diaphragm.

[0159] The diaphragm provided by the present invention adds modified glass fiber to the coating layer. The low expansion coefficient and high thermal stability of the modified glass fiber significantly improve the heat resistance of the diaphragm. In addition, the modified glass fiber and the adhesive are cross-linked during the coating process to form a stable three-dimensional network structure. This network structure not only significantly improves the interfacial bonding and cohesive force of the coating, but also effectively inhibits particle migration and interfacial peeling at high temperatures, giving the coating excellent creep resistance. In addition, the introduction of modified glass fiber also greatly improves the mechanical properties of the coating, such as tensile strength and impact resistance, and reduces the risk of cracking of the coating. The modified glass fiber has the advantages of being green and environmentally friendly. Its production process does not require highly polluting solvents, and the glass fiber itself is recyclable. Compared with traditional polymer fibers, it has lower production energy consumption and a simpler modification process. It is very suitable for large-scale industrial applications, and is particularly suitable for fields such as lithium battery diaphragms and high-temperature protective coatings that have strict requirements on material properties. Therefore, the present invention effectively overcomes some practical problems in the prior art and has high utilization value and use significance.

[0160] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A diaphragm, characterized in that: include: basement membrane; a coating layer disposed on at least one side of the base film; Wherein, the coating comprises modified glass fibers and an adhesive, and the modified glass fibers and the adhesive are cross-linked to form a network structure.

2. The diaphragm according to claim 1, characterized in that The modified glass fiber has one or more of an isocyanate group, an amino group, and an epoxy group.

3. The diaphragm according to claim 1, characterized in that The adhesive includes at least one of polyacrylate, PMMA microspheres, polyurethane, polyvinyl alcohol, styrene, butadiene copolymer, and polyvinylidene fluoride.

4. The diaphragm according to claim 3, characterized in that The adhesive comprises PMMA microspheres, which are core-shell structures. The core of the PMMA microspheres comprises at least one of styrene, acrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polyacrylamide, and the shell comprises acrylic acid monomers.

5. The diaphragm according to claim 1, characterized in that The adhesive has one or more of hydroxyl groups, carboxyl thiol groups, amide groups, amino groups, and epoxy groups.

6. The diaphragm according to claim 1, characterized in that The modified glass fiber has a diameter of 0.5 to 5 μm and a length of 0.5 to 10 μm.

7. The diaphragm according to claim 1, characterized in that The coating comprises the following raw materials in parts by weight: 0.1 to 50 parts of modified glass fiber and 2.5 to 40 parts of adhesive.

8. The diaphragm according to claim 7, characterized in that The coating further comprises 80 to 100 parts of a filler, 0.1 to 3 parts of a dispersant, 0.01 to 3 parts of a wetting agent and 0.5 to 3 parts of a thickener.

9. The diaphragm according to claim 8, characterized in that Include at least one of the following characteristics: The filler includes one or more of alumina, boehmite, barium titanate, barium sulfate, silicon dioxide, magnesium hydroxide, lithium aluminum titanium phosphate, lithium iron phosphate, and ternary positive electrode materials; The dispersant includes one or more of polyphosphate, polycarboxylate, acrylic acid copolymer, and acrylic acid copolymer; The wetting agent includes one or more of an organosilicon wetting agent, an acetylene glycol wetting agent, and a non-ionic wetting agent; The thickener includes one or more of polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose.

10. The diaphragm according to claim 1, wherein The thickness of the coating is 1 to 8 μm.

11. A diaphragm, characterized in that: include: basement membrane; a first coating layer disposed on at least one side of the base film, the first coating layer comprising a filler; The second coating layer is arranged on the first coating layer and / or the base film. The second coating layer includes modified glass fibers and an adhesive. The modified glass fibers and the adhesive are cross-linked to form a network structure.

12. A method for preparing a diaphragm, characterized in that: The following steps are involved: preparing modified glass fibers; Dispersing the modified glass fiber and adhesive in water to prepare a coating slurry; applying the coating slurry on at least one side of a base film; drying the base film coated with the coating slurry to obtain a diaphragm; During the coating process, the modified glass fiber and the adhesive are cross-linked to form a network structure.

13. The method for preparing a diaphragm according to claim 12, characterized in that: The steps of preparing the modified glass fiber include: The glass fibers are ball-milled to obtain ultrafine glass fibers, wherein the diameter of the ball-milled glass fibers is 0.5 to 5 μm and the length is 0.5 to 10 μm; Dispersing the ultrafine glass fibers into water, adding a coupling agent and a catalyst, adjusting the pH of the solution to 4-5, and keeping the solution at 40-80° C.; After the insulation is completed, the modified glass fiber is obtained by filtration and drying.

14. The method for preparing a diaphragm according to claim 13, wherein: In the step of preparing the modified glass fiber, the added amounts of the raw materials are: 100 parts of glass fiber, 0.1 to 50 parts of coupling agent, and 0.1 to 10 parts of catalyst.

15. The method for preparing a diaphragm according to claim 13, wherein: The coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-isocyanatepropyltrimethoxysilane, isocyanate toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

16. The method for preparing a diaphragm according to claim 13, wherein: The catalyst includes one or more of acetic acid, formic acid, dilute hydrochloric acid, and phosphoric acid.

17. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator according to any one of claims 1 to 11 or is prepared by the preparation method according to any one of claims 12 to 16.

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