Battery separator, method for manufacturing the same, and lithium ion battery

Abstract

The application discloses a battery diaphragm, a preparation method thereof and a lithium ion battery, and relates to the technical field of battery diaphragms, in particular to a battery diaphragm, a preparation method thereof and a lithium ion battery. The battery diaphragm comprises a diaphragm base layer, a ceramic layer arranged on at least one side surface of the diaphragm base layer, and a reinforcing coating layer arranged on the surface of the ceramic layer. The reinforcing coating layer comprises a bonding matrix and modified aluminum silicate fibers dispersed in the bonding matrix. The modified aluminum silicate fibers are aluminum silicate fibers which are surface modified by a silane coupling agent. The battery diaphragm uses the aluminum silicate fibers which are surface modified by the silane coupling agent as a reinforcing phase, disperses the aluminum silicate fibers in the bonding matrix, can improve the interfacial bonding force between the aluminum silicate fibers and the bonding matrix, effectively disperses stress concentration, improves the mechanical properties, durability and thermal stability of the battery diaphragm, and when applied to the lithium ion battery, can effectively improve the heat resistance and safety performance of the battery.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in electronic products, energy storage devices, and electric vehicles. With their expanding applications, battery safety has become a critical issue. The separator, a vital component of the battery, primarily prevents short circuits caused by direct contact between the positive and negative electrodes. However, traditional separators often suffer from insufficient mechanical properties and thermal stability, making them prone to failure under high-temperature conditions, leading to battery thermal runaway and safety problems. Therefore, a method is needed to enhance battery thermal stability and mechanical properties to ensure battery safety in high-temperature environments. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a battery separator, a method for preparing the same, and a lithium-ion battery.

[0004] A first aspect of the present invention provides a battery separator comprising:

[0005] Diaphragm base layer;

[0006] A ceramic layer is disposed on at least one surface of the diaphragm base layer;

[0007] A reinforcing coating is disposed on the ceramic layer on the surface opposite to the membrane base layer; the reinforcing coating includes an adhesive matrix and modified aluminum silicate fibers dispersed in the adhesive matrix; the modified aluminum silicate fibers are aluminum silicate fibers surface-modified with a silane coupling agent.

[0008] According to the embodiments of the present invention, the battery separator has at least the following beneficial effects: the battery separator uses aluminum silicate fibers modified with silane coupling agent as the reinforcing phase, and the modified aluminum silicate fibers are uniformly dispersed in the bonding matrix to form a reinforcing coating on the surface of the separator base layer. Among them, aluminum silicate fibers have high strength and high modulus. Introducing them into the coating can significantly improve the strength and toughness of the coating. Specifically, aluminum silicate fibers modified with silane coupling agents are used. The modified aluminum silicate fibers can react with the bonding matrix to form a strong interfacial bond, further improving the mechanical strength and durability of the battery separator and reducing the risk of mechanical damage. In addition, the presence of modified aluminum silicate fibers in the coating can effectively disperse stress, reduce stress concentration, and avoid material peeling and cracking at the interface, thereby improving the overall tensile, puncture, and compression resistance of the separator. Furthermore, aluminum silicate fibers have excellent thermal stability and a high melting point. When the coating is subjected to high temperatures, aluminum silicate fibers can maintain the integrity of its structure and prevent the coating from undergoing significant thermal shrinkage. The skeletal effect of the fibers can also provide additional thermal stability to the coating, ensuring the dimensional stability of the coating at high temperatures, reducing the thermal shrinkage rate of the separator, reducing the possibility of separator melting and deformation, and improving the high-temperature resistance of the battery separator. This battery separator can be further applied to lithium-ion batteries, which can improve the safety of lithium-ion batteries, especially under high temperature or overcharge conditions, effectively preventing the separator from shrinking or being damaged, and preventing internal short circuits in the battery.

[0009] Specifically, under high-temperature environments such as during operation or overcharging of traditional lithium-ion batteries, the separator material may shrink due to thermal effects, leading to pore structure collapse or pore size changes. This affects ion transport and battery performance, and may even cause internal short circuits, posing safety risks. By employing aluminosilicate fibers with high melting points and excellent thermal stability—specifically, surface-modified aluminosilicate fibers with silane coupling agents as a reinforcing phase, uniformly dispersed within the binder matrix to form a reinforcing coating on the separator base layer—this shrinkage phenomenon can be reduced. The modified aluminosilicate fibers, acting as a skeletal structure dispersed within the coating, maintain the integrity of the coating structure at high temperatures, preventing dimensional changes under high-temperature conditions and improving battery safety and reliability.

[0010] In some embodiments of the present invention, the needle penetration strength of the battery separator is 300-500 gf; the ionic conductivity is ≥6.0 mS / cm; and the thermal shrinkage rate is <3% at 130°C.

[0011] In some embodiments of the present invention, the thickness of the reinforcing coating is 1 μm to 4 μm. For example, the thickness of the reinforcing coating can be controlled to be 1 μm, 1.5 μm, 2 μm, 3 μm, 3.5 μm, 4 μm, etc.

[0012] In some embodiments of the present invention, the thickness ratio of the diaphragm base layer, the ceramic layer, and the reinforcing coating is 6-8:0.5-1.5:0.5-1.5.

[0013] In some embodiments of the present invention, the modified aluminosilicate fibers account for 5% to 9% of the mass of the adhesive matrix. Further, the modified aluminosilicate fibers account for 5% to 8%, 6% to 8%, or 7% to 9% of the mass of the adhesive matrix.

[0014] In some embodiments of the present invention, the silane coupling agent contains at least one of amino, hydroxy, and epoxy groups; or, the silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane (KH550), γ-methacryloyloxypropyltrimethoxysilane (KH570), γ-chloropropyltrichlorosilane (CPTMS), γ-glycidoxypropyltrimethoxysilane (KH560), N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (DL602), N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane (KH792), γ-mercaptopropyltrimethoxysilane (KH590), aminopropyltriethoxysilane (APTES), and glycidoxypropyltriethoxysilane (GPTMS). Specifically, one of these agents can be used alone, or two or other combinations thereof can be used. For example, the silane coupling agent can be a combination of γ-aminopropyltriethoxysilane (KH550) and γ-methacryloyloxypropyltrimethoxysilane (KH570), and the mass ratio of KH550 to KH570 can be controlled to be 1:1 to 3:1.

[0015] The surface of aluminosilicate fibers mainly contains silicon-oxygen (Si-O) and hydroxyl (-OH) groups. Silane coupling agents can react and bond with these groups. The hydroxyl groups on the aluminosilicate fibers can react with the epoxy groups of the coupling agent, causing the coupling agent to adhere completely around the fiber. The coupling agent itself has many polar groups, thus achieving surface modification of the aluminosilicate fibers. The above-mentioned surface modification of aluminosilicate fibers using silane coupling agents can generate silicon-oxygen bonds on the fiber surface and introduce functional groups (such as hydroxyl, amino, and epoxy groups). These polar or reactive groups can chemically bond with the binder or form strong interfacial interactions, thereby enhancing the bonding force between the fiber and the binder.

[0016] In some embodiments of the present invention, the adhesive matrix is ​​made of any one of organic coating materials such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). Silane coupling agent-modified aluminosilicate fibers are dispersed in the adhesive matrix. The surface of the modified aluminosilicate fibers carries amino, hydroxyl, or other polar groups. These polar groups can react with polar molecules in the adhesive matrix to form a strong interfacial bond, thereby improving the mechanical strength of the battery separator.

[0017] In some embodiments of the present invention, the mass ratio of the silane coupling agent to the aluminosilicate fiber is 1:1 to 3. For example, the mass ratio of the silane coupling agent to the aluminosilicate fiber may be 1:1, 1:1.5, 1:2, or 1:3.

[0018] In some embodiments of the present invention, the modified aluminosilicate fiber has a fiber diameter of 500–1500 nm and a specific surface area of ​​10–20 m². 2 / g. If the diameter of the modified aluminosilicate fibers is less than 500nm, the preparation difficulty and cost increase, and the fibers may over-accumulate in the coating, affecting the pore structure. If the fiber diameter exceeds 1500nm, the specific surface area decreases, the fiber reinforcement effect weakens, and the uniformity and adhesion of the coating performance are affected. Furthermore, fibers with too small a specific surface area (corresponding to a larger diameter) have insufficient surface contact area, weakening the interfacial adhesion between the fibers and the bonding matrix, affecting the mechanical properties and durability of the coating. Also, a small specific surface area means fewer fibers per unit mass, failing to form a sufficiently dense network structure, which weakens the enhancement effect on the overall strength of the coating. Therefore, controlling the fiber diameter and specific surface area of ​​the modified aluminosilicate fibers within the above ranges can ensure the strength, uniformity, and durability of the enhanced coating, while reducing the preparation difficulty and cost.

[0019] A ceramic layer is disposed on at least one surface of the separator base layer. The ceramic layer is made of inorganic ceramic materials, which improves the high-temperature resistance of the battery separator. First, the inorganic ceramic materials in the ceramic layer, distributed on the separator base layer, can form a rigid framework. Due to their excellent thermal stability, they can effectively prevent the separator from shrinking and melting under thermal runaway conditions, thus improving the thermal stability of the battery separator. Second, the thermal conductivity and other properties of the inorganic ceramic materials in the ceramic layer can further prevent certain thermal runaway points in the battery from expanding into overall thermal runaway, thereby improving battery safety.

[0020] In some embodiments of the present invention, the inorganic ceramic material is selected from one or more of Al2O3, SiO2, TiO2, Al(OH)3, MgO, Mg(OH)2, BrSO4, ZrO2, montmorillonite, and boehmite.

[0021] In some embodiments of the present invention, the inorganic ceramic material in the ceramic layer is selected from amphoteric oxides, i.e., oxides that are alkaline in the presence of strong acids and acidic in the presence of strong bases. For example, the inorganic ceramic material can be at least one of amphiphilic oxides such as Al2O3, TiO2, and ZrO2. By using amphoteric oxides as the inorganic ceramic material, the inorganic ceramic material in the battery separator can partially absorb impurities such as HF generated in the electrolyte due to the presence of trace amounts of water, thereby improving the battery's lifespan.

[0022] In some embodiments of the present invention, the ceramic layer further includes an adhesive. The adhesive may be any one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), or polymethyl methacrylate (PMMA).

[0023] Furthermore, the ceramic layer includes a binder matrix and inorganic ceramic materials dispersed in the binder matrix. The binder matrix is ​​constructed using a binder, and the binder matrix material in the ceramic layer may be the same as or different from the binder matrix material in the reinforcing coating.

[0024] In some embodiments of the present invention, the material of the diaphragm base layer is selected from at least one of polypropylene and polyethylene; and / or, the diaphragm base layer is a porous diaphragm base layer.

[0025] A second aspect of the present invention provides a method for preparing any of the aforementioned battery separators, comprising the following steps:

[0026] A ceramic layer is disposed on at least one surface of the diaphragm base layer;

[0027] Alumina silicate fibers were placed in a silane coupling agent solution for surface modification treatment to obtain modified alumina silicate fibers.

[0028] Modified aluminosilicate fibers are mixed with binders and solvents to prepare a coating slurry;

[0029] The coating slurry is applied to the ceramic layer on the surface away from the membrane base layer and cured to obtain a battery separator.

[0030] The above preparation method involves first modifying the surface of aluminosilicate fibers with a silane coupling agent to imbue the surface with functional groups (generally polar groups, such as hydroxyl or amino groups) for better adhesion to the binder. Specifically, the enhanced chemical interaction between the polar groups on the modified aluminosilicate fibers and the binder improves the mechanical properties of the resulting coating; furthermore, the surface-modified aluminosilicate fibers exhibit better dispersibility, reducing aggregation and improving the uniformity and performance consistency of the coating.

[0031] In some embodiments of the present invention, a ceramic layer is formed on at least one surface of the diaphragm base layer, comprising: preparing a ceramic slurry by mixing raw materials including inorganic ceramic materials and binders with a solvent; then coating the ceramic slurry onto at least one surface of the diaphragm base layer and drying to obtain the ceramic layer. The solvent may be N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), etc.

[0032] In some embodiments of the present invention, before surface modification treatment of the aluminosilicate fibers, the method further includes: preparing aluminosilicate fibers using raw materials comprising an aluminum source, a silicon source, and a grain inhibitor via electrospinning. Specifically, this includes: mixing the aluminum source and the silicon source with an organic solvent, stirring until the solution is clear, and drying to obtain a dry gel; then mixing the dry gel with a solvent, adding a spinning aid, and mixing to obtain a precursor solution; electrospinning the precursor solution to obtain spun fibers, which are then successively dried and heat-treated to obtain aluminosilicate fibers.

[0033] The aluminum source can be anhydrous aluminum chloride, aluminum isopropoxide, aluminum nitrate nonahydrate, etc.; anhydrous aluminum chloride is preferred. Aluminum isopropoxide, as an organoaluminum source, can hydrolyze under specific conditions to generate aluminum oxide; aluminum nitrate nonahydrate can hydrolyze and provide aluminum ions, but it requires dehydration treatment.

[0034] Tetraethyl orthosilicate can be used as both the silicon source and the grain inhibitor. While providing the silicon source, tetraethyl orthosilicate can also inhibit grain formation during the fiber forming process, which helps to control the generated silicon oxide structure and prevent excessively rapid crystallization from increasing fiber brittleness.

[0035] The organic solvent used for mixing with the aluminum source and silicon source can be one or more of the following organic solvents: ethanol, methanol, isopropanol, isopropyl ether, anhydrous methane, etc. For example, a mixture of isopropyl ether and anhydrous methane can be used.

[0036] The solvent used for mixing with the dry gel can be an alcohol solvent, specifically a low alcohol solvent such as methanol, anhydrous ethanol, propanol, or isopropanol. The uniformity of the precursor solution can be adjusted by the solvent to ensure the uniformity of fiber formation.

[0037] The spinning aid can be one or more polymeric spinning aids selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyacrylonitrile (PAN). The addition of the spinning aid increases the viscosity of the precursor solution, which helps to form uniform and continuous fibers during spinning. Alternatively, the spinning aid can be added in the form of a solution prepared by mixing it with a solvent. Using a solvent helps dissolve the spinning aid, facilitates uniform mixing of the aid in the precursor solution, and adjusts the viscosity of the precursor solution to obtain a precursor solution with suitable spinning flowability. The solvent can be N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), etc., and the specific effects on solution viscosity and spinning effect need to be investigated.

[0038] During the preparation of aluminosilicate fibers, the drying temperature can be controlled between 60℃ and 100℃ or between 70℃ and 100℃, such as 60℃, 65℃, 70℃, 80℃, 85℃, 90℃, 100℃, etc.; the heat treatment temperature can be controlled between 700℃ and 900℃, such as 700℃, 720℃, 750℃, 760℃, 800℃, 850℃, 900℃, etc.

[0039] In some embodiments of the present invention, the silane coupling agent solution can be prepared by mixing the silane coupling agent with a solvent, wherein the mass ratio of the silane coupling agent to the solvent can be controlled to be 1:10 to 1:20, such as 1:12, 1:15, 1:18, etc.; the solvent can be anhydrous ethanol or isopropanol.

[0040] In some embodiments of the present invention, when aluminum silicate fibers are placed in a silane coupling agent solution, the mass ratio of silane coupling agent to aluminum silicate fibers is controlled to be 1:1 to 4.

[0041] In some embodiments of the present invention, during the preparation of the coating slurry, the mass ratio of modified aluminum silicate fiber to binder is controlled to be 5% to 9%.

[0042] In some embodiments of the present invention, a coating slurry is prepared by mixing modified aluminosilicate fibers with an adhesive and a solvent. Specifically, this includes: first mixing the adhesive and solvent to obtain an adhesive solution; and then dispersing the modified aluminosilicate fibers in the adhesive solution to obtain the coating slurry. The solvent may be N-methylpyrrolidone (NMP) or N,N-dimethylacetamide (DMAC), and the mass concentration of the adhesive solution may be controlled at 10% to 15%.

[0043] In some embodiments of the present invention, the modified aluminosilicate fibers are dispersed in the binder solution, specifically including: adding the modified aluminosilicate fibers to the binder solution, followed by sequential ultrasonic dispersion and mechanical stirring. If conventional mechanical stirring is used, the modified aluminosilicate fibers may agglomerate, leading to uneven coating reinforcement or even localized failure. By employing a dispersion method combining ultrasonic dispersion and mechanical stirring, the modified aluminosilicate fibers can be uniformly dispersed in the binder solution, ensuring that the aluminosilicate fibers in the reinforced coating are uniformly dispersed within the binder matrix, thereby enhancing the mechanical properties of the battery separator.

[0044] In some embodiments of the present invention, after the coating slurry is applied to the surface of the ceramic layer, thermal curing is employed. After curing, the binder solution forms a cured matrix, and the modified aluminum silicate fibers are uniformly dispersed in the binder matrix, thereby forming a reinforcing coating on the surface of the separator base layer to obtain the battery separator. The thermal curing temperature can be controlled at 150℃~200℃, 160℃~200℃, 170℃~180℃, or 165℃~185℃. By performing thermal curing at around 180℃, the crystallinity and mechanical properties of the binder matrix formed by the cured binder solution can reach a superior state, thereby improving the overall performance of the reinforcing coating.

[0045] A third aspect of the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, wherein the separator is any of the aforementioned battery separators. Detailed Implementation

[0046] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment proposes a battery separator, comprising a separator base layer, a ceramic layer, and a reinforcing coating. The ceramic layer is disposed on both sides of the separator base layer, and the reinforcing coating is disposed on the surface of the ceramic layer facing away from the separator base layer. The reinforcing coating comprises a binder matrix and modified aluminosilicate fibers dispersed in the binder matrix. The modified aluminosilicate fibers are aluminosilicate fibers surface-modified with a silane coupling agent. The silane coupling agent is a mixture of γ-aminopropyltriethoxysilane (KH550) and γ-methacryloyloxypropyltrimethoxysilane (KH570) in a mass ratio of 1:2. The separator base layer is a polyethylene film with a thickness of 7 μm; the reinforcing coating has a thickness of 1 μm, and the mass of the modified aluminosilicate fibers in the reinforcing coating accounts for 5% of the mass of the binder matrix. The binder matrix is ​​made of polyvinylidene fluoride (PVDF).

[0049] The preparation method of the battery separator is as follows:

[0050] S1. Preparation of aluminum silicate fibers. Specifically, this includes: First, weighing 0.4g of anhydrous aluminum chloride and placing it in a 100ml beaker, then adding 0.22ml of tetraethyl orthosilicate using a pipette; next, slowly adding 3.5ml of isopropyl ether and 15ml of anhydrous dichloromethane, stirring magnetically at a constant temperature until the solution becomes clear. The resulting solution is then dried in a 100℃ drying oven to obtain a dry gel. 10.5ml of anhydrous ethanol is poured into the prepared dry gel, followed by the addition of 0.5g of polyvinylpyrrolidone (PVP, molecular weight 1.3 million) and 1.5ml of... N,N-dimethylformamide was stirred until homogeneous to obtain a precursor solution. The precursor solution was then electrospun using a 0.8 mm needle, with a voltage of 23 kV, a flow rate of 2 ml / h, and a distance of 17.6 cm between the needle and the receiving plate. After spinning, the collected spun fibers were placed in an 80°C drying oven for 16 h. The dried fibers were then heat-treated in an 800°C box-type resistance furnace for 1 h to obtain flexible aluminosilicate fibers with a diameter of approximately 600 nm and a specific surface area of ​​approximately 15 m² / g.

[0051] S2. Dissolve the silane coupling agent in anhydrous ethanol at a mass ratio of 1:10 to obtain a silane coupling agent solution. Place the aluminosilicate fibers obtained in step S1 into the silane coupling agent solution at a mass ratio of 1:1 and react at 60°C for 2 hours. Then, dry the solution to obtain modified aluminosilicate fibers with active groups on the surface. Dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 10% PVDF solution. Add the modified aluminosilicate fibers obtained in step S2 to the PVDF solution at a mass ratio of 5% of the PVDF. First, perform ultrasonic dispersion to promote uniform dispersion of the modified aluminosilicate fibers in the solution. Then, mechanically stir for 2.5 hours to ensure uniform dispersion of the modified aluminosilicate fibers in the mixed solution to obtain a coating slurry.

[0052] S3. Using a 7μm thick polyethylene membrane as the separator base layer, the inorganic ceramic material is a combination of alumina (Al2O3) and titanium dioxide (TiO2) in a mass ratio of 7:3. The inorganic ceramic material, binder and solvent DMF are mixed in a mass ratio of 9:1:13.5 to prepare a ceramic slurry. The ceramic slurry is coated on both sides of the separator base layer to form a ceramic layer with a thickness of 1μm. Then, the coating slurry obtained in step S3 is coated on the surface of the ceramic layer. After drying, a reinforcing coating with a thickness of 1μm is obtained. The total thickness of the reinforcing coating on the battery separator is 2μm.

[0053] Example 2

[0054] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that the modified aluminum silicate fiber is added to the PVDF solution according to the amount of modified aluminum silicate fiber being 3% of the mass of PVDF. Other structures and preparation operations are the same as in Embodiment 1.

[0055] Example 3

[0056] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that the modified aluminum silicate fiber is added to the PVDF solution according to the amount of modified aluminum silicate fiber being 8% of the mass of PVDF. Other structures and preparation operations are the same as in Embodiment 1.

[0057] Example 4

[0058] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that the modified aluminum silicate fiber is added to the PVDF solution according to the amount of modified aluminum silicate fiber being 10% of the mass of PVDF. Other structures and preparation operations are the same as in Embodiment 1.

[0059] Example 5

[0060] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that the mass ratio of silane coupling agent to aluminum silicate fiber is 1:0.5, while the other structures and preparation operations are the same as in Embodiment 1.

[0061] Example 6

[0062] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that the mass ratio of silane coupling agent to aluminum silicate fiber is 1:3, while the other structures and preparation operations are the same as in Embodiment 1.

[0063] Example 7

[0064] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that the mass ratio of silane coupling agent to aluminum silicate fiber is 1:4, while the other structures and preparation operations are the same as in Embodiment 1.

[0065] Example 8

[0066] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that a polyethylene film with a thickness of 7 μm is used as the separator base layer, and a ceramic layer with a thickness of 1 μm is first set on both sides of the separator base layer; then the coating slurry obtained in step S3 is coated only on the surface of the ceramic layer on one side, and a reinforced coating with a thickness of 1 μm is obtained after drying.

[0067] Example 9

[0068] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that a polyethylene film with a thickness of 7 μm is used as the separator base layer, and a ceramic layer with a thickness of 1 μm is first set on both sides of the separator base layer; then the coating slurry obtained in step S3 is coated only on the surface of the ceramic layer on one side, and a reinforced coating with a thickness of 2 μm is obtained after drying.

[0069] Example 10

[0070] This embodiment proposes a battery separator. The difference between this embodiment and Embodiment 1 is that a polyethylene film with a thickness of 7 μm is used as the separator base layer, and a ceramic layer with a thickness of 1 μm is first set on both sides of the separator base layer; then the coating slurry obtained in step S3 is coated on the surface of the ceramic layer, and a reinforcing coating with a thickness of 2 μm is obtained after drying treatment. The total thickness of the reinforcing coating on the battery separator is 4 μm.

[0071] Comparative Example 1

[0072] This comparative example presents a battery separator. The difference between this comparative example and Example 1 is that this comparative example uses a 2μm thick PVDF coating instead of the reinforcing coating in Example 1; that is, modified aluminum silicate fibers are not added to the PVDF coating in this comparative example. The other structures are the same as in Example 1. The preparation method of this battery separator is as follows:

[0073] A polyethylene film with a thickness of 7 μm was used as the diaphragm base layer. A ceramic layer with a thickness of 1 μm was first set on both sides of the diaphragm base layer. PVDF was dissolved in water to obtain a PVDF solution, and the PVDF solution was coated on the surface of the ceramic layer. After drying, a PVDF coating with a thickness of 1 μm was prepared.

[0074] Comparative Example 2

[0075] This comparative example presents a battery separator. The difference between this comparative example and Example 1 is that step S2 in the battery separator preparation process differs from that of Example 1. In step S2 of this comparative example, the silane coupling agent, aluminum silicate fiber, and PVDF are directly mixed in a solvent of water to prepare the coating slurry. Other operations are similar to those in Example 1. The specific preparation method is as follows:

[0076] S1, the operation is the same as step S1 in Example 1;

[0077] S2. Dissolve the silane coupling agent in anhydrous ethanol at a mass ratio of 1:10 to obtain a silane coupling agent solution; dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 10% PVDF solution; place the aluminosilicate fiber, silane coupling agent, and PVDF solution obtained in step S1 in a round-bottom flask at a mass ratio of 1:1:20, and perform ultrasonic dispersion and mechanical stirring sequentially to obtain a coating slurry;

[0078] S3. Similar to step S3 in Example 1, a polyethylene film with a thickness of 7 μm is used as the diaphragm base layer. A ceramic layer with a thickness of 1 μm is first set on both sides of the diaphragm base layer. Then, the coating slurry obtained in step S2 is coated on the surface of the ceramic layer and dried to obtain a reinforced coating with a thickness of 1 μm.

[0079] Comparative Example 3

[0080] This comparative example presents a battery separator. The difference between this comparative example and Example 1 is that step S2 in the preparation process of the battery separator in this comparative example differs from that in Example 1. In step S2 of this comparative example, a silane coupling agent is first mixed with PVDF for modification, and then aluminum silicate fibers are added to prepare a coating slurry. Other operations are similar to those in Example 1. The specific preparation method is as follows:

[0081] S1, the operation is the same as step S1 in Example 1;

[0082] S2. Dissolve the silane coupling agent in anhydrous ethanol at a mass ratio of 1:10 to obtain a silane coupling agent solution; dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 10% PVDF solution; place the silane coupling agent solution and PVDF solution in a round-bottom flask at a mass ratio of 1:20 to obtain a mixed solution by ultrasonic dispersion and mechanical stirring; then uniformly coat the mixed solution onto the aluminosilicate fibers and gently push the mixed solution with a glass rod to ensure that the aluminosilicate fibers are fully impregnated by the mixed solution to obtain a coating slurry.

[0083] S3. Similar to step S3 in Example 1, a polyethylene film with a thickness of 7 μm is used as the diaphragm base layer. A ceramic layer with a thickness of 1 μm is first set on both sides of the diaphragm base layer. Then, the coating slurry obtained in step S2 is coated on the surface of the ceramic layer and dried to obtain a reinforced coating with a thickness of 1 μm.

[0084] Comparative Example 4

[0085] This comparative example presents a battery separator. The difference between this comparative example and Example 1 is that the battery separator in this comparative example uses PVDF modified with a silane coupling agent to prepare the coating slurry, and no aluminum silicate fiber is added. The specific preparation method is as follows:

[0086] S1. Dissolve the silane coupling agent in anhydrous ethanol at a mass ratio of 1:10 to obtain a silane coupling agent solution; dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 10% PVDF solution; place the silane coupling agent solution and PVDF solution in a round-bottom flask at a mass ratio of 1:20, and perform ultrasonic dispersion and mechanical stirring sequentially to obtain a PVDF coating slurry modified with silane coupling agent.

[0087] S2. Similar to step S3 in Example 1, a polyethylene film with a thickness of 7 μm is used as the diaphragm base layer. A ceramic layer with a thickness of 1 μm is first set on both sides of the diaphragm base layer. Then, the coating slurry obtained in step S1 is coated on the surface of the ceramic layer and dried to obtain a reinforced coating with a thickness of 1 μm.

[0088] Comparative Example 5

[0089] This comparative example presents a battery separator. The difference between this comparative example and Example 1 is that, in the preparation process of the battery separator in this comparative example, aluminum silicate fiber is directly mixed with PVDF to prepare the coating slurry, without modifying the aluminum silicate fiber with a silane coupling agent. The specific preparation method is as follows:

[0090] S1, the operation is the same as step S1 in Example 1;

[0091] S2. Dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 10% PVDF solution. According to the mass ratio of aluminosilicate fiber to PVDF of 1:20, place the unmodified aluminosilicate fiber and PVDF solution in a round-bottom flask, first perform ultrasonic dispersion to promote the uniform dispersion of aluminosilicate fiber in the solution, and then perform mechanical stirring for 2.5 hours to obtain a PVDF coating slurry containing unmodified aluminosilicate fiber.

[0092] S3. Similar to step S3 in Example 1, a polyethylene film with a thickness of 7 μm is used as the diaphragm base layer. A ceramic layer with a thickness of 1 μm is first set on both sides of the diaphragm base layer. Then, the coating slurry obtained in step S1 is coated on the surface of the ceramic layer and dried to obtain a reinforced coating with a thickness of 1 μm.

[0093] Example 11

[0094] This embodiment proposes a lithium-ion battery, the preparation method of which includes:

[0095] (1) Preparation of positive electrode

[0096] The positive electrode material lithium cobalt oxide, the mixed conductive agent (cobalt trioxide, nickel trioxide and manganese oxide in a mass ratio of 1:1:1), and the binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 98:1.0:1.0. The mixture is then coated onto an Al foil, dried, rolled, and slit to obtain the positive electrode sheet.

[0097] (2) Preparation of negative electrode

[0098] Graphite or silicon-carbon anode material, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are thoroughly mixed in a deionized water solvent system at a mass ratio of 97.8:1.1:1.1. The mixture is then coated onto Cu foil, dried, rolled, and slit to obtain the anode sheet.

[0099] (3) Preparation of electrolyte

[0100] A solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent at a mass ratio of 8:92 is used as the electrolyte for lithium batteries. The non-aqueous organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and ethylene carbonate (VC) in a mass ratio of 25:25:15:31:4.

[0101] (4) Assembly of lithium-ion batteries

[0102] Using the battery separator prepared in Example 1 as the separator in this example, the positive electrode sheet, the separator prepared in step S1, and the negative electrode sheet prepared in step S2 are stacked in sequence, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a safe isolation role, and the electrode assembly is wound up; the electrode assembly is placed in the packaging shell, injected with the electrolyte prepared in step S3 and sealed to obtain a lithium-ion battery.

[0103] Examples 12-20

[0104] Examples 12-20 respectively prepared a lithium-ion battery. The difference between Examples 12-20 and Example 11 is that the battery separator of the lithium-ion battery in Examples 12-20 respectively adopts the battery separator of Examples 2-10, and other operations are the same as in Example 11.

[0105] Comparative Examples 6-10

[0106] A lithium-ion battery was prepared in Comparative Examples 6-10. The difference between Comparative Examples 6-10 and Example 11 is that the battery separator of the lithium-ion battery in Comparative Examples 6-10 is the same as that of Comparative Examples 1-5. Other operations are the same as those in Example 11.

[0107] Performance testing

[0108] The heat shrinkage rate, needle penetration strength and ionic conductivity of the battery separators of Examples 1-10 and Comparative Examples 1-5 were tested respectively.

[0109] The heat shrinkage rate test was conducted at 130℃ for 0.5 hours.

[0110] The method for testing needle penetration strength is as follows: the battery separator is laid flat in the fixture and clamped, and punctured at a rate of (100±10) mm / min. After completion, the sample is removed, and the maximum load of the steel needle penetrating the test piece is read. The instrument automatically calculates the puncture strength. If more than 5 test pieces are used, the average value is taken.

[0111] The test method for ionic conductivity is as follows: it is determined according to the recording method in GB / T 36363 2018 "Polyolefin separators for lithium-ion batteries".

[0112] The performance of the battery diaphragms of each embodiment and comparative example was tested according to the above method, and the results are shown in Table 1. Among them, the thermal shrinkage rate in the MD direction represents the thermal shrinkage rate in the length direction of the battery diaphragm; the thermal shrinkage rate in the TD direction represents the thermal shrinkage rate in the width direction of the battery diaphragm.

[0113] In addition, the thermal stability of the lithium-ion batteries prepared in Examples 11 to 20 and the lithium-ion batteries in Comparative Examples 6 to 10 was tested respectively. The specific test method is as follows:

[0114] Preparation process: Leave it at room temperature (25°C ± 3°C) for 5 min, then discharge it at a constant current of 0.2C to 3.0V and leave it for 5 min; continue to charge it at a constant current and constant voltage of 2C to 4.25V, with a cut-off rate of 1.5C; finally, charge it at a constant current and constant voltage of 1.5C to 4.53V, with a cut-off rate of 0.05C; leave it for 120 min and then use it for testing.

[0115] Testing process: Put the prepared lithium-ion batteries into different ovens, and heat them up to the set temperature (126°C, 127°C, 128°C, 129, 130°C, 132°C, 133°C, 134°C) at a rate of 5 ± 2°C / min, and keep them for 60 min and then stop. Five lithium-ion batteries of Comparative Examples 6 to 10 and Examples 11 to 20 were placed in ovens with different temperatures respectively. During the testing process, the surface temperature, ambient temperature and voltage of the lithium-ion batteries need to be monitored; if the lithium-ion batteries do not catch fire or explode, it means they are qualified. The highest temperature that the tested batteries can withstand is shown in Table 1.

[0116] Table 1 Performance test result data

[0117]

[0118]

[0119] From Table 1 above, by comparing Example 1 and Comparative Example 1, as well as Example 11 and Comparative Example 6, it can be seen that coating the surface of the diaphragm substrate with the aluminosilicate fiber-PVDF composite coating modified by a silane coupling agent can improve the puncture strength and ionic conductivity of the battery diaphragm, reduce the thermal shrinkage rate of the battery diaphragm, and improve the safety performance of the lithium-ion battery. This is because the aluminosilicate fiber as the reinforcing phase can improve the mechanical strength of the PVDF matrix. Therefore, when the coated battery diaphragm is punctured or compressed, it shows higher strength, and significantly improves the thermal stability of the battery diaphragm, reduces shrinkage at high temperatures, and thus can improve the heat resistance and safety performance of the battery.

[0120] Comparing the performance test results of the battery separators in Examples 1 and 2, it is evident that insufficient aluminosilicate fiber content results in limited improvement in needle strength and thermal shrinkage rate. Comparing the performance test results of the battery separators in Examples 1 and 3, it is evident that when the mass ratio of modified aluminosilicate fiber added to the PVDF solution increases, the needle strength, thermal shrinkage rate, and ionic conductivity of the battery separator achieve an optimal balance. Comparing the performance test results of the battery separators in Examples 1 and 4, it is evident that when the fiber content exceeds a certain proportion (e.g., 10%), it may lead to fiber agglomeration and uneven distribution, reducing reinforcement efficiency. Agglomeration may cause a decrease in needle strength and ionic conductivity, resulting in limited performance improvement. Therefore, it is recommended that the mass ratio of aluminosilicate fiber to PVDF be controlled between 5% and 9%, within which the optimal balance between mechanical properties, thermal stability, and electrical conductivity can be achieved.

[0121] Comparing the performance test results of the battery separators in Examples 1 and 5, it can be seen that the silane coupling agent with the highest dosage has the best modification effect, while its needle penetration strength, thermal shrinkage rate, and ionic conductivity are slightly worse, but its cost is higher. Comparing the performance test results of the battery separators in Examples 1, 6, and 7, it can be seen that when the mass ratio of silane coupling agent to aluminosilicate fiber decreases, the needle penetration strength of the battery separator weakens, the thermal shrinkage rate increases, and the ionic conductivity decreases. This is because the surface modification effect of the aluminosilicate fiber may be weakened, leading to a decrease in the bonding strength between the fiber and the PVDF matrix. This decrease in bonding strength will affect the performance of the battery separator. To balance performance and cost, a mass ratio of silane coupling agent to aluminosilicate fiber between 1:1 and 1:3 is recommended, achieving a balanced performance in mechanical properties, thermal stability, and ionic conductivity.

[0122] Comparing the performance test results of the battery separators in Examples 1 and 8-10, it can be seen that applying a 1μm reinforcing coating to each side of the base film (Example 1) effectively improves the needle penetration strength and thermal shrinkage rate while maintaining good air permeability and ionic conductivity, exhibiting a better performance balance. In the case of a 2μm coating on each side (Example 10), although mechanical strength and thermal stability are optimal, the ionic conductivity decreases due to the thicker coating. In comparison, a 1μm coating on one side (Example 8) is more economical and suitable for scenarios requiring cost and process simplification, but its mechanical strength and thermal stability are slightly inferior to the double-sided coating design. A 2μm coating on one side (Example 9) improves mechanical strength, but due to uneven stress distribution, its overall performance is not as good as the double-sided coating. Therefore, the coating method of applying a 1μm coating to each side achieves a good balance between mechanical properties, thermal stability, and ionic conductivity, making it the optimal solution in terms of overall performance.

[0123] Comparing the battery separators of Examples 1 and 2-5, and the lithium-ion batteries of Examples 11 and 7-10, it can be seen that surface modification of aluminosilicate fibers with a silane coupling agent before mixing with PVDF has advantages. This is because in Example 1, surface modification of aluminosilicate fibers with a silane coupling agent is performed first, followed by mixing with PVDF. After surface modification with the silane coupling agent, the surface of the aluminosilicate fibers has functional groups (such as amino or hydroxyl groups). The chemical interaction between these functional groups and PVDF is enhanced, thereby allowing for better bonding with the PVDF matrix and improving the mechanical properties of the coating. Furthermore, the surface-modified aluminosilicate fibers are more easily and uniformly dispersed in PVDF, reducing aggregation and improving the uniformity and performance consistency of the coating, thus enhancing the thermal stability of the battery.

[0124] In Comparative Example 2, when silane coupling agents coexist with PVDF and aluminosilicate fibers, the reaction of the silane coupling agents is insufficient because they may preferentially react with the polar groups in PVDF, reducing the reaction time and opportunity with the aluminosilicate fiber surface, resulting in an unsatisfactory modification effect on the aluminosilicate fiber surface. Furthermore, due to the incomplete modification of the aluminosilicate fiber surface, the bonding force between the aluminosilicate fiber and the PVDF matrix is ​​insufficient, leading to a decrease in the mechanical properties and stability of the coating. In addition, it also affects the fiber dispersion, reduces the uniformity and structural stability of the coating, and consequently reduces the thermal stability of the battery.

[0125] In Comparative Example 3, after the silane coupling agent reacts with PVDF, the polar groups of the silane coupling agent have already combined with PVDF and can no longer effectively react with the hydroxyl or oxides on the surface of aluminosilicate fibers, resulting in insufficient surface modification of aluminosilicate fibers. Since the aluminosilicate fibers are not effectively modified, their bonding force with PVDF is still low, which leads to poor stress transfer efficiency at the interface and affects the mechanical properties of the membrane.

[0126] Aluminosilicate fibers exhibit excellent thermal stability, enhancing the high-temperature resistance of composite materials. Compared to Comparative Example 4, which simply modified PVDF with a silane coupling agent without adding aluminosilicate fibers, the battery separators in each embodiment demonstrate better stability in high-temperature applications (such as batteries). However, in Comparative Example 5, the aluminosilicate fiber surface was not modified with a silane coupling agent, resulting in poor interfacial bonding between the fiber and the PVDF matrix. The relatively inert surface of aluminosilicate fibers lacks polar functional groups that strongly interact with the matrix, leading to the bonding force between the aluminosilicate fibers and the PVDF matrix primarily relying on physical adsorption and mechanical interlocking.

[0127] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A battery separator, characterized in that, include: Diaphragm base layer; A ceramic layer is disposed on at least one surface of the diaphragm base layer; The ceramic layer is made of inorganic ceramic material, which is selected from amphiphilic oxides, and the amphiphilic oxides are selected from at least one of TiO2 and ZrO2 or a combination of at least one of TiO2 and ZrO2 and Al2O3. A reinforcing coating is disposed on the ceramic layer on the surface opposite to the membrane base layer; the reinforcing coating includes an adhesive matrix and modified aluminum silicate fibers dispersed in the adhesive matrix; The modified aluminum silicate fiber is an aluminum silicate fiber that has been surface modified with a silane coupling agent. The mass ratio of the silane coupling agent to the aluminum silicate fiber is 1:1 to 3. The mass ratio of the modified aluminum silicate fiber to the adhesive matrix is ​​5% to 9%.

2. The battery separator according to claim 1, characterized in that, The battery separator has a needle penetration strength of 300~500gf; ionic conductivity ≥6.0 mS / cm; and thermal shrinkage rate <3% at 130℃.

3. The battery separator according to claim 1, characterized in that, The thickness of the reinforcing coating is 1μm to 4μm; and / or, the thickness ratio of the membrane base layer, the ceramic layer and the reinforcing coating is 6 to 8: 0.5 to 1.5: 0.5 to 1.

5.

4. The battery separator according to claim 1, characterized in that, The modified aluminosilicate fibers have a diameter of 500~1500 nm and a specific surface area of ​​10~20 m². 2 / g.

5. The battery separator according to claim 1, characterized in that, The silane coupling agent contains at least one of amino, hydroxy, and epoxy groups; or, the silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-chloropropyltrichlorosilane, γ-glycidoxypropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane, γ-mercaptopropyltrimethoxysilane, aminopropyltriethoxysilane, and epoxypropyltriethoxysilane.

6. The battery separator according to any one of claims 1 to 5, characterized in that, The material of the diaphragm base layer is selected from at least one of polypropylene and polyethylene; and / or, the diaphragm base layer is a porous diaphragm base layer.

7. The method for preparing the battery separator according to any one of claims 1 to 6, characterized in that, Includes the following steps: A ceramic layer is disposed on at least one surface of the diaphragm base layer; Alumina silicate fibers were placed in a silane coupling agent solution for surface modification treatment to obtain modified alumina silicate fibers. Modified aluminosilicate fibers are mixed with binders and solvents to prepare a coating slurry; The coating slurry is applied to the ceramic layer on the surface away from the membrane base layer and cured to obtain a battery separator.

8. The method for preparing the battery separator according to claim 7, characterized in that, The modified aluminum silicate fiber is mixed with a binder and a solvent to prepare a coating slurry. Specifically, the process includes: first, mixing the binder and solvent to obtain a binder solution; and then dispersing the modified aluminum silicate fiber in the binder solution to obtain the coating slurry.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, wherein the separator is the battery separator according to any one of claims 1 to 6.

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