Isolating membrane for lithium ion battery, preparation method of isolating membrane and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly provides an isolating membrane for a lithium ion battery and a preparation method of the isolating membrane. The problems that in the prior art, the dissolution speed of transition metal ions can only be restrained to a certain degree, migration of the transition metal ions to a negative electrode cannot be avoided, and the battery performance still exists are solved. Therefore, the isolating membrane comprises a base membrane and a functional coating located on the surface of the base membrane, the functional coating contains a functionalized MOF material, the functionalized MOF material is an MOF material modified by a functional group, and the functional group is a functional group capable of capturing transition metal ions. The isolating membrane is applied to the lithium battery, transition metal ions in electrolyte can be captured, the probability that the transition metal ions migrate to a negative electrode is reduced, and therefore the battery performance is effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and specifically provides an isolation membrane for lithium-ion batteries and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] In recent years, the new energy industry has flourished, and lithium batteries have been widely used in new energy vehicles, digital products, energy storage and other fields. The positive electrode material is a key factor affecting the performance of lithium batteries. Currently, the most commonly used positive electrode materials are nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium cobalt oxide. During the cycle process, the transition metal in the positive electrode material will dissolve from the positive electrode structure, and the dissolved transition metal ions will migrate to the surface of the negative electrode and be reduced to metal elements, which will accelerate the decomposition of the SEI film, thereby aggravating the attenuation of battery performance, affecting the embedding of Li, forming lithium dendrites, piercing the diaphragm, causing internal short circuits in the battery, and thus causing safety problems.

[0003] In order to solve the problem of transition metal ion dissolution, the current main methods are to inhibit the dissolution of transition metals in the positive electrode materials by coating, doping or regulating the electrolyte components, so as to improve the cycle performance of the battery. However, no matter whether the positive electrode is coated, doped or the electrolyte components are regulated, the dissolution rate can only be inhibited. In the end, the dissolved transition metals will still migrate to the negative electrode surface through the electrolyte, destroying the stability of the SEI film, enhancing the interface impedance and reducing the battery performance.

[0004] Accordingly, this field requires a new technical solution to solve the above technical problems. Summary of the invention

[0005] The present application aims to solve the above-mentioned technical problem, that is, to solve the problem that the prior art can only suppress the dissolution rate of transition metal ions to a certain extent, but cannot prevent the migration of transition metal ions to the negative electrode, and still has the problem of reducing battery performance.

[0006] In a first aspect, the present application provides an isolation membrane for a lithium-ion battery, the isolation membrane comprising a base membrane and a functional coating located on the surface of the base membrane, the functional coating containing a functionalized MOF material, the functionalized MOF material being a MOF material modified by a functional functional group, wherein the functional functional group is a functional group capable of capturing transition metal ions.

[0007] In the preferred technical solution of the above-mentioned separator for lithium-ion batteries, the functional groups are -OH, -NH 2 、-SO 3 H, -SH or more; preferably, the functional groups include at least -SO 3 H.

[0008] In the above-mentioned preferred technical solution of the separator for lithium-ion batteries, the organic ligand of the MOF material includes a first organic ligand, and the functional functional group is contained in the first organic ligand.

[0009] In the above-mentioned preferred technical solution of the separator for lithium-ion batteries, the first organic ligand includes one or more of sodium 2-sulfoterephthalate, 2-aminobenzimidazole, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, tetraminopyrrole, isopropyl mercaptoacetate; and / or, the central metal ion of the MOF material includes one or any combination of zinc ion, cobalt ion, iron ion, zirconium ion, manganese ion, copper ion, chromium ion, scandium ion, vanadium ion, nickel ion, titanium ion, aluminum ion; and / or, the organic ligand of the MOF material further includes a second organic ligand, and the second organic ligand does not contain a functional functional group; the second organic ligand includes one or any combination of p-benzoic acid, trimesic acid, dimethylimidazole, 2,2'-bipyridine-5,5'-dicarboxylic acid, porphyrin, tetracarboxyl porphyrin.

[0010] In the above-mentioned preferred technical solution of the separator for lithium-ion batteries, the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:(0.3 - 10), and preferably the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:(1 - 2).

[0011] In the above-mentioned preferred technical solution of the separator for lithium-ion batteries, the MOF material is a material of the ZIF series, a material of the UiO series, a material of the MIL series or a material of the PCN series; preferably the MOF material is a material of the UiO series, and the functional functional group is -SO 3 H.

[0012] In the above-mentioned preferred technical solution of the separator for lithium-ion batteries, the thickness of the functional coating is 0.5 μm - 5 μm; preferably the thickness of the functional coating is 1 μm - 5 μm.

[0013] In the above-mentioned preferred technical solution of the separator for lithium-ion batteries, the functional coating further includes additives, and the additives include one or more of a dispersant, a wetting agent, a thickener and a pH regulator.

[0014] In a second aspect, the present application provides a method for preparing a separator for preparing the above-mentioned separator for lithium-ion batteries, and the preparation method includes the following steps: Step 1, providing a functional slurry mainly composed of a binder, a functionalized MOF material and a solvent; Step 2, coating the functional slurry on the surface of the base film and drying to obtain the functional coating on the surface of the base film, and preparing a separator.

[0015] In a preferred technical solution of the above method for preparing the separator membrane, the functionalized MOF material is obtained by mixing a metal salt of the MOF material, an organic ligand of the MOF material, and a coordination solvent for reaction, wherein the organic ligand of the MOF material includes at least a first organic ligand, and the first organic ligand contains a functional functional group.

[0016] In a preferred technical solution of the above method for preparing the separator membrane, the mass ratio of the organic ligand of the MOF material to the metal salt of the MOF material is organic ligand of MOF material: metal salt of MOF material = 1: (1 to 2); and / or, the coordination solvent is one or more of water, ethanol, methanol, glycerol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, and formic acid.

[0017] In a preferred technical solution of the above method for preparing the separator membrane, the binder includes one or more of polyvinyl alcohol, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylate, and sodium methylcellulose; and / or, the solvent includes one or more of water, ethanol, methanol, glycerol, acetone, N-methylpyrrolidone, and N,N-dimethylformamide.

[0018] In a preferred technical solution of the above method for preparing the separator membrane, in the slurry of the functionalized coating, the solid content of the slurry is 10% to 50%; and / or, the mass percentage of the functionalized MOF material relative to the solute in the slurry is 70 wt% to 99 wt%, and the mass percentage of the binder relative to the solute in the slurry is 1 wt% to 30 wt%; and / or, the slurry of the functionalized coating further includes additives, and the additives include one or more of a dispersant, a wetting agent, a thickening agent, and a pH regulator, and the mass percentage of the additives relative to the solute in the slurry is 0.5 wt% to 5 wt%; the mass percentage of the functionalized MOF material relative to the solute in the slurry is 70 wt% to 95 wt%, and the mass percentage of the binder relative to the solute in the slurry is 1 wt% to 25 wt%.

[0019] In a third aspect, the present application provides a lithium-ion battery, and the lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and the above separator membrane.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0021] 1. The separator of the present application includes a base film and a functional coating on the surface of the base film. The functional coating contains a functionalized MOF material, which is an MOF material modified by functional functional groups. The functional functional groups in the functionalized MOF material can capture (e.g., by complexation, coordination, or adsorption) transition metal ions in the electrolyte, so that after the transition metal ions dissolve out from the positive electrode, they can be captured, reducing the probability of the transition metal ions reaching the negative electrode and depositing on the negative electrode, thereby effectively improving the battery performance. In addition, the MOF material has a porous structure, which can improve the liquid retention capacity of the battery on the surface of the base film and reduce the internal resistance of the battery, thus effectively improving the long-cycle performance of the battery. And the separator contains the MOF material, which can reduce the thermal shrinkage of the separator, improve the safety performance of the battery, and is lighter in weight, which helps to improve the energy density of the battery.

[0022] 2. The preparation method of the separator of the present application has a simple preparation process and is convenient for production. Detailed implementation manners

[0023] The following describes the preferred implementation manners of the present application. Those skilled in the art should understand that these implementation manners are only used to explain the technical principle of the present application and are not intended to limit the protection scope of the present application.

[0024] In the present application, the term "and / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0025] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or its similar expression below refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b, or c", or, "at least one (item) of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0026] It should be understood that in various embodiments of the present application, the magnitudes of the serial numbers of the above processes do not mean the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "the", and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0028] The weight of the relevant components mentioned in the specification of the embodiments of the present application not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0029] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0030] The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0031] Based on the prior art pointed out in the background art, the problems of solving the dissolution of transition metal ions by means such as positive electrode coating, doping, or regulating the electrolyte components all have the problem that they can only inhibit the dissolution rate of transition metal ions, cannot avoid the migration of transition metal ions to the negative electrode, and there will still be transition metal ions migrating to the negative electrode, and there is still the problem of reducing the battery performance.

[0032] The present application provides a separator for a lithium-ion battery and a preparation method thereof. The separator includes a base film and a functional coating on the surface of the base film. The functional coating contains a functionalized MOF material, and the functionalized MOF material is a MOF material modified by a functional functional group. The functional functional group in the functionalized MOF material can capture the transition metal ions in the electrolyte, so that after the transition metal ions are dissolved from the positive electrode, they can be captured, reducing the probability of the transition metal ions migrating to the negative electrode, and further reducing the probability of the transition metal ions reaching the negative electrode and depositing on the negative electrode, effectively improving the battery performance.

[0033] The present application provides a separator for a lithium-ion battery in a first aspect. The separator includes a base film and a functional coating on the surface of the base film. The functional coating contains a functionalized MOF material, and the functionalized MOF material is a MOF material modified by a functional functional group, and the functional functional group is a functional group capable of capturing transition metal ions.

[0034] It should be noted that the present application does not impose any restrictions on the number of functional coatings. In actual applications, those skilled in the art can set the number of functional coatings according to actual needs. For example, a functional coating is provided only on one surface of the base film, or functional coatings are provided on both surfaces of the base film. Adjustments and changes regarding the number of functional coatings do not deviate from the basic principle of the present application and should be limited within the protection scope of the present application.

[0035] The separator of the present application has a functional coating on the surface of the base film. The functional coating contains a functionalized MOF material, and the functionalized MOF material is a MOF material modified by a functional functional group. The functional functional group in the functionalized MOF material can capture transition metal ions in the electrolyte, so that after the transition metal ions are dissolved out from the positive electrode, they can be captured, reducing the probability of the transition metal ions reaching the negative electrode and depositing on the negative electrode, thereby effectively improving the battery performance. Specifically, the functional functional group can capture the transition metal ions by adsorbing the transition metal ions, or in the form of complexing or coordinating with the transition metal ions, thereby reducing the content of transition metal ions in the electrolyte.

[0036] Preferably, the functional functional group is -OH, -NH 2 、-SO 3 H, -SH, or one or more of them.

[0037] More preferably, the functional functional group at least includes -SO 3 H.

[0038] Preferably, the organic ligand of the MOF material includes a first organic ligand, and the first organic ligand contains a functional functional group. The organic ligand of the MOF material is an organic ligand capable of undergoing a coordination reaction with a metal ion.

[0039] More preferably, the first organic ligand includes one or more of sodium 2-sulfoterephthalate, 2-aminobenzimidazole, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, tetraminopyrrole, and isopropyl mercaptoacetate.

[0040] Further preferably, the organic ligand of the MOF material further includes a second organic ligand, and the second organic ligand does not contain functional functional groups; the second organic ligand includes one or any combination of terephthalic acid, trimesic acid, dimethylimidazole, 2,2'-bipyridine-5,5'-dicarboxylic acid, porphyrin, and tetracarboxyl porphyrin.

[0041] Further preferably, the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:(0.3 - 10).

[0042] Further preferably, the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:(1 - 2).

[0043] Preferably, the central metal ion of the MOF material includes one or any combination of zinc ion, cobalt ion, iron ion, zirconium ion, manganese ion, copper ion, chromium ion, scandium ion, vanadium ion, nickel ion, titanium ion, and aluminum ion.

[0044] Preferably, the MOF material is one or any combination of materials of the ZIF series, UiO series, MIL series, and PCN series.

[0045] Further preferably, the MOF material is a material of the UiO series, and the functional functional group is -SO 3 H.

[0046] Preferably, the base film is a polyethylene separator, a polypropylene separator, a polyimide separator, a cellulose separator, or an inorganic material separator.

[0047] Preferably, the thickness of the functional coating is 0.5 μm - 5 μm.

[0048] Further preferably, the thickness of the functional coating is 1 μm - 5 μm.

[0049] Specifically, in practical applications, the thickness of a single-layer functional coating can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, and any value between any two of the above thickness values. It is preferably to make the thickness of the single-layer functional coating 1 μm - 5 μm to ensure that the separator has better ability to capture transition metal ions.

[0050] By controlling the single-sided coating thickness of the functional coating within the range of 0.5 to 5 μm, the effect of reducing the thermal shrinkage of the separator can be achieved, while ensuring the ability to capture transition metal ions. If the thickness is too thin, the effect of reducing thermal shrinkage cannot be achieved, and at the same time, there are few sites for capturing transition metal ions, resulting in poor effect of capturing transition metal ions. If the thickness is too thick, it will increase the internal resistance of the battery, affect the battery performance, and is also prone to cracking during the coating process.

[0051] Preferably, the functional coating further includes additives, and the additives include one or more of a dispersant, a wetting agent, a thickening agent, and a pH regulator.

[0052] It should be noted that the thickness of the functional coating here is the thickness of a single-layer functional coating.

[0053] In the second aspect, the present application provides a method for preparing a separator for preparing the separator for a lithium-ion battery provided in the first aspect.

[0054] Specifically, the method for preparing the separator of the present application includes the following steps:

[0055] Step 1, providing a functional slurry mainly composed of a binder, a functionalized MOF material, and a solvent.

[0056] Step 2, coating the functional slurry on the surface of the base film and drying to obtain a functional coating on the surface of the base film, thereby preparing the separator.

[0057] The preparation method of the present application is simple, convenient for production, and has low cost.

[0058] Preferably, the functionalized MOF material is obtained by mixing a metal salt of the MOF material, an organic ligand of the MOF material, and a coordination solvent for reaction, wherein the organic ligand of the MOF material includes at least a first organic ligand, and the first organic ligand contains a functional functional group.

[0059] Preferably, the first organic ligand includes one or more of sodium 2-sulfoterephthalate, 2-aminobenzimidazole, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, tetraminopyrrole, and isopropyl mercaptoacetate.

[0060] Preferably, the metal salt includes one or more of zirconium oxychloride octahydrate, zinc nitrate hexahydrate, zirconium tetrachloride, zinc acetate dihydrate, zinc sulfate, zinc chloride, cobalt acetate tetrahydrate, cobalt chloride hexahydrate, and cobalt sulfate heptahydrate.

[0061] Preferably, the organic ligand of the MOF material further includes a second organic ligand, the second organic ligand does not contain functional functional groups, and the second organic ligand includes one or any combination of p-benzoic acid, trimesic acid, dimethylimidazole, 2,2'-bipyridine-5,5'-dicarboxylic acid, porphyrin, and tetracarboxyl porphyrin.

[0062] Preferably, the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:(0.3 to 10).

[0063] More preferably, the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:(1 to 2).

[0064] More preferably, the mass ratio of the first organic ligand to the second organic ligand is the first organic ligand: the second organic ligand = 1:2.

[0065] By controlling the mass ratio of the first organic ligand to the second organic ligand to regulate the number of functional groups, the effect of the separator membrane capturing Fe ions can be better improved. Preferably, the mass ratio of the first organic ligand to the second organic ligand is 1:(1 to 2), and most preferably, the mass ratio of the first organic ligand to the second organic ligand is 1:2.

[0066] Preferably, the mass ratio of the organic ligand of the MOF material to the metal salt of the MOF material is the organic ligand of the MOF material: the metal salt of the MOF material = 1:(1 to 2).

[0067] More preferably, the mass ratio of the organic ligand of the MOF material to the metal salt of the MOF material is the organic ligand of the MOF material: the metal salt of the MOF material = 1:1.

[0068] Preferably, the coordination solvent is one or more of water, ethanol, methanol, glycerol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, and formic acid.

[0069] Preferably, the binder includes one or more of polyvinyl alcohol, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylate, and sodium carboxymethyl cellulose.

[0070] Preferably, the solvent is one or more of water, ethanol, methanol, glycerol, acetone, N-methylpyrrolidone, and N,N-dimethylformamide.

[0071] Preferably, in the slurry of the functionalized coating, the solid content of the slurry is 10% to 50%.

[0072] Controlling the solid content of the slurry at 10% to 50% during the preparation process is convenient for homogenization and coating, can improve the coating quality, and reduce the coating difficulty.

[0073] Preferably, the mass percentage of the functionalized MOF material relative to the solute in the slurry is 70 wt% to 99 wt%, and the mass percentage of the binder relative to the solute in the slurry is 1 wt% to 30 wt%.

[0074] Preferably, the slurry of the functionalized coating further includes additives, the additives include one or more of a dispersant, a wetting agent, a thickening agent, and a pH regulator, and the mass percentage of the additives relative to the solute in the slurry is 0.5 wt% to 5 wt%; the mass percentage of the functionalized MOF material relative to the solute in the slurry is 70 wt% to 95 wt%, and the mass percentage of the binder relative to the solute in the slurry is 1 wt% to 25 wt%.

[0075] In step 2, the functionalized slurry can be coated on the surface of the base film by means of roll coating, dip coating, spraying, etc.

[0076] This application provides a lithium-ion battery in a third aspect. The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and the separator provided in the first aspect.

[0077] The separator of this application and the beneficial effects brought by it will be described in detail below through several specific examples.

[0078] Example 1

[0079] The separator of this embodiment is prepared through the following steps:

[0080] S1: Mix an organic ligand (sodium 2-sulfoterephthalate) and a metal salt (zirconium oxychloride octahydrate) with a mass ratio of 1:1 with a coordination solvent, where the coordination solvent is a mixed solvent of N,N-dimethylformamide and formic acid with a volume ratio of 3:1, react at 150 °C for 24 hours, and obtain a functionalized MOF material, namely sulfonic acid-modified UiO-66, after washing and drying.

[0081] S2: Mix the functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water evenly to obtain a functionalized slurry.

[0082] Among them, the binder is polyacrylate, and the dispersant is polyacrylamide. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate, and polyacrylamide is 80:18:2, and the solid content of the prepared functionalized slurry is 50%.

[0083] S3: Coat the functionalized slurry on two surfaces of a 9-μm base film (polyethylene separator) by gravure coating, with a single-sided coating thickness of 3 μm, and obtain a separator after drying.

[0084] Example 2

[0085] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the single-sided coating thickness in step S3.

[0086] Specifically, the single-sided coating thickness in step S3 of this embodiment is 0.5 μm.

[0087] Example 3

[0088] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the single-sided coating thickness in step S3.

[0089] Specifically, the single-sided coating thickness in step S3 of this embodiment is 1 μm.

[0090] Example 4

[0091] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the single-sided coating thickness in step S3.

[0092] Specifically, the single-sided coating thickness in step S3 of this embodiment is 2 μm.

[0093] Example 5

[0094] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the single-sided coating thickness in step S3.

[0095] Specifically, the single-sided coating thickness in step S3 of this embodiment is 5 μm.

[0096] Example 6

[0097] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the single-sided coating thickness in step S3.

[0098] Specifically, the single-sided coating thickness in step S3 of this embodiment is 0.2 μm.

[0099] Example 7

[0100] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the single-sided coating thickness in step S3.

[0101] Specifically, the single-sided coating thickness in step S3 of this embodiment is 6 μm.

[0102] Example 8

[0103] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only that the components of the organic ligand in step S1 are different.

[0104] Specifically, the organic ligand in step S1 of this embodiment is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-terephthalic acid in a mass ratio of 1:0.33.

[0105] Example 9

[0106] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only that the components of the organic ligand in step S1 are different.

[0107] Specifically, the organic ligand in step S1 of this embodiment is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-terephthalic acid in a mass ratio of 1:1.

[0108] Example 10

[0109] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only that the components of the organic ligand in step S1 are different.

[0110] Specifically, the organic ligand in step S1 of this embodiment is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-terephthalic acid in a mass ratio of 1:2.

[0111] Example 11

[0112] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only that the components of the organic ligand in step S1 are different.

[0113] Specifically, the organic ligand in step S1 of this embodiment is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-terephthalic acid in a mass ratio of 1:3.

[0114] Example 12

[0115] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only that the components of the organic ligand in step S1 are different.

[0116] Specifically, the organic ligand in step S1 of this embodiment is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-terephthalic acid in a mass ratio of 1:4.

[0117] Example 13

[0118] The preparation process of the separator membrane in this example is the same as that in Example 1, and the difference from Example 1 is only that the components of the organic ligand in step S1 are different.

[0119] Specifically, the organic ligand in step S1 of this example is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-benzenedicarboxylic acid in a mass ratio of 1:8.

[0120] Example 14

[0121] The preparation process of the separator membrane in this example is the same as that in Example 1, and the difference from Example 1 is only that the components of the organic ligand in step S1 are different.

[0122] Specifically, the organic ligand in step S1 of this example is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-benzenedicarboxylic acid in a mass ratio of 1:10.

[0123] Example 15

[0124] The preparation process of the separator membrane in this example is the same as that in Example 1, and the difference from Example 1 is only that the components of the organic ligand in step S1 are different and the mass ratio of the organic ligand to the metal salt is different.

[0125] Specifically, the organic ligand in step S1 of this example is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-benzenedicarboxylic acid in a mass ratio of 1:2, and the mass ratio of the organic ligand to the metal salt is 1:2.

[0126] Example 16

[0127] The preparation process of the separator membrane in this example is the same as that in Example 1, and the difference from Example 1 is only that the components of the organic ligand in step S1 are different and the mass ratio of the organic ligand to the metal salt is different.

[0128] Specifically, the organic ligand in step S1 of this example is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-benzenedicarboxylic acid in a mass ratio of 1:2, and the mass ratio of the organic ligand to the metal salt is 1:0.5.

[0129] Example 17

[0130] The preparation process of the separator membrane in this example is the same as that in Example 1, and the difference from Example 1 is only that the components of the organic ligand in step S1 are different and the mass ratio of the organic ligand to the metal salt is different.

[0131] Specifically, in this embodiment, the organic ligand in step S1 is a mixed ligand obtained by mixing monosodium 2-sulfoterephthalate and 1,4-benzenedicarboxylic acid in a mass ratio of 1:2, and the mass ratio of the organic ligand to the metal salt is 1:2.5.

[0132] Example 18

[0133] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the solid content of the functionalized slurry in step S2.

[0134] Specifically, the solid content of the functionalized slurry in step S2 in this embodiment is 10%.

[0135] Example 19

[0136] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the solid content of the functionalized slurry in step S2.

[0137] Specifically, the solid content of the functionalized slurry in step S2 in this embodiment is 20%.

[0138] Example 20

[0139] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the preparation process in step S2.

[0140] Specifically, step S2 in this embodiment is as follows: The functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), and water are mixed evenly to obtain a functionalized slurry. The binder is polyacrylate. In the functionalized slurry, the mass ratio of the functionalized MOF material to polyacrylate is 70:30, and the solid content of the prepared functionalized slurry is 50%.

[0141] Example 21

[0142] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the preparation process in step S2.

[0143] Specifically, step S2 in this embodiment is as follows: The functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), and water are mixed evenly to obtain a functionalized slurry. The binder is polyacrylate. In the functionalized slurry, the mass ratio of the functionalized MOF material to polyacrylate is 80:20, and the solid content of the prepared functionalized slurry is 50%.

[0144] Example 22

[0145] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the preparation process in step S2.

[0146] Specifically, step S2 in this embodiment is as follows: The functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), and water are mixed evenly to obtain a functionalized slurry. The binder is polyacrylate. In the functionalized slurry, the mass ratio of the functionalized MOF material to polyacrylate is 99:1, and the solid content of the prepared functionalized slurry is 50%.

[0147] Example 23

[0148] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the preparation process in step S2.

[0149] Specifically, step S2 in this embodiment is as follows: The functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water are mixed evenly to obtain a functionalized slurry. The binder is polyacrylate. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate to polyacrylamide is 70:25:5, and the solid content of the prepared functionalized slurry is 50%.

[0150] Example 24

[0151] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the preparation process in step S2.

[0152] Specifically, step S2 in this embodiment is as follows: The functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water are mixed evenly to obtain a functionalized slurry. The binder is polyacrylate. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate to polyacrylamide is 90:9.5:0.5, and the solid content of the prepared functionalized slurry is 50%.

[0153] Example 25

[0154] The preparation process of the separator membrane in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is only the preparation process in step S2.

[0155] Specifically, step S2 in this embodiment is specifically as follows: Mix the functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water evenly to obtain a functionalized slurry. The binder is polyacrylate. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate, and polyacrylamide is 98.5:1:0.5, and the solid content of the prepared functionalized slurry is 50%.

[0156] Example 26

[0157] The separator membrane of this embodiment is prepared through the following steps:

[0158] S1: Mix the organic ligand (2-hydroxyterephthalic acid) and the metal salt (zirconium oxychloride octahydrate) with a mass ratio of 1:1 with a coordination solvent. The coordination solvent is a mixed solvent of N,N-dimethylformamide and formic acid with a volume ratio of 3:1. React at 150 °C for 24 hours. After washing and drying, a functionalized MOF material, namely -OH modified UiO-66, is obtained.

[0159] S2: Mix the functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water evenly to obtain a functionalized slurry.

[0160] Among them, the binder is polyacrylate, and the dispersant is polyacrylamide. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate, and polyacrylamide is 80:18:2, and the solid content of the prepared functionalized slurry is 50%.

[0161] S3: Coat the functionalized slurry on both surfaces of a 9-μm base film (polyethylene separator) by gravure coating, with a single-sided coating thickness of 3 μm. After drying, a separator membrane is obtained.

[0162] Example 27

[0163] The separator membrane of this embodiment is prepared through the following steps:

[0164] S1: Dissolve the organic ligand (2-aminobenzimidazole) in DMF to obtain an organic ligand solution, dissolve the metal salt (zinc nitrate hexahydrate) in an equal volume of water to obtain a metal salt solution. The mass ratio of the metal salt to the organic ligand is 1:4. Mix the metal salt solution and the organic ligand solution, stir and react at room temperature for 8 hours. After washing and drying, a functionalized MOF material, namely -NH2 2 modified ZIF8 is obtained.

[0165] S2: Mix the functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water uniformly to obtain a functionalized slurry.

[0166] Among them, the binder is polyacrylate, and the dispersant is polyacrylamide. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate, and polyacrylamide is 80:18:2, and the solid content of the prepared functionalized slurry is 50%.

[0167] S3: Coat the two surfaces of a 9-μm base film (polyethylene separator) with the functionalized slurry by gravure coating, with a single-sided coating thickness of 3 μm, and obtain a separator after drying.

[0168] Example 28

[0169] The separator of this example is prepared through the following steps:

[0170] S1: Mix tetracarboxyl porphyrin, zirconium tetrachloride, and isopropyl mercaptoacetate in a mass ratio of 10:1:35 with a coordination solvent (N,N-dimethylformamide), react at 120°C for 24 hours, and obtain a functionalized MOF material, namely -SH modified PCN-224, after washing and drying.

[0171] S2: Mix the functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water uniformly to obtain a functionalized slurry.

[0172] Among them, the binder is polyacrylate, and the dispersant is polyacrylamide. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate, and polyacrylamide is 80:18:2, and the solid content of the prepared functionalized slurry is 50%.

[0173] S3: Coat the two surfaces of a 9-μm base film (polyethylene separator) with the functionalized slurry by gravure coating, with a single-sided coating thickness of 3 μm, and obtain a separator after drying.

[0174] Comparative Example 1

[0175] The separator of this comparative example is a 9-μm base film (polyethylene separator).

[0176] Comparative Example 2

[0177] The separator of this comparative example is prepared through the following steps:

[0178] S1: Mix an organic ligand (1,4-benzenedicarboxylic acid) and a metal salt (zirconium oxychloride octahydrate) in a mass ratio of 1:1 with a coordination solvent, where the coordination solvent is N,N-dimethylformamide, react at 120 °C for 24 hours, and obtain a functionalized MOF material after washing and drying.

[0179] S2: Mix the functionalized MOF material obtained in step S1, a binder solution (the solid content of the binder is 20%), a dispersant solution (the solid content of the dispersant is 30%), and water evenly to obtain a functionalized slurry.

[0180] Among them, the binder is polyacrylate, the dispersant is polyacrylamide. In the functionalized slurry, the mass ratio of the functionalized MOF material, polyacrylate, and polyacrylamide is 80:18:2, and the solid content of the prepared functionalized slurry is 50%.

[0181] S3: Coat the functionalized slurry on two surfaces of a 9-μm base film (polyethylene diaphragm) by gravure coating, where the single-sided coating thickness is 3 μm, and obtain a separator after drying.

[0182] Test Example 1

[0183] Take the separator samples of Examples 1 to 28 and Comparative Examples 1 and 2, bake them in an oven at 120 °C for 1 h, and calculate the shrinkage rate of the separator after baking. The results are shown in Table 1.

[0184] Specific operation: Clamp the separator between two A4 papers to form a separator sample, place the separator sample in an oven at 120 °C, and bake for 1 h. Among them, the sample size is 150 mm × 150 mm. Shrinkage rate = (size before baking - size after baking) ÷ size before baking × 100%.

[0185] Table 1 Shrinkage rate of the separator after baking in Examples and Comparative Examples

[0186] It can be seen from the experimental data in Table 1 that:

[0187] The shrinkage rates of the separators in Examples 1 - 28 and Comparative Example 2 are much lower than that in Comparative Example 1. From this, it can be known that coating the surface of the base film with a MOF material coating can effectively reduce the thermal shrinkage performance of the separator, and thus improve the safety performance of the battery cell. Therefore, the separator of the present application has good thermal shrinkage performance.

[0188] Test Example 2

[0189] The separator films of Examples 1 to 28 and Comparative Examples 1 and 2 were respectively assembled into lithium-ion batteries, and high-temperature cycle tests were carried out to test the capacity retention rate and the content of Fe ions in the negative electrode after 1000 cycles. The test results are shown in Table 2.

[0190] The assembly steps of the lithium-ion battery are as follows:

[0191] 1. Preparation of the positive electrode sheet: Lithium iron phosphate (LFP), conductive carbon black, binder PVDF and N-methylpyrrolidone were mixed evenly to obtain a positive electrode slurry with a solid content of 65%. Among the positive electrode slurries, the mass ratio of the solid components was lithium iron phosphate: conductive carbon black: PVDF = 96.5:1.5:2. The positive electrode slurry was evenly coated on the surface of the aluminum foil, and the coating surface density was 180 g / m 2 , and the positive electrode sheet was obtained after rolling and slitting.

[0192] 2. Preparation of the negative electrode sheet: Sodium carboxymethyl cellulose was added to deionized water to obtain a colloidal solution, and the negative electrode active material graphite, conductive carbon black and binder styrene-butadiene rubber were evenly dispersed in the colloidal solution to obtain a negative electrode slurry. Among the negative electrode slurries, the mass ratio of the solid components was graphite: conductive carbon black: styrene-butadiene rubber: sodium carboxymethyl cellulose = 95:1.5:2:1.5. The negative electrode slurry was evenly coated on the surface of the copper foil, and the coating surface density was 85 g / m 2 , and the negative electrode sheet was obtained after rolling and slitting.

[0193] 3. Battery assembly: The above-mentioned positive electrode sheet, the separator film of the example or the comparative example, and the negative electrode sheet were wound into an electrode core, and were encapsulated with an aluminum-plastic film. After adding the electrolyte, the battery was obtained after formation, aging and grading.

[0194] Table 2 Data table of cycle test Item Capacity Retention Rate (%) Fe Ion Content (ppm) Example 1 87.5％ 33 ppm Example 2 82％ 62 ppm Example 3 86％ 56 ppm Example 4 86.7％ 40 ppm Example 5 87％ 27 ppm Example 6 81％ 85 ppm Example 7 85％ 25 ppm Example 8 87％ 28 ppm Example 9 88％ 30 ppm Example 10 88.5％ 20 ppm Example 11 83％ 55 ppm Example 12 82.5％ 60 ppm Example 13 81％ 80 ppm Example 14 80.8％ 100 ppm Example 15 87.5％ 32 ppm Example 16 84％ 65 ppm Example 17 87.4％ 35 ppm Example 18 87.6％ 32 ppm Example 19 88％ 30 ppm Example 20 85％ 56 ppm Example 21 86％ 50 ppm Example 22 84％ 60 ppm Example 23 87.5％ 30 ppm Example 24 85％ 45 ppm Example 25 84.6％ 52 ppm Example 26 87.3％ 39 ppm Example 27 86.7％ 44 ppm Example 28 87％ 40 ppm Comparative Example 1 75％ 120 ppm Comparative Example 2 80％ 105 ppm

[0195] It can be seen from the experimental data in Table 2 that:

[0196] 1. Comparing Comparative Example 1 and Comparative Example 2, the battery capacity retention rate of Comparative Example 2 is higher than that of Comparative Example 1, and the Fe ion content of Comparative Example 2 is almost the same as that of Comparative Example 1. It can be seen that coating the MOF material coating on the surface of the base film can improve the cycle performance of the battery to a certain extent, but the improvement of Fe ion dissolution is not significant.

[0197] 2. Comparing Examples 1 to 28 with Comparative Example 2, the battery capacity retention rates of Examples 1 to 28 are all higher than that of Comparative Example 2, and the Fe ion contents of Examples 1 to 28 are much lower than that of Comparative Example 2. It can be seen that coating the MOF material coating modified by functional groups, that is, the functional coating of the present application, on the surface of the base film can effectively improve the problem of Fe ion dissolution and better improve the battery cycle performance.

[0198] 3. Comparing Examples 1 to 7, it can be seen that the thickness of the functionalized coatings of Examples 6, 2, 3, 4, 1, 5, and 7 gradually increases, while the capacity retention rates of the batteries of Examples 6, 2, 3, 4, 1, 5, and 7 first increase and then decrease. Among them, the capacity retention rate of Example 1 is the largest, and its Fe ion content gradually decreases. Thus, it can be known that although the effect of inhibiting the dissolution of Fe ions becomes better with the increase in the thickness of the functionalized coating, if the thickness of the functionalized coating is too thick, it will also affect the cycling performance of the battery. Therefore, it is preferably to make the thickness of the functionalized coating 0.5 μm to 5 μm, more preferably to make the thickness of the functionalized coating 1 μm to 5 μm, and most preferably to make the thickness of the functionalized coating 3 μm.

[0199] 4. Comparing Examples 1, 8 to 14, the capacity retention rates of the batteries of Examples 8, 9, 10, 11, 12, 13, and 14 first increase and then decrease, and their Fe ion contents first decrease and then increase. Thus, it can be known that with the decrease in the proportion of the first organic ligand in the total organic ligands, the inhibitory effect on the dissolution of Fe ions and the cycling performance of the battery also first increase and then decrease. And the data of Example 1 are worse than those of Examples 9 and 10. Thus, it is preferably to control the mass ratio of the first organic ligand to the second organic ligand as the first organic ligand: the second organic ligand = 1:(0 - 10), more preferably to make the first organic ligand: the second organic ligand = 1:(0 - 3), and most preferably to make the first organic ligand: the second organic ligand = 1:(1 - 2).

[0200] 5. Comparing Examples 10, 15 to 17, the data of Example 10 are better than those of Example 15, the data of Example 15 are better than those of Example 17, the data of Example 17 are better than those of Example 16, and the data of Example 16 are much worse than those of Examples 10, 15, and 17. Thus, it can be known that in practical applications, it is preferably to make the mass ratio of the organic ligand of the MOF material to the metal salt of the MOF material as the organic ligand of the MOF material: the metal salt of the MOF material = 1:(1 - 2).

[0201] From the above test examples, it can be known that the separator of the present application can effectively reduce and inhibit the dissolution of transition metal ions, reduce the content of transition metal ions in the battery, thereby improving the cycling performance of the battery. In addition, the MOF material has a porous structure, which can increase the liquid retention capacity of the battery on the surface of the base film and reduce the internal resistance of the battery, thereby effectively improving the long cycling performance of the battery. The MOF material can reduce the thermal shrinkage of the separator, improve the safety performance of the battery, and its mass is lighter, which helps to improve the energy density of the battery.

[0202] So far, the technical solution of the present application has been described in combination with the preferred embodiments. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principle of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present application.

Claims

1. A separator for a lithium ion battery, characterized in that: The isolation membrane includes a base membrane and a functional coating located on the surface of the base membrane, wherein the functional coating contains a functionalized MOF material, wherein the functionalized MOF material is a MOF material modified by a functional functional group, and the functional functional group is a functional group capable of capturing transition metal ions.

2. The separator for lithium-ion battery according to claim 1, characterized in that: The functional groups are one or more of -OH, -NH2, -SO3H, and -SH; preferably, the functional groups include at least -SO3H.

3. The separator for lithium ion battery according to claim 1 or 2, characterized in that: The organic ligand of the MOF material includes a first organic ligand, and the first organic ligand contains the functional group.

4. The separator for lithium-ion battery according to claim 3, characterized in that: The first organic ligand includes one or more of 2-sulfonate terephthalic acid monosodium salt, 2-aminobenzimidazole, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, tetraaminoporphyrin, and isopropyl thioglycolate; And / or, the central metal ion of the MOF material includes one or any combination of zinc ion, cobalt ion, iron ion, zirconium ion, manganese ion, copper ion, chromium ion, scandium ion, vanadium ion, nickel ion, titanium ion and aluminum ion; And / or, the organic ligand of the MOF material further includes a second organic ligand, the second organic ligand does not contain a functional group; the second organic ligand includes one or any combination of benzoic acid, trimesic acid, dimethylimidazole, 2,2'-bipyridine-5,5'-dicarboxylic acid, porphyrin, and tetracarboxy porphyrin.

5. The separator for lithium ion battery according to claim 4, characterized in that: The mass ratio of the first organic ligand to the second organic ligand is first organic ligand: second organic ligand = 1: (0.3-10), preferably the mass ratio of the first organic ligand to the second organic ligand is first organic ligand: second organic ligand = 1: (1-2).

6. The separator for lithium-ion battery according to claim 4, characterized in that: The MOF material is one or any combination of ZIF series materials, UiO series materials, MIL series materials, and PCN series materials; preferably, the MOF material is a UiO series material, and the functional group is -SO3H.

7. The separator for lithium-ion battery according to claim 1, characterized in that: The thickness of the functional coating is 0.5 μm to 5 μm; preferably, the thickness of the functional coating is 1 μm to 5 μm.

8. The separator for lithium-ion battery according to claim 1, characterized in that: The functional coating also includes additives, which include one or more of a dispersant, a wetting agent, a thickener and a pH adjuster.

9. A method for preparing a separator, for preparing the separator for lithium-ion batteries according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1, providing a functionalized slurry mainly composed of a binder, a functionalized MOF material and a solvent; Step 2: coating the functionalized slurry on the surface of the base film and drying it to obtain the functional coating on the surface of the base film to prepare the isolation film.

10. The method for preparing an isolation film according to claim 9, characterized in that: The functionalized MOF material is obtained by mixing and reacting a metal salt of the MOF material, an organic ligand of the MOF material and a coordination solvent, wherein the organic ligand of the MOF material includes at least a first organic ligand, and the first organic ligand contains a functional functional group.

11. The method for preparing an isolation film according to claim 10, characterized in that: The mass ratio of the organic ligand of the MOF material to the metal salt of the MOF material is organic ligand of the MOF material:metal salt of the MOF material=1:(1-2); And / or, the coordination solvent is one or more of water, ethanol, methanol, glycerol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, and formic acid.

12. The method for preparing an isolation film according to claim 9, characterized in that: In the slurry of the functionalized coating, the solid content of the slurry is 10% to 50%; And / or, the mass percentage of the functionalized MOF material relative to the solute in the slurry is 70wt% to 99wt%, and the mass percentage of the binder relative to the solute in the slurry is 1wt% to 30wt%; And / or, the slurry of the functionalized coating further includes additives, the additives include one or more of a dispersant, a wetting agent, a thickener and a pH regulator, and the mass percentage of the additives relative to the solute in the slurry is 0.5wt% to 5wt%; the mass percentage of the functionalized MOF material relative to the solute in the slurry is 70wt% to 95wt%, and the mass percentage of the binder relative to the solute in the slurry is 1wt% to 25wt%.

13. A lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, characterized in that: The isolation membrane is an isolation membrane according to any one of claims 1 to 8 or an isolation membrane prepared by the method for preparing an isolation membrane according to any one of claims 9 to 12.

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