Battery diaphragm, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery diaphragm, a preparation method thereof and a battery. The battery diaphragm provided by the invention comprises a base membrane as well as a first composite material coating and a second composite material coating which are respectively coated on two sides of the base membrane, the first composite material coating comprises an MOF-carbon material compound, the MOF-carbon material compound comprises a carboxylated carbon material and an MOF material, and the second composite material coating comprises an MOF material. When the battery diaphragm is applied to a battery, the first composite material coating faces a positive electrode of the battery, and the second composite material coating faces a negative electrode of the battery. The invention has the effects of improving the performance and cycle life of the battery.

Description

Technical Field

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

[0002] The core structure of the battery consists of a positive electrode, a negative electrode, an electrolyte and a separator. As an important component of the battery, the separator plays the role of isolating the positive and negative electrodes and preventing short circuits and electrolyte loss. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the battery's capacity, cycle and safety performance.

[0003] In related technologies, new separator products are constantly emerging, such as forming a functional coating on a polypropylene film or a polyamide film. However, in actual applications, since the two sides of the separator correspond to the positive electrode side and the negative electrode side, respectively, the functional emphasis of the positive and negative sides is often different. For example, the positive electrode side generally requires higher ionic conductivity and the ability to suppress volume expansion, while the negative electrode side requires better dendrite suppression and interface stabilization. Taking lithium batteries as an example, if the lithium deposition on the negative electrode side is uneven, it may lead to dendrite growth, which will cause a short circuit or even thermal runaway, thereby affecting the performance and cycle life of the battery. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to improve the performance and cycle life of the battery.

[0005] To solve the above problems, the present invention provides a battery separator, a preparation method thereof, and a battery.

[0006] As a first aspect, the present invention provides a battery separator, comprising a base film and a first composite material coating and a second composite material coating respectively coated on both sides of the base film; The material of the first composite material coating layer includes a MOF-carbon material composite, the MOF-carbon material composite includes a carboxylated carbon material and a MOF material, and the material of the second composite material coating layer includes a MOF material.

[0007] Optionally, when the battery separator is applied to a battery, the first composite material coating faces the positive electrode of the battery, and the second composite material coating faces the negative electrode of the battery.

[0008] Optionally, in the first composite material coating, the carboxylated carbon material includes any one or more of carboxylated carbon nanotubes, carboxylated graphene oxide and carboxylated 3D graphene; And / or, in the first composite material coating and the second composite material coating, the MOF material includes any one or more of UIO-66-NH2, ZIF-8-NH2 and MOF-808-NH2.

[0009] Optionally, the first composite material coating and the second composite material coating further include a binder, respectively. The binder includes any one or more of polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate, and polyimide.

[0010] Optionally, the thickness of the first composite material coating layer and the second composite material coating layer is 2 μm to 10 μm respectively.

[0011] As a second aspect, the present invention further provides a method for preparing a battery separator, for preparing the battery separator as described above, the method comprising: Synthesize MOF materials; synthesizing a MOF-carbon material composite by an amide reaction between the MOF material and the carboxylated carbon material, mixing the MOF-carbon material composite with a binder and a second mixed solvent to obtain a first coating liquid, and mixing the MOF material with a binder and a second mixed solvent to obtain a second coating liquid; The first coating liquid and the second coating liquid are respectively coated on both sides of the base film and then dried to obtain the battery separator.

[0012] Optionally, the synthesizing a MOF-carbon material composite by reacting the MOF material and the carboxylated carbon material through an amide reaction comprises: The MOF material and the carboxylated carbon material are dissolved in an organic solvent, mixed evenly, reacted at 60 to 100° C. for 1 to 5 hours, washed and dried to obtain the MOF-carbon material composite.

[0013] Optionally, in the first coating liquid, the mass percentage of the MOF-carbon material composite is 2% to 10%, and the mass percentage of the binder is 5% to 25%; And / or, in the second coating liquid, the mass percentage of the MOF material is 2% to 10%, and the mass percentage of the binder is 5% to 25%.

[0014] Optionally, the MOF material is synthesized by a hydrothermal crystallization method, wherein the time of the hydrothermal crystallization method is 12 to 48 hours and the temperature is 60 to 150°C.

[0015] Optionally, the first coating liquid and the second coating liquid are respectively coated on both sides of the base film by electrospinning.

[0016] As a third aspect, the present invention further provides a battery, which includes the battery separator described in the first aspect, or includes a battery separator prepared by the method for preparing the battery separator described in the second aspect.

[0017] The beneficial effects of the present invention compared to the prior art include: In the battery separator provided by the present invention, different coating materials are used to coat the two sides of the base membrane, and in the first composite material coating on one side, the MOF-carbon material composite has both the high specific surface area, regular pore structure and excellent thermal stability of the MOF material and the excellent conductive properties of its carbon material. Specifically, the high specific surface area and regular pore structure of the MOF material can increase the porosity of the base membrane, provide a fast migration channel for conductive ions (such as lithium ions), and increase the number of lithium ion migration by selectively adsorbing PF6⁻ anions, reduce the interface impedance, and increase the charge and discharge rate. The conductive network of the carboxylated carbon material can accelerate electron conduction and reduce electrode polarization. The rigid structure of the MOF material and the flexible network of the carboxylated carbon material can adapt to the volume change of the battery material during the charge and discharge process, prevent particle rupture, and thus provide mechanical support. In addition, in the second composite material coating on the other side of the base membrane, the MOF layer can preferentially adsorb Li in the electrolyte due to its high specific surface area and polar functional groups. + , inducing uniform nucleation and reducing the local current density, thereby inhibiting dendrite formation.

[0018] Therefore, the present invention employs an asymmetric coating design on both sides of the battery separator, with one side coated with a MOF-carbon material composite and the other with a single MOF material. The two layers work together to achieve a dynamic equilibrium in which conductive ions (such as lithium ions) are rapidly released from one side and orderly deposited on the other. This asymmetric coating design optimizes overall performance, comprehensively improving the thermal stability, mechanical strength, and conductivity of the battery separator, thereby reducing battery resistance and enhancing the battery's high-temperature storage performance, fast-charging performance, and cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of a battery separator in an exemplary embodiment of the present invention; Figure 2 is a schematic diagram of the molecular structure of a MOF-carbon material composite in an exemplary embodiment of the present invention; Figure 3 is a schematic structural diagram of a battery separator of the present invention applied to an exemplary battery; Figure 4 1-2 is a comparison chart of the charging DCR of lithium-ion batteries assembled using the battery separators prepared in Examples 1-9 and Comparative Examples 1-2; Figure 5 This is a comparison chart of the capacity retention of lithium-ion batteries assembled using the battery separators prepared in Examples 1-9 and Comparative Examples 1-2 under storage conditions of 60° C. for 28 days; Figure 61-2 and 1-3 are comparison diagrams of the charge capacity retention rates of lithium-ion batteries assembled using the battery separators prepared in Examples 1-9 and Comparative Examples 1-2 under two different charging modes.

[0020] Description of reference numerals: 1. Positive electrode; 2. Negative electrode; 3. Battery separator; 31. Base film; 32. First composite material coating; 33. Second composite material coating; 4. Electrolyte. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0022] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "including" and its variations used in this document are open inclusions, that is, "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "multiple" means two or more.

[0023] Batteries mainly consist of four core structures: positive electrode, negative electrode, separator and electrolyte. Among them, the positive electrode and negative electrode are responsible for storing and releasing electrical energy respectively, and the electrolyte provides a medium for ion transmission to ensure the normal operation of the battery. The separator plays the role of isolating the positive and negative electrodes and preventing short circuits, while allowing ions to pass through to achieve charging and discharging functions. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the battery's capacity, cycle and safety performance. Therefore, the battery separator material needs to have good conductivity, thermal stability and mechanical strength.

[0024] Metal-Organic Frameworks (MOFs) are a class of crystalline porous materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. They combine the rigidity of inorganic materials with the flexibility of organic materials. They feature a periodic network structure, high porosity, and a large specific surface area. In practical applications, their functionality can be customized by varying the metal center or organic ligands.

[0025] Carboxylated carbon materials refer to materials that have carboxyl functional groups (-COOH) introduced onto the surface of carbon materials through chemical treatment. This process is usually achieved through chemical modification, which makes the originally hydrophobic surface of the carbon material more hydrophilic, enhancing its compatibility with other compounds. The introduction of carboxyl functional groups not only improves the dispersibility and solubility of the carbon material, but also provides active sites for subsequent functional modification.

[0026] An embodiment of the present invention provides a battery separator. Figure 1 FIG. 3 is a schematic structural diagram of a battery separator 3 in an exemplary embodiment of the present invention. Figure 1 As shown, the battery separator 3 in the embodiment of the present invention includes a base film 31 and a first composite material coating 32 and a second composite material coating 33 respectively coated on both sides of the base film 31. The material of the first composite material coating 32 includes a MOF-carbon material composite, which includes a carboxylated carbon material and a MOF material, and the material of the second composite material coating 33 includes a MOF material.

[0027] In this embodiment, the battery separator 3 is coated with different coating materials on both sides of the base membrane 31. In the first composite material coating 32 on one side, the MOF-carbon material composite combines the high specific surface area, regular pore structure and excellent thermal stability of the MOF material with the excellent electrical conductivity of the carbon material. Specifically, the high specific surface area and regular pore structure of the MOF material can increase the porosity of the base membrane 31, providing a good space for conductive ions (such as Li + ) provides a fast migration channel by selectively adsorbing PF6 - The anions increase the number of lithium ion migration, reduce the interface impedance, and increase the charge and discharge rate; while the conductive network of the carboxylated carbon material can accelerate electron conduction and reduce electrode polarization. The rigid structure of the MOF material and the flexible network of the carboxylated carbon material can adapt to the volume change of the electrode material during the charge and discharge process, prevent the particles from breaking, and thus provide mechanical support. In addition, in the second composite material coating 33 on the other side of the base film 31, the MOF layer can preferentially adsorb conductive ions (such as Li) in the electrolyte due to its high specific surface area and polar functional groups. + ), achieving effective and uniform precipitation of lithium ions, and a single MOF material has a lower production cost.

[0028] Therefore, in this embodiment, an asymmetric coating design is adopted on both sides of the battery separator 3, and the two can work together to achieve conductive ions (such as Li + ) in a dynamic balance where one side is quickly detached and the other side is orderly deposited, thereby achieving overall performance optimization through the asymmetric design of the coating on both sides, and comprehensively improving the thermal stability, mechanical strength and conductive properties of the battery separator 3, thereby reducing the resistance of the battery and improving the high-temperature storage performance, fast charging performance and cycle life of the battery.

[0029] In some optional embodiments, when the battery separator 3 is applied to a battery, the first composite material coating 32 faces the positive electrode 1 of the battery, and the second composite material coating 33 faces the negative electrode 2 of the battery.

[0030] It should be noted that batteries primarily rely on the movement of conductive ions between the positive and negative electrodes to achieve charging and discharging. Taking lithium batteries as an example, during the charging process, an external power source applies voltage to the battery, causing the lithium ions in the positive electrode material to gain energy and deintercalate from the positive electrode, passing through the electrolyte and separator to reach the negative electrode, and then embedding into the graphite material of the negative electrode. During the discharge process, the lithium ions deintercalate from the negative electrode, return to the positive electrode through the electrolyte, and release energy.

[0031] In this embodiment, according to the movement direction of the conductive ions inside the battery, the positive electrode side of the battery separator 3 adopts a MOF-carbon material composite as the coating material. The carbon material skeleton provides an electronic conductive network, which is conducive to reducing the interface impedance, and the nanopores of the MOF material selectively adsorb PF6 - The negative electrode uses a single MOF material as the coating material, which is beneficial to fully utilize the structural characteristics of the single MOF material to Li + Adsorption to regulate Li + flux, induces uniform nucleation, avoids local deposition, and realizes Li + Accelerate the release, while the negative electrode side is orderly deposited and Li + Therefore, the present invention achieves a differentiated functional division of labor between the positive and negative electrodes, with the positive electrode focusing on high electron conductivity and the negative electrode on dendrite suppression and interface stability. This can simultaneously solve the problems of ion transport bottlenecks, dendrite growth risks, and interface side reactions in batteries.

[0032] In some optional embodiments, the carboxylated carbon material in the first composite coating 32 includes any one or more of carboxylated carbon nanotubes, carboxylated graphene oxide, and carboxylated 3D graphene. The MOF material in the first composite coating 32 and the second composite coating 33 includes any one or more of UIO-66-NH2, ZIF-8-NH2, and MOF-808-NH2.

[0033] It should be noted that the selection of the type of MOF material should be understood as follows: in the MOF-carbon material composite of the first composite material coating 32, the MOF material of one of its raw materials and the MOF material of the second composite material coating 33 can be selected from any one or more of UIO-66-NH2, ZIF-8-NH2 and MOF-808-NH2, and the MOF materials in the first composite material coating 32 and the second composite material coating 33 can be the same one of the above materials or different ones.

[0034] Specifically, Figure 2 Schematic diagram of the structure of a MOF-carbon material composite prepared in an exemplary embodiment of the present invention. Figure 2 In the figure, the carboxylated carbon material (red area or polyhedral structure area) forms a chemical bond with the MOF material (gray area or framework structure area), resulting in a uniform distribution of the carboxylated carbon material on the surface of the MOF material. In the MOF material of the present invention, amino groups are introduced as functional moieties into the MOF organic network. This modification imparts specific properties and functions to the MOF, allowing the MOF material to form amide bonds with the carboxyl groups of the carboxylated carbon material, thus achieving a more stable chemical bond.

[0035] In some optional embodiments, the first composite material coating 32 and the second composite material coating 33 further include a binder, and the binder includes any one or more of polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate, and polyimide.

[0036] In this optional embodiment, a binder is further added to the first composite material coating 32 and the second composite material coating 33, such as using polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA) or polyimide (PI) as one of the coating materials, which is beneficial to improving the bonding force between the diaphragm and the electrode, and the binder has excellent chemical corrosion resistance, thermal stability and mechanical properties, which can further improve the thermal stability and mechanical properties of the battery diaphragm 3.

[0037] In some optional embodiments, the base film 31 is a polyolefin base film, and the thickness of the polyolefin base film is 5 μm to 15 μm.

[0038] Specifically, the polyolefin-based membrane material includes any one or more of dry-laid mono-stretched polypropylene, dry-laid bi-stretched polypropylene, or wet-laid polyethylene lithium battery separators, with a porosity of 35% to 45%. The polyolefin-based membrane thickness can be 5μm, 8μm, 10μm, 12μm, or 15μm. By controlling the thickness of the base membrane 31 within a reasonable range, the increased internal resistance of the battery caused by using an overly thick separator and the potential for short circuits and other safety issues caused by using an overly thin separator can be mitigated.

[0039] In some optional embodiments, the thickness of the first composite material coating 32 and the second composite material coating 33 are respectively 2 μm to 10 μm.

[0040] In this optional embodiment, by controlling the thickness of the single-sided coating of the base film 31 to 2-10 μm, specifically 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, etc., the phenomenon that an excessively thick coating increases the internal resistance of the battery and an excessively thin coating has insufficient function can be improved.

[0041] Another embodiment of the present invention provides a method for preparing a battery separator, which can be used to prepare the above-mentioned battery separator, and the method comprises the following steps: Step S1: Synthesizing MOF materials.

[0042] Specifically, in some optional embodiments, a metal precursor and an organic ligand can be dissolved in a first mixed solvent and synthesized using a hydrothermal crystallization method. For example, the first mixed solvent can be N,N-dimethylformamide (DMF) and concentrated hydrochloric acid in a volume ratio of 1:(0.01 to 0.1). The metal precursor can be ZrCl₄ or Zn(NO₃)₂·6H₂O₂, and the organic ligand can be 2-aminoterephthalic acid or 2-aminoimidazole. The hydrothermal crystallization method can be performed for 12 to 48 hours at a temperature of 60 to 150°C.

[0043] MOF materials are prepared by reacting metal ions with organic ligands in aqueous solution. Under hydrothermal conditions, the high temperature and high pressure of water promote the reaction between metal ions and organic ligands, forming MOF materials with amino groups.

[0044] Step S2: A MOF material and a carboxylated carbon material are reacted to form a MOF-carbon material composite, and then the MOF-carbon material composite is mixed with a binder and a second mixed solvent to obtain a first coating solution. Simultaneously, the MOF material is mixed with a binder and a second mixed solvent to obtain a second coating solution.

[0045] Specifically, in some optional embodiments, the MOF material and the carboxylated carbon material can be dissolved in an organic solvent, mixed uniformly, reacted at 60 to 100° C. for 1 to 5 hours, and then washed and dried to obtain a MOF-carbon material composite. Exemplarily, the mass ratio of the MOF material to the carboxylated carbon material is (0.5 to 2):1, and the organic solvent can be N,N-dimethylformamide (DMF).

[0046] The MOF material of the present invention and the carboxylated carbon material form a strong chemical bond connection through an amide reaction. Compared with simple physical mixing, chemical bonding can effectively avoid the phenomenon of two-phase separation caused by volume changes, electrolyte swelling or mechanical stress during charging and discharging, thereby effectively inhibiting interface peeling, enhancing interface bonding strength, and improving the cycle stability of the composite material.

[0047] The MOF-carbon material composite is then dispersed in a second mixed solvent to obtain a composite material dispersion, which is then mixed with a binder to obtain a first coating solution. For example, the second mixed solvent can be formed by mixing N,N-dimethylformamide (DMF) and acetone in a volume ratio of 1:(0.4 to 2), and the mass ratio of the second mixed solvent to the MOF-carbon material composite is 1:(0.01 to 0.1). The resulting first coating solution contains 2% to 10% by weight of the MOF-carbon material composite and 5% to 25% by weight of the binder.

[0048] Simultaneously, the MOF material prepared in step S1 is directly dispersed in a second mixed solvent to obtain a MOF material dispersion, which is then mixed with a binder to prepare a second coating solution. Again, as an example, the mass ratio of the second mixed solvent to the MOF material is 1:(0.01 to 0.1). The resulting second coating solution contains 2% to 10% by mass of the MOF material and 5% to 25% by mass of the binder.

[0049] It should be noted that when the solute is dissolved in the solvent, it can be dispersed by ultrasound, and the ultrasound time is 0.5 to 6 hours to improve the final mixing effect.

[0050] S3: The first coating liquid and the second coating liquid are respectively coated on both sides of the base film 31 and then dried to obtain the battery separator 3.

[0051] Specifically, the coating technology may include any one of dip coating, slot extrusion coating, blade coating, spin coating or electrospinning. In some optional embodiments, electrospinning can be used to apply the first coating liquid and the second coating liquid to both sides of the base film 31 respectively. As an example, the temperature of electrospinning is controlled to be 10 to 30°C and the humidity is controlled to be 50 to 70%. The coating obtained by electrospinning technology has a high porosity and good pore connectivity. In the actual operation process, the porosity of the battery separator 3 can be appropriately adjusted by adjusting the processing parameters of electrospinning to meet the requirements of the battery separator 3 for the material porosity.

[0052] After coating, for example, vacuum drying may be performed at a temperature of 40 to 80° C. for 4 to 12 hours to obtain the first composite material coating 32 and the second composite material coating 33 with a thickness of 2 to 10 μm.

[0053] Yet another embodiment of the present invention provides a battery, which includes the battery separator 3 described above, or the battery separator 3 prepared by the method for preparing the battery separator described above.

[0054] Figure 3 This is a schematic diagram of the structure of a battery separator 3 according to an embodiment of the present invention applied to an exemplary battery. Figure 3 As shown, the battery consists of a positive electrode 1, a negative electrode 2, a battery separator 3, and an electrolyte 4. The battery separator 3 is disposed between the positive electrode 1 and the negative electrode 2, with the first composite material coating 32 (not shown) of the battery separator 3 facing the positive electrode 1, and the second composite material coating 33 (not shown) facing the negative electrode 2. The battery separator 3 separates the positive electrode 1 and the negative electrode 2 to prevent short circuits, while allowing lithium ions to pass through while blocking electrons to achieve normal charging and discharging of the battery. In some other embodiments, the battery separator 3 can also securely bond the positive and negative electrode sheets together and be further stacked or wound with the positive and negative electrode sheets to form a battery cell. It should be understood that the battery separator 3 in the embodiments of the present invention can be applied to batteries of various types, such as lithium-ion batteries and sodium-ion batteries.

[0055] The present invention is described in detail below through specific examples and comparative examples: Example 1 (1) Preparation of UiO-66-NH2 A metal solution was prepared by weighing 1.561 g of zirconium chloride (ZrCl4) and dissolving it in 100 mL of N,N-dimethylformamide (DMF). Simultaneously, 1.812 g of 2-aminoterephthalic acid was weighed and dissolved in 90 mL of DMF. 10 mL of concentrated hydrochloric acid (36.5%) was added to prepare an organic ligand solution. The metal solution and ligand solution were each sonicated for 60 minutes to ensure complete dissolution and uniform dispersion.

[0056] The metal solution and organic ligand solution were mixed uniformly and added to a hydrothermal reactor for 48 hours at 120°C. After cooling to room temperature, the mixture was centrifuged and washed three times with DMF and deionized water, respectively, before being vacuum-dried at 60°C for 24 hours to obtain the MOF material, UiO-66-NH2.

[0057] (2) Preparation of MOF-carbon material composites Weigh carboxylated carbon nanotubes (CNTs-COOH) and add them to a three-necked flask containing 50 mL of DMF solvent. Ultrasonic dispersion is performed for 30 minutes. Then, the UiO-66-NH2 prepared in step (1) is added, where the mass ratio of UiO-66-NH2 to CNTs-COOH is 0.5:1. The mixture is stirred under magnetic stirring at 80°C for 3 hours. After washing with acetone and drying, a MOF-carbon material composite is obtained.

[0058] (3) Preparation of the first coating liquid The MOF-carbon material composite particles prepared in step (2) are ultrasonically dispersed in a second mixed solvent of DMF and acetone (7:3) to obtain a composite material dispersion liquid. PVDF powder is added to the second mixed solvent of DMF and acetone (7:3) and ultrasonically dispersed to obtain a PVDF solution. The composite material dispersion liquid and the PVDF solution are then mixed in a certain proportion and ultrasonically dispersed for 6 hours to obtain a first coating liquid. The mass percentage of the MOF-carbon material composite in the first coating liquid is 2%, and the mass percentage of PVDF is 12%.

[0059] (4) Preparation of the second coating liquid The UiO-66-NH2 prepared in (1) was ultrasonically dispersed in a second mixed solvent of DMF and acetone (7:3) to obtain a MOF material dispersion. At the same time, PVDF powder was added to the second mixed solvent of DMF:acetone (7:3) and ultrasonically dispersed to obtain a PVDF solution. The MOF material dispersion was then mixed with the PVDF solution and ultrasonically dispersed for 6 hours to obtain a second coating solution. In the second coating solution, the mass percentage of UiO-66-NH2 was 2%, and the mass percentage of PVDF was 12%.

[0060] (5) Preparation of battery separators The prepared first and second coating liquids were electrospun onto both sides of a polyolefin separator, forming a first and second composite coating, respectively. The thickness of the first and second composite coatings was controlled to 2 μm. The electrospinning temperature was controlled at 20°C and the humidity was controlled at 60%. After electrospinning, the film was dried in a vacuum environment at 60°C for 8 hours to obtain a battery separator.

[0061] Example 2 In this embodiment, the preparation process of the MOF material and the preparation process of the MOF-carbon material composite are the same as those in Example 1, except that: In the first coating liquid, the mass percentage of the MOF-carbon material composite is 5%, and the mass percentage of PVDF is 12%; in the second coating liquid, the mass percentage of UiO-66-NH2 is 5%, and the mass percentage of PVDF is 12%.

[0062] During the preparation of the battery separator, the thickness of the first composite material coating and the second composite material coating was controlled to be 3 μm.

[0063] Example 3 In this embodiment, the preparation process of the MOF material and the preparation process of the MOF-carbon material composite are the same as those in Example 1, except that: In the first coating liquid, the mass percentage of the MOF-carbon material composite is 10%, and the mass percentage of PVDF is 25%; in the second coating liquid, the mass percentage of UiO-66-NH2 is 10%, and the mass percentage of PVDF is 25%.

[0064] During the preparation of the battery separator, the thickness of the first composite material coating and the second composite material coating was controlled to be 4 μm.

[0065] Example 4 (1) Preparation of ZIF-8-NH2 1.488g of Zn(NO₃)₂·6H₂O was weighed and dissolved in 100ml of DMF to obtain a metal solution. Then, 0.270g of 2-aminoimidazole (2-AIM), 1.478g of 2-methylimidazole (2-MIM), and 0.1g of sodium formate were weighed and dissolved in 50ml of deionized water. The mixture was heated at 70°C for 2 hours to obtain an organic ligand solution. The metal solution was quickly added to the organic ligand solution at room temperature and stirred for 0.5 hours. The resulting mixture was then centrifuged and washed with methanol three times, each for 12 hours. Finally, it was dried under vacuum at 80°C for 12 hours to obtain the MOF material ZIF-8-NH₂.

[0066] (2) Preparation of MOF-carbon material composites Carboxylated graphene oxide was weighed and added to a three-necked flask containing 50 mL of DMF. Ultrasonic dispersion was performed for 30 minutes to fully disperse the carboxylated graphene oxide in the DMF. ZIF-8-NH2 was then added at a 1:1 weight ratio of ZIF-8-NH2 to carboxylated graphene oxide. The mixture was reacted at 60°C with magnetic stirring for 5 hours. After washing with acetone and drying, the MOF-carbon composite was obtained.

[0067] (3) Preparation of the first coating liquid The prepared MOF-carbon material composite was ultrasonically dispersed in a second solvent mixture of DMF and acetone (1:2) to obtain a composite dispersion. PMMA powder was then added to the second solvent mixture of DMF and acetone (1:2) and ultrasonically dispersed to obtain a PMMA solution. The composite dispersion and PMMA solution were then mixed in a specific ratio and ultrasonically dispersed for 6 hours to obtain a first coating solution. The first coating solution contained 2% by weight of the MOF-carbon material composite and 5% by weight of PVDF.

[0068] (4) Preparation of the second coating liquid The ZIF-8-NH2 prepared in (1) was ultrasonically dispersed in a second mixed solvent of DMF and acetone (1:2) to obtain a MOF material dispersion. PMMA powder was added to the second mixed solvent of DMF and acetone (1:2) and ultrasonically dispersed to obtain a PMMA solution. The MOF material dispersion and the PMMA solution were then mixed and ultrasonically dispersed for 6 hours to obtain a second coating solution. The mass percentage of ZIF-8-NH2 in the second coating solution was 2%, and the mass percentage of PVDF was 5%.

[0069] (5) Preparation of battery separators The prepared first and second coating liquids were electrospun onto both sides of a polyolefin separator, forming a first and second composite coating, respectively. The thickness of the first and second composite coatings was controlled to 2 μm. The electrospinning temperature was controlled at 10°C and the humidity was controlled at 50%. After electrospinning, the film was dried in a vacuum environment at 80°C for 4 hours to obtain a battery separator.

[0070] Example 5 The difference between this embodiment and embodiment 4 is that: In the first coating liquid, the mass percentage of the MOF-carbon material composite is 5%, and the mass percentage of PMMA is 12%; in the second coating liquid, the mass percentage of ZIF-8-NH2 is 5%, and the mass percentage of PMMA is 12%.

[0071] During the preparation of the battery separator, the thickness of the first composite material coating and the second composite material coating was controlled to be 3 μm.

[0072] Example 6 The difference between this embodiment and embodiment 4 is that: in the first coating liquid, the mass percentage of the MOF-carbon material composite is 10%, and the mass percentage of PMMA is 25%; in the second coating liquid, the mass percentage of ZIF-8-NH2 is 10%, and the mass percentage of PMMA is 25%.

[0073] During the preparation of the battery separator, the thickness of the first composite material coating and the second composite material coating was controlled to be 4 μm.

[0074] Example 7 (1) Preparation of MOF-88-NH2 1.561 g of zirconium chloride (ZrCl4) was weighed and dissolved in 100 mL of a first mixed solvent consisting of N,N-dimethylformamide (DMF) and formic acid in a 1:0.1 volume ratio to obtain a metal solution. 1.812 g of 2-aminoterephthalic acid was then weighed and dissolved in 90 mL of DMF to obtain an organic ligand solution. The metal and organic ligand solutions were ultrasonically treated for 60 minutes, mixed, and then added to a hydrothermal reactor and reacted at 130°C for 48 hours. After cooling to room temperature, the mixture was separated by centrifugation and washed alternately with DMF and deionized water three times. The mixture was then vacuum-dried at 150°C for 12 hours to obtain the white product, MOF-88-NH2.

[0075] (2) Preparation of MOF-carbon material composites Weigh carboxylated graphene oxide and add it to a three-necked flask containing 50 mL of DMF. Ultrasonic dispersion is performed for 30 minutes to fully disperse the carboxylated 3D graphene in DMF. Then, the MOF-88-NH2 prepared in step (1) is added. The mass ratio of MOF-88-NH2 to carboxylated 3D graphene is 2:1. The mixture is stirred under magnetic stirring at 100°C for 1 hour. After washing with acetone and drying, a MOF-carbon material composite is obtained.

[0076] (3) Preparation of the first coating liquid The MOF-carbon material composite prepared in step (2) is ultrasonically dispersed in a second mixed solvent of DMF and acetone (7:3) to obtain a composite material dispersion. PVDF powder is simultaneously added to the second mixed solvent of DMF and acetone (7:3) and ultrasonically dispersed to obtain a PVDF solution. The composite material dispersion is then mixed with the PVDF solution and ultrasonically dispersed for 6 hours to obtain a first coating solution. In the first coating solution, the mass percentage of the MOF-carbon material composite is 10%, and the mass percentage of PVDF is 12%.

[0077] (4) Preparation of the second coating liquid The MOF-88-NH2 prepared in (1) was ultrasonically dispersed in a second mixed solvent of DMF and acetone (7:3) to obtain a MOF material dispersion. PVDF powder was added to the second mixed solvent of DMF:acetone (7:3) and ultrasonically dispersed to obtain a PVDF solution. The MOF material dispersion was then mixed with the PVDF solution and ultrasonically dispersed for 6 hours to obtain a second coating solution. The mass percentage of MOF-88-NH2 in the second coating solution was 10%, and the mass percentage of PVDF was 12%.

[0078] (5) Preparation of battery separators The prepared first and second coating liquids were electrospun onto both sides of a polyolefin separator, forming a first composite coating and a second composite coating, respectively. The thickness of the first and second composite coatings was controlled to 2 μm. The electrospinning temperature was controlled at 30°C and the humidity was controlled at 70%. After electrospinning, the film was dried in a vacuum environment at 40°C for 12 hours to obtain a battery separator.

[0079] Example 8 The difference between this embodiment and embodiment 7 is that: In the first coating liquid, the mass percentage of the MOF-carbon material composite is 5%, and the mass percentage of PVDF is 12%; in the second coating liquid, the mass percentage of MOF-88-NH2 is 5%, and the mass percentage of PVDF is 12%.

[0080] During the preparation of the battery separator, the thickness of the first composite material coating and the second composite material coating was controlled to be 3 μm.

[0081] Example 9 The difference between this embodiment and embodiment 7 is that: In the first coating liquid, the mass percentage of the MOF-carbon material composite is 10%, and the mass percentage of PVDF is 25%; in the second coating liquid, the mass percentage of MOF-88-NH2 is 10%, and the mass percentage of PVDF is 25%.

[0082] During the preparation of the battery separator, the thickness of the first composite material coating and the second composite material coating was controlled to be 4 μm.

[0083] Comparative Example 1 In this comparative example, PVDF powder was added to a second solvent mixture of DMF and acetone (7:3) and ultrasonically dispersed to obtain a PVDF solution. This PVDF solution was then electrospun onto both sides of a polyolefin separator, with the coating thickness controlled to 2 μm. After spinning, the membrane was dried under vacuum at 60°C for 8 hours to obtain a PVDF-coated battery separator.

[0084] Comparative Example 2 In this comparative example, UiO-66-NH2, a MOF-carbon material composite, and a first coating solution were prepared using the method described in Example 1. The prepared first coating solution was then electrospun onto both sides of a polyolefin separator. The electrospun coating thickness was controlled to 2 μm. After spinning, the membrane was dried under vacuum at 60°C for 8 hours to obtain a battery separator coated with the MOF-carbon material composite.

[0085] The battery separators prepared in Examples 1-9 and Comparative Examples 1-2 were subjected to performance tests. Specific performance includes thickness, thermal shrinkage, porosity, and puncture strength. The specific test methods are described in GB / T36363-2018 and the literature Carbohydrate Polymers 234 (2020) 115907; Polymers 15 (2023) 1954. Specific performance data are shown in Table 1: Table 1 Performance data of battery separators prepared in Examples 1-9 and Comparative Examples 1-2

[0086] In Table 1, "-" represents that there is no coating on both sides of the base film, Comparative Example 1 is a battery separator coated on both sides only with PVDF, and Comparative Example 2 is a battery separator coated on both sides only with MOF-carbon material composite + PVDF. As can be seen from Table 1, the basic physical and chemical properties of the battery separators coated on both sides with MOF-carbon material composite + PVDF and MOF material + PVDF, respectively, in Examples 1 to 9 of the present invention have been improved. Among them, compared with the polyolefin base film and the separator coated with PVDF (Comparative Example 1), the porosity and puncture strength of the battery separators prepared in Examples 1 to 9 have been significantly increased, and the thermal shrinkage rate has been significantly reduced. This shows that the mechanical properties and thermal safety performance of the battery separators prepared in Examples 1-9 of the present invention have been significantly improved.

[0087] Furthermore, the battery separators of Examples 1-9 and Comparative Examples 1-2 were assembled into lithium-ion batteries according to the following method.

[0088] (1) Positive electrode sheet: Lithium iron phosphate (LFP), polyvinylidene fluoride (PVDF), and conductive carbon are added to a certain amount of N-methylpyrrolidone, where LFP:PVDF:conductive carbon = 96.2:3:0.8, and stirred in a dry environment to form a uniform positive electrode slurry. The positive electrode slurry is coated on aluminum foil, dried, and rolled to form a positive electrode sheet.

[0089] (2) Negative electrode sheet: Add graphite, sodium hydroxymethyl cellulose, conductive carbon and styrene-butadiene rubber to a certain amount of deionized water (graphite: sodium hydroxymethyl cellulose: conductive carbon: styrene-butadiene rubber = 96:1.0:1.0:2.0), stir to form a uniform negative electrode slurry, apply the negative electrode slurry on copper foil, dry and cold press to make a negative electrode sheet.

[0090] (3) Electrolyte: Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1, and an appropriate amount of LiPF6 was added to make its concentration 1 mol / L, and fluoroethylene carbonate was added to make its mass fraction 3 wt%.

[0091] The positive and negative electrode sheets are sequentially rolled, die-cut, dried, stacked, assembled, and then injected with electrolyte, sealed, formed, and double-sealed to produce a square soft-pack lithium-ion battery.

[0092] The prepared lithium-ion battery was tested for its charging DCR, capacity retention under 28-day storage conditions at 60°C, and two different charging methods. Charging method 1: CC / CV 0.5C to 3.75 V, 0.05C cutoff, SOC 0-80% 96min. Charging method 2: step charge: 1C (0-10% SOC); 2.8C (10-15% SOC); 2.8C (15-20% SOC); 2.7C (20-25% SOC); 2.5C (25-30% SOC); 2.3C (30-35% SOC); 2.05C (35-40% SOC); 1.9C (40-45% SOC); 1.8C (45-50% SOC); 1.72C (50- 55%soc); 1.65C (55-60%soc); 1.54C (60-65%soc); 1.33C (65-70%soc); 1.16C (70-75%soc); 0.95 C (75-80%soc); 0.75C (80-85%soc); 0.5C (85-90%soc); 0.33C (90-95%soc); 0.2C, CVto0.05ln1. SOC 0-80% 24min.

[0093] Figure 4 The DCR of a lithium-ion battery is shown when its state of charge is 80%. DCR specifically reflects the internal resistance of the battery. Figure 4 It can be seen that compared with Comparative Example 1, the charging DCR of the lithium-ion batteries containing the battery separators prepared in Examples 1-9 is slightly reduced, which proves that the conductive properties of the battery separators prepared in the examples of the present invention are improved.

[0094] Figure 5The residual capacity retention rate of the lithium-ion battery after storage at 60°C for 28 days is demonstrated. It can be seen that the high-temperature storage performance of the lithium-ion battery containing the battery separator prepared by Examples 1 to 9 of the present invention is improved, among which the improvement of the high-temperature storage performance of Examples 2, 3, 5, 6, and 9 is more obvious.

[0095] Figure 6 The capacity retention of lithium-ion batteries after 500 charge-discharge cycles at 25°C is demonstrated under two different charging modes. Figure 6 It can be seen that when charging is performed using Charging Mode 1, there is no significant difference in the capacity retention rate between the Examples and the Comparative Examples. When charging is performed using Charging Mode 1, the capacity retention rates of Comparative Examples 1 and 2 deteriorate compared to Examples 1 to 9. This indicates that when the battery separators in Comparative Examples 1 and 2 use symmetrically designed coatings, active lithium precipitation occurs, resulting in a capacity drop, indicating that the lithium ion migration flux on the negative electrode side is significantly weakened. This demonstrates that the fast-charging cycle life of the battery separators prepared using asymmetrically designed coatings in the embodiments of the present invention is improved.

[0096] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A battery separator, characterized in that: The battery separator comprises a base film (31) and a first composite material coating (32) and a second composite material coating (33) respectively coated on both sides of the base film (31); The material of the first composite material coating (32) includes a MOF-carbon material composite, the MOF-carbon material composite includes a carboxylated carbon material and a MOF material, and the material of the second composite material coating (33) includes a MOF material.

2. The battery separator according to claim 1, characterized in that When the battery separator is applied to a battery, the first composite material coating (32) faces the positive electrode (1) of the battery, and the second composite material coating (33) faces the negative electrode (2) of the battery.

3. The battery separator according to claim 1, characterized in that In the first composite material coating (32), the carboxylated carbon material includes any one or more of carboxylated carbon nanotubes, carboxylated graphene oxide, and carboxylated 3D graphene; And / or, in the first composite material coating (32) and the second composite material coating (33), the MOF material includes any one or more of UIO-66-NH2, ZIF-8-NH2 and MOF-808-NH2.

4. The battery separator according to claim 1, characterized in that The first composite material coating (32) and the second composite material coating (33) further comprise a binder respectively, wherein the binder comprises any one or more of polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate and polyimide.

5. The battery separator according to claim 1, characterized in that The thickness of the first composite material coating (32) and the second composite material coating (33) are respectively 2 μm to 10 μm.

6. A method for preparing a battery separator, characterized in that: The method for preparing the battery separator is used to prepare the battery separator according to any one of claims 1 to 5, and the method for preparing the battery separator comprises: Synthesize MOF materials; synthesizing a MOF-carbon material composite by an amide reaction between the MOF material and the carboxylated carbon material, mixing the MOF-carbon material composite with a binder and a second mixed solvent to obtain a first coating liquid, and mixing the MOF material with a binder and a second mixed solvent to obtain a second coating liquid; The first coating liquid and the second coating liquid are respectively coated on both sides of the base film (31), and then dried to obtain the battery separator.

7. The method for preparing a battery separator according to claim 6, wherein: The MOF material and the carboxylated carbon material are reacted to form a MOF-carbon material composite, comprising: The MOF material and the carboxylated carbon material are dissolved in an organic solvent, mixed evenly, reacted at 60 to 100° C. for 1 to 5 hours, washed and dried to obtain the MOF-carbon material composite.

8. The method for preparing a battery separator according to claim 6, wherein: In the first coating liquid, the mass percentage of the MOF-carbon material composite is 2% to 10%, and the mass percentage of the binder is 5% to 25%; And / or, in the second coating liquid, the mass percentage of the MOF material is 2% to 10%, and the mass percentage of the binder is 5% to 25%.

9. The method for preparing a battery separator according to claim 6, wherein: The MOF material is synthesized by a hydrothermal crystallization method, wherein the hydrothermal crystallization time is 12 to 48 hours and the temperature is 60 to 150°C; And / or, the first coating liquid and the second coating liquid are respectively coated on both sides of the base film (31) by electrostatic spinning.

10. A battery, characterized in that: The battery comprises the battery separator according to any one of claims 1 to 5, or comprises a battery separator prepared by the method for preparing a battery separator according to any one of claims 6 to 9.

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