Composite separator for lithium metal battery, preparation method for composite separator, and lithium metal battery

Abstract

The present invention relates to a composite separator for a lithium metal battery, a preparation method for a composite separator, and a lithium metal battery. The composite separator for a lithium metal battery comprises a separator layer and an NF@MOF membrane layer, wherein the NF@MOF membrane layer is an NF membrane on which an MOF material is grown in situ. In the present invention, the separator layer is combined with the NF@MOF membrane layer, and the in-situ grown MOF material provides high ionic conductivity and low interfacial impedance, such that the prepared composite separator integrates high mechanical strength, high flexibility, high electrolyte wettability, a high liquid retention rate and excellent ionic conductivity; and the synergistic effect exerted by the components of the composite separator can promote the uniform deposition and stripping of lithium metal, suppress the growth of lithium dendrites, and prevent separator penetration that may lead to a short circuit or even fire and explosion accidents, thereby prolonging the cycle life of the lithium metal battery and improving the safety performance thereof. Thus, the composite separator of the present invention has broad application prospects in terms of lithium metal batteries.

Description

A lithium metal battery composite separator, its preparation method, and a lithium metal battery

[0001] This application is based on and claims priority to Chinese application CN application number 202410569744.9 filed on May 9, 2024, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to the field of lithium battery technology, and in particular to a lithium metal battery composite separator, its preparation method, and a lithium metal battery. Background Technology

[0003] With the rapid development of lithium-ion battery technology, lithium batteries have been applied to all aspects of social life. Since the current capacity of lithium batteries is approaching the theoretical capacity limit of traditional graphite anodes (372 mAh / g), there is an urgent need to develop anode materials with high theoretical capacity to meet the increasing market demand. Using pure lithium metal directly as the battery anode material is considered the holy grail for lithium-ion battery development. Lithium metal anodes have an extremely high theoretical capacity (3860 mAh / g) and the lowest electrochemical potential (-3.04 V vs. standard hydrogen electrode). When matched with currently mature cathode materials, the energy density of the battery can easily reach over 400 Wh / kg.

[0004] However, lithium metal anode batteries still suffer from severe lithium dendrite growth during actual use, which can lead to short circuits or even explosions, resulting in poor safety of lithium metal batteries. Currently, conventional commercial polypropylene / polyethylene separator products do not have the ability to resist lithium dendrite penetration. Summary of the Invention

[0005] Based on this, and addressing the technical problem that current conventional commercial separator products do not possess the ability to resist lithium dendrite penetration, the purpose of this invention is to provide a lithium metal battery composite separator, its preparation method, and a lithium metal battery. This lithium metal battery composite separator can regulate the uniform diffusion and deposition of lithium metal, has high ionic conductivity and liquid retention capacity, and good mechanical strength and flexibility, thereby achieving the effect of inhibiting lithium dendrite growth and improving the cycle life and safety of lithium metal batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The present invention provides a lithium metal battery composite separator, which includes a separator layer and an NF@MOF film layer, wherein the NF@MOF film layer is an NF film with MOF material grown in situ.

[0008] This invention combines a separator layer with an NF@MOF film layer. Simultaneously, the in-situ grown MOF material provides high ionic conductivity and low interfacial impedance. The resulting composite separator possesses high mechanical strength, high flexibility, high electrolyte wettability and high electrolyte retention, as well as excellent ionic conductivity. The synergistic effect of the components in the composite separator promotes uniform deposition and stripping of lithium metal, inhibits lithium dendrite growth, prevents short circuits or even fires and explosions caused by separator puncture, and improves the cycle life and safety performance of lithium metal batteries. Therefore, this composite separator has broad application prospects in lithium metal batteries.

[0009] As a further improvement of the above-described solution of the present invention, the membrane layer is a polypropylene membrane or a polyethylene membrane; and / or, the NF membrane is composed of polymer fibers, the MOF material is distributed on the surface of the polymer fibers, and the MOF material is connected to the polymer fibers by van der Waals forces and / or hydrogen bonds.

[0010] Furthermore, the diameter of the polymer fibers is 100–1000 nm; and / or, the thickness of the NF membrane is 10–50 μm; and / or, the porosity of the NF membrane is 55%–85%; and / or, the number average molecular weight of the polymer fiber material is 10. 4 ~10 7 g / mol; and / or, the polymer fiber material is at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, and polyvinyl alcohol; and / or, the MOF material is at least one of ZIF-8, ZIF-67, MOF-5, and HKUST-1.

[0011] Furthermore, the mass ratio of the above MOF material to the NF film is (0.1-10):(90.0-99.9).

[0012] The present invention provides a method for preparing the aforementioned lithium metal battery composite separator, comprising the following steps:

[0013] S1. Dissolve the polymer in an organic solvent to obtain a spinning solution, and electrospin the spinning solution to obtain an NF film;

[0014] S2. Prepare the growth solution for MOF material, immerse the NF membrane in the growth solution, then remove the NF membrane, remove excess growth solution and dry it to obtain the NF@MOF membrane;

[0015] S3. Roll press the NF@MOF membrane with the separator layer to obtain a lithium metal battery composite separator.

[0016] As a further improvement to the above-described scheme of the present invention, in step S1, the number-average molecular weight of the polymer is 10. 4 ~10 7g / mol; and / or, the polymer is at least one of polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyimide (PI), and polyvinyl alcohol (PVA);

[0017] And / or, in step S1, the organic solvent is at least one of dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0018] As a further improvement to the above-described scheme of the present invention, in step S1, the mass fraction of the spinning solution is 0.5% to 25%.

[0019] As a further improvement to the above-mentioned solution of the present invention, in step S1, the process parameters of electrospinning are as follows: the distance between the spinning head and the receiver is 10-30cm, the spinning voltage is 10-40KV, the spinning time is 4-20h, the spinning ambient temperature is 20℃-30℃, and the humidity is 40%-70%.

[0020] As a further improvement to the above-mentioned scheme of the present invention, in step S1, the thickness of the NF film is 10-50 μm, the porosity is 55%-85%, and the diameter of the polymer fiber is 100-1000 nm.

[0021] As a further improvement to the above-mentioned solution of the present invention, in step S2, the MOF material is at least one of ZIF-8, ZIF-67, MOF-5, and HKUST-1;

[0022] And / or, in step S2, the NF film is immersed in the growth solution for 3 to 24 hours at a temperature of 20°C to 200°C, and the drying is performed in a vacuum oven at 50°C to 100°C.

[0023] As a further improvement to the above-mentioned solution of the present invention, in step S3, the roll pressing composite is performed by using a hot roll with a temperature of 40°C to 80°C.

[0024] The present invention proposes a lithium metal battery, comprising a lithium anode, a separator, and a cathode, wherein the separator is the aforementioned lithium metal battery composite separator or is prepared by the aforementioned method for preparing a lithium metal battery composite separator.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The lithium metal battery composite separator proposed in this invention includes a separator layer and an NF@MOF membrane layer. The polyethylene / polypropylene separator possesses high mechanical strength and flexibility, but its electrolyte wettability and electrolyte retention performance are generally poor. The NF@MOF membrane layer is a fiber membrane material composed of interlaced fiber filaments. While its tensile strength is relatively low, its extremely high porosity allows it to retain sufficient electrolyte. Furthermore, the uniformly distributed metal cations in the in-situ grown MOF material structure promote the growth of Li-metal alloys under the principle of like charge repulsion. + Rapid passage, suppressing Li + Lithium metal is reduced nearby, leading to the uneven growth of lithium dendrites. This invention combines a separator layer with an NF@MOF film layer. Simultaneously, the in-situ grown MOF material provides high ionic conductivity and low interfacial impedance. The resulting composite separator possesses high mechanical strength, high flexibility, high electrolyte wettability and high electrolyte retention, as well as excellent ionic conductivity. The synergistic effect of the components in the composite separator promotes uniform deposition and stripping of lithium metal, inhibits lithium dendrite growth, prevents short circuits or even fires and explosions caused by separator puncture, and improves the cycle life and safety performance of lithium metal batteries. Therefore, the composite separator described in this invention has broad application prospects in lithium metal batteries.

[0027] 2. This invention uses electrospinning technology to form a polymer solution into a nanofiber membrane of a certain thickness, then grows a metal-organic framework material in situ on the nanofiber membrane to obtain an NF@MOF membrane, and finally presses the NF@MOF membrane and the substrate membrane together using hot rollers to obtain a composite membrane. The preparation process is simple and easy to operate. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 is a SEM image of the PVDF-HFP nanofiber membrane prepared in Example 1 of the present invention;

[0030] Figure 2 is a SEM image of the PVDF-HFP nanofiber membrane prepared in Example 1 of the present invention after in-situ growth of ZIF-8;

[0031] Figure 3 is a schematic diagram of the assembly of the lithium metal battery in an embodiment of the present invention;

[0032] Figure 4 is a comparison chart of the performance test results of Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0033] The above figures include the following reference numerals: 100, positive electrode; 200, Li negative electrode; 300, composite separator. Detailed Implementation

[0034] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0035] It should be noted that in this application, NF membrane is short for nanofiber membrane, which is composed of interlaced and stacked fibers.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0037] As analyzed in the background section of this application, conventional commercial separator products currently do not have the ability to resist lithium dendrite penetration. In order to solve this problem, this application provides a lithium metal battery composite separator, its preparation method, and a lithium metal battery.

[0038] In a typical embodiment of this application, a lithium metal battery composite separator is provided, including a separator layer and an NF@MOF film layer, wherein the NF@MOF film layer is an NF film with MOF material grown in situ.

[0039] The separator layer possesses high mechanical strength and flexibility, but its electrolyte wettability and electrolyte retention performance are generally average. The NF@MOF membrane layer, composed of interlaced fiber filaments, has relatively low tensile strength, but its extremely high porosity allows it to retain sufficient electrolyte. Furthermore, the uniformly distributed metal cations in the in-situ grown MOF material structure promote the growth of Li under the principle of like charge repulsion. + Rapid passage, suppressing Li + Lithium metal is reduced nearby, leading to the uneven growth of lithium dendrites. This invention combines a separator layer with an NF@MOF film layer. Simultaneously, the in-situ grown MOF material provides high ionic conductivity and low interfacial impedance. The resulting composite separator possesses high mechanical strength, high flexibility, high electrolyte wettability and high electrolyte retention, as well as excellent ionic conductivity. The synergistic effect of the components in the composite separator promotes uniform deposition and stripping of lithium metal, inhibits lithium dendrite growth, prevents short circuits or even fires and explosions caused by separator puncture, and improves the cycle life and safety performance of lithium metal batteries. Therefore, the composite separator described in this invention has broad application prospects in lithium metal batteries.

[0040] The aforementioned diaphragm layer and NF@MOF membrane layer are laminated composites, specifically, they can be rolled composites.

[0041] In one embodiment of this application, the membrane layer is a polypropylene membrane or a polyethylene membrane; and / or, the NF membrane is composed of polymer fibers, with MOF material distributed on the surface of the polymer fibers, and the MOF material and the polymer fibers are connected by van der Waals forces and / or hydrogen bonds.

[0042] Polyethylene / polypropylene membranes possess high mechanical strength and flexibility. NF membranes, composed of polymer fibers, have ultra-high porosity to retain sufficient electrolyte. MOF materials are connected to the polymer fibers via van der Waals forces and / or hydrogen bonds, distributed on the surface of the polymer fibers, which helps promote Li... + Rapid passage, suppressing Li + The nearby material is reduced to lithium metal, which then grows unevenly into lithium dendrites.

[0043] In one embodiment of this application, the diameter of the polymer fiber is 100–1000 nm; and / or, the thickness of the NF film is 10–50 μm; and / or, the porosity of the NF film is 55%–85%; and / or, the number average molecular weight of the polymer fiber material is 10. 4 ~10 7 g / mol; and / or, the polymer fiber material is at least one of polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyimide (PI), and polyvinyl alcohol (PVA); and / or, the MOF material is at least one of ZIF-8, ZIF-67, MOF-5, and HKUST-1.

[0044] Controlling the diameter of the polymer fibers within the aforementioned range helps to increase the porosity and specific surface area of ​​the NF membrane, thereby improving the electrolyte wettability and liquid retention capacity, which in turn helps to improve lithium-ion transport efficiency and reduce dendrite formation. Controlling the thickness of the NF membrane within the aforementioned range helps to balance the mechanical strength and lithium-ion transport efficiency of the composite separator. NF membranes with the aforementioned porosity help to further improve the liquid retention rate of the composite separator, providing sufficient ion conduction pathways. Simultaneously, high porosity is conducive to the uniform distribution of lithium ions, reducing the possibility of dendrite growth, thus contributing to improved battery safety and cycle performance. Controlling the number-average molecular weight of the polymer fiber material within the aforementioned range helps to optimize fiber formability, improve fiber diameter uniformity and the stability and toughness of the separator structure, thereby helping to reduce the risk of internal short circuits in the battery. It also facilitates the uniform growth of MOF materials, thus helping to improve the interfacial stability of the separator, which in turn helps to improve the uniform deposition of lithium ions and the cycle performance of the battery. Controlling the type of polymer fiber material within the aforementioned range helps to improve the electrolyte wettability and structural stability of the composite separator. Controlling the type of MOF material within the above-mentioned range helps to improve the ionic conductivity of the composite separator and reduce the transport resistance of lithium ions in the separator. On the other hand, it helps to promote the uniform deposition of lithium ions and suppress dendrite growth, thereby helping to further improve the cycle stability and safety of the battery.

[0045] In one embodiment of this application, the mass ratio of the above-mentioned MOF material to the NF film is (0.1-10):(90.0-99.9).

[0046] Controlling the mass ratio of MOF material to NF membrane within the aforementioned range helps to improve the electrolyte wettability of the composite membrane, retain more electrolyte, and thus enhance the membrane's electrolyte retention capacity and the battery's cycle stability. Furthermore, it helps to promote the development of Li... + Uniform deposition and stripping of ions help to suppress the formation of lithium dendrites.

[0047] In another typical embodiment of this application, a method for preparing the aforementioned lithium metal battery composite separator is provided, comprising the following steps: S1. Dissolving a polymer in an organic solvent to obtain a spinning solution, electrospinning the spinning solution to obtain an NF membrane; S2. Preparing a growth solution for MOF material, immersing the NF membrane in the growth solution, then removing the NF membrane, removing excess growth solution and drying it to obtain an NF@MOF membrane; S3. Roll-pressing the NF@MOF membrane with a separator layer to obtain a lithium metal battery composite separator.

[0048] The lithium metal battery composite separator prepared by the above method can effectively suppress the growth of lithium dendrites, prevent internal short circuits, and improve battery safety. Simultaneously, it exhibits excellent ionic conductivity and electrolyte retention capacity, as well as good mechanical properties, which contribute to improving battery cycle stability. The entire preparation process is relatively simple, easy to scale up for production, and helps reduce the manufacturing cost of the composite separator, thus facilitating its commercial application.

[0049] In one embodiment of this application, in step S1 above, the number-average molecular weight of the polymer is 10. 4 ~10 7 g / mol; and / or, the polymer is at least one of polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyimide (PI), and polyvinyl alcohol (PVA); and / or, in step S1, the organic solvent is at least one of dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0050] Controlling the number-average molecular weight of the polymer within the aforementioned range helps optimize fiber formability, improve fiber diameter uniformity, and enhance the stability and toughness of the separator structure, thereby reducing the risk of internal short circuits in the battery. Furthermore, it promotes uniform growth of the MOF material, improving the interfacial stability of the separator and consequently enhancing the uniform deposition of lithium ions and the battery's cycle performance. Controlling the type of polymer within the aforementioned range also helps improve the electrolyte wettability and structural stability of the composite separator. Controlling the type of organic solvent within the aforementioned range helps increase polymer solubility, resulting in a more uniform spinning solution, which further improves the uniformity of polymer fiber diameter distribution, thus enhancing the electrolyte wettability and structural stability of the composite separator.

[0051] In one embodiment of this application, in step S1 above, the mass fraction of the spinning solution is 0.5% to 25%.

[0052] Controlling the mass fraction of the spinning solution within the above range helps to control the diameter of the polymer fibers within a suitable range and improves the uniformity of the polymer fiber diameter distribution. This, in turn, facilitates the rapid transport of lithium ions and the sufficient wetting of the electrolyte, thereby improving the ionic conductivity and liquid retention capacity of the composite membrane.

[0053] In order to improve the stability and diameter distribution uniformity of polymer fibers, thereby improving the wettability and electrolyte retention capacity of the composite diaphragm, in one embodiment of this application, the electrospinning process parameters in step S1 are as follows: the distance between the spinning head and the receiver is 10-30 cm, the spinning voltage is 10-40 KV, the spinning time is 4-20 h, the spinning ambient temperature is 20℃-30℃, and the humidity is 40%-70%.

[0054] In one embodiment of this application, in step S1 above, the thickness of the NF film is 10-50 μm, the porosity is 55%-85%, and the diameter of the polymer fiber is 100-1000 nm.

[0055] Controlling the thickness of the NF membrane within the aforementioned range helps balance the mechanical strength and lithium-ion transport efficiency of the composite separator. The NF membrane with the aforementioned porosity helps further improve the liquid retention rate of the composite separator, providing ample ion conduction pathways. Simultaneously, high porosity promotes uniform lithium-ion distribution, reducing the possibility of dendrite growth, thereby contributing to improved battery safety and cycle performance. Controlling the diameter of the polymer fibers within the aforementioned range helps increase the porosity and specific surface area of ​​the NF membrane, thereby improving electrolyte wettability and liquid retention capacity, further contributing to enhanced lithium-ion transport efficiency and reduced dendrite formation.

[0056] In one embodiment of this application, in step S2 above, the MOF material is at least one of ZIF-8, ZIF-67, MOF-5, and HKUST-1; and / or, in step S2, the NF film is immersed in the growth solution for 3 to 24 hours, the temperature of the growth solution is 20°C to 200°C, and the drying is carried out in a vacuum oven at 50°C to 100°C.

[0057] Controlling the type of MOF material within the aforementioned range helps to improve the ionic conductivity of the composite membrane and reduce the transport resistance of lithium ions within the membrane. It also helps to promote uniform lithium ion deposition and suppress dendrite growth, thereby further improving the cycle stability and safety of the battery. Controlling the immersion time of the NF membrane in the growth solution within the aforementioned range helps to control the amount of MOF material grown on the NF membrane. This helps to achieve better electrolyte wettability in the composite membrane, retaining more electrolyte and thus enhancing the membrane's electrolyte retention capacity and the battery's cycle stability. Furthermore, it helps to promote the uniform deposition of lithium ions and suppress dendrite growth. + Uniform deposition and stripping of ions help suppress the formation of lithium dendrites. Controlling the temperature of the growth solution within the aforementioned range helps improve the efficiency of MOF material growth on NF films without damaging the NF film structure.

[0058] In order to improve the bonding force between the NF@MOF membrane layer and the separator layer without damaging the NF@MOF membrane layer structure, in one embodiment of this application, the roll pressing composite in step S3 above is performed by hot roll pressing composite using a hot roller at a temperature of 40°C to 80°C.

[0059] In another typical embodiment of this application, a lithium metal battery is provided, including a lithium negative electrode, a separator, and a positive electrode. The separator is the aforementioned lithium metal battery composite separator or is prepared using the aforementioned method for preparing a lithium metal battery composite separator.

[0060] Because the lithium metal battery contains the lithium metal battery composite separator of this application, the lithium metal battery has high rate performance, cycle stability and safety.

[0061] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0062] Example 1

[0063] This embodiment proposes a lithium metal battery composite separator, the preparation method of which includes the following steps:

[0064] S1. PVDF-HFP (number average molecular weight of 4×10⁻⁶) 5 PVDF-HFP (g / mol) was added to DMF and completely dissolved uniformly by magnetic stirring to obtain a PVDF-HFP DMF spinning solution with a polymer PVDF-HFP mass fraction of 10%. Then, the PVDF-HFP DMF spinning solution was spun using electrospinning at a voltage of 17 kV, a receiving distance of 15 cm, and a spinning time of 8 hours to obtain a PVDF-HFP nanofiber membrane. The prepared PVDF-HFP nanofiber membrane was dried in a vacuum oven at 60 °C for later use. The SEM image of the prepared PVDF-HFP nanofiber membrane is shown in Figure 1, where the PVDF-HFP nanofiber membrane has a thickness of 20 μm, a porosity of 65%, and a polymer fiber diameter of 900 nm.

[0065] S2. Preparation of ZIF-8 growth solution: Add 0.01 mol of zinc nitrate hexahydrate to 150 mL of methanol and stir with a magnetic stirrer for 10 minutes to obtain growth solution a; then add 0.04 mol of 2-methylimidazole to 150 mL of methanol and stir with a magnetic stirrer for 30 minutes to obtain growth solution b. First, completely immerse the dried PVDF-HFP nanofiber membrane in growth solution a, seal and let stand for 3 hours. Then, completely pour growth solution b into growth solution a, and let the mixed solution stand at room temperature for 6 hours until ZIF-8 material uniformly grows and coats the surface of PVDF-HFP nanofibers. After the reaction is complete, carefully remove the PVDF-HFP nanofiber membrane, drain off the excess growth solution, and dry it in a vacuum oven at 60℃ to obtain a PVDF-HFP@ZIF-8 membrane, wherein the mass ratio of ZIF-8 to PVDF-HFP nanofiber membrane is 5:95. The SEM image of the PVDF-HFP nanofiber membrane after in-situ growth of ZIF-8 is shown in Figure 2.

[0066] S3. The PVDF-HFP@ZIF-8 membrane and PP separator obtained in step S2 are hot-pressed together by hot rolling. The hot rolling temperature is 70℃, and the distance between the two rollers during hot rolling is the sum of the initial thicknesses of the Celgard2500 separator and the PVDF-HFP@ZIF-8 composite fiber membrane minus 3μm, resulting in the lithium metal battery composite separator material PP@PVDF-HFP@ZIF-8.

[0067] The PP diaphragm used in this embodiment is a commercially available diaphragm, model Celgard2500.

[0068] Example 2

[0069] This embodiment proposes a lithium metal battery composite separator, the preparation method of which includes the following steps:

[0070] S1. PVDF-HFP (number average molecular weight of 4×10⁻⁶) 5 PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of PVDF-HFP of 10%. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 17kV, a receiving distance of 15cm, and a spinning time of 8 hours to obtain a PVDF-HFP nanofiber membrane. The PVDF-HFP nanofiber membrane was dried in a vacuum oven at 60℃ for later use. The thickness of the PVDF-HFP nanofiber membrane was 20μm, the porosity was 65%, and the diameter of the polymer fibers was 900nm.

[0071] S2. Preparation of MOF-5 growth solution: 0.008 mol zinc nitrate hexahydrate and 0.004 mol terephthalic acid were added to 100 mL of N,N-dimethylformamide (DMF) and sonicated until completely dissolved to obtain the MOF-5 growth solution. The dried PVDF-HFP nanofiber membrane was completely immersed in the MOF-5 growth solution, sealed and allowed to stand for 3 hours. Then, 4 mL of triethylamine (TEA) was added dropwise to the mixed solution and magnetically stirred for 5 minutes. The mixture was allowed to stand at room temperature for 6 hours until the MOF-5 material was uniformly grown and coated on the surface of the PVDF-HFP nanofibers. After the reaction was completed, the PVDF-HFP nanofiber membrane was carefully removed, excess growth solution was drained, and the membrane was dried in a vacuum oven at 60 °C to obtain the PVDF-HFP@MOF-5 membrane. The mass ratio of MOF-5 to PVDF-HFP nanofiber membrane was 5:95.

[0072] S3. The PVDF-HFP@MOF-5 membrane and PP separator obtained in step S2 are hot-pressed together by hot rolling. The hot rolling temperature is 70℃, and the distance between the two rollers during hot rolling is the sum of the initial thicknesses of the PP separator and the PVDF-HFP@MOF-5 composite fiber membrane minus 3μm, thus obtaining the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5.

[0073] The PP diaphragm used in this embodiment is a commercially available diaphragm, model Celgard2500.

[0074] Example 3

[0075] This embodiment proposes a lithium metal battery composite separator, the preparation method of which includes the following steps:

[0076] S1. PVDF-HFP (number average molecular weight of 4×10⁻⁶) 5 PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of PVDF-HFP of 10%. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 17kV, a receiving distance of 15cm, and a spinning time of 8 hours to obtain a PVDF-HFP nanofiber membrane. The PVDF-HFP nanofiber membrane was dried in a vacuum oven at 60℃ for later use. The thickness of the PVDF-HFP nanofiber membrane was 20μm, the porosity was 65%, and the diameter of the polymer fibers was 900nm.

[0077] S2. Preparation of HKUST-1 growth solution: Dissolve 0.01 mol of copper nitrate trihydrate completely in 50 mL of anhydrous ethanol to obtain growth solution c; then dissolve 0.006 mol of 1,3,5-benzenetricarboxylic acid completely in 50 mL of anhydrous ethanol to obtain growth solution d. First, completely immerse the dried PVDF-HFP nanofiber membrane in HKUST-1 growth solution c, seal and let stand for 3 hours. Then, pour growth solution d into growth solution c and stir evenly. Subsequently, transfer the PVDF-HFP nanofiber membrane and the mixed solution together to a reaction vessel and let it stand at 80℃ for 10 hours until HKUST-1 material grows uniformly and coats the surface of PVDF-HFP nanofibers. After the reaction is complete, carefully remove the PVDF-HFP nanofiber membrane, drain off the excess growth solution, and dry it in a vacuum oven at 60℃ to obtain PVDF-HFP@HKUST-1 membrane, wherein the mass ratio of HKUST-1 to PVDF-HFP nanofiber membrane is 5:95.

[0078] S3. The PVDF-HFP@HKUST-1 membrane and PP separator obtained in step S2 are hot-pressed together by hot rolling. The hot rolling temperature is 70℃, and the distance between the two rollers during hot rolling is the sum of the initial thicknesses of the PP separator and the PVDF-HFP@HKUST-1 composite fiber membrane minus 3μm, thus obtaining the lithium metal battery composite separator material PP@PVDF-HFP@HKUST-1.

[0079] The PP diaphragm used in this embodiment is a commercially available diaphragm, model Celgard2500.

[0080] Example 4

[0081] The difference from Example 2 is that, in S2, the growth solution of MOF-5 is prepared by adding 0.004 mol of zinc nitrate hexahydrate and 0.002 mol of terephthalic acid to 100 mL of N,N-dimethylformamide (DMF) and sonicating until completely dissolved to obtain the growth solution of MOF-5. The dried PVDF-HFP nanofiber membrane was completely immersed in the MOF-5 growth solution and sealed for 3 hours. Then, 4 mL of triethylamine (TEA) was added dropwise to the mixed solution and magnetically stirred for 5 minutes. The mixture was then left to stand at room temperature for 1 hour until the MOF-5 material was uniformly grown and coated on the surface of the PVDF-HFP nanofibers. After the reaction was complete, the PVDF-HFP nanofiber membrane was carefully removed, excess growth solution was drained, and the membrane was dried in a vacuum oven at 60°C to obtain the PVDF-HFP@MOF-5 membrane. The mass ratio of MOF-5 to PVDF-HFP nanofiber membrane was 0.1:99.9, and the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was finally obtained.

[0082] Example 5

[0083] The difference from Example 2 is that, in S2, the MOF-5 growth solution was prepared as follows: 0.016 mol of zinc nitrate hexahydrate and 0.008 mol of terephthalic acid were added to 100 mL of N,N-dimethylformamide (DMF) and sonicated until completely dissolved to obtain the MOF-5 growth solution. The dried PVDF-HFP nanofiber membrane was completely immersed in the MOF-5 growth solution, sealed, and allowed to stand for 3 hours. Then, 4 mL of triethylamine (TEA) was added dropwise to the mixed solution and magnetically stirred for 5 minutes. The mixture was allowed to stand at room temperature for 12 hours. After the reaction was completed, the PVDF-HFP nanofiber membrane was carefully removed, excess growth solution was drained, and the membrane was dried in a vacuum oven at 60°C to obtain the PVDF-HFP@MOF-5 membrane. The mass ratio of MOF-5 to PVDF-HFP nanofiber membrane was 10:90, and the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was finally obtained.

[0084] Example 6

[0085] The difference from Example 2 is that, in S2, the MOF-5 growth solution was prepared as follows: 0.024 mol of zinc nitrate hexahydrate and 0.012 mol of terephthalic acid were added to 100 mL of N,N-dimethylformamide (DMF) and sonicated until completely dissolved to obtain the MOF-5 growth solution. The dried PVDF-HFP nanofiber membrane was completely immersed in the MOF-5 growth solution, sealed, and allowed to stand for 3 hours. Then, 4 mL of triethylamine (TEA) was added dropwise to the mixed solution and magnetically stirred for 5 minutes. The mixture was allowed to stand at room temperature for 24 hours. After the reaction was completed, the PVDF-HFP nanofiber membrane was carefully removed, excess growth solution was drained, and the membrane was dried in a vacuum oven at 60°C to obtain the PVDF-HFP@MOF-5 membrane. The mass ratio of MOF-5 to PVDF-HFP nanofiber membrane was 15:85, resulting in the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5.

[0086] Example 7

[0087] The difference from Example 2 is that, in S1, PVDF-HFP (number average molecular weight of 4 × 10⁻⁶) is used. 5PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a polymer PVDF-HFP mass fraction of 10%. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 10 kV, a receiving distance of 15 cm, and a spinning time of 8 hours to obtain a PVDF-HFP nanofiber membrane with a porosity of 55% and a polymer fiber diameter of 1000 nm. Finally, the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was obtained.

[0088] Example 8

[0089] The difference from Example 2 is that, in S1, PVDF-HFP (number average molecular weight of 4 × 10⁻⁶) is used. 5 PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of 10% PVDF-HFP. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 40 kV, a receiving distance of 15 cm, and a spinning time of 8 hours to obtain a PVDF-HFP nanofiber membrane with a porosity of 85% and a polymer fiber diameter of 100 nm. Finally, the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was obtained.

[0090] Example 9

[0091] The difference from Example 2 is that, in S1, PVDF-HFP (number average molecular weight of 4 × 10⁻⁶) is used. 5 PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of 10% PVDF-HFP. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 7 kV, a receiving distance of 15 cm, and a spinning time of 8 hours to obtain a PVDF-HFP nanofiber membrane with a porosity of 50% and a polymer fiber diameter of 1500 nm. Finally, the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was obtained.

[0092] Example 10

[0093] The difference from Example 2 is that, in S1, PVDF-HFP (number average molecular weight of 4 × 10⁻⁶) is used. 5PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of 10% PVDF-HFP. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 17 kV, a receiving distance of 15 cm, and a spinning time of 20 hours to obtain a PVDF-HFP nanofiber membrane with a thickness of 50 μm. Finally, the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was obtained.

[0094] Example 11

[0095] The difference from Example 2 is that, in S1, PVDF-HFP (number average molecular weight of 4 × 10⁻⁶) is used. 5 PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of 10% PVDF-HFP. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 17 kV, a receiving distance of 15 cm, and a spinning time of 4 hours to obtain a PVDF-HFP nanofiber membrane with a thickness of 10 μm. Finally, the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was obtained.

[0096] Example 12

[0097] The difference from Example 2 is that, in S1, PVDF-HFP (number average molecular weight of 4 × 10⁻⁶) is used. 5 PVDF-HFP (g / mol) was added to DMF and completely and uniformly dissolved by magnetic stirring to obtain a DMF spinning solution of PVDF-HFP, with a mass fraction of 10% PVDF-HFP. Then, the DMF spinning solution of PVDF-HFP was spun by electrospinning at a voltage of 17 kV, a receiving distance of 15 cm, and a spinning time of 24 hours to obtain a PVDF-HFP nanofiber membrane with a thickness of 60 μm. Finally, the lithium metal battery composite separator material PP@PVDF-HFP@MOF-5 was obtained.

[0098] Example 13

[0099] The difference from Example 2 is that polyacrylonitrile (number average molecular weight of 3 × 10⁻⁶) was used. 5 By replacing PVDF-HFP with g / mol), the final lithium metal battery composite membrane material PP@PAN@MOF-5 was obtained.

[0100] Comparative Example 1

[0101] This comparative example presents a lithium metal battery composite separator, the preparation method of which includes the following steps:

[0102] S1. Add PVDF-HFP to DMF and dissolve PVDF-HFP completely and uniformly by magnetic stirring to obtain a PVDF-HFP DMF spinning solution with a polymer PVDF-HFP mass fraction of 10%. Then, use electrospinning to spin the PVDF-HFP DMF spinning solution, wherein the electrospinning voltage is 17kV, the receiving distance is 15cm, and the spinning time is 8 hours to obtain a PVDF-HFP nanofiber membrane. Place the PVDF-HFP nanofiber membrane in a vacuum oven at 60℃ to dry it for later use.

[0103] S2. The PVDF-HFP nanofiber membrane and PP separator obtained in step S1 are hot-pressed together by hot rolling. The hot rolling temperature is 70℃, and the distance between the two rollers during hot rolling is the sum of the initial thicknesses of the PP separator and the PVDF-HFP nanofiber membrane minus 3μm, thus obtaining the lithium metal battery composite separator material PP@PVDF-HFP.

[0104] The PP diaphragm used in this comparative example is a commercially available diaphragm, model Celgard2500.

[0105] Comparative Example 2

[0106] This comparative example uses commercially available PP membrane material, model Celgard2500.

[0107] Battery manufacturing

[0108] The separator materials of Examples 1 to 13 and Comparative Examples 1 to 2 were cut into rectangles with a length × width of 60 × 50 mm for later use. As shown in Figure 3, the Li negative electrode 200, composite separator 300 and positive electrode 100 were stacked together in sequence to assemble a lithium metal soft-pack dry cell. After completing the tab welding, liquid injection and encapsulation, the lithium metal negative electrode battery was obtained.

[0109] Performance testing

[0110] The lithium metal batteries prepared using the separator materials of Examples 1-13 and Comparative Examples 1-2 were subjected to performance tests. The initial discharge capacity and the number of cycles when the capacity retention rate reached 80% were tested at 0.5CC / 1.0CD. The test results are shown in Table 1.

[0111] Table 1

[0112] As shown in Table 1, the test data reveals that the PP@PVDF-HFP material, compared to commercial PP membranes, exhibits a 100% improvement in cycle performance in lithium metal anode batteries. Furthermore, the cycle performance of PP@PVDF-HFP is further improved by over 50% after in-situ growth of MOF material. This indicates that the components of the composite membrane exert an effective synergistic effect. The commercial PP membrane provides excellent mechanical strength and flexibility; the PVDF-HFP fiber membrane material, prepared by electrospinning, possesses ultra-high porosity, exhibiting excellent electrolyte wettability and retaining a large amount of electrolyte; and the in-situ grown MOF material, with its uniformly arranged metal cations, promotes the growth of Li-metal ions under the principle of like charge repulsion. + It passes through quickly, possesses excellent ionic conductivity, and can suppress Li... + The lithium metal is reduced nearby, leading to the uneven growth of lithium dendrites. This demonstrates the excellent performance and application potential of the composite separator material described in this invention in lithium metal batteries.

[0113] Figure 4 shows a comparison of the performance test results of Examples 1-3 and Comparative Examples 1-2 of the present invention. As can be seen from Figure 4, under the condition that other conditions of the lithium metal battery are kept the same, only different separator materials are used in the tests. The cycle life of the PP@PVDF-HFP@ZIF-8 composite separator material prepared in Example 1 is 174cls@80% in the lithium metal anode battery; the cycle life of the PP@PVDF-HFP@MOF-5 composite separator material prepared in Example 2 is 216cls@80% in the lithium metal anode battery; and the cycle life of the PP@PVDF-HFP@HKUST-1 composite separator material prepared in Example 3 is 212cls@80%. In comparison, the cycle life of the PP@PVDF-HFP material obtained in Comparative Example 1 without in-situ growth of MOF material in the lithium metal anode battery is 114cls@80%; and the cycle life of the commercial PP separator used directly in Comparative Example 2 is only 56cls@80%.

[0114] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A lithium metal battery composite separator, characterized in that, It includes a diaphragm layer and an NF@MOF membrane layer, wherein the NF@MOF membrane layer is an NF membrane with MOF material grown in situ.

2. The lithium metal battery composite separator according to claim 1, characterized in that, The membrane layer is a polypropylene membrane or a polyethylene membrane; and / or, the NF membrane is composed of polymer fibers, the MOF material is distributed on the surface of the polymer fibers, and the MOF material is connected to the polymer fibers by van der Waals forces and / or hydrogen bonds.

3. The lithium metal battery composite separator according to claim 2, characterized in that, The diameter of the polymer fiber is 100-1000 nm; and / or the thickness of the NF membrane is 10-50 μm; and / or the porosity of the NF membrane is 55%-85%. And / or, the polymer fiber material has a number-average molecular weight of 10. 4 ~10 7 g / mol; And / or, the polymer fiber is made of at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, and polyvinyl alcohol; And / or, the MOF material is at least one of ZIF-8, ZIF-67, MOF-5, and HKUST-1.

4. The lithium metal battery composite separator according to any one of claims 1 to 3, characterized in that, The mass ratio of the MOF material to the NF film is (0.1-10):(90.0-99.9).

5. A method for preparing a lithium metal battery composite separator according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Dissolve the polymer in an organic solvent to obtain a spinning solution, and electrospin the spinning solution to obtain an NF film; S2. Prepare a growth solution for MOF material, immerse the NF membrane in the growth solution, then remove the NF membrane, remove excess growth solution and dry it to obtain an NF@MOF membrane; S3. The NF@MOF membrane is rolled and laminated with the separator layer to obtain a lithium metal battery composite separator.

6. The method for preparing the lithium metal battery composite separator according to claim 5, characterized in that, In step S1, the number-average molecular weight of the polymer is 10. 4 ~10 7 g / mol; and / or, the polymer is at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, and polyvinyl alcohol; And / or, in step S1, the organic solvent is at least one of dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The method for preparing the lithium metal battery composite separator according to claim 5, characterized in that, In step S1, the mass fraction of the spinning solution is 0.5% to 25%.

8. The method for preparing the lithium metal battery composite separator according to claim 5, characterized in that, In step S1, the electrospinning process parameters are as follows: the distance between the spinning head and the receiver is 10-30 cm, the spinning voltage is 10-40 KV, the spinning time is 4-20 h, the spinning ambient temperature is 20℃-30℃, and the humidity is 40%-70%.

9. The method for preparing the lithium metal battery composite separator according to claim 5, characterized in that, In step S1, the thickness of the NF membrane is 10-50 μm, the porosity is 55%-85%, and the diameter of the polymer fiber is 100-1000 nm.

10. The method for preparing the lithium metal battery composite separator according to claim 5, characterized in that, In step S2, the MOF material is at least one of ZIF-8, ZIF-67, MOF-5, and HKUST-1; And / or, in step S2, the NF film is immersed in the growth solution for 3 to 24 hours, the temperature of the growth solution is 20°C to 200°C, and the drying is performed in a vacuum oven at 50°C to 100°C.

11. The method for preparing the lithium metal battery composite separator according to claim 5, characterized in that, In step S3, the roll pressing composite is performed using a hot roll pressing composite with a temperature of 40℃~80℃.

12. A lithium metal battery, comprising a lithium anode, a separator, and a cathode, characterized in that: The separator is a lithium metal battery composite separator as described in any one of claims 1 to 4, or is prepared using the method for preparing a lithium metal battery composite separator as described in any one of claims 5 to 11.

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