Electrochemical device, composite diaphragm for electrochemical device and preparation method of composite diaphragm

Abstract

The invention provides an electrochemical device, a composite separator for the electrochemical device and a preparation method of the composite separator for the electrochemical device. The metal-organic framework material is at least distributed on the surface of the cellosilk membrane, and the metal-organic framework material has water absorption; and metal oxide particles or metal sulfide particles directly attached to the surface of the cellosilk membrane and / or the metal-organic framework material. The metal oxide particles or the metal sulfide particles are directly attached to the surface of the metal-organic framework material, so that the polarity of the metal-organic framework material can be improved, and the water absorption and HF adsorption capabilities of the metal-organic framework material are improved. Besides, the metal-organic framework material, the metal oxide particles or the metal sulfide particles have certain thermal stability and incombustibility, so that the thermal shrinkage rate of the composite diaphragm is reduced, and the thermal stability of the composite diaphragm running in a high-temperature environment is improved.

Description

Technical Field

[0001] This invention relates to electrochemical devices, specifically to an electrochemical device, a composite diaphragm for an electrochemical device, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries, as an energy storage device, are an indispensable part of the development and construction of new energy sources. The main components of a lithium-ion power battery are the positive electrode, negative electrode, separator, and electrolyte. Each component performs its specific function to ensure the normal operation of the lithium-ion battery. Among them, the performance of the separator determines the battery's interface structure, internal resistance, and other characteristics, affecting the battery's capacity, cycle life, and safety performance. A high-performance separator plays a crucial role in improving the overall performance of the battery.

[0003] First, the basic performance of the separator must ensure unobstructed ion transport channels between the positive and negative electrodes and good insulation between them. Second, the materials used for the separator need to have certain toughness, mechanical strength, and corrosion resistance, while also being as thin as possible to support the normal manufacturing and use of the battery cell. Finally, the separator needs to have a certain degree of thermal stability, with a small thermal shrinkage rate after heating, to ensure the safety of the battery cell under thermal runaway or high-temperature conditions.

[0004] Currently, the commonly used materials for lithium-ion battery cell separators are PP and PE. A thin ceramic layer is applied to the surface of the separator to increase its strength and thermal stability, and reduce thermal shrinkage under high-temperature environments. However, the commonly used separators still have some drawbacks, such as limited heat resistance, only able to withstand heating temperatures below 120℃. Above 120℃, they are prone to shrinkage, which can cause short circuits between the positive and negative electrodes, further exacerbating the thermal runaway process.

[0005] In existing main separator materials, the separator will undergo thermal shrinkage when the temperature reaches around 130℃. At higher temperatures, the separator shrinkage is severe, leading to a short circuit between the positive and negative electrodes. This will exacerbate cell runaway under thermal runaway conditions. In addition, during the cell manufacturing process, although the electrode plates evaporate most of the moisture through high-temperature baking, trace amounts of moisture remain. At the same time, trace amounts of moisture are also introduced into the electrolyte during electrolyte injection. These trace amounts of moisture in the electrode plates and electrolyte will affect the strength and density of the formed negative electrode SEI film. Furthermore, during cycling, the residual moisture continuously reacts with the SEI film, affecting the long-term performance of the cell. Summary of the Invention

[0006] To address the above problems, the present invention provides a composite membrane for an electrochemical device, comprising: a fiber membrane; a metal-organic framework material, at least distributed on the surface of the fiber membrane, the metal-organic framework material being hygroscopic; and metal oxide particles or metal sulfide particles, directly attached to the surface of the fiber membrane and / or the metal-organic framework material.

[0007] According to this technical solution, the metal oxide particles or metal sulfide particles are polar materials themselves. They adhere to the surface of the metal-organic framework (MOF) material, resulting in a MOF material on the fiber membrane surface that has been modified with metal oxide or metal sulfide particles. This enhances the polarity of the MOF material, improves its adsorption capacity for moisture and HF in the electrolyte or electrode, reduces side reactions of moisture and HF in the electrochemical device, and improves the capacity retention rate of the electrochemical device. Furthermore, the direct adhesion of the metal oxide or metal sulfide particles to the surface of the fiber membrane and / or MOF material improves the stability of the adhesion, reduces the possibility of the MOF and metal oxide or metal sulfide particles detaching from the fiber membrane, reduces the generation of impurities in the electrolyte, and improves the purity of the electrolyte. In addition, metal-organic framework materials, metal oxide particles, or metal sulfide particles themselves have certain thermal stability and non-flammability. When they are attached to the surface of the fiber membrane, they are equivalent to an inorganic coating, forming a certain structural support on the surface of the fiber membrane and having better thermal insulation properties. This optimizes the thermal shrinkage of the composite membrane and improves the thermal stability of the composite membrane in high-temperature environments.

[0008] It should be noted that the "metal oxide particles or metal sulfide particles directly attached to the surface of the fiber membrane and / or metal-organic framework material" described in this embodiment includes: metal oxide particles or metal sulfide particles directly attached to the surface of the metal-organic framework; metal oxide particles or metal sulfide particles directly attached to the surface of the fiber membrane and the surface of the metal-organic framework; and metal oxide particles or metal sulfide particles partially attached to the surface of the metal-organic framework and partially attached to the surface of the fiber membrane and the metal-organic framework, but does not include the case where metal oxide particles or metal sulfide particles are only attached to the surface of the fiber membrane.

[0009] In an optional technical solution of the present invention, the fiber membrane comprises multiple interlaced fiber filaments, and metal-organic framework materials are distributed on the surface of the fiber filaments; the number of metal-organic framework materials attached to a single fiber filament within a length range of 1 μm is not less than 10.

[0010] According to the technical solution, the inventors noted that the density of the distribution of metal-organic framework materials affects the water absorption performance of the fiber membrane. The number of metal-organic framework materials attached to some single fibers within a length range of 1μm is not less than 10, thereby improving the water absorption of a single fiber within a length range of 1μm, so that the composite membrane as a whole has better water absorption performance.

[0011] In an optional technical solution of the present invention, the proportion of metal oxide particles or metal sulfide particles attached to the surface of the fiber membrane is not less than 90% relative to all metal oxide particles or metal sulfide particles, and the distance between the attachment site of the metal oxide particles or metal sulfide particles and the nearest metal-organic framework material is in the range of 0-100 nm.

[0012] According to the technical solution, the inventors noted that metal oxide particles or metal sulfide particles tend to grow near the metal-organic framework material. The metal oxide particles or metal sulfide particles distributed in the 0-100nm range of the metal-organic framework material can use their own polarity to assist the metal-organic framework in adsorption, thereby improving the water absorption performance and HF adsorption performance of the composite membrane.

[0013] In the optional technical solutions of the present invention, the water absorption of the metal-organic framework material is not less than 0.25 g / g, and the water desorption temperature range of the metal-organic framework material is 80-95℃.

[0014] According to this technical solution, when the water absorption capacity of the metal-organic framework material is not less than 0.25 g / g, the composite membrane exhibits excellent water absorption. When applied to electrochemical devices, it demonstrates superior adsorption capacity for water in the electrolyte, preventing side reactions between water in the electrolyte and the negative electrode SEI membrane of the electrochemical device, thereby improving the cycle performance and storage performance of the electrochemical device. During the preparation of the electrochemical device, when the water desorption temperature of the metal-organic framework material is 80-95℃, it ensures that the water adsorbed by the composite membrane can be completely removed during the baking process before electrolyte injection. This guarantees that the composite membrane can fully adsorb water from the electrolyte during subsequent use, further improving the cycle performance and storage performance of the electrochemical device.

[0015] The present invention also provides a method for preparing a composite membrane for an electrochemical device as described above, comprising the following steps: a first composite step: preparing a fiber membrane loaded with a metal-organic framework material; a second composite step: directly attaching metal oxide particles or metal sulfide particles to the surface of the fiber membrane and / or the surface of the metal-organic framework material.

[0016] In an optional technical solution of the present invention, in the first composite step, a fiber membrane loaded with metal-organic framework material is formed by electrospinning; in the second composite step, the fiber membrane loaded with metal-organic framework material is placed in a salt solution corresponding to metal oxide particles or a salt solution corresponding to metal sulfide particles, and after a hydrothermal reaction, corresponding metal oxide particles or metal sulfide particles are generated in situ on the surface of the fiber membrane loaded with metal-organic framework material.

[0017] According to this technical solution, the composite membrane is prepared by hydrothermal synthesis in the second composite step, which has the advantages of simple synthesis steps, low cost, good product dispersibility, and controllable product morphology and size. Furthermore, the prepared crystals are of high quality and require low energy consumption.

[0018] In an optional technical solution of the present invention, the molar ratio between the metal element in the salt solution corresponding to the metal oxide particles or the salt solution corresponding to the metal sulfide particles and the metal element in the metal-organic framework material is 1:4 to 1:6.

[0019] According to this technical solution, the molar ratio of the metal elements in the salt solution corresponding to the metal oxide particles or the salt solution corresponding to the metal sulfide particles to the metal elements in the metal-organic framework material determines the distribution density of the metal oxide particles or metal sulfide particles on the surface of the metal-organic framework material, thus affecting the microstructure of the final composite membrane. Controlling the molar ratio of the metal elements within the specified range prevents, on the one hand, excessive metal oxide particles or metal sulfide particles from covering the surface of the metal-organic framework material, affecting its adsorption performance for moisture and HF; on the other hand, fewer metal oxide particles or metal sulfide particles prevent the metal-organic framework material from completely adsorbing moisture and HF from the electrolyte.

[0020] In the optional technical solution of the present invention, the temperature of the hydrothermal reaction is 100-180℃ and the time of the hydrothermal reaction is 3-5h.

[0021] According to this technical solution, different hydrothermal reaction temperatures lead to different types of products. Extending the hydrothermal reaction time increases the number of metal oxide or metal sulfide particles generated, and these particles exhibit higher crystallinity. Furthermore, different types of metal oxides or metal sulfides require different hydrothermal reaction temperatures. By controlling the temperature and time of the hydrothermal reaction, the amount of metal oxide or metal sulfide particles generated within a specified time can be controlled within a suitable range, ensuring the distribution density of these particles and improving the composite membrane's adsorption capacity for moisture and HF. Controlling the temperature and time of the hydrothermal reaction also allows for the crystallinity of the metal oxide or metal sulfide particles to be kept within a certain range, simultaneously improving the composite performance between these particles and the metal-organic framework material (excessive crystallinity may result in a smoother surface for the metal oxide or metal sulfide particles, reducing the number and accessibility of active sites). In addition, increasing the hydrothermal reaction temperature within a certain range can shorten the reaction time and improve reaction efficiency.

[0022] In the optional technical solutions of the present invention, the material of the fiber membrane is polypropylene, polyethylene, glass fiber, cellulose, polyvinyl alcohol, polyethylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyether ether ketone, polyimide, polyallylamine, polyurethane, polyacrylonitrile, polymethyl methacrylate, polytetraethylene glycol diacrylate, copolymers thereof, or combinations thereof.

[0023] The metal element in the metal-organic framework material is selected from any one of magnesium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc or zirconium.

[0024] The metal oxide type of the metal oxide particles includes any one of MnO2, ZnO, TiO2, NiO, and V2O5.

[0025] The metal sulfide types of the metal sulfide particles include any one of MoS2, ZnS, SnS2, Cu2S, NiS, NiS2, and CoS2.

[0026] According to this technical solution, technicians can flexibly choose the type of fiber membrane, metal-organic framework, metal oxide or metal sulfide according to their needs, which improves the flexibility of composite membrane preparation.

[0027] The present invention also provides an electrochemical device comprising the above-described composite diaphragm for electrochemical devices. Attached Figure Description

[0028] Figure 1 This is a SEM image of the composite membrane used in the electrochemical device under a magnification of 20,000 in an embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This embodiment provides a composite membrane for an electrochemical device, comprising: a fiber membrane; a metal-organic framework material, at least distributed on the surface of the fiber membrane, the metal-organic framework material being water-absorbing; and metal oxide particles or metal sulfide particles, directly attached to the surface of the fiber membrane and / or the metal-organic framework material.

[0031] Through the above method, the metal oxide particles or metal sulfide particles, being polar materials, directly adhere to the surface of the metal-organic framework (MOF) material. This results in the MOF material grown on the fiber membrane surface being modified with metal oxide or metal sulfide particles, enhancing its polarity and improving its adsorption capacity for moisture and HF in the electrolyte or electrode. This reduces side reactions of moisture and HF in the electrochemical device, improving its cycle performance and storage capacity. Furthermore, the direct adhesion of metal oxide or metal sulfide particles to the surface of the fiber membrane and / or MOF material improves adhesion stability, reduces the possibility of MOF and metal oxide or metal sulfide particles detaching from the fiber membrane, reduces the generation of impurities in the electrolyte, and improves the purity of the electrolyte. In addition, metal-organic framework materials, metal oxide particles, or metal sulfide particles themselves have certain thermal stability and non-flammability. When they are attached to the surface of the fiber membrane, they are equivalent to an inorganic coating, forming a certain structural support on the surface of the fiber membrane and having better thermal insulation properties. This optimizes the thermal shrinkage of the composite membrane and improves the thermal stability of the composite membrane in high-temperature environments.

[0032] It should be noted that the "metal oxide particles or metal sulfide particles directly attached to the surface of the fiber membrane and / or metal-organic framework material" described in this embodiment includes: metal oxide particles or metal sulfide particles directly attached to the surface of the metal-organic framework; metal oxide particles or metal sulfide particles directly attached to the surface of the fiber membrane and the surface of the metal-organic framework; and metal oxide particles or metal sulfide particles partially attached to the surface of the metal-organic framework and partially attached to the surface of the fiber membrane and the metal-organic framework, but does not include the case where metal oxide particles or metal sulfide particles are only attached to the surface of the fiber membrane.

[0033] Specifically, the fiber membrane is a nanofiber membrane, abbreviated as NF, also known as a nanofiber membrane or nanofiber filament. Further, the fiber membrane is made of polypropylene, polyethylene, glass fiber, cellulose, polyvinyl alcohol, polyethylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyetheretherketone, polyimide, polyallylamine, polyurethane, polyacrylonitrile, polymethyl methacrylate, polytetraethylene glycol diacrylate, copolymers thereof, or combinations thereof. In this embodiment, "copolymers thereof" refers to copolymers formed by copolymerizing the monomers of polymers such as polypropylene, polyethylene, glass fiber, cellulose, polyvinyl alcohol, polyethylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyetheretherketone, polyimide, polyallylamine, polyurethane, polyacrylonitrile, polymethyl methacrylate, and polytetraethylene glycol diacrylate. "Combinations thereof" refers to any combination of the above copolymers and the above polymers, any combination of copolymers, or any combination of polymers.

[0034] The metal element in the metal-organic framework material is selected from any one of magnesium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, or zirconium; preferably, the metal-organic framework material is MIL-160 (aluminum-based metal-organic framework), ZJU-210 (aluminum-based metal-organic framework), or UIO-66 (molecular formula usually represented as C). 48 H 28 O 32 Zr6 (actual molecular formula may vary depending on specific synthesis conditions and raw materials used), MOF-303 ("MOF-303" refers to a molecular structure of C 20 H 12 O 20 Metal-organic framework materials (MOFs) such as N8Al4, also known as "MOF-303(Al)" or "Al(OH)(HPDC)", are materials with good water absorption. In this embodiment, when the MOF is composited with the fiber membrane, the MOF is not only distributed on the surface of the fiber membrane, but may also be embedded inside the fiber membrane.

[0035] The metal oxide particles can be any one of MnO2, ZnO, TiO2, NiO, or V2O5; the metal sulfide particles can be any one of MoS2, ZnS, SnS2, Cu2S, NiS, NiS2, or CoS2. More preferably, the metal oxide particles or metal sulfide particles are MnO2, ZnO, or MOS2, etc. Technicians can flexibly select the type of fiber membrane, metal-organic framework, metal oxide, or metal sulfide according to their needs, improving the flexibility of composite membrane preparation.

[0036] In a preferred embodiment of the present invention, such as Figure 1 As shown, the fiber membrane contains multiple interlaced fiber filaments, and metal-organic framework materials are distributed on the surface of the fiber filaments; some individual fiber filaments have no fewer than 10 metal-organic framework materials attached within a length range of 1 μm.

[0037] Through the above method, the inventors noticed that the density of the distribution of metal-organic framework materials affects the water absorption performance of the fiber membrane. The number of metal-organic framework materials attached to some single fibers within a length range of 1μm is not less than 10, thereby improving the water absorption of a single fiber within a length range of 1μm, so that the composite membrane as a whole has better water absorption performance.

[0038] In a preferred embodiment of the present invention, the proportion of metal oxide particles or metal sulfide particles attached to the surface of the fiber membrane is not less than 90% relative to all metal oxide particles or metal sulfide particles, and the distance between the attachment site of the metal oxide particles or metal sulfide particles and the nearest metal-organic framework material is in the range of 0-100 nm.

[0039] In this embodiment, metal oxide particles or metal sulfide particles tend to grow near the metal-organic framework material. The distribution of metal oxide particles or metal sulfide particles within the 0-100 nm range of the metal-organic framework material can promote improved water absorption and HF adsorption performance of the composite membrane. In this embodiment, the metal oxide particles or metal sulfide particles exist in the form of fiber rods; preferably, more than 90% of the fiber rods are uniformly distributed on the fiber surface.

[0040] In a preferred embodiment of the present invention, when the water absorption capacity of the metal-organic framework material is not less than 0.25 g / g, the composite membrane exhibits superior water absorption. When applied to an electrochemical device, it demonstrates excellent adsorption capacity for water in the electrolyte, preventing side reactions between water in the electrolyte and the negative electrode SEI membrane of the electrochemical device, thereby improving the cycle performance and storage performance of the electrochemical device. During the preparation of the electrochemical device, when the water desorption temperature of the metal-organic framework material is 80-95°C, it ensures that the water adsorbed by the composite membrane can be completely removed during the baking process before electrolyte injection. This ensures that the composite membrane can fully adsorb water in the electrolyte during subsequent use, further improving the cycle performance and storage performance of the electrochemical device.

[0041] The present invention also provides a method for preparing a composite membrane for an electrochemical device as described above, comprising the following steps: a first composite step: preparing a fiber membrane loaded with a metal-organic framework material; a second composite step: directly attaching metal oxide particles or metal sulfide particles to the surface of the fiber membrane and / or the surface of the metal-organic framework material to obtain a composite membrane for an electrochemical device.

[0042] In a preferred embodiment of the present invention, in the first composite step, the fiber membrane is formed by electrospinning.

[0043] In the second composite step, the fiber membrane is placed in a salt solution corresponding to the metal oxide or a salt solution corresponding to the metal sulfide particles. After a hydrothermal reaction, the corresponding metal oxide particles or metal sulfide particles are generated in situ on the surface of the fiber membrane and / or the surface of the metal-organic framework.

[0044] The composite membrane prepared by hydrothermal synthesis in the second composite step, as described above, has the advantages of simple synthesis steps, low cost, good product dispersibility, and controllable product morphology and size. Furthermore, the prepared crystals are of high quality and require low energy consumption.

[0045] In a preferred embodiment of the present invention, metal oxide particles or metal sulfide particles are preferably distributed on the MOF surface, so that the metal oxide particles and metal sulfide particles can work synergistically to improve the adsorption performance of the composite membrane for water molecules and HF. Technicians can prepare composite membranes with the desired performance by adjusting parameters such as the changes in the amount of each raw material, the pH of the solution, the hydrothermal temperature, and the hydrothermal time during the preparation process.

[0046] In a preferred embodiment of the present invention, the molar ratio between the metal element in the salt solution corresponding to the metal oxide particles or the salt solution corresponding to the metal sulfide particles and the metal element in the metal-organic framework material is 1:4 to 1:6.

[0047] The molar ratio of the metal elements in the salt solution corresponding to the metal oxide particles or the salt solution corresponding to the metal sulfide particles to the metal elements in the metal-organic framework material determines the distribution density of the metal oxide particles or metal sulfide particles on the surface of the metal-organic framework material, thus affecting the microstructure of the final composite membrane. By controlling the molar ratio of the metal elements within the aforementioned range, on the one hand, excessive metal oxide particles or metal sulfide particles are prevented from covering the surface of the metal-organic framework material, affecting its adsorption performance for moisture and HF; on the other hand, fewer metal oxide particles or metal sulfide particles prevent the metal-organic framework material from completely adsorbing moisture and HF from the electrolyte.

[0048] In a preferred embodiment of the present invention, the hydrothermal reaction temperature is 100-180°C and the hydrothermal reaction time is 3-5 hours.

[0049] Different hydrothermal reaction temperatures lead to different types of products. Extending the hydrothermal reaction time increases the number of metal oxide or metal sulfide particles generated, and also increases the crystallinity of these particles. Furthermore, different types of metal oxides or metal sulfides require different hydrothermal reaction temperatures. Technicians can select an appropriate hydrothermal reaction temperature based on the type of metal oxide or metal sulfide. By controlling the temperature and time of the hydrothermal reaction, the amount of metal oxide or metal sulfide particles generated within a specified time can be controlled within a suitable range, ensuring the distribution density of these particles and improving the composite membrane's adsorption capacity for moisture and HF. Controlling the temperature and time of the hydrothermal reaction also allows for the crystallinity of the metal oxide or metal sulfide particles to be controlled within a certain range, while simultaneously improving the composite performance between the metal oxide or metal sulfide particles and the metal-organic framework material (excessive crystallinity may result in a smoother surface for the metal oxide or metal sulfide particles, reducing the number and accessibility of active sites). In this embodiment, the composite membrane prepared at a hydrothermal reaction temperature of 120°C and a time of 4 hours exhibits the best adsorption performance. In addition, increasing the temperature of the hydrothermal reaction within a certain range can shorten the reaction time and improve the reaction efficiency.

[0050] Specifically, this embodiment provides a method for preparing the above-mentioned composite membrane for electrochemical devices, including a first composite step and a second composite step, wherein the first composite step includes the following sub-steps:

[0051] Spinning solution preparation steps: Prepare PVDF solution, and add raw material 1 of MOF with water adsorption properties to PVDF solution;

[0052] Spinning step: The above-prepared spinning solution is electrospun to obtain a nanofiber membrane NF containing raw material 1;

[0053] MOF composite steps: Dissolve MOF raw material 2 in an appropriate amount of water or sodium hydroxide aqueous solution, put in nanofiber NF, and after hydrothermal reaction, obtain a nanofiber membrane loaded with MOF, MOF@NF;

[0054] In the second composite step, the MOF@NF obtained in the first composite step is taken out and immersed in a soluble salt solution of metal oxide or metal sulfide. After hydrothermal reaction, a composite membrane for electrochemical devices - metal oxide particles@MOF@NF or metal sulfide particles@MOF@NF is obtained.

[0055] In this embodiment, the metal-organic framework material is abbreviated as MOF. The first raw material of MOF is a metal source solution (raw material 1 is one or more of a chloride, nitrate, or sulfate salt containing the metal central ion of MOF), and the second raw material of MOF is an organic ligand solution (specifically H2FDC, 2,5-furandicarboxylic acid). Adding the metal source solution during the spinning step and the organic ligand solution during the MOF composite step ensures successful MOF synthesis. The order of the metal source solution addition step and the organic ligand solution addition step cannot be changed. The fiber membrane is made of polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 1.0–1.3 × 10⁻⁶. 6 The solution was prepared by mixing a mixture of dimethylformamide (DMF) and acetone, with a volume ratio of DMF to acetone of 9:1.

[0056] Furthermore, the method for preparing the composite membrane includes the following steps:

[0057] Spinning solution preparation steps: Weigh PVDF and dissolve it in a mixed solution of DMF and acetone to obtain solution 1. Weigh MOF raw material 1 and add it to solution 1 to obtain the spinning solution. Raw material 1 is one or more of chloride, nitrate, or sulfate salts containing the metal center ion of MOF (such as one or more of AlCl3·6H2O, Al(NO3)3·6H2O, or Al2(SO4)3·18H2O). The amount of the central metal element of MOF corresponding to 1g PVDF is controlled to be 0.3-0.8 mmol (i.e., controlling the growth density of MOF in the nanofiber membrane so that the adsorption performance and thermal shrinkage of the composite membrane meet the user's requirements. In some embodiments, 1g PVDF can also be replaced with 1g of other types of fiber membrane materials listed in this embodiment or some other commonly used fiber membrane materials. This embodiment does not limit this).

[0058] Spinning steps: Electrospin the above spinning solution and stabilize the spinning for a certain period of time. Then, remove the nanofiber membrane containing MOF 1 and dry it in an oven.

[0059] MOF compounding steps: Weigh the organic ligand (H2FDC) and dissolve it in NaOH solution, wherein the molar ratio of H2FDC to Al in raw material 1 is 2:1, and the solute concentration of NaOH solution is 0.2 mol / L. After complete dissolution, solution 2 is obtained.

[0060] The nanofiber membrane obtained from the spinning step is placed in solution 2 and subjected to hydrothermal reaction at 100–180°C for 4–18 hours. Afterward, it is removed, washed, and dried to obtain a nanofiber membrane loaded with MOF. Technicians can select an appropriate hydrothermal temperature depending on the type of metal oxide or metal sulfide particles to be synthesized.

[0061] The second composite step: Weigh an appropriate amount of soluble salt of metal oxide or metal sulfide and dissolve it in water to obtain solution 3. The molar ratio of the metal element in the metal oxide or metal sulfide to the metal ion in raw material 1 is 1:4 to 1:6, and the concentration of the metal salt solution is controlled below 0.1 mol / L (controlling the above molar ratio and the concentration of the metal salt solution at the same time can ensure that the growth density of metal oxide particles or metal sulfide particles in the composite membrane is within the specified range, and prevent excessive metal oxide particles or metal sulfide particles).

[0062] The nanofiber membrane obtained from the MOF composite step was placed in solution 3, and after being hydrothermally heated for a sufficient time, it was taken out, washed, and dried to obtain a metal oxide or sulfide@MOF@PVDF composite membrane.

[0063] To better illustrate the technical points of the embodiments of the present invention, the following examples and comparative examples are provided:

[0064] Example 1 (The amount of metal element in the MOF corresponding to 1g PVDF solution is 0.3mmol, and the molar ratio of metal element between KMnO4 and AlCl3·6H2O is 1:4)

[0065] Spinning solution preparation steps: Weigh 1g PVDF, dissolve it in 10ml of a mixed solution of DMF and acetone, wherein the volume ratio of DMF to acetone is 9:1, and dissolve by sonication to obtain solution 1;

[0066] Add 0.3 mmol AlCl3·6H2O to solution 1 to obtain the spinning solution;

[0067] Spinning steps: Electrospinning parameters: Place the spinning solution in a 10mL syringe with a needle inner diameter of 0.8mm. The corresponding outer shell spinning solution feed rate is 1mL / h. Apply a voltage of (17±1)kV. The receiver is 15-18cm away from the needle. The receiver roller speed is (900±50)r / min. Maintain an ambient humidity of (40±1)% and a temperature of (30±2)℃.

[0068] After stabilizing the spinning process for 5 hours under the above electrospinning parameters, the nanofiber membrane was removed and dried in an oven at 60°C for 8 hours to obtain the nanofiber membrane of raw material 1 containing MOF.

[0069] MOF composite steps: Weigh 0.6 mmol H2FDC and dissolve it in 10 ml NaOH solution, where the molar ratio of Al in H2FDC and AlCl3·6H2O is 2:1, and the solute concentration of NaOH solution is 0.2 mol / L. After complete dissolution, solution 2 is obtained.

[0070] The nanofiber membrane obtained from the spinning step was placed in solution 2 and hydrothermally heated at 100°C for 4 hours. It was then removed, washed, and dried.

[0071] Second composite step: Weigh 100 ml of 0.75 mmol / L KMnO4 aqueous solution to obtain solution 3. Place the dried nanofiber membrane from the MOF composite step into solution 3, hydrothermally heat it at 120℃ for 4 h, then remove it, wash and dry it to obtain MnO2@MOF@PVDF composite membrane.

[0072] Comparative Example 1

[0073] The spinning solution preparation and spinning steps in Comparative Example 1 are the same as in Example 1, and will not be repeated here. The difference between Comparative Example 1 and Example 1 is:

[0074] It does not include a second compounding step;

[0075] In the MOF composite step, the nanofiber membrane obtained in the spinning step was immersed in 10 ml of NaOH solution without H2FDC. After hydrothermal treatment at 100℃ for 4 h, the nanofiber membrane was taken out, washed and dried. The solute concentration of the NaOH solution was 0.2 mol / L.

[0076] In Comparative Example 1, the raw materials 2-H2FDC and KMnO4, which did not contain MOF, affected the formation of MOF and the formation of metal oxide particles.

[0077] Comparative Example 2

[0078] The spinning solution preparation step, spinning step, and MOF composite step in Comparative Example 2 are the same as in Example 1, and will not be repeated here. The difference between Comparative Example 2 and Example 1 is:

[0079] In the second composite step, the nanofiber membrane obtained in the MOF composite step was immersed in 100 ml of water and hydrothermally heated at 120°C for 4 h. After removal, washing and drying, comparative example 2 was obtained.

[0080] That is, the composite membrane prepared in Comparative Example 2 contains MOF, but does not contain metal oxide particles or metal sulfide particles.

[0081] Comparative Example 3

[0082] The spinning solution preparation step, spinning step, and second composite step in Comparative Example 3 are the same as in Example 1, and will not be repeated here. The difference between Comparative Example 3 and Example 1 is:

[0083] In the MOF composite step, the nanofiber membrane obtained in the spinning step was immersed in 10 ml of NaOH solution without H2FDC and hydrothermally heated at 100℃ for 4 h. After that, the nanofiber membrane was taken out, washed and dried. The solute concentration of the NaOH solution was 0.2 mol / L.

[0084] In other words, MOF cannot be formed in the composite membrane of Comparative Example 3, but MnO2 particles can be generated.

[0085] Comparative Example 4

[0086] Comparative Example 4 uses a composite 7+2+3 membrane with 2µm CCS and 3µm PCS coated on one side of a commonly used 7µm PP substrate; the effective component of CCS is Al2O3, and the effective component of PCS is PVDF.

[0087] Comparative Example 5

[0088] In Comparative Example 5, the amount of metal element in the MOF corresponding to 1g PVDF solution was 0.2mmol, the molar ratio of metal element between KMnO4 and AlCl3·6H2O was 1:4, and the rest was the same as in Example 1, which will not be repeated here.

[0089] Comparative Example 6

[0090] In Comparative Example 6, the amount of metal element in the MOF corresponding to 1g PVDF solution is 1mmol, the molar ratio of metal element between KMnO4 and AlCl3·6H2O is 1:4, and the rest is the same as in Example 1, so it will not be repeated.

[0091] Comparative Example 7

[0092] In Comparative Example 7, the amount of metal element in the MOF corresponding to 1g PVDF solution was 0.3mmol, the molar ratio of metal element between KMnO4 and AlCl3·6H2O was 1:3, and the rest was the same as in Example 1, so it will not be repeated here.

[0093] Comparative Example 8

[0094] In Comparative Example 8, the amount of metal element in the MOF corresponding to 1g PVDF solution was 0.3mmol, the molar ratio of metal element between KMnO4 and AlCl3·6H2O was 1:7, and the rest was the same as in Example 1, so it will not be repeated here.

[0095] Variations (Other Alternative Solutions)

[0096] Example 2

[0097] The spinning solution preparation step, spinning step, and second composite step in Example 2 are the same as in Example 1, and will not be repeated here. The difference between Example 2 and Example 1 is that the hydrothermal time in the MOF composite step is 8 hours, while other parts of the MOF composite step that are not specifically described are the same as in Example 1.

[0098] Example 3

[0099] The spinning steps in Example 3 are the same as in Example 1, and will not be repeated here. The difference is:

[0100] In the spinning solution preparation step, 1g of PVDF was weighed and dissolved in 10ml of a mixed solution of DMF and acetone, wherein the volume ratio of DMF to acetone was 9:1. The solution was dissolved by sonication to obtain solution 1. 0.8mmol of Al(NO3)3·6H2O was added to solution 1 to obtain the spinning solution.

[0101] In the MOF composite step, 1.6 mmol of H2FDC was weighed and dissolved in 10 ml of NaOH solution. After complete dissolution, solution 2 was obtained. The solute concentration of the NaOH solution was 0.2 mol / L. The other steps were the same as in Example 1.

[0102] In the second composite step, the nanofiber membrane obtained in the MOF composite step was immersed in 267 ml of 0.75 mmol / L KMnO4 solution and hydrothermally heated at 120 °C for 4 h. After removal, washing and drying, Example 3 was obtained.

[0103] The difference between Example 3 and Example 1 is that the amount of metal element in MOF corresponding to 1g PVDF solution is 0.8mmol. The amount of MOF loaded in the fiber membrane increases, but the amount of solution corresponding to the metal oxide increases accordingly. Therefore, the molar ratio between the metal element in KMnO4 and the metal element in MOF is still 0.2mmol:0.8mmol = 1:4.

[0104] Example 4

[0105] The spinning solution preparation step, spinning step, and MOF composite step in Example 4 are the same as in Example 1, and will not be repeated here. The difference is:

[0106] In the second composite step, the nanofiber membrane obtained in the MOF composite step was immersed in 67 ml of 0.75 mmol / L KMnO4 solution and hydrothermally heated at 120 °C for 4 h. After removal, washing and drying, Example 4 was obtained.

[0107] In Example 4, the molar ratio between KMnO4 and the metal elements in MOF is 0.05 mmol:0.3 mmol = 1:6.

[0108] Example 5

[0109] The spinning solution preparation step, spinning step, and MOF composite step in Example 5 are the same as in Example 1, and will not be repeated here. The difference is:

[0110] In the second composite step, a sodium molybdate solution 3 with a concentration of 1.5 mmol / L and a thioacetamide solution 4 with a concentration of 1.5 mmol / L were prepared. The nanofiber membrane obtained in the MOF composite step was immersed in a mixed solution of 50 ml sodium molybdate and 50 ml thioacetamide, and hydrothermally heated at 180°C for 10 h. After that, it was taken out, washed and dried to obtain Example 5.

[0111] The difference between Example 5 and Example 1 is that in the second compounding step, the product generated is molybdenum disulfide (MoS2).

[0112] Example 6

[0113] The spinning solution preparation step, spinning step, and MOF composite step in Example 6 are the same as in Example 1, and will not be repeated here. The difference is:

[0114] In the second composite step, a mixed solution of zinc acetate and hexamethylenetetramine with concentrations of 0.75 mmol / L and 0.5 mmol / L was prepared. The nanofiber membrane obtained in the MOF composite step was immersed in 100 ml of the mixed solution of zinc acetate and hexamethylenetetramine (the concentration of zinc acetate in the mixed solution was 0.75 mmol / L and the concentration of hexamethylenetetramine was 0.5 mmol / L). After hydrothermal treatment at 120 °C for 4 h, it was taken out, washed and dried to obtain Example 6.

[0115] The difference between Example 6 and Example 1 is that in the second compounding step, the product generated is ZnO.

[0116] Regarding the above embodiments and comparative examples, the following studies will investigate their performance in terms of sample characterization of the composite membrane, thermal shrinkage test of the composite membrane, capacity retention rate of the electrochemical device, and water absorption of the electrochemical device.

[0117] Sample Characterization

[0118] The composite membrane prepared in Example 1 was characterized by SEM, such as... Figure 1 As shown, the main body of the composite membrane is composed of interlaced fiber filaments, which is also the main component of the membrane. Scattered white dots are distributed on the surface of the fiber filaments; these white dots are MIL-160 grown on the fiber surface. At SEM magnification of 20,000x or higher, clearly visible white MOF particles are present on the fiber surface. The number of MOF particles within a 1µm length of a single fiber must not be less than 10; otherwise, the spinning conditions and MOF formation conditions are not well controlled. MnO2 exists in the form of fiber rods, with over 90% of the MnO2 adhering to the fiber surface in this form, and the distribution is relatively uniform. MnO2 grows near the MOF.

[0119] [Heat Shrinkage Performance Test]

[0120] To verify the performance of the composite diaphragm for the electrochemical device, the composite diaphragms obtained in Examples 1-6 and Comparative Examples 1-4 were cut into small squares of 2cm x 5cm. Samples were taken along the longitudinal direction of the long side, and the specific width value was measured using a CCD imager and recorded. Then, the diaphragms were kept in a high-temperature oven (the oven temperature was set at 130℃ and 150℃ in this embodiment) for 1 hour. After cooling, the width value of the composite diaphragm was measured again using a CCD imager, and the shrinkage rate of the composite diaphragm in the transverse and longitudinal directions was calculated. The experimental results are shown in Tables 1 and 2 below.

[0121] Table 1. Thermal shrinkage rate of different diaphragms at 130℃

[0122]

[0123]

[0124] Table 2. Heat shrinkage rate of different diaphragms at 150℃

[0125]

[0126] According to the results in Table 1, compared with Comparative Examples 1-4 (transverse shrinkage rate greater than 1%, longitudinal shrinkage rate greater than 2.8%), the transverse shrinkage rate (0.9%) and longitudinal shrinkage rate (1.5%) of Example 1 are both lower. This indicates that the composite membrane prepared in Example 1 has better thermal shrinkage performance at 130℃ than the composite membranes prepared by the coating method in Comparative Example 1 without H2FDC and KMnO4 (which cannot form MOF and MnO2), Comparative Example 2 without KMnO4 (which cannot form MnO2), Comparative Example 3 without H2FDC (which cannot form MOF), and Comparative Example 4. Moreover, compared with the MOF without MnO2 modification in Comparative Example 2, the MOF modified with MnO2 has a lower thermal shrinkage rate, and the thermal shrinkage performance is improved.

[0127] As shown in Table 2, compared to Comparative Examples 1-4 (transverse shrinkage rate greater than 32%, longitudinal shrinkage rate greater than 40%), the transverse shrinkage rate (4.3%) and longitudinal shrinkage rate (6.5%) of Example 1 are both lower. This indicates that the composite membrane prepared in Example 1 has better heat shrinkage performance at 150℃ than the composite membranes prepared in Comparative Example 1 without H2FDC and KMnO4, Comparative Example 2 without KMnO4, Comparative Example 3 with KMnO4 but without H2FDC, and Comparative Example 4 using a coating method. Furthermore, as shown in Tables 1 and 2, within a certain temperature range, the transverse and longitudinal shrinkage rates of the composite membrane increase with increasing temperature.

[0128] Furthermore, comparing Examples 1 and 2, it can be seen that in the MOF composite step, extending the hydrothermal time (from 4h to 8h) resulted in minimal changes in the transverse shrinkage rate (increased by 0.1%) and longitudinal shrinkage rate (increased by 0.3%) of the composite membrane at 130℃. At 150℃, there was no significant difference in the transverse shrinkage rate (increased by 0.8%) and longitudinal shrinkage rate (increased by 0.7%). This is mainly because as the hydrothermal time increases, the amounts of MOF and MnO2 reach a certain level and then stop increasing, resulting in no significant difference in thermal shrinkage rate. Therefore, controlling the hydrothermal time in the MOF composite step to within 4h is preferable, as it shortens the hydrothermal time while ensuring better thermal shrinkage performance.

[0129] Comparing Examples 1 and 3, it can be seen that the amount of Al corresponding to 1g PVDF increased from 0.3mmol to 0.08mmol, and the amount of KMnO4 also increased accordingly. The transverse shrinkage rate and longitudinal shrinkage rate at 130℃ and 150℃ also showed an increasing trend. That is, increasing the distribution density of MOF and MnO2 did not have a significant effect on improving the transverse shrinkage rate and longitudinal shrinkage rate. From the perspective of balancing the heat shrinkage performance of the composite membrane and cost, the concentration of raw materials should be controlled within a reasonable range.

[0130] Comparing Example 1 (molar ratio of KMnO4 to metal elements in MOF is 1:4) and Example 4 (molar ratio of KMnO4 to metal elements in MOF is 1:6), it can be seen that the composite membranes prepared in the two examples have no significant difference in transverse shrinkage rate and longitudinal shrinkage rate at 130℃; the composite membranes prepared in the two examples also have no significant difference in transverse shrinkage rate and longitudinal shrinkage rate at 150℃. The main reason is that although the amount of MOF is increased, the amount of MnO2 is limited, and the thermal shrinkage is not significantly improved. Therefore, the molar ratio of KMnO4 to metal elements in MOF should be reasonably controlled.

[0131] Comparing Examples 1, 5, and 6, it can be seen that the lateral shrinkage rate and longitudinal shrinkage rate of the composite membranes loaded with MnO2, MOS2, and ZnO are not significantly different, and all exhibit good thermal shrinkage performance.

[0132] [Battery Performance Testing]

[0133] To verify the cycle stability of the prepared composite separator, the composite separators prepared in the above comparative examples and embodiments were combined with negative electrode plates, positive electrode plates, and electrolytes to obtain batteries. The capacity retention rate and water absorption of the batteries were tested. The following uses a secondary lithium battery as an example to illustrate the testing process.

[0134] First, a secondary lithium battery is prepared, and the preparation method is as follows:

[0135] Positive electrode preparation: Using Yu Neng's lithium iron phosphate material as the positive electrode active material, the positive electrode material, conductive agent Super P, carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.0:0.5:1.5. The solvent N-methylpyrrolidone (NMP) is added and the mixture is stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, and the positive electrode is prepared by drying, cold pressing, and slitting.

[0136] Negative electrode preparation: Using BTR's artificial graphite as the negative electrode active material, Super P as the conductive agent, sodium carboxymethyl cellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the binder, the negative electrode material, conductive agent acetylene black, carbon nanotubes (CNT), thickener CMC, and binder SBR are mixed at a mass ratio of 96.4:1:1.2:1.4. Deionized water is added as a solvent, and the mixture is stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil, and the positive electrode is prepared through drying, cold pressing, and slitting processes.

[0137] Electrolyte preparation: In an argon-atmospheric glove box with a water content of <10 ppm, battery-grade (referring to purity level meeting battery performance requirements) ethylene carbonate (DOL), propylene carbonate (DMC), ethyl acetate (EA), and vinylene carbonate (VC) were mixed in a volume ratio of 75:15:5:5 to form an organic solvent. Other components were quantitatively added according to the electrolyte composition table below, and the mixture was homogeneous to obtain the electrolyte. The electrolytes used in different examples and comparative examples were completely consistent.

[0138] Membrane preparation: The composite membranes prepared in the above embodiments and comparative examples were used as membranes.

[0139] Preparation of lithium-ion secondary batteries: The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film is wrapped around the separator, dried, and injected with the electrolyte prepared above. After encapsulation, settling, and formation processes, a 1Ah soft-pack battery (i.e., a lithium-ion secondary battery) is finally prepared.

[0140] Capacity retention test

[0141] Capacity retention rate refers to the ratio of the remaining capacity of a battery to its initial capacity after a period of use. The lithium-ion secondary batteries prepared by the above method were activated at 25°C with 0.1C / 0.1C charge-discharge for 3 cycles, and then cycled at 25°C with 0.5C / 0.5C for 2000 cls. The capacity retention rate results are shown in Table 3 below.

[0142] Table 3 Capacity retention of lithium-ion secondary batteries after 2000 cs cycles

[0143] sample Initial capacity of the loop 2000 lap capacity Capacity retention Example 1 4.697 4.340 92.40％ Example 2 4.568 4.223 92.45％ Example 3 4.745 4.383 92.37％ Example 4 4.624 4.272 92.39％ Example 5 4.578 4.231 92.41％ Example 6 4.621 4.264 92.27％ Comparative Example 1 4.721 4.094 86.72％ Comparative Example 2 4.742 4.127 87.04％ Comparative Example 3 4.678 4.085 87.32％ Comparative Example 4 4.656 4.263 86.66％ Comparative Example 5 4.704 4.223 89.78％ Comparative Example 6 4.643 4.282 92.22％ Comparative Example 7 4.598 4.244 92.30％ Comparative Example 8 6.396 5.759 90.04％

[0144] As shown in Table 3, the capacity retention rates in Examples 1-6 are not significantly different, but all are higher than those in Comparative Examples 1-4. This indicates that the composite separator prepared by the method provided in this embodiment has a better capacity retention rate. The reason is:

[0145] Water reacts with lithium salts in the electrolyte to generate HF, which consumes active lithium ions and reduces the battery's energy. Excessive moisture content can damage the density and uniformity of the SEI film, causing lithium ion insertion vacancies to be occupied by the electrolyte solvent, thereby reducing the battery's capacity.

[0146] HF is a highly corrosive acid that can corrode the internal metal parts, battery casing, and seals, leading to problems such as battery swelling and leakage. These problems can affect the battery's capacity retention rate.

[0147] HF can also damage the SEI film, causing irreversible chemical reactions of lithium ions on the negative electrode, further consuming active lithium ions and reducing battery capacity.

[0148] The composite separator provided in this embodiment can adsorb moisture and HF in the electrolyte, thereby helping to maintain battery capacity and ensuring a high capacity retention rate after the battery is discharged under specified conditions. Furthermore, moisture and HF in the battery can damage the performance of the SEI membrane, thus affecting the battery's cycle performance and lifespan. Adsorbing moisture and HF can also improve the battery's cycle performance. In addition, excessive moisture content can lead to slow chemical reactions within the battery, such as the decomposition of lithium salts and damage to the SEI membrane, thereby impairing the battery's storage performance. The corrosiveness of HF also affects the battery's storage performance; adsorbing moisture and HF can also improve the battery's storage performance.

[0149] Water absorption test

[0150] During the membrane fabrication and cell winding processes, the MnO2@MIL-160@NF composite membrane absorbs some moisture. However, during the high-temperature baking process before electrolyte injection, based on typical high-temperature baking conditions (95–105°C and over 12 hours), the moisture absorbed by MIL-160 itself will be fully desorbed. Therefore, when injecting electrolyte into the cell after baking, there is no need to worry about the moisture absorbed by MIL-160 negatively impacting the cell's performance. MnO2 not only promotes the function of the MOF but also has strong adsorption properties for free HF, further reducing internal side reactions within the cell.

[0151] To further verify the adsorption performance of the MnO2@MIL-160@NF composite membrane for moisture and HF, a battery cell that had undergone 2000 cls of cycling at room temperature was disassembled. The Karl Fischer method was used to determine the moisture and hydrofluoric acid content in the residual electrolyte, and the results were compared with those measured before electrolyte injection. The comparison results are shown in the table below.

[0152] Table 4. Growth rates of water content and acid content in the electrolyte.

[0153] sample residual liquid water content Residual acid content Water content growth rate Acid growth rate Example 1 76.5 183.6 194.2％ 135.4％ Example 2 82.3 191.8 216.5％ 145.8％ Example 3 79.4 191.9 205.4％ 146.0％ Example 4 77.83 198.4 201.3％ 150.9％ Comparative Example 1 243.2 580.8 835.4％ 644.6％ Comparative Example 2 156.3 456.4 505.1％ 462.1％ Comparative Example 3 188.4 402.5 601.2％ 363.7％ Comparative Example 4 256.8 718.1 887.7％ 692.5％ Comparative Example 5 112.6 304.7 333.1％ 290.6％ Comparative Example 6 70.6 174.3 171.5％ 123.5％ Comparative Example 7 79.84 180.9 207.1％ 131.9％ Comparative Example 8 124.5 355.6 378.8％ 355.9％

[0154] As shown in the table above, compared to Comparative Examples 1-4, the residual water and residual acid contents in the electrolytes of Examples 1 to 4 were lower, as were the water content growth rate and acid growth rate. This indicates that the MnO2@MIL-160@NF membrane can adsorb free water and HF in the electrolyte, reducing the capacity loss caused by side reactions of water and HF in the cell, thereby improving the long-cycle performance of the cell.

[0155] Based on Tables 1 to 4 above, compared to Example 1, the composite membrane prepared in Comparative Example 5 (with 0.2 mmol of metal element in MOF corresponding to 1 g PVDF) showed increased transverse shrinkage and longitudinal thermal shrinkage at 130°C and 150°C. However, the water content growth rate and acid content growth rate were relatively high, and the capacity retention rate decreased. This indicates that reducing the amount of metal element in MOF in the composite membrane affects the thermal shrinkage rate, capacity retention rate, water content growth rate, and acid content growth rate of the composite membrane. The amount of metal element corresponding to MOF in the composite membrane should be appropriately increased.

[0156] Compared to Example 1, the composite separator prepared in Comparative Example 6 (with 1 mmol of metal element in MOF corresponding to 1 g PVDF) showed no significant changes in lateral shrinkage and longitudinal thermal shrinkage at 130°C and 150°C. The capacity retention rate was not significantly different from that of Examples 3 and 1. The composite separator prepared with 0.3-0.8 mmol of metal element in MOF corresponding to 1 g PVDF was sufficient to meet the requirements for improving battery cycle performance. Therefore, the amount of metal element in MOF corresponding to 1 g PVDF can be controlled to 0.3-0.8 mmol to balance cost and overall performance of the composite separator.

[0157] Compared to Example 1, the composite membrane prepared in Comparative Example 7 (with a metal element molar ratio of 1:3 between KMnO4 and AlCl3·6H2O, meaning the composite membrane has a higher MnO2 content) did not show a significant decrease in lateral shrinkage and longitudinal thermal shrinkage at 130℃ and 150℃. The water content growth rate and acid growth rate decreased, but the improvement in capacity retention was not significant. The composite membrane prepared using a metal element molar ratio of 1:4 between KMnO4 and AlCl3·6H2O is sufficient to meet the requirements.

[0158] Compared to Example 1, the composite separator prepared in Comparative Example 8 (with a metal element molar ratio of 1:7 between KMnO4 and AlCl3·6H2O, meaning a lower MnO2 content in the composite separator) exhibits increased lateral shrinkage and longitudinal thermal shrinkage at 130°C and 150°C. This leads to increased water content and acid growth rates in the battery, deteriorating the overall cycle life and reducing the battery's cycle performance. When the metal element molar ratio between KMnO4 and AlCl3·6H2O is controlled between 1:4 and 1:6, the composite separator exhibits better overall performance.

[0159] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite diaphragm for an electrochemical device, characterized in that, include: Fiber membrane; A metal-organic framework material is at least distributed on the surface of the fiber membrane, and the metal-organic framework material is water-absorbing. as well as Metal oxide particles or metal sulfide particles are directly attached to the surface of the fiber membrane and / or the metal-organic framework material.

2. The composite diaphragm for an electrochemical device according to claim 1, characterized in that, The fiber membrane comprises multiple interlaced fiber filaments, and the metal-organic framework material is distributed on the surface of the fiber filaments; the number of metal-organic framework materials attached to a single fiber filament within a length range of 1 μm is not less than 10.

3. The composite diaphragm for an electrochemical device according to claim 2, characterized in that, The proportion of the metal oxide particles or metal sulfide particles attached to the surface of the fiber membrane is not less than 90% relative to all the metal oxide particles or metal sulfide particles, and the distance between the attachment site of the metal oxide particles or metal sulfide particles and the nearest metal-organic framework material is in the range of 0-100 nm.

4. The composite diaphragm for an electrochemical device according to any one of claims 1 to 3, characterized in that, The water absorption of the metal-organic framework material is not less than 0.25 g / g, and the water desorption temperature range of the metal-organic framework material is 80-95℃.

5. A method for preparing a composite diaphragm for an electrochemical device according to any one of claims 1 to 4, characterized in that, Includes the following steps: First composite step: Prepare fiber membrane loaded with metal-organic framework material; The second composite step involves directly attaching metal oxide particles or metal sulfide particles to the surface of the fiber membrane and / or the surface of the metal-organic framework material.

6. The method for preparing the composite diaphragm for an electrochemical device according to claim 5, characterized in that, In the first composite step, the fiber membrane is formed by electrospinning; In the second composite step, the fiber membrane is placed in a salt solution corresponding to the metal oxide particles or the metal sulfide particles. After a hydrothermal reaction, the corresponding metal oxide particles or metal sulfide particles are generated in situ on the surface of the fiber membrane and / or the surface of the metal-organic framework material.

7. The method for preparing the composite diaphragm for an electrochemical device according to claim 6, characterized in that, The molar ratio between the metal element in the salt solution corresponding to the metal oxide particles or the salt solution corresponding to the metal sulfide particles and the metal element in the metal-organic framework material is 1:4 to 1:

6.

8. The method for preparing the composite membrane for an electrochemical device according to claim 6, characterized in that, The hydrothermal reaction temperature is 100-180℃, and the hydrothermal reaction time is 3-5 hours.

9. The method for preparing the composite diaphragm for an electrochemical device according to claim 5, characterized in that, The fiber membrane is made of polypropylene, polyethylene, glass fiber, cellulose, polyvinyl alcohol, polyethylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyetheretherketone, polyimide, polyallylamine, polyurethane, polyacrylonitrile, polymethyl methacrylate, polytetraethylene glycol diacrylate, copolymers thereof, or combinations thereof. The metal in the metal-organic framework material is selected from any one of magnesium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc or zirconium; The metal oxide type of the metal oxide particles includes any one of MnO2, ZnO, TiO2, NiO, and V2O5; The metal sulfide particles include any one of MoS2, ZnS, SnS2, Cu2S, NiS, NiS2, and CoS2.

10. An electrochemical device, characterized in that, The device comprises a positive electrode, a negative electrode, an electrolyte, and a composite diaphragm for an electrochemical device according to any one of claims 1 to 4.

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