Composite diaphragm and secondary battery and electric device thereof

Abstract

The invention discloses a composite diaphragm and a secondary battery and an electric device thereof, and relates to the technical field of batteries. According to the composite diaphragm provided by the invention, the first coating and the second coating are arranged on at least one side of the porous base membrane, the first coating comprises at least two of the inorganic ceramic, the porous framework material and the flame-retardant microcapsule, and the second coating comprises the polymer particles with the core layer, the middle layer and the shell layer; the crosslinking densities of the polymer A in the core layer, the polymer B in the middle layer and the polymer C in the shell layer are sequentially increased; the obtained composite diaphragm has excellent heat resistance and flame retardance and good cohesiveness, and the interface bonding capacity can be effectively improved; therefore, the cycle performance of the secondary battery prepared subsequently can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite separator and its secondary battery and power-consuming device. Background Technology

[0002] As a core component of rechargeable batteries, the separator primarily functions to separate the positive and negative electrodes, prevent short circuits, and allow ions to pass through. Its performance directly affects the battery's safety, cycle life, and rate performance. With the rapid development of the new energy industry, high energy density, high safety, and long cycle life have become important development directions for rechargeable batteries, placing higher demands on separator performance. Polyolefin separators are widely used due to their good mechanical properties and chemical stability, but they suffer from poor heat resistance (prone to thermal shrinkage above 120℃) and insufficient hydrophilicity (poor electrolyte wettability), making it difficult to meet the requirements of high-safety batteries. To improve these shortcomings, researchers have developed various modified separators, such as coating the base membrane surface with an inorganic ceramic layer to improve heat resistance, or introducing an organic coating to improve hydrophilicity. However, these modified membranes still have the following shortcomings: (1) The interfacial bonding between the coating and the base membrane is weak, and it is easy to peel off under long-term charge-discharge cycles or electrolyte immersion; (2) The function is singular, and it is difficult to meet multiple requirements such as heat resistance, flame retardancy, and high ion conductivity at the same time; (3) The coating structure design is unreasonable, and performance improvement is often achieved by sacrificing porosity, which leads to increased ion transport resistance; (4) There is a lack of effective gradient function design, which makes it impossible to balance the various performance indicators of the membrane. Summary of the Invention

[0003] The purpose of this application is to solve the technical problem that it is difficult for a separator to simultaneously achieve heat resistance and flame retardancy, high ion conduction efficiency and good adhesion. A composite separator with excellent heat resistance and flame retardancy, good electrolyte wettability, excellent adhesion and high ion conductivity is proposed, so that the secondary battery prepared thereafter has excellent cycle performance and low internal resistance, as well as the secondary battery and the power device thereof.

[0004] To achieve the above objectives, a first aspect of this application provides a composite membrane, the composite membrane comprising a porous base membrane and a first coating and a second coating sequentially disposed on at least one side of the porous base membrane; The first coating comprises at least two of inorganic ceramics, porous framework materials, and flame-retardant microcapsules; The second coating comprises polymer particles, the polymer particles comprising a core layer, an intermediate layer and a shell layer, the core layer comprising polymer A, the intermediate layer comprising polymer B, and the shell layer comprising polymer C, wherein the crosslinking density of polymer A, polymer B and polymer C increases sequentially.

[0005] As an embodiment of this application, the thickness of the porous base film is 5μm~16μm.

[0006] As an embodiment of this application, the thickness of the first coating is 1μm~8μm.

[0007] As an embodiment of this application, the thickness of the second coating is 1 μm to 6 μm.

[0008] As an embodiment of this application, the first coating comprises inorganic ceramics, porous framework materials and flame-retardant microcapsules, and the first coating satisfies: 0.6 < Y < 4; Where Y = (B × R) / (D × P); B m 2 / g represents the specific surface area of ​​the porous framework material; R cm 3 / g represents the pore volume of the porous framework material; D nm is the average particle size of the inorganic ceramic; P nm is the shell thickness of the flame-retardant microcapsule.

[0009] As an embodiment of this application, the specific surface area B m of the porous framework material 2 / g is 2000m 2 / g~3000m 2 / g.

[0010] As an embodiment of this application, the pore volume R cm of the porous framework material is... 3 / g is 1.5cm 3 / g~2cm 3 / g.

[0011] As an embodiment of this application, the average particle size D nm of the inorganic ceramic is 100 nm to 150 nm.

[0012] As an embodiment of this application, the shell thickness P nm of the flame-retardant microcapsule is 10 nm to 50 nm.

[0013] As an embodiment of this application, the inorganic ceramic includes at least one of silicon dioxide, aluminum oxide, boehmite, magnesium oxide, and barium sulfate.

[0014] As an embodiment of this application, the surface of the porous framework material has a silane coupling agent, and the intensity ratio of the characteristic peak of the Si-O-Si asymmetric stretching vibration to the characteristic peak of the Si-OH stretching vibration of the porous framework material is ≥1.2.

[0015] As an embodiment of this application, the porous framework material includes MOFs materials, and the MOFs materials include at least one of KAR-F02, ZIF-8, UIO-66, and MOF-177. As an embodiment of this application, the shell of the flame-retardant microcapsule comprises polyurea-formaldehyde resin, and the core layer comprises melamine cyanurate.

[0016] As an embodiment of this application, the core layer of the flame-retardant microcapsules has an average particle size of 0.4 μm to 4.5 μm.

[0017] As an embodiment of this application, the crosslinking density increases by a factor of >20%.

[0018] As an embodiment of this application, polymer A includes isocyanate polymers.

[0019] As an embodiment of this application, the polymer B comprises an acrylate copolymer.

[0020] As an embodiment of this application, the polymer C comprises a cross-linked siloxane polymer.

[0021] As an embodiment of this application, the crosslinking density of polymer A is 0.003 mol / cm³. 3 ~0.005mol / cm 3 .

[0022] As an embodiment of this application, the crosslinking density of polymer B is 0.006 mol / cm³. 3 ~0.008mol / cm 3 .

[0023] As an embodiment of this application, the crosslinking density of the polymer C is 0.009 mol / cm³. 3 ~0.012mol / cm 3 .

[0024] As an embodiment of this application, the thickness ratio of the core layer, intermediate layer and shell layer is (5~6):(2~3):(1~3).

[0025] As an embodiment of this application, the material of the porous base membrane includes any one of polyolefin, polyvinyl alcohol, and polyethylene terephthalate nonwoven fabric.

[0026] As an embodiment of this application, the porous base membrane has pores, and the inner wall of the pore channel has a third coating, the third coating comprising a maleic anhydride monomer grafted polymer, the glass transition temperature of the maleic anhydride monomer grafted polymer being ≥110℃.

[0027] As an embodiment of this application, the ratio of the thickness of the third coating to the average pore size of the porous base film is 1:(1~8).

[0028] As an embodiment of this application, the thickness of the third coating is 50nm~200nm.

[0029] As an embodiment of this application, the average pore size of the porous base film is 200nm~600nm.

[0030] As an embodiment of this application, the porous base membrane has pores, and the inner wall of the pore channels has a fourth coating, the fourth coating comprising an ion-conducting material, the ion-conducting material having an ionic conductivity ≥3×10⁻⁶ at 30°C. -4 S / cm.

[0031] As an embodiment of this application, the ion-conducting material includes at least one of MOFs, COFs, polythiophene, polyaniline, sulfonated polystyrene, crystalline aluminosilicate molecular sieves, layered silicates, metal oxide nanotubes, siloxane-polymer hybrids, graphene, carbon nanotubes, carboxymethyl cellulose, and hydroxyethyl cellulose.

[0032] As an embodiment of this application, the ratio of the thickness of the fourth coating to the average pore size of the porous base film is ≤0.18.

[0033] A second aspect of this application provides a secondary battery, the secondary battery comprising the composite separator described in this application.

[0034] A third aspect of this application provides an electrical device including the secondary battery described in this application.

[0035] Compared with the prior art, the beneficial effects of this application are: The composite separator provided in this application has a first coating and a second coating on at least one side of a porous base membrane. The first coating includes at least two of inorganic ceramics, porous framework materials, and flame-retardant microcapsules, and the second coating includes polymer particles having a core layer, an intermediate layer, and a shell layer. The crosslinking density of polymer A in the core layer, polymer B in the intermediate layer, and polymer C in the shell layer increases sequentially. The resulting composite separator has excellent heat resistance and flame retardancy, as well as good adhesion, which can effectively improve the interfacial bonding ability. This can effectively improve the cycle performance of the secondary battery prepared subsequently. Attached Figure Description

[0036] Figure 1 Here is a SEM image of the composite membrane prepared in Example 1; Figure 2 The figures show the performance of the secondary battery prepared in Example 1 and the secondary battery prepared in Comparative Example 1. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0039] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0040] In one embodiment of this application, a composite membrane is provided, the composite membrane comprising a porous base membrane and a first coating and a second coating sequentially disposed on at least one side of the porous base membrane; The first coating comprises at least two of inorganic ceramics, porous framework materials, and flame-retardant microcapsules; The second coating comprises polymer particles, the polymer particles comprising a core layer, an intermediate layer and a shell layer, the core layer comprising polymer A, the intermediate layer comprising polymer B, and the shell layer comprising polymer C, wherein the crosslinking density of polymer A, polymer B and polymer C increases sequentially.

[0041] The composite separator provided in this application has a first coating and a second coating on at least one side of a porous base membrane. The first coating includes at least two of inorganic ceramics, porous framework materials, and flame-retardant microcapsules, and the second coating includes polymer particles having a core layer, an intermediate layer, and a shell layer. The crosslinking density of polymer A in the core layer, polymer B in the intermediate layer, and polymer C in the shell layer increases sequentially. The resulting composite separator has excellent heat resistance and flame retardancy, as well as good adhesion, which can effectively improve the interfacial bonding ability. This can effectively improve the cycle performance of the secondary battery prepared subsequently.

[0042] In some embodiments, the thickness of the porous base film is 5 μm to 16 μm.

[0043] For example, the thickness of the porous base film can be any point value or a range between any two points between 5μm and 16μm, such as 5μm, 6μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, etc.

[0044] This study found that the thickness of the porous base membrane can affect the ion transport path to a certain extent, thereby affecting the ion conductivity; at the same time, it can also affect the mechanical strength of the composite membrane, thereby affecting the structural stability; when the thickness of the porous base membrane is further selected within the above range, the overall performance of the obtained composite membrane is better, and the cycle performance of the secondary battery prepared subsequently is better.

[0045] In some embodiments, the thickness of the first coating is 1 μm to 8 μm.

[0046] For example, the thickness of the first coating can be any point value between 1μm and 8μm or a range between any two points, such as 1μm, 2μm, 4μm, 6μm, 8μm, etc.

[0047] This study found that the thickness of the first coating affects ion transport resistance to a certain extent, and also affects the heat resistance and flame retardancy of the composite membrane. Furthermore, the thickness of the first coating also affects its bonding ability with the second coating or the porous base membrane. When the thickness of the first coating is further selected within the above-mentioned range, the resulting composite membrane exhibits superior overall performance, and the subsequent secondary battery prepared with it demonstrates better cycle performance. In some embodiments, the thickness of the second coating is 1 μm to 6 μm.

[0048] For example, the thickness of the second coating can be any point value between 1μm and 6μm or a range between any two points, such as 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, etc.

[0049] This study found that the thickness of the second coating affects the ion transport resistance to a certain extent, as well as the wettability of the electrolyte on the composite separator; furthermore, it also affects the structural stability and heat resistance of the composite separator to a certain extent. When the thickness of the second coating is further selected within the above range, the overall performance of the obtained composite separator is better, and the cycle performance of the secondary battery prepared subsequently is better.

[0050] It should be noted that the thickness of the porous base film, the first coating and the second coating are tested as follows: first, the CP is frozen through a diaphragm, and then polished with an argon ion beam for 4.5 hours with an aluminum foil substrate and a polishing voltage of 4 kV; then the thickness is measured using a scanning electron microscope, where EHT=3 kV, WD=6 mm and Aperture Size=30 μm.

[0051] In some embodiments, the first coating comprises inorganic ceramics, porous framework materials, and flame-retardant microcapsules, and the first coating satisfies: 0.6 < Y < 4; Where Y = (B × R) / (D × P); B m 2 / g represents the specific surface area of ​​the porous framework material; R cm 3 / g represents the pore volume of the porous framework material; D nm is the average particle size of the inorganic ceramic; P nm is the shell thickness of the flame-retardant microcapsule.

[0052] This application research found that further selecting the first coating to include inorganic ceramics, porous framework materials, and flame-retardant microcapsules, and limiting the first coating to satisfy 0.6 < (B×R) / (D×P) < 4, the three components have better interaction. On the basis of achieving good heat resistance and flame retardancy, it can also effectively improve the ion conductivity of the composite membrane and improve the wetting performance of the subsequent electrolyte on the composite membrane; thereby effectively improving the cycle performance of the prepared secondary battery and reducing the internal resistance of the secondary battery.

[0053] For example, Y can be any point value between 0.6 and 4 or a range value between any two points, such as 0.6, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, etc.

[0054] In some embodiments, the specific surface area B m of the porous framework material 2 / g is 2000m 2 / g~3000m 2 / g.

[0055] It should be noted that the specific surface area test method of the porous framework material is as follows: the first coating layer of the composite diaphragm is scraped off, then dissolved in an appropriate amount of acetone solvent, allowed to stand for 8 hours, filtered, the filtrate is collected, dried, and the porous framework material is obtained. Then, the specific surface area of ​​the porous framework material is tested by gas adsorption BET method, with nitrogen as the adsorbate. Specifically, the sample pretreatment and degassing conditions are: 220℃ / 2hrs, 250℃ / 2hrs (vacuum degassing); sample volume: 2 / 3 of the bulb volume; determination method: static volumetric method; pressure point range: 0.05~0.35 for conventional samples; adsorbate: nitrogen; temperature control medium: liquid nitrogen; analytical model: multi-point BET.

[0056] For example, the specific surface area of ​​the porous framework material can be 2000 m². 2 / g~3000m 2 Any point value between / g or a range of values ​​between any two points, for example, 2000 m 2 / g、2200 m 2 / g、2400 m 2 / g、2600 m 2 / g、2800 m 2 / g、3000 m 2 / g etc.

[0057] In some embodiments, the pore volume R cm of the porous framework material 3 / g is 1.5 cm 3 / g ~2 cm 3 / g.

[0058] It should be noted that the pore volume test method of the porous framework material is the same as the specific surface area test method of the porous framework material, and the gas adsorption BET method is also used to obtain the pore volume data.

[0059] For example, the pore volume of the porous framework material can be 1.5 cm. 3 / g ~2 cm 3 Any point value between / g or a range between any two points, for example, 1.5 cm. 3 / g, 1.6 cm 3 / g, 1.7 cm 3 / g, 1.8 cm 3 / g, 1.9 cm 3 / g, 2.0 cm 3 / g etc.

[0060] This study found that the specific surface area and pore volume of porous framework materials have varying effects on the adsorption and fixation capacity of electrolytes in subsequent secondary batteries, thus affecting the risk of electrolyte volatilization and combustion at high temperatures, as well as the electrolyte's wetting ability. Furthermore, the specific surface area and pore volume of porous framework materials also affect their thermal stability. Additionally, the specific surface area and pore volume of porous framework materials also influence their adsorption capacity for other substances, such as those with adhesive properties, thereby affecting the bonding performance. When the specific surface area and pore volume of the porous framework material are further selected within the aforementioned ranges, the resulting composite separator exhibits superior overall performance, and the subsequent secondary battery prepared with it demonstrates better cycle performance.

[0061] In some embodiments, the average particle size D nm of the inorganic ceramic is 100 nm to 150 nm.

[0062] It should be noted that the average particle size of the inorganic ceramic is tested as follows: a composite diaphragm is taken, a first coating is scraped off, and then subjected to high-temperature pressure sintering and cooling collection (200MPa Ar gas, sintering temperature 900℃) to obtain inorganic ceramic. Then, particle size analysis laser diffraction is used for testing, with ultrasonic conditions of 35kHz for 3min. Specifically, water, sodium polyacrylate dispersant and inorganic ceramic are mixed evenly in a ratio of 70:10:20, and then ultrasonically treated at a frequency of 35kHz for 3min. Subsequently, the treated mixture is introduced into a Hydro MU2000 sample introduction system for testing, and the rotation speed of the sample introduction system is set to 2400r / min.

[0063] For example, the average particle size of the inorganic ceramic can be any point value between 100 nm and 150 nm or a range value between any two points, such as 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, etc.

[0064] This study found that the average particle size of inorganic ceramics affects the particle packing density, thus influencing the density and uniformity of the heat-resistant network formed in the coating. It also affects the contact area with the electrolyte, thus affecting the electrolyte wettability, and further impacts ion transport resistance. When the average particle size of the inorganic ceramics is further selected within the aforementioned range, the resulting composite separator exhibits superior overall performance, leading to better cycle performance and lower internal resistance in the subsequently fabricated secondary battery.

[0065] In some embodiments, the particle size distribution variation coefficient of the inorganic ceramic is 5% to 15%.

[0066] It should be noted that the particle size distribution variation coefficient of the inorganic ceramic is calculated after testing the particle size using laser diffraction. When its value is within the above range, the particle size distribution of the inorganic ceramic particles is more uniform and there are fewer surface defects, which can make the obtained composite separator have better heat resistance and the subsequent secondary battery has better cycle performance.

[0067] In some embodiments, the shell thickness P nm of the flame-retardant microcapsule is 10 nm to 50 nm.

[0068] It should be noted that the test method for the shell thickness of the flame-retardant microcapsules is as follows: take the composite membrane, scrape off the first coating, then dissolve it in an appropriate amount of acetone solvent, let it stand for 8 hours, filter and collect the solid precipitate, centrifuge at high speed (6000 rpm, relative centrifugal force Fr=10000×g) to obtain flame-retardant microcapsules, and then use transmission electron microscopy to test the shell thickness.

[0069] For example, the shell thickness of the flame-retardant microcapsule can be any point value between 10 nm and 50 nm or a range between any two points, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc.

[0070] This study found that the shell thickness of flame-retardant microcapsules affects the release kinetics of flame-retardant microcapsules and also affects ionic conductivity. When the shell thickness of flame-retardant microcapsules is further selected within the above range, the composite membrane obtained has better overall performance, and the subsequent secondary battery has better cycle performance and lower internal resistance.

[0071] In some embodiments, the inorganic ceramic includes at least one of silicon dioxide, aluminum oxide, boehmite, magnesium oxide, and barium sulfate.

[0072] In some embodiments, the surface of the porous framework material has a silane coupling agent, and the intensity ratio of the characteristic peak of the Si-O-Si asymmetric stretching vibration to the characteristic peak of the Si-OH stretching vibration of the porous framework material is ≥1.2.

[0073] It should be noted that the method for testing the intensity ratio of the Si-O-Si asymmetric stretching vibration characteristic peak to the Si-OH stretching vibration characteristic peak is as follows: after obtaining the porous framework material using the same method as for testing the specific surface area of ​​porous framework materials, Fourier transform infrared spectroscopy is used for testing; specifically, the sample is ground and pressed into a pellet with a thickness of 0.3 mm, and baseline calibration is performed with air as the background at a resolution of 4 cm⁻¹. -1 The number of scans was 32, and the test wavenumber range was 4000 cm⁻¹. -1 ~400cm -1 .

[0074] This study found that introducing a silane coupling agent onto the surface of a porous framework material, with the intensity ratio of the characteristic peak of the Si-O-Si asymmetric stretching vibration to that of the characteristic peak of the Si-OH stretching vibration being ≥1.2, indicates that a certain amount of silane coupling agent has been introduced onto the surface of the porous framework material. This allows the porous framework material to have better compatibility with inorganic ceramics and flame-retardant microcapsules, enabling the three to interact better and improve the overall performance of the composite separator, thereby enhancing the cycle performance of the secondary battery.

[0075] In some embodiments, the intensity ratio of the Si-O-Si asymmetric stretching vibration characteristic peak to the Si-OH stretching vibration characteristic peak of the porous framework material is 1.2 to 1.3.

[0076] In some embodiments, the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane and KH550 silane coupling agent.

[0077] In some embodiments, the porous framework material surface is loaded with a lithium salt electrolyte.

[0078] For example, the lithium salt electrolyte includes at least one of lithium aluminum titanium phosphate (LATP) and lithium oxyphosphate (LiPON).

[0079] This study found that further loading lithium salt electrolytes onto the surface of porous framework materials can more effectively improve the ion conductivity of composite membranes.

[0080] In some embodiments, the porous framework material includes MOFs materials, and the MOFs materials include at least one of KAR-F02, ZIF-8, UIO-66, and MOF-177.

[0081] In some embodiments, the shell of the flame-retardant microcapsule comprises polyurea-formaldehyde resin, and the core layer comprises melamine cyanurate.

[0082] In some embodiments, the core layer of the flame-retardant microcapsules has an average particle size of 0.4 μm to 4.5 μm.

[0083] It should be noted that the test method for the average particle size of the core layer of the flame-retardant microcapsule is as follows: the flame-retardant microcapsule is obtained by using the test method for the shell thickness of the flame-retardant microcapsule, and then tested by transmission electron microscopy.

[0084] For example, the average particle size of the core layer of the flame-retardant microcapsule can be any point value or a range between any two points between 0.4μm and 4.5μm, such as 0.4μm, 1.0μm, 2.0μm, 3.0μm, 4.0μm, 4.5μm, etc.

[0085] This study found that the average particle size of the core layer of flame-retardant microcapsules affects their flame-retardant kinetics and also their heat-resistant flame-retardant effect. When the average particle size of the flame-retardant microcapsules is further selected within the above range, the composite membrane obtained has better overall performance, and the cycle performance of the secondary battery prepared subsequently is better.

[0086] In some embodiments, the core layer of the flame-retardant microcapsule has a mass percentage of 65% to 80%.

[0087] For example, in the flame-retardant microcapsule, the mass percentage of the core layer can be any point value between 65% and 80% or a range between any two points, such as 65%, 68%, 70%, 72%, 75%, 78%, 80%, etc.

[0088] In some embodiments, the crosslinking density increases by a factor of >20%.

[0089] This study found that by selecting crosslinking densities that increase sequentially within the above-mentioned range, the resulting composite separator can effectively suppress electrolyte swelling and also effectively improve the separator's adhesion properties, thereby enhancing the cycle performance of the secondary battery.

[0090] In some embodiments, the crosslinking density increases by a factor greater than 20% and less than or equal to 60%.

[0091] In some embodiments, polymer A comprises isocyanate polymers.

[0092] For example, the isocyanate polymer may be at least one of hexamethylene diisocyanate trimer, isophorone diisocyanate-trimethylolpropane copolymer, and dicyclohexylmethane diisocyanate prepolymer.

[0093] In some embodiments, polymer B comprises an acrylate copolymer.

[0094] For example, the acrylate copolymer may be at least one of methyl methacrylate-butyl acrylate copolymer, hydroxyethyl acrylate-methyl methacrylate copolymer, isooctyl acrylate-maleic anhydride graft copolymer, and butyl acrylate-glycidyl methacrylate copolymer.

[0095] In some embodiments, the polymer C comprises a cross-linked siloxane polymer.

[0096] For example, the cross-linked siloxane polymer may be at least one of vinyltrimethoxysilane-γ-aminopropyltriethoxysilane cocondensation, methyltriethoxysilane-phenyltrimethoxysilane cocondensation, and γ-glycidoxypropyltrimethoxysilane-tetraethoxysilane cocondensation.

[0097] In some embodiments, the crosslinking density of polymer A is 0.003 mol / cm³. 3 ~0.005mol / cm 3 .

[0098] For example, the crosslinking density of polymer A may be 0.003 mol / cm³. 3 ~0.005 mol / cm 3 The value at any point between or between any two points, for example, 0.003 mol / cm. 3 0.004 mol / cm 3 0.005 mol / cm 3 wait.

[0099] In some embodiments, the crosslinking density of polymer B is 0.006 mol / cm³. 3 ~0.008mol / cm 3 .

[0100] For example, the crosslinking density of polymer B may be 0.006 mol / cm³. 3 ~0.008 mol / cm 3 The value at any point between or between any two points, for example, 0.006 mol / cm. 3 0.007 mol / cm 3 0.008 mol / cm 3 wait.

[0101] In some embodiments, the crosslinking density of polymer C is 0.009 mol / cm³. 3 ~0.012mol / cm 3 .

[0102] For example, the crosslinking density of the polymer C may be 0.009 mol / cm³. 3 ~0.012 mol / cm 3 The value at any point between or between any two points, for example, 0.009 mol / cm. 3 0.010 mol / cm 3 0.011 mol / cm 3 0.012 mol / cm 3 wait.

[0103] It should be noted that the crosslinking density of polymers A, B and C was tested as follows: the composite membrane was taken, the second coating was scraped off, and the crosslinking density was tested using the small-angle neutron scattering (SANS) method. The crosslinking density was calculated by comparing the changes in the scattering signal of polymer particles in the tritium-substituted solution with SANA and using the Flory-Rehner model.

[0104] This application research found that by selecting polymers A, B, and C of the above types, and limiting the crosslinking density of polymers A, B, and C to the above range, the second coating can have good adhesion while also having a low swelling rate in the electrolyte, thereby improving the structural stability of the composite membrane; and it has stronger wetting ability in the electrolyte and better ion transport performance; thus achieving better cycle performance of the secondary battery.

[0105] In some embodiments, the thickness ratio of the core layer, intermediate layer and shell layer is (5~6):(2~3):(1~3).

[0106] It should be noted that the test method for the thickness ratio of the core layer, intermediate layer and shell layer is as follows: polymer particles are obtained by referring to the test method for the crosslinking density of polymer A, polymer B and polymer C, and then small-angle neutron scattering (SANS) is used to test them. The strong penetrating power of neutrons is used to directly detect the internal structure of the polymer particles and obtain the corresponding thickness of each layer.

[0107] For example, the thickness ratio of the core layer, intermediate layer and shell layer can be any point value between (5~6): (2~3): (1~3) or a range value between any two points, such as 5:2:1, 5:3:1, 6:2:2, 6:3:3, etc.

[0108] This study found that the thickness ratio of the core layer, intermediate layer, and shell layer affects the bonding performance and electrolyte swelling resistance of the composite separator. When the thickness ratio of the core layer, intermediate layer, and shell layer is further selected within the above range, the cycle performance of the secondary battery prepared subsequently is better.

[0109] In some embodiments, the material of the porous base membrane includes any one of polyolefin, polyvinyl alcohol, and polyethylene terephthalate nonwoven fabric.

[0110] In some embodiments, the porous base membrane has pores, and the inner wall of the pore channels has a third coating, the third coating comprising a maleic anhydride monomer grafted polymer, the maleic anhydride monomer grafted polymer having a glass transition temperature ≥110°C.

[0111] This application research found that by further introducing a third coating, including a maleic anhydride-based monomer-grafted polymer, into the inner wall of the pores of the porous base membrane, and limiting the glass transition temperature of the maleic anhydride-based monomer-grafted polymer to above 110°C, the corresponding maleic anhydride-based monomer-grafted polymer contains a large number of polar groups, which can significantly improve the wettability and interfacial compatibility of the composite separator, thereby improving the cycle performance of the secondary battery.

[0112] In some embodiments, the glass transition temperature of the maleic anhydride monomer-grafted polymer is 110°C to 150°C.

[0113] For example, the glass transition temperature of the maleic anhydride monomer grafted polymer can be any point value between 110°C and 150°C or a range between any two points, such as 110°C, 120°C, 130°C, 140°C, 150°C, etc.

[0114] It should be noted that the test method for the glass transition temperature of the maleic anhydride monomer grafted polymer is as follows: take the composite diaphragm, scrape off the third coating, and measure it by differential scanning calorimetry (DSC). The specific test conditions are: heating rate of 5℃ / min, nitrogen (N2) atmosphere protection, and gas flow rate of 20mL / min.

[0115] In some embodiments, the polymer includes at least one of polyetheretherketone, polyethersulfone, polyetherimide, aromatic polyimide, polyphthalamide, and polytetrafluoroethylene.

[0116] In some embodiments, the maleic anhydride monomers include at least one of maleic anhydride, diethyl maleate, and itaconic anhydride.

[0117] In some embodiments, the ratio of the thickness of the third coating to the average pore size of the porous base film is 1:(1~8).

[0118] For example, the ratio of the thickness of the third coating to the average pore size of the porous base film can be any point value between 1 and (1~8) or a range value between any two points, such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, etc.

[0119] This study found that the thickness of the third coating and the average pore size of the porous base membrane affect the ion conductivity, heat resistance and flame retardancy, as well as the structural stability of the composite membrane. When the ratio of the thickness of the third coating to the average pore size of the porous base membrane is further selected within the above range, the composite membrane has better overall performance, and the cycle performance of the secondary battery prepared subsequently is better.

[0120] In some embodiments, the thickness of the third coating is 50 nm to 200 nm.

[0121] For example, the thickness of the third coating can be any point value between 50 nm and 200 nm or a range between any two points, such as 50 nm, 100 nm, 150 nm, 200 nm, etc.

[0122] This study found that a third coating thickness within the above-mentioned range can better improve the heat resistance and flame retardancy of the composite separator, and also improve the ion conductivity of the composite separator, thereby resulting in better cycle performance of the secondary battery.

[0123] In some embodiments, the average pore size of the porous base film is 200 nm to 600 nm.

[0124] For example, the average pore size of the porous base film can be any point value between 200 nm and 600 nm or a range between any two points, such as 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, etc.

[0125] This study found that when the average pore size of the porous base membrane is within the above-mentioned range, it can not only effectively improve the structural stability of the composite membrane, but also improve the ion conduction efficiency and electrolyte wetting ability, thereby improving the cycle performance of the secondary battery.

[0126] In some embodiments, the porous base membrane has pores, and the inner walls of the pore channels have a fourth coating, the fourth coating comprising an ion-conducting material, the ion-conducting material having an ionic conductivity ≥3×10⁻⁶ at 30°C. -4 S / cm.

[0127] This application research found that introducing a fourth coating into the inner wall of the pore, which includes an ion-conducting substance with an ionic conductivity within a certain range, can further improve the ionic conductivity of the composite membrane.

[0128] It should be noted that the ionic conductivity of the ion-conducting material is tested by using a symmetrical battery with a membrane structure between two copper foils. The test results of the AC impedance spectroscopy (EIS) are obtained by changing the number of layers of the membrane of the ion-conducting material. The test temperature is 30℃, the perturbation voltage is 5mV, and the frequency range is 3mHz~50mHz.

[0129] In some embodiments, the ion-conducting material includes at least one of MOFs, COFs, polythiophene, polyaniline, sulfonated polystyrene, crystalline aluminosilicate molecular sieves, layered silicates, metal oxide nanotubes, siloxane-polymer hybrids, graphene, carbon nanotubes, carboxymethyl cellulose, and hydroxyethyl cellulose.

[0130] For example, the MOFs material includes at least one of KAR-F02, ZIF-8, UIO-66, and MOF-177.

[0131] In some embodiments, the ratio of the thickness of the fourth coating to the average pore size of the porous base film is ≤0.18.

[0132] For example, the ratio of the thickness of the fourth coating to the average pore size of the porous base film can be any point value between ≤0.18 or a range between any two points, such as 0.18, 0.16, 0.14, 0.12, 0.1, 0.08, 0.06, 0.04, 0.02, 0.01, 0.005, etc.

[0133] This study found that the ratio of the thickness of the fourth coating to the average pore size of the porous base membrane affects the ion conduction effect and also affects the structural stability of the composite membrane. When the ratio of the two is further selected within the above range, the overall performance of the resulting composite membrane is better.

[0134] In some embodiments, the porous base membrane has pores, and a third coating is first introduced into the inner wall of the pore channel, followed by a fourth coating.

[0135] In some embodiments, the first coating further includes an adhesive and a wetting agent.

[0136] This application does not impose any special requirements on the selection of adhesives and wetting agents. Exemplarily, the adhesive may be at least one of polyacrylic adhesives and polyurethane adhesives; the wetting agent may be at least one of carboxylate wetting agents, siloxane wetting agents, and polyether wetting agents.

[0137] In some embodiments, the second coating further includes a dispersant and a wetting agent.

[0138] This application does not impose any special requirements on the selection of dispersants and wetting agents. Exemplarily, the dispersant may be at least one of sodium polyacrylate dispersant, polyacrylamide dispersant, sodium citrate dispersant, and sodium carbonate dispersant; the wetting agent may be at least one of carboxylate wetting agents, siloxane wetting agents, and polyether wetting agents.

[0139] In some embodiments, the method for preparing the composite membrane includes the following steps: S1. The porous base membrane is subjected to plasma treatment to obtain the pretreated porous base membrane. S2. The pretreated porous base membrane is immersed in the third coating aqueous solution and heated to form the third coating; wherein, the third coating aqueous solution includes maleic anhydride monomer grafted polymer and benzoyl peroxide; S3. The product obtained in step S2 is placed in an ethanol solution of the fourth coating and microwaved to form the fourth coating; wherein, the ethanol solution of the fourth coating includes an ion-conducting substance. S4. Mix at least two of the inorganic ceramics, porous framework materials, and flame-retardant microcapsules with a binder, add a wetting agent, disperse the mixture in deionized water to form a slurry, coat it on at least one side of the product prepared in step S3, and then dry it to form a first coating. S5. After mixing polymer particles, water, dispersant and wetting agent, add water to form a slurry, and coat it on at least one side of the product prepared in step S3 or on the surface of the first coating to form a second coating, thus obtaining a composite diaphragm.

[0140] In some embodiments, in step S1, the gas used for plasma treatment is oxygen, the power is 200W~400W, the oxygen flow rate is 4sccm~6sccm, and the time is 5min~15min.

[0141] In some embodiments, in step S1, the pore tortuosity of the porous base membrane is 1.3~2.0, and the coefficient of variation of pore size distribution is ≤12%.

[0142] It should be noted that the pore tortuosity and pore size distribution variation coefficient of the porous base membrane were measured by mercury intrusion porosimetry. When they are respectively limited to this range, the composite membrane has better air permeability, which is beneficial to lithium ion transport in the secondary battery.

[0143] It is understandable that by selecting the thickness and average pore size of the porous base membrane, the pore tortuosity and pore size distribution variation coefficient of the porous base membrane at the composite diaphragm end can be changed.

[0144] In some embodiments, in step S2, the heating temperature is 60°C to 80°C and the time is 2 hours to 4 hours.

[0145] In some embodiments, in step S2, the mass percentage of benzoyl peroxide in the third coating aqueous solution is 0.5% to 1.5%.

[0146] In some embodiments, the grafting rate of maleic anhydride monomers in the maleic anhydride-grafted polymer is 1% to 3%.

[0147] In some embodiments, the weight-average molecular weight of the maleic anhydride-based monomer-grafted polymer is 100,000 g / mol to 200,000 g / mol.

[0148] It is understandable that the thickness of the third coating can be changed by adjusting the temperature and time of the heating treatment in step S2.

[0149] It is understandable that the glass transition temperature can be changed by selecting parameters such as the type of maleic anhydride-based monomer graft polymer, the weight-average molecular weight, and the grafting rate of the maleic anhydride-based monomer.

[0150] In some embodiments, in step S3, the microwave processing uses a microwave power of 500W to 800W, a processing time of 5min to 10min, and a temperature range of 100℃ to 120℃.

[0151] It is understandable that the ionic conductivity can be changed by selecting different ion-conducting materials.

[0152] It is understandable that the thickness of the fourth coating can be changed by adjusting the parameters of microwave processing.

[0153] In some embodiments, in step S4, the surface of the porous framework material is further modified with a silane coupling agent.

[0154] In some embodiments, the preparation method of porous framework materials with silane coupling agent surface modification includes the following steps: 1) Preparation of silane coupling agent solution: Prepare a 0.5wt%~2wt% dilute solution of silane coupling agent with anhydrous ethanol, and adjust the pH to 3.5~5.5 with acetic acid; 2) Impregnation modification: The porous framework material is impregnated in the above silane coupling agent solution at a constant temperature of 40℃~70℃ for 4h~6h, then rinsed with ethanol, and dried at room temperature for 12h~24h to obtain a porous framework material with surface modified silane coupling agent.

[0155] It is understandable that by adjusting the type of porous framework material and its pore structure parameters (such as pore size and pore arrangement), the specific surface area and pore volume of the porous framework material can be changed.

[0156] It is understandable that the intensity ratio of Si-O infrared characteristic peaks in porous framework materials can be changed by adjusting the concentration of silane coupling agent, reaction time, and temperature.

[0157] In some embodiments, the method for preparing the flame-retardant microcapsules includes the following steps: 1) Core layer dispersion: Melamine cyanurate (core layer material) was ultrasonically dispersed (power 200±20W, time 10±2min) in deionized water to form a uniform suspension; 2) In-situ polymerization coating: a. Preparation of polyurea-formaldehyde resin monomer: Dissolve isocyanate monomer and diamine monomer in anhydrous ethanol at a molar ratio of 1:1.2 to prepare a 5±1wt% solution, and adjust the pH to 4.0±0.5 with acetic acid; b. Add polyurea-formaldehyde resin monomer to the core suspension to form a shell layer through in-situ polymerization reaction. Reaction conditions: mechanical stirring (300±50 rpm) in a constant temperature water bath at 50℃~80℃ for 2h~4h. 3) After the reaction was completed, the unreacted monomers were removed by centrifugation (8000±500 rpm, 10±2 min), and the mixture was washed three times with ethanol. The flame-retardant microcapsules were then obtained by vacuum drying at 40±5℃ for 12±2 h.

[0158] It is understandable that the shell thickness of flame-retardant microcapsules can be altered by adjusting the concentration of reactant monomers, reaction time, reaction temperature, and stirring rate.

[0159] It is understandable that the thickness of the second coating can be changed by adjusting the coating thickness.

[0160] In some embodiments, the method for preparing the polymer particles includes the following steps: 1) Core layer preparation: Add 0.5wt%~3wt% of emulsifier sodium dodecyl sulfate (SDS), 0.1wt%~0.5wt% of buffer NaHCO3, and deionized water to a four-necked flask. Then, stir at 300rpm~500rpm for 15±5min at 50±5℃, and slowly add core polymer A. Pre-emulsify for 10min~20min, then raise the temperature to 80±5℃. Add dropwise 0.2wt%~0.8wt% of initiator potassium persulfate (KPS) aqueous solution. After the reaction flask wall shows no reflux, raise the temperature to 90±5℃ and hold for 30±5min. Then cool for later use to obtain seed emulsion A. 2) Preparation of the intermediate layer: Add 10 mL of water to 2 ± 0.5 wt% emulsifier SDS, and disperse at 30 ± 5 °C with a stirring speed of 400 rpm to 600 rpm for 10 min to 20 min. Add intermediate layer polymer B, and pre-emulsify for 0.8 h to 1.2 h to obtain pre-emulsified intermediate layer polymer B. Simultaneously add initiator KPS aqueous solution and pre-emulsified intermediate layer polymer B dropwise to seed emulsion A, stir continuously until there is no reflux, then heat to 90 ± 5 °C and hold for 30 ± 5 min, then cool for later use to obtain seed emulsion B; 3) Shell preparation: Initiator KPS aqueous solution and pre-emulsified shell polymer C (prepared using the same method as pre-emulsified intermediate polymer B) were simultaneously added dropwise to seed emulsion B at a constant temperature of 40℃~60℃. The mixture was continuously stirred until no reflux occurred, then heated to 90±5℃ and held at that temperature for 30±5 min. After cooling to 40±5℃, ammonia was added dropwise to adjust the pH to 7~8. The mixture was then filtered and dried to obtain the polymer particles.

[0161] It is understandable that the crosslinking density can be changed by adjusting the types of polymer A, polymer B, and polymer C.

[0162] It is understandable that the thickness ratio of the core layer, intermediate layer, and shell layer can be changed by adjusting the amount of polymer A, polymer B, and polymer C added.

[0163] In one embodiment of this application, a secondary battery is proposed, the secondary battery comprising the composite separator described in this application.

[0164] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector; the positive active material layer includes a positive active material, a positive conductive agent, and a positive binder.

[0165] This application does not limit the positive electrode active material; any known positive electrode active material can be used. For example, the positive electrode active material may be at least one of lithium iron phosphate, lithium manganese iron phosphate, or ternary materials.

[0166] This application does not limit the positive electrode conductive agent; any known positive electrode conductive agent can be used. For example, the positive electrode conductive agent may be at least one of acetylene black, graphene, and carbon nanotubes (CNTs).

[0167] This application does not limit the positive electrode binder; any known positive electrode binder can be used. For example, the positive electrode binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAANa), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0168] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector; the negative active material layer includes a negative active material, a negative conductive agent, and a negative binder.

[0169] This application does not limit the negative electrode active material; any known negative electrode active material can be used. For example, the negative electrode active material may be at least one of artificial graphite, natural graphite, silicon carbide, and silicon oxide.

[0170] This application does not limit the choice of the negative electrode conductive agent; any known negative electrode conductive agent can be used. For example, the negative electrode conductive agent may be at least one of acetylene black, graphene, and carbon nanotubes (CNTs).

[0171] This application does not limit the negative electrode binder; any known negative electrode binder can be used. Exemplarily, the negative electrode binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAANa), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0172] In some embodiments, the secondary battery further includes an electrolyte comprising an organic solvent and a lithium salt.

[0173] This application does not limit the choice of organic solvent; any known organic solvent may be used. For example, the organic solvent may be at least one of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0174] This application does not limit the choice of lithium salt; any known lithium salt can be used. For example, the lithium salt may be at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0175] In some embodiments, the composite separator is disposed between the positive electrode and the negative electrode.

[0176] In one embodiment of this application, an electrical device is provided, which includes the secondary battery described in this application.

[0177] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0178] Example 1 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery includes the following steps: S1. Treatment of porous base membrane: A polyethylene diaphragm with a thickness of 7 μm is selected. The pore tortuosity of the polyethylene diaphragm is 1.6, the average pore size is 0.4 μm, and the pore size distribution variation coefficient is 12%. The base membrane is plasma treated for 10 min (power 300W, oxygen flow rate 5 sccm) to obtain the pretreated porous base membrane. S2. Preparation of the third coating: The pretreated porous base film obtained in step S1 is immersed in an aqueous solution of maleic anhydride-grafted polyether ether ketone (PEEK) containing 1 wt% benzoyl peroxide (in maleic anhydride-grafted PEEK, the grafting rate of maleic anhydride is 2.5%, the weight-average molecular weight of maleic anhydride-grafted PEEK is 120000 g / mol, and the glass transition temperature of maleic anhydride-grafted PEEK is 132℃), and grafted at 70℃ for 3 h to obtain a third coating with a thickness of 150 nm. S3. Preparation of the fourth coating: The product obtained in step S2 is immersed in an ethanol solution of an ion-conducting compound (the ion-conducting compound is KAR-FO2 with an average particle size of 0.1 μm and an ionic conductivity of 4 × 10⁻⁶ at 30 °C). -4 The coating was processed using a microwave-assisted method (microwave conditions: 700W, 6min, 100℃) to obtain a fourth coating with a thickness of 60nm. S4. Preparation of the first coating: Inorganic ceramic (boehmite, average particle size 120 nm) and porous framework material (KAR-F02 modified with KH550 silane coupling agent, specific surface area 2500 m²) are used. 2 / g, pore volume 1.7cm 3 The intensity ratio of the characteristic peak of Si-O-Si asymmetric stretching vibration to that of Si-OH stretching vibration is 1.3, flame-retardant microcapsules (shell layer is polyurea-formaldehyde resin, core layer is melamine cyanurate, core layer mass ratio is 68%, shell layer thickness is 40nm, core layer average particle size is 0.8μm) and binder (polyacrylic adhesive LA133) are mixed in a mass ratio of 70:19:10:1, an appropriate amount of wetting agent (siloxane alkyl wetting agent TEGO 4100) is added, dispersed in deionized water to form a slurry, coated on one side of the product formed in step S3, and dried to form a first coating with a thickness of 3μm; The method for preparing the porous framework material is as follows: the porous framework material KAR-F02 is immersed in a 1.0% KH550 ethanol solution (adjusted to pH 4.0 with acetic acid) at 60℃ for 5 hours, rinsed with ethanol and dried at room temperature for 12 hours to obtain a porous framework material with a surface modified silane coupling agent. The flame-retardant microcapsules were prepared as follows: Melamine cyanurate was ultrasonically dispersed in an aqueous phase (200W, 10min) to form a uniform suspension; 5wt% polyurea-formaldehyde resin monomer (pH=4) was added to the core suspension, and an in-situ polymerization reaction was carried out to form a shell layer under the reaction conditions of 70℃ / 2h / 300rpm, ensuring uniform coating of the core layer by the shell layer. After the reaction was completed, the microcapsules were separated by centrifugation (800rpm / 10min), and unreacted monomers were removed by washing with ethanol. The microcapsules were then dried at 40℃ for 12h to obtain the flame-retardant microcapsules. S5. Preparation of the second coating: Polymer particles, water, dispersant (sodium polyacrylate PAAS), and wetting agent (siloxane alkyl polymer TEGO 4100) were mixed in a mass ratio of 40:50:8:2 to prepare an aqueous slurry, which was then coated onto the substrate surface in an island-like morphology to form a second coating with a thickness of 3 μm; the final composite membrane was obtained (SEM image as shown). Figure 1 (as shown) The polymer particles are prepared as follows: the core layer uses hexamethylene diisocyanate trimer, the middle layer uses methyl methacrylate-butyl acrylate copolymer, and the shell layer uses vinyltrimethoxysilane-γ-aminopropyltriethoxysilane cocondensate. The thickness ratio of the core layer, middle layer, and shell layer is 6:3:1. The polymer particles are formed by emulsion polymerization. 1) Core layer preparation: 1 wt% emulsifier SDS, 0.5 wt% buffer NaHCO3, and deionized water were added to a four-necked flask. The mixture was stirred at 300 rpm for 10 min at 50°C, then polymer A was slowly added. After pre-emulsification for 10 min, the temperature was raised to 80°C. 0.5 wt% initiator KPS aqueous solution was added dropwise. Once there was no reflux on the reaction flask wall, the temperature was raised to 90°C and held for 30 min. The mixture was then cooled for later use to obtain seed emulsion A. 2) Preparation of the intermediate layer: Add 10 mL of water to 2 wt% emulsifier and disperse at 30 °C with stirring at 400 rpm for 10 min. Add polymer B and pre-emulsify for 1 h to obtain pre-emulsified intermediate layer polymer B. Simultaneously add 0.5 wt% initiator KPS aqueous solution and pre-emulsified intermediate layer polymer B to seed emulsion A, stir continuously until there is no reflux, then heat to 90 °C and hold for 30 min, then cool for later use to obtain seed emulsion B; 3) Shell preparation: 0.5 wt% initiator KPS aqueous solution and pre-emulsified shell polymer C (preparation method consistent with pre-emulsified intermediate polymer B) were simultaneously added dropwise to seed emulsion B at a constant temperature of 50℃. The mixture was continuously stirred until no reflux occurred, then heated to 90℃ and held at that temperature for 30 min. After cooling to 40℃, ammonia was added dropwise to adjust the pH to 7. The mixture was then filtered and dried to obtain the polymer particles. The core layer crosslinking density is 0.005 mol / cm³. 3 The cross-linking density of the intermediate layer is 0.008 mol / cm³. 3 The shell crosslinking density is 0.012 mol / cm³. 3 ; S6. Preparation of positive electrode sheet: The positive electrode active material (lithium iron phosphate), positive electrode conductive agent (carbon black), and positive electrode binder (PVDF) are mixed in a weight ratio of 95:2.7:2.3. Then, N-methylpyrrolidone (NMP) is added and mixed thoroughly to obtain a positive electrode slurry. The positive electrode slurry is then coated on both sides onto a (13+1+1) μm carbon-coated aluminum foil. After coating, the electrode sheet is dried, rolled, slit, and cut to obtain the positive electrode sheet. S7. Preparation of the negative electrode sheet: The negative electrode active material (graphite), negative electrode conductive agent (carbon black), and binder (styrene-butadiene rubber) are weighed at a mass ratio of 96:2:2. First, the negative electrode active material and carbon black are mixed for 30 minutes. Then, the binder is added for premixing, fiberization, granulation, and hot rolling to obtain a self-supporting negative electrode sheet. Finally, a 4.5μm copper foil is composited with the electrode sheet by hot rolling. After slitting and cutting, the desired negative electrode sheet is obtained. S8. Preparation of electrolyte: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 1:1:1, then lithium hexafluorophosphate is added, and after mixing evenly, vinylene carbonate is added as an additive; wherein, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 12%, and the mass content of vinylene carbonate is 0.5%; S9. Preparation of secondary batteries: The positive electrode, negative electrode, composite separator and other battery components are assembled and then subjected to processes such as shaping, baking, packaging, liquid injection, formation and capacity testing to obtain secondary batteries.

[0179] Examples 2-3 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the thickness of the porous base film is changed to achieve the parameters in Tables 1 to 3.

[0180] Examples 4-5 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the average pore size of the porous base membrane is changed to achieve the parameters in Tables 1 to 3.

[0181] Examples 6-7 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the amount of slurry applied to the first coating is changed to change the thickness of the first coating, so as to achieve the parameters in Tables 1 to 3.

[0182] Examples 8-9 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the average particle size of the inorganic ceramic is changed to achieve the parameters in Tables 1 to 3.

[0183] Examples 10-11 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the pore structure parameters (such as pore size and pore arrangement angle) of the porous frame material are changed to change the specific surface area and pore volume of the porous frame material, so as to achieve the parameters in Tables 1 to 3.

[0184] Example 12 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the type of porous framework material is changed to achieve the parameters in Tables 1 to 3.

[0185] Examples 13-14 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the amount of shell and core layers added to the flame-retardant microcapsules is changed to change the thickness of the shell and core layers and the mass ratio of the core layer, so as to achieve the parameters in Tables 1 to 3.

[0186] Examples 15-16 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the thickness of the second coating is changed by changing the amount of adhesive and the solid content of the slurry, so as to achieve the parameters in Tables 1 to 3.

[0187] Examples 17-18 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that the amount of polymer A, polymer B and polymer C added and the reaction time are changed during the preparation of polymer particles to change the interlayer thickness ratio of polymer particles, so as to achieve the parameters in Tables 1 to 3.

[0188] Example 19 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that the types of polymer A, polymer B and polymer C are changed to achieve the parameters in Tables 1 to 3.

[0189] Examples 20-21 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that the crosslinking density of polymer A, polymer B and polymer C is changed to achieve the parameters in Tables 1 to 3.

[0190] Examples 22-23 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the heating treatment parameters in the preparation of the third coating are changed to change the thickness of the third coating, so as to achieve the parameters in Tables 1 to 3.

[0191] Example 24 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that the type of maleic anhydride monomer grafted polymer raw material is changed to achieve the parameters in Tables 1 to 3.

[0192] Example 25 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the type of ion-conducting material is changed to achieve the parameters in Tables 1 to 3.

[0193] Example 26 This application provides a composite separator and a secondary battery. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the thickness of the fourth coating is changed by changing the parameters of the microwave treatment, so as to achieve the parameters in Tables 1 to 3.

[0194] Example 27 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that flame-retardant microcapsules are not added, and their amount is supplemented by inorganic ceramics to achieve the parameters in Tables 1 to 3.

[0195] Example 28 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that the amount of silane coupling agent added to the porous framework material is changed to change the intensity ratio of the Si-O infrared characteristic peaks of the porous framework material, so as to achieve the parameters in Tables 1 to 3.

[0196] Example 29 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that a third coating is not introduced to achieve the parameters in Tables 1 to 3.

[0197] Example 30 This application provides a composite separator and a secondary battery. The preparation method of the composite separator and the secondary battery differs from that of Example 1 in that a fourth coating is not introduced to achieve the parameters in Tables 1 to 3.

[0198] Comparative Example 1 This application provides a composite separator and a secondary battery in a comparative example. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the first coating consists only of inorganic ceramics to achieve the parameters in Tables 1 to 3.

[0199] Comparative Example 2 This application provides a composite separator and a secondary battery in a comparative example. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that a first coating is not introduced in order to achieve the parameters in Tables 1 to 3.

[0200] Comparative Example 3 This application provides a composite separator and a secondary battery in a comparative example. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that the crosslinking density of polymer A, polymer B and polymer C is adjusted to achieve the parameters in Tables 1 to 3.

[0201] Comparative Example 4 This application provides a composite separator and a secondary battery in a comparative example. The difference between the preparation method of the composite separator and the secondary battery and that of Example 1 is that a second coating is not introduced in order to achieve the parameters in Tables 1 to 3.

[0202] The thickness h0 μm of the porous base membrane in the examples and comparative examples, the type of porous base membrane, the average pore size r nm of the porous base membrane, the thickness h1 μm of the first coating, the type of inorganic ceramic, the average particle size D nm of the inorganic ceramic, the type of porous framework material, and the specific surface area B m of the porous framework material are all specified. 2 / g, pore volume R cm of porous framework material 3 / g, the intensity ratio IR of the characteristic peak of Si-O-Si asymmetric stretching vibration to that of Si-OH stretching vibration in porous framework materials, the shell thickness P nm of flame-retardant microcapsules, the average particle size d μm of the core layer of flame-retardant microcapsules, the type of shell layer of flame-retardant microcapsules, the type of core layer of flame-retardant microcapsules, the mass percentage of the core layer in the flame-retardant microcapsules W1%, the thickness of the second coating h2 μm, the thickness ratio M of the core layer, intermediate layer and shell layer in the polymer particles, the type and crosslinking density q1 mol / cm 3 The type of polymer B and the crosslinking density q2 mol / cm 3 The type of polymer C and the crosslinking density q3 mol / cm 3 The crosslinking density increases sequentially from the core layer, intermediate layer and shell layer by the magnitude of Wq%, the type of maleic anhydride monomer grafted polymer in the third coating, the ratio of the thickness of the third coating to the average pore size of the porous base membrane n1, the thickness of the third coating h3 nm, the type of ion-conducting substance in the fourth coating, the ionic conductivity of the ion-conducting substance in the fourth coating i S / cm, and the ratio of the thickness of the fourth coating to the average pore size of the porous base membrane n2 are shown in Tables 1-3. Among them, maleic anhydride graft polymer 1 is maleic anhydride grafted polyether ether ketone, and maleic anhydride graft polymer 2 is maleic anhydride grafted polyether imide resin. Polymer A-1 is a hexamethylene diisocyanate trimer, polymer A-2 is an isophorone diisocyanate-trimethylolpropane copolymer, polymer B-1 is a methyl methacrylate-butyl acrylate copolymer, polymer B-2 is a hydroxyethyl acrylate-methyl methacrylate copolymer, polymer C-1 is a vinyltrimethoxysilane-γ-aminopropyltriethoxysilane cocondensate, and polymer C-2 is a γ-glycidoxypropyltrimethoxysilane-tetraethoxysilane cocondensate. Inorganic ceramic 1 is boehmite; Porous framework material 1 is KAR-F02 / KH-550, and porous framework material 2 is ZIF-8 / KH-550; Shell 1 is polyurea-formaldehyde resin, and core 1 is melamine cyanurate (MCA). Table 1 Table 2 Table 3 The performance tests of the composite separators and secondary batteries prepared in the examples and comparative examples include the following aspects: 1. Pore size distribution variation coefficient: The pore size distribution variation coefficient is calculated using the mercury intrusion porosimetry method based on the Washburn equation and the inverse relationship between mercury intrusion pressure and pore size. 2. Heat shrinkage rate: The percentage ratio of the dimensional difference ΔL before and after the diaphragm of a specific size (specifically 50mm×100mm) shrinks after baking at 150℃ for 1 hour to the original size L0 is the heat shrinkage rate, which includes MD heat shrinkage rate and TD heat shrinkage rate. 3. Static contact angle: At room temperature, the droplet is placed on the diaphragm surface using the seated drop method. After it stabilizes, the profile is captured by optical imaging, and the contact angle is calculated. 4. Swelling rate: Weigh the initial mass m0 of a diaphragm of a specific size, then immerse it in a carbonate electrolyte (a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, containing lithium hexafluorophosphate (LiPF6) with a molar concentration of 1.0 mol / L) at 45℃ for 72 hours, and then weigh the mass m1. Swelling rate = (m0-m1) / m0×100%; 5. Adhesion force: The adhesion force between the positive electrode and the separator under hot-pressing conditions of 95℃, 3MPa and 15s was measured using a 180° peeling machine. 6. Puncture strength: The maximum stress that the composite diaphragm can withstand under a 1mm rigid puncture needle is measured using a puncture strength tester. This is the puncture strength of the composite diaphragm. The puncture rate is 50mm / min. 7. Lithium-ion conductivity: The lithium-ion conductivity of a symmetrical battery with a composite separator in the middle and copper foil on both sides is calculated by linearly fitting the EIS test results by changing the number of composite separator layers. 8. DCR Test: In a 25℃ constant temperature room, charge the secondary battery at a constant current of 1C to the upper voltage limit (3.65V), keep the voltage constant and switch to constant voltage charging until the charging current decreases to 0.05C. After resting for 30 minutes, discharge at a constant current of 1C for 30 minutes to bring the battery to 50% SOC. Then discharge at a constant current of 4C for 10 seconds and charge at a constant current of 4C for 10 seconds. Record the voltage drop ΔU and the current difference ΔI. Then DCR = ΔU / ΔI. 9. Cyclic test: In a constant temperature room at 25℃, the secondary battery is charged and discharged at FC / 1C (i.e., a cyclic test procedure of charging at 0.1C current and discharging at 1C current) with a charge and discharge current of 0~100% SOC. The capacity retention rate after 1000 cycles is recorded. The results are shown in Table 4. Table 4 As can be seen from Table 4, when the technical solution provided in this application is adopted, the resulting composite separator has excellent comprehensive performance, and the resulting secondary battery also has excellent comprehensive performance. Specifically, the obtained composite separator has a pore size distribution variation coefficient of less than 15%, a MD thermal shrinkage rate of less than 8.9%, a TD thermal shrinkage rate of less than 8.3%, a static contact angle of less than 30.6°, a swelling rate of less than 7.67%, a lithium-ion conductivity of more than 3.14 ms / cm, an adhesion force of more than 4.3 N / m, and a puncture strength of more than 433.6 gf. The obtained secondary battery has a DCR of less than 16.5 mΩ and a cycle capacity retention rate of more than 85.0%. As can be seen from Examples 1-30 and Comparative Examples 1-4, the technical solutions provided in this application can achieve excellent overall results. In addition, the performance graphs of the secondary batteries prepared in Example 1 and Comparative Example 1 are shown below. Figure 2 As shown.

[0203] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A composite diaphragm, characterized in that, The composite membrane includes a porous base membrane, and a first coating and a second coating sequentially disposed on at least one side of the porous base membrane; The first coating comprises at least two of inorganic ceramics, porous framework materials, and flame-retardant microcapsules; The second coating comprises polymer particles, the polymer particles comprising a core layer, an intermediate layer and a shell layer, the core layer comprising polymer A, the intermediate layer comprising polymer B, and the shell layer comprising polymer C, wherein the crosslinking density of polymer A, polymer B and polymer C increases sequentially.

2. The composite diaphragm according to claim 1, characterized in that, Satisfy at least one of the following: (1) The thickness of the porous base film is 5 μm to 16 μm; (2) The thickness of the first coating is 1 μm to 8 μm; (3) The thickness of the second coating is 1μm~6μm.

3. The composite diaphragm according to claim 1, characterized in that, The first coating comprises inorganic ceramics, porous framework materials, and flame-retardant microcapsules, and the first coating satisfies: 0.6 < Y < 4; Where Y = (B × R) / (D × P); B m 2 / g represents the specific surface area of ​​the porous framework material; Rcm 3 / g represents the pore volume of the porous framework material; D nm is the average particle size of the inorganic ceramic; P nm is the shell thickness of the flame-retardant microcapsule.

4. The composite diaphragm according to claims 1-3, characterized in that, Satisfy at least one of the following: (1) The specific surface area B m of the porous framework material 2 / g is 2000 m 2 / g~3000 m 2 / g; (2) The pore volume R cm of the porous framework material 3 / g is 1.5 cm 3 / g~2.0 cm 3 / g; (3) The average particle size D nm of the inorganic ceramic is 100 nm to 150 nm; (4) The shell thickness P nm of the flame-retardant microcapsule is 10 nm to 50 nm.

5. The composite diaphragm according to claim 1, characterized in that, The surface of the porous framework material has a silane coupling agent, and the intensity ratio of the characteristic peak of the Si-O-Si asymmetric stretching vibration to the characteristic peak of the Si-OH stretching vibration of the porous framework material is ≥1.

2.

6. The composite diaphragm according to claim 1, characterized in that, Satisfy at least one of the following: (1) The inorganic ceramics include at least one of silicon dioxide, alumina, boehmite, magnesium oxide, and barium sulfate; (2) The porous framework material includes MOFs material, and the MOFs material includes at least one of KAR-F02, ZIF-8, UIO-66, and MOF-177; (3) The shell of the flame-retardant microcapsule contains polyurea-formaldehyde resin and the core layer contains melamine cyanurate; (4) The average particle size of the core layer of the flame-retardant microcapsule is 0.4 μm ~ 4.5 μm.

7. The composite diaphragm according to claim 1, characterized in that, The crosslinking density increases by more than 20% sequentially.

8. The composite diaphragm according to claim 1, characterized in that, Satisfy at least one of the following: (1) The polymer A includes isocyanate polymers; (2) The polymer B comprises an acrylate copolymer; (3) The polymer C includes a cross-linked siloxane polymer; (4) The crosslinking density of polymer A is 0.003 mol / cm³. 3 ~0.005mol / cm 3 ; (5) The crosslinking density of polymer B is 0.006 mol / cm³. 3 ~0.008mol / cm 3 ; (6) The crosslinking density of polymer C is 0.009 mol / cm³. 3 ~0.012mol / cm 3 ; (7) The thickness ratio of the core layer, intermediate layer and shell layer is (5~6):(2~3):(1~3); (8) The material of the porous base membrane includes any one of polyolefin, polyvinyl alcohol, and polyethylene terephthalate nonwoven fabric.

9. The composite diaphragm according to claim 1, characterized in that, The porous base membrane has pores, and the inner wall of the pore channel has a third coating, the third coating comprising a maleic anhydride monomer grafted polymer, the glass transition temperature of the maleic anhydride monomer grafted polymer being ≥110℃.

10. The composite diaphragm according to claim 9, characterized in that, The ratio of the thickness of the third coating to the average pore size of the porous base film is 1:(1~8).

11. The composite diaphragm according to claim 10, characterized in that, The thickness of the third coating is 50nm to 200nm; and / or the average pore size of the porous base film is 200nm to 600nm.

12. The composite diaphragm according to claim 1, characterized in that, The porous base membrane has pores, and the inner wall of the pore channels has a fourth coating, the fourth coating comprising an ion-conducting material, the ion-conducting material having an ionic conductivity ≥3×10 at 30°C. -4 S / cm.

13. The composite diaphragm according to claim 12, characterized in that, The ion-conducting material includes at least one of MOFs, COFs, polythiophene, polyaniline, sulfonated polystyrene, crystalline aluminosilicate molecular sieves, layered silicates, metal oxide nanotubes, siloxane-polymer hybrids, graphene, carbon nanotubes, carboxymethyl cellulose, and hydroxyethyl cellulose.

14. The composite diaphragm according to claim 12, characterized in that, The ratio of the thickness of the fourth coating to the average pore size of the porous base film is ≤0.

18.

15. A secondary battery, characterized in that, Includes the composite diaphragm as described in any one of claims 1 to 14.

16. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 15.

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