A separator, a lithium-ion secondary battery, and an electric device

Abstract

The application relates to the technical field of batteries, in particular to a diaphragm, a lithium ion secondary battery and an electric device, the diaphragm comprising a base film and a composite layer arranged on at least one surface of the base film, the composite layer comprising base particles and a polydopamine layer distributed on the surface of the base particles, the base particles comprising an inner core and a silicon dioxide layer distributed on the surface of the inner core, and the inner core comprising carbon nanotubes, the safety performance of the battery under the condition of rapid charging and low temperature is greatly improved under the action of the diaphragm, the formation of lithium dendrites and the internal short circuit and safety risk caused by the penetration of the diaphragm are reduced, the mechanical strength of the diaphragm is improved, and the fast charging capacity and safety performance of the battery are improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a diaphragm, a lithium-ion secondary battery, and an electrical device. Background Art

[0002] The safety of lithium-ion batteries under low-temperature and high-rate charging conditions has long been a research focus. Experimental results show that when the lithium-ion diffusion rate in the negative electrode cannot meet the requirements of rapid charging, a large amount of lithium ions will be deposited in metallic form on the negative electrode surface, increasing the risk of lithium plating. As lithium plating intensifies, the resulting lithium dendrites may penetrate the separator, causing direct contact between the positive and negative electrodes and leading to an internal short circuit. This situation can lead to serious safety hazards such as battery overheating, fire, and even explosion.

[0003] Based on this, how to inhibit lithium plating or lithium dendrites and prevent lithium dendrites from penetrating the diaphragm, thereby improving the safety performance of the battery, especially the safety performance under fast charging and low temperature conditions, is a technical problem that researchers in this field urgently need to solve in the development of lithium-ion batteries. Summary of the Invention

[0004] Therefore, the present application provides a diaphragm, a lithium-ion secondary battery and an electrical device, the purpose of which is to inhibit lithium deposition or lithium dendrites and prevent lithium dendrites from penetrating the diaphragm, thereby improving the safety performance of the battery, especially the safety performance under fast charging and low temperature conditions.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a diaphragm is provided, which includes a base membrane and a composite layer arranged on at least one surface of the base membrane, the composite layer includes matrix particles and a polydopamine layer distributed on the surface of the matrix particles, the matrix particles include an inner core and a silicon dioxide layer distributed on the surface of the inner core, the inner core includes carbon nanotubes, and the silicon dioxide layer includes silicon dioxide.

[0006] Furthermore, the thickness of the silicon dioxide layer is 16 to 60 nm.

[0007] Furthermore, the thickness of the polydopamine layer is 33 to 71 nm.

[0008] Furthermore, the thickness of the separator is 8 to 8.5 μm.

[0009] Furthermore, the added amount of the carbon nanotubes is 150 to 300 mg.

[0010] Furthermore, the silicon dioxide layer also includes phenolic resin.

[0011] Furthermore, the base film includes one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyethylene (PE), polypropylene (PP), polyvinyl pyrrolidone (PVP), and their derivatives.

[0012] Another aspect of the present application provides a lithium-ion secondary battery comprising any of the above-mentioned separators.

[0013] In another aspect of the present application, an electric device is provided, comprising any one of the lithium-ion secondary batteries described above, wherein the lithium-ion secondary battery serves as a power supply for the electric device.

[0014] The diaphragm of the present application has a composite layer arranged on the surface of the base membrane, which, through the combined action of the matrix particles containing carbon nanotubes and silicon dioxide distributed on their surface and the polydopamine layer distributed on the surface of the matrix particles, can not only significantly improve the thermal conductivity of the diaphragm, effectively reduce the temperature difference in the battery cell, thereby reducing the lithium precipitation phenomenon caused by uneven temperature distribution; at the same time, a flame retardant protective layer is formed on the surface of the diaphragm, which significantly improves the flame retardant performance of the diaphragm and prevents the penetration of lithium dendrites; moreover, it can also significantly improve the wettability of the diaphragm, enhance the affinity between the diaphragm and the electrolyte, and contribute to the uniform distribution of the electrolyte, thereby facilitating the uniform distribution of lithium ions on the electrode surface and inhibiting the formation of lithium dendrites; in addition, it can also enhance the tensile strength of the diaphragm, enhance the mechanical stability of the diaphragm, and contribute to improving the diffusion performance of lithium ions and improving the charging and discharging efficiency, so as to enhance the fast charging capability of the battery while effectively resisting the penetration of lithium dendrites. The combined effects of the above greatly improve the safety performance of the battery under fast charging and low temperature conditions, reduce the formation of lithium dendrites and the internal short circuit and safety risks caused by their penetration through the diaphragm, thereby improving both the mechanical strength of the diaphragm and the fast charging capability and safety performance of the battery. DETAILED DESCRIPTION

[0015] The following will clearly and completely describe the concept and technical effects of this application in conjunction with the embodiments to fully understand the purpose, features and effects of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of this application.

[0016] The embodiments of the present application are described in detail below. The described embodiments are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0017] In the description of the present application, the meaning of several is one or more, the meaning of multiple is two or more, greater than, less than, more than, etc. are understood as not including the number, above, below, etc. are understood as including the number. If it is described as first, second, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0018] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0019] If the specific experimental steps or conditions are not specified in the embodiments, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. If the reagent or instrument used is not specified by the manufacturer, it is a conventional reagent product that can be obtained by purchase.

[0020] The existing lithium ion battery has the problem of low safety performance under low temperature and high rate charging conditions. When the lithium ion diffusion speed of the negative electrode cannot meet the demand of fast charging, a large amount of lithium ions will be deposited on the surface of the negative electrode in the form of metal, thereby increasing the risk of lithium precipitation. With the intensification of lithium deposition, lithium dendrites may penetrate the separator, causing direct contact between the positive and negative electrodes, and then causing internal short circuit. This situation may cause battery overheating, fire and even explosion and other serious safety accidents. In addition, uneven temperature distribution is also one of the important factors leading to lithium precipitation.

[0021] In order to solve the above technical problems, according to the first aspect of the present application, a separator is provided, the separator comprises a base film and a composite layer arranged on at least one surface of the base film, the composite layer comprises a base particle and a polydopamine layer distributed on the surface of the base particle, the base particle comprises a core and a silica layer distributed on the surface of the core, the core comprises carbon nanotubes, and the silica layer comprises silicon dioxide.

[0022] The diaphragm of the present application, the composite layer arranged on the surface of the base film, through the combined action of including the base particles containing carbon nanotubes and the silica distributed on the surface thereof and the polydopamine layer distributed on the surface of the base particles, can not only significantly improve the thermal conductivity of the diaphragm, effectively reduce the temperature difference in the battery, thereby reducing the lithium precipitation phenomenon caused by uneven temperature distribution; at the same time, a flame-retardant protective layer is formed on the surface of the diaphragm, which significantly improves the flame-retardant performance of the diaphragm and prevents lithium dendrites from penetrating; moreover, it can also significantly improve the wetting performance of the diaphragm, enhance the affinity between the diaphragm and the electrolyte, and help the uniform distribution of the electrolyte, thereby facilitating the uniform distribution of lithium ions on the surface of the electrode and inhibiting the formation of lithium dendrites; in addition, it can also enhance the tensile strength of the diaphragm, improve the mechanical stability of the diaphragm, and help improve the diffusion performance of lithium ions, improve the charging and discharging efficiency, and enhance the fast charging capability of the battery while effectively resisting the penetration of lithium dendrites. Under the above combined action, the safety performance of the battery under fast charging and low temperature conditions is greatly improved, the formation of lithium dendrites and the internal short circuit and safety risk caused by the penetration of the diaphragm are reduced, and both the mechanical strength of the diaphragm and the fast charging capability and safety performance of the battery are improved.

[0023] In some preferred embodiments, the thickness of the silica layer is 16-60 nm. By controlling the thickness of the silica within the above range, the diaphragm has good flame-retardant performance without affecting the transmission of lithium ions, thereby making the battery have better fast charging capability and safety performance. For example, the thickness of the silica layer can be 16 nm, 20 nm, 30 nm, 35 nm, 40 nm, 60 nm, or within the range consisting of any of the above values.

[0024] In some preferred embodiments, the thickness of the polydopamine layer is 33-71 nm. By controlling the thickness of the polydopamine layer within the above range, the diaphragm has good wetting performance without affecting the transmission of lithium ions, thereby making the battery have better fast charging capability and safety performance. For example, the thickness of the polydopamine layer can be 33 nm, 35 nm, 36 nm, 37 nm, 38 nm, 41 nm, 42 nm, 52 nm, 59 nm, 71 nm, or within the range consisting of any of the above values.

[0025] In some preferred embodiments, the silica layer further includes a phenolic-aldehyde resin. This resin network can be part of the base particles, enhancing the mechanical properties and stability of the diaphragm. For example, the phenolic-aldehyde resin can be one or more of catechol-formaldehyde resin, resorcinol-formaldehyde resin, hydroquinone-formaldehyde resin, o-hydroxybenzoic acid-ethanal resin, m-hydroxybenzoic acid-formaldehyde resin, or p-hydroxybenzoic acid-furfural resin.

[0026] In some preferred embodiments, the carbon nanotube is added in an amount of 150-300 mg. By controlling the amount of carbon nanotube within the above range, the heat transfer performance inside the battery is enhanced, and the temperature distribution is more uniform. For example, the carbon nanotube can be added in an amount of 150 mg, 180 mg, 200 mg, 230 mg, 250 mg, 280 mg, 300 mg, or within a range defined by any of the above values.

[0027] Further, the siloxane precursor includes methoxysilane and / or ethoxysilane. For example, the siloxane precursor includes one or more of tetraethoxysilane, hexaethyldisiloxane, hexamethyldisiloxane, and tetramethyldisiloxane. The carboxylated carbon nanotube can be prepared by conventional methods in the art. For example, the carbon nanotube is mixed with an oxidizing agent and then heated. The oxidizing agent can be concentrated sulfuric acid and / or concentrated nitric acid.

[0028] In some preferred embodiments, the base film includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyethylene (PE), polypropylene (PP), and polyvinylpyrrolidone (PVP), and derivatives thereof. The base film has good wettability and thermal stability when in contact with the electrolyte.

[0029] In some preferred embodiments, the base particles of the present application are prepared by reacting the carboxylated carbon nanotube with a siloxane precursor in the presence of a catalyst. Further, the catalyst includes concentrated ammonia water. The concentration of the concentrated ammonia water can be 25-28%. Further, the siloxane precursor includes methoxysilane and / or ethoxysilane. For example, the siloxane precursor includes one or more of tetraethoxysilane, hexaethyldisiloxane, hexamethyldisiloxane, and tetramethyldisiloxane. The carboxylated carbon nanotube can be prepared by conventional methods in the art. For example, the carbon nanotube is mixed with an oxidizing agent and then heated. The oxidizing agent can be concentrated sulfuric acid and / or concentrated nitric acid.

[0030] In some more preferred embodiments, the method for preparing the base particles includes dissolving the carboxylated carbon nanotube in a solvent, mixing an alkaline substance, stirring until uniform, and then mixing a phenol, a siloxane precursor, and an aldehyde, and then preparing after reaction. Further, the method includes centrifugation, washing, and drying after reaction. Further, the solvent includes an alcohol aqueous solution. For example, the solvent can be an ethanol aqueous solution or a methanol aqueous solution.

[0031] In some more preferred embodiments, the volume ratio of the alkaline substance to the siloxane precursor is 5-15:5-15.

[0032] In certain preferred embodiments, the composite layer is formed by self-polymerization of dopamine on the surface of the substrate particles. In certain more preferred embodiments, the composite layer is prepared by dispersing the substrate particles and dopamine in a solvent and reacting them at room temperature. In more preferred embodiments, the solvent comprises water or a buffer solution. For example, the solvent may be water, Tris-HCl buffer solution, PBS buffer solution, or the like.

[0033] In certain preferred embodiments, the mass ratio of the matrix particles to dopamine is 1-3:1-4.

[0034] In certain preferred embodiments, the reaction further comprises centrifugation, washing and drying.

[0035] In certain preferred embodiments, the method for preparing the diaphragm of the present application comprises dispersing matrix particles having a composite layer on their surface in a solvent, filtering through a base membrane, and drying the diaphragm. The solvent comprises at least one of water, methanol, and ethanol.

[0036] Another aspect of the present application provides a lithium-ion secondary battery comprising any of the above-mentioned separators.

[0037] In another aspect of the present application, an electric device is provided, comprising any one of the lithium-ion secondary batteries described above, wherein the lithium-ion secondary battery serves as a power supply for the electric device.

[0038] Electric equipment refers to any device that can utilize electrical energy and convert it into one or more other forms of energy, such as mechanical energy, thermal energy, or light energy, including electric motors, electric heat generators, and electric light sources. Specifically, these devices include, but are not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, and energy storage systems. Mobile devices include mobile phones, laptops, drones, robot vacuums, and electronic cigarettes. Electric vehicles include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0039] Example 1

[0040] This embodiment provides a diaphragm, and the preparation method thereof is as follows:

[0041] (1) Preparation of carboxylated carbon nanotubes: 1.5 g of carbon nanotubes (CNTs) were added to 125 ml of concentrated nitric acid (68% by weight) and stirred continuously at 120°C for 24 hours. After cooling to room temperature, the mixture was centrifuged and washed several times with deionized water until the solution was neutral. After freeze-drying, the carboxylated carbon nanotubes were obtained.

[0042] (2) Preparation of matrix particles: 150 mg of carboxylated carbon nanotubes were dissolved in a solution containing 20 ml of deionized water and 200 ml of ethanol, followed by the addition of 9 ml of concentrated aqueous ammonia (28% by weight) and stirred vigorously for 5 minutes. Subsequently, 1.28 g of catechol was added to the mixture and stirred until completely dissolved. 5 ml of tetraethoxysilane (TEOS) and 1.8 ml of formaldehyde were then added to the solution in sequence. The solution was then stirred at room temperature for 30 hours using a magnetic stirrer. The resulting black solid powder was collected by centrifugation and thoroughly washed with deionized water and ethanol until the solution was neutral. The powders were vacuum dried at 60°C overnight to obtain carbon nanotube particles coated with a silica layer, referred to as CNTs@SiO2 particles.

[0043] (3) Preparation of the PDA layer: Prepare 100 mL of Tris-HCl buffer solution (10 mmol / L, pH = 8.5) and disperse 150 mg of CNTs@SiO2 particles in it. Add 150 mg of dopamine to the above solution and stir at room temperature for 48 hours to promote the self-polymerization of dopamine on the surface of the CNTs@SiO2 particles to form a polydopamine (PDA) layer. After the reaction is completed, the substrate particles coated with the PDA layer (denoted as CNTs@SiO2@PDA particles) are obtained by centrifugation, washing with water three times, and then freeze-drying.

[0044] (4) Preparation of a membrane: The particles prepared in step (3) were added to 100 mL of a 98% by volume ethanol solution. The resulting suspension, after sonication, was filtered through a 25 mm diameter polypropylene (PP) membrane (base membrane) and dried in an oven at 60°C for 12 hours. A CNTs@SiO2@PDA composite layer was formed on one side of the PP membrane, producing a CNTs@SiO2@PDA membrane. The CNTs@SiO2@PDA membrane was then cut into 19 mm diameter discs.

[0045] This embodiment also provides a method for preparing a lithium-ion secondary battery, comprising the following steps:

[0046] (1) Preparation of electrolyte:

[0047] The electrolyte was prepared in a glove box with water and oxygen contents below 1 ppm. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dried in a vacuum oven at 120°C for 10 h. Lithium bis(trifluoromethanesulfonyl)imide (LiFSI) was first added to a 1:1 (volume ratio) solvent mixture of dimethoxyethane (DME) and 1,3-dioxolane (DOL) and stirred for 2 h to obtain a 0.5 mol / L LiFSI solution. Subsequently, LiTFSI was added and stirred for 4 h to obtain a 1 mol / L LiTFSI solution.

[0048] (2) Positive electrode material preparation:

[0049] 1) A mixed metal salt solution of Ni, Co, Mn, Al is configured, wherein the total molar concentration of metal ions is 2 mol / L; the molar ratio of Ni, Co, Mn, Al satisfies 8:1:0.5:0.5; a sodium hydroxide strong alkali solution with a molar concentration of 4 mol / L is configured as a precipitant, and an ammonia water solution with a concentration of 3.5 mol / L is configured as a complexing agent;

[0050] 2) Pure water, the precipitant and the complexing agent are added to a closed reaction kettle to form a bottom liquid, the pH value of the bottom liquid is controlled to be about 11 by the precipitant, and the ammonia concentration in the bottom liquid is controlled to be about 0.4 mol / L by the complexing agent; the temperature of the co-precipitation reaction system is maintained at about 50°C by a circulating water heating jacket.

[0051] 3) Keep the stirring of the reaction kettle open, the speed is about 400 rpm, keep the nitrogen gas with a flow rate of 20 L / min as a protective gas, add the metal salt mixed solution in step 1), the precipitant and the complexing agent to the reaction kettle through the dropping funnel for co-precipitation reaction. The pH value in the reaction kettle during the reaction is controlled to be about 11, the ammonia concentration during the reaction is 0.6 mol / L, the reaction temperature is maintained at 50°C, and the rotation speed of the reaction kettle is 400 r / min; when the particle size D50 of the slurry in the reaction kettle grows to 10-18 μm, stop the liquid feeding and keep heating and stirring for aging, the aging time is 8 hours, and the aging process is carried out under nitrogen protection.

[0052] 4) The slurry obtained in step 3) is filtered, washed and dried to obtain a high-nickel ternary precursor with a chemical formula of Ni 0.8 Co 0.1 Mn 0.5 Al 0.5 (OH)2, D50 is 13.3 μm;

[0053] 5) The above precursor is uniformly ground and mixed with Li2CO3 in a molar ratio of 1:0.5, and then placed in a muffle furnace for high-temperature calcination at 1000°C for 12h to obtain a LiNi 0.8 Co 0.1 Mn 0.5 Al 0.5 O2 positive electrode material.

[0054] (3) Cell production:

[0055] Positive electrode sheet preparation: the above obtained LiNi 0.8 Co 0.1 Mn 0.5 Al 0.5The O2 positive electrode material, conductive carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and then NMP was added to prepare the slurry. The slurry was then evenly coated on the current collector and dried in a vacuum oven at 100°C to obtain the positive electrode sheet.

[0056] Preparation of the negative electrode: Graphite: CMC: Conductive carbon black: SBR (80:7.5:7.5:5 by mass) was homogenized and evenly coated onto the current collector. The electrode was dried in an oven at 100°C.

[0057] Cell assembly: Assemble the prepared positive electrode sheet, negative electrode sheet, the separator prepared above in this embodiment, and the ionic liquid electrolyte into a battery.

[0058] Examples 2-3

[0059] The preparation process is basically the same as that of Example 1, except that the amount of tetraethoxysilane used in step (2) during the membrane preparation process is adjusted to 10 ml and 15 ml, respectively, to obtain membranes with different silicon dioxide layer thicknesses.

[0060] Examples 4-5

[0061] The preparation process is basically the same as that of Example 1, except that the amount of carboxylated carbon nanotubes in step (1) during the membrane preparation process is adjusted to 200 mg and 300 mg, respectively, to obtain membranes with different silicon dioxide layer thicknesses.

[0062] Examples 6 to 8

[0063] The preparation process is basically the same as that of Example 1, except that the amount of dopamine in step (3) during the membrane preparation process is adjusted to 200 mg, 300 mg, and 400 mg, respectively, to obtain membranes with different polydopamine layer thicknesses.

[0064] Examples 9-10

[0065] The preparation process is basically the same as that of Example 1, except that the type of base film in step (3) of the membrane preparation process is regulated to obtain different membranes.

[0066] Comparative Example 1

[0067] The preparation process is basically the same as that of Example 1, except that step (2) is omitted in the membrane preparation process, and step (3) uses carboxylated carbon nanotubes of the same mass to replace the CNTs@SiO2 particles in Example 1.

[0068] Comparative Example 2

[0069] The preparation process is basically the same as that of Example 1, except that step (3) is omitted in the membrane preparation process, and step (4) uses CNTs@SiO2 particles of the same mass prepared in step (2) to replace the particles prepared in step (3) of Example 1.

[0070] Comparative Example 3

[0071] The preparation process is basically the same as that of Example 1, except that steps (2) and (3) are omitted in the membrane preparation process, and step (4) uses the same mass of carboxylated carbon nanotubes to replace the particles prepared in step (3) of Example 1.

[0072] Comparative Example 4

[0073] The preparation process is basically the same as that of Example 1, except that the diaphragm uses a PP film.

[0074] Table 1 Physical parameters of the diaphragms of various embodiments and comparative examples

[0075]

[0076] " / " means it does not exist

[0077] 1. Determination of physical parameters:

[0078] 1) Thickness of the silicon dioxide layer

[0079] The testing method is as follows: 1 mg of the matrix particles prepared in each Example and Comparative Example 2 was dispersed in 2 ml of ethanol, sonicated for 5 minutes, and the dispersed solution was dropped onto a specially prepared copper grid covered with a thin film to support the sample. The solvent was allowed to evaporate, and the sample was evenly distributed on the grid before TEM imaging. TEM images can be quantitatively analyzed using image analysis software, and statistical analysis can be used to determine the shell thickness of the core-shell structure.

[0080] 2) Thickness of the polydopamine layer

[0081] The testing method is as follows: 1 mg of the PDA-coated substrate particles prepared in each Example and Comparative Example 1 was dispersed in 2 ml of ethanol, sonicated for 5 minutes, and the dispersed solution was dropped onto a specially prepared copper grid covered with a thin film to support the sample. The solvent was allowed to evaporate, and the sample was evenly distributed on the grid before TEM imaging. TEM images can be quantitatively analyzed using image analysis software, and statistical analysis can be used to determine the thickness of the PDA layer.

[0082] 2. Safety performance

[0083] (1) Puncture resistance test

[0084] The diaphragms prepared in each example and comparative example were cut into strips and mounted on the fixed clamp ring of a diaphragm puncture tensile testing machine. A steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm was used to puncture the strips at a rate of (50±5) mm / min. The maximum load at which the needle penetrated the strips was measured. Three points were measured, and the arithmetic average was taken. Five or more strips were tested.

[0085] (2) Tear resistance test

[0086] According to GB / T 1040.3-2006, the tensile strength test of battery separators requires the use of a Type 2 specimen with a width of (15±0.1) mm. During the test, an MTL (PC) tensile testing machine was used. The initial distance between the clamps should be set to (100±5) mm, and the test speed should be controlled at (250±10) mm / min.

[0087] The technical specifications of the MTL (PC) tensile testing machine include a test range of 0-500N (other ranges are optional), a measurement accuracy of 0.3, a travel of 1000mm, a continuously variable test speed of 0.5-500mm / min, and a displacement accuracy of 0.01mm. The tensile testing machine can measure the ratio of the maximum force a diaphragm can withstand before breaking under pure tensile force to the cross-sectional area of ​​the diaphragm under test. This ratio is the tensile strength.

[0088] 3. Battery fast charging performance test:

[0089] The lithium-ion secondary batteries prepared in each example and comparative example were tested for fast-charging performance as follows: At room temperature, a cell with a state of charge (SOC) of 0% was charged at a current density of 0.33C to 4.5V. The capacity at this point was C1. At room temperature, the same cell with a state of charge (SOC) of 0% was charged at a current density of 5C to 4.5V. The capacity at this point was C2. The charge rate performance test metric is capacity retention: fast-charging capacity retention = C2 / C1*100%.

[0090] The test results are shown in Table 2.

[0091] Table 2 Battery rate performance and fast charging performance test results

[0092]

[0093] It can be seen from the above table that, compared with Comparative Examples 1 to 4, the diaphragms prepared in the embodiments of the present application can not only significantly improve the safety performance of the battery, but also maintain a relatively high fast charging performance of the battery.

[0094] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a base film and a composite layer arranged on at least one surface of the base film, the composite layer includes base particles and a polydopamine layer distributed on the surface of the base particles, the base particles include a core and a silicon dioxide layer distributed on the surface of the core, the core includes carbon nanotubes, and the silicon dioxide layer includes silicon dioxide.

2. The diaphragm according to claim 1, characterized in that The thickness of the silicon dioxide layer is 16-60 nm.

3. The diaphragm according to claim 1, characterized in that The thickness of the polydopamine layer is 33-71 nm.

4. The diaphragm according to claim 1, characterized in that The thickness of the separator is 8 to 8.5 μm.

5. The diaphragm according to claim 1, characterized in that The added amount of the carbon nanotubes is 150 to 300 mg.

6. The diaphragm according to claim 1, characterized in that The silica layer also includes a phenolic resin.

7. The diaphragm according to claim 1, characterized in that The base film includes one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyethylene (PE), polypropylene (PP), polyvinyl pyrrolidone (PVP), and derivatives thereof.

8. A lithium ion secondary battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 7.

9. An electrical device, characterized in that: The lithium-ion secondary battery according to claim 8 is included, and the lithium-ion secondary battery serves as a power supply for the electrical equipment.

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