Composite separator and use thereof

Abstract

The present application provides a composite separator and the use thereof. The composite separator comprises a separator substrate and a composite ceramic layer disposed on at least one surface of the separator substrate. The composite ceramic layer comprises at least inorganic nanotubes and ceramic particles, wherein the ceramic particles are an inorganic material that does not comprise lithium; and in the composite ceramic layer, the open porosity of the inorganic nanotubes is 0.3-5%. When used in a battery, the composite separator of the present application not only has good heat resistance, but also has a relatively low moisture content, and can reduce the internal resistance of a lithium-ion battery and improve the rate performance and cycle performance of the lithium-ion battery.

Description

A composite diaphragm and its application Technical Field

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

[0002] In lithium-ion batteries, the separator separates the positive and negative electrodes to prevent them from coming into direct contact and causing a short circuit. Therefore, the performance of the separator directly affects the performance of the lithium-ion battery.

[0003] Currently used polyolefin separators have a low melting point. During the use of lithium-ion batteries, the separator is prone to thermal shrinkage, which can cause the positive and negative electrodes to come into contact and cause a short circuit. This not only reduces the battery's lifespan but also poses a safety hazard.

[0004] To improve the thermal performance of the separator, inorganic particles with higher heat resistance are usually coated on the surface of the polyolefin separator. However, conventional inorganic materials do not have ion conduction capabilities, resulting in low lithium-ion conductivity in the coated film. The current common solution is to add lithium-conducting materials to improve the lithium-ion conductivity of the coated film. However, this also leads to an increase in the moisture content of the coated separator. Since water molecules can react chemically with the active components in the electrolyte, the active components in the electrolyte will undergo chemical degradation, which will affect the performance of the battery.

[0005] Application content

[0006] This application provides a composite separator that, when applied to batteries, not only exhibits excellent heat resistance but also has a low moisture content, thereby improving the rate performance and cycle life of lithium-ion batteries.

[0007] This application provides a battery comprising the aforementioned composite separator, thereby exhibiting excellent safety performance, rate performance, and cycle life.

[0008] In a first aspect, this application provides a composite diaphragm, the composite diaphragm comprising a diaphragm substrate and a composite ceramic layer disposed on at least one surface of the diaphragm substrate;

[0009] The composite ceramic layer comprises at least inorganic nanotubes and ceramic particles; the ceramic particles are inorganic materials that do not contain lithium.

[0010] In the composite ceramic layer, the porosity of the inorganic nanotubes is 0.3-5%.

[0011] Optionally, the ceramic particles include at least one of the following: BaTiO3, HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, TiO2, AlN, Si3N4, BN, TiN, SiC, B4C, and TiC.

[0012] Optionally, the inorganic nanotubes are selected from non-conductive materials.

[0013] Optionally, the inorganic nanotubes include at least one of titanium dioxide nanotubes, silicon nanotubes, halloysite nanotubes, alumina nanotubes, zinc oxide nanotubes, boron nitride nanotubes, and silicon carbide nanotubes.

[0014] Optionally, the inorganic nanotubes comprise 5-60% of the total mass of the composite ceramic layer.

[0015] Optionally, the inner diameter of the inorganic nanotube is 3-150 nm;

[0016] And / or, the length of the inorganic nanotube is 300-5000 nm.

[0017] Optionally, the ratio of the outer diameter to the inner diameter of the inorganic nanotube is 1.5-20:1.

[0018] Optionally, the ratio of the length of the inorganic nanotube to the D50 of the ceramic particle is greater than 0 and not greater than 30.

[0019] Optionally, the composite membrane satisfies at least one of the following:

[0020] a. The thickness of the diaphragm substrate is 5-30 μm;

[0021] b. The thickness of the composite ceramic layer is 0.5-4 μm;

[0022] c. The areal density of the composite ceramic layer is 0.8–6 g / m³. 2 ;

[0023] d. The moisture content of the composite ceramic layer is 800-1700 ppm.

[0024] Optionally, the composite ceramic layer further includes a binder;

[0025] Optionally, the binder content is 3-10% by mass, based on the total mass of the composite ceramic layer.

[0026] Optionally, the composite ceramic layer further includes a silane coupling agent;

[0027] Optionally, the mass percentage of the silane coupling agent is 0.5% to 5.0% based on the total mass of the composite ceramic layer.

[0028] Secondly, this application provides a battery including the composite separator described in the first aspect.

[0029] The composite separator of this application includes a separator substrate and a composite ceramic layer disposed on at least one surface of the separator substrate. The composite ceramic layer includes at least inorganic nanotubes and ceramic particles, and the porosity of the inorganic nanotubes in the composite ceramic layer is 0.3-5%. When applied to batteries, this composite separator not only has excellent heat resistance but also low moisture content and excellent lithium-ion transport performance, which can reduce the internal resistance of lithium-ion batteries and improve their rate performance and cycle performance.

[0030] The battery of this application, due to including the aforementioned separator, has excellent electrochemical performance and can be widely used. Detailed Implementation

[0031] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0032] Existing technologies can improve the heat resistance of polyolefin separators to some extent by applying common ceramic coatings such as alumina and boehmite, or thermoplastic resin coatings such as PVDF, polyimide, and aramid to the surface of the polyolefin separator. However, these methods can also easily reduce the lithium-ion transport performance and increase the internal resistance of lithium-ion batteries.

[0033] To solve the above problems, this application adopts the following technical solution:

[0034] In a first aspect, this application provides a composite diaphragm, the composite diaphragm comprising a diaphragm substrate and a composite ceramic layer disposed on at least one surface of the diaphragm substrate;

[0035] The composite ceramic layer comprises at least inorganic nanotubes and ceramic particles; the ceramic particles are inorganic materials that do not contain lithium.

[0036] In the composite ceramic layer, the porosity of the inorganic nanotubes is 0.3-5%. When applied to batteries, the composite separator of this application not only exhibits excellent heat resistance but also excellent lithium-ion transport performance and lower moisture content. This reduces the internal resistance of lithium-ion batteries and improves their rate performance and cycle performance. The main reasons for this include: Firstly, both the ceramic particles and inorganic nanotubes possess excellent heat resistance, which improves the heat resistance of the composite separator. During battery charging and discharging, the composite separator maintains its intact morphology, preventing short circuits between the positive and negative electrodes caused by thermal shrinkage during charging and discharging. In particular, the inorganic nanotubes have a one-dimensional nanostructure, which further enhances the heat resistance of the composite separator after bonding with the separator substrate. Simultaneously, the ceramic particles are inorganic materials without lithium, resulting in low lithium-ion conductivity, which helps reduce the moisture content of the composite separator. On the other hand, the inorganic nanotube materials in the composite separator can provide abundant lithium-ion transport channels, effectively expanding the porosity of the composite ceramic layer coating and promoting lithium-ion transport performance within the composite ceramic layer. During battery charging and discharging, the porosity of the composite ceramic layer helps increase the transport flux of lithium ions in the coating, contributing to improved cycle performance and rate performance of the lithium battery. Therefore, in the composite ceramic layer, inorganic nanotubes not only provide more channels for lithium-ion transport but also form uniform nanochannels at the separator-electrode interface, enabling uniform lithium-ion transport and reducing transport resistance at the interface, thus lowering the internal resistance of the lithium battery and improving its performance. Furthermore, the density of inorganic nanotube materials is typically lower than that of ceramic nanomaterials, resulting in a lighter separator with a composite ceramic layer compared to a ceramic-coated separator, which is beneficial for increasing the energy density of lithium batteries. Therefore, composite separators including inorganic nanotubes and ceramic particles possess excellent lithium-ion transport performance and heat shrinkage resistance, and when applied to batteries, they can significantly improve the safety, rate performance, cycle performance, and energy density of lithium-ion batteries.

[0037] It is understood that the ceramic particles in this application can also be understood as inorganic materials that have virtually no lithium-ion conductivity, that is, they do not contain lithium, do not have the ability to store lithium, and do not have the ability to conduct lithium ions.

[0038] The applicant also found in the research that when the porosity of inorganic nanotubes in the composite ceramic layer is 0.3-5%, it not only helps to improve the ion transport efficiency of the composite separator and reduce the internal resistance of the battery, thereby improving the electrochemical performance of the battery, but also enables the composite ceramic layer and the separator substrate to have excellent adhesion, preventing the separator substrate from falling off from the composite ceramic layer during the charging and discharging process of the battery, thus effectively improving the safety performance of the battery.

[0039] This application does not impose any particular restrictions on the method of controlling the porosity of inorganic nanotubes in the composite ceramic layer. As long as the above-mentioned characteristics are met, the control method corresponding to the purpose can be freely selected.

[0040] In this application, the surface of the diaphragm substrate refers to the two surfaces of the diaphragm substrate that have the largest area and are arranged opposite each other. This application can form a composite diaphragm by depositing a composite ceramic layer on one surface of the diaphragm substrate, or by depositing composite ceramic layers on both surfaces of the diaphragm substrate.

[0041] This application does not impose any particular limitation on the membrane substrate. The membrane substrate can be a porous membrane commonly used in the art. For example, the membrane substrate can be a polyolefin porous membrane or a polyolefin porous membrane with a coating layer.

[0042] Polyolefin porous membranes can be polyethylene porous membranes, polypropylene porous membranes, or polyethylene-polypropylene multilayer composite membranes. Polyethylene-polypropylene multilayer composite membranes refer to multilayer composite porous membranes formed by stacking polypropylene (PP) and polyethylene (PE) in any order, such as PP-PE-PP three-layer composite membranes, PP-PE two-layer composite membranes, and PP-PP-PE-PP four-layer composite membranes.

[0043] A polyolefin porous membrane with a coating layer refers to a polyolefin porous membrane with a coating layer on at least one surface. The coating layer is not specifically limited in this application; those skilled in the art can select commonly used coating layers according to their needs. For example, the coating layer includes at least one of alumina, boehmite, nanofibers, polyimide, aramid fiber, PMMA, PVDF, and PVDF-HFP. In some embodiments, the polyolefin porous membrane with a coating layer can be an alumina-coated polyolefin porous membrane, a boehmite-coated polyolefin porous membrane, a nanofiber-coated polyolefin porous membrane, a polyimide-coated polyolefin porous membrane, an aramid fiber-coated polyolefin porous membrane, a PMMA-coated polyolefin porous membrane, a PVDF-coated polyolefin porous membrane, or a PVDF-HFP-coated polyolefin porous membrane. The polyolefin porous membrane with a coating layer can also be a polyolefin porous membrane with a mixture of nanofibers and alumina, a polyolefin porous membrane with a mixture of PVDF and alumina, or a polyolefin porous membrane with a mixture of PMMA and alumina.

[0044] In this application, the porosity of inorganic nanotubes refers to the proportion of the pore volume provided by the pores of the inorganic nanotubes in the total volume of the composite ceramic layer. In some embodiments, the porosity of the inorganic nanotubes can be obtained using Equation 1:

[0045] In Equation 1, x represents the total mass based on the composite ceramic layer and the mass percentage of inorganic nanotubes.

[0046] ρ is the tap density of the inorganic nanotubes, in g / cm³. 3 ;

[0047] d1 is the outer diameter of the inorganic nanotube, in nm;

[0048] d2 is the inner diameter of the inorganic nanotube, in nm;

[0049] m1 is the mass of the diaphragm substrate per unit area, in g / cm³. 2 ;

[0050] m2 is the mass of the composite membrane per unit area, in g / cm³. 2 ;

[0051] h represents the thickness of the composite ceramic layer, in cm.

[0052] For example, the porosity of the inorganic nanotubes can be any of 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3%, 3.5%, 4%, 4.5%, and 5%, or a range of any combination thereof. Further, the porosity of the inorganic nanotubes is 0.2-3%.

[0053] In one specific embodiment, the decomposition temperature of the ceramic particles is not lower than 200°C. For example, the ceramic particles include at least one of BaTiO3, HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, TiO2, AlN, Si3N4, BN, TiN, SiC, B4C, and TiC.

[0054] As described above, the ceramic particles have higher heat resistance and mechanical strength, which can further ensure that the composite separator maintains its complete morphology during the charging and discharging process of the battery, and avoid short circuits between the positive and negative electrodes caused by the thermal shrinkage of the composite separator during the charging and discharging process of the battery.

[0055] In one specific embodiment, the inorganic nanotubes include at least one of titanium dioxide nanotubes, silicon nanotubes, halloysite nanotubes, alumina nanotubes, zinc oxide nanotubes, boron nitride nanotubes, and silicon carbide nanotubes. As described above, the inorganic nanotubes have higher mechanical strength, ensuring rapid lithium ion transport within the composite membrane while further ensuring tighter overlap and better adhesion between the nanotubes, resulting in a more robust network structure.

[0056] As a preferred technical solution of this application, to further improve the overall performance of the composite membrane, this application can adjust parameters such as the amount of inorganic nanotubes, the inner diameter and the outer diameter of the inorganic nanotubes.

[0057] In one specific embodiment, the inorganic nanotubes comprise 5-60% of the total mass of the composite ceramic layer.

[0058] For example, based on the total mass of the composite ceramic layer, the mass percentage of inorganic nanotubes can be any or a combination of two of the following: 5%, 10%, 13%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 55%, and 60%. Further, based on the total mass of the composite ceramic layer, the mass percentage of inorganic nanotubes is 10%-50%, and even further, based on the total mass of the composite ceramic layer, the mass percentage of inorganic nanotubes is 13%-50%.

[0059] When the mass percentage of inorganic nanotubes meets the above range, inorganic nanotubes and ceramic particles can form a better particle-nanotube uniformly distributed "point-line" nano-network structure, which enables good adhesion between the composite ceramic coating layer and the membrane substrate, and can improve the lithium-ion transport performance of the composite membrane, resulting in a composite membrane with excellent comprehensive performance.

[0060] In one specific embodiment, the inner diameter of the inorganic nanotube is 3-150 nm.

[0061] For example, the inner diameter of the inorganic nanotube can be any of 3nm, 10nm, 20nm, 40nm, 60nm, 100nm, 130nm, 150nm, or any combination thereof.

[0062] Furthermore, the inner diameter of the inorganic nanotubes is 5-150 nm.

[0063] When the inner diameter of inorganic nanotubes meets the above-mentioned range, it can provide more transport channels for lithium ions, enabling rapid transport of lithium ions in the composite separator. As a result, when the composite separator is applied to a battery, it can further reduce the battery's internal resistance and improve the battery's rate performance and energy density.

[0064] The applicant also discovered that when the length of the inorganic nanotubes is 0.3-5 μm, the inorganic nanotubes can overlap more tightly, resulting in a more uniform and dense distribution of through-holes in the composite ceramic layer. This not only facilitates lithium-ion transport but also enhances the heat resistance of the composite membrane due to the densely packed network structure of the inorganic nanotubes. For example, the length of the inorganic nanotubes can be any or any combination of 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 1.9 μm, 2 μm, 2.3 μm, 2.5 μm, 2.7 μm, 2.9 μm, 3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.5 μm, 4.8 μm, and 5 μm. Further, the length of the inorganic nanotubes is 0.3-2 μm.

[0065] In some implementations, the length of inorganic nanotubes can be obtained in accordance with the industry standard JY / T 0584-2020 "General Rules for Analysis Methods of Scanning Electron Microscopy".

[0066] In one specific embodiment, the ratio of the outer diameter to the inner diameter of the inorganic nanotube is 1.5-20:1.

[0067] The ratio of the outer diameter to the inner diameter of the inorganic nanotube can be any one or any combination of two of the following: 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 10.5:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1; further, the ratio of the outer diameter to the inner diameter of the inorganic nanotube is 2-15:1.

[0068] When the ratio of the outer diameter to the inner diameter of the inorganic nanotubes meets the above-mentioned range, it ensures that lithium ions can be transported quickly in the composite membrane, while also ensuring that the inorganic nanotubes overlap more tightly, adhere better to each other, and form a more robust network structure.

[0069] The inner and outer diameters of the inorganic nanotubes can be determined using conventional techniques known in the art, such as field emission transmission electron microscopy (TEM). Specifically, this includes obtaining a TEM image of the composite ceramic layer according to GB / T 18907-2013 "Microbeam Analysis Electron Microscopy - Selected Area Electron Diffraction Analysis Method". The hollow structure of the inorganic nanotubes can be clearly observed through the TEM image of the composite ceramic layer, and the inner and outer diameters of the inorganic nanotubes can be obtained by measuring with a scale.

[0070] The tap density of inorganic nanotubes can be determined by conventional techniques known in the art, such as by testing according to GBT21354-2008 "General Method for Determination of Tap Density of Powder Products".

[0071] In one specific embodiment, the ratio of the length of the inorganic nanotube to the D50 of the ceramic particle is greater than 0 and not greater than 30.

[0072] For example, the ratio of the length of the inorganic nanotube to the D50 of the ceramic particle can be any or any combination of 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. Further, the ratio of the length of the inorganic nanotube to the D50 of the ceramic particle is ≤20.

[0073] When the length of the inorganic nanotube and the D50 of the ceramic particle satisfy the above relationship, the inorganic nanotube and the ceramic particle can be better matched to obtain a denser composite ceramic layer, thereby improving the overall performance of the composite membrane. It can be understood that in order to prevent the ceramic particles from entering the interior of the inorganic nanotube and affecting the ion transport efficiency of the composite membrane, the inner diameter of the inorganic nanotube should be smaller than the particle size of the ceramic particle.

[0074] In some embodiments of this application, the particle size distribution (SPAN) of the ceramic particles is ≤1.5.

[0075] For example, the particle size distribution of the ceramic particles can be any one of 1.5, 1.4, 1.3, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.3, 0.1, or a range of any two. Further, the particle size distribution of the ceramic particles is 0.8 to 1.5.

[0076] In some implementations, the D10, D50, and D90 of ceramic particles can be tested using a laser force analyzer, and then the particle size distribution SPAN of the ceramic particles can be calculated according to Equation 2.

[0077] SPAN = (D90 - D10) / D50 (Equation 2)

[0078] When the particle size distribution of ceramic particles meets the above-mentioned range, inorganic nanotubes and ceramic particles can be better matched to obtain a denser composite ceramic layer, thereby improving the overall performance of the composite membrane.

[0079] In some embodiments, the particle size of the ceramic particles can be determined using conventional techniques known in the art. For example, the D50, D90, and D10 of the ceramic particles can be characterized using a laser scattering particle size analyzer (Malvin ZEN3690 particle size analyzer). Specifically, this includes dispersing the ceramic particles in pure water and obtaining the D50, D90, and D10 of the ceramic particles. Alternatively, the composite ceramic layer can be scanned using a scanning electron microscope (SEM), and the D50, D90, and D10 of the ceramic particles can be obtained by statistical analysis and calculation of the scanning results (such as using ImageJ software). The particle size corresponding to a cumulative particle size distribution percentage of 10% is the D10 of the ceramic particles, the particle size corresponding to a cumulative particle size distribution percentage of 50% is the D50 of the ceramic particles, and the particle size corresponding to a cumulative particle size distribution percentage of 90% is the D90 of the ceramic particles.

[0080] In some embodiments of this application, the composite membrane satisfies at least one of the following:

[0081] a. The thickness of the diaphragm substrate is 5-30 μm;

[0082] b. The thickness of the composite ceramic layer is 0.5-4 μm;

[0083] c. The areal density of the composite ceramic layer is 0.8–6 g / m³. 2 ;

[0084] d. The moisture content of the composite ceramic layer is 800-1700 ppm.

[0085] Composite separators that meet any of the above conditions can further improve the electrochemical performance of batteries when applied to them.

[0086] The thickness of the composite ceramic layer mentioned above refers to the thickness of a single layer. The thickness of the composite ceramic layer can be determined using conventional techniques known in the art, such as obtaining the thickness according to the test methods specified in national standard GB / T 36363-2018, or by measuring the thickness using a scanning electron microscope. It should be noted that the thickness of the composite ceramic layer refers to the thickness of a single layer; that is, when composite ceramic layers are provided on both surfaces of the diaphragm substrate, the thickness of the composite ceramic layer refers to the thickness of the composite ceramic layer provided on one of the surfaces of the diaphragm substrate.

[0087] The areal density (mass per unit area) of the diaphragm substrate can be determined by conventional techniques known in the art, such as the weighing method. Specifically, the diaphragm substrate can be cut into 10cm×10cm pieces, the sample weight can be weighed, and the areal density of the diaphragm substrate can be calculated.

[0088] The areal density of the composite diaphragm can be determined by conventional techniques known in the art, such as the weighing method. Specifically, the composite diaphragm can be cut into 5cm×5cm pieces, the weight of the samples can be weighed, and the areal density of the composite diaphragm can be calculated.

[0089] In some embodiments of this application, the areal density of the diaphragm substrate is 3.5–10.0 g / m³. 2 The areal density of the composite membrane is 4.3 g / m³. 2 ~16g / m 2 .

[0090] In this application, in order to improve the adhesion between the composite ceramic layer and the diaphragm substrate, and to enable the composite ceramic layer to adhere more tightly to the surface of the diaphragm substrate, the composite ceramic layer also includes an adhesive.

[0091] This application does not specifically limit the adhesive. For example, the adhesive may be at least one of polyacrylate copolymers, polyacrylamide copolymers, polyurethane copolymers, polyimide copolymers, polyetherimide copolymers, polyurea copolymers, and styrene-butadiene rubber copolymers.

[0092] This application does not impose any particular limitation on the mass percentage of the adhesive, and the amount added can be freely selected according to the purpose.

[0093] In some embodiments of this application, the mass percentage of the binder is 3-10% based on the total mass of the composite ceramic layer.

[0094] In this application, in order to improve the heat resistance of the composite ceramic layer, the composite ceramic layer also includes a silane coupling agent.

[0095] In some embodiments of this application, the mass percentage of the silane coupling agent is 0.5% to 5% based on the total mass of the composite ceramic layer.

[0096] In some embodiments, the silane coupling agent is specifically one or more of the following: triethoxymethylsilane, (3-aminopropyl)triethoxysilane, (3-aminopropyl)trimethoxysilane, trimethoxy[3-(methylamino)propyl]silane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, trimethoxy(3,3,3-trifluoropropyl)silane, (3-glycidylpropoxy)trimethoxysilane, 1-[3-(trimethoxysilyl)propyl]urea, diethylenetriaminepropyltrimethoxysilane, and (3-glycidylpropoxy)triethoxysilane, but is not limited to the silane coupling agents described above.

[0097] In the diaphragm of this application, the composite ceramic layer may further include additives such as dispersants, wetting agents, thickeners, and pH adjusters; in the coating solution used to form the composite ceramic layer, dispersants are added for the purpose of improving dispersibility, coatability, or storage stability; in the electrolyte slurry used to form the electrolyte layer, thickeners are added for the purpose of improving storage stability; in the electrolyte slurry used to form the electrolyte layer, wetting agents are added for the purpose of improving coating uniformity; in the coating solution used to form the composite ceramic layer, pH adjusters are added, for example, for the purpose of adjusting pH.

[0098] This application does not specifically limit the dispersant. For example, the dispersant may be at least one of sodium salt of polyacrylate copolymer, ammonium salt of polyacrylate copolymer, and ammonium salt of alkanolate containing acidic groups.

[0099] This application does not specifically limit the thickener. For example, the thickener may be at least one of sodium carboxymethyl cellulose, fumed silica, modified urea polymers, organic modified silicates, organic modified montmorillonite, and organic bentonite.

[0100] This application does not specifically limit the wetting agent. For example, the wetting agent may be at least one of polyether siloxane copolymers, organosilicon twin structure copolymers, polyacrylate copolymers, polyether modified silicone oil copolymers, and polyoxyethylene alkylamine copolymers.

[0101] This application does not specifically limit the pH adjuster. For example, the pH adjuster may be at least one of hydrochloric acid, phosphoric acid, sodium citrate, potassium citrate, sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium carbonate.

[0102] This application does not impose any particular limit on the mass percentage of dispersants, thickeners, wetting agents, and pH adjusters; the amount added can be freely selected according to the purpose.

[0103] In some embodiments of this application, the mass percentage of each additive can be 0.1-3% based on the total mass of the composite ceramic layer;

[0104] Composite separators have superior overall performance and can improve the electrochemical performance of batteries and broaden their application scenarios when applied to them.

[0105] This application does not impose any particular restrictions on the preparation method of the composite diaphragm. As long as the composite diaphragm can meet the above-mentioned characteristic range, the manufacturing method corresponding to the purpose can be freely selected.

[0106] In some embodiments, the composite diaphragm of this application can be prepared by a method including the following steps:

[0107] 1) Disperse inorganic nanotubes and ceramic particles in a solvent to obtain a coating slurry;

[0108] 2) Apply the coating slurry to at least one surface of the diaphragm substrate and dry it to obtain a composite diaphragm.

[0109] The solvent in step 1) can be at least one of water, ethanol, acetone, and N-methylpyrrolidone.

[0110] In some embodiments, at least one of a dispersant, wetting agent, binder and thickener may be added to a solvent in step 1) to form a coating slurry;

[0111] In some embodiments, step 1) may further include: adding a dispersant to a solvent and stirring and dispersing for 10–60 min; then adding inorganic nanotubes and solid electrolyte particles respectively, and continuing to stir and disperse for 10–240 min; then adding a binder and stirring and dispersing for 10–180 min; then adding a thickener and stirring and dispersing for 10–60 min; finally adding a wetting agent and stirring and dispersing for 10–60 min to obtain a coating slurry; the stirring speed can be 1000–5000 r / min, and the solid content of the coating slurry can be ≤45%.

[0112] Secondly, this application provides a battery including the composite separator of the first aspect.

[0113] It is understood that the battery of this application also includes a positive electrode, a negative electrode, and an outer packaging. In this application, the positive electrode, composite separator, and negative electrode can be stacked to obtain an electrode assembly, the electrode assembly is placed in the outer packaging, electrolyte is injected into the outer packaging, and the battery is obtained by sealing.

[0114] The battery of this application, due to the inclusion of the aforementioned composite separator, exhibits excellent electrochemical performance and lifespan, provides a superior user experience, and is suitable for widespread application.

[0115] The present application will be further described below with reference to specific embodiments:

[0116] Example 1

[0117] The composite membrane in this example includes a membrane substrate and a composite ceramic layer disposed on two surfaces of the membrane substrate; the composite ceramic layer includes inorganic nanotubes, ceramic particles, dispersants, binders, thickeners and wetting agents;

[0118] Among them, the inorganic nanotubes are halloysite nanotubes. In the composite ceramic layer, the porosity (P) of the inorganic nanotubes is 1.63%, the inner diameter d2 of the inorganic nanotubes is 20nm, the ratio of the outer diameter to the inner diameter of the inorganic nanotubes (d1:d2) is 3.5:1, and the length (L) of the inorganic nanotubes is 1μm.

[0119] The ceramic particles are alumina nanomaterials with a D50 of 800 nm and a D10 greater than 20 nm. The ratio of the length of the inorganic nanotube to the D50 of the ceramic particles (L:D50) is 1.25.

[0120] Based on the total mass of the composite ceramic layer, the mass percentage of dispersant is 0.3%, the mass percentage of binder is 5%, the mass percentage of thickener is 0.3%, the mass percentage of wetting agent is 0.3%, the mass percentage of inorganic nanotubes (W1) is 30%, and the mass percentage of ceramic particles (W2) is 64.1%.

[0121] The diaphragm substrate is a PE diaphragm with a thickness (h1) of 9 μm and a single-sided thickness (h2) of 2 μm for the composite ceramic layer.

[0122] The battery in this example is prepared by a method including the following steps:

[0123] 1) Preparation of composite membrane

[0124] The dispersant was added to deionized water and stirred for 30 min; inorganic nanotubes and ceramic particles were added separately and stirred for another 60 min; then the binder was added and stirred for 30 min; next, the thickener was added and stirred for 30 min; finally, the wetting agent was added and stirred for 30 min to prepare the coating slurry.

[0125] The coating slurry is applied to both surfaces of the diaphragm substrate by micro-grooving roller coating, and then dried at 80°C to obtain a composite diaphragm including a composite ceramic layer.

[0126] The stirring and dispersing speed was 2000 r / min, the solid content of the coating slurry was 35%, the dispersant was a modified polyamide polymer (KMT-3604, Foshan Kening New Materials Co., Ltd.), the binder was a polyacrylate binder (LIS-S104, Shanghai Sanrui Polymer Materials Co., Ltd.), the thickener was an organic modified bentonite (BP-188L, Shanghai Yantai Industrial Co., Ltd.), and the wetting agent was a polyether modified organosilicon polymer (KMT-5514, Foshan Kening New Materials Co., Ltd.).

[0127] 2) Battery manufacturing

[0128] An electrolytic assembly is obtained by stacking positive electrode, composite separator and negative electrode, and the electrode assembly is placed in aluminum-plastic film and sealed to obtain battery;

[0129] The positive electrode sheet includes an aluminum foil and a positive electrode active layer disposed on the surface of the aluminum foil. The positive electrode active layer includes lithium cobalt oxide, conductive agent Super P, and binder PVDF. The mass ratio of lithium cobalt oxide, conductive agent, and binder is 96:2:2.

[0130] The negative electrode sheet includes a copper foil and a negative electrode active layer disposed on the surface of the copper foil. The negative electrode active layer includes silicon-doped graphite, conductive agent Super P, and binder PAA. The mass ratio of silicon-doped graphite, conductive agent, and binder is 95:2:3.

[0131] The electrolyte includes lithium hexafluorophosphate (LiPF6), EC, DEC and DMC. The concentration of lithium hexafluorophosphate in the electrolyte is 1M, and the volume ratio of EC, DEC and DMC is 1:1:1.

[0132] Example 2-17

[0133] The preparation methods of the composite separators and batteries in Examples 2-15 are basically the same as those in Example 1. The difference is that some parameters are different from those in Example 1 during the preparation of the composite separators, as detailed in Table 1.

[0134] Example 18

[0135] The preparation method of the composite separator and battery in Example 18 is basically the same as that in Example 1. The difference is that the composite separator in this example also includes a silane coupling agent. Based on the total mass of the composite ceramic layer, the mass percentage of the silane coupling agent is 0.3%, which corresponds to the addition of (3-aminopropyl)trimethoxysilane (KH-540, Hangzhou Jessica Chemical Co., Ltd.) as the silane coupling agent in the preparation process of the composite separator.

[0136] Comparative Example 1

[0137] The preparation methods of the composite separator and battery in Comparative Example 1 are basically the same as those in Example 1, except that the composite separator does not include inorganic nanotubes, as shown in Table 1.

[0138] Comparative Example 2

[0139] The preparation methods of the composite separator and battery in Comparative Example 2 are basically the same as those in Example 1, except that the composite separator does not include ceramic particles, as shown in Table 1.

[0140] Comparative Examples 3-4

[0141] The preparation methods of the composite separators and batteries in Comparative Examples 3-4 are basically the same as those in Example 1. The difference is that some parameters are different from those in Example 1 during the preparation of the composite separator, as detailed in Table 1.

[0142] Comparative Example 5

[0143] The preparation methods of the composite separator and battery in Comparative Example 5 are basically the same as those in Example 1, except that the ceramic particles are replaced with lithium aluminum titanium phosphate (LATP), as shown in Table 1.

[0144] Performance testing

[0145] The composite separators and batteries in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 2.

[0146] 1. Heat shrinkage rate

[0147] The thermal shrinkage rate of the composite separator was obtained according to the method specified in the national standard GB / T 36363-2018 "Performance Testing of Lithium-ion Battery Separators". The heat treatment temperature in the oven was 130℃, and the heat treatment time was 1 hour.

[0148] 2. Ratio performance

[0149] The rate performance of the battery was obtained according to the methods specified in the national standard GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles", including the capacity retention rate of the battery at 1C and 3C.

[0150] 3. Cyclic performance

[0151] The cycle performance of the battery was obtained according to the method specified in the national standard GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles", namely, the capacity retention rate of the battery after 1000 charge-discharge cycles at a 1C rate, and the cycle temperature of the assembled battery was high temperature (45℃).

[0152] 4. Hot Box Performance Test

[0153] The battery's thermal safety performance was tested according to the methods specified in national standards GB / T 31485-2015 "Safety Requirements and Test Methods for Power Batteries for Electric Vehicles" and GB / T 31241-2014 "Safety Requirements for Lithium-ion Batteries and Battery Packs for Portable Electronic Products". The test conditions were the safety performance of the battery after being stored in a thermal chamber at 150°C for 10 minutes.

[0154] 5. Thickness

[0155] The cross-section of the composite membrane was scanned using a scanning electron microscope (Hitachi, Japan, model: HITACHI SU8010). Ten random locations were selected to measure the thickness of a single layer of the composite ceramic layer. The average value was then used as the thickness of the single layer of the composite ceramic layer.

[0156] 6. Moisture content

[0157] The moisture content of the composite coated separator was characterized according to the method specified in industry standard TSGX 002—2018 "Ceramic Coated Separator for Power Lithium-ion Batteries Part 2: Moisture Content".

[0158] Table 1:

[0159] Table 2

[0160] As can be seen from Tables 1-2, compared with the comparative examples, the composite separator in this application can significantly improve the rate performance, cycle performance, and safety performance of the battery when applied to it. In particular, by further selecting the relevant parameters of the composite separator, the moisture content of the composite separator can be reduced and the thermal shrinkage performance of the composite separator can be improved, further enhancing the overall performance of the battery. This indicates that by adding inorganic nanotubes to the composite ceramic layer and controlling the porosity of the ceramic particles and inorganic nanotubes in the composite ceramic layer to prepare the composite separator, the electrochemical performance of the battery can be improved.

[0161] Furthermore, as can be seen from Examples 1 and 3, by further selecting the porosity of the inorganic nanotubes in the composite ceramic layer, the thermal shrinkage performance of the composite separator can be further improved, thereby improving the rate performance and cycle performance of the battery.

[0162] As can be seen from Examples 1 and 4, by further selecting the mass percentage of inorganic nanotubes, the moisture content of the composite separator can be further reduced and the thermal shrinkage performance of the composite separator can be improved, thereby improving the rate performance and cycle performance of the battery.

[0163] As can be seen from Examples 1 and 5, further selection of the inner diameter, outer diameter, and mass percentage of inorganic nanotubes can reduce the moisture content of the composite separator, improve the thermal shrinkage performance of the composite separator, and thus improve the rate performance and cycle performance of the battery.

[0164] As can be seen from Examples 1 and 11, the overall performance of the composite membrane can be improved by increasing the length of the inorganic nanotubes, thereby improving the electrochemical performance of the battery.

[0165] As can be seen from Examples 1 and 15, by further selecting the thickness of the composite ceramic layer, the overall performance of the composite separator can be further improved, thereby improving the overall performance of the battery.

[0166] As can be seen from Examples 1 and 18, introducing a silane coupling agent into the composite ceramic layer can further improve the thermal shrinkage performance of the composite separator, thereby improving the overall performance of the battery.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A composite diaphragm, characterized in that, The composite diaphragm includes a diaphragm substrate and a composite ceramic layer disposed on at least one surface of the diaphragm substrate; The composite ceramic layer includes at least inorganic nanotubes and ceramic particles; the ceramic particles are inorganic materials that do not contain lithium. In the composite ceramic layer, the porosity of the inorganic nanotubes is 0.3-5%.

2. The composite diaphragm according to claim 1, characterized in that, The ceramic particles include at least one of the following: BaTiO3, HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, TiO2, AlN, Si3N4, BN, TiN, SiC, B4C, and TiC.

3. The composite diaphragm according to claim 1, characterized in that, The inorganic nanotubes are selected from non-conductive materials; Preferably, the inorganic nanotubes include at least one of titanium dioxide nanotubes, silicon nanotubes, halloysite nanotubes, alumina nanotubes, zinc oxide nanotubes, boron nitride nanotubes, and silicon carbide nanotubes.

4. The composite diaphragm according to claim 1 or 2, characterized in that, Based on the total mass of the composite ceramic layer, the inorganic nanotubes comprise 5-60% by mass.

5. The composite diaphragm according to any one of claims 1-4, characterized in that, The inner diameter of the inorganic nanotubes is 3-150 nm; And / or, the length of the inorganic nanotube is 300-5000 nm.

6. The composite diaphragm according to any one of claims 1-5, characterized in that, The ratio of the outer diameter to the inner diameter of the inorganic nanotube is (1.5-20):

1.

7. The composite diaphragm according to any one of claims 1-6, characterized in that, The ratio of the length of the inorganic nanotube to the D50 of the ceramic particle is greater than 0 and not greater than 30.

8. The composite diaphragm according to any one of claims 1-7, characterized in that, The composite diaphragm must satisfy at least one of the following: a. The thickness of the diaphragm substrate is 5-30 μm; b. The thickness of the composite ceramic layer is 0.5-4 μm; c. The areal density of the composite ceramic layer is 0.8–6 g / m³. 2 ; d. The moisture content of the composite ceramic layer is 800-1700 ppm.

9. The composite diaphragm according to any one of claims 1-8, characterized in that, The composite ceramic layer also includes a binder; Preferably, the binder content is 3-10% by mass, based on the total mass of the composite ceramic layer.

10. The composite diaphragm according to any one of claims 1-9, characterized in that, The composite ceramic layer also includes a silane coupling agent; Preferably, the mass percentage of the silane coupling agent is 0.5% to 5.0% based on the total mass of the composite ceramic layer.

11. A battery, wherein, Includes the composite diaphragm according to any one of claims 1-10.

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