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 an electrolyte layer disposed on at least one surface of the separator substrate, wherein the average roughness of the electrolyte layer is ΔH, where ΔH≤1.0 μm. The electrolyte layer comprises inorganic nanotubes and solid-state electrolyte particles, wherein in the electrolyte layer, the open porosity of the inorganic nanotubes is 0.2-5%. When used in a battery, the composite separator of the present application not only achieves intimate interfacial contact with battery electrodes, a low interfacial porosity and good heat resistance and electrolyte wettability, but also has good lithium-ion transport performance, 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 battery materials, and in particular to a composite separator and its application. Background Technology

[0002] The separator is used to separate the positive and negative electrodes during the electrolysis reaction to prevent short circuits caused by direct contact between the positive and negative electrodes. The separator needs to remain stable in the chemical environment of the battery and not react adversely with the electrolyte or electrode materials to ensure the long-term performance and safety of the battery.

[0003] Currently used polyolefin separators have problems such as low melting point and poor electrolyte wettability. During the use of lithium-ion batteries, the separator is prone to shrinkage, causing the positive and negative electrodes to come into contact and cause a short circuit. This not only reduces the battery's lifespan but also easily leads to safety hazards.

[0004] To increase the melting point, existing technologies improve the heat resistance of the separator and the wettability of the electrolyte by blending it with other inorganic nanofillers with higher melting points and better wettability (such as alumina and silicon dioxide). However, the introduction of inorganic nanofillers can easily affect the interfacial contact between the separator and the battery electrode, and also reduce the lithium-ion transport performance, leading to an increase in the internal resistance of the lithium-ion battery.

[0005] Application content

[0006] This application provides a composite separator that, when applied to a battery, not only has close interfacial contact with the battery electrodes, low interfacial porosity, excellent heat resistance and electrolyte wettability, but also has excellent lithium-ion transport performance. This can reduce the internal resistance of the lithium-ion battery and improve its rate performance, storage stability and cycle performance.

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

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

[0009] The average roughness of the electrolyte layer is ΔH, where ΔH ≤ 1.0 μm. The electrolyte layer comprises inorganic nanotubes and solid electrolyte particles. The porosity of the inorganic nanotubes in the electrolyte layer is 0.2-5%.

[0010] Furthermore, the ratio between the particle size D99 of the solid electrolyte particles and the outer diameter of the inorganic nanotube is 0.3-14.

[0011] Furthermore, the ratio between the length of the inorganic nanotube and the D99 of the solid electrolyte particle is 0.3-18.

[0012] Furthermore, the ratio of the outer diameter to the inner diameter of the inorganic nanotube is 1.5-20:1;

[0013] And / or, the inner diameter of the inorganic nanotube is 3-80 nm;

[0014] And / or, the length of the inorganic nanotube is 300-3000 nm.

[0015] Furthermore, the solid electrolyte particles include at least one of lithium titanium aluminum phosphate and lithium titanium aluminum phosphate doped with doping elements, lithium germanium aluminum phosphate and lithium germanium aluminum phosphate doped with doping elements, and lithium lanthanum zirconium oxide and lithium lanthanum zirconium oxide doped with doping elements.

[0016] Preferably, in the solid electrolyte particles, the doping element includes at least one selected from silicon, tantalum, bismuth, iron, yttrium, indium, lutetium, gallium, rubidium, chromium, iron, aluminum, cerium, strontium, germanium, zinc, magnesium, and tungsten.

[0017] Furthermore, the inorganic nanotubes are selected from non-conductive materials;

[0018] 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.

[0019] Furthermore, based on the total mass of the electrolyte layer, the inorganic nanotubes comprise 5-60% by mass.

[0020] Furthermore, the composite membrane satisfies at least one of the following:

[0021] a. The thickness of the diaphragm substrate is 5-30μm;

[0022] b. The thickness of the electrolyte layer is 0.5-4 μm;

[0023] c. The areal density of the electrolyte layer is 2-5 g / m³ 2 .

[0024] Furthermore, the electrolyte layer also includes a binder;

[0025] Preferably, the binder has a mass percentage of 3-10% based on the total mass of the electrolyte layer.

[0026] Secondly, this application provides a method for preparing a composite separator as described in the first aspect, comprising the following steps:

[0027] S1. A mixed system is prepared by mixing materials including inorganic nanotubes, solid electrolyte particles and dispersing reagents;

[0028] S2. Filter the mixture to obtain a slurry;

[0029] S3. The slurry is coated onto at least one surface of a substrate and dried to obtain the composite separator. In a third aspect, this application provides a battery comprising the composite separator described in the first aspect.

[0030] The composite separator of this application comprises inorganic nanotubes and solid electrolyte particles in its electrolyte layer. By limiting the average roughness ΔH to ≤1.0 μm, it achieves tight interfacial contact with the battery electrodes, resulting in a low interfacial porosity. Furthermore, by limiting the porosity of the inorganic nanotubes to 0.2–5%, the transport resistance of lithium ions at the composite separator-electrode interface is reduced. Therefore, when applied to batteries, this composite separator not only exhibits excellent heat resistance and electrolyte wettability but also superior lithium-ion transport performance, reducing the internal resistance of lithium-ion batteries and thereby improving their rate performance, storage stability, and cycle performance.

[0031] The battery of this application, due to including the aforementioned separator, has excellent electrochemical performance and can be widely used. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments of this application or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 is a surface SEM image (magnification 10K) of the composite diaphragm in Embodiment 2 of this application;

[0034] Figure 2 is a cross-sectional SEM image of the composite diaphragm in Embodiment 2 of this application (magnification of 10K). Detailed Implementation

[0035] 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.

[0036] In a first aspect, this application provides a composite membrane, the composite membrane comprising a membrane substrate and an electrolyte layer disposed on at least one surface of the membrane substrate;

[0037] The average roughness of the electrolyte layer is ΔH, where ΔH ≤ 1.0 μm. The electrolyte layer comprises inorganic nanotubes and solid electrolyte particles. The porosity of the inorganic nanotubes in the electrolyte layer is 0.2-5%.

[0038] When the composite separator of this application is applied to a battery, it not only has close interfacial contact with the battery electrodes, low interfacial porosity, excellent heat resistance and electrolyte wettability, but also has excellent lithium-ion transport performance. This can reduce the internal resistance of lithium-ion batteries and improve their rate performance, storage stability and cycle performance. The main reasons are as follows: First, both solid electrolyte particles and inorganic nanotubes have excellent heat resistance, which can improve the heat resistance of the composite separator. During the charging and discharging process of the battery, the composite separator can maintain its complete morphology, avoiding short circuits between the positive and negative electrodes caused by thermal shrinkage during charging and discharging. In particular, inorganic nanotubes have a one-dimensional nanostructure, which can further improve the heat resistance of the composite separator after bonding with the separator substrate. At the same time, solid electrolyte particles and inorganic nanotubes can also improve the electrolyte wettability of the composite separator. Second, the solid electrolyte particles in the composite separator can promote the lithium-ion transport performance, and during the charging and discharging process of the battery, the solid electrolyte particles can undergo redox reactions with the battery electrodes to form a dense interfacial film on the surface of the composite separator, improving the battery cycle life. While improving performance, the formation of a dense interfacial film can significantly increase the battery's internal resistance, affecting the full release of battery performance (e.g., energy density, rate performance). Inorganic nanotubes not only provide more channels for lithium-ion transport, but also form nanochannels on the surface of the interfacial film during the formation of the solid electrolyte particles, thus transporting lithium ions and preventing a decline in battery performance during the interfacial film formation process. The applicant's research also found that when the porosity of inorganic nanotubes is 0.2-5%, it not only helps to improve the ion transport efficiency of the composite separator and reduce the battery's internal resistance, thereby improving the battery's electrochemical performance, but also enables excellent adhesion between the electrolyte layer and the separator substrate, preventing the separator substrate from detaching from the electrolyte layer during battery charging and discharging, thereby effectively improving the battery's safety performance. Thirdly, the surface smoothness of the electrolyte layer affects the interfacial bonding tightness between the composite separator and the positive and negative electrodes of the battery. If ΔH is greater than 1.0 μm, it will cause large interfacial porosity, affecting the ion transport efficiency at the interface, thereby increasing the internal resistance of the battery and consequently affecting the charge-discharge performance and cycle life of the battery. In addition, large differences in the surface smoothness of the separator will lead to significant differences in the interfacial adhesion mechanical properties between the separator and the electrode, resulting in uneven lithium ion transport at the interface and significant differences in the difficulty of lithium ion release across the entire interface. This will make the battery prone to self-discharge and affect the uniformity of the battery. Therefore, this application improves the interfacial bonding tightness between the composite separator and the electrode by controlling the surface smoothness of the electrolyte layer to make the height difference ΔH of the electrolyte layer ≤ 1.0 μm, thereby further reducing the internal resistance of the battery.

[0039] This application does not impose any particular restrictions on the control methods of the porosity of inorganic nanotubes in the electrolyte layer and the height difference of the electrolyte layer. As long as the above-mentioned characteristics are within the range, the control method corresponding to the purpose can be freely selected.

[0040] In this application, ΔH refers to the average height difference between the highest and lowest points on the surface of the electrolyte layer, which can be obtained by atomic force microscopy.

[0041] In one specific implementation, ΔH is tested through the following process:

[0042] Take a 1cm×1cm composite diaphragm sample and select 16 points for roughness characterization. Calculate the average height difference of each point as the average height difference of the coated diaphragm. The height difference characterization method is performed according to the thin film roughness characterization method specified in the national standard GB / T 31227-2014 "Method for measuring the surface roughness of sputtered thin films using atomic force microscopy".

[0043] 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 an electrolyte layer on one surface of the diaphragm substrate, or by depositing electrolyte layers on both surfaces of the diaphragm substrate.

[0044] 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.

[0045] 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.

[0046] A coated polyolefin porous membrane refers to a polyolefin porous membrane with a coating on at least one surface. The coating is not specifically limited in this application; those skilled in the art can select commonly used coatings as needed. For example, the coating may include at least one of alumina, boehmite, nanofibers, polyimide, aramid fibers, polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF). In some embodiments, the coated polyolefin porous membrane may 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, or a PVDF-coated polyolefin porous membrane. The coated polyolefin porous membrane may also be a polyolefin porous membrane coated with a mixture of nanofibers and alumina, a polyolefin porous membrane coated with a mixture of PVDF and alumina, or a polyolefin porous membrane coated with a mixture of PMMA and alumina.

[0047] 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 electrolyte layer. In some embodiments, the porosity of the inorganic nanotubes can be obtained using Equation 1:

[0048] In Equation 1, x represents the total mass based on the electrolyte layer and the mass percentage of inorganic nanotubes.

[0049] ρ is the tap density of the inorganic nanotubes, in g / cm³. 3 ;

[0050] d1 is the outer diameter of the inorganic nanotube, in nm;

[0051] d2 is the inner diameter of the inorganic nanotube, in nm;

[0052] m1 is the mass of the diaphragm substrate per unit area, in g / cm³. 2 ;

[0053] m2 is the mass of the composite membrane per unit area, in g / cm³. 2 ;

[0054] h is the thickness of the electrolyte layer, in cm.

[0055] For example, the porosity of the inorganic nanotubes can be any one of 0.2%, 0.3%, 0.4%, 0.47%, 0.5%, 0.61%, 0.7%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.1%, 2.3%, 2.5%, 2.7%, 2.86%, 2.9%, 3%, 3.5%, 4%, 4.2%, 4.5%, 5%, or any combination thereof.

[0056] Since the particle size ratio between solid electrolyte particles and inorganic nanotube particles in the composite membrane has a significant impact on the surface morphology smoothness of the electrolyte layer, resulting in a noticeable height difference in the electrolyte layer, in one specific embodiment, this application controls the average roughness to ΔH≤1.0μm through the following means:

[0057] The ratio between the particle size D99 of the solid electrolyte particles and the outer diameter of the inorganic nanotube is 0.3-14.

[0058] And / or, the ratio between the length of the inorganic nanotube and the D99 of the solid electrolyte particle is 0.3-18.

[0059] The outer diameter and length of the inorganic nanotubes can be obtained through SEM testing. In some implementations, the length of the inorganic nanotubes can be obtained according to the industry standard JY / T 0584-2020 "General Rules for Analysis Methods of Scanning Electron Microscopy".

[0060] For example, the ratio between the particle size D99 of the solid electrolyte particles and the outer diameter of the inorganic nanotubes is a range of any one or any two of the following: 14, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.5, 1.22, 1, 0.5, 0.3.

[0061] For example, the ratio between the length of the inorganic nanotube and the D99 of the solid electrolyte particle is a range of any one or any two of the following: 18, 17, 16, 14, 10, 9.5, 9, 8, 7, 6, 5, 4.1, 4, 3, 2.4, 2, 1, 0.7, 0.5, 0.3.

[0062] When the ratio between the particle size D99 of the solid electrolyte particles and the outer diameter of the inorganic nanotubes and / or the length of the inorganic nanotubes and the D99 of the solid electrolyte particles satisfy the above relationship, the inorganic nanotubes and the solid electrolyte can be better matched to obtain a denser electrolyte layer, thereby further improving the overall performance of the composite membrane.

[0063] 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.

[0064] In one specific embodiment, the inner diameter of the inorganic nanotube is 3-80 nm; for example, the inner diameter of the inorganic nanotube can be any one of 3 nm, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 70 nm, 80 nm, or any combination thereof.

[0065] 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.

[0066] The applicant also discovered that when the length of the inorganic nanotubes is 300-3000 nm, the inorganic nanotubes can overlap more tightly, resulting in a more uniform and dense distribution of pores in the electrolyte 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 a combination of any two of the following: 300 nm, 500 nm, 800 nm, 1000 nm, 1200 nm, 1500 nm, 1700 nm, 1900 nm, 2000 nm, 2300 nm, 2500 nm, 2700 nm, 2900 nm, and 3000 nm. Further, the length of the inorganic nanotubes is 300-2000 nm.

[0067] In one specific embodiment, the ratio of the outer diameter to the inner diameter of the inorganic nanotube is 1.5-20:1.

[0068] 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, 1.9:1, 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, 17.3:1, 18:1, 19:1, 20:1; furthermore, the ratio of the outer diameter to the inner diameter of the inorganic nanotube is 2-15:1.

[0069] 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.

[0070] 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 involves obtaining a TEM image of the electrolyte 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 electrolyte layer, and the inner and outer diameters of the inorganic nanotubes can be obtained by measuring with a scale.

[0071] 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".

[0072] The particle size distribution (SPAN) of the solid electrolyte particles is not particularly limited. Based on the consideration of further improving the overall performance of the composite membrane and thereby reducing the angle inside the interface, in some embodiments of this application, the particle size distribution (SPAN) of the solid electrolyte particles is ≤1.5.

[0073] For example, the particle size distribution of the solid electrolyte 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 solid electrolyte particles is 0.8 to 1.5.

[0074] In some implementations, the D10, D50, and D90 of solid electrolyte particles can be tested using a laser particle size analyzer, and then the particle size distribution SPAN of the solid electrolyte particles can be calculated according to Equation 2.

[0075] SPAN = (D90 - D10) / D50 (Equation 2)

[0076] In some embodiments, the particle size of the solid electrolyte particles can be determined using conventional techniques known in the art. For example, the D50, D90, and D10 of the solid electrolyte particles can be characterized using a laser scattering particle size analyzer (Malvin ZEN3690 particle size analyzer). Specifically, this includes dispersing the solid electrolyte particles in pure water and obtaining the D50, D90, and D10 of the solid electrolyte particles. Alternatively, the electrolyte layer can be scanned using a scanning electron microscope (SEM), and the D50, D90, and D10 of the solid electrolyte 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 solid electrolyte particles, the particle size corresponding to a cumulative particle size distribution percentage of 50% is the D50 of the solid electrolyte particles, and the particle size corresponding to a cumulative particle size distribution percentage of 90% is the D90 of the solid electrolyte particles.

[0077] In one specific embodiment, the solid electrolyte particles include at least one of lithium titanium aluminum phosphate and lithium titanium aluminum phosphate doped with a doping element, lithium germanium aluminum phosphate and lithium germanium aluminum phosphate doped with a doping element, lithium lanthanum zirconium oxide and lithium lanthanum zirconium oxide doped with a doping element, and lithium lanthanum zirconium tantalum oxide and lithium lanthanum zirconium oxide doped with a doping element; the doping element in the solid electrolyte particles includes at least one of silicon, tantalum, bismuth, iron, yttrium, indium, lutetium, gallium, rubidium, chromium, iron, aluminum, cerium, strontium, germanium, zinc, magnesium, and tungsten.

[0078] In one specific embodiment, the inorganic nanotubes are selected from non-conductive materials.

[0079] In some embodiments, 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.

[0080] As described above, the solid electrolyte particles exhibit higher heat resistance and mechanical strength, further ensuring the composite separator maintains its intact morphology during battery charging and discharging. This prevents short circuits between the positive and negative electrodes caused by thermal shrinkage of the composite separator during charging and discharging. The inorganic nanotubes described above are non-conductive materials, avoiding micro-short circuits caused by conductive materials. Furthermore, the higher mechanical strength of these inorganic nanotubes ensures rapid lithium-ion transport within the composite separator while also ensuring tighter overlap and better adhesion between the nanotubes, resulting in a more robust network structure.

[0081] In one specific embodiment, the inorganic nanotubes comprise 5-60% of the total mass of the electrolyte layer.

[0082] For example, based on the total mass of the electrolyte layer, the mass percentage of inorganic nanotubes can be any or any combination of 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 electrolyte layer, the mass percentage of inorganic nanotubes is 10%-50%, and even further, based on the total mass of the electrolyte layer, the mass percentage of inorganic nanotubes is 13%-50%.

[0083] When the mass percentage of inorganic nanotubes meets the above range, inorganic nanotubes and solid electrolyte particles can form a better particle-nanotube uniformly distributed "point-line" nanonetwork 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.

[0084] In some embodiments of this application, the composite membrane satisfies at least one of the following:

[0085] a. The thickness of the diaphragm substrate is 5-30μm;

[0086] b. The thickness of the electrolyte layer is 0.5-4 μm.

[0087] c. The areal density of the electrolyte layer is 2-5 g / m³ 2 .

[0088] Composite separators that meet any of the above conditions can further improve the electrochemical performance of batteries when applied to them.

[0089] The thickness of the electrolyte layer mentioned above refers to the thickness of a single electrolyte layer. The thickness of the electrolyte layer can be determined using conventional techniques known in the art, such as obtaining the thickness of the electrolyte layer according to the test methods specified in national standard GB / T 36363-2018, or by measuring the thickness of the electrolyte layer using scanning electron microscopy. It should be noted that the electrolyte layer thickness refers to the thickness of a single electrolyte layer; that is, when electrolyte layers are provided on both surfaces of the membrane substrate, the thickness of the electrolyte layer refers to the thickness of the electrolyte layer provided on one of the surfaces of the membrane substrate.

[0090] The areal density 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.

[0091] 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.

[0092] In some embodiments of this application, the areal density of the diaphragm substrate is 3.5–10.0 g / m³. 2 .

[0093] In this application, in order to improve the adhesion between the electrolyte layer and the diaphragm substrate, and to enable the electrolyte layer to adhere more tightly to the surface of the diaphragm substrate, the electrolyte layer also includes an adhesive.

[0094] 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.

[0095] 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.

[0096] In some embodiments of this application, the mass percentage of the binder is 3-10% based on the total mass of the electrolyte layer.

[0097] In the diaphragm of this application, the electrolyte 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 to improve dispersibility, coatability, or storage stability. In the electrolyte slurry used to form the electrolyte layer, thickeners are added to improve storage stability. In the electrolyte slurry used to form the electrolyte layer, wetting agents are added to improve coating uniformity. In the coating solution used to form the composite ceramic layer, pH adjusters are added, for example, to adjust the 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 is 0.1-3% based on the total mass of the electrolyte 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] Thirdly, this application provides a method for preparing a composite separator, comprising the following steps:

[0106] S1. A mixed system is prepared by mixing materials including inorganic nanotubes, solid electrolyte particles and dispersing reagents;

[0107] S2. Filter the mixture to obtain a slurry;

[0108] S3. The slurry is coated onto at least one surface of the substrate and dried to obtain a composite diaphragm.

[0109] In one specific embodiment, the preparation of the composite membrane may include the following process:

[0110] S1. Add inorganic nanotubes to the dispersing agent, mill and disperse at high speed to obtain an inorganic nanotube dispersion system; add solid electrolyte material to the inorganic nanotube dispersion system, and continue to disperse at high speed to obtain a mixed system.

[0111] S2. Filter the above mixture through a 500-800 mesh filter to remove agglomerated large particles and obtain a slurry;

[0112] S3. The slurry is coated onto at least one surface of the substrate, and after drying, a composite diaphragm is obtained.

[0113] The dispersing agent in step S1 can be at least one of water, ethanol, acetone, and N-methylpyrrolidone.

[0114] In some embodiments, at least one of a dispersant, a wetting agent, a binder, and a thickener may be added to the dispersant to form a mixed system in step S3;

[0115] In some embodiments, step S1 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 mill 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; and finally adding a wetting agent and stirring and dispersing for 10–60 min to obtain a coating slurry.

[0116] In some embodiments, the stirring and dispersing speed can be 1000–5000 r / min;

[0117] In some embodiments, the solid content of the coating slurry can be ≤45wt%.

[0118] Thirdly, this application provides a battery including the composite separator of the first aspect.

[0119] 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.

[0120] 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.

[0121] The present application will be further described below with reference to specific embodiments:

[0122] Example 1

[0123] The composite membrane in this example includes a membrane substrate and an electrolyte layer disposed on two surfaces of the membrane substrate; the electrolyte layer includes inorganic nanotubes, solid electrolyte particles, dispersant, binder, thickener and wetting agent;

[0124] Among them, the inorganic nanotubes are halloysite nanotubes. In the electrolyte layer, the porosity (P) of the inorganic nanotubes is 1.22%, the inner diameter d2 of the inorganic nanotubes is 20 nm, 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 1 μm; the average roughness of the electrolyte layer is ΔH = 0.4 μm.

[0125] The solid electrolyte particles are lithium aluminum titanium phosphate (LATP), with a particle size distribution (SPAN) of 0.9, a particle size distribution (D10) greater than 20 nm, a length-to-D99 ratio (L:D99) of 1.25 for the inorganic nanotubes, and a ratio (D99:d1) of 10 between the D99 particle size of the solid electrolyte particles and the outer diameter of the inorganic nanotubes.

[0126] Based on the total mass of the electrolyte 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 solid electrolyte particles (W2) is 64.1%.

[0127] 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 electrolyte layer.

[0128] The battery in this example is prepared by a method including the following steps:

[0129] 1) Preparation of composite membrane

[0130] The dispersant was added to deionized water and stirred for 30 min. Inorganic nanotubes were added separately and dispersed at high speed by shearing and by sand milling for 60 min. The sand mill was removed, and then solid electrolyte particles were added 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. The mixture was then filtered through a 500-800 mesh screen to remove large agglomerated particles, thus preparing the coating slurry.

[0131] 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 an electrolyte layer.

[0132] 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.).

[0133] 2) Battery manufacturing

[0134] 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;

[0135] 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.

[0136] 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.

[0137] 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.

[0138] Example 2-15

[0139] 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.

[0140] Comparative Example 1

[0141] 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.

[0142] Comparative Example 2

[0143] 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 solid electrolyte particles, as shown in Table 1.

[0144] Comparative Example 3

[0145] The preparation methods of the composite separator and battery in Comparative Example 3 are basically the same as those in Example 1, except that some parameters are different from those in Example 1, as detailed in Table 1.

[0146] Comparative Example 4

[0147] The preparation methods of the composite separator and battery in Comparative Example 4 are basically the same as those in Example 1, except that:

[0148] 1) In the preparation of the composite membrane, the dispersant was added to deionized water and stirred for 30 min; inorganic nanotubes were added separately and dispersed by high-speed shearing and sand milling for 60 min. The sand mill was removed, and then solid electrolyte particles were added and stirred for another 60 min; then the binder was added and stirred for 30 min; then 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.

[0149] Some other parameters differ from those in Example 1, as detailed in Table 1.

[0150] Performance testing

[0151] 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.

[0152] 1. Morphological characteristics

[0153] SEM images of the composite diaphragm were obtained according to the methods specified in industry standard JY / T 0584-2020 "General Rules for Analysis Methods of Scanning Electron Microscopy".

[0154] Figure 1 is a surface SEM image of the composite membrane in Embodiment 2 of this application; Figure 2 is a cross-sectional SEM image of the composite membrane in Embodiment 2 of this application. As can be seen from Figure 1, the surface of the composite membrane has a granular structure and a tubular structure, indicating that the electrolyte layer of the composite membrane includes inorganic nanotubes and solid electrolyte particles; as can be seen from Figure 2, the interface of the composite membrane has two distinct layers, indicating that the composite membrane includes a membrane substrate and an electrolyte layer disposed on at least one surface of the membrane substrate.

[0155] 2. Heat shrinkage rate

[0156] 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.

[0157] 3. Ratio performance

[0158] 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.

[0159] 4. Cyclic performance

[0160] The cycle performance of the battery, namely the capacity retention rate after 1000 cycles at a 1C rate, is 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".

[0161] 5. Hot Box Performance Test

[0162] 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.

[0163] 6. Thickness

[0164] 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 electrolyte layer. The average value was then used as the thickness of the single electrolyte layer.

[0165] 7. Battery storage performance (self-discharge) characterization

[0166] The self-discharge performance of composite membrane assembled batteries was tested according to the methods specified in the national standard GB / T 31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles".

[0167] 8. Low temperature performance

[0168] The ambient temperature for battery testing was adjusted to -20℃ using a high and low temperature control chamber. Then, the low-temperature discharge 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". Specifically, the battery discharge performance at -20℃ was tested at a 1C rate.

[0169] Table 1:

[0170] Table 2

[0171] As shown in Table 1, compared with the comparative example, the composite separator in this application can significantly improve the rate performance, cycle performance, storage performance, and safety performance of the battery when applied to a battery. This indicates that by adding inorganic nanotubes to the electrolyte layer and controlling the porosity of the inorganic nanotubes in the electrolyte layer to prepare the composite separator, the electrochemical performance of the battery can be improved.

[0172] Furthermore, as can be seen from Examples 1-2 and Examples 6 and 9, further selection of the mass percentage of inorganic nanotubes can improve the peel strength and thermal shrinkage performance of the composite separator, thereby improving the rate performance and cycle performance of the battery.

[0173] As can be seen from Examples 1 and 7-8, the ratio of the length of the inorganic nanotube to the D99 of the solid electrolyte particles can affect the thermal shrinkage performance of the composite membrane, and affect the rate performance, cycle performance, storage performance and low-temperature discharge performance of the lithium battery assembled using the composite membrane.

[0174] As can be seen from Example 1 and Comparative Example 4, by further selecting the ratio between the particle size D99 of the solid electrolyte particles and the outer diameter of the inorganic nanotubes, the average roughness of the composite film can be affected, which in turn affects the rate performance, cycle performance, storage performance and low-temperature discharge performance of the lithium battery.

[0175] As can be seen from Examples 1 and Examples 4-5 and 13, by further selecting the inner diameter of inorganic nanotubes, the rate performance, cycle performance, storage performance and low-temperature discharge performance of the battery can be improved.

[0176] As can be seen from Examples 1 and 7-8, 14, the heat shrinkage resistance of the composite separator can be improved by increasing the length of the inorganic nanotubes, and the rate performance, storage performance, cycle performance and low-temperature discharge performance of the lithium battery assembled with the composite separator can be improved.

[0177] 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

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