Composite separator and use thereof

Abstract

A composite separator and the use thereof. The composite separator comprises a separator substrate and an electrolyte layer arranged on at least one surface of the separator substrate, wherein the electrolyte layer at least comprises inorganic nanotubes and solid electrolyte particles; and in the electrolyte layer, the through-hole ratio of the inorganic nanotubes is 0.2-5%. When used in a battery, the composite separator not only has good heat resistance and electrolyte wettability, but also has good lithium-ion transport performance, and thus can reduce the internal resistance of a lithium-ion battery and improve the rate capability and cycle performance of the lithium-ion battery.

Description

A composite diaphragm and its application Technical Field

[0001] The embodiments of the present application relate to a composite diaphragm and its application, belonging to the field of energy technology. Background Art

[0002] The diaphragm is placed between the positive and negative electrodes of a lithium-ion battery to prevent direct contact between the two electrodes, which could cause a short circuit. The performance of the diaphragm directly impacts the performance of the lithium-ion battery. However, currently used polyolefin diaphragms suffer from low melting points and poor electrolyte wettability. During the use of lithium-ion batteries, the diaphragm easily shrinks, causing contact between the positive and negative electrodes and resulting in a short circuit. This not only shortens the battery's lifespan but also poses a safety hazard.

[0003] To address this issue, existing technologies have employed coatings of common ceramics, such as alumina and boehmite, or thermoplastic resins, such as PVDF, polyimide, and aramid, on the surface of polyolefin separators to improve their heat resistance and electrolyte wettability. However, this approach can reduce lithium ion transport performance and increase the internal resistance of lithium-ion batteries.

[0004] Summary of the Invention

[0005] The present application provides a composite diaphragm, which, when applied to a battery, not only has excellent heat resistance and electrolyte wettability, but also has excellent lithium ion transmission performance, can reduce the internal resistance of the lithium ion battery, and improve the rate performance and cycle performance of the lithium ion battery.

[0006] The present application provides a battery, which includes the above-mentioned composite separator, so that the battery has excellent safety performance, rate performance and cycle performance.

[0007] The present application provides a composite diaphragm, wherein the composite diaphragm comprises a diaphragm substrate and an electrolyte layer provided on at least one surface of the diaphragm substrate;

[0008] The electrolyte layer comprises at least inorganic nanotubes and solid electrolyte particles;

[0009] In the electrolyte layer, the through-porosity of the inorganic nanotubes is 0.2-5%.

[0010] The composite separator as described above, wherein the mass percentage of the inorganic nanotubes is 5-60% based on the total mass of the electrolyte layer.

[0011] The composite diaphragm as described above, wherein the inner diameter of the inorganic nanotubes is 3-150 nm.

[0012] The composite diaphragm as described above, wherein the ratio of the outer diameter of the inorganic nanotube to the inner diameter of the inorganic nanotube is (1.5-20):1.

[0013] The composite membrane as described above, wherein the length of the inorganic nanotubes is 0.3-5 μm.

[0014] The composite separator as described above, wherein the ratio of the length of the inorganic nanotubes to the D50 of the solid electrolyte particles is greater than 0 and not greater than 30.

[0015] The composite membrane as described above, wherein the particle size distribution of the solid electrolyte particles is ≤1.5.

[0016] The composite diaphragm as described above, wherein the composite diaphragm satisfies at least one of the following conditions:

[0017] a. The thickness of the diaphragm substrate is 5-30 μm;

[0018] b. The thickness of the electrolyte layer is 0.5-4 μm.

[0019] The composite separator as described above, wherein the electrolyte layer further comprises at least one of a dispersant, a wetting agent, a binder and a thickener.

[0020] The composite diaphragm as described above, wherein the composite diaphragm satisfies at least one of the following conditions:

[0021] a. Based on the total mass of the electrolyte layer, the mass percentage of the binder is 3-10%;

[0022] b. Based on the total mass of the electrolyte layer, the mass percentage of the dispersant is 0.1-1.5%;

[0023] c. Based on the total mass of the electrolyte layer, the mass percentage of the thickener is 0.1-3%;

[0024] d. Based on the total mass of the electrolyte layer, the mass percentage of the wetting agent is 0.1-1.5%.

[0025] The present application provides a battery, which includes the composite separator as described above.

[0026] The composite diaphragm of the present application comprises a diaphragm substrate and an electrolyte layer disposed on at least one surface of the diaphragm substrate. The electrolyte layer comprises at least inorganic nanotubes and solid electrolyte particles, and the inorganic nanotubes in the electrolyte layer have a through-porosity of 0.2-5%. When used in batteries, this composite diaphragm not only exhibits excellent heat resistance and electrolyte wettability, but also exhibits excellent lithium ion transport properties, thereby reducing the internal resistance of lithium-ion batteries and improving their rate performance and cycle performance.

[0027] The battery of the present application, because it includes the above-mentioned separator, has excellent electrochemical performance and can be widely promoted and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a surface SEM image of the composite diaphragm in Example 2 of the present application (magnification is 10K);

[0029] FIG2 is a cross-sectional SEM image of the composite diaphragm in Example 2 of the present application (magnification is 10K). DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] A first aspect of the present application provides a composite diaphragm, the composite diaphragm comprising a diaphragm substrate and an electrolyte layer disposed on at least one surface of the diaphragm substrate;

[0032] The electrolyte layer includes at least inorganic nanotubes and solid electrolyte particles;

[0033] In the electrolyte layer, the through-porosity of the inorganic nanotubes is 0.2 to 5%.

[0034] In this application, the surface of the diaphragm substrate refers to the two surfaces of the diaphragm substrate with the largest area and arranged opposite each other. In this application, an electrolyte layer can be arranged on one surface of the diaphragm substrate to form a composite diaphragm, or an electrolyte layer can be arranged on both surfaces of the diaphragm substrate to form a composite diaphragm.

[0035] The present application does not particularly limit the diaphragm substrate, and the diaphragm substrate may be a porous membrane commonly used in the art. For example, the diaphragm substrate may be a polyolefin porous membrane, or a polyolefin porous membrane provided with a coating layer.

[0036] The polyolefin porous membrane may be a polyethylene porous membrane, a polypropylene porous membrane, or a polyethylene-polypropylene multilayer composite membrane. The polyethylene-polypropylene multilayer composite membrane refers to a multilayer composite porous membrane formed by stacking polypropylene (PP) and polyethylene (PE) in any order, for example, a PP-PE-PP three-layer composite membrane, a PP-PE two-layer composite membrane, or a PP-PP-PE-PP four-layer composite membrane.

[0037] The polyolefin porous membrane provided with a coating layer refers to a polyolefin porous membrane having at least one surface provided with a coating layer. The coating layer is not particularly limited and can be selected according to demand. The coating layer commonly used in the art can be, for example, a coating layer comprising at least one of aluminum oxide, boehmite, nanofiber, polyimide, PMMA, and PVDF. For example, the polyolefin porous membrane provided with a coating layer can be aluminum oxide coated polyolefin porous membrane, boehmite coated polyolefin porous membrane, nanofiber coated polyolefin porous membrane, polyimide coated polyolefin porous membrane, PMMA coated polyolefin porous membrane, or PVDF coated polyolefin porous membrane; the polyolefin porous membrane provided with a coating layer can also be a polyolefin porous membrane coated with a mixture of nanofiber and aluminum oxide, a polyolefin porous membrane coated with a mixture of PVDF and aluminum oxide, or a porous membrane coated with a mixture of PMMA and aluminum oxide.

[0038] The electrolyte layer of the present application includes at least inorganic nanotubes and solid electrolyte particles. The present application does not specifically limit the material of the inorganic nanotubes. The inorganic nanotubes can be tubular inorganic nanomaterials commonly used in the art. For example, the inorganic nanotubes can be at least one of titanium dioxide nanotubes, silicon nanotubes, halloysite nanotubes, aluminum oxide nanotubes, zinc oxide nanotubes, boron nitride nanotubes and silicon carbide nanotubes. The present application does not specifically limit the solid electrolyte particles. The solid electrolyte can be a solid electrolyte commonly used in the art. For example, the solid electrolyte can be at least one of LATP, LAGP, LLZO and LLZTO. Further, the solid electrolyte can be LATP.

[0039] In this application, the through-porosity of the inorganic nanotubes refers to the ratio of the pore volume provided by the through-pores of the inorganic nanotubes to the total volume of the electrolyte layer. In some embodiments, the through-porosity of the inorganic nanotubes can be obtained by formula 1:

[0040] In formula 1, x is the mass percentage of the inorganic nanotubes based on the total mass of the electrolyte layer;

[0041] ρ is the tap density of inorganic nanotubes, g / cm 3 ;

[0042] d1 is the outer diameter of the inorganic nanotube, nm;

[0043] d2 is the inner diameter of the inorganic nanotube, nm;

[0044] m1 is the mass of the diaphragm substrate per unit area, g / cm 2 ;

[0045] m2 is the mass of the composite diaphragm per unit area, g / cm 2 ;

[0046] h is the thickness of the electrolyte layer, cm.

[0047] Among them, the inner diameter and outer diameter of the inorganic nanotubes can be determined by conventional techniques known in the art, for example, they can be obtained by field emission transmission electron microscopy (TEM), specifically including: obtaining a TEM image of the electrolyte layer in accordance with GB / T18907-2013 "Microbeam analysis electron microscopy transmission electron microscope selected area electron diffraction analysis method", through the TEM image of the electrolyte layer, the hollow structure of the inorganic nanotubes can be clearly observed, and the inner diameter and outer diameter of the inorganic nanotubes can be obtained by measuring with a ruler.

[0048] The tap density of the inorganic nanotubes can be determined by conventional techniques known in the art, for example, by testing according to GBT 21354-2008, “General method for determination of tap density of powder products”.

[0049] The mass per unit area of ​​the separator substrate can be determined by conventional techniques known in the art, such as the weighing method. Specifically, the separator substrate can be cut into 5 cm×5 cm pieces, the sample weight can be weighed, and the mass per unit area of ​​the separator substrate can be obtained by calculation.

[0050] The mass per unit area of ​​the composite membrane can be determined by conventional techniques known in the art, such as the weighing method. Specifically, the composite membrane can be cut into 5 cm×5 cm pieces, the sample weight can be weighed, and the mass per unit area of ​​the composite membrane can be obtained by calculation.

[0051] The thickness of the electrolyte layer can be determined by conventional techniques known in the art, such as obtaining the thickness of the electrolyte layer according to the test method specified in the national standard GB / T 36363-2018, or obtaining the thickness of the electrolyte layer by scanning electron microscopy. It should be noted that the electrolyte layer thickness refers to the thickness of a single electrolyte layer. That is, when the electrolyte layer is provided on both surfaces of the separator substrate, the electrolyte layer thickness refers to the thickness of the electrolyte layer provided on one surface of the separator substrate.

[0052] For example, the through-porosity of the inorganic nanotubes can be in a range of any one 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%, 5%, or any combination thereof. Furthermore, the through-porosity of the inorganic nanotubes is 0.2-3%.

[0053] In the present application, both the solid electrolyte particles and the inorganic nanotubes have excellent heat resistance, which can improve the heat resistance of the composite diaphragm. During the charge and discharge process of the battery, the composite diaphragm can still maintain its complete morphology, avoiding the short circuit between the positive and negative electrodes caused by the heat shrinkage of the composite diaphragm during the charge and discharge process of the battery. In particular, the inorganic nanotubes have a one-dimensional nanostructure, which can further improve the heat resistance of the composite diaphragm after bonding with the diaphragm substrate; at the same time, the solid electrolyte particles and the inorganic nanotubes can also improve the electrolyte wettability of the composite diaphragm.

[0054] Furthermore, the solid electrolyte in the composite membrane can promote the transmission performance of lithium ions, and during the charge and discharge process of the battery, the solid electrolyte can undergo redox reactions with the battery electrodes, forming a dense interface film on the surface of the composite membrane, thereby improving the cycle performance of the battery. However, the formation of a dense interface film can also lead to a significant increase in the internal resistance of the battery, affecting the complete release of battery performance (such as energy density and rate performance). Inorganic nanotubes can not only provide more channels for the transmission of lithium ions, but also form nanochannels on the surface of the interface film during the process of the solid electrolyte particles forming the interface film, and transmit lithium ions, thereby avoiding the degradation of battery performance during the formation of the interface film. Therefore, the composite membrane including inorganic nanotubes and solid electrolyte particles has excellent lithium ion transmission performance and heat shrinkage resistance. When applied to batteries, it can significantly improve the safety performance, rate performance, cycle performance and energy density of lithium-ion batteries.

[0055] The inventors also discovered that when the through-porosity of the inorganic nanotubes in the electrolyte layer is 0.2-5%, it not only helps improve the ion transmission efficiency of the composite separator, reducing the internal resistance of the battery, thereby improving the battery's electrochemical performance, but also ensures excellent adhesion between the electrolyte layer and the separator substrate, preventing the separator substrate and the electrolyte layer from falling off during the battery's charge and discharge process, thereby effectively improving the battery's safety performance. Therefore, when the composite separator of the present application is used in a battery, it can significantly improve the battery's safety performance, rate performance, cycle performance, and energy density.

[0056] The present application does not impose any particular restrictions on the method for regulating the through-porosity of the inorganic nanotubes in the electrolyte layer. As long as the aforementioned characteristics are met, a regulating method corresponding to the purpose can be freely selected.

[0057] As a preferred technical solution of this application, to further improve the overall performance of the composite separator, this application can control parameters such as the amount of inorganic nanotubes used, the inner diameter and outer diameter of the inorganic nanotubes. In some embodiments of this application, the weight percentage of the inorganic nanotubes is 5-60% based on the total weight of the electrolyte layer.

[0058] For example, the mass percentage of the inorganic nanotubes based on the total mass of the electrolyte layer may be any one of 5%, 10%, 13%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 55%, 60%, or any two thereof. Furthermore, the mass percentage of the inorganic nanotubes based on the total mass of the electrolyte layer may be 10%-50%, and further, the mass percentage of the inorganic nanotubes based on the total mass of the electrolyte layer may be 13%-50%.

[0059] When the mass percentage of the inorganic nanotubes meets the above range, the inorganic nanotubes and the solid electrolyte particles can form a better "point-line" nanonetwork structure with uniform distribution of particles and nanotubes, so that good adhesion performance is obtained between the solid electrolyte composite coating layer and the diaphragm substrate, and the lithium ion transmission performance of the composite diaphragm can be improved, thereby obtaining a composite diaphragm with excellent comprehensive performance.

[0060] In some embodiments of the present application, the inner diameter of the inorganic nanotube is 3-150 nm. For example, the inner diameter of the inorganic nanotube can be any one of 3 nm, 10 nm, 20 nm, 40 nm, 60 nm, 100 nm, 130 nm, and 150 nm, or a range consisting of any two thereof.

[0061] Furthermore, the inner diameter of the inorganic nanotube is 5-150 nm.

[0062] When the inner diameter of the inorganic nanotubes meets the above range, it can provide more transmission channels for lithium ions, enabling lithium ions to be quickly transmitted in the composite diaphragm, so that when the composite diaphragm is applied to the battery, it can further reduce the internal resistance of the battery and improve the battery's rate performance and energy density.

[0063] In some embodiments of the present application, the ratio of the outer diameter of the inorganic nanotube to the inner diameter of the inorganic nanotube is (1.5-20):1.

[0064] The ratio of the outer diameter of the inorganic nanotube to the inner diameter of the inorganic nanotube can be any one of 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, and 20:1, or a range consisting of any two of the above. Further, the ratio of the outer diameter of the inorganic nanotube to the inner diameter of the inorganic nanotube is (2-15):1.

[0065] When the ratio of the outer diameter to the inner diameter of the inorganic nanotubes meets the above range, while ensuring the rapid transmission of lithium ions in the composite separator, it further ensures that the inorganic nanotubes are more closely overlapped and better bonded to each other, and the network structure formed is stronger.

[0066] The inventors also discovered that when the length of the inorganic nanotubes is 0.3-5 μm, the inorganic nanotubes can overlap more closely, making the through-pore distribution of the inorganic nanotubes in the electrolyte layer more uniform and dense, which is not only more conducive to the transmission of lithium ions, but also the network structure formed by the dense stacking of the inorganic nanotubes is more conducive to improving the heat resistance of the composite separator. For example, the length of the inorganic nanotubes can be in the range of any one 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, or any two thereof. Furthermore, the length of the inorganic nanotubes is 0.3-2 μm.

[0067] In some embodiments, the length of the inorganic nanotubes can be obtained according to the industry standard JY / T 0584-2020 "General Rules for Scanning Electron Microscope Analysis Methods".

[0068] In some embodiments of the present application, the ratio of the length of the inorganic nanotube to the D50 of the solid electrolyte particle is greater than 0 and not greater than 30.

[0069] For example, the ratio of the length of the inorganic nanotubes to the D50 of the solid electrolyte particles can be any one of 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, and 1, or any two thereof. Furthermore, the ratio of the length of the inorganic nanotubes to the D50 of the solid electrolyte is ≤20.

[0070] When the length of the inorganic nanotubes and the D50 of the solid electrolyte particles satisfy the above relationship, the inorganic nanotubes and the solid electrolyte can be better matched to obtain a tighter electrolyte layer, thereby improving the overall performance of the composite membrane.

[0071] In some embodiments of the present application, the particle size distribution (SPAN) of the solid electrolyte particles is ≤1.5.

[0072] For example, the particle size distribution of the solid electrolyte particles may 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 consisting of any two thereof. Furthermore, the particle size distribution of the solid electrolyte particles is 0.8 to 1.5.

[0073] In some embodiments, the D10, D50, and D90 of the solid electrolyte particles can be measured by a laser force analyzer, and then the particle size distribution SPAN of the solid electrolyte particles can be calculated according to Formula 2;

[0074] SPAN = (D90 - D10) / D50 Formula 2.

[0075] When the particle size distribution of the solid electrolyte particles meets the above range, the inorganic nanotubes and the solid electrolyte particles can be better matched to obtain a tighter electrolyte layer, thereby improving the overall performance of the composite separator.

[0076] In some embodiments, the particle size of the solid electrolyte particles can be determined by conventional techniques known in the art. For example, a laser scattering particle size analyzer (Malvern ZEN3690 particle size analyzer) can be used to characterize the D50, D90, and D10 of the solid electrolyte particles, specifically including dispersing the solid electrolyte particles in pure water to obtain the D50, D90, and D10 of the solid electrolyte particles; the electrolyte layer can also be scanned by a scanning electron microscope (SEM), and the D50, D90, and D10 of the solid electrolyte can be obtained by statistically analyzing and calculating the scanning results (such as Image J software analysis and calculation). The particle size corresponding to the cumulative particle size distribution percentage reaching 10% is the D10 of the solid electrolyte particle, the particle size corresponding to the cumulative particle size distribution percentage reaching 50% is the D50 of the solid electrolyte particle, and the particle size corresponding to the cumulative particle size distribution percentage reaching 90% is the D90 of the solid electrolyte particle.

[0077] In some embodiments of the present application, when the composite membrane satisfies at least one of the following:

[0078] a. The thickness of the diaphragm substrate is 5-30 μm;

[0079] b. When the thickness of the electrolyte layer is 0.5 to 4 μm, the resulting composite separator can further enhance the electrochemical performance of the battery when used in the battery. The thickness of the electrolyte layer refers to the thickness of a single electrolyte layer.

[0080] In the present application, in order to improve the adhesion between the electrolyte layer and the separator substrate so that the electrolyte layer can be more closely attached to the surface of the separator substrate, the electrolyte layer further includes at least one of a dispersant, a wetting agent, a binder and a thickener.

[0081] The present application does not particularly limit the binder. For example, the binder can be at least one of polyacrylate copolymers, polyacrylamide copolymers, polyurethane copolymers, polyimide copolymers, polyetherimide copolymers, polyurea copolymers and styrene-butadiene rubber copolymers.

[0082] The present application does not particularly limit the dispersant. For example, the dispersant can be at least one of a sodium salt of a polyacrylate copolymer, an ammonium salt of a polyacrylate copolymer, and an ammonium salt of an alkanoate containing an acidic group.

[0083] The present application does not particularly limit the thickener. For example, the thickener can be at least one of sodium carboxymethyl cellulose, fumed silica, modified urea polymers, organic-modified silicates, organic-modified montmorillonites, and organic bentonites.

[0084] The present application does not particularly limit the wetting agent. For example, the wetting agent can be at least one of polyether siloxane copolymers, silicone twin structure copolymers, polyacrylate copolymers, polyether modified silicone oil copolymers and polyoxyethylene alkylamine copolymers.

[0085] The present application does not impose any particular limitation on the percentage by mass of the binder, dispersant, thickener, and wetting agent, and the added content may be freely selected according to the purpose.

[0086] As a preferred technical solution of this application, when the composite diaphragm meets at least one of the following:

[0087] a. Based on the total mass of the electrolyte layer, the mass percentage of the binder is 3-10%;

[0088] b. Based on the total mass of the electrolyte layer, the mass percentage of the dispersant is 0.1-1.5%;

[0089] c. Based on the total mass of the electrolyte layer, the mass percentage of the thickener is 0.1-3%;

[0090] d. Based on the total mass of the electrolyte layer, when the mass percentage of the wetting agent is 0.1-1.5%, the composite separator has better comprehensive performance. When applied to batteries, it can improve the electrochemical performance of the battery and broaden the application scenarios of the battery.

[0091] For example, based on the total mass of the electrolyte layer, the mass percentage of the binder can be any one of 3%, 4%, 5%, 7%, 9%, 10%, or a range consisting of any two thereof;

[0092] Based on the total mass of the electrolyte layer, the mass percentage of the dispersant is any one of 0.1%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, or a range consisting of any two thereof;

[0093] Based on the total mass of the electrolyte layer, the mass percentage of the thickener is any one of 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2.5%, 3%, or a range consisting of any two thereof;

[0094] The mass percentage of the wetting agent based on the total mass of the electrolyte layer is any one of 0.1%, 0.5%, 0.7%, 0.9%, 1.2%, 1.5%, or a range consisting of any two of them.

[0095] The present application does not impose any particular restrictions on the preparation method of the composite diaphragm. As long as a composite diaphragm that meets the various characteristic ranges described above is produced, the manufacturing method corresponding to the purpose can be freely selected.

[0096] In some embodiments, the composite membrane of the present application can be prepared by a method comprising the following steps:

[0097] 1) dispersing inorganic nanotubes and solid electrolyte particles in a solvent to obtain a coating slurry;

[0098] 2) The coating slurry is placed on at least one surface of the diaphragm substrate and dried to obtain a composite diaphragm.

[0099] The solvent in step 1) may be at least one of water, ethanol, acetone and N-methylpyrrolidone;

[0100] In some embodiments, in step 1), at least one of a dispersant, a wetting agent, a binder, and a thickener may be added to the solvent to form a coating slurry;

[0101] In some embodiments, step 1) may further include: adding a dispersant to a solvent and stirring and dispersing for 10 to 60 minutes; then adding inorganic nanotubes and solid electrolyte particles respectively, and continuing to stir and disperse for 10 to 240 minutes; then adding a binder and stirring and dispersing for 10 to 180 minutes; then adding a thickener and stirring and dispersing for 10 to 60 minutes; finally adding a wetting agent and stirring and dispersing for 10 to 60 minutes to obtain a coating slurry; the stirring and dispersing speed may be 1000 to 5000 r / min, and the solid content of the coating slurry may be ≤45%.

[0102] A second aspect of the present application provides a battery comprising the composite separator of the first aspect.

[0103] It is understood that the battery of the present application also includes a positive electrode sheet, a negative electrode sheet, and an outer packaging. In the present application, the positive electrode sheet, the composite separator, and the negative electrode sheet can be stacked to obtain an electrode assembly, which is then placed in an outer packaging, and an electrolyte is injected into the outer packaging, which is then sealed to obtain a battery.

[0104] Since the battery of the present application includes the above-mentioned composite diaphragm, it has excellent electrochemical performance and service life, and provides excellent user experience, and is suitable for wide promotion and application.

[0105] The technical solution of this application is described in detail below through specific embodiments.

[0106] Example 1

[0107] The battery of this embodiment is prepared by a method comprising the following steps:

[0108] 1) Preparation of composite diaphragm

[0109] The dispersant was added to deionized water and stirred and dispersed for 30 minutes; the inorganic nanotubes and solid electrolyte particles were added separately and stirred and dispersed for 60 minutes; the binder was then added and stirred and dispersed for 30 minutes; the thickener was then added and stirred and dispersed for 30 minutes; and finally the wetting agent was added and stirred and dispersed for 30 minutes to prepare a coating slurry;

[0110] The coating slurry is applied to both surfaces of the separator substrate by micro-concave roller coating, and then dried at 80° C. to obtain a composite separator including an electrolyte layer;

[0111] 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 (Kemite 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 organically modified bentonite (BP-188L, Shanghai Yantai Industrial Co., Ltd.), and the wetting agent was a polyether-modified silicone polymer (Kemite KMT-5514, Foshan Kening New Materials Co., Ltd.);

[0112] The inorganic nanotube is a halloysite nanotube, the inner diameter d2 of the inorganic nanotube is 20 nm, the ratio of the outer diameter of the inorganic nanotube to the inner diameter of the inorganic nanotube (d1:d2) is 3.5:1, and the length (L) of the inorganic nanotube is 1 μm;

[0113] The solid electrolyte particles are LATP, the particle size distribution (SPAN) of the solid electrolyte particles is 0.9, and the ratio of the length of the inorganic nanotubes to the D50 of the solid electrolyte particles (L:D50) is 1.67;

[0114] In the electrolyte layer, the porosity (P) of the inorganic nanotubes is 1.22%. Based on the total mass of the electrolyte layer, the mass percentage of the dispersant is 0.3%, the mass percentage of the binder is 5%, the mass percentage of the thickener is 0.3%, the mass percentage of the wetting agent is 0.3%, the mass percentage of the inorganic nanotubes (W1) is 30%, and the mass percentage of the solid electrolyte particles (W2) is 64.1%.

[0115] The separator substrate is a PE separator, the thickness (h1) of the separator substrate is 9 μm, and the thickness of the electrolyte layer on one side (h2) is 2 μm.

[0116] 2) Battery preparation

[0117] The positive electrode sheet, the composite separator and the negative electrode sheet are stacked to obtain an electrolytic assembly, and the electrode assembly is placed in an aluminum-plastic film and sealed to obtain a battery;

[0118] 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, a conductive agent Super P, and a binder PVDF. The mass ratio of lithium cobalt oxide, the conductive agent, and the binder is 96:2:2.

[0119] 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, a conductive agent Super P, and a binder PAA. The mass ratio of the silicon-doped graphite, the conductive agent, and the binder is 95:2:3.

[0120] The electrolyte includes lithium hexafluorophosphate (LiPF6), EC, DEC and DMC. In the electrolyte, the concentration of lithium hexafluorophosphate is 1M, and the volume ratio of EC, DEC and DMC is 1:1:1.

[0121] Examples 2-12, Comparative Examples 1-4

[0122] The preparation methods of the batteries of Examples 2-12 and Comparative Examples 1-4 are basically the same as those of Example 1, except that some parameters in the preparation process of the composite separator are different from those of Example 1, as shown in Table 1 for details.

[0123] Performance Testing

[0124] The following performance tests were performed on the composite membranes and batteries in the examples and comparative examples. The results are shown in Table 2.

[0125] 1. Morphology characterization

[0126] The SEM image of the composite diaphragm was obtained according to the method specified in the industry standard JY / T 0584-2020 "General Rules for Scanning Electron Microscope Analysis Methods".

[0127] Figure 1 is a surface SEM image of the composite membrane in Example 2 of the present application; Figure 2 is a cross-sectional SEM image of the composite membrane in Example 2 of the present application. As can be seen from Figure 1, the surface of the composite membrane has granular and tubular structures, 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 a distinct two-layer structure, indicating that the composite membrane includes a membrane substrate and an electrolyte layer disposed on at least one surface of the membrane substrate.

[0128] 2. Thermal shrinkage

[0129] The thermal shrinkage of the composite separator was determined using the method specified in the national standard GB / T 36363-2018, "Lithium-ion Battery Separator Performance Test." The heat treatment temperature in the oven was 130°C and the heat treatment time was 1 hour.

[0130] 3. Rate performance

[0131] The battery rate performance 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", including the battery capacity retention rate at 1C and 3C respectively.

[0132] 4. Cycle performance

[0133] The battery cycle performance 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", that is, the capacity retention rate of the battery after 1000 cycles at a rate of 1C.

[0134] 5. Hot box performance test

[0135] The hot box safety performance of the battery is tested in accordance with the methods specified in the 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 are that the battery is stored in a hot box at 150°C for 10 minutes.

[0136] 6. Thickness

[0137] The cross section of the composite membrane was scanned by a scanning electron microscope (Hitachi, Japan, model: HITACHI SU8010), and 10 locations were randomly selected to measure the thickness of the electrolyte layer. The average value was the thickness of the electrolyte layer.

[0138] 7. Peel strength

[0139] The peel strength of the electrolyte layer in the composite diaphragm was tested according to the method specified in the national standard GBT 2792-2014 "Test method for peel strength of adhesive tape".

[0140] 8. Low temperature performance

[0141] The ambient temperature of the battery test is adjusted to -20°C using a high and low temperature control box, and then the low-temperature discharge performance of the battery 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", that is, the battery discharge performance at -20°C is tested at a rate of 1C.

[0142] Table 1

[0143] Table 2

[0144] As can be seen from Table 1, compared with the comparative example, the composite membrane in the embodiment of the present application can significantly improve the battery's rate performance, cycle performance, low-temperature performance, and safety performance when used in the battery; in particular, by further selecting the relevant parameters of the composite membrane, the peel strength and thermal shrinkage performance of the composite membrane can be improved, further improving the overall performance of the battery. This shows that the present application can improve the electrochemical performance of the battery by adding inorganic nanotubes to the electrolyte layer and controlling the through-porosity of the inorganic nanotubes in the electrolyte layer to prepare the composite membrane;

[0145] Furthermore, it can be seen from Examples 1 and 3 that by further selecting the through-porosity of the inorganic nanotubes in the electrolyte layer, the peel strength and thermal shrinkage performance of the composite separator can be further improved, thereby improving the rate performance, cycle performance, and low-temperature performance of the battery;

[0146] As can be seen from Examples 1-2 and Example 6, 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, cycle performance, and low-temperature performance of the battery;

[0147] It can be seen from Examples 1 and 7 that by further selecting the inner diameter of the inorganic nanotubes, the peel strength and thermal shrinkage performance of the composite separator can be improved, thereby improving the rate performance, cycle performance and low-temperature performance of the battery;

[0148] It can be seen from Examples 1 and 8 that the overall performance of the composite diaphragm can be improved by adjusting the length of the inorganic nanotubes, thereby improving the electrochemical performance of the battery;

[0149] It can be seen from Examples 1 and 9 that the ratio of the length of the inorganic nanotubes to the D50 of the solid electrolyte particles can affect the overall performance of the composite separator, and thus affect the overall performance of the battery;

[0150] It can be seen from Examples 1 and 10 that when the particle size distribution of the solid electrolyte meets a specific range, the composite separator has better peel strength and thermal shrinkage performance. When the composite separator is used in a battery, it can improve the electrochemical performance of the battery.

[0151] It can be seen from Example 1 and Example 12 that by further selecting the thickness of the electrolyte layer, the comprehensive performance of the composite separator can be further improved, thereby improving the comprehensive performance of the battery.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A composite diaphragm, wherein: The composite diaphragm includes a diaphragm substrate and an electrolyte layer disposed on at least one surface of the diaphragm substrate; The electrolyte layer comprises at least inorganic nanotubes and solid electrolyte particles; In the electrolyte layer, the through-porosity of the inorganic nanotubes is 0.2-5%.

2. The composite diaphragm according to claim 1, wherein Based on the total mass of the electrolyte layer, the mass percentage of the inorganic nanotubes is 5-60%.

3. The composite diaphragm according to claim 1 or 2, wherein: The inner diameter of the inorganic nanotube is 3-150 nm.

4. The composite diaphragm according to any one of claims 1 to 3, wherein: The ratio of the outer diameter of the inorganic nanotube to the inner diameter of the inorganic nanotube is (1.5-20):

1.

5. The composite diaphragm according to any one of claims 1 to 4, wherein: The length of the inorganic nanotubes is 0.3-5 μm.

6. The composite diaphragm according to any one of claims 1 to 5, wherein: The ratio of the length of the inorganic nanotube to the D50 of the solid electrolyte particle is greater than 0 and not greater than 30.

7. The composite diaphragm according to any one of claims 1 to 6, wherein: The particle size distribution of the solid electrolyte particles is ≤1.

5.

8. The composite diaphragm according to any one of claims 1 to 7, wherein: The composite diaphragm satisfies at least one of the following: a. The thickness of the diaphragm substrate is 5-30 μm; b. The thickness of the electrolyte layer is 0.5-4 μm.

9. The composite diaphragm according to any one of claims 1 to 8, wherein: The electrolyte layer further includes at least one of a dispersant, a wetting agent, a binder, and a thickener.

10. The composite diaphragm according to claim 9, wherein The composite diaphragm satisfies at least one of the following: a. Based on the total mass of the electrolyte layer, the mass percentage of the binder is 3-10%; b. Based on the total mass of the electrolyte layer, the mass percentage of the dispersant is 0.1-1.5%; c. Based on the total mass of the electrolyte layer, the mass percentage of the thickener is 0.1-3%; d. Based on the total mass of the electrolyte layer, the mass percentage of the wetting agent is 0.1-1.5%.

11. A battery, wherein: The composite diaphragm comprises the composite diaphragm according to any one of claims 1 to 10.

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