Composite separator, preparation method therefor and battery

Abstract

Disclosed in the present invention are a composite separator, a preparation method therefor and a battery. The composite separator comprises a ceramic-fiber layer. The ceramic-fiber layer comprises inorganic ceramic particles and a one-dimensional material toughening agent. The inorganic ceramic particles comprise a first inorganic ceramic. The first inorganic ceramic is nitride inorganic ceramic. In the present invention, the one-dimensional material toughening agent is used for toughening the inorganic ceramic particles, so that the strength of the separator can be greatly improved, and the separator is not easy to break etc. Further, because the inorganic ceramic particles comprise nitride inorganic ceramic, the composite separator has good insulation, excellent high-temperature resistance and good heat conduction performance, so that while the composite separator has good insulation, the original shape of the separator can be well maintained even at high temperature, contact between positive and negative electrodes is avoided, the safety performance of the battery is effectively improved. Moreover, compared with other inorganic ceramics, nitride inorganic ceramic has lower density, so that the overall mass of the battery can be controlled to the maximum extent.

Description

Composite diaphragm, preparation method thereof, and battery

[0001] This application is based on the Chinese patent application with application number 202311274716.6 and application date September 28, 2023, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this application as a reference. Technical Field

[0002] The invention belongs to the technical field of batteries and relates to a composite diaphragm and a preparation method thereof, and a battery. Background Art

[0003] With the increasing promotion of electric vehicles and the widespread application of portable electronic devices, people have put forward higher requirements on battery life, energy density, fast charging performance and safety performance. Among them, it is particularly important to ensure that the battery has good safety performance.

[0004] In batteries, the performance of the diaphragm plays an important role in ensuring the safety of the battery. The diaphragm needs to have good strength and heat resistance to ensure effective isolation of the positive and negative electrodes. If the mechanical properties of the diaphragm are poor and it is damaged during use or shrinks when subjected to high temperatures, it will cause the positive and negative electrodes to contact and cause short circuits, explosions and other problems.

[0005] To improve the strength and heat resistance of the separator, existing technologies generally coat both sides of the lithium-ion battery polymer separator with inorganic ceramic materials. Using a gravure coating process, inorganic functional ceramic materials are then applied to both sides of the polyolefin separator to form a ceramic composite separator. This utilizes the heat resistance of inorganic ceramics to improve the separator's high-temperature deformation resistance and strength. However, because the ceramic layer is generally very thin and provides limited support, the separator will still shrink significantly at high temperatures, leading to direct contact between the positive and negative electrodes of the battery, resulting in a large-scale short circuit, which can cause the battery to burn and explode.

[0006] Therefore, providing a high-strength diaphragm while ensuring that it has good shrinkage resistance at high temperatures is a technical problem that needs to be solved urgently.

[0007] Summary of the Invention

[0008] In view of the above problems existing in the prior art, the object of the present invention is to provide a composite diaphragm and a preparation method thereof and a battery.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a composite diaphragm, comprising a ceramic-fiber layer, wherein the ceramic-fiber layer comprises inorganic ceramic particles and a one-dimensional material toughening agent, wherein the inorganic ceramic particles comprise a first inorganic ceramic, and the first inorganic ceramic is a nitride inorganic ceramic.

[0011] The present invention provides a composite separator that utilizes a one-dimensional material toughening agent to toughen inorganic ceramic particles, significantly increasing the separator's strength and making it less susceptible to breakage. Furthermore, because the inorganic ceramic particles contain nitride inorganic ceramics, which exhibit excellent insulation, high-temperature resistance, and thermal conductivity, the composite separator not only possesses excellent insulation properties but also maintains its original shape even at high temperatures, preventing contact between the positive and negative electrodes and effectively improving battery safety.

[0012] Moreover, compared with other inorganic ceramics, nitride inorganic ceramics have lower density, so the overall quality of the battery can be controlled to the greatest extent.

[0013] The composite diaphragm of the present invention has good flexibility and can be applied to the field of flexible devices.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] Preferably, the diameter of the one-dimensional material toughening agent is 2 nm-20 nm and / or 0.1 μm-10 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, etc. Preferably, when the one-dimensional material toughening agent is a nanotube, the diameter of the nanotube is 2 nm-20 nm, for example, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 15 nm, 17 nm, 18 nm or 20 nm, etc.

[0016] Preferably, the length of the one-dimensional material toughener is 1 mm-100 mm, for example, 1 mm, 3 mm, 5 mm, 8 mm, 10 mm, 12.5 mm, 15 mm, 18 mm, 20 mm, 23 mm, 26 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm or 100 mm, etc., preferably 1 mm-80 mm, more preferably 2 mm-50 mm.

[0017] Preferably, based on the total mass of the ceramic-fiber layer as 100%, the mass proportion of the one-dimensional material toughening agent is 5%-25%, for example, 5%, 7%, 10%, 12.5%, 15%, 18%, 20%, 22% or 25%, etc.

[0018] Preferably, the one-dimensional material toughening agent is selected from at least one of a one-dimensional inorganic material and a one-dimensional organic material.

[0019] Preferably, the one-dimensional inorganic material includes at least one of aluminum oxide fibers, silicon dioxide fibers, zirconium dioxide fibers, boron nitride fibers, boron nitride nanotubes, glass fibers, titanium dioxide nanotubes, and zirconium dioxide nanotubes. The one-dimensional inorganic fibers are selected to be heat-resistant, as they can resist deformation at high temperatures, further ensuring the high-temperature resistance and high strength of the composite diaphragm.

[0020] Preferably, the mass proportion of the one-dimensional inorganic material in the one-dimensional material toughening agent is 50%-100%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, etc. Wherein, the mass proportion of the one-dimensional inorganic material in the one-dimensional material toughening agent being 100% means that the one-dimensional material toughening agent is all one-dimensional inorganic material.

[0021] Preferably, the one-dimensional organic fiber comprises at least one of nylon fiber, polyvinylidene fluoride fiber, polyimide fiber, polyphenylene sulfide fiber, polyvinylidene fluoride-hexafluoropropylene fiber, and polyvinylidene fluoride-chlorotrifluoroethylene fiber. The one-dimensional organic fiber is selected to be heat-resistant, as it can resist deformation at high temperatures, further ensuring the high-temperature resistance and high strength of the composite separator.

[0022] Preferably, the mass proportion of the one-dimensional organic material in the one-dimensional material toughening agent is 0%-50%, for example, 0%, 0.05%, 0.1%, 0.5%, 1%, 3%, 5%, 7%, 10%, 12.5%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 33%, 36%, 40%, 45% or 50%, etc. Wherein, the mass proportion of the one-dimensional organic material in the one-dimensional material toughening agent being 0% means that the one-dimensional material toughening agent does not contain a one-dimensional organic material.

[0023] Preferably, the particle size of the inorganic ceramic particles is 0.1μm-5μm, for example, 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, etc.

[0024] Preferably, based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 75%-95%, for example, 75%, 76%, 77%, 78%, 80%, 82%, 85%, 88%, 90%, 91%, 92%, 93% or 95%, etc.

[0025] As a preferred technical solution of the composite diaphragm of the present invention, the nitride inorganic ceramic includes at least one of boron nitride, aluminum nitride, silicon nitride, titanium nitride and magnesium nitride.

[0026] Preferably, the boron nitride includes hexagonal boron nitride and / or N-type cubic boron nitride.

[0027] Preferably, the inorganic ceramic also includes a second inorganic ceramic, which includes at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, molybdenum-doped silicon dioxide, zirconium boride, zirconium nitride ceramics, silicon boride, vanadium boride, titanium boride, magnesium boride, lithium lanthanum zirconium oxide, lithium lanthanum titanate oxide, tantalum-doped lithium lanthanum zirconium oxide, aluminum-doped lithium lanthanum zirconium oxide, lithium germanium phosphorus-sulfur compound, lithium phosphorus-sulfur-chloride and lithium aluminum germanium phosphate.

[0028] Preferably, the mass of the second inorganic ceramic accounts for 0%-95% of the mass of the first inorganic ceramic and does not contain 0%, for example, 0.05%, 0.1%, 0.5%, 1%, 3%, 5%, 7%, 10%, 12.5%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 33%, 36%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, etc.

[0029] As a preferred technical solution of the composite diaphragm of the present invention, the ceramic-fiber layer also includes a polymer binder, and the polymer binder includes polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE), polymethyl methacrylate (PMMA), polyacrylic acid (PAA), polyacrylonitrile (PAN), perfluorosulfonic acid resin (Nafion-H), perfluorosulfonic acid resin lithium (Nafion-Li), thermoplastic polyurethane (TPU), polyphenylene sulfide (PPS), polyethyleneimine (PEI), polyethyl cyanoacrylate (PCA), polyvinylene carbonate (PEC), polypropylene carbonate (PPC), polyvinyl carbonate (PVC), polymalonate substances, polysuccinate substances, polyimide (PI) and polyethersulfone polyethersulfone (PESU) at least one.

[0030] In one embodiment, the lithium perfluorosulfonic acid resin is prepared as follows: 10 g of the perfluorosulfonic acid resin is added to 100 ml of lithium hydroxide solution (lithium hydroxide concentration is 1 mol / L), stirred for 24 h to 48 h, and then filtered and dried to obtain the lithium perfluorosulfonic acid resin.

[0031] Preferably, the polymalonate material includes at least one of polypentylene malonate (PPM), polyethylene malonate (PEM), polypropylene malonate (PTM) and polyhexylene malonate (PHM).

[0032] Preferably, the polysuccinate material includes polyethylene succinate (PES) and / or polypropylene succinate.

[0033] Preferably, the mass proportion of the polymer binder in the ceramic-fiber layer is 0%-10%, for example, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0034] Preferably, the ceramic-fiber layer further comprises a dispersant.

[0035] Preferably, the dispersant comprises at least one of phenolic resin, polyvinyl pyrrolidone and polyethylene glycol.

[0036] Preferably, the mass proportion of the dispersant in the ceramic-fiber layer is 1%-5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0037] As a preferred technical solution for the composite separator described herein, a polymer layer is further provided on at least one surface of the ceramic-fiber layer. This polymer layer, through direct contact with the positive and negative electrodes, improves interfacial compatibility, improves the battery's interfacial performance, and effectively reduces interfacial internal resistance. Furthermore, the polymer layer further enhances the flexibility of the composite separator, making it more suitable for use in flexible devices.

[0038] Preferably, the thickness of the polymer layer is 0 μm-10 μm and does not include 0 μm, for example, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, etc.

[0039] Preferably, the polymer types in the polymer layer include at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylic acid, polyacrylonitrile, perfluorosulfonic acid resin, perfluorosulfonic acid resin lithium, thermoplastic polyurethane, polyphenylene sulfide, polyethyleneimine, polyethyl cyanoacrylate, polyvinylene carbonate, polypropylene carbonate, polyvinyl carbonate, polymalonate substances, polysuccinate substances, polyimide, polyetherimide and polyethersulfone.

[0040] Preferably, the polymalonate material includes at least one of polypentylene malonate, polyethylene malonate, polypropylene malonate and polyhexylene malonate.

[0041] Preferably, the polysuccinate material includes polyethylene succinate and / or polypropylene succinate.

[0042] Preferably, the porosity of the composite membrane is 5%-90%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0043] Preferably, the thickness of the composite diaphragm is 1 μm-100 μm, for example, 1 μm, 2.5 μm, 5 μm, 7 μm, 8 μm, 10 μm, 12.5 μm, 15 μm, 17 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm or 100 μm, etc.

[0044] In a second aspect, the present invention provides a method for preparing the composite diaphragm according to the first aspect, characterized in that the preparation method is selected from any one of method one and method two.

[0045] The method 1 comprises:

[0046] The raw materials for preparing the composite diaphragm are ball-milled and mixed, and then cold-pressed to obtain the composite diaphragm;

[0047] The second method includes:

[0048] Prepare a slurry including raw materials for preparing a composite diaphragm, a polymer binder and an organic solvent,

[0049] For example, a polymer binder can be mixed with an organic solvent to obtain a glue solution;

[0050] Adding raw materials for preparing a composite diaphragm to the glue solution, dispersing the raw materials uniformly to obtain a slurry, forming a film on a substrate using a tape casting method and volatilizing the organic solvent to obtain a composite diaphragm;

[0051] Wherein, the raw materials for preparing the composite diaphragm in method 1 and method 2 include inorganic ceramic particles and one-dimensional material toughening agent.

[0052] As a preferred technical solution of the preparation method of the composite diaphragm described in the present invention, in the method one, the ball-to-material ratio of ball milling is (6-10):1, for example, 6:1, 7:1, 8:1, 9:1 or 10:1; the rotation speed is 200rpm-600rpm, for example, 200rpm, 220rpm, 240rpm, 260rpm, 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm or 600rpm; the time is 4h-24h, for example, 4h, 6h, 8h, 9h, 10h, 12h, 13h, 15h, 18h, 20h, 22h or 24h, etc.

[0053] Preferably, in the method one, the cold pressing pressure is 5 MPa-30 MPa, for example, 5 MPa, 5.5 MPa, 6 MPa, 6.5 MPa, 7 MPa, 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa, 9.5 MPa, 10 MPa, 12 MPa, 15 MPa, 17.5 MPa, 20 MPa, 23 MPa, 26 MPa, 28 MPa or 30 MPa, etc.; the cold pressing time is 10 min-60 min, for example, 10 min, 12 min, 14 min, 15 min, 18 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc.

[0054] Preferably, in the second method, the method of forming a film on a substrate using the slurry by tape casting is: applying the slurry to the surface of the substrate, and coating the slurry on the surface of the substrate by using a scraper or a wire rod.

[0055] Preferably, in the second method, the organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, nitrogen methyl pyrrolidone, acetonitrile, ethanol and acetone.

[0056] Preferably, in the second method, the slurry further comprises a dispersant. By adding the dispersant to the slurry, the ceramic particles and fibers can be better dispersed in the slurry to avoid agglomeration.

[0057] Preferably, in the second method, the raw materials and dispersant for preparing the composite diaphragm are added in the following order: a one-dimensional material toughening agent is added, and then the dispersant and inorganic ceramic particles are added in sequence.

[0058] In a third aspect, the present invention provides a battery comprising a positive electrode, a negative electrode and a separator, wherein the separator is located between the positive electrode and the negative electrode to isolate the positive electrode from the negative electrode, and the separator is the composite separator described in the first aspect or the composite separator prepared by the method described in the second aspect.

[0059] Preferably, the battery is an all-solid-state battery or a semi-solid-state battery.

[0060] Preferably, a flexible interface is formed between the composite separator and the positive electrode through the polymer layer and / or between the composite separator and the negative electrode through the polymer layer.

[0061] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (1) The present invention utilizes a one-dimensional material toughening agent to toughen the inorganic ceramic particles, which can significantly improve the strength of the diaphragm and make it less prone to breakage. At the same time, because the inorganic ceramic particles contain nitride inorganic ceramics, which have good insulation, excellent high-temperature resistance and good thermal conductivity, the composite diaphragm has good insulation while being able to maintain its original shape even at high temperatures, avoiding contact between the positive and negative electrodes and effectively improving the safety performance of the battery. Moreover, compared with other inorganic ceramics, nitride inorganic ceramics have a lower density, so the overall quality of the battery can be controlled to the greatest extent.

[0064] (2) The composite diaphragm of the present invention has good flexibility and can be applied in the field of flexible devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG1 is a schematic structural diagram of a composite diaphragm in one embodiment of the present invention, wherein: 1 is inorganic ceramic particles; 2 is a one-dimensional material toughening agent. DETAILED DESCRIPTION

[0066] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0067] Example 1

[0068] A composite diaphragm, the structural schematic diagram of which is shown in Figure 1, includes a ceramic-fiber layer, the ceramic-fiber layer includes inorganic ceramic particles 1 and a one-dimensional material toughening agent 2, the inorganic ceramic particles 1 are a first inorganic ceramic, the first inorganic ceramic is hexagonal boron nitride (BN) particles (particle size D50 is 0.5μm), and the one-dimensional material toughening agent 2 is BN fiber (length 50mm); based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 80%, and the mass of the one-dimensional material toughening agent accounts for 20%.

[0069] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0070] After being ball-milled to uniformity, hexagonal BN particles and BN fibers were placed in a press and cold-pressed at a pressure of 5 MPa for 45 minutes to obtain a composite diaphragm.

[0071] The ball-to-material ratio of the ball mill is 7:1, the ball milling speed is 300 rpm, and the time is 12 h.

[0072] Example 2

[0073] A composite diaphragm includes a ceramic-fiber layer, wherein the ceramic-fiber layer includes inorganic ceramic particles and a one-dimensional material toughening agent, wherein the inorganic ceramic particles are a first inorganic ceramic, which is aluminum nitride (AlN) particles (particle size D50 is 1 μm), and the one-dimensional material toughening agent is BN fiber (length is 20 mm); based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 90%, and the mass of the one-dimensional material toughening agent accounts for 10%.

[0074] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0075] After ball-milling, AlN particles and BN fibers were placed in a press and cold-pressed at a pressure of 15 MPa for 30 minutes to obtain a composite diaphragm.

[0076] The ball-to-material ratio of the ball mill is 9:1, the ball milling speed is 400 rpm, and the time is 7 h.

[0077] Example 3

[0078] A composite diaphragm includes a ceramic-fiber layer, wherein the ceramic-fiber layer includes inorganic ceramic particles and a one-dimensional material toughening agent, wherein the inorganic ceramic particles are a first inorganic ceramic, which is silicon nitride (Si3N4) particles (particle size D50 is 2μm), and the one-dimensional material toughening agent is BN fiber (length 75mm); based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 75%, and the mass of the one-dimensional material toughening agent accounts for 25%.

[0079] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0080] After ball-milling Si3N4 particles and BN fibers, they were placed in a press and cold-pressed at a pressure of 25 MPa for 30 min to obtain a composite diaphragm.

[0081] The ball-to-material ratio of the ball mill is 6:1, the ball milling speed is 200 rpm, and the time is 20 h.

[0082] Example 4

[0083] A composite diaphragm includes a ceramic-fiber layer, wherein the ceramic-fiber layer includes inorganic ceramic particles, a one-dimensional material toughening agent and a polymer binder, wherein the inorganic ceramic particles are a first inorganic ceramic, which is N-type cubic phase BN particles (particle size D50 is 0.5 μm), the one-dimensional material toughening agent is BN nanotubes (diameter is 10 nm, length is 10 mm), and the polymer binder is polyvinylidene fluoride (PVDF); based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 75%, the mass of the one-dimensional material toughening agent accounts for 20%, and the mass of the polymer binder accounts for 5%.

[0084] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0085] PVDF is dissolved in nitrogen methyl pyrrolidone (NMP) to form a glue solution, BN nanotubes are added to the glue solution and dispersed evenly, and then N-type cubic phase BN particles are added and dispersed evenly to obtain a slurry;

[0086] The slurry was dropped onto the surface of a polytetrafluoroethylene plate, and the slurry was coated on the substrate surface with a scraper and dried to volatilize the NMP. The membrane material was then removed to obtain a composite diaphragm.

[0087] Example 5

[0088] A composite diaphragm includes a ceramic-fiber layer, wherein the ceramic-fiber layer includes inorganic ceramic particles, a one-dimensional material toughening agent and a polymer binder, the inorganic ceramic particles include a first inorganic ceramic and a second inorganic ceramic, the first inorganic ceramic is N-type cubic phase (BN) particles (particle size D50 is 4 μm), the second inorganic ceramic is alumina particles (particle size D50 is 1.5 μm), the one-dimensional material toughening agent is aluminum oxide fiber (length 80 mm), and the polymer binder is polyethylene oxide (PEO); based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 75% (wherein the mass of the second inorganic ceramic accounts for 50% of the mass of the first inorganic ceramic), the mass of the one-dimensional material toughening agent accounts for 15%, and the mass of the polymer binder accounts for 10%.

[0089] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0090] PEO is dissolved in acetonitrile to form a glue solution, aluminum oxide fibers are added to the glue solution and dispersed evenly, and then N-type cubic phase BN particles and aluminum oxide particles are added and dispersed evenly to obtain a slurry;

[0091] The slurry was dropped onto the surface of a polytetrafluoroethylene plate, and the slurry was coated on the substrate surface using a scraper. After drying to volatilize the NMP, a composite diaphragm was obtained.

[0092] Example 6

[0093] A composite diaphragm includes a ceramic-fiber layer, wherein the ceramic-fiber layer includes inorganic ceramic particles, a one-dimensional material toughening agent, a polymer binder and a dispersant, wherein the inorganic ceramic particles are a first inorganic ceramic, the first inorganic ceramic is titanium nitride particles (particle size D50 is 2.5 μm), the one-dimensional material toughening agent is silica fiber (length 15 mm) and nylon fiber (length 65 mm), the polymer binder is polymethyl methacrylate (PMMA), and the dispersant is a phenolic resin; based on the total mass of the ceramic-fiber layer as 100%, the mass proportion of the inorganic ceramic particles is 75%, the mass proportion of the silica fiber is 10%, the mass proportion of the nylon fiber is 10%, the mass content of the polymer binder is 3%, and the mass content of the dispersant is 2%.

[0094] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0095] PMMA is dissolved in acetone to form a glue solution, silica fiber and nylon fiber are added to the glue solution and dispersed evenly, and then titanium nitride and a dispersant are added and dispersed evenly to obtain a slurry;

[0096] The slurry is dropped onto the surface of a polytetrafluoroethylene plate, and the slurry is coated on the surface of the substrate using a scraper. After drying to evaporate the acetone, a composite diaphragm is obtained.

[0097] Example 7

[0098] A composite diaphragm is different from Example 1 only in that a polymer layer is provided on the surface of the ceramic-fiber layer, the polymer in the polymer layer is polyvinylidene fluoride (PVDF), and the thickness of the polymer layer is 3 μm.

[0099] The preparation method of the composite diaphragm provided in this embodiment comprises the following steps:

[0100] After ball-milling, hexagonal BN particles and BN fibers were uniformly placed in a press and cold-pressed at a pressure of 10 MPa for 10 minutes to obtain a membrane material.

[0101] The ball-to-material ratio of the ball milling was 8:1, the ball milling speed was 500 rpm, and the time was 15 h.

[0102] Dissolve PVDF in NMP to obtain a polymer glue;

[0103] The polymer glue is coated on the surface of the membrane material, and after drying, a polymer layer is formed on the surface of the membrane material to obtain a composite diaphragm.

[0104] Example 8

[0105] A composite diaphragm and a preparation method thereof, which differ from Example 1 only in that the amount of hexagonal BN particles and BN fibers used is changed so that in the composite diaphragm, based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 70%, and the mass of the one-dimensional material toughening agent accounts for 30%.

[0106] Example 9

[0107] A composite diaphragm and a preparation method thereof, which differ from Example 1 only in that the amount of hexagonal BN particles and BN fibers used is changed so that in the composite diaphragm, based on the total mass of the ceramic-fiber layer as 100%, the mass of the inorganic ceramic particles accounts for 97%, and the mass of the one-dimensional material toughening agent accounts for 3%.

[0108] Comparative Example 1

[0109] A composite diaphragm and a preparation method thereof, which differ from Example 1 only in that, in the preparation method, BN fibers are replaced with hexagonal BN of equal mass, so that the composite diaphragm does not contain BN fibers.

[0110] Comparative Example 2

[0111] A composite diaphragm and a preparation method thereof, which differ from Example 1 only in that, in the preparation method, hexagonal BN is replaced with BN fibers of equal mass, so that the composite diaphragm does not contain hexagonal BN.

[0112] Application Example 1

[0113] A lithium-ion battery comprises a positive electrode, a negative electrode, a separator (the composite separator of Example 1) and an electrolyte, and a method for preparing the lithium-ion battery comprises the following steps:

[0114] According to the mass ratio of lithium iron phosphate (LFP): SuperP:PVDF = 8:1:1, LFP, Super P and PVDF were dispersed in DMF and the solid content was controlled to 60% to obtain a positive electrode slurry. The positive electrode slurry was coated on aluminum foil with a scraper with a thickness of 100 μm and dried for use.

[0115] The electrolyte composition is: 1 mol / L LiPF6 as electrolyte and a mixture of EC:DMC (volume ratio) = 1:1 as solvent.

[0116] A lithium sheet with a thickness of 100 μm was used as the counter electrode and a button cell of model 2032 was assembled in an inert gas glove box with a water and oxygen content of less than 0.1 ppm.

[0117] Application Example 2-9

[0118] A lithium ion battery differs from Application Example 1 only in that the composite diaphragms of Examples 2-9 are used to replace the composite diaphragm of Example 1.

[0119] Application Comparative Example 1-2

[0120] A lithium ion battery differs from Application Example 1 only in that the composite diaphragms of Comparative Examples 1-2 are used to replace the composite diaphragms of Example 1.

[0121] Performance testing:

[0122] (1) Diaphragm thickness: Use a micrometer to measure the thickness of the diaphragm.

[0123] (2) Porosity of the diaphragm: The porosity of the diaphragm was tested using a mercury intrusion instrument.

[0124] (3) Thermal shrinkage of the diaphragm: Place the diaphragm in a 150°C oven, keep it warm for 1 hour, then take it out. Record the size of the sample before and after heating, and obtain the thermal shrinkage through the area change.

[0125] (4) Tensile strength at break of the diaphragm: The tensile strength at break of the diaphragm was tested using a universal mechanical properties testing machine at a speed of 10 mm / min, with reference to GB / T1040.

[0126] (5) Discharge capacity: The charge and discharge test was performed at room temperature with a current density of 0.1C.

[0127] The thickness, porosity, thermal shrinkage and tensile strength at break of the composite membranes of Examples 1-9 and Comparative Examples 1-2 were tested according to the above test methods. The test results are shown in Table 1.

[0128] The discharge capacity of the lithium-ion batteries corresponding to Examples 1-9 and Comparative Examples 1-2 was tested, and the results are shown in Table 2.

[0129] Table 1

[0130] Table 2

[0131] By comparing Example 1 with Examples 8-9, it can be seen that there is an optimal range for the amount of one-dimensional material toughening agent used. If the amount of toughening agent used is too little or too much, it will lead to a greater thermal shrinkage rate and a decrease in the tensile strength at break, resulting in a decrease in the electrochemical performance of the battery assembled using it. The capacity of the battery in Application Example 8-9 is lower than that in Application Example 1.

[0132] By comparing Example 1 with Comparative Example 1, it can be seen that the diaphragm of Comparative Example 1 does not contain a one-dimensional material toughening agent and cannot toughen the ceramic particles, resulting in a larger shrinkage rate of the diaphragm, a significant decrease in strength, and easy breakage, which causes safety problems.

[0133] By comparing Example 1 with Comparative Example 2, it can be seen that the diaphragm of Comparative Example 2 does not contain inorganic ceramic particles, which results in a larger shrinkage rate of the diaphragm and a significant decrease in strength.

[0134] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A composite diaphragm, characterized in that: The composite diaphragm comprises a ceramic-fiber layer, wherein the ceramic-fiber layer comprises inorganic ceramic particles and a one-dimensional material toughening agent, wherein the inorganic ceramic particles comprise a first inorganic ceramic, and the first inorganic ceramic is a nitride inorganic ceramic.

2. The composite diaphragm according to claim 1, characterized in that: The diameter of the one-dimensional material toughening agent is 2nm-20nm and / or 0.1μm-10μm; preferably, when the one-dimensional material toughening agent is a nanotube, the diameter of the nanotube is 2nm-20nm; Preferably, the length of the one-dimensional material toughening agent is 1 mm-100 mm, preferably 1 mm-80 mm, more preferably 2 mm-50 mm; Preferably, based on the total mass of the ceramic-fiber layer being 100%, the mass proportion of the one-dimensional material toughening agent is 5%-25%.

3. The composite diaphragm according to claim 1 or 2, characterized in that: The one-dimensional material toughening agent is selected from at least one of a one-dimensional inorganic material and a one-dimensional organic material; Preferably, the one-dimensional inorganic material comprises at least one of aluminum oxide fiber, silicon dioxide fiber, zirconium dioxide fiber, boron nitride fiber, boron nitride nanotube, glass fiber, titanium dioxide nanotube and zirconium dioxide nanotube; Preferably, the mass proportion of the one-dimensional inorganic material in the one-dimensional material toughening agent is 50%-100%; Preferably, the one-dimensional organic fiber comprises at least one of nylon fiber, polyvinylidene fluoride fiber, polyimide fiber, polyphenylene sulfide fiber, polyvinylidene fluoride-hexafluoropropylene fiber and polyvinylidene fluoride-chlorotrifluoroethylene fiber; Preferably, the mass proportion of the one-dimensional organic material in the one-dimensional material toughening agent is 0%-50%; Preferably, the particle size of the inorganic ceramic particles is 0.1 μm-5 μm; Preferably, based on the total mass of the ceramic-fiber layer being 100%, the mass of the inorganic ceramic particles accounts for 75%-95%; Preferably, the nitride inorganic ceramic includes at least one of boron nitride, aluminum nitride, silicon nitride, titanium nitride and magnesium nitride; Preferably, the boron nitride includes hexagonal boron nitride and / or N-type cubic boron nitride; Preferably, the inorganic ceramic further includes a second inorganic ceramic, and the second inorganic ceramic includes at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, molybdenum-doped silicon dioxide, zirconium boride, zirconium nitride ceramics, silicon boride, vanadium boride, titanium boride, magnesium boride, lithium lanthanum zirconium oxide, lanthanum titanate lithium oxide, tantalum-doped lithium lanthanum zirconium oxide, aluminum-doped lithium lanthanum zirconium oxide, lithium germanium phosphorus-sulfur compound, lithium phosphorus-sulfur-chloride compound and lithium germanium aluminum phosphate; Preferably, the mass of the second inorganic ceramic accounts for 0%-95% of the mass of the first inorganic ceramic and does not include 0%.

4. The composite diaphragm according to any one of claims 1 to 3, characterized in that: The ceramic-fiber layer also includes a polymer binder, and the polymer binder includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluorochloroethylene, polymethyl methacrylate, polyacrylic acid, polyacrylonitrile, perfluorosulfonic acid resin, perfluorosulfonic acid resin lithium, thermoplastic polyurethane, polyphenylene sulfide, polyethyleneimine, polyethyl cyanoacrylate, polyvinylene carbonate, polypropylene carbonate, polyvinyl carbonate, polymalonate, polysuccinate, polyimide and polyether sulfone; Preferably, the polymalonate material includes at least one of polypentylene malonate, polyethylene malonate, polypropylene malonate and polyhexylene malonate; Preferably, the polysuccinate-based material includes polyethylene succinate and / or polypropylene succinate. alcohol esters; Preferably, the polymer binder accounts for 0%-10% by weight in the ceramic-fiber layer and does not contain 0%.

5. The composite diaphragm according to any one of claims 1 to 4, characterized in that: The ceramic-fiber layer also includes a dispersant; Preferably, the dispersant comprises at least one of phenolic resin, polyvinyl pyrrolidone and polyethylene glycol; Preferably, the mass proportion of the dispersant in the ceramic-fiber layer is 1%-5%.

6. The composite diaphragm according to any one of claims 1 to 5, characterized in that: A polymer layer is also provided on at least one side surface of the ceramic-fiber layer; Preferably, the thickness of the polymer layer is 0 μm-10 μm and does not include 0 μm; Preferably, the polymer type in the polymer layer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylic acid, polyacrylonitrile, perfluorosulfonic acid resin, perfluorosulfonic acid resin lithium, thermoplastic polyurethane, polyphenylene sulfide, polyethyleneimine, polyethyl cyanoacrylate, polyvinylene carbonate, polypropylene carbonate, polyvinyl carbonate, polymalonate substances, polysuccinate substances, polyimide, polyether ester imide and polyether sulfone; Preferably, the polymalonate material includes at least one of polypentylene malonate, polyethylene malonate, polypropylene malonate and polyhexylene malonate; Preferably, the polysuccinate-based material includes polyethylene succinate and / or polypropylene succinate.

7. The composite diaphragm according to any one of claims 1 to 6, characterized in that: The porosity of the composite membrane is 5%-90%, preferably 40%-80%; preferably, the thickness of the composite membrane is 1 μm-100 μm.

8. A method for preparing a composite diaphragm according to any one of claims 1 to 7, characterized in that: The preparation method is selected from any one of method 1 and method 2, The method 1 comprises: The raw materials for preparing the composite diaphragm are ball-milled and mixed, and then cold-pressed to obtain the composite diaphragm; The second method comprises: Preparing a slurry including raw materials for preparing a composite diaphragm, a polymer binder and an organic solvent, forming a film on a substrate using the slurry by a tape casting method and volatilizing the organic solvent to obtain a composite diaphragm; Wherein, the raw materials for preparing the composite diaphragm in method 1 and method 2 include inorganic ceramic particles and one-dimensional material toughening agent.

9. The preparation method according to claim 8, characterized in that: In the method 1, the ball-to-material ratio of the ball mill is (6-10):1, the rotation speed is 200rpm-600rpm, and the time is 4h-24h; Preferably, in the method, the ball milling speed is 200 rpm-400 rpm, and the time is 5 h-24 h; Preferably, in the method 1, the cold pressing pressure is 5MPa-30MPa, and the cold pressing time is 10min-60min; Preferably, in the second method, the method of forming a film on a substrate by using the slurry by tape casting is: applying the slurry to the surface of the substrate, and coating the slurry on the surface of the substrate by using a scraper or a wire rod; Preferably, in the second method, the organic solvent comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide, nitrogen methyl pyrrolidone, acetonitrile, ethanol and acetone; Preferably, in the second method, the slurry further comprises a dispersant; Preferably, in the second method, the raw materials for preparing the composite diaphragm and the dispersant are added in the following order: First, add the one-dimensional material toughening agent, and then add the dispersant and inorganic ceramic particles in sequence.

10. A battery comprising a positive electrode, a negative electrode and a separator, wherein the separator is located between the positive electrode and the negative electrode to isolate the positive electrode from the negative electrode, characterized in that: The diaphragm is a composite diaphragm according to any one of claims 1 to 7 or a composite diaphragm prepared by the method of claim 8 or 9; Preferably, the battery is an all-solid-state battery or a semi-solid-state battery; Preferably, a flexible interface is formed between the composite separator and the positive electrode through the polymer layer and / or between the composite separator and the negative electrode through the polymer layer.

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