Composite separator, manufacturing method therefor, and battery

Abstract

Disclosed are a composite separator, a manufacturing method therefor, and a battery. The composite separator comprises a ceramic matrix layer and base membranes located on the surfaces of the two sides of the ceramic matrix layer, the ceramic matrix layer comprising ceramic particles, the ceramic particles comprising first ceramic, and the first ceramic being nitride inorganic ceramic; and the outer surfaces of the two sides of the composite separator are both the base membranes. In the present invention, the part of the composite separator in direct contact with the positive and negative electrodes has good compatibility, thus improving the battery interface performance and effectively reducing the interface resistance. Additionally, the use of the nitride inorganic ceramic allows for the maximum control on the overall quality of the battery, as well as the inhibition of the high-temperature shrinkage rate of the separator, thus preventing the contact of the positive and negative electrodes and improving the battery safety performance.

Description

Composite diaphragm, preparation method thereof, and battery

[0001] This application is based on the Chinese patent application with application number 202311273169.X 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] Because all-solid-state batteries or semi-solid-state batteries contain no or only a small amount of liquid electrolyte, their safety performance is greatly improved compared to liquid batteries. Among them, all-solid-state batteries use solid electrolytes instead of liquid electrolytes, so that only solid phase exists inside the battery. Semi-solid-state batteries use solid electrolytes to replace part of the liquid electrolyte, so that solid electrolyte and liquid electrolyte coexist in the semi-solid-state battery.

[0004] Liquid batteries typically include a diaphragm, whose primary function is to separate the positive and negative electrodes of the battery, preventing contact and short circuits. Furthermore, the diaphragm itself is porous, allowing electrolyte ions to pass through. Solid-state or semi-solid-state batteries typically use a solid electrolyte membrane as a key component to isolate the positive and negative electrodes and provide ion conduction. The solid electrolytes used in solid electrolyte membranes are primarily categorized as polymer solid electrolytes, inorganic ceramic solid electrolytes, and composites of the two.

[0005] Polymer solid electrolytes are a type of polymer film material that can transport lithium ions and effectively isolate the positive and negative electrodes from short circuits. Their main components are polymers and lithium-containing substances.

[0006] Inorganic ceramic solid electrolytes mainly include sulfide ceramic solid electrolytes, oxide ceramic solid electrolytes and halide ceramic solid electrolytes. Inorganic ceramic solid electrolytes can rely on their own structural characteristics to transport lithium ions while avoiding direct contact between the positive and negative electrodes.

[0007] Among the methods for preparing solid-state electrolyte layers, a currently popular method is to coat both sides of the lithium-ion battery polymer separator with an inorganic ceramic material. Using a gravure coating process, inorganic functional ceramic materials are then coated on both sides of the polyolefin separator to form a ceramic composite separator, also known as the solid-state electrolyte layer. This ceramic composite separator is made of inorganic ceramic materials on both sides facing the positive and negative electrodes. Inorganic ceramic particles are a type of inorganic non-metallic material formed by forming and high-temperature sintering natural or synthetic compounds. They have advantages such as high melting point, high hardness, wear resistance, and oxidation resistance. However, this also leads to poor interfacial compatibility with the positive and negative electrodes, resulting in large interfacial impedance in all-solid-state or semi-solid-state batteries.

[0008] Therefore, providing a separator suitable for solid-state batteries or semi-solid-state batteries so that it has good compatibility with the positive and negative electrodes and low interface impedance is a technical problem that needs to be solved urgently.

[0009] Summary of the Invention

[0010] 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.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a composite diaphragm, comprising a ceramic base layer and base membranes located on both sides of the ceramic base layer, wherein the ceramic base layer comprises ceramic particles, wherein the ceramic particles comprise a first ceramic, wherein the first ceramic is a nitride inorganic ceramic;

[0013] The outer surfaces on both sides of the composite diaphragm are both the base membranes.

[0014] In the composite diaphragm of the present invention, since the outermost side is a base film, the composition of the base film is generally a polymer. By utilizing the high elasticity of the polymer, the compatibility of the part of the composite diaphragm in direct contact with the positive and negative electrodes is good, which improves the interface performance of the battery and can effectively reduce the interface resistance. The use of nitride inorganic ceramics in the composite diaphragm plays a key role in improving the comprehensive performance of the composite diaphragm. Specifically: First, compared with other inorganic ceramics, nitride inorganic ceramics have a lower density, so the overall quality of the battery can be controlled to the maximum extent; second, nitride inorganic ceramics have good insulation properties, which can avoid direct contact between the positive and negative electrodes; third, nitride inorganic ceramics have excellent high temperature resistance, which improves the high temperature shrinkage resistance of the diaphragm. At the same time, it has good thermal conductivity and can conduct heat to other parts in a relatively short time. Therefore, it can play a good supporting role at high temperatures, avoid battery short circuits caused by diaphragm deformation, and ensure the safety performance of the battery at high temperatures.

[0015] The composite diaphragm of the present invention is applied to all-solid-state batteries or semi-solid-state batteries, and can improve the safety performance of the battery without significantly sacrificing the electrochemical performance.

[0016] The composite membrane of the present invention has a flexible interfacial layer on its surface, ensuring good contact between the electrolyte and the electrodes. This system effectively addresses issues of ionic conductivity and interfacial impedance, thereby improving the electrochemical performance of the battery. Furthermore, due to its excellent flexibility, the composite membrane is suitable for application in the field of flexible devices.

[0017] 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.

[0018] Preferably, the nitride inorganic ceramic includes at least one of boron nitride, aluminum nitride, silicon nitride, titanium nitride and magnesium nitride, preferably boron nitride.

[0019] In the present invention, the main component of the ceramic diaphragm is a polymer, and the boron atoms in the boron nitride can form Lewis acid sites in the polymer. Therefore, when the lithium salt passes through the composite diaphragm layer, the lithium ions can pass through quickly.

[0020] Preferably, the boron nitride includes at least one of hexagonal boron nitride and N-type cubic boron nitride.

[0021] As a preferred technical solution of the composite diaphragm described in the present invention, the ceramic particles also include a second ceramic, which includes at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, molybdenum-doped silicon dioxide, zirconium boride, zirconium nitride compounds, silicon boride, vanadium boride, titanium boride, magnesium boride and inorganic ceramic solid electrolytes.

[0022] Preferably, the zirconium nitride compound includes at least one of ZrN, o-Zr3N4, and c-Zr3N4;

[0023] Preferably, the inorganic ceramic solid electrolyte includes at least one of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanate oxide (LLTO), tantalum-doped lithium lanthanum zirconium oxide (LLZTO), aluminum-doped lithium lanthanum zirconium oxide (LLZAO), lithium germanium phosphorous sulfide (LGPS), lithium phosphorous sulfur chloride (LPSCl) and lithium aluminum germanium phosphate (LAGP).

[0024] Preferably, the mass of the second ceramic accounts for 0%-95% of the mass of the first ceramic and does not contain 0%, such as 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., preferably 50%-80%.

[0025] Preferably, the particle size D50 of the first ceramic is 0.2μm-2μm, for example, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm or 2μm, etc.; the particle size D50 of the second ceramic is 0.2μm-2μm, for example, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm or 2μm, etc.

[0026] Preferably, the ratio of the particle size D50 of the first ceramic to the particle size D50 of the second ceramic is 1:(0.5-2), for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:1, 1:1.5, or 1:2. When the ratio of the particle size D50 of the first ceramic to the particle size D50 of the second ceramic is 1:(0.5-2), it is beneficial to improve the interfacial contact between the two ceramics, thereby improving the high temperature resistance and interfacial compatibility of the composite separator, thereby enhancing the electrochemical performance of the battery.

[0027] Preferably, the ceramic matrix layer further comprises a polymer binder, and the polymer binder binds the ceramic particles together.

[0028] Preferably, the polymer binder includes at least one of 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 and polyimide (PI).

[0029] 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.

[0030] Preferably, the polymalonate material includes at least one of polypentylene malonate (PPM), polyethylene malonate (PEM), polypropylene malonate (PTM) and polyhexylene malonate (PHM).

[0031] Preferably, the polysuccinate material includes polyethylene succinate (PES) and / or polypropylene succinate.

[0032] Preferably, in the ceramic matrix layer, the mass proportion of ceramic particles is 5%-95%, for example, 5%, 6%, 8%, 10%, 12%, 13%, 15%, 17%, 20%, 23%, 26%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, and preferably 50%-90%. If the mass proportion of ceramic particles is too low, the thermal shrinkage resistance of the composite diaphragm may be affected. If the mass proportion of ceramic particles is too high, it may make it difficult to achieve uniform distribution of ceramic particles in the ceramic matrix layer.

[0033] Preferably, the porosity of the ceramic matrix layer is 5%-90%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, etc., preferably 40%-70%.

[0034] Preferably, the thickness of the ceramic base layer is 5 μm-20 μm, for example, 5 μm, 7 μm, 8 μm, 10 μm, 12.5 μm, 15 μm, 17 μm or 20 μm.

[0035] It should be noted that when the ceramic matrix layer does not contain ceramic particles (such as LLZO) that can conduct active ions (such as lithium ions), the ceramic matrix layer should have a certain porosity to ensure good ion transmission performance. At this time, the composite diaphragm is porous.

[0036] Preferably, the base film is a polymer base film, preferably including any one of a porous polyethylene film (PE base film), a porous polypropylene film (PP base film), a porous polyethylene / polypropylene film (PE / PP base film) and a porous polyimide film (PI base film).

[0037] Preferably, the thickness of the base films on both sides of the ceramic base layer is independently 5 μm-20 μm, for example, 5 μm, 7 μm, 8 μm, 10 μm, 12.5 μm, 15 μm, 17 μm or 20 μm.

[0038] In the present invention, the base films on both sides of the ceramic base layer may be made of the same or different types, for example, the same polymer material or different polymer materials, and those skilled in the art may select the material according to their needs.

[0039] In a second aspect, the present invention provides a method for preparing the composite diaphragm according to the first aspect, the preparation method comprising the following steps:

[0040] preparing a ceramic slurry including ceramic particles;

[0041] The ceramic slurry is coated on the surface of the first base film to form a ceramic slurry layer, and the ceramic slurry layer is covered with a second base film. After drying, the composite diaphragm is obtained.

[0042] In one embodiment, ceramic particles and a polymer binder are dispersed in a solvent to obtain a ceramic slurry.

[0043] The preparation method of the present invention is simple, can achieve interface softening, is compatible with the process system of existing solid-state batteries or semi-solid-state batteries, and can be put into production quickly.

[0044] Preferably, the drying is vacuum drying.

[0045] Preferably, the drying temperature is 50°C-80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C; the drying time is 12-26h, for example, 12h, 14h, 15h, 17h, 18h, 19h, 20h, 22h, 24h or 26h.

[0046] 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 a composite separator as described in the first aspect or a composite separator prepared by the preparation method as described in the second aspect.

[0047] Preferably, the battery is an all-solid-state battery or a semi-solid-state battery.

[0048] Preferably, a flexible interface is formed between the composite membrane and the positive electrode and / or between the composite membrane and the negative electrode, the composite membrane has good compatibility with the positive and negative electrodes, the interface impedance is low, and the battery exhibits good electrochemical performance.

[0049] 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.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) The composite separator of the present invention has good compatibility with the portion in direct contact with the positive and negative electrodes, improving the interfacial properties of the battery and effectively reducing interfacial resistance. Furthermore, the use of inorganic nitride ceramics can maximize control of the overall quality of the battery while suppressing the high-temperature shrinkage of the separator, effectively preventing contact between the positive and negative electrodes and improving the safety of the battery.

[0052] (2) The composite diaphragm of the present invention can be applied to all-solid-state batteries or semi-solid-state batteries, thereby improving battery safety without significantly sacrificing electrochemical performance. The composite diaphragm of the present invention has a thermal shrinkage rate of less than 5.3% at 150°C, and the battery discharge capacity is greater than 153 mAh / g.

[0053] (3) The composite membrane of the present invention has a flexible interfacial layer on its surface, which enables good contact between the electrolyte and the electrode. This system can effectively solve the problems of ionic conductivity and interfacial impedance, thereby improving the electrochemical performance of the battery. The interfacial impedance of the battery assembled using this system after one cycle is below 52Ω. At the same time, due to the good flexibility of the composite membrane, it can be applied in the field of flexible devices.

[0054] (4) The preparation method of the present invention is simple, can achieve interface softening, and is compatible with the existing process system of solid-state batteries or semi-solid-state batteries, and can be put into production quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG1 is a schematic structural diagram of a composite diaphragm of the present invention. DETAILED DESCRIPTION

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0057] In the embodiments of the present invention, the base film used can be prepared by methods disclosed in the prior art, or can be a commercially available product.

[0058] Example 1

[0059] This embodiment provides a composite diaphragm, the structural diagram of which is shown in FIG1 . The composite diaphragm includes a ceramic base layer 1 and base films 2 located on both sides of the ceramic base layer 1. The ceramic base layer 1 includes ceramic particles and a polymer binder. The ceramic particles include a first ceramic and a second ceramic. The first ceramic is hexagonal BN particles (particle size D50 is 0.5 μm), the second ceramic is LLZO (particle size D50 is 0.5 μm), and the polymer binder is PVDF. The outer surfaces of both sides of the composite diaphragm are base films 2.

[0060] In the ceramic matrix layer 1, the mass proportion of ceramic particles is 70%, and the mass proportion of polymer binder is 30%;

[0061] In the ceramic particles, the mass of the second ceramic accounts for 60% of the mass of the first ceramic;

[0062] The thickness of the ceramic base layer 1 is 10 μm, and the thickness of the base films 2 on both sides is 7 μm.

[0063] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0064] PVDF, hexagonal BN particles, and LLZO were mixed and dispersed in DMF solvent. The resulting slurry was coated on a 7 μm thick diaphragm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. The surface was then covered with another 7 μm thick diaphragm. The membrane was first dried at room temperature and then dried in a vacuum oven at 60°C for 24 hours. The composite membrane was then removed.

[0065] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polyethylene membrane.

[0066] Example 2

[0067] This embodiment provides a composite diaphragm, comprising a ceramic base layer and base films located on both sides of the ceramic base layer. The ceramic base layer includes ceramic particles and a polymer binder. The ceramic particles include a first ceramic and a second ceramic. The first ceramic is AlN particles (particle size D50 is 0.5 μm), and the second ceramic is Al2O3 (particle size D50 is 0.3 μm). The polymer binder is PVDF. Both sides of the outer surface of the composite diaphragm are base films.

[0068] In the ceramic matrix layer, the mass proportion of ceramic particles is 80%, and the mass proportion of polymer binder is 20%;

[0069] In the ceramic particles, the mass of the second ceramic accounts for 50% of the mass of the first ceramic;

[0070] The thickness of the ceramic base layer is 15 μm, and the thickness of the base films on both sides is 5 μm.

[0071] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0072] PVDF, AlN particles, and Al2O3 were dispersed in DMF solvent, and the resulting slurry was coated on a 5μm thick diaphragm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. Then, another 5μm thick diaphragm was covered on the surface, dried at room temperature, and then placed in a vacuum oven at 60°C for 24 hours to obtain a composite diaphragm.

[0073] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polypropylene membrane.

[0074] Example 3

[0075] This embodiment provides a composite diaphragm, comprising a ceramic base layer and base films located on both sides of the ceramic base layer, wherein the ceramic base layer comprises ceramic particles and a polymer binder, wherein the ceramic particles are N-type cubic phase BN particles (particle size D50 is 1 μm), and the polymer binder is PVDF; both sides of the outer surface of the composite diaphragm are base films;

[0076] In the ceramic matrix layer, the mass proportion of ceramic particles is 55%, and the mass proportion of polymer binder is 45%;

[0077] The thickness of the ceramic base layer is 7 μm, and the thickness of the base films on both sides is 7 μm.

[0078] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0079] PVDF and N-type cubic phase BN particles were dispersed in DMF solvent, and the resulting slurry was coated on a 7μm thick diaphragm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. Then, another 7μm thick diaphragm was covered on the surface, dried at room temperature, and then placed in a vacuum oven at 60°C for 24 hours to obtain a composite diaphragm.

[0080] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polyethylene / polypropylene membrane.

[0081] Example 4

[0082] This embodiment provides a composite diaphragm, comprising a ceramic base layer and base films located on both sides of the ceramic base layer, wherein the ceramic base layer comprises ceramic particles and a polymer binder, wherein the ceramic particles are AlN particles (particle size D50 is 0.4 μm), and the polymer binder is PVDF; both sides of the outer surface of the composite diaphragm are base films;

[0083] In the ceramic matrix layer, the mass proportion of ceramic particles is 65%, and the mass proportion of polymer binder is 35%;

[0084] The thickness of the ceramic base layer is 18 μm, and the thickness of the base films on both sides is 7 μm.

[0085] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0086] PVDF and AlN particles were dispersed in DMF solvent, and the resulting slurry was coated on a 7 μm thick diaphragm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. Then, another 7 μm thick diaphragm was covered on the surface, dried at room temperature, and then placed in a vacuum oven at 60°C for 24 hours to obtain a composite diaphragm.

[0087] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polyimide membrane.

[0088] Example 5

[0089] This embodiment provides a composite diaphragm, comprising a ceramic base layer and base films located on both sides of the ceramic base layer, wherein the ceramic base layer comprises ceramic particles and a polymer binder, wherein the ceramic particles are Si3N4 particles (particle size D50 is 0.5 μm), and the polymer binder is PVDF; both sides of the outer surface of the composite diaphragm are base films;

[0090] In the ceramic matrix layer, the mass proportion of ceramic particles is 75%, and the mass proportion of polymer binder is 25%;

[0091] The thickness of the ceramic base layer is 12 μm, and the thickness of the base films on both sides is 7 μm.

[0092] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0093] PVDF and Si3N4 particles were dispersed in DMF solvent, and the resulting slurry was coated on a 7μm thick diaphragm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. Then, another 7μm thick diaphragm was covered on the surface, dried at room temperature, and then placed in a vacuum oven at 60°C for 24 hours to obtain a composite diaphragm.

[0094] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polyethylene membrane.

[0095] Example 6

[0096] This embodiment provides a composite diaphragm, comprising a ceramic base layer and base films located on both sides of the ceramic base layer, wherein the ceramic base layer comprises ceramic particles and a polymer binder, wherein the ceramic particles comprise a first ceramic and a second ceramic, wherein the first ceramic is hexagonal BN particles (particle size D50 is 1.7 μm), the second ceramic is LLZTO (particle size D50 is 1 μm), and the polymer binder is PVDF; both sides of the outer surface of the composite diaphragm are base films;

[0097] In the ceramic matrix layer, the mass proportion of ceramic particles is 93%, and the mass proportion of polymer binder is 7%;

[0098] In the ceramic particles, the mass of the second ceramic accounts for 40% of the mass of the first ceramic;

[0099] The thickness of the ceramic base layer is 6 μm, and the thickness of the base films on both sides are 10 μm and 5 μm respectively.

[0100] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0101] PVDF, hexagonal BN particles, and LLZTO were mixed and dispersed in DMF solvent. The resulting slurry was coated on a 10 μm thick diaphragm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. The surface was then covered with another 5 μm thick diaphragm. The membrane was first dried at room temperature and then dried in a vacuum oven at 70°C for 15 hours. The composite membrane was then removed.

[0102] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polyethylene membrane.

[0103] Example 7

[0104] This embodiment provides a composite diaphragm, comprising a ceramic base layer and base films located on both sides of the ceramic base layer. The ceramic base layer includes ceramic particles and a polymer binder. The ceramic particles include a first ceramic and a second ceramic. The first ceramic is N-type cubic phase BN particles (particle size D50 is 0.3 μm), the second ceramic is ZrB2 (particle size D50 is 0.4 μm), and the polymer binder is PVDF. Both sides of the outer surface of the composite diaphragm are base films.

[0105] In the ceramic matrix layer, the mass proportion of ceramic particles is 30%, and the mass proportion of polymer binder is 70%;

[0106] In the ceramic particles, the mass of the second ceramic accounts for 85% of the mass of the first ceramic;

[0107] The thickness of the ceramic base layer is 10 μm, and the thickness of the base films on both sides is 8 μm.

[0108] This embodiment also provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0109] PVDF, N-type cubic phase BN particles and ZrB2 were dispersed in DMF solvent, and the resulting slurry was coated on a diaphragm with a thickness of 8 μm. The thickness of the ceramic layer was adjusted by controlling the thickness of the scraper. Then, another diaphragm with a thickness of 8 μm was used to cover the surface. The membrane was first dried at room temperature and then dried in a vacuum oven at 80°C for 12 hours. The composite membrane was then taken out.

[0110] The diaphragm used in the preparation method of this embodiment is also the base membrane, specifically a porous polypropylene membrane.

[0111] Example 8

[0112] The difference from Example 1 is that the mass of the second ceramic accounts for 30% of the mass of the first ceramic.

[0113] Example 9

[0114] The difference from Example 1 is that the mass of the second ceramic accounts for 90% of the mass of the first ceramic.

[0115] Example 10

[0116] The difference from Example 1 is that the particle size D50 of the hexagonal BN particles is 2 μm. At this time, the ratio of the particle size D50 of the first ceramic particles to the particle size D50 of the second ceramic particles is 1:0.25.

[0117] Example 11

[0118] The difference from Example 1 is that the particle size D50 of LLZO is 2 μm. In this case, the ratio of the particle size D50 of the first ceramic to the particle size D50 of the second ceramic is 1:4.

[0119] Example 12

[0120] The difference from Example 1 is that the hexagonal BN particles are replaced by magnesium nitride particles.

[0121] Comparative Example 1

[0122] The difference from Example 1 is that in the ceramic matrix layer, the mass proportion of ceramic particles is 97%, and the mass proportion of polymer binder is 3%.

[0123] Comparative Example 2

[0124] This comparative example is a pure polypropylene film (PP membrane), which is also the base film in Example 2.

[0125] Comparative Example 3

[0126] This comparative example is a single-layer ceramic diaphragm purchased from Enjie Co., Ltd.

[0127] Comparative Example 4

[0128] The difference from Example 1 is that the ceramic particles are only LLZO particles, and the mass of the LLZO particles in this comparative example is the same as the total mass of the ceramic particles in Example 1.

[0129] The porosity of the separators of Examples 1-12 and Comparative Examples 1-4 was tested. The results are shown in Table 1.

[0130] The thermal shrinkage of the separators of Examples 1-12 and Comparative Examples 1-4 was tested at a temperature of 150° C. The results are shown in Table 1.

[0131] Batteries were assembled using the separators of the embodiments and comparative examples and tested, specifically including:

[0132] 1. Assemble the battery:

[0133] 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 to obtain a positive electrode.

[0134] The electrolyte composition is: 1 mol / L LiPF6 as electrolyte and a mixture of EC:DMC (volume ratio) = 1:1 as solvent.

[0135] Using a lithium sheet with a thickness of 100 μm as the counter electrode, the positive electrode, counter electrode, separator and electrolyte were assembled into a button battery with a model number of 2032 in an inert gas glove box with a water and oxygen content of less than 0.1 ppm.

[0136] 2. Test the discharge capacity of the battery: Perform charge and discharge tests at room temperature with a current density of 0.1C.

[0137] 3. Test interface impedance:

[0138] The above-mentioned button cell model 2032 was used as the test object. The EIS program was called through the electrochemical workstation, and the frequency range was set to 1 Hz to 1 MHz to test the interfacial impedance after one cycle.

[0139] The test results are shown in Table 1.

[0140] Table 1

[0141] As shown in Table 1, the method of the present invention, by placing the ceramic matrix layer on the inside and the base membrane on the outside, and adding at least a nitride inorganic ceramic to the ceramic matrix layer, can effectively improve the high-temperature resistance of the separator, reduce the interfacial impedance of the battery, and improve the electrochemical performance of the battery. The composite separator of the present invention has a thermal shrinkage rate of less than 5.3% at 150°C, an interfacial impedance of less than 52Ω after one cycle, and a discharge capacity of more than 153mAh / g.

[0142] By comparing Example 1 with Examples 8-9, it can be seen that the mass ratio of the first ceramic and the second ceramic will affect the performance of the composite ceramic. When the mass of the second ceramic accounts for 50%-80% of the mass of the first ceramic, it is more conducive to improving high temperature resistance, reducing interface internal resistance and increasing the discharge capacity of the battery.

[0143] By comparing Example 1 with Examples 10-11, it can be seen that the ratio of the particle size D50 of the first ceramic to the particle size D50 of the second ceramic will affect the performance of the composite ceramic. When the ratio of the particle size D50 of the first ceramic to the particle size D50 of the second ceramic is 1:(0.5-2), it is beneficial to improve the interface contact between the two ceramics, thereby improving the high temperature resistance and interface compatibility of the composite diaphragm, and improving the electrochemical performance of the battery.

[0144] By comparing Example 1 and Example 12, it can be seen that the type of nitride inorganic ceramic will affect the properties of the composite diaphragm and thus affect the electrochemical performance of the battery assembled therewith. Since the main component of the ceramic diaphragm is a polymer, the boron atoms in boron nitride can form Lewis acid sites in the polymer. Therefore, when the lithium salt passes through the composite diaphragm layer, the lithium ions can pass through quickly, thereby improving the lithium ion conductivity and thus improving the electrochemical performance of the battery.

[0145] A comparison of Example 1 and Comparative Example 1 shows that when the mass ratio of ceramic particles exceeds 95%, the ceramic matrix layer is difficult to form a film, the adhesion is reduced, and a composite separator with a "sandwich" structure cannot be formed. Moreover, when the content of ceramic particles in the entire suspension system exceeds 95%, sedimentation occurs, making it difficult to form a stable suspension system, which in turn affects the uniformity of the dispersion of ceramic particles in the ceramic matrix layer. These factors lead to a significant decline in the performance of the battery assembled with the separator of Comparative Example 1.

[0146] The diaphragms used in Comparative Examples 2 and 3 are commercially available base membranes and ceramic diaphragms, respectively, which have poor high temperature resistance and wettability. Therefore, when used in batteries, they have problems with poor thermal stability and interface compatibility, which leads to a decrease in electrochemical performance.

[0147] By comparing Example 1 with Comparative Example 4, it can be seen that the use of nitride inorganic ceramics is beneficial to improving high temperature resistance. At the same time, it can be seen from Table 1 that the coordinated use of nitride ceramics and LLZO also plays a positive role in reducing the interface internal resistance and improving the capacity of the battery.

[0148] 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 includes a ceramic base layer and base films located on both sides of the ceramic base layer, the ceramic base layer includes ceramic particles, the ceramic particles include a first ceramic, and the first ceramic is a nitride inorganic ceramic; The outer surfaces on both sides of the composite diaphragm are the base membranes.

2. The composite diaphragm according to claim 1, characterized in that: 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 at least one of hexagonal boron nitride and N-type cubic boron nitride.

3. The composite diaphragm according to claim 1 or 2, characterized in that: The ceramic particles also include a second ceramic, which includes at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, molybdenum-doped silicon dioxide, zirconium boride, zirconium nitride compounds, silicon boride, vanadium boride, titanium boride, magnesium boride and an inorganic ceramic solid electrolyte; Preferably, the zirconium nitride compound includes at least one of ZrN, o-Zr3N4, and c-Zr3N4; Preferably, the inorganic ceramic solid electrolyte includes at least one of 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.

4. The composite diaphragm according to claim 3, characterized in that: The mass of the second ceramic accounts for 0%-95% of the mass of the first ceramic and does not include 0%, preferably 50%-80%; Preferably, the particle size D50 of the first ceramic is 0.2 μm-2 μm, and the particle size D50 of the second ceramic is 0.2 μm-2 μm; Preferably, the ratio of the particle size D50 of the first ceramic to the particle size D50 of the second ceramic is 1:(0.5-2).

5. The composite diaphragm according to any one of claims 1 to 4, characterized in that: The ceramic matrix layer also includes a polymer binder, and the polymer binder binds the ceramic particles together; Preferably, the polymer binder includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, 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 and polyimide; Preferably, the polymalonate material includes at least one of polypentylene malonate, polyethylene malonate, polypropylene malonate and polyhexylene malonate; Preferably, the polysuccinate material includes polyethylene succinate and / or polypropylene succinate; Preferably, in the ceramic matrix layer, the mass proportion of ceramic particles is 5%-95%, preferably 50%-90%.

6. The composite diaphragm according to any one of claims 1 to 5, characterized in that: The thickness of the ceramic matrix layer is 5 μm-20 μm.

7. The composite diaphragm according to any one of claims 1 to 6, characterized in that: The base film is a polymer base film, preferably including any one of a porous polyethylene film, a porous polypropylene film, a porous polyethylene / polypropylene film and a porous polyimide film; Preferably, the thickness of the base films on both sides of the ceramic base layer is independently 5 μm-20 μm.

8. A method for preparing a composite diaphragm according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: preparing a ceramic slurry including ceramic particles; The ceramic slurry is applied to the surface of the first base film to form a ceramic slurry layer, and the second base film is covered The ceramic slurry layer is dried to obtain the composite diaphragm.

9. The preparation method according to claim 8, characterized in that: The drying is vacuum drying; Preferably, the drying temperature is 50° C.-80° C., and the drying time is 12-26 hours.

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 as described in any one of claims 1 to 7 or a composite diaphragm prepared by the preparation method as described in any one of claims 8 to 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 and / or between the composite separator and the negative electrode.

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