Ceramic composite diaphragm and battery

Abstract

The invention provides a ceramic composite diaphragm and a battery. The ceramic composite diaphragm comprises a base membrane and a ceramic coating arranged on the surface of at least one side of the base membrane, wherein the ceramic coating comprises ceramic powder and graft modified polyvinyl alcohol; the graft modified polyvinyl alcohol comprises acrylic ester graft modified polyvinyl alcohol, and the mass ratio of hydroxyl in the graft modified polyvinyl alcohol is 2%-10%. The ceramic composite diaphragm provided by the invention has low moisture content, and the peel strength between the ceramic coating and the base membrane is high.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a ceramic composite diaphragm and a battery. Background Art

[0002] With the expansion of the commercial lithium-ion battery market, the requirements for safety and performance are constantly increasing. One of the keys to providing high safety and high performance is the diaphragm. Traditional polyolefin diaphragms can no longer meet the high safety requirements of current users for lithium-ion batteries. Ceramic composite diaphragms coated with ceramic coatings have greatly improved oxidation resistance, high temperature resistance, and safety, and have become the mainstream of current lithium-ion battery technology.

[0003] The moisture content of the ceramic composite diaphragm will affect the safety and performance of the lithium-ion battery. In order to reduce the moisture content of the ceramic composite diaphragm, the existing technology generally uses hydrophobic adhesives to reduce the water absorption. However, the hydrophobic adhesive basically relies on the van der Waals force to achieve the bonding effect, which is difficult to meet the high adhesion requirements between the ceramic coating and the polyolefin diaphragm. In the actual lithium battery winding production process, the ceramic composite diaphragm is prone to ceramic coating powder shedding, which affects the normal processing and production of lithium batteries, and is also prone to cause internal self-discharge and micro-short circuit problems in the battery, greatly reducing the safety and cycle performance of lithium batteries.

[0004] Therefore, it is necessary to develop a ceramic composite diaphragm that can improve the peel strength between the ceramic coating and the base membrane while maintaining a low moisture content in the ceramic composite diaphragm, thereby improving the electrochemical safety and performance of the ceramic composite diaphragm. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a ceramic composite diaphragm and a battery. The ceramic composite diaphragm can improve the peel strength between the ceramic coating and the base film while maintaining a low moisture content, thereby improving electrochemical safety and performance.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a ceramic composite diaphragm, the ceramic composite diaphragm comprising a base film and a ceramic coating disposed on at least one side of the base film, the ceramic coating comprising ceramic powder and grafted modified polyvinyl alcohol;

[0008] The grafted modified polyvinyl alcohol includes acrylate grafted modified polyvinyl alcohol, and the mass percentage of hydroxyl groups in the acrylate grafted modified polyvinyl alcohol is 2% to 10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0009] In the present invention, acrylate grafted modified polyvinyl alcohol is prepared by grafting acrylate onto polyvinyl alcohol, thereby making up for the deficiency of hydrophobic adhesive in peel strength; grafting acrylate onto the polyvinyl alcohol molecular chain can significantly reduce the water absorption of polyvinyl alcohol; the ceramic composite diaphragm prepared by adding acrylate grafted modified polyvinyl alcohol can improve the peel strength between the ceramic coating and the base film while maintaining a low moisture content, improve the electrochemical safety and performance, and meet the processing and performance requirements of lithium batteries.

[0010] In a second aspect, the present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet and the ceramic composite diaphragm as described in the first aspect.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The ceramic composite diaphragm of the present invention has low moisture content, high peel strength between the ceramic coating and the base film, and can meet the processing and use performance requirements of lithium batteries; the ceramic composite diaphragm has low production cost and is suitable for large-scale production. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0014] The present invention provides a ceramic composite diaphragm, which comprises a base film and a ceramic coating arranged on at least one side of the base film, wherein the ceramic coating comprises ceramic powder and grafted modified polyvinyl alcohol;

[0015] The grafted modified polyvinyl alcohol includes acrylate grafted modified polyvinyl alcohol, and the mass percentage of hydroxyl groups in the acrylate grafted modified polyvinyl alcohol is 2% to 10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0016] In the present invention, the mass proportion of hydroxyl groups in the acrylate grafted modified polyvinyl alcohol is 2% to 10%. If the mass proportion of hydroxyl groups in the acrylate grafted modified polyvinyl alcohol is too low, the acrylate grafted modified polyvinyl alcohol fails to play its role in improving the peel strength of the ceramic coating; if the mass proportion of hydroxyl groups in the acrylate grafted modified polyvinyl alcohol is too high, the moisture content of the ceramic composite diaphragm will be high. Acrylate grafted modified polyvinyl alcohol is prepared by grafting acrylate onto polyvinyl alcohol, which makes up for the deficiency of the existing adhesive in peel strength while significantly reducing the water absorption of polyvinyl alcohol; the ceramic composite diaphragm prepared by adding acrylate grafted modified polyvinyl alcohol can improve the peel strength between the ceramic coating and the base film while maintaining a low moisture content, improve electrochemical safety and performance, and meet the processing and performance requirements of lithium batteries.

[0017] In the present invention, at least one side of the base membrane refers to at least one of the two sides of the base membrane with the largest surface area and arranged opposite to each other. In the present invention, a ceramic coating can be arranged on one side of the base membrane to form a ceramic composite diaphragm, and a ceramic coating can also be arranged on both sides of the base membrane to form a ceramic composite diaphragm.

[0018] Preferably, the grafted mass proportion of acrylate in the acrylate grafted modified polyvinyl alcohol is 70% to 90%, for example, it can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90% or the range of any two thereof.

[0019] In the present invention, the grafted mass proportion of acrylate in the acrylate grafted modified polyvinyl alcohol is obtained by theoretical calculation, specifically, in the preparation of acrylate grafted modified polyvinyl alcohol, the total mass of acrylate and polyvinyl alcohol input is 100%, wherein the mass proportion of acrylate is.

[0020] When the grafted mass ratio of acrylate in the acrylate grafted modified polyvinyl alcohol meets the above range, it is beneficial to further ensure the peel strength and moisture content of the coating.

[0021] Preferably, the acrylic acid ester includes any one or a combination of at least two of hydroxyethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate or styrene acrylate.

[0022] The acrylate grafted modified polyvinyl alcohol in the present invention can be obtained through commercial channels or prepared by using an existing grafting method. For example, the acrylate grafted modified polyvinyl alcohol can be prepared by the following method: polyvinyl alcohol, acrylate, sodium hydroxide and water are mixed to form a mixed system, the mixed system is reacted at a temperature of 60 to 100° C. for 1 to 24 hours under a nitrogen environment, and water is removed after sufficient reaction to obtain the acrylate grafted modified polyvinyl alcohol. However, the present invention is not limited thereto.

[0023] Preferably, the alcoholysis degree of polyvinyl alcohol is 60% to 80%, for example, it can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80% or any two thereof.

[0024] The weight average molecular weight of the polyvinyl alcohol is not particularly limited in the present invention. Preferably, the weight average molecular weight of the polyvinyl alcohol is 10000-80000, for example, it can be 10000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, 55000, 60000, 65000, 70000, 75000, 80000, or any two thereof. The weight average molecular weight of the polyvinyl alcohol can be obtained by an existing test method, such as gel permeation chromatography (GPC).

[0025] Preferably, based on the total mass of polyvinyl alcohol, acrylate, sodium hydroxide and water being 100%, the mass proportion of the sodium hydroxide is 0.2% to 0.5%.

[0026] Preferably, based on the total mass of polyvinyl alcohol, acrylate, sodium hydroxide and water being 100%, the mass proportion of water may be 50% to 70%.

[0027] Preferably, based on the total mass of the ceramic coating being 100%, the mass proportion of the acrylate graft-modified polyvinyl alcohol is 2% to 8%, and more preferably 2% to 6%.

[0028] When the mass proportion of acrylate grafted modified polyvinyl alcohol meets the above range, it is beneficial to further provide sufficient adhesion to the ceramic powder and improve the peel strength of the coating.

[0029] Exemplarily, based on the total mass of the ceramic coating as 100%, the mass proportion of the acrylate grafted modified polyvinyl alcohol can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or a range consisting of any two of them.

[0030] Further preferably, the total mass of the ceramic coating is 100%, and the mass proportion of the acrylate grafted modified polyvinyl alcohol is 3.0% to 4.5%.

[0031] Preferably, based on the total mass of the ceramic coating being 100%, the mass proportion of the ceramic powder is 92% to 98%, and more preferably 92% to 96%.

[0032] When the mass proportion of the ceramic powder meets the above range, it is conducive to forming a suitable coating pore size and porosity between the ceramic powders. At the same time, the ceramic powder can form a good ratio with the grafted modified polyvinyl alcohol to further improve the peel strength between the coating and the base film, thereby improving the electrochemical performance.

[0033] Exemplarily, with the total mass of the ceramic coating as 100%, the mass proportion of the ceramic powder can be 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or a range consisting of any two of them.

[0034] The ceramic powder in the ceramic layer is not particularly limited as long as it is electrochemically stable. That is, the ceramic powder does not undergo oxidation and / or reduction within the operating voltage range applied to the electrochemical device (e.g., 0 to 5 V for Li / Li+), and the ceramic powder can be used without special restrictions in the present invention. From the perspective of helping to improve the ionic conductivity of the electrolyte, preferably, the ceramic powder includes any one of aluminum oxide, boehmite, silicon oxide, magnesium oxide, barium sulfate or barium titanate, or a combination of at least two thereof.

[0035] The present invention has no particular limitation on the shape of the ceramic powder, which may be any existing ceramic powder shape, for example, any one or a combination of at least two of spherical, elliptical, quasi-spherical, plate-like or flake-like shapes.

[0036] Preferably, the particle size of the ceramic powder is 0.2 μm to 3.0 μm, for example, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or a range consisting of any two thereof.

[0037] When the particle size of the ceramic powder meets the above range, it is beneficial to form a uniform thickness of the coating while providing the pore size and porosity of the coating, thereby improving the battery cycle performance and safety performance. The particle size of the ceramic powder can be determined by conventional techniques known in the art. For example, a laser scattering particle size analyzer (European and American Topsizer type particle size analyzer) can be used to characterize the particle size of the ceramic powder, specifically including dispersing the ceramic powder in pure water, obtaining the D50 of the ceramic powder as the particle size of the ceramic powder, and the D50 of the ceramic powder refers to the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, which is the D50 of the ceramic powder; the composite ceramic layer can also be scanned by a scanning electron microscope (SEM), and the average particle size of the ceramic powder can be obtained by statistically analyzing and calculating the scanning results (such as Image J software analysis and calculation).

[0038] Preferably, the surface density of the ceramic composite diaphragm is 1.15 to 2.5 times the surface density of the base membrane, for example, 1.15 times, 1.2 times, 1.4 times, 1.6 times, 1.8 times, 2.0 times, 2.2 times, 2.4 times, 2.5 times or a range consisting of any two of them.

[0039] By making the surface density of the ceramic composite diaphragm and the surface density of the base membrane satisfy the above relationship, the ceramic composite diaphragm has better ion permeability and lower internal resistance, while ensuring the adhesion of the ceramic coating and improving battery performance.

[0040] The surface density can be determined by conventional techniques known in the art, such as the weighing method. Specifically, the sample membrane (base membrane or ceramic composite membrane) to be tested can be cut into 10 cm×10 cm pieces, the sample weight can be weighed, and the mass per unit area of ​​the sample membrane can be calculated to obtain the surface density of the base membrane (in g / m 2 ).

[0041] In the ceramic composite diaphragm of the present invention, the ceramic coating may further include additives such as a dispersant and a wetting agent. In the coating solution for forming the ceramic coating, a dispersant is added for the purpose of improving dispersibility, coating properties or storage stability. In the coating solution for forming the ceramic coating, a wetting agent is added, for example, for the purpose of improving affinity with a porous substrate.

[0042] The present invention does not particularly limit the dispersant. For example, the dispersant can be selected from any one of sodium polyacrylate, ammonium polyacrylate, carboxylates, hexametaphosphates or sulfonates, or a combination of at least two thereof.

[0043] The present invention does not particularly limit the wetting agent. For example, the wetting agent can be selected from any one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether or polyether-modified polysiloxane, or a combination of at least two thereof.

[0044] The present invention does not impose any particular limitation on the mass percentage of additives such as dispersants and wetting agents, and the added content corresponding to the purpose can be freely selected.

[0045] Exemplarily, based on the total mass of the ceramic coating as 100%, the mass proportion of the dispersant is 0.5% to 3.0%, for example, it can be 0.5%, 0.8%, 1.1%, 1.4%, 1.7%, 2.0%, 2.3%, 2.7%, 3.0% or any two thereof.

[0046] Exemplarily, based on the total mass of the ceramic coating as 100%, the mass proportion of the wetting agent is 0.5% to 1.5%, for example, it can be 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5% or a range consisting of any two of them.

[0047] Furthermore, in the separator of the present invention, if the porous substrate having a plurality of pores is a conventional porous substrate used for electrochemical devices, it is not limited to a specific kind of porous substrate. Exemplarily, the base film includes a polyolefin porous film.

[0048] Preferably, the polyolefin porous membrane can be selected from polyethylene microporous membrane, polypropylene microporous membrane, polybutylene microporous membrane, polymethylpentene microporous membrane or a multilayer (two or more layers) composite membrane formed by any two or more thereof in any stacking order.

[0049] The present invention does not particularly limit the thickness of the polyolefin porous membrane. Based on the viewpoints of mechanical strength and internal resistance, the thickness is preferably between 1 μm and 5000 μm, more preferably between 5 μm and 20 μm. For example, it can be 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 20 μm or any two thereof.

[0050] The present invention does not particularly limit the average pore size and porosity of the polyolefin porous membrane, but based on the viewpoints of mechanical strength, ion permeability and electrochemical safety, it is preferably a porosity between 30% and 65%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or any two of them; the average pore size is preferably in the range of 20nm to 100nm, for example, it can be 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or any two of them. In addition, the pore structure of the polyolefin porous membrane is formed by the interlaced connection of a number of fibrils, which are formed by the polymer being stretched and oriented during the preparation process, and the preparation method of the polyolefin porous membrane is not particularly limited.

[0051] Hereinafter, a preferred preparation method for manufacturing the ceramic composite diaphragm of the present invention is described below. However, the present invention is not limited thereto.

[0052] Exemplarily, the method for preparing the ceramic composite diaphragm comprises the following steps:

[0053] (1) Mixing materials including ceramic powder, graft-modified polyvinyl alcohol and a solvent to obtain a ceramic slurry.

[0054] (2) coating the ceramic slurry obtained in step (1) on at least one surface of the base membrane and drying the slurry to obtain the ceramic composite diaphragm.

[0055] Preferably, the solvent includes at least one of deionized water, N-N dimethylformamide (DMF), N-N methylpyrrolidone (NMP), N-N dimethylacetamide (DMAC) or tetrahydrofuran (THF).

[0056] Based on the considerations of ceramic slurry stability and coating uniformity, preferably, the solid content of the ceramic slurry is 20% to 50%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any two thereof.

[0057] Preferably, before step (2), the method may further include filtering the obtained ceramic slurry.

[0058] Exemplarily, the filter mesh number used for filtration is 200-400 mesh, so as to remove particles with excessively large particle size and metal foreign matter in the slurry to improve coating uniformity and safety of use. The filter mesh number can be, for example, 200 mesh, 220 mesh, 240 mesh, 260 mesh, 280 mesh, 300 mesh, 320 mesh, 340 mesh, 360 mesh, 380 mesh, 400 mesh or a range consisting of any two of them.

[0059] In addition, the ceramic slurry prepared in step (1) may be coated on at least one side of the surface of the base film using conventional coating methods known in the art, such as dip coating, die coating, roller coating or a combination thereof.

[0060] The present invention also provides a battery, comprising a positive electrode sheet, a negative electrode sheet and at least one of the ceramic composite diaphragms described above.

[0061] The ceramic composite diaphragm of the present invention can be used as a diaphragm between the positive electrode sheet and the negative electrode sheet.

[0062] The battery provided by the present invention is any device that can undergo electrochemical reactions, for example, it can include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, capacitors (such as supercapacitors), etc. Specifically, lithium secondary batteries can be preferably used in secondary batteries, including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries, etc.

[0063] Specifically, the battery may be a lithium secondary battery.

[0064] Specifically, the battery includes a positive electrode sheet, a negative electrode sheet and the above-mentioned ceramic composite diaphragm. The ceramic composite diaphragm is spaced between the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from contacting and short-circuiting. At the same time, during the charge and discharge process of the battery, the ceramic composite diaphragm allows active lithium ions to pass through. The active lithium ions pass through the diaphragm and migrate back and forth between the positive and negative electrodes to be deintercalated in the positive and negative electrodes to realize the charge and discharge process of the battery.

[0065] As mentioned above, the surface of the base film of the above-mentioned ceramic composite diaphragm is provided with a lithium replenishing layer, which can effectively release active lithium ions during the charge and discharge process of the battery. The released active lithium ions participate in the charge and discharge process of the battery, thereby replenishing the battery with lithium and compensating for the irreversible lithium loss generated during the charge and discharge process of the battery, thereby improving the coulomb efficiency of the battery in the first week, reducing the internal resistance of the battery, and improving the cycle performance of the battery.

[0066] Generally, the positive electrode sheet includes a positive electrode collector and a positive electrode coating located on at least one side surface of the positive electrode collector. The positive electrode coating can be provided on one side surface of the positive electrode collector, or on both the front and back sides of the positive electrode collector.

[0067] Specifically, the positive electrode current collector may be a conventional positive electrode current collector in the art, for example, the positive electrode current collector may include aluminum foil, but is not limited thereto.

[0068] Specifically, the positive electrode coating layer may include a positive electrode active material layer including a positive electrode active material, a first conductive agent, and a first binder.

[0069] Among them, the positive electrode active material can be a conventional positive electrode active material in the art, for example, the positive electrode active material includes a lithium-containing active material, and the lithium-containing active material can include one or more of nickel-cobalt-manganese ternary material (NCM), lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel manganese oxide, lithium-rich manganese-based solid solution or lithium manganese oxide, etc.

[0070] The first conductive agent may be a conventional conductive material in the art. For example, the first conductive agent may include one or more of conductive carbon black (SuperP), acetylene black, graphene, Ketjen black or carbon fiber, but is not limited thereto.

[0071] Among them, the first binder can be a conventional bonding material in the art, for example, the first binder can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinyl pyrrolidone or polyurethane, but is not limited thereto.

[0072] Specifically, based on 100% of the total mass of the positive electrode active material layer, the mass fraction of the positive electrode active material may be 70% to 99%, the mass fraction of the first conductive agent may be 0.5% to 15%, and the mass fraction of the first binder may be 0.5% to 15%.

[0073] In addition, the negative electrode sheet includes a negative electrode collector and a negative electrode coating present on at least one side of the negative electrode collector. The negative electrode coating can be provided on one side of the negative electrode collector, or on both the positive and negative sides of the negative electrode collector.

[0074] Specifically, the negative electrode current collector may be a conventional negative electrode current collector in the art, for example, the negative electrode current collector may include copper foil, but is not limited thereto.

[0075] Specifically, the negative electrode coating layer may include a negative electrode active material layer including a negative electrode active material, a second conductive agent, and a second binder.

[0076] The negative electrode active material may include graphite and / or silicon-based materials, and the silicon-based materials may include silicon-carbon and / or silicon-oxygen materials, but are not limited thereto.

[0077] The second conductive agent may be a conventional conductive material in the art. For example, the second conductive agent may include one or more of conductive carbon black (SuperP), acetylene black, Ketjen black, carbon fiber or graphene, but is not limited thereto.

[0078] Among them, the second binder can be a conventional bonding material in the art. For example, the second binder can include one or more of PVDF, polyacrylic acid (PAA), carboxymethyl cellulose, styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, sodium polyacrylate, polyacrylonitrile copolymers or polyacrylic acid copolymers, but is not limited thereto.

[0079] Specifically, based on the total mass of the negative electrode active material layer, the mass fraction of the negative electrode active material may be 70% to 99%, the mass fraction of the second conductive agent may be 0.5% to 15%, and the mass fraction of the second binder may be 0.5% to 15%.

[0080] Exemplarily, the positive electrode sheet can be prepared by conventional methods in the art, such as by a coating method. For example, the preparation process of the positive electrode sheet includes: dispersing the components for forming the positive electrode coating, such as the positive electrode active material, the first conductive agent, the first binder, etc., in a first solvent, wherein the first solvent includes, for example, N-methylpyrrolidone (NMP), to prepare a positive electrode slurry; applying the positive electrode material to the surface of the positive electrode collector, and after drying, rolling and other processes, forming a positive electrode coating on the surface of the positive electrode collector to obtain a positive electrode sheet.

[0081] Illustratively, the negative electrode sheet can be prepared by conventional methods in the art, such as by a coating method. For example, the preparation process of the negative electrode sheet includes: dispersing the components for forming the negative electrode coating, such as the negative electrode active material, the second conductive agent, the second binder, etc., in a second solvent, the second solvent includes, for example, water (specifically, deionized water can be used), to prepare a negative electrode slurry; applying the negative electrode material to the surface of the negative electrode collector, and after drying, rolling and other processes, forming a negative electrode coating on the surface of the negative electrode collector to obtain a negative electrode sheet.

[0082] Generally, a battery includes a cell and a package that packages the cell, and the cell includes the above-mentioned positive electrode sheet, separator and negative electrode sheet. The cell can be a wound cell, that is, the positive electrode sheet, separator and negative electrode sheet are stacked in sequence and then wound to form a wound cell (rolled core); or, the cell can also be a laminated cell, that is, the cell includes a plurality of stacked positive electrode sheets and a plurality of negative electrode sheets, which are staggered and separated by a separator.

[0083] In the embodiments of the present application, the package body may be a conventional packaging material in the art. For example, the package body may include a soft packaging material (ie, the battery may be a soft packaging battery). The soft packaging material may include, for example, an aluminum-plastic film, but is not limited thereto.

[0084] In addition, the battery also includes an electrolyte, which may be a conventional electrolyte in the art, specifically a non-aqueous electrolyte.

[0085] For example, the electrolyte may include an organic solvent, an electrolyte salt, and an additive.

[0086] The organic solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC) or ethyl propyl carbonate (EPC).

[0087] Among them, the electrolyte salt may include a lithium salt, and the lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium bis(difluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0088] The additive may include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN) or adiponitrile (ADN).

[0089] Illustratively, the battery can be manufactured according to conventional methods in the art. For example, after assembling the positive electrode sheet, the separator and the negative electrode sheet into a battery cell, the battery cell is packaged with a packaging body, and then the battery is manufactured after processes such as liquid injection and formation. These processes are all conventional operations in the battery preparation process in the art and are not particularly limited.

[0090] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes 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.

[0091] The technical solution provided by the present invention will be clearly and completely described below in conjunction with examples and comparative examples. Obviously, the specific implementation methods described are only part of the implementation methods of the present invention, rather than all the implementation methods.

[0092] The materials used in the present invention can be purchased from the market or prepared by conventional methods; unless otherwise specified, the materials used in the present invention are as follows:

[0093] Polyethylene porous membrane: prepared by Shenzhen Xingyuan Material Technology Co., Ltd., with a thickness of 11 μm and a porosity of 46%.

[0094] Acrylate grafted modified polyvinyl alcohol: commissioned Hunan Gaorui Power Materials Co., Ltd. to prepare as follows:

[0095] (1) Acrylate grafted modified polyvinyl alcohol A: methyl methacrylate grafted modified polyvinyl alcohol, wherein the mass proportion of hydroxyl group is 6.1%, the mass proportion of methyl methacrylate grafted is 80%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0096] (2) Acrylate grafted modified polyvinyl alcohol B: Butyl acrylate grafted modified polyvinyl alcohol, wherein the mass proportion of hydroxyl group is 6.1%, the mass proportion of grafted butyl acrylate is 80%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0097] (3) Acrylate grafted modified polyvinyl alcohol C: polyvinyl alcohol grafted modified with isooctyl acrylate, wherein the mass proportion of hydroxyl group is 6.1%, the mass proportion of grafted isooctyl acrylate is 80%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0098] (4) Acrylate grafted modified polyvinyl alcohol D: methyl methacrylate grafted modified polyvinyl alcohol, wherein the mass proportion of hydroxyl group is 3.0%, the mass proportion of methyl methacrylate grafted is 90%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0099] (5) Acrylate grafted modified polyvinyl alcohol E: methyl methacrylate grafted modified polyvinyl alcohol, wherein the mass proportion of hydroxyl group is 9.1%, the mass proportion of methyl methacrylate grafted is 70%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0100] (6) Acrylate grafted modified polyvinyl alcohol F: polyvinyl alcohol grafted modified with methyl methacrylate, wherein the mass proportion of hydroxyl group is 5.4%, the mass proportion of grafted methyl methacrylate is 80%, the alcoholysis degree of the raw material polyvinyl alcohol is 60%, and the weight average molecular weight is 70,000.

[0101] (7) Acrylate grafted modified polyvinyl alcohol G: methyl methacrylate grafted modified polyvinyl alcohol, wherein the mass proportion of hydroxyl group is 6.7%, the mass proportion of methyl methacrylate grafted is 80%, the alcoholysis degree of the raw material polyvinyl alcohol is 80%, and the weight average molecular weight is 70,000.

[0102] (8) Acrylate grafted modified polyvinyl alcohol H: polyvinyl alcohol grafted modified with methyl methacrylate, wherein the mass proportion of hydroxyl group is 10.6%, the mass proportion of grafted methyl methacrylate is 65%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0103] (9) Acrylate grafted modified polyvinyl alcohol I: methyl methacrylate grafted modified polyvinyl alcohol, wherein the mass proportion of hydroxyl group is 1.5%, the mass proportion of methyl methacrylate grafted is 95%, the alcoholysis degree of the raw material polyvinyl alcohol is 70%, and the weight average molecular weight is 70,000.

[0104] Example 1

[0105] This embodiment provides a ceramic composite diaphragm and a battery, as follows:

[0106] 1) Ceramic composite diaphragm

[0107] The ceramic composite diaphragm includes a base membrane and ceramic coatings arranged on both sides of the base membrane, the base membrane is a polyethylene porous membrane (thickness of 11 μm, porosity of 46%), and the thickness of the ceramic coatings on both sides is 3 μm;

[0108] The ceramic coating includes the following components by mass percentage: ceramic powder (boehmite, particle size 0.9 μm) 94.4%, acrylate grafted modified polyvinyl alcohol A 4.3%, dispersant (ammonium polyacrylate dispersant, brand DP03, manufacturer Beijing Xidema) 0.8%, wetting agent (alkylphenol polyoxyethylene ether, brand YDP-2129, manufacturer Hunan Guangxin) 0.5%.

[0109] The ceramic composite diaphragm is prepared by the following method:

[0110] (1) The ceramic powder, dispersant and deionized water were stirred and uniformly mixed, and then the acrylate grafted modified polyvinyl alcohol A and the wetting agent were added and continued to be stirred and dispersed uniformly, and then filtered through a 300-mesh filter to obtain the ceramic slurry, wherein the solid content of the ceramic slurry was 36.5%.

[0111] (2) The ceramic slurry prepared in step (1) is coated on both sides of the polyethylene porous membrane, and then dried in an oven at 70° C. to form a ceramic coating, thereby obtaining the ceramic composite diaphragm.

[0112] 2) Battery

[0113] The battery is prepared by the following method: stacking a positive electrode sheet, the ceramic composite diaphragm and a negative electrode sheet to obtain an electrolytic assembly, placing the electrode assembly in an aluminum-plastic film, and sealing to obtain a battery;

[0114] The positive electrode sheet includes an aluminum foil and a positive electrode active layer arranged on the surface of the aluminum foil, the positive electrode active layer includes lithium cobalt oxide, a conductive agent (conductive carbon black Super P), and a binder (PVDF), and the mass ratio of lithium cobalt oxide, the conductive agent, and the binder is 96:2:2;

[0115] The negative electrode sheet includes a copper foil and a negative electrode active layer arranged on the surface of the copper foil, the negative electrode active layer includes silicon-doped graphite, a conductive agent (conductive carbon black SuperP), and a binder (PAA), and the mass ratio of the silicon-doped graphite, the conductive agent, and the binder is 95:2:3;

[0116] The electrolyte includes lithium hexafluorophosphate, EC, DEC and DMC. In the electrolyte, the concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of EC, DEC and DMC is 1:1:1.

[0117] Example 2

[0118] This embodiment provides a ceramic composite diaphragm and a battery, which differ from Embodiment 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with acrylate grafted modified polyvinyl alcohol B of the same mass, and other conditions are the same as those in Embodiment 1.

[0119] Example 3

[0120] This embodiment provides a ceramic composite diaphragm and a battery, which differ from Embodiment 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with acrylate grafted modified polyvinyl alcohol C of the same mass, and other conditions are the same as those in Embodiment 1.

[0121] Example 4

[0122] This embodiment provides a ceramic composite diaphragm and battery, which differ from Example 1 only in that the mass percentage of acrylate grafted modified polyvinyl alcohol A in the ceramic coating is adjusted to 1.5%, and the mass percentage of ceramic powder (boehmite, particle size 0.9 μm) is adjusted to 97.2%. Other conditions are the same as those in Example 1.

[0123] Example 5

[0124] This embodiment provides a ceramic composite diaphragm and battery, which differs from Example 1 only in that the mass percentage of acrylate grafted modified polyvinyl alcohol A in the ceramic coating is adjusted to 2%, and the mass percentage of ceramic powder (boehmite, particle size 0.9 μm) is adjusted to 96.7%. Other conditions are the same as those in Example 1.

[0125] Example 6

[0126] This embodiment provides a ceramic composite diaphragm and battery, which differ from Example 1 only in that the mass percentage of acrylate grafted modified polyvinyl alcohol A in the ceramic coating is adjusted to 6.8%, and the mass percentage of ceramic powder (boehmite, particle size 0.9 μm) is adjusted to 91.9%, and other conditions are the same as Example 1.

[0127] Example 7

[0128] This embodiment provides a ceramic composite diaphragm and battery, which differ from Example 1 only in that the mass percentage of acrylate grafted modified polyvinyl alcohol A in the ceramic coating is adjusted to 8%, and the mass percentage of ceramic powder (boehmite, particle size 0.9 μm) is adjusted to 90.7%. Other conditions are the same as those in Example 1.

[0129] Example 8

[0130] This embodiment provides a ceramic composite diaphragm and battery, which differ from Example 1 only in that the mass percentage of acrylate grafted modified polyvinyl alcohol in the ceramic coating is adjusted to 9%, and the mass percentage of ceramic powder (boehmite, particle size 0.9 μm) is adjusted to 89.7%. Other conditions are the same as in Example 1.

[0131] Example 9

[0132] This embodiment provides a ceramic composite diaphragm and a battery, which are different from the embodiment 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with the acrylate grafted modified polyvinyl alcohol D of the same mass, and other conditions are the same as those of the embodiment 1.

[0133] Example 10

[0134] This embodiment provides a ceramic composite diaphragm and a battery, which are different from the embodiment 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with the acrylate grafted modified polyvinyl alcohol E of the same mass, and other conditions are the same as those in the embodiment 1.

[0135] Embodiment 11

[0136] This embodiment provides a ceramic composite diaphragm and a battery, which are different from the embodiment 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with acrylate grafted modified polyvinyl alcohol F of the same mass, and other conditions are the same as those in the embodiment 1.

[0137] Example 12

[0138] This embodiment provides a ceramic composite diaphragm and a battery, which differ from Embodiment 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with acrylate grafted modified polyvinyl alcohol G of the same mass, and other conditions are the same as those in Embodiment 1.

[0139] Embodiment 13

[0140] This embodiment provides a ceramic composite diaphragm and a battery, which differ from the embodiment 1 only in that the coating amount of the ceramic slurry is adjusted so that the thickness of the ceramic coating on both sides is 5 μm, and other conditions are the same as those in the embodiment 1.

[0141] Comparative Example 1

[0142] This comparative example provides a ceramic composite diaphragm and a battery, which differ from Example 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with acrylate grafted modified polyvinyl alcohol H of the same mass, and other conditions are the same as those in Example 1.

[0143] Comparative Example 2

[0144] This comparative example provides a ceramic composite diaphragm and a battery, which differ from Example 1 only in that the acrylate grafted modified polyvinyl alcohol A is replaced with acrylate grafted modified polyvinyl alcohol I of the same mass, and other conditions are the same as those in Example 1.

[0145] Comparative Example 3

[0146] This comparative example provides a ceramic composite diaphragm and a battery, which differ from Example 1 only in that the acrylate grafted modified polyvinyl alcohol A in the ceramic coating is replaced with acrylamide grafted modified polyvinyl alcohol of the same mass;

[0147] The acrylamide-modified polyvinyl alcohol is prepared by the following method: 20 parts by weight of polyvinyl alcohol (with a degree of alcoholysis of 70% and a weight-average molecular weight of 70,000) and 120 parts by weight of water are mixed, stirred, heated to 80°C, and kept warm for 2 hours, 80 parts by weight of acrylamide are added, 60 ml of a sodium persulfate aqueous solution with a mass percentage concentration of 0.05% is slowly added dropwise, and after the addition is completed, the solution is dispersed on a wheel for 3 hours. After the reaction is completed, the product solution is washed with acetone to remove unreacted small molecules; the organic solid phase is taken out after suction filtration, and is dried at a constant temperature of 55°C to a constant mass; it is then washed with dimethyl sulfoxide to remove acrylamide homopolymer in the organic phase; the filtrate is taken out by suction filtration, and the filtrate is washed with acetone to precipitate acrylamide-grafted modified polyvinyl alcohol, which is suction filtered and dried at a constant temperature of 55°C to obtain the acrylamide-modified polyvinyl alcohol.

[0148] Other conditions are the same as in Example 1.

[0149] The following performance tests were performed on the ceramic composite diaphragms and batteries provided in Examples 1 to 13 and Comparative Examples 1 to 3.

[0150] Moisture content: The ceramic composite diaphragm is placed in an environment with a dew point of -50°C for 2 hours, then 0.3g of the sample is cut, placed in a glass bottle and sealed with a bottle cap with an aluminum-coated film, and then the Karl Fischer method commonly used in the lithium battery industry is used to test the moisture content in the ceramic composite diaphragm. The moisture content value is obtained by testing at 150°C for 5 minutes.

[0151] Peel strength: Mark the A side and B side on both sides of the ceramic composite diaphragm respectively, then cut them into 15mm wide sample strips, stick both sides on 3M tape (width 15mm), and then use a Tester automatic tensile machine to perform a 180° peel test on the A side and the B side respectively. The test conditions are: peel speed of 100mm / min, gauge length of 100mm, and the peel strength is obtained.

[0152] Cycle capacity retention rate: The cycle performance of the battery is tested in accordance with 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 500 cycles of charge and discharge at a rate of 1C. The cycle temperature of the assembled battery is room temperature (25°C).

[0153] The test results are shown in Table 1 below:

[0154] Table 1

[0155]

[0156]

[0157] From the content of Table 1, it can be seen that the water content of the ceramic composite diaphragm provided by the present invention is ≤740ppm, and the peel strength of the A surface and the B surface are both ≥73N / m. Preferably, the water content of the ceramic composite diaphragm is ≤700ppm, and the peel strength of the A surface and the B surface are both ≥80N / m.

[0158] By comparing Example 1 with Examples 4-8, it can be seen that, based on the total mass of the ceramic coating being 100%, the ceramic composite diaphragm prepared by the mass proportion of the acrylate grafted modified polyvinyl alcohol being within a specific range has low water content, high peel strength and better performance.

[0159] It can be seen from Example 1 and Examples 9-10 that the ceramic composite diaphragms prepared by grafting polyvinyl alcohol with acrylate in which the grafted mass proportion of acrylate is 70% to 90% have lower water content, higher peel strength and better performance.

[0160] Compared with Example 1, if the mass proportion of hydroxyl groups in the acrylate-grafted modified polyvinyl alcohol is too high (Comparative Example 1), the moisture content of the ceramic coating on the prepared ceramic composite diaphragm is too high.

[0161] Compared with Example 1, if the mass proportion of hydroxyl groups in the acrylate-grafted modified polyvinyl alcohol is too low (Comparative Example 2), the peel strength of the ceramic coating on the prepared ceramic composite diaphragm is too low.

[0162] Compared with Example 1, if the acrylate grafted modified polyvinyl alcohol is replaced by acrylamide grafted modified polyvinyl alcohol (Comparative Example 3), the prepared ceramic composite diaphragm has a higher moisture content and a lower peel strength.

[0163] The applicant declares that the present invention illustrates a ceramic composite diaphragm and a battery of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A ceramic composite diaphragm, characterized in that: The ceramic composite diaphragm comprises a base film and a ceramic coating disposed on at least one surface of the base film, wherein the ceramic coating comprises ceramic powder and grafted modified polyvinyl alcohol; The graft-modified polyvinyl alcohol includes acrylate-grafted polyvinyl alcohol, and the mass percentage of hydroxyl groups in the acrylate-grafted polyvinyl alcohol is 2% to 10%.

2. The ceramic composite diaphragm according to claim 1, characterized in that: The grafted mass proportion of acrylate in the acrylate grafted modified polyvinyl alcohol is 70% to 90%.

3. The ceramic composite diaphragm according to claim 1 or 2, characterized in that: The acrylic acid ester includes any one of hydroxyethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate or styrene acrylate, or a combination of at least two thereof.

4. The ceramic composite diaphragm according to any one of claims 1 to 3, characterized in that: Taking the total mass of the ceramic coating as 100%, the mass proportion of the acrylate grafted modified polyvinyl alcohol is 2% to 8%.

5. The ceramic composite diaphragm according to any one of claims 1 to 4, characterized in that: Taking the total mass of the ceramic coating as 100%, the mass of the ceramic powder accounts for 92% to 98%.

6. The ceramic composite diaphragm according to any one of claims 1 to 5, characterized in that: The ceramic powder includes any one of aluminum oxide, boehmite, silicon oxide, magnesium oxide, barium sulfate or barium titanate, or a combination of at least two of them.

7. The ceramic composite diaphragm according to any one of claims 1 to 6, characterized in that: The particle size of the ceramic powder is 0.2 μm to 3.0 μm.

8. The ceramic composite diaphragm according to any one of claims 1 to 7, characterized in that: The surface density of the ceramic composite diaphragm is 1.15 to 2.5 times the surface density of the base membrane.

9. The ceramic composite diaphragm according to any one of claims 1 to 8, characterized in that: The base film includes a polyolefin porous film.

10. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet and the ceramic composite diaphragm according to any one of claims 1 to 9.

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