Composite separator and lithium-ion battery

Abstract

In order to overcome the problem in the existing technology that a non-fluorinated separator binder has low bonding force, resulting in low bonding strength between an electrode sheet and a composite separator prepared and obtained by using the separator binder, a composite separator and a lithium-ion battery are provided. The composite separator comprises a base film, a non-conductive particle coating layer located on the surface of the base film, and a bonding layer located on the surface of the non-conductive particle coating layer. The bonding layer comprises a separator adhesive, the separator adhesive comprising a granular polymer, and the average particle size D1 of the granular polymer being 0.2-6μm. The non-conductive particle coating layer comprises non-conductive particles, and the average particle size D2 of the non-conductive particles is 0.1-2μm. The average particle size D1 of the granular polymer and the average particle size D2 of the non-conductive particles satisfy: D1 / D2≥0.4. The composite separator has both excellent air permeability and bonding strength with an electrode sheet.

Description

A composite separator and lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 202411435485.7, filed on October 15, 2024, entitled "A Composite Separator and a Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of secondary battery technology, specifically relating to a composite separator and a lithium-ion battery using the composite separator. Background Technology

[0003] Lithium-ion batteries are a type of rechargeable battery with broad application prospects. Due to their high energy density, long lifespan, small size, maintenance-free operation, and environmental friendliness, they are favored by various industries and have expanded from mobile phones and laptops to electric bicycles, electric vehicles, energy storage, and various portable devices, making them an ideal mobile power source.

[0004] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. The separator is one of the key internal components, and its function is to separate the positive and negative electrodes to prevent them from coming into direct contact and short-circuiting.

[0005] Currently, the separators used in lithium-ion batteries are generally polyolefin porous membranes. Because these polyolefin porous membranes have a low melting point, when the battery temperature rises due to internal or external factors, the polyolefin porous membrane will shrink or melt, causing the positive and negative electrodes to come into direct contact, leading to a short circuit in the battery, and subsequently causing accidents such as battery combustion and explosion.

[0006] To address these issues, a common approach is to coat inorganic particles onto the surface of a separator substrate using polymer binders to create a composite separator. For example, ceramic particles can be coated onto the separator substrate to form a ceramic / polymer composite separator, leveraging the heat resistance of the ceramic particles to reduce thermal shrinkage of the separator. Simultaneously, a separator binder is applied to the ceramic coating surface to bond the separator to the positive and negative electrode plates, thus securing the battery structure.

[0007] Currently, the most commonly used membrane adhesives on the market are polyvinylidene fluoride (PVDF). However, PVDF adhesives suffer from problems such as scarce upstream fluorine resources, difficulties in recycling, and serious environmental pollution caused by decomposition products. Therefore, using non-fluorinated membrane adhesives to bond the membrane to the electrode is a trend in the industry. However, existing non-fluorinated membrane adhesives (such as polyacrylate adhesives) have low adhesion strength, resulting in low bonding strength between the composite membrane prepared using these adhesives and the electrode. Summary of the Invention

[0008] The technical problem to be solved by this application is that the existing non-fluorinated membrane adhesives have low adhesion, and the composite membranes prepared using the membrane adhesives have low bonding strength with the electrodes. This application provides a composite membrane and a lithium-ion battery.

[0009] To solve the above-mentioned technical problems, this application provides a composite membrane, including a base membrane, a non-conductive particle coating on the surface of the base membrane, and an adhesive layer on the surface of the non-conductive particle coating;

[0010] The adhesive layer includes a diaphragm adhesive, which includes a particulate polymer with an average particle size D1 of 0.2-6 μm.

[0011] The non-conductive particle coating comprises non-conductive particles, wherein the average particle size D2 of the non-conductive particles is 0.1-2 μm;

[0012] The average particle size D1 of the particulate polymer and the average particle size D2 of the non-conductive particles satisfy the following:

[0013] D1 / D2≥0.4.

[0014] Preferably, the average particle size D1 of the particulate polymer and the average particle size D2 of the non-conductive particles satisfy the following condition: 0.4 ≤ D1 / D2 ≤ 100.

[0015] Preferably, the glass transition temperature (Tg) of the particulate polymer is 10-90°C.

[0016] Preferably, the particulate polymer is a polymer comprising at least one of vinyl monomer units, (meth)acrylate monomer units, maleate monomer units, itaconic acid ester monomer units, maleimide monomer units, and (meth)acrylamide monomer units.

[0017] Preferably, the vinyl monomer unit is selected from at least one of aliphatic vinyl hydrocarbon compound units, alicyclic vinyl hydrocarbon compound units, aromatic vinyl hydrocarbon compound units, alkene and propyl compound units, and vinyl compound units containing heteroatoms;

[0018] The (meth)acrylate monomer unit is selected from at least one of methacrylate monomer units and acrylate monomer units.

[0019] The maleic ester monomer unit includes at least one of maleic acid C1-C12 monoalkyl ester or maleic acid C1-C12 dialkyl ester;

[0020] The itaconic acid ester monomer unit includes at least one of itaconic acid C1-C12 monoester and itaconic acid C1-C12 dieester;

[0021] The maleimide monomer unit includes at least one of maleimide monomer unit, C1-C12 alkyl-substituted maleimide monomer unit, and C6-C16 aryl-substituted maleimide monomer unit;

[0022] The (meth)acrylamide monomer unit includes at least one of the following: (meth)acrylamide monomer unit, N-methyl(meth)acrylamide monomer unit, N-butylacrylamide monomer unit, acetylacetone acrylamide monomer unit, N-hydroxymethyl(meth)acrylamide monomer unit, N,N'-methylenebis[(meth)acrylamide] monomer unit, cinnamamide monomer unit, N,N-dimethylacrylamide monomer unit, N,N-dibenzylacrylamide monomer unit, methacryloylformamide monomer unit, N-methylN-vinylacetamide monomer unit, and N-vinylpyrrolidone monomer unit.

[0023] Preferably, the thickness of the non-conductive particle coating is 0.5-4 μm.

[0024] Preferably, the areal density of the adhesive layer is 0.1-0.6 g / m³. 2 .

[0025] Preferably, the non-conductive particle coating comprises non-conductive particles, a ceramic binder, and selectively added rheology modifiers, dispersants, and wetting agents;

[0026] In the non-conductive particle coating, the weight ratio of non-conductive particles, ceramic binder, sodium carboxymethyl cellulose, dispersant, and wetting agent is (88-96.3):(3-15):(0-3):(0-2):(0-2).

[0027] Preferably, the base film is selected from at least one of polyethylene base film, polypropylene base film, polypropylene-polyethylene-polypropylene laminated base film or non-woven fabric base film;

[0028] And / or, the thickness of the base film is 3-12 μm.

[0029] Secondly, this application provides a lithium-ion battery, including the composite separator as described above.

[0030] Through extensive research, the applicant discovered that the particulate polymer in the adhesive layer formed on the surface of the non-conductive particle coating is extremely prone to embedding into the gaps between the non-conductive particles within the coating. During the subsequent hot-pressing process of the composite separator and electrode, insufficient contact between the particulate polymer in the adhesive layer and the electrode easily occurs, resulting in low bonding strength between the composite separator and the electrode. To address this issue, the applicant set the adhesive layer of the composite separator to 0.1-0.6 g / m³. 2Within this range, by combining particulate polymers with an average particle size D1 of 0.4-3 μm and non-conductive particles with an average particle size D2 of 0.1-2 μm, and limiting D1 / D2 ≥ 0.4, the composite diaphragm can simultaneously possess excellent air permeability and bonding strength with the electrode. Detailed Implementation

[0031] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0032] In the description of this application, the term "monomer unit" refers to the corresponding unit of the monomer structure formed on a polymer chain segment after a monomer participates in polymerization. The term "average particle size" refers to the volume average particle size D of the particles. V 50.

[0033] The composite membrane provided in this application includes a base membrane, a non-conductive particle coating on the surface of the base membrane, and an adhesive layer on the surface of the non-conductive particle coating.

[0034] The adhesive layer includes a diaphragm adhesive, which includes a particulate polymer with an average particle size D1 of 0.4-3 μm.

[0035] The non-conductive particle coating comprises non-conductive particles, wherein the average particle size D2 of the non-conductive particles is 0.1-2 μm;

[0036] The average particle size D1 of the particulate polymer and the average particle size D2 of the non-conductive particles satisfy the following:

[0037] D1 / D2≥0.4.

[0038] According to this application, in the adhesive layer, the average particle size D1 of the particulate polymer is 0.2-6 μm. Specifically, the average particle size D1 of the particulate polymer can be 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.1 μm, 2.4 μm, 2.5 μm, 2.8 μm, 3 μm, 4 μm, 5 μm, or 6 μm. Preferably, the average particle size D1 of the particulate polymer is 0.2-5 μm. In the composite separator provided in this application, if the average particle size D1 of the particulate polymer is greater than 6 μm or less than 0.1 μm, the bonding strength between the composite separator and the electrode will be significantly reduced. The reason is speculated to be that if D1 is greater than 6μm, the particulate polymer is easy to fall off after it forms on the surface of the non-conductive particulate coating, thus leading to a decrease in bonding strength; if D1 is less than 0.1μm, the particulate polymer is more likely to embed into the non-conductive particulate coating, thus leading to a decrease in bonding strength.

[0039] Meanwhile, for the composite diaphragm provided in this application, the areal density of the adhesive layer on its surface is 0.1-0.6 g / m³. 2 Specifically, the areal density of the adhesive layer can be 0.1 g / m³. 2 0.2g / m 2 0.3g / m 2 0.4g / m 2 0.5g / m 2 0.6g / m 2 Preferably, the areal density of the adhesive layer is 0.1-0.3 g / m³. 2 In this application, if the areal density of the adhesive layer is not within the above-mentioned range, it will lead to a decrease in the air permeability of the composite diaphragm or insufficient bonding strength between it and the electrode.

[0040] According to this application, the glass transition temperature (Tg) of the particulate polymer can vary within a wide range. Preferably, the Tg of the particulate polymer is 10-90°C. More preferably, it is 20-80°C.

[0041] The particulate polymer in this application can be made using existing non-fluorinated adhesives for bonding diaphragms and electrodes, such as polyacrylate adhesives, the preparation methods of which are known to those skilled in the art. In this application, preferably, the particulate polymer is a polymer comprising at least one of vinyl monomer units, (meth)acrylate monomer units, maleate monomer units, itaconic acid ester monomer units, maleimide monomer units, and (meth)acrylamide monomer units.

[0042] Furthermore, the vinyl monomer unit is selected from at least one of aliphatic vinyl hydrocarbon compound units, alicyclic vinyl hydrocarbon compound units, aromatic vinyl hydrocarbon compound units, allyl compound units, and vinyl compound units containing heteroatoms.

[0043] The aliphatic vinyl hydrocarbon compounds include, but are not limited to, alkenes having 2-12 carbon atoms (exemplarily including, but not limited to: ethylene, propylene, butene, isobutene, pentene, heptene, diisobutene, octene, dodecene, octadecene), α-olefins having 3-24 carbon atoms, and dienes having 4-12 carbon atoms (exemplarily including, but not limited to: butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, and 1,7-octadiene). The alicyclic vinyl hydrocarbon compounds include, but are not limited to, monocyclic or bicyclic alkenes having 6-15 carbon atoms (exemplarily including, but not limited to: cyclohexene, vinylcyclohexene, and ethimide-bicycloheptene), monocyclic or bicyclic dienes having 5-12 carbon atoms (exemplarily including, but not limited to: cyclopentadiene, cycloheptadiene, bicyclopentadiene, and bicycloheptadiene), and terpenoids (exemplarily including, but not limited to: limonene and indene). The aromatic vinyl hydrocarbon compounds include, but are not limited to, styrene and substituted styrene, wherein the substituted styrene includes, but is not limited to, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotonylstyrene, divinylbenzene, divinyltoluene, divinylxylbenzene, trivinylbenzene, vinylnaphthalene, and p-tert-butylstyrene.

[0044] Vinyl compounds containing heteroatoms include, but are not limited to, vinyl (thio) ethers, vinyl sulfones, acrylonitrile, methacrylonitrile, cyanostyrene, 4-vinylpyridine, 2-vinylpyridine, vinylimidazole, N-vinylpyrrole, and N-vinylthiopyrrolidone.

[0045] The (meth)acrylate monomer unit is selected from at least one of methacrylate monomer units and acrylate monomer units. The (meth)acrylate monomers include, but are not limited to: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, carboxyethyl acrylate, methyl methacrylate, and so on. Ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono[(meth)acrylate] ester, (methyl (Meth)aminoethyl acrylate, (meth)acrylate dimethylaminoethyl acrylate, (meth)acrylate diethylaminoethyl acrylate, tert-butylaminoethyl methacrylate, (meth)acrylate glycidyl acrylate, (meth)acrylate tetrahydrofuran ester, ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethoxylated ethylene glycol diacrylate, ethoxylated ethylene glycol dimethacrylate, allyl methacrylate, diallyl phthalate, diallyl adipate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol diacrylate At least one of the following: ester, pentaerythritol dimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, aminoethyl acrylate, aminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, and tert-butylaminoethyl methacrylate.

[0046] The maleate ester monomer unit includes at least one of C1-C12 monoalkyl esters or C1-C12 dialkyl esters of maleic acid. As is known to those skilled in the art, C1-C12 indicates a carbon number of 1-12. Specifically, the maleate ester monomer may include at least one of monomethyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, monopropyl maleate, dipropyl maleate, monobutyl maleate, dibutyl maleate, monooctyl maleate, and dioctyl maleate.

[0047] The itaconic acid ester monomer unit includes at least one of itaconic acid C1-C12 monoester and itaconic acid C1-C12 diester. Specifically, the itaconic acid ester monomer may include at least one of itaconic acid monomethyl ester, itaconic acid dimethyl ester, itaconic acid monoethyl ester, itaconic acid diethyl ester, itaconic acid monobutyl ester, itaconic acid dibutyl ester, itaconic acid monooctyl ester, and itaconic acid dioctyl ester.

[0048] The maleimide monomer unit includes at least one of maleimide, C1-C12 alkyl-substituted maleimide, and C6-C16 aryl-substituted maleimide.

[0049] The (meth)acrylamide monomer unit includes at least one of the following: (meth)acrylamide monomer unit, N-methyl(meth)acrylamide monomer unit, N-butylacrylamide monomer unit, acetylacetone acrylamide monomer unit, N-hydroxymethyl(meth)acrylamide monomer unit, N,N'-methylenebis[(meth)acrylamide] monomer unit, cinnamamide monomer unit, N,N-dimethylacrylamide monomer unit, N,N-dibenzylacrylamide monomer unit, methacryloylformamide monomer unit, N-methylN-vinylacetamide monomer unit, and N-vinylpyrrolidone monomer unit.

[0050] In this application, the preparation method of the particulate polymer is not particularly limited, and can be any one of emulsion polymerization, suspension polymerization, dispersion polymerization, or precipitation polymerization, as long as the particle size and glass transition temperature of the prepared particulate polymer meet the specified particle size range. The particulate polymer in this application can also be commercially available; a particulate polymer product with the desired average particle size D1 and glass transition temperature can be selected.

[0051] According to this application, the adhesive layer in the composite diaphragm is formed by a diaphragm adhesive containing the aforementioned particulate polymer. The method for forming the adhesive layer can be existing, for example, by coating the diaphragm adhesive onto a non-conductive particulate coating using a conventional coating process. It should be noted that, as mentioned above, the areal density of the coated adhesive layer must be between 0.1 and 0.6 g / m³. 2 Within the range.

[0052] In this application, the non-conductive particle coating includes non-conductive particles, a ceramic binder, and selectively added rheology modifiers, dispersants, and wetting agents.

[0053] Rheology modifiers may include at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate, and lithium polyacrylate.

[0054] Non-conductive particles are well known to those skilled in the art. Specifically, non-conductive particles are particles that are non-conductive, insoluble in water used as a dispersion medium in slurries, and in non-aqueous electrolytes used in secondary batteries, and can maintain their shape. Furthermore, due to their electrochemical stability, non-conductive particles remain stable within the separator under the operating environment of secondary batteries. Various inorganic particles and heat-resistant organic particles can be used as non-conductive particles.

[0055] Examples of inorganic particles include oxide particles such as hydrated alumina, aluminum oxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, and alumina-silicon dioxide composite oxides; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; sparingly soluble ionic crystal particles such as calcium carbonate, barium titanate, barium sulfate, calcium fluoride, and barium fluoride; and clay microparticles such as talc and montmorillonite.

[0056] Examples of heat-resistant organic particles include cross-linked polymers such as polyethylene, polystyrene, polydivinylbenzene, and styrene-divinylbenzene copolymers, as well as various cross-linked polymer particles such as polyimide, polyamide, polyamide-imide, melamine resin, phenolic resin, and benzoguanamine-formaldehyde condensate, and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide. The difference between these heat-resistant organic particles and the aforementioned granular polymers is that, unlike granular polymers which possess adhesive properties, heat-resistant organic particles do not.

[0057] In this application, inorganic particles are preferred as non-conductive particles, and boehmite, hydrated alumina, and aluminum oxide are more preferred.

[0058] According to this application, the average particle size D2 of the non-conductive particles is 0.1-2 μm. Specifically, the average particle size D2 of the non-conductive particles can be 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, or 2 μm. Preferably, the average particle size D2 of the non-conductive particles is 0.2-1.5 μm. In the composite separator provided in this application, if the average particle size D2 of the non-conductive particles is greater than 2 μm, it is not conducive to balancing the heat resistance of the composite separator and the volumetric energy density of the battery. If the average particle size D2 of the non-conductive particles is less than 0.1 μm, it will lead to an excessive increase in the gas permeability of the composite separator, a decrease in gas permeability, resulting in excessively high internal resistance of the battery and poor battery performance.

[0059] Importantly, in this application, the average particle size D1 of the particulate polymer and the average particle size D2 of the non-conductive particles satisfy the condition: D1 / D2 ≥ 0.4. Through extensive research, the applicant of this application has creatively combined the aforementioned particulate polymer and non-conductive particles with specific average particle sizes, maintaining the areal density of the adhesive layer at 0.1-0.6 g / m³. 2 Within this range, it can effectively prevent the particulate polymer in the adhesive layer formed on the surface of the non-conductive particle coating from embedding into the gaps between the non-conductive particles in the non-conductive particle coating. This ensures that during the subsequent hot pressing of the composite separator and the electrode, the particulate polymer in the adhesive layer and the electrode achieve sufficient contact, improving the bonding strength between the composite separator and the electrode. Furthermore, the aforementioned composite separator also exhibits excellent air permeability.

[0060] Preferably, the average particle size D1 of the particulate polymer and the average particle size D2 of the non-conductive particles satisfy: 0.4≤D1 / D2≤100, more preferably 0.6≤D1 / D2≤60.

[0061] According to this application, the thickness of the non-conductive particulate coating is 0.5-4 μm, preferably 0.5-3 μm. When the thickness of the non-conductive particulate coating is less than 0.5 μm, it will lead to a decrease in the heat resistance of the composite separator, and the prepared battery will have a greater safety risk. When the thickness of the non-conductive particulate coating is greater than 4 μm, it will result in an excessively thick composite separator, and the prepared battery will have a lower energy density.

[0062] The role of the ceramic binder in the non-conductive particle coating is to bond the non-conductive particles to the base film. The ceramic binder used in this application can be any existing ceramic binder, and ceramic binders with the required particle size and glass transition temperature can be obtained directly through commercial purchase.

[0063] The wetting agent can be any of the existing wetting agents, such as any one or a mixture of several of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether and polyether modified polysiloxane.

[0064] The dispersant can be any of the existing dispersants, such as sodium polyacrylate.

[0065] In this application, the weight ratio of non-conductive particles, ceramic binder, rheology modifier, dispersant, and wetting agent in the non-conductive particle coating is (88-96.3):(3-15):(0-3):(0-2):(0-2). In this application, the above weight ratio represents the weight ratio between the substances, not a percentage. Preferably, the weight ratio of non-conductive particles, ceramic binder, rheology modifier, dispersant, and wetting agent in the non-conductive particle coating is (88-96.3):(3-15):(0.5-3):(0.1-2):(0.1-2).

[0066] As is known to those skilled in the art, the aforementioned non-conductive particulate coating is prepared from a non-conductive particulate slurry. For example, the non-conductive particulate slurry can be coated onto a base film and dried in an oven.

[0067] This application does not impose any particular limitation on the base film. The base film can be a polymer membrane commonly used in the art. For example, the base film can be selected from polyethylene base film, polypropylene base film, polypropylene-polyethylene composite base film or non-woven base film. Among them, polypropylene-polyethylene composite base film refers to the base film formed by laminating polypropylene and polyethylene. This application does not limit the lamination order and number of polypropylene and polyethylene. It can be a polypropylene-polyethylene double-layer base film, a polypropylene-polyethylene-polypropylene triple-layer base film, or a polypropylene-polyethylene-polypropylene quadruple-layer base film.

[0068] Preferably, the base film is selected from at least one of polyethylene base film, polypropylene base film, polypropylene-polyethylene-polypropylene laminated base film, or nonwoven base film.

[0069] The thickness of the base film can vary within a wide range; preferably, the thickness of the base film is 3-12 μm.

[0070] Secondly, this application provides a lithium-ion battery, including the composite separator as described above.

[0071] The composite diaphragm provided in this application has excellent air permeability and bonding strength with the electrode sheet.

[0072] The present application will be further illustrated by the following examples.

[0073] Example 1

[0074] The battery in this embodiment is prepared by a method including the following steps:

[0075] 1) Diaphragm adhesive

[0076] Use SL814 from Shenzhen Haodian Technology Co., Ltd.

[0077] 2) Preparation of the diaphragm

[0078] A non-conductive particle slurry was prepared by mixing 93.4 parts of non-conductive boehmite powder, 6 parts of ceramic binder (SWA610 from Shenzhen Haodian Technology Co., Ltd.), 0.3 parts of dispersant sodium polyacrylate, 1 part of sodium carboxymethyl cellulose, and 0.3 parts of wetting agent alkylphenol polyoxyethylene ether. The non-conductive particle slurry was coated on one surface of a 9 μm thick polyethylene base film and dried in an oven at 50 °C to form a non-conductive particle coating on the base film surface.

[0079] The membrane adhesive from step 1) is applied to the surface of the non-conductive particle coating and dried to obtain the adhesive layer.

[0080] The specific parameters of the particulate polymer, adhesive layer, non-conductive particles, non-conductive particle coating and base film are shown in Table 1.

[0081] 3) Preparation of the positive electrode

[0082] N-methylpyrrolidone is used to disperse positive electrode active particles lithium nickel cobalt manganese oxide (NCM523), conductive carbon black Super P, and binder polyvinylidene fluoride to form a positive electrode slurry. The positive electrode slurry is uniformly coated onto Al foil by coating. After baking and rolling processes, a positive electrode including a positive electrode active layer is obtained.

[0083] The mass ratio of the positive electrode active particles, conductive agent, and binder is 97.5:1.0:1.5.

[0084] 4) Preparation of the negative electrode

[0085] A negative electrode slurry is formed by dispersing deionized water with artificial graphite, conductive carbon black Super P, sodium carboxymethyl cellulose as a binder, and styrene-butadiene latex. Then, a negative electrode active layer is formed on the surface of the negative electrode current collector by coating, baking, and rolling processes to obtain the negative electrode.

[0086] The mass ratio of the negative electrode active particles, conductive agent, and binder (sodium carboxymethyl cellulose to styrene-butadiene latex in a mass ratio of 1:1.5) is 96.5:1.0:2.5.

[0087] 5) Battery manufacturing

[0088] The positive electrode, the aforementioned composite separator, and the negative electrode are stacked in sequence after the electrode is prepared, and then wound to obtain the battery cell. The battery cell is placed in an aluminum-plastic film, and electrolyte is injected into the bare battery cell. After vacuum sealing, standing, formation, shaping, and capacity testing, the battery is obtained.

[0089] The electrolyte includes lithium hexafluorophosphate, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the ratio of ethylene carbonate:methyl ethyl carbonate:diethyl carbonate is 3:2:5, and the concentration of lithium hexafluorophosphate is 1 mol / L.

[0090] Examples 2-7, Comparative Examples 1-6

[0091] The composite separator and battery were prepared according to the method of Example 1, except that the parameters of the particulate polymer, the adhesive layer, the non-conductive particles and the non-conductive particle coating were adjusted according to Table 1 (wherein, particulate polymers and non-conductive particles of different particle sizes were selected as shown in Table 1).

[0092] Table 1

[0093] Performance testing

[0094] The performance test results of the composite membranes in the examples and comparative examples are shown in Table 2.

[0095] 1. Diaphragm air permeability enhancement test

[0096] Refer to the air permeability test in GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries":

[0097] Three separator pieces were cut longitudinally from the membrane roll at 150mm intervals. If the separator width was ≥100mm, the sample size was 100mm × 100mm; if the separator width was <100mm, the sample size was 100mm × separator width. The separator was placed in the test head of an air permeability meter with a suitable testing range for air permeability time testing. The average of the three test results was taken as the air permeability time of the separator, in s / 100cc. The separator air permeability increment was the difference between the air permeability time of the separator coated with non-conductive particles and binder and the air permeability time of the polyolefin-based membrane, in s / 100cc.

[0098] 2. Peel strength test

[0099] The composite separator and positive electrode sheet prepared using the scheme described in this application were cut into strips of 20mm*100mm. They were cold-pressed for 60s at 95℃ and 2MPa, and then subjected to a 180° peel strength test using an electronic tensile testing machine. The test results were taken as the average of three samples.

[0100] Table 2

[0101] As can be seen from the test results in Table 2, the composite membrane provided in this application can effectively improve air permeability and bonding strength. When the average particle size D1 of the particulate polymer, the areal density of the adhesive layer, the average particle size D2 of the non-conductive particles, and the ratio of D1 / D2 are not within the range disclosed in this application, the air permeability and bonding strength of the composite membrane decrease to varying degrees.

[0102] Specifically, comparing the test results of Examples 1-7 with Comparative Example 1, it can be seen that if the ratio of D1 / D2 is too small, the peel strength between the composite diaphragm and the electrode will decrease significantly, and its air permeability will also decrease to some extent.

[0103] Comparing the test results of Examples 1-7 with those of Comparative Examples 2 and 3, it can be seen that under the scheme of this application, if the average particle size D1 of the particulate polymer is too small, the air permeability of the composite membrane will increase significantly, and the air permeability will decrease significantly. Conversely, if the average particle size D1 of the particulate polymer is too large, the peel strength between the composite membrane and the electrode will decrease significantly.

[0104] Comparing the test results of Examples 1-7 with Comparative Example 4, it can be seen that under the scheme of this application, if the average particle size D2 of the non-conductive particles is too small, the air permeability of the composite membrane will increase significantly and the air permeability will decrease significantly.

[0105] Comparing the test results of Examples 1-7 with those of Comparative Examples 5 and 6, it can be seen that if the areal density of the adhesive layer is too small, the peel strength between the composite diaphragm and the electrode will decrease significantly; if the areal density of the adhesive layer is too large, the air permeability of the composite diaphragm will increase significantly, and the air permeability will decrease significantly.

[0106] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite diaphragm, characterized in that, It includes a base film, a non-conductive particle coating on the surface of the base film, and an adhesive layer on the surface of the non-conductive particle coating; The adhesive layer includes a diaphragm adhesive, which comprises a particulate polymer with an average particle size D1 of 0.2-6 μm; the particulate polymer is a non-fluorinated adhesive. The non-conductive particle coating comprises non-conductive particles, wherein the average particle size D2 of the non-conductive particles is 0.2-1.5 μm; The areal density of the adhesive layer is 0.1-0.3 g / m³. 2 ; The average particle size D1 of the particulate polymer and the average particle size D2 of the non-conductive particles satisfy the following condition: 0.6 ≤ D1 / D2 ≤ 60. The glass transition temperature (Tg) of the particulate polymer is 10-90℃.

2. The composite diaphragm according to claim 1, characterized in that, The particulate polymer is a polymer comprising at least one of vinyl monomer units, (meth)acrylate monomer units, maleate monomer units, itaconic acid ester monomer units, maleimide monomer units, and (meth)acrylamide monomer units.

3. The composite diaphragm according to claim 2, characterized in that, The vinyl monomer unit is selected from at least one of aliphatic vinyl hydrocarbon compound units, alicyclic vinyl hydrocarbon compound units, aromatic vinyl hydrocarbon compound units, allyl compound units, and vinyl compound units containing heteroatoms; The (meth)acrylate monomer unit is selected from at least one of methacrylate monomer units and acrylate monomer units; The maleic ester monomer unit includes at least one of maleic acid C1-C12 monoalkyl ester or maleic acid C1-C12 dialkyl ester; The itaconic acid ester monomer unit includes at least one of itaconic acid C1-C12 monoester and itaconic acid C1-C12 dieester; The maleimide monomer unit includes at least one of maleimide monomer unit, C1-C12 alkyl-substituted maleimide monomer unit, and C6-C16 aryl-substituted maleimide monomer unit; The (meth)acrylamide monomer unit includes at least one of the following: (meth)acrylamide monomer unit, N-methyl(meth)acrylamide monomer unit, N-butylacrylamide monomer unit, acetylacetone acrylamide monomer unit, N-hydroxymethyl(meth)acrylamide monomer unit, N,N'-methylenebis[(meth)acrylamide] monomer unit, cinnamamide monomer unit, N,N-dimethylacrylamide monomer unit, N,N-dibenzylacrylamide monomer unit, methacryloylformamide monomer unit, N-methylN-vinylacetamide monomer unit, and N-vinylpyrrolidone monomer unit.

4. The composite diaphragm according to claim 1, characterized in that, The thickness of the non-conductive particle coating is 0.5-4 μm.

5. The composite diaphragm according to claim 1 or 4, characterized in that, The non-conductive particle coating includes non-conductive particles, a ceramic binder, and selectively added rheology modifiers, dispersants, and wetting agents; In the non-conductive particle coating, the weight ratio of non-conductive particles, ceramic binder, rheology modifier, dispersant and wetting agent is (88-96.3):(3-15):(0-3):(0-2):(0-2).

6. The composite diaphragm according to claim 1, characterized in that, The base film is selected from at least one of polyethylene base film, polypropylene base film, polypropylene-polyethylene-polypropylene laminated base film or non-woven fabric base film; And / or, the thickness of the base film is 3-12 μm.

7. A lithium-ion battery, characterized in that, Includes the composite diaphragm as described in any one of claims 1-6.

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