Use of binder in preparation of surface coating of secondary battery separator, separator and battery

Abstract

Provided in the present invention are the use of a binder in the preparation of a surface coating of a secondary battery separator, a separator and a battery. In the use, the binder comprises polymer particles, and the volume average particle size Dv50 of the polymer particles and the thickness L of the coating satisfy the following relationship: 1.3≤Dv50 / L≤4; in addition, the volume average particle diameter Dv10 of the polymer particles is not less than the thickness L of the coating. The separator obtained by means of the use has excellent adhesion, air permeability and heat resistance.

Description

Application of a binder in preparing surface coating layer of secondary battery separator, separator and battery

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on July 16, 2024, with application number 202410953725.6 and application name “Application of a binder in the preparation of a surface coating layer of a secondary battery separator, a separator and a battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the field of new energy technology, and in particular to an application of a binder in preparing a surface coating layer of a secondary battery separator, a separator and a battery. Background Art

[0003] Lithium-ion batteries are rechargeable batteries with broad application prospects. Their high energy density, long lifespan, compact size, maintenance-free operation, and environmental friendliness have made them popular across various industries. Currently, lithium-ion batteries are being used in applications ranging from mobile phones and laptops to electric bicycles, electric vehicles, energy storage, and various portable devices.

[0004] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. The separator is a key internal component of a lithium-ion battery, separating the positive and negative electrodes and preventing them from contacting and causing a short circuit. Currently, the separators used in lithium-ion batteries are mostly polyolefin porous membranes. However, 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 direct contact between the positive and negative electrodes, resulting in a short circuit, which can lead to accidents such as battery combustion and explosion.

[0005] To address these issues, a binder and inorganic particles are typically prepared into a coating slurry, which is then applied to the surface of a separator substrate to form a coating layer. Furthermore, a binder layer is applied to the surface of the coating layer away from the separator, forming a separator comprising a binder layer, a coating layer, and a separator substrate. Inorganic particles with excellent heat resistance can reduce the thermal shrinkage of the separator substrate, thereby preventing short circuits caused by contact between the positive and negative electrodes due to increased battery temperature. The binder layer is used to bond the positive electrode to the separator and / or the negative electrode to the separator, thereby fixing the battery structure. However, the binder layer reduces the air permeability of the separator, thereby increasing the internal resistance of the battery.

[0006] Therefore, there is a need to provide a separator having excellent adhesion, air permeability, and heat resistance.

[0007] Summary of the Invention

[0008] In order to improve the performance of the diaphragm in the prior art so that it has excellent adhesion, air permeability and heat resistance, the present invention provides the use of a binder in the preparation of a surface coating layer of a secondary battery diaphragm, and a diaphragm obtained based on the application, which has excellent adhesion, air permeability and heat resistance.

[0009] The present invention provides a battery comprising the above-mentioned separator, so the battery has excellent service life and safety performance, and the internal resistance of the battery is low.

[0010] The present invention provides an application of a binder in preparing a surface coating layer of a secondary battery separator, wherein the binder comprises polymer particles, and the volume average particle size Dv50 of the polymer particles and the thickness L of the coating layer satisfy the following relationship:

[0011] 1.3≤Dv50 / L≤4;

[0012] Furthermore, the volume average particle diameter Dv10 of the polymer particles is not less than the thickness L of the coating layer.

[0013] Preferably, the coating layer has a thickness of 0.5-4 μm.

[0014] Preferably, the volume average particle size Dv50 of the polymer particles is 0.65-16 μm.

[0015] Preferably, the volume average particle size Dv10 of the polymer particles is greater than or equal to 0.5 μm and less than 16 μm.

[0016] Preferably, the glass transition temperature of the polymer particles is 30-90°C.

[0017] Preferably, the polymer particles include at least one of (meth)acrylate monomer units, vinyl monomer units, maleate monomer units, itaconate monomer units, maleimide monomer units, monomer units with carboxyl groups, monomer units with sulfonic acid groups, monomer units with phosphoric acid groups, monomer units with hydroxyl groups, monomer units with amino groups, monomer units with epoxy groups, (meth)acrylamide monomer units, and monomer units containing cyano groups.

[0018] In addition, the present invention further provides a diaphragm, comprising a diaphragm substrate and a coating layer disposed on at least one surface of the diaphragm substrate;

[0019] The coating layer includes non-conductive particles and a binder, the binder includes polymer particles, and at least some of the polymer particles protrude from the coating layer;

[0020] The volume average particle size Dv50 of the polymer particles and the thickness L of the coating layer satisfy the following relationship:

[0021] 1.3≤Dv50 / L≤4;

[0022] Furthermore, in the polymer particles, the proportion Nv of the total volume of the polymer particles having a particle size smaller than the thickness of the coating layer in the total volume of the polymer particles satisfies the following relationship:

[0023] Nv≤10%.

[0024] Preferably, the coating layer has a thickness of 0.5-4 μm;

[0025] and / or, in the coating layer, the volume average particle size Dv50 of the polymer particles is 0.65-16 μm;

[0026] and / or, in the coating layer, the volume average particle size Dv10 of the polymer particles is not less than the thickness L of the coating layer;

[0027] and / or, the polymer particles have a glass transition temperature of 30-90° C.;

[0028] And / or, the polymer particles include at least one of (meth)acrylate monomer units, vinyl monomer units, maleate monomer units, itaconate monomer units, maleimide monomer units, monomer units having carboxyl groups, monomer units having sulfonic acid groups, monomer units having phosphoric acid groups, monomer units having hydroxyl groups, monomer units having amino groups, monomer units having epoxy groups, (meth)acrylamide monomer units, and monomer units containing cyano groups;

[0029] and / or, the ratio of the volume average particle size Dv50 of the non-conductive particles to the volume average particle size Dv50 of the polymer particles is 1:1.1-5;

[0030] and / or, in the coating layer, the volume average particle size Dv50 of the non-conductive particles is 0.1-1.8 μm;

[0031] And / or, the non-conductive particles include at least one of inorganic particles or heat-resistant organic particles.

[0032] Preferably, in the coating layer, the mass ratio of the polymer particles to the non-conductive particles is 1-40:60-99.

[0033] The present invention provides a battery, wherein the battery comprises the separator as described above.

[0034] The diaphragm prepared using the binder application method provided herein, or the diaphragm provided herein, can improve the adhesion between the diaphragm and the electrode while maintaining excellent air permeability, thereby extending the battery's service life while maintaining low internal resistance. The diaphragm also exhibits excellent heat resistance. The battery of the present invention, incorporating the aforementioned diaphragm, exhibits excellent safety and service life, and has a low internal resistance, making it suitable for widespread application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments of the present invention or related technologies. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0036] FIG1 is a schematic structural diagram of a diaphragm in some embodiments of the present invention;

[0037] FIG2 is a schematic diagram of a heat shrinkage test of the diaphragm of the present invention.

[0038] Explanation of reference numerals: 1: diaphragm substrate; 2: coating layer; 21: polymer particles. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] To achieve the object of the present invention, the present invention first provides an application of a binder in preparing a surface coating layer of a secondary battery separator, wherein the binder comprises polymer particles, and the volume average particle size Dv50 of the polymer particles and the thickness L of the coating layer satisfy the following relationship:

[0041] 1.3≤Dv50 / L≤4;

[0042] Furthermore, the volume average particle diameter Dv10 of the polymer particles is not less than the thickness L of the coating layer.

[0043] The applicant has improved the air permeability and bonding strength of the separator to a certain extent by combining two granular polymers of different particle sizes. However, these properties still require further improvement. To further improve the air permeability and bonding strength of the separator, the present invention further enhances the air permeability and bonding strength of the separator by adjusting the polymer particle size and ensuring a specific relationship between the particle size and the coating thickness.

[0044] In the present invention, those skilled in the art can adjust the thickness of the coating layer according to actual needs, as long as the particle size of the polymer particles and the thickness of the coating layer satisfy the aforementioned relationship.

[0045] Based on the consideration of optimizing the energy density of the battery, it is not favorable for the thickness of the coating layer to be too thick. However, the thinning of the coating layer is not conducive to the heat resistance of the diaphragm. Therefore, when reducing the thickness of the coating layer, it is necessary to ensure that the thermal shrinkage of the diaphragm will not increase significantly. In the present invention, preferably, the thickness of the coating layer is 0.5-4μm. At this time, the thickness of the coating layer is thin, which is conducive to optimizing the energy density of the battery. In the present invention, it will not significantly increase the thermal shrinkage of the diaphragm. At the same time, it can also achieve high bonding strength and air permeability, and improve the mechanical properties of the diaphragm, thereby extending the service life of the battery. Exemplarily, the thickness of the coating layer can be any one of 0.5μm, 1μm, 1.3μm, 2μm, 2.5μm, 3μm, 4μm, and a range consisting of any two of them.

[0046] It should be noted that in the present invention, the thickness of the coating layer refers to the thickness of the coating layer on one side of the diaphragm substrate. Those skilled in the art may form the coating layer on one or both sides of the diaphragm substrate, depending on process requirements. If the coating layer is formed on both sides of the diaphragm substrate, the thickness of the coating layer on each side of the diaphragm substrate may be independently within the above range.

[0047] As known to those skilled in the art, the thickness of the coating layer can be controlled by a coating machine. In actual operation, it is only necessary to set the target thickness parameter on the coating machine.

[0048] In the present invention, the volume average particle size Dv50 of the polymer particles can vary within a wide range, as long as the Dv50 of the polymer particles and the thickness L of the coating layer satisfy the relationship of 1.3 ≤ Dv50 / L ≤ 4. For example, Dv50 / L can be any one of 1.3, 1.5, 1.8, 2, 2.5, 3, 3.2, 3.5, 4, or a range consisting of any two thereof.

[0049] According to the present invention, preferably, the volume average particle size Dv50 of the polymer particles is 0.65-16 μm, preferably 1-16 μm. For example, the volume average particle size Dv50 of the polymer particles can be any one of 0.65 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 13 μm, and 16 μm, or a range consisting of any two thereof. If the volume average particle size Dv50 of the polymer particles is too large or too small, the effect of improving the bonding strength will be reduced.

[0050] Furthermore, as mentioned above, the volume average particle size Dv10 of the polymer particles is not less than the thickness L of the coating layer. It is understandable that those skilled in the art will select a specific coating layer thickness L according to actual needs, and based on this, select a binder in which the volume average particle size Dv10 of the polymer particles is not less than L. In a preferred embodiment of the present invention, when the coating layer thickness is 0.5-4 μm, the lower limit of the Dv10 of the polymer particles is 0.5 μm, that is, when the coating layer thickness is 0.5 μm. Correspondingly, it is well known to those skilled in the art that the Dv10 of the polymer particles is less than their Dv50, that is, in a preferred embodiment of the present invention, when the Dv50 of the polymer particles is 0.65-16 μm, the upper limit of the Dv10 of the polymer particles is less than 16 μm, that is, when the Dv50 of the polymer particles is 16 μm. In summary, in the present invention, the Dv10 of the polymer particles is not less than the thickness L of the coating layer, and is less than the Dv50 of the polymer particles. More preferably, the volume average particle size Dv10 of the polymer particles is 0.5 μm or more and less than 16 μm, more preferably 1 to 5 μm.

[0051] When the volume average particle size Dv50 and Dv10 of the polymer particles and the thickness L of the coating layer meet the above relationship, the bonding strength between the separator and the electrode can be further improved, the internal structure of the battery can be stabilized, and the service life of the battery can be extended. At the same time, the permeability of the separator can be improved.

[0052] The method for measuring the volume average particle diameters Dv50 and Dv10 of the polymer particles in the above binder is well known to those skilled in the art, for example, by using a conventional laser particle size analyzer for detection.

[0053] Preferably, the glass transition temperature of the polymer particles is 30-90° C. For example, the glass transition temperature of the polymer particles can be any one of 30° C., 40° C., 45° C., 60° C., 65° C., 75° C., 80° C., 90° C., or a range consisting of any two thereof.

[0054] The glass transition temperature (GTT) refers to the temperature at which a material transitions from a glassy state to a highly elastic state. When the GTT of polymer particles is within this range, it significantly improves the bond strength between the diaphragm and the electrode, further enhancing the diaphragm's heat resistance and matching the diaphragm's processing temperature, reducing processing difficulty.

[0055] The method for measuring the glass transition temperature of the polymer particles in the binder is well known to those skilled in the art, for example, by using a conventional differential scanning calorimeter.

[0056] In the present invention, the polymer particles may be polymers commonly used in the art for diaphragm binders, which are generally obtained by polymerization of monomers having unsaturated bonds, and the monomers are present in the polymer after polymerization in the form of monomer units. Preferably, the polymer particles include at least one of (meth)acrylate monomer units, vinyl monomer units, maleate monomer units, itaconate monomer units, maleimide monomer units, monomer units having carboxyl groups, monomer units having sulfonic acid groups, monomer units having phosphoric acid groups, monomer units having hydroxyl groups, monomer units having amino groups, monomer units having epoxy groups, (meth)acrylamide monomer units, and monomer units containing cyano groups.

[0057] According to the present invention, the (meth)acrylate monomer unit is obtained by polymerizing a (meth)acrylate monomer, and the (meth)acrylate monomer can be methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate , at least one of n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 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, pentaerythritol dimethacrylate, pentaerythritol triacrylate, and pentaerythritol trimethacrylate.

[0058] The vinyl-containing monomer unit is obtained by polymerizing a vinyl-containing monomer, and the vinyl-containing monomer can be selected from at least one of aliphatic vinyl hydrocarbon compounds, alicyclic vinyl hydrocarbon compounds, aromatic vinyl hydrocarbon compounds, allyl compounds and vinyl compounds containing heteroatoms (for example, at least one of vinyl esters, vinyl (thio) ethers, vinyl ketones and vinyl sulfones).

[0059] Specifically, the aliphatic vinyl hydrocarbon compound can be selected from at least one of C2-C12 alkenes (e.g., ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, and octadecene), C3-C24 α-olefins, and C4-C12 diolefins (e.g., butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, and 1,7-octadiene). As is well known to those skilled in the art, C2-C12 alkenes refer to chain-like alkenes containing 2 to 12 carbon atoms. The following description is similar and will not be repeated here.

[0060] The alicyclic vinyl hydrocarbon compound can be selected from at least one of C6-C15 monocyclic or bicyclic olefins (e.g., cyclohexene, vinylcyclohexene, ethylidene bicycloheptene), C5-C12 monocyclic or bicyclic dienes (e.g., cyclopentadiene, cycloheptadiene, dicyclopentadiene, bicycloheptadiene), and terpene compounds (e.g., limonene and indene).

[0061] The aromatic vinyl hydrocarbon compound can be selected from substituted or unsubstituted styrenes, and the substituted styrenes can be, for example, at least one of α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylstyrene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, vinylnaphthalene, and tert-butylstyrene.

[0062] Likewise, the maleate monomer unit is obtained by polymerizing a maleate monomer, and the maleate monomer can be selected from at least one of a C1-C12 monoalkyl maleate and a C1-C12 dialkyl maleate.

[0063] The (meth)acrylamide monomer unit is obtained by polymerizing a (meth)acrylamide monomer, which can be selected from at least one of acrylamide, methacrylamide, C1-C12 alkyl-substituted acrylamide, and C6-C18 aryl-substituted acrylamide. Preferably, the (meth)acrylamide monomer is selected from at least one of acrylamide, methacrylamide, N-methylacrylamide, N-butylacrylamide, acetylacetonatoacrylamide, N-methylolacrylamide, N,N'-methylenedimethylacrylamide, cinnamamide, N,N-dimethylacrylamide, N,N-dibenzylacrylamide, methacryloylformamide, N-methyl-N-vinylacetamide, and N-vinylpyrrolidone.

[0064] The itaconate monomer unit is obtained by polymerizing itaconate monomers, and the itaconate monomers can be selected from at least one of itaconate C1-C12 monoesters and itaconate C1-C12 diesters.

[0065] The maleimide monomer unit is obtained by polymerizing a maleimide monomer, and the maleimide monomer can be selected from at least one of maleimide, C1-C12 alkyl-substituted maleimide, and C6-C16 aryl-substituted maleimide.

[0066] The monomer unit having a carboxyl group is obtained by polymerizing a monomer having a carboxyl group, and the monomer having a carboxyl group can be selected from at least one of a C3-C30 unsaturated monocarboxylic acid (for example, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, cinnamic acid), a C3-C30 unsaturated dicarboxylic acid (for example, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid), a C3-C30 unsaturated dicarboxylic anhydride (for example, maleic anhydride, citraconic anhydride), and a C3-C30 unsaturated dicarboxylic acid monoalkyl ester (the monoalkyl group can be a monoalkyl group having 1 to 24 carbon atoms, and the C3-C30 unsaturated dicarboxylic acid monoalkyl ester can be, for example, monomethyl maleate, monooctadecyl maleate, monoethyl fumarate, monobutyl itaconate, ethylene glycol itaconate, and monoeicosyl citrate).

[0067] The monomer unit having a sulfonic acid group is obtained by polymerizing a monomer having a sulfonic acid group, and the monomer having a sulfonic acid group can be selected from C2-C14 olefin sulfonic acids (such as vinyl sulfonic acid, methallyl sulfonic acid, allyl sulfonic acid, methylvinyl sulfonic acid), styrene sulfonic acid, styrene sulfonic acid alkyl derivatives (the alkyl group can have 2-24 carbon atoms, such as α-methylstyrene sulfonic acid), C5-C18 sulfohydroxyalkyl acrylates or C5-C18 sulfohydroxyalkyl methacrylates (such as sulfopropyl methacrylate, 2-hydroxy-3-methylacrylate), At least one of acryloyloxypropylsulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxy-2-hydroxypropanesulfonic acid), C5-C18 sulfoalkyl methacrylamide (for example, 2-methacryloyl-2,2-dimethylethanesulfonic acid, 2-methacryloyl-2-methylpropanesulfonic acid, 3-methacryloyl-2-hydroxypropanesulfonic acid), and C3-C18 alkyl allyl sulfosuccinic acid (for example, propyl allyl sulfosuccinic acid, butyl allyl sulfosuccinic acid, and 2-ethylhexyl-allyl sulfosuccinic acid).

[0068] The monomer having a sulfonic acid group may also be a vinyl monomer having a sulfonic acid group. The vinyl monomer having a sulfonic acid group may be in the form of a salt, such as at least one of an alkali metal salt (lithium salt, sodium salt and potassium salt, etc.), an amine salt or a quaternary ammonium salt.

[0069] The monomer unit having a phosphate group is obtained by polymerizing a monomer having a phosphate group, and the monomer having a phosphate group can be selected from acryloyloxyalkyl phosphate monoester, methacryloyloxyalkyl phosphate monoester, acryloyloxyalkyl phosphate monoester, methacryloyloxyalkyl phosphate monoester, acryloyloxyalkyl phosphate, methacryloyloxyalkyl phosphate, acryloyloxyalkyl phosphate, methacryloyloxyalkyl phosphate, and methacryloyloxyalkyl phosphate. The alkyl group can have 1 to 24 carbon atoms, for example, it can be at least one of 2-hydroxyethylacryloyl phosphate, 2-hydroxyethylmethacryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate, and 2-acryloyloxyethyl phosphoric acid.

[0070] The monomer having a phosphate group may also be a vinyl monomer having a phosphate group. The vinyl monomer having a phosphate group may be in the form of a salt, such as at least one of an alkali metal salt (lithium salt, sodium salt, potassium salt, etc.), an amine salt, or a quaternary ammonium salt.

[0071] The monomer unit having a hydroxyl group is obtained by polymerizing a monomer having a hydroxyl group, and the monomer having a hydroxyl group can be selected from a vinyl monomer having a hydroxyl group, for example, it can be at least one of hydroxystyrene, N-hydroxymethyl acrylamide, N-hydroxymethyl methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, allyl alcohol, methallyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-butene-3-ol, 2-butene-1-ol, 2-butene-1,4-diol, propargyl alcohol, 2-hydroxyethyl propenyl ether and sucrose allyl ether.

[0072] The monomer unit having an amino group is obtained by polymerizing a monomer having an amino group, and the monomer having an amino group can be selected from at least one of aminoethyl acrylate, aminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, N-aminoethylacrylamide, N-aminoethyl(methyl)acrylamide, allylamine, methallylamine, morpholinoethyl acrylate, morpholinoethyl methacrylate, 4-vinylpyridine, 2-vinylpyridine, crotylamine, N,N-dimethylaminostyrene, α-acetamidomethyl acrylate, vinylimidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, N-arylphenylenediamine, aminocarbazole, aminothiazole, aminoindole, aminopyrrole, aminoimidazole, aminomercaptothiazole and monomer salts thereof.

[0073] The monomer unit having an epoxy group is obtained by polymerizing a monomer having an epoxy group. The monomer having an epoxy group can be selected from a vinyl monomer having an epoxy group and having 6 to 18 carbon atoms, for example, it can be at least one of glycidyl methacrylate, glycidyl methacrylate, tetrahydrofuran acrylate, tetrahydrofuran methacrylate, and allyl glycidyl ester.

[0074] The monomer unit containing a cyano group is obtained by polymerizing a monomer having a cyano group. The monomer having a cyano group can be selected from a vinyl monomer having a cyano group and having 3 to 10 carbon atoms, for example, at least one of acrylonitrile, methacrylonitrile, cyanostyrene, and cyanoacrylate.

[0075] More preferably, the polymer particles are selected from one or more of styrene-(meth)acrylate copolymers, acrylonitrile-(meth)acrylate copolymers, butadiene-styrene copolymers, and (meth)acrylate copolymers.

[0076] The preparation method, glass transition temperature, and particle size control methods of the above-mentioned polymer particles are well known to those skilled in the art, or can be known to those skilled in the art based on existing technologies. For example, the glass transition temperature can be controlled by controlling the composition and ratio of the polymerized monomers, and the particle size of the polymer particles can be controlled by controlling the solid content during the synthesis process, the stirring speed (for example, a speed of 3000 rpm to 20,000 rpm can be selected according to the different material compositions of the binder), and other conditions. Generally, the higher the speed, the smaller the particle size of the polymer particles.

[0077] The present invention does not particularly limit the membrane substrate. The membrane substrate can be a polymer membrane commonly used in the art. For example, the membrane substrate can be selected from a polyethylene base film, a polypropylene base film, a polypropylene-polyethylene composite base film or a non-woven fabric base film, wherein the polypropylene-polyethylene composite base film refers to a base film formed by laminating polypropylene and polyethylene. The present invention does not limit the stacking order and number of layers of polypropylene and polyethylene. It can be a polypropylene-polyethylene double-layer base film, a polypropylene-polyethylene-polypropylene three-layer base film, or a polypropylene-polyethylene-polyethylene-polypropylene four-layer base film.

[0078] The method of forming a coating layer on the surface of the separator substrate is well known in the art. For example, a slurry including a binder is coated on the separator surface by a coating machine. The slurry may contain non-conductive particles in addition to the binder.

[0079] The non-conductive particles used in the separator are well known to those skilled in the art. Specifically, the non-conductive particles are non-conductive, insoluble in water used as a dispersion medium in the slurry and in the non-aqueous electrolyte of the secondary battery, and capable of maintaining their shape. Furthermore, the non-conductive particles are electrochemically stable and therefore remain stably present in the separator under the operating environment of the secondary battery. Examples of the non-conductive particles include various inorganic particles and heat-resistant organic particles.

[0080] Examples of the 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-silica composite oxides; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; insoluble ionic crystal particles such as calcium carbonate, barium titanate, barium sulfate, calcium fluoride, and barium fluoride; and clay particles such as talc and montmorillonite.

[0081] Examples of heat-resistant organic particles include cross-linked polymer particles such as polyethylene, polystyrene, polydivinylbenzene, and styrene-divinylbenzene copolymers, as well as cross-linked polymer particles such as polyimide, polyamide, polyamide-imide, melamine resin, phenolic resin, and benzoguanamine-formaldehyde condensates, and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide. Heat-resistant organic particles differ from the aforementioned polymer particles in that, while polymer particles have binding properties, heat-resistant organic particles do not have binding properties.

[0082] In the present invention, the non-conductive particles are preferably inorganic particles, and more preferably alumina.

[0083] When the slurry contains non-conductive particles, as is well known to those skilled in the art, the volume average particle size Dv50 of the non-conductive particles is smaller than the thickness L of the coating layer, so that the non-conductive particles are filled as much as possible within the coating layer without protruding from the surface of the coating layer. Preferably, the ratio of the volume average particle size Dv50 of the non-conductive particles to the thickness L of the coating layer is 1:1.1-5; more preferably, it can be any one of 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or a combination thereof.

[0084] In the present invention, the non-conductive particles preferably have a volume average particle size (Dv50) of 0.1-1.8 μm. For example, the Dv50 of the non-conductive particles can be any one of 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, and 1.8 μm, or a range consisting of any two thereof. Using non-conductive particles with such Dv50s, a coating layer of suitable thickness can be prepared, thereby increasing the energy density of the battery and extending the battery life.

[0085] If non-conductive particles are added to the slurry, the amount of non-conductive particles added can vary within a wide range. Preferably, the mass ratio of the polymer particles to the non-conductive particles is 1-40:60-99, more preferably 3-30:70-97, and even more preferably 3-20:70-94. It should be noted that the above mass ratios are ratios of parts by mass, not mass percentages.

[0086] In addition, other additives and other ingredients may be selectively added to the slurry according to specific needs. The selectively added additives and related processes are well known to those skilled in the art and will not be described in detail in the present invention.

[0087] FIG1 is a schematic diagram of the structure of a diaphragm in some embodiments of the present invention. As shown in FIG1 , the second aspect of the present invention further provides a diaphragm, the diaphragm comprising a diaphragm substrate 1 and a coating layer 2 disposed on at least one surface of the diaphragm substrate 1;

[0088] The coating layer 2 includes non-conductive particles and a binder, the binder includes polymer particles 21, and at least part of the polymer particles 21 protrudes from the coating layer 2;

[0089] The volume average particle size Dv50 of the polymer particles 21 and the thickness L of the coating layer 2 satisfy the following relationship:

[0090] 1.3≤Dv50 / L≤4;

[0091] Furthermore, in the polymer particles 21, the proportion Nv of the total volume of the polymer particles 21 having a particle size smaller than the thickness of the coating layer 2 in the total volume of the polymer particles 21 satisfies the following relationship:

[0092] Nv≤10%.

[0093] The diaphragm substrate 1 is as described above and will not be described again here.

[0094] The coating layer 2 is formed by coating the surface of the separator with a slurry containing non-conductive particles and a binder. The volume average particle size (Dv50) of the non-conductive particles is smaller than the thickness (L) of the coating layer 2. Preferably, the ratio of the volume average particle size (Dv50) of the non-conductive particles to the thickness (L) of the coating layer 2 is 1:1.1-5; more preferably, the ratio can be any one of 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or a combination thereof.

[0095] The volume average particle size Dv50 of the polymer particles 21 and the thickness L of the coating layer 2 satisfy the following relationship:

[0096] 1.3≤Dv50 / L≤4.

[0097] Furthermore, in the polymer particles 21, the proportion Nv of the total volume of the polymer particles 21 having a particle size smaller than the thickness of the coating layer 2 in the total volume of the polymer particles 21 satisfies the following relationship:

[0098] Nv≤10%.

[0099] In the present invention, the proportion Nv of the total volume of the polymer particles 21 having a particle size smaller than the thickness of the coating layer 2 in the total volume of the polymer particles 21 can be obtained by observing the cross-section of the diaphragm with an electron microscope, and then counting the "total volume of the polymer particles 21 having a particle size smaller than the thickness of the coating layer 2 (the particles are spherical, and the volume of a single particle is calculated after measuring the diameter)" and the "total volume of the polymer particles 21", and then calculating the ratio Nv between the two. When Nv ≤ 10%, it can be understood that among the polymer particles 21, the total volume of the polymer particles 21 that are smaller than the thickness of the coating layer 2 is not greater than 10%. For the convenience of actual operation and calculation, in the present invention, "Nv ≤ 10%" is reflected by "Dv10 of the polymer particles 21 in the binder is not less than the thickness L of the coating layer 2".

[0100] In the coating layer 2, the volume average particle diameter Dv50 and Dv10 of the polymer particles 21 can be measured based on the volume average particle diameter Dv50 and Dv10 of the polymer particles 21 in the binder used when preparing the coating layer 2. Similarly, the thickness of the coating layer 2 can be measured based on the thickness applied when preparing the coating layer 2.

[0101] As previously mentioned, preferably, the coating layer 2 has a thickness of 0.5-4 μm. Similarly, preferably, the volume average particle size Dv50 of the polymer particles 21 is 0.65-16 μm, more preferably 1-16 μm. The range of values ​​for the volume average particle size Dv10 of the polymer particles 21 is as previously described and will not be further elaborated here.

[0102] Similarly, the glass transition temperature of the polymer particles 21 and the material of the polymer particles 21 are as described above. Preferably, the ratio of the volume average particle size Dv50 of the non-conductive particles to the thickness L of the coating layer 2 is 1:1.1-5. Specifically, the volume average particle size Dv50 of the non-conductive particles and the material of the non-conductive particles are as described above.

[0103] As mentioned above, preferably, in the coating layer 2, the mass ratio of the polymer particles 21 to the non-conductive particles is 1-40:60-99, more preferably 3-30:70-97, and even more preferably 3-20:70-94. Similarly, the above mass ratio is the ratio of the two parts by mass, not the mass percentage.

[0104] The present invention provides a diaphragm, wherein the coating layer 2 includes non-conductive particles and a binder, and the binder includes polymer particles 21. The diaphragm has excellent heat resistance and can shrink less when the battery temperature rises, which can reduce the risk of short circuit caused by contact between the positive and negative electrodes and improve the safety performance of the battery. In particular, because the volume average particle size Dv50, Dv10 of the polymer particles 21 and the thickness L of the coating layer 2 meet a specific relationship, the bonding strength between the diaphragm and the positive and / or negative electrodes can be effectively improved (with the same amount of binder, the diaphragm of the present invention has better bonding strength with the positive and / or negative electrodes, or, with the same bonding strength between the diaphragm and the positive and / or negative electrodes, the amount of binder used is lower), better fixes the battery structure, and prolongs the battery life while maintaining a low internal resistance of the battery. At the same time, the air permeability of the diaphragm can be guaranteed. Therefore, the diaphragm of the present invention has excellent air permeability, adhesion and heat resistance, which can prolong the battery life, improve the battery safety performance and reduce the battery internal resistance.

[0105] In some embodiments of the present invention, the diaphragm can be prepared by a method comprising the following steps:

[0106] Non-conductive particles and a binder are prepared into a slurry, which is then coated on at least one surface of the diaphragm substrate 1 , and dried to form a diaphragm including a coating layer 2 .

[0107] A third aspect of the present invention provides a battery comprising the separator according to the first aspect.

[0108] It is understood that the battery also includes a positive electrode, a negative electrode, an electrolyte, and a battery casing. In the present invention, the positive electrode, the separator, and the negative electrode can be stacked to form a laminated battery cell, which is then placed in a battery casing and the electrolyte is injected into the battery casing to form a laminated battery cell. Alternatively, the positive electrode, the separator, and the negative electrode can be stacked and then wound to form a wound battery cell, which is then placed in a battery casing and the electrolyte is injected into the battery casing to form a wound battery cell.

[0109] Since the battery of the present invention includes the separator of the first aspect, the battery has excellent safety performance and service life, and the internal resistance of the battery is low, and can be widely promoted and applied.

[0110] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0111] Example 1

[0112] The battery of this embodiment is prepared by a method comprising the following steps:

[0113] 1) Preparation of binder

[0114] Step 1: Mix 20 parts of monomer with 0.5 parts of dilauroyl peroxide, stir and dissolve evenly to form a mixed monomer; the monomers used in this embodiment are a mixture of styrene, butyl acrylate, isooctyl acrylate, and divinylbenzene, with a mass ratio of 80:15:4:1;

[0115] Step 2: Dissolve polyvinyl alcohol 1788 in 80 parts of deionized water to prepare a dispersant aqueous solution with a dispersant concentration of 0.5 wt%;

[0116] Step 3: Pour the mixed solution from the first step into the dispersant aqueous solution from the second step, and homogenize into an oil-water dispersion using a high-speed homogenizer at a speed of 10,000 rpm;

[0117] Step 4: After nitrogen flow for 30 minutes, the temperature was raised to 75°C and the polymerization time was 6 hours. After the polymerization was completed, an aqueous dispersion of styrene-acrylate copolymer with a solid content of 25% was obtained. The Dv50 of the polymer particles in the aqueous dispersion was 5 μm and the Dv10 was 3.5 μm using a laser particle size analyzer (LS-909, OMEC).

[0118] The glass transition temperature (Tg) of the polymer particles in the aqueous dispersion was measured using a differential scanning calorimeter (DSC 3500 Sirius) and was found to be 55°C.

[0119] 2) Preparation of diaphragm

[0120] preparing a slurry of non-conductive particles and a binder, and coating the slurry on one surface of a diaphragm substrate to form a diaphragm including a coating layer;

[0121] The specific parameters of the non-conductive particles and the separator are shown in Table 1 , where the amount of polymer particles added is the solid content of the binder in the aqueous dispersion state;

[0122] 3) Preparation of positive electrode

[0123] N-methylpyrrolidone is used to disperse positive electrode active particles of 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 evenly coated on Al foil by coating. After baking and roller pressing, a positive electrode including a positive electrode active layer is obtained.

[0124] Among them, the mass ratio of positive electrode active particles, conductive agent and binder is 97.5:1.0:1.5.

[0125] 4) Preparation of negative electrode

[0126] Deionized water is used to disperse negative electrode active particles of artificial graphite, conductive carbon black Super P, a binder of sodium carboxymethyl cellulose, and styrene-butadiene latex to form a negative electrode slurry; then a negative electrode active layer is formed on the surface of the negative electrode current collector through coating, baking, and roller pressing processes to obtain a negative electrode;

[0127] Among them, the mass ratio of the negative electrode active particles, the conductive agent and the binder (the mass ratio of sodium carboxymethyl cellulose to styrene-butadiene latex is 1:1.5) is 96.5:1.0:2.5.

[0128] 5) Battery preparation

[0129] The prepared positive electrode, separator, and negative electrode are stacked in sequence and then wound to obtain a battery cell, which is placed in an aluminum-plastic film. The electrolyte is injected into the bare battery cell, and the battery is obtained after vacuum packaging, static standing, formation, shaping, and capacity testing.

[0130] The electrolyte includes lithium hexafluorophosphate, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, wherein the ratio of ethylene carbonate:ethyl methyl carbonate:diethyl carbonate is 3:2:5, and the concentration of lithium hexafluorophosphate is 1 mol / L.

[0131] Example 2

[0132] The preparation method of the battery of this embodiment is basically the same as that of Example 1, except that:

[0133] The monomers and the proportions thereof for preparing the adhesive are: acrylonitrile, isooctyl acrylate, methacrylic acid, and trimethylolpropane triacrylate, and the mass ratio thereof is: 95:3:1:1.

[0134] The polymer particles in the binder had a Dv50 of 3 μm, a Dv10 of 1.5 μm, and a glass transition temperature Tg of 90°C.

[0135] Example 3

[0136] The preparation method of the battery of this embodiment is basically the same as that of Example 1, except that:

[0137] The monomers and the proportions thereof for preparing the adhesive are: methyl methacrylate, n-octyl methacrylate, and trimethylolpropane triacrylate, and the mass ratio thereof is: 45:54:1.

[0138] The polymer particles in the binder had a Dv50 of 6 μm, a Dv10 of 4.1 μm, and a glass transition temperature Tg of 30°C.

[0139] Examples 4-13

[0140] The preparation method of the battery of this embodiment is basically the same as that of Example 3. By adjusting the ratio of monomers and reaction conditions including the homogenization speed, the glass transition temperature and particle size of the polymer particles in the binder are adjusted and tested, as shown in Table 1.

[0141] Comparative Examples 1-3

[0142] The binder was prepared according to the method of Example 3, except that the glass transition temperature and particle size of the polymer particles in the binder were adjusted by adjusting the monomer ratio and reaction conditions including the homogenization speed, and then tested, as shown in Table 1.

[0143] A separator and a battery were prepared using the binder prepared above according to the method of Example 3.

[0144] Table 1

[0145] Performance Testing

[0146] The following performance tests were performed on the separators and batteries in the examples and comparative examples, and the results are shown in Table 2.

[0147] 1. Diaphragm air permeability value-added test

[0148] Refer to the air permeability test in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries":

[0149] Cut three membrane pieces from the film roll, spaced 150mm apart longitudinally. If the membrane width is ≥100mm, the sample size is 100mm x 100mm; if the membrane width is <100mm, the sample size is 100mm x membrane width. Place the membrane in the test head of a permeability tester suitable for the test range and test the permeability time. The average of the three test results is used as the membrane permeability time, expressed in seconds per 100cc. The membrane permeability increment is the difference between the permeability time of the coated membrane and the permeability time of the membrane substrate, expressed in seconds per 100cc.

[0150] 2. Thermal shrinkage test

[0151] Refer to the thermal shrinkage test in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries":

[0152] A stainless steel plate and two pieces of quantitative filter paper were placed in the middle of an oven, and the temperature of the stainless steel plate and filter paper was controlled to reach (130 ± 1)°C. Figure 2 is a schematic diagram of the heat shrinkage test of the diaphragm of the present invention. The longitudinal and transverse directions of the diaphragm are marked in Figure 2. The longitudinal and transverse lengths of the sample were measured using a length measuring instrument with appropriate resolution according to actual needs. The diaphragm was then flattened and placed on one of the quantitative filter papers on the stainless steel plate in the middle of a forced-air constant temperature oven. After completion, the diaphragm was pressed down with another piece of quantitative filter paper. The constant temperature oven door was closed, and the timer was started, maintaining the temperature at 130°C for 1 hour.

[0153] After heating, remove the separator and wait for it to return to room temperature before measuring the length of the longitudinal and transverse markings again. Calculate the shrinkage of the separator in the longitudinal and transverse directions using the following formula. The average of the three test results is used as the thermal shrinkage of the separator.

[0154] MD%=100%*(L z0 -L z ) / L z0 ,

[0155] TD%=100%*(L h0 -L h ) / L h0 ,

[0156] Where:

[0157] MD%: thermal shrinkage in the longitudinal direction of the diaphragm, %;

[0158] TD%: thermal shrinkage in the transverse direction of the diaphragm, %;

[0159] L z0 : The length of the diaphragm in the longitudinal direction before heating, in millimeters (mm);

[0160] L z : The length of the diaphragm in the longitudinal direction after heating, in millimeters (mm);

[0161] L h0 : The length of the diaphragm in the transverse direction before heating, in millimeters (mm);

[0162] L h : The length of the diaphragm in the transverse direction after heating, in millimeters (mm).

[0163] 3. Peel strength test

[0164] The diaphragm and positive electrode sheet prepared by the scheme of the present invention were cut into 20mm*100mm strips respectively, cold pressed for 60s at 95℃ and 2MPa, and subjected to 180° peel strength test using an electronic tensile testing machine. The test results were taken as the average value of 3 samples.

[0165] 4. Battery internal resistance test

[0166] The positive electrode, negative electrode and separator prepared by the scheme of the present invention were used to assemble 503040-550mAh batteries. After the battery cores were divided into different capacities, the AC internal resistance was tested using an AC low resistance tester.

[0167] Table 2

[0168] According to Tables 1 and 2, comparing the test results of Example 4 with Comparative Example 1, it can be seen that the separator obtained using the application method provided by the present invention has higher peel strength and lower thermal shrinkage, demonstrating better heat resistance. At the same time, its air permeability value-added and internal resistance do not increase significantly. If the ratio of the polymer particles' Dv50 to the coating layer thickness L is too high, the separator's bonding strength will be significantly reduced. Furthermore, combining the test results of Example 3 and Comparative Example 2, it can be seen that if the ratio of the polymer particles' Dv50 to the coating layer thickness L is too low, not only will the separator's bonding strength be significantly reduced, but its air permeability value-added and internal resistance will also increase.

[0169] From the test results of Comparative Example 4 and Comparative Example 3, it can be seen that if the total volume of polymer particles with a particle size smaller than the thickness of the coating layer accounts for Nv greater than 10% of the total volume of the polymer particles (or the volume average particle size Dv10 of the polymer particles is smaller than the thickness L of the coating layer), the bonding strength of the diaphragm will also be significantly reduced.

[0170] By comparing the test results of Example 4, Example 8 and Comparative Examples 1 and 2, it can be seen that the higher the glass transition temperature of the polymer particles, the lower the peel strength tends to be. However, compared with the comparative examples, the peel strength can still be improved.

[0171] Each embodiment in this specification is described in a related manner. Similar parts between the embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences from other embodiments. The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. Application of a binder in preparing a surface coating layer of a secondary battery separator, characterized in that: The binder includes polymer particles, and the volume average particle size Dv50 of the polymer particles and the thickness L of the coating layer satisfy the following relationship: 1.3≤Dv50 / L≤4; Furthermore, the volume average particle diameter Dv10 of the polymer particles is not less than the thickness L of the coating layer.

2. Use of the binder according to claim 1 in preparing a surface coating layer of a secondary battery separator, characterized in that: The coating layer has a thickness of 0.5-4 μm.

3. Use of the binder according to claim 1 or 2 in preparing a surface coating layer of a secondary battery separator, characterized in that: The volume average particle size Dv50 of the polymer particles is 0.65-16 μm.

4. Use of the binder according to any one of claims 1 to 3 in preparing a surface coating layer of a secondary battery separator, characterized in that: The volume average particle size Dv10 of the polymer particles is greater than or equal to 0.5 μm and less than 16 μm.

5. Use of the binder according to any one of claims 1 to 4 in preparing a surface coating layer of a secondary battery separator, characterized in that: The glass transition temperature of the polymer particles is 30-90°C.

6. Use of the binder according to any one of claims 1 to 5 in preparing a surface coating layer of a secondary battery separator, characterized in that: The polymer particles include at least one of (meth)acrylate monomer units, vinyl monomer units, maleate monomer units, itaconate monomer units, maleimide monomer units, monomer units with carboxyl groups, monomer units with sulfonic acid groups, monomer units with phosphoric acid groups, monomer units with hydroxyl groups, monomer units with amino groups, monomer units with epoxy groups, (meth)acrylamide monomer units, and monomer units containing cyano groups.

7. A diaphragm, characterized in that: The diaphragm includes a diaphragm substrate and a coating layer disposed on at least one surface of the diaphragm substrate; The coating layer includes non-conductive particles and a binder, the binder includes polymer particles, and at least part of the polymer particles protrude from the coating layer; The volume average particle size Dv50 of the polymer particles and the thickness L of the coating layer satisfy the following relationship: 1.3≤Dv50 / L≤4; Furthermore, among the polymer particles, the polymer particles having a particle size smaller than the thickness of the coating layer are The proportion Nv of the meter volume in the total volume of the polymer particles satisfies the following relationship: Nv≤10%.

8. The diaphragm according to claim 7, characterized in that The coating layer has a thickness of 0.5-4 μm; And / or, in the coating layer, the volume average particle size Dv50 of the polymer particles is 0.65-16 μm; and / or, in the coating layer, the volume average particle size Dv10 of the polymer particles is not less than the thickness L of the coating layer; and / or, the glass transition temperature of the polymer particles is 30-90° C.; And / or, the polymer particles include at least one of (meth)acrylate monomer units, vinyl monomer units, maleate monomer units, itaconate monomer units, maleimide monomer units, monomer units with carboxyl groups, monomer units with sulfonic acid groups, monomer units with phosphoric acid groups, monomer units with hydroxyl groups, monomer units with amino groups, monomer units with epoxy groups, (meth)acrylamide monomer units, and monomer units containing cyano groups; and / or, the ratio of the volume average particle size Dv50 of the non-conductive particles to the thickness L of the coating layer is 1:1.1-5; And / or, in the coating layer, the volume average particle size Dv50 of the non-conductive particles is 0.1-1.8 μm; And / or, the non-conductive particles include at least one of inorganic particles or heat-resistant organic particles.

9. The diaphragm according to claim 7 or 8, characterized in that In the coating layer, the mass ratio of the polymer particles to the non-conductive particles is 1-40:60-99.

10. A battery, characterized in that: The battery comprises a diaphragm prepared by the application method of any one of claims 1 to 6, or a diaphragm according to any one of claims 7 to 9.

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