Separator and battery

Abstract

A separator and a battery. The separator comprises a base membrane and an adhesive layer located on at least one side surface of the base membrane; the thickness of the base membrane is 3-6 µm, and the thickness of the adhesive layer is 0.5-1.5 µm; the adhesive layer comprises a first polymer binder and non-conductive particles; a ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4): 1; the average particle size D503 of the non-conductive particles is 0.15-0.8 µm; and the peel strength between the adhesive layer and the base membrane is 10 N / m or more. The separator has a small thickness, a low thermal shrinkage rate, and a high adhesion strength to electrode sheets, thereby ensuring high energy density and safety of the battery.

Description

A separator and a battery

[0001] The present application claims priority to the Chinese patent application No. 2024113709715, filed on September 29, 2024, and entitled "A separator and a battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to a separator, in particular to a separator, a preparation method thereof and a battery, and belongs to the technical field of batteries. BACKGROUND

[0003] Lithium ion battery is a rechargeable battery with wide application prospect, high energy density, long service life, small size, no maintenance, environmental friendliness, and is favored by various industries. It has gone from mobile phones, notebook computers and other fields to electric bicycles, electric vehicles, energy storage and various portable device fields, and is an ideal mobile power supply.

[0004] Lithium ion battery is generally composed of positive electrode, negative electrode, separator, electrolyte and battery shell. The separator is one of the key inner components, which separates the positive and negative electrodes of the battery to prevent the positive and negative electrodes from contacting and short-circuiting. The separator used in the current lithium ion battery is generally a polyolefin porous membrane. Since the melting point of the polyolefin porous membrane is relatively low, when the temperature of the battery rises due to internal or external factors, the polyolefin porous membrane will shrink or melt, causing the positive and negative electrodes to directly contact, leading to battery short circuit, and further causing battery combustion and explosion accidents.

[0005] In order to solve these problems, inorganic particles are usually coated on the surface of the separator substrate by using a polymer adhesive to make a composite separator. For example, ceramic particles are coated on the surface of the separator substrate to make a ceramic / polymer composite separator, hoping to use the heat resistance of the ceramic particles to reduce the thermal shrinkage of the separator. At the same time, a layer of polymer adhesive, such as polyvinylidene fluoride (PVDF), is coated on the surface of the ceramic coating for bonding the separator and the positive and negative electrode sheets, playing a role in fixing the structure of the battery. Although the method of coating an additional adhesive layer has a better bonding effect, the adhesive is prone to form a film on the surface of the separator, resulting in a decrease in the air permeability of the separator, further increasing the internal resistance of the battery, and leading to the deterioration of the cycle performance of the battery. In addition, the current lithium ion battery has higher and higher requirements for energy density, which puts higher and higher requirements on the thickness of the separator. However, reducing the thickness of the separator will greatly increase its thermal shrinkage, seriously affecting the safety performance of the battery.

[0006] Based on the above problems, the technical personnel in the field urgently need to develop a separator with thin thickness and low thermal shrinkage to improve the energy density and safety performance of the battery. SUMMARY

[0007] The present application provides a separator with small thickness, low heat shrinkage and high adhesion strength between the electrode sheet, thereby ensuring high energy density and safety performance of the battery.

[0008] The present application provides a method for preparing a separator with small thickness, low heat shrinkage and good adhesion to the electrode sheet, and the method is simple and easy to operate.

[0009] The present application also provides a battery comprising the above separator, with high energy density and safety performance.

[0010] The present application provides a separator comprising a base film and an adhesive layer on at least one side surface of the base film; the thickness of the base film is 3-6 μm, and the thickness of the adhesive layer is 0.5-1.5 μm.

[0011] The adhesive layer comprises a first polymer binder and non-conductive particles; the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1; the average particle size D503 of the non-conductive particles is 0.15-0.8 μm; and the peeling strength between the adhesive layer and the base film is 10 N / m or more.

[0012] The separator as described above, wherein the average particle size D501 of the first polymer binder is 1-6 μm.

[0013] And / or, the glass transition temperature Tg1 of the first polymer binder is 45-95℃.

[0014] The separator as described above, wherein the mass percentage of the first polymer binder in the adhesive layer is 3%-15%.

[0015] And / or, the first polymer binder is obtained by polymerization of a monomer containing an unsaturated bond, wherein,

[0016] The monomer containing an unsaturated bond comprises one or more of a vinyl monomer, a (meth)acrylate monomer, a maleate monomer, an itaconate monomer, a maleimide monomer, and a (meth)acrylamide monomer.

[0017] And / or, the monomer containing an unsaturated bond comprises one or more of a monomer with carboxyl group, a monomer with sulfonic acid group, a monomer with phosphoric acid group, a monomer with hydroxyl group, a monomer with amino group, a monomer with epoxy group, and a monomer with cyano group.

[0018] The separator as described above, wherein the ratio of the average particle size D503 of the non-conductive particles to the average particle size D501 of the first polymer binder is 1:2.3-20.

[0019] The diaphragm as described above, wherein the average particle size D103 of the non-conductive particles is 0.05-0.6 μm, and the average particle size D903 of the non-conductive particles is 0.5-2 μm.

[0020] The diaphragm as described above, wherein the mass percentage of the non-conductive particles in the adhesive layer is 70%-93.4%.

[0021] Preferably, the non-conductive particles include one or more of alumina, aluminum trioxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, organic polymer microspheres, and organic polymer fibers. When the non-conductive particles are organic polymer fibers, the average particle size refers to the diameter of the polymer fibers.

[0022] The diaphragm as described above, wherein the adhesive layer further includes a second polymer binder, and the average particle size D502 of the second polymer binder is 0.05-1 μm.

[0023] Preferably, the average particle size of the second polymer binder is less than 1 μm.

[0024] Preferably, the Tg2 of the second polymer binder is 20°C or lower.

[0025] Preferably, the second polymer binder includes at least one of polyacrylate and styrene-butadiene latex.

[0026] Preferably, the mass percentage of the second polymer binder in the adhesive layer is 3%-10%.

[0027] The diaphragm as described above, wherein the adhesive layer further includes a rheological modifier and / or an auxiliary agent, the auxiliary agent includes a wetting agent and / or an antifoaming agent; wherein the rheological modifier includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyacrylate; and / or the mass percentage of the rheological modifier in the adhesive layer is 0.5%-3%; and / or the mass percentage of the auxiliary agent in the adhesive layer is 0.1%-2%; and / or the base film includes a polyolefin film and / or a non-woven fabric film, the polyolefin film includes a polyethylene-based film and / or a polypropylene-based film.

[0028] The diaphragm as described above, wherein the heat shrinkage rate of the diaphragm after being baked at 130°C±5°C for 60 min±5 min is less than 5%.

[0029] Preferably, the air permeability of the diaphragm is not higher than 50 s / 100 cc.

[0030] The application also provides a separator, comprising a base film and an adhesive layer on at least one side surface of the base film; the thickness of the base film is 3-6 μm, and the thickness of the adhesive layer is 0.5-1.5 μm.

[0031] The adhesive layer comprises a first polymer binder, non-conductive particles and a second polymer binder; the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1; the average particle size D503 of the non-conductive particles is 0.15-0.8 μm; the average particle size D502 of the second polymer binder is 0.05-1 μm, and the size range of the second polymer binder is less than 1.

[0032] Preferably, the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1.

[0033] Preferably, the average particle size D501 of the first polymer binder is 1-6 μm.

[0034] And / or, the glass transition temperature Tg1 of the first polymer binder is 45-95℃.

[0035] Preferably, the mass percentage of the first polymer binder in the adhesive layer is 3%-15%.

[0036] And / or, the first polymer binder is obtained by polymerization of a monomer containing an unsaturated bond, wherein,

[0037] The monomer containing an unsaturated bond comprises one or more of a vinyl monomer, a (meth)acrylate monomer, a maleate monomer, an itaconate monomer, a maleimide monomer and a (meth)acrylamide monomer.

[0038] And / or, the monomer containing an unsaturated bond comprises one or more of a monomer having a carboxyl group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, a monomer having a hydroxyl group, a monomer having an amino group, a monomer having an epoxy group and a monomer having a cyano group.

[0039] Preferably, the ratio of the average particle size D503 of the non-conductive particles to the average particle size D501 of the first polymer binder is 1:(2.3-20).

[0040] Preferably, the average particle size D103 of the non-conductive particles is 0.05-0.6 μm, and the average particle size D903 of the non-conductive particles is 0.5-2 μm.

[0041] And / or, the mass percentage of the non-conductive particles in the adhesive layer is 70%-93.4%.

[0042] And / or, the non-conductive particles include one or more of alumina, aluminum trioxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, organic polymer microspheres, and organic polymer fibers.

[0043] Preferably, the Tg2 of the second polymer binder is 20℃ or lower;

[0044] And / or, the second polymer binder includes at least one of polyacrylate and styrene-butadiene latex.

[0045] And / or, the mass percentage of the second polymer binder in the adhesive layer is 3% to 10%.

[0046] The separator as described above, wherein the adhesive layer further includes a rheological modifier and / or an auxiliary agent, the auxiliary agent including a wetting agent and / or an antifoaming agent; wherein the rheological modifier includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyacrylate; and / or the mass percentage of the rheological modifier in the adhesive layer is 0.5% to 3%; and / or the mass percentage of the auxiliary agent in the adhesive layer is 0.1% to 2%; and / or the base film includes a polyolefin film and / or a non-woven fabric film, the polyolefin film including a polyethylene-based film and / or a polypropylene-based film.

[0047] The separator as described above, wherein the heat shrinkage rate of the separator after being baked at 130℃±5℃ for 60min±5min is less than 5%;

[0048] And / or, the air permeability value of the separator is not higher than 50s / 100cc.

[0049] The present application provides a battery, wherein the battery includes a positive electrode sheet, a negative electrode sheet, and a separator as described above, the separator being located between the positive electrode sheet and the negative electrode sheet.

[0050] The battery as described above, wherein,

[0051] The adhesive force between the separator and the positive electrode sheet is not lower than 1.5N / m;

[0052] And / or, the adhesive force between the separator and the negative electrode sheet is not lower than 0.5N / m;

[0053] And / or, the battery is a lithium ion battery.

[0054] The separator, the preparation method of the separator and the battery provided by the application have a base film and an adhesive layer with a thickness significantly lower than the thickness of the corresponding parts of the existing separator. To overcome the problems caused by the reduction of the thickness of the base film and the adhesive layer, the first polymer binder with an average particle size D501 greater than the thickness of the adhesive layer is used in the application, the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1, the average particle size D503 of the non-conductive particles is 0.15-0.8 μm, and the peeling strength between the adhesive layer and the base film is controlled to be greater than or equal to 10 N / m. In the case of the base film and the adhesive layer with the above thickness, the adhesion between the separator and the positive and negative electrode sheets can be effectively realized, and the problem of the increase of the thermal shrinkage rate of the separator caused by the reduction of the thickness of the base film and the adhesive layer can be effectively inhibited, so that the high energy density and safety of the battery can be ensured. DETAILED DESCRIPTION

[0055] To make the person skilled in the art better understand the scheme of the application, the application is further described in detail below. The following specific embodiments are only used to describe the principles and characteristics of the application, and the examples are used to explain the application, but not to limit the scope of the application. Based on the embodiments of the application, all other embodiments obtained by the person skilled in the art without creative labor are within the scope of protection of the application.

[0056] The application provides a separator, which comprises a base film and an adhesive layer on at least one side surface of the base film; the thickness of the base film is 3-6 μm, and the thickness of the adhesive layer is 0.5-1.5 μm; the adhesive layer comprises a first polymer binder and non-conductive particles; the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1; the average particle size D503 of the non-conductive particles is 0.15-0.8 μm; and the peeling strength between the adhesive layer and the base film is greater than or equal to 10 N / m.

[0057] The separator of the application is composed of a base film and an adhesive layer, and the adhesive layer is located on at least one side surface of the base film, that is, the adhesive layer can be adhered to one side of the base film or both sides of the base film.

[0058] The thickness of the base film in the embodiments of the application is 3-6 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm, etc.

[0059] The thickness of the adhesive layer in the embodiments of the present application is 0.5-1.5 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm, etc.

[0060] The components in the adhesive layer in the embodiments of the present application include a first polymer binder, and the average particle size D501 of the first polymer binder is greater than the thickness of the adhesive layer. The average particle size D50 refers to the volume distribution average particle size Dv50, i.e. the particle size corresponding to the cumulative particle size distribution percentage of 50%.

[0061] Specifically, the average particle size D501 of the first polymer binder in the embodiments of the present application can be obtained by measuring the first polymer binder by a laser particle size analyzer or the like. After the preparation of the separator, the average particle size of the first polymer binder in the adhesive layer of the separator can be tested by the following steps: testing the separator by using SEM, testing the average particle size of at least 20 particles, and then taking the average value as the final test result.

[0062] According to the present application, the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1. When the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is within the above range, it is beneficial to improve the adhesion strength between the separator and the electrode sheet, inhibit the thermal shrinkage of the separator, and ensure the air permeability of the separator. If the ratio is too large, in the case of a thin adhesive layer (0.5-1.5 μm), there may be a problem of the first polymer binder falling off due to the excessively large average particle size D501 of the first polymer binder, which in turn causes the adhesion strength between the separator and the electrode sheet to decrease, and the inhibitory effect on the thermal shrinkage of the separator to decrease. If the ratio is too small, it is not conducive to improving the adhesion strength between the separator and the electrode sheet, and the air permeability of the separator will also decrease to some extent.

[0063] Preferably, the average particle size D501 of the first polymer binder is 1-6 μm, and specifically, for example, the average particle size D501 of the first polymer binder can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm, etc.

[0064] In the present application, preferably, the glass transition temperature Tg1 of the first polymer binder is 45-95 ℃, for example, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃ or 95 ℃, etc.

[0065] The glass transition temperature refers to the temperature at which the material inside changes from a glassy state to a high-elasticity state. When the glass transition temperature of the polymer particles is within the above range, it is very beneficial to improve the bonding strength between the separator and the electrode sheet, and can further improve the heat resistance of the separator, and can also match the processing temperature of the separator, reducing the processing difficulty.

[0066] The measurement method of the glass transition temperature of the polymer particles in the above binder is well known to those skilled in the art, for example, using a conventional differential scanning calorimeter for detection.

[0067] The glass transition temperature Tg1 of the first polymer binder is within the above range, which can effectively improve the heat resistance of the separator while ensuring the adhesion of the first polymer binder, thereby further reducing the thermal shrinkage of the separator, and avoiding the shrinkage or melting of the separator caused by the increase in battery temperature, thereby improving the safety of the battery.

[0068] The present application has the advantages that, in the case of a small thickness of the base film and the bonding layer in the separator, the separator has low thermal shrinkage, high air permeability, and good adhesion to the electrode sheet. The application of the separator to the battery can improve the energy density, cycle performance, and safety of the battery. The inventors believe that the reason may be that the average particle size of the first polymer binder is appropriate, which can be uniformly dispersed in the bonding layer, avoiding the first polymer binder from falling off from the bonding layer, ensuring the structure of the separator, and improving the safety of the battery. Moreover, the first polymer binder is dispersed and embedded in the bonding layer, and the hot pressing does not form a film, especially when the ratio of the average particle size D501 of the first polymer binder to the thickness of the bonding layer is (1.3-4):1, which can effectively avoid the decrease in air permeability of the separator, thereby ensuring the migration rate of ions in the battery and improving the cycle performance of the battery. Controlling the peeling strength between the bonding layer and the base film to be above 10 N / m can effectively ensure the close combination between the bonding layer and the base film, and also effectively inhibit the thermal shrinkage of the separator. In addition, the low thickness of the base film and the separator can avoid the increase in internal resistance of the battery, shorten the migration path length of ions between the positive and negative electrodes, and thereby improve the energy density of the battery.

[0069] In a specific embodiment, the mass percentage of the first polymer binder in the bonding layer is 3%-15%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, etc. When the mass percentage of the first polymer binder in the bonding layer is within the above range, the first polymer binder can make the separator have high adhesion, low thermal shrinkage, and high air permeability, and can avoid the decrease in air permeability of the separator caused by too high content of the first polymer binder, or the insufficient adhesion of the separator caused by too low content of the first polymer binder, thereby greatly improving the cycle performance and safety of the battery.

[0070] In the present application, the mass percentage content of the first polymer binder in the adhesive layer can be based on the mass percentage content of the first polymer binder in the slurry when the adhesive layer is prepared.

[0071] In one specific embodiment, the first polymer binder is obtained by polymerization of a monomer containing an unsaturated bond.

[0072] Specifically, the monomer containing an unsaturated bond can include one or more of a vinyl monomer, a (meth)acrylate monomer, a maleate monomer, an itaconate monomer, a maleimide monomer, and a (meth)acrylamide monomer.

[0073] In addition, the monomer containing an unsaturated bond can include one or more of a monomer having a carboxyl group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, a monomer having a hydroxyl group, a monomer having an amino group, a monomer having an epoxy group, and a monomer having a cyano group.

[0074] The vinyl monomer of the present application includes, but is not limited to, an aliphatic vinyl hydrocarbon compound, an alicyclic vinyl hydrocarbon compound, an aromatic vinyl hydrocarbon compound, an allyl compound, and a vinyl compound containing a heteroatom (exemplarily including, but not limited to, a vinyl ester, a vinyl (thio)ether, a vinyl ketone, a vinyl sulfone);

[0075] Among them, the aliphatic vinyl hydrocarbon compound includes, but is not limited to, an alkene having 2-12 carbon atoms (exemplarily including, but not limited to, ethylene, propylene, butylene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene), an α-olefin having 3-24 carbon atoms, a diene having 4-12 carbon atoms (exemplarily including, but not limited to, butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, and 1,7-octadiene);

[0076] The alicyclic vinyl hydrocarbon compound includes, but is not limited to, a monocyclic or bicyclic alkene having 6-15 carbon atoms (exemplarily including, but not limited to, cyclohexene, vinylcyclohexene, and ethylidenebicycloheptene), a monocyclic or bicyclic diene having 5-12 carbon atoms (exemplarily including, but not limited to, cyclopentadiene, cycloheptadiene, dicyclopentadiene, and dicycloheptadiene), a terpene compound (exemplarily including, but not limited to, limonene and indene);

[0077] Aromatic vinyl hydrocarbons include, but are not limited to, styrene and substituted styrenes, which include, by way of example, but not limitation, a-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylstyrene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, vinyl naphthalene, p-t-butylstyrene.

[0078] The (meth)acrylate monomers of the embodiments of the present application include methacrylate and acrylate, which include, by way of example, but not limitation, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, isoamyl 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, t-butyl methacrylate, n-amyl methacrylate, isoamyl 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, pentaerythritol trimethacrylate.

[0079] The maleate monomers of the embodiments of the present application include, by way of example, but not limitation, C1-C12 monoalkyl maleate and C1-C12 dialkyl maleate.

[0080] The itaconate monomers of the embodiments of the present application include, by way of example, but not limitation, C1-C12 monoester itaconate and C1-C12 diester itaconate.

[0081] The maleimide monomers of the embodiments of the present application include, by way of example, but not limitation, maleimide, C1-C12 alkyl-substituted maleimide, C6-C16 aryl-substituted maleimide.

[0082] The (meth)acrylamide monomer of the present embodiment exemplarily includes, but is not limited to, (meth)acrylamide, N-methyl (meth)acrylamide, N-butyl acrylamide, acetoacetoxy acrylamide, N-hydroxymethyl (meth)acrylamide, N,N'-methylenebis[(meth)acrylamide], cinnamamide, N,N-dimethyl acrylamide, N,N-dibenzyl acrylamide, methacryloyl formamide, N-methyl N-vinyl acetamide and N-vinyl pyrrolidone, C1-C12 alkyl-substituted acrylamide, C6-C18 aryl-substituted acrylamide, and the like.

[0083] The monomer having a carboxyl group of the present embodiment includes, but is not limited to, an unsaturated monocarboxylic acid having 3 to 30 carbon atoms (exemplarily including, but not limited to, (meth)acrylic acid (containing acrylic acid and / or methacrylic acid, hereinafter the same), crotonic acid, isocrotonic acid, and cinnamic acid, and the like), an unsaturated dicarboxylic acid (anhydride) having 3 to 30 carbon atoms (exemplarily including, but not limited to, maleic acid (anhydride), fumaric acid, itaconic acid, citraconic acid (anhydride), and mesaconic acid, and the like), a monoalkyl (1 to 24 carbon atoms) ester of an unsaturated dicarboxylic acid having 3 to 30 carbon atoms (exemplarily including, but not limited to, monomethyl maleate, monooctadecyl maleate, monoethyl fumarate, monobutyl itaconate, ethylene glycol monoether of itaconic acid, and monoeicosyl citraconate, and the like), and the like; the vinyl monomer having a carboxyl group can also be in the form of a salt, such as an alkali metal salt (lithium salt, sodium salt, and potassium salt, and the like), an amine salt, or a quaternary ammonium salt.

[0084] The monomer having a sulfonic acid group of the present embodiment includes, but is not limited to, an olefin sulfonic acid having 2 to 14 carbon atoms (exemplarily including, but not limited to, vinyl sulfonic acid, (meth)allyl sulfonic acid, and methyl vinyl sulfonic acid, and the like), styrene sulfonic acid and alkyl (2 to 24 carbon atoms) derivatives thereof (exemplarily including, but not limited to, α-methyl styrene sulfonic acid, and the like), a (meth)acrylic acid sulfobutyl (hydroxy) alkyl ester having 5 to 18 carbon atoms (exemplarily including, but not limited to, sulfopropyl (meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl sulfonic acid, 2-(meth)acryloyloxyethane sulfonic acid, and 3-(meth)acryloyloxy-2-hydroxypropane sulfonic acid, and the like), a sulfobutyl (hydroxy) alkyl (meth)acrylamide having 5 to 18 carbon atoms (exemplarily including, but not limited to, 2-(meth)acryloylamino-2,2-dimethylethane sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, 3-(meth)acrylamido-2-hydroxypropane sulfonic acid), an alkyl (3 to 18 carbon atoms) allyl sulfosuccinic acid (exemplarily including, but not limited to, propyl allyl sulfosuccinic acid, butyl allyl sulfosuccinic acid, 2-ethylhexyl-allyl sulfosuccinic acid); the vinyl monomer having a sulfonic acid group can also be in the form of a salt, such as an alkali metal salt (lithium salt, sodium salt, and potassium salt, and the like), an amine salt, or a quaternary ammonium salt.

[0085] The monomer having a phosphoric acid group of the present embodiment includes, but is not limited to, (meth)acryloyloxyalkyl phosphoric acid monoester (alkyl group having 1 to 24 carbon atoms) (exemplarily including, but not limited to, 2-hydroxyethyl (meth)acryloyl phosphate and phenyl-2-propenoyloxyethyl phosphate, etc.), (meth)acryloyloxyalkyl phosphoric acid (alkyl group having 1 to 24 carbon atoms, exemplarily including, but not limited to, 2-propenoyloxyethyl phosphoric acid); the vinyl monomer having a phosphoric acid group can also be in the form of a salt, such as an alkali metal salt (lithium salt, sodium salt, and potassium salt, etc.), an amine salt, or a quaternary ammonium salt.

[0086] The monomer having a hydroxyl group of the present embodiment includes, but is not limited to, a vinyl monomer having a hydroxyl group: hydroxystyrene, N-hydroxymethyl (meth)acrylamide, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, polyethylene glycol mono[(meth)acrylate], (meth)allyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-buten-3-ol, 2-buten-1-ol, 2-buten-1,4-diol, propargyl alcohol, 2-hydroxyethyl propylene ether, and sucrose allyl ether, etc.

[0087] The monomer having an amino group of the present embodiment includes, but is not limited to, aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, t-butylaminoethyl methacrylate, N-aminoethyl (meth)acrylamide, (meth)allylamine, morpholinoethyl (meth)acrylate, 4-vinylpyridine, 2-vinylpyridine, crotylamine, N,N-dimethylaminostyrene, α-acetylamino methyl acrylate, vinyl imidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, N-arylphenylenediamine, aminocarbazole, aminothiazole, aminoindole, aminopyrrole, aminimidazole, aminomercaptothiazole, and a monomeric salt thereof.

[0088] The monomer having an epoxy group of the present embodiment includes, but is not limited to, a vinyl monomer having an epoxy group and having 6 to 18 carbon atoms: glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl glycidyl ester.

[0089] The monomer having a cyano group of the present embodiment includes, but is not limited to, a vinyl monomer having a cyano group and having 3 to 10 carbon atoms: (meth)acrylonitrile, cyanostyrene, and cyanoacrylate.

[0090] In one specific embodiment, the second polymer binder is at least one of a polyacrylate, which is polymerized from at least one acrylate or methacrylate monomer, and a styrene-butadiene latex, which is copolymerized from at least butadiene and styrene. The monomers used to prepare the first polymer binder can also be copolymerized when preparing the second polymer binder.

[0091] According to the present application, the average particle size D503 of the non-conductive particles in the adhesive layer is less than the thickness of the adhesive layer, and specifically, the average particle size D503 of the non-conductive particles in the adhesive layer is 0.15-0.8 μm. For example, it can be specifically 0.15 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm, etc. More preferably, the average particle size D103 of the non-conductive particles is 0.05-0.6 μm, and the average particle size D903 of the non-conductive particles is 0.5-2 μm. In the case where the thickness of the base film of the separator is 3-6 μm, and the thickness of the adhesive layer is 0.5-1.5 μm, if the average particle size D503 of the non-conductive particles exceeds 0.8 μm, it will result in a significant increase in the heat shrinkage of the separator.

[0092] Preferably, the ratio of the average particle size D503 of the non-conductive particles to the average particle size D501 of the first polymer binder is 1:(2.3-20). In the case where the thickness of the base film of the separator is 3-6 μm, and the thickness of the adhesive layer is 0.5-1.5 μm, when the ratio of the average particle size D503 of the non-conductive particles to the average particle size D501 of the first polymer binder is 1:(2.3-20), the heat shrinkage of the separator can be better inhibited, and the good air permeability can be maintained.

[0093] Specifically, the average particle size of the non-conductive particles of the present application can be directly obtained from the supplier at the time of purchase. The average particle size of the non-conductive particles coated on the base film can be tested by the following steps: using a scanning electron microscope (SEM) test to test the separator, testing the average particle size of at least 20 particles, and then taking the average value as the final test result.

[0094] The mass percentage of the non-conductive particles in the adhesive layer described above is 70%-93.4%. For example, it can be specifically 70%, 75%, 80%, 85%, 90% or 93.4%, etc. When the mass percentage of the non-conductive particles in the adhesive layer is within the above range, the mechanical strength and thermal stability of the separator can be effectively improved, so that the heat shrinkage of the separator is lower, thereby enabling the safety of the battery to be more optimal.

[0095] In the present application, in one specific embodiment, the non-conductive particles can include inorganic ceramic particles and / or organic polymer particles, and specifically can include one or more of alumina, aluminum trioxide, boehmite, silica, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, organic polymer microspheres, and organic polymer fibers. The alumina of the present application includes hydrated alumina. When the non-conductive particles are selected from the above-mentioned materials, the non-conductive particles can better improve the mechanical strength and thermal stability of the separator, further reduce the thermal shrinkage of the separator, and further improve the safety of the battery. The above-mentioned non-conductive particles can be obtained by commercial purchase. As known by those skilled in the art, the D503, D103, and D903 values of the non-conductive particles can be obtained from the supplier when purchased. In the present application, non-conductive particles with appropriate parameters can be used.

[0096] As described above, in the present application, the peeling strength between the adhesive layer and the base film is 10 N / m or more. To achieve effective adhesion between the adhesive layer and the base film, the adhesive layer further includes a second polymer binder. In the present application, by adjusting the second polymer binder in the adhesive layer or the construction process thereof, the peeling strength between the final adhesive layer and the base film can be 10 N / m or more.

[0097] In the present application, the type of the second polymer binder can be the commonly used binder for adhering non-conductive particles on the surface of the separator, for example, at least one of a polyacrylate binder and a styrene-butadiene latex binder can be used.

[0098] In the present application, the average particle size D502 of the second polymer binder is 0.05-1 μm.

[0099] According to the present application, the span of the second polymer binder is less than 1, preferably less than 0.8, and specifically can be less than 0.6, less than 0.5, etc. At this time, it is beneficial to further inhibit the thermal shrinkage of the separator.

[0100] As known in the prior art, the span is expressed as SPAN=(D90-D10) / D50.

[0101] In the present application, by controlling the peeling strength between the adhesive layer and the base film to be 10 N / m or more, the separator can have a low thermal shrinkage rate when the thickness of the base film is 3-6 μm and the thickness of the adhesive layer is 0.5-1.5 μm.

[0102] According to the present application, the peeling strength between the above-mentioned adhesive layer and the base film can be tested by the method known in the prior art, for example, by the test method described in the performance test section of the present application.

[0103] In one embodiment, the adhesive layer further comprises a second polymer binder, which comprises at least one of polyacrylate, styrene-butadiene latex. When the second polymer binder is further included in the adhesive layer, the second polymer binder can bind the non-conductive particles and the first polymer binder and other components in the adhesive layer, avoid the components in the adhesive layer from falling off, improve the stability of the adhesive layer, and the second polymer binder can enhance the adhesion between the adhesive layer and the substrate, so that the structure of the separator is stable, the positive and negative electrode sheets of the battery are not displaced due to the falling off of the adhesive layer from the surface of the substrate, and the safety of the battery is improved.

[0104] Preferably, the mass percentage of the second polymer binder in the adhesive layer is 3% to 10%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc. When the mass percentage of the second polymer binder in the adhesive layer is within the above range, the adhesive layer can be firmly attached to the surface of the substrate, thereby further improving the safety of the battery, and the excessive second polymer binder can be avoided to cause the air permeability of the separator to decrease, thereby more greatly improving the cycle performance of the battery.

[0105] Preferably, the Tg2 of the second polymer binder is 20°C or lower.

[0106] The second polymer binder satisfying the above requirements of the present application can be obtained by self-preparation or purchased from the market, and has an average particle size of 0.05 to 1 μm, a span of 0.4 to 0.9, and a glass transition temperature of -50 to 20°C.

[0107] The second polymer binder of the present application can be prepared by emulsion polymerization, and the specific preparation method is as follows:

[0108] 0.1-3 parts of a surfactant and 300-400 parts of deionized water are weighed into a stirring container, 100-200 parts of monomers are added, the stirring speed is controlled at 200±50 rpm, and the mixture is heated to 74±1°C, then 0.2-2 parts of an initiator is added, the stirring is maintained at 469-79°C for 3-6 h, and then the temperature is increased to 74-84°C, and the reaction is continued for 3-5 h to obtain a second polymer binder emulsion with a solid content of 20-40%.

[0109] Based on the above preparation method, the corresponding monomers can be selected and the process conditions can be fine-tuned by the person skilled in the art according to the type of the binder to be prepared, for example, the styrene-butadiene latex second polymer binder or the polyacrylate second polymer binder.

[0110] The monomers for preparing the styrene-butadiene latex include at least one aromatic vinyl monomer selected from styrene units, α-methylstyrene units, vinyltoluene units, 2-vinylnaphthalene units, methylvinyl naphthalene units, vinylanthracene units, and methylvinyl anthracene units, and at least one conjugated diene monomer selected from 1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene, 1,3-cyclopentadiene, and 1,3-hexadiene. Other modifying monomers can also be added as needed. The amounts of the monomers can be selected and adjusted as needed by those skilled in the art during preparation.

[0111] The monomers for preparing the polyacrylate include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, isobutyl acrylate, butyl (meth)acrylate, 2-isooctyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, hexylol lactate, benzyl acrylate, and ethylene glycol diacrylate. Other monomers such as divinyl benzene can also be added as needed. The amounts of the monomers can be selected and adjusted as needed by those skilled in the art during preparation.

[0112] The surfactant can be at least one of emulsifiers commonly used in emulsion polymerization, such as sodium lauryl sulfate, potassium lauryl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium dodecyl polyoxyethylene ether sulfate, ammonium dodecyl polyoxyethylene ether sulfate, sodium dodecyl benzene sulfonate, fatty alcohol polyoxyethylene ether, and alkyl phenol polyoxyethylene ether.

[0113] The initiator can be at least one of initiators commonly used in emulsion polymerization, such as persulfate salts, combinations of persulfate salts and bisulfite, and combinations of peroxides and bisulfite.

[0114] As another embodiment of the present application, the separator includes a base film and an adhesive layer on at least one side surface of the base film; the thickness of the base film is 3 to 6 μm, and the thickness of the adhesive layer is 0.5 to 1.5 μm.

[0115] The adhesive layer includes a first polymeric binder, non-conductive particles, and a second polymeric binder; the ratio of the average particle size D501 of the first polymeric binder to the thickness of the adhesive layer is (1.3 to 4):1; the average particle size D503 of the non-conductive particles is 0.15 to 0.8 μm; the average particle size D502 of the second polymeric binder is 0.05 to 1 μm, and the size distribution of the second polymeric binder is less than 1.

[0116] In the present application, when the thickness of the base film is 3-6 μm, the thickness of the adhesive layer is 0.5-1.5 μm, and the average particle size D501 of the first polymer adhesive is greater than the thickness of the adhesive layer, the average particle size D502 of the second polymer adhesive is controlled to be 0.05-1 μm, and the span of the second polymer adhesive is less than 1, so that excellent heat resistance and low thermal shrinkage can be achieved even when the overall thickness of the separator is thin.

[0117] As described above, the ratio of the average particle size D501 of the first polymer adhesive to the thickness of the adhesive layer is (1.3-4):1. When the ratio of the average particle size D501 of the first polymer adhesive to the thickness of the adhesive layer is within the above range, it is beneficial to improve the adhesive strength between the separator and the electrode sheet, inhibit the thermal shrinkage of the separator, and ensure the gas permeability of the separator. If the ratio is too large, in the case of a thin adhesive layer (0.5-1.5 μm), there can be a problem of the first polymer adhesive falling off due to the excessively large average particle size D501 of the first polymer adhesive, which in turn leads to a decrease in the adhesive strength between the separator and the electrode sheet, and a decrease in the inhibitory effect on the thermal shrinkage of the separator. If the ratio is too small, it is not beneficial to improve the adhesive strength between the separator and the electrode sheet, and the gas permeability of the separator will also decrease to some extent.

[0118] Preferably, the average particle size D501 of the first polymer adhesive is 1-6 μm, and specifically, for example, the average particle size D501 of the first polymer adhesive can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, or 6 μm, etc.

[0119] Preferably, in the present application, the glass transition temperature Tg1 of the first polymer adhesive is 45-95℃, for example, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, or 95℃, etc.

[0120] The application has low thermal shrinkage and high air permeability and good adhesion to the electrode sheet in the case of small thickness of the base film and the adhesive layer in the separator. The application can improve the energy density, cycle performance and safety of the battery. The inventor believes that the reason may be that the average particle size of the first polymer binder is appropriate, which can be uniformly dispersed in the adhesive layer, avoiding the first polymer binder from falling off from the adhesive layer, ensuring the structure of the separator and improving the safety of the battery. Moreover, the first polymer binder is dispersed and inlaid in the adhesive layer, and the hot pressing will not form a film, especially when the ratio of the average particle size D501 of the first polymer binder to the thickness of the adhesive layer is (1.3-4):1, which can effectively avoid the decrease of the air permeability of the separator, thereby ensuring the ion migration rate in the battery and improving the cycle performance of the battery. The average particle size D502 of the second polymer binder is controlled to be 0.05-1 μm, and the diameter distance of the second polymer binder is less than 1. Through the joint action of the first polymer binder, the second polymer binder and the non-conductive particles, the close combination between the adhesive layer and the base film can be effectively ensured, and the thermal shrinkage of the separator can also be effectively inhibited.

[0121] In the present embodiment, the content and the specific substance of the first polymer binder in the adhesive layer are as described above, and will not be repeated here.

[0122] According to the application, the average particle size D503 of the non-conductive particles in the adhesive layer is less than the thickness of the adhesive layer. Preferably, the ratio of the average particle size D503 of the non-conductive particles to the average particle size D501 of the first polymer binder is 1:(2.3-20). If the average particle size D503 of the non-conductive particles exceeds 0.8 μm, the thermal shrinkage of the separator will be significantly increased.

[0123] Preferably, the average particle size D103 of the non-conductive particles is 0.05-0.6 μm, and the average particle size D903 of the non-conductive particles is 0.5-2 μm. In this case, the non-conductive particles and the second polymer binder with the above-mentioned average particle size and diameter distance can better cooperate, realizing excellent heat resistance and low thermal shrinkage of the separator at a lower thickness.

[0124] When the thickness of the base film of the separator is 3-6 μm, the thickness of the adhesive layer is 0.5-1.5 μm, the average particle size D502 of the second polymer binder is 0.05-1 μm, the diameter distance is less than 1, and the ratio of the average particle size D503 of the non-conductive particles to the average particle size D501 of the first polymer binder is 1:(2.3-20), the first polymer binder, the non-conductive particles and the second polymer binder can better inhibit the thermal shrinkage of the separator and maintain good air permeability.

[0125] In the present embodiment, the content of the non-conductive particles and the specific substances that can be used are as described above, and will not be repeated here.

[0126] Preferably, the Tg2 of the second polymer binder is 20°C or lower.

[0127] The content of the second polymer binder and the specific substances that can be used are as described above, and will not be repeated here.

[0128] In the present embodiment, the first polymer binder can be used as the main adhesive component for bonding the separator and the electrode sheet, i.e. the separator is mainly bonded to the electrode sheet through the first polymer binder in the adhesive layer. The second polymer binder can be mainly used for bonding the non-conductive particles and the first polymer binder (particles) and other components in the adhesive layer, to improve the stability of the adhesive layer, and can also be used together with the first polymer binder as the adhesive material for bonding the separator and the electrode sheet, to improve the bonding force between the separator and the electrode sheet.

[0129] In a specific embodiment, the adhesive layer further comprises a rheological modifier and / or an auxiliary agent, and the auxiliary agent comprises a wetting agent and / or a defoaming agent; wherein the rheological modifier comprises one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyacrylate. The rheological modifier of the present embodiment can adjust the viscosity of the adhesive layer slurry, facilitating the coating of the adhesive layer slurry on the base film, so as to obtain a separator with high stability. The wetting agent of the present embodiment can make the adhesive layer slurry more easily spread uniformly on the base film, so as to make the adhesive layer more uniform, thereby better controlling the thickness of the adhesive layer. The defoaming agent of the present embodiment can eliminate the bubbles generated in the adhesive layer slurry and the coating process, preventing defects in the separator, and facilitating the subsequent application of the separator.

[0130] In a specific embodiment, the mass percentage content of the rheological modifier in the adhesive layer is 0.5% to 3%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%, etc.; and / or, the mass percentage content of the auxiliary agent in the adhesive layer is 0.1% to 2%, such as 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%, etc. When the mass percentage contents of the rheological modifier and the auxiliary agent in the adhesive layer are within the above ranges, respectively, the coating process of the adhesive layer is easier, and a separator with fewer defects can be prepared, which is beneficial to the application of the separator in the battery.

[0131] In a specific embodiment, the base film comprises a polyolefin film and / or a non-woven fabric film, and the polyolefin film comprises a polyethylene-based film and / or a polypropylene-based film. When the base film is selected from the above materials, the separator has high air permeability, which can ensure the rapid migration of ions between the positive and negative electrodes, thereby ensuring the electrochemical performance of the battery.

[0132] In a specific embodiment, the heat shrinkage of the separator is less than 5% after being baked at 130℃±5℃ for 60min±5min. The heat shrinkage of the separator within the above range can prevent the positive and negative electrodes of the battery from directly contacting each other, avoid short circuit of the battery, and thus improve the safety of the battery.

[0133] Specifically, the heat shrinkage of the separator of the embodiments of the present application can be obtained by referring to the heat shrinkage test in GB / T 36363-2018 “Polyolefin Separator for Lithium Ion Battery”:

[0134] The stainless steel plate and two pieces of filter paper are placed in the middle position of the oven, and the temperature is controlled to make the stainless steel plate and the filter paper reach (130±1)℃. The longitudinal and transverse directions of the separator are marked, and the length measuring instrument with the corresponding resolution is used to measure the length of the longitudinal and transverse directions of the sample, respectively. Then, the separator is placed flat on one of the filter papers in the middle of the stainless steel plate in the air-blast thermostat, and the other filter paper is used to press it. After that, the door of the thermostat is closed, and the time is started. The temperature is kept at 130℃ for 1h.

[0135] After heating, the separator is taken out, and after the separator returns to room temperature, the marked length of the longitudinal and transverse directions is measured again. The shrinkage of the longitudinal and transverse directions of the separator is calculated according to the following formula, and the average of three test results is taken as the heat shrinkage of the separator.

[0136] MD% = 100% * (L z0 -L z ) / L z0 ,

[0137] TD% = 100% * (L h0 -L h ) / L h0 ,

[0138] In the formula:

[0139] MD%: heat shrinkage in the longitudinal direction of the separator, %;

[0140] TD%: heat shrinkage in the transverse direction of the separator, %;

[0141] L z0 : length in the longitudinal direction of the separator before heating, unit: millimeter (mm);

[0142] L z : length in the longitudinal direction of the separator after heating, unit: millimeter (mm);

[0143] L h0 : length in the transverse direction of the separator before heating, unit: millimeter (mm);

[0144] Lh : the length of the separator after heating in the transverse direction, in millimeters (mm).

[0145] In one specific embodiment, the air permeability of the separator is not higher than 50 s / 100cc. The air permeability of the separator is within the above range, and the ions in the battery can quickly pass through the separator to achieve rapid migration between the positive and negative electrodes, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0146] Specifically, the air permeability of the separator of the embodiments of the present application can be tested by the following steps.

[0147] First, the air permeation time of the base film and the coated separator is tested according to GB / T 36363-2018 "Polyolefin Separator for Lithium Ion Battery".

[0148] Three pieces of separator are cut from the film roll at a longitudinal interval of 150 mm. If the width of the separator is ≥100 mm, the sample size is 100 mm x 100 mm, and if the width of the separator is <100 mm, the sample size is 100 mm x the width of the separator. The separator is placed in the test head of the air permeation instrument suitable for testing to test the air permeation time, and the average of three test results is taken as the air permeation time of the separator, in s / 100cc.

[0149] The air permeability of the separator is the difference between the air permeation time of the coated separator and the air permeation time of the base film, in s / 100cc.

[0150] The present application provides a preparation method of the above-mentioned separator, comprising the following steps: coating a slurry containing a first polymer binder on at least one side surface of the base film to form a bonding layer, thereby obtaining the separator.

[0151] Specifically, the first polymer binder is mixed with water in a specified ratio to prepare a slurry containing the first polymer binder, and then the slurry is coated on at least one side surface of the base film to obtain a bonding layer after drying, i.e., a separator comprising a base film and a bonding layer.

[0152] Further, when the bonding layer further comprises a second polymer binder, non-conductive particles, a rheology modifier, and an auxiliary agent, the first polymer binder, the second polymer binder, the non-conductive particles, the rheology modifier, the auxiliary agent, and water are mixed in a specified ratio to obtain the bonding layer slurry.

[0153] The ratio of the mass of water to the total weight of solids in the bonding layer slurry of the embodiments of the present application is (2.5-5):1, so that the solid content of the bonding layer slurry is 25%-45%.

[0154] The embodiments of the present application do not limit the specific method of mixing the first polymer binder with water, for example, stirring, ultrasonic, etc. can be selected according to actual needs.

[0155] The specific parameters of coating are not limited in the embodiments of the present application, and can be selected according to actual needs.

[0156] The specific parameters of drying are not limited in the embodiments of the present application, and can be selected according to actual needs.

[0157] The preparation method of the present application can attach the adhesive layer to the surface of the base film, and prepare the separator with small thickness, low thermal shrinkage rate and high air permeability, so as to ensure the high energy density, cycle performance and safety of the battery. Moreover, the preparation method is simple in process, easy to operate and low in cost, and is conducive to the industrialized production of the separator.

[0158] The present application provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, and the separator as described above, and the separator is located between the positive electrode sheet and the negative electrode sheet.

[0159] The battery of the embodiments of the present application can be a lithium ion battery or a sodium ion battery, etc. When the battery of the embodiments of the present application is a lithium ion battery, the lithium ion battery of the embodiments of the present application comprises a positive electrode sheet, and the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode current collector is generally an aluminum foil. The positive electrode active material comprises at least one of lithium transition metal oxides such as LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, LiNi x Co y Mn 1-x-y O2, wherein 0 < x < 1 and 0 < y < 1.

[0160] The lithium ion battery of the embodiments of the present application comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder, wherein the negative electrode current collector is generally a copper foil, and the negative electrode active material is selected from one or more of graphite, hard carbon, soft carbon, mesocarbon microbeads, silicon-based negative electrode material and lithium-containing metal composite oxide material.

[0161] The selection of the conductive agent and the binder in the positive electrode active material layer and the negative electrode active material layer of the embodiments of the present application can be conventional materials in the field.

[0162] In a specific embodiment, the adhesion between the separator and the positive electrode sheet is not less than 1.5 N / m; and / or, the adhesion between the separator and the negative electrode sheet is not less than 0.5 N / m. When the adhesion between the separator and the positive and negative electrode sheets is within the above range respectively, the separator can be adhered to the positive and negative electrode sheets, so as to fix the structure of the battery, avoid the displacement of the positive and negative electrode sheets in the battery to cause the separator to be pierced, and avoid the direct contact between the positive and negative electrode sheets, thereby improving the safety of the battery.

[0163] For the purposes of the present application, the technical solutions and advantages will be more apparent, the technical solutions of the present application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0164] The present application will be further described below through specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used in the following are conventional reagents, conventional materials and conventional instruments, which are commercially available. The reagents and materials involved can also be synthesized by conventional synthesis methods.

[0165] Example 1

[0166] The preparation method of the diaphragm of the present embodiment comprises the following steps:

[0167] 1. Polymerize the monomer containing unsaturated bond to obtain the first polymer binder, and the preparation process is as follows:

[0168] First step: mix 20 parts of monomer with 0.5 parts of peroxide dilauryl, stir and dissolve uniformly to form a mixed monomer; the monomer used in the present embodiment is a mixture of styrene, butyl acrylate, isooctyl acrylate and divinylbenzene, with a mass ratio of 93:3:3:1;

[0169] Second step: dissolve polyvinyl alcohol 1788 in 80 parts of deionized water to prepare a dispersant aqueous solution, and the dispersant concentration is 0.5wt%;

[0170] Third step: pour the mixed solution of the first step into the dispersant aqueous solution of the second step, and use a high-speed homogenizer to homogenize into an oil-water dispersion at a speed of 5000 revolutions per minute;

[0171] Fourth step: after 30 minutes of nitrogen blowing, polymerize at a temperature of 75℃ for 6 hours, and obtain a first polymer binder aqueous dispersion with a solid content of 25% after polymerization is completed.

[0172] 2. The second polymer binder, and the preparation process is as follows:

[0173] Take 0.1 parts of sodium dodecyl sulfate and 350 parts of deionized water into a stirring container, add 85 parts of styrene, 65 parts of butadiene, control the stirring speed at 150±50 rpm, heat to 74±1°C under stirring, then add 0.8 parts of initiator, keep 74±1°C for 6h, then raise the temperature to 79±1°C, continue to react for 3h, to obtain a second polymer binder emulsion with solid content of 30%, average particle size D502 of 0.8μm, span of 0.9, and glass transition temperature Tg2 of 12°C.

[0174] 3. Mix the first polymer binder, the second polymer binder, the hydrated alumina, the sodium carboxymethyl cellulose, the auxiliary agent, and water to obtain a bonding layer slurry, then coat the slurry on both sides of the polyvinyl film, and dry to obtain the separator;

[0175] The thickness of the polyvinyl film is 6μm, and the thickness of the bonding layer on one side of the polyvinyl film is 1.5μm.

[0176] In the bonding layer, the average particle size D501 of the first polymer binder is 6μm, the ratio of the average particle size of the first polymer binder to the thickness of the bonding layer is 4:1, and the glass transition temperature Tg1 of the first polymer binder is 80°C.

[0177] The mass percentage of the first polymer binder is 8%, the mass percentage of the second polymer binder is 6%, the mass percentage of the hydrated alumina (with average particle size D503 of 0.5μm, D103 of 0.2μm, and D903 of 1.2μm) is 84.5%, the mass percentage of the sodium carboxymethyl cellulose is 1%, and the mass percentage of the auxiliary agent is 0.5%.

[0178] Example 2

[0179] The preparation method of the separator of the present example is substantially the same as that of Example 1, except that the raw material composition for preparing the first polymer binder is a mixture of styrene, butyl acrylate, isooctyl acrylate, and divinylbenzene with a mass ratio of 95:1:2:2.

[0180] The monomer raw material composition for preparing the second polymer binder is a mixture of methyl methacrylate, butyl acrylate, isooctyl acrylate, and divinylbenzene with a mass ratio of 55:40:4:1.

[0181] The first polymer binder, the second polymer binder, the non-conductive particles, and the separator are adjusted according to the values in Table 1.

[0182] Example 3

[0183] The preparation method of the separator of the present example is substantially the same as that of Example 1, except that the raw material composition for preparing the first polymer binder is a mixture of styrene, butyl acrylate, isooctyl acrylate, and divinylbenzene in a mass ratio of 79:10:10:1.

[0184] The monomer raw material composition for preparing the second polymer binder is a mixture of methyl methacrylate, butyl acrylate, isooctyl acrylate, and ethylene glycol diacrylate in a mass ratio of 20:65:14:1.

[0185] The first polymer binder, the second polymer binder, the non-conductive particles, and the separator are adjusted according to the values in Table 1.

[0186] Examples 4-8 and Comparative Examples 1-4

[0187] The preparation method of the separator of the present example is substantially the same as that of Example 1, except that the first polymer binder, the second polymer binder, the non-conductive particles, and the separator are adjusted according to the values in Table 1.

[0188] Table 1

[0189] Test Example 1

[0190] The separators of the examples and comparative examples are tested for thermal shrinkage, air permeability, and the bonding strength between the adhesive layer and the base film:

[0191] Thermal shrinkage test

[0192] The thermal shrinkage test is performed in accordance with GB / T 36363-2018 “Polyolefin separators for lithium ion batteries”. The specific method includes: placing a stainless steel plate and two pieces of quantitative filter paper in the middle position of an oven, and controlling the temperature to make the stainless steel plate and the filter paper reach (130±1)℃. Mark the longitudinal and transverse directions of the separator, and then use a length measuring instrument with the appropriate resolution to measure the length of the longitudinal and transverse directions of the sample, respectively. Then, place the separator flat on one of the quantitative filter papers on the stainless steel plate in the middle of the air-blast constant temperature oven, and press it with the other quantitative filter paper. Close the oven door and start the time calculation. Keep the temperature at 130℃ for 1h.

[0193] After heating is completed, the separator is taken out, and after the separator returns to room temperature, the marked lengths of the longitudinal and transverse directions are measured again. The shrinkage rates of the longitudinal and transverse directions of the separator are calculated according to the following formula, and the average of three test results is taken as the thermal shrinkage rate of the separator. MD% = 100% * (L z0 -L z ) / L z0 , TD% = 100% * (L h0 -Lh ) / L h0 ,

[0194] In the formula:

[0195] MD%: heat shrinkage rate in the longitudinal direction of the separator, %;

[0196] TD%: heat shrinkage rate in the transverse direction of the separator, %;

[0197] L z0 : length in the longitudinal direction of the separator before heating, in millimeters (mm);

[0198] L z : length in the longitudinal direction of the separator after heating, in millimeters (mm);

[0199] L h0 : length in the transverse direction of the separator before heating, in millimeters (mm);

[0200] L h : length in the transverse direction of the separator after heating, in millimeters (mm).

[0201] Air permeability test

[0202] The air permeation time of the base film and the coated separator was tested according to GB / T 36363-2018 "Polyolefin Separator for Lithium Ion Battery". The specific method includes: cutting 3 pieces of separator from the film roll with a longitudinal interval of 150 mm, if the width of the separator is ≥100 mm, taking the sample size as 100 mm x 100 mm, if the width of the separator is <100 mm, taking the sample size as 100 mm x the width of the separator. The separator is placed in the test head of the air permeation instrument suitable for the test range to test the air permeation time, and the average value of 3 test results is taken as the air permeation time of the separator, in s / 100cc.

[0203] The air permeation value of the separator is the difference between the air permeation time of the coated separator and the air permeation time of the base film, in s / 100cc.

[0204] Adhesion strength test between the adhesive layer and the base film:

[0205] Test equipment:

[0206] Tensile testing machine: sensor range <200 N; sensor resolution 0.01 N, accuracy ±0.5%;

[0207] Support: steel plate with a thickness ≥1 mm, smooth and flat surface, length ≥150 mm, width ≥25 mm;

[0208] Test tape: single-sided tape with adhesion 0.4±0.05 N / mm, width 19±0.5 mm;

[0209] General double sided tape: width > 20 mm, < support width

[0210] Roller: 2.5 kg smooth rubber roller

[0211] Test sample:

[0212] Cut 3 pieces of 300 mm x 50 mm rectangular samples from the separators prepared in the foregoing examples and comparative examples. If the width is between 20-50 mm, the sample size is: 300 mm x separator width.

[0213] Test procedure:

[0214] Apply the general double sided tape with width > 20 mm to one end of the support flatly, the length of the general double sided tape is 120 mm. Remove the surface layer of the general double sided tape. Apply the adhesive layer of the separator sample to the general double sided tape flatly, roll back and forth with the roller at least 3 times to expel the air between the general double sided tape and the sample. Apply the test tape to the surface of the base film of the separator sample flatly, roll back and forth with the roller at least 3 times (the length of the test tape is 200-250 mm). There should be no bubbles or folds at the bonding sites between the adhesive layer and the general double sided tape, between the base film and the test tape. Peel the test tape outside the support from the coating, stop peeling when the coating is peeled to about 10 mm from the end with the general double sided tape.

[0215] Adjust the test parameters of the tensile testing machine, the test speed is 50 ± 5 mm / min, the peeling length is 100 ± 10 mm, the clamp distance is 120 ± 10 mm, the test width is 19 mm, and the front and end 25% (25 mm) are removed. After adjusting the parameters, clamp the end of the support without the double sided tape with the lower clamp, and clamp the test tape with the upper clamp. Pay attention to the sample when clamping the sample, and make sure that the sample is vertical. Start the test. After the test is completed, read the average peeling strength value of the interface as the 180° adhesive strength value of the sample. Take the average value of 3 samples as the 180° adhesive strength of the sample, with the unit of N / m.

[0216] The test results obtained are shown in Table 2.

[0217] Test Example 2

[0218] The separators of the examples and comparative examples were combined with positive electrode sheets, negative electrode sheets and electrolyte to prepare lithium ion batteries, specifically: the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3O2(NCM523), conductive material CNT, conductive carbon black and binder (polyvinylidene fluoride) PVDF are dispersed in a solvent NMP in a mass ratio of 94:2:2:2 to obtain a positive active material layer slurry; the positive active material layer slurry is uniformly coated on the surface of the positive current collector aluminum foil, and after drying, rolling, baking, slitting and spot welding of the tabs, a positive electrode sheet is obtained.

[0219] The negative active material artificial graphite, conductive agent conductive carbon black, CNT, sodium carboxymethyl cellulose and binder SBR are dispersed in deionized water in a mass ratio of 95:1.25:1.25:1.25:1.25, and uniformly stirred to obtain a negative active material layer slurry; the negative active material layer slurry is uniformly coated on the surface of the negative current collector copper foil, and after drying, rolling, baking, slitting and spot welding of the tabs, a negative electrode sheet is obtained.

[0220] An electrolyte is prepared in a glove box, the glove box is filled with argon with a purity of 99.999%, the moisture in the glove box is controlled to be ≤0.1 ppm, and the temperature is controlled to be at room temperature, ethylene carbonate (EC) and diethyl carbonate (DEC), methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC:DMC:DEC=3:5:2, then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1.2 mol / L, and after uniform mixing, an electrolyte is obtained.

[0221] The prepared positive electrode sheet, negative electrode sheet and separator are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet, the cell is placed in an aluminum plastic film after winding, dried, injected with electrolyte, sealed, and subjected to processes such as standing, formation, two-sealing, and capacity grading to obtain a lithium ion battery.

[0222] The adhesion of the separator to the positive electrode sheet and the adhesion of the separator to the negative electrode sheet are tested, and the test results are shown in Table 2.

[0223] Table 2

[0224] As can be seen from the test results in Table 2, in the separator provided in the present application, the adhesion strength between the adhesion layer and the base film is high, the adhesion between the separator and the electrode sheet is high, and the thermal shrinkage rate and the air permeability value of the separator itself are low, showing excellent air permeability and heat shrinkage resistance.

[0225] Specifically, as can be seen from Comparative Example 4 and Comparative Example 4, in the case of the low base film and adhesion layer thickness of the present application, if the average particle size D503 of the non-conductive particles exceeds 0.8 μm, the thermal shrinkage rate of the separator will increase significantly.

[0226] As can be seen from the test results of Comparative Examples 4 and Comparative Example 3, if the span of the second polymer binder exceeds 1, the adhesion strength of the base film to the bonding layer will be significantly reduced, and the thermal shrinkage of the separator will be significantly increased.

[0227] As can be seen from the test results of Comparative Examples 1, 2, 4 and Comparative Examples 1 and 2, if the ratio of the average particle size D501 of the first polymer binder to the thickness of the bonding layer is not within the range of 1.3-4, the adhesion of the separator to the pole piece will be significantly reduced.

[0228] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions described in the foregoing examples can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A diaphragm, characterized by The adhesive layer includes a first polymer binder and non-conductive particles; a ratio of an average particle diameter D501 of the first polymer binder to a thickness of the adhesive layer is (1.3-4):1; an average particle diameter D503 of the non-conductive particles is 0.15-0.8 μm; and a peeling strength between the adhesive layer and the base film is 10 N / m or more. The average particle diameter D501 of the first polymer binder is 1-6 μm.

2. The separator according to claim 1, characterized in that The glass transition temperature Tg1 of the first polymer binder is 45-95 °C. The mass percentage content of the first polymer binder in the adhesive layer is 3-15 %; 3. The separator of claim 1, wherein The monomer containing an unsaturated bond includes one or more of a vinyl monomer, a (meth)acrylate monomer, a maleate monomer, an itaconate monomer, a maleimide monomer, and a (meth)acrylamide monomer. The monomer containing an unsaturated bond includes one or more of a monomer having a carboxyl group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, a monomer having a hydroxyl group, a monomer having an amino group, a monomer having an epoxy group, and a monomer having a cyano group. The ratio of the average particle diameter D503 of the non-conductive particles to the average particle diameter D501 of the first polymer binder is 1:(2.3-20). The average particle diameter D103 of the non-conductive particles is 0.05-0.6 μm, and the average particle diameter D903 of the non-conductive particles is 0.5-2 μm.

4. The separator of claim 1, wherein The mass percentage content of the non-conductive particles in the adhesive layer is 70-93.4 %.

5. The diaphragm of claim 4, wherein, The non-conductive particles include one or more of alumina, aluminum sesquioxide, boehmite, silica, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, organic polymer microspheres, and organic polymer fibers.

6. The separator of claim 1, wherein The adhesive layer further includes a second polymer binder having an average particle diameter D502 of 0.05-1 μm. The second polymer binder has a particle size of less than 1.

7. The separator according to any one of claims 1 to 6, wherein The second polymer binder has a Tg2 of 20 °C or less.

8. The diaphragm of claim 7, wherein, The second polymer binder includes at least one of a polyacrylate and a styrene-butadiene latex.

9. The diaphragm of claim 6 or 7, wherein, The mass percentage content of the second polymer binder in the adhesive layer is 3-10 %.

10. The septum of claim 7, wherein, The adhesive layer includes a first polymer binder and non-conductive particles; a ratio of an average particle diameter D501 of the first polymer binder to a thickness of the adhesive layer is (1.3-4):1; an average particle diameter D503 of the non-conductive particles is 0.15-0.8 μm; and a peeling strength between the adhesive layer and the base film is 10 N / m or more. ​ 11. A diaphragm characterized by, ​ The adhesive layer includes a first polymer binder, non-conductive particles, and a second polymer binder; a ratio of an average particle diameter D501 of the first polymer binder to a thickness of the adhesive layer is (1.3-4):1; an average particle diameter D503 of the non-conductive particles is 0.15-0.8 μm; an average particle diameter D502 of the second polymer binder is 0.05-1 μm, and a diameter distance of the second polymer binder is less than 1.

12. The diaphragm of claim 11, wherein, The average particle diameter D501 of the first polymer binder is 1-6 μm. And / or, a glass transition temperature Tg1 of the first polymer binder is 45-95 °C.

13. The septum of claim 12, wherein, A mass percentage content of the first polymer binder in the adhesive layer is 3%-15%; And / or, the first polymer binder is obtained by polymerization of a monomer containing an unsaturated bond, wherein, The monomer containing an unsaturated bond includes one or more of a vinyl monomer, a (meth)acrylate monomer, a maleate monomer, an itaconate monomer, a maleimide monomer, and a (meth)acrylamide monomer; And / or, the monomer containing an unsaturated bond includes one or more of a monomer having a carboxyl group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, a monomer having a hydroxyl group, a monomer having an amino group, a monomer having an epoxy group, and a monomer having a cyano group.

14. The separator according to any one of claims 11 to 13, wherein A ratio of the average particle diameter D503 of the non-conductive particles to the average particle diameter D501 of the first polymer binder is 1:(2.3-20).

15. The diaphragm of claim 14, wherein, The average particle diameter D103 of the non-conductive particles is 0.05-0.6 μm, and the average particle diameter D903 of the non-conductive particles is 0.5-2 μm. And / or, a mass percentage content of the non-conductive particles in the adhesive layer is 70%-93.4%; And / or, the non-conductive particles include one or more of alumina, aluminum trioxide, boehmite, silica, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, organic polymer microspheres, and organic polymer fibers.

16. The septum of claim 11, wherein The Tg2 of the second polymer binder is 20 °C or lower; And / or, the second polymer binder includes at least one of a polyacrylate and a styrene-butadiene latex. And / or, a mass percentage content of the second polymer binder in the adhesive layer is 3%-10%.

17. A battery, characterized by A separator according to any one of claims 1-10 or a separator according to any one of claims 11-16 is disposed between a positive electrode sheet and a negative electrode sheet.

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