Battery separator, secondary battery and electric device

Abstract

The present application belongs to the technical field of new energy. Disclosed are a battery separator, a secondary battery and an electric device. The battery separator of the present application comprises a separator substrate and a coating arranged on at least one surface of the separator substrate, wherein the coating comprises an aramid fiber layer and adhesive polymer particles, and the aramid fiber layer comprises a first surface and a second surface, which are arranged face to face, the first surface of the aramid fiber layer being in contact with the separator substrate, and the adhesive polymer particles being embedded into the aramid fiber layer and forming dotted bulges on the second surface of the aramid fiber layer. The battery separator of the present application shows good adhesion performance on positive and negative electrode sheets, has a high separator rupture temperature, good air permeability, good compressibility, a good electrolyte infiltration effect and low impedance, and is not only applicable to the preparation of a fast-charge and / or high-power battery, but also capable of ensuring that a battery has good safety.

Description

Battery separators, secondary batteries and electrical equipment

[0001] Cross-references

[0002] This application is related to a Chinese application filed on January 10, 2024, the invention name of which is "Battery Separator, Secondary Battery and Electrical Equipment", application number 202410039739.7, and the entire contents of the application are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of new energy technology and relates to battery separators, secondary batteries and electrical equipment. Background Art

[0004] Battery separators isolate the positive and negative electrodes, preventing them from contact and causing short circuits. Their ion transport capacity is directly related to the overall performance of the battery. Currently, separators are primarily made by coating a porous polyolefin substrate with a heat-resistant coating of aluminum oxide or boehmite. However, these heat-resistant coatings are inherently heavy, hindering lightweight battery development, and their ability to increase the membrane rupture temperature is limited.

[0005] Aramid is lightweight and heat-resistant, and can effectively solve the above-mentioned problems of alumina or boehmite heat-resistant coatings. However, aramid itself does not have adhesive properties, and a layer of adhesive coating needs to be applied to the surface of the aramid coating, or an adhesive polymer needs to be added and dissolved in the coating liquid used to prepare the aramid coating. However, the process of applying a layer of adhesive coating on the surface of the aramid coating is complicated, and it will result in a low porosity, poor air permeability, and poor ion transmission capacity of the pure aramid coating, which is not suitable for the preparation of fast-charging and high-power batteries; and adding and dissolving an adhesive polymer in the coating liquid used to prepare the aramid coating will result in essentially no gap between the aramid coating and the electrode plate, which will in turn result in the electrolyte being unable to quickly penetrate into the interior of the battery during injection, resulting in poor wetting. Moreover, the aramid coating thus obtained has weak compressibility, which results in the electrode plate easily wrinkling when the electrode plate expands and squeezes the diaphragm during charging and discharging, causing cycle failure. Summary of the Invention

[0006] In response to the above-mentioned problems, the present application aims to provide a battery separator, a secondary battery, and an electrical device. The battery separator not only exhibits excellent adhesion and a high rupture temperature, but also exhibits excellent air permeability, good compressibility, and low impedance. When the battery separator is fabricated into a secondary battery, a gap is formed between the separator and the electrode plates, providing a channel for electrolyte infiltration.

[0007] In a first aspect, the present application provides a battery separator, comprising a separator substrate and a coating provided on at least one side of the separator substrate;

[0008] The coating comprises an aramid layer and adhesive polymer particles;

[0009] The aramid layer has a first surface and a second surface opposite to each other, wherein the first surface of the aramid layer contacts the diaphragm matrix, and the adhesive polymer particles are embedded in the aramid layer and form dot-shaped protrusions on the second surface of the aramid layer.

[0010] In some embodiments, the average height of the dot-shaped protrusions is 1 to 10 μm.

[0011] In some embodiments, the area of ​​the dot-shaped protrusions accounts for 2% to 30% of the area of ​​the second surface of the aramid layer.

[0012] In some embodiments, the battery separator further satisfies at least one of conditions (1) to (4):

[0013] (1) The compression rate of the battery separator is 5% to 42%;

[0014] (2) The air permeability of the battery separator is less than or equal to 250s;

[0015] (3) The impedance of the battery separator is less than or equal to 3.9 ohm;

[0016] (4) The rupture temperature of the battery separator is greater than or equal to 158°C.

[0017] In some embodiments, the swelling rate of the adhesive polymer particles in a polar solvent is ≤800wt.% and the dissolution rate is ≤60wt.%, wherein the polar solvent includes at least one of an amide organic solvent and a sulfone organic solvent, and the swelling rate and dissolution rate test conditions are 25°C and 24h.

[0018] In some embodiments, the amide organic solvent includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and hexamethylphosphoric triamide, and the sulfone organic solvent includes at least one of sulfolane and dimethyl sulfoxide.

[0019] In some embodiments, the adhesive polymer particles include a cross-linked polymer, and the cross-linked polymer includes at least one of cross-linked polymethyl methacrylate, cross-linked polyacrylate, cross-linked acrylic ester copolymer, cross-linked vinylidene fluoride-hexafluoropropylene copolymer, cross-linked styrene-butadiene rubber, cross-linked styrene-propylene rubber, cross-linked polyurethane, cross-linked epoxy resin, and cross-linked ethylene-vinyl acetate copolymer.

[0020] In some embodiments, the material of the aramid layer includes at least one of aramid 1313 and aramid 1414 .

[0021] In a second aspect, the present application provides a secondary battery comprising the battery separator.

[0022] In a third aspect, the present application provides an electric device, comprising the secondary battery, wherein the secondary battery is used as a power supply for the electric device.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) For the battery separator of the present application, on the one hand, since the adhesive polymer particles are embedded in the aramid layer, the density of the aramid layer of the battery separator is reduced, the air permeability is improved, and the impedance is reduced; on the other hand, these adhesive polymer particles form point-shaped protrusions on the second surface of the aramid layer away from the separator substrate, which not only forms a gap between the separator and the electrode plate, providing a channel for the infiltration of the electrolyte, ensuring that the electrolyte can quickly penetrate into the interior of the battery with a good infiltration effect, but also makes the separator have good compressibility, which can provide space for the expansion of the electrode plate during the battery charging and discharging process, and avoid the electrode plate squeezing the separator and causing wrinkles to cause cycle failure.

[0025] (2) The battery separator of the present application has good adhesion to the positive and negative electrodes, high membrane rupture temperature, good air permeability, good compressibility, good electrolyte infiltration effect, and low impedance. It is not only suitable for preparing fast-charging and / or high-power type batteries, but also ensures that the battery has good safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic structural diagram of the battery separator obtained in Example 1, wherein 1 is a separator substrate, 2 is a coating layer, 21 is an aramid layer, and 22 is adhesive polymer particles. DETAILED DESCRIPTION

[0027] In order to better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific embodiments and comparative examples. Its purpose is to understand the content of the present application in detail, rather than to limit the present application. All other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present application. The experimental reagents and instruments involved in the implementation of this application are all commonly used ordinary reagents and instruments unless otherwise specified.

[0028] According to a first aspect of the present application, a battery separator is provided, comprising a separator substrate and a coating provided on at least one side of the separator substrate;

[0029] The coating comprises an aramid layer and adhesive polymer particles;

[0030] The aramid layer has a first surface and a second surface that are opposite to each other. The first surface of the aramid layer contacts the diaphragm matrix. The adhesive polymer particles are embedded in the aramid layer and form dot-shaped protrusions on the second surface of the aramid layer.

[0031] The battery separator of the present application possesses the characteristics of aramid and adhesive polymer because it contains aramid and adhesive polymer particles, thus having a high membrane rupture temperature and good adhesion. On the one hand, because the adhesive polymer particles are embedded in the aramid layer, the density of the aramid layer of the battery separator is reduced, the air permeability is improved, and the impedance is reduced; on the other hand, these adhesive polymer particles form dot-shaped protrusions on the second surface of the aramid layer, creating a gap between the separator and the electrode plate, providing a channel for the infiltration of the electrolyte, ensuring that the electrolyte can quickly penetrate into the interior of the battery, and the infiltration effect is good; at the same time, these adhesive polymer particles are also compressible, which can provide space for the expansion of the electrode plate during the battery charging and discharging process, preventing the electrode plate from squeezing the separator and causing wrinkles and cycle failure.

[0032] The battery separator of the present application has good adhesion with the positive and negative electrode sheets, high membrane rupture temperature, good air permeability, good compressibility, good electrolyte infiltration effect, and low impedance. It is not only suitable for preparing fast-charging and / or high-power type batteries, but also ensures that the battery has good safety.

[0033] In some embodiments, the average height of the dot-like protrusions is 1 to 10 μm, such as 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, or a range formed by any two of the above values. This not only allows the electrolyte to quickly penetrate into the battery, resulting in a better wetting effect, but also improves the compressibility of the coating and the compression rate, reducing the impact of the coating on ion transport, ensuring the appropriate thickness of the diaphragm, and facilitating the improvement of battery energy density. The average height of the dot-like protrusions can be measured by the following test method:

[0034] The 3D mode of the Keyence LJ-X8000 device was used to place the battery separator sample flat on the stage. The height from the highest point of the point-like protrusion in the sample coating to the second surface of the aramid layer of the coating was measured using the 3D mode. 32 protrusion points were randomly counted continuously, and the average value was taken as the average height of the point-like protrusions.

[0035] In some embodiments, the area of ​​the dot-shaped protrusions on the second surface of the aramid layer accounts for 2% to 30%, such as 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 27%, 30%, or a range formed by any two of the above values, so as to achieve a higher coating compression rate, a higher adhesion between the separator and the positive and negative electrode sheets, better air permeability, and lower impedance. The area ratio of the dot-shaped protrusions on the second surface of the aramid layer can be measured by the following test method:

[0036] The 2D mode of the Keyence LJ-X8000 device was used to place the battery separator sample flat on the stage and scan the 1cm surface of the sample coating in 2D mode. 2In the coating area, calculate the area ratio of all point-like protrusions on the scanning area, and continuously randomly count 32 areas. The average value is taken as the area ratio of the point-like protrusions on the aramid layer surface.

[0037] In some embodiments, the average depth of the adhesive polymer particles embedded in the aramid layer is 0.2 to 5 μm, such as 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or a range formed by any two of the above values. The average depth of the adhesive polymer particles embedded in the aramid layer within the above range can further improve the adhesion of the coating and reduce the possibility of powder loss. The average depth of the adhesive polymer particles embedded in the aramid layer can be measured by the following test method:

[0038] The cross-section of the battery separator sample was cut using an argon ion polishing cutting device, and the cut section was further photographed using a scanning electron microscope. The vertical distance from the lowest point of the embedded particle to the second surface of the aramid layer was measured on a computer, and 32 embedded particle points were continuously counted, and the average was taken as the average depth of the adhesive polymer particles embedded in the aramid layer.

[0039] In some embodiments, the compressibility of the battery separator is 5% to 42%, such as 5%, 10%, 15%, 30%, 42%, or a range formed by any two of the above values. The compressibility of the battery separator can be measured by the following method: measuring the initial thickness of the separator h0, the thickness of the positive electrode sheet m, and the thickness of the negative electrode sheet n, laminating the sheets in the order of one positive electrode sheet, one separator, and one negative electrode sheet, and then hot pressing the sheets after lamination. The hot pressing parameters are as follows: pressure 3 MPa, temperature 90°C, time 15 seconds; measuring the sum of the thicknesses s of the positive electrode sheet, separator, and negative electrode sheet after hot pressing; separator compression ratio = 1-(smn) / h0.

[0040] In some embodiments, the battery separator has an air permeability value of less than or equal to 250 s, such as 250 s, 200 s, 150 s, 50 s, or a range formed by any two of these values. The air permeability value of the separator can be measured using a Gurley tester using the following parameters: a 20-ounce internal air cylinder, a 1.0 square inch round hole, and 100 cc of air.

[0041] In some embodiments, the impedance of the battery separator is less than or equal to 3.9 ohm, such as 3.9 ohm, 3.5 ohm, 2.5 ohm, 1.5 ohm, 1.05 ohm, 1.00 ohm, 0.95 ohm, 0.90 ohm or the range formed by any two of the above values. The impedance of the separator can be measured by the following method: the symmetrical battery is assembled with the structure of the first copper foil + blue glue + separator + second copper foil (the coating of the separator is fixedly assembled to the second copper foil), and the center of the blue glue is punched with a circular hole with a diameter of 12 mm (the actual effective area through which lithium ions can pass); the number of separator layers is designed to be 1 layer, 2 layers, 3 layers, and 4 layers respectively, and 3 symmetrical battery parallel samples are made for each layer of separator, which are then dried and packaged with liquid; the symmetrical battery impedance is tested using an electrochemical workstation at a test frequency of 3 MHZ to 200 MHZ; the impedance values ​​obtained from the symmetrical battery test corresponding to 1 layer, 2 layers, 3 layers, and 4 layers of separators are linearly fitted, and the slope of the straight line is defined as the separator impedance.

[0042] In some embodiments, the battery separator has a rupture temperature greater than or equal to 158°C, such as 158°C, 160°C, 170°C, 185°C, 200°C, 215°C, 231°C, or a range formed by any two of the above values. The rupture temperature of the separator can be measured by the following method: TMA tester, with a specimen size of 8 mm, a fixed load of 50 mN, and a heating rate of 5°C / min. The separator is tested in the machine direction (MD) and the transverse direction (TD) respectively, and the peak temperature of the TMA curve is taken as the separator rupture temperature.

[0043] In some embodiments, the average thickness of the coating is 1.2 to 14 μm, such as 1.2 μm, 2 μm, 5 μm, 7 μm, 10 μm, 13 μm, 14 μm, or a range formed by any two of the above values. The average thickness of the coating can be measured by the following test method:

[0044] The cross section of the coated diaphragm was cut using an argon ion polishing cutting device, and the cut section was further photographed using a scanning electron microscope. The vertical distance from the highest point of the embedded particle to the first surface of the aramid layer was measured on a computer, and 32 particle points were continuously counted, and the average was taken as the average thickness of the coating.

[0045] The aramid layer is typically produced using an aramid coating solution, which is obtained by dissolving aramid in a polar solvent. By adding adhesive polymer particles with a low solubility rate to the aramid coating solution, the adhesive polymer particles can be embedded in the resulting aramid layer, forming dot-like protrusions on the second surface of the aramid layer.

[0046] In some embodiments, the dissolution rate of the adhesive polymer particles in a polar solvent is ≤ 60 wt.% (e.g., 60 wt.%, 50 wt.%, 40 wt.%, 30 wt.%, 20 wt.%, 10 wt.%, 5 wt.%, 1 wt.%, 0.5 wt.%, 0, or a range formed by any two of the above values). The dissolution rate is tested at 25° C. for 24 hours to ensure that the adhesive polymer particles are embedded in the formed aramid layer and form dot-shaped protrusions on the second surface of the aramid layer. When testing the dissolution rate of the adhesive polymer particles in a polar solvent, a mass ratio of the adhesive polymer particles to the polar solvent can be selected to be 100:1.

[0047] In some embodiments, the swelling ratio of the adhesive polymer particles in a polar solvent is ≤ 800 wt.% (e.g., 800 wt.%, 600 wt.%, 400 wt.%, 200 wt.%, 100 wt.%, 50 wt.%, 30 wt.%, 20 wt.%, 10 wt.%, 5 wt.%, 0, or a range formed by any two of the above values). The swelling ratio is tested at 25° C. for 24 hours to ensure minimal dimensional change before and after drying of the coating during the preparation process. When testing the swelling ratio of the adhesive polymer particles in a polar solvent, a mass ratio of adhesive polymer particles to polar solvent can be selected to be 100:1.

[0048] As an example, the polar solvent includes at least one of an amide organic solvent and a sulfone organic solvent. Alternatively, the amide organic solvent includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and hexamethylphosphoric triamide; and the sulfone organic solvent includes at least one of sulfolane and dimethyl sulfoxide. However, the polar solvent is not limited thereto.

[0049] As an example, the adhesive polymer particles include cross-linked polymers, and the cross-linked polymers include at least one of cross-linked polymethyl methacrylate, cross-linked polyacrylate, cross-linked acrylic ester copolymer, cross-linked vinylidene fluoride-hexafluoropropylene copolymer, cross-linked styrene-butadiene rubber, cross-linked styrene-propylene rubber, cross-linked polyurethane, cross-linked epoxy resin, and cross-linked ethylene-vinyl acetate copolymer.

[0050] As an example, the material of the aramid layer includes at least one of aramid 1313 and aramid 1414. However, the material of the aramid layer is not limited thereto.

[0051] In some embodiments, a method for preparing a battery separator comprises the following steps:

[0052] Prepare aramid polymer solution;

[0053] preparing a dispersion of adhesive polymer particles;

[0054] The aramid polymer solution and the adhesive polymer particle dispersion solution are mixed and dispersed to obtain a coating solution;

[0055] The obtained coating liquid is coated on the surface of the separator substrate, placed in water for phase inversion, and then dried and rolled up to obtain a battery separator.

[0056] Optionally, the mass concentration of aramid in the aramid polymer solution is 1.5% to 30%, such as 1.5%, 5%, 10%, 15%, 20%, 25%, 30% or a range formed by any two of the above values.

[0057] Optionally, the solvent in the aramid polymer solution includes a polar solvent, which includes at least one of an amide organic solvent and a sulfone organic solvent, wherein the amide organic solvent includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and hexamethylphosphoric triamide, and the sulfone organic solvent includes at least one of cyclopentane sulfone and dimethyl sulfoxide.

[0058] In one embodiment, a method for preparing an aramid polymer solution includes the following steps: adding a cosolvent and phenylenediamine to a polar solvent under protective gas protection for dissolution, controlling the process temperature to be -30°C to 20°C (e.g., -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, or a range formed by any two of the above values), then adding phthaloyl chloride while stirring at a temperature of -15°C to 60°C (e.g., -15°C, -10°C, 0°C, 10°C, 30°C, 50°C, 60°C, or a range formed by any two of the above values), wherein the molar ratio of phenylenediamine to phthaloyl chloride is 0.5:1 to 1:0.5 (e.g., 0.5:1, 0.8:1, 1:1, 1:0.2, 1:0.5, or a range formed by any two of the above values), and adding a neutralizer after the reaction reaches a predetermined time for neutralization to obtain an aramid polymer solution.

[0059] Optionally, the addition of phthaloyl chloride to the completion of the reaction takes 0.5 to 8 hours, such as 0.5 hours, 1 hour, 3 hours, 5 hours, 8 hours, or a range formed by any two of the above values. Optionally, the protective gas used includes at least one of nitrogen and an inert gas. Optionally, the polar solvent used includes at least one of an amide organic solvent and a sulfone organic solvent, wherein the amide organic solvent includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and hexamethylphosphoric triamide; and the sulfone organic solvent includes at least one of sulfolane and dimethyl sulfoxide. Optionally, the cosolvent includes at least one of lithium chloride and calcium chloride. Optionally, the neutralizer includes at least one of sodium hydroxide, calcium hydroxide, and potassium hydroxide. Optionally, the mass of the cosolvent is 2% to 20% of the total mass of the aramid polymer solution, such as 2%, 5%, 10%, 15%, 20%, or a range formed by any two of the above values. When the aramid polymer solution is aramid 1313, the phenylenediamine used is m-phenylenediamine, and the phthaloyl chloride used is isophthaloyl chloride. When the aramid polymer solution is aramid 1414, the phenylenediamine used is p-phenylenediamine, and the phthaloyl chloride used is terephthaloyl chloride. When the aramid polymer solution is a mixed polymer solution of aramid 1313 and aramid 1414, it can be prepared by the following method: mixing and dispersing the aramid 1313 and aramid 1414 polymer solutions to obtain a polymer solution of aramid 1313 and aramid 1414.

[0060] Optionally, the mass concentration of the adhesive polymer in the adhesive polymer particle dispersion is 5% to 50%, such as 5%, 10%, 20%, 30%, 40%, 50% or a range formed by any two of the above values.

[0061] Optionally, the average particle size of the adhesive polymer particles in the adhesive polymer particle dispersion is 2 to 12 μm, such as 2 μm, 5 μm, 7 μm, 10 μm, 12 μm or a range formed by any two of the above values.

[0062] Optionally, the solvent in the adhesive polymer particle dispersion includes a polar solvent, the polar solvent including at least one of an amide organic solvent and a sulfone organic solvent, wherein the amide organic solvent is at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and hexamethylphosphoric triamide, and the sulfone organic solvent includes at least one of sulfolane and dimethyl sulfoxide. In one embodiment, the adhesive polymer particles include a cross-linked polymer, wherein the cross-linked polymer includes at least one of cross-linked polymethyl methacrylate, cross-linked polyacrylate, cross-linked acrylic acid ester copolymer, cross-linked vinylidene fluoride-hexafluoropropylene copolymer, cross-linked styrene-butadiene rubber, cross-linked styrene-propylene rubber, cross-linked polyurethane, cross-linked epoxy resin, and cross-linked ethylene-vinyl acetate copolymer.

[0063] In one embodiment, a method for preparing a dispersion of adhesive polymer particles includes the following steps: weighing adhesive polymer particles, adding them to a polar solvent, and dispersing them to obtain a dispersion of adhesive polymer particles. Optionally, the average particle size of the adhesive polymer particles is 2 to 12 μm, such as 2 μm, 5 μm, 7 μm, 10 μm, 12 μm, or a range formed by any two of these values. The average particle size of the adhesive polymer particles can be measured using a Malvern particle size analyzer, and the measured Dv50 value is used as the average particle size of the particles.

[0064] Optionally, the mass ratio of the aramid polymer solution to the adhesive polymer particle dispersion is 1:12 to 500:1, such as 1:12, 1:1, 10:1, 50:1, 100:1, 300:1, 500:1 or a range formed by any two of the above values.

[0065] Optionally, the coating method includes at least one of gravure roller coating, blade coating, and dip coating.

[0066] In some embodiments, the membrane substrate comprises a porous polyolefin membrane substrate. As an example, the porous polyolefin membrane substrate comprises at least one of a porous polyethylene membrane substrate and a porous polypropylene membrane substrate. The membrane substrate can be selected from a composite substrate formed from two or more of the aforementioned substrates, such as a porous polyethylene and polypropylene composite substrate.

[0067] In some embodiments, the porosity of the membrane matrix is ​​20% to 80%, such as 20%, 30%, 40%, 50%, 60%, 70%, 80% or a range formed by any two of the above values.

[0068] In a second aspect, the present application provides a secondary battery comprising the above-mentioned battery separator.

[0069] In some embodiments, the secondary battery includes at least one of a wound soft-pack battery, a wound aluminum shell battery, a wound cylindrical battery, a laminated soft-pack battery, a laminated aluminum shell battery, and the like.

[0070] In a third aspect, the present application provides an electrical device, comprising the above-mentioned secondary battery, wherein the above-mentioned secondary battery is used as a power supply for the electrical device.

[0071] In order to clearly understand the technical solution of the present application, the present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be understood as limiting the scope of protection claimed in the present application.

[0072] The following examples and comparative examples are prepared using the following raw materials:

[0073] The preparation method of cross-linked acrylic ester multi-polymer powder is as follows:

[0074] 1. The first main monomers are styrene, methyl methacrylate, and butyl methacrylate, with a mass ratio of 6:1:1. The first functional monomers are methyl hydroxymethylacrylate and divinylbenzene, with a mass ratio of 1:2, and a mass ratio of 5:1 between the first main monomer and the first functional monomer. The emulsifier is polysorbate 80, with the total amount of the emulsifier being 4 wt% of the total monomer mass. The first main monomer, the first functional monomer, and the emulsifier are mixed and then added with water to form a first reaction solution with a total monomer concentration of 30%. The first initiator is ammonium persulfate, which is prepared as a 0.8 mol / L aqueous solution for later use.

[0075] 2. The second main monomers are selected from acrylonitrile, ethyl acrylate, butyl acrylate, and isooctyl acrylate, and the mass ratio of each monomer is 5:1:1:2; the second functional monomers are selected from methacrylic acid, N-hydroxymethyl acrylamide, and polyethylene glycol (200) diacrylate, and the mass ratio thereof is 1:3:1, and the mass ratio of the second main monomer to the second functional monomer is 10:1; the second initiator is selected from benzoyl peroxide, and the addition amount is 0.2% of the total monomers. The second main monomer, the second functional monomer, the second initiator and the organic solvent dimethyl carbonate are mixed to form a second reaction solution with a total monomer concentration of 30%.

[0076] 3. Add the first reaction liquid into the reactor and heat it to 85°C, gradually add the ammonium persulfate initiator solution dropwise, the addition time is controlled to 2h, and the reaction is continued for 2 hours after the addition is completed; continue to add the second reaction liquid dropwise, control the total monomer mass ratio of the first reaction liquid to the total monomer mass of the second reaction liquid to be 3:1, and control the addition time of the second reaction liquid to be 1 hour. After the addition is completed, keep the temperature at 85°C for 1 hour to obtain a synthetic emulsion for standby use.

[0077] 4. A crosslinking agent, ethyl orthosilicate, was added to the synthesized emulsion at a concentration of 0.4% by weight of the total monomers. The emulsion was dried in a spray dryer at 140°C to obtain a crosslinked acrylic ester multipolymer powder. The average particle size D50 of the powder was 30 μm.

[0078] 5. The powder is further passed through a jet mill. By controlling the gas flow rate, gas flow rate, feed pressure, and pulverization pressure of the jet mill, cross-linked acrylic ester multi-polymer powders with different particle sizes of D50 ranging from 1 to 18 μm can be obtained.

[0079] The preparation method of cross-linked polymethyl methacrylate powder is as follows:

[0080] 1. Water, emulsifier (OP-10: sodium dodecylbenzenesulfonate = 1:1), sodium dodecylbenzenesulfonate, and methyl methacrylate were mixed in a ratio of 66.75:3:0.25:30 to form an emulsion. The temperature was raised to 80°C, and the initiator was added dropwise. The addition was completed within 2 hours. The reaction was kept warm for 4 hours to obtain a polymethyl methacrylate emulsion.

[0081] 2. A crosslinking agent, ethyl orthosilicate, was added to the synthetic emulsion at a concentration of 0.4% by weight of the total monomers. The emulsion was dried in a spray dryer at 140°C to obtain polymethyl methacrylate powder. The average particle size D50 of the powder was 30 μm.

[0082] 3. The powder is further passed through a jet mill. By controlling the gas flow rate, gas flow rate, feed pressure, and pulverizing pressure of the jet mill, cross-linked polymethyl methacrylate powders with different particle sizes of D50 ranging from 1 to 18 μm can be obtained.

[0083] The preparation method of cross-linked vinylidene fluoride-hexafluoropropylene copolymer powder is as follows:

[0084] At room temperature, 1 kg of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, Arkema, LBG brand) powder was placed in an aluminum foil bag, and the air was replaced with nitrogen before irradiation. The irradiation source was Co-60, and the irradiation dose was 60 kGy to obtain a cross-linked intermediate product. The cross-linked intermediate product was further heated to 180°C, maintained at a constant temperature for 10 minutes, and then cooled to room temperature at a cooling rate of 10°C / min to obtain a cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer.

[0085] Unless otherwise specified, the components and raw materials used in the examples and comparative examples of the present application are all commercially available raw materials, and the raw materials used in each parallel experiment are all of the same kind.

[0086] Example 1

[0087] This embodiment provides a battery separator, the preparation method of which includes the following steps:

[0088] (1) Weighing 10.00 kg of N-methylpyrrolidone and adding it to a container, adding 3.120 kg of m-phenylenediamine and 0.949 kg of calcium chloride as a co-solvent to dissolve them under nitrogen protection, controlling the process temperature at -20°C, then adding 5.858 kg of isophthaloyl chloride while stirring at 15°C, reacting for 40 minutes, and adding calcium hydroxide to neutralize, thereby obtaining an aramid polymer solution (i.e., aramid 1313 polymer solution);

[0089] (2) Weighing 2.500 kg of cross-linked acrylate copolymer powder with an average particle size of 7 μm, adding 10.00 kg of N-methylpyrrolidone, and stirring at 25° C. for 2 h to obtain a dispersion of adhesive polymer particles;

[0090] (3) adding all of the adhesive polymer particle dispersion prepared in step (2) to the aramid polymer solution prepared in step (1), mixing and stirring for 20 minutes to obtain a coating solution;

[0091] (4) A wet-process polyethylene porous diaphragm substrate with a thickness of 9 μm and a porosity of 40% was selected. The micro-concave roller parameters were adjusted, and the coating liquid was applied to one of the two surfaces of the diaphragm substrate. The substrate was then placed in a water bath for phase inversion, dried, and rolled up to obtain a battery separator. The schematic diagram of the resulting battery separator structure is shown in FIG1 . The total thickness is 16 μm, the average height of the dot-like protrusions is 5 μm, and the area of ​​the dot-like protrusions on the second surface of the aramid layer (i.e., the surface facing away from the diaphragm substrate) accounts for 6% of the area.

[0092] Example 2

[0093] The difference from Example 1 is that 3.120 kg of p-phenylenediamine is used instead of 3.120 kg of m-phenylenediamine, and 5.858 kg of terephthaloyl chloride is used instead of 5.858 kg of isophthaloyl chloride, and the obtained aramid polymer liquid is aramid 1414 polymer liquid; in the obtained battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0094] Example 3

[0095] The difference from Example 1 is that the average particle size of the cross-linked acrylate copolymer powder is 2 μm, and the amount of the cross-linked acrylate copolymer powder is adjusted; in the obtained battery separator, the average height of the point-like protrusions is 1 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0096] Example 4

[0097] The difference from Example 1 is that the average particle size of the cross-linked acrylate copolymer powder is 12 μm, and the amount of the cross-linked acrylate copolymer powder is adjusted; in the obtained battery separator, the average height of the point-like protrusions is 10 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0098] Example 5

[0099] The difference from Example 1 is that the average particle size of the cross-linked acrylate copolymer powder is 1 μm, and the amount of the cross-linked acrylate copolymer powder is adjusted; in the obtained battery separator, the average height of the point-like protrusions is 0.5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0100] Example 6

[0101] The difference from Example 1 is that the average particle size of the cross-linked acrylate copolymer powder is 18 μm, and the amount of the cross-linked acrylate copolymer powder is adjusted; in the obtained battery separator, the average height of the point-like protrusions is 12 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0102] Example 7

[0103] The difference from Example 1 is that the amount of cross-linked acrylate copolymer powder is reduced; in the resulting battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 2%.

[0104] Example 8

[0105] The difference from Example 1 is that the amount of cross-linked acrylate copolymer powder is increased; in the resulting battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 30%.

[0106] Example 9

[0107] The difference from Example 1 is that the amount of cross-linked acrylate copolymer powder is reduced; in the resulting battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 1%.

[0108] Example 10

[0109] The difference from Example 1 is that the amount of cross-linked acrylate copolymer powder is increased; in the resulting battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 35%.

[0110] Example 11

[0111] The difference from Example 1 is that the cross-linked acrylic ester multipolymer powder is completely replaced by cross-linked polymethyl methacrylate powder with an equal weight average particle size of 7 μm; in the obtained battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0112] Example 12

[0113] The difference from Example 1 is that the cross-linked acrylic ester multipolymer powder is completely replaced by cross-linked polyvinylidene fluoride-hexafluoropropylene powder with an equal weight average particle size of 7 μm; in the obtained battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0114] Example 13

[0115] The difference from Example 1 is that 10.00 kg of N,N-dimethylacetamide is used to completely replace N-methylpyrrolidone in step (1), and 10.00 kg of N,N-dimethylacetamide is used to completely replace N-methylpyrrolidone in step (2); in the obtained battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0116] Example 14

[0117] The difference from Example 1 is that 10.00 kg of N,N-dimethylformamide is used to completely replace N-methylpyrrolidone in step (1), and 10.00 kg of N,N-dimethylformamide is used to completely replace N-methylpyrrolidone in step (2); in the obtained battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0118] Example 15

[0119] The difference from Example 1 is that in step (1), 10.00 kg of cyclopentane sulfone is used to completely replace N-methylpyrrolidone, and in step (2), 10.00 kg of cyclopentane sulfone is used to completely replace N-methylpyrrolidone; in the obtained battery separator, the average height of the point-like protrusions is 5 μm, and the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the separator substrate) accounts for 6% of the area.

[0120] Comparative Example 1

[0121] The difference from Example 1 is that steps (2) and (3) are not performed, and the aramid polymer solution obtained in step (1) is directly used as the coating solution in step (4); the thickness of the obtained battery separator is 11 μm.

[0122] Comparative Example 2

[0123] The difference from Example 1 is that the coating liquid used is different. The preparation method of the coating liquid of this comparative example includes the following steps:

[0124] Weigh 49.59 kg of ultrapure water, 0.19 kg of sodium polyacrylate dispersant and 8 kg of carboxymethyl cellulose (CMC) solution, mix and stir for 20 minutes, add 38.5 kg of alumina powder, stir again for 30 minutes, add 4.62 kg of Japan Ruiong BM-900B binder, stir for 20 minutes, and finally add 0.1 kg of wetting agent and continue stirring for 20 minutes to obtain a coating liquid (i.e., alumina diaphragm coating liquid).

[0125] Comparative Example 3

[0126] The difference from Example 1 is that the coating liquid used is different. The preparation method of the coating liquid of this comparative example includes the following steps:

[0127] Weigh 49.59 kg of ultrapure water, 0.19 kg of sodium polyacrylate dispersant and 8 kg of CMC solution, mix and stir for 20 minutes, add 38.5 kg of alumina powder, stir again for 30 minutes, add 3.85 kg of cross-linked acrylic ester multipolymer powder, the average particle size of which is 7 μm, stir for 40 minutes, add 4.62 kg of Japan Ruiong BM-900B binder, stir for 20 minutes, and finally add 0.1 kg of wetting agent and continue stirring for 20 minutes to obtain a coating liquid (i.e., alumina diaphragm coating liquid).

[0128] The coated diaphragms prepared in the examples and comparative examples were subjected to the following performance tests, and the results are recorded in Table 1:

[0129] (1) Adhesion between coating and electrode: A layer of diaphragm and a layer of positive electrode sheet (ternary NCM positive electrode sheet) or negative electrode sheet (artificial graphite negative electrode sheet) are stacked and hot pressed after stacking. The hot pressing parameters are as follows: pressure 3 MPa, temperature 90 °C, time 15 s; the hot pressed positive or negative electrode sheet + diaphragm unit is cut into 50 mm wide strips, and the diaphragm and electrode on the strips are subjected to a 180° peel test using an electronic tensile testing machine to obtain the adhesion between the diaphragm and the electrode.

[0130] (2) Diaphragm compression rate: Use a micrometer to measure the initial thickness of the diaphragm h0, the thickness of the positive electrode sheet m, and the thickness of the negative electrode sheet n. Lamination is performed in the order of one positive electrode sheet, one diaphragm, and one negative electrode sheet. After lamination, hot pressing is performed using the following parameters: pressure 3 MPa, temperature 90°C, and time 15 s. The sum of the thicknesses of the positive electrode sheet, diaphragm, and negative electrode sheet after hot pressing is measured (s). The compression rate of the diaphragm bond coat is 1-(smn) / h0.

[0131] (3) Thermal shrinkage of the diaphragm: The diaphragm was cut into a size of MD×TD=100mm×100mm. The sample was clamped with A4 paper on the top and bottom, placed in a 130℃ oven and baked for 1 hour. The MD size of the sample after baking was measured with a film ruler as x and the TD size as y. The units of x and y are mm. The shrinkage in the MD direction is (100-x)%, and the shrinkage in the TD direction is (100-y)%.

[0132] (4) Diaphragm rupture temperature: TMA tester, sample size 8 mm, fixed load 50 mN, heating rate 5 ° C / min, test the diaphragm in MD and TD directions respectively, and take the peak temperature of the thermomechanical analysis (TMA) curve as the membrane melting temperature.

[0133] (5) Diaphragm air permeability: Gurley tester, tester parameters: 20 ounce built-in cylinder, 1.0 square inch round hole, 100cc air.

[0134] (6) Symmetrical battery diaphragm impedance: The symmetrical battery is assembled with the structure of first copper foil + blue glue + diaphragm + second copper foil (the coating 2 of the diaphragm is fixedly mounted on the second copper foil), and a circular hole with a diameter of 12 mm is punched in the center of the blue glue (the actual effective area through which lithium ions can pass); the number of diaphragm layers is designed to be 1 layer, 2 layers, 3 layers, and 4 layers respectively, and 3 symmetrical battery parallel samples are made for each layer of diaphragm, which are then dried and sealed with liquid; the symmetrical battery impedance is tested using an electrochemical workstation with a test frequency of 3 MHz to 200 MHz; the impedance values ​​obtained from the symmetrical battery test corresponding to 1 layer, 2 layers, 3 layers, and 4 layers of diaphragms are linearly fitted, and the slope of the straight line is defined as the diaphragm impedance.

[0135] Table 1

[0136] The separators described in the examples and comparative examples are stacked in order with the positive and negative electrode sheets so that the separator is located between the positive and negative electrode sheets. The cells are wound, hot-pressed, and welded to the tabs to obtain a bare cell. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10°C for 24 hours. The electrolyte is injected into the dried cell, and the cell is allowed to stand, undergo formation, and undergo capacity separation to complete the preparation of a lithium-ion soft-pack battery.

[0137] The preparation of the positive electrode sheet includes the following steps:

[0138] The positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1 ) O2, conductive agent acetylene black and binder polyvinylidene fluoride are mixed uniformly in a mass ratio of 94:3:3, and dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed slurry is coated on both sides of aluminum foil, baked, roll-pressed, and cut into pieces to obtain a positive electrode sheet;

[0139] The preparation of the negative electrode sheet includes the following steps:

[0140] The negative electrode active material graphite, the conductive agent acetylene black, the thickener carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) were mixed uniformly in a mass ratio of 96.2:1.2:1.2:1.4, and dispersed in deionized water to form a uniform black slurry. The mixed slurry was coated on both sides of the copper foil, and then baked, rolled, and cut into pieces to obtain the negative electrode sheet;

[0141] The preparation of the electrolyte includes the following steps:

[0142] At room temperature, in an argon-filled glove box (H2O<1ppm, O2<1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1:1 and The molecular sieve is used to remove water to obtain a mixed solvent, and then LiPF6 is added and mixed evenly to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0143] The performance of the obtained lithium-ion soft-pack battery was tested. The specific test items, test methods and results (see Table 2) are as follows:

[0144] (1) 25°C Cycling Performance Test: At 25±2°C, the lithium-ion soft-pack batteries obtained in each embodiment and comparative example were subjected to charge and discharge cycling tests at a charge and discharge rate of 1C / 1C in the range of 2.5 to 4.25V, and the number of cycles when the battery capacity retention rate was 80% was recorded. Capacity retention rate (%) = discharge specific capacity at the last cycle / discharge specific capacity at the first cycle * 100%;

[0145] (2) Battery thermal failure temperature test: At 25℃±2, fully charge the battery to 4.3V, let it stand for 1 hour, then take it out and place it in a thermal runaway test box. The initial temperature of the test box is set to 30℃±2℃. After standing for 1 hour, heat it at a rate of 10℃ / min. After heating to 100℃, keep it warm and let it stand for 30 minutes. Continue to heat it at a rate of 1℃ / min. After each 10℃ increase, let it stand for 30 minutes until the battery thermal runaway ignites. The temperature at which the battery thermal runaway ignites is recorded and defined as the battery thermal failure temperature.

[0146] Table 2

[0147] The battery separators of each embodiment of the present application have a bonding force with the positive electrode greater than or equal to 0.2 N / m, a bonding force with the negative electrode greater than or equal to 0.5 N / m, a separator compression rate of 5% to 42%, a shrinkage rate in the MD direction of more than 1.3%, a shrinkage rate in the TD direction greater than or equal to 0.85%, a membrane rupture temperature greater than or equal to 158°C, an air permeability value less than or equal to 250s, and an impedance less than or equal to 3.9 ohm.

[0148] By comparing Examples 1, 3 to 6, it can be seen that when the average height of the point-like protrusions is in the range of 1 to 10 μm, it is beneficial to improve the adhesion between the battery separator and the positive and negative electrodes, the compression rate of the separator, the MD direction shrinkage rate, the TD direction shrinkage rate, the membrane rupture temperature, the air permeability value and the balance of impedance, so that the comprehensive performance of the separator is better, and the cycle performance and safety performance of the battery prepared using the separator are improved.

[0149] From a comparison of Examples 1, 7 to 10, it can be seen that when the area of ​​the point-like protrusions on the second surface of the aramid layer (i.e., the surface away from the diaphragm substrate) accounts for 2% to 30%, it is beneficial to improve the adhesion between the battery diaphragm and the positive and negative electrodes, the compression rate of the diaphragm, the MD direction shrinkage rate, the TD direction shrinkage rate, the membrane rupture temperature, the air permeability value and the balance of impedance, so that the comprehensive performance of the diaphragm is better, and the cycle performance and safety performance of the battery prepared using the diaphragm are improved.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A battery separator, comprising a separator substrate and a coating provided on at least one surface of the separator substrate; The coating includes an aramid layer and adhesive polymer particles; The aramid layer has a first surface and a second surface that are oppositely disposed, wherein, A first surface of the aramid layer contacts the separator substrate, and at least a part of the adhesive polymer particles are embedded in the aramid layer and form dot-like protrusions on a second surface of the aramid layer.

2. The battery separator according to claim 1, wherein an average height of the dot-like protrusions is 1 to 10 μm.

3. The battery separator according to claim 1, wherein an area ratio of the dot-like protrusions on the second surface of the aramid layer is 2% to 30%.

4. The battery separator according to claim 1, wherein a compression ratio of the separator is 5% to 42%.

5. The battery separator according to claim 1, wherein an air permeability value of the separator is less than or equal to 250 s.

6. The battery separator according to claim 1, wherein an impedance of the separator is less than or equal to 3.9 ohm.

7. The battery separator according to claim 1, wherein a membrane breakage temperature of the separator is greater than or equal to 158 °C.

8. The battery separator according to claim 1, wherein a swelling rate of the adhesive polymer particles in a polar solvent is ≤800 wt.% and a dissolution rate is ≤60 wt.%, wherein the polar solvent includes at least one of amide organic solvents and sulfone organic solvents, and test conditions for the swelling rate and the dissolution rate are 25 °C and 24 h.

9. The battery separator according to claim 8, wherein the amide organic solvents include at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and hexamethylphosphoric triamide, and the sulfone organic solvents include at least one of sulfolane and dimethyl sulfoxide.

10. The battery separator according to claim 1, wherein the adhesive polymer particles include crosslinked polymers, and the crosslinked polymers include at least one of crosslinked polymethyl methacrylate, crosslinked polyacrylate, crosslinked acrylate multi-copolymer, crosslinked vinylidene fluoride-hexafluoropropylene copolymer, crosslinked styrene-butadiene rubber, crosslinked styrene-acrylic rubber, crosslinked polyurethane, crosslinked epoxy resin, and crosslinked ethylene-vinyl acetate copolymer.

11. The battery separator according to claim 1, wherein a material of the aramid layer includes at least one of aramid 1313 and aramid 1414.

12. The battery separator according to claim 1, wherein an average depth of the adhesive polymer particles embedded in the aramid layer is 0.2 to 5 μm.

13. The battery separator according to claim 1, wherein an average thickness of the coating is 1.2 to 14 μm.

14. The battery separator according to claim 1, wherein a porosity of the separator substrate is 20% to 80%.

15. A secondary battery, comprising the battery separator according to any one of claims 1 to 14.

16. An electrical device, comprising the secondary battery according to claim 15, and the secondary battery is used as a power supply for the electrical device.

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