Spray-coated separator having polymer secondary aggregates uniformly distributed in spray points, preparation method therefor, and battery

Abstract

Disclosed in the present invention are a spray-coated separator having polymer secondary aggregates uniformly distributed in spray points, a preparation method therefor, and a battery. The spray-coated separator comprises a separator substrate and a spray coating coated on at least one side surface of the separator substrate, wherein the spray coating is composed of a plurality of spray points, a plurality of uniformly distributed polymer secondary aggregates are contained in the spray points, the average diameter D50 of the spray points is 300-600 μm, the proportion of the effective bonding area of any spray point is greater than or equal to 60%, and the compression ratio of the spray coating is greater than or equal to 20%. In the present invention, by regulating and controlling the morphology of the spray points, the bonding efficiency of each single spray point is improved, and therefore the utilization rate of a polymer resin can be effectively improved, and the desired bonding effect can be achieved with minimum material consumption; thus, the production cost can be effectively reduced.

Description

Spray-coated diaphragm with uniform distribution of polymer secondary aggregates in spraying points, preparation method thereof, and battery Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a spray-coated separator with polymer secondary aggregates uniformly distributed within a spraying point, a preparation method thereof, and a battery. Background Art

[0002] With the implementation and promotion of the "Dual Carbon" policy, the new energy vehicle industry has experienced rapid growth, directly propelling the industry from a policy-driven to a market-driven trajectory, entering the fast lane. Currently, 98% of electric vehicles are powered by lithium-ion batteries. The lithium-ion battery industry still requires significant research and development in areas such as safety, energy density, and cycle life.

[0003] Lithium-ion battery separators, a key material in lithium-ion batteries, are typically coated on one or more sides of a microporous base membrane with a functional layer having adhesive properties. This layer can bond the positive and negative electrodes, improve the interface between the separator and the positive and negative electrodes, and enhance lithium ion flow. It also increases the hardness of the battery cell, thereby improving battery safety and cycle life. Commonly used coating materials in the market include polyvinylidene fluoride homopolymer or copolymer (PVDF), polymethyl methacrylate polymer (PMMA), and acrylate polymers. Common coating processes include micro-gravure roller coating and high-speed rotary spraying. High-speed rotary spraying is widely used in lithium-ion power battery systems because it can effectively control coating coverage and reduce battery internal resistance. The spray point, a key component of the spray coating, has a direct impact on the performance of the lithium-ion battery due to its morphology.

[0004] Currently, common spray-coated diaphragms focus on parameters such as spray point size and coverage, without specifying specific requirements for spray point morphology. The most common spray point morphology on the market is the hollow structure described in patent CN 114094283 A. This hollow structure is formed by a raised portion enclosing the hollow portion, with the interior of the raised portion enclosing the hollow portion. However, this structure has a small effective bonding area, limited bond strength, and is difficult to improve. Furthermore, the raised portions are densely packed, hindering ion passage.

[0005] Summary of the Invention

[0006] In view of this, the present invention provides a spray-coated diaphragm with uniformly distributed polymer secondary aggregates within the spraying point, a preparation method thereof, and a battery. By regulating the morphology of the spraying point, the bonding efficiency of a single spraying point is improved, the utilization rate of the polymer resin can be effectively improved, the desired bonding effect can be achieved with a minimum amount of material, and the production cost can be effectively reduced.

[0007] To achieve the above objectives, the present invention provides, in a first aspect, a spray-coated diaphragm having uniformly distributed polymer secondary agglomerates within a spray point, comprising a diaphragm substrate and a spray coating applied to at least one surface of the diaphragm substrate; the spray coating comprises a plurality of spray points, each of which contains a plurality of uniformly distributed polymer secondary agglomerates, wherein the average diameter D50 of the spray points is 300-600 μm, the effective bonding area of ​​any spray point accounts for ≥60%, and the compression rate of the spray coating is ≥20%;

[0008] Among them, D50 represents the diameter corresponding to when the cumulative spray point diameter distribution percentage reaches 50%;

[0009] The effective bonding area ratio of any spraying point is the ratio of the coverage area of ​​all polymer secondary aggregates within the spraying point to the area of ​​the spraying point;

[0010] Compression ratio of spray coating = ((thickness of spray-coated diaphragm before hot pressing - thickness of spray-coated diaphragm after hot pressing) - (thickness of substrate before hot pressing - thickness of substrate after hot pressing)) / thickness of spray coating × 100%.

[0011] According to any embodiment of the first aspect of the present invention, the average diameter D50 of the spraying point is 400-500 μm, the effective bonding area of ​​any spraying point accounts for ≥65%, and the compression rate of the sprayed coating is ≥30%.

[0012] According to any embodiment of the first aspect of the present invention, the thickness of the sprayed coating is 0.5 μm-10 μm.

[0013] According to any embodiment of the first aspect of the present invention, the effective bonding coefficient K of the spray coating prepared by the polymer is ≥ 1.5, where K is the slope of the fitted straight line between the bonding strength between the prepared spray coating and the corresponding amount of glue applied, reflecting the effectiveness of the polymer resin; and / or

[0014] The air permeability increase of the spray coating is ≤15s / 100cc.

[0015] According to any embodiment of the first aspect of the present invention, the spray coating comprises: 80 to 100 parts by mass of a polymer; 2 to 20 parts by mass of a binder; and 0.01 to 3 parts by mass of a dispersant.

[0016] According to any embodiment of the first aspect of the present invention, the polymer includes at least one of polyvinylidene fluoride homopolymer (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polyvinylidene fluoride-methyl methacrylate copolymer (PVDF-PMMA), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-acrylic acid copolymer, polymethyl methacrylate (PMMA), polyethylene (PE), and acrylate polymer.

[0017] According to any embodiment of the first aspect of the present invention, the binder includes at least one of carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, and acrylonitrile multipolymer.

[0018] According to any embodiment of the first aspect of the present invention, the dispersant includes at least one of ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, acrylic acid-polyurethane and polyethylene glycol.

[0019] According to any embodiment of the first aspect of the present invention, the separator substrate comprises a base film and an optional inorganic coating layer;

[0020] The base film is selected from at least one of polyethylene film, polypropylene film, polyimide film, polyvinylidene fluoride film, polyvinylidene fluoride-hexafluoropropylene film, polyamide film, and polyethylene terephthalate film;

[0021] The inorganic coating is composed of an inorganic material, and the inorganic material is selected from at least one of silicon dioxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, calcium oxide, boehmite, aluminum nitride, boron nitride, barium sulfate, calcium fluoride, and barium fluoride.

[0022] According to any embodiment of the first aspect of the present invention, the base film has a thickness of 3 μm to 25 μm and a porosity of 20% to 80%.

[0023] A second aspect of the present invention provides a method for preparing a spray-coated diaphragm having uniformly distributed polymer secondary aggregates within a spraying point, comprising the following steps:

[0024] Preparation of polymer slurry: Water and dispersant are stirred and mixed uniformly to obtain a first mixed solution at a stirring speed of 20-500 rpm for 5-30 minutes; polymer is added to the first mixed solution and mixed uniformly to obtain a second mixed solution, which is then ground using the following grinding parameters: grinding times 1-6 times, grinding speed 100-1500 rpm, grinding flow rate 10-100 mL / min, and grinding zirconium bead size 0.4-1.0 mm to obtain a third mixed solution; finally, a binder is added and mixed uniformly to obtain a polymer slurry;

[0025] The properties of the polymer slurry are as follows: the solid content of the polymer slurry is 10-20%, the particle size of the polymer slurry is D10≤3μm, 3μm<D50≤6μm, and D97≤12μm;

[0026] The spherical index of polymer particles in the polymer slurry is ψ≥1.3, Where D(4,3) is the volume average particle size of the polymer particles; D(3,2) is the surface area average particle size of the polymer particles;

[0027] Preparation of spray-coated diaphragm: The polymer slurry is applied to the surface of at least one side of the diaphragm substrate by rotary spraying to obtain a spray coating. The rotary spraying parameters are: coating speed 100-300m / min, slurry flow rate 1500-15000mL / min, and spraying speed 5000-15000rpm.

[0028] Drying: A high temperature-low temperature two-stage drying method is adopted, with the high temperature drying temperature being 60-90°C and the low temperature drying temperature being 55-85°C, to obtain a spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within the spraying point.

[0029] According to any embodiment of the second aspect of the present invention, the amount of glue applied is 0.05-1.5g / m 2 .

[0030] The third aspect of the present invention provides a battery, comprising a spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within the spraying points provided by the first aspect of the present invention or a spray-coated diaphragm prepared by the preparation method of the spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within the spraying points provided by the second aspect of the present invention.

[0031] Beneficial effects: The spray-coated diaphragm provided by the present invention has polymer secondary aggregates uniformly distributed within the spraying point. The spraying point morphology is regulated by controlling the slurry particle morphology and destroying its sphericity. The polymer secondary aggregate particles are uniformly distributed within the spraying point, and the effective bonding area within the spraying point accounts for ≥60%. By regulating the spraying point morphology, the bonding efficiency of a single spraying point is improved, the utilization rate of the polymer resin can be effectively improved, the desired bonding effect can be achieved with a minimum amount of material, and the production cost can be effectively reduced.

[0032] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0034] FIG1 is a scanning electron microscope image of the raw material acrylate polymer in Example 1 (accelerating voltage EHT=1 kV, working distance WD=5.8-6.1 mm, SE2 detector);

[0035] FIG2 is a scanning electron microscope image of the spraying point in Example 1;

[0036] FIG3 is a scanning electron microscope image of the raw material PVDF-HFP in Example 2;

[0037] FIG4 is a scanning electron microscope image of the spraying point in Example 2;

[0038] FIG5 is a scanning electron microscope image of the spraying point in Comparative Example 1. DETAILED DESCRIPTION

[0039] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0040] In a first aspect, the present invention provides a spray-coated diaphragm having uniformly distributed polymer secondary aggregates within spray points, comprising a diaphragm substrate and a spray coating applied to at least one surface of the diaphragm substrate; the spray coating comprises a plurality of spray points, each of which contains a plurality of uniformly distributed polymer secondary aggregates, wherein the average diameter D50 of the spray points is 300-600 μm, the effective bonding area of ​​any spray point accounts for ≥60%, and the compression rate of the spray coating is ≥20%;

[0041] Among them, D50 represents the diameter corresponding to when the cumulative major axis size distribution percentage of the spray points reaches 50%;

[0042] The effective bonding area ratio of any spraying point is the ratio of the coverage area of ​​all polymer secondary aggregates within the spraying point to the area of ​​the spraying point;

[0043] Compression ratio of spray coating = ((thickness of spray-coated diaphragm before hot pressing - thickness of spray-coated diaphragm after hot pressing) - (thickness of substrate before hot pressing - thickness of substrate after hot pressing)) / thickness of spray coating × 100%.

[0044] The following details are provided:

[0045] Diaphragm substrate:

[0046] The separator substrate may be a base film without a coating layer or a base film coated with an inorganic coating layer, without any particular limitation.

[0047] In an embodiment of the present invention, there is no particular restriction on the type of the diaphragm substrate, and it can be selected according to actual needs; preferably, the diaphragm substrate can be selected from one or more of polyethylene film, polypropylene film, polyimide film, polyvinylidene fluoride film, polyvinylidene fluoride-hexafluoropropylene film, polyamide film, and polyethylene terephthalate film.

[0048] In an embodiment of the present invention, the inorganic coating is composed of an inorganic material. There is no particular restriction on the type of the inorganic material and it can be selected according to actual needs. Preferably, the inorganic material can be selected from one or more of silicon dioxide (SiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), zirconium oxide (ZrO2), titanium oxide (TiO2), calcium oxide (CaO), boehmite (AlOOH), aluminum nitride (AlN), boron nitride (BN), barium sulfate (BaSO4), calcium fluoride (CaF2), and barium fluoride (BaF2).

[0049] The thickness of the separator substrate may be 3 μm to 25 μm, and preferably 5 μm to 16 μm.

[0050] The porosity of the diaphragm substrate may be 20% to 80%, preferably 30% to 60%.

[0051] Spray coating:

[0052] The spray coating is composed of a plurality of spraying points, which are composed of a plurality of polymer secondary agglomerates, and the polymer secondary agglomerates are formed by agglomeration of polymer primary particles.

[0053] The secondary polymer agglomerates of the present invention are evenly distributed within the spraying point.

[0054] The average diameter D50 of the sprayed spots is 300-600 μm, preferably 400-500 μm.

[0055] The definition of spray point diameter D50 is similar to that of particle size D50, indicating that spray points with diameters larger than it account for 50%, and spray points with diameters smaller than it also account for 50%, reflecting the average diameter of the spray points.

[0056] Method for measuring the diameter of the spraying point: The projected shape of the spraying point on the substrate is regarded as an ellipse, and the major axis size of the ellipse is used as the diameter of the spraying point. Specifically: a photo of the spraying point is taken with a scanning electron microscope, and the outline of the spraying point can be marked by software (such as Image J and other image processing software), and the major axis size of the outline is measured.

[0057] Measurement method of spray point diameter D50: For each sample, count the diameters of 100 spray points and arrange them from small to large. The diameter of the 50th spray point is D50.

[0058] The spray point size is the long axis size of the spray point. The narrower the spray point size distribution range, the more uniform the spray point and the better the bonding performance. When the spray point is too small, the bonding area between the spray point and the electrode is small, the single point bonding is weak, and there is basically no bonding effect. When the spray point is too large, the spray point coverage is too large, affecting the ion permeability performance.

[0059] The effective bonding area of ​​any spraying point accounts for ≥60%, preferably ≥65%, such as 70%, 75%, 80%, 85%, 90%, 95%...;

[0060] Effective bonding area ratio = ratio of the coverage area ∑A of all polymer secondary aggregates within the spraying point to the area S of the spraying point.

[0061] ∑A is the sum of the projected areas of each polymer secondary agglomerate on the substrate within the spraying point. The projected areas of each polymer secondary agglomerate on the substrate within the spraying point are tested and then summed. The test method for the projected area of ​​polymer secondary agglomerates on the substrate is as follows: arbitrarily select a spraying point, take a photo of the spraying point at 200 magnification using a scanning electron microscope, and use software (such as Image J or other image processing software) to mark the edge range of the polymer secondary agglomerate. The area of ​​this range is the projected area of ​​the polymer secondary agglomerate on the substrate. The method for marking the edge range of the secondary agglomerate is as follows: starting from a certain point on the edge of the secondary agglomerate, draw a line around the edge of the secondary agglomerate. The requirement is that the angle of all line segments is less than 180° (the internal angle between each line segment and the previous line segment is less than 180°). When the line segment angle is greater than 180°, the line segment directly connected to the starting point is disconnected. The line segments enclose a closed area, i.e., the range, and its area is the projected area of ​​the secondary agglomerate.

[0062] S is the projected area of ​​the spray point on the substrate. The test method is: take a photo of the spray point using a scanning electron microscope (e.g., at 200x magnification), and use software (such as Image J or other image processing software) to mark the outline of the spray point. The area enclosed by the outline is the projected area of ​​the spray point on the substrate.

[0063] The proportion of effective bonding area within the spraying point is the ratio of the coverage area of ​​the polymer resin within the spraying point to the area of ​​the spraying point. The larger the proportion of effective bonding area within the spraying point, the more uniform the distribution of the polymer resin, and the better the bonding effect of the spraying point, which can effectively improve material utilization and reduce costs.

[0064] The compression rate of the spray coating is ≥20%, preferably ≥30%, such as 40%, 50%, 60%, 70%, 80%, 90%...;

[0065] Compression ratio of spray coating = ((thickness of spray-coated diaphragm before hot pressing - thickness of spray-coated diaphragm after hot pressing) - (thickness of substrate before hot pressing - thickness of substrate after hot pressing)) / thickness of spray coating × 100%.

[0066] The coating thickness is measured by the difference method. First, use a micrometer to test the thickness of the substrate, and then test the thickness of the coated diaphragm. The difference between the thickness of the coated diaphragm and the thickness of the substrate is the coating thickness.

[0067] The hot pressing is performed using a flat hot press, and the hot pressing conditions are: hot pressing temperature 50°C-95°C, pressure 6.5 MPa, and hot pressing time 90s.

[0068] The compression rate is used to indirectly characterize the accumulation state of the secondary aggregates of the polymer resin in the spraying point. A high compression rate indicates that the secondary aggregates are loosely accumulated and the membrane permeability is good.

[0069] In an embodiment of the present invention, the thickness of the spray coating is 0.5 μm-10 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, ..., 8 μm, 9 μm, and 10 μm. The spray coating thickness is controlled within the range of 0.5 μm-10 μm. If the thickness is too thin, the adhesion performance will be poor; if the thickness is too thick, the spray coating thickness will be uneven, the coating will easily fall off, and the ion penetration performance will be poor.

[0070] In an embodiment of the present invention, the effective bonding coefficient K of the polymer spray coating is ≥1.5, where K is the slope of the fitting straight line between the bonding strength between the prepared spray coating and the corresponding glue coating amount, reflecting the effectiveness of the polymer resin, for example, K is 1.6, 1.7, 1.8, ..., 3.0.

[0071] The bonding strength between the spray coatings is the bonding strength between the spray coatings of the spray-coated diaphragm. The test method can be: cut the spray-coated diaphragm into two samples of 200mm×25mm in size, overlap the spray coatings and place them together, then clamp them between two A4 papers, and use a laminator for laminating (equipment model is SKY 325R6), the laminating temperature is 100℃, the laminating speed is 5mm / s, the ends of the two bonded diaphragms are peeled off and placed on the upper and lower clamps of the tensile testing machine, force is applied in two directions, the speed of the tensile machine is 50mm / min, and the test value is the bonding strength.

[0072] The K value test method is: for the same slurry, different glue coating amounts are made, for example, 0.2g / m 2 , 0.4g / m 2 , 0.6g / m 2 , 0.8g / m 2 , 1.0g / m 2 The samples were then tested for their corresponding bonding strength (unit N / m) between the spray coatings, and then (for example, using Origin software) the amount of glue (unit g / m 2 ) as the horizontal coordinate and the bonding strength (unit: N / m) as the vertical coordinate for straight line fitting. The slope of the fitted straight line is the K value.

[0073] In an embodiment of the present invention, the air permeability increment of the spray coating is ≤15s / 100cc, for example, 2s / 100cc, 5s / 100cc, 6s / 100cc, 8s / 100cc, 10s / 100cc, 12s / 100cc, etc.

[0074] The added permeability of the spray coating = the permeability of the spray-coated membrane - the permeability of the substrate.

[0075] The air permeability can be tested by methods known in the art. As a specific example, the air permeability can be tested according to the method specified in GB / 1038.

[0076] In an embodiment of the present invention, the components of the spray coating include: 80 to 100 parts by mass of a polymer; 2 to 20 parts by mass of a binder; and 0.01 to 3 parts by mass of a dispersant.

[0077] In the embodiment of the present invention, the type of binder is not particularly limited and can be selected according to actual needs; preferably, the binder can be selected from one or more of carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, and acrylonitrile copolymer.

[0078] In the embodiment of the present invention, the type of dispersant is not particularly limited and can be selected according to actual needs; preferably, the dispersant can be selected from one or more of ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, acrylic acid-polyurethane and polyethylene glycol.

[0079] The battery separator provided by the embodiments of the present invention can be used in various types of batteries. Therefore, there is no particular limitation on the type of battery and the separator can be selected according to actual needs. Preferably, the separator can be used in secondary batteries, particularly those containing liquid electrolytes, such as lithium-ion batteries and sodium-ion batteries.

[0080] In a second aspect, the present invention provides a method for preparing a spray-coated diaphragm having uniformly distributed polymer secondary aggregates within a spraying point, comprising the following steps:

[0081] Preparation of polymer slurry: water and dispersant are stirred and mixed uniformly to obtain a first mixed solution at a stirring speed of 20-500 rpm and a stirring time of 5-30 min; polymer is added to the first mixed solution and mixed uniformly to obtain a second mixed solution, which is then subjected to grinding treatment with grinding parameters as follows: grinding times 1-6 times, grinding speed 100-1500 rpm, grinding flow rate 10-100 mL / min, and grinding zirconium bead size 0.4-1.0 mm to obtain a third mixed solution, and finally a binder is added and mixed uniformly to obtain a polymer slurry;

[0082] The properties of the polymer slurry are as follows: the solid content of the polymer slurry is 10-20%, and the solid content of the slurry is adjusted by adjusting the amount of water added. The adjustment of the solid content affects the movement of the polymer particles during the drying process of the spray coating. When the solid content is high, the water content is small, and the coating can be dried in a shorter time, which can reduce the movement of the polymer particles and make the polymer particles more evenly distributed in the spraying point; the particle size of the polymer slurry is D10≤3μm, 3μm<D50≤6μm, and D97≤12μm;

[0083] The particle sizes D10, D50, and D97 of the polymer slurry can be tested using a laser particle size analyzer.

[0084] The spherical index of polymer particles (secondary aggregates) in the polymer slurry is ψ≥1.3, Where D(4,3) is the volume average particle size of the polymer particles (secondary aggregates), and D(3,2) is the surface area average particle size of the polymer particles (secondary aggregates);

[0085] The volume average particle size and surface area average particle size of the polymer particles were obtained by Malvern laser particle size analyzer.

[0086] As ψ approaches 1, the slurry particle shape becomes more regular and closer to spherical; conversely, as ψ deviates further from 1, the slurry particle shape becomes less regular. By destroying the sphericity of the raw material through the grinding process, the sphericity index is high. This results in poor polymer particle flowability during the spray slurry atomization, transfer to the substrate surface, and drying process. This allows the polymer particles to be evenly distributed and loosely packed within the spray point, achieving an effective bonding area of ​​≥60% within any spray point and a spray coating compression rate of ≥20%.

[0087] Preparation of spray-coated diaphragm: The polymer slurry is applied to the surface of at least one side of the diaphragm substrate by rotary spraying to obtain a spray coating. The rotary spraying parameters are: coating speed 100-300m / min, slurry flow rate 1500-15000mL / min, and spraying speed 5000-15000rpm.

[0088] Drying: A high temperature-low temperature two-stage drying method is adopted, with the high temperature drying temperature being 60-90°C and the low temperature drying temperature being 55-85°C, to obtain a spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within the spraying point.

[0089] First, high-temperature drying is used to quickly remove the moisture from the slurry, reduce the flow time of the polymer particles during the drying process, and make the polymer particles evenly distributed within the spraying point.

[0090] The slurry particle size, sphericity, solid content, drying conditions, etc. affect the morphology of the spray point and thus affect the proportion of effective bonding area; the particle size affects the accumulation of secondary agglomerates in the spray point. If the particles are too small, they are densely packed and have a low compression rate.

[0091] According to the method provided in the second aspect of the embodiment of the present invention, a spray-coated diaphragm with uniformly distributed polymer secondary agglomerates within the spraying point according to any embodiment of the first aspect of the present invention can be obtained.

[0092] The third aspect of the present invention provides a battery, comprising a spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within the spraying points provided by the first aspect of the embodiment of the present invention, or a spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within the spraying points prepared by the preparation method provided by the second aspect of the embodiment of the present invention.

[0093] In an embodiment of the present invention, the battery is a lithium-ion secondary battery or a sodium-ion secondary battery.

[0094] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0095] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the art.

[0096] The high-speed rotary spraying machine is a DS-800-01PCS isolation film spraying machine manufactured by Yuanbiao in Hong Kong, China.

[0097] Example 1: Preparation of spray slurry: 85kg of water and 0.15kg of dispersant were weighed and stirred at 200rpm for 30min to obtain a first mixed solution; 15kg of acrylate polymer (SF001 powder of Yanyi New Material, Figure 1 is a morphology of the raw material) was added to the first mixed solution, first slowly stirred at 300rpm for 30min, then quickly stirred at 800rpm for 40min, and finally slowly stirred at 300rpm for 20min to obtain a second mixed solution after stirring; the second mixed solution was then ground 3 times, the grinding speed was 600rpm, the grinding flow rate was 40mL / min, the grinding zirconium bead size was 0.6-0.8mm, and a third mixed solution was obtained after grinding; finally, 1.5kg of polyacrylic acid binder was added to the third mixed solution, and the finished slurry was obtained after stirring at 50rpm for 30min. The slurry solid content, particle size, and spherical index were tested, and the test results are shown in Table 1 below.

[0098] Preparation of spray diaphragm: The prepared spray slurry is fed into the feeding tank of a high-speed rotary sprayer through an automatic feeding system and then applied to one side of a 12μm, 52% porosity polyethylene wet-process base membrane by rotary spraying. The coating speed is 150m / min, the spray slurry flow rate is 5000mL / min, and the spraying speed is 9000rpm. The coated diaphragm is dried at two temperatures, high at 75°C and low at 70°C, to obtain the coated diaphragm. The coating amount is 0.5g / m 2 , the coating thickness is 3.2μm. Figure 2 shows the distribution of secondary agglomerates of acrylate polymer within the spraying point.

[0099] The spray point size, effective bonding area within the spray point, coating compressibility, effective bonding coefficient K, and coating permeability increment of the coated diaphragm were tested and calculated. The parameters are shown in Table 1. The test method of the effective bonding coefficient K is as follows: using the slurry prepared in Example 1, adjusting the spray slurry flow rate, and keeping other coating process parameters unchanged, respectively, the coating amount is 0.2g / m 2 , 0.4g / m 2 , 0.6g / m 2 , 0.8g / m 2 , 1.0g / m 2 The diaphragm is prepared and its corresponding bonding strength is tested. A graph is drawn with the amount of glue applied as the horizontal axis and the bonding strength as the vertical axis, and fitting is performed. The fitting slope is the K value.

[0100] Example 2: Preparation of spray slurry: 88 kg of water and 0.12 kg of dispersant were weighed and stirred at 500 rpm for 30 min to obtain a first mixed solution; 12 kg of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, Sinochem Blue Sky 2707 powder, Figure 3 is a morphology of the raw materials) was added to the first mixed solution, first slowly stirred at 300 rpm for 30 min, then quickly stirred at 1200 rpm for 60 min, and finally slowly stirred at 300 rpm for 30 min to obtain a second mixed solution after stirring; the second mixed solution was then ground twice, the grinding speed was 500 rpm, the grinding flow rate was 30 mL / min, the grinding zirconium bead size was 0.6-0.8 mm, and a third mixed solution was obtained after grinding; finally, 0.6 kg of polyacrylic acid binder was added to the third mixed solution, and the mixture was stirred at 50 rpm for 30 min to obtain a finished slurry, and the slurry solid content, particle size, and spherical index were tested. The test results are shown in Table 1 below.

[0101] Preparation of spray diaphragm: The prepared spray slurry was fed into the feeding tank of a high-speed rotary sprayer through an automatic feeding system and then applied to one side of a 12μm, 52% porosity polyethylene wet-process base membrane by rotary spraying. The coating speed was 100m / min, the spray slurry flow rate was 3600mL / min, and the spraying speed was 9000rpm. The coated diaphragm was dried at two temperatures, 70°C and 65°C, to obtain the coated membrane. The coating weight was 0.6g / m 2 , the coating thickness is 3.5μm. Figure 4 shows the distribution of PVDF-HFP secondary agglomerates within the spraying point.

[0102] The spray point size, effective bonding area within the spray point, coating compressibility, effective bonding coefficient K, and coating permeability increment of the coated diaphragm were tested and calculated. The parameters are shown in Table 1. The test method of the effective bonding coefficient K is as follows: using the slurry prepared in Example 2, adjusting the spray slurry flow rate, and keeping other coating process parameters unchanged, respectively, the coating amount is 0.2g / m 2 , 0.4g / m 2 , 0.6g / m 2 , 0.8g / m 2 , 1.0g / m 2 The diaphragm was tested and its bonding strength was 0.35N / m, 0.74N / m, 1.2N / m, 1.4N / m and 1.83N / m respectively. Then a graph was drawn with the amount of glue applied as the horizontal coordinate and the bonding strength as the vertical coordinate, and the graph was fitted. The straight line was Y=1.81X+0.018, and the fitting slope of 1.81 was the K value.

[0103] Comparative Example 1: Preparation of spray slurry: 95 kg of water and 0.05 kg of dispersant were weighed and stirred at 500 rpm for 30 min to obtain a first mixed solution; 5 kg of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, Sinochem Blue Sky 2707 powder, Figure 3) was added to the first mixed solution, first slowly stirred at 300 rpm for 30 min, then quickly stirred at 1000 rpm for 60 min, and finally slowly stirred at 300 rpm for 30 min to obtain a second mixed solution after stirring; 0.5 kg of polyacrylic acid binder was directly added to the second mixed solution without grinding, and stirred at 50 rpm for 30 min to obtain a finished slurry, and the slurry solid content, particle size, and spherical index were tested. The test results are shown in Table 1 below.

[0104] Preparation of spray diaphragm: The prepared spray slurry was fed into the feeding tank of a high-speed rotary sprayer through an automatic feeding system and then applied to one side of a 12μm, 52% porosity polyethylene wet-process base membrane by rotary spraying. The coating speed was 80m / min, the spray slurry flow rate was 3600mL / min, and the spraying speed was 9000rpm. The coated diaphragm was dried at 60°C to obtain the coated membrane. The coating amount was 0.6g / m 2 , the coating thickness is 5.7μm. Figure 5 shows the distribution of PVDF-HFP secondary agglomerates within the spraying point.

[0105] The spray point size, effective bonding area within the spray point, coating compressibility, effective bonding coefficient K, and coating air permeability increment of the coated diaphragm were tested and calculated, and the parameters are shown in Table 1. The effective bonding coefficient K was tested using the slurry prepared in Comparative Example 1, using the same method as in Example 2.

[0106] Comparative Example 2: Preparation of spray slurry: 90 kg of water and 0.3 kg of dispersant were weighed and stirred at 500 rpm for 30 min to obtain a first mixed solution; 10 kg of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, Sinochem Blue Sky 2707 powder, Figure 3) was added to the first mixed solution, first slowly stirred at 300 rpm for 30 min, then quickly stirred at 1000 rpm for 60 min, and finally slowly stirred at 300 rpm for 30 min to obtain a second mixed solution after stirring; the second mixed solution was then ground 20 times, the grinding speed was 300 rpm, the grinding flow rate was 10 L / min, the grinding zirconium bead size was 0.4-0.6 mm, and a third mixed solution was obtained after grinding; 0.5 kg of polyacrylic acid binder was added to the third mixed solution, and the finished slurry was obtained by stirring at 50 rpm for 30 min. The slurry solid content, particle size, and spherical index were tested, and the test results are shown in Table 1 below.

[0107] Preparation of spray diaphragm: The prepared spray slurry was fed into the feeding tank of a high-speed rotary sprayer through an automatic feeding system and then applied to one side of a 12μm, 52% porosity polyethylene wet-process base membrane by rotary spraying. The coating speed was 100m / min, the spray slurry flow rate was 3600mL / min, and the spraying speed was 9000rpm. The coated diaphragm was dried at 65℃ to obtain the coated membrane. The coating amount was 0.6g / m 2 , the coating thickness is 1.2μm.

[0108] The spray point size, effective bonding area within the spray point, coating compressibility, effective bonding coefficient K, and coating air permeability increment of the coated diaphragm were tested and calculated. The parameters are shown in Table 1. The effective bonding coefficient K was tested using the slurry prepared in Comparative Example 2, using the same method as in Example 2.

[0109] Table 1

[0110] Comparing Example 2 and Comparative Example 1, the same materials are used. Due to the different batching processes, Comparative Example 1 is not ground, the slurry particle size is generally larger, D50 and D97 are both beyond the required range, the spherical index ψ is less than 1.3, and the particle morphology is mostly maintained as spherical particles. Moreover, due to the low solid content of the slurry and the slow drying rate (slow vehicle speed and low drying temperature), the particles move to the edge during the drying process to form a dense accumulation. Therefore, the spraying point obtained by spraying in Comparative Example 1 is a quasi-annular spraying point, and the effective bonding area within the spraying point accounts for only 40%.

[0111] Comparing Example 2 and Comparative Example 2, the same materials are used. Due to the different batching processes, Comparative Example 2 undergoes a higher degree of grinding treatment, the overall slurry particle size is smaller, D50 exceeds the required range, the polymer particles are close to the initial particle size, the polymer particle morphology is closer to a spherical shape, and the spherical index ψ is less than 1.3. The spraying points obtained by spraying in Comparative Example 2 are quasi-annular spraying points, and the effective bonding area within the spraying points accounts for 52%. Due to the small particle size and the dense accumulation between the particles, the coating compression rate is only 17.5%.

[0112] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A spray-coated membrane with uniform distribution of polymer secondary aggregates within the spray point, characterized in that: include: a diaphragm substrate, and A spray coating applied to at least one surface of the diaphragm substrate, The spray coating is composed of a number of spray points, each of which contains a number of evenly distributed polymer secondary agglomerates, wherein the average diameter D50 of the spray points is 300-600 μm, the effective bonding area of ​​any spray point accounts for ≥60%, and the compression rate of the spray coating is ≥20%; Among them, D50 represents the diameter corresponding to when the cumulative spray point diameter distribution percentage reaches 50%; The effective bonding area ratio of any spraying point is the ratio of the coverage area of ​​all polymer secondary aggregates in the spraying point to the area of ​​the spraying point; Compression rate of spray coating = ((thickness of spray-coated diaphragm before hot pressing - thickness of spray-coated diaphragm after hot pressing) - (thickness of substrate before hot pressing - thickness of substrate after hot pressing)) / thickness of spray coating × 100%.

2. The spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to claim 1, characterized in that: The average diameter D50 of the spraying point is 400-500μm, the effective bonding area of ​​any spraying point accounts for ≥65%, and the compression rate of the spray coating is ≥30%.

3. The spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to claim 1, characterized in that: The effective bonding coefficient K of the polymer spray coating is ≥ 1.5, where K is the slope of the straight line fitting the bonding strength between the spray coatings and the corresponding amount of glue applied, reflecting the effectiveness of the polymer resin; and / or The air permeability increase of the spray coating is ≤15s / 100cc.

4. A spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to any one of claims 1 to 3, characterized in that: Spray coatings include: Polymer, 80-100 parts by mass; Binder, 2 to 20 parts by weight; Dispersant: 0.01 to 3 parts by mass.

5. The spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to claim 4, characterized in that: The polymer includes at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-methyl methacrylate copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-acrylic acid copolymer, polymethyl methacrylate, polyethylene, and acrylate polymer; and / or The binder comprises at least one of carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, and acrylonitrile multipolymer; and / or The dispersant includes ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, acrylic acid-polyurethane and polyethylene glycol. at least one of alcohols.

6. A spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to any one of claims 1 to 3, characterized in that: The diaphragm substrate comprises a base film and an optional inorganic coating, wherein the base film is selected from at least one of a polyethylene film, a polypropylene film, a polyimide film, a polyvinylidene fluoride film, a polyvinylidene fluoride-hexafluoropropylene film, a polyamide film, and a polyethylene terephthalate film; The inorganic coating is composed of inorganic materials, and the inorganic material is selected from at least one of silicon dioxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, calcium oxide, boehmite, aluminum nitride, boron nitride, barium sulfate, calcium fluoride, and barium fluoride.

7. The spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to claim 6, characterized in that: The thickness of the diaphragm substrate is 3 μm to 25 μm, and the porosity is 20% to 80%; and / or The thickness of the spray coating is 0.5 μm-10 μm.

8. A method for preparing a spray-coated diaphragm with uniform distribution of polymer secondary aggregates in the spraying point according to any one of claims 1 to 7, characterized in that: The following steps are involved: Preparation of polymer slurry: stirring and mixing water and dispersant to obtain a first mixed solution, the stirring speed is 20-500rpm, and the stirring time is 5-30min; adding polymer to the first mixed solution and mixing to obtain a second mixed solution, and then grinding, the grinding parameters are: grinding times 1-6 times, grinding speed 100-1500rpm, grinding flow rate 10-100mL / min, grinding zirconium bead size 0.4-1.0mm, to obtain a third mixed solution, and finally adding a binder and mixing to obtain a polymer slurry; The properties of the polymer slurry are as follows: the solid content of the polymer slurry is 10-20%, the particle size of the polymer slurry is D10≤3μm, 3μm<D50≤6μm, D97≤12μm; The spherical index of the polymer particles in the polymer slurry is ψ≥1.3, Wherein D(4,3) is the volume average particle size of the polymer particles; D(3,2) is the surface area average particle size of the polymer particles; Preparation of spray-coated diaphragm: The polymer slurry is applied to the surface of at least one side of the diaphragm substrate by rotary spraying to obtain a spray coating. The rotary spraying parameters are: coating speed 100-300m / min, slurry flow rate 1500-15000mL / min, and spraying speed 5000-15000rpm; Drying: A high temperature-low temperature two-stage drying method is adopted, the high temperature drying temperature is 60-90°C, and the low temperature drying temperature is 55-85°C, so as to obtain a spray-coated diaphragm with uniform distribution of polymer secondary agglomerates in the spraying point.

9. The preparation method according to claim 8, characterized in that: The glue coating amount is 0.05g / m 2 -1.5g / m 2 .

10. A battery, characterized in that: A spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within a spray point, comprising the spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within a spray point as described in any one of claims 1-7 or the spray-coated diaphragm with uniform distribution of polymer secondary agglomerates within a spray point as described in claim 8 or 9.

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