Battery separator and preparation method therefor, and battery

Abstract

The present invention provides a battery separator and a preparation method therefor, and a battery. The battery separator provided by the present invention comprises a base film and a coating coated on one or both sides of the base film, wherein the coating comprises fluorine-free polymeric resin particles and ceramic particles; the fluorine-free polymeric resin particles are in the morphology of primary particles or the morphology of secondary agglomerates; the fluorine-free polymeric resin particles are spherical and dispersed in the ceramic particles; and the surface density ρ0 of the coating, the thickness h0 of the coating, the average radius r of the fluorine-free polymeric resin particles, the volume V1 of the fluorine-free polymeric resin particles in the coating, the number N0 of the fluorine-free polymeric resin particles, the density ρ of a fluorine-free polymeric resin, and the coating density ρ1 of a pure ceramic coating satisfy the following relationship. The battery separator provided by the present invention has a coating having good adhesion, high consistency, strong stability and good heat resistance.

Description

Battery separator, preparation method thereof, and battery Technical Field

[0001] The present invention relates to the field of batteries, and more particularly, to a battery separator and a preparation method thereof, as well as a battery comprising the battery separator. Background Art

[0002] With the development of lithium-ion battery technology, the requirements for diaphragms are increasing. Therefore, the development of diaphragms is no longer limited to base membranes, and the functionality of coatings is increasingly valued, such as coating modifications that require adhesion, heat resistance, and electrolyte affinity. This provides a technical route for the development of diaphragms.

[0003] Existing technologies often use PVDF as a bonding layer. PVDF itself can serve as a binder for the positive electrode in batteries and is a material with certain bonding properties. Based on current market trends, spray coating is often used to attach PVDF to the surface of the ceramic diaphragm to achieve the bonding function.

[0004] However, due to the high melting point of PVDF (≥135°C), the conditions for achieving its adhesion are also higher, requiring higher temperatures and pressures to achieve adhesion between the diaphragm and the electrode. Moreover, its own formed particle size is small, and only by forming agglomerates of a certain size in the form of agglomerates can it have a significant bonding effect. Because the agglomerates are formed later and the particle size of the agglomerates cannot be controlled, the size and morphology of the agglomerates vary greatly. Therefore, the consistency and stability of PVDF are very weak, which means that when PVDF is used as the bonding layer, the structure is unstable and easy to fall off, thus affecting the bonding effect. It is also difficult to ensure the consistency of the coating. Whether it is the stacking density or the morphology of the agglomerates on the coating, there are obvious differences, making it difficult to control the coverage rate and making the coating impossible to control at both the microscopic and macroscopic levels.

[0005] Summary of the Invention

[0006] In view of the above problems, the present invention uses ceramic particles and fluorine-free polymer resin particles for mixing and formulating, comprehensively considers and adjusts factors such as the coating surface density, ceramic particle size, fluorine-free polymer resin particle size, and ceramic thickness, and ultimately forms a coating with good adhesion, high consistency, strong stability, and good heat resistance.

[0007] Specifically, the present invention provides a battery separator having a coating with good adhesion, high consistency, good stability and good heat resistance, a preparation method thereof, and a battery including the battery separator.

[0008] The present invention provides a battery separator, comprising a base film and a coating applied on one or both sides of the base film, wherein:

[0009] The coating contains: no fluorine polymer resin particles, no ceramic particles;

[0010] The fluorine-free polymer resin particles are in the form of primary particles or secondary aggregates, and are spherically dispersed in the ceramic particles.

[0011] The coating area density ρ0, the coating thickness h0, the average radius r of the non-fluorinated polymer resin particles, the volume V1 occupied by the non-fluorinated polymer resin particles in the coating, the number N0 of the non-fluorinated polymer resin particles, the density ρ of the non-fluorinated polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship:

[0012] The present invention also provides a method for preparing a battery separator, which is used to prepare the battery separator provided by the present invention. However, the preparation of the battery separator provided by the present invention is not limited to the preparation method provided by the present invention. The method includes:

[0013] 1) Dispersing ceramic powder in water and grinding it with a sand mill to form a dispersion;

[0014] 2) adding a fluorine-free polymer resin in an emulsion state to the dispersion, adding a binder, and passing through an 80-200 mesh sieve to form a finished slurry;

[0015] 3) According to the required coating thickness, the finished slurry is coated on one or both sides of the base film using a gravure roller or a wire rod. After the finished slurry is coated on the surface of the base film, it is dried in an oven to obtain a battery separator with a coating film;

[0016] Wherein, in step 1), the speed of sand milling dispersion is 500-1500 rpm, and the time of sand milling dispersion is 10-60 min; after step 1), the dispersion liquid is cooled under low-speed stirring to maintain the temperature of the dispersion liquid at ≤70°C, wherein the stirring rate of low-speed stirring is 20-300 rpm;

[0017] The finished slurry prepared in step 2) is continuously stirred at a low speed from the time the mixture is prepared to the time it is put into use, so that the finished slurry is always in dynamic equilibrium, and the rotation speed of the low-speed stirring is 10-800 rpm; from the start of step 2) to the time the finished slurry is put into use, the slurry is maintained at a temperature between 5°C and 70°C; a stirring tank having stirring blades on both the upper and lower layers is used for low-speed stirring, and the radii of the stirring blades on the upper and lower layers are different;

[0018] In step 3), in the battery separator, the coating surface density ρ0, the coating thickness h0, the average radius r of the fluorine-free polymer resin particles, the volume V1 occupied by the fluorine-free polymer resin particles in the coating, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship:

[0019] Preferably, in the coating of step 3), high-speed coating is used, and the speed of the high-speed coating is 50-250 m / min; the drying temperature is 50-100° C., preferably 60-90° C.; and the drying time is ≥5 s.

[0020] The present invention also provides a battery, comprising: a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the separator is the battery separator provided by the present invention.

[0021] The technical solution provided by the present invention can achieve a coated diaphragm with good adhesion, consistency, stability and heat resistance, and can achieve a balance among the four properties. The coating surface of the diaphragm has good adhesion properties and is firmly attached to the electrode sheet, which is beneficial to the assembly of the battery cell and the improvement of the battery energy density. The ceramic stacking thickness of the coating surface is highly consistent, thereby improving the consistency of the battery cell performance and increasing the cycle life of the battery. The resin particles should be stably fixed on the coating. If the resin particles are detached, it will affect the assembly of the battery cell and the cycle life of the battery. The diaphragm has good thermal shrinkage performance, which is beneficial to improving battery safety. However, the inventors found that in the prior art, these four properties are often difficult to balance. For example, the improvement of the coating adhesion performance will lead to a decrease in the coating stability and heat resistance, and will also cause the coating consistency to deteriorate. Therefore, the present invention provides a solution for a battery diaphragm, which achieves the balance and consideration of the four properties by controlling various parameters of the coating, thereby improving the quality and efficiency of the back-end battery cell assembly, improving the energy density and cycle life of the battery, and benefiting the safety of the battery. The present invention also provides one of the preparation methods for preparing such a diaphragm. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a schematic diagram of a coating structure of a battery separator provided in an embodiment of the present invention;

[0023] FIG2 is a planar SEM image of the coating film of the battery separator of Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a battery separator, comprising a base film and a coating applied on one or both sides of the base film, wherein:

[0025] The coating contains: no fluorine polymer resin particles, no ceramic particles;

[0026] The fluorine-free polymer resin particles are in the form of primary particles or secondary aggregates, and are spherically dispersed in the ceramic particles.

[0027] The coating area density ρ0, the coating thickness h0, the average radius r of the non-fluorinated polymer resin particles, the volume V1 occupied by the non-fluorinated polymer resin particles in the coating, the number N0 of the non-fluorinated polymer resin particles, the density ρ of the non-fluorinated polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship:

[0028] In the above relationship, V1 represents the volume of the spherical segment (ie, the volume occupied by the non-fluorinated polymer resin particles in the coating), and N0 represents the number of the non-fluorinated polymer resin particles.

[0029] As shown in Figure 2, if the coating is located on both sides of the base film, the coating thickness h0 = (cb) / 2. If the coating is located on only one side of the base film, the coating thickness h0 is the difference between the thickness of the battery separator and the thickness of the base film. Specifically, the value of h0 can be determined by preparing a cross-sectional sample of the battery separator at 21°C ± 4°C and a humidity of ≤ 65% RH. The cross-sectional electron micrograph is obtained using a Zeiss SIGMA 300 electron microscope. The thickness of the ceramic deposited layer within the single coating layer is measured at five random locations on the image, and the average value is taken as the value of h0.

[0030] Spherical segment volume V1 = (π / 3)(3r-h) × h 2 , h is the height of the spherical segment, h = h0. It is important to note that 2r = D = D50, where r is the radius of the fluorine-free polymer resin particle and D is the diameter. D - h0 > 0. D50 depends on the choice of fluorine-free polymer resin raw material. Specifically, the D50 value can be determined by the raw material itself or by taking five random samples of the fluorine-free polymer resin particles and calculating the average value using the aforementioned electron microscopy method.

[0031] ρ and ρ1 are fixed values ​​determined by the fluorine-free polymer resin and ceramic materials. Specifically, ρ is determined by the properties of the raw materials, while ρ1 is determined by the density and particle size of the ceramic. ρ can be measured using the fluorine-free polymer resin raw material or by separating and collecting the fluorine-free polymer resin particles in the coating. Measurement can also be performed using an electronic scale and a graduated cylinder.

[0032] ρ1 can be obtained by using ceramic particles, coating them into a film using a gravure roller or a wire rod, and then measuring the surface density of the film using an electronic scale and a steel ruler. The ceramic particles used are ceramic particles used as coating raw materials, or ceramic particles extracted from a diaphragm coating. The method for extracting ceramic particles from a diaphragm is not particularly limited. For example, the coating or diaphragm can be dissolved in a solvent to extract ceramic particles. Specifically: the first step is to disperse the ceramic particles in water to form an ordinary ceramic slurry; the second step is to coat the ceramic slurry into a film using a gravure roller or a wire rod of corresponding dry thickness; the third step is to measure the surface density of the coating using an electronic scale and a steel ruler to obtain ρ1.

[0033] ρ0 is the surface density of the coating, which is calculated using the above formula.

[0034] Regarding N0, first count the number of fluorine-free polymer resin particles within the field of view of the electron microscope under a 1000x electron microscope, and then convert it to the number of fluorine-free polymer resin particles contained in 1m2 of the diaphragm based on the field of view of the electron microscope. (For example: using the aforementioned electron microscope method, count the average number of fluorine-free polymer resin particles in 5 electron microscope images at 1000x magnification, calculate the field of view of the electron microscope at this magnification, and then convert it to the number of fluorine-free polymer resin particles per unit area using the unit, i.e. 1m2 2 The number of particles on the area N0).

[0035] Among them, the coating surface density ρ0 is 0-20g / m 2 The coating thickness h0 is between 0.1×10 -6 -10×10 -6 The average radius r of the fluorine-free polymer resin particles is between 1×10 -6 -4.5×10 -6 m, the volume occupied by the fluorine-free polymer resin particles in the coating is V1≥0m 3 The number of fluorine-free polymer resin particles N0 ≥ 1 (an integer), and the density ρ of the fluorine-free polymer resin is 0.5×10 6 -2.0×10 6 g / m 3 The coating density ρ1 of pure ceramic coating is between 0.5×10 6 -2.0×10 6 g / m 3 between.

[0036] It should be noted that when ρ0, h0, r, V1, N0, ρ, and ρ1 are substituted into the relational formula, the units should not be used for calculation. The relational formula and range proposed in the present invention are designed based on the numerical relationship of these parameters and are not affected by whether the dimensions are equal.

[0037] The fluorine-free polymer resin particles are spherical in shape, which offers excellent structural stability and greater consistency in the coating. Sphericity can be characterized using the aspect ratio method: aspect ratio S = longest diameter through the particle interior / shortest diameter perpendicular to the longest diameter. When S ≤ 2, the particles are spherical.

[0038] The primary particle morphology may be a primary particle morphology with consistent internal and external components, or a primary particle morphology with a core-shell structure.

[0039] The fluorine-free polymer resin has a certain degree of cross-linking and a low glass transition temperature (Tg), preferably 40-100°C; if the Tg is too low, the structure will be unstable and the structure will easily disintegrate or the sphere will collapse and deform; if the Tg is too high, the adhesion of the sphere will be reduced and the defect of soft battery cell will be easily generated.

[0040] The fluorine-free polymer resin has a certain swelling property, and the swelling rate is preferably 10-200%, more preferably 10-100%. As a polymer material, if the swelling rate is too small, it will affect the battery cell's ability to retain liquid; if the swelling rate is too large, it will easily lead to defects such as high air permeability and thickness expansion after the electrode is immersed in the electrolyte, affecting the battery's cycle performance, and even causing the electrode to lose adhesion after being immersed in the electrolyte.

[0041] The fluorine-free polymer resin preferably has a glass transition temperature of 45-70° C. and a swelling ratio of 10-100%.

[0042] Preferred are at least one of poly(meth)acrylate polymers, SBR (styrene-butadiene rubber) microspheres, PI (polyimide) water-soluble microspheres, and PAA (polyacrylate) modified microspheres. Poly(meth)acrylate polymers formed in one piece are particularly preferred. Acrylate polymers have a very low softening point (~50°C), which significantly reduces adhesion requirements. Furthermore, their high distribution consistency and uniformity in the coating significantly improve the adhesion of the coating (approximately 2-10 times that of PVDF). The material formed by modifying the molecular surface of the acrylate polymer with hydrophilic groups (abbreviated as poly(meth)acrylate polymer) significantly improves its hydrophilicity, making it more difficult to disperse and more stable in aqueous solvents than PVDF. In particular, the large primary particle size and low density of these particles allow them to form a stable mosaic structure in the coating, thereby reducing the coating's weight while significantly improving adhesion and stability.

[0043] The average particle size (D50) of the fluorine-free polymer resin particles is preferably 2-9 μm.

[0044] The ceramic particles can be selected from at least one of aluminum oxide, boehmite, barium titanate, calcium oxide, magnesium oxide, zinc oxide, zirconium oxide, and silicon oxide. When the ceramic particles are a mixture of multiple substances, the amounts of the different substances can be in any ratio, as long as the total amount meets the ceramic particle dosage requirements. Preferably, the ceramic powder is boehmite.

[0045] The average particle size (D50) of the ceramic particles is 0.1-4.0 μm, preferably 0.2-1.5 μm. Smaller particle sizes improve thermal shrinkage performance. The ceramic particles should be free of sharp protrusions to prevent them from disrupting the polymer structure. Smaller particle sizes lead to poorer dispersion in the slurry. A particle size below 0.1 μm increases the slurry particle size, risking poor coating consistency.

[0046] The present invention also provides a method for preparing a battery separator, wherein the method comprises the following steps:

[0047] Step 1) dispersing ceramic powder in water and sand-grinding the powder in a sand mill to form a dispersion;

[0048] Step 2) adding a fluorine-free polymer resin liquid in an emulsion state to the dispersion liquid, adding a binder, and passing through an 80-200 mesh sieve to form a finished slurry;

[0049] Step 3) According to the required coating thickness, the finished slurry is coated on one or both sides of the base film using a gravure roller or a wire rod. After the finished slurry is coated on the surface of the base film, it is dried in an oven to obtain a battery separator with a coating film;

[0050] Wherein, in step 1), the speed of sand milling dispersion is 500-1500 rpm, and the time of sand milling dispersion is 10-60 min; after step 1), the dispersion liquid is cooled under low-speed stirring to maintain the temperature of the dispersion liquid at ≤70°C, wherein the stirring rate of low-speed stirring is 20-300 rpm;

[0051] The finished slurry prepared in step 2) is continuously stirred at a low speed from the time the mixture is prepared to the time it is put into use, so that the finished slurry is always in dynamic equilibrium, and the rotation speed of the low-speed stirring is 10-800 rpm; from the start of step 2) to the time the finished slurry is put into use, the slurry is maintained at a temperature between 5°C and 70°C; a stirring tank having stirring blades on both the upper and lower layers is used for low-speed stirring, and the radii of the stirring blades on the upper and lower layers are different;

[0052] In step 3), in the battery separator, the coating surface density ρ0, the coating thickness h0, the average radius r of the fluorine-free polymer resin particles, the volume V1 occupied by the fluorine-free polymer resin particles in the coating, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship:

[0053] The fluorine-free polymer resin liquid in an emulsion state used in the above method is not limited to being commercially available or self-produced. The self-produced method includes mixing fluorine-free polymer resin powder, a surfactant, and water, and then dispersing and stirring to form the fluorine-free polymer resin liquid in an emulsion state. Commercially available fluorine-free polymer resin liquids in an emulsion state include, for example: the poly(meth)acrylate polymer liquid used in Examples 1-3, purchased from Shenzhen Haodian Technology Co., Ltd., with the trademark SWA709, having a glass transition temperature of 55°C, a swelling rate of 70%, and a poly(meth)acrylate polymer concentration of 25%; the poly(meth)acrylate polymer liquid used in Example 4, purchased from Japan Ruiong Co., Ltd., with the trademark BM5000, having a glass transition temperature of 54°C, a swelling rate of 97%, and a poly(meth)acrylate polymer concentration of 19%; the poly(meth)acrylate polymer liquid used in Example 5, purchased from Sichuan Jundile Materials Co., Ltd., with the trademark FS400, having a glass transition temperature of 68°C, a swelling rate of 68%, and a poly(meth)acrylate polymer concentration of 30%.

[0054] The fluorine-free polymeric resin emulsion preferably does not undergo structural decomposition or deformation at a pH of ≥5 and ≤10 (all commercially available poly(meth)acrylate polymers meet this condition). This is because aqueous ceramic solutions are generally alkaline, and a fluorine-free polymeric resin solution with an excessively low pH will partially degrade upon mixing with ceramics, resulting in structural instability. The average particle size D50 of the fluorine-free polymeric resin powder in the fluorine-free polymeric resin emulsion is 2-9 μm, while the average particle size D50 of the ceramic powder is 0.4-4.0 μm.

[0055] Furthermore, after step 1), the dispersion temperature is maintained at ≤70°C because excessively high temperatures can affect the performance of the coating. High-speed dispersion or grinding processes can cause the dispersion to heat up, and the fluorine-free polymer resin material should be added only after the temperature has dropped to ≤70°C. A dispersion temperature exceeding 70°C can soften and cling to the fluorine-free polymer resin particles, preventing them from maintaining a spherical shape. This can affect the coating's adhesion and heat resistance.

[0056] The finished slurry prepared in step 2) is continuously stirred at a low speed from the completion of the configuration to the time of being put into use. The reason for keeping the finished slurry in dynamic equilibrium is to prevent the fluorine-free polymer resin particles and the ceramic particles from being delaminated, which causes the fluorine-free polymer resin particles to float after coating. The floating not only affects the consistency of the coating, but also affects the stability of the coating structure, thereby easily causing large particles to fall off, such as so-called powdering and poor bonding. Use double paddles (i.e., both the upper and lower layers of the stirring tank have stirring blades) for stirring, and the radius of the upper and lower stirring blades (r 上 , r 下 ) should be different, that is, the radius ratio r 上 / r 下 ≠1, the purpose is to form a differential speed, so that the organic particles and inorganic particles are evenly dispersed, eliminating aggregation, and improving the stability and consistency of the coating, wherein the rotation speed of the low-speed stirring is 10-800rpm. High-speed stirring will cause the slurry to foam, thereby affecting the consistency of the coating. The reason for maintaining the slurry between 5°C and 70°C from the beginning of this step until the finished slurry is put into use is that if the temperature is too high, the structure of the fluorine-free polymer resin particles will soften and stick together, and it will not be able to maintain a complete spherical shape, which will affect the adhesion and heat resistance of the coating.

[0057] In the coating of step 3), high-speed coating (50-250 m / min) is preferably applied due to the high stability of the finished slurry.

[0058] The present invention has no particular limitation on the base film, and the base film can be selected with reference to existing lithium-ion battery separators. Typically, the base film can be a polyolefin base film, such as a polypropylene base film, a polyethylene base film, etc. As a preferred embodiment, the base film is a polyethylene base film.

[0059] The base film may have a thickness of 5-12 μm. The coating may have a thickness of 1-5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0060] In the above method, the average particle size D50 of the fluorine-free polymer resin particles is preferably 2-9 μm; the average particle size D50 of the ceramic powder is preferably 0.4-1.5 μm.

[0061] Based on the total weight of the finished slurry, the fluorine-free polymer resin powder accounts for 0.5-10 weight %; the ceramic powder accounts for 15-40 weight %, more preferably 20-35 weight %.

[0062] The drying temperature is 50-100° C., and the drying time is ≥5s.

[0063] The present invention has no particular limitations on the surfactant, water, and binder, and their amounts. Commonly used products in the art, such as those disclosed in CN115117559 A, and their proportions, can be used. For example, the surfactant comprises surfactant A and surfactant B, wherein surfactant A is a polyether siloxane copolymer and surfactant B is a polysiloxane. The binder is selected from at least one of polyacrylic acid, polyvinyl alcohol, polyvinyl ethyl ether, polymethyl methacrylate, polyvinyl acetate, and polyurethane, preferably polyacrylic acid. Based on the total weight of the finished slurry, surfactant A comprises 0.06-0.5% by weight, surfactant B comprises 0.1-0.5% by weight, water comprises 40-60% by weight, and the binder comprises 5-10% by weight.

[0064] The present invention also provides a battery, comprising: a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the separator is the battery separator provided by the present invention.

[0065] The battery separator provided by the present invention has a coating with good adhesion, high consistency, strong stability, and good heat resistance. The coating has an adhesion strength of ≥0.6N / m, a consistency R ≤0.5μm, a probability of particle drop ≤3%, and a thermal shrinkage rate ≤5%.

[0066] The present invention will be further described below with reference to the examples, but the scope of the present invention is not limited to these examples.

[0067] Example

[0068] In the following examples and comparative examples, the binder is polyacrylic acid emulsion purchased from Hunan Gaorui Power Materials Co., Ltd. with the brand name LIB-S105B.

[0069] In the following examples and comparative examples, parts are by weight unless otherwise specified.

[0070] The following Examples 1-5 are used to illustrate the battery separator and the preparation method thereof of the present invention.

[0071] Example 1

[0072] 1) 30 parts of boehmite (D50: 0.8 μm) was dispersed in 54 parts of water and dispersed by sand milling (1000 rpm for 30 minutes) to form a dispersion; the dispersion was cooled while stirring at a low speed (150 rpm) to maintain the dispersion temperature at ≤70°C.

[0073] 2) adding 6 parts of an emulsion poly(meth)acrylate polymer liquid (pH 6.5, glass transition temperature 55° C., swelling ratio 70%, D50 of poly(meth)acrylate polymer 4.5 μm, poly(meth)acrylate polymer concentration 25%) to the dispersion, and adding 10 parts of a binder, and passing through a 200-mesh sieve to form a finished slurry;

[0074] The finished slurry is stirred at a low speed (300 rpm) using a double-paddle (i.e., both the upper and lower layers of the stirring tank have stirring blades) from the time it is made until it is used in the next step, and the radius of the upper and lower stirring blades (r 上 , r 下 ) satisfies the “radius ratio r 上 / r 下 ≠1" relationship, and from step 2) until the finished slurry is used in the next step, the slurry is kept between 5-70°C.

[0075] 3) According to the required coating thickness, the finished slurry is coated on both sides of a 7 μm thick base film using a gravure roller or a wire rod. After the finished slurry is coated on the surface of the base film, it is dried in an oven (drying temperature of 75° C. for 10 seconds) to obtain a battery separator B1 with a coated film;

[0076] Wherein, in step 3), in the battery separator, the coating surface density ρ0, the coating thickness h0, the average radius r of the fluorine-free polymer resin particles, the volume V1 occupied by the fluorine-free polymer resin particles in the coating, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship:

[0077] The measurement methods of the above parameters are as described in the present invention and will not be repeated here. The measured data are shown in Table 1 below.

[0078] Example 2: In this example, except for changing the parameters shown in Table 1, the method is the same as that of Example 1 to prepare a battery separator B2 with a coating film; the prepared battery separator satisfies the formula of the present invention.

[0079] Example 3: In this example, except for changing the parameters shown in Table 1, the method is the same as that of Example 1 to prepare a battery separator B3 with a coating film; the prepared battery separator satisfies the formula of the present invention.

[0080] Example 4: In this example, in addition to changing the parameters shown in Table 1, the parameters of the poly(meth)acrylate polymer liquid used in step 2) are as follows: pH 7.9, glass transition temperature 54°C, swelling ratio 97%, D50 of poly(meth)acrylate polymer 4.5 μm, concentration of poly(meth)acrylate polymer 25%, and the method is the same as in Example 1 to obtain a battery separator B4 with a coating film.

[0081] Example 5: In this example, in addition to changing the parameters shown in Table 1, the parameters of the poly(meth)acrylate polymer liquid used in step 2) are as follows: pH 9.4, glass transition temperature 68°C, swelling ratio 68%, D50 of poly(meth)acrylate polymer 9 μm, concentration of poly(meth)acrylate polymer 25%, and the method is the same as in Example 1 to prepare a battery separator B5 with a coating film.

[0082] Example 6: Except that boehmite is replaced by a mixture of boehmite and BaTiO3 (mass ratio 3:1) in step 1), the performance parameters of the poly(meth)acrylate polymer liquid in step 2 are as follows: pH 6.5, glass transition temperature 45°C, swelling ratio 150%, D50 of poly(meth)acrylate polymer 2.2 μm, concentration of poly(meth)acrylate polymer 25%, and the amount of each substance is changed according to Table 1. The rest is the same as Example 1, and a battery separator B6 with a coating film is obtained.

[0083] Example 7: Except that in step 1), boehmite is replaced by a mixture of boehmite and BaTiO3 (mass ratio 9:1), in step 2, the performance parameters of the poly(meth)acrylate polymer liquid are as follows: pH 6.5, glass transition temperature 76°C, swelling ratio 88%, D50 of poly(meth)acrylate polymer 3 μm, concentration of poly(meth)acrylate polymer 25%, and the amounts of each substance are changed according to Table 1. The rest is the same as in Example 1, and a battery separator B7 with a coating film is prepared.

[0084] Example 8: Except that in step 1), boehmite is replaced by a mixture of boehmite and BaTiO3 (mass ratio 9:5), and in step 2, the poly(meth)acrylate polymer liquid is replaced by an SBR (styrene-butadiene rubber) microsphere solution, the performance parameters are as follows: pH 7.2, glass transition temperature 88°C, swelling rate 30%, D50 of SBR (styrene-butadiene rubber) microspheres 2.5μm, concentration of SBR (styrene-butadiene rubber) microspheres 25%, and the amount of each substance is changed according to Table 1. The rest is the same as in Example 1, and a battery separator B8 with a coating film is prepared.

[0085] Example 9: Except that in step 1), boehmite is replaced by a mixture of boehmite and BaTiO3 (mass ratio 3:1), and in step 2, the poly(meth)acrylate polymer liquid is replaced by a PI (polyimide) water-soluble microsphere solution, the performance parameters are as follows: pH is 6.8, glass transition temperature is 90°C, swelling rate is 55%, D50 of PI (polyimide) water-soluble microspheres is 4.5μm, the concentration of PI (polyimide) water-soluble microspheres is 25%, and the amount of each substance is changed according to Table 1. The rest is the same as Example 1, and a battery separator B9 with a coating film is prepared.

[0086] Comparative Example 1: In this comparative example, a battery separator C1 with a coating film was prepared in the same manner as in Example 1, except that PVDF liquid prepared from PVDF powder was used instead of the poly(meth)acrylate polymer liquid.

[0087] The preparation method of PVDF liquid is as follows: 1.5 parts of PVDF powder, 0.005 parts of polysiloxane surfactant and 4.5 parts of water are mixed to prepare 6 parts of PVDF liquid.

[0088] PVDF powder was purchased from East Sunshine Company with brand number 2600.

[0089] In this comparative example, since the morphology of the PVDF balls is unstable, the density of PVDF cannot be calculated, and thus this comparative example is not applicable to the formula of the present invention.

[0090] Comparative Example 2-3: Except that some parameter data as shown in Table 1 below are different from those in Example 1, the dispersion formed in step 1) is directly mixed without cooling in the next step, and the finished slurry is stirred at a low speed (300 rpm) using a single paddle from the time of preparation to the time of use in the next step, i.e., the paddle radius ratio r is 0.001mm. 上 / r 下 =1", and the same method as in Example 1 was used to prepare a battery separator C2-3 with a coating film.

[0091] Comparative Example 4: Except for the type of fluorine-free polymer resin being different from that in Example 8, the rest are the same as those in Example 8. The performance parameters of the poly(meth)acrylate polymer liquid used in this comparative example are as follows: pH 6.5, glass transition temperature 38°C, swelling rate 244%, D50 of the poly(meth)acrylate polymer 1 μm, and concentration of the poly(meth)acrylate polymer 25%.

[0092] Comparative Example 5: Except for the type of fluorine-free polymer resin being different from that in Example 8, the rest are the same as those in Example 8. The performance parameters of the poly(meth)acrylate polymer liquid used in this comparative example are as follows: pH 6.5, glass transition temperature of -37°C, swelling rate of 300%, D50 of the poly(meth)acrylate polymer of 4.5 μm, and concentration of the poly(meth)acrylate polymer of 25%.

[0093] Comparative Example 6: In this comparative example, except for changing the parameters shown in Table 1, the method is the same as Example 1 to prepare a battery separator C6 with a coating film; the prepared battery separator does not meet the formula of the present invention.

[0094] Table 1 Parameter data of B1-B9 and C2-C6

[0095] The performance of battery separators B1-B9 and C2-C6 was tested using the following test methods. The test results are shown in Table 2 below.

[0096] (1) Adhesion:

[0097] Adhesion as referred to in this invention refers to the tightness and uniformity of the adhesion between the battery separator and the battery electrode during assembly of the battery cell. Specifically, adhesion is evaluated according to the following method: Tests are conducted with reference to the requirements of GB / T 2792.

[0098] 1) stacking A4 paper and a separator in the order of A4 paper / separator / separator / A4 paper, with the separator coatings facing each other;

[0099] 2) The stacked A4 paper and separator are subjected to thermoplastic treatment at a temperature of 100°C;

[0100] 3) Cut the thermoplasticized membrane into strips with a length of 200 mm and a width of 25 mm. The distance between the clamps is (100 ± 5) mm, and the test speed is (50 ± 10) mm / min.

[0101] (2) Consistency:

[0102] The term "consistency" as used herein refers to the uniformity and consistency of the ceramic particle packing within a mixed coating of fluorine-free polymer resin particles and ceramic particles. The presence of larger particles of fluorine-free polymer resin can reduce the uniformity of the ceramic particle packing, adversely affecting the mechanical uniformity of the coating.

[0103] Use foam with a certain resilience and density (the present invention uses a beauty egg made of polyurethane foam), place the prepared battery separator on a horizontal table, fix the separator with one hand, and use foam with the other hand to wipe the membrane surface from left to right 6-8 times, so that the PMMA particles can be removed from the coating without damaging the ceramic layer, thereby obtaining the thickness of the ceramic layer and monitoring it. In particular, the consistency can be evaluated in the following way: prepare a cross-sectional sample of the battery separator at 21°C ± 4°C and humidity ≤ 65% RH, and take a photograph of the cross-sectional electron microscope using a Zeiss SIGMA 300 electron microscope. On the picture, measure the thickness of the single-coating ceramic stacking layer at any 10 positions, and calculate the range R (max-min) of the thickness of these 10 positions. If R ≤ 0.5 μm, it means good consistency.

[0104] (3) Stability:

[0105] The stability referred to in the present invention refers to the degree to which the fluorine-free polymer resin particles are firmly embedded in the coating.

[0106] In particular, stability can be evaluated in the following way: after the finished battery separator passes through a 90-degree angle roller 20 times, random samples are taken, and 1000-fold electron microscope pictures (500-5000 times can be taken) are taken to count the probability of particle falling (number of PMMA or PVDF particles falling / total number of PMMA or PVDF particles).

[0107] (4) Heat resistance:

[0108] The heat resistance referred to in the present invention refers to the thermal shrinkage performance of the battery separator. In particular, the heat resistance can be evaluated by measuring the thermal shrinkage rate according to the method specified in GB / T12027-2004, and taking the average of the thermal shrinkage rate in the TD direction and the thermal shrinkage rate in the MD direction.

[0109] Table 2 Performance test results of B1-B5 and C1-C3

[0110] It can be seen from the data in Table 2 that the battery separator provided by the present invention has a coating with good adhesion, high consistency, strong stability and good heat resistance.

[0111] However, the battery separator prepared in Comparative Example 1 uses PVDF, which easily floats on the surface of the coating, making the coating very unstable, and the coating has a high thermal shrinkage rate and poor heat resistance.

[0112] As can be seen from Tables 1 and 2, regardless of how the various parameters vary, when the condition of "0.8ρ1 ≤ ρ0 / h0 ≤ 1.2ρ1" is met, the coating exhibits the advantages of good adhesion, high consistency, strong stability, and excellent heat resistance. However, when these conditions are not met, these advantages are no longer present. Other parameters in the embodiments not limited by ρ, ρ0, and h0 can be adjusted within the ranges provided by the present invention to achieve the condition of "0.8ρ1 ≤ ρ0 / h0 ≤ 1.2ρ1", but achieving this condition is not essential.

[0113] The battery separator provided by the present invention is not limited to being prepared by the preparation method provided by the present invention, and the battery separators in accordance with the present invention obtained by other methods should all fall within the scope of protection of the claims of the present invention.

[0114] At the same time, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

Claims

1. A battery separator, comprising a base film and a coating coated on one or both sides of the base film, characterized in that: The coating contains: fluorine-free polymer resin particles and ceramic particles; The fluorine-free polymer resin particles are in the form of primary particles or secondary aggregates, and the fluorine-free polymer resin particles are spherically dispersed in the ceramic particles. The coating surface density ρ0, the coating thickness h0, the average radius r of the non-fluorinated polymer resin particles, the volume V1 occupied by the non-fluorinated polymer resin particles in the coating, the number N0 of the non-fluorinated polymer resin particles, the density ρ of the non-fluorinated polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship: 0.8ρ1≤ρ0 / h0≤1.2ρ1; The fluorine-free polymer resin has a glass transition temperature of 40-100° C. and a swelling rate of 10-200%; N0 is the number of fluorine-free polymer resin particles counted under a 1K electron microscope, and then converted to 1m according to the area. 2 The amount of fluorine-free polymer resin particles contained in the separator.

2. The battery separator according to claim 1, wherein The glass transition temperature of the fluorine-free polymer resin is 45-70° C., and the swelling rate is 10-100%.

3. The battery separator according to claim 1, wherein The fluorine-free polymer resin is a poly(meth)acrylate polymer.

4. The battery separator according to claim 1, wherein The average particle size D50 of the fluorine-free polymer resin particles is 2-9 μm.

5. The battery separator according to claim 1, wherein The ceramic particles are at least one selected from the group consisting of aluminum oxide, boehmite, barium titanate, calcium oxide, magnesium oxide, zinc oxide, zirconium oxide, and silicon oxide.

6. The battery separator according to claim 5, wherein: The ceramic particles are boehmite.

7. The battery separator according to claim 1, wherein The average particle size D50 of the ceramic particles is 0.1-4.0 μm.

8. A method for preparing a battery separator, characterized in that: The method comprises the following steps: Step 1) dispersing ceramic powder in water, and dispersing by sand milling to form a dispersion; Step 2) adding a fluorine-free polymer resin liquid in an emulsion state to the dispersion liquid, adding a binder, and passing through a 80-200 mesh sieve to form a finished slurry; Step 3) according to the required coating thickness, the finished slurry is coated on one or both sides of the base film using a gravure roller or a wire rod. After the finished slurry is coated on the surface of the base film, it is dried in an oven to obtain a battery separator with a coating; Wherein, in step 1), the rotation speed of the sand milling dispersion is 500-1500rpm, and the sand milling dispersion time is 10-60min; after step 1), the dispersion is cooled under low-speed stirring so that the temperature of the dispersion is maintained at ≤70°C, wherein the stirring rate of the low-speed stirring is 20-300rpm; The finished slurry prepared in step 2) is continuously stirred at a low speed from the completion of the preparation to before it is put into use, so that the finished slurry is always in dynamic equilibrium, and the rotation speed of the low-speed stirring is 10-800rpm; from step 2) to before the finished slurry is put into use, the slurry is kept at 5°C-70°C; a stirring tank with stirring blades on both the upper and lower layers is used for low-speed stirring, and the radii of the stirring blades on the upper and lower layers are different; In step 3), in the battery separator, the coating surface density ρ0, the coating thickness h0, the average radius r of the fluorine-free polymer resin particles, the volume V1 occupied by the fluorine-free polymer resin particles in the coating, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the coating density ρ1 of the pure ceramic coating satisfy the following relationship: 0.8ρ1≤ρ0 / h0≤1.2ρ1; The fluorine-free polymer resin has a glass transition temperature of 40-100° C. and a swelling rate of 10-200%; N0 is the number of fluorine-free polymer resin particles counted under a 1K electron microscope, and then converted to 1m according to the area. 2 The amount of fluorine-free polymer resin particles contained in the separator.

9. The preparation method according to claim 8, wherein: The fluorine-free polymer resin liquid in the emulsion state will not undergo structural decomposition or deformation under the conditions of pH ≥ 5 and pH ≤ 10; the average particle size D50 of the fluorine-free polymer resin powder in the fluorine-free polymer resin liquid in the emulsion state is 2-9 μm; The average particle size D50 of the ceramic powder is 0.4-4.0 μm.

10. The preparation method according to claim 8, wherein: Based on the total weight of the finished slurry, the fluorine-free polymer resin powder accounts for 0.5-10% by weight, and the ceramic powder accounts for 15-40% by weight.

11. The preparation method according to claim 10, wherein: Based on the total weight of the finished slurry, the fluorine-free polymer resin powder accounts for 5-10% by weight; and the ceramic powder accounts for 20-35% by weight.

12. The preparation method according to claim 8, wherein: In the coating of step 3), high-speed coating is used, and the speed of the high-speed coating is 50-250 m / min; The drying temperature is 50-100° C. and the drying time is ≥5s.

13. The preparation method according to claim 12, wherein: The drying temperature is 60-90°C.

14. A battery comprising: A positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, wherein the separator is a battery separator as described in any one of claims 1 to 7.

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