Battery separator, method for manufacturing the same, and battery

Abstract

The present invention provides a battery separator, a method for manufacturing the same, and a battery. The battery separator provided by the present invention includes a base film and a coating layer coated on one side or both sides of the base film. The coating layer 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. The fluorine-free polymer resin particles are spherically dispersed in the ceramic particles. The surface density ρ0 of the coating layer, the thickness h0 of the coating layer, 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 layer, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the density ρ1 of the coating layer of the pure ceramic coating layer satisfy the following relationship. The battery separator provided by the present invention has a coating layer with good adhesiveness, high consistency, strong stability, and good heat resistance.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and more specifically, to a battery separator, a method for manufacturing the same, and a battery including the battery separator.

Background Art

[0002] With the development of lithium-ion battery technology, the requirements for separators are increasing. Therefore, the development of separators is not limited to the base film, and the functions of the coating layer are being increasingly emphasized. For example, the modification of the coating layer such as the adhesiveness, heat resistance, and electrolyte affinity of the coating layer is required, which provides a technical route for the development of separators. In the prior art, PVDF is often adopted as the adhesive layer. PVDF itself can be used as an adhesive for the positive electrode in a battery and is a material with a certain degree of adhesiveness. According to the current market development, spray coating is often performed to attach PVDF to the surface of the ceramic separator to achieve the adhesive function.

[0003] However, since PVDF has a high melting point (≥135°C), the conditions for achieving its adhesiveness are also higher, and higher temperature and pressure are required to achieve the adhesion between the separator and the electrode tab. And since the particle size of the particles formed by PVDF itself is small, in order to achieve an obvious adhesive effect, it is necessary to form aggregates of a certain size in the form of aggregates. The aggregates are formed in the later stage, and since the particle size of the aggregates cannot be controlled, the differences in the size and shape of the aggregates are large, whereby both the consistency and stability of PVDF are weak. Due to the above reasons, when PVDF is adopted as the adhesive layer, the structure becomes unstable and it is easy to fall off powder, which affects the adhesive effect, and it is also difficult to guarantee the consistency of the coating layer. Whether it is the deposited density or the aggregated form in the coating layer, there are obvious differences, whereby it becomes difficult to control the coverage rate, and the coating layer cannot be controlled microscopically or macroscopically.

Summary of the Invention

[0004] In view of the above problems, the present invention prepares by mixing ceramic particles and fluorine-free polymer resin particles, and finally forms a coating layer with good adhesiveness, high consistency, strong stability and good heat resistance by comprehensively considering and adjusting factors such as the surface density of the coating layer, the particle size of the ceramic particles, the particle size of the fluorine-free polymer resin particles, and the thickness of the ceramic.

[0005] Specifically, the present invention provides a battery separator having a coating layer with good adhesiveness, high consistency, good stability and good heat resistance, a manufacturing method thereof, and a battery including the battery separator.

[0006] The present invention provides a battery separator, which includes a base film and a coating layer coated on one or both sides of the base film. The coating layer 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 surface density ρ0 of the coating layer, the thickness h0 of the coating layer, 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 layer, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the density ρ1 of the pure ceramic coating layer satisfy the following relationship.

Equation

[0007] The present invention further provides a manufacturing method of a battery separator for manufacturing the battery separator provided by the present invention. However, to achieve the battery separator provided by the present invention, it is not limited to the manufacturing method provided by the present invention. The method includes 1) dispersing ceramic powder in water and performing sand mill dispersion using a sand mill to form a dispersion; 2) adding an emulsion-like fluorine-free polymer resin liquid to the dispersion, adding an adhesive, and passing through a sieve of 80-200 meshes to form a finished slurry. 3) According to the required thickness of the coating layer, use a gravure roll or a wire bar to coat the finished slurry on one or both sides of the base film. After coating the finished slurry on the surface of the base film, dry it in an oven to obtain a battery separator with a coating film. In step 1), the rotation speed of the sand mill dispersion is 500 - 1500 rpm, the time of the sand mill dispersion is 10 - 60 min. After step 1) is completed, cool the dispersion while stirring it at a low speed, maintain the temperature of the dispersion at ≤70°C, and the stirring speed of the low-speed stirring is 20 - 300 rpm. The finished slurry prepared in step 2) continues to be stirred at a low speed from the completion of preparation to the start of use, always keeping the finished slurry in a dynamic equilibrium. The rotation speed of the low-speed stirring is 10 - 800 rpm. From the start of step 2) to the start of use of the finished slurry, maintain the slurry between 5°C and 70°C, and use a stirring tank with stirring blades on both the upper and lower layers to stir at a low speed, and the radii of the stirring blades on the upper and lower layers are different. In step 3), for the battery separator, the surface density ρ0 of the coating layer, the thickness h0 of the coating layer, 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 layer, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the density ρ1 of the pure ceramic coating layer satisfy the following relationship.

Number

[0008] Preferably, in the coating of step 3), high-speed coating is used, 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. The present invention further provides a battery, which includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte. The separator is the battery separator provided by the present invention.

[0009] The technical solution provided by the present invention can achieve a coating separator with good adhesiveness, consistency, stability, and heat resistance, and can balance the four properties. When the surface of the separator coating layer has good adhesiveness, the bonding with the electrode sheet is strong, which is beneficial to the assembly of the cell and the increase of the battery energy density. When the consistency of the deposition thickness of the ceramics on the surface of the coating layer is high, it further improves the consistency of the cell properties and increases the cycle life of the battery. The resin particles need to be stably fixed in the coating layer. If the resin particles deviate, it will affect the assembly of the cell and the cycle life of the battery. Good heat shrinkage properties of the separator are beneficial to the improvement of battery safety. However, the inventors have found that in the prior art, usually, it is difficult to balance these four properties. For example, improving the adhesiveness of the coating layer leads to a decrease in the stability and heat resistance properties of the coating layer, and the consistency of the coating layer also deteriorates. Therefore, the present invention provides a technical solution for a battery separator. By controlling the multi-faceted parameters of the coating layer, the coexistence and balance of the four properties are achieved, thereby improving the quality and efficiency of the subsequent cell assembly, increasing the energy density and cycle life of the battery, and being beneficial to the safety of the battery. The present invention further provides one of the manufacturing methods for manufacturing the separator.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying out the Invention

[0011] The present invention provides a battery separator. The battery separator includes a base film and a coating layer coated on one or both sides of the base film. The coating layer 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 surface density ρ0 of the coating layer, the thickness h0 of the coating layer, 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 layer, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the density ρ1 of the pure ceramic coating layer satisfy the following relationship.

Equation

[0012] In the above relational expression, V1 represents the volume of the spherical segment (i.e., the volume occupied by the fluorine-free polymer resin particles in the coating layer), and N0 represents the number of the fluorine-free polymer resin particles. As shown in Figure 2, when the coating layer is on both sides of the base film, the thickness h0 of the coating layer = (c - b) / 2, and when the coating layer is on one side of the base film, the thickness h0 of the coating layer is the difference between the thickness of the battery separator and the thickness of the base film. In particular, the value of h0 can be determined as follows. A cross-sectional sample of the battery separator is prepared under the conditions of 21°C ± 4°C and humidity ≤ 65% RH, photographed by an electron microscope of the ZEISS SIGMA 300 type, an electron micrograph of the cross-section is taken, and in the photograph, the thickness of the ceramic deposition layer in any five single-layer coating layers is measured, and the average value is taken as the value of h0. The volume of the spherical segment is V1 = (π / 3)(3R - h)×h 2 where H is the height of the spherical segment, h = h0, and it should be noted that 2r = D = D50 here, r is the radius of the sphere of the fluorine-free polymer resin particles, D is the diameter, D - h0 > 0, and D50 is determined by the selection of the raw material of the fluorine-free polymer resin. In particular, the value of D50 can be determined from the raw material, or as described above, five samples of the fluorine-free polymer resin particles can be taken by an electron microscope and measured by calculating the average value.

[0013] ρ and ρ1 are fixed values determined by the fluorine-free polymer resin and the ceramic material. Specifically, ρ is determined from the properties of the raw materials, and ρ1 is determined from the density and particle size of the ceramic. ρ may be measured using the raw materials of the fluorine-free polymer resin, or the fluorine-free polymer resin particles in the coating layer may be separated and collected and measured using an electronic balance and a graduated cylinder.

[0014] ρ1 is obtained by coating a film using ceramic particles with a gravure roll or a wire bar, and then measuring the areal density of the film using an electronic balance and a steel rule. The ceramic particles used are either the ceramic particles as the raw materials of the coating layer or the ceramic particles extracted from the separator coating layer. The method for extracting ceramic particles from the separator is not particularly limited. For example, the ceramic particles may be extracted by dissolving the coating layer or the separator in a solvent. Specifically, as the first step, the ceramic particles are dispersed in water to prepare a normal ceramic slurry. As the second step, the ceramic slurry is coated with a gravure roll or a wire bar corresponding to the thickness after drying to form a film. As the third step, the areal density of the coating layer is measured using an electronic balance and a steel rule to obtain ρ1. ρ0 is the areal density of the coating layer and is calculated by the above formula.

[0015] Regarding N0, first, the number of fluorine-free polymer resin particles within the field of view area of the electron microscope is counted using a 1000-fold electron microscope, and then it may be converted to the number of fluorine-free polymer resin particles contained in 1 m 2 of the separator from the field of view area of the electron microscope. (For example, as described above, using an electron microscope, the average value of the number of fluorine-free polymer resin particles in 5 electron micrographs at a magnification of 1000 is counted, the field of view area of the electron microscope at that magnification is calculated, and then the number of fluorine-free polymer resin particles per unit area, that is, the number of particles N0 per 1 m 2 area, is subjected to unit conversion.)

[0016] Among them, the areal density ρ0 of the coating layer is 0 to 20 g / m 2is between, and the thickness h0 of the coating layer is 0.1×10 -6 ~10×10 -6 is between, and the average radius r of the fluorine-free polymer resin particles is 1×10 -6 ~4.5×10 -6 is between m, and the volume V1 of the fluorine-free polymer resin particles occupying the coating layer is V1≧0m 3 is, and the number N0 of the fluorine-free polymer resin particles is 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 is between, and the density ρ1 of the pure ceramic coating layer is 0.5×10 6 ~2.0×10 6 g / m 3 is between.

[0017] Note that when substituting ρ0, h0, R, V1, N0, ρ, ρ1 into the relational expression, the units should not be substituted for calculation. The relational expressions and ranges proposed by the present invention are designed based on the numerical relationships of these parameters and are not affected by whether the dimensions are equal. The fluorine-free polymer resin particles are in a spherical form, and the spherical form has excellent structural stability and higher consistency in the coating layer. The sphericity can be characterized by the aspect ratio method, that is, the aspect ratio S = the longest diameter passing through the inside of the particle / the short diameter perpendicular to the longest diameter, and S≦2 indicates that the particles are in a spherical form. The primary particle form may be a primary particle form in which the internal component and the external component are the same, or a primary particle form with a core-shell structure.

[0018] The fluorine-free polymer resin has a certain degree of crosslinking degree and a low glass transition temperature (TG), preferably 40~100°C. If TG is too low, the structure becomes unstable, and it is easy for the structure to disintegrate or the sphere to collapse and deform. If TG is too high, the adhesiveness of the sphere decreases, and defects such as the cells becoming soft are likely to occur.

[0019] The fluorine-free polymer resin has a certain degree of swellability, and the degree of swelling is preferably 10 to 200%, more preferably 10 to 100%. As a polymer material, if the degree of swelling is too small, it will affect the liquid retention ability of the cell. If the degree of swelling is too large, after the electrode plate is immersed in the electrolyte, the increase value of air permeability will be high, and defects such as the thickness expanding are likely to occur, which will affect the cycle characteristics of the battery, and may even lose adhesiveness after being immersed in the electrolyte.

[0020] The fluorine-free polymer resin has a glass transition temperature of 45 to 70°C, and the degree of swelling is preferably 10 to 100%.

[0021] The fluorine-free polymer resin is preferably at least one of poly(meth)acrylate polymer, SBR (styrene-butadiene rubber) microspheres, and PI (polyimide) water-soluble microspheres, PAA (polyacrylate) modified microspheres. The poly(meth)acrylate polymer obtained by primary molding is particularly preferred. Since the acrylate polymer has a low softening point (~50°C), it greatly reduces the adhesion conditions, and because of the high consistency and uniformity of the distribution in the coating layer, the adhesion effect of the coating layer is greatly enhanced (about 2 to 10 times that of PVDF). The poly(meth)acrylate polymer obtained by grafting a hydrophilic group on the molecular surface of the acrylate polymer (abbreviation: poly(meth)acrylate polymer) has greatly improved hydrophilicity, and the ease and stability of dispersion in an aqueous solvent are superior to those of PVDF. In particular, since the particles have a large primary particle size and a low density, a stable fitting structure can be formed in the coating layer, so that the weight per gram of the coating layer can be reduced, and the adhesiveness and stability can be greatly enhanced.

[0022] The average particle diameter (D50) of the fluorine-free polymer resin particles is preferably 2 to 9 μm.

[0023] The ceramic particles may be selected from at least one of alumina, boehmite, barium titanate, calcium oxide, magnesium oxide, zinc oxide, zirconium oxide, and silicon oxide. When the ceramic particles are a mixture of a plurality of substances, the respective usage amounts of the different substances may be in any ratio as long as the total amount satisfies the usage limit of the ceramic particles. Preferably, the ceramic powder is boehmite.

[0024] The average particle size (D50) of the ceramic particles is 0.1 to 4.0 μm, preferably 0.2 to 1.5 μm. The smaller the particle size, the higher the thermal shrinkage property. The crystal of the ceramic particles should not have obvious sharp protrusions in order to avoid the protrusions from destroying the structure of the polymer. The smaller the particle size, the worse the dispersibility of the particles in the slurry. When it is less than or equal to 0.1 μm, the particle size of the slurry becomes large, and there is a risk that the uniformity of the coating layer becomes poor.

[0025] The present invention further provides a method for manufacturing a battery separator, and the method includes: Step 1) dispersing ceramic powder in water, performing sand mill dispersion using a sand mill to form a dispersion; Step 2) adding an emulsion state fluorine-free polymer resin liquid to the dispersion, adding an adhesive, and passing through a sieve of 80 to 200 meshes to form a finished slurry; Step 3) coating the finished slurry on one or both sides of a base film using a gravure roll or a wire bar according to the required thickness of the coating layer, drying in an oven after coating the finished slurry on the surface of the base film to obtain a battery separator with a coating layer. In Step 1), the rotation speed of the sand mill dispersion is 500 to 1500 rpm, the time of the sand mill dispersion is 10 to 60 min. After Step 1 is completed, the dispersion is cooled while being stirred at a low speed, and the temperature of the dispersion is maintained at ≤70 °C, and the stirring speed of the low-speed stirring is 20 to 300 rpm. The finished product slurry prepared in step 2) continues to be stirred at a low speed from the completion of preparation to the start of use, keeping the finished product slurry in a dynamic equilibrium at all times. The rotation speed of the low-speed stirring is 10 to 800 rpm. From the start of step 2) to the start of use of the finished product slurry, the slurry is maintained between 5°C and 70°C. Low-speed stirring is carried out using a stirring tank with stirring blades in both the upper and lower layers, and the radii of the stirring blades in the upper and lower layers are different. In step 3), for the battery separator, the surface density ρ0 of the coating layer, the thickness h0 of the coating layer, 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 layer, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the density ρ1 of the pure ceramic coating layer of the coating layer satisfy the following relationships.

Number

[0026] The fluorine-free polymer resin liquid in emulsion state used in the above method is not limited to those obtained by commercial purchase or self-production. The self-production method includes mixing fluorine-free polymer resin powder, surfactant and water, dispersing and stirring them to form a fluorine-free polymer resin liquid in emulsion state. As commercially available fluorine-free polymer resin liquids in emulsion state, for example, the poly(meth)acrylate polymer liquid with product number SWA709, glass transition temperature of 55 °C, swelling degree of 70%, and poly(meth)acrylate polymer concentration of 25%, which was purchased from Shenzhen Haodyne Technology Co., Ltd and used in Examples 1 to 3; the poly(meth)acrylate polymer liquid with product number BM5000, glass transition temperature of 54 °C, swelling degree of 97%, and poly(meth)acrylate polymer concentration of 19%, which was purchased from Zeon Corporation of Japan and used in Example 4; the poly(meth)acrylate polymer liquid with product number FS400, glass transition temperature of 68 °C, swelling degree of 68%, and poly(meth)acrylate polymer concentration of 30%, which was purchased from Sichuan Indigo Materials Science and Technology Group CO., Ltd and used in Example 5 can be mentioned.

[0027] Preferably, the fluorine-free polymer resin liquid in emulsion state does not undergo structural decomposition or deformation under the conditions of pH ≥ 5 and pH ≤ 10 (all of the above commercially available poly(meth)acrylate polymer liquids meet this condition). The reason is that the aqueous solution of ceramics is often basic, and if the fluorine-free polymer resin liquid with too low pH is mixed with ceramics, part of the structure will be denatured, resulting in an unstable structure. The average particle size D50 of the fluorine-free polymer resin powder in the fluorine-free polymer resin liquid in emulsion state is 2 to 9 μm, and the average particle size D50 of the ceramics powder is 0.4 to 4.0 μm.

[0028] After step 1) is completed, the reason for maintaining the temperature of the dispersion liquid at ≤70°C is that if the temperature is too high, it will affect the properties of the coating film. Since processes such as high-speed dispersion or grinding raise the temperature of the dispersion liquid, it is necessary to add the fluorine-free polymer resin material after the temperature drops to ≤70°C. When the temperature of the dispersion liquid exceeds 70°C, the structure of the fluorine-free polymer resin particles softens and blocking occurs, and they can no longer maintain a perfect spherical shape, which further affects the adhesiveness and heat resistance of the coating layer.

[0029] For the finished product slurry prepared in step 2), low-speed stirring should be continued from the completion of preparation to the start of use to always keep the finished product slurry in a dynamic equilibrium. The reason is to prevent the fluorine-free polymer resin particles and ceramic particles from separating and the fluorine-free polymer resin particles from floating up after coating. Floating up affects the uniformity of the coating layer and the stability of the coating layer structure, making so-called powder falling such as the dropping of large particles and poor adhesion likely to occur. Stir with two paddles (that is, there are stirring blades in both the upper and lower layers of the stirring tank.), and the radii (r 上 , r 下 ) of the stirring blades in the upper and lower layers need to be different, that is, the ratio of the radii r 上 / r 下 ≠1. The purpose is to uniformly disperse the organic and inorganic particles, eliminate the aggregation phenomenon, and improve the stability and uniformity of the coating layer by generating a speed difference. The rotation speed of the low-speed stirring is 10~800 rpm. High-speed stirring affects the uniformity of the coating layer by generating bubbles in the slurry. The reason for maintaining the slurry at 5°C~70°C from the start of this step to the start of use of the finished product slurry is that if the temperature is too high, the structure of the fluorine-free polymer resin particles softens and blocking occurs, and they can no longer maintain a perfect spherical shape, which further affects the adhesiveness and heat resistance of the coating layer.

[0030] In the coating in step 3), since the stability of the finished product slurry is high, preferably high-speed coating (50~250 m / min) is applied. The base film of the present invention is not particularly limited and can be selected with reference to conventional lithium-ion battery separators. Usually, the base film may be a polyolefin base film such as a polypropylene base film or a polyethylene base film. In a preferred embodiment, the base film is a polyethylene base film.

[0031] The thickness of the base film may be 5 to 12 μm. The thickness of the coating layer may be 1 to 5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0032] In the above method, the average particle diameter D50 of the fluorine-free polymer resin particles is preferably 2 to 9 μm. The average particle diameter D50 of the ceramic powder is preferably 0.4 to 1.5 μm.

[0033] Based on the total weight of the finished slurry, the fluorine-free polymer resin powder is 0.5 to 10% by weight, and the ceramic powder is 15 to 40% by weight, more preferably 20 to 35% by weight.

[0034] The drying temperature is 50 to 100 °C, and the drying time is ≧5 s.

[0035] The present invention has no particular limitation on the surfactant, water, adhesive, and their usage amounts, and products generally used in this field, for example, the products disclosed in CN115117559A, and their ratios may be used. For example, the surfactant includes surfactant A and surfactant B. Surfactant A is a polyether siloxane copolymer, and surfactant B is a polysiloxane. The adhesive is at least one selected from 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 is 0.06 to 0.5% by weight, surfactant B is 0.1 to 0.5% by weight, water is 40 to 60% by weight, and the adhesive is 5 to 10% by weight.

[0036] The present invention provides a battery, which includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, and the separator is the battery separator provided by the present invention.

[0037] The battery separator provided by the present invention has a coating layer with good adhesiveness, high consistency, strong stability, and good heat resistance. The adhesion strength of the coating layer is ≥ 0.6 N / m, the consistency R is ≤ 0.5 μm, the probability of particle dropping is ≤ 3%, and the heat shrinkage rate is ≤ 5%.

[0038] The present invention will be further described with reference to the following examples, but the scope of the present invention is not limited to these examples.

Examples

[0039] In the following examples and comparative examples, the adhesive is a polyacrylate emulsion, purchased from Hunan Gaorui Power Source Materials Co., Ltd., and the product number is LIB-S105B. In the following examples and comparative examples, unless otherwise specified, "parts" refers to parts by weight. The following Examples 1 to 5 are used to illustrate the battery separator of the present invention and its manufacturing method.

[0040] Example 1 1) 30 parts of boehmite (D50 is 0.8 μm) was dispersed in 54 parts of water, and sand mill dispersion was carried out using a sand mill (the rotation speed was 1000 rpm and the time was 30 min) to form a dispersion. The dispersion was cooled by stirring at a low speed (150 rpm), and the temperature of the dispersion was maintained at ≤ 70 °C.

[0041] 2) 6 parts of an emulsion state poly(meth)acrylate polymer liquid (pH is 6.5, glass transition temperature is 55 °C, swelling degree is 70%, D50 of the poly(meth)acrylate polymer is 4.5 μm, and the concentration of the poly(meth)acrylate polymer is 25%) was added to the above dispersion, 10 parts of an adhesive was added, and it was passed through a 200-mesh sieve to form a finished slurry.

[0042] The above-mentioned finished product slurry is stirred at a low speed (300 rpm) with two paddles (i.e., there are stirring blades in both the upper and lower layers of the stirring tank) from the completion of preparation until it is used in the next step, and the radii (r 上 and r 下 ) of the stirring blades in the upper and lower layers satisfy the relationship of "the ratio of radii r 上 / r 下 ≠1", and the slurry is maintained between 5 and 70 °C from the start of step 2) until the finished product slurry is used in the next step.

[0043] 3) According to the required thickness of the coating layer, the finished product slurry is coated on both sides of a base film with a thickness of 7 μm using a gravure roll or a wire bar. After the finished product slurry is coated on the surface of the base film and then dried in an oven (the drying temperature was 75 °C and the time was 10 s), a battery separator B1 with a coated film was obtained.

[0044] In step 3), for the battery separator, the surface density ρ0 of the coating layer, the thickness h0 of the coating layer, 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 layer, the number N0 of the fluorine-free polymer resin particles, the density ρ of the fluorine-free polymer resin, and the density ρ1 of the coating layer of the pure ceramic coating layer satisfy the following relationship.

Equation

[0045] The measurement methods of the above parameters are as described in the present invention, and will not be elaborated here. The measured data are shown in Table 1 below.

[0046] Example 2: In this example, except that the parameters shown in Table 1 were changed, a battery separator B2 with a coated film was manufactured by the same method as in Example 1, and the manufactured battery separator satisfies the formula of the present invention.

[0047] Example 3: In this example, except that the parameters shown in Table 1 were changed, a battery separator B3 with a coating film was manufactured in the same manner as in Example 1, and the manufactured battery separator satisfies the formula of the present invention.

[0048] Example 4: In this example, the parameters shown in Table 1 were changed. Regarding the parameters of the poly(meth)acrylate polymer liquid used in step 2), the pH was 7.9, the glass transition temperature was 54°C, the swelling degree was 97%, the D50 of the poly(meth)acrylate polymer was 4.5 μm, and the concentration of the poly(meth)acrylate polymer was 25%. Except for this, a battery separator B4 with a coating film was manufactured in the same manner as in Example 1.

[0049] Example 5: In this example, the parameters shown in Table 1 were changed. Regarding the parameters of the poly(meth)acrylate polymer liquid used in step 2), the pH was 9.4, the glass transition temperature was 68°C, the swelling degree was 68%, the D50 of the poly(meth)acrylate polymer was 9 μm, and the concentration of the poly(meth)acrylate polymer was 25%. Except for this, a battery separator B5 with a coating film was manufactured in the same manner as in Example 1.

[0050] Example 6: In step 1), boehmite was changed to a mixture of boehmite and BaTiO3 (mass ratio 3:1). In step 2), regarding the characteristic parameters of the poly(meth)acrylate polymer liquid, the pH was 6.5, the glass transition temperature was 45°C, the swelling degree was 150%, the D50 of the poly(meth)acrylate polymer was 2.2 μm, and the concentration of the poly(meth)acrylate polymer was 25%. Except for changing the usage amounts of each substance according to Table 1, a battery separator B6 with a coating film was manufactured in the same manner as in Example 1.

[0051] Example 7: In step 1), boehmite was changed to a mixture of boehmite and BaTiO3 (mass ratio 9:1). In step 2), regarding the characteristic parameters of the poly(meth)acrylate polymer liquid, the pH was 6.5, the glass transition temperature was 76 °C, the swelling degree was 88%, the D50 of the poly(meth)acrylate polymer was 3 μm, the concentration of the poly(meth)acrylate polymer was 25%, and except for changing the usage amounts of each substance according to Table 1, a battery separator B7 with a coating film was manufactured in the same manner as in Example 1.

[0052] Example 8: In step 1), boehmite was changed to a mixture of boehmite and BaTiO3 (mass ratio 9:5). In step 2), the poly(meth)acrylate polymer liquid was changed to an SBR (styrene-butadiene rubber) microsphere solution. Regarding the characteristic parameters, the pH was 7.2, the glass transition temperature was 88 °C, the swelling degree was 30%, the D50 of the SBR (styrene-butadiene rubber) microspheres was 2.5 μm, the concentration of the SBR (styrene-butadiene rubber) microspheres was 25%, and except for changing the usage amounts of each substance according to Table 1, a battery separator B8 with a coating film was manufactured in the same manner as in Example 1.

[0053] Example 9: In step 1), boehmite was changed to a mixture of boehmite and BaTiO3 (mass ratio 3:1). In step 2, the poly(meth)acrylate polymer liquid was changed to a PI (polyimide) water-soluble microsphere solution. Regarding the characteristic parameters, the pH was 6.8, the glass transition temperature was 90 °C, the swelling degree was 55%, the D50 of the PI (polyimide) water-soluble microspheres was 4.5 μm, the concentration of the PI (polyimide) water-soluble microspheres was 25%, and except for changing the usage amounts of each substance according to Table 1, a battery separator B9 with a coating film was manufactured in the same manner as in Example 1.

[0054] Comparative Example 1: In this comparative example, a battery separator C1 with a coating film was produced in the same manner as in Example 1, except that a self-made PVDF made from PVDF powder was used instead of the poly(meth)acrylate polymer liquid. The PVDF liquid was prepared by mixing 1.5 parts of PVDF powder, 0.005 parts of a polysiloxane surfactant, and 4.5 parts of water to obtain 6 parts of PVDF liquid.

[0055] The PVDF powder was purchased from Dongyangguang Co., Ltd. and had the product number 2600. In this comparative example, the morphology of the PVDF sphere is unstable, so the density of PVDF cannot be calculated, and the comparative example is not applicable to the formula of the present invention.

[0056] Comparative Examples 2-3: Some of the parameter data shown in Table 1 below are different from Example 1. In step 1) of slurry preparation, the dispersion is formed, and then the mixing operation of the next step is performed directly without cooling. Also, the finished slurry is stirred at a low speed (300 rpm) with one paddle from the time it is made to the time it is used in the next step. That is, the stirring paddle has a radius ratio r 上 / r 下 Battery separators C2 to C3 with coating film were produced in the same manner as in Example 1, except that the relationship ".times. ...

[0057] Comparative Example 4: The same as Example 8 except that the type of non-fluorine-containing polymer resin was different from that of Example 8. The characteristic parameters of the poly(meth)acrylate polymer liquid used in this comparative example were pH 6.5, glass transition temperature 38°C, swelling degree 244%, D50 of the poly(meth)acrylate polymer 1 μm, and concentration of the poly(meth)acrylate polymer 25%.

[0058] Comparative Example 5: It was the same as Example 8 except that the type of the fluorine-free polymer resin was different from that of Example 8. Regarding the characteristic parameters of the poly(meth)acrylate polymer liquid used in this comparative example, the pH was 6.5, the glass transition temperature was -37 °C, the swelling degree was 300%, the D50 of the poly(meth)acrylate polymer was 4.5 μm, and the concentration of the poly(meth)acrylate polymer was 25%. Comparative Example 6: In this comparative example, a battery separator C6 with a coating film was manufactured by the same method as in Example 1 except that the parameters shown in Table 1 were changed, and the manufactured battery separator did not satisfy the formula of the present invention.

[0059]

Table 1

[0060] The characteristics of battery separators B1 to B9 and C2 to C6 were measured, and the measurement methods were as follows. The measurement results are shown in Table 2.

[0061] (1) Adhesiveness: The adhesiveness referred to in the present invention is the degree of adhesion and uniformity of adhesion between the battery separator and the battery electrode plate when assembling the cell. In particular, the adhesiveness was evaluated according to the method of measuring with reference to the requirements of GB / T 2792. 1) A4 paper and the separator were laminated in the order of A4 paper / separator / separator / A4 paper, and the separator coating layers were opposed to each other. 2) The laminated A4 paper and separator were thermoplastically treated at a temperature of 100 °C. 3) The thermoplastically treated separator was cut into long strips with a length of 200 mm and a width of 25 mm, the distance between the clamps was (100 ± 5) mm, and the measurement speed was (50 ± 10) mm / min.

[0062] (2) Conformity: The consistency referred to in the present invention is the degree of uniformity and coincidence of the deposition of ceramic particles in the mixed coating layer of fluorine-free polymer resin particles and ceramic particles. The presence of large particles of fluorine-free polymer resin deteriorates the uniformity of the deposition of ceramic particles and has an adverse effect on the uniformity of the mechanical structure of the coating layer. Using a foam having a certain degree of repulsive force and density (in the present invention, a beauty sponge made of a polyurethane foam was used), the manufactured battery separator was placed on a horizontal table, the separator was fixed with one hand, and the foam was used with the other hand to wipe the film surface from left to right 6 to 8 times, so as to remove PMMA particles from the coating layer without damaging the ceramic layer, thereby obtaining the thickness of the ceramic layer and monitoring it. In particular, the consistency can be evaluated by preparing a cross-sectional sample of the battery separator under the conditions of 21°C ± 4°C and humidity ≤ 65% RH and taking an electron micrograph of the cross-section with an electron microscope of the ZEISS SIGMA 300 type. In the photograph, the thickness of the ceramic deposition layer of any 10 single-layer coating layers is measured, the range R (max - min) of the thickness of these 10 locations is calculated, and when R ≤ 0.5 μm, it indicates good consistency.

[0063] (3) Stability: The stability referred to in the present invention is the degree of firmness of the fluorine-free polymer resin particles embedded in the coating layer.

[0064] In particular, the stability can be evaluated by randomly sampling after passing the finished battery separator through a roll with a winding angle of 90 degrees 20 times, taking an electron micrograph at 1000 times (it may also be 500 - 5000 times), and counting the probability of particle falling (the number of fallen PMMA or PVDF particles / the total number of PMMA or PVDF particles).

[0065] (4) Heat resistance: The heat resistance referred to in the present invention is the heat shrinkage characteristic of the battery separator. In particular, the heat resistance can be evaluated by measuring the heat shrinkage rate, which is measured according to the method specified in GB / T12027-2004, and the average value of the heat shrinkage rate in the TD direction and the heat shrinkage rate in the MD direction is taken.

[0066]

Table 2

[0067] From the data in Table 2, it can be seen that the battery separator provided by the present invention has a coating layer with good adhesiveness, high consistency, strong stability, and good heat resistance.

[0068] On the other hand, for the battery separator manufactured in Comparative Example 1, since PVDF is used, PVDF is likely to float to the surface of the coating layer, resulting in the coating layer being very unstable, and the heat shrinkage rate of the coating layer becoming high, and the heat resistance becoming poor.

[0069] From Table 1 and Table 2, it can be seen that no matter how each parameter changes, when the condition of "0.8ρ1≦ρ0 / h0≦1.2ρ1" is satisfied, the coating layer can have the advantages of good adhesiveness, high consistency, strong stability, and good heat resistance simultaneously. On the other hand, if the above condition is not satisfied, the advantages of being able to have them simultaneously will be lost. Other parameters not restricted by ρ, ρ0, h0 in the examples can be adjusted within the range provided by the present invention to achieve the condition of "0.8ρ1≦ρ0 / h0≦1.2ρ1", but it is not necessary for achieving the above condition.

[0070] The battery separator provided by the present invention is not limited to being manufactured by the manufacturing method provided by the present invention, and all battery separators that meet the present invention obtained by other methods should be included in the protection scope of the claims of the present invention. In addition, the present invention can have a plurality of other embodiments. Those skilled in the art can make various corresponding changes and modifications without departing from the gist and essence of the present invention. All of these corresponding changes and modifications should be included in the scope of the claims of the present invention.

Claims

1. A battery separator, comprising: a base film and a coating layer coated on one or both sides of the base film, wherein the coating layer 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, the fluorine-free polymer resin particles are spherically dispersed in the ceramic particles, The areal density ρ of the coating layer ０ , the thickness h of the coating layer ０ , the average radius r of the fluorine-free polymer resin particles, the volume V occupied by the fluorine-free polymer resin particles in the coating layer １ , the number N of the fluorine-free polymer resin particles ０ , the density ρ of the fluorine-free polymer resin, and the density ρ of the coating layer of the pure ceramic coating layer １ satisfy the following relationship 【Number 1】 the fluorine-free polymer resin has a glass transition temperature of 40 to 100 °C and a swelling degree of 10 to 200%, N ０ is the number of fluorine-free polymer resin particles in a 1K electron microscope, and after statistical analysis, it is the number of fluorine-free polymer resin particles contained in a separator of 1 m 2 converted from the area. The battery separator is characterized by this.

2. The battery separator according to claim 1, wherein the fluorine-free polymer resin has a glass transition temperature of 45 to 70 °C and a swelling degree of 10 to 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 diameter D50 of the fluorine-free polymer resin particles is 2 to 9 μm.

5. The battery separator according to claim 1, wherein the ceramic particles are at least one selected from the group consisting of alumina, 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 diameter D50 of the ceramic particles is 0.1 to 4.0 μm.

8. A method for manufacturing a battery separator, comprising: Step 1) dispersing ceramic powder in water, performing sand mill dispersion using a sand mill to form a dispersion; Step 2) adding an emulsion-like fluorine-free polymer resin liquid and an adhesive to the dispersion, passing through a sieve of 80 to 200 mesh to form a finished slurry; Step 3) coating the finished slurry on one or both sides of a base film according to the required thickness of the coating layer, drying in an oven after coating the finished slurry on the surface of the base film to obtain a battery separator with a coating layer; in Step 1), the rotation speed of the sand mill dispersion is 500 to 1500 rpm, and the time of the sand mill dispersion is 10 to 60 min. After step 1) is completed, the dispersion is cooled while being stirred at a low speed, and the temperature of the dispersion is maintained at ≤ 70°C. The stirring speed of the low-speed stirring is 20 to 300 rpm. The finished product slurry prepared in step 2) continues to be stirred at a low speed from the completion of preparation to the start of use, keeping the finished product slurry in a dynamic equilibrium at all times. The rotation speed of the low-speed stirring is 10 to 800 rpm. From the start of step 2) to the start of use of the finished product slurry, the slurry is maintained between 5°C and 70°C. Low-speed stirring is carried out using a stirring tank with stirring blades in both the upper and lower layers, and the radii of the stirring blades in the upper and lower layers are different. In step 3), the battery separator has a surface density ρ of the coating layer ０ , a thickness h of the coating layer ０ , an average radius r of the fluorine-free polymer resin particles, a volume V occupied by the fluorine-free polymer resin particles in the coating layer １ , a number N of the fluorine-free polymer resin particles ０ , a density ρ of the fluorine-free polymer resin, and a density ρ of the coating layer of the pure ceramic coating layer １ satisfy the following relationship: 【Number 2】 The fluorine-free polymer resin has a glass transition temperature of 40 to 100°C and a swelling degree of 10 to 200%. N ０ is the number of fluorine-free polymer resin particles in a 1 K electron microscope, and is the number of fluorine-free polymer resin particles contained in a separator of 1 m 2 converted from the area after counting, and is characterized by the manufacturing method.

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

10. Based on the total weight of the finished product slurry, the fluorine-free polymer resin powder is 0.5 to 10% by weight, and the ceramic powder is 15 to 40% by weight. The manufacturing method according to claim 8.

11. Based on the total weight of the finished product slurry, the fluorine-free polymer resin powder is 5 to 10% by weight, and the ceramic powder is 20 to 35% by weight. The manufacturing method according to claim 10.

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

13. The manufacturing method according to claim 12, wherein the drying temperature is 60 to 90°C.

14. 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 according to any one of claims 1 to 7. The battery is characterized by this.

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