Mixed particles for coating lithium ion battery diaphragm and lithium ion battery composite diaphragm

Abstract

The invention discloses a mixed particle for coating a lithium ion battery diaphragm and a lithium ion battery composite diaphragm, and belongs to the technical field of diaphragms. The mixed particles for coating the lithium battery diaphragm comprise first particles and second particles, the first particles comprise clusters formed by first inorganic particles, second inorganic particles and elastic colloid particles; the first inorganic particles are inorganic oxide particles, and the median diameter D50 of the first inorganic particles is 0.8-1.0 [mu] m; the second inorganic particles are inorganic oxide particles, and the median particle size D50 of the second inorganic particles is 0.2-0.4 mu m; the median particle size D50 of the elastic colloidal particles is 6.0 [mu] m-8. 0 [mu] m; the second particles comprise second inorganic particles; the particle size of the mixed particles is in bimodal distribution, and the particle size difference value of the bimodal peak value is 3.0-6.0 [mu] m. The mixed particles are coated on the surface of the base membrane, so that the problems of edge collapse and middle depression of the membrane surface can be obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a kind of mixed particles for coating lithium ion battery separator, slurry, lithium ion battery composite separator and preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in mobile electronic devices and electric vehicles due to their high energy density, long life and good charging performance. The performance and safety of lithium ion batteries not only depend on the chemical reactions and material properties inside the battery, but also closely related to the performance of the battery separator. The battery separator is located between the positive and negative electrodes, its main function is to prevent physical contact between the positive and negative electrodes, while allowing lithium ions to pass through. Therefore, the flatness, mechanical strength and heat resistance of the battery separator are important factors affecting the performance and life of the battery.

[0003] The existing lithium battery separator mainly coats inorganic matter on the substrate to improve the mechanical strength and functionality of the separator. However, the existing technology still faces challenges in terms of flatness, especially the middle depression and edge collapse of the separator when dealing with large width separators. These problems can cause internal short circuit of the battery, affecting the performance and safety of the battery.

[0004] The existing technology has limitations in improving the mechanical strength and heat resistance of the separator. When using high molecular polymer and high viscosity binder for coating, the other properties of the separator may be sacrificed, such as electrical conductivity and flatness.

[0005] CN104064708A discloses a lithium ion secondary battery separator, including a separator film and a plurality of porous insulating layers including inorganic particles and a binder disposed on at least one surface of the separator film. The average particle size of inorganic particles in each porous insulating layer gradually increases in the direction from the surface of the separator film to the electrode sheet, i.e. by coating small size particles on the surface of the separator first, then coating large size particles, to improve the thermal shrinkage of the separator. Although this solution can improve thermal shrinkage to some extent, it is difficult to improve the flatness of the separator, especially the middle depression and edge collapse, by coating inorganic particles from small to large size.

[0006] CN117937052A discloses a separator and a non-aqueous secondary battery including the separator, the separator includes a separator substrate and a heat-resistant coating layer disposed on at least one side surface of the separator substrate, the heat-resistant coating layer includes inorganic particles and a polymer binder; by adjusting the D V 90 range of inorganic particles, and the ratio of D V 90 / D V 10, for example, the particle size D V 90 of inorganic particles is 0.05 μm to 1.5 μm, and the particle size of the inorganic particles satisfies 1 ≤ D V90 / D V 10≤9.7, the flatness of the separator can be improved; the packing density of the small particle size inorganic particles in the heat-resistant coating can also be improved, the thermal stability of the separator at high temperature is improved, that is, the thermal shrinkage rate of the separator is reduced, and the safety performance of the battery is improved. However, in this scheme, although the thermal shrinkage rate of the separator can be improved to a large extent, the size of the inorganic particles used is small, and a small inorganic particle coating usually leads to an increase in the moisture content of the separator, which also leads to the fact that the separator does not meet the requirements.

[0007] CN117578031A discloses a ceramic slurry containing flaky ceramic particles, a thickening agent, a dispersant, a binder and a solvent for coating a separator, controlling the viscosity of the thickening agent aqueous solution and the particle size, thickness and specific surface area of the flaky ceramic particles, and the slurry coated base film can obtain a separator with a smooth surface and a low friction coefficient.

[0008] However, some existing high polymer material mixing and adding techniques may affect other performances of the battery, such as affecting the conductivity and capacity of the battery.

[0009] Therefore, in order to improve the safety of the separator and maintain the performance of the battery, the development of a separator with low thermal shrinkage and smooth film surface is still the direction of continuous research by researchers in the field. SUMMARY

[0010] 1. Problem to be solved In view of the technical problem of the ceramic-coated lithium ion battery separator that the film surface edge collapses and the middle part is depressed in different environments, the purpose of the present application is to provide a composite separator with a coating layer with a smooth film surface and low thermal shrinkage. In order to achieve this purpose, the present application first provides a mixed particle used as a coating material, which has rigidity and toughness. The use of the mixed particle to prepare a slurry to coat the separator can obtain a separator with high flatness and low thermal shrinkage.

[0011] On this basis, the present application provides a slurry made of mixed particles for coating a separator.

[0012] Finally, the present application provides a separator coated with the above-mentioned slurry, which has the characteristics of low thermal shrinkage and smooth film surface. When used in a lithium ion battery, it has high safety without affecting the performance of the battery itself.

[0013] 2. Technical scheme In order to solve the above-mentioned problems, the present application provides the following technical scheme: [Hybrid particles] The first aspect of the present application provides a hybrid particle for coating a lithium battery separator, comprising a first particle and a second particle; The first particle comprises a cluster of a first inorganic particle, a second inorganic particle and an elastic colloidal particle; the first inorganic particle is an inorganic oxide particle, and the median particle size D50 is 0.8-1.0 μm; the second inorganic particle is an inorganic oxide particle, and the median particle size D50 is 0.2-0.4 μm; and the elastic colloidal particle has a median particle size D50 of 6.0-8.0 μm. The second particle comprises a second inorganic particle. The particle size of the mixed particle is in a bimodal distribution, and the particle size difference between the two peaks is 3.0-6.0 μm.

[0014] The present application studies find that, in the prior art, when the inorganic particles are coated on the surface of the separator by using a polymer binder, the strength and flexibility of the polymer and the inorganic particles after coating are insufficient, and it is difficult to improve the phenomenon of collapse at the edge and depression in the middle of the film surface. The present application innovatively uses an elastic colloidal particle with a specific particle size as part of the support framework, and uses the first inorganic particle and the second inorganic particle with different particle sizes in cooperation with the elastic colloidal particle, so that the mixed particle is in a bimodal distribution with a particle size difference between the two peaks of 3.0-6.0 μm, and the mixed particle has both the larger-size cluster particle, i.e. the first particle, which can play a supporting and pressure-resistant supporting role, and the smaller-size second particle which can play a role of filling pores and improving the pore spacing; the cluster particle is bonded with the first inorganic particle of large size, and a part of the second inorganic particle of small size is also bonded at the gap, which can greatly reduce the large gap formed between the elastic colloidal particle and the first inorganic particle of large size; the cooperation of the cluster particle and the second inorganic particle with the bimodal peak particle size makes the film surface not only maintain a certain strength, but also have the effect of uniform stress distribution, effectively solving the problems of collapse at the edge and depression in the middle of the film surface, and obtaining a flat and heat-stable separator.

[0015] As a preferred embodiment of any of the technical solutions of the first aspect of the present application, the D10 of the mixed particle is 0.15-0.35 μm (for example, it can be 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm or 0.35 μm), the median particle size D50 is 2.0-3.5 μm (for example, it can be 2.0 μm, 2.5 μm, 3.0 μm or 3.5 μm), and the D90 is 8.0-10.0 μm (for example, it can be 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm or 10.0 μm). The above particle size can ensure that the large particles and the small particles are uniformly distributed in the mixed particle and are not prone to aggregation.

[0016] Preferably, the D10 of the mixed particle is 0.20-0.30 μm, the median particle size D50 is 2.5-3.0 μm, and the D90 is 8.5-9.0 μm.

[0017] As a preferred embodiment of any one of the technical solutions of the first aspect of the present application, the elastic colloidal particles are selected from one or more of an acrylate resin, a silicone glue, a polyurethane glue, or an epoxy resin modified glue, and preferably the elastic colloidal particles are an acrylate resin. The molecular weight of the elastic colloidal particles is 200 W to 350 W, and preferably 250 W to 350 W.

[0018] Within the above-mentioned molecular weight range, the adhesion of the elastic colloidal particles and the influence on the air permeability after being coated on the base film can be ensured, and the cycle rate of the separator is not affected. As a preferred embodiment of any one of the technical solutions of the first aspect of the present application, the particle size of the elastic colloidal particles is D10: 3.5 μm to 5.8 μm, D50: 6.0 μm to 8.0 μm, and D90: 9.0 μm to 11.0 μm. The elastic colloidal particles having the above-mentioned particle size can ensure the air permeability of the coated separator and also ensure the flexibility and supportability of the separator.

[0019] As a preferred embodiment of any one of the technical solutions of the first aspect of the present application, the particle size DMAX of the elastic colloidal particles is 12.0 μm to 14.0 μm. When the size of the elastic colloidal particles is too large, the possibility of the cluster particles being too large increases, which can cause unevenness of the film surface. Therefore, it is necessary to control the maximum size of the elastic colloidal particles.

[0020] As a preferred embodiment of any one of the technical solutions of the first aspect of the present application, the first inorganic particles or the second inorganic particles are selected from one or more of alumina, boehmite, magnesium oxide, silicon oxide, and titanium oxide. Preferably, the first inorganic particles or the second inorganic particles are boehmite. The first inorganic particles or the second inorganic particles play a supporting role in the mixed particles, and the use of the above-mentioned inorganic particles can provide excellent thermal stability and mechanical strength.

[0021] As a preferred embodiment of any of the technical solutions of the first aspect of the present application, the particle size of the first inorganic particles is D10: 0.25-0.45 μm (for example, it can be 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, or 0.45 μm), D50: 0.8-1.0 μm (for example, it can be 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, or 1.0 μm), and D90: 1.5-1.8 μm (for example, it can be 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, or 1.8 μm); and the particle size of the second inorganic particles is D10: 0.05-0.18 μm (for example, it can be 0.05 μm, 0.1 μm, 0.15 μm, or 0.18 μm), D50: 0.20-0.40 μm (for example, it can be 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, or 0.4 μm), and D90: 0.5-1.0 μm (for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1.0 μm).

[0022] As a preferred embodiment of any of the technical solutions of the first aspect of the present application, the mass ratio of the sum of the mass of the first inorganic particles and the mass of the second inorganic particles to the mass of the elastic colloidal particles in the mixed particles is (27-34):(1.5-2.5), which can be preferably (27-34):(1.5-2.0), and further preferably (27-30):(1.5-2.0). The mass ratio of the first inorganic particles to the second inorganic particles in the mixed particles is 2:(0.8-1.2), preferably 2:(0.9-1.1), and further preferably 2:1.

[0023] It is worth noting that the particle ratio in the mixed particles plays a decisive role in the porosity of the clusters in the mixed particles and the spacing size when the mixed particles are coated on the surface of the separator: When the ratio of the elastic colloidal particles in the mixed particles is too high, the elastic colloidal particles will occupy the supporting space of the inorganic particles, reduce the rigidity of the coating, and cause the separator to shrink more easily at high temperatures, so that the basic performance of the separator does not meet the requirements.

[0024] When the ratio of the elastic colloidal particles in the mixed particles is too low, the pores of the base film are blocked, the air permeability of the separator is reduced, and the ion conductivity of the battery is affected; When the mass ratio of the first inorganic particles to the second inorganic particles in the mixed particles is too small, the number of large particles in the mixed particles is small, and the number of small particles is large, and too many small particles can cause the separator to have too high moisture and be difficult to apply; When the mass ratio of the first inorganic particles and the second inorganic particles in the mixed particles is too large, the pores between the large particles adhered to the elastic colloidal particles in the mixed particles are too large, and the gap between the mixed particles when coated on the surface of the separator is too large, resulting in a high thermal shrinkage of the separator, which is not conducive to the safety of the separator.

[0025] Preferably, the mass ratio of the first inorganic particles and the second inorganic particles in the mixed particles is 2: (0.9-1.1). The defined addition ratio better increases the retention rate of the cycle capacity of the battery, and the thermal shrinkage rate is <5%. The above-mentioned ratio of the first inorganic particles and the second inorganic particles can ensure that the gap between the particles is within a certain range, and the particle size interval and the pore are more stable, which can better reduce the space for the movement of the polymer chain segment at high temperature (shrinkage of the film) to maintain the stability of the thermal shrinkage, and the stable pore structure can delay the drying of the electrolyte, thereby increasing the retention rate. In some examples, the mass ratio of the first inorganic particles and the second inorganic particles is too high, the large particles are too many and the small particles are too few, the distance between the large particles is large, and the shrinkage rate is high during the heating process; in other examples, the mass ratio of the first inorganic particles and the second inorganic particles is too low, the large particles are too few and the small particles are too many, the distance between the particles is small, and the shrinkage rate of the separator is too low during the heating process, the internal resistance of the separator is high, and the ion passing rate of the separator is also reduced.

[0026] [Preparation method of mixed particles] The second aspect of the present application provides a preparation method of the mixed particles according to any one of the first aspect of the present application, comprising the following steps: First mixing step: mixing the first inorganic particles with the elastic colloidal particles; The purpose of this step is to uniformly bond the large-size first inorganic particles on the surface of the elastic colloidal particles to form a structure in which large particles are bonded on the surface of the elastic particles, at this time, there are still large gaps between the large-size first inorganic particles on the surface of the elastic colloidal particles, which cannot be directly used for coating the separator; Second mixing step: adding the second inorganic particles to the particles obtained after the first mixing step and mixing and dispersing to obtain mixed particles; In this step, the added second inorganic particles are small in size, a part of the second inorganic particles are used to fill the gaps between the large-size first inorganic particles on the surface of the elastic colloidal particles to form clusters with large size and elasticity; another part of the second inorganic particles still scatter in the mixed particles, which are used to fill the gaps between the cluster particles when coating the separator to reduce the thermal shrinkage rate of the separator.

[0027] As a preferred embodiment of any one of the second aspect of the present application, the mixing speed in the first mixing step is 800-1500 rpm.

[0028] As a preferred embodiment of any of the technical solutions of the second aspect of the present application, the speed of mixing in the second mixing step is 800-1500 rpm.

[0029] As a preferred embodiment of any of the technical solutions of the second aspect of the present application, the first inorganic particles are mixed with the elastic colloidal particles after being treated with ammonium hydroxide. After being treated with ammonium hydroxide, the first inorganic particles repel each other due to the negative charges on the surface of the first inorganic particles, and a potential balance is formed between the first inorganic particles. When the elastic colloidal particles are mixed with the first inorganic particles, the dispersion and distribution of the first inorganic particles on the surface of the elastic colloidal particles are facilitated, and the agglomeration between the first inorganic particles is less likely to occur. In addition, the elastic colloidal particles are more uniformly distributed on the surface of the boehmite due to the combination of the elastic colloidal particles and the hydroxyl groups on the surface of the boehmite through hydrogen bonds, thereby improving the collapse of the edge and the depression of the middle of the membrane surface, and improving the performance and safety of the battery.

[0030] Preferably, the mass ratio of the ammonium hydroxide to the first inorganic particles is 0.005-0.01:1.

[0031] Preferably, the mixing condition in the first mixing step is mixing in pure water (ammonium hydroxide is added first, and then the inorganic particles are added).

[0032] Preferably, the mixing condition in the second mixing step is high-speed dispersion, and the inorganic particles and the elastic colloidal particles are uniformly distributed.

[0033] In some cases, the mixed particles obtained can be dried by using the drying methods in the prior art, for example, by using freeze-drying, vacuum drying, etc.

[0034] [Slurry of mixed particles] The third aspect of the present application provides a slurry of mixed particles for coating a lithium battery separator, which comprises the mixed particles according to any of the technical solutions of the first aspect of the present application and a binder; and the solid content of the slurry is 29%-35% (for example, it can be 29%, 30%, 31%, 32%, 33%, 34%, or 35%). The solid content is conducive to forming a coating layer with good flatness and low thermal shrinkage after the slurry is coated on the surface of the separator.

[0035] As a preferred embodiment of any of the technical solutions of the third aspect of the present application, the binder comprises an acrylic binder and an acrylate binder.

[0036] As a preferred embodiment of any of the technical solutions of the third aspect of the present application, the slurry of mixed particles further comprises a wetting agent. Preferably, the wetting agent is a polyalkylene oxide wetting agent, and more preferably, the wetting agent is a polyether-modified polysiloxane.

[0037] As a preferred embodiment of any of the technical solutions of the third aspect of the present application, the slurry comprises:

[0038] As a preferred embodiment of any of the third aspect of the present application, the ammonium hydroxide has a solid content of 50%, and the viscosity of the acrylic binder is generally less than 50 mPa·s, for example, the viscosity is 22-25 mPa·s, and there is no special restriction on the manufacturer and model, and a conventional 45% acrylic emulsion can be purchased.

[0039] As a preferred embodiment of any of the third aspect of the present application, the viscosity of the acrylic ester binder is 1000-1200 mPa·s, and the solid content is 20-25%. In the slurry, it plays a role in reducing the shrinkage of the separator at high temperature and improving the peeling strength.

[0040] [Preparation method of mixed particle slurry] The fourth aspect of the present application provides a preparation method of the mixed particle slurry of any of the third aspect of the present application, comprising the following steps: The acrylic binder, the acrylic ester binder and the polyalkylene oxide wetting agent are added to the mixed particles obtained by any of the third aspect of the present application, and the slurry is obtained after uniform dispersion.

[0041] [Composite separator] The fifth aspect of the present application provides a composite separator, comprising a base film and a coating layer located on both sides of the base film; The coating layer comprises the mixed particles of any of the first aspect of the present application; the thickness of the coating layer is 1-5 μm, preferably 1-3 μm.

[0042] The prior art process cannot make the high molecular material and inorganic particles be limitedly distributed in the coating layer. In the present application, due to the bimodal distribution of the particle size of the mixed particles, the small-size second inorganic particles fill the pores between the elastic colloidal particles and the large-size first inorganic particles on the cluster particles, and the pores between the cluster particles, so that the coating layer has large-size cluster particles for filling the recessed parts of the separator, small-size second inorganic particles for paving on the flat parts of the separator, and forms a relatively dense and small-gap coating layer on the surface of the separator, while ensuring the high flatness and low thermal shrinkage of the separator.

[0043] Preferably, the single-sided thickness of the coating layer is 2±0.5 μm. For example, 1.5-2.5 μm, 1.6-2.4 μm, 1.8-2.2 μm.

[0044] As a preferred embodiment of any of the fifth aspect of the present application, the base film is selected from one of polyethylene (PE), polypropylene (PP), polyamide (PA), polyimide (PI), and aramid (AF); The porosity of the base film is 35-55%; The thickness of the base film is 3-10 μm.

[0045] It is worth noting that the mixed particles of the present application are particularly suitable for base films with a porosity of 35% to 55%. When applied to base films with too low porosity and too high porosity, although the flatness and depression problems of the separator can still be improved, the disadvantage of too high air permeability value will be caused.

[0046] Preferably, the porosity is selected from any of the following groups: 40% to 55%, 43% to 55%, 45% to 55%, 48% to 55%, 50% to 55%; 40% to 50%, 43% to 50%, 45% to 50%, 48% to 50%; 40% to 45%, 43% to 45%; 40% to 43%.

[0047] Most preferably, the porosity of the base film is 40% to 43%.

[0048] Preferably, the thickness of the base film is 5 to 10 μm, more preferably 7 to 9 μm.

[0049] As a preferred embodiment of any of the technical solutions of the fifth aspect of the present application, the coating further comprises an acrylic binder, an acrylate binder and a wetting agent.

[0050] [Method for preparing the composite separator] The sixth aspect of the present application provides a method for preparing the composite separator of any of the technical solutions of the fifth aspect of the present application, comprising the step of coating the slurry of any of the technical solutions of the third aspect of the present application on both sides of the separator by using a gravure roll coating process.

[0051] As a preferred embodiment of any of the technical solutions of the sixth aspect of the present application, the temperature of the coating process is 80±10℃, and the coating speed is 120±20 m / min.

[0052] Preferably, the temperature of the coating process is 75 to 90℃.

[0053] Preferably, the coating speed is 110 to 130 m / min.

[0054] [Lithium ion battery] The seventh aspect of the present application provides a lithium ion battery, comprising: a positive electrode; a negative electrode; an electrolyte; and the composite separator of any of the fifth aspect of the present application.

[0055] As a preferred embodiment of any of the technical solutions of the seventh aspect of the present application, the positive electrode is selected from one of high-nickel ternary, lithium iron phosphate and lithium cobaltate.

[0056] As a preferred embodiment of any of the technical solutions of the seventh aspect of the present application, the negative electrode is selected from one of natural graphite, artificial graphite, silicon-based materials, and lithium metal.

[0057] As a preferred embodiment of any of the technical solutions of the seventh aspect of the present application, the electrolyte is selected from one of a conventional lithium salt, a high-concentration electrolyte (LiFSI), and a solid / semi-solid electrolyte.

[0058] 3. Beneficial effects Compared with the prior art, the present application has the following beneficial effects: (1) The mixed particles for coating the lithium battery separator provided by the present application use an elastic colloid with a specific particle size as part of the support framework, and the first inorganic particles and the second inorganic particles with different sizes are used in combination with the elastic colloid. The mixed particles have a proper size and a bimodal particle size difference in the range of 3.0-6.0 μm, which makes the distribution state (proper spacing of large and small particles) and structure of the mixed particles as a coating more stable. After being coated on the base film, the mixed particles can significantly improve the strength and support of the separator. The distribution state of the elastic colloid directly contacting and bonding with the large particles (first inorganic particles) plays a strong supporting role, and the small particle size inorganic particles (second inorganic particles) fully fill the gaps between the elastic colloid and the large particle inorganic particles, making the entire coating more compact after being coated, thereby improving the collapse and flatness of the film surface and effectively solving the problems of edge collapse and middle depression of the separator after being placed in different environments. At the same time, the coating of the mixed particles can improve the flatness, hardness, and heat resistance of the separator without affecting other performance of the battery. (2) Further, the overall size of the mixed particles is controlled in the range of D10 0.15-0.35 μm, median particle size D50 2.0-3.5 μm, and D90 8.0-10.0 μm, which is beneficial for the mixed particles to be applied to a base film with a porosity of 35%-55%. The coating of the mixed particles can improve the flatness, hardness, and heat resistance of the separator without affecting other performance (such as air permeability) of the battery. (3) The molecular weight of the elastic colloid particles is 200 W-350 W, which can ensure the adhesion of the elastic colloid particles and the influence on the air permeability after being coated on the base film, and ensure that the cycle rate of the separator is not affected. (4) The preparation method of the mixed particles of the present application adopts a two-step mixing process. First, large-sized first inorganic particles are mixed with elastic colloidal particles, so that the first inorganic particles are uniformly bonded to the surface of the elastic particles, forming a structure in which large particles are bonded to the surface of the elastic particles. Then, the particle structure is mixed with small-sized second inorganic particles, so that a part of the second inorganic particles are used to fill the gaps between the large-sized first inorganic particles on the surface of the elastic colloidal particles, forming clusters with large size and elasticity. Another part of the second inorganic particles still scatters in the mixed particles, and is used to fill the gaps between the cluster particles when the separator is coated. The mixed particles prepared by the two-step mixing process have a bimodal distribution of particle size, and can effectively improve the technical problems of the collapse of the edge and the depression of the middle of the separator film, and reduce the thermal shrinkage rate of the separator.

[0059] (5) The composite separator of the present application has a significantly improved effect of reducing the collapse of the edge and the depression of the middle of the film, while ensuring the high flatness and low thermal shrinkage rate of the separator.

[0060] (6) In some preferred embodiments of the present application, different particle sizes of inorganic particles and polymer particles are selected and mixed in a specific process to optimize the distribution state of the inorganic particles and the polymer particles to form mixed particles. The specific distribution state and the spacing of the particles of different sizes in the mixed particles can significantly improve the strength and support of the separator after the mixed particles are coated on the base film as a coating, and the battery conductivity and capacity performance are more excellent. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is a schematic diagram of the composite separator prepared in Example 1 of the present application; Figure 2 is a particle size distribution diagram of the mixed particles of Example 1 of the present application; Figure 3 is a particle size distribution diagram of the mixed particles of Example 2 of the present application; Figure 4 is a particle size distribution diagram of the mixed particles of Example 3 of the present application; Figure 5 is a particle size distribution diagram of the mixed particles of Comparative Example 1 of the present application; Figure 6 is a particle size distribution diagram of the mixed particles of Comparative Example 2 of the present application; Figure 7 is a particle size distribution diagram of the mixed particles of Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0063] Unless otherwise indicated, conventional conditions or manufacturer's recommendations were used in the examples. Where used reagents or instruments are not specified, they are conventional products available commercially.

[0064] As used herein, the term "about" is used to provide flexibility to a numerical range endpoint by providing support for a somewhat greater or lesser inclusion of the numerical value as appropriate for a given term, measurement or value. One of skill in the art can readily determine what is "about" in a given context.

[0065] Concentrations, amounts, and other numerical data can be presented herein in a range format. It is to be understood that such range format is used only for convenience and brevity and should be construed as having been followed to the rightmost significant figure of the numerical value that immediately precedes such range format. However, this range format is not to be construed as a representation that the numerical values are continuous within the stated range. To the contrary, specific numerical values within the described range are not implied or should not be inferred. Any numerical value, however, can be expressed as approximately or approximately by applying the term about to the numerical value. For example, about 1 to about 4.5 should be interpreted as meaning that the numerical value can be anywhere within the range from 1 to 4.5, including the individual numbers (e.g., 2, 3, 4) and sub-ranges (e.g., 1-3, 2-4, etc.) within the range. The same principles apply to ranges that are stated only in one numerical value, such as "less than about 4.5," which should be interpreted to include all of the values and ranges described above. In addition, this interpretation should apply regardless of the breadth of the range or the characteristics being described.

[0066] Instrument: Test Method: Particle Size: Laser Particle Size Analyzer Using a laser particle size analyzer (Dandong Bettersize, BT-2600E), select wet method to test, fully stir the slurry to be tested, take an appropriate amount into a beaker, dilute with pure water, and stir evenly, put into an ultrasonic cleaner, ultrasonic for 8 minutes, when prompted to add sample, slowly add the diluted slurry into the wet sample injector with a dropper, and observe the light shielding degree, light shielding degree 8-10, test to get the D V 10 (D10), D V 50 (D50), D V 90 (D90).

[0067] Flatness: Wave Edge Tester Cut the finished product diaphragm sample with a length of 1.5 m and place it on the designated position on the wave edge tester (Shenzhen Weijiang Test Technology Co., Ltd.), start the instrument to automatically search for the edge test, the laser starts from the left edge of the film as the starting point, moves to the right end of the film, and locates the end point. At this time, the screen displays the diaphragm width, and the laser returns. After the laser returns to the starting point, the actual wave edge measurement is performed. As the measurement proceeds, the screen interface displays the real-time state of the film surface fluctuation. After the test is completed, the laser returns to zero. According to the test chart, the numbers at the left, middle and right positions on the chart are read respectively, and the wave edge is calculated: Median value: median diaphragm height difference (the distance value between the middle lowest point and the overall highest point); Edge value: edge diaphragm height difference (the distance value between the edge lowest point and the overall highest point).

[0068] Flatness: The maximum deformation value (unit: mm) in the above measured values.

[0069] Heat shrinkage: electric heating air drying oven According to the requirements of GB / T36363-2018, cut a sample with a size of 10 cm x 10 cm, mark the horizontal TD and vertical MD on the sample, measure the horizontal and vertical width with a full-automatic image measurement projector (Kunshan Gaoping Precision Instrument Co., Ltd., GP-300C), clamp the sample between two sealed A4 papers, place the sample in a 150℃ oven for 1h, and then measure the horizontal and vertical width with a full-automatic image measurement projector after the sample returns to room temperature. Measure 3 times and take the average value: MD heat shrinkage (%) = (MD length before heating - MD length after heating) ÷ MD length before heating x 100%.

[0070] Conductivity test: The electrochemical impedance spectroscopy (EIS) test system is tested according to the method specified in NB / T10827-2021. A sample with a size of φ19mm (φ19mm represents that the diameter of the circular sample is 19mm) is cut, and a CR2016 button cell positive and negative electrode shell is assembled into a button cell, wherein the electrolyte is LiPF61mol / L, EC:EMC=3:7, and VC=2.0wt%. The button cell is assembled in the order of negative electrode shell, separator, gasket (φ15.8*0.5mm, i.e. the diameter of the gasket is 15.8mm and the thickness is 0.5mm), wave spring, and positive electrode shell, 4 drops of electrolyte are dropped using a 1mL dropper to fully wet the separator, sealed with a sealing machine, and the electrolyte on the surface of the button cell is wiped clean with alcohol, and placed for 3h. Turn on the electrochemical workstation (Metrohm, PGSTAT204), select “impedance test” for testing, wherein the lower limit of the frequency is 10000Hz, the upper limit of the frequency is 100000Hz, and the current is 100mA. The resistance values of the batteries composed of one, two, three, and four layers of separators are tested, and three sets of parallel data are tested for each group of samples. The slope of the curve with a fitting degree of ≥0.99 is the resistance value R (Ω) of the separator, and the ion conductivity of the separator is d / (R*A) (S / cm), wherein d is the thickness of the separator, the unit is cm, and A is the effective area of the gasket, the unit is cm 2 .

[0071] The application will be further described below in combination with specific examples.

[0072] Example 1 In this example, mixed particles, slurry and composite separator are prepared, and the specific raw materials and components are as follows:

[0073] Step one: preparation of mixed particles (1) uniformly disperse the first inorganic particles and ammonium hydroxide dispersant in pure water; (2) add elastic colloidal particles to the above mixture, mix under high-speed (1000rpm) dispersion conditions for 40min; (3) add the second inorganic particles to the mixture, and disperse at high speed (1000rpm) for 20min to obtain the mixed particles.

[0074] Step two: preparation of mixed particle slurry (4) add acrylic acid binder, acrylic ester binder and wetting agent to the mixed particles obtained in step (3), and stir uniformly to obtain coating slurry A, and the solid content of the slurry is 32.48%.

[0075] Step three: preparation of composite separator (5) The coating slurry A was coated on both sides of the polyethylene (PE) base film with a porosity of 40% and a thickness of 9 μm by using the gravure roll coating process, and the coating thickness was controlled at 2 μm on each side. During the coating process, the temperature was controlled at 85°C, and the coating speed was 130 m / min, thereby obtaining the composite separator.

[0076] Step four: Test of the properties of the mixed particles and the composite separator The coated composite separator was tested: (6) The coverage of the small particles (second inorganic particles) on the elastic colloidal particles and the coverage of the large particles (first inorganic particles) on the elastic colloidal particles in the mixed particles were observed by using the scanning electron microscope. The results showed that part of the mixed particles were cluster particles with a larger size, and part of the mixed particles were second inorganic particles with a smaller size. The coverage of the large particles on the elastic colloidal particles was about 76%, and the coverage of the small particles on the elastic colloidal particles was about 72%. It was observed that the distance between the particles was in the range of 50-100 nm.

[0077] (7) Test of the particle size of the mixed particles in the coating slurry A The schematic diagram of the mixed particles is shown in Figure 1 .

[0078] As shown in Figure 2 , the results showed that the particle size of the mixed particles was in a bimodal distribution, in which D10 was 0.210 μm, D50 was 2.513 μm, and D90 was 8.235 μm. The difference between the particle sizes of the two peaks was about 5.2 μm.

[0079] (8) The flatness of the coated film was tested, the thermal shrinkage rate was tested, and the electrical conductivity was tested.

[0080] The flatness test results showed that there was no obvious collapse at the edge of the film surface, and there was no concave phenomenon in the middle part, and the flatness was ≤1 mm. The thermal shrinkage rate test results showed that the shrinkage degree of the separator was less than 5% in the MD direction at 150°C for 1 h, and the specific values are shown in Table 1.

[0081] Example 2 In this example, mixed particles, a slurry and a composite separator were prepared, and the specific raw materials and components are as follows:

[0082] Step one: Preparation of the mixed particles (1) The first inorganic particles and the ammonium hydroxide dispersant were uniformly dispersed in pure water; (2) The elastic colloidal particles were added to the above mixture, and the mixture was mixed at a high speed (1000 rpm) for 40 min; (3) The second inorganic particles were added to the mixture, and the mixture was dispersed at a high speed (1000 rpm) for 20 min, thereby obtaining the mixed particles.

[0083] Step two: preparation of mixed particle slurry (4) Add acrylic binder, acrylate binder and wetting agent to the mixed particles obtained in step (3), and stir uniformly to obtain coating slurry B, with a solid content of 32.6%.

[0084] Step three: preparation of composite separator (5) Use gravure roll coating process to coat both sides of the coating slurry B on a polyethylene (PE) substrate with a porosity of 38% and a thickness of 9 μm, and control the coating thickness on one side to be 2 μm. During the coating process, the temperature is controlled at 90°C, and the coating speed is 110 m / min. The composite separator is obtained.

[0085] Step four: test of properties of mixed particles and composite separator The coated composite separator is tested: (6) Estimate the coverage of small particles on the elastic colloidal particles and the coverage of large particles on the elastic colloids in the mixed particles by scanning electron microscopy observation. The results show that part of the mixed particles are larger size cluster particles, and part are smaller size second inorganic particles. The coverage of large particles on the elastic colloids is about 77%, and the coverage of small particles on the elastic colloidal particles is about 70%. The particle spacing is observed to be in the range of about 50-100 nm.

[0086] (7) Test the size of the mixed particles of coating slurry B As shown in Figure 3 , the results show that the particle size of the mixed particles is bimodal distribution, with D10 of 0.2606 μm, D50 of 2.712 μm, D90 of 8.713 μm, and a particle size difference of the bimodal peaks of about 4.4 μm.

[0087] (8) Test the flatness of the coated film, the thermal shrinkage rate, and the electrical conductivity.

[0088] The flatness test results show that there is no obvious collapse at the edge of the film surface, and there is no concave phenomenon in the middle, with a flatness of ≤1 mm. The thermal shrinkage rate test results show that the deformability of the separator is less than 5% at 150°C, and the specific values are shown in Table 1.

[0089] Example 3 In this example, mixed particles, slurry and composite separator are prepared, and the specific raw materials and components are as follows:

[0090] Step one: preparation of mixed particles (1) Disperse the first inorganic particles and ammonium hydroxide dispersant uniformly in pure water; (2) Adding elastic colloidal particles to the above mixture, mixing for 40 min under high speed (1000 rpm) dispersion condition; (3) Adding second inorganic particles to the mixture, mixing for 20 min under high speed (1000 rpm) dispersion condition to obtain mixed particles.

[0091] Step two: Preparation of mixed particle slurry (4) Adding acrylic binder, acrylate binder and wetting agent to the mixed particles obtained in step (3), and stirring uniformly to obtain coating slurry C, with solid content of 32.02%.

[0092] Step three: Preparation of composite separator (5) Using gravure roll coating process to coat coating slurry C on both sides of a polyethylene (PE) substrate with porosity of 42% and thickness of 9 μm, and controlling the coating thickness on one side to be 2 μm. During the coating process, the temperature is controlled at 80℃, and the coating speed is 120 m / min, to obtain a composite separator.

[0093] Step four: Test of properties of mixed particles and composite separator The coated composite separator is tested: (6) Estimating the coverage of small particles on elastic colloidal particles and the coverage of large particles on elastic colloidal particles in the mixed particles by SEM observation method. The results show that part of the mixed particles are large-sized cluster particles, and part of them are small-sized second inorganic particles; the coverage of large particles on elastic colloidal particles is about 75%, and the coverage of small particles on elastic colloidal particles is about 75%. It is observed that the particle spacing is about 50-100 nm.

[0094] (7) Test of particle size of mixed particles of coating slurry C As Figure 4 , the results show that the particle size of the mixed particles is bimodal distribution, in which D10 is 0.212 μm, D50 is 2.531 μm, D90 is 8.615 μm, and the particle size difference of the bimodal peaks is about 5.0 μm.

[0095] (8) Test of flatness of coated film surface, heat resistance, and conductivity.

[0096] The flatness test results show that there is no obvious collapse at the edge of the film surface, and there is no concave phenomenon in the middle, and the flatness is ≤1 mm. The heat shrinkage test results show that the deformability of the separator is less than 5% at 150℃, and the specific values are shown in Table 1.

[0097] Comparative Example 1 In this comparative example, mixed particles, slurry and composite separator are prepared, and the specific raw materials and components are as follows:

[0098] Steps 1 and 2 combined: Preparation of mixed granular slurry (1) Mix the first inorganic particles and the second inorganic particles; (2) Add ammonium hydroxide (dispersant) to the above mixture and mix; (3) Add acrylic binder, acrylate binder and wetting agent to the mixed particles obtained in step (2) and stir until uniform; (4) Add elastic colloidal particles and mix for 20 min under high speed (1000 rpm) dispersion conditions to obtain coating slurry D with a solid content of 32.98%.

[0099] Step 3: Preparation of the composite membrane (5) The coating slurry D was coated on both sides of a polyethylene (PE) substrate with a porosity of 40% and a thickness of 9 μm using a gravure roller coating process. The coating thickness on one side was controlled at 2 μm. During the coating process, the temperature was controlled at 85℃ and the coating speed was 130 m / min to obtain a composite diaphragm.

[0100] Step 4: Testing the properties of mixed particles and composite membranes The coated composite membrane was then tested. (6) The coverage of small particles and large particles on the elastic colloidal particles in the mixed particles was estimated by scanning electron microscopy. The results showed that some of the mixed particles were large-sized cluster particles and some were small-sized secondary inorganic particles. The coverage of large particles on the elastic colloidal particles was about 61%, and the coverage of small particles on the elastic colloidal particles was about 73%. It was observed that the interparticle spacing was mostly less than 50 nm.

[0101] (7) Test of particle size of coating slurry D like Figure 5 As shown, the results indicate that the particle size of the mixed particles exhibits a bimodal distribution, with D10 being 0.412 μm, D50 being 4.838 μm, and D90 being 11.293 μm. The difference in particle size between the peak values ​​of the two peaks is approximately 3.7 μm.

[0102] (8) Conduct tests on the flatness of the coated film surface, the heat shrinkage rate, and the electrical conductivity.

[0103] The flatness test results showed that there was still collapse at the edges of the membrane surface and concavity in the middle, with a flatness greater than 1 mm. The heat shrinkage test results showed that the membrane could deform by more than 5% at 150℃ for 1 hour, and the specific values ​​are shown in Table 1.

[0104] Conclusion: When the ratio of large to small particles is 1:1, an excessively high proportion of small particles will result in excessive air and moisture permeability and excessive internal resistance in the diaphragm.

[0105] Comparative Example 2 The comparative example prepared a mixed particle, slurry and composite diaphragm, the specific raw materials and components are as follows:

[0106] Step one: preparation of mixed particles (1) uniformly disperse the first inorganic particles and ammonium hydroxide dispersant in pure water; (2) add elastic colloidal particles to the above mixture, mix under high speed (1000 rpm) dispersion condition for 40 min; (3) add the second inorganic particles to the mixture, disperse at high speed (1000 rpm) for 20 min, to obtain the mixed particles.

[0107] Step two: preparation of mixed particle slurry (4) add acrylic adhesive, acrylic ester adhesive and wetting agent to the mixed particles obtained in step (3), stir uniformly to obtain coating slurry E, the solid content is 32.23%.

[0108] Step three: preparation of composite diaphragm (5) use gravure roll coating process to coat the coating slurry E on both sides of the polyethylene (PE) substrate with a porosity of 40% and a thickness of 9 μm, control the coating thickness on one side to be 2 μm. During the coating process, the temperature is controlled at 85°C, and the coating speed is 130 m / min, to obtain the composite diaphragm.

[0109] Step four: test the properties of mixed particles and composite diaphragm Test the coated composite diaphragm: (6) estimate the coverage of small particles on elastic colloidal particles and the coverage of large particles on elastic colloidal particles in the mixed particles by scanning electron microscope observation method; the results show that part of the mixed particles are larger size cluster particles, and part are smaller size second inorganic particles; the coverage of large particles on elastic colloidal particles is about 80%, and the coverage of small particles on elastic colloidal particles is about 50%. It is observed that the particle spacing is mostly greater than 100 nm.

[0110] (7) test the size of mixed particles of coating slurry E See Figure 6 The results show that the particle size of the mixed particles is bimodal distribution, in which D10 is 0.205 μm, D50 is 2.393 μm, D90 is 7.261 μm, and the particle size difference of the bimodal peaks is about 3.8 μm.

[0111] (8) test the flatness of the coated film, the thermal shrinkage rate and the conductivity.

[0112] The flatness test results show that there is collapse at the edge of the membrane surface and depression in the middle, and the flatness is >1 mm. The thermal shrinkage test results show that the deformability of the separator is >5% at 150°C for 1 h, and the specific values are shown in Table 1.

[0113] Conclusion: When the ratio of large and small particles is 3:1, the thermal shrinkage will increase and the deformation of the separator will increase if the ratio of large particles is too high.

[0114] Comparative Example 3 The specific raw materials and components of this comparative example are as follows:

[0115] Steps: (1) The first inorganic particles and ammonium hydroxide (dispersant) were uniformly dispersed in pure water; (2) The second inorganic particles were added to the mixture, and high-speed (1000 rpm) dispersion was performed for 20 min to obtain mixed particles, wherein the mixed particles were normally distributed (see Figure 7 ) with a size of D10: 0.232 μm; D50: 0.495 μm; and D90: 1.753 μm.

[0116] (3) The mixed particles obtained were added with acrylic binder, acrylic ester binder, and wetting agent, and after uniform stirring, coating slurry F was obtained, with a solid content of 32.33%.

[0117] (4) The coating slurry F was coated on both sides of a polyethylene (PE) separator base film with a porosity of 40% and a thickness of 9 μm using a gravure roll coating process, and the coating thickness was controlled at 2 μm on one side. During the coating process, the temperature was controlled at 85°C, and the coating speed was 130 m / min, to obtain a composite separator.

[0118] Test results: see Table 1.

[0119] The flatness test results show that there is collapse at the edge of the membrane surface and depression in the middle, and the flatness is >1 mm. The thermal shrinkage test results show that the deformability of the separator is ≤5% at 150°C for 1 h.

[0120] Conclusion: When no elastic particles are added, the mixed particles are unimodal distribution, the gap between the particles becomes smaller, the resistance increases, and the support force becomes poor.

[0121] Comparative Example 4 The specific raw materials and components of this comparative example are as follows:

[0122] Steps: (1) The first inorganic particles and ammonium hydroxide (dispersant) were uniformly dispersed in pure water; (2) Adding elastic colloidal particles to the above mixture, mixing for 40 min under high-speed (1000 rpm) dispersion condition to obtain mixed particles, wherein the mixed particle size is: D10: 0.351 μm; D50: 0.895 μm; D90: 2.799 μm; (3) Adding acrylic binder, acrylate binder and wetting agent to the obtained mixed particles, stirring uniformly to obtain coating slurry G, and the solid content of the coating slurry G is 33.48%. (4) Using a gravure roll coating process, the coating slurry G is coated on both sides of a polyethylene (PE) separator base film with a porosity of 40% and a thickness of 9 μm, and the coating thickness is controlled to be 2 μm on a single side. During the coating process, the temperature is controlled to be 85°C, and the coating speed is 130 m / min, to obtain a composite separator.

[0123] Test results: see Table 1.

[0124] The flatness test results show that there is a collapse on the edge of the film surface, and the middle part is concave, and the flatness is >1. The heat shrinkage test results show that the deformability of the separator is >5% at 150°C for 1 h.

[0125] Conclusion: When no small particles are added, the gap between the particles is too large, the heat shrinkage is high, and the deformation of the separator after heating is serious.

[0126] Comparative Example 5 The specific raw materials and components of this comparative example are as follows:

[0127] Steps: (1) Uniformly dispersing the second inorganic particles and ammonium hydroxide (dispersant) in pure water; (2) Adding elastic colloidal particles to the above mixture, mixing for 40 min under high-speed dispersion condition; (3) The obtained mixed particles are normally distributed (D10: 0.152 μm; D50: 0.395 μm; D90: 1.253 μm), and acrylic binder, acrylate binder and wetting agent are added, and the coating slurry H is obtained after stirring uniformly, and the solid content of the coating slurry H is 32.48%.

[0128] (4) Using a gravure roll coating process, the coating slurry H is coated on both sides of a polyethylene (PE) separator base film with a porosity of 40% and a thickness of 9 μm, and the coating thickness is controlled to be 2 μm on a single side. During the coating process, the temperature is controlled to be 85°C, and the coating speed is 130 m / min, to obtain a composite separator.

[0129] Test results: see Table 1.

[0130] The flatness test result shows that there is collapse at the edge of the film surface and depression in the middle, and the flatness is >1mm. The heat resistance test result shows that the deformability of the diaphragm is ≤5% at 150℃ for 1h.

[0131] Conclusion: Without increasing the particle size, the gap between the particles becomes smaller, the resistance increases, and the diaphragm support force becomes poor.

[0132] The test performance data of each diaphragm in the above examples and comparative examples are shown in Table 1 below: Table 1 Summary of test performance data of each in the examples and comparative examples

[0133] The results of Examples 1-3 show that the performance and flatness of the diaphragm are best improved when the size ratio of the inorganic particles is about 2:1, the slurry is prepared by the two-step mixing method, and then coated.

[0134] Comparative Example 2 shows that when the proportion of the first inorganic particles is too high, the flatness of the coated diaphragm is improved, but the improvement is limited, and the thermal shrinkage rate (MD) is >5%.

[0135] Comparative Examples 3-5 show that the elastic particles, the first inorganic particles, and the second inorganic particles are indispensable, otherwise the ideal bimodal distribution of the mixed particles cannot be formed, and the flatness of the coated diaphragm is not significantly improved.

[0136] The above content is a schematic description of the present application and its embodiments, which is not restrictive. The examples shown are only one of the embodiments of the present application, and the actual implementation is not limited thereto. Therefore, if a person skilled in the art is inspired by it, without departing from the purpose of the present application, similar embodiments and examples can be designed without creative design, which should belong to the protection scope of the present application.

Claims

1. Mixed particles for coating a lithium-ion battery separator, characterized in that, comprise a first particle and a second particle; the first particle comprises a cluster of a first inorganic particle, a second inorganic particle and an elastic colloidal particle; the first inorganic particle is an inorganic oxide particle with a median particle size D50 of 0.8 μm to 1.0 μm; the second inorganic particle is an inorganic oxide particle with a median particle size D50 of 0.2 μm to 0.4 μm; the elastic colloidal particle has a median particle size D50 of 6.0 μm to 8.0 μm; the second particle comprises a second inorganic particle; the particle size of the mixed particles is in a bimodal distribution, and the particle size difference between the two peaks of the bimodal distribution is 3.0 μm to 6.0 μm.

2. The mixed particles according to claim 1, characterized in that, the D10 of the mixed particles is 0.15 μm to 0.35 μm, the median particle size D50 is 2.0 μm to 3.5 μm, and the D90 is 8.0 μm to 10.0 μm.

3. The mixed particles according to claim 1, characterized in that, the elastic colloidal particle is selected from one or more of an acrylate resin, a silicone glue, a polyurethane glue or an epoxy resin modified glue, and the molecular weight of the elastic colloidal particle is 200 W to 350 W, preferably 250 W to 350 W; the particle size of the elastic colloidal particle is D10: 3.5 μm to 5.8 μm, D50: 6.0 μm to 8.0 μm, D90: 9.0 μm to 11.0 μm, and DMAX: 12.0 μm to 14.0 μm.

4. The mixed particles of claim 1, wherein the first inorganic particle or the second inorganic particle is selected from one or more of alumina, boehmite, magnesium oxide, silicon oxide and titanium oxide; optionally, the particle size of the first inorganic particle is D10: 0.25 μm to 0.45 μm, D50: 0.8 μm to 1.0 μm, and D90: 1.5 μm to 1.8 μm; and the particle size of the second inorganic particle is D10: 0.05 μm to 0.18 μm, D50: 0.2 μm to 0.4 μm, and D90: 0.5 μm to 1.0 μm.

5. The mixed particles of claim 1, wherein the mass ratio of the first inorganic particle and the second inorganic particle to the elastic colloidal particle in the mixed particles is (27 to 34):(1.5 to 2.5); the mass ratio of the first inorganic particle to the second inorganic particle in the mixed particles is 2:(0.8 to 1.2).

6. The method of producing the mixed granules according to any one of claims 1 to 5, characterized by, comprising the following steps: a first mixing step of mixing the first inorganic particle with the elastic colloidal particle; a second mixing step of adding the second inorganic particle to the particles obtained after the first mixing step and mixing and dispersing to obtain the mixed particles.

7. The production method according to claim 6, wherein the first inorganic particle is treated with ammonium hydroxide before being mixed with the elastic colloidal particle.

8. A mixed particle slurry for coating a lithium battery separator, characterized by, comprising the mixed particles according to any one of claims 1 to 5 and a binder; the solid content of the slurry is 29% to 35%.

9. A composite separator, characterized by, comprising a base film and a coating layer on both sides of the base film; the coating layer comprises the mixed particles according to any one of claims 1 to 5; the thickness of the coating layer is 1 μm to 5 μm; the thickness of the base film is 3 μm to 10 μm.

10. A lithium-ion battery, characterized by, comprising: a positive electrode; a negative electrode; an electrolyte; and the composite separator according to claim 9.

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