Composite coated separator and preparation method therefor, and lithium-ion battery comprising same

Abstract

A composite coated separator and a preparation method therefor, and a lithium-ion battery comprising same. The composite coated separator comprises a substrate film and a coating layer formed on at least one surface of the substrate film, wherein the coating layer comprises aramid fibers and an inorganic filler, the inorganic filler fills in a three-dimensional network structure formed by the aramid fibers, and the filling rate of the coating layer is 80-98%, the filling rate of the coating layer being equal to 100% × (1 - area of the inorganic filler exposed on the surface of the coating layer / area of the coating layer). In the composite coating separator, the filling rate of the inorganic filler in the coating layer is appropriate, and the coating layer has the characteristics of high temperature resistance, air permeability and low tendency for powder shedding.

Description

Composite coated diaphragm and preparation method thereof, and lithium ion battery containing the same Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a composite coating diaphragm for lithium ion batteries and a preparation method thereof. Background Art

[0002] The separator is a key component of lithium-ion batteries, primarily serving as a lithium ion pathway and electronic insulation. Polyolefins (such as PE and PP) are currently the primary material used in commercial lithium-ion battery separators. While they offer advantages in chemical stability, mechanical properties, and cost, as lithium-ion batteries continue to gain traction in electric vehicles, polyolefins' shortcomings in high-temperature resistance and electrolyte wettability have become increasingly prominent, severely reducing the safety performance of lithium-ion batteries and particularly hindering their application in power batteries.

[0003] A common approach to addressing these issues is to apply a high-temperature-resistant and liquid-friendly coating to one or both sides of a polyolefin substrate membrane. The coating is primarily made of inorganic materials or organic polymers. A mixed coating of these inorganic and organic materials can achieve both high-temperature resistance and liquid-friendly properties. However, the coating's air permeability, high-temperature resistance, and powder shedding directly impact its performance. Therefore, research on separator coatings is crucial.

[0004] Summary of the Invention

[0005] The primary purpose of the present invention is to provide a composite coated separator, a method for preparing the same, and a lithium-ion battery containing the same, to overcome the existing problem of the coating layer's inability to achieve a balance between high-temperature resistance, air permeability, and powder shedding resistance. The inventors discovered that by mixing aramid fibers with inorganic fillers to form a coating layer, and maintaining the coating layer filling ratio within a specific range, a coated separator with balanced high-temperature resistance, air permeability, and powder shedding resistance can be obtained.

[0006] The specific plan is:

[0007] A composite coated diaphragm comprises a substrate film and a coating layer formed on at least one surface of the substrate film, wherein the coating layer comprises aramid and an inorganic filler, wherein the inorganic filler is filled in a three-dimensional network structure formed by the aramid, and the coating layer filling rate is 80% to 98%, wherein the coating layer filling rate = 100% × (1-the area of ​​the exposed inorganic filler on the surface of the coating layer / the area of ​​the coating layer).

[0008] In one embodiment, the composite coated diaphragm of the present invention has an air permeability increase per unit thickness of the coating layer of less than 35s / 100cc / μm; the composite coated diaphragm has a heat shrinkage rate in the MD direction of less than 5% and a heat shrinkage rate in the TD direction of less than 1% under the conditions of 120°C and 1h, and a powder loss rate of less than 0.5%.

[0009] In one embodiment of the composite coated diaphragm of the present invention, the substrate film has a thickness of 4-20 μm, an air permeability of 50-500 s / 100 cc, and a porosity of 40-55%; and the coating layer has a thickness of 1-4 μm.

[0010] In one embodiment of the composite coated diaphragm of the present invention, the inorganic filler is selected from at least one of a ceramic material, a nanowire material, or a nanotube material; the ceramic material is selected from one or more of Al2O3, SiO2, TiO2, ZrO2, BaTiO3, MgO, CaO, AlOOH, and SiC; the nanowire material is selected from one or more of carbon nanowires, attapulgite, silver nanowires, boron carbide nanowires, nanocellulose, copper hydroxide nanowires, silicon monoxide nanowires, and hydroxyapatite nanowires; the nanotube material is selected from one or more of carbon nanotubes, silver nanotubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, and hydroxyapatite nanotubes;

[0011] In one embodiment of the composite coated separator of the present invention, the inorganic filler is an inorganic particle having a hydroxyl functional group on the surface; and the particle size of the inorganic filler is 0.01 to 0.5 μm.

[0012] A composite coated diaphragm comprises a substrate film and a coating layer formed on at least one surface of the substrate film. The slurry forming the coating layer comprises an aramid stock solution and an inorganic filler. The rotational viscosity of the aramid stock solution is 2000-4000 mPa·s.

[0013] In one embodiment of the composite coated diaphragm of the present invention, the solid content of the slurry forming the coating layer is 4wt% to 5wt%; the aramid stock solution includes at least one of poly(m-phenylene isophthalamide) and poly(p-phenylene terephthalamide) and a solvent, and the solvent is N-methylpyrrolidone.

[0014] In one embodiment of the composite coated diaphragm of the present invention, the aramid stock solution further comprises an auxiliary agent, which is one or more of CaCl2, KOH, LiCl and pyridine, and the mass content of the auxiliary agent in the aramid stock solution is ≤10%.

[0015] A method for preparing a composite coated diaphragm comprises the following steps:

[0016] An inorganic filler is blended with an organic solvent, subjected to a first high-speed dispersion, and then mixed with an aramid stock solution and subjected to a second high-speed dispersion to obtain a slurry for forming the coating layer; the aramid stock solution has a rotational viscosity of 2000 to 4000 mPa·s, the solid content of the slurry for forming the coating layer is 4 wt% to 5 wt%, the rotation speed of the first high-speed dispersion is 6500 to 10000 r / min, and the time of the first high-speed dispersion is 10 to 60 minutes; the rotation speed of the second high-speed dispersion is 6500 to 10000 r / min, and the time of the second high-speed dispersion is 10 to 60 minutes, and the first high-speed dispersion speed is the same as the second high-speed dispersion speed;

[0017] The slurry is coated on one side or both sides of a substrate film to obtain a composite coating separator.

[0018] In one embodiment of the method for preparing the composite coated diaphragm of the present invention, the organic solvent is N-methylpyrrolidone.

[0019] A lithium-ion battery comprises the composite coated diaphragm or the composite coated diaphragm prepared by the above preparation method.

[0020] Beneficial effects of the present invention:

[0021] The present invention provides a composite coated diaphragm, the coating layer has a suitable filling rate, and the coating layer has the characteristics of high temperature resistance, air permeability and non-powdering properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a schematic diagram of the area where the surface inorganic material is located in the electron microscope photograph of the coating layer of Example 1 selected using the manual selection function of imageJ software.

[0023] The actual area size of the field of view shown in FIG1 is 1024 μm×692 μm.

[0024] Among them, 1-32 are the areas where the surface inorganic material is located in the electron microscope photograph of the coating layer of Example 1, which are selected by manual selection function of imageJ software. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described in detail below. The following implementation methods are implemented based on the technical solution of the present invention and provide a detailed implementation process. However, the protection scope of the present invention is not limited to the following implementation methods. In the following implementation methods, structures or experimental methods without specifying specific conditions are generally based on conventional conditions.

[0026] The present invention provides a composite coated diaphragm, comprising a substrate film and a coating layer formed on at least one surface of the substrate film, wherein the coating layer comprises aramid and an inorganic filler, wherein the inorganic filler is filled in a three-dimensional network structure formed by the aramid, and the coating layer filling rate is 80% to 98%, wherein the coating layer filling rate = 100% × (1-the area of ​​the exposed inorganic filler on the surface of the coating layer / the area of ​​the coating layer).

[0027] The present invention mixes aramid fibers with inorganic materials to form a coating layer. When the filling rate of the coating layer is within a specific range, a coated diaphragm that is resistant to high temperatures, breathable, and anti-powdering can be obtained.

[0028] The present invention does not specifically limit the material of the substrate film; for example, it may be made of polyolefins (such as PE and PP), or it may be a coated substrate film. The present invention also does not specifically limit the thickness of the substrate film; for example, it may be 4-20 μm, preferably 12-14 μm; the air permeability may be, for example, 50-500 s / 100 cc, and the porosity may be 40-55%. Those skilled in the art can prepare the substrate film of the present invention based on existing techniques.

[0029] In the present invention, the coating layer is coated on one side or both sides of the substrate film, that is, the diaphragm of the present invention may include one coating layer coated on one surface of the base film, or may include two coating layers, respectively coated on the two surfaces of the base film, which is not particularly limited in the present invention.

[0030] In one embodiment, the aramid of the present invention is at least one of poly(m-phenylene isophthalamide) (aramid 1313) and poly(p-phenylene terephthalamide) (aramid 1414, aramid II).

[0031] In one embodiment, the inorganic filler of the present invention is selected from ceramic materials, nanowire materials or nanotube materials. The ceramic material can be selected from one or a combination of Al2O3, SiO2, TiO2, ZrO2, BaTiO3, MgO, CaO, AlOOH, and SiC; the nanowire material can be selected from one or more of carbon nanowires, attapulgite, nanosilver wire, boron carbide nanowire, nanocellulose, copper hydroxide nanowire, silicon monoxide nanowire, and hydroxyapatite nanowire; the nanotube material can be selected from one or more of carbon nanotubes, nanosilver tubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, and hydroxyapatite nanotubes; the particle size of the inorganic filler is 0.2 to 0.5 μm, and the inorganic seasoning is preferably an inorganic filler having hydroxyl functional groups on the surface, and the inorganic filler is, for example, an inorganic particle.

[0032] In one embodiment, the thickness of the coating layer of the present invention is 1-4 μm, and the permeability increase per unit thickness of the coating layer is less than 35s / 100cc / μm; the composite coated diaphragm has a heat shrinkage rate in the MD direction of less than 5% under the conditions of 120°C and 1h, a heat shrinkage rate in the TD direction of less than 1%, and a powder loss rate of less than 0.5%.

[0033] The present invention also provides a composite coated diaphragm, comprising a substrate film and a coating layer formed on at least one surface of the substrate film, wherein the slurry forming the coating layer comprises an aramid stock solution and an inorganic filler, and the rotational viscosity of the aramid stock solution is 2000 to 4000 mPa·s.

[0034] By limiting the rotational viscosity of the aramid stock solution, the present invention can ensure that the resulting coating layer has better porosity and enhanced air permeability. Therefore, the composite coated diaphragm of the present invention has excellent physical properties.

[0035] The present invention does not specifically limit the material of the substrate film; for example, it may be made of polyolefins (such as PE and PP), or it may be a coated substrate film. The present invention also does not specifically limit the thickness of the substrate film; for example, it may be 4-20 μm, preferably 12-14 μm; the air permeability may be, for example, 50-500 s / 100 cc, and the porosity may be 40-55%. Those skilled in the art can prepare the substrate film of the present invention based on existing techniques.

[0036] In the present invention, the coating layer is coated on one side or both sides of the substrate film, that is, the diaphragm of the present invention may include one coating layer coated on one surface of the base film, or may include two coating layers, respectively coated on the two surfaces of the base film, which is not particularly limited in the present invention.

[0037] In the present invention, the slurry forming the coating layer includes an aramid stock solution and an inorganic filler. Of course, the slurry contains a solvent, which can be derived from the aramid stock solution or added separately. In one embodiment, the inorganic filler and the solvent are pre-dispersed, then mixed with the aramid stock solution and dispersed again. In one embodiment, the rotation speed of the pre-dispersion of the inorganic filler and the solvent is 6500-10000r / min, and the dispersion speed of the mixed solution of the inorganic filler and the aramid stock solution is 6500-10000r / min. Pre-dispersion of the inorganic filler and dispersion of the mixed solution of the inorganic filler and the aramid stock solution are performed within this speed range, so that the resulting coating layer has high temperature resistance and the coating layer is not easy to fall off. In another embodiment, the solvent is N-methylpyrrolidone (NMP).

[0038] In the present invention, the rotational viscosity of the aramid stock solution is 2000-4000 mPa·s, so that the coating layer has better porosity and the coating layer has better air permeability per unit thickness.

[0039] In one embodiment, the aramid stock solution of the present invention includes at least one of poly(m-phenylene isophthalamide) (aramid 1313) and poly(p-phenylene terephthalamide) (aramid 1414, aramid II) and a solvent, such as N-methylpyrrolidone (NMP). Thus, at least one of poly(m-phenylene isophthalamide) (aramid 1313) and poly(p-phenylene terephthalamide) (aramid 1414, aramid II) is dissolved in the solvent to form a yellow, transparent, uniform liquid.

[0040] In another embodiment, the aramid stock solution further contains an additive, such as one or more of CaCl2, KOH, LiCl and pyridine, and the mass content of the additive is ≤10%.

[0041] The aramid stock solutions with different rotational viscosity values ​​of the present invention may be commercially available products, and the present invention is not particularly limited thereto.

[0042] In one embodiment, the inorganic filler of the present invention is selected from ceramic materials, nanowire materials or nanotube materials. The ceramic material can be selected from one or a combination of Al2O3, SiO2, TiO2, ZrO2, BaTiO3, MgO, CaO, AlOOH, and SiC; the nanowire material can be selected from one or more of carbon nanowires, attapulgite, nanosilver wire, boron carbide nanowire, nanocellulose, copper hydroxide nanowire, silicon monoxide nanowire, and hydroxyapatite nanowire; the nanotube material can be selected from one or more of carbon nanotubes, nanosilver tubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, and hydroxyapatite nanotubes; the particle size of the inorganic filler is 0.2 to 0.5 μm, and the inorganic filler is preferably an inorganic material having hydroxyl functional groups on the surface, and the inorganic filler is, for example, an inorganic particle.

[0043] In the present invention, the solid content of the slurry forming the coating layer is 4wt% to 5wt%, so that the coating layer has good high temperature resistance and is not easy to fall off. If the solid content of the slurry forming the coating layer is too high, the coating layer will be too thick and prone to problems such as sagging and wrinkling, and will also increase energy consumption and production costs; if the solid content of the slurry forming the coating layer is too low, it may cause the coating layer to be weak, affecting the performance and service life of the coating layer. If the solid content of the slurry is too low, the high temperature resistance of the coating layer will be poor; if the solid content of the slurry is too high, the air permeability of the coating layer will be poor.

[0044] In one embodiment, the coating layer filling rate of the present invention is 80% to 98%. Wherein, the coating layer filling rate = 100% × (1-the area of ​​the inorganic material exposed on the surface of the coating layer / the area of ​​the coating layer). The present invention simultaneously regulates the rotational viscosity of the aramid stock solution and the solid content of the slurry forming the coating layer, combined with controlling the first high-speed dispersion speed (dispersion of the inorganic filler and the solvent) and the second high-speed dispersion speed (dispersion of the inorganic filler and the aramid stock solution) to be the same within a specific range, thereby obtaining a composite coating diaphragm with a filling rate of 80% to 98%, achieving a balance between air permeability, high temperature resistance and powder loss rate. If the coating layer filling rate is too low, the coating layer is prone to defects such as powder loss and poor air permeability; if the coating layer filling rate is too high, the coating layer has poor high temperature resistance.

[0045] The present invention also provides a method for preparing a composite coated diaphragm, comprising the following steps:

[0046] An inorganic filler is blended with an organic solvent, subjected to a first high-speed dispersion, and then mixed with an aramid stock solution and subjected to a second high-speed dispersion to obtain a slurry for forming the coating layer; the aramid stock solution has a rotational viscosity of 2000 to 4000 mPa·s, the solid content of the slurry for forming the coating layer is 4 wt% to 5 wt%, the rotation speed of the first high-speed dispersion is 6500 to 10000 r / min, and the time of the first high-speed dispersion is 10 to 60 minutes; the rotation speed of the second high-speed dispersion is 6500 to 10000 r / min, and the time of the second high-speed dispersion is 10 to 60 minutes, and the first high-speed dispersion speed and the second high-speed dispersion speed are the same;

[0047] The slurry is coated on one side or both sides of a substrate film to obtain a composite coating separator.

[0048] The present invention does not particularly limit the preparation method of the substrate film, and conventional preparation methods in the art may be used.

[0049] In the present invention, the inorganic filler is first blended with a solvent. The inorganic filler has been described in detail above and will not be repeated here. In one embodiment, the solvent is an organic solvent, such as N-methylpyrrolidone (NMP). The mixture of the inorganic filler and the solvent is subjected to a first high-speed dispersion, wherein the speed of the first high-speed dispersion is 6500-10000 r / min and the time of the first high-speed dispersion is 10-60 minutes. The speed of the first high-speed dispersion is the same as the speed of the second high-speed dispersion.

[0050] Then, the dispersed mixture of the inorganic filler and the solvent is mixed with the aramid stock solution. The aramid stock solution has been described in detail above and will not be repeated here. In one embodiment, the mass ratio of the inorganic filler to the aramid stock solution is (1-6):25, specifically, it can be 4:25, and the mass ratio of aramid to the solvent in the aramid stock solution is (1-3):45, specifically, it can be 1:45. The mixture of the inorganic filler and the aramid stock solution is subjected to a second high-speed dispersion, the rotation speed of the second high-speed dispersion is 6500-10000r / min, and the time of the second high-speed dispersion is 10-60min. The rotation speed of the first high-speed dispersion can be the same as the rotation speed of the second high-speed dispersion.

[0051] The present invention limits the high-speed dispersion speed to 6500-10000r / min, so that the resulting coating layer is not easy to shed powder. If the dispersion speed is too low, it will lead to the presence of large lumps and aggregates in the coating layer slurry, affecting subsequent processing and performance, making the coating layer filling rate too low, and the coating film prone to shed powder; conversely, if the dispersion speed is too high, it may cause excessive shearing of the slurry, destroying its internal structure, reducing its stability and rheological properties, and further making the coating layer filling rate too high and the coating film poor in high-temperature resistance. The first high-speed dispersion speed is the same as the second high-speed dispersion speed, which is conducive to the stability control of the slurry. If the speeds are different, the slurry stability deteriorates and the coating film sheds powder at an increased rate.

[0052] Generally speaking, the high-speed dispersion speed requirement of the slurry by the blade coating method, the gravure roller coating method, and the slot extrusion coating method is usually between 5000-10000 r / min. The high-speed dispersion speed of the present invention is 6500-10000 r / min, thus meeting the dispersibility requirements of the slurry by the blade coating method, the gravure roller coating method, and the slot extrusion coating method.

[0053] Generally speaking, blade coating, gravure coating, and slot die coating methods generally require a slurry solid content of 3wt% to 5wt%. The slurry of the present invention has a solid content of 4wt% to 5wt%, thus meeting the slurry solid content requirements of blade coating, gravure coating, and slot die coating methods.

[0054] Therefore, in the composite coated diaphragm of the present invention, the ceramic filling rate of the coating layer is appropriate, the coating layer has the characteristics of high temperature resistance, air permeability and non-powdering, and has excellent performance.

[0055] The technical solution of the present invention will be further described below through specific examples. Unless otherwise specified, the following "%" refers to weight percentage.

[0056] raw material:

[0057] Aramid stock solutions with different rotational viscosity values ​​are available on the market.

[0058] Test method:

[0059] (1) Powder loss rate test method

[0060] Cut 100 10cm x 10cm coated separators, vacuum-dry them at 60°C for 12 hours, and weigh the total weight (G1). Each of the coated separators was rinsed in propylene carbonate (PC), then washed sequentially with pure water and anhydrous ethanol. The 100 separators were vacuum-dried at 60°C for 12 hours, and weighed the total weight (G2). The powder loss rate = (G1 - G2) / G1 × 100%. (Reference: Xiao Qiong, Li Lianhong, Wang Xianyou. A method for preparing a positive electrode sheet for a lithium iron phosphate power battery [P]. Hubei: CN105720267A, 2016-06-29)

[0061] (2) Coating layer filling rate

[0062] ImageJ software was used to determine the inorganic material coverage on the coating surface, and thus the coating filling rate. Since the inorganic material is usually distributed as a single layer on the coating surface and its area is smaller than the coating area, the coating filling rate can be indirectly evaluated by the amount of exposed inorganic material on the surface.

[0063] Test method for the coverage of exposed inorganic material on the coating surface: Use the manual selection function of imageJ software to select the area where the surface inorganic material is located in the electron microscope photo of the coating layer (as shown in Figure 1), add the selected area to the ROI Manager, and use the measure function to calculate the area of ​​each selection. The coverage of the exposed inorganic material on the coating surface is obtained by calculating the ratio of the sum of the areas of all selected areas (i.e., the area of ​​the exposed inorganic material on the coating surface) to the total field of view area (i.e., the area of ​​the coating layer), and then the coating filling rate is obtained.

[0064] Filling rate of coating layer = 100% x (1 - area of ​​inorganic material exposed on the surface of coating layer / area of ​​coating layer).

[0065] (3) Thermal shrinkage test method:

[0066] The test was conducted according to the requirements of GB / T36363-2018. A 100 mm x 100 mm sample was removed from the polyolefin microporous separator and placed in a forced air oven at 120°C for 1 hour. The thermal shrinkage rate can be calculated using the following formula.

[0067] MD heat shrinkage (%) = |(MD length before heating - MD length after heating) ÷ MD length before heating | × 100

[0068] TD heat shrinkage (%) = |(TD length before heating - TD length after heating) ÷ TD length before heating | × 100

[0069] (4) Air permeability test method:

[0070] The increase in air permeability per unit thickness of the coating layer = (air permeability of the entire coated membrane after coating - air permeability of the substrate membrane) / coating thickness.

[0071] Air permeability can be tested according to the method specified in GB / 1038.

[0072] Example 1

[0073] 8g of 0.3μm Al2O3 inorganic filler was mixed with 50mL of N-methylpyrrolidone (NMP) and dispersed at 8500rpm for 30 minutes. The mixture was then mixed with 200g of aramid stock solution with a rotational viscosity of 3000mPa·s and dispersed at the same high-speed dispersion speed for another 30 minutes to obtain a slurry with a solids content of 4.65%. The slurry was then coated onto a 13.5μm substrate film using a gravure roller (coating thickness of 3μm). The coating fill factor, air permeability, thermal shrinkage, and powder loss rate were measured.

[0074] According to the preparation method of Example 1, the composite coated diaphragms of Examples 2-14 and Comparative Examples 1-9 were prepared. The values ​​of the variables and the test results obtained in each example and comparative example are shown in Table 1.

[0075] Table 1

[0076] As shown in Table 1, when the aramid stock solution rotational viscosity value, slurry solid content, and rotation speed are all within a specific range, the filling rate is controlled within 80%-98%. It is found that when the filling rate is within 80%-98%, the three properties of high temperature resistance, air permeability, and powder loss rate are balanced.

[0077] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

Claims

1. A composite coated diaphragm, comprising a substrate film and a coating layer formed on at least one surface of the substrate film, characterized in that: The coating layer includes aramid and inorganic filler, and the inorganic filler is filled in the three-dimensional network structure formed by the aramid. The coating layer filling rate is 80% to 98%, and the coating layer filling rate = 100% × (1-the area of ​​the exposed inorganic filler on the surface of the coating layer / the area of ​​the coating layer); wherein the permeability increase per unit thickness of the coating layer is less than 35s / 100cc / μm; the composite coated diaphragm has a heat shrinkage rate of less than 5% in the MD direction and less than 1% in the TD direction under the conditions of 120°C and 1h, and a powder loss rate of less than 0.5%; the thickness of the coating layer is 1-4μm.

2. The composite coated diaphragm according to claim 1, characterized in that: The substrate film has a thickness of 4-20 μm, an air permeability of 50-500 s / 100 cc, and a porosity of 40-55%.

3. The composite coated diaphragm according to claim 1, characterized in that: The inorganic filler is selected from at least one of ceramic materials, nanowire materials or nanotube materials; the ceramic material is selected from one or more of Al2O3, SiO2, TiO2, ZrO2, BaTiO3, MgO, CaO, AlOOH, SiC; the nanowire material is selected from one or more of carbon nanowires, attapulgite, nanosilver wire, boron carbide nanowire, nanocellulose, copper hydroxide nanowire, silicon monoxide nanowire, hydroxyapatite nanowire; the nanotube material is selected from one or more of carbon nanotubes, nanosilver tubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, hydroxyapatite nanotubes.

4. The composite coated diaphragm according to claim 1, characterized in that: The inorganic filler is inorganic particles with hydroxyl functional groups on the surface; the particle size of the inorganic filler is 0.01-0.5 μm.

5. The composite coated diaphragm according to claim 1, characterized in that: The slurry for forming the coating layer comprises aramid stock solution and inorganic filler, and the rotational viscosity of the aramid stock solution is 2000-4000 mPa·s.

6. The composite coated diaphragm according to claim 5, characterized in that: The solid content of the slurry forming the coating layer is 4wt% to 5wt%; the aramid stock solution includes at least one of poly(m-phenylene isophthalamide) and poly(p-phenylene terephthalamide) and a solvent, and the solvent is N-methylpyrrolidone.

7. The composite coated diaphragm according to claim 5, characterized in that: The aramid stock solution also includes an auxiliary agent, which is one or more of CaCl2, KOH, LiCl and pyridine, and the mass content of the auxiliary agent in the aramid stock solution is ≤10%.

8. The method for preparing the composite coated diaphragm according to claim 1, characterized in that: The steps include: The inorganic filler is mixed with an organic solvent, and a first high-speed dispersion is performed, and then mixed with an aramid stock solution, and a second high-speed dispersion is performed to obtain a slurry for forming the coating layer; the rotational viscosity of the aramid stock solution is 2000-4000 mPa·s, the solid content of the slurry for forming the coating layer is 4wt%-5wt%, the rotation speed of the first high-speed dispersion is 6500-10000 r / min, and the time of the first high-speed dispersion is 10-60 min; The second high-speed dispersion speed is 6500-10000r / min, the second high-speed dispersion time is 10-60min, and the first high-speed dispersion speed is the same as the second high-speed dispersion speed; the slurry is coated on one side or both sides of the substrate film to obtain a composite coated diaphragm.

9. The method for preparing the composite coated diaphragm according to claim 8, characterized in that: The organic solvent is N-methylpyrrolidone.

10. A lithium ion battery, characterized in that: Comprising the composite coated diaphragm as described in claim 1.

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